Down-regulation of microRNA-206 in striated muscle of mdx mice improves muscle function.

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 DESCRIPTION (provided by applicant): Duchenne muscular dystrophy (DMD) is a severe muscle wasting disease and the most prevalent inherited muscle disorder worldwide. It is caused by a mutation in the dystrophin gene, which normally encodes an important structural and signaling protein located at the muscle membrane. In DMD, the dystrophin protein is absent or present at low levels within the body, rendering the muscle susceptible to damage. DMD patients lose motor function over time and die prematurely from respiratory or cardiac failure. Current treatments are merely palliative and do not target the underlying cause. Gene therapy strategies aimed at replacing or correcting mutated genes have shown promise for DMD. Recombinant adeno-associated viruses (AAVs) are popular gene delivery vehicles due to their non-pathogenic nature and ability to establish long-term and efficient gene transfer. Still, restoring dystrophin fails to completely alleviate motor deficits and prevent fatigue after mild activity. While DMD is caused by a mutation in a single gene, many secondary disease mechanisms are involved, such as ischemia, fibrosis and abnormal regeneration. A strategy that addresses multiple pathological mechanisms may provide greater benefit. MicroRNAs (miRNAs or miRs) are small, regulatory RNA molecules that inhibit their target genes. A skeletal muscle-restricted miRNA, miR-206, is highly up-regulated in dystrophic muscle. While its function after disease onset is not well-understood, multiple miR-206 targets have shown therapeutic benefit for DMD, such as vascular endothelial growth factor A (VEGF-A) and utrophin. Down-regulation of miR-206 and its detrimental effect on corrective mechanisms thus presents a novel strategy for treating DMD. This proposal aims to characterize the therapeutic efficacy of a recombinant AAV vector carrying an antisense sequence against miR-206 (AAV-anti-miR-206), exploring its impact on two secondary pathological mechanisms. Functional ischemia is a major contributor to the dystrophic phenotype and exacerbates muscle damage. To better understand the role of AAV-anti-miR-206 on muscle vascularization, the first Aim will investigate its ability to increase the expression of proven therapeutic target VEGF-A. These experiments will also determine if AAV-anti-miR-206 can recapitulate blood vessel growth, function and integrity associated with VEGF-A treatment. Increasing membrane stability using utrophin, a dystrophin paralog, can delay DMD progression and improve motor function. To determine if AAV-anti-miR-206 influences muscle structural integrity and pathology, the second Aim will explore its effect on utrophin expression. The proposed experiments will determine if this treatment improves overall muscle pathology and prevents further damage. Together these Aims will provide a better understanding of miR-206 function and explore a novel, multifunctional therapeutic strategy for DMD.