The Transport of Nutritional Heme in Animal Development

 描述（由申请人提供）：本提案的长期目标是确定人类营养中血红素稳态的细胞和分子决定因素。血红素是血红素铁被吸收的肠细胞和血红素铁被回收的巨噬细胞的生物可利用铁的重要来源。在人体肠道中，膳食血红素比无机铁更容易吸收，并且是西方饮食中大部分身体铁的来源。此外，超过70%的身体铁以血红素的形式存在于血红蛋白中。血红素中的铁通过巨噬细胞吞噬溶酶体中的衰老红细胞的吞噬作用再循环。到目前为止，血红素在人肠道和网状内皮系统巨噬细胞中转运的基因和途径仍然不清楚。作为一种疏水性和细胞毒性的辅因子，血红素必须通过特定的细胞内和细胞间途径以高度受控的方式通过膜转运。在最后一个供资期之前，纽约血红素进口商的身份不明。我们建立了线虫秀丽隐杆线虫是一个很好的动物模型，以确定血红素转运途径，因为它合成了大量的血红素蛋白与人类同源物，但不合成血红素从头。利用C.在上一个资助周期中，我们成功地鉴定了第一个真核血红素输入/转运蛋白HRG 1及其相应的人类同源物，这一发现为动物中血红素转运和贩运提供了第一个初步框架。HRG 1对于巨噬细胞铁稳态是必不可少的，并且在衰老RBC的吞噬作用期间将血红素从吞噬溶酶体转运到细胞质-这一过程称为红细胞吞噬作用（Cell Metabolism 2013）。重要的是，我们的研究表明，人类的HRG 1变体在血红素转运方面存在缺陷。本研究旨在阐明血红素转运HRG 1在分子、细胞和生物体水平的确切机制。我们试图验证这样的假设：HRG 1是难以捉摸的人类肠道血红素转运蛋白，也是重要的血红素运输网络的一部分。我们将利用（a）细胞生物学方法建立HRG 1作为肠血红素转运蛋白;（B）遗传学方法阐明HRG 1变体在人类铁代谢障碍中的分子后果;（c）生物化学方法揭示HRG 1的其他上游和下游相互作用，包括功能性血红素运输网络。我们的目标是获得一个全面的了解途径介导血红素运输哺乳动物，迄今为止，仍然知之甚少。

 DESCRIPTION (provided by applicant): The long-term goals of this proposal are to define the cellular and molecular determinants of heme homeostasis in human nutrition. Heme is a significant source of bioavailable iron for enterocytes where heme-iron is absorbed and for macrophages where heme-iron is recycled. In the human intestine, dietary heme is more easily absorbed than inorganic iron and is the source for the majority of body iron from a western diet. Moreover, over 70% of the total body iron is present as heme in hemoglobin. Iron from heme is recycled by phagocytosis of senescent red blood cells in the phagolysosome of macrophages. As of yet, the genes and pathways responsible for heme transport in the human intestine and macrophages of the reticuloendothelial system remain poorly defined. As a hydrophobic and cytotoxic cofactor, heme must be transported in a highly controlled manner through membranes via specific intra- and inter-cellular pathways. Prior to the last funding period, the identity of ny heme importer was unknown. We established that the roundworm Caenorhabditis elegans is an excellent animal model to identify heme transport pathways because it synthesizes a large number of hemoproteins with human homologs but does not synthesize heme de novo. By exploiting the heme auxotrophy of C. elegans in the previous grant cycle, we successfully identified the first eukaryotic heme importer/transporter, HRG1, and its corresponding human homolog, a discovery which provided the first preliminary framework for heme transport and trafficking in animals. HRG1 is essential for macrophage iron homeostasis and transports heme from the phagolysosome to the cytoplasm during phagocytosis of senescent RBCs - a process called erythrophagocytosis (Cell Metabolism 2013). Importantly, our studies reveal that a HRG1 variant in humans is defective in heme transport. The studies in this proposal are designed to elucidate the precise mechanisms of heme transport by HRG1 at the molecular, cellular, and organismal levels. We seek to test the hypothesis that HRG1 is the elusive human intestinal heme transporter and part of an essential heme trafficking network. We will utilize (a) a cell biological approach to establish HRG1 as the intestinal heme transporter; (b) a genetic approach to elucidate the molecular consequence of HRG1 variants in human iron metabolism disorders; and (c) a biochemical approach to uncover additional upstream and downstream interactors of HRG1 comprising a functional heme trafficking network. Our goal is to obtain a comprehensive understanding of the pathways which mediate heme transport in mammals that have, heretofore, remained poorly understood.