Sulfatides and Glycolipids in Platelets and Endothelial Cells

Abstract

Sulfatides are sulfated glycolipids which are negatively charged and thought to influence receptor mediated activities. Sulfatides have the capacity to provide a surface for the initiation of in vitro coagulation tests and these acidic lipids represent the potential biological surface for the initiation of the contact and intrinsic systems in vivo. Several sulfatides have been demonstrated in blood platelets. We have investigated sulfatides and other glycolipids in endothelial cells and platelets in order to define the cellular sources for sulfatides that would be available for influencing hemostasis. Endothelial cells were derived from primary cultures of human umbilical veins and human platelets were obtained from freshly-collected blood. Cellular lipids were extracted by the Folch method. Sulfatides and glycolipids were purified by silicic acid chromatography, separated by thin-layer chromatography, and quantitated by the assay of sphingosine. Glycolipids were also analyzed by HPLC. Globoside was found to be the predominant glycolipid in endothelial cells while lactosyl ceramide was the predominant glyco-lipid in platelets. Sulfatides were detected by two approaches: 1) Sulfatide synthesis by the incorporation of [35S]-Sulfate; 2) The specific binding of [125I]-thrombospondin and [125I]-von Willebrand’s factor (vWF) to sulfatides separated by thin-layer chromatography (TLC). Several sulfatides were identified in endothelial cells and platelets by virtue of the incorporation of [35S]-sulfate into glycolipids separated by TLC. [125I]-TSP and [125I]-vWF bound to the glycolipids that had incorporated [35S]-sulfate. [35S]-sulfate was primarily incorporated into sulfated galactosyl ceramide but both cells also synthesized complex glycolipids. TSP and vWF were shown to bind to sulfated galactosyl ceramide, a band that comigrated with glycosyl ceramide as well as with two more complex sulfatides in both cells. However, differences in sulfatide synthesis and binding of TSP to sulfatides were observed in endothelial cells from that in platelets. The study indicates that endothelial cells and platelets contain several sulfatides and thus are potential sources for sulfatides for the initiation of coagulation.