Bone marrow CD73⁺ mesenchymal stem cells display increased stemness <i>in vitro</i> and promote fracture healing <i>in vivo</i>.

Abstract

Mesenchymal stem cells (MSCs) are multipotent and considered to be of great potential for regenerative medicine. We could show recently (Breitbach, Kimura et al. 2018) that a subpopulation of MSCs as well as sinusoidal endothelial cells (sECs) in the bone marrow (BM) of CD73-EGFP reporter mice could be labeled <i>in vivo</i>. We took advantage of this model to explore the plasticity and osteogenic potential of CD73-EGFP⁺ MSCs <i>in vitro</i> and their role in the regenerative response upon bone lesion <i>in vivo</i>. Herein we show that isolated CD73-EGFP⁺ MSCs displayed more pronounced stemness and stronger <i>in vitro</i> differentiation capacity into the osteogenic lineage compared to CD73-EGFP^- MSCs. In a bone fracture model, endogenous BM-resident CD73-EGFP⁺ MSCs were found to migrate to the fracture site and differentiate into cartilage and bone cells. Our analysis also showed that CD73-EGFP⁺ sECs contributed to the neovascularization of the fracture site. In addition, grafting of CD73-EGFP⁺ MSCs into acute bone lesions revealed their capacity to differentiate into chondrocytes and osteocytes <i>in vivo</i> and their contribution to callus formation in the regeneration process of fracture healing. Thus, CD73⁺ MSCs display enhanced stemness and osteogenic differentiation potential <i>in vitro</i> and <i>in vivo</i> illustrating a prominent role of the CD73⁺ MSC subpopulation to promote fracture repair.