1.
Employing neuronal networks to investigate the pathophysiological basis of abnormal cortical oscillations in Alzheimer's disease.
Abstract
This paper describes an investigation into the pathophysiological causes of abnormal cortical oscillations in Alzheimer's disease (AD) using two heterogeneous neuronal network models. The effect of excitatory circuit disruption on the betaband power (13-30 Hz) using a conductance-based network model of 200 neurons is assessed. Then, the neural correlates of abnormal cortical oscillations in different frequency bands based on a larger network model of 1000 neurons consisting of different types of cortical neurons is also analyzed. The results show that, despite the heterogeneity of the network models, the beta band power is significantly affected by excitatory neural and synaptic loss. Secondly, the results of modeling a functional impairment in the excitatory circuit shows that beta band power exhibits the most decrease compared with other bands. Previous biological experiments on different types of cultural excitatory neurons show that cortical neuronal death is mediated by dysfunctional ionic behavior that might specifically contribute to the pathogenesis of p-amyloid peptide (Ap)-induced neuronal death in AD. Our study also shows that beta band power was the first affected component when the modeled excitatory circuit begins to lose neurons and synapses. Alpha (8-12 Hz), gamma (30-50 Hz) and Full frequency (1-70 Hz) band power are affected in a later stage when more severe synaptic loss occurs.
- PMID:
- 22254743
- [PubMed - in process]
Dual Effect of Beta-Amyloid on α7 and α4β2 Nicotinic Receptors Controlling the Release of Glutamate, Aspartate and GABA in Rat Hippocampus.
Source
Department of Drug Sciences, Centre of Excellence in Applied Biology, University of Pavia, Pavia, Italy.
Abstract
BACKGROUND:
We previously showed that beta-amyloid (Aβ), a peptide considered as relevant to Alzheimer's Disease, is able to act as a neuromodulator affecting neurotransmitter release in absence of evident sign of neurotoxicity in two different rat brain areas. In this paper we focused on the hippocampus, a brain area which is sensitive to Alzheimer's Disease pathology, evaluating the effect of Aβ (at different concentrations) on the neurotransmitter release stimulated by the activation of pre-synaptic cholinergic nicotinic receptors (nAChRs, α4β2 and α7 subtypes). Particularly, we focused on some neurotransmitters that are usually involved in learning and memory: glutamate, aspartate and GABA.
METHODOLOGY/FINDINGS:
WE USED A DUAL APPROACH: in vivo experiments (microdialysis technique on freely moving rats) in parallel to in vitro experiments (isolated nerve endings derived from rat hippocampus). Both in vivo and in vitro the administration of nicotine stimulated an overflow of aspartate, glutamate and GABA. This effect was greatly inhibited by the highest concentrations of Aβ considered (10 µM in vivo and 100 nM in vitro). In vivo administration of 100 nM Aβ (the lowest concentration considered) potentiated the GABA overflow evoked by nicotine. All these effects were specific for Aβ and for nicotinic secretory stimuli. The in vitro administration of either choline or 5-Iodo-A-85380 dihydrochloride (α7 and α4β2 nAChRs selective agonists, respectively) elicited the hippocampal release of aspartate, glutamate, and GABA. High Aβ concentrations (100 nM) inhibited the overflow of all three neurotransmitters evoked by both choline and 5-Iodo-A-85380 dihydrochloride. On the contrary, low Aβ concentrations (1 nM and 100 pM) selectively acted on α7 subtypes potentiating the choline-induced release of both aspartate and glutamate, but not the one of GABA.
CONCLUSIONS/SIGNIFICANCE:
The results reinforce the concept that Aβ has relevant neuromodulatory effects, which may span from facilitation to inhibition of stimulated release depending upon the concentration used.
- PMID:
- 22253754
- [PubMed - in process]
- PMCID: PMC3256170
Role of amino acid hydrophobicity, aromaticity, and molecular volume on IAPP(20-29) amyloid self-assembly.
Source
Department of Chemistry, University of Rochester, Rochester, New York 14627.
