Department of Plastic and Reconstructive Surgery, Department of Pediatrics, Department of Anesthesiology and Pain Medicine, Chungnam National University Hospital, Daejeon, 35015, Republic of Korea.
Department of Medical Science, Department of Physiology, Department of Anatomy, Brain Research Institute, Chungnam National University School of Medicine, Daejeon, 35015, Republic of Korea.
Mol Brain. 2018 Feb 27;11(1):11. doi: 10.1186/s13041-018-0354-y.
Neuropathic pain is a complex, chronic pain state characterized by hyperalgesia, allodynia, and spontaneous pain. Accumulating evidence has indicated that the microglial Toll-like receptor 4 (TLR4) and autophagy are implicated in neurodegenerative diseases, but their relationship and role in neuropathic pain remain unclear. In this study, we examined TLR4 and its association with autophagic activity using a chronic constriction injury (CCI)-induced neuropathic pain model in wild-type (WT) and TLR4-knockout (KO) mice. The mice were assigned into four groups: WT-Contralateral (Contra), WT-Ipsilateral (Ipsi), TLR4 KO-Contra, and TLR4 KO-Ipsi. Behavioral and mechanical allodynia tests and biochemical analysis of spinal cord tissue were conducted following CCI to the sciatic nerve. Compared with the Contra group, mechanical allodynia in both the WT- and TLR4 KO-Ipsi groups was significantly increased, and a marked decrease of allodynia was observed in the TLR4 KO-Ipsi group. Although glial cells were upregulated in the WT-Ipsi group, no significant change was observed in the TLR4 KO groups. Moreover, protein expression and immunoreactive cell regulation of autophagy (Beclin 1, p62) were significantly increased in the neurons, but not microglia, of WT-Ipsi group compared with the WT-Contra group. The level of PINK1, a marker for mitophagy was increased in the neurons of WT, but not in TLR4 KO mice. Together, these results show that TLR4-mediated p62 autophagic impairment plays an important role in the occurrence and development of neuropathic pain. And what is more, microglial TLR4-mediated microglial activation might be indirectly coupled to neuronal autophage.
神经病理性疼痛是一种以痛觉过敏、感觉异常和自发性疼痛为特征的复杂慢性疼痛状态。越来越多的证据表明，小胶质细胞 Toll 样受体 4（TLR4）和自噬与神经退行性疾病有关，但它们在神经病理性疼痛中的关系和作用尚不清楚。在这项研究中，我们使用慢性缩窄性损伤（CCI）诱导的神经病理性疼痛模型，在野生型（WT）和 TLR4 敲除（KO）小鼠中检查了 TLR4 及其与自噬活性的关系。将小鼠分为四组：WT-对侧（Contra）、WT-同侧（Ipsi）、TLR4 KO-对侧（Contra）和 TLR4 KO-同侧（Ipsi）。CCI 后对坐骨神经进行行为学和机械性感觉异常测试以及脊髓组织的生化分析。与 Contra 组相比，WT 和 TLR4 KO 的 Ipsi 组的机械性感觉异常明显增加，而 TLR4 KO 的 Ipsi 组的感觉异常明显减少。尽管 WT-Ipsi 组的神经胶质细胞上调，但 TLR4 KO 组没有观察到明显变化。此外，与 WT-Contra 组相比，WT-Ipsi 组神经元中自噬（Beclin 1、p62）的蛋白表达和免疫反应性细胞调节显著增加，而小胶质细胞中则没有。神经元中 PINK1（一种线粒体自噬标志物）的水平在 WT 中增加，但在 TLR4 KO 小鼠中则没有。总之，这些结果表明，TLR4 介导的 p62 自噬障碍在神经病理性疼痛的发生和发展中起重要作用。更重要的是，小胶质细胞 TLR4 介导的小胶质细胞激活可能与神经元自噬间接偶联。
