In vitro dissection of the pathogenic mechanisms of muscle fribrosis in duchenne dystrophy

The principal goal of this study is to increase understanding of pro-fibrotic mechanisms in dystrophic muscle by reconstructing, in an in vitro muscle cell-fibroblast culture model, the various steps of ECM deposition. Fibrosis is a complex mechanism not completely understood, triggered for repairing the injured tissue and for isolating it from the healthy surroundings. We expect that our in vitro studies will help to better understand which are the major players in muscle fibrosis. Furthermore, our studies will provide clues to the development of anti-fibrotic therapies that, in the absence of specific treatments, may improve muscle function and slow disease progression in DMD and other muscular dystrophies. We performed this study in order to investigate whether ECM components contribute to the severe fibrosis observed in DMD skeletal muscle. We analyzed several ECM components as transcripts and proteins in primary DMD and control myotube culture. In particular we evaluated TGF-β1, myostatin, decorin, MMP-2, MMP-9, TIMP-1, -2, -3, collagens I and VI. We have found that transcript expression and protein modulation of several ECM components is altered in DMD muscle cells in vitro indicating their contribute to the pathological process. To probe profibrotic mechanisms in DMD muscle we isolated fibroblasts from DMD and control biopsies and induced transdifferentiation to myofibroblasts by TGF-β1 treatment. The study has revealed several differences between fibroblasts from DMD muscle and those from normal muscle, particularly as regards factors likely to affect ECM turnover. This study confirms that fibroblasts and myofibroblasts play a major role in muscle fibrosis and suggests that DMD fibroblasts have a profibrotic phenotype accentuated by TGF-β1 treatment.