Native and aspirin-triggered lipoxins control innate immunity by inducing proteasomal degradation of TRAF6

The Gene Signature of Activated M-CSF-Primed Human Monocyte-Derived Macrophages Is IL-10-Dependent

During inflammatory responses, monocytes are recruited into inflamed tissues, where they become monocyte-derived macrophages and acquire pro-inflammatory and tissue-damaging effects in response to the surrounding environment. In fact, monocyte-derived macrophage subsets are major pathogenic cells in inflammatory pathologies. Strikingly, the transcriptome of pathogenic monocyte-derived macrophage subsets resembles the gene profile of macrophage colony-stimulating factor (M-CSF)-primed monocyte-derived human macrophages (M-MØ). As M-MØ display a characteristic cytokine profile after activation (IL10high TNFlow IL23low IL6low), we sought to determine the transcriptional signature of M-MØ upon exposure to pathogenic stimuli. Activation of M-MØ led to the acquisition of a distinctive transcriptional profile characterized by the induction of a group of genes (Gene set 1) highly expressed by pathogenic monocyte-derived macrophages in COVID-19 and whose presence in tumor-associated macrophages (TAM) correlates with the expression of macrophage-specific markers (CD163, SPI1) and IL10. Indeed, Gene set 1 expression was primarily dependent on ERK/p38 and STAT3 activation, and transcriptional analysis and neutralization experiments revealed that IL-10 is not only required for the expression of a subset of genes within Gene set 1 but also significantly contributes to the idiosyncratic gene signature of activated M-MØ. Our results indicate that activation of M-CSF-dependent monocyte-derived macrophages induces a distinctive gene expression profile, which is partially dependent on IL-10, and identifies a gene set potentially helpful for macrophage-centered therapeutic strategies.

Tespa1 Deficiency Dampens Thymus-Dependent B-Cell Activation and Attenuates Collagen-Induced Arthritis in Mice

Thymocyte-expressed, positive selection-associated 1 (Tespa1) plays an important role in both T cell receptor (TCR)-driven thymocyte development and in the FcεRI-mediated activation of mast cells. Herein, we show that lack of Tespa1 does not impair B cell development but dampens the in vitro activation and proliferation of B cells induced by T cell-dependent (TD) antigens, significantly reduces serum antibody concentrations in vivo, and impairs germinal center formation in both aged and TD antigen-immunized mice. We also provide evidence that dysregulated signaling in Tespa1-deficient B cells may be linked to CD40-induced TRAF6 degradation, and subsequent effects on 1-phosphatidylinositol-4,5-bisphosphate phosphodiesterase gamma-2 (PLCγ2) phosphorylation, MAPK activation, and calcium influx. Furthermore, we demonstrate that Tespa1 plays a critical role in pathogenic B cells, since Tespa1-deficient chimeric mice showed a lower incidence and clinical disease severity of collagen-induced arthritis. Overall, our study demonstrates that Tespa1 is essential for TD B cell responses, and suggests an important role for Tespa1 during the development of autoimmune arthritis.

Platelets, inflammation and anti-inflammatory effects of antiplatelet drugs in ACS and CAD

Platelets play a pivotal role in chronic inflammation leading to progression of atherosclerosis and acute coronary events. Recent discoveries on novel mechanisms and platelet-dependent inflammatory targets underpin the role of platelets to maintain a chronic inflammatory condition in cardiovascular disease. There is strong and clinically relevant crosslink between chronic inflammation and platelet activation. Antiplatelet therapy is a cornerstone in the prevention and treatment of acute cardiovascular events. The benefit of antiplatelet agents has mainly been attributed to their direct anti-aggregatory impact. Some anti-inflammatory off-target effects have also been described. However, it is unclear whether these effects are secondary due to inhibition of platelet activation or are caused by direct distinct mechanisms interfering with inflammatory pathways. This article will highlight novel platelet associated targets that contribute to inflammation in cardiovascular disease and elucidate mechanisms by which currently available antiplatelet agents evolve anti-inflammatory capacities, in particular by carving out the differential mechanisms directly or indirectly affecting platelet mediated inflammation. It will further illustrate the prognostic impact of antiplatelet therapies by reducing inflammatory marker release in recent cardiovascular trials.

Suppressor of Cytokine Signaling 2 Negatively Regulates NK Cell Differentiation by Inhibiting JAK2 Activity

Suppressor of cytokine signaling (SOCS) proteins are negative regulators of cytokine responses. Although recent reports have shown regulatory roles for SOCS proteins in innate and adaptive immunity, their roles in natural killer (NK) cell development are largely unknown. Here, we show that SOCS2 is involved in NK cell development. SOCS2^−/− mice showed a high frequency of NK cells in the bone marrow and spleen. Knockdown of SOCS2 was associated with enhanced differentiation of NK cells in vitro, and the transplantation of hematopoietic stem cells (HSCs) into congenic mice resulted in enhanced differentiation in SOCS2^−/− HSCs. We found that SOCS2 could inhibit Janus kinase 2 (JAK2) activity and JAK2-STAT5 signaling pathways via direct interaction with JAK2. Furthermore, SOCS2^−/− mice showed a reduction in lung metastases and an increase in survival following melanoma challenge. Overall, our findings suggest that SOCS2 negatively regulates the development of NK cells by inhibiting JAK2 activity via direct interaction.

