Towards investigating apolipoprotein E genotypes on the metabolism of long chain fatty acids

长链多不饱和脂肪酸（LC-PUFA）几乎完全由饮食提供。它们对于维持细胞膜的物理性质和诱导许多不同细胞类型的基因表达或抑制是重要的。LC-PUFA主要通过含有载脂蛋白E （APOE）蛋白的循环脂蛋白传递到器官。该蛋白在人体内存在三种亚型，即APOE2、APOE3和APOE4。我们最近在人类APOE4携带者中发现，LC-PUFA在血浆总脂中的分布存在不平衡。这些不平衡可能会使LC-PUFA的细胞含量失调，从而导致基因表达或抑制功能障碍。由于APOE在许多不同类型的细胞中表达，转基因小鼠敲入人类APOE基因型为研究APOE亚型在LC-PUFA稳态中的细胞来源依赖性作用提供了独特的工具。因此，我们的目的是阐明APOE基因型在LC-PUFA代谢和基因表达或抑制中的作用。为此，我们将使用携带人类APOE2、APOE3或APOE4基因型的转基因小鼠。在我们的第一个实验中，我们将使用三种碳13非放射性脂肪酸（示踪剂）在一个月内精确监测这些脂肪酸的代谢。在我们的第二个实验中，我们将给小鼠喂食以下四种饮食中的一种：A)控制饮食，B)富含omega-3 LC-PUFA的饮食，C)缺乏omega-3 LC-PUFA和其他omega-3脂肪酸的饮食，D)高脂肪饮食，会产生类似人类的脂蛋白水平。由于这些饲料会改变肝脏、心脏和白色脂肪组织等器官的细胞含量，我们将量化LC-PUFA中的细胞含量，量化脂肪酸转运体和脂肪酸受体基因的表达，并量化它们各自的蛋白质水平。这项工作将有助于更好地了解一种特定的基因-饮食相互作用（LC-PUFA通过APOE基因型）如何改变LC-PUFA的全身稳态。考虑到LC-PUFA在细胞中的调节作用，这是一个重要的研究问题。

Long-chain polyunsaturated fatty acids (LC-PUFA) are provided almost exclusively by the diet. They are important to maintain the physical nature of cell membranes and induce gene expression or repression in many different cell types. LC-PUFA are mainly delivered to organs by circulating lipoproteins that contains apolipoprotein E (APOE) protein. There are three existing isoforms of this protein in human namely APOE2, APOE3 and APOE4. We have recently shown in humans carriers of APOE4 that there are imbalances in the distribution of LC-PUFA in plasma total lipids. These imbalances potentially deregulate the cellular content in LC-PUFA and hence induce dysfunctions in gene expression or repression. Since APOE is expressed in many different types of cells, transgenic mice knock-in for human APOE genotypes provide unique tools to study the cellular source-dependant role of APOE isoforms in LC-PUFA homeostasis. Therefore, our objective is to elucidate the role(s) of APOE genotypes on LC-PUFA metabolism and gene expression or repression. To do so, we will use transgenic mice carrying human APOE2, APOE3 or APOE4 genotype. In our first experiment, we will use three carbon 13 non-radioactive fatty acids (tracers) to monitor precisely the metabolism of these fatty acids over one month. In our second experiment, we will feed the mice one of the four following diets: A) a control diet, B) a diet enriched in omega-3 LC-PUFA, C) a diet deprived in omega-3 LC-PUFA and other omega-3 fatty acids and D) a high-fat diet that will produce human-like lipoprotein levels. Because these diets will change the cellular content of organs such as liver, heart and white adipose tissue, we will quantify the cellular content in LC-PUFA and quantify the expression of fatty acid transporters and fatty acid receptor genes and quantify their respective protein levels. This work will contribute to better understand how one specific gene-by-diet interaction (LC-PUFA by APOE genotypes) change the whole body homeostasis in LC-PUFA. This is an important question to investigate considering the regulatory role of LC-PUFA in the cells.