Murine Models of Heme Metabolism and Iron Recycling

描述（由申请人提供）：人体近三分之二的铁以血红蛋白的形式存在，每个红细胞含有超过十亿个血红素形式的铁原子。因此，遗传或获得性血红蛋白合成缺陷，包括地中海贫血、血红蛋白病、缺铁和炎症性贫血是最普遍的人类疾病，这并不奇怪。重要的是，每天约3600亿红细胞（500万/秒）合成血红蛋白所需的约25毫克铁，大部分来自网状内皮系统（RES）巨噬细胞分解代谢的老化红细胞中的血红素铁的再循环；在稳定状态下，膳食中血红素和非血红素铁的吸收仅贡献1-2毫克/天的系统性铁经济，其中高达三分之二被吸收为血红素铁。然而，尽管RES铁循环和肠血红素吸收的重要性，巨噬细胞和肠上皮细胞中血红素跨膜运输的分子途径在很大程度上仍然未知。这在很大程度上是由于鉴定哺乳动物细胞中血红素特异性转运蛋白的技术困难，以及无法将这些发现转化为整个生物体。最近，我们的合作者利用秀丽隐杆线虫，绕过了哺乳动物细胞存在的几个技术障碍，发现了一种蛋白质，血红素反应基因1 (hrg-1)，它具有血红素转运蛋白的功能。我们的初步体外和体内实验数据有力地表明，hrg-1的哺乳动物同源物HRG1参与巨噬细胞铁循环、肠道血红素吸收以及红细胞和肝细胞血红素代谢。在这里，我们建议通过研究Hrg1在巨噬细胞和肠上皮细胞中对血红素和铁的反应，以及吞噬红细胞和炎症的调节来研究小鼠体内的功能，所有这些都调节全身铁代谢，并参与常见营养性、获得性和遗传性贫血的发病机制。此外，我们将直接检验Hrg1对…至关重要的假设

DESCRIPTION (provided by applicant): Nearly two-thirds of the body's iron endowment is in the form of hemoglobin and each red blood cell contains more than a billion iron atoms in the form of heme. Consequently, it is not surprising that inherited or acquired defects in hemoglobin synthesis, including the thalassemias, hemoglobinopathies, iron deficiency, and the anemia of inflammation are among the most prevalent human afflictions. Importantly, most of the ~25 mg of iron required to synthesize the hemoglobin in ~360 billion RBCs each day (5 million/sec) derives from recycling of heme-iron from aged RBCs catabolized by reticuloendothelial system (RES) macrophages; at steady state, dietary heme and non-heme iron absorption contribute only 1-2 mg/day to the systemic iron economy, and up to two-thirds of this is absorbed as heme-iron. Nevertheless, despite the importance of RES iron recycling and intestinal heme absorption, the molecular pathways of transmembrane heme transport in macrophages and intestinal epithelial cells have, for the most part, remained unknown. This is in large part due to technical difficulties in identifying heme-specific transporters in mammalian cells and the inability to translate these finding to whole organisms. Recently, using C. elegans, which bypasses several of the technical hurdles presented by mammalian cells, our collaborators identified a protein, heme-responsive gene 1 (hrg-1), which functions a heme transporter. Our preliminary in vitro and in vivo data strongly suggest that the mammalian ortholog of hrg-1, HRG1, is involved in macrophage iron recycling, intestinal heme absorption, as well as intraerythroid and hepatocellular heme metabolism. Here, we propose to investigate the in vivo function of Hrg1 in the mouse by examining its regulation in macrophages and intestinal epithelial cells in response to heme and iron, as phagocytosed red blood cells, as well inflammation, all of which modulate systemic iron metabolism and contribute to the pathogenesis of common nutritional, acquired, and inherited anemias. In addition, we will directly test the hypothesis that Hrg1 is essential for macrophage iron recycling, intestinal heme absorption, and intraerythroid iron metabolism using conditional gene targeting technology in the mouse. We expect that the collective results will yield substantial insight into these hitherto obscure aspects of heme and iron biology that are critical to our understanding and rational treatment of these common diseases.