Abstract
BackgroundSelf-assembly of the amyloid-β (Aβ) peptide into aggregates, ranging from small oligomers to amyloid fibrils, is fundamentally linked with Alzheimer’s disease (AD). However it is clear that not all forms of Aβ are equally harmful, and that linking a specific aggregate to toxicity also depends on the assays and model systems used [1, 2]. Indeed, though a central postulate of the amyloid cascade hypothesis, there remain many gaps in our understanding regarding the links between Aβ deposition and neurodegeneration.MethodsIn this study we utilized BRI2-Aβ fusion technology and rAAV2/1 based somatic brain transgenesis to examine Aβ aggregates that form from selective expression of individual mutant Aβ species in vivo. In parallel we generated PhiC31-based transgenic Drosophila melanogaster expressing WT and mutant Aβ40 and Aβ42, fused to the Argos signal peptide and placed under the GAL4-upstream activation sequence (UAS) expression system in order to assess the extent of Aβ42-induced toxicity as well as to interrogate the combined effect of different forms of Aβ40 and Aβ42 species.ResultsWhen expressed in the mouse brain for 6 months, Aβ42 E22G, Aβ42 E22Q/D23N, and Aβ42 WT formed amyloid aggregates consisting of some diffuse material as well as cored plaques, whereas other mutants formed predominantly diffuse amyloid deposits. Moreover, while Aβ40WT showed no distinctive phenotype, Aβ40 E22G and E22Q/D23N formed unique aggregates that accumulated in mouse brains. This is the first evidence that mutant Aβ40 overexpression leads to deposition under certain conditions. Interestingly, we found that mutant Aβ42 E22G, E22Q, and S26C, but not Aβ40, were toxic to the eye of the flies and exacerbated their behavior. In contrast, flies expressing a copy of Aβ40 (wild type [WT] or mutants) in addition to Aβ42 WT, showed improved phenotypes, suggesting possible protective qualities for Aβ40.ConclusionsThese studies suggest that some Aβ40 mutants form unique amyloid aggregates in mouse brains, despite being protective against Aβ42 toxicity in Drosophila, which highlights the significance of using different systems for a better understanding of AD pathogenicity and more accurate screening for new potential therapies.