Steroid-resistant Airway Research Articles

Small extracellular vesicles derived from human mesenchymal stem cells prevent Th17-dominant neutrophilic airway inflammation via immunoregulation on Th17 cells

Type 17 helper T cells (Th17)-dominant neutrophilic airway inflammation is critical in the pathogenesis of steroid-resistant airway inflammation such as severe asthma. Small extracellular vesicles (sEV) derived from human mesenchymal stem cells (MSCs) display extensive therapeutic effects and advantages in many diseases. However, the role of MSC-sEV in Th17-dominant neutrophilic airway inflammation and the related mechanisms are still poorly studied. Here we found that MSC-sEV significantly alleviated the infiltration of inflammatory cells in peribronchial interstitial tissues and reduced levels of inflammatory cells, especially neutrophils, in bronchoalveolar lavage fluids (BALF) of mice with neutrophilic airway inflammation. Consistently, MSC-sEV significantly decreased levels of IL-17A in BALF and Th17 in lung tissues. Furthermore, we found that labelled MSC-sEV were taken up by human CD4+ T cells most obviously at 12 h after incubation, and distributed mostly in mouse lungs. More importantly, potential signaling pathways involved in the MSC-sEV mediated inhibition of Th17 polarization were found using RNA sequencing. Using Western blot, JAK2-STAT3 pathway was identified as an important role in the inhibition of Th17 polarization by MSC-sEV. We found that proteins in MSC-sEV were mostly involved in the therapeutic effects of MSC-sEV. In total, our study suggested that MSC-sEV could be a potential therapeutic strategy for the treatment of neutrophilic airway inflammation.

Inhibition of Spleen Tyrosine Kinase Restores Glucocorticoid Sensitivity to Improve Steroid-Resistant Asthma.

Background: Regulation or restoration of therapeutic sensitivity to glucocorticoids is important in patients with steroid-resistant asthma. Spleen tyrosine kinase (Syk) is activated at high levels in asthma patients and mouse models, and small-molecule Syk inhibitors such as R406 show potent anti-inflammatory effects in the treatment of immune inflammatory diseases. Several downstream signaling molecules of Syk are involved in the glucocorticoid response, so we hypothesized that R406 could restore sensitivity to dexamethasone in severe steroid-resistant asthma. Objective: To discover the role of the Syk inhibitor R406 in glucocorticoid resistance in severe asthma. Methods: Steroid-resistant asthma models were induced by exposure of C57BL/6 mice to house dust mite (HDM) and β-glucan and by TNF-α administration to the bronchial epithelial cell line BEAS-2B. We evaluated the role of the Syk inhibitor R406 in dexamethasone (Dex)-insensitive airway inflammation. Pathological alterations and cytokines in the lung tissues and inflammatory cells in BALF were assessed. We examined the effects of Dex or R406 alone and in combination on the phosphorylation of MAPKs, glucocorticoid receptor (GR) and Syk, as well as the transactivation and transrepression induced by Dex in mouse lung tissues and BEAS-2B cells. Results: Exposure to HDM and β-glucan induced steroid-resistant airway inflammation. The Syk inhibitor R406 plus Dex significantly reduced airway inflammation compared with Dex alone. Additionally, TNF-α-induced IL-8 production in BEAS-2B cells was not completely inhibited by Dex, while R406 markedly promoted the anti-inflammatory effect of Dex. Compared with Dex alone, R406 enhanced Dex-mediated inhibition of the phosphorylation of MAPKs and GR-Ser226 induced by allergens or TNF-α in vivo and in vitro. Moreover, R406 also restored the impaired expression and nuclear translocation of GRα induced by TNF-α. Then, the activation of NF-κB and decreased HDAC2 activity in the asthmatic model were further regulated by R406, as well as the expression of GILZ. Conclusions: The Syk inhibitor R406 improves sensitivity to dexamethasone by modulating GR. This study provides a reference for the development of drugs to treat severe steroid-resistant asthma.

Short palate, lung, and nasal epithelial clone 1 (SPLUNC1) level determines steroid-resistant airway inflammation in aging.

