Elastin expression in very severe human COPD

Does lysozyme play a role in the pathogenesis of COPD?

Elastic fiber injury is an important process in the pathogenesis of chronic obstructive pulmonary disease (COPD), particularly with regard to the development of pulmonary emphysema. Damage to these fibers results in uneven distribution of mechanical forces in the lung, leading to dilatation and rupture of alveolar walls. While the role of various enzymes and oxidants in this process has been well-documented, we propose that a previously unsuspected agent, lysozyme, may contribute significantly to the changes in elastic fibers observed in this disease. Studies from our laboratory have previously shown that lysozyme preferentially binds to elastic fibers in human emphysematous lungs. On the basis of this finding, it is hypothesized that the attachment of lysozyme to these fibers enhances their susceptibility to injury, and further impairs the transfer of mechanical forces in the lung, leading to increased alveolar wall damage and enhanced progression of COPD. The hypothesized effects of lysozyme are predicated on its interaction with hyaluronan (HA), a long-chain polysaccharide that is found in close proximity to elastic fibers. By preventing the binding of HA to elastic fibers in COPD, lysozyme may interfere with the protective effect of this polysaccharide against enzymes and oxidants that degrade these fibers. Furthermore, the loss of the hydrating effect of HA on these fibers may impair their elastic properties, greatly increasing the probability of their fragmentation in response to mechanical forces. The proposed hypothesis may explain why the content of HA is significantly lower in the lungs of COPD patients. It may also contribute to the design of clinical trials involving the use of exogenously administered HA as a potential treatment for COPD.

A large lung gene expression study identifying fibulin-5 as a novel player in tissue repair in COPD

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a progressive, incurable lung disease characterised by abnormal tissue repair causing emphysema and small airways fibrosis. Since current therapy cannot modify this abnormal repair, it is crucial to unravel its underlying molecular mechanisms. Unbiased analysis of genome-wide gene expression profiles in lung tissue provides a powerful tool to investigate this.

METHODS

We performed genome-wide gene expression profiling in 581 lung tissue samples from current and ex-smokers with (n=311) and without COPD (n=270). Subsequently, quantitative PCR, western blot and immunohistochemical analyses were performed to validate our main findings.

RESULTS

112 genes were found to be upregulated in patients with COPD compared with controls, whereas 61 genes were downregulated. Among the most upregulated genes were fibulin-5 (FBLN5), elastin (ELN), latent transforming growth factor β binding protein 2 (LTBP2) and microfibrillar associated protein 4 (MFAP4), all implicated in elastogenesis. Our gene expression findings were validated at mRNA and protein level. We demonstrated higher ELN gene expression in COPD lung tissue and similar trends for FBLN5 and MFAP4, and negative correlations with lung function. FBLN5 protein levels were increased in COPD lung tissue and cleaved, possibly non-functional FBLN5 protein was present. Strong coexpression of FBLN5, ELN, LTBP2 and MFAP4 in lung tissue and in silico analysis indicated cofunctionality of these genes. Finally, colocalisation of FBLN5, MFAP4 and LTBP2 with elastic fibres was demonstrated in lung tissue.

CONCLUSIONS

We identified a clear gene signature for elastogenesis in COPD and propose FBLN5 as a novel player in tissue repair in COPD.

Similar matrix alterations in alveolar and small airway walls of COPD patients

Background

Remodelling in COPD has at least two dimensions: small airway wall thickening and destruction of alveolar walls. Recent studies indicate that there is some similarity between alveolar and small airway wall matrix remodelling. The aim of this study was to characterise and assess similarities in alveolar and small airway wall matrix remodelling, and TGF-β signalling in COPD patients of different GOLD stages.

Methods

Lung tissue sections of 14 smoking controls, 16 GOLD II and 19 GOLD IV patients were included and stained for elastin and collagens as well as hyaluronan, a glycosaminoglycan matrix component and pSMAD2.

Results

Elastin was significantly decreased in COPD patients not only in alveolar, but also in small airway walls. Interestingly, both collagen and hyaluronan were increased in alveolar as well as small airway walls. The matrix changes were highly comparable between GOLD stages, with collagen content in the alveolar wall increasing further in GOLD IV. A calculated remodelling index, defined as elastin divided over collagen and hyaluronan, was decreased significantly in GOLD II and further lowered in GOLD IV patients, suggesting that matrix component alterations are involved in progressive airflow limitation. Interestingly, there was a positive correlation present between the alveolar and small airway wall stainings of the matrix components, as well as for pSMAD2. No differences in pSMAD2 staining between controls and COPD patients were found.

