Role of laminin in maintenance of type II pneumocyte morphology and function

Development and Functional Characterization of Fetal Lung Organoids

Preterm infants frequently suffer from pulmonary complications due to a physiological and structural lung immaturity resulting in significant morbidity and mortality. Novel in vitro and in vivo models are required to study the underlying mechanisms of late lung maturation and to facilitate the development of new therapeutic strategies. Organoids recapitulate essential aspects of structural organization and possibly organ function, and can be used to model developmental and disease processes. We aimed at generating fetal lung organoids (LOs) and to functionally characterize this in vitro model in comparison to primary lung epithelial cells and lung explants ex vivo. LOs were generated with alveolar and endothelial cells from fetal rat lung tissue, using a Matrigel-gradient and air-liquid-interface culture conditions. Immunocytochemical analysis showed that the LOs consisted of polarized epithelial cell adhesion molecule (EpCAM)-positive cells with the apical membrane compartment facing the organoid lumen. Expression of the alveolar type 2 cell marker, RT2-70, and the Club cell marker, CC-10, were observed. Na⁺ transporter and surfactant protein mRNA expression were detected in the LOs. First time patch clamp analyses demonstrated the presence of several ion channels with specific electrophysiological properties, comparable to vital lung slices. Furthermore, the responsiveness of LOs to glucocorticoids was demonstrated. Finally, maturation of LOs induced by mesenchymal stem cells confirmed the convenience of the model to test and establish novel therapeutic strategies. The results showed that fetal LOs replicate key biological lung functions essential for lung maturation and therefore constitute a suitable in vitro model system to study lung development and related diseases.

Characterization of pulmonary cell growth parameters in a continuous perfusion microfluidic environment

In vitro models of the alveolo-pulmonary barrier consist of microvascular endothelial cells and alveolar epithelial cells cultured on opposing sides of synthetic porous membranes. However, these simple models do not reflect the physiological microenvironment of pulmonary cells, wherein cells are exposed to a complex milieu of mechanical and soluble stimuli. In this report, we studied alveolar epithelial (A549) and microvascular endothelial (HMEC-1) cells within varying microfluidic environments as a first step towards building a microfluidic analog of the gas-exchange interface. We fabricated polydimethylsiloxane (PDMS) microdevices for parallel studies of cell growth under multiple flow rates. Cells adhered and proliferated in the microculture chambers for shear stresses up to approximately 2 x 10(-3) dynes/cm(2), corresponding to media turnover rates of approximately 53 seconds. Proliferation of these cells into confluent monolayers and expression of cell-specific markers (SP-A and CD-31) demonstrated successful pulmonary cell culture in microscale devices, a first for alveolar epithelial cells. These results represent the initial steps towards the development of microfluidic analogs of the alveolo-pulmonary barrier and tissue engineering of the lung.

Modulation of endotoxin-induced neutrophil transendothelial migration by alveolar epithelium in a defined bilayer model

Within the alveolus, epithelial cells, due to their close association with endothelial cells, can potentially influence endothelial cell responsiveness during inflammation and their interaction with leukocytes. To investigate this, three lung epithelial cell lines (A549, Calu-3, or NCI-H441) were grown with endothelium on opposing surfaces of Transwell filters and the formation and stability of bilayers was rigorously evaluated. All epithelial lines disrupted endothelial monolayer formation on filters with 3- or 5-microm pores by breaching the filter, and this occurred regardless of seeding density, matrix composition, or duration of culture. Endothelial disruption was not detectable by electrical resistance or permeability measurements but required cell-specific staining with immunofluorescence and microscopy. Distinct bilayers formed only on filters with 0.4-microm pores and only with A549 cells and human umbilical vein endothelial cells. Endotoxin (lipopolysaccharide [LPS]) stimulation of bilayers (4 hours) enhanced neutrophil transendothelial migration, but this was significantly decreased compared with the response of endothelium grown alone, irrespective of whether LPS exposure was via the epithelial or endothelial side of the bilayer. Down-modulation required epithelial-endothelial approximation and was not seen when these cells were separated by 0.5 to 1 mm. This study defines optimal conditions required for generation of intact bilayers of lung epithelial cells with endothelium for the study of leukocyte-transendothelial migration. Furthermore, it was demonstrated that lung epithelial cells can modulate endothelial cell responsiveness to an environmental inflammatory stimulus such as LPS and thus may have an important role in minimizing excessive and deleterious neutrophilic inflammation in the lung alveolus.

Integrins β1, α6, and α3contribute to mechanical strain-induced differentiation of fetal lung type II epithelial cells via distinct mechanisms

Mechanical forces regulate lung maturation in the fetus by promoting type II epithelial differentiation. However, the cell surface receptors that transduce these mechanical cues into cellular responses remain largely unknown. When distal lung type II epithelial cells isolated from embryonic day 19 rat fetuses were cultured on flexible plates coated with laminin, fibronectin, vitronectin, collagen, or elastin and exposed to a level of mechanical strain (5%) similar to that observed in utero, transmembrane signaling responses were induced under all conditions, as measured by ERK activation. However, mechanical stress maximally increased expression of the type II cell differentiation marker surfactant protein C when cells were cultured on laminin substrates. Strain-induced alveolar epithelial differentiation was inhibited by interfering with cell binding to laminin using soluble laminin peptides (IKVIV or YIGSR) or blocking antibodies against integrin β1, α3, or α6. Additional studies were carried out with substrates coated directly with different nonactivating anti-integrin antibodies. Blocking integrin β1and α6binding sites inhibited both cell adhesion and differentiation, whereas inhibition of α3prevented differentiation without altering cell attachment. These data demonstrate that various integrins contribute to mechanical control of type II lung epithelial cell differentiation on laminin substrates. However, they may act via distinct mechanisms, including some that are independent of their cell anchoring role.

Effects of vascular endothelial growth factor on isolated fetal alveolar type II cells

Previous investigations gained from in vivo or lung explant studies suggested that VEGF is an autocrine proliferation and maturation factor for developing alveolar type II cells. The objective of this work was to determine whether VEGF exerted its growth and maturation effects directly on isolated type II cells. These were isolated from 19-day fetal rat lung and cultured in defined medium. The presence of VEGF receptor-2 was assessed in cultured cells at the pre- and posttranslational levels. Recombinant VEGF(165), formerly found to be active on lung explants, failed to enhance type II cell proliferation estimated by thymidine and 5-bromo-2'-deoxy-uridine incorporation. It increased choline incorporation in saturated phosphatidylcholine by 27% but did not increase phospholipid surfactant pool size. VEGF (100 ng/ml) left unchanged the transcript level of surfactant proteins (SP)-A, SP-C, and SP-D but increased SP-B transcripts to four times the control steady-state level. VEGF slightly retarded, but did not prevent, the in vitro transdifferentiation of type II into type I cells, as assessed by immunolabeling of the type I cell marker T1alpha. We conclude that, with the exception of SP-B expression, which appears to be controlled directly, the previously observed effects of this VEGF isoform on type II cells are likely to be exerted indirectly through reciprocal paracrine interactions involving other lung cell types.

