A role for glycogen synthase kinase-3 in antagonizing mycobacterial immune evasion by negatively regulating IL-10 induction

A Protective Role of Canonical Wnt/β-Catenin Pathway in Pathogenic Bacteria-Induced Inflammatory Responses

Inflammation is a complex host defensive response against various disease-associated pathogens. A baseline extent of inflammation is supposed to be tightly associated with a sequence of immune-modulated processes, resulting in the protection of the host organism against pathogen invasion; however, as a matter of fact is that an uncontrolled inflammatory cascade is the main factor responsible for the host damage, accordingly suggesting a significant and indispensable involvement of negative feedback mechanism in modulation of inflammation. Evidence accumulated so far has supported a repressive effect of the canonical Wnt/β-catenin pathway on microbial-triggered inflammation via diverse mechanisms, although that consequence is dependent on the cellular context, types of stimuli, and cytokine environment. It is of particular interest and importance to comprehend the precise way in which the Wnt/β-catenin pathway is activated, due to its essential anti-inflammatory properties. It is assumed that an inflammatory milieu is necessary for initiating and activating this signaling, implying that Wnt activity is responsible for shielding tissues from overwhelming inflammation, thus sustaining a balanced physiological condition against bacterial infection. This review gathers the recent efforts to elucidate the mechanistic details through how Wnt/β-catenin signaling modulates anti-inflammatory responses in response to bacterial infection and its interactions with other inflammatory signals, which warrants further study for the development of specific interventions for the treatment of inflammatory diseases. Further clinical trials from different disease settings are required.

Inhibition of glycogen synthase kinase-3β protects against collagen type II-induced arthritis associated with the inhibition of miR155/24 and inflammation and upregulation of apoptosis in rats

MicroRNAs have been implicated in the pathogenesis of rheumatoid arthritis (RA) and their syntheses are modulated by glycogen synthase kinase-3β (GSK-3β). Therefore, we hypothesised that the GSK-3β inhibitor, TDZD-8 can protect against collagen-induced arthritis (CIA) via downregulating miR155 and miR-24 expression. Rats were randomly allocated into four groups (n = 6) as follows: Control, Control + TDZD-8 (1 mg/kg), CIA, and CIA + TDZD-8. Rats were sacrificed after 6 weeks. We observed in the model group (CIA) significant (p<.05) increase in arthritis score and serum levels of RA biomarkers, which were significantly (p < .05) inhibited by TDZD-8. TDZD-8 also significantly (p<.05) inhibited CIA-induced synovial tissue levels of miR155, miR-24, and inflammation. In addition, a significant (p<.05) modulation of biomarkers of survival (Bcl-2) and apoptosis (cleaved caspase-3) by TDZD-8 was observed. Thus, TDZD-8 protects against CIA in rats for a period of 6 weeks, which is associated with the inhibition of miR155/24 and inflammation, and apoptosis augmentation.

Berberine inhibits IFN-γ signaling pathway in DSS-induced ulcerative colitis

Aims

The potential signaling pathways and core genes in ulcerative colitis (UC) were investigated in this study. Furthermore, potential mechanisms of BBR in treating UC were also explored.

Methods

Expression profiling by array of UC patients were obtained from Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) were determined with the differential analysis. The biological functions of DEGs were analyzed through the Database for Annotation, Visualization and Integrated Discovery (DAVID). The Gene Set Enrichment Analysis (GSEA) was applied to analyze the expression differences between two different phenotype sample sets. Dextran sulfate sodium (DSS) was applied to establish UC model of mice and lipopolysaccharide (LPS) was utilized to induce inflammatory damage of NCM460 cells. Therapeutic effects of berberine (BBR) on disease performance, pathologic changes and serum supernatant indices were analyzed in vivo. To further investigate the potential mechanisms of BBR in treating UC, the expression of genes and proteins in vivo and in vitro were examined by RT-qPCR, immunohistochemical staining and western blotting.

Results

Immune-inflammatory genes were identified and up-regulated significantly in UC patients. In addition, IFN-γ signaling pathway and its core genes were significantly up-regulated in the phenotype of UC. All disease performance and the pathologic changes of UC in mice were evidently ameliorated by BBR treatment. The pro-inflammatory cytokines of serum, including CXCL9, CXCL1, IL-17 and TNF-α, in UC mice were significantly reduced by treatment of BBR. In terms of mechanisms of BBR in treating UC, the pro-inflammatory and immune-related genes, encoding IFN-γ, IRF8, NF-κB and TNF-α decreased significantly in UC mice followed by BBR treatment. Meanwhile, the expression of IFN-γ and its initiated targets, including IRF8, Ifit1, Ifit3, IRF1, were suppressed significantly by BBR treatment in vivo. The blocking of IFN-γ in vitro led to the silence of IFN-γ signaling pathway after exposure to BBR. Furthermore, the blocking of IFN-γ in vitro led to the silence of IFN-γ signaling pathway after exposure to BBR.

Conclusion

BBR holds anti-inflammatory activity and can treat UC effectively. The anti-inflammatory property of BBR is tightly related to the suppression of IFN-γ signaling pathway, which is crucial in immune-inflammatory responses of the colon mucosa.

Host factors subverted by Mycobacterium tuberculosis: Potential targets for host directed therapy

INTRODUCTION

Despite new approaches in the diagnosis and treatment of tuberculosis (TB), it continues to be a major health burden. Several immunotherapies that potentiate the immune response have come up as adjuncts to drug therapies against drug resistant TB strains; however, there needs to be an urgent appraisal of host specific drug targets for improving their clinical management and to curtail disease progression. Presently, various host directed therapies (HDTs) exist (repurposed drugs, nutraceuticals, monoclonal antibodies and immunomodulatory agents), but these mostly address molecules that combat disease progression.

