Agarose plug instillation causes goblet cell metaplasia by activating EGF receptors in rat airways

Smoking and COVID-19: What we know so far

The ongoing COVID-19 pandemic has placed a spotlight on infectious diseases and their associations with host factors and underlying conditions. New data on the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) virus are entering the public domain at a rapid rate such that their distillation often lags behind. To minimise weak associations becoming perceived as established paradigms, it is imperative that methodologies and outputs from different studies are appropriately critiqued and compared. In this review, we examine recent data on a potential relationship between smoking and COVID-19. While the causal role of smoking has been firmly demonstrated in regard to lung cancer and chronic obstructive pulmonary disease, such associations have the benefit of decades' worth of multi-centre epidemiological and mechanistic data. From our analysis of the available studies to date, it appears that a relationship is emerging in regard to patients with a smoking history having a higher likelihood of developing more severe symptoms of COVID-19 disease than non-smokers. Data on whether COVID-19 has a greater incidence in smokers than non-smokers is thus far, contradictory and inconclusive. There is therefore a need for some caution to be exercised until further research has been conducted in a wider range of geographical settings with sufficient numbers of patients that have been carefully phenotyped in respect of smoking status and adequate statistical control for confounding factors.

IL-19 Up-Regulates Mucin 5AC Production in Patients With Chronic Rhinosinusitis via STAT3 Pathway

The mucin gene, MUC5AC, is highly expressed both in chronic respiratory inflammatory diseases and inflammatory bowel disease where mucin secretion is regulated by members of the interleukin IL-20 subfamily. This study was conducted to determine the roles and mechanisms of IL-19, a member of the IL-20 subfamily, in regulating MUC5AC production in chronic rhinosinusitis (CRS). We analyzed the expression of mucin and MUC5AC in the nasal mucosa of patients with CRS through periodic acid Schiff (PAS) staining and immunohistochemical examination. Real-time quantitative PCR, ELISA, confocal microscopy and western blotting were used to measure MUC5AC expression in primary human nasal epithelium cells (PHNECs) stimulated with recombinant human IL-19 (rhIL-19), IL-19 receptor siRNA transfection or a control. The involvement of the STAT3 signaling pathway was examined using cryptotanshinone (CRY, an inhibitor of STAT3). Mucin and MUC5AC were significantly increased in mucosa of CRS patients with/without nasal polyps compared to mucosa isolated from controls who had no CRS, but there were no significant differences between these two groups. Pretreatment with rhIL-19 up-regulated the expression of MUC5AC levels in PHNECs. Knockdown of IL-20R2 and pretreatment with CRY attenuated MUC5AC production induced by rhIL-19. We propose that IL-19 up-regulates MUC5AC-induced mucin production via the STAT3 pathway in CRS, highlighting the important role IL-19 may play in mucin production in chronic respiratory diseases.

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.

Prevention of intubation-induced mucosal damage using a tube coated with 2-methacryloyloxyethyl phosphorylcholine polymer

BACKGROUND AND OBJECTIVE

Tracheal intubation is associated with various complications that include epithelial injury. Abrasion of the fragile tracheal epithelium can occur at the points of contact between the tube and mucosa subject to respiratory movement. In this original experiment, we examined the mucosal protective effect of coating endotracheal tubes with poly[2-methacryloyloxyethl phosphorylcholine (MPC)-co-n-butyl methacrylate] (PMB).

METHODS

We prepared four types of tubes: tube A (control, no coating), tube B (two coats, 0.5% PMB), tube C (10 coats, 0.5% PMB) or tube D (one coat, 5% PMB). Twenty-nine beagle dogs were divided into four groups and orally intubated with tube A, B, C or D for 4±0.5 h. The cuffs of extubated tubes were stained with haematoxylin. Paraffin sections from tracheal walls in contact with the inflated cuff were stained with haematoxylin/eosin and periodic acid-Schiff.

RESULTS

Cuffs of tubes A and B were strongly stained with haematoxylin because of attached epithelial cells. Stained areas in those of tubes C and D were significantly reduced. Histological analysis showed that a single coat of 5% PMB prevented epithelial abrasion and proliferation of goblet cells. Excess tracheal mucus was observed in the tube A group, but not in the tube D group.

CONCLUSION

Tracheal epithelial damage caused by intubation was greatly reduced or eliminated by PMB coating on the surface of the tracheal tube.