Heterocellular cultures of pulmonary alveolar epithelial cells grown on laminin-5 supplemented matrix

The pulmonary alveolar epithelium consists of alveolar type I (AT1) and alveolar type II (AT2) cells. Interactions between these two cell types are necessary for alveolar homeostasis and remodeling. These interactions have been difficult to study in vitro because current cell culture models of the alveolar epithelium do not provide a heterocellular population of AT1 and AT2 cells for an extended period of time in culture. In this study, a new method for obtaining heterocellular cultures of AT1- and AT2-like alveolar epithelial cells maintained for 7 d on a rat tail collagen-fibronectin matrix supplemented with laminin-5 is described. These cultures contain cells that appear by their morphology to be either AT1 cells (larger flattened cells without lamellar bodies) or AT2 cells (smaller cuboidal cells with lamellar bodies). AT1-like cells stain for the type I cell marker aquaporin-5, whereas AT2-like cells stain for the type II cell markers surfactant protein C or prosurfactant protein C. AT1/AT2 cell ratios, cell morphology, and cell phenotype-specific staining patterns seen in 7-d-old heterocellular cultures are similar to those seen in alveoli in situ. This culture system, in which a mixed population of phenotypically distinct alveolar epithelial cells are maintained, may facilitate in vitro studies that are more representative of AT1-AT2 cell interactions that occur in vivo.

Laminin alpha 5 is required for lobar septation and visceral pleural basement membrane formation in the developing mouse lung

Laminin alpha/beta/gamma heterotrimers are the major noncollagenous components of all basement membranes. To date, five alpha, three beta, and three gamma chains have been identified. Laminin alpha 5 is expressed early in lung development and colocalizes with laminin alpha1. While laminin alpha1 expression in the lung is restricted to the embryonic period, laminin alpha 5 expression persists throughout embryogenesis and adulthood. Targeted mutation of the mouse laminin alpha 5 gene Lama5 causes embryonic lethality at E14-E17 associated with exencephaly, syndactyly, placentopathy, and kidney defects, all attributable to abnormal basement membranes. In this investigation, lung development in Lama5(-/-) mice up to E16.5 was examined. We observed normal lung branching morphogenesis and vasculogenesis, but incomplete lobar septation and absence of the visceral pleura basement membrane. Preservation of branching morphogenesis was associated with ectopic deposition of laminin alpha 4 in the airway basement membrane. Perturbation of pleural basement membrane formation and right lung septation correlated with absence of laminin alpha 5, which was found to be the only laminin alpha chain present in the normal visceral pleura basement membrane. Our finding of normal lung branching morphogenesis with abnormal lobar septation demonstrates that these processes are not obligatorily linked.

Maintenance of the differentiated type II cell characteristics by culture on an acellular human amnion membrane

We have developed a Culture system for guinea pig alveolar type II cells using an epithelium-denuded human amnion membrane as a substratum. The differentiated morphology was maintained for 3 wk by both air-interface feeding and immersion feeding when type II cells were cultured on the basement membrane side of the amnion with fibroblasts on the opposite side (coculture). Functionally high levels of surfactant protein B (SP-B) and C (SP-C) messenger ribonucleic acids (mRNAs) were expressed even after the 3-wk cultivation and surfactant protein A mRNA was detected on day 10 of the culture. The differentiation was also maintained when fibroblasts were cultured on lower chambers of the culture plates (separate culture). In contrast, culture of type II cells without fibroblasts (monoculture) could not preserve the mature morphology. When the monoculture was supplemented with keratinocyte growth factor or hepatocyte growth factor, a monolayer of rather cuboidal type II cells with apical microvilli was maintained. However, the percent area of lamellar bodies in these cells was significantly less than that in freshly isolated type II cells, and mRNA expressions of SP-B and SP-C were also considerably suppressed. These findings suggest that other growth factors or combinations of these factors are necessary for the maintenance of the differentiated phenotype. As substratum, a permeable collagen membrane or a thin gel layer of Engelbreth-Holm-Swarm mouse sarcoma extracts did not preserve the mature characteristics. This culture system using an acellular human amnion membrane may provide novel models for research in type II cells.

Recovery of rat type II cell surfactant components during primary cell culture

A culture system designed to maintain the differentiated characteristics of rat type II cells based on protocols used for human fetal lung pneumocytes was investigated. Type II cells were isolated either from adult rats with elastase (adult type II cells) or from young rats (4-11 days postnatal) with collagenase and trypsin (young type II cells) and were incubated with dexamethasone (Dex, 10 nM) and cAMP (0.1 mM). By day 4 of culture with hormone treatment, the mRNA levels in adult type II cells were less than 3% of day 0 values, whereas surfactant protein (SP)-A protein content was 26%. However, young type II cells maintained lamellar bodies and microvilli and secreted phospholipid in response to ATP. SP-A, -B, and -C mRNA levels were elevated to 159, 350, and 39%, respectively, of day 0 values with a synergistic response to Dex and cAMP, whereas SP-A protein content rose to 119%. Surfactant mRNA and protein did not recover in cells cultured without hormones. This cell culture system restored surfactant components in rat type II cells.

Maintenance of the differentiated type II cell characteristics by culture on an acellular human amnion membrane

We have developed a Culture system for guinea pig alveolar type II cells using an epithelium-denuded human amnion membrane as a substratum. The differentiated morphology was maintained for 3 wk by both air-interface feeding and immersion feeding when type II cells were cultured on the basement membrane side of the amnion with fibroblasts on the opposite side (coculture). Functionally high levels of surfactant protein B (SP-B) and C (SP-C) messenger ribonucleic acids (mRNAs) were expressed even after the 3-wk cultivation and surfactant protein A mRNA was detected on day 10 of the culture. The differentiation was also maintained when fibroblasts were cultured on lower chambers of the culture plates (separate culture). In contrast, culture of type II cells without fibroblasts (monoculture) could not preserve the mature morphology. When the monoculture was supplemented with keratinocyte growth factor or hepatocyte growth factor, a monolayer of rather cuboidal type II cells with apical microvilli was maintained. However, the percent area of lamellar bodies in these cells was significantly less than that in freshly isolated type II cells, and mRNA expressions of SP-B and SP-C were also considerably suppressed. These findings suggest that other growth factors or combinations of these factors are necessary for the maintenance of the differentiated phenotype. As substratum, a permeable collagen membrane or a thin gel layer of Engelbreth-Holm-Swarm mouse sarcoma extracts did not preserve the mature characteristics. This culture system using an acellular human amnion membrane may provide novel models for research in type II cells.

Connexin expression by alveolar epithelial cells is regulated by extracellular matrix

Extracellular matrix (ECM) proteins promote attachment, spreading, and differentiation of cultured alveolar type II epithelial cells. The present studies address the hypothesis that the ECM also regulates expression and function of gap junction proteins, connexins, in this cell population. Expression of cellular fibronectin and connexin (Cx) 43 increase in parallel during early type II cell culture as Cx26 expression declines. Gap junction intercellular communication is established over the same interval. Cells plated on a preformed, type II cell-derived, fibronectin-rich ECM demonstrate accelerated formation of gap junction plaques and elevated gap junction intercellular communication. These effects are blocked by antibodies against fibronectin, which cause redistribution of Cx43 protein from the plasma membrane to the cytoplasm. Conversely, cells cultured on a laminin-rich ECM, Matrigel, express low levels of Cx43 but high levels of Cx26, reflecting both transcriptional and translational regulation. Cx26 and Cx43 thus demonstrate reciprocal regulation by ECM constituents.

TGF-beta1 and fibroblast growth factor-1 modify fibroblast growth factor-2 production in type II cells

Fibroblast growth factor (FGF)-2, which stimulates DNA synthesis by type II cells in the lung, has been shown to be regulated by transforming growth factor (TGF)-beta1, an important inflammatory cytokine, in vascular epithelium. The goal of this study was to determine if FGF-2 production by alveolar type II cells is modulated by TGF-beta1 or FGF-1, which also stimulates DNA synthesis by type II cells. Isolated rat type II cells were exposed to 0-40 ng/ml of TGF-beta1 or 0-500 ng/ml of FGF-1 in serum-free medium for 1-5 days. With a specific immunoassay, significant increases of FGF-2 protein in type II cell lysates to levels above those in control cells were achieved after 1 day of exposure to 100 ng/ml of FGF-1 and after 3 days of treatment with 8 ng/ml of TGF-beta1. Similarly, transcripts for FGF-2 were dramatically increased above those in control cells with TGF-beta1 or FGF-1, as were those for FGF receptor-1. These results demonstrate important regulatory links between FGF-2 and both TGF-beta1 and FGF-1 in the alveolar epithelium that could contribute to the regulation of normal cell turnover, development, and the repair processes after injury in the lung.

