Endotoxin tolerance impairs IL-1 receptor-associated kinase (IRAK) 4 and TGF-beta-activated kinase 1 activation, K63-linked polyubiquitination and assembly of IRAK1, TNF receptor-associated factor 6, and IkappaB kinase gamma and increases A20 expression

A20 is critical for the induction of Pam3CSK4-tolerance in monocytic THP-1 cells

A20 functions to terminate Toll-like receptor (TLR)-induced immune response, and play important roles in the induction of lipopolysacchride (LPS)-tolerance. However, the molecular mechanism for Pam3CSK4-tolerance is uncertain. Here we report that TLR1/2 ligand Pam3CSK4 induced tolerance in monocytic THP-1 cells. The pre-treatment of THP-1 cells with Pam3CSK4 down-regulated the induction of pro-inflammatory cytokines induced by Pam3CSK4 re-stimulation. Pam3CSK4 pre-treatment also down-regulated the signaling transduction of JNK, p38 and NF-κB induced by Pam3CSK4 re-stimulation. The activation of TLR1/2 induced a rapid and robust up-regulation of A20, suggesting that A20 may contribute to the induction of Pam3CSK4-tolerance. This hypothesis was proved by the observation that the over-expression of A20 by gene transfer down-regulated Pam3CSK4-induced inflammatory responses, and the down-regulation of A20 by RNA interference inhibited the induction of tolerance. Moreover, LPS induced a significant up-regulation of A20, which contributed to the induction of cross-tolerance between LPS and Pam3CSK4. A20 was also induced by the treatment of THP-1 cells with TNF-α and IL-1β. The pre-treatment with TNF-α and IL-1β partly down-regulated Pam3CSK4-induced activation of MAPKs. Furthermore, pharmacologic inhibition of GSK3 signaling down-regulated Pam3CSK4-induced A20 expression, up-regulated Pam3CSK4-induced inflammatory responses, and partly reversed Pam3CSK4 pre-treatment-induced tolerance, suggesting that GSK3 is involved in TLR1/2-induced tolerance by up-regulation of A20 expression. Taken together, these results indicated that A20 is a critical regulator for TLR1/2-induced pro-inflammatory responses.

Morphine induced exacerbation of sepsis is mediated by tempering endotoxin tolerance through modulation of miR-146a

Development of tolerance to endotoxin prevents sustained hyper inflammation during systemic infections. Here we report for the first time that chronic morphine treatment tempers endotoxin tolerance resulting in persistent inflammation, septicemia and septic shock. Morphine was found to down-regulate endotoxin/LPS induced miR-146a and 155 in macrophages. However, only miR-146a over expression, but not miR-155 abrogates morphine mediated hyper-inflammation. Conversely, antagonizing miR-146a (but not miR-155) heightened the severity of morphine-mediated hyper-inflammation. These results suggest that miR-146a acts as a molecular switch controlling hyper-inflammation in clinical and/or recreational use of morphine.

Evaluation of selected binding domains for the analysis of ubiquitinated proteomes

Ubiquitination is an abundant post-translational modification that consists of covalent attachment of ubiquitin to lysine residues or the N-terminus of proteins. Mono- and polyubiquitination have been shown to be involved in many critical eukaryotic cellular functions and are often disrupted by intracellular bacterial pathogens. Affinity enrichment of ubiquitinated proteins enables global analysis of this key modification. In this context, the use of ubiquitin-binding domains is a promising but relatively unexplored alternative to more broadly used immunoaffinity or tagged affinity enrichment methods. In this study, we evaluated the application of eight ubiquitin-binding domains that have differing affinities for ubiquitination states. Small-scale proteomics analysis identified ~200 ubiquitinated protein candidates per ubiquitin-binding domain pull-down experiment. Results from subsequent Western blot analyses that employed anti-ubiquitin or monoclonal antibodies against polyubiquitination at lysine 48 and 63 suggest that ubiquitin-binding domains from Dsk2 and ubiquilin-1 have the broadest specificity in that they captured most types of ubiquitination, whereas the binding domain from NBR1 was more selective to polyubiquitination. These data demonstrate that with optimized purification conditions, ubiquitin-binding domains can be an alternative tool for proteomic applications. This approach is especially promising for the analysis of tissues or cells resistant to transfection, of which the overexpression of tagged ubiquitin is a major hurdle.

