Transforming growth factor type beta 1 increases the expression of angiotensin II receptor type 2 by a SMAD- and p38 MAPK-dependent mechanism in skeletal muscle

Excessive deposition of extracellular matrix (ECM) proteins, a condition known as fibrosis, is a hallmark of Duchenne muscular dystrophy. Among the factors that trigger muscle fibrosis are transforming growth factor beta (TGF-) and angiotensin II (Ang-II). Ang-II belongs to the renin-angiotensin system, and its biological effects are exerted by Ang-II receptors type 1 and type 2 (AT-1 and AT-2, respectively). This study aims to determine the effect of TGF-1 on the expression of AT-1 and AT-2 receptor in skeletal muscle. C2C12 myoblasts exposed to TGF-1 showed a dose-dependent increase in AT-2 expression but with no effect on AT-1 levels. Injection of TGF-1 in the skeletal muscle of mice increased the levels of AT-2 and ECM protein but unchanged AT-1 levels. We also detected higher expression levels of AT-2 receptor in dystrophic skeletal muscle of mdx mice than in normal mice. The induction of AT-2 was mediated by the canonical TGF- pathway because under the inhibitory conditions of the kinase activity of TGF receptor I or the knockdown of Smad2/3 levels, TGF--induced AT-2 receptor increase was strongly inhibited. Furthermore, we demonstrated that p38MAPK activity in response to TGF- is also required for AT-2 increase as evaluated by a p38MAPK inhibitor. Our results show that the levels of AT-2 but not AT-1 receptor are modulated by the pro-fibrotic factor TGF-1 in myoblasts and mouse skeletal muscle. This finding suggests that AT-2 might be involved in the physiopathology of fibrosis in dystrophic skeletal muscle. (c) 2013 BioFactors, 39(4):467-475, 2013