New insight into the molecular mechanisms of corticosteroid resistance in asthma

Although corticosteroids are very efficient in managing asthma and other inflammatory diseases, a small percentage of patients affected by “severe asthma” fail to respond even to high doses of oral glucocorticoids. It is therefore important to try to understand the potential mechanisms behind this insensitivity to corticosteroid therapy in order to be able to effectively control asthma in this patient subset. We have decided to focus on one particular channel called K[subscript Ca]3.1, a calcium-activated potassium channel. First, emerging evidence in the literature to date has strongly supported a significant role for K[subscript Ca]3.1 channel in the pathophysiology of asthma. K[subscript Ca]3.1 channel is expressed by several inflammatory and structural airway cells including mast cells and human bronchial smooth muscle (HBSM). Therefore these channels might serve as new targets for the treatment of lung diseases. Here we established a cellular model of corticosteroid insensitivity consisting of primary HBSM cells exposed to two cytokines TNF-α and IFN-γ. Under these conditions, HBSMC exhibit a marked production of different pro-asthmatic chemokines like CCL5, CX3CL1, CCL11 and CXCL10 that are completely resistant to corticosteroid treatment. In this model, we found that although K[subscript Ca]3.1 channel expression did not change between healthy control, asthmatic and COPD subjects, K[subscript Ca]3.1 channel blockers (ICA-17043 and TRAM-34) were able to inhibit the production of corticosteroid-resistant chemokines either directly via the suppression of gene expression or indirectly via the restoration of the anti-inflammatory action of fluticasone. We also found that K[subscript Ca]3.1 channel blockers restored cell sensitivity to corticosteroid in cytokine-treated HBSMC by re-establishing the transactivation function of fluticasone via the prevention of dephosphorylation of Glucocorticoid Receptors (GRα) at Ser[superscript 211] and induction of anti-inflammatory genes such as Glucocorticoid-induced leucine zipper (GILZ). The likely mechanism of this restoration of corticosteroid sensitivity by K[subscript Ca]3.1 channel blockers is via the inhibition of protein phosphatase 5 (PP5) expression found to be up-regulated in steroid resistant conditions

The Plant Derivative Compound A Inhibits the Production of Corticosteroid-resistant Chemokines by 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 TNFα/IFNγ for 24 hr in the presence or absence of CpdA. ELISA and qPCR assays were used to assess the effect of CpdA on chemokine expression. Activation of GRα by CpdA was assessed by qPCR, immunostaining and receptor antagonism using RU486. An effect of CpdA on the transcription factor IRF-1 was investigated using immunoblot, immunostaining and 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 Glucocorticoid-induced Leucine Zipper (GILZ) while transiently inducing MAPK phosphatase 1 (MKP-1) at both mRNA and protein levels. CpdA inhibitory action was not associated with GRαnuclear translocation nor prevented by RU486 antagonism. Activation of IRF-1 by TNFα/IFNγ 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

Bidirectional counter-regulation of human lung mast cell and airway smooth muscle beta2-adrenoceptors

Human lung mast cells (HLMCs) play a central role in asthma pathogenesis through their relocation to the airway smooth muscle (ASM) bundles. β2 adrenoceptor (β2-AR)-agonists are used to relieve bronchoconstriction in asthma, but may reduce asthma control, particularly when used as monotherapy. We hypothesized that HLMC and human ASM cell (HASMC) responsiveness to β2-AR agonists would be attenuated when HLMCs are in contact with HASMCs. Cells were cultured in the presence of the short-acting β2-agonist albuterol, and the long-acting β2-agonists formoterol and olodaterol. Constitutive and FcεRI-dependent HLMC histamine release, HASMC contraction, and β2-AR phosphorylation at Tyr(350) were assessed. Constitutive HLMC histamine release was increased in HLMC-HASMC coculture and this was enhanced by β2-AR agonists. Inhibition of FcεRI-dependent HLMC mediator release by β2-agonists was greatly reduced in HLMC-HASMC coculture. These effects were reversed by neutralization of stem cell factor (SCF) or cell adhesion molecule 1 (CADM1). β2-AR agonists did not prevent HASMC contraction when HLMCs were present, but this was reversed by fluticasone. β2-AR phosphorylation at Tyr(350) occurred within 5 min in both HLMCs and HASMCs when the cells were cocultured, and was inhibited by neutralizing SCF or CADM1. HLMC interactions with HASMCs via CADM1 and Kit inhibit the potentially beneficial effects of β2-AR agonists on these cells via phosphorylation of the β2-AR. These results may explain the potentially adverse effects of β2-ARs agonists when used for asthma therapy. Targeting SCF and CADM1 may enhance β2-AR efficacy, particularly in corticosteroid-resistant patients

Increased β2-adrenoceptor phosphorylation in airway smooth muscle in severe asthma: possible role of mast cell-derived growth factors.

