P20.4 Antithetic role of miR-21 and miR-29 in the progression of fibrosis in Duchenne muscular dystrophy

Abstract

Muscle fibrosis that progressively replaces muscle fibers in severe muscular dystrophies and chronic myopathies is characterized by excessive deposition of collagen and other extracellular matrix (ECM) proteins. Recent data indicate a major involvement of microRNAs in regulation of pro- and anti-fibrotic genes. In particular, persistent over-expression of miR-21 perturbs tissue repair and contributes to tissue fibrosis; furthermore, induction of miR-21 expression by TGF-beta 1 treatment indicates that it may mediate TGF-beta 1 fibrogenic activity. In fibrotic diseases reduced miR-29 expression correlates with increased expression of collagens and ECM-related genes, while in skeletal muscle it acts as pro-myogenic factor during muscle cell differentiation, suggesting a major role of miR-29 in ECM deposition and remodelling and in muscle regeneration. To define the role of miR-21 and miR-29 in Duchenne muscle dystrophy (DMD), we evaluated their expression in DMD muscles and in muscle-derived fibroblasts and myoblasts. Our results show significant increase of miR-21 expression in DMD fibroblasts, more marked after TGF-beta 1 treatment, and significant reduction of miR-29a and miR-29c expression in myoblasts. In DMD fibroblasts we also observed changes in miR-21 target genes including Pten and Sprouty-1, that were significantly reduced and collagen I and VI that were significantly increased. In DMD fibroblasts, along with miR-21 increase, there was also an increase in soluble collagen production; the fibrinolytic system uPa/plasmin, involved in ECM remodelling of damaged skeletal muscle and in regulation of miR-21 expression, was altered, and plasmin activity was reduced. All these aspects indicate a pro-fibrotic modification in ECM homeostasis. Our results show that miR-21 and miR-29 play opposed roles in muscle fibrosis and suggest that pharmacological modulation of their expression may have therapeutic potential for muscle fibrosis.