Phenotypic Improvement of Dystrophic Muscles by rAAV/Microdystrophin Vectors Is Augmented by Igf1 Codelivery
The absence of dystrophin in Duchenne muscular dystrophy (DMD) leads to sarcolemmal instability and enhances the susceptibility of muscle fibers to contraction-induced injury. Various viral vectors have been used to deliver mini- and microdystrophin expression cassettes to muscles of dystrophin deficient mdx mice, significantly increasing both the morphological and the functional properties of the muscles. However, dystrophin delivery to adult mdx mice has not yielded a complete rescue of the dystrophic phenotype. Here we investigated a novel strategy involving dual gene transfer of recombinant adeno-associated viral vectors expressing either microdystrophin (rAAV-MDys) or a muscle-specific isoform of Igf-1 (rAAV-mIgf-1). Injection of mdx muscles with rAAV-MDys reduced myofiber degeneration and turnover and increased their resistance to mechanical injury, but did not increase muscle mass or force generation. Injection of mdx muscles with rAAV-mIgf-1 led to increased muscle mass, but did not provide protection against mechanical injury or halt myofiber degeneration, leading to loss of the vector over time. In contrast, co-injection of the rAAV-MDys and rAAV-mIgf-1 vectors resulted in increased muscle mass and strength, reduced myofiber degeneration, and increased protection against contraction-induced injury. These results suggest that a dual-gene, combinatorial strategy could enhance the efficacy of gene therapy of DMD.