Regulation of acute inflamation by oncostatin M receptor-beta

Although the interleukin (IL)-6 related cytokine Oncostatin M (OSM) affects a variety of inflammatory events associated with disease progression, the function of OSM in the face of an inflammatory challenge remains unclear. In this thesis a peritoneal model of inflammation, in association with in vitro studies using human primary cell lines, has been used to define the influence of OSM on chemokine-mediated leukocyte recruitment. When compared to wild type mice (WT) the induction of peritoneal inflammation in Oncostatin M receptor-beta deficient mice (OSMR-KO) resulted in enhanced monocytic cell trafficking, with no differences in neutrophil or lymphocyte recruitment observed, suggesting that OSM control of leukocyte recruitment is functionally distinct from that of IL-6. Subsequent in vitro studies and an in vivo appraisal of inflammatory chemokine expression following peritoneal inflammation inferred that OSM regulation of CCL5 might account for the observed difference in monocytic cell trafficking. The OSM-mediated control of CCL5 is clearly distinct from the actions of IL-6, which acts as a more prominent in vivo regulator of CCL2 expression than OSM. Mechanistically, these studies inferred a hitherto unidentified interplay between OSM-mediated STAT signalling and NF-kappaB activation. In this respect, EMSA analysis of nuclear extracts from peritoneal membranes isolated during course of the inflammatory response showed that OSMR-KO mice display an enhanced profile of NF-kappaB activation as compared to WT mice. Initial in vivo appraisal of the role of OSMRg-mediated signalling in repeated episodes of inflammation and associated tissue damage suggest that OSM continues to regulate monocytic cell trafficking throughout recurrent inflammatory episodes and does not play a significant role in inflammation-associated peritoneal tissue damage, again a finding clearly distinct from the observed effects of IL-6 in tissue injury. These findings suggest that activation of gp 130 by IL-6 and OSM trigger distinct inflammatory responses to affect individual aspects of leukocyte trafficking

The Pivotal Role of Macrophages in Metabolic Distress

Obesity is a prevalent condition with several associated co-morbidities including the development of metabolic diseases. In obesity there is immune cell infiltration into the white adipose tissue and this is associated with the generation of inflammation and insulin resistance (IR). A large majority of the infiltrating leukocytes in obese adipose tissue are pro-inflammatory macrophages, which upon activation induce a switch in metabolism from oxidative phosphorylation, as is utilised by macrophages in lean adipose tissue, towards aerobic glycolysis. The signalling pathways evoked in the recruited macrophages induce the release of pro-inflammatory cytokines, in signalling pathways which directly interfere with insulin signalling and thus induce a state of IR. As macrophages appear to play such a pivotal role in the generation of IR and are the largest leukocyte population in the adipose tissue, they provide a promising therapeutic target. Indeed, there are several strategies currently being studied to induce a ‘switch’ in macrophages associated with obese adipose tissue, towards the phenotype of those associated with lean adipose tissue, with arguably the most promising being those strategies designed to target the metabolic pathways within the macrophages. This chapter will discuss the polarisation and activation of macrophages within lean and obese adipose tissue and how these cells can be targeted therapeutically

Btk Regulated Macrophage Polarization in Response to Lipopolysaccharide

Bacterial Lipopolysaccharide (LPS) is a strong inducer of inflammation and does so by inducing polarization of macrophages to the classic inflammatory M1 population. Given the role of Btk as a critical signal transducer downstream of TLR4, we investigated its role in M1/M2 induction. In Btk deficient (Btk−\−) mice we observed markedly reduced recruitment of M1 macrophages following intraperitoneal administration of LPS. Ex vivo analysis demonstrated an impaired ability of Btk−/− macrophages to polarize into M1 macrophages, instead showing enhanced induction of immunosuppressive M2-associated markers in response to M1 polarizing stimuli, a finding accompanied by reduced phosphorylation of STAT1 and enhanced STAT6 phosphorylation. In addition to STAT activation, M1 and M2 polarizing signals modulate the expression of inflammatory genes via differential activation of transcription factors and regulatory proteins, including NF-κB and SHIP1. In keeping with a critical role for Btk in macrophage polarization, we observed reduced levels of NF-κB p65 and Akt phosphorylation, as well as reduced induction of the M1 associated marker iNOS in Btk−/− macrophages in response to M1 polarizing stimuli. Additionally enhanced expression of SHIP1, a key negative regulator of macrophage polarisation, was observed in Btk−/− macrophages in response to M2 polarizing stimuli. Employing classic models of allergic M2 inflammation, treatment of Btk−/− mice with either Schistosoma mansoni eggs or chitin resulted in increased recruitment of M2 macrophages and induction of M2-associated genes. This demonstrates an enhanced M2 skew in the absence of Btk, thus promoting the development of allergic inflammation