Conclusions

In conclusion, remodelling in the alveolar and small airway wall in COPD is markedly similar and already present in moderate COPD. Notably, alveolar collagen and a remodelling index relate to lung function.

Chemosensory functions for pulmonary neuroendocrine cells

The mammalian airways are sensitive to inhaled stimuli, and airway diseases are characterized by hypersensitivity to volatile stimuli, such as perfumes, industrial solvents, and others. However, the identity and function of the cells in the airway that can sense volatile chemicals remain uncertain, particularly in humans. Here, we show that solitary pulmonary neuroendocrine cells (PNECs), which are morphologically distinct and physiologically undefined, might serve as chemosensory cells in human airways. This conclusion is based on our finding that some human PNECs expressed members of the olfactory receptor (OR) family in vivo and in primary cell culture, and are anatomically positioned in the airway epithelium to respond to inhaled volatile chemicals. Furthermore, apical exposure of primary-culture human airway epithelial cells to volatile chemicals decreased levels of serotonin in PNECs, and the led to the release of the neuropeptide calcitonin gene-related peptide (CGRP) to the basal medium. These data suggest that volatile stimulation of PNECs can lead to the secretion of factors that are capable of stimulating the corresponding receptors in the lung epithelium. We also found that the distribution of serotonin and neuropeptide receptors may change in chronic obstructive pulmonary disease, suggesting that increased PNEC-dependent chemoresponsiveness might contribute to the altered sensitivity to volatile stimuli in this disease. Together, these data indicate that human airway epithelia harbor specialized cells that respond to volatile chemical stimuli, and may help to explain clinical observations of odorant-induced airway reactions.

Long-term IL-33-producing epithelial progenitor cells in chronic obstructive lung disease

Chronic obstructive lung disease is characterized by persistent abnormalities in epithelial and immune cell function that are driven, at least in part, by infection. Analysis of parainfluenza virus infection in mice revealed an unexpected role for innate immune cells in IL-13-dependent chronic lung disease, but the upstream driver for the immune axis in this model and in humans with similar disease was undefined. We demonstrate here that lung levels of IL-33 are selectively increased in postviral mice with chronic obstructive lung disease and in humans with very severe chronic obstructive pulmonary disease (COPD). In the mouse model, IL-33/IL-33 receptor signaling was required for Il13 and mucin gene expression, and Il33 gene expression was localized to a virus-induced subset of airway serous cells and a constitutive subset of alveolar type 2 cells that are both linked conventionally to progenitor function. In humans with COPD, IL33 gene expression was also associated with IL13 and mucin gene expression, and IL33 induction was traceable to a subset of airway basal cells with increased capacities for pluripotency and ATP-regulated release of IL-33. Together, these findings provide a paradigm for the role of the innate immune system in chronic disease based on the influence of long-term epithelial progenitor cells programmed for excess IL-33 production.

Inhaled steroids modulate extracellular matrix composition in bronchial biopsies of COPD patients: a randomized, controlled trial

RATIONALE

Smoking and inflammation contribute to the pathogenesis of chronic obstructive pulmonary disease (COPD), which involves changes in extracellular matrix. This is thought to contribute to airway remodeling and airflow obstruction. We have previously observed that long-term treatment with inhaled corticosteroids can not only reduce bronchial inflammation, but can also attenuate lung function decline in moderate-severe COPD. We hypothesized that inhaled corticosteroids and current smoking modulate bronchial extracellular matrix components in COPD.

OBJECTIVE

To compare major extracellular matrix components (elastic fibers; proteoglycans [versican, decorin]; collagens type I and III) in bronchial biopsies 1) after 30-months inhaled steroids treatment or placebo; and 2) between current and ex-smokers with COPD.

METHODS

We included 64 moderate-severe, steroid-naive COPD patients (24/40 (ex)-smokers, 62±7 years, 46 (31-54) packyears, post-bronchodilator forced expiratory volume in one second (FEV1) 62±9% predicted) at baseline in this randomized, controlled trial. 19 and 13 patients received 30-months treatment with fluticasone or placebo, respectively. Bronchial biopsies collected at baseline and after 30 months were studied using (immuno)histochemistry to evaluate extracellular matrix content. Percentage and density of stained area were calculated by digital image analysis.

