Autosomal-dominant hemochromatosis is associated with a mutation in the ferroportin (SLC11A3) gene

Ferroportin in the progression and prognosis of hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is the fifth most common malignant tumor in men and the seventh in women and understanding the molecular mechanisms of HCC and establishing more effective therapies are critical and urgent issues. Our objective was to study the expression of ferroportin in hepatocellular carcinoma (HCC) tissue samples and the relationship between ferroportin expression and HCC characteristics.

METHODS

Sixty HCC tissues and their corresponding para-cancer liver tissues (PCLT) were obtained from sixty HCC patients who had undergone hepatectomy in the Second Xiangya Hospital of Central South University. Ten normal liver tissue samples were also obtained as a control. Immunohistochemistry (IHC) was performed to analyze the ferroportin expression in HCC, and the relationship between ferroportin expression and HCC clinical pathological characteristics also was analyzed. For the evaluation of IHC results, the comprehensive scoring criteria were met according to the staining intensity and the number of positive staining cells. Western blotting was performed to detect the expression level of ferroportin in HCC cell lines.

RESULTS

Ferroportin expression in HCC tissue was significantly lower compared to PCLT and normal liver tissue (P <0.05). Moreover, ferroportin expression was related to liver cancer cell de-differentiation, the severity degree in TNM staging, Edmondson-Steiner grading, intrahepatic metastasis and portal vein invasion. In addition, high expression of ferroportin was observed in normal human liver cell lines L02 and HL7702, whereas weak positive expression and even negative expression of ferroportin were observed in HCC cell lines FOCUS, MHCC-97H, HepG2 and SMMC-7721. Furthermore, among the four kinds of HCC cell lines, the expression level of ferroportin was the lowest in MHCC-97H cells.

CONCLUSIONS

Ferroportin expression level declines along with the progression of liver cancer, suggesting that the reduction of ferroportin may serve as an important marker for poor HCC prognosis and as a new therapeutic target.

Effect of Nerium oleander (N.O.) leaves extract on serum hepcidin, total iron, and infiltration of ED1 positive cells in albino rat

To gain insight into the hepatohistological alterations in noninjured rat liver, Nerium oleander (N.O.) leaves extract was injected intramuscularly to induce an acute phase reaction (APR). Histopathological changes were studied after 3, 12, and 24 h time course of sterile muscle abscess. Tissue integrity and any infiltration of inflammatory cells in the liver were investigated by Hematoxylin and Eosin and ED1 peroxidase stainings. The administration of N.O. leaves extract (10 mL/kg) in H & E stained sections showed a general vacuolization of cytoplasm resulting loss of polarity with prominent nucleoli after 3 h of induction. At 12 h, eccentric nuclei were also observed in the sections. Marked infiltration of leucocytes with predominate macrophages was also found after 24 h as seen by ED1 positive staining. In the present study, a possible relationship between serum hepcidin and total iron level was also investigated in vivo. An early increase of hepcidin and total iron level (3 h) with a maximum at 12 h (P < 0.01; P < 0.001) was observed. These changes indicate that sterile muscle abscess may induce APR resulting in hepatic damage which is evident with the recruitment of inflammatory cells into the organ.

Ferristatin II promotes degradation of transferrin receptor-1 in vitro and in vivo

Previous studies have shown that the small molecule iron transport inhibitor ferristatin (NSC30611) acts by down-regulating transferrin receptor-1 (TfR1) via receptor degradation. In this investigation, we show that another small molecule, ferristatin II (NSC8679), acts in a similar manner to degrade the receptor through a nystatin-sensitive lipid raft pathway. Structural domains of the receptor necessary for interactions with the clathrin pathway do not appear to be necessary for ferristatin II induced degradation of TfR1. While TfR1 constitutively traffics through clathrin-mediated endocytosis, with or without ligand, the presence of Tf blocked ferristatin II induced degradation of TfR1. This effect of Tf was lost in a ligand binding receptor mutant G647A TfR1, suggesting that Tf binding to its receptor interferes with the drug’s activity. Rats treated with ferristatin II have lower TfR1 in liver. These effects are associated with reduced intestinal ⁵⁹Fe uptake, lower serum iron and transferrin saturation, but no change in liver non-heme iron stores. The observed hypoferremia promoted by degradation of TfR1 by ferristatin II appears to be due to induced hepcidin gene expression.

Absorption of manganese and iron in a mouse model of hemochromatosis

Hereditary hemochromatosis, an iron overload disease associated with excessive intestinal iron absorption, is commonly caused by loss of HFE gene function. Both iron and manganese absorption are regulated by iron status, but the relationships between the transport pathways of these metals and how they are affected by HFE-associated hemochromatosis remain poorly understood. Loss of HFE function is known to alter the intestinal expression of DMT1 (divalent metal transporter-1) and Fpn (ferroportin), transporters that have been implicated in absorption of both iron and manganese. Although the influence of HFE deficiency on dietary iron absorption has been characterized, potential effects on manganese metabolism have yet to be explored. To investigate the role of HFE in manganese absorption, we characterized the uptake and distribution of the metal in Hfe^−/− knockout mice after intravenous, intragastric, and intranasal administration of ⁵⁴Mn. These values were compared to intravenous and intragastric administration of ⁵⁹Fe. Intestinal absorption of ⁵⁹Fe was increased and clearance of injected ⁵⁹Fe was also increased in Hfe^−/− mice compared to controls. Hfe^−/− mice displayed greater intestinal absorption of ⁵⁴Mn compared to wild-type Hfe^+/+ control mice. After intravenous injection, the distribution of ⁵⁹Fe to heart and liver was greater in Hfe^−/− mice but no remarkable differences were observed for ⁵⁴Mn. Although olfactory absorption of ⁵⁴Mn into blood was unchanged in Hfe^−/− mice, higher levels of intranasally-instilled ⁵⁴Mn were associated with Hfe^−/− brain compared to controls. These results show that manganese transport and metabolism can be modified by HFE deficiency.

Zebrafish erythropoiesis and the utility of fish as models of anemia

Erythrocytes contain oxygen-carrying hemoglobin to all body cells. Impairments in the generation of erythrocytes, a process known as erythropoiesis, or in hemoglobin synthesis alter cell function because of decreased oxygen supply and lead to anemic diseases. Thus, understanding how erythropoiesis is regulated during embryogenesis and adulthood is important to develop novel therapies for anemia. The zebrafish, Danio rerio, provides a powerful model for such study. Their small size and the ability to generate a large number of embryos enable large-scale analysis, and their transparency facilitates the visualization of erythroid cell migration. Importantly, the high conservation of hematopoietic genes among vertebrates and the ability to successfully transplant hematopoietic cells into fish have enabled the establishment of models of human anemic diseases in fish. In this review, we summarize the current progress in our understanding of erythropoiesis on the basis of zebrafish studies and highlight fish models of human anemias. These analyses could enable the discovery of novel drugs as future therapies.

