Transforming growth factor (TGF)-β1 is a known factor in
angiotensin II (Ang II)-mediated cardiac
fibrosis after
myocardial infarction (MI).
Hypoxia inducible factor-1 (Hif-1α) was recently demonstrated to involve in the tissue
fibrosis and influenced by Ang II. However, whether Hif-1α contributed to the Ang II-mediated cardiac
fibrosis after MI, and whether interaction or synergetic roles between Hif-1α and TGF-β pathways existed in the process was unclear. In vitro, cardiac cells were incubated under
hypoxia or Ang II to mimic ischaemia. In vivo,
valsartan was intravenously injected into Sprague-Dawley rats with MI daily for 1 week; saline and
hydralazine (another
anti-hypertensive agent like
valsartan) was used as control. The
fibrosis-related
proteins were detected by Western blotting. Cardiac structure and function were assessed with multimodality methods. We demonstrated in vitro that
hypoxia would induce the up-regulation of Ang II, TGF-β/Smad and Hif-1α, which further induced
collagen accumulation. By blocking with
valsartan, a blocker of Ang II type I (AT1) receptor, we confirmed that the up-regulation of TGF-β/Smad and Hif-1α was through the Ang II-mediated pathway. By administering TGF-β or
dimethyloxalylglycine, we determined that both TGF-β/Smad and Hif-1α contributed to Ang II-mediated
collagen accumulation and a synergetic effect between them was observed. Consistent with in vitro results,
valsartan significantly attenuated the expression of TGF-β/Smad, Hif-1α and
fibrosis-related
protein in rats after MI. Heart function, infarcted size, wall thickness as well as myocardial vascularization of ischaemic hearts were also significantly improved by
valsartan compared with saline and
hydralazine. Our study may provide novel insights into the mechanisms of Ang II-induced cardiac
fibrosis as well as into the cardiac protection of
valsartan.