Lipid-dependent two-step interfacially-driven Aβ 1–40 aggregation mechanism

Abstract

Specific interactions between amyloid-β (Aβ) peptides and membrane lipids are increasingly recognized as key contributors to Alzheimer’s disease (AD) pathogenesis. Cholesterol (Chol), a major component of neuronal membranes — whose levels decline with aging but in AD occurred an altered Chol metabolism and asymmetric distribution, particularly between neuronal and synaptosomal membranes – plays a central role in modulating membrane properties and Aβ–membrane interactions. While Chol has been proposed to facilitate both membrane disruption and local Aβ aggregation, its precise role in fibrillation remains controversial. To address this issue, we investigated Aβ 1–40 aggregation using model membrane systems composed of POPC, sphingomyelin (bSM or 24:1 SM), and increasing amounts of Chol. Both monomeric and oligomeric preparations of Aβ 1-40 were used. Across all systems, time-resolved spectroscopy, fluorescence microscopy, dot blot, and TEM analyses revealed that Chol is necessary—but not sufficient —for full Aβ 1–40 aggregation. While Chol-rich bilayers promoted initial peptide anchoring and oligomerization, the progression to fibrillar structures critically depended on the presence of liquid-disordered membrane phases. Moreover, Aβ-induced vesicle disruption, lipid recruitment, and bilayer perturbations demonstrate that lipids act as active modulators—not passive scaffolds—of fibrillogenesis. Our findings support a surface-mediated aggregation mechanism in which Chol-rich membranes serve as catalytic platforms, increasing local peptide concentration and reducing diffusional dimensionality. Complementary experiments with acetylcholinesterase showed additional modulatory pathways. These findings advance our mechanistic understanding of Aβ aggregation at biological interfaces and offer broader implications for interface-driven self-assembly processes in complex colloidal systems.