Extracellular Ca2+ Promotes Odontoblastic Differentiation of Dental Pulp Stem Cells via BMP2‐Mediated Smad1/5/8 and Erk1/2 Pathways

Ca(2+) is the main element of many pulp capping materials that are used to promote the regeneration of tertiary dentin, but the underlying molecular mechanism is not clear. In this study, we found that Ca(2+) increased the expression of the odontoblastic differentiation marker gene DSPP and promoted odontoblastic differentiation and mineralization of DPSCs, but inhibited ALP activity. Ca(2+) increases the expression of endogenous BMP2, which activates the Smad1/5/8 pathway and promotes the Smad1-Runx2 and Runx2-DSPP interaction in DPSCs. Inhibition of Smad1/5/8 with dorsomorphin partially blocked Runx2 activity; however, inhibition of the BMP2 receptor with Noggin nearly fully suppressed Runx2 activity. These results indicate that Ca(2+) promotes cell differentiation mainly via BMP2-mediated Smad-dependent and Smad-independent pathways. We then determined that the phosphorylation level of Erk1/2, but not JNK or p38, was significantly increased as a result of Ca(2+) stimulation. Blockage of Erk1/2 was found to inhibit Runx2 activity, indicating that Ca(2+) triggers the Erk1/2 pathway, which subsequently regulates Runx2 activity. In addition, inhibition of Erk1/2 differentially attenuated the phosphorylation levels of Smad1/5/8 and Smad2/3. Collectively, this study demonstrates that Ca(2+) activates the BMP2-mediated Smad1/5/8 and Erk1/2 pathways in DPSCs and that Smad1/5/8 and Erk1/2 signaling converge at Runx2 to control the odontoblastic differentiation of DPSCs.