STAT3 mediates hepatic hepcidin expression and its inflammatory stimulation

Modelling Systemic Iron Regulation during Dietary Iron Overload and Acute Inflammation: Role of Hepcidin-Independent Mechanisms

Systemic iron levels must be maintained in physiological concentrations to prevent diseases associated with iron deficiency or iron overload. A key role in this process plays ferroportin, the only known mammalian transmembrane iron exporter, which releases iron from duodenal enterocytes, hepatocytes, or iron-recycling macrophages into the blood stream. Ferroportin expression is tightly controlled by transcriptional and post-transcriptional mechanisms in response to hypoxia, iron deficiency, heme iron and inflammatory cues by cell-autonomous and systemic mechanisms. At the systemic level, the iron-regulatory hormone hepcidin is released from the liver in response to these cues, binds to ferroportin and triggers its degradation. The relative importance of individual ferroportin control mechanisms and their interplay at the systemic level is incompletely understood. Here, we built a mathematical model of systemic iron regulation. It incorporates the dynamics of organ iron pools as well as regulation by the hepcidin/ferroportin system. We calibrated and validated the model with time-resolved measurements of iron responses in mice challenged with dietary iron overload and/or inflammation. The model demonstrates that inflammation mainly reduces the amount of iron in the blood stream by reducing intracellular ferroportin transcription, and not by hepcidin-dependent ferroportin protein destabilization. In contrast, ferroportin regulation by hepcidin is the predominant mechanism of iron homeostasis in response to changing iron diets for a big range of dietary iron contents. The model further reveals that additional homeostasis mechanisms must be taken into account at very high dietary iron levels, including the saturation of intestinal uptake of nutritional iron and the uptake of circulating, non-transferrin-bound iron, into liver. Taken together, our model quantitatively describes systemic iron metabolism and generated experimentally testable predictions for additional ferroportin-independent homeostasis mechanisms.

The importance of iron in many physiological processes relies on its ability to participate in reduction-oxidation reactions. This property also leads to potential toxicity if concentrations of free iron are not properly managed by cells and tissues. Multicellular organisms therefore evolved intricate regulatory mechanisms to control systemic iron levels. A central regulatory mechanism is the binding of the hormone hepcidin to the iron exporter ferroportin, which controls the major fluxes of iron into blood plasma. Here, we present a mathematical model that is fitted and validated against experimental data to simulate the iron content in different organs following dietary changes and/or inflammatory states, or genetic perturbation of the hepcidin/ferroportin regulatory system. We find that hepcidin mediated ferroportin control is essential, but not sufficient to quantitatively explain several of our experimental findings. Thus, further regulatory mechanisms had to be included in the model to reproduce reduced serum iron levels in response to inflammation, the preferential accumulation of iron in the liver in the case of iron overload, or the maintenance of physiological serum iron concentrations if dietary iron levels are very high. We conclude that hepcidin-independent mechanisms play an important role in maintaining systemic iron homeostasis.

Silkworm feces extract improves iron deficiency anemia via suppressing hepcidin expression and promoting iron-regulatory proteins expression

In this study, we aimed to explore the preventive efficacy of SFE toward iron deficiency anemia in rats and clarify the underlying mechanisms. Findings suggest that SFE may be an efficient oral iron supplement to ameliorate iron deficiency anemia.

Regulation of the Iron Homeostatic Hormone Hepcidin

Iron is required for many biological processes but is also toxic in excess; thus, body iron balance is maintained through sophisticated regulatory mechanisms. The lack of a regulated iron excretory mechanism means that body iron balance is controlled at the level of absorption from the diet. Iron absorption is regulated by the hepatic peptide hormone hepcidin. Hepcidin also controls iron release from cells that recycle or store iron, thus regulating plasma iron concentrations. Hepcidin exerts its effects through its receptor, the cellular iron exporter ferroportin. Important regulators of hepcidin, and therefore of systemic iron homeostasis, include plasma iron concentrations, body iron stores, infection and inflammation, and erythropoiesis. Disturbances in the regulation of hepcidin contribute to the pathogenesis of many iron disorders: hepcidin deficiency causes iron overload in hereditary hemochromatosis and nontransfused β-thalassemia, whereas overproduction of hepcidin is associated with iron-restricted anemias seen in patients with chronic kidney disease, chronic inflammatory diseases, some cancers, and inherited iron-refractory iron deficiency anemia. This review summarizes our current understanding of the molecular mechanisms and signaling pathways involved in the control of hepcidin synthesis in the liver, a principal determinant of plasma hepcidin concentrations.

Differences in hepatic expression of iron, inflammation and stress-related genes in patients with nonalcoholic steatohepatitis

 Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide. We have previously shown that hepatic reticuloendothelial system (RES) iron deposition is associated with an advanced degree of nonalcoholic steatohepatitis (NASH) in humans. In this study, we aimed to determine differentially expressed genes related to iron overload, inflammation and oxidative stress pathways, with the goal of identifying factors associated with NASH progression. Seventy five patients with NAFLD were evaluated for their biochemical parameters and their liver tissue analyzed for NASH histological characteristics. Gene expression analysis of pathways related to iron homeostasis, inflammation and oxidative stress was performed using real-time PCR. Gene expression was compared between subjects based on disease status and presence of hepatic iron staining. We observed increased gene expression of hepcidin (HAMP) (2.3 fold, p = 0.027), transmembrane serine proteinase 6 (TMPRSS6) (8.4 fold, p = 0.003), signal transducer and activator of transcription 3 (STAT3) (5.5 fold, p = 0.004), proinflammatory cytokines; IL-1? (2.7 fold, p = 0.046) and TNF-? (3.8 fold, p = 0.001) in patients with NASH. TMPRSS6, a negative regulator of HAMP, is overexpressed in patients with NASH and HIF1? (hypoxia inducible factor-1) is downregulated. NAFLD patients with hepatic iron deposition exhibited higher hepcidin expression (3.1 fold, p = 0.04) but lower expression of cytokines. In conclusion, we observed elevated hepatic HAMP expression in patients with NASH and in NAFLD patients who had hepatic iron deposition, while proinflammatory cytokines displayed elevated expression only in patients with NASH, suggesting a regulatory role for hepcidin in NAFL to NASH transition and in mitigating inflammatory responses.

Antimicrobial Activity of Mesenchymal Stem Cells: Current Status and New Perspectives of Antimicrobial Peptide-Based Therapies

While mesenchymal stem cells (MSCs)-based therapy appears to be promising, there are concerns regarding possible side effects related to the unwanted suppression of antimicrobial immunity leading to an increased risk of infection. Conversely, recent data show that MSCs exert strong antimicrobial effects through indirect and direct mechanisms, partially mediated by the secretion of antimicrobial peptides and proteins (AMPs). In fact, MSCs have been reported to increase bacterial clearance in preclinical models of sepsis, acute respiratory distress syndrome, and cystic fibrosis-related infections. This article reviews the current evidence regarding the direct antimicrobial effector function of MSCs, focusing mainly on the role of MSCs-derived AMPs. The strategies that might modulate the expression and secretion of these AMPs, leading to enhanced antimicrobial effect, are highlighted. Furthermore, studies evaluating the presence of AMPs in the cargo of extracellular vesicles (EVs) are underlined as perspective opportunities to develop new drug delivery tools. The antimicrobial potential of MSCs-derived EVs can also be heightened through cell conditioning and/or drug loading. Finally, improving the pharmacokinetics and delivery, in addition to deciphering the multi-target drug status of AMPs, should synergistically lead to key advances against infections caused by drug-resistant strains.

