Year 3

Human orofacial bone-derived mesenchymal stem cells (OMSCs) showed distinct differentiation traits from mesenchymal stem cells (MSCs) derived from long bones, mouse OMSCs have not been isolated due to technical difficulties, which in turn precludes using mouse models to study orofacial diseases. We developed techniques to isolate mouse OMSCs derived from mandibles and verified their MSC characteristics by single colony formation, multi-lineage differentiation, and in vivo tissue regeneration. Activated T-lymphocytes impaired OMSCs via the Fas/Fas ligand pathway, as occur in long bone MSCs. Furthermore, we found that OMSCs are distinct from long bone MSCs with respect to regulating T-lymphocyte survival and proliferation. Our data suggest that OMSCs are a unique population of MSCs and have a role in systemic immunity.

Embryologic development and amalgamations of the complex array of bones and cartilage in the craniofacial region have revealed that the molecular mechanisms controlling skeletogenesis in the orofacial bones are quietly unique and different from in the axial and appendicular bones. The discrepancy in bone development between orofacial bones and long axial/appendicular bones give rises to specific diseases in the orofacial bone region, such as periodontitis, cherubism, and hyperparathyroid jaw tumor syndrome, which only affect the jaw bones. Therefore, it is not surprising to find that human OMSCs are distinct from BMMSCs in terms of differentiation traits and immunoregulation. MSC mediated bone formation involves in both donor and recipient cells, but only recipient cells contribute to marrow element formation. Our study suggests that both OMSCs and host cells contribute to bone formation in vivo.

Ex vivo-expanded BMMSCs are capable of suppressing the T-lymphocyte proliferation and activity in vitro, which provides a foundation for using BMMSC transplantation to treat T-cell-associated disorders, such as acute graft-versus-host-disease (GvHD) in mice and humans. In addition, we found activated T-lymphocyte induced apoptosis of BMMSCs through the Fas/FasL pathway. Our data suggest that OVX induced T lymphocyte activation may contribute to OMSC damage. Although T lymphocyte activation in OVX condition is a major factor for promoting osteoclast function and inhibiting osteoblast function, we can’t exclude other factors that may also contribute to OMSC deficiency in OVX mice. The immune-modulatory property is related to a high level NO production induced by IFN via enhanced iNOS expression in BMMSCs. In this report, mouse OMSCs showed a stronger suppressive effect on proliferation of anti-CD3 antibody-activated T cells, but only partially inhibited T cell proliferation by anti-IFN antibody and the iNOS inhibitor, 1400W. These highly immunosuppressive properties of OMSCs may provide an advantage for tissue engineering in the orofacial region. Surprisingly, mouse OMSCs produced larger amounts of NO than mouse BMMSCs, indicating that OMSCs are more responsive to inflammatory cytokine(s)-induced NO production. We also found that OMSCs were capable of keeping naïve splenocytes including T cell survival more effectively than BMMSCs. Therefore, it is necessary to continue elucidating underlying mechanisms of the interplay between OMSCs and immunity using established various mouse models.

Bisphosphonates (BPs) have been used for the clinical treatment of bone diseases with increased bone resorption such as osteoporosis and malignant diseases like multiple myeloma or metastasis to the bone. However, there is increasing evidence associate bisphosphonates treatment with osteonecrosis of the jaws. The detail mechanism of bisphosphonate-related osteonecrosis of the jaws (BRONJ) is unclear and it is very difficult to be treated. In present study, we generated large animal model of BRONJ in miniature pig and treated with allogeneic bone marrow mesenchymal stem cell (BMMSCs) transfusion. Of the 9 miniature pigs received BPs treatment and tooth extraction, 6 pigs disclosed BRONJ with exposed bone. The level of CD4+CD25+ T cells, foxp3+ T cells in the peripheral blood was decreased, while the level of γδ T cells and IL-17 were increased. After MSCs infusion, mucosal and bone healing were achieved, changes in immunity recovered. These findings obtained in a clinically relevant large-animal model of BRONJ provide evidence of the connection of BPs treatment and osteonecrosis of the jaw, as well as the immunity-based mechanism of BRONJ.