Glycosylphosphatidylinositol anchor analogues sequester cholesterol and reduce prion formation

A hallmark of prion diseases is the conversion of the hostencoded prion protein (PrP^C where C is cellular) into an alternatively folded, disease-related isoform (PrP^Sc, where Sc is scrapie), the accumulation of which is associated with synapse degeneration and ultimately neuronal death. The formation of PrP^Sc is dependent upon the presence of PrP^C in specific, cholesterol-sensitive membrane microdomains, commonly called lipid rafts. PrP^C 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 PrP^Sc 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 PrP^Sc formation. The effect of glucosamine-PI on PrP^Sc formation was also reversed by the addition of platelet-activating factor. Glucosamine-PI caused the displacement of PrP^C from lipid rafts and reduced expression of PrP^C at the cell surface, putative sites for PrP^Sc formation. We propose that treatment with glucosamine-PI modifies local micro-environments that control PrP^C expression and activation of PLA₂ and subsequently inhibits PrP^Sc formation.