The role of FIT2 in VLDL assembly, hepatic triglyceride homeostasis, and lipoprotein atherogenicity

FIT2 在 VLDL 组装、肝甘油三酯稳态和脂蛋白致动脉粥样硬化中的作用

• 批准号: 10638637
• 负责人: JEFFREY L. BRODSKY
• 金额: $ 18.98万
• 依托单位: NEW YORK UNIVERSITY SCHOOL OF MEDICINE
• 依托单位国家: 美国
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-04-06 至 2027-03-31
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/10638637
• 关键词: Acceleration; Adipocytes; Affect; Anabolism; Apolipoproteins; Arterial Fatty Streak; Atherosclerosis; Biogenesis; Biological Assay; Cell Culture System; Cell Line; Cell secretion; Cells; Cholesterol; Cholesterol Esters; Chylomicrons; Circulation; Clinic; Collaborations; Coronary heart disease; Data; Databases; Degradation Pathway; Endoplasmic Reticulum; Endothelial Cells; Engineering; Enterocytes; Event; Fatty Acids; Fatty acid glycerol esters; Generations; Goals; Golgi Apparatus; Heart Diseases; Hepatic; Hepatocyte; High Fat Diet; Homeostasis; Human; Hypertriglyceridemia; In Vitro; Incubated; International; Kinetics; Lipids; Lipoproteins; Liver; LoxP-flanked allele; Macrophage; Mediating; Membrane; Membrane Lipids; Membrane Proteins; Metabolic; Metabolism; Modeling; Molecular; Mus; Myocardial Infarction; Names; Outcome; Output; Paper; Pathogenicity; Pathway interactions; Peripheral; Pharmaceutical Preparations; Pilot Projects; Plasma; Play; Predisposition; Production; Property; Protein Secretion; Proteins; Publications; Publishing; Research Personnel; Rodent Model; Role; Sampling; Severities; Smooth Endoplasmic Reticulum; Source; Steatohepatitis; System; Testing; Tissues; Transcript; Triglycerides; Very low density lipoprotein; Vesicle; Work; atherogenesis; biological adaptation to stress; clinically relevant; defined contribution; endoplasmic reticulum stress; experience; fatty liver disease; hypercholesterolemia; in vivo; microsomal triglyceride transfer protein; mouse model; non-alcoholic fatty liver disease; nonalcoholic steatohepatitis; novel; overexpression; particle; protein degradation; transcriptomics

This R01 application focuses on the mechanisms that control the generation of very low density lipoproteins (VLDLs) in liver cells. Prior work from the MPIs, which has resulted in 15 publications, established that a major mechanism controlling the secretion and circulation of VLDL is the regulated degradation of apolipoprotein (apoB) in the endoplasmic reticulum (ER). This metabolically orchestrated event requires the ER-associated degradation (ERAD) pathway, which was named and first elucidated by MPI Brodsky. In contrast, when neutral lipids (primarily triacylglycerols; TGs) are sufficient, apoB is co-translationally lipidated by MTP, and the nascent VLDL particles are expanded by lipids sourced from ER-resident lipid droplets (LDs). The re-modelled VLDL particles are next packaged into COPII vesicles for delivery to the Golgi and then secreted into the medium from hepatic cells (in vitro) or from liver hepatocytes into the circulation (in vivo). In contrast to these pathways that control the levels of VLDL, the factors that regulate the concentration and composition of lipids assembled onto apoB in the ER are poorly characterized. However, recent results generated by the MPIs and colleagues indicate that an ER-resident membrane protein, FIT2, plays a significant role in controlling TG assembly onto apoB in vitro and in vivo. Specifically, the preliminary data outlined in this application—which were made possible by the generation of novel rodent models and engineered VLDL secreting cell lines—strongly suggest that FIT2 regulates both the concentration and composition of apoB-associated lipids, as well as the atherogenicity of VLDL. Based on these and other new data, the following hypotheses will be tested: 1) FIT2 deficiency will increase ER membrane lipid content along with the generation of TG-depleted VLDL; 2) FIT2 delivers LDs into the ER, which are then integrated into VLDL particles in either an MTP-dependent or independent manner; and, 3) the level of FIT2 activity is a previously unappreciated determinant for the severity of fatty liver disease (NAFLD), steatohepatitis (NASH), and atherosclerosis. Because the efficiency of FIT2-mediated loading of TG onto VLDL also impacts hepatic lipid levels in the ER, FIT2 deficiency may also lead to lipid dysregulation in the ER and toxic stress responses. Moreover, the delivery of lipid-rich VLDLs could be limited by another ER-associated factor, KLHL12, that helps form specialized VLDL- resident COPII vesicles. Thus, another hypothesis is that native KLHL12 levels constrain the capacity of FIT2- supported delivery of VLDL from hepatic cells, thus exacerbating ER stress. Overall, besides dissecting how FIT2 regulates NASH, NAFLD, VLDL biogenesis, hepatic TG homeostasis, and lipoprotein atherogenicity, the clinical relevance of this project also includes the integration of transcriptomic data from the recently generated models with analogous databases obtained from human livers and atherosclerotic plaques. Toward all of these goals, the project benefits from deep and complementary expertise of the MPIs along with the experience of long-term collaborators with a substantial track record in studying lipoprotein metabolism.

