Activation of G protein-coupled parathyroid hormone receptors in rat incisor odontoblasts promotes mineralization via cyclic adenosine monophosphate, not Ca2+ signalling: In vitro study.

Aim: Parathyroid hormone (PTH) and its Gα_s-coupled receptors, PTH receptor, mediate odontoblast differentiation; however, the detailed intracellular adenylyl cyclase-mediated signalling pathway mediated by the PTH-PTH receptor axis remains to be elucidated. Therefore, we measured the intracellular levels of cyclic adenosine monophosphate (cAMP) in living single odontoblasts.

Methodology: We obtained acutely isolated odontoblasts from newborn Wistar rats and analysed the mineralization ability by Alizarin red staining. Intracellular-free Ca²⁺ concentration was measured using a fluorescent Ca²⁺ indicator, whereas intracellular cAMP levels were examined by a mNeon Green-based cAMP sensor.

Results: Granulated PTH was detected in the vascular area of the dental pulp periphery. Application of the non-selective PTH receptor agonist DPC AJ1951 increased cAMP levels in odontoblasts. This increase was significantly inhibited by the non-selective PTH receptor antagonist 4185-v and the adenylyl cyclase inhibitor SQ 22536. However, applying the non-selective PTH receptor agonist DPC AJ1951 did not increase the intracellular Ca²⁺ concentration without extracellular Ca²⁺. In mineralization assays, PTH promoted mineralization by odontoblasts. The mineralization was inhibited by SQ 22536 and 4185-v but not by the phospholipase C inhibitor U73122.

Conclusion: Thus, the present study suggests that PTH from the bloodstream functionally activates the Gα_s-coupled PTH receptor in odontoblasts, which plays an essential role in dentinogenesis.