Current understanding of iron homeostasis Anderson, Gregory J; Frazer, David M
The American journal of clinical nutrition,
12/2017, Letnik:
106, Številka:
Suppl 6
Journal Article
Recenzirano
Odprti dostop
Iron is an essential trace element, but it is also toxic in excess, and thus mammals have developed elegant mechanisms for keeping both cellular and whole-body iron concentrations within the optimal ...physiologic range. In the diet, iron is either sequestered within heme or in various nonheme forms. Although the absorption of heme iron is poorly understood, nonheme iron is transported across the apical membrane of the intestinal enterocyte by divalent metal-ion transporter 1 (DMT1) and is exported into the circulation via ferroportin 1 (FPN1). Newly absorbed iron binds to plasma transferrin and is distributed around the body to sites of utilization with the erythroid marrow having particularly high iron requirements. Iron-loaded transferrin binds to transferrin receptor 1 on the surface of most body cells, and after endocytosis of the complex, iron enters the cytoplasm via DMT1 in the endosomal membrane. This iron can be used for metabolic functions, stored within cytosolic ferritin, or exported from the cell via FPN1. Cellular iron concentrations are modulated by the iron regulatory proteins (IRPs) IRP1 and IRP2. At the whole-body level, dietary iron absorption and iron export from the tissues into the plasma are regulated by the liver-derived peptide hepcidin. When tissue iron demands are high, hepcidin concentrations are low and vice versa. Too little or too much iron can have important clinical consequences. Most iron deficiency reflects an inadequate supply of iron in the diet, whereas iron excess is usually associated with hereditary disorders. These disorders include various forms of hemochromatosis, which are characterized by inadequate hepcidin production and, thus, increased dietary iron intake, and iron-loading anemias whereby both increased iron absorption and transfusion therapy contribute to the iron overload. Despite major recent advances, much remains to be learned about iron physiology and pathophysiology.
Microglia-mediated neuroinflammation is one of the most significant features in a variety of central nervous system (CNS) disorders such as traumatic brain injury, stroke, and many neurodegenerative ...diseases. Microglia become polarized upon stimulation. The two extremes of the polarization are the neuron-destructive proinflammatory M1-like and the neuron-regenerative M2-like phenotypes. Thus, manipulating microglial polarization toward the M2 phenotype is a promising therapeutic approach for CNS repair and regeneration. It has been reported that nanoparticles are potential tools for regulating microglial polarization. Gold nanoclusters (AuNCs) could penetrate the blood-brain barrier and have neuroprotective effects, suggesting the possibility of utilizing AuNCs to regulate microglial polarization and improve neuronal regeneration in CNS. In the current study, AuNCs functionalized with dihydrolipoic acid (DHLA-AuNCs), an antioxidant with demonstrated neuroprotective roles, were prepared, and their effects on polarization of a microglial cell line (BV2) were examined. DHLA-AuNCs effectively suppressed proinflammatory processes in BV2 cells by inducing polarization toward the M2-like phenotype. This was associated with a decrease in reactive oxygen species and reduced NF-kB signaling and an improvement in cell survival coupled with enhanced autophagy and inhibited apoptosis. Conditioned medium from DHLA-AuNC-treated BV2 cells was able to enhance neurogenesis in both the neuronal cell line N2a and in an ex vivo brain slice stroke model. The direct treatment of brain slices with DHLA-AuNCs also ameliorated stroke-related tissue injury and reduced astrocyte activation (astrogliosis). This study suggests that by regulating neuroinflammation to improve neuronal regeneration, DHLA-AuNCs could be a potential therapeutic agent in CNS disorders.
Hephaestin is a vertebrate multicopper ferroxidase important for the transfer of dietary iron from intestinal cells to the blood. Hephaestin is mutated in the sex-linked anemia mouse, resulting in ...iron deficiency. However, sex-linked anemia mice still retain some hephaestin ferroxidase activity. They survive, breed, and their anemia improves with age. To gain a better understanding of the role of hephaestin in iron homeostasis, we used the Cre-lox system to generate knockout mouse models with whole body or intestine-specific (Villin promoter) ablation of hephaestin. Both types of mice were viable, indicating that hephaestin is not essential and that other mechanisms, multicopper ferroxidase-dependent or not, must compensate for hephaestin deficiency. The knockout strains, however, both developed a microcytic, hypochromic anemia, suggesting severe iron deficiency and confirming that hephaestin plays an important role in body iron acquisition. Consistent with this, the knockout mice accumulated iron in duodenal enterocytes and had reduced intestinal iron absorption. In addition, the similarities of the phenotypes of the whole body and intestine-specific hephaestin knockout mice clarify the important role of hephaestin specifically in intestinal enterocytes in maintaining whole body iron homeostasis. These mouse models will serve as valuable tools to study the role of hephaestin and associated proteins in iron transport in the small intestine and other tissues.
Genital herpes simplex infection affects more than 500 million people worldwide. We have previously shown that COR-1, a therapeutic HSV-2 polynucleotide vaccine candidate, is safe and well tolerated ...in healthy subjects.
Here, we present a single center double-blind placebo-controlled, randomized phase I/IIa trial of COR-1 in HSV-2 positive subjects in which we assessed safety and tolerability as primary endpoints, and immunogenicity and therapeutic efficacy as exploratory endpoints.
Forty-four HSV-2+ subjects confirmed by positive serology or pathology, and positive qPCR during baseline shedding, with a recurrent genital HSV-2 history of at least 12 months including three to nine reported lesions in 12 months prior to screening, aged 18 to 50 years females and males with given written informed consent, were randomized into two groups. Three immunizations at 4-week intervals and one booster immunization at 6 months, each of 1 mg COR-1 DNA or placebo, were administered intradermally as two injections of 500 μg each to either one forearm or both forearms.
