Epigenetic mechanisms silence a disintegrin and metalloprotease 33 expression in bronchial epithelial cells

BACKGROUND

A disintegrin and metalloprotease 33 (ADAM33) polymorphism is strongly associated with asthma and bronchial hyperresponsiveness. Although considered to be a mesenchymal cell-specific gene, recent reports have suggested epithelial expression of ADAM33 in patients with severe asthma.

OBJECTIVES

Because dysregulated expression of ADAM33 can contribute to disease pathogenesis, we characterized the mechanism or mechanisms that control its transcription and investigated ADAM33 expression in bronchial biopsy specimens and brushings from healthy and asthmatic subjects.

METHODS

The ADAM33 promoter and CpG island methylation were analyzed by using bioinformatics, luciferase reporters, and bisulfite sequencing of genomic DNA. Epithelial-mesenchymal transition was induced by using TGF-beta1. ADAM33 mRNA was scrutinized in bronchial biopsy specimens and brushings by using reverse transcriptase-quantitative polymerase chain reaction, melt-curve analysis, and direct sequencing.

RESULTS

The predicted ADAM33 promoter (-550 to +87) had promoter transcriptional activity. Bisulfite sequencing showed that the predicted promoter CpG island (-362 to +80) was hypermethylated in epithelial cells but hypomethylated in ADAM33-expressing fibroblasts. Treatment of epithelial cells with 5-aza-deoxycytidine caused demethylation of the CpG island and induced ADAM33 expression. In contrast, phenotypic transformation of epithelial cells through a TGF-beta-induced epithelial-mesenchymal transition was insufficient to induce ADAM33 expression. ADAM33 mRNA was confirmed in bronchial biopsy specimens, but no validated signal was detected in bronchial brushings from healthy or asthmatic subjects.

CONCLUSION

The ADAM33 gene contains a regulatory CpG island within its promoter, the methylation status of which tightly controls its expression in a cell type-specific manner. ADAM33 repression is a stable feature of airway epithelial cells, irrespective of disease.

The role of a soluble TNFalpha receptor fusion protein (etanercept) in corticosteroid refractory asthma: a double blind, randomised, placebo controlled trial

AIM

Tumour necrosis factor alpha (TNFalpha) is a cytokine recognised as a therapeutic target in chronic inflammatory diseases.

METHODS

A randomised, double blind, placebo controlled parallel group trial is reported of etanercept (an IgG1-TNF p75 receptor fusion protein), administered once weekly for 12 weeks in 39 patients with severe corticosteroid refractory asthma. Efficacy was measured by change from the pretreatment baseline in Asthma Related Quality of Life (AQLQ) and Asthma Control (ACQ) Questionnaire scores (the primary endpoints), lung function, peak expiratory flow (PEF) and bronchial hyperresponsiveness (BHR). Sputum and serum inflammatory cells and cytokines, serum albumin and C reactive protein (CRP) as biomarkers of inflammation were also assessed.

RESULTS

There was a small but significant difference in reduction of ACQ scores between treatment and placebo (-1.11 (95% CI -1.56 to -0.75) and -0.52 (95% CI -0.97 to -0.07), respectively, p = 0.037). There was no significant difference in improvements in AQLQ scores, lung function, PEF, BHR or exacerbation rates between the groups. Minor adverse events, including injection site pain and skin rashes, were more frequent with etanercept. There was a significant reduction in sputum macrophages and CRP, and increases in serum TNFalpha and albumin following treatment, but not in other laboratory parameters.

CONCLUSION

Etanercept therapy over 12 weeks demonstrated only a small but significant improvement in asthma control and systemic inflammation, as measured by serum albumin and CRP. Larger randomised, placebo controlled trials are required to clarify the role of TNFalpha antagonism in subjects with severe refractory asthma.

Cellular localization of interleukin 13 receptor alpha2 in human primary bronchial epithelial cells and fibroblasts

BACKGROUND

Interleukin (IL) 13 is a key cytokine in asthma, regulating fibrosis, airway remodeling, induction of immunoglobulin E synthesis by B cells, bronchial hyperresponsiveness, and mucus production. IL-13 signals through the type II IL-4 receptor (IL-4R), which is composed of the IL-4Ralpha and the IL-13Ralpha1 chains. Another IL-13 binding chain, IL-13Ralpha2, binds IL-13 with high affinity but has no known signaling capability and is thought to serve as a decoy receptor providing tight regulation of IL-13 responses.

