Inflammation-induced up-regulation of hepcidin and down-regulation of ferroportin transcription are dependent on macrophage polarization

HFE-Related Hemochromatosis May Be a Primary Kupffer Cell Disease

Iron overload can lead to increased deposition of iron and cause organ damage in the liver, the pancreas, the heart and the synovium. Iron overload disorders are due to either genetic or acquired abnormalities such as excess transfusions or chronic liver diseases. The most common genetic disease of iron deposition is classic hemochromatosis (HH) type 1, which is caused by mutations of HFE. Other rare forms of HH include type 2A with mutations at the gene hemojuvelin or type 2B with mutations in HAMP that encodes hepcidin. HH type 3, is caused by mutations of the gene that encodes transferrin receptor 2. Mutations of SLC40A1 which encodes ferroportin cause either HH type 4A or HH type 4B. In the present review, an overview of iron metabolism including absorption by enterocytes and regulation of iron by macrophages, liver sinusoidal endothelial cells (LSECs) and hepatocyte production of hepcidin is presented. Hereditary Hemochromatosis and the current pathogenetic model are analyzed. Finally, a new hypothesis based on published data was suggested. The Kupffer cell is the primary defect in HFE hemochromatosis (and possibly in types 2 and 3), while the hepcidin-relative deficiency, which is the common underlying abnormality in the three types of HH, is a secondary consequence.

P. Gingivalis induce macrophage polarization by regulating hepcidin expression in chronic apical periodontitis

INTRODUCTION

Hepcidin, a central regulatory molecule of iron metabolism, is upregulated through the IL-6/STAT3 signaling pathway in inflammatory and infectious states, contributing to the pathogenesis of various diseases. In chronic apical periodontitis (CAP), Porphyromonas gingivalis (P. gingivalis) and its lipopolysaccharides (LPS) activate various immune responses in vivo, contributing to disease progression. This study evaluated the role and mechanism of hepcidin in P. gingivalis-induced bone tissue damage in CAP, focusing on its promotion of macrophage M1 polarization via the IL-6/STAT3 signaling pathway.

METHODS

We analyzed a GSE77459 dataset from the GEO database, containing data from inflammatory and normal dental pulp tissues. RT-qPCR and immunofluorescence staining were used to detect the expression of hepcidin in human CAP tissues and its relationship with macrophages. Mouse bone marrow derived macrophages (BMDMs) were cultured in vitro and stimulated with P. gingivalis LPS. The effects of Stattic on macrophage hepcidin expression, IL-6 expression, STAT3 phosphorylation, and macrophage polarization were detected by ELISA, western blotting, RT-qPCR, and flow cytometry, respectively.

RESULTS

Hepcidin expression in human inflammatory dental pulp tissues was upregulated via the IL-6/STAT3 pathway and correlated with macrophage polarization. Hepcidin-encoding genes were found to be highly expressed and primarily associated with M1 macrophages in CAP tissues. In vitro experiments revealed that P. gingivalis LPS stimulation induced macrophages to express hepcidin through the IL-6/STAT3 pathway and polarize to M1. Additionally, the IL-6/STAT3 pathway inhibitor Stattic suppressed these changes.

CONCLUSIONS

Our study demonstrates that in CAP, macrophages highly express hepcidin, which subsequently alters macrophage metabolism, regulates M1 polarization, and leads to bone tissue destruction.

Iron Deficiency in Preschool Children with Chronic Rhinitis

Introduction: Iron deficiency (ID) has been intricately linked with various inflammatory diseases. Chronic rhinitis stands as one of most common respiratory inflammation disorders in children. This study aimed to investigate the prevalence of ID among preschool children with chronic rhinitis and to explore the association between ID and chronic rhinitis in this population. Methods: This cross-sectional study included children aged 3 to 7 years diagnosed with chronic rhinitis. ID was defined as transferrin saturation <20%, with absolute ID being defined as ferritin <15 ng/mL. Logistic regression analyses were performed to identify factors associated with ID. Results: A total of 72 children with chronic rhinitis were included, revealing a prevalence of ID of 47.2%. Only 5.9% children with ID exhibited absolute ID. Multivariate analysis revealed that neutrophils (odds ratio [OR] = 1.205, 95% confidence interval [CI] = 1.013-1.433, P = 0.035) and monocytes (OR = 1.803, 95% CI = 1.198-2.713, P = 0.005) were independently and significantly associated with ID. Conclusion: This study revealed a notable prevalence of ID in the preschool children with chronic rhinitis. The significant association between neutrophils and monocytes with ID implied an intricate involvement of innate immunity in the manifestation of ID.