[Pharmacological treatment of hyperinflation]

Introduction Lung hyperinflation leads to breathlessness, limitation in exercise capacity and tolerance, and impaired quality of life. Thus, it is important to target this key and characteristic feature of COPD. Current knowledge Available pharmacological approaches rely mainly on bronchodilators, in particular beta2 agonists and anticholinergic agents. These treatments act through the reduction of expiratory airflow limitation. However, changes in classical indices of airflow obstruction do not accurately predict effects on hyperinflation and symptoms. The decrease in operating lung volumes (as reflected by inspiratory capacity or functional residual capacity) at rest and during exercise is one of the mechanisms by which these treatments improve quality of life and maybe also decrease the impact of exacerbations. The effect of beta2 agonists on hyperinflation might be amplified by concurrent treatment with inhaled corticosteroids. Perspectives The effect of new treatments targeting airways inflammation on hyperinflation remains to be explored. Conclusions Measuring the reduction in the degree of lung hyperinflation allows a better understanding of the symptomatic effect of COPD pharmacological treatments.

ERK/p44p42 mitogen-activated protein kinase mediates EGF-stimulated proliferation of conjunctival goblet cells in culture

PURPOSE

To determine whether activation of the ERK pathway by EGF leads to rat and human goblet cell proliferation.

METHODS

The conjunctiva was removed from male Sprague-Dawley rats. Human conjunctiva was removed during ocular surgery. The tissue was minced and goblet cells were grown. The cells were stimulated with EGF (10(-7) M) for 1 and 5 minutes and Western blot analysis was performed with an antibody against phosphorylated EGFR, to measure the activation of the EGF receptor (EGFR). The cells were incubated with EGF (10(-7) M) for 24 hours, and cell proliferation was measured by WST-8. Inhibitors were added either 20 minutes before EGF or 2 hours after. The cells were stimulated with EGF (10(-7) M) for 1 minute to 24 hours. The number of cells expressing phosphorylated ERK (pERK) in the nucleus and Ki-67 was determined by immunofluorescence.

RESULTS

EGF increased the activation of EGFR in rat conjunctival goblet cells. EGF-stimulated proliferation was inhibited by the EGFR inhibitor AG1478 and the MEK inhibitor U0126 in rat and human cultured goblet cells. EGF caused the translocation of pERK to the nucleus in a biphasic manner. Inhibition of the second peak with U0126 prevented proliferation. EGF-stimulated goblet cells progressed through the cell cycle expressing pERK in the nucleus.

CONCLUSIONS

EGF stimulated human and rat conjunctival goblet cell proliferation by activating the EGFR. EGFR stimulated ERK causing its biphasic translocation to the nucleus. The second peak response is responsible for cell proliferation, but the role of the first peak is not known.

Survival after lung volume reduction in chronic obstructive pulmonary disease: insights from small airway pathology

RATIONALE

COPD is associated with reduced life expectancy.

OBJECTIVES

To determine the association between small airway pathology and long-term survival after lung volume reduction in chronic obstructive pulmonary disease (COPD) and the effect of corticosteroids on this pathology.

METHODS

Patients with severe (GOLD-3) and very severe (GOLD-4) COPD (n = 101) were studied after lung volume reduction surgery. Respiratory symptoms, quality of life, pulmonary function, exercise tolerance, chest radiology, and corticosteroid treatment status were assessed preoperatively. The severity of luminal occlusion, wall thickening, and the presence of small airways containing lymphoid follicles were determined in resected lung tissue. Kaplan-Meier survival analysis and Cox proportional hazards models were used to determine the relationship between survival and small airway pathology. The effect of corticosteroids on this pathology was assessed by comparing treated and untreated groups.

MEASUREMENTS AND MAIN RESULTS

The quartile of subjects with the greatest luminal occlusion, adjusted for covariates, died earlier than subjects who had the least occlusion (hazard ratio, 3.28; 95% confidence interval, 1.55-6.92; P = 0.002). There was a trend toward a reduction in the number of airways containing lymphoid follicles (P = 0.051) in those receiving corticosteroids, with a statistically significant difference between the control and oral +/- inhaled corticosteroid-treated groups (P = 0.019). However, corticosteroid treatment had no effect on airway wall thickening or luminal occlusion.

CONCLUSIONS

Occlusion of the small airways by inflammatory exudates containing mucus is associated with early death in patients with severe emphysema treated by lung volume reduction surgery. Corticosteroid treatment dampens the host immune response in these airways by reducing lymphoid follicles without changing wall thickening and luminal occlusion.

