STAT1 is required for iNOS activation, but not IL-6 production in murine fibroblasts

The aryl hydrocarbon receptor controls mesenchymal stromal cell-mediated immunomodulation via ubiquitination of eukaryotic elongation factor-2 kinase

Mesenchymal stem cells (MSCs) have great therapeutic advantages due to their immunosuppressive properties. The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor whose signaling plays an important role in the immune system. AHR may be involved in the regulation of MSC-associated immunomodulatory functions. However, the mechanisms by which AHR controls the immunosuppressive functions of MSCs are not well understood. Here, we report that Ahr-deficient MSCs show decreased therapeutic efficacy against graft-versus-host disease (GVHD) compared to wild-type (WT)-MSCs. This was probably due to decreased iNOS protein expression, which is a key regulatory enzyme in MSC immunomodulation. The expression of eukaryotic elongation factor 2 kinase (eEF2K), which inhibits the elongation stage of protein synthesis, is significantly increased in the Ahr-deficient MSCs. Inhibition of eEF2K restored iNOS protein expression. AHR is known to act as an E3 ligase together with CUL4B. We observed constitutive binding of AHR to eEF2K. Consequently, ubiquitination and degradation of eEF2K were inhibited in Ahr-deficient MSCs and by the AHR antagonist CH223191 in WT-MSCs. In summary, AHR regulates the immunomodulatory functions of MSCs through ubiquitination of eEF2K, thereby controlling iNOS protein synthesis and its product, nitric oxide levels.

High-Dose Acetaminophen with N-acetylcysteine Rescue Inhibits M2 Polarization of Tumor-Associated Macrophages

High-dose acetaminophen (AAP) with N-acetylcysteine (NAC) rescue is among the few treatments that has shown activity in phase I trials without achieving dose-limiting toxicity that has not progressed to evaluation in later line studies. While the anti-tumor effects of AAP/NAC appear not to be mediated by glutathione depletion and free radical injury, the mechanism of anti-tumor effects of AAP/NAC has not been definitively characterized. In vitro, the effects of AAP/NAC were evaluated on bone marrow derived macrophages. Effects of AAP on IL-4/STAT6 (M2) or IFN/LPS/STAT1 (M1) signaling and downstream gene and protein expression were studied. NAC reversed the AAP toxicity in the normal liver but did not reverse AAP cytotoxicity against tumor cells in vitro. AAP/NAC selectively inhibited IL-4-induced STAT6 phosphorylation but not IFN/LPS-induced STAT1 phosphorylation. Downstream, AAP/NAC inhibited IL-4 induction of M2-associated genes and proteins but did not inhibit the IFN/LPS induction of M1-associated genes and proteins. In vivo, AAP/NAC inhibited tumor growth in EF43.fgf4 and 4T1 triple-negative breast tumors. Flow cytometry of tumor-associated macrophages revealed that AAP/NAC selectively inhibited M2 polarization. The anti-tumor activity of high-dose AAP/NAC is lost in macrophage-depleted mouse syngeneic tumor models, suggesting a macrophage-dependent mechanism of action. In conclusion, our study is the first to show that high-dose AAP/NAC has profound effects on the tumor immune microenvironment that facilitates immune-mediated inhibition of tumor growth.

Innate immunity in rickettsial infections

Rickettsial agents are a diverse group of alpha-proteobacteria within the order Rickettsiales, which possesses two families with human pathogens, Rickettsiaceae and Anaplasmataceae. These obligate intracellular bacteria are most frequently transmitted by arthropod vectors, a first step in the pathogens' avoidance of host cell defenses. Considerable study of the immune responses to infection and those that result in protective immunity have been conducted. Less study has focused on the initial events and mechanism by which these bacteria avoid the innate immune responses of the hosts to survive within and propagate from host cells. By evaluating the major mechanisms of evading innate immunity, a range of similarities among these bacteria become apparent, including mechanisms to escape initial destruction in phagolysosomes of professional phagocytes, those that dampen the responses of innate immune cells or subvert signaling and recognition pathways related to apoptosis, autophagy, proinflammatory responses, and mechanisms by which these microbes attach to and enter cells or those molecules that trigger the host responses. To illustrate these principles, this review will focus on two common rickettsial agents that occur globally, Rickettsia species and Anaplasma phagocytophilum.

Localized cytotoxic T cell-associated antigen 4 and antioxidant islet encapsulation alters macrophage signaling and induces regulatory and anergic T cells to enhance allograft survival

The loss of functional β-cell mass is a hallmark of type 1 diabetes. Islet transplantation represents a promising alternative approach, but immune-mediated graft destruction remains a major challenge. We sought to use islet encapsulation technologies to improve graft survival and function without systemic immunosuppression. We hypothesized islet encapsulation with nanothin coatings consisting of tannic acid (TA), an antioxidant; poly(N-vinylpyrrolidone) (PVPON), a biocompatible polymer; and cytotoxic T cell-associated antigen 4 immunoglobulin (CTLA-4-Ig), an inhibitory immune receptor, will elicit localized immunosuppression to prolong islet allograft function and suppress effector T cell responses. In the absence of systemic immunosuppression, we demonstrated (PVPON/TA/CTLA-4-Ig)-encapsulated NOD.Rag islet grafts maintain function significantly longer than control IgG-containing (PVPON/TA/IgG) and nonencapsulated controls after transplantation into diabetic C57BL/6 mice. This protection coincided with diminished proinflammatory macrophage responses mediated by signal transducer and activator of transcription 1 signaling, decreased proinflammatory T cell effector responses, and CTLA-4-Ig-specific concomitant increases in anergic CD4+ T cells and regulatory T cells. Our results provide evidence that conjugation of CTLA-4-Ig to (PVPON/TA) coatings can suppress T cell activation, enhance regulatory T cell populations, prolong islet allograft survival, and induce localized immunosuppression after transplantation.

