Cholesterol-dependent modulation of β-amyloid 1-40 peptide aggregation by membrane organization.

HYPOTHESIS: Cholesterol (chol) is a key lipid for nervous system development and function. While aging is associated with reduced brain chol, Alzheimer's disease (AD) is characterized by altered chol metabolism and asymmetric membrane distribution, particularly between neuronal body and synaptic compartments. The impact of these changes on β-amyloid (Aβ) aggregation, a central event in AD pathogenesis, remains unclear-especially under physiologically low Aβ concentrations. We hypothesize that Aβ nucleation in colloidal systems requires chol as an initial anchoring site, but that progression toward fibril formation is modulated by the system's interfacial properties.

EXPERIMENTS: To test this hypothesis, we employed biomimetic colloidal systems in the form of large and giant unilamellar vesicles (LUVs and GUVs) composed of POPC, brain sphingomyelin (bSM), and varying chol levels. By selectively modifying membrane composition to modulate membrane order and interfacial organization, we created distinct physicochemical environments. A combination of fluorescence spectroscopy, fluorescence microscopy, transmission electron microscopy, and dot blot assays was used to monitor Aβ1-40 aggregation dynamics and structural states, complemented by molecular dynamics simulations.

FINDINGS: We found that chol is essential to initiate Aβ 1-40 oligomerization. However, when chol levels were held constant but lipid composition was altered -by removing POPC or bSM, or replacing bSM with SM 24:1-Aβ aggregation outcomes varied significantly. These results demonstrate that while chol is necessary to initiate Aβ aggregation, the interfacial properties of the colloidal system govern its progression to fibril formation, revealing a novel interfacial mechanism linking membrane organization and peptide aggregation.