Cytokines induce an early steroid resistance in airway smooth muscle cells: novel role of interferon regulatory factor-1

Inflammatory endotypes of adenoidal hypertrophy based on a cluster analysis of biomarkers

OBJECTIVE

To identify adenoid inflammatory endotypes based on inflammatory markers, match endotypes to phenotypes, and predict endotypes.

METHODS

This cross-sectional study included 72 children with adenoid hypertrophy. Thirteen inflammatory markers and total immunoglobulin E (TIgE) in adenoid tissue were analyzed using Luminex and enzyme-linked immunosorbent assay (ELISA) for performing cluster analysis. Correlation analysis was used to examine the characteristics of each cluster. Receiver operating characteristic (ROC) curve analysis was performed to screen for preoperative characteristic data with predictive value for adenoid inflammation endotype.

RESULTS

The patients were divided into four clusters. Cluster 1 exhibited non-type 2 signatures with low inflammatory marker concentrations, except for the highest expression of Th1-related cytokines. Cluster 2 showed a non-type 2 endotype with the highest concentration of interleukin (IL)-17A and IL-22. Cluster 3 exhibited moderate type 2 inflammation, with the highest concentration of neutrophil factors. Cluster 4 demonstrated significant type 2 inflammation and moderate neutrophil levels. The proportions of AR and serum TIgE levels increased from clusters 1 to 4, and there was a gradual increase in the prevalence of chronic sinusitis from low to high neutrophilic inflammation. The area under the ROC curve for serum TIgE was higher than those for combined or other separate preoperative characteristics for predicting non-type 2 and type 2 inflammation in the adenoid tissue.

CONCLUSIONS

The evaluation of cytokines in adenoid tissue revealed four endotypes. Serum TIgE level was an important indicator of the endotype of adenoid inflammation. Identification of adenoid inflammatory endotypes can facilitate targeted treatment decisions.

Synergy between Interleukin-1β, Interferon-γ, and Glucocorticoids to Induce TLR2 Expression Involves NF-κB, STAT1, and the Glucocorticoid Receptor

Glucocorticoids act via the glucocorticoid receptor (GR; NR3C1) to downregulate inflammatory gene expression and are effective treatments for mild to moderate asthma. However, in severe asthma and virus-induced exacerbations, glucocorticoid therapies are less efficacious, possibly due to reduced repressive ability and/or the increased expression of proinflammatory genes. In human A549 epithelial and primary human bronchial epithelial cells, toll-like receptor (TLR)-2 mRNA and protein were supra-additively induced by interleukin-1β (IL-1β) plus dexamethasone (IL-1β+Dex), interferon-γ (IFN-γ) plus dexamethasone (IFN-γ+Dex), and IL-1β plus IFN-γ plus dexamethasone (IL-1β+IFN-γ+Dex). Indeed, ∼34- to 2100-fold increases were apparent at 24 hours for IL-1β+IFN-γ+Dex, and this was greater than for any single or dual treatment. Using the A549 cell model, TLR2 induction by IL-1β+IFN-γ+Dex was antagonized by Org34517, a competitive GR antagonist. Further, when combined with IL-1β, IFN-γ, or IL-1β+IFN-γ, the enhancements by dexamethasone on TLR2 expression required GR. Likewise, inhibitor of κB kinase 2 inhibitors reduced IL-1β+IFN-γ+Dex-induced TLR2 expression, and TLR2 expression induced by IL-1β+Dex, with or without IFN-γ, required the nuclear factor (NF)-κB subunit, p65. Similarly, signal transducer and activator of transcription (STAT)-1 phosphorylation and γ-interferon-activated sequence-dependent transcription were induced by IFN-γ These, along with IL-1β+IFN-γ+Dex-induced TLR2 expression, were inhibited by Janus kinase (JAK) inhibitors. As IL-1β+IFN-γ+Dex-induced TLR2 expression also required STAT1, this study reveals cooperation between JAK-STAT1, NF-κB, and GR to upregulate TLR2 expression. Since TLR2 agonism elicits inflammatory responses, we propose that synergies involving TLR2 may occur within the cytokine milieu present in the immunopathology of glucocorticoid-resistant disease, and this could promote glucocorticoid resistance. SIGNIFICANCE STATEMENT: This study highlights that in human pulmonary epithelial cells, glucocorticoids, when combined with the inflammatory cytokines interleukin-1β (IL-1β) and interferon-γ (IFN-γ), can synergistically induce the expression of inflammatory genes, such as TLR2. This effect involved positive combinatorial interactions between NF-κB/p65, glucocorticoid receptor, and JAK-STAT1 signaling to synergistically upregulate TLR2 expression. Thus, synergies involving glucocorticoid enhancement of TLR2 expression may occur in the immunopathology of glucocorticoid-resistant inflammatory diseases, including severe asthma.

Calpeptin may reverse glucocorticoid-resistance of allergic rhinitis associated with cigarette smoke exposure by down-regulating interferon regulatory factor 1

Cigarette smoke exposure is an important factor in chronic inflammation in patients with allergic rhinitis (AR); however, the relationship between cigarette smoke and AR-related glucocorticoid resistance requires further study. In mice, calpeptin significantly reduces inflammation of the lower respiratory tract caused by cigarette smoke, but whether it can treat glucocorticoid-resistant AR caused by cigarette smoke requires further research. In this study, we confirmed that cigarette smoke exposure can aggravate the Th2 inflammatory response in AR leading to glucocorticoid resistance. The underlying mechanism may be related to decreased expression of DNA methyltransferase 3a (Dnmt3a), and increased expression of interferon regulatory factor 1 (IRF1). In addition, we found that calpeptin can inhibit the expression of IRF1 and thus treat AR-associated glucocorticoid resistance in rats exposed to cigarette smoke. These data suggest that calpeptin may downregulate IRF1 and therefore treat glucocorticoid resistance in AR-associated with cigarette smoke exposure.

Airway smooth muscle in contractility and remodeling of asthma: potential drug target mechanisms

INTRODUCTION

Asthma is characterized by enhanced airway contractility and remodeling where airway smooth muscle (ASM) plays a key role, modulated by inflammation. Understanding the mechanisms by which ASM contributes to these features of asthma is essential for the development of novel asthma therapies.

AREAS COVERED

Inflammation in asthma contributes to a multitude of changes within ASM including enhanced airway contractility, proliferation, and fibrosis. Altered intracellular calcium ([Ca²⁺]_i) regulation or Ca²⁺ sensitization contributes to airway hyperreactivity. Increased airway wall thickness from ASM proliferation and fibrosis contributes to structural changes seen with asthma.

EXPERT OPINION

ASM plays a significant role in multiple features of asthma. Increased ASM contractility contributes to hyperresponsiveness, while altered ASM proliferation and extracellular matrix production promote airway remodeling both influenced by inflammation of asthma and conversely even influencing the local inflammatory milieu. While standard therapies such as corticosteroids or biologics target inflammation, cytokines, or their receptors to alleviate asthma symptoms, these approaches do not address the underlying contribution of ASM to hyperresponsiveness and particularly remodeling. Therefore, novel therapies for asthma need to target abnormal contractility mechanisms in ASM and/or the contribution of ASM to remodeling, particularly in asthmatics resistant to current therapies.

Distinct spatial and temporal roles for Th1, Th2, and Th17 cells in asthma

Immune response in the asthmatic respiratory tract is mainly driven by CD4⁺ T helper (Th) cells, represented by Th1, Th2, and Th17 cells, especially Th2 cells. Asthma is a heterogeneous and progressive disease, reflected by distinct phenotypes orchestrated by τh2 or non-Th2 (Th1 and Th17) immune responses at different stages of the disease course. Heterogeneous cytokine expression within the same Th effector state in response to changing conditions in vivo and interlineage relationship among CD4⁺ T cells shape the complex immune networks of the inflammatory airway, making it difficult to find one panacea for all asthmatics. Here, we review the role of three T helper subsets in the pathogenesis of asthma from different stages, highlighting timing is everything in the immune system. We also discuss the dynamic topography of Th subsets and pathogenetic memory Th cells in asthma.