Density and substrata are important in lung type II cell transdifferentiation in vitro

Morphological techniques and metabolic cell marker assays were used to study the transdifferentiation of pulmonary type II epithelial cells to type I-like cells in vitro. In the lung this process is important during remodelling and alveolar repair. Type II cell phenotype was best maintained over eight days when densely packed cells were plated out on a commercially available extracellular matrix. Such cells retained type II cell characteristics (lamellar bodies, high activities of gamma glutamyl transpeptidase and alkaline phosphatase) but expressed low levels of rT1(40) a surface protein marker of type I cells. In contrast, low density cultures, irrespective of substratum, exhibited rapid cell spreading, loss of lamellar bodies, loss of type II cell enzyme markers and expressed high levels or rT1(40). Conditions have been described whereby the same isolate of type II cells can be used to produce differential epithelial phenotypes and use can be made of this for further characterisation or to investigate the effect of toxins on different lung cell types in vitro.

Peptide growth factors regulate insulin-like growth factor binding protein production by fetal rat lung fibroblasts

Insulin-like growth factor (IGF) binding proteins (IGFBPs) are expressed in fetal lung and may provide important post-translational regulation of IGF-induced mitogenesis during lung organogenesis. Because of the observation that growth factors can control cell growth through regulation of IGFBPs, we examined IGFBP production by fetal lung fibroblasts following stimulation by peptide growth factors important for fetal lung growth and development. Fetal lung fibroblasts were cultured in serum-free medium supplemented with various growth factors for up to 48 h, and IGFBPs in conditioned medium (CM) were analyzed by ligand blot and immunoblot techniques. Accumulation of CM IGFBP-3 was increased and IGFBP-2 decreased by incubation with either keratinocyte growth factor (KGF) or epidermal growth factor (EGF). The effect of these factors on IGFBP-3 accumulation increased with time but the effects of KGF on CM IGFBP-2 decreased over 48 h of incubation. CM IGFBP-4 was increased by 24 and 48 h incubation with basic fibroblast growth factor (bFGF; 2.1- and 2.7-fold increases at 24 and 48 h, respectively) and platelet-derived growth factor-BB (PDGF-BB; 4.2- and 14.9-fold increases at 24 and 48 h, respectively), and 48 h incubation with EGF (6.3-fold increase). In 48-h coincubation experiments, EGF in combination with PDGF-BB or with bFGF, and bFGF in combination with PDGF-BB, resulted in IGFBP-4 accumulations twice that expected from a summation of the effects of either growth factor alone (IGFBP-4 increased 9.8-, 4.0-, and 1.8-fold by PDGF-BB, EGF, and bFGF, respectively; and 27.1-, 37.3-, and 13.0-fold by PDGF-BB plus EGF, PDGF-BB plus bFGF, and EGF plus bFGF, respectively). These results suggest synergistic effects of these growth factors on IGFBP-4 accumulation in fetal lung fibroblast CM. Because IGFBPs are known to regulate DNA synthesis, we speculate that peptide growth factors may alter cell proliferation in fetal lung, in part through their effect on IGFBPs.

Cholera toxin stimulates type II pneumocyte proliferation by a cyclic AMP-independent mechanism

Cholera toxin (CT) stimulated DNA synthesis by low-density primary cultures of adult rat type II pneumocytes (T2P) in a dose-dependent manner, either in the presence or the absence of serum. In the presence of 1% rat serum, 1 microgram/ml CT also stimulated a 50% increase in cell number over 8 days of incubation (P<0.01); this was in addition to a 2-fold increase in cell number induced by the serum alone (P<0.05). The same dose of CT also elevated intracellular cAMP and the total activity of protein kinase A (both P<0.01), suggesting toxin stimulation of T2P proliferation by a cAMP-dependent mechanism. However, the effect of CT on DNA synthesis could not be mimicked by 8-bromoadenosine 3':5'-cyclic monophosphate (8-bromo-cAMP), nor by N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate (dibutyryl-cAMP), each tested over a wide range of concentrations. l-Isoproterenol stimulated surfactant secretion by over 5-fold (P<0. 01), but neither the beta-agonist, forskolin nor 3-isobutyl-1-methylxanthine had any significant effect on DNA synthesis. The purified B-subunit of CT stimulated DNA synthesis to the same degree as did the holotoxin, either in the presence or the absence of rat serum. In contrast, the purified A-subunit had no significant effect. These data suggest that cholera toxin stimulates type II pneumocyte proliferation through a mechanism that is independent of cAMP, protein kinase A and toxin-catalyzed ADP-ribosylation.

Sulfation of extracellular matrices modifies growth factor effects on type II cells on laminin substrata

The alveolar basement membrane contains a variety of extracellular matrix (ECM) molecules, including laminin and sulfated glycosaminoglycans of proteoglycans. These mixtures exist within microdomains of differing levels of sulfate, which may specifically interact to be key determinants of the known capacity of the type II cell to respond to certain growth factors. Isolated type II cells were exposed to either acidic fibroblast growth factor (FGF-1), basic fibroblast growth factor (FGF-2), or keratinocyte growth factor (KGF; FGF-7) on culture wells precoated with laminin alone or in combination with chondroitin sulfate (CS), high-molecular-weight heparin, or their desulfated forms. Desulfated heparin significantly elevated FGF-1- and FGF-2-stimulated DNA synthesis, whereas desulfated CS and N-desulfated heparin elevated FGF-7-stimulated DNA synthesis by type II cells on laminin substrata. When FGF-1 was mixed into the various test matrix substrata, DNA synthesis was significantly increased in all cases. These results demonstrated that decreased levels of sulfate in ECM substrata act to upregulate responses to heparin-binding growth factors by alveolar epithelial cells on laminin substrata.

Modulation of laminin integrin receptors in the postnatal and adult rat lung

Recent studies have shown that type II pneumocytes, at birth and day 3 postnatally, have a diffuse distribution and localize at alveolar 'corners' between 3 and 7 days. Since alpha 3 beta 1 and alpha 6 beta 1 are laminin-binding receptors that are well expressed by rat type II alveolar epithelial cells, we postulated that they may play a role in the localization of the cells in the alveolus. To begin the evaluation of this hypothesis, we studied the temporal and spatial expression of the alpha 3, alpha 6, and beta 1 integrin subunit protein and mRNA in whole rat lungs during postnatal development by immunofluorescence, confocal microscopy, and Northern blot analysis. The temporal expression of proteins analyzed by immunochemistry, with integrin subunit specific antibodies, increased during the 3- to 7-day postnatal period and in adult lungs. Densitometric values of the alpha 3, alpha 6, and beta 1 mRNA expression, normalized to 28S rRNA, quadrupled from day 1 to day 3 postnatally. The mRNA expression of different integrin chains was elevated 1.5- to threefold from days 5 to 7 postnatally compared to day 1 levels. The alpha 3 and alpha 6 integrin subunit mRNA decreased to newborn levels in adult lungs, whereas the beta 1 integrin mRNA in adult lungs was expressed at approximately 50% of its level in newborn lungs. We postulate that the increases in alpha 3, alpha 6, and beta 1 integrin mRNA expression during the early neonatal period may be important for the spatial distribution of type II pneumocytes.

