Uncovering mechanical mechanisms of traumatic axonal injury

项目概要/摘要 脑震荡或轻度创伤性脑损伤 (mTBI) 每年影响美国约 200 万人 直到最近才被认为是一个重大健康问题。这种伤害绝不是“轻微”的，因为它会导致 许多人存在持续的认知功能障碍。此外，人们越来越担心可能会出现 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 病理生理作用。尽管 mTBI 产生了影响，但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，越来越多的证据表明创伤性轴索损伤 (TAI) 在单次和重复性 mTBI 中发挥着重要作用。拟议工作的目标是研究 TAI 与单次和重复性 mTBI 相关的机制。这将使用综合方法来完成 计算模型的体外实验。我们的特征良好的体外 TAI 模型已被使用 进行开创性观察，确定随后在大样本中发现的 TAI 机制 动物和人类 TBI。建议使用该模型来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响应来控制微管 (MT) 失效。自从 所有单独的失效事件都无法在原位访问，这是一种定量超微结构计算模型 轴突将用于指导和解释实验工作。 目标 1 将侧重于确定 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 的解离。一种新颖的计算模型，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将集中于 tau 和轴突 MT 解聚、磷酸化/易位的时空演化 TAI 后的退化或恢复。将在一段时间内使用与目标 1 相同的体外测量 使用确定的损伤阈值参数的时间过程。目标 3 将检查轴突脆弱性至第二个 受伤。该漏洞将根据 MT 稳定性、tau 易位和轴突能力进行评估 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基于以下的脆弱性标准 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 单次和重复性创伤性轴突损伤的生物力学阈值和新机制 与人类轻度 TBI 相关。

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.