Uncovering mechanical mechanisms of traumatic axonal injury

项目概要/摘要 在美国，脑震荡或轻度创伤性脑损伤（mTBI）每年影响约200万人。 直到最近才被认为是一个重大的健康问题。这种伤害绝不是“轻微的”，因为它会引起 在许多人中持续存在认知功能障碍。此外，人们越来越担心， 一次mTBI后的脆弱期，在此期间，第二次mTBI可能引起极大夸大的 病理生理效应尽管mTBI的影响，该领域才刚刚开始确定机制， 特别是对于重复性mTBI。尽管如此，有越来越多的证据表明创伤性轴突损伤 (TAI)在单次和重复性mTBI中起重要作用。本文的目标是研究TAI 与单次和重复性mTBI相关的机制。这将采用以下综合办法： 体外实验与计算机建模。我们的良好表征的体外TAI模型已被用于 进行开创性的观察，以确定随后在大范围内发现的TAI机制， 动物和人类TBI。使用这个模型，建议检查基本的生物力学阈值 通过检查对拉伸损伤的非线性粘弹性反应来控制微管（MT）失效。以来 所有的个别故障事件不能在原位访问，一个定量的超微结构计算模型， 轴突将被用来指导和解释实验工作。 目标1将集中于确定TAI失效的急性机制作为应变和应变率的函数。电子 显微镜，免疫荧光和轴突内钙的变化将用于检查机械 MT的断裂和微管稳定蛋白tau的解结合。一种新的计算模型，基于 在轴突的三维超微结构上，确定整个轴突水平的损伤阈值， 纳米水平，考虑到MT-tau结合，tau扩散和MT预张力。目标2将集中于 MT解聚、tau蛋白和轴突磷酸化/易位时空演变 TAI后的退化或恢复。目标1中的相同体外测量将在一段时间内使用 时间过程使用识别的损伤阈值参数。目标3将检查轴突的脆弱性， 损伤这种脆弱性将根据MT稳定性、tau易位和轴突的能力进行评估， 在第一次受伤后恢复。将确定MT失效的应变和应变率阈值。一 根据tau、MT的磷酸化密度的时空演变的计算模型 聚合动力学和应力分布将被开发，以预测脆弱性标准， 应力、应变率、MT长度和二次损伤时间。预计生成的数据将揭示 生物力学阈值和单一和重复性创伤性轴突损伤的新机制， 与人类轻度创伤性脑损伤有关

Project Summary/Abstract Affecting approximately 2 million people in the US each year, concussion or mild traumatic brain injury (mTBI) has only recently been recognized as a major health issue. This injury is by no means `mild' since it induces persisting cognitive dysfunction in many individuals. Moreover, there is increasing concern that there may be a period of vulnerability after one mTBI, during which time a second mTBI may induce greatly exaggerated pathophysiological effects. Despite the impact of mTBI, the field has only just begun to identify mechanisms, especially with regards to repetitive mTBI. Nonetheless, there is mounting evidence that traumatic axonal injury (TAI) plays an important role in single and repetitive mTBI. The goal of the proposed work is to study TAI mechanisms that are relevant to single and repetitive mTBI. This will be done using an integrated approach of in vitro experimentation with computational modeling. Our well-characterized in vitro TAI model has been used to make seminal observations identifying mechanisms of TAI that have subsequently been found in large animal and human TBI. Using this model it is proposed to examine the fundamental biomechanical thresholds that govern microtubule (MT) failure by examining the non-linear viscoelastic response to stretch injury. Since all the individual failure events cannot be accessed in situ, a quantitative ultrastructural computational model of the axon will be used to guide and interpret experimental work. Aim 1 will focus on identifying acute mechanisms of TAI failure as a function of strain and strain rate. Electron microscopy, immunofluorescence and changes in intra-axonal calcium will be used to examine mechanical breaking of MTs and unbinding of the microtubule stabilizing protein tau. A novel computational model, based on the three-dimensional ultrastructure of the axon, identify injury thresholds at the level of the whole axon and nanometer level taking into account MT-tau binding, tau diffusion and MT pretension. Aim 2 will concentrate on the spatio-temporal evolution of MT depolymerization, phosphorylation / translocation of tau and axon degeneration or recovery following TAI. The same in vitro measures from Aim 1 will be used over a temporal time course using identified injury threshold parameters. Aim 3 will examine axon vulnerability to a second injury. This vulnerability will be assessed in relation to MT stability, tau translocation and an axons ability to recover following the first injury. A strain and strain rate threshold for MT failure will be determined. A computational model following the spatiotemporal evolution of phosphorylated densities of tau, MT polymerization kinetics and stress distributions will be developed to predict vulnerability criterion based on stress, strain rate, MT length and time to a second injury. It is anticipated that the data generated will reveal biomechanical thresholds and new mechanisms of single and repetitive traumatic axonal injury that will be relevant to mild TBI in humans.