Cytochrome P-450 monooxygenase,epoxide hydrolase and flavin monooxygenase activities in clara cells and alveolar type II cells isolated from rabbit

The activities of several enzymes which metabolize xenobiotics were measured and compared in freshly isolated rabbit Clara cells (50–70% purity) and alveolar type II cells (80–95% purity) or microsomal preparations from the isolated cell fractions. The presence of 1 mM nicotinamide in protease and cell isolation buffers increased significantly 7-ethoxycoumarin (7-EC) deethylase and epoxide hydrolase activities in the isolated Clara and type II cells. Isolated Clara cell fractions metabolized 7-EC to umbelliferone at a rate of 241 ± 27 pmoles/mg prot/min (mean ± S.E., N=5), while the 7-EC deethylation rate in type II cells was 111 ± 15 pmoles/mg prot/min. Coumarin hydroxylation activity, however, was more than ten times greater in the Clara cells than in the type II cells on a per mg cellular protein basis. N-oxidation of N,N-dimethylaniline, catalyzed by a flavin monooxygenase, was about 2 times as great in microsomes of Clara cells as in microsomes of type II cells. Epoxide hydrolase activity with benzo(a)pyrene 4,5-oxide as substrate was about 10 times higher in Clara cells than in type II cells. Because of the greater cellular, structural and functional heterogeneity in lung, differential distribution of enzymes responsible for xenobiotic metabolism in this tissue may contribute to cell selective chemical toxicity and carcinogenesis.Abbreviations 7-EC 7-ethoxycoumarin - DMA N,N-dimethylaniline     

Metabolism of 2-acetylaminofluorene by clara cells,type II cells and alveolar macrophages isolated from rabbit lung,and use of a new chamber incubation mutagenicity test system

Clara cells, alveolar type II cells and pulmonary alveolar macrophages (PAM) were isolated in high yield from rabbit lung. The purity of the cell fractions was 80–90%, 98% and above 99%, respectively. Cytochrome P-450 total content was determined in microsomes from freshly prepared cells. The Clara cells contained significantly more cytochrome P-450 than was found in whole lung microsomes. Furthermore, the cytochrome content of the Clara cells was 2 -fold higher than in the type II cells and 4 -fold higher than in the macrophages. 2-aminofluorene (AF) was the major metabolite in all preparations when intact cells were incubated with 2-acetylaminofuorene (AAF). The PAMs produced AF in the highest rates, while the Clara cells showed the largest rates of cytochrome P-450-dependent, ring hydroxylation of AAF. Mutagenic activation of AAF by isolated lung cells was assayed with a chamber-incubation method. The Clara cells were far more active than the type II cells in this respect, while the macrophages were inactive.Abbreviations AAF 2-acetylaminofluorene - AF 2-aminofluorene - DMSO dimethyl sulfoxide - NBT nitro blue tetrazolium - 7-OH-AAF 7-hydroxy-AAF - 9-OH-AAF 9-hydroxy-AAF     

<Emphasis Type="Italic">In vivo</Emphasis> Cre/loxP Mediated Recombination in Mouse Clara Cells

In small airways, Clara cells are the main epithelial cell type and play an important physiological role in surfactant production, protection against environmental agents, regulation of inflammatory and immune responses in the respiratory system. Thus, Clara cells are involved in lung homeostasis and pathologies like asthma, Chronic Obstructive Pulmonary Diseases (COPD) or cancers. To date, Clara cells implication in these pathological processes remains largely enigmatic. The engineering of a transgenic strain mouse allowing specific gene invalidation in Clara cells may be of interest to improve our knowledge about the genes involved in these diseases. By using the Cre/loxP strategy we report the engineering of a transgenic mouse strain with expression of Cre recombinase under the control of the Clara Cell Secretory Protein (CCSP) promoter. Specific staining and immuno-histochemistry performed after breeding with reporter mice revealed that CCSP drives a functional Cre expression specifically in Clara cells. This mouse strain is a powerful tool for Cre-loxP-mediated conditional recombination in the lung and represents a new tool to study Clara cell physiology.     

