Airway smooth muscle cell as an inflammatory cell: lessons learned from interferon signaling pathways

Effects of Nigella sativa Oil Fractions on Reactive Oxygen Species and Chemokine Expression in Airway Smooth Muscle Cells

BACKGROUND

many previous studies have demonstrated the therapeutic potential of N. sativa total oil fractions, neutral lipids (NLs), glycolipids (GLs), phospholipids (PLs), and unsaponifiable (IS) in asthma patients. We therefore tested its effect on airway smooth muscle (ASM) cells by observing its ability to regulate the production of glucocorticoid (GC)-insensitive chemokines in cells treated with TNF-α/IFN-γ, and its antioxidative and reactive oxygen species (ROS) scavenging properties.

MATERIALS AND METHODS

the cytotoxicity of N. sativa oil fractions was assessed using an MTT assay. ASM cells were treated with TNF-α/IFN-γ for 24 h in the presence of different concentrations of N. sativa oil fractions. An ELISA assay was used to determine the effect of N. sativa oil fractions on chemokine production (CCL5, CXCL-10, and CXCL-8). The scavenging effect of N. sativa oil fractions was evaluated on three reactive oxygen species (ROS), O₂•^-, OH•, and H₂O₂.

RESULTS

our results show that different N. sativa oil fractions used at 25 and 50 µg/mL did not affect cell viability. All fractions of N. sativa oil inhibited chemokines in a concentration-dependent manner. Interestingly, the total oil fraction showed the most significant effect of chemokine inhibition, and had the highest percentage of ROS scavenging effect.

CONCLUSION

these results suggest that N. sativa oil modulates the proinflammatory actions of human ASM cells by inhibiting the production of GC-insensitive chemokines.

Circular RNA circ_0002594 regulates PDGF-BB-induced proliferation and migration of human airway smooth muscle cells via sponging miR-139-5p/TRIM8 in asthma

BACKGROUND

Asthma is a chronic respiratory disease characterised by the contraction of smooth muscle and remodelling of the airway wall, which is correlated with increased airway smooth muscle mass. Circular RNA (circRNA) circ_0002594 has been reported as a pro-inflammatory factor in allergic asthma. Therefore, this study is designed to explore the role and mechanism of circ_0002594 in human airway smooth muscle cells (HASMC) proliferation and metastasis.

METHODS

Cell proliferative ability, invasion, and migration were detected by 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide (MTT), 5-ethynyl-2'-deoxyuridine (EdU), Transwell, and Wound healing assays. The protein levels of E-cadherin, N-cadherin, and tripartite motif 8 (TRIM8) were detected by western blot assay. The levels of interleukin-6 (IL-6) and IL-13 were detected using Enzyme-linked immunosorbent assays (ELISA). Levels of circ_0002594, microRNA-139-5p (miR-139-5p), TRIM8 were determined by real-time quantitative polymerase chain reaction (RT-qPCR). The binding between miR-139-5p and circ_0002594 or TRIM8 was predicted by Circinteractome or Starbase v2.0, and then verified by a dual-luciferase reporter and RNA Immunoprecipitation (RIP) assays.

RESULTS

Platelet-derived growth factor-BB (PDGF-BB) could trigger HASMC proliferation, metastasis, and inflammation. Circ_0002594 and TRIM8 were elevated in asthma patients and PDGF-BB-treated HASMC, and the miR-139-5p level was decreased. Furthermore, circ_0002594 knockdown could suppress PDGF-BB- stimulated HASMC damage. Mechanism analysis exhibited that circ_0002594 could regulate TRIM8 expression through sponging miR-139-5p.

CONCLUSION

Our findings revealed that circ_0002594 could act as a regulator in the airway remodelling during asthma development partly by the miR-139-5p/TRIM8 axis, hinting at an underlying therapeutic strategy for asthma.

