Ironing out the wrinkles in host defense: interactions between iron homeostasis and innate immunity

Post-diagnostic multivitamin supplement use and colorectal cancer survival: A prospective cohort study

BACKGROUND

Use of multivitamin supplements has been associated with lower incidence of colorectal cancer (CRC). However, its influence on CRC survival remains unknown.

METHODS

Among 2424 patients with stage I-III CRC who provided detailed information about multivitamin supplements in the Nurses' Health Study and Health Professionals Follow-up Study, the authors calculated multivariable hazard ratios (HRs) of multivitamin supplements for all-cause and CRC-specific mortality according to post-diagnostic use and dose of multivitamin supplements.

RESULTS

During a median follow-up of 11 years, the authors documented 1512 deaths, among which 343 were of CRC. Compared to non-users, post-diagnostic users of multivitamin supplements at a dose of 3-5 tablets/week had lower CRC-specific mortality (HR, 0.55; 95% confidence interval [CI], 0.36-0.83, p = .005), and post-diagnostic users at doses of 3-5 and 6-9 tablets/week had lower all-cause mortality (HR, 0.81; 95% CI, 0.67-0.99, p = .04; HR, 0.79; 95% CI, 0.70-0.88), p < .001). The dose-response analysis showed a curvilinear relationship for both CRC-specific (pnonlinearity < .001) and all-cause mortality (pnonlinearity = .004), with the maximum risk reduction observed at 3-5 tablets/week and no further reduction at higher doses. Compared to non-users in both pre- and post-diagnosis periods, new post-diagnostic users at dose of <10 tablets/week had a lower all-cause mortality (HR, 0.81; 95% CI, 0.71-0.94, p = .005), whereas new users at a dose of ≥10 tablets/week (HR, 1.58; 95% CI, 1.07-2.33) and discontinued users (HR, 1.35; 95% CI, 1.14-1.59) had a higher risk of mortality.

CONCLUSIONS

Use of multivitamin supplements at a moderate dose after a diagnosis of nonmetastatic CRC is associated with lower CRC-specific and overall mortality, whereas a high dose (≥10 tablets/week) use is associated with higher CRC-specific mortality.

The effect of red blood cell disorders on male fertility and reproductive health

Male infertility is defined as a failure to conceive after 12 months of unprotected intercourse owing to suspected male reproductive factors. Non-malignant red blood cell disorders are systemic conditions that have been associated with male infertility with varying severity and strength of evidence. Hereditary haemoglobinopathies and bone marrow failure syndromes have been associated with hypothalamic-pituitary-gonadal axis dysfunction, hypogonadism, and abnormal sperm parameters. Bone marrow transplantation is a potential cure for these conditions, but exposes patients to potentially gonadotoxic chemotherapy and/or radiation that could further impair fertility. Iron imbalance might also reduce male fertility. Thus, disorders of hereditary iron overload can cause iron deposition in tissues that might result in hypogonadism and impaired spermatogenesis, whereas severe iron deficiency can propagate anaemias that decrease gonadotropin release and sperm counts. Reproductive urologists should be included in the comprehensive care of patients with red blood cell disorders, especially when gonadotoxic treatments are being considered, to ensure fertility concerns are appropriately evaluated and managed.

Iron metabolism: An emerging therapeutic target underlying the anti-Alzheimer's disease effect of ginseng

Finding neuroprotective drugs with fewer side effects and more efficacy has become a major problem as the global prevalence of Alzheimer's disease (AD) rises. Natural drugs have risen to prominence as potential medication candidates. Ginseng has a long history of use in China, and it has a wide range of pharmacological actions that can help with neurological issues. Iron loaded in the brain has been linked to AD pathogenesis. We reviewed the regulation of iron metabolism and its studies in AD and explored how ginseng might regulate iron metabolism and prevent or treat AD. Researchers utilized network pharmacology analysis to identify key factive components of ginseng that protect against AD by regulating ferroptosis. Ginseng and its active ingredients may benefit AD by regulating iron metabolism and targeting ferroptosis genes to inhibit the ferroptosis process. The results present new ideas for ginseng pharmacological studies and initiatives for further research into AD-related drugs. To provide comprehensive information on the neuroprotective use of ginseng to modulate iron metabolism, reveal its potential to treat AD, and provide insights for future research opportunities.

Association of iron-related biomarkers with severity and mortality in COVID-19 patients

BACKGROUND

Nutritional deficiency is associated with weaken immune system and increased susceptibility to infection. Among other nutrients, several trace elements have been shown to regulate immune responses. Iron is one of the most abundant trace elements present in our body, which is required in various biological processes. Iron has an immunomodulatory function and thus influence the susceptibility to the course and outcome of a variety of viral infections. So, this present study was aimed to study relations of different iron-related biomarkers in association to severity and mortality in SARS-CoV-2 patients.

MATERIALS AND METHODS

A total of 150 individuals infected with COVID-19 and 50 healthy individuals were recruited. Cases were divided based on severity (mild, moderate, and severe) and outcome (discharged or deceased). Serum iron, TIBC, ferritin, transferrin, transferrin saturation levels were analyzed by the direct colourimetric method.

RESULTS

In cases the median levels of serum iron, TIBC, transferrin, transferrin saturation and ferritin are 29 µg/dL, 132.53 µg/dL, 106.3 mg/dL, 17.74 % and 702.9 ng/dL respectively. Similarly, in controls the median levels of serum iron, TIBC, transferrin, transferrin saturation and ferritin are 53 µg/dL, 391.88 µg/dL, 313.51 mg/dL, 12.81 % and 13.52 ng/dL respectively. On comparing the cases with the controls, a significant lower level of iron, TIBC, and transferrin were found in the cases along with the significant higher levels of ferritin and transferrin saturation. On comparing the Receiver operating characteristic (ROC) curves of Iron, Ferritin, Transferrin, Transferrin sat % and TIBC in relation to survival in COVID-19 patients it was found that iron, followed by transferrin and ferritin has the highest area under the curve (AUC) with 74 %, 63 % and 61 % respectively. Further, in pairwise analysis of ROC curve, a significant difference was found between the Iron-transferrin (p < 0.01), iron-TIBC (p < 0.001) and transferrin-ferritin (P < 0.01). The multiple regression model based on Iron and transferrin outperformed any other combination of variables via stepwise AIC selection with an AUC of 98.2 %. The cutoff point according to Youden's J index is characterized with a sensitivity of 98 % and a specificity of 96.8 %, indicating that iron along with transferrin can be a useful marker that may contribute to a better assessment of survival chances in COVID-19.

CONCLUSION

Our study demonstrated a significantly decreased levels of iron, TIBC, & transferrin and a significantly increased levels of ferritin and transferrin saturation in COVID-19 patients when compared with controls. Further, Iron and transferrin were observed to be a good predictor of mortality in patients with COVID-19. From the above analysis we confirm that iron-related biomarkers play an important role in the development of oxidative stress and further lead to activation of the cytokine storm. So, continuous monitoring of these parameters could be helpful in the early detection of individuals developing the severe disease and can be used to decrease mortality in upcoming new waves of COVID-19.