Macrophage Polarization and Osteoporosis: A Review

Over 200 million people suffer from osteoporosis worldwide. Individuals with osteoporosis have increased rates of bone resorption while simultaneously having impaired osteogenesis. Most current treatments for osteoporosis focus on anti-resorptive methods to prevent further bone loss. However, it is important to identify safe and cost-efficient treatments that not only inhibit bone resorption, but also stimulate anabolic mechanisms to upregulate osteogenesis. Recent data suggest that macrophage polarization may contribute to osteoblast differentiation and increased osteogenesis as well as bone mineralization. Macrophages exist in two major polarization states, classically activated macrophages (M1) and alternatively activated macrophage (M2) macrophages. The polarization state of macrophages is dependent on molecules in the microenvironment including several cytokines and chemokines. Mechanistically, M2 macrophages secrete osteogenic factors that stimulate the differentiation and activation of pre-osteoblastic cells, such as mesenchymal stem cells (MSC’s), and subsequently increase bone mineralization. In this review, we cover the mechanisms by which M2 macrophages contribute to osteogenesis and postulate the hypothesis that regulating macrophage polarization states may be a potential treatment for the treatment of osteoporosis.

PACT-mediated PKR activation acts as a hyperosmotic stress intensity sensor weakening osmoadaptation and enhancing inflammation

The inability of cells to adapt to increased environmental tonicity can lead to inflammatory gene expression and pathogenesis. The Rel family of transcription factors TonEBP and NF-κB p65 play critical roles in the switch from osmoadaptive homeostasis to inflammation, respectively. Here we identified PACT-mediated PKR kinase activation as a marker of the termination of adaptation and initiation of inflammation in Mus musculus embryonic fibroblasts. We found that high stress-induced PACT-PKR activation inhibits the interaction between NF-κB c-Rel and TonEBP essential for the increased expression of TonEBP-dependent osmoprotective genes. This resulted in enhanced formation of TonEBP/NF-κB p65 complexes and enhanced proinflammatory gene expression. These data demonstrate a novel role of c-Rel in the adaptive response to hyperosmotic stress, which is inhibited via a PACT/PKR-dependent dimer redistribution of the Rel family transcription factors. Our results suggest that inhibiting PACT-PKR signaling may prove a novel target for alleviating stress-induced inflammatory diseases.

Essential oil of Artemisia argyi suppresses inflammatory responses by inhibiting JAK/STATs activation

ETHNOPHARMACOLOGICAL RELEVANCE

Artemisia argyi is a herbal medicine traditionally used in Asia for the treatment of bronchitis, dermatitis and arthritis. Recent studies revealed the anti-inflammatory effect of essential oil in this plant. However, the mechanisms underlying the therapeutic potential have not been well elucidated. The present study is aimed to verify its anti-inflammatory effect and investigate the probable mechanisms.

MATERIALS AND METHODS

The essential oil from Artemisia argyi (AAEO) was initially tested against LPS-induced production of inflammatory mediators and cytokines in RAW264.7 macrophages. Protein and mRNA expressions of iNOS and COX-2 were determined by Western blotting and RT-PCR analysis, respectively. The effects on the activation of MAPK/NF-κB/AP-1 and JAK/STATs pathway were also investigated by western blot. Meanwhile, in vivo anti-inflammatory effect was examined by histologic and immunohistochemical analysis in TPA-induced mouse ear edema model.

RESULTS

The results of in vitro experiments showed that AAEO dose-dependently suppressed the release of pro-inflammatory mediators (NO, PGE₂ and ROS) and cytokines (TNF-α, IL-6, IFN-β and MCP-1) in LPS-induced RAW264.7 macrophages. It down-regulated iNOS and COX-2 protein and mRNA expression but did not affect the activity of these two enzymes. AAEO significantly inhibited the phosphorylation of JAK2 and STAT1/3, but not the activation of MAPK and NF-κB cascades. In animal model, oral administration of AAEO significantly attenuated TPA-induced mouse ear edema and decreased the protein level of COX-2.

CONCLUSION

AAEO suppresses inflammatory responses via down-regulation of the JAK/STATs signaling and ROS scavenging, which could contribute, at least in part, to the anti-inflammatory effect of AAEO.

Monocytic myeloid-derived suppressor cells regulate T-cell responses against vaccinia virus

Vaccinia virus (VV) can potently activate NK- and T-cell responses, leading to efficient viral control and generation of long-lasting protective immunity. However, immune responses against viral infections are often tightly controlled to avoid collateral damage and systemic inflammation. We have previously shown that granulocytic myeloid-derived suppressor cells (g-MDSCs) can suppress the NK-cell response to VV infection. It remains unknown what regulates T-cell responses to VV infection in vivo. In this study, we first showed that monocytic MDSCs (m-MDSCs), but not g-MDSCs, from VV-infected mice could directly suppress CD4⁺ and CD8⁺ T-cell activation in vitro. We then demonstrated that defective recruitment of m-MDSCs to the site of VV infection in CCR2^-/- mice enhanced VV-specific CD8⁺ T-cell response and that adoptive transfer of m-MDSCs into VV-infected mice suppressed VV-specific CD8⁺ T-cell activation, leading to a delay in viral clearance. Mechanistically, we further showed that T-cell suppression by m-MDSCs is mediated by indication of iNOS and production of NO upon VV infection, and that IFN-γ is required for activation of m-MDSCs. Collectively, our results highlight a critical role for m-MDSCs in regulating T-cell responses against VV infection and may suggest potential strategies using m-MDSCs to modulate T-cell responses during viral infections.

Ly6Chi monocytes regulate T cell responses in viral hepatitis

Viral hepatitis remains a global health challenge despite recent progress in the development of more effective therapies. Although virus-specific CD8⁺ and CD4⁺ T cell responses are essential for viral clearance, it remains largely unknown what regulates T cell-mediated viral clearance. Thus, a better understanding of the regulation of anti-viral T cell immunity would be critical for the design of more effective therapies for viral hepatitis. Using a model of adenovirus-induced hepatitis, here we showed that adenoviral infection induced recruitment of Ly6C^hi monocytes to the liver in a CCR2-dependent manner. These recruited Ly6C^hi monocytes suppressed CD8⁺ and CD4⁺ T cell responses to adenoviral infection, leading to a delay in viral clearance. In vivo depletion of Ly6C^hi monocytes markedly enhanced anti-viral T cell responses and promoted viral clearance. Mechanistically, we showed that induction of iNOS and the production of NO by Ly6C^hi monocytes are critical for the suppression of T cell responses. In addition, a contact-dependent mechanism mediated by PD-1 and PD-L1 interaction is also required for T cell suppression by Ly6C^hi monocytes. These findings suggest a critical role for Ly6C^hi monocytes in the regulation of T cell immunity in viral hepatitis and may provide new insights into development of more effective therapies for treating viral hepatitis based on targeting the immunosuppressing monocytes.

