Transcriptional regulation of cytokine function in airway smooth muscle cells

Immunological factors, important players in the development of asthma

Asthma is a heterogeneous disease, and its development is the result of a combination of factors, including genetic factors, environmental factors, immune dysfunction and other factors. Its specific mechanism has not yet been fully investigated. With the improvement of disease models, research on the pathogenesis of asthma has made great progress. Immunological disorders play an important role in asthma. Previously, we thought that asthma was mainly caused by an imbalance between Th1 and Th2 immune responses, but this theory cannot fully explain the pathogenesis of asthma. Recent studies have shown that T-cell subsets such as Th1 cells, Th2 cells, Th17 cells, Tregs and their cytokines contribute to asthma through different mechanisms. For the purpose of the present study, asthma was classified into distinct phenotypes based on airway inflammatory cells, such as eosinophilic asthma, characterized by predominant eosinophil aggregates, and neutrophilic asthma, characterized by predominant neutrophil aggregates. This paper will examine the immune mechanisms underlying different types of asthma, and will utilize data from animal models and clinical studies targeting specific immune pathways to inform more precise treatments for this condition.

Immunoglobulin A promotes IL-6 and IL-8 production, proliferation, and migration by the human bronchial smooth muscle cells

Immunoglobulin A (IgA) is important in biological defense, mainly in the mucosal area, and plays pathogenic roles in various diseases by activating both inflammatory and structural cells. The current study aimed to validate the effects of IgA on the human bronchial smooth muscle cell (BSMC), which plays a major role in airway inflammation and remodeling. Serum IgA induced interleukin (IL)-6 and IL-8 production at both mRNA and protein levels, and enhanced cell proliferation and migration by the BSMCs. The synthetic phenotype markers were regulated and the contractile phenotype markers were downregulated by serum IgA. Mitogen-activated protein kinase, phosphatidylinositol 3-kinase/Akt, and nuclear factor-κB pathways were involved in IgA-induced IL-6 and IL-8 production. The BSMCs expressed transferrin receptor (TfR), and TfR siRNA transfection inhibited IL-6 and IL-8 production by serum IgA. In summary, serum IgA is a potent activator of the BSMCs at least partially via TfR.

Transgenic overexpression of α7 integrin in smooth muscle attenuates allergen‐induced airway inflammation in a murine model of asthma

Asthma is a chronic inflammatory disorder of the lower airways characterized by modulation of airway smooth muscle (ASM) function. Infiltration of smooth muscle by inflammatory mediators is partially regulated by transmembrane integrins and the major smooth muscle laminin receptor α7β1 integrin plays a critical role in the maintenance of ASM phenotype. The goal of the current study was to investigate the role of α7 integrin in asthma using smooth muscle‐specific α7 integrin transgenic mice (TgSM‐Itgα7) using both acute and chronic OVA sensitization and challenge protocols that mimic mild to severe asthmatic phenotypes. Transgenic over‐expression of the α7 integrin in smooth muscle resulted in a significant decrease in airway resistance relative to controls, reduced the total number of inflammatory cells and substantially inhibited the production of crucial Th2 and Th17 cytokines in airways. This was accompanied by decreased secretion of various inflammatory chemokines such as eotaxin/CCL11, KC/CXCL3, MCP‐1/CCL2, and MIP‐1β/CCL4. Additionally, α7 integrin overexpression significantly decreased ERK1/2 phosphorylation in the lungs of TgSM‐Itgα7 mice and affected proliferative, contractile, and inflammatory downstream effectors of ERK1/2 that drive smooth muscle phenotype in the lung. Taken together, these results support the hypothesis that enhanced expression of α7 integrin in vivo inhibits allergic inflammation and airway resistance. Moreover, we identify ERK1/2 as a potential target by which α7 integrin signals to regulate airway inflammation. We conclude that identification of therapeutics targeting an increase in smooth muscle α7 integrin expression could serve as a potential novel treatment for asthma.

