Investigating the role of Wnt signaling in pulp stem cells

Objectives: The present study exploits a multipotent pulp-derived stem cell line, the A4 clone, to investigate the role of the Wnt canonical pathway in relation with the acquisition of odontoblastic phenotypic markers.

Methods: Assuming that cell confluence may represent a critical step in the competency of cells to respond to differentiating cues, the status of various phenotypic markers was assessed according to the cell density through PCR and immunocytochemistry assays. We further examined the expression of these markers upon cell exposure to BIO, an activator of the Wnt canonical pathway.

Results: Irrespective of cell density A4 cells express typical markers of the neural crest-derived odontogenic lineage (Lhx6, Lhx7, Pax9, Msx2), as well as various ligands, inhibitors and effectors of the Wnt canonical pathway. We observed that the establishment of cellular contacts triggered a "switch-off" of the Wnt canonical pathway together with the up regulation of DMP1 and type I collagen. Further, both E-cadherin and N-cadherin were induced, likely sustaining homotypic interactions between committed stem cells. Importantly, DMP1, E-cadherin and N-cadherin mRNA levels failed to increase when the Wnt canonical pathway was kept active with BIO.

Conclusions: These results show that the “switch-off” of the Wnt pathway associated with cell confluence unlocks DMP1 expression and represents an important step in the acquisition of dental stem cell competency.