Cholesterol, a modulator of membrane-associated Abeta-fibrillogenesis and neurotoxicity

Recent studies have suggested that cholesterol, an important determinant of the physical state of biological membranes, plays a significant role in the development of Alzheimer's disease. We have employed in situ scanning probe microscopy, fluorescence anisotropy, and electron microscopy to investigate how cholesterol levels within total brain lipid bilayers effect amyloid beta-peptide (Abeta)-assembly. Fluorescence anisotropy measurements revealed that the relative fluidity of the total brain lipid membranes was influenced by the level of cholesterol and the addition of Abeta40 resulted in a decrease in the overall vesicle fluidity. In situ scanning probe microscopy performed on supported planar bilayers of total brain lipid revealed a correlation between membrane fluidity, as influenced by cholesterol level, and the extent of Abeta-insertion and subsequent fibrillogenesis. These observations were consistent with fluorescence microscopy studies of PC-12 and SH-SY5Y cell lines exposed to exogenous Abeta, which revealed an inverse correlation between membrane cholesterol level, and Abeta-cell surface binding and subsequent cell death. These results collectively suggest that Abeta-cell surface interactions are mediated by cellular cholesterol levels, the distribution of cholesterol throughout the cell, and membrane fluidity.