The Transport of Nutritional Heme in Animal Development

动物发育中营养血红素的运输

基本信息

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
项目类别：
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

项目摘要

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障碍。膳食血红素（铁原卟啉 IX）是生物可利用铁的重要来源，但负责人类肠细胞中血红素运输和利用的基因和途径仍然难以捉摸。在人类中，体内 60% 以上的铁以血红蛋白中的血红素形式存在。血红素中的铁通过衰老红细胞的吞噬作用和巨噬细胞中血红蛋白的蛋白水解作用而被回收。与肠细胞类似，巨噬细胞中血红素跨吞噬溶酶体膜的转运和利用途径尚不清楚。由于血红素是一种疏水性、细胞毒性大环化合物，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转运，包括血红素摄取、运输和隔离。我们已经证明，线虫秀丽隐杆线虫是识别血红素转运途径的优秀动物模型，因为它合成大量与人类同源物的血红素蛋白，但不从头合成血红素。蠕虫需要膳食血红素来生长和繁殖。因此，线虫模型提供了一个干净的遗传背景，没有内源性血红素，并且能够从外部操纵细胞内血红素的代谢通量。利用秀丽隐杆线虫作为血红素营养缺陷的遗传动物模型，我们鉴定了 HRG-1，第一个真核血红素输入/转运蛋白（Nature 2008）。 HRG-1 是一种在人类中保守的通透酶，可结合和运输血红素。线虫和人类 HRG-1 蛋白共定位于内溶酶体区室。斑马鱼中 HRG-1 的敲除会导致脑积水、卵黄管缺陷和贫血，而这些表型可被蠕虫 HRG-1 完全挽救。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识别血红素稳态途径的真正模型。本提案中的研究旨在阐明 HRG-1 在分子、细胞和有机体水平上转运血红素的精确机制。我们试图检验这样的假设：HRG-1 介导的血红素转运是动物血红素稳态调节网络的一个组成部分。我们将利用结构-功能方法来识别负责血红素转运的 HRG-1 的功能元件，利用细胞生物学方法将 HRG-1 建立为血红素-铁回收的囊泡转运蛋白，并利用系统方法来识别复杂的调控因子。将 HRG-1 与有机血红素运输相结合的电路。我们的目标是全面了解调节哺乳动物血红素稳态的途径，而迄今为止，人们对这些途径仍知之甚少。公共健康相关性：缺铁是世界上第一大营养障碍，而血红素是人类食用的铁的生物利用度最高的形式。确定血红素如何转运以合成含铁和血红素的蛋白质，将有助于设计专门针对缺铁个体（包括孕妇和婴儿）的基于合成血红素的“营养保健品”。确定血红素铁回收产生血红蛋白的分子基础将为合成人造血液提供新的策略。