APOE e4 negative regulation of microglia-astrocytes crosstalk in Alzheimer's disease

阿尔茨海默病（Alzheimer's disease，AD）是最常见的神经退行性疾病。小胶质细胞在 支持正常的CNS功能，但在疾病中可能导致神经变性。我们确定 稳态（M0）和神经变性（MGnD）小胶质细胞，也称为疾病相关小胶质细胞 (DAM)，这是由TGF β的相互抑制和APOE信号的诱导调节，在不同的细胞中， 神经退行性小鼠模型，包括AD。然而，这两种主要表型的作用以及它们如何 影响疾病进展仍然是一个主要问题。重要的是，靶向小胶质细胞APOE信号恢复 在急性和慢性脑缺血模型中与神经保护相关的小胶质细胞的稳态特征 神经变性APOE信号以细胞自主方式抑制PU.1和TGFβ信号。人类 APOE有三种变体：ε2、ε3和ε4。APOE ε4是晚发性阿尔茨海默病最强的遗传风险因素 疾病（负载）。我们的初步数据显示：1）人源化APOE在小胶质细胞中PU.1的表达增加 ε4小鼠; 2）APOE ε4在小胶质细胞中的表达损害小胶质细胞反应以诱导MGnD表型， 3)缺失小胶质细胞APOE ε4恢复APP/PS1小鼠与星形胶质细胞相关的MGnD表型 向Ab斑募集和减少神经炎斑。这些数据表明，APOE ε4信号转导 是APP/PS1小鼠小胶质细胞中的关键调节通路。基于这些发现，我们假设， 载脂蛋白E ε4携带者，载脂蛋白E ε4“锁定”小胶质细胞在其稳态，导致受损的吞噬功能， 功能和失调的小胶质细胞-星形胶质细胞串扰，这可能会产生根本性的后果， AD发展。我们将在以下目标中阐述我们的假设： 目的1：确定APOE ε4在小胶质细胞转录调控中的作用及其与小胶质细胞的相互作用。 AD患者和携带不同APOE等位基因的非痴呆患者的星形胶质细胞。我们将决定 人APOE ε4影响细胞应答、相互作用途径和功能的转录特征， 调节，重点是小胶质细胞和星形胶质细胞。 目的2：在单细胞分辨率下观察APOE ε4小胶质细胞和星形胶质细胞的空间差异。我们 将验证小胶质细胞和星形胶质细胞基因表达的差异在大脑中，使用免疫组化， 特异性标记和多重抗错荧光原位杂交（MERFISH）。 总之，本研究旨在验证APOE ε4是否损害转录、空间和功能 AD脑中MGnD-小胶质细胞的调节及其与星形胶质细胞的串扰。

Alzheimer’s disease (AD) is the most prevalent neurodegenerative disorder. Microglia play an essential role in supporting normal CNS functions, but in disease may contribute to neurodegeneration. We identified homeostatic (M0) and neurodegenerative (MGnD) microglia, also referred to as disease associated microglia (DAM), that are regulated by the reciprocal suppression of TGFb and induction of APOE signaling in different neurodegenerative mouse models including AD. However, the role of these two major phenotypes and how they affect disease progression remains a major question. Importantly, targeting microglial APOE signaling restored the homeostatic signature of microglia associated with neuroprotection in acute and chronic models of neurodegeneration. APOE signaling suppressed PU.1 and TGFβ signaling in a cell-autonomous manner. Human APOE has three variants: ε2, ε3, and ε4. APOE ε4 is the strongest genetic risk factor for late-onset Alzheimer’s disease (LOAD). Our preliminary data show: 1) Increased expression of PU.1 in microglia from humanized APOE ε4 mice; 2) Expression of APOE ε4 in microglia impaired microglial response to induce a MGnD phenotype and 3) Deletion of microglial APOE ε4 restored MGnD phenotype in APP/PS1 mice associated with astrocytes recruitment towards Ab-plaques and reduction in neuritic plaques. These data indicate that APOE ε4 signaling is a crucial regulatory pathway in microglia in APP/PS1 mice. Based on these findings, we hypothesize that in APOE ε4 carriers, APOE ε4 ‘locks’ microglia in their homeostatic state leading to impaired phagocytic functions and dysregulated microglia-astrocyte crosstalk, which could have fundamental consequences for AD development. We will address our hypothesis in the following aims: Aim 1: Determine the role of APOE ε4 on transcriptional regulation of microglia and their crosstalk with astrocytes in AD and non-demented subjects carrying different APOE alleles. We will determine whether human APOE ε4 affects transcriptional signatures of cellular response, interactive pathways, and functional regulation, focusing on microglia and astrocytes. Aim 2: Validate the spatial differences in APOE ε4 microglia and astrocytes at single-cell resolution. We will validate the differences in microglia and astrocytic gene expression in brain, using immunohistochemistry of specific markers and multiplexed error-robust fluorescence in situ hybridization (MERFISH). IN SUMMARY, this study aims to validate whether APOE ε4 impairs transcriptional, spatial, and functional regulation of MGnD-microglia and their crosstalk with astrocytes in AD brain.