Yousuf Muhammad Saad, Zubkow Kasia, Tenorio Gustavo, Kerr Bradley
Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB T6G 2E1, Canada.
Department of Anesthesiology and Pain Medicine, University of Alberta, Edmonton, AB T6G 2G3, Canada.
Neuroscience. 2017 Mar 6;344:178-186. doi: 10.1016/j.neuroscience.2016.12.046. Epub 2017 Jan 3.
Patients with multiple sclerosis (MS) often complain of neuropathic pain. According to the Gate Control Theory of Pain, spinal networks of GABAergic inhibitory interneurons are important in modulating nociceptive inputs from the periphery. Na+-K+-2Cl- co-transporter 1 (NKCC1) and K+-Cl- co-transporter 2 (KCC2) generally dictate the tone of GABA/glycine inhibition by regulating intracellular chloride concentrations. In this study, we investigated the role of NKCC1 and KCC2 in neuropathic pain observed in the animal model, experimental autoimmune encephalomyelitis (EAE), a commonly used model to study the pathophysiology of MS. Quantitative real-time polymerase chain reactions (qRT-PCR) analysis revealed no change in NKCC1 mRNA transcripts in dorsal root ganglia throughout EAE disease course. However, NKCC1 and KCC2 mRNA levels in the dorsal spinal cord were significantly reduced at disease onset and peak only to recover by the chronic time point. Similarly, Western blot data revealed a significant downregulation of NKCC1 and KCC2 in the dorsal spinal cord at disease onset but an upregulation of NKCC1 protein in the dorsal root ganglia at this time point. Treatment with bumetanide, an NKCC inhibitor, had no effect on mechanical hypersensitivity seen in mice with EAE even though it reversed the changes in the levels of NKCC1 and KCC2. We noted that bumetanide treatment, while effective at reversing the changes in monomeric KCC2 levels was ineffective at reversing the changes in oligomeric KCC2 which remained repressed. These results indicate that mechanical hypersensitivity in EAE is not mediated by altered levels of NKCC1.
多发性硬化症（MS）患者常诉说有神经性疼痛。根据疼痛的闸门控制理论，γ-氨基丁酸（GABA）能抑制性中间神经元的脊髓网络在调节来自外周的伤害性输入方面很重要。钠-钾-2氯协同转运蛋白1（NKCC1）和钾-氯协同转运蛋白2（KCC2）通常通过调节细胞内氯离子浓度来决定GABA/甘氨酸抑制的强度。在本研究中，我们调查了NKCC1和KCC2在动物模型实验性自身免疫性脑脊髓炎（EAE）中观察到的神经性疼痛中的作用，EAE是一种常用于研究MS病理生理学的模型。定量实时聚合酶链反应（qRT-PCR）分析显示，在整个EAE病程中，背根神经节中NKCC1 mRNA转录本没有变化。然而，背脊髓中NKCC1和KCC2的mRNA水平仅在疾病发作和高峰期显著降低，到慢性期时恢复。同样，蛋白质印迹数据显示，在疾病发作时，背脊髓中NKCC1和KCC2显著下调，但此时背根神经节中NKCC1蛋白上调。用布美他尼（一种NKCC抑制剂）治疗对EAE小鼠的机械性超敏反应没有影响，尽管它逆转了NKCC1和KCC2水平的变化。我们注意到，布美他尼治疗虽然能有效逆转单体KCC2水平的变化，但对逆转仍受抑制的寡聚体KCC2的变化无效。这些结果表明，EAE中的机械性超敏反应不是由NKCC1水平的改变介导的。