AREAS COVERED

The current review discusses major Mycobacterium tuberculosis (M. tuberculosis) survival paradigms inside the host and presents a plethora of host targets subverted by M. tuberculosis which can be further explored for future HDTs. The host factors unique to M. tuberculosis infection (in humans) have also been identified through an in-silico interaction mapping.

EXPERT OPINION

HDTs could become the next-generation adjunct therapies in order to counter antimicrobial resistance and virulence, as well as to reduce the duration of existing TB treatments. However, current scientific efforts are largely directed toward combatants rather than host molecules co-opted by M. tuberculosis for its survival. This might drive the immune system to a hyper-inflammatory condition; therefore, we emphasize that host factors subverted by M. tuberculosis, and their subsequent neutralization, must be considered for development of better HDTs.

Inhibition of GSK3β protects against collagen type II-induced arthritis associated with a decrease in synovial leukocyte infiltration and inhibition of endoplasmic reticulum stress and autophagy biomarkers

We sought to determine whether TDZD-8, the inhibitor of the glycogen synthase kinase-3β (GSK3β), can protect the synovial membrane of the knee joint against injuries induced by collagen type II immunization (CIA) possibly via the downregulation of synovial leukocyte infiltration, endoplasmic reticulum stress (ERS), and autophagy. The model group of rats (CIA) were immunized over a period of 3 weeks with collagen type II, whereas the treated group of rats (CIA + TDZD-8) were treated with TDZD-8 (1 mg/kg) for 21 days after the completion of the immunization regimen. All rats were then killed at week 6. Harvested synovial tissues were prepared for immunohistochemistry staining, and synovial homogenates were assayed for biomarkers of ERS, autophagy, apoptosis, and cell survival and proliferation. In addition, blood samples were assayed for biomarkers of arthritis. Synovial tissue images showed that CIA enhanced leukocyte recruitment as demonstrated by an increased CD45+ (leukocyte common antigen) immunostaining, which was markedly decreased by TDZD-8. TDZD-8 also significantly (P < .05) inhibited collagen-induced autophagy biomarkers Beclin-1 and LC3II, the ERS biomarkers GRP-78, IRE1-α, XBPIs, and eIF2a, and the survival protein Bcl-2. Whereas, the collagen-induced proliferative biomarkers Akt and mTOR were not inhibited by TDZD-8, and CIA inhibited the apoptotic proteins CHOP and cleaved caspase-3, which were augmented by TDZD-8. We further demonstrated a significant (P < .05) correlation between autoantibodies generated during the course of arthritis and biomarkers of ERS and autophagy. We conclude that TDZD-8 inhibits CIA and decreases synovial leukocyte infiltration, ERS, and autophagy, which is independent of Akt/mTOR signalling.

Defective Antigen Presentation Leads to Upregulation of PD1 and IL-10 in HIV-TB Co-Infection

Human immunodeficiency virus-tuberculosis (HIV-TB) co-infection poses a challenge to the immunologists in developing new diagnostic and therapeutic tools. Mechanisms behind the breakdown of the immune defense of the co-infected individual are poorly known. Numerous studies in HIV alone have revealed the role of PD1, TAP, and IL-10, but not in co-infection. The interaction of the 2 distinct bugs, which is resulting in domination over the host immune system, is still a lacuna. Hence, we aimed to portray functions of IL-10, TAP, and PD1 molecules in HIV-TB co-infection. Co-culture cells challenged with γ-irradiated M.Tb under various conditions resulted in high interleukin (IL)-10 secretion and high percentage of PD1 expression on CD8 T cells, which might be due to defective antigen presentation of TAP on dendritic cells and macrophages. Herein our observations provide an insight into the escape mechanisms by M.Tb in HIV-infected individuals from the host immune responses leading to TB co-infection.

GSK3β inhibition attenuates LPS-induced IL-6 expression in porcine adipocytes

IL-6 is not only a proinflammatory cytokine associated with inflammatory responses but also a regulator on the energy and glucose metabolism in adipose tissue. Glycogen synthase kinase 3β (GSK3β) has fundamental roles in the regulation of pro- and anti-inflammatory cytokines production. However, the regulatory role for GSK3β in the pig inflammatory response in adipocytes remains unknown. We show here that SB216763 and LPS increased the phosphorylation of GSK3β (Ser9), and decreased the phosphorylation of GS (Ser641) in adipocytes. The activity of porcine GSK3β was inhibited by SB216763, an inhibitor of GSK3β, attenuated the production of IL-6 in LPS-stimulated adipocytes. Additionally, the essential core region of the pig IL-6 promoter located at -191 bp to -59 bp, and an NF-κBp65 element in this region was responsible for IL-6 promoter activity. The transcription activity of NF-κBp65 was activated by LPS stimulation, and the GSK3β inhibition repressed LPS-induced luciferase activity of the IL-6 promoter. Furthermore, LPS increased p65 binding to the NF-κB site, and GSK3β inhibition had no effect on the association of NF-κBp65 with IL-6 gene promoter after LPS treatment. These results demonstrate that GSK3β has important regulatory roles in the LPS-induced inflammatory response of IL-6 production in pig adipocytes.

