Pathology of traumatic injury to CNS axons

描述(申请人提供)：在美国，每年有200万人遭受创伤性脑损伤的折磨，其中许多人由于弥漫性轴突损伤而患有持续性神经残疾。在创伤性脑损伤中，轴突的剪切或伸展会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导致延迟而不是立即的轴突切开，所以在轴突切开之前有机会进行治疗干预。为了阐明创伤性轴突损伤的细胞机制并确定治疗靶点，我们将进行小鼠动态视神经拉伸损伤，准确复制创伤期间人脑轴突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验证我们的工作假说，即创伤性轴突损伤后钙痛的激活会导致微管损伤和轴突运输障碍，除非这一点被逆转，否则将导致轴突切断和神经元凋亡。在目标1中，我们将评估轴突顺行和逆行快速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害的时间进程。在目标2中，我们将通过微管相关蛋白的降解来建立钙蛋白激活和轴突运输中断之间的机制联系。在目标3中，我们将验证我们的假设，即视神经轴突轴突运输的长期中断会导致视网膜神经节细胞(RGCs)的凋亡。在目标4中，我们将使用高表达IGF-1的小鼠和外源性IGF-1治疗来确定提高IGF-1水平是否可以通过延缓RGC凋亡和上调细胞骨架蛋白合成来逆转轴突损伤后的运输障碍。由于中枢神经系统轴突的再生仍然是一个难以实现的目标，因此在轴突切断术发生之前干预创伤性轴突损伤的病理级联是至关重要的。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，这在目前全脑轴突损伤模型中是不可能的。通过利用这些独特的优势，我们希望找出轴突病理中的关键介质和新的治疗策略，以便在轴突切断之前有效地维持脆弱的神经元和修复轴突损伤。

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.