Transforming growth factor beta 1 gene expression in human airways

Mycoplasma pneumoniae infection increases airway collagen deposition in a murine model of allergic airway inflammation

Mycoplasma pneumoniae (Mp) has been linked to chronic asthma. Airway remodeling (e.g., airway collagen deposition or fibrosis) is one of the pathological features of chronic asthma. However, the effects of respiratory Mp infection on airway fibrosis in asthma remain unclear. In the present study, we hypothesized that respiratory Mp infection may increase the airway collagen deposition in a murine model of allergic airway inflammation in part through upregulation of transforming growth factor (TGF)-beta1. Double (2 wk apart) inoculations of Mp or saline (control) were given to mice with or without previous allergen (ovalbumin) challenges. On days 14 and 42 after the last Mp or saline, lung tissue and bronchoalveolar lavage (BAL) fluid were collected for analyses of collagen and TGF-beta1 at protein and mRNA levels. In allergen-naïve mice, Mp did not alter airway wall collagen. In allergen-challenged mice, Mp infections did not change airway wall collagen deposition on day 14 but increased the airway collagen on day 42; this increase was accompanied by increased TGF-beta1 protein in the airway wall and reduced TGF-beta1 protein release from the lung tissue into BAL fluid. Our results suggest that Mp infections could modulate airway collagen deposition in a murine model of allergic airway inflammation with TGF-beta1 involved in the collagen deposition process.

Cellular and molecular mechanisms in chronic obstructive pulmonary disease: an overview

In the last decade, the analysis of bronchial biopsies and lung parenchyma obtained from chronic obstructive pulmonary disease (COPD) patients compared with those from smokers with normal lung function and non-smokers has provided new insights on the role of the different inflammatory and structural cells, their signalling pathways and mediators, contributing to a better knowledge of the pathogenesis of COPD. This review summarizes and discusses the lung pathology of COPD patients with emphasis on inflammatory cell phenotypes that predominate in different clinical conditions. In bronchial biopsies, a cascade of events takes place during progression from mild-to-severe disease. T lymphocytes, particularly CD8+ cells and macrophages are the prevalent inflammatory cells in the lung of healthy smokers and patients with mild COPD, while total and activated neutrophils predominate in severe COPD. The number of CD4+, CD8+ cells and macrophages expressing nuclear factor-kappa B (NF-kappaB), STAT-4 and IFN-gamma proteins as well as endothelial adhesion molecule-1 in endothelium is increased in mild/moderate disease. In contrast, activated neutrophils (MPO+ cells) and increased nitrotyrosine immunoreactivity develops in severe COPD. In bronchial biopsies obtained during COPD exacerbations, some studies have shown an increased T cell and granulocyte infiltration. Regular treatment with high doses of inhaled glucocorticoids does not significantly change the number of inflammatory cells in bronchial biopsies from patients with moderate COPD. The profile in lung parenchyma is similar to bronchial biopsies. 'Healthy' smokers and mild/moderate diseased patients show increased T lymphocyte infiltration in the peripheral airways. Pulmonary emphysema is associated with a general increase of inflammatory cells in the alveolar septa. The molecular mechanisms driving the lymphocyte and neutrophilic prevalence in mild and severe disease, respectively, needs to be extensively studied. Up-regulation of pro-inflammatory transcription factors NF-kappaB and STAT-4 in mild, activated epithelial and endothelial cells in the more severe disease may contribute to this differential prevalence of infiltrating cells.

Proteome annotations and identifications of the human pulmonary fibroblast

We hereby report on a three year project initiative undertaken by our research team encompassing large-scale protein expression profiling and annotations of human primary lung fibroblast cells. An overview is given of proteomic studies of the fibroblast target cell involved in several diseases such as asthma, idiopatic pulmonary disease, and COPD. It has been the objective within our research team to map and identify the protein expressions occurring in both activated-, as well as resting cell states. The JGGL database www.2DDB.org has been built around these data, allowing advanced hypothesis building using the interactive query bioinformatic tools developed. Gene ontology has been applied to these annotations, classifying and correlating protein expressions to function. The localization as well as the biological processes involved for the annotations are being presented including an annotation-, and sequence-identification strategy, resulting in close to 2000 protein identities. Both gel based, high resolution 2D-gels, and liquid-phase separation (three-dimensional HPLC), as well as the combination of gel- and LC-based approaches (1D-gels and nano-capillary LC, reversed-phase) were utilized. Protein sequencing and structure identities were acquired by a combination of MALDI-, and electrospray-mass spectrometry techniques. Phenotypical and morphological characterizations were also made for this human disease target cell in both stimulated- and resting-cell states. The use of functional assays that demonstrate the key regulating role of growth factors and cytokine stimuli such as PDGF, TGF-beta, and EGF and the effect of ECM molecules such as Biglycan, are also presented and discussed.

Mediators of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a major and increasing global health problem that is now a leading cause of death. COPD is associated with a chronic inflammatory response, predominantly in small airways and lung parenchyma, which is characterized by increased numbers of macrophages, neutrophils, and T lymphocytes. The inflammatory mediators involved in COPD have not been clearly defined, in contrast to asthma, but it is now apparent that many lipid mediators, inflammatory peptides, reactive oxygen and nitrogen species, chemokines, cytokines, and growth factors are involved in orchestrating the complex inflammatory process that results in small airway fibrosis and alveolar destruction. Many proteases are also involved in the inflammatory process and are responsible for the destruction of elastin fibers in the lung parenchyma, which is the hallmark of emphysema. The identification of inflammatory mediators and understanding their interactions is important for the development of anti-inflammatory treatments for this important disease.

Fibrogenic cytokine levels in bronchoalveolar lavage aspirates 15 years after exposure to sulfur mustard

Over 100,000 Iranian war veterans suffer from chronic effects of mustard gas exposure. Sulfur mustard was used by Iraq during the Iraqi-imposed war on Iran (between 1980 and 1988). The major complaints of these patients are mild interstitial fibrosis and bronchiolitis. We aimed to determine the state of fibrosis progression and assessed transforming growth factor (TGF)-β1 levels in pulmonary samples and in bronchoalveolar lavage (BAL) aspirates. A total of 126 war veterans confirmed for lung disease were assessed and compared with three control groups: 1) 64 veterans not exposed to chemical agents, 2) 12 idiopathic pulmonary fibrosis civilian patients, and 3) 33 normal persons. BAL was performed via a flexible fiber-optic bronchoscope and the standard manual method. Total protein was measured by Bradford assay, and samples were corrected with regard to coefficients. Samples were concentrated 15-fold by lyophilization and resolubilization. Samples were double-checked using an ELISA test kit. The Mann-Whitney test was used for the data analysis using commercial software. We detected that significant differences between TGF-β1 levels between the case group and control group 1 ( P = 0.001) and control group 3 ( P = 0.003). No significant differences were found between the case group and control group 2 ( P = 0.57). Inflammation and fibrotic processes in lung tissue of patients exposed to sulfur mustard may be progressive so IFN-γ may be a useful drug to these patients' treatment.

Epithelial expression of profibrotic mediators in a model of allergen-induced airway remodeling

Airway remodeling, including subepithelial fibrosis, is a characteristic feature of asthma and likely contributes to the pathogenesis of airway hyperresponsiveness. We examined expression of genes related to airway wall fibrosis in a model of chronic allergen-induced airway dysfunction using laser capture microdissection and quantitative real-time PCR. BALB/c mice were sensitized and subjected to chronic ovalbumin exposure over a 12-wk period, after which they were rested and then harvested 2 and 8 wk after the last exposure. Chronic allergen-exposed mice had significantly increased indices of airway remodeling and airway hyperreactivity at all time points, although no difference in expression of fibrosis-related genes was found when mRNA extracted from whole lung was examined. In contrast, fibrosis-related gene expression was significantly upregulated in mRNA obtained from microdissected bronchial wall at 2 wk after chronic allergen exposure. In addition, when bronchial wall epithelium and smooth muscle were separately microdissected, gene expression of transforming growth factor-beta1 and plasminogen activating inhibitor-1 were significantly upregulated only in the airway epithelium. These data suggest that transforming growth factor-beta1 and other profibrotic mediators produced by airway wall, and specifically, airway epithelium, play an important role in the pathophysiology of airway remodeling.

