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

Abstract

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.