Inhibition of cholesterol recycling impairs cellular PrPSc propagation

The infectious agent in prion diseases consists of an aberrantly folded isoform of the cellular prion protein (PrP^c), termed PrP^Sc, which accumulates in brains of affected individuals. Studies on prion-infected cultured cells indicate that cellular cholesterol homeostasis influences PrP^Sc propagation. Here, we demonstrate that the cellular PrP^Sc content decreases upon accumulation of cholesterol in late endosomes, as induced by NPC-1 knock-down or treatment with U18666A. PrP^c trafficking, lipid raft association, and membrane turnover are not significantly altered by such treatments. Cellular PrP^Sc formation is not impaired, suggesting that PrP^Sc degradation is increased by intracellular cholesterol accumulation. Interestingly, PrP^Sc propagation in U18666A-treated cells was partially restored by overexpression of rab 9, which causes redistribution of cholesterol and possibly of PrP^Sc to the trans-Golgi network. Surprisingly, rab 9 overexpression itself reduced cellular PrP^Sc content, indicating that PrP^Sc production is highly sensitive to alterations in dynamics of vesicle trafficking.