Aims: Thrombomodulin (TM), a potent anticoagulant, is not detected in quiescent vascular smooth muscle cells (VSMCs). In diseased vessels, VSMC expresses TM, but the mechanisms are unclear. This study examined molecular mechanisms for TM expression in VSMCs.
Methods and results: Platelet-derived growth factor-BB (PDGF-BB) induced TM expression in cultured human aortic VSMCs. PDGF-induced TM is functional in activating protein C. TM induction was eliminated by inhibitors of Src kinase, phosphatidylinositol 3-kinase (PI3-kinase), and mammalian target of rapamycin (mTOR) and by expressing dominant-negative Akt while expressing active Akt-stimulated TM expression. PDGF-BB activated the TM promoter, and the deletion of a sequence segment -394/-255 drastically reduced TM promoter activity. Transcription factor E26 transformation-specific sequence-1 (Ets-1) was upregulated by PDGF-BB in a PI3-kinase- and mTOR-dependent manner. RNA interference of Ets-1 inhibited PDGF induction of TM, and overexpressing Ets-1 increased TM expression. Chromatin immunoprecipitation and electrophoretic mobility shift assay detected increased Ets-1 binding to the TM promoter after PDGF treatment. Following carotid artery ligation of C57/BL6 mice, PDGF-BB and TM were co-expressed in the media and neointima.
Conclusion: In VSMCs, PDGF-BB stimulates TM expression that is mainly mediated by Ets-1 via the Src kinase/PI3-kinase/Akt/mTOR signalling pathway. Furthermore, PDGF-BB may regulate TM expression in VSMCs during vascular remodelling.