Role of hepcidin in the setting of hypoferremia during acute inflammation

Induced Disruption of the Iron-Regulatory Hormone Hepcidin Inhibits Acute Inflammatory Hypoferraemia

Withdrawal of iron from serum (hypoferraemia) is a conserved innate immune antimicrobial strategy that can withhold this critical nutrient from invading pathogens, impairing their growth. Hepcidin (Hamp1) is the master regulator of iron and its expression is induced by inflammation. Mice lacking Hamp1 from birth rapidly accumulate iron and are susceptible to infection by blood-dwelling siderophilic bacteria such as Vibrio vulnificus. In order to study the innate immune role of hepcidin against a background of normal iron status, we developed a transgenic mouse model of tamoxifen-sensitive conditional Hamp1 deletion (termed iHamp1-KO mice). These mice attain adulthood with an iron status indistinguishable from littermate controls. Hamp1 disruption and the consequent decline of serum hepcidin concentrations occurred within hours of a single tamoxifen dose. We found that the TLR ligands LPS and Pam3CSK4 and heat-killed Brucella abortus caused an equivalent induction of inflammation in control and iHamp1-KO mice. Pam3CSK4 and B. abortus only caused a drop in serum iron in control mice, while hypoferraemia due to LPS was evident but substantially blunted in iHamp1-KO mice. Our results characterise a powerful new model of rapidly inducible hepcidin disruption, and demonstrate the critical contribution of hepcidin to the hypoferraemia of inflammation.

Relationships of iron metabolism with insulin resistance and glucose levels in young and healthy adults

AIMS

Several biomarkers within the iron metabolism pathway have been related to the occurrence of diabetes mellitus, but underlying mechanisms are unknown. The aim of our study was to investigate the differential relationships of iron metabolism with a broad range of diabetes markers in young and healthy adults.

DESIGN

2160 participants aged 25 to 41years were enrolled in a population-based study. Established cardiovascular disease, diabetes or a body mass index >35kg/m(2) were exclusion criteria. Multivariable linear regression models were built to assess the associations of ferritin and transferrin saturation (TSAT) with blood levels of glucagon-like peptide-1 (GLP-1), insulin, homeostatic model assessment-insulin resistance (HOMA-IR), fasting plasma glucose (FPG) and hemoglobin A1c (HbA1c).

RESULTS

Median (interquartile range) age was 37 (31, 40) years. In multivariable linear regression analyses, β-coefficients (95% confidence intervals) per 1-SD increase in ferritin were 0.04 (0.02; 0.07, p=0.0008) for GLP-1, 0.06 (0.04; 0.08, p<0.0001) for insulin, 0.07 (0.04; 0.09, p<0.0001) for HOMA-IR, 0.004 (-0.00; 0.01, p=0.07) for FPG and -0.003 (-0.01; -0.00, p=0.07) for HbA1c. β-coefficients (95% CI) per 1-SD increase in TSAT were -0.07 (-0.09; -0.05, p<0.0001) for GLP-1, -0.06 (-0.08; -0.04, p<0.0001) for insulin, -0.07(-0.09; -0.05, p<0.0001) for HOMA-IR, -0.01 (-0.01; -0.00, p<0.0001) for FPG and -0.01 (-0.01; -0.00, p=0.0004) for HbA1c.

CONCLUSIONS

Markers of insulin resistance are strongly related with markers of iron metabolism in healthy subjects. These relationships were inconsistent and weaker for short-term and long-term glucose levels. These results may provide insights in the relationships between iron metabolism and diabetes occurrence.

The effect of the competitive season in professional basketball on inflammation and iron metabolism

Following acute physical activity, blood hepcidin concentration appears to increase in response to exercise-induced inflammation, but the long-term impact of exercise on hepcidin remains unclear. Here we investigated changes in hepcidin and the inflammation marker interleukin-6 to evaluate professional basketball players' response to a season of training and games. The analysis also included vitamin D (25(OH)D3) assessment, owing to its anti-inflammatory effects. Blood samples were collected for 14 players and 10 control non-athletes prior to and after the 8-month competitive season. Athletes' performance was assessed with the NBA efficiency score. At the baseline hepcidin correlated with blood ferritin (r = 0.61; 90% CL ±0.31), but at the end of the season this correlation was absent. Compared with the control subjects, athletes experienced clear large increases in hepcidin (50%; 90% CI 15-96%) and interleukin-6 (77%; 90% CI 35-131%) and a clear small decrease in vitamin D (-12%; 90% CI -20 to -3%) at the season completion. Correlations between change scores of these variables were unclear (r = -0.21 to 0.24, 90% CL ±0.5), but their uncertainty generally excluded strong relationships. Athletes were hence concluded to have experienced acute inflammation at the beginning but chronic inflammation at the end of the competitive season. At the same time, the moderate correlation between changes in vitamin D and players' performance (r = 0.43) was suggestive of its beneficial influence. Maintaining the appropriative concentration of vitamin D is thus necessary for basketball players' performance and efficiency. The assessment of hepcidin has proven to be useful in diagnosing inflammation in response to chronic exercise.

