Cholesterol, a modulator of membrane-associated Aβ-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 (A beta)-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 A beta 40 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 fibrillogenesis. These observations were consistent with fluorescence microscopy studies of PC-12 and SH-SY5Y cell lines exposed to exogenous A beta, which revealed an inverse correlation between membrane cholesterol level, and A beta -cell surface binding and subsequent cell death. These results collectively suggest that A beta -cell surface interactions are mediated by cellular cholesterol levels, the distribution of cholesterol throughout the cell, and membrane fluidity. (C) 2001 Academic Press.