metalloproteinase (MMP) enzymes MMP-3 and MMP-9 have relevance to the
chronic structural airway changes in asthma. These proteinases can be
generated by structural and inflammatory cells, and have the ability to
degrade proteoglycans and thus potentially enhance airway fibrosis and
smooth muscle proliferation through their ability to release and
activate latent matrix bound growth factors.
for MMP-3 and MMP-9 as well as for mast cells, eosinophils, and
neutrophils was undertaken in acetone fixed and glycolmethacrylate
embedded endobronchial biopsy specimens obtained by fibreoptic
bronchoscopy under local anaesthesia. The findings from 17 asthmatic subjects (nine with mild to moderate non-steroid treated
asthma and eight with chronic persistent steroid-dependent asthma) were
compared with those from eight healthy controls. The cell associated
MMP immunoreactivity was co-localised to mast cells, eosinophils, or
neutrophils and represented as cells/mm2, based on the area
of the biopsy specimen. Extracellular matrix immunoreactivity was
assessed by an image analysis system and visually with ranking and the
two approaches were compared.
specimens from asthmatic subjects contained significantly more
eosinophils (p<0.001) than those from the non-asthmatic subjects. Both
MMP-9 and MMP-3 immunoreactivity could be identified in endobronchial
biopsy specimens. Gelatinase B (MMP-9) immunoreactivity was prominent
within the extracellular matrix as well as exhibiting distinct cell
immunoreactivity which predominantly co-localised to neutrophils.
Stromelysin (MMP-3) was co-localised to mast cells, eosinophils, and
neutrophils as well as being present in the epithelium, the lamina
reticularis and, to a lesser extent, the extracellular matrix. There
was no significant difference in the extent of matrix immunoreactivity
for either MMP-3 or MMP-9 between healthy controls or subjects with
mild or severe asthma.
immunostaining cannot distinguish between active and inactive forms of
MMPs, the presence of MMP-3 and MMP-9 within endobronchial biopsy
specimens, the co-localisation to inflammatory cells of relevance to
asthma (mast cells and eosinophils), and the identification of matrix
binding, indicative of MMP-matrix interactions, points to the potential
for disease related changes in MMP release that influence airway
remodelling in asthma.
The characteristics of human asthma are chronic inflammation and airway remodeling. Hyaluronan (HA), a major extracellular matrix component, accumulates during inflammatory lung diseases including asthma. Hyaluronan fragments stimulate macrophages to produce inflammatory cytokines. We hypothesized that HA and its receptors would play a role in human asthma.
To investigate the role of HA and HA binding proteins in human asthma.
Twenty-one subjects with asthma and 25 normal control subjects underwent bronchoscopy with endobronchial biopsy and bronchoalveolar lavage (BAL). Fibroblasts were cultured, HA and HA synthase expression was determined at baseline and after exposure to several mediators relevant to asthma pathobiology. The expression of HA binding proteins, CD44, TLR2 and TLR4 on BAL macrophages was determined by flow cytometry. IL-8 production by macrophages in response to HA fragment stimulation was compared.
Airway fibroblasts from asthma patients produced significantly increased concentrations of lower molecular weight HA compared to those of normal fibroblasts. Hyaluronan synthase 2 mRNA was markedly increased in asthmatic fibroblasts. Asthmatic macrophages showed a decrease in cell surface CD44 expression and an increase in TLR2 and TLR4 expression. Macrophages from asthmatic subjects showed an increase in responsiveness to low molecular weight HA stimulation, as demonstrated by increased IL-8 production.
HA homeostasis is deranged in asthma with increased production by fibroblasts and decreased CD44 expression on alveolar macrophages. Upregulation of TLR2 and TLR4 on macrophages with increased sensitivity to HA fragments suggests a novel pro-inflammatory mechanism by which persistence of HA fragments could contribute to chronic inflammation and airway remodeling in asthma.
Asthma; Hyaluronan; Cytokines; Fibroblasts; Macrophages
Background: Obliterative bronchiolitis in chronic rejection of lung allografts is characterised by airway epithelial damage and fibrosis. The process whereby normal epithelium is lost and replaced by fibroblastic scar tissue is poorly understood, but recent findings suggest that epithelial cells can become fibroblasts through epithelial-mesenchymal transition (EMT). It is hypothesised that EMT occurs in lung allografts and plays a potential role in airway remodelling.
Methods: Sixteen stable lung transplant recipients underwent bronchoscopy with bronchoalveolar lavage (BAL), endobronchial biopsies, and bronchial brushings. Biopsy sections were stained for the fibroblast marker S100A4. Brushings were cultured on collagen, stained with anti-S100A4, and examined for further EMT markers including matrix metalloproteinase (MMP) zymographic activity and epithelial invasion through collagen coated filters.
Results: A median 15% (0–48%) of the biopsy epithelium stained for S100A4 in stable lung transplant recipients and MMP-7 co-localisation was observed. In non-stimulated epithelial cultures from lung allografts, S100A4 staining was identified with MMP-2 and MMP-9 production and zymographic activity. MMP total protein and activity was increased following stimulation with transforming growth factor (TGF)-ß1. Non-stimulated transplant epithelial cells were invasive and penetration of collagen coated filters increased following TGF-ß1 stimulation.
Conclusions: This study provides evidence of EMT markers in lung allografts of patients without loss of lung function. The EMT process may represent a final common pathway following injury in more common diseases characterised by airway remodelling.
To prospectively apply an automated, quantitative 3-D approach to imaging and airway analysis to assess airway remodeling in asthma.
