Angiotensin II type 1 receptor, but no type 2 receptor, interferes with the insulin-induced nitric oxide production in HUVECs

Objective: Two subtypes of angiotensin II (ATII) receptor have been defined on the basis of their differential pharmacological and biochemical properties: ATII-type1 receptors (AT 1-R) and ATII-type2 receptors (AT 2-R). It has been hypothesized that part of the protective effects on the cardiovascular system of AT 1-R blockers is mediated by an ATII-mediated overstimulation of AT 2-R. We hypothesized that the inhibition of AT 1-R has a stronger impact on insulin-induced nitric oxide (NO) production than ATII-mediated overstimulation of AT 2-R. Therefore we studied the effect of the inhibition of AT 1-R and AT 2-R on ATII-mediated actions in Human Umbilical Vein Endothelial Cells (HUVECs). Methods: We analyzed the phosphorylation state of IRS1 at Ser 616 and Ser 312 and on tyrosines after preincubation with PD123319, an inhibitor of AT 2-R, alone and in combination whit losartan, an inhibitor of AT 1-R. In addition we measured eNOS and Akt activation through the evaluation of their phosphorylation at Ser 1177 and Ser 473 sites respectively. Results: ATII induces IRS-1 phosphorylation at Ser 312 and Ser 616 through the activation of JNK and ERK 1/2, resulting in the inhibition of the insulin-induced phosphorylation of IRS1 tyrosines, Akt and eNOS. Treatment of HUVECs with AT 1-R inhibitor restored the insulin signaling leading to NO production, whereas AT 2-R inhibitor did not have effects on NO production in presence of ATII. Conclusion: Our results demonstrate that in presence of AT 1-R antagonist, the AT 2-R blockage does not modify the effect obtained with the AT 1-R inhibition alone. Therefore, a possible positive role of an AT 2-R overstimulation in condition of AT 1-R antagonism seems to be irrelevant. © 2011 Elsevier Ireland Ltd.