Comprehensive genomic profiling in diabetic nephropathy reveals the predominance of proinflammatory pathways

Despite advances in the treatment of diabetic nephropathy (DN), currently available therapies have not prevented the epidemic of progressive chronic kidney disease (CKD). The morbidity of CKD, and the inexorable increase in the prevalence of end-stage renal disease, demands more effective approaches to prevent and treat progressive CKD. We undertook next-generation sequencing in a rat model of diabetic nephropathy to study in depth the pathogenic alterations involved in DN with progressive CKD. We employed the obese, diabetic ZS rat, a model that develops diabetic nephropathy, characterized by progressive CKD, inflammation, and fibrosis, the hallmarks of human disease. We then used RNA-seq to examine the combined effects of renal cells and infiltrating inflammatory cells acting as a pathophysiological unit. The comprehensive systems biology analysis of progressive CKD revealed multiple interactions of altered genes that were integrated into morbid networks. These pathological gene assemblies lead to renal inflammation and promote apoptosis and cell cycle arrest in progressive CKD. Moreover, in what is clearly a major therapeutic challenge, multiple and redundant pathways were found to be linked to renal fibrosis, a major cause of kidney loss. We conclude that systems biology applied to progressive CKD in DN can be used to develop novel therapeutic strategies directed to restore critical anomalies in affected gene networks.

IRAK4 kinase activity is not required for induction of endotoxin tolerance but contributes to TLR2-mediated tolerance

Prior exposure to LPS induces "endotoxin tolerance" that reprograms TLR4 responses to subsequent LPS challenge by altering expression of inflammatory mediators. Endotoxin tolerance is thought to limit the excessive cytokine storm and prevent tissue damage during sepsis but renders the host immunocompromised and susceptible to secondary infections. Tolerance initiated via one TLR can affect cellular responses to challenge via the same TLR ("homotolerance") or through different TLRs ("heterotolerance"). IRAK4, an essential component of the MyD88-dependent pathway, functions as a kinase and an adapter, activating subsets of divergent signaling pathways. In this study, we addressed mechanistically the role of IRAK4 kinase activity in TLR4- and TLR2-induced tolerance using macrophages from WT versus IRAK4(KDKI) mice. Whereas IRAK4 kinase deficiency decreased LPS signaling, it did not prevent endotoxin tolerance, as endotoxin pretreatment of WT and IRAK4(KDKI) macrophages inhibited LPS-induced MAPK phosphorylation, degradation of IκB-α and recruitment of p65 to the TNF-α promoter, expression of proinflammatory cytokines, and increased levels of A20 and IRAK-M. Pretreatment of WT macrophages with Pam3Cys, a TLR2-TLR1 agonist, ablated p-p38 and p-JNK in response to challenge with Pam3Cys and LPS, whereas IRAK4(KDKI) macrophages exhibited attenuated TLR2-elicited homo- and heterotolerance at the level of MAPK activation. Thus, IRAK4 kinase activity is not required for the induction of endotoxin tolerance but contributes significantly to TLR2-elicited homo- and heterotolerance.

Toll-like receptor polymorphisms, inflammatory and infectious diseases, allergies, and cancer

