Hypoxia inhibits hepcidin expression in HuH7 hepatoma cells via decreased SMAD4 signaling

Inhibition of ALK3-mediated signalling pathway protects against acetaminophen-induced liver injury

Acetaminophen (APAP)-induced liver injury is one of the most prevalent causes of acute liver failure (ALF). We assessed the role of the bone morphogenetic protein (BMP) type I receptors ALK2 and ALK3 in APAP-induced hepatotoxicity. The molecular mechanisms that regulate the balance between cell death and survival and the response to oxidative stress induced by APAP was assessed in cultured human hepatocyte-derived (Huh7) cells treated with pharmacological inhibitors of ALK receptors and with modulated expression of ALK2 or ALK3 by lentiviral infection, and in a mouse model of APAP-induced hepatotoxicity. Inhibition of ALK3 signalling with the pharmacological inhibitor DMH2, or by silencing of ALK3, showed a decreased cell death both by necrosis and apoptosis after APAP treatment. Also, upon APAP challenge, ROS generation was ameliorated and, thus, ROS-mediated JNK and P38 MAPK phosphorylation was reduced in ALK3-inhibited cells compared to control cells. These results were also observed in an experimental model of APAP-induced ALF in which post-treatment with DMH2 after APAP administration significantly reduced liver tissue damage, apoptosis and oxidative stress. This study shows the protective effect of ALK3 receptor inhibition against APAP-induced hepatotoxicity. Furthermore, findings obtained from the animal model suggest that BMP signalling might be a new pharmacological target for the treatment of ALF.

Weak response of bovine hepcidin induction to iron through decreased expression of Smad4

Hepcidin negatively regulates systemic iron levels by inhibiting iron entry into the circulation. Hepcidin production is increased in response to an increase in systemic iron via the activation of the bone morphogenetic protein (BMP) pathway. Regulation of hepcidin expression by iron status has been proposed on the basis of evidence mainly from rodents and humans. We evaluated the effect of iron administration on plasma hepcidin concentrations in calves and the expression of bovine hepcidin by the BMP pathway in a cell culture study. Hematocrit as well as levels of blood hemoglobin and plasma iron were lower than the reference level in calves aged 1-4 weeks. Although intramuscular administration of iron increased iron-related parameters, plasma hepcidin concentrations were unaffected. Treatment with BMP6 increased hepcidin expression in human liver-derived cells but not in bovine liver-derived cells. A luciferase-based reporter assay revealed that Smad4 was required for hepcidin reporter transcription induced by Smad1. The reporter activity of hepcidin was lower in the cells transfected with bovine Smad4 than in those transfected with murine Smad4. The lower expression levels of bovine Smad4 were responsible for the lower activity of the hepcidin reporter, which might be due to the instability of bovine Smad4 mRNA. In fact, the endogenous Smad4 protein levels were lower in bovine cells than in human and murine cells. Smad4 also confers TGF-β/activin-mediated signaling. Induction of TGF-β-responsive genes was also lower after treatment with TGF-β1 in bovine hepatocytes than in human hepatoma cells. We revealed the unique regulation of bovine hepcidin expression and the characteristic TGF-β family signaling mediated by bovine Smad4. The present study suggests that knowledge of the regulatory expression of hepcidin as well as TGF-β family signaling obtained in murine and human cells is not always applicable to bovine cells.

Beneficial effect of roxadustat on early posttransplant anemia and iron utilization in kidney transplant recipients: a retrospective comparative cohort study

Background

Although posttransplant anemia (PTA) is a common complication after kidney transplant, it has not been thoroughly evaluated for appropriate treatment. Roxadustat can stimulate erythropoiesis by increasing erythropoietin (EPO) production and improving the utilization of iron. However, there are currently a few case reports describing its effect on PTA in kidney transplant recipients (KTRs). Our purpose was to evaluate the efficacy and safety of roxadustat in KTRs with PTA.

Methods

In this retrospective study, KTRs with early PTA were divided into a roxadustat group, erythropoiesis-stimulating agent (ESA) group, and untreated group (neither roxadustat nor ESA) according to the treatment prescribed by their physicians. We compared the levels of hemoglobin (Hb), creatinine, lipids, hepcidin, intact fibroblast growth factor 23 (iFGF23) and iron-related indices, at baseline and different time points posttransplant. Outcome was assessed at both month 3 and month 12 posttransplant. Adverse events during the treatment course were also recorded.

Results

A total of 57 KTRs were included (n=22 roxadustat group, n=13 ESA group, n=22 untreated group). There was no difference in age, sex, body mass index, dialysis method and duration, donor type among three groups at baseline. The mean Hb levels at month 3 posttransplant (128.00±19.62 vs. 118.59±11.60 g/L, P=0.048) and the average change in Hb levels from week 2 to month 3 (48.05±22.53 vs. 31.45±12.96 g/L, P=0.005) in the roxadustat group were significantly higher than those in the untreated group. However, there was no significant difference in the above indices between the roxadustat and ESA groups. At month 3, the total iron binding capacity (TIBC) and levels of transferrin were significantly higher while levels of ferritin, hepcidin and iFGF23 were significantly lower in the roxadustat group than in other groups (P<0.05). No significant difference was found in creatinine or estimated glomerular filtration rate (eGFR) levels among the three groups at month 3. During the follow-up, no adverse events related to roxadustat were reported.

Conclusions

Administration of roxadustat in KTRs with early PTA could elevate Hb levels effectively and safely by enhancing endogenous EPO production and improving iron utilization. Further randomized studies with larger sample size are necessary to verify our results.

Novel insights into alcoholic liver disease: Iron overload, iron sensing and hemolysis

The liver is the major target organ of continued alcohol consumption at risk and resulting alcoholic liver disease (ALD) is the most common liver disease worldwide. The underlying molecular mechanisms are still poorly understood despite decades of scientific effort limiting our abilities to identify those individuals who are at risk to develop the disease, to develop appropriate screening strategies and, in addition, to develop targeted therapeutic approaches. ALD is predestined for the newly evolving translational medicine, as conventional clinical and health care structures seem to be constrained to fully appreciate this disease. This concept paper aims at summarizing the 15 years translational experience at the Center of Alcohol Research in Heidelberg, namely based on the long-term prospective and detailed characterization of heavy drinkers with mortality data. In addition, novel experimental findings will be presented. A special focus will be the long-known hepatic iron accumulation, the somewhat overlooked role of the hematopoietic system and novel insights into iron sensing and the role of hepcidin. Our preliminary work indicates that enhanced red blood cell (RBC) turnover is critical for survival in ALD patients. RBC turnover is not primarily due to vitamin deficiency but rather to ethanol toxicity directly targeted to erythrocytes but also to the bone marrow stem cell compartment. These novel insights also help to explain long-known aspects of ALD such as mean corpuscular volume of erythrocytes (MCV) and elevated aspartate transaminase (GOT/AST) levels. This work also aims at identifying future projects, naming unresolved observations, and presenting novel hypothetical concepts still requiring future validation.

