Radial extracorporeal shockwave promotes subchondral bone stem/progenitor cell self-renewal by activating YAP/TAZ and facilitates cartilage repair in vivo

Background Radial extracorporeal shockwave (r-ESW), an innovative and noninvasive technique, is gaining increasing attention in regenerative medicine due to its mechanobiological effects. Subchondral bone stem/progenitor cells (SCB-SPCs), originating from the pivotal zone of the osteochondral unit, have been shown to have multipotency and self-renewal properties. However, thus far, little information is available regarding the influences of r-ESW on the biological properties of SCB-SPCs and their therapeutic effects in tissue regeneration. Methods SCB-SPCs were isolated from human knee plateau osteochondral specimens and treated with gradient doses of r-ESW in a suspension stimulation system. The optimized parameters for SCB-SPC self-renewal were screened out by colony-forming unit fibroblast assay (CFU-F). Then, the effects of r-ESW on the proliferation, apoptosis, and multipotency of SCB-SPCs were evaluated. Moreover, the repair efficiency of radial shockwave-preconditioned SCB-SPCs was evaluated in vivo via an osteochondral defect model. Potential mechanisms were explored by western blotting, confocal laser scanning, and high-throughput sequencing. Results The CFU-F data indicate that r-ESW could augment the self-renewal of SCB-SPCs in a dose-dependent manner. The CCK-8 and flow cytometry results showed that the optimized shockwave markedly promoted SCB-SPC proliferation but had no significant influence on cell apoptosis. Radial shockwave exerted no significant influence on osteogenic capacity but strongly suppressed adipogenic ability in the current study. For chondrogenic potentiality, the treated SCB-SPCs were mildly enhanced, while the change was not significant. Importantly, the macroscopic scores and further histological analysis strongly demonstrated that the in vivo therapeutic effects of SCB-SPCs were markedly improved post r-ESW treatment. Further analysis showed that the cartilage-related markers collagen II and proteoglycan were expressed at higher levels compared to their counterpart group. Mechanistic studies suggested that r-ESW treatment strongly increased the expression of YAP and promoted YAP nuclear translocation in SCB-SPCs. More importantly, self-renewal was partially blocked by the YAP-specific inhibitor verteporfin. Moreover, the high-throughput sequencing data indicated that other self-renewal-associated pathways may also be involved in this process. Conclusion We found that r-ESW is capable of promoting the self-renewal of SCB-SPCs in vitro by targeting YAP activity and strengthening its repair efficiency in vivo, indicating promising application prospects.