Iron metabolism: current facts and future directions

Iron metabolism has been intensively examined over the last decade and there are many new players in this field which are worth to be introduced. Since its discovery many studies confirmed role of liver hormone hepcidin as key regulator of iron metabolism and pointed out liver as the central organ of system iron homeostasis. Liver cells receive multiple signals related to iron balance and respond by transcriptional regulation of hepcidin expression. This liver hormone is negative regulator of iron metabolism that represses iron efflux from macrophages, hepatocytes and enterocytes by its binding to iron export protein ferroportin. Ferroportin degradation leads to cellular iron retention and decreased iron availability. At level of a cell IRE/IRP (iron responsive elements/iron responsive proteins) system allows tight regulation of iron assimilation that prevents an excess of free intracellular iron which could lead to oxidative stress and damage of DNA, proteins and lipid membranes by ROS (reactive oxygen species). At the same time IRE/IRP system provides sufficient iron in order to meet the metabolic needs.

Recently a significant progress in understanding of iron metabolism has been made and new molecular participants have been characterized. Article gives an overview of the current understanding of iron metabolism: absorption, distribution, cellular uptake, release, and storage. We also discuss mechanisms underlying systemic and cellular iron regulation with emphasis on central regulatory hormone hepcidin.

Reduced sensitivity of the ferroportin Q248H mutant to physiological concentrations of hepcidin

Ferroportin Q248H mutation has an allele frequency of 2.2-13.4% in African populations and is associated with a mild tendency to increased serum ferritin in the general population. Some investigators have reported that ferroportin Q248H is degraded after exposure to hepcidin in exactly the same manner as wild-type ferroportin, but supraphysiological concentrations of hepcidin were used. The aim of our study was to determine whether ferroportin Q248H may have reduced sensitivity to physiological concentrations of hepcidin. The sensitivity of ferroportin Q248H to hepcidin was determined in 293T cells transiently expressing ferroportin using immunoblotting and fluorescence analysis. Ferritin concentrations were measured in these cells and also in human primary monocytes derived from humans with different ferroportin genotypes. The effect of Q248H on serum iron measures was examined in patients with sickle cell anemia. Immunoblotting and fluorescence analysis showed decreased sensitivity of ferroportin Q248H to physiological concentrations of hepcidin. Lower ferritin concentrations were observed after incubation with iron and hepcidin in 293T cells expressing ferroportin Q248H and in primary monocytes from ferroportin Q248H subjects. In sickle cell anemia, ferroportin Q248H heterozygotes had lower serum ferritin concentrations than wild-type subjects, consistent with enhanced iron release by macrophage ferroportin Q248H. A clinical benefit of ferroportin Q248H was suggested by lower echocardiographic estimates of pulmonary artery pressure in patients carrying mutant alleles. In conclusion, our results suggest that ferroportin Q248H protein is resistant to physiological concentrations of hepcidin and that this mutation has discernible effects on iron metabolism-related clinical complications of sickle cell anemia. They provide a mechanistic explanation for the effect of ferroportin Q248H on iron status in individuals of African descent and suggest that these changes in iron metabolism may be beneficial under certain disease-specific circumstances. (ClinicalTrials.gov Identifier:NCT00011648).

A precious metal: Iron, an essential nutrient for all cells

Iron is an important cofactor required for a number of essential cell functions and hence is a vital nutrient. However, iron can also be dangerous as a catalyst of free radical reactions. Accordingly, intracellular iron homeostasis and body iron balance are tightly regulated. In this review, we presented an overview of the remarkable new insights that over the last years have been gained into the multifaceted and sophisticated molecular mechanisms controlling iron acquisition, storage and release. We also reviewed the data about nutrition-related abnormalities of iron metabolism, such as iron overload and deficiency. Finally, we discussed how pathogenic microorganisms and host cells compete for iron, a battle whose outcome has a relevant role in infectious disease.

Pharmacology of iron transport

Elucidating the molecular basis for the regulation of iron uptake, storage, and distribution is necessary to understand iron homeostasis. Pharmacological tools are emerging to identify and distinguish among different iron transport pathways. Stimulatory or inhibitory small molecules with effects on iron uptake can help characterize the mechanistic elements of iron transport and the roles of the transporters involved in these processes. In particular, iron chelators can serve as potential pharmacological tools to alleviate diseases of iron overload. This review focuses on the pharmacology of iron transport, introducing iron transport membrane proteins and known inhibitors.

Hereditary hemochromatosis restores the virulence of plague vaccine strains

Nonpigmented Yersinia pestis (pgm) strains are defective in scavenging host iron and have been used in live-attenuated vaccines to combat plague epidemics. Recently, a Y. pestis pgm strain was isolated from a researcher with hereditary hemochromatosis who died from laboratory-acquired plague. We used hemojuvelin-knockout (Hjv(-/-)) mice to examine whether iron-storage disease restores the virulence defects of nonpigmented Y. pestis. Unlike wild-type mice, Hjv(-/-) mice developed lethal plague when challenged with Y. pestis pgm strains. Immunization of Hjv(-/-) mice with a subunit vaccine that blocks Y. pestis type III secretion generated protection against plague. Thus, individuals with hereditary hemochromatosis may be protected with subunit vaccines but should not be exposed to live-attenuated plague vaccines.

Mechanisms of mammalian iron homeostasis

Iron is vital for almost all organisms because of its ability to donate and accept electrons with relative ease. It serves as a cofactor for many proteins and enzymes necessary for oxygen and energy metabolism, as well as for several other essential processes. Mammalian cells utilize multiple mechanisms to acquire iron. Disruption of iron homeostasis is associated with various human diseases: iron deficiency resulting from defects in the acquisition or distribution of the metal causes anemia, whereas iron surfeit resulting from excessive iron absorption or defective utilization causes abnormal tissue iron deposition, leading to oxidative damage. Mammals utilize distinct mechanisms to regulate iron homeostasis at the systemic and cellular levels. These involve the hormone hepcidin and iron regulatory proteins, which collectively ensure iron balance. This review outlines recent advances in iron regulatory pathways as well as in mechanisms underlying intracellular iron trafficking, an important but less studied area of mammalian iron homeostasis.

Hooked! Modeling human disease in zebrafish

Zebrafish have been widely used as a model system for studying developmental processes, but in the last decade, they have also emerged as a valuable system for modeling human disease. The development and function of zebrafish organs are strikingly similar to those of humans, and the ease of creating mutant or transgenic fish has facilitated the generation of disease models. Here, we highlight the use of zebrafish for defining disease pathways and for discovering new therapies.