Apolipoprotein E deficiency leads to the polarization of splenic macrophages towards M1 phenotype by increasing iron content

Apolipoprotein E (ApoE) plays a crucial role in iron homeostasis in the body, while macrophages are the principal cells responsible for handling iron in mammals. However, it is unknown whether ApoE can affect the functional subtypes and the iron handling capacity of splenic macrophages (SM). Here, we investigated the effects of ApoE deficiency (ApoE-/-) on the polarization and iron content of SM and its potential mechanisms. ApoE-/- was found to induce a significant increase in the expressions of M1 marker genes CD86, IL-1β, IL-6, IL-12, TNF-α and iNOS and a reduction in M2 marker genes CD206, Arg-1, IL-10 and Ym-1 in SM of mice aged 28 weeks, Meanwhile, ApoE-/- caused a significant increase in iron content and expression of ferritin, transferrin receptor 1 (TfR1), iron regulatory protein 1 (IRP1) and heme oxygenase-1 (HO-1) and a reduction in ferroportin1 (Fpn1) in spleen and/or SM of mice aged 28 weeks. It was concluded that ApoE-/- can increase iron content through increased iron uptake mediated by TfR/ IRPs and decreased iron release mediated by Fpn1, leading to polarization of the SM to M1 phenotype.

Iron scavenging and myeloid cell polarization

Myeloid cells that populate all human organs and blood are a versatile class of innate immune cells. They are crucial for sensing and regulating processes as diverse as tissue homeostasis and inflammation and are frequently characterized by their roles in either regulating or promoting inflammation. Recent studies in cultured cells and mouse models highlight the role of iron in skewing the functional properties of myeloid cells in tissue damage and repair. Here, we review certain emerging concepts on how iron influences and determines myeloid cell polarization in the context of its uptake, storage, and metabolism, including in conditions such as multiple sclerosis (MS), sickle cell disease, and tumors.

Evaluation of the expression of genes associated with iron metabolism in peripheral blood mononuclear cells from Type 2 diabetes mellitus patients

AIMS

Type 2 Diabetes (T2DM) has been linked to ferroptosis. This study aimed to assess expression levels of genes linked with iron metabolism in peripheral blood mononuclear cells (PBMCs) from T2DM patients and to investigate the association of these expression levels with anthropometric and clinical parameters.

METHODS

Gene expression of iron metabolism genes (Ferritin Light Chain, FTL; Ferritin Heavy Chain, FTH1; Transferrin Receptor, TFRC; Divalent Metal Transporter 1, SLC11A2; Ferroportin, SLC40A1) in archival PBMCs was assessed using quantitative real-time PCR assays. Correlations of gene expression with anthropometric/biochemical patient data were evaluated.

RESULTS

The study included 36 (18 male/18 female) T2DM patients and 45 (28 male/17 female) normoglycemic (NGT) subjects with a mean age of 38.1 ± 6.8 years and 47.6 ± 8.6 years respectively. Relative expression of FTL was significantly lower in T2DM females compared to that in NGT females (P = 0.027). Relative expression of SLC40A1 was significantly lower in the T2DM group (P = 0.043) and in the T2DM females (P = 0.021). Relative expression of SLC11A2 was negatively correlated with systolic blood pressure in T2DM male patients. Relative expression of SLC40A1 was negatively associated with serum phosphorous and positively associated with serum thyroid stimulating hormone in male T2DM patients.

CONCLUSIONS

Our findings indicate a reduction in the expression of FTL in perimenopausal T2DM females. Also, in male T2DM patients and NGT subjects, biochemical markers are significantly correlated with the expression of FTL, FTH1, SLC11A2, and SLC40A1 in PBMCs.

Early innate immune responses in European sea bass (Dicentrarchus labrax L.) following Tenacibaculum maritimum infection

Introduction

The marine aquaculture industry has been witnessing a worldwide emergence of tenacibaculosis, a poorly understood bacterial disease caused by Tenacibaculum maritimum that affects commercially important fish. So far, knowledge on the T. maritimum virulence mechanisms is scarce and the pathogen-host interaction operating in tenacibaculosis remain to be disclosed. This study aimed at contributing to a better understanding of this disease, by evaluating the early innate immune response triggered in European sea bass (Dicentrarchus labrax) by a bath-challenge with T. maritimum.

Methods

Groups of sea bass were bath-challenged with T. maritimum (challenged fish) or mock-challenged. Undisturbed fish were used as controls (time 0). Samples of blood, liver and mucosal organs (skin, gills and posterior-intestine) were collected at 0 h (control) and at 6, 24, 48 and 72 h post-challenge (n=12). Mucosal organs were used for analyzing the expression of immune-related genes by RT-qPCR, as well as blood samples for assessing haematological and innate humoral parameters and liver for oxidative stress assessment.

