The effect of neutrophil protenase enzymes on the release of mucus from feline and human airway cultures

Expression/Activation of PAR-1 in Airway Epithelial Cells of COPD Patients: Ex Vivo/In Vitro Study

The role of PAR-1 expression and activation was described in epithelial cells from the central and distal airways of COPD patients using an ex vivo/in vitro model. PAR-1 immunoreactivity was studied in epithelial cells from surgical specimens of the central and distal airways of COPD patients and healthy control (HC). Furthermore, PAR-1 expression and activation were measured in both the human bronchial epithelial cell line (16HBE) and normal human bronchial epithelial cells (NHBEs) exposed to cigarette smoke extract (CSE) (10%) or thrombin. Finally, cell proliferation, apoptosis, and IL-8 release were detected in stimulated NHBEs. We identified higher levels of PAR-1 expression/activation in epithelial cells from the central airways of COPD patients than in HC. Active PAR-1 increased in epithelial cells from central and distal airways of COPD, with higher levels in COPD smokers (correlated with pack-years) than in COPD ex-smokers. 16HBE and NHBEs exposed to CSE or thrombin showed increased levels of active PAR-1 (localized in the cytoplasm) than baseline conditions, while NHBEs treated with thrombin or CSE showed increased levels of IL-8 proteins, with an additional effect when used in combination. Smoking habits generate the upregulation of PAR-1 expression/activation in airway epithelial cells, and promoting IL-8 release might affect the recruitment of infiltrating cells in the airways of COPD patients.

Proteases, Mucus, and Mucosal Immunity in Chronic Lung Disease

Dysregulated protease activity has long been implicated in the pathogenesis of chronic lung diseases and especially in conditions that display mucus obstruction, such as chronic obstructive pulmonary disease, cystic fibrosis, and non-cystic fibrosis bronchiectasis. However, our appreciation of the roles of proteases in various aspects of such diseases continues to grow. Patients with muco-obstructive lung disease experience progressive spirals of inflammation, mucostasis, airway infection and lung function decline. Some therapies exist for the treatment of these symptoms, but they are unable to halt disease progression and patients may benefit from novel adjunct therapies. In this review, we highlight how proteases act as multifunctional enzymes that are vital for normal airway homeostasis but, when their activity becomes immoderate, also directly contribute to airway dysfunction, and impair the processes that could resolve disease. We focus on how proteases regulate the state of mucus at the airway surface, impair mucociliary clearance and ultimately, promote mucostasis. We discuss how, in parallel, proteases are able to promote an inflammatory environment in the airways by mediating proinflammatory signalling, compromising host defence mechanisms and perpetuating their own proteolytic activity causing structural lung damage. Finally, we discuss some possible reasons for the clinical inefficacy of protease inhibitors to date and propose that, especially in a combination therapy approach, proteases represent attractive therapeutic targets for muco-obstructive lung diseases.

β2-integrin LFA1 mediates airway damage following neutrophil transepithelial migration during respiratory syncytial virus infection

Respiratory syncytial virus (RSV) bronchiolitis is the most common cause of infant hospital admissions, but there is limited understanding of the mechanisms of disease, and no specific antiviral treatment. Using a novel in vitro primary transepithelial neutrophil migration model and innovative imaging methods, we show that RSV infection of nasal airway epithelium increased neutrophil transepithelial migration and adhesion to infected epithelial cells, which is associated with epithelial cell damage and reduced ciliary beat frequency, but also with a reduction in infectious viral load.Following migration, RSV infection results in greater neutrophil activation, degranulation and release of neutrophil elastase into the airway surface media compared to neutrophils that migrated across mock-infected nasal epithelial cells. Blocking of the interaction between the ligand on neutrophils (the β₂-integrin LFA-1) for intracellular adhesion molecule (ICAM)-1 on epithelial cells reduced neutrophil adherence to RSV-infected cells and epithelial cell damage to pre-infection levels, but did not reduce the numbers of neutrophils that migrated or prevent the reduction in infectious viral load.These findings have provided important insights into the contribution of neutrophils to airway damage and viral clearance, which are relevant to the pathophysiology of RSV bronchiolitis. This model is a convenient, quantitative preclinical model that will further elucidate mechanisms that drive disease severity and has utility in antiviral drug discovery.

Neutrophil-Airway Epithelial Interactions Result in Increased Epithelial Damage and Viral Clearance during Respiratory Syncytial Virus Infection

This study shows that the RSV-infected human airway drives changes in the behavior of human neutrophils, including increasing activation markers and delaying apoptosis, that result in greater airway damage and viral clearance.

