Divergent Mechanisms Utilized by SOCS3 to Mediate Interleukin-10 Inhibition of Tumor Necrosis Factor α and Nitric Oxide Production by Macrophages

Forskolin-mediated cAMP activation upregulates TNF-α expression despite NF-κB downregulation in LPS-treated Schwann cells

Although Schwann cells have been found to play a key role in inflammation and repair following nerve injury, the exact pathway is still unknown. To explore the mechanism by which Schwann cells exert their effects in the neuron microenvironment, we investigated two main inflammatory pathways: the NF-κB and cAMP pathways, and their downstream signaling molecules. In this study, lipopolysaccharide (LPS), a bacterial endotoxin, was used to activate the NF-κB pathway, and forskolin, a plant extract, was used to activate the cAMP pathway. The rat RT4-D6P2T Schwann cell line was treated with 0.1, 1, or 10 μg/mL of LPS, with or without 2 μM of forskolin, for 1, 3, 12, and 24 hours to determine the effects of elevated cAMP levels on LPS-treated cell viability. To investigate the effects of elevated cAMP levels on the expression of downstream signaling effector proteins, specifically NF-κB, TNF-α, AKAP95, and cyclin D3, as well as TNF-α secretion, RT4-D6P2T cells were incubated in the various treatment combinations for a 3-hour time period. Overall, results from the CellTiter-Glo viability assay revealed that forskolin increased viability in cells treated with smaller doses of LPS for 1 and 24 hours. For all time points, 10 μg/mL of LPS noticeably reduced viability regardless of forskolin treatment. Results from the Western blot analysis revealed that, at 10 μg/mL of LPS, forskolin upregulated the expression of TNF-α despite a downregulation of NF-κB, which was also accompanied by a decrease in TNF-α secretion. These results provide evidence that cAMP might regulate TNF-α expression through alternate pathways. Furthermore, although cAMP activation altered AKAP95 and cyclin D3 expression at different doses of LPS, there does not appear to be an association between the expression of AKAP95 or cyclin D3 and the expression of TNF-α. Exploring the possible interactions between cAMP, NF-κB, and other key inflammatory signaling pathways might reveal a potential therapeutic target for the treatment of nerve injury and inflammation.

IL-10 dependent adaptation allows macrophages to adjust inflammatory responses to TLR4 stimulation history

During an infection, innate immune cells must adjust nature and strength of their responses to changing pathogen abundances. To determine how stimulation of the pathogen sensing TLR4 shapes subsequent macrophage responses, we systematically varied priming and restimulation concentrations of its ligand KLA. We find that different priming strengths have very distinct effects at multiple stages of the signaling response, including receptor internalization, MAPK activation, cytokine and chemokine production, and nuclear translocation and chromatin association of NFκB and IκB members. In particular, restimulation-induced TNF-α production required KLA doses equal to or greater than those used for prior exposure, indicating that macrophages can detect and adaptively respond to changing TLR4 stimuli. Interestingly, while such adaptation was dependent on the anti-inflammatory cytokine IL-10, exogenous concentrations of IL-10 corresponding to those secreted after strong priming did not exert suppressive effects on TNF-α without such prior priming, confirming the critical role of TLR4 stimulation history.

Agent-based vs. equation-based multi-scale modeling for macrophage polarization

Macrophages show high plasticity and result in heterogenic subpopulations or polarized states identified by specific cellular markers. These immune cells are typically characterized as pro-inflammatory, or classically activated M1, and anti-inflammatory, or alternatively activated M2. However, a more precise definition places them along a spectrum of activation where they may exhibit a number of pro- or anti-inflammatory roles. To understand M1-M2 dynamics in the context of a localized response and explore the results of different mathematical modeling approaches based on the same biology, we utilized two different modeling techniques, ordinary differential equation (ODE) modeling and agent-based modeling (ABM), to simulate the spectrum of macrophage activation to general pro- and anti-inflammatory stimuli on an individual and multi-cell level. The ODE model includes two hallmark pro- and anti-inflammatory signaling pathways and the ABM incorporates similar M1-M2 dynamics but in a spatio-temporal platform. Both models link molecular signaling with cellular-level dynamics. We then performed simulations with various initial conditions to replicate different experimental setups. Similar results were observed in both models after tuning to a common calibrating experiment. Comparing the two models' results sheds light on the important features of each modeling approach. When more data is available these features can be considered when choosing techniques to best fit the needs of the modeler and application.

Less Severe Sepsis in Cecal Ligation and Puncture Models with and without Lipopolysaccharide in Mice with Conditional Ezh2-Deleted Macrophages (LysM-Cre System)

Despite a previous report on less inflammatory responses in mice with an absence of the enhancer of zeste homologue 2 (Ezh2), a histone lysine methyltransferase of epigenetic regulation, using a lipopolysaccharide (LPS) injection model, proteomic analysis and cecal ligation and puncture (CLP), a sepsis model that more resembles human conditions was devised. As such, analysis of cellular and secreted protein (proteome and secretome) after a single LPS activation and LPS tolerance in macrophages from Ezh2 null (Ezh2^flox/flox; LysM-Cre^cre/-) mice (Ezh2 null) and the littermate control mice (Ezh2^fl/fl; LysM-Cre^-/-) (Ezh2 control) compared with the unstimulated cells from each group indicated fewer activities in Ezh2 null macrophages, especially by the volcano plot analysis. Indeed, supernatant IL-1β and expression of genes in pro-inflammatory M1 macrophage polarization (IL-1β and iNOS), TNF-α, and NF-κB (a transcription factor) were lower in Ezh2 null macrophages compared with the control. In LPS tolerance, downregulated NF-κB compared with the control was also demonstrated in Ezh2 null cells. In CLP sepsis mice, those with CLP alone and CLP at 2 days after twice receiving LPS injection, representing sepsis and sepsis after endotoxemia, respectively, symptoms were less severe in Ezh2 null mice, as indicated by survival analysis and other biomarkers. However, the Ezh2 inhibitor improved survival only in CLP, but not LPS with CLP. In conclusion, an absence of Ezh2 in macrophages resulted in less severe sepsis, and the use of an Ezh2 inhibitor might be beneficial in sepsis.

The Regulatory Roles of Ezh2 in Response to Lipopolysaccharide (LPS) in Macrophages and Mice with Conditional Ezh2 Deletion with LysM-Cre System

The responses of macrophages to lipopolysaccharide (LPS) might determine the direction of clinical manifestations of sepsis, which is the immune response against severe infection. Meanwhile, the enhancer of zeste homologue 2 (Ezh2), a histone lysine methyltransferase of epigenetic regulation, might interfere with LPS response. Transcriptomic analysis on LPS-activated wild-type macrophages demonstrated an alteration of several epigenetic enzymes. Although the Ezh2-silencing macrophages (RAW264.7), using small interfering RNA (siRNA), indicated a non-different response to the control cells after a single LPS stimulation, the Ezh2-reducing cells demonstrated a less severe LPS tolerance, after two LPS stimulations, as determined by the higher supernatant TNF-α. With a single LPS stimulation, Ezh2 null (Ezh2flox/flox; LysM-Crecre/−) macrophages demonstrated lower supernatant TNF-α than Ezh2 control (Ezh2fl/fl; LysM-Cre−/−), perhaps due to an upregulation of Socs3, which is a suppressor of cytokine signaling 3, due to the loss of the Ezh2 gene. In LPS tolerance, Ezh2 null macrophages indicated higher supernatant TNF-α and IL-6 than the control, supporting an impact of the loss of the Ezh2 inhibitory gene. In parallel, Ezh2 null mice demonstrated lower serum TNF-α and IL-6 than the control mice after an LPS injection, indicating a less severe LPS-induced hyper-inflammation in Ezh2 null mice. On the other hand, there were similar serum cytokines after LPS tolerance and the non-reduction of serum cytokines after the second dose of LPS, indicating less severe LPS tolerance in Ezh2 null mice compared with control mice. In conclusion, an absence of Ezh2 in macrophages resulted in less severe LPS-induced inflammation, as indicated by low serum cytokines, with less severe LPS tolerance, as demonstrated by higher cytokine production, partly through the upregulated Socs3.