Glucocorticoid Insensitivity in Asthma: The Unique Role for Airway Smooth Muscle Cells

Although most patients with asthma symptoms are well controlled by inhaled glucocorticoids (GCs), a subgroup of patients suffering from severe asthma respond poorly to GC therapy. Such GC insensitivity (GCI) represents a profound challenge in managing patients with asthma. Even though GCI in patients with severe asthma has been investigated by several groups using immune cells (peripheral blood mononuclear cells and alveolar macrophages), uncertainty exists regarding the underlying molecular mechanisms in non-immune cells, such as airway smooth cells (ASM) cells. In asthma, ASM cells are among the targets of GC therapy and have emerged as key contributors not only to bronchoconstriction but also to airway inflammation and remodeling, as implied by experimental and clinical evidence. We here summarize the current understanding of the actions/signaling of GCs in asthma, and specifically, GC receptor (GR) “site-specific phosphorylation” and its role in regulating GC actions. We also review some common pitfalls associated with studies investigating GCI and the inflammatory mediators linked to asthma severity. Finally, we discuss and contrast potential molecular mechanisms underlying the impairment of GC actions in immune cells versus non-immune cells such as ASM cells.

Th1 cytokines synergize to change gene expression and promote corticosteroid insensitivity in pediatric airway smooth muscle

Background

Corticosteroids remain a key therapy for treating children with asthma. Patients with severe asthma are insensitive, resistant, or refractory to corticosteroids and have poorly controlled symptoms that involve airway inflammation, airflow obstruction, and frequent exacerbations. While the pathways that mediate corticosteroid insensitivity in asthma remain poorly defined, recent studies suggest that enhanced Th1 pathways, mediated by TNFα and IFNγ, may play a role. We previously reported that the combined effects of TNFα and IFNγ promote corticosteroid insensitivity in developing human airway smooth muscle (ASM).

Methods

To further understand the effects of TNFα and IFNγ on corticosteroid sensitivity in the context of neonatal and pediatric asthma, we performed RNA sequencing (RNA-seq) on human pediatric ASM treated with fluticasone propionate (FP), TNFα, and/or IFNγ.

Results

We found that TNFα had a greater effect on gene expression (~ 1000 differentially expressed genes) than IFNγ (~ 500 differentially expressed genes). Pathway and transcription factor analyses revealed enrichment of several pro-inflammatory responses and signaling pathways. Interestingly, treatment with TNFα and IFNγ augmented gene expression with more than 4000 differentially expressed genes. Effects of TNFα and IFNγ enhanced several pro-inflammatory genes and pathways related to ASM and its contributions to asthma pathogenesis, which persisted in the presence of corticosteroids. Co-expression analysis revealed several gene networks related to TNFα- and IFNγ-mediated signaling, pro-inflammatory mediator production, and smooth muscle contractility. Many of the co-expression network hubs were associated with genes that are insensitive to corticosteroids.

Conclusions

Together, these novel studies show the combined effects of TNFα and IFNγ on pediatric ASM and implicate Th1-associated cytokines in promoting ASM inflammation and hypercontractility in severe asthma.

Identification of Key Signaling Pathways and Genes in Eosinophilic Asthma and Neutrophilic Asthma by Weighted Gene Co-Expression Network Analysis

Background: Asthma is a heterogeneous disease with different subtypes including eosinophilic asthma (EA) and neutrophilic asthma (NA). However, the mechanisms underlying the difference between the two subtypes are not fully understood.

Methods: Microarray datasets (GSE45111 and GSE137268) were acquired from Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) in induced sputum between EA (n = 24) and NA (n = 15) were identified by “Limma” package. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses and Gene set enrichment analysis (GSEA) were used to explore potential signaling pathways. Weighted gene co-expression network analysis (WGCNA) were performed to identify the key genes that were strongly associated with EA and NA.

Results: A total of 282 DEGs were identified in induced sputum of NA patients compared with EA patients. In GO and KEGG pathway analyses, DEGs were enriched in positive regulation of cytokine production, and cytokine-cytokine receptor interaction. The results of GSEA showed that ribosome, Parkinson’s disease, and oxidative phosphorylation were positively correlated with EA while toll-like receptor signaling pathway, primary immunodeficiency, and NOD-like receptor signaling pathway were positively correlated with NA. Using WGCNA analysis, we identified a set of genes significantly associated NA including IRFG, IRF1, STAT1, IFIH1, IFIT3, GBP1, GBP5, IFIT2, CXCL9, and CXCL11.

Conclusion: We identified potential signaling pathways and key genes involved in the pathogenesis of the asthma subsets, especially in neutrophilic asthma.

Human Lung Mast Cells Impair Corticosteroid Responsiveness in Human Airway Smooth Muscle Cells

The mechanisms underlying corticosteroid insensitivity in severe asthma have not been elucidated although some indirect clinical evidence points toward a role of mast cells. Here, we tested the hypothesis that mast cells can drive corticosteroid insensitivity in airway smooth muscle cells, a key player in asthma pathogenesis. Conditioned media from resting or FcεR1-activated human lung mast cells were incubated with serum-deprived ASM cells (1:4 dilution, 24 h) to determine their impact on the anti-inflammatory action of fluticasone on ASM cell chemokine expression induced by TNFα (10 ng/ml). Conditioned media from FcεR1-activated mast cells (but not that from non-activated mast cells or control media) significantly reduced the ability of 100 nM fluticasone to suppress ASM TNFα-dependent CCL5 and CXCL10 production at both mRNA and protein levels. In contrast, fluticasone inhibition of CXCL-8 production by TNFα was still preserved in the presence of activated mast cell conditioned media. Transcriptomic analysis validated by individual qPCR assays revealed that activated mast cell conditioned media dramatically reduced the number of anti-inflammatory genes induced by fluticasone in ASM cells. Our study demonstrates for the first time that conditioned media from FcεR1-activated mast cells blunt the anti-inflammatory action of corticosteroids in ASM cells by altering their transactivation properties. Because infiltration of mast cells within the ASM bundles is a defining feature of asthma, mast cell-derived mediators may contribute to the glucocorticoid insensitivity present in severe asthma.

A phase 2 multiple ascending dose study of the inhaled pan-JAK inhibitor nezulcitinib (TD-0903) in severe COVID-19

Severe coronavirus disease 2019 (COVID-19) is characterised by pneumonia with excessive systemic inflammation, referred to as a “cytokine storm” [1–3]. Dexamethasone treatment decreases mortality in patients with COVID-19 receiving respiratory support and is standard of care for severe COVID-19 [4, 5]. However, pulmonary inflammation, which drives COVID-19 morbidity and mortality [3], can persist despite corticosteroid use [6, 7]. Janus kinase (JAK) inhibition blocks signalling by many cytokines in diverse cell types, offering broad immunomodulation [8]. The oral JAK-1/2 inhibitor baricitinib combined with the antiviral remdesivir shows clinical efficacy in patients with severe COVID-19 [9]. Direct delivery of JAK inhibition to the lung via inhalation could overcome corticosteroid-resistant pulmonary inflammation [10], offering the potential for improved responses while minimising risk of excessive systemic immunosuppression. The novel inhaled pan-JAK inhibitor nezulcitinib (TD-0903) was designed to target all JAK isoforms (JAK1, JAK2, JAK3, TYK2; −log inhibition constant ≥9.2) and optimise delivery to the lungs while limiting systemic exposure (R. Sana and co-workers; unpublished results: abstract submitted to ERS International Congress, 2021). We report results from the completed part 1 of a 2-part phase 2 trial (NCT04402866) in hospitalised patients with severe COVID-19.

The inhaled lung-selective pan-JAK inhibitor nezulcitinib appears generally well tolerated in hospitalised patients with severe #COVID-19, with trends for improved oxygenation and clinical status, shortened hospitalisation, and fewer deaths versus placebohttps://bit.ly/35Xs1Rf

Potential Role of Mast Cells in Regulating Corticosteroid Insensitivity in Severe Asthma

The mechanisms driving corticosteroid insensitivity in asthma are still unclear although evidence points toward a potential role of lung mast cells. Indeed, a number of in vitro studies using various cell types showed that different mediators produced by activated mast cells, including cytokines, have the capacity to interfere with the therapeutic action of corticosteroids. In patients with severe allergic refractory asthma, the anti-IgE monoclonal antibody (mAb), Omalizumab, has been shown to be associated with a marked reduction in inhaled and systemic use of corticosteroids, further suggesting a key role of mast cells in the poor response of patients to these drugs. The present chapter will discuss the possible underlying mechanisms by which mast cells could contribute to reducing corticosteroid sensitivity seen in patients with severe asthma.

