1 Departments of Anaesthesiology and Neurobiology, Duke University Medical Centre, Durham, NC, 27710, USA.
2 Centre for Translational Neuromedicine, University of Rochester Medical Centre, Rochester, NY, 14642, USA.
Brain. 2014 Aug;137(Pt 8):2193-209. doi: 10.1093/brain/awu140. Epub 2014 Jun 11.
Accumulating evidence suggests that spinal cord astrocytes play an important role in neuropathic pain sensitization by releasing astrocytic mediators (e.g. cytokines, chemokines and growth factors). However, it remains unclear how astrocytes control the release of astrocytic mediators and sustain late-phase neuropathic pain. Astrocytic connexin-43 (now known as GJ1) has been implicated in gap junction and hemichannel communication of cytosolic contents through the glial syncytia and to the extracellular space, respectively. Connexin-43 also plays an essential role in facilitating the development of neuropathic pain, yet the mechanism for this contribution remains unknown. In this study, we investigated whether nerve injury could upregulate connexin-43 to sustain late-phase neuropathic pain by releasing chemokine from spinal astrocytes. Chronic constriction injury elicited a persistent upregulation of connexin-43 in spinal astrocytes for >3 weeks. Spinal (intrathecal) injection of carbenoxolone (a non-selective hemichannel blocker) and selective connexin-43 blockers (connexin-43 mimetic peptides (43)Gap26 and (37,43)Gap27), as well as astroglial toxin but not microglial inhibitors, given 3 weeks after nerve injury, effectively reduced mechanical allodynia, a cardinal feature of late-phase neuropathic pain. In cultured astrocytes, TNF-α elicited marked release of the chemokine CXCL1, and the release was blocked by carbenoxolone, Gap26/Gap27, and connexin-43 small interfering RNA. TNF-α also increased connexin-43 expression and hemichannel activity, but not gap junction communication in astrocyte cultures prepared from cortices and spinal cords. Spinal injection of TNF-α-activated astrocytes was sufficient to induce persistent mechanical allodynia, and this allodynia was suppressed by CXCL1 neutralization, CXCL1 receptor (CXCR2) antagonist, and pretreatment of astrocytes with connexin-43 small interfering RNA. Furthermore, nerve injury persistently increased excitatory synaptic transmission (spontaneous excitatory postsynaptic currents) in spinal lamina IIo nociceptive synapses in the late phase, and this increase was suppressed by carbenoxolone and Gap27, and recapitulated by CXCL1. Together, our findings demonstrate a novel mechanism of astrocytic connexin-43 to enhance spinal cord synaptic transmission and maintain neuropathic pain in the late-phase via releasing chemokines.
越来越多的证据表明，脊髓星形胶质细胞通过释放星形胶质细胞介质（如细胞因子、趋化因子和生长因子）在神经病理性疼痛敏化中发挥重要作用。然而，星形胶质细胞如何控制星形胶质细胞介质的释放并维持晚期神经病理性疼痛仍然不清楚。星形胶质细胞连接蛋白 43（现在称为 GJ1）已被牵连到通过神经胶质合胞体的细胞溶质内容物的缝隙连接和半通道通讯，以及分别到细胞外空间。连接蛋白 43在促进神经病理性疼痛的发展中也起着至关重要的作用，但这种贡献的机制尚不清楚。在这项研究中，我们研究了神经损伤是否可以通过从脊髓星形胶质细胞中释放趋化因子来上调连接蛋白 43 以维持晚期神经病理性疼痛。慢性缩窄性损伤引起脊髓星形胶质细胞中的连接蛋白 43 持续上调超过 3 周。在神经损伤后 3 周给予脊髓（鞘内）注射 carbenoxolone（一种非选择性半通道阻滞剂）和选择性连接蛋白 43 阻滞剂（连接蛋白 43 模拟肽（43）Gap26 和（37,43）Gap27），以及星形胶质细胞毒素而不是小胶质细胞抑制剂，可有效减轻机械性痛觉过敏，这是晚期神经病理性疼痛的主要特征。在培养的星形胶质细胞中，TNF-α引起趋化因子 CXCL1 的明显释放，该释放被 carbenoxolone、Gap26/Gap27 和连接蛋白 43 小干扰 RNA 阻断。TNF-α还增加了星形胶质细胞培养物中的连接蛋白 43 表达和半通道活性，但不增加缝隙连接通讯。从皮质和脊髓制备的星形胶质细胞培养物。脊髓注射 TNF-α 激活的星形胶质细胞足以诱导持续的机械性痛觉过敏，而这种痛觉过敏被 CXCL1 中和、CXCL1 受体（CXCR2）拮抗剂和星形胶质细胞用连接蛋白 43 小干扰 RNA 预处理所抑制。此外，神经损伤持续增加脊髓 lamina IIo 伤害感受突触中的兴奋性突触传递（自发性兴奋性突触后电流）在晚期，这种增加被 carbenoxolone 和 Gap27 抑制，并通过 CXCL1 再现。总之，我们的研究结果表明，星形胶质细胞连接蛋白 43 通过释放趋化因子增强脊髓突触传递并维持晚期神经病理性疼痛的一种新机制。