RESULTS

30-Months inhaled steroids increased the percentage stained area of versican (9.6% [CI 0.9 to 18.3%]; p = 0.03) and collagen III (20.6% [CI 3.8 to 37.4%]; p = 0.02) compared to placebo. Increased collagen I staining density correlated with increased post-bronchodilator FEV1 after inhaled steroids treatment (Rs = 0.45, p = 0.04). There were no differences between smokers and ex-smokers with COPD in percentages and densities for all extracellular matrix proteins.

CONCLUSIONS

These data show that long-term inhaled corticosteroids treatment partially changes the composition of extracellular matrix in moderate-severe COPD. This is associated with increased lung function, suggesting that long-term inhaled steroids modulate airway remodeling thereby potentially preventing airway collapse in COPD. Smoking status is not associated with bronchial extracellular matrix proteins.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00158847.

A cytokine axis regulates elastin formation and degradation

Underlying the dynamic regulation of tropoelastin expression and elastin formation in development and disease are transcriptional and post-transcriptional mechanisms that have been the focus of much research. Of particular importance is the cytokine-governed elastin regulatory axis in which the pro-elastogenic activities of transforming growth factor β-1 (TGFβ1) and insulin-like growth factor-I (IGF-I) are opposed by anti-elastogenic activities of basic fibroblast growth factor (bFGF/FGF-2), heparin-binding epidermal growth factor-like growth factor (HB-EGF), EGF, PDGF-BB, TGFα, tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β and noncanonical TGFβ1 signaling. A key mechanistic feature of the regulatory axis is that cytokines influence elastin formation through effects on the cell cycle involving control of cyclin-cyclin dependent kinase complexes and activation of the Ras/MEK/ERK signaling pathway. In this article we provide an overview of the major cytokines/growth factors that modulate elastogenesis and describe the underlying molecular mechanisms for their action on elastin production.

Pro-inflammatory phenotype of COPD fibroblasts not compatible with repair in COPD lung

Chronic obstructive pulmonary disease (COPD) is characterized by loss of elastic fibres from small airways and alveolar walls, with the decrease in elastin increasing with disease severity. It is unclear why there is a lack of repair of elastic fibres. We have examined fibroblasts cultured from lung tissue from subjects with or without COPD to determine if the secretory profile explains lack of tissue repair. In this study, fibroblasts were cultured from lung parenchyma of patients with mild COPD [Global initiative for chronic Obstructive Lung Disease (GOLD) 1, n= 5], moderate to severe COPD (GOLD 2–3, n= 12) and controls (non-COPD, n= 5). Measurements were made of proliferation, senescence-associated β-galactosidase-1, mRNA expression of IL-6, IL-8, MMP-1, tropoelastin and versican, and protein levels for IL-6, IL-8, PGE_2, tropoelastin, insoluble elastin, and versican. GOLD 2–3 fibroblasts proliferated more slowly (P < 0.01), had higher levels of senescence-associated β-galactosidase-1 (P < 0.001) than controls and showed significant increases in mRNA and/or protein for IL-6 (P < 0.05), IL-8 (P < 0.01), MMP-1 (P < 0.05), PGE₂ (P < 0.05), versican (P < 0.05) and tropoelastin (P < 0.05). mRNA expression and/or protein levels of tropoelastin (P < 0.01), versican (P < 0.05), IL-6 (P < 0.05) and IL-8 (P < 0.05) were negatively correlated with FEV1% of predicted. Insoluble elastin was not increased. In summary, fibroblasts from moderate to severe COPD subjects display a secretory phenotype with up-regulation of inflammatory molecules including the matrix proteoglycan versican, and increased soluble, but not insoluble, elastin. Versican inhibits assembly of tropoelastin into insoluble elastin and we conclude that the pro-inflammatory phenotype of COPD fibroblasts is not compatible with repair of elastic fibres.

Imaging alveolar-duct geometry during expiration via ³He lung morphometry

Acinar geometry has been the subject of several morphological and imaging studies in the past; however, surprisingly little is known about how the acinar microstructure changes when the lung inflates or deflates. Lung morphometry with hyperpolarized (3)He diffusion MRI allows non-destructive evaluation of lung microstructure and acinar geometry, which has important applications in understanding basic lung physiology and disease. In this study, we have measured the alveolar and acinar duct sizes at physiologically relevant volumes by (3)He lung morphometry in six normal, excised, and unfixed canine lungs. Our results imply that, during a 37% decrease in lung volume, the acinar duct radius decreases by 19%, whereas the alveolar depth increases by 9% (P < 0.0001 and P < 0.05, respectively via paired t-tests with a Bonferroni correction). A comparison to serial sections under the microscope validates the imaging results and opens the door to in vivo human studies of lung acinar geometry and physiology during respiration using (3)He lung morphometry.