Iron Deprivation Modulates the Exoproteome in Paracoccidioides brasiliensis

Fungi of the Paracoccidioides genus are the etiological agents of the systemic mycosis paracoccidioidomycosis and, when in the host, they find a challenging environment that is scarce in nutrients and micronutrients, such as Fe, which is indispensable for the survival of the pathogen. Previous studies have shown that fungi of this genus, in response to Fe deprivation, are able to synthesize and capture siderophores (Fe³⁺ chelators), use Fe-containing host proteins as a source of the metal, and use a non-canonical reductive pathway for Fe³⁺ assimilation. Despite all of these findings, there are still gaps that need to be filled in the pathogen response to metal deprivation. To contribute to the knowledge related to this subject, we obtained the exoproteome of Paracoccidioides brasiliensis (Pb18) undergoing Fe deprivation and by nanoUPLC-MS^E. One hundred forty-one proteins were identified, and out of these, 64 proteins were predicted to be secreted. We also identified the regulation of several virulence factors. Among the results, we highlight Cyb5 as a secreted molecule of Paracoccidioides in the exoproteome obtained during Fe deprivation. Cyb5 is described as necessary for the Fe deprivation response of Saccharomyces cerevisiae and Aspergillus fumigatus. Experimental data and molecular modeling indicated that Cyb5 can bind to Fe ions in vitro, suggesting that it can be relevant in the arsenal of molecules related to iron homeostasis in P. brasiliensis.

HCV-Induced Immunometabolic Crosstalk in a Triple-Cell Co-Culture Model Capable of Simulating Systemic Iron Homeostasis

Iron is crucial to the regulation of the host innate immune system and the outcome of many infections. Hepatitis C virus (HCV), one of the major viral human pathogens that depends on iron to complete its life cycle, is highly skilled in evading the immune system. This study presents the construction and validation of a physiologically relevant triple-cell co-culture model that was used to investigate the input of iron in HCV infection and the interplay between HCV, iron, and determinants of host innate immunity. We recorded the expression patterns of key proteins of iron homeostasis involved in iron import, export and storage and examined their relation to the iron regulatory hormone hepcidin in hepatocytes, enterocytes and macrophages in the presence and absence of HCV. We then assessed the transcriptional profiles of pro-inflammatory cytokines Interleukin-6 (IL-6) and interleukin-15 (IL-15) and anti-inflammatory interleukin-10 (IL-10) under normal or iron-depleted conditions and determined how these were affected by infection. Our data suggest the presence of a link between iron homeostasis and innate immunity unfolding among liver, intestine, and macrophages, which could participate in the deregulation of innate immune responses observed in early HCV infection. Coupled with iron-assisted enhanced viral propagation, such a mechanism may be important for the establishment of viral persistence and the ensuing chronic liver disease.

On Iron Metabolism and Its Regulation

Iron is a critical metal for several vital biological processes. Most of the body’s iron is bound to hemoglobin in erythrocytes. Iron from senescent red blood cells is recycled by macrophages in the spleen, liver and bone marrow. Dietary iron is taken up by the divalent metal transporter 1 (DMT1) in enterocytes and transported to portal blood via ferroportin (FPN), where it is bound to transferrin and taken up by hepatocytes, macrophages and bone marrow cells via transferrin receptor 1 (TfR1). While most of the physiologically active iron is bound hemoglobin, the major storage of most iron occurs in the liver in a ferritin-bound fashion. In response to an increased iron load, hepatocytes secrete the peptide hormone hepcidin, which binds to and induces internalization and degradation of the iron transporter FPN, thus controlling the amount of iron released from the cells into the blood. This review summarizes the key mechanisms and players involved in cellular and systemic iron regulation.

Amelioration of Murine Macrophage Activation Syndrome by Monomethyl Fumarate in Both a Heme Oxygenase 1-Dependent and Heme Oxygenase 1-Independent Manner

OBJECTIVE

Macrophage activation syndrome (MAS) is characterized by increased serum levels of ferritin and heme oxygenase 1 (HO-1), and yet no known function is ascribed to these molecules in MAS. Because HO-1 is antiinflammatory, we hypothesized that pharmacologic activation of HO-1 could ameliorate MAS disease activity. Dimethyl fumarate (DMF), a treatment approved by the US Food and Drug Administration for multiple sclerosis, activates HO-1. Monomethyl fumarate (MMF) is the active metabolite of DMF. We therefore evaluated whether MMF could elicit HO-1-dependent therapeutic improvements in a murine model of MAS.

METHODS

We induced MAS by repeated activation of Toll-like receptor 9 (TLR-9) in wild-type and myeloid-specific HO-1-deficient mice. MMF was administered twice daily to test its efficacy. We assessed organ weights, serum cytokine levels, histologic features of the spleen and liver tissue, and complete blood cell counts to evaluate disease activity. Statistical testing was performed using Student's t-test or by 2-way analysis of variance as appropriate.

RESULTS

The presence of HO-1 was required for the majority of TLR-9-induced interleukin-10 (IL-10). IL-10 production in TLR-9-induced MAS was found to correlate with the myeloid-HO-1 gene dose in myeloid cells (P < 0.001). MMF treatment increased the levels of HO-1 in splenic macrophages by ~2-fold (P < 0.01), increased serum levels of IL-10 in an HO-1-dependent manner in mice with TLR-9-induced MAS (P < 0.005), and improved multiple disease parameters in both an HO-1-dependent and HO-1-independent manner.

CONCLUSION

TLR-9-induced production of IL-10 is regulated by HO-1 activity both in vitro and in vivo. Therapeutic enhancement of the HO-1/IL-10 axis in a murine model was able to significantly ameliorate MAS disease activity. These results suggest that HO-1 may be viable as a MAS therapeutic target, and treatment with DMF and MMF should be considered in future investigations of MAS therapy.

Flipside of the Coin: Iron Deficiency and Colorectal Cancer

Iron deficiency, with or without anemia, is the most frequent hematological manifestation in individuals with cancer, and is especially common in patients with colorectal cancer. Iron is a vital micronutrient that plays an essential role in many biological functions, in the context of which it has been found to be intimately linked to cancer biology. To date, however, whereas a large number of studies have comprehensively investigated and reviewed the effects of excess iron on cancer initiation and progression, potential interrelations of iron deficiency with cancer have been largely neglected and are not well-defined. Emerging evidence indicates that reduced iron intake and low systemic iron levels are associated with the pathogenesis of colorectal cancer, suggesting that optimal iron intake must be carefully balanced to avoid both iron deficiency and iron excess. Since iron is vital in the maintenance of immunological functions, insufficient iron availability may enhance oncogenicity by impairing immunosurveillance for neoplastic changes and potentially altering the tumor immune microenvironment. Data from clinical studies support these concepts, showing that iron deficiency is associated with inferior outcomes and reduced response to therapy in patients with colorectal cancer. Here, we elucidate cancer-related effects of iron deficiency, examine preclinical and clinical evidence of its role in tumorigenesis, cancer progression and treatment response. and highlight the importance of adequate iron supplementation to limit these outcomes.

