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Vitamin a Modulation of Iron Homeostasis : the Role of Iron Regulatory Proteins

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Vitamin a Modulation of Iron Homeostasis : the Role of Iron Regulatory Proteins Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1-1-2006 Vitamin A modulation of iron homeostasis : the role of iron regulatory proteins Stacy Eileen Schroeder Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Recommended Citation Schroeder, Stacy Eileen, "Vitamin A modulation of iron homeostasis : the role of iron regulatory proteins" (2006). Retrospective Theses and Dissertations. 19096. https://lib.dr.iastate.edu/rtd/19096 This Thesis is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Vitamin A modulation of iron homeostasis: the role of iron regulatory proteins by Stacy Eileen Schroeder A thesis submitted to the graduate faculty in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Major: Nutrition Program of ~t-~dy Committee: Kevin Schalinske, Major Professor Manj u Reddy Mary Ackermann Iowa State University Ames, Iowa 2006 11 Graduate College Iowa State University This is to certify that the master's thesis of Stacy Eileen Schroeder has met the thesis requirements ofIowa State University Signatures have been redacted for privacy 111 TABLE OF CONTENTS LIST OF FIGURES ..................................................................................................... v LIST OF TABLES ...................................................................................................... vi LIST OF ABBREVIATIONS ...................................................................................vu ABSTRACT...............................................................................................................viii CHAPTER 1 -GENERAL INTRODUCTION ........................................................1 THESIS ORGANIZATION RESEARCH QUESTIONS CHAPTER 2 —REVIEW OF LITERATURE .......................................................... 4 IRON HOMEOSTASIS 4 Function and Metabolic Usage 4 Requirements 6 Absorption 7 Divalent metal transporter-1 7 Copper containing ferroxidases: ceruloplasmin and hephaestin 9 Ferroportin 10 Transport and Cellular Uptake 11 Transferrin 11 Transferrin receptors 12 Storage 14 Ferritin 14 Iron Regulatory Proteins 15 Other Iron Regulation Factors 17 Hepcidin 17 Hr~ 20 DISRUPTIONS OF IRON HOMEOSTASIS 21 Deficiency 21 Iron-deficiency anemia 21 Illness and cytokines 22 Toxicity 24 Hemochromatosis 25 Oxidative stress 26 Interactions with Other Nutrients 27 Copper 27 Ascorbic acid 28 Vitamin A 28 LITERATURE CITED..............................................................................................32 iv CHAPTER 3 -IRON REGULATORY PROTEINS PLAY A ROLE IN VITAMIN A MODULATION OF IRON HOMEOSTASIS .................................47 ABSTRACT 47 INTRODUCTION 48 MA'1'~;RIALS AND METHODS 50 Chemicals 50 Cell Culture and Study Design 50 Animals and Experifnental Design 52 Hematocrit Determination 53 Hemoglobin Determination 54 Measurement of Liver Vitamin A 54 Analysis of Liver Non-he~ne Iron 55 Determination of Ferritin and TYansfeYYin Receptor Abundance 55 Analysis of Iron Regulatory Protein Activity and Abundance 56 Statistical Analysis 57 RESULTS 57 DISCUSSION 59 ACKNOWLEDGEMENTS 62 FIGURE LEGENDS 63 TABLES Aim FIGUxES 67 CHAPTER 4 —GENERAL CONCLUSIONS .........................................................77 SUMMARY AND CONCLUSIONS 77 RECOMMENDATIONS FOR FUTURE RESEARCH 79 LITERATURE_CITED .............................................................................................. SO V LIST OF FIGURES Figure 2.1 Diagram of iron cycle 5 Figure 2.2 Cellular iron metabolism 8 Figure 2.3 Diagram of the role of hepcidin 19 Figure 2.4 Role of inflammation in iron regulation 23 Figure 2.5 Hypothetical scheme for iron-induced carcinogenesis 26 Figure 3.1 Post-transcriptional regulation of ferritin and transferrin receptor 69 (TfR) by iron regulatory proteins Figure 3.2 Animal study design flow chart 70 Figure 3.3 Retinoic acid (RA) mediation of ferritin abundance in human 71 hepatoma cells Figure 3.4 Regulation of iron regulatory protein (IRP) -RNA binding activity 72 in hepatoma cells treated with varying doses of retinoic acid (RA) Figure 3.5 Retinoic acid (RA) modulation of iron regulatory protein (IRP) — 73 RNA binding activity in iron deficient or sufficient hepatoma cells Figure 3.6 Transferrin receptor (TfR) abundance is significantly inhibited in 74 rats consuming iron deficient diets Figure 3.7 Modulation of ferritin abundance with iron deficiency and retinoic 75 acid (RA) supplementation Figure 3.8 Retinoic acid (RA) inhibits iron or vitamin A deficiency mediated 