Potential Use of Patient-Specific Induced Pluripotent Stem Cell for Liver Fibrosis Thalassemia Treatment Management

Thalassemia is the most common inherited single gene blood disease worldwide and present a significant health problem in the world. Approximately, 1.5% of the global populations (An estimated 80–90 million people) are carriers of β-thalassemia. Around 5% of Indonesia population is thought to carry the thalassemia gene. The globin imbalance in β-thalassemia major causes hemolysis and ineffective erythropoiesis which results in anemia leading to increases of iron absorption. Furthermore, repeated blood transfusion and long-term increased iron absorption will lead to excessive accumulation of iron in vital organs, especially in the liver, causes liver fibrosis then leading to liver disease. Iron overload can be controlled by iron chelating drugs with the risk of side effects; therefore, a breakthrough is needed. Stem cell technology has a potential to provide novel insight in thalassemia major, through induced pluripotent stem cells (iPSCs) who has the ability to differentiate into hepatic stellate cells (HSCs)-like cells. iPSCs derived HSC-like cells (iPSC-HSCs) present the phenotypic and functional characteristics of HSCs. The utilization of iPSCs is a new option in personalized thalassemia management.

Effect of Recombinant Human Erythroferrone Protein on Hepcidin Gene (Hamp1) Expression in HepG2 and HuH7 Cells

Iron is essential for all living organisms. It is strictly controlled by iron transporters, transferrin receptors, ferroportin and hepcidin. Erythroferrone (ERFE) is an iron-regulatory hormone which is highly expressed in erythroblasts by erythropoietin (EPO) stimulation and osteoblasts independently of EPO by sequestering bone morphogenetic proteins and inhibiting hepatic hepcidin expression. Although the hepcidin suppressive function of ERFE is known, its receptors still require investigation. Here, we aim to identify ERFE receptors on the HepG2 and Huh7 cells responsible for ERFE. Recombinant ERFE (rERFE) was first produced in HEK293 cells transfected with pcDNA3.1 + ERFE, then purified and detected by Western blot. The liver cells were treated with an rERFE-rich medium of transfected HEK293 cells and a purified rERFE-supplemented medium at various time points, and hepcidin gene (Hamp1) expression was determined using qRT-PCR. The results show that 37-kD rERFE was expressed in HEK293 cells. Hamp1 was suppressed at 3 h and 6 h in Huh7 cells after rERFE treatments (p < 0.05), then restored to the original levels. Hamp1 was activated after treatment with purified rERFE for 24 h and 48 h. Together, these results reveal that ERFE suppressed Hamp1 expression in liver cells, possibly acting on membrane ERFE receptor, which in Huh7 cells was more sensitive to the ERFE concentrate.

A Novel Choice to Correct Inflammation-Induced Anemia in CKD: Oral Hypoxia-Inducible Factor Prolyl Hydroxylase Inhibitor Roxadustat

Anemia is a complication of chronic kidney disease (CKD), primarily due to insufficient secretion of erythropoietin (EPO) by the kidney. Erythropoiesis-stimulating agents (ESAs) are used to treat anemia associated with chronic kidney disease. A poor response to ESAs has been associated with inflammation. Inflammation can affect erythrocytes and its production in many ways, but mainly through the inflammatory cytokine IL-6 to stimulate the synthesis of hepcidin in the liver. Hepcidin causes iron insufficiency, which causes erythrocytes to fail to mature normally. In addition, inhibition of bone marrow erythroid precursor cells by inflammatory cytokines such as IL-1 and TNF-α also affects bone marrow hematopoiesis. These cytokines are also important factors leading to EPO resistance. Roxadustat is a new drug for the treatment of renal anemia. In addition to promoting the production of EPO, clinical trials have shown that it can significantly reduce hepcidin and can potentially be used for the treatment of inflammation-induced anemia in CKD.

IL-1 beta-mediated macrophage-hepatocyte crosstalk upregulates hepcidin under physiological low oxygen levels

In mammals, the iron masterswitch hepcidin efficiently controls iron recycling by the macrophage-liver axis but the exact interplay between macrophages and hepatocytes remains poorly understood. We here study hepcidin response during macrophage differentiation as well as the macrophage-hepatocyte crosstalk and its subsequent effects on hepatocyte hepcidin using an in vitro co-culture model that mimics the physiological liver microenvironment. We show that macrophage differentiation strongly induces hepcidin by 60-fold both in THP1 macrophages and primary isolated monocyte-derived macrophages. Removal of H₂O₂ by catalase or inhibition of NOX2 efficiently blocked hepcidin induction. After differentiation, macrophage hepcidin accounted for 10% of total hepatocyte hepcidin and did not respond to low oxygen levels. In contrast, co-culture of differentiated macrophages with Huh7 cells significantly induced hepatocyte hepcidin, which was further potentiated under low oxygen levels. Hepatocyte hepcidin was also upregulated when Huh7 cells were solely exposed to macrophage-conditioned hypoxic medium. A cytokine screen identified macrophage secreted IL-1β as major inducer of hepcidin in hepatocytes. In confirmation, treatment of Huh7 cells with the IL-1 receptor antagonist (anakinra) completely blunted macrophage-mediated hepcidin transcription in hepatocytes. Finally, detailed analysis of potentially involved signaling pathways points toward STAT3 and CEBPδ-mediated hepcidin induction independent of IL-6. In conclusion, our study demonstrates a strong NOX2-mediated hepcidin induction during macrophage differentiation. These differentiated macrophages are able to efficiently induce hepatocyte hepcidin mainly through secretion of IL-1β. Our data highlight a hitherto unrecognized role of macrophage-hepatocyte crosstalk for a joint and oxygen-dependent hepcidin production through STAT3 and CEBPδ.

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Hepcidin is strongly induced during NOX2-mediated macrophage differentiation in a H₂O₂-dependent manner.

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In contrast to hepatocyte hepcidin, macrophage hepcidin transcription is not modulated by low O₂ level.

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Macrophage released IL1-β strongly induces hepatocyte hepcidin via STAT3 signaling.

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IL1-β mediated hepatocyte hepcidin induction is independent of IL-6.

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Despite the mandatory requirement of STAT3, CEBPδ also involved in IL1-β induced hepatocyte hepcidin transcription.

