Vascular endothelial growth factor induces expression of connective tissuegrowth factor via KDR, Flt1, and phosphatidylinositol 3-kinase-Akt-dependent pathways in retinal vascular cells

Fibroblastic proliferation accompanies many angiogenesis-related retinal an d systemic diseases. Since connective tissue growth factor (CTGF) is a pote nt mitogen for fibrosis, extracellular matrix production, and angiogenesis, we have studied the effects and mechanism by which vascular endothelial gr owth factor (VEGF) regulates CTGF gene expression in retinal capillary cell s. In our study, VEGF increased CTGF mRNA levels in a time and concentratio n-dependent manner in bovine retinal endothelial cells and pericytes, witho ut the need of new protein synthesis and without altering mRNA stability. V EGF activated the tyrosine receptor phosphorylation of KDR and Flt1 and inc reased the binding of phosphatidylinositol 3-kinase (PIS-kinase) p85 subuni t to KDR and Flt1, both of which could mediate CTGF gene induction. VEGF-in duced CTGF expression was mediated primarily by PI3-kinase activation, wher eas PKC and ERK pathways made only minimal contributions. Furthermore, over expression of constitutive active Akt was sufficient to induce CTGF gene ex pression, and inhibition of Akt activation by overexpressing dominant negat ive mutant of Akt abolished the VEGF-induced CTGF expression. These data su ggest that VEGF can increase CTGF gene expression in bovine retinal capilla ry cells via KDR or Fit receptors and the activation of PI3-kinase-Akt path way independently of PKC or Ras-ERK pathway, possibly inducing the fibrosis observed in retinal neovascular diseases.