Pulmonary fibroblasts from COPD patients show an impaired response of elastin synthesis to TGF-β1

Insufficiency of tissue repair by pulmonary fibroblasts may contribute to the decrease in elastic fibres in chronic obstructive pulmonary disease (COPD). In this study, the repair function of COPD fibroblasts was assessed by examining the response to transforming growth factor (TGF)-β1. Primary pulmonary fibroblasts were cultured from lung tissue of COPD patients and smoking control subjects. Cellular proliferation was measured with Alamar Blue reduction method. Levels of tropoelastin mRNA and soluble elastin was measured using real-time RT-PCR and Fastin elastin assay respectively. The percentage of increase in proliferation and elastin production after TGF-β1 (1 ng/ml) treatment was calculated for fibroblasts from each subject. COPD fibroblasts showed slower proliferation than control fibroblasts, and a reduced response to TGF-β1 stimulation. The promotive effect of TGF-β1 on elastin synthesis in control fibroblasts was significantly diminished in fibroblasts from COPD patients. Our findings indicate that COPD lung fibroblasts have a significantly decreased response to TGF-β1 in terms of proliferation and elastin production.

Oxidative modifications of the C-terminal domain of tropoelastin prevent cell binding

Tropoelastin (TE), the soluble monomer of elastin, is synthesized by elastogenic cells, such as chondrocytes, fibroblasts, and smooth muscle cells (SMCs). The C-terminal domain of TE interacts with cell receptors, and these interactions play critical roles in elastic fiber assembly. We recently found that oxidation of TE prevents elastic fiber assembly. Here, we examined the effects of oxidation of TE on cell interactions. We found that SMCs bind to TE through heparan sulfate (HS), whereas fetal lung fibroblasts (WI-38 cells) bind through integrin α(v)β(3) and HS. In addition, we found that oxidation of TE by peroxynitrite (ONOO(-)) prevented binding of SMCs and WI-38 cells and other elastogenic cells, human dermal fibroblasts and fetal bovine chondrocytes. Because the C-terminal domain of TE has binding sites for both HS and integrin, we examined the effects of oxidation of a synthetic peptide derived from the C-terminal 25 amino acids of TE (CT-25) on cell binding. The CT-25 peptide contains the only two Cys residues in TE juxtaposed to a cluster of positively charged residues (RKRK) that are important for cell binding. ONOO(-) treatment of the CT-25 peptide prevented cell binding, whereas reduction of the CT-25 peptide had no effect. Mass spectrometric and circular dichroism spectroscopic analyses showed that ONOO(-) treatment modified both Cys residues in the CT-25 peptide to sulfonic acid derivatives, without altering the secondary structure. These data suggest that the mechanism by which ONOO(-) prevents cell binding to TE is by introducing negatively charged sulfonic acid residues near the positively charged cluster.

The role of matrix metalloproteinase-9 in cigarette smoke-induced emphysema

RATIONALE

Matrix metalloprotease (MMP)-9 is an elastolytic endopeptidase produced by activated macrophages that may be involved in the development of human pulmonary emphysema and could be inhibited with existing compounds. Mouse models have demonstrated that excess MMP-9 production can result in permanent alveolar destruction.

OBJECTIVES

To determine if MMP-9 causes cigarette smoke-induced emphysema using MMP-9 knockout mice and human samples.

METHODS

Mouse lungs were analyzed for inflammation and airspace enlargement using a mainstream smoke-exposure model. Human macrophage mRNA was isolated from subjects with emphysema by laser capture microdissection. Human blood monocyte mRNA was isolated from subjects with greater than 30 pack-year smoking history. Human gene expression was determined by quantitative polymerase chain reaction and compared with emphysema severity determined by automated computed tomography analysis. Plasma Clara cell secretory protein and surfactant protein-D were quantified to measure ongoing lung injury.

