Interaction of amyloid precursor protein and beta-secretase on the cell surface

Accumulation of amyloid-beta-peptide (Abeta) in senile plaques is a characteristic feature for Alzheimer's disease. The amyloid precursor protein (APP) is cleaved sequentially by beta-site APP-cleaving enzyme (BACE) and gamma-secretase to release Abeta. Recent data indicate that production, clearance, and aggregation of Aß are highly dependent on the specific neuronal subcellular localization wherein Aß is generated. We tested the hypothesis that APP and BACE are co-localized within lipid domains (e.g. lipid rafts) on the cell surface.

We used Total internal reflection fluorescence microscopy (TIRFM) combined with non-radiative energy transfer (FRET) measurements in order to examine co-localization of the amyloid precursor protein (APP) and the bet-site APP-cleaving enzyme (BACE) in human glioblastoma and mouse N2a cells. Our findings suggest that both proteins are co-localized within whole cells (depending on the intracellular amount of cholesterol) and to a much lesser extent on the plasma membranes. Functional consequences of cholesterol depletion upon APP processing were investigated. Analysis of sAPP-alpha, sAPP-beta and Abeta by Mesoscale multi-spot assay indicated alteration of cleavage upon cholesterol depletion.