Omar Tliba

IL-13 enhances agonist-evoked calcium signals and contractile responses in airway smooth muscle.

Growing evidence suggests that interleukin (IL)‐13, a Th2‐type cytokine, plays a critical role in the development of bronchial hyper‐responsiveness (BHR), an essential feature of asthma, although the underlying mechanisms remain unknown. In the present study, we investigated whether IL‐13 directly affects airway smooth muscle (ASM) function. In murine tracheal rings, IL‐13 (100 ng ml−1, 24 h) significantly increased both the carbachol‐ and KCl‐induced maximal force generation without affecting ASM sensitivity. In cultured human ASM cells, IL‐13 (50 ng ml−1, 24 h) also augmented cytosolic calcium levels to bradykinin, histamine and carbachol by 60, 35 and 26%, respectively. The present study demonstrates that IL‐13 may promote BHR by directly modulating ASM contractility, an effect that may be due to enhanced G protein‐coupled receptor (GPCR)‐associated calcium signaling.

Vitamin D inhibits growth of human airway smooth muscle cells through growth factor‐induced phosphorylation of retinoblastoma protein and checkpoint kinase 1

Background and purpose:  Airway remodelling in asthma is manifested, in part, as increased airway smooth muscle (ASM) mass, reflecting myocyte proliferation. We hypothesized that calcitriol, a secosteroidal vitamin D receptor (VDR) modulator, would inhibit growth factor‐induced myocyte proliferation.

Vitamin D and glucocorticoids differentially modulate chemokine expression in human airway smooth muscle cells

Chemokines play a critical role in the pathogenesis of asthma and facilitate the recruitment of inflammatory cells in the airways. Evidence now suggests that airway smooth muscle (ASM) may serve as a source of chemokines in inflamed airways. Although vitamin D has potent anti‐inflammatory properties in vitro in some cell types, its effects on ASM cells remain unclear. Here, we investigated whether 1α, 25‐dihydroxy vitamin D3 (calcitriol) modulated chemokine production in ASM.

Tumor necrosis factor α modulates airway smooth muscle function via the autocrine action of interferon β

Current evidence suggests that tumor necrosis factor α (TNFα) and the family of interferons (IFNs) synergistically regulate many cellular responses that are believed to be critical in chronic inflammatory diseases, although the underlying mechanisms of such interaction are complex, cell-specific, and not completely understood. In this study, TNFα in a time-dependent manner activated both janus tyrosine kinase 1 and Tyk2 tyrosine kinase and increased the nuclear translocation of interferon-regulatory factor-1, STAT1, and STAT2 in human airway smooth muscle cells. In cells transfected with a luciferase reporter, TNFα stimulated γ-activated site-dependent gene transcription in a time- and concentration-dependent manner. Using neutralizing antibodies to IFNβ and TNFα receptor 1, we show that TNFα-induced secretion of IFNβ mediated γ-activated site-dependent gene expression via activation of TNFα receptor 1. In addition, neutralizing antibody to IFNβ also completely abrogated the activation of interferon stimulation response element-dependent gene transcription induced by TNFα. Secreted IFNβ acted as a negative regulator of TNFα-induced interleukin-6 expression, while IFNβ augmented TNFα-induced RANTES (regulated on activation normal T cell expressed and secreted) secretion but had little effect on TNFα-induced intercellular adhesion molecule-1 expression. Furthermore TNFα, a modest airway smooth muscle mitogen, markedly induced DNA synthesis when cells were treated with neutralizing anti-IFNβ. Together these data show that TNFα, via the autocrine action of IFNβ, differentially regulates the expression of proinflammatory genes and DNA synthesis.

Noncontractile Functions of Airway Smooth Muscle Cells in Asthma

Although pivotal in regulating bronchomotor tone in asthma, airway smooth muscle (ASM) also modulates airway inflammation and undergoes hypertrophy and hyperplasia, contributing to airway remodeling in asthma. ASM myocytes secrete or express a wide array of immunomodulatory mediators in response to extracellular stimuli, and in chronic severe asthma, increases in ASM mass may render the airway irreversibly obstructed. Although the mechanisms by which ASM secretes cytokines and chemokines are the same as those regulating immune cells, there exist unique ASM signaling pathways that may provide novel therapeutic targets. This review provides an overview of our current understanding of the proliferative as well as the synthetic properties of ASM.

Airway Smooth Muscle as an Immunomodulatory Cell

Although pivotal in regulating bronchomotor tone in asthma, airway smooth muscle (ASM) also modulates airway inflammation in asthma. ASM myocytes secrete or express a wide array of immunomodulatory mediators in response to extracellular stimuli, and in chronic severe asthma, increases in ASM mass may also render the airway irreversibly obstructed. Although the mechanisms by which ASM secretes cytokines and chemokines are shared with those regulating immune cells, there exist unique ASM signaling pathways that may provide novel therapeutic targets. This review provides an overview of our current understanding of the proliferative as well as synthetic properties of ASM.

