Heme trafficking and its impact on systemic iron homeostasis

这个项目的目标是研究血红素运输如何影响全身铁稳态。25 mg的 每天需要铁来维持红细胞生成，仅1-2 mg/d从胃肠道吸收，1-2 mg/d从胃肠道吸收。 当铁通过胃肠道、皮肤和肾粘膜细胞脱落而丢失时，大多数铁被回收。传统 一种观点认为，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，然后是铁， 其通过膜铁转运蛋白输出为转铁蛋白，以递送至肝脏（用于储存）或骨髓（用于新生红细胞）。 细胞生产）。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）。在西方分析中，FLVCR高表达 在十二指肠、肝脏和巨噬细胞中，这些组织对铁的吸收和运输至关重要; 除了红细胞发育不全之外，小鼠在这些部位具有过量的铁（Science 319：825-828，2008）。这些 观察，加上体外细胞系和原代巨噬细胞的研究，使我们假设血红素，而不是 只有铁是被贩卖的。该赠款将定义FLVCR结构，并识别其出口机制 血红素血红素结合蛋白，如血红素结合蛋白和白蛋白，使用诱变分析，非洲爪蟾 卵母细胞研究和电子晶体学。我们将确定铁是如何调节细胞间 定位FLVCR以帮助全身铁平衡。此外，我们还将从红色中确定血红素的命运 通过研究来自Flvcrflox/flox;LysM-cre小鼠的巨噬细胞， 体外和体内;通过研究Flvcrflox/flox;alb-cre小鼠确定血红素一旦递送到肝脏的命运; 确定肝细胞是否可以通过FLVCR分泌血红素进入胆汁，允许铁离开身体;并探索 这些发现在溶血、慢性炎症和血色病模型中的意义。 总之，这些研究应该表明，铁的生理调节是更加错综复杂的 比以前欣赏。

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.