SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Human iron metabolism

27

BACKGROUND: Growth differentiation factor 15 (GDF15), a divergent TGFβ superfamily, has recently been implicated in the modulation of iron homeostasis, acting as an upstream negative regulator of hepcidin, the key iron regulatory hormone produced primarily by hepatocytes. However, little is known about possible roles that GDF15 might play in the regulation of iron homeostasis and development of hyperferritinemia in children with hemophagocytic lymphohistiocytosis (HLH). PROCEDURES: We compared serum GDF15 level and mRNA expressions of GDF15 and key molecules of iron metabolism, and made correlations between their expressions in children with HLH and control children. RESULTS: Serum GDF15 level was remarkably higher in HLH group than that in controls, with median serum concentration of 1,700 and 260 pg/ml, respectively (P < 0.001). In addition, GDF15 mRNA was significantly upregulated but independent of hypoxia-inducible factor-mediated oxygen signaling pathway. More importantly, GDF15 induction was positively correlated to upregulation of ferroportin, the only cellular iron exporter, and to upregulation of ferritin heavy chain. CONCLUSIONS: Our study suggests that GDF15 induction helps suppress further activation of macrophages in stressful physiologic states as HLH, and is intimately implicated in the development of hyperferritinemia by modulating the hepcidin-ferroportin axis, resulting in enhanced ferroportin-mediated iron efflux. Pediatr Blood Cancer © 2013 Wiley Periodicals, Inc.

Concepts: Regulation of gene expression, Iron deficiency anemia, Hematology, Ferroportin, Anemia of chronic disease, Hepcidin, Human iron metabolism, Gene expression

26

The management and understanding of hereditary hemochromatosis have evolved with recent advances in iron biology and the associated discovery of numerous genes involved in iron metabolism. HFE-related (type 1) hemochromatosis remains the most frequent form, characterized by C282Y mutation homozygosity. Rare forms of hereditary hemochromatosis include type 2 (A and B, juvenile hemochromatosis caused by HJV and HAMP mutation), type 3 (related to TFR2 mutation), and type 4 (A and B, ferroportin disease). The diagnostic evaluation relies on comprehension of the involved pathophysiologic defect, and careful characterization of the phenotype, which gives clues to guide appropriate genetic testing.

Concepts: Human iron metabolism, Genotype, DNA, Gene, Natural selection, Biology, Evolution, Genetics

23

The transferrin receptor (TfR1), which mediates cellular iron uptake through clathrin-dependent endocytosis of iron-loaded transferrin, plays a key role in iron homeostasis. Since the number of TfR1 molecules at the cell surface is the rate-limiting step for iron entry into cells and is essential to prevent iron overload, TfR1 expression is precisely controlled at multiple levels. In this review, we have discussed the latest advances in the molecular regulation of TfR1 expression and we have considered current understanding of TfR1 function beyond its canonical role in providing iron for erythroid precursors and rapidly proliferating cells.

Concepts: Iron deficiency anemia, Transferrin receptor, Cell nucleus, Endocytosis, Organism, Human iron metabolism, Iron metabolism, DNA

18

Hearing loss in the US adult population is linked to hospitalization, poorer self-reported health, hypertension, diabetes, and tobacco use. Because iron deficiency anemia (IDA) is a common and easily correctable condition, further understanding of the association between IDA and all types of hearing loss in a population of US adults may help to open new possibilities for early identification and appropriate treatment.

Concepts: Biology, Serum iron, Iron deficiency, Iron, Human iron metabolism, Transferrin, Hemoglobin, Iron deficiency anemia

18

Iron is a functional component of oxygen transport and energy production in humans and therefore is a critically important micronutrient for sport and exercise performance. Athletes, particularly female athletes participating in endurance sport, are at increased risk of compromised iron status due to heightened iron losses through menstruation and exercise-induced mechanisms associated with endurance activity. Conventionally oral iron supplementation is used in prevention or/and treatment of iron deficiency. However, this approach has been criticised because of the side effects and increased risk of iron toxicity associated with the use of supplements. Thus, more recently there has been a growing interest in using dietary modification rather than the use of supplements to improve iron status of athletes. Dietary iron treatment methods include the prescription of an iron-rich diet, or/and haem iron-based diet, dietary advice counselling and inclusion of novel iron-rich products into the daily diet. Although studies using dietary modification are still scarce, current literature suggests that dietary iron interventions can assist in maintaining iron status in female athletes, especially during intensive training and competition. Future research should focus on the most efficient method(s) of dietary modification for improvement of iron status and whether these approaches can have a favourable impact on sports and exercise performance.

Concepts: Improve, Iron deficiency, Hemoglobin, Human iron metabolism, Iron, Heme, Iron supplements, Human

16

Inadequate nutrition has a severe impact on health in India. According to the WHO, iron deficiency is the single most important nutritional risk factor in India, accounting for more than 3% of all disability-adjusted life years (DALYs) lost. We estimate the social costs of iron deficiency anemia (IDA) in 6-59-month-old children in India in terms of intangible costs and production losses.