Hepcidin in chronic kidney disease anemia

Chronic kidney disease (CKD) is associated with several complications that worsen with progression of disease; anemia, disturbances in iron metabolism and inflammation are common features. Inflammatory response starts early, releasing pro-inflammatory cytokines, acute phase reactants and hepcidin. Hepcidin production is modulated by several factors, as hypoxia/anemia, erythropoietin and erythropoiesis products, transferrin saturation (TSAT) and liver iron levels, which are altered in CKD. Treatment of CKD anemia is based on pharmaceutical intervention, with erythropoietic stimulating agents and/or iron supplementation; however, in spite of the erythropoietic benefits, this therapy, on a regular basis, involves risks, namely iron overload. To overcome these risks, some therapeutic approaches are under study to target CKD anemia. Considering the actual alerts about risk of iron overload in dialysis patients, inhibition of hepcidin, the central key player in iron homeostasis, could be a pivotal strategy in the management of CKD anemia.

The transcriptional regulation of an antimicrobial peptide hepcidin1 in Oryzias melastigma upon EE2 exposure involved in a new pathway with a novel transcriptional regulatory element HepERE

17α-ethinylestradiol (EE2) exerts endocrine disrupting effect and immunotoxic effect on marine animals, including modulation of hepcidin expression. The antimicrobial peptide hepcidin displays a crucial role in innate immunity in fish against invading pathogens. It is known that the transcription of hepcidin in mammals is individually regulated by many stimuli, including inflammation, iron overload, anemia or hypoxia, through several distinct molecular pathways. The canonical mechanism for endocrine disrupting effects is mediated by an estrogen receptor (ER) and estrogen responsive element (ERE), whereas the underlying mechanism for immunotoxic effect is still unclear. In this study, a hepcidin from Oryzias melastigma (OM-hep1) was found to be down-regulated upon EE2 exposure and was associated with ERα. Unlike the revealed signaling pathways for hepcidin regulation in mammals, it was revealed by promoter activity analysis that the OM-hep1 transcription was not associated with canonical immune-associated and hormone-associated regulatory elements, known as the nuclear factor κB (NF-κB), signal transducer and activator of transcription 3 (STAT3), ERE and estrogen-related receptor responsive element (ERRE). Further analysis through a series of base mutations revealed a short fragment from -315 to -289 bp on the OM-hep1 promoter with high activity. This fragment was composed of a putative ERE-like element (23 bases) plus an adjacent down-streamed four bases motif GTGT. Replacement of either of the core bases (GGTCA) of ERE-like or GTGT motif showed non-activity and non-response to EE2 exposure, thus a new hepcidin-associated element named as HepERE was revealed. Evidences from electrophoretic mobility shift assay (EMSA) and surface plasmon resonance (SPR) assay demonstrated that the EE2-mediated down-regulation of OM-hep1 expression was associated with ERα binding to HepERE but not classical ERE. Taken together, a novel signaling pathway was revealed and the regulatory mechanism associated with the ERα and HepERE element on immunomodulation of OM-hep1 expression upon EE2 exposure was first reported here.

Inducible Nitric Oxide Synthase Is a Key Host Factor for Toxoplasma GRA15-Dependent Disruption of the Gamma Interferon-Induced Antiparasitic Human Response

Although Toxoplasma virulence mechanisms targeting gamma interferon (IFN-γ)-induced cell-autonomous antiparasitic immunity have been extensively characterized in mice, the virulence mechanisms in humans remain uncertain, partly because cell-autonomous immune responses against Toxoplasma differ markedly between mice and humans. Despite the identification of inducible nitric oxide synthase (iNOS) as an anti-Toxoplasma host factor in mice, here we show that iNOS in humans is a pro-Toxoplasma host factor that promotes the growth of the parasite. The GRA15 Toxoplasma effector-dependent disarmament of IFN-γ-induced parasite growth inhibition was evident when parasite-infected monocytes were cocultured with hepatocytes. Interleukin-1β (IL-1β), produced from monocytes in a manner dependent on GRA15 and the host's NLRP3 inflammasome, combined with IFN-γ to strongly stimulate iNOS expression in hepatocytes; this dramatically reduced the levels of indole 2,3-dioxygenase 1 (IDO1), a critically important IFN-γ-inducible anti-Toxoplasma protein in humans, thus allowing parasite growth. Taking the data together, Toxoplasma utilizes human iNOS to antagonize IFN-γ-induced IDO1-mediated cell-autonomous immunity via its GRA15 virulence factor.IMPORTANCE Toxoplasma, an important intracellular parasite of humans and animals, causes life-threatening toxoplasmosis in immunocompromised individuals. Gamma interferon (IFN-γ) is produced in the host to inhibit the proliferation of this parasite and eventually cause its death. Unlike mouse disease models, which involve well-characterized virulence strategies that are used by Toxoplasma to suppress IFN-γ-dependent immunity, the strategies used by Toxoplasma in humans remain unclear. Here, we show that GRA15, a Toxoplasma effector protein, suppresses the IFN-γ-induced indole-2,3-dioxygenase 1-dependent antiparasite immune response in human cells. Because NLRP3-dependent production of IL-1β and nitric oxide (NO) in Toxoplasma-infected human cells is involved in the GRA15-dependent virulence mechanism, blocking NO or IL-1β production in the host could represent a novel therapeutic approach for treating human toxoplasmosis.

DNA methylation of hepatic iron sensing genes and the regulation of hepcidin expression

Production of the iron regulatory peptide hepcidin is tightly controlled by a network of proteins in hepatocytes that sense levels of iron in the circulation (as diferric-transferrin) and in tissues (in ferritin). Human studies show high variability in the normal range of serum hepcidin levels. We have postulated that this may, in part, be related to inter-individual variability in the expression of genes in the iron sensing pathway, potentially governed by epigenetic factors. Here, we have investigated whether genes encoding hepatic iron sensing proteins and hepcidin are regulated by DNA methylation. Experiments were performed on two human hepatoma cell lines, HepG2 cells and Huh7 cells. Basal expression of TFR2 and HAMP was significantly lower in Huh7 cells compared with HepG2 cells. Analysis of bisulphite-converted DNA from Huh7 cells revealed partial methylation of TFR2 (alpha transcript), which could result in gene silencing. Demethylation using 5-aza-2’-deoxycitidine (AZA) increased TFR2 mRNA expression in Huh7. PCR analysis of bisulphite-converted HAMP promoter DNA, using methylation-specific primers, revealed no differences between cell lines. However, HAMP mRNA expression in Huh7 was increased by AZA treatment, suggesting that methylation of one or more iron sensing genes may indirectly influence HAMP expression. Our study provides evidence that DNA methylation might control expression of HAMP and other hepatic iron sensing genes, and indicates that epigenetic influences on iron homeostasis warrant further investigation.

