Modulation of cholesterol, farnesylpyrophosphate, and geranylgeranylpyrophosphate in neuroblastoma SH-SY5Y-APP695 cells: Impact on amyloid beta-protein production

There is keen interest in the role of the isoprenoids farnesylpyrophosphate (FPP) and geranylgeranylpyrophosphate (GGPP) in protein prenylation and cell function in Alzheimer's disease (AD). We recently reported elevated FPP and GGPP brain levels and increased gene expression of FPP synthase (FPPS) and GGPP synthase (GGPPS) in the frontal cortex of AD patients. Cholesterol levels and gene expression of 3-hydroxy-3-methylglutarylcoenzyme A reductase were similar in AD and control samples, suggesting that homeostasis of FPP and GGPP but not cholesterol is specifically targeted in brain tissue of AD patients (Neurobiol Dis 2009 35:251-257). In the present study, it was determined if cellular levels of FPP, GGPP, and cholesterol affect beta-amyloid (Aâ) abundance in SHSY5Y cells, expressing human APP695. Cells were treated with different inhibitors of the mevalonate/isoprenoid/cholesterol pathway. FPP, GGPP, cholesterol, and Aβ1-40 levels were determined, and activities of farnesyltransferase and geranylgeranyltransferase I were measured. Inhibitors of different branches of the mevalonate/isoprenoid/cholesterol pathway as expected reduced cholesterol and isoprenoid levels in neuroblastoma cells. Aβ1-40 levels were selectively reduced by cholesterol synthesis inhibitors but not by inhibitors of protein isoprenylation, indicating that changes in cholesterol levels per se and not isoprenoid levels account for the observed modifications in Aβ production.