Toll-like receptors (TLRs) are germ-line-encoded innate immune sensors that recognize conserved microbial structures and host alarmins and signal expression of MHC proteins, costimulatory molecules, and inflammatory mediators by macrophages, neutrophils, dendritic cells, and other cell types. These processes activate immediate and early mechanisms of innate host defense, as well as initiate and orchestrate adaptive immune responses. Several single-nucleotide polymorphisms (SNPs) within the TLR genes have been associated with altered susceptibility to infectious, inflammatory, and allergic diseases, and have been found to play a role in tumorigenesis. Critical advances in our understanding of innate immune functions and genome-wide association studies (GWAS) have uncovered complex interactions of genetic polymorphisms within TLRs and environmental factors. However, conclusions obtained in the course of such analyses are restricted by limited power of many studies that is likely to explain controversial findings. Further, linkages to certain ethnic backgrounds, gender, and the presence of multigenic effects further complicate the interpretations of how the TLR SNPs affect immune responses. For many TLRs, the molecular mechanisms by which SNPs impact receptor functions remain unknown. In this review, I have summarized current knowledge about the TLR polymorphisms, their impact on TLR signaling, and associations with various inflammatory, infectious, allergic diseases and cancers, and discussed the directions of future scientific research.

Dissociation of endotoxin tolerance and differentiation of alternatively activated macrophages

Endotoxin tolerance is a complex phenomenon characterized primarily by decreased production of proinflammatory cytokines, chemokines, and other inflammatory mediators, whereas the expression of other genes are induced or unchanged. Endotoxin tolerance is induced by prior exposure of murine macrophages/human monocytes, experimental animals, or people to TLR ligands. Although recent studies reported a possible relationship between endotoxin tolerance and differentiation of alternatively activated macrophages (AA-MΦs or M2), we show in this study that LPS pretreatment of IL-4Rα(-/-) and STAT6(-/-) macrophages, which fail to develop into AA-MΦs, resulted in tolerance of proinflammatory cytokines, as well as molecules and chemokines previously associated with AA-MΦs (e.g., arginase-1, mannose receptor, CCL2, CCL17, and CCL22). In contrast to LPS, wild-type (WT) MΦs pretreated with IL-4, the prototype inducer of AA-MΦs, did not induce endotoxin tolerance with respect to proinflammatory cytokines, AA-MΦ-associated chemokines, negative regulators, NF-κB binding and subunit composition, and MAPKs; conversely, IL-13(-/-) macrophages were tolerized equivalently to WT MΦs by LPS pretreatment. Further, IL-4Rα deficiency did not affect the reversal of endotoxin tolerance exerted by the histone deacetylase inhibitor trichostatin A. Like WT mice, 100% of LPS-tolerized IL-4Rα-deficient mice survived LPS + d-galactosamine-induced lethal toxicity and exhibited decreased serum levels of proinflammatory cytokines and AA-MΦ-associated chemokines induced by LPS challenge compared with nontolerized mice. These data indicate that the signaling pathways leading to endotoxin tolerance and differentiation of AA-MΦs are dissociable.

IL-33 causes selective mast cell tolerance to bacterial cell wall products by inducing IRAK1 degradation

Mast cells are important cellular constituents of epithelial-mesenchymal interactions, densely located at sites of microbial entry into the host where they are continuously exposed to products from commensals. In order to avoid excessive activation and the associated pathology, mast cell responses to TLR agonists must be tightly regulated. Here, we show that exposure in vitro to subactivating levels of the epithelial cell product, IL-33, renders mast cells insensitive to bacterial cell wall products. Mast cell responsiveness to Ag, cytoplasmic dsDNA, and TLR7/8 agonists is unaffected or enhanced by IL-33. The IL-33-induced mast cell selective tolerance requires the IL-33 receptor ST2 and peritoneal mast cells from St2(-/-) mice display a constitutively activated phenotype, demonstrated by increased expression of activation markers including CD11b and CD28. IL-33 exposure neither affects the levels of TLR4, MyD88, TIRAP, IL-1R associated kinase 2 (IRAK2), or IRAK4, nor induces persistent A20 or Tollip expression, but potently causes ST2-dependent IRAK1 degradation. We show that while IRAK2 is redundant for TLR4 signaling, IRAK1 is essential for TLR4 signaling in mast cells. We suggest that IL-33 produced during homeostasis retains mast cells in an unresponsive state to bacterial cell wall products via IRAK1 degradation, thus preventing chronic inflammation and tissue destruction.

