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P2Y12 receptors in spinal microglia are required for neuropathic pain after peripheral nerve injury.

ABSTRACT: Extracellular nucleotides have been implicated as signaling molecules used by microglia to sense adverse physiological conditions, such as neuronal damage. They act through purinoceptors, especially the G-protein-coupled P2Y receptor P2Y(12)R. Emerging evidence has indicated that activated spinal microglia responding to nerve injury are key cellular intermediaries in the resulting highly debilitating chronic pain state, namely neuropathic pain. However, the role of microglial P2Y(12)Rs in neuropathic pain remains unknown. Here, we show that the level of P2Y(12)R mRNA expression was markedly increased in the spinal cord ipsilateral to the nerve injury and that this expression was highly restricted to ionized binding calcium adapter molecule 1-positive microglia. An increase in the immunofluorescence of P2Y(12)R protein in the ipsilateral spinal cord was also observed after nerve injury, and P2Y(12)R-positive cells were double labeled with the microglial marker OX-42. Blocking spinal P2Y(12)R by the intrathecal administration of its antagonist AR-C69931MX prevented the development of tactile allodynia (pain hypersensitivity to innocuous stimuli), a hallmark of neuropathic pain syndrome. Furthermore, mice lacking P2ry(12) (P2ry(12)(-/-)) displayed impaired tactile allodynia after nerve injury without any change in basal mechanical sensitivity. Moreover, a single intrathecal administration of AR-C69931MX or oral administration of clopidogrel (a P2Y(12)R blocker clinically in use) to nerve-injured rats produced a striking alleviation of existing tactile allodynia. Together, our findings indicate that activation of P2Y(12)Rs in spinal microglia may be a critical event in the pathogenesis of neuropathic pain and suggest that blocking microglial P2Y(12)R might be a viable therapeutic strategy for treating neuropathic pain.

SUBMITTER: Tozaki-Saitoh H

PROVIDER: S-EPMC6670742 | biostudies-literature | 2008 May

REPOSITORIES: biostudies-literature

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P2Y12 receptors in spinal microglia are required for neuropathic pain after peripheral nerve injury.

Tozaki-Saitoh Hidetoshi H Tsuda Makoto M Miyata Hiroyuki H Ueda Kazuaki K Kohsaka Shinichi S Inoue Kazuhide K

The Journal of neuroscience : the official journal of the Society for Neuroscience 20080501 19

Extracellular nucleotides have been implicated as signaling molecules used by microglia to sense adverse physiological conditions, such as neuronal damage. They act through purinoceptors, especially the G-protein-coupled P2Y receptor P2Y(12)R. Emerging evidence has indicated that activated spinal microglia responding to nerve injury are key cellular intermediaries in the resulting highly debilitating chronic pain state, namely neuropathic pain. However, the role of microglial P2Y(12)Rs in neurop ...[more]

PMID: 18463248

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Project description:Peripheral nerve injury alters the expression of hundreds of proteins in dorsal root ganglia (DRG). Targeting some of these proteins has led to successful treatments for acute pain, but not for sustained postoperative neuropathic pain. The latter may require targeting multiple proteins. Since a single microRNA (miR) can affect the expression of multiple proteins, here, we describe an approach to identify chronic neuropathic pain-relevant miRs. We used two variants of the spared nerve injury (SNI): Sural-SNI and Tibial-SNI and found distinct pain phenotypes between the two. Both models induced strong mechanical allodynia, but only Sural-SNI rats maintained strong mechanical and cold allodynia, as previously reported. In contrast, we found that Tibial-SNI rats recovered from mechanical allodynia and never developed cold allodynia. Since both models involve nerve injury, we increased the probability of identifying differentially regulated miRs that correlated with the quality and magnitude of neuropathic pain and decreased the probability of detecting miRs that are solely involved in neuronal regeneration. We found seven such miRs in L3-L5 DRG. The expression of these miRs increased in Tibial-SNI. These miRs displayed a lower level of expression in Sural-SNI, with four having levels lower than those in sham animals. Bioinformatics analysis of how these miRs could affect the expression of some ion channels supports the view that, following a peripheral nerve injury, the increase of the 7 miRs may contribute to the recovery from neuropathic pain while the decrease of four of them may contribute to the development of chronic neuropathic pain. The approach used resulted in the identification of a small number of potentially neuropathic pain relevant miRs. Additional studies are required to investigate whether manipulating the expression of the identified miRs in primary sensory neurons can prevent or ameliorate chronic neuropathic pain following peripheral nerve injuries. To identify the miRs that were differentially dysregulated between Tibial-SNI and Sural-SNI, we first performed 12 microarrays in a limited number of samples (in four individual DRGs per group: Sham, Tibial-SNI and Sural-SNI; two L3-DRG and two L4-DRG). Then, miRs identified as having differential expression were corroborated with real time qRT-PCR in RNA isolated from individual DRGs (L3, L4 and L5) derived from 4 rats per group (not presented here, but in the manuscript).

Project description:Background Neuropathic pain is a major pathology of the central nervous system associated with neuroinflammation. Ryk (receptor-like tyrosine kinase) receptors act as repulsive axon-guidance molecules during development of central nervous system and neural injury. Increasing evidence suggests the potential involvement of Wnt/Ryk (wingless and Int) signaling in the pathogenesis of neuropathic pain. However, its underlying mechanism remains unknown. Results The expression and location of Ryk receptor as well as its ligand Wnt1 were detected by qPCR, Western blot, and immunohistochemistry. We found that Ryk, a specific Wnt receptor, was expressed in IB4+ (Isolectin B4) and CGRP+ (calcitonin gene-related peptide) dorsal root ganglia neurons and their ascending unmyelinated fibers in the dorsal horn of the spinal cord. Ryk was upregulated after spinal nerve ligation surgery. Wnt1 was also increased in activated astrocytes in the dorsal horn after spinal nerve ligation. The presynaptic mechanism of Ryk in regulation of neuropathic pain was determined by electrophysiology in spinal slice. Spinal nerve ligation model was established, and the therapeutic potential of inhibiting Ryk receptor was determined. Spine-specific blocking of the Wnt/Ryk receptor signaling attenuated the spinal nerve ligation-induced mechanical allodynia but not thermal hyperalgesia. Further, it also blocked Ca2+-dependent signals including CaMKII and PKCγ, subsequent release of CCL2 (CCR-like protein) in the dorsal horn. An in vitro study showed that inactivating Ryk receptors with anti-Ryk antibodies or lentiviral Ryk shRNA led to the inactivation of Wnt1 for excitatory synaptic transmission in spinal slices and subsequent decrease in CCL2 expression in the dorsal root ganglia neurons. Conclusion These studies demonstrate the existence of critical crosstalk between astrocytes and unmyelinated fibers, which indicate the presynaptic mechanism of Ryk in cytokine transmission of neuropathic pain and the therapeutic potential for Wnt/Ryk signaling pathway in the treatment of neuropathic pain.

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P2Y12 receptors in spinal microglia are required for neuropathic pain after peripheral nerve injury.

Publications

P2Y12 receptors in spinal microglia are required for neuropathic pain after peripheral nerve injury.

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