Results

An increased expression of il-1β, il8, mmp9 and hamp1 was detected in all mucosal organs of infected fish when compared with control and mock-challenged fish, suggesting a pro-inflammatory response against T. maritimum transversal to all organs. The faster induction of these pro-inflammatory genes was observed in the gills. Regarding the systemic response, challenged fish presented neutrophilia, monocytosis, signs of anemia, and a decrease of bactericidal and lysozyme activities in plasma. Almost no variations were observed regarding hepatic oxidative stress.

Discussion/Conclusions

The present study suggests that T. maritimum induces a local innate immune response upon bath infection not only in the skin of European sea bass, but also in the gills and posterior-intestine, likely triggered by the T. maritimum's capacity to adhere, colonize and damage these organs that can function as entry ways to bacteria, leading ultimately to the seen host's systemic response.

Polymorphisms Related to Iron Homeostasis Associate with Liver Disease in Chronic Hepatitis C

Dysregulation of iron metabolism in chronic hepatitis C (CHC) is a significant risk factor for hepatic cirrhosis and cancer. We studied if known genetic variants related to iron homeostasis associate with liver disease progression in CHC. Retrospective analysis included 249 CHC patients qualified for antiviral therapy between 2004 and 2014. For all patients, nine SNPs within HFE, TFR2, HDAC2, HDAC3, HDAC5, TMPRSS6, and CYBRD1 genes were genotyped. Expression of selected iron-related genes, was determined with qRT-PCR in 124 liver biopsies, and mRNA expression of co-inhibitory receptors (PD-1, Tim3, CTLA4) was measured in 79 liver samples. CYBRD1 rs884409, HDAC5 rs368328, TFR2 rs7385804, and TMPRSS6 rs855791 associated with histopathological changes in liver tissue at baseline. The combination of minor allele in HDAC3 rs976552 and CYBRD1 rs884409 linked with higher prevalence of hepatocellular carcinoma (HCC) during follow up (OR 8.1 CI 2.2-29.2; p = 0.001). Minor allele in HDAC3 rs976552 associated with lower hepatic expression of CTLA4. Tested polymorphisms related to iron homeostasis associate with histopathological changes in the liver. The presence of both HDAC3 rs976552 G and CYBRD1 rs884409 G alleles correlates with HCC occurrence, especially in the group of patients with elevated AST (>129 IU/L). rs976552 in HDAC3 could impact immunological processes associated with carcinogenesis in CHC.

Induction of Hepcidin Expression in the Renal Cortex of Sickle Cell Disease Mice

In patients with sickle cell disease (SCD), chronic hemolysis and frequent blood transfusions cause iron overload and accumulation in the kidneys. The iron deposition is found in the renal cortex and correlates with the severity of hemolysis. In this study, we observed a significant accumulation of iron in the renal cortex of a mouse model of SCD, and assessed the expression of the proteins involved in maintaining renal iron homeostasis. Despite the intracellular iron accumulation, the levels of the transferrin receptor in the kidneys were increased, but the levels of the iron exporter ferroportin were not altered in SCD mice. Ferroportin is regulated by hepcidin, which binds to it and promotes its degradation. We found reduced serum hepcidin levels but increased renal hepcidin production in SCD mice. Furthermore, we observed significant macrophage infiltration and increased expression of intercellular adhesion molecule 1 in the endothelial cells of the kidneys in SCD mice. These observations correlated with elevated levels of proinflammatory cytokines IL-1β and IL-6, which can potentially stimulate hepcidin expression. Taken together, our results demonstrate that in individuals with SCD, a renal inflammation state induces renal hepcidin production that blocks the upregulation of ferroportin levels, resulting in dysregulation of iron homeostasis in the kidney and iron deposition in the renal cortex.

The Chelating Ability of Plant Polyphenols Can Affect Iron Homeostasis and Gut Microbiota

In the past decades, many studies have widely examined the effects of dietary polyphenols on human health. Polyphenols are well known for their antioxidant properties and for their chelating abilities, by which they can be potentially employed in cases of pathological conditions, such as iron overload. In this review, we have highlighted the chelating abilities of polyphenols, which are due to their structural specific sites, and the differences for each class of polyphenols. We have also explored how the dietary polyphenols and their iron-binding abilities can be important in inflammatory/immunomodulatory responses, with a special focus on the involvement of macrophages and dendritic cells, and how they might contribute to reshape the gut microbiota into a healthy profile. This review also provides evidence that the axes “polyphenol–iron metabolism–inflammatory responses” and “polyphenol–iron availability–gut microbiota” have not been very well explored so far, and the need for further investigation to exploit such a potential to prevent or counteract pathological conditions.

Repression of the iron exporter ferroportin may contribute to hepatocyte iron overload in individuals with type 2 diabetes

OBJECTIVE

Hyperferremia and hyperferritinemia are observed in patients and disease models of type 2 diabetes mellitus (T2DM). Likewise, patients with genetic iron overload diseases develop diabetes, suggesting a tight link between iron metabolism and diabetes. The liver controls systemic iron homeostasis and is a central organ for T2DM. Here, we investigate how the control of iron metabolism in hepatocytes is affected by T2DM.