METHODS

In this study, we investigated the cellular localization of IL-13Ralpha2 in human primary bronchial epithelial cells and fibroblasts using flow cytometry and confocal microscopy, as well as the in vivo expression of IL-13Ralpha2 in the human bronchial mucosa by means of immunohistochemistry.

RESULTS

IL-13Ralpha2 is predominantly an intracellular rather than a membrane-bound molecule in both human primary bronchial epithelial cells and fibroblasts and displays a diffuse granular cytoplasmic distribution in both cell types. IL-13Ralpha2 protein is expressed in vivo in the human bronchial mucosa with its expression being higher in bronchial epithelial cells than bronchial fibroblasts both in vivo and in vitro.

CONCLUSIONS

IL-13Ralpha2 is expressed by both human primary bronchial epithelial cells and fibroblasts as an intracellular protein with a diffuse cytoplasmic distribution. In vivo, IL-13Ralpha2 is expressed in the human airway mucosa mainly by bronchial epithelial cells.

Enhancement of neutrophil function by the bronchial epithelium stimulated by epidermal growth factor

The bronchial epithelium is an important physical barrier that regulates physiological processes including leukocyte trafficking. The aim of the present study was to elucidate the mechanisms whereby the bronchial epithelium, stimulated by epidermal growth factor (EGF) as part of a response to acute or chronic injury, could activate and chemoattract human neutrophils. Subconfluent human bronchial epithelial (16HBE) cells were stimulated with EGF to mimic the in vivo events after injury. The effect of the resulting EGF-conditioned media (CM) was compared with that of basal-CM with respect to neutrophil activation and chemotaxis. Such findings were then confirmed using primary bronchial epithelial cells (PBECs) from healthy volunteers. EGF-CM from 16HBE cells caused increased expression of CD11b/CD66b and CD62L loss on neutrophils when compared with basal-CM. EGF-CM contained significant neutrophil chemotactic activity involving granulocyte-macrophage colony-stimulating factor and interleukin-8 that was potentiated by leukotriene B(4). This was dependent on neutrophil phosphatidylinositol-3-kinase activation and Akt phosphorylation, with partial regulation by phospholipase D, but not mammalian target of rapamycin. Consistent with these observations, EGF-CM derived from PBECs displayed increased chemotactic activity. The present results suggest that the enhanced chemotactic activity of the epidermal growth factor-conditioned epithelium can enhance neutrophil-mediated immunity during acute injury, while during continued injury and repair, as in chronic asthma, this could contribute to persistent neutrophilic inflammation.

IFN-gamma-induced protein 10 is a novel biomarker of rhinovirus-induced asthma exacerbations

Background

Rhinovirus-induced acute asthma is the most frequent trigger for asthma exacerbations.

Objective

We assessed which inflammatory mediators were released from bronchial epithelial cells (BECs) after infection with rhinovirus and then determined whether they were also present in subjects with acute virus-induced asthma, with the aim to identify a biomarker or biomarkers for acute virus-induced asthma.

Methods

BECs were obtained from bronchial brushings of steroid-naive asthmatic subjects and healthy nonatopic control subjects. Cells were infected with rhinovirus 16. Inflammatory mediators were measured by means of flow cytometry with a cytometric bead array. Subjects with acute asthma and virus infection were recruited; they were characterized clinically by using lung function tests and had blood taken to measure the inflammatory mediators identified as important by the BEC experiments.

Results

IFN-γ–induced protein 10 (IP-10) and RANTES were released in the greatest quantities, followed by IL-6, IL-8, and TNF-α. Dexamethasone treatment of BECs only partially suppressed IP-10 and TNF-α but was more effective at suppressing RANTES, IL-6, and IL-8. In acute clinical asthma serum IP-10 levels were increased to a greater extent in those with acute virus-induced asthma (median of 604 pg/mL compared with 167 pg/mL in those with non–virus-induced acute asthma, P < .01). Increased serum IP-10 levels were predictive of virus-induced asthma (odds ratio, 44.3 [95% CI, 3.9-100.3]). Increased serum IP-10 levels were strongly associated with more severe airflow obstruction (r = −0.8; P < .01).

Conclusions

IP-10 release is specific to acute virus-induced asthma.

Clinical implications

Measurement of serum IP-10 could be used to predict a viral trigger to acute asthma.