Asthma and its heterogeneity change with age. Increased airspace neutrophil numbers contribute to severe steroid-resistant asthma exacerbation in the elderly, which correlates with the changes seen in adults with asthma. However, whether that resembles the same disease mechanism and pathophysiology in aged and adults is poorly understood. Here, we sought to address the underlying molecular mechanism of steroid-resistant airway inflammation development and response to corticosteroid (Dex) therapy in aged mice. To study the changes in inflammatory mechanism, we used a clinically relevant treatment model of house-dust mite (HDM)-induced allergic asthma and investigated lung adaptive immune response in adult (20–22 wk old) and aged (80–82 wk old) mice. Our result indicates an age-dependent increase in airway hyperresponsiveness (AHR), mixed granulomatous airway inflammation comprising eosinophils and neutrophils, and Th1/Th17 immune response with progressive decrease in frequencies and numbers of HDM-bearing dendritic cells (DC) accumulation in the draining lymph node (DLn) of aged mice as compared with adult mice. RNA-Seq experiments of the aged lung revealed short palate, lung, and nasal epithelial clone 1 (SPLUNC1) as one of the steroid-responsive genes, which progressively declined with age and further by HDM-induced inflammation. Moreover, we found increased glycolytic reprogramming, maturation/activation of DCs, the proliferation of OT-II cells, and Th2 cytokine secretion with recombinant SPLUNC1 (rSPLUNC1) treatment. Our results indicate a novel immunomodulatory role of SPLUNC1 regulating metabolic adaptation/maturation of DC. An age-dependent decline in the SPLUNC1 level may be involved in developing steroid-resistant airway inflammation and asthma heterogeneity.

Cutting Edge: Steroid Responsiveness in Foxp3+ Regulatory T Cells Determines Steroid Sensitivity during Allergic Airway Inflammation in Mice.

Glucocorticoids are a highly effective first-line treatment option for many inflammatory diseases, including asthma. Some patients develop a steroid-resistant condition, yet, the cellular and molecular mechanisms underlying steroid resistance remain largely unknown. In this study, we used a murine model of steroid-resistant airway inflammation and report that combining systemic dexamethasone and intranasal IL-27 is able to reverse the inflammation. Foxp3+ regulatory T cells (Tregs) were required during dexamethasone/IL-27 treatment of steroid-resistant allergic inflammation, and importantly, direct stimulation of Tregs via glucocorticoid or IL-27 receptors was essential. Mechanistically, IL-27 stimulation in Tregs enhanced expression of the agonistic glucocorticoid receptor-α isoform. Overexpression of inhibitory glucocorticoid receptor-β isoform in Tregs alone was sufficient to elicit steroid resistance in a steroid-sensitive allergic inflammation model. Taken together, our results demonstrate for the first time, to our knowledge, that Tregs are instrumental during steroid resistance and that manipulating steroid responsiveness in Tregs may represent a novel strategy to treat steroid refractory asthma.

Chitin induces steroid-resistant airway inflammation and airway hyperresponsiveness in mice

BackgroundPrevious reports have shown that pathogen-associated patterns (PAMPs) induce the production of interleukin (IL)-1β in macrophages. Moreover, studies using mouse models also suggest that chitin, which acts as a PAMP, induces adjuvant effects and eosinophilic infiltration in the lung. Thus, we investigated the effects of inhaled chitin in mouse models. MethodsWe developed mouse models of inhaled chitin particle-induced airway inflammation and steroid-resistant ovalbumin (OVA)-induced airway inflammation. Some experimental groups of mice were treated additionally with dexamethasone (DEX). Murine alveolar macrophages (AMs), which were purified from bronchoalveolar lavage (BAL) fluids, were incubated with chitin, and treated with or without DEX. ResultsThe numbers of total cells, AMs, lymphocytes, eosinophils, and neutrophils among BAL-derived cells, as well as the IL-1β levels in BAL fluids and the numbers of IL-1β-positive cells in lung, were significantly increased by chitin stimulation. Airway hyperresponsiveness (AHR) was aggravated in mice of the chitin inflammation model compared to control animals. The production of IL-1β was significantly increased in murine AMs by chitin treatment, but DEX administration did not inhibit this chitin-induced IL-1β production. Furthermore, in mouse models, DEX treatment inhibited the OVA-induced airway inflammation and AHR but not the airway inflammation and AHR induced by chitin or the combination of OVA and chitin. ConclusionsThese results suggest that inhaled chitin induces airway inflammation, AHR, and the production of IL-1β. Furthermore, our findings demonstrate for the first time that inhaled chitin induces steroid-resistant airway inflammation and AHR. Inhaled chitin may contribute to features of steroid-resistant asthma.