Perinatal increases in TGF-α disrupt the saccular phase of lung morphogenesis and cause remodeling: microarray analysis

Transforming growth factor-α (TGF-α) and its receptor, the epithelial growth factor receptor (EGFR), have been associated with lung remodeling in premature infants with bronchopulmonary dysplasia (BPD). The goal of this study was to target TGF-α overexpression to the saccular phase of lung morphogenesis and determine early alterations in gene expression. Conditional lung-specific TGF-α bitransgenic mice and single-transgene control mice were generated. TGF-α overexpression was induced by doxycycline (Dox) treatment from embryonic day 16.5 (E16.5) to E18.5. After birth, all bitransgenic pups died by postnatal day 7 (P7). Lung histology at E18.5 and P1 showed abnormal lung morphogenesis in bitransgenic mice, characterized by mesenchymal thickening, vascular remodeling, and poor apposition of capillaries to distal air spaces. Surfactant levels (saturated phosphatidylcholine) were not reduced in bitransgenic mice. Microarray analysis was performed after 1 or 2 days of Dox treatment during the saccular (E17.5, E18.5) and alveolar phases (P4, P5) to identify genes induced by EGFR signaling that were shared or unique to each phase. We found 196 genes to be altered (>1.5-fold change; P < 0.01 for at least 2 time points), with only 32% similarly altered in both saccular and alveolar phases. Western blot analysis and immunostaining showed that five genes selected from the microarrays (egr-1, SP-B, SP-D, S100A4, and pleiotrophin) were also increased at the protein level. Pathological changes in TGF-α-overexpressing mice bore similarities to premature infants born in the saccular phase who develop BPD, including remodeling of the distal lung septae and arteries.

MUC5AC, a gel-forming mucin accumulating in gallstone disease, is overproduced via an epidermal growth factor receptor pathway in the human gallbladder

Despite evidence that mucin overproduction is critical in the pathogenesis of gallstones, the mechanisms triggering mucin production in gallstone disease are unknown. Here, we tested the potential implication of an inflammation-dependent epidermal growth factor receptor (EGF-R) pathway in the regulation of gallbladder mucin synthesis. In gallbladder tissue sections from subjects with cholesterol gallstones, mucus accumulation was associated with neutrophil infiltration and with increased expressions of EGF-R and of tumor necrosis factor-alpha (TNF-alpha). In primary cultures of human gallbladder epithelial cells, TNF-alpha induced EGF-R overexpression. In the presence of TNF-alpha, EGF-R ligands (either EGF or transforming growth factor-alpha) caused significant increases in MUC5AC mRNA and protein production, whereas expression of the other gallbladder mucins MUC1, MUC3, and MUC5B was unchanged. In addition, on gallbladder tissue sections from subjects with gallstones, increased MUC5AC immunoreactivity was detected in the epithelium and within mucus gel in the lumen. Studies in primary cultures demonstrated that MUC5AC up-regulation induced by the combination of TNF-alpha with EGF-R ligands was completely blunted by inhibitors of EGF-R tyrosine kinase and mitogen-activated protein/extracellular signal-related kinase kinase. In conclusion, an inflammation-dependent EGF-R cascade causes overproduction of the gel-forming mucin MUC5AC, which accumulates in cholesterol gallstone disease. The ability to interrupt this cascade is of potential interest in the prevention of cholesterol gallstones.

The inhibitory effects of rebamipide on cigarette smoke-induced airway mucin production

Cigarette smoke may be the main cause of chronic bronchitis. Exposure of cigarette smoke induces the recruitment of inflammatory cells in the airway epithelium, and release of the tumor necrosis factor alpha (TNFalpha) from airways. Previous reports have shown that cigarette smoke induces goblet cell metaplasia by activating an epidermal growth factor receptor (EGFR) cascade, and that this results in mucin production. Rebamipide (2-(4-chlorobenzoylamino)-3-[2(1H)-quinolinon-4-yl] propionic acid, OPC-12759) directly inhibits the production of superoxide (O2-) and inhibits proinflammatory cytokines (such as TNFalpha and IL-8). In the present study, we aimed to analyze the inhibitory effects of rebamipide on TNFalpha and EGFR activation after cigarette smoke treatment in vitro and in vivo. NCl-H292 cells and Sprague-Dawley rats were used for in vitro and in vivo studies. In vitro studies, cigarette smoke solution was found to increase TNFalpha secretion, and EGFR-specific tyrosine phosphorylation, and to elevate MUC5AC production. These effects were inhibited dose-dependently by pretreatment with rebamipide (MUC5AC protein levels were inhibited from 44% to 17%, P<0.05). In vivo studies, cigarette smoke was found to cause inflammatory cell recruitment and to increase the secretion of TNFalpha in bronchoalveolar lavage (BAL) fluids (from 198+/-78 to 2270+/-158 pg/ml, P<0.01). Moreover, the pretreatment of rats with rebamipide inhibited goblet cell metaplasia and TNFalpha secretion, dose-dependently (from 2270+/-158 to 1377+/-112 pg/ml, P<0.05). In conclusion, the exposure of airway epithelium to cigarette smoke-induced TNFalpha production, neutrophil recruitment, activated EGFR, and caused MUC5AC mucin synthesis. Moreover, rebamipide was found to prevent this cigarette smoke-induced TNFalpha release, and mucin production.