Organ-specific immune profiling of Leishmania donovani-infected hamsters

Visceral leishmaniasis (VL) is a neglected disease with a broad spectrum of clinical manifestations and involvement of visceral organs. Organ-specific immune response against the Leishmania donovani (Ld) complex is not yet understood due to the unavailability of an appropriate experimental model. In reference to our recent work on comparing the hamster model with VL patients, it is now possible to understand immune profiling in different visceral organs. This may offer an answer to varying parasite loads in different visceral organs in the same host. Herein, we analysed a panel of immune markers (Th-2/Th-1) in visceral organs of Ld-infected hamsters and quantified parasitic load in the same tissues using qPCR assay. In spleen, liver, bone marrow and lymph node (mesenteric) from Ld-infected hamsters, the parasite burden was quantified along with mRNA expression of a panel of Th-2 and Th-1 type immune markers, namely IL-10, IL-4, Arginase-I, GATA-3, SOCS-3, IL-12, IFN-γ, iNOS, T-bet and SOCS-5. A clear dichotomy was absent between Th-2 and Th-1 type immune markers and the major players of this immune response were IFN-γ, IL-10, T-bet, GATA-3, SOCS-5 and SOCS-3.

Impact of Plasticizer on the Intestinal Epithelial Integrity and Tissue-Repairing Ability within Cells in the Proximity of the Human Gut Microbiome

Toxicological research into the impact of plasticizer on different organs has been reported in the past few decades, while their effects on shifting the gut microbiota and immune cells homeostasis in zebrafish were only studied recently. However, studies on the impact of plasticizer on human gut microbiota are scarce. In this study, we co-incubated healthy human fecal microbiota with different concentrations of Di(2-ethylhexyl) phthalate (DEHP) and di-iso-nonyl phthalate (DINP), analyzed microbial composition by 16S rDNA sequencing, and compared the influence of their derived microbiomes on the human enterocyte (HT-29) and murine macrophage (RAW264.7) cell lines. Microbial diversity is reduced by DEHP treatment in a dose-dependent manner. DEHP treatment reduced the phyla Firmicutes/Bacteroidetes ratio, while DINP treatment promoted Proteobacteria. Expressions of tight/adherens junction genes in HT-29 and anti-inflammatory genes in RAW264.7 were down-regulated by plasticizer-co-incubated microbiota derived metabolites. Overall, it is observed that selected plasticizers at high dosages can induce compositional changes in human microbiota. Metabolites from such altered microbiota could affect the tight junction integrity of the intestinal epithelium and upset macrophage differentiation homeostasis in proximity. Chronic exposure to these plasticizers may promote risks of dysbiosis, leaky gut or the exacerbation of intestinal inflammation.

SOCS3-microtubule interaction via CLIP-170 and CLASP2 is critical for modulation of endothelial inflammation and lung injury

Proinflammatory cytokines such as IL-6 induce endothelial cell (EC) barrier disruption and trigger an inflammatory response in part by activating the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway. The protein suppressor of cytokine signaling-3 (SOCS3) is a negative regulator of JAK-STAT, but its role in modulation of lung EC barrier dysfunction caused by bacterial pathogens has not been investigated. Using human lung ECs and EC-specific SOCS3 knockout mice, we tested the hypothesis that SOCS3 confers microtubule (MT)-mediated protection against endothelial dysfunction. SOCS3 knockdown in cultured ECs or EC-specific SOCS3 knockout in mice resulted in exacerbated lung injury characterized by increased permeability and inflammation in response to IL-6 or heat-killed Staphylococcus aureus (HKSA). Ectopic expression of SOCS3 attenuated HKSA-induced EC dysfunction, and this effect required assembled MTs. SOCS3 was enriched in the MT fractions, and treatment with HKSA disrupted SOCS3-MT association. We discovered that-in addition to its known partners gp130 and JAK2-SOCS3 interacts with MT plus-end binding proteins CLIP-170 and CLASP2 via its N-terminal domain. The resulting SOCS3-CLIP-170/CLASP2 complex was essential for maximal SOCS3 anti-inflammatory effects. Both IL-6 and HKSA promoted MT disassembly and disrupted SOCS3 interaction with CLIP-170 and CLASP2. Moreover, knockdown of CLIP-170 or CLASP2 impaired SOCS3-JAK2 interaction and abolished the anti-inflammatory effects of SOCS3. Together, these findings demonstrate for the first time an interaction between SOCS3 and CLIP-170/CLASP2 and reveal that this interaction is essential to the protective effects of SOCS3 in lung endothelium.

SOCS Proteins Participate in the Regulation of Innate Immune Response Caused by Viruses

The host immune system has multiple innate immune receptors that can identify, distinguish and react to viral infections. In innate immune response, the host recognizes pathogen-associated molecular patterns (PAMP) in nucleic acids or viral proteins through pathogen recognition receptors (PRRs), especially toll-like receptors (TLRs) and induces immune cells or infected cells to produce type I Interferons (IFN-I) and pro-inflammatory cytokines, thus when the virus invades the host, innate immunity is the earliest immune mechanism. Besides, cytokine-mediated cell communication is necessary for the proper regulation of immune responses. Therefore, the appropriate activation of innate immunity is necessary for the normal life activities of cells. The suppressor of the cytokine signaling proteins (SOCS) family is one of the main regulators of the innate immune response induced by microbial pathogens. They mainly participate in the negative feedback regulation of cytokine signal transduction through Janus kinase signal transducer and transcriptional activator (JAK/STAT) and other signal pathways. Taken together, this paper reviews the SOCS proteins structures and the function of each domain, as well as the latest knowledge of the role of SOCS proteins in innate immune caused by viral infections and the mechanisms by which SOCS proteins assist viruses to escape host innate immunity. Finally, we discuss potential values of these proteins in future targeted therapies.

Suppressors of Cytokine Signaling (SOCS)1 and SOCS3 Proteins Are Mediators of Interleukin-10 Modulation of Inflammatory Responses Induced by Chlamydia muridarum and Its Major Outer Membrane Protein (MOMP) in Mouse J774 Macrophages

The immunopathology of chlamydial diseases is exacerbated by a broad-spectrum of inflammatory mediators, which we reported are inhibited by IL-10 in macrophages. However, the chlamydial protein moiety that induces the inflammatory mediators and the mechanisms by which IL-10 inhibits them are unknown. We hypothesized that Chlamydia major outer membrane protein (MOMP) mediates its disease pathogenesis, and the suppressor of cytokine signaling (SOCS)1 and SOCS3 proteins are mediators of the IL-10 inhibitory actions. Our hypothesis was tested by exposing mouse J774 macrophages to chlamydial stimulants (live Chlamydia muridarum and MOMP) with and without IL-10. MOMP significantly induced several inflammatory mediators (IL-6, IL-12p40, CCL5, CXCL10), which were dose-dependently inhibited by IL-10. Chlamydial stimulants induced the mRNA gene transcripts and protein expression of SOCS1 and SOCS3, with more SOCS3 expression. Notably, IL-10 reciprocally regulated their expression by reducing SOCS1 and increasing SOCS3. Specific inhibitions of MAPK pathways revealed that p38, JNK, and MEK1/2 are required for inducing inflammatory mediators as well as SOCS1 and SOCS3. Chlamydial stimulants triggered an M1 pro-inflammatory phenotype evidently by an enhanced nos2 (M1 marker) expression, which was skewed by IL-10 towards a more M2 anti-inflammatory phenotype by the increased expression of mrc1 and arg1 (M2 markers) and the reduced SOCS1/SOCS3 ratios. Neutralization of endogenously produced IL-10 augmented the secretion of inflammatory mediators, reduced SOCS3 expression, and skewed the chlamydial M1 to an M2 phenotype. Inhibition of proteasome degradation increased TNF but decreased IL-10, CCL5, and CXCL10 secretion by suppressing SOCS1 and SOCS3 expressions and dysregulating their STAT1 and STAT3 transcription factors. Our data show that SOCS1 and SOCS3 are regulators of IL-10 inhibitory actions, and underscore SOCS proteins as therapeutic targets for IL-10 control of inflammation for Chlamydia and other bacterial inflammatory diseases.

Functional characterization of IL-10 and its receptor subunits in a perciform fish, the mandarin fish, Siniperca chuatsi

Interleukin (IL)-10 is an immune-regulatory cytokine with multiple functions. In the current study, IL-10 and its two receptors, IL-10R1 and IL-10R2 were identified in mandarin fish, Siniperca chuatsi. The inhibitory effect of mandarin fish IL-10 was investigated on pro-inflammatory cytokine expression and the ligand-receptor relationship. This IL-10 possesses conserved cysteine residues, predicted α-helices and a typical IL-10 family signature motif, similar to its mammalian orthologue, and IL-10R1 harbours predicted JAK1 and STAT3 binding sites in the intracellular region. The fish IL-10 and IL-10R1 exhibit high expression levels in several immune-related organs/tissues, such as spleen, trunk kidney and head kidney, and IL-10R2 possesses a constitutive expression pattern. The expression of IL-10 shows significant increase in spleen from infectious spleen and kidney necrosis virus (ISKNV) infected mandarin fish, where the two receptors also exhibit different levels of induced expression. Mandarin fish IL-10 also exhibits significant response to the stimulation of LPS, PHA and PMA, with the two receptors exhibiting an interesting decrease in expression following the treatment of PMA. The pro-inflammatory cytokines, IL-6, IL-1β, IL-8, TNF-α, show diminished up-regulation in LPS-stimulated splenocytes pre-incubated with IL-10, indicating the anti-inflammatory roles of mandarin fish IL-10. In EPC cells transfected with different combinations of receptors, IL-10 can enhance the expression of suppressor of cytokine signalling 3 (SOCS3) only when IL-10R1 and IL-10R2 are both expressed, suggesting the participation of the two receptors in signal transduction of mandarin fish IL-10. Similar results are observed with the usage of chimeric receptors, IL-10R1/CRFB1 and IL-10R2/CRFB5. Overall, mandarin fish IL-10 shares conserved ligand-receptor system and the prototypical inhibitory activities on pro-inflammatory cytokine expression with mammalian IL-10, implying the evolutionary conservation of this cytokine.