A Transcriptional Regulatory Map of Iron Homeostasis Reveals a New Control Circuit for Capsule Formation in Cryptococcus neoformans

Iron is essential for the growth of the human fungal pathogen Cryptococcus neoformans within the vertebrate host, and iron sensing contributes to the elaboration of key virulence factors, including the formation of the polysaccharide capsule. C. neoformans employs sophisticated iron acquisition and utilization systems governed by the transcription factors Cir1 and HapX. However, the details of the transcriptional regulatory networks that are governed by these transcription factors and connections to virulence remain to be defined. Here, we used chromatin immunoprecipitation followed by next-generation sequencing (ChIP-seq) and transcriptome analysis (RNA-seq) to identify genes directly regulated by Cir1 and/or HapX in response to iron availability. Overall, 40 and 100 genes were directly regulated by Cir1, and 171 and 12 genes were directly regulated by HapX, under iron-limited and replete conditions, respectively. More specifically, we found that Cir1 directly controls the expression of genes required for iron acquisition and metabolism, and indirectly governs capsule formation by regulating specific protein kinases, a regulatory connection not previously revealed. HapX regulates the genes responsible for iron-dependent pathways, particularly under iron-depleted conditions. By analyzing target genes directly bound by Cir1 and HapX, we predicted the binding motifs for the transcription factors and verified that the purified proteins bind these motifs in vitro Furthermore, several direct target genes were coordinately and reciprocally regulated by Cir1 and HapX, suggesting that these transcription factors play conserved roles in the response to iron availability. In addition, biochemical analyses revealed that Cir1 and HapX are iron-containing proteins, implying that the regulatory networks of Cir1 and HapX may be influenced by the incorporation of iron into these proteins. Taken together, our identification of the genome-wide transcriptional networks provides a detailed understanding of the iron-related regulatory landscape, establishes a new connection between Cir1 and kinases that regulate capsule, and underpins genetic and biochemical analyses that reveal iron-sensing mechanisms for Cir1 and HapX in C. neoformans.

Saraca asoca seed extract treatment recovers the trace elements imbalances in experimental murine visceral leishmaniasis

Saraca asoca is an important plant species of India having variety of medicinal activity such as antiviral, anti-diabetic, antimicrobial, anti-inflammatory, anti-cancer etc. Indian Kala-azar (KA) or visceral leishmaniasis (VL) is a protozoan parasitic disease caused by Leishmania sp and is endemic in Indian subcontinent. VL mainly targets the poorest people who have been suffering from deficiency in protein, nutrients and essential trace elements which ultimately leads to immunodeficiency. Essential trace element, Zinc (Zn) controls multiple aspects of innate and adaptive immunity while Iron (Fe) is required for various cellular activities. Bromine (Br) is important for assembly of collagen IV scaffolds in tissue development and helps in signalling and Copper (Cu) performs several functions related to immune system. Intra-cardiac blood was collected from the experimental BALB/c mice groups including (a) healthy control, (b) infected control, (c) Saraca asoca seed extract (Sa-SE) treated groups. The trace elements level in blood of mice was measured by Energy Dispersive X-Ray Fluorescence technique. Interestingly, the decreased level of Zn, Fe and Br as well as increased level of Cu in diseased state came back to almost normal range upon treatment with Sa-SE. The trace elements imbalances thus were almost restored to normalcy by treating the experimental BALB/c mice with ethanolic seed extract of Saraca asoca.

Role of Dietary Flavonoids in Iron Homeostasis

Balancing systemic iron levels within narrow limits is critical for human health, as both iron deficiency and overload lead to serious disorders. There are no known physiologically controlled pathways to eliminate iron from the body and therefore iron homeostasis is maintained by modifying dietary iron absorption. Several dietary factors, such as flavonoids, are known to greatly affect iron absorption. Recent evidence suggests that flavonoids can affect iron status by regulating expression and activity of proteins involved the systemic regulation of iron metabolism and iron absorption. We provide an overview of the links between different dietary flavonoids and iron homeostasis together with the mechanism of flavonoids effect on iron metabolism. In addition, we also discuss the clinical relevance of state-of-the-art knowledge regarding therapeutic potential that flavonoids may have for conditions that are low in iron such as anaemia or iron overload diseases.

Hepcidin mediated iron homoeostasis as immune regulator in visceral leishmaniasis patients

AIM

Iron is key ingredient for immunosurveillance and host-pathogen interaction. Intracellular pathogen steals the iron from the host, but how parasite orchestrates iron acquisition and affects immune responses remains controversial. We aimed to study the iron homoeostasis in visceral leishmaniasis (VL) and its influence on immune machinery.

METHODS AND RESULTS

This study was performed on purified monocytes and T cells, peripheral blood mononuclear cells and splenic aspirates for transcriptional analyses of iron homoeostasis (hepcidin, DMT1, transferrin receptor, ferroportin) and immune modulations (IFN-γ, HLA-DR, IL-10, iNOS, IL-6). Serum/plasma was used for determination of iron, total/transferrin iron-binding capacity and anti-leishmania antibody titres in cases. We report that VL-induced perturbation in iron homoeostasis may cause immune dysfunctions. VL cases had decreased iron uptake by transferrin-dependent and transferrin-independent routes while elevated hepcidin, degraded sole iron exporter ferroportin. Therefore, it appears that perturbation in iron homoeostasis has essential role in HLA-DR mediated antigen presentation and innate armoury by downregulating iNOS as well as altering IFN-γ, IL-6 and IL-10 profiles.

CONCLUSION

The iron homoeostasis by hepcidin can serve as one of the crucial determinants for regulating immune cell signalling; therefore, targeting iron metabolism, specifically hepcidin alone or in combination with agonists, can serve to clear infection.

[Iron and susceptibility to infections]

Iron is essential for proper functioning of the host immune system as well as an essential nutrient for growth of various pathogens. Iron deficiency increases infection susceptibility, specially those due to intracellular pathogens. At the opposite, excess iron stores could increase the virulence of some pathogens. Hepcidin synthesis is increased during the acute inflammation phase; leading to decreased iron intestinal absorption and retention of the metal within macrophages. This is considered to result from a defense mechanism of the child to limit the availability of iron for extracellular pathogens. On the other hand, iron affect innate immune responses by influencing IFN-γ or NF-kB pathways in macrophages. Consequently, iron enhances host resistance to intracellular pathogens but excess iron may alter immune system.

