Presenilin deficiency results in cellular cholesterol accumulation by impairment of protein glycosylation and NPC1 function.

Presenilin (PS) proteins represent the catalytic subunits of γ-secretase, and play a critical role in the generation of the Amyloid β (Aβ) peptide and the pathogenesis of Alzheimer’s disease (AD). Indeed, mutations in presenilin 1 (PS1) or PS2 are a major cause of early onset familial Alzheimer’s disease (FAD). However, PS proteins also exert multiple functions beyond Aβ generation. In this study, we examine the individual roles of PS1 and PS2 in cellular cholesterol metabolism. Deletion of PS1 or PS2 in mouse models led to cholesterol accumulation in cerebral neurons. Cholesterol accumulation was also observed in lysosomes of embryonic fibroblasts from PS1-KO and PS2-KO mice, and associated with decreased expression of the Niemann-Pick type C1 (NPC1) protein involved in intracellular cholesterol transport at late endosome/lysosome. Mass spectrometry and complementary biochemical methods also revealed abnormal N-glycosylation of NPC1 and several other membrane proteins in PS1-KO and PS2-KO cells. Interestingly, pharmacological inhibition of N-glycosylation resulted in intracellular cholesterol accumulation prominently in lysosomes as well as decrease of NPC1 expression in wild-type MEFs, thereby resembling the changes in PS1-KO and PS2-KO MEFs. In turn, treatment of PS1-KO and PS2-KO MEFs with a chaperone inducer, Arimoclomol, attenuated decrease of NPC1 and rescued the lysosomal cholesterol accumulation. Additionally, the intracellular cholesterol accumulation in PS1-KO and PS2-KO MEFs was prevented by NPC1 overexpression. Collectively, these data indicate that PS/γ-secretase dysfunction results in an impairment of protein N-glycosylation, which eventually causes NPC1 decrease and intracellular cholesterol accumulation. 3'RNASeq of mouse embryonic fibroblasts with PS1- or PS2-deficiency compared with controls. Biological replicates Comparative gene expression profiling analysis of RNA-seq data for mouse embryonic fibroblasts derived from WT, Psen1-, Psen2-KO mice