Beta Amyloid Precursor Protein ~ Current Research TOP 100 Publications on Beta Amyloid Precursor Protein ~ Tau Protein Blog
Stem Cell Res Ther. 2011 Aug 30;2(4):36. [Epub ahead of print]
Soluble amyloid precursor protein: a novel proliferation factor of adult progenitor cells of ectodermal and mesodermal origin.
Abstract
ABSTRACT:
INTRODUCTION:
Soluble amyloid precursor protein alpha (sAPPalpha) is a proteolyte of APP cleavage by alpha-secretase. The significance of the cleavage and the physiological role of sAPPalpha are unknown. A crystal structure of a region of the amino terminal of sAPPalpha reveals a domain that is similar to cysteine-rich growth factors. While a previous study implicates sAPPalpha in the regulation of neural progenitor cell proliferation in the subventricular zone of adult mice, the ubiquitous expression of APP suggests that its role as a growth factor might be broader.
METHODS:
sAPPalpha and alpha-secretase activities were determined in neural progenitor cells (NPCs), mesenchymal stem cells and human decidua parietalis placenta stem cells. Inhibition of alpha-secretase was achieved by treatment with the matrixmetalloproteinase inhibitor GM6001, and proliferative was determined using clonogenic and immunocytochemical analysis of cell-lineage markers. Recovery of proliferation was achieved by supplementing GM6001-treated cells with recombinant soluble APPalpha. Expression of APP and its cellular localization in the subventricular zone was determined by Western blot and immunohistochemical analyses of APP wild type and knockout tissue. Alterations in pERK and pAKT expression as a function of soluble APPalpha production and activity in NPCs was determined by Western blot analysis.
RESULTS:
Here we show that sAPPalpha is a proliferation factor of adult NPCs, mesenchymal stem cells (MSCs) and human placenta-derived stem cells (hdpPSC). Inhibition of alpha-secretase activity reduces proliferation of these stem cell populations in a dose-dependent manner. Stem cell proliferation can be recovered by the addition of sAPPalpha in a dose-dependent manner, but not of media depleted of sAPPalpha. Importantly, sAPPalpha operates independently of the prominent proliferation factors epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF), but in association with ERK signaling and MAP-kinase signaling pathways. Levels of sAPPalpha and putative alpha-secretase, ADAM10, are particularly high in the subventricular zone of adult mice, suggesting a role for sAPPalpha in regulation of NPCs in this microenvironment.
CONCLUSIONS:
These results determine a physiological function for sAPPalpha and identify a new proliferation factor of progenitor cells of ectodermal and mesodermal origin. Further, our studies elucidate a potential pathway for sAPPalpha signaling through MAP kinase activation.
J Biol Chem. 2011 Aug 25. [Epub ahead of print]
Substrate sequence influences {gamma}-secretase modulator activity: role of the transmembrane domain of the amyloid precursor protein.
Source
University of California San Diego, United States;
Abstract
A subset of non-steroidal anti-inflammatory drugs (NSAIDs) modulates the γ-cleavage site in the amyloid precursor protein (APP) to selectively reduce production of Aβ42. It is unclear precisely how these γ-secretase modulators (GSMs) act to preferentially spare Aβ40 production as well as Notch processing and signaling. In an effort to determine the substrate requirements in NSAID/GSM activity, we determined the effects of sulindac sulfide and flurbiprofen on γ-cleavage of artificial constructs containing several γ-secretase substrates. Using Flag-tagged constructs that expressed extracellularly-truncated APP, Notch-1 or CD44, we found that these substrates have different sensitivities to sulindac sulfide. γ-Secretase cleavage of APP was altered by sulindac sulfide, but CD44 and Notch-1 were either insensitive or only minimally altered by this compound. Using chimeric APP constructs, we observed that the transmembrane domain (TMD) of APP played a pivotal role in determining drug sensitivity. Substituting the APP TMD with that of APLP2 retained the sensitivity to γ-cleavage modulation, but replacing TMDs from Notch-1 or ErbB4 rendered the resultant molecules insensitive to drug treatment. Specifically, the GxxxG motif within APP appeared to be critical to GSM activity. Consequently, the modulatory effects on γ-cleavage appears to be substrate dependent. We hypothesize that the substrate present in the γ-secretase complex influences the conformation of the complex, such that the binding site of GSMs is either stabilized or less favorable to influence the cleavage of the respective substrates.
J Biol Chem. 2011 Aug 25. [Epub ahead of print]
Lysine 624 of the amyloid precursor protein (APP) is a critical determinant of amyloid {beta} peptide length: support for a sequential model of {gamma}-secretase intramembrane proteolysis and regulation by the APP juxtamembrane region.
Kukar TL, Ladd TB, Robertson P, Pintchovski SA, Moore B, Bann MA, Ren Z, Jansen-West K, Malphrus K, Eggert S,Maruyama H, Cottrell BA, Das P, Basi GS, Koo EH, Golde TE.
Source
Emory University, United States;
Abstract
γ-Secretase is a multi-protein intramembrane-cleaving aspartyl protease (I-CLiP) that catalyzes the final cleavage of the amyloid β precursor protein (APP) to release the amyloid beta peptide (Aβ). Aβ is the primary component of senile plaques in Alzheimers disease (AD), and its mechanism of production has been intensely studied. γ-Secretase executes multiple cleavages within the transmembrane domain of APP with cleavages producing Aβ and the APP intracellular domain (AICD) referred to as γ and ε, respectively. The heterogeneous nature of the γ-cleavage that produces various Aβ peptides is highly relevant to AD, as increased production of Aβ 1-42 is genetically and biochemically linked to the development of AD. We have identified an amino acid in the juxtamemembrane region of APP, lysine 624 based on APP695 numbering (position 28 relative to Aβ) that plays a critical role in determining the final length of Aβ peptides released by γ-secretase. Mutation of this lysine to alanine (K28A) shifts the primary site of γ-secretase cleavage from 1-40 to 1-33, without significant changes to ε-cleavage. These results further support a model where ε-cleavage occurs first, followed by sequential proteolysis of the remaining transmembrane fragment, but extend these observations by demonstrating that charged residues at the luminal boundary of the APP transmembrane domain limit processivity of γ-Secretase.
PLoS One. 2011;6(8):e23600. Epub 2011 Aug 15.
Soluble Beta-amyloid precursor protein is related to disease progression in amyotrophic lateral sclerosis.
Source
Department of Neurology, University of Ulm, Ulm, Germany.
Abstract
BACKGROUND:
Biomarkers of disease progression in amyotrophic lateral sclerosis (ALS) could support the identification of beneficial drugs in clinical trials. We aimed to test whether soluble fragments of beta-amyloid precursor protein(sAPPα and sAPPß) correlated with clinical subtypes of ALS and were of prognostic value.
METHODOLOGY/PRINCIPAL FINDINGS:
In a cross-sectional study including patients with ALS (N = 68) with clinical follow-up data over 6 months, Parkinson's disease (PD, N = 20), and age-matched controls (N = 40), cerebrospinal fluid (CSF) levels of sAPPα a, sAPPß and neurofilaments (NfH(SMI35)) were measured by multiplex assay, Progranulin by ELISA. CSF sAPPα and sAPPß levels were lower in ALS with a rapidly-progressive disease course (p = 0.03, and p = 0.02) and with longer disease duration (p = 0.01 and p = 0.01, respectively). CSF NfH(SMI35) was elevated in ALS compared to PD and controls, with highest concentrations found in patients with rapid disease progression (p<0.01). High CSF NfH(SMI3) was linked to low CSF sAPPα and sAPPß (p = 0.001, and p = 0.007, respectively). The ratios CSF NfH(SMI35)/CSF sAPPα,-ß were elevated in patients with fast progression of disease (p = 0.002 each). CSF Progranulin decreased with ongoing disease (p = 0.04).
CONCLUSIONS:
This study provides new CSF candidate markers associated with progression of disease in ALS. The data suggest that a deficiency of cellular neuroprotective mechanisms (decrease of sAPP) is linked to progressive neuro-axonal damage (increase of NfH(SMI35)) and to progression of disease.
J Biol Chem. 2011 Aug 18. [Epub ahead of print]
Ubiquilin-1 is a molecular chaperone for the amyloid precursor protein.
Source
The University of Texas Medical Branch, United States;
Abstract
Alzheimer s disease (AD) is associated with extracellular deposition of proteolytic fragments of amyloid precursor protein(APP). Although mutations in APP and proteases that mediate its processing are known to result in familial, early-onset forms of AD, the mechanisms underlying the more common sporadic, yet genetically complex, forms of the disease are still unclear. Four single nucleotide polymorphisms (SNPs) within the ubiquilin-1 gene have been shown to be genetically associated with AD, implicating its gene product in the pathogenesis of late-onset AD. However, genetic linkage between ubiquilin-1 and AD has not been confirmed in studies examining different populations. Here we show that regardless of genotype, ubiquilin-1 protein levels are significantly decreased in late-onset AD patient brains, suggesting that diminished ubiquilin function may be a common denominator in AD progression. Our interrogation of putative ubiquilin-1 activities based on sequence similarities to proteins involved in cellular quality control showed that ubiquilin-1 can be biochemically defined as a bona fide molecular chaperone and that this activity is capable of preventing the aggregation of APP both in vitro and in live neurons. Furthermore, we show that reduced activity of ubiquilin-1 results in augmented production of pathogenic APP fragments as well as increased neuronal death. Our results support the notion that ubiquilin-1 chaperone activity is necessary to regulate the production of APP and its fragments, and that diminished ubiquilin-1 levels may contribute to AD pathogenesis.
Dement Geriatr Cogn Disord. 2011 Aug 13;32(1):45-54. [Epub ahead of print]
Clinical Course of Patients with Familial Early-Onset Alzheimer's Disease Potentially Lacking Senile Plaques Bearing the E693Δ Mutation in Amyloid Precursor Protein.
Source
Department of Geriatrics and Neurology, Osaka City University Graduate School of Medicine, Osaka, Japan.
Abstract
Background/Aims: Oligomeric amyloid β (Aβ) is currently considered to induce Alzheimer's disease (AD). We examined 2 patients with familial AD who possessed the Osaka (E693Δ) mutation in amyloid precursor protein. To the best of our knowledge, these patients are the first AD cases presumably affected with Aβ oligomers in the absence of senile plaques, and they support the Aβ oligomer hypothesis. Methods: We evaluated the clinical course, neuropsychological data, cerebrospinal fluid biomarker levels, magnetic resonance imaging (MRI) scans, fluorodeoxyglucose-positron emission tomography (PET) scans, and Pittsburgh compound B (PiB)-PET images of these patients. Results: In the early stages, these patients developed memory disturbances in a similar rate to patients with sporadic AD. Despite their memory disturbances, both patients showed only limited brain atrophy on MRI and little amyloid accumulation on PiB-PET. Subsequent to the development of memory disturbances, both patients suffered from motor dysfunction, probably due to cerebellar ataxia, and, within a few years, the patients fell into an apallic state. Conclusions: Familial AD patients with Osaka (E693Δ) mutation show severe dementia, cerebellar ataxia, and gait disturbances.
Copyright © 2011 S. Karger AG, Basel.
IUBMB Life. 2011 Aug 10. doi: 10.1002/iub.512. [Epub ahead of print]
Intracellular trafficking of the β-secretase and processing of amyloid precursor protein.
Source
Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Melbourne, Victoria, Australia.
Abstract
The main component of the amyloid plaques found in the brains of those with Alzheimer's disease (AD) is a polymerized form of the β-amyloid peptide (Aβ) and is considered to play a central role in the pathogenesis of this neurodegenerative disorder. Aβ is derived from the proteolytic processing of the amyloid precursor protein (APP). Beta site APP-cleaving enzyme, BACE1 (also known as β-secretase) is a membrane-bound aspartyl protease responsible for the initial step in the generation of Aβ peptide and is thus a prime target for therapeutic intervention. Substantive evidence now indicates that the processing of APP by BACE1 is regulated by the intracellular sorting of the enzyme and, moreover, perturbations in these intracellular trafficking pathways have been linked to late-onset AD. In this review, we highlight the recent advances in the understanding of the regulation of the intracellular sorting of BACE1 and APP and illustrate why the trafficking of these cargos represent a key issue for understanding the membrane-mediated events associated with the generation of the neurotoxic Aβ products in AD. © 2011 IUBMB IUBMB Life, 2011.
Copyright © 2011 International Union of Biochemistry and Molecular Biology, Inc.
PLoS One. 2011;6(7):e22857. Epub 2011 Jul 29.
Secreted human amyloid precursor protein binds semaphorin 3a and prevents semaphorin-induced growth cone collapse.
Magdesian MH, Gralle M, Guerreiro LH, Beltrão PJ, Carvalho MM, da S Santos LE, de Mello FG, Reis RA, Ferreira ST.
Source
Institute of Medical Biochemistry, Program in Biochemistry and Cellular Biophysics, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
Abstract
The amyloid precursor protein (APP) is well known for giving rise to the amyloid-β peptide and for its role in Alzheimer's disease. Much less is known, however, on the physiological roles of APP in the development and plasticity of the central nervous system. We have used phage display of a peptide library to identify high-affinity ligands of purified recombinant human sAPPα(695) (the soluble, secreted ectodomain from the main neuronal APP isoform). Two peptides thus selected exhibited significant homologies with the conserved extracellular domain of several members of the semaphorin (Sema) family of axon guidance proteins. We show that sAPPα(695) binds both purified recombinant Sema3A and Sema3A secreted by transfected HEK293 cells. Interestingly, sAPPα(695) inhibited the collapse of embryonic chicken (Gallus gallus domesticus) dorsal root ganglia growth cones promoted by Sema3A (K(d)≤8·10(-9) M). Two Sema3A-derived peptides homologous to the peptides isolated by phage display blocked sAPPα binding and its inhibitory action on Sema3A function. These two peptides are comprised within a domain previously shown to be involved in binding of Sema3A to its cellular receptor, suggesting a competitive mechanism by which sAPPα modulates the biological action of semaphorins.
Proc Natl Acad Sci U S A. 2011 Aug 23;108(34):E559-68. Epub 2011 Aug 8.
ADP ribosylation factor 6 (ARF6) controls amyloid precursor protein (APP) processing by mediating the endosomal sorting of BACE1.
Sannerud R, Declerck I, Peric A, Raemaekers T, Menendez G, Zhou L, Veerle B, Coen K, Munck S, De Strooper B, Schiavo G, Annaert W.
Source
Laboratory of Membrane Trafficking and Laboratory for Research on Neurodegenerative Diseases, Center for Human Genetics, Catholic University of Leuven, and Department of Molecular and Developmental Genetics, Vlaams Instituut voor Biotechnologie, Gasthuisberg, B-3000 Leuven, Belgium.
Abstract
Amyloid β (Aβ) peptides, the primary constituents of senile plaques and a hallmark in Alzheimer's disease pathology, are generated through the sequential cleavage of amyloid precursor protein (APP) by β-site APP cleaving enzyme 1 (BACE1) and γ-secretase. The early endosome is thought to represent a major compartment for APP processing; however, the mechanisms of how BACE1 encounters APP are largely unknown. In contrast to APP internalization, which is clathrin-dependent, we demonstrate that BACE1 is sorted to early endosomes via a route controlled by the small GTPase ADP ribosylation factor 6 (ARF6). Altering ARF6 levels or its activity affects endosomal sorting of BACE1, and consequently results in altered APP processing and Aβ production. Furthermore, sorting of newly internalized BACE1 from ARF6-positive towards RAB GTPase 5 (RAB5)-positive early endosomes depends on its carboxyterminal short acidic cluster-dileucine motif. This ARF6-mediated sorting of BACE1 is confined to the somatodendritic compartment of polarized neurons in agreement with Aβ peptides being primarily secreted from here. These results demonstrate a spatial separation between APP and BACE1 during surface-to-endosome transport, suggesting subcellular trafficking as a regulatory mechanism for this proteolytic processing step. It thereby provides a novel avenue to interfere with Aβ production through a selective modulation of the distinct endosomal transport routes used by BACE1 or APP.
J Neurochem. 2011 Aug 9. doi: 10.1111/j.1471-4159.2011.07419.x. [Epub ahead of print]
FE65 Proteins Regulate NMDA Receptor Activation-induced Amyloid Precursor ProteinProcessing.
Source
Genetics and Aging Research Unit, MassGeneral Institute for Neurodegenerative Disease, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, USA Department of Neurology, Tufts University School of Medicine, Caritas St. Elizabeth's Medical Center, Brighton, MA USA Mayo Clinic Jacksonville, FL, USA.
Abstract
Amyloid precursor protein (APP) family members and their proteolytic products are implicated in normal nervous system function and Alzheimer's disease pathogenesis. APP processing and Aβ secretion are regulated by neuronal activity. Various data suggest that NMDA receptor (NMDAR) activity plays a role in both non-amyloidogenic and amyloidogenic APP processing depending on whether synaptic or extrasynaptic NMDARs are activated, respectively. The APP-interacting FE65 proteins modulate APP trafficking and processing in cell lines, but little is known about their contribution to APP trafficking and processing in neurons, either in vivo or in vitro. In this study, we examined the contribution of the FE65 protein family to APP trafficking and processing in WT and FE65/FE65L1 double knockout neurons under basal conditions and following NMDAR activation. We report that FE65 proteins facilitate neuronal Aβ secretion without affecting APP fast axonal transport to presynaptic terminals. In addition, FE65 proteins facilitate an NMDAR-dependent non-amyloidogenic APP processing pathway. Generation of high-molecular weight (HMW) species bearing an APP C-terminal epitope was also observed following NMDAR activation. These HMW species require proteasomal and calpain activities for their accumulation. Recovery of APP polypeptide fragments from electroeluted HMW species having molecular weights consistent with calpain I cleavage of APP suggests that HMW species are complexes formed from APP metabolic products. Our results indicate that the FE65 proteins contribute to physiological APP processing and accumulation of APP metabolic products resulting from NMDAR activation.
Journal of Neurochemistry © 2011 International Society for Neurochemistry.
Protein Cell. 2011 Jul;2(7):573-84. Epub 2011 Aug 6.
Pharmacological applications of a novel neoepitope antibody to a modified amyloid precursor protein-derived beta-secretase product.
Source
Department of Neurology, Merck Research Laboratory, West Point, PA, 19486, USA, Guoxin_wu@merck.com.
Abstract
We have previously described a novel artificial NFEV β-secretase (BACE1) cleavage site, which when introduced into the amyloid-β precursor protein (APP), significantly enhances APP cleavage by BACE1 in in vitro and cellular assays. In this study, we describe the identification and characterization of a single chain fragment of variable region (scFv), specific to the EV neo-epitope derived from BACE1 cleavage of the NFEV-containing peptide, and its conversion to IgG1. Both the scFv displayed on phage and EV-IgG1 show exquisite specificity for binding to the EV neoepitope without cross-reactivity to other NFEV containing peptides or WT-APP KMDA cleavage products. EV-IgG1 can detect as little as 0.3 nmol/L of the EV peptide. EV-IgG1 antibody was purified, conjugated with alkaline phosphatase and utilized in various biological assays. In the BACE1 enzymatic assay using NFEV substrate, a BACE1 inhibitor MRK-3 inhibited cleavage with an IC(50) of 2.4 nmol/L with excellent reproducibility. In an APP_NFEV stable SH-SY5Y cellular assay, the EC(50) for inhibition of EV-Aβ peptide secretion with MRK-3 was 236 nmol/L, consistent with values derived using an EV polyclonal antibody. In an APP_NFEV knock-in mouse model, both Aβ_EV40 and Aβ_EV42 peptides in brain homogenate showed excellent gene dosage dependence. In conclusion, the EV neoepitope specific monoclonal antibody is a novel reagent for BACE1 inhibitor discovery for both in vitro, cellular screening assays and in vivo biochemical studies. The methods described herein are generally applicable to novel synthetic substrates and enzyme targets to enable robust screening platforms for enzyme inhibitors.
J Biol Chem. 2011 Aug 3. [Epub ahead of print]
Structural basis for matrix metalloproteinase-2 (MMP-2)-selective inhibitory action of {beta}-amyloid precursor protein-derived inhibitor.
Source
Graduate School of Nanobioscience, Yokohama City University, Japan.