Novel Comprehensive Bioinformatics Approaches to Determine the Molecular Genetic Susceptibility Profile of Moderate and Severe Asthma

Background: Asthma is a chronic inflammatory condition linked to hyperresponsiveness in the airways. There is currently no cure available for asthma, and therapy choices are limited. Asthma is the result of the interplay between genes and the environment. The exact molecular genetic mechanism of asthma remains elusive. Aims: The aim of this study is to provide a comprehensive, detailed molecular etiology profile for the molecular factors that regulate the severity of asthma and pathogenicity using integrative bioinformatics tools. Methods: The GSE43696 omnibus gene expression dataset, which contains 50 moderate cases, 38 severe cases, and 20 healthy controls, was used to investigate differentially expressed genes (DEGs), susceptible chromosomal loci, gene networks, pathways, gene ontologies, and protein–protein interactions (PPIs) using an intensive bioinformatics pipeline. Results: The PPI network analysis yielded DEGs that contribute to interactions that differ from moderate-to-severe asthma. The combined interaction scores resulted in higher interactions for the genes STAT3, AGO2, COL1A1, CLCN6, and KSR for moderate asthma and JAK2, INSR, ERBB2, NR3C1, and PTK6 for severe asthma. Enrichment analysis (EA) demonstrated differential enrichment between moderate and severe asthma phenotypes; the ion transport regulation pathway was significantly enhanced in severe asthma phenotypes compared to that in moderate asthma phenotypes and involved PER2, GCR, IRS-2, KCNK7, KCNK6, NOX1, and SCN7A. The most enriched common pathway in both moderate and severe asthma is the development of the glucocorticoid receptor (GR) signaling pathway followed by glucocorticoid-mediated inhibition of proinflammatory and proconstrictory signaling in the airway of smooth muscle cell pathways. Gene sets were shared between severe and moderate asthma at 16 chromosome locations, including 17p13.1, 16p11.2, 17q21.31, 1p36, and 19q13.2, while 60 and 48 chromosomal locations were unique for both moderate and severe asthma, respectively. Phylogenetic analysis for DEGs showed that several genes have been intersected in phases of asthma in the same cluster of genes. This could indicate that several asthma-associated genes have a common ancestor and could be linked to the same biological function or gene family, implying the importance of these genes in the pathogenesis of asthma. Conclusion: New genetic risk factors for the development of moderate-to-severe asthma were identified in this study, and these could provide a better understanding of the molecular pathology of asthma and might provide a platform for the treatment of asthma.

FGF2, an Immunomodulatory Factor in Asthma and Chronic Obstructive Pulmonary Disease (COPD)

The fibroblast growth factor 2 (FGF2) is a potent mitogenic factor belonging to the FGF family. It plays a role in airway remodeling associated with chronic inflammatory airway diseases, including asthma and chronic obstructive pulmonary disease (COPD). Recently, research interest has been raised in the immunomodulatory function of FGF2 in asthma and COPD, through its involvement in not only the regulation of inflammatory cells but also its participation as a mediator between immune cells and airway structural cells. Herein, this review provides the current knowledge on the biology of FGF2, its expression pattern in asthma and COPD patients, and its role as an immunomodulatory factor. The potential that FGF2 is involved in regulating inflammation indicates that FGF2 could be a therapeutic target for chronic inflammatory diseases.

Glucocorticoid resistance in chronic diseases

Glucocorticoids are involved in several responses triggered by a variety of environmental and physiological stimuli. These hormones have a wide-range of regulatory effects in organisms. Synthetic glucocorticoids are extensively used to suppress allergic, inflammatory, and immune disorders. Although glucocorticoids are highly effective for therapeutic purposes, some patients chronically treated with glucocorticoids can develop reduced glucocorticoid sensitivity or even resistance, increasing patient vulnerability to exaggerated inflammatory responses. Glucocorticoid resistance can occur in several chronic diseases, including asthma, major depression, and cardiovascular conditions. In this review, we discuss the complexity of the glucocorticoid receptor and the potential role of glucocorticoid resistance in the development of chronic diseases.

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.

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.

Refractory asthma: mechanisms, targets, and therapy

Asthma is a common medical condition affecting 300 million people worldwide. Airway inflammation, smooth muscle bronchoconstriction leading to airflow obstruction, and mucous hypersecretion are clinical hallmarks of asthma. The NHLBI Expert Panel Report 3 recommends inhaled corticosteroids (ICS) for patients with moderate to severe persistent asthma. Inhaled corticosteroids (ICS) target gene transcription through their interactions with the glucocorticoid (GC) receptor (GR) at the glucocorticoid response element (GRE). The GC/GR complex enhances anti-inflammatory but inhibits pro-inflammatory mediator production. Classically, asthma has been described as a Th2-associated eosinophil-predominant disease, but recently alternative models have been described including a Th17-mediated neutrophil-predominant phenotype resulting in patients with more severe disease who may be less responsive to steroids. Additional mechanisms of steroid resistance include increased activity of GR phosphorylating kinases which modify the interactions of GR with transcription factors to inhibit the ability of GR to bind with GRE, leading to an increase in pro-inflammatory gene transcription. Oxidative stress also affects the balance between pro-inflammatory and anti-inflammatory gene transcription through the modification of transcription factors and cofactors (such as PI3K) leading to the inhibition of histone deacetylase 2. Continued investigations into the mechanisms behind glucocorticoid resistance will lead to novel treatments that improve control of severe refractory asthma.

