Leukotrienes modulate cytokine release from dendritic cells

Zileuton Alleviates Radiation-Induced Cutaneous Ulcers via Inhibition of Senescence-Associated Secretory Phenotype in Rodents

Radiation-induced cutaneous ulcers are a challenging medical problem for patients receiving radiation therapy. The inhibition of cell senescence has been suggested as a prospective strategy to prevent radiation ulcers. However, there is no effective treatment for senescent cells in radiation ulcers. In this study, we investigated whether zileuton alleviated radiation-induced cutaneous ulcer by focusing on cell senescence. We demonstrate increased cell senescence and senescence-associated secretory phenotype (SASP) in irradiated dermal fibroblasts and skin tissue. The SASP secreted from senescent cells induces senescence in adjacent cells. In addition, 5-lipoxygenase (5-LO) expression increased in irradiated dermal fibroblasts and skin tissue, and SASP and cell senescence were regulated by 5-LO through p38 phosphorylation. Finally, the inhibition of 5-LO following treatment with zileuton inhibited SASP and mitigated radiation ulcers in animal models. Our results demonstrate that inhibition of SASP from senescent cells by zileuton can effectively mitigate radiation-induced cutaneous ulcers, indicating that inhibition of 5-LO might be a viable strategy for patients with this condition.

Role of arachidonic acid-derived eicosanoids in intestinal innate immunity

Arachidonic acid (ARA), an n-6 essential fatty acid, plays an important role in human and animal growth and development. The ARA presents in the membrane phospholipids can be released by phospholipase A2. These free arachidonic acid molecules are then used to produce eicosanoids through three different pathways. Previous studies have demonstrated that eicosanoids have a wide range of physiological functions. Although they are generally considered to be pro-inflammatory molecules, recent advances have elucidated they have an effect on innate immunity via regulating the development, and differentiation of innate immune cells and the function of the intestinal epithelial barrier. Here, we review eicosanoids generation in intestine and their role in intestinal innate immunity, focusing on intestinal epithelial barrier, innate immune cell in lamina propria (LP) and their crosstalk.

Differences in cNOS/iNOS Activity during Resistance to Trypanosoma cruzi Infection in 5-Lipoxygenase Knockout Mice

Infection with the protozoan Trypanosoma cruzi causes Chagas disease and consequently leads to severe inflammatory heart condition; however, the mechanisms driving this inflammatory response have not been completely elucidated. Nitric oxide (NO) is a key mediator of parasite killing in T. cruzi-infected mice, and previous studies have suggested that leukotrienes (LTs) essentially regulate the NO activity in the heart. We used infected 5-lipoxygenase-deficient mice (5-LO^−/−) to explore the participation of nitric oxide synthase isoforms, inducible (iNOS) and constitutive (cNOS), in heart injury, cytokine profile, and oxidative stress during the early stage of T. cruzi infection. Our evidence suggests that the cNOS of the host is involved in the resistance of 5-LO^−/− mice during T. cruzi infection. iNOS inhibition generated a remarkable increase in T. cruzi infection in the blood and heart of mice, whereas cNOS inhibition reduced cardiac parasitism (amastigote nests). Furthermore, this inhibition associates with a higher IFN-γ production and lower lipid peroxidation status. These data provide a better understanding about the influence of NO-interfering therapies for the inflammatory response toward T. cruzi infection.

Therapeutic potential of lipids obtained from γ-irradiated PBMCs in dendritic cell-mediated skin inflammation

BACKGROUND

Since numerous pathological conditions are evoked by unwanted dendritic cell (DC) activity, therapeutic agents modulating DC functions are of great medical interest. In regenerative medicine, cellular secretomes have gained increasing attention and valuable immunomodulatory properties have been attributed to the secretome of γ-irradiated peripheral blood mononuclear cells (PBMCs). Potential effects of the PBMC secretome (PBMCsec) on key DC functions have not been elucidated so far.

