Human neutrophil elastase releases cell surface mucins from primary cultures of hamster tracheal epithelial cells

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.

Involvement of the MAP kinase ERK2 in MUC1 mucin signaling

MUC1 mucin is a receptor-like glycoprotein expressed abundantly in various cancer cell lines as well as in glandular secretory epithelial cells, including airway surface epithelial cells. The role of this cell surface mucin in the airway is not known. In an attempt to understand the signaling mechanism of MUC1 mucin, we established a stable cell line from COS-7 cells expressing a chimeric receptor consisting of the extracellular and transmembrane domains of CD8 and the cytoplasmic (CT) domain of MUC1 mucin (CD8/MUC1 cells). We previously observed that treatment of these cells with anti-CD8 antibody resulted in tyrosine phosphorylation of the CT domain of the chimera. Here we report that treatment of CD8/MUC1 cells with anti-CD8 resulted in activation of extracellular signal-regulated kinase (ERK) 2 as assessed by immunoblotting, kinase assay, and immunocytochemistry. The activation of ERK2 was completely blocked either by a dominant negative Ras mutant or in the presence of a mitogen-activated protein kinase kinase (MEK) inhibitor. We conclude that tyrosine phosphorylation of the CT domain of MUC1 mucin leads to activation of a mitogen-activated protein kinase pathway through the Ras-MEK-ERK2 pathway. Combined with the existing data by others, it is suggested that one of the roles of MUC1 mucin may be regulation of cell growth and differentiation via a common signaling pathway, namely the Grb2-Sos-Ras-MEK-ERK2 pathway.

Muc1 mucins on the cell surface are adhesion sites for Pseudomonas aeruginosa

Recently, we cloned and characterized a full-length cDNA of the hamster Muc1 gene, the expression of which appears to be associated with secretory cell differentiation (Park HR, Hyun SW, and Kim KC. Am J Respir Cell Mol Biol 15: 237-244, 1996). The role of Muc1 mucins in the airway, however, is unknown. In this study, we investigated whether cell surface mucins are adhesion sites for Pseudomonas aeruginosa. Chinese hamster ovary (CHO) cells not normally expressing Muc1 mucin were stably transfected with the hamster Muc1 cDNA, and binding to P. aeruginosa was examined. Our results showed that 1) stably transfected CHO cells expressed both Muc1 mRNA and Muc1 mucins based on Northern and Western blot analyses, 2) Muc1 mucins present on the cell surface were degraded by neutrophil elastase, and 3) expression of Muc1 mucins on the cell surface resulted in a significant increase in adhesion of P. aeruginosa that was completely abolished by either proteolytic cleavage with neutrophil elastase or deletion of the extracellular domain by mutation. We conclude that Muc1 mucins expressed on the surface of CHO cells serve as adhesion sites for P. aeruginosa, suggesting a possible role for these glycoproteins in the early stage of airway infection and providing a model system for studying epithelial cell responses to bacterial adhesion that leads to airway inflammation in general and cystic fibrosis in particular.

Lipopolysaccharide Induces Mucus Cell Metaplasia in Mouse Lung

A murine model of lipopolysaccharide (LPS)-induced airway inflammation and epithelial cell phenotypic change, and the time courses of these events are described. A single intratracheal instillation of Pseudomonas aeruginosa LPS in mice resulted in massive recruitment of neutrophils to the lung 2 d after treatment as assessed by differential cell counts of the inflammatory cells in bronchoalveolar lavage fluid and histologic assessment of hematoxylin and eosin (H&E)-stained lung sections. The LPS-induced neutrophilic inflammation subsided substantially on Day 4 and essentially vanished by Day 7. Airway epithelial mucus cells were not detected by Alcian blue periodic acid-Schiff staining until Day 4 after LPS treatment and became more abundant in number as well as in mucus content on Day 7. The expression of Muc5ac messenger RNA (mRNA) as well as glycoprotein was enhanced on Day 2, peaked on Day 4, and decreased on Day 7, whereas enhanced expression of mucin core 2 beta6 N-acetylglucosaminyltransferase (C2GnT)-M mRNA was not detected until Day 4 and peaked on Day 7. The expression of C2GnT-L mRNA in the lung, a marker for activated leukocytes as well as mucus cells, peaked on Day 2 and remained moderately high until Day 7. C2GnT-L mRNA expression in LPS-treated lung correlated with the presence of neutrophils and the appearance of mucus cells in the airway epithelium. We conclude that mucus cell metaplasia and hyperplasia can be generated in mouse lungs with a single intratracheal instillation of LPS. In addition, C2GnT-M may serve as a marker for mucus cells in mouse lung. This LPS-induced mucus cell metaplasia and hyperplasia model should be useful for the study of Pseudomonas-induced airway mucus hypersecretory diseases.

Squamous differentiation downregulates Muc1 mucin in hamster tracheal surface epithelial cell

To investigate whether the squamous differentiation of primary hamster tracheal epithelial cell, which is induced by retinoic acid deficiency or chronic PMA treatment, regulates Muc1 expression, we first produced and characterized a monoclonal antibody against hamster tracheal Muc1 mucin using pGEX-Muc1 fusion protein as an antigen and the changes of Muc1 mucin expression was determined by Western blot. Squamous differentiation downregulated the expression of Muc1 mucin from HTSE cells. The decrease in the immunoreactivity of Muc1 mucin was parallel to the decrease in the immunoreactivity of high molecular weight mucin, which is secreted from HTSE cells. The data from the present study implicate a possible role of Muc1 mucin in squamous differentiation of HTSE cells.

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.

ATP induced MUC5AC release from human airways in vitro

BACKGROUND

Chronic airway diseases are often associated with marked mucus production, however, little is known about the regulation of secretory activity by locally released endogenous mediators.

AIM

This investigation was performed to determine the release of MUC5AC mucin from human bronchial preparations using the purinergic agonists adenosine 5'-triphosphate (ATP) and uridine 5'-triphosphate (UTP).

METHODS

Immunohistochemical and immunoradiometric assays (IRMA) were used to detect the MUC5AC mucin. Immunohistochemical analysis were performed using individual 1-13 M1 and 21 M1 MAbs recognizing a recombinant M1 mucin partially encoded by the MUC5AC gene. IRMA measurments were performed using a mixture of eight anti-M1 mucin MAbs (PM8), which included both 1-13 M1 and 21 M1 MAbs. Lysozyme and protein were also measured in the biological fluids derived from human bronchial preparations obtained from patients who had undergone surgery for lung carcinoma.

RESULTS

The anti-M1 monoclonal antibodies labelled epithelial goblet cells. After challenge of human bronchial preparations with ATP, the goblet cells exhibited less staining. In contrast, UTP did not alter the immunolabelling of goblet cells. MUC5AC mucin in the bronchial fluids derived from ATP-challenged preparations was increased while UTP had no effect on release. ATP did not alter either the quantities of lysozyme or protein detected in the biological fluids.

CONCLUSION

These results suggest that ATP may regulate epithelial goblet cell secretion of MUC5AC mucin from human airways in vitro.

Serine proteinase inhibitor therapy in alpha(1)-antitrypsin inhibitor deficiency and cystic fibrosis

Proteinase-antiproteinase imbalances are recognized in several diseases including the two most common lethal hereditary disorders of white populations, alpha(1)-antitrypsin (alpha(1)-AT) deficiency and cystic fibrosis (CF). In alpha(1)-AT deficiency, the type Z variant of alpha(1)-AT forms polymers in the endoplasmic reticulum of hepatocytes resulting in liver disease in childhood. The block in alpha(1)-AT processing in hepatocytes significantly reduces levels of circulating alpha(1)-AT. This may lead in young adults to panacinar emphysema due to insufficient protection of the lower respiratory tract from neutrophil elastase, permitting progressive destruction of the alveoli. In CF, chronic bacterial lung infections due to impaired mucociliary clearance lead to a vigorous influx of neutrophils in the airways. Released levels of neutrophil serine proteinases, particularly elastase, exceed the antiproteinase capacity of endogenous serine proteinase inhibitors in the airways. Progressive proteolytic impairment of multiple defense pathways in addition to endobronchial obstruction and airway wall destruction are thought to be responsible for the reduced life expectancy in CF patients. Strategies to augment the antiproteinase defenses in the airways of patients with severe alpha(1)-AT deficiency or CF include the intravenous or aerosol administration of serine proteinase inhibitors. Studies in both patient groups using plasma-derived or transgenic alpha(1)-AT, recombinant secretory leukoprotease inhibitor or synthetic elastase inhibitors show promising results concerning drug safety and efficacy.

