Stem Cells of the Apical Papilla Regulate Trigeminal Neurite Outgrowth and Targeting through a BDNF-Dependent Mechanism

Abstract

Regenerative endodontic procedures have become a valuable alternative for the treatment of immature teeth with pulp necrosis. In addition to resolution of periradicular pathosis and promotion of continued root development, positive vitality testing has been observed in some regenerative clinical cases. Importantly, the positive response to electric stimulation of the regenerated tissue requires targeting of periradicular axons into the previously empty root canal space. However, the mechanism by which this process occurs is largely unknown. Since stem cells of the apical papilla (SCAP) have been proposed to populate the root canal following regenerative endodontic procedures, we hypothesized that SCAP regulate neurite outgrowth and axonal targeting. To test this hypothesis, we established primary co-cultures of human SCAP and rat trigeminal neurons, and performed neurite outgrowth assays using ELISA and confocal microscopy to determine the effect of increasing concentration of SCAP on the total neurite outgrowth and axonal targeting. In addition, we evaluated whether SCAP evoked axonal targeting in vivo using a matrigel subcutaneous implant assay. Data were analyzed by ANOVA with Bonferroni's post hoc test, and significance was set at p < 0.05. The results demonstrated that SCAP release a soluble factor that regulates neurite outgrowth from cultured trigeminal neurons. Next, we demonstrated that this effect is completely abolished by pretreatment with a neutralizing antibody to brain-derived neurotrophic factor (BDNF), but not by antibodies to other neurotrophins. Further, SCAP release BDNF in a concentration-dependent manner as detected by ELISA, and trigger directed axonal targeting both in vitro and in vivo as demonstrated by microfluidic and matrigel implant experiments, respectively. Collectively, these results suggest that SCAP may be responsible for the chemical signal driving axons to target regenerated tissue via a BDNF-dependent mechanism.

Disclosing the physiology of pulp tissue for vital pulp therapy

“…Promotes neuronal growth and axonal targeting and may bind to glycosaminoglycans, which is a possible mechanism for interaction and storage in the extracellular dentine matrix (De Almeida et al 2014). Glial cell line-derived growth factor (GDNF)…”

Stem Cells of Dental Origin: Current Research Trends and Key Milestones towards Clinical Application

“…A recent study [145] demonstrated that SCAP release BDNF responsible for triggering directed axonal targeting both in vitro and in vivo , as shown by microfluidic and Matrigel implant experiments. Yu et al also detected several neurotrophic factors in SCAP secretome, including Midkine (MDK), Pleiotrophin (PTN), Mesencephalic Astrocyte-Derived Neurotrophic Factor (MANF), Neuroblast Differentiation-Associated Protein (AHNAK), and Neurophilin 2 (NRP2).…”

Enhanced regeneration potential of mobilized dental pulp stem cells from immature teeth

“…In addition, BDNF and NGF are well known to be involved in both the differentiation of new neurons and the protection/survival of established differentiated cells (Gu et al, 2009;Li et al, 2009;Salgado et al, 2010). Notably, BDNF regulates trigeminal neurite outgrowth (de Almeida et al, 2014). The survival of endothelial cells is promoted by MMP-3 and VEGF by their antiapoptotic actions (Gera et al, 1999;Chavakis and Dimmeler, 2002;Zheng et al, 2009), while GDNF also inhibits cell death in dental pulp (Gale et al, 2011).…”