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).

脂质稳态对细胞至关重要，这种平衡的破坏可能导致脂质超载疾病， 例如与肥胖相关的疾病。脂质稳态主要在内质网（ER）中协调，内质网是最大的脂质网。 细胞内的膜系统。内质网是公认的膜和分泌蛋白合成场所， 由“未折叠蛋白反应”（UPR）保护的过程。最近的研究表明，互补 和相互关联的途径，我们称之为“脂毒性保护反应”（LPR），平行作用以维持 ER 脂质 体内平衡。然而，与 UPR 相比，LPR 的分子方面的知识仍然处于初级阶段。这里 我们描述了通过我们最近确定的调查来克服这一知识差距的研究 哺乳动物 FIT2 蛋白是 ER 脂质稳态的关键守护者。 FIT2 是一种神秘的 ER 蛋白，具有至关重要的作用。 对细胞健康和功能的重要性，与内质网稳态和脂质代谢有关，但缺乏 确定的功能。经过多年的努力和生化杰作，我们发现FIT2是一种酰基辅酶A 内质网中分解代谢脂酰辅酶A（脂肪酸的活化形式）的二磷酸酶。我们的初步数据 表明这种活性可能位于管腔小叶上，对于细胞健康和活力至关重要。 FIT2 的缺失会引发内质网应激，并且在我们建立的小鼠模型中会引发肝损伤。我们的发现开辟了新天地 并提出了许多有关 FIT2 和 LPR 的重要问题。在这里，我们建议通过使用 跨学科方法。目标 1 将通过破译 LPR 在分子水平上的机制 FIT2 在 ER 中脂肪酰辅酶 A 分解代谢的生化机制。我们将生物化学和结构结合起来 生物学方法回答：酶的催化机制是什么？ FIT2 对 ER 腔底物有活性吗？ 其活性是否受脂质代谢物（例如二酰基甘油、DAG）调节？产生的代谢物的命运是什么 FIT2 活动？目标 2 将通过阐明 FIT2 和 LPR 的关系来确定细胞水平上的 LPR 机制 与其他 ER 应激保护途径相结合。具体来说，我们将解决：FIT2如何机制触发 普遍定期审议？哺乳动物 UPR 通路是否依赖于 FIT2 活性？ FIT2/LPR 和 UPR 可用于癌症的治疗目的，例如那些对 ER 功能有高要求的癌症，例如 肝细胞癌和多发性骨髓瘤？目标 3 将确定 LPR 在生理水平上的机制 通过确定 FIT2 如何维持哺乳动物肝脏中的脂质稳态。我们已经生成了缺乏 FIT2 的小鼠 肝细胞，初步研究表明这些小鼠存在 ER 应激、肝细胞脂质储存增加、 脂质分泌和肝脏疾病的迹象。我们将机械地剖析这种表型，以阐明 FIT2 的作用 细胞脂质代谢所需。完成这些目标将揭示快速的酶促机制如何在 LPR 保护细胞并维持脂质稳态。它还将揭示人类疾病的发病机制，例如 作为 FIT2 缺陷的罕见人类疾病和涉及 ER 脂质代谢的更常见代谢疾病， 对肝脏脂肪变性和严重依赖内质网的癌症（如肝癌和多发性骨髓瘤）的影响。