Targeting IL-17A/glucocorticoid synergy to CSF3 expression in neutrophilic airway diseases.

IL-17A plays a critical role in the pathogenesis of steroid-resistant neutrophilic airway inflammation, which is a hallmark of severe asthma and chronic obstructive pulmonary disease (COPD). Through RNA sequencing analysis of transcriptomes of human airway smooth muscle cells treated with IL-17A, dexamethasone (DEX, a synthetic glucocorticoid drug), alone or in combination, we identified a group of genes that are synergistically induced by IL-17A and DEX, including the neutrophil-promoting cytokine CSF3. In type-17 (Th17/IL-17Ahi) preclinical models of neutrophilic severe asthma (acute and chronic) and COPD, although DEX treatment was able to reduce the expression of neutrophil-mobilizing CXCL1 and CXCL2 in lung tissue, CSF3 expression was upregulated by DEX treatment. We found that DEX treatment alone failed to alleviate neutrophilic airway inflammation and pathology, and even exacerbated the disease phenotype when CSF3 was highly induced. Disruption of the IL-17A/DEX synergy by IL-17A inhibition with anti-IL-17A mAb or cyanidin-3-glucoside (C3G, a small-molecule IL-17A blocker) or depletion of CSF3 effectively rendered DEX sensitivity in type-17 preclinical models of neutrophilic airway diseases. Our study elucidates what we believe is a novel mechanism of steroid resistance in type-17 neutrophilic airway inflammation and offers an effective steroid-sparing therapeutic strategy (combined low-dose DEX and C3G) for treating neutrophilic airway diseases.

Lipopolysaccharide induces steroid-resistant exacerbations in a mouse model of allergic airway disease collectively through IL-13 and pulmonary macrophage activation.

Acute exacerbations of asthma represent a major burden of disease and are often caused by respiratory infections. Viral infections are recognized as significant triggers of exacerbations; however, less is understood about the how microbial bioproducts such as the endotoxin (lipopolysaccharide (LPS)) trigger episodes. Indeed, increased levels of LPS have been linked to asthma onset, severity and steroid resistance. The goal of this study was to identify mechanisms underlying bacterial-induced exacerbations by employing LPS as a surrogate for infection. We developed a mouse model of LPS-induced exacerbation on the background of pre-existing type-2 allergic airway disease (AAD). LPS-induced exacerbation was characterized by steroid-resistant airway hyperresponsiveness (AHR) and an exaggerated inflammatory response distinguished by increased numbers of infiltrating neutrophils/macrophages and elevated production of lung inflammatory cytokines, including TNFα, IFNγ, IL-27 and MCP-1. Expression of the type-2 associated inflammatory factors such as IL-5 and IL-13 were elevated in AAD but not altered by LPS exposure. Furthermore, AHR and airway inflammation were no longer suppressed by corticosteroid (dexamethasone) treatment after LPS exposure. Depletion of pulmonary macrophages by administration of 2-chloroadenosine into the lungs suppressed AHR and reduced IL-13, TNFα and IFNγ expression. Blocking IL-13 function, through either IL-13-deficiency or administration of specific blocking antibodies, also suppressed AHR and airway inflammation. We present evidence that IL-13 and innate immune pathways (in particular pulmonary macrophages) contribute to LPS-induced exacerbation of pre-existing AAD and provide insight into the complex molecular processes potentially underlying microbial-induced exacerbations.

