Altered production of extra-cellular matrix components by muscle-derived Duchenne muscular dystrophy fibroblasts before and after TGF-β1 treatment

To probe pro-fibrotic mechanisms in dystrophic muscle, we isolated primary fibroblasts from Duchenne muscular dystrophy (DMD) and control muscle biopsies and induced transdifferentiation in myofibroblasts by transforming growth factor β1 (TGF-β1) treatment. We compared proliferating activity, soluble collagen production, and transcript and protein levels of decorin, myostatin, TGF-β1, matrix metalloproteinase-1 (MMP-1; interstitial collagenase), MMP-2 (gelatinase), MMP-3 (stromelysin), MMP-7 (matrilysin), and the tissue inhibitors of metalloproteinases inhibitors (TIMPs) 1-4, in fibroblasts and myofibroblasts. Principal differences included a significantly greater proliferation rate and soluble collagen production, a significant upregulation of decorin, myostatin and MMP-7 transcripts and proteins, and a significant downregulation of MMP-1 and TIMP-3 transcripts (with MMP-1 protein being reduced as shown by enzyme-linked immunosorbent assay and TIMP-3 protein apparently being reduced on Western blot), in untreated DMD fibroblasts compared with controls. TGF-β1 transdifferentiation significantly lowered decorin and myostatin and significantly increased TGF-β1 transcript and protein, significantly increased MMP-1 and TIMP-3, and significantly lowered MMP-7 transcript and protein in DMD cells compared with pretreatment controls. The differences between DMD and control fibroblasts showed that DMD fibroblasts had a profibrotic phenotype, accentuated by TGF-β1 treatment. Dystrophin absence itself could exert a direct influence on the homeostasis of the extracellular matrix (ECM) by allowing leakage of cellular components to the extracellular space or by abnormal cellular uptake of extracellular growth factors, cytokines, or enzymes influencing muscle fibroblasts either directly by altering adhesion properties or indirectly by interactions with molecules released into the ECM by muscle or inflammatory cells. The transdifferentiation of muscle fibroblasts might serve as a simplified model of fibrosis for further elucidation of the mechanisms of muscle fibrosis and for testing possible anti-fibrotic agents.