Secretory proteins of the lung in rodents: immunocytochemistry

The reactivity of rabbit antisera to rat lung secretory proteins with other rodent species was evaluated by immunocytochemistry. Rabbit anti-rat surfactant apoprotein antiserum reacts with the cytoplasm of rat, mouse, and hamster type II pneumocytes and is specific for these cells. Rabbit antiserum to rat Clara cell secretory proteins stains rat, mouse, and hamster Clara cells. Rabbit antisera specific to the two antigenic types of rat Clara cell antigens were also both reactive with rat, mouse, and hamster Clara cells. An antiserum to the non-serum proteins of hamster lung lavage was also prepared and shown to be specifically reactive with hamster Clara cells. The availability of specific reagents for secretory proteins of rodent lungs is expected to facilitate studies of the respective cell types in various pathologic states.     

Isolation of viable type II alveolar epithelial cells by flow cytometry

We developed a new method for isolating viable type II cells from fractionated and unfractionated lung cell suspensions by flow cytometry using acridine orange (AO). Fischer-344 rat lungs were dispersed into single-cell suspensions by a technique that yields a high number of cells (4-5 X 10(8) cells/lung, congruent to 85% viable), congruent to 11% of which are type II cells. Elutriated fractions from the lung cell preparation and parent, unfractionated cell suspensions were incubated with 1.0-0.02 micrograms/ml AO and analyzed by flow cytometry. Parameters analyzed included axial light loss (ALL) and red fluorescence (RF). Based on their unique RF, attributable to AO staining of type II cell lamellar bodies, and their ALL characteristics, type II pneumocytes were sorted from elutriated fractions to greater than 95% purity. Using the same approach, type II pneumocytes were sorted from unfractionated lung cell suspensions at greater than or equal to 85% purity. The viabilities of the type II alveolar epithelial cells isolated by this method range from 85% to 95%, and the ultrastructural features of the sorted cells were unaltered by AO labeling or sorting.     

Identification and isolation of mouse type II cells on the basis of intrinsic expression of enhanced green fluorescent protein

The unique morphology and cell-specific expression of surfactant genes have been used to identify and isolate alveolar type II epithelial cells. Because these attributes can change during lung injury, a novel method was developed for detecting and isolating mouse type II cells on the basis of transgenic expression of enhanced green fluorescence protein (EGFP). A line of transgenic mice was created in which EGFP was targeted to type II cells under control of the human surfactant protein (SP)-C promoter. Green fluorescent cells that colocalized by immunostaining with endogenous pro-SP-C were scattered throughout the parenchyma. EGFP was not detected in Clara cell secretory protein-expressing airway epithelial cells or other nonlung tissues. Pro-SP-C immunostaining diminished in lungs exposed to hyperoxia, consistent with decreased expression and secretion of intracellular precursor protein. In contrast, type II cells could still be identified by their intrinsic green fluorescence, because EGFP is not secreted. Type II cells could also be purified from single-cell suspensions of lung homogenates using fluorescence-activated cell sorting. Less than 1% of presorted cells exhibited green fluorescence compared with >95% of the sorted population. As expected for type II cells, ultrastructural analysis revealed that the sorted cells contained numerous lamellar bodies. SP-A, SP-B, and SP-C mRNAs were detected in the sorted population, but T1alpha and CD31 (platelet endothelial cell adhesion molecule) were not, indicating enrichment of type II epithelial cells. This method will be invaluable for detecting and isolating mouse type II cells under a variety of experimental conditions.     

The effects of interleukin-8 on airway smooth muscle contraction in cystic fibrosis

Background

Clara cells are the epithelial progenitor cell of the small airways, a location known to be important in many lung disorders. Although migration of alveolar type II and bronchiolar ciliated epithelial cells has been examined, the migratory response of Clara cells has received little attention.