The RNA-binding protein Mex-3B plays critical roles in the development of steroid-resistant neutrophilic airway inflammation

While most asthma can be treated with steroids, about 10%, called severe asthma, is refractory to steroids. It has recently been shown that in a subgroup of severe asthma cases, neutrophils that infiltrate into the airways play an important role in inflammation. However, the mechanisms underlying this increased neutrophil infiltration are not well understood. Here, using a mouse model of steroid-resistant neutrophilic inflammation, we show that mice deficient for the RNA-binding protein Mex-3B have significantly less neutrophil infiltration in the airways than wild-type mice. We further demonstrate that Mex-3B post-transcriptionally upregulates CXCL2, a chemokine that induces neutrophil chemotaxis and migration. Moreover, we show that treatment with either anti-CXCL2 antibody or anti-Mex-3B antisense oligonucleotide suppresses neutrophilic allergic airway inflammation. These results suggest that Mex-3B-mediated induction of CXCL2 is crucial for steroid-resistant neutrophilic allergic airway inflammation. Our findings suggest new strategies for therapeutic intervention in steroid-resistant severe asthma.

Combined treatment with SB203580 and dexamethasone suppresses non-typeable Haemophilus influenzae-induced Th17 inflammation response in murine allergic asthma

Accumulating evidence suggests that non-typeable Haemophilus influenzae (NTHi) infection drives the development of steroid-resistant allergic airway disease (SRAAD), exacerbates clinical symptoms, worsens quality of life, and accounts for most of the related healthcare burden. The poor understanding of the pathogenesis of SRAAD deters the development of more effective therapeutic strategies. Here, we established a murine model of NTHi infection-induced exacerbation of allergic airway disease. We showed that NTHi infection drove Th 17-mediated pulmonary neutrophilic inflammation, aggravated airway hyper-responsiveness, and upset the balance of MUC5AC and MUC5B expression. Dexamethasone treatment effectively inhibited the features of allergic airway disease but failed to reduce NTHi-induced exacerbation, which was associated with the hyper-phosphorylation of p38 mitogen-activated protein kinase (MAPK). Interestingly, inhibition of p38 using a specific inhibitor (SB203580) only partly suppressed the airway hyper-responsiveness and mucus hyper-secretion but failed to abrogate the infection-induced neutrophilic inflammatory response in SRAAD. However, SB203580 and dexamethasone co-treatment substantially suppressed all the features of NTHi-induced SRAAD. Our findings highlight the importance of p38 MAPK in the pathogenesis of NTHi-induced steroid resistance, and this combined treatment approach may be a novel strategy against steroid-resistant asthma.

Development of highly potent glucocorticoids for steroid-resistant severe asthma

Clinical application of inhaled glucocorticoids (GCs) has been hampered in the case of steroid-resistant severe asthma. To overcome this limitation, we have developed a series of highly potent GCs, including VSGC12, VSG158, and VSG159 based on the structural insight into the glucocorticoid receptor (GR). Particularly, VSG158 exhibits a maximal repression of lung inflammation and is 10 times more potent than the currently most potent clinical GC, Fluticasone Furoate (FF), in a murine model of asthma. More importantly, VSG158 displays a unique property to reduce neutrophilic inflammation in a steroid-resistant airway inflammation model, which is refractory to clinically available GCs, including dexamethasone and FF. VSG158 and VSG159 are able to deliver effective treatments with reduced off-target and side effects. In addition, these GCs also display pharmacokinetic properties that are suitable for the inhalation delivery method for asthma treatment. Taken together, the excellent therapeutic and side-effect profile of these highly potent GCs holds promise for treating steroid-resistant severe asthma.

A Non-canonical Pathway with Potential for Safer Modulation of Transforming Growth Factor-β1 in Steroid-Resistant Airway Diseases

SummaryImpaired therapeutic responses to anti-inflammatory glucocorticoids (GC) in chronic respiratory diseases are partly attributable to interleukins and transforming growth factor β1 (TGF-β1). However, previous efforts to prevent induction of GC insensitivity by targeting established canonical and non-canonical TGF-β1 pathways have been unsuccessful. Here we elucidate a TGF-β1 signaling pathway modulating GC activity that involves LIM domain kinase 2-mediated phosphorylation of cofilin1. Severe, steroid-resistant asthmatic airway epithelium showed increased levels of immunoreactive phospho-cofilin1. Phospho-cofilin1 was implicated in the activation of phospholipase D (PLD) to generate the effector(s) (lyso)phosphatidic acid, which mimics the TGF-β1-induced GC insensitivity. TGF-β1 induction of the nuclear hormone receptor corepressor, SMRT (NCOR2), was dependent on cofilin1 and PLD activities. Depletion of SMRT prevented GC insensitivity. This pathway for GC insensitivity offers several promising drug targets that potentially enable a safer approach to the modulation of TGF-β1 in chronic inflammatory diseases than is afforded by global TGF-β1 inhibition.