Socs1 and Socs3 degrades Traf6 via polyubiquitination in LPS-induced acute necrotizing pancreatitis

Mechanisms involved in inflammatory development during acute pancreatitis (AP) are largely vague, especially in the transformation of acute edematous pancreatitis (AEP) into acute necrotizing pancreatitis (ANP). This current study aims to investigate the functions of Traf6 in different AP models in vitro and in vivo, and to identify the possible regulatory mechanism in the progression of inflammation from mild to severe. Our data revealed that the level of Traf6 expression was significantly increased in the mild AP induced by caerulein, and the upregulation of Traf6 played a protective role in acinar cells against caerulein-induced apoptosis. In contrast, only Traf6 protein but not mRNA was downregulated in the severe ANP induced by combination treatment of caerulein and LPS. Mechanistic studies showed that LPS upregulated the levels of Socs1 and Socs3 expressions in acinar cells, Socs1 and Socs3 interacted Traf6 directly and degraded Traf6 protein via polyubiquitination, thereby counteracted the protective function of Traf6. In vivo study further showed that combination treatment of caerulein and LPS failed to induce an ANP model in the TLR4 knockout mice, and the level of Traf6 expression in the pancreatic tissues remained the same as that from the acute edematous pancreatitis (AEP) mouse. Taken together, our study reveals that Traf6 functioned as a protective factor in the progression of AP, and LPS-induced Socs1 and Socs3 exacerbate mild AP to severe AP, which provides evidence for developing a new therapeutic target to combat AP.

Regulation of Macrophage, Dendritic Cell, and Microglial Phenotype and Function by the SOCS Proteins

Macrophages are innate immune cells of dynamic phenotype that rapidly respond to external stimuli in the microenvironment by altering their phenotype to respond to and to direct the immune response. The ability to dynamically change phenotype must be carefully regulated to prevent uncontrolled inflammatory responses and subsequently to promote resolution of inflammation. The suppressor of cytokine signaling (SOCS) proteins play a key role in regulating macrophage phenotype. In this review, we summarize research to date from mouse and human studies on the role of the SOCS proteins in determining the phenotype and function of macrophages. We will also touch on the influence of the SOCS on dendritic cell (DC) and microglial phenotype and function. The molecular mechanisms of SOCS function in macrophages and DCs are discussed, along with how dysregulation of SOCS expression or function can lead to alterations in macrophage/DC/microglial phenotype and function and to disease. Regulation of SOCS expression by microRNA is discussed. Novel therapies and unanswered questions with regard to SOCS regulation of monocyte-macrophage phenotype and function are highlighted.

Mechanisms of nonsteroidal anti-inflammatory drugs in cancer prevention

Various clinical and epidemiologic studies show that nonsteroidal anti-inflammatory drugs (NSAIDs), including aspirin and cyclooxygenase inhibitors (COXIBs) help prevent cancer. Since eicosanoid metabolism is the main inhibitory targets of these drugs the resulting molecular and biological impact is generally accepted. As our knowledge base and technology progress we are learning that additional targets may be involved. This review attempts to summarize these new developments in the field.

Predictive in silico off-target profiling in drug discovery

Drug action can be rationalized as interaction of a molecule with proteins in a regulatory network of targets from a specific biological system. Both drug and side effects are often governed by interaction of the drug molecule with many, often unrelated, targets. Accordingly, arrays of protein–ligand interaction data from numerous in vitro profiling assays today provide growing evidence of polypharmacological drug interactions, even for marketed drugs. In vitro off-target profiling has therefore become an important tool in early drug discovery to learn about potential off-target liabilities, which are sometimes beneficial, but more often safety relevant. The rapidly developing field of in silico profiling approaches is complementing in vitro profiling. These approaches capitalize from large amounts of biochemical data from multiple sources to be exploited for optimizing undesirable side effects in pharmaceutical research. Therefore, current in silico profiling models are nowadays perceived as valuable tools in drug discovery, and promise a platform to support optimally informed decisions.

Distinct signaling cascades elicited by different formyl peptide receptor 2 (FPR2) agonists

The formyl peptide receptor 2 (FPR2) is a remarkably versatile transmembrane protein belonging to the G-protein coupled receptor (GPCR) family. FPR2 is activated by an array of ligands, which include structurally unrelated lipids and peptide/proteins agonists, resulting in different intracellular responses in a ligand-specific fashion. In addition to the anti-inflammatory lipid, lipoxin A4, several other endogenous agonists also bind FPR2, including serum amyloid A, glucocorticoid-induced annexin 1, urokinase and its receptor, suggesting that the activation of FPR2 may result in potent pro- or anti-inflammatory responses. Other endogenous ligands, also present in biological samples, include resolvins, amyloidogenic proteins, such as beta amyloid (Aβ)-42 and prion protein (Prp)_106–126, the neuroprotective peptide, humanin, antibacterial peptides, annexin 1-derived peptides, chemokine variants, the neuropeptides, vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP)-27, and mitochondrial peptides. Upon activation, intracellular domains of FPR2 mediate signaling to G-proteins, which trigger several agonist-dependent signal transduction pathways, including activation of phospholipase C (PLC), protein kinase C (PKC) isoforms, the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) pathway, the mitogen-activated protein kinase (MAPK) pathway, p38MAPK, as well as the phosphorylation of cytosolic tyrosine kinases, tyrosine kinase receptor transactivation, phosphorylation and nuclear translocation of regulatory transcriptional factors, release of calcium and production of oxidants. FPR2 is an attractive therapeutic target, because of its involvement in a range of normal physiological processes and pathological diseases. Here, we review and discuss the most significant findings on the intracellular pathways and on the cross-communication between FPR2 and tyrosine kinase receptors triggered by different FPR2 agonists.

Lipoxins, resolvins and protectins: new leads for the treatment of asthma

BACKGROUND

The pathobiology of asthma is characterized by the production of pro-inflammatory eicosanoids that play important roles in regulating airway responses. Recognition of the biosynthetic pathways and sites of action for 5-lipoxygenase-derived leukotrienes has led to the successful development of two different classes of asthma therapeutics.

OBJECTIVES

In this review, we describe structurally distinct lipid mediators derived from arachidonic acid and ω-3 fatty acids that have anti-inflammatory and pro-resolving actions. These counter-regulatory lipid mediators are generated in the airway during asthma and defects in their production are associated with disease severity.

CONCLUSION

These natural small molecules are rapidly inactivated, but serve as rationale templates for the design of stable analogues with protective actions that could serve as new therapeutic leads for asthma.