Neutrophil elastase causes MUC5AC mucin synthesis via EGF receptor, ERK and NF-kB pathways in A549 cells

BACKGROUND

Neutrophil elastase (NE) was found to increase the respiratory mucin gene, MUC5AC, although the molecular mechanisms of this process remain unknown. We attempted to determine the signal transduction pathway through which NE induces MUC5AC gene expression in bronchial epithelial cells.

METHODS

A fragment of 1.3 Kb MUC5AC promoter which had been cloned into the pGL3-Basic luciferase vector was transfected to the A549 cells. By measuring the luciferase activity, we were able to evaluate the MUC5AC promoter activity in A549 cells. The involvement of mitogen-activated protein kinases (MAPK) was confirmed by Western blotting. To confirm the involvement of nuclear factorkappaB (NF-kB), we used site-directed mutagenesis and electrophoretic mobility shift assay (EMSA) autoradiogram. The MUC5AC mRNA expression was confirmed by RT-PCR.

RESULTS

NE increased the transcriptional activity of the MUC5AC promoter in A549 cells. The increased transcriptional activity of the MUC5AC promoter by NE was found to be associated with increased NF-kB activity. Site-directed mutagenesis showed that the transfection of the mutated NF-kB binding sites from the PGL3-MUC5AC-3752 promoter luciferase reporter plasmid decreased the luciferase activity after NE stimulation. Among the MAPKs, only extracellular signal-regulated kinases (ERK) were involved in this NE-induced MUC5AC mucin expression. RT-PCR also showed that NE increased MUC5AC mRNA. An EMSA autoradiogram revealed that NE induced NF-kB:DNA binding.

CONCLUSIONS

These results indicate that human NE induces MUC5AC mucin through the epidermal growth factor receptor (EGF-R), ERK, and NF-kB pathways in A549 cells.

E-cadherin promotes EGFR-mediated cell differentiation and MUC5AC mucin expression in cultured human airway epithelial cells

In previous work, we showed that epidermal growth factor receptor (EGFR) activation causes mucin expression in airway epithelium in vivo and in human NCI-H292 airway epithelial cells and normal human bronchial epithelial (NHBE) cells in vitro. Here we show that the cell surface adhesion molecule, E-cadherin, promotes EGFR-mediated mucin production in NCI-H292 cells in a cell density- and cell cycle-dependent fashion. The addition of the EGFR ligand, transforming growth factor (TGF)-alpha, increased MUC5AC protein expression markedly in dense, but not in sparse, cultures. MUC5AC-positive cells in dense cultures contained 2 N DNA content and did not incorporate bromodeoxyuridine, suggesting that they develop via cell differentiation and that a surface molecule involved in cell-cell contact is important for EGFR-mediated mucin production. In support of this hypothesis, in dense cultures of NCI-H292 cells and in NHBE cells at air-liquid interface, blockade of E-cadherin-mediated cell-cell contacts decreased EGFR-dependent mucin production. E-cadherin blockade also increased EGFR-dependent cell proliferation and TGF-alpha-induced EGFR tyrosine phosphorylation in dense cultures of NCI-H292 cells, suggesting that E-cadherin promotes EGFR-dependent mucin production and inhibits EGFR-dependent cell proliferation via modulation of EGFR phosphotyrosine levels. Furthermore, in dense cultures, E-cadherin blockade decreased the rate of EGFR tyrosine dephosphorylation, implicating an E-cadherin-dependent protein tyrosine phosphatase in EGFR dephosphorylation. Thus E-cadherin promotes EGFR-mediated cell differentiation and MUC5AC production, and our results suggest that this occurs via a pathway involving protein tyrosine phosphatase-dependent EGFR dephosphorylation.

Titanium dioxide particle-induced goblet cell hyperplasia: association with mast cells and IL-13

Background

Inhalation of particles aggravates respiratory symptoms including mucus hypersecretion in patients with chronic airway disease and induces goblet cell hyperplasia (GCH) in experimental animal models. However, the underlying mechanisms remain poorly understood.

Methods

To understand this, the numbers of goblet cells, Muc5ac (+) expressing epithelial cells and IL-13 expressing mast cells were measured in the trachea of sham or TiO₂ particles – treated rats using periodic acid-Schiff, toluidine blue and immunohistochemical staining. RT-PCR for Muc-1, 2 and 5ac gene transcripts was done using RNA extracted from the trachea. Differential cell count and IL-13 levels were measured in bronchoalveolar lavage (BAL) fluid. In pretreatment groups, cyclophosphamide (CPA) or dexamethasone (DEX) was given before instillation of TiO₂. TiO₂ treatment markedly increased Muc5ac mRNA expression, and Muc5ac (+) or PAS (+) epithelial cells 48 h following treatment.