METHODS

Perls Prussian blue staining was applied to analyze iron distribution in liver biopsies of T2DM patients. To identify molecular mechanisms underlying hepatocyte iron accumulation we established cellular models of insulin resistance by treatment with palmitate and insulin.

RESULTS

We show that a subset of T2DM patients accumulates iron in hepatocytes, a finding mirrored in a hepatocyte model of insulin resistance. Iron accumulation can be explained by the repression of the iron exporter ferroportin upon palmitate and/or insulin treatment. While during palmitate treatment the activation of the iron regulatory hormone hepcidin may contribute to reducing ferroportin protein levels in a cell-autonomous manner, insulin treatment decreases ferroportin transcription via the PI3K/AKT and Ras/Raf/MEK/ERK signaling pathways.

CONCLUSION

Repression of ferroportin at the transcriptional and post-transcriptional level may contribute to iron accumulation in hepatocytes observed in a subset of patients with T2DM.

Hepcidin Alleviates LPS-Induced ARDS by Regulating the Ferritin-Mediated Suppression of Ferroptosis

ABSTRACT

The effects of ferroptosis, an iron-dependent cell death, on acute respiratory distress syndrome (ARDS) remain largely elusive. Hepcidin, encoded by the HAMP gene, affects inflammation, and iron homeostasis. The present study aimed to investigate whether hepcidin protects against ferroptosis in lipopolysaccharide (LPS)-induced ARDS. Our results confirmed that ferroptosis aggravated lung inflammation and damage in LPS-induced ARDS. Hepcidin defended against ferroptosis, with results similar to those of the ferroptosis inhibitor ferrostatin-1 (Fer-1). Moreover, hepcidin decreased iron uptake, as determined by Transferrin Receptor 1 (TfR1) expression levels, and increased iron storage, based on ferritin heavy chain (FTH) expression. The effects of hepcidin on the A549 cell line were in line with the in vivo results. In addition, we used si-FTH to knock down FTH expression and found that this suppressed the ability of hepcidin to protect against ferroptosis. Collectively, our data suggest that hepcidin inhibits ferroptosis by increasing FTH expression in LPS-induced ARDS; thus, hepcidin may represent a possible treatment targeting ferroptosis.

Crosstalk between Acidosis and Iron Metabolism: Data from In Vivo Studies

Iron absorption requires an acidic environment that is generated by the activity of the proton pump gastric H(+)/K(+)ATPase (ATP4), expressed in gastric parietal cells. However, hepcidin, the iron regulatory peptide that inhibits iron absorption, unexpectedly upregulates ATP4 and increases gastric acidity. Thus, a concept of link between acidosis and alterations in iron metabolism, needs to be explored. We investigated this aspect in-vivo using experimental models of NH4Cl-induced acidosis and of an iron-rich diet. Under acidosis, gastric ATP4 was augmented. Serum hepcidin was induced and its mRNA level was increased in the liver but not in the stomach, a tissue where hepcidin is also expressed. mRNA and protein levels of intestinal DMT1(Divalent Metal Transporter 1) and ferroportin were downregulated. Serum iron level and transferrin saturation remained unchanged, but serum ferritin was significantly increased. Under iron-rich diet, the protein expression of ATP4A was increased and serum, hepatic and gastric hepcidin were all induced. Taken together, these results provide evidence of in-vivo relationship between iron metabolism and acidosis. For clinical importance, we speculate that metabolic acidosis may contribute in part to the pathologic elevation of serum hepcidin levels seen in patients with chronic kidney disease. The regulation of ATP4 by iron metabolism may also be of interest for patients with hemochromatosis.

Nutritional immunity: the impact of metals on lung immune cells and the airway microbiome during chronic respiratory disease

Nutritional immunity is the sequestration of bioavailable trace metals such as iron, zinc and copper by the host to limit pathogenicity by invading microorganisms. As one of the most conserved activities of the innate immune system, limiting the availability of free trace metals by cells of the immune system serves not only to conceal these vital nutrients from invading bacteria but also operates to tightly regulate host immune cell responses and function. In the setting of chronic lung disease, the regulation of trace metals by the host is often disrupted, leading to the altered availability of these nutrients to commensal and invading opportunistic pathogenic microbes. Similarly, alterations in the uptake, secretion, turnover and redox activity of these vitally important metals has significant repercussions for immune cell function including the response to and resolution of infection. This review will discuss the intricate role of nutritional immunity in host immune cells of the lung and how changes in this fundamental process as a result of chronic lung disease may alter the airway microbiome, disease progression and the response to infection.