IL-10/STAT3/SOCS3 Axis Is Involved in the Anti-inflammatory Effect of Benznidazole

Anti-parasitic treatment for Chagas disease mainly relies on benznidazole, which is virtually the only drug available in the market. Besides its anti-parasitic effects, benznidazole has anti-inflammatory properties. In this work we studied the mechanisms involved in the latter, demonstrating the participation of the IL-10/STAT3/SOCS3 pathway. To achieve this goal, the anti-inflammatory properties of benznidazole were studied using an in vitro model of cardiomyocyte primary culture stimulated with LPS. LPS increased both SOCS3 expression and STAT3 phosphorylation. The addition of benznidazole increased their expression even further. Specific inhibition of STAT3 precluded this effect, suggesting a role for STAT3 in the increase of SOCS3 expression induced by benznidazole. To assess the participation of SOCS3 in the anti-inflammatory effect of benznidazole, we accomplished specific knockdown of SOCS3 with siRNA. Silencing of SOCS3 in cardiomyocytes precluded the inhibitory effects of benznidazole on TNF-α, IL-6, iNOS expression and NO release. Moreover, in the absence of SOCS3, benznidazole could neither prevent IKK phosphorylation nor IκBα degradation, supporting the notion that SOCS3 is required for the benznidazole-mediated inhibition of the NF-κB pathway. Previously, we demonstrated that IL-10 increases the expression of SOCS3 in cultured cardiomyocytes. Here, we found that benznidazole shows a trend to increased IL-10 expression. To evaluate whether benznidazole increased SOCS3 in an IL-10-dependent manner, cardiomyocytes from IL-10 knockout mice were pre-treated with benznidazole and stimulated with LPS. Benznidazole neither inhibited NO release nor avoid IKK phosphorylation or IκBα degradation, showing that IL-10 is required for benznidazole-mediated inhibition of NF-κB. Moreover, exogenous addition of IL-10 to IL-10 knockout cardiomyocytes restored the inhibitory effect of benznidazole on NO release. The results reported herein show, for the first time, that the IL-10/STAT3/SOCS3 axis is involved in the anti-inflammatory effects of benznidazole. These findings may add up to new therapeutic strategies for chronic Chagas disease given its inflammatory nature.

Activation of Sphingosine-1-Phosphate Receptor 1 in the Spinal Cord Produces Mechanohypersensitivity Through the Activation of Inflammasome and IL-1β Pathway

Sphingosine-1-phosphate (S1P) receptor 1 subtype (S1PR1) activation by its ligand S1P in the dorsal horn of the spinal cord causes mechanohypersensitivity. The cellular and molecular pathways remain poorly understood. We report that the activation of S1PR1 with an intrathecal injection of the highly selective S1PR1 agonist SEW2871 led to the development of mechanoallodynia by activating the nod-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome (increased expression of NLRP3, cleaved caspase 1 and mature IL-1β) in the dorsal horn of the spinal cord. The functional S1PR1 antagonist FTY720 blocked NLRP3 activation and IL-1β production. Moreover, inhibiting IL-10 signaling with an intrathecal injection of an anti-IL-10 antibody attenuated the beneficial effects exerted by FTY720. This finding suggests that disrupting S1PR1 signaling engages beneficial IL-10-dependent pathways. Notably, we found that mice with astrocyte-specific deletions of S1pr1 did not develop mechanoallodynia after intrathecal injection of SEW2871 and exhibited decreased levels of cleaved caspase 1, identifying astrocytes as a key cellular locus for S1PR1 activity. Our findings provide novel mechanistic insights on how S1PR1 activation in the spinal cord contributes to the development of nociception while identifying the cellular substrate for these activities. PERSPECTIVE: This study is the first to link the activation of NLRP3 and IL-1β signaling in the spinal cord and S1PR1 signaling in astrocytes to the development of S1PR1-evoked mechanoallodynia. These findings provide critical basic science insights to support the development of therapies targeted toward S1PR1.

Post-operative immune suppression is mediated via reversible, Interleukin-10 dependent pathways in circulating monocytes following major abdominal surgery

Introduction

Post-operative infections occur frequently following major surgery. The magnitude of the post-operative immune response is associated with an increased risk of post-operative infections, although the mechanisms driving post-operative immune-dysfunction and the potential reversibility of this response with immune stimulants are not well understood. This study aims to describe the immediate immune response to major surgery and establish links to both post-operative infection and functional aspects of immune dysregulation. We also investigate the potential of clinically available immune stimulants to reverse features of post-operative immune-dysfunction.

Methods

Patients over 45 years old undergoing elective gastro-intestinal surgery with planned post-operative surgical ICU admission were recruited. The expression of selected genes was determined pre-operatively and at 2, 24 and 48 hours post-operatively using qRT-PCR. Circulating levels of Interleukin-10 protein were determined by ELISA. Peri-operative cell surface monocyte HLA-DR (mHLA-DR) expression was determined using flow cytometry. Gene expression and mHLA-DR levels were determined in healthy monocytes cultured in peri-operative serum with and without neutralising antibodies and immune stimulants.

Results

119 patients were recruited; 44 developed a post-operative infection. Interleukin-10 mRNA and protein increased 4-fold post-operatively (P<0.0001), peaking within 2 hours of the procedure. Higher post-operative Interleukin-10 mRNA (P = 0.007) and protein (P = 0.001) levels were associated with an increased risk of infection. Cell surface mHLA-DR expression fell post-operatively (P<0.0001). Reduced production, rather than intracellular sequestration, accounted for the post-operative decline in cell surface mHLA-DR expression. Interleukin-10 antibody prevented the decrease in mHLA-DR expression observed when post-operative serum was added to healthy monocytes. GM-CSF and IFN-γ prevented the decline in mHLA-DR production through distinct pathways.

Conclusions

Monocyte dysfunction and features of immune suppression occur frequently after major surgery. Greater post-operative Interleukin-10 production is associated with later infection. Interleukin-10 is an important mediator of post-operative reductions in mHLA-DR expression, while clinically available immune stimulants can restore mHLA-DR levels.

Identification of two Stat3 variants lacking a transactivation domain in grass carp: New insights into alternative splicing in the modification of teleost Stat3 signaling

Signal transducer and activator of transcription 3 (STAT3) is a member of the STAT family in response to cytokines and growth factors. In mammals, alternative splicing of STAT3 generates STAT3α and STAT3β, which have distinct and overlapping functions. In the previous study, we have identified two spliceforms of Stat3α (Stat3α1 and Stat3α2) possessing all functional domains of Stat3 in grass carp (Ctenopharyngodon idella). In the present study, two Stat3β variants (Stat3β1 and Stat3β2) without C-terminal transactivation domain were isolated from this species, and their transcripts were ubiquitously expressed in all examined tissues with the highest levels in liver. Further studies showed that Stat3β1/2 had the ability to translocate into the nucleus upon activation, indicating their roles in transcriptional regulation. In support of this notion, grass carp Stat3β1 and Stat3β2 displayed the abilities to inhibit Interleukin-10 (Il-10) signaling and competitively impaired the transcriptional activities of Stat3α1/2. In particular, similar to their mammalian counterparts, grass carp Stat3β1 and Stat3β2 could enhance Stat3α1/2 phosphorylation upon cytokine stimulation. Interestingly, stat3β1 and stat3β2 transcripts were also found in zebrafish (Danio rerio) and goldfish (Carassius auratus), and each variant in these teleosts is generated through similar alternative splicing events, including exon skipping and intron retention. This highlights a conserved splicing event of stat3 gene during vertebrate evolution and indicates a potential physiological significance of generating unique Stat3 variants in fish. These results, along with the findings regarding Stat3α1/2, demonstrate the existence of Stat3 isoforms with functional diversity and redundancy in teleosts. It leads to the hypothesis that teleost-specific spliceforms of Stat3 gene may contribute to the complexity of Stat3 signaling in fishes, thereby benefiting them to adapt to evolution and environmental changes.