Abstract
Aromatic amino acids strongly promote cross-β amyloid formation; whether the amyloidogenicity of aromatic residues is due to high hydrophobicity and β-sheet propensity or formation of stabilizing π-π interactions has been debated. To clarify the role of aromatic residues on amyloid formation, the islet amyloid polypeptide 20-29 fragment [IAPP(20-29)], which contains a single aromatic residue (Phe 23), was adopted as a model. The side chain of residue 23 does not self-associate in cross-β fibrils of IAPP(20-29) (Nielsen et al., Angew Chem Int Ed 2009;48:2118-2121), allowing investigation of the amyloidogenicity of aromatic amino acids in a context where direct π-π interactions do not occur. We prepared variants of IAPP(20-29) in which Tyr, Leu, Phe, pentafluorophenylalanine (F5-Phe), Trp, cyclohexylalanine (Cha), α-naphthylalanine (1-Nap), or β-naphthylalanine (2-Nap) (in order of increasing peptide hydrophobicity) were incorporated at position 23 (SNNXGAILSS-NH2), and the kinetic and thermodynamic effects of these mutations on cross-β self-assembly were assessed. The Tyr, Leu, and Trp 23 variants failed to readily self-assemble at concentrations up to 1.5 mM, while the Cha 23 mutant fibrillized with attenuated kinetics and similar thermodynamic stability relative to the wild-type Phe 23 peptide. Conversely, the F5-Phe, 1-Nap, and 2-Nap 23 variants self-assembled at enhanced rates, forming fibrils with greater thermodynamic stability than the wild-type peptide. These results indicate that the high amyloidogenicity of aromatic amino acids is a function of hydrophobicity, β-sheet propensity, and planar geometry and not the ability to form stabilizing or directing π-π bonds. Proteins 2012;. © 2011 Wiley Periodicals, Inc.
Copyright © 2011 Wiley Periodicals, Inc.
- PMID:
- 22253015
- [PubMed - as supplied by publisher]
Hexafluoroisopropanol induces self-assembly of β-amyloid peptides into highly ordered nanostructures.
Source
Council of Scientific and Industrial Research, Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad, 500 007, India.
Abstract
Deposition of insoluble fibrillar aggregates of β-amyloid (Aβ) peptides in the brain is a hallmark of Alzheimer's disease. Apart from forming fibrils, these peptides also exist as soluble aggregates. Fibrillar and a variety of nonfibrillar aggregates of Aβ have also been obtained in vitro. Hexafluoroisopropanol (HFIP) has been widely used to dissolve Aβ and other amyloidogenic peptides. In this study, we show that the dissolution of Aβ40, 42, and 43 in HFIP followed by drying results in highly ordered aggregates. Although α-helical conformation is observed, it is not stable for prolonged periods. Drying after prolonged incubation of Aβ40, 42, and 43 peptides in HFIP leads to structural transition from α-helical to β-conformation. The peptides form short fibrous aggregates that further assemble giving rise to highly ordered ring-like structures. Aβ16-22, a highly amyloidogenic peptide stretch from Aβ, also formed very similar rings when dissolved in HFIP and dried. HFIP could not induce α-helical conformation in Aβ16-22, and rings were obtained from freshly dissolved peptide. The rings formed by Aβ40, 42, 43, and Aβ16-22 are composed of the peptides in β-conformation and cause enhancement in thioflavin T fluorescence, suggesting that the molecular architecture of these structures is amyloid-like. Our results clearly indicate that dissolution of Aβ40, 42 and 43 and the amyloidogenic fragment Aβ16-22 in HFIP results in the formation of annular amyloid-like structures. Copyright © 2012 EuropeanPeptide Society and John Wiley & Sons, Ltd.
Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.
- PMID:
- 22252985
- [PubMed - as supplied by publisher]
The Microtubule-Associated Protein 1A (MAP1A) is an Early Molecular Target of Soluble Aβ-Peptide.
Source
Neurobiology Research Unit 9201, Center for Integrated Molecular Brain Imaging (CIMBI), Copenhagen University Hospital, Rigshospitalet, Blegdamsvej 9, 2100, Copenhagen, Denmark.
Abstract
A progressive accumulation of amyloid β-protein (Aβ) is widely recognized as a pathological hallmark of Alzheimer's disease (AD). Substantial progress has been made toward understanding the neurodegenerative cascade initiated by small soluble species of Aβ and recent evidence supports the notion that microtubule rearrangements may be proximate to neuritic degeneration and deficits in episodic declarative memory. Here, we examined primary cortical neurons for changes in markers associated with synaptic function following exposure to sublethal concentrations of non-aggregated Aβ-peptide. This data show that soluble Aβ species at a sublethal concentration induce degradation of the microtubule-associated protein 1A (MAP1A) without concurrently affecting dendritic marker MAP2 and/or the pre-synaptic marker synaptophysin. In addition, MAP1A was found to highly co-localize with the postsynaptic density-95 (PSD-95) protein, proposing that microtubule perturbations might be central for the Aβ-induced neuronal dysfunctions as PSD-95 plays a key role in synaptic plasticity. In conclusion, this study suggests that disruption of MAP1A could be a very early manifestation of Aβ-mediated synaptic dysfunction-one that presages the clinical onset of AD by years. Moreover, our data support the notion of microtubule-stabilizing agents as effective AD drugs.
