Wnt/β-catenin inhibits dental pulp stem cell differentiation

Dental pulp stem cells (DPSCs) are a unique precursor population isolated from post-natal human dental pulp and have the ability to regenerate a reparative dentin-like complex. Canonical Wnt signaling plays a critical role in tooth development and stem cell self-renewal through β-catenin. In this study, the regulation of odontoblast-like differentiation of DPSCs by canonical Wnt signaling was examined. DPSCs were stably transduced with canonical Wnt-1 or the active form of β-catenin, with retrovirus-mediated infection. Northern blot analysis found that Wnt-1 strongly induced the expression of matricellular protein osteopontin, and modestly enhanced the expression of type I collagen in DPSCs. Unexpectedly, Wnt-1 inhibited alkaline phosphatase (ALP) activity and the formation of mineralized nodules in DPSCs. Moreover, overexpression of β-catenin was also sufficient to suppress the differentiation and mineralization of DPSCs. In conclusion, our results suggest that canonical Wnt signaling negatively regulates the odontoblast-like differentiation of DPSCs. Abbreviations used: DPSC, dental pulp stem cell; ALP, alkaline phosphatase; BSP, bone sialoprotein; MSC, mesenchymal stem cell; β-GP, β- glycerophosphate; APC, adenomatous polyposis coli; GSK-3β, glycogen synthase kinase-3β; LRP, LDL receptor-related protein; Tcf, T-cell factor; LEF, lymphoid enhancer factor; FCS, fetal calf serum; AA, L-ascorbic acid 2-phosphate; α-MEM, α-modified Eagle's medium; PBS, phosphate-buffered saline; HA, hemagglutinin; ON, osteonectin; OPN, osteopontin.