Valsartan regulates the interaction of angiotensin II type 1 receptor and endothelial nitric oxide synthase via Src/PI3K/Akt signalling

Valsartan, a selective angiotensin II type 1 receptor (AT(1)R) blocker, has beneficial effects in the cardiovascular system in part by its increase of nitric oxide (NO) bioavailability, yet the mechanisms are unclear. We investigated the molecular mechanisms underlying this effect in endothelial cells (ECs). NO production was examined by Griess reagent assay, DAF-2 DA fluorescence staining and cGMP ELISA kits. Protein interaction was determined by western blotting and immunoprecipitation. Treating bovine or human aortic ECs with valsartan increased NO production, as evidenced by elevated level of stable NO metabolites and intracellular cGMP. Valsartan increased the phosphorylation but not the protein level of endothelial NO synthase (eNOS). Inhibition of phosphoinositide-3 kinase (PI3K)/Akt and Src pathways by specific inhibitors suppressed valsartan-induced NO release. In addition, valsartan increased the tyrosine residue phosphorylation of AT(1)R, which was attenuated by inhibition of Src but not PI3K activities. Valsartan also suppressed the interaction of eNOS and AT(1)R, which was blocked by Src or PI3K inhibition. Valsartan-induced NO production in ECs is mediated through Src/PI3K/Akt-dependent phosphorylation of eNOS. Valsartan-induced AT(1)R phosphorylation depends on Src but not PI3K, whereas valsartan-induced suppression of AT(1)R-eNOS interaction depends on Src/PI3K/Akt signalling. These results indicate a novel vasoprotective mechanism of valsartan in upregulating NO production in ECs.