METHODS

We used a hapten-mediated murine model of contact hypersensitivity (CH) to study the effects of PBMCsec on DCs in vivo. Effects of PBMCsec on human DCs were investigated in monocyte-derived DCs (MoDC) and ex vivo skin cultures. DCs were phenotypically characterised by transcriptomics analyses and flow cytometry. DC function was evaluated by cytokine secretion, antigen uptake, PBMC proliferation and T-cell priming.

FINDINGS

PBMCsec significantly alleviated tissue inflammation and cellular infiltration in hapten-sensitized mice. We found that PBMCsec abrogated differentiation of MoDCs, indicated by lower expression of classical DC markers CD1a, CD11c and MHC class II molecules. Furthermore, PBMCsec reduced DC maturation, antigen uptake, lipopolysaccharides-induced cytokine secretion, and DC-mediated immune cell proliferation. Moreover, MoDCs differentiated with PBMCsec displayed diminished ability to prime naïve CD4+T-cells into TH1 and TH2 cells. Furthermore, PBMCsec modulated the phenotype of DCs present in the skin in situ. Mechanistically, we identified lipids as the main biomolecule accountable for the observed immunomodulatory effects.

INTERPRETATION

Together, our data describe DC-modulatory actions of lipids secreted by stressed PBMCs and suggest PBMCsec as a therapeutic option for treatment of DC-mediated inflammatory skin conditions.

FUNDING

This research project was supported by the Austrian Research Promotion Agency (Vienna, Austria; grant "APOSEC" 862068; 2015-2019) and the Vienna Business Agency (Vienna, Austria; grant "APOSEC to clinic" 2343727).

Advanced Glycation End-Products-, C-Type Lectin- and Cysteinyl/ Leukotriene-Receptors in Distinct Mesenchymal Stromal Cell Populations: Differential Transcriptional Profiles in Response to Inflammation

OBJECTIVES

We aimed at characterizing the transcription profiles of immunological receptors associated with the biology of mesenchymal stromal cells (MSCs).

MATERIALS AND METHODS

In this experimental study, quantitative real time-polymerase chain reaction (qRTPCR) was performed to establish the transcription profiles of advanced glycation end-products (RAGE) receptor, C-type lectin receptors (CLRs, including DECTIN-1, DECTIN-2 and MINCLE), leukotriene B4 (LTB4) receptors (BLT1 and BLT2) and cysteinyl leukotrienes (CysLTs) receptors (CYSLTR1 and CYSLTR2) in distinct populations of MSCs grown under basic or inflammatory conditions.

RESULTS

MSCs derived from adipose tissue (AT), foreskin (FSK), Wharton's jelly (WJ) and bone marrow (BM) exhibited significantly different transcription levels for these genes. Interestingly, these transcription profiles substantially changed following exposure of MSCs to inflammatory signals.

CONCLUSIONS

Collectively, for the first time, our data highlights that MSCs depending on their tissue-source, present several relevant receptors potentially involved in the regulation of inflammatory and immunological responses. Understanding the roles of these receptors within MSCs immunobiology will incontestably improve the efficiency of utilization of MSCs during cell-based therapies.

Oxidation by neutrophils-derived HOCl increases immunogenicity of proteins by converting them into ligands of several endocytic receptors involved in antigen uptake by dendritic cells and macrophages

The initiation of adaptive immune responses to protein antigens has to be preceded by their uptake by antigen presenting cells and intracellular proteolytic processing. Paradoxically, endocytic receptors involved in antigen uptake do not bind the majority of proteins, which may be the main reason why purified proteins stimulate at most weak immune responses. A shared feature of different types of adjuvants, capable of boosting immunogenicity of protein vaccines, is their ability to induce acute inflammation, characterized by early influx of activated neutrophils. Neutrophils are also rapidly recruited to sites of tissue injury or infection. These cells are the source of potent oxidants, including hypochlorous acid (HOCl), causing oxidation of proteins present in inflammatory foci. We demonstrate that oxidation of proteins by endogenous, neutrophils-derived HOCl increases their immunogenicity. Upon oxidation, different, randomly chosen simple proteins (yeast alcohol dehydrogenase, human and bovine serum albumin) and glycoproteins (human apo-transferrin, ovalbumin) gain the ability to bind with high affinity to several endocytic receptors on antigen presenting cells, which seems to be the major mechanism of their increased immunogenicity. The mannose receptor (CD206), scavenger receptors A (CD204) and CD36 were responsible for the uptake and presentation of HOCl-modified proteins by murine dendritic cells and macrophages. Other scavenger receptors, SREC-I and LOX-1, as well as RAGE were also able to bind HOCl-modified proteins, but they did not contribute significantly to these ligands uptake by dendritic cells because they were either not expressed or exhibited preference for more heavily oxidised proteins. Our results indicate that oxidation by neutrophils-derived HOCl may be a physiological mechanism of conferring immunogenicity on proteins which in their native forms do not bind to endocytic receptors. This mechanism might enable the immune system to detect infections caused by pathogens not recognized by pattern recognition receptors.