Cutting Edge: Suppression of GM-CSF Expression in Murine and Human T Cells by IL-27:suppression of GM-CSF expression in murine and human T cells by IL-27

GM-CSF is a potent pro-inflammatory cytokine that plays a pathogenic role in the CNS inflammatory disease, EAE. As IL-27 ameliorates EAE, we hypothesised that IL-27 suppresses GM-CSF expression by T cells. We found that IL-27 suppressed GM-CSF expression in CD4(+) and CD8(+) T cells in splenocyte and purified T cell cultures. IL-27 suppressed GM-CSF in Th1, but not Th17 cells. IL-27 also suppressed GM-CSF expression by human T cells in non-polarised and Th1 but not Th17 polarised PBMC cultures. In vivo, IL-27p28 deficiency resulted in increased GM-CSF expression by CNS infiltrating T cells during Toxoplasma gondii infection. While in vitro suppression of GM-CSF by IL-27 was independent of IL-2 suppression, IL-10 up-regulation or SOCS3 signalling, we observed that IL-27-driven suppression of GM-CSF was STAT1 dependent. Our findings demonstrate that IL-27 is a robust negative regulator of GM-CSF expression in T cells which likely inhibits T cell pathogenicity in CNS inflammation

The helminth T2 RNase v1 promotes metabolic homeostasis in an IL-33– and group 2 innate lymphoid cell–dependent mechanism

Induction of a type 2 cellular response in the white adipose tissue leads to weight loss and improves glucose homeostasis in obese animals. Injection of obese mice with recombinant helminth-derived Schistosoma mansoni egg-derived v1 (v1), a potent inducer of type 2 activation, improves metabolic status involving a mechanism reliant upon release of the type 2 initiator cytokine IL-33. IL-33 initiates the accumulation of group 2 innate lymphoid cells (ILC2s), eosinophils, and alternatively activated macrophages in the adipose tissue. IL-33 release from cells in the adipose tissue is mediated by the RNase activity of v1; however, the ability of v1 to improve metabolic status is reliant upon effective binding of v1 to CD206. We demonstrate a novel mechanism for RNasemediated release of IL-33 inducing ILC2-dependent improvements in the metabolic status of obese animals.— Hams, E., Bermingham, R., Wurlod, F. A., Hogan, A. E., O’Shea, D., Preston, R. J., Rodewald, H.-R., McKenzie, A. N. J., Fallon, P. G. The helminth T2 RNase v1 promotes metabolic homeostasis in an IL-33– and group 2 innate lymphoid cell–dependent mechanism

The Hydroxylase Inhibitor Dimethyloxallyl Glycine Attenuates Endotoxic Shock Via Alternative Activation of Macrophages and IL-10 Production by B1 Cells

Localized tissue hypoxia is a feature of infection and inflammation, resulting in the upregulation of the transcription factors HIF-1α and NF-κB via inhibition of oxygen sensing hydroxylase enzymes. Previous studies have demonstrated a beneficial role for the hydroxylase inhibitor dimethyloxallyl glycine (DMOG) in inflammatory conditions, including experimental colitis, by regulating the activity of HIF-1 and NF-κB. We have demonstrated in vivo that pre-treatment with DMOG attenuates systemic LPS-induced activation of the NF-κB pathway. Furthermore, mice treated with DMOG had significantly increased survival in LPS-induced shock. Conversely, in models of polymicrobial sepsis, DMOG exacerbates disease severity. DMOG treatment of mice promotes M2 polarization in macrophages within the peritoneal cavity, resulting in the downregulation of pro-inflammatory cytokines such as TNFα. In addition, in vivo DMOG treatment upregulates IL-10 expression, specifically in the peritoneal B-1 cell population. This study demonstrates cell type specific roles for hydroxylase inhibition in vivo and provides insight into the mechanism underlying the protection conveyed by DMOG in models of endotoxic shock