Association of serum cytokines levels, interleukin 10 -1082G/A and interferon-γ +874T/A polymorphisms with atopic asthma children from Saudi Arabia

The aim of this study was to clarify the role of IL-4, IL-10, IL-13 and interferon (IFN) -γ levels in atopic asthma patients by studying the relation between their serum levels and severity of the disease. The effect of IL-10 -1082G/A and IFN-γ +874T/A SNPs was also studied. The study included 200 atopic children with asthma and 50 age- and gender matched healthy children as controls. The levels of both IL-4 and IL-13 were significantly (p<0.001) higher, while IFN-γ was significantly (p<0.001) lower in patients compared to that of the controls. There was a significant effect of gene polymorphisms of IL-10 (p<0.05) and IFN-γ (p<0.001) in occurrence of atopic asthma and increased IgE level. Polymorphism of IFN-γ gene had an effect on the serum level of IFN-γ. In conclusion, IFN-γ gene polymorphism at position +874 and IL-10 gene polymorphism at position -1082A/G are genetic determinants which contribute to susceptibility to atopic asthma in children from Saudi Arabia.

Comparison of TNF antagonism by etanercept and dexamethasone on airway epithelium and remodeling in an experimental model of asthma

BACKGROUND

The aim of the study was to compare the influence of TNF antagonism and corticosteroid treatment on epithelial, smooth muscle and basement membrane component of airway remodeling in an experimental murine model of chronic asthma.

METHODS

We used 30 BALB/c mice. Group 1 not exposed to ovalbumin or any medication was designated as control group. Chronic asthma model was achieved in the other three groups with intraperitoneal (IP) and inhaled ovalbumin. Then, Group 2 received IP saline, Group 3 received IP dexamethasone and Group 4 received IP etanercept. Epithelial, subepithelial smooth muscle and basement membrane thickness as well as goblet cells and mast cells were examined on samples isolated from left lung.

RESULTS

Etanercept treatment led to thinner epithelial and basement membrane layer and lower goblet and mast cell number than untreated asthmatic mice (p<0.001, p=0.001, p=0.005 and p=0.03 respectively). Neither epithelial and basement membrane thickness nor mast cell number was different among mice treated with etanercept and dexamethasone (p=0.38, p=0.79 and p=0.51 respectively). However, etanercept group was associated with thicker subepithelial muscle layer but lower goblet cell number (p<0.001 and p=0.04 respectively) than dexamethasone group.

CONCLUSIONS

Corticosteroids are more effective in decreasing smooth muscle mass while TNF antagonists in reducing goblet cell number in animal model of asthma. Therefore, further research is needed to assess the synergistic use of TNF antagonism and dexamethasone for more rational remodeling control.

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.

Caveolin-1 in cytokine-induced enhancement of intracellular Ca(2+) in human airway smooth muscle

Diseases such as asthma are characterized by airway hyperresponsiveness. Enhanced airway smooth muscle (ASM) intracellular Ca(2+) ([Ca(2+)](i)) response to agonist stimulation leading to increased airway constriction has been suggested to contribute to airway hyperresponsiveness. Caveolae are flask-shaped plasma membrane invaginations that express the scaffolding protein caveolin and contain multiple proteins important in [Ca(2+)](i) signaling (e.g., agonist receptors, ion channels). We recently demonstrated that caveolae and caveolin-1 are important in [Ca(2+)](i) regulation in human ASM. Proinflammatory cytokines such as tumor necrosis factor (TNF)-α and interleukin (IL)-13 modulate [Ca(2+)](i) in ASM. We hypothesized that cytokine upregulation of caveolar signaling in ASM contributes to enhanced agonist-induced [Ca(2+)](i) in inflammation. Enzymatically dissociated human ASM cells were exposed to medium (control), 20 ng/ml TNF-α, or 50 ng/ml IL-13 for 24 h. Caveolae-enriched membrane fractions displayed substantial increase in caveolin-1 and -2 expressions by TNF-α and IL-13. Transfection with caveolin-1-mRed DNA substantially accelerated and increased plasma membrane caveolin-1 expression by TNF-α and to a lesser extent by IL-13. Caveolin-1 enhancement was inhibited by nuclear factor-κB and mitogen-activated protein kinase inhibitors. In fura 2-loaded ASM cells, [Ca(2+)](i) responses to 1 μM ACh, 10 μM histamine, or 10 nM bradykinin were all exaggerated by TNF-α as well as IL-13 exposure. However, disruption of caveolae using caveolin-1 suppression via small-interfering RNA resulted in significant blunting of agonist-induced [Ca(2+)](i) responses of vehicle and TNF-α-exposed cells. These functional data were correlated to the presence of TNFR(1) receptor (but not the IL-4/IL-13 receptor) within caveolae. Overall, these results indicate that caveolin-1 plays an important role in airway inflammation by modulating the effect of specific cytokines on [Ca(2+)](i).