Important lessons learned from studies on the pharmacology of glucocorticoids in human airway smooth muscle cells: Too much of a good thing may be a problem

Glucocorticoids (GCs) are the treatment of choice for chronic inflammatory diseases such as asthma. Despite proven effective anti-inflammatory and immunosuppressive effects, long-term and/or systemic use of GCs can potentially induce adverse effects. Strikingly, some recent experimental evidence suggests that GCs may even exacerbate some disease outcomes. In asthma, airway smooth muscle (ASM) cells are among the targets of GC therapy and have emerged as key contributors not only to bronchoconstriction, but also to airway inflammation and remodeling, as implied by experimental and clinical evidence. We here will review the beneficial effects of GCs on ASM cells, emphasizing the differential nature of GC effects on pro-inflammatory genes and on other features associated with asthma pathogenesis. We will also summarize evidence describing how GCs can potentially promote pro-inflammatory and remodeling features in asthma with a specific focus on ASM cells. Finally, some of the possible solutions to overcome these unanticipated effects of GCs will be discussed.

[TNF-α Decreased Corticosteroid Responsiveness in Mice Models of Airway Inflammation Induced by Double Strand RNA and/or Tobacco Smoke Exposure]

Reduction of corticosteroid responsiveness is one of the important clinical problems in chronic obstructive pulmonary disease (COPD). In this study, we determined the effects of neutralization of tumor necrosis factor-α (TNF-α) on corticosteroid insensitivity in mice models of airway inflammation induced by poly(I:C) and tobacco smoke (TS) exposure. Mice (male A/J strain, 5 weeks old) were exposed to TS for 10 d, or TS for 11 d and poly(I:C) for 3 d. Anti-TNF-α antibody was intranasally treated once every other day 2 h before the TS exposure, and dexamethasone 21-phosphate (DEX) was treated 30 min before the TS or poly(I:C) exposure. On the next day of the last stimulation, mice were sacrificed. The combination treatment of DEX and TNF-α neutralization was significantly attenuated the increase of the numbers of inflammatory cells in BALF and the TNF-α mRNA expression levels induced by TS and poly(I:C) exposure, even though TNF-α neutralization alone had little effect. These data indicated that neutralization of TNF-α restores corticosteroid responsiveness. Therefore, our study suggests that targeting TNF-α signaling pathway provides a new therapeutic approach to corticosteroid refractory airway diseases.

Th1 cytokines TNF-α and IFN-γ promote corticosteroid resistance in developing human airway smooth muscle

Corticosteroids (CSs) are commonly used to manage wheezing and asthma in pediatric populations. Although corticosteroids are effective in alleviating airway diseases, some children with more moderate-severe asthma phenotypes show CS resistance and exhibit significant airflow obstruction, persistent inflammation, and more frequent exacerbations. Previous studies have demonstrated that Th1 cytokines, such as TNF-α and IFN-γ, promote CS resistance in adult human airway smooth muscle (ASM). In the present study, using a human fetal ASM cell model, we tested the hypothesis that TNF-α/IFN-γ induces CS resistance. In contrast to TNF-α or IFN-γ alone, the combination of TNF-α/IFN-γ blunted the ability of fluticasone propionate (FP) to reduce expression of the chemokines CCL5 and CXCL10 despite expression of key anti-inflammatory glucocorticoid receptor target genes being largely unaffected by TNF-α/IFN-γ. Expression of the NF-κB subunit p65 and phosphorylation of Stat1 were elevated in cells treated with TNF-α/IFN-γ, an effect that remained in the presence of FP. siRNA knockdown studies demonstrated the effects of TNF-α/IFN-γ on increased p65 are mediated by Stat1, a transcription factor activated by IFN-γ. Expression of TNFAIP3, a negative regulator of NF-κB activity, was not altered by TNF-α/IFN-γ. However, the effects of TNF-α/IFN-γ were partially reduced by overexpression of TNFAIP3 but did not influence p65 expression. Together, these data suggest that IFN-γ augments the effects of TNF-α on chemokines by enhancing expression of key inflammatory pathways in the presence of CS. Interactions between TNF-α- and IFN-γ-mediated pathways may promote inflammation in asthmatic children resistant to CSs.

Air pollution and resistance to inhaled glucocorticoids: Evidence, mechanisms and gaps to fill

Substantial evidence indicates that cigarette smoke exposure induces resistance to glucocorticoids, the primary maintenance medication in asthma treatment. Modest evidence also suggests that air pollution may reduce the effectiveness of these critical medications. Cigarette smoke, which has clear parallels with air pollution, has been shown to induce glucocorticoid resistance in asthma and it has been speculated that air pollution may have similar effects. However, the literature on an association of air pollution with glucocorticoid resistance is modest to date. In this review, we detail the evidence for, and against, the effects of air pollution on glucocorticoid effectiveness, focusing on results from epidemiology and controlled human exposure studies. Epidemiological studies indicate a correlation between increased air pollution exposure and worse asthma symptoms. But these studies also show a mix of beneficial and harmful effects of glucocorticoids on spirometry and asthma symptoms, perhaps due to confounding influences, or the induction of glucocorticoid resistance. We describe mechanisms that may contribute to reductions in glucocorticoid responsiveness following air pollution exposure, including changes to phosphorylation or oxidation of the glucocorticoid receptor, repression by cytokines, or inflammatory pathways, and epigenetic effects. Possible interactions between air pollution and respiratory infections are also briefly discussed. Finally, we detail a number of therapies that may boost glucocorticoid effectiveness or reverse resistance in the presence of air pollution, and comment on the beneficial effects of engineering controls, such as air filtration and asthma action plans. We also call attention to the benefits of improved clean air policy on asthma. This review highlights numerous gaps in our knowledge of the interactions between air pollution and glucocorticoids to encourage further research in this area with a view to reducing the harm caused to those with airways disease.

CD38/cADPR Signaling Pathway in Airway Disease: Regulatory Mechanisms

Asthma is an inflammatory disease in which proinflammatory cytokines have a role in inducing abnormalities of airway smooth muscle function and in the development of airway hyperresponsiveness. Inflammatory cytokines alter calcium (Ca²⁺) signaling and contractility of airway smooth muscle, which results in nonspecific airway hyperresponsiveness to agonists. In this context, Ca²⁺ regulatory mechanisms in airway smooth muscle and changes in these regulatory mechanisms encompass a major component of airway hyperresponsiveness. Although dynamic Ca²⁺ regulation is complex, phospholipase C/inositol tris-phosphate (PLC/IP3) and CD38-cyclic ADP-ribose (CD38/cADPR) are two major pathways mediating agonist-induced Ca²⁺ regulation in airway smooth muscle. Altered CD38 expression or enhanced cyclic ADP-ribosyl cyclase activity associated with CD38 contributes to human pathologies such as asthma, neoplasia, and neuroimmune diseases. This review is focused on investigations on the role of CD38-cyclic ADP-ribose signaling in airway smooth muscle in the context of transcriptional and posttranscriptional regulation of CD38 expression. The specific roles of transcription factors NF-kB and AP-1 in the transcriptional regulation of CD38 expression and of miRNAs miR-140-3p and miR-708 in the posttranscriptional regulation and the underlying mechanisms of such regulation are discussed.