Hypoxia enhances H2O2-mediated upregulation of hepcidin: Evidence for NOX4-mediated iron regulation

The exact regulation of the liver-secreted peptide hepcidin, the key regulator of systemic iron homeostasis, is still poorly understood. It is potently induced by iron, inflammation, cytokines or H₂O₂ but conflicting results have been reported on hypoxia. In our current study, we first show that pronounced (1%) and mild (5%) hypoxia strongly induces hepcidin in human Huh7 hepatoma and primary liver cells predominantly at the transcriptional level via STAT3 using two hypoxia systems (hypoxia chamber and enzymatic hypoxia by the GOX/CAT system). SiRNA silencing of JAK1, STAT3 and NOX4 diminished the hypoxia-mediated effect while a role of HIF1α could be clearly ruled out by the response to hypoxia-mimetics and competition experiments with a plasmid harboring the oxygen-dependent degradation domain of HIF1α. Specifically, hypoxia drastically enhances the H₂O₂-mediated induction of hepcidin strongly pointing towards an oxidase as powerful upstream control of hepcidin. We finally provide evidences for an efficient regulation of hepcidin expression by NADPH-dependent oxidase 4 (NOX4) in liver cells. In summary, our data demonstrate that hypoxia strongly potentiates the peroxide-mediated induction of hepcidin via STAT3 signaling pathway. Moreover, oxidases such as NOX4 or artificially overexpressed urate oxidase (UOX) can induce hepcidin. It remains to be studied whether the peroxide-STAT3-hepcidin axis simply acts to continuously compensate for oxygen fluctuations or is directly involved in iron sensing per se.

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Hypoxia strongly induces hepcidin via STAT3 signaling.

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HIF1α is not involved in hepcidin regulation under hypoxia.

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Hypoxia enhances hydrogen peroxide-mediated hepcidin induction.

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Oxidases, such as NOX4 are powerful inducers of hepcidin.

Does Hypoxia Cause Carcinogenic Iron Accumulation in Alcoholic Liver Disease (ALD)?

Alcoholic liver disease (ALD) is a leading health risk worldwide. Hepatic iron overload is frequently observed in ALD patients and it is an important and independent factor for disease progression, survival, and the development of primary liver cancer (HCC). At a systemic level, iron homeostasis is controlled by the liver-secreted hormone hepcidin. Hepcidin regulation is complex and still not completely understood. It is modulated by many pathophysiological conditions associated with ALD, such as inflammation, anemia, oxidative stress/H₂O_2, or hypoxia. Namely, the data on hypoxia-signaling of hepcidin are conflicting, which seems to be mainly due to interpretational limitations of in vivo data and methodological challenges. Hence, it is often overlooked that hepcidin-secreting hepatocytes are physiologically exposed to 2–7% oxygen, and that key oxygen species such as H₂O₂ act as signaling messengers in such a hypoxic environment. Indeed, with the recently introduced glucose oxidase/catalase (GOX/CAT) system it has been possible to independently study hypoxia and H₂O₂ signaling. First preliminary data indicate that hypoxia enhances H₂O₂-mediated induction of hepcidin, pointing towards oxidases such as NADPH oxidase 4 (NOX4). We here review and discuss novel concepts of hypoxia signaling that could help to better understand hepcidin-associated iron overload in ALD.

Effects of cranberry (Vaccinum macrocarpon) supplementation on iron status and inflammatory markers in rowers

Background

The aim of this study was to analyze the effect of supplementation with cranberry (Vaccinum macrocarpon) on the levels of pro-inflammatory cytokines, hepcidin and selected markers of iron metabolism in rowers subjected to exhaustive exercise.

Methods

This double-blind study included 16 members of the Polish Rowing Team. The subjects were randomly assigned to the supplemented group (n = 9), receiving 1200 mg of cranberry extract for 6 weeks, or to the placebo group (n = 7). The participants performed a 2000-m test on a rowing ergometer at the beginning and at the end of the preparatory camp. Blood samples were obtained from the antecubital vein prior to each exercise test, one minute after completing the test, and after a 24-h recovery period. The levels of hepcidin, interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-alpha), ferritin, iron, soluble transferrin receptor (sTfR) and myoglobin were determined, along with total iron-binding capacity (TIBC), unbound iron-binding capacity (UIBC) and total antioxidant capacity (TAC).

Results

Both prior and after the supplementation, a significant post-exercise increase in the concentration of IL-6 was observed in both groups. At the end of the study period, cranberry-supplemented athletes presented with significantly higher resting, post-exercise and post-recovery levels of TAC than the controls. However, a significant exercise-induced increase in the concentrations of TNF-alpha, myoglobin and hepcidin was observed solely in the control group.

Conclusion

Supplementation with cranberry extract contributed to a significant strengthening of antioxidant potential in individuals exposed to strenuous physical exercise. However, supplementation did not exert direct effects on other analyzed parameters: inflammatory markers and indices of iron metabolism (TNF-alpha, hepcidin and myoglobin).

Molecular pathogenesis and clinical consequences of iron overload in liver cirrhosis

BACKGROUND

The liver, as the main iron storage compartment and the place of hepcidin synthesis, is the central organ involved in maintaining iron homeostasis in the body. Excessive accumulation of iron is an important risk factor in liver disease progression to cirrhosis and hepatocellular carcinoma. Here, we review the literature on the molecular pathogenesis of iron overload and its clinical consequences in chronic liver diseases.

DATA SOURCES

PubMed was searched for English-language articles on molecular genesis of primary and secondary iron overload, as well as on their association with liver disease progression. We have also included literature on adjuvant therapeutic interventions aiming to alleviate detrimental effects of excessive body iron load in liver cirrhosis.

RESULTS

Excess of free, unbound iron induces oxidative stress, increases cell sensitivity to other detrimental factors, and can directly affect cellular signaling pathways, resulting in accelerated liver disease progression. Diagnosis of liver cirrhosis is, in turn, often associated with the identification of a pathological accumulation of iron, even in the absence of genetic background of hereditary hemochromatosis. Iron depletion and adjuvant therapy with antioxidants are shown to cause significant improvement of liver functions in patients with iron overload. Phlebotomy can have beneficial effects on liver histology in patients with excessive iron accumulation combined with compensated liver cirrhosis of different etiology.

CONCLUSION

Excessive accumulation of body iron in liver cirrhosis is an important predictor of liver failure and available data suggest that it can be considered as target for adjuvant therapy in this condition.

Regulation of Hepcidin by Erythropoiesis: The Story So Far

Hepcidin is the master regulator of systemic iron homeostasis, facilitating iron balance by controlling intestinal iron absorption and recycling. Hepcidin levels are suppressed when erythropoiesis is stimulated, for example following acute blood loss, appropriately enhancing cellular iron export to the plasma to support production of new red blood cells. However, persistent increased and ineffective erythropoiesis, for example in thalassemia, results in sustained elevations in iron absorption, which cause iron overload with associated organ toxicities. The ligands, receptors, and canonical pathways by which iron loading and inflammation upregulate hepcidin expression have been largely established. However, although several mechanisms have been proposed, the means by which erythropoiesis causes hepcidin suppression have been unclear. The erythroid-derived hormone erythroferrone appears to be a convincing candidate for the link between increased erythropoiesis and hepcidin suppression. If confirmed to be clinically and physiologically relevant in humans, potentiation or inhibition of erythroferrone activity could be a crucial pharmaceutical strategy.

