Interaction between angiotensin II and Smad proteins in fibroblasts in failing heart and in vitro

Abstract

Angiotensin II (angiotensin) and transforming growth factor (TGF)-β 1 play an important role in cardiac fibrosis. We examined Smad proteins in 8-wk post-myocardial infarction (MI) rat hearts. AT 1 blockade (losartan) attenuated the activation of TGF-β 1 in target tissues. Losartan administration (8 wk, 15 mg · kg−1· day−1) normalized total Smad 2 overexpression in infarct scar and remnant heart tissue and normalized Smad 4 in infarct scar. Phosphorylated Smad 2 (P-Smad 2) staining decreased in cytosol from failing heart vs. the control, which was normalized by losartan, suggesting augmented P-Smad 2 movement into nuclei in untreated failing hearts. Using adult primary rat fibroblasts treated with angiotensin (10−6 M), we noted rapid translocation (15 min) of P-Smad 2 into the nuclei from the cytosol. Nuclear P-Smad 2 protein level increased with angiotensin treatment, which was blocked by losartan. We conclude that angiotensin may influence total Smad 2 and 4 expression in post-MI heart failure and that angiotensin treatment is associated with rapid P-Smad 2 nuclear translocation in isolated fibroblasts. This study suggests that cross talk between angiotensin and Smad signaling is associated with fibrotic events in post-MI hearts.