A functional interplay between 5-lipoxygenase and μ-calpain affects survival and cytokine profile of human Jurkat T lymphocyte exposed to simulated microgravity

A growing body of evidence strongly indicates that both simulated and authentic weightlessness exert a broad range of effects on mammalian tissues and cells, including impairment of immune cell function and increased apoptotic death. We previously reported that microgravity-dependent activation of 5-lipoxygenase (5-LOX) might play a central role in the initiation of apoptosis in human T lymphocytes, suggesting that the upregulation of this enzyme might be (at least in part) responsible for immunodepression observed in astronauts during space flights. Herein, we supplement novel information about the molecular mechanisms underlying microgravity-triggered apoptotic cell death and immune system deregulation, demonstrating that under simulated microgravity human Jurkat T cells increase the content of cytosolic DNA fragments and cytochrome c (typical hallmarks of apoptosis) and have an upregulated expression and activity of µ-calpain. These events were paralleled by the unbalance of interleukin- (IL-) 2 and interferon- (INF-) γ, anti- and proapoptotic cytokines, respectively, that seemed to be dependent on the functional interplay between 5-LOX and µ-calpain. Indeed, we report unprecedented evidence that 5-LOX inhibition reduced apoptotic death, restored the initial IL-2/INF-γ ratio, and more importantly reverted µ-calpain activation induced by simulated microgravity.

Effects of zileuton on the development of autoimmune myocarditis in an experimental rat model

BACKGROUND

Myocarditis is associated with high morbidity and mortality in childhood, but the pathogenesis of this disease is still unclear. Current knowledge indicates that complex immunopathogenic mechanisms are involved. It is understood that leukotrienes play an important role in the inflammation associated with asthma, and recent reports indicate that leukotrienes participate in immune processes and in autoimmunity.

OBJECTIVE

The aim of this study was to assess the role of leukotriene synthesis in the development of myocardial inflammation and necrosis during myocarditis.

METHODS

The effect of zileuton, a leukotriene synthesis inhibitor, was assessed in an experimental model of autoimmune myocarditis in rats. Healthy adult (10-week-old) male Wistar albino rats were randomly divided into 3 groups. Groups A and B received injections of 1.0 mg porcine cardiac myosin to induce autoimmune myocarditis and group C (the control group) received phosphate-buffered saline. Group B also received zileuton by oral gavage at 100 mg/kg · d(-1). Myocardial inflammation was assessed biochemically via serum concentrations of creatine kinase MB subunit (CK-MB) and troponin T. Cardiac tissue was assessed macroscopically (0 = no inflammation; 1 = a small discolored focus; 2 = diffuse discolored areas covering less than half of the cardiac surface; 3 = diffuse discolored areas covering more than half of the cardiac surface) and microscopically (0 = no inflammation; 1 = ⪯5% infiltration; 2 = 5% to <10% infiltration; 3 = 10% to < 20% infiltration; 4 = >20% infiltration).