Granulocyte-macrophage colony-stimulating factor negatively regulates early IL-10-mediated responses

Aim:

Treatment of inflammatory disorders relies on the intervention in immune responses thereby restoring homeostasis. IL-10 is a cytokine with therapeutic potential, but until now has not been as successful as previously anticipated. A reason for this may be that IL-10 responsiveness depends on the environment of the inflamed tissue. In this study we investigated whether GM-CSF is able to influence IL-10-mediated responses.

Methodology:

Dendritic cells and macrophages were differentiated from mouse bone marrow and treated or depleted from GM-CSF prior to analyze their response to IL-10. Activity was assessed by measuring cytokine expression upon lipopolysaccharide stimulation, IL-10-induced signaling and down-stream gene expression.

Conclusion:

This study describes that GM-CSF negatively regulates IL-10-mediated responses.

Over the last couple of decades inflammatory disorders, like autoimmune disease and allergies, are becoming more prevalent in the western world. These inflammatory disorders are characterized by uncontrolled immune responses against harmless antigens or commensal bacteria. Treatment of these diseases relies on the intervention in inflammatory responses and thereby restoring the balance of the immune system. One approach used in the clinic to balance the immune system is by treating patients with molecules used by our own immune system to suppress inflammation, such as IL-10. However, treatment with IL-10 has not been as successful as previously anticipated. In this study we show that a particular signaling molecule of the immune system that contributes to inflammation negatively affects the response of immune cells toward IL-10 and thereby could contribute to the low efficacy of IL-10 treatment.

Ammonium trichloro [1,2-ethanediolato-O,O']-tellurate cures experimental visceral leishmaniasis by redox modulation of Leishmania donovani trypanothione reductase and inhibiting host integrin linked PI3K/Akt pathway

In an endeavor to search for affordable and safer therapeutics against debilitating visceral leishmaniasis, we examined antileishmanial potential of ammonium trichloro [1,2-ethanediolato-O,O']-tellurate (AS101); a tellurium based non toxic immunomodulator. AS101 showed significant in vitro efficacy against both Leishmania donovani promastigotes and amastigotes at sub-micromolar concentrations. AS101 could also completely eliminate organ parasite load from L. donovani infected Balb/c mice along with significant efficacy against infected hamsters (˃93% inhibition). Analyzing mechanistic details revealed that the double edged AS101 could directly induce apoptosis in promastigotes along with indirectly activating host by reversing T-cell anergy to protective Th1 mode, increased ROS generation and anti-leishmanial IgG production. AS101 could inhibit IL-10/STAT3 pathway in L. donovani infected macrophages via blocking α4β7 integrin dependent PI3K/Akt signaling and activate host MAPKs and NF-κB for Th1 response. In silico docking and biochemical assays revealed AS101's affinity to form thiol bond with cysteine residues of trypanothione reductase in Leishmania promastigotes leading to its inactivation and inducing ROS-mediated apoptosis of the parasite via increased Ca2+ level, loss of ATP and mitochondrial membrane potential along with metacaspase activation. Our findings provide the first evidence for the mechanism of action of AS101 with excellent safety profile and suggest its promising therapeutic potential against experimental visceral leishmaniasis.

SOCS Proteins as Regulators of Inflammatory Responses Induced by Bacterial Infections: A Review

Severe bacterial infections can lead to both acute and chronic inflammatory conditions. Innate immunity is the first defense mechanism employed against invading bacterial pathogens through the recognition of conserved molecular patterns on bacteria by pattern recognition receptors (PRRs), especially the toll-like receptors (TLRs). TLRs recognize distinct pathogen-associated molecular patterns (PAMPs) that play a critical role in innate immune responses by inducing the expression of several inflammatory genes. Thus, activation of immune cells is regulated by cytokines that use the Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling pathway and microbial recognition by TLRs. This system is tightly controlled by various endogenous molecules to allow for an appropriately regulated and safe host immune response to infections. Suppressor of cytokine signaling (SOCS) family of proteins is one of the central regulators of microbial pathogen-induced signaling of cytokines, principally through the inhibition of the activation of JAK/STAT signaling cascades. This review provides recent knowledge regarding the role of SOCS proteins during bacterial infections, with an emphasis on the mechanisms involved in their induction and regulation of antibacterial immune responses. Furthermore, the implication of SOCS proteins in diverse processes of bacteria to escape host defenses and in the outcome of bacterial infections are discussed, as well as the possibilities offered by these proteins for future targeted antimicrobial therapies.

Identification and functional evaluation of two STAT3 variants in grass carp: Implication for the existence of specific alternative splicing of STAT3 gene in teleost

A STAT family member, STAT3, becomes activated as a DNA binding protein in response to cytokines and growth factors. In teleost, STAT3 cDNA has been cloned and identified in a few species, but only a single STAT3 transcript is revealed in these studies. In the present study, two variants of STAT3 gene generated by alternative splicing were isolated from grass carp and nominated as STAT3α1 and STAT3α2 based on the homology with their mammalian orthologs. In particular, the homologs of STAT3α1/2 were also found in various fish species, including zebrafish, takifugu, tilapia, medaka and goldfish. Intriguingly, sequence alignment and genomic structure analysis revealed that fish STAT3α1/2 are generated through similar alternative splicing events, implying the potential physiological significance of generating STAT3 variants in fish. Grass carp STAT3α1/2 (gcSTAT3α1/2) were ubiquitously expressed although the transcript levels of STAT3α2 were markedly higher than STAT3α1 in all examined tissues. In vivo and in vitro studies showed that the expression patterns of these two variants were similar under the stimulation of immune stimuli. To reveal the role of gcSTAT3α1/2 in fish immunity, their phosphorylation and involvement in IL-17A/F1 mRNA expression were demonstrated in grass carp peripheral blood lymphocytes upon LPS or PHA challenge, providing evidence for the functional conservation of STAT3 signaling in fish. These findings also raise a question of whether both gcSTAT3α1/2 participate in transcriptional regulation in fish. Actually, our results showed that both of them had the ability to translocate into the nucleus upon activation, and to amplify IL-10 signaling, indicating the existence of STAT3 isoforms with functional redundancy in teleost.

Re-evaluation of IL-10 signaling reveals novel insights on the contribution of the intracellular domain of the IL-10R2 chain

Interleukin-10 (IL-10) is an anti-inflammatory cytokine that plays a key role in maintaining immune homeostasis. IL-10-mediated responses are triggered upon binding to a heterodimeric receptor complex consisting of IL-10 receptor (IL-10R)1 and IL-10R2. Engagement of the IL-10R complex activates the intracellular kinases Jak1 and Tyk2, but the exact roles of IL-10R2 and IL-10R2-associated signaling via Tyk2 remain unclear. To elucidate the contribution of IL-10R2 and its signaling to IL-10 activity, we re-evaluated IL-10-mediated responses on bone marrow-derived dendritic cells, macrophages and mast cells. By using bone marrow from IL-10R-/- mice it was revealed that IL-10-mediated responses depend on both IL-10R1 and IL-10R2 in all three cell types. On the contrary, bone marrow-derived cells from Tyk2-/- mice showed similar responses to IL-10 as wild-type cells, indicating that signaling via this IL-10R2-associated kinase only plays a limited role. Tyk2 was shown to control the amplitude of STAT3 activation and the up-regulation of downstream SOCS3 expression. SOCS3 up-regulation was found to be cell-type dependent and correlated with the lack of early suppression of LPS-induced TNF-α in dendritic cells. Further investigation of the IL-10R complex revealed that both the extracellular and intracellular domains of IL-10R2 influence the conformation of IL-10R1 and that both domains were required for transducing IL-10 signals. This observation highlights a novel role for the intracellular domain of IL-10R2 in the molecular mechanisms of IL-10R activation.

Pro- and anti-inflammatory responses of peripheral blood mononuclear cells induced by Staphylococcus aureus and Pseudomonas aeruginosa phages

The ability of bacteriophages to kill bacteria is well known, as is their potential use as alternatives to antibiotics. As such, bacteriophages reach high doses locally through infection of their bacterial host in the human body. In this study we assessed the gene expression profile of peripheral blood monocytes from six donors for twelve immunity-related genes (i.e. CD14, CXCL1, CXCL5, IL1A, IL1B, IL1RN, IL6, IL10, LYZ, SOCS3, TGFBI and TNFA) induced by Staphylococcus aureus phage ISP and four Pseudomonas aeruginosa phages (i.e. PNM, LUZ19, 14-1 and GE-vB_Pae-Kakheti25). The phages were able to induce clear and reproducible immune responses. Moreover, the overall immune response was very comparable for all five phages: down-regulation of LYZ and TGFBI, and up-regulation of CXCL1, CXCL5, IL1A, IL1B, IL1RN, IL6, SOCS3 and TNFA. The observed immune response was shown to be endotoxin-independent and predominantly anti-inflammatory. Addition of endotoxins to the highly purified phages did not cause an immune response comparable to the one induced by the (endotoxin containing) phage lysate. In addition, the use of an intermediate level of endotoxins tipped the immune response to a more anti-inflammatory response, i.e. up-regulation of IL1RN and a strongly reduced expression of CXCL1 and CXCL5.