Using the Pulmonary Workstation (VIDA Diagnostics) that enables quantitative airway segment measurements of low-dose, thin section (0.625-1.25 mm) multidetector-row CT (MDCT), we compared airway wall thickness (WT) and area (WA) in 123 subjects participating in a prospective multicenter cohort study, NIH Severe Asthma Research Program (SARP): severe asthma (n=63), mild-moderate asthma (n=35), and normal (n=25). A subset of these subjects underwent fiberoptic bronchoscopy and endobronchial biopsies (n=32). WT and WA were corrected for total airway diameter and area - WT%, WA%.
Subjects with severe asthma had significantly greater WT% than mild-moderate asthma and normals [17.2±1.5 v 16.5±1.6, p=0.014 and 16.3±1.2, p=0.031, respectively] and greater WA% compared to mild-moderate asthma and normal [56.6±2.9 v 54.7±3.3, p=.005 and 54.6±2.4, p=0.003, respectively]. Both WT% and WA% were inversely correlated with baseline FEV1% (r=-0.39, p<0.0001 and -0.40, p<0.0001, respectively) and positively correlated with response to bronchodilator (r=0.28, p=0.002 and r=0.35, p<0.0001, respectively). Airway epithelial thickness on biopsy correlated with WT% (r=0.47, p=0.007) and WA% (r=0.52, p=0.003). In the same individual, there is considerable regional heterogeneity in airway wall thickness.
Severe asthmatics have thicker airway walls on MDCT than mild asthmatics or normals, which correlates with pathologic measures of remodeling and the degree of airflow obstruction. MDCT may be a useful technique for assessing airway remodeling in asthma, but overlap among groups limits the diagnostic value in individual subjects.
Asthma; airway remodeling; chest CT
Rationale: Excessive deposition of extracellular matrix occurs in proximal airways of individuals with asthma, but fibrosis in distal lung has not been observed. Whether differing fibrotic capacities of fibroblasts from these two regions contribute to this variability is unknown.
Objectives: We compared morphologic and functional characteristics of fibroblasts isolated from proximal airways and distal lung parenchyma to determine phenotypic differences.
Methods: Concurrent proximal airway and distal lung biopsies were obtained by bronchoscopy from subjects with asthma to isolate airway and distal lung fibroblasts, respectively. The following characteristics were compared: morphology, proliferation, α-smooth muscle actin expression, and synthesis of procollagen type I and eotaxin-1.
Results: Airway fibroblasts (AFs) are morphologically distinct from distal lung fibroblasts (DLFs): they are larger (2.3-fold greater surface area vs. matched DLFs; p = 0.02), stellate in appearance, and with more cytoplasmic projections compared with the spindle-shaped DLFs. AFs synthesized more procollagen type I than did DLFs at baseline (twofold higher; p = 0.003) and after transforming growth factor-β stimulation (1.4-fold higher; p = 0.02). Similarly, AFs produced more eotaxin-1 than did DLFs at baseline (2.5-fold higher; p = 0.004) and after interleukin-13 stimulation (13-fold higher; p = 0.0001). In contrast, DLFs proliferate more than AFs with serum stimulation (about sixfold greater; p = 0.03). Unstimulated DLFs also expressed more α-smooth muscle actin than did corresponding AFs (p = 0.006).
Conclusions: These studies suggest that at least two phenotypes of fibroblast exist in the lung. These phenotypic differences may partially explain the variable responses to injury and repair between proximal airways and distal lung/parenchyma in asthma and other respiratory diseases.
asthma; fibroblast; interleukin 13; remodeling; transforming growth factor β
Rationale: Airway smooth muscle (SM) of patients with asthma exhibits a greater velocity of shortening (Vmax) than that of normal subjects, and this is thought to contribute to airway hyperresponsiveness. A greater Vmax can result from increased myosin activation. This has been reported in sensitized human airway SM and in models of asthma. A faster Vmax can also result from the expression of specific contractile proteins that promote faster cross-bridge cycling. This possibility has never been addressed in asthma.
Objectives: We tested the hypothesis that the expression of genes coding for SM contractile proteins is altered in asthmatic airways and contributes to their increased Vmax.
Methods: We quantified the expression of several genes that code for SM contractile proteins in mild allergic asthmatic and control human airway endobronchial biopsies. The function of these contractile proteins was tested using the in vitro motility assay.
Measurements and Main Results: We observed an increased expression of the fast myosin heavy chain isoform, transgelin, and myosin light chain kinase in patients with asthma. Immunohistochemistry demonstrated the expression of these genes at the protein level. To address the functional significance of this overexpression, we purified tracheal myosin from the hyperresponsive Fisher rats, which also overexpress the fast myosin heavy chain isoform as compared with the normoresponsive Lewis rats, and found a faster rate of actin filament propulsion. Conversely, transgelin did not alter the rate of actin filament propulsion.
Conclusions: Selective overexpression of airway smooth muscle genes in asthmatic airways leads to increased Vmax, thus contributing to the airway hyperresponsiveness observed in asthma.
asthma; airway hyperresponsiveness; gene expression; smooth muscle; myosin
Background: Airway remodelling is a characteristic feature of chronic asthma and there is evidence that an airway imbalance between levels of matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinases-1 (TIMP-1) is associated with airway remodelling. On this basis, we hypothesised that polymorphisms in the MMP-9 and TIMP-1 genes were associated with the disease process.