Aspirin and immune system

The time-tested gradual exploration of aspirin's diverse pharmacological properties has made it the most reliable therapeutic agent worldwide. In addition to its well-argued anti-inflammatory effects, many new and exciting data have emerged regarding the role of aspirin in cells of the immune system and certain immunopathological states. For instance, aspirin induces tolerogenic activity in dendritic cells and determines the fate of naive T cells to regulatory phenotypes, which suggests its immunoregulatory potential in relevance to immune tolerance. It also displays some intriguing traits to modulate the innate and adaptive immune responses. In this article, the immunomodulatory relation of aspirin to different immune cells, such as neutrophils, macrophages, dendritic cells (DCs), natural killer (NK) cells, and the T and B lymphocytes has been highlighted. Moreover, the clinical prospects of aspirin in terms of autoimmunity, allograft rejection and immune tolerance have also been outlined.

Tumor necrosis factor-related genes and colon and rectal cancer

Tumor necrosis factor-α (TNF) is a promoter of inflammation. Genes in the TNF pathway include tumor necrosis factor receptor superfamily member 1A (TNFRSF1A), TNF receptor-associated factor 2 (TRAF2), mitogen activated protein kinase 8 (MAPK8), 14 (MAPK14), and mitogen activated protein kinase kinase kinase 7 (MAP3K7), nuclear factor of activated-T-5 (NFAT5) cells and NFAT activated protein with ITAM motif 1 ﹛NFAM1). Data from population-based studies of colon cancer (cases=1,555; controls=1,956) and rectal cancer (cases=754; controls=959) were used. We observed that MAP3K7 rs13208824 was associated with reduced colon cancer risk (OR 0.83, 95% CI 0.71, 0.98 dominant model), TNF rs1800630 was associated with an increased colon cancer risk (OR 1.19 95% CI 1.03, 1.38 for CA/AAvsCC), and TNFRSF1A rs4149570 was associated with reduced risk (OR 0.79 95% CI 0.64, 0.96 TTvsGG). For rectal cancer MAPK8 rs10508901 was associated with increased risk (OR 1.45 95% CI 1.05, 1.99 AA vs CC/CA; NFAT5 (rs12447326 and rs16959025) was associated with a 40% reduced risk for the recessive model. Aspirin/NSAID interacted with MAP3K7 (colon cancer) and with MAPK14, NFAT5, and TRAF2 (rectal cancer); smoking cigarettes interacted with NFAM1 and NFAT2 (colon cancer) and MAPK8, NFAT5, and TNFRSF1A (rectal cancer); BMI interacted with NFAM1 and NFAT5 (colon cancer) and with MAPK8 and TNFRSF1A (rectal cancer). A genotype summary score showed a threefold increased risk of dying with higher mutational load. Although few independent associations were detected, aspirin/NSAID, cigarette smoking, and BMI influenced genes in this pathway. These data suggest pathways through which TNF-signaling operates.

The SOCS2 ubiquitin ligase complex regulates growth hormone receptor levels

Growth Hormone is essential for the regulation of growth and the homeostatic control of intermediary metabolism. GH actions are mediated by the Growth Hormone Receptor; a member of the cytokine receptor super family that signals chiefly through the JAK2/STAT5 pathway. Target tissue responsiveness to GH is under regulatory control to avoid excessive and off-target effects upon GHR activation. The suppressor of cytokine signalling 2 (SOCS) is a key regulator of GHR sensitivity. This is clearly shown in mice where the SOCS2 gene has been inactivated, which show 30–40% increase in body length, a phenotype that is dependent on endogenous GH secretion. SOCS2 is a GH-stimulated, STAT5b-regulated gene that acts in a negative feedback loop to downregulate GHR signalling. Since the biochemical basis for these actions is poorly understood, we studied the molecular function of SOCS2. We demonstrated that SOCS2 is part of a multimeric complex with intrinsic ubiquitin ligase activity. Mutational analysis shows that the interaction with Elongin B/C controls SOCS2 protein turnover and affects its molecular activity. Increased GHR levels were observed in livers from SOCS2^−/− mice and in the absence of SOCS2 in in vitro experiments. We showed that SOCS2 regulates cellular GHR levels through direct ubiquitination and in a proteasomally dependent manner. We also confirmed the importance of the SOCS-box for the proper function of SOCS2. Finally, we identified two phosphotyrosine residues in the GHR to be responsible for the interaction with SOCS2, but only Y487 to account for the effects of SOCS2. The demonstration that SOCS2 is an ubiquitin ligase for the GHR unveils the molecular basis for its physiological actions.

ShRNA-mediated silencing of the TRAF6 gene inhibits LPS/TLR4 signaling in vitro

AIM: To investigate the impact of small hairpin RNA (shRNA)-mediated silencing of the tumor necrosis factor receptor-associated factor 6 (TRAF6) gene on the lipopolysaccharide (LPS)/toll-like receptor (TLR) 4 signaling pathway in vitro.

METHODS: ShRNA sequences targeting the TRAF6 gene were designed, synthesized and used to construct eukaryotic expression plasmids. After transfection of the recombinant plasmids into RAW264.7 cells, cell proliferation was measured by methyl thiazolyl tetrazolium (MTT) assay. Inflammatory cellular models were established by LPS stimulation. Levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and transforming growth factor-β1 (TGF-β1) in the supernatants, mRNA expression of TRAF6, interleukin-6 (IL-6) and cyclooxygenase-2 (COX-2), protein expression of TRAF6, and translocation of NF-κB were assayed by ELISA, real-time quantitative PCR and Western blot, respectively.

RESULTS: The mRNA and protein expression of TRAF6 was lower in cells transfected with TRAF6-shRNA1 or TRAF6-shRNA2 (79.17% and 68.74%, respectively) compared to other groups. Therefore, cells transfected with pGCsi-TRAF6-shRNA1 or 2 were used for subsequent experiments. TRAF6 knockdown significantly inhibited the proliferation of RAW264.7 cells within 72 h after transfection, reduced the production of pro-inflammatory cytokines and mediators including TNF-α, IL-1β, IL-6 and COX-2, and inhibited NF-κB nuclear translocation. Moreover, TRAF6 knockdown could suppress the release of TGF-β1 at the protein level.

