title: 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.
authors.affiliation: Department of Molecular and System Pharmacology, Graduate School of Pharmaceutical Sciences, Kyushu University, Higashi, Fukuoka 812-8582, Japan.
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Tozaki-Saitoh
authors.forename: Makoto
authors.initials: M
authors.lastname: Tsuda
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Miyata
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Ueda
authors.forename: Shinichi
authors.initials: S
authors.lastname: Kohsaka
authors.forename: Kazuhide
authors.initials: K
authors.lastname: Inoue
mesh_terms: D000249:Adenosine Monophosphate / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D000284:Administration, Oral; D000818:Animals; D000077144:Clopidogrel; D006941:Hyperesthesia / Q000503:physiopathology / Q000517:prevention & control; D007278:Injections, Spinal; D008297:Male; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D017628:Microglia / Q000378:metabolism*; D009437:Neuralgia / Q000209:etiology*; D058919:Purinergic P2 Receptor Antagonists; D051381:Rats; D017208:Rats, Wistar; D018048:Receptors, Purinergic P2 / Q000172:deficiency / Q000378:metabolism*; D058925:Receptors, Purinergic P2Y12; D013116:Spinal Cord / Q000378:metabolism*; D013127:Spinal Nerves / Q000293:injuries* / Q000378:metabolism*; D013988:Ticlopidine / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D015854:Up-Regulation
chemical_list: D008565:Membrane Proteins; C553058:P2ry12 protein, rat; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; D058925:Receptors, Purinergic P2Y12; D000249:Adenosine Monophosphate; C117446:cangrelor; D000077144:Clopidogrel; D013988:Ticlopidine