Local genetic and environmental factors in asthma disease pathogenesis: chronicity and persistence mechanisms

While asthma is an inflammatory disorder of the airways usually associated with atopy, an important additional component is involvement of the epithelium and underlying mesenchyme acting as a trophic unit (EMTU). In addition to allergens, a wide range of environmental factors interact with the EMTU, such as virus infections, environmental tobacco smoke and pollutants, to initiate tissue damage and aberrant repair responses that are translated into remodelling of the airways. While candidate gene association studies have revealed polymorphic variants that influence asthmatic inflammation, positional cloning of previously unknown genes is identifying a high proportion of novel genes in the EMTU. Dipeptidyl peptidase (DPP) 10 and disintegrin and metalloproteinase (ADAM)33 are newly identified genes strongly associated with asthma that are preferentially expressed in the airway epithelium and underlying mesenchyme, respectively. Also of increasing importance is the recognition that genes associated with asthma and atopy have important interactions with the environment through epigenetic mechanisms that influence their expression. This type of research will not only identify biomarkers of different types of asthma across the full range of phenotypic expression, but will also identify novel therapeutic targets that could influence the natural history of the heterogenes lung disease.

Effect of IL-13 receptor alpha2 levels on the biological activity of IL-13 variant R110Q

BACKGROUND

IL-13 is a key cytokine associated with the asthmatic phenotype. IL-13 signals via its cognate receptor, a complex of IL-13 receptor (IL-13R) alpha 1 chain with IL-4 receptor alpha; however, a second protein, IL-13Ralpha2, also binds IL-13. Recently a polymorphic variant of IL-13 (R110Q) has been shown to be associated with atopy.

OBJECTIVE

To investigate the binding properties of this IL-13 variant to its cognate receptors.

METHODS

We used surface plasmon resonance to measure the binding kinetics of R110Q to its receptors. Primary human fibroblasts were grown from endobronchial biopsies obtained from volunteers. Receptor levels were measured by fluorescence-activated cell sorting.

RESULTS

There was no significant difference in the binding of R110Q with soluble human IL-13Ralpha1 compared with IL-13 (32 +/- 5 nmol/L and 36 +/- 7 nmol/L, respectively; P = .625). However, a small but significant difference was observed in the binding of R110Q to soluble human IL-13Ralpha2 compared with IL-13 (840 +/- 87 pmol/L and 1.1 +/- .05 nmol/L, respectively; P = .04). We observed that primary human lung fibroblasts expressed different levels of IL-13Ralpha2. Eotaxin release from fibroblasts expressing low IL-13Ralpha2 levels was significantly higher in response to R110Q compared with IL-13. This was not evident in cells that had high baseline IL-13Ralpha2 levels.

CONCLUSION

These results suggest that relatively small changes in functional properties of a ligand combined with variation in receptor levels in vivo can result in significant differences in responsiveness.

CLINICAL IMPLICATIONS

Expression of R110Q and low IL-13Ralpha2 levels can result in important biological differences that may have clinical relevance in an atopic environment.

Expression of genes involved in oxidative stress responses in airway epithelial cells of smokers with chronic obstructive pulmonary disease

RATIONALE

The molecular mechanisms involved in airway oxidative stress responses reported in healthy smokers and in those with chronic obstructive pulmonary disease (COPD) are poorly understood.

OBJECTIVES

To assess the expression of genes involved in oxidative stress responses in the bronchial epithelium of smokers with or without COPD and in relation to disease severity.

METHODS

Global gene expression was assessed in bronchial brushings in 38 subjects with COPD, 14 healthy nonsmokers, and 18 healthy smokers.

RESULTS

Gene expression analysis using Affymetrix arrays revealed mRNAs representing 341 out of 642 oxidative stress genes from two predefined gene sets to be differentially expressed in healthy nonsmokers when compared with healthy smokers, and 200 differentially expressed oxidative genes in subjects with COPD when compared with healthy smokers. Gene set enrichment analysis showed that pathways involved in oxidant/antioxidant responses were among the most differentially expressed gene pathways in smoking individuals, with further differences seen in COPD. Distinct, nonlinear gene expression patterns were identified across the severity spectrum of COPD, which correlated with the presence of certain transcription factor binding sites in their promoters. Significant changes in oxidant response genes observed in vivo were reproduced in vitro using primary bronchial epithelial cells from the same donors cultured at an air-liquid interface and exposed to cigarette smoke extract.

CONCLUSIONS

Cigarette smoke induces significant changes in oxidant defense responses; some of these are further amplified, but not in a linear fashion, in individuals who develop COPD.