Methods: A number of MMP-9 and TIMP-1 gene polymorphisms were examined in an adult white Australian population of mild (n = 259), moderate (n = 213) and severe (n = 71) asthmatics and non-asthmatic controls (n = 406) using PCR-RFLP and PCR-SSCP analyses.
Results: MMP-9 –1562C>T and 836G>A (Arg279Gln) were not associated with asthma (p⩾0.15) or asthma severity (p⩾0.13), and TIMP-1 434T>C (Phe124Phe) was not associated with asthma in women (p = 0.094) or men (p = 0.207). In this population, MMP-9 –861C>T and TIMP-1 323C>T (Pro87Pro) were not informative (with minor allele frequencies of <1%), and MMP-9 –1702T>A and TIMP-1 595C>T (Ser178Phe) were not detectable. However, a novel polymorphism was detected in the TIMP-1 gene 536C>T (Ile158Ile) which was significantly associated with asthma in women (p = 0.011; OR = 5.54, 95% CI 1.66 to 34.4) but not in men (p = 1.0). 536C>T was found to be in linkage disequilibrium with 434T>C, and haplotype analysis supported an association with asthma (p = 0.014).
Conclusions: This is the first reported association between a polymorphism in the TIMP-1 gene and asthma, and supports the hypothesis that the protease/antiprotease balance has an important role in this common disease.
Genetic variants influencing lung function or immune system may be involved in the development of asthma and/or its symptoms. Matrix metalloproteinases (MMPs) contribute to both normal and pathological tissue remodeling and also act as regulatory molecules by processing cytokines or adhesion molecules. In animal models, growing evidences suggest that MMPs play important roles in asthma phenotypes. Some MMP genes (e.g. MMP-9 and MMP-12) have recently been shown to be associated with asthma in Caucasian populations. We investigated whether single nucleotide polymorphisms (SNPs) in MMP-7 and MMP-12 could affect the susceptibility to and clinical phenotypes of asthma in the Japanese population.
We conducted a case-control study between SNPs in MMP-7 and MMP-12 genes and asthma-related phenotypes using childhood and adult Japanese populations (653 childhood asthma patients and 423 controls, and 428 adult asthma patients and 646 controls, respectively). To investigate the effects of amino acid substitutions by SNPs on MMPs' enzymatic activity, MMP activity assays were performed using commercially available kits based on fluorescence resonance energy transfer (FRET) peptide. We also evaluated the effect of 3’UTR SNP in MMP-7 on its mRNA stability and the effect of SNP in MMP-12 on its antimicrobial activity.
We found that, in the Japanese population, SNPs of MMP-7 (rs10502001, G/A, Arg77His; rs14983, C/T, 3’UTR) (P = 0.006; odds ratio (OR), 1.46; 95% confidential interval (CI), 1.126-1.903) and MMP-12 (rs652438, A/G, Asn357Ser) (P = 0.015; OR, 1.60; 95% CI, 1.002-2.556) showed significant association with adult and childhood asthma, respectively. We also found that the SNP (rs652438) in MMP-12 was associated with severity in adult asthma (P = 0.010). Using supernatant from cultured HEK293 cells stably transfected with the pcDNA3.1(+)-MMP-7 or MMP-12 as MMP proteins, we evaluated activation kinetics, rate of proteolytic cleavage of FRET peptide, Michaelis constant, and substrate specificity of the enzyme. In this system, we couldn't detect the functional effects of amino acid substitutions by SNPs on the enzymatic activity.
Our association study suggested that genetic variants of MMP7 and MMP12 conferred risk for development of asthma in the Japanese population.
Airway wall remodelling and inflammation are features of chronic asthma. Transforming growth factor β (TGF‐β) has been implicated in these processes.
To determine the effect of allergen challenge on airway inflammation and remodelling and whether TGF‐β isoforms and the Smad signalling pathways are involved.
Thirteen patients with atopic asthma underwent inhalational challenge with 0.9% saline, followed by allergen 3–4 weeks later. After both challenges, fibreoptic bronchoscopy was undertaken to obtain bronchial biopsies and tissue samples were processed for immunohistochemistry and examined by microscopy.
Forced expiratory volume in 1 s (FEV1) fell after allergen challenge (mean (SE) −28.1 (0.9)% at 30 min with a late response at 7 hours (−23.0 (1.2)%). Allergen challenge caused an increase in neutrophils and eosinophils in the bronchial mucosa compared with saline. Sub‐basement membrane (SBM) thickness did not change after allergen, but tenascin deposition in SBM was increased. Intranuclear (activated) Smad 2/3 and Smad 4 detected by immunohistochemistry were increased after allergen challenge in epithelial and subepithelial cells of bronchial biopsies. No inhibitory Smad (Smad 7) protein was detected. TGF‐β isoforms 1, 2 and 3 were expressed predominantly in bronchial epithelium after saline and allergen challenges, but only TGF‐β2 expression was increased after allergen. Double immunostaining showed an increase in TGF‐β2 positive eosinophils and neutrophils but not in TGF‐β1 positive eosinophils and neutrophils after allergen challenge.
TGF‐β2 may contribute to the remodelling changes in allergic asthma following single allergen exposure.
Chronic obstructive pulmonary disease (COPD) is characterized by chronic inflammation and structural alterations (ie, tissue remodeling) throughout the conducting airways, parenchyma, and pulmonary vasculature. Matrix metalloproteinases (MMPs) are extracellular degrading enzymes that play a critical role in inflammatory cell infiltration and tissue remodeling, but the influence of the agents that are used for the treatment of COPD on the production of MMPs is not well understood.