Silicon-based quantum dots induce inflammation in human lung cells and disrupt extracellular matrix homeostasis

Quantum dots (QDs) are nanocrystalline semiconductor materials that have been tested for biological applications such as cancer therapy, cellular imaging and drug delivery, despite the serious lack of information of their effects on mammalian cells. The present study aimed to evaluate the potential of Si/SiO2 QDs to induce an inflammatory response in MRC-5 human lung fibroblasts. Cells were exposed to different concentrations of Si/SiO2 QDs (25-200 μg·mL(-1)) for 24, 48, 72 and 96 h. The results obtained showed that uptake of QDs was dependent on biocorona formation and the stability of nanoparticles in various biological media (minimum essential medium without or with 10% fetal bovine serum). The cell membrane damage indicated by the increase in lactate dehydrogenase release after exposure to QDs was dose- and time-dependent. The level of lysosomes increased proportionally with the concentration of QDs, whereas an accumulation of autophagosomes was also observed. Cellular morphology was affected, as shown by the disruption of actin filaments. The enhanced release of nitric oxide and the increase in interleukin-6 and interleukin-8 protein expression suggested that nanoparticles triggered an inflammatory response in MRC-5 cells. QDs decreased the protein expression and enzymatic activity of matrix metalloproteinase (MMP)-2 and MMP-9 and also MMP-1 caseinase activity, whereas the protein levels of MMP-1 and tissue inhibitor of metalloproteinase-1 increased. The present study reveals for the first time that silicon-based QDs are able to generate inflammation in lung cells and cause an imbalance in extracellular matrix turnover through a differential regulation of MMPs and tissue inhibitor of metalloproteinase-1 protein expression.

Inducible nitric oxide synthase (iNOS) regulatory region variation in non-human primates

Inducible nitric oxide synthase (iNOS) is an enzyme that plays a key role in intracellular immune response against respiratory infections. Since various species of nonhuman primates exhibit different levels of susceptibility to infectious respiratory diseases, and since variation in regulatory regions of genes is thought to play a key role in expression levels of genes, two candidate regulatory regions of iNOS were mapped, sequenced, and compared across five species of nonhuman primates: African green monkeys (Chlorocebus sabaeus), pig-tailed macaques (Macaca nemestrina), cynomolgus macaques (Macaca fascicularis), Indian rhesus macaques (Macaca mulatta), and Chinese rhesus macaques (M. mulatta). In addition, we conducted an in silico analysis of the transcription factor binding sites associated with genetic variation in these two candidate regulatory regions across species. We found that only one of the two candidate regions showed strong evidence of involvement in iNOS regulation. Specifically, we found evidence of 13 conserved binding site candidates linked to iNOS regulation: AP-1, C/EBPB, CREB, GATA-1, GATA-3, NF-AT, NF-AT5, NF-κB, KLF4, Oct-1, PEA3, SMAD3, and TCF11. Additionally, we found evidence of interspecies variation in binding sites for several regulatory elements linked to iNOS (GATA-3, GATA-4, KLF6, SRF, STAT-1, STAT-3, OLF-1 and HIF-1) across species, especially in African green monkeys relative to other species. Given the key role of iNOS in respiratory immune response, the findings of this study might help guide the direction of future studies aimed to uncover the molecular mechanisms underlying the increased susceptibility of African green monkeys to several viral and bacterial respiratory infections.

6-Dehydrogingerdione restrains lipopolysaccharide-induced inflammatory responses in RAW 264.7 macrophages

6-Dehydrogingerdione (6-DG), one important component of ginger, has been reported to possess some medical effects, such as antitumor and antiatherosclerosis. Herein, the anti-inflammatory effects of 6-DG against lipopolysaccharides (LPS) induced pro-inflammation mediators in RAW 264.7 cells were investigated. Results show that 6-DG significantly attenuated inducible nitric oxide synthase (iNOS, NOS2), cyclooxygenase-2 (COX-2), interleukin-1β (IL-1β), interleukin 6 (IL-6), and tumor necrosis factor-α (TNF-α) in the LPS-mediated murine macrophages (RAW 264.7 cells). 6-DG inhibited LPS-induced phosphorylation of both p38 and nuclear factor of κ light polypeptide gene enhancer in B-cells inhibitor-α (IκBα), which further prevented p-p65 nuclear factor-κB (NF-κB-p65) translocation to the nucleus. Moreover, 6-DG increased the ratio of phosphorylated signal transducers and activators of transcription 1 (p-STAT1)/p-STAT3 and down-regulated the gene expression of IL-1β, IL-6, and IL-10.

Phytoestrogens mediated anti-inflammatory effect through suppression of IRF-1 and pSTAT1 expressions in lipopolysaccharide-activated microglia

Microglial activation has been implicated in various neurological disorders, including Alzheimer's disease, Parkinson's disease, multiple sclerosis, and HIV encephalopathy. Phytoestrogens have been shown to be neuroprotective in neurotoxicity models; however, their effect on microglia has not been well established. In the current study, we report that the soy phytoestrogens, genistein, daidzein, and coumestrol, decreased nitric oxide (NO) production induced by lipopolysaccharide (LPS) in the rat microglial cell line (HAPI). The levels of inducible NO synthase (iNOS) mRNA and protein expression were also reduced. Transcription factors known to govern iNOS expression including interferon regulatory factor-1 (IRF-1) and phosphorylated STAT1 were down regulated. These observations explain, at least in part, the inhibitory effect of phytoestrogens on NO production. The levels of monocyte chemoattractant protein-1 and interleukin-6 mRNA, proinflammatory chemokine and cytokine associated with various neurological disorders, were also reduced following LPS stimulation when HAPI cells were pretreated with phytoestrogens. Hence, genistein, daidzein, and coumestrol could serve as anti-inflammatory agents and may have beneficial effects in the treatment of neurodegenerative diseases.

