Airway Wall Remodeling In Asthma Research Articles

Amygdalin alleviated TGF-β-induced epithelial-mesenchymal transition in bronchial epithelial cells

ObjectiveTransforming growth factor-beta TGF-β-induced epithelial-mesenchymal transition (EMT) in bronchial epithelial cells contributes to airway wall remodeling in asthma. This study aims to explore the role of amygdalin, an active ingredient in bitter almonds, in TGF-β-induced EMT in bronchial epithelial cells and to elucidate the possible mechanisms underlying its biological effects. MethodsAn asthmatic mouse model was established through ovalbumin induction. Primary mouse bronchial epithelial cells and a human bronchial epithelial cell line were incubated with transforming growth factor-beta (TGF-β) to induce EMT, whose phenotype of cells was evaluated by the expressions of EMT markers [alpha-smooth muscle actin (α-SMA), vimentin, and fibronectin] and cell migration capacity. A co-immunoprecipitation assay was performed to assess the ubiquitination of heparanase (HPSE). ResultsIn asthmatic model mice, amygdalin treatment relieved airway wall remodeling and decreased expressions of EMT markers (α-SMA and vimentin). In TGF-β-treated bronchial epithelial cells, amygdalin treatment decreased the mRNA and protein levels of EMT markers (α-SMA, vimentin, and fibronectin) without impairing cell viability. Through the Swiss Target Prediction database, HPSE was screened as a candidate downstream target for amygdalin. HPSE overexpression further promoted TGF-β-induced EMT while the HPSE inhibitor suppressed TGF-β-induced EMT in bronchial epithelial cells. In addition, HPSE overexpression reversed the inhibitory effect of amygdalin on TGF-β-induced EMT in bronchial epithelial cells. The following mechanism exploration revealed that amygdalin downregulated HPSE expression by enhancing ubiquitination. ConclusionOur study showed that amygdalin inhibited TGF-β-induced EMT in bronchial epithelial cells and found that the anti-EMT activity of amygdalin might be related to its regulatory effect on HPSE expression.

Zinc salicylate reduces airway smooth muscle cells remodelling by blocking mTOR and activating p21(Waf1/Cip1)

Asthma is characterized by chronic inflammation and tissue remodeling of the airways. Remodeling is resistant to pharmaceutical therapies. This study investigated the effect of zinc salicylate-methylsulfonylmethane (Zn-Sal-MSM) compared to zinc salicylate (Zn-Sal), or sodium salicylate (Na-Sal), or zinc chloride (ZnCl2) on remodeling parameters of human airway smooth muscle cells (ASMC). Human ASMC obtained from asthma patients (n=7) and non-asthma controls (n=7) were treated with one of the reagents. Cell proliferation and viability was determined by direct cell counts and MTT assay. The expression of and phosphorylation proteins was determined by Western-blotting, ELISA, immunofluorescence, and mass spectrometry. Extracellular matrix deposition by ELISA. Zn-Sal-MSM, Zn-Sal and Na-Sal (0.1–100 µg/mL) significantly reduced PDGF-BB-induced proliferation in a concentration dependent manner, while ZnCl2 was toxic. The reduced proliferation correlated with increased expression of the cell cycle inhibitor p21(Waf1/Cip1), and reduced activity of Akt, p70S6K, and Erk1/2. Zn-Sal-MSM, Zn-Sal, but not Na-Sal reduced the deposition of fibronectin and collagen type-I. Furthermore, Zn-Sal-MSM reduced the mitochondria specific COX4 expression. Mass spectrometry indicated that Zn-Sal-MSM modified the expression of several signaling proteins and zinc-dependent enzymes. In conclusion, Zn-Sal-MSM and Zn-Sal potentially prevent airway wall remodeling in asthma by inhibition of both the Erk1/2 and mTOR signaling pathways.

Immunologic and Non-Immunologic Mechanisms Leading to Airway Remodeling in Asthma.

