BDNF/TrkB Is a Crucial Regulator in the Inflammation-Mediated Odontoblastic Differentiation of Dental Pulp Stem Cells

The odontoblastic differentiation of dental pulp stem cells (DPSCs) associated with caries injury happens in an inflammatory context. We recently demonstrated that there is a link between inflammation and dental tissue regeneration, identified via enhanced DPSC-mediated dentinogenesis in vitro. Brain-derived neurotrophic factor (BDNF) is a nerve growth factor-related gene family molecule which functions through tropomyosin receptor kinase B (TrkB). While the roles of BDNF in neural tissue repair and other regeneration processes are well identified, its role in dentinogenesis has not been explored. Furthermore, the role of BDNF receptor-TrkB in inflammation-induced dentinogenesis remains unknown. The role of BDNF/TrkB was examined during a 17-day odontogenic differentiation of DPSCs. Human DPSCs were subjected to odontogenic differentiation in dentinogenic media treated with inflammation inducers (LTA or TNF & alpha;), BDNF, and a TrkB agonist (LM22A-4) and/or antagonist (CTX-B). Our data show that BDNF and TrkB receptors affect the early and late stages of the odontogenic differentiation of DPSCs. Immunofluorescent data confirmed the expression of BDNF and TrkB in DPSCs. Our ELISA and qPCR data demonstrate that TrkB agonist treatment increased the expression of dentin matrix protein-1 (DMP-1) during early DPSC odontoblastic differentiation. Coherently, the expression levels of runt-related transcription factor 2 (RUNX-2) and osteocalcin (OCN) were increased. TNF & alpha;, which is responsible for a diverse range of inflammation signaling, increased the levels of expression of dentin sialophosphoprotein (DSPP) and DMP1. Furthermore, BDNF significantly potentiated its effect. The application of CTX-B reversed this effect, suggesting TrkB`s critical role in TNF & alpha;-mediated dentinogenesis. Our studies provide novel findings on the role of BDNF-TrkB in the inflammation-induced odontoblastic differentiation of DPSCs. This finding will address a novel regulatory pathway and a therapeutic approach in dentin tissue engineering using DPSCs.