MicroRNA-29 Overexpression Delivered By Adeno-Associated Virus Suppresses Fibrosis in mdx:utrn+/- Mice (S61.003)

OBJECTIVE: To demonstrate the degree of muscle fibrosis in mdx:utrn +/- mice and in dystrophin-deficient patient-derived muscle biopsies, correlate changes with microRNA-29 (miR-29), and develop anti-fibrotic therapy using miR-29 delivered by adeno-associated virus (AAV). BACKGROUND: Duchenne muscular dystrophy (DMD) is caused by dystrophin deficiency resulting in muscle loss and progressive weakness, and fibrotic scarring. Muscle fibrosis impairs blood flow and excludes endomysial-derived constituents hampering muscle repair and regeneration. Fibrosis contributes to limb contractures and loss of ambulation. Irrespective of the success of gene restoration (molecular or pharmacologic), functional improvement mandates reduction of muscle fibrosis. mRNA-29 is a potential gene regulator and an ideal candidate for reducing muscle fibrosis. DESIGN/METHODS: Connective tissue was quantified from muscle biopsies of dystrophin-deficient patients, the mdx or mdx:utrn +/- mouse models. Endomysial fibrosis was quantified using Sirius Red-stained sections analyzed by NIH ImageJ Software. 59-nuclease assays were used to measure miR-29 expression correlated with levels of fibrosis. AAV was used to deliver miR-29 into mouse muscle via intramuscular injection. RESULTS: Endomysial connective tissue levels were uniformly increased in the muscles of mdx mice, and in muscle biopsies from DMD patients. Findings correlated with downregulation of miR-29a and miR-29c in the mouse disease model, and in patient biopsies. Initial findings from mdx:utrn +/- mouse muscles treated with AAV-miR29c suggest a favorable anti-fibrotic response that is varied among the treatment groups. CONCLUSIONS: Demonstration of increased fibrosis and decreased miR-29 expression in mdx:utrn +/- mice and dystrophin-deficient patients validates the mouse model as being representative of the human disease. Initial results using AAV-delivered miR29 as an anti-fibrotic therapy suggest that significant beneficial effects can be achieved with further optimization. These data provide a rationale for overexpression of miR-29 to reduce fibrosis in translational, preclinical studies in mdx:utrn +/- mice in preparation for clinical trials. Study Supported by: NIH Ruth L. Kirschstein National Research Service Award (F32) Disclosure: Dr. Meadows has nothing to disclose. Dr. Kota has nothing to disclose. Dr. Malik has nothing to disclose. Dr. Clark has nothing to disclose. Dr. Sahenk has received research support from Sarepta Therapeutics. Dr. Harper has nothing to disclose. Dr. Mendell has received research support from Sarepta Therapeutics Inc.