Regulation of hepcidin expression by inflammation-induced activin B

Activin B is induced in response to inflammation in the liver and enhances hepcidin expression, but the source of activin B and the molecular mechanism underlying hepcidin induction are not clear yet. Lipopolysaccharide (LPS)-induced inflammation induced inhibin βB but not inhibin α or inhibin βA expression in the liver, implicating activin B induction. Immunoreactive inhibin βB was detected in endothelial cells and Kupffer cells in LPS-treated liver. Activin B, but not activin A or activin AB, directly increased hepcidin expression. Activin B induced phosphorylation and activation of Smad1/5/8, the BMP-regulated (BR)-Smads. The stimulation of hepcidin transcription by activin B was mediated by ALK2 and ActRIIA, receptors for the TGF-β family. Unexpectedly, activin B-induced hepcidin expression and BR-Smad phosphorylation were resistant to the effects of LDN-193189, an ALK2/3/6 inhibitor. ALK2 and ActRIIA complex formation in response to activin B may prevent the approach of LDN-193189 to ALK2 to inhibit its activity. Activin B also induced phosphorylation of Smad2/3, the TGF-β/activin-regulated (AR)-Smad, and increased expression of connective tissue growth factor, a gene related to liver fibrogenesis, through ALK4 and ActRIIA/B. Activin B-induced activation of the BR-Smad pathway was also detected in non-liver-derived cells. The present study reveals the broad signaling of activin B, which is induced in non-parenchymal cells in response to hepatic inflammation, in hepatocytes.

Heparanase Overexpression Reduces Hepcidin Expression, Affects Iron Homeostasis and Alters the Response to Inflammation

Hepcidin is the key regulator of systemic iron availability that acts by controlling the degradation of the iron exporter ferroportin. It is expressed mainly in the liver and regulated by iron, inflammation, erythropoiesis and hypoxia. The various agents that control its expression act mainly via the BMP6/SMAD signaling pathway. Among them are exogenous heparins, which are strong hepcidin repressors with a mechanism of action not fully understood but that may involve the competition with the structurally similar endogenous Heparan Sulfates (HS). To verify this hypothesis, we analyzed how the overexpression of heparanase, the HS degrading enzyme, modified hepcidin expression and iron homeostasis in hepatic cell lines and in transgenic mice. The results showed that transient and stable overexpression of heparanase in HepG2 cells caused a reduction of hepcidin expression and of SMAD5 phosphorylation. Interestingly, the clones showed also altered level of TfR1 and ferritin, indices of a modified iron homeostasis. The heparanase transgenic mice showed a low level of liver hepcidin, an increase of serum and liver iron with a decrease in spleen iron content. The hepcidin expression remained surprisingly low even after treatment with the inflammatory LPS. The finding that modification of HS structure mediated by heparanase overexpression affects hepcidin expression and iron homeostasis supports the hypothesis that HS participate in the mechanisms controlling hepcidin expression.

The SMAD Pathway Is Required for Hepcidin Response During Endoplasmic Reticulum Stress

Hepcidin, the iron hormone, is regulated by a number of stimulatory and inhibitory signals. The cAMP responsive element binding protein 3-like 3 (CREB3L3) mediates hepcidin response to endoplasmic reticulum (ER) stress. In this study we asked whether hepcidin response to ER stress also requires the small mother against decapentaplegic (SMAD)-1/5/8 pathway, which has a major role in hepcidin regulation in response to iron and other stimuli. We analyzed hepcidin mRNA expression and promoter activity in response to ER stressors in HepG2 cells in the presence of the bone morphogenetic protein (BMP) type I receptor inhibitor LDN-193189, mutated hepcidin promoter or small interfering RNA against different SMAD proteins. We then used a similar approach in vivo in wild-type, Smad1/5, or Creb3l3^-/- animals undergoing ER stress. In vitro, LDN-193189 prevented hepcidin mRNA induction by different ER stressors. Seemingly, mutation of a BMP-responsive element in the hepcidin promoter prevented ER stress-mediated up-regulation. Moreover, in vitro silencing of SMAD proteins by small interfering RNA, in particular SMAD5, blunted hepcidin response to ER stress. On the contrary, hepcidin induction by ER stress was maintained when using antibodies against canonical BMP receptor ligands. In vivo, hepcidin was induced by ER stress and prevented by LDN-193189. In addition, in Smad1/5 knockout mice, ER stress was unable to induce hepcidin expression. Finally, in Creb3l3 knockout mice, in response to ER stress, SMAD1/5 were correctly phosphorylated and hepcidin induction was still appreciable, although to a lesser extent as compared with the control mice. In conclusion, our study indicates that hepcidin induction by ER stress involves the central regulatory SMAD1/5 pathway.

Orphan nuclear receptor SHP regulates iron metabolism through inhibition of BMP6-mediated hepcidin expression

Small heterodimer partner (SHP) is a transcriptional corepressor regulating diverse metabolic processes. Here, we show that SHP acts as an intrinsic negative regulator of iron homeostasis. SHP-deficient mice maintained on a high-iron diet showed increased serum hepcidin levels, decreased expression of the iron exporter ferroportin as well as iron accumulation compared to WT mice. Conversely, overexpression of either SHP or AMP-activated protein kinase (AMPK), a metabolic sensor inducing SHP expression, suppressed BMP6-induced hepcidin expression. In addition, an inhibitory effect of AMPK activators metformin and AICAR on BMP6-mediated hepcidin gene expression was significantly attenuated by ablation of SHP expression. Interestingly, SHP physically interacted with SMAD1 and suppressed BMP6-mediated recruitment of the SMAD complex to the hepcidin gene promoter by inhibiting the formation of SMAD1 and SMAD4 complex. Finally, overexpression of SHP and metformin treatment of BMP6 stimulated mice substantially restored hepcidin expression and serum iron to baseline levels. These results reveal a previously unrecognized role for SHP in the transcriptional control of iron homeostasis.

S-Propargyl-Cysteine, a Novel Hydrogen Sulfide Donor, Inhibits Inflammatory Hepcidin and Relieves Anemia of Inflammation by Inhibiting IL-6/STAT3 Pathway

Anemia of inflammation (AI) is clinically prevalent and greatly threatens public health. Traditional remedies have raised controversy during clinical practice, calling for alternative therapies. We have recently found that hydrogen sulfide (H₂S) inhibits inflammatory hepcidin, the critical mediator of AI. However, due to the chemical property of H₂S, there remains an urgent need for a stable H₂S donor in AI treatment. Here we reported that S-propargyl-cysteine (SPRC), a novel water-soluble H₂S donor, suppressed hepatic hepcidin and corrected hypoferremia induced by lipopolysaccharide. The effects of SPRC were reversed by inhibition of cystathionine γ-lyase, one of the major endogenous H₂S synthases. Moreover, SPRC reduced serum hepcidin, improved transferrin saturation, and maintained erythrocyte membrane integrity in a chronic mouse AI model. Consistently, splenomegaly was ameliorated and splenic iron accumulation relieved. Mechanism study indicated that serum IL-6 content and hepatic Il-6 mRNA were decreased by SPRC, in parallel with reduced hepatic JAK2/STAT3 activation. On the whole, our data reveal the inhibition of inflammatory hepcidin by SPRC, and suggest SPRC as a potential remedy against AI.