Anti-Inflammatory Activity of 4-((1R,2R)-3-Hydroxy-1-(4-hydroxyphenyl)-1-methoxypropan-2-yl)-2-methoxyphenol Isolated from Juglans mandshurica Maxim. in LPS-Stimulated RAW 264.7 Macrophages and Zebrafish Larvae Model

Juglans mandshurica Maxim., a traditional folk medicinal plant, is widely distributed in Korea and China. In our previous study, we isolated a new phenylpropanoid compound, 4-((1R,2R)-3-hydroxy-1-(4-hydroxyphenyl)-1-methoxypropan-2-yl)-2-methoxyphenol (HHMP), from J. mandshurica. In the present study, we evaluated the anti-inflammatory activity of HHMP on lipopolysaccharide (LPS)-stimulated RAW 264.7 cells and zebrafish larvae. HHMP significantly inhibited LPS-induced nitric oxide (NO) and prostaglandin E₂ production in a dose-dependent manner. Moreover, HHMP treatment considerably suppressed LPS-induced expression of inducible nitric oxide synthase and cyclooxygenase-2. We also demonstrated the mechanisms of HHMP inhibition of inflammatory responses in LPS-stimulated RAW 264.7 cells via Western blot analysis and immunofluorescence staining. Furthermore, HHMP significantly inhibited NO production in LPS-stimulated zebrafish larvae. Consequently, we established that HHMP significantly inhibited the LPS-induced activation of NF-κB and MAPK and the nuclear translocation of p65 in RAW 264.7 cells. Taken together, our findings demonstrate the effect of HHMP on LPS-induced inflammatory responses in vitro and in vivo, suggesting its potential to be used as a natural anti-inflammatory agent.

Serum metabonomic study of the effects of Huofeitong tablet on rats with COPD

Chronic obstructive pulmonary disease (COPD) is a common respiratory disease. The Huofeitong tablet (HFTT), a Chinese compound medicine, exhibits an unambiguous therapeutic effect on COPD. However, the mechanism of its therapeutic effect on COPD is unclear. This study aimed to investigate the effect of HFTT on COPD and its mechanism. The changes in pulmonary function and the inflammatory factors in rats were determined via histopathology and bronchoalveolar lavage fluid. The mechanism of HFTT in COPD treatment was revealed using UPLC-Q-TOF-MS/MS and multivariate statistical analysis. Results showed that after HFTT treatment, the lung function began to recover, the lung tissue improved, and the TNF-α and IL-6 levels decreased, suggesting that HFTT had a therapeutic effect on COPD. In addition, 12 potential biomarkers, including malonate, urea-1-carboxylate, pyruvate, l-cysteate, glutathione, 2-deoxy-α-d-ribose1-phosphate, 3-fumarylpyruvate, 3-maleylpyruvate, 2-inosose, urate, allantoin, and inosine were screened. They associated with COPD development and concentrated in glutathione metabolism, glyoxylate and dicarboxylate metabolism, secondly concentrated in pyruvate metabolism, glycolysis/gluconeogenesis, pentose phosphate pathway, citrate cycle, glycine, serine and threonine metabolism, inositol phosphate, and purine metabolism. This study contributes to the development and application of HFTT in COPD treatment and provides a theoretical basis for COPD diagnosis, prevention, and treatment.

Eupatilin alleviates airway remodeling via regulating phenotype plasticity of airway smooth muscle cells

Childhood asthma is a common chronic airway disease, and its severe form remains a challenge. Eupatilin is a bioactive natural flavone that has been found to possess potential anti-asthma activity. However, the roles of eupatilin in asthma remain to be elucidated. In the present study, airway smooth muscle cells (ASMCs) were applied for the in vitro investigation since their phenotype plasticity make great contribution to airway remodeling during asthma pathogenesis. Our results showed that eupatilin suppressed the transforming growth factor β1 (TGF-β1)-induced proliferation and migration of ASMCs. Exposure of ASMCs to eupatilin increased the expressions of contractile markers smooth muscle α-actin (α-SMA) and myocardin, whereas expressions of extracellular matrix (ECM) proteins type I collagen (Coll I) and fibronectin were reduced. Furthermore, eupatilin treatment reversed the activation of nuclear factor-κ B (NF-κB), signal transducer and activator of transcription 3 (STAT3) and AKT pathways caused by TGF-β1 in ASMCs. These findings suggested that eupatilin might attenuate airway remodeling via regulating phenotype plasticity of ASMCs.