Iron Metabolism in the Tumor Microenvironment: Contributions of Innate Immune Cells

Cells of the innate immune system are a major component of the tumor microenvironment. They play complex and multifaceted roles in the regulation of cancer initiation, growth, metastasis and responses to therapeutics. Innate immune cells like neutrophils and macrophages are recruited to cancerous tissues by chemotactic molecules released by cancer cells and cancer-associated stromal cells. Once they reach the tumor, they can be instructed by a network of proteins, nucleic acids and metabolites to exert protumoral or antitumoral functions. Altered iron metabolism is a feature of cancer. Epidemiological studies suggest that increased presence of iron and/or iron binding proteins is associated with increased risks of cancer development. It has been shown that iron metabolism is involved in shaping the immune landscapes in inflammatory/infectious diseases and cancer-associated inflammation. In this article, we will dissect the contribution of macrophages and neutrophils to dysregulated iron metabolism in malignant cells and its impact on cancer growth and metastasis. The mechanisms involved in regulating the actions of macrophages and neutrophils will also be discussed. Moreover, we will examine the effects of iron metabolism on the phenotypes of innate immune cells. Both iron chelating and overloading agents are being explored in cancer treatment. This review highlights alternative strategies for management of iron content in cancer cells by targeting the iron donation and modulation properties of macrophages and neutrophils in the tumor microenvironment.

C-FGF23 peptide alleviates hypoferremia during acute inflammation

Hypoferremia results as an acute phase response to infection and inflammation aiming to reduce iron availability to pathogens. Activation of toll-like receptors (TLR), the key sensors of the innate immune system, induces hypoferremia mainly through the rise of the iron hormone hepcidin. Conversely, stimulation of erythropoiesis suppresses hepcidin expression via induction of the erythropoietin-responsive hormone erythroferrone. Iron deficiency stimulates transcription of the osteocyte- secreted protein FGF23. Here we hypothesized that induction of FGF23 in response to TLR4 activation is a potent contributor to hypoferremia and, thus, impairment of its activity may alleviate hypoferremia induced by lipopolysaccharide (LPS), a TLR 4 agonist. We used the C-terminal tail of FGF23 to impair endogenous full-length FGF23 signaling in wildtype mice, and investigated its impact on hypoferremia. Our data show that FGF23 is induced as early as pro-inflammatory cytokines in response to LPS, followed by upregulation of hepcidin and downregulation of erythropoietin (Epo) expression in addition to decreased serum iron and transferrin saturation. Further, LPS-induced hepatic and circulating hepcidin were significantly reduced by FGF23 signaling disruption. Accordingly, iron sequestration in liver and spleen caused by TLR4 activation was completely abrogated by FGF23 signaling inhibition, resulting in alleviation of serum iron and transferrin saturation deficit. Taken together, our studies highlight for the first time that inhibition of FGF23 signaling alleviates LPS-induced acute hypoferremia.

Dioscin elicits anti-tumour immunity by inhibiting macrophage M2 polarization via JNK and STAT3 pathways in lung cancer

Tumour‐associated macrophage (TAM) is an important component in tumour microenvironment. Generally, TAM exhibits the function of M2‐like macrophage, which was closely related to angiogenesis and tumour progression. Dioscin, a natural steroidal saponin, has shown its powerful anti‐tumour activity recently. However, the mechanism of dioscin involved in immune regulation is still obscure. Here, we observed dioscin induced macrophage M2‐to‐M1 phenotype transition in vitro and inhibited IL‐10 secretion. Meanwhile, the phagocytosis of macrophages was enhanced. In subcutaneous lung tumour models, dioscin inhibited the augmentation of M2 macrophage populations. Furthermore, dioscin down‐regulated STAT3 and JNK signalling pathways in macrophages in vitro. In BMDMs, activating JNK and inhibiting STAT3 induce macrophages to M1 polarization while inhibiting JNK and activating STAT3 to M2 polarization. Additionally, condition mediums from dioscin‐pre‐treated macrophages inhibited the migration of 3LL cells and the tube‐formation capacity of HUVECs. What's more, dioscin‐mediated macrophage polarization inhibited the in vivo metastasis of 3LL cells. In conclusion, dioscin may act as a new anti‐tumour agent by inhibiting TAMs via JNK and STAT3 pathways in lung cancer.

