Smad 1/5 Is Involved in Bone Morphogenetic Protein-2-induced Odontoblastic Differentiation in Human Dental Pulp Cells

Introduction: Bone morphogenetic protein-2 (BMP-2) is a member of the transforming growth factor-beta (TGF-beta) superfamily, which has a broad range of activities that affect many different cell types. Previous research has suggested that BMP-2 induces the differentiation of human dental pulp cells (DPCs) into odontoblast-like cells. However, the mechanism by which BMP-2 induces odontoblastic differentiation has not yet been established. In the present study, we examined the involvement of the BMP/Smad pathway in mediating odontoblastic differentiation in DPCs. Methods: Levels of phosphorylated and unphosphorylated Smad 1/5 were quantified by Western blot analysis in response to BMP-2 and the BMP signaling inhibitor noggin. Some nuclear translocation of Smad 1/5 was also observed by immunofluorescence staining in isolated DPCs treated with BMP-2. The effects of noggin on the BMP-2-induced odontoblastic differentiation of DPCs were determined by alkaline phosphatase activity assay, and the expression of odontoblastic markers was evaluated by reverse transcription polymerase chain reaction analysis and Western blotting. Results: We found that BMP-2 induced the phosphorylation and nuclear translocation of Smad 1/5. In addition, noggin significantly inhibited alkaline phosphatase activity and odontoblastic differentiation and reduced the formation of mineralized nodules in BMP-2-treated DPCs. Conclusions: These findings suggest that Smad 1/5 is involved in BMP-2-induced odontoblastic differentiation in DPCs. (J Endod 2012;38:66-71)