Biosynthesis of sulfated extracellular matrices by alveolar type II cells increases with time in culture

The aim of this study was to determine the extent to which sulfate incorporated into biosynthesized basement membrane (BM) components increased as isolated type II cells progress toward a more type I cell-like phenotype from 7 to 21 days in culture. Specific sulfate cytochemistry, using high iron diamine, showed that type I-like cells in 21-day cultures deposited a more highly sulfated extracellular matrix. Biosynthetic labeling experiments using [35S]cysteine or [35S]sulfate as precursors confirmed the increased capacity of 21-day type I-like cells to biosynthesize sulfated BM components compared with type II-like cells in 7-day cultures, including a novel sulfated laminin. These biochemical changes in sulfation of BM components coincide with the established phenotypic transition from type II to type I cells during prolonged culture. More importantly, the data suggest that regulation of sulfation constitutes a potential mechanism by which type I and type II cells alter their environment in such a manner as to stabilize phenotype and modulate responses to growth factors.

E1A-induced immortalization of rat type II alveolar epithelial cells

Using a retroviral vector expressing the adenoviral 12S E1A gene product the authors have immortalized rat type II alveolar epithelial cells. For a period of time, the immortalized cells retain many of the ultrastructural characteristics of type II cells in situ, including the presence of lamellar bodies. By 250 days in culture, however, neither lamellar bodies, SP-A, nor a phospholipid profile characteristic of surfactant were present. The cell bind the lectin Maclura pomifera and stably express cytokeratins and the E1A gene product. The cell line also has a diploid karyotype, exhibits contact inhibition of growth, and does not grow in soft agar. E1A-immortalized cell lines should prove useful as models for study of certain aspects of type II alveolar epithelial cell function.

Immunocytochemical evidence for a modulation of galectin 3 (Mac-2), a carbohydrate binding protein, in pulmonary fibrosis

Galectin 3 is endogenous mammalian carbohydrate-binding protein with affinity for terminal beta-galactose residues, polylactosamine glycans, and ABH-blood group carbohydrate epitopes. To determine the distribution and regulation of galectin 3 during pulmonary injury, which is known to be accompanied by profound changes in the carbohydrate moieties of cell surface glycoproteins of alveolar cells, a rat model of irradiation-induced lung inflammation and repair was used. Immunocytochemistry showed that in normal rat lungs, galectin 3 was localized to alveolar macrophages, with weaker staining of bronchial epithelial cells. Shortly after irradiation-induced lung injury, when there is active proliferation of type II alveolar epithelial cells and re-epithelialization of alveolar basement membranes by type I cells, the total galectin concentration in the lung increased dramatically. This increase was due in part to an increased population of galectin 3-positive interstitial and alveolar macrophages. In addition, galectin 3 was expressed prominently at the surface of the newly formed type I alveolar epithelium and to lesser extent at the apical surface of type II cells. These findings suggest that the increased synthesis and secretion of galectin 3 during irradiation-induced lung injury, together with ligation of secreted lectin at the surface of alveolar epithelial cells, may play roles in pulmonary alveolar epithelial expansion and differentiation during injury and repair.

Regulation of the beta 2 subunit chain of laminin in developing rabbit fetal lung tissue

Laminins are a family of basement membrane-associated heterotrimeric proteins that are important in mediating the growth, migration, and differentiation of a variety of cell types. The beta 2 subunit chain is a component of several laminin isoforms, e.g., laminin-3, laminin-4, laminin-7, and possibly other, as yet uncharacterized laminin isoforms. Utilizing monoclonal antibodies directed against the beta 2 subunit chain of laminin, we detected this protein in fetal, neonatal, and adult lung tissues. The relative amount of laminin beta 2 subunit chain in fetal lung tissue increased as gestation proceeded, reaching its peak around the time of alveolar type II cell differentiation in the rabbit. The laminin beta 2 subunit chain was localized in early gestational age rabbit fetal lung tissue primarily in basement membranes of prealveolar ducts, airways, and smooth muscle cells of airways and arterial blood vessels. A rabbit laminin beta 2 cDNA was generated using RT-PCR and utilized as a probe in northern blot analysis to characterize the levels of laminin beta 2 mRNA in developing rabbit lung tissue. Similar to the pattern of laminin beta 2 protein induction observed in fetal lung tissue, laminin beta 2 mRNA levels were maximal late in gestation. Utilizing a laminin beta 2 chain cRNA probe and in situ hybridization, we detected laminin beta 2 mRNA in the epithelial cells of prealveolar ducts, the alveolar wall, and airways, as well as in connective tissue cells, and the smooth muscle cells of airways and blood vessels in fetal and adult lung tissues. In addition, using an in vitro explant model, we determined that alveolar type II cells are capable of synthesizing laminin beta 2 subunit mRNA and depositing this laminin subunit chain in the basement membrane beneath type II cells. The results of this study are suggestive that the laminin beta 2 chain may be involved in alveolar epithelial cell differentiation.

Impaired surfactant synthesis in fetal type II lung cells from gsd/gsd rats

The importance of intracellular glycogen for surfactant synthesis was investigated in fetal type II lung cells isolated from rats with a glycogen storage disorder, designated gsd/gsd. Compared to cells from a control Wistar strain, cultured gsd/gsd pneumocytes were glycogenrich and contained fewer and smaller lamellar inclusions. Freshly isolated cells from day 19-21 fetuses of control rats demonstrated the expected gestational rise and fall of cellular glycogen seen in intact fetal lungs. At day 20, when tissue glycogen peaks, cellular glycogen content was 48 and 70 nmol glucose/micrograms DNA in isolated type II cells of control and gsd/gsd lungs, respectively. In control cells, while active glycogen phosphorylase changed from 35 to 65% of total during 24 h of culture, glycogen fell 85%. In contrast, gsd/gsd cell phosphorylase was not activated, phosphorylase kinase activity was nondetectable, and glycogen per cell remained unchanged. [3H]Choline incorporation into total PC and disaturated PC (DSPC) was 50 and 62% lower, respectively, in gsd/gsd type II cells compared to controls in the absence of exogenous substrate. Cellular content of the surfactant-associated protein SP-A was similar in control and gsd/gsd cells at day 20, and increased 3- to 4-fold during a subsequent 24-h interval of tissue culture. These results suggest that PC synthesis is dramatically impaired in type II cells in which glycogen cannot be mobilized, but SP-A is synthesized at normal rates. This work characterizes the isolated gsd/gsd fetal type II cell and supports its use in future studies to determine the importance and relative utilization of specific nonglycogen substrates.

Characterization of alpha 1, beta 1, and gamma 1 laminin subunits during rabbit fetal lung development

Laminin-1 is an extracellular matrix protein composed of three polypeptide chains that are designated alpha 1, beta 1, and gamma 1. We investigated the expression of laminin alpha 1, beta 1, and gamma 1 subunit chains during several stages of rabbit fetal lung development. Utilizing polyclonal antibodies directed against human placental laminin and immunoblot analysis, we found that the highest levels of laminin alpha 1, beta 1, and gamma 1 subunit chains in the fetal lung were present on day 26 of gestation (term = 31 days), coincident with the initiation of alveolar epithelial cell differentiation. Levels of the laminin chains were approximately five times higher in fetal lung at day 26 of gestation than in adult lung tissue. Different temporal patterns of laminin alpha 1, beta 1, and gamma 1 subunit chain expression were observed, data suggestive that the chains are independently regulated during lung development. Laminin was localized to the basement membranes of bronchi, bronchioles, prealveolar ducts, and blood vessels in fetal lung tissue, as shown by immunostaining with polyclonal laminin antibodies. A similar staining pattern was observed in adult lung tissue, but the alveolar wall was also stained. Laminin was also observed surrounding a few mesenchymal cells in fetal lung on day 19 of gestation; the number of positive mesenchymal cells increased with lung development. Laminin alpha 1 subunit chains, detected using a monoclonal antibody, were present in the basement membranes of bronchi, bronchioles, prealveolar ducts, and blood vessels in fetal lung tissue. No laminin alpha 1 chain staining was observed in the mesenchyme of early fetal lung tissue. Using a monoclonal antibody, laminin beta 1 subunit chains were immunolocalized in the basement membranes of bronchi, bronchioles, in prealveolar ducts, and surrounding some mesenchymal cells in fetal lung tissue. Laminin alpha 1 and beta 1 subunit chains in adult lung tissue were present in basement membranes of airways, blood vessels, and alveoli. Thus, changes in the localization and accumulation of laminin near the time of alveolar type I and type II epithelial cell differentiation suggest that laminin may play a role in mediating the differentiation of these cell types during rabbit fetal lung development.