Targeting the networks that underpin contiguous immunity in asthma and chronic obstructive pulmonary disease

Recent advances in the field of innate immunity have driven an important reappraisal of the role of these processes in airway disease. Various strands of evidence indicate that resident cells, such as macrophages and epithelial cells, have central importance in the initiation of inflammation. Macrophage activation has the potential to regulate not just typical aspects of innate immunity but also, via a variety of intricate cell-cell networks, adaptive responses and responses characterized by Th2-type cytokine production. In turn, such adaptive immune processes modify the phenotype and function of the innate immune system. Cooperative responses between monocytic cells and tissue cells are likely to be crucial to the generation of effective inflammatory responses, and a realization of the importance of these networks is providing a new way of identifying antiinflammatory therapies. Importantly, the repeated cycles of allergic and nonallergic inflammation that comprise chronic human airway disease are not necessarily well described by current terminology, and we propose and describe a concept of contiguous immunity, in which continual bidirectional cross-talk between innate and adaptive immunity describes disease processes more accurately.

The genetics of asthma: ADAM33 as an example of a susceptibility gene

The ability to identify novel disease genes by positional cloning led to the identification of a disintegrin and metalloprotease (ADAM)33 gene on chromosome 20p13 as a susceptibility gene for asthma. Case-control and family-based association studies have mostly confirmed a link between ADAM33 and asthma. Its restricted expression to mesenchymal cells as well as its association with bronchial hyperresponsiveness and accelerated decline in lung function over time point strongly to its involvement in the structural airway components of asthma, such as remodeling. Extensive alternative splicing, expression during branching morphogensis in the developing fetus, impaired lung function in childhood, the production of a soluble form linked to chronic asthma, and tight epigenetic regulation indicate a level of complexity in the way ADAM33 influences disease phenotype. Its recent association with chronic obstructive pulmonary disease as well as with asthma and lung development points to functions relating to airway wall modeling and remodeling as a general morphogenetic repair gene rather than being restricted to asthma.

Cysteinyl leukotrienes synergize with growth factors to induce proliferation of human bronchial fibroblasts

BACKGROUND

Cysteinyl leukotrienes (cys-LTs) are potent asthma-related mediators that function through their G protein-coupled receptors, cys-LT receptor type 1 (CysLT1R) and cys-LT receptor type 2 (CysLT2R).

OBJECTIVE

Because many G protein-coupled receptors transactivate the epidermal growth factor receptor (EGFR) through metalloprotease-mediated ligand shedding, we investigated the effects of cys-LTs on signal transduction and proliferation of bronchial fibroblasts.

METHODS

Human bronchial fibroblasts were grown from biopsy specimens of healthy subjects. Mitogenesis was assessed on the basis of tritiated methylthymidine incorporation.

RESULTS

Leukotriene (LT) D(4) alone did not increase mitogenesis but dose-dependently increased thymidine incorporation and cell proliferation in the presence of epidermal growth factor (EGF). The enhancement was not prevented by CysLT1R antagonists (MK-571 and montelukast) or by a dual antagonist (BAY u9773), which is consistent with the lack of detectable mRNA for CysLT1R and CysLT2R in bronchial fibroblasts. LTD(4) did not cause EGFR transphosphorylation nor was the synergism blocked by the metalloprotease inhibitor GM6001. The EGFR-selective kinase inhibitor AG1478 suppressed the synergy between LTD(4) and EGF but had no effect on synergistic interactions of LTD(4) with other receptor tyrosine kinase growth factors. The effect of LTD(4) involved a pertussis toxin-sensitive and protein kinase C-mediated intracellular pathway, leading to sustained growth factor-dependent phosphorylation of extracellular signal-regulated kinase 1/2 and protein kinase B (PKB/Akt).

CONCLUSION

Cys-LTs do not transactivate EGFR but have a broader capability to synergize with receptor tyrosine kinase pathways.

CLINICAL IMPLICATIONS

This study implies a critical role of cys-LTs in airway fibrosis in asthma and other chronic airway diseases, which might not be blocked by therapy with current LT receptor antagonists.

Shotgun proteomic analysis of human-induced sputum

Induced sputum is a readily accessible biological fluid whose composition may alter as a consequence of disease. To date, however, the proteins that routinely populate this biofluid are largely unknown, in part due to the technical difficulties in processing such mucin-rich samples. To provide a catalogue of sputum proteins, we have surveyed the proteome of human-induced sputum (sputome). A combination of 2-D gel analysis and GeLC-MS/MS allowed a total of 191 human proteins to be confidently assigned. In addition to the expected components, several hitherto unreported proteins were found to be present, including three members of the annexin family, kallikreins 1 and 11, and peroxiredoxins 1, 2 and 5. Other sets of proteins identified included four proteins previously annotated as hypothetical or conserved hypothetical. Taken together, these data represent the first extensive survey of the proteome of induced sputum and provide a platform for future identification of biomarkers of lung disease.

