Role of bone marrow-derived progenitor cells in the maintenance and regeneration of dental mesenchymal tissues.

While dental mesenchymal stem cells are well-studied, the origin of these cells is still unclear. Bone marrow-derived cells (BMDCs) have the potential to engraft into several tissues after injury, but whether they can become dental tissue-specific progenitor cells under normal conditions and the relationship of these cells to the tissue-resident cells are unknown. Thus, we transplanted green fluorescent protein (GFP)-labeled BMDCs into irradiated wild-type mice. We found that the engraftment of BMDCs participated in the regeneration and differentiated into periodontal specific cells after injury. Under normal conditions, there were more BMDCs engrafting into the dental mesenchymal tissue than other organs, in which the expression of stromal cell-derived factor-1 (SDF-1) was significantly higher than in other organs, and the engraftment of cells increased with time. A small fraction of GFP+ cells maintained the mesenchymal stem cell phenotype positive for CD105, CD106, and CD90, which were significantly less than the tissue-resident stem cells; meanwhile, GFP+/CD45+ cells were rare. Isolation and characterization of the dental pulp cells showed that the number of GFP+/Ki67+ cells were greater than the GFP-/Ki67+ cells. In addition, some GFP+ cells differentiated into the dental-specific cells and expressed dental-specific proteins, and can be found in the odontoblast layer after implantation of the apical bud. In conclusion, these data suggest that bone marrow progenitor cells communicate with dental tissues and become tissue-specific mesenchymal progenitor cells to maintain tissue homeostasis.