Apoptosis inducers endotoxin and Fas-ligation enhance the expression of vascular endothelial growth factor in human endothelial cells

Endothelial cells in culture were exposed during four hours to the apoptosis inducing agents endotoxin (lipopolysaccharide, LPS) and Fas-ligand mimicking antibody in various concentrations. With addition of a deletion primer as internal standard a competitive RT-PCR was performed to measure semi-quantitatively the expression of mRNA of Vascular endothelial growth factor (VEGF). It appeared that endothelial cells survive increasing amounts of LPS and show a concentration- and time-dependent increase in the expression of VEGF-mRNA. The same effect was found with Fas-ligation, although at high concentrations Fas-ligation induced no further increase, but even a decrease of VEGF expression, possibly related to cell damage. Apoptotic cells were rarely observed after LPS-stimulation, but simultaneous incubation with a blocking antibody to VEGF resulted in a significant increase in apoptosis. We hypothesize that endothelial cells are resistant to apoptosis induction by autocrine expression of VEGF under stress conditions.