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

总结 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 通过密集的毛细血管网络输送的血液营养物质的调节供应。 因此，精确控制通过脑微循环的血流对于神经元的发育至关重要。 健康然而，血液在毛细血管网内分布的机制 仍然知之甚少。加深我们对这一过程的理解至关重要，因为它越来越多地 认识到脑血流动力学的破坏是脑缺血最早的病理事件之一， 小血管疾病周细胞是壁细胞，其围绕内皮细胞形成血管内皮细胞。 毛细血管。我们广泛的初步数据表明，第一次，周细胞位于第一， 第四级毛细血管分支响应于管腔压力变化而收缩和舒张。这 观察表明由毛细网络产生的阻力不是恒定的， 均匀的，而是可变的和动态的，铸造了一个新的光对血流调节。 具体地说，我们已经发现，压力诱导的收缩周细胞从事自分泌 表皮生长因子受体（EGFR）激活，随后三磷酸肌醇（IP 3） 信号传导和瞬时受体电位典型3（TRPC 3）激活。使用一个完善的 CADASIL是一种遗传性小血管疾病，我们进一步提出， 致病机制抑制EGFR在周细胞中的活化，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颖的，最先进的实验 方法使用完整的动物，天然组织和新鲜分离的细胞，辅以 复杂的计算模型利用我们新开发的加压小动脉- 毛细血管离体制备，目的1将探索EGFR如何通过腔内压力活化， 激动剂诱导的血管收缩有助于γ1磷脂酶C（PLCγ1）激活和IP 3- 依赖性Ca 2+信号。目的2将确定EGFR和PLCγ1激活与细胞凋亡之间的联系机制。 TRPC 3通道开放，导致膜去极化和收缩。最后利用 CADASIL作为框架的细胞外基质破坏特征，Aim 3将提供第一个 深入了解EGFR及其上游调控周细胞收缩性的机制 调节剂TIMP 3，一种基质金属蛋白酶抑制剂，和ADAM 17，一种金属蛋白酶， 介导EGFR配体HB-EGF的脱落。拟议的工作有可能提供一个 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 为了解脑小血管疾病提供了基础。

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.