Insight into Stage-Specific Effects of Fibroblast Growth Factor Signaling on Dental Pulp Cells

Odontoblast differentiation and reparative dentinogenesis are dependent on multiple signaling molecules, including members of Fibroblast Growth Factor (FGF) family. Previous studies have demonstrated both positive and negative effects of FGFs on odontoblast differentiation in dental pulp. However, the underlying cellular and molecular mechanisms of these opposite effects are unclear. Therefore, the overall goal of the studies outlined in this dissertation was to gain insight into the cellular and molecular mechanisms of the effects of FGF signaling on mineralization and dentinogenesis of pulp cells. To approach this goal, we used dental pulp cultures derived from the coronal portion of unerupted molars from various transgenic mice, which display stage-specific activation of transgenes during odontoblast differentiation. Our observations showed that exposure of progenitors and cells at early stages of odontoblast differentiation stimulated/accelerated their differentiation into functional odontoblasts, expressing high levels of Dmp1 and DMP1-GFP, and low levels of Dspp and DSPP-Cerulean. Additional exposure maintained cells as functional odontoblasts and prevented their differentiation into mature odontoblasts, expressing high levels of Dspp and DSPP-Cerulean and producing mineralized matrix. Withdrawal of FGF2 resulted in complete recovery of mineralization and differentiation of functional odontoblasts into mature odontoblasts. Analysis of FACS-sorted 2.3-GFP- (progenitors) and 2.3-GFP+ (cells at early stages of differentiation) cells confirmed that FGF2 stimulated/accelerated their differentiation into functional odontoblasts, while prevented their differentiation into fully differentiated odontoblasts. Finally, our results showed that stimulatory effects of FGF2 were mediated by activation of the FGFR, MEK/Erk1/2 and BMP/BMPR signaling pathways, whereas inhibitory effects were mediated by re-activation of the FGFR and MEK/Erk1/2 pathways with negative roles in odontoblast differentiation. Taken together, our results demonstrated the stage-specificity of the effects of FGF2 on odontoblast differentiation, suggesting that FGF2 is a viable growth factor for dentin regeneration.