Mechanisms Mediating the Enhanced Gene Transcription of P2X3 Receptor by Calcitonin Gene-related Peptide in Trigeminal Sensory Neurons

Abstract

The molecular mechanisms underlying migraine pain remain unclear and probably require sustained facilitation in pain-sensing P2X 3 receptors gated by extracellular ATP in nociceptive sensory neurons. The major migraine mediator calcitonin generelated peptide (CGRP) is known to sensitize P2X 3 receptors to increase impulse flow to brainstem trigeminal nuclei. This process is mediated via changes in the expression and function of P2X 3 receptors initially through enhanced trafficking and, later, perhaps through augmented synthesis of P2X 3 receptors. To clarify the mechanisms responsible for CGRP-evoked long lasting alterations in P2X 3 receptors, we used as a model mouse trigeminal ganglion neurons in culture. CGRP activated Ca 2؉ -calmodulin-dependent kinase II, which became localized to the perimembrane region and neuronal processes, a phenomenon already apparent after 30 min and accompanied by a parallel increase in cAMP-response element-binding protein (CREB) phosphorylation and nuclear translocation. These effects triggered increased P2X 3 receptor transcription and were prevented by expressing a dominant negative form of CREB. Increased P2X 3 receptor synthesis was partly mediated by endogenous brain-derived neurotrophic factor (BDNF) because of its block by anti-BDNF antibodies and mimicry by exogenous BDNF. Immunocytochemistry experiments indicated distinct subpopulations of BDNF-or CGRP-sensitive trigeminal neurons with only partial overlap. The present data indicate a novel mechanism for enhancing P2X 3 receptor expression and function in trigeminal sensory neurons by CGRP via CREB phosphorylation. BDNF was an intermediate to extend the sensitizing effect of CGRP also to CGRP-insensitive neurons. This combinatorial action could serve as a powerful process to amplify and prolong pain mediated by P2X 3 receptors.Sensitization of sensory neurons represents the key phenomenon for generating chronic pain that remains relatively refractory to standard treatment (1). Current theories predict that chronic pain is brought about by a gain in the expression and function of sensory nociceptors that enhance their signal flow to the brain to ensure the long lasting nature of this process (2). Clarification of the novel gene expression profiles associated to pain should, therefore, be useful to target emerging molecules (and mechanisms) and for designing new analgesics. Previous studies (3) aimed at detecting changes in transcriptome patterns during pain conditions have provided only a limited description of the global alterations because of the complexity of pain pathologies and signal pathways.Migraine is a classical example of chronic, relapsing pain triggered by local release of endogenous pain mediators, such as the neuropeptide calcitonin gene-related peptide (CGRP) 2 (4, 5) that induces long lasting trigeminal neuronal sensitization (6) and novel gene transcription in sensory neurons (7-9). CGRPmediated signals are transduced at the cell membrane by activation of a G-protein-coupled receptor complex (composed b...

Nucleotide homeostasis and purinergic nociceptive signaling in rat meninges in migraine-like conditions

“…Whereas in the presence of CGRP, we did not find modifications of the rate of ATP degradation we cannot exclude that the rate of nucleotide degradation could be controlled by other migraine-related active molecules, operating via gene transcription [22], which needs observation over the longer time scales.…”

“…Most of the trigeminal sensory nerves innervating meninges express ATP-gated P2X3 receptors and also contain CGRP [45]. We showed previously CGRP induced upregulation of ATP-gated P2X3 receptors [21][22][23] and the inhibitory action of CGRP on nicotinic receptors [46] suggesting various effects of this neuropeptide related to migraine pathology. We also found a significantly enhanced P2X3-mediated signaling in trigeminal neurons of transgenic mouse expressing human mutated gene responsible for familial type migraine [16] and the inhibitory action of the popular anti-migraine agent naproxen on P2X3 receptors [47].…”

“…We showed previously that CGRP induced a delayed upregulation of the pain-transducing ATP-gated P2X3 receptors [21][22][23] suggesting the possible explanation for migraine-related nociceptive firing in the trigeminal system. Thus, our previous studies suggested that P2X3 receptors are likely inducers of migraine pain [18,23].…”

Targeted Taste Cell-specific Overexpression of Brain-derived Neurotrophic Factor in Adult Taste Buds Elevates Phosphorylated TrkB Protein Levels in Taste Cells, Increases Taste Bud Size, and Promotes Gustatory Innervation

“…Another plausible mechanism for BDNF function in the peripheral taste system might be related to its function in the pain transduction and nociceptive system (51). It was shown that calcitonin gene-related peptide (CGRP) promoted P2X3 transcription in trigeminal sensory neurons.…”

P2Y purinergic receptors: New targets for analgesic and antimigraine drugs

“…As a final outcome, recovery from P2X3 receptor desensitization is accelerated, and P2X3 activity is consequently increased [15,16,17]. Moreover, an increased expression of P2X3 receptors in TG neurons was observed upon algogen application in vitro [15,18], or following induction of trigeminalassociated pain in vivo ( Fig. 1) [19,20].…”