Maintenance of differentiated phenotype by mouse type 2 pneumocytes in serum-free primary culture

An improved method has been developed for separation of an enriched population of mouse type 2 pneumocytes, based on differential adherence and size fractionation of cells dissociated with trypsin. These cells were successfully maintained in primary culture in serum-free medium MCDB 201 supplemented with albumin, transferrin, and lipids. Whereas type 2 pneumocytes in serum-supplemented culture undergo phenotypic transformation into adherent flattened cells that resemble type 1 pneumocytes, this did not occur in serum-free culture. Both the morphology of the type 2 pneumocytes and their expression of surfactant protein A were maintained for at least 6 days in vitro. However, rapid loss of differentiated characteristics was induced by exposure of the cells to normal mouse serum. This was accompanied by a striking decrease in spontaneous DNA synthesis as assessed by incorporation of tritiated thymidine. When cultured in serum-free medium, the behavior of the type 2 pneumocytes on various extracellular matrix components was different from that reported for serum-supplemented culture. Serum-free culture of type 2 pneumocytes may offer significant advantages for evaluation of the secretory activities of these cells in vitro.

Vitamin D stimulates DNA synthesis in alveolar type-II cells

Alveolar type-II cells are responsible for alveolar epithelial cell proliferation during growth and development and in response to lung injury. Based on the observation of abnormal lung development in rachitic rat pups and the expression of receptors for vitamin D by fetal alveolar epithelial cells, the present study examined the influence of 1,25-dihydroxy vitamin D (DHD) on the proliferation of primary cultures of fetal, neonatal and adult alveolar epithelial cells. The ontogony of vitamin D responsiveness was examined, using fetal (days 18, 19 and 22 = term), neonatal (days 7 and 18) alveolar epithelial cells as well as adult alveolar type-II cells. Maximal stimulation of [3H]thymidine incorporation occurred in neonatal d18 cells: (250 +/- 4.8%, n = 4, P < 0.05). Incubation of adult type-II cells, in the presence of 10(-9) M DHD increased thymidine incorporation into DNA (149.1 +/- 33.2%, mean +/- S.E., n = 3, P < 0.001) compared to control cells maintained in basal medium. Exposure to DHD also increased thymidine incorporation after stimulation with a mixture of conventional progression factors (insulin (10 micrograms/ml) (I), cholera toxin (10 micrograms/ml) (C) and EGF (20 ng/ml) (E)) (349.4 +/- 42.9% vs. 213.5 +/- 23.6%, n = 6, P < 0.005). Autoradiographic labeling indices of adult type-II cells increased from 3.1 +/- 0.6% for cells cultured in basal medium to 7.2 +/- 1.7% in cells exposed to DHD from the time of plating and I, C, E from 20-68 h in culture (n = 4, P < 0.05). Although no increase in the number of adult type-II cells was observed in these experiments, flow cytometric analysis of nuclear DNA content revealed an increased proportion of cells in the S and G2 phases of the cell cycle (basal: S = 2.6%, G2/M = 3.0%, DHD+GF: S = 4.7%, G2/M = 5.6%, P < 0.05 for each comparison). These data demonstrate that vitamin D3 is a growth factor for alveolar type-II cells and suggest the possibility that local elaboration of vitamin D may provide a novel mechanism of modulation of epithelial proliferation in the context of lung development and repair.

A novel laminin E8 cell adhesion site required for lung alveolar formation in vitro

Basement membrane-adherent type II alveolar cells isolated from lung assemble into lumen-containing cellular spheres which retain the correct polarity and thereby approximate the earliest fetal stage of alveolar morphogenesis. The molecular basis of this process, determined in initial experiments to be attributable mainly to the large heterotrimeric glycoprotein laminin, was probed with laminin proteolytic fragments, antibodies, and synthetic peptides. The carboxy-terminal fragment E8, but not equimolar amounts of fragment P1, blocked alveolar formation. To pursue this observation, we used several anti-E8 antibodies and identified one, prepared against A chain residues 2179-2198 ("SN-peptide") from the first loop of the G domain, as inhibitory. These results were confirmed by use of SN-peptide alone and further defined by trypsin digestion of SN-peptide to the sequence SINNNR. This conserved site promoted divalent cation dependent adhesion of both type II alveolar and HT1080 cells, was inhibitable with equimolar amounts of fragment E8 but not P1, and derives from a form of laminin present in fetal alveolar basement membranes. These studies point to an important novel cell adhesion site in the laminin E8 region with a key role in lung alveolar morphogenesis.

Electron and fluorescence microscopic investigations on composition and structure of the epithelial basement membrane of the human inferior nasal concha

Light and electron microscopic as well as immunohistochemical investigations were performed on the basement membrane (BM) of the nasal mucosa from the inferior nasal conchae of 20 patients, aged 15-50 years. Two of the patients served as controls. Clinical disorders requiring the turbinectomies were hyperplastic nasal inferior conchae (17 patients) and immobile cilia syndrome (1 patient). In all cases light microscopy demonstrated a 10-15 microns thick homogeneous BM underneath an intact epithelium. Electron microscopic findings revealed a typical subepithelial basal lamina (BL). The remaining parts of the BM consisted of single, isolated 25-mm-thick collagenous fibrils. Only a few cells and small unmyelinated nerves occurred in this layer. Immunohistochemical investigations showed BL components (collagen type IV, laminin, nidogen and heparan sulfate proteoglycan) directly underneath the epithelium. Collagen types I, III, V, and VI could also be demonstrated immunohistochemically in the remaining parts of the BM. Collagen type VII was allocated to the anchor filaments beneath the BL. This special BM is presumed to contribute to mechanical stabilization of the epithelium. The significance of the BL and the subepithelial connective tissue for the behavior of the epithelium--e.g. direction of differentiation--are discussed.

