Mesenchymal stem cells promote endothelial progenitor cell migration, vascularization, and bone repair in tissue-engineered constructs via activating CXCR2-Src-PKL/Vav2-Rac1.

Tissue-engineered constructs (TECs) hold great promise for treating large bone defects. Incorporated mesenchymal stem cells (MSCs) can facilitate the vascularization of TECs. Nevertheless, the underlying mechanism remains ambiguous. Here we analyzed the roles of C-X-C chemokine receptor 2 (CXCR2) and its downstream signal pathways in MSC-induced endothelial progenitor cell (EPC) migration. Transwell assays and immunofluorescence staining were performed for cell migration analysis in vitro and in vivo, respectively. A series of signal inhibitors and short hairpin RNA was used for screening essential signaling molecules. We found that blockade of CXCR2 abolished the migration of EPCs toward MSCs as well as subsequent vascularization and bone repair in TECs. Moreover, screening results suggested that steroid receptor coactivator (Src) acted as a predominant downstream effector of CXCR2. Further molecular biologic and histomorphological experiments revealed that the action of Src required the phosphorylation of ras-related C3 botulinum toxin substrate 1 (Rac1), which was pivotal for the development of lamellipodia and filopodia. The phosphorylation and colocalization of paxillin kinase linker (PKL) and vav guanine nucleotide exchange factor 2 (Vav2) were essential for the activation of Rac1. Therefore, we demonstrated that MSCs promoted EPC migration via activating CXCR2 and its downstream Src-PKL/Vav2-Rac1 signaling pathway. These findings unveiled the molecular mechanism in the vascularization of TECs and were expected to provide novel targets for efficacy improvement.-Li, Z., Yang, A., Yin, X., Dong, S., Luo, F., Dou, C., Lan, X., Xie, Z., Hou, T., Xu, J., Xing, J. Mesenchymal stem cells promote endothelial progenitor cell migration, vascularization, and bone repair in tissue-engineered constructs via activating CXCR2-Src-PKL/Vav2-Rac1.