| Objective To investigate the potential regulatory role of angiotensin type 2 receptor (AT2R) and vitamin D receptor (VDR) in fibrosis of skeletal muscle in mice. Methods Grip strength tests were performed on 16-week-old wild type (WT) and AT2R(-/-) mice, 12-week-old AT2R(-/-) mice, and AT2R(-/-)/VDR(-/-) (DKO) mice. The wet weight ratio and the molecular expressions of fibrotic and profibrotic factors were measured in hindlimb muscles of mice. Results (1) Compared to to those in WT mice, there was no significant difference in the wet weight ratio of the hindlimb skeletal muscles in AT2R(-/-) mice. However, the mRNA expressions of fibronectin (FN), CTGF, VEGF (P<0.05), and MSTN displayed the decreasing trend. The protein expressions of TGF-β and Col-IV were significantly down-regulated (P<0.05) associated with a marked reduce in content of MSTN (P<0.05) in skeletal muscle of AT2R(-/-) mice. (2) In a comparison with AT2R(-/-) mice, the DKO mice showed the significant up-regulation (P<0.05) in protein expressions of the fibrotic indicators including Col-IV, TGF-?, and VEGF, along with a profound elevation in protein expression of Renin (P<0.05). The immunofluorescence detection indicated that the relative fluorescence intensity and the fluorescence area of FN were both enhanced in the gastrocnemius muscle of DKO mice (P<0.05). Conclusion The knockout of AT2R gene might alleviate the degree of muscle fibrosis in mice. Importantly, VDR ablation exacerbates skeletal muscle fibrosis in AT2R knockout mice, which is, at least partially, attributed to the over-activity of renin-angiotensin system that may lead to enhance fibrosis of tissues. |