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

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

Iron Homeostasis and Inflammatory Status in Mice Deficient for the Cystic Fibrosis Transmembrane Regulator

BACKGROUND

Cystic Fibrosis (CF) is a frequent and lethal autosomal recessive disease caused by mutations in the gene encoding the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). Patients with CF suffer from chronic infections and severe inflammation, which lead to progressive pulmonary and gut diseases. Recently, an expanding body of evidence has suggested that iron homeostasis was abnormal in CF with, in particular, systemic iron deficiency and iron sequestration in the epithelium airway. The molecular mechanisms responsible for iron dysregulation and the relationship with inflammation in CF are unknown.

METHODS AND RESULTS

We assessed the impact of CFTR deficiency on systemic and tissue iron homeostasis as well as inflammation in wildtype and CFTR knockout (KO) mice. First, in contrast to the systemic and intestinal inflammation we observed in the CFTR KO mice, we reported the absence of lung phenotype with regards to both inflammation and iron status. Second, we showed a significant decrease of plasma ferritin levels in the KO mice, as in CF patients, likely caused by a decrease in spleen ferritin levels. However, we measured unchanged plasma iron levels in the KO mice that may be explained by increased intestinal iron absorption.

CONCLUSION

These results indicate that in CF, the lung do not predominantly contributes to the systemic ferritin deficiency and we propose the spleen as the major organ responsible for hypoferritinemia in the KO mouse. These results should provide a better understanding of iron dysregulation in CF patients where treating or not iron deficiency remains a challenging question.

Ironing out Ferroportin

Maintaining physiologic iron concentrations in tissues is critical for metabolism and host defense. Iron absorption in the duodenum, recycling of iron from senescent erythrocytes, and iron mobilization from storage in macrophages and hepatocytes constitute the major iron flows into plasma for distribution to tissues, predominantly for erythropoiesis. All iron transfer to plasma occurs through the iron exporter ferroportin. The concentration of functional membrane-associated ferroportin is controlled by its ligand, the iron-regulatory hormone hepcidin, and fine-tuned by regulatory mechanisms serving iron homeostasis, oxygen utilization, host defense, and erythropoiesis. Fundamental questions about the structure and biology of ferroportin remain to be answered.

The microbiota shifts the iron sensing of intestinal cells

The amount of iron in the diet directly influences the composition of the microbiota. Inversely, the effects of the microbiota on iron homeostasis have been little studied. So, we investigate whether the microbiota itself may alter host iron sensing. Duodenal cytochrome b and divalent metal transporter 1, involved in apical iron uptake, are 8- and 10-fold, respectively, more abundant in the duodenum of germ-free (GF) mice than in mice colonized with a microbiota. In contrast, the luminal exporter ferroportin is 2-fold less abundant in GF. The overall signature of microbiota on iron-related proteins is similar in the colon. The colonization does not modify systemic parameters as plasma transferrin saturation (20%), plasma ferritin (150 ng/L), and liver (85 µg/g) iron load. Commensal organisms (Bacteroides thetaiotaomicron VPI-5482 and Faecalibacterium prausnitzii A2-165) and a probiotic strain (Streptococcus thermophilus LMD-9) led to up to 12-fold induction of ferritin in colon. Our data suggest that the intestinal cells of GF mice are depleted of iron and that following colonization, the epithelial cells favor iron storage. This study is the first to demonstrate that gut microbes induce a specific iron-related protein signature, highlighting new aspects of the crosstalk between the microbiota and the intestinal epithelium.

