Characterization of Stable Hypoxia-Preconditioned Dental Pulp Stem Cells: Implication for Pulp Regeneration

Abstract

Background: Dental pulp stem cells (DPSCs) have been developed as a potential source of mesenchymal stem cells (MSCs) for regeneration of dental pulp and other tissues. However, further strategies to isolate highly functional DPSCs beyond the colony-forming methods are required. Our clinical study has demonstrated safety and efficacy of DPSCs isolated by G-CSF-induced mobilization and cultured under normoxia (mobilized DPSCs, MDPSCs) for pulp regeneration. It is well known that the oxygen concentration is closely linked to the maintenance of stemness. Thus, in this investigation, hypoxia-preconditioned DPSCs (hpDPSCs) was characterized to develop and improve the clinical utility for regeneration of dental pulp in endodontics.Methods: Colony-forming DPSCs were isolated and preconditioned with hypoxia in a stable closed cultured system and compared with MDPSCs isolated from the individual dog teeth. We examined the proliferation rate, migration potential, anti-apoptotic activity and gene expression of the stem cell markers and angiogenic/neurotrophic factors. Trophic effects of the conditioned medium (CM) were also evaluated. In addition, the expression of immunomodulatory molecules upon stimulation with IFN-γ were investigated. The pulp regenerative potential and transplantation safety of hpDPSCs were further assessed in pulpectomized teeth in dogs by histological and immunohistochemical analyses and by chemistry of blood and urine. tests Results: hpDPSCs demonstrated higher proliferation rate and expression of a major regulator of oxygen homeostasis, HIF-1α, and a stem cell marker, CXCR-4. The direct migratory activity of hpDPSCs in response to G-CSF was significantly higher than MDPSCs. The CM of hpDPSCs stimulated neurite extension. However, there were no changes in angiogenic, migration and anti-apoptotic activities compared with the CM of MDPSCs. The expression of immunomodulatory gene, PTGE was significantly up-regulated by IFN gamma in hpDPSCs compared with MDPSCs. However, no difference in nitric oxide was observed. The regenerated pulp tissue was quantitatively and qualitatively similar in hpDPSC transplants compared with MDPSC transplants in dog teeth. There was no evidence of toxicity or adverse events of the hpDPSC transplantation Conclusions: These results demonstrated that hpDPSCs improved stem cell properties compared to MDPSCs, suggesting their potential clinical utility for pulp regeneration.