CONCLUSION: TRAF6 knockdown can, to some extent, inhibit early inflammatory response stimulated by LPS. TRAF6 may become a potential therapeutic target for many inflammation-related diseases.

Suppressor of cytokine signaling 2 is a feedback inhibitor of TLR-induced activation in human monocyte-derived dendritic cells

Dendritic cells (DCs) are key players in initiating and directing the immune response. Therefore, their activation state and functional differentiation need to be tightly controlled. The activating stimuli and their signaling networks have long been an area of focus in DC research. Recent investigations have also shed light on the mechanisms of counterregulation and fine-tuning of DC functions. One class of proteins involved in these processes is the family of suppressors of cytokine signaling (SOCS), whose members were originally described as feedback inhibitors of cytokine-induced JAK/STAT signaling. Essential roles in DC function have been assigned to SOCS1 and SOCS3. In this article, we show that SOCS2 also is involved in DC regulation. In human and in murine DCs, SOCS2 is a highly TLR-responsive gene, which is expressed in a time-delayed fashion beginning 8 h after TLR ligation. Functionally, silencing of SOCS2 in DCs results in hyperphosphorylation of STAT3 at later time points. As a consequence, SOCS2-deficient DCs secrete increased amounts of the cytokines IL-1β and IL-10, both being transcriptional targets of STAT3. We propose a model in which SOCS2 acts as a negative regulator of TLR-induced DC activation. The delayed expression of SOCS2 provides a mechanism of late-phase counterregulation and limitation of inflammation-driving DC activity.

High pancreatic n-3 fatty acids prevent STZ-induced diabetes in fat-1 mice: inflammatory pathway inhibition

OBJECTIVE

Because of confounding factors, the effects of dietary n-3 polyunsaturated fatty acids (PUFA) on type 1 diabetes remain to be clarified. We therefore evaluated whether fat-1 transgenic mice, a well-controlled experimental model endogenously synthesizing n-3 PUFA, were protected against streptozotocin (STZ)-induced diabetes. We then aimed to elucidate the in vivo response at the pancreatic level.

RESEARCH DESIGN AND METHODS

β-Cell destruction was produced by multiple low-doses STZ (MLD-STZ). Blood glucose level, plasma insulin level, and plasma lipid analysis were then performed. Pancreatic mRNA expression of cytokines, the monocyte chemoattractant protein, and GLUT2 were evaluated as well as pancreas nuclear factor (NF)-κB p65 and inhibitor of κB (IκB) protein expression. Insulin and cleaved caspase-3 immunostaining and lipidomic analysis were performed in the pancreas.

RESULTS

STZ-induced fat-1 mice did not develop hyperglycemia compared with wild-type mice, and β-cell destruction was prevented as evidenced by lack of histological pancreatic damage or reduced insulin level. The prevention of β-cell destruction was associated with no proinflammatory cytokine induction (tumor necrosis factor-α, interleukin-1β, inducible nitric oxide synthase) in the pancreas, a decreased NF-κB, and increased IκB pancreatic protein expression. In the fat-1-treated mice, proinflammatory arachidonic-derived mediators as prostaglandin E₂ and 12-hydroxyeicosatetraenoic acid were decreased and the anti-inflammatory lipoxin A₄ was detected. Moreover, the 18-hydroxyeicosapentaenoic acid, precursor of the anti-inflammatory resolvin E1, was highly increased.

CONCLUSIONS

Collectively, these findings indicate that fat-1 mice were protected against MLD-STZ-induced diabetes and pointed out for the first time in vivo the beneficial effects of n-3 PUFA at the pancreatic level, on each step of the development of the pathology-inflammation, β-cell damage-through cytokine response and lipid mediator production.

Effect of lipoxin A₄ on IL-1β production of monocytes and its possible mechanism in severe preeclampsia

This study examined in vitro effect of lipoxin A(4) (LXA(4)) on interleukin-1β (IL-1β) production of monocytes and its possible mechanism in severe preeclampsia (PE). Peripheral venous blood was drawn from 15 patients with severe preeclampsia (PE group) and 20 normal pregnant women (control group) to prepare monocytes which were then treated with LXA(4) at different concentrations of 0, 10, 100 nmol/L respectively. IL-1β level in the supernatant of monocytes was detected by enzyme linked immunoassay. The [Ca(2+)](i) of monocytes was measured by laser scanning confocal microscopy. The results showed that the IL-1β level and the [Ca(2+)](i) of monocytes in the PE group were significantly higher than those in the control group. LXA(4) significantly decreased the generation of IL-1β in a dose-dependent manner in the PE group. After treatment with 100-nmol/L LXA(4), in the PE group, the [Ca(2+)](i) concentration of monocytes was significantly reduced. It was concluded that LXA(4) may inhibit the IL-1β production of monocytes from severe preeclampsia women by inhibiting extracellular calcium influx.

Lipoxin A4 impairment of apoptotic signaling in macrophages: implication of the PI3K/Akt and the ERK/Nrf-2 defense pathways

Lipoxin A(4) (LXA(4)) is an endogenous lipid mediator that requires transcellular metabolic traffic for its synthesis. The targets of LXA(4) on neutrophils are well described, contributing to attenuation of inflammation. However, effects of lipoxins on macrophage are less known, particularly the action of LXA(4) on the regulation of apoptosis of these cells. Our data show that pretreatment of human or murine macrophages with LXA(4) at the concentrations prevailing in the course of resolution of inflammation (nanomolar range) significantly inhibits the apoptosis induced by staurosporine, etoposide and S-nitrosoglutathione or by more pathophysiological stimuli, such as LPS/IFNgamma challenge. The release of mitochondrial mediators of apoptosis and the activation of caspases was abrogated in the presence of LXA(4). In addition to this, the synthesis of reactive oxygen species induced by staurosporine was attenuated and antiapoptotic proteins of the Bcl-2 family accumulated in the presence of lipoxin. Analysis of the targets of LXA(4) identified an early activation of the PI3K/Akt and ERK/Nrf-2 pathways, which was required for the observation of the antiapoptotic effects of LXA(4). These data suggest that the LXA(4), released after the recruitment of neutrophils to sites of inflammation, exerts a protective effect on macrophage viability that might contribute to a better resolution of inflammation.