PEGylated IL-10 Activates Kupffer Cells to Control Hypercholesterolemia

Interleukin-10 (IL-10) is a multifunctional cytokine that exerts potent context specific immunostimulatory and immunosuppressive effects. We have investigated the mechanism by which PEGylated rIL-10 regulates plasma cholesterol in mice and humans. In agreement with previous work on rIL-10, we report that PEGylated rIL-10 harnesses the myeloid immune system to control total plasma cholesterol levels. We have discovered that PEG-rMuIL-10’s dramatic lowering of plasma cholesterol is dependent on phagocytotic cells. In particular, PEG-rHuIL-10 enhances cholesterol uptake by Kupffer cells. In addition, removal of phagocytotic cells dramatically increases plasma cholesterol levels, suggesting for the first time that immunological cells are implicitly involved in regulating total cholesterol levels. These data suggest that treatment with PEG-rIL-10 potentiates endogenous cholesterol regulating cell populations not currently targeted by standard of care therapeutics. Furthermore, we show that IL-10’s increase of Kupffer cell cholesterol phagocytosis is concomitant with decreases in liver cholesterol and triglycerides. This leads to the reversal of early periportal liver fibrosis and facilitates the restoration of liver health. These data recommend PEG-rIL-10 for evaluation in the treatment of fatty liver disease and preventing its progression to non-alcoholic steatohepatitis. In direct confirmation of our in vivo findings in the treatment of hypercholesterolemic mice with PEG-rMuIL-10, we report that treatment of hypercholesterolemic cancer patients with PEG-rHuIL-10 lowers total plasma cholesterol by up to 50%. Taken together these data suggest that PEG-rIL-10’s cholesterol regulating biology is consistent between mice and humans.

The rLrp of Mycobacterium tuberculosis inhibits proinflammatory cytokine production and downregulates APC function in mouse macrophages via a TLR2-mediated PI3K/Akt pathway activation-dependent mechanism

We demonstrate that Mycobacterium tuberculosis recombinant leucine-responsive regulatory protein (rLrp) inhibits lipopolysaccharide (LPS)-induced tumor necrosis factor alpha (TNF-α), interleukin-6, and interleukin-12 production and blocks the nuclear translocation of subunits of the nuclear-receptor transcription factor NF-κB (Nuclear factor-kappa B). Moreover, rLrp attenuated LPS-induced DNA binding and NF-κB transcriptional activity, which was accompanied by the degradation of inhibitory IκBα and a consequent decrease in the nuclear translocation of the NF-κB p65 subunit. RLrp interfered with the LPS-induced clustering of TNF receptor-associated factor 6 and with interleukin-1 receptor-associated kinase 1 binding to TAK1. Furthermore, rLrp did not attenuate proinflammatory cytokines or the expression of CD86 and major histocompatibility complex class-II induced by interferon-gamma in the macrophages of Toll-like receptor 2 deletion (TLR2^-/-) mice and in protein kinase b (Akt)-depleted mouse cells, indicating that the inhibitory effects of rLrp were dependent on TLR2-mediated activation of the phosphatidylinositol 3-OH kinase (PI3K)/Akt pathway. RLrp could also activate the PI3K/Akt pathway by stimulating the rapid phosphorylation of PI3K, Akt, and glycogen synthase kinase 3 beta in macrophages. In addition, 19 amino acid residues in the N-terminus of rLrp were determined to be important and required for the inhibitory effects mediated by TLR2. The inhibitory function of these 19 amino acids of rLrp raises the possibility that mimetic inhibitory peptides could be used to restrict innate immune responses in situations in which prolonged TLR signaling has deleterious effects. Our study offers new insight into the inhibitory mechanisms by which the TLR2-mediated PI3K/Akt pathway ensures the transient expression of potent inflammatory mediators.

Interleukin-10 modulates pulmonary neutrophilic inflammation induced by cigarette smoke exposure

AIM OF THE STUDY

Interleukin (IL)-10 is an anti-inflammatory cytokine, but its role in cigarette smoke (CS)-induced inflammation and chronic obstructive pulmonary disease (COPD) has not been fully elucidated. The purpose of this study was to investigate the effect of IL-10 deficiency on CS-induced pulmonary inflammation in mice in vivo and in vitro.

MATERIALS AND METHODS

IL-10-deficient and wild-type control mice with a C57BL6/J genetic background were exposed to CS, and inflammatory cells in bronchoalveolar lavage fluid (BALF) and mRNA of cytokines in lung were evaluated with enzyme-linked immunosorbent assay (ELISA) and reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

During 12 days of daily CS exposure to wild-type mice, neutrophil counts in BAL fluid and tumor necrosis factor (TNF)-α mRNA expression were increased, peaked at day 8, and then declined on day 12 when the level of IL-10 reached its peak. In IL-10-deficient mice, neutrophil recruitment and TNF-α mRNA levels induced by CS exposure were significantly greater than those in wild-type mice. Keratinocyte-derived chemokine (KC; murine ortholog of human CXCL8) and granulocyte macrophage colony-stimulating factor (GM-CSF) mRNA levels or matrix metalloproteinase(MMP)-9 protein levels were not correlated with neutrophil count.

CONCLUSIONS

IL-10 had a modulatory effect on CS-induced pulmonary neutrophilic inflammation and TNF-α expression in mice in vivo and therefore appears to be an important endogenous suppressor of airway neutrophilic inflammation.

Adenosine 5'-monophosphate-activated protein kinase regulates IL-10-mediated anti-inflammatory signaling pathways in macrophages

AMP-activated protein kinase (AMPK) is a conserved serine/threonine kinase with a critical function in the regulation of metabolic pathways in eukaryotic cells. Recently, AMPK has been shown to play an additional role as a regulator of inflammatory activity in leukocytes. Treatment of macrophages with chemical AMPK activators, or forced expression of a constitutively active form of AMPK, results in polarization to an anti-inflammatory phenotype. In addition, we reported previously that stimulation of macrophages with anti-inflammatory cytokines such as IL-10, IL-4, and TGF-β results in rapid activation of AMPK, suggesting that AMPK contributes to the suppressive function of these cytokines. In this study, we investigated the role of AMPK in IL-10-induced gene expression and anti-inflammatory function. IL-10-stimulated wild-type macrophages displayed rapid activation of PI3K and its downstream targets Akt and mammalian target of rapamycin complex (mTORC1), an effect that was not seen in macrophages generated from AMPKα1-deficient mice. AMPK activation was not impacted by treatment with either the PI3K inhibitor LY294002 or the JAK inhibitor CP-690550, suggesting that IL-10-mediated activation of AMPK is independent of PI3K and JAK activity. IL-10 induced phosphorylation of both Tyr(705) and Ser(727) residues of STAT3 in an AMPKα1-dependent manner, and these phosphorylation events were blocked by inhibition of Ca(2+)/calmodulin-dependent protein kinase kinase β, an upstream activator of AMPK, and by the mTORC1 inhibitor rapamycin, respectively. The impaired STAT3 phosphorylation in response to IL-10 observed in AMPKα1-deficient macrophages was accompanied by reduced suppressor of cytokine signaling 3 expression and an inadequacy of IL-10 to suppress LPS-induced proinflammatory cytokine production. Overall, our data demonstrate that AMPKα1 is required for IL-10 activation of the PI3K/Akt/mTORC1 and STAT3-mediated anti-inflammatory pathways regulating macrophage functional polarization.

