Ion Channel Formation by Amyloid-β42 Oligomers but not Amyloid-β40 in Cellular Membranes

A central hallmark of Alzheimer's disease (AD) is the presence of extracellular amyloid plaques chiefly consisting of amyloid-β (Aβ) peptides in the brain interstitium. Aβ largely exists in two isoforms, 40 or 42 amino acids long, while a large body of evidence points to Aβ(1-42) rather than Aβ(1-40) as the cytotoxic form. One proposed mechanism by which Aβ exerts toxicity is the formation of ion channel pores that disrupt intracellular Ca2+ homeostasis. However, previous studies using membrane mimetics have not identified any notable difference in the channel-forming properties between Aβ(1-40) and Aβ(1-42). Here, we tested whether a more physiological environment-membranes excised from HEK293 cells of neuronal origin-would reveal differences in the relative channel-forming ability of monomeric, oligomeric, and fibrillar forms of both Aβ(1-40) and Aβ(1-42). Aβ preparations were characterized with transmission electron microscopy and Thioflavin-T fluorescence. Aβ was then exposed to the extracellular face of excised membranes and transmembrane currents were monitored using patch-clamp. Our data indicated that Aβ(1-42) assemblies in oligomeric preparations form voltage-independent, non-selective ion channels. In contrast, Aβ(1-40) oligomers, fibres and monomers did not form channels. Ion channel conductance results suggested that Aβ(1-42) oligomers—but not monomers and fibres—formed 3 distinct pore structures with 1.7, 2.1, and 2.4 nm pore diameters. Our findings demonstrate that only Aβ(1-42) contains unique structural features that facilitate membrane insertion and channel formation, now aligning ion channel formation with the differential neurotoxic effect of Aβ(1-40) and Aβ(1-42) in AD.Life Science initiative, Queen Mary, University of London and Biotechnology and Biological Sciences Research Council Grant BB/M023877/1