RSSTol2 gene trap integrations in the zebrafish amyloid precursor protein genes appa and aplp2 reveal accumulation of secreted APP at the embryonic veins.
Source
Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA 50011; Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011.
Abstract
The single spanning transmembrane amyloid precursor protein (APP) and its proteolytic product, amyloid-beta (Aβ)peptide, have been intensely studied due to their role in the pathogenesis of Alzheimer's disease. However, the biological role of the secreted ectodomain of APP, which is also generated by proteolytic cleavage, is less well understood. Here, we report Tol2 RFP transposon gene trap integrations in the zebrafish amyloid precursor protein a (appa) and amyloid precursor-like protein 2 (aplp2) genes. The transposon integrations are predicted to disrupt the appa and aplp2 genes to primarily produce secreted ectodomains of the corresponding proteins that are fused to RFP. Our results indicate the Appa-RFP and Aplp2 fusion proteins are likely secreted from the central nervous system and accumulate in the embryonic veins independent of blood flow. The zebrafish appa and aplp2 transposon insertion alleles will be useful for investigating the biological role of the secreted form of APP. Developmental Dynamics, 2011. © 2011 Wiley Periodicals, Inc.
Copyright © 2011 Wiley Periodicals, Inc.
- PMID:
- 22275008
- [PubMed - as supplied by publisher]
The effects of vitamin A supplementation for 3 months on adult rat nigrostriatal axis: Increased monoamine oxidase enzyme activity, mitochondrial redox dysfunction, increased β-amyloid(1-40) peptide and TNF-α contents, and susceptibility of mitochondria to an in vitro H(2)O(2) challenge.
Source
Centro de Estudos em Estresse Oxidativo (Lab. 32), Departamento de Bioquímica, ICBS, Universidade Federal do Rio Grande do Sul, rua Ramiro Barcelos, 2600-Anexo, CEP 90035-003, Porto Alegre, RS, Brazil.
Abstract
Even though vitamin A has been viewed as an antioxidant molecule, recent findings demonstrate that such vitamin elicits pro-oxidant effects in vivo. Moreover, vitamin A supplements utilization may increase mortality rates among healthy subjects. However, the mechanism by which vitamin A elicits such effects remains to be better analyzed. In this regard, we investigated here the consequences of vitamin A supplementation at 500, 1000, or 2500IU/kgday(-1) for 3 months on adult rat substantia nigra and striatum total and mitochondrial redox state (both oxidative and nitrosative stress markers), electron transfer chain activity, monoamine oxidase (MAO) enzyme activity, endoplasmic reticulum stress marker (BiP), α- and β-synucleins, β-amyloid peptide (1-40), dopamine D2 receptor (D2R), receptor for advanced glycation end products (RAGE), caspase-3 and caspase-8 enzyme activity and tumor necrosis factor-α (TNF-α) levels. Also, nigrostriatal mitochondria were isolated and challenged with 50μM H(2)O(2)in vitro after vitamin A supplementation and complexes I-III, II-III, and IV enzyme activity was recorded. We observed both total and mitochondrial oxidative and nitrosative stress, increased MAO enzyme activity, and increased levels of α-synuclein, β-amyloid peptide, RAGE, and TNF-α, but decreased D2R in both rat brain areas. Furthermore, vitamin A supplementation induced a decrease in nigral, but not striatal, β-synuclein levels in this work. Moreover, mitochondria isolated from both substantia nigra and striatum of vitamin A-treated rats were more sensitive to H(2)O(2) than control mitochondria as assessed through the in vitro assay. Overall, these data may be useful to explain how vitamin A elicits neurotoxic effects chronically.
Copyright © 2012. Published by Elsevier Inc.
- PMID:
- 22274401
- [PubMed - as supplied by publisher]
Self-Assembly of Aβ-based Peptide Amphiphiles with Double Hydrophobic Chains.
