Role of Sphingomyelin in Lipoprotein Metabolism

性状（由申请方提供）：鞘磷脂（SM）是血浆中仅次于磷脂酰胆碱（PC）的最丰富的磷脂，是细胞膜筏的重要组分。虽然最近的流行病学研究表明，血浆中高SM水平增加动脉粥样硬化的风险，但其潜在机制尚不清楚，因为SM的正常功能尚未阐明。我们建议，由于其独特的结构，并定位在细胞的外表面，SM保护细胞膜的完整性，通过抑制磷脂酶和脂质过氧化反应。此外，我们提出，由于其亲和力的胆固醇，SM调节细胞胆固醇稳态和逆转胆固醇转运。这些功能的失调可导致炎症并促进动脉粥样硬化。在目的1中，我们提出了测试的假设，SM调节胆固醇逆向转运，重点是它的作用，在流出的巨噬细胞的胆固醇，并在酯化胆固醇的LCAT。新的假设，SM作为一个伴侣的胆固醇在ABCG 1转运介导的外流将进行探讨。将研究SM在生理系统中调节LCAT的作用。在目标2中，我们将研究SM通过抑制促炎脂质如溶血PC、花生四烯酸、氧化磷脂和氧化固醇的形成而作为抗炎脂质的假设。SM竞争性抑制所有酶，利用PC作为底物的假设将测试分泌型磷脂酶和内皮脂肪酶。SM在促炎性氧化PC和氧固醇生成中的抑制作用将在脂蛋白和细胞膜中进行测试。将在骨髓特异性SM缺陷小鼠中研究SM缺陷对巨噬细胞和中性粒细胞功能的影响，包括细胞因子产生和超氧化物生成。在目标3中，SM和神经酰胺在细胞胆固醇稳态中的作用将通过确定它们对细胞区室之间以及细胞与其环境之间的胆固醇运输的影响来研究。这些研究将为这种重要磷脂的生理作用提供新的见解，并可能确定对抗炎症和动脉粥样硬化的新治疗靶点。公共卫生相关性：鞘磷脂（SM）是一种存在于血浆和细胞外膜中的特殊脂质分子，本文拟对其生理作用进行研究。他们将特别关注SM作为抗炎分子的作用，保护细胞免受环境的侵害。这些研究不仅可以导致对炎症和心脏病机制的新理解，还可以导致更好的治疗策略。 首先，是否有任何巨噬细胞途径的胆固醇代谢，是向上或向下调节的消融ABCG 1？细胞胆固醇含量、胆固醇酯酶、ACAT、ABCA 1或可能的SR-B1可能会发生变化，从而影响外排。第二，存在影响外排的其他机制，特别是自发转移，Rothblat等人已经证明其在某些情况下是重要的（ATVB 2006 26：541-7）和由apo E介导的外排（ATVB 2006 26：157-62）。最后，通过测量培养基和细胞胆固醇含量的非放射性示踪剂方法，将流出量与胆固醇的净变化进行比较将是有用的。放射性示踪剂揭示了FC离开细胞的速度，但没有揭示有多少未标记的胆固醇从培养基中的供体重新进入细胞。

DESCRIPTION (provided by applicant): Sphingomyelin (SM) is the most abundant phospholipid in plasma next to phosphatidylcholine (PC), and is an essential component of cell membrane rafts. Although recent epidemiologic studies suggest that high SM levels in plasma increase the risk of atherosclerosis, the underlying mechanisms are unknown, because the normal functions of SM have not been elucidated. We propose that, because of its unique structure, and localization in the outer surface of cells, SM protects the integrity of cell membranes by inhibiting the phospholipase and lipid peroxidation reactions. Furthermore, we propose that because of its affinity to cholesterol, SM regulates cell cholesterol homeostasis and reverse cholesterol transport. Dysregulation of these functions could lead to inflammation and promote atherosclerosis. In Aim 1, we propose to test the hypothesis that SM regulates reverse cholesterol transport, focusing on its role in the efflux of cholesterol from macrophages, and in the esterification of cholesterol by LCAT. The novel hypothesis that SM acts as a chaperone for cholesterol during ABCG1 transporter-mediated efflux will be explored. The role of SM in the regulation of LCAT in physiological systems will be studied. In Aim 2, we will investigate the hypothesis that SM acts as an anti-inflammatory lipid by inhibiting the formation of pro-inflammatory lipids such as lyso PC, arachidonate, oxidized phospholipids and oxysterols. The hypothesis that SM competitively inhibits all enzymes that utilize PC as substrate will be tested with respect to secretory phospholipases and endothelial lipase. The inhibitory role of SM in the generation of pro-inflammatory oxidized PCs and oxysterols will be tested in lipoproteins and cell membranes. The effect of SM deficiency on the macrophage and neutrophil function, including cytokine production and superoxide generation, will be studied in myeloid-specific SM-deficient mice. In Aim 3, the role of SM and ceramide in cellular cholesterol homeostasis will be studied by determining their effects on cholesterol trafficking between cellular compartments and between cells and their environment. These studies will provide novel insights into the physiological role of this important phospholipid, and could possibly identify novel therapeutic targets against inflammation and atherosclerosis. PUBLIC HEALTH RELEVANCE: The studies proposed here will investigate the physiological role of sphingomyelin (SM) a special lipid molecule prevalent in plasma and in outer cell membrane. They will specifically focus on the role of SM as an ant-inflammatory molecule that protects cells against environmental insults. These studies could lead not only to new understanding of mechanisms of inflammation and heart disease, but also to better therapeutic strategies. First, are there any macrophage pathways for cholesterol metabolism that are up- or down regulated by ablation of ABCG1? There could be changes in cellular cholesterol content, cholesterol esterases, ACAT, ABCA1, or possibly SR-B1 that could affect efflux. Second, there are other mechanisms that effect efflux, particularly spontaneous transfer, which Rothblat et al have shown to be important in some contexts (ATVB 2006 26:541-7) and efflux mediated by apo E (ATVB 2006 26:157-62). Lastly, it would be useful to compare efflux with net change in cholesterol by a non radio tracer method that would measure both medium and cellular cholesterol content. Radio tracers reveal how fast FC leaves the cell but not how much unlabeled cholesterol re enters the cell from donors in the medium.