Separation of bovine bronchial epithelial cell subpopulations by density centrifugation: a method to isolate ciliated and nonciliated cell fractions

Increased expression of transforming growth factor-beta1 in small airway epithelium from tobacco smokers and patients with chronic obstructive pulmonary disease (COPD)

Tobacco smoke is believed to cause small airway disease and then chronic obstructive pulmonary disease (COPD), but the molecular mechanisms by which small airway obstruction occurs remain unknown. To study the gene expression levels of transforming growth factor (TGF)-beta1, a potent fibrogenic factor, in small airway epithelium from smokers and patients with COPD, we harvested highly pure samples of epithelial cells from small airways under direct vision by using an ultrathin bronchofiberscope BF-2.7T (outer diameter 2.7 mm with a biopsy channel of 0.8 mm in diameter). The expression levels of TGF-beta1 were evaluated by reverse transcription-polymerase chain reaction (RT-PCR). The mRNA levels of TGF-beta1 corrected by beta-actin transcripts were significantly higher in the smoking group and patients with COPD than those in nonsmokers (p < 0.01). Furthermore, among smokers and patients with COPD, TGF-beta1 mRNA levels correlated positively with the extent of smoking history (pack-years) and the degree of small airway obstruction as assessed by measurements of flow-volume curves. Immunocytochemistry of the cells demonstrated more intense stainings for TGF-beta1 in samples from smokers and patients with COPD than from nonsmokers. Spontaneously released immunoreactive TGF-beta1 levels from cultured epithelial cells were more elevated in subjects with a history of smoking and patients with COPD than in nonsmokers. Our study showed a close link between smoking and expression of TGF-beta1 in small airways. Our results also suggested that small airway epithelial cells might be involved in obstructive changes found in smokers and patients with COPD.

Visualization of labile zinc and its role in apoptosis of primary airway epithelial cells and cell lines

The respiratory epithelium is vulnerable to noxious substances, resulting in the shedding of cells and decreased protection. Zinc (Zn), an antioxidant and cytoprotectant, can suppress apoptosis in a variety of cells. Here we used the novel Zn-specific fluorophore Zinquin to visualize and quantify labile intracellular Zn in respiratory epithelial cells. Zinquin fluorescence in isolated ciliated tracheobronchial epithelial cells and intact epithelium from sheep and pigs revealed an intense fluorescence in the apical and mitochondria-rich cytoplasm below the cilia. Zinquin fluorescence was quenched by the Zn chelator N,N,N', N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) and increased by the Zn ionophore pyrithione. We also assessed whether changes in intracellular labile Zn would influence susceptibility of these cells to apoptosis by hydrogen peroxide. Our results confirm that Zn deficiency enhanced hydrogen peroxide-induced caspase activation from 1.24 +/- 0.12 to 2.58 +/- 0.53 units. microg protein(-1). h(-1) (P </= 0.05); Zn supplementation suppressed these effects. These findings are consistent with the hypothesis that Zn protects upper respiratory epithelial cells and may have implications for human asthma where there is hypozincemia and epithelial damage.

Increased expression of inflammatory mediators in small-airway epithelium from tobacco smokers

To study the inflammatory responses of small-airway epithelium in smokers, we harvested enough living epithelial cells (1.97 x 10(6) +/- 0.74 x 10(6)) with a new ultrathin fiberscope from the very peripheral airways of 22 current smokers and 17 subjects who never smoked after informed consent was obtained. The cells were keratin positive and composed mainly of nonciliated cells. The expression levels of inflammatory markers [interleukin (IL)-8 and intercellular adhesion molecule (ICAM)-1] were evaluated with RT-PCR. The magnitude of the mRNA levels corrected by beta-actin transcripts of IL-8 and ICAM-1 was significantly higher in the smokers than in the nonsmokers (P < 0.001). Furthermore, among current smokers, IL-8 mRNA levels correlated positively with the extent of smoking history [in pack. years (packs/day x no. of years of smoking); r = 0.754, P < 0.001]. Spontaneously released IL-8 and soluble ICAM-1 levels (n = 12) from cultured epithelial cells were elevated in subjects with a smoking history than in those without it (IL-8, 1,580 +/- 29.6 vs. 354 +/- 39.4 pg. 10(6) cells(-1). 24 h(-1); P < 0.001; soluble ICAM-1, 356.0 +/- 45.9 vs. 112.9 +/- 12.9 pg. 10(6) cells(-1). 24 h(-1); P < 0.01 by Student's t-test ). In contrast, the epithelial cells from the main bronchi did not show such differences between smokers and nonsmokers. Our study highlighted a close link between smoking and the expression of inflammatory mediators such as IL-8 and ICAM-1 in small airways. Our results also suggested that this new ultrathin bronchofiberscope promised a good approach for the evaluation of cellular changes in the small airways.

