NOTUM plays a bidirectionally modulatory role in the odontoblastic differentiation of human stem cells from the apical papilla through the WNT/ß-catenin signaling pathway.

ABSTRACT

OBJECTIVE: Notum is a secreted deacylase, which is crucial for tooth dentin development in mice. This study aimed to investigate the effect of NOTUM on the odontoblastic differentiation of human stem cells from the apical papilla (hSCAPs), to reveal the potential value of NOTUM in pulp-dentin complex regeneration. DESIGN: The expression pattern of NOTUM in human tooth germs and during in vitro odontoblastic differentiation of hSCAPs was evaluated by immunohistochemical staining, and quantitative polymerase chain reaction, respectively. To manipulate the extracellular NOTUM level, ABC99 or small interfering RNA was used to down-regulate it, while recombinant NOTUM protein was added to up-regulate it. The effects of changing NOTUM level on the odontoblastic differentiation of hSCAPs and its interaction with the WNT/ß-catenin signaling pathway were studied using alkaline phosphatase staining, alizarin red staining, quantitative polymerase chain reaction, and western blot. RESULTS: NOTUM was observed in the apical papilla of human tooth germs. During in vitro odontoblastic differentiation of hSCAPs, NOTUM expression initially increased, while the WNT/ß-catenin pathway was activated. Downregulation of NOTUM hindered odontoblastic differentiation. Recombinant NOTUM protein had varying effects on odontoblastic differentiation depending on exposure duration. Continuous addition of the protein inhibited both odontoblastic differentiation and the WNT/ß-catenin pathway. However, applying the protein solely in the first 3 days enhanced odontoblastic differentiation and up-regulated the WNT/ß-catenin pathway. CONCLUSION: NOTUM demonstrated a bidirectional impact on in vitro odontoblastic differentiation of hSCAPs, potentially mediated by the WNT/ß-catenin pathway. These findings suggest its promising potential for pulp-dentin complex regeneration.