Cobalt Chloride Enhances the Stemness of Human Dental Pulp Cells

Hypoxia is a factor in controlling stem cell stemness. We investigated if cobalt chloride (CoCl2), a chemical agent that mimics hypoxia in vitro, affected human dental pulp cell (hDPC) stemness by examining cell proliferation, stem cell marker expression, and osteogenic differentiation.hDPCs were cultured with or without 25 or 50 μmol/L CoCl2. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was used to determine cell proliferation. The number of STRO-1+ cells was determined by flow cytometry. The messenger RNA expression of the stem cell markers REX1, OCT4, SOX2, and NANOG and the osteogenic-associated genes ALP, COLI, and RUNX2 were evaluated using reverse transcription polymerase chain reaction or real-time polymerase chain reaction. Osteogenic differentiation was assessed by alkaline phosphatase (ALP) activity and mineralization assays.Although 25 and 50 μmol/L CoCl2 suppressed hDPC proliferation, 50 μmol/L CoCl2 increased the number of STRO-1+ cells. Moreover, CoCl2 dose dependently induced stem cell marker expression. Additionally, CoCl2 treatment suppressed osteogenic-associated gene expression, ALP activity, and calcium deposition. The addition of apigenin, a hypoxia-inducible factor 1-alpha inhibitor, reversed the inhibitory effect of CoCl2 on ALP activity.This study indicated that CoCl2 may enhance hDPC stemness.