Safety and cellular assessment of bronchial brushing in airway diseases

Bronchial brushing is a useful method for morphological and functional studies of bronchial epithelial cells (BECs) in various diseases. This technique has been found to be generally safe, but its safety in asthma and chronic bronchitis has not been fully assessed. The purpose of this study was to determine 1, whether bronchial brushing is a safe method in asthmatic and chronic bronchitis patients of differing severity and 2, to characterize the BECs obtained in terms of number, viability and purity. We evaluated 25 asthmatics of variable severity, 19 chronic bronchitis patients and 26 normal volunteers. Bronchoscopy and bronchial brushing were performed in a standardized manner by the same investigator. Safety was assessed by clinical follow-up of all subjects; continuous monitoring of arterial oxygen saturation during the procedure with a digital oximeter was carried out in a subsample of subjects. No complications were observed clinically during the procedure. There was a minimal fall in arterial oxygen saturation without a significant difference between the three groups of subjects. A consistent number of BECs was recovered and their viability, assessed by the trypan blue exclusion test, in asthmatics and chronic bronchitis patients was significantly lower than in controls (P < 0.05). Bronchial brushing is well tolerated and may be a valuable method of obtaining BECs in asthmatic and chronic bronchitis patients.

Phenol sulfotransferase expression in the airways: enzymological and immunohistochemical demonstration

Phenol (aryl) sulfotransferases (PSTs) provide a conjugative pathway that detoxifies hydroxylated aromatic xenobiotics by esterification with sulfate. Both human and bovine airways have been reported to use this pathway, and in this investigation the bovine system is examined. PST activity in tracheal through fourth generation bronchial mucosal cytosols was 0.1-0.35 nmol/mg protein/min. Activity was generally greater in more distal bronchi and in parenchymal extracts, which contained 0.6-3 nmol/mg/min PST activity. Comparison of the PST activities of bronchial and parenchymal cytosols indicated similar pH activity profiles, although steady state kinetic measurements revealed different Km values for the acceptor substrate 2-naphthol (13.7 microM for bronchial, 31.3 microM for parenchymal). Anion exchange chromatography indicated two PST isoforms being expressed in different ratios. Immunoblot analysis with mouse anti-bovine PST revealed a closely spaced doublet at 32 kDa in both bronchial mucosal and parenchymal cytosolic extracts; however, this doublet was unequally stained in parenchymal extracts. Immunohistochemical analyses revealed faint positive staining of the tracheobronchial epithelium. Greatest immunostaining was observed in the nonciliated secretory epithelial cells of the bronchioles, whereas surrounding smooth muscle, endothelial cells, and alveoli were immunonegative. These results are consistent with the known locations of other detoxification enzymes within the airways.