Cross-talk among myeloid-derived suppressor cells, macrophages, and tumor cells impacts the inflammatory milieu of solid tumors

MDSC and macrophages are present in most solid tumors and are important drivers of immune suppression and inflammation. It is established that cross-talk between MDSC and macrophages impacts anti-tumor immunity; however, interactions between tumor cells and MDSC or macrophages are less well studied. To examine potential interactions between these cells, we studied the impact of MDSC, macrophages, and four murine tumor cell lines on each other, both in vitro and in vivo. We focused on IL-6, IL-10, IL-12, TNF-α, and NO, as these molecules are produced by macrophages, MDSC, and many tumor cells; are present in most solid tumors; and regulate inflammation. In vitro studies demonstrated that MDSC-produced IL-10 decreased macrophage IL-6 and TNF-α and increased NO. IL-6 indirectly regulated MDSC IL-10. Tumor cells increased MDSC IL-6 and vice versa. Tumor cells also increased macrophage IL-6 and NO and decreased macrophage TNF-α. Tumor cell-driven macrophage IL-6 was reduced by MDSC, and tumor cells and MDSC enhanced macrophage NO. In vivo analysis of solid tumors identified IL-6 and IL-10 as the dominant cytokines and demonstrated that these molecules were produced predominantly by stromal cells. These results suggest that inflammation within solid tumors is regulated by the ratio of tumor cells to MDSC and macrophages and that interactions of these cells have the potential to alter significantly the inflammatory milieu within the tumor microenvironment.

Identification of grass carp IL-10 receptor subunits: functional evidence for IL-10 signaling in teleost immunity

Although the functions of teleost IL-10 have been preliminarily determined, functional evidence for its receptor signaling is lacking. Particularly, the identity of fish IL-10 receptor 2 (IL-10R2) is ambiguous. Cytokine receptor family member b4 (CRFB4) and CRFB5 are likely the ortholog of mammalian IL-10R2. In this study, grass carp CRFB4 (gcCRFB4) and gcCRFB5 cDNAs were isolated and characterized. The relatively high expression levels of grass carp IL10 receptor 1 (gcIL-10R1), gcCRFB4 and gcCRFB5 in immune tissues and cells implied their importance in fish immunity. Accordingly, gcIL-10R1, gcCRFB4 and gcCRFB5 were overexpressed in a grass carp kidney cell line to identify the IL-10 receptor subunits upon grass carp IL-10 (gcIL-10) treatment. Results showed that gcIL-10R1 was essential for gcIL-10 stimulation on STAT3 activation and grass carp suppressor of cytokine signaling 3 (gcSOCS3) promoter activity, and also indicated that gcCRFB4 but not gcCRFB5 might be the ortholog of mammalian IL-10R2. Furthermore, mutation of a putative STAT3-binding element in gcSOCS3 promoter attenuated the stimulation of gcIL-10 on gcSOCS3 promoter activity, indicating that gcIL-10 may modulate gcSOCS3 transcription at least partly via STAT3 activation. This notion was further supported by our observation that gcIL-10 was able to induce STAT3 phosphorylation and STAT3 inhibitor could abolish the upregulation of gcSOCS3 mRNA expression by gcIL-10 in grass carp head kidney leukocytes. Taken together, this study for the first time functionally characterized the teleost IL-10 receptor subunits and clarified the conservation of fish IL-10 signaling during evolution, thus laying the ground for further understanding the critical immune events led by IL-10 in teleost.

Infection-induced IL-10 and JAK-STAT: A review of the molecular circuitry controlling immune hyperactivity in response to pathogenic microbes

Generation of effective immune responses against pathogenic microbes depends on a fine balance between pro- and anti-inflammatory responses. Interleukin-10 (IL-10) is essential in regulating this balance and has garnered renewed interest recently as a modulator of the response to infection at the JAK-STAT signaling axis of host responses. Here, we examine how IL-10 functions as the “master regulator” of immune responses through JAK-STAT, and provide a perspective from recent insights on bacterial, protozoan, and viral infection model systems. Pattern recognition and subsequent molecular events that drive activation of IL-10-associated JAK-STAT circuitry are reviewed and the implications for microbial pathogenesis are discussed.

SOCS1/3 expression levels in HSV-1-infected, cytokine-polarized and -unpolarized macrophages

Macrophage subtypes are characterized as proinflammatory (M1) or immunomodulatory and tissue remodeling (M2). Since macrophages play a pivotal role in controlling Herpes simplex virus type-1 (HSV-1) replication, effects of HSV-1 by 24 h of infection were determined in murine J774A.1 macrophages unpolarized (M0) or polarized to either an M1 or M2 phenotype. Morphology, cell viability, and expression of CD14 (co-receptor for lipopolysaccharide), CD86 (B7.2-immune co-stimulatory molecule), and suppressors of cytokine signaling (SOCS1 and SOCS3) were determined. M1 macrophages were flattened and vacuolated, while M2 cells appeared elongated with a few vacuoles. Compared with unpolarized M0 cells, M1 cells showed a 31% decrease in viability, a 2-fold increase in the number of CD14(+)-CD86(+) cells, no change in SOCS1 expression, and an 11-fold decrease in SOCS3 expression. M2 cells exhibited a 9% decrease in viability, a 26.0% decrease in the number of CD14(+)-CD86(+) cells, and no change in SOCS1/SOCS3 expression levels compared with M0 cells. After HSV-1 infection, all phenotypes appeared rounded, cell viabilities decreased as did numbers of M1 cells expressing CD14 and CD86. At 24 h after infection, M0 control and M2 cells showed greater virus yield than did the M1 cells, presumably reflecting the loss of viable M1 cells. SOCS1 expression was predominant in uninfected M1-polarized cells and in virus-infected control (M0) cells. SOCS1/SOCS3 expression ratio was 7:1 in uninfected M1 macrophages and approached 1:1 in M1 cells at 24 h after infection with HSV-1. In contrast, little differences were seen in SOCS1/SOCS3 expression ratios in uninfected M2-polarized cells or virus-infected M2 cells. These observations suggest that SOCS1/SOCS3 expression ratios can be used to characterize HSV-1-infected and uninfected macrophages.

IL-10 inhibits the NF-κB and ERK/MAPK-mediated production of pro-inflammatory mediators by up-regulation of SOCS-3 in Trypanosoma cruzi-infected cardiomyocytes

Trypanosoma cruzi (T. cruzi) infection produces an intense inflammatory response which is critical for the control of the evolution of Chagas’ disease. Interleukin (IL)-10 is one of the most important anti-inflammatory cytokines identified as modulator of the inflammatory reaction. This work shows that exogenous addition of IL-10 inhibited ERK1/2 and NF-κB activation and reduced inducible nitric oxide synthase (NOS2), metalloprotease (MMP) -9 and MMP-2 expression and activities, as well as tumour necrosis factor (TNF)-α and interleukin (IL)-6 expression, in T. cruzi-infected cardiomyocytes. We found that T. cruzi and IL-10 promote STAT3 phosphorylation and up-regulate the expression of suppressor of cytokine signalling (SOCS)-3 thereby preventing NF-κB nuclear translocation and ERK1/2 phosphorylation. Specific knockdown of SOCS-3 by small interfering RNA (siRNA) impeded the IL-10-mediated inhibition of NF-κB and ERK1/2 activation. As a result, the levels of studied pro-inflammatory mediators were restored in infected cardiomyocytes. Our study reports the first evidence that T. cruzi up- regulates SOCS-3 expression and highlights the relevance of IL-10 in the modulation of pro-inflammatory response of cardiomyocytes in Chagas’ disease.

The immuno-regulatory impact of orally-administered Hypericum perforatum extract on Balb/C mice inoculated with H1n1 influenza A virus

Hypericumperforatum (H. perforatum) ethanol extract has been found to inhibit lipopolysaccharide-induced production of inflammatory mediators and cytokines in cultured macrophages. Therefore, it may be able to protect the host from excessive inflammation during viral infection. In the current study, the immune-regulatory effect of H. perforatum extract was evaluated in A549 lung epithelial cells and BALB/c mice exposed to Influenza A/PR/8/34 H1N1 virus. In A549 cells, the extract (30 µg/mL) significantly inhibited influenza virus induced monocyte chemotactic protein (MCP)-1 and interferon-γ induced protein 10 kD (IP-10), but dramatically increased interleukin-6 (IL-6). In mice inoculated intranasally with 10^7.9 EID₅₀ of Influenza A/PR/8/34 H1N1 (high dose), daily oral treatment of H. perforatum extract at a rate of 110 mg/kg of body weight increased lung viral titer, bronchoalveolar lavage (BAL) pro-inflammatory cytokine and chemokine levels, and the infiltration of pro-inflammatory cells in the lung 5 days post-inoculation, as compared to ethanol vehicle treated mice. Transcription of suppressor of cytokine signaling 3 (SOCS3) was increased by H. perforatum extract both in A549 cells and BALB/c mice, which could have interrupted anti-viral immune response and thus led to the inefficient viral clearance and increased lung inflammation. H. perforatum treatment resulted in minor reduction in viral titer without affecting body weight when mice were inoculated with a lower dose (~10^5.0 EID₅₀) and H. perforatum was applied in the later phase of infection. Mice challenged intranasally with high dose of influenza virus (10^7.9 EID₅₀) suffered from a higher mortality rate when dosed with H. perforatum extract. In conclusion, the current study showed that SOCS3 elevation by H. perforatum may cause impaired immune defense against influenza virus infection and lead to higher mortality.

