Dog tracheal epithelial cells in culture synthesize sulfated macromolecular glycoconjugates and release them from the cell surface upon exposure to extracellular proteinases

Retargeting the coxsackievirus and adenovirus receptor to the apical surface of polarized epithelial cells reveals the glycocalyx as a barrier to adenovirus-mediated gene transfer

Lumenal delivery of adenovirus vectors (AdV) results in inefficient gene transfer to human airway epithelium. The human coxsackievirus and adenovirus receptor (hCAR) was detected by immunofluorescence selectively at the basolateral surfaces of freshly excised human airway epithelial cells, suggesting that the absence of apical hCAR constitutes a barrier to adenovirus-mediated gene delivery in vivo. In transfected polarized Madin-Darby canine kidney cells, wild-type hCAR was expressed selectively at the basolateral membrane, whereas hCAR lacking the transmembrane and/or cytoplasmic domains was expressed on both the basolateral and apical membranes. Cells expressing apical hCAR still were not efficiently transduced by AdV applied to the apical surface. However, after the cells were treated with agents that remove components of the apical surface glycocalyx, AdV transduction occurred. These results indicate that adenovirus can infect via receptors located at the apical cell membrane but that the glycocalyx impedes interaction of AdV with apical receptors.

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.

Partial liquid ventilation with perfluorocarbon in acute lung injury: light and transmission electron microscopy studies

Liquid ventilation using perfluorocarbon has been shown to improve gas exchange in animal models of acute lung injury as well as in children with acute respiratory distress syndrome. This study was designed to define structural features of lung injury following partial liquid ventilation (PLV) using light and transmission electron microscopy in a rabbit model of acute respiratory distress. Animals were treated with either conventional mechanical ventilation (CMV-gas) (n = 6) or PLV (n = 5) for 4 h after the induction of acute lung injury with saline lavage. Control animals were killed after the lung injury. PLV significantly improved alveolar-arterial oxygen tension and the oxygen index compared with CMV (P < 0.05). Morphometric studies using light microscopy show less alveolar hemorrhage, less edema, and fewer hyaline membranes in the PLV group (P < 0.05). Polymorphonuclear leukocyte sequestration in lung capillaries (11.4 +/- 1.5 versus 19.2 +/- 3 x 10(8)/ml, P < 0.05, PLV versus CMV) and migration into airspaces (3.1 +/- 1.2 versus 4.5 +/- 1.1 x 10(8)/ml, P < 0.05, PLV versus CMV) were lower in the gravity-dependent lung regions. There were fewer alveolar macrophages in the PLV group compared with other groups (P < 0.05). Fluorescence microscopy analysis shows fewer type II alveolar epithelial cells in the CMV group and brighter type II cells in the PLV group. Transmission electron microscopy studies show more alveolar wall damage in the CMV group, with type II cells detached from their basement membrane with fewer surfactant-containing lamellar bodies. We conclude that quantitative histologic analysis shows less lung damage and inflammation when perfluorocarbon is combined with CMV in the management of acute respiratory distress syndrome.

Biosynthesis of mucins in bovine trachea: identification of the major radiolabelled species

Bovine trachea in organ culture secretes mucus containing a 'high-density' (1.46 g/ml) and a 'low-density' (1.37 g/ml) mucin similar to those identified previously in bovine respiratory secretions [Hovenberg, Carlstedt and Davies (1997) Biochem. J. 321, 117-123]. After pulse-labelling, autoradiography showed uptake of [35S]sulphate by both epithelial goblet cells and submucosal glands, while [3H]proline was mainly incorporated into the ciliated surface epithelial cells. After 24 h of radiolabelling, neither the high- nor the low-density mucin in the secreted mucus gel was heavily radiolabelled with the precursors. In contrast, a population of molecules banding at 1.50 g/ml was heavily radiolabelled with [35S]sulphate. This component was smaller than the high-density mucin from the mucus gel and was insensitive to reduction or digestion with chondroitin ABC lyase or heparan sulphate lyase. The molecules yielded two populations of high-Mr glycopeptides upon trypsin digestion, were sensitive to keratanase and endo-beta-galactosidase digestion and contained O-linked glycans. Extracts of the surface epithelium and submucosal tissue after radiolabelling showed that the high- and low-density mucins in the tissue were also poorly radiolabelled. Thus, under these conditions, the radiolabelled precursors were not effectively incorporated into the large oligomeric mucins but into a high-Mr monomeric species. This study suggests that data obtained in investigations where mucins are radiolabelled and studied without further separation into distinct components may rather reflect the turnover of this 'novel' monomeric species than the large oligomeric mucins.