Expression of iron regulatory proteins in full-term swine placenta

In swine, even though the pregnant sows were with iron abundance, the inborn iron reserve of piglets was compromised. This indicates the insufficiency of molecular machinery involved in local placental iron flux. Here, we investigated the expression of iron regulatory proteins like hepcidin and ferroportin and also their association with iron reserve, inflammation and oxidative stress in placenta of full-term pregnant sows (n = 6). Amplification and sequencing of placental DNA confirmed the presence of hepcidin (MN579557) and ferroportin (MN565887) sequences and their 100% identity with existing GenBank data. Real-time amplification of placental mRNA revealed significant higher expression of hepcidin (p < .05) than ferroportin. Western blot analysis of placental tissues revealed specific bands for both hepcidin (~8 kDa) and ferroportin (~62 kDa) molecules. Immunohistochemistry revealed the immunoreactivity for both proteins in the cytoplasm and membrane of trophoblastic cells of the placenta. Hepcidin and ferroportin expressions were positively associated with placental non-haem iron reserve (p < .0001; p = .033), lipid peroxidation (p = .0060; p < .0001) and reactive oxygen species level (p = .0092; p = .0292). Hepcidin expression was positively associated with interleukin - 6 (p = .0002) and interferon gamma (p < .0001) expressions but ferroportin expression was negatively associated with interleukin-6 (p = .0005), interleukin-1β (p = .0226) and interferon gamma (p = .0059) expressions. This indicates hepcidin and ferroportin may have a role in controlling the local placental iron flux by acting as a molecular bridge between iron trafficking and inflammation.

The role of hepcidin and iron homeostasis in atherosclerosis

Atherosclerotic cardiovascular disease is a major burden on global health and a leading cause of death worldwide. The pathophysiology of this chronic disease is complex, involving inflammation, lipoprotein oxidation and accumulation, plaque formation, and calcification. In 1981, Dr. Jerome Sullivan formulated the 'Iron Hypothesis', suggesting that higher levels of stored iron promote cardiovascular diseases, whereas iron deficiency may have an atheroprotective effect. This hypothesis has stimulated research focused on clarifying the role of iron in the development of atherosclerosis. However, preclinical and clinical studies have produced contradictory results and the observation that patients with hemochromatosis do not appear to have an increased risk of atherosclerosis seemed incongruous with Sullivan's initial hypothesis. The 'paradox' of systemic iron overload not being accompanied by an increased risk for atherosclerosis led to a refinement of the iron hypothesis focusing on intracellular macrophage iron. More recent in vitro and animal studies have elucidated the complex signaling pathways regulating iron, with a particular focus on hepcidin, the master regulator of body iron homeostasis. Bone morphogenetic protein (BMP) signaling is the major pathway that is required for induction of hepcidin expression in response to increasing levels of iron. Strong links between iron homeostasis, BMP signaling, inflammation and atherosclerosis have been established in both mechanistic and human studies. This review summarizes the current understanding of the role of iron homeostasis and hepcidin in the development of atherosclerosis and discusses the BMP-hepcidin-ferroportin axis as a novel therapeutic target for the treatment of cardiovascular disease.

H-Ferritin is essential for macrophages' capacity to store or detoxify exogenously added iron

Macrophages are central cells both in the immune response and in iron homeostasis. Iron is both essential and potentially toxic. Therefore, iron acquisition, transport, storage, and release are tightly regulated, by several important proteins. Cytosolic ferritin is an iron storage protein composed of 24 subunits of either the L- or the H-type chains. H-ferritin differs from L-ferritin in the capacity to oxidize Fe²⁺ to Fe³⁺. In this work, we investigated the role played by H-ferritin in the macrophages’ ability to respond to immune stimuli and to deal with exogenously added iron. We used mice with a conditional deletion of the H-ferritin gene in the myeloid lineage to obtain bone marrow-derived macrophages. These macrophages had normal viability and gene expression under basal culture conditions. However, when treated with interferon-gamma and lipopolysaccharide they had a lower activation of Nitric Oxide Synthase 2. Furthermore, H-ferritin-deficient macrophages had a higher sensitivity to iron-induced toxicity. This sensitivity was associated with a lower intracellular iron accumulation but a higher production of reactive oxygen species. These data indicate that H-ferritin modulates macrophage response to immune stimuli and that it plays an essential role in protection against iron-induced oxidative stress and cell death.

Regulation of tissue iron homeostasis: the macrophage "ferrostat"

Iron is an essential element for multiple fundamental biological processes required for life; yet iron overload can be cytotoxic. Consequently, iron concentrations at the cellular and tissue level must be exquisitely governed by mechanisms that complement and fine-tune systemic control. It is well appreciated that macrophages are vital for systemic iron homeostasis, supplying or sequestering iron as needed for erythropoiesis or bacteriostasis, respectively. Indeed, recycling of iron through erythrophagocytosis by splenic macrophages is a major contributor to systemic iron homeostasis. However, accumulating evidence suggests that tissue-resident macrophages regulate local iron availability and modulate the tissue microenvironment, contributing to cellular and tissue function. Here, we summarize the significance of tissue-specific regulation of iron availability and highlight how resident macrophages are critical for this process. This tissue-dependent regulation has broad implications for understanding both resident macrophage function and tissue iron homeostasis in health and disease.