Transgenic HFE-dependent induction of hepcidin in mice does not require transferrin receptor-2

Hereditary hemochomatosis (HH) is caused by mutations in several genes, including HFE and transferrin receptor-2 (TFR2). Loss of either protein decreases expression of the iron regulatory hormone hepcidin by the liver, leading to inappropriately high iron uptake from the diet, and resulting in systemic iron overload. In tissue culture, overexpressed HFE and TFR2 physically interact. Hepatocellular overexpression of Hfe in vivo increases hepcidin expression, despite an associated decrease in Tfr2. On this basis, we hypothesized that Tfr2 would not be required for Hfe-dependent up-regulation of hepcidin. We show that hepatocellular overexpression of Hfe in Tfr2(Y245X/Y245X) mice leads to hepcidin induction eventuating in iron deficiency and a hypochromic, microcytic anemia. Furthermore, coimmunoprecipitation studies using liver lysates did not provide evidence for physical interaction between Hfe and Tfr2 in vivo. In conclusion, we demonstrate that Tfr2 is not essential for Hfe-mediated induction of hepcidin expression, supporting the possibility that TFR2 may regulate iron metabolism in an HFE-independent manner.

Ferroportin-mediated iron transport: expression and regulation

The distinguishing feature between iron homeostasis in single versus multicellular organisms is the need for multicellular organisms to transfer iron from sites of absorption to sites of utilization and storage. Ferroportin is the only known iron exporter and ferroportin plays an essential role in the export of iron from cells to blood. Ferroportin can be regulated at many different levels including transcriptionally, post-transcriptionally, through mRNA stability and post-translationally, through protein turnover. Additionally, ferroportin may be regulated in both cell-dependent and cell-autonomous fashions. Regulation of ferroportin is critical for iron homeostasis as alterations in ferroportin may result in either iron deficiency or iron overload. This article is part of a Special Issue entitled: Cell Biology of Metals.

The long history of iron in the Universe and in health and disease

BACKGROUND

Not long after the Big Bang, iron began to play a central role in the Universe and soon became mired in the tangle of biochemistry that is the prima essentia of life. Since life's addiction to iron transcends the oxygenation of the Earth's atmosphere, living things must be protected from the potentially dangerous mix of iron and oxygen. The human being possesses grams of this potentially toxic transition metal, which is shuttling through his oxygen-rich humor. Since long before the birth of modern medicine, the blood-vibrant red from a massive abundance of hemoglobin iron-has been a focus for health experts.

SCOPE OF REVIEW

We describe the current understanding of iron metabolism, highlight the many important discoveries that accreted this knowledge, and describe the perils of dysfunctional iron handling.

GENERAL SIGNIFICANCE

Isaac Newton famously penned, "If I have seen further than others, it is by standing upon the shoulders of giants". We hope that this review will inspire future scientists to develop intellectual pursuits by understanding the research and ideas from many remarkable thinkers of the past.

MAJOR CONCLUSIONS

The history of iron research is a long, rich story with early beginnings, and is far from being finished. This article is part of a Special Issue entitled Transferrins: Molecular mechanisms of iron transport and disorders.

Cellular transport and homeostasis of essential and nonessential metals

Metals can have a number of detrimental or beneficial effects in the cell, but first they must get in. Organisms have evolved transport mechanisms to get metals that are required, or essential into the cell. Nonessential metals often enter the cell through use of the machinery provided for essential metals. Much work has been done to advance our understanding of how these metals are transported across plasma and organelle membranes. This review provides an overview of essential and nonessential metal transport and homeostatic processes.

Effect of hereditary haemochromatosis genotypes and iron overload on other trace elements

PURPOSE

Hereditary haemochromatosis is a common genetic disorder involving dysregulation of iron absorption. There is some evidence to suggest that abnormal iron absorption and metabolism may influence the status of other important trace elements. In this study, the effect of abnormal HFE genotypes and associated iron overload on the status of other trace elements was examined.

METHODS

Dietary data and blood samples were collected from 199 subjects (mean age = 55.4 years; range = 21-81 years). Dietary intakes, serum selenium, copper and zinc concentrations and related antioxidant enzymes (glutathione peroxidase and superoxide dismutase) in subjects with normal HFE genotype (n = 118) were compared to those with abnormal HFE genotype, with both normal iron status (n = 42) and iron overload (n = 39).

RESULTS

For most dietary and biochemical variables measured, there were no significant differences between study groups. Red cell GPx was significantly higher in male subjects with normal genotypes and normal iron status compared to those with abnormal genotypes and normal iron status (P = 0.03) or iron overload (P = 0.001). Red cell GPx was also highest in normal women and significantly lower in the abnormal genotype and normal iron group (P = 0.016), but not in the iron overload group (P = 0.078).

CONCLUSION

Although it may not be possible to exclude a small effect between the genotype groups on RBC GPx, overall, haemochromatosis genotypes or iron overload did not appear to have a significant effect on selenium, copper or zinc status.

Zebrafish as a model for normal and malignant hematopoiesis

Zebrafish studies in the past two decades have made major contributions to our understanding of hematopoiesis and its associated disorders. The zebrafish has proven to be a powerful organism for studies in this area owing to its amenability to large-scale genetic and chemical screening. In addition, the externally fertilized and transparent embryos allow convenient genetic manipulation and in vivo imaging of normal and aberrant hematopoiesis. This review discusses available methods for studying hematopoiesis in zebrafish, summarizes key recent advances in this area, and highlights the current and potential contributions of zebrafish to the discovery and development of drugs to treat human blood disorders.

Hepcidin and ferroportin: the new players in iron metabolism

Systemic iron homeostasis is regulated by the interaction of the peptide hormone, hepcidin and the iron exporter, ferroportin. Mutations in FPN1, the gene that encodes ferroportin, result in iron-overload disease that shows dominant inheritance and variation in phenotype. The inheritance of ferroportin-linked disorders can be explained by the finding that ferroportin is a multimer and the product of the mutant allele participates in multimer formation. The nature of the ferroportin mutant can explain the variation in phenotype, which is due to either decreased iron export activity or decreased ability to be downregulated by hepcidin. Iron export through ferroportin is determined by the concentration of ferroportin in plasma membrane, which is the result of both synthetic and degradation events. Ferroportin degradation can occur by hepcidin-dependent and hepcidin-independent internalization. Ferroportin expression is regulated transcriptionally and posttranslationally.

