Mechanisms of human mesenchymal stromal cells during bone regeneration are impacted by the associated biomaterial

摘要

Introduction: Despite bone capacity to regenerate after injury, incomplete consolidation concerns 1 million persons per year. Cell engineering involving human bone marrow mesenchymal stromal cells (hBM-MSCs) associated with biomaterials emerge as a new strategy to repair this defect. hBM-MSCs are used for their ability to induce new bone formation. Nevertheless, mechanisms stay poorly known and heterogeneities are observed as a function of the donor but also of the associated scaffolds Wl. In our study, we assessed the impact of biomaterials on mechanisms of hBM-MSCs during bone regeneration. Materials and methods: In our study, two biomaterials commonly used in clinic were studied. The synthetic hydroxyapatite/beta-tricalcium-phosphate scaffold (HA/pTCP) and the biologic gamma-irradiated-processed bone allograft (Tutoplast~® process Bone [TPB]). hBM-MSCs were collected from 3 donors. One million cells were injected on 8 mg of biomaterial implanted subcutaneously in SCID mice. Control group received only biomaterials. We quantified ectopic bone formation, cell attachment and evaluated their direct and paracrine roles. Results: Histological analysis showed higher bone and bone marrow formation in vivo when hBM-MSCs were combined with TPB. This was associated to a better vascularization and cell attachment on this biomaterial. One day post-graft almost all hBM-MSCs were present on TPB, whereas only half of them were found on HA/βTCP. Cell loss on HA/βTCP does not appear to be due to a higher apoptosis or inflammation. In fact, non-adherent cells were found on muscle and skin adjacent to the biomaterial during 72 hours. In contrast, most of the adherent cells survive up to 6 weeks on biomaterials; so we decide to assess their function in vivo. Interestingly, as early as 2 weeks hBM-MSCs highly expressed Runx2, BSP and OC when combined with TPB. Otherwise, they are able to chemoattract and induce osteogenic differentiation of mouse cells independently of the type of biomaterial. To better understand scaffold impact on cell adhesion and osteoblastic differentiation, we performed in vitro tests. Our results indicate that cell adhesion was 3.5 times better on TPB while both biomaterials were able to induce osteoblastic cell differentiation. Discussion: These results indicate that bone and bone marrow formation correlate with the number of adherent hBM-MSCs on the biomaterial. TPB microenvironment favors cell attachment which can be explained in part by its higher outer accessible area. This appears to keep grafted cells alive and so promote their capacity to induce vascularization and bone regeneration through a direct role and a paracrine effect. Conclusion: The clinical choice of associated scaffold is critical for good bone repair by preserving grafted cells and their osteogenic potential.