Transforming growth factor-beta2 induces bronchial epithelial mucin expression in asthma

The transforming growth factor (TGF)-beta family is important for tissue repair in pathological conditions including asthma. However, little is known about the impact of either TGF-beta1 or TGF-beta2 on asthmatic airway epithelial mucin expression. We evaluated bronchial epithelial TGF-beta1 and TGF-beta2 expression and their effects on mucin expression, and the role of TGF-beta1 or TGF-beta2 in interleukin (IL)-13-induced mucin expression. Epithelial TGF-beta1, TGF-beta2, and mucin expression were evaluated in endobronchial biopsies from asthmatics and normal subjects. The effects of TGF-beta1 or TGF-beta2 on mucin MUC5AC protein and mRNA expression, and the impact of IL-13 on epithelial TGF-beta1, TGF-beta2, and MUC5AC were determined in cultured bronchial epithelial cells from endobronchial brushings of both subject groups. In biopsy tissue, epithelial TGF-beta2 expression levels were higher than TGF-beta1 in both asthmatics and normals. TGF-beta2, but not TGF-beta1, was increased in asthmatics compared with normals, and significantly correlated with mucin expression. TGF-beta2, but not TGF-beta1, increased mucin expression in cultured epithelial cells from both subject groups. IL-13 increased the release of TGF-beta2, but not TGF-beta1, from epithelial cells. A neutralizing TGF-beta2 antibody partially inhibited IL-13-induced mucin expression. These data suggest that TGF-beta2 production by asthmatic bronchial epithelial cells may increase airway mucin expression. IL-13-induced mucin expression may occur in part through TGF-beta2 up-regulation.

Interleukin-10 production genotype protects against acute persistent rejection after lung transplantation

BACKGROUND

Our previous studies demonstrated that cytokine gene polymorphisms are related to acute rejection in pediatric heart transplantation; a decreased tumor necrosis factor (TNF)-alpha production genotype combined with an increased or intermediate interleukin (IL)-10 production genotype was associated with the smallest incidence of acute rejection. The objective of this study was to determine whether cytokine genotypes TNF-alpha, IL-10, IL-6, interferon-gamma, and transforming growth factor beta were associated with acute persistent rejection after lung transplantation.

METHODS

Cytokine genotyping was performed in 119 adult lung transplantation recipients who underwent surveillance transbronchial biopsies during their first year after transplantation. We categorized recipients with acute persistent rejection if they had 2 consecutive biopsy specimens at >/=Grade A2 despite anti-rejection treatment. We performed cytokine genotyping using the polymerase chain reaction-sequence specific primers technique, with a commercially available kit.

RESULTS

We analyzed the IL-10 genotype in 116 patients. For the increased IL-10 production genotype, 7 of 20 patients (35%) were persistent rejecters. In comparison, 57 of 96 patients (59%) with intermediate or decreased IL-10 production genotype had acute persistent rejection (p = 0.046). For IL-10 haplotypes associated with intermediate IL-10 production, 30 of 45 patients with GCC/ACC haplotype (67%) had acute persistent rejection compared with 10 of 22 patients with GCC/ATA (45%). In the patients with intermediate IL-10 production, 17 of 22 (77%) with IL-10 GCC/ACC and IL-6 G/C had acute persistent rejection, whereas only 2 of 7 patients (29%) with IL-10 GCC/ATA and IL-6 G/G had acute persistent rejection (p = 0.018).

CONCLUSIONS

In lung transplant recipients, the increased IL-10 production genotype protects against acute persistent rejection when compared with the intermediate or decreased IL-10 production genotypes. The intermediate IL-10 production genotype in lung transplant recipients can be differentiated into 2 haplotype responses, with the GCC/ACC haplotype associated more with acute persistent rejection. In lung transplant recipients, the immunomodulatory effects of IL-6 are differentiated in the G/C and G/G alleles in conjunction with IL-10 haplotypes, with G/C being associated with more acute persistent rejection in conjunction with the IL-10 GCC/ACC haplotype. Future pharmacogenomic models may incorporate these associations with acute persistent rejection in lung transplant recipients to formulate individualized therapeutic regimens.

Regulation of TGF-beta 1-induced connective tissue growth factor expression in airway smooth muscle cells

Transforming growth factor (TGF)-beta may play an important role in airway remodeling, and the fibrogenic effect of TGF-beta may be mediated through connective tissue growth factor (CTGF) release. We investigated the role of MAPKs and phosphatidylinositol 3-kinase (PI3K) and the effects of inflammatory cytokines on TGF-beta-induced CTGF expression in human airway smooth muscle cells (ASMC). We examined whether Smad signal was involved in the regulatory mechanisms. TGF-beta 1 induced a time- and concentration-dependent expression of CTGF gene and protein as analyzed by real-time RT-PCR and Western blot. Inhibition of ERK and c-jun NH(2)-terminal kinase (JNK), but not of p38 MAPK and PI3K, blocked the effect of TGF-beta 1 on CTGF mRNA and protein expression and on Smad2/3 phosphorylation. T helper lymphocyte 2-derived cytokines, IL-4 and IL-13, attenuated TGF-beta 1-stimulated mRNA and protein expression of CTGF and inhibited TGF-beta 1-stimulated ERK1/2 and Smad2/3 activation in ASMC. The proinflammatory cytokines tumor necrosis factor-alpha and IL-1 beta reduced TGF-beta 1-stimulated mRNA expression of CTGF but did not inhibit TGF-beta-induced Smad2/3 phosphorylation. TGF-beta 1-stimulated CTGF expression is mediated by mechanisms involving ERK and JNK pathways and is downregulated by IL-4 and IL-13 through modulation of Smad and ERK signals.

A Lung Tissue Bank for Gene Expression Studies in Chronic Obstructive Pulmonary Disease

A bank of surgically resected human lung tissues frozen at -70 degrees C after being inflated with support medium for cutting frozen tissue and a separate group inflated with fixative and embedded in paraffin has been established for studies of chronic obstructive pulmonary disease. The present report concerns the quality of RNA that can be extracted from these frozen and fixed tissue samples and from cells obtained from them by laser capture microdissection. The results show that the RNA yield was 257+/-183 ng/mg and 77+/-56 ng/mg from randomly selected frozen and paraffin-embedded tissue, respectively. Intact 18S and 28S rRNA subunits were present in 11/23 frozen and 2/6 paraffin-embedded specimens. The 375-bp actin and 296-bp glyceraldehdye 3-phosphate dehydrogenase targets were amplified by reverse transcription-PCR from both sources and the 983-bp glyceraldehdye 3-phosphate dehydrogenase and 499-bp nonhousekeeping integrin-linked kinase targets from frozen tissue. The minimal amount of RNA required for reverse transcription-PCR of 296-bp glyceraldehdye 3-phosphate dehydrogenase target was 29 pg from frozen tissue when RNA subunits were present and 144 pg when these subunits were absent compared to 0.8 ng from paraffin-embedded tissue. Ten laser pulses were required to laser capture sufficient cells from frozen tissue to detect amplification of the 375-bp actin target while more pulses were required for equivalent amplification from paraffin-embedded tissue. Storage time had no detectable effect on RNA quality. We conclude that both frozen and paraffin-embedded tissues as well as laser-captured cells are suitable for gene expression studies but frozen tissue offered greater sensitivity.