Asthma increases worldwide without any definite reason and patient numbers double every 10 years. Drugs used for asthma therapy relax the muscles and reduce inflammation, but none of them inhibited airway wall remodeling in clinical studies. Airway wall remodeling can either be induced through pro-inflammatory cytokines released by immune cells, or direct binding of IgE to smooth muscle cells, or non-immunological stimuli. Increasing evidence suggests that airway wall remodeling is initiated early in life by epigenetic events that lead to cell type specific pathologies, and modulate the interaction between epithelial and sub-epithelial cells. Animal models are only available for remodeling in allergic asthma, but none for non-allergic asthma. In human asthma, the mechanisms leading to airway wall remodeling are not well understood. In order to improve the understanding of this asthma pathology, the definition of “remodeling” needs to be better specified as it summarizes a wide range of tissue structural changes. Second, it needs to be assessed if specific remodeling patterns occur in specific asthma pheno- or endo-types. Third, the interaction of the immune cells with tissue forming cells needs to be assessed in both directions; e.g., do immune cells always stimulate tissue cells or are inflamed tissue cells calling immune cells to the rescue? This review aims to provide an overview on immunologic and non-immunologic mechanisms controlling airway wall remodeling in asthma.

Comparison of Airway Wall Remodeling in Asthma and COPD: Biopsy Findings

Bronchial remodeling is currently known to affect not only patients with asthma, but also COPD patients. Some studies have demonstrated that basement membrane thickening and destruction of the bronchial epithelium are also found in COPD. The aim of the study was to compare the basement membrane thickness (BMT) and epithelial damage in biopsy specimens from patients with asthma and COPD. The study was performed in 20 subjects with asthma and 12 subjects with COPD, who had not been treated with corticosteroids for at least 3 months before study enrollment. Subjects' characteristics were based on the results of clinical assessment, allergic skin-prick tests, lung function testing, and methacholine bronchial challenge. All subjects underwent bronchoscopy with forceps biopsies of bronchial mucosa. Light-microscope and semi-automatic software were used to measure BMT in hematoxylin-eosin stained sections. Total (denudation) and partial epithelial damage were assessed independently by 2 pathologists. The mean BMT in subjects with asthma was 12.54 ± 2.8 μm, and only 7.81 ± 2.0 μm in COPD patients (P < .001). Overall percentage of the basement membrane length lined with damaged epithelium was 45 ± 20% in the asthma group and 47 ± 22% in the COPD group (difference not significant). Complete and partial epithelial damage did not differ between the groups. BMT might be a histopathological parameter helpful in distinguishing asthma and COPD patients, whereas the extent and pattern of epithelial damage is not.

Possible role of differential growth in airway wall remodeling in asthma

Airway remodeling in patients with chronic asthma is characterized by a thickening of the airway walls. It has been demonstrated in previous theoretical models that this change in thickness can have an important mechanical effect on the properties of the wall, in particular on the phenomenon of mucosal folding induced by smooth muscle contraction. In this paper, we present a model for mucosal folding of the airway in the context of growth. The airway is modeled as a bilayered cylindrical tube, with both geometric and material nonlinearities accounted for via the theory of finite elasticity. Growth is incorporated into the model through the theory of morphoelasticity. We explore a range of growth possibilities, allowing for anisotropic growth as well as different growth rates in each layer. Such nonuniform growth, referred to as differential growth, can change the properties of the material beyond geometrical changes through the generation of residual stresses. We demonstrate that differential growth can have a dramatic impact on mucosal folding, in particular on the critical pressure needed to induce folding, the buckling pattern, as well as airway narrowing. We conclude that growth may be an important component in airway remodeling.

S45 Functional KCa3.1 K+ channels are required for human fibrocyte migration

BackgroundFibrocytes are bone marrow-derived CD34+ collagen I+ cells present in peripheral blood that are implicated in the pathogenesis of tissue remodelling and fibrosis in both asthma and pulmonary fibrosis. Ion...