IL-13 receptor alpha 2: a regulator of IL-13 and IL-4 signal transduction in primary human fibroblasts

BACKGROUND

IL-13 and IL-4 share many functional properties as a result of their use of a common receptor complex comprising IL-13 receptor alpha 1 (IL-13Ralpha1) and IL-4 receptor alpha (IL-4Ralpha). The nonsignaling receptor IL-13 receptor alpha 2 (IL-13Ralpha2) binds IL-13 with high affinity and specificity and is believed to be a decoy receptor for IL-13.

OBJECTIVE

We sought to examine the inhibitory effects of soluble and membrane-bound IL-13Ralpha2 on IL-13- and IL-4-mediated effects.

METHODS

Primary human fibroblasts were grown from endobronchial biopsy specimens obtained from volunteers. Upregulation of IL-13Ralpha2 mRNA was measured by means of RT-PCR, and the level of surface expression was measured by means of FACS.

RESULTS

We found that a recombinant soluble form of IL-13Ralpha2 blocked the effects of IL-13, but not IL-4, in fibroblasts in vitro. However, we found that the transmembrane form of IL-13Ralpha2 could attenuate both IL-13 and IL-4 responses, even though the response to TNF-alpha was unaffected. Furthermore, we found that IL-13Ralpha2 became associated with IL-4Ralpha in the presence of IL-4. Addition of a blocking antibody to the extracellular domain of IL-13Ralpha2 restored responses of both IL-13 and IL-4.

CONCLUSION

The ability of IL-13Ralpha2 to regulate IL-4 was previously unrecognized in primary airway cells. These data reveal a novel role for IL-13Ralpha2 as a negative regulator of both IL-13 and IL-4 signaling in human bronchial fibroblasts.

CLINICAL IMPLICATIONS

It appears that IL-13Ralpha2 might be a powerful suppressor of TH2-mediated responses and thus represents a potential therapeutic target for the treatment of asthma.

Role of deficient type III interferon-lambda production in asthma exacerbations

Rhinoviruses are the major cause of asthma exacerbations, and asthmatics have increased susceptibility to rhinovirus and risk of invasive bacterial infections. Here we show deficient induction of interferon-lambdas by rhinovirus in asthmatic primary bronchial epithelial cells and alveolar macrophages, which was highly correlated with severity of rhinovirus-induced asthma exacerbation and virus load in experimentally infected human volunteers. Induction by lipopolysaccharide in asthmatic macrophages was also deficient and correlated with exacerbation severity. These results identify previously unknown mechanisms of susceptibility to infection in asthma and suggest new approaches to prevention and/or treatment of asthma exacerbations.

IL-4 receptor alpha is an important modulator of IL-4 and IL-13 receptor binding: implications for the development of therapeutic targets

IL-4 is a key cytokine associated with allergy and asthma. Induction of cell signaling by IL-4 involves interaction with its cognate receptors, a complex of IL-4Ralpha with either the common gamma-chain or the IL-13R chain alpha1 (IL-13Ralpha1). We found that IL-4 bound to the extracellular domain of IL-4Ralpha (soluble human (sh)IL-4Ralpha) with high affinity and specificity. In contrast with the sequential mechanism of binding and stabilization afforded by IL-4Ralpha to the binding of IL-13 to IL-13Ralpha1, neither common gamma-chain nor IL-13Ralpha1 contributed significantly to the stabilization of the IL-4:IL-4Ralpha complex. Based on the different mechanisms of binding and stabilization of the IL-4R and IL-13R complexes, we compared the effects of shIL-4Ralpha and an IL-4 double mutein (R121D/Y124D, IL-4R antagonist) on IL-4- and IL-13-mediated responses. Whereas IL-4R antagonist blocked responses to both cytokines, shIL-4Ralpha only blocked IL-4. However, shIL-4Ralpha stabilized and augmented IL-13-mediated STAT6 activation and eotaxin production by primary human bronchial fibroblasts at suboptimal doses of IL-13. These data demonstrate that IL-4Ralpha plays a key role in the binding affinity of both IL-13R and IL-4R complexes. Under certain conditions, shIL-4Ralpha has the potential to stabilize binding IL-13 to its receptor to augment IL-13-mediated responses. Thus, complete understanding of the binding interactions between IL-4 and IL-13 and their cognate receptors may facilitate development of novel treatments for asthma that selectively target these cytokines without unpredicted or detrimental side effects.