Therapeutic Advances in Regulating the Hepcidin/Ferroportin Axis

The interaction between hepcidin and ferroportin is the key mechanism involved in regulation of systemic iron homeostasis. This axis can be affected by multiple stimuli including plasma iron levels, inflammation and erythropoietic demand. Genetic defects or prolonged inflammatory stimuli results in dysregulation of this axis, which can lead to several disorders including hereditary hemochromatosis and anaemia of chronic disease. An imbalance in iron homeostasis is increasingly being associated with worse disease outcomes in many clinical conditions including multiple cancers and neurological disorders. Currently, there are limited treatment options for regulating iron levels in patients and thus significant efforts are being made to uncover approaches to regulate hepcidin and ferroportin expression. These approaches either target these molecules directly or regulatory steps which mediate hepcidin or ferroportin expression. This review examines the current status of hepcidin and ferroportin agonists and antagonists, as well as inducers and inhibitors of these proteins and their regulatory pathways.

MiR-20b Down-Regulates Intestinal Ferroportin Expression In Vitro and In Vivo

Ferroportin (FPN) is the only known cellular iron exporter in mammalian. However, post-transcriptional regulation of intestinal FPN has not yet been completely understood. In this study, bioinformatics algorithms (TargetScan, PicTar, PITA, and miRanda) were applied to predict, screen and obtain microRNA-17 family members (miR-17, miR-20a, miR-20b, and miR-106a) targeting FPN, ‘seed sequence’ and responding binding sites on the 3′untranslated region (3′UTR) region of FPN. Dual-luciferase reporter assays revealed miRNA-17 family members’ mimics decreased the luciferase activity, whereas their inhibitors increased the luciferase activity. Compared with the FPN 3′UTR wild type reporter, co-transfection of a miRNA-17 family members’ over-expression plasmids and FPN 3′UTR mutant reporters enhanced the luciferase activity in HCT116 cells. Transfection with miR-20b overexpression plasmid significantly enhanced its expression, and it inhibited endogenous FPN protein expression in Caco-2 cells. Additionally, tail-vein injection of miR-20b resulted in increasing duodenal miR-20b expression, decreasing duodenal FPN protein expression, which was closely related to lower plasma iron level in mice. Taken together, these data suggest that the miR-20b is identified to regulate intestinal FPN expression in vitro and in vivo, which will provide a potential target for intestinal iron exportation.

Twenty Years of Ferroportin Disease: A Review or An Update of Published Clinical, Biochemical, Molecular, and Functional Features

Iron overloading disorders linked to mutations in ferroportin have diverse phenotypes in vivo, and the effects of mutations on ferroportin in vitro range from loss of function (LOF) to gain of function (GOF) with hepcidin resistance. We reviewed 359 patients with 60 ferroportin variants. Overall, macrophage iron overload and low/normal transferrin saturation (TSAT) segregated with mutations that caused LOF, while GOF mutations were linked to high TSAT and parenchymal iron accumulation. However, the pathogenicity of individual variants is difficult to establish due to the lack of sufficiently reported data, large inter-assay variability of functional studies, and the uncertainty associated with the performance of available in silico prediction models. Since the phenotypes of hepcidin-resistant GOF variants are indistinguishable from the other types of hereditary hemochromatosis (HH), these variants may be categorized as ferroportin-associated HH, while the entity ferroportin disease may be confined to patients with LOF variants. To further improve the management of ferroportin disease, we advocate for a global registry, with standardized clinical analysis and validation of the functional tests preferably performed in human-derived enterocytic and macrophagic cell lines. Moreover, studies are warranted to unravel the definite structure of ferroportin and the indispensable residues that are essential for functionality.

Modulating Iron for Metabolic Support of TB Host Defense

Tuberculosis (TB) is the world's biggest infectious disease killer. The increasing prevalence of multidrug-resistant and extensively drug-resistant TB demonstrates that current treatments are inadequate and there is an urgent need for novel therapies. Research is now focused on the development of host-directed therapies (HDTs) which can be used in combination with existing antimicrobials, with a special focus on promoting host defense. Immunometabolic reprogramming is integral to TB host defense, therefore, understanding and supporting the immunometabolic pathways that are altered after infection will be important for the development of new HDTs. Moreover, TB pathophysiology is interconnected with iron metabolism. Iron is essential for the survival of Mycobacterium tuberculosis (Mtb), the bacteria that causes TB disease. Mtb struggles to replicate and persist in low iron environments. Iron chelation has therefore been suggested as a HDT. In addition to its direct effects on iron availability, iron chelators modulate immunometabolism through the stabilization of HIF1α. This review examines immunometabolism in the context of Mtb and its links to iron metabolism. We suggest that iron chelation, and subsequent stabilization of HIF1α, will have multifaceted effects on immunometabolic function and holds potential to be utilized as a HDT to boost the host immune response to Mtb infection.