Nucleotide-induced PMN adhesion to cultured epithelial cells: possible role of MUC1 mucin

Accumulation of intraluminal polymorphonuclear leukocytes (PMN) is a hallmark of inflammatory diseases of the airways. Extracellular nucleotides stimulate PMN adhesion to human main pulmonary artery endothelial cells (HPAEC) by a purinoceptor-mediated mechanism. We investigated the effects of nucleotides on adhesion of freshly isolated human PMN to cultured human tracheobronchial epithelial cells (HBEC). We found that extracellular ATP and UTP were much less effective in stimulating PMN adhesion to HBEC compared with HPAEC, whereas the bacterial chemotactic peptide N-formyl-Met-Leu-Phe stimulated PMN adhesion to both cell types to an equal degree. We investigated several mechanisms that might account for decreased nucleotide-induced PMN adhesion to HBEC. The ectonucleotidase-resistant ATP analog adenosine 5'-O-(3-thiotriphosphate) was also ineffective in stimulating PMN adhesion to HBEC, indicating that degradation of ATP by ectonucleotidase(s) was not responsible for altered PMN adhesion. HBEC responded to ATP and UTP with increased intracellular calcium, indicating that these cells are capable of purinoceptor-mediated responses. We found that ATP and UTP also did not stimulate PMN adhesion to Chinese hamster ovary (CHO) cells, which had been stably transfected with the gene for hamster Muc1, a cell-associated mucin. However, ATP and UTP did stimulate adhesion of PMN to nontransfected CHO cells. These results suggested that MUC1 mucin modulates PMN adhesion to epithelium. We found that cultured HBEC expressed more mRNA and protein for MUC1 mucin than did HPAEC. We conclude that extracellular nucleotides are less effective in stimulating PMN adhesion to epithelial cells than to endothelial cells and that overexpression of hamster Muc1 mucin inhibits nucleotide-induced PMN adhesion to CHO cells.

Inhibition of mucin release from airway goblet cells by polycationic peptides

In the present study, we investigated whether polycationic peptides affect mucin release from cultured airway goblet cells. Confluent primary hamster tracheal surface epithelial cells were metabolically radiolabeled with [(3)H]glucosamine for 24 h and chased for 30 min in the presence of varying concentrations of either poly-L-arginine (PLA) or poly-L-lysine (PLL) to assess the effects on [(3)H]mucin release. Possible cytotoxicity by the polycations was assessed by measuring lactate dehydrogenase release, (51)Cr release, and cell exfoliation. The results were as follows: 1) both PLA and PLL inhibited mucin release in a dose-dependent fashion; 2) there was no significant difference in either lactate dehydrogenase release, (51)Cr release, or the number of floating cells between control and treatment groups; 3) the effects of both PLA and PLL on mucin release were completely blocked by neutralizing the positive charges either by pretreatment with heparin or by N-acetylation of the polycations; and 4) both PLA and PLL completely masked the stimulatory effect of ATP on mucin release. We conclude that these polycationic peptides can inhibit mucin release from airway goblet cells without any apparent cytotoxicity, and the inhibitory effect seems to be attributable to their positive charges. These are the first nonsteroidal agents, to the best of our knowledge, that have been shown to inhibit mucin release from airway goblet cells.

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.

Recombinant human Monocyte/Neutrophil elastase inhibitor protects rat lungs against injury from cystic fibrosis airway secretions

Human monocyte/neutrophil elastase inhibitor (M/NEI) is a fast-acting stoichiometric inhibitor of neutrophil elastase (NE), cathepsin-G, and proteinase-3. Recombinant M/NEI (rM/NEI) was evaluated with a rat model of NE-induced lung damage. rM/NEI was found to protect against pulmonary injury caused by instilled human NE or by a preparation from airway secretions (sputum) of cystic fibrosis patients (CF sol). Human NE instilled into rat lungs produced dose-dependent hemorrhage and increased epithelial permeability, whereas NE incubated in vitro with rM/NEI did neither. Similarly, hemorrhage was induced by CF sol, but not by CF sol incubated in vitro with rM/NEI. To examine its distribution and survival time in airways, rM/NEI was labeled with the fluorochrome Texas Red (rM/NEI-TR) and instilled into rat lungs. Confocal microscopy showed that rM/NEI-TR could be detected on large airways (300 microm) at 5 min, 1 h, 4 h, and 24 h after instillation. Pretreating rats with rM/NEI was found to provide extended protection upon subsequent NE challenge, reducing hemorrhage by 98, 96, and 73%, respectively, at 1, 4, and 24 h after rM/NEI pretreatment. Pretreating rats with rM/NEI similarly conferred protection against subsequent exposure to CF sol, reducing hemorrhage by 95, 86, and 87%, respectively, at 1, 4, and 24 h after pretreatment. The findings that rM/NEI (1) mitigates protease-induced lung injury and (2) remains present and active in the lungs for 24 h after instillation strongly support its potential for treating patients with neutrophil protease-induced inflammatory lung damage, such as occurs in CF and other diseases.

CFTR antisense phosphorothioate oligodeoxynucleotides (S-ODns) induce tracheo-bronchial mucin (TBM) mRNA expression in human airway mucosa

Mucus hypersecretion is a critical component of cystic fibrosis (CF) pathogenesis. The effects of dysfunction of the cystic fibrosis transmembrane regulator (CFTR) on mucin expression were examined using the tracheo-bronchial mucin (TBM) gene as an indicator. TBM mRNA expression was assessed in a human bronchial epithelial cell line (HBE1) and human nasal mucosal explants in vitro. Antisense phosphorothioate oligodeoxynucleotides (S-ODN) to TBM suppressed baseline expression of TBM mRNA in both systems, but had no effect on glyceraldehyde phosphate dehydrogenase mRNA (GAPDH) expression. Sense and missense (multiple scrambled control oligonucleotides) S-ODNs had no effect. 8Br-cAMP and PGE1 significantly elevated TBM mRNA expression. These increases were also specifically inhibited by the antisense S-ODNs. In order to induce a CF-like state, S-ODN to CFTR were added to explants. Antisense CFTR S-ODNs were anticipated to reduce the expression of cellular CFTR protein, and the level of CFTR function. Antisense, but not sense or missense, CFTR S-ODN significantly increased TBM mRNA expression. These data suggest that mucin hypersecretion in CF may be a direct consequence of CFTR dysfunction; the specific mechanism through which this effect is mediated is not known.

Identification and characterization of high molecular-mass mucin-like glycoproteins in the plasma membrane of airway epithelial cells

A previous lectin binding study demonstrated the presence of high molecular-mass mucin-like glycoproteins (HMGP) on the surface of hamster tracheal surface epithelial (HTSE) secretory cells (Proc. Natl. Acad. Sci. USA 1987;84:9304). In the present study, we intended to isolate and characterize these HMGP from the plasma membrane of the primary HTSE cells and then to determine whether or not these membrane HMGP are Muc-1 mucins, a type of mucins originally discovered on the surface of some carcinomas. A subcellular fraction enriched with the plasma membrane was obtained using a sucrose density gradient centrifugation. This fraction contained high molecular-mass glycoconjugates which were excluded from Sepharose CL-4B gel. Biochemical characterization of these glycoconjugates revealed the following characteristics: (1) susceptibility to both pronase and mild alkaline treatments, but totally resistant to proteoglycan-digesting enzymes; (2) partitioning in the detergent phase of Triton X-114 and resistance to digestion by phosphatidylinositol phospholipase C or D; (3) a buoyant density of 1.5 g/ml based on CsCl density gradient centrifugation; (4) polydispersity in terms of both size and charge density; and (5) lack of immunoreactivity with an anti-Muc-1 mucin antibody. We conclude that the plasma membrane of HTSE cells at confluence contains HMGP, which seem to be the integral membrane proteins but different from Muc-1 mucins, and that these membrane HMGP appear to share some similarities with secreted mucins in terms of size and charge.

