Cryo-electron microscopy structure of an SH3 amyloid fibril and model of the molecular packing.
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Amyloid fibrils are assemblies of misfolded proteins and are associated with pathological conditions such as Alzheimer's disease and the spongiform encephalopathies. In the amyloid diseases, a diverse group of normally soluble proteins self-assemble to form insoluble fibrils. X-ray fibre diffraction studies have shown that the protofilament cores of fibrils formed from the various proteins all contain a cross-beta-scaffold, with beta-strands perpendicular and beta-sheets parallel to the fibre axis. We have determined the threedimensional structure of an amyloid fibril, formed by the SH3 domain of phosphatidylinositol-3'-kinase, using cryo-electron microscopy and image processing at 25 A resolution. The structure is a double helix of two protofilament pairs wound around a hollow core, with a helical crossover repeat of approximately 600 A and an axial subunit repeat of approximately 27 A. The native SH3 domain is too compact to fit into the fibril density, and must unfold to adopt a longer, thinner shape in the amyloid form. The 20x40-A protofilaments can only accommodate one pair of flat beta-sheets stacked against each other, with very little inter-strand twist. We propose a model for the polypeptide packing as a basis for understanding the structure of amyloid fibrils in general. (+info)
Dynamics of plaque formation in Alzheimer's disease.
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Plaques that form in the brains of Alzheimer patients are made of deposits of the amyloid-beta peptide. We analyze the time evolution of amyloid-beta deposition in immunostained brain slices from transgenic mice. We find that amyloid-beta deposits appear in clusters whose characteristic size increases from 14 microm in 8-month-old mice to 22 microm in 12-month-old mice. We show that the clustering has implications for the biological growth of amyloid-beta by presenting a growth model that accounts for the experimentally observed structure of individual deposits and predicts the formation of clusters of deposits and their time evolution. (+info)
Improvement by nefiracetam of beta-amyloid-(1-42)-induced learning and memory impairments in rats.
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1. We have previously demonstrated that continuous i.c.v. infusion of amyloid beta-peptide (A beta), the major constituent of senile plaques in the brains of patients with Alzheimer's disease, results in learning and memory deficits in rats. 2. In the present study, we investigated the effects of nefiracetam [N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl) acetamide, DM-9384] on A beta-(1-42)-induced learning and memory deficits in rats. 3. In the A beta-(1-42)-infused rats, spontaneous alternation behaviour in a Y-maze task, spatial reference and working memory in a water maze task, and retention of passive avoidance learning were significantly impaired as compared with A beta-(40-1)-infused control rats. 4. Nefiracetam, at a dose range of 1-10 mg kg(-1), improved learning and memory deficits in the A beta-(1-42)-infused rats when it was administered p.o. 1 h before the behavioural tests. 5. Nefiracetam at a dose of 3 mg kg(-1) p.o. increased the activity of choline acetyltransferase in the hippocampus of A beta-(1-42)-infused rats. 6. Nefiracetam increased dopamine turnover in the cerebral cortex and striatum of A beta-(1-42)-infused rats, but failed to affect the noradrenaline, serotonin and 5-hydroxyindoleacetic acid content. 7. These results suggest that nefiracetam may be useful for the treatment of patients with Alzheimer's disease. (+info)
Competition of Abeta amyloid peptide and apolipoprotein E for receptor-mediated endocytosis.
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The genetic polymorphism of apolipoprotein E (apoE) is associated with the age of onset and relative risk of Alzheimer's disease (AD). In contrast to apoE3, the wild type allele, apoE4 confers an increased risk of late-onset AD. We demonstrate that the beta-amyloid peptide isoforms Abeta (1-28), Abeta (1-40), and Abeta (1-43) compete for the cellular metabolism of apoE3 and apoE4 containing beta-very low density lipoproteins. An antibody raised against Abeta (1-28) cross-reacted with recombinant apoE. Epitope mapping revealed positive amino acid clusters as common epitopes of Abeta (13 through 17; HHQKL) and apoE (residues 144 through 148; LRKRL), both regions known to be heparin binding domains. Abeta in which amino acids 13 through 17 (HHQKL) were replaced by glycine (GGQGL) failed to compete with the cellular uptake of apoE enriched betaVLDL. These observations indicate that Abeta and apoE are taken up into cells by a common pathway involving heparan sulfate proteoglycans. (+info)
beta-amyloid load is not influenced by the severity of cardiovascular disease in aged and demented patients.
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BACKGROUND AND PURPOSE: This study was conducted to analyze the association between reported risk factors for Alzheimer's disease, apolipoprotein E epsilon4 allele, and cardiovascular disease and neuropathological changes essential for the diagnosis of Alzheimer's disease. METHODS: Our data are based on clinical and postmortem evaluations of a cohort of nondemented (n=118) and demented (n=107) individuals. A cardiovascular index was calculated at autopsy to estimate the extent of cardiovascular disease. Neuropathological lesions such as senile/neuritic plaques, neurofibrillary tangles, beta-amyloid load, cerebral amyloid angiopathy, and the load of paired helical filaments were determined. RESULTS: The aforementioned neuropathological lesions did not show any positive significant correlation with cardiovascular index. In contrast, the extent of Alzheimer's lesions was significantly higher in those nondemented and demented patients carrying the apolipoprotein E epsilon4 allele than in those without this allele. CONCLUSIONS: Our results demonstrate that the apolipoprotein E epsilon4 allele, but not cardiovascular disease, indeed influences the extent of Alzheimer's lesions seen in the brain tissue of demented patients as well as asymptomatic controls. (+info)
Increased poly(ADP-ribosyl)ation of nuclear proteins in Alzheimer's disease.