Investigation into the Antigenic Properties and Contributions to Growth in Blood of the Meningococcal Haemoglobin Receptors, HpuAB and HmbR

Acquisition of iron from host complexes is mediated by four surface-located receptors of Neisseria meningitidis. The HmbR protein and heterodimeric HpuAB complex bind to haemoglobin whilst TbpBA and LbpBA bind iron-loaded transferrin and lactoferrin complexes, respectively. The haemoglobin receptors are unevenly distributed; disease-causing meningococcal isolates encode HmbR or both receptors while strains with only HpuAB are rarely-associated with disease. Both these receptors are subject to phase variation and 70–90% of disease isolates have one or both of these receptors in an ON expression state. The surface-expression, ubiquity and association with disease indicate that these receptors could be potential virulence factors and vaccine targets. To test for a requirement during disease, an hmbR deletion mutant was constructed in a strain (MC58) lacking HpuAB and in both a wild-type and TbpBA deletion background. The hmbR mutant exhibited an identical growth pattern to wild-type in whole blood from healthy human donors whereas growth of the tbpBA mutant was impaired. These results suggest that transferrin is the major source of iron for N. meningitidis during replication in healthy human blood. To examine immune responses, polyclonal antisera were raised against His-tagged purified-recombinant variants of HmbR, HpuA and HpuB in mice using monolipopolysaccharide as an adjuvant. Additionally, monoclonal antibodies were raised against outer membrane loops of HmbR presented on the surface of EspA, an E. coli fimbrial protein. All antisera exhibited specific reactivity in Western blots but HmbR and HpuA polyclonal sera were reactive against intact meningococcal cells. None of the sera exhibited bactericidal activity against iron-induced wild-type meningococci. These findings suggest that the HmbR protein is not required during the early stages of disease and that immune responses against these receptors may not be protective.

Iron Regulatory Proteins Mediate Host Resistance to Salmonella Infection

Macrophages are essential for systemic iron recycling, and also control iron availability to pathogens. Iron metabolism in mammalian cells is orchestrated posttranscriptionally by iron-regulatory proteins (IRP)-1 and -2. Here, we generated mice with selective and combined ablation of both IRPs in macrophages to investigate the role of IRPs in controlling iron availability. These animals are hyperferritinemic but otherwise display normal clinical iron parameters. However, mutant mice rapidly succumb to systemic infection with Salmonella Typhimurium, a pathogenic bacterium that multiplies within macrophages, with increased bacterial burdens in liver and spleen. Ex vivo infection experiments indicate that IRP function restricts bacterial access to iron via the EntC and Feo bacterial iron-acquisition systems. Further, IRPs contain Salmonella by promoting the induction of lipocalin 2, a host antimicrobial factor that inhibits bacterial uptake of iron-laden siderophores, and by suppressing the ferritin iron pool. This work reveals the importance of the IRPs in innate immunity.

Regulation of Iron Metabolism by Hepcidin under Conditions of Inflammation

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

Ceruloplasmin and Hypoferremia: Studies in Burn and Non-Burn Trauma Patients

OBJECTIVE

Normal iron handling appears to be disrupted in critically ill patients leading to hypoferremia that may contribute to systemic inflammation. Ceruloplasmin (Cp), an acute phase reactant protein that can convert ferrous iron to its less reactive ferric form facilitating binding to ferritin, has ferroxidase activity that is important to iron handling. Genetic absence of Cp decreases iron export resulting in iron accumulation in many organs. The objective of this study was to characterize iron metabolism and Cp activity in burn and non-burn trauma patients to determine if changes in Cp activity are a potential contributor to the observed hypoferremia.

MATERIAL AND METHODS

Under Brooke Army Medical Center Institutional Review Board approved protocols, serum or plasma was collected from burn and non-burn trauma patients on admission to the ICU and at times up to 14 days and measured for indices of iron status, Cp protein and oxidase activity and cytokines.

RESULTS

Burn patients showed evidence of anemia and normal or elevated ferritin levels. Plasma Cp oxidase activity in burn and trauma patients were markedly lower than controls on admission and increased to control levels by day 3, particularly in burn patients. Plasma cytokines were elevated throughout the 14 days study along with evidence of an oxidative stress. No significant differences in soluble transferrin receptor were noted among groups on admission, but levels in burn patients were lower than controls for the first 5 days after injury.

CONCLUSION

This study further established the hypoferremia and inflammation associated with burns and trauma. To our knowledge, this is the first study to show an early decrease in Cp oxidase activity in burn and non-burn trauma patients. The results support the hypothesis that transient loss of Cp activity contributes to hypoferremia and inflammation. Further studies are warranted to determine if decreased Cp activity increases the risk of iron-induced injury following therapeutic interventions such as transfusions with blood that has undergone prolonged storage in trauma resuscitation.

