Iron-induced expression of bone morphogenic protein 6 in intestinal cells is the main regulator of hepatic hepcidin expression in vivo

Diagnosis and management of anemia in pediatric inflammatory bowel diseases: Clinical practice guidelines on behalf of the SIGENP IBD Working group

Anemia is one of the most frequent extra-intestinal manifestations of inflammatory bowel disease. Insidious onset, variability of symptoms and lack of standardized screening practices may increase the risk of underestimating its burden in children with IBD. Despite its relevance and peculiarity in everyday clinical practice, this topic is only dealt with in a few documents specifically for the pediatric field. The aim of the current guidelines is therefore to provide pediatric gastroenterologists with a practical update to support the clinical and therapeutic management of children with IBD and anemia. A panel of 19 pediatric gastroenterologists and 1 pediatric hematologist with experience in the field of pediatric IBD was agreed by IBD Working group of the Italian Society of Gastroenterology, Hepatology and Nutrition (SIGENP) to produce the present article outlining practical clinical approaches to the pediatric patient with IBD and anemia. The levels of evidence and recommendations have been defined for each part of the statement according to the GRADE system.

Reduced Plasma Bone Morphogenetic Protein 6 Levels in Sepsis and Septic Shock Patients

Infectious diseases are associated with low iron levels and the induction of hepcidin, the primary protein regulating cellular iron export. Bone morphogenetic protein 6 (BMP6), a key regulator of hepcidin expression, has not yet been analyzed in the plasma of patients with systemic inflammatory response syndrome (SIRS) or sepsis. An analysis of 38 SIRS, 39 sepsis, and 78 septic shock patients revealed similar levels of BMP6 in sepsis and septic shock, which were lower compared to patients with SIRS and healthy controls. Plasma BMP6 levels did not correlate with procalcitonin and C-reactive protein levels in patients with SIRS or sepsis/septic shock. Neither bacterial nor SARS-CoV-2 infections affected plasma BMP6 levels. There was no difference in BMP6 levels between ventilated and non-ventilated patients, or between patients with and without dialysis. Vasopressor therapy did not alter BMP6 levels. Survivors had plasma BMP6 levels similar to non-survivors. Due to the high variability of plasma BMP6 levels, these analyses have limited clinical relevance. Iron, ferritin, and transferrin levels were known in at least 50% of patients but did not correlate with plasma BMP6 levels. In conclusion, this study showed normal BMP6 plasma levels in SIRS, which are reduced in patients with sepsis and septic shock. This suggests that the commonly observed increase in hepcidin levels and the decline in iron levels in SIRS, sepsis, and septic shock are not due to higher BMP6.

An emerging class of new therapeutics targeting TGF, Activin, and BMP ligands in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an often fatal condition, the primary pathology of which involves loss of pulmonary vascular perfusion due to progressive aberrant vessel remodeling. The reduced capacity of the pulmonary circulation places increasing strain on the right ventricle of the heart, leading to death by heart failure. Currently, licensed therapies are primarily vasodilators, which have increased the median post-diagnosis life expectancy from 2.8 to 7 years. Although this represents a substantial improvement, the search continues for transformative therapeutics that reverse established disease. The genetics of human PAH heavily implicates reduced endothelial bone morphogenetic protein (BMP) signaling as a causal role for the disease pathobiology. Recent approaches have focused on directly enhancing BMP signaling or removing the inhibitory influence of pathways that repress BMP signaling. In this critical commentary, we review the evidence underpinning the development of two approaches: BMP-based agonists and inhibition of activin/GDF signaling. We also address the key considerations and questions that remain regarding these approaches.

The role of iron in host-microbiota crosstalk and its effects on systemic glucose metabolism

Iron is critical for the appearance and maintenance of life on Earth. Almost all organisms compete or cooperate for iron acquisition, demonstrating the importance of this essential element for the biological and physiological processes that are key for the preservation of metabolic homeostasis. In humans and other mammals, the bidirectional interactions between the bacterial component of the gut microbiota and the host for iron acquisition shape both host and microbiota metabolism. Bacterial functions influence host iron absorption, whereas the intake of iron, iron deficiency and iron excess in the host affect bacterial biodiversity, taxonomy and function, resulting in changes in bacterial virulence. These consequences of the host-microbial crosstalk affect systemic levels of iron, its storage in different tissues and host glucose metabolism. At the interface between the host and the microbiota, alterations in the host innate immune system and in circulating soluble factors that regulate iron (that is, hepcidin, lipocalin 2 and lactoferrin) are associated with metabolic disease. In fact, patients with obesity-associated metabolic dysfunction and insulin resistance exhibit dysregulation in iron homeostasis and alterations in their gut microbiota profile. From an evolutionary point of view, the pursuit of two important nutrients - glucose and iron - has probably driven human evolution towards the most efficient pathways and genes for human survival and health.

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.

Ferric carboxymaltose in patients with pulmonary arterial hypertension and iron deficiency: a long-term study

BACKGROUND

Pulmonary arterial hypertension (PAH) is a progressive disease with limited survival. Iron deficiency (ID) correlates with disease severity and mortality. While oral iron supplementation was shown to be insufficient in such patients, the potential impact of parenteral iron on clinical measures warrants further investigation.

METHODS

We retrospectively analysed the long-term effects of intravenous ferric carboxymaltose (FCM) on iron status and clinical measures in patients with PAH and ID [ferritin < 100 μg/L or ferritin 100-300 μg/L and transferrin saturation (TSAT) < 20%] who were on stable targeted PAH therapy, compared with matched controls without ID. Patients with ID received a single infusion of FCM (500 to 1000 mg). Clinical measures monitored included exercise capacity, World Health Organization (WHO) functional class, ESC/ERS risk status, and hospitalizations. The observation period was up to 18 months.

RESULTS

One hundred and seventeen patients (mean age 60.9 ± 16.1 years; 64.1% females) with confirmed PAH and on stable targeted therapy for ≥3 months were included (58 with and 59 patients without ID who did not receive FCM). In patients with ID, iron supplementation with FCM resulted in an immediate and sustained improvement of iron status for up to 18 months (serum iron, ferritin, TSAT, all P < 0.01). Fourteen patients in the FCM group received a second FCM infusion after 9.6 ± 4.8 months due to recurrent ID. At 6 and 18 months after FCM infusion, 6 min walk distance improved from 377.5 ± 15.9 at baseline to 412.5 ± 15.1 and 400.8 ± 14.5 m, respectively (both P < 0.05). WHO functional class (P < 0.05) and ESC/ERS risk status also improved, and there was a reduction of hospitalizations for worsening PAH in the 12 months post vs. prior to iron repletion (P = 0.029). No significant changes were observed in the control group. FCM was well tolerated in all patients, with no severe adverse events.

CONCLUSIONS

In addition to targeted therapy, correction of ID by parenteral iron supplementation with FCM appears feasible and safe, has sustained effects on iron status, and may improve the clinical status and hospitalization rates in patients with PAH. Larger controlled studies are required to confirm this finding.