Comparison between ELISA and gel-filtration assay for the quantitation of airway mucins

In this study, we developed immunoassay methods for the more convenient and effective detection of rat tracheal mucin and the results were compared with those of [3H]glucosamine based gel-filtration method. A monoclonal anti-rat tracheal mucin antibody, mAbRT03, which specifically recognizes rat tracheal mucins, was used throughout in this study. To induce mucin secretion, varying concentrations of ATP (0-2 mM) were applied to the primary rat tracheal surface epithelial (RTSE) cell culture which had been metabolically radiolabeled with [3H]glucosamine and the secretion of mucin was analyzed both by the immunoassay and the gel-filtration chromatography methods. For the immunoassay, the following two procedures were employed. 1) Simple ELISA; the culture spent media were directly coated onto the assay plate and the immunoreactivity with mAbRT03 was assessed from the standard curve generated with the purified rat mucin. 2) Inhibition ELISA; A known amount of the purified rat mucin was coated onto the assay plate and then ATP-stimulated culture spent media were added to inhibit the immunoreactivity with mAbRT03. The contents of mucin in the sample were calculated from the standard inhibition curve which was generated with the purified rat mucin. The assay results obtained from the immunoassays were identical with those from the gel-filtration methods. The present result indicates that ELISA can be substituted for the laborious, time-consuming gel-filtration assay in studying the regulation of airway mucin release from cultured airway epithelial cells.

Sialomucin complex in the rat respiratory tract: a model for its role in epithelial protection

The pulmonary epithelium has a multitude of specialized functions, which depend on regulated growth and differentiation of several cell types. One such function is the synthesis and secretion of mucins, which offer the epithelium protection from and a means for removal of noxious environmental factors. Sialomucin complex (SMC) is a heterodimeric glycoprotein consisting of a mucin subunit (ASGP-1, ascites sialoglycoprotein-1) and a transmembrane protein (ASGP-2) with two epidermal-growth-factor-like domains. SMC was originally discovered in a highly metastatic rat mammary adenocarcinoma and has been implicated in metastasis and in the protection of the tumour cells from natural killer cells. It can also act as a ligand for the receptor tyrosine kinase 185(neu), suggesting that it is bifunctional as well as heterodimeric. SMC is expressed on the epithelium of rat conducting airways, with the highest levels occurring in the proximal trachea and progressively decreasing into the bronchioles. Airway SMC consists of two forms: a soluble form that lacks the C-terminal cytoplasmic and transmembrane domains and accounts for about 70% of the total, and a membrane-associated form that has the C-terminal domains. Immunocytochemical analyses show that SMC is predominantly present on the apical surfaces of the airway epithelium, but not in goblet cells. Soluble form can be removed from the trachea by rinsing, suggesting that a fraction of the protein is adsorbed to the apical surface. Based on these results, we propose a protective mechanism in which membrane and soluble forms of SMC are produced by airway luminal epithelial cells to provide a cell-associated epithelial glycoprotein barrier that also serves as an interface with flowing mucus. In support of this mechanism, we demonstrated secretion of soluble SMC by primary cultures of tracheal epithelial cells. This model suggests that SMC is a critical element in the protective barrier of the airway epithelium.

Abnormal mucous cell phenotype induced by neutrophil elastase in hamster bronchi

Bronchial mucous cell metaplasia (MCM) is a histologic component of chronic mucus hypersecretion. The hamster model of elastase-induced MCM appears to involve an irreversible conversion of Clara cells to mucous cells. The present study questioned whether the mucous cells seen in hamster bronchi exposed to neutrophil elastase produce and maintain a form of glycoconjugate secretory product different from that normally found in mucous cells or Clara cells. Ultrastructural cytochemistry using the gold-labeled lectin HPA revealed a difference in the cell surface and stored secretory granules of elastase-derived mucous cells compared to normal mucous cells and Clara cells at 3 weeks and 4 months following exposure. The results suggest that elastase irreversibly alters the glycoconjugate character of the Clara cells normally present so that they produce an abnormal form of mucus. Because secreted glycoconjugates can affect the rate of mucociliary clearance and receptor-mediated binding of microorganisms, this change in phenotype may be involved in the pathogenesis of diseases associated with chronic mucus hypersecretion in humans.

Diurnal variations in tear glycoproteins: evidence for an epithelial origin for the major non-reducible > or = 450 kDa sialoglycoprotein(s)

PURPOSE

To characterize the nature and origin of changes in tear glycoproteins accompanying eye closure.

METHODS

Reflex (R) and overnight closed (C) eye tears collected by capillary tubes were centrifuged with the resulting R pellets (primarily desquamated epithelial cells) and C pellets (primarily PMN and some epithelial cells) extracted in acidic PBS. Extracts and supernatants were separated by size-exclusion HPLC and/or SDS-PAGE. Gels were stained or blotted and immune- or lectin-probed. An HPLC glycoprotein fraction of > or = 450 kDa isolated from all four sources was characterized before and after partial deglycosylation, using antibodies specific to known mucin and carbohydrate epitopes. Immunofluorescence microscopy was carried out on human conjunctiva, using as probe a MAb to salivary mucin specific for a sialyl Lea epitope, which was found to cross-react specifically with the major non-reducible high molecular weight sialoglycoproteins (SGs) in tears. These SGs were immunoprecipitated and blot-probed along with tissue extracts.

RESULTS

R fluid contained minor amounts of numerous glycoproteins, including probably several of inducible lacrimal secretory origin. Results confirmed sIgA as the principal source of the intense reducible glycoprotein bands common to C fluid. Smaller amounts of free secretory component and serum glycoproteins were also visualized. The HPLC fraction (> or = 450 kDa) consisted of four major non-reducible glycoproteins. In R fluid, this fraction (< 1% total protein) consisted primarily of two entities: a 450-500 kDa SG and a larger asialoglycoprotein. The SG accounts for as much as 85% of the total protein in the R pellet extract. C fluid was associated with a selective increase in SGs and a shift in distribution to two SGs > 500 kDa. All SGs exhibited a common antigenicity reacting specifically with the MAb for the sialyl Lea epitope. SGs indistinguishable in size and antigenicity were recovered in epithelial extracts. Immunofluorescence microscopy revealed that reactivity was localized to the epithelial plasma membrane, increasing in intensity from basal to apical cells. Although these SGs exhibited some properties in common with MUC1, immunological and other data suggest a unique SG.

CONCLUSIONS

Tear glycoproteins are derived from four principal sources. In R fluid, an inducible lacrimal secretion predominates. In C fluid, a constitutive sIgA secretion predominates, augmented by a serum exudate and SGs derived at least in part from the epithelium. In R fluid and pellet extracts, the SGs consist primarily of a 450-500 kDa species that is most probably derived from the plasma membrane. Larger antigenically related SGs are prevalent in C fluid.