Human iPSC-MSCs prevent steroid-resistant neutrophilic airway inflammation via modulating Th17 phenotypes

BackgroundHuman induced pluripotent stem cells-derived mesenchymal stem cells (iPSC-MSCs) have been shown to be effective in Type 2 helper T cells (Th2)-dominant eosinophilic allergic airway inflammation. However, the role of iPSC-MSCs in Type 17 helper T cells (Th17)-dominant neutrophilic airway inflammation remains poorly studied. Therefore, this study was to explore the effects of iPSC-MSCs on an experimental mouse model of steroid-resistant neutrophilic airway inflammation and further determine the underlying mechanisms.MethodsA mouse model of neutrophilic airway inflammation was established using ovalbumin (OVA) and lipopolysaccharide (LPS). Human iPSC-MSCs were systemically administered, and the lungs or bronchoalveolar lavage fluids (BALF) were collected at 4 h and 48 h post-challenge. The pathology and inflammatory cell infiltration, the T helper cells, T helper cells-associated cytokines, nuclear transcription factors and possible signaling pathways were evaluated. Human CD4+ T cells were polarized to T helper cells and the effects of iPSC-MSCs on the differentiation of T helper cells were determined.ResultsWe successfully induced the mouse model of Th17 dominant neutrophilic airway inflammation. Human iPSC-MSCs but not dexamethasone significantly prevented the neutrophilic airway inflammation and decreased the levels of Th17 cells, IL-17A and p-STAT3. The mRNA levels of Gata3 and RORγt were also decreased with the treatment of iPSC-MSCs. We further confirmed the suppressive effects of iPSC-MSCs on the differentiation of human T helper cells.ConclusionsiPSC-MSCs showed therapeutic potentials in neutrophilic airway inflammation through the regulation on Th17 cells, suggesting that the iPSC-MSCs could be applied in the therapy for the asthma patients with steroid-resistant neutrophilic airway inflammation.

Refractory airway type 2 inflammation in a large subgroup of asthmatic patients treated with inhaled corticosteroids

Airway type 2 inflammation is usually corticosteroid sensitive, but the role of type 2 inflammation as a mechanism of asthma in patients receiving high-dose inhaled corticosteroids (ICSs) is uncertain. We sought to determine whether airway type 2 inflammation persists in patients treated with ICSs and to evaluate the clinical features of patients with steroid-resistant airway type 2 inflammation. We used quantitative PCR to generate a composite metric of type 2 cytokine gene expression (type 2 gene mean [T2GM]) in induced sputum cells from healthy control subjects, patients with severe asthma receiving ICSs (n=174), and patients with nonsevere asthma receiving ICSs (n=85). We explored relationships between asthma outcomes and T2GM values and the utility of noninvasive biomarkers of airway T2GM. Sputum cell T2GM values in asthmatic patients were significantly increased and remained high after treatment with intramuscular triamcinolone. We used the median T2GM value as a cutoff to classify steroid-treated type 2-low and steroid-resistant type 2-high (srT2-high) subgroups. Compared with patients with steroid-treated type 2-low asthma, those with srT2-high asthma were older and had more severe asthma. Blood eosinophil cell counts predicted srT2-high asthma when body mass index was less than 40kg/m2 but not when it was 40kg/m2 or greater, whereas blood IgE levels strongly predicted srT2-high asthma when age was less than 34years but not when it was 34years or greater. Despite ICS therapy, many asthmatic patients have persistent airway type 2 inflammation (srT2-high asthma), and these patients are older and have more severe disease. Body weight and age modify the performance of blood-based biomarkers of airway type 2 inflammation.

