Critical aggregation concentration for the formation of early Amyloid-β (1–42) oligomers

The oligomers formed during the early steps of amyloid aggregation are thought to be responsible for the neurotoxic damage associated with Alzheimer’s disease. It is therefore of great interest to characterize this early aggregation process and the aggregates formed, especially for the most significant peptide in amyloid fibrils, Amyloid-β(1–42) (Aβ42). For this purpose, we directly monitored the changes in size and concentration of initially monomeric Aβ42 samples, using Fluorescence Correlation Spectroscopy. We found that Aβ42 undergoes aggregation only when the amount of amyloid monomers exceeds the critical aggregation concentration (cac) of about 90 nM. This spontaneous, cooperative process resembles surfactants self-assembly and yields stable micelle-like oligomers whose size (≈50 monomers, R h ≈ 7–11 nm) and elongated shape are independent of incubation time and peptide concentration. These findings reveal essential features of in vitro amyloid aggregation, which may illuminate the complex in vivo processWe thank the Ministerio de Ciencia e Innovación, the Ministerio de Economía y Competitividad, and the Xunta de Galicia for their financial support (CTQ2010-21369, CTQ2014-59020-R, GPC2013-052, R2014/051, ED431B 2016/024, ED431D R2016/007). S.F. thanks the Xunta de Galicia for her research scholarshipS