Plasminogen Activation by Airway Smooth Muscle Is Regulated by Type I Collagen

Plasmin, the activated protease product of plasminogen, is involved in collagen remodeling, and is strongly implicated in asthma pathophysiology by recent genome-wide association studies. This study examines plasminogen "activation" by airway smooth muscle cells, and its regulation in a fibrotic environment created by culture on type I collagen and incubation with transforming growth factor (TGF)-β. Urokinase plasminogen activator (uPA) activity was detected in the supernatants of human airway smooth muscle cell cultures maintained in serum-free conditions. Incubation with plasminogen (1.5-50.0 μg/ml, 24 h) increased plasmin activity in a concentration-dependent manner (P < 0.001). uPA activity was higher in cultures maintained on fibrillar type I collagen substrata than in those on plastic, as was plasmin activity after incubation with plasminogen (20 μg/ml). Pretreatment with TGF-β (100 pM) for 18 hours inhibited plasminogen activation by airway smooth muscle cells maintained on plastic, but not on collagen. TGF-β stimulated an increase in the level of uPA mRNA in airway smooth muscle cells grown on collagen, but not on plastic. Reducing the levels of β1-integrin collagen receptor, using interference RNA, attenuated plasmin formation by airway smooth muscle cells grown on collagen, and restored the inhibitory effect of TGF-β. This study shows that airway smooth muscle activation of plasminogen by uPA is accelerated in a collagen-rich environment in which the inhibitory effect of TGF-β is attenuated in association with greater uPA expression induced via β1-integrin signaling. These findings suggest that the plasminogen-activation system involving uPA has the potential to contribute to airway wall remodeling in asthma.

Collagen impairs glucocorticoid actions in airway smooth muscle through integrin signalling

Airway wall remodelling in asthma is characterised by a number of structural changes, including an increase in the volume of airway smooth muscle (ASM), and the abundance of the extracellular matrix (ECM) protein, collagen, is increased. We have investigated the mechanism of collagen-induced glucocorticoid resistance of proliferation, and migration of ASM. ASM cultured from human airways has been seeded on to either type I monomeric collagen or a laminin pentapeptide, YIGSR. The role of alpha2beta1 integrin in the collagen-induced glucocorticoid resistance was investigated using a function blocking monoclonal antibody. Culture of ASM on collagen I, but not laminin, led to a greater proliferative response that was insensitive to regulation by dexamethasone (100 nM). The anti-migratory effects of the glucocorticoid, fluticasone propionate (1 nM) were also impaired by contact of ASM with collagen. The impaired anti-mitogenic action of dexamethasone was associated with a failure to reduce the levels of the rate-limiting cell cycle regulatory protein, cyclin D1. When signalling through the alpha2beta1 integrin was reduced, dexamethasone-mediated reductions in proliferation and cyclin D1 levels were restored. In the collagen-rich microenvironment of the inflamed and fibrotic asthmatic airway, integrin/ECM interactions may contribute to glucocorticoid resistance.

