The mitochondrial protein OPA1 regulates the quiescent state of adult muscle stem cells

Regulation of quiescence is essential for adult stem cell maintenance, longevity and sustained regeneration potential. Our studies have uncovered that physiological and transient changes in mitochondrial shape regulate the quiescent state of adult muscle stem cells (MuSCs). We show that mitochondria in MuSCs rapidly fragment in response to an activation stimulus, via a systemic HGF/mTOR mechanism, to drive the exit from deep quiescence. Deletion of the mitochondrial fusion protein OPA1 and forced mitochondrial fragmentation is sufficient to transition MuSCs into G-alert quiescence causing premature activation and depletion upon a stimulus. Loss of OPA1 activates a glutathione (GSH) redox signaling pathway that promotes cell-cycle progression, myogenic gene expression and commitment. MuSCs with chronic OPA1 loss and mitochondrial fragmentation, leading to mitochondrial dysfunction, continue to reside in a primed state but acquire severe cell cycle defects. Additionally, we provide evidence that OPA1 decline and impaired mitochondrial dynamics may contribute to age-related MuSC dysfunction. These findings reveal a fundamental role for OPA1 and mitochondrial dynamics in establishing the quiescent state and activation potential of adult stem cells. Comparative gene expression profiling analysis of RNA-seq data for freshly FACS sorted muscle stem cells from OPA1-WT and OPA1-KO mice at 8-10 weeks