Understanding the impact of capillary obstructions on brain angio-architecture and function

背景资料。毛细血管是营养和气体交换的主要场所，大脑包含数公里的毛细血管，以满足其对能量的苛刻需求。毛细血管网络被认为是维持大脑功能的关键，因为随着年龄的增长而出现的认知减退和某些神经退行性疾病与大脑毛细血管的丧失相关。大脑的毛细血管网络被低估的一个方面是它很容易阻塞，即使是在健康的动物身上也是如此。最近的研究表明，在任何给定的时刻，都会有一小部分毛细血管受阻。这并不令人惊讶，因为毛细血管天生就是狭窄的低压管道，必须通过相对较大的血细胞。虽然这些障碍中的大多数在几秒钟到几分钟内就被清除了，但有一小部分毛细血管仍然被堵塞的时间要长得多。我们最近发现，30%的持续性梗阻的毛细血管在21天内被修剪，而不是通过长出新的毛细血管来补偿。这导致了局部血液流动的长期扰动。利用这些信息，我们能够模拟和预测健康小鼠随年龄增长的毛细血管丢失，这与经验数据非常一致。鉴于这些新的发现，我们仍然没有很好的机制了解这些毛细血管障碍是如何被清除的，甚至它们对大脑功能有什么影响。初步发现和一般假设。来自我的实验室的初步数据表明，通过环境浓缩或药物作用来增加神经活动，可以增强梗阻清除，减少毛细血管损失。基于这些发现，我们假设，通过迄今尚不清楚的电路或分子机制，神经活动的增加对于清除障碍和维持大脑中的毛细血管血流至关重要。方法论方法。我们将成像自然发生的毛细血管阻塞或通过注射荧光微球来诱导它们，这会阻塞一小部分毛细血管，而不会导致可检测到的细胞死亡。小鼠的大脑将在活体或死后在脑切片中进行成像，以评估梗阻清除和毛细血管修剪率。我们将使用药理学、遗传学(病毒、Cre-Lox小鼠)、光学和化学遗传学方法来测试我们的三个主要目标：目标1：确定神经元活动在清除毛细血管障碍中的作用以及涉及哪些特定神经回路。目的2：了解神经活动如何通过影响毛细血管张力和血流来清除障碍。目的3：确定毛细血管阻塞对脑功能的影响/意义。意义重大。这项研究将为微循环障碍对脑功能的影响和调节其清除的机制提供基础知识，以便设计新的策略来维持健康的微循环系统，并在一生中保护大脑功能。

Background. Capillaries are the primary site of nutrient and gas exchange and the brain contains kilometers of capillaries to meet its energetically demanding needs. Capillary networks are assumed to be critical for maintaining brain function since decrements in cognition that occur with aging and certain neurodegenerative diseases correlate with the loss of brain capillaries. One underappreciated aspect of the brain's capillary network is that it is prone to obstruction, even in healthy animals. Recent studies have shown that at any given moment, a small fraction of capillaries are obstructed. This is not surprising since capillaries are inherently narrow, low pressure tubes that must pass relatively large blood cells. While the majority of these obstructions clear within seconds to minutes, a fraction of capillaries remain obstructed for much longer. We have recently shown that 30% of capillaries with persistent obstructions are pruned over 21 day period and are not compensated for by sprouting new capillaries. This led to a prolonged perturbation in local flow blood. Using this information, we were able to model and predict capillary loss with aging in healthy mice which fell closely in line with empirical data. In light of these new findings, we still do not have a good mechanistic understanding of how these capillary obstructions are cleared, or even what impact they have on brain function. Preliminary findings and general hypothesis. Pilot data from my lab indicate that increasing neural activity through environmental enrichment or pharmacology enhances obstruction clearance and reduces capillary loss. Based on these findings, we hypothesize that bouts of increased neural activity, through an as of yet understood circuit or molecular mechanism, is critical for clearing obstructions and maintaining capillary blood flow in the brain. Methodological approach. We will image naturally occurring capillary obstructions or induce them with injection of fluorescent microspheres, which blocks a small fraction of capillaries and do not lead to detectable cell death. The mouse brain will be imaged in vivo or post-mortem in brain sections to assess obstruction clearance and capillary pruning rates. We will use pharmacological, genetic (viruses, Cre-Lox mice), optical and chemo-genetic approaches to test our 3 broad aims: Aim 1: Define the role of neuronal activity in clearing capillary obstructions and what specific neural circuits are involved. Aim 2: Understand how neural activity dislodges obstructions by influencing capillary tone and blood flow. Aim 3: Determine the impact/significance of capillary obstructions on brain function. Significance. This research will provide fundamental knowledge regarding the impact of micro-circulatory obstructions on brain function and the mechanisms that regulate their removal, so that new strategies can be devised to maintain a healthy microcirculatory system and preserve brain function throughout life.