Capillary control of cerebral blood flow, and its disruption in small vessel disease

摘要 神经元缺乏能量储备，因此它们的生存依赖于不间断的、动态的 血液中营养物质的调节供应，这些营养物质通过密集的毛细血管网络输送。 因此，精确控制通过大脑微循环的血液流动对神经元来说是必不可少的。 健康。然而，血液在毛细血管网络中分布的机制 人们对此仍然知之甚少。增进我们对这一进程的理解是至关重要的，因为它日益 认识到脑血流动力学紊乱是脑部疾病最早的病理事件之一。 小血管疾病。周细胞是包裹形成血管内皮细胞的壁细胞。 毛细血管。我们广泛的初步数据首次显示，周细胞位于第一到 四级毛细血管分支对管腔压力变化有收缩和松弛的反应。这 观察表明，毛细网络产生的阻力不是恒定的， 均匀的，但更多的是可变的和动态的，为血流调节提供了新的曙光。 具体地说，我们发现压力诱导的周细胞收缩与自分泌相结合。 激活表皮生长因子受体(EGFR)，随后激活三磷酸肌醇(IP3) 信号转导和瞬时受体电位规范3(TRPC3)激活。使用一种成熟的 遗传性小血管疾病CADASIL小鼠模型的建立，我们进一步提出 致病机制抑制周细胞内EGFR的激活，导致毛细血管血液受损 流量自动调节。为了测试这些想法，我们进行了各种各样的新奇的、最先进的实验 使用完整的动物、自然组织和新分离的细胞的方法，并辅之以 复杂的计算模型。利用我们新开发的加压微动脉- 毛细血管体外准备，目标1将探索EGFR如何通过腔内压力和 激动剂诱导的血管收缩参与γ-1磷脂酶C(γ-1)的激活和IP3- 依赖的钙信号。AIM 2将确定将表皮生长因子受体和PLCγ1激活联系到 TRPC3通道开放引起膜去极化和收缩。最后，使用 以CADASIL的细胞外基质破坏特征为框架，AIM 3将提供第一个 EGFR及其上游调控周细胞收缩的机制 调节因子TIMP3，一种基质金属蛋白酶抑制剂，和ADAM17，一种金属蛋白酶， 调节EGFR配体HB-EGF的脱落。拟议的工作有可能提供一种 关于周细胞如何控制毛细血管血流分布的范式转变观点，因此，应该 为了解脑部小血管疾病奠定了基础。

Summary Neurons lack energy reserves and thus their survival depends on an uninterrupted, dynamically regulated supply of blood-borne nutrients, which are delivered through a dense capillary network. Precise control of the blood flow through the brain microcirculation is therefore essential for neuronal health. However, the mechanisms through which blood is distributed within the capillary network remains poorly understood. Furthering our understanding of this process is critical, as it is increasingly appreciated that disruption of brain hemodynamics is one of the earliest pathological events in cerebral small vessel diseases. Pericytes are mural cells that wrap around the endothelial cells forming the capillaries. Our extensive preliminary data show for the first time that pericytes located on the first to fourth order capillary branches constrict and relax in response to luminal pressure changes. This observation implies that the resistance created by the capillary network is not constant and homogeneous, but rather variable and dynamic, casting a new light on blood flow regulation. Specifically, we have found that pressure-induced constriction in pericytes engages the autocrine activation of the epidermal growth factor receptor (EGFR), subsequent inositol trisphosphate (IP3) signaling, and transient receptor potential canonical 3 (TRPC3) activation. Using a well-established genetic mouse model of CADASIL, a hereditary form of small vessel disease, we further propose that pathogenic mechanisms depress the EGFR activation in pericytes, resulting in impaired capillary blood flow autoregulation. To test these ideas, we engage a wide variety of novel, state-of-the-art experimental approaches using intact animals, native tissue, and freshly isolated cells, complemented by sophisticated computational modeling. Taking advantage of our newly developed pressurized arteriole- capillary ex vivo preparation, Aim 1 will explore how EGFR activation by intraluminal pressure and agonist-induced vasoconstriction contributes to γ1 phospholipase C (PLCγ1) activation and IP3- dependent Ca2+ signals. Aim 2 will determine the mechanism linking EGFR and PLCγ1 activation to TRPC3 channel opening to cause membrane depolarization and constriction. Finally, using extracellular matrix disruptions characteristic of CADASIL as a framework, Aim 3 will provide the first insights into the mechanisms by which pericyte contractility is regulated by EGFR and its upstream regulators TIMP3, a matrix metalloproteinase inhibitor, and ADAM17, a metalloproteinase that mediates shedding of the EGFR ligand, HB-EGF. The proposed work has the potential to provide a paradigm-shifting view on how pericytes control capillary blood flow distribution, and as such, should provide the foundation for understanding small vessel diseases of the brain.