Slow-Binding Inhibition of Mycobacterium tuberculosis Shikimate Kinase by Manzamine Alkaloids

Tuberculosis represents a significant public health crisis. There is an urgent need for novel molecular scaffolds against this pathogen. We screened a small library of marine-derived compounds against shikimate kinase from Mycobacterium tuberculosis ( MtSK), a promising target for antitubercular drug development. Six manzamines previously shown to be active against M. tuberculosis were characterized as MtSK inhibitors: manzamine A (1), 8-hydroxymanzamine A (2), manzamine E (3), manzamine F (4), 6-deoxymanzamine X (5), and 6-cyclohexamidomanzamine A (6). All six showed mixed noncompetitive inhibition of MtSK. The lowest K_I values were obtained for 6 across all MtSK-substrate complexes. Time-dependent analyses revealed two-step, slow-binding inhibition. The behavior of 1 was typical; initial formation of an enzyme-inhibitor complex (EI) obeyed an apparent K_I of ∼30 μM with forward ( k₅) and reverse ( k₆) rate constants for isomerization to an EI* complex of 0.18 and 0.08 min^-1, respectively. In contrast, 6 showed a lower K_I for the initial encounter complex (∼1.5 μM), substantially faster isomerization to EI* ( k₅ = 0.91 min^-1), and slower back conversion of EI* to EI ( k₆ = 0.04 min^-1). Thus, the overall inhibition constants, K_I*, for 1 and 6 were 10 and 0.06 μM, respectively. These findings were consistent with docking predictions of a favorable binding mode and a second, less tightly bound pose for 6 at MtSK. Our results suggest that manzamines, in particular 6, constitute a new scaffold from which drug candidates with novel mechanisms of action could be designed for the treatment of tuberculosis by targeting MtSK.

Lysophosphatidylcholine Promotes Phagosome Maturation and Regulates Inflammatory Mediator Production Through the Protein Kinase A-Phosphatidylinositol 3 Kinase-p38 Mitogen-Activated Protein Kinase Signaling Pathway During Mycobacterium tuberculosis Infection in Mouse Macrophages

Tuberculosis is caused by the infectious agent Mycobacterium tuberculosis (Mtb). Mtb has various survival strategies, including blockade of phagosome maturation and inhibition of antigen presentation. Lysophosphatidylcholine (LPC) is a major phospholipid component of oxidized low-density lipoprotein and is involved in various cellular responses, such as activation of second messengers and bactericidal activity in neutrophils. In this study, macrophages were infected with a low infectious dose of Mtb and treated with LPC to investigate the bactericidal activity of LPC against Mtb. In macrophages infected with Mtb strain, H37Ra or H37Rv, LPC suppressed bacterial growth; however, this effect was suppressed in bone marrow-derived macrophages (BMDMs) isolated from G2A (a G protein-coupled receptor involved in some LPC actions) knockout mice. LPC also promoted phagosome maturation via phosphatidylinositol 3 kinase (PI3K)–p38 mitogen-activated protein kinase (MAPK)-mediated reactive oxygen species production and intracellular Ca²⁺ release during Mtb infection. In addition, LPC induced increased levels of intracellular cyclic adenosine monophosphate (cAMP) and phosphorylated glycogen synthase kinase 3 beta (GSK3β) in Mtb-infected macrophages. Protein kinase A (PKA)-induced phosphorylation of GSK3β suppressed activation of NF-κB in LPC-treated macrophages during Mtb infection, leading to decreased secretion of pro-inflammatory cytokines and increased secretion of anti-inflammatory cytokines. These results suggest that LPC can effectively control Mtb growth by promoting phagosome maturation via cAMP-induced activation of the PKA–PI3K–p38 MAPK pathway. Moreover, LPC can regulate excessive production of pro-inflammatory cytokines associated with bacterial infection of macrophages.

Glycogen Synthase Kinase 3α Is the Main Isoform That Regulates the Transcription Factors Nuclear Factor-Kappa B and cAMP Response Element Binding in Bovine Endothelial Cells Infected with Staphylococcus aureus

Glycogen synthase kinase 3 (GSK3) is a constitutive enzyme implicated in the regulation of cytokine expression and the inflammatory response during bacterial infections. Mammals have two GSK3 isoforms named GSK3α and GSK3β that plays different but often overlapping functions. Although the role of GSK3β in cytokine regulation during the inflammatory response caused by bacteria is well described, GSK3α has not been found to participate in this process. Therefore, we tested if GSK3α may act as a regulatory isoform in the cytokine expression by bovine endothelial cells infected with Staphylococcus aureus because this bacterium is one of the major pathogens that cause tissue damage associated with inflammatory dysfunction. Interestingly, although both isoforms were phosphorylated–inactivated, we consistently observed a higher phosphorylation of GSK3α at Ser21 than that of GSK3β at Ser9 after bacterial challenge. During a temporal course of infection, we characterized a molecular switch from pro-inflammatory cytokine expression (IL-8), promoted by nuclear factor-kappa B (NF-κB), at an early stage (2 h) to an anti-inflammatory cytokine expression (IL-10), promoted by cAMP response element binding (CREB), at a later stage (6 h). We observed an indirect effect of GSK3α activity on NF-κB activation that resulted in a low phosphorylation of CREB at Ser133, a decreased interaction between CREB and the co-activator CREB-binding protein (CBP), and a lower expression level of IL-10. Gene silencing of GSK3α and GSK3β with siRNA indicated that GSK3α knockout promoted the interaction between CREB and CBP that, in turn, increased the expression of IL-10, reduced the interaction of NF-κB with CBP, and reduced the expression of IL-8. These results indicate that GSK3α functions as the primary isoform that regulates the expression of IL-10 in endothelial cells infected with S. aureus.

