Central post-stroke pain (CPSP) is a chronic and intolerable neuropathic pain syndrome following a cerebral vascular insult, which negatively impacts the quality of life of stroke survivors but currently lacks efficacious treatments. Though its underlying mechanism remains unclear, clinical features of hyperalgesia and allodynia indicate central sensitization due to excessive neuroinflammation. Recently, the crosslink between neuroinflammation and endoplasmic reticulum (ER) stress has been identified in diverse types of diseases. Nevertheless, whether this interaction contributes to pain development remains unanswered. Epoxyeicosatrienoic acids (EETs)/soluble epoxy hydrolase inhibitors (sEHi) are emerging targets that play a significant role in pain and neuroinflammatory regulation. Moreover, recent studies have revealed that EETs are effective in attenuating ER stress. In this study, we hypothesized that ER stress around the stroke site may activate glial cells and lead to further inflammatory cascades, which constitute a positive feedback loop resulting in central sensitization and CPSP. Additionally, we tested whether EETs/sEHi could attenuate CPSP by suppressing ER stress and neuroinflammation, as well as their vicious cycle, in a rat model of CPSP. Young male SD rats were used to induce CPSP using a model of thalamic hemorrhage and were then treated with TPPU (sEHi) alone or in combination with 14,15-EET or 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE, the EET antagonist), tunicamycin (Tm, ER stress inducer), or 4-PBA (ER stress inhibitor). Nociceptive behaviors, ER stress markers, JNK and p38 (two well-recognized inflammatory kinases of mitogen-activated protein kinase (MAPK) signaling) expression, and glial cell activation were assessed. In addition, some healthy rats were intrathalamically microinjected with Tm or lipopolysaccharide (LPS) to test the interaction between ER stress and neuroinflammation in central pain. Analysis of the perithalamic lesion tissue from the brain of CPSP rats demonstrated decreased soluble epoxy hydrolase (sEH) expression, which was accompanied by increased expression of ER stress markers, including BIP, p-IRE, p-PERK, and ATF6. In addition, inflammatory kinases (p-p38 and p-JNK) were upregulated and glial cells were activated. Intrathalamic injection of sEHi (TPPU) increased the paw withdrawal mechanical threshold (PWMT), reduced hallmarks of ER stress and MAPK signaling, and restrained the activation of microglia and astrocytes around the lesion site. However, the analgesic effect of TPPU was completely abolished by 14,15-EEZE. Moreover, microinjection of Tm into the thalamic ventral posterior lateral (VPL) nucleus of healthy rats induced mechanical allodynia and activated MAPK-mediated neuroinflammatory signaling; lipopolysaccharide (LPS) administration led to activation of ER stress along the injected site in healthy rats. The present study provides evidence that the interaction between ER stress and neuroinflammation is involved in the mechanism of CPSP. Combined with the previously reported EET/sEHi effects on antinociception and neuroprotection, therapy with agents that target EET signaling may serve as a multi-functional approach in central neuropathic pain by attenuating ER stress, excessive neuroinflammation, and subsequent central sensitization. The use of these agents within a proper time window could not only curtail further nerve injury but also produce an analgesic effect.

中文翻译：

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EETs/sEHi 通过阻断中风后疼痛模型中内质网应激和神经炎症之间的交联来减轻伤害感受

中枢性卒中后疼痛 (CPSP) 是脑血管损伤后的一种慢性且无法忍受的神经性疼痛综合征，对中风幸存者的生活质量产生负面影响，但目前缺乏有效的治疗方法。尽管其潜在机制仍不清楚，但痛觉过敏和异常性疼痛的临床特征表明过度神经炎症导致中枢敏感。最近，已经在多种疾病中发现了神经炎症和内质网 (ER) 应激之间的交联。然而，这种相互作用是否有助于疼痛的发展仍然没有答案。环氧二十碳三烯酸 (EET)/可溶性环氧水解酶抑制剂 (sEHi) 是在疼痛和神经炎症调节中发挥重要作用的新兴靶点。而且，最近的研究表明，EET 可有效减轻 ER 压力。在这项研究中，我们假设中风部位周围的 ER 应激可能会激活神经胶质细胞并导致进一步的炎症级联反应，从而构成一个正反馈回路，导致中枢敏化和 CPSP。此外，我们在 CPSP 大鼠模型中测试了 EET/sEHi 是否可以通过抑制 ER 应激和神经炎症以及它们的恶性循环来减弱 CPSP。年轻雄性 SD 大鼠使用丘脑出血模型诱导 CPSP，然后单独使用 TPPU (sEHi) 或与 14,15-EET 或 14,15-epoxyeicosa-5(Z)-enoic acid (14 ,15-EEZE，EET 拮抗剂）、衣霉素（Tm，ER 应激诱导剂）或 4-PBA（ER 应激抑制剂）。伤害感受行为、ER 压力标记、评估了 JNK 和 p38（丝裂原活化蛋白激酶 (MAPK) 信号传导的两种公认的炎症激酶）表达和神经胶质细胞活化。此外，一些健康大鼠在丘脑内显微注射 Tm 或脂多糖 (LPS)，以测试 ER 应激与中枢性疼痛中神经炎症之间的相互作用。对来自 CPSP 大鼠大脑的丘脑周围病变组织的分析表明，可溶性环氧水解酶 (sEH) 的表达降低，同时伴随着 ER 应激标志物的表达增加，包括 BIP、p-IRE、p-PERK 和 ATF6。此外，炎症激酶（p-p38 和 p-JNK）被上调，神经胶质细胞被激活。sEHi (TPPU) 的丘脑内注射增加了缩爪机械阈值 (PWMT)，降低了 ER 应激和 MAPK 信号传导的标志，并抑制病变部位周围小胶质细胞和星形胶质细胞的活化。然而，14,15-EEZE完全消除了TPPU的镇痛作用。此外，将 Tm 微量注射到健康大鼠的丘脑腹后外侧 (VPL) 核可诱导机械性异常性疼痛并激活 MAPK 介导的神经炎症信号；脂多糖 (LPS) 给药导致健康大鼠沿注射部位激活 ER 应激。本研究提供的证据表明，ER 应激和神经炎症之间的相互作用参与了 CPSP 的机制。结合先前报道的 EET/sEHi 对镇痛和神经保护的影响，使用靶向 EET 信号传导的药物治疗可以通过减轻 ER 应激作为中枢神经性疼痛的多功能方法，过度的神经炎症和随后的中枢敏化。在适当的时间窗口内使用这些药物不仅可以减少进一步的神经损伤，还可以产生镇痛作用。