Biological and Immunological Aspects of Iron Deficiency Anemia in Cancer Development: A Narrative Review

Iron Deficiency Anemia (IDA) is a universal health problem and a risk factor for the development of cancer. IDA changes the microenvironment of the human body by affecting both the biological and immunological systems. It increases DNA damage and genomic instability by different mechanisms. IDA is one of the leading causes of the imbalance between different antioxidant enzymes as well as enzymes involved in DNA damage and DNA repair systems of the body. It can affect the biogenesis/expression of microRNAs. IDA interrupts the oxidative phosphorylation energy metabolism and intestinal Cytochrome-P450 systems. It also disturbs multicellular signaling pathways involved in cell survival and helps in tumor angiogenesis. Moreover, IDA is also responsible for the functional deterioration of innate and adaptive immune systems that lead to immunological dysfunctions against invading pathogens. Genomic instability and immunological dysfunctions are the hallmarks of cancer development. In this review, we will review the evidence linking IDA to increased cancer risk.

Siderophore-mediated iron acquisition and modulation of host-bacterial interactions

Iron is an essential micronutrient for most life forms including the majority of resident bacteria of the microbiota and their mammalian hosts. Bacteria have evolved numerous mechanisms to competitively acquire iron within host environments, such as the secretion of small molecules known as siderophores that can solubilize iron for bacterial use. However, siderophore biosynthesis and acquisition is not a capability equally harbored by all resident bacteria. Moreover, the structural diversity of siderophores creates variability in the susceptibility to host mechanisms that serve to counteract siderophore-mediated iron acquisition and limit bacterial growth. As a result, the differential capabilities to acquire iron among members of a complex microbial community carry important implications for the growth and function of resident bacteria. Siderophores can also directly influence host function by modulating cellular iron homeostasis, further providing a mechanism by which resident bacteria may influence their local environment at the host-microbial interface. This review will explore the putative mechanisms by which siderophore production by resident bacteria in the intestines may influence microbial community dynamics and host-bacterial interactions with important implications for pathogen- and microbiota-driven diseases including infection, inflammatory bowel diseases and colorectal cancer.

Hepcidin-mediated iron sequestration protects against bacterial dissemination during pneumonia

Gram-negative pneumonia is a dangerous illness, and bacterial dissemination to the bloodstream during the infection is strongly associated with death. Antibiotic resistance among the causative pathogens has resulted in diminishing treatment options against this infection. Hepcidin is the master regulator of extracellular iron availability in vertebrates, but its role in the context of host defense is undefined. We hypothesized that hepcidin-mediated depletion of extracellular iron during Gram-negative pneumonia protects the host by limiting dissemination of bacteria to the bloodstream. During experimental pneumonia, hepcidin was induced in the liver in an IL-6-dependent manner and mediated a rapid decline in plasma iron. In contrast, hepcidin-deficient mice developed a paradoxical increase in plasma iron during infection associated with profound susceptibility to bacteremia. Incubation of bacteria with iron-supplemented plasma enhanced bacterial growth in vitro, and systemic administration of iron to WT mice similarly promoted increased susceptibility to bloodstream infection. Finally, treatment with a hepcidin analogue restored hypoferremia in hepcidin-deficient hosts, mediated bacterial control, and improved outcomes. These data show hepcidin induction during pneumonia to be essential to preventing bacterial dissemination by limiting extracellular iron availability. Hepcidin agonists may represent an effective therapy for Gram-negative infections in patients with impaired hepcidin production or signaling.

Leishmania and its quest for iron: An update and overview

Parasites of genus Leishmania are the causative agents of complex neglected diseases called leishmaniasis and continue to be a significant health concern globally. Iron is a vital nutritional requirement for virtually all organisms, including pathogenic trypanosomatid parasites, and plays a crucial role in many facets of cellular metabolism as a cofactor of several enzymes. Iron acquisition is essential for the survival of parasites. Yet parasites are also vulnerable to the toxicity of iron and reactive oxygen species. The aim of this review is to provide an update on the current knowledge about iron acquisition and usage by Leishmania species. We have also discussed about host strategy to modulate iron availability and the strategies deployed by Leishmania parasites to overcome iron withholding defences and thus favour parasite growth within host macrophages. Since iron plays central roles in the host's response and parasite metabolism, a comprehensive understanding of the iron metabolism is beneficial to identify potential viable therapeutic opportunities against leishmaniasis.

On the translocation of bacteria and their lipopolysaccharides between blood and peripheral locations in chronic, inflammatory diseases: the central roles of LPS and LPS-induced cell death

We have recently highlighted (and added to) the considerable evidence that blood can contain dormant bacteria. By definition, such bacteria may be resuscitated (and thus proliferate). This may occur under conditions that lead to or exacerbate chronic, inflammatory diseases that are normally considered to lack a microbial component. Bacterial cell wall components, such as the endotoxin lipopolysaccharide (LPS) of Gram-negative strains, are well known as potent inflammatory agents, but should normally be cleared. Thus, their continuing production and replenishment from dormant bacterial reservoirs provides an easy explanation for the continuing, low-grade inflammation (and inflammatory cytokine production) that is characteristic of many such diseases. Although experimental conditions and determinants have varied considerably between investigators, we summarise the evidence that in a great many circumstances LPS can play a central role in all of these processes, including in particular cell death processes that permit translocation between the gut, blood and other tissues. Such localised cell death processes might also contribute strongly to the specific diseases of interest. The bacterial requirement for free iron explains the strong co-existence in these diseases of iron dysregulation, LPS production, and inflammation. Overall this analysis provides an integrative picture, with significant predictive power, that is able to link these processes via the centrality of a dormant blood microbiome that can resuscitate and shed cell wall components.

Emergent Transcriptomic Technologies and Their Role in the Discovery of Biomarkers of Liver Transplant Tolerance

Liver transplantation offers a unique window into transplant immunology due, in part, to the considerable proportion of recipients who develop immunological tolerance to their allograft. Biomarkers are able to identify and predict such a state of tolerance, and thereby able to establish suitable candidates for the minimization of hazardous immunosuppressive therapies, are not only of great potential clinical benefit but might also shed light on the immunological mechanisms underlying tolerance and rejection. Here, we review the emergent transcriptomic technologies serving as drivers of biomarker discovery, we appraise efforts to identify a molecular signature of liver allograft tolerance, and we consider the implications of this work on the mechanistic understanding of immunological tolerance.

