Deciphering Mechanisms for Triglyceride and Cholesterol Transport

项目1：甘油三酯和胆固醇转运的解密机制 总结/摘要 项目1的研究人员致力于探索脂蛋白代谢的基本机制， 健康和疾病。他们发现一种内皮细胞蛋白GPIHBP 1，负责转运 脂蛋白脂酶（LPL）的毛细血管腔; LPL-GPIHBP 1复合物是至关重要的边缘， 沿着毛细血管的富含磷脂酰肌醇的脂蛋白（TRL）; GPIHBP 1保护LPL免受自发性和 ANGPTL 4催化的解折叠/失活。他们的努力已经产生了超过60种出版物，其中许多反映了 致力于了解人类疾病。例如，他们发现GPIHBP 1突变导致 发现了一种由GPIHBP 1自身抗体引起的新的人类疾病-乳糜微粒血症。 最近，项目1的研究人员和同事确定了LPL-GPIHBP 1复合物的结构。期间 在接下来的5年里，项目1的研究人员将追求两个独立的目标。一是持续追求 血管内脂解的研究，建立在GPIHBP 1-LPL复合物结构的基础上。的 结构，沿着新试剂，新方法和专家合作者，已经使血管内 脂肪分解比以往任何时候都更令人兴奋。关键目标包括定义GPIHBP 1-LPL所需的氨基酸残基 相互作用，探索具体的“乳糜微粒血症突变”的机制，了解获得性 LPL的功能多态性，定义GPIHBP 1的酸性结构域在稳定LPL中的作用， 解折叠/失活，检查GPIHBP 1的酸性结构域在从硫酸乙酰肝素募集LPL中的功能 蛋白聚糖结合位点的内皮下空间，并研究如何ANGPTL 4启动展开 和LPL的失活。我们还将确定与Fab相关的GPIHBP 1和LPL的结构 LPL特异性单克隆抗体5D2的片段。我们的第二个目标是调查 巨噬细胞中的胆固醇和巨噬细胞处理胆固醇的机制。初步 研究，项目1的研究人员发现，巨噬细胞释放，质膜出芽，许多30- 70纳米颗粒。通过NanoSIMS成像，这些颗粒高度富集胆固醇，包括 可被细菌溶细胞素检测到的代谢活性“可接近胆固醇”（例如，ALO-D4）。的发现 富含胆固醇的颗粒从巨噬细胞中“萌芽”，这引起了许多问题。粒子的作用是什么 萌芽？这些粒子的组成是什么？颗粒出芽是否受到监管？与项目合作 2和3，项目1将调查不同环境中巨噬细胞颗粒的数量和组成 (e.g.,固醇饥饿、胆固醇负荷、LXR激动剂治疗和LXR、ABCA 1或 ABCG1）。初步的NanoSIMS成像研究表明，高密度脂蛋白在卸载中是有效的。 胆固醇从巨噬细胞衍生的颗粒，这意味着巨噬细胞颗粒出芽可能与 逆转胆固醇转运和动脉粥样硬化斑块中胆固醇负载细胞的出现。

Project 1: Deciphering Mechanisms for Triglyceride and Cholesterol Transport SUMMARY/ABSTRACT Project 1 investigators have devoted their careers to exploring basic mechanisms of lipoprotein metabolism in health and disease. They discovered that an endothelial cell protein, GPIHBP1, is responsible for transporting lipoprotein lipase (LPL) to the capillary lumen; that the LPL–GPIHBP1 complex is crucial for the margination of triglyceride-rich lipoproteins (TRLs) along capillaries; and that GPIHBP1 protects LPL from spontaneous and ANGPTL4-catalyzed unfolding/inactivation. Their efforts have resulted in >60 publications, many reflecting a commitment to understanding human disease. For example, they identified GPIHBP1 mutations causing chylomicronemia and uncovered a new human disease—chylomicronemia from GPIHBP1 autoantibodies. Recently, Project 1 investigators and coworkers determined the structure of the LPL–GPIHBP1 complex. During the next 5 years, Project 1 investigators will pursue two independent objectives. The first is to pursue ongoing studies of intravascular lipolysis, building on insights from the structure of the GPIHBP1–LPL complex. That structure, along with new reagents, new methodologies, and expert collaborators, have made intravascular lipolysis more exciting than ever. Key goals include defining amino acid residues required for GPIHBP1–LPL interactions, exploring mechanisms underlying specific “chylomicronemia mutations,” understanding a gain-of- function polymorphism in LPL, defining the role of GPIHBP1’s acidic domain in stabilizing LPL from unfolding/inactivation, examining the function of GPIHBP1’s acidic domain in recruiting LPL from heparan sulfate proteoglycan binding sites in the subendothelial spaces, and investigating how ANGPTL4 initiates the unfolding and inactivation of LPL. We will also determine the structure of GPIHBP1 and LPL in association with an Fab fragment of the LPL–specific monoclonal antibody 5D2. Our second objective is to investigate the distribution of cholesterol in macrophages and the mechanisms by which macrophages dispose of cholesterol. In preliminary studies, Project 1 investigators found that macrophages release, by plasma membrane budding, numerous 30– 70-nm particles. By NanoSIMS imaging, these particles are highly enriched in cholesterol, including the metabolically active “accessible cholesterol” detectable by bacterial cytolysins (e.g., ALO-D4). The finding that cholesterol-rich particles “bud” from macrophages raises many questions. What is the function of particle budding? What is the composition of these particles? Is particle budding regulated? In collaboration with projects 2 and 3, project 1 will investigate the numbers and composition of macrophage particles in different settings (e.g., sterol starvation, cholesterol loading, LXR agonist treatment, and deficiencies of LXRs, ABCA1, or ABCG1). Preliminary NanoSIMS imaging studies showed that high-density lipoproteins are effective in unloading cholesterol from macrophage-derived particles, implying that macrophage particle budding could be relevant to reverse cholesterol transport and the emergence of cholesterol-laden cells in atherosclerotic plaques.