The present study aimed to examine the influence of tiotropium bromide hydrate (TBH) on the production of MMPs from lung fibroblasts (LFs) induced by transforming growth factor (TGF)-β in vitro.
LFs, at a concentration of 5 × 105 cells·mL−1, were stimulated with TGF-β in the presence of various concentrations of TBH. MMP-1 and MMP-2 levels in culture supernatants were examined by enzyme-linked immunosorbent assay (ELISA), and MMP messenger ribonucleic acid (mRNA) expression was examined by real-time polymerase chain reaction (RT-PCR). The influence of TBH on TGF-β signaling pathways was also analyzed by examining Smad activation and signaling protein phosphorylation by ELISA.
TBH at more than 15 pg·mL−1 inhibited the production of MMP-1 and MMP-2, but not tissue inhibitor of matrix metalloproteinase (TIMP)-1 and TIMP-2, from LFs, after TGF-β stimulation. TBH also suppressed MMP mRNA expression through the inhibition of Smad activation and signaling protein, extracellular-signal-regulated kinase (ERK) 1 and 2, and c-Jun N-terminal kinase (JNK), phosphorylation.
These results may suggest that TBH suppresses MMP production from LFs, through interference of TGF-β-mediated signaling pathways and results in favorable modification of the clinical status of COPD.
tiotropium bromide; matrix metalloproteinases; lung fibroblast; TGF-β; inhibition; in vitro
Airway remodelling is thought to be under the control of a complex group of molecules belonging to the Transforming Growth Factor (TGF)-superfamily. The Bone Morphogenetic Proteins (BMPs) belong to this family and have been shown to regulate fibrosis in kidney and liver diseases. However, the role of BMPs in lung remodelling remains unclear. BMPs may regulate tissue remodelling in asthma by controlling TGF-β-induced profibrotic functions in lung fibroblasts.
Cell cultures were exposed to TGF-β1 alone or in the presence of BMP-4 or BMP-7; control cultures were exposed to medium only. Cell proliferation was assessed by quantification of the incorporation of [3H]-thymidine. The expression of the mRNA encoding collagen type I and IV, tenascin C and fibronectin in normal human lung fibroblasts (NHLF) was determined by real-time quantitative PCR and the main results were confirmed by ELISA. Cell differentiation was determined by the analysis of the expression of α-smooth muscle actin (α-SMA) by western blot and immunohistochemistry. The effect on matrix metalloproteinase (MMP) activity was assessed by zymography.
We have demonstrated TGF-β1 induced upregulation of mRNAs encoding the extracellular matrix proteins, tenascin C, fibronectin and collagen type I and IV when compared to unstimulated NHLF, and confirmed these results at the protein level. BMP-4, but not BMP-7, reduced TGF-β1-induced extracellular matrix protein production. TGF-β1 induced an increase in the activity of the pro-form of MMP-2 which was inhibited by BMP-7 but not BMP-4. Both BMP-4 and BMP-7 downregulated TGF-β1-induced MMP-13 release compared to untreated and TGF-β1-treated cells. TGF-β1 also induced a myofibroblast-like transformation which was partially inhibited by BMP-7 but not BMP-4.
Our study suggests that some regulatory properties of BMP-7 may be tissue or cell type specific and unveil a potential regulatory role for BMP-4 in the regulation of lung fibroblast function.
Little is known about vitamin D status and its effect on asthma pathophysiology in children with severe, therapy-resistant asthma (STRA).
Relationships between serum vitamin D, lung function, and pathology were investigated in pediatric STRA.
Serum 25-hydroxyvitamin D [25(OH)D3] was measured in 86 children (mean age, 11.7 yr): 36 with STRA, 26 with moderate asthma (MA), and 24 without asthma (control subjects). Relationships between 25(OH)D3, the asthma control test (ACT), spirometry, corticosteroid use, and exacerbations were assessed. Twenty-two of 36 children with STRA underwent fiberoptic bronchoscopy, bronchoalveolar lavage, and endobronchial biopsy with assessment of airway inflammation and remodeling.
Measurements and Main Results
25(OH)D3 levels (median [IQR]) were significantly lower in STRA (28 [22–38] nmol/L) than in MA (42.5 [29–63] nmol/L) and control subjects (56.5 [45–67] nmol/L) (P < 0.001). There was a positive relationship between 25(OH)D3 levels and percent predicted FEV1 (r = 0.4, P < 0.001) and FVC (r = 0.3, P = 0.002) in all subjects. 25(OH)D3 levels were positively associated with ACT (r = 0.6, P < 0.001), and inversely associated with exacerbations (r=−0.6, P < 0.001) and inhaled steroid dose (r=−0.39, P = 0.001) in MA and and STRA. Airway smooth muscle (ASM) mass, but not epithelial shedding or reticular basement membrane thickness, was inversely related to 25(OH)D3 levels (r=−0.6, P = 0.008). There was a positive correlation between ASM mass and bronchodilator reversibility (r = 0.6, P = 0.009) and an inverse correlation between ASM mass and ACT (r = −0.7, P < 0.001).
Lower vitamin D levels in children with STRA were associated with increased ASM mass and worse asthma control and lung function. The link between vitamin D, airway structure, and function suggests vitamin D supplementation may be useful in pediatric STRA.
vitamin D; asthma; remodeling; airway smooth muscle; pediatrics
Airway wall remodelling and inflammation are features of chronic asthma. Transforming growth factor β (TGF-β) has been implicated in these processes.