Mucins secreted by a transformed cell line derived from human tracheal gland cells

High-molecular-mass glycoconjugates are secreted by the continuous cell line MM-39, which has been obtained from cultured human tracheal gland cells transformed by simian virus 40. They were purified on Sepharose(R) CL-4B and then by two steps of density-gradient centrifugation. High-molecular-mass glycoproteins resistant to digestion by hyaluronidase, chondroitin ABC lyase and heparitinase were obtained, in addition to hyaluronic acid and proteoglycans. They were susceptible to beta-elimination. They contained polylactosaminoglycan chains as well as carbohydrate chains with a terminal sialic acid in the NeuAc alpha2-3 sequence. Most of them have a buoyant density of 1.45 g/ml in CsCl-density-gradient centrifugation, except for MUC1. The MM-39 cells were also characterized by a high expression of MUC1 and MUC4 genes, but they did not express MUC2, MUC3, MUC5B and MUC5AC. Therefore the MM-39 cells synthesized mucin-like glycoproteins as well as lysozyme and mucous proteinase inhibitor [Merten, Kammouni, Renaud, Birg, Mattéi and Figarella (1996) Am. J. Respir. Cell. Mol. Biol. 15, 520-528]; they should be considered as having a mixed, both serous and mucous, phenotype.

Transmission electron microscopy of the epithelium of distal airways and pulmonary parenchyma of the goat lung

Lungs from eight goats of mixed sexes and breeds (Cashmere, Nubian and Toggenburg) aged between 10 and 48 months were used in this study. Tissues from lung parenchyma were minced and routinely prepared for transmission electron microscopy (TEM) after using different methods of fixation. Thick sections were examined with a light microscope and samples, to include terminal bronchioles, respiratory bronchioles, alveolar ducts and alveolar membrane, were selected for ultrathin sectioning. Six cell types, ciliated, non-ciliated bronchiolar epithelial, mucus-producing, alveolar Type I, alveolar Type II and capillary endothelial cell were identified and characterised cytologically. It was established that the cell population in the distal airways is similar to that observed in other domestic mammals. The mucus-producing cell, which appears to be a common cell type in the distal airways of man and Rhesus monkey, was encountered particularly in adult goats in the present study. This study has also established that the Clara cell of the goat shows some cytological differences from those of some other mammalian species by having a large amount of SER, particularly in the apical region. Lipid vacuoles were seen to be a feature of the alveolar Type II cells; these do not appear to have been reported in other mammalian species. The study has provided a basic understanding of the morphological features of the cell population of the epithelium lining the distal airways in the goat's respiratory tract. The difference in junctional complexes between the various alveolar epithelial cells perhaps signify a different pattern of intercellular transport, thus influencing the pathogenesis and resolution of alveolar pulmonary edema.

Simultaneous expression of keratan sulphate epitope (a sulphated poly-N-acetyllactosamine) and blood group ABH antigens in papillary carcinomas of the human thyroid gland

The monoclonal antibody 5-D-4 recognizes heavily sulphated forms of keratan sulphate epitope. It reacted strongly with the cell surfaces of most thyroid papillary carcinomas from all the individuals examined, independently of the blood group of the patients. Cells of follicular variants of papillary carcinomas were also labelled by 5-D-4. In contrast, no labelling with this antibody was observed in other types of thyroid neoplasms, or in normal tissues. The reactivity of 5-D-4 with papillary carcinomas was markedly reduced or abolished by prior digestion with endo-beta-galactosidase, keratanase II, or N-glycosidase F. Although keratanase digestion had no effect on 5-D-4 labelling, it revealed the binding sites of Griffonia simplicifolia agglutinin II (GSA-II), which recognizes terminal N-acetylglucosamine in a limited number of carcinoma cells from some individuals. Blood group ABH antigens, which are simultaneously expressed together with keratan sulphate epitope in cancer cells, were eliminated by digestion with endo-beta-galactosidase and N-glycosidase F, but were resistant to keratanase and keratanase II treatment. These results indicate that keratan sulphate oligosaccharides are cancer-associated and are probably oncofoetal antigens, as are the blood group antigens in human thyroid glands. The results suggests that poly-N-acetyllactosamine, which is ubiquitously and consistently produced in papillary carcinomas, is modified in two different ways: sulphation on the 6-position of at least some units of either galactose or N-acetylglucosamine or both, and decoration of non-reducing termini with the blood group antigens. Along with the endo-beta-galactosidase-GSA-II labelling procedure, labelling with 5-D-4 may be a useful diagnostic means for distinguishing papillary carcinoma from other types of thyroid neoplasms.

