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      Tumor necrosis factor α modulates sodium-activated potassium channel SLICK in rat dorsal horn neurons via p38 MAPK activation pathway

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          Abstract

          The dorsal horn (DH) of the spinal cord is the integrative center that processes and transmits pain sensation. Abnormal changes in ion channel expression can enhance the excitability of pain-related DH neurons. Sodium-activated potassium (K Na) channels are highly expressed particularly in the central nervous system; however, information about whether rat DH neurons express the SLICK channel protein is lacking, and the direct effects on SLICK in response to inflammation and the potential signaling pathway mediating such effects are yet to be elucidated. Here, using cultured DH neurons, we have shown that tumor necrosis factor-α inhibits the total outward potassium current I K and the K Na current predominantly as well as induces a progressive loss of firing accommodation. However, we found that this change in channel activity is offset by the p38 inhibitor SB202190, thereby suggesting the modulation of SLICK channel activity via the p38 MAPK pathway. Furthermore, we have demonstrated that the tumor necrosis factor-α modulation of K Na channels does not occur at the level of SLICK channel gating but arises from possible posttranslational modification.

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          Most cited references 20

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          MAP kinase and pain.

          Mitogen-activated protein kinases (MAPKs) are important for intracellular signal transduction and play critical roles in regulating neural plasticity and inflammatory responses. The MAPK family consists of three major members: extracellular signal-regulated kinases (ERK), p38, and c-Jun N-terminal kinase (JNK), which represent three separate signaling pathways. Accumulating evidence shows that all three MAPK pathways contribute to pain sensitization after tissue and nerve injury via distinct molecular and cellular mechanisms. Activation (phosphorylation) of MAPKs under different persistent pain conditions results in the induction and maintenance of pain hypersensitivity via non-transcriptional and transcriptional regulation. In particular, ERK activation in spinal cord dorsal horn neurons by nociceptive activity, via multiple neurotransmitter receptors, and using different second messenger pathways plays a critical role in central sensitization by regulating the activity of glutamate receptors and potassium channels and inducing gene transcription. ERK activation in amygdala neurons is also required for inflammatory pain sensitization. After nerve injury, ERK, p38, and JNK are differentially activated in spinal glial cells (microglia vs astrocytes), leading to the synthesis of proinflammatory/pronociceptive mediators, thereby enhancing and prolonging pain. Inhibition of all three MAPK pathways has been shown to attenuate inflammatory and neuropathic pain in different animal models. Development of specific inhibitors for MAPK pathways to target neurons and glial cells may lead to new therapies for pain management. Although it is well documented that MAPK pathways can increase pain sensitivity via peripheral mechanisms, this review will focus on central mechanisms of MAPKs, especially ERK.
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            Acute p38-mediated modulation of tetrodotoxin-resistant sodium channels in mouse sensory neurons by tumor necrosis factor-alpha.

            Tumor necrosis factor-alpha (TNFalpha) is a proinflammatory cytokine involved in the development and maintenance of inflammatory and neuropathic pain conditions. TNFalpha can have long-lasting effects by regulating the expression of a variety of inflammatory mediators, including other cytokines and TNFalpha itself. However, the speed with which TNFalpha induces tactile and thermal hypersensitivity suggests that transcriptional regulation cannot fully account for its sensitizing effects, and some recent findings suggest that TNFalpha may act directly on primary afferent neurons to induce pain hypersensitivity. In the present study, we show that peripheral administration of TNFalpha induces thermal hypersensitivity in wild-type mice but not in transient receptor potential vanilloid receptor TRPV1(-/-) mice. In contrast, TNFalpha produced equivalent mechanical hypersensitivity in TRPV1(-/-) mice and wild-type littermates, suggesting a role for TRPV1 in TNFalpha-induced thermal, but not mechanical, hypersensitivity. Because tetrodotoxin (TTX)-resistant Na+ channels are a critical site of modulation underlying mechanical hypersensitivity in inflammatory and neuropathic pain conditions, we tested the effects of TNFalpha on these channels in isolated mouse dorsal root ganglion (DRG) neurons. We report that acute application of TNFalpha rapidly enhances TTX-resistant Na+ currents in isolated DRG neurons. This potentiation of TTX-resistant currents by TNFalpha is dramatically reduced in DRG neurons from TNF receptor 1 (TNFR1) knock-out mice and is blocked by the p38 mitogen-activated protein kinase inhibitor SB202190 [4-(4-fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)1H-imidazole]. Mechanical hypersensitivity induced by peripherally applied TNFalpha is also significantly reduced by SB202190. These results suggest that TNFalpha may induce acute peripheral mechanical sensitization by acting directly on TNFR1 in primary afferent neurons, resulting in p38-dependent modulation of TTX-resistant Na+ channels.
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              Regulating excitability of peripheral afferents: emerging ion channel targets.

              The transmission and processing of pain signals relies critically on the activities of ion channels that are expressed in afferent pain fibers. This includes voltage-gated channels, as well as background (or leak) channels that collectively regulate resting membrane potential and action potential firing properties. Dysregulated ion channel expression in response to nerve injury and inflammation results in enhanced neuronal excitability that underlies chronic neuropathic and inflammatory pain. Pharmacological modulators of ion channels, particularly those that target channels on peripheral neurons, are being pursued as possible analgesics. Over the past few years, a number of different types of ion channels have been implicated in afferent pain signaling. Here we give an overview of recent advances on sodium, calcium, potassium and chloride channels that are emerging as especially attractive targets for the treatment of pain.
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                Author and article information

                Journal
                J Pain Res
                J Pain Res
                Journal of Pain Research
                Journal of Pain Research
                Dove Medical Press
                1178-7090
                2017
                25 May 2017
                : 10
                : 1265-1271
                Affiliations
                [1 ]Medical School of Southeast University
                [2 ]Department of Orthopaedics, Zhongda Hospital, Southeast University, Nanjing, People’s Republic of China
                Author notes
                Correspondence: Xiao-Tao Wu, Department of Orthopaedics, Zhongda Hospital, Southeast University, 87 Dingjia Bridge, Nanjing Shi, Jiangsu Sheng 210009, People’s Republic of China, Email wuxiaotao@ 123456medmail.com.cn
                Article
                jpr-10-1265
                10.2147/JPR.S132185
                5449117
                © 2017 Wang et al. This work is published and licensed by Dove Medical Press Limited

                The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License ( http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed.

                Categories
                Original Research

                Anesthesiology & Pain management

                p38 mapk, slick channel, neuropathic pain, dorsal horn, tnf-α

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