Methods

Using a modification of existing procedures for Clara cell isolation, we examined mouse Clara cells and a mouse Clara-like cell line (C22) for adhesion to and migration toward matrix substrate gradients, to establish the nature and integrin dependence of migration in Clara cells.

Results

We observed that Clara cells adhere preferentially to fibronectin (Fn) and type I collagen (Col I) similar to previous reports. Migration of Clara cells can be directed by a fixed gradient of matrix substrates (haptotaxis). Migration of the C22 cell line was similar to the Clara cells so integrin dependence of migration was evaluated with this cell line. As determined by competition with an RGD containing-peptide, migration of C22 cells toward Fn and laminin (Lm) 511 (formerly laminin 10) was significantly RGD integrin dependent, but migration toward Col I was RGD integrin independent, suggesting that Clara cells utilize different receptors for these different matrices.

Conclusion

Thus, Clara cells resemble alveolar type II and bronchiolar ciliated epithelial cells by showing integrin mediated pro-migratory changes to extracellular matrix components that are present in tissues after injury.     

Formation of genotoxic products from N-nitrosoheptamethyleneimine (NHMI), 4-(Methylnitrosamino)-1-(3-Pyridyl)-1-Butanone (NNK) and N′-Nitrosonornicotine (NNN) by isolated rabbit lung cells

The genotoxic potentials of N-nitrosoheptamethyleneimine (NHMI), 4-(methylnitrosamino)-1-(3 pyridyl)-1-butanone (NNK) and N-nitrosonornicotine (NNN) were studied in fresh preparations of Clara cells and type II cells isolated by centrifugal elutriation and density gradient centrifugation, and macrophages from rabbit lung. The activation of the compounds to bacterial mutagens was assayed in the Salmonella mutagenicity test using strains of TA 100 and TA 1530 preincubated with test chemicals and cells placed in chambers with nucleopore membranes to separate cells and bacteria. Unscheduled DNA synthesis was measured by incorporation of [³H]-thymidine in the cells after exposure to the compounds. NHMI, NNK and NNN were not activated to bacterial mutagens by Clara cells, type II cells or macrophages, presumably because the reactive metabolites generated were not released into the incubation medium. However, NHMI and NNK increased unscheduled DNA synthesis in Clara cells, and the highest repair activity was found after incubation with NNK. The effect of NNN was only marginal. This indicates that NHHI and NNK are genotoxic in the rabbit lung and that the Clara cells are involved in the metabolic activation of these compounds.Abbreviations NHMI N-nitrosoheptamethyleneimine - NNK 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone - NNN N-nitrosonornicotine Supported by a grant and a fellowship (R.B.) from the Royal Norwegian Council for Scientific and Industrial Research.     

Differential susceptibilities of isolated hamster lung cell types to amiodarone toxicity

Treatment of cardiac dysrhythmias with the iodinated benzofuran derivative amiodarone (AM) is limited by pulmonary toxicity. The susceptibilities of different lung cell types of male Golden Syrian hamsters to AM-induced cytotoxicity were investigated in vitro. Bronchoalveolar lavage and protease digestion to release cells, followed by centrifugal elutriation and density gradient centrifugation, resulted in preparations enriched with alveolar macrophages (98%), alveolar type II cells (75-85%), and nonciliated bronchiolar epithelial (Clara) cells (35-50%). Alveolar type II cell and Clara cell preparations demonstrated decreased viability (by 0.5% trypan blue dye exclusion) when incubated with 50 microM AM for 36 h, and all AM-treated cell preparations demonstrated decreased viability when incubated with 100 or 200 microM AM. Based on a viability index ((viability of AM-treated cells/viability of controls) x 100%), the Clara cell fraction was significantly (p<0.05) more susceptible than all of the other cell types to 50 microM AM. However, AM cytotoxicity was greatest (p<0.05) in alveolar macrophages following incubation with 100 or 200 microM AM. There was no difference between any of the enriched cell preparations in the amount of drug accumulated following 24 h of incubation with 50 microM AM, whereas alveolar macrophages accumulated the most drug during incubation with 100 microM AM. Thus, the most susceptible cell type was dependent on AM concentration. AM-induced cytotoxicity in specific cell types may initiate processes leading to inflammation and pulmonary fibrosis.     