In situ preparation of rat tracheal basal cells

The primary function of basal cells is to attach columnar epithelium to the basal lamina. They may also have limited stem cell potential, but very little is known of other biological functions. Basal cells lie on the basal lamina beneath the ciliated and secretory cells and do not reach the surface of the epithelium. The position of the cell beneath the ciliated and secretory cell epithelium makes their in situ study difficult. In order to further aid in the study of basal cells, we have developed an in situ preparation technique in which ciliated and secretory cells are removed. Treatment of rat tracheas with a 20 mM Na2 EDTA solution, pH 7.4, results in partial removal of columnar epithelium from the basal lamina. The percent of denuded columnar epithelial cells per mm of basal lamina is 43.9 +/- 7.8% at 60 min, 47.6 +/- 8.4% at 90 min, and 52.6 +/- 2.7% at 120 min. The viability of the exposed basal cells was the same at both 60 and 90 min of treatment (79.4 +/- 7.8 and 78.0 +/- 8.5, respectively). Morphologically, the exposed basal cells are attached to the basal lamina by hemidesmosomes and are similar to those in the intact animal.

Attenuated fibroblast sheath around the basement membrane zone in the trachea

In the connective tissue underlying the epithelium of the airways, there are thin attenuated cells that appear to be fibroblasts. These cells are close to the basal lamina and delineate an area equivalent to the basement membrane zone (BMZ). Using the mean data from transversely and longitudinally sectioned attenuated fibroblasts, we estimate that the diameter of the attenuated fibroblast is approximately 28.0 microns and its thickness 0.55 microns. Serial sections indicate there are pores of various sizes in the attenuated fibroblast. Also, the presence of cell segments less than 5 microns in length suggests there are processes from the edge of the cell which would give it a stellate appearance. These large flat cells form a sheath covering 66 to 70% of the BMZ at an average distance of 1.9 microns from the basal lamina. In addition, they make contact with the basal lamina approximately 7,000 times per mm2 of basal lamina. The majority of the contacts with the basal lamina are beneath basal cells. Cells of the attenuated fibroblast sheath are probably associated with lung morphogenesis, wound healing, and development of the BMZ. Their existence as a sheath demonstrates an anatomical unit associated with fibroblast-epithelial cell interactions in airway epithelium.

A technique to harvest viable tracheobronchial epithelial cells from living human donors

The ability to obtain airway epithelial cells from the lower respiratory tract in living human donors will facilitate study of the biologic properties of these cells. We report our experience harvesting tracheobronchial epithelial cells from living human donors by brushing the mucosal surface of the trachea and mainstem bronchi. Cells were obtained on 21 occasions from 18 healthy adult subjects under direct vision with a brush-tipped catheter during fiberoptic bronchoscopy. The average number of cells harvested per subject was 14 +/- 2 x 10(6), and cell viability determined by trypan blue exclusion averaged 36 +/- 4%. Of note, cell viability was significantly enhanced when lidocaine was confined to the nares. Lidocaine was also observed to diminish cell viability in vitro in a dose-dependent fashion. Morphologic and staining properties were used to classify harvested cells into the three major cell types present in the mucosa (i.e., ciliated, secretory, and basal cells). All three subtypes were obtained. The percentage of ciliated, secretory, and basal-like cells was 24 +/- 2%, 11 +/- 1%, 29 +/- 1%, respectively, while the remaining 36% were difficult to type. In one subject in whom brushing was performed on three occasions over a 7-wk period, the percentage of each of the three subtypes was similar across procedures. Harvested cells could be successfully placed in primary culture with a plating efficiency of 50 to 60% and could be subcultured for up to seven passages. Acutely dissociated cells could be used to study the beta-adrenergic receptor adenylyl cyclase system since they produced cAMP in response to isoproterenol.(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming growth factor-beta stimulates the expression of desmosomal proteins in bronchial epithelial cells