We determined the effect of allergen challenge on airway inflammation and remodelling and whether TGF-β isoforms and the Smad signalling pathways were involved.
Thirteen atopic asthmatics underwent inhalational challenge with 0.9% saline (SC), followed by allergen (AC) 3-4 weeks later. After both challenges, fiberoptic bronchoscopy was undertaken in order to obtain bronchial biopsies and tissue samples were processed for immunohistochemistry and examined by microscopy.
FEV1 fell after AC (−28.1 % ± 0.92, mean ± SEM, at 30 minutes) with a late response at 7 hours (−23.0% ± 1.23). AC caused an increase in neutrophils (p=0.016) and eosinophils (p=0.01) in the bronchial mucosa when compared with SC. Sub-basement membrane (SBM) thickness did not change after AC, but tenascin deposition in SBM was increased (p=0.02). Intranuclear (activated) Smad 2/3 and Smad 4 detected by immunohistochemistry were increased after AC in epithelial and subepithelial cells of bronchial biopsies. No inhibitory Smad (Smad 7) protein was detected. TGF-β isoforms 1, 2 and 3 were expressed predominantly in bronchial epithelium both after saline or allergen, but only TGF-β2 expression was increased after AC (p=0.03). Using double-immunostaining, an increase in TGF-β2-positive eosinophils (p=0.01) and neutrophils (p=0.04), but not in TGF-β1 positive eosinophils and neutrophils, was also found after AC.
TGF-β2 may contribute to the remodelling changes in allergic asthma following single allergen exposure; further detailed studies will be needed.
Asthma wall remodelling; allergen challenge; transforming growth factor-beta isoforms
Matrix metalloproteinases (MMPs) modulate development, inflammation, and repair in lungs. Tissue inhibitors of MMPs (TIMPs) interact with MMPs, controlling the intensity and nature of the response to injury. Absence of MMP-9, -2, and -8 activities is associated with altered lung inflammation during allergic sensitization. To test the hypothesis that the absence of TIMP-1 enhances allergic lung inflammation, airway hyperreactivity (AHR), and lung remodeling in asthma, we studied TIMP-1 null (TIMP-1 KO) mice and their WT controls using an ovalbumin (OVA) asthma model. TIMP-1 KO mice, compared to WT controls, developed an asthma phenotype characterized by AHR, pronounced cellular lung infiltrates, greater reduction in lung compliance, enhanced Th2 cytokine mRNA and protein expression, and altered collagen lung content associated with enhanced MMP-9 activity. Our findings support the hypothesis that TIMP-1 plays a protective role by preventing AHR and modulating inflammation, remodeling, and cytokine expression in an animal model of asthma.
Asthma; Bronchial hyperreactivity; TIMP-1; MMPs; Airway remodeling; Intercellular matrix
Rationale: Despite long-term therapy with corticosteroids, patients with severe asthma develop irreversible airway obstruction.
Objectives: To evaluate if there are structural and functional differences in the airway epithelium in severe asthma associated with airway remodeling.
Methods: In bronchial biopsies from 21 normal subjects, 11 subjects with chronic bronchitis, 9 subjects with mild asthma, and 31 subjects with severe asthma, we evaluated epithelial cell morphology: epithelial thickness, lamina reticularis (LR) thickness, and epithelial desquamation. Levels of retinoblastoma protein (Rb), Ki67, and Bcl-2 were measured, reflecting cellular proliferation and death. Terminal deoxynucleotidyl-mediated dUTP nick end labeling (TUNEL) was used to study cellular apoptosis.
Measurements and Main Results: Airway epithelial and LR thickness was greater in subjects with severe asthma compared with those with mild asthma, normal subjects, and diseased control subjects (p = 0.009 and 0.033, respectively). There was no significant difference in epithelial desquamation between groups. Active, hypophosphorylated Rb expression was decreased (p = 0.002) and Ki67 was increased (p < 0.01) in the epithelium of subjects with severe asthma as compared with normal subjects, indicating increased cellular proliferation. Bcl-2 expression was decreased (p < 0.001), indicating decreased cell death suppression. There was a greater level of apoptotic activity in the airway biopsy in subjects with severe asthma as compared with the normal subjects using the TUNEL assay (p = 0.002), suggesting increased cell death.
Conclusions: In subjects with severe asthma, as compared with subjects with mild asthma, normal subjects, and diseased control subjects, we found novel evidence of increased cellular proliferation in the airway contributing to a thickened epithelium and LR. These changes may contribute to the progressive decline in lung function and airway remodeling in patients with severe asthma.