Bone morphogenetic protein 6-mediated crosstalk between endothelial cells and hepatocytes recapitulates the iron-sensing pathway in vitro

Liver sinusoidal endothelial cell–derived bone morphogenetic protein 6 (BMP6) and the BMP6–small mothers against decapentaplegic homolog (SMAD) signaling pathway are essential for the expression of hepcidin, the secretion of which is considered the systemic master switch of iron homeostasis. However, there are continued controversies related to the strong and direct suppressive effect of iron on hepatocellular hepcidin in vitro in contrast to in vivo conditions. Here, we directly studied the crosstalk between endothelial cells (ECs) and hepatocytes using in vitro coculture models that mimic hepcidin signaling in vivo. Huh7 cells were directly cocultured with ECs, and EC conditioned media (CM) were also used to culture Huh7 cells and primary mouse hepatocytes. To explore the reactions of ECs to surrounding iron, they were grown in the presence of ferric ammonium citrate and heme, two iron-containing molecules. We found that both direct coculture with ECs and EC-CM significantly increased hepcidin expression in Huh7 cells. The upstream SMAD pathway, including phosphorylated SMAD1/5/8, SMAD1, and inhibitor of DNA binding 1, was induced by EC-CM, promoting hepcidin expression. Efficient blockage of this EC-mediated hepcidin upregulation by an inhibitor of the BMP6 receptor ALK receptor tyrosine kinase 2/3 or BMP6 siRNA identified BMP6 as a major hepcidin regulator in this coculture system, which highly fits the model of hepcidin regulation by iron in vivo. In addition, EC-derived BMP6 and hepcidin were highly sensitive to levels of not only ferric iron but also heme as low as 500 nM. We here establish a hepatocyte–endothelial coculture system to fully recapitulate iron regulation by hepcidin using EC-derived BMP6.

Effect of hepcidin antagonists on anemia during inflammatory disorders

Iron is an essential element for the mammalian body however, its homeostasis must be regulated accurately for appropriate physiological functioning. Alterations in physiological iron levels can lead to moderate to severe iron disorders like chronic and acute iron deficiency (anemia) or iron overload. Hepcidin plays an important role in regulating homeostasis between circulating iron and stored iron in the cells as well as the absorption of dietary iron in the intestine. Inflammatory disorders restrict iron absorption from food due to increased circulating levels of hepcidin. Increased production of hepcidin causes ubiquitination of ferroportin (FPN) leading to its degradation, thereby retaining iron in the spleen, duodenal enterocytes, macrophages, and hepatocytes. Hepcidin inhibitors and antagonists play a consequential role to ameliorate inflammation-associated anemia. Many natural and synthesized compounds, able to reduce hepcidin expression during inflammation have been identified in recent years. Few of which are currently at various phases of clinical trial. This article comprises a comprehensive review of therapeutic approaches for the efficient treatment of anemia associated with inflammation. Many strategies have been developed targeting the hepcidin-FPN axis to rectify iron disorders. Hepcidin modulation with siRNAs, antibodies, chemical compounds, and plant extracts provides new insights for developing advanced therapeutics for iron-related disorders. Hepcidin antagonist's treatment has a high potential to improve iron status in patients with iron disorders, but their clinical success needs further recognition along with the identification and application of new therapeutic approaches.

Portuguese Consensus on Diagnosis, Treatment, and Management of Anemia in Pediatric Inflammatory Bowel Disease

Anemia is a common extraintestinal manifestation of inflammatory bowel disease (IBD), both in pediatric and in adult patients. Iron deficiency is the main cause of anemia in patients with IBD. Anemia is a clinically relevant comorbidity, with impact on patients' quality of life and it should be timely diagnosed and adequately treated. Currently, an active treatment approach is the recommended strategy, with evidence showing efficacy and safety of intravenous iron formulations. However, evidence in pediatric age remains scarce and no clinical recommendations exist for the diagnosis and treatment of this particular age group. The present document represents the first national consensus on the management of anemia in pediatric IBD and is therefore particularly relevant. The authors anticipate that the proposed recommendations will be useful in daily clinical practice for diagnosing and managing iron deficiency and iron-deficiency anemia in the pediatric population with IBD.

Cold atmospheric plasma treatment inhibits growth in colorectal cancer cells

Plasma oncology is a relatively new field of research. Recent developments have indicated that cold atmospheric plasma (CAP) technology is an interesting new therapeutic approach to cancer treatment. In this study, p53 wildtype (LoVo) and human p53 mutated (HT29 and SW480) colorectal cancer cells were treated with the miniFlatPlaSter - a device particularly developed for the treatment of tumor cells - that uses the Surface Micro Discharge (SMD) technology for plasma production in air. The present study analyzed the effects of plasma on colorectal cancer cells in vitro and on normal colon tissue ex vivo. Plasma treatment had strong effects on colon cancer cells, such as inhibition of cell proliferation, induction of cell death and modulation of p21 expression. In contrast, CAP treatment of murine colon tissue ex vivo for up to 2 min did not show any toxic effect on normal colon cells compared to H2O2 positive control. In summary, these results suggest that the miniFlatPlaSter plasma device is able to kill colorectal cancer cells independent of their p53 mutation status. Thus, this device presents a promising new approach in colon cancer therapy.

Bone Morphogenetic Protein-6 Inhibits Fibrogenesis in Scleroderma Offering Treatment Options for Fibrotic Skin Disease

BMP6 is known to be crucial for regulating embryonic skin development. This study assessed the role of BMP6 in dermal fibrosis. We detected that BMP6 is significantly increased in skin-derived fibroblasts of patients with localized scleroderma. Moreover, it was shown that BMP6 significantly impacts proliferation, migration, cytoskeletal organization, and collagen expression, as well as activity of the major pro-fibrogenic transcription factor AP-1 in dermal fibroblasts. The importance of BMP6 in dermal fibrosis was further confirmed in an in vivo model of dermal fibrosis in which BMP6-deficient mice showed significantly enhanced fibrosis compared with wild-type mice. Conversely, application of recombinant BMP6 significantly ameliorated dermal fibrosis in this preclinical bleomycin-induced sclerosis model, and herewith provided proof of concept for the successful treatment of this fibrotic skin disease.

BMP6-induced modulation of the tumor micro-milieu

Melanoma is the deadliest form of skin cancer with rising incidence, creating a significant health problem. We discovered increased expression of bone morphogenetic protein 6 (BMP6) in melanoma cells and tissues, and observed that BMP6 deficiency caused significantly delayed tumor onset and decelerated tumor progression in a melanoma mouse model. Moreover, we determined that BMP6 inhibits dermal mast cell recruitment and found that mast cell-derived mediators significantly reduced melanoma growth in vitro. In line with this, mast cell deficiency accelerated tumor onset and progression in a melanoma mouse model. Analysis of human melanoma tissues revealed a strong negative correlation between melanoma proliferation and mast cell infiltration. This study elucidates a novel role of BMP6-induced modulation of the tumor microenvironment.

Cold atmospheric plasma (CAP) activates angiogenesis-related molecules in skin keratinocytes, fibroblasts and endothelial cells and improves wound angiogenesis in an autocrine and paracrine mode

BACKGROUND

Cold atmospheric plasma (CAP) emerged as a novel therapeutic field with applications developed for bacterial sterilization, wound healing and cancer treatment. For clinical implementation it is important to know how CAP works and which molecular changes occur after the CAP treatment. Vascularization is an important step during wound healing, however, the effects of CAP on wound angiogenesis are not well examined so far. Furthermore, it has not been investigated, whether CAP primarily affects endothelial cells directly or via paracrine mechanisms to modulate the vasculature.

OBJECTIVE

This study concentrates on the influence of CAP on angiogenesis-related molecules in human epidermal keratinocytes, dermal fibroblasts and endothelial cells.

METHODS

CAP was generated by the MicroPlaSter ß® plasma torch system and CAP effects on angiogenesis were determined in vitro and in vivo.

RESULTS

We observed that CAP significantly induces the expression of Artemin, EGF, EG-VEGF (PK1), Endothelin-1 (ET-1), FGF-2 (FGF basic), IL-8 (CXCL8) and uPA in keratinocytes and Angiogenin (ANG), Endostatin (Col18A1), MCP-1 (CCL2), MMP-9, TIMP-1, uPA and VEGF in fibroblasts. In addition, CAP activates the expression of Angiopoietin-2 (Ang-2), Angiostatin (PLG), Amphiregulin (AR), Endostatin, FGF-2 and angiogenic-involved receptor expression of FGF R1 and VEGF R1 in HUVEC endothelial cells. It was also demonstrated that supernatants collected from CAP activated fibroblasts and keratinocytes elevate tube formation by endothelial cells and FGF-2 appears to be an important pro-angiogenic factor that controls vascularization via paracrine mechanisms. Mouse experiments supplement that CAP promotes angiogenesis during wound healing in vivo.

