间充质干细胞（MSCs）移植促进骨缺损再生，但其机制尚不完全清楚，尤其是供体MSCs移植后的大量凋亡和其促进宿主组织再生之间的“矛盾”现象尚未得到阐明。课题组前期研究发现，供体MSCs能够通过调控宿主MSCs成骨分化功能促进骨再生；同时，凋亡MSC所释放的凋亡小体能够促进正常MSCs的成骨分化；进一步研究显示，MSCs释放的凋亡小体中含有miR-26a并且其能够促进MSCs成骨分化。由此推测，供体MSCs通过释放凋亡小体转运miR-26a促进宿主MSCs成骨分化及骨再生。本研究拟从MSCs释放的凋亡小体对骨再生的促进作用、凋亡小体对宿主MSCs成骨分化功能的调控、凋亡小体转运miR-26a调控宿主MSCs功能、miR-26a对MSCs功能调控的机制四部分探讨MSCs释放的凋亡小体促进骨缺损再生的机制。本研究有望揭示MSCs治疗的新机制，为MSCs移植治疗的临床应用提供重要理论和实验依据。

Transplantation of mesenchymal stem cells (MSCs) promotes bone regeneration. However, the underlying mechanisms are still not fully understood. Especially, the “paradox” between the large-scale apoptosis after transplantation and the promoting effects on regeneration is still unknown. Our previous studies found that, donor MSCs could promote bone regeneration by modulating the osteogenic differentiation potentials of recipient MSCs. Meanwhile, the apoptotic bodies released by apoptotic MSCs could promote osteogenic differentiation of normal MSCs. Moreover, the apoptotic bodies released by MSCs contained miR-26a, which was demonstrated to promote osteogenic differentiation of MSCs. Therefore, based on these evidences, we hypothesize that the apoptotic bodies released by donor MSCs transferred miR-26a to promote osteogenic differentiation of recipient MSCs and bone regeneration. This study will conduct four parts to explore the mechanisms underlying apoptotic body-mediated bone regeneration. The four parts include the promoting effects on bone regeneration generated by MSC-derived apoptotic bodies, regulation of recipient MSC functions by apoptotic bodies, regulation of recipient MSC functions by apoptotic body-derived miR-26a, mechanisms underlying MSC functional regulation by miR-26a. This study hopefully reveals the new mechanisms underlying MSC therapy and provides important theory and experimental evidences for clinical application.