Gαs-Coupled CGRP Receptor Signaling Axis from the Trigeminal Ganglion Neuron to Odontoblast Negatively Regulates Dentin Mineralization

Abstract

An inflammatory response following dental pulp injury and/or infection often leads to neurogenic inflammation via the axon reflex. However, the detailed mechanism underlying the occurrence of the axon reflex in the dental pulp remains unclear. We sought to examine the intracellular cyclic adenosine monophosphate (cAMP) signaling pathway in odontoblasts via the activation of Gs protein-coupled receptors and intercellular trigeminal ganglion (TG) neuron–odontoblast communication following direct mechanical stimulation of TG neurons. Odontoblasts express heterotrimeric G-protein α-subunit Gαs and calcitonin receptor-like receptors. The application of an adenylyl cyclase (AC) activator and a calcitonin gene-related peptide (CGRP) receptor agonist increased the intracellular cAMP levels ([cAMP]i) in odontoblasts, which were significantly inhibited by the selective CGRP receptor antagonist and AC inhibitor. Mechanical stimulation of the small-sized CGRP-positive but neurofilament heavy chain-negative TG neurons increased [cAMP]i in odontoblasts localized near the stimulated neuron. This increase was inhibited by the CGRP receptor antagonist. In the mineralization assay, CGRP impaired the mineralization ability of the odontoblasts, which was reversed by treatment with a CGRP receptor antagonist and AC inhibitor. CGRP establishes an axon reflex in the dental pulp via intercellular communication between TG neurons and odontoblasts. Overall, CGRP and cAMP signaling negatively regulate dentinogenesis as defensive mechanisms.

Piezo1-pannexin-1-P2X3 axis in odontoblasts and neurons mediates sensory transduction in dentinal sensitivity

“…NCXs and PMCAs in odontoblasts are functionally coupled with high pH stimulation-induced Ca 2+ mobilization, which is important for physiological and high-pH-induced dentinogenesis ( Kimura et al, 2016 , 2021 ). Our recent results also indicate “retrograde” communication between neurons and odontoblasts via neuropeptides, such as calcitonin gene-related peptide (CGRP), released from nerve terminals (i.e., axon reflex) during neurogenic inflammation in the dental pulp ( Saito et al, 2022 ).…”

Sensory nerves, but not sympathetic nerves, promote reparative dentine formation after dentine injury via CGRP‐mediated angiogenesis: An in vivo study

“…In contrast to findings that CGRP directly promotes the proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells via the Wnt/β‐catenin signalling pathway (Jia et al., 2019; Wan et al., 2021), CGRP exhibits an inhibitory effect on DPSC proliferation and does not affect differentiation of DPSCs (Michot et al., 2020; Moore et al., 2022). An odontoblast‐neuron co‐culture study also revealed that CGRP signalling negatively regulates dentinogenesis as a defensive mechanism (Saito et al., 2022), which suggests that CGRP exerts different effects on different types of stem cells. Hence, CGRP may act on other components in the local microenvironment to promote healing in the dental pulp.…”

Intracellular cAMP Signaling Pathway via Gs Protein-Coupled Receptor Activation in Rat Primary Cultured Trigeminal Ganglion Cells

“…In accordance, our results showed that NF-H-positive TG cells are Gα s protein-positive. In our previous study, we reported CGRP release from peptidergic C neurons of TG, but not NF-H-positive neurons, into the extracellular space following mechanical stimulation of the neurons [ 22 ].…”