Macroscopic distribution pathways of apoE in CNS

描述(申请人提供)：载脂蛋白E(ApoE)是中枢神经系统中脂类的运输和新陈代谢所必需的。在载脂蛋白E的三种亚型(E2、E3和E4)中，E4是阿尔茨海默病(AD)的主要危险因素。在正常情况下，人们高度认识到 专门的成熟神经元将apoE的产生外包给星形胶质细胞，但apoE传递到神经元的机制尚不清楚。最近，一种促进间质液体(ISF)对流的全脑通路被证明在清除神经活动的副产物，包括淀粉样β蛋白方面发挥了重要作用。这一脑脊液(CSF)通道的血管周围系统我们建议测试这一想法，即淋巴系统也作为向神经元输送必要物质的全脑分配路径。我们选择测试载脂蛋白E的这一概念，因为脑载脂蛋白E独立于外周载脂蛋白E，脑脊液可能是载脂蛋白E的来源，而且因为脂质失调是AD的主要危险因素。我们的初步数据显示，(1)脂化的apoE(Lip-apoE)由淋巴系统循环，并通过动脉周围的流入进入脑内；(2)意外的是，荧光标记的Lip-apoE在穿透动脉(E4&lt；E3&lt；E2)周围的区域呈同型分布，(3)随着年龄的增长和Aqp4-/-小鼠，apoE的淋巴分布急剧减少。我们假设，淋巴系统对于全脑范围内apoE向神经元的分布是至关重要的，该系统的年龄相关故障使远离动脉的神经元无法获得形成和维持突触所需的胆固醇和必要的脂质。我们建议通过实验方法对这一新的全脑载脂蛋白E分布途径进行基本分析，主要目标如下：目标1将表征载脂蛋白E亚型的宏观传递和分布。目的2评估衰老和水通道蛋白4对条件诱导型Aqp4-/-和对照组小鼠载脂蛋白E亚型宏观分布的影响。目的3将使用特异性受体阻断抗体确定载脂蛋白E受体在宏观载脂蛋白E递送中的作用。我们假设apoE受体捕获apoE的效果取决于apoE亚型的不同，从而导致不同的分布图，而在衰老和Aqp4-/-动物中动脉周围对流脑脊液流入的减少将减少apoE的分布。这一概念的含义是，apoE在全脑范围内淋巴分布的失败导致了apoE亚型特异性相关疾病，包括脑淀粉样血管病(CAA)和AD。我们希望，这些研究将产生全新的靶点，通过改善载脂蛋白E的淋巴分布来减缓甚至预防AD相关的神经认知下降，而载脂蛋白E是一个迄今被忽视的靶点。

DESCRIPTION (provided by applicant): Apolipoprotein E (apoE) is essential for the transport and metabolism of lipids in the CNS. Of the three apoE isoforms (E2, E3 and E4), E4 is a major risk factor for Alzheimer's disease (AD). Under normal conditions, it is recognized that the highly specialized mature neurons outsource apoE production to astrocytes, but the mechanism for apoE delivery to neurons remains unclear. Recently, a brain-wide pathway that facilitates convective flow of interstitial fluid (ISF) was shown to play a major role in clearance of by-products of neural activity, including amyloid-beta. This perivascular system of cerebrospinal fluid (CSF) channels-termed the glymphatic system- allows solute exchange with parenchymal ISF by three main pathways: (1) influx of CSF via the peri-arterial space, (2) astrocytic aquaporin 4 (AQP4)-dependent convective flow of ISF through the brain parenchyma, and (3) efflux via para-venous clearance. We propose to test the idea that the glymphatic system also serves as a brain-wide distribution path for the delivery of essential substances to neurons. We choose to test this concept for apoE, since brain apoE is independent of peripheral apoE, CSF could be a source of apoE and because lipid dysregulation is a major risk factor for AD. Our pilot data show, (1) that lipidated apoE (lip-apoE) was circulated by the glymphatic system and entered brain ISF via peri-arterial influx; (2) unexpectedly, fluorescently-tagged lip-apoE was distributed in an isoform specific pattern of zones around penetrating arteries (E4< E3 < E2), and (3) glymphatic distribution of apoE was sharply reduced in aging and in Aqp4-/- mice. We hypothesize that the glymphatic system is critical for brain-wide distribution of apoE to neurons and that age-related failure of this system deprives neurons, located distant to the arteries, access to cholesterol and essential lipids needed for formation and maintenance of synapses. We propose to generate a basic analysis on this novel brain-wide pathway of apoE distribution by an experimental approach centered on the following objectives: Aim 1 will characterize the macroscopic delivery and distribution of apoE isoforms. Aim 2 will assess the effect of aging and AQP4 on the macroscopic distribution of apoE isoforms in conditional inducible Aqp4-/- and control mice. Aim 3 will determine the role of apoE receptors in the macroscopic apoE delivery using specific receptor blocking antibodies. We hypothesize that apoE receptors trap apoE with different efficacy dependent on the apoE isoforms, resulting in the differential distribution profiles, and that reduced peri-arterial convective CSF influx in aging and Aqp4-/- animals will reduce apoE distribution. The implication of the proposed concept is that failure of brain-wide glymphatic distribution of apoE contributes to apoE isoform specific related disorders, including cerebral amyloid angiopathy (CAA) and AD. Our hope is that these studies will generate entirely novel targets for slowing or even preventing AD related neurocognitive decline by improving the glymphatic distribution of apoE, a target that has been ignored so far.