RESULTS

Twenty-four rats were divided equally into 3 groups. All rats survived the duration of the study. After 21 days, all rats were euthanized. No significant differences were found between groups A and B in terms of serum concentrations of CK-MB or troponin T. The microscopic pathology score was significantly lower in group B (myosin + zileuton) than in group A (myosin only) (0.12 [0.35] vs 1.25 [1.03]; P = 0.023). The microscopic pathology score was significantly higher in group A than in group C (1.25 [1.03] vs 0; P < 0.01), but the difference between groups B and C was not statistically significant. The macroscopic pathology score was significantly higher in group A than in group B (1.37 [0.91] vs 0.37 [0.51]; P = 0.029). The macroscopic pathology score was significantly higher in group A than in group C (1.37 [0.91] vs 0; P < 0.01). There was no significant difference in macroscopic scores between groups B and C (0.37 [0.51] vs 0).

CONCLUSIONS

In this study of the effects of zileuton in an experimental rat model of autoimmune myocarditis, no significant differences were found in the serum concentrations of the biochemical markers in the 2 groups administered myosin. However, lower macroscopic and microscopic inflammation scores in the zileuton-treated group (group B) compared with the group administered only myosin (group A) suggest that zileuton, a leukotriene-synthesis inhibitor, may suppress the development of experimental autoimmune myocarditis in rats.

Efferocytosis promotes suppressive effects on dendritic cells through prostaglandin E2 production in the context of autoimmunity

Introduction

Efferocytosis is a crucial process by which apoptotic cells are cleared by phagocytes, maintaining immune tolerance to self in the absence of inflammation. Peripheral tolerance, lost in autoimmune processes, may be restored by the administration of autologous dendritic cells loaded with islet apoptotic cells in experimental type 1 diabetes.

Objective

To evaluate tolerogenic properties in dendritic cells induced by the clearance of apoptotic islet cells, thus explaining the re-establishment of tolerance in a context of autoimmunity.

Methods

Bone marrow derived dendritic cells from non-obese diabetic mice, a model of autoimmune diabetes, were generated and pulsed with islet apoptotic cells. The ability of these cells to induce autologous T cell proliferation and to suppress mature dendritic cell function was assessed, together with cytokine production. Microarray experiments were performed using dendritic cells to identify differentially expressed genes after efferocytosis.

Results

Molecular and functional changes in dendritic cells after the capture of apoptotic cells were observed. 1) Impaired ability of dendritic cells to stimulate autologous T cell proliferation after the capture of apoptotic cells even after proinflammatory stimuli, with a cytokine profile typical for immature dendritic cells. 2) Suppressive ability of mature dendritic cell function. 3) Microarray-based gene expression profiling of dendritic cells showed differential expression of genes involved in antigen processing and presentation after efferocytosis. 4) Prostaglandin E2 increased production was responsible for immunosuppressive mechanism of dendritic cells after the capture of apoptotic cells.

Conclusions

The tolerogenic behaviour of dendritic cells after islet cells efferocytosis points to a mechanism of silencing potential autoreactive T cells in the microenvironment of autoimmunity. Our results suggest that dendritic cells may be programmed to induce specific immune tolerance using apoptotic cells; this is a viable strategy for a variety of autoimmune diseases.

Leukotriene C(4) prevents the complete maturation of murine dendritic cells and modifies interleukin-12/interleukin-23 balance

Leukotriene C(4) is an important mediator in the development of inflammatory reactions and ischaemia. Previous studies have shown that leukotriene C(4) is able to modulate the function of dendritic cells (DCs) and induce their chemotaxis from skin to lymph node. In this study, we decided to evaluate the modulation exerted by leukotriene C(4) on DCs, depending on their status of activation. We showed for the first time that leukotriene C(4) stimulates endocytosis both in immature and lipopolysaccharide (LPS) -activated DCs. Moreover, it suppressed the interleukin-12p70 (IL-12p70) release, but induces the secretion of IL-23 by DCs activated with LPS and promotes the expansion of T helper type 17 (Th17) lymphocytes. Furthermore, blocking the release of IL-23 reduced the percentages of CD4(+) T cells producing IL-17 in a mixed lymphocyte reaction. Ours results suggest that leukotriene C(4) interferes with the complete maturation of inflammatory DCs in terms of phenotype and antigen uptake, while favouring the release of IL-23, the main cytokine involved in the maintenance of the Th17 profile.