Novel method for isolation of murine clara cell secretory protein-expressing cells with traces of stemness

Clara cells are non-ciliated, secretory bronchiolar epithelial cells that serve to detoxify harmful inhaled substances. Clara cells also function as stem/progenitor cells for repair in the bronchioles. Clara cell secretory protein (CCSP) is specifically expressed in pulmonary Clara cells and is widely used as a Clara cell marker. In addition CCSP promoter is commonly used to direct gene expression into the lung in transgenic models. The discovery of CCSP immunoreactivity in plasma membranes of airway lining cells prompted us to explore the possibility of enriching Clara cells by flow cytometry. We established a novel and simple method for the isolation of CCSP-expressing cell Clara cells using a combination of mechanical and enzymatic dissociation followed by flow cytometry sorting technology. We showed that ～25% of dissociated cells from whole lung expressed CCSP. In the resulting preparation, up to 98% of cells expressed CCSP. Notably, we found that several common stem cell markers including CD44, CD133, Sca-1 and Sox2 were expressed in CCSP(+) cells. Moreover, CCSP(+) cells were able to form spheroid colonies in vitro with 0.97‰ efficiency. Parallel studies in vivo confirmed that a small population of CCSP(-)expressing cells in mouse airways also demonstrates stem cell-like properties such as label retention and harboring rare bronchioalveolar stem cells (BASCs) in terminal bronchioles (TBs). We conclude that CCSP(+) cells exhibit a number of stem cell-like features including stem cell marker expression, bronchosphere colony formation and self-renewal ability. Clara cell isolation by flow cytometry sorting is a useful method for investigating the function of primary Clara cells in stem cell research and mouse models.     

The increase of microRNA-21 during lung fibrosis and its contribution to epithelial-mesenchymal transition in pulmonary epithelial cells

Background

The excess and persistent accumulation of fibroblasts due to aberrant tissue repair results in fibrotic diseases such as idiopathic pulmonary fibrosis. Recent reports have revealed significant changes in microRNAs during idiopathic pulmonary fibrosis and evidence in support of a role for microRNAs in myofibroblast differentiation and the epithelial-mesenchymal transition in the context of fibrosis. It has been reported that microRNA-21 is up-regulated in myofibroblasts during fibrosis and promotes transforming growth factor-beta signaling by inhibiting Smad7. However, expression changes in microRNA-21 and the role of microRNA-21 in epithelial-mesenchymal transition during lung fibrosis have not yet been defined.

Methods

Lungs from saline- or bleomycin-treated C57BL/6 J mice and lung specimens from patients with idiopathic pulmonary fibrosis were analyzed. Enzymatic digestions were performed to isolate single lung cells. Lung epithelial cells were isolated by flow cytometric cell sorting. The expression of microRNA-21 was analyzed using both quantitative PCR and in situ hybridization. To induce epithelial-mesenchymal transition in culture, isolated mouse lung alveolar type II cells were cultured on fibronectin-coated chamber slides in the presence of transforming growth factor-β, thus generating conditions that enhance epithelial-mesenchymal transition. To investigate the role of microRNA-21 in epithelial-mesenchymal transition, we transfected cells with a microRNA-21 inhibitor. Total RNA was isolated from the freshly isolated and cultured cells. MicroRNA-21, as well as mRNAs of genes that are markers of alveolar epithelial or mesenchymal cell differentiation, were quantified using quantitative PCR.

