Expression and localization of hepcidin in macrophages: A role in host defense against tuberculosis

Department of Microbiology, The Ohio State University, Columbus, OH 43210, USA.
Journal of Leukocyte Biology (Impact Factor: 4.29). 11/2007; 82(4):934-45. DOI: 10.1189/jlb.0407216
Source: PubMed


Hepcidin is an antimicrobial peptide produced by the liver in response to inflammatory stimuli and iron overload. Hepcidin regulates iron homeostasis by mediating the degradation of the iron export protein ferroportin 1, thereby inhibiting iron absorption from the small intestine and release of iron from macrophages. Here, we examined the expression of hepcidin in macrophages infected with the intracellular pathogens Mycobacterium avium and Mycobacterium tuberculosis. Stimulation of the mouse RAW264.7 macrophage cell line and mouse bone marrow-derived macrophages with mycobacteria and IFN-gamma synergistically induced high levels of hepcidin mRNA and protein. Similar results were obtained using the human THP-1 monocytic cell line. Stimulation of macrophages with the inflammatory cytokines IL-6 and IL-beta did not induce hepcidin mRNA expression. Iron loading inhibited hepcidin mRNA expression induced by IFN-gamma and M. avium, and iron chelation increased hepcidin mRNA expression. Intracellular protein levels and secretion of hepcidin were determined by a competitive chemiluminescence ELISA. Stimulation of RAW264.7 cells with IFN-gamma and M. tuberculosis induced intracellular expression and secretion of hepcidin. Furthermore, confocal microscopy analyses showed that hepcidin localized to the mycobacteria-containing phagosomes. As hepcidin has been shown to possess direct antimicrobial activity, we investigated its activity against M. tuberculosis. We found that hepcidin inhibited M. tuberculosis growth in vitro and caused structural damage to the mycobacteria. In summary, our data show for the first time that hepcidin localizes to the phagosome of infected, IFN-gamma-activated cells and has antimycobacterial activity.

