MicroRNA-206 Downregulation Improves Therapeutic Gene Expression and Motor Function in mdx Mice

Abstract

Duchenne muscular dystrophy (DMD) is a severe muscle-wasting disorder caused by a mutation in the dystrophin gene. Numerous gene therapies have been developed to replace or repair the defective dystrophin gene; however, these treatments cannot restore the full-length protein or completely resolve dystrophic symptoms. Secondary pathological mechanisms, such as functional ischemia and fibrosis, are thought to exacerbate the primary defect and cause the profound muscle degeneration found in dystrophic muscle. Surrogate therapies utilizing alternative therapeutic genes, or "booster genes," such as VEGFA and utrophin, seek to address these secondary mechanisms and have shown impressive benefit in mdx mice. A skeletal muscle-specific microRNA, miR-206, is particularly overexpressed in dystrophic muscle and inhibits the expression of known booster genes. Thus, we aimed to determine if miR-206 contributes to dystrophic pathology by repressing beneficial gene expression. Here, we show that AAV-mediated expression of a miR-206 decoy target effectively downregulated miR-206 expression and increased endogenous therapeutic gene expression in mature mdx muscle. Furthermore, treatment significantly improved motor function and dystrophic pathology in mdx mice. In summary, we have identified a contributing factor to the dystrophic phenotype and characterized a novel therapeutic avenue for DMD.