Hypoxia-inducible factor-2α mediates the adaptive increase of intestinal ferroportin during iron deficiency in mice

BACKGROUND & AIMS

Iron deficiency and iron overload affect over a billion people worldwide. Dietary iron absorption in the small intestine is required for systemic iron homeostasis. Ferroportin (FPN) is the only characterized, mammalian, basolateral iron exporter. Despite the importance of FPN in maintaining iron homeostasis, its in vivo mechanisms of regulation are unclear.

METHODS

Systemic iron homeostasis was assessed in mice with intestine-specific disruption of genes encoding the von Hippel-Lindau tumor suppressor protein (Vhl), hypoxia-inducible factor (HIF)-1α, HIF-2α, and aryl hydrocarbon nuclear translocator (ARNT).

RESULTS

We observed biphasic regulation of Fpn during iron deficiency. Fpn was rapidly induced under conditions of low iron, which required the transcription factor HIF-2α. Targeted disruption of HIF-2α in the intestine inhibited Fpn induction in mice with low iron, through loss of transcriptional activation. Analysis of the Fpn promoter and in vivo chromatin immunoprecipitation assays demonstrated that HIF-2α directly binds to the Fpn promoter and induces its expression, indicating a mechanism of transcriptional regulation of Fpn following changes in systemic levels of iron. During chronic iron deficiency, FPN protein levels also increased, via increased stability through a HIF-2α-independent pathway.

CONCLUSIONS

In mice, expression of the gene that encodes Fpn and its protein levels are regulated by distinct pathways to provide a rapid and sustained response to acute and chronic iron deficiency. Therapies that target FPN might be developed for patients with iron-related disorders.

Gene therapy by allele selection in a mouse model of beta-thalassemia

To be of therapeutic use, autologous stem cells derived from patients with inherited genetic disorders require genetic modification via gene repair or insertion. Here, we present proof of principle that, for diseases associated with dominant alleles (gain-of-function or haploinsufficient loss-of-function), disease allele–free ES cells can be derived from afflicted individuals without genome manipulation. This approach capitalizes on the derivation of uniparental cells, such as parthenogenetic (PG) ES cell lines from disease allele–free gametes. Diploid mammalian uniparental embryos with only maternally (oocyte-) or paternally (sperm-)derived genomes fail early in development due to the nonequivalence of parental genomes caused by genomic imprinting. However, these uniparental embryos develop to the blastocyst stage, allowing the derivation of ES cell lines. Using a mouse model for dominant beta-thalassemia, we developed disease allele–free PG ES cell lines from the oocytes of affected animals. Phenotype correction was obtained in donor-genotype recipients after transplantation of in vitro hematopoietic ES cell derivatives. This genetic correction strategy without gene targeting is potentially applicable to any dominant disease. It could also be the sole approach for larger or more complex mutations that cannot be corrected by homologous recombination.

The molecular basis of iron overload disorders and iron-linked anemias

Iron homeostasis in vertebrates requires coordination between cells that export iron into plasma and those that utilize or store plasma iron. The coordination of iron acquisition and utilization is mediated by the interaction of the peptide hormone hepcidin and the iron exporter ferroportin. Hepcidin levels are increased during iron sufficiency and inflammation and are decreased in hypoxia or erythropoiesis. Hepcidin is a negative regulator of iron export. Hepcidin binds to cell surface ferroportin inducing ferroportin degradation and decreasing cellular iron export. Genetic disorders of iron overload of iron-linked anemia can be explained by changes in the level of hepcidin or ferroportin and of the ability of ferroportin to be internalized by hepcidin.

Ferroportin disease: a systematic meta-analysis of clinical and molecular findings

BACKGROUND & AIMS

Classical ferroportin disease is characterized by hyperferritinemia, normal transferrin saturation, and iron overload in macrophages. A non-classical form is characterized by additional hepatocellular iron deposits and a high transferrin saturation. Both forms demonstrate autosomal dominant transmission and are associated with ferroportin gene (SLC40A1) mutations. SLC40A1 encodes a cellular iron exporter expressed in macrophages, enterocytes, and hepatocytes. The aim of the analysis is to determine the penetrance of SLC40A1 mutations and to evaluate in silico tools to predict the functional impairment of ferroportin mutations as an alternative to in vitro studies.

METHODS

We conducted a systematic review of the literature and meta-analysis of the biochemical presentation, genetics, and pathology of ferroportin disease.

RESULTS

Of the 176 individuals reported with SLC40A1 mutations, 80 were classified as classical phenotype with hyperferritinemia and normal transferrin saturation. The non-classical phenotype with hyperferritinemia and elevated transferrin saturation was present in 53 patients. The remaining patients had normal serum ferritin or the data were reported incompletely. Despite an increased hepatic iron concentration in all biopsied patients, significant fibrosis or cirrhosis was present in only 11%. Hyperferritinemia was present in 86% of individuals with ferroportin mutations. Bio-informatic analysis of ferroportin mutations showed that the PolyPhen score has a sensitivity of 99% and a specificity of 67% for the discrimination between ferroportin mutations and polymorphisms.

CONCLUSIONS

In contrast to HFE hemochromatosis, ferroportin disease has a high penetrance, is genetically heterogeneous and is rarely associated with fibrosis. Non-classical ferroportin disease is associated with a higher risk of fibrosis and a more severe overload of hepatic iron.

Measurement of serum hepcidin-25 levels as a potential test for diagnosing hemochromatosis and related disorders

BACKGROUND

Iron overload syndromes include a wide spectrum of genetic and acquired conditions. Recent studies suggest suppressed hepcidin synthesis in the liver to be the molecular basis of hemochromatosis. However, a liver with acquired iron overload synthesizes an adequate amount of hepcidin. Thus, hepcidin could function as a biochemical marker for differential diagnosis of iron overload syndromes.

METHODS

We measured serum iron parameters and hepcidin-25 levels followed by sequencing HFE, HJV, HAMP, TFR2, and SLC40A1 genes in 13 Japanese patients with iron overload syndromes. In addition, we performed direct measurement of serum hepcidin-25 levels using liquid chromatography-tandem mass spectrometry in 3 Japanese patients with aceruloplasminemia and 4 Italians with HFE hemochromatosis.

RESULTS

One patient with HJV hemochromatosis, 2 with TFR2 hemochromatosis, and 3 with ferroportin disease were found among the 13 Japanese patients. The remaining 7 Japanese patients showed no evidence for genetic basis of iron overload syndrome. As far as the serum hepcidin-25 was concerned, seven patients with hemochromatosis and 3 with aceruloplasminemia showed markedly decreased serum hepcidin-25 levels. In contrast, 3 patients with ferroportin disease and 7 with secondary iron overload syndromes showed serum hepcidin levels parallel to their hyperferritinemia. Patients with iron overload syndromes were divided into 2 phenotypes presenting as low and high hepcidinemia. These were then associated with their genotypes.

