Lipotoxic Protective Response of the Endoplasmic Reticulum

内质网的脂毒性保护反应

• 批准号: 10376867
• 负责人: ROBERT V FARESE
• 金额: $ 14.9万
• 依托单位: HARVARD SCHOOL OF PUBLIC HEALTH
• 依托单位国家: 美国
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-04-01 至 2022-09-01
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/10376867
• 关键词: Acyl Coenzyme A; Address; Adipose tissue; Affect; Apoptosis; Binding; Biochemical; Biochemical Reaction; Biochemistry; Biology; Catabolism; Cell Compartmentation; Cell physiology; Cells; Chronic; Data; Defect; Diglycerides; Disease; Endoplasmic Reticulum; Enzymes; Equilibrium; Exhibits; Face; Family; Fatty Acids; Fatty Liver; Genes; Health; Hepatocyte; Homeostasis; Human; In Vitro; Investigation; Knowledge; Lead; Light; Link; Lipids; Liver; Liver diseases; Location; Malignant Neoplasms; Malignant neoplasm of liver; Mammalian Cell; Measures; Mediating; Membrane; Membrane Fluidity; Metabolic; Metabolic Diseases; Mohr-Tranebjaerg syndrome; Molecular; Multiple Myeloma; Mus; Muscle; Normal Cell; Obesity; Organelles; PPAR alpha; Pathogenesis; Pathway interactions; Phenotype; Physiological; Primary carcinoma of the liver cells; Process; Proteins; Research; Role; System; Therapeutic; Tissues; Transmembrane Domain; Work; Yeasts; base; biological adaptation to stress; biological systems; endoplasmic reticulum stress; gene synthesis; human disease; interdisciplinary approach; lipid metabolism; liver injury; membrane synthesis; mouse model; response; sensor; structural biology; tumor metabolism

Lipid homeostasis is crucially important for cells, and disruptions in this balance can lead to diseases of lipid overload, such as obesity-related disorders. Lipid homeostasis is mainly coordinated in the endoplasmic reticulum (ER), the largest membrane system in cells. The ER is a well-recognized location for synthesis of membrane and secreted proteins, processes that are safeguarded by the “unfolded protein response” (UPR). Recent studies suggest that a complementary and interrelated pathway, which we term the “lipotoxic protective response” (LPR), acts in parallel to maintain ER lipid homeostasis. In contrast to the UPR, however, knowledge of the molecular aspects of the LPR remain rudimentary. Here we describe studies to overcome this knowledge gap through investigations through our recent identification of the mammalian FIT2 protein as a key guardian of ER lipid homeostasis. FIT2 has been a mysterious ER protein, of crucial importance for cell health and function, that was implicated in ER homeostasis and lipid metabolism but lacked an identified function. After years of effort and a biochemical tour de force, we have discovered that FIT2 is an acyl-CoA diphosphatase enzyme that catabolizes fatty acyl-CoAs, the activated forms of fatty acids, in the ER. Our preliminary data indicate that this activity may be localized on the luminal leaflet and is crucially important for cell health and viability. Absence of FIT2 triggers ER stress and, in a mouse model we have generated, liver injury. Our findings break new ground and raise many important questions about FIT2 and the LPR. Here we propose to answer these questions by using an interdisciplinary approach. Aim 1 will determine mechanisms of the LPR at the molecular level by deciphering the biochemical mechanism for FIT2’s catabolism of fatty acyl-CoA in the ER. We will combine biochemical and structural biology approaches to answer: What is the enzyme’s catalytic mechanism? Is FIT2 active towards ER luminal substrates? Is its activity regulated by lipid metabolites (e.g., diacylglycerol, DAG)? What is the fate of the metabolites generated by FIT2 activity? Aim 2 will determine mechanisms of the LPR at the cellular level by elucidating how FIT2 and the LPR are integrated with other ER stress protection pathways. Specifically, we will address: How does FIT2 mechanistically trigger the UPR? Does the mammalian UPR pathway depend on FIT2 activity? Can the interdependency of the FIT2/LPR and the UPR be exploited for therapeutic purposes in cancer, for example those with high demands on ER function, such hepatocellular carcinoma and multiple myeloma? Aim 3 will determine mechanisms of the LPR at the physiological level by determining how FIT2 maintains lipid homeostasis in mammalian liver. We have generated mice lacking FIT2 in hepatocytes, and preliminary studies indicate these mice have ER stress, increases in hepatocyte lipid storage, defects in lipid secretion, and signs of liver disease. We will mechanistically dissect this phenotype to elucidate how FIT2 is required in cellular lipid metabolism. Completion of these aims will reveal how a fast, enzymatic mechanism functions in the LPR to protect cells and maintain lipid homeostasis. It will also shed light on the pathogenesis of human disease, such as the rare human disorder of FIT2 deficiency and more common metabolic diseases involving ER lipid metabolism, with implications for both liver steatosis and cancers that rely heavily of the ER (such as liver cancer and multiple myeloma).

