Mechanisms of rapid paravascular fluid transport in the brain

描述（由申请人提供）：今年在美国，近八十万人将罹患中风，成为全国第三大死因。脑水肿是大面积脑梗死患者死亡的主要原因。在那些患有大脑中动脉大中风的人中，在事件发生后的第一周内死亡率接近80%。对于脑水肿的直接缓解，目前还没有持续有效的非手术疗法。由于中风后的脑水肿是由患病脑组织内的离子和水的运动驱动的，因此临床有效治疗方法的发展将取决于对脑组织中水和溶质运动的分子机制的更完整理解。大脑没有传统的淋巴系统，因此代谢废物通过沿着基底层（一种围绕脑毛细血管的鞘）的运输从脑细胞外液中清除。以前的研究表明，流体流动沿着基板与蛛网膜下CSF室，构成了“血管旁液体运输途径”，作为一个事实上的脑淋巴系统的功能。然而，这种血管旁液体转运的机制和分子基础仍然缺乏特征。我建议利用传统的组织学方法，体外电生理学和体内2-光子显微镜来表征这种血管旁液体转运途径的力学和分子基础。我目前的初步数据表明，这种血管旁液体运输是定向的，与流体从皮质表面向内移动沿着穿透小动脉的水平，脑毛细血管。在具体目标1中，我将确定是否向内的血管旁运输遵循穿透小动脉，而向外清除细胞外液遵循小静脉。在具体目标2中，我将测试这种定向运输是否由动脉搏动机械驱动。我还提出了初步的数据表明，小鼠缺乏水通道蛋白-4（AQP 4）水通道表现出减少血管旁液体转运。在具体目标3中，我将评估星形胶质细胞NKCC 1离子共转运蛋白和AQP 4水通道的活性是否有助于血管周围终足的定向水通量，从而有助于定向血管旁通量。拟议的研究将探讨脑中的水和溶质流动的机制，除了他们的妥协条件下的脑缺血，并可能有重要的临床意义治疗这种情况。 公共卫生相关性：大中风死亡的主要原因是脑水肿，脑组织肿胀，没有直接有效的非手术治疗。脑水肿是大脑中适当的水运动的破坏，对大脑中水运动的调节方式的理解不足阻碍了开发有效治疗方法的努力。在这里，目的是确定水如何沿着大脑血管的外部流动，并确定这种流动的停止是否有助于中风后的脑水肿。

DESCRIPTION (provided by applicant): This year in the U.S., close to 800,000 people will suffer a stroke, making it the third leading cause of death nationwide. The major cause of death in patients with large cerebral infarctions is cerebral edema. Among those suffering large middle cerebral artery strokes, mortality rates approach 80% within the first week following the event. No consistently effective non-surgical therapy exists for the direct relief of cerebral edema. Because cerebral edema following stroke is driven by the movement of ions and water within diseased brain tissue, progress in the development of clinically effective treatments will depend upon a more complete understanding of the molecular mechanisms governing water and solute movement in brain tissue. The brain does not have a conventional lymphatic system, so metabolic waste is cleared from brain extracellular fluid by its transport along the basal lamina, a sheath that surrounds brain capillaries. Previous studies suggest that fluid flow along the basal lamina communicates with the subarachnoid CSF compartment, constituting a 'paravascular fluid transport pathway' that functions as a de facto brain lymphatic system. However, the mechanics and molecular basis of this paravascular fluid transport remain poorly characterized. I propose to utilize both conventional histological approaches, ex vivo electrophysiology and in vivo 2-photon microscopy to characterize the mechanics and molecular basis of this paravascular fluid transport pathway. I present preliminary data demonstrating that this paravascular fluid transport is directional, with fluid from the cortical surface moving inward along penetrating arterioles to the level of cerebral capillaries. In Specific Aim 1, I will determine whether inward paravascular transport follows penetrating arterioles while outward clearance of extracellular fluid follows venules. In Specific Aim 2 I will test whether this directional transport is driven mechanically by arterial pulsation. I also present preliminary data demonstrating that mice lacking the aquaporin-4 (AQP4) water channel exhibit reduced paravascular fluid transport. In Specific Aim 3, I will evaluate whether the activity of the astrocytic NKCC1 ion co-transporter and the AQP4 water channel facilitate directional water flux across perivascular endfeet, thus contributing to directional paravascular flux. The proposed studies will explore the mechanisms governing water and solute flow in the brain, in addition to their compromise under conditions of cerebral ischemia, and may have important clinical implications for the treatment of this condition. PUBLIC HEALTH RELEVANCE: The major cause of death from large strokes is cerebral edema, a swelling of brain tissue for which there is no direct and effective non-surgical treatment. Cerebral edema is a disruption of proper water movement in the brain, and a poor understanding of the way that water movement is regulated in the brain hampers efforts to develop effective treatments. Here, the aim is to define how water flows along the outside of blood vessels in the brain, and to determine if the stoppage of this flow contributes to cerebral edema following stroke.