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.

Differential regulation of cytokine and chemokine expression by MK2 and MK3 in airway smooth muscle cells

BACKGROUND

Airway smooth muscle (ASM) contributes to local inflammation and plays an immunomodulatory role in airway diseases. This is partially regulated by p38 mitogen-activated protein kinase (MAPK), which further activates two closely related isoforms of the MAPK-activated protein kinases (MKs), MK2 and MK3. The MKs have similar substrate specificities but less is known about differences in their functional responses. This study was undertaken to identify differential downstream inflammatory targets of MK2 and MK3 signaling and assess cross-talk between the MAPK pathway and NF-κB signaling relevant to ASM function.

METHODS

Wild-type and kinase-deficient MK2 (MK2^WT, MK2^KR) and MK3 (MK3^WT, MK3^3A) were expressed in human ASM cells stimulated for 20 h with 10 ng/ml each interleukin (IL)-1β, tumor necrosis factor (TNF)-α and interferon (IFN)-γ. Inflammatory mediator secretion was assessed by Luminex assays and ELISA. Signaling pathway activation was monitored by Western blotting.

RESULTS

Expression of these MKs and stimulation with 10 ng/ml IL-1β, TNFα and IFNγ for 20 h did not affect secretion of multiple cytokines including IL-4, IL-5, IL-13 and monocyte chemotactic protein (MCP)-1/CCL2 but did differentially affect the secretion of regulated upon activation, normal T cell expressed and secreted (RANTES)/CCL5, IL-6 and granulocyte macrophage-colony stimulating factor (GM-CSF). RANTES/CCL5 secretion was decreased by MK2^WT or MK3^WT and stimulated by inhibition of MK2 or MK3 activity with expression of the kinase-deficient enzymes MK2^KR or MK3^3A. IL-6 and GM-CSF secretion was decreased by inhibition of MK2 activity with MK2^KR and while MK3^WT had no effect, the kinase-deficient MK3^3A further decreased secretion of these mediators. Cross-talk of the MKs with other signaling pathways was investigated by examining NF-κB activation, which was inhibited by expression of MK3 but not affected by MK2.

CONCLUSIONS

These results suggest an inhibitory role for MK2 and MK3 activity in RANTES/CCL5 secretion and cross-talk of MK3 with NF-κB to regulate IL-6 and GM-CSF. These findings differentiate MK2 and MK3 function in ASM cells and provide insight that may enable selective targeting of MKs in ASM to modulate local inflammation in airway disease.

Large-scale profiling of signalling pathways reveals an asthma specific signature in bronchial smooth muscle cells

Background

Bronchial smooth muscle (BSM) cells from asthmatic patients maintain in vitro a distinct hyper-reactive (“primed”) phenotype, characterized by increased release of pro-inflammatory factors and mediators, as well as hyperplasia and/or hypertrophy. This “primed” phenotype helps to understand pathogenesis of asthma, as changes in BSM function are essential for manifestation of allergic and inflammatory responses and airway wall remodelling.

Objective

To identify signalling pathways in cultured primary BSMs of asthma patients and non-asthmatic subjects by genome wide profiling of differentially expressed mRNAs and activated intracellular signalling pathways (ISPs).

Methods

Transcriptome profiling by cap-analysis-of-gene-expression (CAGE), which permits selection of preferentially capped mRNAs most likely to be translated into proteins, was performed in human BSM cells from asthmatic (n=8) and non-asthmatic (n=6) subjects and OncoFinder tool were then exploited for identification of ISP deregulations.

