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Published on: August 10, 2018
Transient muscle expression of mitoARCUS in mice leads to sustained reductions in pathogenic mtDNA and reduces
Sandra R Bacman1, Wendy Shoop2, C Spencer Henley-Beasley3
1Department of Neurology, University of Miami Miller School of Medicine, 1600 NW 10th Avenue, Miami, FL 33136, USA.
Abstract:
Mitochondrial myopathies are often caused by heteroplasmic mutations in the mitochondrial DNA (mtDNA). In muscle, biochemical, pathological, and clinical impairments are observed only when the ratios of mutant/wild-type mtDNA are high. Because reductions in mutant mtDNA loads are essentially permanent, we reasoned that transient expression of a therapeutic mitochondrial nuclease could be sufficient to permanently alter heteroplasmy. We expressed a mitochondrial targeted gene editing nuclease (mitoARCUS) via intramuscular injection of lipid nanoparticle (LNP)/mRNA complexes in a mouse model of mtDNA disease (m.5024C>T in the mt-tRNAAla gene). Transient expression of mitoARCUS in the tibialis anterior (TA) led to a robust decrease in mtDNA mutation load, which was maintained up to 42 weeks after injection. A molecular marker of the mitochondrial defect in this model, namely low levels of mt-tRNAAla, were markedly improved in treated muscles. Muscle force assessment in situ after repeated stimulation showed that fatigability was improved in the treated TA. Finally, we showed that multi-muscle injections can alter mtDNA heteroplasmy essentially in whole limbs. These results demonstrate that transient expression of mitoARCUS via LNP/mRNA intramuscular injections have long-lasting positive effects in muscles afflicted with mitochondrial myopathy.
Insights
Transient expression of a mitochondrial-targeted nuclease (mitoARCUS) via lipid nanoparticle/mRNA injections permanently reduced mitochondrial DNA mutation loads in a mouse model of mitochondrial myopathy.
Area of Science:
- Mitochondrial biology
- Gene therapy
- Neuromuscular disorders
Background:
- Mitochondrial myopathies stem from heteroplasmic mutations in mitochondrial DNA (mtDNA).
- Disease manifestation in muscle correlates with high mutant/wild-type mtDNA ratios.
- Reductions in mutant mtDNA are typically permanent.
Purpose of the Study:
- To investigate if transient expression of a mitochondrial-targeted gene editing nuclease (mitoARCUS) can permanently alter mtDNA heteroplasmy.
- To assess the therapeutic potential of mitoARCUS delivered via lipid nanoparticle (LNP)/mRNA complexes in a mouse model of mtDNA disease.
Main Methods:
- Intramuscular injection of LNP/mRNA complexes encoding mitoARCUS into the tibialis anterior (TA) muscle of mice with an m.5024C>T mtDNA mutation.
- Assessment of mtDNA mutation load, mt-tRNA levels, and muscle force (fatigability) over time.
- Evaluation of multi-muscle injection efficacy for altering mtDNA heteroplasmy in limb muscles.
Main Results:
- Transient mitoARCUS expression led to a sustained, robust decrease in mtDNA mutation load up to 42 weeks post-injection.
- Levels of mt-tRNA Ala, a marker of mitochondrial dysfunction, significantly improved in treated muscles.
- Muscle fatigability was improved in treated TA muscles, and multi-muscle injections altered heteroplasmy in entire limbs.
Conclusions:
- Transient expression of mitoARCUS via LNP/mRNA intramuscular injections achieves long-lasting reductions in mtDNA mutation load.
- This approach demonstrates significant therapeutic potential for treating mitochondrial myopathies.
- MitoARCUS delivery offers a promising strategy for permanent heteroplasmy correction in affected muscles.
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