Species differences in the physical and transport properties of airway secretions

The clearance of airway secretions is vital in protecting the mammalian lung from pollution and infection. Diverse animal models have been used to study lung diseases associated with impaired secretion clearance. The extrapolation of data from animal models to humans is based on the assumption that there are structural and functional similarities in the airway epithelium and secretions. This manuscript reviews regulation of mucus secretion as well as the physical and transport properties of respiratory mucus. As tracheal size increases, the rigidity of airway secretions decreases, and rigidity is inversely correlated with mucociliary transportability. These differences are placed in the context of previously reported species and regional differences in transepithelial potential difference and the tracheobronchial epithelial cell population. Tracheal mucus transport velocity varies with the species studied and has been shown to positively correlate with tracheal surface area. A progressive increase in the rate of mucus transport from the small to the large airways has also been reported. The reduction in mucus rigidity from small to large airways could be one of the mechanisms responsible for velocity gradients, which facilitate mucociliary transport. Because airway dimensions, rather than anatomic level of the airway, may better predict epithelial secretory response, studies to assess the physiologic responses in human airways require the use of an animal model with a similar-sized airway.

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.

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.

Secretory proteins and glycoconjugates synthesized by human tracheal gland cells in culture

To study the proteins and glycoconjugates synthesized by serous cells from human tracheal glands (HTG), isolated HTG cells were cultured in the presence of radiolabeled precursors 14C-proline, Na2(35)SO4, and 3H-fucose. The secretory 14C/35S/3H-radiolabeled proteins and glycoproteins, de novo synthesized by HTG cells, were analyzed by gel filtration chromatography. We observed the incorporation of 14C-proline into antileukoprotease and an unknown 30 kD protein, and the incorporation of 35SO4-- and 3H-fucose into high molecular weight glycoconjugates and sulfoconjugates (M(r) > 1,000,000) and into components with apparent M(r) of approximately 250 and 100 kD. After specific chemical and enzymatic treatment, the 35S- and 3H-glycoconjugates were shown to be -O-linked mucin-like glycoproteins and proteoglycans. These results show that cultured HTG cells synthesize some of the macromolecules identified in bronchial secretions.

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.

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.

Chondroitin sulfate in sputum from patients with cystic fibrosis and chronic bronchitis

In order to ascertain whether or not the presence of glycosaminoglycans in sputa of patients suffering from chronic bronchial disorders was related to tracheobronchial infection, an electrophoretic procedure was set up. The different acidic macromolecular components of sputum, namely nucleic acids, glycosaminoglycans, and bronchial glycopeptides could be identified in proteolyzed sputum using agarose electrophoresis before and after the action of different enzymes: nucleases, chondroitinases, hyaluronidase and heparinase. This procedure was used to analyze 13 sputum samples from patients suffering from cystic fibrosis (CF) and 12 sputum samples from patients suffering from chronic bronchitis. Chondroitin sulfate was identified in 11 infected sputum samples from patients with CF and also in the noninfected sputum from a patient with chronic bronchitis. These data suggest a relationship between the presence of chondroitin sulfate proteoglycans in sputum and severe tracheobronchial infection in CF.

Differential adhesion of Pseudomonas aeruginosa to human respiratory epithelial cells in primary culture

Human nasal polyps in outgrowth culture were used to study the Pseudomonas aeruginosa adhesion to respiratory cells. By scanning electron microscopy, P. aeruginosa were seen associated with ciliated cells, but by transmission electron microscopy, bacteria were never seen at the interciliary spaces or attached along cilia, but were identified trapped at the extremities of cilia, usually as bacterial aggregates. A fibronectin-containing fibrillar material was seen associated with aggregated bacteria. By time-lapse video microscopy, bacteria were seen to aggregate in the culture medium following their addition to the culture wells. Progressively, these aggregates were trapped by cilia or attached to migrating cells of a lower cell layer that protruded beneath the upper layer cells, at the outgrowth periphery. P. aeruginosa adhesion to these lower cell layer migrating cells was significantly higher than to ciliated or nonciliated cells of the upper cell layer. Migrating cells were intensely labeled by the complexes Con A and arachis hypogea agglutinin (PNA)-FITC, in contrast to the other cells. The percentage of PNA-labeled cells with attached bacteria was significantly higher than that without bacteria. These results suggest that changes of cell surface glycoconjugates related with cell migration may favor P. aeruginosa adhesion to respiratory cells.