该 R01 应用重点关注控制极低密度脂蛋白生成的机制 (VLDL) 存在于肝细胞中。 MPI 之前的工作已发表 15 份出版物，确定了一个主要的 控制VLDL分泌和循环的机制是载脂蛋白的调节降解 (apoB) 在内质网 (ER) 中。这种代谢精心安排的事件需要与 ER 相关的 降解（ERAD）途径，由 MPI Brodsky 命名并首次阐明。相反，当中性时 脂质（主要是三酰甘油；TG）就足够了，apoB 通过 MTP 共翻译脂质化，并且新生的 VLDL 颗粒通过来自内质网驻留脂滴 (LD) 的脂质进行扩增。重新建模的VLDL 接下来，颗粒被包装到 COPII 囊泡中，输送到高尔基体，然后分泌到培养基中 肝细胞（体外）或从肝脏肝细胞进入循环（体内）。与这些途径相反 控制 VLDL 的水平，这是调节脂质浓度和组成的因素 ER 中的 apoB 的特征很少。然而，MPI 及其同事最近得出的结果表明 内质网驻留膜蛋白 FIT2 在控制 TG 组装到 apoB 上发挥着重要作用 体外和体内。具体来说，本申请中概述的初步数据是由 新型啮齿动物模型和工程 VLDL 分泌细胞系的产生——强烈表明 FIT2 调节 apoB 相关脂质的浓度和组成，以及动脉粥样硬化性 极低密度脂蛋白。根据这些和其他新数据，将检验以下假设：1) FIT2 缺陷将 随着 TG 耗尽的 VLDL 的产生，内质网膜脂含量增加； 2) FIT2 将 LD 传递到 ER，然后以 MTP 依赖或独立的方式整合到 VLDL 颗粒中；和， 3) FIT2活性水平是脂肪肝疾病严重程度的一个之前未被认识到的决定因素 （NAFLD）、脂肪性肝炎（NASH）和动脉粥样硬化。 因为 FIT2 介导的 TG 加载到 VLDL 上的效率也会影响 ER 中的肝脂质水平， FIT2 缺乏还可能导致 ER 中的脂质失调和毒性应激反应。此外，交货 富含脂质的 VLDL 的形成可能受到另一种 ER 相关因子 KLHL12 的限制，该因子有助于形成专门的 VLDL- 常驻 COPII 囊泡。因此，另一个假设是天然 KLHL12 水平限制了 FIT2-的能力。 支持肝细胞输送 VLDL，从而加剧 ER 应激。总的来说，除了剖析如何 FIT2 调节 NASH、NAFLD、VLDL 生物发生、肝脏 TG 稳态和脂蛋白动脉粥样硬化性 该项目的临床相关性还包括整合最近生成的转录组数据 具有从人类肝脏和动脉粥样硬化斑块获得的类似数据库的模型。朝着这一切 目标，该项目受益于 MPI 深厚且互补的专业知识以及 在研究脂蛋白代谢方面拥有丰富记录的长期合作者。