CONCLUSIONS

Taken together, these results suggest that CAP modulates angiogenesis-involved factors via autocrine and paracrine mechanisms and may be used to affect angiogenesis during wound healing.

Anemia of Inflammation: A Review

Impaired iron homeostasis and the suppressive effects of proinflammatory cytokines on erythropoiesis, together with alterations of the erythrocyte membrane that impair its survival, cause anemia of inflammation. Recent epidemiologic studies have connected inflammatory anemia with critical illness, obesity, aging, kidney failure, cancer, chronic infection, and autoimmune disease. The proinflammatory cytokine, interleukin-6, the iron regulatory hormone, hepcidin, and the iron exporter, ferroportin, interact to cause iron sequestration in the setting of inflammation. Although severe anemia is associated with adverse outcomes in critical illness, experimental models suggest that iron sequestration is part of a natural defense against pathogens.

Endothelial cells produce bone morphogenetic protein 6 required for iron homeostasis in mice

Bone morphogenetic protein 6 (BMP6) signaling in hepatocytes is a central transcriptional regulator of the iron hormone hepcidin that controls systemic iron balance. How iron levels are sensed to regulate hepcidin production is not known, but local induction of liver BMP6 expression by iron is proposed to have a critical role. To identify the cellular source of BMP6 responsible for hepcidin and iron homeostasis regulation, we generated mice with tissue-specific ablation of Bmp6 in different liver cell populations and evaluated their iron phenotype. Efficiency and specificity of Cre-mediated recombination was assessed by using Cre-reporter mice, polymerase chain reaction of genomic DNA, and quantitation of Bmp6 messenger RNA expression from isolated liver cell populations. Localization of the BMP co-receptor hemojuvelin was visualized by immunofluorescence microscopy. Analysis of the Bmp6 conditional knockout mice revealed that liver endothelial cells (ECs) expressed Bmp6, whereas resident liver macrophages (Kupffer cells) and hepatocytes did not. Loss of Bmp6 in ECs recapitulated the hemochromatosis phenotype of global Bmp6 knockout mice, whereas hepatocyte and macrophage Bmp6 conditional knockout mice exhibited no iron phenotype. Hemojuvelin was localized on the hepatocyte sinusoidal membrane immediately adjacent to Bmp6-producing sinusoidal ECs. Together, these data demonstrate that ECs are the predominant source of BMP6 in the liver and support a model in which EC BMP6 has paracrine actions on hepatocyte hemojuvelin to regulate hepcidin transcription and maintain systemic iron homeostasis.

Lower hepatic iron storage associated with obesity in mice can be restored by decreasing body fat mass through feeding a low-fat diet

High-fat diet (HFD)-induced obesity has been reported to result in low hepatic iron storage. In the current study, we tested the hypothesis that these obesity-related changes in hepatic iron status could be reversed by decreasing adiposity by feeding a low-fat diet. Five-week-old C57BL/6 mice were assigned to 3 groups: the LL group was fed a control diet for 31 weeks, the HH group was fed a HFD for 31 weeks, and the HL group was fed the HFD for 15 weeks and then switched to the control diet for 16 weeks. The fat mass of the HL group decreased by 3.2 g from the 14th to the 30th weeks. Fat mass was significantly different among the groups (11.4, 15.8, and 37.5 g in the LL, HH, and HL groups, respectively; P< .001). The liver iron concentration of the HL group was similar to that of the LL group, which was about 30% higher than that of the HH group (74.2, 72.7, and 55.7 μg/g in the LL, HL, and HH groups, respectively; P< .05). Duodenal cytochrome b messenger RNA (mRNA) levels were higher in the HL group than in the HH group. Although bone morphogenetic protein 6 (Bmp6) mRNA levels showed no significant differences in the liver, duodenal Bmp6 mRNA levels were significantly lower in the HH group compared with the LL and HL groups. Liver Smad1/5 proteins were differentially activated: the HH group had significantly less phosphorylated Smads than did the LL and HL groups. Our data demonstrate that hepatic iron storage levels are closely related to body adiposity, and reducing body fat mass through feeding a lower-fat diet to HFD-induced obese mice restores liver iron storage.

Hepcidin-Dependent Regulation of Erythropoiesis during Anemia in a Teleost Fish, Dicentrarchus labrax

Anemia is a common disorder, characterized by abnormally low levels of red blood cells or hemoglobin. The mechanisms of anemia development and response have been thoroughly studied in mammals, but little is known in other vertebrates, particularly teleost fish. In this study, different degrees of anemia were induced in healthy European sea bass specimens (Dicentrarchus labrax) and at pre-determined time points hematological parameters, liver iron content and the expression of genes involved in iron homeostasis and hematopoiesis, with particular attention on hepcidins, were evaluated. The experimental anemia prompted a decrease in hamp1 expression in all tested organs, in accordance to an increased need for iron absorption and mobilization, with slight increases in hamp2 in the kidney and intestine. The liver was clearly the major organ involved in iron homeostasis, decreasing its iron content and showing a gene expression profile consistent with an increased iron release and mobilization. Although both the spleen and head kidney are involved in erythropoiesis, the spleen was found to assume a more preponderant role in the recovery of erythrocyte levels. The intestine was also involved in the response to anemia, through the increase of iron transporting genes. Administration of Hamp1 or Hamp2 mature peptides showed that only Hamp1 affects hematological parameters and liver iron content. In conclusion, the molecular mechanisms of response to anemia present in sea bass are similar to the ones described for mammals, with these results indicating that the two hepcidin types from teleosts assume different roles during anemia.

Association of hepatic oxidative stress and iron dysregulation with HCC development after interferon therapy in chronic hepatitis C

BACKGROUND

Oxidative stress may play pathogenic roles in the mechanisms underlying chronic hepatitis C (CHC). The impact of excessive oxidative stress and iron dysregulation on the development of hepatocellular carcinoma (HCC) after interferon therapy has not been established.

METHODS

We investigated the impact of oxidative stress and iron deposition on HCC development after therapy with pegylated interferon (PegIFN)+ribavirin in CHC patients. Systemic and intracellular iron homeostasis was evaluated in liver tissues, peripheral blood mononuclear cells and sera.

RESULTS

Of 203 patients enrolled, 13 developed HCC during the 5.6-year follow-up. High hepatic 8-hydroxy-2-deoxyguanosine (8-OHdG) levels were significantly associated with HCC development in multivariate analysis (p=0.0012) which was also significantly correlated with severity of hepatic iron deposition before therapy (p<0.0001). Systemic and intracellular iron regulators of hepcidin and F-box and leucine-rich repeat protein 5 (FBXL5) expression levels were significantly suppressed in CHC patients (p=0.0032 and p=0.016, respectively) despite their significantly higher levels of serum iron and ferritin compared with controls. However, intracellular iron regulators of FBXL5 and iron regulatory proteins were regulated in balance with hepatic iron deposition. Significant correlations were observed among IL-6, bone morphogenetic protein 6, hepcidin and ferroportin, as regards systemic iron regulation.

CONCLUSIONS

Measurement of hepatic oxidative stress before antiviral therapy is useful for the prediction of HCC development after interferon therapy. Low baseline levels of the intracellular iron regulators of FBXL5 in addition to a suppressed hepcidin level might be associated with severe hepatic iron deposition in CHC patients.