Expression of growth factors by airway epithelial cells in a model of chronic asthma: regulation and relationship to subepithelial fibrosis

BACKGROUND

Growth factors produced by airway epithelial cells may be important in the pathogenesis of subepithelial fibrosis, a distinctive lesion of chronic human asthma.

OBJECTIVE

To examine the relationship between the development of subepithelial fibrosis and the expression of transforming growth factor-beta 1 (TGF-beta 1) and ligands for the epidermal growth factor receptor.

METHODS

BALB/c mice sensitized to ovalbumin were chronically challenged by inhalation of low levels of antigen, leading to development of subepithelial fibrosis and other changes of airway wall remodelling. Growth factor expression was assessed by immunohistochemistry and enzyme immunoassay.

RESULTS

Allergic sensitization directly correlated with airway epithelial expression of both the cleaved, potentially biologically active form of TGF-beta 1 and of amphiregulin in response to allergen challenge. Accumulation of TGF-beta 1 was related to remodelling of the airway wall in chronic asthma, whereas expression of amphiregulin did not exhibit a similar relationship. Production of epithelial cell-derived TGF-beta 1 appeared to be regulated by IL-13, while both IL-13 and CD4(+) T cells regulated accumulation of TGF-beta 1. In contrast to results reported in high-level exposure models of airway fibrosis, eosinophils did not appear to be a significant source of TGF-beta 1.

CONCLUSION

Airway epithelial cell-derived TGF-beta 1 has a potentially crucial role in the development of airway wall remodelling in asthma. Immunological mechanisms may regulate the release and accumulation of TGF-beta 1.

Immunomodulatory cytokines in asthmatic inflammation

The development of asthmatic inflammation involves a complex array of cytokines that promote the recruitment and activation of a number of different immune cells. While factors involved in initiating and establishing inflammation are well characterized, the process by which this pro-inflammatory cascade is regulated is less well understood. The identification and characterization of immunomodulatory cytokines in asthma has been a difficult proposition. Many of the putative regulatory factors have pleiotropic bioactivities and have been characterized as pro-inflammatory in association with certain pathologic conditions. This chapter addresses the potential role of several endogenous factors which appear to attenuate asthmatic inflammation. Understanding the integration of these factors into the regulation of the inflammatory process will likely result in novel therapeutic approaches.

Expression of transforming growth factor beta1 in bronchial biopsies in asthma and COPD

The role of transforming growth factor beta1 (TGF beta1) in airway remodeling in asthma and chronic obstructive pulmonary disease (COPD) has not been fully described. To evaluate the possible pathogenetic role of TGF beta1 in asthma and COPD, immunohistochemical expression of TGF beta1 was described in bronchial biopsies from patients with asthma and COPD compared with healthy individuals. Twelve subjects with asthma, 13 subjects with COPD, and 10 healthy individuals enrolled in the study. Bronchial biopsies were stained with hematoxylin and eosin and anti-TGF beta1 antibody. As a result, immunoreactive TGF beta1 was mainly localized in association with connective tissue in all groups. The staining intensity was not statistically different among the groups in bronchial epithelium, whereas it was significantly higher in the group of asthma in the submucosa. Because there is evidence showing a significant increase of staining intensity in the submucosa from asthmatics but not from subjects with COPD, we may conclude that TGF beta1 may play a significant role in pathogenesis of asthma but not in COPD.

Transforming Growth Factor-β 1 and Extracellular Matrix-Associated Fibronectin Expression in Pulmonary Lymphangioleiomyomatosis

STUDY OBJECTIVES

Lymphangioleiomyomatosis (LAM) is a rare disorder of unknown etiology, affecting almost exclusively women of childbearing age, that is associated with the proliferation of spindle cells and cystic changes in the affected lung. The underlying processes that contribute to this disease are poorly understood. Transforming growth factor (TGF)-beta(1) is a potent cytokine that promotes mesenchymal cell proliferation and regulates the synthesis of extracellular matrix (ECM) components, particularly fibronectins. Herein, we evaluate the expression of TGF beta(1) and matrix-associated fibronectin in lung specimens demonstrating LAM.

DESIGN

Lung biopsy specimens that were confirmed to contain pathologic LAM cells were obtained from 13 patients. The specimens were submitted to immunohistochemical evaluation for TGF beta(1) and fibronectin, as well as the typical markers of LAM cells. Healthy lung parenchyma surrounding resected neoplasms was studied in a parallel fashion as control tissues.

MEASUREMENTS AND RESULTS

In all 13 LAM cases and in healthy lung parenchyma, we demonstrated that TGF beta(1) localized consistently to airway epithelial cells. However, in LAM tissues, matrix-associated TGF beta(1) was also consistently found in regions containing pathologic LAM cells. Notably, more abundant TGF beta(1) was observed in highly cellular areas compared to the walls of chronic cystic regions in LAM tissues. Fibronectin, a matrix component that is strongly expressed in response to active TGF beta(1) was found to consistently colocalize with this protein in these highly cellular regions, supporting TGF beta(1) activity in these regions. The markers of proliferating LAM cells, including proliferating cell nuclear antigen, were also markedly present in these highly cellular LAM regions.

CONCLUSION

These studies suggest that the proliferation of aberrant LAM cells may be associated with altered regional expression of TGF beta(1) and related ECM proteins.

Transforming growth factor-beta and its role in asthma

Transforming growth factor-beta (TGF-beta) is an important fibrogenic and immunomodulatory factor that may play a role in the structural changes observed in the asthmatic airways. In vitro as well as in vivo studies have evidenced a dual role for TGF-beta: it can either function as a pro- or anti-inflammatory cytokine on inflammatory cells, participating into the initiation and resultion of inflammatory and immune responses in the airways. TGF-beta is also involved in the remodelling of the airway wall, and has in particular been related to the subepithelial fibrosis. TGF-beta is produced in the airways by inflammatory cells infiltrated in the bronchial mucosa, as well as by structural cells of the airway wall including fibroblasts, epithelial, endothelial and smooth muscle cells. By releasing TGF-beta, these different cell types may then participate into the increased levels of TGF-beta observed in bronchoalveolar lavage fluid from asthmatic patients. Taken together, these results suggest that TGF-beta may play a role in inflammation in asthma. However, as its role is dual in the modulation of inflammation, further studies are needed to elucidate the precise role of TGF-beta in the airways.

GM-CSF increases airway smooth muscle cell connective tissue expression by inducing TGF-beta receptors

Fibrosis around the smooth muscle of asthmatic airway walls leads to irreversible airway obstruction. Bronchial epithelial cells release granulocyte/macrophage colony-stimulating factor (GM-CSF) in asthmatics and are in close proximity to airway smooth muscle cells (ASMC). The findings in this study demonstrate that GM-CSF induces confluent, prolonged, serum-deprived cultures of ASMC to increase expression of collagen I and fibronectin. GM-CSF also induced ASMC to increase the expression of transforming growth factor (TGF)-beta receptors type I, II, and III (TbetaR-I, TbetaR-II, TbetaR-III), but had no detectable effect on the release of TGF-beta1 by the same ASMC. The presence of GM-CSF also induced the association of TGF-beta1 with TbetaR-III, which enhances binding of TGF-beta1 to TbetaR-II. The induction of TbetaRs was parallel to the increased induction of phosphorylated Smad2 (pSmad2) and connective tissue growth factor (CTGF), indicative of TGF-beta-mediated connective tissue synthesis. Dexamethasone decreased GM-CSF-induced TbetaR-I, TbetaR-II, TbetaR-III, pSmad2, CTGF, collagen I, and fibronectin. In conclusion, GM-CSF increases the responsiveness of ASMC to TGF-beta1-mediated connective tissue expression by induction of TbetaRs, which is inhibited by corticosteroids.

