The Transport of Nutritional Heme in Animal Development

动物发育中营养血红素的运输

• 批准号: 8054236
• 负责人: Iqbal Hamza
• 金额: $ 29.22万
• 依托单位: UNIV OF MARYLAND, COLLEGE PARK
• 依托单位国家: 美国
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-04-01 至 2014-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8054236
• 关键词: Anemia; Animal Model; Animals; Binding; Bioavailable; Biological; Biological Assay; Blood Substitutes; Caenorhabditis elegans; Candidate Disease Gene; Cell Line; Cell membrane; Cell model; Cells; Chimera organism; Complex; Consumption; Defect; Development; Diffuse; Digestion; Elements; Enterocytes; Erythrocytes; Erythrophagocytosis; Funding; Gene Expression; Genes; Genetic; Genetic Screening; Goals; Growth; Heme; Heme Iron; Hemeproteins; Hemoglobin; Homeostasis; Homologous Gene; Human; Hydrocephalus; Individual; Infant; Iron; Lead; Ligand Binding; M cell; Mammalian Cell; Mammals; Measures; Mediating; Membrane; Membrane Protein Traffic; Metabolic; Modeling; Molecular; Mothers; Mus; Nature; Nematoda; Nutraceutical; Nutrition Disorders; Nutritional; Pathway interactions; Patients; Phagocytosis; Phagolysosome; Phenotype; Protein Biosynthesis; Proteins; RNA; RNA Interference; Recycling; Reporter; Reporter Genes; Reproduction; Saccharomyces cerevisiae; Site; Source; Structure; System; Testing; Transgenic Organisms; Tube; Variant; Yeasts; Zebrafish; analog; auxotrophy; base; cytotoxic; design; heme 1; iron (III) reductase; iron protoporphyrin IX; macrophage; mutant; nutrition; paralogous gene; permease; positional cloning; pregnant; prototype; public health relevance; response; senescence; small hairpin RNA; trafficking; uptake; zinc mesoporphyrin

DESCRIPTION (provided by applicant): The long-term objective of our studies is to define the cellular and molecular determinants of heme homeostasis in human nutrition. Iron deficiency is the most common nutritional disorder. Dietary heme (iron-protoporphyrin IX) is a significant source of bioavailable iron, but the genes and pathways responsible for heme transport and utilization in human enterocytes remain elusive. In humans, greater than 60% of total body iron is present as heme in hemoglobin. Iron from heme is recycled by phagocytosis of senescent red blood cells and proteolytic digestion of hemoglobin in macrophages. Similar to enterocytes, the pathways for heme transport and utilization across the phagolysosomal membrane in macrophages are unknown. Since heme is a hydrophobic, cytotoxic macrocycle, we assert that heme does not passively diffuse through membranes but is actively transported via specific intra- and inter-cellular pathways that comprise heme uptake, trafficking, and sequestration. We have demonstrated 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. Worms require dietary heme for growth and reproduction. Thus, the worm model provides a clean genetic background devoid of endogenous heme and the ability to externally manipulate the metabolic flux of intracellular heme. Utilizing C. elegans as a genetic animal model of heme auxotrophy, we identified HRG-1, the first eukaryotic heme importer/ transporter (Nature 2008). HRG-1 is a permease that is conserved in humans and binds and transports heme. The worm and human HRG-1 proteins co-localize to the endo-lysosomal compartment. Knockdown of hrg-1 in zebrafish causes hydrocephalus, yolk tube defects, and anemia - phenotypes that are fully rescued by worm HRG-1. These studies established a conserved model for cellular heme transport and validated C. elegans as a bona fide model for the identification of heme homeostasis pathways. The studies in this proposal are designed to elucidate the precise mechanisms of heme transport by HRG-1 at the molecular, cellular, and organismal levels. We seek to test the hypothesis that heme transport mediated by HRG-1 is an integral component of the heme homeostasis regulatory network in animals. We will utilize a structure-function approach to identify the functional elements of HRG-1 responsible for heme transport, a cell biological approach to establish HRG-1 as the vesicular transporter for heme-iron recycling, and a systems approach to identify the complex regulatory circuit which integrates HRG-1 with organismal heme trafficking. Our goal is to obtain a comprehensive understanding of the pathways which mediate heme homeostasis in mammals that have, heretofore, remained poorly understood. PUBLIC HEALTH RELEVANCE: Iron deficiency is the world's number one nutritional disorder, and heme is the most bioavailable form of iron for human consumption. Identification of how heme is transported for the synthesis of proteins containing iron and heme will permit the design of synthetic heme-based "nutraceuticals" specifically targeted to iron-deficient individuals including pregnant mothers and infants. Identifying the molecular basis of heme-iron recycling to produce hemoglobin will lead to new strategies for the synthesis of artificial blood.

描述（由申请人提供）：我们研究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。缺铁是最常见的营养失调。膳食血红素（铁-原卟啉IX）是生物可利用铁的重要来源，但人类肠细胞中负责血红素运输和利用的基因和途径尚不清楚。人体中，超过60%的铁以血红蛋白中的血红素的形式存在。血红素中的铁通过衰老红细胞的吞噬和巨噬细胞中血红蛋白的蛋白水解消化而循环利用。与肠细胞类似，巨噬细胞中血红素在吞噬溶酶体膜上的转运和利用途径尚不清楚。由于血红素是一种疏水、细胞毒性的大循环，我们断言血红素不会被动地通过膜扩散，而是通过特定的细胞内和细胞间途径主动运输，包括血红素摄取、运输和封存。我们已经证明，秀丽隐杆线虫是一个很好的动物模型，以确定血红素运输途径，因为它合成大量的血红蛋白与人类同源，但不合成血红素从头。蠕虫的生长和繁殖需要膳食血红素。因此，蠕虫模型提供了一个干净的遗传背景，缺乏内源性血红素和外部操纵细胞内血红素代谢通量的能力。利用秀丽隐杆线虫作为血红素营养不良的遗传动物模型，我们鉴定出HRG-1，这是第一个真核血红素进口/转运体（Nature 2008）。HRG-1是一种在人体中保守的渗透酶，可以结合和运输血红素。蠕虫和人HRG-1蛋白共定位于内溶酶体腔室。在斑马鱼中敲低hrg-1会导致脑积水、卵黄管缺陷和贫血——这些表型完全由蠕虫hrg-1拯救。这些研究建立了细胞血红素运输的保守模型，并验证了秀丽隐杆线虫作为鉴定血红素稳态途径的真正模型。本研究旨在阐明HRG-1在分子、细胞和机体水平上转运血红素的确切机制。我们试图测试由HRG-1介导的血红素运输是动物血红素稳态调节网络的一个组成部分的假设。我们将利用结构-功能方法来确定HRG-1负责血红素运输的功能元件，利用细胞生物学方法来确定HRG-1作为血红素铁循环的囊泡转运体，并利用系统方法来确定将HRG-1与有机血红素运输结合在一起的复杂调控回路。我们的目标是全面了解介导哺乳动物血红素稳态的途径，迄今为止，人们对这些途径知之甚少。