Abstract 8877: Redefining the Role of Angiotensin II Type 1 and Type 2 Receptors in Cardiomyocyte Apoptosis
Purpose of the study: Angiotensin II exerts its effects by activating its receptors, primarily type 1 (AT1R) and type 2 (AT2R). The role of AT1R and AT2R in cardiomyocyte apoptosis remains controversial. To define the precise role of AT1R and AT2R on cardiomyocyte biology, we studied the apoptotic response of AT1R or AT2R overexpression in HL-1 cardiomyocytes. Materials and
Methods: HL-1 cells were transfected with AT1R and AT2R cDNA, and cell apoptosis and the expressions of apoptotic genes, NADPH oxidase, ROS, iNOS and eNOS were detected in this study.
Results: We observed that AT1R overexpression increased endogenous AT2R expression, but AT2R overexpression did not affect endogenous AT1R expression. Caspase-3 staining, cell cycle analysis and Bax/Bcl2 Western analysis indicated that overexpression of AT1R or AT2R resulted in cardiomyocyte apoptosis (Fig A). Further, we observed that AT1R overexpression significantly increased Nox2, p47phox and p67phox (subunits of NADPH oxidase) and ROS generation; in contrast, AT2R overexpression decreased p67phox expression without significant effect on other NADPH oxidase subunits or ROS generation (Fig B). Both AT1R and AT2R overexpression markedly increased iNOS expression (AT2R>AT1R) (Fig B). To delineate the contribution of upregulation of AT2R by AT1R overexpression and subsequent increase in iNOS resulting in apoptosis in cardiomyocytes; AT1R over-expressing cells were treated with AT2R blocker PD133319; this treatment significantly inhibited AT1R overexpression-induced iNOS and apoptosis.
Conclusion: These findings suggest that AT2R overexpression induces cardiomyocyte apoptosis via iNOS upregulation; AT1R overexpression induces cardiomyocyte apoptosis at least in part via endogenous AT2R increase and resultant upregulation of iNOS.
- © 2011 by American Heart Association, Inc.