Dystrophin Gene Editing Stability Is Dependent on Dystrophin Levels in Skeletal but Not Cardiac Muscles
Gene editing is often touted as a permanent method for correcting mutations, but its long-term benefits in Duchenne muscular dystrophy (DMD) may depend on sufficiently high editing efficiencies to halt muscle degeneration. Here we explored the persistence of dystrophin expression following rAAV6:CRISPR/Cas9-mediated multi-exon deletion/reframing in systemically injected 2- and 11-week old dystrophic mice, and show that induction of low dystrophin levels persists for several months in cardiomyocytes, but not in skeletal muscles, where myofibers remain susceptible to necrosis and regeneration. While gene-correction efficiency in both muscle types was enhanced with increased ratios of gRNA- to nuclease vectors, obtaining high-dystrophin levels in skeletal muscles via multi-exon deletion remained challenging. In contrast, when AAV-microdystrophin was co-delivered with editing components, long-term gene-edited dystrophins persisted in both muscle types. These results suggest that the high rate of necrosis and regeneration in skeletal muscles, compared with the relative stability of dystrophic cardiomyocytes, caused the rapid loss of edited genomes. Consequently, stable dystrophin expression in DMD skeletal muscles will require either highly efficient gene editing or the use of co-treatment s that decrease skeletal muscle degeneration.