Role of APin during amelogenesis

Objectives: APin was previously suggested to have a functional role in the mineralization and maturation of enamel. The purpose of this study was to investigate the biological function and signaling pathway of APin during ameloblast differentiation and enamel mineralization. Methods: We examined the expression of the APin and BMPR-1B protein during tooth development in mice using immunofluroence. A high-density protein microarray was performed to identify the other proteins interacting with APin. The expression of identified genes was investigated by RT-PCR after the silencing or over-expression of APin. The alkaline phosphatase (ALP) activity was measured and the level of mineralization was also determined by staining the calcified nodules with Alizarin red S stain. After the treatment of BMP-2 recombinant protein and BMP receptor 1B (BMPR-1B) siRNA transfection into the ALCs, expression of APin and Smad 1/5/8 was evaluated by RT-PCR and western blot. Results: APin and BMPR-1B protein were not expressed in presecretory ameloblast but strongly expressed in mature ameloblast. The mineralization and the ALP activity were increased by the treatment of APin recombinant protein and the APin over-expression in the ALCs. The silencing of APin decreased the expression of BMPR-1B, EF hand calcium binding protein 2, MMP-20 and Smad 1/5/8 in the ALCs, whereas their expression were up-regulated markedly when APin was over-expressed. The expression of APin, BMPR-1B, Smad 1/5/8 and MMP-20 was also increased by the treatment of BMP2 recombinant protein in ALCs. Conclusion: These results indicate that APin augmented enamel mineralization and its function might be mediated through the BMP signal transduction pathway via BMPR-1B. This work was supported by RO1-2006-000-10581-0 from the Basic Research Program of The Korea Science & Engineering Foundation.