Correlation between airway responsiveness and proteoglycan production by bronchial fibroblasts from normal and asthmatic subjects

Asthma is characterized by an airway remodeling process involving altered extracellular matrix deposition such as collagen, fibronectin and proteoglycans. Proteoglycans determine tissue mechanical properties and are involved in many important biological aspects. Not surprisingly, it has been suggested that proteoglycan deposition may alter airway properties in asthma including airway hyperresponsiveness. In chronically inflamed airway tissues, fibroblasts likely represent an activated fibrotic phenotype that contributes to the excessive deposition of different extracellular matrix components. To investigate whether this was the case for proteoglycans, the production of hyaluronan, perlecan, versican, small heparan sulphate proteoglycans (HSPGs), decorin and biglycan was quantified in the culture medium of primary bronchial fibroblast cultures, established from four normal and six asthmatic subjects. Values were further correlated to the airway responsiveness (PC(20) methacholine) of donor subjects. Fibroblasts from subjects with the most hyperresponsive airways produced up to four times more total proteoglycans than cells from subjects with less hyperresponsive or normoresponsive airways. We observed a significant negative correlation between the PC(20) and perlecan, small HSPGs and biglycan, while such correlation was absent for decorin and close to significant for hyaluronan and versican. Altered proteoglycan metabolism by bronchial fibroblasts may contribute to the increased proteoglycan deposition in the bronchial mucosa and to airway hyperresponsiveness characterizing asthma.

beta-Actin and GAPDH housekeeping gene expression in asthmatic airways is variable and not suitable for normalising mRNA levels

BACKGROUND

The use of reverse transcription-polymerase chain reaction (RT-PCR) to measure mRNA levels has led to the common use of beta-actin and GAPDH housekeeping genes as denominators for comparison of samples. Expression of these genes is assumed to remain constant, so normalising for variations in processing and signal quantitation. However, it is well documented that beta-actin and GAPDH expression is upregulated with proliferation, activation, and differentiation. We hypothesised that airway samples which differ in their cellular profiles and activation status have different levels of expression of GAPDH and beta-actin.

METHODS

The mRNA for beta-actin, GAPDH, and interleukin (IL)-2 was measured in bronchoalveolar lavage (BAL) fluid cells and endobronchial biopsy tissue by competitive RT-PCR in a cross sectional study of 26 normal controls and 92 asthmatic subjects.

RESULTS

For both BAL fluid cells and biopsy tissue, asthmatics overall had reduced expression of GAPDH and beta-actin mRNA. In asthmatic subjects not using inhaled corticosteroids (ICS), GAPDH mRNA levels in both BAL fluid and biopsy tissue, and beta-actin mRNA in BAL fluid cells were 10 times lower than samples from both normal controls and from asthmatic subjects using ICS. beta-Actin mRNA in biopsy specimens showed the same pattern of expression, but asthmatic subjects not using ICS were not significantly different from those receiving ICS treatment. IL-2 mRNA levels did not differ between the subject or treatment groups but, when expressed as a ratio with beta-actin, significant differences were seen.

CONCLUSIONS

beta-Actin and GAPDH used as denominators of gene expression quantitation in asthma research can cause confounding. Housekeeping genes need careful validation before their use in such quantitative mRNA assays.

DNA microarray analysis of transforming growth factor-beta and related transcripts in nasal biopsies from patients with allergic rhinitis

Decreased activity of anti-inflammatory cytokines like transforming growth factor (TGF)-beta may contribute to allergic inflammation. In vivo effects of TGF-beta-effects are difficult to infer from local concentrations, since TGF-beta-effects depend on a complex system of regulatory proteins and receptors. Instead the effects of TGF-beta might be inferred by examining TGF-beta-inducible transcripts. In this study DNA microarrays were used to examine local expression of TGF-beta, TGF-beta-regulatory and -inducible transcripts in nasal biopsies from patients with symptomatic allergic rhinitis and healthy controls. In addition, nasal fluids were analysed with cytological and immunological methods. Nasal fluid eosinophils, albumin, eosinophil granulae proteins and IgE, but not TGF-beta, were higher in patients than in controls. DNA microarray analysis of nasal mucosa showed expression of transcripts encoding TGF-beta, TGF-beta-regulatory proteins and -receptors at variable levels in patients and controls. By comparison, analysis of 28 TGF-beta-inducible transcripts indicated that 23 of these had lower measurement values in patients than in controls, while one was higher, and the remaining four were absent in both patients and controls. In summary, TGF-beta and a complex system of regulatory genes and receptors are expressed in the nasal mucosa. Low expression of TGF-beta-inducible transcripts may indicate decreased TGF-beta activity in allergic rhinitis. DNA microarray analysis may be a way to study cytokine effects in vivo.

Interleukin-4- and interleukin-13-enhanced transforming growth factor-beta2 production in cultured human bronchial epithelial cells is attenuated by interferon-gamma

Cytokines derived from lymphocytes are believed to play key roles in a variety of diseases, including airway diseases such as asthma. The current study was designed to evaluate the hypothesis that cytokines derived from Th2 cells, interleukin (IL)-4 and IL-13, might contribute to tissue remodeling by modulating the production of transforming growth factor (TGF)-beta. In addition, the ability of interferon (IFN)-gamma, a cytokine derived from Th1 cells that can antagonize many effects of IL-4 and IL-13, was also assessed for its effects on TGF-beta production. IL-4 and IL-13 both stimulated production of TGF-beta2 release from human bronchial epithelial cells in a time- and concentration-dependent manner. Both with and without acidification, TGF-beta2 were detected. Neither TGF-beta1 nor TGF-beta3 was released. In contrast to the stimulatory effect on human bronchial epithelial cells, neither IL-4 nor IL-13 stimulated release of any TGF-beta isoform from human lung fibroblasts. IFN-gamma reduced both basal, IL-4-, and IL-13-stimulated release of TGF-beta2 in human bronchial epithelial cells. The stimulatory effects of IL-4 and IL-13 and the inhibitory effect of IFN-gamma on TGF-beta2 release were paralleled by mRNA levels, as assessed by real-time reverse transcriptase-polymerase chain reaction (RT-PCR). In summary, the Th2-derived cytokines, IL-4 and IL-13, can stimulate production of TGF-beta from airway epithelial cells but not from lung fibroblasts. IFN-gamma, in contrast, can inhibit TGF-beta2 release both under basal conditions and following IL-4 or IL-13 stimulation. The ability of these cytokines to modulate TGF-beta release may contribute to both normal airway repair and to the development of subepithelial fibrosis in asthma.

Interleukin-4 and tumour necrosis factor-alpha inhibit transforming growth factor-beta production in a human bronchial epithelial cell line: possible relevance to inflammatory mechanisms in chronic obstructive pulmonary disease

OBJECTIVE

Human bronchial epithelial cells are known to secrete an array of inflammatory cytokines including tumour necrosis factor-alpha (TNF-alpha) and interleukin (IL)-4, which may play a role in immune responses in lung diseases such as chronic obstructive pulmonary disease (COPD). However, the regulatory mechanisms governing cytokine production in bronchial epithelia in COPD are largely unknown. Transforming growth factor-beta (TGF-beta) is an anti-inflammatory cytokine and is involved in airway repair. The purpose of this study was to study the effect of TNF-alpha and IL-4 (pro-inflammatory cytokines known to be up-regulated in COPD), on the production of TGF-beta (a negative regulator of inflammation) by epithelial cells.

METHODOLOGY

A bronchial epithelial cell line was used as an in vitro culture model (16HBE). Cell cultures were stimulated with various combinations of TNF-alpha and IL-4 (20 ng/mL) for 24 h. Transforming growth factor-beta production was measured by flow cytometry, enzyme-linked immunosorbent assay and immunohistochemistry.