Plasmodium berghei NK65 in Combination with IFN-γ Induces Endothelial Glucocorticoid Resistance via Sustained Activation of p38 and JNK

Malaria-associated acute respiratory distress syndrome (MA-ARDS) is an often lethal complication of malaria. Currently, no adequate therapy for this syndrome exists. Although glucocorticoids (GCs) have been used to improve clinical outcome of ARDS, their therapeutic benefits remain unclear. We previously developed a mouse model of MA-ARDS, in which dexamethasone treatment revealed GC resistance. In the present study, we investigated GC sensitivity of mouse microvascular lung endothelial cells stimulated with interferon-γ (IFN-γ) and Plasmodium berghei NK65 (PbNK65). Upon challenge with IFN-γ alone, dexamethasone inhibited the expression of CCL5 (RANTES) by 90% and both CCL2 (MCP-1) and CXCL10 (IP-10) by 50%. Accordingly, whole transcriptome analysis revealed that dexamethasone differentially affected several gene clusters and in particular inhibited a large cluster of IFN-γ-induced genes, including chemokines. In contrast, combined stimulation with IFN-γ and PbNK65 extract impaired inhibitory actions of GCs on chemokine release, without affecting the capacity of the GC receptor to accumulate in the nucleus. Subsequently, we investigated the effects of GCs on two signaling pathways activated by IFN-γ. Dexamethasone left phosphorylation and protein levels of signal transducer and activator of transcription 1 (STAT1) unhampered. In contrast, dexamethasone inhibited the IFN-γ-induced activation of two mitogen-activated protein kinases (MAPK), JNK, and p38. However, PbNK65 extract abolished the inhibitory effects of GCs on MAPK signaling, inducing GC resistance. These data provide novel insights into the mechanisms of GC actions in endothelial cells and show how malaria may impair the beneficial effects of GCs.

Glucocorticoid and cytokine crosstalk: Feedback, feedforward, and co-regulatory interactions determine repression or resistance

Inflammatory signals induce feedback and feedforward systems that provide temporal control. Although glucocorticoids can repress inflammatory gene expression, glucocorticoid receptor recruitment increases expression of negative feedback and feedforward regulators, including the phosphatase, DUSP1, the ubiquitin-modifying enzyme, TNFAIP3, or the mRNA-destabilizing protein, ZFP36. Moreover, glucocorticoid receptor cooperativity with factors, including nuclear factor-κB (NF-κB), may enhance regulator expression to promote repression. Conversely, MAPKs, which are inhibited by glucocorticoids, provide feedforward control to limit expression of the transcription factor IRF1, and the chemokine, CXCL10. We propose that modulation of feedback and feedforward control can determine repression or resistance of inflammatory gene expression toglucocorticoid.

Protein phosphatase 5 mediates corticosteroid insensitivity in airway smooth muscle in patients with severe asthma

BACKGROUND

The mechanisms driving glucocorticoid (GC) insensitivity in patients with severe asthma are still unknown. Recent evidence suggests the existence of GC-insensitive pathways in airway smooth muscle (ASM) caused by a defect in GC receptor (GRα) function. We examined whether other mechanisms could potentially explain the reduced sensitivity of ASM cells to GC in severe asthmatics.

METHODS

Airway smooth muscle cells from healthy and severe asthmatic subjects were treated with TNF-α and responses to corticosteroids in both cohorts were compared by ELISA, immunoblot, immunohistochemistry and real-time PCR. Immunohistochemistry and flow cytometry assays were used to assess the expression of the protein phosphatase PP5 in endobronchial biopsies and ASM cells.

RESULTS

The production of CCL11 and CCL5 by TNF-α was insensitive to both fluticasone and dexamethasone in ASM cells from severe asthmatic compared to that in healthy subjects. Fluticasone-induced GRα nuclear translocation, phosphorylation at serine 211 and expression of GC-induced leucine zipper (GILZ) were significantly reduced in ASM cells from severe asthmatics compared to responses in healthy subjects. Levels of PP5 were increased in ASM cells from severe asthmatics and PP5 knockdown using siRNA restored fluticasone repressive action on chemokine production and its ability to induce GRα nuclear translocation and GRE-dependent GILZ expression. In vivo PP5 expression was also increased in the ASM bundles in endobronchial biopsies in severe asthmatics.

CONCLUSIONS

PP5-dependent impairment of GRα function represents a novel mechanism driving GC insensitivity in ASM in severe asthma.

Long-acting β2-agonists promote glucocorticoid-mediated repression of NF-κB by enhancing expression of the feedback regulator TNFAIP3

Glucocorticoids, or corticosteroids, are effective treatments for many chronic inflammatory diseases, and in mild/moderate asthma, long-acting β₂-adrenoceptor agonists (LABAs) enhance the efficacy of inhaled corticosteroids (ICSs) more than increasing the ICS dose. In human bronchial epithelial, BEAS-2B, cells, expression of TNFα-induced protein-3 (TNFAIP3), or A20, a dual-ubiquitin ligase that provides feedback inhibition of NF-κB, was induced by budesonide, an ICS, and formoterol, a LABA, and was further enhanced by budesonide-formoterol combination. The proinflammatory cytokine TNF induced TNFAIP3 and TNF expression. Whereas subsequent budesonide treatment enhanced TNF-induced TNFAIP3 and reduced TNF expression, formoterol amplified these differential effects. In primary human airway smooth muscle cells, TNFAIP3 expression was induced by TNF. This was largely unaffected by budesonide but was acutely enhanced by budesonide-formoterol combination. In BEAS-2B cells, TNF recruited RELA, the main NF-κB transactivating subunit, to a 3' region of the TNF gene. RELA binding was reduced by budesonide, was further reduced by formoterol cotreatment, and was associated with reduced RNA polymerase II recruitment to the TNF gene. This is consistent with reduced TNF expression. TNFAIP3 knockdown enhanced TNF expression in the presence of TNF, TNF plus budesonide, and TNF plus budesonide-formoterol combination and confirms feedback inhibition. A luciferase reporter containing the TNF 3' RELA binding region recapitulated TNF inducibility and was inhibited by an IκB kinase inhibitor and TNFAIP3 overexpression. Repression of reporter activity by budesonide was increased by formoterol and involved TNFAIP3. Thus LABAs may improve the anti-inflammatory properties of ICSs by augmenting TNFAIP3 expression to negatively regulate NF-κB.

DUSP1 Maintains IRF1 and Leads to Increased Expression of IRF1-dependent Genes: A MECHANISM PROMOTING GLUCOCORTICOID INSENSITIVITY

Although the mitogen-activated protein kinase (MAPK) phosphatase, DUSP1, mediates dexamethasone-induced repression of MAPKs, 14 of 46 interleukin-1β (IL1B)-induced mRNAs were significantly enhanced by DUSP1 overexpression in pulmonary A549 cells. These include the interferon regulatory factor, IRF1, and the chemokine, CXCL10. Of these, DUSP1-enhanced mRNAs, 10 including CXCL10, were IRF1-dependent. MAPK inhibitors and DUSP1 overexpression prolonged IRF1 expression by elevating transcription and increasing IRF1 mRNA and protein stability. Conversely, DUSP1 silencing increased IL1B-induced MAPK phosphorylation while significantly reducing IRF1 protein expression at 4 h. This confirms a regulatory network whereby DUSP1 switches off MAPKs to maintain IRF1 expression. There was no repression of IRF1 expression by dexamethasone in primary human bronchial epithelial cells, and in A549 cells IL1B-induced IRF1 protein was only modestly and transiently repressed. Although dexamethasone did not repress IL1B-induced IRF1 protein expression at 4-6 h, silencing of IL1B plus dexamethasone-induced DUSP1 significantly reduced IRF1 expression. IL1B-induced expression of CXCL10 was largely insensitive to dexamethasone, whereas other DUSP1-enhanced, IRF1-dependent mRNAs showed various degrees of repression. With IL1B plus dexamethasone, CXCL10 expression was also IRF1-dependent, and expression was reduced by DUSP1 silencing. Thus, IL1B plus dexamethasone-induced DUSP1 maintains expression of IRF1 and the IRF1-dependent gene, CXCL10. This is supported by chromatin immunoprecipitation showing IRF1 recruitment to be essentially unaffected by dexamethasone at the CXCL10 promoter or at the promoters of more highly repressed IRF1-dependent genes. Since IRF1-dependent genes, such as CXCL10, are central to host defense, these data may help explain the reduced effectiveness of glucocorticoids during asthma exacerbations.