Results

The concentration of IL-13 in BAL fluids was higher in TiO₂ treated – rats when compared to those in sham rats (p < 0.05). Pretreatment with cyclophosphamide (CPA) decreased the number of neutrophils and eosinophils in BAL fluid of TiO₂ treated – rats (p < 0.05), but affected neither the percentage of PAS (+) cells, nor IL-13 levels in the BAL fluids (p > 0.05). In contrast, pretreatment with dexamethasone (DEX) diminished the percentage of PAS (+) cells and the levels of IL-13 (p < 0.05). TiO₂ treatment increased the IL-13 (+) mast cells (p < 0.05) in the trachea, which was suppressed by DEX (p < 0.05), but not by CPA pretreatment (p > 0.05). In addition there were significant correlations of IL-13 (+) rate of mast cells in the trachea with IL-13 concentration in BAL fluid (p < 0.01) and with the percentage of Muc5ac (+) cells in the sham and TiO₂ treated rats (p < 0.05).

Conclusion

In conclusion, TiO₂ instillation induces GCH and Muc5ac expression, and this process may be associated with increased production of IL-13 by mast cells.

Role of neutrophils in mucus hypersecretion in COPD and implications for therapy

Airway mucus hypersecretion is a serious and presently untreatable symptom of COPD. Over the past several years, emerging evidence has implicated epidermal growth factor receptor (EGFR) expression and activation in mucin production by airway epithelial (goblet) cells. Activated neutrophils recruited to the airways (and their secreted products) play several key roles in EGFR-dependent mucus hypersecretion: (i) activated neutrophils secrete tumor necrosis factor (TNF)-alpha, which induces EGFR expression in airway epithelial cells; (ii) activated neutrophils release reactive oxygen species, which activate EGFR; (iii) neutrophil elastase cleaves the EGFR proligand, pro-transforming growth factor (TGF)-alpha, releasing mature TGF alpha which activates EGFR in a ligand-dependent fashion; and (iv) neutrophil elastase causes potent goblet cell degranulation. The secretion of active products by neutrophils appears carefully regulated. The local release of neutrophil elastase requires close contact between the neutrophil and another cell, mediated by surface adhesion molecules, thus limiting proteolysis to the immediate pericellular environment. In the airway lumen, neutrophils undergo apoptosis and are cleared by macrophages without releasing their intracellular contents. In contrast, neutrophils that die by necrosis disgorge proteases and reactive oxygen species into the lumen. In COPD, conditions within the airway lumen promote neutrophil necrosis. It is concluded that neutrophil death via necrosis leads to the high concentrations of free neutrophil elastase and reactive oxygen species in the sputum of patients with airway neutrophilia and mucus hypersecretion. Inflammatory cells (neutrophils), molecules (neutrophil elastase and reactive oxygen species), signaling pathways (EGFR), and cellular processes (neutrophil necrosis) contribute to mucus hypersecretion in COPD, and are potential targets for therapy. Interventions that target EGFR, neutrophil elastase, and reactive oxygen species exist and can be evaluated as treatments for neutrophil-dependent mucus hypersecretion.

fMLP causes degranulation followed by regranulation in rat nasal glands

OBJECTIVE

To determine the mechanism of mucus production by nasal glands.

STUDY DESIGN

Because neutrophilic inflammation is associated with mucus hypersecretion in disease states, here we examine the role of neutrophil recruitment in mucous cell degranulation and regranulation in rat nasal glands.

METHODS

N-formyl-methionyl-leucyl-phenylalanine (fMLP) was aerosolized intranasally in rats (n = 5), and its effects on degranulation and regranulation of submucosal glands were evaluated by Alcian blue/periodic acid-Schiff (AB/PAS) staining and by immunolocalization of neutrophils and epidermal growth factor receptor (EGF-R).

RESULTS

In control subjects, glands were filled with mucin. After fMLP inhalation, degranulation, 31.7 +/- 0.8% (P <.01), was maximal at 2 to 4 hours. By 24 to 48 hours after fMLP inhalation, degranulation had decreased to 10.3 +/- 0.6% (P <.05), indicating that regranulation of mucous glycoconjugates was occurring. After fMLP inhalation, neutrophils around submucosal glands increased within 0.5 hours from 1.4 +/- 0.1 to 9.5 +/- 0.3 per 0.0032 mm2 (P <.05). In control subjects, EGF-R protein was expressed near acinar ducts, 16.4 +/- 0.7% of gland area, and increased to 30.9 +/- 0.9% (P <.05) 24 to 48 hours after fMLP inhalation. Nasal pretreatment with a selective EGF-R tyrosine kinase inhibitor (BIBX1522, 15 mg/kg bid) prevented regranulation at 24 hours after fMLP inhalation (degranulation 27.8 +/- 0.3%, P <.05, compared to 24 hours after fMLP alone), indicating that inhibition of EGF-R activation had prevented regranulation after fMLP inhalation.

