The Role of BMP Signaling in Mediating Stimulatory Effects of FGF-FGFR Signaling on Odontoblast Differentiation in Dental Pulp

Odontoblast differentiation is dependent on multiple signaling molecules, including growth factors stored in the extracellular dentin matrix. Our previous studies have demonstrated that Fibroblast Growth Factor 2 (FGF2) exerted stage-specific effects on odontoblast differentiation in primary dental pulp cultures. FGF2 stimulated differentiation of functional odontoblasts expressing high levels of Dmp1 from early progenitors but inhibited the terminal differentiation of functional odontoblasts to fully differentiated odontoblasts expressing high levels of Dspp. These stimulatory effects involved activation of FGFR and ERK1/2, and increased levels of expression of Bmp2, Runx2, and Osx (components of BMP signaling) suggesting the involvement of BMP signaling in FGF2-induced Dspp expression. Therefore, the overall goal of the studies outlined in this thesis was to examine the role of BMP signaling in stimulatory effects of FGF signaling on odontoblast differentiation of dental pulp cells. We showed that BMP2 did not affect the extent of mineralization but rapidly (within ~12-24 hrs) stimulated expression of Dspp and intensity of DSPP-Cerulean transgene in a concentration-dependent manner without affecting the percentage of DSPP-Cerulean+ odontoblasts. In contrast to Dspp, BMP2 rapidly (within ~24-48 hrs) decreased expression of Dmp1, Bsp, DMP1-mCherry, and BSP-GFP in a concentration-dependent manner. Inhibition of the BMP and FGF signaling pathways by noggin and SU5402, respectively, did not have marked effects on the extent of mineralization but decreased expression of Dspp stimulated by these growth factors. These inhibitory effects were long-lasting and observed up to 14 days after removal of the growth factors. Additional experiments in primary bone marrow stromal cells cultures demonstrated that early and limited exposure to BMP2 did not affect mineralization but decreased expression of Dmp1, Bsp, and respective transgenes. Taken together, our results demonstrated that activation of the canonical BMP signaling pathway during the proliferation phase of in vitro growth resulted in significant increases in the expression of Dspp, and these increases were mediated via reciprocal interaction of the BMP and FGF signaling pathways. These data will further elucidate the perspectives of using both FGF2 and BMP2 in dentin regeneration applications