In vitro induction of type II pneumocyte-related differentiation in a clonal fetal bronchiolo-alveolar epithelial cell line (M3E3/C3)

The aim of the present study is to investigate the differentiation of a cloned fetal Syrian hamster lung epithelial cell line, M3E3/C3, to assume morphological and biochemical features of Type II pneumocytes (phospholipid synthesis). The use of a soft agar overlay and a differentiation medium, based on RPMI 1640 combined with hormone supplements, increased the cellular content of phosphatidylcholine (PC) from 48.6% in the conventional culture without any of these factors (referred to as 'control') to 64.7% (p < 0.02). The other cell membrane-associated components, phosphatidylethanolamine (p < 0.05), sphingomyelin (p < 0.001), phosphatidylserine (n. s.), phosphatidic acid (p < 0.02) and phosphatidylinositol (p < 0.02) decreased. The content of phosphatidylglycerol showed no essential change (from 11.2% to 8.4%) and the content of disaturated phospholipids decreased from 32.0 to 23.4 micrograms/10(6) cells (p < 0.002). The phospholipid pattern of these differentiated cells is in rough accordance with that of primary isolated Type II pneumocytes. They incorporated 3H-choline over a period of four hours at a higher rate in the Type II pneumocyte-specific phospholipids, PC and dipalmitoyl-phosphatidylcholine (DPPC), than the undifferentiated control. The radiolabelling of PC and DPPC in the differentiated cells, after 3 hours of incubation with 3H-choline, was about 3.2-fold and 2.2-fold, respectively, higher than that in the control cells (p < 0.001). Intracytoplasmatic phospholipid granules were evident in the differentiated cells by light and fluorescence microscopy (modified Papanicolaou stain, Phosphin 3 R fluorescence). Furthermore, the differentiated cells had a high activity of alkaline phosphatase, whereas the control cells showed only little activity of this enzyme. Ultrastructurally, many concentric multilayered osmiophilic bodies, well developed Golgi apparatuses and many cytoplasmic protrusions comparable to microvilli, were detectable in the cuboidal shaped differentiated cells. The control cells remained wide and flattened on the plastic surface and produced a fibrillar extracellular matrix. In the simultaneously studied fetal lung fibroblasts none of these specific features were noted. These results indicate a specific differentiation capacity of the clonal fetal cell line, M3E3/C3, by closely resembling Type II pneumocytes.

Type IV collagen production by rat pulmonary alveolar epithelial cells

Maintenance and repair of the pulmonary alveolar basement membrane are critical processes for preserving normal alveolar structure and function. To elucidate the mechanisms that control type IV collagen production by pulmonary alveolar epithelial cells, type II pneumocytes from rat lungs were isolated and maintained in tissue culture as monolayers. Using Northern blot analysis and metabolic labeling, we found that the cultured epithelial cells express type IV collagen mRNA and incorporate [3H]proline into type IV collagen. To determine the effects of phenotype on control of type IV collagen synthesis, we took advantage of the well-described observation that isolated type II cells lose their distinctive type II features when cultured on plastic in serum-containing medium for 7 days and assume an appearance more like that of type I epithelial cells. We found that [3H]proline incorporation into type IV collagen increased from day 1 to day 2 and thereafter decreased gradually up to day 7. Despite this decrease in [3H]proline incorporation, type IV collagen mRNA increased over the same period. If the loss of type II cell characteristics was prevented by culturing the cells in EHS matrix, a basement membrane-like extracellular matrix, there was little increase in relative abundance of type IV collagen mRNA as compared with cells cultured on plastic. We therefore conclude that type IV collagen production by isolated pulmonary alveolar epithelial cells is controlled, at least in part, by translational or post-translational mechanisms. Furthermore, the full type II cell phenotype is not required for expression of type IV collagen genes.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of integrin cell adhesion receptors on normal bronchial epithelial cells and lung cancer cells in vitro and in vivo

The interactions of bronchial epithelial cells with the basement membrane control cell morphology, differentiation, and proliferation in addition to having a major role in malignant transformation. Since these interactions are mediated by the integrin family of cell adhesion receptors, we characterized the integrin repertoire and adhesive properties of normal human bronchial epithelial cells in culture and cell lines derived from nine lung carcinomas using subunit-specific monoclonal antibodies. In addition, the integrin repertoire of three of the transformed cell lines was reexamined after the cells formed tumor nodules in immunodeficient mice. Bronchial epithelial cells in culture expressed multiple integrin subunits with the capability of binding to collagen and laminin (alpha 2, alpha 3, and alpha 6) and at least two subunits that are capable of mediating adhesion to fibronectin (alpha 3 and an alpha v-containing integrin). The alpha v beta 3 vitronectin receptor was not present. This distribution closely mimicked that seen by bronchial epithelial cells in situ. Cell lines derived from transformed pulmonary epithelial cells showed great heterogeneity with respect to integrin expression--some showing fewer, some greater, and some the same types of integrins as nontransformed epithelial cells. Only slight changes in integrin expression were seen in tumor cells propagated in immunodeficient mice. Although the adhesion characteristics of the transformed cells mirrored their adhesion receptor profile, no correlation between integrin profile and the ability to grow in SCID mice was observed. This study defines the integrin repertoire of human bronchial epithelial cells and sets the stage for future investigations exploring how the regulation and signal transduction mechanisms of these receptors might affect important pulmonary processes such as bronchial cell differentiation, wound healing, and malignant transformation.

Polarity reversal of inside-out thyroid follicles cultured on the surface of a reconstituted basement membrane matrix

When cultured in suspension, epithelial thyroid cells organized into inside-out follicles. We studied the behavior of these structures after seeding on polystyrene, type I collagen, and reconstituted basement membrane (RBM) gel. When seeded on plastic, type I collagen or mixed type I collagen-RBM gel, inside-out follicles attached and spread, forming polarized cell monolayers. In contrast, on thick RBM gel, inside-out follicles attached penetrated into the gel, and reorganized into properly oriented follicular structures. Polarity of the cell layer was progressively inverted while, after adhesion, cells penetrated the soft RBM gel. In the process of reorientation, cells with hybrid polarity were observed. The fraction of the apical pole which was not yet in the gel showed an inside-out orientation, while a modified orientation was observed in contact with the RBM gel. Cells which had penetrated completely in the matrix formed a new apical pole and displayed an opposite orientation of their polarity. A continuous basement membrane was observed, lining the basal cell surface when native RBM gel was present in the substratum.

Extracellular matrix proteins regulate morphologic and biochemical properties of tracheal gland serous cells through integrins

The extracellular matrix has been shown to influence the differentiation of epithelial cells. To identify cues from the extracellular matrix controlling the differentiation of tracheal gland serous cells, we examined the effects of culturing these cells on various extracellular matrix proteins. Bovine tracheal gland (BTG) serous cells attached to Type IV collagen (COL IV), laminin (LM), and fibronectin (FN) in a concentration-dependent manner. Morphologic analysis showed that cells formed confluent monolayers on COL IV or LM, whereas on FN, cells formed birefringent spheres. Metabolic labeling experiments showed that [35S]methionine-labeled protein bands at 68, 105, and 120 kD were prominent when cells were grown on COL IV or LM, but were lost or reduced when the cells were grown on FN. COL IV also enhanced the expression of proteins at 14, 16.5, 18, and 21.5 kD. Attachment to all substrates was inhibited by an antibody directed against beta 1 integrins. This antibody precipitated several integrin heterodimers from a BTG cell membrane extract, caused partial retraction of cells from all substrates, and strongly suppressed the expression of COL IV- and LM-dependent proteins. Control experiments indicated that the latter did not require conspicuous changes in cell shape. These results show that some biochemical properties of serous cells are regulated by integrin-mediated effects of extracellular matrix proteins in vitro and suggest that similar regulation may occur during normal development and remodeling of the glands in vivo.