Results

CAGE revealed >600 RNAs differentially expressed in asthma vs control cells (p≤0.005), with asthma samples showing a high degree of similarity among them. Comprehensive ISP activation analysis revealed that among 269 pathways analysed, 145 (p<0.05) or 103 (p<0.01) are differentially active in asthma, with profiles that clearly characterize BSM cells of asthmatic individuals. Notably, we identified 7 clusters of coherently acting pathways functionally related to the disease, with ISPs down-regulated in asthma mostly targeting cell death-promoting pathways and up-regulated ones affecting cell growth and proliferation, inflammatory response, control of smooth muscle contraction and hypoxia-related signalization.

Conclusions

These first-time results can now be exploited toward development of novel therapeutic strategies targeting ISP signatures linked to asthma pathophysiology.

Agrimonolide from Agrimonia pilosa suppresses inflammatory responses through down-regulation of COX-2/iNOS and inactivation of NF-κB in lipopolysaccharide-stimulated macrophages

BACKGROUND

Agrimonolide from Agrimonia pilosa showed a strong anti-inflammatory activity, and the present study aims to reveal potential mechanisms on molecular level explaining its anti-inflammatory effect.

HYPOTHESIS/PURPOSE

To investigate the mechanism of anti-inflammatory activity of agrimonolide.

STUDY DESIGN

Anti-inflammatory activity of agrimonolide in cells was applied.

METHODS

Anti-inflammatory activity of agrimonolide isolated from Agrimonia pilosa was evaluated using lipopolysaccharide (LPS) stimulated RAW 264.7 cell models. The productions of IL-1β, IL-6, TNF-α and NO were determined by ELISA and nitrite analysis, respectively. The expressions of iNOS and COX-2 were measured by western blotting and RT-PCR analysis.

RESULTS

The pre-treatment with agrimonolide significantly reduced the levels of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α), as well as attenuated the expression of iNOS and COX-2 in LPS-stimulated macrophages. Furthermore, agrimonolide inhibited the activation of JNK and p38 MAPKs and decreased the activation of JAK-STAT and NF-κB in LPS-stimulated macrophages.

CONCLUSION

The present study suggested that agrimonolide exerted anti- inflammatory activity, at least in part, via suppressing LPS-induced activation of JAK-STATs and p38 MAPKs signaling pathway.

Interleukin-33 promotes inflammatory cytokine production in chronic airway inflammation

Interleukin (IL)-33, belonging to the IL-1 family, is a novel cytokine that plays an important role in several chronic inflammatory diseases. Its role in chronic airway inflammation that develops into COPD is widely unknown. To determine this, we identified the expression of IL-33 in human bronchial epithelial layer and detected the inflammatory effects of IL-33 stimulation and the relative signaling pathways in human bronchial epithelial (HBE) cells and peripheral blood mononuclear cells (PBMCs), respectively. In this study, the expression of IL-33 in human bronchial epithelial layer was upregulated in COPD patients compared with normal controls. The expressions of IL-6 and IL-8 were also increased in both HBE cells and PBMCs, stimulated by IL-33 alone or combining the cigarette smoke extract (CSE). And the increased expressions could be partially blocked by ST2-Fc and IL-1RacP-Fc in both HBE cells and PBMCs. The p42/p44 ERK inhibitor in HBE cells and the p38 MAPK inhibitor in PBMCs exerted similar effects. Our data showed that IL-33 could induce and enhance the expression of IL-6 and IL-8 in HBE cells and PBMCs of COPD patients via ST2/IL-1RacP pathway and MAPKs pathway. Thus, the IL-33 is a promoter of chronic airway inflammation that contributes to COPD development.

