Evaluation of mesenchymal stem cell modulation of trigeminal neuronal responses to cold

- Cold stimulus to teeth reaches the activation threshold for TRPA1 and TRPM8.
- TRPA1- and TRPM8- and ATP-mediated inward currents in trigeminal neurons are enhanced by SCAP co-culture.
- Conditioned media from SCAP exposed to 15 °C activate P2X3 and/or P2X2/3 in trigeminal neurons.

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. 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. TG neurons co-cultured with SCAP demonstrated increased TRPA1-mediated (p < 0.01) and TRPM8-mediated inward current densities (p < 0.01) at 24 h 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). These data suggest that SCAP release trophic factors that act on afferent neurons to enhance cold-sensitive ion channel activity.