Stimulated activation of platelet-derived growth factor receptor in vivo in balloon-injured arteries: A link between angiotensin II and intimal thickening

Background: Growth factors such as platelet-derived growth factor (PDGF) have been postulated to be important mediators of neointimal formation in balloon-injured artery. Binding of growth factors to their receptors activates intrinsic receptor tyrosine kinase, resulting in tyrosine phosphorylation of receptors themselves and cellular substrate proteins. We investigated in vive activities of growth factors by determining the extent of tyrosine phosphorylation of growth factor receptors and substrate proteins in injured artery. Methods and Results: Rat balloon-injured carotid artery was analyzed for phosphotyrosine content of PDGF α- and β-receptors, epidermal growth factor (EGF) receptors, and insulin receptor substrate-1 (IRS-1) by immunoprecipitation and anti-phosphotyrosine Western blot. The development of intimal thickening after deendothelializing balloon catheterization of rat carotid artery was accompanied by transient twofold to threefold increases in the extent of tyrosyl phosphorylation of PDGF α- and β-receptors but not EGF receptor or IRS-1. The AT₁ angiotensin II (Ang II) receptor antagonist TCV-116 markedly inhibited both tyrosyl phosphorylation of PDGF α- and β-receptors and intimal thickening. The AT₁ antagonist reduced mRNA levels of both PDGF-A and -B chains in injured arteries. Conclusions: The present study provides direct evidence for increased PDGF activities in injured artery in situ and the involvement of Ang II in stimulated activation of PDGF receptors. These results are consistent with the pathogenetic role for PDGF in intimal thickening.