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Mol Ther. 2015 Oct;23(10):1592-9. doi: 10.1038/mt.2015.126. Epub 2015 Jul 10.

MitoTALEN: A General Approach to Reduce Mutant mtDNA Loads and Restore Oxidative Phosphorylation Function in Mitochondrial Diseases.

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Department of Neurology, University of Miami Miller School of Medicine Miami, Miami, Florida, USA.
Division of Human Genetics, Department of Pediatrics, The Children's Hospital of Philadelphia and University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, USA.
Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California, USA.
Sylvester Comprehensive Cancer Center, University of Miami Miller School of Medicine, Miami, Florida, USA.
Department of Cell Biology, University of Miami Miller School of Medicine, Miami, Florida, USA.


We have designed mitochondrially targeted transcription activator-like effector nucleases or mitoTALENs to cleave specific sequences in the mitochondrial DNA (mtDNA) with the goal of eliminating mtDNA carrying pathogenic point mutations. To test the generality of the approach, we designed mitoTALENs to target two relatively common pathogenic mtDNA point mutations associated with mitochondrial diseases: the m.8344A>G tRNA(Lys) gene mutation associated with myoclonic epilepsy with ragged red fibers (MERRF) and the m.13513G>A ND5 mutation associated with MELAS/Leigh syndrome. Transmitochondrial cybrid cells harbouring the respective heteroplasmic mtDNA mutations were transfected with the respective mitoTALEN and analyzed after different time periods. MitoTALENs efficiently reduced the levels of the targeted pathogenic mtDNAs in the respective cell lines. Functional assays showed that cells with heteroplasmic mutant mtDNA were able to recover respiratory capacity and oxidative phosphorylation enzymes activity after transfection with the mitoTALEN. To improve the design in the context of the low complexity of mtDNA, we designed shorter versions of the mitoTALEN specific for the MERRF m.8344A>G mutation. These shorter mitoTALENs also eliminated the mutant mtDNA. These reductions in size will improve our ability to package these large sequences into viral vectors, bringing the use of these genetic tools closer to clinical trials.

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