Mechanism of axon guidance after injury to the central nervous system.

为了探讨中枢神经系统(CNS)损伤神经元轴突引导的机制，我们利用基因芯片技术筛选了神经营养因子刺激后表达变化的基因。我们得到了100多个基因，显示出增强的表达。我们专注于几个有望在轴突指导中发挥作用的基因，并决定进行详细的分析。我们发现嵌合体参与了神经元对某些抑制分子的脱敏。神经营养素作用后，嵌合体蛋白在小脑颗粒神经元中的表达增强。当嵌合体异位过度表达时，髓鞘相关糖蛋白对轴突生长的抑制作用降低到对照水平。相反，先前暴露于神经营养素的影响被使用siRNA的嵌合体基因敲除而消除。因此，嵌合体可能促进中枢神经系统损伤后轴突的再生。此外，我们还对另一个基因--排斥性引导分子(RGM)感兴趣。RGMa抑制哺乳动物中枢神经系统突起生长的机制依赖于Rho/Rho-Kinase通路的激活。在成年大鼠脊髓的少突胶质细胞、有髓纤维和神经元中观察到RGMa的表达，并在脊髓损伤后的损伤部位周围诱导表达。我们开发了一种RGMa抗体，在体外可以有效地阻断RGMa的作用。脊髓半横断大鼠鞘内注射抗体可显著促进皮质脊髓束轴突生长，促进功能恢复。因此，RGMa在限制中枢神经系统损伤后轴突再生方面发挥了重要作用，RGMa抗体在以中枢神经系统再生失败为特征的临床条件下提供了一种可能的治疗手段。

To explore the mechanism of axon guidance of the injured neurons in the cetral nervous system (CNS), we screened the genes whose expression was changed after stimulation with neurotrophins using microarray technique. We got more than one hundred genes that showed enhanced expression. We focus on several genes that are expected to play a role in axon guidance, and decide to perform detailed analysis. We found that chimaerins are involved in desensitization of the neurons to some inhibitory molecules. The expression of chimaerins are enhanced in the cerebellar granule neurons after exposure to neurotrophins. When chimaerins are ectopically overexpressed, inhibition of neurite outgrowth by myelin-associated glycoprotein is reduced to the control level. In contrast, the effect of prior exposure to neurotrophins is abolished by the gene knockdown of chimaerins using siRNA. Thus, chimaerins may promote axon regeneration after injury to the CNS. In addition, we are interested in another gene, repulsive guidance molecule (RGM). RGMa inhibits mammalian CNS neurite outgrowth by a mechanism dependent on the activation of the Rho/Rho-kinase pathway. RGMa expression is observed in oligodendrocytes, myelinated fibers, and neurons of the adult rat spinal cord, and is induced around the injury site following spinal cord injury. We developed an antibody to RGMa that efficiently blocks the effect of RGMa in vitro. Intrathecal administration of the antibody to rats with thoracic spinal cord hemisection results in significant axonal growth of the corticospinal tract, and improves functional recovery. Thus, RGMa plays an important role in limiting axonal regeneration after CNS injury, and the RGMa antibody offers a possible therapeutic agent in clinical conditions characterized by a failure of CNS regeneration.