GSK-3Beta-Dependent Activation of GEF-H1/ROCK Signaling Promotes LPS-Induced Lung Vascular Endothelial Barrier Dysfunction and Acute Lung Injury

The bacterial endotoxin or lipopolysaccharide (LPS) leads to the extensive vascular endothelial cells (EC) injury under septic conditions. Guanine nucleotide exchange factor-H1 (GEF-H1)/ROCK signaling not only involved in LPS-induced overexpression of pro-inflammatory mediator in ECs but also implicated in LPS-induced endothelial hyper-permeability. However, the mechanisms behind LPS-induced GEF-H1/ROCK signaling activation in the progress of EC injury remain incompletely understood. GEF-H1 localized on microtubules (MT) and is suppressed in its MT-bound state. MT disassembly promotes GEF-H1 release from MT and stimulates downstream ROCK-specific GEF activity. Since glycogen synthase kinase (GSK-3beta) participates in regulating MT dynamics under pathologic conditions, we examined the pivotal roles for GSK-3beta in modulating LPS-induced activation of GEF-H1/ROCK, increase of vascular endothelial permeability and severity of acute lung injury (ALI). In this study, we found that LPS induced human pulmonary endothelial cell (HPMEC) monolayers disruption accompanied by increase in GSK-3beta activity, activation of GEF-H1/ROCK signaling and decrease in beta-catenin and ZO-1 expression. Inhibition of GSK-3beta reduced HPMEC monolayers hyper-permeability and GEF-H1/ROCK activity in response to LPS. GSK-3beta/GEF-H1/ROCK signaling is implicated in regulating the expression of beta-catenin and ZO-1. In vivo, GSK-3beta inhibition attenuated LPS-induced activation of GEF-H1/ROCK pathway, lung edema and subsequent ALI. These findings present a new mechanism of GSK-3beta-dependent exacerbation of lung micro-vascular hyper-permeability and escalation of ALI via activation of GEF-H1/ROCK signaling and disruption of intracellular junctional proteins under septic condition.

Glycogen synthase kinase-3 (GSK3) regulates TNF production and haemocyte phagocytosis in the immune response of Chinese mitten crab Eriocheir sinensis

Glycogen synthase kinase-3 (GSK3) is a serine/threonine protein kinase firstly identified as a regulator of glycogen synthesis. Recently, it has been proved to be a key regulator of the immune reaction. In the present study, a GSK3 homolog gene (designated as EsGSK3) was cloned from Chinese mitten crab, Eriocheir sinensis. The open reading frame (ORF) was 1824 bp, which encoded a predicted polypeptide of 607 amino acids. There was a conserved Serine/Threonine Kinase domain and a DNA binding domain found in EsGSK3. Phylogenetic analysis showed that EsGSK3 was firstly clustered with GSK3-β from oriental river prawn Macrobrachium nipponense in the invertebrate branch, while GSK3s from vertebrates formed the other distinct branch. EsGSK3 mRNA transcripts could be detected in all tested tissues of the crab including haepatopancreas, eyestalk, muscle, gonad, haemocytes and haematopoietic tissue with the highest expression level in haepatopancreas. And EsGSK3 protein was mostly detected in the cytoplasm of haemocyte by immunofluorescence analysis. The expression levels of EsGSK3 mRNA increased significantly at 6 h after Aeromonas hydrophila challenge (p < 0.05) in comparison with control group, and then gradually decreased to the initial level at 48 h (p > 0.05). The mRNA expression of lipopolysaccharide-induced tumor necrosis factor (TNF)-α factor (EsLITAF) was also induced by A. hydrophila challenge. However, the mRNA expression of EsLITAF and TNF-α production was significantly suppressed after EsGSK3 was blocked in vivo with specific inhibitor lithium, while the phagocytosis of crab haemocytes was significantly promoted. These results collectively demonstrated that EsGSK3 could regulate the innate immune responses of E. sinensis by promoting TNF-α production and inhibiting haemocyte phagocytosis.

Virulence-dependent induction of interleukin-10-producing-tolerogenic dendritic cells by Mycobacterium tuberculosis impedes optimal T helper type 1 proliferation

Mycobacterium tuberculosis inhibits optimal T helper type 1 (Th1) responses during infection. However, the precise mechanisms by which virulent M. tuberculosis limits Th1 responses remain unclear. Here, we infected dendritic cells (DCs) with the virulent M. tuberculosis strain H37Rv or the attenuated strain H37Ra to investigate the phenotypic and functional alterations in DCs and resultant T-cell responses. H37Rv-infected DCs suppressed Th1 responses more strongly than H37Ra-infected DCs. Interestingly, H37Rv, but not H37Ra, impaired DC surface molecule expression (CD80, CD86 and MHC class II) due to prominent interleukin-10 (IL-10) production while augmenting the expression of tolerogenic molecules including PD-L1, CD103, Tim-3 and indoleamine 2,3-dioxygenase on DCs in a multiplicity-of-infection (MOI) -dependent manner. These results indicate that virulent M. tuberculosis drives immature DCs toward a tolerogenic phenotype. Notably, the tolerogenic phenotype of H37Rv-infected DCs was blocked in DCs generated from IL-10^-/- mice or DCs treated with an IL-10-neutralizing monoclonal antibody, leading to restoration of Th1 polarization. These findings suggest that IL-10 induces a tolerogenic DC phenotype. Interestingly, p38 mitogen-activated protein kinase (MAPK) activation predominantly mediates IL-10 production; hence, H37Rv tends to induce a tolerogenic DC phenotype through expression of tolerogenic molecules in the p38 MAPK-IL-10 axis. Therefore, suppressing the tolerogenic cascade in DCs is a novel strategy for stimulating optimal protective T-cell responses against M. tuberculosis infection.

Enzyme Activity Assays for Protein Kinases: Strategies to Identify Active Substrates

Protein kinases are an important class of enzymes and drug targets. New opportunities to discover medicines for neglected diseases can be leveraged by the extensive kinase tools and knowledge created in targeting human kinases. A valuable tool for kinase drug discovery is an enzyme assay that measures catalytic function. The functional assay can be used to identify inhibitors, estimate affinity, characterize molecular mechanisms of action (MMOAs) and evaluate selectivity. However, establishing an enzyme assay for a new kinases requires identification of a suitable substrate. Identification of a new kinase's endogenous physiologic substrate and function can be extremely costly and time consuming. Fortunately, most kinases are promiscuous and will catalyze the phosphotransfer from ATP to alternative substrates with differing degrees of catalytic efficiency. In this manuscript we review strategies and successes in the identification of alternative substrates for kinases from organisms responsible for many of the neglected tropical diseases (NTDs) towards the goal of informing strategies to identify substrates for new kinases. Approaches for establishing a functional kinase assay include measuring auto-activation and use of generic substrates and peptides. The most commonly used generic substrates are casein, myelin basic protein, and histone. Sequence homology modeling can provide insights into the potential substrates and the requirement for activation. Empirical approaches that can identify substrates include screening of lysates (which may also help identify native substrates) and use of peptide arrays. All of these approaches have been used with a varying degree of success to identify alternative substrates.