CONCLUSION

Determining serum hepcidin-25 levels may aid differential diagnosis of iron overload syndromes prior to genetic analysis.

Ferroportin and erythroid cells: an update

In recent years there have been major advances in our knowledge of the regulation of iron metabolism that have had implications for understanding the pathophysiology of some human disorders like beta-thalassemia and other iron overload diseases. However, little is known about the relationship among ineffective erythropoiesis, the role of iron-regulatory genes, and tissue iron distribution in beta-thalassemia. The principal aim of this paper is an update about the role of Ferroportin during human normal and pathological erythroid differentiation. Particular attention will be given to beta-thalassemia and other diseases with iron overload. Recent discoveries indicate that there is a potential for therapeutic intervention in beta-thalassemia by means of manipulating iron metabolism.

Hemizygous deletion of COL3A1, COL5A2, and MSTN causes a complex phenotype with aortic dissection: a lesson for and from true haploinsufficiency

Aortic dilatation/dissection (AD) can occur spontaneously or in association with genetic syndromes, such as Marfan syndrome (MFS; caused by FBN1 mutations), MFS type 2 and Loeys-Dietz syndrome (associated with TGFBR1/TGFBR2 mutations), and Ehlers-Danlos syndrome (EDS) vascular type (caused by COL3A1 mutations). Although mutations in FBN1 and TGFBR1/TGFBR2 account for the majority of AD cases referred to us for molecular genetic testing, we have obtained negative results for these genes in a large cohort of AD patients, suggesting the involvement of additional genes or acquired factors. In this study we assessed the effect of COL3A1 deletions/duplications in this cohort. Multiplex ligation-dependent probe amplification (MLPA) analysis of 100 unrelated patients identified one hemizygous deletion of the entire COL3A1 gene. Subsequent microarray analyses and sequencing of breakpoints revealed the deletion size of 3,408,306 bp at 2q32.1q32.3. This deletion affects not only COL3A1 but also 21 other known genes (GULP1, DIRC1, COL5A2, WDR75, SLC40A1, ASNSD1, ANKAR, OSGEPL1, ORMDL1, LOC100129592, PMS1, MSTN, C2orf88, HIBCH, INPP1, MFSD6, TMEM194B, NAB1, GLS, STAT1, and STAT4), mutations in three of which (COL5A2, SLC40A1, and MSTN) have also been associated with an autosomal dominant disorder (EDS classical type, hemochromatosis type 4, and muscle hypertrophy). Physical and laboratory examinations revealed that true haploinsufficiency of COL3A1, COL5A2, and MSTN, but not that of SLC40A1, leads to a clinical phenotype. Our data not only emphasize the impact/role of COL3A1 in AD patients but also extend the molecular etiology of several disorders by providing hitherto unreported evidence for true haploinsufficiency of the underlying gene.

Suppression of SLC11A2 expression is essential to maintain duodenal integrity during dietary iron overload

Iron is essential for the survival of mammals, but iron overload causes fibrosis and carcinogenesis. Reduced iron absorption and regulated release into circulation in duodenal mucosa constitute two major mechanisms of protection against dietary iron overload; however, their relative contribution remains elusive. To study the significance of the former process, we generated SLC11A2 transgenic mice (TGs) under the control of the chicken beta-actin promoter. TGs were viable and fertile, and displayed no overt abnormalities up to 20 months. No significant difference in iron concentration was observed in major solid organs between TGs and their wild-type littermates, suggesting that increased number of iron transporters does not lead to increased iron absorption. To test the sensitivity to iron overload, TGs and wild-type mice were fed with an iron-rich diet containing 2% ferric citrate. Iron supplementation caused suppression of endogenous duodenal SLC11A2 expression, down-regulation of duodenal ferroportin, and overexpression of hepatic hepcidin, precluding excessive iron uptake both in the TGs and wild-type mice. However, iron-treated TGs revealed increased mortality, resulting from oxidative mucosal damage leading to hemorrhagic erosion throughout the whole intestinal area. These findings suggest that reduced iron release from duodenal cells into circulation plays a role in mitigating excessive iron uptake from the diet and that finely regulated duodenal absorption is essential to protect intestinal mucosa from iron-induced oxidative damage.

Ferroportin (SLC40A1) Q248H mutation is associated with lower circulating plasma tumor necrosis factor-alpha and macrophage migration inhibitory factor concentrations in African children

BACKGROUND

Iron deficiency and the Q248H mutation in the gene, SLC40A1, that encodes for the cellular iron exporter, ferroportin, are both common in African children. The iron status of macrophages influences the pro-inflammatory response of these cells. We hypothesized that Q248H mutation may modify the inflammatory response by influencing iron levels within macrophages.

METHODS

The Q248H mutation and circulating concentrations of ferritin, C-reactive protein and selected pro-inflammatory cytokines (interleukin-12, interferon-gamma, TNF-alpha, and macrophage migration inhibitory factor) and anti-inflammatory cytokines (interleukin-4 and interleukin-10) were measured in 69 pre-school children recruited from well-child clinics in Harare, Zimbabwe.

RESULTS

In multivariate analysis, both ferroportin Q248H and ferritin <10ug/L were associated with significantly lower circulating concentrations of tumor necrosis factor-alpha. Ferroportin Q248H but not low iron stores was associated with lower circulating macrophage migration inhibitory factor as well. Anti-inflammatory cytokine levels were not significantly associated with either ferroportin Q248H or iron status.

CONCLUSIONS

Ferroportin Q248H and low iron stores are both associated with lower circulating tumor necrosis factor-alpha, while only ferroportin Q248H is associated with lower circulating macrophage migration inhibitory factor. Whether the reduced production of tumor necrosis factor-alpha observed in ferroportin Q248H heterozygotes may be of significance in anemia of chronic disease is yet to be determined.

Hepatocyte-targeted HFE and TFR2 control hepcidin expression in mice

Hereditary hemochromatosis is caused by mutations in the hereditary hemochromatosis protein (HFE), transferrin-receptor 2 (TfR2), hemojuvelin, hepcidin, or ferroportin genes. Hepcidin is a key iron regulator, which is secreted by the liver, and decreases serum iron levels by causing the down-regulation of the iron transporter, ferroportin. Mutations in either HFE or TfR2 lower hepcidin levels, implying that both HFE and TfR2 are necessary for regulation of hepcidin expression. In this study, we used a recombinant adeno-associated virus, AAV2/8, for hepatocyte-specific expression of either Hfe or Tfr2 in mice. Expression of Hfe in Hfe-null mice both increased Hfe and hepcidin mRNA and lowered hepatic iron and Tf saturation. Expression of Tfr2 in Tfr2-deficient mice had a similar effect, whereas expression of Hfe in Tfr2-deficient mice or of Tfr2 in Hfe-null mice had no effect on liver or serum iron levels. Expression of Hfe in wild-type mice increased hepcidin mRNA and lowered iron levels. In contrast, expression of Tfr2 had no effect on wild-type mice. These findings suggest that Hfe is limiting in formation of the Hfe/Tfr2 complex that regulates hepcidin expression. In addition, these studies show that the use of recombinant AAV vector to deliver genes is a promising approach for studying physiologic consequences of protein complexes.

