Assessing the role of APOE in glial lipid droplet metabolism and function

摘要 阿尔茨海默病（Alzheimer's disease，AD）是老年人致残和依赖性的主要原因之一 是美国第六大死亡原因。迟发性AD是最常见的形式， 超过99%的AD病例发生在65岁以后。最强的遗传风险因素发展 晚发性AD携带APOE4等位基因载脂蛋白E（APOE）主要由神经胶质细胞表达， 脑中的脂蛋白，是由星形胶质细胞和小胶质细胞分泌的脂蛋白颗粒的主要蛋白组分。 脂蛋白颗粒提供了胶质细胞和神经元之间脂质转运的双向机制。许多 最近的研究表明，神经系统脂质的不平衡与以下风险的增加有关： 发展AD。然而，APOE 4影响细胞脂质稳态的机制是 不完全理解。我们最近发现，在胶质细胞中，APOE可以运输到细胞质脂滴， (LDs)而不是在脂蛋白颗粒上进行分泌。我们假设APOE在之前 通过直接作用于星形胶质细胞和小胶质细胞中的LD，在细胞脂质代谢中发挥未被认识的作用。 星形胶质细胞在过氧化脂质代谢中发挥重要作用，而小胶质细胞是主要的先天性 中枢神经系统的免疫效应细胞。在目标1中，我们将测试调节APOE在 星形胶质细胞对细胞脂质组成、代谢和脂质过氧化的影响。在目标2中，我们将测试效果 调节小胶质细胞中的APOE对细胞脂质组成、代谢和炎症的影响。在目标3中， 我将通过开发一个社区资源来填补一个关键的知识空白，该资源将各种LD可视化和量化。 不同基因型和年龄的小鼠的脑区和细胞类型。总之，这些研究将导致 关于APOE 4表达导致增加的细胞和分子机制的新见解 迟发性AD的风险。这项工作也可能导致识别新的药物靶点， 治疗AD。

ABSTRACT Alzheimer’s disease (AD) is one of the predominant causes of disability and dependency among older people, and the sixth leading cause of death in the United States. Late-onset AD is the most common form, with more than 99% of AD cases occurring after age 65. The strongest genetic risk factor for developing late-onset AD is carrying the APOE4 allele. Apolipoprotein E (APOE) is primarily expressed by glial cells in the brain and is the major protein component of lipoprotein particles secreted by astrocytes and microglia. Lipoprotein particles provide a bidirectional mechanism of lipid transport between glia and neurons. Many recent studies suggest that a disequilibrium in nervous system lipids is associated with increased risk of developing AD. However, the mechanisms by which APOE4 affects cellular lipid homeostasis are incompletely understood. We recently discovered that in glia, APOE can traffic to cytoplasmic lipid droplets (LDs) rather than undergoing secretion on lipoprotein particles. We hypothesize that APOE plays previously unrecognized roles in cellular lipid metabolism by acting directly on LDs in astrocytes and microglia. Astrocytes play important roles in metabolizing peroxidated lipids, while microglia are the primary innate immune effector cells of the central nervous system. In Aim 1, we will test the effect of modulating APOE in astrocytes on cellular lipid composition, metabolism, and lipid peroxidation. In Aim 2, we will test the effect of modulating APOE in microglia on cellular lipid composition, metabolism, and inflammation. In Aim 3, we will fill a key knowledge gap by developing a community resource visualizing and quantifying LDs in various brain regions and cell types in mice of different genotypes and ages. Together, these studies will lead to new insights about the cellular and molecular mechanism by which expression of APOE4 leads to increased risk of late-onset AD. This work could also lead to the identification of novel drug targets for preventing and treating AD.