Respiratory syncytial virus (RSV) is a major cause of pediatric respiratory disease. Large numbers of neutrophils are recruited into the airways of children with severe RSV disease. It is not clear whether or how neutrophils enhance recovery from disease or contribute to its pathology. Using an in vitro model of the differentiated airway epithelium, we found that the addition of physiological concentrations of neutrophils to RSV-infected nasal cultures was associated with greater epithelial damage with lower ciliary activity, cilium loss, less tight junction expression (ZO-1), and more detachment of epithelial cells than is seen with RSV infection alone. This was also associated with a decrease in infectious virus and fewer RSV-positive cells in cultures after neutrophil exposure than in preexposure cultures. Epithelial damage in response to RSV infection was associated with neutrophil activation (within 1 h) and neutrophil degranulation, with significantly greater cellular expression of CD11b and myeloperoxidase and higher levels of neutrophil elastase and myeloperoxidase activity in apical surface media than in media with mock-infected airway epithelial cells (AECs). We also recovered more apoptotic neutrophils from RSV-infected cultures (>40%) than from mock-infected cultures (<5%) after 4 h. The results of this study could provide important insights into the role of neutrophils in host response in the airway.

IMPORTANCE This study shows that the RSV-infected human airway drives changes in the behavior of human neutrophils, including increasing activation markers and delaying apoptosis, that result in greater airway damage and viral clearance.

The human tubal lavage proteome reveals biological processes that may govern the pathology of hydrosalpinx

Hydrosalpinx, the blockage of fallopian tubes, can result from pelvic inflammatory disease. Hydrosalpinx is a cause of infertility and negatively impacts in vitro fertilization. To better understand the pathobiology of hydrosalpinx, we compared the proteome of lavages from disease vs. healthy fallopian tubes. Results indicate a disruption of redox homeostasis and activation of the complement system, immune cell infiltration, and phagocytosis; pathways that may drive tubal injury. To our surprise among the most prominent proteins with hydrosalpinx was mesothelin (MSLN), which until now has only been associated with epithelial malignancies. Analogous to mesothelioma and ovarian carcinoma, a significant increase of MSLN was detected in plasma from patients with hydrosalpinx. This finding suggests MSLN may provide clinical diagnosis in lieu of the current approaches that require invasive imaging. Importantly, these findings implicate MSLN in a benign disease, indicating that the activation and role of MSLN is not restricted to cancer.

The impact of alpha-1 antitrypsin augmentation therapy on neutrophil-driven respiratory disease in deficient individuals

Alpha-1 antitrypsin (AAT) is the most abundant serine protease inhibitor circulating in the blood. AAT deficiency (AATD) is an autosomal codominant condition affecting an estimated 3.4 million individuals worldwide. The clinical disease associated with AATD can present in a number of ways including COPD, liver disease, panniculitis and antineutrophil cytoplasmic antibody vasculitis. AATD is the only proven genetic risk factor for the development of COPD, and deficient individuals who smoke are disposed to more aggressive disease. Principally, AAT is a serine protease inhibitor; however, over the past number of years, the assessment of AAT as simply an antiprotease has evolved, and it is now recognized that AAT has significant anti-inflammatory properties affecting a wide range of cells, including the circulating neutrophil.

Mucin Production and Hydration Responses to Mucopurulent Materials in Normal versus Cystic Fibrosis Airway Epithelia

RATIONALE

Cystic fibrosis (CF) airways disease produces a mucoobstructive lung phenotype characterized by airways mucus plugging, epithelial mucous cell metaplasia/hyperplasia, chronic infection, and inflammation. Simultaneous biochemical and functional in vivo studies of mucin synthesis and secretion from CF airways are not available. In vitro translational models may quantitate differential CF versus normal mucin and fluid secretory responses to infectious/inflammatory stimuli.

OBJECTIVES

We tested the hypothesis that CF airways exhibit defective epithelial fluid, but not mucin, secretory responses to bacterial/inflammatory host products.

METHODS

Well-differentiated primary human bronchial epithelial cultures were exposed to supernatant from mucopurulent material (SMM) from human CF airways as a test of bacterial/inflammatory host product stimulus. Human bronchial epithelia (HBE) with normal CF transmembrane conductance regulator function were compared with ΔF508/ΔF508 CF HBE.

MEASUREMENTS AND MAIN RESULTS

Acute (up to 60 min) SMM exposure promoted mucin secretion, but mucins were degraded by the proteolytic enzymes present in SMM. Chronic SMM exposure induced upregulation of mucin synthesis and storage and generated absolute increases in basal and stimulated mucin release in normal and CF cultures. These responses were similar in normal and CF cultures. In contrast, SMM produced a coordinated CF transmembrane conductance regulator-mediated Cl- secretory response in normal HBE, but not in CF HBE. The absence of the fluid secretory response in CF produced quantitatively more dehydrated mucus.

CONCLUSIONS

Our study reveals the interplay between regulation of mucin and fluid secretion rates in inflamed versus noninflamed conditions and why a hyperconcentrated mucus is produced in CF airways.

Role of Proteases in Lung Disease: A Brief Overview

Proteases play an important role in health and disease of the lung. In the normal lungs, proteases maintain their homeostatic functions that regulate processes like its regeneration and repair. Dysregulation of proteases–antiproteases balance is crucial in the manifestation of different types of lung diseases. Chronic inflammatory lung pathologies are associated with a marked increase in protease activities. Thus, in addition to protease activities, inhibition of anti-proteolytic control mechanisms are also important for effective microbial infection and inflammation in the lung. Herein, we briefly summarize the role of different proteases and to some extent antiproteases in regulating a variety of lung diseases.