Tidal stretches differently regulate the contractile and cytoskeletal elements in intact airways

Recent reports suggest that tidal stretches do not cause significant and sustainable dilation of constricted intact airways ex vivo. To better understand the underlying mechanisms, we aimed to map the physiological stretch-induced molecular changes related to cytoskeletal (CSK) structure and contractile force generation through integrin receptors. Using ultrasound, we measured airway constriction in isolated intact airways during 90 minutes of static transmural pressure (Ptm) of 7.5 cmH2O or dynamic variations between Ptm of 5 and 10 cmH20 mimicking breathing. Integrin and focal adhesion kinase activity increased during Ptm oscillations which was further amplified during constriction. While Ptm oscillations reduced β-actin and F-actin formation implying lower CSK stiffness, it did not affect tubulin. However, constriction was amplified when the microtubule structure was disassembled. Without constriction, α-smooth muscle actin (ASMA) level was higher and smooth muscle myosin heavy chain 2 was lower during Ptm oscillations. Alternatively, during constriction, overall molecular motor activity was enhanced by Ptm oscillations, but ASMA level became lower. Thus, ASMA and motor protein levels change in opposite directions due to stretch and contraction maintaining similar airway constriction levels during static and dynamic Ptm. We conclude that physiological Ptm variations affect cellular processes in intact airways with constriction determined by the balance among contractile and CSK molecules and structure.

Cigarette smoke-induced mitochondrial fragmentation and dysfunction in human airway smooth muscle

The balance between mitochondrial fission and fusion is crucial for mitochondria to perform its normal cellular functions. We hypothesized that cigarette smoke (CS) disrupts this balance and enhances mitochondrial dysfunction in the airway. In nonasthmatic human airway smooth muscle (ASM) cells, CS extract (CSE) induced mitochondrial fragmentation and damages their networked morphology in a concentration-dependent fashion, via increased expression of mitochondrial fission protein dynamin-related protein 1 (Drp1) and decreased fusion protein mitofusin (Mfn) 2. CSE effects on Drp1 vs. Mfn2 and mitochondrial network morphology involved reactive oxygen species (ROS), activation of extracellular signal-regulated kinase (ERK), phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt), protein kinase C (PKC) and proteasome pathways, as well as transcriptional regulation via factors such as NF-κB and nuclear erythroid 2-related factor 2. Inhibiting Drp1 prevented CSE effects on mitochondrial networks and ROS generation, whereas blocking Mfn2 had the opposite, detrimental effect. In ASM from asmatic patients, mitochondria exhibited substantial morphological defects at baseline and showed increased Drp1 but decreased Mfn2 expression, with exacerbating effects of CSE. Overall, these results highlight the importance of mitochondrial networks and their regulation in the context of cellular changes induced by insults such as inflammation (as in asthma) or CS. Altered mitochondrial fission/fusion proteins have a further potential to influence parameters such as ROS and cell proliferation and apoptosis relevant to airway diseases.

Vitamin D supplementation reduces airway hyperresponsiveness and allergic airway inflammation in a murine model

BACKGROUND

Asthma is a chronic disease associated with airway hyperresponsiveness (AHR), airway obstruction and airway remodelling. NF-κB is a transcriptional factor that regulates and co-ordinates the expression of various inflammatory genes. The NF-κB subunits, p50 and Rel-A, are translocated to the nucleus by importin α3 and importin α4. There is growing evidence that vitamin D is a potent immunomodulator. However, the evidence for beneficial or adverse effects of vitamin D in asthma is still unclear.

OBJECTIVE

In this study, we examined the effect of vitamin D status on AHR, airway inflammation and cytokines in the bronchoalveolar lavage fluid (BALF) in a murine model of allergic asthma.

METHODS

Female BALB/c mice were fed with special vitamin D-deficient or vitamin D-sufficient (2000 IU/kg) or vitamin D-supplemented (10,000 IU/kg) diet for 13 weeks. Mice were sensitized and challenged with ovalbumin (OVA). The effect of vitamin D on lung histology, AHR, T regulatory cells (Tregs) and BALF cytokines was examined. The expression of importin-α3 and Rel-A in the lung of OVA-sensitized mice was analysed using immunofluorescence.

