Investigating the Role of Chronic OPA1 Loss in Muscle Stem Cell Maintenance and Activity

Abstract

Adult muscle stem cells (MuSCs) play a crucial role in tissue regeneration, yet the mechanisms governing their dysfunction and depletion during aging remain unclear. However, during aging, regulators of mitochondrial dynamics, a key regulator of MuSC activity and fate, decline in expression. This loss of mitochondrial fission and fusion modulators has been associated with premature aging phenotypes in whole muscle and MuSC dysregulation with age. To date, how mitochondrial dynamics contribute to senescent and aged-like phenotypes in MuSCs has not been fully described. Our lab has previously implemented a Pax7CreERT2 inducible system to conditionally knock-out the mitochondrial fusion protein OPA1 specifically within MuSCs (OPA1-KO) and found that with chronic loss of OPA1, MuSCs have enhanced activation kinetics, significant proliferation defects, and evidence of mitochondrial dysfunction. In this current work, we sought to address the role of chronic OPA1 loss in MuSCs, particularly in the contexts of aging and senescence. We found that with chronic loss of OPA1, MuSCs accumulate biomarkers of senescence, experience cell cycle dysregulation at the transcriptional level, and have a dysregulated metabolome. However, the proliferative defects associated with chronic OPA1 ablation may be partially mitigated via supplementation of exogenous metabolites. Notably, at 9 months of OPA1 loss, the phenotype of MuSC dysfunction was found to progress to the extent of stem cell depletion basally. Further, whole-muscle defects were observed at this time, including the onset of a muscle wasting phenotype (with a reduction in the myofiber cross-sectional area and the number of myonuclei per myofiber) and increased fatiguability of the muscle. These findings suggest that mitochondrial dynamics are a critical regulator of MuSC activity and maintenance in an aging context, and that whole muscle health during aging is dependent on the presence of functional MuSCs. This research offers novel therapeutic insight that may be leveraged to improve muscle stem cell health and function with age