Understanding the pathophysiology of severe asthma to generate new therapeutic opportunities

Although asthma is defined in terms of reversibility of airflow obstruction, as the disease becomes more severe and chronic, it adopts different characteristics, including a degree of fixed airflow obstruction and corticosteroid refractoriness. Underlying these phenotypes is evidence of airway wall remodeling, which should be distinguished from the increase in smooth muscle linked to airways hyperresponsiveness. Aberrant epithelial-mesenchymal communication leads to a chronic wound scenario, which is characterized by activation of the epithelial-mesenchymal trophic unit, epithelial damage, the laying down of new matrix, and greater involvement of neutrophils in the inflammatory response. In allergic asthmatic patients who remain symptomatic despite high-dose corticosteroid therapy, blockade of IgE with omalizumab confers appreciable clinical benefit. Chronic severe asthma is also accompanied by a marked increase in TNF-alpha production that might contribute to corticosteroid refractoriness. Based on this, TNF blockade with the soluble fusion protein entanercept produces improvement in asthma symptoms, lung function, and quality of life paralleled by a marked reduction in airways hyperresponsiveness. Identification of novel susceptibility genes, such as a disintegrin and metalloprotease 33 (ADAM33), will provide further targets against which to direct novel therapies for asthma, especially at the more severe end of the disease spectrum.

CD40 ligation protects bronchial epithelium against oxidant-induced caspase-independent cell death

CD40 and its ligand regulate pleiotropic biological responses, including cell proliferation, differentiation, and apoptosis. In many inflammatory lung diseases, tissue damage by environmental or endogenous oxidants plays a major role in disease pathogenesis. As the epithelial barrier is a major target for these oxidants, we postulated that CD40, the expression of which is increased in asthma, plays a role in the regulation of apoptosis of bronchial epithelial cells exposed to oxidants. Using 16HBE 14o- cells exposed to oxidant stress, we found that ligation of CD40 (induced by G28-5 monoclonal antibodies) enhanced cell survival and increased the number of cells in G2/M (interphase between DNA synthesis and mitosis) of the cell cycle. This was associated with NF-kappaB and activator protein-1 activation and increased expression of the inhibitor of apoptosis, c-IAP1. However, oxidant stress-induced apoptosis was found to be caspase- and calpain-independent implicating CD40 ligation as a regulator of caspase-independent cell death. This was confirmed by the demonstration that CD40 ligation prevented mitochondrial release and nuclear translocation of apoptosis inducing factor. In conclusion, we demonstrate a novel role for CD40 as a regulator of epithelial cell survival against oxidant stress. Furthermore, we have identified, for the first time, an endogenous inhibitory pathway of caspase-independent cell death.

ADAM33: a newly identified gene in the pathogenesis of asthma

There is much to find out about this fascinating and complex molecule in relation to the development and progression of asthma. Added to it are three further new asthma/allergy genes identified by positional cloning: PDH Finger Protein II (PHF11) on chromosome 13q14, which encodes NY-REN-34 a protein first described in patients with renal cell carcinoma [67]; Dipeptidyl diptidase 10 (DDP10) on chromosome 2q14 [68]; and G protein-coupled receptor for asthma susceptibility (GPRA) on chromosome 7p [69]. For each of these genes, as is the case for ADAM33, determining their normal function(s) and how these become disordered in asthma is the future challenge.

Enhanced upregulation of smooth muscle related transcripts by TGF beta2 in asthmatic (myo) fibroblasts

BACKGROUND

Transforming growth factor beta (TGF beta) upregulates a number of smooth muscle specific genes in (myo)fibroblasts. As asthma is characterised by an increase in airway smooth muscle, we postulated that TGFbeta(2) favours differentiation of asthmatic (myo)fibroblasts towards a smooth muscle phenotype.

METHODS

Primary fibroblasts were grown from bronchial biopsy specimens from normal (n = 6) and asthmatic (n = 7) donors and treated with TGF beta2 to induce myofibroblast differentiation. The most stable genes for normalisation were identified using RT-qPCR and the geNorm software applied to a panel of 12 "housekeeping" genes. Expression of alpha-smooth muscle actin (alpha SMA), heavy chain myosin (HCM), calponin 1 (CPN 1), desmin, and gamma-actin were measured by RT-qPCR. Protein expression was assessed by immunocytochemistry and western blotting.