Abstract
Two peptide-amphiphiles (PAs), 2C12-Lys-Aβ(12-17) and C12-Aβ(11-17)-C12, were constructed with two alkyl chains attached to a key fragment of amyloid β-peptide (Aβ(11-17)) at different positions. The two alkyl chains of 2C12-Lys-Aβ(12-17) were attached to the same terminus of Aβ(12-17), while the two alkyl chains of C12-Aβ(11-17)-C12 were separately attached to each terminus of Aβ(11-17). The self-assembly behavior of both the PAs in aqueous solutions was studied at 25 °C and at pHs 3.0, 4.5, 8.5 and 11.0, focusing on the effects of the attached positions of hydrophobic chains to Aβ(11-17) and the net charge quantity of Aβ(11-17) head group. Cryogenic transmission electron microscopy and atomic force microscopy show that 2C12-Lys-Aβ(12-17) self-assembles into long stable fibrils over the entire pH range, while C12-Aβ(11-17)-C12 forms short twisted ribbons and lamellae by adjusting pHs. The above fibrils, ribbons and lamellae are generated by the lateral association of nanofibrils. Circular dichroism spectroscopy suggests the formation of β-sheet structure with twist and disorder to different extents in the aggregates of both the PAs. Some of the C12-Aβ(11-17)-C12 molecules adopt turn conformation with the weakly charged peptide sequence, and the fourier transform infrared spectroscopy indicates that the turn content increases with the pH increase. This work provides additional basis for the manipulations of the PA's nanostructures and will lead to the development of tunable nanostructure materials.
- PMID:
- 22272929
- [PubMed - as supplied by publisher]
Flavonoids protect cerebrovascular endothelial cells through Nrf2 and PI3K from β-amyloid peptide-induced oxidative damage.
Source
School of Public Health and Family Medicine, Capital Medical University, China, 100069.
Abstract
β-amyloid peptides (Aβ) induced cerebrovascular dysfunction has been recognized as a vital factor involved in the pathogenesis of neurodegeneration. Genistein, a flavonoid, has antioxidative properties to prevent neurodegeneration induced by β-amyloid peptides. In this study, we were investigating whether genistein could antagonize oxidative damage induced by β-amyloid peptide 25-35 (Aβ25-35) in bEND.3 cells, and also identifying the potential neuroprotective targets of genistein. Vitamin E was used as the positive control. The bEND.3 cells were pre-incubated with/out genistein or vitamin E for 2 h followed by the incubation with 25 μM Aβ25-35 for another 24 h. The reactive oxygen species (ROS), nitrotyrosine, cell redox state, mRNA or protein expressions of the factors on Nrf2 signaling pathway were measured after Aβ25-35 treatment. The results showed that genistein alleviated the increase of ROS and nitrotyrosine production induced by Aβ25-35, and maintained bEND.3 cell redox state by increasing GSH level and GSH/GSSG. Genistein could reverse the down-regulation of total protein and mRNA expression of NF-E2-related factor 2 (Nrf2), nuclear Nrf2, γ-glutamylcysteine synthetase (γ-GCS), phosphatidylinositol 3-kinase (PI3K) induced by Aβ25-35; while PI3K inhibitor LY294002 could attenuate the activation effects of genistein on Nrf2, especially for the promotion of nuclear translocation. These results suggested that genistein could protect cerebrovascular endothelial cells from Aβ25-35-induced oxidative damage. The potential mechanisms might be associated with the activation of Nrf2 signaling pathway by modulating PI3K activity.
- PMID:
- 22272764
- [PubMed - as supplied by publisher]
Hippocampal BDNF Expression in a Tau Transgenic Mouse Model.
Source
Max-Planck Institute für Biologie des Alterns/Max-Planck Institute for Biology of Ageing, Gleueler Strasse 50a, D-50931 Köln, Germany. sylvie.burnouf@age.mpg.de.
Abstract
Alzheimer's disease (AD) is a neurodegenerative disorder characterized by extracellular accumulation of amyloiddeposits and intracellular neurofibrillary tangles (NFT) composed of hyperphosphorylated Tau proteins. Brain-derived neurotrophic factor (BDNF) is a neurotrophic factor playing a critical role in hippocampal synaptic plasticity and memory and whose levels have been shown reduced in AD brains. While recent data support a pivotal role of β-amyloid peptidestowards BDNF decrease, whether Tau pathology impacts on BDNF expression remains unknown so far. In the present study, we have evaluated this relationship using quantitative PCR, Western blot and ELISA in the THY-Tau22 transgenic strain, known to display a progressive development of both hippocampal AD-like Tau pathology and memory impairments. We observed that Tau pathology was not associated with down-regulation of BDNF at the protein and mRNA levels in this model, suggesting that the alteration of BDNF homeostasis observed in AD patients' brains might rather be ascribed to amyloid pathology.