RESULTS

Vitamin D deficiency was associated with higher AHR in OVA-sensitized and challenged mice than those in vitamin D-sufficient mice. This was accompanied with marked signs of airway remodelling, high BALF eosinophilia, increased BALF pro-inflammatory cytokines, reduced BALF IL-10 levels, reduced blood Tregs, increased expression of importin-α3 and Rel-A in the lung tissue. Vitamin D supplementation attenuated the pro-inflammatory effects, but did not completely reverse the features of allergic airway inflammation.

CONCLUSION AND CLINICAL RELEVANCE

Vitamin D could be beneficial as an adjunct therapy in the treatment of allergic asthma.

Resveratrol attenuates the release of inflammatory cytokines from human bronchial smooth muscle cells exposed to lipoteichoic acid in chronic obstructive pulmonary disease

During bacterial infections, pathogen-associated molecular patterns (PAMPs) induce cytokine/chemokine release in immunoactive cells. This increases corticosteroid-resistant airway inflammation in chronic obstructive pulmonary disease (COPD) and leads to exacerbations. Anti-inflammatory therapies other than corticosteroids are required and resveratrol is currently under discussion. Resveratrol is an activator of sirtuins, which are class III histone deacetylases (HDACs). We suggested that human airway smooth muscle cells (HASMCs) release COPD-associated cytokines/chemokines in response to lipoteichoic acid (LTA), a major PAMP of gram-positive bacteria and that resveratrol is superior to the corticosteroid dexamethasone in suppressing these cytokines/chemokines. Cultivated HASMCs of patients with COPD were pre-incubated with resveratrol or dexamethasone before stimulation with LTA. CCL2, GM-CSF, IL-6 and IL-8 were analysed in culture supernatants by enzyme-linked immunosorbent assay. Drug effects were investigated in the absence and presence of trichostatin A (TSA), an inhibitor of class I/II HDACs, and EX527, an inhibitor of the sirtuin SIRT1. LTA induced robust cytokine/chemokine release. Resveratrol was superior to dexamethasone in reducing CCL-2, IL-6 and IL-8 in LTA-exposed HASMCs of patients with COPD. Both drugs were equally effective in reducing GM-CSF. Resveratrol effects were partially reversed by EX527 but not by TSA. Dexamethasone effects were partially reversed by TSA but not by EX527. We conclude that HASMCs contribute to the increase in airway inflammation in COPD exacerbations caused by gram-positive bacterial infections. Our data suggest resveratrol as an alternative anti-inflammatory therapy in infection-induced COPD exacerbations. Resveratrol and corticosteroids suppress cytokine/chemokine expression through activation of SIRT1 or interaction with class I/II HDACs, respectively, in HASMCs.

TNFα induces expression of HIF-1α mRNA and protein but inhibits hypoxic stimulation of HIF-1 transcriptional activity in airway smooth muscle cells

Airway smooth muscle cells (ASMCs) participate in tissue remodeling characteristic of airway inflammatory diseases like asthma. Inflammation and hypoxia pathways are often interconnected and the regulatory subunit of the hypoxia inducible factor, HIF-1α, has been recently shown to be induced by cytokines. Here we investigate the effect of individual or combined treatment of ASMCs with the inflammatory mediator TNFα and/or hypoxia on the expression of HIF-1α, HIF-1 targets and inflammation markers. TNFα enhances HIF-1α protein and mRNA levels, under both normoxia and hypoxia. TNFα-mediated induction of HIF-1α gene transcription is repressed by inhibition of the NF-κB pathway. Despite the up-regulation of HIF-1α protein, the transcription of HIF-1 target genes remains low in the presence of TNFα at normoxia and is even reduced at hypoxia. We show that the reduction in HIF-1 transcriptional activity by TNFα is due to inhibition of the interaction of HIF-1α with ARNT and subsequent blocking of its binding to HREs. Comparison between hypoxia and TNFα for their effects on the expression of inflammatory markers shows significant differences: hypoxia up-regulates the expression of IL-6, but not RANTES or ICAM, and reduces the induction of VCAM by TNFα. Finally, ex vivo treatment of rabbit trachea strips with TNFα increases HIF-1α protein levels, but reduces the expression of HIF-1 targets under hypoxia. Overall, TNFα induces HIF-1α mRNA synthesis via an NF-κB dependent pathway but inhibits binding of HIF-1α to ARNT and DNA, while hypoxia and TNFα have distinct effects on ASMC inflammatory gene expression.