Suppressor of cytokine signaling 2 regulates IL-15-primed human NK cell function via control of phosphorylated Pyk2

NK cells are capable of killing virus-infected or tumor cells and producing IFN-gamma. Resting NK cells, however, have only minimal cytolytic activity and secrete a low level of IFN-gamma. The cytokine IL-15 can promote the expression of effector functions by resting NK cells. In this study, we demonstrate that suppressor of cytokine signaling 2 (SOCS2) has a novel role in IL-15-primed human NK cell function. SOCS2 expression was upregulated in NK cells following stimulation with IL-15. During IL-15-mediated NK cell priming, SOCS2 interacted with phosphorylated proline-rich tyrosine kinase 2 (Pyk2) at tyrosine 402 (p-Pyk2(Tyr402)) and induced the proteasome-mediated degradation of p-Pyk2(Tyr402) via ubiquitination. Knockdown of SOCS2 resulted in the accumulation of p-Pyk2(Tyr402) and blocked NK cell effector functions. In addition, NK cell cytolytic activity and IFN-gamma production were inhibited by overexpression of the wild-type of Pyk2 but not by the overexpression of tyrosine 402 mutant of Pyk2. These results suggest that SOCS2 regulates human NK cell effector functions via control of phosphorylated Pyk2 depending on IL-15 existence.

Proteasomal Degradation of Indoleamine 2,3-Dioxygenase in CD8 Dendritic Cells is Mediated by Suppressor of Cytokine Signaling 3 (SOCS3)

Indoleamine 2,3-dioxygenase (IDO) catalyzes the initial and rate-limiting step of tryptophan catabolism in a specific pathway, resulting in a series of extracellular messengers collectively known as kynurenines. IDO has been recognized as an authentic regulator of immunity not only in mammalian pregnancy, but also in infection, autoimmunity, inflammation, allergy, transplantation, and neoplasia. Its suppressive effects are mostly mediated by dendritic cells (DCs) and involve tryptophan deprivation and/or production of kynurenines, which act on IDO-negative DCs as well as CD4⁺ and CD8⁺ T cells. We have found that mouse IDO contains two tyrosine residues within two distinct putative immunoreceptor tyrosine-based inhibitory motifs, VPY₁₁₅CEL and LLY₂₅₃EGV. We have also found that Suppressor of Cytokine Signaling 3 (SOCS3)—known to interact with phosphotyrosine-containing peptides and be selectively induced by interleukin 6 (IL-6)—binds mouse IDO, recruits the ECS (Elongin-Cullin-SOCS) E3 ligase, and targets the IDO/SOCS3 complex for proteasomal degradation. This event underlies the ability of IL-6 to convert otherwise tolerogenic, IDO-competent DCs into immunogenic cells. Thus onset of immunity in response to antigen within an early inflammatory context demands that IDO be degraded in tolerogenic DCs. These studies support the finding that IDO is regulated by proteasomal degradation in response to immunogenic and inflammatory stimuli.

Therapeutic anti-inflammatory potential of formyl-peptide receptor agonists

The need for novel anti-inflammatory drugs justifies the search for innovative targets that could satisfy this goal. For quite some time now, we have proposed the study of endogenous anti-inflammation as a distinctive approach to the discovery of new drugs. This approach requires development of new compounds that activate specific receptor targets to downregulate the cellular and tissue pathways operative in the host during inflammation. Here we dwell on a family of G-protein coupled receptors (GPCR) termed FPRs, acronym for formyl-peptide receptors. With three and seven members in man and mouse, respectively, these receptors harness many biological functions, spanning odour perception and hair growth, to the control of multiple facets (pain; cell migration; oxidative burst; xenobiotic engulfment) of the inflammatory reaction. We focus on FPR biology with particular attention to molecules able to produce pharmacological effects by interacting with these GPCRs, describing endogenous agonists of FPRs and, more relevantly, the current development of synthetic agonists. Besides being potential leads for the development of the anti-inflammatory therapeutics of the future, these compounds could also help clarify the properties and roles that each FPR might play in the complex network of pathways that is inflammation. We conclude that FPR2 agonists could be valid warhorses for defining a novel philosophy for anti-inflammatory drug discovery programmes: mimicking - with new compounds - the way our body disposes of inflammation could be a viable approach to regulate aberrant inflammatory responses as in the case of several chronic rheumatic and cardiovascular pathologies.

Modulation of dendritic cell responses by parasites: a common strategy to survive

Parasitic infections are one of the most important causes of morbidity and mortality in our planet and the immune responses triggered by these organisms are critical to determine their outcome. Dendritic cells are key elements for the development of immunity against parasites; they control the responses required to eliminate these pathogens while maintaining host homeostasis. However, there is evidence showing that parasites can influence and regulate dendritic cell function in order to promote a more permissive environment for their survival. In this review we will focus on the strategies protozoan and helminth parasites have developed to interfere with dendritic cell activities as well as in the possible mechanisms involved.

