Immunomodulation of TGF-beta1 in mdx mouse inhibits connective tissue proliferation in diaphragm but increases inflammatory response: Implications for antifibrotic therapy

Irreversible connective tissue proliferation in muscle is a pathological hallmark of Duchenne muscular dystrophy (DMD), a genetic degenerative muscle disease due to lack of the sarcolemmal protein dystrophin. Focal release of transforming growth factor-beta1 (TGF-β1) is involved in fibrosis development. Murine muscular dystrophy (mdx) is genetically homologous to DMD and histopathological alterations comparable to those in DMD muscles occur in diaphragm of older mdx mice. To investigate the early development of fibrosis and TGF-β1 involvement, we assessed diaphragms in 6-36-week-old mdx and C57/BL6 (control) mice for fibrosis, and used real-time PCR and ELISA to determine TGF-β1 expression. Significantly greater fibrosis and TGF-β1 expression were found in mdx from the 6th week. Mice treated with neutralizing antibody against TGF-β1 had lower levels of TGF-β1 protein, reduced fibrosis, unchanged muscles fiber degeneration/regeneration, but increased inflammatory cells (CD4 + lymphocytes). These data demonstrate early and progressive fibrosis in mdx diaphragm accompanied by TGF-β1 upregulation. Reduction of TGF-β1 appears promising as a therapeutic approach to muscle fibrosis, but further studies are required to evaluate long term effects of TGF-β1 immunomodulation on the immune system.