Nutritional iron turned inside out: intestinal stress from a gut microbial perspective

Iron is abundantly present on earth, essential for most microorganisms and crucial for human health. Human iron deficiency that is nevertheless highly prevalent in developing regions of the world can be effectively treated by oral iron administration. Accumulating evidence indicates that excess of unabsorbed iron that enters the colonic lumen causes unwanted side effects at the intestinal host-microbiota interface. The chemical properties of iron, the luminal environment and host iron withdrawal mechanisms, especially during inflammation, can turn the intestine in a rather stressful milieu. Certain pathogenic enteric bacteria can, however, deal with this stress at the expense of other members of the gut microbiota, while their virulence also seems to be stimulated in an iron-rich intestinal environment. This review covers the multifaceted aspects of nutritional iron stress with respect to growth, composition, metabolism and pathogenicity of the gut microbiota in relation to human health. We aim to present an unpreceded view on the dynamic effects and impact of oral iron administration on intestinal host-microbiota interactions to provide leads for future research and other applications.

Alternative splicing contributes to the coordinated regulation of ferritin subunit levels in Bactrocera dorsalis (Hendel)

A constant ratio of ferritin heavy chain homolog (HCH) and light chain homolog (LCH) subunits seems to be required to compose the ferritin heteropolymer protein in insects. However, the mechanism by which insect LCH genes regulate protein levels remains unclear. We report that alternative promoters and alternative splicing contribute to maintaining a constant ratio of the two subunits, BdFer1HCH and BdFer2LCH (ferritin 1 HCH and ferritin 2 LCH), in Bactrocera dorsalis, a notorious quarantine pest. The genes BdFer1HCH and BdFer2LCH were identified with a series of potential transcription factor binding sites and were shown to be clustered within the genome in a "head to head" fashion. Thus, we unearthed a potential post-transcriptional mechanism to regulate the levels of LCH subunits, and confirmed that the expressions of BdFer1HCH and BdFer2LCH were induced by 20-hydroecdysone, iron overload, and immune challenge.

Transport proteins promoting Escherichia coli pathogenesis

Escherichia coli is a genetically diverse species infecting hundreds of millions of people worldwide annually. We examined seven well-characterized E. coli pathogens causing urinary tract infections, gastroenteritis, pyelonephritis and haemorrhagic colitis. Their transport proteins were identified and compared with each other and a non-pathogenic E. coli K12 strain to identify transport proteins related to pathogenesis. Each pathogen possesses a unique set of protein secretion systems for export to the cell surface or for injecting effector proteins into host cells. Pathogens have increased numbers of iron siderophore receptors and ABC iron uptake transporters, but the numbers and types of low-affinity secondary iron carriers were uniform in all strains. The presence of outer membrane iron complex receptors and high-affinity ABC iron uptake systems correlated, suggesting co-evolution. Each pathovar encodes a different set of pore-forming toxins and virulence-related outer membrane proteins lacking in K12. Intracellular pathogens proved to have a characteristically distinctive set of nutrient uptake porters, different from those of extracellular pathogens. The results presented in this report provide information about transport systems relevant to various types of E. coli pathogenesis that can be exploited in future basic and applied studies.

Stenotrophomonas maltophilia virulence and specific variations in trace elements during acute lung infection: implications in cystic fibrosis

Metal ions are necessary for the proper functioning of the immune system, and, therefore, they might have a significant influence on the interaction between bacteria and host. Ionic dyshomeostasis has been recently observed also in cystic fibrosis (CF) patients, whose respiratory tract is frequently colonized by Stenotrophomonas maltophilia. For the first time, here we used an inductively mass spectrometry method to perform a spatial and temporal analysis of the pattern of changes in a broad range of major trace elements in response to pulmonary infection by S. maltophilia. To this, DBA/2 mouse lungs were comparatively infected by a CF strain and by an environmental one. Our results showed that pulmonary ionomic profile was significantly affected during infection. Infected mice showed increased lung levels of Mg, P, S, K, Zn, Se, and Rb. To the contrary, Mn, Fe, Co, and Cu levels resulted significantly decreased. Changes of element concentrations were correlated with pulmonary bacterial load and markers of inflammation, and occurred mostly on day 3 post-exposure, when severity of infection culminated. Interestingly, CF strain – significantly more virulent than the environmental one in our murine model - provoked a more significant impact in perturbing pulmonary metal homeostasis. Particularly, exposure to CF strain exclusively increased P and K levels, while decreased Fe and Mn ones. Overall, our data clearly indicate that S. maltophilia modulates pulmonary metal balance in a concerted and virulence-dependent manner highlighting the potential role of the element dyshomeostasis during the progression of S. maltophilia infection, probably exacerbating the harmful effects of the loss of CF transmembrane conductance regulator function. Further investigations are required to understand the biological significance of these alterations and to confirm they are specifically caused by S. maltophilia.

Suppression of iron-regulatory hepcidin by vitamin D

The antibacterial protein hepcidin regulates the absorption, tissue distribution, and extracellular concentration of iron by suppressing ferroportin-mediated export of cellular iron. In CKD, elevated hepcidin and vitamin D deficiency are associated with anemia. Therefore, we explored a possible role for vitamin D in iron homeostasis. Treatment of cultured hepatocytes or monocytes with prohormone 25-hydroxyvitamin D or active 1,25-dihydroxyvitamin D decreased expression of hepcidin mRNA by 0.5-fold, contrasting the stimulatory effect of 25-hydroxyvitamin D or 1,25-dihydroxyvitamin D on related antibacterial proteins such as cathelicidin. Promoter-reporter and chromatin immunoprecipitation analyses indicated that direct transcriptional suppression of hepcidin gene (HAMP) expression mediated by 1,25-dihydroxyvitamin D binding to the vitamin D receptor caused the decrease in hepcidin mRNA levels. Suppression of HAMP expression was associated with a concomitant increase in expression of the cellular target for hepcidin, ferroportin protein, and decreased expression of the intracellular iron marker ferritin. In a pilot study with healthy volunteers, supplementation with a single oral dose of vitamin D (100,000 IU vitamin D2) increased serum levels of 25D-hydroxyvitamin D from 27±2 ng/ml before supplementation to 44±3 ng/ml after supplementation (P<0.001). This response was associated with a 34% decrease in circulating levels of hepcidin within 24 hours of vitamin D supplementation (P<0.05). These data show that vitamin D is a potent regulator of the hepcidin-ferroportin axis in humans and highlight a potential new strategy for the management of anemia in patients with low vitamin D and/or CKD.

Antimicrobial peptide β-defensin-1 expression is upregulated in Alzheimer's brain

Background

The human β-defensins (hBDs) are a highly conserved family of cationic antimicrobial and immunomodulatory peptides expressed primarily by epithelial cells in response to invasion by bacteria, fungi and some viruses. To date, the most studied members of this family of peptides are hBD-1, -2, and -3. Expression of hBD-1 and -2 has been demonstrated previously in cultured microglia and astrocytes of both mouse and human brain. Unlike inducible hBD-2 and -3, hBD-1 is constitutively expressed and is not generally upregulated by proinflammatory factors. In this study, we investigated whether hBDs, as active components of the innate immune response, are affected by pathological events in the Alzheimer’s disease (AD) brain. We assessed the expression of hBD-1, -2, and -3 in tissue obtained at autopsy from AD and age-matched control brains.