Identification of IFN-γ and IL-27 as Critical Regulators of Respiratory Syncytial Virus-Induced Exacerbation of Allergic Airways Disease in a Mouse Model.

Respiratory syncytial virus (RSV) infection induces asthma exacerbations, which leads to worsening of clinical symptoms and may result in a sustained decline in lung function. Exacerbations are the main cause of morbidity and mortality associated with asthma, and significantly contribute to asthma-associated healthcare costs. Although glucocorticoids are used to manage exacerbations, some patients respond to them poorly. The underlying mechanisms associated with steroid-resistant exacerbations remain largely unknown. We have previously established a mouse model of RSV-induced exacerbation of allergic airways disease, which mimics hallmark clinical features of asthma. In this study, we have identified key roles for macrophage IFN-γ and IL-27 in the regulation of RSV-induced exacerbation of allergic airways disease. Production of IFN-γ and IL-27 was steroid-resistant, and neutralization of IFN-γ or IL-27 significantly suppressed RSV-induced steroid-resistant airway hyperresponsiveness and airway inflammation. We have previously implicated activation of pulmonary macrophage by TNF-α and/or MCP-1 in the mechanisms of RSV-induced exacerbation. Stimulation of pulmonary macrophages with TNF-α and/or MCP-1 induced expression of both IFN-γ and IL-27. Our findings highlight critical roles for IFN-γ and IL-27, downstream of TNF-α and MCP-1, in the mechanism of RSV-induced exacerbation. Thus, targeting the pathways that these factors activate may be a potential therapeutic approach for virus-induced asthma exacerbations.

Role for NLRP3 Inflammasome-mediated, IL-1β-Dependent Responses in Severe, Steroid-Resistant Asthma.

Severe, steroid-resistant asthma is the major unmet need in asthma therapy. Disease heterogeneity and poor understanding of pathogenic mechanisms hampers the identification of therapeutic targets. Excessive nucleotide-binding oligomerization domain-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome and concomitant IL-1β responses occur in chronic obstructive pulmonary disease, respiratory infections, and neutrophilic asthma. However, the direct contributions to pathogenesis, mechanisms involved, and potential for therapeutic targeting remain poorly understood, and are unknown in severe, steroid-resistant asthma. To investigate the roles and therapeutic targeting of the NLRP3 inflammasome and IL-1β in severe, steroid-resistant asthma. We developed mouse models of Chlamydia and Haemophilus respiratory infection-mediated, ovalbumin-induced severe, steroid-resistant allergic airway disease. These models share the hallmark features of human disease, including elevated airway neutrophils, and NLRP3 inflammasome and IL-1β responses. The roles and potential for targeting of NLRP3 inflammasome, caspase-1, and IL-1β responses in experimental severe, steroid-resistant asthma were examined using a highly selective NLRP3 inhibitor, MCC950; the specific caspase-1 inhibitor Ac-YVAD-cho; and neutralizing anti-IL-1β antibody. Roles for IL-1β-induced neutrophilic inflammation were examined using IL-1β and anti-Ly6G. Chlamydia and Haemophilus infections increase NLRP3, caspase-1, IL-1β responses that drive steroid-resistant neutrophilic inflammation and airway hyperresponsiveness. Neutrophilic airway inflammation, disease severity, and steroid resistance in human asthma correlate with NLRP3 and IL-1β expression. Treatment with anti-IL-1β, Ac-YVAD-cho, and MCC950 suppressed IL-1β responses and the important steroid-resistant features of disease in mice, whereas IL-1β administration recapitulated these features. Neutrophil depletion suppressed IL-1β-induced steroid-resistant airway hyperresponsiveness. NLRP3 inflammasome responses drive experimental severe, steroid-resistant asthma and are potential therapeutic targets in this disease.

Mechanisms Mediating Pediatric Severe Asthma and Potential Novel Therapies.