76 induction of iron regulatory protein (IRP) -RNA binding activity in rats V1 LIST OF TABLES Table 2.1 Summary of characteristics of epidemiological. studies on ~9 vitamin A deficiency and anemia Table 3.1 . Iron indices hematocrit, hemoglobin, and liver non-heme iron 67 in rats Table 3.2 Hepatic vitamin A concentration in rats 68 Vll LIST OF ABBREVIATIONS c-acon cytosolic aconitase CD163 hemoglobin scavenger receptor Cp ceruloplasmin DcytB duodenal cytochrome b DMSO dimethyl sulfoxide (Me2S0) DMT1 divalent metal transporter 1 eALAS erythroid 5-aminolaevulinate synthase EDTA ethylenediaminetetraacetate FPNl ferroportin 1 H heavy (ferritin) HFE gene encoding a majorhistocompatibility complex class I-like protein HPLC high performance liquid chromatography IL interleukin IRE iron response element IRP iron regulatory protein L light (ferritin) m-acon mitochondrial aconitase MHC major histocompatibility class mRNA messenger RNA MTP1 gene coding for FPN1 PMSF phenylmethylsulphonylfluoride RA a11-trans-retinoic acid RAR retinoic acid receptor RDA recommended dietary allowance RE reticuloendothelial ROS reactive oxygen species TCA trichloroacetic acid TfR transferrin receptor TNF tumor necrosis factor UL tolerable upper intake level Vlll ABSTRACT Iron homeostasis is essential in preventing iron toxicity and deficiency. Several nutrients have been shown to have interactions with iron, specifically vitamin A. A few recently discovered proteins play crucial roles in maintaining iron homeostasis. One central group of governing proteins is known as the iron regulatory proteins (IRPs). Understanding how Il2Ps respond to altered cellular concentrations of other nutrients may be vital for the treatment or prevention of iron toxicity and deficiency. These studies were conducted to determine if IRPs play a role the perturbation of iron homeostasis in vitamin A deficiency and supplementation. In human hepatoma (HepG2) cells we found that IRP-RNA binding activity was induced when cells were treated with an iron chelator and slightly repressed when administered retinoic acid (RA). Hence, we used a rat model to determine the role of IRPs in iron deficiency, vitamin A deficiency and a combination of these deficiencies. Acute iron deficiency in rats significantly induced hepatic IRP-RNA binding activity and reduced hepatic ferritin to undetectable amounts. Furthermore, we found RA supplementation inhibited the increase in IlZP-.RNA binding activity to a level not significantly different from the control. This inhibition of IRP-RNA binding activity by RA supplementation was correlated with a 34°Io reduction in transferrin receptor (TfR) abundance and a partial restoration of hepatic ferritin abundance. Our additional studies utilizing HepG2 cells provided evidence that RA mediates ferritin in adose-dependant manner. These findings suggest that IRPs play a role in vitamin A mediated alterations of iron homeostasis; providing insight. into prevention and treatment of iron deficiency and rationale for cautioning retinoid users of the potential for hepatic iron accumulation. 1 CHAPTER 1 -GENERAL INTRODUCTION THESIS ORGANIZATION The material in this thesis is organized into four main chapters. Chapter one is designed to provide the reader with an organizational overview of the entire document and present the research questions the author addressed throughout the paper. Chapter two is an extensive review of the literature pertaining to the author's research in cellular iron homeostasis and its regulation by iron regulatory proteins and nutrients, specifically vitamin A. A list of references for chapter 2 are provided following the section. The author's research,, investigating the role of iron regulatory proteins in the perturbation of iron homeostasis by vitamin A status alterations constitutes chapter three. The content of chapter three will be submitted to The Journal of Nutrition for publication. General conclusions and ideas for future research paths encompass chapter four. The final portion of the thesis provides a list of the literature referenced throughout chapter 3. RESEARCH QUESTIONS Associations between vitamin A status and iron homeostasis have been documented for nearly a century (Koessler et al., 1926). Both human and animal models have been utilized to document the various outcomes of this nutrient-nutrient interaction. Table 2.1 provides a noteworthy list of human studies that have documented the vitamin A deficiency mediated alterations of iron status indices. Rat studies on vitamin A deficiency have found hampered iron incorporation into erythrocytes (Gardner et al., 1979) and perturbed maternal iron status which causes
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