No serious adverse events, life-threatening events or deaths occurred throughout the study. As expected, HSV-2 infected subjects displayed gD2-specific antibody titers prior to immunization. COR-1 was associated with a reduction in viral shedding after booster administration compared with baseline.
This study confirms the previously demonstrated safety of COR-1 in humans and indicates a potential for use of COR-1 as a therapy to reduce viral shedding in HSV-2 infected subjects.
The mechanisms responsible for disturbed iron homoeostasis in hereditary haemochromatosis are poorly understood. However, results of some studies indicate a link between hepcidin, a liver-derived ...peptide, and intestinal iron absorption, suggesting that this molecule could play a part in hepatic iron overload. To investigate this possible association, we studied the hepatic expression of the gene for hepcidin (HAMP) and a gene important in iron transport (IREG1) in patients with haemochromatosis, in normal controls, and in Hfe-knockout mice.
We extracted total RNA from the liver tissue of 27 patients with HFE-associated haemochromatosis, seven transplant donors (controls), and Hfe-knockout mice. HAMP and IREG1 mRNA concentrations were examined by ribonuclease protection assays and expressed relative to the housekeeping gene GAPD.
There was a significant decrease in HAMP expression in untreated patients compared with controls (5·4-fold, 95% CI 3·3–7·5; p<0·0001) despite significantly increased iron loading. Similarly, we noted a decrease in Hamp expression in iron-loaded Hfe-knockout mice. Hepatic IREG1 expression was greatly upregulated in patients with haemochromatosis (1·8-fold, 95% CI 1·5–2·2; p=0·002). There was a significant correlation between hepatic iron concentration and expression of HAMP (r=0·59, p=0·02) and IREG1 (r=0·67, p=0·007) in untreated patients.
Lack of HAMP upregulation in HFE-associated haemochromatosis despite significant hepatic iron loading indicates that HFE plays an important part in the regulation of hepcidin expression in response to iron overload. Our results imply that the liver is important in the pathophysiology of HFE-associated haemochromatosis. Furthermore, the increase in hepatic IREG1 expression in haemochromatosis suggests that IREG1 could function to facilitate the removal of excess iron from the liver.
Iron is crucial for many biological functions, but quantitatively the most important use of iron is in the production of hemoglobin in red blood cell precursors. The amount of iron in the plasma, and ...hence its availability for hemoglobin synthesis, is determined by the liver-derived iron regulatory hormone hepcidin. When the iron supply to erythroid precursors is limited, as often occurs during stimulated erythropoiesis, these cells produce signals to inhibit hepatic hepcidin production, thereby increasing the amount of iron that enters the plasma. How stimulated erythropoiesis suppresses hepcidin production is incompletely understood, but erythroferrone, Gdf15 and Twsg1 have emerged as candidate regulatory molecules. To further examine the relationship between erythropoiesis and the candidate erythroid regulators, we have studied five mouse models of anemia, including two models of β-thalassemia (Hbbth3/+ and RBC14), the hemoglobin deficit mouse (hbd), dietary iron deficient mice and mice treated with phenylhydrazine to induce acute hemolysis. Hematological parameters, iron status and the expression of Erfe (the gene encoding erythroferrone), Gdf15 and Twsg1 in the bone marrow and spleen were examined. Erfe expression was the most consistently upregulated of the candidate erythroid regulators in all of the mouse models examined. Gene expression was particularly high in the bone marrow and spleen of iron deficient animals, making erythroferrone an ideal candidate erythroid regulator, as its influence is strongest when iron supply to developing erythroid cells is limited. Gdf15 expression was also upregulated in most of the anemia models studied although the magnitude of the increase was generally less than that of Erfe. In contrast, very little regulation of Twsg1 was observed. These results support the prevailing hypothesis that erythroferrone is a promising erythroid regulator and demonstrate that Erfe expression is stimulated most strongly when the iron supply to developing erythroid cells is compromised.
β-thalassemia major causes ineffective erythropoiesis and chronic anemia and is associated with iron overload due to both transfused iron and increased iron absorption, the latter mediated by ...suppression of the iron-regulatory hormone hepcidin. We sought to determine whether, in β-thalassemia major, transfusion-mediated inhibition of erythropoiesis dynamically affects hepcidin. We recruited 31 chronically transfused patients with β-thalassemia major and collected samples immediately before and 4 to 8 days after transfusion. Pretransfusion hepcidin was positively correlated with hemoglobin and ferritin and inversely with erythropoiesis. The hepcidin-ferritin ratio indicated hepcidin was relatively suppressed given the degree of iron loading. Posttransfusion, hemoglobin and hepcidin increased, and erythropoietin and growth differentiation factor-15 decreased. By multiple regression, pre- and posttransfusion hepcidin concentrations were both associated positively with hemoglobin, inversely with erythropoiesis, and positively with ferritin. Although men and women had similar pretransfusion hemoglobin, men had significantly increased erythropoiesis and lower hepcidin, received a lower transfusion volume per liter blood volume, and experienced a smaller posttransfusion reduction in erythropoiesis and hepcidin rise. Age of blood was not associated with posttransfusion hemoglobin or ferritin change. Hepcidin levels in patients with β-thalassemia major dynamically reflect competing influences from erythropoiesis, anemia, and iron overload. Measurement of these indices could assist clinical monitoring.
• In β-thalassemia major, hepcidin levels are simultaneously associated with erythropoiesis and iron loading pre- and posttransfusion.• Transfusion improves anemia, suppressing erythropoiesis and in turn increasing hepcidin in patients with β-thalassemia major.
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