TRIAL REGISTRATION NUMBER

UMIN 000001031.

Enhanced expression of BMP6 inhibits hepatic fibrosis in non-alcoholic fatty liver disease

OBJECTIVE

Bone morphogenetic protein 6 (BMP6) has been identified as crucial regulator of iron homeostasis. However, its further role in liver pathology including non-alcoholic fatty liver disease (NAFLD) and its advanced form non-alcoholic steatohepatitis (NASH) is elusive. The aim of this study was to investigate the expression and function of BMP6 in chronic liver disease.

DESIGN

BMP6 was analysed in hepatic samples from murine models of chronic liver injury and patients with chronic liver diseases. Furthermore, a tissue microarray comprising 110 human liver tissues with different degree of steatosis and inflammation was assessed. BMP6-deficient (BMP6(-/-)) and wild-type mice were compared in two dietary NASH-models, that is, methionine choline-deficient (MCD) and high-fat (HF) diets.

RESULTS

BMP6 was solely upregulated in NAFLD but not in other murine liver injury models or diseased human livers. In NAFLD, BMP6 expression correlated with hepatic steatosis but not with inflammation or hepatocellular damage. Also, in vitro cellular lipid accumulation in primary human hepatocytes induced increased BMP6 expression. MCD and HF diets caused more hepatic inflammation and fibrosis in BMP6(-/-) compared with wild-type mice. However, only in the MCD and not in the HF diet model BMP6(-/-) mice developed marked hepatic iron overload, suggesting that further mechanisms are responsible for protective BMP6 effect. In vitro analysis revealed that recombinant BMP6 inhibited the activation of hepatic stellate cells (HSCs) and reduced proinflammatory and profibrogenic gene expression in already activated HSCs.

CONCLUSIONS

Steatosis-induced upregulation of BMP6 in NAFLD is hepatoprotective. Induction of BMP6-signalling may be a promising antifibrogenic strategy.

Effects of cold atmospheric plasma (CAP) on ß-defensins, inflammatory cytokines, and apoptosis-related molecules in keratinocytes in vitro and in vivo

Cold atmospheric plasma (CAP) has been gaining increasing interest as a new approach for the treatment of skin diseases or wounds. Although this approach has demonstrated promising antibacterial activity, its exact mechanism of action remains unclear. This study explored in vitro and in vivo whether CAP influences gene expression and molecular mechanisms in keratinocytes. Our results revealed that a 2 min CAP treatment using the MicroPlaSter ß in analogy to the performed clinical studies for wound treatment induces expression of IL-8, TGF-ß1, and TGF-ß2. In vitro and in vivo assays indicated that keratinocyte proliferation, migration, and apoptotic mechanisms were not affected by the CAP treatment under the applied conditions. Further, we observed that antimicrobial peptides of the ß-defensin family are upregulated after CAP treatment. In summary, our results suggest that a 2 min application of CAP induces gene expression of key regulators important for inflammation and wound healing without causing proliferation, migration or cell death in keratinocytes. The induction of ß-defensins in keratinocytes describes an absolutely new plasma strategy. Activation of antimicrobial peptides supports the well-known antibacterial effect of CAP treatment, whereas the mechanism of ß-defensin activation by CAP is not investigated so far.

Potential roles of BMP9 in liver fibrosis

Liver fibrosis is a common phenomenon that is associated with several pathologies and is characterized by excessive extracellular matrix deposition that leads to progressive liver dysfunction. Bone morphogenetic protein 9 (BMP9) is the most recently discovered member of the BMP family. BMP9 bound with high affinity to activin receptor-like kinase 1 (ALK1) and endoglin in non-parenchymal liver cells. In addition, BMP9 activated Smad1/Smad5/Smad8 and induced the expression of the target genes inhibitor of differentiation 1 (Id1), hepcidin, Snail and the co-receptor endoglin in liver cells. Although the role of BMP9 in liver fibrosis is currently poorly understood, the presence of BMP9-activated proteins and its target genes have been reported to be associated with liver fibrosis development. This review summarizes the indirect connection between BMP9 and liver fibrosis, with a focus on the BMP9 signaling pathway members ALK1, endoglin, Id1, hepcidin and Snail. The observations on the role of BMP9 in regulating liver fibrosis may help in understanding the pathology mechanisms of liver disease. Furthermore, BMP9 could be served as a potent biomarker and the target of potential therapeutic drugs to treat hepatocytes fibrosis.

Exogenous BMP7 corrects plasma iron overload and bone loss in Bmp6-/- mice

PURPOSE

Iron overload accelerates bone loss in mice lacking the bone morphogenetic protein 6 (Bmp6) gene, which is the key endogenous regulator of hepcidin, iron homeostasis gene. We investigated involvement of other BMPs in preventing haemochromatosis and subsequent osteopenia in Bmp6-/- mice.

METHODS

Iron-treated wild-type (WT) and Bmp6-/- mice were analysed for hepcidin messenger RNA (mRNA) and tissue and blood BMP levels by quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR), immunohistochemistry, Western blot, enzyme-linked immunosorbent assay (ELISA) and proximity extension assay. BMPs labeled with technetium-99m were used in pharmacokinetic studies.

RESULTS

In WT mice, 4 h following iron challenge, liver Bmp6 and hepcidin expression were increased, while expression of other Bmps was not affected. In parallel, we provided the first evidence that BMP6 circulates in WT mice and that iron increased the BMP6 serum level and the specific liver uptake of (99m)Tc-BMP6. In Bmp6-/- mice, iron challenge led to blunted activation of liver Smad signaling and hepcidin expression with a delay of 24 h, associated with increased Bmp5 and Bmp7 expression and increased Bmp2, 4, 5 and 9 expression in the duodenum. Liver Bmp7 expression and increased circulating BMP9 eventually contributed to the late hepcidin response. This was further supported by exogenous BMP7 therapy resulting in an effective hepcidin expression followed by a rapid normalisation of plasma iron values and restored osteopenia in Bmp6-/- mice.

CONCLUSION

In Bmp6-/- mice, iron activated endogenous compensatory mechanisms of other BMPs that were not sufficient for preventing hemochromatosis and bone loss. Administration of exogenous BMP7 was effective in correcting the plasma iron level and bone loss, indicating that BMP6 is an essential but not exclusive in vivo regulator of iron homeostasis.

Disordered hepcidin-ferroportin signaling promotes breast cancer growth

Iron homeostasis is strictly governed in mammals; however, disordered iron metabolism (such as excess iron burden) is recognized as a risk factor for various types of diseases including cancers. Burgeoning evidence indicates that the central signaling of iron homeostasis, the hepcidin-ferroportin axis, is misregulated in cancers. Nonetheless, the mechanisms of misregulated expression of iron-related genes along this signaling in cancers remain largely unknown. In the current study, we found increased levels of serum hepcidin in breast cancer patients. Reduction of hepatic hepcidin through administration of heparin restrained tumorigenic properties of breast tumor cells. Mechanistic investigation revealed that increased iron, bone morphogenetic protein-6 (BMP6) and interleukin-6 (IL-6) jointly promoted the synthesis of hepatic hepcidin. Tumor hepcidin expression was marginally increased in breast tumors relative to adjacent tissues. In contrast, tumor ferroportin concentration was greatly reduced in breast tumors, especially in malignant tumors, compared to adjacent tissues. Elevation of ferroportin concentration inhibited cell proliferation in vitro and in vivo by knocking down tumor hepcidin expression. Additionally, increased IL-6 was demonstrated to jointly enhance the tumorigenic effects of iron through enforcing cell growth. Our combined data overall deciphered the machinery that altered the hepcidin-ferroportin signaling in breast cancers. Thus, targeting the hepcidin-ferroportin signaling would represent a promising therapeutics to restrain breast cancer growth.