Social Stress Enhances Allergen-Induced Airway Inflammation in Mice and Inhibits Corticosteroid Responsiveness of Cytokine Production

Chronic psychosocial stress exacerbates asthma, but the underlying mechanisms remain poorly understood. We hypothesized that psychosocial stress aggravates allergic airway inflammation by altering innate immune cell function. The effects of stress on airway inflammation, lung function, and glucocorticoid responsiveness were studied in a novel in vivo murine model of combined social disruption stress and allergic sensitization. The effects of corticosterone were assessed on cytokine profile and glucocorticoid receptor activation in LPS-stimulated spleen cell cultures in vitro. Airway inflammation resolved 48 h after a single allergen provocation in sensitized control mice, but not in animals that were repeatedly exposed to stress before allergen challenge. The enhanced eosinophilic airway inflammation 48 h after allergen challenge in these mice was associated with increased levels of IL-5, GM-CSF, IgG1, thymus-activated and regulatory chemokine, TNF-α, and IL-6 in the airways and a diminished inhibition of these mediators by corticosterone in LPS-stimulated splenocyte cultures in vitro. Stress-induced reduction of the corticosteroid effects paralleled increased p65 expression and a decreased DNA-binding capability of the glucocorticoid receptor in vitro. Furthermore, glucocorticoid receptor mRNA and protein expression in the lungs of mice exposed to both stress and allergen was markedly reduced in comparison with that in either condition alone or in naive mice. Thus, exposure to repeated social stress before allergen inhalation enhances and prolongs airway inflammation and alters corticosterone responsiveness. We speculate that these effects were mediated at least in part by impaired glucocorticoid receptor expression and function.

Inhibition of Tumor Necrosis Factor-α-Inducible Inflammatory Genes by Interferon-γ Is Associated with Altered Nuclear Factor-κB Transactivation and Enhanced Histone Deacetylase Activity

Airway smooth muscle (ASM) cells can act as effector cells in the initiation and/or perpetuation of airway inflammation in asthma by producing various inflammatory chemokines or cytokines. Previous studies from our laboratory and others showed that the combination of tumor necrosis factor-α (TNFα) and interferon-γ (IFNγ) or endogenous IFNβ results in a synergistic induction of various pro-inflammatory genes, including CD38 and regulated upon activation normal T-cell expressed and secreted (RANTES), in ASM cells. In contrast to these studies, we found that IFNγ (1000 U/ml) markedly inhibited TNFα-induced expression of interleukin (IL)-6, IL-8, and eotaxin by 66.29 ± 3.33, 43.86 ± 7.11, and 63.25 ± 6.46%, respectively. These genes were also found to be NF-κB-dependent in that TNFα-induced expression of IL-6, IL-8, and eotaxin was dose-dependently inhibited by the selective IKKβ inhibitor 4-(2′-aminoethyl)amino-1,8-dimethylimidazo[1,2-a]quinoxaline (BMS-345541) (1-30 μM). Using a luciferase reporter construct containing κB sites, we found that IFNγ (10-1000 U/ml) inhibits NF-κB-dependent gene transcription in a dose-dependent manner. Moreover, IFNγ failed to affect TNFα-induced IκKβ phosphorylation or IκB degradation as well as nuclear NF-κB/DNA interaction. It is noteworthy that IFNγ decreases TNFα-induced histone acetyl transferase (HAT) and increases histone deacetylase (HDAC) activities. Finally, trichostatin A, an HDAC inhibitor, prevents IFNγ inhibitory action on TNFα-induced gene expression. Together, our data indicate that IFNγ is a potent inhibitor of specific TNFα-inducible inflammatory genes by acting on NF-κB transactivation via the modulation of HDAC function.

Glucocorticoid Receptor Interacting Protein-1 Restores Glucocorticoid Responsiveness in Steroid-Resistant Airway Structural Cells

Glucocorticoid (GC) insensitivity represents a profound challenge in managing patients with asthma. The mutual inhibition of transcriptional activity between GC receptor (GR) and other regulators is one of the mechanisms contributing to GC resistance in asthma. We recently reported that interferon regulatory factor (IRF)-1 is a novel transcription factor that promotes GC insensitivity in human airway smooth muscle (ASM) cells by interfering with GR signaling (Tliba et al., Am J Respir Cell Mol Biol 2008;38:463-472). Here, we sought to determine whether the inhibition of GR function by IRF-1 involves its interaction with the transcriptional co-regulator GR-interacting protein 1 (GRIP-1), a known GR transcriptional co-activator. We here found that siRNA-mediated GRIP-1 depletion attenuated IRF-1-dependent transcription of the luciferase reporter construct and the mRNA expression of an IRF-1-dependent gene, CD38. In parallel experiments, GRIP-1 silencing significantly reduced GR-mediated transactivation activities. Co-immunoprecipitation and GST pull-down assays showed that GRIP-1, through its repression domain, physically interacts with IRF-1 identifying GRIP-1 as a bona fide transcriptional co-activator for IRF-1. Interestingly, the previously reported inhibition of GR-mediated transactivation activities by either TNF-alpha and IFN-gamma treatment or IRF-1 overexpression was fully reversed by increasing cellular levels of GRIP-1. Together, these data suggest that the cellular accumulation of IRF-1 may represent a potential molecular mechanism mediating altered cellular response to GC through the depletion of GRIP-1 from the GR transcriptional regulatory complexes.

Is Airway Smooth Muscle the “Missing Link” Modulating Airway Inflammation in Asthma?

Airway smooth muscle (ASM) plays a central role in regulating bronchomotor tone in patients with asthma. New evidence, however, suggests that ASM may also orchestrate and perpetuate airway inflammation by promoting the recruitment, activation, and trafficking of inflammatory cells in the airways. This review addresses the immunomodulatory function of ASM and highlights how such function may have therapeutic implications in the management of asthma.