Interleukin-10 Family and Tuberculosis: An Old Story Renewed

The interleukin-10 (IL-10) family of cytokines consists of six immune mediators, namely IL-10, IL-19, IL-20, IL-22, IL-24 and IL-26. IL-10, IL-22, IL-24 and IL-26 are critical for the regulation of host defense against Mycobacterium tuberculosis infections. Specifically, IL-10 and IL-26 can suppress the antimycobacterial immunity and promote the survival of pathogen, while IL-22 and IL-24 can generate protective responses and inhibit the intracellular growth of pathogen. Knowledge about the new players in tuberculosis immunology, namely IL-10 family, can inform novel immunity-based countermeasures and host directed therapies against tuberculosis.

The Role of GSK3β in the Regulation of IL-10 and IL-12 Production Induced by Lipopolysaccharide in PK-15 Cells

Glycogen synthase kinase-3β (GSK3β) plays a fundamental role in the inflammatory response by controlling the balance between pro- and anti-inflammatory cytokine production induced by lipopolysaccharide (LPS). However, the inflammatory roles of different porcine GSK3β isoforms in response to LPS remain unknown. In this study, the activity of porcine GSK3β was inhibited in response to LPS stimulation through increased serine 9 phosphorylation of GSK3β, which increased the production of interleukin (IL)-10 and IL-12 in PK-15 cells. However, treatment with an inhibitor of GSK3β, lithium chloride, significantly increased the production of IL-10 and IL-12 compared with the untreated control and significantly decreased the production of IL-10 and IL-12 compared with LPS stimulation. Moreover, all four glycogen synthase kinase-3 transcripts had positive roles in the production of IL-10 and IL-12 to varying degrees, suggesting their importance in the LPS-induced inflammatory response in pigs.

GSK3β-dependent inhibition of AMPK potentiates activation of neutrophils and macrophages and enhances severity of acute lung injury

Although AMP-activated protein kinase (AMPK) is involved in regulating carbohydrate and lipid metabolism, activated AMPK also plays an anti-inflammatory role in many cell populations. However, despite the ability of AMPK activation to diminish the severity of inflammatory responses, previous studies have found that AMPK activity is diminished in LPS-treated neutrophils and also in lungs of mice with LPS-induced acute lung injury (ALI). Since GSK3β participates in regulating AMPK activity, we examined potential roles for GSK3β in modulating LPS-induced activation of neutrophils and macrophages and in influencing severity of ALI. We found that GSK3β-dependent phosphorylation of T479-AMPK was associated with pT172 dephosphorylation and inactivation of AMPK following TLR4 engagement. GSK3β inhibitors BIO (6-bromoindirubin-3'-oxime), SB216763, or siRNA knockdown of GSK3β, but not the PI3K/AKT inhibitor LY294002, prevented Thr172-AMPK dephosphorylation. Exposure to LPS resulted in rapid binding between IKKβ and AMPKα, and phosphorylation of S485-AMPK by IKKβ. These results suggest that IKKβ-dependent phosphorylation of S485-AMPK was an essential step in subsequent phosphorylation and inactivation AMPK by GSK3β. Inhibition of GSK3β activity delayed IκBα degradation and diminished expression of the proinflammatory TNF-α in LPS-stimulated neutrophils and macrophages. In vivo, inhibition of GSK3β decreased the severity of LPS-induced lung injury as assessed by development of pulmonary edema, production of TNF-α and MIP-2, and release of the alarmins HMGB1 and histone 3 in the lungs. These results show that inhibition of AMPK by GSK3β plays an important contributory role in enhancing LPS-induced inflammatory responses, including worsening the severity of ALI.

A Wnt/β-catenin negative feedback loop represses TLR-triggered inflammatory responses in alveolar epithelial cells

Increasing evidence has demonstrated that the epithelial cells in the lung play crucial roles in regulating certain inflammatory responses by modulating Wnt signaling during microbial infection. However, the anti-microbial functions of Wnt signaling in alveolar epithelial cells remain elusive. In this report, we show that Wnt/β-catenin signaling is repressed in A549 alveolar epithelial cells during a Toll-like receptor ligand stimulation with Mycobacterium bovis Bacillus Calmette-Guerin (BCG) or lipopolysaccharide (LPS). In addition to activating TLR signaling, a stimulation of BCG or LPS led to the up-regulation of a Wnt receptor Frizzled-1, cytosolic GSK3β and Axin, and the down-regulation of nuclear β-catenin, lymphoid enhancer factor 1 and transcription factor 4. While an enhancement of β-catenin activity suppressed the TLR signal response, and substantially led to alleviate the TLR ligand-induced pro-inflammatory responses. Importantly, gain and loss of function studies by overexpressing or silencing of TLR signaling adaptor, myeloid differentiation primary response gene 88 (MyD88) further demonstrated an inverse relationship between TLR signaling and canonical Wnt signaling in A549 cells. These data imply that Wnt/β-catenin signaling acts as a negative feedback loop to suppress inflammation in alveolar epithelial cells, and averts cell injury from excessive inflammatory reactions. This study thus reveals a novel immunoregulatory mechanism in alveolar epithelial cells in response to bacterial infection.