- PMID:
- 22252785
- [PubMed - as supplied by publisher]
Small surfactant-like peptides can drive soluble proteins into active aggregates.
Abstract
ABSTRACT:
BACKGROUND:
Inactive protein inclusion bodies occur commonly in Escherichia coli (E. coli) cells expressing heterologous proteins. Previously several independent groups have found that active protein aggregates or pseudo inclusion bodies can be induced by a fusion partner such as a cellulose binding domain from Clostridium cellulovorans (CBDclos) when expressed in E. coli. More recently we further showed that a short amphipathic helical octadecapeptide 18A (EWLKAFYEKVLEKLKELF) and a short beta structure peptide ELK16 (LELELKLKLELELKLK) have a similar property.
RESULTS:
In this work, we explored a third type of peptides, surfactant-like peptides, for performing such a "pulling-down" function. One or more of three such peptides (L6KD, L6K2, DKL6) were fused to the carboxyl termini of model proteins including Aspergillus fumigatus amadoriase II (AMA, all three peptides were used), Bacillus subtilis lipase A (LipA, only L6KD was used, hereinafter the same), Bacillus pumilus xylosidase (XynB), and green fluorescent protein (GFP), and expressed in E. coli. All fusions were found to predominantly accumulate in the insoluble fractions, with specific activities ranging from 25% to 92% of the native counterparts. Transmission electron microscopic (TEM) and confocal fluorescence microscopic analyses confirmed the formation of protein aggregates in the cell. Furthermore, binding assays with amyloid-specific dyes (thioflavin T and Cong red) to the AMA-L6KD aggregate and the TEM analysis of the aggregate following digestion with protease K suggested that the AMA-L6KD aggregate may contain structures reminiscent of amyloids, including a fibril-like structure core.
CONCLUSIONS:
This study shows that the surfactant-like peptides L6KD and it derivatives can act as a pull-down handler for converting soluble proteins into active aggregates, much like 18A and ELK16. These peptide-mediated protein aggregations might have important implications for protein aggregation in vivo, and can be explored for production of functional biopolymers with detergent or other interfacial activities.
- PMID:
- 22251949
- [PubMed - as supplied by publisher]
Prolonged elevation in hippocampal Aβ and cognitive deficits following repeated endotoxin exposure in the mouse.
Source
Texas Christian University, College of Science and Engineering, Department of Psychology, 2800 S. University Drive, Fort Worth, TX 76129, USA.
Abstract
Alzheimer's disease (AD) is characterized by neuronal cell death and atrophy in regions of the adult brain, including the hippocampus and cortex, due to formation of amyloid beta (Aβ) plaques and neurofibrillary tangles. The presence of these pathologies can limit normal signaling properties and ultimately lead to learning and memory deficits. Chronic inflammation has been implicated in the onset and progression of these AD-related pathologies. Our study was designed to assess the effects of peripheral inflammation on pathologies associated with AD by using the bacterial endotoxin lipopolysaccharide (LPS). C57BL/6J mice were given intraperitoneal injections of LPS or saline for 1, 3, or 7 consecutive days. Hippocampal tissue from animals receiving LPS contained significantly higher levels of Aβ1-42, apeptide component of AD plaques, than did those from saline control animals. Central and peripheral pro-inflammatory cytokine levels were increased following a single injection of LPS, but retuned to baseline levels before cognitive testing began. We show that one injection of LPS leads to sickness behavior, but 7 consecutive days does not, indicating tolerance to the endotoxin. Cognitive testing was then conducted to determine if whether deficits from increased Aβ1-42 was evident. Results from both Morris water maze and contextual fear conditioning revealed cognitive deficits in LPS-treated mice. In summary, multiple injections of LPS resulted in increased Aβ1-42 in the hippocampus and cognitive deficits in mice.