RESULTS

Exposure to TNF-alpha significantly up-regulated production of IL-4 from cultured epithelial cells. Unstimulated cells spontaneously released TGF-beta. Exposure to TNF-alpha and IL-4 significantly inhibited production of TGF-beta. The inhibitory effects of TNF-alpha and IL-4 on TGF-beta synthesis were summative.

CONCLUSIONS

The inhibitory effect of IL-4 and TNF-alpha on production of the regulatory cytokine TGF-beta in a bronchial epithelial cell line suggests that such mechanisms may contribute to the progression of the inflammatory response and compromise repair processes in inflammatory lung diseases such as COPD.

Localisation of transforming growth factor β1 and β3 mRNA transcripts in normal and fibrotic human lung

BACKGROUND

Transforming growth factor β1 is implicated in the pathogenesis of lung fibrosis. It promotes extracellular matrix accumulation by increasing procollagen synthesis and reducing degradation. TGFβ1 gene and protein expression increase in experimental lung fibrosis, and TGFβ1 antibodies attenuate fibrosis in mice. The role of other TGFβ isoforms is unclear. This study aimed to localise TGFβ1 and TGFβ3 gene expression in fibrotic human lung and compare it with that in normal human lung.

METHODS

Lung tissue from patients with cryptogenic fibrosing alveolitis and fibrosis associated with systemic sclerosis was examined by in situ hybridisation. Macroscopically normal lung from carcinoma resections was used as control tissue. Digoxigenin labelled riboprobes were synthesised from TGFβ isoform specific cDNA templates.

RESULTS

The digoxigenin labelled riboprobes were sensitive and permitted precise cellular localisation of mRNA transcripts. TGFβ1 and TGFβ3 mRNA transcripts were widespread in normal lung and localised to alveolar macrophages and bronchiolar epithelium. TGFβ1 but not TGFβ3 mRNA was detected in mesenchymal and endothelial cells. In fibrotic lung tissue mRNA transcripts for both isoforms were also detected in metaplastic type II cells. TGFβ1 gene expression was enhanced in some patients. TGFβ3 was expressed in fibrotic lung but was not consistently altered compared with controls.

CONCLUSION

TGFβ1mRNA transcripts were localised in normal and fibrotic human lung and TGFβ3 gene expression in human lung fibrosis was shown for the first time. The results suggest that TGFβ1 may play the predominant role in pathogenesis. It is suggested that TGFβ1 should be the primary target of anticytokine treatments for pulmonary fibrosis.

Activation of the TGF-beta/activin-Smad2 pathway during allergic airway inflammation

Changes in the levels of transforming growth factor (TGF)-beta cytokines or receptors observed during the progression of several inflammatory and fibrotic disorders have been used to implicate these cytokines in the pathophysiology of these diseases. Although correlative, these studies were inconclusive because they were unable to demonstrate actual continuous TGF-beta-mediated signaling in the involved tissues. We reasoned that the phosphorylation state and subcellular localization of Smad2, the intracellular effector of TGF-beta/activin-mediated signaling, could be used as a marker of active signaling mediated by these cytokines in situ. We therefore used an experimental model of ovalbumin-induced allergic airway inflammation and were able to demonstrate a dramatic increase in the numbers of bronchial epithelial, alveolar, and infiltrating inflammatory cells expressing nuclear phosphorylated Smad2 within the allergen-challenged lungs. This was accompanied by strong upregulation of the activin receptor ALK-4/ActR-IB and redistribution of the TGF-beta responsive ALK-5/TbetaR-I. Although levels of TGF-beta1, TGF-beta2, and TGF-beta3 messenger RNA (mRNA) were marginally altered, the level of activin mRNA was strongly upregulated during the inflammatory response. Our data illustrate the usefulness of antiphosphorylated Smad antibodies in demonstrating active TGF- beta/activin-mediated signaling in vivo and strongly suggest that activin/Smad-mediated signaling could be a critical contributor in the pathophysiology of allergic pulmonary diseases.

Localisation of transforming growth factor beta1 and beta3 mRNA transcripts in normal and fibrotic human lung

BACKGROUND

Transforming growth factor beta1 is implicated in the pathogenesis of lung fibrosis. It promotes extracellular matrix accumulation by increasing procollagen synthesis and reducing degradation. TGFbeta1 gene and protein expression increase in experimental lung fibrosis, and TGFbeta1 antibodies attenuate fibrosis in mice. The role of other TGFbeta isoforms is unclear. This study aimed to localise TGFbeta1 and TGFbeta3 gene expression in fibrotic human lung and compare it with that in normal human lung.

METHODS

Lung tissue from patients with cryptogenic fibrosing alveolitis and fibrosis associated with systemic sclerosis was examined by in situ hybridisation. Macroscopically normal lung from carcinoma resections was used as control tissue. Digoxigenin labelled riboprobes were synthesised from TGFbeta isoform specific cDNA templates.

RESULTS

The digoxigenin labelled riboprobes were sensitive and permitted precise cellular localisation of mRNA transcripts. TGFbeta1 and TGFbeta3 mRNA transcripts were widespread in normal lung and localised to alveolar macrophages and bronchiolar epithelium. TGFbeta1 but not TGFbeta3 mRNA was detected in mesenchymal and endothelial cells. In fibrotic lung tissue mRNA transcripts for both isoforms were also detected in metaplastic type II cells. TGFbeta1 gene expression was enhanced in some patients. TGFbeta3 was expressed in fibrotic lung but was not consistently altered compared with controls.

CONCLUSION

TGFbeta1 mRNA transcripts were localised in normal and fibrotic human lung and TGFbeta3 gene expression in human lung fibrosis was shown for the first time. The results suggest that TGFbeta1 may play the predominant role in pathogenesis. It is suggested that TGFbeta1 should be the primary target of anticytokine treatments for pulmonary fibrosis.

Increased expression of transforming growth factor-beta1 in small airway epithelium from tobacco smokers and patients with chronic obstructive pulmonary disease (COPD)

Tobacco smoke is believed to cause small airway disease and then chronic obstructive pulmonary disease (COPD), but the molecular mechanisms by which small airway obstruction occurs remain unknown. To study the gene expression levels of transforming growth factor (TGF)-beta1, a potent fibrogenic factor, in small airway epithelium from smokers and patients with COPD, we harvested highly pure samples of epithelial cells from small airways under direct vision by using an ultrathin bronchofiberscope BF-2.7T (outer diameter 2.7 mm with a biopsy channel of 0.8 mm in diameter). The expression levels of TGF-beta1 were evaluated by reverse transcription-polymerase chain reaction (RT-PCR). The mRNA levels of TGF-beta1 corrected by beta-actin transcripts were significantly higher in the smoking group and patients with COPD than those in nonsmokers (p < 0.01). Furthermore, among smokers and patients with COPD, TGF-beta1 mRNA levels correlated positively with the extent of smoking history (pack-years) and the degree of small airway obstruction as assessed by measurements of flow-volume curves. Immunocytochemistry of the cells demonstrated more intense stainings for TGF-beta1 in samples from smokers and patients with COPD than from nonsmokers. Spontaneously released immunoreactive TGF-beta1 levels from cultured epithelial cells were more elevated in subjects with a history of smoking and patients with COPD than in nonsmokers. Our study showed a close link between smoking and expression of TGF-beta1 in small airways. Our results also suggested that small airway epithelial cells might be involved in obstructive changes found in smokers and patients with COPD.

The pathology of asthma: brief review

The presence of chronic airway inflammation in asthmatic patients has been known for over a century, but the relationship of this inflammatory process to the pathogenesis of reversible airflow obstruction and non-specific bronchial hyperresponsiveness remains unclear. In recent years, the increasing ability to sample the lower respiratory tract of living asthmatic patients, coupled with revolutionary advances in immunology and molecular biology, has resulted in extensive evaluation of inflammatory cells and mediators implicated in the pathogenesis of asthma. In addition, there is increasing recognition that airway remodeling, characterized by thickening of all compartments of the airway wall, may have profound consequences on the mechanics of airway narrowing in asthma and contribute to the chronicity and progression of the disease. In this brief review, I will describe the gross and microscopic pathology of asthma, the process of airway remodeling and its functional consequences, and speculate on future directions to improve our understanding of the structural changes of asthma and their pathogenic role.