TLR3 regulates mycobacterial RNA-induced IL-10 production through the PI3K/AKT signaling pathway

Cytokine induction in response to Mycobacterium tuberculosis (Mtb) infection is critical for pathogen control, by (i) mediating innate immune effector functions and (ii) instructing specific adaptive immunity. IL-10 is an important anti-inflammatory cytokine involved in pathogenesis of tuberculosis (TB). Here, we show that TLR3, a sensor of extracellular viral or host RNA with stable stem structures derived from infected or damaged cells, is essential for Mtb-induced IL-10 production. Upon Mycobacterium bovis Bacillus Calmette-Guérin (BCG) infection, TLR3(-/-) macrophages expressed lower IL-10 but higher IL-12p40 production, accompanied by reduced phosphorylation of AKT at Ser473. BCG-infected TLR3(-/-) mice exhibited reduced IL-10 but elevated IL-12 expression compared to controls. Moreover, higher numbers of splenic Th1 cells and reduced pulmonary bacterial burden and tissue damage were observed in BCG-infected TLR3(-/-) mice. Finally, BCG RNA induced IL-10 in macrophages via TLR3-mediated activation of PI3K/AKT. Our findings demonstrate a critical role of TLR3-mediated regulation in the pathogenesis of mycobacterial infection involving mycobacterial RNA, which induces IL-10 through the PI3K/AKT signaling pathway.

A role for interleukin-17A in modulating intracellular survival of Mycobacterium bovis bacillus Calmette-Guérin in murine macrophages

Interleukin 17A IL-17A is a crucial immunomodulator in various chronic immunological diseases including rheumatoid arthritis and inflammatory bowel disease. The cytokine has also been demonstrated to control the pathogenesis of the Mycobacterium tuberculosis by dysregulating production of cytokines and chemokines and promoting granuloma formation. Whether IL-17A regulates innate defence mechanisms of macrophages in response to mycobacterial infection remains to be elucidated. In the current report, we investigated the effects of IL-17A on modulating the intracellular survival of Mycobacterium bovis bacillus Calmette-Guérin (BCG) in RAW264.7 murine macrophages. We observed that IL-17A pre-treatment for 24 hr was able to synergistically enhance BCG-induced nitric oxide (NO) production and inducible nitric oxide synthase expression in dose- and time-dependent manners. We further delineated the mechanisms involved in this synergistic reaction. IL-17A was found to specifically enhanced BCG-induced phosphorylation of Jun N-terminal kinase (JNK), but not of extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase. By using a specific JNK inhibitor (SP600125), we found that the production of NO in BCG-infected macrophages was significantly suppressed. Taken together, we confirmed the involvement of the JNK pathway in IL-17A-enhanced NO production in BCG-infected macrophages. We further demonstrated that IL-17A significantly enhanced the clearance of intracellular BCG by macrophages through an NO-dependent killing mechanism. In conclusion, our study revealed an anti-mycobacterial role of IL-17A through priming the macrophages to produce NO in response to mycobacterial infection.

Regulatory role of GSK-3 β on NF- κ B, nitric oxide, and TNF- α in group A streptococcal infection

Group A streptococcus (GAS) imposes a great burden on humans. Efforts to minimize the associated morbidity and mortality represent a critical issue. Glycogen synthase kinase-3β (GSK-3β) is known to regulate inflammatory response in infectious diseases. However, the regulation of GSK-3β in GAS infection is still unknown. The present study investigates the interaction between GSK-3β, NF-κB, and possible related inflammatory mediators in vitro and in a mouse model. The results revealed that GAS could activate NF-κB, followed by an increased expression of inducible nitric oxide synthase (iNOS) and NO production in a murine macrophage cell line. Activation of GSK-3β occurred after GAS infection, and inhibition of GSK-3β reduced iNOS expression and NO production. Furthermore, GSK-3β inhibitors reduced NF-κB activation and subsequent TNF-α production, which indicates that GSK-3β acts upstream of NF-κB in GAS-infected macrophages. Similar to the in vitro findings, administration of GSK-3β inhibitor in an air pouch GAS infection mouse model significantly reduced the level of serum TNF-α and improved the survival rate. The inhibition of GSK-3β to moderate the inflammatory effect might be an alternative therapeutic strategy against GAS infection.

Role of glycogen synthase kinase-3 beta in the inflammatory response caused by bacterial pathogens

Glycogen synthase kinase 3β (GSK3β) plays a fundamental role during the inflammatory response induced by bacteria. Depending on the pathogen and its virulence factors, the type of cell and probably the context in which the interaction between host cells and bacteria takes place, GSK3β may promote or inhibit inflammation. The goal of this review is to discuss recent findings on the role of the inhibition or activation of GSK3β and its modulation of the inflammatory signaling in monocytes/macrophages and epithelial cells at the transcriptional level, mainly through the regulation of nuclear factor-kappaB (NF-κB) activity. Also included is a brief overview on the importance of GSK3 in non-inflammatory processes during bacterial infection.

A role for c-Myc in regulating anti-mycobacterial responses

c-Myc (Myc) is a well known transcription factor that regulates many essential cellular processes; however, its role in modulating immunity is not known. Here, we showed different species of mycobacteria can induce Myc expression via ERK1/2 and JNK activation. Unexpectedly, the induced Myc is localized in the cytoplasm but not in the nucleus. This induced Myc expression is associated with the induction of TNF-α and IL-6 and with the suppression of intracellular mycobacterial growth. To delineate the underlying mechanisms, we demonstrated that Myc enhances IRAK1 degradation, leading to specific activations of ERK1/2 and p38 MAPK but not Akt, and reduces IκBα protein recovery upon degradation. Hence, our findings may provide insights into a potential role for Myc in regulating the antimicrobial responses.