Copyright © 2012. Published by Elsevier B.V.
DNA immunization with HBsAg-based particles expressing a B cell epitope ofamyloid β-peptide attenuates disease progression and prolongs survival in a mouse model of Alzheimer's disease.
Source
Immunotherapeutics Unit, Laboratory of Molecular Biology and Immunology, United States.
Abstract
Alzheimer's disease (AD) is an incurable and progressive neurodegenerative senile disorder associated with the brain accumulation of Aβ plaques. Although vaccines that reduce Aβ plaques can control AD, the rationale for their use at the onset of the disease remains debatable. Old humans and mice usually respond poorly to vaccines due to presumably age-related immunological impairments. Here, we report that by modifying vaccines, the poor responsiveness of old mice can be reversed. Unlike the Aβ peptide vaccine, DNA immunizations with the amino-terminal Aβ(1-11) fragment exposed on the surface of HBsAg particles elicit high levels of anti-Aβ antibody both in young and old mice. Importantly, in AD model 3xTgAD mice, the vaccine reduced Aβ plaques, ameliorated cognitive impairments and, surprisingly, significantly increased life span. Hence, we propose that vaccines targeting Aβ(1-11) can efficiently combat AD-induced pathological alterations and provide survival benefit in patients with AD.
Copyright © 2012. Published by Elsevier Ltd.
Oligomeric Intermediates in Amyloid Formation: Structure Determination and Mechanisms of Toxicity.
Abstract
Oligomeric intermediates are non-fibrillar polypeptide assemblies that occur during amyloid fibril formation and that are thought to underlie the aetiology of amyloid diseases, such as Alzheimer's disease, Parkinson's disease and Huntington's disease. Focusing primarily on the oligomeric states formed from Alzheimer's disease β-amyloid (Aβ)peptide, this review will make references to other polypeptide systems, highlighting common principles or sequence-specific differences. The covered topics include the structural properties and polymorphism of oligomers, the biophysical mechanism of peptide self-assembly and its role for pathogenicity in amyloid disease. Oligomer-dependent toxicity mechanisms will be explained along with recently emerging possibilities of interference.
Copyright © 2011. Published by Elsevier Ltd.
Amyloid-Derived Peptide Forms Self-Assembled Monolayers on Gold Nanoparticle with a Curvature-Dependent β-Sheet Structure.
Abstract
Using a combination of Fourier transform infrared (FTIR) spectroscopy and solid state nuclear magnetic resonance (SSNMR) techniques, the secondary structure of peptides anchored on gold nanoparticles of different sizes is investigated. The structure of the well studied CALNN-capped nanoparticles is compared to the structure of nanoparticles capped with a new cysteine-terminated peptide, CFGAILSS. The design of that peptide is derived from the minimal amyloidogenic sequence FGAIL of the human islet polypeptide amylin. We demonstrate that CFGAILSS forms extended fibrils in solution. When constrained at a nanoparticle surface, CFGAILSS adopts a secondary structure markedly different from CALNN. Taking into account the surface selection rules, the FTIR spectra of CFGAILSS-capped gold nanoparticles indicate the formation of β-sheets which are more prominent for 25 nm diameter nanoparticles than for 5 nm nanoparticles. No intermolecular 13C-13C dipolar coupling is detected with rotational resonance SSNMR for CALNN-capped nanoparticles while CALNN is in a random coil configuration. Coupling is detected for CFGAILSS-capped gold nanoparticles, however, consistent with an intermolecular 13C-13C distance of 5.0 Å ± 0.3 Å in agreement with intermolecular hydrogen bonding in a parallel β-sheet structure.
β-Amyloid peptide is internalized into chick retinal neurons and alters the distribution of myosin Vb.
Source
Instituto de Bioquímica Médica - Universidade Federal do Rio de Janeiro; Departamento de Biociências da Atividade Física - Escola da Educação Física e Desportos - Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, 21941-902, Brazil.