One-month exposure to inhaled endotoxin produces a dose-dependent increase in stored mucosubstances in rat intrapulmonary airways

This study examined the production of stored mucosubtances in rats after repeated exposure to aerosolized endotoxin, a common contaminant of bioaerosols. Male Fischer 344 rats were exposed to aerosolized saline (sham control) or endotoxin (target concentrations of 0.05, 0.5, and 5.0 micrograms/m3) for 3 h/day, 5 days/week for 4 weeks. Following the final exposure, the left lung of each animal was lavaged and the right lung and nasal cavity were fixed with buffered formalin. Morphometric examination of Alcian blue/Periodic acid Schiffs-stained (AB/PAS) lung sections demonstrated dose-dependent increases in stored intraepithelial mucosubstances in the intrapulmonary airways of endotoxin-exposed rats. Threefold and eightfold increases in stored mucosubstances were observed in generation 5 airways of animals exposed to 0.5 or 5.0 microgram/m3 endotoxin, respectively (p < .05). This mucous cell metaplasia in the intrapulmonary airways was not accompanied by evidence of lung inflammation or increased AB/PAS-staining high molecular weight material in lavage fluid. Furthermore, despite significant deposition of endotoxin aerosols (mass median aerodynamic diameter of 1.9 microns) in the nasal cavity, no significant changes in stored mucosubstances were observed in the nasal septum. In animals repeatedly exposed to 5.0 micrograms/m3 endotoxin and allowed to recover for 1 month, stored mucosubstances in the intrapulmonary airway were still more than fivefold greater than control values. Thus, in rats, repeated exposure to inhaled endotoxin produced a persistent mucous cell metaplasia only in the intrapulmonary airways.

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

Neutrophils may be central in the pathogenesis of several airway diseases. The effect of two neutrophil products upon mucus release from feline and human airways was examined in vitro. Neutrophil elastase (HNE) and cathepsin G (HCG) were equipotent in stimulating mucus release from feline trachea. A potential mechanism of the mucus release was studied by exposure to HNE and various inhibitors of serine proteases or eicosanoid metabolism. Coincubation with the serine protease inhibitor, chloromethylketone, completely blocked HNE-stimulated mucus release. The putative selective cyclooxygenase inhibitor, ibuprofen, did not alter HNE-stimulated mucus release. The phospholipase A2 inhibitor, bromophenacyl bromide, and various lipoxygenase inhibitors blocked HNE-stimulated mucus release by 30-40%. The effect of HNE upon mucus release from human upper and lower airways was also examined. HNE stimulated greater mucus release from human bronchi than from nasal mucosa. The cellular source of the mucus was investigated in feline trachea and human upper airway by quantitation of mucus using enzyme assays for a specific mucous cell marker (monoclonal antibody 7F-10). HNE stimulated the release of 7F-10 detectable mucus, and after coincubation with chloromethylketone this stimulation was blocked. These data demonstrate that neutrophil products may alter airway mucus secretion and that altered eicosanoid metabolism may partially mediate these effects. Additionally, the lower airways appear more responsive to HNE than upper airways.

Effect of floating a gel matrix on mucin release in cultured airway epithelial cells

Confluent cultures of primary hamster tracheal surface epithelial (HTSE) cells grown on a thick collagen gel are highly enriched with secretory cells and constitutively release mucins. In the present experiment, we examined the possible effect of mechanical strain of cultured HTSE cells on the release of mucin. The mechanical strain of cells was accomplished by several methods: 1) by floating the gel from the culture dish by rimming; 2) by treatment with EGTA which interrupts intercellular tight junctions; 3) by treatment with collagenase which disrupts the cell-matrix adhesion; and 4) by mechanically flexing the collagen gel matrix. All these conditions caused increases of mucin release without damage on the plasma membrane. We conclude that a number of mechanical strains which might alter cell shape can stimulate mucin release from cultured HTSE cells. Such a mechanism might be operative in the physiological regulation of airway goblet cell mucin secretion where mechanical strains may be induced on epithelial cells by underlying smooth muscles.

Nucleotide regulation of goblet cells in human airway epithelial explants: normal exocytosis in cystic fibrosis

The regulation of mucin secretion by airway goblet cells is poorly understood and the receptor-based regulatory mechanisms have not been described in human airways. In the present study, we report that extracellular triphosphate nucleotides regulate the rate of granule release from goblet cells in both normal and cystic fibrosis (CF) airway epithelial explants. Explants isolated from nasal and tracheobronchial tissues were mounted in perfusion chambers and the secretory activity was assessed by videomicroscopic determination of degranulation in single goblet cells and by ELISA determination of mucins secreted into the mucosal perfusate. Baseline degranulation was measured at 0.05 degranulation events (DE)/min. In normal goblet cells, mucosal ATP (10(-4) M, n = 17) induced a biphasic secretory response comprising 29.1 +/- 4.9 DE during the first 5 min, with an initial rate of 118.2 +/- 10.2 DE/min. Mucosal UTP (10(-4) M, n = 9) induced a similar response to ATP (initial rate: 89.2 +/- 23.9 DE/min, 17.9 +/- 5.1 DE in 5 min), but mucosal 2-MeSATP was not an effective agonist (initial rate: 1.5 +/- 1.4 DE/min, 2.3 +/- 0.5 DE in 5 min). Determination of mucins by ELISA confirmed that both ATP and UTP induced similar secretory responses but that 2-MeSATP was not effective. In CF explants, mucosal UTP (10(-4) M, n = 6) induced similar responses to those observed in normal tissues (initial rate: 82.5 +/- 27.5 DE/min, 18.8 +/- 4.1 DE in 5 min). We conclude that human nasal and tracheobronchial goblet cells are stimulated by mucosal nucleotides, probably via a 5'-nucleotide receptor, and that this response is unaffected by CF.

Elastase causes secretory discharge in bronchi of hamsters with elastase-induced secretory cell metaplasia

A single intratracheal instillation of human neutrophil elastase (HNE) into hamsters causes granule discharge from bronchial secretory cells followed by marked accumulation of granules, visible by light microscopy at 21 days and persisting through 18 months. To determine whether persistence of this secretory cell metaplasia (SCM) is due to inability of the metaplastic secretory cells to secrete their granules, hamsters having HNE-induced SCM were challenged with the potent secretagogue HNE. Four groups of 10 hamsters each received 300 micrograms HNE intratracheally. Twenty-one days later, hamsters were intratracheally treated with HNE or saline; the groups were designated HNE-HNE and HNE-SAL, respectively. Hamsters were killed 2 h or 21 days following the second treatment. Using light microscopy, nucleated epithelial cells were counted in plastic sections of the left main intrapulmonary bronchus. Cells were classified as ciliated (C), basal (B), indeterminate (IN), or secretory. Secretory cells were subcategorized as S0 (0 granules), S1 (1-4 granules), S2 (> or = 5 granules with intervening cytoplasm), and S3 (abundant granules completely filling the cytoplasm). At 2 h, S3 cell frequency in the HNE-HNE group was 13.0 +/- 2.2 (% mean +/- SE), significantly lower than in the 2 h HNE-SAL group (31.1 +/- 4.5). Concomitantly, higher cell frequencies were seen in the other secretory categories of the HNE-HNE group compared to the HNE-SAL group; S2 17.1 +/- 1.9 compared to 9.4 +/- 1.9, S1 2.4 +/- 0.4 compared to 1.1 +/- 0.5, and S0 2.4 +/- 0.5 compared to 1.1 +/- 0.5, respectively. The S3 cell frequency of the 21-day HNE-HNE group was 25.4 +/- 4.7, increased significantly compared to the 2 h HNE-HNE group; this change was concomitant with significant decrease in the frequency of the S0 secretory cells. Cell frequencies of C, B, and IN were not affected by treatment or time. It is concluded that metaplastic secretory cells discharge their granules in response to HNE; SCM returns to its original state after HNE rechallenge; persistent SCM is not due to the inability of metaplastic secretory cells to discharge their granules.