Abstract
Unlike other synthetic or physiological inhibitors for matrix metalloproteinases (MMPs), the β-amyloid precursor protein-derived inhibitory peptide (APP-IP) having ISYGNDALMP sequence has a high selectivity toward MMP-2. Our previous study identified amino acid residues of MMP-2 essential for its selective inhibition by APP-IP, and also demonstrated that the N to C direction of the decapeptide inhibitor relative to the substrate-binding cleft of MMP-2 is opposite to that of substrate. However, detailed interactions between the two molecules remained to be clarified. Here, we determined the crystal structure of the catalytic domain of MMP-2 in complex with APP-IP. We found that APP-IP in the complex is indeed embedded into the substrate-binding cleft of the catalytic domain in the N to C direction opposite to that of substrate. With the crystal structure, it was first clarified that the aromatic side chain of Tyr(3) of the inhibitor is accommodated into the S1' pocket of the protease, and the carboxylate group of Asp(6) of APP-IP coordinates bidentately to the catalytic zinc of the enzyme. The Ala(7) to Pro(10) and Tyr(3) to Ile(1) strands of the inhibitor extend into the non-prime and the prime sides of the cleft, respectively. Therefore, the decapeptide inhibitor has long-range contact with the substrate-binding cleft of the protease. This mode of interaction is probably essential for the high MMP-2-selectivity of the inhibitor, because MMPs share a common architecture in the vicinity of the catalytic center but whole structures of their substrate-binding clefts have sufficient variety for the inhibitor to distinguish MMP-2 from other MMPs.
Neurol Sci. 2011 Jul 29. [Epub ahead of print]
Effects of conjugated linoleic acid on cleavage of amyloid precursor protein via PPARγ
Source
School of Pharmaceutical Sciences, Rm 211, Sun Yat-sen University, 132 Waihuan East Road, Higher Education Mega Center, Guangzhou, 510006, Guangdong, China.
Abstract
Conjugated linoleic acid (CLA) plays important roles in physiological conditions. The aim of present study was to explore the effects of CLA on the cleavage of amyloid precursor protein (APP) and the potential mechanism involved. The effects of CLA on intracellular APP, BACE1 (β-site APP Cleaving Enzyme1, BACE1), a disintegrin and metalloprotease (ADAM10) and extracellular sAPPα (soluble) were analyzed by RT-PCR, Western blot and ELISA in SH-SY5Y cells. Our study indicated that CLA significantly decreased the expression of BACE1 and increased the extracellular secretion of sAPPα, but not affected the levels of APP and ADAM10. The study also revealed that the nuclear receptor peroxisome proliferators activated receptor γ (PPARγ) played an important role in the CLA-induced intracellular BACE1 decrease, as well as the extracellular sAPPα increase through knockdown of PPARγ transcription using siRNA. We hypothesize that CLA acts as an agonist or ligand, which binds with PPARγ and leads to the increase in APP cleavage via α-secretase-mediated pathway and the decrease in the deposition of Aβ.
J Biol Chem. 2011 Jul 27. [Epub ahead of print]
Prion protein interacts with bace1 and differentially regulates its activity towards wild type and swedish mutant amyloid precursor protein.
Griffiths HH, Whitehouse IJ, Baybutt H, Brown D, Kellett KA, Jackson CD, Turner AJ, Piccardo P, Manson JC, Hooper NM.
Source
University of Leeds, United Kingdom;
Abstract
In Alzheimers disease (AD) amyloid-beta (Abeta) peptides derived from the amyloid precursor protein (APP) accumulate in the brain. Cleavage of APP by the beta-secretase BACE1 is the rate-limiting step in the production of Abeta. We have reported previously that the cellular prion protein (PrPC) inhibited the action of BACE1 towards wild type human APP (APPWT) in cellular models and that the levels of endogenous murine Abeta were significantly increased in PrPC null mice brain. Here we have investigated the molecular and cellular mechanisms underlying this observation. PrPC interacted directly with the pro-domain of the immature Golgi-localised form of BACE1. This interaction decreased BACE1 at the cell surface and in endosomes, where it preferentially cleaves APPWT, but increased it in the Golgi, where it preferentially cleaves APP with the Swedish mutation (APPSwe). In transgenic mice expressing human APP with the Swedish and Indiana familial AD mutations (APPSwe,Ind), PrPC deletion had no influence on APP proteolytic processing, Abeta plaque deposition, levels of soluble Abeta or Abeta oligomers. In cells, although PrPC inhibited the action of BACE1 on APPWT, it did not inhibit BACE1 activity towards APPSwe. The differential subcellular location of the BACE1 cleavage of APPSwe relative to APPWT provides an explanation for the failure of PrPC deletion to affect Abeta accumulation in APPSwe,Ind mice. Thus, while PrPC exerts no control on cleavage of APPSwe by BACE1, it has a profound influence on the cleavage of APPWT suggesting that PrPC may be a key protective player against sporadic AD.
J Neurosci. 2011 Jul 27;31(30):10836-10846.
LRAD3, A Novel Low-Density Lipoprotein Receptor Family Member That ModulatesAmyloid Precursor Protein Trafficking.
Ranganathan S, Noyes NC, Migliorini M, Winkles JA, Battey FD, Hyman BT, Smith E, Yepes M, Mikhailenko I, Strickland DK.
Source
Center for Vascular and Inflammatory Diseases and the Departments of Surgery and Physiology, University of Maryland School of Medicine, Baltimore, Maryland 21201, Alzheimer's Disease Research Laboratory, Department of Neurology, Massachusetts General Institute for Neurodegenerative Disease, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts 02129, and the Department of Neurology and Center for Neurodegenerative Disease, Emory University School of Medicine, Atlanta, Georgia 30322.
Abstract
We have identified a novel low-density lipoprotein (LDL) receptor family member, termed LDL receptor class A domain containing 3 (LRAD3), which is expressed in neurons. The LRAD3 gene encodes an ∼50 kDa type I transmembrane receptor with an ectodomain containing three LDLa repeats, a transmembrane domain, and a cytoplasmic domain containing a conserved dileucine internalization motif and two polyproline motifs with potential to interact with WW-domain-containing proteins. Immunohistochemical analysis of mouse brain reveals LRAD3 expression in the cortex and hippocampus. In the mouse hippocampal-derived cell line HT22, LRAD3 partially colocalizes with amyloid precursor protein (APP) and interacts with APP as revealed by coimmunoprecipitation experiments. To identify the portion of APP that interacts with LRAD3, we used solid-phase binding assays that demonstrated that LRAD3 failed to bind to a soluble APP fragment (sAPPα) released after α-secretase cleavage. In contrast, C99, the β-secretase product that remains cell associated, coprecipitated with LRAD3, confirming that regions within this portion of APP are important for associating with LRAD3. The association of LRAD3 with APP increases the amyloidogenic pathway of APP processing, resulting in a decrease in sAPPα production and increased Aβ peptide production. Pulse-chase experiments confirm that LRAD3 expression significantly decreases the cellular half-life of mature APP. These results reveal that LRAD3 influences APP processing and raises the possibility that LRAD3 alters APP function in neurons, including its downstream signaling.
Biosci Trends. 2011 Jun;5(3):129-38.
Gastrodia elata modulates amyloid precursor protein cleavage and cognitive functions in mice.
Abstract
Gastrodia elata (Tianma) is a traditional Chinese medicine often used for the treatment of headache, convulsions, hypertension, and cardiovascular diseases. The vasodilatory actions of Tianma led us to investigate its specific effects on memory and learning as well as on Alzheimer's disease (AD)-related signaling. We conducted a radial arm water maze analysis and the novel object recognition test to assess the cognitive functions of Tianma-treated mice. Our data show that Tianma enhances cognitive functions in mice. Further investigations revealed that Tianma enhances the α-secretase-mediated proteolytic processing of the amyloid precursor protein (App) that precludes the amyloid-β peptide production and supports the non-amyloidogenic processing of App which is favorable in AD treatment. We hypothesize that Tianma promotes cognitive functions and neuronal survival by inhibiting β-site App-cleaving enzyme 1 activity and promoting the neuroprotective α-secretase activity.
Cell Adh Migr. 2011 Jul 1;5(4). [Epub ahead of print]
The roles of amyloid precursor protein (APP) in neurogenesis: Implications to pathogenesis and therapy of Alzheimer disease.
Source
National Neuroscience Institute; Singapore.
Abstract
The amyloid-beta (Aβ) peptide is the derivative of amyloid precursor protein (APP) generated through sequential proteolytic processing by β- and γ-secretases. Excessive accumulation of Aβ, the main constituent of amyloid plaques, has been implicated in the etiology of Alzheimer's disease (AD). It was found recently that the impairments of neurogenesis in brain were associated with the pathogenesis of AD. Furthermore recent findings implicated that APP could function to influence proliferation of neural progenitor cells (NPC) and might regulate transcriptional activity of various genes. Studies demonstrated that influence of neurogenesis by APP is conferred differently via its two separate domains, soluble secreted APPs (sAPPs, mainly sAPPα) and APP intracellular domain (AICD). The sAPPα was shown to be neuroprotective and important to neurogenesis, whereas AICD was found to negatively modulate neurogenesis. Furthermore, it was demonstrated recently that microRNA could function to regulate APP expression, APP processing, Aβ accumulation and subsequently influence neurotoxicity and neurogenesis related to APP, which was implicated to AD pathogenesis, especially for sporadic AD. Based on data accumulated, secretase balances were proposed. These secretase balances could influence the downstream balance related to regulation of neurogenesis by AICD and sAPPα as well as balance related to influence of neuron viability by Aβ and sAPPα. Disruption of these secretase balances could be culprits to AD onset.
J Neurosci. 2011 Jul 20;31(29):10427-31.
Ablation of cellular prion protein does not ameliorate abnormal neural network activity or cognitive dysfunction in the j20 line of human amyloid precursor protein transgenic mice.
Source
Gladstone Institute of Neurological Disease and Department of Neurology, University of California, San Francisco, San Francisco, California 94158.
Abstract
Previous studies suggested that the cellular prion protein (PrP(c)) plays a critical role in the pathogenesis of Alzheimer's disease (AD). Specifically, amyloid-β (Aβ) oligomers were proposed to cause synaptic and cognitive dysfunction by binding to PrP(c). To test this hypothesis, we crossed human amyloid precursor protein (hAPP) transgenic mice from line J20 onto a PrP(c)-deficient background. Ablation of PrP(c) did not prevent the premature mortality and abnormal neural network activity typically seen in hAPPJ20 mice. Furthermore, hAPPJ20 mice with or without PrP(c) expression showed comparably robust abnormalities in learning and memory and in other behavioral domains at 6-8 months of age. Notably, these abnormalities are not refractory to therapeutic manipulations in general: they can be effectively prevented by interventions that prevent Aβ-dependent neuronal dysfunction also in other lines of hAPP transgenic mice. Thus, at least in this model, PrP(c) is not an important mediator of Aβ-induced neurological impairments.
FASEB J. 2011 Jul 11. [Epub ahead of print]
An alternative metabolic pathway of amyloid precursor protein C-terminal fragments via cathepsin B in a human neuroglioma model.
Source
*Department of Pharmacology, Faculty of Medicine, Saitama Medical University, Saitama, Japan;
Abstract
γ-Secretase catalyzes the cleavage of the intramembrane region of the Alzheimer amyloid precursor protein (APP), generating p3, amyloid-β peptide (Aβ), and the APP intracellular domain (AICD). Although a γ-secretase inhibitor has been shown to cause an accumulation of the APP C-terminal fragments (CTFs) α and β and to decrease levels of p3 or Aβ and AICD, we found that treatment with a lysosomotropic weak base, such as chloroquine or ammonium chloride, caused simultaneous accumulation of both CTFs and AICD, suggesting that lysosomal proteases are also involved in processing of APP. This observation was reinforced by the results that cysteine protease inhibitor E-64d and cathepsin B specific inhibitor CA-074Me caused the accumulation of both CTFs and AICD with no change in known secretase activities. γ-Secretase preferentially cleaved phosphorylated CTFs to produce Aβ, but cathepsin B degraded CTFs regardless of phosphorylation. Our results suggest that cathepsin B plays novel roles in the metabolism of APP and that an inhibition of APP phosphorylation is an attractive therapeutic target for Alzheimer's disease.-Asai, M., Yagishita, S., Iwata, N., Saido, T. C., Ishiura, S., Maruyama, K. An alternative metabolic pathway of amyloid precursor protein C-terminal fragments via cathepsin B in a human neuroglioma model.
PLoS One. 2011;6(6):e20405. Epub 2011 Jun 22.
Increased secreted amyloid precursor protein-α (sAPPα) in severe autism: proposal of a specific, anabolic pathway and putative biomarker.
Source
Department of Psychiatry, Institute of Psychiatric Research, Indiana University School of Medicine, Indianapolis, Indiana, United States of America.
Abstract
Autism is a neurodevelopmental disorder characterized by deficits in verbal communication, social interactions, and the presence of repetitive, stereotyped and compulsive behaviors. Excessive early brain growth is found commonly in some patients and may contribute to disease phenotype. Reports of increased levels of brain-derived neurotrophic factor (BDNF) and other neurotrophic-like factors in autistic neonates suggest that enhanced anabolic activity in CNS mediates this overgrowth effect. We have shown previously that in a subset of patients with severe autism and aggression, plasma levels of the secreted amyloid-β (Aβ) precursor protein-alpha form (sAPPα) were significantly elevated relative to controls and patients with mild-to-moderate autism. Here we further tested the hypothesis that levels of sAPPα and sAPPβ (proteolytic cleavage products of APP by α- and β-secretase, respectively) are deranged in autism and may contribute to an anabolic environment leading to brain overgrowth. We measured plasma levels of sAPPα, sAPPβ, Aβ peptides and BDNF by corresponding ELISA in a well characterized set of subjects. We included for analysis 18 control, 6 mild-to-moderate, and 15 severely autistic patient plasma samples. We have observed that sAPPα levels are increased and BDNF levels decreased in the plasma of patients with severe autism as compared to controls. Further, we show that Aβ1-40, Aβ1-42, and sAPPβ levels are significantly decreased in the plasma of patients with severe autism. These findings do not extend to patients with mild-to-moderate autism, providing a biochemical correlate of phenotypic severity. Taken together, this study provides evidence that sAPPα levels are generally elevated in severe autism and suggests that these patients may have aberrant non-amyloidogenic processing of APP.
Curr Med Chem. 2011;18(22):3314-21.
Current Drug Targets for Modulating Alzheimer's Amyloid Precursor Protein: Role of Specific Micro-RNA Species.
Source
Department of Psychiatry, Indiana University School of Medicine, 791Union Drive, Indianapolis IN 46202, USA. dlahiri@iupui.edu.
Abstract
Alzheimer's disease (AD) is the most common form of dementia in the United States and is increasing in prevalence every year throughout the world. Recent clinical trial failures highlight the need for further insights into the molecular events that underlie the neurobiology of AD. Pathological aberrations in AD are believed to result, in part, from excess accumulation of amyloid-beta peptide (Aβ), a product of Aβ precursor protein (APP). Targeting APP levels would then be expected to reduce Aβ production in all forms of AD. Therefore, clarifying the regulatory network that governs APP expression is likely to reveal molecular players that could serve as novel drug targets. This review highlights recent work demonstrating the involvement of microRNA (miRNA) in this regulatory network. MiRNA are small, non-coding RNA that interact with target mRNA at sites of imperfect complementarity and mediate translational inhibition or transcript destabilization. We first review the neurobiology of AD and describe current therapeutic strategies. We then review transcriptional and post-transcriptional mechanisms utilized by cells to control APP expression. We conclude by highlighting recent work, including our own, which suggests miRNA are integral components of this regulatory framework and potential targets for future AD therapeutics.
J Biol Chem. 2011 Aug 26;286(34):29748-57. Epub 2011 Jun 29.
Crystal Structure of the E2 Domain of Amyloid Precursor Protein-like Protein 1 in Complex with Sucrose Octasulfate.
Source
From the Department of Pharmacology, Yale School of Medicine, New Haven, Connecticut 06520.
Abstract
Missense mutations in the amyloid precursor protein (APP) gene can cause familial Alzheimer disease. It is thought that APP and APP-like proteins (APLPs) may play a role in adhesion and signal transduction because their ectodomains interact with components of the extracellular matrix. Heparin binding induces dimerization of APP and APLPs. To help explain how these proteins interact with heparin, we have determined the crystal structure of the E2 domain of APLP1 in complex with sucrose octasulfate (SOS). A total of three SOS molecules are bound to the E2 dimer. Two SOSs are bound inside a narrow intersubdomain groove, and the third SOS is bound near the two-fold axis of the protein. Mutational analyses show that most residues interacting with SOS also contribute to heparin binding, although in varying degrees; a deep pocket, defined by His-376, Lys-422, and Arg-429, and an interfacial site between Lys-314 and its symmetry mate are most important in the binding of the negatively charged polysaccharide. Comparison with a lower resolution APP structure shows that all key heparin binding residues are conserved and identically positioned, suggesting that APLP1 and APP may bind heparin similarly. In transfected HEK-293 cells, mutating residues responsible for heparin binding causes little change in the proteolysis of APP by the secretases. However, mutating a pair of conserved basic residues (equivalent to Arg-414 and Arg-415 of APLP1) immediately adjacent to the heparin binding site affects both the maturation and the processing of APP.
.
Proc Natl Acad Sci U S A. 2011 Jul 19;108(29):11848-53. Epub 2011 Jun 28.
Site-specific characterization of threonine, serine, and tyrosine glycosylations ofamyloid precursor protein/amyloid {beta}-peptides in human cerebrospinal fluid.
Halim A, Brinkmalm G, Rüetschi U, Westman-Brinkmalm A, Portelius E, Zetterberg H, Blennow K, Larson G, Nilsson J.
Source
Department of Clinical Chemistry and Transfusion Medicine, Institute of Biomedicine, University of Gothenburg, SE-413 45 Gothenburg, Sweden.
Abstract
The proteolytic processing of human amyloid precursor protein (APP) into shorter aggregating amyloid β (Aβ)-peptides, e.g., Aβ1-42, is considered a critical step in the pathogenesis of Alzheimer's disease (AD). Although APP is a well-known membrane glycoprotein carrying both N- and O-glycans, nothing is known about the occurrence of released APP/Aβ glycopeptides in cerebrospinal fluid (CSF). We used the 6E10 antibody and immunopurified Aβ peptides and glycopeptides from CSF samples and then liquid chromatography-tandem mass spectrometry for structural analysis using collision-induced dissociation and electron capture dissociation. In addition to 33 unglycosylated APP/Aβ peptides, we identified 37 APP/Aβ glycopeptides with sialylated core 1 like O-glycans attached to Thr(-39, -21, -20, and -13), in a series of APP/AβX-15 glycopeptides, where X was -63, -57, -52, and -45, in relation to Asp1 of the Aβ sequence. Unexpectedly, we also identified a series of 27 glycopeptides, the Aβ1-X series, where X was 20 (DAEFRHDSGYEVHHQKLVFF), 19, 18, 17, 16, and 15, which were all uniquely glycosylated on Tyr10. The Tyr10 linked O-glycans were (Neu5Ac)(1-2)Hex(Neu5Ac)HexNAc-O- structures with the disialylated terminals occasionally O-acetylated or lactonized, indicating a terminal Neu5Acα2,8Neu5Ac linkage. We could not detect any glycosylation of the Aβ1-38/40/42 isoforms. We observed an increase of up to 2.5 times of Tyr10 glycosylated Aβ peptides in CSF in six AD patients compared to seven non-AD patients. APP/Aβ sialylated O-glycans, including that of a Tyr residue, the first in a mammalian protein, may modulate APP processing, inhibiting the amyloidogenic pathway associated with AD.
Proc Natl Acad Sci U S A. 2011 Jul 12;108(28):11686-91. Epub 2011 Jun 27.
Altered temporal patterns of anxiety in aged and amyloid precursor protein (APP) transgenic mice.
Source
Department of Neuroscience, Institute for Behavioral Medicine Research, Ohio State University Medical Center, Columbus, OH 43210, USA. tracy.bedrosian@osumc.edu
Abstract
Both normal aging and dementia are associated with dysregulation of the biological clock, which contributes to disrupted circadian organization of physiology and behavior. Diminished circadian organization in conjunction with the loss of cholinergic input to the cortex likely contributes to impaired cognition and behavior. One especially notable and relatively common circadian disturbance among the aged is "sundowning syndrome," which is characterized by exacerbated anxiety, agitation, locomotor activity, and delirium during the hours before bedtime. Sundowning has been reported in both dementia patients and cognitively intact elderly individuals living in institutions; however, little is known about temporal patterns in anxiety and agitation, and the neurobiological basis of these rhythms remains unspecified. In the present study, we explored the diurnal pattern of anxiety-like behavior in aged and amyloid precursor protein (APP) transgenic mice. We then attempted to treat the observed behavioral disturbances in the aged mice using chronic nightly melatonin treatment. Finally, we tested the hypothesis that time-of-day differences in acetylcholinesterase and choline acetyltransferase expression and general neuronal activation (i.e., c-Fos expression) coincide with the behavioral symptoms. Our results show a temporal pattern of anxiety-like behavior that emerges in elderly mice. This behavioral pattern coincides with elevated locomotor activity relative to adult mice near the end of the dark phase, and with time-dependent changes in basal forebrain acetylcholinesterase expression. Transgenic APP mice show a similar behavioral phenomenon that is not observed among age-matched wild-type mice. These results may have useful applications to the study and treatment of age- and dementia-related circadian behavioral disturbances, namely, sundowning syndrome.