In alcoholic cirrhosis, low-serum hepcidin levels associate with poor long-term survival

BACKGROUND & AIMS

Iron constitutes a potentially toxic element and consequently, hepatic iron overload may accelerate liver disease progression and development of hepatocellular carcinoma (HCC). Hepcidin is the central negative regulator of iron metabolism that is produced primarily by the liver.

METHODS

To study the prognostic significance of serum hepcidin, we assessed the influence of baseline serum hepcidin levels on the outcome of a French cohort encompassing 237 patients with alcoholic cirrhosis prospectively followed up in the setting of HCC screening.

RESULTS

Hepcidin values correlated weakly with serum ferritin levels (r = 0.33) and hepatic iron scores (r = 0.3). After a median follow-up of 68 months, patients with baseline lower hepcidin level had a higher risk of HCC occurrence [hazard ratio, HR = 1.76 (1.01-3.06), P = 0.031] and overall death [HR = 1.63 (1.07-2.44), P = 0.019]. According to Cox multivariate analyses, lower hepcidin levels were independently associated with death [HR = 2.84 (1.29-6.25), P = 0.009] along with higher Child-Pugh score while HCC occurrence was mainly associated with clinical confounders interfering with iron metabolism (older age and higher BMI, adjusted P-value for hepcidin = 0.119).

CONCLUSIONS

In conclusion, low-serum hepcidin levels in patients with alcoholic cirrhosis bear a long-term prognostic significance warranting further explorations.

Combination therapy of menstrual derived mesenchymal stem cells and antibiotics ameliorates survival in sepsis

INTRODUCTION

Sepsis is a clinical syndrome associated with a severe systemic inflammation induced by infection. Although different anti-microbial drugs have been used as treatments, morbidity and mortality rates remain high. Mesenchymal stem cells (MSCs) derived from the bone marrow have demonstrated a partial protective effect in sepsis. Menstrual derived MSCs (MenSCs) emerge as an attractive candidate because they present important advantages over other sources, including improved proliferation rates and paracrine response under specific stress conditions. Here, we evaluate their therapeutic effect in a polymicrobial severe sepsis model.

METHODS

The antimicrobial activity of MenSCs was determined in vitro through direct and indirect bacterial growth assays and the measurement of the expression levels of different antimicrobial peptides (AMPs) by quantitative reverse transcription-polymerase chain reaction. The therapeutic effect of MenSCs was determined in the cecal ligation and puncture (CLP) mouse model. Mice were then treated with antibiotics (AB) or MenSCs alone or in combination. The survival rates and histological and biochemical parameters were evaluated, and the systemic levels of pro- and anti-inflammatory cytokines as well as the response of specific lymphocyte subsets were determined by flow cytometry.

RESULTS

MenSCs exerted an important antimicrobial effect in vitro, mediated by a higher expression of the AMP-hepcidin. In the CLP mouse model, MenSCs in synergy with AB (a) improved the survival rate (95 %) in comparison with saline (6 %), AB (73 %), and MenSCs alone (48 %) groups; (b) enhanced bacterial clearance in the peritoneal fluids and blood; (c) reduced organ injuries evaluated by lower concentrations of the liver enzymes alanine aminotransferase and aspartate aminotransferase; and (d) modulated the inflammatory response through reduction of pro- and anti-inflammatory cytokines without significant loss of T and B lymphocytes.

CONCLUSIONS

We conclude that MenSCs in combination with AB enhance survival in CLP-induced sepsis by acting on multiples targets. MenSCs thus constitute a feasible approach for the future clinical treatment of sepsis.

Oxidative stress and the homeodynamics of iron metabolism

Iron and oxygen share a delicate partnership since both are indispensable for survival, but if the partnership becomes inadequate, this may rapidly terminate life. Virtually all cell components are directly or indirectly affected by cellular iron metabolism, which represents a complex, redox-based machinery that is controlled by, and essential to, metabolic requirements. Under conditions of increased oxidative stress—i.e., enhanced formation of reactive oxygen species (ROS)—however, this machinery may turn into a potential threat, the continued requirement for iron promoting adverse reactions such as the iron/H2O2-based formation of hydroxyl radicals, which exacerbate the initial pro-oxidant condition. This review will discuss the multifaceted homeodynamics of cellular iron management under normal conditions as well as in the context of oxidative stress.

Circulating factors are involved in hypoxia-induced hepcidin suppression

Hepcidin transcription is strongly down-regulated under hypoxic conditions, however whether hypoxia inhibits hepcidin directly or indirectly is still unknown. We investigated the time course of hypoxia-mediated hepcidin down-regulation in vivo in healthy volunteers exposed to hypobaric hypoxia at high altitude and, based on the hypothesis that circulating factors are implicated in hepcidin inhibition, we analyzed the effect of sera of these volunteers exposed to normoxia and hypoxia on hepcidin expression in Huh-7 cell lines. Hypoxia led to a significant hepcidin down-regulation in vivo that was almost complete within 72h of exposure and followed erythropoietin induction. This delay in hepcidin down-regulation suggests the existence of soluble factor/s regulating hepcidin production. We then stimulated HuH-7 cells with normoxic and hypoxic sera to analyze the effects of sera on hepcidin regulation. Hypoxic sera had a significant inhibitory effect on hepcidin promoter activity assessed by a luciferase assay, although the amount of such decrease was not as relevant as that observed in vivo. Cellular mRNA analysis showed that a number of volunteers' sera inhibited hepcidin expression, concurrently with ID1 inhibition, suggesting that inhibitory factor(s) may act through the SMAD-pathway.

Hepcidin and sports anemia

Iron is an important mineral element used by the body in a variety of metabolic and physiologic processes. These processes are highly active when the body is undergoing physical exercises. Prevalence of exercise-induced iron deficiency anemia (also known as sports anemia) is notably high in athletic populations, particularly those with heavy training loads. The pathogenesis of sports anemia is closely related to disorders of iron metabolism, and a more comprehensive understanding of the mechanism of iron metabolism in the course of physical exercises could expand ways of treatment and prevention of sports anemia. In recent years, there have been remarkable research advances regarding the molecular mechanisms underlying changes of iron metabolism in response to physical exercises. This review has covered these advances, including effects of exercise on duodenum iron absorption, serum iron status, iron distribution in organs, erythropoiesis, and hepcidin’s function and its regulation. New methods for the treatment of exercise-induced iron deficiency are also discussed.