The antitumor effect of the toll-like receptor 3 ligand polyinosinic-cytidylic acid as an adjuvant

Although polyinosinic-polycytidylic acid (poly(I:C)) has been applied in tumor immunity as a Toll-like receptor 3 (TLR3) ligand, the interaction between poly(I:C) and TLR3 is still unclear, as are the mechanisms underlying the antitumor effect of poly(I:C). Our aim was to investigate the interaction between poly(I:C) and TLR3, as well as the mechanisms underlying the antitumor effect of poly(I:C). NK92 cells were maintained in medium (untreated group), or medium containing E7(44-62) (E7 group) or E7(44-62)+poly(I:C) (poly(I:C)/E7 group), and we measured the expression of TLR3 mRNA, p-p65, and IκB-α protein. The cells were first incubated in medium alone or medium containing TLR3 monoclonal antibody, and then in medium containing poly(I:C)/E7. Finally, we measured the level of interferon-beta (INF-β) in the supernatant and determined the tumor cell-killing effect of the NK92 cells. At 1 h, the expression of TLR3 mRNA in the poly(I:C)/E7 group was markedly higher than that in the untreated and E7 groups (P < 0.05). When compared with the poly(I:C)/E7 group, the expression of IκB-α was dramatically increased in the E7 and untreated groups, and the expression of p-p65 was dramatically decreased in the E7 and untreated groups (all P < 0.05). At 24 h, INF-β content and tumor cell-killing activity in the poly(I:C)/E7 group were markedly higher than those in the untreated group (P < 0.001, <0.05, respectively). Treatment with TLR3 monoclonal antibody significantly inhibited poly(I:C)/E7-induced INF-β secretion and tumor cell-killing activity in NK92 cells (P < 0.001, <0.05, respectively). The interaction between poly(I:C) and TLR3 plays an important role in the antitumor immunity of NK92 cells. In addition, the interaction between poly(I:C) and TLR3 increases INF-β expression, which may be attributed to the activation of NFκB.

HangAmDan-B, an ethnomedicinal herbal mixture, suppresses inflammatory responses by inhibiting Syk/NF-κB and JNK/ATF-2 pathways

HangAmDan-B (HAD-B) is a powdered mixture of eight ethnopharmacologically characterized folk medicines that is prescribed for solid masses and cancers in Korea. In view of the finding that macrophage-mediated inflammation is a pathophysiologically important phenomenon, we investigated whether HAD-B modulates inflammatory responses and explored the associated molecular mechanisms. The immunomodulatory activity of HAD-B in toll-like receptor-activated macrophages induced by lipopolysaccharide (LPS) was assessed by measuring nitric oxide (NO) and prostaglandin E(2) (PGE(2)) levels. To identify the specific transcription factors (such as nuclear factor [NF]-κB and signaling enzymes) targeted by HAD-B, biochemical approaches, including kinase assays and immunoblot analysis, were additionally employed. HAD-B suppressed the production of PGE(2) and NO in LPS-activated macrophages in a dose-dependent manner. Furthermore, the extract ameliorated HCl/EtOH-induced gastritis symptoms. Moreover, HAD-B significantly inhibited LPS-induced mRNA expression of inducible NO synthase and cyclooxygenase (COX)-2. Interestingly, marked inhibition of NF-κB and activating transcription factor was observed in the presence of HAD-B. Data from direct kinase assays and immunoblot analysis showed that HAD-B suppresses activation of the upstream signaling cascade involving spleen tyrosine kinase, Src, p38, c-Jun N-terminal kinase, and transforming growth factor β-activated kinase 1. Finally, kaempferol, but not quercetin or resveratrol was identified as a bioactive compound in HAD-B. Therefore, our results suggest that HAD-B possesses anti-inflammatory activity that contributes to its anticancer property.

