Pathology of traumatic injury to CNS axons

描述（由申请人提供）：在美国，创伤性脑损伤每年折磨200万人，其中许多人由于弥漫性轴索损伤而遭受持续性神经功能障碍。在创伤性脑损伤期间，轴突的剪切或拉伸引发进行性轴突损伤，最终导致轴突切断和神经元死亡。因为创伤性损伤最常引起延迟而不是立即的轴突切断，所以在轴突切断之前存在治疗干预的机会。为了阐明创伤性轴突损伤的细胞机制并确定治疗靶点，我们将在小鼠中进行动态视神经牵张损伤，准确复制创伤性损伤期间人脑中轴突所经历的损伤的生物力学。我们建议使用这个已建立的中枢神经系统轴突损伤模型来检验我们的工作假设，即创伤性轴突损伤后钙蛋白酶的激活会导致微管损伤和轴突运输受损，除非逆转，否则将导致轴突切断和神经元凋亡。在目标1中，我们将评估顺行和逆行快速轴突运输作为损伤严重程度的函数，并建立相对于轴突切断的运输损伤的时间过程。在目标2中，我们将通过微管相关蛋白的降解建立钙蛋白酶激活和轴突运输中断之间的机制联系。在目标3中，我们将测试我们的假设，即视神经轴突中轴突运输的长期中断导致视网膜神经节细胞（RGC）的凋亡。在目标4中，我们将使用IGF-1过表达小鼠和外源性IGF-1治疗，以确定是否IGF-1水平的升高可以逆转轴突损伤后的转运障碍，通过延迟RGC凋亡和上调细胞骨架蛋白的合成。由于中枢神经系统轴突的再生仍然是一个难以捉摸的目标，它是至关重要的，以干预病理级联的创伤性轴突损伤轴突切断术发生之前。视神经牵张损伤模型允许轴突病理与机械损伤参数或细胞体反应之间的相关性，这在全脑轴突损伤模型中是目前不可能的。通过利用这些独特的优势，我们希望确定轴突病理学中的关键介质和新的治疗策略，以有效地维持脆弱的神经元和修复轴突损伤前轴突切断。

DESCRIPTION (provided by applicant): Traumatic brain injury afflicts 2 million people each year in the United States, many of whom suffer persistent neurological disability as a result of diffuse axonal injury. Shearing or stretching of axons during traumatic brain injury initiates progressive axonal damage, ultimately leading to axotomy and neuronal death. Because traumatic injury most often causes delayed rather than immediate axotomy, the opportunity exists to intervene therapeutically prior to axotomy. To elucidate the cellular mechanisms underlying traumatic axonal injury and identify therapeutic targets, we will perform dynamic optic nerve stretch injury in mice, accurately replicating the biomechanics of injury experienced by axons in the human brain during traumatic injury. We propose to use this established model of central nervous system axonal injury to test our working hypothesis that activation of calpains after traumatic axonal injury causes microtubule damage and impairment of axonal transport which, unless reversed, will lead to axotomy and neuronal apoptosis. In Aim 1, we will evaluate anterograde and retrograde fast axonal transport as a function of injury severity and establish the time course of transport impairment relative to axotomy. In Aim 2, we will establish a mechanistic link between calpain activation and interruption of axonal transport via degradation of microtubule-related proteins. In Aim 3, we will test our hypothesis that prolonged disruption of axonal transport in optic nerve axons leads to apoptosis of retinal ganglion cells (RGCs). In Aim 4, we will use IGF-1 overexpressing mice and exogenous IGF-1 treatment to determine whether elevation of IGF-1 levels can reverse transport impairment after axonal injury by delaying RGC apoptosis and upregulating cytoskeletal protein synthesis. Because regeneration of central nervous system axons remains an elusive goal, it is vital to intervene in the pathologic cascade of traumatic axonal injury before axotomy occurs. The optic nerve stretch injury model allows correlations between axonal pathology and either mechanical injury parameters or the cell body response that are not currently possible in whole-brain axonal injury models. By exploiting these unique advantages, we hope to identify key mediators in axonal pathology and novel therapeutic strategies to effectively sustain the vulnerable neuron and repair axonal damage prior to axotomy.