Untangling the mechanisms of white matter damage in cerebral hypoperfusion

白色物质占人类大脑的一半以上，其正常功能对于神经元之间的快速通信至关重要。在衰老和痴呆期间发生的白色物质损伤与慢性脑血流量降低（灌注不足）有关，并且似乎涉及疾病发作后不同时间血管和周围脑组织中多种细胞类型的复杂变化。理解这些过程的进展一直受到无法跟踪细胞随时间变化的限制，并且缺乏对主要目标之一少突胶质细胞（包裹神经元的细胞，使其能够发送快速信号）实际上是如何受损的理解。然而，我们的新方法将在理解白色物质如何受损方面取得重大突破。我们开发了一种新的方法，使我们能够对清醒小鼠的一个主要白色物质束--胼胝体--中不同的脑细胞和血管成像。我们的方法将这些新测量的数据输入脑切片实验中，以确定潜在的机制，然后再测试干扰这些机制是否可以保护活小鼠在慢性脑灌注不足期间免受白色物质损伤。通过在这两种方法之间进行重要的对话，我们的目标是解开白色物质在慢性脑血流量降低期间受损的过程，并确定可能的治疗靶点。我们将首先测量清醒小鼠慢性脑灌注不足模型期间白色物质氧合（缺氧）的减少，以及死后组织中的脑组织和细胞损伤。然后，我们将在脑切片中重现这些氧合水平，以了解白色细胞中的机制受到这种缺氧水平的影响。为了了解灌注不足期间细胞功能如何变化，我们将跟踪由于大量白色物质细胞（少突胶质细胞，神经元，小胶质细胞-大脑的常驻免疫细胞-和血管）灌注不足而引起的体内功能变化，以了解哪些细胞首先受到影响，以更好地了解哪些细胞可能是白色物质损伤的主要驱动因素。利用这些信息，我们将在脑切片中测试缺氧是否会对这些细胞造成与灌注不足相同的损害，或者是否还涉及其他可能的途径--例如特定分子从血液泄漏到大脑中，然后，我们将应用不同的药物来确定操纵我们发现在炎症中被破坏的通路对不同细胞的影响。脑切片，必要时使用组合治疗来保护不同的细胞类型。以这种方式设计的干预措施最终将在体内进行测试，看看它们是否可以保留血管和少突胶质细胞的功能。因此，我们的方法将使以前不可能在体内的功能特性的变化，发生在脑灌注不足，通知详细询问导致细胞损伤的机制。它将使干预措施的设计能够从一开始就考虑不同药物对不同细胞类型的影响，然后允许在完整动物中测试这些设计的功效。我们希望它能对慢性低灌注对白色物质的影响有一个强有力的新认识，对了解人类小血管疾病和白色物质损伤的进展具有巨大的潜在临床意义。

White matter makes up over half of the human brain and its proper function is critical for fast communication between neurons. White matter damage that occurs during ageing and dementia is linked to chronically lowered brain blood flow (hypoperfusion) and appears to involve complex changes in multiple cell types in blood vessels and surrounding brain tissue at different times after disease onset. Progress in understanding these processes has been restricted by an inability to track cellular changes over time, and a lack of understanding of how one of the major targets, oligodendrocytes (cells which ensheath neurons allowing them to send fast signals), actually are damaged. However, our novel approach will allow major breakthroughs in understanding how white matter becomes damaged. We developed a new method that allows us to image different brain cells and blood vessels in a major white matter tract - the corpus callosum - of awake mice. Our approach feeds data from these new measurements into experiments in brain slices that allow underlying mechanisms to be identified, before in turn testing whether interfering with these mechanisms protects live mice from experiencing white matter damage during chronic cerebral hypoperfusion. By engaging a vital dialogue between these two approaches, we aim to untangle the processes by which white matter becomes damaged during chronically lowered brain blood flow and identify possible therapeutic targets. We will first measure the reduction in white matter oxygenation (hypoxia) during a model of chronic cerebral hypoperfusion in awake mice, and characterise tissue and cell damage in post mortem tissue. We will then recreate these levels of oxygenation in brain slices to understand what mechanisms in white matter cells are impacted by this level of hypoxia. To understand how cell function changes during hypoperfusion, we will track, in vivo functional changes due to hypoperfusion in lots of white matter cells (oligodendrocytes, neurons, microglia - the brain's resident immune cell - and blood vessels) to understand which cells are first affected, to better understand which cells might be primary drivers of white matter damage. Using this information, we will test, in brain slices, if hypoxia causes the same damage to these cells as does hypoperfusion, or whether other possible pathways are also involved - such as leakage of specific molecules into the brain from the blood, or release of molecules associated with inflammation.We will then apply different drugs to determine the effects on different cells of manipulating the pathways which we find are disrupted in brain slices, where necessary using a combination of treatments to protect different cell types. Interventions designed this way will finally be tested in vivo to see if they can preserve both vascular and oligodendrocyte function. Our approach will therefore enable previously impossible in vivo functional characterisation of the changes that occur during cerebral hypoperfusion to inform detailed interrogation of mechanisms leading to cell damage. It will enable design of interventions that account, from the onset, for the effect of different drugs on different cell types and then allow testing of the efficacy of these designs in the intact animal. We expect it to lead to a powerful new understanding of the effect of chronic hypoperfusion on white matter, with huge potential clinical relevance for understanding the progression of small vessel disease and white matter damage in humans.