Relationship between iron overload and nonalcoholic fatty liver disease: An update

As a component of the multiple hits, iron overload plays an important role in the development of nonalcoholic fatty liver disease (NAFLD). Iron overload could affect glucose, lipid, energy metabolism and inflammatory reaction. This paper reviews the relationship between iron overload and nonalcoholic fatty liver disease, in order to clarify how and why iron overload influences the progression of NAFLD.

Transforming Growth Factor β1 (TGF-β1) Activates Hepcidin mRNA Expression in Hepatocytes

The hepatic hormone hepcidin is the master regulator of systemic iron homeostasis. Its expression level is adjusted to alterations in iron levels, inflammatory cues, and iron requirements for erythropoiesis. Bone morphogenetic protein 6 (BMP6) contributes to the iron-dependent control of hepcidin. In addition, TGF-β1 may stimulate hepcidin mRNA expression in murine hepatocytes and human leukocytes. However, receptors and downstream signaling proteins involved in TGF-β1-induced hepcidin expression are still unclear. Here we show that TGF-β1 treatment of mouse and human hepatocytes, as well as ectopic expression of TGF-β1 in mice, increases hepcidin mRNA levels. The hepcidin response to TGF-β1 depends on functional TGF-β1 type I receptor (ALK5) and TGF-β1 type II receptor (TβRII) and is mediated by a noncanonical mechanism that involves Smad1/5/8 phosphorylation. Interestingly, increasing availability of canonical Smad2/3 decreases TGF-β1-induced hepcidin regulation, whereas the BMP6-hepcidin signal was enhanced, indicating a signaling component stoichiometry-dependent cross-talk between the two pathways. Although ALK2/3-dependent hepcidin activation by BMP6 can be modulated by each of the three hemochromatosis-associated proteins: HJV (hemojuvelin), HFE (hemochromatosis protein), and TfR2 (transferrin receptor 2), these proteins do not control the ALK5-mediated hepcidin response to TGF-β1. TGF-β1 mRNA levels are increased in mouse models of iron overload, indicating that TGF-β1 may contribute to hepcidin synthesis under these conditions. In conclusion, these data demonstrate that a complex regulatory network involving TGF-β1 and BMP6 may control the sensing of systemic and/or hepatic iron levels.

Hepcidin: A Promising Therapeutic Target for Iron Disorders: A Systematic Review

Iron is required for most forms of organisms, and it is the most essential element for the functions of many iron-containing proteins involved in oxygen transport, cellular respiration, DNA replication, and so on. Disorders of iron metabolism are associated with diverse diseases, including anemias (e.g., iron-deficiency anemia and anemia of chronic diseases) and iron overload diseases, such as hereditary hemochromatosis and β-thalassemia. Hepcidin (encoded by Hamp gene) is a peptide hormone synthesized by hepatocytes, and it plays an important role in regulating the systematic iron homeostasis. As the systemic iron regulator, hepcidin, not only controls dietary iron absorption and iron egress out of iron storage cells, but also induces iron redistribution in various organs. Deregulated hepcidin is often seen in a variety of iron-related diseases including anemias and iron overload disorders. In the case of iron overload disorders (e.g., hereditary hemochromatosis and β-thalassemia), hepatic hepcidin concentration is significantly reduced.Since hepcidin deregulation is responsible for iron disorder-associated diseases, the purpose of this review is to summarize the recent findings on therapeutics targeting hepcidin.Continuous efforts have been made to search for hepcidin mimics and chemical compounds that could be used to increase hepcidin level. Here, a literature search was conducted in PubMed, and research papers relevant to hepcidin regulation or hepcidin-centered therapeutic work were reviewed. On the basis of literature search, we recapitulated recent findings on therapeutic studies targeting hepcidin, including agonists and antagonists to modulate hepcidin expression or its downstream signaling. We also discussed the molecular mechanisms by which hepcidin level and iron metabolism are modulated.Elevating hepcidin concentration is an optimal strategy to ameliorate iron overload diseases, and also to relieve β-thalassemia phenotypes by improving ineffective erythropoiesis. Relative to the current conventional therapies, such as phlebotomy and blood transfusion, therapeutics targeting hepcidin would open a new avenue for treatment of iron-related diseases.

Activin B Induces Noncanonical SMAD1/5/8 Signaling via BMP Type I Receptors in Hepatocytes: Evidence for a Role in Hepcidin Induction by Inflammation in Male Mice

Induction of the iron regulatory hormone hepcidin contributes to the anemia of inflammation. Bone morphogenetic protein 6 (BMP6) signaling is a central regulator of hepcidin expression in the liver. Recently, the TGF-β/BMP superfamily member activin B was implicated in hepcidin induction by inflammation via noncanonical SMAD1/5/8 signaling, but its mechanism of action and functional significance in vivo remain uncertain. Here, we show that low concentrations of activin B, but not activin A, stimulate prolonged SMAD1/5/8 signaling and hepcidin expression in liver cells to a similar degree as canonical SMAD2/3 signaling, and with similar or modestly reduced potency compared with BMP6. Activin B stimulates hepcidin via classical activin type II receptors ACVR2A and ACVR2B, noncanonical BMP type I receptors activin receptor-like kinase 2 and activin receptor-like kinase 3, and SMAD5. The coreceptor hemojuvelin binds to activin B and facilitates activin B-SMAD1/5/8 signaling. Activin B-SMAD1/5/8 signaling has some selectivity for hepatocyte-derived cells and is not enabled by hemojuvelin in other cell types. Liver activin B mRNA expression is up-regulated in multiple mouse models of inflammation associated with increased hepcidin and hypoferremia, including lipopolysaccharide, turpentine, and heat-killed Brucella abortus models. Finally, the activin inhibitor follistatin-315 blunts hepcidin induction by lipopolysaccharide or B. abortus in mice. Our data elucidate a novel mechanism for noncanonical SMAD activation and support a likely functional role for activin B in hepcidin stimulation during inflammation in vivo.

A review of iron studies in overweight and obese children and adolescents: a double burden in the young?

INTRODUCTION

The connection between iron and excessive adiposity has received much research interest. Although children and adolescents have unique developmental phases and nutritional demands, to date, reviews of iron in the overweight (OW) and obese (OB) have combined studies of children and adults or have focussed on adults.

PURPOSE

The aim of this review was to critically evaluate studies of the relationship between iron and OW and obesity in children and adolescents, with emphasis on iron status, oral iron response, dietary intake and systemic inflammatory markers.

METHODS

A PubMed search was conducted to identify relevant articles published up to December 2015. Combinations of the following keywords were used: iron, OW, OB, children, adolescents, diet, hepcidin, inflammation, fortification, supplementation, weight loss, trace elements, obesity, iron deficiency (ID), minerals.

