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Principal Investigator: James F. Collins
Organization: UNIVERSITY OF FLORIDA
Fiscal Year: 2022
Award: $100,000
Funding agency: National Institute of Diabetes and Digestive and Kidney Diseases
Project Summary
Iron is an essential nutrient for rats, mice, and humans, yet iron in excess is toxic. Iron deficiency (ID) and iron
overload (IO) thus result in severe homeostatic perturbations. Since iron excretion is inefficient and unregulated,
intestinal iron absorption dictates overall body iron levels. Dietary iron exists mainly as non-heme and heme iron,
and both contribute significantly to iron nutriture. Non-heme iron absorption by duodenal enterocytes critically
relies on the iron importer divalent metal-ion transporter 1 (DMT1) and the iron exporter ferroportin (FPN).
Mechanisms of heme-iron absorption have not been clarified. Inappropriately elevated absorption of heme and
non-heme iron underlies iron loading in the genetic disorders hereditary hemochromatosis (HH) and β-
thalassemia (βthal). Iron overload can cause liver disease, arthropathies, osteoporosis, cardiomyopathy,
diabetes mellitus and impotence. HH is caused by mutations in genes that regulate transcription of the Hamp
gene in hepatocytes. Hamp encodes the iron-regulatory hormone hepcidin, which regulates serum iron content
by modulating FPN levels in duodenal enterocytes and reticuloendothelial macrophages (which store iron). The
most common gene mutated in HH is homeostatic iron regulator (HFE). In the U.S., ~1:300 adults of Northern
European descent is homozygous for HFE mutations1, significantly increasing risk for severe liver disease2. HH
can also be caused by mutations in Hamp which impair production of the functional hormone. βthal is an iron-
loading anemia, typified by ineffective erythropoiesis, due to β-globin gene mutations, and disordered iron
metabolism. Elevated iron absorption (due to low hepcidin) and frequent blood transfusion both contribute to iron
loading. In a transfusion-independent form of the disease, βthal intermedia (βTI), excessive iron absorption is
the main contributor to iron loading. In HH and βTI, increased FPN activity (due to low hepcidin) depletes
intracellular iron from duodenal enterocytes, which upregulates DMT1. The mechanism of DMT1 induction
involves a transcript variant that contains an iron-responsive element (+IRE) in the 3’ UTR. When iron is low, this
+IRE variant is stabilized by binding of an iron-regulatory protein (IRP) to the IRE motif thus stabilizing the
transcript and increasing translation. High DMT1 and FPN thus precipitate excessive iron absorption. In Aim 1,
we seek to mitigate iron loading in Hamp KO and Th3/+ mice by targeting the +IRE DMT1 mRNA using our Folic
Acid-coupled Ginger Nanoparticle-derived Lipid Vector (FA-GDLV) siRNA delivery system. We further seek to
ascertain if non-heme and heme-iron absorption are coordinately regulated to maintain iron homeostasis under
physiological conditions and to clarify whether this regulation goes awry in ID and IO (in Aim 2). Additional
experimentation will elucidate whether DMT1 and FPN modulate heme-iron absorption and contribute to iron
loading in HH (in Aim 3). Ambiguities in mechanisms and regulation of heme-iron absorption cannot be resolved
using mouse models, since mice inefficiently absorb heme iron. We thus developed Sprague-Dawley (SD) rat
models of heme-iron absorption and HH (Hamp KO), thus allowing this investigation to proceed in this direction.
Terms: <21+ years old><3' Untranslated Regions><3'UTR><Adult><Adult Human><Anemia><Assimilations><Autoregulation><B-globin><B-thalassemia><Binding><Blood Serum><Blood Transfusion><Body Tissues><Cardiomyopathies><Common Rat Strains><Coupled><Development><Diabetes Mellitus><Diet><Dietary Iron><Disease><Disorder><Duodenum><Elements><Endocrine Gland Secretion><Enteral><Enteric><Enterocytes><Erythropoiesis><European><Excretory function><Experimental Models><Fe absorption><Fe deficiency><Fe element><Fe metabolism><Fe overload><Ferroprotoporphyrin><Folate><Folic Acid><Gene Alteration><Gene Inactivation><Gene Mutation><Gene Silencing><Gene Transcription><Genes><Genetic Alteration><Genetic Change><Genetic Diseases><Genetic Transcription><Genetic defect><Ginger><Heme><Heme Iron><Hepatic Cells><Hepatic Disorder><Hepatic Parenchymal Cell><Hepatocyte><Hepc peptide><Hereditary hemochromatosis><Homeostasis><Hormones><Human><Hydroxyl><Hydroxyl Radical><Impairment><Impotence><Intestinal><Intestines><Investigation><Ions><Iron><Iron Metabolism Disorders><Iron Overload><Iron Regulatory Factor><Iron-Regulatory Proteins><Iron-Response Proteins><Isoforms><Joint Diseases><Lipids><Liver><Liver Cells><Liver diseases><Mediating><Membrane><Messenger RNA><Metabolic Pathway><Mice><Mice Mammals><Micronutrients><Modeling><Modern Man><Molecular><Molecular Interaction><Murine><Mus><Mutate><Mutation><Myocardial Diseases><Myocardial Disorder><Myocardiopathies><Mφ><Nutrient><Nutritional><Oral Administration><Oral Drug Administration><Osteoporosis><Oxides><Pathway interactions><Peptide Hormone Gene><Physiologic><Physiological><Physiological Homeostasis><Process><Production><Protein Isoforms><Proteins><Protoheme><Pteroylglutamic Acid><RNA Expression><Rat><Rats Mammals><Rattus><Reaction><Regulation><Repression><Risk><Role><Serum><Short interfering RNA><Siderophilin><Small Interfering RNA><Sprague-Dawley Rats><System><Testing><Therapeutic Hormone><Therapeutic Intervention><Tissues><Transcript><Transcription><Transferrin><Transfusion><Translations><Up-Regulation><Upregulation><Variant><Variation><Vitamin M><Zingiber officinale><absorption><adulthood><apical membrane><arthropathic><arthropathies><arthropathy><beta Globin><beta Thalassemia><beta thalassemia intermedia><bowel><cytotoxic><developmental><diabetes><dietary><dietary Fe><dietary heme><diets><divalent metal><erythroid development><excretion><ferroheme><ferroportin><ferroportin1 protein><genetic condition><genetic disorder><genome mutation><hepatic body system><hepatic disease><hepatic organ system><hepatopathy><hepcidin><impotent><in vivo><in vivo evaluation><in vivo testing><intervention therapy><intraoral drug delivery><iron absorption><iron deficiency><iron disorder><iron metabolism><joint disorder><knock-down><knockdown><liver disorder><mRNA><macrophage><membrane structure><metal transporting protein 1><mouse model><murine model><mutant><myocardium disease><myocardium disorder><nano particle><nano-sized particle><nanoparticle><nanosized particle><nutritional heme><nutritious><oxidative damage><oxidative injury><p-Thalassemia><pathway><peptide hormone><pre-clinical><preclinical><prevent><preventing><promoter><promotor><siRNA><siRNA delivery><social role><solute carrier family 40 (iron-regulated transporter), member 1><thalassemia intermedia><therapeutic agent development><therapeutic development><transcriptional silencing><vector><vitamin Bc><β-globin><β-thalassemia><β-thalassemia intermedia>