A novel inflammatory pathway mediating rapid hepcidin-independent hypoferremia

Regulation of iron metabolism and innate immunity are tightly interlinked. The acute phase response to infection and inflammation induces alterations in iron homeostasis that reduce iron supplies to pathogens. The iron hormone hepcidin is activated by such stimuli causing degradation of the iron exporter ferroportin and reduced iron release from macrophages, suggesting that hepcidin is the crucial effector of inflammatory hypoferremia. Here, we report the discovery of an acute inflammatory condition that is mediated by Toll-like receptors 2 and 6 (TLR2 and TLR6) and which induces hypoferremia in mice injected with TLR ligands. Stimulation of TLR2/TLR6 triggers profound decreases in ferroportin messenger RNA and protein expression in bone marrow-derived macrophages, liver, and spleen of mice without changing hepcidin expression. Furthermore, C326S ferroportin mutant mice with a disrupted hepcidin/ferroportin regulatory circuitry respond to injection of the TLR2/6 ligands FSL1 or PAM3CSK4 by ferroportin downregulation and a reduction of serum iron levels. Our findings challenge the prevailing role of hepcidin in hypoferremia and suggest that rapid hepcidin-independent ferroportin downregulation in the major sites of iron recycling may represent a first-line response to restrict iron access for numerous pathogens.

An Evaluation of the Correlation between Hepcidin Serum Levels and Disease Activity in Inflammatory Bowel Disease

Aim. While there are many well-defined serological markers for inflammatory bowel disease (IBD), there is limited evidence that they positively affect clinical outcomes. This study aimed to evaluate the correlation between hepcidin serum levels and disease activity in IBD. Materials and Methods. Eighty-five consecutive IBD patients were enrolled in the study. Hepcidin serum levels were assessed using an enzyme-linked immunosorbent assay (ELISA) and were compared with disease activity as well as the interleukin-6 (IL-6) and C-reactive protein (CRP) levels. Results. The mean hepcidin serum levels in Crohn's disease (CD) patients in remission and in the active phase were 3837 ± 1436 and 3752 ± 1274 pg/mL, respectively (P = 0.613). The mean hepcidin serum levels in ulcerative colitis (UC) patients in remission and in the active phase were 4285 ± 8623 and 3727 ± 1176 pg/mL, respectively (P = 0.241). Correlation analysis between inflammatory markers and hepcidin serum levels indicated that there was no correlation between hepcidin levels and IL-6 (P = 0.582) or CRP (P = 0.783). Conclusion. As an acute-phase protein, hepcidin seems to have a lower efficacy than other parameters in the detection of activation in IBD.

Regulation of iron uptake in primary culture rat hepatocytes: the role of acute-phase cytokines

Decreased serum and increased hepatic iron uptake is the hallmark of acute-phase (AP) response. Iron uptake is controlled by iron transport proteins such as transferrin receptors (TfRs) and lipocalin 2 (LCN-2). The current study aimed to understand the regulation of iron uptake in primary culture hepatocytes in the presence/absence of AP mediators. Rat hepatocytes were stimulated with different concentrations of iron alone (0.01, 0.1, 0.5 mM) and AP cytokines (interleukin 6 [IL-6], IL-1β, tumor necrosis factor α) in the presence/absence of iron (FeCl3: 0.1 mM). Hepatocytes were harvested at different time points (0, 6, 12, 24 h). Total mRNA and proteins were extracted for reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot. A significant iron uptake was detected with 0.1 mM iron administration with a maximum (133.37 ± 4.82 µg/g of protein) at 24 h compared with control and other iron concentrations. This uptake was further enhanced in the presence of AP cytokines with a maximum iron uptake (481 ± 25.81 µg/g of protein) after concomitant administration of IL-6 + iron to cultured hepatocytes. Concomitantly, gene expression of LCN-2 and ferritin subunits (light- and heavy-chain ferritin subunits) was upregulated by iron or/and AP cytokines with a maximum at 24 h both at mRNA and protein levels. In contrast, a decreased TfR1 level was detected by IL-6 and iron alone, whereas combination of iron and AP cytokines (mainly IL-6) abrogated the downregulation of TfR1. An increase in LCN-2 release into the supernatant of cultured hepatocytes was observed after addition of iron/AP cytokines into the medium. This increase in secretion was further enhanced by combination of IL-6 + iron. In conclusion, iron uptake is tightly controlled by already present iron concentration in the culture. This uptake can be further enhanced by AP cytokines, mainly by IL-6.

