Mass spectrometric analysis reveals an increase in plasma membrane polyunsaturated phospholipid species upon cellular cholesterol loading

Here we used electrospray ionization mass spectrometry for quantitative det ermination of lipid molecular species in human fibroblasts and their plasma membrane incorporated into enveloped viruses. Both influenza virus selecti ng ordered domains and vesicular stomatitis virus (VSV) depleted of such do mains [Scheiffele, P., et al. (1999) J. Biol. Chem. 274, 2038-2044] were an alyzed. The major difference between influenza and VSV was found to be a ma rked enrichment of glycosphingolipids in the former. The effect of chronic cholesterol loading on viral lipid composition was studied in Niemann-Pick type C (NPC) fibroblasts. Both NPC-derived influenza and VSV virions contai ned increased amounts of cholesterol. Furthermore, polyunsaturated phosphat idylcholine, phosphatidylethanolamine, and phosphatidylserine were enriched in NPC-derived virions at the expense of the monounsaturated ones. When no rmal fibroblasts were acutely loaded with cholesterol using cyclodextrin co mplexes, an adjustment toward increasingly unsaturated phospholipid species was observed, most clearly for phosphatidylcholine and sphingomyelin. Our results provide evidence that (1) glycosphingolipids are enriched in domain s through which influenza virus buds, (2) chronic cholesterol accumulation increases the cholesterol content of both glycosphingolipid-enriched and in tervening plasma membrane domains, and (3) an increase in membrane choleste rol content is accompanied by an increased level of polyunsaturated species of the major membrane phospholipids. We suggest that remodeling of phospho lipids toward higher unsaturation may serve as both an acute and a long-ter m adaptive mechanism in human cellular membranes against cholesterol excess .