Quercetin prevents ethanol-induced iron overload by regulating hepcidin through the BMP6/SMAD4 signaling pathway

Emerging evidence has demonstrated that chronic ethanol exposure induces iron overload, enhancing ethanol-mediated liver damage. The purpose of this study was to explore the effects of the naturally occurring compound quercetin on ethanol-induced iron overload and liver damage, focusing on the signaling pathway of the iron regulatory hormone hepcidin. Adult male C57BL/6J mice were pair-fed with isocaloric-Lieber De Carli diets containing ethanol (accounting for 30% of total calories) and/or carbonyl iron (0.2%) and treated with quecertin (100 mg/kg body weight) for 15 weeks. Mouse primary hepatocytes were incubated with ethanol (100 mM) and quercetin (100 μM) for 24 h. Mice exposed to either ethanol or iron presented significant fatty infiltration and iron deposition in the liver; these symptoms were exacerbated in mice cotreated with ethanol and iron. Quercetin attenuated the abnormity induced by ethanol and/or iron. Ethanol suppressed BMP6 and intranuclear SMAD4 as well as decreased hepcidin expression. These effects were partially alleviated by quercetin supplementation in mice and hepatocytes. Importantly, ethanol caused suppression of SMAD4 binding to the HAMP promoter and of hepcidin messenger RNA expression. These effects were exacerbated by anti-BMP6 antibody and partially alleviated by quercetin or human recombinant BMP6 in cultured hepatocytes. In contrast, co-treatment with iron and ethanol, especially exposure of iron alone, activated BMP6/SMAD4 pathway and up-regulated hepcidin expression, which was also normalized by quercetin in vivo. Quercetin prevented ethanol-induced hepatic iron overload different from what carbonyl iron diet elicited in the mechanism, by regulating hepcidin expression via the BMP6/SMAD4 signaling pathway.

Hepcidin and the iron enigma in HCV infection

An estimated 30-40% of patients with chronic hepatitis C have elevated serum iron, transferrin saturation, and ferritin levels. Clinical data suggest that iron is a co-morbidity factor for disease progression following HCV infection. Iron is essential for a number of fundamental metabolic processes in cells and organisms. Mammalian iron homeostasis is tightly regulated and this is maintained through the coordinated action of sensory and regulatory networks that modulate the expression of iron-related proteins at the transcriptional and/or posttranscriptional levels. Disturbances of iron homeostasis have been implicated in infectious disease pathogenesis. Viruses, similarly to other pathogens, can escape recognition by the immune system, but they need iron from their host to grow and spread. Hepcidin is a 25-aa peptide, present in human serum and urine and represents the key peptide hormone, which modulates iron homeostasis in the body. It is synthesized predominantly by hepatocytes and its mature form is released in circulation. In this review, we discuss recent advances in the exciting crosstalk of molecular mechanisms and cell signaling pathways by which iron and hepcidin production influences HCV-induced liver disease.

Hypoxia-inducible factors link iron homeostasis and erythropoiesis

Iron is required for efficient oxygen transport, and hypoxia signaling links erythropoiesis with iron homeostasis. Hypoxia induces a highly conserved signaling pathway in cells under conditions of low levels of O2. One component of this pathway, hypoxia-inducible factor (HIF), is a transcription factor that is highly active in hypoxic cells. The first HIF target gene characterized was EPO, which encodes erythropoietin-a glycoprotein hormone that controls erythropoiesis. In the past decade, there have been fundamental advances in our understanding of how hypoxia regulates iron levels to support erythropoiesis and maintain systemic iron homeostasis. We review the cell type-specific effects of hypoxia and HIFs in adaptive response to changes in oxygen and iron availability as well as potential uses of HIF modulators for patients with iron-related disorders.

Iron homeostasis in the liver

Iron is an essential nutrient that is tightly regulated. A principal function of the liver is the regulation of iron homeostasis. The liver senses changes in systemic iron requirements and can regulate iron concentrations in a robust and rapid manner. The last 10 years have led to the discovery of several regulatory mechanisms in the liver that control the production of iron regulatory genes, storage capacity, and iron mobilization. Dysregulation of these functions leads to an imbalance of iron, which is the primary cause of iron-related disorders. Anemia and iron overload are two of the most prevalent disorders worldwide and affect over a billion people. Several mutations in liver-derived genes have been identified, demonstrating the central role of the liver in iron homeostasis. During conditions of excess iron, the liver increases iron storage and protects other tissues, namely, the heart and pancreas from iron-induced cellular damage. However, a chronic increase in liver iron stores results in excess reactive oxygen species production and liver injury. Excess liver iron is one of the major mechanisms leading to increased steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma.

Nuclear expression of Smad proteins and its prognostic significance in clear cell renal cell carcinoma

Smad2, Smad3, and Smad4 are components of the transforming growth factor β signaling pathway associated with tumorigenesis. The expression of these proteins is associated with tumor progression and prognosis of many cancers. This study aimed to evaluate the nuclear expression of Smad2, Smad3, and Smad4 in clear cell renal cell carcinoma and to assess the clinical significance and prognostic value of their expression patterns. The nuclear expression levels of Smads were evaluated in 637 cases of clear cell renal cell carcinomas using immunohistochemistry. To determine the statistical significance of Smad expression in clear cell renal cell carcinoma, each of the cases were divided into 2 groups (low and high expression groups) according to the extent of nuclear staining. Nuclear expressions of Smad3 and Smad4 were inversely correlated with the patient's age, the nuclear grade, the tumor size, and the pTNM stage. The Smad3-low and Smad4-low groups showed significantly shorter cancer-specific and progression-free survival times. Furthermore, multivariate analysis showed that both Smad3 and Smad4 were independent predictors for progression-free survival (P = .008 and P = .022, respectively). However, Smad2 expression was not related to clinicopathologic parameters and patients' survival. These results suggest that nuclear expressions of Smad3 and Smad4 were related to prognosis of clear cell renal cell carcinoma patients and may serve as novel prognostic markers in clear cell renal cell carcinoma patients.

Regulatory effects of Cu, Zn, and Ca on Fe absorption: the intricate play between nutrient transporters

Iron is an essential nutrient for almost every living organism because it is required in a number of biological processes that serve to maintain life. In humans, recycling of senescent erythrocytes provides most of the daily requirement of iron. In addition, we need to absorb another 1–2 mg Fe from the diet each day to compensate for losses due to epithelial sloughing, perspiration, and bleeding. Iron absorption in the intestine is mainly regulated on the enterocyte level by effectors in the diet and systemic regulators accessing the enterocyte through the basal lamina. Recently, a complex meshwork of interactions between several trace metals and regulatory proteins was revealed. This review focuses on advances in our understanding of Cu, Zn, and Ca in the regulation of iron absorption. Ascorbate as an important player is also considered.