- PMID:
- 22272617
- [PubMed - as supplied by publisher]
Pharmacological inhibition of PKR in APPswePS1dE9 mice transiently prevents inflammation at 12 months of age but increases Aβ42 levels in the late stages of the Alzheimer's disease.
Source
Research Group on Brain Aging, GReViC EA 3808, 6 rue de la Milétrie BP 199, 86034 Poitiers Cedex, France. guylene.page@univ-poitiers.fr.
Abstract
The double-stranded RNA-dependent protein kinase (PKR) is switched on by a wide range of stimuli, including theamyloid peptide. Then, PKR transmits signals to the translational machinery, apoptosis and inflammatory signaling pathways by interacting with some adapters. In virus-infected cells, PKR engages the nucleus factor κB (NF-κB) pathway. In many models of Alzheimer's disease (AD) and patients with AD, PKR was activated. Furthermore, there is strong evidence implicating the inflammatory process in the AD brain. However, the PKR involvement in inflammatory responses in AD is not elucidated. Based on our previous in vitro results, the aim of this study was to evaluate the effects of a pharmacological inhibition of PKR in inflammation in APPswePS1dE9 transgenic mice. Our results showed that PKR inhibition prevented the NF-κB activation and production of tumor necrosis factor alpha (TNFα) and interleukin (IL)-1β at 12 months of age without decrease of Aβ42 levels and memory deficits. Surprisingly, PKR inhibition failed to prevent IL-1β-mediated inflammation and induced a great increase in β-amyloid peptide (Aβ42) levels at 18 months of age. In this model, our findings highlight the lack of relationship between inflammation and Aβ42 levels. Moreover, the age-dependent inflammatory response must be carefully taken into account in the establishment of an anti-inflammatory therapy in AD.
- PMID:
- 22272616
- [PubMed - as supplied by publisher]
Trehalose protects from aggravation of amyloid pathology induced by isoflurane anesthesia in APPswe mutant mice.
Source
Department of Neurobiology, Hospital Ramón y Cajal , Ctra. de Colmenar Km. 9 , Madrid 28034. Spain. maria.a.mena@hrc.es.
Abstract
There is an open controversy about the role of surgery and anesthesia in the pathogenesis of Alzheimer's disease (AD). Clinical studies have shown a high prevalence of these procedures in subjects with AD but the interpretation of these studies is difficult because of the co-existence of multiple variables. Experimental studies in vitro and in vivo have shown that small molecular weight volatile anesthetics enhance amyloidogenesis in vitro and produce behavioral deficits and brain lesions similar to those found in patients with AD. We examined the effect of co-treatment with trehalose on isoflurane-induced amyloidogenesis in mice. WT and APPswe mice, of 11 months of age, were exposed to 1% isoflurane, 3 times, for 1.5 hours each time and sacrificed 24 hours after their last exposure to isoflurane. The right hemi-brain was used for histological analysis and the contra-lateral hemi-brain used for biochemical studies. In this study, we have shown that repetitive exposure to isoflurane in pre-symptomatic mature APPswe mice increases apoptosis in hippocampus and cerebral cortex, enhances astrogliosis and the expression of GFAP and that these effects are prevented by co-treatment with trehalose, a disaccharide with known effects as enhancer of autophagy. We have also confirmed that in our model the co-treatment with trehalose increases the expression of autophagic markers as well as the expression of chaperones. Co-treatment with trehalose reduces the levels of β amyloid peptide aggregates, tau plaques and levels of phospho-tau. Our study, therefore, provides new therapeutic avenues that could help to prevent the putative pro-amyloidogenic properties of small volatile anesthetics.
- PMID:
- 22272607
- [PubMed - as supplied by publisher]
Calorimetric investigation of copper(II) binding to Aβ peptides: thermodynamics of coordination plasticity.
Source
Department of Chemistry, East Carolina University, 300 Science and Technology, Greenville, NC, 27858, USA.
