Association of active γ-secretase complex with lipid rafts

Cholesterol has been implicated in the pathogenesis of Alzheimer's disease ( AD). Although the underlying mechanisms are not yet clear, several studies have provided evidence for the involvement of cholesterol-rich lipid rafts in the production of amyloid beta peptide (A beta), the major component of amyloid deposits in AD. In this regard, the gamma-secretase complex is responsible for the final cleavage event in the processing of beta-amyloid precursor protein (beta APP), resulting in A beta generation. The gamma-secretase complex is a multiprotein complex composed of presenilin, nicastrin (NCT), APH-1, and PEN-2. Recent reports have suggested that gamma-secretase activity is predominantly localized in lipid rafts, and presenilin and NCT have been reported to be localized in lipid rafts. In this study, various biochemical methods, including coimmunoprecipitation, in vitro gamma-secretase assay, and methyl-beta-cyclodextrin (M beta CD) treatment, are employed to demonstrate that all four components of the active endogenous gamma-secretase complex, including APH-1 and PEN-2, are associated with lipid rafts in human neuroblastoma cells (SH-SY5Y). Treatment with statins, 3-hydroxy-3- methylglutaryl-CoA-reductase inhibitors, significantly decreased the association of the beta-secretase complex with lipid rafts without affecting the distribution of flotillin-1. This effect was partially abrogated by the addition of geranylgeraniol. These results suggest that both cholesterol and protein isoprenylation influence the active gamma-secretase complex association with lipid rafts.