Airway Gland Structure and Function

Submucosal glands contribute to airway surface liquid (ASL), a film that protects all airway surfaces. Glandular mucus comprises electrolytes, water, the gel-forming mucin MUC5B, and hundreds of different proteins with diverse protective functions. Gland volume per unit area of mucosal surface correlates positively with impaction rate of inhaled particles. In human main bronchi, the volume of the glands is ∼ 50 times that of surface goblet cells, but the glands diminish in size and frequency distally. ASL and its trapped particles are removed from the airways by mucociliary transport. Airway glands have a tubuloacinar structure, with a single terminal duct, a nonciliated collecting duct, then branching secretory tubules lined with mucous cells and ending in serous acini. They allow for a massive increase in numbers of mucus-producing cells without replacing surface ciliated cells. Active secretion of Cl(-) and HCO3 (-) by serous cells produces most of the fluid of gland secretions. Glands are densely innervated by tonically active, mutually excitatory airway intrinsic neurons. Most gland mucus is secreted constitutively in vivo, with large, transient increases produced by emergency reflex drive from the vagus. Elevations of [cAMP]i and [Ca(2+)]i coordinate electrolyte and macromolecular secretion and probably occur together for baseline activity in vivo, with cholinergic elevation of [Ca(2+)]i being mainly responsive for transient increases in secretion. Altered submucosal gland function contributes to the pathology of all obstructive diseases, but is an early stage of pathogenesis only in cystic fibrosis.

Neutrophil elastase induces MUC5AC secretion via protease-activated receptor 2

Mucus hypersecretion is a major manifestation in patients with chronic inflammatory airway diseases, and mucin5AC (MUC5AC) protein is a major component of airway mucus. Previous studies have demonstrated that neutrophil elastase (NE) stimulates the secretion of MUC5AC from airway epithelial cells, however, the mechanism is poorly understood. NE is a known ligand for protein active receptors (PARs), which have been confirmed to participate in releasing MUC5AC in the airways. However, the role of PARs in NE-induced MUC5AC secretion remains unclear. We demonstrated that airway goblet-like Calu-3 cells express PAR1, PAR2, and PAR3 with a predominant level of PAR2. NE can increase PAR2 expression and MUC5AC release. In our study, we showed that NE binding to PAR2 can increase the cytosolic calcium concentration and subsequently activate PKC, leading to MUC5AC secretion. In order to investigate the mechanism of increased cytosolic calcium in Calu-3 cells, thapsigargin was used to exhaust the endoplasmic reticulum (ER) calcium pools, and 2-aminoethoxydiphenyl borate was used to inhibit the function of the store-operated calcium entry (SOCE) channels in the plasma membrane. We found that the NE-induced increase in intracellular calcium concentration is derived from release of the ER calcium pool and its subsequent calcium internal flux from the extracellular space via SOCE channels, which is dependent on sufficient levels of extracellular calcium.

NAD(P)H quinone oxidoreductase 1 regulates neutrophil elastase-induced mucous cell metaplasia

Mucous cell metaplasia (MCM) and neutrophil-predominant airway inflammation are pathological features of chronic inflammatory airway diseases. A signature feature of MCM is increased expression of a major respiratory tract mucin, MUC5AC. Neutrophil elastase (NE) upregulates MUC5AC in primary airway epithelial cells by generating reactive oxygen species, and this response is due in part to upregulation of NADPH quinone oxidoreductase 1 (NQO1) activity. Delivery of NE directly to the airway triggers inflammation and MCM and increases synthesis and secretion of MUC5AC protein from airway epithelial cells. We hypothesized that NE-induced MCM is mediated in vivo by NQO1. Male wild-type and Nqo1-null mice (C57BL/6 background) were exposed to human NE (50 μg) or vehicle via oropharyngeal aspiration on days 1, 4, and 7. On days 8 and 11, lung tissues and bronchoalveolar lavage (BAL) samples were obtained and evaluated for MCM, inflammation, and oxidative stress. MCM, inflammation, and production of specific cytokines, granulocyte-macrophage colony-stimulating factor, macrophage inflammatory protein-2, interleukin-4, and interleukin-5 were diminished in NE-treated Nqo1-null mice compared with NE-treated wild-type mice. However, in contrast to the role of NQO1 in vitro, we demonstrate that NE-treated Nqo1-null mice had greater levels of BAL and lung tissue lipid carbonyls and greater BAL iron on day 11, all consistent with increased oxidative stress. NQO1 is required for NE-induced inflammation and MCM. This model system demonstrates that NE-induced MCM directly correlates with inflammation, but not with oxidative stress.

