Angiotensin II stimulates the synthesis of vascular endothelial growth factor through the p38 mitogen activated protein kinase pathway in cultured mouse podocytes

Abstract

Angiotensin II (Ang-II) and vascular endothelial growth factor (VEGF) have an important role in the pathogenesis of diabetic nephropathy, but the signaling cascade of VEGF regulation in response to Ang-II in podocytes is largely unknown. In these experiments, we looked at the effect of Ang-II on the production of VEGF, and investigated whether VEGF production depends on the p38 mitogen activated protein kinase (MAPK) pathway in cultured mouse podocytes. Incubation of podocytes with Ang-II induced a rapid increase in VEGF mRNA expression and protein synthesis as well as its transcriptional activity in an Ang-II dose-dependent manner. To further define the role of angiotensin type 1 (AT1) and type 2 (AT2) receptors involved in Ang-II-mediated VEGF synthesis, the effects of selective AT1 and AT2 receptor antagonists were evaluated. Prior treatment with losartan significantly inhibited VEGF mRNA and protein synthesis induced by Ang-II, which suggests that the AT1 receptor is involved in Ang-II-mediated VEGF synthesis. Furthermore, stimulation of the cells with Ang-II increased both phosphorylation of p38 MAPK and MAP kinase kinase 3/6 (MKK3/6). Additionally, Ang-II enhanced the DNA binding activity to cAMP response element binding protein (CREB) and phosphorylation of CREB. In addition, to investigate the role of p38 MAPK in Ang-II-induced VEGF synthesis, podocytes were pretreated with or without the p38 MAPK inhibitor, SB203580 for 24 h to observe whether Ang-II-mediated VEGF synthesis was inhibited by blocking p38 MAPK. The addition of SB203580 led to a marked inhibition of the increased VEGF mRNA and protein production induced by Ang-II in a dose-dependent manner. Taken together, these results suggest that Ang-II stimulates the synthesis of VEGF in podocytes and the production of VEGF induced by Ang-II is mediated, in part, through the activation of the p38 MAPK pathway.