Although a rare disease, severe therapy-resistant asthma in children is a cause of significant morbidity and results in utilization of approximately 50% of health-care resources for asthma. Improving control for children with severe asthma is, therefore, an urgent unmet clinical need. As a group, children with severe asthma have severe and multiple allergies, steroid resistant airway eosinophilia, and significant structural changes of the airway wall (airway remodeling). Omalizumab is currently the only add-on therapy that is licensed for use in children with severe asthma. However, limitations of its use include ineligibility for approximately one-third of patients because of serum IgE levels outside the recommended range and lack of clinical efficacy in a further one-third. Pediatric severe asthma is thus markedly heterogeneous, but our current understanding of the different mechanisms underpinning various phenotypes is very limited. We know that there are distinctions between the factors that drive pediatric and adult disease since pediatric disease develops in the context of a maturing immune system and during lung growth and development. This review summarizes the current data that give insight into the pathophysiology of pediatric severe asthma and will highlight potential targets for novel therapies. It is apparent that in order to identify novel treatments for pediatric severe asthma, the challenge of undertaking mechanistic studies using age appropriate experimental models and airway samples from children needs to be accepted to allow a targeted approach of personalized medicine to be achieved.

Impaired induction of Slc26a4 promotes respiratory acidosis and severe, steroid-resistant asthma

Abstract CO2 produced by systemic cellular respiration is hydrated into carbonic acid (H2CO3) that dissociates into H+ and HCO3−. These are transported in the plasma to the lungs where HCO3− is converted back into H2CO3 and CO2 that are expelled through breathing. Evidence suggests that dysfunction of the mechanisms that govern these processes may result in the development of respiratory acidosis (RA) and the cardinal features of severe, steroid-resistant (SSR) asthma. Reduced lung function, which occurs in SSR asthma, impairs removal of volatile H2CO3 and CO2, resulting in acid accumulation and increased arterial PaCO2. Patients with severe asthma often develop complications from increased PaCO2, which skews the PaCO2/HCO3− ratio resulting in increased H+ concentration and reduced pH. We developed three mouse models of respiratory infection and ovalbumin-induced SSR allergic airways disease (SSRAAD) that are highly representative of SSR asthma in humans. We used these models to show a role for impaired homeostatic acid-base balance in SSR asthma. All three infections suppress the induction of the expression of the chloride (Cl−)/HCO− pump, Slc26a4, in the airway mucosa in AAD. Importantly, SSRAAD is associated with increased levels of free H+ ions in bronchoalveolar lavage fluid. Administration of Slc26a4-specific siRNA in steroid-sensitive AAD, which mimics the effect of decreased Slc26a4 responses in SSRAAD, induced RA and steroid-resistant airway inflammation and AHR. Importantly, treatment of RA with NaHCO3 during infection-induced SSRAAD suppressed steroid-resistant AHR. Thus, we have identified a previously unrecognised role for deficient Slc26a4 responses that result in the development of RA and the pathogenesis of SSRAAD.

Bromodomain and Extra Terminal (BET) Inhibitor Suppresses Macrophage-Driven Steroid-Resistant Exacerbations of Airway Hyper-Responsiveness and Inflammation.

BackgroundExacerbations of asthma are linked to significant decline in lung function and are often poorly controlled by corticosteroid treatment. Clinical investigations indicate that viral and bacterial infections play crucial roles in the onset of steroid-resistant inflammation and airways hyperresponsiveness (AHR) that are hallmark features of exacerbations. We have previously shown that interferon γ (IFNγ) and lipopolysaccharide (LPS) cooperatively activate pulmonary macrophages and induce steroid-resistant airway inflammation and AHR in mouse models. Furthermore, we have established a mouse model of respiratory syncytial virus (RSV)-induced exacerbation of asthma, which exhibits macrophage-dependent, steroid-resistant lung disease. Emerging evidence has demonstrated a key role for bromo- and extra-terminal (BET) proteins in the regulation of inflammatory gene expression in macrophages. We hypothesised that BET proteins may be involved in the regulation of AHR and airway inflammation in our steroid-resistant exacerbation models.Methodology/Principal FindingsWe investigated the effects of a BET inhibitor (I-BET-762) on the development of steroid-resistant AHR and airway inflammation in two mouse models. I-BET-762 administration decreased macrophage and neutrophil infiltration into the airways, and suppressed key inflammatory cytokines in both models. I-BET treatment also suppressed key inflammatory cytokines linked to the development of steroid-resistant inflammation such as monocyte chemoattractant protein 1 (MCP-1), keratinocyte-derived protein chemokine (KC), IFNγ, and interleukin 27 (IL-27). Attenuation of inflammation was associated with suppression of AHR.Conclusions/SignificanceOur results suggest that BET proteins play an important role in the regulation of steroid-resistant exacerbations of airway inflammation and AHR. BET proteins may be potential targets for the development of future therapies to treat steroid-resistant inflammatory components of asthma.