epithelium; desquamation; airflow obstruction
The asthma susceptibility gene, a disintegrin and metalloprotease-33 (ADAM33), is selectively expressed in mesenchymal cells, and the activity of soluble ADAM33 has been linked to angiogenesis and airway remodeling. Transforming growth factor (TGF)-β is a profibrogenic growth factor, the expression of which is increased in asthma, and recent studies show that it enhances shedding of soluble ADAM33. In this study, we hypothesized that TGF-β also affects ADAM33 expression in bronchial fibroblasts in asthma. Primary fibroblasts were grown from bronchial biopsies from donors with and those without asthma, and treated with TGF-β2 to induce myofibroblast differentiation. ADAM33 expression was assessed using quantitative RT-PCR and Western blotting. To examine the mechanisms whereby TGF-β2 affected ADAM33 expression, quantitative methylation-sensitive PCR, chromatin immunoprecipitation, and nuclear accessibility assays were conducted on the ADAM33 promoter. We found that TGF-β2 caused a time- and concentration-dependent reduction in ADAM33 mRNA expression in normal and asthmatic fibroblasts, affecting levels of splice variants similarly. TGF-β2 also induced ADAM33 protein turnover and appearance of a cell-associated C-terminal fragment. TGF-β2 down-regulated ADAM33 mRNA expression by causing chromatin condensation around the ADAM33 promoter with deacetylation of histone H3, demethylation of H3 on lysine-4, and hypermethylation of H3 on lysine-9. However, the methylation status of the ADAM33 promoter did not change. Together, these data suggest that TGF-β2 suppresses expression of ADAM33 mRNA in normal or asthmatic fibroblasts. This occurs by altering chromatin structure, rather than by gene silencing through DNA methylation as in epithelial cells. This may provide a mechanism for fine regulation of levels of ADAM33 expression in fibroblasts, and may self-limit TGF-β2–induced ectodomain shedding of ADAM33.
a disintegrin and metalloprotease-33; myofibroblast; transforming growth factor-β; histone modification
Background: The most characteristic structural change evident in endobronchial biopsies in asthma, even in mild disease, is subepithelial collagen deposition within the lamina reticularis. This has been associated with progressive loss of lung function and the persistence of airway hyperresponsiveness, and has been linked to airway fibroblast proliferation. A potent fibroproliferative factor in bronchoalveolar lavage fluid in asthma is fibroblast growth factor-2 (FGF-2). FGF-2 is a member of a family of heparin binding growth factors that bind to heparan sulphate proteoglycans (HSPG), an important determinant of FGF-2 activity. This study compared the level of expression and distribution of FGF-2 in relation to HSPG in bronchial tissue from normal and asthmatic subjects.
Methods: The distribution of FGF-2 and HSPG in intact and cleaved forms in endobronchial biopsies from normal and asthmatic subjects was examined using an immunohistochemical approach. A novel ELISA based method was developed to detect solubilisation of FGF-2 following addition of heparin and heparitinase to bronchial tissue slices.
Results: Immunohistochemical analysis showed that FGF-2 was co-localised to HSPG in epithelial and endothelial basement membranes. Epithelial FGF-2, but not HSPG, was significantly more abundant in patients with mild asthma than in normal subjects. In vitro experiments indicated that FGF-2 was released from binding sites in the tissue by heparin and heparitinase I.
Conclusions: FGF-2 is bound by HSPG in bronchial tissue. The mast cell, through the release of heparin and endoglycosidase, may make a unique contribution to tissue remodelling in allergic asthma.
Rationale: Aberrant airway smooth muscle cell (ASMC) function and overexpression of transforming growth factor (TGF)-β, which modulates ASMC proliferative and inflammatory function and induces oxidant release, are features of asthma. Nuclear factor E2-related factor 2 (Nrf2) activates antioxidant genes conferring protection against oxidative stress.
Objectives: To determine the role of Nrf2 in ASMCs and its modulation by TGF-β, and compare Nrf2 activity in ASMCs from subjects with severe and nonsevere asthma and healthy subjects.
Methods: ASMCs were cultured from airways of subjects without asthma, and from airway biopsies from patients with severe and nonsevere asthma. We studied Nrf2 activation on antioxidant gene expression and proliferation, the effect of TGF-β on Nrf2 transcriptional activity, and the impact of Nrf2 activation on TGF-β–mediated proliferation and IL-6 release. Nrf2–antioxidant response elements binding and Nrf2-dependent antioxidant gene expression was determined in asthmatic ASMCs.
Measurements and Main Results: Activation of Nrf2 led to up-regulation of the antioxidant genes heme oxygenase (HO)-1, NAD(P)H:quinone oxidoreductase, and manganese superoxide dismutase, and a reduction in proliferation. TGF-β reduced Nrf2-mediated antioxidant gene transcription through induction of activating transcription factor-3 expression. Nrf2 activation attenuated TGF-β–mediated reduction in HO-1, ASMC proliferation, and IL-6 release. Nrf2–antioxidant response elements binding was reduced in ASMCs from patients with severe asthma compared with ASMCs from patients with nonsevere asthma and normal subjects. HO-1 expression was reduced in ASMCs from patients with both nonsevere and severe asthma compared with healthy subjects.
Conclusions: Nrf2 regulates antioxidant responses and proliferation in ASMCs and is inactivated by TGF-β. Nrf2 reduction may underlie compromised antioxidant protection and aberrant ASM function in asthma.
asthma; airway smooth muscle; nuclear factor E2-related factor 2; transforming growth factor-β; antioxidant
Transforming growth factor-β (TGF-β) is thought to play a role in the pathobiological progression of ovarian cancer because this peptide hormone is overexpressed in cancer tissue, plasma, and peritoneal fluid. In the current study, we investigated the role of the TGF-β/Smad3 pathway in ovarian cancer metastasis by regulation of an epithelial-to-mesenchymal transition. When cancer cells were cultured on plastic, TGF-β1, TGF-β2, and TGF-β3 induced pro–matrix metalloproteinase (MMP) secretion, loss of cell-cell junctions, down-regulation of E-cadherin, up-regulation of N-cadherin, and acquisition of a fibroblastoid phenotype, consistent with an epithelial-to-mesenchymal transition. Furthermore, Smad3 small interfering RNA transfection inhibited TGF-β–mediated changes to a fibroblastic morphology, but not MMP secretion. When cancer cells were cultured on a three-dimensional collagen matrix, TGF-β1, TGF-β2, and TGF-β3 stimulated both pro-MMP and active MMP secretion and invasion. Smad3 small interfering RNA transfection of cells cultured on a collagen matrix abrogated TGF-β–stimulated invasion and MMP secretion. Analysis of Smad3 nuclear expression in microarrays of serous benign tumors, borderline tumors, and cystadenocarcinoma revealed that Smad3 expression could be used to distinguish benign and borderline tumors from carcinoma (P = 0.006). Higher Smad3 expression also correlated with poor survival (P = 0.031). Furthermore, a direct relationship exists between Smad3 nuclear expression and expression of the mesenchymal marker N-cadherin in cancer patients (P = 0.0057). Collectively, these results implicate an important role for the TGF-β/Smad3 pathway in mediating ovarian oncogenesis by enhancing metastatic potential.
