Bimodal concentration-dependent effect of thrombin on endothelial cell proliferation and growth factor release in culture

Background. The role of thrombin in the stimulation of endothelial cell (EC) proliferation is controversial. The aim of this study was to investigate if thrombin regulates cell proliferation and production of platelet-derived growth factor (PDGF), bovine fibroblast growth factor (bFGF), and transforming growth factor β1 (TGF-β1) by bovine aortic ECs. Methods. ECs, obtained from thoracic aortas of calves, were stimulated with thrombin at various concentrations (from 0.05 to 1.0 IU/ml) in serum free culture. Mitogenic activity of thrombin on ECs was determined by tritiated thymidine uptake. The release of PDGF, bFGF, and TGF-β1 was assessed by ELISA. PDGF release was confirmed by Western blot and bFGF and TGF-β1 mRNA expression was determined by polymerase chain reaction (PCR). Results. Thrombin at high concentrations did not cause any increase in EC proliferation after 72 h of culture and induced inhibition of EC proliferation after 96 h and 8 days of culture. It induced a decrease in PDGF release and an increase in TGF-β1 release. Thrombin at low concentrations induced a significant increase in EC proliferation at 72 h, 96 h, and 8 days of culture. It induced an increase in PDGF release and a decrease in TGF-β1 release. bFGF release was higher than control at all thrombin concentrations. These data were confirmed by Western blot and PCR studies. Conclusions. Thrombin regulates EC growth through the inhibition of EC proliferation at high concentrations and through the stimulation of EC proliferation at low physiological concentrations. EC proliferation is partially mediated by autocrine production of PDGF, bFGF, and TGF-β1. © 2001 Academic Press.