Utilization of Exogenous Ceramide for the Synthesis of Sphingolipids in Cultured SV40-Transformed Rat Schwann Cells

Abstract

Homogeneous SV40-transformed rat Schwann cell lines were prepared from cultured primary Schwann cells (Chen and Chen, 1983). Cultured transformed Schwann cells actively synthesize sphingomyelin and glucosylceramide, as well as myelin-associated sulfatide, galactosylceramide and highly sialylated gangliosides. In this report we used ¹⁴C-palmitoyl sphingosine (¹⁴C-ceramide) as a precursor to investigate the biosynthesis of sphingolipids in these cells. In cultured human skin fibroblasts, degradation of ceramide internalized via LDL-mediated and liposomal uptake is compartmentalized (Sutrina and Chen, 1982). The presence of lysosomal and nonlysosomal ceramidases in cultured Schwann cells, suggests that hydrolysis of internalized ceramide can take place in different compartments. Therefore, in addition to the utilization of intact ceramide for the sphingolipids synthesis, we have investigated whether internalized ceramide is hydrolyzed by different ceramidases and the resulting fatty acid moiety can then be utilized for the glycerolipid synthesis. We also examined the regulation of these two lipid synthetic pathways.