RESULTS

Phospholipase A2 and ubiquitin C were identified as the most stably expressed and practically useful genes for normalisation of gene expression during myofibroblast differentiation. TGF beta2 induced mRNA expression for all five smooth muscle related transcripts; alpha SMA, HCM and CPN 1 protein were also increased but desmin protein was not detectable. Although there was no difference in basal expression, HCM, CPN 1 and desmin were induced to a significantly greater extent in asthmatic fibroblasts than in those from normal controls (p = 0.041 and 0.011, respectively).

CONCLUSIONS

Although TGF beta2 induced the transcription of several smooth muscle related genes, not all were translated into protein. Thus, while TGF beta2 is unable to induce a bona fide smooth muscle cell phenotype, it may "prime" (myo)fibroblasts for further differentiation, especially if the cells are derived from asthmatic airways.

The contribution of transforming growth factor-beta and epidermal growth factor signalling to airway remodelling in chronic asthma

Asthma is increasing in prevalence in the developing world, affecting approximately 10% of the world's population. It is characterised by chronic lung inflammation and airway remodelling associated with wheezing, shortness of breath, acute bronchial hyperresponsiveness to a variety of innocuous stimuli and a more rapid decline in lung function over time. Airway remodelling, involving proliferation and differentiation of mesenchymal cells, particularly myofibroblasts and smooth muscle cells, is generally refractory to corticosteroids and makes a major contribution to disease chronicity. Transforming growth factor-beta is a potent profibrogenic factor whose expression is increased in the asthmatic airways and is a prime candidate for the initiation and persistence of airway remodelling in asthma. This review highlights the role of transforming growth factor-beta in the asthmatic lung, incorporating biosynthesis, signalling pathways and functional outcome. In vivo, however, it is the balance between transforming growth factor-beta and other growth factors, such as epidermal growth factor, which will determine the extent of fibrosis in the airways. A fuller comprehension of the actions of transforming growth factor-beta, and its interaction with other signalling pathways, such as the epidermal growth factor receptor signalling cascade, may enable development of therapies that control airway remodelling where there is an unmet clinical need.

Altered protein tyrosine phosphorylation in asthmatic bronchial epithelium

A disease-related, corticosteroid-insensitive increase in the expression of epidermal growth factor (EGF) receptor (EGFR) tyrosine kinase in asthmatic bronchial epithelium has been shown previously by the current authors. To determine whether this is associated with enhanced intracellular signalling, the aim of this study was to evaluate epithelial tyrosine phosphorylation. Bronchial biopsies were analysed for the presence of phosphotyrosine by immunohistochemistry. Bronchial epithelial cells were exposed to EGF, hydrogen peroxide or tumour necrosis factor-alpha in vitro for measurement of tyrosine phosphorylated signalling intermediates and interleukin (IL)-8 release. Phosphotyrosine was increased significantly in the epithelium of severe asthmatics when compared with controls or mild asthmatics; however, in mild asthma, phosphotyrosine levels were significantly decreased when compared with controls. There was no significant difference between phosphotyrosine levels before or after 8 weeks of treatment with budesonide. Stimulation of bronchial epithelial cells resulted in tyrosine phosphorylation of several proteins, including EGFR, Shc and p42/p44 mitogen-activated protein kinase. In the presence of salbutamol, a transient partial suppression of EGFR phosphorylation occurred, whereas dexamethasone was without effect. Neither salbutamol nor dexamethasone inhibited EGF-stimulated IL-8 release. These data indicate that regulation of protein tyrosine kinase activity is abnormal in severe asthma. The epidermal growth factor receptor and/or other tyrosine kinase pathways may contribute to persistent, corticosteroid-unresponsive inflammation in severe asthma.

Epithelial-mesenchymal communication in the pathogenesis of chronic asthma

Although Th-2-mediated inflammation is a key therapeutic target in asthma, its relationship to altered structure and functions of the airways is largely unknown. In addition to inflammation, asthma is a disorder involving the airway epithelium that is more vulnerable to environmental injury and responds to this by impaired healing. This establishes a chronic wound scenario that is capable of sustaining chronic inflammation as well as remodeling. This response occurs as a consequence of activation of the epithelial-mesenchymal unit, involving reciprocal activities of growth factors belonging to the fibroblast growth factor, epidermal growth factor, and transforming growth factor-beta families. The observation that structural changes in the airways in children at or before the onset of asthma occurs irrespective of inflammation might suggest that premodeling is required before Th-2 inflammatory responses can be sustained. Once established, altered function of constitutive airway cells, including fibroblasts, smooth muscle, nerves, and the epithelium, provides an abnormal microenvironment in which to generate a separate set of signals that underpin the acute/subacute inflammation characteristic of asthma exacerbations, triggered by viruses, pollutants, and allergens.