Proteases and cystic fibrosis

Cystic fibrosis is the most common, inherited fatal disease in Caucasians. The major cause of morbidity and mortality is chronic lung disease due to infection and inflammation in the airways leading to bronchiectasis and respiratory failure. The signature pathologic features of CF lung disease including abnormal mucus obstructing airways, chronic infection with Staphylococcus aureus, Pseudomonas aeruginosa and other gram negative bacteria, and a robust neutrophil-dominant airway inflammation, are exacerbated by unopposed proteases present at high concentrations in the ASL. There is strong evidence that proteases, particularly neutrophil elastase, contribute to the pathology of CF by impairing mucociliary clearance, interfering with innate immune functions, and perpetuating neutrophilic inflammation. The mechanisms employed by proteases to impact airway function in CF will be reviewed.

Mucins in the mucosal barrier to infection

The mucosal tissues of the gastrointestinal, respiratory, reproductive, and urinary tracts, and the surface of the eye present an enormous surface area to the exterior environment. All of these tissues are covered with resident microbial flora, which vary considerably in composition and complexity. Mucosal tissues represent the site of infection or route of access for the majority of viruses, bacteria, yeast, protozoa, and multicellular parasites that cause human disease. Mucin glycoproteins are secreted in large quantities by mucosal epithelia, and cell surface mucins are a prominent feature of the apical glycocalyx of all mucosal epithelia. In this review, we highlight the central role played by mucins in accommodating the resident commensal flora and limiting infectious disease, interplay between underlying innate and adaptive immunity and mucins, and the strategies used by successful mucosal pathogens to subvert or avoid the mucin barrier, with a particular focus on bacteria.

Mucin overproduction in chronic inflammatory lung disease

Mucus overproduction and hypersecretion are commonly observed in chronic inflammatory lung disease. Mucins are gel-forming glycoproteins that can be stimulated by a variety of mediators. The present review addresses the mechanisms involved in the upregulation of secreted mucins. Mucin induction by neutrophil elastase, bacteria, cytokines, growth factors, smoke and cystic fibrosis transmembrane conductance regulator malfunction are also discussed.

Characterizing mucous cell remodeling in cystic fibrosis: relationship to neutrophils

RATIONALE

Relatively few studies have characterized mucous cells or mucins in detail in cystic fibrosis (CF), and the relationship between mucous cell abnormalities and neutrophilic inflammation is uncertain.

OBJECTIVES

To characterize mucous cell phenotypes and mucin profiles in CF and to determine if neutrophils accumulate around goblet cells in the epithelium and gland acini in the submucosa.

METHODS

Bronchial biopsies were collected from 7 subjects with CF and 15 control subjects, and the morphology of mucous cells was measured. Immunostains for gel-forming mucins and neutrophil elastase were quantified.

MEASUREMENTS AND MAIN RESULTS

Goblet cell size was increased in CF (p = 0.004), but the number of goblet cells was normal. The volume of submucosal glands was fourfold higher than normal (p = 0.031), but the proportion of mucous and serous cells in CF glands was normal. The patterns of expression of gel-forming mucins in epithelial and submucosal compartments in CF were similar to normal. Although neutrophil elastase immunostaining was intense in the epithelium in CF, neutrophils were largely absent around gland acini in the submucosa.

CONCLUSION

The most prominent pathologic feature in the CF airway is an increase in submucosal gland volume, but serous cell transdifferentiation to mucous cells does not occur, nor are gland acini inflamed with neutrophils. The mechanism for increased submucosal gland volume in CF deserves further study.

Relationship between secretory leukocyte protease inhibitor levels in bronchoalveolar lavage fluid and postoperative pulmonary complications in patients with esophageal cancer

BACKGROUND

We investigated whether secretory leukocyte protease inhibitor (SLPI) is associated with pulmonary complications after esophagectomy.

METHODS

We measured serial changes in the SLPI concentration in the bronchoalveolar lavage fluid (BALF) of 34 patients who underwent and examined the relationship between SLPI and postoperative morbidity.

RESULTS

Fifteen (44%) of 34 patients (high group) had a BALF SLPI concentration >90,000 pg/mL at the end of the surgery (postoperative day [POD] 0). There was no significant difference between the high group and other 19 patients (low group) with respect to age, sex, preoperative comorbid conditions, tumor stage, surgical technique, operating time, or blood loss volume. Days of intubation and pulmonary complication rate were significantly increased in the high group compared with the low group. Logistic regression analysis revealed that the BALF SLPI level on POD 0 was significant for pulmonary complications.

CONCLUSIONS

Our results indicate that assaying SLPI levels in BALF can be useful for the prediction of pulmonary complications after esophagectomy.