脂质稳态对于细胞本质上至关重要，这种平衡的破坏会导致脂质过载疾病， 例如与肥胖有关的疾病。脂质稳态主要在最大的内质网中协调（ER） 细胞中的膜系统。 ER是一个公认的膜和分泌蛋白质的位置， 由“未折叠的蛋白质反应”（UPR）保护的过程。最近的研究表明是一个完整的 和相互关联的途径，我们将其称为“脂肪毒性保护反应”（LPR），并平行起作用以维持ER脂质 稳态。但是，与UPR相反，了解LPR的分子方面仍然是基本的。这里 我们描述了通过我们最近确定的研究来克服这一知识差距的研究 哺乳动物FIT2蛋白是ER脂质稳态的关键监护人。 Fit2一直是一种神秘的ER蛋白质，至关重要 对于细胞健康和功能的重要性，这是在ER稳态和脂质代谢中实现的，但缺乏 确定的功能。经过多年的努力和生化巡回赛的力量，我们发现Fit2是酰基辅酶A ER中脂肪酸激活形式的脂肪酰基酸会分解脂肪酸的双磷酸酶。我们的初步数据 表明该活性可以定位在腔叶上，对于细胞健康和生存能力至关重要。 缺乏FIT2会触发ER应力，在小鼠模型中，我们已经产生了肝损伤。我们的发现破裂了 并提出有关FIT2和LPR的许多重要问题。在这里，我们建议通过使用 跨学科方法。 AIM 1将通过破译在分子水平上确定LPR的机制 ER中FIT2的脂肪酰辅酶A的分解代谢的生化机制。我们将结合生化和结构 生物学方法可以回答：酶的催化机制是什么？ Fit2对ER腔底物有效吗？ 它的活性是否由脂质代谢产物（例如二酰基甘油，DAG）调节？由什么代谢产生的代谢物的命运是什么 Fit2活动？ AIM 2将通过阐明FIT2和LPR的方式来确定LPR在细胞水平上的机制 与其他ER应力保护途径集成。具体来说，我们将解决：FIT2如何机械触发 UPR？哺乳动物UPR途径是否取决于FIT2活性？ fit2/lpr的相互依赖性和可以 为了治疗目的，请探索UPR，例如那些对ER功能的需求较高的人，例如 肝细胞癌和多发性骨髓瘤？ AIM 3将确定LPR在物理水平上的机制 通过确定FIT2如何保持哺乳动物肝脏中的脂质稳态。我们已经产生了缺乏fit2的老鼠 肝细胞和初步研究表明这些小鼠具有ER应力，肝细胞脂质储存的增加，缺陷 脂质分泌和肝病的迹象。我们将机械剖析此表型以阐明Fit2的方式 在细胞脂质代谢中需要。这些目标的完成将揭示快速的酶机制在 LPR保护细胞并保持脂质稳态。它还将阐明人类疾病的发病机理 作为罕见的FIT2缺乏症和更常见的代谢疾病，涉及ER脂质代谢， 对大大依赖ER的肝脏脂肪变性和癌症的影响（例如肝癌和多发性骨髓瘤）。