Endogenous laminin is required for human airway smooth muscle cell maturation

BackgroundAirway smooth muscle (ASM) contraction underlies acute bronchospasm in asthma. ASM cells can switch between a synthetic-proliferative phenotype and a contractile phenotype. While the effects of extracellular matrix (ECM) components on modulation of ASM cells to a synthetic phenotype have been reported, the role of ECM components on maturation of ASM cells to a contractile phenotype in adult lung is unclear. As both changes in ECM components and accumulation of contractile ASM are features of airway wall remodelling in asthma, we examined the role of the ECM protein, laminin, in the maturation of contractile phenotype in human ASM cells.MethodsHuman ASM cells were made senescence-resistant by stable expression of human telomerase reverse transcriptase. Maturation to a contractile phenotype was induced by 7-day serum deprivation, as assessed by immunoblotting for desmin and calponin. The role of laminin on ASM maturation was investigated by comparing the effects of exogenous laminin coated on culture plates, and of soluble laminin peptide competitors. Endogenous expression of laminin chains during ASM maturation was also measured.ResultsMyocyte binding to endogenously expressed laminin was required for ASM phenotype maturation, as laminin competing peptides (YIGSR or GRGDSP) significantly reduced desmin and calponin protein accumulation that otherwise occurs with prolonged serum deprivation. Coating of plastic cell culture dishes with different purified laminin preparations was not sufficient to further promote accumulation of desmin or calponin during 7-day serum deprivation. Expression of α2, β1 and γ1 laminin chains by ASM cells was specifically up-regulated during myocyte maturation, suggesting a key role for laminin-2 in the development of the contractile phenotype.ConclusionWhile earlier reports suggest exogenously applied laminin slows the spontaneous modulation of ASM to a synthetic phenotype, we show for the first time that endogenously expressed laminin is required for ASM maturation to the contractile phenotype. As endogenously expressed laminin chains α2, β1 and γ1 are uniquely increased during myocyte maturation, these laminin chains may be key in this process. Thus, human ASM maturation appears to involve regulated endogenous expression of a select set of laminin chains that are essential for accumulation of contractile phenotype myocytes.

Mechanical strain enhances proteoglycan message in fibroblasts from asthmatic subjects.

Remodelling of the asthmatic airway includes increased deposition of proteoglycan (PG) molecules. One of the stimuli driving airway remodelling may be excessive mechanical stimulation. We hypothesized that fibroblasts from asthmatic patients would respond to excessive mechanical strain with up-regulation of message for PGs. We obtained fibroblasts from asthmatic patients (AF) and normal volunteers (NF) using endobronchial biopsy. Cells were maintained in culture until the fifth passage and then grown on a flexible collagen-coated membrane. Using the Flexercell device, cells were then subjected to cyclic stretch at 30% amplitude at 1 Hz for 24 h. Control cells were unstrained. Total RNA was extracted from the cell layer and quantitative RT-PCR performed for decorin, lumican and versican mRNA. In unstrained cells, the expression of decorin mRNA was greater in AF than NF. With strain, NF showed increased expression of versican mRNA and AF showed increased expression of versican and decorin mRNA. The relative increase in versican mRNA expression with strain was greater in AF than NF. These data support the hypothesis that proteoglycan message is increased in asthmatic fibroblasts subject to mechanical strain. This finding has implications for the mechanisms governing airway wall remodelling in asthma.

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

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

Inhibition of chemokine production from human airway smooth muscle cells by fluticasone, budesonide and beclomethasone

Human airway smooth muscle cells (HASMC) contribute to the process of airway wall remodelling in asthma by virtue of their secretory functions. This study was performed to investigate the effectiveness of the commonly used steroids beclomethasone, budesonide and fluticasone in downregulating HASMC production of RANTES and IL-8. HASMC ( n=5) were cultured from dissected bronchi using collagenase digestion. Confluent HASMC were exposed to TNFα and IL-1β (10 ng/ml) for 24 h. All stimulations were set with and without pre-treatment with beclomethasone, budesonide or fluticasone for 2 h at concentrations of 10 −9–10 −6 M. IL-8 and RANTES mRNA expression was assessed by RT-PCR and protein secretion was determined by ELISA. Pre-treatment with beclomethasone, budesonide or fluticasone reduced TNFα- and IL-1β-stimulated IL-8 and RANTES release from HASMC in a dose dependent manner. However, beclomethasone was 22–28% less effective than fluticasone and budesonide in inhibiting chemokine production. TNFα- and IL-1β-induced RANTES and IL-8 expression was reduced on the transcriptional level by pre-treatment with fluticasone and budesonide. The results suggest that the topical steroids fluticasone, budesonide and to a lesser extent beclomethasone may have beneficial effects on airway inflammation in asthma by reducing RANTES and IL-8-induced leukocyte infiltration into the airway wall.