The structure and airway biology of mast cell proteinases

Recent studies have led to a rapid expansion of knowledge concerning the structure and biology of the two major mast cell proteinases, tryptase and chymase. Tryptase is an abundant, trypsin-like enzyme found in the secretory granules of all human lung mast cells. The subunits of the heparin-associated tryptase tetramer appear to be the products of a multigene family whose intron-exon organization is unique and is not closely related to that of other mast cell or leukocyte serine proteinases. In vitro studies suggest that tryptases may participate in lung and airway responses by regulating airway neuropeptide activity, bronchomotor tone, and fibroblast mitogenesis. Mast cell chymases are chymotrypsin-like proteinases related closely to neutrophil cathepsin G and lymphocyte granzymes. The cDNA-derived structures of tryptase and chymase suggest that the two enzymes may differ in modes of activation from proenzyme forms, although the mature enzymes are packaged and released together. Chymase expression appears to be limited to a subset of human lung mast cells most prevalent in the airway submucosa. Possible roles for chymase include inactivation of sensory neuropeptides, regulation of submucosal gland secretion, and potentiation of histamine-induced vascular permeability.

Mucins in cat airway secretions

Mucous secretions were obtained from cat tracheas that had received [3H]glucose and [35S]sulphate to radiolabel mucus glycoproteins biosynthetically. Samples were collected under resting ('basal') conditions as well as after pilocarpine stimulation and were separated into gel and sol phases by centrifugation. Macromolecules were partially purified by using gel chromatography on Sepharose CL-4B, and the species that were eluted with the void volume were then separated into two major populations with isopycnic density-gradient centrifugation in CsCl. The major component from the gel phase of pilocarpine-induced secretions had a buoyant density typical of mucins and was observed as linear and apparently flexible chains by electron microscopy. Reduction of disulphide bonds gave subunits that could be further cleaved by trypsin digestion into components of approximately the same size as the high-Mr glycopeptides obtained from other mucins after this treatment. In contrast, the dominant species in the gel phase of the 'basal' secretion had a significantly higher buoyant density than expected for mucins and was largely unaffected by reduction, as studied by gel chromatography. The macromolecules were fragmented by trypsin, suggesting that they contain a polypeptide backbone. This more dense component also predominated in the sol phase both from the 'basal' secretions and from the pilocarpine-released secretions. Digestion with DNAase, chondroitin ABC lyase or heparan sulphate lyase had no effect, which shows that this component is not DNA, a dermatan sulphate/chondroitin sulphate or a heparan sulphate proteoglycan. In contrast, endo-beta-galactosidase and keratanase caused some fragmentation, suggesting that the molecules contain some linkages of the poly-(N-acetyl-lactosamine) type, although the degradation was not as extensive as expected for keratan sulphate. Treatment with alkaline borohydride resulted in extensive fragmentation of the high-Mr glycopeptides from both components, indicating that the glycans were oligosaccharides that were probably O-linked. The monosaccharide compositions of both components were consistent with that expected for mucins. The data are in keeping with the major component from the pilocarpine-stimulated gel secretions being a mucus glycoprotein and the more dense component being a mucin-like molecule, possibly related to the keratanase-sensitive material isolated from canine trachea by Varsano, Basbaum, Forsberg, Borson, Caughey & Nadel [(1987) Exp. Lung Res. 13, 157-184].