Enhanced suppressor of cytokine signaling 3 in arthritic cartilage dysregulates human chondrocyte function

OBJECTIVE

To determine the expression of suppressor of cytokine signaling 3 (SOCS-3) in human articular chondrocytes and its functional consequences.

METHODS

Chondrocytes were isolated from the cartilage of patients with osteoarthritis (OA), patients with rheumatoid arthritis (RA), and trauma patients and from the healthy cartilage of patients with a femoral neck fracture. The human chondrocyte cell line G6 and primary bovine chondrocytes were used in validation experiments. SOCS-3 messenger RNA (mRNA) expression was measured by quantitative polymerase chain reaction, and SOCS-3 protein levels were determined by Western blotting and immunohistochemical analysis. To ascertain the role of SOCS-3 in the chondrocyte response to interleukin-1β (IL-1β) or lipopolysaccharide (LPS), the expression of SOCS3 was either reduced by small interfering RNA or enhanced by viral transduction.

RESULTS

The expression of SOCS-3 mRNA (but not that of SOCS-1 mRNA) was significantly enhanced in chondrocytes obtained from OA cartilage (mean ± SD ΔC(t) 3.4 ± 1.0) and RA cartilage (ΔC(t) 3.4 ± 1.4) compared with cartilage obtained from patients with femoral neck fracture (ΔC(t) 5.3 ± 1.2). The expression of SOCS3 correlated significantly with that of other genes known to be expressed in arthritic chondrocytes, such as MMP13 (r = 0.743), ADAMTS4 (r = 0.779), and ADAMTS5 (r = 0.647), and an inverse relationship was observed with COL2A1 (r = -0.561). Up-regulation of SOCS-3 by IL-1 in G6 chondrocytes and its spontaneous expression in OA chondrocytes were reduced by mithramycin, a specific inhibitor of transcription factor Sp-1. Overexpression of SOCS-3 in bovine chondrocytes reduced IL-1- and LPS-induced nitric oxide production and insulin-like growth factor 1-induced proteoglycan synthesis. Interestingly, a similar impairment of function was observed in OA chondrocytes, which was partially restored by SOCS-3 gene knockdown.

CONCLUSION

This study demonstrated that both SOCS-3 mRNA and SOCS-3 protein are expressed in human arthritic chondrocytes and affect cellular responses involved in cartilage pathology.

Systemic treatment with the inhibitory neurotransmitter γ-aminobutyric acid aggravates experimental autoimmune encephalomyelitis by affecting proinflammatory immune responses

Transcriptomic and proteomic analyses of multiple sclerosis (MS) lesions indicate alterations in the gamma-aminobutyric acid (GABA) inhibitory system, suggesting its involvement in the disease process. To further elucidate the role of GABA in central nervous system (CNS) inflammation in vivo, the chronic myelin oligodendrocyte glycoprotein (MOG)(35-55) experimental autoimmune encephalomyelitis (EAE) model was used. Daily GABA injections (200mg/kg) from day 3 onwards significantly augmented disease severity, which was associated with increased CNS mRNA expression levels of tumor necrosis factor alpha (TNF-α) and interleukin (IL)-6. GABA-treated mice showed enhanced MOG-dependent proliferation and were skewed towards a T helper 1 phenotype. Moreover, in vitro, the lipopolysaccharide (LPS)-induced increase in interleukin (IL)-6 production by macrophages was enhanced at low GABA concentrations (0.03-0.3mM). In sharp contrast to exogenous GABA administration, endogenous GABA increment by systemic treatment with the GABA-transaminase inhibitor vigabatrin (250mg/kg) had prophylactic as well as therapeutic potential in EAE. Together, these results indicate an immune amplifying role of GABA in neuroinflammatory diseases like MS.

The inhibition of lipopolysaccharide-induced macrophage inflammation by 4 compounds in Hypericum perforatum extract is partially dependent on the activation of SOCS3

Our previous studies found that 4 compounds, namely pseudohypericin, amentoflavone, quercetin, and chlorogenic acid, in Hypericum perforatum ethanol extract synergistically inhibited lipopolysaccharide (LPS)-induced macrophage production of prostaglandin E2 (PGE2). Microarray studies led us to hypothesize that these compounds inhibited PGE2 production by activating suppressor of cytokine signaling 3 (SOCS3). In the current study, siRNA was used to knockdown expression of SOCS3 in RAW 264.7 macrophages and investigated the impact of H. perforatum extract and the 4 compounds on inflammatory mediators and cytokines. It was found that the SOCS3 knockdown significantly compromised the inhibition of PGE2 and nitric oxide (NO) by the 4 compounds, but not by the extract. The 4 compounds, but not the extract, decreased interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), while both lowered interleukine-1β. SOCS3 knockdown further decreased IL-6 and TNF-α. Pseudohypericin was the major contributor to the PGE2 and NO inhibition in cells treated with the 4 compounds, and its activity was lost with the SOCS3 knockdown. Cyclooxygenase-2 (COX-2) and inducible NO synthase protein expression were not altered by the treatments, while COX-2 activity was decreased by the extract and the 4 compounds and increased by SOCS3 knockdown. In summary, it was demonstrated that the 4 compounds inhibited LPS-induced PGE2 and NO through SOCS3 activation. The reduction of PGE2 can be partially attributed to COX-2 enzyme activity, which was significantly elevated with SOCS3 knockdown. At the same time, these results also suggest that constituents in H. perforatum extract were alleviating LPS-induced macrophage response through SOCS3 independent mechanisms.

Notch signal suppresses Toll-like receptor-triggered inflammatory responses in macrophages by inhibiting extracellular signal-regulated kinase 1/2-mediated nuclear factor κB activation

Multiple signaling pathways are involved in the tight regulation of Toll-like receptor (TLR) signaling, which is important for the tailoring of inflammatory response to pathogens in macrophages. It is widely accepted that TLR signaling can activate Notch pathway; however, whether full activation of Notch signaling can feedback modulate TLR signaling pathway so as to control inflammation response remains unclear. Here, we demonstrated that stimulation with TLR ligands up-regulated Notch1 and Notch2 expression in macrophages. The expression of Notch target genes including Hes1 and Hes5 was also induced in macrophages by LPS, suggesting that TLR4 signaling enhances the activation of Notch pathway. Importantly, overexpression of constituted active form of Notch1 (NICD1) and Notch2 (NICD2) suppressed production of TLR4-triggered proinflammatory cytokines such as TNF-α and IL-6 but promoted production of antiinflammatory cytokine IL-10, which is dependent on the PEST domain of NICD. In addition, NICD1 and NICD2 suppressed TLR-triggered ERK phosphorylation, which is indispensable for Notch-mediated inhibition of TLR4-triggered proinflammatory cytokine production. Furthermore, activation of Notch signaling inhibited NF-κB transcription activity by MyD88/TRAF6 and TRIF pathways, which was dependent on ERK activity. Therefore, our results showed that Notch signaling negatively regulates TLR-triggered inflammation responses, revealing a new mechanism for negative regulation of TLR signaling via Notch pathway.

Deciphering the pathways of death of Histoplasma capsulatum-infected macrophages: implications for the immunopathogenesis of early infection

Apoptosis of leukocytes is known to strongly influence the immunopathogenesis of infection. In this study, we dissected the death pathways of murine macrophages (MΦs) infected with the intracellular pathogen Histoplasma capsulatum. Yeast cells caused apoptosis of MΦs at a wide range of multiplicity of infection, but smaller inocula resulted in delayed detection of apoptosis. Upon infection, caspases 3 and 1 were activated, and both contributed to cell death; however, only the former was involved in apoptosis. The principal driving force for apoptosis involved the extrinsic pathway via engagement of TNFR1 by TNF-α. Infected MΦs produced IL-10 that dampened apoptosis. The chronology of TNF-α and IL-10 release differed in vitro. The former was detected by 2 h postinfection, and the latter was not detected until 8 h postinfection. In vivo, the lungs of TNFR1(-/-) mice infected for 1 d contained fewer apoptotic MΦs than wild-type mice, whereas the lungs of IL-10(-/-) mice exhibited more. Blockade of apoptosis by a pan-caspase inhibitor or by simvastatin sharply reduced the release of TNF-α but enhanced IL-10. However, these treatments did not modify the fungal burden in vitro over 72 h. Thus, suppressing cell death modulated cytokine release but did not alter the fungal burden. These findings provide a framework for the early pathogenesis of histoplasmosis in which yeast cell invasion of lung MΦs engenders apoptosis, triggered in part in an autocrine TNF-α-dependent manner, followed by release of IL-10 that likely prevents apoptosis of newly infected neighboring phagocytes.

