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

ABSTRACT: 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.

ORGANISM(S): Mus musculus

PROVIDER: GSE208326 | GEO | 2022/08/24

REPOSITORIES: GEO

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Project description:Many stem cell populations exist in a quiescent state in vivo, exiting quiescence and entering the cell cycle in response to specific stimuli. In the case of skeletal muscle, the muscle stem cells (MuSCs, or “satellite cells”) are quiescent under normal homeostatic conditions and undergo activation and cell cycle entry in response to muscle fiber damage. Quiescent MuSCs are also much more potent than their proliferating progeny in assays of stem cell transplantation. In recent years, it has become increasingly apparent that the quiescent state is both actively maintained and dynamically regulated. However, most of the analyses of quiescent MuSCs have come from cells that have been removed from their niche in vivo, purified by fluorescence activated cell sorting, and then assay ex vivo. Although such cells are still in the quiescent state under these conditions, there is no doubt that significant biochemical changes will occur during the isolation and purification process. Thus, we have sought to examine the true in vivo quiescent state by analyzing the transcriptome of MuSCs. To achieve that, we have used techniques to label actively transcribing RNA in vivo using nucleoside analogs. In mice in which the enzyme uracil phosphoribosyltransferase (UPRT) is expressed specifically in MuSCs, administration of 4-thiouracil (4TU), which is converted to thiouridine (TU) by UPRT, resulted in labelling of MuSC transcripts, and the transcriptome could be analyzed following pull-down of TU-tagged RNA. Varying the timing of 4TU administration revealed the dynamic regulation of different subsets of transcripts. Notably, labeling transcripts during the isolation procedure revealed very active transcription of specific subsets of genes. Nevertheless, the ex vivo transcriptome remained largely reflective of the in vivo transcriptome. Using the transcriptional inhibitor, α-amanitin, we were also able to show that there was little difference between the steady-state transcript levels of the most highly expressed genes when comparing the ex vivo transcriptome with the in vivo transcriptome. Together, these data provide a novel view of the molecular regulation of the quiescent state at the transcriptional level, demonstrate the utility of these tools for probing transcriptional dynamics in vivo, and provide an invaluable resource for understanding stem cell state transitions.

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

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