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: 8541530
• 负责人: Janis L Abkowitz
• 金额: $ 1.05万
• 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/8541530
• 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（由申请人提供）：该项目的目标是研究血红素运输如何影响全身铁稳态。由于每天需要 25 毫克铁来维持红细胞的生成，因此只有 1-2 毫克/天从胃肠道吸收，并且 1-2 毫克/天通过脱落的胃肠道、皮肤和肾粘膜细胞损失，大多数铁是回收。传统观点认为，当巨噬细胞吞噬衰老红细胞时，它们的血红蛋白被降解为血红素，然后是铁，铁通过铁转运蛋白输出到转铁蛋白，输送到肝脏（用于储存）或骨髓（用于新红细胞的产生）。在之前的研究中，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)。根据西方分析，FLVCR 在十二指肠、肝脏和巨噬细胞中高度表达，这些组织对铁的吸收和运输至关重要； Flvcr 缺失的小鼠除了出现红细胞再生障碍外，这些部位还含有过量的铁（Science 319:825-828, 2008）。这些观察结果，加上对细胞系和原代巨噬细胞的体外研究，使我们推测血红素（而不仅仅是铁）被贩运。这笔资助将使用诱变分析、非洲爪蟾卵母细胞研究和电子晶体学来定义 FLVCR 结构并辨别其将血红素输出到血红素结合蛋白（如血红素结合蛋白和白蛋白）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Flvcrflox/flox；LysM-cre小鼠的体外和体内巨噬细胞，确定红细胞被巨噬细胞摄取后血红素的命运。通过研究 Flvcrflox/flox;alb-cre 小鼠，确定血红素一旦输送到肝脏后的命运；确定肝细胞是否可以通过 FLVCR 将血红素分泌到胆汁中，从而允许铁排出体外；并探讨这些发现在溶血、慢性炎症和血色素沉着症模型中的意义。这些研究共同表明，铁的生理调节比以前认识的更加复杂。 公众健康相关性：全身铁平衡很大程度上取决于巨噬细胞铁的回收（人每天 20-25 毫克），最低限度取决于饮食中铁的摄入量（每天 1-2 毫克）。目前的概念是，红细胞中的血红素被转化为铁，然后再循环到骨髓中形成新的红细胞或运输到肝脏进行储存。我们的数据挑战了这一公认的范式；证明血红素（而不仅仅是铁）被贩运；并表明这种运输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症的临床表现。