Bone morphogenetic proteins as regulators of iron metabolism

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-beta (TGF-β) superfamily of signaling molecules. In addition to protean roles in embryonic development, germ-line specification, and cellular differentiation, a central role in iron homeostasis has recently been demonstrated for certain BMPs. Specifically, BMP6 serves to relate hepatic iron stores to the hepatocellular expression of the iron-regulatory hormone hepcidin. This regulation occurs via cellular SMAD-signaling molecules and is strongly modulated by the BMP coreceptor hemojuvelin (HJV). Mutations in certain genes influencing signaling to hepcidin via the BMP/SMAD pathway are associated with human disorders of iron metabolism, such as hereditary hemochromatosis and iron-refractory iron-deficiency anemia. Evidence suggests that signals in addition to iron stores influence hepcidin expression via the BMP/SMAD pathway. This review summarizes the details of BMP/SMAD signaling, with a particular focus on its role in iron homeostasis and iron-related diseases.

Potential roles of bone morphogenetic protein (BMP)-9 in human liver diseases

Bone morphogenetic proteins (BMP-2 to BMP-15) belong to the Transforming Growth Factor (TGF)-β superfamily and, besides their well-documented roles during embryogenesis and bone formation, some of them have recently been described to be involved in the pathogenesis of different organs, including the liver. The role of BMPs in liver damage responses including hepatocellular carcinoma (HCC) development has only begun to be addressed and strong evidence supports the concept of a pro-tumorigenic role of BMP signaling in HCC cells. BMP-9 (also termed Growth and Differentiation Factor (GDF)-2) represents the most recently discovered member of the BMP family. We have previously demonstrated that in HCC patient samples BMP-9 expression was positively associated with the tumor seize (“T stage”) and that it enhanced cell migration and induced epithelial to mesenchymal transition (EMT) in HCC cells in vitro. In another study we recently found that BMP-9 promotes growth in HCC cells, but not in non-transformed hepatocytes. Published as well as unpublished results obtained with primary hepatocytes support the concept of a dual function of BMP-9 in the liver: while in primary, non-malignant cells BMP-9 stabilizes the epithelial phenotype and inhibits proliferation, in HCC cells it induces cell growth and the acquisition of a migratory phenotype. In this review article we summarize current knowledge about BMPs in liver diseases, with special focus on the role of BMP-9 in HCC development and progression, that may provide new clues for a better understanding of the contribution of BMP-signaling to chronic liver diseases.

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.

Modulation of stemness in a human normal intestinal epithelial crypt cell line by activation of the WNT signaling pathway

The small intestine consists of two histological compartments composed of the crypts and the villi. The function of the adult small intestinal epithelium is mediated by four different types of mature cells: enterocytes, goblet, enteroendocrine and Paneth. Undifferentiated cells reside in the crypts and produce these four types of mature cells. The niche-related Wnt and Bmp signaling pathways have been suggested to be involved in the regulation and maintenance of the stem cell microenvironment. In our laboratory, we isolated the first normal human intestinal epithelial crypt (HIEC) cell model from the human fetal intestine and in this study we investigated the expression of a panel of intestinal stem cell markers in HIEC cells under normal culture parameters as well as under conditions that mimic the stem cell microenvironment. The results showed that short term stimulation of HIEC cells with R-spondin 1 and Wnt-3a±SB-216763, a glycogen synthase kinase 3β (GSK3β) inhibitor, induced β-catenin/TCF activity and expression of the WNT target genes, cyclin D2 and LGR5. Treatment of HIEC cells with noggin, an antagonist of BMP signaling, abolished SMAD2/5/8 phosphorylation. Inducing a switch from inactive WNT/active BMP toward active WNT/inactive BMP pathways was sufficient to trigger a robust intestinal primordial stem-like cell signature with predominant LGR5, PHLDA1, PROM1, SMOC2 and OLFM4 expression. These findings demonstrate that even fully established cultures of intestinal cells can be prompted toward a CBC stem cell-like phenotype. This model should be useful for studying the regulation of human intestinal stem cell self-renewal and differentiation.

Parenteral vs. oral iron: influence on hepcidin signaling pathways through analysis of Hfe/Tfr2-null mice

Treatment for iron deficiency anemia can involve iron supplementation via dietary or parenteral routes that result in different cellular iron distributions. The effect of the administered iron on the iron regulatory system and hepcidin in the liver has not been well studied. Hepcidin, the liver-expressed central iron-regulatory peptide, is itself regulated through the bone morphogenetic protein (BMP)/SMAD signaling pathway. Specifically, Bmp6 expression is upregulated in response to iron and induces hepcidin through phosphorylation of Smad1/5/8. The hemochromatosis-associated proteins Hfe and transferrin receptor 2 (Tfr2) are known upstream regulators of hepcidin, although their precise roles are still unclear. To investigate the mechanisms of this regulation and the roles of the Hfe and Tfr2, we subjected wild-type, Hfe(-/-), Tfr2(-/-), and Hfe(-/-)/Tfr2(-/-) mice to iron loading via dietary or parenteral routes. Systematic analysis demonstrated that Tfr2 is required for effective upregulation of Bmp6 in response to hepatocyte iron, but not nonparenchymal iron. Hfe is not required for Bmp6 upregulation, regardless of iron localization, but rather, is required for efficient downstream transmission of the regulatory signal. Our results demonstrate that Hfe and Tfr2 play separate roles in the regulatory responses to iron compartmentalized in different cell types and further elucidates the regulatory mechanisms controlling iron homeostasis.

Hepcidin production in response to iron is controlled by monocyte-derived humoral factors

Hepcidin, which is mainly produced by the liver, is the key regulator in iron homeostasis. Hepcidin expression is up-regulated by iron loading in vivo, but the mechanism underlying this process is not completely understood. In the present study, we investigated the mechanism, following the hypothesis that hepcidin production in response to iron loading is regulated by extra-hepatic iron sensors. We measured serum hepcidin concentrations and iron indices in Wistar rats treated with saccharated ferric oxide (SFO). Human hepatoma-derived HepG2 cells were stimulated using SFO-administered rat sera, and co-cultured with rat spleen cells, human monocyte-derived THP-1 cells, or human monocytes with diferric transferrin (holo-Tf), and hepcidin concentrations in the conditioned media were measured. SFO elevated rat serum hepcidin concentrations. SFO-treated rat sera increased hepcidin production from HepG2 cells, and this induction correlated with serum hepcidin levels, but not with iron indices. Holo-Tf up-regulated hepcidin concentrations in media from HepG2 cells co-cultured with rat spleen cells, THP-1 cells, or human monocytes with or without cell-to-cell contacts, while holo-Tf did not up-regulate hepcidin from HepG2 cells alone. Our results suggest the existence of humoral factors capable of inducing hepcidin production that are secreted by extra-hepatic cells, such as reticuloendothelial monocytes, in response to iron.