Abstract
The most common neurodegenerative disorder afflicting the aging human population is Alzheimer's disease. A major hallmark of Alzheimer's disease is dementia from a loss of neuronal function, attributed to the presence and accumulation of β-amyloid peptide into senile plaques. Preceding senile plaque formation, abnormalities in axons can be observed as changes in morphologies and intracellular trafficking. Recently, it has been recognized that β-amyloid also accumulates within neurons and this intraneuronal β-amyloid accumulation has been reported to be critical in the disruption of synapses and cognitive function. Here we report on the internalization of a fluorescently labeled β-amyloidpeptide into cultured chick retinal neurons. The pattern of β-amyloid distribution during the time course of incubation is reminiscent of the endocytic pathway. Furthermore, the distribution of the internalized β-amyloid peptide converges with that of myosin Vb and both relocalize from the axon to cell body. These observations are consistent with the hypothesis that Alzheimer's disease proceeds as a result of an imbalance between β-amyloid production and β-amyloid clearance, suggesting a role for myosin Vb in this process. © 2012 Wiley Periodicals, Inc.
Copyright © 2012 Wiley Periodicals, Inc.
A novel study on amyloid beta peptide 40, 42 and 40/42 ratio in Saudi autistics.
Abstract
ABSTRACT: Objectives: We examined whether plasma concentrations of amyloid beta (Abeta) as protein derivatives play a central role in the etiology of autistic features. Design and Methods: Concentrations of human Abeta (1-42), Abeta (1-40), and Abeta (40/42) in the plasma of 52 autistic children (aged 3-16 years) and 36 age-matched control subjects were determined by using the ELISA technique and were compared. Results: Compared to control subjects, autistic children exhibited significantly lower concentrations of both Abeta (1-40) and Abeta (1-42) and lower Abeta (40/42) concentration ratio. Receiver operating characteristics curve (ROC) analysis showed that these measurements of Abeta peptides showed high specificity and sensitivity in distinguishing autistic children from control subjects. Conclusions: Lower concentrations of Abeta (1-42) and Abeta (1-40) were attributed to loss of Abeta equilibrium between the brain and blood, an imbalance that may lead to failure to draw Abeta from the brain and/or impairment of beta- and gamma- secretase's concentration or kinetics as enzymes involving in Abeta production.
Aβ delays fibrin clot lysis by altering fibrin structure and attenuating plasminogen binding to fibrin.
Source
Laboratory of Neurobiology and Genetics, The Rockefeller University, New York, NY, United States.
Abstract
Alzheimer's disease is characterized by the presence of increased levels of the beta-amyloid peptide (Aβ) in the brain parenchyma and cerebral blood vessels. This accumulated Aβ can bind to fibrin(ogen) and render fibrin clots more resistant to degradation. Here, we demonstrate that Aβ(42) specifically binds to fibrin and induces a tighter fibrin network characterized by thinner fibers and increased resistance to lysis. Aβ(42)-induced structural changes cannot be the sole mechanism of delayed lysis, however, since Aβ overlaid on normal pre-formed clots also binds to fibrin and delays lysis without altering clot structure. In this regard, we show that Aβ interferes with the binding of plasminogen to fibrin, which could impair plasmin generation and fibrin degradation. Indeed, plasmin generation by tPA, but not streptokinase, is slowed in fibrin clots containing Aβ(42), and clot lysis by plasmin, but not trypsin, is delayed. Notably, plasmin and tPA activities, as well as tPA-dependent generation of plasmin in solution, are not decreased in the presence of Aβ(42). Our results indicate the existence of two mechanisms of Aβ(42) involvement in delayed fibrinolysis: 1) through the induction of a tighter fibrin network composed of thinner fibers; and 2) through inhibition of plasmin(ogen)'s binding to fibrin.
Peptides for therapy and diagnosis of Alzheimer's disease.
Source
Dieter Willbold, Forschungszentrum Jülich, ICS-6, D-52425 Jülich, Germany. d.willbold@fz-juelich.de.
Abstract
Alzheimer's disease (AD) is a progressive neurodegenerative disorder with devastating effects. The greatest risk factor to develop AD is age. Today, only symptomatic therapies are available. Additionally, AD can be diagnosed with certainty only post mortem, whereas the diagnosis "probable AD" can be established earliest when severe clinical symptoms appear. Specific neuropathological changes like neurofibrillary tangles and amyloid plaques define AD. Amyloid plaques are mainly composed of the amyloid-β peptide (Aβ). Several lines of evidence suggest that the progressive concentration and subsequent aggregation and accumulation of Aβ play a fundamental role in the disease progress. Therefore, substances which bind to Aβ and influence aggregation thereof are of great interest. An enormous number of organic substances for therapeutic purposes are described. This review focuses on peptides developed for diagnosis and therapy of AD and discusses the pre- and disadvantages of peptide drugs.