Genetic mechanisms and modifying factors in hereditary hemochromatosis

Primary iron overload is one of the most common inherited diseases worldwide. Several genetic mutations underlie the various forms of the disease, which have similar pathophysiological profiles but distinct clinical presentations. Patients with hereditary hemochromatosis absorb too much iron from the diet, which accumulates over time within parenchymal cells. This accumulation leads to eventual organ failure as a consequence of iron-mediated formation of free radicals. The mechanism underlying this excessive absorption of iron is a sensing defect caused by the reduced formation of hepcidin, the master regulator of iron homeostasis, as a consequence of mutations in the genes encoding several membrane-bound signaling molecules present on hepatocytes. A considerable number of carriers of these specific genetic mutations, however, do not develop iron overload, indicating that additional genetic and environmental factors modify the severity and clinical penetrance of disease. In affected patients, early initiation of treatment by phlebotomy can prevent organ damage. Genetic screening of first-degree relatives can be also used to identify individuals at risk. Our expanding knowledge of the regulation of iron metabolism and the role of factors that modify the severity of the disease may lead to the design of new and improved treatments.

Ferroportin is a manganese-responsive protein that decreases manganese cytotoxicity and accumulation

Although manganese (Mn) is an essential trace element for human development and growth, chronic exposure to excessive Mn levels can result in psychiatric and motor disturbances, referred to as manganism. However, there are no known mechanism(s) for efflux of excess Mn from mammalian cells. Here, we test the hypothesis that the cytoplasmic iron (Fe) exporter ferroportin (Fpn) may also function as a Mn exporter to attenuate Mn toxicity. Using an inducible human embryonic kidney (HEK293T) cell model, we examined the influence of Fpn expression on Mn-induced cytotoxicity and intracellular Mn concentrations. We found that induction of an Fpn-green fluorescent protein fusion protein in HEK293T cells was cytoprotective against several measures of Mn toxicity, including Mn-induced cell membrane leakage and Mn-induced reductions in glutamate uptake. Fpn-green fluorescent protein mediated cytoprotection correlated with decreased Mn accumulation following Mn exposure. Thus, Fpn expression reduces Mn toxicity concomitant with reduced Mn accumulation. To determine if mammalian cells may utilize Fpn in response to increased intracellular Mn concentrations and toxicity, we assessed endogenous Fpn levels in Mn-exposed HEK293T cells and in mouse brain in vivo. We find that 6 h of Mn exposure in HEK293T cells is associated with a significant increase in Fpn levels. Furthermore, mice exposed to Mn showed an increase in Fpn levels in both the cerebellum and cortex. Collectively, these results indicate that (i) Mn exposure promotes Fpn protein expression, (ii) Fpn expression reduces net Mn accumulation, and (iii) reduces cytotoxicity associated with exposure to this metal.

Stoichiometries of transferrin receptors 1 and 2 in human liver

Mutations in either the hereditary hemochromatosis protein, HFE, or transferrin receptor 2, TfR2, result in a similarly severe form of the most common type of iron overload disease called hereditary hemochromatosis. Models of the interactions between HFE, TfR1, and TfR2 imply that these proteins are present in different molar concentrations in the liver, where they control expression of the iron regulatory hormone, hepcidin, in response to body iron loading. The aim of this study was to determine in vivo levels of mRNA by quantitative RT-PCR and concentrations of these proteins by quantitative immunoblotting in human liver tissues. The level of TfR2 mRNA was 21- and 63-fold higher than that of TfR1 and HFE, respectively. Molar concentration of TfR2 protein was the highest and determined to be 1.95 nmol/g protein in whole cell lysates and 10.89 nmol/g protein in microsomal membranes. Molar concentration of TfR1 protein was 4.5- and 6.1-fold lower than that of TfR2 in whole cell lysates and membranes, respectively. The level of HFE protein was below 0.53 nmol/g of total protein. HFE is thus present in substoichiometric concentrations with respect to both TfR1 and TfR2 in human liver tissue. This finding supports a model, in which availability of HFE is limiting for formation of complexes with TfR1 or TfR2.

Hepcidin revisited, disulfide connectivity, dynamics, and structure

Hepcidin is a tightly folded 25-residue peptide hormone containing four disulfide bonds, which has been shown to act as the principal regulator of iron homeostasis in vertebrates. We used multiple techniques to demonstrate a disulfide bonding pattern for hepcidin different from that previously published. All techniques confirmed the following disulfide bond connectivity: Cys(1)-Cys(8), Cys(3)-Cys(6), Cys(2)-Cys(4), and Cys(5)-Cys(7). NMR studies reveal a new model for hepcidin that, at ambient temperatures, interconverts between two different conformations, which could be individually resolved by temperature variation. Using these methods, the solution structure of hepcidin was determined at 325 and 253 K in supercooled water. X-ray analysis of a co-crystal with Fab appeared to stabilize a hepcidin conformation similar to the high temperature NMR structure.

The molecular basis of hepcidin-resistant hereditary hemochromatosis

The interaction between the hormone hepcidin and the iron exporter ferroportin (Fpn) regulates plasma iron concentrations. Hepcidin binds to Fpn and induces its internalization and degradation, resulting in decreased iron efflux from cells into plasma. Fpn mutations in N144, Y64N, and C326 residue cause autosomal dominant disease with parenchymal iron overload, apparently due to the resistance of mutant Fpn to hepcidin-mediated internalization. To define the mechanism of resistance, we generated human Fpn constructs bearing the pathogenic mutations. The mutants localized to the cell surface and exported iron normally, but were partially or completely resistant to hepcidin-mediated internalization and continued to export iron despite the presence of hepcidin. The primary defect with exofacial C326 substitutions was the loss of hepcidin binding, which resulted in the most severe phenotype. The thiol form of C326 was essential for interaction with hepcidin, suggesting that C326-SH homology is located in or near the binding site of hepcidin. In contrast, N144 and Y64 residues were not required for hepcidin binding, but their mutations impaired the subsequent internalization of the ligand-receptor complex. Our observations explain why the mutations in C326 Fpn residue produce a severe form of hemochromatosis with iron overload at an early age.

