Hunting and mountain sheep: Do current harvest practices affect horn growth?

The influence of human harvest on evolution of secondary sexual characteristics has implications for sustainable management of wildlife populations. The phenotypic consequences of selectively removing males with large horns or antlers from ungulate populations have been a topic of heightened concern in recent years. Harvest can affect size of horn-like structures in two ways: (a) shifting age structure toward younger age classes, which can reduce the mean size of horn-like structures, or (b) selecting against genes that produce large, fast-growing males. We evaluated effects of age, climatic and forage conditions, and metrics of harvest on horn size and growth of mountain sheep (Ovis canadensis ssp.) in 72 hunt areas across North America from 1981 to 2016. In 50% of hunt areas, changes in mean horn size during the study period were related to changes in age structure of harvested sheep. Environmental conditions explained directional changes in horn growth in 28% of hunt areas, 7% of which did not exhibit change before accounting for effects of the environment. After accounting for age and environment, horn size of mountain sheep was stable or increasing in the majority (~78%) of hunt areas. Age-specific horn size declined in 44% of hunt areas where harvest was regulated solely by morphological criteria, which supports the notion that harvest practices that are simultaneously selective and intensive might lead to changes in horn growth. Nevertheless, phenotypic consequences are not a foregone conclusion in the face of selective harvest; over half of the hunt areas with highly selective and intensive harvest did not exhibit age-specific declines in horn size. Our results demonstrate that while harvest regimes are an important consideration, horn growth of harvested male mountain sheep has remained largely stable, indicating that changes in horn growth patterns are an unlikely consequence of harvest across most of North America.

Biological relevance of antler, horn, and pronghorn size in records programs

Long-term datasets are becoming increasingly important for assessing population- and species-level responses to a changing environment. Programs that record morphological measurements of horns, antlers, and pronghorns were established in the early- to mid-20th century to collect biological information about animals that possess large horns, antlers, or pronghorns, which could be used to assess the effectiveness of conservation efforts for large mammals in North America. The general relevance of record books has been questioned because of the minimum size requirements for inclusion in a record book, which may mask trends when changes in the population occur. We compared trends in size of antlers, horns, and pronghorns through time using records from three records programs with different minimum size requirements to evaluate the influence of entry requirements on temporal trends. We also investigated whether horn, antler, or pronghorn size affected the probability of specimens being submitted to a records program. Only two of 17 categories exhibited less-pronounced trends in the record book with the highest size requirements for entry, and in two categories trends were more pronounced. Although societal interest in submitting eligible specimens increased slightly over time in one of six categories, the probability of voluntary entry was largely random and not affected by year of harvest or size of specimen. In contrast to previous criticisms, trends in record books should not be expected to represent the size of all males within a population. Instead, our evaluation indicates that the records programs we examined can provide a useful resource for assessing long-term changes in phenotypic characteristics of ungulates, but importantly, they represent the respective range of sizes within which each program collects data.

Source-gated transistors for order-of-magnitude performance improvements in thin-film digital circuits

Ultra-large-scale integrated (ULSI) circuits have benefited from successive refinements in device architecture for enormous improvements in speed, power efficiency and areal density. In large-area electronics (LAE), however, the basic building-block, the thin-film field-effect transistor (TFT) has largely remained static. Now, a device concept with fundamentally different operation, the source-gated transistor (SGT) opens the possibility of unprecedented functionality in future low-cost LAE. With its simple structure and operational characteristics of low saturation voltage, stability under electrical stress and large intrinsic gain, the SGT is ideally suited for LAE analog applications. Here, we show using measurements on polysilicon devices that these characteristics lead to substantial improvements in gain, noise margin, power-delay product and overall circuit robustness in digital SGT-based designs. These findings have far-reaching consequences, as LAE will form the technological basis for a variety of future developments in the biomedical, civil engineering, remote sensing, artificial skin areas, as well as wearable and ubiquitous computing, or lightweight applications for space exploration.