- PMID:
- 22236121
- [PubMed - as supplied by publisher]
Amyloid-β oligomers induce differential gene expression in adult human brain slices.
Source
Federal University of Rio de Janeiro, Brazil;
Abstract
Cognitive decline in Alzheimers disease (AD) is increasingly attributed to the neuronal impact of soluble oligomers of theamyloid-β peptide (AβOs). Current knowledge on the molecular and cellular mechanisms underlying the toxicity of AβOs stems largely from rodent-derived cell/tissue culture experiments or from transgenic models of AD, which do not necessarily recapitulate the complexity of the human disease. Here, we used DNA microarray and RT-PCR to investigate changes in transcription in adult human cortical slices exposed to sub-lethal doses of AβOs. Results revealed a set of 27 genes that showed consistent differential expression upon exposure of slices from three different donors to AβOs. Functional classification of differentially expressed genes revealed that AβOs impact pathways important for neuronal physiology and known to be dysregulated in AD, including vesicle trafficking, cell adhesion, actin cytoskeleton dynamics and insulin signaling. Most genes (70%) were down-regulated by AβO treatment, suggesting a predominantly inhibitory effect on the corresponding pathways. Significantly, AβOs induced downregulation of synaptophysin, a presynaptic vesicle membrane protein, suggesting a mechanism by which oligomers cause synapse failure. Results provide insight into early mechanisms of pathogenesis of AD, and suggest that the neuronal pathways affected by AβOs may be targets for development of novel diagnostic or therapeutic approaches.
Structural Basis of β-Amyloid-Dependent Synaptic Dysfunctions.
Source
Max Planck Research Unit for Enzymology of Protein Folding, & MLU, Weinbergweg 22, 06120 Halle (Saale) (Germany).
Abstract
Learn about Alzheimer: The molecular conformation of a toxic β-amyloid oligomer structure was determined by NMR spectroscopy. The measurements show a N-terminal β strand that controls the partitioning between oligomer and protofibril formation. Targeting the N-terminus of the peptide neutralizes Aβ-dependent neuronal dysfunctions. The data have important implications for understanding the structural basis of Alzheimer's disease.
Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
[Compensatory function of transthyretin in Alzheimer's disease].
Abstract
Alzheimer's disease (AD) is the most common form of age-related primary neurodegenerative diseases characterized by progressive memory loss, aphasia, and intellectual and mental breakdown. Pathogenesis of AD is based on the early synaptic dysfunction following neurodegeneration and neuronal death. According to modern concepts, the development of neuropathological processes is due to progressively deposited intermediates of amyloid fibrils that represent oligomers consisting of short peptide named amyloid beta protein (Abeta). In this context, it is reasonable to propose that one of the compensatory mechanisms of AD might be inhibition of Abeta oligomerization by sequestration or clearance of Abeta. Experiments with transgenic animals and epidemiological studies demonstrate that major protein of cerebrospinal fluid, transthyretin, is a natural neuroprotector that inhibits Abeta amyloid formation and restore cognitive functions. The study of Abeta-transthyretin complexes allowed to create peptides that are mimetics of transthyretin. These mimetics inhibit amyloid formation in vitro and, therefore, could be used in therapeutic treatment of AD.
- PMID:
- 22232933
- [PubMed - in process]
Characterization of Insulin Degrading Enzyme and Other Amyloid-β Degrading Proteases in Human Serum: A Role in Alzheimer's Disease?
Source
Departments of Pharmacology and Experimental Therapeutics, Boston University Medical Campus, Boston, MA, USA Departments of Anesthesiology, The Second People's Hospital of Shenzhen, PR China.
Abstract
Sporadic Alzheimer's disease (AD) patients have low amyloid-β peptide (Aβ) clearance in the central nervous system. The peripheral Aβ clearance may also be important but its role in AD remains unclear. We aimed to study the Aβ degrading proteases including insulin degrading enzyme (IDE), angiotensin converting enzyme (ACE) and others in blood. Using the fluorogenic substrate V (a substrate of IDE and other metalloproteases), we showed that human serum degraded the substrate V, and the activity was inhibited by adding increasing dose of Aβ. The existence of IDE activity was demonstrated by the inhibition of insulin, amylin, or EDTA, and further confirmed by immunocapture of IDE using monoclonal antibodies. The involvement of ACE was indicated by the ability of the ACE inhibitor, lisinopril, to inhibit the substrate V degradation. To test the variations of substrate V degradation in humans, we used serum samples from a homebound elderly population with cognitive diagnoses. Compared with the elderly who had normal cognition, those with probable AD and amnestic mild cognitive impairment (amnestic MCI) had lower peptidase activities. Probable AD or amnestic MCI as an outcome remained negatively associated with serum substrate V degradation activity after adjusting for the confounders. The elderly with probable AD had lower serum substrate V degradation activity compared with those who had vascular dementia. The blood proteases mediating Aβ degradation may be important for the AD pathogenesis. More studies are needed to specify each Aβ degrading protease in blood as a useful biomarker and a possible treatment target for AD.
