The Effects of GDNF on Peripheral Nerve Regeneration

描述（申请人提供）：尽管手术重建及时细致，但创伤性近端周围神经损伤后的恢复往往很差。失去神经支配超过一年的肌肉表现为纤维化和运动端板的丧失，即使再生的轴突到达运动目标，也不能有效地再神经支配。为了优化周围神经损伤后的恢复，研究人员一直在寻找能够提高轴突再生速度并在损伤后适当地引导再生的运动轴突沿着运动路径和感觉轴突沿着感觉路径的药物。外源性给药神经营养因子和神经亲免疫素配体已显示出不同的神经再生功效。神经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周围神经损伤范式中得到严格检验。为了解决这些问题，我们开发了两种不同的转基因小鼠系，它们在中枢神经系统或外周肌肉中具有良好的GDNF过表达模式。此外，这些小鼠在其大部分运动和感觉轴突表达增强的黄色荧光蛋白，或仅在少数外周运动神经表达增强的绿色荧光蛋白，从而实现对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，从形态学和功能上比较了近端和远端周围神经压迫和修复的横断损伤中中枢或外周GDNF过表达的神经再生效果。我们还将研究gdnf介导的下游信号通路和gdnf介导的神经再生转录调控。在aim 2a中，通过神经移植或端侧修复，评估了中枢和外周来源的GDNF过表达在急性或延迟方式修复的横断损伤中的神经增强作用。在目的2b中，我们研究了GDNF和FK506对坐骨神经横断损伤端到端修复后神经再生的组织学和机制上的加性作用。除了建立最有效刺激周围神经损伤后再生的GDNF递送途径外，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生-这是一个与周围神经外科医生具有极端临床相关性的概念。我们将确定哪一种营养支持来源，目标或途径衍生的在将再生轴突定向到适当的目标方面影响最大。

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.