Regulation of IL-1β-induced NFκB by hydroxylases links key hypoxic and inflammatory signaling pathways

Hypoxia is a prominent feature of chronically inflamed tissues. Oxygen-sensing hydroxylases control transcriptional adaptation to hypoxia through the regulation of hypoxia-inducible factor (HIF) and nuclear factor ?B (NF-?B), both of which can regulate the inflammatory response. Furthermore, pharmacologic hydroxylase inhibitors reduce inflammation in multiple animal models. However, the underlying mechanism(s) linking hydroxylase activity to inflammatory signaling remains unclear. IL-1ß, a major proinflammatory cytokine that regulates NF-?B, is associated with multiple inflammatory pathologies. We demonstrate that a combination of prolyl hydroxylase 1 and factor inhibiting HIF hydroxylase isoforms regulates IL-1ß-induced NF-?B at the level of (or downstream of) the tumor necrosis factor receptor-associated factor 6 complex. Multiple proteins of the distal IL-1ß-signaling pathway are subject to hydroxylation and form complexes with either prolyl hydroxylase 1 or factor inhibiting HIF. Thus, we hypothesize that hydroxylases regulate IL-1ß signaling and subsequent inflammatory gene expression. Furthermore, hydroxylase inhibition represents a unique approach to the inhibition of IL-1ß-dependent inflammatory signaling

MHCII-mediated dialog between group 2 innate lymphoid cells and CD4+ T cells potentiates type 2 immunity and promotes parasitic helminth expulsion

Group 2 innate lymphoid cells (ILC2s) release interleukin-13 (IL-13) during protective immunity to helminth infection and detrimentally during allergy and asthma. Using two mouse models to deplete ILC2s in vivo, we demonstrate that T helper 2 (Th2) cell responses are impaired in the absence of ILC2s. We show that MHCII-expressing ILC2s interact with antigen-specific T cells to instigate a dialog in which IL-2 production from T cells promotes ILC2 proliferation and IL-13 production. Deletion of MHCII renders IL-13-expressing ILC2s incapable of efficiently inducing Nippostrongylus brasiliensis expulsion. Thus, during transition to adaptive T cell-mediated immunity, the ILC2 and T cell crosstalk contributes to their mutual maintenance, expansion and cytokine production. This interaction appears to augment dendritic-cell-induced T cell activation and identifies a previously unappreciated pathway in the regulation of type-2 immunity

Toll-like Receptor 3 L412F Polymorphism Promotes a Persistent Clinical Phenotype in Pulmonary Sarcoidosis

Background: Sarcoidosis is a multisystemic disorder of unknown etiology, characterised by the presence of non-caseating granulomas in target organs. In ninety percent of cases, there is thoracic involvement. Fifty to seventy percent of pulmonary sarcoidosis patients will experience acute, self-limiting disease. For the subgroup of patients who develop persistent disease, no targeted therapy is currently available. Aim: To investigate the potential of the single nucleotide polymorphism (SNP), Toll-like receptor 3 Leu412Phe (TLR3 L412F; rs3775291), as a causative factor in the development of, and in disease persistence in pulmonary sarcoidosis. To investigate the functionality of TLR3 L412F in vitro in primary human lung fibroblasts from pulmonary sarcoidosis patients. Methods: Cohorts of Irish sarcoidosis patients (n=228), healthy Irish controls (n = 263) and a secondary cohort of American sarcoidosis patients (n=123) were genotyped for TLR3 L412F. Additionally, the effect of TLR3 L412F in primary lung fibroblasts from pulmonary sarcoidosis patients was quantitated following TLR3 activation in the context of cytokine and type I interferon production, TLR3 expression, and apoptotic- and fibroproliferative-responses. Results: We report a significant association between TLR3 L412F and persistent clinical disease in two cohorts of Irish and American Caucasians with pulmonary sarcoidosis. Furthermore, activation of TLR3 in primary lung fibroblasts from 412F-homozygous pulmonary sarcoidosis patients resulted in reduced IFN-â and TLR3 expression, reduced apoptosis- and dysregulated fibroproliferative-responses compared with TLR3 wild-type patients. Conclusions: This study identifies defective TLR3 function as a previously unidentified factor in persistent clinical disease in pulmonary sarcoidosis and reveals TLR3 L412F as a candidate biomarker