CONCLUSIONS

Degranulation of rat nasal glands by fMLP is followed by regranulation; regranulation depends on a neutrophil-associated EGF-R cascade.

Interleukin-9 induces mucous cell metaplasia independent of inflammation

Interleukin-9 (IL-9) has been strongly implicated in the pathogenesis of asthma, including the overproduction of mucus, in humans and in animal models. We evaluated the inflammatory changes associated with the upregulation of mucus production by examining the time course of inflammation after daily intratracheal IL-9 administration to naive C57Bl6 mice for 9 d. IL-9 induced an asthmatic phenotype, which in general took several days to develop, as assessed by the measurement of airway hyperresponsiveness, pulmonary inflammation, and serum immunoglobulin E. However, within 24 h of a single dose of IL-9, muc5ac mRNA upregulation occurred, and increased numbers of periodic acid Schiff/Alcian blue-positive mucous cells appeared. This response occurred before the development of an inflammatory cell influx and was the result of epithelial metaplasia. It seemed that IL-9 evoked mucous cell metaplasia independent of IL-13 because mRNA tissue evaluation indicated that muc5ac upregulation preceded any increase in IL-13 mRNA expression or detectable levels of IL-13 in the brochoalveolar lavage fluid. Therefore, the upregulation of IL-13 by IL-9 may be responsible for the amplification of mucus production but is not required for its initiation. IL-9 seems to directly stimulate mucous cell metaplasia without the requirement of inflammatory cell influx.

High levels of sulfated mucins in bronchoalveolar lavage fluid of ICU patients with ventilator-associated pneumonia

OBJECTIVE

To compare the levels of sulfated mucins in bronchoalveolar lavage fluid (BALF) in ICU patients with ventilator-associated pneumonia (VAP) with those in non-infectious controls, i.e., ventilated ICU patients without VAP, and nonventilated patients.

DESIGN AND SETTING

Prospective study in a mixed intensive care unit and outpatient clinic of a university hospital.

PATIENTS

The study included 56 ventilated ICU patients with VAP, 21 ventilated ICU patients without VAP, and 26 nonventilated outpatients with no pulmonary infection.

MEASUREMENTS AND RESULTS

Total cell count and differential cell count of BALF samples were determined, and sulfated mucin levels were measured. For this we used the monoclonal antibody F2 against the sulfated Lewis C structure (SO(3)-3Galbeta1-3GlcNAc). Sulfated mucin levels were significantly increased in ICU patients with VAP than in those without VAP and nonventilated patients. No statistical difference was found between the two groups of ICU patients regarding APACHE II score and the duration of mechanical ventilation prior to the bronchoalveolar lavage.

CONCLUSIONS

The increased levels of sulfated mucins in ICU patients with VAP are associated with infection and not with ventilation. The increase in sulfated mucins may favor the persistence of those micro-organisms that possess mucin sulfatase activity, which enable them to survive within the mucus, especially Pseudomonas aeruginosa.

Expression of epidermal growth factor receptor and its ligands in chronic sinusitis

The epidermal growth factor receptor (EGF-R) system plays a crucial role in mucus production in vitro and in rats. However, the role of the EGF-R system in humans is not known. We compared the localization of EGF-R and its ligands (epidermal growth factor and transforming growth factor alpha) in the epithelia of sinuses with chronic sinusitis and in those of healthy controls. Immunohistochemical techniques were employed to identify the presence of EGF-R and its ligands in the sinus mucosa. We found EGF-R in goblet cells, basal cells, and submucosal gland cells, but not in ciliated cells. Immunoreactivity for both epidermal growth factor and transforming growth factor alpha was found in the epithelial cells and inflammatory cells and in some submucosal gland cells. There was stronger staining of EGF-R and its ligand proteins in chronic sinusitis specimens than in controls. The interrelated localization of EGF-R and its ligands suggests a role in mucus production in the epithelium of the sinus mucosa.