Identification of circulating fibrocytes as precursors of bronchial myofibroblasts in asthma.

The mechanisms contributing to airway wall remodeling in asthma are under investigation to identify appropriate therapeutic targets. Bronchial myofibroblasts would represent an important target because they play a crucial role in the genesis of subepithelial fibrosis, a characteristic feature of the remodeling process, but their origin is poorly understood. We hypothesized that they originate from fibrocytes, circulating cells with the unique characteristic of expressing the hemopoietic stem cell Ag CD34 and collagen I. In this study we show that allergen exposure induces the accumulation of fibrocyte-like cells in the bronchial mucosa of patients with allergic asthma. These cells are CD34-positive; express collagen I and alpha-smooth muscle actin, a marker of myofibroblasts; and localize to areas of collagen deposition below the epithelium. By tracking labeled circulating fibrocytes in a mouse model of allergic asthma, we provide evidence that fibrocytes are indeed recruited into the bronchial tissue following allergen exposure and differentiate into myofibroblasts. We also show that human circulating fibrocytes acquire the myofibroblast phenotype under in vitro stimulation with fibrogenic cytokines that are produced in exaggerated quantities in asthmatic airways. These results indicate that circulating fibrocytes may function as myofibroblast precursors and may contribute to the genesis of subepithelial fibrosis in asthma.

Correlation of Reticular Basement Membrane Thickness and Airway Wall Remodeling in Asthma

Correlation of Reticular Basement Membrane Thickness and Airway Wall Remodeling in Asthma

The relationship of reticular basement membrane thickness to airway wall remodeling in asthma.

Assessment of airway wall remodeling in asthma is difficult in vivo. The thickness of deposited extracellular matrix proteins below the epithelium, the reticular basement membrane, can be assessed by bronchial biopsy of proximal airways. The aim of this study was to determine the relationship between the thickness of the reticular basement membrane in a sample equivalent to a central airway biopsy and the dimensions of the airway wall measured on transverse sections of both central and peripheral airways. Large and small cartilaginous and membranous airways from persons who had died from asthma (fatal asthma, n = 5) or from nonrespiratory causes with asthma (nonfatal asthma, n = 5) or without asthma (control subjects, n = 5) were studied. Reticular basement membrane thickness correlated with the percentage of smooth muscle, submucosal mucous gland, and inner wall area (p < 0.05) in large cartilaginous airways, and with inner wall area and area of smooth muscle (p < 0.01) in small cartilaginous airways, but was not related to airway wall dimensions in membranous airways. These findings show that reticular basement membrane thickness of central airways, which may be assessed by endobronchial biopsy, is correlated with airway remodeling in cartilaginous airways but not with airway wall dimensions of membranous airways.

Reduced airway distensibility, fixed airflow limitation, and airway wall remodeling in asthma.

The airways of individuals with asthma are less distensible than normal and it has been assumed that this may be due to airway remodeling associated with chronic inflammation, although there are currently no available data directly relating these two aspects of asthma. We have therefore carried out a study of the relationship between airway distensibility (DeltaVD) and subepithelial reticular basement membrane (RBM) thickening as an index of airway remodeling, in a group of patients with relatively mild but symptomatic asthma. Our methods included a cross-sectional study of DeltaVD in patients with mild to moderate atopic asthma, with matched airway biopsy for structural components. We confirmed that DeltaVD was lower in patients with asthma than in normal individuals (19.8 +/- 1.1 versus 24.1 +/- 1.5; p < 0.05) and that RBM thickness was increased in patients with asthma (9.1 +/- 2.2 versus 7.7 +/- 1.2 microm; p < 0.01). There was a negative correlation between DeltaVD and RBM thickness in asthma (r = -0.37, p = 0.03) and positive correlations between percent predicted postbronchodilator large and small airway function (for percent predicted FEV(1 )versus DeltaVD, r = 0.59, p < 0.001). We conclude that, cross-sectionally, DeltaVD was related to airway remodeling (RBM thickening) and airflow limitation (percent predicted large and small airway function). Our findings support the hypothesis that DeltaVD is a physiologic test that is reflective of airway remodeling.