Transforming growth factor-beta 1 (TGF-beta 1) has been shown to induce squamous differentiation of cultured airway epithelial cells. It has also been shown to increase expression of matrix proteins and integrin receptors in cell culture of these and other cells. However, it is unknown if TGF-beta 1 affects expression of genes encoding intercellular junctional proteins. Therefore, we have investigated the effect of TGF-beta 1 on the expression of proteins and mRNAs for desmoplakins (DPs) I and II, desmosomal plaque proteins. Fibronectin, known to be induced by TGF-beta 1 was used as a positive control and tubulin as a negative control. Twenty-four hours after TGF-beta 1 stimulation, DP I and II mRNA levels assessed by Northern blotting analysis had increased significantly (DP I mRNA, 1.8-fold, P less than 0.05; DP II mRNA, 2.4-fold, P less than 0.04), thereby indicating pretranslational regulation of DP expression. By comparison, mRNA for fibronectin increased 8.1-fold whereas mRNA for tubulin was unchanged. Immunofluorescence using the monoclonal anti-DP I and II antibodies revealed dramatic increased expression of punctate DP structures after exposure to TGF-beta 1. Immunoblot analyses with polyclonal anti-DP I antibodies showed increased levels of both DP I (250 kD) and DP II (215 kD), with the DP I increase being more pronounced (DP I, 2.5-fold; DP II, 1.4-fold at 48 h relative to controls), suggesting translational regulation by TGF-beta 1. This study therefore demonstrates the ability of TGF-beta 1 to alter cellular phenotype by altering expression of proteins involved in intercellular junctions.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum-free culture of fractionated bovine bronchial epithelial cells

Procedures for the serum-free culture of a density fractionated population of bovine bronchial epithelial cells have been established. Epithelial cells dispersed by protease digestion were fractionated by density equilibrium centrifugation, followed by plating of the small basal-like population on type I collagen-coated culture dishes. Two or three passages of 1:4 split enriched for a population of actively dividing cells, which could be stored in liquid nitrogen for subsequent use. Clonal growth assays revealed optimum proliferation using a 1:1 mixture of medium RPMI 1640 and LHC-9, a medium employed for human bronchial epithelial cells. Cellular growth rate, which was 0.6 to 1.3 doublings per day depending on the cell preparation, was conveniently decreased by supplementing LHC-9 medium with less than 50% RPMI. In contrast to airway epithelial cell cultures from other species, serum stimulated the growth of bovine bronchial epithelial cells in this system. Transforming growth factor beta 1, however, inhibited growth and induced differentiation into a squamous phenotype. Also in contrast with other systems, the bovine cells were resistant to growth inhibition by 100 nM tetradecanoyl phorbol acetate or 1 microM calcium ionophore A23187. Combination of phorbol ester with ionophore decreased mitotic activity, although induction of squamous morphology was not observed. Therefore, growth inhibition and squamous differentiation were not tightly coupled in this system. Finally, biologically synthesized matrix deposited by these cells stimulated growth rate. This culture system will therefore be useful in assessing the activities of both soluble and matrix-associated factors in the absence of serum.

Attachment characteristics of bovine bronchial epithelial cells to extracellular matrix components

Attachment of cells to extracellular matrix (ECM) plays an important role in the regulation of cell growth and differentiated function. We hypothesized that bronchial epithelial cells preferentially attach to ECM proteins and utilize specific receptors for ECM proteins. Bronchial epithelial cells were obtained from bovine lung by protease digestion. Both freshly isolated and cultured bronchial epithelial cells were plated onto plastic petri dishes coated with bovine serum albumin, type I collagen, type IV collagen, fibronectin, laminin, ECM synthesized by cultured bronchial epithelial cells, or uncoated. Freshly isolated cells demonstrated significant attachment to ECM but weak attachment to other matrix proteins. Cultured bronchial epithelial cells attached well to ECM; however, they had relatively increased attachment to type I collagen, type IV collagen, fibronectin, and laminin compared to freshly isolated cells. To determine whether the attachment of bronchial epithelial cells is arginine-glycine-aspartic acid (RGD)-mediated, an RGD-containing peptide known to block attachment mediated by many integrin receptors was added to the media (400 micrograms/ml). There was no inhibition of attachment of freshly isolated cells; however, there was significant but not complete inhibition of the attachment of the cultured cells to type IV collagen, laminin, and fibronectin, but not to type I collagen or ECM. Thus, freshly isolated bronchial epithelial cells readily adhere to ECM, and the attachment does not appear to be mediated by RGD-dependent receptors. Cultured bronchial epithelial cells demonstrate increased attachment to component proteins of ECM, and this attachment is, in part, to RGD-dependent receptors.