Tumour necrosis factor (TNFalpha) as a novel therapeutic target in symptomatic corticosteroid dependent asthma

BACKGROUND

Tumour necrosis factor alpha (TNFalpha) is a major therapeutic target in a range of chronic inflammatory disorders characterised by a Th1 type immune response in which TNFalpha is generated in excess. By contrast, asthma is regarded as a Th2 type disorder, especially when associated with atopy. However, as asthma becomes more severe and chronic, it adopts additional characteristics including corticosteroid refractoriness and involvement of neutrophils suggestive of an altered inflammatory profile towards a Th1 type response, incriminating cytokines such as TNFalpha.

METHODS

TNFalpha levels in bronchoalveolar lavage (BAL) fluid of 26 healthy controls, 42 subjects with mild asthma and 20 with severe asthma were measured by immunoassay, and TNFalpha gene expression was determined in endobronchial biopsy specimens from 14 patients with mild asthma and 14 with severe asthma. The cellular localisation of TNFalpha was assessed by immunohistochemistry. An open label uncontrolled clinical study was then undertaken in 17 subjects with severe asthma to evaluate the effect of 12 weeks of treatment with the soluble TNFalpha receptor-IgG1Fc fusion protein, etanercept.

RESULTS

TNFalpha levels in BAL fluid, TNFalpha gene expression and TNFalpha immunoreative cells were increased in subjects with severe corticosteroid dependent asthma. Etanercept treatment was associated with improvement in asthma symptoms, lung function, and bronchial hyperresponsiveness.

CONCLUSIONS

These findings may be of clinical significance in identifying TNFalpha as a new therapeutic target in subjects with severe asthma. The effects of anti-TNF treatment now require confirmation in placebo controlled studies.

ADAM33: a newly identified protease involved in airway remodelling

Asthma is a complex disorder in which major genetic and environmental factors interact to both initiate the disease and modify its progression. While asthma is recognised as a disorder of the conducting airways characterised by Th2-directed inflammation, it is being increasingly apparent that alteration of the structural cells of the airways (airway remodelling) is also fundamental to disease chronicity and severity. The gene ADAM33, encoding a novel member of a identified as an asthma susceptibility gene as the result of a positional cloning effort in a cohort of families recruited form the UK and USA. Subsequent genetic studies have now provided evidence that ADAM33 may be involved in determining lung function throughout life, associated with early life lung function as well as increased decline therapeutic intervention in asthma and future work will focus on the mechanisms by which it alters lung function and bronchial hyperresponsiveness.

Epithelial stress and structural remodelling in childhood asthma

BACKGROUND

In adult asthma the bronchial epithelium shows high expression of the epidermal growth factor receptor (EGFR) and the cyclin dependent kinase inhibitor, p21waf, linked to ongoing stress and injury.

METHODS

To determine if these are early markers of disease, sections of bronchial specimens obtained post mortem or by bronchoscopy from non-asthmatic (n = 7), moderate (n = 7), or severe (n = 9) asthmatic children aged 5-15 years were examined immunohistochemically. All severe and one moderately asthmatic children were receiving inhaled corticosteroids.

RESULTS

The lamina reticularis of the asthmatic biopsy sections was found to be thicker (p = 0.01) than normal with increased deposition of collagen III (p = 0.007); submucosal eosinophil numbers did not differ between groups. As in adults, there was an asthma-related increase in epithelial EGFR (p<0.002) but there was no evidence of proliferation, with Ki67 being reduced (p = 0.001) and p21waf increased (p<0.004). The thickness of the lamina reticularis was significantly correlated with epithelial EGFR (rho = 0.77, p<0.001).

CONCLUSIONS

These data provide evidence that, in asthmatic children, the epithelium is stressed or injured without significant eosinophilic inflammation. This change in the epithelial phenotype is associated with collagen deposition in the lamina reticularis, suggesting that the epithelial mesenchymal trophic unit is active early in, and may contribute to, the pathogenesis of asthma.