Timing and synchrony of births in bighorn sheep: implications for reintroduction and conservation

Context Timing (mean birthdate) and synchrony (variance around that date) of births can influence survival of young and growth in ungulate populations. Some restored populations of ungulates may not adjust these life-history characteristics to environments of release sites until several years after release, which may influence success of reintroductions. Aims We quantified timing and synchrony of births from 2005 to 2007 in four populations of reintroduced bighorn sheep (Ovis canadensis) occupying two ecoregions (Central Basin and Range and Wasatch and Uinta Mountains) in Utah, USA, to investigate whether bighorns would adjust these life-history characteristics to environmental conditions of the two ecoregions. We also compared timing and synchrony of births for bighorns in their source herd (Antelope Island) with bighorns in an ecologically similar release site (Stansbury Mountains) during 2006 and 2007. Methods We relocated female bighorns to record birthdates of young, and observed groups of collared bighorns to quantify use of elevation by those ungulates. We also calculated the initiation, rate and timing of peak green-up by ecoregion, using the normalised difference vegetation index. Key results We quantified 274 birthdates, and although only separated by 57 km, bighorn populations occupying the Central Basin and Range Mountains gave birth an average of 29 days earlier than did those on the Wasatch and Uinta Mountains, which corresponded with the initiation of vegetation green-up. Additionally, bighorn sheep on the Stansbury Mountains (ecologically similar release site) gave birth at similar times as did bighorns on Antelope Island (source area). Conclusions Populations of bighorn sheep that were reintroduced into adjacent ecoregions adjusted timing of births to environments and green-up of vegetation in restoration areas. Timing and synchrony of births for reintroduced bighorn sheep in an ecologically similar release site were the same as those of their source area. Implications Consideration should be given to the adjustment of timing and synchrony of births when reintroducing bighorns, especially when animals are released into different ecoregions. Also, biologists should select release sites that are ecologically similar to source areas, thereby reducing potential negative effects of animals adjusting timing and synchrony of births to environmental conditions of restoration areas.

Coculture of Embryonic Stem Cells with Pulmonary Mesenchyme: A Microenvironment That Promotes Differentiation of Pulmonary Epithelium

Coculture of stem/progenitor cells with mature cells or tissues can drive their differentiation toward required lineages. Thus, we hypothesized that coculture of murine embryonic stem (ES) cells with embryonic mesenchyme from distal lung promotes the differentiation of pneumocytes. Murine ES cells were differentiated to embryoid bodies (EBs) and cultured for 5 or 12 days with pulmonary mesenchyme from embryonic day 11.5 or 13.5 murine embryos, in direct contact or separated by a membrane. Controls included EBs cultured alone or with embryonic gut mesenchyme. Histology revealed epithelium-lined channels in directly cocultured EBs, whereas EBs grown alone showed little structural organization. The lining cells expressed cytokeratin and thyroid transcription factor 1, an early developmental marker in pulmonary epithelium. Differentiation of type II pneumocytes specifically was demonstrated by the presence of surfactant protein C (SP-C) in some of the epithelial cells. None of these markers was seen in EBs cultured alone or with embryonic gut mesenchyme. Indirect coculture of EBs with lung mesenchyme resulted in a 14-fold increase in SP-C gene expression. Thus, provision of an appropriate microenvironment, in the form of pulmonary mesenchyme, appears to promote the differentiation of ES cells toward lung epithelium. Our findings may have applications in regenerative medicine strategies and the engineering of lung tissue.

Rat alveolar type II cells inhibit lung fibroblast proliferation in vitro

Fibroblasts stimulate alveolar type II epithelial cell differentiation and proliferation in vitro and during lung development. However, little is known about the effects of adult type II cells on fibroblasts. We investigated the effect of adult rat type II cells on proliferation of adult human lung fibroblasts. Fibroblasts were suspended within rat tail collagen which was gelled on a floating polycarbonate filter, and type II cells were cultured on Matrigel. In this coculture system, alveolar type II cells inhibited fibroblast proliferation and indomethacin blocked the inhibitory effect on fibroblast growth. Prostaglandin (PG) E2, the major PG secreted by type II cells, inhibited fibroblast proliferation and was increased during the period of inhibition of fibroblast proliferation. Incubation with arachidonate showed that most of the PGE2 in the coculture system was produced by the fibroblasts. In addition, we found that rat type II cells also inhibited rat fibroblasts and that inhibition of fibroblast growth by type II cells could be stimulated by keratinocyte growth factor. We conclude that in this coculture system, type II cells inhibit fibroblast proliferation by secreting a factor(s) that stimulates PGE2 production by fibroblasts, and that PGE2 directly inhibits fibroblast proliferation.