Reactivity of alveolar epithelial cells in primary culture with type I cell monoclonal antibodies

An understanding of the process of alveolar epithelial cell growth and differentiation requires the ability to trace and analyze the phenotypic transitions that the cells undergo. This analysis demands specific phenotypic probes to type II and, especially, type I pneumocytes. To this end, monoclonal antibodies have been generated to type I alveolar epithelial cells using an approach designed to enhance production of lung-specific clones from a crude lung membrane preparation. The monoclonal antibodies were screened by a combination of enzyme-linked immunosorbent assay and immunohistochemical techniques, with the determination of type I cell specificity resting primarily on immunoelectron microscopic localization. Two of these new markers of the type I pneumocyte phenotype (II F1 and VIII B2) were used to analyze primary cultures of type II cells growing on standard tissue culture plastic and on a variety of substrata reported to affect the morphology of these cells in culture. On tissue culture plastic, the antibodies fail to react with early (days 1 to 3) type II cell cultures. The cells become progressively more reactive with time in culture to a plateau of approximately 6 times background by day 8, with a maximum rate of increase between days 3 and 5. This finding is consistent with the hypothesis that type II cells in primary culture undergo at least partial differentiation into type I cells. Type II cells grown on laminin, which reportedly delays the loss of type II cell appearance, and on fibronectin, which has been reported to facilitate cell spreading and loss of type II cell features, develop the type I cell markers during cultivation in vitro with kinetics similar to those on uncoated tissue culture plastic. Cells on type I collagen and on tissue culture-treated Nuclepore filters, which have been reported to support monolayers with type I cell-like morphology, also increase their expression of the II F1 and VIII B2 epitopes around days 3 to 5. Taken together with available morphologic information, these data suggest that expression of different alveolar epithelial cell phenotypic markers by type II cells in primary culture may be independently regulated. The monoclonal antibody probes described in this report should prove useful in the continued investigation of the mechanisms and regulation of alveolar epithelial cell differentiation.

Comparison of effects of epidermal and insulin-like growth factors, gastrin releasing peptide and retinoic acid on fetal lung cell growth and maturation in vitro

The role in cell multiplication and maturation of several factors present in the late fetal lung was explored on isolated fetal rat pulmonary fibroblasts and alveolar epithelial type II cells cultivated in serum-free medium. The low degree of reciprocal contamination of each cell population was assessed by immunocytochemistry. Epidermal Growth Factor (EGF) stimulated thymidine incorporation and DNA accumulation in both cell types. In type II cells, it increased labeled-choline incorporation into surfactant phosphatidylcholine (PC), consistently with previous data obtained with lung explant cultures, but not into non-surfactant PC. Insulin-like growth factor (IGF)-I slightly stimulated DNA accumulation in fibroblasts although it did not significantly stimulate thymidine incorporation, contrary to IGF-II which presented a dose-dependent stimulating activity of thymidine incorporation. Neither IGF-I nor IGF-II stimulated type II cell growth. IGFs thus appear to primarily control the growth of lung mesenchyme. In type II cells, they stimulated the most non-surfactant PC biosynthesis. Gastrin releasing peptide (GRP) which was recently reported to promote fetal lung growth in vivo and to stimulate surfactant biosynthesis in lung organ culture revealed as a growth factor for type II cells only, at concentrations below 10(-9) M. At concentration 10(-8) M, although it did not affect DNA synthesis, GRP tended to increase surfactant and non-surfactant-PC biosynthesis. Retinoic acid inhibited thymidine incorporation into type II cells on a dose-dependent manner but nevertheless enhanced surfactant-PC biosynthesis to a similar extent as EGF. It is suggested that retinoic acid may represent a differentiation or maturation factor for the alveolar epithelium.

Type II alveolar epithelial eicosanoid metabolism: predominance of cyclooxygenase pathways and transcellular lipoxygenase metabolism in co-culture with neutrophils

Arachidonic acid (AA) metabolism was studied in freshly isolated type II alveolar epithelial cells of rabbits. Substantial basal secretion of prostanoids with predominance of prostaglandin (PG) I2 was noted. Challenge with the calcium ionophore A23187 resulted in a time- and dose-dependent increase in the generation of all AA cyclooxygenase products to severalfold values following the rank order of 12-heptadecatrienoic acid (12-HHT) greater than PGI2 greater than PGE2 greater than or equal to thromboxane A2 greater than PGF2 alpha approximately PGD2. Even larger augmentation of prostanoid generation was evoked by challenge with free exogenous AA. Generation of the different AA cyclooxygenase products was inhibited by acetylsalicylic acid with IC50 in the range between 250 and 500 microM. In addition to the prostanoid release, ionophore-challenged type II pneumocytes liberated substantial amounts of AA lipoxygenase products with leukotriene (LT) B4 greater than 15-hydroxyeicosatetraenoic acid (HETE) greater than 12-HETE greater than 5-HETE. Generation of LTs and HETEs was markedly increased upon simultaneous disposal of free exogenous AA. No omega-oxidation of LTB4 was noted, and no evidence for secretion of intact LTA4 was obtained. The epithelial cells displayed avid uptake of exogenously offered LTA4 with subsequent enzymatic conversion to LTB4. Co-stimulation of pneumocytes with neutrophils (PMN) resulted in an amplification of LTB4 generation, paralleled by a decrease in nonenzymatic decay products of PMN-derived LTA4; both phenomena were dose dependent on the pneumocyte-PMN ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Culture of fetal alveolar epithelial type II cells in serum-free medium

A serum-free culture medium (defined medium = DM) was elaborated by adding to Eagle's minimum essential medium (MEM), non-essential amino acids, transferrin, putrescine, tripeptide glycyl-histidyl-lysine, somatostatin, sodium selenite, ethanolamine, phosphoethanolamine, sodium pyruvate, and metal trace elements. This medium was tested for its ability to support sustained surfactant biosynthesis in fetal alveolar epithelial type II cells. For up to 8 days, ultrastructure was maintained with persistence of lamellar inclusion bodies. Thymidine incorporation into DNA was enhanced about 50% in DM as compared with MEM, whereas it was enhanced 300% in 10% fetal bovine serum. With DM, the incorporation of tritiated choline into phosphatidylcholine (PC) of isolated surfactant material was about twice that with MEM. Deletion experiments evidenced the prominent role of pyruvate, transferrin, and selenium in the stimulation of surfactant PC biosynthesis. The addition of biotin to DM enhanced surfactant PC biosynthesis slightly and nonsurfactant PC biosynthesis markedly. The presence of nucleosides seemed unfavorable to the synthesis of surfactant PC. Type II cells responded to the addition of epidermal growth factor and insulinlike growth factor-I both by increased thymidine incorporation into DNA and choline incorporation into PC. It is concluded that DM represents a useful tool for cultivating type II cells without loss of their specialized properties and for studying the regulation of cell proliferation and surfactant biosynthesis in a controlled environment.

Cellular changes in the lungs of adrenalectomized rats following left pneumonectomy

The time course and nature of the cellular response to left pneumonectomy, with or without prior adrenalectomy, were evaluated in the right lungs of male Sprague-Dawley rats using morphometric techniques. Animals were studied at days 2, 5, and 14 following pneumonectomy, intervals prior to, during the course of, and following significant compensatory changes in right lung mass. The postoperative increase in right lung mass and volume in pneumonectomized animals involved minimal changes in the ratios of most tissue components, when compared to the lungs of sham-operated controls. A transient disproportionate increase in type II cell volume and epithelial thickness was evident on day 14. Postpneumonectomy changes in the type II epithelium were accentuated in the lungs of adrenalectomized-pneumonectomized animals. Adrenalectomy 5 days prior to pneumonectomy resulted in a substantial increase in the volume of all right lung tissue components, associated with thickening of the alveolar wall and with increases in the volume of both cellular and noncellular interstitium. Effects of adrenalectomy on the endothelium also were evident. In both adrenal-intact and adrenalectomized animals, pneumonectomy increased alveolar number by day 14 but had no effect on the volume of individual alveoli. These results confirm a coordinated pattern of compensatory growth following pneumonectomy in the adrenal-intact rat. The data further suggest that in adrenalectomized animals compensatory lung growth is more poorly synchronized, with pronounced postoperative elevations in volume of the interstitial and type II epithelial compartments leading to increased thickness of the alveolar wall. Adrenal hormones thus appear to be required for coordination and control of compensatory lung growth and for rapid restoration of normal tissue structure.

