Mechanisms of rapid paravascular fluid transport in the brain

描述(申请人提供)：今年在美国，将有近80万人罹患中风，成为全国第三大死因。大面积脑梗塞患者的主要死亡原因是脑水肿。在遭受大脑中动脉大面积中风的患者中，在事件发生后的第一周内死亡率接近80%。目前还没有持续有效的非手术治疗方法来直接缓解脑水肿。由于卒中后的脑水肿是由病变脑组织内的离子和水的运动所驱动的，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全面的了解。大脑没有传统的淋巴系统，所以新陈代谢废物通过基底层的运输从脑细胞外液体中清除出来。基底层是包裹着大脑毛细血管的鞘。以前的研究表明，沿着基底板的液体流动与蛛网膜下腔的脑脊液相通，构成了一条“血管旁液体运输途径”，起着事实上的脑淋巴系统的作用。然而，这种血管旁液体运输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双光子显微镜来表征这一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，这种血管旁液体的运输是定向的，液体从皮质表面沿着穿透小动脉向内移动到大脑毛细血管水平。在特定的目标1中，我将确定是否穿透小动脉后向内的血管旁运输，而细胞外液体的向外清除跟随小静脉。在具体目标2中，我将测试这种定向运输是否是由动脉搏动机械驱动的。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。在具体目标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血管周围终末足部的定向水流量，从而促进定向血管旁流量。这些拟议的研究将探索脑内水和溶质流动的调节机制，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。 公共卫生相关性：大面积中风的主要死亡原因是脑水肿，这是一种脑组织肿胀，没有直接有效的非手术治疗方法。脑水肿是大脑中正常的水运动的中断，对水运动在大脑中的调节方式缺乏了解，阻碍了开发有效治疗方法的努力。在这里，目的是确定水是如何沿着大脑血管外部流动的，并确定这种流动的停止是否会导致中风后的脑水肿。

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.