Regulation of myocardial interleukin-6 expression by p53 and STAT1

Cardiovascular diseases are a major cause of morbidity and mortality worldwide. The interferon inducible transcriptional activator signal transducer and activator of transcription-1 (STAT1) and p53 are two critical transcriptional factors that have pivotal roles in cardiac biology and pathology. Here we describe a novel interplay between these two key players that critically regulate the levels of the pleiotropic interleukin 6 (IL6) in the heart. We provide in vivo evidence to demonstrate that, in cardiac tissues, STAT1 is a positive regulator of IL6 expression and it competes with the suppressive effect of p53 to sustain basal IL6 levels. Induction of IL6 expression in response to interferon gamma (IFNγ), a well-characterized activator of STAT1, parallels that of STAT1 phosphorylation and induction of STAT1 target genes, such as the interferon regulatory factor-1 (IRF-1), major histocompatibility complex class II transactivator (C2ta), and β2-microglobulin (B2m). Furthermore, hearts from STAT1 knockout mice fail to induce IL6 expression in response to IFNγ. More importantly, we showed that this regulatory system is not functional in mouse embryonic fibroblasts, suggesting that activation of IL6 expression by STAT1 may be tissue specific. IL6 is a major effector of inflammation and cardiac hypertrophy, two major processes involved in heart failure, and therefore, understanding the molecular mechanisms regulating IL6 expression will enable better therapies and treatments for cardiovascular disease patients.

Intestinal myofibroblasts produce nitric oxide in response to combinatorial cytokine stimulation

Inflammatory bowel disease (IBD) patients display elevated levels of intraluminal nitric oxide (NO). NO can react with other molecules to form toxic compounds, which has led to the idea that NO may be an important mediator of IBD. However, the cellular source of NO and how its production is regulated in the intestine are unclear. In this study we aimed to determine if intestinal myofibroblasts produce NO in response to the IBD-associated cytokines IL-1β, TNFα, and IFNγ. Intestinal myofibroblasts were isolated from mice and found to express inducible nitric oxide synthase (iNOS) mRNA, but not endothelial NOS or neuronal NOS. Individual treatment of myofibroblasts with IL-1β, TNFα, or IFNγ had no effect on NO production, but stimulation with combinations of these cytokines synergistically increased iNOS mRNA and protein expression. Treatment with TNFα or IFNγ increased cell surface expression of IFNγRI or TNFRII, respectively, suggesting that these cytokines act in concert to prime NO production by myofibroblasts. Impairment of NF-κB activity with a small molecule inhibitor was sufficient to prevent increased expression of IFNγRI or TNFRII, and inhibition of Akt, JAK/STAT, or NF-κB blocked nearly all NO production induced by combinatorial cytokine treatment. These data indicate that intestinal myofibroblasts require stimulation by multiple cytokines to produce NO and that these cytokines act through a novel pathway involving reciprocal cytokine receptor regulation and signaling by Akt, JAK/STAT, and NF-κB.

Cytomegalovirus impairs antiviral CD8+ T cell immunity by recruiting inflammatory monocytes

Inflammatory monocytes are key early responders to infection that contribute to pathogen-host interactions in diverse ways. Here, we report that the murine cytomegalovirus-encoded CC chemokine, MCK2, enhanced CCR2-dependent recruitment of these cells to modulate antiviral immunity, impairing virus-specific CD8(+) T cell expansion and differentiation into effector cytotoxic T lymphocytes, thus reducing the capacity to eliminate viral antigen-bearing cells and slowing viral clearance. Adoptive transfer of inflammatory monocytes into Ccr2(-/-)Ccl2(-/-) mice impaired virus antigen-specific clearance. Cytomegalovirus therefore enhances a natural CCR2-dependent immune regulatory network to modulate adaptive immunity via nitric oxide production, reminiscent of the monocytic subtype of myeloid-derived suppressor cells primarily implicated in cancer immunomodulation.

Activated expression of the chemokine Mig after chemotherapy contributes to chemotherapy-induced bone marrow suppression and lethal toxicity

Alterations in gene expression after chemotherapy may potentially help to identify mediators that induce suppression or regeneration in bone marrow. This paper reports our observation that the expression of the chemokine monokine induced by IFN-γ (Mig) and its receptor CXCR3 was significantly activated in mice after treatment with the chemotherapeutic agent 5-fluorouracil (5-FU). The neutralization of antibodies against the activated Mig increased the survival rate and accelerated BM recovery after chemotherapy. In addition, elevation of Mig plasma levels after 5-FU treatment corresponded with increased mortality. The cell cycle-inhibiting effect of the prophylactic administration of Mig protected hematopoietic progenitor cells (HPCs) from 1-β-d-arabinofuranosylcytosine in spleen colony assays and enhanced the irradiated recipients' survival. In CXCR3(-/-) mice, Mig did not propagate BM suppression, indicating that the suppressive effect of Mig is dependent on CXCR3. On the one hand, Mig stimulated p70 S6K and Erk1/2 pathways in mesenchymal stroma cells, inhibiting mesenchymal stroma cell-dependent HPC expansion. Moreover, Mig suppressed the STAT5 pathway in HPCs, inhibiting leukocyte differentiation. Our results strongly suggest that Mig contributes to the acute lethal toxicity arising from 5-FU administration. Neutralization of Mig may offer new strategies to alleviate BM toxicity with potentially dramatic implications for chemotherapy.