R753Q polymorphism inhibits Toll-like receptor (TLR) 2 tyrosine phosphorylation, dimerization with TLR6, and recruitment of myeloid differentiation primary response protein 88

The R753Q polymorphism in the Toll-IL-1 receptor domain of Toll-like receptor 2 (TLR2) has been linked to increased incidence of tuberculosis and other infectious diseases, but the mechanisms by which it affects TLR2 functions are unclear. Here, we studied the impact of the R753Q polymorphism on TLR2 expression, hetero-dimerization with TLR6, tyrosine phosphorylation, and recruitment of myeloid differentiation primary response protein (MyD) 88 and MyD88 adapter-like (Mal). Complementation of HEK293 cells with transfected WT or R753Q TLR2 revealed their comparable total levels and only minimal changes in cell surface expression of the mutant species. Notably, even a 100-fold increase in amounts of transfected R753Q TLR2 versus WT variant did not overcome the compromised ability of the mutant TLR2 to activate nuclear factor κB (NF-κB), indicating that a minimal decrease in cell surface levels of the R753Q TLR2 cannot account for the signaling deficiency. Molecular modeling studies suggested that the R753Q mutation changes the electrostatic potential of the DD loop and results in a discrete movement of the residues critical for protein-protein interactions. Confirming these predictions, biochemical assays demonstrated that R753Q TLR2 exhibits deficient agonist-induced tyrosine phosphorylation, hetero-dimerization with TLR6, and recruitment of Mal and MyD88. These proximal signaling deficiencies correlated with impaired capacities of the R753Q TLR2 to mediate p38 phosphorylation, NF-κB activation, and induction of IL-8 mRNA in transfected HEK293 cells challenged with inactivated Mycobacterium tuberculosis or mycobacterial components. Thus, the R753Q polymorphism renders TLR2 signaling-incompetent by impairing its tyrosine phosphorylation, dimerization with TLR6, and recruitment of Mal and MyD88.

Age-related defects in TLR2 signaling diminish the cytokine response by alveolar macrophages during murine pneumococcal pneumonia

Alveolar macrophages (AMs) are the first immune cells to respond to an invading pathogen and coordinate the inflammatory response within the lungs. Studies suggest that macrophages exhibit age-related deficiencies in Toll-like receptor (TLR) function; however, the impact of this dysfunction during pneumonia, the leading cause of infectious death in the elderly, and the underlying mechanisms responsible remain unclear. We examined disease severity in young, mature, and aged BALB/cBy mice following intratracheal infection with the Gram-positive bacteria Streptococcus pneumoniae (Spn). Both mature and aged mice failed to clear bacteria and as a result had increased mortality, tissue damage and vascular leakage. Early production of TNFα, IL-1β, and IL-6 during pneumonia declined with age and was associated with an inability of isolated AMs to respond to pneumococcal cell wall (CW) and ethanol-killed Spn ex vivo. Total levels of TLR1 were unaffected by age and TLR2 surface expression was slightly yet significantly increased on aged AMs suggesting that intracellular TLR signaling defects were responsible for the age-related decline in cytokine responsiveness. Following infection of isolated AMs with live Spn, a significant age-related decline in TLR2-induced phosphorylation of p65 NFκB, JNK and p38 MAPK, and an increase in ERK phosphorylation was observed by immunoblotting. These data are the first to demonstrate that TLR2-dependent recognition of Spn by aged AMs is impaired and is associated with a delayed pro-inflammatory cytokine response in vivo along with enhanced susceptibility to pneumococcal pneumonia.

Identification and characterization of IL-1 receptor-associated kinase-4 (IRAK-4) in half-smooth tongue sole Cynoglossus semilaevis

As a crucial component in TLR/IL-1R signaling pathways, IRAK-4 plays a central role in innate and adaptive immunity. In the present study, the cDNA of IRAK-4 was cloned for the first time from half-smooth tongue sole (Cynoglossus semilaevis). The full-length cDNA of csIRAK-4 was 2149 bp and contained a 168 bp 5' UTR, a 580 bp 3' UTR and a 1401 bp CDS. The predicted protein sequence of csIRAK-4 had two typical domains, a death domain (DD) at the N terminus and a serine/threonine/tyrosine protein kinase domain (STYKc) at the C terminus. RT-PCR showed that csIRAK-4 mRNA was detected in all tested tissues, especially in immune-related organs, gonads and brain. After injected with inactivated Vibrio anguillarum, the expressions of csIRAK-4 were up-regulated significantly (P<0.05) in spleen and head kidney. During development, csIRAK-4 was expressed at all selected stages and low-level expression was detected at metamorphosis. Taken together, the present study indicated that csIRAK-4 played a crucial role in immune responses and might be involved in the process of development.