Neutrophil elastase induces mucin production by ligand-dependent epidermal growth factor receptor activation

Neutrophil products are implicated in hypersecretory airway diseases. To determine the mechanisms linking a proteolytic effect of human neutrophil elastase (HNE) and mucin overproduction, we examined the effects of HNE on MUC5AC mucin production in human airway epithelial (NCI-H292) cells. Stimulation with HNE for 5-30 min induced MUC5AC production 24 h later, which was prevented by HNE serine active site inhibitors, implicating a proteolytic effect of HNE. MUC5AC induction was preceded by epidermal growth factor receptor (EGFR) tyrosine phosphorylation and was prevented by selective EGFR tyrosine kinase inhibitors, implicating EGFR activation. HNE-induced MUC5AC production was inhibited by a neutralizing transforming growth factor-alpha (TGF-alpha, an EGFR ligand) antibody and by a neutralizing EGFR antibody but not by oxygen free radical scavengers, further implicating TGF-alpha and ligand-dependent EGFR activation in the response. HNE decreased pro-TGF-alpha in NCI-H292 cells and increased TGF-alpha in cell culture supernatant. From these results, we conclude that HNE-induced MUC5AC mucin production occurs via its proteolytic activation of an EGFR signaling cascade involving TGF-alpha.

IL-13-induced Clara cell secretory protein expression in airway epithelium: role of EGFR signaling pathway

Previous work showed that the Th2 cytokine interleukin (IL)-13 induces goblet cell metaplasia via an indirect mechanism involving the expression and subsequent activation of epidermal growth factor receptor (EGFR). Because Clara cell secretory protein (CCSP) expression has been reported in cells that express mucins, we examined the effect of IL-13 on CCSP gene and protein expression in pathogen-free rat airways and in pulmonary mucoepidermoid NCI-H292 cells. Intratracheal instillation of IL-13 induced CCSP mRNA in epithelial cells without cilia within 8-16 h, maximal between 24 and 48 h; CCSP immunostaining increased in a time-dependent fashion, maximal at 48 h. The CCSP immunostaining was localized in nongranulated secretory cells and goblet cells and in the lumen. Pretreatment with the selective EGFR tyrosine kinase inhibitor BIBX1522, cyclophosphamide (an inhibitor of bone marrow leukocyte mobilization), or a blocking antibody to IL-8 prevented CCSP staining. Treatment of NCI-H292 cells with the EGFR ligand transforming growth factor-alpha, but not with IL-13 alone, induced CCSP gene and protein expression. Selective EGFR tyrosine kinase inhibitors, BIBX1522 and AG1478, prevented CCSP expression in NCI-H292 cells, but the platelet-derived growth factor receptor tyrosine kinase inhibitor AG1295 had no effect. These findings indicate that IL-13 induces CCSP expression via an EGFR- and leukocyte-dependent pathway.

Remodeling of the airway epithelium in asthma

Several pathologic changes occur in the airway epithelium in asthma, but the relationship between these changes and the initiation and progression of asthma remains poorly understood. One possibility is that changes in the structure and function of the epithelium induced by environmental exposure in genetically susceptible subjects represent primary pivotal events that occur early in the pathogenesis of asthma. Alternatively, these epithelial changes may occur simply as a consequence of pivotal early events in other systems, such as immune deviation in childhood to a helper T cell type 2 (Th2) subtype of CD4(+) cells. Epithelial desquamation in asthma represents a pathologic change that is frequently cited as important for the mechanisms of airway remodeling and airway hyperresponsiveness. Desquamation of the epithelium may not represent true pathology, however, but may instead be an artifact of tissue sampling and handling. Evidence is more firm for other pathologic changes in the epithelium. For example, goblet cell numbers are increased in asthma, leading to increases in stored mucins in the epithelium and in secreted mucins in sputum. The functional consequences of these changes include sputum production and airway narrowing, which lead to asthma exacerbations. Currently available data suggest that an important mechanism for goblet cell hyperplasia in asthma is the action of Th2 cytokines. Improved understanding of epithelial goblet cell abnormalities in asthma will hopefully lead to novel therapies for mucin hypersecretion, which is an important cause of morbidity and mortality.

Epidermal growth factor receptor signaling mediates regranulation of rat nasal goblet cells

BACKGROUND

Mucus hypersecretion is a common response to inflammation in the lower airways and is a hallmark of chronic rhinitis.

OBJECTIVE

The purpose of this study was to elucidate the mechanisms of regranulation (mucus production) of goblet cells in nasal epithelium.

METHODS

Because neutrophils induce an epidermal growth factor (EGFR) cascade, we induced degranulation of goblet cells in rat nasal respiratory epithelium by means of intranasal inhalation of N-formyl-methionyl-leucyl-phenylalanine (fMLP), and we examined regranulation of the goblet cells and the role of EGFR inhibitors and neutrophils in the regranulation process.