Abstract
Metal ions have been shown to play a critical role in β-amyloid (Aβ) neurotoxicity, thus prompting an intense investigation into the formation of metal-Aβ complexes. Isothermal titration calorimetry (ITC) has been widely used to determine binding constants (K) for a variety of metal-protein interactions, including those in metal-Aβ complexes. In this study, ITC was used to more fully quantify the thermodynamics (K, ΔG, ΔH, and TΔS) of Cu(2+) binding to Aβ16, N-acetyl-Aβ16, Aβ28, N-acetyl-Aβ28, and Aβ28 variants (H6A, H13A, H14A) at pH 7.4 and 37 °C. After deconvolution of competing reactions, K for Aβ16 was found to be 1.1 (±0.13) × 10(9) and is in strong agreement with literature values measured under similar conditions. Further, a similar K value was obtained at two additional concentrations of competing ligand, suggesting that ternary complex formation is not significant. The acetylated peptide analogs reveal a marked decrease in the overall free energy upon binding, which is the result of less favorable enthalpic and entropic contributions. Circular dichroism spectroscopy shows conformational changes that are consistent with these results. Most importantly, data for Aβ28 variants lacking a potential Cu(2+)-binding histidine residue reveal that the overall free energy of binding remains constant, which is the result of entropy/enthalpy compensation. These data provide fundamental thermodynamic evidence for coordination plasticity in Cu(2+) binding to Aβ and other intrinsically disorderedpeptides.
Temporal course of cerebrospinal fluid dynamics and amyloid accumulation in the aging rat brain from three to thirty months.
Abstract
ABSTRACT: BACKGROUND: Amyloid accumulation in the brain parenchyma is a hallmark of Alzheimer's disease (AD) and is seen in normal aging. Alterations in cerebrospinal fluid (CSF) dynamics are also associated with normal aging and AD. This study analyzed CSF volume, production and turnover rate in relation to amyloid-beta peptide (Abeta) accumulation in the aging rat brain. Methods: Aging Fischer 344/Brown-Norway hybrid rats at 3, 12, 20, and 30 months were studied. CSF production was measured by ventriculo-cisternal perfusion with blue dextran in artificial CSF; CSF volume by MRI; and CSF turnover rate by dividing the CSF production rate by the volume of the CSF space. Abeta40 and Abeta42 concentrations in the cortex and hippocampus were measured by ELISA. Results: There was a significant linear increase in total cranial CSF volume with age: 3-20 months (p<0.01); 3-30 months (p<0.001). CSF production rate increased from 3-12 months (p<0.01) and decreased from 12-30 months (p<0.05). CSF turnover showed an initial increase from 3 months (9.40 day-1) to 12 months (11.30 day-1) and then a decrease to 20 months (10.23 day-1) and 30 months (6.62 day-1). Abeta40 and Abeta42 concentrations in brain increased from 3-30 months (p<0.001). Both Abeta42 and Abeta40 concentrations approached a steady state level by 30 months. Conclusions: In young rats there is no correlation between CSF turnover and Abeta brain concentrations. After 12 months, CSF turnover decreases as brain Abeta continues to accumulate. This decrease in CSF turnover rate may be one of several clearance pathway alterations that influence age-related accumulation of brain amyloid.
Hydrogen exchange mass spectrometry as an analytical tool for the analysis ofamyloid fibrillogenesis.
Source
Center for Insoluble Protein Structure and Interdisciplinary Nanoscience Center (iNANO) at the Department of Molecular Biology, Science Park, University of Aarhus, Gustav Wieds Vej 10c, 8000 Aarhus C, Denmark.
Abstract
In this study, we have used glucagon as a model system for analyzing amyloid fibrillogenesis by hydrogen exchange MALDI mass spectrometry (HXMS). The hydrogen exchange mass spectrometry data correlated well with the traditional method based on Thioflavin T fluorescence and provided quantitative information by measuring the fibrillating molecules directly. The hydrogen exchange mass spectrometry data collected during fibrillogenesis revealed that glucagon fibrillation was a two component system showing an on/off type of interaction where only monomeric and fibrils were present without any substantial amount of intermediate species. This was evident by the extensive deuteration of the monomer and protection of the entire 29 residue glucagon peptide upon fibrillation.. The method complements the traditional procedures and has the potential to provide new information with respect to the nature of transient species, the structure of the growing fibrils and the mechanism of formation.
