Glial interleukin-1β upregulates neuronal sodium channel 1.7 in trigeminal ganglion contributing to temporomandibular joint inflammatory hypernociception in rats

Zhang et al. Journal of Neuroinflammation (2018) 15:117 https://doi.org/10.1186/s12974-018-1154-0 RESEARCH Open Access Glial interleukin-1β upregulates neuronal sodium channel 1.7 in trigeminal ganglion contributing to temporomandibular joint inflammatory hypernociception in rats Peng Zhang1,2,3, Rui-Yun Bi4 and Ye-Hua Gan1,2,3* Abstract Background: The proinflammatory cytokine interleukin-1β (IL-1β) drives pain by inducing the expression of inflammatory mediators; however, its ability to regulate sodium channel 1.7 (Nav1.7), a key driver of temporomandibular joint (TMJ) hypernociception, remains unknown. IL-1β induces cyclooxygenase-2 (COX-2) and prostaglandin E2 (PGE2). We previously showed that PGE2 upregulated trigeminal ganglionic Nav1.7 expression. Satellite glial cells (SGCs) involve in inflammatory pain through glial cytokines. Therefore, we explored here in the trigeminal ganglion (TG) whether IL-1β upregulated Nav1.7 expression and whether the IL-1β located in the SGCs upregulated Nav1.7 expression in the neurons contributing to TMJ inflammatory hypernociception. Methods: We treated rat TG explants with IL-1β with or without inhibitors, including NS398 for COX-2, PF-04418948 for EP2, and H89 and PKI-(6-22)-amide for protein kinase A (PKA), or with adenylate cyclase agonist forskolin, and used realtime PCR, Western blot, and immunohistofluorescence to determine the expressions or locations of Nav1.7, COX-2, cAMP response element-binding protein (CREB) phosphorylation, and IL-1β. We used chromatin immunoprecipitation to examine CREB binding to the Nav1.7 promoter. Finally, we microinjected IL-1β into the TGs or injected complete Freund’s adjuvant into TMJs with or without previous microinjection of fluorocitrate, an inhibitor of SGCs activation, into the TGs, and evaluated nociception and gene expressions. Differences between groups were examined by one-way analysis of variance (ANOVA) or independent samples t test. Results: IL-1β upregulated Nav1.7 mRNA and protein expressions in the TG explants, whereas NS398, PF-04418948, H89, or PKI-(6-22)-amide could all block this upregulation, and forskolin could also upregulate Nav1.7 mRNA and protein expressions. IL-1β enhanced CREB binding to the Nav1.7 promoter. Microinjection of IL-1β into the TGs or TMJ inflammation both induced hypernociception of TMJ region and correspondingly upregulated COX-2, phosphoCREB, and Nav1.7 expressions in the TGs. Moreover, microinjection of fluorocitrate into the TGs completely blocked TMJ inflammation-induced activation of SGCs and the upregulation of IL-1β and COX-2 in the SGCs, and phospho-CREB and Nav1.7 in the neurons and alleviated inflammation-induced TMJ hypernociception. (Continued on next page) * Correspondence: 1 Central Laboratory, Peking University School and Hospital of Stomatology, 22 Zhongguancun Avenue South, Haidian District, Beijing 100081, China 2 Department of Oral & Maxillofacial Surgery, Peking University School and Hospital of Stomatology, 22 Zhongguancun Avenue South, Haidian District, Beijing 100081, China Full list of author information is available at the end of the article © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Zhang et al. Journal of Neuroinflammation (2018) 15:117 Page 2 of 16 (Continued from previous page) Conclusions: Glial IL-1β upregulated neuronal Nav1.7 expression via the crosstalk between signaling pathways of the glial IL-1β/COX-2/PGE2 and the neuronal EP2/PKA/CREB/Nav1.7 in TG contributing to TMJ inflammatory hypernociception. Keywords: IL-1β, Nav1.7, Trigeminal ganglion, Satellite glial cells, Neuron, TMJ, Inflammatory hypernociception, CREB, COX-2, Background The tetrodotoxin-sensitive (TTX-S) voltage-gated sodium channel 1.7 (Nav1.7), whose principal α-subunit is encoded by the sodium channel voltage-gated type IX alpha subunit (SCN9A) gene, is highly expressed in the trigeminal ganglia (TG), dorsal root ganglia (DRG), sympathetic ganglia, and peripheral terminals of painsensing nociceptors [1, 2]. Nav1.7 amplifies weak stimuli in neurons and acts as a threshold channel for firing action potentials [3, 4]. Mutations in the SCN9A gene which lead to a gain of Nav1.7 function are associated with primary erythromelalgia [5] and paroxysmal extreme pain disorder [6], while mutations in the SCN9A gene which lead to a loss of Nav1.7 function are associated with congenital insensitivity to pain [7]. Nav1.7 plays an important role in inflammatory pain. In addition to increasing the TTX-S current (mainly include Nav1.3 and Nav1.7), Nav1.7 mRNA and protein expressions are upregulated in the DRG in a hindpaw inflammation model in rats [8]. Moreover, the role of Nav1.7 in inflammatory hypernociception is supported by knockout and knockdown studies in mice. Nociceptor-specific Nav1.7 knockout abrogates inflammation-induced mechanical and thermal hyperalgesia [9], while Nav1.7 knockdown in primary afferent neurons prevents inflammation-induced hyperalgesia [10]. We have shown that TG Nav1.7 is involved in temporomandibular joint (TMJ) inflammatory hypernociception [11]. However, Nav1.7 regulation remains poorly understood. While two studies have shown that Nav1.7 is regulated in the DRG by nerve growth factor (NGF) [12] and tumor necrosis factor-α (TNF-α) [13], the mechanisms remain to be elucidated. Proinflammatory cytokines might be important Nav1.7 regulators. Many proinflammatory mediators, including interleukin-1 and interleukin-6 (IL-1 and IL-6), TNF-α, NGF, serotonin, and prostaglandins are increased after tissue inflammation [14]. Interleukin-1β (IL-1β), a member of IL-1 family, as the first discovered cytokine [15] is associated with peripheral sensitization [16] and the development and maintenance of inflammatory pain [17, 18]. IL-1β injection produces mechanical hypernociception in rats [19]. IL-1 receptor antagonist (IL-1ra) administration significantly reduces IL-1β-induced enhancement of nociceptive neuron responses [20] and inflammatory hyperalgesia [21]. IL-1β can increase nociceptor excitability by relieving resting slow inactivation of tetrodotoxin-resistant (TTX-R) voltage-gated sodium channels, enhancing the persistent TTX-R current near threshold levels, and increasing the TTX-S sodium current amplitude [16]. IL-1β-induced hyperalgesia is prevented by anti-NGF antibodies [17]. We hypothesized that IL-1β might modulate Nav1.7 expression to contribute to inflammator (...truncated)