Neutrophil elastase stimulates MUC1 gene expression through increased Sp1 binding to the MUC1 promoter

We previously reported MUC1 was a cell surface receptor for Pseudomonas aeruginosa, and binding of bacteria to cells was significantly reduced by pretreatment with neutrophil elastase (NE) (Lillehoj EP, Hyun SW, Kim BT, Zhang XG, Lee DI, Rowland S, and Kim KC. Am J Physiol Lung Cell Mol Physiol 280: L181-L187, 2001). The current study was conducted to ascertain NE effects on MUC1 gene transcription, and MUC1 protein synthesis and degradation. A549 human lung carcinoma cells treated with NE exhibited significantly higher MUC1 protein levels in detergent lysates compared with cells treated with vehicle alone. Also, MUC1 protein shed into cell-conditioned medium was rapidly and completely degraded by NE. Actinomycin D blocked NE-stimulated increase in MUC1 protein expression, suggesting a mechanism of increased gene transcription that was confirmed by measurement of quantitatively greater MUC1 mRNA levels in NE-treated cells compared with controls. However, NE did not alter MUC1 mRNA stability, implying increased de novo transcription induced by the protease. NE increased promoter activity in A549 cells transfected with MUC1 gene promoter-luciferase reporter plasmid. This effect of NE was completely blocked by mithramycin A, an inhibitor of Sp1, as well as mutation of one of the putative Sp1 binding sites in MUC1 promoter located at -99/-90 relative to transcription initiation site. EMSA revealed NE enhanced binding of Sp1 to this 10-bp segment in a time-dependent manner. These results indicate the increase in MUC1 gene transcription by NE is mediated through increase in Sp1 binding to -99/-90 segment of MUC1 promoter.

Neutrophil elastase induces mucus cell metaplasia in mouse lung

Goblet cell hyperplasia in the superficial airway epithelia is a signature pathological feature of chronic bronchitis and cystic fibrosis. In these chronic inflammatory airway diseases, neutrophil elastase (NE) is found in high concentrations in the epithelial lining fluid. NE has been reported to trigger mucin secretion and increase mucin gene expression in vitro. We hypothesized that chronic NE exposure to murine airways in vivo would induce goblet cell metaplasia. Human NE (50 microg) or PBS saline was aspirated intratracheally by male Balb/c (6 wk of age) mice on days 1, 4, and 7. On days 8, 11, and 14, lung tissues for histology and bronchoalveolar lavage (BAL) samples for cell counts and cytokine levels were obtained. NE induced Muc5ac mRNA and protein expression and goblet cell metaplasia on days 8, 11, and 14. These cellular changes were the result of proteolytic activity, since the addition of an elastase inhibitor, methoxysuccinyl Ala-Ala-Pro-Val chloromethylketone (AAPV-CMK), blocked NE-induced Muc5ac expression and goblet cell metaplasia. NE significantly increased keratinocyte-derived chemokine and IL-5 in BAL and increased lung tissue inflammation and BAL leukocyte counts. The addition of AAPV-CMK reduced these measures of inflammation to control levels. These experiments suggest that NE proteolytic activity initiates an inflammatory process leading to goblet cell metaplasia.

Neutrophil elastase increases MUC4 expression in normal human bronchial epithelial cells

In chronic obstructive pulmonary diseases, the airway epithelium is chronically exposed to neutrophil elastase, an inflammatory protease. The cellular response to neutrophil elastase dictates the balance between epithelial injury and repair. Key regulators of epithelial migration and proliferation are the ErbB receptor tyrosine kinases, including the epidermal growth factor receptor. In this context, we investigated whether neutrophil elastase may regulate expression of MUC4, a membrane-tethered mucin that has recently been identified as a ligand for ErbB2, the major heterodimerization partner of the epidermal growth factor receptor. In normal human bronchial epithelial cells, neutrophil elastase increased MUC4 mRNA levels in both a concentration- and time-dependent manner. RNA stability assays revealed that neutrophil elastase increased MUC4 mRNA levels by prolonging the mRNA half-life from 5 to 21 h. Neutrophil elastase also increased MUC4 glycoprotein levels as determined by Western analysis, using a monoclonal antibody specific for a nontandem repeat MUC4 sequence. Therefore, airway epithelial cells respond to neutrophil elastase exposure by increasing expression of MUC4, a potential activator of epithelial repair mechanisms.

Regulation of protease-activated receptor-1 in mononuclear cells by neutrophil proteases

Neutrophils and mononuclear cells are implicated in the pathogenesis of several inflammatory conditions including chronic obstructive pulmonary disease (COPD). Neutrophil-derived serine proteases, such as cathepsin G (CG) and neutrophil elastase (NE), may interact with mononuclear cells via protease-activated receptors (PARs) which are seven-transmembrane G protein-coupled receptors activated by proteolytic cleavage of the extracellular N-terminus, and which, on activation, induce the release of several mediators and cytokines. We determined whether CG and NE could affect PAR-1 expression and function in mononuclear cells. Human blood mononuclear cells were isolated from 20 healthy donors. Surface and intracellular receptor expression and calcium mobilisation (using the calcium chelator, FLUO3-AM) were studied by fluorescence-assisted cell sorting (FACS analysis). Positive controls, i.e. thrombin (0.1-100 mU/ml) and the PAR-1-activating peptide SFLLRN (100 microM) induced a rapid and transient intemalisation of PAR-1 in monocytes and lymphocytes. CG but not NE had a similar effect. By contrast, in monocytes intracellular calcium mobilisation was induced by thrombin and SFLLRN but not by CG and NE. Thus, CG can induce intracellular PAR-1 sequestration without activation of the receptor, and may act as an antagonist and prevent subsequent activation of PAR-1 in mononuclear cells. These findings may be of relevance to the pathogenesis of COPD.