Caveolin-2-deficient mice show increased sensitivity to endotoxemia

Caveolin proteins are structural components of caveolae and are involved in the regulation of many biological processes. Recent studies have shown that caveolin-1 modulates inflammatory responses and is important for sepsis development. In the present study, we show that caveolin-1 and caveolin-2 have opposite roles in lipopolysaccharide (LPS)-induced sepsis using caveolin-deficient (Cav-1 (-/-) and Cav-2 (-/-) ) mice for each of these proteins. While Cav-1 (-/-) mice displayed delayed mortality following challenge with LPS, Cav-2 (-/-) mice were more sensitive to LPS compared to wild-type (WT). With Cav-2 (-/-) mice, this effect was associated with increased intestinal injury and increased intestinal permeability. This negative outcome was also correlated with enhanced expression of iNOS in epithelial intestinal cells, and enhanced production of nitric oxide (NO). By contrast, Cav-1 (-/-) mice demonstrated a decrease in iNOS expression with decreased NO production, but no alteration in intestinal permeability. The differential expression of iNOS was associated with a significant increase of STAT-1 activation in these mice. Intestinal cells of Cav-2 (-/-) mice showed increased phosphorylation of STAT-1 at tyrosine 701 compared to wild-type. However, Cav-1 (-/-) mice-derived intestinal cells showed decreased levels of phosphorylation of STAT-1 at tyrosine 701. Since caveolin-2 is almost completely absent in Cav-1 (-/-) mice, we conclude that it is not just the absence of caveolin-2 that is responsible for the observed effects, but that the balance between caveolin-1 and caveolin-2 is important for iNOS expression and ultimately for sepsis outcome.

Carbon monoxide from CORM-2 reduces HMGB1 release through regulation of IFN-β/JAK2/STAT-1/INOS/NO signaling but not COX-2 in TLR-activated macrophages

Reduction of high-mobility group box 1 (HMGB1) and NO levels may be important therapeutic strategy for treatment of sepsis. Recently, we found that carbon monoxide (CO) can reduce HMGB1 levels in septic animal models. Here, we tried to elucidate the molecular machinery of how CO inhibits HMGB1 release in toll-like receptor (TLR)-activated macrophages. Carbon monoxide-releasing molecule 2 (CORM-2) specifically inhibited the expression of iNOS (NO), but not of cyclooxygenase 2 (COX-2) (PGE₂) in RAW 264.7 cells activated either by peptidoglycan (TLR-2 agonist), polyinosinic-polycytidylic acid (TLR-3 agonist), or LPS (TLR-4 agonist); this inhibition seemed to be mediated via the JAK2/STAT1 pathway. Treatment with neutralizing antibody to IFN-β, a JAK2 inhibitor (AG490), or a STAT1 inhibitor (fludarabine) selectively inhibited iNOS, but not COX-2 in this system. Moreover, deletion of STAT1 by siRNA also showed preferential inhibition of iNOS but not COX-2 in LPS-treated cells. Carbon monoxide-releasing molecule 2 reduced IFN-β production and phosphorylation of JAK2 and STAT1 in LPS-activated RAW264.7 cells. Carbon monoxide-releasing molecule 2 failed to inhibit iNOS and HMGB1 levels in the presence of recombinant IFN-β and NO donor (NOC-18), respectively. Finally, plasma levels of HMGB1 and iNOS protein expression in lung tissues of cecal ligation and puncture-induced septic mice were decreased in the presence of CORM-2. Taken together, it is concluded that CO selectively inhibits iNOS over COX-2, at least through IFNβ/JAK2/STAT1 signals, and this regulation plays an important role in the CORM-2-mediated inhibitory effect on HMGB1 release in macrophages.

Enhanced induction of LPS-induced fibroblast MCP-1 by interferon-gamma: involvement of JNK and MAPK phosphatase-1

IFN-gamma has significant immunoregulatory activity and plays an important role in both innate and adaptive immunity. Additive effects of IFN-gamma and the Toll-like receptor ligand LPS has been investigated in macrophages, but in fibroblasts is incompletely understood. IFN-gamma and LPS synergistically induced MCP-1 and NO release in primary murine dermal fibroblasts. IFN-gamma enhanced LPS-induced JNK and p38 MAPK phosphorylation but had no effect on NF-kappaB activity. The induction of both MCP-1 and NO was attenuated by inhibition of JNK but not p38 MAPK. Serine 727 STAT1 phosphorylation by IFN-gamma was increased by LPS, and this was also attenuated by inhibition of JNK but not p38 MAPK. IFN-gamma inhibited the basal expression of MAPK phosphatase-1, a negative regulator of MAPK signaling pathway. These results suggest that enhancement of LPS-induced JNK activation by IFN-gamma associated with inhibition of MAPK phosphatase-1 may be one of the mechanisms of additive effects between IFN-gamma and LPS in fibroblasts.

Identification of discrete tumor-induced myeloid-derived suppressor cell subpopulations with distinct T cell-suppressive activity

The induction of CD11b(+)Gr-1(+) myeloid-derived suppressor cells (MDSCs) is an important immune-evading mechanism used by tumors. However, the exact nature and function of MDSCs remain elusive, especially because they constitute a heterogeneous population that has not yet been clearly defined. Here, we identified 2 distinct MDSC subfractions with clear morphologic, molecular, and functional differences. These fractions consisted of either mononuclear cells (MO-MDSCs), resembling inflammatory monocytes, or low-density polymorphonuclear cells (PMN-MDSCs), akin to immature neutrophils. Interestingly, both MO-MDSCs and PMN-MDSCs suppressed antigen-specific T-cell responses, albeit using distinct effector molecules and signaling pathways. Blocking IFN-gamma or disrupting STAT1 partially impaired suppression by MO-MDSCs, for which nitric oxide (NO) was one of the mediators. In contrast, while IFN-gamma was strictly required for the suppressor function of PMN-MDSCs, this did not rely on STAT1 signaling or NO production. Finally, MO-MDSCs were shown to be potential precursors of highly antiproliferative NO-producing mature macrophages. However, distinct tumors differentially regulated this inherent MO-MDSC differentiation program, indicating that this phenomenon was tumor driven. Overall, our data refine tumor-induced MDSC functions by uncovering mechanistically distinct MDSC subpopulations, potentially relevant for MDSC-targeted therapies.

Structure-function relationships in the IL-17 receptor: implications for signal transduction and therapy

IL-17 is the defining cytokine of a newly-described "Th17" population that plays critical roles in mediating inflammation and autoimmunity. The IL-17/IL-17 receptor superfamily is the most recent class of cytokines and receptors to be described, and until recently very little was known about its function or molecular biology. However, in the last year important new insights into the composition and dynamics of the receptor complex and mechanisms of downstream signal transduction have been made, which will be reviewed here.