Matrix-driven pneumocyte differentiation

This commentary presents evidence in support of a hypothesis that adult mammalian alveolar epithelial basement membrane possesses functional and structural domains that determine sites at which type I and type II cells localize. The hypothesis provides a framework for understanding how, after normal repair of the epithelium, a constant ratio of type I and type II cells, and the localization of the cell types is maintained.

Structural and functional relationships between type II pneumocytes and components of extracellular matrices

Type II pneumocytes of the pulmonary alveolus are dynamic cells with multiple functional capabilities in vivo, including secretion of surface-active lipoproteins and cell renewal of the epithelial lining of the alveolus, involving its differentiation into another cell type (the type I pneumocyte). The factors that influence and control these processes, which are vital to the function of the alveolus, have begun to be more clearly understood in recent years, in large part because of the development of adequate in vitro systems, which permit the manipulation of relevant variables. These appear to be a complex interaction between insoluble components of extracellular matrices, principally of the basement membrane, and soluble factors that include hormones and growth factors. This review focuses particularly on those components of extracellular matrices that specifically and nonspecifically impact on type II cell function, and it attempts to bring together the diverse technical approaches used to define and examine these relationships cytochemically and functionally.

Effects of transforming growth factor-beta on collagen synthesis by fetal rat lung epithelial cells

Studies were performed to characterize the effects of acute and chronic exposure to transforming growth factor-beta (TGF-beta) on collagen biosynthesis by fetal rat lung epithelial (FRLE) cells, a cell line established from the fetal rat lung alveolar epithelial cell. Neither condition of exposure to TGF-beta stimulated cell growth, but both conditions increased total protein synthesis. Quantitative evaluation by carboxymethyl-Trisacryl chromatography revealed that FRLE cells synthesized types I, III, IV, and V collagen under all circumstances. Acute and chronic exposure to TGF-beta increased total collagen production approximately 50% and 300%, respectively, with the increases in total collagen production exceeding those of total protein synthesis. In addition, these analyses indicated that the production of types I and III molecules was stimulated to a greater extent than was the synthesis of types IV and V molecules. Both experimental conditions increased the ratio of secreted to cell-associated molecules for types I and III molecules, decreased this ratio for type IV collagen, but minimally affected the culture distribution of type V collagen. Additionally, both conditions of exposure to TGF-beta were found to increase the proportion of the homotrimeric forms of types I and V molecules relative to their heterotrimeric counterparts. Thus, these studies establish that TGF-beta selectively and type-specifically alters collagen production without affecting growth in an epithelial cell line of fetal rat lung origin.

Immunocytochemical localization of laminin in hamster tracheal epithelial cell cultures

EM examination of 28 day cultures of enzymatically dissociated hamster tracheal epithelial (HTE) cells grown on collagen coated millipore filters reveals that fragments of basal lamina may be present at the basal plasmalemma. Since the basal lamina consists of several major components including type IV collagen, heparan sulfate proteoglycans, entactin/nidogen, and laminin, questions naturally arise concerning the presence of such a structure in this cell culture system. When immunocytochemical procedures utilizing anti-laminin antibody and PAP techniques are carried out with paraffin sections of HTE culture at 1,2,3, and 4 weeks in vitro, LM analysis reveals that a thin, dense line of reaction product is present between the basal surface of the HTE cells and the underlying collagen substrate. Immunoblotting evaluation carried out with supernatants of 7d HTE cell homogenates and HTE cell conditioned media also indicate that laminin is being produced by the tracheal cells. Thus, the presence of basal lamina-like fragments, the immunocytochemical localization of laminin, and immunoblot identification of laminin in hamster tracheal epithelial cell cultures, suggest that, although basal lamina components may be produced by HTE cells, at the time points tested, they are not yet being organized into a complete basal lamina.

Expression of urokinase-type plasminogen activator by rat pulmonary alveolar epithelial cells

Intra-alveolar fibrin deposition accompanies many forms of inflammatory lung injury. Appropriate clearance of this fibrin matrix is important for normal healing and remodeling. The local generation of plasmin by the action of plasminogen activators (PAs) represents a pivotal step in the fibrinolytic process. To investigate whether the alveolar epithelium plays a role in the modulation of intra-alveolar fibrinolysis, we have studied PA regulation by rat pulmonary alveolar epithelial cells. We have found large quantities of PA activity both in conditioned media and cell lysates from epithelial monolayers in culture. Casein-plasminogen zymography reveals that this PA activity migrates as a tight doublet with an apparent mol wt of 45 kD, clearly distinct from rat tissue-type PA (tPA, greater than 68 kD). Analysis of freshly isolated type II alveolar epithelial cells demonstrates readily measurable PA activity in cell lysates, as well as expression of urokinase-type PA (uPA) mRNA on Northern blot analysis. Upregulation of PA activity occurs progressively with time in culture as the alveolar epithelial cells lose type II cell characteristics and become more flattened. Stimulation of alveolar epithelial cell monolayers with lipopolysaccharide or tumor necrosis factor increases levels of secreted PA activity. The relative abundance of uPA mRNA was shown to change in parallel with PA activity during in vitro differentiation or after exposure to inflammatory mediators. Thus, alveolar epithelial cells are likely an important source of uPA in the lung, the expression of which is influenced by the state of cellular differentiation as well as the presence of inflammatory mediators.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of a reconstituted basement membrane on expression of surfactant apoproteins in cultured adult rat alveolar type II cells

Pulmonary surfactant, which is composed of phospholipids and three lung-specific apoproteins, is synthesized and secreted by alveolar type II cells. Previous work from this laboratory (Biochim. Biophys. Acta 1987; 931:143-156) has shown that cell-extracellular matrix interactions and cuboidal cell shape affect both the ultrastructural appearance and pattern of phospholipids synthesized by cultured rat type II cells. In the present study, we have examined the effects of cell-matrix interactions and cell shape on the ability of adult rat type II cells to express the surfactant apoproteins in culture. Isolated adult rat type II cells were cultured for 2, 4, and 8 days on either tissue culture plastic, on an extract of the Engelbreth-Holm-Swarm (EHS) tumor, or on laminin-coated plastic dishes. Expression of surfactant proteins A, B, and C (SP-A, SP-B, and SP-C) was evaluated by Northern analysis using specific rat cDNA probes for these mRNAs. SP-A content was determined by enzyme-linked immunosorbent assay using a polyclonal antibody raised against rat SP-A purified from lavage. Type II cells cultured on plastic dishes assumed an attenuated morphology soon after being placed in culture. Except for an occasional positive signal on day 2 of culture, these cells were uniformly negative for the presence of mRNA for SP-A, SP-B, or SP-C. Type II cells cultured on plastic did not contain SP-A. In contrast, type II cells cultured on EHS gels formed three-dimensional aggregates on the surface of the substratum; these aggregates were composed of polarized cells that had their apical surfaces directed inward. Type II cells cultured on this substratum showed a positive signal for mRNA for all three surfactant proteins; the abundance of these mRNAs, however, was significantly below that seen in freshly isolated type II cells. While the abundance of mRNA for SP-A and SP-B steadily increased with time in culture under these conditions, the abundance of SP-C mRNA decreased, suggesting that SP-C is regulated independently of SP-A and SP-B. These cultures were also positive for SP-A content, which increased with increasing time in culture. Type II cells cultured on laminin-coated dishes initially spread more slowly across the culture surface than cells on plastic, but were extremely attenuated by day 8 in culture. These cells contained neither SP-A, nor mRNA for any of the three surfactant proteins.(ABSTRACT TRUNCATED AT 400 WORDS)