engleski

Cholesterol levels modulate trafficking of APP and BACE1 in Niemann-Pick type C cells

Background and objectives: Processing of the amyloid precursor protein (APP) by beta-secretase (BACE1) in endosomes results in formation of amyloid-beta (Abeta) peptide, the central molecule in Alzheimer’s disease (AD) pathogenesis. Accumulation of Abeta peptide in the brain has also been observed in Niemann-Pick Type C disease (NPC), an inherited neurodegenerative disorder of lipid accumulation. We have demonstrated that increased Abeta levels in CHO-NPC1 null cells are due to cholesterol dependent increased cleavage of APP by BACE1 (Malnar et al. 2010). Moreover, we have observed that CHO-NPC1 null cells show sequestration of APP/BACE1 within enlarged endosomes (Malnar et al. 2012). In this work, we investigated the role of cholesterol levels on APP/BACE1 trafficking in NPC model cell. Methods: APP and BACE1 trafficking was analyzed by immunofluorescent confocal microscopy. Cholesterol was depleted by growing CHO-NPC1 null cells in the media containing a lipid-deficient serum, by statin-treatment and by methyl-beta-cyclodextrin (MbetaC)-treatment. To load cholesterol in CHOwt cells we used two different approaches: U18666A-treatment and MbetaC-cholesterol treatment. Additionally, we analyzed the localization of APP protein in U18666A-treated primary cortical neurons. Results: We demonstrate that cholesterol-depletion corrects APP and BACE1 misstrafficking in CHO-NPC1 null cells, while cholesterol loading shows altered APP/BACE1 trafficking even in non NPC1-deficient environment. Conclusions: Our results indicate that increased formation of Abeta in NPC disease is due to cholesterol-mediated altered endocytic trafficking of APP and BACE1. Our findings support previous notion that altered endocytic trafficking may be the primary defect in AD and that increased cholesterol level, such as in NPC disease and sporadic AD, may be the upstream effector that drives these events.

Cholesterol; APP; BACE1; Niemann-Pick type C; Alzheimer's disease

nije evidentirano