2013 Volume 56 Issue 3 Pages 231-238
Purpose: Undifferentiated ectomesenchymal cells in damaged pulp tissue differentiate into odontoblasts, forming reparative dentin. Elucidation of the molecular mechanism of differentiation from undifferentiated ectomesenchymal cells into odontoblasts is critical for the development of vital pulp therapy for conservative dental treatment. The Wnt family, secreted glycoproteins, has recently attracted attention as a key factor for the differentiation of various types of cell during wound healing of pulp. The Wnt family has been demonstrated to play an important role in the formation of reparative dentin as well as in the process of tooth development. Signal transduction through the canonical Wnt/β-catenin pathway in Wnt signaling has been elucidated in detail. Lithium chloride (LiCl) inhibits the GSK3β activity of cells and promotes the accumulation of β-catenin in the nuclei, causing pseudo-activation of the canonical Wnt/β-catenin pathway. Thus, LiCl is applied to various cells to investigate the effects of Wnt. In this study, the role of the canonical Wnt/β-catenin pathway in the differentiation from undifferentiated ectomesenchymal cells into odontoblasts was examined by investigating the effects of LiCl on cultured primary dental pulp cells. Methods: Cultured primary dental pulp cells isolated from rat lower incisors were used in this study. The cells were treated with LiCl (10 mmol/l) for 2 days and cultured for 20 days. Morphological analysis of alkaline phosphatase and von Kossa stainings were performed in the cells. Total RNA isolated from the cells was used for examination of odontoblastic phenotypes including alkaline phosphatase (ALP), dentin sialophosphoprotein (DSPP), osteocalcin, and ectodin with real-time PCR. Further, to examine the effects of LiCl on the Wnt/β-catenin pathway in dental pulp cells, western blotting analysis for detecting β-catenin phosphorylation in the cells was carried out. Results: Phosphorylation of β-catenin was inhibited by LiC1 in cultured pulp cells, suppressing odontoblast differentiation and mineralized dentin-like nodule formation. Expressions of ALP, DSPP, and osteocalcin mRNA were reduced by the addition of LiCl, whereas the expression of ectodin, an antagonist of Wnt and BMP, was enhanced by the addition of LiCl. Conclusion: Odontoblast differentiation and dentin formation are regulated through the canonical Wnt/β-catenin pathway involving ectodin. In addition, a negative feedback mechanism through ectodin exists in this pathway.