J Med Chem. 2011 Aug 25;54(16):5836-57. Epub 2011 Jul 29.
From Fragment Screening to In Vivo Efficacy: Optimization of a Series of 2-Aminoquinolines as Potent Inhibitors of Beta-Site Amyloid Precursor Protein Cleaving Enzyme 1 (BACE1).
Cheng Y, Judd TC, Bartberger MD, Brown J, Chen K, Fremeau RT, Hickman D, Hitchcock SA, Jordan B, Li V, Lopez P,Louie SW, Luo Y, Michelsen K, Nixey T, Powers TS, Rattan C, Sickmier EA, St Jean DJ, Wahl RC, Wen PH, Wood S.
Source
Chemistry Research and Discovery, §Department of Molecular Structure, ∥Department of Neuroscience, ⊥Department of HTS and Molecular Pharmacology, #Department of Pharmacokinetics and Drug Metabolism, Amgen Inc. , One Amgen Center Drive, Thousand Oaks, California 91320, United States.
Abstract
Using fragment-based screening of a focused fragment library, 2-aminoquinoline 1 was identified as an initial hit for BACE1. Further SAR development was supported by X-ray structures of BACE1 cocrystallized with various ligands and molecular modeling studies to expedite the discovery of potent compounds. These strategies enabled us to integrate the C-3 side chain on 2-aminoquinoline 1 extending deep into the P2' binding pocket of BACE1 and enhancing the ligand's potency. We were able to improve the BACE1 potency to subnanomolar range, over 10(6)-fold more potent than the initial hit (900 μM). Further elaboration of the physical properties of the lead compounds to those more consistent with good blood-brain barrier permeability led to inhibitors with greatly improved cellular activity and permeability. Compound 59 showed an IC(50) value of 11 nM on BACE1 and cellular activity of 80 nM. This compound was advanced into rat pharmacokinetic and pharmacodynamic studies and demonstrated significant reduction of Aβ levels in cerebrospinal fluid (CSF).
J Mol Neurosci. 2011 Jun 21. [Epub ahead of print]
Selective Interaction of Amyloid Precursor Protein with Different Isoforms of Neural Cell Adhesion Molecule.
Source
Key Laboratory of Developmental Genes and Human Disease, Ministry of Education, Institute of Life Science, Southeast University, Nanjing, 210009, China.
Abstract
Compare to the thoroughly studied beta-amyloid, the physiological function of amyloid precursor protein (APP) is not well understood. We now had identified neural cell adhesion molecule (NCAM)-140 as a potential interaction partner of APP. Our data indicated that NCAM-140, but not NCAM-180, binds to the conserved central extracellular domain of APP. We also found that the phosphorylation levels of ERK1 and ERK2 were increased when cells were co-transfected with NCAM-140 and APP indicate that the interaction between NCAM-140 and APP may involve the MAPK pathway. These findings demonstrated that NCAM-140 interacts with APP, potentially playing a role in neurite outgrowth and neural development.
J Neurochem. 2011 Sep;118(5):677-9. doi: 10.1111/j.1471-4159.2011.07353.x.
Going the wrong road: Fyn and targeting of amyloid precursor protein to lipid rafts.
Source
Deutsches Institut für Demenzprävention (DIDP), Experimental Neurology, Medical Campus of the Saarland University, Homburg, Germany Department of Medical Chemistry, Biochemistry and Biotechnology, The Medical School, University of Milano, Milano, Italy.
Neurochem Int. 2011 Aug;59(1):59-64. Epub 2011 Jun 7.
Bilobalide regulates soluble amyloid precursor protein release via phosphatidyl inositol 3 kinase-dependent pathway.
Source
Department of Anatomy, Guangzhou Medical University, Guangzhou 510182, China.
Abstract
Bilobalide (BB) is a sesquiterpenoid extracted from Ginkgo biloba leaves. An increasing number of studies have demonstrated its neuroprotective effects. The neuroprotective mechanisms may be associated with modulation of intracellular signaling cascades such as the phosphatidyl inositol 3-kinase (PI3K) pathway. Using differentiated SH-SY5Y cells, this study investigated whether BB modulation of intracellular signaling pathways, such as the protein kinase C (PKC) and PI3K pathways, contributes to amyloid precursor protein (APP) metabolism, a key event in the pathogenesis of Alzheimer's disease (AD). We demonstrated in this study that BB enhanced the secretion of α-secretase-cleaved soluble amyloid precursor protein (sAPPα, a by-product of non-amyloidogenic processing of APP) and decreased the β amyloid protein (Aβ, a by-product of amyloidogenic processing of APP) via PI3K-dependent pathway. The PI3K pathway mediated the rapid effect of BB on APP processing possibly via regulation of intracellular APP trafficking. After longer time BB incubation (12h), this effect was reinforced by PI3K pathway-mediated up-regulation of disintegrin and metalloproteinase domain-containing protein 10 (ADAM10, an α-secretase candidate). Given the strong association between APP metabolism and AD pathogenesis, the ability of BB to regulate APP processing suggests its potential use in AD prevention.
Copyright © 2011 Elsevier B.V. All rights reserved.
FASEB J. 2011 Sep;25(9):3146-56. Epub 2011 Jun 13.
Interaction between amyloid precursor protein and Nogo receptors regulates amyloid deposition.
Source
1 Department of Neurosciences, Lerner Research Institute, Cleveland Clinic, 9500 Euclid Ave./NC30, Cleveland, OH 44195, USA. yanr@ccf.org.
Abstract
Excessive production or accumulation of β-amyloid (Aβ) peptides in human brains leads to increased amyloid deposition and cognitive dysfunction, which are invariable pathological features in patients with Alzheimer's disease (AD). Many cellular factors can regulate the production of Aβ. In this study, we show that a family of proteins named Nogo receptor proteins (NgR1 to NgR3) regulates Aβ production via interaction with amyloid precursor protein (APP). Further mapping of the interacting domain indicates that a small region adjacent to the BACE1 cleavage site of APP mediates interaction of APP with Nogo receptor proteins. Our results also indicate that increased interaction between Nogo receptor and APP reduces surface expression of APP and favors processing of APP by BACE1. When NgR2 was ablated in AD transgenic mice expressing Swedish APP and PS1ΔE9, amyloid deposition was clearly reduced (0.66% of total measured area in APP(swe)/PS1ΔE9/NgR2(-/-) mice vs. 0.76% of total measured area in APP(swe)/PS1ΔE9 mice). Our results demonstrate that down-regulation of NgR expression is a potential approach for inhibiting amyloid deposition in AD patients.-Zhou, X., Hu, X., He, W., Tang, X., Shi, Q., Zhang, Z., Yan, R. Interaction between amyloid precursor protein and Nogo receptors regulates amyloid deposition.
Int J Immunopathol Pharmacol. 2011 Apr-Jun;24(2):529-34.
Platelet amyloid precursor protein isoform expression in Alzheimer's disease: evidence for peripheral marker.
Abstract
Alzheimer's disease (AD) is a chronic neurodegenerative disorder characterized by a progressive cognitive and memory decline. Among peripheral markers of AD, great interest has been focused on the amyloid precursor protein (APP). In this regard, platelets represent an important peripheral source of APP since it has been demonstrated that the three major isoforms, that are constituted of 770, 751 and 695 aa residues, are inserted in the membrane of resting platelets. APP 751 and APP 770 contain a Kunitz-type serine protease inhibitor domain (APP KPI) and APP 695 lacks this domain. To address this issue, we first examined the platelet APP isoform mRNAs prospectively as biomarker for the diagnosis of AD by means of real-time quantitative PCR, and then evaluated the correlation between APP mRNA expression levels and cognitive impairment of enrolled subjects. Differential gene expression measurements in the AD patient group (n=18) revealed a significant up-regulation of APP TOT (1.52-fold), APP KPI (1.32-fold), APP 770 (1.33-fold) and APP 751 (1.26-fold) compared to controls (n=22). Moreover, a statistically significant positive correlation was found between APP mRNA levels (TOT, KPI, 770 and 751) and cognitive impairment. Since AD definitive diagnosis still relies on pathological evaluation at autopsy, the present results are consistent with the hypothesis that platelet APP could be considered a potential reliable peripheral marker for studying AD and could contribute to define a signature for the presence of AD pathology.
Biochemistry. 2011 Jul 19;50(28):6208-16. Epub 2011 Jun 24.
Protein interactions among Fe65, the low-density lipoprotein receptor-related protein, and the amyloid precursor protein.
Source
Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0378, United States.
Abstract
The adapter protein Fe65 has been proposed to be the link between the intracellular domains of the amyloid precursor protein, APP (AICD), and the low-density lipoprotein receptor-related protein (LRP-CT). Functional linkage between these two proteins has been established, and mutations within LRP-CT affect the amount of Aβ produced from APP. Previous work showed that AICD binds to protein interaction domain 2 (PID2) of Fe65. Although the structure of PID1 was determined recently, all attempts to demonstrate LRP-CT binding to this domain failed. We used biophysical experiments and binding studies to investigate the binding among these three proteins. Full-length Fe65 bound more weakly to AICD than did N-terminally truncated forms; however, the intramolecular domain-domain interactions that had been proposed to inhibit binding could not be observed using amide H-D exchange. Surprisingly, when LRP-CT is phosphorylated at Tyr4507, it bound to Fe65 PID1 despite the fact that this domain belongs to the Dab-like subclass of PIDs that are not supposed to be phosphorylation-dependent. Mutation of a critical arginine abolished binding, providing further proof of the phosphorylation dependence. Fe65 PID1 thus provides a link between the Dab-like class and the IRS-like class of PIDs and is the first Dab-like family member to show phosphorylation-dependent binding.
J Phys Chem B. 2011 Jul 28;115(29):9224-35. Epub 2011 Jun 29.
Effects of Cu Ions and Explicit Water Molecules on the Copper Binding Domain ofAmyloid Precursor Protein APP(131-189): A Molecular Dynamics Study.
Source
Department of Chemistry and Chemical Biology, McMaster University , Hamilton, Ontario, Canada L8S 4M1.
Abstract
Amyloid precursor protein (APP) is a cell-surface trans-membrane glycoprotein that appears to play an important role in in vivo Cu ion homeostasis. This protein includes a copper-binding-domain (CuBD) fragment consisting of residues 124-189, of which His147, His151, Tyr168, and possibly Met170 comprise the explicit Cu-binding site (CuBS). Molecular dynamics (MD) simulations are carried out on Cu-free and Cu-bound APP models, based on crystal structures including residues 131-189 obtained from the Protein Data Bank, to confirm the site of Cu-ion binding and to elucidate the effects of the oxidation state of the Cu ions (default GROMACS parameters modeled only the electrostatic binding to the Cu ions at the CuBS) and explicit water molecules on the conformational properties of the 131-189 residue portion of the CuBD. MD trajectory analysis demonstrated a conformational change of Met170. The sulfur atom of Met170 moves closer to the Cu(II) ion and away from Cu(I), and this change may play an important role in the reduction of Cu(II) and the release of Cu(I). Two explicit water molecules were included in the MD simulations. These water molecules that bind strongly to the Cu ions via their lone pair electrons result in a significant modification of the binding interactions with the other residues at the CuBS.
J Biol Chem. 2011 Aug 5;286(31):27741-50. Epub 2011 Jun 6.
Metalloprotease Meprin {beta} Generates Nontoxic N-terminal Amyloid Precursor Protein Fragments in Vivo.
Jefferson T, Causevic M, Auf dem Keller U, Schilling O, Isbert S, Geyer R, Maier W, Tschickardt S, Jumpertz T, Weggen S,Bond JS, Overall CM, Pietrzik CU, Becker-Pauly C.
Source
From Cell and Matrix Biology, Johannes Gutenberg-University, 55128 Mainz, Germany.
Abstract
Identification of physiologically relevant substrates is still the most challenging part in protease research for understanding the biological activity of these enzymes. The zinc-dependent metalloprotease meprin β is known to be expressed in many tissues with functions in health and disease. Here, we demonstrate unique interactions between meprin β and the amyloid precursor protein (APP). Although APP is intensively studied as a ubiquitously expressed cell surface protein, which is involved in Alzheimer disease, its precise physiological role and relevance remain elusive. Based on a novel proteomics technique termed terminal amine isotopic labeling of substrates (TAILS), APP was identified as a substrate for meprin β. Processing of APP by meprin β was subsequently validated using in vitro and in vivo approaches. N-terminal APP fragments of about 11 and 20 kDa were found in human and mouse brain lysates but not in meprin β(-/-) mouse brain lysates. Although these APP fragments were in the range of those responsible for caspase-induced neurodegeneration, we did not detect cytotoxicity to primary neurons treated by these fragments. Our data demonstrate that meprin β is a physiologically relevant enzyme in APP processing.
J Biol Chem. 2011 Jul 22;286(29):26166-77. Epub 2011 Jun 3.
Loss of Cleavage at {beta}'-Site Contributes to Apparent Increase in {beta}-Amyloid Peptide (A{beta}) Secretion by {beta}-Secretase (BACE1)-Glycosylphosphatidylinositol (GPI) Processing of Amyloid Precursor Protein.
Source
From the Departments of Neurobiology, Neurology, and Pathology, The University of Chicago, Chicago, Illinois 60637.
Abstract
Several lines of evidence implicate lipid raft microdomains in Alzheimer disease-associated β-amyloid peptide (Aβ) production. Notably, targeting β-secretase (β-site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1)) exclusively to lipid rafts by the addition of a glycosylphosphatidylinositol (GPI) anchor to its ectodomain has been reported to elevate Aβ secretion. Paradoxically, Aβ secretion is not reduced by the expression of non-raft resident S-palmitoylation-deficient BACE1 (BACE1-4C/A (C474A/C478A/C482A/C485A)). We addressed this apparent discrepancy in raft microdomain-associated BACE1 processing of APP in this study. As previously reported, we found that expression of BACE1-GPI elevated Aβ secretion as compared with wild-type BACE1 (WTBACE1) or BACE1-4C/A. However, this increase occurred without any difference in the levels of APP ectodomain released following BACE1 cleavage (soluble APPβ), arguing against an overall increase in BACE1 processing of APP per se. Further analysis revealed that WTBACE1 cleaves APP at β- and β'-sites, generating +1 and +11 β-C-terminal fragments and secreting intact as well as N-terminally truncated Aβ. In contrast, three different BACE1-GPI chimeras preferentially cleaved APP at the β-site, mainly generating +1 β-C-terminal fragment and secreting intact Aβ. As a consequence, cells expressing BACE1-GPI secreted relatively higher levels of intact Aβ without an increase in BACE1 processing of APP. Markedly reduced cleavage at β'-site exhibited by BACE1-GPI was cell type-independent and insensitive to subcellular localization of APP or the pathogenic KM/NL mutant. We conclude that the apparent elevation in Aβ secretion by BACE1-GPI is mainly attributed to preferential cleavage at the β-site and failure to detect +11 Aβ species secreted by cells expressing WTBACE1.
J Biol Chem. 2011 Jul 8;286(27):24264-74. Epub 2011 May 23.
Soluble amyloid precursor protein induces rapid neural differentiation of human embryonic stem cells.
Source
Department of Neurobiology and Behavior and Institute for Memory Impairments and Neurological Disorders, University of California, Irvine, California 92697, USA.
Abstract
Human embryonic stem cells (hESCs) offer tremendous potential for not only treating neurological disorders but also for their ability to serve as vital reagents to model and investigate human disease. To further our understanding of a key protein involved in Alzheimer disease pathogenesis, we stably overexpressed amyloid precursor protein (APP) in hESCs. Remarkably, we found that APP overexpression in hESCs caused a rapid and robust differentiation of pluripotent stem cells toward a neural fate. Despite maintenance in standard hESC media, up to 80% of cells expressed the neural stem cell marker nestin, and 65% exhibited the more mature neural marker β-3 tubulin within just 5 days of passaging. To elucidate the mechanism underlying the effects of APP on neural differentiation, we examined the proteolysis of APP and performed both gain of function and loss of function experiments. Taken together, our results demonstrate that the N-terminal secreted soluble forms of APP (in particular sAPPβ) robustly drive neural differentiation of hESCs. Our findings not only reveal a novel and intriguing role for APP in neural lineage commitment but also identify a straightforward and rapid approach to generate large numbers of neurons from human embryonic stem cells. These novel APP-hESC lines represent a valuable tool to investigate the potential role of APP in development and neurodegeneration and allow for insights into physiological functions of this protein.
Curr Alzheimer Res. 2011 May 23. [Epub ahead of print]
Alpha-Secretase Cleavage of the Amyloid Precursor Protein: Proteolysis Regulated by Signaling Pathways and Protein Trafficking.
Source
German Center for Neurodegenerative Diseases, 80336 Munich, Germany and 2the Adolf Butenandt- Institute, Biochemistry, Ludwig-Maximilians-University, 80336 Munich, Germany. stefan.lichtenthaler@med.uni-muenchen.de.
Abstract
α-secretase is the name for a metalloprotease activity, which is assumed to play a key role in the prevention of the molecular mechanisms underlying Alzheimer's disease (AD). Proteases similar to α- secretase are essential for a wide range of biological processes, such as cell adhesion and embryonic development. The molecular culprit in AD is the amyloid β peptide (Aβ), which derives from the amyloid precursor protein (APP) through sequential cleavage by the two proteases β and γ-secretase. In contrast, α-secretase, which is the metalloprotease ADAM10, cleaves APP within the Aβ domain, thus preventing Aβ generation. Additionally, it produces a secreted APP ectodomain with neurotrophic and neuroprotective properties. An increase in α-secretase cleavage is considered a therapeutic approach for AD, but the molecular mechanisms regulating α-secretase cleavage are only partly known. Protein kinase C and mitogen-activated protein kinase constitute central signaling hubs for the regulation of α-secretase cleavage. Additionally, recent studies increasingly demonstrate that the correct spatial and temporal localization of the two membrane proteins APP and α-secretase is essential for efficient α-secretase cleavage of APP. This review highlights the role of signaling pathways and protein trafficking in the control of APP α-secretase cleavage.
Prog Neurobiol. 2011 May 12. [Epub ahead of print]
Development of Alzheimer-disease neuroimaging-biomarkers using mouse models with amyloid-precursor protein-transgene expression.
Source
Department of Psychiatry, University of Rostock, Rostock, Germany; DZNE, German Center for Neurodegenerative Diseases, Rostock, Germany.
Abstract
There are important recent developments in Alzheimer's disease (AD) translational research, especially with respect to the imaging of amyloid pathology in vivo using MRI and PET technologies. Here we exploit the most widely used transgenic mouse models of amyloid pathology in order to relate the imaging findings to our knowledge about the histopathological phenotype of these models. The development of new diagnostic criteria of AD necessitates the use of biological markers to diagnose AD even in the absence of overt dementia or early symptomatic mild cognitive impairment. The validity of the diagnosis will depend on the availability of an in vivo marker to reflect underlying neurobiological changes of AD. Transgenic models with essential features of AD pathology and mechanisms provide a test setting for the development and evaluation of new biological imaging markers. Among the best established imaging markers of amyloid pathology in transgenic animals are high-field MRI of brain atrophy, proton spectroscopy of neurochemical changes, high-field MRI of amyloid plaque load, and in vivo plaque imaging using radio-labelled ligands with PET. We discuss the implications of our findings as well as the methodological limitations and the specific requirements of these technologies. We furthermore outline future directions of transgene-imaging research. Transgene imaging is an emerging area of translational research that implies strong multi- and interdisciplinary collaborations. It will become ever more valuable with the introduction of new diagnostic standards and novel treatment approaches which will require valid and reliable biological markers to improve the diagnosis and early treatment of AD patients.
Copyright © 2011. Published by Elsevier Ltd.
FASEB J. 2011 Sep;25(9):2937-46. Epub 2011 May 19.
Inhibitors of {gamma}-secretase stabilize the complex and differentially affect processing of amyloid precursor protein and other substrates.
Source
1 Departments of Psychiatry and Neuroscience, Mt. Sinai School of Medicine, New York University, One Gustave L. Levy Pl., Box 1229, New York, NY 10029, USA. nikos.robakis@mssm.edu.