Consequences of long-term inflammation. Airway remodeling

Airway inflammation may not account for all the clinical manifestations of asthma. Airway remodeling, which is thought to be a result of airway chronic inflammation, may help fill this void. Remodeling is described for fatal and nonfatal asthmatics including changes in smooth muscle, collagen deposition, noncollagenous matrix, and mucus glands. This article also reviews the correlation of airway remodeling with clinical, physiologic and biologic data, experimental models of airways remodeling, and effect of therapy on airway remodeling. Throughout, it is emphasized that the concept of airway remodeling is a dynamic process that is active and potentially progressive in asthmatic patients but that may be prevented by appropriate therapy.

Inflammation and repair processes in chronic obstructive pulmonary disease

COPD is characterized by chronic inflammation and injury of both the airways and the parenchymal structures of the lung. These processes are associated with ongoing repair. Whether repair leads to restoration of normal tissue architecture or to altered tissue structure with loss of function depends on complex interrelationships of a variety of interacting mediators. The possibility that repair processes can be modulated by exogenous agents raises the possibility that therapeutic strategies aimed at repair can be effective. Such strategies offer tremendous promise both for slowing the relentlessly progressive natural history which most often characterizes COPD and, possibly, for restoring lung function. Rennard SI. Inflammation and repair processes in chronic obstructive pulmonary disease.

Extracellular matrix deposition by primary human lung fibroblasts in response to TGF-beta1 and TGF-beta3

Increased collagen and extracellular matrix (ECM) deposition within the lung is a characteristic feature of lung fibrosis. Transforming growth factor (TGF)-beta isoforms play a pivotal role in the production of collagen and ECM. In this study, we investigated the effects of TGF-beta1 and TGF-beta3 on the main processes controlling ECM deposition using primary human lung fibroblasts. We analyzed 1) collagen metabolism by [3H]proline incorporation, 2) matrix metalloproteinase (MMP) expression by substrate gel zymography, and 3) tissue inhibitor of metalloproteinases (TIMP) expression by Western blot analysis. TGF-beta1 and TGF-beta3 increased the percentage of secreted collagens in supernatants of primary fibroblasts from 8.0 +/- 1.2 (control) to 23.6 +/- 4.6 and 22.3 +/- 1.3%, respectively. The collagen percentage in deposited ECM was increased from 5.8 +/- 0.3 (control) to 9.0 +/- 0.5 and 8.8 +/- 0.5% by TGF-beta1 and TGF-beta3, respectively. Secretion of MMP-1 (interstitial collagenase) by fibroblasts was reduced by both TGF-beta isoforms, whereas secretion of MMP-2 (gelatinase A) was unaffected by either of the two isoforms. Both TGF-beta isoforms increased TIMP-1 protein expression, whereas TIMP-2 protein was decreased. We thus conclude that TGF-beta1 and TGF-beta3 are equally potent in increasing ECM deposition. Their fibrotic effect in lung fibroblasts results from 1) an increase in the secretion and deposition of total ECM and collagens, 2) a decrease in MMP-1 secretion, and 3) an increase of TIMP-1 expression.

Transforming growth factor beta1 and recruitment of macrophages and mast cells in airways in chronic obstructive pulmonary disease

Chronic airways inflammation is one of the features of chronic obstructive pulmonary disease (COPD). We demonstrated previously that bronchiolar epithelium in COPD contains increased numbers of macrophages and mast cells. Transforming growth factor beta1 (TGF-beta1) may be involved in this influx because it has chemotactic activity for macrophages and mast cells. In this study, we examined expression patterns of TGF-beta1, TGF-beta receptors type I and II (TGF-betaRI and TGF-betaRII) by immunohistochemistry and mRNA in situ hybridization in peripheral lung tissue of 14 current or ex-smokers with COPD (FEV1 < 75%) and 14 without COPD (FEV1 > 84%). In both groups, TGF-beta1 and its receptors are present in airway and alveolar epithelial cells, airway and vascular smooth muscle cells, and tissue and alveolar CD68(+) cells (considered herein to be macrophages). In subjects with COPD, a semiquantitative analysis revealed approximately twofold higher levels of TGF-beta1 mRNA and protein in bronchiolar and alveolar epithelium (p < 0.02) as compared with subjects without COPD. With regard to bronchiolar epithelial cells, we found a significant correlation between TGF-beta1 mRNA and protein expression (r = 0.62; p < 0.002), and between the FEV1 of all subjects together and TGF-beta1 protein (r = -0.60; p < 0.0002) and mRNA (r = -0.67; p < 0. 002) levels. The epithelial expression of TGF-beta1 mRNA and TGF-beta1 protein correlates with the number of intraepithelial macrophages (both: r = 0.44; p < 0.03) whereas intraepithelial mast cell numbers correlate with epithelial TGF-beta1 mRNA expression. These data suggest a role for TGF-beta1 in recruiting macrophages into the airway epithelium in COPD.

Co-localization of immunoreactive transforming growth factor-beta 1 and decorin in bronchial biopsies from asthmatic and normal subjects

Airway wall remodelling is an established pathological feature of asthma but its causes are not well understood. One cytokine of potential relevance is transforming growth factor-beta1 (TGF-beta 1). The immunolocalization of TGF-beta 1 and of its small binding proteoglycan decorin have been examined in the airways of normal subjects and atopic asthmatics. Bronchial biopsy specimens were obtained by fibreoptic bronchoscopy, processed into glycolmethacrylate resin, and stained immunohistochemically using specific antibodies. Immunoreactive TGF-beta 1 was principally localized extracellularly in association with subepithelial connective tissue. Some staining of bronchial epithelial cells was also evident, but otherwise there was little intracellular staining. The overall pattern of immunohistochemical staining was indistinguishable in biopsy specimens from asthmatic and control subjects. Comparison of adjacent sections demonstrated the co-localization of immunoreactivity for TGF-beta 1 and decorin in the mucosa. It is concluded that immunoreactive TGF-beta 1 in human airways is principally extracellular and that matrix-associated TGF-beta 1 is likely to be bound at least in part to decorin. This interaction may provide a reservoir of TGF-beta 1 that can be released in an active form in response to appropriate stimuli.

Interleukin-10 and transforming growth factor-beta promoter polymorphisms in allergies and asthma

Interleukin-10 (IL-10) and transforming growth factor beta (TGF-beta) are inhibitory for B and T cells, IgE production, and mast cell proliferation, and they induce apoptosis in eosinophils. These cytokines are therefore candidate genes which could contribute to the development of asthma or allergies. We investigated the hypothesis that polymorphic nucleotides within the IL-10 and TGF-beta gene promoters would link to the expression of allergies and asthma. DNA taken from families with an asthmatic proband was examined for base exchanges by single-stranded conformational polymorphism (SSCP). We demonstrated the presence of a polymorphism in the promoter region of the IL-10 gene and four in the TGF-beta gene promoters (3 in TGF-beta1 and 1 in TGF-beta2). The IL-10 gene polymorphism was a C-to-A exchange 571 base pairs upstream from the translation start site and was present between consensus binding sequences for Sp1 and elevated total serum. This polymorphism was associated with elevated total serum IgE in subjects heterozygotic or homozygotic for this base exchange (p < 0.009). The base exchange at -509 (from the transcription initiation site) in the TGF-beta promoter also linked to elevated total IgE (p < 0.01). This polymorphism represented a C-to-T base exchange which induced a YY1 consensus sequence and is present in a region of the promoter associated with negative transcription regulation.

