Non-senescent, conventional marker-negative geriatric muscle stem cells identified by new CD63/CD200 markers [scRNA-seq]

During aging, the accumulation of senescent cells has a pivotal role in age-related dysfunctions. At geriatric age, the emergence of muscle stem cells (MuSCs) exhibiting senescence markers identified in vitro studies have been reported. However, whether they are in cellular senescence and thus have lost their function is unclear, due to the lack of specific marker for senescent cells. Here, by tracing genetically labeled MuSCs throughout life, we found an unknown MuSC population termed GERI-MuSCs that lost conventional MuSC markers at geriatric age. Although they have several known senescence features, they retain considerable functionalities of in vitro proliferation and in vivo myogenesis, suggesting they are not in cellular senescence. These results highlight the potential discrepancies between aging process in vivo and cellular senescence characterized in vitro. Importantly, we found new markers, CD63 and CD200, inclusive of GERI-MuSCs, which provide a crucial tool for a deeper investigation on in vivo senescence. Single-cell RNA-sequencing analysis was performed using isolated YFP-positive cells of the limb skeletal muscle of Pax7-CreERT2;Rosa-YFP mice by FACS. 10 to 14 months old mice are used as middle-aged for control and more than 28 months old mice are used as geriatric-aged. DHT (dihydrotestosterone) comtained silastic tube was implanted to geriatric mice for 1 and 4 weeks and vehicle implanted mice for 4 weeks was used as control.