- PMID:
- 22267952
- [PubMed]
- PMCID: PMC3261750
- [Available on 2012/4/30]
Biochemical inhibition of ATase1 and ATase2 activity reduces BACE1 levels and Aβ generation.
Source
University of Wisconsin-Madison, United States.
Abstract
The cellular levels of β-site APP cleaving enzyme 1 (BACE1), the rate-limiting enzyme for the generation of the Alzheimer's disease (AD) amyloid β-peptide (Aβ), are tightly regulated by two ER-based acetyl-CoA:lysine acetyltransferases, ATase1 and ATase2. Here we report that both acetyltransferases are expressed in neurons and glial cells, and are up-regulated in the brain of AD patients. We also report the identification of first and second generation compounds that inhibit ATase1/ATase2 and down-regulate the expression levels as well as activity of BACE1. The mechanism of action involves competitive and non-competitive inhibition as well as generation of unstable intermediates of the ATases that undergo degradation.
Phosphorylation of the amyloid-β peptide at serine 8 attenuates its clearance via insulin degrading and angiotensin converting enzymes.
Source
University of Bonn, Germany;
Abstract
Accumulation of amyloid β-peptides (Aβ) in the brain is a common pathological feature of Alzheimer's disease (AD). Aggregates of Aβ are neurotoxic and appear to be critically involved in the neurodegeneration during AD pathogenesis. Accumulation of Aβ could be caused by increased production as indicated by several mutations in the amyloidprecursor protein or the γ-secretase components presenilin-1 or -2 that cause familial early onset AD. However, recent data also indicate a decreased clearance rate of Aβ in AD brains. We recently demonstrated that Aβ undergoes phosphorylation by extracellular or cell surface localized protein kinase A, leading to increased aggregation. Here we provide evidence that phosphorylation of monomeric Aβ at serine residue 8 also decreases its clearance by microglial cells. By using mass spectrometry, we demonstrate that phosphorylation at serine 8 inhibits the proteolytic degradation of monomeric Aβ by the insulin degrading enzyme (IDE), a major Aβ degrading enzyme released from microglial cells. Phosphorylation also decreased the degradation of Aβ by the angiotensin converting enzyme (ACE). In contrast, Aβ degradation by plasmin was largely unaffected by phosphorylation. Thus, phosphorylation of Aβ could play a dual role in Aβ metabolism. It decreases its proteolytic clearance and also promotes its aggregation. The inhibition of extracellular Aβ phosphorylation, stimulation of cell-surface protease expression and/or increasing their activity could be explored to promote Aβ degradation in AD therapy or prevention.
Assessment of the range of the HIV-1 infectivity enhancing effect of individual human semen specimen and the range of inhibition by EGCG.
Abstract
ABSTRACT: Recently, it has been shown that human ejaculate enhances human immunodeficiency virus 1 (HIV-1) infectivity. Enhancement of infectivity is conceived to be mediated by amyloid filaments from peptides that are proteolytically released from prostatic acid phosphatase (PAP), termed Semen-derived Enhancer of Virus Infection (SEVI). The aim of this study was to test the range of HIV-1 infectivity enhancing properties of a large number of individual semen samples (n=47) in a TZM-bl reporter cell HIV infection system. We find that semen overall increased infectivity to 156% of the control experiment without semen, albeit with great inter- and intraindividual variability (range -53%-363%). Using transmission electron microscopy, we provide evidence for SEVI fibrils in fresh human semen for the first time. Moreover, we confirm that the infectivity enhancing property can be inhibited by the major green tea ingredient epigallocatechin-3-gallate (EGCG) at non-toxic concentrations. The median inhibition of infection by treatment with 0.4 mM EGCG was 70.6% (p<0.0001) in our cohort. Yet, there were substantial variations of inhibition and in a minority of samples, infectivity enhancement was not inhibited by EGCG treatment at all. Thus, topical application of EGCG may be a feasible additional measure to prevent the sexual transmission of HIV. However, the reasons for the variability in the efficacy of the abrogation of semen-mediated enhancement of HIV-1 infectivity and EGCG efficacy have to be elucidated before therapeutic trials can be conducted.
Wild-type amyloid beta 1-40 peptide induces Vascular Smooth Muscle Cell death independently from Matrix Metalloprotease activity.
