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      The Interaction Between Spinal PDGFRβ and μ Opioid Receptor in the Activation of Microglia in Morphine-Tolerant Rats

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          Abstract

          Purpose

          Opioid tolerance remains a challenging problem, which limits prolonged drug usage in clinics. Previous studies have shown a fundamental role of platelet-derived growth factor receptor β submit (PDGFRβ) in morphine tolerance. The aim of this study was to investigate the mechanisms of spinal PDGFRβ activation in morphine tolerance.

          Methods

          Rats were treated with morphine for 7 days and the effect of drug was evaluated by tail-flick latency test. By using Western blot and real-time PCR, the interaction between μ opioid receptor (MOR) and PDGFRβ in microglia activation, as well as related signaling pathways during morphine tolerance were investigated.

          Results

          Chronic PDGFRβ agonist could induce microglia activation in spinal cord and decrease the analgesic effect of morphine. PDGFRβ inhibitor suppressed microglia activation during the development of morphine tolerance. Furthermore, antagonizing MOR could effectively inhibit the phosphorylations of PDGFRβ and JNK. Blocking PDGFRβ had no influence on JNK signaling, while JNK inhibitor could decrease the phosphorylation of PDGFRβ.

          Conclusion

          These results provide direct evidence that repeatedly activating MOR by morphine could induce the transactivation of PDGFRβ via JNK MAPK in spinal cord, which leads to microglia activation during the development of morphine tolerance.

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          Most cited references 21

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          Chronic morphine induces downregulation of spinal glutamate transporters: implications in morphine tolerance and abnormal pain sensitivity.

          Tolerance to the analgesic effects of an opioid occurs after its chronic administration, a pharmacological phenomenon that has been associated with the development of abnormal pain sensitivity such as hyperalgesia. In the present study, we examined the role of spinal glutamate transporters (GTs) in the development of both morphine tolerance and associated thermal hyperalgesia. Chronic morphine administered through either intrathecal boluses or continuous infusion induced a dose-dependent downregulation of GTs (EAAC1 and GLAST) in the rat's superficial spinal cord dorsal horn. This GT downregulation was mediated through opioid receptors because naloxone blocked such GT changes. Morphine-induced GT downregulation reduced the ability to maintain in vivo glutamate homeostasis at the spinal level, because the hyperalgesic response to exogenous glutamate was enhanced, including an increased magnitude and a prolonged time course, in morphine-treated rats with reduced spinal GTs. Moreover, the downregulation of spinal GTs exhibited a temporal correlation with the development of morphine tolerance and thermal hyperalgesia. Consistently, the GT inhibitor l-trans-pyrrolidine-2-4-dicarboxylate (PDC) potentiated, whereas the positive GT regulator riluzole reduced, the development of both morphine tolerance and thermal hyperalgesia. The effects from regulating spinal GT activity by PDC were at least in part mediated through activation of the NMDA receptor (NMDAR), because the noncompetitive NMDAR antagonist MK-801 blocked both morphine tolerance and thermal hyperalgesia that were potentiated by PDC. These results indicate that spinal GTs may contribute to the neural mechanisms of morphine tolerance and associated abnormal pain sensitivity by means of regulating regional glutamate homeostasis.
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            Japanese encephalitis virus induces matrix metalloproteinase-9 expression via a ROS/c-Src/PDGFR/PI3K/Akt/MAPKs-dependent AP-1 pathway in rat brain astrocytes