Dysregulated inflammation as a risk factor for pneumonia in the elderly

Advances in modern medicine have led to an increase in the median life span and an expansion of the world's population over the age of 65. With increasing numbers of the population surviving to the extreme of age, those at risk for the development of pneumonia will approach 2 billion by the year 2050. Numerous age-related changes in the lung likely contribute to the enhanced occurrence of pneumonia in the elderly. Inflammation in the elderly has been shown to increase risk prior to infection; age-associated inflammation enhances bacterial ligand expression in the lungs which increases the ability of bacteria to attach and invade host cells. Conversely, the elaboration of the acute inflammatory response during early infection has been found to decrease with age resulting in a delayed immune response and diminished bacterial killing. Finally, the resolution of the inflammatory response during the convalescent stage back to "baseline" is often prolonged in the elderly and associated with negative outcomes, such as adverse cardiac events. The focus of this review will be to discuss our current understanding of the potential mechanisms by which dysregulated inflammation (both prior to and following an infectious insult) enhances susceptibility to and severity of community acquired pneumonia (CAP) in the elderly with an emphasis on pneumococcal pneumonia, the leading cause of CAP.

Anti-inflammatory activity of ethanol extract derived from Phaseolus angularis beans

ETHNOPHARMACOLOGICAL SIGNIFICANCE

Phaseolus angularis Wight (adzuki bean) is an ethnopharmacologically well-known folk medicine that is prescribed for infection, edema, and inflammation of the joints, appendix, kidney and bladder in Korea, China and Japan.

AIM OF STUDY

The anti-inflammatory effect of this plant and its associated molecular mechanisms will be investigated.

MATERIALS AND METHODS

The immunomodulatory activity of Phaseolus angularis ethanol extract (Pa-EE) in toll like receptor (TLR)-activated macrophages induced by ligands such as lipopolysaccharide (LPS), Poly (I:C), and pam3CSK was investigated by assessing nitric oxide (NO) and prostaglandin (PG)E(2) levels. To identify which transcription factors such as nuclear factor (NF)-κB and their signaling enzymes can be targeted to Pa-EE, biochemical approaches including reporter gene assays, immunoprecipitation, kinase assays, and immunoblot analyses were also employed. Finally, whether Pa-EE was orally available, ethanol (EtOH)/hydrochloric acid (HCl)-induced gastritis model in mice was used.

RESULTS

Pa-EE dose-dependently suppressed the release of PGE(2) and NO in LPS-, Poly(I:C)-, and pam3CSK-activated macrophages. Pa-EE strongly down-regulated LPS-induced mRNA expression of inducible NO synthase (iNOS) and cyclooxygenase (COX)-2. Interestingly, Pa-EE markedly inhibited NF-κB, activator protein (AP)-1, and cAMP response element binding protein (CREB) activation; further, according to direct kinase assays and immunoblot analyses, Pa-EE blocked the activation of the upstream signaling molecules spleen tyrosine kinase (Syk), p38, and transforming growth factor β-activated kinase 1 (TAK1). Finally, orally administered Pa-EE clearly ameliorated EtOH/HCl-induced gastritis in mice.

CONCLUSION

Our results suggest that Pa-EE can be further developed as a promising anti-inflammatory remedy because it targets multiple inflammatory signaling enzymes and transcription factors.