Methods

Fixed and frozen choroid plexus and the CA1 region of the hippocampus were obtained at autopsy from individuals diagnosed with AD, or from age-matched control brains without diagnosed neurodegenerative disease. Histopathologically diagnosed AD brain tissue was obtained for our study. Immunocytochemical analysis was performed using affinity purified polyclonal antibodies directed against hBD-1, -2, or -3. TaqMan gene expression assays were used to quantify the mRNA of hBD-1, -2, and -3 in the choroid plexus and hippocampus. Immunocytochemical detection of iron deposits was achieved using a modified Perl’s stain for redox-active iron. In vitro experiments were performed on human primary oral epithelial cells to model the human choroid plexus epithelial response to ferric chloride. Cells were then exposed to ferric chloride added to selected wells at 0, 1, or 10 mM concentrations for 24 h at 37°C. Total mRNA was isolated to quantify hBD-1 mRNA expression by RTqPCR.

Results

hBD-1 peptide is apparent in astrocytes of the AD hippocampus and hippocampal neurons, notably within granulovacuolar degeneration structures (GVD). A higher level of hBD-1 was also seen in the choroid plexus of AD brain in comparison to age-matched control tissue. Increased expression of hBD-1 mRNA was observed only in the choroid plexus of the AD brain when compared to expression level in age-matched control brain. Redox-active iron was also elevated in the AD choroid plexus and in vitro addition of Fe⁺³Cl₃ to cultured epithelial cells induced hBD-1 mRNA expression.

Conclusions

Our findings suggest interplay between hBD-1 and neuroimmunological responses in AD, marked by microglial and astrocytic activation, and increased expression of the peptide within the choroid plexus and accumulation within GVD. As a constitutively expressed component of the innate immune system, we propose that hBD-1 may be of considerable importance early in the disease process. We also demonstrate that increased iron deposition in AD may contribute to the elevated expression of hBD-1 within the choroid plexus. These findings represent a potentially important etiological aspect of Alzheimer’s disease neuropathology not previously reported.

The effect of bacterial challenge on ferritin regulation in the yellow fever mosquito, Aedes aegypti

Secreted ferritin is the major iron storage and transport protein in insects. Here, we characterize the message and protein expression profiles of yellow fever mosquito (Aedes aegypti) ferritin heavy chain homologue (HCH) and light chain homologue (LCH) subunits in response to iron and bacterial challenge. In vivo experiments demonstrated tissue-specific regulation of HCH and LCH expression over time post-blood meal (PBM). Transcriptional regulation of HCH and LCH was treatment specific, with differences in regulation for naïve versus mosquitoes challenged with heat-killed bacteria (HKB). Translational regulation by iron regulatory protein (IRP) binding activity for the iron-responsive element (IRE) was tissue-specific and time-dependent PBM. However, mosquitoes challenged with HKB showed little change in IRP/IRE binding activity compared to naïve animals. The changes in ferritin regulation and expression in vivo were confirmed with in vitro studies. We challenged mosquitoes with HKB followed by a blood meal to determine the effects on ferritin expression, and demonstrate a synergistic, time-dependent regulation of expression for HCH and LCH.

Dynamic transcript profiling of Candida albicans infection in zebrafish: a pathogen-host interaction study

Candida albicans is responsible for a number of life-threatening infections and causes considerable morbidity and mortality in immunocompromised patients. Previous studies of C. albicans pathogenesis have suggested several steps must occur before virulent infection, including early adhesion, invasion, and late tissue damage. However, the mechanism that triggers C. albicans transformation from yeast to hyphae form during infection has yet to be fully elucidated. This study used a systems biology approach to investigate C. albicans infection in zebrafish. The surviving fish were sampled at different post-infection time points to obtain time-lapsed, genome-wide transcriptomic data from both organisms, which were accompanied with in sync histological analyses. Principal component analysis (PCA) was used to analyze the dynamic gene expression profiles of significant variations in both C. albicans and zebrafish. The results categorized C. albicans infection into three progressing phases: adhesion, invasion, and damage. Such findings were highly supported by the corresponding histological analysis. Furthermore, the dynamic interspecies transcript profiling revealed that C. albicans activated its filamentous formation during invasion and the iron scavenging functions during the damage phases, whereas zebrafish ceased its iron homeostasis function following massive hemorrhage during the later stages of infection. Most of the immune related genes were expressed as the infection progressed from invasion to the damage phase. Such global, inter-species evidence of virulence-immune and iron competition dynamics during C. albicans infection could be crucial in understanding control fungal pathogenesis.

Iron status evaluation as a marker of postoperative joint infection: a pilot study

We evaluated the effect of different inflammatory conditions on iron status and, as a consequence, the possible use of iron markers as indicators of infection in the diagnosis of postoperative prosthetic orthopaedic joint infections. The study population was consisted of 26 patients undergoing revision of total hip or total knee joint arthroplasty and subdivided into three groups according to the cause of prosthesis implant failure: 10 as having had previous infection (Group A), 10 patients were categorized as having infection (Group B); and the remaining 6 (Group C) as not having infection. These patients were assayed for mean corpuscular haemoglobin concentration (MCHC) and serum values of iron (Fe), ferritin (Fer), transferrin (Tf), soluble transferrin receptor (sTfR), and transferrin saturation (sat Tf). Septic patients display statistically significant lower serum iron concentration, higher sTfR and ferritin levels, lower, but not statistically significant, MCHC compared to non septic ones. Little differences were observed for Tf, sat Tf, tibc, TfR index, among the three groups of patients. Our study suggests that iron status parameters, in particular serum iron, ferritin, sTfR and TfR index, could be useful tools for the early detection and the diagnosis of orthopaedic prosthetic joint infections.

Iron levels change in larval Heliothis virescens tissues following baculovirus infection

Inductively coupled plasma mass spectrometry and (59)Fe radiotracers were used to investigate changes in levels of Fe in the tissues of 4th instar Heliothis virescens larvae following infection with Helicoverpa zea single nucleopolyhedrovirus (HzSNPV) or with Autographa californica multiple nucleopolyhedrovirus. Baculovirus infection led to significant changes in hemolymph Fe levels late in infection. (24)Na radiotracer ingested by 4th instar larvae was rapidly cleared to nearly undetectable levels 6 h post-ingestion. In contrast, (59)Fe radiotracer fed to 4th instar larvae declined within the first few hours of ingestion and then remained constant at approximately 60% of the initial tracer activity. While Fe radiotracer levels among larval tissues changed, whole insect tracer levels did not decline from 6 to 60 h post-ingestion. Tissues from HzSNPV larvae had higher radiotracer levels in the hemolymph and midgut 36 and 60 h post-infection. The protein-bound/free ratio of (59)Fe was significantly higher in baculovirus infected hemolymph than in uninfected hemolymph at 60 h post-infection, indicating that Fe released from damaged cells is protein-bound. In both studies, hemolymph Fe levels were higher in HzSNPV infected larvae. This first study of tissue Fe levels during viral infection of an insect clearly demonstrates that Fe homeostasis is substantially disrupted.

