Citations

AbstractBackgroundMutation of the m. 8993 T > G ATP6 subunit of ATP synthase causes a maternally inherited Leigh Syndrome (LS), a rapidly fatal encephalomyelopathy in childhood called and related Neuropathy, Ataxia and Retinitis Pigmentosa (NARP) in adults. There is no cure, and relevant animal models are few. Here we describe a novel ATP6 mouse model of LS and preclinical efficacy of a gene therapy approach to neutralize the ATP6 mutation by competition with a mitochondrial targeted adeno‐associated virus serotype 9 (AAV9) vector containing wild‐type ATP6.MethodsLS transgenic mice with an ATP6 mutation were developed by microinjecting AAV2 modified by a COX8 mitochondrial targeting sequence (MTS) into mouse blastocysts to deliver the human ATP6 gene with a T > G mutation at position 8993 of the mitochondrial genome, responsible for clinical LS DNA, protein, and metabolic assays confirmed functional gene delivery and in depth physiological/clinical assessments supported germline transmission of an LS phenotype. Rescue of LS in this model was evaluated after intravenous injection of mito‐targeted AAV9 containing wild‐type ATP6 followed by reevaluation of phenotypes.ResultsLS transgenic mice expressed mutant ATP6 protein in multiple relevant tissues including brain, eye, liver. Mutant ATP6 incorporated into Complex V and conferred decreased ATP synthase efficiency. Mice exhibited hallmarks of the human disease with one or multiple systemic symptoms including early death, paralysis, hunching, vision loss and seizures over six generations. Necropsy revealed spongiform encephalopathy, retinal degeneration, and cardiomegaly. Rescue by mitochondrially directed AAV9 containing wild type ATP6 after disease onset conferred prolonged survival and reduced paralysis. When administered prior to disease onset all treated ATP6 mice survived with evidence of globally improved function.ConclusionsThe results are consistent with efficient delivery and expression of foreign genes in mitochondria by AAV vectors directed by MTS and support further development of such strategies via intravenous injection of mitochondrial targeted AAV9 to deliver corrective genes.

Abstract Mutations in mitochondrial genes are primary causes of multiple inherited disorders, especially affecting tissues with high aerobic energy demands such as the eye, brain, heart, and skeletal muscles. Such mitochondrial diseases are untreatable, have poor prognoses, and relevant animal models are few. Here we microinjected into the mouse blastocyst an adeno-associated virus (AAV) that we redirected to mitochondria to deliver the mutant human adenosine triphosphate (ATP) synthase subunit 6 gene (m.8993T>G) responsible for Maternally Inherited Leigh Syndrome, a neurologic disease renowned for causing rapidly fatal encephalomyelopathy in childhood or Neuropathy, Ataxia and Retinitis Pigmentosa in adults. Mice bred over six generations exhibited hallmarks of the human disease with one or multiple systemic symptoms including early death, paralysis, hunching, vision loss and seizures. Necropsy revealed spongiform encephalopathy, retinal degeneration, and cardiomegaly. Intravenous injection of a mitochondrially directed AAV serotype 9 vector containing wild-type ATP6 after disease onset, conferred prolonged survival and reduced paralysis. When administered prior to disease onset, all treated mice survived, and visual and motor function improved. These results support further development of gene therapy strategies involving intravenous delivery of mito-targeted AAV9.