TGF-β1 re-programs TLR4 signaling in L. donovani infection: enhancement of SHP-1 and ubiquitin-editing enzyme A20

Visceral leishmaniasis (VL), caused by Leishmania donovani, is a major health concern in India. It represents T-helper type 2 (Th2) bias of cytokines in active state and Th1 bias at cure. However, the role of the parasite in regulating Toll-like receptor (TLR)-mediated macrophage activation in VL patients remains elusive. In this report, we demonstrated that later stages of L. donovani infection rendered tolerance to macrophages, leading to incapability for the production of inflammatory cytokines like tumor necrosis factor (TNF)-α and interleukin (IL)-1β in response to TLR stimulation. Overexpression of transforming growth factor (TGF)-β(1), but not IL-10, resulted in suppressed lipopolysaccharide (LPS)-induced production of TNF-α and downregulation of TLR4 expression in L. donovani-infected macrophages. Recombinant human (rh)TGF-β(1) markedly enhanced tyrosine phosphatase (Src homology region 2 domain-containing phosphatase-1) activity, but inhibited IL-1 receptor-activated kinase (IRAK)-1 activation. Addition of neutralizing TGF-β(1) antibody reversed these effects, and thus suggesting the pivotal role of TGF-β(1) in promoting refractoriness for LPS in macrophages. Surprisingly, the use of a tyrosine phosphatase inhibitor (sodium orthovanadate, Na(3)VO(4)) promoted IRAK-1 activation, confirming the negative inhibitory role of tyrosine phosphatase in macrophage activation. Furthermore, rhTGF-β(1) induced tolerance in infected macrophages by reducing inhibitory protein (IκBα) degradation in a time-dependent manner. In addition, short interfering RNA studies proved that overexpression of A20 ubiquitin-editing protein complex induced inhibitory activity of TGF-β(1) on LPS-mediated nuclear factor-κB activation. Thus, these findings suggest that TGF-β(1) promotes overexpression of A20 through tyrosine phosphatase activity that ensures transient activation of inflammatory signaling pathways in macrophages in active L. donovani infection.

Induction of endotoxin tolerance in vivo inhibits activation of IRAK4 and increases negative regulators IRAK-M, SHIP-1, and A20

TLRs mediate host defense against microbial pathogens by eliciting production of inflammatory mediators and activating expression of MHC, adhesion, and costimulatory molecules. Endotoxin tolerance limits excessive TLR-driven inflammation during sepsis and reprograms macrophage responses to LPS, decreasing expression of proinflammatory cytokines without inhibiting anti-inflammatory and antimicrobial mediators. Molecular mechanisms of reprogramming of TLR4 signaling upon in vivo induction of endotoxin tolerance are incompletely understood. We used an in vivo model of endotoxin tolerance, whereby C57BL/6 mice were i.p.-inoculated with LPS or PBS, followed by in vitro challenge of peritoneal or splenic macrophages with LPS to examine activation of IRAK4 and expression of negative regulatory molecules. Administration of LPS in vivo-induced endotoxin tolerance in peritoneal and splenic macrophages, as evidenced by decreased degradation of IκBα, suppressed phosphorylation of p38 and reduced expression of TNF-α, IL-6, and KC mRNA upon in vitro LPS challenge. Macrophages from control and endotoxin-tolerant mice exhibited comparable TLR4 mRNA levels and similar expression of IL-1RA and IL-10 genes. Endotoxin tolerization in vivo blocked TLR4-driven IRAK4 phosphorylation and activation in macrophages, while increasing expression of IRAK-M, SHIP-1, A20 mRNA, and A20 protein. Thus, induction of endotoxin tolerance in vivo inhibits expression of proinflammatory mediators via impaired activation of IRAK4, p38, and NF-κB and increases expression of negative regulators of TLR4 pathways.