T-bet is induced by interferon-γ to mediate chemokine secretion and migration in human airway smooth muscle cells

An inappropriate balance between T-helper (Th)1 and Th2 cytokine production underlies inflammatory changes that result in airway disease. Expression of the T-box transcription factor T-bet regulates differentiation of Th cells and production of Th1 cytokines, particularly IFNγ. T-bet-deficient mice develop airway hyperreactivity, undergo airway remodeling, and exhibit defects in IFNγ production while overproducing Th2 cytokines. T-bet is also reduced in the airways of asthmatic patients, suggesting loss of T-bet expression or activity promotes development of inflammatory airway disease. We present novel data demonstrating T-bet expression is induced in human airway smooth muscle cells (ASMC) by IFNγ. This IFNγ-stimulated expression of T-bet is dependent on signaling through JAK2 and signal transducers and activators of transcription 1 (STAT1) and activates T-bet-dependent DNA binding activity. Expression of T-bet stimulates IFNγ-stimulated IFNγ expression, secretion, and promoter activity, while inhibiting IFNγ-stimulated release of chemokines including monocyte chemoattractant protein (MCP)-1/CCL2, regulated on activation normal T-expressed and secreted (RANTES)/CCL5, and eotaxin/CCL11. This is accompanied by changes in expression of the chemokine receptors CCR3 and IL12Rβ2 and TNFα. T-bet expression also reduces chemotactic migration of ASMC in response to serum and PDGF, which contributes to airway hyperplasia. These results are the first to identify T-bet expression and activity in a structural cell of the lung and may provide new insights into therapeutic targets for inflammatory airway disease.

Interferons modulate mitogen-induced protein synthesis in airway smooth muscle

Severe asthma is characterized by increased airway smooth muscle (ASM) mass due, in part, to ASM cell growth and contractile protein expression associated with increased protein synthesis. Little is known regarding the combined effects of mitogens and interferons on ASM cytosolic protein synthesis. We demonstrate that human ASM mitogens including PDGF, EGF, and thrombin stimulate protein synthesis. Surprisingly, pleiotropic cytokines IFN-beta and IFN-gamma, which inhibit ASM proliferation, also increased cytosolic protein content in ASM cells. Thus IFN-beta alone significantly increased protein synthesis by 1.62 +/- 0.09-fold that was further enhanced by EGF to 2.52 +/- 0.17-fold. IFN-gamma alone also stimulated protein synthesis by 1.91 +/- 0.15-fold; treatment of cells with PDGF, EGF, and thrombin in the presence of IFN-gamma stimulated protein synthesis by 2.24 +/- 0.3-, 1.25 +/- 0.17-, and 2.67 +/- 0.34-fold, respectively, compared with growth factors alone. The mammalian target of rapamycin (mTOR)/S6 kinase 1 (S6K1) inhibition with rapamycin inhibited IFN- and EGF-induced protein synthesis, suggesting that IFN-induced protein synthesis is modulated by mTOR/S6K1 activation. Furthermore, overexpression of tumor suppressor protein tuberous sclerosis complex 2 (TSC2), which is an upstream negative regulator of mTOR/S6K1 signaling, also inhibited mitogen-induced protein synthesis in ASM cells. IFN-beta and IFN-gamma stimulated miR143/145 microRNA expression and increased SM alpha-actin accumulation but had little effect on ASM cell size. In contrast, EGF increased ASM cell size but had little effect on miR143/145 expression. Our data demonstrate that both IFNs and mitogens stimulate protein synthesis but have differential effects on cell size and contractile protein expression and suggest that combined effects of IFNs and mitogens may contribute to ASM cell growth, contractile protein expression, and ASM remodeling in asthma.