Asthma is a chronic inflammatory lung disease, and airway remodeling denotes the pathophysiologic modifications of normal airway wall structure, including changes in the composition and organization of the airway wall's cellular and molecular constituents. These structural alterations are largely irreversible in chronic severe asthma and lead to symptoms associated with chronic airflow limitation. However, the pathogenetic mechanisms leading to these responses remain unclear. According to recent reports, lung-resident fibroblasts and smooth muscle cells have been implicated in the pathogenesis of airway remodeling. Myofibroblasts are proposed to be the primary effector cells of lung fibrotic responses and are characterized by expression of α-smooth muscle actin (α-SMA) stress fibers. Transforming growth factor (TGF)-β is known to induce the transformation of fibroblasts to myofibroblasts. Protease activated receptor (PAR)-2, a G-protein-coupled receptor activated by serine proteases such as trypsin and mast cell tryptase has been recognized as a key molecule in inflammation and fibrotic changes. We hypothesized that activation of PAR-2 induces TGF-β and α-SMA expression and hence may be one of the potential mechanisms of airway remodeling in asthma.
Cultured human lung fibroblasts (MRC5) were exposed to trypsin (5 nM) or a specific activating peptide, PAR-2AP. Secreted TGF-β was measured using ELISA. Cell associated α-SMA was assessed by Western blot analysis and immunostaining and activation of downstream signaling pathways was assessed by Western analysis.
Activation of PAR-2 by trypsin or PAR-2AP induced TGF-β secretion that peaked between 4 and 8 hours. These were correlated with activations of c-fos and c-jun. Induction of α-SMA expression peaked between 4 and 24 hours. Treatment with trypsin or PAR-2AP also induced phosphorylation of GSK-3β on serine 9 and nuclear translocation of β-catenin.
Activation of PAR-2 induces TGF-β secretion through the AP-1 transcription factor complex leading to myofibroblast transformation via the GSK-3β/β-Catenin Pathway.
Extracellular matrix (ECM) turnover is controlled by the synthetic rate of matrix proteins, including type I collagen, and their enzymatic degradation by matrix metalloproteinases (MMPs). Fibrosis is characterized by an unbalanced accumulation of ECM leading to organ dysfunction as observed in systemic sclerosis. We previously reported that proteasome inhibition (PI) in vitro decreases type I collagen and enhances MMP-1 production by human fibroblasts, thus favoring an antifibrotic fibroblast phenotype. These effects were dominant over the pro-fibrotic phenotype induced by transforming growth factor (TGF)-β. Here we investigate the molecular events responsible for the anti-fibrotic phenotype induced in fibroblasts by the proteasome inhibitor bortezomib.
The steady-state mRNA levels of COL1A1, COL1A2, TIMP-1, MMP-1, and MMP-2 were assessed by quantitative PCR in human dermal fibroblasts cultured in the presence of TGF-β, bortezomib, or both. Transient fibroblast transfection was performed with wild-type and mutated COL1A1 and MMP-1 promoters. Chromatin immunoprecipitation, electrophoretic mobility shift assay (EMSA), and DNA pull-down assays were used to assess the binding of c-Jun, SP1, AP2, and Smad2 transcription factors. Immunoblotting and immunofluorescent microscopy were performed for identifying phosphorylated transcription factors and their cellular localization.
Bortezomib decreased the steady-state mRNA levels of COL1A1 and COL1A2, and abrogated SP1 binding to the promoter of COL1A2 in both untreated and TGF-β-activated fibroblasts. Reduced COL1A2 expression was not due to altered TGF-β-induced Smad2 phosphorylation, nuclear translocation, or binding to the COL1A2 promoter. In contrast to collagen, bortezomib specifically increased the steady-state mRNA levels of MMP-1 and enhanced the binding of c-Jun to the promoter of MMP-1. Furthermore, disruption of the proximal AP-1-binding site in the promoter of MMP-1 severely impaired MMP-1 transcription in response to bortezomib.
By altering the binding of at least two transcription factors, c-Jun and SP1, proteasome inhibition results in increased production of MMP-1 and decreased synthesis of type I collagen in human dermal fibroblasts. Thus, the antifibrotic phenotype observed in fibroblasts submitted to proteasome inhibition results from profound modifications in the binding of key transcription factors. This provides a novel rationale for assessing the potential of drugs targeting the proteasome for their anti-fibrotic properties.
Rationale: Asthma is characterized by increases in airway resistance, pulmonary remodeling, and lung inflammation. The cytokine transforming growth factor (TGF)-β has been shown to have a central role in asthma pathogenesis and in mouse models of allergic airway disease.