Proliferation, differentiation and ciliary beating of human respiratory ciliated cells in primary culture

The growth, differentiation, ciliary beating pattern and frequency of human respiratory ciliated cells in primary culture were studied by scanning and transmission electron microscopy and by videomicroscopy. The epithelial cells were obtained as outgrowth from explants of adult nasal polyps. When the explants were grown on type-I and type-IV collagen substrates in a standard serum-free, hormone-supplemented medium, a high percentage of ciliated cells (range 29 +/- 5% to 37 +/- 6%) was present within 2 days of culture. After 5 days of culture, the percentage of ciliated cells near the explant was 51 +/- 5%. Most of the cultured ciliated cells (85%) were characterized by individual cilia showing a coordinated movement during the beat cycle and a beating frequency (13.3 +/- 1.3 Hz) similar to that reported in vivo. In the other 15% of the ciliated cells, the dyskinetic cilia were aggregated into clumps and characterized by a rigid and planar bending movement and a lower (P less than 0.01) beating frequency (10.7 +/- 1.4 Hz). It is suggested that the latter type of cell, already described during fetal development, might be an intermediate type of ciliated cell which appears temporarily during the surface respiratory epithelial differentiation.

Inhibition of human neutrophil elastase by ICI 200,355

To examine the pathogenetic role of neutrophil elastase in airway hypersecretion, we have studied the novel inhibitor of this enzyme, [4-(4-bromophenylsulfonylcarbamoyl)benzoyl-L-valyl-L-proline 1 (RS)-(1-trifluroacetyl-2-methylprolyl)amide] (ICI 200, 355). This compound was a potent (Ki = 0.6 +/- 0.22 nM) inhibitor of human neutrophil elastase and a much weaker inhibitor of other hydrolases. ICI 200,355 also inhibited the ongoing destruction of insoluble elastin by human neutrophil elastase. ICI 200,355 produced a concentration-dependent inhibition of the secretory response induced by human neutrophil elastase (10(-8) M), with an IC50 of 1.6 x 10(-8) M. ICI 200,355 had no effect on baseline secretion or on the secretory response to chymase, cathepsin G or Pseudomonas aeruginosa elastase. Thus, ICI 200,355 appears to be a useful tool for investigating the role of human neutrophil elastase in inflammatory disorders associated with hypersecretion, such as cystic fibrosis, chronic bronchitis, and asthma.

Sulfated O-glycoproteins secreted by guinea pig trachea in organ culture

Organ culture of guinea pig trachea was performed in the presence of [35S]sulfate in order to characterize the sulfated glycoproteins released from the respiratory epithelium and mucosa. The sulfated macromolecules that were synthesized during a 6-h incorporation were separated by CsBr density-gradient centrifugation and gel-filtration chromatography successively. Most of the sulfated secreted macromolecules corresponded to a population of glycoproteins sensitive to reductive beta-elimination but resistant to both chondroitinase ABC and heparinase. These glycoproteins had different buoyant densities (ranging from 1.48 g/ml to 1.16 g/ml) and could be subfractionated according to molecular mass. A major part of the radioactivity was incorporated into high-molecular-mass mucins that were excluded from a Sepharose CL-2B column and did not penetrate into polyacrylamide gel in PAGE. However, a mixture of sulfated O-glycoproteins of much lower molecular mass was also characterized in addition to low amounts of chondroitin sulfate. Epithelial goblet cells are the predominant mucin-containing cells of the respiratory guinea pig trachea. Our results suggest that a wide range of sulfated O-glycoproteins are secreted by the guinea pig tracheal mucosa.

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.

Dog mast cell chymase: molecular cloning and characterization

We cloned and characterized a cDNA coding for the complete amino acid sequence of dog mast cell chymase. The cDNA was identified by screening a dog mastocytoma cDNA library with an oligonucleotide probe based on the amino acid sequence of a fragment of dog mastocytoma chymase. The deduced amino acid sequence reveals a putative 21-residue prepropeptide followed by a catalytic domain of 228 residues. The primary structure of the preproenzyme shares features with rat mucosal mast cell chymase (RMCP II), several lymphocyte-associated proteases, and neutrophil cathepsin G. The common characteristics include an apparent activation peptide terminating in glutamic acid, strict conservation of an octapeptide (residues 9-16) in the N-terminal portion of the catalytic domain, and the presence of only six cysteines available for intramolecular disulfide bond formation. However, dog chymase differs in being modified by N-glycosylation. Although the dog chymase catalytic domain exhibits a similar level of sequence identity when compared with both RMCP II and the rat connective tissue mast cell chymase RMCP I (58% and 61%, respectively), the dog enzyme most closely resembles RMCP I in its high predicted net charge (+16) and in the presence of serine at the base of its putative primary substrate binding pocket. The dog chymase differs strikingly from dog mast cell tryptase in the preprosequence and in the structure of the catalytic domain. Therefore, chymase appears not to be closely related to tryptase and may not share a mechanism of activation, even though both enzymes are packaged and released together.