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Experimental studies indicate that overactivation of the DNA repair protein poly(ADP-ribose) polymerase (PARP) in response to oxidative damage to DNA can cause cell death due to depletion of NAD+. Oxidative damage to DNA and other macromolecules has been reported to be increased in the brains of patients with Alzheimer's disease. In the present study we sought evidence of PARP activation in Alzheimer's disease by immunostaining sections of frontal and temporal lobe from autopsy material of 20 patients and 10 controls, both for PARP itself and for its end-product, poly(ADP-ribose). All of the brains had previously been subjected to detailed neuropathological examination to confirm the diagnosis of Alzheimer's disease or, in the controls, to exclude Alzheimer's disease-type pathology. Double immunolabelling for poly(ADP-ribose) and microtubule-associated protein 2 (MAP2), glial fibrillary-acidic protein (GFAP), CD68, A beta-protein or tau was used to assess the identity of the cells with poly(ADP-ribose) accumulation and their relationship to plaques and neurofibrillary tangles. Both PARP- and poly(ADP-ribose)-immunolabelled cells were detected in a much higher proportion of Alzheimer's disease (20 out of 20) brains than of control brains (5 out of 10) (P = 0.0018). Double-immunolabelling for poly(ADP-ribose) and markers of neuronal, astrocytic and microglial differentiation (MAP2, GFAP and CD68, respectively) showed many of the cells containing poly(ADP-ribose) to be neurons. Most of these were small pyramidal neurons in cortical laminae 3 and 5. A few of the cells containing poly(ADP-ribose) were astrocytes. No poly(ADP-ribose) accumulation was detected in microglia. Double-immunolabelling for poly(ADP-ribose) and tau or A beta-protein indicated that the cells with accumulation of poly(ADP-ribose) did not contain tangles and relatively few occurred within plaques. Our findings indicate that there is enhanced PARP activity in Alzheimer's disease and suggest that pharmacological interventions aimed at inhibiting PARP may have a role in slowing the progression of the disease. (+info)
Regulation of beta-amyloid secretion by FE65, an amyloid protein precursor-binding protein.
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The principal component of Alzheimer's amyloid plaques, Abeta, derives from proteolytic processing of the Alzheimer's amyloid protein precursor (APP). FE65 is a brain-enriched protein that binds to APP. Although several laboratories have characterized the APP-FE65 interaction in vitro, the possible relevance of this interaction to Alzheimer's disease has remained unclear. We demonstrate here that APP and FE65 co-localize in the endoplasmic reticulum/Golgi and possibly in endosomes. Moreover, FE65 increases translocation of APP to the cell surface, as well as both alphaAPPs and Abeta secretion. The dramatic (4-fold) FE65-dependent increase in Abeta secretion suggests that agents which inhibit the interaction of FE65 with APP might reduce Abeta secretion in the brain and therefore be useful for preventing or slowing amyloid plaque formation. (+info)
The cell death-promoting gene DP5, which interacts with the BCL2 family, is induced during neuronal apoptosis following exposure to amyloid beta protein.
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DP5, which contains a BH3 domain, was cloned as a neuronal apoptosis-inducing gene. To confirm that DP5 interacts with members of the Bcl-2 family, 293T cells were transiently co-transfected with DP5 and Bcl-xl cDNA constructs, and immunoprecipitation was carried out. The 30-kDa Bcl-xl was co-immunoprecipitated with Myc-tagged DP5, suggesting that DP5 physically interacts with Bcl-xl in mammalian cells. Previously, we reported that DP5 is induced during neuronal apoptosis in cultured sympathetic neurons. Here, we analyzed DP5 gene expression and the specific interaction of DP5 with Bcl-xl during neuronal death induced by amyloid-beta protein (A beta). DP5 mRNA was induced 6 h after treatment with A beta in cultured rat cortical neurons. The protein encoded by DP5 mRNA showed a specific interaction with Bcl-xl. Induction of DP5 gene expression was blocked by nifedipine, an inhibitor of L-type voltage-dependent calcium channels, and dantrolene, an inhibitor of calcium release from the endoplasmic reticulum. These results suggested that the induction of DP5 mRNA occurs downstream of the increase in cytosolic calcium concentration caused by A beta. Moreover, DP5 specifically interacts with Bcl-xl during neuronal apoptosis following exposure to A beta, and its binding could impair the survival-promoting activities of Bcl-xl. Thus, the induction of DP5 mRNA and the interaction of DP5 and Bcl-xl could play significant roles in neuronal degeneration following exposure to A beta. (+info)