Arabinosylated lipoarabinomannan skews Th2 phenotype towards Th1 during Leishmania infection by chromatin modification: involvement of MAPK signaling

The parasitic protozoan Leishmania donovani is the causative organism for visceral leishmaniasis (VL) which persists in the host macrophages by deactivating its signaling machinery resulting in a critical shift from proinflammatory (Th1) to an anti-inflammatory (Th2) response. The severity of this disease is mainly determined by the production of IL-12 and IL-10 which could be reversed by use of effective immunoprophylactics. In this study we have evaluated the potential of Arabinosylated Lipoarabinomannan (Ara-LAM), a cell wall glycolipid isolated from non pathogenic Mycobacterium smegmatis, in regulating the host effector response via effective regulation of mitogen-activated protein kinases (MAPK) signaling cascades in Leishmania donovani infected macrophages isolated from BALB/C mice. Ara-LAM, a Toll-like receptor 2 (TLR2) specific ligand, was found to activate p38 MAPK signaling along with subsequent abrogation of extracellular signal-regulated kinase (ERKs) signaling. The use of pharmacological inhibitors of p38MAPK and ERK signaling showed the importance of these signaling pathways in the regulation of IL-10 and IL-12 in Ara-LAM pretreated parasitized macrophages. Molecular characterization of this regulation of IL-10 and IL-12 was revealed by chromatin immunoprecipitation assay (CHIP) which showed that in Ara-LAM pretreated parasitized murine macrophages there was a significant induction of IL-12 by selective phosphorylation and acetylation of histone H3 residues at its promoter region. While, IL-10 production was attenuated by Ara-LAM pretreatment via abrogation of histone H3 phosphorylation and acetylation at its promoter region. This Ara-LAM mediated antagonistic regulations in the induction of IL-10 and IL-12 genes were further correlated to changes in the transcriptional regulators Signal transducer and activator of transcription 3 (STAT3) and Suppressor of cytokine signaling 3 (SOCS3). These results demonstrate the crucial role played by Ara-LAM in regulating the MAPK signaling pathway along with subsequent changes in host effector response during VL which might provide crucial clues in understanding the Ara-LAM mediated protection during Leishmania induced pathogenesis.

Interleukin-10 and immunity against prokaryotic and eukaryotic intracellular pathogens

The generation of an effective immune response against an infection while also limiting tissue damage requires a delicate balance between pro- and anti-inflammatory responses. Interleukin-10 (IL-10) has potent immunosuppressive effects and is essential for regulation of immune responses. However, the immunosuppressive properties of IL-10 can also be exploited by pathogens to facilitate their own survival. In this minireview, we discuss the role of IL-10 in modulating intracellular bacterial, fungal, and parasitic infections. Using information from several different infection models, we bring together and highlight some common pathways for IL-10 regulation and function that cannot be fully appreciated by studies of a single pathogen.

Effect of anaphylactic shock on suppressors of cytokine signaling

The pathophysiologic mechanisms of anaphylactic shock still remain unclear. In this study, we investigated the changes of expression and translation of SOCS1/SOCS3 in the heart, lungs, kidney, liver and spleen from patients who died of anaphylactic shock. Samples from the same viscera of 8 patients who died of anaphylactic shock and 8 healthy controls who died from accidents were collected in the present study. The level of IgE was measured in heart, and SOCS1/ SOCS3 mRNA and protein expression were determined by RT-PCR and immunohistochemistry, respectively. As a result, the higher IgE level was detected in the blood samples from the patients' heart than the control. SOCS1 and SOCS3 protein were significantly increased in the kidney and liver than the control. After anaphylactic shock, the expression of SOCS1 and SOCS3 mRNA were also increased. The expression level of SOCS3 mRNA was higher than that of SOCS1 in all viscera, and both were the highest in liver and kidney. There was a positive correlation between SOCS1 mRNA and SOCS3 mRNA in liver and kidney after anaphylactic shock. Our results indicate that SOCS1 and SOCS3 may play a regulatory role in anaphylactic shock viscera injury processes during anaphylactic shock.

The PPE18 protein of Mycobacterium tuberculosis inhibits NF-κB/rel-mediated proinflammatory cytokine production by upregulating and phosphorylating suppressor of cytokine signaling 3 protein

Mycobacterium tuberculosis bacteria are known to suppress proinflammatory cytokines like IL-12 and TNF-α for a biased Th2 response that favors a successful infection and its subsequent intracellular survival. However, the signaling pathways targeted by the bacilli to inhibit production of these cytokines are not fully understood. In this study, we demonstrate that the PPE18 protein of M. tuberculosis inhibits LPS-induced IL-12 and TNF-α production by blocking nuclear translocation of p50, p65 NF-κB, and c-rel transcription factors. We found that PPE18 upregulates the expression as well as tyrosine phosphorylation of suppressor of cytokine signaling 3 (SOCS3), and the phosphorylated SOCS3 physically interacts with IκBα-NF-κB/rel complex, inhibiting phosphorylation of IκBα at the serine 32/36 residues by IκB kinase-β, and thereby prevents nuclear translocation of the NF-κB/rel subunits in LPS-activated macrophages. Specific knockdown of SOCS3 by small interfering RNA enhanced IκBα phosphorylation, leading to increased nuclear levels of NF-κB/rel transcription factors vis-a-vis IL-12 p40 and TNF-α production in macrophages cotreated with PPE18 and LPS. The PPE18 protein did not affect the IκB kinase-β activity. Our study describes a novel mechanism by which phosphorylated SOCS3 inhibits NF-κB activation by masking the phosphorylation site of IκBα. Also, this study highlights the possible mechanisms by which the M. tuberculosis suppresses production of proinflammatory cytokines using PPE18.

Elevated maternal soluble Gp130 and IL-6 levels and reduced Gp130 and SOCS-3 expressions in women complicated with preeclampsia

Increased inflammatory response plays a significant role in the vascular pathophysiology in preeclampsia. However, the mechanism for increased inflammatory response in preeclampsia is largely unknown. Interleukin (IL)-6 levels are elevated in women with preeclampsia. IL-6 and its receptors, IL-6R and glycoprotein (gp)130, play a critical role in mediating antiinflammatory response via induction of SOCS-3 (suppressor of cytokine signaling-3). However, IL-6 receptor levels and expressions have not been studied in preeclampsia. In this study, we measured IL-6 and its 2 soluble receptors, soluble IL-6R and soluble gp130, in maternal plasma from normal and preeclamptic pregnant women and found that not only IL-6 but also soluble gp130 levels were significantly higher in preeclamptic women than in normotensive pregnant controls. We further examined IL-6R, gp130, and SOCS-3 expressions in maternal vessels and leukocytes and found that gp130 and SOCS-3 expressions were downregulated in both vessel endothelium and leukocytes from preeclampsia. Different patterns for IL-6R and gp130 expressions were found. IL-6R expression was also downregulated in leukocytes from preeclampsia. Our results suggest that increased plasma soluble gp130/soluble IL-6R/IL-6 ratio and reduced membrane transsignaling gp130 expression could contribute to decreased SOCS-3 expression and subsequent reduction in SOCS-3 antiinflammatory activity in women with preeclampsia. Thus, reduced gp130 and SOCS-3 expressions may offer, at least in part, a plausible explanation of reduced antiinflammatory protection in the maternal vascular system in preeclampsia.

Suppressor of cytokine signaling 3 inhibits LPS-induced IL-6 expression in osteoblasts by suppressing CCAAT/enhancer-binding protein {beta} activity

Suppressor of cytokine signaling 3 (SOCS3) is an important intracellular protein that inhibits cytokine signaling in numerous cell types and has been implicated in several inflammatory diseases. However, the expression and function of SOCS3 in osteoblasts are not known. In this study, we demonstrated that SOCS3 expression was transiently induced by LPS in osteoblasts, and apparently contributed to the inhibition of IL-6 induction by LPS treatment. We found that tyrosine 204 of the SOCS box, the SH2 domain, and the N-terminal kinase inhibitory region (KIR) of SOCS3 were all involved in its IL-6 inhibition. Furthermore, we demonstrated that CCAAT/enhancer-binding protein (C/EBP) β was activated by LPS (increased DNA binding activity), and played a key role in LPS-induced IL-6 expression in osteoblasts. We further provided the evidence that SOCS3 functioned as a negative regulator for LPS response in osteoblasts by suppressing C/EBPβ DNA binding activity. In addition, tyrosine 204 of the SOCS box, the SH2 domain, and the N-terminal kinase inhibitory region (KIR) of SOCS3 were all required for its C/EBPβ inhibition. These findings suggest that SOCS3 by interfering with C/EBPβ activation may have an important regulatory role during bone-associated inflammatory responses.