Glycosylphosphatidylinositol anchor analogues sequester cholesterol and reduce prion formation

Abstract

A hallmark of prion diseases is the conversion of the hostencoded prion protein (PrPC where C is cellular) into an alternatively folded, disease-related isoform (PrPSc, where Sc is scrapie), the accumulation of which is associated with synapse degeneration and ultimately neuronal death. The formation of PrPSc is dependent upon the presence of PrPC in specific, cholesterol-sensitive membrane microdomains, commonly called lipid rafts. PrPC is targeted to these lipid rafts because it is attached to membranes via a glycosylphosphatidylinositol anchor. Here, we show that treatment of prion-infected neuronal cell lines (ScN2a, ScGT1, or SMB cells) with synthetic glycosylphosphatidylinositol analogues, glucosamine-phosphatidylinositol (glucosamine-PI) or glucosamine 2-O-methyl inositol octadecyl phosphate, reduced the PrPSc content of these cells in a dose-dependent manner. In addition, ScGT1 cells treated with glucosamine-PI did not transmit infection following intracerebral injection to mice. Treatment with glucosamine-PI increased the cholesterol content of ScGT1 cell membranes and reduced activation of cytoplasmic phospholipase A2 (PLA2), consistent with the hypothesis that the composition of cell membranes affects key PLA2-dependent signaling pathways involved in PrPSc formation. The effect of glucosamine-PI on PrPSc formation was also reversed by the addition of platelet-activating factor. Glucosamine-PI caused the displacement of PrPC from lipid rafts and reduced expression of PrPC at the cell surface, putative sites for PrPSc formation. We propose that treatment with glucosamine-PI modifies local micro-environments that control PrPC expression and activation of PLA2 and subsequently inhibits PrPSc formation. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.