Concepts: Iron, Nutrition, Health, Human iron metabolism, Transferrin, Malnutrition, Hemoglobin, Iron deficiency anemia

15

Regulation of iron metabolism and innate immunity are tightly interlinked. The acute phase response to infection and inflammation induces alterations in iron homeostasis that reduce iron supplies to pathogens. The iron-hormone hepcidin is activated by such stimuli causing degradation of the iron exporter ferroportin and reduced iron release from macrophages, suggesting that hepcidin is the crucial effector of inflammatory hypoferremia. Here we report the discovery of an acute inflammatory condition that is mediated by Toll-like receptor (TLR) 2 and TLR6 and which induces hypoferremia in mice injected with TLR ligands. Stimulation of TLR2/TLR6 triggers profound decreases in ferroportin mRNA and protein expression in bone marrow-derived macrophages, liver and spleen of mice without changing hepcidin expression. Furthermore, C326S ferroportin mutant mice with a disrupted hepcidin/ferroportin regulatory circuitry respond to injection of the TLR2/6 ligands FSL1 or PAM3CSK4 by ferroportin down regulation and a reduction of serum iron levels. Our findings challenge the prevailing role of hepcidin in hypoferremia and suggest that rapid hepcidin-independent ferroportin down regulation in the major sites of iron recycling may represent a first line response to restrict iron access for numerous pathogens.

Concepts: Hepcidin, Ferroportin, Iron deficiency anemia, Iron metabolism, Iron deficiency, Iron, Human iron metabolism, Immune system

12

Delayed umbilical cord clamping has been shown to improve iron stores in infants to 6 months of age. However, delayed cord clamping has not been shown to prevent iron deficiency or anemia after 6 months of age.

Concepts: Clinical research, Transferrin, Fetus, Bone marrow, Hemoglobin, Clinical trial, Human iron metabolism, Umbilical cord

11

Iron metabolism is regulated by transcriptional and post-transcriptional mechanisms. The mRNA of the iron-controlling gene, transferrin receptor 1 (TfR1), has long been believed to be negatively regulated by a yet-unidentified endonuclease. Here, we show that the endonuclease Regnase-1 is critical for the degradation of mRNAs involved in iron metabolism in vivo. First, we demonstrate that Regnase-1 promotes TfR1 mRNA decay. Next, we show that Regnase-1(-/-) mice suffer from severe iron deficiency anemia, although hepcidin expression is downregulated. The iron deficiency anemia is induced by a defect in duodenal iron uptake. We reveal that duodenal Regnase-1 controls the expression of PHD3, which impairs duodenal iron uptake via HIF2α suppression. Finally, we show that Regnase-1 is a HIF2α-inducible gene and thus provides a positive feedback loop for HIF2α activation via PHD3. Collectively, these results demonstrate that Regnase-1-mediated regulation of iron-related transcripts is essential for the maintenance of iron homeostasis.

Concepts: DNA, Iron metabolism, Iron deficiency, Iron, Transferrin, Protein, Iron deficiency anemia, Human iron metabolism

9

Iron is an essential component of the erythrocyte protein hemoglobin and is crucial to oxygen transport in vertebrates. In the steady state, erythrocyte production is in equilibrium with erythrocyte removal. In various pathophysiological conditions, however, erythrocyte life span is compromised severely, which threatens the organism with anemia and iron toxicity. Here we identify an on-demand mechanism that clears erythrocytes and recycles iron. We show that monocytes that express high levels of lymphocyte antigen 6 complex, locus C1 (LY6C1, also known as Ly-6C) ingest stressed and senescent erythrocytes, accumulate in the liver via coordinated chemotactic cues, and differentiate into ferroportin 1 (FPN1, encoded by SLC40A1)-expressing macrophages that can deliver iron to hepatocytes. Monocyte-derived FPN1(+)Tim-4(neg) macrophages are transient, reside alongside embryonically derived T cell immunoglobulin and mucin domain containing 4 (Timd4, also known as Tim-4)(high) Kupffer cells (KCs), and depend on the growth factor Csf1 and the transcription factor Nrf2 (encoded by Nfe2l2). The spleen, likewise, recruits iron-loaded Ly-6C(high) monocytes, but these do not differentiate into iron-recycling macrophages, owing to the suppressive action of Csf2. The accumulation of a transient macrophage population in the liver also occurs in mouse models of hemolytic anemia, anemia of inflammation, and sickle cell disease. Inhibition of monocyte recruitment to the liver during stressed erythrocyte delivery leads to kidney and liver damage. These observations identify the liver as the primary organ that supports rapid erythrocyte removal and iron recycling, and uncover a mechanism by which the body adapts to fluctuations in erythrocyte integrity.

Concepts: Hemolytic anemia, White blood cell, Human iron metabolism, Liver, Anemia, Immune system, Hemoglobin, Red blood cell