Increased HGF and c-Met in muscle tissues of polymyositis and dermatomyositis patients: beneficial roles of HGF in muscle regeneration.

We investigated the expression of hepatocyte growth factor (HGF), which has mitogenic and anti-fibrotic activities, in muscle tissue of polymyositis/dermatomyositis (PM/DM) patients, as well as its functional roles in cultured myoblasts. Immunohistochemistry in muscle from PM/DM patients revealed that HGF was expressed predominantly on infiltrating mononuclear cells and that muscle cells expressed the receptor c-met. Cultured myoblasts produced HGF; which was increased by IL-1alpha but suppressed by TGF-beta and dexamethasone. Exogenous HGF induced myoblast proliferation and reduced procollagen type I production. Furthermore, HGF enhanced the gene expression of muscle regulatory factors MyoD and Myf5, while suppressing expression of fibrosis-related genes, connective tissue growth factor and alpha-smooth muscle actin. Although dexamethasone showed contrasting effects to HGF on the expression of these genes, co-treatment with HGF ameliorated the effects of dexamethasone. Taking the beneficial roles of HGF into consideration, administration of HGF might contribute to muscle regeneration in PM/DM especially under corticosteroid treatment.