RESULTS AND CONCLUSION

A higher prevalence of ID, or risk of ID, among OW and OB children and adolescents has been consistently observed. Chronic inflammation caused by excessive adiposity offers a plausible explanation for this finding, rather than dietary factors. However, future studies must employ screening for the presence of both acute and chronic infections and inflammatory conditions and report other factors such as pubertal status. Intervention studies, although few, indicate that OW and OB children and adolescents have reduced response to oral iron. Further trials are needed to explore the connection between body fat mass, inflammatory proteins and iron absorption, together with the effect of weight loss on iron status in iron-deficient OW and OB children and adolescents.

Homocysteine upregulates hepcidin expression through BMP6/SMAD signaling pathway in hepatocytes

Subjects with severe hyperhomocysteinemia have hypoferric anemia and excessive iron deposition in the liver. Hepcidin, the central regulator of iron homeostasis, plays a key role in iron metabolism. However, the regulation of homocysteine (Hcy) on hepcidin is largely unclear. We conducted experiments in HepG2 cells to identify the mechanisms with which Hcy modulates hepcidin expression. We found that treatment with Hcy dose-dependently increased both hepcidin transcript levels and protein levels, as assessed by quantitative real-time reverse-transcriptase polymerase chain reaction and western blotting, respectively. Hcy also activated BMP6 signaling and increased the phosphorylation of SMAD1/5/8 in HepG2 cells. We found that Hcy's effect on hepcidin expression was impaired by the knockdown of BMP6 and its receptors ALK2/3/6 with siRNAs. These results demonstrated that Hcy up-regulated hepcidin expression through the BMP6/SMAD pathway, suggesting a novel mechanism underlying the hyperhomocysteinemia-associated perturbation of iron homeostasis.

Ceramide Induces Human Hepcidin Gene Transcription through JAK/STAT3 Pathway

Changes in lipid metabolism and iron content are observed in the livers of patients with fatty liver disease. The expression of hepcidin, an iron-regulatory and acute phase protein synthesized by the liver, is also modulated. The potential interaction of lipid and iron metabolism is largely unknown. We investigated the role of lipid intermediate, ceramide in the regulation of human hepcidin gene, HAMP. Human hepatoma HepG2 cells were treated with cell-permeable ceramide analogs. Ceramide induced significant up-regulation of HAMP mRNA expression in HepG2 cells. The effect of ceramide on HAMP expression was mediated through transcriptional mechanisms because it was completely blocked with actinomycin D treatment. Reporter assays also confirmed the activation of 0.6 kb HAMP promoter by ceramide. HepG2 cells treated with ceramide displayed increased phosphorylation of STAT3, JNK, and NF-κB proteins. However, ceramide induced the binding of STAT3, but not NF-κB or c-Jun, to HAMP promoter, as shown by the chromatin immunoprecipitation assays. The mutation of STAT3 response element within 0.6 kb HAMP promoter region significantly inhibited the stimulatory effect of ceramide on HAMP promoter activity. Similarly, the inhibition of STAT3 with a pan-JAK kinase inhibitor and STAT3 siRNA pool also diminished the induction of both HAMP promoter activity and mRNA expression by ceramide. In conclusion, we have shown a direct role for ceramide in the activation of hepatic HAMP transcription via STAT3. Our findings suggest a crosstalk between lipid and iron metabolism in the liver, which may contribute to the pathogenesis of obesity-related fatty liver disease.

High Sulfation and a High Molecular Weight Are Important for Anti-hepcidin Activity of Heparin

Heparins are efficient inhibitors of hepcidin expression even in vivo, where they induce an increase of systemic iron availability. Heparins seem to act by interfering with BMP6 signaling pathways that control the expression of liver hepcidin, causing the suppression of SMAD1/5/8 phosphorylation. The anti-hepcidin activity persists also when the heparin anticoagulant property is abolished or reduced by chemical reactions of oxidation/reduction (glycol-split, Gs-Heparins) or by high sulfation (SS-Heparins), but the structural characteristics needed to optimize this inhibitory activity have not been studied in detail. To this aim we analyzed three different heparins (Mucosal Heparin, the Glycol split RO-82, the partially desulfated glycol-split RO-68 and the oversulfated SSLMWH) and separated them in fractions of molecular weight in the range 4–16 kD. Since the distribution of the negative charges in heparins contributes to the activity, we produced 2-O- and 6-O-desulfated heparins. These derivatives were analyzed for the capacity to inhibit hepcidin expression in hepatic HepG2 cells and in mice. The two approaches produced consistent results and showed that the anti-hepcidin activity strongly decreases with molecular weight below 7 kD, with high N-acetylation and after 2-O and 6-O desulfation. The high sulfation and high molecular weight properties for efficient anti-hepcidin activity suggest that heparin is involved in multiple binding sites.

Hydrogen Sulfide Attenuates Inflammatory Hepcidin by Reducing IL-6 Secretion and Promoting SIRT1-Mediated STAT3 Deacetylation

AIMS

Anemia of inflammation is quite prevalent in hospitalized patients with poor prognosis. Concerns about the effectiveness and safety of iron supplementation have arisen, driving the demand for alternative therapies. Induction of hepatic hepcidin, the master hormone of iron homeostasis, causes anemia under inflammatory conditions. Previous studies indicated that hydrogen sulfide (H2S), the third gasotransmitter and a well-known regulator of inflammation, may inhibit the secretion of inflammatory cytokines. We thus investigated the effect of H2S on inflammatory hepcidin induction.

RESULTS

H2S suppressed lipopolysaccharide (LPS)-induced hepcidin production and regulated iron homeostasis in mice by decreasing serum interleukin-6 (IL-6) and Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) activation; similar results were obtained in Huh7 cells exposed to conditioned medium from LPS-challenged THP-1 macrophages. Intriguingly, we found H2S also attenuated hepcidin levels in Huh7 cells and mouse primary hepatocytes in a sirtuin 1 (SIRT1)-dependent manner. By promoting SIRT1 expression and stabilizing SIRT1-STAT3 interactions, H2S ameliorated IL-6-induced STAT3 acetylation, resulting in reduced hepcidin production. Inhibition and silencing of SIRT1 diminished H2S-mediated suppression of hepcidin, as opposed to SIRT1 activation and overexpression. Consistent results were observed in vivo. Furthermore, knockout of cystathionine γ-lyase (CSE), an endogenous H2S synthase, exaggerated inflammatory hepcidin expression in mice.

INNOVATION

For the first time, we elucidated the effects and possible mechanisms of H2S on inflammatory hepcidin and established a novel regulatory link between SIRT1 and hepcidin.

CONCLUSION

Our work demonstrates that H2S attenuates inflammation-induced hepatic hepcidin via multipathways and suggests new treatment strategies for anemia of inflammation.

Modulation of hepcidin to treat iron deregulation: potential clinical applications

The secreted peptide hormone hepcidin regulates systemic and local iron homeostasis through degradation of the iron exporter ferroportin. Dysregulation of hepcidin leads to altered iron homeostasis and development of pathological disorders including hemochromatosis, and iron loading and iron restrictive anemias. Therapeutic modulation of hepcidin is a promising method to ameliorate these conditions. Several approaches have been taken to enhance or reduce the effects of hepcidin in vitro and in vivo. Based on these approaches, hepcidin modulating drugs have been developed and are undergoing clinical evaluation. In this article we review the rationale for development of these drugs, the data concerning their safety and efficacy, their therapeutic uses, and potential future prospects.

