Premature aging of skeletal stem/progenitor cells rather than osteoblasts causes bone loss with mechanosensation decline

Distinct skeletal stem/progenitor cells (SSPCs) have been identified in the bone marrow, growth plate, and periosteum, which are indispensable for the maintenance and remodeling of the adult skeleton. However, the decline of which cell types are responsible for age-related bone loss and what characteristic changes of these cells during aging remain to be determined. Here, we constructed premature skeletal aging models by depleting metalloproteinase Zmpste24 (Z24) in mice and found that Prx1-dependent, but not Osx-dependent, Z24 deletion caused significant bone loss. Single-cell RNA sequencing (scRNA-seq) revealed that Prx1-expressing cells in the periosteum (pSSPCs) and growth plate (gpSSPCs) significantly declined in progeria mice. Consistent with aggrecan (Acan) expression in gpSSPCs but not pSSPCs, Acan-linked Z24 depletion only caused trabecular bone loss. Chromatin and transcriptional profiling demonstrate that premature aged SSPCs gain apoptotic signaling pathway and mechanosensation decline. Moreover, SSPCs increased after physical exersice and Z24 depletion’s effects on cellular apoptosis and extracellular matrix expression were reverted by mechanical stimuli. Overall, this study identifies that Z24 deficiency-induced impairment of mechanosensation in SSPCs causes bone loss, shedding new insight on how physical exercise can be used to improve bone quality and prevent bone aging. Medium-intensity treadmill exercise was performed for 5 weeks at 8-week-old.Then bones of 13-week-old exercised and sedentary mice after bone marrow was flushed were collected and ground with liquid nitrogen to extract the RNA.