Andrographolide Restores Steroid Sensitivity To Block Lipopolysaccharide/IFN-γ-Induced IL-27 and Airway Hyperresponsiveness in Mice.

LPS and IFN-γ alone or in combination have been implicated in the development of steroid resistance. Combined LPS/IFN-γ strongly upregulates IL-27 production, which has been linked to steroid-resistant airway hyperresponsiveness (AHR). Andrographolide, a bioactive molecule isolated from the plant Andrographis paniculata, has demonstrated anti-inflammatory and antioxidant properties. The present study investigated whether andrographolide could restore steroid sensitivity to block LPS/IFN-γ-induced IL-27 production and AHR via its antioxidative property. The mouse macrophage cell line Raw 264.7, mouse primary lung monocytes/macrophages, and BALB/c mice were treated with LPS/IFN-γ, in the presence and absence of dexamethasone and/or andrographolide. Levels of IL-27 in vitro and in vivo were examined and mouse AHR was assessed. Dexamethasone alone failed to inhibit LPS/IFN-γ-induced IL-27 production and AHR in mice. Andrographolide significantly restored the suppressive effect of dexamethasone on LPS/IFN-γ-induced IL-27 mRNA and protein levels in the macrophage cell line and primary lung monocytes/macrophages, mouse bronchoalveolar lavage fluid and lung tissues, and AHR in mice. LPS/IFN-γ markedly reduced the nuclear level of histone deacetylase (HDAC)2, an essential epigenetic enzyme that mediates steroid anti-inflammatory action. LPS/IFN-γ also decreased total HDAC activity but increased the total histone acetyltransferase/HDAC activity ratio in mouse lungs. Andrographolide significantly restored nuclear HDAC2 protein levels and total HDAC activity, and it diminished the total histone acetyltransferase/HDAC activity ratio in mouse lungs exposed to LPS/IFN-γ, possibly via suppression of PI3K/Akt/HDAC2 phosphorylation, and upregulation of the antioxidant transcription factor NF erythroid-2-related factor 2 level and DNA binding activity. Our data suggest that andrographolide may have therapeutic value in resensitizing steroid action in respiratory disorders such as asthma.

Molecular Mechanisms of Airway Hyperresponsiveness in a Murine Model of Steroid-Resistant Airway Inflammation.

IL-13 and IL-17A, produced mainly by Th2 and Th17 cells, respectively, have an influential role in asthma pathogenesis. We examined the role of IL-13 and IL-17A in mediating airway hyperresponsiveness (AHR), lung inflammation, and mucus metaplasia in a dual Th2/Th17 model of asthma. IL-13 and/or IL-17A were neutralized using mAbs. Th2/Th17 adoptive transfer induced a mixed asthma phenotype characterized by elevated eosinophilia and neutrophilia, tissue inflammation, mucus metaplasia, and AHR that were partially reversible with steroid treatment. Pulmonary inflammation and quasi-static lung compliance were largely unaffected by neutralization of IL-13 and/or IL-17A. However, neutralization of IL-13 alone or in combination with IL-17A significantly attenuated AHR and mucus metaplasia. Further, STAT6 activation was attenuated following IL-13 and IL-13/IL-17A Ab treatment. We next assessed the role of STAT6 in Th2/Th17-mediated allergic airway disease using STAT6(-/-) mice. STAT6(-/-) mice adoptively transferred with Th2/Th17 cells had decreased AHR compared with controls. These data suggest that IL-13 drives AHR and mucus metaplasia in a STAT6-dependent manner, without directly contributing to airway or tissue inflammation. IL-17A independently contributes to AHR, but it only partially mediates inflammation and mucus metaplasia in a mixed Th2/Th17 model of steroid-resistant asthma.