Aggregating Human Platelets Stimulate Expression of Vascular Endothelial Growth Factor in Cultured Vascular Smooth Muscle Cells Through a Synergistic Effect of Transforming Growth Factor-β 1 and Platelet-Derived Growth Factor AB

Abstract

Background —Vascular endothelial growth factor (VEGF), an endothelial mitogen and chemoattractant, has been implicated in the recovery of the endothelium after balloon injury. The increased expression of VEGF in vascular smooth muscle cells (SMC) at sites of injury suggests that this cell type may be a major cellular source of VEGF. This study examined whether aggregating platelets stimulate VEGF expression in cultured SMC. Methods and Results —VEGF expression in SMC was assessed by Northern blot analysis and by reverse transcription followed by polymerase chain reaction and the release of VEGF by Western blot analysis and immunoassay. Platelet-derived products (PDP) released by aggregating human platelets time-dependently and concentration-dependently enhanced VEGF mRNA levels, mainly that coding for the soluble splice variant VEGF 165/164 , and stimulated the release of VEGF protein. These effects were potentiated by transient acidification of PDP, which release bioactive transforming growth factor (TGF)-β 1 , and mimicked by platelet-derived growth factor (PDGF) AB and TGF-β 1 in a synergistic manner. Both a TGF-β–neutralizing antibody and a PDGF-neutralizing antibody significantly attenuated the effect of acidified PDP on VEGF production. Conclusions —Aggregating human platelets induce VEGF mRNA expression in cultured SMC and the subsequent release of VEGF protein. This effect can be attributed to a supra-additive action of PDGF AB and TGF-β 1 and may represent a novel mechanism by which platelets contribute to the recovery of the endothelial lining at sites of balloon-injured arteries.