Effect of acute and chronic inflammatory stimuli on expression of protease-activated receptors 1 and 2 in alveolar macrophages

BACKGROUND

Protease-activated receptors 1 and 2 (PAR-1 and PAR-2) are 7-transmembrane G protein-coupled receptors activated by serine proteases in many cell types, including monocytes-macrophages, leading to the production of pro-inflammatory mediators, cytokines, and growth factors.

OBJECTIVE

We determined the influence of chronic smoking and asthma on the expression of PAR-1 and PAR-2 receptors on alveolar macrophages (AMs).

METHODS

We used RT-PCR and immunocytochemistry with confocal microscopy to determine mRNA and protein expression of PAR-1 and PAR-2 in AMs obtained from healthy smokers, asthmatic patients, and healthy subjects. In addition, we examined the effect of IL-1beta and LPS.

RESULTS

PAR1 mRNA was decreased, whereas PAR2 mRNA was increased in 24-hour cultured AMs from smokers when compared with values in AMs from healthy subjects. Paradoxically, there was a higher degree of PAR-1 protein staining in AMs from smokers, whereas PAR-2 staining was similar in smokers and healthy subjects. PAR-1 and PAR-2 mRNA and protein expression were similar in asthmatic patients and control subjects. IL-1beta and LPS had no effect on PAR1 and PAR2 gene expression by AMs.

CONCLUSIONS

There is a dissociation between gene and protein expression of PAR-1 and PAR-2. PAR-1 protein overexpression in AMs from smokers might be important in the pathophysiology of chronic airways disease.

Airway mucus: its components and function

The airway surface liquid (ASL), often referred to as mucus, is a thin layer of fluid covering the luminal surface of the airway. The major function of mucus is to protect the lung through mucociliary clearance against foreign particles and chemicals entering the lung. The mucus is comprised of water, ions, and various kinds of macromolecules some of which possess the protective functions such as anti-microbial, anti-protease, and anti-oxidant activity. Mucus glycoproteins or mucins are mainly responsible for the viscoelastic property of mucus, which is crucial for the effective mucociliary clearance. There are at least eight mucin genes identified in the human airways, which will potentially generate various kinds of mucin molecules. At present, neither the exact structures of mucin proteins nor their regulation are understood although it seems likely that different types of mucins are involved in different functions and might also be associated with certain airway diseases. The fact that mucins are tightly associated with various macromolecules present in ASL seems to suggest that the defensive role of ASL is determined not only by these individual components but rather by a combination of these components. Collectively, mucins in ASL may be compared to aircraft carriers carrying various types of weapons in defense of airbome enemies.

Neutrophil elastase induces MUC5AC gene expression in airway epithelium via a pathway involving reactive oxygen species

Neutrophil-predominant airway inflammation and mucus obstruction of the airways are major pathologic features of chronic airway diseases, including cystic fibrosis and chronic bronchitis. Neutrophils release elastase, a serine protease that impairs mucociliary clearance and stimulates goblet cell metaplasia and mucin production. We previously reported that neutrophil elastase increases expression of a major respiratory mucin gene, MUC5AC, by enhancing mRNA stability. However, the molecular mechanisms of elastase-regulated MUC5AC expression are not known. We hypothesized that reactive oxygen species, generated by elastase treatment, mediate MUC5AC gene expression. To test this hypothesis, A549, a respiratory epithelial cell line, was treated with elastase in the presence or absence of the oxygen radical scavenger, dimethylthiourea, or the iron chelator, desferrioxamine. MUC5AC mRNA levels were assessed by Northern analysis. Both antioxidants significantly inhibited elastase-induced MUC5AC gene expression. Dimethylthiourea also inhibited the neutrophil elastase (NE)-induced increase in MUC5AC expression in normal human bronchial epithelial cells. To determine whether elastase treatment generated reactive oxygen species, A549 and normal human bronchial epithelial cells were loaded with dichlorodihydrofluorescein, a fluorescent indicator of oxidative stress. NE treatment increased cellular fluorescence in both cell types, indicating generation of intracellular reactive oxygen species. We conclude that NE treatment increases MUC5AC gene expression by an oxidant-dependent mechanism.

Regulation of secretion from mucous and serous cells in the excised ferret trachea

Mucus hypersecretion is an important characteristic of many airway diseases. Mucin is the major component of mucus, and is secreted from surface goblet cells of the airway epithelium and mucous cells of submucosal glands. Lysozyme is an enzyme secreted by serous cells of airway submucosal glands. We hypothesized that secretagogues acting through different pathways would have different effects on tracheal mucin and lysozyme secretion. We used a sandwich enzyme-linked lectin assay (ELLA) to measure mucin-like glycoprotein secretion and a spectrophotometric method to measure lysozyme secretion from isolated ferret tracheal segments. We evaluated the secretory response to four secretagogues; prostaglandin F(2alpha) (PGF(2alpha)), adenosine triphosphate (ATP), methacholine (MCh), and human neutrophil elastase (HNE). Each agent stimulated mucin and lysozyme secretion. The relative potency was PGF(2alpha)< or =ATP<MCh<HNE for mucin and ATP< or =PGF(2alpha)<MCh<HNE for lysozyme secretion. We showed that there is an anatomic gradient for constitutive and stimulated mucin and lysozyme secretion with the distal tracheal segments secreting more mucin and lysozyme per gram of tissue than the proximal segments. This robust model system can be used to evaluate the regulation of airway mucous and serous cell secretion and to assess the effect of agents that might alter the secretory response. We confirm that on an equimolar basis, HNE is one of the most potent mucus secretagogues.