Abnormal corticosteroid signalling in airway smooth muscle: mechanisms and perspectives for the treatment of severe asthma

Growing in vivo evidence supports the concept that airway smooth muscle produces various immunomodulatory factors that could contribute to asthma pathogenesis via the regulation of airway inflammation, airway narrowing and remodelling. Targeting ASM using bronchial thermoplasty has provided undeniable clinical benefits for patients with uncontrolled severe asthma who are refractory to glucocorticoid therapy. The present review will explain why the failure of glucocorticoids to adequately manage patients with severe asthma could derive from their inability to affect the immunomodulatory potential of ASM. We will support the view that ASM sensitivity to glucocorticoid therapy can be blunted in severe asthma and will describe some of the factors and mechanisms that could be responsible for glucocorticoid insensitivity.

Bronchoprotection and bronchorelaxation in asthma: New targets, and new ways to target the old ones

Despite over 50years of inhaled beta-agonists and corticosteroids as the default management or rescue drugs for asthma, recent research suggests that new therapeutic options are likely to emerge. This belief stems from both an improved understanding of what causes and regulates airway smooth muscle (ASM) contraction, and the identification of new targets whose inhibition or activation can relax ASM. In this review we discuss the recent findings that provide new insight into ASM contractile regulation, a revolution in pharmacology that identifies new ways to "tune" G protein-coupled receptors to improve therapeutic efficacy, and the discovery of several novel targets/approaches capable of effecting bronchoprotection or bronchodilation.

Glucocorticoid and TNF signaling converge at A20 (TNFAIP3) to repress airway smooth muscle cytokine expression

Airway smooth muscle is a major target tissue for glucocorticoid (GC)-based asthma therapies, however, molecular mechanisms through which the GC receptor (GR) exerts therapeutic effects in this key airway cell type have not been fully elucidated. We previously identified the nuclear factor-κB (NF-κB) inhibitor, A20 (TNFAIP3), as a mediator of cytokine repression by glucocorticoids (GCs) in airway epithelial cells and defined cooperative regulation of anti-inflammatory genes by GR and NF-κB as a key mechanistic underpinning of airway epithelial GR function. Here, we expand on these findings to determine whether a similar mechanism is operational in human airway smooth muscle (HASM). Using HASM cells derived from normal and fatal asthma samples as an in vitro model, we demonstrate that GCs spare or augment TNF-mediated induction of A20 (TNFAIP3), TNIP1, and NFKBIA, all implicated in negative feedback control of NF-κB-driven inflammatory processes. We applied chromatin immunoprecipitation and reporter analysis to show that GR and NF-κB directly regulate A20 expression in HASM through cooperative induction of an intronic enhancer. Using overexpression, we show for the first time that A20 and its interacting partner, TNIP1, repress TNF signaling in HASM cells. Moreover, we applied small interfering RNA-based gene knockdown to demonstrate that A20 is required for maximal cytokine repression by GCs in HASM. Taken together, our data suggest that inductive regulation of A20 by GR and NF-κB contributes to cytokine repression in HASM.

Adenoviral delivery of recombinant soluble human tumor necrosis factor receptor 1 partially normalized mouse model of asthma

BACKGROUND

Tumor necrosis factor α (TNF-α) is a proinflammatory cytokine that has been implicated in the airway pathology of asthma and result in resistance to hormone therapy. Tumor necrosis factor α inhibitors have become a major research focus in the treatment of asthma.

METHODS

Recombinant adenovirus (Ad-sTNFR1-IgGFc) expressing a fusion protein (sTNFR1-IgGFc), which was consisted of the soluble extracellular region of TNF receptor 1 and Fc fragment of IgG (sTNFR1-IgGFc), was used to transduce primary human airway smooth muscle cells (HASMCs). Enzyme-linked immunosorbent assay, flow cytometry, and immunocytochemistry confirmed the expression of sTNFR1-IgGFc. MTT was used to test the effect of sTNFR1-IgGFc to antagonism TNF-α-induced proliferates of HASMCs. To investigate the in vivo effectiveness of sTNFR1-IgGFc, mouse model of asthma was established. Ad-sTNFR1-IgGFc was delivered to the lung via nasal spray. Expression of sTNFR1-IgGFc in the tissue was confirmed by in situ hybridization and immunohistochemistry. The 2 major cell types that are involved in the inflamed asthmatic airway, neutrophils and eosinophils, in bronchoalveolar lavage fluid were observed.

RESULTS

The sTNFR1-IgGFc isolated from transduced HASMC culture supernatant was able to antagonize HASMC proliferation stimulated by TNF-α. Asthma-induced pathologies and alterations in the cell composition in bronchoalveolar lavage fluid were reduced in mice subjected to Ad-sTNFR1-IgGFc therapy.

CONCLUSIONS

The soluble extracellular region of TNF receptor 1 and Fc fragment of IgG was able to functionally antagonize TNF-α in vitro and showed promise as a therapeutic agent for the localized treatment of severe refractory asthma.

Effect of the plant derivative Compound A on the production of corticosteroid-resistant chemokines in airway smooth muscle cells

Preclinical models of human conditions including asthma showed the therapeutic potential of Compound A (CpdA), a dissociated glucocorticoid (GC) receptor (GRα) ligand. Whether CpdA inhibits GC resistance, a central feature of severe asthma, has not been addressed. We investigated whether CpdA modulates cytokine-induced GC resistance in human airway smooth muscle (ASM) cells. Healthy and asthmatic ASM cells were treated with TNF-α/IFN-γ for 24 hours in the presence or absence of CpdA. ELISA and quantitative PCR assays were used to assess the effect of CpdA on chemokine expression. Activation of GRα by CpdA was assessed by quantitative PCR, immunostaining, and receptor antagonism using RU486. An effect of CpdA on the transcription factor interferon regulatory factor 1 (IRF-1) was investigated using immunoblot, immunostaining, and small interfering RNA (siRNA) knockdown. CpdA inhibited production of fluticasone-resistant chemokines CCL5, CX3CL1, and CXCL10 at protein and mRNA levels in both asthmatic and healthy cells. CpdA failed to induce expression of GC-induced Leucine Zipper while transiently inducing mitogen-activated protein kinase phosphatase 1 (MKP-1) at both mRNA and protein levels. CpdA inhibitory action was not associated with GRα nuclear translocation, nor was it prevented by RU486 antagonism. Activation of IRF-1 by TNF-α/IFN-γ was inhibited by CpdA. IRF-1 siRNA knockdown reduced cytokine-induced CCL5 and CX3CL1 production. siRNA MKP-1 prevented the inhibitory effect of CpdA on cytokine-induced CXCL10 production. For the first time, we show that CpdA inhibits the production of GC-resistant chemokines via GRα-independent mechanisms involving the inhibition of IRF-1 and up-regulation of MKP-1. Thus, targeting CpdA-sensitive pathways in ASM cells represents an alternative therapeutic approach to treat GC resistance in asthma.

Neutralizing TNFα restores glucocorticoid sensitivity in a mouse model of neutrophilic airway inflammation

Asthma is a heterogeneous disorder, evidenced by distinct types of inflammation resulting in different responsiveness to therapy with glucocorticoids (GCs). Tumor necrosis factor α (TNFα) is involved in asthma pathogenesis, but anti-TNFα therapies have not proven broadly effective. The effects of anti-TNFα treatment on steroid resistance have never been assessed. We investigated the role of TNFα blockade using etanercept in the responsiveness to GCs in two ovalbumin-based mouse models of airway hyperinflammation. The first model is GC sensitive and T helper type 2 (Th2)/eosinophil driven, whereas the second reflects GC-insensitive, Th1/neutrophil-predominant asthma subphenotypes. We found that TNFα blockade restores the therapeutic effects of GCs in the GC-insensitive model. An adoptive transfer indicated that the TNFα-induced GC insensitivity occurs in the non-myeloid compartment. Early during airway hyperinflammation, mice are GC insensitive specifically at the level of thymic stromal lymphopoietin (Tslp) transcriptional repression, and this insensitivity is reverted when TNFα is neutralized. Interestingly, TSLP knockout mice displayed increased inflammation in the GC-insensitive model, suggesting a limited therapeutic application of TSLP-neutralizing antibodies in subsets of patients suffering from Th2-mediated asthma. In conclusion, we demonstrate that TNFα reduces the responsiveness to GCs in a mouse model of neutrophilic airway inflammation. Thus antagonizing TNFα may offer a new strategy for therapeutic intervention in GC-resistant asthma.