The purpose of this study was to investigate whether growth factors produced by activated human lung mast cells (HLMCs) impair β2 -adrenoceptor (β2 -AR) function in human airway smooth muscle (ASM) cells. Protein array analysis confirmed the presence of various growth factors, including transforming growth factor (TGF)-β1, in the supernatants of high-affinity IgE receptor (FcεRI)-activated HLMCs which, when applied to ASM cells, impaired albuterol-induced cyclic adenosine monophosphate (cAMP) production, an effect that was prevented following neutralization of TGF-β1. This blunted β2 -AR response was reproduced by treating ASM cells with TGF-β1 or fibroblast growth factor (FGF)-2, which induced β2 -AR phosphorylation at tyrosine residues Tyr141 and Tyr350 , and significantly reduced the maximal bronchorelaxant responses to isoproterenol in human precision cut lung slices (PCLS). Finally, ASM cells isolated from severe asthmatics displayed constitutive elevated β2 -AR phosphorylation at both Tyr141 and Tyr350 and a reduced relaxant response to albuterol. This study shows for the first time that abnormal β2 -AR phosphorylation/function in ASM cells that is induced rapidly by HLMC-derived growth factors, is present constitutively in cells from severe asthmatics

ST2 expression and release by the bronchial epithelium is downregulated in asthma

Background: The airway epithelium plays an important role in wound repair, host defense and is involved in the immunopathogenesis of asthma. Genome wide association studies have described associations between ST2/Interleukin (IL)-33 genes in asthma, but its role in bronchial epithelium is unclear. Methods: ST2 expression was examined in subjects with asthma and healthy controls in bronchial epithelium from biopsies (n = 27 versus n = 9) and brushings (n = 34 versus n = 20) by immunohistochemistry and RNA-Seq. In human primary bronchial epithelial cells ST2 mRNA and protein expression were assessed by qPCR, flow cytometry, Western blotting, and immunofluorescence. IL-33 function in epithelial cells was examined by intracellular calcium measurements, wound healing assays, and synthetic activation by gene array and ELISA. Results: Bronchial epithelial ST2 protein expression was significantly decreased in biopsies in subjects with asthma compared to healthy controls (P =.039). IL1RL1 gene expression in bronchial brushes was not different between health and disease. In vitro primary bronchial epithelial cells expressed ST2 and IL-33 stimulation led to an increase in intracellular calcium, altered gene expression, but had no effect upon wound repair. Epithelial cells released sST2 spontaneously, which was reduced following stimulation with TNFα or poly-IC. Stimulation by TNFα or poly-IC did not affect the total ST2 expression by epithelial cell whereas surface ST2 decreased in response to TNFα, but not poly-IC. Conclusion: In asthma, bronchial epithelium protein expression of ST2 is decreased. Our in vitro findings suggest that this decrease might be a consequence of the pro-inflammatory environment in asthma or in response to viral infection

HMGB1 is upregulated in the airways in asthma and potentiates airway smooth muscle contraction via TLR4

[First paragraph] Asthma is characterized by variable airflow obstruction, airway hyperresponsiveness, and inflammation. Airway smooth muscle (ASM) contributes to asthma pathophysiology via hypercontractility, increased mass, and inflammatory mediator release.1 Clinical studies and animal models demonstrate a role for high-mobility group box 1 (HMGB1) and its receptors in airway inflammation and asthma.2 ; 3 HMGB1's activity and receptor interactions is determined by its redox state, with oxidation rendering HMGB1 inactive.4 We have investigated the redox state of airway HMGB1 and the role of HMGB1 in ASM function

NADPH oxidase 4 over-expression is associated with epithelial ciliary dysfunction in neutrophilic asthma

BACKGROUND: Bronchial epithelial ciliary dysfunction is an important feature of asthma. We sought to determine the role in asthma of neutrophilic inflammation and NADPH oxidases in ciliary dysfunction. METHODS: Bronchial epithelial ciliary function was assessed by video-microscopy in fresh ex vivo epithelial strips from asthmatics stratified by their sputum cell differentials and in cultures from healthy controls and asthmatics. Bronchial epithelial oxidative damage was determined by 8-oxo-dG expression. NOX/DUOX expression was assessed in bronchial epithelial cells by microarrays, with NOX4, DUOX1/2 expression assessed in bronchial biopsies. Ciliary dysfunction following NADPH oxidase inhibition, using GKT137831, was evaluated in fresh epithelial strips from asthmatics and a murine model of ovalbumin sensitisation and challenge. RESULTS: Ciliary beat frequency was impaired in asthmatics with sputum neutrophilia (n=11) versus those without (n=10) (5.8 [0.6] versus 8.8 [0.5]Hz; P=0.003) and was correlated with sputum neutrophil count (r=-0.70; P<0.001). Primary bronchial epithelial cells expressed DUOX1/2 and NOX4. 8-oxo-dG and NOX4, were elevated in neutrophilic versus non-neutrophilic asthmatics, DUOX1 was elevated in both, and DUOX2 was elevated in non-neutrophilic asthma in vivo. In primary epithelial cultures ciliary dysfunction did not persist, although NOX4 expression and reactive oxygen species generation was increased from subjects with neutrophilic asthma. GKT137831 both improved ciliary function in ex vivo epithelial strips (n=13), relative to the intensity of neutrophilic inflammation, and abolished ciliary dysfunction in the murine asthma model without a reduction in inflammation. CONCLUSIONS: Ciliary dysfunction is increased in neutrophilic asthma associated with increased NOX4 expression and is attenuated by NADPH oxidase inhibition