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

ObjectiveTwo subtypes of angiotensin II (ATII) receptor have been defined on the basis of their differential pharmacological and biochemical properties: ATII-type1 receptors (AT1-R) and ATII-type2 receptors (AT2-R). It has been hypothesized that part of the protective effects on the cardiovascular system of AT1-R blockers is mediated by an ATII-mediated overstimulation of AT2-R.We hypothesized that the inhibition of AT1-R has a stronger impact on insulin-induced nitric oxide (NO) production than ATII-mediated overstimulation of AT2-R. Therefore we studied the effect of the inhibition of AT1-R and AT2-R on ATII-mediated actions in Human Umbilical Vein Endothelial Cells (HUVECs).MethodsWe analyzed the phosphorylation state of IRS1 at Ser616 and Ser312 and on tyrosines after preincubation with PD123319, an inhibitor of AT2-R, alone and in combination whit losartan, an inhibitor of AT1-R. In addition we measured eNOS and Akt activation through the evaluation of their phosphorylation at Ser1177 and Ser473 sites respectively.ResultsATII induces IRS-1 phosphorylation at Ser312 and Ser616 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 AT1-R inhibitor restored the insulin signaling leading to NO production, whereas AT2-R inhibitor did not have effects on NO production in presence of ATII.ConclusionOur results demonstrate that in presence of AT1-R antagonist, the AT2-R blockage does not modify the effect obtained with the AT1-R inhibition alone. Therefore, a possible positive role of an AT2-R overstimulation in condition of AT1-R antagonism seems to be irrelevant.