Involvement of a signal transduction mechanism in ATP-induced mucin release from cultured airway goblet cells

Release of mucins from cultured airway surface epithelial cells can be stimulated by extracellular ATP via a P2-purinergic receptor-mediated mechanism (K. C. Kim and B. C. Lee. 1991. Br. J. Pharmacol. 103:1053-1056). In this report, we studied the mechanism by which extracellular ATP induces the mucin release. We found that: (1) ATP increased both mucin release and generation of inositol phosphates in a dose-dependent fashion, and their dose-effect relationships were almost superimposed; (2) the increases in both mucin release and the phosphatidylinositol phosphate (PI) turnover by extracellular ATP were partially, but almost equally, blocked by the pretreatment with pertussis toxin (42% for mucin release and 44% for PI turnover). We conclude that in cultured airway goblet cells extracellular ATP stimulates mucin release by a signal transduction mechanism, which seems to involve coupling of ATP-activated P2 purinoceptors with phospholipase C, at least in part, via pertussis toxin-sensitive GTP-binding proteins. This may be an important finding in understanding the regulation of mucin release by airway goblet cells, since a number of agents present in the airway could influence this signal transduction pathway and subsequently modulate the mucin secretion.

Secretory leukocyte protease inhibitor in cystic fibrosis

Cystic fibrosis (CF) is a genetic disorder that leads to a defect in chloride ion transport and results in pancreatic and pulmonary insufficiency. The pulmonary disease is characterized by bacterial colonization and inflammation with excessive levels of neutrophils and neutrophil elastase within the lung. Neutrophil elastase is considered to be one of the major mediators of the pulmonary damage. Secretory leukocyte protease inhibitor (SLPI) is a natural anti-protease found in the upper airways and has been successfully produced by recombinant technology. SLPI is effective in reducing elastase-induced damage in vitro and in vivo and has recently been administered safely as an aeroeol to CF patients with evidence of biochemical efficacy.

Changes in the carbohydrate content of airway epithelium induced by human neutrophil elastase in the hamster

Hamster airway epithelial secretory cells were investigated by light and electron microscopic cytochemistry to study possible changes in their carbohydrate content induced by human neutrophil elastase (HNE), an agent known to cause replacement of Clara cells by mucous cells in hamster bronchi. Characterization of secretory cell carbohydrates by the AB/PAS, PA-TCH-SP, HID-TCH-SP, and LID-TCH-SP sequences indicated the existence of periodate-reactive acidic glycoconjugates, but the absence of sulfated or carboxylated glycoconjugates in both treated and control animals. Differences were seen in the quality and quantity of historeactive carbohydrates throughout various regions in the lower respiratory tract. This was especially evident in the HNE-treated animals. It is concluded that the HNE-induced expression of the mucous cell phenotype is associated with an increase in the amount of neutral and acidic nonsulfated and noncarboxylated polysaccharides stored in the secretory granules of these cells.

Induction of emphysema and bronchial mucus cell hyperplasia by intratracheal instillation of lipopolysaccharide in the hamster

The aim of this study was to determine whether lipopolysaccharide-induced elastase release from recruited neutrophils in the hamster lung would induce emphysema, measured by mean linear intercept (Lm) and bronchial mucus cell hyperplasia (BMCH), scored in tissue sections stained with periodic acid-Schiff. Lipopolysaccharide (LPS) was instilled transorally twice a week for up to 5 weeks in hamsters. At 4 weeks after seven LPS instillations, Lm amounted to 87.6 +/- 1.2 microns, while it was 68.3 +/- 1.5 microns after seven saline instillations (P less than 0.01). At 6 months after the sixth LPS instillation, the Lm of these lungs was 83.3 +/- 1.6 microns, indicating irreversible tissue destruction. LPS-treated hamsters showed marked to severe BMCH, which was most evident in large intrapulmonary airways. Instillations of highly selective inhibitor of hamster PMN elastase resulted in 50 per cent inhibition of LPS-induced emphysema. The development of BMCH was inhibited by approximately 35 per cent by this agent. To study the response in time of cellular infiltration after a single LPS instillation, the lungs of groups of four hamsters were lavaged at different time points. PMN recruitment showed peak values at 4 and 48 h after LPS instillation and returned to baseline values at 96 h. Simultaneous intratracheal instillation of LPS and anti-TNF alpha antiserum resulted in a considerable reduction of neutrophil influx into bronchoalveolar spaces in the first 6 h after instillation.

MUC1 mucin mRNA expression in cultured human nasal and bronchial epithelial cells

The MUC1 mucin mRNA, for which the cDNA was previously cloned from human breast and pancreatic tissues, was found to be expressed in nasal and bronchial epithelial cell primary cultures from cystic fibrotic, atopic, and normal individuals. Sequence analysis of cDNA clones from the CF/T43 cystic fibrosis nasal epithelial cell line revealed only insignificant differences in the 3' untranslated region of the mRNA when compared with the pancreas and breast mucin cDNAs.

Interactions between airway epithelium and mediators of inflammation

Epithelial cells lining the respiratory airways classically are considered to be "target" cells, responding to exposure to a variety of inflammatory mediators by altering one or several of their functions, such as mucin secretion, ion transport, or ciliary beating. Specific responses of epithelial cells in vivo or in vitro to many of these inflammatory mediators are discussed. Recent studies have indicated that airway epithelial cells also can act as "effector" cells, responding to a variety of exogenous and/or endogenous stimuli by generating and releasing additional mediators of inflammation, such as eicosanoids, reactive oxygen species, and cytokines. Many of these epithelial-derived substances can diffuse away and affect neighboring cells and tissues, or can act, via autocrine or paracrine mechanisms, to affect structure and function of epithelial cells themselves. Studies dealing with airway epithelium as a source of inflammatory mediators and related compounds also are discussed.

Cyclic AMP-independent secretion of mucin by SW1116 human colon carcinoma cells. Differential control by Ca2+ ionophore A23187 and arachidonic acid

The regulation of mucin secretion by SW1116 human colon carcinoma cells has been studied using monoclonal antibody 19-9, which has previously been used to detect mucin in the serum of cancer and cystic fibrosis patients. We found that SW1116 cells constitutively secrete considerable amounts of mucin as the predominant glycoprotein. The secretion of mucin by these cells is independent of cyclic AMP levels, but can be further stimulated by the Ca2+ ionophore A23187. However, arachidonic acid and its metabolites inhibit mucin secretion. Electron microscope studies reveal that the mucin is located near the plasma membrane as well as in vesicular and lysosome-like structures. However, the secretion pathway of mucin is different than that of the lysosomal contents, since arachidonic acid, while inhibiting mucin secretion, actually activates the secretion of the lysosomal enzyme beta-glucuronidase. We suggest that the mechanism of mucin secretion by SW1116 cells occurs by a pathway different from common exocytosis, and possibly by more than one pathway. The response of mucin secretion by SW1116 cells to common secretagogues resembles that of epithelial cells obtained from cystic fibrosis patients. Thus SW1116 cells are an especially interesting system for studying processes related to pathological states associated with excessive constitutive secretion of mucin.

Interaction between secretory leucocyte proteinase inhibitor and bronchial mucins or glycopeptides. Physiopathological implications for the protection of mucins against proteolysis by human leucocyte elastase

The interaction of secretory leucocyte proteinase inhibitor with bronchial mucins and glycopeptides was studied by means of c.d. spectroscopy. The interaction with mucins was characterized by an increase in organized structure of alpha-helical type, as evidenced by the appearance in the difference spectra of two positive bands at 208 and 218 nm. This phenomenon was correlated with the amount of inhibitor present in the mixtures, suggesting that the change was inherent to the inhibitor. Surprisingly, when the inhibitor was mixed with acid glycopeptides, difference c.d. spectra showed a decrease in organized structure, characterized by a negative minimum at 196 nm. Glycopeptides treated with neuraminidase gave similar profiles of difference spectra in three different mixtures, indicating that the interaction was smaller. The interaction between the inhibitor and mucins was also studied for its ability to modify in vitro the proteolytic activity of human leucocyte elastase. Mucins alone were degraded by that proteinase into glycopeptides of Mr 400,000-500,000, whereas mucins mixed with inhibitor before adding elastase were proteolysed to a lesser extent. These data demonstrate that the secretory leucocyte proteinase inhibitor interacts with mucins and consequently is capable of protecting the mucins against proteolysis by elastase.