Source
Paris 6 Pierre et Marie Curie University, UR4, Stress, vieillissement et Inflammation 7 quai Saint-Bernard, 75252 Paris, France Cancer Research Center, Sanford-Burnham Medical Research Institute, La Jolla, California 92037, United States of America.
Abstract
Cerebral amyloid angiopathy (CAA) is an important cause of intracerebral hemorrhages in the elderly, characterized byamyloid-β (Aβ) peptide accumulating in central nervous system blood vessels. Within the vessel walls, Aβ peptidedeposits (composed mainly of wild-type (WT)Aβ(1-40) peptide in sporadic forms) induce impaired adhesion of vascular smooth muscle cells (VSMCs) to the extracellular matrix (ECM) associated to their degeneration. This process often results in a loss of blood vessel wall integrity and ultimately translates into cerebral ischemia and micro-hemorrhages, both clinical features of CAA. In this study, we decipher the molecular mechanism of MMP-2 activation in WT-Aβ(1-40) -treated VSMC and provide evidence that matrix metalloprotease (MMP) activity, although playing a critical role in cell detachment disrupting ECM components, is not involved in the wild-type Aβ(1-40) -induced degeneration of VSMCs. Indeed, whereas this peptide clearly induced VSMC apoptosis, neither preventing MMP-2 activity, nor hampering the expression of membrane-type1 MMP, or preventing tissue inhibitors of MMPs-2 (TIMP-2) recruitment (two proteins evidenced here as involved in MMP-2 activation), reduced the number of dead cells. Even the use of broad-range MMP inhibitors (GM6001 and Batimastat) did not affect WT-Aβ(1-40) -induced cell apoptosis. Our results, contrast those obtained using the Aβ(1-40) Dutch variant suggesting a link between MMP-2 activity, VSMC mortality and degradation of specific matrix components, indicate that the ontogenesis of the Dutch familial and sporadic forms of CAAs is different. ECM degradation and VSMC degeneration would be tightly connected in the Dutch familial form while being two independent processes in sporadic forms of CAA. © 2012 The Authors Aging Cell © 2012 Blackwell Publishing Ltd/Anatomical Society of Great Britain and Ireland.
Copyright © 2012 Blackwell Publishing Ltd/Anatomical Society of Great Britain and Ireland.
Measurement of Altered AβPP Isoform Expression in Frontal Cortex of Patients with Alzheimer's Disease by Absolute Quantification Real-Time PCR.
Source
University of Vermont, Department of Medicine, Burlington, VT, USA.
Abstract
Enzymatic cleavage of amyloid-β protein precursor (AβPP) produces amyloid-β (Aβ) peptides which form the insoluble cortical plaques characteristic of Alzheimer's disease (AD). AβPP is post-transcriptionally processed into three major isoforms with differential cellular and tissue expression patterns. Changes in AβPP isoform expression may be indicative of disease pathogenesis in AD, but accurately measuring AβPP gene isoforms has been difficult to standardize, reproduce, and interpret. In light of this, we developed a set of isoform specific absolute quantification real time PCR standards that allow for quantification of transcript copy numbers for total AβPP and all three major isoforms (AβPP695, AβPP751, and AβPP770) in addition to glyceraldehyde-3-dehydrogenase (GAPDH) and examined expression patterns in superior frontal gyrus (SFG) and cerebellar samples from patients with (n = 12) and without AD (n = 10). Both total AβPP and AβPP695 transcripts were significantly decreased in SFG of patients with AD compared to control (p = 0.037 and p = 0.034, respectively). AβPP751 and AβPP770 transcripts numbers were not significantly different between AD and control (p > 0.15). There was trend for decreased percentage AβPP695 (p = 0.051) and increased percentage AβPP770 (p = 0.013) expression in SFG of patients with AD. GAPDH transcripts levels were also decreased significantly in the SFG of patients with AD compared to control (p = 0.005). Decreasing total AβPP and AβPP695 copy number was associated with increased plaque burden and decreased cognitive function. In this study we describe a simple procedure for measuring AβPP isoform transcripts by real-time PCR and confirm previous studies showing altered AβPP isoform expression patterns in AD.
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 beta band 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.
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.
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.
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.
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.
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