P.245 - Potential role of exosomes in skeletal muscle fibrosis

Abstract

Muscle fibrosis, the end point of most severe muscle diseases, is characterized by excessive connective tissue proliferation that progressively replaces muscle fibres. We have previously shown that cellular and circulating microRNAs (miRNAs) are involved in the process and, in particular, that the expression of the pro-fibrotic miR-21 is increased in Duchenne muscle dystrophy (DMD) fibroblasts and the anti-fibrotic miR-29 is significantly reduced in DMD myoblasts. Exosomes, small vesicles secreted by several cell types, in addition to proteins, contain mRNAs and miRNAs, and are actively involved in cell-cell communication. We characterized exosome release by DMD muscle-derived fibroblasts and exosome up-take by control muscle-derived fibroblasts, and investigated the role of exosomes and of miRNAs transported by exosomes. In exosomes derived from DMD fibroblasts a focused miRNA array analysis showed high levels of miR-199a, as also observed in fibrotic conditions affecting other tissues. DMD fibroblast-derived exosomes added to control fibroblasts induced increased expression of the fibrotic markers α-SMA, collagen 1, fibronectin, TIMP-1 and TGF-beta-1, increased production of soluble collagens, and increased cell proliferation. To confirm that these changes are related to miR-199a and to secondary reduction in caveolin-1, a known target gene of miR-199a, we transfected control fibroblasts with miR-199a mimic observing, as consequence, increased expression of the fibrosis markers. On the contrary, transfection with miR-199a inhibitor caused reduction of these markers. Our results suggest that DMD fibroblast-derived exosomes induces an activated pro-fibrotic phenotype in control fibroblasts. Our findings also indicate that the phenotypic conversion of fibroblasts to myofibroblasts, typical of fibrosis, can be induced by exosomes produced by DMD fibroblasts, pointing to miR-199a as potential therapeutic target for reducing fibrosis.