MitoTALEN reduces mutant mtDNA load and restores tRNAAla levels in a mouse model of heteroplasmic mtDNA mutation

Mutations in the mitochondrial DNA ( mtDNA) are responsible for several metabolic disorders, commonly involving muscle and the central nervous system(1). Because of the critical role of mtDNA in oxidative phosphorylation, the majority of pathogenic mtDNA mutations are heteroplasmic, co-existing with wild-type molecules(1). Using a mouse model with a heteroplasmic mtDNA mutation(2), we tested whether mitochondrialtargeted TALENs (mitoTALENs)(3,4) could reduce the mutant mtDNA load in muscle and heart. AAV9-mitoTALEN was administered via intramuscular, intravenous, and intraperitoneal injections. Muscle and heart were efficiently transduced and showed a robust reduction in mutant mtDNA, which was stable over time. The molecular defect, namely a decrease in transfer RNA(Ala) levels, was restored by the treatment. These results showed that mitoTALENs, when expressed in affected tissues, could revert disease-related phenotypes in mice.