Physiology and pathophysiology of iron in hemoglobin-associated diseases

Iron overload and iron toxicity, whether because of increased absorption or iron loading from repeated transfusions, can be major causes of morbidity and mortality in a number of chronic anemias. Significant advances have been made in our understanding of iron homeostasis over the past decade. At the same time, advances in magnetic resonance imaging have allowed clinicians to monitor and quantify iron concentrations noninvasively in specific organs. Furthermore, effective iron chelators are now available, including preparations that can be taken orally. This has resulted in substantial improvement in mortality and morbidity for patients with severe chronic iron overload. This paper reviews the key points of iron homeostasis and attempts to place clinical observations in patients with transfusional iron overload in context with the current understanding of iron homeostasis in humans.

Matriptase-2 is essential for hepcidin repression during fetal life and postnatal development in mice to maintain iron homeostasis

Iron is an essential element required for development and survival of all living organisms. In fetuses, maternofetal iron transfer across the placenta is essential for growth and development. In neonates, efficient intestinal iron absorption is required to scavenge as much iron as possible from the low-iron-content milk. During these periods, efficient iron mobilization is ensured by the downregulation of the iron regulatory hormone hepcidin by as-yet uncharacterized molecular mechanisms. Here we demonstrate that the recently described hepcidin repressor-the serine protease matriptase-2 (encoded by Tmprss6)-is responsible for this repression throughout development, with its deficiency leading to increased hepcidin levels triggering iron deficiency and anemia starting in utero. This result might have implications for a better understanding of iron homeostasis during early development in iron-refractory iron deficiency anemia patients, who present with microcytic anemia caused by hyperhepcidinemia, and of questions about the role of matriptase-2 in human neonates.

Regulation of mammalian siderophore 2,5-DHBA in the innate immune response to infection

Bacteria can utilize a mammalian host siderophore to usurp host iron; however, the host can respond by down-regulating siderophore expression and up-regulating expression of an inhibitory siderophore-binding protein.

Competition for iron influences host–pathogen interactions. Pathogens secrete small iron-binding moieties, siderophores, to acquire host iron. In response, the host secretes siderophore-binding proteins, such as lipocalin 24p3, which limit siderophore-mediated iron import into bacteria. Mammals produce 2,5-dihydroxy benzoic acid, a compound that resembles a bacterial siderophore. Our data suggest that bacteria use both mammalian and bacterial siderophores. In support of this idea, supplementation with mammalian siderophore enhances bacterial growth in vitro. In addition, mice lacking the mammalian siderophore resist E. coli infection. Finally, we show that the host responds to infection by suppressing siderophore synthesis while up-regulating lipocalin 24p3 expression via TLR signaling. Thus, reciprocal regulation of 24p3 and mammalian siderophore is a protective mechanism limiting microbial access to iron.

Hepcidin-dependent and hepcidin-independent regulation of erythropoiesis in a mouse model of anemia of chronic inflammation

Increased hepcidin antimicrobial peptide correlates with hypoferremia and anemia in various disease states, but its requirement for anemia of inflammation has not been adequately demonstrated. Anemia of inflammation is usually described as normocytic and normochromic, while diseases associated with over expression of hepcidin, alone, are often microcytic and hypochromic. These differences in erythrocyte parameters suggest anemia in many inflammatory states may not be fully explained by hepcidin-mediated iron sequestration. We used turpentine-induced sterile abscesses to model chronic inflammation in mice with targeted disruption of Hepcidin 1 [Hepc1 (-/-)] or its positive regulator, Interleukin-6 [IL-6 (-/-)], to determine whether these genes are required for features characteristic of anemia of inflammation. Although hemoglobin levels did not decline in Hepc1 (-/-) mice with sterile abscesses, erythrocyte numbers were significantly reduced compared to untreated Hepc1 (-/-) mice. In contrast, both hemoglobin concentration and erythrocyte number declined significantly in wild type and IL-6 (-/-) mice with sterile abscesses. Both Hepc1 (-/-) and IL-6 (-/-) mice had increased erythrocyte mean cell volume and mean cell hemoglobin following sterile abscesses, while wild types had no change. Thus, IL-6 (-/-) mice with sterile abscesses exhibit an intermediate phenotype between wild type and Hepc1 (-/-). Our results demonstrate the requirement of Hepc1 for the development of anemia in this rodent model. Simultaneously, our results demonstrate hepcidin-independent effects of inflammation on the suppression of erythropoiesis. Our results suggest chronic anemia associated with inflammation may benefit from interventions protecting erythrocyte number in addition to anti-hepcidin interventions aimed at enhancing iron availability.