The phosphoinositide-3-kinase-Akt signaling pathway is important for Staphylococcus aureus internalization by endothelial cells

Internalization of Staphylococcus aureus in bovine endothelial cells (BEC) is increased by tumor necrosis factor alpha stimulation and NF-κB activation. Because the phosphoinositide-3-kinase (PI3K)-Akt signaling pathway also modulates NF-κB activity, we considered whether the internalization of S. aureus by BEC is associated with the activity of PI3K and Akt. We found a time- and multiplicity of infection-dependent phosphorylation of Akt on Ser473 in BEC infected with S. aureus. This phosphorylation was inhibited by LY294002 (LY), indicating the participation of PI3K. Inhibition of either PI3K with LY or wortmannin, or Akt with SH-5, strongly reduced the internalization of S. aureus. Transfection of BEC with a dominant-negative form of the Akt gene significantly decreased S. aureus internalization, whereas transfection with the constitutively active mutant increased the number of internalized bacterium. Inhibition of PDK1 activity with OSU-03012 did not affect the level of S. aureus internalization, demonstrating that phosphorylation of Akt on Thr308 is not important for this process. Compared to the untreated control, the adherence of S. aureus to the surface of BEC was unaltered when cells were transfected or incubated with the pharmacological inhibitors. Furthermore, Akt activation by internalized S. aureus triggered a time-dependent phosphorylation of glycogen synthase kinase-3α (GSK-3α) on Ser21 and GSK-3β on Ser9 that was partially inhibited with SH-5. Finally, treatment of BEC with LY prior to S. aureus infection inhibited the NF-κB p65 subunit phosphorylation on Ser536, indicating the involvement of PI3K. These results suggest that PI3K-Akt activity is important for the internalization of S. aureus and phosphorylation of GSK-3α, GSK-3β, and NF-κB.

Interleukin-17A differentially modulates BCG induction of cytokine production in human blood macrophages

The pathogenesis of Mtb depends in part on cytokine cross-regulation between macrophages and T cells in host immunity. Th17 cells produce IL-17A to induce granuloma formation and to restrict mycobacterial dissemination. IL-17A also mediates cytokine responses induced by proinflammatory cytokines such as TNF-α. Our previous results showed that BCG induces IL-6, IL-10, and TNF-α via activity of protein kinases, including dsRNA-activated serine/threonine protein kinase and glycogen synthase kinase-3 in primary human monocytes. Therefore, we investigated whether IL-17A, upon its induction by BCG, plays an additional role to aid the production of downstream proinflammatory cytokines in macrophages. Here, we showed that IL-17A enhanced IL-6 mRNA and protein levels inducible by BCG in a time- and dose-dependent manner, whereas it had no effect on IL-10 and TNF-α production. We also demonstrated that IL-17A activated the phosphorylation of ERK1/2 triggered by BCG. With the use of a specific chemical inhibitor of a MAPK/ERK-activating kinase (MEK1/2), we confirmed the correlation between the enhanced ERK1/2 activation and augmented IL-6 production. Additionally, we revealed that IL-17A acts in concert with BCG-induced TNF-α to enhance the level of IL-6 synthesis. Taken together, our results suggest a significant role of IL-17A to serve as a modulator of cytokine expression in innate immune response during mycobacterial infection.

Differential effects of Radix Paeoniae Rubra (Chishao) on cytokine and chemokine expression inducible by mycobacteria

Background

Upon initial infection with mycobacteria, macrophages secrete multiple cytokines and chemokines, including interleukin-6 (IL-6), IL-8 and tumor necrosis factor-α (TNF-α), to mediate host immune responses against the pathogen. Mycobacteria also induce the production of IL-10 via PKR activation in primary human monocytes and macrophages. As an anti-inflammatory cytokine, over-expression of IL-10 may contribute to mycobacterial evasion of the host immunity. Radix Paeoniae Rubra (RPR, Chishao), a Chinese medicinal herb with potentials of anti-inflammatory, hepatoprotective and neuroprotective effects, is used to treat tuberculosis. This study investigates the immunoregulatory effects of RPR on primary human blood macrophages (PBMac) during mycobacterial infection.

Methods

The interaction of Bacillus Calmette-Guerin (BCG) with PBMac was used as an experimental model. A series of procedures involving solvent extraction and fractionation were used to isolate bioactive constituents in RPR. RPR-EA-S1, a fraction with potent immunoregulatory effects was obtained with a bioactivity guided fractionation scheme. PBMac were treated with crude RPR extracts or RPR-EA-S1 before BCG stimulation. The expression levels of IL-6, IL-8, IL-10 and TNF-α were measured by qPCR and ELISA. Western blotting was used to determine the effects of RPR-EA-S1 on signaling kinases and transcriptional factors in the BCG-activated PBMac.

Results

In BCG-stimulated macrophages, crude RPR extracts and fraction RPR-EA-S1 specifically inhibited IL-10 production while enhanced IL-8 expression at both mRNA and protein levels without affecting the expressions of IL-6 and TNF-α. Inhibition of BCG-induced IL-10 expression by RPR-EA-S1 occurred in a dose- and time-dependent manner. RPR-EA-S1 did not affect the phosphorylation of cellular protein kinases including MAPK, Akt and GSK3β. Instead, it suppressed the degradation of IκBα in the cytoplasm and inhibited the translocation of transcription factor NF-κB1 p50 to the nucleus.

Conclusion

RPR crude extracts and its fraction RPR-EA-S1 inhibited anti-inflammatory cytokine IL-10 and enhanced pro-inflammatory chemokine IL-8 expression in BCG-activated PBMac. The inhibitory effects of RPR-EA-S1 on IL-10 expression in BCG-activated PBMac may be due to the reduced nuclear translocation of NF-κB1 p50.