Janus kinase 3 inhibitor WHI-P154 in macrophages activated by bacterial endotoxin: differential effects on the expression of iNOS, COX-2 and TNF-alpha

Bacterial endotoxin is a potent inducer of inflammatory response, including the induction of inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) production, and the expression of cyclo-oxygenase (COX)-2 and tumor necrosis factor (TNF)-alpha in inflammatory cells. In the present study, we investigated the effects of pharmacological inhibition of Janus kinase (JAK) 3 on the production of these proinflammatory molecules in macrophages exposed to bacterial endotoxin (lipopolysaccharide; LPS). JAK3 inhibitors WHI-P154 (4-(3'-bromo-4'-hydroxylphenyl)-amino-6,7-dimethoxyquinazoline) and its derivative WHI-P131 inhibited LPS-induced iNOS expression and NO production in a dose-dependent manner. WHI-P154 inhibited the activation of signal transducer and activator of transcription (STAT) 1 and the expression of iNOS mRNA but it had no effect on iNOS mRNA decay when determined by actinomycin D assay. The JAK3 inhibitor had no effect on COX-2 expression, and TNF-alpha production was slightly inhibited only at higher drug concentrations (30 microM). In addition, WHI-P154 inhibited iNOS expression and NO production also in human epithelial cells. Our results suggest that JAK3 inhibition modulates human and murine iNOS expression and NO production in response to inflammatory stimuli.

Novel role of IL-6/SIL-6R signaling in the expression of inducible nitric oxide synthase (iNOS) in murine B16, metastatic melanoma clone F10.9, cells

Inducible nitric oxide synthase (iNOS) has been shown to be frequently expressed in melanomas; up-regulation of this enzyme is though to be associated with tumor progression. In this study, we investigated whether diverse cytokines such as: IL-6, TNF-alpha, IL-1beta, IFN-gamma and IL6RIL6 (a highly active fusion protein of the soluble form of the IL-6R (sIL-6R) and IL-6) enhance the iNOS gene expression in B16/F10.9 murine metastatic melanoma cells. An increase at iNOS expression and NO production was observed with the co-treatment of IL6RIL6 plus TNF-alpha. Gel shift and reporter gene analyses revealed that IL6RIL6 selectively activated AP-1; while TNF-alpha increased the activities of both NF-kappaB and AP-1. Persistent activation of AP-1 was also seen in cells treated with IL6RIL6 plus TNF-alpha. Stimulation of cells with IL6RIL6/TNF-alpha resulted in the activation of mitogen-activated protein kinases (MAPK) such as c-Jun N-terminal kinase (JNK) and p38, and the abrogation by pretreatment with JNK or p38 MAPK inhibitor. IL6RIL6 or IL6RIL6/TNFalpha-inducible AP-1 binding increase was supershifted by anti-c-Jun or c-Fos antibodies, and the activation of c-Jun and c-Fos was dependent on JNK and p38, respectively. These results suggest that IL-6/sIL-6R/gp130 complex signaling has an unexpected positive effect on iNOS gene expression through JNK/p38 MAPK mediated-AP-1 activation in melanoma cells.

The IL-17 cytokine family

IL-17A and its receptor are the founding members of a recently described cytokine family, with unique sequences and functions in the immune system and elsewhere. Consisting of six ligands (IL-17A-F) and five receptors (IL-17RA-IL-17RE) in mammals, these molecules have distinct primary amino acid structures with only minimal homology to other cytokine families. By far the best studied of these cytokines to date are IL-17A and its receptor, IL-17RA. IL-17A is produced primarily by T cells, and is the hallmark cytokine of a newly defined T helper cell subset that appears to be involved in generation of autoimmunity. Despite its production by the adaptive immune system, IL-17A exhibits proinflammatory activities similar to innate immune cytokines such as IL-1beta and TNF-alpha and appears to play important and nonredundant roles in regulating granulocytes in vivo. As a result, IL-17A also plays key roles in host defense. In contrast to the restricted expression of IL-17A, the IL-17RA receptor is ubiquitously expressed, and thus most cells are potential physiological targets of IL-17A. This chapter describes the major molecular properties, biological activities, and known signaling pathways of the IL-17 family, with an emphasis on IL-17A and IL-17RA.

A role for Stat1 in the regulation of lipopolysaccharide-induced interleukin-1beta expression

Because the induction of interleukin-1beta (IL-1beta) is critical to antibacterial host defenses and its excessive generation is a prominent component of sepsis, regulation of this proinflammatory cytokine is a critical factor in the immune response to lipopolysaccharide (LPS). We previously showed that LPS-induced IL-1beta expression was regulated by a Stat1-dependent, nitric oxide (NO)-mediated mechanism. Subsequent in vivo studies showed that whereas Stat1 had a role in the downregulation of IL-1beta expression, it had a more significant effect on its initial induction. Although both interferon-beta (IFN-beta) and IFN-gamma activate Stat1, the early appearance of IFN-beta in the circulation after LPS administration suggested its pivotal role in Stat1-mediated IL-1beta expression in vivo. Further in vitro analysis of peritoneal macrophages from IFN-beta (/), Stat1(/), and caspase-1(/) mice and their wild-type controls following LPS stimulation demonstrated that IL-1beta mRNA was expressed in these mice but not in macrophages from MyD88(/) mice. Despite the presence of IL-1beta mRNA, IL-1beta protein was markedly reduced in the absence of Stat1 activation in macrophages derived from IFN-beta (/) and Stat1(/) mice or in the absence of caspase-1 activity, which itself was dependent on Stat1 activation. These studies support the hypothesis that the expression of IL-1beta requires both the MyD88-dependent induction of IL-1beta mRNA and pro-IL-1beta as well as the MyD88-independent, Stat1-mediated processing of that gene product into active cytokine.