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.

Mucus glycoproteins from 'normal' human tracheobronchial secretion

Mucous secretions were collected from tracheas of patients undergoing minor surgery under general anaesthesia with tracheal intubation, and mucus glycoproteins were isolated by using isopycnic density-gradient centrifugation in CsCl/guanidinium chloride. 'Whole' mucins were excluded from a Sepharose CL-2B gel, whereas subunits obtained after reduction were included. Trypsin digestion of subunits afforded high-Mr glycopeptides (T-domains), which were further included in the gel. The latter fragments are heterogeneous and comprise two or three populations, as indicated by gel chromatography and ion-exchange h.p.l.c. Rate-zonal centrifugation showed that the 'whole' mucins are polydisperse in size, with a weight-average Mr of (14-16) x 10(6). The macromolecules were observed by electron microscopy, as linear and apparently flexible thread-like structures. Subunits and T-domains had weight-average contour lengths of 490 nm and 160 nm respectively. It is concluded that mucus glycoproteins are present in secretions from the healthy lower respiratory tract. The 'whole' tracheal mucins are assembled from subunits, which in turn can be fragmented into high-Mr glycopeptides corresponding to the oligosaccharide domains typically found in mucus glycoproteins. The size and macromolecular architecture of the tracheal mucins is thus similar to that observed for mucins from human cervical mucus, chronic bronchitic sputum and pig stomach, providing yet another example of this general design of these macromolecules, i.e. subunits assembled end-to-end into very large linear and flexible macromolecules.

The uptake of radiolabelled precursors of mucus glycoconjugates by secretory tissues in the feline trachea

1. We gave one of three radiolabelled precursors of mucus glycoconjugates ([3H]proline, [3H]glucose and [35S]sulphate) into the tracheas of anaesthetized cats for 3 h. In other cats [35S]sulphate was given by intravenous injection. 2. After a further 2 h, tracheas were removed and fixed. Serial actions were cut and alternate sections were stained with Haematoxylin and Eosin or prepared as unstained autoradiographs. Points on submucosal gland and surface epithelium were chosen with a grid on photomicrographs of the stained sections. Absorbance, which is proportional to autoradiographic grain density, was estimated on corresponding points on unstained autoradiographs by flying-spot microdensitometry. 3. With [3H]proline as precursor, the grain densities were greater over surface epithelium than over submucosal gland. With [3H]glucose, grain densities were greater over the surface epithelium in three cases, equal in one and greater over submucosal gland in the last. [35S]Sulphate, given either into the tracheal segment or intravenously, yielded grain densities that were greater over the submucosal glands than over surface epithelium. 4. The areas of submucosal gland the surface epithelium were estimated by point counting and the total content of radioactivity in the two structures estimated by multiplying mean absorbance by area. Ratios of the total radiolabel in surface epithelium to that in submucosal gland were consistently high when [3H]proline was the precursor and low with [35S]sulphate, given by either route. [3H]Glucose gave intermediate ratios. 5. Secretions washed from the trachea were subjected to gel-exclusion chromatography. Washings from tracheas labelled with [3H]proline contained some molecules eluting in the void volume of a Sepharose CL-4B column (suggesting a relative molecular mass of greater than 10(6) Da), but more of the radiolabel eluted in three peaks in the partially included volume. Density gradient ultracentrifugation of the void volume material gave radiolabelled peaks at densities of approximately 1.60 and 1.50 g ml-1, consistent with glycosylated proteins, as well as less dense material (less than 1.30 g ml-1), probably proteins with little or no glycosylation. 6. We discuss the justification of using these radiolabelled precursors to give relatively selective labelling of secretory products from submucosal gland and surface epithelium.