RESULTS

In the control state Alcian blue/periodic acid-Schiff and mucin MUC5AC staining was present. Degranulation was induced in the nasal septal epithelium 4 hours after intranasal inhalation of fMLP (10(-7) mol/L); 48 hours later, goblet-cell regranulation was complete. In the control state EGFR protein staining was absent in the epithelium, but after fMLP-induced degranulation, EGFR protein was expressed. After pretreatment with BIBX1522, a selective EGFR tyrosine kinase inhibitor, fMLP-induced degranulation was unaffected, but goblet-cell regranulation was prevented completely.

CONCLUSION

These data suggest a role for the EGFR cascade in neutrophil-dependent production of goblet-cell mucins. Proving this theory will require the use of selective EGFR inhibitors in clinical studies of nasal hypersecretory states.

Role of epidermal growth factor receptor activation in regulating mucin synthesis

Healthy individuals have few goblet cells in their airways, but in patients with hypersecretory diseases goblet-cell upregulation results in mucus hypersecretion, airway plugging, and death. Multiple stimuli produce hypersecretion via epidermal growth factor receptor (EGFR) expression and activation, causing goblet-cell metaplasia from Clara cells by a process of cell differentiation. These cells are also believed to be the cells of origin of non-small-cell lung cancer, but this occurs via cell multiplication. The mechanisms that determine which pathway is chosen are critical but largely unknown. Although no effective therapy exists for hypersecretion at present, the EGFR cascade suggests methods for effective therapeutic intervention.

Relationship of epidermal growth factor receptors to goblet cell production in human bronchi

To determine the relationship of epidermal growth factor receptor (EGFR) expression to mucin synthesis in human airways, we examined EGFR and MUC5AC expression at both gene and protein levels using in situ hybridization and immunohistochemical analysis in human bronchi. Bronchial mucosal biopsy specimens were obtained from 12 asthmatic subjects and 11 healthy subjects. In asthmatic airways, EGFR mRNA was expressed in the airway epithelium. EGFR immunoreactivity staining patterns varied among the asthmatic airways: staining was positive mainly in goblet cells, in basal cells, or in both. In contrast, healthy airways showed little expression of EGFR mRNA; EGFR immunoreactivity was observed mainly in goblet cells. In parallel to EGFR expression, MUC5AC mRNA expression was greater in asthmatic airways; mucous glycoconjugates that stained positively with Alcian blue/PAS were also increased in asthmatic airways. Ciliated cells were negative for EGFR and MUC5AC both in asthmatic and in healthy subjects at both mRNA and protein levels. There was a significant positive correlation between EGFR immunoreactivity and the area of MUC5AC-positive staining in both asthmatics and healthy subjects. These findings suggest a sequence of events by which EGFR activation is involved in mucin expression in asthmatic airway epithelium.

IL-13 induces mucin production by stimulating epidermal growth factor receptors and by activating neutrophils

Mucus hypersecretion contributes to the morbidity and mortality in acute asthma. Both T helper 2 (Th2) cytokines and epidermal growth factor receptor (EGFR) signaling have been implicated in allergen-induced goblet cell (GC) metaplasia. Present results show that a cascade of EGFR involving neutrophils is implicated in interleukin (IL)-13-induced mucin expression in GC. Treatment with a selective EGFR tyrosine kinase inhibitor prevented IL-13-induced GC metaplasia dose dependently and completely. Instillation of IL-13 also induced tumor necrosis factor-alpha protein expression, mainly in infiltrating neutrophils. Control airway epithelium contained few leukocytes, but intratracheal instillation of IL-13 resulted in time-dependent leukocyte recruitment by IL-13-induced IL-8-like chemoattractant expression in airway epithelium. Pretreatment with an inhibitor of leukocytes in the bone marrow (cyclophosphamide) or with a blocking antibody to IL-8 prevented both IL-13-induced leukocyte recruitment and GC metaplasia. These findings indicate that EGFR signaling is involved in IL-13-induced mucin production. They suggest a potential therapeutic role for inhibitors of the EGFR cascade in the hypersecretion that occurs in acute asthma.

Barrett's metaplasia

The rate of oesophageal adenocarcinoma is increasing in the western world and has a poor prognosis mainly because individuals present at a late stage. Attempts to intervene at an early stage of tumour progression have not proven cost effective, although lesions identified during surveillance programmes have a better prognosis. As a consequence, there has been renewed interest in strategies that might prevent the precursor lesion Barrett's oesophagus. Furthermore, there is an improved understanding of genetic and environmental interactions necessary for the clonal expansion and propagation of metaplastic premalignant lesions. Clearly, three mechanisms promote cancer progression--inheritance of germ-line mutations or polymorphisms, sporadic mutagenesis, and local epigenetic alterations. Locally produced cytokines and bile acids in the refluxate create a microenvironment that sets the scene for metaplastic transformation of the oesophageal epithelium, mainly by directly affecting metaplastic stem cells.