Therapeutic Albumin Binding to Remove Amyloid-β
Source
Instituto Grifols S.A., Research & Development Area, Polígon Llevant, Parets del Vallès, Barcelona, Spain.
Abstract
Clearance of plasma amyloid-β (Aβ) through plasma exchange and replacement with therapeutic albumin to facilitate net Aβ efflux from the brain to plasma is a novel approach for the treatment of Alzheimer's disease. Therefore, thorough characterization of the capacity of therapeutic albumin to bind Aβ is warranted. In this study, Aβ40 and Aβ42 were quantified by commercial ELISA or Araclon ABtest® in samples of Grifols' therapeutic albumin (Albutein®) 5%, 20%, and 25%. The capacity of Albutein® to bind Aβ was assessed by: a) ELISA in serially diluted therapeutic albumin (0-45 mg/ml protein concentration) to which 80 pg/ml of synthetic Aβ peptide (sAβ40 or sAβ42) were added; b) ELISA in samples of the therapeutic albumin containing serially diluted sAβ40 or sAβ42 (60-400 pg/ml); and c) surface plasmon resonance (SPR) for sAβ42 binding. The Aβ content in Albutein® was below the quantification threshold of the ELISA tests (<25 to <62.5 pg/ml) and ABtest® (<3.125 pg/ml). Quantification of exogenously added sAβ42 decreased in parallel with increasing protein concentration (59-78% at 45 mg/ml albumin). Recovery of sAβ serially diluted in Albutein® was ∼60% for sAβ40 and ∼70% for sAβ42, but was ∼100% in control samples without albumin. The KD by SPR analysis for sAβ42 interaction with Albutein® was 1.72 ± 0.24 × 10-6 M. In conclusion, Grifols' therapeutic albumin has undetectable content of Aβ40 and Aβ42. Moreover, Grifols' therapeutic albumin consistently binds peptides containing the primary sequence of human Aβ.
Amyloid-β Protein Precursor Regulates Phosphorylation and Cellular Compartmentalization of Microtubule Associated Protein Tau.
Source
Dipartimento di Oncologia, Biologia e Genetica, Università degli Studi di Genova, Genova, Italy.
Abstract
Tau is a multifunctional protein detected in different cellular compartments in neuronal and non-neuronal cells. When hyperphosphorylated and aggregated in atrophic neurons, tau is considered the culprit for neuronal death in familial and sporadic tauopathies. With regards to Alzheimer's disease (AD) pathogenesis, it is not yet established whether entangled tau represents a cause or a consequence of neurodegeneration. In fact, it is unquestionably accepted thatamyloid-β protein precursor (AβPP) plays a pivotal role in the genesis of the disease, and it is postulated that the formation of toxic amyloid-β peptides from AβPP is the primary event that subsequently induces abnormal tau phosphorylation. In this work, we show that in the brain of AD patients there is an imbalance between the nuclear and the cytoskeletal pools of phospho-tau. We observed that in non-AD subjects, there is a stable pool of phospho-tau which remains strictly confined to neuronal nuclei, while nuclear localization of phospho-tau is significantly underrepresented in neurons of AD patients bearing neurofibrillary tangles. A specific phosphorylation of tau is required during mitosis in vitro and in vivo, likely via a Grb2-ERK1/2 signaling cascade. In differentiated neuronal A1 cells, the overexpression of AβPP modulates tau phosphorylation, altering the ratio between cytoskeletal and nuclear pools, and correlates with cell death. Altogether our data provide evidence that AβPP, in addition to amyloid formation, modulates the phosphorylation of tau and its subcellular compartmentalization, an event that may lead to the formation of neurofibrillary tangles and to neurodegeneration when occurring in postmitotic neurons.
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