Interaction of the hereditary hemochromatosis protein HFE with transferrin receptor 2 is required for transferrin-induced hepcidin expression

The mechanisms that allow the body to sense iron levels in order to maintain iron homeostasis are unknown. Patients with the most common form of hereditary iron overload have mutations in the hereditary hemochromatosis protein HFE. They have lower levels of hepcidin than unaffected individuals. Hepcidin, a hepatic peptide hormone, negatively regulates iron efflux from the intestines into the blood. We report two hepatic cell lines, WIF-B cells and HepG2 cells transfected with HFE, where hepcidin expression responded to iron-loaded transferrin. The response was abolished when endogenous transferrin receptor 2 (TfR2) was suppressed or in primary hepatocytes lacking either functional TfR2 or HFE. Furthermore, transferrin-treated HepG2 cells transfected with HFE chimeras containing only the alpha3 and cytoplasmic domains could upregulate hepcidin expression. Since the HFE alpha3 domain interacts with TfR2, these results supported our finding that TfR2/HFE complex is required for transcriptional regulation of hepcidin by holo-Tf.

Investigation of the biophysical and cell biological properties of ferroportin, a multipass integral membrane protein iron exporter

Ferroportin is a multipass membrane protein that serves as an iron exporter in many vertebrate cell types. Ferroportin-mediated iron export is controlled by the hormone hepcidin, which binds ferroportin, causing its internalization and degradation. Mutations in ferroportin cause a form of the iron overload hereditary disease hemochromatosis. Relatively little is known about ferroportin's properties or the mechanism by which mutations cause disease. In this study, we expressed and purified human ferroportin to characterize its biochemical/biophysical properties in solution and conducted cell biological studies in mammalian cells. We found that purified detergent-solubilized ferroportin is a well-folded monomer that binds hepcidin. In cell membranes, the N- and C-termini were both cytosolic, implying an even number of transmembrane regions, and ferroportin was mainly localized to the plasma membrane. Hepcidin addition resulted in a redistribution of ferroportin to intracellular compartments that labeled with early endosomal and lysosomal, but not Golgi, markers and that trafficked along microtubules. An analysis of 16 disease-related ferroportin mutants revealed that all were expressed and trafficked to the plasma membrane but that some were resistant to hepcidin-induced internalization. The characterizations reported here form a basis upon which models for ferroportin's role in regulating iron homeostasis in health and disease can be interpreted.

Evolutionary mutant models for human disease

Although induced mutations in traditional laboratory animals have been valuable as models for human diseases, they have some important limitations. Here, we propose a complementary approach to discover genes and mechanisms that might contribute to human disorders: the analysis of evolutionary mutant models in which adaptive phenotypes mimic maladaptive human diseases. If the type and mode of action of mutations favored by natural selection in wild populations are similar to those that contribute to human diseases, then studies in evolutionary mutant models have the potential to identify novel genetic factors and gene-by-environment interactions that affect human health and underlie human disease.

Hepcidin regulation of iron transport

The discovery of hepcidin as a key regulator of iron homeostasis has advanced our current knowledge of this field. Liver-derived hepcidin peptide is secreted in response to iron and inflammation and interacts with the iron export protein ferroportin. This review summarizes recent advances discussed at the Symposium. A particular focus is on molecular interactions between hepcidin and ferroportin, the regulation of hepcidin expression by iron and inflammation, and emerging methods to measure serum hepcidin in human populations.

Hereditary hemochromatosis in the post-HFE era

Following the discovery of the HFE gene in 1996 and its linkage to the iron overload disorder hereditary hemochromatosis (HH) there have been profound developments in our understanding of the pathogenesis of the biochemical and clinical manifestations of a number of iron overload disorders. This article provides an update of recent developments and key issues relating to iron homeostasis and inherited disorders of iron overload, with emphasis on HFE-related HH, and is based on the content of the American Association for the Study of Liver Diseases Single-Topic Conference entitled "Hemochromatosis: What has Happened After HFE?" which was held at the Emory Convention Center in Atlanta, September 7-9, 2007.

Intracellular iron transport and storage: from molecular mechanisms to health implications

Maintenance of proper "labile iron" levels is a critical component in preserving homeostasis. Iron is a vital element that is a constituent of a number of important macromolecules, including those involved in energy production, respiration, DNA synthesis, and metabolism; however, excess "labile iron" is potentially detrimental to the cell or organism or both because of its propensity to participate in oxidation-reduction reactions that generate harmful free radicals. Because of this dual nature, elaborate systems tightly control the concentration of available iron. Perturbation of normal physiologic iron concentrations may be both a cause and a consequence of cellular damage and disease states. This review highlights the molecular mechanisms responsible for regulation of iron absorption, transport, and storage through the roles of key regulatory proteins, including ferroportin, hepcidin, ferritin, and frataxin. In addition, we present an overview of the relation between iron regulation and oxidative stress and we discuss the role of functional iron overload in the pathogenesis of hemochromatosis, neurodegeneration, and inflammation.

Zebrafish in hematology: sushi or science?

After a decade of the "modern era" of zebrafish hematology research, what have been their major contributions to hematology and what challenges does the model face? This review argues that, in hematology, zebrafish have demonstrated their suitability, are proving their utility, have supplied timely and novel discoveries, and are poised for further significant contributions. It presents an overview of the anatomy, physiology, and genetics of zebrafish hematopoiesis underpinning their use in hematology research. Whereas reverse genetic techniques enable functional studies of particular genes of interest, forward genetics remains zebrafish's particular strength. Mutants with diverse and interesting hematopoietic defects are emerging from multiple genetic screens. Some mutants model hereditary blood diseases, occasionally leading to disease genes first; others provide insights into developmental hematology. Models of malignant hematologic disorders provide tools for drug-target and pharmaceutics discovery. Numerous transgenic zebrafish with fluorescently marked blood cells enable live-cell imaging of inflammatory responses and host-pathogen interactions previously inaccessible to direct observation in vivo, revealing unexpected aspects of leukocyte behavior. Zebrafish disease models almost uniquely provide a basis for efficient whole animal chemical library screens for new therapeutics. Despite some limitations and challenges, their successes and discovery potential mean that zebrafish are here to stay in hematology research.

Non-HFE hemochromatosis: genetics, pathogenesis, and clinical management

Recent advances in our understanding of iron metabolism and the epidemiology of iron overload disorders have shown that hereditary forms of hemochromatosis can result from mutations in several iron metabolism genes other than HFE, including Hamp, HJV, TFR2, and SCL40A. These "non-HFE" forms of hemochromatosis are much rarer than HFE-related hemochromatosis but exhibit a similar phenotype, and with the exception of ferroportin disease, a similar pattern of inheritance and parenchymal iron accumulation. Therefore, these diseases can be thought of as variant forms of a primary hepatic iron overload syndrome; thus, a unified approach can be used for evaluation and diagnosis. Management generally consists of periodic phlebotomies until iron is depleted.

