Heme trafficking and its impact on systemic iron homeostasis

血红素运输及其对全身铁稳态的影响

• 批准号: 8257066
• 负责人: Janis L Abkowitz
• 金额: $ 33.93万
• 依托单位: UNIVERSITY OF WASHINGTON
• 依托单位国家: 美国
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-05-01 至 2015-04-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8257066
• 关键词: Albumins; Bile fluid; Cell Line; Cells; Chronic; Clinical; Complex; Data; Diet; Duodenum; Equilibrium; Erythrocytes; Feline Leukemia Virus; Gastrointestinal tract structure; Goals; Grant; Heme; Heme Iron; Hemochromatosis; Hemoglobin; Hemolysis; Hemopexin; Hepatocyte; Homeostasis; In Vitro; Inflammation; Ingestion; Iron; Kidney; Kupffer Cells; Liver; Marrow; Modeling; Mus; Mutagenesis; Persons; Physiological; Process; Production; Recycling; Regulation; Science; Site; Skin; Structure; Subgroup; Tissues; Transferrin; Xenopus oocyte; absorption; electron crystallography; extracellular; gastrointestinal; heme-binding protein; in vivo; insight; macrophage; metal transporting protein 1; public health relevance; receptor; senescence; tool; trafficking

DESCRIPTION (provided by applicant): The goal of this project is to study how heme trafficking might impact systemic iron homeostasis. As 25 mg of iron is required daily to maintain red cell production, only 1-2 mg/d is absorbed from the GI tract, and 1-2 mg/d is lost through sloughed gastrointestinal, skin and kidney mucosal cells, most iron is recycled. The traditional view is that when macrophages engulf senescent red cells, their hemoglobin is degraded to heme then iron, which is exported via ferroportin to transferrin for delivery to the liver (for storage) or to the marrow (for new red cell production). In previous studies, we determined that the feline leukemia virus-C receptor, FLVCR, specifically exports heme from cells (Cell 118:757-66, 2004). On western analysis, FLVCR is highly expressed in the duodenum, liver and macrophage, tissues critical for iron absorption and trafficking; and Flvcr-deleted mice have excess iron at these sites, in addition to red cell aplasia (Science 319:825-828, 2008). These observations, plus studies of cell lines and primary macrophages in vitro, led us to hypothesize that heme, not only iron, is trafficked. This grant will define FLVCR structure and discern the mechanism by which it exports heme to heme-binding proteins, such as hemopexin and albumin, using mutagenesis analyses, Xenopus oocytes studies, and electron crystallography. We will determine how iron regulates the intercellular localization of FLVCR to aid systemic iron balance. In addition, we will determine the fate of heme from red cells after the cells are ingested by macrophages by studying macrophages from Flvcrflox/flox;LysM-cre mice in vitro and in vivo; determine the fate of heme once delivered to liver by studying Flvcrflox/flox;alb-cre mice; determine if hepatocytes can secrete heme via FLVCR into the bile permitting iron to exit the body; and explore the implications of these findings in models of hemolysis, chronic inflammation, and hemochromatosis. Together these studies should demonstrate that the physiologic regulation of iron is more intricate and complex than previously appreciated. PUBLIC HEALTH RELEVANCE: Systemic iron balance largely depends on macrophage iron recycling (20-25 mg/d in persons) and minimally on the ingestion of iron in the diet (1-2 mg/day). The current concept is that heme from red cells is converted to iron, then recycled to the marrow to make new red cells or transported to the liver for storage. Our data challenge this accepted paradigm; demonstrate that heme, and not only iron, is trafficked; and suggest that this trafficking could help regulate systemic iron balance and/or modify the clinical manifestations of hemolysis, chronic inflammation and hemochromatosis.

描述(由申请者提供)：本项目的目标是研究血红素贩运如何影响全身铁稳态。由于每天需要25毫克的铁来维持红细胞的产生，每天只有1-2毫克的铁从胃肠道吸收，1-2毫克的铁每天通过萎靡不振的胃肠道、皮肤和肾脏粘膜细胞流失，因此大多数铁是循环利用的。传统的观点认为，当巨噬细胞吞噬衰老的红细胞时，它们的血红蛋白被降解为血红素，然后铁通过铁蛋白输出到转铁蛋白，然后输送到肝脏(用于储存)或骨髓(用于产生新的红细胞)。在以前的研究中，我们确定猫白血病病毒-C受体FLVCR特异性地从细胞中输出血红素(Cell 118：757-66,2004)。根据Western分析，FLVCR在十二指肠、肝脏和巨噬细胞中高表达，这些组织对铁的吸收和运输至关重要；Flvcr基因缺失的小鼠除了红细胞再生障碍性贫血外，还在这些部位存在过量的铁(Science 319：825-828,2008)。这些观察，加上对细胞系和体外原代巨噬细胞的研究，使我们假设血红素不仅是铁，而且是被贩卖的。这笔赠款将通过突变分析、非洲爪哇卵母细胞研究和电子结晶学，定义FLVCR的结构，并识别它将血红素输出到血红素结合蛋白(如血凝素和白蛋白)的机制。我们将确定铁如何调节FLVCR的细胞间定位，以帮助全身铁平衡。此外，我们将通过研究Flvcrflx/FLOX的巨噬细胞来确定红细胞中的血红素的命运；通过研究Flvcrflx/Flox的巨噬细胞在体外和体内的实验研究LysM-cre小鼠；通过研究Flvcrflx/Flox来确定一旦血红素进入肝脏后的命运；通过研究Alb-cre小鼠；确定肝细胞是否可以通过FLVCR将血红素分泌到胆汁中并允许铁排出体外；并探索这些发现在溶血、慢性炎症和血色沉着模型中的意义。总而言之，这些研究应该证明，铁的生理调节比之前所认识的更加复杂和复杂。 与公众健康相关：全身铁平衡在很大程度上取决于巨噬细胞铁的循环(人体每天20-25毫克)，最低限度取决于饮食中铁的摄入量(1-2毫克/天)。目前的概念是，红血球中的血红素转化为铁，然后循环到骨髓中制造新的红血球，或者运输到肝脏进行储存。我们的数据挑战了这一公认的范式；证明了血红素，而不仅仅是铁，被贩卖；并表明这种贩卖可能有助于调节全身铁平衡和/或改变溶血、慢性炎症和血色素沉着的临床表现。