Peripheral blood IRF1 expression as a marker for glucocorticoid sensitivity

OBJECTIVE

Despite of the common usage of glucocorticoids (GCs), a significant portion of asthma patients exhibit GC insensitivity. This could be mediated by diverse mechanisms, including genomics. Recent work has suggested that measuring changes in gene expression may provide more predictive information about GC insensitivity than baseline gene expression alone, and that expression changes in peripheral blood may be reflective of those in the airway.

METHODS

We performed in silico discovery using gene expression omnibus (GEO) data that evaluated GC effect on gene expression in multiple tissue types. Subsequently, candidate genes whose expression levels are affected by GC were examined in cell lines and in primary cells derived from human airway and blood.

RESULTS

Through gene expression omnibus analysis, we identified interferon regulator factor 1 (IRF1), whose expression is affected by GC treatment in airway smooth muscle cells, normal human bronchial epithelial (NHBE) cells, and lymphoblastoid cell lines (LCLs). Significant IRF1 downregulation post GC exposure was confirmed in two cultured airway epithelial cell lines and primary NHBE cells (P<0.05). We observed large interindividual variation in GC-induced IRF1 expression changes among primary NHBE cells tested. Significant downregulation of IRF1 was also observed in six randomly selected LCLs (P<0.05), with variable degrees of downregulation among different samples. In peripheral blood mononuclear cells obtained from healthy volunteers, variable downregulation of IRF1 by GC was also shown. NFKB1, a gene whose expression is known to be downregulated by GC and the degree of downregulation of which is reflective of GC response, was used as a control in our study. IRF1 shows more consistent downregulation across tissue types when compared with NFKB1.

CONCLUSION

Our results suggest that GC-induced IRF1 gene expression changes in peripheral blood could be used as a marker to reflect GC response in the airway.

Cytokine-induced loss of glucocorticoid function: effect of kinase inhibitors, long-acting β(2)-adrenoceptor [corrected] agonist and glucocorticoid receptor ligands

Acting on the glucocorticoid receptor (NR3C1), glucocorticoids are widely used to treat inflammatory diseases. However, glucocorticoid resistance often leads to suboptimal asthma control. Since glucocorticoid-induced gene expression contributes to glucocorticoid activity, the aim of this study was to use a 2 × glucocorticoid response element (GRE) reporter and glucocorticoid-induced gene expression to investigate approaches to combat cytokine-induced glucocorticoid resistance. Pre-treatment with tumor necrosis factor-α (TNF) or interleukin-1β inhibited dexamethasone-induced mRNA expression of the putative anti-inflammatory genes RGS2 and TSC22D3, or just TSC22D3, in primary human airway epithelial and smooth muscle cells, respectively. Dexamethasone-induced DUSP1 mRNA was unaffected. In human bronchial epithelial BEAS-2B cells, dexamethasone-induced TSC22D3 and CDKN1C expression (at 6 h) was reduced by TNF pre-treatment, whereas DUSP1 and RGS2 mRNAs were unaffected. TNF pre-treatment also reduced dexamethasone-dependent 2×GRE reporter activation. This was partially reversed by PS-1145 and c-jun N-terminal kinase (JNK) inhibitor VIII, inhibitors of IKK2 and JNK, respectively. However, neither inhibitor affected TNF-dependent loss of dexamethasone-induced CDKN1C or TSC22D3 mRNA. Similarly, inhibitors of the extracellular signal-regulated kinase, p38, phosphoinositide 3-kinase or protein kinase C pathways failed to attenuate TNF-dependent repression of the 2×GRE reporter. Fluticasone furoate, fluticasone propionate and budesonide were full agonists relative to dexamethasone, while GSK9027, RU24858, des-ciclesonide and GW870086X were partial agonists on the 2×GRE reporter. TNF reduced reporter activity in proportion with agonist efficacy. Full and partial agonists showed various degrees of agonism on RGS2 and TSC22D3 expression, but were equally effective at inducing CDKN1C and DUSP1, and did not affect the repression of CDKN1C or TSC22D3 expression by TNF. Finally, formoterol-enhanced 2×GRE reporter activity was also proportional to agonist efficacy and functionally reversed repression by TNF. As similar effects were apparent on glucocorticoid-induced gene expression, the most effective strategy to overcome glucocorticoid resistance in this model was addition of formoterol to high efficacy NR3C1 agonists.

Heterogeneity in mechanisms influencing glucocorticoid sensitivity: the need for a systems biology approach to treatment of glucocorticoid-resistant inflammation

Glucocorticoids (GCs) have impressive anti-inflammatory and immunosuppressive effects and show a diversity of actions across a variety of cell phenotypes. Implicit in efforts to optimize GCs as anti-inflammatory agents for any or all indications is the notion that the relevant mechanism(s) of action of GCs are fully elucidated. However, recent advances in understanding GC signalling mechanisms have revealed remarkable complexity and contextual dependence, calling into question whether the mechanisms of action are sufficiently well-described to embark on optimization. In the current review, we address evidence for differences in the mechanism of action in different cell types and contexts, and discuss contrasts in mechanisms of glucocorticoid insensitivity, with a focus on asthma and Chronic Obstructive Pulmonary Disease (COPD). Given this complexity, we consider the potential breadth of impact and selectivity of strategies directed to reversing the glucocorticoid insensitivity.

Functional proteomics for the characterization of impaired cellular responses to glucocorticoids in asthma

In chronic airway inflammatory disorders, such as asthma, glucocorticoid (GC) insensitivity is a challenging clinical problem associated with life-threatening disease progression and the potential development of serious side effects. The mechanism of steroid resistance in asthma remains unclear and may be multifactorial. Excluding noncompliance with GC treatment, abnormal steroid pharmacokinetics, and rare genetic defects in the glucocorticoid receptor (GR), the majority of GC insensitivity in asthma can be attributed to secondary defects related to GR function. Airway inflammatory cells obtained from patients with GC-resistant asthma show a number of abnormalities in cell immune responses to GC, which suggests that there is a causative defect in GR signaling in GC-resistant cells that could be further elucidated by a functional and molecular proteomics approach. Since T cells, eosinophils, and monocytes play a major role in the pathogenesis of airway inflammation, most of the work published to date has focused on these cell types as the primary therapeutic targets in GC-insensitive asthma. We herein review several distinct techniques for the assessment of (1) the cellular response to GCs including the effect of GCs on cell viability, adhesion, and mediator release; (2) the functionality of GC receptors, including phosphorylation of the GR, nuclear translocation, and binding activities; and (3) the characterization of proteins differentially expressed in steroid-resistant cells by comparative 2DE-gel electrophoresis-based techniques and mass spectrometry. These comprehensive approaches are expected to reveal novel candidates for biomarkers of steroid insensitivity, which may lead to the development of effective therapeutic interventions for patients with chronic steroid-resistant asthma.

Basal p38 mitogen-activated protein kinase regulates unliganded glucocorticoid receptor function in airway smooth muscle cells

Like many steroid receptors, the glucocorticoid (GC) receptor (GR) is a phosphoprotein. Although there are multiple phosphorylation sites critical for GR transcriptional activity (i.e., serine [S]203, S211, and S226), their respective role in driving GR functions is highly cell specific. We have recently identified protein phosphatase 5 as an essential Ser/Thr phosphatase responsible for impairing GR function via S211 dephosphorylation in airway smooth muscle (ASM) cells. Because p38 mitogen-activated protein kinase (MAPK) directly phosphorylates GR in different cell types in a stimulus- and cell-dependent manner, we investigated the role of p38 MAPK on GR phosphorylation and function in ASM cells. Cells were transfected with 100 nM p38 MAPK small interfering RNA or 2 μg MAPK kinase 3 expression vector (a specific kinase that directly activates p38 MAPK) in the presence or absence of fluticasone (100 nM) and/or p38 MAPK pharmacological inhibitor SB203580. We found that p38 MAPK blockade positively regulates GR nuclear translocation and GR-dependent induction of the steroid-target gene GC-induced leucine zipper in a hormone-independent manner. We also found that p38 MAPK-dependent regulation of GR functions was associated with a differential action on GR phosphorylation at S203 and S211 residues. This study demonstrated that the inactive state of GR in resting conditions is not only ensured by the absence of the GC ligand but also by p38 MAPK-dependent phosphorylation of unliganded GR at specific residues, which appears to be important in determining the overall GC responsiveness of ASM cells.