Airway epithelial cell mucin release: immunologic quantitation and response to platelet-activating factor

Mucus production is an integral component of airway mucosal inflammation. Platelet-activating factor (PAF) is a phospholipid mediator implicated in the pathogenesis of many inflammatory processes, including airway inflammation. PAF functions as a mucus secretagogue when mucus is quantitated as radiolabeled glycoconjugates released from airway organ cultures. To more directly assess the interaction of PAF and airway epithelial mucous cell secretion, we used primary feline tracheal epithelial cell cultures and an immunoassay for a specific mucous cell secretory vesicle component. Cultured tracheal epithelial cells were shown to synthesize and secrete glycoconjugates with mucin characteristics. These mucin-type glycoconjugates were immunoreactive with a mucous cell-specific antibody. Localization of this antibody to components of the secretory vesicles of cultured epithelial cells was confirmed by electron microscopic immunogold labeling. Using this monoclonal antibody, an immunoassay was developed to quantitate release of immunoreactive material into cell culture media. Exposure of cultures to PAF produced a concentration-dependent, prompt release of immunoreactive material. Concentration-dependent inhibition of this effect was demonstrated by coincubation with the PAF receptor antagonists, WEB 2086 and Ro 19-3704. A component of the signal transduction pathway for PAF effects was studied in cultured tracheal epithelial cells by coincubation of PAF with nordihydroguaiaretic acid (NDGA), a combined lipoxygenase and cyclooxygenase inhibitor, or p-bromophenacyl bromide (BPB), an inhibitor of cellular arachidonic acid release. Both NDGA and BPB blocked PAF-stimulated mucin release in a concentration-dependent manner. These studies demonstrate a direct airway epithelial mucous cell secretagogue effect that appears to be dependent upon airway epithelial PAF receptors and altered cellular lipid metabolism. These findings suggest a direct and potent mechanism for goblet cell secretion during airway inflammation.

Resistance of hamster bronchiolar epithelium to neutrophil elastase: investigation by cell surface lectin cytochemistry

An intratracheal instillation of human neutrophil elastase (HNE) causes accumulation of an excess number of secretory granules in the epithelial secretory cells lining the hamster bronchus. This chronic lesion, which we refer to as secretory cell metaplasia (SCM), is not seen in the trachea or bronchioles. Because luminal cell surface lectin binding is much higher in the trachea than in the bronchus, we concluded that tracheal resistance may be due to a protective glycoconjugate coat. In the present ultrastructural study, we analyzed the lectin-binding capability of bronchiolar epithelial cells to determine whether their luminal cell surface glycoconjugate layer is similar to tracheal epithelial cells. None of the six ferritin-conjugated lectins showed higher binding in bronchioles compared to the bronchus, suggesting that a high level of surface oligosaccharides is not necessary for resistance to the metaplastic effects of HNE. HNE caused a significant reduction in bronchiolar surface binding of the gold-labeled, secretory cell-specific lectin, Helix pomatia agglutinin. The principal granulated secretory cell type in bronchioles was ultrastructurally similar to a form of bronchial Clara cell that converts to a mucous cell phenotype in response to HNE. The results suggest that absence of bronchiolar SCM is not attributable to a protective layer of cell surface oligosaccharides, a lack of cellular contact by HNE, or the presence of a morphologically distinct population of epithelial cells in bronchioles.

Characterization of Pseudomonas aeruginosa adherence to cultured hamster tracheal epithelial cells

This study reports an in vitro system that allows the convenient study of both microenvironmental and bacterial factors affecting adherence of Pseudomonas aeruginosa to tracheal epithelium. Primary cultures of mixed ciliated and nonciliated epithelial cells isolated from hamster tracheas were grown on collagen-coated multiwell plates containing 10(5) epithelial cells/well at confluence. When 10(7) 14C-labeled P. aeruginosa (nonmucoid, strain Y-4) suspensions were added to each well, 8.13 +/- 2.6% (mean +/- SD) of the initial inoculum bound to the cultured cells, an amount comparable to that measured using suspensions of human tracheal epithelial cells and the same bacteria. The bacteria adhered preferentially to the cultured cells rather than to an acellular collagen matrix. Five additional nonmucoid strains of P. aeruginosa also bound well to the cultured cells, while two mucoid strains were less adherent. Strains of two other gram-negative bacteria, Pseudomonas maltophilia and Klebsiella pneumoniae, did not bind significantly, emphasizing the bacterial species specificity of the adherence interaction being measured. The binding interaction with P. aeruginosa was both pH-sensitive and altered by the presence of the divalent cation calcium. Thus, the in vitro assay system described provides a consistent surface of tracheal epithelial cells that binds P. aeruginosa in a specific manner and can be used to examine the effects of bacterial variables and microenvironmental conditions that may be present in the human airway.

Critical variables controlling cell proliferation in primary cultures of rat tracheal epithelial cells

The purpose of our experiments was to examine variables affecting early events in the establishment of rat tracheal epithelial (RTE) cultures as well as factors regulating long-term RTE cell growth. The experiments showed that when RTE cells were seeded into complete serum-free medium between 13 and 30% of the seeded cells attached. Of the seeded cells, only approximately 2% entered into DNA synthesis and underwent repeated cell divisions to form colonies containing greater than 20 cells. Coating the dishes with extracellular matrix components had little effect on cell attachment or colony forming efficiency (CFE). However, coating the dishes with fetal bovine serum markedly increased CFE. The media components bovine serum albumin and bovine pituitary extract were shown to be important in promoting cell attachment as well as CFE. Cholera toxin on the other hand had no effect on cell attachment but significantly increased CFE. These and other studies showed that cell attachment and cell proliferation are independently regulated. Studies on long-term culture growth indicated that the number of progeny produced per colony forming unit (CFU) is inversely proportional to the number of CFUs seeded. Inasmuch as the cultures did not become confluent under any of the culture conditions tested and media obtained from high density cultures were shown to be growth inhibitory, these findings suggest that a diffusible growth restraining factor is being produced by the cultures limiting clonal expansion. Experiments showing growth inhibitory effects of media conditioned by high cell density cultures support this interpretation. The putative factor reaches critical concentrations earlier in cultures seeded with high numbers of CFU than in cultures seeded with low numbers of CFU. Because the cultures are known to produce transforming growth factor-beta, this growth regulator probably plays a role in controlling RTE cell proliferation. However, it is likely than other events, such as depletion of growth factors from the media, also are significant in regulating the growth of the cultures.

Use of a monoclonal antibody enzyme-linked immunosorbent assay to measure human respiratory glycoprotein production in vitro

High-molecular-weight glycoprotein from human airway cultures was used to generate murine monoclonal antibodies, one of which recognizes a high-molecular-weight, hyaluronidase-resistant glycoprotein localized by immunofluorescent microscopy and immunogold electron microscopy to the secretory granules of human airway submucosal gland mucous cells and goblet cells. This monoclonal antibody was used to develop an enzyme-linked immunosorbent assay (ELISA) that was adapted to the study of respiratory glycoprotein secretion from human airways in vitro. Using the assay, the effect of a known mucus secretagogue, the cholinergic agonist methacholine, was studied on explant cultures of tissue from human bronchus or from human nasal mucosa. In studies of human bronchus explants, methacholine, 100 and 10 microM, stimulated increased secretion of respiratory glycoprotein (RGP) by 109 +/- 8% (n = 14; P less than 0.001) and 96 +/- 14% (n = 9; P less than 0.001), respectively, above control values. In studies of human nasal turbinate mucosal explants, methacholine, 100 and 10 microM, stimulated increased secretion of RGP by 75 +/- 28% (n = 7; P less than 0.01) and 70 +/- 21% (n = 4; P less than 0.01) above control values. An ELISA for the measurement of RGP secretion may provide a sensitive and more specific method for the performance of in vitro studies of RGP secretion from human tissues.

