Analysis for the maintenance of neuropathic pain regulated by protein degradation.

外周组织损伤、炎症或神经损伤会引起持续性疼痛超敏反应，如痛觉过敏和异常性疼痛。在慢性压迫性坐骨神经损伤大鼠中，鞘内应用poteasome抑制剂可减轻痛敏和异常性疼痛，这表明通过遍在蛋白-蛋白酶体系统的选择性蛋白降解可能在持续性疼痛的突触修饰中发挥作用。我们以前证明，谷氨酸受体的NMDA亚型的激活和随后产生的一氧化氮（NO）的神经元型NO合酶（nNOS）在脊髓参与维持神经病理性疼痛。本实验研究了泛素-蛋白酶体系统相关分子Fbx 2、CHIP、Mdm 2、UCHL 1和Usp 14在神经病理性疼痛和炎症性疼痛中的表达水平。泛素连接酶Fbx 2、CHIP和Mdm 2分别泛素化NMDA谷氨酸受体、nNOS和突触后密度95（PSD 95）的NR 1亚基。UCHL 1和Usp 14是去泛素化酶。L5脊神经切断后7 d脊髓Mdm 2 mRNA表达增加。Mdm 2介导的PSD 95降解可能影响神经病理性疼痛中nNOS与NMDA谷氨酸受体的相互作用以及AMPA谷氨酸受体的表达和内化。另一方面，足底注射完全弗氏佐剂诱导炎性疼痛后1天，脊髓中Fbx 2 mRNA的表达增加。Fbx 2泛素化NR 1的后转位胞外域，NR 1的降解可能参与炎性疼痛的发生。这些结果表明，神经病理性疼痛和炎症性疼痛可能是通过泛素-蛋白酶体系统的动态变化的突触组成，如谷氨酸受体和nNOS维持。

Persistent pain hypersensitivity such as hyperalgesia and allodynia is produced by peripheral tissue injury, inflammation or nerve injury. Interthecal application of poteasome inhibitors in rats with chronic constriction sciatic nerve injury attenuated hyperalgesia and allodynia, suggesting that the selective protein degradation via ubiquitin-proteasome system may play a role in synaptic modifications for persistent pain. We previously demonstrated that the activation of NMDA subtype of glutamate receptor and subsequent production of nitric oxide (NO) by neuronal NO synthase (nNOS) in the spinal cord are involved in the maintenance of neuropathic pain. Here, we studied the expression level of ubiquitin-proteasome system related molecules, Fbx2, CHIP, Mdm2, UCHL1 and Usp14, in mouse spinal cord during neuropathic pain and inflammatory pain. Ubiquitin ligases, Fbx2, CHIP and Mdm2, ubiquitinate NR1 subunit of NMDA glutamate receptor, nNOS and post-synaptic density 95 (PSD95), respectively. UCHL1 and Usp14 are de-ubiquitinating enzymes. The expression of Mdm2 mRNA was increased in the spinal cord 7 days after nerve injury produced by L5 spinal nerve transection. The degradation of PSD95 via Mdm2 may affect the interaction between nNOS and NMDA glutamate receptor and the surface expression and internalization of AMPA glutamate receptor in neuropathic pain. On the other hand, the expression of Fbx2 mRNA was increased in the spinal cord 1 day after inflammatory pain induced by intraplantar injection of complete Freund's adjuvant. Fbx2 ubiquitinates NR1 in the retrotranslocated ectodomain, and the degradation of NR1 may involve in the inflammatory pain. These results suggest that both neuropathic pain and inflammatory pain may be maintained by dynamic change of synaptic composition such as glutamate receptors and nNOS through the ubiquitin-proteasome system.