The methyltransferase WBSCR22/Merm1 enhances glucocorticoid receptor function and is regulated in lung inflammation and cancer

Glucocorticoids (GC) regulate cell fate and immune function. We identified the metastasis-promoting methyltransferase, metastasis-related methyltransferase 1 (WBSCR22/Merm1) as a novel glucocorticoid receptor (GR) regulator relevant to human disease. Merm1 binds the GR co-activator GRIP1 but not GR. Loss of Merm1 impaired both GR transactivation and transrepression by reducing GR recruitment to its binding sites. This was accompanied by loss of GR-dependent H3K4Me3 at a well characterized promoter. Inflammation promotes GC resistance, in part through the actions of TNFα and IFNγ. These cytokines suppressed Merm1 protein expression by driving ubiquitination of two conserved lysine residues. Restoration of Merm1 expression rescued GR transactivation. Cytokine suppression of Merm1 and of GR function was also seen in human lung explants. In addition, striking loss of Merm1 protein was observed in both inflammatory and neoplastic human lung pathologies. In conclusion, Merm1 is a novel regulator of chromatin structure affecting GR recruitment and function, contributing to loss of GC sensitivity in inflammation, with suppressed expression in pulmonary disease.

The respiratory syncytial virus (RSV) nonstructural proteins mediate RSV suppression of glucocorticoid receptor transactivation

Respiratory syncytial virus (RSV)-induced bronchiolitis in infants is not responsive to glucocorticoids. We have shown that RSV infection impairs glucocorticoid receptor (GR) function. In this study, we have investigated the mechanism by which RSV impairs GR function. We have shown that RSV repression of GR-induced transactivation is not mediated through a soluble autocrine factor. Knock-down of mitochondrial antiviral signaling protein (MAVS), but not retinoic acid-inducible gene 1 (RIG-I) or myeloid differentiation primary response gene 88 (MyD88), impairs GR-mediated gene activation even in mock-infected cells. Over-expression of the RSV nonstructural protein NS1, but not NS2, impairs glucocorticoid-induced transactivation and viruses deleted in NS1 and/or NS2 are unable to repress glucocorticoid-induction of the known GR regulated gene glucocorticoid-inducible leucine zipper (GILZ). These data suggest that the RSV nonstructural proteins mediate RSV repression of GR-induced transactivation and that inhibition of the nonstructural proteins may be a viable target for therapy against RSV-related disease.

Dominance of the strongest: inflammatory cytokines versus glucocorticoids

Pro-inflammatory cytokines are involved in the pathogenesis of many inflammatory diseases, and the excessive expression of many of them is normally counteracted by glucocorticoids (GCs), which are steroids that bind to the glucocorticoid receptor (GR). Hence, GCs are potent inhibitors of inflammation, and they are widely used to treat inflammatory diseases, such as asthma, rheumatoid arthritis and inflammatory bowel disease. However, despite the success of GC therapy, many patients show some degree of GC unresponsiveness, called GC resistance (GCR). This is a serious problem because it limits the full therapeutic exploitation of the anti-inflammatory power of GCs. Patients with reduced GC responses often have higher cytokine levels, and there is a complex interplay between GCs and cytokines: GCs downregulate pro-inflammatory cytokines while cytokines limit GC action. Treatment of inflammatory diseases with GCs is successful when GCs dominate. But when cytokines overrule the anti-inflammatory actions of GCs, patients become GC insensitive. New insights into the molecular mechanisms of GR-mediated actions and GCR are needed for the design of more effective GC-based therapies.

Functional KCa3.1 channels regulate steroid insensitivity in bronchial smooth muscle cells

Identifying the factors responsible for relative glucocorticosteroid (GC) resistance present in patients with severe asthma and finding tools to reverse it are of paramount importance. In asthma we see in vivo evidence of GC-resistant pathways in airway smooth muscle (ASM) bundles that can be modeled in vitro by exposing cultured ASM cells to TNF-α/IFN-γ. This action drives GC insensitivity via protein phosphatase 5-dependent impairment of GC receptor phosphorylation. In this study, we investigated whether KCa3.1 ion channels modulate the activity of GC-resistant pathways using our ASM model of GC insensitivity. Immunohistochemical staining of endobronchial biopsies revealed that KCa3.1 channels are localized to the plasma membrane and nucleus of ASM in both healthy controls and asthmatic patients, irrespective of disease severity. Western blot assays and immunofluorescence staining confirmed the nuclear localization of KCa3.1 channels in ASM cells. The functional importance of KCa3.1 channels in the regulation of GC-resistant chemokines induced by TNF-α/IFN-γ was assessed using complementary inhibitory strategies, including KCa3.1 blockers (TRAM-34 and ICA-17043) or KCa3.1-specific small hairpin RNA delivered by adenoviruses. KCa3.1 channel blockade led to a significant reduction of fluticasone-resistant CX3CL1, CCL5, and CCL11 gene and protein expression. KCa3.1 channel blockade also restored fluticasone-induced GC receptor-α phosphorylation at Ser(211) and transactivation properties via the suppression of cytokine-induced protein phosphatase 5 expression. The effect of KCa3.1 blockade was evident in ASM cells from both healthy controls and asthmatic subjects. In summary, KCa3.1 channels contribute to the regulation of GC-resistant inflammatory pathways in ASM cells: blocking KCa3.1 channels may enhance corticosteroid activity in severe asthma.

Glucocorticoid insensitivity as a source of drug targets for respiratory disease

Glucocorticoids (corticosteroids) are effective and clinically useful medicines for repressing inflammation in lung disease; however, the number of respiratory conditions that have been recognized to be refractory or insensitive to glucocorticoids is on the rise--either due to an inherent difference in the glucocorticoid sensitivity as part of the disease process or due to exogenous stressors such as cigarette smoke and other oxidative insults. Independent of causality, the aim of future therapeutic advances to conquer this frontier will no doubt be based on our growing knowledge of molecular mechanisms underlying glucocorticoid insensitivity in respiratory diseases. The current article aims to highlight the key molecular mechanisms responsible for glucocorticoid insensitivity in asthma and COPD. This new knowledge will ultimately allow us to enhance lung health by restoring glucocorticoid responsiveness in respiratory disease. In this way, our increased understanding of corticosteroid insensitivity can be exploited as a source of drug targets for respiratory disease in the future.

IL-17 inhibits adipogenesis in part via C/EBPα, PPARγ and Krüppel-like factors

IL-17 is an inflammatory cytokine associated with anti-microbial host defense and pathogenesis of autoimmune diseases. Obesity is considered to be an inflammatory condition, but how cytokines and fat metabolism are interconnected remains poorly understood. Mesenchymal stem cells can differentiate into adipocytes, which serve as depots for stored fat. Despite the pro-inflammatory properties of IL-17, both IL-17- and IL-17RA-deficient mice are overweight. Consistently, IL-17 suppresses maturation of cells with adipogenic potential. However, the mechanism underlying IL-17-mediated inhibition is not defined. In this study, we addressed this question by evaluating the impact of IL-17 on a variety of transcription factors (TFs) that control adipogenesis, using 3T3-L1 cells to model adipocyte differentiation. Surprisingly, IL-17 does not suppress adipogenesis via C/EBPβ and C/EBPδ, TFs often considered to be central regulators of adipogenesis. Rather, IL-17 suppresses expression of several pro-adipogenic TFs, including PPARγ and C/EBPα. Moreover, we found that IL-17 regulates expression of several members of the Krüppel-like family (KLF). Specifically, IL-17 suppresses KLF15, a pro-adipogenic TF, and enhances expression of KLF2 and KLF3, which are anti-adipogenic. Thus, IL-17 suppresses adipogenesis at least in part through the combined effects of TFs that regulate adipocyte differentiation.

Thiazolidinediones inhibit airway smooth muscle release of the chemokine CXCL10: in vitro comparison with current asthma therapies

BACKGROUND

Activated mast cells are present within airway smooth muscle (ASM) bundles in eosinophilic asthma. ASM production of the chemokine CXCL10 plays a role in their recruitment. Thus the effects of glucocorticoids (fluticasone, budesonide), long-acting β2-agonists (salmeterol, formoterol) and thiazolidinediones (ciglitazone, rosiglitazone) on CXCL10 production by ASM cells (ASMC) from people with and without asthma were investigated in vitro.