Cold atmospheric plasma (CAP) changes gene expression of key molecules of the wound healing machinery and improves wound healing in vitro and in vivo

Cold atmospheric plasma (CAP) has the potential to interact with tissue or cells leading to fast, painless and efficient disinfection and furthermore has positive effects on wound healing and tissue regeneration. For clinical implementation it is necessary to examine how CAP improves wound healing and which molecular changes occur after the CAP treatment. In the present study we used the second generation MicroPlaSter ß® in analogy to the current clinical standard (2 min treatment time) in order to determine molecular changes induced by CAP using in vitro cell culture studies with human fibroblasts and an in vivo mouse skin wound healing model. Our in vitro analysis revealed that the CAP treatment induces the expression of important key genes crucial for the wound healing response like IL-6, IL-8, MCP-1, TGF-ß1, TGF-ß2, and promotes the production of collagen type I and alpha-SMA. Scratch wound healing assays showed improved cell migration, whereas cell proliferation analyzed by XTT method, and the apoptotic machinery analyzed by protein array technology, was not altered by CAP in dermal fibroblasts. An in vivo wound healing model confirmed that the CAP treatment affects above mentioned genes involved in wound healing, tissue injury and repair. Additionally, we observed that the CAP treatment improves wound healing in mice, no relevant side effects were detected. We suggest that improved wound healing might be due to the activation of a specified panel of cytokines and growth factors by CAP. In summary, our in vitro human and in vivo animal data suggest that the 2 min treatment with the MicroPlaSter ß® is an effective technique for activating wound healing relevant molecules in dermal fibroblasts leading to improved wound healing, whereas the mechanisms which contribute to these observed effects have to be further investigated.

The small molecule, genistein, increases hepcidin expression in human hepatocytes

Hepcidin, a peptide hormone that decreases intestinal iron absorption and macrophage iron release, is a potential drug target for patients with iron overload syndromes because its levels are inappropriately low in these individuals. Endogenous stimulants of Hepcidin transcription include bone morphogenic protein 6 (BMP6) and interleukin-6 (IL-6) by effects on mothers against decapentaplegic homolog (Smad)4 or signal transducer and activator of transcription (Stat)3, respectively. We conducted a small-scale chemical screen in zebrafish embryos to identify small molecules that modulate hepcidin expression. We found that treatment with the isoflavone, genistein, from 28-52 hours postfertilization in zebrafish embryos enhanced Hepcidin transcript levels, as assessed by whole-mount in situ hybridization and quantitative real-time reverse-transcriptase polymerase chain reaction. Genistein's stimulatory effect was conserved in human hepatocytes: Genistein treatment of HepG2 cells increased both Hepcidin transcript levels and promoter activity. We found that genistein's effect on Hepcidin expression did not depend on estrogen receptor signaling or increased cellular iron uptake, but was impaired by mutation of either BMP response elements or the Stat3-binding site in the Hepcidin promoter. RNA sequencing of transcripts from genistein-treated hepatocytes indicated that genistein up-regulated 68% of the transcripts that were up-regulated by BMP6; however, genistein raised levels of several transcripts involved in Stat3 signaling that were not up-regulated by BMP6. Chromatin immunoprecipitation and ELISA experiments revealed that genistein enhanced Stat3 binding to the Hepcidin promoter and increased phosphorylation of Stat3 in HepG2 cells.

CONCLUSION

Genistein is the first small-molecule experimental drug that stimulates Hepcidin expression in vivo and in vitro. These experiments demonstrate the feasibility of identifying and characterizing small molecules that increase Hepcidin expression. Genistein and other candidate molecules may subsequently be developed into new therapies for iron overload syndromes.

Mammalian iron homeostasis in health and disease: uptake, storage, transport, and molecular mechanisms of action

Iron is a crucial factor for life. However, it also has the potential to cause the formation of noxious free radicals. These double-edged sword characteristics demand a tight regulation of cellular iron metabolism. In this review, we discuss the various pathways of cellular iron uptake, cellular iron storage, and transport. Recent advances in understanding the reduction and uptake of non-transferrin-bound iron are discussed. We also discuss the recent progress in the understanding of transcriptional and translational regulation by iron. Furthermore, we discuss recent advances in the understanding of the regulation of cellular and systemic iron homeostasis and several key diseases resulting from iron deficiency and overload. We also discuss the knockout mice available for studying iron metabolism and the related human conditions.

Murine mutants in the study of systemic iron metabolism and its disorders: an update on recent advances

Many past and recent advances in the field of iron metabolism have relied upon the use of mouse models of disease. These models have arisen spontaneously in breeder colonies or have been engineered for global or conditional ablation or overexpression of select genes. Full phenotypic characterization of these models typically involves maintenance on iron-loaded or -deficient diets, treatment with oxidative or hemolytic agents, breeding to other mutant lines or other stresses. In this review, we focus on systemic iron biology and the contributions that mouse model-based studies have made to the field. We have divided the field into three broad areas of research: dietary iron absorption, regulation of hepcidin expression and cellular iron metabolism. For each area, we begin with an overview of the current understanding of key molecular and cellular determinants then discuss recent advances. Finally, we conclude with brief comments on prospects for future study. This article is part of a Special Issue entitled: Cell Biology of Metals.

High-fat diet causes iron deficiency via hepcidin-independent reduction of duodenal iron absorption

Obesity is often associated with disorders of iron homeostasis; however, the underlying mechanisms are not fully understood. Hepcidin is a key regulator of iron metabolism and may be responsible for obesity-driven iron deficiency. Herein, we used an animal model of diet-induced obesity to study high-fat-diet-induced changes in iron homeostasis. C57BL/6 mice were fed a standard (SD) or high-fat diet (HFD) for 8 weeks, and in addition, half of the mice received high dietary iron (Fe+) for the last 2 weeks. Surprisingly, HFD led to systemic iron deficiency which was traced back to reduced duodenal iron absorption. The mRNA and protein expressions of the duodenal iron transporters Dmt1 and Tfr1 were significantly higher in HFD- than in SD-fed mice, indicating enterocyte iron deficiency, whereas the mRNA levels of the duodenal iron oxidoreductases Dcytb and hephaestin were lower in HFD-fed mice. Neither hepatic and adipose tissue nor serum hepcidin concentrations differed significantly between SD- and HFD-fed mice, whereas dietary iron supplementation resulted in increased hepatic hepcidin mRNA expression and serum hepcidin levels in SD as compared to HFD mice. Our study suggests that HFD results in iron deficiency which is neither due to intake of energy-dense nutrient poor food nor due to increased sequestration in the reticulo-endothelial system but is the consequence of diminished intestinal iron uptake. We found that impaired iron absorption is independent of hepcidin but rather results from reduced metal uptake into the mucosa and discordant oxidoreductases expressions despite enterocyte iron deficiency.

Prevalence and management of anemia in children, adolescents, and adults with inflammatory bowel disease

BACKGROUND

Children and adolescents with inflammatory bowel disease (IBD) are more likely to have Crohn's disease (CD) than ulcerative colitis (UC) and their disease tends to be more extensive and severe than in adults. We hypothesized that the prevalence of anemia would therefore be greater in children and adolescents than in adults attending IBD outpatient clinics.

METHODS

Using the WHO age-adjusted definitions of anemia we assessed the prevalence, severity, type, and response to treatment of anemia in patients attending pediatric, adolescent, and adult IBD clinics at our hospital.

RESULTS

The prevalence of anemia was 70% (41/59) in children, 42% (24/54) in adolescents, and 40% (49/124) in adults (P < 0.01). Overall, children (88% [36/41]) and adolescents (83% [20/24]) were more often iron-deficient than adults (55% [27/49]) (P < 0.01). Multivariate logistic regression showed that both active disease (odds ratio [OR], 4.7 95% confidence interval [CI], 2.5, 8.8) and attending the pediatric clinic (OR 3.7; 95% CI, 1.6, 8.4) but not the adolescent clinic predicted iron deficiency anemia. Fewer iron-deficient children (13% [5/36]) than adolescents (30% [6/20]) or adults (48% [13/27]) had been given oral iron (P < 0.05); none had received intravenous iron compared with 30% (6/20) adolescents and 41% (11/27) adults (P < 0.0001).

CONCLUSIONS

Anemia is even more common in children than in older IBD patients. Oral iron was given to half of adolescents and adults but, despite similar tolerance and efficacy, only a quarter of children with iron-deficient anemia. Reasons for the apparent underutilization of iron therapy include a perceived lack of benefit and concerns about side effects, including worsening of IBD activity.