Abstract
γ-Secretase inhibitors (GSIs) are drugs used in research to inhibit production of Aβ and in clinical trials to treat Alzheimer's disease (AD). They inhibit proteolytic activities of γ-secretase noncompetitively by unknown mechanisms. Here, we used cortical neuronal cultures expressing endogenous levels of enzymes and substrates to study the effects of GSIs on the structure and function of γ-secretase. We show that GSIs stabilize the interactions between the C-terminal fragment of presenilin (PS-CTF), the central component of the γ-secretase complex, and its partners the APH-1/nicastrin and PS1-NTF/PEN-2 subcomplexes. This stabilization dose-dependently correlates with inhibition of N-cadherin cleavage, a process limited by enzyme availability. In contrast, production of amyloid precursor protein (APP) intracellular domain (AICD) is insensitive to low concentrations of GSIs and is limited by substrate availability. Interestingly, APP is processed by both PS1- and PS2-containing γ-secretase complexes, while N-cadherin and ephrinB1 are processed only by PS1-containing complexes. Paradoxically, low concentrations of GSIs specifically increased the levels of Aβ without affecting its catabolism, indicating increased Aβ production. Our data reveal a mechanism of γ-secretase inhibition by GSIs and provide evidence that distinct γ-secretase complexes process specific substrates. Furthermore, our observations have implications for GSIs as therapeutics because processing of functionally important substrates may be inhibited at lower concentrations than Aβ.-Barthet, G., Shioi, J., Shao, Z., Ren, Y., Georgakopoulos, A., Robakis, N. K. Inhibitors of γ-secretase stabilize the complex and differentially affect processing of amyloid precursor protein and other substrates.
J Forensic Sci. 2011 May 19. doi: 10.1111/j.1556-4029.2011.01814.x. [Epub ahead of print]
Axonal Injury in Young Pediatric Head Trauma: A Comparison Study of β-amyloid Precursor Protein (β-APP) Immunohistochemical Staining in Traumatic and Nontraumatic Deaths*
Source
Office of the Chief Medical Examiner (OCME), Urban County Government Center, Louisville, KY. Office of the Chief Medical Examiner, State of Maryland, Baltimore, MD. Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, MD. Departments of Pathology and Neurology, The Johns Hopkins University School of Medicine, Baltimore, MD. Department of Pediatrics, University of Maryland, Baltimore, MD. Key Laboratory of Evidence Science, China University of Political Science and Law, Beijing, China.
Abstract
We tested the independent utility of β- amyloid precursor protein (β-APP) immunohistochemical staining as evidence of brain trauma in the deaths of young children. Blinded reviewers retrospectively reviewed immunostained brain tissues from homicidal deaths, age-matched control cases without evidence of trauma, as well as cases of sudden infant death syndrome (SIDS). The reviewers correctly identified five of the seven cases with documented inflicted head trauma. However, one of seven age-matched control cases and one of 10 SIDS/sudden unexplained death in infancy (SUDI) cases demonstrated staining patterns similar to those seen in cases of inflicted trauma. We discuss these cases and the circumstances surrounding them with the intent to explain the difficulties associated with immunohistological interpretation of axonal injury. Although the utility of β-APP is quite powerful if not confounded by global hypoxic-ischemic injury, ultimately, β-APP studies should be only one piece of information in the determination of cause and manner of death.
© 2011 American Academy of Forensic Sciences.
FASEB J. 2011 Sep;25(9):3208-18. Epub 2011 May 18.
Neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) slows down Alzheimer's disease-like pathology in amyloid precursor protein-transgenic mice.
Rat D, Schmitt U, Tippmann F, Dewachter I, Theunis C, Wieczerzak E, Postina R, van Leuven F, Fahrenholz F, Kojro E.
Source
1 Institute of Pharmacy and Biochemistry, Johannes Gutenberg University, Becherweg 30, D-55128 Mainz, Germany. kojro@uni-mainz.de.
Abstract
Pituitary adenylate cyclase-activating polypeptide (PACAP) has neuroprotective and neurotrophic properties and is a potent α-secretase activator. As PACAP peptides and their specific receptor PAC1 are localized in central nervous system areas affected by Alzheimer's disease (AD), this study aims to examine the role of the natural peptide PACAP as a valuable approach in AD therapy. We investigated the effect of PACAP in the brain of an AD transgenic mouse model. The long-term intranasal daily PACAP application stimulated the nonamyloidogenic processing of amyloid precursor protein(APP) and increased expression of the brain-derived neurotrophic factor and of the antiapoptotic Bcl-2 protein. In addition, it caused a strong reduction of the amyloid β-peptide (Aβ) transporter receptor for advanced glycation end products (RAGE) mRNA level. PACAP, by activation of the somatostatin-neprilysin cascade, also enhanced expression of the Aβ-degrading enzyme neprilysin in the mouse brain. Furthermore, daily PAC1-receptor activation via PACAP resulted in an increased mRNA level of both the PAC1 receptor and its ligand PACAP. Our behavioral studies showed that long-term PACAP treatment of APP[V717I]-transgenic mice improved cognitive function in animals. Thus, nasal application of PACAP was effective, and our results indicate that PACAP could be of therapeutic value in treating AD.-Rat, D., Schmitt, U., Tippmann, F., Dewachter, I., Theunis, C., Wieczerzak, E, Postina, R., van Leuven, F., Fahrenholz, F., Kojro, E. Neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) slows down Alzheimer's disease-like pathology in amyloid precursor protein-transgenic mice.
Hum Cell. 2011 Jun;24(2):104-11. Epub 2011 May 17.
Establishment and characterization of RNA-edited serotonin 2C receptor isoform cell models and alteration of amyloid precursor protein ectodomain secretion in HEK293 APPSwe cells.
Source
School of Pharmacy, Shanghai Jiao Tong University, Shanghai, 200240, China.
Abstract
RNA editing is a mechanism for generating molecular diversity by altering the genetic code at the level of RNA. The 5-HT(2C) receptor is the only G protein-coupled receptor known to be edited. It has been reported that the non-edited 5-HT(2C) receptor stimulates secretion of the APP metabolite APP ectodomain (APPs). However, it remains unknown whether RNA-edited 5-HT(2C) receptors can also affect APPs secretion. In this study, cDNAs of five non-edited or partially/fully edited 5-HT(2C) receptor isoforms (INI, VNI, VNV, VSV and VGV) were stably transfected into HEK293APPSwe cells to detect the cell proliferation and APPs secretion. The results demonstrated that the overexpression of INI and VNI caused increased proliferation of host cells while VNV, VSV and VGV caused inverse effects (P < 0.01). Compared with both control and non-edited isoform INI, APPs levels were significantly increased in the four edited 5-HT(2C) receptor isoforms, VNI (P < 0.05), VNV (P < 0.05), VSV (P < 0.05) and VGV (P < 0.01). These results suggest that the RNA editing of the 5-HT(2C) receptor may affect APPs secretion through different signaling pathways related to cell growth and protein processing, and that these cell models will provide appropriate useful information to study the association between the RNA editing of the serotonin 5-HT(2C) receptor and APP metabolism.
Mol Cell Neurosci. 2011 Jul;47(3):223-32. Epub 2011 May 4.
ERK1-independent α-secretase cut of β-amyloid precursor protein via M1 muscarinic receptors and PKCα/ε.
Source
Université de Nice-Sophia-Antipolis, Institut de Neuro-Médecine Moléculaire, Unité Mixte de Recherche, 6097 Centre National de la Recherche Scientifique, Equipe labellisée Fondation pour la Recherche Médicale, 660 route des lucioles, Sophia-Antipolis, 06560 Valbonne, France.
Abstract
The amyloid precursor protein (βAPP) undergoes several proteolytic cleavages. While β- and γ-secretases are responsible for the production of the 40-43 amino-acid long amyloid β peptide (Aβ), the α-secretase cut performed by the disintegrins ADAM10 and ADAM17, occurs in the middle of the Aβ sequence, thereby preventing its formation and leading to the secretion of the large sAPPα neuroprotective fragment. Here we showed that a series of M1 muscarinic receptor agonists dose-dependently stimulated sAPPα secretion without interfering with βAPP subcellular distribution. Carbachol- and PDBu-induced sAPPα secretions were blocked by the general PKC inhibitor GF109203X. We established that HEK293 and rhabdhomyosarcoma cells overexpressing constitutively active (CA) PKCα or PKCε secrete increased amounts of sAPPα while those expressing PKCδ were unable to modify sAPPα recovery. Conversely, the overexpression of PKCα or PKCε dominant negative (DN) constructs abolished PDBU-stimulated sAPPα secretion, whereas DN-PKCδ remained inert. In agreement, PKCα knockout lowered sAPPα recovery in primary cultured fibroblasts. We also demonstrated that the regulated α-secretase processing of βAPP is not controlled by the Extracellular-Regulated Kinase-1/MAP-ERK Kinase (ERK1/MEK) cascade and likely does not require ADAM17 phosphorylation on its threonine735 residue. Because the muscarinic-dependent α-secretase-like processing of PrP(c) is fully dependent on ADAM17 phosphorylation on its threonine735 residue by ERK1, these results indicate that a single extracellular signal triggers ADAM17-dependent regulated cleavages of βAPP and PrP(c) through distinct signalling cascades. This opens new potential therapeutic strategies aimed, in the context of Alzheimer's disease, at selectively activating ADAM17 towards βAPP without affecting the cleavages of its numerous other substrates.
Copyright © 2011 Elsevier Inc. All rights reserved.
Curr Alzheimer Res. 2011 Jun 1;8(4):385-92.
Tolfenamic Acid Interrupts the De Novo Synthesis of the β-Amyloid Precursor Proteinand Lowers Amyloid Beta Via a Transcriptional Pathway.
Source
Department of Biomedical and Pharmaceutical Sciences, University of Rhode Island, Fogarty Hall 41 Lower College Rd. Kingston, RI 02881; USA. nzawia@uri.edu.
Abstract
Amyloid beta (Aβ) peptides are related to the pathogenesis of Alzheimer's disease (AD). The search for therapeutic strategies that lower these peptides has mainly focused on the proteolytic processing of the β-amyloid precursor protein(APP), and other post-transcriptional pathways. The transcription factor specificity protein 1 (Sp1) is vital for the regulation of several genes involved in AD including APP and the beta site APP cleaving enzyme 1 (BACE1). We have previously reported that tolfenamic acid promotes the degradation of Sp1 protein (SP1) in pancreatic human cancer cells and mice tumors. This study examines the ability of tolfenamic acid to reduce SP1 levels, and thereby decrease APP transcription and Aβ levels in rodent brains. Tolfenamic acid was administered by oral gavage to C57BL/6 mice at variable dosages and for different time periods. Results have shown that tolfenamic acid was able to down regulate brain protein levels of SP1, APP, and Aβ. These findings demonstrate that interference with upstream transcriptional pathways can lower pathogenic intermediates associated with AD, and thus tolfenamic acid represents a novel approach for the development of a therapeutic intervention for AD.
PLoS One. 2011 Apr 27;6(4):e18754.
Amyloid precursor protein is trafficked and secreted via synaptic vesicles.
Source
Department of Membrane Biophysics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.
Abstract
A large body of evidence has implicated amyloid precursor protein (APP) and its proteolytic derivatives as key players in the physiological context of neuronal synaptogenesis and synapse maintenance, as well as in the pathology of Alzheimer's Disease (AD). Although APP processing and release are known to occur in response to neuronal stimulation, the exact mechanism by which APP reaches the neuronal surface is unclear. We now demonstrate that a small but relevant number of synaptic vesicles contain APP, which can be released during neuronal activity, and most likely represent the major exocytic pathway of APP. This novel finding leads us to propose a revised model of presynaptic APP trafficking that reconciles existing knowledge on APP with our present understanding of vesicular release and recycling.
Int J Alzheimers Dis. 2011 Mar 17;2011:134971.
Impacts of membrane biophysics in Alzheimer's disease: from amyloid precursor protein processing to aβ Peptide-induced membrane changes.
Source
Department of Biological Engineering, University of Missouri, Columbia, MO 65211, USA.
Abstract
An increasing amount of evidence supports the notion that cytotoxic effects of amyloid-β peptide (Aβ), the main constituent of senile plaques in Alzheimer's disease (AD), are strongly associated with its ability to interact with membranes of neurons and other cerebral cells. Aβ is derived from amyloidogenic cleavage of amyloid precursor protein(AβPP) by β- and γ-secretase. In the nonamyloidogenic pathway, AβPP is cleaved by α-secretases. These two pathways compete with each other, and enhancing the non-amyloidogenic pathway has been suggested as a potential pharmacological approach for the treatment of AD. Since AβPP, α-, β-, and γ-secretases are membrane-associated proteins, AβPP processing and Aβ production can be affected by the membrane composition and properties. There is evidence that membrane composition and properties, in turn, play a critical role in Aβ cytotoxicity associated with its conformational changes and aggregation into oligomers and fibrils. Understanding the mechanisms leading to changes in a membrane's biophysical properties and how they affect AβPP processing and Aβ toxicity should prove to provide new therapeutic strategies for prevention and treatment of AD.
J Neurochem. 2011 Sep;118(5):879-90. doi: 10.1111/j.1471-4159.2011.07296.x. Epub 2011 May 25.
Fyn kinase regulates the association between amyloid precursor protein and Dab1 by promoting their localization to detergent-resistant membranes.
Source
Department of Neuroscience, Georgetown University Medical Center, Washington, District of Columbia, USA Department of Neurology, Georgetown University Medical Center, Washington, District of Columbia, USA.
Abstract
J. Neurochem. (2011) 118, 879-890. ABSTRACT: The adaptor protein Disabled1 (Dab1) interacts with amyloid precursor protein (APP) and decreases its pathological processing, an effect mediated by Fyn tyrosine kinase. Fyn is highly enriched in lipid rafts, a major site of pathological APP processing. To investigate the role of Fyn in the localization and phosphorylation of APP and Dab1 in lipid rafts, we isolated detergent-resistant membrane (DRM) fractions from wild-type and Fyn knock-out mice. In wild-type mice, all of the Fyn kinase, 17% of total APP, and 33% of total Dab1 were found in DRMs. Nearly all of the tyrosine phosphorylated forms of APP and Dab1 were in DRMs. APP and Dab1 co-precipitated both in and out of DRM fractions, indicating an association that is independent of subcellular localization. Fyn knock-out mice had decreased APP, Dab1, and tyrosine-phosphorylated Dab1 in DRMs but increased co-immunoprecipitation of DRM APP and Dab1. Expression of phosphorylation deficient APP or Dab1 constructs revealed that phosphorylation of APP increases, whereas phosphorylation of Dab1 decreases, the interaction between APP and Dab1. Consistent with these observations, Reelin treatment led to increased Dab1 phosphorylation and decreased association between APP and Dab1. Reelin also caused increased localization of APP and Dab1 to DRMs, an effect that was not seen in Fyn knock-out neurons. These findings suggest that Reelin treatment promotes the localization of APP and Dab1 to DRMs, and affects their phosphorylation by Fyn, thus regulating their interaction.
© 2011 The Authors. Journal of Neurochemistry © 2011 International Society for Neurochemistry.
Mol Neurodegener. 2011 Apr 28;6(1):27.
Biology and pathophysiology of the amyloid precursor protein.
Source
Huffington Center on Aging and Department of Molecular & Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA. huiz@bcm.edu.
Abstract
ABSTRACT: The amyloid precursor protein (APP) plays a central role in the pathophysiology of Alzheimer's disease in large part due to the sequential proteolytic cleavages that result in the generation of β-amyloid peptides (Aβ). Not surprisingly, the biological properties of APP have also been the subject of great interest and intense investigations. Since our 2006 review, the body of literature on APP continues to expand, thereby offering further insights into the biochemical, cellular and functional properties of this interesting molecule. Sophisticated mouse models have been created to allow in vivo examination of cell type-specific functions of APP together with the many functional domains. This review provides an overview and update on our current understanding of the pathobiology of APP.
Anesth Analg. 2011 Jul;113(1):145-52. Epub 2011 Apr 25.
The potential dual effects of anesthetic isoflurane on hypoxia-induced caspase-3 activation and increases in β-site amyloid precursor protein-cleaving enzyme levels.
Source
Geriatric Anesthesia Research Unit, Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Harvard Medical School, 149 13th St., Room 4310, Charlestown, MA 02129-2060, USA.
Abstract
BACKGROUND:
β-Amyloid protein (Aβ) accumulation, caspase activation, apoptosis, and hypoxia-induced neurotoxicity have been suggested to be involved in Alzheimer disease neuropathogenesis. Aβ is produced from amyloid precursor protein through proteolytic processing by the aspartyl protease β-site amyloid precursor protein-cleaving enzyme (BACE) and γ-secretase. Inhaled anesthetics have long been considered to protect against neurotoxicity. However, recent studies have suggested that the inhaled anesthetic isoflurane may promote neurotoxicity by inducing caspase activation and apoptosis, and by increasing levels of BACE and Aβ. We therefore sought to determine whether isoflurane can induce concentration-dependent dual effects on hypoxia-induced caspase-3 activation and increases in BACE levels: protection versus promotion.
METHODS:
H4 human neuroglioma cells were treated with hypoxia (3% O(2)) alone, different concentrations of isoflurane (0.5% and 2%), and the combination of hypoxia and 0.5% or 2% isoflurane. The levels of caspase-3 cleavage (activation), BACE, and Bcl-2 were determined by Western blot analysis.
RESULTS:
We show for the first time that treatment with 0.5% isoflurane for 8 hours attenuated, whereas treatment with 2% isoflurane for 8 hours enhanced, hypoxia-induced caspase-3 activation and increases in BACE levels. The 2% isoflurane treatment also enhanced a hypoxia-induced decrease in Bcl-2 levels.
CONCLUSIONS:
These results suggest a potential concept that isoflurane has dual effects (protection versus promotion) on hypoxia-induced toxicity, which may act through Bcl-2 family proteins. These findings could lead to more systematic studies to determine the potential dual effects of anesthetics on Alzheimer disease-associated neurotoxicity.
PMID:
BMC Physiol. 2011 Apr 25;11:7.
Expression of human amyloid precursor protein in the skeletal muscles of Drosophila results in age- and activity-dependent muscle weakness.
Source
Molecular and Cellular Biology Program, University of Massachusetts, Amherst, MA 01003, USA.
Abstract
BACKGROUND:
One of the hallmarks of Alzheimer's disease, and several other degenerative disorders such as Inclusion Body Myositis, is the abnormal accumulation of amyloid precursor protein (APP) and its proteolytic amyloid peptides. To better understand the pathological consequences of inappropriate APP expression on developing tissues, we generated transgenic flies that express wild-type human APP in the skeletal muscles, and then performed anatomical, electrophysiological, and behavioral analysis of the adults.
RESULTS:
We observed that neither muscle development nor animal longevity was compromised in these transgenic animals. However, human APP expressing adults developed age-dependent defects in both climbing and flying. We could advance or retard the onset of symptoms by rearing animals in vials with different surface properties, suggesting that human APP expression-mediated behavioral defects are influenced by muscle activity. Muscles from transgenic animals did not display protein aggregates or structural abnormalities at the light or transmission electron microscopic levels. In agreement with genetic studies performed with developing mammalian myoblasts, we observed that co-expression of the ubiquitin E3 ligase Parkin could ameliorate human APP-induced defects.
CONCLUSIONS:
These data suggest that: 1) ectopic expression of human APP in fruit flies leads to age- and activity-dependent behavioral defects without overt changes to muscle development or structure; 2) environmental influences can greatly alter the phenotypic consequences of human APP toxicity; and 3) genetic modifiers of APP-induced pathology can be identified and analyzed in this model.
EMBO Mol Med. 2011 May;3(5):291-302. doi: 10.1002/emmm.201100138. Epub 2011 Apr 15.
Amyloid precursor protein mutation E682K at the alternative β-secretase cleavage β'-site increases Aβ generation.
Zhou L, Brouwers N, Benilova I, Vandersteen A, Mercken M, Van Laere K, Van Damme P, Demedts D, Van Leuven F,Sleegers K, Broersen K, Van Broeckhoven C, Vandenberghe R, De Strooper B.
Source
Department for Developmental and Molecular Genetics, VIB, Leuven, Belgium.
Abstract
BACE1 cleaves the amyloid precursor protein (APP) at the β-cleavage site (Met(671) -Asp(672) ) to initiate the generation of amyloid peptide Aβ. BACE1 is also known to cleave APP at a much less well-characterized β'-cleavage site (Tyr(681) -Glu(682) ). We describe here the identification of a novel APP mutation E682K located at this β'-site in an early onset Alzheimer's disease (AD) case. Functional analysis revealed that this E682K mutation blocked the β'-site and shifted cleavage of APP to the β-site, causing increased Aβ production. This work demonstrates the functional importance of APP processing at the β'-site and shows how disruption of the balance between β- and β'-site cleavage may enhance the amyloidogenic processing and consequentially risk for AD. Increasing exon- and exome-based sequencing efforts will identify many more putative pathogenic mutations without conclusive segregation-based evidence in a single family. Our study shows how functional analysis of such mutations allows to determine the potential pathogenic nature of these mutations. We propose to classify the E682K mutation as probable pathogenic awaiting further independent confirmation of its association with AD in other patients.