Emerging mediators of airway smooth muscle dysfunction in asthma

Phenotypic changes in airway smooth muscle are integral to the pathophysiological changes that constitute asthma - namely inflammation, airway wall remodelling and bronchial hyperresponsiveness. In vitro and in vivo studies have shown that the proliferative, secretory and contractile functions of airway smooth muscle are dysfunctional in asthma. These functions can be modulated by various mediators whose levels are altered in asthma, derived from inflammatory cells or produced by airway smooth muscle itself. In this review, we describe the emerging roles of the CXC chemokines (GROs, IP-10), Th17-derived cytokines (IL-17, IL-22) and semaphorins, as well as the influence of viral infection on airway smooth muscle function, with a view to identifying new opportunities for therapeutic intervention in asthma.

TLR2 ligand engagement upregulates airway smooth muscle TNFα-induced cytokine production

Airway inflammation and respiratory infections are important factors contributing to disease exacerbation in chronic airway diseases such as asthma and chronic obstructive pulmonary disease. Airway smooth muscle (ASM) cells express Toll-like receptors (TLRs) and may be involved in the amplification of airway inflammatory responses during infectious exacerbations. We determined whether infectious stimuli (mimicked using Pam3CSK4, a synthetic bacterial lipopeptide that binds to TLR2/TLR1) further enhance ASM cell inflammatory responses to TNFα in vitro and the signaling pathways involved. Human ASM cells were pretreated for 1 h with Pam3CSK4 (1 μg/ml) in the absence or presence of TNFα (10 ng/ml), and IL-6 and IL-8 release was measured after 24 h. As expected, stimulation with Pam3CSK4 or TNFα alone induced significant IL-6 and IL-8 release. Furthermore, Pam3CSK4 significantly increased TNFα-induced IL-6 and IL-8 mRNA expression and protein release and neutrophil chemotactic activity. The potentiating effect of Pam3CSK4 on TNFα-induced inflammatory responses was not due to enhanced TLR2 expression nor did it involve augmentation of NF-κB or MAPK signaling pathways. Rather, Pam3CSK4 induced cAMP response element (CRE) binding protein phosphorylation and induced CRE-mediated transcriptional regulation, suggesting that Pam3CSK4 and TNFα are acting in concert to enhance ASM cytokine secretion via parallel transcriptional pathways. Our findings suggest that ASM cells may be involved in the amplification of airway inflammatory responses during infectious exacerbations in chronic airway disease.

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.

Isoprostanes and asthma

Isoprostanes are prostaglandin (PG)-like compounds generated in vivo following oxidative stress by non-enzymatic peroxidation of polyunsaturated fatty acids, including arachidonic acid. They are named based on their prostane ring structure and by the localization of hydroxyl groups on the carbon side chain; these structural differences result in a broad array of isoprostane molecules with varying biological properties. Generation of specific isoprostanes is also regulated by host cell redox conditions; reducing conditions favor F₂-isoprostane production while under conditions with deficient antioxidant capacity, D₂- and E₂-isoprostanes are formed. F₂-isoprostanes (F₂-isoP) are considered reliable markers of oxidative stress in pulmonary diseases including asthma. Importantly, F₂-isoP and other isoprostanes function as ligands for PG receptors, and potentially other receptors that have not yet been identified. They have been reported to have important biological properties in many organs. In the lung, isoprostanes regulate cellular processes affecting airway smooth muscle tone, neural secretion, epithelial ion flux, endothelial cell adhesion and permeability, and macrophage adhesion and function. In this review, we will summarize the evidence that F₂-isoP functions as a marker of oxidative stress in asthma, and that F₂-isoP and other isoprostanes exert biological effects that contribute to the pathogenesis of asthma. This article is part of a Special Issue entitled Biochemistry of Asthma.

