Role of Myelin in Spinal Cord Regeneration

描述（由申请人提供）：成人CNS中轴突再生的主要障碍之一是与髓鞘相关的抑制剂，如MAG。然而，如果神经元cAMP水平升高，则在培养物和体内的抑制环境中，轴突生长都可以被促进，无论是用类似物如db cAMP还是通过用神经营养素引发神经元。发生自发CNS轴突再生的一种情况是背根神经节轴突，如果同一神经元（背根神经节（DRG）神经元）的外周分支在一周前受损-条件损伤（CL）效应，其是cAMP依赖性的。cAMP和CL效应都依赖于转录，上调的一个基因是精氨酸酶I（Arg I），这是多胺合成的关键。多胺，亚精胺，可以克服MAG在培养中的抑制作用，并促进视神经再生在体内。此外，亚精胺通过hypusinating真核起始因子5A（eIF 5A）激活激酶CDK 5促进再生，导致CDK 5激活剂p35的翻译增加。在目标1a中，将鉴定响应于多胺而活化的CDK 5底物，并表征其在克服抑制和促进体内再生中的作用。目的1b将解决神经营养因子和MAG信号通路之间的串扰，重点是MAG阻断神经营养因子激活小GT3，Rap 1的能力。强有力的初步数据表明，cAMP和CL效应都需要轴突中的局部翻译以促进抑制环境中的再生。在目标2中，将鉴定在CL和用db cAMP处理后的过程中增加的mRNA和微小RNA。在目的3中，将表征（过表达、敲低）在两种条件后增加的那些mRNA和微小RNA在培养物中MAG存在下促进再生和在体内促进再生中的可能作用。通过本提案中描述的实验，我们不仅将进一步理解已知促进体内再生的试剂的作用机制，而且将鉴定新试剂。这反过来将揭示新的干预和药物开发的目标，以促进轴突再生体内。

DESCRIPTION (provided by applicant): One of the major obstacles to axonal regeneration in the adult CNS is inhibitors associated with myelin, such as MAG. However, axonal growth can be encouraged in an inhibitory environment both in culture and in vivo if the neuronal cAMP levels are elevated, either with analogues such as db cAMP or by priming neurons with neurotrophins. One situation where spontaneous CNS axon regeneration does occur is of dorsal root ganglion axons if the peripheral branch of the same neuron, the dorsal root ganglion (DRG) neuron, is lesioned one week before - the conditioning lesion (CL) effect, which is cAMP dependent. Both the cAMP and the CL effects are dependent on transcription and one gen that is up-regulated is for the enzyme Arginase I (Arg I), which is key in the synthesis of polyamines. The polyamine, spermidine, can overcome inhibition by MAG in culture and promotes optic nerve regeneration in vivo. Furthermore, spermidine promotes regeneration by activating the kinase CDK5 by hypusinating the eukaryotic initiation factor 5A (eIF5A), resulting in an increase in translation of the CDK5 activator p35. In Aim 1a the CDK5 substrates that are activated in response to polyamine will be identified and characterized for their role in overcoming inhibition and promoting regeneration in vivo. Aim 1b will address the cross-talk between the neurotrophin and MAG signaling pathway, focusing on the ability of MAG to block the activation of the small GTPase, Rap1, by neurotrophin. Strong preliminary data suggest that both the cAMP and CL effects require local translation in the axon to promote regeneration in an inhibitory environment. In Aim 2 mRNA and microRNAs that increase in the processes after both a CL and treatment with db cAMP will be identified. In Aim 3 those mRNAs and microRNAs that increase after both conditions will be characterized (over-expression, knock-down) for a possible role in promoting regeneration in the presence of MAG in culture and in promoting regeneration in vivo. Through the experiments described in this proposal not only will our understanding be advanced of the mechanism of action of agents known to promote regeneration in vivo but novel agents will be identified. This in turn will reveal novel targets for intervention and drug development to promote axonal regeneration in vivo.