Mice with a selective impairment of IFN-gamma signaling in macrophage lineage cells demonstrate the critical role of IFN-gamma-activated macrophages for the control of protozoan parasitic infections in vivo

IFN-gamma has long been recognized as a cytokine with potent and varied effects in the immune response. Although its effects on specific cell types have been well studied in vitro, its in vivo effects are less clearly understood because of its diverse actions on many different cell types. Although control of multiple protozoan parasites is thought to depend critically on the direct action of IFN-gamma on macrophages, this premise has never been directly proven in vivo. To more directly examine the effects of IFN-gamma on cells of the macrophage lineage in vivo, we generated mice called the "macrophages insensitive to IFN-gamma" (MIIG) mice, which express a dominant negative mutant IFN-gamma receptor in CD68+ cells: monocytes, macrophages, dendritic cells, and mast cells. Macrophage lineage cells and mast cells from these mice are unable to respond to IFN-gamma, whereas other cells are able to produce and respond to this cytokine normally. When challenged in vitro, macrophages from MIIG mice were unable produce NO or kill Trypanosoma cruzi or Leishmania major after priming with IFN-gamma. Furthermore, MIIG mice demonstrated impaired parasite control and heightened mortality after T. cruzi, L. major, and Toxoplasma gondii infection, despite an appropriate IFN-gamma response. In contrast, MIIG mice displayed normal control of lymphocytic choriomeningitis virus, despite persistent insensitivity of macrophages to IFN-gamma. Thus, the MIIG mouse formally demonstrates for the first time in vivo, the specific importance of direct, IFN-gamma mediated activation of macrophages for controlling infection with multiple protozoan parasites.

Suppressors of cytokine signaling (SOCS) in T cell differentiation, maturation, and function

Cytokines are key modulators of T cell biology, but their influence can be attenuated by suppressors of cytokine signaling (SOCS), a family of proteins consisting of eight members, SOCS1-7 and CIS. SOCS proteins regulate cytokine signals that control the polarization of CD4(+) T cells into Th1, Th2, Th17, and T regulatory cell lineages, the maturation of CD8(+) T cells from naïve to "stem-cell memory" (Tscm), central memory (Tcm), and effector memory (Tem) states, and the activation of these lymphocytes. Understanding how SOCS family members regulate T cell maturation, differentiation, and function might prove critical in improving adoptive immunotherapy for cancer and therapies aimed at treating autoimmune and infectious diseases.

Lipoxins: resolutionary road

The resolution of inflammation is an active process controlled by endogenous mediators with selective actions on neutrophils and monocytes. The initial phase of the acute inflammatory response is characterized by the production of pro-inflammatory mediators followed by a second phase in which lipid mediators with pro-resolution activities may be generated. The identification of these mediators has provided evidence for the dynamic regulation of the resolution of inflammation. Among these endogenous local mediators of resolution, lipoxins (LXs), lipid mediators typically formed during cell-cell interaction, were the first to be recognized. More recently, families of endogenous chemical mediators, termed resolvins and protectins, were discovered. LXs and aspirin-triggered LXs are considered to act as 'braking signals' in inflammation, limiting the trafficking of leukocytes to the inflammatory site. LXs are actively involved in the resolution of inflammation stimulating non-phlogistic phagocytosis of apoptotic cells by macrophages. Furthermore, LXs have emerged as potential anti-fibrotic mediators that may influence pro-fibrotic cytokines and matrix-associated gene expression in response to growth factors. Here, we provide a review and an update of the biosynthesis, metabolism and bioactions of LXs and LX analogues, and the recent studies on their therapeutic potential as promoters of resolution and fibro-suppressants.

SOCS2 influences LPS induced human monocyte-derived dendritic cell maturation

Dendritic cells (DCs) are highly specific antigen presenting cells, which link innate and adaptive immune responses and participate in protecting hosts from invading pathogens. DCs can be generated in vitro by culturing human monocytes with GM-CSF and IL-4 followed by LPS induced DC maturation. We set out to study the suppressor of cytokine signaling (SOCS) proteins during maturation and activation of human monocyte-derived DCs from peripheral blood in vitro. We found that the expression of SOCS2 mRNA and protein is dramatically up-regulated during DC maturation. Silencing of SOCS2 using siRNA, inhibited DC maturation as evidenced by a decreased expression of maturation markers such as CD83, co-stimulatory molecules CD40, CD86 and HLA-DR. Furthermore, silencing of SOCS2 decreased LPS induced activation of MAP kinases (SAKP/JNK, p38, ERK), IRF3, decreased the translocation of the NF-kappaB transcription factor and reduced downstream gene mRNA expression. These results suggest a role for SOCS2 in the MyD88-dependent and -independent TLR4 signaling pathways. In conclusion, our results demonstrate that SOCS2 is required for appropriate TLR4 signaling in maturating human DCs via both the MyD88-dependent and -independent signaling pathway.

12/15-lipoxygenase counteracts inflammation and tissue damage in arthritis

Eicosanoids are essential mediators of the inflammatory response and contribute both to the initiation and the resolution of inflammation. Leukocyte-type 12/15-lipoxygenase (12/15-LO) represents a major enzyme involved in the generation of a subclass of eicosanoids, including the anti-inflammatory lipoxin A(4) (LXA(4)). Nevertheless, the impact of 12/15-LO on chronic inflammatory diseases such as arthritis has remained elusive. By using two experimental models of arthritis, the K/BxN serum-transfer and a TNF transgenic mouse model, we show that deletion of 12/15-LO leads to uncontrolled inflammation and tissue damage. Consistent with these findings, 12/15-LO-deficient mice showed enhanced inflammatory gene expression and decreased levels of LXA(4) within their inflamed synovia. In isolated macrophages, the addition of 12/15-LO-derived eicosanoids blocked both phosphorylation of p38MAPK and expression of a subset of proinflammatory genes. Conversely, 12/15-LO-deficient macrophages displayed significantly reduced levels of LXA(4), which correlated with increased activation of p38MAPK and an enhanced inflammatory gene expression after stimulation with TNF-alpha. Taken together, these results support an anti-inflammatory and tissue-protective role of 12/15-LO and its products during chronic inflammatory disorders such as arthritis.