A mouse model of anemia of inflammation: complex pathogenesis with partial dependence on hepcidin

An injection of heat-killed Brucella abortus in mice causes prolonged anemia with features similar to human anemia of inflammation. Ablation of hepcidin ameliorates anemia of inflammation in this model and allows faster recovery.

Do prenatal immune activation and maternal iron deficiency interact to affect neurodevelopment and early behavior in rat offspring?

Infection and iron deficiency are common during pregnancy and studies have described altered brain development in the offspring as a result of these individual maternal exposures. Both exposures have been identified as risk factors for schizophrenia yet they have never been modeled simultaneously. We developed a rat model of prenatal immune activation on a background of maternal iron deficiency to determine whether these factors interact to affect neurodevelopment and early behavior in offspring. Pregnant rats were placed on iron sufficient (IS) or iron deficient (ID) diets from E2 to P7, and administered LPS or saline on E15/16. Iron was reduced in liver, spleen, serum and placenta from ID dams by E15. LPS administration on E15 caused greater induction of serum interleukin-6 and tumor necrosis factor-α in ID dams compared to IS dams. Offspring (P0, P7) from ID dams had reduced iron in spleen, liver and brain compared to IS, which normalized by P21. Pups from ID dams showed differences in forelimb grasp and acoustic startle, whilst pups from LPS dams displayed differences in grip ability, geotaxis reflex, cliff avoidance and acoustic startle. Offspring from LPS dams displayed reduced locomotor activity at P7 and P60; offspring from ID dams showed no change. Our findings show effects of prenatal LPS and maternal iron deficiency were additive, such that offspring exposed to both insults displayed more neurodevelopmental abnormalities than offspring exposed to one alone. Yet surprisingly there was no interaction between factors, suggesting independent mechanisms of action.

Inflammation regulates TMPRSS6 expression via STAT5

TMPRSS6 is a regulated gene, with a crucial role in the regulation of iron homeostasis by inhibiting hepcidin expression. The main regulator of iron homeostasis, the antimicrobial peptide hepcidin, which also has a role in immunity, is directly upregulated by inflammation. In this study, we analyzed whether inflammation is also a modulator of TMPRSS6 expression in vitro and in vivo and we determined the mechanism of this regulation A Human Hepatoma cell line was treated with interleukin-6 and mice were injected with lipopolysaccharide and TMPRSS6 expression and the regulatory mechanism were addressed. In this study, we demonstrate that inflammation downregulates TMPRSS6 expression in vitro and in vivo. The downregulation of Tmprss6 by inflammation in mice is not dependent on the Bmp-Smad pathway but occurs through a decrease in Stat5 phosphorylation. Moreover, Stat5 positively regulates Tmprss6 expression directly by binding to a Stat5 element located on the Tmprss6 promoter. Importantly, our results highlight the functional role of inflammatory modulation of TMPRSS6 expression in the regulation of hepcidin. TMPRSS6 inhibition via decreased STAT5 phosphorylation may be an additional mechanism by which inflammation stimulates hepcidin expression to regulate iron homeostasis and immunity.

Iron in intracellular infection: to provide or to deprive?

Due to their chemical versatility, transition metals were incorporated as cofactors for several basic metabolic pathways in living organisms. This same characteristic makes them potentially harmful, since they can be engaged in deleterious reactions like Fenton chemistry. As such, organisms have evolved highly specialized mechanisms to supply their own metal needs while keeping their toxic potential in check. This dual character comes into play in host-pathogen interactions, given that the host can either deprive the pathogen of these key nutrients or exploit them to induce toxicity toward the invading agent. Iron stands as the prototypic example of how a metal can be used to limit the growth of pathogens by nutrient deprivation, a mechanism widely studied in Mycobacterium infections. However, the host can also take advantage of iron-induced toxicity to control pathogen proliferation, as observed in infections caused by Leishmania. Whether we may harness either of the two pathways for therapeutical purposes is still ill-defined. In this review, we discuss how modulation of the host iron availability impacts the course of infections, focusing on those caused by two relevant intracellular pathogens, Mycobacterium and Leishmania.