Effects of iron loading on muscle: genome-wide mRNA expression profiling in the mouse

Background

Hereditary hemochromatosis (HH) encompasses genetic disorders of iron overload characterized by deficient expression or function of the iron-regulatory hormone hepcidin. Mutations in 5 genes have been linked to this disease: HFE, TFR2 (encoding transferrin receptor 2), HAMP (encoding hepcidin), SLC40A1 (encoding ferroportin) and HJV (encoding hemojuvelin). Hepcidin inhibits iron export from cells into plasma. Hemojuvelin, an upstream regulator of hepcidin expression, is expressed in mice mainly in the heart and skeletal muscle. It has been suggested that soluble hemojuvelin shed by the muscle might reach the liver to influence hepcidin expression. Heart muscle is one of the target tissues affected by iron overload, with resultant cardiomyopathy in some HH patients. Therefore, we investigated the effect of iron overload on gene expression in skeletal muscle and heart using Illumina™ arrays containing over 47,000 probes. The most apparent changes in gene expression were confirmed using real-time RT-PCR.

Results

Genes with up-regulated expression after iron overload in both skeletal and heart muscle included angiopoietin-like 4, pyruvate dehydrogenase kinase 4 and calgranulin A and B. The expression of transferrin receptor, heat shock protein 1B and DnaJ homolog B1 were down-regulated by iron in both muscle types. Two potential hepcidin regulatory genes, hemojuvelin and neogenin, showed no clear change in expression after iron overload.

Conclusion

Microarray analysis revealed iron-induced changes in the expression of several genes involved in the regulation of glucose and lipid metabolism, transcription and cellular stress responses. These may represent novel connections between iron overload and pathological manifestations of HH such as cardiomyopathy and diabetes.

Non-HFE haemochromatosis

Non-HFE hereditary haemochromatosis (HH) refers to a genetically heterogeneous group of iron overload disorders that are unlinked to mutations in the HFE gene. The four main types of non-HFE HH are caused by mutations in the hemojuvelin, hepcidin, transferrin receptor 2 and ferroportin genes. Juvenile haemochromatosis is an autosomal recessive disorder and can be caused by mutations in either hemojuvelin or hepcidin. An adult onset form of HH similar to HFE-HH is caused by homozygosity for mutations in transferrin receptor 2. The autosomal dominant iron overload disorder ferroportin disease is caused by mutations in the iron exporter ferroportin. The clinical characteristics and molecular basis of the various types of non-HFE haemochromatosis are reviewed. The study of these disorders and the molecules involved has been invaluable in improving our understanding of the mechanisms involved in the regulation of iron metabolism.

SLC40A1 Q248H allele frequencies and Q248H-associated risk of non-HFE iron overload in persons of sub-Saharan African descent

The ferroportin polymorphism SLC40A1 Q248H (exon 6, cDNA 744G-->T; Gln248His) occurs in persons of sub-Saharan African descent with and without iron overload, and is associated with elevated serum ferritin concentrations (SF). However, the risk of iron overload associated with Q248H has not been defined. We tabulated previously reported Q248H allele frequency estimates in African-Americans and Native Africans, and computed the risk of iron overload associated with Q248H in subjects who lacked HFE C282Y. The aggregate Q248H allele frequency in 1038 African-Americans in two cohorts from Alabama and one cohort each from Washington, DC and California was 0.0525 (95% CI: 0.0451, 0.0652); there was no significant difference in frequencies across these cohorts. The aggregate frequency in 259 Natives from southeast Africa in two cohorts was 0.0946 (95% CI: 0.0694, 0.1198); the difference between the frequencies of these cohorts was not significant. The aggregate Q248H frequencies in African-Americans and Native Africans differed significantly (0.0525 vs. 0.0946, respectively; p=0.0021). There were reports of 24 unrelated African-Americans and 15 unrelated Native Africans without HFE C282Y who had iron overload. In African-Americans, the odds ratio (OR) of Q248H-associated risk of iron overload using 610 C282Y-negative control subjects unselected for SF was 1.57 (95% CI: 0.52, 4.72; p=0.29). In Native Africans, the OR using 208 control subjects unselected for SF was 1.05 (95% CI: 0.28, 3.90; p=0.58). We conclude that the frequency of SLC40A1 Q248H is significantly lower in African-Americans than in Native Africans. Although OR estimates of iron overload in African-Americans and Native Africans with Q248H were greater than unity, the increased OR were not statistically significant.

The flatiron mutation in mouse ferroportin acts as a dominant negative to cause ferroportin disease

Ferroportin disease is caused by mutation of one allele of the iron exporter ferroportin (Fpn/IREG1/Slc40a1/MTP1). All reported human mutations are missense mutations and heterozygous null mutations in mouse Fpn do not recapitulate the human disease. Here we describe the flatiron (ffe) mouse with a missense mutation (H32R) in Fpn that affects its localization and iron export activity. Similar to human patients with classic ferroportin disease, heterozygous ffe/+ mice present with iron loading of Kupffer cells, high serum ferritin, and low transferrin saturation. In macrophages isolated from ffe/+ heterozygous mice and through the use of Fpn plasmids with the ffe mutation, we show that Fpn(ffe) acts as a dominant negative, preventing wild-type Fpn from localizing on the cell surface and transporting iron. These results demonstrate that mutations in Fpn resulting in protein mislocalization act in a dominant-negative fashion to cause disease, and the Fpn(ffe) mouse represents the first mouse model of ferroportin disease.

Iron Overload (with Attention to Genetic Testing and Diagnosis/Management of HFE Wild Type Patients)

The discovery of the HFE, HJV, HAMP, TfR2, and SLC40A1 genes and preliminary understanding of their roles in iron homeostasis have contributed tremendously to our understanding of the pathogenesis of genetic hemochromatosis. Although several new models of iron metabolism have been proposed, some key "sensor" steps of iron absorption in the enterocytes and of iron storage in hepatocytes and other cells remain unclear. A diagnosis of non-HFE genetic hemochromatosis should be considered in patients with unexplained iron overload who do not have the common mutations in the HFE genes. Phenotypic evaluation such as liver biopsy and measurement of hepatic iron concentration remain important in non-HFE hemochromatosis because mutations in other genes are rare and there are no other available noninvasive tests to confirm the diagnosis. Phlebotomy remains the mainstay of therapy also for non-HFE hemochromatosis. However, phlebotomy may not be well tolerated in certain forms of non-HFE hemochromatosis such as "ferroportin disease."