Macrophage Cholesterol Efflux During Inflammation

巨噬细胞具有多种调节胆固醇平衡的机制。 吸收/合成和输出。最重要的是促进外流的运输机制 过量的胆固醇进入细胞外受体。清除多余的胆固醇在血管壁中是至关重要的， 巨噬细胞摄取脂蛋白衍生的脂质可导致病理性胆固醇负荷 缺乏足够的清除系统。三磷酸腺苷结合盒(ABC)超家族的两个成员 跨膜转运蛋白ABCA1和Abcg1在预防胆固醇脂类中发挥关键作用 巨噬细胞中的蓄积。广泛的研究表明，ABCA1促进两者的外流 胆固醇和磷脂到低脂载脂蛋白，特别是载脂蛋白A-L。相比之下，出现了Abcg1 通过将细胞内胆固醇重新分配到质膜结构域来促进外流 由高密度脂蛋白去除，但不是血脂贫乏的载脂蛋白A-L。因此，影响载脂蛋白A-L脂化状态的因素可能 调节这两种转运蛋白的活性。在炎症期间，高密度脂蛋白经历了广泛的重塑 这会导致颗粒的产生，这些颗粒的大小、电荷和载脂蛋白都发生了显著的变化 脂肪含量。这些变化主要是由急性时相反应物血清淀粉样蛋白A引起的 (SaA)和IIA组分泌型磷脂酶A2。从多个实验室收集证据， 包括我们的，已经确定SAA，无论是以急性时相高密度脂蛋白或无脂形式提供的，都可以 促进巨噬细胞胆固醇外流。在初步数据中，我们提供了证据，证明在 胆固醇酯转运蛋白、磷脂耗竭的高密度脂蛋白颗粒由IIA组的sPLA2可导致 产生细小的、耗尽脂质的高密度脂蛋白颗粒。我们的目标是表明，急性肺炎的一个主要后果是 时相反应是从外周动员胆固醇的增加，并加速 巨噬细胞的胆固醇逆向运输。我们假设SAA和sPLA2促进巨噬细胞 通过修饰高密度脂蛋白受体和通过与巨噬细胞的直接相互作用，脂质外流。为了测试这一点 假设，我们提出了以下具体目标：1)证明炎症诱导 高密度脂蛋白的重塑产生底物，增强ABCA1和Abcg1依赖的外流；2) 探讨SAA和sPLA2促进巨噬细胞胆固醇外流的机制(S)；3) 测试SAA通过ABCA1和/或防止动脉粥样硬化性脂质堆积的假设 Abcg1依赖的机制。

Macrophages possess a number of mechanisms to regulate the balance between cholesterol uptake/synthesis and export. Of major importance are transport mechanisms that promote the efflux of excess cholesterol to extracellular acceptors. The removal of excess cholesterol is critical in the vessel wall, where macrophage uptake of lipoprotein-derived lipid can lead to a pathological cholesterol load in the absence of sufficient removal systems. Two members of the ATP binding cassette (ABC) superfamily of transmembrane transporters, ABCA1 and ABCG1, play critical roles in preventing cholesterol lipid accumulation in macrophages. Extensive studies have shown that ABCA1 promotes efflux of both cholesterol and phospholipids to lipid-poor apolipoproteins, in particular, apoA-l. In contrast, ABCG1 appears to promote efflux by redistributing intracellular cholesterol to plasma membrane domains accessible for removal by HDL, but not lipid-poor apoA-l. Thus, factors that affect the lipidated state of apoA-l may modulate the activity of these two transporters. During inflammation, HDL undergoes extensive remodeling that leads to the generation of particles that are significantly altered in size, charge, and apolipoprotein and lipid content. These alterations are primarily brought about by the acute phase reactants serum amyloid A (SAA) and Group IIA secretory phospholipase A2. Accumulating evidence from multiple laboratories, including ours, has established that SAA, either delivered as acute phase HDL or in a lipid-free form, can enhance macrophage cholesterol efflux. In Preliminary Data, we provide evidence that in the presence of cholesterol ester transfer protein, phospholipid depletion of HDL particles by Group IIA sPLA2 can lead to the generation of small, lipid-depleted HDL particles. We aim to show that a major consequence of the acute phase response is an increase in the mobilization of cholesterol from the periphery, and an accelerated rate of macrophage reverse cholesterol transport. We hypothesize that SAA and sPLA2 promote macrophage lipid efflux by modifying HDL acceptors and through direct interactions with macrophage cells. To test this hypothesis, we propose the following Specific Aims: 1) To demonstrate that inflammation-induced remodeling of HDL generates substrates that enhance ABCA1 and ABCG1-dependent efflux; 2) To investigate the mechanism(s) by which SAA and sPLA2 promote macrophage cholesterol efflux; and 3) To test the hypothesis that SAA protects against atherosclerotic lipid accumulation through an ABCA1 and/or ABCG1 -dependent mechanism.