The hypoxia-inducible factor-C/EBPα axis controls ethanol-mediated hepcidin repression

Hepcidin is a liver-derived peptide hormone and the master regulator of systemic iron homeostasis. Decreased hepcidin expression is a common feature in alcoholic liver disease (ALD) and in mouse models of ethanol loading. Dysregulation of hepcidin signaling in ALD leads to liver iron deposition, which is a major contributing factor to liver injury. The mechanism by which hepcidin is regulated following ethanol treatment is unclear. An increase in liver hypoxia was observed in an acute ethanol-induced liver injury model. The hypoxic response is controlled by a family of hypoxia-inducible transcription factors (HIFs), which are composed of an oxygen-regulated alpha subunit (HIFα) and a constitutively present beta subunit, aryl hydrocarbon receptor nuclear translocator (HIFβ/Arnt). Disruption of liver HIF function reversed the repression of hepcidin following ethanol loading. Mouse models of liver HIF overexpression demonstrated that both HIF-1α and HIF-2α contribute to hepcidin repression in vivo. Ethanol treatment led to a decrease in CCAAT-enhancer-binding protein alpha (C/EBPα) protein expression in a HIF-dependent manner. Importantly, adenoviral rescue of C/EBPα in vivo ablated the hepcidin repression in response to ethanol treatment or HIF overexpression. These data provide novel insight into the regulation of hepcidin by hypoxia and indicate that targeting HIFs in the liver could be therapeutic in ALD.

Influence of low oxygen tensions on macrophage polarization

Microenvironmental conditions in infected, inflamed or damaged tissues are characterized by low levels of oxygen (hypoxia) and nutrients. Myeloid cells (mostly macrophages and neutrophils) account for 95% of the cells newly recruited into inflammatory sites, and exert their effector functions under these restrictive conditions. In the case of macrophages, adaptation to the surrounding tissue environment is underlined by their huge metabolic and functional plasticity, which allows them to critically participate in the maintenance of tissue homeostasis and the initiation and resolution of inflammatory processes under hypoxic conditions. Therefore, alterations in oxygen availability directly affect the macrophage functional state (polarization), a phenomenon that has been already illustrated in pathologies like cancer, atherosclerosis and obesity. This review summarizes recent advances on the molecular basis of macrophage sensing and response to changes in oxygen pressure, emphasizing the link among the hypoxia-induced signalling pathways, macrophage polarization and inflammatory pathologies.

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.

Inhibition of hepcidin transcription by growth factors

The hepatic peptide hormone hepcidin controls the duodenal absorption of iron, its storage, and its systemic distribution. Hepcidin production is often insufficient in chronic hepatitis C and alcoholic liver disease, leading to hyperabsorption of iron and its accumulation in the liver. Hepatocyte growth factor (HGF) and epidermal growth factor (EGF) mediate hepatic regeneration after liver injury. We examined the effect of these growth factors on hepcidin synthesis by hepatocytes. HGF and EGF treatment of primary mouse hepatocytes, as well as EGF administration in mice, suppressed hepcidin messenger RNA (mRNA) synthesis. The suppression of hepcidin by these growth factors was transcriptional, and was mediated by a direct effect of HGF and EGF on the bone morphogenetic protein (BMP) pathway regulating hepcidin synthesis. We further show that growth factors interfered with nuclear localization of activated sons of mothers against decapentaplegic (Smad) and increased the nuclear pool of the BMP transcriptional corepressor TG-interacting factor (TGIF). In a kinase screen with small-molecule kinase inhibitors, inhibitors in the PI3 kinase pathway and in the mitogen-activated ERK kinase/extracellular signal-regulated kinase (MEK/ERK) pathway prevented HGF suppression of hepcidin in primary mouse hepatocytes.

CONCLUSION

HGF and EGF suppress hepatic hepcidin synthesis, in part through PI3 kinase MEK/ERK kinase pathways which may be modulating the nuclear localization of BMP pathway transcriptional regulators including activated Smads1/5/8 and the corepressor TGIF. EGF, HGF, and possibly other growth factors that activate similar pathways may contribute to hepcidin suppression in chronic liver diseases, promote iron accumulation in the liver, and exacerbate the destructive disease processes.

Hypoxia and cytokines regulate carbonic anhydrase 9 expression in hepatocellular carcinoma cells in vitro

AIM: To study the expression of carbonic anhydrase (CA) 9 in human hepatocellular carcinoma (HCC) cells.

METHODS: We studied CA9 protein, CA9 mRNA and hypoxia-inducible factor-1 alpha (HIF-1α) protein levels in Hep3B cells exposed in different parallel approaches. In one of these approaches, HCC cells were exposed to extreme in vitro hypoxia (24 h 0.1% O₂) without or with interleukin (IL)-1, IL-6, tumor necrosis factor-alpha (TNF-α) and transforming growth factor-beta (TGF-β) stimulation for the same hypoxic exposure time or exposed to normoxic oxygenation conditions without or with cytokine stimulation.

RESULTS: The tumour cell line analysed showed a strong hypoxic CA9 mRNA expression pattern in response to prolonged severe hypoxia with cell-line specific patterns and a marked induction of CA9 protein in response to severe hypoxia. These results were paralleled by the results for HIF-1α protein under identical oxygenation conditions with a similar expression tendency to that displayed during the CA9 protein expression experimental series. Continuous stimulation with the cytokines, IL-1, IL-6, TNF-α and TGF-β, under normoxic conditions significantly increased the carbonic anhydrase 9 expression level at both the protein and mRNA level, almost doubling the CA9 mRNA and CA9 and HIF-1α protein expression levels found under hypoxia. The findings from these experiments indicated that hypoxia is a positive regulator of CA9 expression in HCC, and the four signal transduction pathways, IL-1, IL-6, TNF-α and TGF-β, positively influence CA9 expression under both normoxic and hypoxic conditions.

CONCLUSION: These findings may potentially be considered in the design of anti- cancer therapeutic approaches involving hypoxia-induced or cytokine stimulatory effects on expression. In addition, they provide evidence of the stimulatory role of the examined cytokine families resulting in an increase in CA9 expression under different oxygenation conditions in human cancer, especially HCC, and on the role of the CA9 gene as a positive disease regulator in human cancer.

