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

为探讨中枢神经系统（CNS）损伤神经元轴突导向的机制，我们利用基因芯片技术筛选了神经营养素刺激后表达变化的基因。我们得到了超过一百个基因，显示出增强的表达。我们专注于几个基因，预计将发挥作用，轴突的指导，并决定进行详细的分析。我们发现，嵌合蛋白参与了神经元对某些抑制性分子的脱敏。神经营养素作用后小脑颗粒神经元嵌合蛋白表达增强。当嵌合蛋白异位过表达时，髓鞘相关糖蛋白对轴突生长的抑制作用降低到对照水平。相比之下，先前暴露于神经营养因子的作用通过使用siRNA敲除嵌合蛋白的基因而消除。因此，嵌合蛋白可以促进CNS损伤后的轴突再生。此外，我们对另一个基因，排斥导向分子（RGM）感兴趣。RGMa通过依赖于Rho/Rho-激酶途径的激活的机制抑制哺乳动物CNS神经突生长。RGMa表达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，并且在脊髓损伤后在损伤部位周围被诱导。我们开发了在体外有效阻断RGMa作用的RGMa抗体。对胸脊髓半切大鼠鞘内给予抗体可导致皮质脊髓束的显著轴突生长，并改善功能恢复。因此，RGMa在CNS损伤后限制轴突再生中起重要作用，并且RGMa抗体在以CNS再生失败为特征的临床病症中提供了可能的治疗剂。

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.