J Neuropathol Exp Neurol. 2011 May;70(5):360-76.
Brain oligomeric β-amyloid but not total amyloid plaque burden correlates with neuronal loss and astrocyte inflammatory response in amyloid precursor protein/tau transgenic mice.
DaRocha-Souto B, Scotton TC, Coma M, Serrano-Pozo A, Hashimoto T, Serenó L, Rodríguez M, Sánchez B, Hyman BT,Gómez-Isla T.
Source
Neurology Department, Massachusetts General Hospital, Harvard University, Boston, Massachusetts 02114, USA.
Abstract
It has long been assumed that β-amyloid (Aβ) had to assemble into fibrillar amyloid plaques to exert its neurotoxic effects in Alzheimer disease. An alternative hypothesis is that soluble oligomers ofAβ play a much larger role in neuronal damage than the insoluble component. We have tested these competing hypotheses in vivo by studying the clinicopathologic correlates of oligomeric Aβ species and classic fibrillar amyloid plaques in the brains of double-transgenic APP-tau mice up to 17 months of age. Biochemical and immunohistochemical measures of brain oligomeric Aβ exponentially increased with age. Oligomeric Aβ load correlated with morphological markers of fibrillar Aβ deposition. In contrast to total amyloid plaque burden, the amount of oligomeric Aβ deposits labeled by the conformational epitope-specific antibody Nab61 closely correlated with neuronal loss and numbers of astrocytes in the entorhinal cortex and the CA1 hippocampal subfield. However, like other morphological Aβ measurements, brain oligomeric Aβ burden did not correlate well with memory deficits in these mice. The number of glial fibrillary acidic protein-positive astrocytes in entorhinal cortex and CA1 most tightly correlated with memory impairment and neuronal cell loss. Based on these findings, we hypothesize that the astrocyte response, which is likely triggered by brain oligomeric Aβ accumulation, adversely affects cognition and might also contribute to neuronal cell death in this model.
PLoS One. 2011 Mar 31;6(3):e17966.
Herpes simplex virus dances with amyloid precursor protein while exiting the cell.
Source
Department of Pathology and Laboratory Medicine, Alpert Medical School of Brown University, Providence, Rhode Island, United States of America.
Abstract
Herpes simplex type 1 (HSV1) replicates in epithelial cells and secondarily enters local sensory neuronal processes, traveling retrograde to the neuronal nucleus to enter latency. Upon reawakening newly synthesized viral particles travel anterograde back to the epithelial cells of the lip, causing the recurrent cold sore. HSV1 co-purifies with amyloid precursor protein (APP), a cellular transmembrane glycoprotein and receptor for anterograde transport machinery that when proteolyzed produces A-beta, the major component of senile plaques. Here we focus on transport inside epithelial cells of newly synthesized virus during its transit to the cell surface. We hypothesize that HSV1 recruits cellular APP during transport. We explore this with quantitative immuno-fluorescence, immuno-gold electron-microscopy and live cell confocal imaging. After synchronous infection most nascent VP26-GFP-labeled viral particles in the cytoplasm co-localize with APP (72.8+/-6.7%) and travel together with APP inside living cells (81.1+/-28.9%). This interaction has functional consequences: HSV1 infection decreases the average velocity of APP particles (from 1.1+/-0.2 to 0.3+/-0.1 µm/s) and results in APP mal-distribution in infected cells, while interplay with APP-particles increases the frequency (from 10% to 81% motile) and velocity (from 0.3+/-0.1 to 0.4+/-0.1 µm/s) of VP26-GFP transport. In cells infected with HSV1 lacking the viral Fc receptor, gE, an envelope glycoprotein also involved in viral axonal transport, APP-capsid interactions are preserved while the distribution and dynamics of dual-label particles differ from wild-type by both immuno-fluorescence and live imaging. Knock-down of APP with siRNA eliminates APP staining, confirming specificity. Our results indicate that most intracellular HSV1 particles undergo frequent dynamic interplay with APP in a manner that facilitates viral transport and interferes with normal APP transport and distribution. Such dynamic interactions between APP and HSV1 suggest a mechanistic basis for the observed clinical relationship between HSV1 seropositivity and risk of Alzheimer's disease.
Cysteine 27 variant of the delta-opioid receptor affects amyloid precursor proteinprocessing through altered endocytic trafficking.
Sarajärvi T, Tuusa JT, Haapasalo A, Lackman JJ, Sormunen R, Helisalmi S, Roehr JT, Parrado AR, Mäkinen P, Bertram L, Soininen H, Tanzi RE, Petäjä-Repo UE, Hiltunen M.
Source
Institute of Clinical Medicine-Neurology, University of Eastern Finland, and Department of Neurology, Kuopio University Hospital, FI-70211 Kuopio, Finland.
Abstract
Agonist-induced activation of the δ-opioid receptor (δOR) was recently shown to augment β- and γ-secretase activities, which increased the production of β-amyloid peptide (Aβ), known to accumulate in the brain tissues of Alzheimer's disease (AD) patients. Previously, the δOR variant with a phenylalanine at position 27 (δOR-Phe27) exhibited more efficient receptor maturation and higher stability at the cell surface than did the less common cysteine (δOR-Cys27) variant. For this study, we expressed these variants in human SH-SY5Y and HEK293 cells expressing exogenous or endogenous amyloid precursor protein (APP) and assessed the effects on APP processing. Expression of δOR-Cys27, but not δOR-Phe27, resulted in a robust accumulation of the APP C83 C-terminal fragment and the APP intracellular domain, while the total soluble APP and, particularly, the β-amyloid 40 levels were decreased. These changes upon δOR-Cys27 expression coincided with decreased localization of APP C-terminal fragments in late endosomes and lysosomes. Importantly, a long-term treatment with a subset of δOR-specific ligands or a c-Src tyrosine kinase inhibitor suppressed the δOR-Cys27-induced APP phenotype. These data suggest that an increased constitutive internalization and/or concurrent signaling of the δOR-Cys27 variant affects APP processing through altered endocytic trafficking of APP.
J Mol Biol. 2011 Jun 3;409(2):189-201. Epub 2011 Apr 2.
The crystal structure of death receptor 6 (DR6): a potential receptor of the amyloid precursor protein (APP).
Source
Leibniz Institute for Age Research-Fritz Lipmann Institut, Protein Crystallography Group, Beutenbergstr. 11, 07745 Jena, Germany.
Abstract
Death receptors belong to the tumor necrosis factor receptor (TNFR) super family and are intimately involved in the signal transduction during apoptosis, stress response and cellular survival. Here we present the crystal structure of recombinantly expressed death receptor six (DR6), one family member that was recently shown to bind to the amyloid precursor protein (APP) and hence to be probably involved in the development of Alzheimer's disease. The extracellular cysteine rich region of DR6, the typical ligand binding region of all TNFRs, was refined to 2.2 Å resolution and shows that its four constituting cysteine rich domains (CRDs) are arranged in a rod-like overall structure, which presents DR6-specific surface patches responsible for the exclusive recognition of its ligand(s). Based on the structural data, the general ligand binding modes of TNFRs and molecular modeling experiments we were able to elucidate structural features of the potential DR6-APP signaling complex.
Copyright © 2011 Elsevier Ltd. All rights reserved.
J Biol Chem. 2011 May 27;286(21):18414-25. Epub 2011 Apr 1.
Age-dependent accumulation of soluble amyloid beta (Abeta) oligomers reverses the neuroprotective effect of soluble amyloid precursor protein-alpha (sAPP(alpha)) by modulating phosphatidylinositol 3-kinase (PI3K)/Akt-GSK-3beta pathway in Alzheimer mouse model.
Jimenez S, Torres M, Vizuete M, Sanchez-Varo R, Sanchez-Mejias E, Trujillo-Estrada L, Carmona-Cuenca I, Caballero C,Ruano D, Gutierrez A, Vitorica J.
Source
Departamento Bioquímica y Biología Molecular, Facultad de Farmacia, Universidad de Sevilla, 41012 Sevilla, Spain.
Abstract
Neurotrophins, activating the PI3K/Akt signaling pathway, control neuronal survival and plasticity. Alterations in NGF, BDNF, IGF-1, or insulin signaling are implicated in the pathogenesis of Alzheimer disease. We have previously characterized a bigenic PS1×APP transgenic mouse displaying early hippocampal Aβ deposition (3 to 4 months) but late (17 to 18 months) neurodegeneration of pyramidal cells, paralleled to the accumulation of soluble Aβ oligomers. We hypothesized that PI3K/Akt/GSK-3β signaling pathway could be involved in this apparent age-dependent neuroprotective/neurodegenerative status. In fact, our data demonstrated that, as compared with age-matched nontransgenic controls, the Ser-9 phosphorylation of GSK-3β was increased in the 6-month PS1×APP hippocampus, whereas in aged PS1×APP animals (18 months), GSK-3β phosphorylation levels displayed a marked decrease. Using N2a and primary neuronal cell cultures, we demonstrated that soluble amyloid precursor protein-α (sAPPα), the predominant APP-derived fragment in young PS1×APP mice, acting through IGF-1 and/or insulin receptors, activated the PI3K/Akt pathway, phosphorylated the GSK-3β activity, and in consequence, exerted a neuroprotective action. On the contrary, several oligomeric Aβ forms, present in the soluble fractions of aged PS1×APP mice, inhibited the induced phosphorylation of Akt/GSK-3β and decreased the neuronal survival. Furthermore, synthetic Aβ oligomers blocked the effect mediated by different neurotrophins (NGF, BDNF, insulin, and IGF-1) and sAPPα, displaying high selectivity for NGF. In conclusion, the age-dependent appearance of APP-derived soluble factors modulated the PI3K/Akt/GSK-3β signaling pathway through the major neurotrophin receptors. sAPPα stimulated and Aβ oligomers blocked the prosurvival signaling. Our data might provide insights into the selective vulnerability of specific neuronal groups in Alzheimer disease.
Eur J Cell Biol. 2011 Apr 1. [Epub ahead of print]
The amyloid precursor protein and its homologues: Structural and functional aspects of native and pathogenic oligomerization.
Source
Institut für Chemie und Biochemie, Freie Universität Berlin, Thielallee 63, 14195 Berlin, Germany.
Abstract
Over the last 25 years, remarkable progress has been made not only in identifying key molecules of Alzheimer's disease but also in understanding their meaning in the pathogenic state. One hallmark of Alzheimer pathology is the amyloid plaque. A major component of the extracellular deposit is the amyloid-β (Aβ) peptide which is generated from its larger precursor molecule, i.e., the amyloid precursor protein (APP) by consecutive cleavages. Processing is exerted by two enzymes, i.e., the β-secretase and the γ-secretase. We and others have found that the self-association of the amyloid peptide and the dimerization and oligomerization of these proteins is a key factor under native and pathogenic conditions. In particular, the Aβ homodimer represents a nidus for plaque formation and a well defined therapeutic target. Further, dimerization of the APP was reported to increase generation of toxic Aβ whereas heterodimerization with its homologues amyloid precursor like proteins (APLP1 and APLP2) decreased Aβ formation. This review mainly focuses on structural features of the homophilic and heterophilic interactions among APP family proteins. The proposed contact sites are described and the consequences of protein dimerization on their functions and in the pathogenesis of Alzheimer's disease are discussed.
Copyright © 2011 Elsevier GmbH. All rights reserved.
Mol Cell Endocrinol. 2011 Jun 6;339(1-2):72-80. Epub 2011 Mar 31.
Thyroid hormone suppression of β-amyloid precursor protein gene expression in the brain involves multiple epigenetic regulatory events.
Source
Department of Physiology and Biophysics, Robert Wood Johnson Medical School, UMDNJ, Piscataway, NJ 08854, USA.
Abstract
Thyroid hormone (T3) suppresses cerebral gene expression of the β-amyloid precursor protein (APP), an integral membrane protein that plays a key role in the onset and progression of Alzheimer's disease. However, the mechanisms by which T3 signaling pathways inhibit APP gene transcription in the brain remain unclear. By carrying out chromatin immunoprecipitation with neuroblastoma cells and primary rat brain tissue, we show for the first time that thyroid hormone receptors (TRs) directly bind at the APP gene in vivo at a promoter region containing a negative T3-response element. We further show that T3 treatment decreases both histone H3 acetylation and histone H3 lysine 4 methylation at the APP promoter and that chemical inhibitors of histone deacetylases and histone lysine demethylase abrogate T3-dependent APP silencing. Our findings thus suggest that TRs actively facilitate T3-dependent silencing of APP gene expression via the recruitment of distinct histone modifying enzymes associated with transcriptional repression.
Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.
FEBS Lett. 2011 Apr 20;585(8):1243-8. Epub 2011 Mar 30.
Alterations of cyclin dependent kinase 5 expression and phosphorylation in amyloid precursor protein (APP)-transfected PC12 cells.
Source
Department of Cellular Signaling, Mossakowski Medical Research Centre Polish Academy of Sciences, Pawinskiego 5, 02-106 Warsaw, Poland. grzegorz@cmdik.pan.pl
Abstract
The aim of the present study was to analyse the alterations of cyclin dependent kinase 5 (Cdk5) expression and phosphorylation in PC12 cells overexpressing amyloid precursor protein (APP). Our results demonstrated enhanced cell death and increased levels of mRNA for the Cdk5 gene in APP-transfected cells. Significantly decreased phosphorylation of Cdk5 at Tyr15 was observed in APPsw cells, which is responsible for a reduction in Cdk5 activity. Cdk5-dependent phosphorylation of glycogen synthase kinase-3β (Gsk-3β) at Ser9 was also decreased, which can lead to the increase of Gsk-3β activity and hyperphosphorylation of MAP tau. Our results demonstrate for the first time, a deregulation of Cdk5 phosphorylation in APP-transfected cells.
Copyright © 2011 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.
Annu Rev Neurosci. 2011;34:185-204.
Amyloid precursor protein processing and Alzheimer's disease.
Source
Department of Neurology, Johns Hopkins Bayview Medical Center, USA. robrien@jhmi.edu
Abstract
Alzheimer's disease (AD), the leading cause of dementia worldwide, is characterized by the accumulation of the β-amyloid peptide (Aβ) within the brain along with hyperphosphorylated and cleaved forms of the microtubule-associated protein tau. Genetic, biochemical, and behavioral research suggest that physiologic generation of the neurotoxic Aβ peptide from sequential amyloid precursor protein (APP) proteolysis is the crucial step in the development of AD. APP is a single-pass transmembrane protein expressed at high levels in the brain and metabolized in a rapid and highly complex fashion by a series of sequential proteases, including the intramembranous γ-secretase complex, which also process other key regulatory molecules. Why Aβ accumulates in the brains of elderly individuals is unclear but could relate to changes in APP metabolism or Aβ elimination. Lessons learned from biochemical and genetic studies of APP processing will be crucial to the development of therapeutic targets to treat AD.
J Biol Chem. 2011 May 6;286(18):15989-97. Epub 2011 Mar 22.
Large quantities of Abeta peptide are constitutively released during amyloid precursor protein metabolism in vivo and in vitro.
Moghekar A, Rao S, Li M, Ruben D, Mammen A, Tang X, O'Brien RJ.
Source
Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Abstract
The metabolism of the amyloid precursor protein (APP) has been extensively investigated because its processing generates the amyloid-β-peptide (Aβ), which is a likely cause of Alzheimer disease. Much prior research has focused on APP processing using transgenic constructs and heterologous cell lines. Work to date in native neuronal cultures suggests that Aβ is produced in very large amounts. We sought to investigate APP metabolism and Aβ production simultaneously under more physiological conditions in vivo and in vitro using cultured rat cortical neurons and live pigs. We found in cultured neurons that both APP and Aβ are secreted rapidly and at extremely high rates into the extracellular space (2-4 molecules/neuron/s for Aβ). Little APP is degraded outside of the pathway that leads to extracellular release. Two metabolic pools of APP are identified, one that is metabolized extremely rapidly (t1/2;) = 2.2 h), and another, surface pool, composed of both synaptic and extrasynaptic elements, that turns over very slowly. Aβ release and accumulation in the extracellular medium can be accounted for stoichiometrically by the extracellular release of β-cleaved forms of the APP ectodomain. Two α-cleavages of APP occur for every β-cleavage. Consistent with the results seen in cultured neurons, an extremely high rate of Aβ production and secretion from the brain was seen in juvenile pigs. In summary, our experiments show an enormous and rapid production and extracellular release of Aβ and the soluble APP ectodomain. A small, slowly metabolized, surface pool of full-length APP is also identified.
PLoS One. 2011 Mar 22;6(3):e18006.
The intracellular threonine of amyloid precursor protein that is essential for docking of Pin1 is dispensable for developmental function.
Source
Department of Microbiology and Immunology, Einstein College of Medicine, Bronx, New York, United States of America.
Abstract
BACKGROUND:
Processing of Aβ-precursor protein (APP) plays an important role in Alzheimer's Disease (AD) pathogenesis. Thr residue at amino acid 668 of the APP intracellular domain (AID) is highly conserved. When phosphorylated, this residue generates a binding site for Pin1. The interaction of APP with Pin1 has been involved in AD pathogenesis.
METHODOLOGY/PRINCIPAL FINDINGS:
To dissect the functions of this sequence in vivo, we created an APP knock-in allele, in which Thr(668) is replaced by an Ala (T(668)A). Doubly deficient APP/APP-like protein 2 (APLP2) mice present postnatal lethality and neuromuscular synapse defects. Previous work has shown that the APP intracellular domain is necessary for preventing early lethality and neuromuscular junctions (NMJ) defects. Crossing the T(668)A allele into the APLP2 knockout background showed that mutation of Thr(668) does not cause a defective phenotype. Notably, the T(668)A mutant APP is able to bind Mint1.
CONCLUSIONS/SIGNIFICANCE:
Our results argue against an important role of the Thr(668) residue in the essential function of APP in developmental regulation. Furthermore, they indicate that phosphorylation at this residue is not functionally involved in those APP-mediated functions that prevent (NMJ) defects and early lethality in APLP2 null mice.
Behav Brain Res. 2011 Sep 12;222(1):169-75. Epub 2011 Apr 1.
Spatial learning and memory impairment and increased locomotion in a transgenicamyloid precursor protein mouse model of Alzheimer's disease.
Source
Department of Psychological Sciences, 210 McAlester Hall, University of Missouri, Columbia, MO 65211, USA.
Abstract
This study provides an examination of spatial learning and a behavioral assessment of irritability and locomotion in TgCRND8 mice, an amyloid precursor protein transgenic model of Alzheimer's disease. Performance was assessed using the Barnes maze, the touch escape test, and an open-field test. While past research focused primarily on 2-5-month-old TgCRND8 mice, the present study used an older age cohort (9-month-old female mice), in addition to a 4-month-old cohort of both transgenic (Tg) and wildtype female mice. Both younger and older Tg mice displayed poor spatial learning in the Barnes maze task compared to their wildtype littermates, as demonstrated by significantly longer latencies and more errors both during acquisition and at a 2-week retest. No differences in irritability were found between Tg and control mice in the younger cohort; however, older Tg mice displayed significantly higher irritability compared with wildtype littermates, as measured by the touch escape test. Additionally, Tg mice of both age cohorts showed increased locomotion and slowed habituation during a 60-min open-field test over 3 days of testing. These results demonstrate that TgCRND8 mice show significant deficits in spatial and nonspatial behavioral tasks at advanced stages of amyloid pathology.
Copyright © 2011 Elsevier B.V. All rights reserved.
J Mol Biol. 2011 May 20;408(5):879-95. Epub 2011 Mar 31.
Molecular determinants and thermodynamics of the amyloid precursor proteintransmembrane domain implicated in Alzheimer's disease.
Source
Department of Structural and Chemical Biology, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029, USA.
Abstract
The deposition of toxic amyloid-β (Aβ) peptide aggregates in the brain is a hallmark of Alzheimer's disease. The intramembrane proteolysis by γ-secretase of the amyloid precursor protein β-carboxy-terminal fragment (APP-βCTF) constitutes the final step in the production of Aβ peptides. Mounting evidence suggests that APP-βCTF is a transmembrane domain (TMD) dimer, and that dimerization might modulate the production of Aβ species that are prone to aggregation and are therefore most toxic. We combined experimental and computational approaches to study the molecular determinants and thermodynamics of APP-βCTF dimerization, and we produced a unifying structural model that reconciles much of the published data. Using a cell assay that exploits a dimerization-dependent activator of transcription, we identified specific dimerization-affecting mutations located mostly at the N-terminus of the TMD of APP-βCTF. The ability of selected mutants to affect the dimerization of full-length APP-βCTF was confirmed by fluorescence resonance energy transfer experiments. Free-energy estimates of the wild type and mutants of the TMD of APP-βCTF derived from enhanced molecular dynamics simulations showed that the dimeric state is composed of different arrangements, in which either (709)GXXXA(713) or (700)GXXXG(704)GXXXG(708) interaction motifs can engage in symmetric or asymmetric associations. Mutations along the TMD of APP-βCTF were found to modulate the relative free energy of the dimeric configurations and to differently affect the distribution of interfaces within the dimeric state. This observation might have important biological implications, since dimers with a different arrangement of the transmembrane helices are likely to be recognized differently by γ-secretase and to lead to a variation in Aβ levels.