Collagen deposition in large airways may not differentiate severe asthma from milder forms of the disease

Chronic airway inflammation and remodeling, including fibrosis, have been proposed as important contributors to asthma pathophysiology. Previous studies of airway fibrosis have been performed mainly in mild and moderate asthmatics at the subepithelial "basement membrane" (SBM) level. The current study was designed to evaluate the large airway SBM thickness and submucosal collagen deposition, as measured by three different collagen staining methods, in endobronchial biopsies from 17 severe, nine moderate, and seven mild asthmatics, as well as eight normal control subjects. Tissue eosinophils and transforming growth factor-beta (TGF-beta) immunoreactivity were also examined. There were no statistically significant differences in the SBM thickness, submucosal collagen deposition, eosinophil numbers, or TGF-beta positive cells among the three groups of asthmatics and the normal control subjects. It was only when examining all asthmatics (n = 33) together, that a modestly thickened SBM (p = 0.04), as evaluated by collagen type III immunostaining, was observed as compared with normal control subjects. Despite this difference, no significant differences were found in the amount of submucosal collagen deposition and the number of eosinophils or TGF-beta expressing cells when comparing total asthmatics and normal control subjects. Additionally, no significant correlations were found between collagen deposition and eosinophil count, TGF-beta expression level, FEV1, or duration of asthma. These results suggest that although increased collagen deposition in the SBM at the large airway level is a characteristic of asthma, it may not explain the differences in severity of asthma.

Inhibition of serum and transforming growth factor beta (TGF-beta1)-induced DNA synthesis in confluent airway smooth muscle by heparin

1. Airway remodelling occurs in asthma and involves an increase in airway smooth muscle mass through cell proliferation and hypertrophy. Increased eosinophil density in the airways is a feature of asthma. Eosinophils exhibiting activation in the airways of asthmatics also exhibit increased expression of transforming growth factor beta (TGF-beta1). We have examined the capacity of TGF-beta1 and epidermal growth factor (EGF) to influence airway smooth muscle division and the effect of heparin on TGF-beta1. EGF and serum-induced smooth muscle DNA synthesis in confluent airway smooth muscle cells (ASMC) as an indication of entry into S phase preceding mitogenesis. 2. ASMC were obtained from cell populations growing out from explanted bovine trachealis muscle sections. Cell division was monitored in sparse plated cells by direct cell counting following nuclear staining. Cell DNA synthesis in confluent cells was monitored by uptake of [3H]-thymidine. 3. TGF-beta1 (100 microM) inhibited FBS (10%)-induced smooth muscle division in sparsely plated cells (40%). TGF-beta1 (100 pM) increased cell DNA synthesis (200%) in confluent cells in the presence of bovine serum albumin (BSA, 0.25%). EGF (0.7 nM) also increased airway smooth muscle DNA synthesis (69%) in the presence of BSA (0.25%). The facilitatory effect of TGF-beta1 was observed between 1-100 pM, while that of EGF was observed between 20 200 pM. 4. Heparin inhibited serum and TGF-beta1-induced DNA synthesis in confluent ASMC (55%), consistent with our previous observation of inhibition of division in sparsely populated ASMC (Kilfeather et al., 1995a). This action of heparin was observed between concentrations of 1-100 microg ml(-1). Heparin did not inhibit DNA synthesis in response to EGF. An anti-mitogenic effect of heparin was also observed against responses to combined exposure to TGF-beta1 and EGF. 5. There was a clear inhibitory effect of heparin in absolute terms against serum-induced division in cells plated at 10, 20 and 45 x 10(3) cells cm(-2). The inhibitory effect of heparin was also observed at a plating density of 45,000 cells cm(-2) when responses to serum were expressed as fold-stimulation of basal DNA synthesis. 6. These findings demonstrate a potential role of TGF-beta1, EGF and heparin-related molecules in regulation of airway smooth muscle division.

Expression of epidermal growth factor and epidermal growth factor receptor immunoreactivity in the asthmatic human airway

Chronic airway inflammation, one of the pathophysiologic features of bronchial asthma, is suspected to be responsible for irreversible pathological changes of airways, called airway remodeling. To examine the mechanisms of airway remodeling in asthma, we investigated the expression of epidermal growth factor (EGF) and its receptor immunohistochemically in asthmatic human airways. Airway specimens from seven patients with asthma were obtained from autopsied and surgically resected lungs. Control specimens were obtained from lungs of eight subjects without asthma and other pulmonary complications at autopsy. We stained those specimens by the avidin-biotin-peroxidase complex (ABC) method with anti-human polyclonal EGF antibody and monoclonal EGF receptor antibodies. Three different portions of airways-large bronchi (about 1 cm in diameter), small bronchi (about 3 mm in diameter), and peripheral airways (less than 2 mm in diameter)-were examined. The thickness of the bronchial smooth muscle and basement membrane was significantly greater in the asthmatic airways than in controls. Clear immunoreactivities of EGF were widely observed on bronchial epithelium, glands, and smooth muscle in asthmatic airways. In the controls, the bronchial epithelium and the bronchial glands partially expressed faint EGF immunoreactivity. For the EGF receptor, clear immunoreactivities were also observed on bronchial epithelium, glands, smooth muscle, and basement membrane in asthmatic airways. In control airways, only part of the bronchial epithelium and smooth muscle weakly expressed EGF receptor immunoreactivity. These results suggest a possible contribution of EGF to the pathophysiology of bronchial asthma, including airway remodeling.

Inhaled corticosteroid reduced lamina reticularis of the basement membrane by modulation of insulin-like growth factor (IGF)-I expression in bronchial asthma

BACKGROUND

Pathological studies of bronchial biopsy specimens have confirmed the apparent thickening of lamina reticularis of the epithelial basement membrane. Corticosteroids have proven to be most effective in modifying airway inflammation. However, there is not much data on the effects of corticosteroid-treatment on the basement membrane.

OBJECTIVE

To investigate the effects of inhaled beclomethasone dipropionate (BDP) on the thickness of basement membrane and cellular infiltration into the bronchial mucosa, and the expression of growth factors in patients with asthma.

METHODS

We studied bronchial biopsies from 24 asthmatic patients before and after treatment with inhaled BDP, 400 microg twice a day or placebo, for 6 months in a double-blind manner. Each subject recorded daily asthma symptoms and peak expiratory flow (PEF). Lung function and bronchial responsiveness to methacholine were measured before and after treatment. The thickness of the basement membrane was determined by electron microscopy. Inflammatory cells and the expression of growth factors were examined by immunohistochemistry in endobronchial biopsy specimens.

RESULTS

After 6 months of treatment, we observed a significant improvement of asthma symptoms (P<0.01), PEF (P<0.01), diurnal variation of PEF (P<0.05), and airway responsiveness (P< 0.05) in the BDP group compared with the placebo group. This was accompanied by a significant decrease in the thickness of the lamina reticularis (P < 0.001), and in the number of activated eosinophils (P<0.01), T-lymphocytes (P<0.01), and fibroblasts (P < 0.05) in BDP-treated patients. There was also a reduction in the expression of insulin-like growth factor (IGF)-I (P < 0.01). Significant correlation was found between the IGF-I expression and collagen thickening (rs = 0.34, P<0.01), and the number of fibroblasts (rs = 0.45, P < 0.01).

CONCLUSION

These results suggest that corticosteroid treatment in asthma can reduce the lamina reticular thickness by modulation of IGF-I expression with consequent inhibition of the airway infiltration by inflammatory cells, and therefore may help to prevent remodelling of the airways.

Expression of growth factors and remodelling of the airway wall in bronchial asthma

BACKGROUND

Bronchial asthma is characterised by airway structural changes, including mucosal inflammatory infiltration and subepithelial collagen deposition, that may represent the morphological basis for the chronicity of the disease. The relationship between airway wall thickness and growth factors in asthma has not been elucidated.

