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Modified low density lipoproteins suppress production of a platelet-derived growth factor-like protein by cultured endothelial cells.

Cultured endothelial cells (EC) produce a platelet-derived growth factor-like protein (PDGF-c) that stimulates the growth of cultured cells of mesenchymal origin. We have examined the effect of native plasma low density lipoprotein (LDL) and chemically modified LDL on production of PDGF-c by EC. Acetyl-LDL, but not native LDL, suppressed the production of PDGF-c by bovine aortic EC. Half-maximal inhibition was observed at a concentration of 25-75 micrograms of cholesterol per ml, and maximal inhibition (0-25% of control) at 150 micrograms of cholesterol per ml. EC treated with acetyl-LDL showed no morphological damage, there was no change in cell number, and the effect on production of PDGF-c was substantially reversed upon removal of the acetyl-LDL. The observed inhibition of PDGF-c production was specific, since total cellular and secreted protein synthesis were unaffected by acetyl-LDL. Acetyl-LDL suppressed PDGF-c production in both bovine aortic and human umbilical vein EC, but not in rat heart EC. This cell specificity correlated with the presence of scavenger receptors as measured by degradation of 125I-labeled acetyl-LDL and uptake of fluorescently labeled acetyl-LDL. Dimethylpropanediamine-LDL, a cationic modified lipoprotein, also inhibited PDGF-c production. The inhibition by both types of modified LDL was accompanied by significant intracellular cholesterol accumulation, suggesting a role for EC lipid composition in the regulation of production of PDGF-c.