Thrombin causes vascular endothelial growth factor expression in vascular smooth muscle cells - Role of reactive oxygen species

Vascular endothelial growth factor (VEGF) has been implicated in the reendo thelialization of the vascular wall after balloon injury. This study invest igated whether thrombin, which is formed during activation of the coagulati on cascade at sites of vascular injury, upregulates VEGF expression in vasc ular smooth muscle cells (VSMCs). VEGF expression was assessed in native an d cultured VSMCs by Northern blot analysis and reverse transcription-polyme rase chain reaction and the release of VEGF protein by immunoassay. alpha - Thrombin time- and concentration-dependently increased VEGF mRNA levels, ma inly that mRNA coding for the soluble splice variant VEGF(164/165), and sti mulated the release of VEGF protein. These effects required the proteolytic activity of thrombin and were mimicked by a thrombin receptor activating-p eptide. Upregulation of VEGF expression was also induced by conditioned med ium from alpha -thrombin-stimulated VSMCs. Both the early and the delayed a lpha -thrombin-induced VEGF expressions were attenuated by antioxidants and by diphenyleneiodonium. alpha -Thrombin-induced VEGF release was significa ntly reduced by a platelet-derived growth factor (PDGF)-, a transforming gr owth factor (TGF)-beta-, and a basic fibroblast growth factor (bFGF)-neutra lizing antibody. Thrombin caused a redox-sensitive upregulation of expressi on of VEGF in VSMCs through a direct and an indirect effect, which was depe ndent on the endogenous formation of PDGF, TGF-beta, and bFGF. Upregulation of VEGF expression may represent an important mechanism by which the coagu lation cascade contributes to the regeneration of the endothelial lining at sites of balloon injury.