Altered Toll-like receptor 2-mediated endotoxin tolerance is related to diminished interferon beta production

Induction of endotoxin tolerance leads to a reduced inflammatory response after repeated challenge by LPS and is important for resolution of inflammation and prevention of tissue damage. Enterobacterial LPS is recognized by the TLR4 signaling complex, whereas LPS of some non-enterobacterial organisms is capable of signaling independently of TLR4 utilizing TLR2-mediated signal transduction instead. In this study we report that Porphyromonas gingivalis LPS, a TLR2 agonist, fails to induce a fully endotoxin tolerant state in a human monocytic cell line (THP-1) and mouse bone marrow-derived macrophages. In contrast to significantly decreased production of human IL-8 and TNF-α and, in mice, keratinocyte-derived cytokine (KC), macrophage inflammatory protein-2 (MIP-2), and TNF-α after repeated challenge with Escherichia coli LPS, cells repeatedly exposed to P. gingivalis LPS responded by producing less TNF-α but sustained elevated secretion of IL-8, KC, and MIP-2. Furthermore, in endotoxin-tolerant cells, production of IL-8 is controlled at the signaling level and correlates well with NF-κB activation, whereas TNF-α expression is blocked at the gene transcription level. Interferon β plays an important role in attenuation of chemokine expression in endotoxin-tolerized cells as shown in interferon regulatory factor-3 knock-out mice. In addition, human gingival fibroblasts, commonly known not to display LPS tolerance, were found to be tolerant to repeated challenge by LPS if pretreated with interferon β. The data suggest that the inability of the LPS-TLR2 complex to induce full endotoxin tolerance in monocytes/macrophages is related to diminished production of interferon β and may partly explain the involvement of these LPS isoforms in the pathogenesis of chronic inflammatory diseases.

Contrasting ocular effects of local versus systemic endotoxin

PURPOSE. A marked cellular infiltrate has been observed when endotoxin (lipopolysaccharide [LPS]) is injected into the mouse eye, but systemically injected LPS does not produce a comparable effect. Several hypotheses were tested to reconcile this discordance. METHODS. BALB/c mice were injected intravitreally (ivt) or intraperitoneally (ip) with Escherichia coli LPS. Uveitis was assessed by traditional and intravital microscopy. Cytokine levels in the eye, plasma, or spleen were measured by single or multiplex ELISA assays. RESULTS. The eye's higher sensitivity was confirmed to local LPS exposure, as 250 ng ivt LPS produced a brisk leukocytic infiltrate whereas ip injection of 100 μg LPS did not. The hypothesis was tested that the lack of a cellular infiltrate after ip LPS is explained by less induction of cytokines in the eye, but surprisingly, ip LPS resulted in comparable cytokine levels to ivt LPS. The hypothesis was disproved that the eye's sensitivity to local LPS is due to lack of expression of intracellular inhibitors of LPS such as A20, IRAK-M, or SARM. Finally, the hypothesis that systemic LPS inhibits diapedesis was tested by injection of LPS ip and ivt simultaneously, a strategy that did not significantly reduce leukocyte rolling or sticking in iris vessels but blocked the cellular infiltrate normally seen with ivt LPS. CONCLUSIONS. Systemic and local LPS exposures produce discordant effects within the murine eye. The hypothesis that systemic LPS desensitizes leukocytes to the stimuli responsible for transmigration offers a plausible explanation for this discordance.

Epigenetics, bioenergetics, and microRNA coordinate gene-specific reprogramming during acute systemic inflammation

Acute systemic inflammation from infectious and noninfectious etiologies has stereotypic features that progress through an initiation (proinflammatory) phase, an adaptive (anti-inflammatory) phase, and a resolution (restoration of homeostasis) phase. These phase-shifts are accompanied by profound and predictable changes in gene expression and metabolism. Here, we review the emerging concept that the temporal phases of acute systemic inflammation are controlled by an integrated bioenergy and epigenetic bridge that guides the timing of transcriptional and post-transcriptional processes of specific gene sets. This unifying connection depends, at least in part, on redox sensor NAD(+)-dependent deacetylase, Sirt1, and a NF-κB-dependent p65 and RelB feed-forward and gene-specific pathway that generates silent facultative heterochromatin and active euchromatin. An additional level of regulation for gene-specific reprogramming is generated by differential expression of miRNA that directly and indirectly disrupts translation of inflammatory genes. These molecular reprogramming circuits generate a dynamic chromatin landscape that temporally defines the course of acute inflammation.