Mechanisms of rapid paravascular fluid transport in the brain

描述（由申请人提供）：今年在美国，近80万人将遭受中风，使其成为全国第三大死亡原因。脑水肿是大面积脑梗死患者死亡的主要原因。在大的大脑中动脉中风患者中，在事件发生后的第一周内死亡率接近80%。没有一致有效的非手术治疗存在直接缓解脑水肿。由于脑卒中后脑水肿是由病变脑组织内离子和水的运动驱动的，因此临床有效治疗的进展将取决于对控制脑组织中水和溶质运动的分子机制的更全面理解。大脑没有传统的淋巴系统，因此代谢废物从脑细胞外液中被清除，它沿着基底层（一种包围着脑毛细血管的鞘）运输。先前的研究表明，沿着基底膜的液体流动与蛛网膜下腔CSF室相通，构成了一个“血管旁液体运输通道”，其功能实际上相当于脑淋巴系统。然而，这种血管旁流体运输的力学和分子基础仍然不清楚。我建议利用传统的组织学方法，离体电生理学和体内双光子显微镜来表征这种血管旁液体运输途径的力学和分子基础。我提供的初步数据表明，这种血管旁液体运输是有方向性的，液体从皮质表面沿着穿透性小动脉向内移动到脑毛细血管水平。在特异性目标1中，我将确定向内的血管旁运输是否遵循穿透小动脉，而细胞外液的向外清除是否遵循小静脉。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。我还提供了初步数据，表明缺乏水通道蛋白-4 （AQP4）水通道的小鼠表现出血管旁液体运输减少。在Specific Aim 3中，我将评估星形细胞NKCC1离子共转运体和AQP4水通道的活性是否促进了血管周围终足的定向水通量，从而有助于定向血管旁通量。拟议的研究将探索脑内水和溶质流动的控制机制，以及它们在脑缺血条件下的妥协，并可能对这种情况的治疗具有重要的临床意义。

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.