P2 purinoceptor regulation of mucin release by airway goblet cells in primary culture

1. The effects of adenine analogues on mucin release by airway goblet cells have been examined in a hamster primary tracheal epithelial cell culture. 2. Adenosine, a P1 receptor agonist, had no effect on mucin release even at 2 mM, while ATP, a P2 receptor agonist, stimulated mucin release in a dose-dependent fashion with an apparent EC50 of 20 microM. The relative potency order among adenine nucleotides was ATP greater than ADP greater than AMP = adenosine. 3. ATP gamma S, a non-hydrolyzable analogue of ATP, was equipotent with ATP in stimulating mucin release. The potency order among some ATP analogues was ATP greater than 2-methylthio ATP greater than alpha, beta-methylene ATP greater than beta, gamma-methylene ATP. Reactive blue 2, a putative P2 gamma-purinoceptor antagonist, did not block the ATP-induced mucin release. 4. The present results indicate that mucin release by airway goblet cells is stimulated by extracellular ATP via P2 receptor-mediated mechanism. We suggest that this mechanism may be important in the physiological regulation of airway goblet cell mucin release in vivo.

Mucin-like glycoproteins secreted from cultured hamster tracheal surface epithelial cells: their hydrophobic nature and amino acid composition

Confluent cultures of primary hamster tracheal surface epithelial cells synthesize and secrete high molecular weight mucin-like glycoproteins (HMW MLGP). Secreted HMW MLGP are highly associated with various lipids, indicating that they are extremely hydrophobic. These HMW MLGP are also associated with varying amounts of "small" glycoproteins via hydrophobic interactions and they can be dissociated by heat and detergent treatments. HMW MLGP free of these "small" glycoconjugates have a buoyant density of 1.5 g/ml and can enter 4% but not 7.5% gels during SDS-polyacrylamide gel electrophoresis. Amino acid composition analysis of HMW MLGP free of these "small" glycoproteins shows that they are relatively rich in serine, threonine, and proline, but the total content of these amino acids seems somewhat lower than that of in vivo airway mucins.

Lectin cytochemistry reveals differences between hamster trachea and bronchus in the composition of epithelial surface glycoconjugates and in the response of secretory cells to neutrophil elastase

Hamsters exposed to an intratracheal instillation of human neutrophil elastase (HNE) accumulate an abnormally high number of secretory granules in bronchial but not tracheal epithelial cells. We employed lectin cytochemistry to investigate possible differences in the epithelial cell surface glycoconjugate layer in trachea compared to bronchus which might explain the regional dissimilarity in response to HNE. Portions of glutaraldehyde-fixed trachea and bronchi were incubated in one of several ferritin-labeled lectins prior to embedding for transmission electron microscopy. Lectins from Ricinus communis, Helix pomatia, and Triticum vulgaris bound to the surface of tracheal secretory cells in moderate to profuse amounts, while most bronchial secretory cells showed little or no label with these lectins. Gold-labeled Helix pomatia agglutinin (HPA), a lectin specific for secretory cells, showed a decrease in surface binding to all tracheal secretory cell types within 2 h of HNE instillation, compared to saline controls. In contrast, the majority of bronchial secretory cells showed an HNE-induced increase in surface label from extremely low levels in saline controls. The low levels of lectin binding to bronchial cells, in contrast to the trachea, may indicate the lack of a protective surface glycoconjugate coat, thus explaining the vulnerability of these cells to HNE. The rise in number of accessible HPA binding sites on the surface of bronchial secretory cells exposed to HNE may represent an important event in the pathologic accumulation of secretory granules by these cells.

Hydrophobicity of mucin-like glycoproteins secreted by cultured tracheal epithelial cells: association with lipids

Confluent cultures of primary hamster tracheal surface epithelial cells are highly enriched with secretory cells resembling airway goblet cells. The cultures secrete lipids, most of which appear to be associated with high-molecular-weight mucinlike glycoproteins (HMW MLGP). In the present communication, we examined the nature of the association and analyzed the lipids associated with the secreted HMW MLGP. The HMW MLGP purified in the presence of 4 M guanidinium HCl were highly associated with lipids. When these HMW MLGP were gel filtered using a Sepharose CL-4B column in the presence of detergents, more than 97% of the associated lipids were dissociated from HMW MLGP and eluted in fractions with Kd = 0.70. On the other hand, when [3H]palmitic acid-labeled spent medium was gel filtered, column elution profiles varied among elution buffers, a major change being an appearance of a 3H peak at Kd = 0.70 in the presence of 50 mM sodium acetate, phosphate-buffered saline (PBS), or PBS/sodium dodecyl sulfate, but not with 4 M guanidinium HCl. Lipids associated with MMW MLGP under a "physiological" condition consisted of neutral, phospho-, and glycolipids. We conclude that (1) HMW MLGP secreted from cultured airway epithelial cells are extremely hydrophobic and associated with a variety of lipids, mostly via noncovalent binding, and (2) the degree of the lipid association seems to depend on the ionic environment of the solution.

Neutrophil elastase and cathepsin G stimulate secretion from cultured bovine airway gland serous cells

To investigate the hypothesis that neutrophil proteases stimulate airway gland secretion, we studied the effect of human cathepsin G and elastase on secretion of 35S-labeled macromolecules from cultured bovine airway gland serous cells. Both proteases stimulated secretion in a concentration-dependent fashion with a threshold of greater than or equal to 10(-10) M. Elastase was more potent than cathepsin G, causing a maximal secretory response of 1,810 +/- 60% over baseline at 10(-8) M. The maximal response to cathepsin G (1,810 +/- 70% over baseline at 10(-7) M) was similar to the maximal response to elastase. These responses were greater than 10-fold larger than the response to other agonists such as histamine. Protease-induced secretion was noncytotoxic and required catalytically active enzymes. The predominant sulfated macromolecule released by proteases was chondroitin sulfate proteoglycan. Immunocytochemical staining demonstrated chondroitin sulfate in cytoplasmic granules and decreased granular staining after stimulation of cells with elastase. The neutrophil proteases also degraded the proteoglycan released from serous cells. Cathepsin G and elastase in supernatant obtained by degranulation of human peripheral neutrophils also caused a secretory response. Thus, neutrophil proteases stimulate airway gland serous cell secretion of chondroitin sulfate proteoglycan and degrade the secreted product. These findings suggest a potential role for neutrophil proteases in the pathogenesis of increased and abnormal submucosal gland secretions in diseases associated with inflammation and neutrophil infiltration of the airways.

Characterization of guinea pig tracheal epithelial cells maintained in biphasic organotypic culture: cellular composition and biochemical analysis of released glycoconjugates

An air-liquid interface (biphasic) primary culture system in which guinea pig tracheal epithelial cells maintain morphologic characteristics of differentiated epithelium has been developed in this laboratory. In this report, we compared quantitatively cell populations of 8-day cultures to those of epithelial mucosa in intact trachea. In addition, high molecular weight glycoconjugates released by the cultured cells were isolated and characterized. Quantitative morphometric analysis revealed similar volume densities of ciliated, secretory, basal, and "other" cells in cultures and in intact tracheal surface epithelium, although the cultures tended to have smaller cells and contained fewer basal cells. High molecular weight glycoconjugates released apically by cell cultures and excluded from Sepharose CL-4B columns contained approximately 5% hyaluronic acid but undetectable amounts of other proteoglycans, such as chondroitin sulfate, heparan sulfate, and dermatan sulfate. The hyaluronidase-resistant glycoconjugates exhibited a peak buoyant density at 1.49 g/ml on cesium chloride density gradient centrifugation and were shown to contain mucin-type carbohydrate to peptide linkages (i.e., GalNAc to ser/thr) and an amino acid composition typical of respiratory mucins. The results indicate that this organotypic cell culture system mimics quite closely morphology of mucosal epithelium in intact airways and that the cells release high molecular weight glycoconjugates with biochemical properties of mucin-type glycoproteins. Thus, this in vitro system appears well-suited for studies of mucin secretion and other functions of respiratory epithelial cells.