The bronchial microcirculation in asthma.

Airway wall remodelling in asthma involves a number of changes including increased vascularity, vasodilation and microvascular leakage. Evidence suggests that the number and size of bronchial vessels is increased in patients with asthma compared with normal controls. In particular, there may be increased numbers of vessels in patients with fatal asthma. Treatment with inhaled corticosteroids is now known to reduce this vascularity. Bronchial vessels may undergo proliferation in response to inflammatory stimuli. Many factors can induce angiogenesis including a range of mediators and growth factors. Others can cause a vascular response by causing vasodilation and microvascular leakage. Airway wall oedema is likely to be important in asthma but has not yet been quantified. It is thought that mast cells play a key role in modulating these vascular remodelling changes by releasing cytokines and growth factors. Many key issues remain to be resolved before we fully understand the role of the bronchial microcirculation in asthma. In the future, novel therapies may be directed towards angiogenesis, vasodilation and microvascular leakage.

Cartilaginous airway dimensions and airflow obstruction in human lungs.

Airway wall remodeling in asthma and chronic obstructive pulmonary disease (COPD) can have a profound effect on the function of the airways. We tested the hypothesis that airflow obstruction and estimates of peripheral airway inflammation correlate with airway wall thickness and the amount of bronchial smooth muscle in cartilaginous airways. In addition, we estimated the theoretical relation between airway dimensions and airway resistance with a computational model. Lung tissue was obtained from 72 patients with different degrees of COPD who were operated on for a solitary peripheral lung lesion. In 341 transversely cut cartilaginous airway sections we measured airway size and airway wall dimensions. Inflammatory changes from the same lungs were scored in noncartilaginous airways. Preoperatively measured maximum expiratory flows and the response to a bronchodilator were correlated with airway wall dimensions. Maximum expiratory flow, the reversibility of airflow obstruction, and peripheral airway inflammation were significantly related to the airway wall area but not to the smooth muscle area. We conclude that airflow obstruction and its reversibility in COPD is in part caused by thickening of the cartilaginous airway wall and is related to inflammatory changes.

Regulation of Airway Wall Remodeling: Prospects for the Development of Novel Antiasthma Drugs

Publisher Summary This chapter describes the evidence for airway wall remodeling in asthma, discusses the pathogenesis of these changes, and identify potential therapeutic approaches to arresting the remodeling process. There is a clear requirement for the development of methodology that allows assessment of airway wall thickening because of smooth muscle hyperplasia/hypertrophy in living subjects. This is expected to facilitate studies examining therapeutic interventions to determining the reversibility of the remodeling process. Also the intracellular signaling pathways that subserve airway smooth muscle proliferation have not been fully defined nor have the key endogenous mitogens been identified. The difficulty in proposing intracellular signaling as a useful target for antiasthma drugs that would prevent airway wall remodeling is in the potential lack of specificity. It seems likely that many of the signals used by airway smooth muscle cells in the transduction of proliferative stimuli can also be common to other cell types. Further studies to elucidate the precise signaling cascade used by this cell type are required to identify whether unique regulatory sites exist. Characterization of phenotypic modulation in airway smooth muscle cells may reveal novel ways of reducing proliferative responses. If airway smooth muscle cells switch to the synthetic phenotype prior to cell-cycle progression, as do vascular smooth muscle cells, then blocking such phenotypic changes could prevent proliferation in a specific manner. Each of the elements of the airway wall remodeling process may be considered as a target for therapeutic intervention. The acute changes are likely to respond to existing anti-inflammatory treatments for asthma, primarily glucocorticoids.