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Available from: William C Florence, Apr 26, 2014
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    • "We think that in our severe COPD patient group, the decrease in serum hepcidin levels is related to hypoxemia rather than inflammation. In another study it was shown that hepcidin is also produced in mouse macrophages infected with intracellular Mycobacteria [28]. However, there are conflicting findings about the serum hepcidin level related to acute and chronic inflammation in the literature. "
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    ABSTRACT: Hepcidin has a regulatory role in inflammation, the immune system, and iron metabolism. It has been shown that proinflammatory cytokine interleukin 6 (IL-6) is an important inducer of hepcidin synthesis during infection and inflammation. Aim of the work To study the relationship between serum hepcidin level and hypoxemia in the COPD patients and its relation to COPD severity. Patients and methods A prospective case control study to compare serum hepcidin levels and other parameters in 70 COPD patients treated at the Pulmonology Department, King Fahad Hospital Dammam, with 34 age and sex matched healthy controls. All subjects participating in the study underwent a complete physical examination and detailed pulmonary function tests (PFTs). A sample from the radial artery for arterial blood gas analysis was done. As well as a panel of other tests including hemoglobin, hematocrit (hct), Iron, CRP, ferritin and total iron binding capacity. A hepcidin prohormone enzyme immunoassay kit (RE 54051, IBL) was used for serum hepcidin measurement. Results COPD patients had significantly lower serum hepcidin level compared to the control group (204.60 ± 53.12 and 280.81 ± 50.61, respectively). Furthermore there was a significantly greater reduction in serum hepcidin level in patients with severe COPD compared to patients with mild COPD. A positive correlation was found between serum hepcidin levels and arterial oxygen saturation (SaO2, %) and FEV1 level (P = 0.005). There was a negative correlation between serum hepcidin level and the ages of patients and packs of cigarettes consumed per year (P = 0.003). Conclusion Our study demonstrated a significant reduction in serum hepcidin levels in COPD patients, and the degree of reduction correlated with the severity of COPD and hypoxemia.
    Full-text · Article · Oct 2014
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    • "Because pathogens such as bacteria utilize iron to maintain growth, restriction of circulating iron concentrations provides an important host response to systemic infection (Drakesmith and Prentice, 2012). However, for pathogens such as M. tb that attempt to evade immune surveillance at the intracellular level, accumulation of iron within this environment may promote the growth of internalized pathogens such as Salmonella typhimurium (Nairz et al., 2007), M. tb (Schaible et al., 2002; Sow et al., 2007, 2009), and Chlamydia psittaci (Paradkar et al., 2008). Conversely, innate immune and viral stimuli are known to stimulate the expression of HAMP (Sow et al., 2009; Armitage et al., 2011). "
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    ABSTRACT: Immunomodulatory responses to the active form of vitamin D (1,25-dihydroxyvitamin D, 1,25D) have been recognized for many years, but it is only in the last 5 years that the potential role of this in normal human immune function has been recognized. Genome-wide analyses have played a pivotal role in redefining our perspective on vitamin D and immunity. The description of increased vitamin D receptor (VDR) and 1α-hydroxylase (CYP27B1) expression in macrophages following a pathogen challenge, has underlined the importance of intracrine vitamin D as key mediator of innate immune function. It is now clear that both macrophages and dendritic cells (DCs) are able to respond to 25-hydroxyvitamin D (25D), the major circulating vitamin D metabolite, thereby providing a link between the function of these cells and the variations in vitamin D status common to many humans. The identification of hundreds of primary 1,25D target genes in immune cells has also provided new insight into the role of vitamin D in the adaptive immune system, such as the modulation of antigen-presentation and T cells proliferation and phenotype, with the over-arching effects being to suppress inflammation and promote immune tolerance. In macrophages 1,25D promotes antimicrobial responses through the induction of antibacterial proteins, and stimulation of autophagy and autophagosome activity. In this way variations in 25D levels have the potential to influence both innate and adaptive immune responses. More recent genome-wide analyses have highlighted how cytokine signaling pathways can influence the intracrine vitamin D system and either enhance or abrogate responses to 25D. The current review will discuss the impact of intracrine vitamin D metabolism on both innate and adaptive immunity, whilst introducing the concept of disease-specific corruption of vitamin D metabolism and how this may alter the requirements for vitamin D in maintaining a healthy immune system in humans.
    Full-text · Article · Apr 2014 · Frontiers in Physiology
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    • "Based on this observed induction of hepcidin production, we tested whether purified hepcidin-25 antimicrobial peptide might exert anti-gonococcal activity. Although it reportedly lacks strong antibacterial action against clinical strains of Escherichia coli and Klebsiella pneumoniae [39], hepcidin-25 seems to have some activity against Mycobacterium tuberculosis [40]. In order to learn if hepcidin-25 could kill gonococci, we compared its activity to a model cationic antimicrobial peptide (polymyxin B; PMB) that has potent anti-gonococcal activity in vitro [25]. "
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    ABSTRACT: Neisseria gonorrhoeae is a strict human pathogen that causes the sexually transmitted infection termed gonorrhea. The gonococcus can survive extracellularly and intracellularly, but in both environments the bacteria must acquire iron from host proteins for survival. However, upon infection the host uses a defensive response by limiting the bioavailability of iron by a number of mechanisms including the enhanced expression of hepcidin, the master iron-regulating hormone, which reduces iron uptake from the gut and retains iron in macrophages. The host also secretes the antibacterial protein NGAL, which sequesters bacterial siderophores and therefore inhibits bacterial growth. To learn whether intracellular gonococci can subvert this defensive response, we examined expression of host genes that encode proteins involved in modulating levels of intracellular iron. We found that N. gonorrhoeae can survive in association (tightly adherent and intracellular) with monocytes and macrophages and upregulates a panel of its iron-responsive genes in this environment. We also found that gonococcal infection of human monocytes or murine macrophages resulted in the upregulation of hepcidin, NGAL, and NRAMP1 as well as downregulation of the expression of the gene encoding the short chain 3-hydroxybutyrate dehydrogenase (BDH2); BDH2 catalyzes the production of the mammalian siderophore 2,5-DHBA involved in chelating and detoxifying iron. Based on these findings, we propose that N. gonorrhoeae can subvert the iron-limiting innate immune defenses to facilitate iron acquisition and intracellular survival.
    Full-text · Article · Jan 2014 · PLoS ONE
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