Virus-induced differential expression of nuclear receptors and coregulators in dendritic cells: implication to interferon production

We investigated mRNA expression of 49 nuclear hormone receptors (NRs) and 35 transcriptional coregulators in mouse bone marrow-derived dendritic cells (DCs) upon infection with Newcastle Disease virus (NDV) or murine cytomegalovirus (MCMV). These viruses regulated mRNA expression of some NRs among which NOR1 and LXRα were highly induced at mRNA and protein levels. Exogenous expression of the latter NRs repressed IRF3- or IRF7-induced transactivation of the interferon β promoter and NDV infection further potentiated their repressive effect. The viral infection also significantly regulated mRNA expression of some coregulators, including HDAC1. Toll-like receptor ligands regulated NR and coregulator mRNA expression similar to the viruses. Thus, NRs and coregulators are integral components of DC-organizing anti-viral response wherein NOR1 and LXRα participate in regulating interferon production.

Lipid metabolism in myelinating glial cells: lessons from human inherited disorders and mouse models

The integrity of central and peripheral nervous system myelin is affected in numerous lipid metabolism disorders. This vulnerability was so far mostly attributed to the extraordinarily high level of lipid synthesis that is required for the formation of myelin, and to the relative autonomy in lipid synthesis of myelinating glial cells because of blood barriers shielding the nervous system from circulating lipids. Recent insights from analysis of inherited lipid disorders, especially those with prevailing lipid depletion and from mouse models with glia-specific disruption of lipid metabolism, shed new light on this issue. The particular lipid composition of myelin, the transport of lipid-associated myelin proteins, and the necessity for timely assembly of the myelin sheath all contribute to the observed vulnerability of myelin to perturbed lipid metabolism. Furthermore, the uptake of external lipids may also play a role in the formation of myelin membranes. In addition to an improved understanding of basic myelin biology, these data provide a foundation for future therapeutic interventions aiming at preserving glial cell integrity in metabolic disorders.

Ir-LBP, an ixodes ricinus tick salivary LTB4-binding lipocalin, interferes with host neutrophil function

Background

During their blood meal, ticks secrete a wide variety of proteins that can interfere with their host's defense mechanisms. Among these proteins, lipocalins play a major role in the modulation of the inflammatory response.

Methodology/Principal Findings

We previously identified 14 new lipocalin genes in the tick Ixodes ricinus. One of them codes for a protein that specifically binds leukotriene B4 with a very high affinity (Kd: ±1 nM), similar to that of the neutrophil transmembrane receptor BLT1. By in silico approaches, we modeled the 3D structure of the protein and the binding of LTB4 into the ligand pocket. This protein, called Ir-LBP, inhibits neutrophil chemotaxis in vitro and delays LTB4-induced apoptosis. Ir-LBP also inhibits the host inflammatory response in vivo by decreasing the number and activation of neutrophils located at the tick bite site. Thus, Ir-LBP participates in the tick's ability to interfere with proper neutrophil function in inflammation.

Conclusions/Significance

These elements suggest that Ir-LBP is a “scavenger” of LTB4, which, in combination with other factors, such as histamine-binding proteins or proteins inhibiting the classical or alternative complement pathways, permits the tick to properly manage its blood meal. Moreover, with regard to its properties, Ir-LBP could possibly be used as a therapeutic tool for illnesses associated with an increased LTB4 production.

5-Lipoxygenase-derived lipid mediators are not required for the development of NSAID-induced inflammatory bowel disease in IL-10-/- mice