Progesterone receptor membrane component-1 regulates hepcidin biosynthesis

Iron homeostasis is tightly regulated by the membrane iron exporter ferroportin and its regulatory peptide hormone hepcidin. The hepcidin/ferroportin axis is considered a promising therapeutic target for the treatment of diseases of iron overload or deficiency. Here, we conducted a chemical screen in zebrafish to identify small molecules that decrease ferroportin protein levels. The chemical screen led to the identification of 3 steroid molecules, epitiostanol, progesterone, and mifepristone, which decrease ferroportin levels by increasing the biosynthesis of hepcidin. These hepcidin-inducing steroids (HISs) did not activate known hepcidin-inducing pathways, including the BMP and JAK/STAT3 pathways. Progesterone receptor membrane component-1 (PGRMC1) was required for HIS-dependent increases in hepcidin biosynthesis, as PGRMC1 depletion in cultured hepatoma cells and zebrafish blocked the ability of HISs to increase hepcidin mRNA levels. Neutralizing antibodies directed against PGRMC1 attenuated the ability of HISs to induce hepcidin gene expression. Inhibiting the kinases of the SRC family, which are downstream of PGRMC1, blocked the ability of HISs to increase hepcidin mRNA levels. Furthermore, HIS treatment increased hepcidin biosynthesis in mice and humans. Together, these data indicate that PGRMC1 regulates hepcidin gene expression through an evolutionarily conserved mechanism. These studies have identified drug candidates and potential therapeutic targets for the treatment of diseases of abnormal iron metabolism.

Commensal Bacteria-induced Interleukin 1β (IL-1β) Secreted by Macrophages Up-regulates Hepcidin Expression in Hepatocytes by Activating the Bone Morphogenetic Protein Signaling Pathway

The liver hormone hepcidin is the central regulator of systemic iron metabolism. Its increased expression in inflammatory states leads to hypoferremia and anemia. Elucidation of the mechanisms that up-regulate hepcidin during inflammation is essential for developing rational therapies for this anemia. Using mouse models of inflammatory bowel disease, we have shown previously that colitis-associated hepcidin induction is influenced by intestinal microbiota composition. Here we investigate how two commensal bacteria, Bifidobacterium longum and Bacteroides fragilis, representative members of the gut microbiota, affect hepcidin expression. We found that supernatants of a human macrophage cell line infected with either of the bacteria up-regulated hepcidin when added to a human hepatocyte cell line. This activity was abrogated by neutralization of IL-1β. Moreover, purified IL-1β increased hepcidin expression when added to the hepatocyte line or primary human hepatocytes and when injected into mice. IL-1β activated the bone morphogenetic protein (BMP) signaling pathway in hepatocytes and in mouse liver, as indicated by increased phosphorylation of small mothers against decapentaplegic proteins. Activation of BMP signaling correlated with IL-1β-induced expression of BMP2 in human hepatocytes and activin B in mouse liver. Treatment of hepatocytes with two different chemical inhibitors of BMP signaling or with a neutralizing antibody to BMP2 prevented IL-1β-induced up-regulation of hepcidin. Our results clarify how commensal bacteria affect hepcidin expression and reveal a novel connection between IL-1β and activation of BMP signaling. They also suggest that there may be differences between mice and humans with respect to the mechanism by which IL-1β up-regulates hepcidin.

Hepcidin-induced hypoferremia is a critical host defense mechanism against the siderophilic bacterium Vibrio vulnificus

Hereditary hemochromatosis, an iron overload disease caused by a deficiency in the iron-regulatory hormone hepcidin, is associated with lethal infections by siderophilic bacteria. To elucidate the mechanisms of this susceptibility, we infected wild-type and hepcidin-deficient mice with the siderophilic bacterium Vibrio vulnificus and found that hepcidin deficiency results in increased bacteremia and decreased survival of infected mice, which can be partially ameliorated by dietary iron depletion. Additionally, timely administration of hepcidin agonists to hepcidin-deficient mice induces hypoferremia that decreases bacterial loads and rescues these mice from death, regardless of initial iron levels. Studies of Vibrio vulnificus growth ex vivo show that high iron sera from hepcidin-deficient mice support extraordinarily rapid bacterial growth and that this is inhibited in hypoferremic sera. Our findings demonstrate that hepcidin-mediated hypoferremia is a host defense mechanism against siderophilic pathogens and suggest that hepcidin agonists may improve infection outcomes in patients with hereditary hemochromatosis or thalassemia.

Genetics, Genetic Testing, and Management of Hemochromatosis: 15 Years Since Hepcidin

The discovery of hepcidin in 2000 and the subsequent unprecedented explosion of research and discoveries in the iron field have dramatically changed our understanding of human disorders of iron metabolism. Today, hereditary hemochromatosis, the paradigmatic iron-loading disorder, is recognized as an endocrine disease due to the genetic loss of hepcidin, the iron hormone produced by the liver. This syndrome is due to unchecked transfer of iron into the bloodstream in the absence of increased erythropoietic needs and its toxic effects in parenchymatous organs. It is caused by mutations that affect any of the proteins that help hepcidin to monitor serum iron, including HFE and, in rarer instances, transferrin-receptor 2 and hemojuvelin, or make its receptor ferroportin, resistant to the hormone. In Caucasians, C282Y HFE homozygotes are numerous, but they are only predisposed to hemochromatosis; complete organ disease develops in a minority, due to alcohol abuse or concurrent genetic modifiers that are now being identified. HFE gene testing can be used to diagnose hemochromatosis in symptomatic patients, but analyses of liver histology and full gene sequencing are required to identify patients with rare, non-HFE forms of the disease. Due to the central pathogenic role of hepcidin, it is anticipated that nongenetic causes of hepcidin loss (eg, end-stage liver disease) can cause acquired forms of hemochromatosis. The mainstay of hemochromatosis management is still removal of iron by phlebotomy, first introduced in 1950s, but identification of hepcidin has not only shed new light on the pathogenesis of the disease and the approach to diagnosis, but etiologic therapeutic applications from these advances are now foreseen.

Isocitrate treatment of acute anemia of inflammation in a mouse model

Acute and severe anemia of inflammation (AI) is a common complication of various clinical syndromes, including fulminant infections, critical illness with multiorgan failure, and exacerbations of autoimmune diseases. Building on recent data showing beneficial results with isocitrate treatment for chronic low-grade AI in a rat model, we used a mouse model of acute and severe AI induced by intraperitoneal heat-killed Brucella abortus to determine if isocitrate would be effective in this more stringent application. Inflamed mice treated with isocitrate developed an early but transient improvement in hemoglobin compared to solvent-treated controls, with a robust improvement on day 7, and only a trend towards improvement by day 14. Reticulocyte counts were increased in treated mice transiently, with no significant difference by day 21. Serum erythropoietin (EPO) levels were similar in treated versus control mice, indicating that isocitrate increased sensitivity to EPO. Serum and tissue iron levels showed no significant differences between the treated and control mice, ruling out improved iron availability as the cause of the increased response to endogenous EPO. Compared to the milder rat model, much higher doses of isocitrate were required for a relatively modest benefit.

