Chylomicrons and endothelial biology

摘要 动脉粥样硬化的第一步是血管内皮细胞的跨内皮运动和内皮下积聚。 脂蛋白脂质内皮细胞（EC）转运LDL涉及两种受体：清道夫受体BI（SR-BI） 和激活素样激酶1（ALK 1）。我们发现EC也通过SR-BI内化未消化的乳糜微粒， 在溶酶体中加工它们，导致一些脂质作为脂滴储存，并释放小的细胞外基质。 囊泡（sEV），其导致巨噬细胞中的脂质积聚。虽然许多人认为乳糜微粒是 非致动脉粥样硬化和太大而不能穿过EC屏障，这个概念现在已经过时， 脂蛋白进入动脉是受体介导的过程。本项目的总体目标是确定 EC乳糜微粒摄取如何影响EC生物学，将脂质输送到动脉，并加速动脉粥样硬化。在 目的1，我们建议确定富含磷脂酰肌醇的脂蛋白如何影响脂质通过血管的转移， 内皮细胞我们提供的初步数据表明，N-末端apoB 18具有单独的配体结合， ALK 1和SR-BI的区域。我们将确定是否脂蛋白大小或载脂蛋白B的长度决定暴露， 这两个不同的地区。我们还将确定来自乳糜微粒调节的EC的sEV如何引起脂质过氧化， 在巨噬细胞中的积累，并确定从对照和 乳糜微粒处理的EC。在目标2中，我们提出了体内研究，以确定EC-乳糜微粒的作用， 组织脂质转运和动脉粥样硬化的摄取途径。我们提供的初步数据表明， 在脂蛋白脂酶（LpL）缺陷小鼠中积累的乳糜微粒增加动脉粥样硬化。我们将使用 基因修饰小鼠和敲除策略，以评估LDL和乳糜微粒脂质的摄取， 动脉，并将评估是否更广泛的动脉粥样硬化在小鼠与联合缺乏LpL和 LDL受体是由于高乳糜微粒血症。最后，我们将确定AAV介导的 apoB 18的过表达降低了体内EC对apoB脂蛋白的摄取并改变了动脉粥样硬化。完成 这些研究有望改变我们对乳糜微粒与血管疾病关系的看法， 动脉粥样硬化脂质积聚的新途径，并说明了一种可能的方法，以防止 阻止这些脂质进入动脉

ABSTRACT The first steps in atherosclerosis are the transendothelial movement and subendothelial accumulation of lipoprotein lipid. Endothelial cell (EC) transcytosis of LDL involves two receptors, scavenger receptor-BI (SR-BI) and activin-like kinase 1 (ALK1). We showed that ECs also internalize undigested chylomicrons via SR-BI and process them in lysosomes, leading to storage of some lipid as lipid droplets and the release of small extracellular vesicles (sEVs) that cause lipid accumulation in macrophages. While many have considered chylomicrons as non-atherogenic and too large to cross the EC barrier, this concept is now outdated with the understanding that lipoprotein entry into the artery is a receptor-mediated process. The overall goal of this project is to determine how EC chylomicron uptake affects EC biology, delivers lipids to the artery, and accelerates atherosclerosis. In Aim 1, we propose to determine how triglyceride-rich lipoproteins affect lipid transfer across the vascular endothelium. We provide preliminary data suggesting that N-terminal apoB18 has separate ligand binding regions for ALK1 and SR-BI. We will determine whether lipoprotein size or apoB length determines exposure of these two different regions. We also will determine how sEVs from chylomicron-conditioned ECs cause lipid accumulation in macrophages and determine the differences between sEVs released from control and chylomicron-treated ECs. In Aim 2, we propose in vivo studies to determine the role of the EC-chylomicron uptake pathway in tissue lipid delivery and atherosclerosis. We provide preliminary data suggesting that chylomicrons that accumulate in lipoprotein lipase (LpL) deficient mice increase atherosclerosis. We will use genetically modified mice and knockdown strategies to assess the uptake of LDL and chylomicron lipids into arteries and will assess whether more extensive atherosclerosis in mice with combined deficiency of LpL and the LDL receptor is due to hyperchylomicronemia. Finally, we will determine whether AAV-mediated overexpression of apoB18 reduces EC uptake of apoB lipoproteins in vivo and alters atherosclerosis. Completion of the proposed studies promises to alter our view of the relationship of chylomicrons to vascular disease, define a novel pathway for arterial accumulation of atherogenic lipids, and illustrate a possible approach to prevent these lipids from entering the artery.