MEASUREMENTS AND MAIN RESULTS

Mice deficient in MMP-9 develop the same degree of cigarette smoke-induced inflammation and airspace enlargement as strain-matched controls. Macrophages are the predominant source of MMP-9 production in human emphysema specimens and similar quantities of macrophage MMP-9 mRNA is present in areas of lung with and without emphysema. Circulating monocytes produce more MMP-9 in individuals with advanced emphysema severity despite no correlation of MMP-9 with markers of ongoing lung damage.

CONCLUSIONS

These results suggest that MMP-9 in humans who smoke is similar to smoke-exposed mice, where MMP-9 is present in emphysematous lung but not correlated with the emphysema. To the degree that the mechanisms of emphysema in humans who smoke resemble the mouse model, these data suggest specific inhibition of MMP-9 is unlikely to be an effective therapy for cigarette smoke-induced emphysema. Clinical trial registered with www.clinicaltrials.gov (NCT 00757120).

Oxidative and nitrosative modifications of tropoelastin prevent elastic fiber assembly in vitro

Elastic fibers are extracellular structures that provide stretch and recoil properties of tissues, such as lungs, arteries, and skin. Elastin is the predominant component of elastic fibers. Tropoelastin (TE), the precursor of elastin, is synthesized mainly during late fetal and early postnatal stages. The turnover of elastin in normal adult tissues is minimal. However, in several pathological conditions often associated with inflammation and oxidative stress, elastogenesis is re-initiated, but newly synthesized elastic fibers appear abnormal. We sought to determine the effects of reactive oxygen and nitrogen species (ROS/RNS) on the assembly of TE into elastic fibers. Immunoblot analyses showed that TE is oxidatively and nitrosatively modified by peroxynitrite (ONOO(-)) and hypochlorous acid (HOCl) and by activated monocytes and macrophages via release of ONOO(-) and HOCl. In an in vitro elastic fiber assembly model, oxidatively modified TE was unable to form elastic fibers. Oxidation of TE enhanced coacervation, an early step in elastic fiber assembly, but reduced cross-linking and interactions with other proteins required for elastic fiber assembly, including fibulin-4, fibulin-5, and fibrillin-2. These findings establish that ROS/RNS can modify TE and that these modifications affect the assembly of elastic fibers. Thus, we speculate that oxidative stress may contribute to the abnormal structure and function of elastic fibers in pathological conditions.

Palifermin induces alveolar maintenance programs in emphysematous mice

RATIONALE

Emphysema is characterized by destruction of alveoli with ensuing airspace enlargement and loss of alveoli. Induction of alveolar regeneration is still a major challenge in emphysema therapy.

OBJECTIVES

To investigate whether therapeutic application of palifermin (DeltaN23-KGF) is able to induce a regenerative response in distal lung parenchyma after induction of pulmonary emphysema.

METHODS

Mice were therapeutically treated at three occasions by oropharyngeal aspiration of 10 mg DeltaN23-KGF per kg body weight after induction of emphysema by porcine pancreatic elastase.

MEASUREMENTS AND MAIN RESULTS

Airflow limitation associated with emphysema was largely reversed as assessed by noninvasive head-out body plethysmography. Porcine pancreatic elastase-induced airspace enlargement and loss of alveoli were partially reversed as assessed by design-based stereology. DeltaN23-KGF induced proliferation of epithelium, endothelium, and fibroblasts being associated with enhanced differentiation as well as increased expression of vascular endothelial growth factor, vascular endothelial growth factor receptors, transforming growth factor (TGF)-beta1, TGF-beta2, (phospho-) Smad2, plasminogen activator inhibitor-1, and elastin as assessed by quantitative reverse transcriptase-polymerase chain reaction, Western blotting, and immunohistochemistry. DeltaN23-KGF induced the expression of TGF-beta1 in and release of active TGF-beta1 from primary mouse alveolar epithelial type 2 (AE2) cells, murine AE2-like cells LA-4, and cocultures of LA-4 and murine lung fibroblasts (MLF), but not in MLF cultured alone. Recombinant TGF-beta1 but not DeltaN23-KGF induced elastin gene expression in MLF. Blockade of TGF-signaling by neutralizing antibody abolished these effects of DeltaN23-KGF in LA-4/MLF cocultures.

CONCLUSIONS

Our data demonstrate that therapeutic application of DeltaN23-KGF has the potential to induce alveolar maintenance programs in emphysematous lungs and suggest that the regenerative effect on interstitial tissue is linked to AE2 cell-derived TGF-beta1.