International Union of Basic and Clinical Pharmacology. LXXIII. Nomenclature for the formyl peptide receptor (FPR) family

Formyl peptide receptors (FPRs) are a small group of seven-transmembrane domain, G protein-coupled receptors that are expressed mainly by mammalian phagocytic leukocytes and are known to be important in host defense and inflammation. The three human FPRs (FPR1, FPR2/ALX, and FPR3) share significant sequence homology and are encoded by clustered genes. Collectively, these receptors bind an extraordinarily numerous and structurally diverse group of agonistic ligands, including N-formyl and nonformyl peptides of different composition, that chemoattract and activate phagocytes. N-formyl peptides, which are encoded in nature only by bacterial and mitochondrial genes and result from obligatory initiation of bacterial and mitochondrial protein synthesis with N-formylmethionine, is the only ligand class common to all three human receptors. Surprisingly, the endogenous anti-inflammatory peptide annexin 1 and its N-terminal fragments also bind human FPR1 and FPR2/ALX, and the anti-inflammatory eicosanoid lipoxin A4 is an agonist at FPR2/ALX. In comparison, fewer agonists have been identified for FPR3, the third member in this receptor family. Structural and functional studies of the FPRs have produced important information for understanding the general pharmacological principles governing all leukocyte chemoattractant receptors. This article aims to provide an overview of the discovery and pharmacological characterization of FPRs, to introduce an International Union of Basic and Clinical Pharmacology (IUPHAR)-recommended nomenclature, and to discuss unmet challenges, including the mechanisms used by these receptors to bind diverse ligands and mediate different biological functions.

The effect of Lipoxin A4 on the interaction between macrophage and osteoblast: possible role in the treatment of aseptic loosening

Background

Aseptic loosening (AL) is the main problem of total joints replacement (TJR) by the implantation of permanently prosthetic components. In vitro and in vivo studies have clearly demonstrated that wear debris and its byproducts could trigger inflammation in the peri-implant tissue. Lipoxins (LXs) are endogenous eicosanoids synthesized locally from arachidonate acid (AA) at sites of inflammation and mediate pro-resolving activity. A number of studies have demonstrated the effect of LXA₄ to counteract inflammation in different cell and animal models, but till now, no relative report about the role of LXs in progress or prevention of AL.

Methods

Murine RAW264.7 macrophage cell line and MC3T3-E1 osteoblasts (OB) cell line were purchased. Co-cultured model of these two cell lines was established. To explore the effect of exogenous Lipoxin A₄ (LXA₄) on polymethylmethacrylate (PMMA) induced inflammation, pro-inflammatory cytokines including TNF-α, IL-1β, PGE₂ and GM-CSF were measured by ELISA kits and bone resorption was quantified by measuring calcium release from 5-day-old mice calvaria in vitro. To determine further the endogenous effect of LXA₄, cells were co-cultured and with or without 15-lipoxygease (15-LO) blocking by 15-LO siRNA. Both real-time PCR and western blotting were applied to confirm the inhibitory efficiency of 15-LO by siRNA.

Results

0.1 mg/ml, 0.5 mg/ml and 1.0 mg/ml PMMA showed a time-dependent manner to trigger production of all the pro-inflammatory cytokines studied. Exogenous 0–100 nM LXA₄ presented an inhibitory effect on both generation of above cytokines and PMMA stimulated calvarial bone resorption with a dose-dependent manner. LXA₄ in supernatant from neither rest macrophages nor macrophages cultured alone exposing to PMMA was detectable. In co-cultured cells challenged by PMMA, LXA₄ was increased significantly, while, this enhance could be partly inhibited by 15-LO siRNA. When LXA₄ generation was blocked with 15-LO siRNA, the PMMA induced pro-inflammatory cytokines were elevated and bone resorption was accelerated.

Conclusion

In the present study, we demonstrated that LXA₄ had a favorable inhibitory effect on PMMA-induced inflammation in a macrophage and OB co-culture system.

Synthesis of lipoxin A4 by 5-lipoxygenase mediates PPARgamma-dependent, neuroprotective effects of rosiglitazone in experimental stroke

Peroxisome proliferator-activated receptors gamma (PPARgamma) are nuclear receptors with essential roles as transcriptional regulators of glucose and lipid homeostasis. PPARgamma are also potent anti-inflammatory receptors, a property that contributes to the neuroprotective effects of PPARgamma agonists in experimental stroke. The mechanism of these beneficial actions, however, is not fully elucidated. Therefore, we have explored further the actions of the PPARgamma agonist rosiglitazone in experimental stroke induced by permanent middle cerebral artery occlusion (MCAO) in rodents. Rosiglitazone induced brain 5-lipoxygenase (5-LO) expression in ischemic rat brain, concomitantly with neuroprotection. Rosiglitazone also increased cerebral lipoxin A(4) (LXA(4)) levels and inhibited MCAO-induced production of leukotriene B4 (LTB(4)). Furthermore, pharmacological inhibition and/or genetic deletion of 5-LO inhibited rosiglitazone-induced neuroprotection and downregulation of inflammatory gene expression, LXA(4) synthesis and PPARgamma transcriptional activity in rodents. Finally, LXA(4) caused neuroprotection, which was partly inhibited by the PPARgamma antagonist T0070907, and increased PPARgamma transcriptional activity in isolated nuclei, showing for the first time that LXA(4) has PPARgamma agonistic actions. Altogether, our data illustrate that some effects of rosiglitazone are attributable to de novo synthesis of 5-LO, able to induce a switch from the synthesis of proinflammatory LTB(4) to the synthesis of the proresolving LXA(4). Our study suggests novel lines of study such as the interest of lipoxin-like anti-inflammatory drugs or the use of these molecules as prognostic and/or diagnostic markers for pathologies in which inflammation is involved, such as stroke.

Lipoxins as an immune-escape mechanism

Here, we discuss the mechanisms of repression of signaling pathways that are triggered by Lipoxin (LX) and are responsible for control of pro-inflammatory response during chronic phase of Toxoplasma gondii infection. We also discuss this mechanism from the perspective of the pathogen, which pirates the host's lipoxygenase machinery to its own advantage as a probable immune-escape mechanism. Pro-inflammatory mediators such as IL-12, IFN-gamma and TNF are essential in controlling parasite growth during T. gondii infection. However, it is clear that exacerbated production of these cytokines results in host tissue damage. LX, an anti-inflammatory eicosanoid, plays an important role in regulation of immune response to T. gondii.