Objectives: To determine the contribution of TGF-β to airway hyperresponsiveness (AHR), we examined the time course, source, and isoform specificity of TGF-β production in an in vivo mouse asthma model. To then elucidate the function of TGF-β in AHR, inflammation, and pulmonary fibrosis, we examined the effects of blocking TGF-β signaling with neutralizing antibody.
Methods: Mice were sensitized and challenged with ovalbumin (OVA) to establish allergic airway disease. TGF-β activity was neutralized by intranasal administration of monoclonal antibody.
Measurements and Main Results: TGF-β1 protein levels were increased in OVA-challenged lungs versus naive controls, and airway epithelial cells were shown to be a likely source of TGF-β1. In addition, TGF-β1 levels were elevated in OVA-exposed IL-5–null mice, which fail to recruit eosinophils into the airways. Neutralization of TGF-β1 with specific antibody had no significant effect on airway inflammation and eosinophilia, although anti–TGF-β1 antibody enhanced OVA-induced AHR and suppressed pulmonary fibrosis.
Conclusions: These data show that TGF-β1 is the main TGF-β isoform produced after OVA challenge, with a likely cellular source being the airway epithelium. The effects of blocking TGF-β1 signaling had differential effects on AHR, fibrosis, and inflammation. While TGF-β neutralization may be beneficial to abrogating airway remodeling, it may be detrimental to lung function by increasing AHR.
lung; mice; hypersensitivity; cytokines
Chronic inflammation in asthmatic airways leads to bronchial hyper-responsiveness (BHR) and the development of structural changes. Important features of remodeling include the formation of subepithelial fibrosis due to increased collagen deposition in the reticular basement membrane. Transforming growth factor (TGF)-β might be a central mediator of tissue fibrosis and remodeling.
Materials and Methods:
Immunohistochemistry was used to measure collagen III deposition and TGF-β1 expression in biopsies from patients with long-standing asthma treated with inhaled corticosteroids, patients with recently diagnosed asthma, and control subjects. Computer-assisted image analysis was used to evaluate total basement membrane (TBM) thickness.
Asthmatics, particularly those with long-standing asthma, had thicker TBMs than healthy subjects. Collagen III deposition was comparable in the studied groups. BHR was not correlated with features of mucosal inflammation and was lower in steroid-treated patients with long-standing asthma than in subjects with newly diagnosed asthma untreated with steroids. Epithelial TGF-β1 expression negatively correlated with collagen III deposition and TBM thickness.
The study showed that TBM thickness, but not collagen III deposition, could be a differentiating marker of asthmatics of different disease duration and treatment. The lack of correlation between BHR and features of mucosal inflammation suggests the complexity of BHR development. Corticosteroids can reduce BHR in asthmatics, but it seems to be less effective in reducing subepithelial fibrosis. The role of epithelial TGF-β1 needs to be further investigated since the possibility that it plays a protective and anti-inflammatory role in asthmatic airways cannot be excluded.
bronchial hyper-responsiveness; subepithelial fibrosis; airway remodeling; transforming growth factor-β
In severe asthma bronchial epithelial cells are damaged and detached, and it has been proposed that such damage might lead to the bronchial hyperresponsiveness that characterises asthma. To investigate the relation between airway hyperresponsiveness and epithelial damage, biopsy specimens of the bronchial mucus membrane were obtained at fibreoptic bronchoscopy from 11 patients with mild atopic asthma and airway hyperresponsiveness (provocative concentration of methacholine causing a 20% fall in FEV1 (PC20) less than 1.0 mg/ml), and from 17 healthy non-atopic subjects who did not have airway hyperresponsiveness (PC20 methacholine greater than 8.0 mg/ml). Observers who were blind to the presence or absence of asthma examined the biopsy specimens by light and electron microscopy. Epithelial cells, intercellular spaces, and goblet cells were counted. Intercellular junctional complexes were examined, and a semiquantitative assessment was made of ciliary loss, non-parallel central ciliary filaments, and vacuoles in ciliated cells. There were no differences between the asthmatic and healthy groups in any of these measurements. These findings indicate that airway hyperresponsiveness may be present when there is no apparent change in the structure of the bronchial epithelium.
The mechanisms that initiate allergic lung inflammation are relevant to expression of diseases such as asthma, but the factors underlying resolution of inflammation are equally important. Previously, we demonstrated the importance of matrix metalloproteinase 2 (MMP2) for airway egression of lung eosinophils, a critical anti-inflammatory mechanism without which mice are rendered highly susceptible to lethal asphyxiation. Here we show that leukocyte MMP9 is the dominant airway MMP controlling inflammatory cell egression. The allergic lung phenotype of MMP9−/− mice was similar to WT and was not altered by concomitant deletion of the MMP2 gene (double knockout; dko). However, inflammatory cells accumulated aberrantly in the lungs of allergen-challenged MMP9−/− and dko mice and fewer eosinophils and neutrophils were present in bronchoalveolar lavage. These aberrant cellular trafficking patterns were explained by disruption of transepithelial chemokine gradients, in MMP2−/− mice affecting only eotaxin (CCL11), but in MMP9−/− and dko mice involving eotaxin, MARC (CCL7), and TARC (CCL17). Thus, by establishing multiple transepithelial chemokine gradients, MMP9 is broadly implicated in the resolution of allergic inflammation, an essential protective mechanism that overlaps with a more limited role played by MMP2.
chemotaxis; cytokines; gelatinase B; matrix metalloproteinase-9