Metalloreductase Steap3 coordinates the regulation of iron homeostasis and inflammatory responses

BACKGROUND

Iron and its homeostasis are intimately related to inflammatory responses, but the underlying molecular mechanisms are poorly understood. We investigated the role of Steap3 in regulating iron homeostasis in macrophages, and the effects of Steap3 depletion on host inflammatory responses.

DESIGN AND METHODS

We analyzed bone marrow-derived macrophages and primary cultured hepatocytes from Steap3(-/-) mouse models to investigate the roles of Steap3 in coordinately regulating iron homeostasis and inflammatory responses. First, we examined iron distribution and iron status in cells deficient in Steap3, as well as the requirement for the Steap3 gene during inflammatory responses. Secondly, we analyzed the regulation of Steap3 expression by inflammatory stimuli and thus, the influence of these stimuli on iron distribution and homeostasis.

RESULTS

We found that Steap3 mRNA was expressed at high levels in macrophages and hepatocytes. Steap3 deficiency led to impaired iron homeostasis, causing abnormal iron distribution and a decreased availability of cytosolic iron in macrophages. Among STEAP family members, Steap3 mRNA was uniquely down-regulated in macrophages stimulated by lipopolysaccharides. To determine whether Steap3 regulated iron homeostasis during inflammatory stress, we treated Steap3(-/-) mice with lipopolysaccharide, which produced greater iron accumulation in the vital tissues of these mice compared to in the tissues of wild-type controls. Furthermore, Steap3 depletion led to impaired induction of interferon-β, monocyte chemoattractant protein-5, and interferon induced protein-10 in macrophages via the TLR4-mediated signaling pathway.

CONCLUSIONS

Steap3 is important in regulating both iron homeostasis and TLR4-mediated inflammatory responses in macrophages. Steap3 deficiency causes abnormal iron status and homeostasis, which leads to impaired TLR4-mediated inflammatory responses in macrophages. Following inflammatory stimuli, Steap3 depletion causes dysregulated iron sequestration and distribution. Our results provide important insights into the function of Steap3 as a coordinate regulator of both iron homeostasis and innate immunity.

Mammalian siderophores, siderophore-binding lipocalins, and the labile iron pool

Bacteria use tight-binding, ferric-specific chelators called siderophores to acquire iron from the environment and from the host during infection; animals use proteins such as transferrin and ferritin to transport and store iron. Recently, candidate compounds that could serve endogenously as mammalian siderophore equivalents have been identified and characterized through associations with siderocalin, the only mammalian siderophore-binding protein currently known. Siderocalin, an antibacterial protein, acts by sequestering iron away from infecting bacteria as siderophore complexes. Candidate endogenous siderophores include compounds that only effectively transport iron as ternary complexes with siderocalin, explaining pleiotropic activities in normal cellular processes and specific disease states.

Proteomic cornerstones of hematopoietic stem cell differentiation: distinct signatures of multipotent progenitors and myeloid committed cells

Regenerative tissues such as the skin epidermis, the intestinal mucosa or the hematopoietic system are organized in a hierarchical manner with stem cells building the top of this hierarchy. Somatic stem cells harbor the highest self-renewal activity and generate a series of multipotent progenitors which differentiate into lineage committed progenitors and subsequently mature cells. In this report, we applied an in-depth quantitative proteomic approach to analyze and compare the full proteomes of ex vivo isolated and FACS-sorted populations highly enriched for either multipotent hematopoietic stem/progenitor cells (HSPCs, Lin(neg)Sca-1(+)c-Kit(+)) or myeloid committed precursors (Lin(neg)Sca-1(-)c-Kit(+)). By employing stable isotope dimethyl labeling and high-resolution mass spectrometry, more than 5000 proteins were quantified. From biological triplicate experiments subjected to rigorous statistical evaluation, 893 proteins were found differentially expressed between multipotent and myeloid committed cells. The differential protein content in these cell populations points to a distinct structural organization of the cytoskeleton including remodeling activity. In addition, we found a marked difference in the expression of metabolic enzymes, including a clear shift of specific protein isoforms of the glycolytic pathway. Proteins involved in translation showed a collective higher expression in myeloid progenitors, indicating an increased translational activity. Strikingly, the data uncover a unique signature related to immune defense mechanisms, centering on the RIG-I and type-1 interferon response systems, which are installed in multipotent progenitors but not evident in myeloid committed cells. This suggests that specific, and so far unrecognized, mechanisms protect these immature cells before they mature. In conclusion, this study indicates that the transition of hematopoietic stem/progenitors toward myeloid commitment is accompanied by a profound change in processing of cellular resources, adding novel insights into the molecular mechanisms at the interface between multipotency and lineage commitment.

Intra-graft expression of genes involved in iron homeostasis predicts the development of operational tolerance in human liver transplantation

Following organ transplantation, lifelong immunosuppressive therapy is required to prevent the host immune system from destroying the allograft. This can cause severe side effects and increased recipient morbidity and mortality. Complete cessation of immunosuppressive drugs has been successfully accomplished in selected transplant recipients, providing proof of principle that operational allograft tolerance is attainable in clinical transplantation. The intra-graft molecular pathways associated with successful drug withdrawal, however, are not well defined. In this study, we analyzed sequential blood and liver tissue samples collected from liver transplant recipients enrolled in a prospective multicenter immunosuppressive drug withdrawal clinical trial. Before initiation of drug withdrawal, operationally tolerant and non-tolerant recipients differed in the intra-graft expression of genes involved in the regulation of iron homeostasis. Furthermore, as compared with non-tolerant recipients, operationally tolerant patients exhibited higher serum levels of hepcidin and ferritin and increased hepatocyte iron deposition. Finally, liver tissue gene expression measurements accurately predicted the outcome of immunosuppressive withdrawal in an independent set of patients. These results point to a critical role for iron metabolism in the regulation of intra-graft alloimmune responses in humans and provide a set of biomarkers to conduct drug-weaning trials in liver transplantation.

The role of iron in the immune response to bacterial infection

My laboratory has been interested for some time in the influence of iron, a nutrient that is essential for both microbial pathogens and their mammalian hosts, on the course of infectious disease. Our studies indicate that alterations in the expression of host molecules that sequester or transport iron can have direct effects on pathogen growth and can also have an impact on the ability to mount normal immune responses. We have elucidated the mechanistic basis for some of these observations, and have started to apply our findings in strategies to control abnormalities of inflammation and iron metabolism. I will review here what we have learned about the interactions between iron and immunity and discuss the implications of the information that we have acquired.

