Dataset Information

The astrocyte-targeted therapy by Bushi for the neuropathic pain in mice.

ABSTRACT:

Background

There is accumulating evidence that the activation of spinal glial cells, especially microglia, is a key event in the pathogenesis of neuropathic pain. However, the inhibition of microglial activation is often ineffective, especially for long-lasting persistent neuropathic pain. So far, neuropathic pain remains largely intractable and a new therapeutic strategy for the pain is still required.

Methods/principal findings

Using Seltzer model mice, we investigated the temporal aspect of two types of neuropathic pain behaviors, i.e., thermal hyperalgesia and mechanical allodynia, as well as that of morphological changes in spinal microglia and astrocytes by immunohistochemical studies. Firstly, we analyzed the pattern of progression in the pain behaviors, and found that the pain consisted of an "early induction phase" and subsequent "late maintenance phase". We next analyzed the temporal changes in spinal glial cells, and found that the induction and the maintenance phase of pain were associated with the activation of microglia and astrocytes, respectively. When Bushi, a Japanese herbal medicine often used for several types of persistent pain, was administered chronically, it inhibited the maintenance phase of pain without affecting the induction phase, which was in accordance with the inhibition of astrocytic activation in the spinal cord. These analgesic effects and the inhibition of astrocytic activation by Bushi were mimicked by the intrathecal injection of fluorocitrate, an inhibitor of astrocytic activation. Finally, we tested the direct effect of Bushi on astrocytic activation, and found that Bushi suppressed the IL-1β- or IL-18-evoked ERK1/2-phosphorylation in cultured astrocytes but not the ATP-evoked p38- and ERK1/2-phosphorylation in microglia in vitro.

Conclusions

Our results indicated that the activation of spinal astrocytes was responsible for the late maintenance phase of neuropathic pain in the Seltzer model mice and, therefore, the inhibition of astrocytic activation by Bushi could be a useful therapeutic strategy for treating neuropathic pain.

SUBMITTER: Shibata K

PROVIDER: S-EPMC3158083 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Neuropathic pain, a debilitating pain condition, is a common consequence of damage to the nervous system. Optimal treatment of neuropathic pain is a major clinical challenge because the underlying mechanisms remain unclear and currently available treatments are frequently ineffective. Emerging lines of evidence indicate that peripheral nerve injury converts resting spinal cord glia into reactive cells that are required for the development and maintenance of neuropathic pain. However, the mechanisms underlying reactive astrogliosis after nerve injury are largely unknown. In the present study, we investigated cell proliferation, a critical process in reactive astrogliosis, and determined the temporally restricted proliferation of dorsal horn astrocytes in rats with spinal nerve injury, a well-known model of neuropathic pain. We found that nerve injury-induced astrocyte proliferation requires the Janus kinase-signal transducers and activators of transcription 3 signalling pathway. Nerve injury induced a marked signal transducers and activators of transcription 3 nuclear translocation, a primary index of signal transducers and activators of transcription 3 activation, in dorsal horn astrocytes. Intrathecally administering inhibitors of Janus kinase-signal transducers and activators of transcription 3 signalling to rats with nerve injury reduced the number of proliferating dorsal horn astrocytes and produced a recovery from established tactile allodynia, a cardinal symptom of neuropathic pain that is characterized by pain hypersensitivity evoked by innocuous stimuli. Moreover, recovery from tactile allodynia was also produced by direct suppression of dividing astrocytes by intrathecal administration of the cell cycle inhibitor flavopiridol to nerve-injured rats. Together, these results imply that the Janus kinase-signal transducers and activators of transcription 3 signalling pathway are critical transducers of astrocyte proliferation and maintenance of tactile allodynia and may be a therapeutic target for neuropathic pain.

Project description:BackgroundNeuropathic pain is caused by sensory nerve injury, but effective treatments are currently lacking. Microglia are activated in the spinal dorsal horn after sensory nerve injury and contribute to neuropathic pain. Accordingly, molecules expressed by these cells are considered potential targets for therapeutic strategies. Our previous gene screening study using a mouse model of motor nerve injury showed that the G-protein-coupled receptor 34 gene (GPR34) is induced by nerve injury. Because GPR34 is now considered a microglia-enriched gene, we explored the possibility that it might be involved in microglial activation in the dorsal horn in a mouse model of neuropathic pain.MethodsmRNA expression of GPR34 and pro-inflammatory molecules was determined by quantitative real-time PCR in wild-type and GPR34-deficient mice with L4 spinal nerve injury. In situ hybridization was used to identify GPR34 expression in microglia, and immunohistochemistry with the microglial marker Iba1 was performed to examine microglial numbers and morphology. Mechanical sensitivity was evaluated by the von Frey hair test. Liquid chromatography-tandem mass spectrometry quantified expression of the ligand for GPR34, lysophosphatidylserine (LysoPS), in the dorsal horn, and a GPR34 antagonist was intrathecally administrated to examine the effect of inhibiting LysoPS-GPR34 signaling on mechanical sensitivity.ResultsGPR34 was predominantly expressed by microglia in the dorsal horn after L4 nerve injury. There were no histological differences in microglial numbers or morphology between WT and GPR34-deficient mice. However, nerve injury-induced pro-inflammatory cytokine expression levels in microglia and pain behaviors were significantly attenuated in GPR34-deficient mice. Furthermore, the intrathecal administration of the GPR34 antagonist reduced neuropathic pain.ConclusionsInhibition of GPR34-mediated signal by GPR34 gene deletion reduced nerve injury-induced neuropathic pain by suppressing pro-inflammatory responses of microglia without affecting their morphology. Therefore, the suppression of GPR34 activity may have therapeutic potential for alleviating neuropathic pain.