Copyright © 2011 Elsevier Ltd. All rights reserved.
Neurobiol Dis. 2011 Jul;43(1):176-83. Epub 2011 Apr 3.
Decreased expression of GGA3 Protein in Alzheimer's disease frontal cortex and increased co-distribution of BACE with the amyloid precursor protein.
Source
Department of Pathology, The University of Melbourne, Parkville, Victoria, Australia.
Abstract
BACE initiates the amyloidogenic processing of the amyloid precursor protein (APP) that results in the production of Aβ peptides associated with Alzheimer's disease (AD). Previous studies have indicated that BACE is elevated in the frontal cortex of AD patients. Golgi-localized γ-ear containing ADP ribosylation factor-binding proteins (GGA) control the cellular trafficking of BACE and may alter its levels. To investigate a link between BACE and GGA expression in AD, frontal cortex samples from AD (N = 20) and healthy, age-matched controls (HC, N =17) were analyzed by immunoblotting. After normalization to the neuronal marker β-tubulin III, the data indicate an average two-fold increase of BACE protein (p = 0.01) and a 64% decrease of GGA3 in the AD group compared to the HC (p = 0.006). GGA1 levels were also decreased in AD, but a statistical significance was not achieved. qRT-PCR analysis of GGA3 mRNA showed no difference between AD and HC. There was a strong correlation between GGA1 and GGA3 in both AD and HC, but no correlation between BACE and GGA levels. Subcellular fractionation of AD cortex with low levels of GGA proteins showed an alteration of BACE distribution and extensive co-localization with APP. These data suggest that altered compartmentalization of BACE in AD promotes the amyloidogenic processing of APP.
Copyright © 2011 Elsevier Inc. All rights reserved.
Int J Dev Neurosci. 2011 Jun;29(4):389-96. Epub 2011 Mar 31.
Arsenic affects expression and processing of amyloid precursor protein (APP) in primary neuronal cells overexpressing the Swedish mutation of human APP.
Source
Department of Biochemistry, Faculty of Medicine, University of San Luis Potosí, Av. V. Carranza 2405, Col. Los Filtros, 78210 San Luis Potosí, S.L.P., Mexico.
Abstract
Arsenic poisoning due to contaminated water and soil, mining waste, glass manufacture, select agrochemicals, as well as sea food, affects millions of people world wide. Recently, an involvement of arsenic in Alzheimer's disease (AD) has been hypothesized (Gong and O'Bryant, 2010). The present study stresses the hypothesis whether sodium arsenite, and its main metabolite, dimethylarsinic acid (DMA), may affect expression and processing of the amyloid precursor protein(APP), using the cholinergic cell line SN56.B5.G4 and primary neuronal cells overexpressing the Swedish mutation of APP, as experimental approaches. Exposure of cholinergic SN56.B5.G4 cells with either sodium arsenite or DMA decreased cell viability in a concentration- and exposure-time dependent manner, and affected the activities of the cholinergic enzymes acetylcholinesterase and choline acetyltransferase. Both sodium arsenite and DMA exposure of SN56.B5.G4 cells resulted in enhanced level of APP, and sAPP in the membrane and cytosolic fractions, respectively. To reveal any effect of arsenic on APP processing, the amounts of APP cleavage products, sAPPβ, and β-amyloid (Aβ) peptides, released into the culture medium of primary neuronal cells derived from transgenic Tg2576 mice, were assessed by ELISA. Following exposure of neuronal cells by sodium arsenite for 12h, the membrane-bound APP level was enhanced, the amount of sAPPβ released into the culture medium was slightly higher, while the levels of Aβ peptides in the culture medium were considerably lower as compared to that assayed in the absence of any drug. The sodium arsenite-induced reduction of Aβ formation suggests an inhibition of the APP γ-cleavage step by arsenite. In contrast, DMA exposure of neuronal cells considerably increased formation of Aβ and sAPPβ, accompanied by enhanced membrane APP level. The DMA-induced changes in APP processing may be the result of the enhanced APP expression. Alternatively, increased Aβ production may also be due to stimulation of caspase activity by arsenic compounds, or failure in Aβ degradation. In summary, the present report clearly demonstrates that sodium arsenite and DMA affect processing of APP in vitro.
Copyright © 2011 ISDN. Published by Elsevier Ltd. All rights reserved.
BMC Genomics. 2011 Mar 24;12:160.
Comparative transcriptome profiling of amyloid precursor protein family members in the adult cortex.
Source
Department of Bioinformatics and Functional Genomics, Institute of Pharmacy and Molecular Biotechnology, Heidelberg University, Im Neuenheimer Feld 364, D-69120 Heidelberg, Germany.
Abstract
BACKGROUND:
The β-amyloid precursor protein (APP) and the related β-amyloid precursor-like proteins (APLPs) undergo complex proteolytic processing giving rise to several fragments. Whereas it is well established that Aβ accumulation is a central trigger for Alzheimer's disease, the physiological role of APP family members and their diverse proteolytic products is still largely unknown. The secreted APPsα ectodomain has been shown to be involved in neuroprotection and synaptic plasticity. The γ-secretase-generated APP intracellular domain (AICD) functions as a transcriptional regulator in heterologous reporter assays although its role for endogenous gene regulation has remained controversial.
RESULTS:
To gain further insight into the molecular changes associated with knockout phenotypes and to elucidate the physiological functions of APP family members including their proposed role as transcriptional regulators, we performed DNA microarray transcriptome profiling of prefrontal cortex of adult wild-type (WT), APP knockout (APP-/-), APLP2 knockout (APLP2-/-) and APPsα knockin mice (APPα/α) expressing solely the secreted APPsα ectodomain. Biological pathways affected by the lack of APP family members included neurogenesis, transcription, and kinase activity. Comparative analysis of transcriptome changes between mutant and wild-type mice, followed by qPCR validation, identified co-regulated gene sets. Interestingly, these included heat shock proteins and plasticity-related genes that were both down-regulated in knockout cortices. In contrast, we failed to detect significant differences in expression of previously proposed AICD target genes including Bace1, Kai1, Gsk3b, p53, Tip60, and Vglut2. Only Egfr was slightly up-regulated in APLP2-/- mice. Comparison of APP-/- and APPα/α with wild-type mice revealed a high proportion of co-regulated genes indicating an important role of the C-terminus for cellular signaling. Finally, comparison of APLP2-/- on different genetic backgrounds revealed that background-related transcriptome changes may dominate over changes due to the knockout of a single gene.
CONCLUSION:
Shared transcriptome profiles corroborated closely related physiological functions of APP family members in the adult central nervous system. As expression of proposed AICD target genes was not altered in adult cortex, this may indicate that these genes are not affected by lack of APP under resting conditions or only in a small subset of cells.
J Neurosci Res. 2011 Jun;89(6):822-32. doi: 10.1002/jnr.22618. Epub 2011 Mar 23.
Decrease in brain soluble amyloid precursor protein β (sAPPβ) in Alzheimer's disease cortex.
Source
Department of Neurology, Merck Research Laboratory, West Point, Pennsylvania. guoxin_wu@merck.com
Abstract
Amyloid-β peptide (Aβ) is generated by sequential cleavage of the amyloid precursor protein (APP) by β-site amyloid precursor protein cleaving enzyme 1 (β-secretase, or BACE1) and γ-secretase. Several reports demonstrate increased BACE1 enzymatic activity in brain and cerebrospinal fluid (CSF) from Alzheimer's disease (AD) subjects, suggesting that an increase in BACE1-mediated cleavage of APP drives amyloid pathophysiology in AD. BACE1 cleavage of APP leads to the generation of a secreted N-terminal fragment of APP (sAPPβ). To relate BACE1 activity better to endogenous APP processing in AD and control brains, we have directly measured brain sAPPβ levels using a novel APP β-site specific enzyme-linked immunosorbent assay. We demonstrate a significant reduction in brain cortical sAPPβ levels in AD compared with control subjects. In the same brain samples, BACE1 activity was unchanged, full-length APP and sAPPα levels were significantly reduced, and Aβ peptides were significantly elevated. In conclusion, a reduction in cortical brain sAPPβ together with unchanged BACE1 activity suggests that this is due to reduced full-length APP substrate in late-stage AD subjects. These results highlight the need for multiparameter analysis of the amyloidogenic process to understand better AD pathophysiology in early vs. late-stage AD.
J Mol Neurosci. 2011 Sep;45(1):5-9. Epub 2011 Mar 22.
Amyloid Precursor Protein Gene (APP) Variation in Late-Onset Alzheimer's Disease.
Miar A, Alvarez V, Corao AI, Díaz M, Alonso B, Martínez C, Calatayud MT, Menéndez M, Morís G, Coto E.
Source
Genética Molecular, Hospital Universitario Central Asturias, 33006, Oviedo, Spain.
Abstract
Mutations in the beta-amyloid precursor protein gene (APP) have been found in familial early-onset Alzheímer's disease (AD). DNA variants at several genes have been linked to the risk of developing the most common late-onset form of AD (LOAD). A few studies analyzed the contribution of APP variants to LOAD, with negative or conflicting results. We determined the variation in the 18 APP exons and flanking intronic sequences in a total of 350 LOAD patients from Spain. A total of 13 nucleotide changes were found and 6 were new and not found among 340 healthy controls, including the only missense change (D243N). The in silico analysis suggested that none of them would have an effect on pre-mRNA splicing or protein folding (D243N). Patients and controls were also genotyped for three APP promoter polymorphisms, and none of them was significantly associated with LOAD. We concluded that APP variants would not contribute to the risk of developing LOAD in our population.
Zhong Xi Yi Jie He Xue Bao. 2011 Mar;9(3):292-8.
[Effects of early intervention with Huannao Yicong formula effective components on behavior and cholinergic system of β-amyloid precursor protein transgenic mice].
[Article in Chinese]
Source
Geratology Center, Xiyuan Hospital, China Academy of Chinese Medical Sciences, Beijing 100091, China.
Abstract
OBJECTIVE:
To observe the effects of early intervention with effective components from a Chinese herbal formula (Huannao Yicong formula, HNYCF) on behavior and related indicators of cholinergic system in β-amyloid precursor protein (APP) transgenic mice.
METHODS:
Sixty 3-month-old APP695 V717I transgenic mice were randomly divided into model group, high-dose HNYCF group (2.80 g/(kg·d)), low-dose HNYCF group (1.40 g/(kg·d)) and donepezil group (0.65 mg/(kg·d)), with 15 mice in each group. Fifteen non-transgenic mice of the same genetic background were used as normal group. The model group and normal group were fed with equal volume of distilled water by gavage. After 6-month continuous medication, the Morris water maze and the passive avoidance test were used to detect the visual spatial learning and memory ability of each mouse. Then the mice were decapitated and their cerebral cortex and hippocampus were isolated to homogenate by sonication. Contents of acetylcholine (ACh) and acetylcholinesterase (AChE) and choline acetyltransferase (ChAT) activity in the homogenate were determined by enzyme-linked immunosorbent assay, and protein contents of cerebral cortex and hippocampus were measured by Coomassie brilliant blue method.
RESULTS:
Compared with the model group, high- and low-dose HNYCF and donepezil hydrochloride all improved spatial learning of APP mice in the Morris water maze. The ratio of swimming distance in the central area in the high-dose HNYCF group was longer than that in the model group (P<0.05). In the passive avoidance test, high- and low-dose HNYCF and donepezil hydrochloride improved memory function of APP mice by improving the escape latency and reducing the number of errors (P<0.05, P<0.01). High- and low-dose HNYCF and donepezil hydrochloride reduced the content of AChE, increased the activity of ChAT (P<0.01, P<0.05) and improved the content of ACh in hippocampus (P<0.05); high- and low-dose HNYCF and donepezil hydrochloride increased the content of ACh in cortex (P<0.05). Donepezil hydrochloride reduced the content of AChE in cortex (P<0.05), however, high- and low-dose HNYCF had no obvious influence (P>0.05). High- and low-dose HNYCF increased the content of ChAT in cortex (P<0.05), whereas donepezil hydrochloride had no obvious influence (P>0.05).
CONCLUSION:
Early intervention with HNYCF effective components can improve the learning and memory ability of APP transgenic mice. The mechanism may be related to enhancing the function of cholinergic system.
Biol Pharm Bull. 2011;34(2):290-4.
Amyloid precursor protein binding protein Fe65 is cleaved by caspases during DNA damage-induced apoptosis.
Source
Department of Biochemistry, Faculty of Pharmaceutical Science, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278–8510, Japan.
Abstract
Caspases cleave several cellular proteins to execute cell death by apoptosis. The identification of novel substrates of caspases could provide an important clue for elucidation of new apoptosis signaling pathways. In this study, we tested whether an amyloid precursor protein (APP) binding protein Fe65 is proteolytically degraded in neuronal cell death by apoptosis, using a neuron-like cell line, human neuroblastoma SH-SY5Y cells. When treated with DNA damaging agents, etoposide (ETP) and camptothecin (CPT), SH-SY5Y cells underwent apoptosis in a dose-dependent manner. Interestingly, Fe65 (97 kDa) was cleaved to a 65 kDa product during DNA damage-induced apoptosis. Furthermore, the cleavage of Fe65 was accompanied by activation of caspases-9 and -3. The restriction cleavage of Fe65 was completely suppressed by the treatment with a pan-caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp(OMe) fluoromethylketone (z-VAD-fmk). These results reveal the restriction cleavage of Fe65 by caspases during DNA damage-induced apoptosis. Since Fe65 has been shown to suppress APP processing to amyloid β (Aβ) production, our findings may provide a new insight into the molecular mechanism by which DNA damage induces Aβ production and subsequent neuronal cell death in Alzheimer's disease (AD).
J Neurochem. 2011 Jun;117(5):779-96. doi: 10.1111/j.1471-4159.2011.07248.x. Epub 2011 Apr 14.
Regulated intramembrane proteolysis--lessons from amyloid precursor proteinprocessing.
Source
DZNE-German Center for Neurodegenerative Diseases, Adolf-Butenandt-Institute, Biochemistry, Ludwig-Maximilians-University, Munich, Germany.
Abstract
Regulated intramembrane proteolysis (RIP) controls the communication between cells and the extracellular environment. RIP is essential in the nervous system, but also in other tissues. In the RIP process, a membrane protein typically undergoes two consecutive cleavages. The first one results in the shedding of its ectodomain. The second one occurs within its transmembrane domain, resulting in secretion of a small peptide and the release of the intracellular domain into the cytosol. The proteolytic cleavage fragments act as versatile signaling molecules or are further degraded. An increasing number of membrane proteins undergo RIP. These include growth factors, cytokines, cell adhesion proteins, receptors, viral proteins and signal peptides. A dysregulation of RIP is found in diseases, such as leukemia and Alzheimer's disease. One of the first RIP substrates discovered was the amyloid precursor protein (APP). RIP processing of APP controls the generation of the amyloid β-peptide, which is believed to cause Alzheimer's disease. Focusing on APP as the best-studied RIP substrate, this review describes the function and mechanism of the APP RIP proteases with the goal to elucidate cellular mechanisms and common principles of the RIP process in general.
© 2011 The Authors. Journal of Neurochemistry © 2011 International Society for Neurochemistry.
J Clin Endocrinol Metab. 2011 Jun;96(6):1783-8. Epub 2011 Mar 16.
Insulin suppresses the expression of amyloid precursor protein, presenilins, and glycogen synthase kinase-3beta in peripheral blood mononuclear cells.
Source
Division of Endocrinology, Diabetes, and Metabolism, State University of New York at Buffalo and Kaleida Health, Buffalo, New York 14209, USA. pdandona@KaleidaHealth.org
Abstract
OBJECTIVE:
Our objective was to determine whether peripheral blood mononuclear cells express amyloid precursor protein (APP) and other mediators involved in the pathogenesis of Alzheimer's disease and whether their expression is suppressed by insulin.
RESEARCH DESIGN AND METHODS:
Ten obese type 2 diabetic patients were infused with insulin (2 U/h with 100 ml 5% dextrose/h) for 4 h. Patients were also infused with 5% dextrose/h or normal physiological saline for 4 h, respectively, on two other days as controls. Blood samples were obtained at 0, 2, 4, and 6 h.
RESULTS:
Insulin infusion significantly suppressed the expression of APP, presenilin-1, presenilin-2, and glycogen synthase kinase-3β in peripheral blood mononuclear cells. Dextrose and saline infusions did not alter these indices. Insulin infusion also caused significant parallel reductions in nuclear factor-κB binding activity and plasma concentrations of serum amyloid A and intercellular adhesion molecule-1.
CONCLUSIONS:
A low dose infusion of insulin suppresses APP, presenilin-1, presenilin-2, and glycogen synthase kinase-3β, key proteins involved in the pathogenesis of Alzheimer's disease, in parallel with exerting its other antiinflammatory effects.
Acta Biochim Pol. 2011;58(1):11-8. Epub 2011 Mar 15.
Chromatin acetylation, β-amyloid precursor protein and its binding partner FE65 in DNA double strand break repair.
Source
Centre for Radiobiology and Biological Dosimetry, Institute of Nuclear Chemistry and Technology, Warszawa, Poland. i.szumiel@ichtj.waw.pl
Abstract
Among post-translational modifications of chromatin proteins taking place in DNA double strand break (DSB) repair, acetylation plays a prominent role. This review lists several facts and hypotheses concerning this process. Lack of acetyltransferase TIP60 (HIV-Tat interacting protein of 60 kDa) activity results in cells with defective DSB repair. The enzyme is present in the nucleus in a multimeric protein complex. TIP60 dependent activation of ATM (ataxia telangiectasia mutated kinase) is an early event in the response to DNA breakage. Other important acetylations are those of histones H4 and γH2AX. Correct reconstruction of the damaged site is critical for survival and prevention of genetic and epigenetic changes in the cell that may affect the function of its daughter cells. Recently, two proteins with previously unsuspected functions in DSB repair have been identified as active in this process: Alzheimer β-amyloid precursor protein (APP) and its binding partner FE65, β-amyloid precursor binding protein. Their participation in DSB repair in both neuronal and non-neuronal cells is related to acetylation carried out by the acetyltransferase complex. The same function is ascribed to heterochromatin protein 1 (HP1). So far, the relations (if any) between TIP60 activation by HP1 and by the FE65 complex remain unidentified.
Neuropharmacology. 2011 Jul-Aug;61(1-2):69-79. Epub 2011 Mar 12.
5-HT(4) receptor agonist mediated enhancement of cognitive function in vivo andamyloid precursor protein processing in vitro: A pharmacodynamic and pharmacokinetic assessment.
Source
Department of Pharmacology, Theravance Inc., 901 Gateway Boulevard, South San Francisco, CA 94080, USA. fshen@theravance.com
Abstract
There remains an urgent need for therapeutic agents that provide improved symptomatic treatment and attenuate disease progression in patients with Alzheimer's disease (AD). 5-HT(4) receptors are widely expressed in those CNS areas which receive substantial cholinergic input and are involved in cognition. The ability of 5-HT(4) receptor agonists to increase acetylcholine (ACh) release and reduce cognitive impairment in both animals and humans has been demonstrated. In addition, 5-HT(4) receptor agonist modulation of levels of the amyloid precursor protein (APP) derived peptides, soluble amyloid precursor protein (sAPPα) and amyloid beta protein (Aβ) in the CNS has been reported. In this study, the preclinical properties of three structurally-distinct 5-HT(4) receptor selective agonists, PRX-03140, velusetrag and TD-8954, were studied to assess their potential for symptomatic and disease-modifying benefit in the treatment of AD. All three compounds exhibited high affinity for the rat 5-HT(4) receptor but could be discriminated on the basis of their agonist activity. In cAMP accumulation and sAPPα secretion assays using recombinant HEK293f-5-HT(4(d))-APP(695) cells, velusetrag and TD-8954 were potent, full agonists, relative to 5-HT, whereas PRX-03140 was a partial agonist (intrinsic activity 18%, relative to 5-HT). In a guinea pig colon isolated tissue preparation, TD-8954 exhibited lower intrinsic activity than velusetrag, and PRX-03140 had negligible agonist activity. In the rat Morris water maze (MWM) cognition test, velusetrag and TD-8954 (0.1 mg/kg), but not PRX-03140 (0.03-1 mg/kg), significantly reversed the scopolamine-induced spatial learning deficit via activation of 5-HT(4) receptors. Coadministration of subefficacious doses of the acetylcholinesterase inhibitor (AChEi), donepezil (0.1 mg/kg, i.p.), and either velusetrag or TD-8954 (0.01 mg/kg i.p.) resulted in reversal of the scopolamine-induced cognitive deficit. Pharmacokinetic data indicated that the CNS penetration for all three 5-HT(4) receptor agonists was relatively low. However, the pharmacodynamic-pharmacokinetic relationships in the MWM model for velusetrag and TD-8954 were consistent with their respective receptor pharmacology (binding affinity and intrinsic efficacy) and CNS penetration properties. Collectively, these findings support a potential role for potent and efficacious 5-HT(4) receptor agonists in the treatment of AD.