Results

The lung epithelial cells isolated from the bleomycin-induced lung fibrosis model system had decreased expression of epithelial marker genes, whereas the expression of mesenchymal marker genes was increased. MicroRNA-21 was significantly upregulated in isolated lung epithelial cells during bleomycin-induced lung fibrosis and human idiopathic pulmonary fibrosis. MicroRNA-21 was also upregulated in the cultured alveolar epithelial cells under the conditions that enhance epithelial-mesenchymal transition. Exogenous administration of a microRNA-21 inhibitor prevented the increased expression of vimentin and alpha-smooth muscle actin in cultured primary mouse alveolar type II cells under culture conditions that induce epithelial-mesenchymal transition.

Conclusions

Our experiments demonstrate that microRNA-21 is increased in lung epithelial cells during lung fibrosis and that it promotes epithelial-mesenchymal transition.     

Identification of calcium-dependent phospholipid-binding proteins (annexins) from guinea pig alveolar type II cells

A new group of calcium-regulating proteins, called annexins or Ca⁺⁺-dependent phospholipid-binding proteins (PLBP), have been detected in different species, organs and cell types. In the present study, we have identified and quantitated PLBP from guinea pig lung, lavage fluid and alveolar type II cells to elucidate the possible role of PLBP in lung surfactant biogenesis and secretion. Lungs were lavaged and type II cells from lavaged lung were isolated by elastase digestion and purified by centrifugal elutriation. For the quantitative identification of PLBP, we performed ELISA assays and Western blot analysis by using an antiserum raised in guinea pigs against a pure rabbit lung 36 kDa PLBP. The lavage fluid, cytosol from lung and type II cells contained 784,167 and 435 ng per mg protein, respectively, of PLBP. The SDS-PAGE electrophoretic pattern and Western blot confirmed that all lung samples have band corresponding to a 36 kDa protein. This indicates that both alveolar type II cells and lavage fluid have higher levels of PLBP than whole lung cytosol.     

Localization of pulmonary carbonyl reductase in guinea pig and mouse: enzyme histochemical and immunohistochemical studies.

We studied the localization of carbonyl reductase (E.C. 1.1.1.184) in guinea pig and mouse lung by enzyme histochemistry and immunohistochemistry, using antibodies against the guinea pig lung enzyme which crossreacted with the lung enzymes of both animals. Carbonyl reductase activity was detectable in the bronchiolar epithelial cells of small airways and in alveolar cells. In the immunohistochemical staining for carbonyl reductase, the reaction was strongest in the non-ciliated bronchiolar cells (Clara cells) and was weak in the ciliated cells and type II alveolar pneumocytes. Injection of a single dose of naphthalene led to significant impairment of carbonyl reductase activity and of microsomal mixed-function oxidase activities in mouse lung, with a marked decrease in both activity and immunoreactive staining in the bronchiolar epithelial cells. The results indicate that carbonyl reductase is localized primarily in the Clara cells, which are known to be sites of pulmonary drug metabolism.     

A quantitative method for separation of livingHydra cells

Summary We describe a rapid method for the isolation of large numbers of livingHydra cells of defined cell type in an isotonic cell medium (Gierer et al. 1972). Intact animals are enzymatically dissociated into a single cell suspension and the various cell types separated in less than one hour by counterflow centrifugation elutriation. Cell loss is minimal. RNA isolated from various fractions can be probed with cell type specific cDNA-clones.     

Increased gene expression of lung marker proteins in the homeobox B3-overexpressed fetal lung cell line M3E3/C3.

Homeobox (Hox)-containing factors have been shown to play regulatory roles on lung development. Although HoxB3 gene expression is detected in the prenatal lung during development, its function has not been clarified precisely. We constructed an expression vector of a hamster HoxB3 coding region, which was cloned from hamster fetal lung cell line M3E3/C3. Sixteen-base deletion was found in the hamster HoxB3 coding sequence when compared with the mouse sequence. Under conditions of differentiation, cells transfected transiently with HoxB3 augmented the retinol-induced gene expression of Clara cell-specific secretory protein, whereas the cells showed reduced expression of surfactant-associated protein C. These alterations were attenuated by the transfection with HoxB3 antisense nucleotide. The results show that the cells with overexpressed HoxB3 were reinforced to have characteristics of Clara cells but did not have the characteristics of alveolar type II cells, and that HoxB3 played a stimulatory role on Clara cell differentiation in M3E3/C3 cells. In addition, the expression of Clara cell-specific secretory protein and surfactant-associated protein C genes was enhanced upon transfer of cells to collagen substrate, suggesting that collagen substrate has some regulatory functions on lung cell differentiation through cell adhesion.     