Acute acetaminophen intoxication leads to hepatic iron loading by decreased hepcidin synthesis

Acetaminophen (APAP), a major cause of acute liver injury in the Western world, is mediated by metabolism and oxidative stress. Recent studies have suggested a role for iron in potentiating APAP-induced liver injury although its regulatory mechanism is not completely understood. The current study was designed to unravel the iron-regulating pathways in mice after APAP-induced hepatotoxicity. Mice with severe injury showed a significant increase in liver iron concentration and oxidative stress. Concurrently, the plasma concentration of hepcidin, the key regulator in iron metabolism, and hepatic hepcidin antimicrobial peptide (Hamp) mRNA expression levels were significantly reduced. We showed that hepcidin transcription was inhibited via several hepcidin-regulating factors, including the bone morphogenetic protein/small mother against decapentaplegic (BMP/SMAD) pathway, CCAAT/enhancer-binding protein α (C/EBPα), and possibly also via erythropoietin (EPO). Downregulation of the BMP/SMAD signaling pathway was most likely caused by hypoxia-inducible factor 1α (HIF-1α), which was increased in mice with severe APAP-induced liver injury. HIF-1α stimulates cleaving of hemojuvelin, the cofactor of the BMP receptor, thereby blocking BMP-induced signaling. In addition, gene expression levels of C/ebpα were significantly reduced, and Epo mRNA expression levels were significantly increased after APAP intoxication. These factors are regulated through HIF-1α during oxidative stress and suggest that HIF-1α is a key modulator in reduced hepcidin transcription after APAP-induced hepatotoxicity. In conclusion, acute APAP-induced liver injury leads to activation of HIF-1α, which results in a downregulation in hepcidin expression through a BMP/SMAD signaling pathway and through C/EBPα inhibition. Eventually, this leads to hepatic iron loading associated with APAP cytotoxicity.

Severe microcytic anemia but increased erythropoiesis in mice lacking Hfe or Tfr2 and Tmprss6

Cell surface proteins Hfe, Tfr2, hemojuvelin and Tmprss6 play key roles in iron homeostasis. Hfe and Tfr2 induce transcription of hepcidin, a small peptide that promotes the degradation of the iron transporter ferroportin. Hemojuvelin, a co-receptor for bone morphogenic proteins, induces hepcidin transcription through a Smad signaling pathway. Tmprss6 (also known as matriptase-2), a membrane serine protease that has been found to bind and degrade hemojuvelin in vitro, is a potent suppressor of hepcidin expression. In order to examine if Hfe and Tfr2 are substrates for Tmprss6, we generated mice lacking functional Hfe or Tfr2 and Tmprss6. We found that double mutant mice lacking functional Hfe or Tfr2 and Tmprss6 exhibited a severe iron deficiency microcytic anemia phenotype mimicking the phenotype of single mutant mice lacking functional Tmprss6 (Tmprss6msk/msk mutant) demonstrating that Hfe and Tfr2 are not substrates for Tmprss6. Nevertheless, the phenotype of the mice lacking Hfe or Tfr2 and Tmprss6 differed from Tmprss6 deficient mice alone, in that the double mutant mice exhibited much greater erythropoiesis. Hfe and Tfr2 have been shown to play important roles in the erythron, independent of their role in regulating liver hepcidin transcription. We demonstrate that lack of functional Tfr2 and Hfe allows for increased erythropoiesis even in the presence of high hepcidin expression, but the high levels of hepcidin levels significantly limit the availability of iron to the erythron, resulting in ineffective erythropoiesis. Furthermore, repression of hepcidin expression by hypoxia was unaffected by the loss of functional Hfe, Tfr2 and Tmprss6.

Alcohol Activates TGF-Beta but Inhibits BMP Receptor-Mediated Smad Signaling and Smad4 Binding to Hepcidin Promoter in the Liver

Hepcidin, a key regulator of iron metabolism, is activated by bone morphogenetic proteins (BMPs). Mice pair-fed with regular and ethanol-containing L. De Carli diets were employed to study the effect of alcohol on BMP signaling and hepcidin transcription in the liver. Alcohol induced steatosis and TGF-beta expression. Liver BMP2, but not BMP4 or BMP6, expression was significantly elevated. Despite increased BMP expression, the BMP receptor, and transcription factors, Smad1 and Smad5, were not activated. In contrast, alcohol stimulated Smad2 phosphorylation. However, Smad4 DNA-binding activity and the binding of Smad4 to hepcidin promoter were attenuated. In summary, alcohol stimulates TGF-beta and BMP2 expression, and Smad2 phosphorylation but inhibits BMP receptor, and Smad1 and Smad5 activation. Smad signaling pathway in the liver may therefore be involved in the regulation of hepcidin transcription and iron metabolism by alcohol. These findings may help to further understand the mechanisms of alcohol and iron-induced liver injury.

Hepatic hypoxia-inducible factor-2 down-regulates hepcidin expression in mice through an erythropoietin-mediated increase in erythropoiesis

BACKGROUND

Iron metabolism, regulated by the iron hormone hepcidin, and oxygen homeostasis, dependent on hypoxia-inducible factors, are strongly interconnected. We previously reported that in mice in which both liver hypoxia-inducible factors-1 and -2 are stabilized (the hepatocyte von Hippel-Lindau knockout mouse model), hepcidin expression was strongly repressed and we hypothesized that hypoxia-inducible factor-2 could be the major regulatory component contributing to the hepcidin down-regulation.

DESIGN AND METHODS

We generated and analyzed hepatocyte-specific knockout mice harboring either hypoxia-inducible factor-2α deficiency (Hif2a knockout) or constitutive hypoxia-inducible factor-2α stabilization (Vhlh/Hif1a knockout) and ex vivo systems (primary hepatocyte cultures). Hif2a knockout mice were fed an iron-deficient diet for 2 months and Vhlh/Hif1a knockout mice were treated with neutralizing erythropoietin antibody.

RESULTS

We demonstrated that hypoxia-inducible factor-2 is dispensable in hepcidin gene regulation in the context of an adaptive response to iron-deficiency anemia. However, its overexpression in the double Vhlh/Hif1a hepatocyte-specific knockout mice indirectly down-regulates hepcidin expression through increased erythropoiesis and erythropoietin production. Experiments in primary hepatocytes confirmed the non-autonomous role of hypoxia-inducible factor-2 in hepcidin regulation.

CONCLUSIONS

While our results indicate that hypoxia-inducible factor-2 is not directly involved in hepcidin repression, they highlight the contribution of hepatic hypoxia-inducible factor-2 to the repression of hepcidin through erythropoietin-mediated increased erythropoiesis, a result of potential clinical interest.

Hepcidin: A Critical Regulator of Iron Metabolism during Hypoxia

Iron status affects cognitive and physical performance in humans. Recent evidence indicates that iron balance is a tightly regulated process affected by a series of factors other than diet, to include hypoxia. Hypoxia has profound effects on iron absorption and results in increased iron acquisition and erythropoiesis when humans move from sea level to altitude. The effects of hypoxia on iron balance have been attributed to hepcidin, a central regulator of iron homeostasis. This paper will focus on the molecular mechanisms by which hypoxia affects hepcidin expression, to include a review of the hypoxia inducible factor (HIF)/hypoxia response element (HRE) system, as well as recent evidence indicating that localized adipose hypoxia due to obesity may affect hepcidin signaling and organismal iron metabolism.