Cell iron status influences macrophage polarization

Macrophages play crucial roles in innate immune response and in the priming of adaptive immunity, and are characterized by their phenotypic heterogeneity and plasticity. Reprogramming intracellular metabolism in response to microenvironmental signals is required for M1/M2 macrophage polarization and function. Here we assessed the influence of iron on the polarization of the immune response in vivo and in vitro. Iron-enriched diet increased M2 marker Arg1 and Ym1 expression in liver and peritoneal macrophages, while iron deficiency decreased Arg1 expression. Under LPS-induced inflammatory conditions, low iron diet exacerbated the proinflammatory response, while the IL-12/IL-10 balance decreased with iron-rich diet, thus polarizing toward type 2 response. Indeed, in vitro macrophage iron loading reduced the basal percentage of cells expressing M1 co-stimulatory CD86 and MHC-II molecules. Further, iron loading of macrophages prevented the pro-inflammatory response induced by LPS through reduction of NF-κB p65 nuclear translocation with decreased iNOS, IL-1β, IL-6, IL-12 and TNFα expression. The increase of intracellular iron also reduced LPS-induced hepcidin gene expression and abolished ferroportin down-regulation in macrophages, in line with macrophage polarization. Thus, iron modulates the inflammatory response outcome, as elevated iron levels increased M2 phenotype and negatively regulated M1 proinflammatory LPS-induced response.

Apolipoprotein A-I mimetic peptide 4F suppresses tumor-associated macrophages and pancreatic cancer progression

Pancreatic cancer is an aggressive malignancy that is unresponsive to conventional radiation and chemotherapy. Therefore, development of novel immune therapeutic strategies is urgently needed. L-4F, an Apolipoprotein A-I (ApoA-I) mimetic peptide, is engineered to mimic the anti-inflammatory and anti-oxidative functionalities of ApoA-I. In this work, H7 cells were orthotopically implanted in C57BL/6 mice and treated with L-4F. Then, pancreatic cancer progression and the inflammatory microenvironment were investigated in vivo. The cytotoxicity of L-4F toward H7 cells was assessed in vitro. Furthermore, we investigated the effects of L-4F on macrophage polarization by analyzing the polarization and genes of mouse bone marrow-derived macrophages in vitro. The results show that L-4F substantially reduced the tumorigenicity of H7 cells. L-4F inhibited inflammation by reducing the accumulation of inflammatory cells, such as IL-17A-, IL-4-, GM-CSF-, IL-1β-, and IL-6-producing cells and Th1 and Th17. Notably, L-4F also decreased the percentage of macrophages in tumor tissues, especially M2 macrophages (CD11b⁺F4/80⁺CD206⁺), which was also confirmed in vitro. Additionally, the expression of the M2 marker genes Arg1, MRC1, and CCL22 and the inflammatory genes IL-6, iNOS, and IL-12 was decreased by L-4F, indicating that L-4F prevents M2 type macrophage polarization. However, L-4F could not directly attenuate H7 cell invasion or proliferation and did not induce apoptosis. In addition, L-4F potently down-regulated STAT3, JNK and ERK signaling pathways but not affects the phosphorylation of p38 in RAW 264.7 cells. These results suggest that L-4F exhibits an effective therapeutic effect on pancreatic cancer progression by inhibiting tumor-associated macrophages and inflammation.

Correlation of HAMP gene polymorphisms and expression with the susceptibility and length of hospital stays in Taiwanese children with Kawasaki disease

Kawasaki disease (KD) is a form of systemic vasculitis. Regarding its pathogenesis, HAMP gene encoding hepcidin, which is significant for iron metabolism, has a vital function. In this study, we recruited a total of 381 KD patients for genotyping. Data from 997 subjects (500 subjects from cohort 1; 497 subjects from cohort 2) were used for analysis. Using TaqMan allelic discrimination, we determined five tag SNPs (rs916145, rs10421768, rs3817623, rs7251432, and rs2293689). Treatment outcome data related to such clinical phenotypes as coronary artery lesions (CAL), coronary artery aneurysms (CAA), and intravenous immunoglobulin (IVIG) effects were also collected. Furthermore, we measured plasma hepcidin levels with an enzyme-linked immunosorbent assay. We found that HAMP gene polymorphism (rs7251432, and rs2293689) was significantly correlated with KD risk and that plasma hepcidin levels both before and after IVIG treatment had a significantly positive correlation with length of hospital stays (R = 0.217, p = 0.046 and R = 0.381, p < 0.0001, respectively). In contrast, plasma hepcidin levels has a negative correlation with KD patients' albumin levels (R = -0.27, p < 0.001) prior to IVIG treatment. This study's findings indicate that HAMP might have a role in the disease susceptibility, as well as its expressions correlated length of hospital stays, and albumin levels in Taiwanese children with KD.