Copyright © 2011 Elsevier Ltd. All rights reserved.
EMBO Rep. 2011 Mar;12(3):180-1.
Mediator: the missing link in amyloid precursor protein nuclear signalling.
Source
Institute of Molecular & Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, UK. a.j.turner@leeds.ac.uk
Molecules. 2011 Mar 2;16(3):2084-96.
Luteolin isolated from the medicinal plant Elsholtzia rugulosa (Labiatae) prevents copper-mediated toxicity in β-amyloid precursor protein Swedish mutation overexpressing SH-SY5Y cells.
Source
Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100050, China.
Abstract
Luteolin, a 3',4',5,7-tetrahydroxyflavone, is a plant flavonoid and pharmacologically active agent that has been isolated from several plant species. In the present study, the effects of luteolin obtained from the medicinal plant Elsholtzia rugulosa and the related mechanisms were examined in an Alzheimer's disease (AD) cell model. In this model, copper was used to exacerbate the neurotoxicity in β-amyloid precursor protein Swedish mutation stably overexpressed SH-SY5Y cells (named "APPsw cells" for short). Based on this model, we demonstrated that luteolin increased cell viability, reduced intracellular ROS generation, enhanced the activity of SOD and reversed mitochondrial membrane potential dissipation. Inhibition of caspase-related apoptosis was consistently involved in the neuroprotection afforded by luteolin. Furthermore, it down-regulated the expression of AβPP and lowered the secretion of Aβ₁₋₄₂. These results indicated that luteolin from the Elsholtzia rugulosa exerted neroprotective effects through mechanisms that decrease AβPP expression, lower Aβ secretion, regulate the redox imbalance, preserve mitochondrial function, and depress the caspase family-related apoptosis.
Am J Physiol Cell Physiol. 2011 Jun;300(6):C1502-12. Epub 2011 Mar 2.
Dysregulation of Ca2+ signaling in astrocytes from mice lacking amyloid precursor protein.
Source
Dept. of Physiology, University of Maryland School of Medicine, 685 W. Baltimore Street, Baltimore, MD 21201, USA.
Abstract
The relationship between altered metabolism of the amyloid-β precursor protein (APP) and Alzheimer's disease is well established but the physiological roles of APP still remain unclear. Here, we studied Ca(2+) signaling in primary cultured and freshly dissociated cortical astrocytes from APP knockout (KO) mice and from Tg5469 mice overproducing by five- to sixfold wild-type APP. Resting cytosolic Ca(2+) (measured with fura-2) was not altered in cultured astrocytes from APP KO mice. The stored Ca(2+) evaluated by measuring peak amplitude of cyclopiazonic acid [CPA, endoplasmic reticulum (ER) Ca(2+) ATPase inhibitor]-induced Ca(2+) transients in Ca(2+)-free medium was significantly smaller in APP KO astrocytes than in wild-type cells. Store-operated Ca(2+) entry (SOCE) activated by ER Ca(2+) store depletion with CPA was also greatly reduced in APP KO astrocytes. This reflected a downregulated expression in APP KO astrocytes of TRPC1 (C-type transient receptor potential) and Orai1 proteins, essential components of store-operated channels (SOCs). Indeed, silencer RNA (siRNA) knockdown of Orai1 protein expression in wild-type astrocytes significantly attenuated SOCE. SOCE was also essentially reduced in freshly dissociated APP KO astrocytes. Importantly, knockdown of APP with siRNA in cultured wild-type astrocytes markedly attenuated ATP- and CPA-induced ER Ca(2+) release and extracellular Ca(2+) influx. The latter correlated with downregulation of TRPC1. Overproduction of APP in Tg5469 mice did not alter, however, the stored Ca(2+) level, SOCE, and expression of TRPC1/4/5 in cultured astrocytes from these mice. The data demonstrate that the functional role of APP in astrocytes involves the regulation of TRPC1/Orai1-encoded SOCs critical for Ca(2+) signaling.
Int J Cancer. 2011 Mar 1. doi: 10.1002/ijc.26028. [Epub ahead of print]
The impact of amyloid precursor protein signalling and histone deacetylase inhibition on neprilysin expression in human prostate cells.
Source
Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom.
Abstract
The zinc metallopeptidase, neprilysin (NEP), is an endothelin-1 degrading enzyme whose expression is extensively downregulated in prostate cancer. The expression of NEP in neuronal cells is regulated by intramembrane proteolysis of the amyloid precursor protein (APP) through its intracellular domain (AICD) facilitating histone acetylation of the NEP promoter and gene transcription. The present study has examined whether similar mechanisms operate in prostate cell lines. The expression of APP and its processing enzymes (β- and γ-secretases) was examined in a number of prostate cell lines, and the effect of γ-secretase inhibition was explored on NEP expression and activity. The potential interaction of AICD with the NEP promoter was examined by chromatin immunoprecipitation. Our results indicated that all key components involved in APP processing were expressed in prostate cancer cell lines but suppression of AICD production using a γ-secretase inhibitor did not decrease NEP expression and activity, and no direct AICD-NEP promoter interaction could be detected. However, histone deacetylase inhibitors (valproate and trichostatin A) caused a 2- to 3-fold increase in NEP expression in PC-3 cells, and combinatorial treatment with the DNA demethylating agent, AzaC, further increased NEP expression levels. Although AICD is detectable in prostate cell lines, it does not appear to regulate NEP by AICD-mediated signalling. Apart from promoter de-methylation, the data suggest that histone acetylation may facilitate partial re-activation of NEP expression in advanced prostate cancer cells. Upregulation of this tumour-suppressing protein may provide a novel therapeutic strategy in prostate cancer.
Copyright © 2011 UICC.
Commun Integr Biol. 2010 Nov;3(6):499-503. Epub 2010 Nov 1.
Post-transcriptional regulation of amyloid precursor protein by microRNAs and RNA binding proteins.
Source
INMM-CNR Istituto di Neurobiologia e Medicina Molecolare; IRCSS; Fondazione Santa Lucia.
Abstract
Amyloid Precursor Protein (APP) and its proteolytic product amyloid beta (Aβ) are critical in the pathogenesis of Alzheimer's Disease (AD). APP gene duplication and transcriptional upregulation are linked to AD. In addition, normal levels of APP appear to be required for some physiological functions in the developing brain. Several studies in mammalian cell lines and primary neuron cultures indicate that RNA binding proteins and microRNAs interacting with regulatory regions of the APP mRNA modulate expression of APP post-transcriptionally. However, when the various mechanisms of APP post-transcriptional regulation are recruited and which of them are acting in a synergistic fashion to balance APP protein levels, is unclear. Recent studies suggest that further investigation of the molecules and pathways involved in APP post-transcriptional regulation are warranted.
Atherosclerosis. 2011 May;216(1):54-8. Epub 2011 Jan 26.
Attenuated atherogenesis in apolipoprotein E-deficient mice lacking amyloid precursor protein.
Source
Division of Pharmacology, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Wilrijk, Belgium.
Abstract
OBJECTIVE:
Recent evidence suggests that amyloid precursor protein (APP) is overexpressed in atherosclerosis-prone regions of mouse aorta. We therefore investigated in the present study whether APP has a role in the progression and composition of atherosclerotic plaques.
METHODS AND RESULTS:
Apolipoprotein E-deficient (apoE(-/-)) mice were crossbred with animals lacking APP (APP(-/-)). After 16 weeks on a Western-type diet, apoE(-/-) and APP(-/-)/apoE(-/-) mice showed similar cholesterol levels. However, atherosclerotic plaque size was significantly reduced in the distal thoracic aorta (90% reduction) and abdominal aorta (75% reduction) of APP(-/-)/apoE(-/-) mice as compared to apoE(-/-). Plaques at the level of the aortic valves were not different in size, but showed a more stable phenotype in APP(-/-)/apoE(-/-) mice, as indicated by a reduced macrophage content, an increased amount of collagen and a thicker fibrous cap.
CONCLUSION:
Our findings provide evidence that lack of APP attenuates atherogenesis and leads to plaque stability.
Neurobiol Dis. 2011 Jun;42(3):349-59. Epub 2011 Feb 17.
Loss of amyloid precursor protein in a mouse model of Niemann-Pick type C disease exacerbates its phenotype and disrupts tau homeostasis.
Source
Department of Neuroscience, MRC Centre for Neurodegeneration Research, King's College London, Institute of Psychiatry, De Crespigny Park, London SE5 8AF, UK.
Abstract
Niemann-Pick type C disease (NPC) is a lysosomal storage disorder which, at the cellular level, shows amyloid Aβ and tau pathologies comparable to those seen in the AD brain. Here, we have investigated, in a mouse model of NPC, the impact of removing the source of Aβ, namely APP, on the disease phenotype and on the expression levels and phosphorylation patterns of tau. We reasoned that removing APP from the NPC brain might help to unveil its impact on the disease phenotype and shed light on the mechanisms governing the interaction, both physiological and pathological, between APP function and tau homeostasis, at least in NPC. We show that, unexpectedly, loss of APP in NPC mice leads to poorer neuromuscular coordination and cumulative survival rates; exacerbation of their cholesterol abnormalities; higher levels of astrocytosis and dysregulation of tau homeostasis. Our results are consistent with a mechanism of neurodegeneration in the NPC and AD brains in which cholesterol dysregulation is a key early pathogenic event affecting tau homeostasis in parallel with, and independently of, amyloid accumulation.
Copyright © 2011 Elsevier Inc. All rights reserved.
Neuroscience. 2011 Apr 28;180:305-13. Epub 2011 Feb 12.
Yokukansan, a traditional Japanese medicine, ameliorates memory disturbance and abnormal social interaction with anti-aggregation effect of cerebral amyloid β proteins in amyloid precursor protein transgenic mice.
Fujiwara H, Takayama S, Iwasaki K, Tabuchi M, Yamaguchi T, Sekiguchi K, Ikarashi Y, Kudo Y, Kase Y, Arai H, Yaegashi N.
Source
Department of Traditional Asian Medicine, Tohoku University Graduate School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai 980-8574, Japan.
Abstract
The deposition of amyloid β protein (Aβ) is a consistent pathological hallmark of Alzheimer's disease (AD) brains. Therefore, inhibition of Aβ aggregation in the brain is an attractive therapeutic and preventive strategy in the development of disease-modifying drugs for AD. An in vitro study demonstrated that yokukansan (YKS), a traditional Japanese medicine, inhibited Aβ aggregation in a concentration-dependent manner. An in vivo study demonstrated that YKS and Uncaria hook (UH), a constituent of YKS, prevented the accumulation of cerebral Aβ. YKS also improved the memory disturbance and abnormal social interaction such as increased aggressive behavior and decreased social behavior inamyloid precursor protein transgenic mice. These results suggest that YKS is likely to be a potent and novel therapeutic agent to prevent and/or treat AD, and that this may be attributed to UH.
Neurosci Lett. 2011 Apr 4;492(3):155-9. Epub 2011 Feb 15.
P2 receptor stimulation induces amyloid precursor protein production and secretion in rat cortical astrocytes.
Source
Research Service 151, Miami VAMC, 1201 NW 16th Street, Miami, FL 33125, United States. Minh.Tran@va.gov
Abstract
Amyloid precursor protein (APP) is ubiquitously expressed in a variety of tissues but is predominantly expressed in the brain. The expression of APP has been well studied in neurons but little is known about its presence in astrocytes. The study presented here shows that purinergic signaling is involved in the production and secretion of APP in primary cultures of rat cortical astrocytes. Extracellular ATP caused an increase in APP production and release in a time- and concentration-dependent manner and was inhibited by antagonists of P2 receptors. Further agonist and antagonist studies revealed involvement of P2Y2 and P2Y4 receptors in nucleotide-stimulated production and release of APP. In addition, signaling studies with various protein kinase inhibitors demonstrated that blockade of mitogen-activated protein kinases, but not Akt, inhibited nucleotide-stimulated APP expression and release. These results indicate that APP production and secretion can be regulated by activation of P2Y2/4 receptors coupled to protein kinase signaling pathways and suggest that astrocytes can be a potential source of APP.
Published by Elsevier Ireland Ltd.
PLoS One. 2011 Jan 27;6(1):e16301.
Secreted amyloid precursor protein β and secreted amyloid precursor protein α induce axon outgrowth in vitro through Egr1 signaling pathway.
Source
INSERM U894, Paris, France.
Abstract
BACKGROUND:
sAPPα released after α secretase cleavage of Amyloid Precursor Protein (APP) has several functions including the stimulation of neurite outgrowth although detailed morphometric analysis has not been done. Two domains involved in this function have been described and are present in sAPPβ released at the first step of amyloid peptide cleavage, raising the possibility that sAPPβ could also stimulate neurite outgrowth. We investigated the morphological effects of sAPPα and sAPPβ on primary neurons and identified a key signaling event required for the changes observed.
METHODOLOGY/PRINCIPAL FINDINGS:
Final concentrations of 50 to 150 nM bacterial recombinant sAPPα or sAPPβ added to primary neuronal cultures after 1 day in vitro decreased cell adhesion 24 hours later and primary dendrite length 96 hours later. 150 nM sAPPα and sAPPβ induced a similar increase of axon outgrowth, although this increase was already significant at 100 nM sAPPα. These morphological changes induced by sAPPs were also observed when added to differentiated neurons at 5 days in vitro. Real time PCR and immunocytochemistry showed that sAPPα and sAPPβ stimulated Egr1 expression downstream of MAPK/ERK activation. Furthermore, in primary neurons from Egr1 -/- mice, sAPPs affected dendritic length but did not induce any increase of axon length.
CONCLUSION/SIGNIFICANCE:
sAPPα and sAPPβ decrease cell adhesion and increase axon elongation. These morphological changes are similar to what has been observed in response to heparan sulfate. The sAPPα/sAPPβ stimulated increase in axon growth requires Egr1 signaling. These data suggest that sAPPβ is not deleterious per se. Since sAPPβ and sAPPα are present in the embryonic brain, these two APP metabolites might play a role in axon outgrowth during development and in response to brain damage.
EMBO Rep. 2011 Mar;12(3):216-22. Epub 2011 Feb 4.
Mediator is a transducer of amyloid-precursor-protein-dependent nuclear signalling.
Source
Department of Molecular Medicine, Institute of Biotechnology, University of Texas Health Science Center at San Antonio, 15355 Lambda Drive, San Antonio, Texas 78245, USA.
Abstract
Regulated intramembrane proteolysis of the amyloid precursor-protein (APP) produces both a characterstic amyloid-β peptide that contributes to neuritic plaque formation and neurodegeneration in Alzheimer disease and a small APP intracellular domain (AICD) that transcriptionally activates genes implicated in Alzheimer disease pathology. Although the biochemical events leading to amyloidogenic APP processing at the cell membrane have been described in detail, comparably little is known about the mechanistic basis of AICD-dependent gene regulation in the nucleus. In this study, we show that the AICD activates transcription by targeting MED12, an RNA polymerase II transcriptional Mediator subunit that is implicated in human cognitive development. The AICD binds to MED12/Mediator in vitro and in vivo. Disruption of the AICD/MED12 interaction inhibits AICD transactivation potential and expression of AICD target genes. Mediator, in a MED12-dependent manner, occupies only AICD-bound promoter DNA, indicating that the AICD recruits Mediator to activate transcription. These results identify the MED12 interface in Mediator as a crucial transducer of AICD transactivation and a potential therapeutic target in Alzheimer disease.
J Neurosci. 2011 Feb 2;31(5):1837-49.
Sphingolipid storage affects autophagic metabolism of the amyloid precursor proteinand promotes Abeta generation.
Source
Department of Neurology, University of Bonn, 53127 Bonn, Germany.
Abstract
Deposition of amyloid β peptides (Aβs) in extracellular amyloid plaques within the human brain is a hallmark of Alzheimer's disease (AD). Aβ derives from proteolytic processing of the amyloid precursor protein (APP) by β- and γ-secretases. The initial cleavage by β-secretase results in shedding of the APP ectodomain and generation of APP C-terminal fragments (APP-CTFs), which can then be further processed within the transmembrane domain by γ-secretase, resulting in release of Aβ. Here, we demonstrate that accumulation of sphingolipids (SLs), as occurs in lysosomal lipid storage disorders (LSDs), decreases the lysosome-dependent degradation of APP-CTFs and stimulates γ-secretase activity. Together, this results in increased generation of both intracellular and secreted Aβ. Notably, primary fibroblasts from patients with different SL storage diseases show strong accumulation of potentially amyloidogenic APP-CTFs. By using biochemical, cell biological, and genetic approaches, we demonstrate that SL accumulation affects autophagic flux and impairs the clearance of APP-CTFs. Thus, accumulation of SLs might not only underlie the pathogenesis of LSDs, but also trigger increased generation of Aβ and contribute to neurodegeneration in sporadic AD.
J Neuroimmune Pharmacol. 2011 Feb 2. [Epub ahead of print]
HIV-1 gp120-Induced Axonal Injury Detected by Accumulation of β-Amyloid Precursor Protein in Adult Rat Corpus Callosum.
Zhang J, Liu J, Katafiasz B, Fox H, Xiong H.
Source
Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198-5880, USA.
Abstract
HIV-1 brain infection induces neurodegeneration. While most studies focus on HIV-1-mediated neuronal injury, relatively few have investigated HIV-1-associated white matter damage. Corpus callosum (CC) is one of frequently involved white matter structures in HIV-1-associated white matter damage. Utilizing a model of ex vivo treatment of brain slice containing CC with HIV-1 glycoprotein 120 (gp120), we examined axonal injury by analyzing β-amyloid precursor protein (β-APP) accumulation in the axon. Incubation of CC slice with gp120 produced a significant higher density of β-APP in the CC tissue compared with non-gp120-treated controls, suggesting the presence of axonal damage in the CC. The gp120-induced CC axonal damage was blocked by a chemokine CXCR4 receptor antagonist T140 but not by an NMDA receptor blocker MK801 as demonstrated by Western blot analysis of β-APP, indicating that gp120 evokes the CC axonal injury through CXCR4 receptor. Immunocytochemical studies revealed a surprisingly high density of CXCR4-positive immunoreactivity in the CC. The CXCR4-positive labeling was distributed along the nerve fibers. Moreover, double labeling of anti-CXCR4 with either anti-neuronal nuclei or anti-myelin/oligodendrocyte-specific protein antibody revealed co-localization of CXCR4 and myelin/oligodendrocytes in some fiber-like structures, inferring that some neurons and oligodendrocytes in the CC express CXCR4. Taken together, these results indicate that gp120 induced axonal damage via CXCR4 in the CC.
Biophys J. 2011 Feb 2;100(3):711-9.
Evidence from solid-state NMR for nonhelical conformations in the transmembrane domain of the amyloid precursor protein.
Source
Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA.
Abstract
The amyloid precursor protein (APP) is subject to proteolytic processing by γ-secretase within neuronal membranes, leading to Alzheimer's disease-associated β-amyloid peptide production by cleavage near the midpoint of the single transmembrane (TM) segment of APP. Conformational properties of the TM segment may affect its susceptibility to γ-secretase cleavage, but these properties have not been established definitively, especially in bilayer membranes with physiologically relevant lipid compositions. In this article, we report an investigation of the APP-TM conformation, using (13)C chemical shifts obtained with two-dimensional solid-state NMR spectroscopy as site-specific conformational probes. We find that the APP-TM conformation is not a simple α-helix, particularly at 37°C in multilamellar vesicles with compositions that mimic the composition of neuronal cell membranes. Instead, we observe a mixture of helical and nonhelical conformations at the N- and C-termini and in the vicinity of the γ-cleavage site. Conformational plasticity of the TM segment of APP may be an important factor in the γ-secretase cleavage mechanism.
Copyright © 2011 Biophysical Society. Published by Elsevier Inc. All rights reserved.
Ann Neurol. 2011 Jan;69(1):47-64. doi: 10.1002/ana.22308.
SORCS1 alters amyloid precursor protein processing and variants may increase Alzheimer's disease risk.