Acidosis affects tumor cell survival through modulation of nitric oxide release

The influence of environmental pH on the production of tumoricidal free radical nitric oxide (NO) was investigated in mouse fibrosarcoma L929 and rat glioma C6 cell lines. A combination of IFN-gamma and IL-1 induced a significant NO release and subsequent reduction of cell viability in tumor cell lines. Acidification of cell culture medium reduced tumor cell NO production in a pH-dependent manner. While the inhibitory effect of acidosis on NO production in C6 cells was associated with a further decrease in cell viability, it completely rescued L929 cells from NO-dependent apoptotic and necrotic death. Acidic pH diminished IFN-gamma+ IL-1-induced expression of inducible NO synthase (iNOS) mRNA and protein, and abolished the activation of iNOS transcription factor IRF-1 in L929 cells. Moreover, extracellular acidosis significantly impaired cytokine-induced phosphorylation of MAP kinase p44/42 (ERK1/2) and subsequent expression of transcription factor c-Fos in L929 cells. Finally, mild acidosis (pH 6.8) augmented, while severe acidosis (pH 6.0) reduced, IFN-gamma-induced iNOS activation/NO release and NO-dependent anticancer activity of rat and mouse macrophages. Taken together, our findings indicate that modulation of macrophage and tumor cell iNOS by an acidic microenvironment might influence the progression of NO-sensitive solid tumors.

Lentivirus infection causes neuroinflammation and neuronal injury in dorsal root ganglia: pathogenic effects of STAT-1 and inducible nitric oxide synthase

Distal sensory polyneuropathy (DSP) is currently the most common neurological complication of HIV infection in the developed world and is characterized by sensory neuronal injury accompanied by inflammation, which is clinically manifested as disabling pain and gait instability. We previously showed that feline immunodeficiency virus (FIV) infection of cats caused DSP together with immunosuppression in cats, similar to that observed in HIV-infected humans. In this study, we investigated the pathogenic mechanisms underlying the development of FIV-induced DSP using feline dorsal root ganglia (DRG) cultures, consisting of neurons, Schwann cells, and macrophages. FIV-infected cultures exhibited viral Ags (p24 and envelope) in macrophages accompanied by neuronal injury, indicated by neurite retraction, neuronal loss and decreased soma size, compared with mock-infected (control) cultures. FIV infection up-regulated inducible NO synthase (iNOS), STAT-1, and TNF-alpha mRNA levels in DRG cultures. Increased STAT-1 and iNOS mRNA levels were also observed in DRGs from FIV-infected animals relative to mock-infected controls. Similarly, immunolabeling studies of DRGs from FIV-infected animals showed that macrophages were the principal sources of STAT-1 and iNOS protein production. The iNOS inhibitor aminoguanidine reduced nitrotyrosine and protein carbonyl levels, together with preventing neuronal injury in FIV-infected DRG cultures. The present studies indicate that FIV infection of DRGs directly contributes to axonal and neuronal injury through a mechanism involving macrophage immune activation, which is mediated by STAT-1 and iNOS activation.

SOCS1/JAB Likely Mediates the Protective Effect of Cardiotrophin-1 Against Lipopolysaccharide-Induced Left Ventricular Dysfunction In Vivo

BACKGROUND

Suppressor of cytokine signaling 1 (SOCS1) is a negative regulator of cytokine signaling whose expression is induced in the rat heart by cardiotrophin-1 (CT-1). Sepsis-induced myocardial depression results from the expression of inducible nitric oxide synthase (iNOS) evoked by inflammatory cytokines.

METHODS AND RESULTS

The effect of CT-1 on lipopolysaccharide (LPS)-induced cardiac dysfunction was examined in a rat model of sepsis. In the absence of CT-1, LPS (1 mg/kg ip) elicited a reduction of systolic function and dilation of the ventricular cavity within 3-6 h after administration. These physiological effects were accompanied by increased ventricular phosphorylation of signal transducers and activators of transcription (STAT) 1 and STAT3, activation of nuclear factor-kappaB and expression of iNOS mRNA. Notably, administration of CT-1 (20 microg/kg iv) immediately prior to LPS significantly inhibited all of these LPS-induced changes. To determine whether SOCS1 expression in cardiomyocytes is sufficient to inhibit LPS- and cytokine-induced expression of iNOS mRNA, the effects of forced expression of SOCS1 in cultured neonatal cardiomyocytes were investigated using an adenovirus-mediated transfection system. Forced expression of SOCS1 significantly inhibited iNOS transcription induced by LPS, tumor necrosis factor-alpha or interferon-gamma.

CONCLUSIONS

CT-1-mediated expression of SOCS1 in cardiomyocytes may be a useful target for preventing sepsis-induced myocardial depression.

Inducible nitric oxide synthase activation by interleukin-17

Interleukin-17 (IL-17) is a proinflammatory T cell cytokine presumably involved in physiological responses to infection, but also in immunopathology of autoimmune disorders such as rheumatoid arthritis. The proinflammatory action of IL-17 depends considerably on its ability to trigger the expression of inducible nitric oxide (NO) synthase (iNOS), an enzyme responsible for the generation of cytotoxic and immunoregulatory free radical NO. Here we discuss the role of IL-17 in the cytokine network controlling iNOS expression, and analyze signaling pathways employed by IL-17 for the initiation of iNOS gene transcription. We also propose biological consequences of IL-17-mediated NO release that could be relevant for the mechanisms or therapy of autoimmune and inflammatory disorders.

STAT-1 and c-Fos interaction in nitric oxide synthase-2 gene activation

Interferon-gamma (IFN-gamma) is required for induction of the human nitric oxide synthase-2 (NOS2) gene in lung epithelium. Although the human NOS2 promoter region contains many cytokine-responsive elements, the molecular basis of induction is only partially understood. Here, the major cis-regulatory elements that control IFN-gamma-inducible NOS2 gene transcription in human lung epithelial cells are identified as composite response elements that bind signal transducer and activator of transcription 1 (STAT-1) and activator protein 1 (AP-1), which is comprised of c-Fos, Fra-2, c-Jun, and JunD. Notably, IFN-gamma activation of the human NOS2 promoter is shown to require functional AP-1 regulatory region(s), suggesting a role for AP-1 activation/binding in the IFN-gamma induction of genes. We show that c-Fos interacts with STAT-1 after IFN-gamma activation and the c-Fos/STAT-1 complex binds to the gamma-activated site (GAS) element in close proximity to AP-1 sites located at 4.9 kb upstream of the transcription start site. Taken together, our findings support a model in which a physical interaction between c-Fos and STAT-1 participates in NOS2 gene transcriptional activation.

