The Biological Role of Heme in Human Nutrition

世界上五分之四的人可能缺铁，这使得营养性缺铁最严重 常见的营养障碍。尽管大量的实验和营养数据支持一种基本的 血红素(铁原卟啉IX)作为生物可利用的铁来源在人类营养中的作用，途径 血红素的吸收和利用目前尚不清楚。从细胞生物学的角度来看，血红素是 许多重要生物学过程中的辅基，在真核生物中，它是在 线粒体基质。因为血红素是一种疏水分子，由于其固有的特性而具有细胞毒性。 过氧化物酶活性，我们假设，血红素不仅通过脂双层扩散，而且是活跃的 通过特定的细胞内途径运输。我们建议使用CANONOHABDI炎动物模型 为了确定血红素运输的细胞途径和调节血红素运输的分子， 因为这种动物是已知的唯一不能合成血红素的遗传性动物模型。 需要血红素来维持新陈代谢过程。由于线虫缺乏制造血红素的能力，它提供了 美国具有干净的遗传背景，不含内源性血红素，并有能力从外部控制 血红素的代谢流。因此，线虫是一种专性的血红素营养缺陷型动物，将成为一种优秀的动物。 研究膳食中的血红素吸收以及细胞内运输、封存的模型 并整合到关键的血色素蛋白中。血红素运输的细胞途径将在C. 从正向遗传筛选中分离的突变体表型簇的生化特征 检测血红素水平和血红素蛋白活性，评估生存能力和追踪血红素在肝脏中的转运 动物的血红素类似物，并用电子在超微结构水平上测定血红素的分布 显微镜。突变基因的分子特性将通过对突变基因进行分类来确定 遗传互补组，使用SNPs定位突变基因，通过 RNA干扰和基因拯救，并通过对候选基因的测序来确定分子损伤。 从我们的DMA微阵列中鉴定出的线虫中受血红素调控的基因将被表征为 通过实时定量聚合酶链式反应和RNA印迹分析定量验证基因亚群，确定其功能 通过RNA干扰获得候选基因，并确定这些基因的时间和空间表达 通过合成转录和翻译报告基因融合来响应血红素的产物。这个 这些研究的结果将为真核生物中的血红素动态平衡和 可能有助于开发以血红素为基础的针对人类铁缺乏的营养干预措施，以及 针对加剧铁缺乏的人类蠕虫感染的潜在药物靶点。

Four out of five people in the world may be iron-deficient, making nutritional iron deficiency the most common nutritional disorder. Although considerable experimental and nutritional data support an essential role for heme (iron-protoporphyrin IX) as a bioavailable source of iron in human nutrition, the pathways for heme absorption and utilization are currently unknown. From a cell biological perspective, heme is the prosthetic group for many important biological processes, and in eukaryotes it is synthesized in the mitochondrial matrix. Because heme is a hydrophobic molecule and is cytotoxic due to its intrinsic peroxidase activity, we hypothesize that heme does not merely diffuse through lipid bilayers but is actively transported via specific intracellular pathways. We propose to use the animal model, Caenorhabditis elegans, to identify the cellular pathways for heme transport and the molecules mediating heme trafficking, because this animal is the only known genetic animal model that is unable to synthesize heme eye no^o albeit requiring heme to sustain metabolic processes. Since C. elegans lacks the ability to make heme, it provides us with a clean genetic background devoid of endogenous heme, and the capacity to externally control the metabolic flux of heme. Thus, C. elegans is an obligate heme auxotroph and will be an excellent animal model to study dietary heme absorption as well as intracellular heme trafficking for transport, sequestration and incorporation into critical hemoproteins. The cellular pathways for heme transport will be mapped in C. elegans by characterizing phenoclusters of mutants isolated from forward genetic screens by biochemically assaying for heme levels and hemoprotein activity, evaluating viability and tracking heme transport in live animals with heme analogs, and determining heme distribution at the ultrastructural level using electron microscopy. The molecular identities of the mutated genes will be determined by categorizing mutants in genetic complementation groups, mapping the mutated genes using SNPs, localizing the mutant gene by RNA interference and gene rescue, and by sequencing candidate genes to determine the molecular lesion. The heme regulated genes in C. elegans, identified from our DMA microarrays, will be characterized by quantitatively validating subsets of genes by real-time PCR and RNA blot analysis, determining the function of the candidate genes by RNA interference, and defining the temporal and spatial expression of these gene products in response to heme by synthesizing transcriptional and translational reporter gene fusions. The results from these studies will provide new mechanistic insights into heme homeostasis in eukaryotes and may aid in the development of heme-based nutritional interventions for human iron deficiency, and potential drug targets for human helminthic infections that exacerbate iron deficiency.