METHODS

Confluent serum-deprived cells were treated with the agents before and during cytokine stimulation for 0-24 h. CXCL10 protein/mRNA, IκB-α levels and p65 activity were measured using ELISA, RT PCR, immunoblotting and p65 activity assays respectively. Data were analysed using ANOVA followed by Fisher's post-hoc test.

RESULTS

Fluticasone and/or salmeterol at 1 and 100 nM inhibited CXCL10 release induced by IL-1β and TNF-α, but not IFNγ or all three cytokines (cytomix). The latter was also not affected by budesonide and formoterol. In asthmatic ASMC low salmeterol, but not formoterol, concentrations increased cytomix-induced CXCL10 release and at 0.01 nM enhanced NF-κB activity. Salmeterol 0.1 nM together with fluticasone 0.1 and 10 nM still increased CXCL10 release. The thiazolidinediones ciglitazone and rosiglitazone (at 25 and 100 μM) inhibited cytomix-induced CXCL10 release but these inhibitory effects were not prevented by the PPAR-g antagonist GW9662. Ciglitazone did not affect early NF-κB activity and CXCL10 mRNA production.

CONCLUSIONS

Thus the thiazolidinediones inhibited asthmatic ASMC CXCL10 release under conditions when common asthma therapies were ineffective or enhanced it. They may provide an alternative strategy to reduce mast cell-ASM interactions and restore normal airway physiology in asthma.

Corticosteroid-induced gene expression in allergen-challenged asthmatic subjects taking inhaled budesonide

BACKGROUND AND PURPOSE

Inhaled corticosteroids (ICS) are the cornerstone of asthma pharmacotherapy and, acting via the glucocorticoid receptor (GR), reduce inflammatory gene expression. While this is often attributed to a direct inhibitory effect of the GR on inflammatory gene transcription, corticosteroids also induce the expression of anti-inflammatory genes in vitro. As there are no data to support this effect in asthmatic subjects taking ICS, we have assessed whether ICS induce anti-inflammatory gene expression in subjects with atopic asthma.

EXPERIMENTAL APPROACH

Bronchial biopsies from allergen-challenged atopic asthmatic subjects taking inhaled budesonide or placebo were subjected to gene expression analysis using real-time reverse transcriptase-PCR for the corticosteroid-inducible genes (official gene symbols with aliases in parentheses): TSC22D3 [glucocorticoid-induced leucine zipper (GILZ)], dual-specificity phosphatase-1 (MAPK phosphatase-1), both anti-inflammatory effectors, and FKBP5 [FK506-binding protein 51 (FKBP51)], a regulator of GR function. Cultured pulmonary epithelial and smooth muscle cells were also treated with corticosteroids before gene expression analysis.

KEY RESULTS

Compared with placebo, GILZ and FKBP51 mRNA expression was significantly elevated in budesonide-treated subjects. Budesonide also increased GILZ expression in human epithelial and smooth muscle cells in culture. Immunostaining of bronchial biopsies revealed GILZ expression in the airways epithelium and smooth muscle of asthmatic subjects.

CONCLUSIONS AND IMPLICATIONS

Expression of the corticosteroid-induced genes, GILZ and FKBP51, is up-regulated in the airways of allergen-challenged asthmatic subjects taking inhaled budesonide. Consequently, the biological effects of corticosteroid-induced genes should be considered when assessing the actions of ICS. Treatment modalities that increase or decrease GR-dependent transcription may correspondingly affect corticosteroid efficacy.

Network analysis identifies a putative role for the PPAR and type 1 interferon pathways in glucocorticoid actions in asthmatics

BACKGROUND

Asthma is a chronic inflammatory airway disease influenced by genetic and environmental factors that affects ~300 million people worldwide, leading to ~250,000 deaths annually. Glucocorticoids (GCs) are well-known therapeutics that are used extensively to suppress airway inflammation in asthmatics. The airway epithelium plays an important role in the initiation and modulation of the inflammatory response. While the role of GCs in disease management is well understood, few studies have examined the holistic effects on the airway epithelium.

METHODS

Gene expression data were used to generate a co-transcriptional network, which was interrogated to identify modules of functionally related genes. In parallel, expression data were mapped to the human protein-protein interaction (PPI) network in order to identify modules with differentially expressed genes. A common pathways approach was applied to highlight genes and pathways functionally relevant and significantly altered following GC treatment.

RESULTS

Co-transcriptional network analysis identified pathways involved in inflammatory processes in the epithelium of asthmatics, including the Toll-like receptor (TLR) and PPAR signaling pathways. Analysis of the PPI network identified RXRA, PPARGC1A, STAT1 and IRF9, among others genes, as differentially expressed. Common pathways analysis highlighted TLR and PPAR signaling pathways, providing a link between general inflammatory processes and the actions of GCs. Promoter analysis identified genes regulated by the glucocorticoid receptor (GCR) and PPAR pathways as well as highlighted the interferon pathway as a target of GCs.

CONCLUSIONS

Network analyses identified known genes and pathways associated with inflammatory processes in the airway epithelium of asthmatics. This workflow illustrated a hypothesis generating experimental design that integrated multiple analysis methods to produce a weight-of-evidence based approach upon which future focused studies can be designed. In this case, results suggested a mechanism whereby GCs repress TLR-mediated interferon production via upregulation of the PPAR signaling pathway. These results highlight the role of interferons in asthma and their potential as targets of future therapeutic efforts.

Cytokines alter glucocorticoid receptor phosphorylation in airway cells: role of phosphatases

Corticosteroid insensitivity (CSI) represents a profound challenge in managing patients with asthma. We recently demonstrated that short exposure of airway smooth muscle cells (ASMCs) to proasthmatic cytokines drastically reduced their responsiveness to glucocorticoids (GCs), an effect that was partially mediated via interferon regulatory factor-1, suggesting the involvement of additional mechanisms (Am J Respir Cell Mol Biol 2008;38:463-472). Although GC receptor (GR) can be phosphorylated at multiple serines in the N-terminal region, the major phosphorylation sites critical for GR transcriptional activity are serines 211 (Ser211) and 226 (Ser226). We tested the novel hypothesis that cytokine-induced CSI in ASMCs is due to an impaired GR phosphorylation. Cells were treated with TNF-α (10 ng/ml) and IFN-γ (500 UI/ml) for 6 hours and/or fluticasone (100 nm) added 2 hours before. GR was constitutively phosphorylated at Ser226 but not at Ser211 residues. Cytokines dramatically suppressed fluticasone-induced phosphorylation of GR on Ser211 but not on Ser226 residues while increasing the expression of Ser/Thr protein phosphatase (PP)5 but not that of PP1 or PP2A. Transfection studies using a reporter construct containing GC responsive elements showed that the specific small interfering RNA-induced mRNA knockdown of PP5, but not that of PP1 or PP2A, partially prevented the cytokine suppressive effects on GR-meditated transactivation activity. Similarly, cytokines failed to inhibit GC-induced GR-Ser211 phosphorylation when expression of PP5 was suppressed. We propose that the novel mechanism that proasthmatic cytokine-induced CSI in ASMCs is due, in part, to PP5-mediated impairment of GR-Ser211 phosphorylation.

Targeting airway smooth muscle in airways diseases: an old concept with new twists

Airway smooth muscle (ASM) manifests a hyper-responsive phenotype in airway disorders such as asthma. ASM also modulates immune responses by secreting mediators and expressing cell-surface molecules that promote recruitment of inflammatory cells to the lungs. The aim of the current article is to highlight therapeutics that may modulate ASM responses in airway disorders and exacerbations.

Airway smooth muscle and immunomodulation in acute exacerbations of airway disease

Airway smooth muscle (ASM) manifests a hyperresponsive phenotype in airway disorders such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis. Current evidence also suggests that ASM modulates immune responses by secreting mediators and expressing cell surface molecules. Such processes amplify or dampen inflammation by inflammatory cells in the airways or by altering cellular responses to viruses, bacteria, or pathogens known to exacerbate airways diseases.