P2Y(12) receptor Upregulation in activated microglia is a gateway of p38 signaling and neuropathic pain
ABSTRACT Microglia in the spinal cord may play an important role in the development and maintenance of neuropathic pain. A metabotropic ATP receptor, P2Y(12), has been shown to be expressed in spinal microglia constitutively and be involved in chemotaxis. Activation of p38 mitogen-activated protein kinase (MAPK) occurs in spinal microglia after nerve injury and may be related to the production of cytokines and other mediators, resulting in neuropathic pain. However, it remains unknown whether any type of P2Y receptor in microglia is involved in the activation of p38 MAPK and the pain behaviors after nerve injury. Using the partial sciatic nerve ligation (PSNL) model in the rat, we found that P2Y(12) mRNA and protein increased in the spinal cord and peaked at 3 d after PSNL. Double labeling studies revealed that cells expressing increased P2Y(12) mRNA and protein after nerve injury were exclusively microglia. Both pharmacological blockades by intrathecal administration of P2Y(12) antagonist and antisense knockdown of P2Y(12) expression suppressed the development of pain behaviors and the phosphorylation of p38 MAPK in spinal microglia after PSNL. The intrathecal infusion of the P2Y(12) agonist 2-(methythio) adenosine 5'-diphosphate trisodium salt into naive rats mimicked the nerve injury-induced activation of p38 in microglia and elevated pain behaviors. These data suggest a new mechanism of neuropathic pain, in which the increased P2Y(12) works as a gateway of the following events in microglia after nerve injury. Activation of this receptor by released ATP or the hydrolyzed products activate p38 MAPK pathway and may play a crucial role in the generation of neuropathic pain.
- SourceAvailable from: Kristina Hoffmann
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- "Next, we have attempted to identify the mechanism of action of P2Y 12 R antagonists for alleviating CFA-induced mechanical hyperalgesia in rats. Previous studies indicated an upregulation of P2Y 12 R mRNA in microglia cells of the spinal cord in neuropathic models using either semi-quantitative RT-PCR (Kobayashi et al., 2008) or in situ hybridization histochemistry (Kobayashi et al., 2008, 2012). In our experiments, a massive upregulation of P2Y 12 R mRNA was detected 48 h after CFA injection in the hind paw in parallel with the robust induction of the proinflammatory cytokine IL-1β, indicating a rapid cytokine response at the periphery. "
ABSTRACT: In this study the role of P2Y12 receptors (P2Y12R) were explored in rodent models of inflammatory and neuropathic pain and in acute thermal nociception. In correlation with their activity to block the recombinant human P2Y12R, the majority of P2Y12R antagonists alleviated mechanical hyperalgesia dose-dependently, following intraplantar CFA injection, and after partial ligation of the sciatic nerve in rats. They also caused an increase in thermal nociceptive threshold in the hot plate test. Among the six P2Y12R antagonists evaluated in the pain studies, the selective P2Y12 receptor antagonist PSB-0739 was most potent upon intrathecal application. P2Y12R mRNA and IL-1β protein were time-dependently overexpressed in the rat hindpaw and lumbar spinal cord following intraplantar CFA injection. This was accompanied by the upregulation of TNF-α, IL-6 and IL-10 in the hindpaw. PSB-0739 (0.3 mg/kg i.t.) attenuated CFA-induced expression of cytokines in the hindpaw and of IL-1β in spinal cord. Subdiaphragmatic vagotomy and the α7 nicotinic acetylcholine receptor antagonist MLA occluded the effect of PSB-0739 (i.t.) on pain behavior and peripheral cytokine induction. Denervation of sympathetic nerves by 6-OHDA pretreatment did not affect the action of PSB-0739. PSB-0739, in an analgesic dose, did not influence motor coordination and platelet aggregation. Genetic deletion of the P2Y12R in mice reproduced the effect of P2Y12R antagonists on mechanical hyperalgesia in inflammatory and neuropathic pain models, on acute thermal nociception and on the induction of spinal IL-1β. Here we report the robust involvement of the P2Y12R in inflammatory pain. The anti-hyperalgesic effect of P2Y12R antagonism could be mediated by the inhibition of both central and peripheral cytokine production and involves α7-receptor mediated efferent pathways.Neurobiology of Disease 06/2014; 70. DOI:10.1016/j.nbd.2014.06.011 · 5.20 Impact Factor
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- "It seems there may be multiple activation states whereby microglia do change the manner with which they participate in neural plastic changes, but do not reach a morphologically activated phenotype. The p38 MAPK pathway can be activated by a host of molecules known to increase pain sensitivity, including the proinflammatory cytokines TNFí µí»¼ and IL-1í µí»½, CCL2 (also known as monocyte chemoattractant protein 1 (MCP-1)), fractalkine (CX3CL1), inducible nitric oxide synthase (iNOS), and matrix metalloprotease-9 (MMP-9) as well as the ATP receptors P2X4 and P2X7        . As shown in Figure 2, some of these microglial activators, such as ATP, CCL2, fractalkine, and MMP-9, could be released from primary afferent neurons  . "
ABSTRACT: Microglia are regarded as macrophages in the central nervous system (CNS) and play an important role in neuroinflammation in the CNS. Microglial activation has been strongly implicated in neurodegeneration in the brain. Increasing evidence also suggests an important role of spinal cord microglia in the genesis of persistent pain, by releasing the proinflammatory cytokines tumor necrosis factor-alpha (TNF α ), Interleukine-1beta (IL-1 β ), and brain derived neurotrophic factor (BDNF). In this review, we discuss the recent findings illustrating the importance of microglial mediators in regulating synaptic plasticity of the excitatory and inhibitory pain circuits in the spinal cord, leading to enhanced pain states. Insights into microglial-neuronal interactions in the spinal cord dorsal horn will not only further our understanding of neural plasticity but may also lead to novel therapeutics for chronic pain management.Neural Plasticity 08/2013; 2013:753656. DOI:10.1155/2013/753656 · 3.60 Impact Factor
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- "Two studies have revealed that P2Y12Rs are key regulators of neuropathic pain (Kobayashi et al., 2008; Tozaki-Saitoh et al., 2008). Intrathecally administered P2Y12R antagonists, such as MRS2395 and AR-C69931MX, and an antisense oligonucleotide for P2Y12R, significantly suppressed development of neuropathic pain after PNI (Kobayashi et al., 2008; Tozaki- Saitoh et al., 2008). A crucial finding was established in P2Y12R-knockout mice, which failed to show tactile allodynia (Tozaki-Saitoh et al., 2008). "
ABSTRACT: Many pathological processes within the central nervous system are mediated by complex interactions between neurons and resident glial cells. In the case of painful peripheral neuropathy, spinal microglia react and undergo a series of changes that directly influence the establishment of neuropathic pain states. Purinergic signaling has been shown to be at the center of this reactivity, and here we review recent mechanistic advances describing the importance of microglial P2 receptors and their interactions with neuronal populations in the development of neuropathic pain. © Wiley Periodicals, Inc.Glia 01/2013; 61(1). DOI:10.1002/glia.22379 · 6.03 Impact Factor