Genetic mutations in dystrophin manifest in Duchenne muscular dystrophy (DMD), the most commonly inherited muscle disease. Here, we report on reprogramming of fibroblasts from two DMD mouse models into induced myogenic progenitor cells (iMPCs) by MyoD overexpression in concert with small molecule treatment. DMD iMPCs proliferate extensively, while expressing myogenic stem cell markers including Pax7 and Myf5. Additionally, DMD iMPCs readily give rise to multinucleated myofibers that express mature skeletal muscle markers; however, they lack DYSTROPHIN expression. Utilizing an exon skipping-based approach with CRISPR/Cas9, we report on genetic correction of the dystrophin mutation in DMD iMPCs and restoration of protein expression in vitro. Furthermore, engraftment of corrected DMD iMPCs into the muscles of dystrophic mice restored DYSTROPHIN expression and contributed to the muscle stem cell reservoir. Collectively, our findings report on a novel in vitro cellular model for DMD and utilize it in conjunction with gene editing to restore DYSTROPHIN expression in vivo.

Satellite cells, the stem cells of skeletal muscle tissue, hold a prodigious regeneration capacity. However, low satellite cell yield from autologous or donor-derived muscles precludes adoption of satellite cell transplantation for the treatment of muscle diseases including Duchenne muscular dystrophy (DMD). To address this limitation, here we investigated whether sufficient quantity of satellite cells can be produced in allogeneic or xenogeneic animal hosts. First, we report on exclusive satellite cell production in intraspecies mouse chimeras by injection of CRISPR/Cas9-corrected DMD-induced pluripotent stem cells (iPSCs) into blastocysts carrying an ablation system of host Pax7+ satellite cells. Additionally, injection of genetically-corrected DMD-iPSCs into rat blastocysts produced interspecies rat-mouse chimeras harboring mouse muscle stem cells that efficiently restored dystrophin expression in DMD mice. This study thus provides a proof-of-principle for the generation of therapeutically-competent stem cells between divergent species, raising the possibility of procuring human stem cells in large animals for regenerative medicine purposes.