Saturated fatty acids induce post-transcriptional regulation of HAMP mRNA via AU-rich element-binding protein, human antigen R (HuR)

Iron is implicated in fatty liver disease pathogenesis. The human hepcidin gene, HAMP, is the master switch of iron metabolism. The aim of this study is to investigate the regulation of HAMP expression by fatty acids in HepG2 cells. For these studies, both saturated fatty acids (palmitic acid (PA) and stearic acid (SA)) and unsaturated fatty acid (oleic acid (OA)) were used. PA and, to a lesser extent, SA, but not OA, up-regulated HAMP mRNA levels, as determined by real-time PCR. To understand whether PA regulates HAMP mRNA at the transcriptional or post-transcriptional level, the transcription inhibitor actinomycin D was employed. PA-mediated induction of HAMP mRNA expression was not blocked by actinomycin D. Furthermore, PA activated HAMP 3'-UTR, but not promoter, activity, as shown by reporter assays. HAMP 3'-UTR harbors a single AU-rich element (ARE). Mutation of this ARE abolished the effect of PA, suggesting the involvement of ARE-binding proteins. The ARE-binding protein human antigen R (HuR) stabilizes mRNA through direct interaction with AREs on 3'-UTR. HuR is regulated by phosphorylation-mediated nucleo-cytoplasmic shuttling. PA activated this process. The binding of HuR to HAMP mRNA was also induced by PA in HepG2 cells. Silencing of HuR by siRNA abolished PA-mediated up-regulation of HAMP mRNA levels. PKC is known to phosphorylate HuR. Staurosporine, a broad-spectrum PKC inhibitor, inhibited both PA-mediated translocation of HuR and induction of HAMP expression. Similarly, rottlerin, a novel class PKC inhibitor, abrogated PA-mediated up-regulation of HAMP expression. In conclusion, lipids mediate post-transcriptional regulation of HAMP throughPKC- and HuR-dependent mechanisms.

Low Serum Hepcidin in Patients with Autoimmune Liver Diseases

Hepcidin, a liver hormone, is important for both innate immunity and iron metabolism regulation. As dysfunction of the hepcidin pathway may contribute to liver pathology, we analysed liver hepcidin mRNA and serum hepcidin in patients with chronic liver diseases. Hepcidin mRNA levels were determined in liver biopsies obtained from 126 patients with HCV (n = 21), HBV (n = 23), autoimmune cholestatic disease (primary biliary cirrhosis and primary sclerosing cholangitis; PBC/PSC; n = 34), autoimmune hepatitis (AIH; n = 16) and non-alcoholic fatty liver disease (NAFLD; n = 32). Sera sampled on the biopsy day from the same patients were investigated for serum hepcidin levels. Hepatic hepcidin mRNA levels correlated positively with ferritin and negatively with serum γ-GT levels. However, no correlation was found between serum hepcidin and either ferritin or liver hepcidin mRNA. Both serum hepcidin and the serum hepcidin/ferritin ratio were significantly lower in AIH and PBC/PSC patients’ sera compared to HBV, HCV or NAFLD (P<0.001 for each comparison) and correlated negatively with serum ALP levels. PBC/PSC and AIH patients maintained low serum hepcidin during the course of their two-year long treatment. In summary, parallel determination of liver hepcidin mRNA and serum hepcidin in patients with chronic liver diseases shows that circulating hepcidin and its respective ratio to ferritin are significantly diminished in patients with autoimmune liver diseases. These novel findings, once confirmed by follow-up studies involving bigger size and better-matched disease subgroups, should be taken into consideration during diagnosis and treatment of autoimmune liver diseases.

The Potential Role of Iron and Copper in Pediatric Obesity and Nonalcoholic Fatty Liver Disease

Obesity is a rapidly growing health problem and is paralleled by a multitude of comorbidities, including nonalcoholic fatty liver disease (NAFLD). NAFLD has become the most common chronic liver disease in both adults and children. The current understanding of NAFLD is still fragmentary. While simple steatosis is characterized by the interplay between excessive free fatty acid accumulation and hepatic insulin resistance, the progression to NASH has been related to oxidative stress and a proinflammatory state with dysbalanced adipokine, cytokine levels, and endotoxin-mediated immune response. In addition, oxidative stress has been suggested to play a central role for the sequelae leading to NASH. Trace elements are critical in regulatory, immunologic, and antioxidant functions resulting in protection against inflammation and peroxidation and consequently against the known comorbidities of obesity. Disruptions of the metal detoxification processes located in the liver are plausibly related to NAFLD development via oxidative stress. Perturbations of iron and copper (Cu) homeostasis have been shown to contribute to the pathogenesis of NAFLD. This review presents current data from pediatric studies. In addition, data from adult studies are summarized where clinical relevance may be extrapolated to pediatric obesity and NAFLD.

Adaptation of iron requirement to hypoxic conditions at high altitude

Adequate acclimatization time to enable adjustment to hypoxic conditions is one of the most important aspects for mountaineers ascending to high altitude. Accordingly, most reviews emphasize mechanisms that cope with reduced oxygen supply. However, during sojourns to high altitude adjustment to elevated iron demand is equally critical. Thus in this review we focus on the interaction between oxygen and iron homeostasis. We review the role of iron 1) in the oxygen sensing process and erythropoietin (Epo) synthesis, 2) in gene expression control mediated by the hypoxia-inducible factor-2 (HIF-2), and 3) as an oxygen carrier in hemoglobin, myoglobin, and cytochromes. The blood hormone Epo that is abundantly expressed by the kidney under hypoxic conditions stimulates erythropoiesis in the bone marrow, a process requiring high iron levels. To ensure that sufficient iron is provided, Epo-controlled erythroferrone that is expressed in erythroid precursor cells acts in the liver to reduce expression of the iron hormone hepcidin. Consequently, suppression of hepcidin allows for elevated iron release from storage organs and enhanced absorption of dietary iron by enterocytes. As recently observed in sojourners at high altitude, however, iron uptake may be hampered by reduced appetite and gastrointestinal bleeding. Reduced iron availability, as observed in a hypoxic mountaineer, enhances hypoxia-induced pulmonary hypertension and may contribute to other hypoxia-related diseases. Overall, adequate systemic iron availability is an important prerequisite to adjust to high-altitude hypoxia and may have additional implications for disease-related hypoxic conditions.

Lipopolysaccharides upregulate hepcidin in neuron via microglia and the IL-6/STAT3 signaling pathway

Neuroinflammation is closely related to brain iron homeostasis. Our previous study demonstrated that lipopolysaccharides (LPS) can regulate expression of iron-regulatory peptide hepcidin; however, the mechanism is undefined. Here, we demonstrated that intracerebroventricular injection of LPS in rat brain upregulated hepcidin and downregulated ferroportin 1 in the cortex and substantia nigra. LPS increased hepcidin expression in neurons only when they were co-cultured with BV-2 microglia, and the upregulation was suppressed by IL-6 neutralizing antibody in vitro. In addition, IL-6 but not IL-1α, IL-1β, or tumor necrosis factor-alpha increased hepcidin expression and signal transducer and activator of transcription 3 (STAT3) phosphorylation in cortical neurons and MES23.5 dopaminergic neurons. These effects were blocked by the STAT3 inhibitor, stattic. Our results show that neurons are the major source of increased hepcidin expression in response to LPS challenge but microglia play a key mediator role by releasing IL-6 and recruiting the STAT3 pathway. We conclude that LPS upregulates hepcidin expression in neurons via microglia and the IL-6/STAT3 signaling pathway.