Secretion and gene expression of secretory leukocyte protease inhibitor by human airway submucosal glands

Submucosal glands were isolated within 4 h of death from tracheae and bronchi obtained from autopsied lungs, and the secretory response of secretory leukocyte protease inhibitor (SLPI) was examined with ELISA and a secretory index. Although human neutrophil elastase (HNE) at low concentrations increased SLPI secretion above the control level (i.e., 149% of control level at 10(-11) M), HNE at high concentrations significantly decreased it below the control level (i.e., 16% of control level at 10(-7) M). The decrease in SLPI concentration was shown to result from the degradation of SLPI by excessive HNE. Methacholine induced significant secretion (i.e., 363% of control level at 10(-5) M) that was abolished by both M(1) and M(3) receptor antagonists. A semiquantitative analysis of SLPI mRNA by RT-PCR and Southern blot showed that compared with the superficial epithelium, submucosal glands had a 30-fold or higher level of SLPI mRNA. Both HNE and methacholine significantly increased the level of SLPI mRNA in submucosal glands in a dose-dependent manner (i.e., 357% of control level at 10(-7) M and 175% of control level at 10(-5) M, respectively). These findings indicate that human airway submucosal glands can transcribe 30-fold or more SLPI mRNA than the superficial epithelium and that SLPI mRNA transcription and secretion are regulated by both HNE and muscarinic receptors.

Human neutrophil elastase releases two pools of mucinlike glycoconjugate from tracheal submucosal gland cells

Neutrophil elastase can contribute to the pathogenesis of increased airway reactivity and excess mucus secretion in many pulmonary diseases. Ten nanomolar human neutrophil elastase (HNE) effectively empties airway serous cells, raising the question of why HNE is not equally effective at emptying mucous cells of their stored mucin because total release of mucin granules is not seen in postmortem examination of even the most severe disease. To better resolve the mucus secretagogue action of HNE, we measured secretion of mucinlike glycoconjugates (MGCs) released from freshly isolated swine tracheal submucosal gland cells in fractions of the superfusate acquired every 2 min. Six to fifty nanomolar HNE released a fixed quantity of MGCs at an increasing rate with increasing concentrations of enzyme, an action consistent with the release of cell surface mucinlike molecules. The polycation poly-L-lysine (1 microg/ml) released a similar transient of MGCs. A steady-state doubling of MGC rate of release was seen as long as 100 nM HNE was present, but this stimulus represented less than a 1% release of stored MGCs/min and was consistent with release of mucin vesicles from cell stores. Both actions of HNE were inhibited by the specific inhibitors L-680833 and DMP-777 but not by 30 microM erythromycin. Therefore, HNE release of MGCs from tracheal submucosal glands is limited by both the fixed quantity of the MGCs in the transient pool and by the small steady-state response to the higher concentrations of enzyme.

Respiratory Syncytial Virus Stimulates Neutrophil Degranulation and Chemokine Release

Neutrophil infiltration of the airways is a common finding in respiratory syncytial virus (RSV) bronchiolitis. Neutrophil-derived chemokines and neutrophil granule contents can cause further inflammation, hyperresponsiveness, and damage of the airways. In this study, peripheral blood neutrophils incubated with RSV (multiplicity of infection (MOI) = 10) induced IL-8, macrophage inflammatory protein (MIP)-1α, MIP-1β, and myeloperoxidase (MPO) release. In contrast, LPS induced only chemokine but not MPO release. RSV-induced chemokine and MPO release was noncytotoxic as assessed by trypan blue exclusion. The mechanism of RSV-induced chemokine release was shown to be transcription dependent since cytokine mRNA synthesis was increased with RSV stimulation and the process was inhibited by actinomycin-D. In addition, the effect of dexamethasone (dex) on mediator release was also studied. Dex significantly inhibited chemokine release but did not inhibit MPO release. The mechanism of inhibition of the release of these chemokines is probably posttranscriptional since the mRNA synthesis was not inhibited by dex. We conclude that the release of chemokines (IL-8, MIP-1α, MIP-1β) and granule enzymes (MPO) by RSV-stimulated neutrophils may contribute to the pulmonary pathology in RSV bronchiolitis. These in vitro findings showing that dex failed to consistently inhibit all the RSV-induced release of neutrophil inflammatory mediators may explain the variable efficacy of corticosteroids in the treatment of RSV bronchiolitis.

