Role of Cerebrovascular cells in tau processing following traumatic brain injury

脑外伤（TBI）的一个突出病理特征是脑内 过度磷酸化和聚集的tau物质。Tau是一种细胞质蛋白，据信 仅限于神经元的细胞内区室。然而，最近的几项研究调查了 tau蛋白在脑细胞外区室中的存在和作用，并已表明增加 细胞外环境中单体tau蛋白的水平在脑梗死的发病机制中起主要作用。 神经退行性tau蛋白病事实上，有报道称，脑中细胞外tau蛋白水平与 与TBI的临床结果相关。尽管细胞外tau蛋白的流行和潜在的重要性， 神经退行性疾病，很少了解细胞外tau蛋白是如何加工和消除的 从大脑中。我们的研究表明，脑血管壁细胞（周细胞和平滑肌细胞） 参与细胞外tau蛋白的加工和消除。与其他神经退行性疾病 我们观察到，在反复轻度脑缺血后， TBI（r-mTBI）。此外，来自r-mTBI动物的分离的脑血管不太能够内化， 比未受伤的动物。据我们所知，这些是第一次观察到扰动的研究， 脑创伤背景下的壁细胞表达和tau蛋白加工。重要的是，除了壁细胞， 在我们的小鼠r-mTBI模型中，我们观察到总tau蛋白、磷酸化tau蛋白和 低聚tau蛋白此外，我们发现，tau蛋白从大脑中的消除减少， 与野生型小鼠相比，转基因壁细胞耗尽的动物。我们认为脑血管壁 细胞作为处理和消除细胞外脑液中tau蛋白的途径， 这些细胞在TBI中的过度增殖导致tau病理学和神经变性。本项目的目标是确定 脑血管壁细胞对TBI中观察到的tau病理学的贡献。具体目标是 建议是，1）在壁细胞耗尽动物和人TBI中检查壁细胞状态和tau病理 2）评估壁细胞在tau降解和消除中的作用以及r-mTBI对这些的影响 3）确定壁细胞在血管旁（胶质淋巴）tau清除和血管周围tau清除中的作用。 r-mTBI后tau从脑中排出。为了确定TBI后的壁细胞状态，tau摄取和 将在来自壁细胞耗尽的动物的分离的血管系统中检查各种壁细胞标记物 和人类脑外伤样本为了了解壁细胞对tau蛋白分布的影响， 将在来自r-mTBI动物的分离的脑脉管系统中评价tau的降解，并且将在来自r-mTBI动物的分离的脑脉管系统中评价tau的消除。 将在壁细胞耗尽的动物和r-mTBI小鼠中检查脑。最后，为了了解 在r-TBI后，我们将检查血管旁细胞对脑液中细胞外tau蛋白运动的影响， （胶质淋巴）tau蛋白清除和血管周围tau蛋白从壁细胞耗尽的动物和r- mTBI小鼠。拟议的研究将促进我们对tau蛋白加工和消除的理解， 细胞外脑液，并确定脑血管壁细胞对tau病理学的贡献， 神经退行性表型。

One of the prominent pathological features of traumatic brain injury (TBI) is the accumulation of hyperphosphorylated and aggregated tau species in the brain. Tau is a cytoplasmic protein which is believed to be restricted to the intracellular compartment of neurons. However, several recent studies have investigated the existence and role for tau in the extracellular compartments of the brain, and have indicated that increased levels of monomeric tau in the extracellular environment play a major role in the pathogenesis of neurodegenerative tauopathies. In fact, it has been reported that extracellular tau levels in the brain correlate with clinical outcome in TBI. Despite the prevalence and potential importance of extracellular tau in neurodegenerative disease, there is little understanding of how extracellular tau is processed and eliminated from the brain. Our studies demonstrate that brain vascular mural cells (pericytes and smooth muscle cells) are involved in the processing and elimination of extracellular tau. Consistent with other neurodegenerative disorders, we observed a progressive decline in cerebrovascular mural cell expression following repetitive mild TBI (r-mTBI) in mice. Moreover, isolated brain vessels from r-mTBI animals were less able to internalize and process tau than non-injured animals. To our knowledge, these are the first studies to observe perturbations in mural cell expression and tau processing in the context of brain trauma. Importantly, alongside the mural cell disruptions in our mouse r-mTBI model, we observed an accumulation of total tau, phosphorylated tau, and oligomeric tau species in the brain. Additionally, we showed that tau elimination from the brain is reduced in transgenic mural-cell depleted animals compared to wild-type mice. We propose that brain vascular mural cells serve as a pathway for processing and eliminating tau from extracellular brain fluids and that disruption of these cells in TBI leads to tau pathology and neurodegeneration. The objective of this project is to determine the contribution of brain vascular mural cells to the tau pathology observed in TBI. The specific aims of this proposal are, 1) examine mural cell status and tau pathology in mural-cell depleted animals and human TBI brains, 2) evaluate the role of mural cells in tau degradation and elimination and the impact of r-mTBI on these processes, and 3) determine the role of mural cells in paravascular (glymphatic) tau clearance and perivascular tau drainage from the brain following r-mTBI. To determine mural cell status following TBI, tau uptake and various mural cell markers will be examined in isolated cerebrovasculature from mural-cell depleted animals and human TBI brain specimens. To understand the influence of mural cells on tau disposition, tau degradation will be evaluated in isolated brain vasculature from r-mTBI animals and tau elimination from the brain will be examined in mural-cell depleted animals and r-mTBI mice. Lastly, to understand the impact of mural cells on extracellular tau movement in brain fluids following r-TBI, we will examine both paravascular (glymphatic) tau clearance and perivascular tau drainage from the brain in mural-cell depleted animals and r- mTBI mice. The proposed studies will advance our understanding of tau processing and elimination from extracellular brain fluids and determine the contribution of brain vascular mural cells to tau pathology and the neurodegenerative phenotype following TBI.