Exogenous control of the expression of Group I CD1 molecules competent for presentation of microbial nonpeptide antigens to human T lymphocytes

Group I CD1 (CD1a, CD1b, and CD1c) glycoproteins expressed on immature and mature dendritic cells present nonpeptide antigens (i.e., lipid or glycolipid molecules mainly of microbial origin) to T cells. Cytotoxic CD1-restricted T lymphocytes recognizing mycobacterial lipid antigens were found in tuberculosis patients. However, thanks to a complex interplay between mycobacteria and CD1 system, M. tuberculosis possesses a successful tactic based, at least in part, on CD1 downregulation to evade CD1-dependent immunity. On the ground of these findings, it is reasonable to hypothesize that modulation of CD1 protein expression by chemical, biological, or infectious agents could influence host's immune reactivity against M. tuberculosis-associated lipids, possibly affecting antitubercular resistance. This scenario prompted us to perform a detailed analysis of the literature concerning the effect of external agents on Group I CD1 expression in order to obtain valuable information on the possible strategies to be adopted for driving properly CD1-dependent immune functions in human pathology and in particular, in human tuberculosis.

The role of the transcription factor CREB in immune function

CREB is a transcription factor that regulates diverse cellular responses, including proliferation, survival, and differentiation. CREB is induced by a variety of growth factors and inflammatory signals and subsequently mediates the transcription of genes containing a cAMP-responsive element. Several immune-related genes possess this cAMP-responsive element, including IL-2, IL-6, IL-10, and TNF-α. In addition, phosphorylated CREB has been proposed to directly inhibit NF-κB activation by blocking the binding of CREB binding protein to the NF-κB complex, thereby limiting proinflammatory responses. CREB also induces an antiapoptotic survival signal in monocytes and macrophages. In T and B cells, CREB activation promotes proliferation and survival and differentially regulates Th1, Th2, and Th17 responses. Finally, CREB activation is required for the generation and maintenance of regulatory T cells. This review summarizes current advances involving CREB in immune function--a role that is continually being defined.

Isolation and identification of anti-inflammatory constituents from Ligusticum chuanxiong and their underlying mechanisms of action on microglia

Stroke is the third most common cause of death worldwide. Recent findings showed that the severity of cerebrovascular diseases including ischemic stroke correlates with inflammation mediated responses in the neural cells. During ischemia, inflammatory mediators including tumor necrosis factor-alpha (TNF-α) and nitric oxide are produced by microglia, which play a central role in the pathogenesis of the disease. Ligusticum chuanxiong (LCX) is a commonly used traditional Chinese medicine (TCM) for empiric treatment of cerebrovascular and cardiovascular diseases for many centuries. By applying a bioactivity-guided fractionation scheme, two compounds with inhibition on neuroinflammation were isolated from LCX. Using chromatographic and spectrometric methods, they were identified to be senkyunolide A and Z-ligustilide. They could inhibit the production of proinflammatory mediators in lipopolysaccharide (LPS)-stimulated murine BV-2 microglial cells and human peripheral blood monocyte derived macrophages. In addition, both compounds protected Neuro-2a cells from neuroinflammatory toxicity induced by the conditioned culture media produced by LPS-stimulated BV-2 cells. The underlying mechanisms of action of senkyunolide A were further delineated. Its inhibitory effects were shown to be independent of the phosphorylation of mitogen-activated protein kinases (MAPK) and translocation of nuclear factor kappa B (NF-κB). However, senkyunolide A could increase the degradation of TNF-α mRNA and reduce its half life by 43%. In conclusion, bioactivity-guided fractionation is an effective way of isolating bioactive compounds from medicinal herbs. In addition, senkyunolide A and Z-ligustilide isolated from LCX may be considered as potential complementary drug candidates for treating inflammatory processes associated with cerebrovascular diseases.

Identification of the bioactive constituent and its mechanisms of action in mediating the anti-inflammatory effects of black cohosh and related Cimicifuga species on human primary blood macrophages

Cimicifuga species have been used as traditional medicinal herbs to treat inflammation and symptoms associated with menopause in Asia, Europe, and North America. However, the underlying mechanism of their anti-inflammatory effects remains to be investigated. With bioactivity guided purification involving the use of partitioning extraction and high performance liquid chromatography, we isolated one of the key bioactive constituents from the rhizome extracts of Cimicifuga racemosa. By NMR spectroscopy, the molecule was identified to be cimiracemate A (1). This compound (140 muM) suppressed the lipopolysaccharide-induced TNF-alpha production in the blood macrophages by 47 +/- 19% and 58 +/- 30% at LPS concentrations of 1 ng/mL and 10 ng/mL, respectively. The anti-inflammatory activity of compound 1 may be due to its modulation of a signaling mitogen activated protein kinase and transcription factor nuclear factor-kappaB activities. Compound 1 was found in other Cimicifuga species. Our data indicate that compound 1 or its chemical analogues may have the potential to be further developed as a new class of therapeutic agent.

Innate and adaptive immune responses regulated by glycogen synthase kinase-3 (GSK3)

In just a few years, the view of glycogen synthase kinase-3 (GSK3) has been transformed from an obscure enzyme seldom encountered in the immune literature to one implicated in an improbably large number of roles. GSK3 is a crucial regulator of the balance between pro- and anti-inflammatory cytokine production in both the periphery and the central nervous system, so that GSK3 inhibitors such as lithium can diminish inflammation. GSK3 influences T-cell proliferation, differentiation and survival. Many effects stem from GSK3 regulation of critical transcription factors, such as NF-kappaB, NFAT and STATs. These discoveries led to the rapid application of GSK3 inhibitors to animal models of sepsis, arthritis, colitis, multiple sclerosis and others, demonstrating their potential for therapeutic intervention.