The mechanism of γ-Secretase dysfunction in familial Alzheimer diseaseMutations in presenilin (PSEN) and amyloid precursor protein (APP) cause dominant early-onset Alzheimer's disease (AD), but the mechanism involved is debated. Here, such mutations are shown to alter γ-secretase activity, leading to changes in Aβ peptide cleavage patterns.

The amyloid peptides Ab 40 and Ab 42 of Alzheimer's disease are thought to contribute differentially to the disease process. Although Ab 42 seems more pathogenic than Ab 40 , the reason for this is not well understood. We show here that small alterations in the Ab 42 :Ab 40 ratio dramatically affect the biophysical and biological properties of the Ab mixtures reflected in their aggregation kinetics, the morphology of the resulting amyloid fibrils and synaptic function tested in vitro and in vivo. A minor increase in the Ab 42 :Ab 40 ratio stabilizes toxic oligomeric species with intermediate conformations. The initial toxic impact of these Ab species is synaptic in nature, but this can spread into the cells leading to neuronal cell death. The fact that the relative ratio of Ab peptides is more crucial than the absolute amounts of peptides for the induction of neurotoxic conformations has important implications for anti-amyloid therapy. Our work also suggests the dynamic nature of the equilibrium between toxic and non-toxic intermediates.

Background: Amyloid ␤ peptide plays a role in Alzheimer disease. Results: Interaction of amyloid ␤ peptides with 40 and 42 amino acids has consequences for oligomer formation. Conclusion: Increased production of amyloid ␤ peptide with 42 amino acids affects the behavior of the entire amyloid ␤ peptide pool. Significance: This might explain the synaptotoxic effect observed with a shift in amyloid ␤ peptide production.

We provide a validated and rapid protocol for the solubilization of amyloid β-peptide (Aβ). This procedure involves sequential solubilization using structure-breaking organic solvents hexafluoroisopropanol and DMSO followed by column purification. The low solubility and tendency of Aβ to aggregate considerably impede the in vitro handling and biophysical or biological investigation of Aβ, despite the interest in this peptide because of its implication in Alzheimer's disease. The main advantage of the proposed protocol over others is that it results in standardized aggregate-free Aβ peptide samples that are biocompatible for cell culture studies and yield reproducible aggregation kinetics and cytotoxicities. This three-step protocol also enables the co-solubilization of the longer Aβ42 variant with Aβ40 in ratios relevant to Alzheimer's disease.

BACE1 cleaves the amyloid precursor protein (APP) at the β-cleavage site (Met671–Asp672) to initiate the generation of amyloid peptide Aβ. BACE1 is also known to cleave APP at a much less well-characterized β′-cleavage site (Tyr681–Glu682). 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.

Current therapeutic approaches under development for Alzheimer disease, including γ-secretase modulating therapy, aim at increasing the production of Aβ(1-38) and Aβ(1-40) at the cost of longer Aβ peptides. Here, we consider the aggregation of Aβ(1-38) and Aβ(1-43) in addition to Aβ(1-40) and Aβ(1-42), in particular their behavior in mixtures representing the complex in vivo Aβ pool. We demonstrate that Aβ(1-38) and Aβ(1-43) aggregate similar to Aβ(1-40) and Aβ(1-42), respectively, but display a variation in the kinetics of assembly and toxicity due to differences in short timescale conformational plasticity. In biologically relevant mixtures of Aβ, Aβ(1-38) and Aβ(1-43) significantly affect the behaviors of Aβ(1-40) and Aβ(1-42). The short timescale conformational flexibility of Aβ(1-38) is suggested to be responsible for enhancing toxicity of Aβ(1-40) while exerting a cyto-protective effect on Aβ(1-42). Our results indicate that the complex in vivo Aβ peptide array and variations thereof is critical in Alzheimer disease, which can influence the selection of current and new therapeutic strategies.

a b s t r a c tAggregated forms of the amyloid-b peptide are hypothesized to act as the prime toxic agents in Alzheimer disease (AD). The in vivo amyloid-b peptide pool consists of both C-and N-terminally truncated or mutated peptides, and the composition thereof significantly determines AD risk. Other variations, such as biotinylation, are introduced as molecular tools to aid the understanding of disease mechanisms. Since these modifications have the potential to alter key aggregation properties of the amyloid-b peptide, we present a comparative study of the aggregation of a substantial set of the most common in vivo identified and in vitro produced amyloid-b peptides. Structured summary of protein interactions:Amyloid beta and Amyloid beta bind by fluorescence technology (View Interaction: 1, 2, 3, 4, 5) Amyloid beta and Amyloid beta bind by transmission electron microscopy (View Interaction: 1, 2) Amyloid beta and Amyloid beta bind by filter binding (View Interaction: 1,2,3)

No abstract