Wnt/B-catenin Signaling Regulates Dental Pulp Stem Cell Properties

Objectives: 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 b-catenin. While DPSCs have great potential for dentin regeneration and tooth repair, molecular regulation of DPSC differentiation is poorly understood. The objective of this study was to examine whether Wnt signaling regulates DPSC differentiation and stem cell properties.

Methods: DPSCs isolated from human adult third molar were stably transduced with canonical Wnt-1 or the active form of b-catenin using retrovirus-mediated infection. Following selection, confluent cell layers were induced to differentiate toward an odontoblast-like lineage with ascorbic acid, dexamethasone and b-glycerophosphate. Post-differentiation analysis included staining for calcium mineral and alkaline phosphatase (ALP) and analysis of osteogenic lineage markers osteonectin, osteopontin, bone sialoprotein, and collagen I.

Results: Northern blot analysis found that Wnt-1 strongly induced the expression of matricellular protein osteopontin (OPN) 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 by more than 80% when compared to control DPSCs. Moreover, over-expression of b-catenin was also sufficient to suppress differentiation and mineralization.

Conclusion: Our results are the first demonstration that canonical Wnt/b-catenin signaling negatively regulates the odontoblast-like differentiation of DPSCs and may help to maintain their stem cell properties. Studies of crystal nucleation suggest that OPN is a potent inhibitor of mineral crystal growth at high concentrations. Thus, it is possible that the induction of OPN by Wnt-1 may play a role in the suppression of mineral formation in DPSCs.

Research supported by R01DE-016513 and T32DE-007057.