Tubular dentin formation by TGF-β/BMP signaling in dental epithelial cells.

Objectives: This study aimed to identify formation of tubular dentin induced by transforming growth factor-β (TGF-β) and bone morphogenic protein (BMP) signaling pathway in dental epithelial cells.

Methods: We collected conditioned medium (CM) of rTGF-β1/rBMP-2-treated HAT-7 and treated to MDPC-23 cells. The expression levels of odontoblast differentiation markers, KLF4, DMP1, and DSP were evaluated by real-time PCR and Western blot analysis. To evaluate whether CM of rTGF-β1/rBMP-2 induces tubular dentin formation, we made a beagle dog tooth defect model.

Results: Here, we show that Cpne7 is regulated by Smad4-dependent TGF-β1/BMP2 signaling pathway in dental epithelial cells. CM of rTGF-β1/rBMP-2 treated HAT-7 or rCPNE7 raises the expression levels of KLF4, DMP1, and DSP in MDPC-23 cells. When rTGF-β1 or rBMP-2 is directly treated to MDPC-23 cells, however, expression levels of Cpne7-regulated genes remain unchanged. In a beagle dog defect model, application of rTGF-β1/BMP2-treated CM resulted in tubular tertiary dentin mixed with osteodentin at cavity-prepared sites, while rTGF-β1 group exhibited homogenous osteodentin.

Conclusions: Taken together, Smad4-dependent TGF-β1/BMP2 signaling regulates Cpne7 in dental epithelial cells, and CPNE7 protein secreted from pre-ameloblasts mediates odontoblast differentiation via epithelial-mesenchymal interaction.