The effects of local anaesthetic agents upon mucus secretion in the feline trachea in vivo

The actions of lignocaine and tetrodotoxin (TTX) in a tracheal segment of the cat were tested on secretion of mucus macromolecules radiolabelled with 35S and 3H. Lignocaine, 4.3-43 mM, given into the segment, caused a concentration dependent increase of secretion of 3H-and 35S-labelled macromolecules. At 43 mM, lignocaine increased secretion: delta 3H = +433 +/- 191%, delta 35S = +327 +/- 34.5% (n = 8). This effect lessened over 15-45 min. Atropine (1 mg/kg) had little effect on these responses. All concentrations of lignocaine tested (4.3-43 mM) abolished the effect of vagus nerve stimulation on secretion and diminished the effect of a submaximal concentration of pilocarpine (5 microM) in the segment in a dose-dependent manner. TTX in the segment did not alter the resting secretion. At 50 microM it abolished, and at 10 microM diminished, vagal control of secretion without affecting the secretory response to pilocarpine. The study shows that lignocaine, in concentrations which block vagal control of secretion (greater than or equal to 4.3 mM), stimulates the release of mucus macromolecules. Resting secretion is unaltered by TTX, and so does not appear to be under neurogenic inhibition. Larger concentrations of lignocaine (greater than or equal to 13 mM) also diminish pilocarpine-induced secretion, whereas TTX may inhibit nervous control of mucus secretion selectively. The results suggest that clinical anaesthesia of the airways with lignocaine may stimulate mucus secretion.

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.

Roles of mast cell proteases in airways

The mast cell proteases tryptase and chymase have long been known to constitute one-fifth of the total protein in mast cells. However, their biological functions have not been easy to study because of the difficulty in obtaining sufficient amounts of the enzymes to study their biological functions. Recently, we have been fortunate to have available a permanent line of dog mastocytoma cells to purify both enzymes to homogeneity, and we have used the purified enzymes in two ways. First, in a series of biological studies, we have discovered unique and potent actions of the enzymes that may provide important insights into the pathogenesis of diseases such as asthma and cystic fibrosis. Important biological activities are also likely to exist in other tissues. Because of their structures, mast cell proteases are likely to act in proximity to their sites of release. Thus, the presence and amounts of tryptase and chymase in specific loci may play important roles in tissue responses. In diseases such as asthma and cystic fibrosis, there is evidence that the expression of these mast cell enzymes changes, and these changes have important pathogenetic implications. Second, we have begun to perform structural studies of the enzymes. The recent cloning of tryptase by our group should assist in the better understanding of its functions. Crystallography of the pure proteins should provide further insights and could be the basis of rational development of potent and selective drugs that will inhibit their actions.

Turnover of cell-surface macromolecules in cultured dog tracheal epithelial cells

We studied the metabolism of sulfated cell-surface macromolecules in dog tracheal epithelial cells in primary culture. To examine the time-course and rate of appearance of sulfated macromolecules at the cell surface, the cells were pulsed with 35SO4 for short periods (5-15 min), and the incubation medium was sampled for spontaneously released macromolecules (basal secretions) and for release induced by trypsin (trypsin-accessible secretions). Trypsin-accessible 35S-labeled macromolecules appeared on the cell surface within 5-10 min, increased linearly, and plateaued by 40 min; the median transit time for 35S-labeled macromolecules to reach the cell surface was 21 min. 35S-labeled macromolecules in basal secretions increased with a similar time-course, reaching a plateau by 40 min. Incorporation of [3H]serine into the protein moiety of trypsin-accessible macromolecules occurred more slowly; trypsin-accessible 3H-labeled macromolecules were barely detectable at 1 h and increased to a maximum after 2 h, suggesting the presence of a preformed pool of nonsulfated core protein. Pretreatment with cycloheximide, an inhibitor of protein synthesis, decreased trypsin-accessible 35S-labeled macromolecules log-linearly depending on the duration of pretreatment providing an estimate of the rate of depletion of the core protein pool (t1/2 = 32 min). During continuous exposure to 35SO4, 35S-labeled macromolecules accumulated on the cell surface (trypsin-accessible compartment) for 16 h, at which point the cell-surface pool was saturated (t1/2 = 7.5 h). After pulse-labeling the cells with 35SO4 for 15 min, the 35S-labeled macromolecules disappeared continuously from the cell surface (t1/2 = 4.6 h), and 79% of the radioactivity was recovered in the medium as nondialyzable macromolecules. Release of the 35S-labeled macromolecules from the cell surface was abolished at 4 degrees C, indicative of an energy-dependent process, but multiple proteinase inhibitors did not affect the release. We conclude that sulfate is metabolized rapidly into epithelial cell-surface macromolecules, which accumulate continuously into a relatively large cell-surface pool, before they are released by an undefined energy-dependent mechanism.