METHODS

Bronchial biopsy specimens were obtained from 21 asthmatic patients and eight healthy subjects and the basement membrane thickness was measured by light microscopy and electron microscopy. At the same time the numbers of eosinophils and fibroblasts were assessed and the expression of transforming growth factor beta 1 (TGF-beta 1), platelet derived growth factor (PDGF), and insulin like growth factor (IGF) I in the bronchial mucosa was examined by immunostaining. The relationship between the degree of thickening of the subepithelial layer and both the clinical data and pulmonary function were also investigated.

RESULTS

The basement membrane of the asthmatic patients was thicker than that of the healthy controls (median 8.09 versus 4.02 microns). Electron microscopic examination of the basement membrane revealed thickening of the subepithelial lamina reticularis; this thickening significantly correlated with the number of fibroblasts in the submucosa in the asthmatic subjects (rs = 0.88) but not in the controls (rs = 0.70). There was a significantly higher number of eosinophils in the airways of the asthmatic subjects than in the healthy subjects (EG1 + cells: 52.0 versus 2.0/mm2, EG2 + cells: 56.0 versus 1.5/mm2). The expression of each growth factor in the bronchial mucosa was similar in asthmatic and healthy subjects (TGF-beta 1: 18.0% versus 16.0%, PDGF: 37.0% versus 32.5%, IGF-I: 15.0% versus 8.0%). A weak but statistically significant correlation was found between the number of fibroblasts and the expression of TGF-beta 1 in asthmatic subjects (rs = 0.50). There was a significant correlation between the thickness of the subepithelial layer in asthmatic subjects and the attack score (rs = 0.58) and a significant inverse correlation between the subepithelial collagen thickness in asthmatic subjects and airway hypersensitivity (rs = -0.65).

CONCLUSIONS

These findings indicate that the thickening of the subepithelial layer in bronchial asthma is due to an increase in fibroblasts, and that the thickness of the subepithelial collagen appears to be linked to an increase in bronchial responsiveness and exacerbation of clinical manifestations.

Eosinophil-associated TGF-beta1 mRNA expression and airways fibrosis in bronchial asthma

The histopathology of bronchial asthma is associated with structural changes within the airways, including subepithelial fibrosis, as well as chronic eosinophilic inflammation. The mechanisms responsible for this tissue remodeling, and in particular the role of inflammatory cells, remain to be established. Transforming growth factor-beta (TGF-beta) is a potent profibrotic cytokine which may contribute to the thickening of the reticular lamina by the deposition of collagen fibers. To investigate the molecular mechanisms underlying these structural changes, we have investigated the expression of TGF-beta1 mRNA and immunoreactivity within the bronchial mucosa of mild to severe asthmatic individuals and normal control subjects using the techniques of in situ hybridization and immunocytochemistry. As eosinophils are prominent within the asthmatic airway and are known to synthesize pro-inflammatory cytokines, the presence of TGF-beta1 mRNA and immunoreactive protein in eosinophils was also examined. Asthmatic individuals exhibited a greater expression of TGF-beta1 mRNA and immunoreactivity in the airways submucosa than normal control subjects (P < 0.05), and these increases were directly related to the severity of the disorder. The extent of airways fibrosis, as detected histochemically, was also increased in asthmatics compared with normal control subjects (P < 0.005). In asthmatic subjects, the presence of subepithelial fibrosis was associated with the severity of the disease and correlated with the decline in forced expiratory volume in 1 s (r2 = 0.78; P < 0.05). Within the asthmatic airways, EG2-positive eosinophils represented the major source of TGF-beta1 mRNA and immunoreactivity. These results provide evidence that TGF-beta1 may play a role in the fibrotic changes occurring within asthmatic airways and that activated eosinophils are a major source of this cytokine.

Transforming growth factor-beta expression in mucosal biopsies in asthma and chronic bronchitis

We assessed whether transforming growth factor-beta (TGF-beta), a fibrogenic growth factor, may be involved in remodeling of asthma and chronic bronchitis; its expression was compared with that of epidermal growth factor (EGF) and granulocyte macrophage colony-stimulating factor (GM-CSF) in bronchial mucosal biopsies from 13 normal subjects, 24 asthmatics, and 19 patients with chronic bronchitis. TGF-beta immunoreactivity was highly increased in epithelium and submucosa of those with bronchitis and to a lesser extent in asthmatics. By comparison, with normal subjects, EGF immunoreactivity was significantly increased in the epithelium of bronchitic subjects and submucosa of asthmatics, and, GM-CSF immunoreactivity was increased in both epithelial and submucosal cells of asthmatics and to a lesser extent in submucosa of bronchitics. A significant correlation was found between the number of epithelial or submucosal cells expressing TGF-beta in both asthma and chronic bronchitis and basement membrane thickness and fibroblast number. No such correlation was found for EGF or GM-CSF. in situ hybridization for TGF-beta 1 mRNA confirmed the results obtained by immunohistochemistry. By combining in situ hybridization and immunohistochemistry, it was found that eosinophils and fibroblasts were synthetizing TGF-beta in asthma and bronchitis. These data suggest that TGF-beta, but not EGF or GM-CSF, is involved in airways remodeling in asthma and chronic bronchitis.

Transforming growth factor-beta 1 in asthma. Measurement in bronchoalveolar lavage fluid

Airway wall remodeling is an established pathological feature in asthma. Its causes are not well understood, but one mediator of potential relevance is transforming growth factor-beta 1 (TGF-beta 1). We have measured levels of immunoreactive TGF-beta 1 in bronchoalveolar lavage (BAL) fluid from clinically stable atopic asthmatics and healthy control subjects. We have also examined the influence of allergen exposure on TGF-beta 1 release in the airways using a segmental bronchoprovocation model, with BAL performed at two time points following endobronchial allergen and sham saline challenges. Basal concentrations of TGF-beta 1 were significantly higher in asthmatics than control subjects (median 8.0 versus 5.5 pg/ml, p = 0.027). Following segmental bronchoprovocation, concentrations of TGF-beta 1 at the allergen- and saline-challenged sites were not significantly different after 10 min, (31.3 versus 25.0 pg/ml, p = 0.78), but after 24 h there were significantly higher TGF-beta 1 concentrations at the allergen-challenged sites (46.0 versus 21.5 pg/ml, p = 0.017). We conclude that basal TGF-beta 1 levels in the airways are elevated in atopic asthma and that these levels increase further in response to allergen exposure. These findings are consistent with the hypothesis that TGF-beta 1 is implicated in airway wall remodeling in asthma.

The structural and functional consequences of chronic allergic inflammation of the airways

Although asthma is generally considered a form of reversible airway obstruction, there is evidence that chronic allergic inflammation can lead to structural changes in the airway and a degree of progressive fixed airway obstruction. More importantly, these structural changes can lead to airway hyper-responsiveness. The structural consequences of chronic allergic inflammation are secondary to cellular proliferation and reorganization of the connective tissue constituents of the airway wall. Smooth muscle proliferation and hypertrophy may increase the potential for smooth muscle shortening against the elastic loads provided by lung parenchymal recoil and airway mucosal folding. Resident airway cells, as well as inflammatory cells, produce mediators, cytokines and growth factors that stimulate production of connective tissue proteins and proteoglycans that cause airway remodelling and altered mechanical function. Thickening of the airway wall internal to the smooth muscle layer can amplify the effect of smooth muscle shortening on airway calibre, and it could also stiffen the airway making it less distensible. Thickening of the airway wall external to the muscle can uncouple the airway from the distending force applied by the lung parenchyma. Early and aggressive anti-inflammatory medication may alter the natural history of asthma by preventing the structural changes that are a consequence of chronic allergic inflammation.