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.

Downregulation of hemojuvelin prevents inhibitory effects of bone morphogenetic proteins on iron metabolism in hepatocellular carcinoma

Recently, we revealed that bone morphogenetic protein (BMP) 4 is increased in hepatocellular carcinoma (HCC). Furthermore, latest reports described BMPs, in particular BMP6, as important regulators of hepcidin expression in iron homeostasis. Therefore, we aimed to unravel why enhanced BMP expression in HCC patients does not lead to severe changes in iron metabolism. Initial analysis of the BMP4 and BMP6 expression patterns revealed enhanced expression on mRNA and protein level in HCC cell lines and tissue samples compared with primary human hepatocytes (PHHs) and normal liver tissues. However and interestingly, hepcidin expression was reduced in HCC cell lines and tissues. Analysis of BMP6 receptor expression revealed loss of BMP6-specific receptor subunit in HCC. To identify a possible regulatory mechanism causing lack of reaction to BMP4 we analyzed the expression of hemojuvelin (HJV), which is involved in iron metabolism as BMP co-receptor. HJV expression was markedly decreased in HCC cell lines and tissues. HJV promoter analysis revealed potential HNF-1α and snail-binding sites, but functional analysis ruled out that these transcriptional regulators or promoter methylation are the cause of HJV downregulation in HCC. However, we identified AU-rich elements in the HJV 3'-untranslated region and revealed significantly faster decay of HJV mRNA in HCC cells as compared with PHH indicating decreased mRNA-stability as the reason for the loss of HJV expression in HCC.

Iron regulation of hepcidin despite attenuated Smad1,5,8 signaling in mice without transferrin receptor 2 or Hfe

BACKGROUND & AIMS

HFE and transferrin receptor 2 (TFR2) are each necessary for the normal relationship between body iron status and liver hepcidin expression. In murine Hfe and Tfr2 knockout models of hereditary hemochromatosis (HH), signal transduction to hepcidin via the bone morphogenetic protein 6 (Bmp6)/Smad1,5,8 pathway is attenuated. We examined the effect of dietary iron on regulation of hepcidin expression via the Bmp6/Smad1,5,8 pathway using mice with targeted disruption of Tfr2, Hfe, or both genes.

METHODS

Hepatic iron concentrations and messenger RNA expression of Bmp6 and hepcidin were compared with wild-type mice in each of the HH models on standard or iron-loading diets. Liver phospho-Smad (P-Smad)1,5,8 and Id1 messenger RNA levels were measured as markers of Bmp/Smad signaling.

RESULTS

Whereas Bmp6 expression was increased, liver hepcidin and Id1 expression were decreased in each of the HH models compared with wild-type mice. Each of the HH models also showed attenuated P-Smad1,5,8 levels relative to liver iron status. Mice with combined Hfe/Tfr2 disruption were most affected. Dietary iron loading increased hepcidin and Id1 expression in each of the HH models. Compared with wild-type mice, HH mice demonstrated attenuated (Hfe knockout) or no increases in P-Smad1,5,8 levels in response to dietary iron loading.

CONCLUSIONS

These observations show that Tfr2 and Hfe are each required for normal signaling of iron status to hepcidin via the Bmp6/Smad1,5,8 pathway. Mice with combined loss of Hfe and Tfr2 up-regulate hepcidin in response to dietary iron loading without increases in liver Bmp6 messenger RNA or steady-state P-Smad1,5,8 levels.

Conditional disruption of mouse HFE2 gene: maintenance of systemic iron homeostasis requires hepatic but not skeletal muscle hemojuvelin

Mutations of the HFE2 gene are linked to juvenile hemochromatosis, a severe hereditary iron overload disease caused by chronic hyperabsorption of dietary iron. HFE2 encodes hemojuvelin (Hjv), a membrane-associated bone morphogenetic protein (BMP) coreceptor that enhances expression of the liver-derived iron regulatory hormone hepcidin. Hjv is primarily expressed in skeletal muscles and at lower levels in the heart and the liver. Moreover, a soluble Hjv form circulates in plasma and is thought to act as a decoy receptor, attenuating BMP signaling to hepcidin. To better understand the regulatory function of Hjv, we generated mice with tissue-specific disruption of this protein in hepatocytes or in muscle cells. The hepatic ablation of Hjv resulted in iron overload, quantitatively comparable to that observed in ubiquitous Hjv-/- mice. Serum iron and ferritin levels, transferrin saturation, and liver iron content were significantly (P < 0.001) elevated in liver-specific Hjv-/- mice. Hepatic Hjv mRNA was undetectable, whereas hepcidin expression was markedly suppressed (12.6-fold; P < 0.001) and hepatic BMP6 mRNA up-regulated (2.4-fold; P < 0.01), as in ubiquitous Hjv-/- counterparts. By contrast, the muscle-specific disruption of Hjv was not associated with iron overload or altered hepcidin expression, suggesting that muscle Hjv mRNA is dispensable for iron metabolism. Our data do not support any significant iron-regulatory function of putative muscle-derived soluble Hjv in mice, at least under physiological conditions.

CONCLUSION

The hemochromatotic phenotype of liver-specific Hjv-/- mice suggests that hepatic Hjv is necessary and sufficient to regulate hepcidin expression and control systemic iron homeostasis.

Iron deficiency and raised hepcidin in idiopathic pulmonary arterial hypertension: clinical prevalence, outcomes, and mechanistic insights

OBJECTIVES

This study sought to understand the prevalence and clinical relevance of iron deficiency in patients with idiopathic pulmonary arterial hypertension (IPAH).

BACKGROUND

Iron availability influences the pulmonary vascular response to hypoxia in humans and may be significant in the pathogenesis of IPAH.

METHODS

Iron deficiency, defined by raised levels of soluble transferrin receptor (sTfR), was investigated in 98 patients with IPAH. Hepcidin and erythropoietin (EPO) levels were also measured. The effect of bone morphogenetic protein (BMP) receptor knockdown on BMP-6-stimulated hepcidin production was assessed in human hepatoma HepG2 cells. Relationships between sTfR and exercise capacity, functional class, and all-cause mortality were analyzed.

RESULTS

Circulating sTfR levels were raised in 63% of IPAH patients, indicating significant iron deficiency. Consistent with this, iron, ferritin, and transferrin saturation levels were reduced and red cell distribution width increased, without overt anemia. Hepcidin correlated inversely with sTfR and positively with increasing ferritin. Hepcidin was inappropriately raised in IPAH independent of the inflammatory marker interleukin-6. EPO levels were also raised and correlated inversely with hepcidin. BMP receptor-type 2 (BMPR2) knockdown in HepG2 cells increased BMP-6-stimulated hepcidin expression. sTfR increased with World Health Organization functional class (p < 0.05), correlated negatively with exercise capacity (p = 0.027), and values >28.1 nmol/l independently predicted survival (p = 0.011).

CONCLUSIONS

Iron deficiency is common in IPAH patients and associated with disease severity and poor clinical outcome. Inappropriately raised hepcidin levels, which impair iron absorption from the gut, may be a factor.

Pathways for the regulation of hepcidin expression in anemia of chronic disease and iron deficiency anemia in vivo

BACKGROUND

Increased levels of hepcidin, the master regulator of iron homeostasis, contribute to the diversion of iron underlying the anemia of chronic disease. Yet hepcidin levels are low in anemia of chronic disease with concomitant true iron deficiency. Here we clarify the different underlying pathways regulating hepcidin expression under these conditions in vivo.

DESIGN AND METHODS

We used rat models of iron deficiency anemia, anemia of chronic disease and anemia of chronic disease with concomitant true iron deficiency and investigated upstream signaling pathways controlling hepcidin transcription in the liver. Protein and mRNA levels of iron metabolism genes and genes involved in SMAD1/5/8 and STAT3 signaling were determined by RT-PCR, Western blotting and immunohistochemistry.