Human lung mast cells: purification and characterization

Detailed studies of the biochemistry and pharmacology of mast cell-mediated inflammatory disorders have been hampered by the inability to purify human mast cells. We now report techniques to purify human lung mast cells to apparent homogeneity. The major purification steps are: 1) dispersion of lung fragments into a single-cell suspension with enzyme combinations (pronase-chymopapain, collagenase-elastase); 2) partial purification by countercurrent centrifugation elutriation (CCE); and 3) affinity column chromatography. Enzymatic dispersion yielded suspensions with congruent to 10(6) mast cells per gram of lung parenchyma in purities of 1.2 to 9.7%. Dispersed mast cells responded comparably to those in parent lung fragments to challenge with anti-human IgG and pharmacologic agonists. Elutriation of lung cell suspensions yielded mast cell-enriched fractions with purities up to 70%. High purity mast cell fractions were combined, passively sensitized with purified human penicillin (BPO)-specific IgE, and purified by a BPO-affinity column chromatography procedure. Post elutriation mast cell purities of 29 +/- 3.5% were increased to 84 +/- 3% (range 65 to 98%) by the affinity column. Short-term (24 hr) culture of column-purified mast cells allowed adherence of non-mast cell contaminants to tissue culture plates, further increasing purity (up to 100%). Purified mast cells were intact and functional as assessed by dye exclusion, survival in short-term culture, IgE-mediated histamine release, and modulation of release by the pharmacologic agonists adenosine, IBMX, prostaglandin E2, and fenoterol.     

Monoclonal antibody isolation of type II pneumocytes

A monoclonal antibody that identifies a membrane molecule unique in rat lung for type II alveolar epithelial cells was used to isolate these cells from enzymatically dispersed lung cells by fluorescence-activated cell sorting. Although multistep physical separation techniques have permitted the isolation of large quantities of these cells and flow cytometry has been used by others to isolate lamellar body-containing cells, the application of this antibody-directed sorting has distinct advantages. Because the marker molecule is expressed on immature type II cells prior to the development of lamellar bodies, the antibody will also permit their isolation and study.     

l7Rn6 encodes a novel protein required for clara cell function in mouse lung development

The highly secretory Clara cells play a pivotal role in protecting the lung against inflammation and oxidative stress. This study reports the positional cloning of a novel protein required for Clara cell physiology in mouse lung development. The perinatal lethal N-ethyl-N-nitrosourea-induced l7Rn6(4234SB) allele contained a nonsense mutation in the previously hypothetical gene NM_026304 on chromosome 7. Whereas l7Rn6 mRNA levels were indistinguishable from wild type, l7Rn6(4234SB) homozygotes exhibited decreased expression of the truncated protein, suggesting protein instability. During late gestation, l7Rn6 was widely expressed in the cytoplasm of lung epithelial cells, whereas perinatal expression was restricted to the bronchiolar epithelium. Homozygosity for the l7Rn6(4234SB) allele did not affect early steps in lung patterning, growth, or cellular differentiation. Rather, mutant lungs demonstrated severe emphysematous enlargement of the distal respiratory sacs at birth. Clara cell pathophysiology was evident from decreased cytoplasmic CCSP and SP-B protein levels, enlargement and disorganization of the Golgi complex, and formation of aberrant vesicular structures. Additional support for a role in the secretory pathway derived from l7Rn6 localization to the endoplasmic reticulum. Thus, l7Rn6 represents a novel protein required for organization and/or function of the secretory apparatus in Clara cells in mouse lung.