Heme trafficking and recycling in iron metabolism

铁代谢中的血红素运输和回收

• 批准号: 10440269
• 负责人: Iqbal Hamza
• 金额: $ 15.45万
• 依托单位: UNIV OF MARYLAND, COLLEGE PARK
• 依托单位国家: 美国
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-07-01 至 2022-08-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/10440269
• 关键词: Adult; Anemia; Animal Genetics; Animal Model; Antiparasitic Agents; Biological; Biological Assay; Blood; Bone Marrow; Caenorhabditis elegans; Candidate Disease Gene; Cells; Chloroquine; Clinical; Co-Immunoprecipitations; Crystallization; Cytoplasm; Cytosol; Degradation Pathway; Development; Dichloromethylene Diphosphonate; Drug Metabolic Detoxication; Elements; Embryo; Erythrocytes; Erythrophagocytosis; Erythropoiesis; FTH1 gene; Ferritin; Funding; Genes; Genetic; Genetic Transcription; Goals; Hematology; Heme; Heme Iron; Hemoglobin; Homeostasis; Homologous Gene; Human; Human body; Hydrophobicity; Impairment; In Situ; Ingestion; Investigation; Iron; Lead; Ligation; Liver; Lysosomal Storage Diseases; Lysosomes; Mammals; Mediating; Membrane; Metabolism; Molecular; Monitor; Mus; Mutation; Nutrient; Nutrition Disorders; Organ; Organism; Oxygenases; Pathway interactions; Perinatal mortality demographics; Phagocytosis; Phagolysosome; Pharmacology; Physiological; Production; Proteins; RNA Interference; Recycling; Regulation; Reticuloendothelial System; Role; Sickle Cell Anemia; Spleen; Technology; Testing; Time; Toxic effect; Transgenic Mice; Variant; auxotrophy; base; cofactor; cytotoxic; design; feeding; genetic approach; hemozoin; in vivo; inhibitor; iron deficiency; iron metabolism; macrophage; metal transporting protein 1; prevent; protein complex; response; senescence; trafficking; transcriptome sequencing

The long-term goals of this proposal are to define heme transport and recycling in iron metabolism. Iron deficiency is the most common nutritional disorder in the world. The most common clinical manifestation of iron deficiency is anemia due to impaired hemoglobinization of red blood cells (RBCs). This is because over 70% of iron in the human body is used as heme in hemoglobin production. In healthy adults, about 90% of body iron is derived from recycled heme-iron. Each day, reticuloendothelial system (RES) macrophages recycle heme-iron by ingesting almost 5 million senescent or damaged RBCs per second; the bone marrow utilizes this recycled iron to produce new RBCs. As a consequence genetic defects in macrophage iron recycling result in anemia. Despite the importance of heme in iron recycling, the pathways responsible for heme transport and trafficking in RES macrophages remain poorly understood. After erythrophagocytosis, the iron is enzymatically released from heme by heme oxygenases (HMOX1) in the cytosol. This iron can either be stored in ferritin (FTH1) or exported out of the cell by ferroportin (FPN1) to be reutilized for new RBC production in the bone marrow. Consequently, genetic disruption in HMOX1, FPN1, and FTH1 – steps in the heme-iron recycling pathway – causes embryonic lethality in mice. We identified the first eukaryotic heme importer/transporter, HRG1 and showed that it is essential for transporting heme from the macrophage phagolysosome into the cytoplasm in macrophages. Our recent studies show that HRG1-deficient mice are viable even though they are incapable of recycling heme-iron and accumulate 10-fold excess heme within macrophages. The mice are tolerant to heme toxicity because they sequester heme inside lysosomes, which become 10-100 times larger than normal, by forming hemozoin - large multimeric heme crystals heretofore only identified in blood-feeding organisms to detoxify heme. Heme tolerance requires a fully-operational heme degradation pathway as haploinsufficiency of HMOX1 combined with HRG1 deficiency causes perinatal lethality, demonstrating a synthetic lethal interaction. Our exciting results suggest the existence of a previously unanticipated pathway for heme detoxification and tolerance in mammals. The studies in this proposal are designed to uncover the molecular basis of HRG1-mediated heme tolerance. We will test the hypotheses that heme tolerance is conferred by the coordinated regulation of heme transport by HRG1 and its genetic and physical interactions with heme degradation and additional components of the heme trafficking machinery. We will utilize (a) a genetic approach to elucidate the regulatory mechanisms of hemozoin formation and heme tolerance; and (b) a cell biological approach to identify the mechanisms for the synthetic lethal interactions between HRG1 and HMOX1. Our goals are to acquire a deep understanding for the molecular basis for heme trafficking and recycling and its role in heme tolerance in mammals.

该提案的长期目标是定义铁代谢中的血红素运输和回收。缺铁是世界上最常见的营养失调症。缺铁最常见的临床表现是红细胞（RBC）血红蛋白化受损导致的贫血。这是因为人体内70%以上的铁在血红蛋白生产中被用作血红素。在健康成年人中，约 90% 的体内铁来自回收的血红素铁。每天，网状内皮系统 (RES) 巨噬细胞每秒摄入近 500 万个衰老或受损的红细胞来回收血红素铁；骨髓利用这种回收的铁来产生新的红细胞。因此，巨噬细胞铁回收的遗传缺陷会导致贫血。尽管血红素在铁回收中很重要，但 RES 巨噬细胞中负责血红素运输和贩运的途径仍然知之甚少。噬红细胞作用后，铁通过细胞质中的血红素加氧酶 (HMOX1) 从血红素中释放出来。这种铁可以储存在铁蛋白 (FTH1) 中，也可以通过铁转运蛋白 (FPN1) 输出到细胞外，以便在骨髓中重新利用以产生新的红细胞。因此，HMOX1、FPN1 和 FTH1（血红素铁循环途径中的步骤）的基因破坏会导致小鼠胚胎死亡。我们鉴定了第一个真核血红素输入/转运蛋白 HRG1，并表明它对于将血红素从巨噬细胞吞噬溶酶体转运到巨噬细胞的细胞质中至关重要。我们最近的研究表明，HRG1 缺陷的小鼠虽然无法回收血红素铁并在巨噬细胞内积累 10 倍过量的血红素，但仍能存活。小鼠对血红素毒性具有耐受性，因为它们通过形成疟原虫色素将血红素隔离在溶酶体内，溶酶体比正常情况大10-100倍。迄今为止，这种大型多聚血红素晶体仅在食血生物体中发现，可以解毒血红素。血红素耐受性需要一个完全可操作的血红素降解途径，因为 HMOX1 的单倍体不足与 HRG1 缺陷相结合会导致围产期死亡，这证明了合成致死相互作用。我们令人兴奋的结果表明，哺乳动物中存在以前未预料到的血红素解毒和耐受途径。本提案中的研究旨在揭示 HRG1 介导的血红素耐受的分子基础。我们将测试以下假设：血红素耐受性是由 HRG1 对血红素运输的协调调节及其与血红素降解和血红素运输机制的其他组成部分的遗传和物理相互作用赋予的。我们将利用（a）遗传学方法来阐明疟原虫色素形成和血红素耐受性的调节机制； (b) 一种细胞生物学方法，用于鉴定 HRG1 和 HMOX1 之间合成致死相互作用的机制。我们的目标是深入了解血红素运输和回收的分子基础及其在哺乳动物血红素耐受性中的作用。