Mechanisms of receptor binding and cellular activation by the epidermal growth factor ligand family

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Involvement of the epidermal growth factor receptor in epithelial repair in asthma

Epithelial damage and airway remodeling are consistent features of bronchial asthma and are correlated with disease chronicity, severity, and bronchial hyperreactivity. To examine the mechanisms that control bronchial epithelial repair, we investigated expression of the epidermal growth factor receptor (c-erbB1, EGFR) in asthmatic bronchial mucosa and studied repair responses in vitro. In biopsies from asthmatic subjects, areas of epithelial damage were frequently observed and exhibited strong EGFR immunostaining. EGFR expression was also high in morphologically intact asthmatic epithelium. Using image analysis, EGFR immunoreactivity (% of total epithelial area, median (range) was found to increase from 9.4 (4.1–20.4) in normal subjects (n=10) to 18.4 (9.3–28.9) in mild asthmatics (P<0.01, n=13) and 25.4 (15.4–31.8) in severe asthmatics (P<0.00, n=5). Epithelial EGFR immunoreactivity remained elevated in patients treated with corticosteroids and was positively correlated with subepithelial reticular membrane thickening. Using 16HBE 14o- bronchial epithelial cells, we found that EGF accelerated repair of scrape-wounded monolayers and that the EGFR-selective inhibitor, tyrphostin AG1478, inhibited both EGF-stimulated and basal wound closure whereas dexamethasone was without effect. Intrinsic activation of the EGFR was confirmed by analysis of tyrosine phosphorylated proteins, which revealed a rapid, damage-induced phosphorylation of the EGFR, irrespective of the presence of exogenous EGF. To assess the relationship between EGFR-mediated repair and tissue remodeling, release of the profibrogenic mediator TGF-ß2 was also measured. Scrape wounding increased release of TGF-ß2 from epithelial monolayers and EGF had no additional stimulatory effect. However, when repair was retarded with AG1478, the amount of TGF-ß2 increased significantly. These data indicate that the EGFR may play an important role in bronchial epithelial repair in asthma and that impairment of this function may augment airway remodeling

Invited lecture: activation of the epithelial mesenchymal trophic unit in the pathogenesis of asthma

Background: A recent NIH Workshop and an ERS Task Force concluded that more work was needed to understand mechanisms of severe and chronic asthma. This report describes a series of studies that identify aberrant epithelial mesenchymal signalling in the airways as an important event in maintaining inflammation and driving remodelling in response to environmental injury. Methods: Immunohistochemistry, genotyping and functional studies conducted on cultured asthmatic cells and mucosal biopsies were used to identify biochemical pathways involved in epithelial injury and repair in asthma and their relationship to disease severity. Results: Our findings suggest that the asthmatic state results from an interaction between a susceptible epithelium and Th-2-mediated inflammation to alter the communication between the epithelium and the underlying mesenchyme - the epithelial mesenchymal trophic unit - leading to disease persistence, airway remodelling and refractoriness to corticosteroid treatment. Conclusions: Asthma is more than an inflammatory disorder, but requires engagement of important signalling pathways involved in epithelial repair and tissue remodelling. These pathways involving EGFRs and TGF-Rs provide targets against which to develop novel therapies for chronic 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 synthesisby 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-4R? and the IL-13R?1 chains. Another IL-13 binding chain, IL-13R?2, 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-13R?2 in human primary bronchial epithelial cells and fibroblasts using flow cytometry and confocal microscopy, as well as the in vivo expression of IL-13R?2 in the human bronchial mucosa by means of immunohistochemistry.Results: IL-13R?2 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-13R?2 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-13R?2 is expressed by both human primary bronchial epithelial cells and fibroblasts as an intracellular protein with a diffuse cytoplasmic distribution. In vivo, IL-13R?2 is expressed in the human airway mucosa mainly by bronchial epithelial cells

The role of the epidermal growth factor receptor in sustaining neutrophil inflammation in severe asthma

Background The extent of epithelial injury in asthma is reflected by expression of the epidermal growth factor receptor (EGFR), which is increased in proportion to disease severity and is corticosteroid refractory. Although the EGFR is involved in epithelial growth and differentiation, it is unknown whether it also contributes to the inflammatory response in asthma.Objectives Because severe asthma is characterized by neutrophilic inflammation, we investigated the relationship between EGFR activation and production of IL-8 and macrophage inhibitory protein-1 alpha (MIP-1?) using in vitro culture models and examined the association between epithelial expression of IL-8 and EGFR in bronchial biopsies from asthmatic subjects.Methods H292 or primary bronchial epithelial cells were exposed to EGF or H2O2 to achieve ligand-dependent and ligand-independent EGFR activation; IL-8 mRNA was measured by real-time PCR and IL-8 and MIP-1? protein measured by enzyme-linked immunosorbent assay (ELISA). Epithelial IL-8 and EGFR expression in bronchial biopsies from asthmatic subjects was examined by immunohistochemistry and quantified by image analysis.Results Using H292 cells, EGF and H2O2 increased IL-8 gene expression and release and this was completely suppressed by the EGFR-selective tyrosine kinase inhibitor, AG1478, but only partially by dexamethasone. MIP-1? release was not stimulated by EGF, whereas H2O2 caused a 1.8-fold increase and this was insensitive to AG1478. EGF also significantly stimulated IL-8 release from asthmatic or normal primary epithelial cell cultures established from bronchial brushings. In bronchial biopsies, epithelial IL-8, MIP-1?, EGFR and submucosal neutrophils were all significantly increased in severe compared to mild disease and there was a strong correlation between EGFR and IL-8 expression (r = 0.70, P < 0.001).Conclusions These results suggest that in severe asthma, epithelial damage has the potential to contribute to neutrophilic inflammation through enhanced production of IL-8 via EGFR- dependent mechanisms

The three A's in asthma - airway smooth muscle, airway remodeling & angiogenesis

Asthma affects more than 300 million people worldwide and its prevalence is still rising. Acute asthma attacks are characterized by severe symptoms such as breathlessness, wheezing, tightness of the chest, and coughing, which may lead to hospitalization or death. Besides the acute symptoms, asthma is characterized by persistent airway inflammation and airway wall remodeling. The term airway wall remodeling summarizes the structural changes in the airway wall: epithelial cell shedding, goblet cell hyperplasia, hyperplasia and hypertrophy of the airway smooth muscle (ASM) bundles, basement membrane thickening and increased vascular density. Airway wall remodeling starts early in the pathogenesis of asthma and today it is suggested that remodeling is a prerequisite for other asthma pathologies. The beneficial effect of bronchial thermoplasty in reducing asthma symptoms, together with the increased potential of ASM cells of asthmatics to produce inflammatory and angiogenic factors, indicate that the ASM cell is a major effector cell in the pathology of asthma. In the present review we discuss the ASM cell and its role in airway wall remodeling and angiogenesis