Expression and function of the inducible costimulator ligand B7-H2 in human airway smooth muscle cells

BACKGROUND

B7-H2 is a ligand for the inducible costimulator (ICOS). The aim of this study was to examine the expression and function of B7-H2 in human airway smooth muscle (ASM) cells and compare them with those of CD40 or OX40 ligand (OX40L).

METHODS

Expression of B7-H2, CD40 and OX40L in ASM cells and their respective counterparts in T cells was analyzed by RT-PCR or flow cytometry. The modulating effect of polyinosinic-polycytidylic acid (poly I:C) on expression of B7-H2, CD40 and OX40L was also examined. The function of these three molecules was evaluated by virtue of adhesion of anti-CD3-activated T cells, IL-6 and IL-8 production and DNA synthesis.

RESULTS

ASM cells constitutively expressed B7-H2, CD40 and OX40L that mediated adhesion of activated T cells expressing ICOS, CD40L and OX40. ASM cells responded to poly I:C with upregulated expression of B7-H2, CD40 and OX40L and displayed enhanced adhesion of activated T cells. Functional analysis performed on untreated ASM cells showed that engagement of B7-H2 with ICOS-Ig clearly induced DNA synthesis, whereas that of CD40 or OX40L with trimeric CD40L or OX40-Ig greatly increased IL-6 and IL-8 production. These responses were enhanced in poly I:C-treated ASM cells.

CONCLUSIONS

The data demonstrate that ASM cells express functionally active B7-H2, CD40 and OX40L and suggest that B7-H2-dependent signaling may play an active role in a proliferative response rather than in cytokine and chemokine production. In addition, the modulation of B7-H2, CD40 and OX40L expression and function by poly I:C may have important implications for the function of virus-infected ASM cells.

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.

Transcriptional regulation of cytokine function in airway smooth muscle cells

The immuno-modulatory properties of airway smooth muscle have become of increasing importance in our understanding of the mechanisms underlying chronic inflammation and structural remodeling of the airway wall in asthma and chronic obstructive pulmonary disease (COPD). ASM cells respond to many cytokines, growth factors and lipid mediators to produce a wide array of immuno-modulatory molecules which may in turn orchestrate and perpetuate the disease process in asthma and COPD. Despite numerous studies of the cellular effects of cytokines on cultured ASM, few have identified intracellular signaling pathways by which cytokines modulate or induce these cellular responses. In this review we provide an overview of the transcriptional mechanisms as well as intracellular signaling pathways regulating cytokine functions in ASM cells. The recent discovery of toll-like receptors in ASM cells represents a significant development in our understanding of the immuno-modulatory capabilities of ASM cells. Thus, we also review emerging evidence of the inflammatory response to toll-like receptor activation in ASM cells.

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.

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

BACKGROUND AND PURPOSE

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 1alpha, 25-dihydroxy vitamin D3 (calcitriol) modulated chemokine production in ASM.

EXPERIMENTAL APPROACH

Human ASM cell cultures were derived from tracheal samples taken during surgery. ASM cells were treated with tumour necrosis factor alpha (TNFalpha) and/or interferon gamma (IFNgamma) for 24 h in the presence of calcitriol and/or the glucocorticoid fluticasone added 2 h before. RANTES (regulated upon activation, normal T-cell expressed and secreted), interferon-inducible protein 10 (IP-10) and fractalkine (FKN) levels in cell supernatants were measured by ELISA.

KEY RESULTS

In TNFalpha-treated cells, calcitriol inhibited RANTES and IP-10 secretion in a concentration-dependent manner. FKN levels were negligible. In TNFalpha/IFNgamma-treated cells, whereas fluticasone or calcitriol alone partially inhibited RANTES secretion (by 38 and 20%, respectively), the combination of both drugs additively inhibited RANTES secretion (by 60%). No effect was observed on IP-10 secretion. Whereas fluticasone enhanced FKN secretion (by 50%), calcitriol significantly decreased FKN levels (by 50%). Interestingly, calcitriol blocked the stimulatory effect of fluticasone on FKN secretion, which was inhibited by 60% with the combination of calcitriol and fluticasone.

CONCLUSIONS AND IMPLICATIONS

These findings suggest that vitamin D uniquely modulates human ASM expression of chemokines and may exert some beneficial effects in the treatment of steroid-resistant patients with asthma.