Processing body accumulation in aged muscle stem cells contributes to impaired self-renewal

Stem cell exhaustion is a pillar of aging hallmarks, mediated by an inability of the body’s stem cells to self-renew. In skeletal muscle, impaired self-renewal of muscle stem cells (MuSCs) manifests as a progressive decline in muscle regenerative capacities, leading to functional dependence in the aged. Self-renewal depends on preventing degradation of factors mediating pluripotency during division, thereby averting differentiation, however, mechanisms underlying the inability of MuSCs to self-renew in the aged are unknown. Here, we show processing bodies (p-bodies) accumulate in MuSCs isolated from old mice. As p-bodies canonically represent cellular depots for RNA degradation, our findings suggest age-related changes to RNA degradation may contribute to impaired self-renewal of old MuSCs. To investigate the consequence of p-body enrichment in old MuSCs on self-renewal, we utilized a computational-based lineage analysis termed Dynamo following single cell RNA-sequencing of MuSCs isolated from young and old mice. Dynamo incorporates the velocity of RNA to generate transcriptional vector fields, allowing for inference of lineage specification. Moreover, through characterization of each cell’s transcriptome, this framework also allows for investigation of changes to lineage specification as a result of genetic perturbation. We found that manipulation of scaffold proteins mediating p-body formation resulted in a pronounced effect on lineage specification. Specifically, our results showed that upregulation of LSM14a mRNA processing body assembly factor ( LSM14a) in young MuSCs resulted in a loss of cycling-related gene expression, and subsequently promoted differentiation. Moreover, we found that downregulation of LSM14a in old MuSCs oriented transcriptional vector fields towards a self-renewing phenotype and away from differentiation, mediated by increased expression of cycling-related genes and decreases in differentiation-related genes. Together, the accumulation of p-bodies in old MuSCs coupled with the ability of p-bodies to facilitate self-renewal, suggests that targeted interventions focusing on p-body assembly may be therapeutic in restoring old MuSC self-renewal, and thereby regenerative capacities in the aged. This study was supported by NIA R01 AG061005 (FA), NIA R01 AG052978 (FA), and NIEHS R01 ES025529 (FA). Postdoctoral fellowship funding provided by P30AG024827 (ZH). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.