Amelogenin Activates the Wnt/b-catenin Pathway

Objectives: Canonical Wnt signaling plays a critical role in tooth development. While amelogenin is essential to proper enamel development, the mechanism for regulation of Wnt signaling pathway by amelogenin is yet to be studied. The aim of this study was to investigate the spatial distribution of Wnt signaling in postnatal tissue by using a β-catenin reporter mouse (TOPGAL) and to evaluate that amelogenin has signaling activity in isolated mouse calvarial cells and human periodontal ligament (PDL) cells. Methods: We examined the regulatory function of canonical Wnt signaling by amelogenin in TOPGAL transgenic mice. These mice express a β-galactosidase trans gene under the control of a LEF/TCF and β-catenin inducible promoter so that Wnt activity can be detected by X-gal staining. To further investigate the molecular mechanisms involved in β-catenin signaling pathway, isolated osteoblasts and PDL cells were exposed to full-length recombinant mouse amelogenin and evaluated for phenotypic changes and β-catenin signaling using a TOPFLASH and LacZ reporter gene. Results: Intense X-gal staining for β-catenin signaling in TOPGAL mouse was observed throughout the periodontal ligament and root surface. Upon treatment of these isolated osteoblasts with amelogenin at 3.0 and 5.0 µg/ml there was a dose dependent statistically significant increase in LacZ reporter activity. In the PDL cells, amelogenin also stimulates the LacZ reporter activity of the TOPFLASH construct by four fold and induced a marked increase in the level of activated β-catenin transcription factor. Conclusion: In these in vitro models, we show that amelogenin can activate β-catenin signaling. With the TOPGAL transgenic mouse we also show that amelogenin expression in vivo is localized mainly around the root, PDL, and alveolar bone.