Lipopolysaccharide-mediated modulation of cytochromes P450 in Stat1 null mice

Signal transducer and activator of transcription (Stat), a family of transcriptional factors, has been demonstrated to play a critical role in gene regulation in response to inflammatory cytokines, such as interferon and interleukin-6. Inflammatory cytokines and bacterial endotoxin are known to suppress, in most of cases, the constitutive or induced cytochromes P450 (P450) in animals and humans. However, it is not clear if the suppression of P450 by cytokines is through the Stat-signaling pathway. In the present study, we determined whether Stat1 is involved in lipopolysaccharide (LPS)-mediated modulation of P450 in mouse liver. In both Stat1(+/+) (wild type) and Stat1(-/-) (null) mice, a single dose of LPS treatment (1 mg/kg of body weight, i.p.) significantly reduced the expression of CYP3A11, 2C29, and 1A2 mRNA to 8 to 40% of the control levels as determined by real-time quantitative reverse transcription-polymerase chain reaction. The reduction was supported by Western blot analysis. In contrast, LPS significantly induced the level of CYP4A10 mRNA in both Stat1(+/+) (338% of control) and Stat1(-/-) mice (264% of control). Although suppression of mRNA levels of CYP2E1, and 2D9 was not observed in either LPS-treated Stat1 null or wild-type animals, LPS treatment resulted in a reduction of CYP2E1 protein content, which was more significant in Stat1(+/+) (23% of control) than in Stat1(-/-) mice (67% of control). Consistent with this result, the chlorzoxazone 6-hydroxylase and lauric acid 11-hydroxylase activities, as CYP2E1 representative activities, were reduced markedly by LPS in Stat1(+/+) but not in Stat1(-/-) mice. The ethoxyresorufin O-deethylase activity, as a representative CYP1A activity, was also reduced significantly only in LPS-treated Stat1(+/+) mice. These data clearly demonstrate that LPS-mediated modulation of CYP3A11, 2B10, 2C29, 1A2, and 4A10 in mouse liver is Stat1-independent. However, the significant difference between the LPS-treated Stat1(+/+) and Stat1(-/-) mice in the levels of CYP2E1 protein and activity as well as in the activity level of CYP1A suggests that Stat1 may be indirectly involved in the post-transcriptional modulation of these two mouse P450 enzymes.

Immunosuppressants leflunomide and mycophenolic acid inhibit fibroblast IL-6 production by distinct mechanisms

Mycophenolic acid (MPA) and A77 1726, the active components of the immunosuppressants mycophenolate mophetil and leflunomide, respectively, in a dose-dependent manner inhibited interferon (IFN)-gamma/LPS-induced interleukin (IL)-6 release in confluent cultures of mouse L929 fibrosarcoma cells. In addition, both drugs markedly reduced the production of the free radical gas nitric oxide (NO), without affecting the viability of L929 cells. The inhibitors of NO synthase, aminoguanidine and L-NMMA, but not L-NMMA inactive counterpart D-NMMA, mimicked the effects of A77 1726 and MPA on IL-6 generation in L929 fibroblasts. Furthermore, NO-releasing substance SNP completely reverted IL-6 accumulation in L929 cultures treated with A77 1726, while only partial recovery of IL-6 production was observed in the presence of MPA. MPA, but not A77 1726, significantly suppressed NO-independent IL-6 release triggered by cAMP-elevating agent rolipram. Thus, while A77 1726 effect on IL-6 production was mediated through concomitant reduction of NO synthesis, MPA action was mainly independent of the interference with NO generation. Finally, both agents inhibited IFN-gamma/LPS-triggered IL-6 production in mouse primary fibroblasts, but not in mouse peritoneal macrophages, indicating cell-specificity of this novel anti-inflammatory action of A77 1726 and MPA.

Maxadilan, the vasodilator/immunomodulator from Lutzomyia longipalpis sand fly saliva, stimulates haematopoiesis in mice

Protozoal parasites of the genus Leishmania are transmitted to their vertebrate host within the saliva of the sand fly during a blood meal. The saliva of the sand fly Lutzomyia longipalpis contains maxadilan, a potent vasodilator and immunomodulator. Maxadilan has been shown to enhance the virulence of L. major in all strains of laboratory mice when injected along with the organism. Increased haematopoiesis has been associated with enhanced susceptibility to Leishmania organisms. Here, we show that maxadilan alone stimulates bone marrow haematopoiesis through its ability to stimulate interleukin-6 production by bone marrow stromal cells. Moreover, these effects of maxadilan are mediated through the interaction of maxadilan with the pituitary adenylate cyclase activating polypeptide receptor. These data suggest that increasing haematopoiesis may be yet another way that maxadilan enhances susceptibility of mice to Leishmania infection.

Tumor-infiltrating macrophages induce apoptosis in activated CD8(+) T cells by a mechanism requiring cell contact and mediated by both the cell-associated form of TNF and nitric oxide

We have investigated the ability of different cells present in murine tumors to induce apoptosis of activated CD8(+) T cells in vitro. Tumor cells do not induce apoptosis of T cells; however, macrophages that infiltrate tumors are potent inducers of apoptosis. Tumor macrophages express cell surface-associated TNF, TNF type I (CD120a) and II (CD120b) receptors, and, upon contact with T cells which induces release of IFN-gamma from T cells, secrete nitric oxide. Killing of T cells in vitro is blocked by Abs to IFN-gamma, TNF, CD120a, or CD120b, or N-methyl-L-arginine. In concert with that finding, tumor macrophages isolated from either TNF type I or type II receptor -/- mice are not proapoptotic and do not produce nitric oxide upon contact with activated T cells. Control macrophages do not express TNF receptors or release nitric oxide. Tumor cells or tumor-derived macrophages do not express FasL, and blocking Abs to either Fas or FasL have no effect on macrophage-mediated T cell killing. These results demonstrate that macrophages which infiltrate tumors are highly proapoptotic and may be responsible for elimination of activated antitumor T cells within the tumor bed.