Spinal IL-33/ST2 Signaling Contributes to Neuropathic Pain via Neuronal CaMKII–CREB and Astroglial JAK2–STAT3 Cascades in Mice

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Background:Emerging evidence indicates that nerve damage–initiated neuroinflammation and immune responses, which are evidenced by the up-regulation of proinflammatory cytokines, contribute to the development of neuropathic pain. This study investigated the role of spinal interleukin (IL)-33 and its receptor ST2 in spared nerve injury (SNI)-induced neuropathic pain.Methods:The von Frey test and acetone test were performed to evaluate neuropathic pain behaviors (n = 8 to 12), and Western blot (n = 4 to 6), immunohistochemistry, real-time polymerase chain reaction (n = 5), and Bio-Plex (n = 5) assays were performed to understand the molecular mechanisms.Results:Intrathecal administration of ST2-neutralizing antibody or ST2 gene knockout (ST2−/−) significantly attenuated the SNI-induced mechanical and cold allodynia. On the 7th day after SNI, the expression of spinal IL-33 and ST2 was increased by 255.8 ± 27.3% and 266.4 ± 83.5% (mean ± SD), respectively. Mechanistic studies showed that the increased expression of the spinal N-methyl-D-aspartate (NMDA) receptor subunit 1 after SNI was reduced by ST2 antibody administration or ST2−/−. The induction of nociceptive behaviors in naive mice due to recombinant IL-33 was reversed by the noncompetitive NMDA antagonist MK-801. ST2 antibody administration or ST2−/− markedly inhibited the increased activation of the astroglial janus kinase 2 (JAK2)–signal transducer and activator of transcription 3 (STAT3) cascade and the neuronal calcium–calmodulin-dependent kinase II (CaMKII)–cyclic adenosine monophosphate response element–binding protein (CREB) cascade after SNI. Moreover, intrathecal pretreatment with the CaMKII inhibitor KN-93 or the JAK2–STAT3 cascade inhibitor AG490 attenuated recombinant IL-33-induced nociceptive behaviors and NMDA subunit 1 up-regulation in naive mice.Conclusion:Spinal IL-33/ST2 signaling contributes to neuropathic pain by activating the astroglial JAK2–STAT3 cascade and the neuronal CaMKII–CREB cascade.

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