Reitz C, Tokuhiro S, Clark LN, Conrad C, Vonsattel JP, Hazrati LN, Palotás A, Lantigua R, Medrano M, Z Jiménez-Velázquez I, Vardarajan B, Simkin I, Haines JL, Pericak-Vance MA, Farrer LA, Lee JH, Rogaeva E, George-Hyslop PS,Mayeux R.
Source
The Taub Institute for Research on Alzheimer's Disease and the Aging Brain, Columbia University, New York, NY, USA.
Abstract
OBJECTIVE:
Sorting mechanisms that cause the amyloid precursor protein (APP) and the β-secretases and γ-secretases to colocalize in the same compartment play an important role in the regulation of Aβ production in Alzheimer's disease (AD). We and others have reported that genetic variants in the Sortilin-related receptor (SORL1) increased the risk of AD, that SORL1 is involved in trafficking of APP, and that underexpression of SORL1 leads to overproduction of Aβ. Here we explored the role of one of its homologs, the sortilin-related VPS10 domain containing receptor 1 (SORCS1), in AD.
METHODS:
We analyzed the genetic associations between AD and 16 SORCS1-single nucleotide polymorphisms (SNPs) in 6 independent data sets (2,809 cases and 3,482 controls). In addition, we compared SorCS1 expression levels of affected and unaffected brain regions in AD and control brains in microarray gene expression and real-time polymerase chain reaction (RT-PCR) sets, explored the effects of significant SORCS1-SNPs on SorCS1 brain expression levels, and explored the effect of suppression and overexpression of the common SorCS1 isoforms on APP processing and Aβ generation.
RESULTS:
Inherited variants in SORCS1 were associated with AD in all datasets (0.001 < p < 0.049). In addition, SorCS1 influenced APP processing. While overexpression of SorCS1 reduced γ-secretase activity and Aβ levels, the suppression of SorCS1 increased γ-secretase processing of APP and the levels of Aβ.
INTERPRETATIONS:
These data suggest that inherited or acquired changes in SORCS1 expression or function may play a role in the pathogenesis of AD.
Copyright © 2010 American Neurological Association.
Comment in
Ann Neurol. 2011 Jan;69(1):8-10. doi: 10.1002/ana.22342.
Targeting amyloid precursor protein.
Comment on
Int J Dev Neurosci. 2011 Apr;29(2):107-14. Epub 2011 Jan 26.
Activity-induced dendrite and dendritic spine development in human amyloid precursor protein transgenic mice.
Source
Department of Anatomy, Histology and Embryology, Semmelweis University Medical School, Tűzoltó u. 58, H-1450 Budapest, Hungary. dralpar@gmx.net
Abstract
The amyloid precursor protein is essential for proper neuronal function but an imbalance in processing or metabolism or its overexpression lead to severe malfunction of the brain. The present study focused on dendritic morphology of hippocampal neurons in mice overexpressing the wild-type human amyloid precursor protein (hAPP). In addition, we examined whether enhanced physical activity may affect hAPP-related morphological changes. Overexpression of hAPP resulted in significant enlargement of dendrites, especially within the basal dendritic field but had no effect on spine density. Enhanced physical activity only moderately potentiated hAPP induced changes in dendritic size. Physical activity dependent increases in spine density were, however, augmented by hAPP overexpression. The results suggest that enhanced levels of wild-type hAPP do not result in degenerative changes of neuronal morphology, but rather promote dendritic growth.
Copyright © 2011 ISDN. Published by Elsevier Ltd. All rights reserved.
J Biol Chem. 2011 Mar 18;286(11):8717-21. Epub 2011 Jan 25.
A single tyrosine residue in the amyloid precursor protein intracellular domain is essential for developmental function.
Source
Department of Microbiology and Immunology, Einstein College of Medicine, Bronx, New York 10461, USA.
Abstract
The Aβ-precursor protein (APP) intracellular domain is highly conserved and contains many potentially important residues, in particular the (682)YENPTY(687) motif. To dissect the functions of this sequence in vivo, we created an APP knock-in allele mutating Tyr(682) to Gly (Y682G). Crossing this allele to APP-like protein 2 (APLP2) knock-out background showed that mutation of Tyr(682) results in postnatal lethality and neuromuscular synapse defects similar to doubly deficient APP/APLP2 mice. Our results demonstrate that a single residue in the APP intracellular region, Tyr(682), is indispensable for the essential function of APP in developmental regulation.
FASEB J. 2011 Apr;25(4):1295-305. Epub 2011 Jan 21.
Local cholesterol increase triggers amyloid precursor protein-Bace1 clustering in lipid rafts and rapid endocytosis.
Marquer C, Devauges V, Cossec JC, Liot G, Lécart S, Saudou F, Duyckaerts C, Lévêque-Fort S, Potier MC.
Source
Centre de Recherche de l'Institut du Cerveau et de la Moelle, UPMC, INSERM UMR-S975, Centre National de la Recherche Scientifique (CNRS) UMR7225, Hôpital de la Pitié-Salpêtrière, Paris, France.
Abstract
Amyloid peptide (Aβ) is generated by sequential cleavage of the amyloid precursor protein (APP) by β-secretase (Bace1) and γ-secretase. Aβ production increases after plasma membrane cholesterol loading through unknown mechanisms. To determine how APP-Bace1 proximity affects this phenomenon, we developed a fluorescence lifetime imaging microscopy-Förster resonance energy transfer (FLIM-FRET) technique for visualization of these molecules either by epifluorescence or at the plasma membrane only using total internal reflection fluorescence. Further, we used fluorescence correlation spectroscopy to determine the lipid rafts partition of APP-yellow fluorescent protein (YFP) and Bace1-green fluorescent protein (GFP) molecules at the plasma membrane of neurons. We show that less than 10 min after cholesterol exposure, Bace1-GFP/APP-mCherry proximity increases selectively at the membrane and APP relocalizes to raft domains, preceded by rapid endocytosis. After longer cholesterol exposures, APP and Bace1 are found in proximity intracellularly. We demonstrate that cholesterol loading does not increase Aβ production by having a direct impact on Bace1 catalytic activity but rather by altering the accessibility of Bace1 to its substrate, APP. This change in accessibility is mediated by clustering in lipid rafts, followed by rapid endocytosis.
J Neurosci. 2011 Jan 19;31(3):1032-7.
Drosophila amyloid precursor protein-like is required for long-term memory.
Source
Genes and Dynamics of Memory Systems, Neurobiology Unit, Centre National de la Recherche Scientifique, Ecole Supérieure de Physique et de Chimie Industrielles, 75005 Paris, France.
Abstract
The amyloid precursor protein (APP) plays an important role in Alzheimer's disease (AD), a progressive neurodegenerative pathology that first manifests as a decline of memory. While the main hypothesis for AD pathology centers on the proteolytic processing of APP, very little is known about the physiological function of the APP protein in the adult brain. Likewise, whether APP loss of function contributes to AD remains unclear. Drosophila has been used extensively as a model organism to study neuronal function and pathology. In addition, many of the molecular mechanisms underlying memory are thought to be conserved from flies to mammals, prompting us to study the function of APPL, the fly APP ortholog, during associative memory. It was previously shown that APPL expression is highly enriched in the mushroom bodies (MBs), a specialized brain structure involved in olfactory memory. We analyzed memory in flies in which APPL expression has been silenced specifically and transiently in the adult MBs. Our results show that in adult flies, APPL is not required for learning but is specifically involved in long-term memory, a long lasting memory whose formation requires de novo protein synthesis and is thought to require synaptic structural plasticity. These data support the hypothesis that disruption of normal APP function may contribute to early AD cognitive impairment.
Neuroscience. 2011 Mar 17;177:207-22. Epub 2011 Jan 9.
Differential expression and redox proteomics analyses of an Alzheimer disease transgenic mouse model: effects of the amyloid-β peptide of amyloid precursor protein(Ξ).
Robinson RA, Lange MB, Sultana R, Galvan V, Fombonne J, Gorostiza O, Zhang J, Warrier G, Cai J, Pierce WM, Bredesen DE, Butterfield DA.
Source
Department of Chemistry, Center of Membrane Sciences, University of Kentucky, Lexington, KY 40506, USA.
Abstract
Among the pathological factors known to be associated with Alzheimer disease (AD), oxidative stress induced by the amyloid-β peptide (Aβ) has been demonstrated to play a key role in human brain and animal models of AD. Recently, we reported elevated levels of oxidative damage in the brain of a transgenic (Tg) AD mouse model with Swedish and Indiana familial AD mutations in human amyloid precursor protein (APP) [PDAPP mice, line J20], as evidenced by increased levels of protein carbonyls, 3-nitrotyrosine, and protein-bound 4-hydroxy-2-nonenal. This oxidative damage was dependent on the methionine 35 residue within the Aβ peptide. Further insight into the molecular pathways affected in this Tg model of AD may be gained with discovery-based proteomics studies; therefore, two-dimensional gel-based expression proteomics was performed to compare differences in brain protein levels of J20 Tg mice with non-transgenic (NTg) littermate controls. Based on our studies, we identified six proteins that had significantly increased levels in J20 Tg relative to NTg mice: calcineurin subunit B type 1, ρ GDP-dissociation inhibitor 1, T-complex protein 1 subunit α A, α-enolase, peptidyl-prolyl cis-trans isomerase (Pin-1), and ATP synthase subunit α mitochondrial. Several of these proteins have previously been implicated in in vitro and in vivo models and subjects with AD. Additionally, using redox proteomics analyses we identified two oxidatively-modified proteins: phosphatidylethanolamine-binding protein 1 and Pin-1 with decreased levels of protein 3-nitrotyrosine in J20 Tg mice relative to NTg. Western blotting and immunoprecipitation analyses were used to validate proteomics results. Overall, these studies provide information about changes in the brain proteome as a result of Aβ deposition and clues with which to further direct studies on elucidating AD pathogenesis.
Copyright © 2011 IBRO. Published by Elsevier Ltd. All rights reserved.
Brain Res. 2011 Mar 10;1378:137-43. Epub 2011 Jan 6.
The neuroprotective domains of the amyloid precursor protein, in traumatic brain injury, are located in the two growth factor domains.
Source
Discipline of Anatomy and Pathology, School of Medical Sciences, University of Adelaide, South Australia, Australia.
Abstract
The amyloid precursor protein (APP) is known to increase following traumatic brain injury (TBI). This increase in levels of APP may be deleterious to outcome due to the production of neurotoxic Aβ. Conversely, this upregulation may be beneficial as cleavage of APP via the alternative non-amyloidogenic pathway produces the soluble α form of APP (sAPPα), which is known to have many neuroprotective and neurotrophic functions. Indeed it has previously been shown that treatment with sAPPα following a diffuse injury in rats improves outcome. However, the exact location within the sAPPα molecule which contains this neuroprotective activity has yet to be determined. The sAPPα peptide can consist of up to 6 domains, with the main isoform in the brain missing the 4th and 5th. Of the remaining domains, the D1 and D6a domains seem the most likely as they have been shown to have beneficial actions in vitro. This present study examined the effects of in vivo posttraumatic administration via an intracerebroventricular injection of the D1, D2 and D6a domains of sAPPα on outcome following moderate-impact acceleration TBI in rats. While treatment with either the D1 or D6a domains was found to significantly improve motor and cognitive outcome, as assessed on the rotarod and Y maze, treatment with the D2 domain had no effect. Furthermore axonal injury was reduced in D1 and D6a domain treated animals, but not those that received the D2 domain. As the D1 and D6a domains contain a heparin binding region while the D2 domain does not, this suggests that sAPPα mediates its neuroprotective response through its ability to bind to heparin sulfate proteoglycans.
Crown Copyright © 2011. Published by Elsevier B.V. All rights reserved.
J Neurochem. 2011 Mar;116(5):916-25. doi: 10.1111/j.1471-4159.2010.07070.x. Epub 2011 Jan 12.
Plasmalogen synthesis is regulated via alkyl-dihydroxyacetonephosphate-synthase byamyloid precursor protein processing and is affected in Alzheimer's disease.
Grimm MO, Kuchenbecker J, Rothhaar TL, Grösgen S, Hundsdörfer B, Burg VK, Friess P, Müller U, Grimm HS,Riemenschneider M, Hartmann T.
Source
Neurodegeneration and Neurobiology, Deutsches Institut für DemenzPrävention (DIDP), Homburg, Germany. marcus.grimm@uks.eu
Abstract
Lipids play an important role as risk or protective factors in Alzheimer's disease, which is characterized by amyloid plaques composed of aggregated amyloid-beta. Plasmalogens are major brain lipids and controversially discussed to be altered in Alzheimer's disease (AD) and whether changes in plasmalogens are cause or consequence of AD pathology. Here, we reveal a new physiological function of the amyloid precursor protein (APP) in plasmalogen metabolism. The APP intracellular domain was found in vivo and in vitro to increase the expression of the alkyl-dihydroxyacetonephosphate-synthase (AGPS), a rate limiting enzyme in plasmalogen synthesis. Alterations in APP dependent changes of AGPS expression result in reduced protein and plasmalogen levels. Under the pathological situation of AD, increased amyloid-beta level lead to increased reactive oxidative species production, reduced AGPS protein and plasmalogen level. Accordingly, phosphatidylethanol plasmalogen was decreased in the frontal cortex of AD compared to age matched controls. Our findings elucidate that plasmalogens are decreased as a consequence of AD and regulated by APP processing under physiological conditions.
© 2011 The Authors. Journal of Neurochemistry © 2011 International Society for Neurochemistry.
Neurobiol Aging. 2011 Mar;32(3):556.e13-23. Epub 2010 Dec 31.
Amyloid precursor protein (APP) processing genes and cerebrospinal fluid APP cleavage product levels in Alzheimer's disease.
Bekris LM, Galloway NM, Millard S, Lockhart D, Li G, Galasko DR, Farlow MR, Clark CM, Quinn JF, Kaye JA, Schellenberg GD, Leverenz JB, Seubert P, Tsuang DW, Peskind ER, Yu CE.
Source
Geriatric Research, Education and Clinical Center (GRECC), VA Puget Sound Health Care System, Seattle, WA, USA. lbekris@u.washington.edu
Abstract
The aim of this exploratory investigation was to determine if genetic variation within amyloid precursor protein (APP) or its processing enzymes correlates with APP cleavage product levels: APPα, APPβ or Aβ42, in cerebrospinal fluid (CSF) of cognitively normal subjects or Alzheimer's disease (AD) patients. Cognitively normal control subjects (n = 170) and AD patients (n = 92) were genotyped for 19 putative regulatory tagging SNPs within 9 genes (APP, ADAM10, BACE1, BACE2, PSEN1, PSEN2, PEN2, NCSTN and APH1B) involved in the APP processing pathway. SNP genotypes were tested for their association with CSF APPα, APPβ, and Aβ42, AD risk and age-at-onset while taking into account age, gender, race and APOE ε4. After adjusting for multiple comparisons, a significant association was found between ADAM10 SNP rs514049 and APPα levels. In controls, the rs514049 CC genotype had higher APPα levels than the CA, AA collapsed genotype, whereas the opposite effect was seen in AD patients. These results suggest that genetic variation within ADAM10, an APP processing gene, influences CSF APPα levels in an AD specific manner.
Copyright © 2011 Elsevier Inc. All rights reserved.
Neurobiol Aging. 2010 Dec 28. [Epub ahead of print]
Duplication of amyloid precursor protein (APP), but not prion protein (PRNP) gene is a significant cause of early onset dementia in a large UK series.
McNaughton D, Knight W, Guerreiro R, Ryan N, Lowe J, Poulter M, Nicholl DJ, Hardy J, Revesz T, Lowe J, Rossor M,Collinge J, Mead S.
Source
MRC Prion Unit, Department of Neurodegenerative Disease, UCL Institute of Neurology, Queen Square, London, UK.
Abstract
Amyloid precursor protein gene (APP) duplications have been identified in screens of selected probands with early onset familial Alzheimer's disease (FAD). A causal role for copy number variation (CNV) in the prion protein gene (PRNP) in prion dementias is not known. We aimed to determine the prevalence of copy number variation in APP and PRNP in a large referral series, test a screening method for detection of the same, and expand knowledge of clinical phenotype. We used a 3-tiered screening assay for APP and PRNP duplication (exonic real-time quantitative polymerase chain reaction [exon-qPCR], fluorescent microsatellite quantitative PCR [fm-q-PCR], and Illumina array [Illumina Inc., San Diego, CA, USA]) for analysis of a heterogeneous referral series comprising 1531 probands. Five of 1531 probands screened showed APP duplication, a similar prevalence to APP missense mutation. Real-time quantitative PCR and fluorescent microsatellite quantitative PCR were similar individually but are theoretically complementary; we used Illumina arrays as our reference assay. Two of 5 probands were from an autosomal dominant early onset Alzheimer's disease (familial Alzheimer's disease) pedigree. One extensive, noncontiguous duplication on chromosome 21 was consistent with an unbalanced translocation not including the Down's syndrome critical region. Seizures were prominent in the other typical APP duplications. A range of imaging, neuropsychological, cerebrospinal fluid, and pathological findings are reported that extend the known phenotype. APP but not PRNP duplication is a significant cause of early onset dementia in the UK. The recognized phenotype may be expanded to include the possibility of early seizures and apparently sporadic disease which, in part, may be due to different mutational mechanisms. The pros and cons of our screening method are discussed.
Copyright © 2010 Elsevier Inc. All rights reserved.
Alzheimers Res Ther. 2010 Dec 29;2(6):36.
Amyloid precursor protein selective gamma-secretase inhibitors for treatment of Alzheimer's disease.
Basi GS, Hemphill S, Brigham EF, Liao A, Aubele DL, Baker J, Barbour R, Bova M, Chen XH, Dappen MS, Eichenbaum T,Goldbach E, Hawkinson J, Lawler-Herbold R, Hu K, Hui T, Jagodzinski JJ, Keim PS, Kholodenko D, Latimer LH, Lee M,Marugg J, Mattson MN, McCauley S, Miller JL, Motter R, Mutter L, Neitzel ML, Ni H, Nguyen L, Quinn K, Ruslim L, Semko CM, Shapiro P, Smith J, Soriano F, Szoke B, Tanaka K, Tang P, Tucker JA, Ye XM, Yu M, Wu J, Xu YZ, Garofalo AW, Sauer JM, Konradi AW, Ness D, Shopp G, Pleiss MA, Freedman SB, Schenk D.
Source
Elan Pharmaceuticals, Inc, 180 Oyster Point Blvd, S, San Francisco, CA 94080, USA. guriq.basi@neotopebio.com.
Abstract
ABSTRACT : INTRODUCTION : Inhibition of gamma-secretase presents a direct target for lowering Aβ production in the brain as a therapy for Alzheimer's disease (AD). However, gamma-secretase is known to process multiple substrates in addition to amyloid precursor protein (APP), most notably Notch, which has limited clinical development of inhibitors targeting this enzyme. It has been postulated that APP substrate selective inhibitors of gamma-secretase would be preferable to non-selective inhibitors from a safety perspective for AD therapy. METHODS : In vitro assays monitoring inhibitor potencies at APP γ-site cleavage (equivalent to Aβ40), and Notch ε-site cleavage, in conjunction with a single cell assay to simultaneously monitor selectivity for inhibition of Aβ production vs. Notch signaling were developed to discover APP selective gamma-secretase inhibitors. In vivo efficacy for acute reduction of brain Aβ was determined in the PDAPP transgene model of AD, as well as in wild-type FVB strain mice. In vivo selectivity was determined following seven days x twice per day (b.i.d.) treatment with 15 mg/kg/dose to 1,000 mg/kg/dose ELN475516, and monitoring brain Aβ reduction vs. Notch signaling endpoints in periphery. RESULTS : The APP selective gamma-secretase inhibitors ELN318463 and ELN475516 reported here behave as classic gamma-secretase inhibitors, demonstrate 75- to 120-fold selectivity for inhibiting Aβ production compared with Notch signaling in cells, and displace an active site directed inhibitor at very high concentrations only in the presence of substrate. ELN318463 demonstrated discordant efficacy for reduction of brain Aβ in the PDAPP compared with wild-type FVB, not observed with ELN475516. Improved in vivo safety of ELN475516 was demonstrated in the 7d repeat dose study in wild-type mice, where a 33% reduction of brain Aβ was observed in mice terminated three hours post last dose at the lowest dose of inhibitor tested. No overt in-life or post-mortem indications of systemic toxicity, nor RNA and histological end-points indicative of toxicity attributable to inhibition of Notch signaling were observed at any dose tested. CONCLUSIONS : The discordant in vivo activity of ELN318463 suggests that the potency of gamma-secretase inhibitors in AD transgenic mice should be corroborated in wild-type mice. The discovery of ELN475516 demonstrates that it is possible to develop APP selective gamma-secretase inhibitors with potential for treatment for AD.
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