Neutrophil elastase increases MUC5AC mRNA and protein expression in respiratory epithelial cells

Chronic neutrophil-predominant inflammation and hypersecretion of mucus are common pathophysiological features of cystic fibrosis, chronic bronchitis, and viral- or pollution-triggered asthma. Neutrophils release elastase, a serine protease, that causes increased mucin production and secretion. The molecular mechanisms of elastase-induced mucin production are unknown. We hypothesized that as part of this mechanism, elastase upregulates expression of a major respiratory mucin gene, MUC5AC. A549, a human lung carcinoma cell line that expresses MUC5AC mRNA and protein, and normal human bronchial epithelial cells in an air-liquid interface culture were stimulated with neutrophil elastase. Neutrophil elastase increased MUC5AC mRNA levels in a time-dependent manner in both cell culture systems. Neutrophil elastase treatment also increased MUC5AC protein levels in A549 cells. The mechanism of MUC5AC gene regulation by elastase was determined in A549 cells. The induction of MUC5AC gene expression required serine protease activity; other classes of proteases had no effect on MUC5AC gene expression. Neutrophil elastase increased MUC5AC mRNA levels by enhancing mRNA stability. This is the first report of mucin gene regulation by this mechanism.

Unique role of allergens and the epithelium in asthma

The respiratory epithelium has been regarded as an inert barrier separating the human airway from the external world. Equally allergens have been perceived to be environmental proteins which interact with immunocompetent cells, activate inflammatory cells via IgE and promote the allergic response. However many allergens are biochemically active and are able to increase epithelial permeability and to stimulate epithelial cells to produce cytokines, adhesion receptors and MHC Class II expression. Thus the biochemical properties of allergens are likely to be important in enhancing the allergic responses and disease.

Neutrophil elastase promotes rapid exocytosis in human airway gland cells by producing cytosolic Ca2+ oscillations

The molecular and ionic mechanisms responsible for the regulation of mucus exocytosis in human airway gland cells remain poorly defined. To determine whether dynamic changes of intracellular free Ca2+ concentration [Ca2+]i can promote different exocytotic responses, we monitored dynamic changes in [Ca2+]i and secretory granule (SG) exocytosis in individual human tracheal submucosal serous gland (HTG) cells. These changes were in response to exposure of the cells to three different secretagogues associated with airway inflammation and disease: human neutrophil elastase (HNE), histamine, and ATP. Dynamic changes in [Ca2+]i from single cells were determined with Indo-1/AM using quantitative UV laser microspectrofluorometry. The rate of SG exocytosis was measured in single cells by fluorescence videomicroscopy of SG degranulation and by the ELISA method. Exposure of HTG cells to a low concentration of HNE (1.0 microM) caused a high rate of SG exocytosis (52% decrease in the initial quinacrine fluorescence) during the first 8-min stimulation period compared with that observed following exposure of the cells to 100 microM histamine (10% decrease) or 100 microM ATP (6% decrease). In contrast to a rapid and transient rise in [Ca2+]i induced by histamine (1.0-100 microM) and ATP (10-100 microM), HNE (0.01-1 microM) generated asynchronous oscillations in [Ca2+]i over the first 8-min period. Depletion of internal Ca2+ stores with thapsigargin (500 nM) induced a significant reduction (P < 0.01) in the observed increases in [Ca2+]i upon addition of each of the secretagogues, but did not greatly affect the SG exocytotic responses. Interestingly, the removal of extracellular Ca2+ (+5 mM EGTA) significantly reduced (P < 0.01) both the [Ca2+]i increases and the rate of SG exocytosis following exposure to the secretagogues. We also demonstrate that the influx of extracellular Ca2+ and [Ca2+]i oscillations rather than the absolute level of [Ca2+]i regulate the rapid onset and extent of exocytotic responses to HNE in airway gland cells. Taken together, these results provide strong evidence that [Ca2+]i is a critical intracellular messenger in the regulation of exocytosis process in human airway gland cells.

Regulation of Mucin Secretion in the Ferret Trachea

Mucin is the major component of mucus and can be used as a marker for mucus secretion. The purpose of this study was to develop an in vitro method to evaluate the regulation of mucin secretion. To do this, we used a sandwiched enzyme-linked lectin assay to measure mucin secretion from isolated ferret tracheal segments. This assay entailed coating microtiter plate wells with dolichos biflorus agglutinin and detecting the bound mucin that was secreted into a buffer solution by the tracheal segments. We used this method to evaluate the secretory response to four secretogogues: prostaglandin F2α (PGF2α), adenosine triphosphate (ATP), methacholine, and human neutrophil elastase (HNE). Each agent stimulated mucin secretion above baseline secretion (ATP ( p = 0.022), PGF2α ( p = 0.009), and HNE ( p < 0.05)), and the relative potency of these secretogogues was PGF2α ≤ ATP < MCh < HNE. We also demonstrated that there is an anatomic gradient for both constitutive and stimulated mucin secretion, with the distal tracheal segments secreting more mucin per gram of weight than the proximal segments. This fairly simple and reproducible technique can be used to evaluate the regulation of mucin secretion in the airway and to assess the efficacy of agents that might alter the secretory response.