Mesenchymal Stem Cell Modulation of Trigeminal Neuronal Responses to Cold

Objectives: Tissue engineering protocols, such as regenerative endodontic procedures (REPs), comprise biologically based procedures designed to restore normal physiologic function. For REPs, the goal is reconstitution of the pulp-dentin complex by delivering mesenchymal stem cells (MSCs), including the stem cells of the apical papilla (SCAP) into a root canal system. Many patients regain cold sensitivity after REPs, but the mechanism is not understood. We hypothesized that SCAP modulate nociceptive function through a paracrine mechanism that activates cold-sensitive ion channels in neurons.

Methods: We established a co-culture system with human SCAP and rat trigeminal (TG) sensory neurons in order to determine the effect of SCAP co-culture on neuronal responses using whole-cell patch-clamp electrophysiology.
Results: Application of Endo Ice on the occlusal surface of a REP restoration resulted in a temperature decrease to temperatures that activate the cold-sensitive ion channels TRPM8 and TRPA1. TG neurons co-cultured with SCAP demonstrated increased TRPA1-mediated (p<0.01) and TRPM8-mediated inward current densities (p<0.01) at 24h in co-culture. Cold stimulation to SCAP significantly increased ATP release (p<0.01), and supernatant collected after cold stimulation to SCAP was able to activate cultured TG neurons. Co-culture with SCAP significantly increased sustained ATP-evoked inward current density (p<0.05)


Conclusions: These data suggest that SCAP release trophic factors that act on afferent neurons to enhance cold-sensitive ion channel activity. In this study, we performed in vitro experiments that investigated potential non-hydrodynamic mechanisms that could underlie the detection of noxious cold stimulus following REPs .