Leukotrienes are potent lipid mediators derived from the metabolism of arachidonic acid by the enzyme 5-lipoxygenase (5-LO). Elevated levels of the proinflammatory leukotriene LTB(4) have been found in preclinical models of inflammatory bowel disease (IBD) as well as in colon tissue from individuals with IBD. We therefore determined the extent to which absence of 5-LO-derived lipid mediators would alter the colitis in IL-10(-/-) mice, a model of human IBD. IL-10(-/-)/5-LO(-/-) mice were generated and were healthy. Absence of 5-LO did not alter the development of spontaneous colitis in IL-10-deficient mice. We then evaluated the extent to which absence of 5-LO would alter the development of NSAID-induced colitis in IL-10(-/-) mice. Absence of 5-LO did not delay the onset or alter the severity of inflammation in NSAID-treated IL-10(-/-) mice. At an early time point, 3 days after NSAID treatment was initiated, a qualitative increase in the number of dendritic cells and CD4(+) T cells was noted in the colons of IL-10(-/-)/5-LO(-/-); however, this difference was no longer present after 14 days of NSAID treatment. Absence of 5-LO did not alter the degree of neutrophil infiltration into the in this model. Absence of 5-LO does not alter the development of IFN-gamma producing Th1-type CD4(+) T cells or IL-17 producing CD4(+) T cells. Absence of 5-LO-derived mediators did not alter the expression of the adhesion molecules ICAM-1 and P-selectin. Development of colitis in IL-10(-/-) mice was associated with increased levels of the 5-LO-derived anti-inflammatory lipoxin LXA(4). These studies demonstrate that 5-LO-derived leukotrienes are not required for the development or maintenance of spontaneous or NSAID-induced colonic inflammation in IL-10(-/-) mice.

Increased interleukin-10 production and Th2 skewing in the absence of 5-lipoxygenase

Eicosanoids (prostaglandins and leukotrienes) are important mediators of inflammatory responses. These lipid mediators may also regulate the production of peptide mediators of the immune system. In this study, we investigated the effect of the absence of 5-lipoxygenase (5-LO)-derived leukotrienes on interleukin (IL)-10 production. IL-10 is a key regulator of immune and inflammatory responses, and previous studies have suggested that prostaglandins effect their immunosuppressive functions in part by stimulation of IL-10 production. We therefore investigated whether leukotriene production would have a similar role in regulation of IL-10 production. We have made the striking observation that absence of 5-LO-derived leukotrienes results in increased IL-10 production with a concomitant decrease in the production of pro-inflammatory cytokines, including tumour necrosis factor (TNF)-alpha and IL-12. Moreover, T-cell cytokine production in the absence of 5-LO-derived leukotrienes results in increased IL-4 production and decreased interferon (IFN)-gamma production. This may be in part secondary to increased IL-10 production and its effects on dendritic cell function resulting in altered T-cell differentiation. These findings indicate that, in addition to the central role leukotrienes play in the acute inflammatory response, endogenous leukotrienes are also important regulators of inflammatory cytokine production, via regulation of IL-10 production and in vivo differentiation of T cells.

Expression of 5-lipoxygenase (5-LOX) in T lymphocytes

5-Lipoxygenase (5-LOX) is the key enzyme responsible for the synthesis of the biologically active leukotrienes. Its presence has been reported in cells of the myeloid lineage and B lymphocytes but has not been formally defined in T lymphocytes. In this study, we provide evidence for 5-LOX expression on both transcriptional and translational levels in highly purified peripheral blood T cells as well as in human T lymphoblastoid cell lines (MOLT4 and Jurkat). Messenger RNA (mRNA) of 5-LOX was amplified by conventional reverse transcription-polymerase chain reaction (RT-PCR; MOLT4 and Jurkat cells) and by in situ RT-PCR (T lymphocytes). 5-LOX protein expression was confirmed by Western blot and immunofluorescence studies. 5-LOX was present primarily in the cytoplasm with some nuclear localization and was translocated to the nuclear periphery after culture in a mitosis-supporting medium. Fluorescence-activated cell sorter analysis of different T-lymphocyte populations, including CD4, CD8, CD45RO, CD45RA, T helper type 2, and T-cell receptor-alphabeta and -gammadelta expressing cells, did not identify a differential distribution of the enzyme. Purified peripheral blood T lymphocytes were incapable of synthesizing leukotrienes in the absence of exogenous arachidonic acid. Jurkat cells produced leukotriene C(4) and a small amount of leukotriene B(4) in response to CD3-CD28 cross-linking. This synthesis was abolished by two inhibitors of leukotriene synthesis, MK-886 and AA-861. The presence of 5-LOX in T lymphocytes but the absence of endogenous lipoxygenase metabolite production compared to Jurkat cells may constitute a fundamental difference between resting peripheral lymphocytes and leukaemic cells.