Does airway smooth muscle express an inflammatory phenotype in asthma?

In addition to hyperresponsiveness in asthma, airway smooth muscle (ASM) also manifests an inflammatory phenotype characterized by augmented expression of mediators that enhance inflammation, contribute to tissue remodelling and augment leucocyte trafficking and activity. Our present review summarizes contemporary understanding of ASM-derived mediators and their paracrine and autocrine actions in airway diseases.

Essential role of NF-κB and AP-1 transcription factors in TNF-α-induced TSLP expression in human airway smooth muscle cells

Human airway smooth muscle (HASM) cells are a rich source of inflammatory mediators that may propagate the airway inflammatory responses. Recent studies from our laboratory and others demonstrate that HASM cells express the proallergic cytokine thymic stromal lymphopoietin (TSLP) in vitro and in vivo. Compelling evidence from in vitro studies and animal models suggest that the TSLP is a critical factor sufficient and necessary to induce or maintain the allergic airway inflammation. Despite of an immense interest in pathophysiology of TSLP in allergic inflammation, the triggers and mechanisms of TSLP expression remain inadequately understood. In this study, we found that TNF-α upregulates the TSLP mRNA and induces high levels of TSLP protein release in primary human ASM cells. Interestingly, TNF-α induced the TSLP promoter activity ( P < 0.05; n = 4) in HASM that was mediated by upstream NF-κB and activator protein-1 (AP-1) binding sites. Mutation in NF-κB and AP-1 binding sites completely abrogated the effect of TNF-α-mediated TSLP promoter activity and so did the expression of a dominant-negative mutant construct of IκB kinase. Furthermore, the peptide inhibitors of IκB kinase or NF-κB inhibited the TNF-α-induced TSLP protein release ( P < 0.05; n = 3) in HASM. Collectively, our data suggest a novel important biological role for NF-κB pathway in TNF-α-induced TSLP expression in HASM and recommend this as a prime target for anti-inflammatory drugs.

Pro-inflammatory mechanisms of muscarinic receptor stimulation in airway smooth muscle

BACKGROUND

Acetylcholine, the primary parasympathetic neurotransmitter in the airways, plays an important role in bronchoconstriction and mucus production. Recently, it has been shown that acetylcholine, by acting on muscarinic receptors, is also involved in airway inflammation and remodelling. The mechanism(s) by which muscarinic receptors regulate inflammatory responses are, however, still unknown.

METHODS

The present study was aimed at characterizing the effect of muscarinic receptor stimulation on cytokine secretion by human airway smooth muscle cells (hASMc) and to dissect the intracellular signalling mechanisms involved. hASMc expressing functional muscarinic M2 and M3 receptors were stimulated with the muscarinic receptor agonist methacholine, alone, and in combination with cigarette smoke extract (CSE), TNF-α, PDGF-AB or IL-1β.

RESULTS

Muscarinic receptor stimulation induced modest IL-8 secretion by itself, yet augmented IL-8 secretion in combination with CSE, TNF-α or PDGF-AB, but not with IL-1β. Pretreatment with GF109203X, a protein kinase C (PKC) inhibitor, completely normalized the effect of methacholine on CSE-induced IL-8 secretion, whereas PMA, a PKC activator, mimicked the effects of methacholine, inducing IL-8 secretion and augmenting the effects of CSE. Similar inhibition was observed using inhibitors of IκB-kinase-2 (SC514) and MEK1/2 (U0126), both downstream effectors of PKC. Accordingly, western blot analysis revealed that methacholine augmented the degradation of IκBα and the phosphorylation of ERK1/2 in combination with CSE, but not with IL-1β in hASMc.

CONCLUSIONS

We conclude that muscarinic receptors facilitate CSE-induced IL-8 secretion by hASMc via PKC dependent activation of IκBα and ERK1/2. This mechanism could be of importance for COPD patients using anticholinergics.

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.