            Background Japanese encephalitis virus (JEV) infection is a major cause of acute encephalopathy in children, which destroys central nervous system (CNS) cells, including astrocytes and neurons. Matrix metalloproteinase (MMP)-9 has been shown to degrade components of the basal lamina, leading to disruption of the blood-brain barrier (BBB) and to contribute to neuroinflammatory responses in many neurological diseases. However, the detailed mechanisms of JEV-induced MMP-9 expression in rat brain astrocytes (RBA-1 cells) are largely unclear. Methods In this study, the effect of JEV on expression of MMP-9 was determined by gelatin zymography, western blot analysis, RT-PCR, and promoter assay. The involvement of AP-1 (c-Jun and c-Fos), c-Src, PDGFR, PI3K/Akt, and MAPKs in these responses were investigated by using the selective pharmacological inhibitors and transfection with siRNAs. Results Here, we demonstrate that JEV induces expression of pro-form MMP-9 via ROS/c-Src/PDGFR/PI3K/Akt/MAPKs-dependent, AP-1 activation in RBA-1 cells. JEV-induced MMP-9 expression and promoter activity were inhibited by pretreatment with inhibitors of AP-1 (tanshinone), c-Src (PP1), PDGFR (AG1296), and PI3K (LY294002), and by transfection with siRNAs of c-Jun, c-Fos, PDGFR, and Akt. Moreover, JEV-stimulated AP-1 activation was inhibited by pretreatment with the inhibitors of c-Src, PDGFR, PI3K, and MAPKs. Conclusion From these results, we conclude that JEV activates the ROS/c-Src/PDGFR/PI3K/Akt/MAPKs pathway, which in turn triggers AP-1 activation and ultimately induces MMP-9 expression in RBA-1 cells. These findings concerning JEV-induced MMP-9 expression in RBA-1 cells imply that JEV might play an important role in CNS inflammation and diseases.
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              Calcium/Ask1/MKK7/JNK2/c-Src signalling cascade mediates disruption of intestinal epithelial tight junctions by dextran sulfate sodium.

              Disruption of intestinal epithelial tight junctions is an important event in the pathogenesis of ulcerative colitis. Dextran sodium sulfate (DSS) induces colitis in mice with symptoms similar to ulcerative colitis. However, the mechanism of DSS-induced colitis is unknown. We investigated the mechanism of DSS-induced disruption of intestinal epithelial tight junctions and barrier dysfunction in Caco-2 cell monolayers in vitro and mouse colon in vivo. DSS treatment resulted in disruption of tight junctions, adherens junctions and actin cytoskeleton leading to barrier dysfunction in Caco-2 cell monolayers. DSS induced a rapid activation of c-Jun N-terminal kinase (JNK), and the inhibition or knockdown of JNK2 attenuated DSS-induced tight junction disruption and barrier dysfunction. In mice, DSS administration for 4 days caused redistribution of tight junction and adherens junction proteins from the epithelial junctions, which was blocked by JNK inhibitor. In Caco-2 cell monolayers, DSS increased intracellular Ca(2+) concentration, and depletion of intracellular Ca(2+) by 1,2-bis-(o-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid tetrakis(acetoxymethyl ester) (BAPTA/AM) or thapsigargin attenuated DSS-induced JNK activation, tight junction disruption and barrier dysfunction. Knockdown of apoptosis signal-regulated kinase 1 (Ask1) or MKK7 blocked DSS-induced tight junction disruption and barrier dysfunction. DSS activated c-Src by a Ca2+ and JNK-dependent mechanism. Inhibition of Src kinase activity or knockdown of c-Src blocked DSS-induced tight junction disruption and barrier dysfunction. DSS increased tyrosine phosphorylation of occludin, zonula occludens-1 (ZO-1), E-cadherin and β-catenin. SP600125 abrogated DSS-induced tyrosine phosphorylation of junctional proteins. Recombinant JNK2 induced threonine phosphorylation and auto-phosphorylation of c-Src. The present study demonstrates that Ca(2+)/Ask1/MKK7/JNK2/cSrc signalling cascade mediates DSS-induced tight junction disruption and barrier dysfunction.
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                Author and article information

                Journal
                J Pain Res
                J Pain Res
                JPR
                jpainres
                Journal of Pain Research
                Dove
                1178-7090
                17 July 2020
                2020
                : 13
                : 1803-1810
                Affiliations
                [1 ]Department of Anesthesiology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology , Wuhan, People’s Republic of China
                Author notes
                Correspondence: Feng Gao Department of Anesthesiology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology , 1095 Jiefang Ave, Wuhan430030, People’s Republic of China Email fgao@tjh.tjmu.edu.cn
                Article
                255221
                10.2147/JPR.S255221
                7381827
                © 2020 Li 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. For permission for commercial use of this work, please see paragraphs 4.2 and 5 of our Terms ( https://www.dovepress.com/terms.php).

                Page count
                Figures: 4, References: 31, Pages: 8
                Funding
                This study was supported by the National Natural Science Foundation of China (Nos. 81974168, 81771191, 81471143).
                Categories
                Original Research

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