Insect transferrins: multifunctional proteins

BACKGROUND

Many studies have been done evaluating transferrin in insects. Genomic analyses indicate that insects could have more than one transferrin. However, the most commonly studied insect transferrin, Tsf1, shows greatest homology to mammalian blood transferrin.

SCOPE OF REVIEW

Aspects of insect transferrin structure compared to mammalian transferrin and the roles transferrin serves in insects are discussed in this review.

MAJOR CONCLUSIONS

Insect transferrin can have one or two lobes, and can bind iron in one or both. The iron binding ligands identified for the lobes of mammalian blood transferrin are generally conserved in the lobes of insect transferrins that have an iron binding site. Available information supports that the form of dietary iron consumed influences the regulation of insect transferrin. Although message is expressed in several tissues in many insects, fat body is the likely source of hemolymph transferrin. Insect transferrin is a vitellogenic protein that is down-regulated by Juvenile Hormone. It serves a role in transporting iron to eggs in some insects, and transferrin found in eggs appears to be endowed from the female. In addition to the roles of transferrin in iron delivery, this protein also functions to reduce oxidative stress and to enhance survival of infection.

GENERAL SIGNIFICANCE

Future studies in Tsf1 as well as the other insect transferrins that bind iron are warranted because of the roles of transferrin in preventing oxidative stress, enhancing survival to infections and delivering iron to eggs for development. This article is part of a Special Issue entitled Transferrins: Molecular mechanisms of iron transport and disorders.

Hepcidin expression and iron parameters change in Type 2 diabetic patients

AIM

Iron may contribute to the pathogenesis of Type 2 diabetes mellitus (DM). The aim of this study was to determine iron regulator hepcidin and iron metabolic parameters in Type 2 DM patients, the relationships among them were evaluated in this specific sub-groups.

MATERIALS AND METHODS

The study included sixty-four people: 34 cases of diabetes and 30 age-matched controls. Serum hepcidin, IL-6, hsCRP, ferritin, sTfR, EPO as well as other clinical parameters were detected, and the associations between hepcidin levels and iron/inflammatory parameters were analyzed in diabetes and the controls.

RESULTS

Serum ferritin and hepcidin levels in diabetic patients were significant higher than the controls (p<0.001 respectively). A positive correlation between hepcidin and ferritin, as well as between ferritin and IL-6 levels was existed in diabetes and the control groups (p<0.001 respectively).

CONCLUSION

All of these data demonstrated that the higher hepcidin levels in diabetic patients may be due to those higher ferritin and IL-6 levels, the elevated hepcidin might have adaptive value through down-regulated iron absorb and play an important role in pathogenesis of Type 2 DM.

Regulation of francisella tularensis virulence

Francisella tularensis is one of the most virulent bacteria known and a Centers for Disease Control and Prevention Category A select agent. It is able to infect a variety of animals and insects and can persist in the environment, thus Francisella spp. must be able to survive in diverse environmental niches. However, F. tularensis has a surprising dearth of sensory and regulatory factors. Recent advancements in the field have identified new functions of encoded transcription factors and greatly expanded our understanding of virulence gene regulation. Here we review the current knowledge of environmental adaptation by F. tularensis, its transcriptional regulators and their relationship to animal virulence.

Iron and the immune system

Iron and immunity are closely linked: firstly by the fact that many of the genes/proteins involved in iron homoeostasis play a vital role in controlling iron fluxes such that bacteria are prevented from utilising iron for growth; secondly, cells of the innate immune system, monocytes, macrophages, microglia and lymphocytes, are able to combat bacterial insults by carefully controlling their iron fluxes, which are mediated by hepcidin and ferroportin. In addition, lymphocytes play an important role in adaptive immunity. Thirdly, a variety of effector molecules, e.g. toll-like receptors, NF-κB, hypoxia factor-1, haem oxygenase, will orchestrate the inflammatory response by mobilising a variety of cytokines, neurotrophic factors, chemokines, and reactive oxygen and nitrogen species. Pathologies, where iron loading and depletion occur, may adversely affect the ability of the cell to respond to the bacterial insult.

Iron and immunity: immunological consequences of iron deficiency and overload

The influence of iron on immune function has been long appreciated. However, the molecular basis for this interaction is less well understood. Recently, there have been several important advances that have shed light on the mechanisms that regulate mammalian iron metabolism. The new insights provide a conceptual framework for understanding and manipulating the cross-talk between iron homeostasis and the immune system. This article will review what is currently known about how disturbances of iron metabolism can affect immunity and how activation of the immune system can lead to alterations in iron balance.

Cross-talk between iron homeostasis and intestinal inflammation

Recent publications from my laboratory have highlighted the important influence of altered iron homeostasis on the inflammatory response to intestinal bacteria. Here, I provide commentary on one of those papers, "Selective modulation of TLR4-activated inflammatory responses by altered iron homeostasis in mice", which was published in the Journal of Clinical Investigation in November, 2009. It describes experiments that point to a previously unappreciated role for intracellular iron in the regulation of Toll-like receptor 4 signaling, and also demonstrates the potential therapeutic application of this information in a novel anti-inflammatory strategy based on manipulating iron balance. Our findings indicate that further investigation of the cross-talk between iron homeostasis and inflammation will yield new insights into the pathogenesis of chronic inflammatory diseases and may suggest new treatment approaches for these conditions.

Selective modulation of TLR4-activated inflammatory responses by altered iron homeostasis in mice

Mice deficient in the hemochromatosis gene, Hfe, have attenuated inflammatory responses to Salmonella infection associated with decreased macrophage TNF-alpha and IL-6 biosynthesis after exposure to LPS. In this study, we show that the abnormal cytokine production is related to impaired TLR4 signaling. Despite their abnormal response to LPS, Hfe KO macrophages produced amounts of TNF-alpha similar to those in WT cells after TLR2 stimulation. Consistent with this finding, LPS-induced activation of Mal/MyD88-dependent events was normal in the mutant macrophages. However, LPS-induced IFN-beta expression, a TRAM/TRIF-dependent response activated by TLR4, was reduced by Hfe deficiency. This reduction could be replicated in WT macrophages with the use of iron chelators. In contrast, TLR3-activated expression of IFN-beta, a TRIF-dependent response, was normal in Hfe KO macrophages and was unaffected by iron chelation. Our data suggest that low intracellular iron selectively impairs signaling via the TLR4/TRAM/TRIF pathway proximal to TRIF and results in reduced LPS-induced cytokine expression. Furthermore, by mimicking the altered iron metabolism associated with Hfe deficiency, we found that 3 different inhibitors of hepcidin attenuated Salmonella-induced and noninfectious enterocolitis. Thus, manipulation of iron homeostasis could represent a new therapeutic approach to controlling inflammation.