Iron, inflammation and invasion of cancer cells

Chronic inflammation is associated with the metastasis of tumor cells evolving from a benign tumor to disseminating cancer. Such a metastatic progression is fostered by the angiogenesis propelled by various mediators interacting at the site of tumor growth. Angiogenesis causes two major changes that are assisted by altered glycosylation and neo-antigen presentation by the cancer cells. The angiogenesis-promoted pathological changes include enhanced inflammation and degradation of tissue matrices releasing tumor cells from the site of its origin. The degraded tumor cells release the neo-antigens resulting from altered glycosylation. Presentation of neo-antigens to T cells escalates metastasis and inflammation. Inflammasome activation and inflammation in several infections are regulated by iron. Based on the discrete reports, we propose a link between iron, inflammation, angiogenesis and tumor growth. Knowing the link better may help us formulate a novel strategy for cancer immunotherapy.

The small molecule ferristatin II induces hepatic hepcidin expression in vivo and in vitro

Previous studies have shown that administration of ferristatin II to rats is associated with decreased serum iron, reduced transferrin saturation, and increased hepatic hepcidin expression. BMP and IL-6 signaling act via Smad and Stat3 transcription factors, respectively, to increase expression of hepcidin, the master regulator of iron metabolism. In this study, we aimed to explore the underlying mechanism of ferristatin II action on hepcidin production. We found that ferristatin II greatly increased hepcidin expression both in vivo and in vitro. In the rat liver, ferristatin II treatment decreased expression of Smad downstream targets Smad7 and Id1 and increased expression of Stat3 downstream targets α-2-macroglobulin, α-1-acid glycoprotein, and C-reactive peptide. Ferristatin II also increased Stat3 phosphorylation in the rat liver without affecting serum or hepatic IL-6 levels. It is unclear whether the Stat3 activation observed in vivo is a cause or a consequence to hepcidin induction. Reporter gene expression studies demonstrated that ferristatin II synergized with BMP6 and IL-6 to enhance hepcidin expression in vitro. However, this synergy was not due to activation of either Smad or Stat3 signaling, raising the possibility that ferristatin II may activate a novel pathway for hepcidin regulation.

Regulation of Iron Metabolism by Hepcidin under Conditions of Inflammation

Iron is a redox-active metal required as a cofactor in multiple metalloproteins essential for a host of life processes. The metal is highly toxic when present in excess and must be strictly regulated to prevent tissue and organ damage. Hepcidin, a molecule first characterized as an antimicrobial peptide, plays a critical role in the regulation of iron homeostasis. Multiple stimuli positively influence the expression of hepcidin, including iron, inflammation, and infection by pathogens. In this Minireview, I will discuss how inflammation regulates hepcidin transcription, allowing for sufficient concentrations of iron for organismal needs while sequestering the metal from infectious pathogens.

Analysis of IL-22 contribution to hepcidin induction and hypoferremia during the response to LPS in vivo

The anaemia of chronic disease (ACD) results from inflammation-mediated up-regulation of the iron regulatory hormone hepcidin, with the consequent sequestration of iron limiting its availability for erythropoiesis. The inflammatory cytokine IL-6, a regulator of hepcidin, has been implicated in this process. Recent in vivo and in vitro studies indicate that IL-22 is also able to stimulate hepcidin expression. We aimed to determine if IL-22 had a role in causing the hypoferremia associated with the inflammatory response. Wild-type and Il22-knockout mice were subjected to an acute inflammatory stimulus via administration of LPS and the response of hepcidin and iron homeostasis was analysed. In the absence of IL-22, there was a response of hepcidin, resulting in a reduction in serum iron levels. However, the hypoferremic response to LPS was slightly blunted in mice lacking IL-22, suggesting that, during LPS-mediated inflammation, IL-22 may play a minor role in mediating the hypoferremic response. These results may have implications for the treatment and management of the ACD.

HJV and HFE Play Distinct Roles in Regulating Hepcidin

AIMS

Hereditary hemochromatosis (HH) is an iron overload disease that is caused by mutations in HFE, HJV, and several other genes. However, whether HFE-HH and HJV-HH share a common pathway via hepcidin regulation is currently unclear. Recently, some HH patients have been reported to carry concurrent mutations in both the HFE and HJV genes. To dissect the roles and molecular mechanisms of HFE and/or HJV in the pathogenesis of HH, we studied Hfe(-/-), Hjv(-/-), and Hfe(-/-)Hjv(-/-) double-knockout mouse models.

RESULTS

Hfe(-/-)Hjv(-/-) mice developed iron overload in multiple organs at levels comparable to Hjv(-/-) mice. After an acute delivery of iron, the expression of hepcidin (i.e., Hamp1 mRNA) was increased in the livers of wild-type and Hfe(-/-) mice, but not in either Hjv(-/-) or Hfe(-/-)Hjv(-/-) mice. Furthermore, iron-induced phosphorylation of Smad1/5/8 was not detected in the livers of Hjv(-/-) or Hfe(-/-)Hjv(-/-) mice.

INNOVATION

We generated and phenotypically characterized Hfe(-/-)Hjv(-/-) double-knockout mice. In addition, because they faithfully phenocopy clinical HH patients, these mouse models are an invaluable tool for mechanistically dissecting how HFE and HJV regulate hepcidin expression.

CONCLUSIONS

Based on our results, we conclude that HFE may depend on HJV for transferrin-dependent hepcidin regulation. The presence of residual hepcidin in the absence of HFE suggests either the presence of an unknown regulator (e.g., TFR2) that is synergistic with HJV or that HJV is sufficient to maintain basal levels of hepcidin.

Hepcidin Levels Are Increased in Patients with Acute Ischemic Stroke: Preliminary Report

BACKGROUND

Our current understanding of iron balance in acute ischemic stroke (AIS) is still limited. The objective of this study was to evaluate levels of iron homeostasis proteins-hepcidin (25-amino acid form) and soluble hemojuvelin (sHJV) together with hepcidin/sHJV ratio (Hepc/sHJV) and soluble transferrin receptor (sTfR) in patients with AIS. In addition, the effect of timing of blood collection, type of stroke treatment, and scores on the National Institutes of Health Stroke Scale were investigated.

METHODS

Participants comprised 31 patients diagnosed with AIS and 20 matched healthy controls. Venous blood samples were drawn on the first day and on the seventh day after stroke onset. Individuals who had experienced a stroke were subdivided according to type of treatment (thrombolysis group, n = 12 versus nonthrombolysis group, n = 19). Plasma hepcidin, sHJV, and sTfR levels were determined by the enzyme-linked immunosorbent assay method.

RESULTS

We found that plasma hepcidin levels were significantly higher in ischemic stroke patients compared with the control group (median, 19.82 versus 12.62 ng/mL, P = .04). Furthermore, levels of hepcidin on the seventh day (1 week after diagnosis) were significantly higher in patients treated with thrombolysis than in patients not treated with thrombolysis (median, 22.16 versus 16.21 ng/mL, P = .04).