Oxygen metabolites stimulate release of high-molecular-weight glycoconjugates by cell and organ cultures of rodent respiratory epithelium via an arachidonic acid-dependent mechanism

Several common pulmonary disorders characterized by mucus hypersecretion and airway obstruction may relate to increased levels of inhaled or endogenously generated oxidants (O2 metabolites) in the respiratory tract. We found that O2 metabolites stimulated release of high-molecular-weight glycoconjugates (HMG) by respiratory epithelial cells in vitro through a mechanism involving cyclooxygenase metabolism of arachidonic acid. Noncytolytic concentrations of chemically generated O2 metabolites (purine + xanthine oxidase) stimulated HMG release by cell and explant cultures of rodent airway epithelium, an effect which is inhibitable by coaddition of specific O2 metabolite scavengers or inhibitors of arachidonic acid metabolism. Addition of O2 metabolites to epithelial cells provoked production of PGF2a, an effect also inhibitable by coaddition of O2 metabolite scavengers or inhibitors of arachidonic acid metabolism. Finally, addition of exogenous PGF2a to cell cultures stimulated HMG release. We conclude that O2 metabolites increase release of respiratory HMG through a mechanism involving cyclooxygenase metabolism of arachidonic acid with production mainly of PGF2a. This mechanism may be fundamental to the pathogenesis of a variety of lung diseases associated with hypersecretion of mucus and/or other epithelial fluids, as well as a basic cellular response to increased oxidants.

Regulation of differentiation and keratin protein expression by vitamin A in primary cultures of hamster tracheal epithelial cells

Hamster tracheal epithelial (HTE) cells maintained in primary culture show the induction of specific keratin species under vitamin A-deficient conditions. A comparison was made between the morphology and the expression of keratins in HTE cells in vivo and in primary culture with and without vitamin A. HTE cells cultured in serum-free, vitamin A-supplemented medium formed a simple cuboidal, ciliated monolayer and produced four simple epithelial keratins (7, 8, 18, and 19). In contrast, vitamin A-deficient HTE cells, which were squamous-like and stratified in culture, produced a more complex keratin pattern, with the induction of four additional keratin species (5, 6, 14, and 17). A keratin pair whose expression serves as a marker of stratified epithelia was induced, as well as a single keratin species unique to lesions of squamous metaplasia in vitamin A-deficient hamster tracheal organ cultures. Thus it appears that HTe cells retain the ability to respond to a deficiency in vitamin A through squamous differentiation and increased keratin production when removed from the intact organ and maintained in primary culture in a chemically defined medium. This system may be useful for the study of mechanisms underlying the squamous differentiation of respiratory epithelial cells in the development of bronchogenic tumors.

Mechanisms of airway goblet cell mucin release: studies with cultured tracheal surface epithelial cells

Confluent hamster tracheal surface epithelial (HTSE) cells in primary culture are enriched with secretory cells that synthesize and release mucins. Using this cell culture system, we investigated possible mechanisms of goblet cell mucin release by altering the media bathing the apical surface of HTSE cells: medium hyperosmolarity decreased mucin release, whereas hypo-osmolarity increased release without causing a cytoplasmic leak due to plasma membrane damage. A Ca2+ ionophore, A23187, did not influence mucin release. Both acidic (pH less than 4) and basic (pH greater than 9) media caused significant increases in mucin release secondary to cell membrane damage. Physiologic concentrations of chemical mediators such as prostaglandins (PGE2 and PGF2 alpha) and leukotrienes (LTC4 and LTD4) did not influence mucin release. Both elastase and cathepsin G derived from human neutrophils caused marked increases in release, whereas trypsin from the porcine pancreas produced a small increase only at a high concentration. We conclude that mucin release by cultured airway goblet cells can be enhanced by: (1) irritant gases, (2) luminal fluid osmolarity, (3) pharmacologic concentrations of LTC4 and LTD4, and (4) cationic proteases, each presumably acting by different mechanisms. Each of these mechanisms may play a role in epithelial mucin secretion associated with airway inflammation.

Elastase inhibitor. Characterization of the human elastase inhibitor molecule associated with monocytes, macrophages, and neutrophils

A fast-acting inhibitor of serine elastase has been detected at high levels in human neutrophils, fresh monocytes, matured monocytes, and macrophages. The elastase inhibitor was isolated from large scale cultures of the monocyte-like cell line U937 by DNase chromatography, disulfide exchange, Phenyl-Sepharose, Red A-agarose, and DEAE HPLC chromatography with an average yield of 480 micrograms from 1.8 x 10(10) cells. The isolated polypeptide was verified as elastase inhibitor by its ability to (a) form a covalent complex with elastase; and (b) inhibit the elastinolytic activity of elastase. The purified elastase inhibitor molecule is unique, i.e., physiochemical and/or functional properties distinguish it from all other serine proteinase inhibitors. Treatment with iodoacetamide abrogates the ability of the molecule to form a complex with elastase, thereby providing evidence for the presence of an essential cysteine residue. Based on functional criteria, this elastase inhibitor has been grouped with the proteinase inhibitors of the serpin superfamily. The purified elastase inhibitor is a single polypeptide of Mr approximately 42,000. The NH2 terminus appears to be blocked. Compositional analyses indicates five cysteine residues per molecule of approximately 360 amino acid residues. Negligible levels of carbohydrate were detected on gas-liquid chromatography. This finding and the insensitivity of the molecule to peptide N-glycosidase F treatment strongly indicate that the elastase inhibitor is a nonglycosylated protein.

Human neutrophil elastase causes glycoconjugate release from the epithelial cell surface of hamster trachea in organ culture

It is known that human neutrophil elastase (HNE) treatment of hamster tracheal explants causes the release of glycoconjugates, most of which appear to have the characteristics of mucus glycoproteins. This study was designed to determine the origin of HNE-induced glycoconjugate release from 1-day-old cultures of adult hamster trachea. After confirming that HNE treatment released glycoconjugates from cultures labeled with tritiated glucosamine, light microscopic autoradiograms and electron micrographs were prepared. Untreated cultures and cultures treated with inactivated HNE served as controls. HNE treatment caused a 40 to 50% decrease in the silver grain count on the external apical surfaces of secretory cells (p less than 0.05) and ciliated cells (p less than 0.01). Silver grain counts in secretory and ciliated cell cytoplasm, submucosa, and nontissue background were not significantly different from controls. The percentage of nongranulated secretory cells and the number of secretory granules in granulated secretory cells were similar in the HNE-treated and untreated controls. There was no evidence of constitutive release of radiolabeled glycoproteins, or of discharge of secretory granules from the secretory cells. We conclude that HNE releases mucins and other glycoconjugates from the external surfaces of both secretory and ciliated cells in tracheal organ culture.

Secretions from primary hamster tracheal surface epithelial cells in culture: mucin-like glycoproteins, proteoglycans, and lipids

Surface epithelial cells dissociated from hamster tracheas and grown on a thick collagen gel in the presence of 5% fetal bovine serum become highly enriched with secretory cells at confluence. In the present communication, we have analyzed secretory products from this primary hamster tracheal surface epithelial (HTSE) cell culture. The secreted glycoconjugates included high-molecular-weight mucin-like glycoproteins (HMW MLGP) and proteoglycans that comprised 22% and 5% of the total [3H]glycoconjugates secreted when [3H]glucosamine was added as a metabolic precursor. Among the proteoglycans were hyaluronic acids (53%), heparan sulfate proteoglycans (29%), and chrondroitin sulfate proteoglycans (18%). Chondroitin sulfates were mostly 4-sulfated. On the other hand, the secreted lipids included cholesterol, phospholipids, and glycolipids, and most of them were associated with HMW MLGP.