Abstract
Cardiac myocyte apoptosis underlies the pathophysiology of cardiomyopathy, and plays a critical role in the transition from myocardial hypertrophy to heart failure. Angiotensin II (Ang II) induces cardiac myocyte apoptosis and hypertrophy which contribute to heart failure possibly through enhanced oxidative stress; however, the mechanisms underlying the activation of both pathways and their interactions remain unclear. In the present study, we have investigated whether overexpression of the antioxidant protein heme oxygenase‐1 (HO‐1) protects against apoptosis and hypertrophy in cultured rat cardiac myocytes treated with Ang II. Our findings demonstrate that Ang II (100 nM, 24 h) alone upregulates HO‐1 expression and induces both myocyte hypertrophy and apoptosis, assessed by measuring terminal deoxynucleotidyltransferase dUTP nick‐end labelling (TUNEL) staining, caspase‐3 activity and mitochondrial membrane potential. Ang II elicited apoptosis was augmented in the presence of tin protoporphyrin, an inhibitor of HO activity, while HO‐1 gene transfer to myocytes attenuated Ang II‐mediated apoptosis but not hypertrophy. Adenoviral overexpression of HO‐1 was accompanied by a significant increase in Ang II induced phosphorylation of Akt, however, Ang II‐mediated p38 mitogen activated protein kinase (MAPK) phosphorylation was attenuated. Inhibition of phosphotidylinositol‐3‐kinase enhanced myocyte apoptosis elicited by Ang II, however, p38^MAPK^ inhibition had no effect, suggesting that overexpression of HO‐1 protects myocytes via augmented Akt activation and not through modulation of p38^MAPK^ activation. Our findings identify the signalling pathways by which HO‐1 gene transfer protects against apoptosis and suggest that overexpression of HO‐1 in cardiomyopathies may delay the transition from myocyte hypertrophy to heart failure. J. Cell. Physiol. 209: 1–7, 2006. © 2006 Wiley‐Liss, Inc.