The Effects of GDNF on Peripheral Nerve Regeneration

描述（由申请人提供）：尽管及时和细致的手术重建，近端创伤性周围神经损伤后的恢复通常很差。失神经支配超过一年的肌肉的特征是纤维化和运动终板的丧失，即使再生轴突到达其运动靶点，也不能有效地重新神经支配。已经寻求能够增加轴突再生速率并在损伤后适当地引导再生的运动轴突沿着运动路径和引导再生的感觉轴突沿着感觉路径的试剂，以优化外周神经损伤的恢复。外源性神经营养因子和neuroimmunophilin配体的管理已被证明是可变的神经再生功效。胶质源性神经营养因子（GDNF）是一种特别有效的运动神经元存活因子，在周围神经损伤后的恢复中显示出一定的益处。然而，GDNF对轴突再生的速率和特异性（运动与感觉）的影响、其给药途径的重要性及其作用机制尚未在临床相关的外周神经损伤范例中进行严格测试。为了解决这些问题，我们已经开发了两个不同的系的转基因小鼠与GDNF过表达的中枢神经系统或外周肌肉的良好特征的模式。此外，这些小鼠在其大部分运动和感觉轴突中表达增强的黄色荧光蛋白或仅在少数外周运动神经中表达绿色荧光蛋白，以实现神经再生的连续跟踪。在我们的具体目标中，我们使用这些小鼠模型来研究神经损伤后中枢或外周GDNF过表达的神经增强作用。在目的1a和1b中，在近端和远端周围神经挤压和修复的横断损伤之间，从形态学和功能上比较了中枢或外周GDNF过表达的神经再生作用。我们还将研究GDNF介导的下游信号通路和GDNF介导的转录调控参与神经再生。在目的2a中，在用神经移植物或端侧修复以急性或延迟方式修复的横断损伤中评价来自中枢和外周来源的GDNF过表达的神经增强作用。在目的2b中，我们研究了GDNF和FK 506对坐骨神经横断损伤端端修复后神经再生的组织学和机制的累加效应。除了建立GDNF递送途径，外周或中枢，这将最有效地刺激周围神经损伤后的再生，在目标3中，我们利用我们的转基因模型来研究优先运动神经再支配-一个与周围神经外科医生具有极端临床相关性的概念。我们将确定营养支持的来源，目标或路径衍生的最有影响力的指导再生轴突到他们适当的目标。

DESCRIPTION (provided by applicant): Despite timely and meticulous surgical reconstruction, recovery following proximal traumatic peripheral nerve injuries is often poor. Muscles that are denervated for over a year are characterized by fibrosis and loss of motor end plates and cannot be effectively reinnervated even when regenerating axons reach their motor targets. Agents capable of increasing the rate of axonal regeneration and appropriately directing regenerating motor axons down motor paths and sensory axons down sensory paths after injury have been sought to optimize recovery from peripheral nerve injuries. The exogenous administration of neurotrophic factors and neuroimmunophilin ligands have demonstrated variable neuroregenerative efficacy. Glial-derived neurotrophic factor (GDNF) is an especially potent motor neuron survival factor that has shown some benefit in recovery following peripheral nerve injury. However, the effects of GDNF on the rate and specificity (motor vs. sensory) of axonal regeneration, the importance of its route of administration, and its mechanism of action have not been rigorously tested in clinically relevant peripheral nerve injury paradigms. To address these issues, we have developed two distinct lines of transgenic mice with well-characterized patterns of GDNF overexpression in the central nervous system or peripheral muscle. In addition, these mice express enhanced yellow fluorescent protein in most of their motor and sensory axons or green fluorescent protein in only a few peripheral motor nerves to enable serial tracking of nerve regeneration. In our specific aims we use these murine models to study the neuroenhancing effects of central or peripheral GDNF overexpression following nerve injury. In aims 1a and 1b, the neuroregenerative effects of central or peripheral GDNF overexpression are compared between proximal and distal peripheral nerve crush and repaired transection injuries both morphologically and functionally. We will also study GDNF-mediated downstream signaling pathways and GDNF-mediated transcriptional regulation involved in nerve regeneration. In aim 2a the neuroenhancing effects of GDNF overexpression from central and peripheral sources are evaluated in transection injuries repaired in an acute or delayed fashion with nerve grafts or end- to-side repair. In aim 2b we study the additive effects of GDNF and FK506 on nerve regeneration both histologically and mechanistically following end-to-end repair of sciatic nerve transection injury. In addition to establishing the route of GDNF delivery, peripheral- or central-, that will most effectively stimulate regeneration after peripheral nerve injury, in aim 3 we utilize our transgenic model to study preferential motor reinnervation - a concept with extreme clinical relevance to peripheral nerve surgeons. We will determine which source of trophic support, target- or pathway-derived has the most influence in directing regenerating axons to their appropriate targets.