CONCLUSIONS

The study provides evidence that AIS is associated with increased hepcidin levels. Stroke treatment may have an influence on hepcidin synthesis.

Mutual interaction between iron homeostasis and obesity pathogenesis

Obesity is identified as an important medical problem. One of the pathologic conditions observed in obesity is systemic iron deficiency and hypoferremia. Along with a large number of studies indicating disturbed iron homeostasis in obesity, recent data indicate a cause-effect relationship between iron status and obesity-related pathologies. The primary objective of the article is to consider two aspects of the iron-obesity interplay: (1) the mechanisms leading to impaired iron balance, and (2) the pathways of iron participation in obesity-related pathogenesis. While considering disturbance of iron homeostasis in obesity, a number of potential mechanisms of hypoferremia are proposed. At the same time, the inflammation of obesity and obesity-related hepcidin and lipocalin 2 hyperproduction seem to be the most probable reasons of obesity-related hypoferremia. Oversecretion of these proteins leads to iron sequestration in reticuloendothelial system cells. The latter also leads to increased adipose tissue iron content, thus producing preconditions for adverse effects of local iron overload. Being a redox-active metal, iron is capable of inducing oxidative stress as well as endoplasmic reticulum stress, inflammation and adipose tissue endocrine dysfunction. Iron-mediated mechanisms of toxicity may influence aspects of obesity pathogenesis possibly even leading to obesity aggravation. Thus, a mutual interaction between disturbance in iron homeostasis and obesity pathogenesis is proposed. All sides of this interaction should be considered to design new therapeutic approaches to the treatment of disturbed iron homeostasis in obesity.

Hepcidin: regulation of the master iron regulator

Iron, an essential nutrient, is required for many diverse biological processes. The absence of a defined pathway to excrete excess iron makes it essential for the body to regulate the amount of iron absorbed; a deficiency could lead to iron deficiency and an excess to iron overload and associated disorders such as anaemia and haemochromatosis respectively. This regulation is mediated by the iron-regulatory hormone hepcidin. Hepcidin binds to the only known iron export protein, ferroportin (FPN), inducing its internalization and degradation, thus limiting the amount of iron released into the blood. The major factors that are implicated in hepcidin regulation include iron stores, hypoxia, inflammation and erythropoiesis. The present review summarizes our present knowledge about the molecular mechanisms and signalling pathways contributing to hepcidin regulation by these factors.

Hepatic hepcidin protects against polymicrobial sepsis in mice by regulating host iron status

BACKGROUND

Hepcidin is a master regulator of iron metabolism primarily produced by the liver. Markedly increased hepcidin levels have been observed in septic individuals, while decreased hepatic hepcidin expression has been demonstrated in liver diseases that tend to develop into sepsis. However, the role of liver hepcidin in sepsis remains unknown.

METHODS

Mouse hepatic hepcidin expression was silenced using adenovirus-mediated hepcidin-specific short hairpin RNA injected via the tail vein. Sepsis was induced by cecal ligation and puncture, and the outcome (n = 23 for hepcidin knockdown mice, n = 15 for controls) and pathogenic changes (n = 5) related to sepsis were evaluated. The impact of alteration of iron status on the survival rate of hepatic hepcidin knockdown mice (n = 18 to 19) was also investigated.

RESULTS

Disruption of liver hepcidin expression increased serum iron level (537.8 ± 28.1 μg/dl [mean ± SD] vs. 235.9 ± 62.2 μg/dl; P < 0.05) and reduced iron content in the spleen macrophages at the steady state. Hepatic hepcidin knockdown mice not only showed increased 7-day mortality (73.9% vs. 46.7%; P < 0.05), but also had exacerbated organ damage and oxidative stress, as well as compromised host inflammatory responses and bacterial clearance at 24 h after polymicrobial sepsis. Treating the hepatic hepcidin knockdown mice with low-iron diet plus iron chelation decreased systemic iron content (serum level: 324.0 ± 67.4 μg/dl vs. 517.4 ± 13.4 μg/dl; P < 0.05) and rescued the mice from lethal sepsis (7-day survival: 36.8% vs. 83.3%; P < 0.01).

CONCLUSIONS

Hepatic hepcidin plays an important role in sepsis through regulation of iron metabolism. The findings may have potential therapeutic implications for liver diseases in which hepcidin expression is decreased.

Update on iron metabolism and molecular perspective of common genetic and acquired disorder, hemochromatosis

Iron is an essential component of erythropoiesis and its metabolism is tightly regulated by a variety of internal and external cues including iron storage, tissue hypoxia, inflammation and degree of erythropoiesis. There has been remarkable improvement in our understanding of the molecular mechanisms of iron metabolism past decades. The classical model of iron metabolism with iron response element/iron response protein (IRE/IRP) is now extended to include hepcidin model. Endogenous and exogenous signals funnel down to hepcidin via wide range of signaling pathways including Janus Kinase/Signal Transducer and Activator of Transcription 3 (JAK/STAT3), Bone Morphogenetic Protein/Hemojuvelin/Mothers Against Decapentaplegic Homolog (BMP/HJV/SMAD), and Von Hippel Lindau/Hypoxia-inducible factor/Erythropoietin (VHL/HIF/EPO), then relay to ferroportin, which directly regulates intra- and extracellular iron levels. The successful molecular delineation of iron metabolism further enhanced our understanding of common genetic and acquired disorder, hemochromatosis. The majority of the hereditary hemochromatosis (HH) patients are now shown to have mutations in the genes coding either upstream or downstream proteins of hepcidin, resulting in iron overload. The update on hepcidin centered mechanisms of iron metabolism and their clinical perspective in hemochromatosis will be discussed in this review.

A HAMP promoter bioassay system for identifying chemical compounds that modulate hepcidin expression

Hepcidin is the central regulator of systemic iron homeostasis; dysregulation of hepcidin expression causes various iron metabolic disorders, including hereditary hemochromatosis and anemia of inflammation. To identify molecules that modulate hepcidin expression, we developed a bioassay system for hepcidin gene (HAMP) promoter activity by stable transfection of Hep3B hepatoma cells with an expression plasmid in which EGFP was linked to a 2.5-kb human HAMP promoter. Interleukin 6, bone morphogenetic protein 6 (BMP-6), and oncostatin M, well-characterized stimulators of the HAMP promoter, strongly enhanced the green fluorescence intensity of these cells. Dorsomorphin, heparin, and cobalt chloride, known inhibitors of hepcidin expression, significantly suppressed green fluorescence intensity, and these inhibitory effects were more prominent when the cells were stimulated with BMP-6. Employing this system, we screened 1,280 biologically active small molecules and found several candidate inhibitors of hepcidin expression. Apomorphine, benzamil, etoposide, CGS-15943, kenpaullone, and rutaecarpine (all at 10 μmol/L) significantly inhibited hepcidin mRNA expression by Hep3B cells without affecting cell viability. CGS-15943 was the strongest suppressor of BMP-6-induced hepcidin-25 secretion in these cells. We conclude that our newly developed hepcidin promoter bioassay system is useful for identifying and evaluating compounds that modulate hepcidin expression.