Uncovering mechanical mechanisms of traumatic axonal injury

项目摘要/摘要 在美国，每年大约有200万人受到脑震荡或轻度创伤性脑损伤的影响 直到最近才被认为是一个主要的健康问题。这种伤害绝不是“轻微的”，因为它会引起 许多人持续存在认知功能障碍。此外，人们越来越担心，可能会有一个 一次mTBI后的脆弱期，在此期间，第二次mTBI可能会导致严重夸大 病理生理效应。尽管有大规模毁灭性武器的影响，该领域才刚刚开始确定机制， 尤其是关于重复的mTBI。尽管如此，越来越多的证据表明创伤性轴突损伤 (TAI)在单纯性和重复性mTBI中起重要作用。拟议工作的目标是研究TAI 与单次和重复性mTBI相关的机制。这将使用一种综合的方法来完成 体外实验与计算建模。我们特征良好的体外TAI模型已用于 进行开创性的观察，确定TAI的机制，随后在 动物和人类的脑外伤。利用这个模型，提出了检测基本生物力学阈值的方法。 它通过检测拉伸损伤的非线性粘弹性反应来控制微管(MT)的失效。自.以来 所有单独的故障事件都不能就地访问，这是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 将使用显微镜、免疫荧光和轴突内钙的变化来检查机械 MTS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和 纳米级考虑了MT-tau结合、tau扩散和MT预张力。目标2将专注于 MT解聚、tau和轴突磷酸化/易位的时空演变 TAI后的退变或恢复。来自目标1的相同的体外测量将在时间上使用 使用已识别的损伤阈值参数的时间进程。Aim 3将检查第二个轴突的脆弱性 受伤。这一脆弱性将通过MT稳定性、tau易位和轴突能力进行评估 在第一次受伤后恢复。将确定MT失效的应变和应变率阈值。一个 Tau、MT磷酸化密度时空演化的计算模型 将开发聚合动力学和应力分布来预测易损性准则 应力、应变率、MT长度和第二次损伤的时间。预计生成的数据将揭示 单纯性和重复性创伤性轴索损伤的生物力学阈值和新机制 与人类轻度脑损伤有关。

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.