RESULTS

SMAD1/5/8 phosphorylation and in parallel hepcidin mRNA expression were increased in anemia of chronic disease but significantly down-regulated in anemia of chronic disease with concomitant iron deficiency, either on the basis of phlebotomy or dietary iron restriction. Iron deficiency resulted in reduced bone morphogenetic protein-6 expression and impaired SMAD1/5/8 phosphorylation and trafficking, two key events for hepcidin transcription. Reduced SMAD1/5/8 activity in association with phlebotomy was paralleled by increased expression of the inhibitory factor, SMAD7, dietary iron restriction appeared to impair hepcidin transactivating SMAD pathways via reduction of membrane bound hemojuvelin expression.

CONCLUSIONS

This study evaluated hepcidin signaling pathways in anemia of chronic disease with/without concomitant iron deficiency in vivo. While iron deficiency in general decreased bone morphogenetic protein-6 expression, phlebotomy or dietary iron restriction inhibited inflammation driven SMAD1/5/8 mediated hepcidin formation by different pathways, indicating alternate hierarchic signaling networks as a function of the mode and kinetics of iron deficiency. Nonetheless, iron deficiency inducible regulatory pathways can reverse inflammation mediated stimulation of hepcidin expression.

Serum and liver iron differently regulate the bone morphogenetic protein 6 (BMP6)-SMAD signaling pathway in mice

The bone morphogenetic protein 6 (BMP6)-SMAD signaling pathway is a central regulator of hepcidin expression and systemic iron balance. However, the molecular mechanisms by which iron is sensed to regulate BMP6-SMAD signaling and hepcidin expression are unknown. Here we examined the effects of circulating and tissue iron on Bmp6-Smad pathway activation and hepcidin expression in vivo after acute and chronic enteral iron administration in mice. We demonstrated that both transferrin saturation and liver iron content independently influence hepcidin expression. Although liver iron content is independently positively correlated with hepatic Bmp6 messenger RNA (mRNA) expression and overall activation of the Smad1/5/8 signaling pathway, transferrin saturation activates the downstream Smad1/5/8 signaling cascade, but does not induce Bmp6 mRNA expression in the liver. Hepatic inhibitory Smad7 mRNA expression is increased by both acute and chronic iron administration and mirrors overall activation of the Smad1/5/8 signaling cascade. In contrast to the Smad pathway, the extracellular signal-regulated kinase 1 and 2 (Erk1/2) mitogen-activated protein kinase (Mapk) signaling pathway in the liver is not activated by acute or chronic iron administration in mice.

CONCLUSION

Our data demonstrate that the hepatic Bmp6-Smad signaling pathway is differentially activated by circulating and tissue iron to induce hepcidin expression, whereas the hepatic Erk1/2 signaling pathway is not activated by iron in vivo.

Regulation of cellular iron metabolism

Iron is an essential but potentially hazardous biometal. Mammalian cells require sufficient amounts of iron to satisfy metabolic needs or to accomplish specialized functions. Iron is delivered to tissues by circulating transferrin, a transporter that captures iron released into the plasma mainly from intestinal enterocytes or reticuloendothelial macrophages. The binding of iron-laden transferrin to the cell-surface transferrin receptor 1 results in endocytosis and uptake of the metal cargo. Internalized iron is transported to mitochondria for the synthesis of haem or iron–sulfur clusters, which are integral parts of several metalloproteins, and excess iron is stored and detoxified in cytosolic ferritin. Iron metabolism is controlled at different levels and by diverse mechanisms. The present review summarizes basic concepts of iron transport, use and storage and focuses on the IRE (iron-responsive element)/IRP (iron-regulatory protein) system, a well known post-transcriptional regulatory circuit that not only maintains iron homoeostasis in various cell types, but also contributes to systemic iron balance.

BMP signaling modulates hepcidin expression in zebrafish embryos independent of hemojuvelin

Hemojuvelin (Hjv), a member of the repulsive-guidance molecule (RGM) family, upregulates transcription of the iron regulatory hormone hepcidin by activating the bone morphogenetic protein (BMP) signaling pathway in mammalian cells. Mammalian models have identified furin, neogenin, and matriptase-2 as modifiers of Hjv's function. Using the zebrafish model, we evaluated the effects of hjv and its interacting proteins on hepcidin expression during embryonic development. We found that hjv is strongly expressed in the notochord and somites of the zebrafish embryo and that morpholino knockdown of hjv impaired the development of these structures. Knockdown of hjv or other hjv-related genes, including zebrafish orthologs of furin or neogenin, however, failed to decrease hepcidin expression relative to liver size. In contrast, overexpression of bmp2b or knockdown of matriptase-2 enhanced the intensity and extent of hepcidin expression in zebrafish embryos, but this occurred in an hjv-independent manner. Furthermore, we demonstrated that zebrafish hjv can activate the human hepcidin promoter and enhance BMP responsive gene expression in vitro, but is expressed at low levels in the zebrafish embryonic liver. Taken together, these data support an alternative mechanism for hepcidin regulation during zebrafish embryonic development, which is independent of hjv.

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

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

Diagnosis and management of iron deficiency anemia in patients with IBD

Anemia is the most prevalent extraintestinal complication of IBD. It can affect quality of life and ability to work, and can also increase the hospitalization rate in patients with IBD. Although the causes of anemia in IBD are multifactorial, iron deficiency anemia (IDA) is the most common. Assessment of the iron status of patients who have a condition associated with inflammation, such as IBD, by using common biochemical values is insufficient. However, new indices of iron metabolism (for instance ferritin:transferrin receptor ratio, reticulocyte hemoglobin content or percentage of hypochromic red blood cells) may help to improve the assessment of iron status in patients with IBD. The treatment of IDA traditionally involves oral iron supplementation. However, because of extensive gastrointestinal adverse effects, and data showing that the use of oral iron in IBD may be associated with disease exacerbation, current guidelines suggest that iron supplementation in IBD should be administered intravenously. This Review provides an overview of iron homeostasis in health before discussing diagnostic and therapeutic strategies for IDA in patients with IBD.

Increased BMP6 levels in the brains of Alzheimer's disease patients and APP transgenic mice are accompanied by impaired neurogenesis

During aging and in the progression of Alzheimer's disease (AD), synaptic plasticity and neuronal integrity are disturbed. In addition to the alterations in plasticity in mature neurons, the neurodegenerative process in AD has been shown to be accompanied by alterations in neurogenesis. Members of the bone morphogenetic protein (BMP) family of growth factors have been implicated as important regulators of neurogenesis and neuronal cell fate determination during development; however, their role in adult neurogenesis and in AD is less clear. We show here by qRT-PCR analysis that BMP6 mRNA levels were significantly increased in the hippocampus of human patients with AD and in APP transgenic mice compared to controls. Immunoblot and immunohistochemical analyses confirmed that BMP6 protein levels were increased in human AD brains and APP transgenic mouse brains compared to controls and accumulated around hippocampal plaques. The increased levels of BMP6 were accompanied by defects in hippocampal neurogenesis in AD patients and APP transgenic mice. In support of a role for BMP6 in defective neurogenesis in AD, we show in an in vitro model of adult neurogenesis that treatment with amyloid-β(1-42) protein (Aβ) resulted in increased expression of BMP6, and that exposure to recombinant BMP6 resulted in reduced proliferation with no toxic effects. Together, these results suggest that Aβ-associated increases in BMP6 expression in AD may have deleterious effects on neurogenesis in the hippocampus, and therapeutic approaches could focus on normalization of BMP6 levels to protect against AD-related neurogenic deficits.