Correcting a pathogenic mouse mitochondrial DNA mutation by base editing
Primary mitochondrial disorders are most often caused by deleterious mutations in the mtDNA. Here, we harnessed a mitochondrial base editor, DdCBE, to introduce a compensatory edit (m.5081G?A) in a mouse model that carries the pathological m.5024C?T mutation in the mitochondrial tRNAAla gene. For this, the DdCBE gene construct was packaged in recombinant AAV9 and systemically injected into mice. We found that total mt-tRNAAla levels, which are drastically reduced by the mutation, are restored by the m.5081G?A edit in a dose-dependent manner. However, an excessive expression of DdCBE also induces extensive mtDNA off-target editing, counteracting this positive outcome. To address this, we optimized the dosage to maximize the amount of compensatory edit generated with minimal off-target editing. These results show that mitochondrial base editors are promising candidates for gene therapy for mitochondrial disorders, but their expression need to be carefully controlled. Overall design: tRNA-Seq datasets were generated from mouse embryonic fibriblasts (MEF) and mouse tissues investigate the impact of correcting a pathogenic mutation in the mitochondrial tRNA-Ala gene by base editing.