SOCS3 drives proteasomal degradation of indoleamine 2,3-dioxygenase (IDO) and antagonizes IDO-dependent tolerogenesis

Despite their common ability to activate intracellular signaling through CD80/CD86 molecules, cytotoxic T lymphocyte antigen 4 (CTLA-4)-Ig and CD28-Ig bias the downstream response in opposite directions, the latter promoting immunity, and CTLA-4-Ig tolerance, in dendritic cells (DCs) with opposite but flexible programs of antigen presentation. Nevertheless, in the absence of suppressor of cytokine signaling 3 (SOCS3), CD28-Ig-and the associated, dominant IL-6 response-become immunosuppressive and mimic the effect of CTLA-4-Ig, including a high functional expression of the tolerogenic enzyme indoleamine 2,3-dioxygenase (IDO). Here we show that forced SOCS3 expression antagonized CTLA-4-Ig activity in a proteasome-dependent fashion. Unrecognized by previous studies, IDO appeared to possess two tyrosine residues within two distinct putative immunoreceptor tyrosine-based inhibitory motifs, VPY(115)CEL and LLY(253)EGV. We found that SOCS3-known to interact with phosphotyrosine-containing peptides and be selectively induced by CD28-Ig/IL-6-would bind IDO and target the IDO/SOCS3 complex for ubiquitination and subsequent proteasomal degradation. This event accounted for the ability of CD28-Ig and IL-6 to convert otherwise tolerogenic, IDO-competent DCs into immunogenic cells. Thus onset of immunity in response to antigen within an early inflammatory context requires that IDO be degraded in tolerogenic DCs. In addition to identifying SOCS3 as a candidate signature for mouse DC subsets programmed to direct immunity, this study demonstrates that IDO undergoes regulatory proteolysis in response to immunogenic stimuli.

Uncontrolled airway inflammation in lung disease represents a defect in counter-regulatory signaling

Counter-regulatory lipid mediators are generated during airway inflammation to promote resolution. Defects in the production of these lipid mediators have now been associated with several diseases of persistent airway inflammation. Lipoxins are the lead members of this class of anti-inflammatory and proresolving chemical mediators. Recently, several new families of fatty acid-derived counter-regulatory mediators have been discovered, including the resolvins and protectins. Diminished formation of these endogenous protective signals would interrupt the natural resolution of inflammation. Here, we review how rapidly emerging information on lipoxins, resolvins and protectins is providing new insights into the pathophysiology of chronic airway inflammation in several common illnesses, including asthma.

The potential role of suppressors of cytokine signaling in the attenuation of inflammatory reaction and alveolar bone loss associated with apical periodontitis

Inflammatory cytokines contribute to periapical tissue destruction. Their activity is potentially regulated by suppressors of cytokine signaling (SOCS), which downregulate signal transduction as part of an inhibitory feedback loop. We investigated the expression of the cytokines tumor necrosis factor alpha (TNF-alpha); interleukin (IL)-10 and RANKL; and SOCS-1, -2, and -3 by real-time polymerase chain reaction in 57 periapical granulomas and 38 healthy periapical tissues. Periapical granulomas exhibited significantly higher SOCS-1, -2, and -3, TNF-alpha, IL-10, and RANKL messenger RNA levels when compared with healthy controls. Significant positive correlations were found between SOCS1 and IL-10 and between SOCS3 and IL-10. Significant inverse correlations were observed between SOCS1 and TNF-alpha, SOCS1 and RANKL, and SOCS3 and TNF-alpha. Increased SOCS-1, -2, and -3 messenger RNA levels in periapical granulomas may be related to the downregulation of inflammatory cytokines in these lesions; therefore, SOCS molecules may play a role in the dynamics of periapical granulomas development.

Role of hypercytokinemia in NF-kappaB p50-deficient mice after H5N1 influenza A virus infection

During H5N1 influenza virus infection, proinflammatory cytokines are markedly elevated in the lungs of infected hosts. The significance of this dysregulated cytokine response in H5N1-mediated pathogenesis remains to be determined. To investigate the influence of hypercytokinemia, or "cytokine storm," a transgenic mouse technology was used. The classical NF-kappaB pathway regulates the induction of most proinflammatory cytokines. Deletion of the p50 subunit leads to a markedly reduced expression of the NF-kappaB-regulated cytokines and chemokines. Here we show that H5N1 influenza virus infection of this transgenic mouse model resulted in a lack of hypercytokinemia but not in altered pathogenesis.

The immunobiology of the innate response to Toxoplasma gondii

Toxoplasma gondii is a unique intracellular parasite. It can infect a variety of cells in virtually all warm-blooded animals. It has a worldwide distribution and, overall, around one-third of people are seropositive for the parasite, with essentially the entire human population being at risk of infection. For most people, T. gondii causes asymptomatic infection but the parasite can cause serious disease in the immunocompromised and, if contracted for the first time during pregnancy, can cause spontaneous abortion or congenital defects, which have a substantial emotional, social and economic impact. Toxoplasma gondii provokes one of the most potent innate, pro-inflammatory responses of all infectious disease agents. It is also a supreme manipulator of the immune response so that innate immunity to T. gondii is a delicate balance between the parasite and its host involving a coordinated series of cellular interactions involving enterocytes, neutrophils, dendritic cells, macrophages and natural killer cells. Underpinning these interactions is the regulation of complex molecular reactions involving Toll-like receptors, activation of signalling pathways, cytokine production and activation of anti-microbial effector mechanisms including generation of reactive nitrogen and oxygen intermediates.

SOCS regulation of the JAK/STAT signalling pathway

The suppressor of cytokine signalling (SOCS) proteins were, as their name suggests, first described as inhibitors of cytokine signalling. While their actions clearly now extend to other intracellular pathways, they remain key negative regulators of cytokine and growth factor signalling. In this review we focus on the mechanics of SOCS action and the complexities of the mouse models that have underpinned our current understanding of SOCS biology.