Elevated expression of surfactant proteins in newborn rats during adaptation to hyperoxia

The mechanisms whereby lung adaptation to hyperoxia occurs in the newborn period are incompletely understood. Pulmonary surfactant has been implicated in lung protection against hyperoxic injury, and elevated expression of certain surfactant proteins occurs in lungs of adult rats during adaptation to sublethal oxygen (85% O(2)). Here we report that newborn rats, which can adapt to even higher levels of hyperoxia (100% O(2)) than do adult rats, manifest changes in the lung surfactant proteins (SP), especially SP-A and SP-D. In newborn rats exposed to hyperoxia on Days 3 through 10 of life, lung messenger RNAs (mRNAs) for SP-A and SP-B gradually and progressively increased, relative to levels in age-matched, air-exposed newborns, over this 8-d period. By contrast, SP-C and SP-D mRNAs were maximally increased relative to values in simultaneously air-exposed control rats after 4 d of exposure. Lung mRNA for CC-10, a protein specific for Clara cells, was greater in hyperoxia-exposed rats than in air-exposed control rats on Day 4 of exposure, but not on other days. Lung mRNA for thyroid transcription factor (TTF)-1 was marginally increased on Days 1, 2, 4, and 6, and significantly increased on Day 8. Both SP-A and SP-D proteins were increased in lung lavage samples taken from hyperoxia-exposed newborns, relative to those taken from air-exposed controls, with the greatest increases occurring on Days 6 and 8 of exposure. However, the patterns of increase of the proteins were not identical to those of the respective mRNAs. In situ hybridization studies demonstrated increases in SP-D, and to a lesser extent in SP-A, in peripheral lung tissues from oxygen-exposed newborns. Taken together, these data indicate that specific surfactant proteins are upregulated at both the pretranslational and post-translational levels in distal lung epithelium during adaptation to hyperoxia in the newborn rat.

Lung fibroblasts improve differentiation of rat type II cells in primary culture

Epithelial-mesenchymal interactions mediate prenatal lung morphogenesis and differentiation, yet little is known about their effects in the adult. In this study we have examined the influence of cocultured lung fibroblasts on rat alveolar type II cell differentiation in primary culture. Type II cells that were co-cultured with lung fibroblasts showed significant increases in messenger RNA (mRNA) levels of surfactant protein (SP)-A, SP-B, SP-C, and SP-D. Metabolic labeling and immunohistochemistry demonstrated that these mRNAs were translated and processed. Addition of 10(-7) M dexamethasone (DEX) to cocultures antagonized the effects of the fibroblasts on SP-A and SP-C, but significantly augmented the effects on SP-B; expression of SP-D was unaffected. Coculture of type II cells with lung fibroblasts also increased acetate incorporation into phospholipids 10-fold, which was antagonized by DEX. Keratinocyte growth factor (KGF) mimicked the effects of lung fibroblasts on SP gene expression, but KGF neutralizing antibodies only partially reduced the effects of lung fibroblasts. KGF increased acetate incorporation into surfactant phospholipids, and the addition of DEX augmented this response. Together, our observations suggest that epithelial--mesenchymal interactions affect type II cell differentiation in the adult lung, and that these effects are partially mediated by KGF.

Overexpression of tumor necrosis factor-alpha produces an increase in lung volumes and pulmonary hypertension

Tumor necrosis factor (TNF)-alpha is a key proinflammatory cytokine that is thought to be important in the development of pulmonary fibrosis, whereas its role in pulmonary emphysema has not been as thoroughly documented. In the present study, TNF-alpha was overexpressed in alveolar type II cells under the control of the human surfactant protein C promoter. In this report, we further characterized the pulmonary abnormalities and provided a physiological assessment of these mice. Histopathology of the lungs revealed chronic inflammation, severe alveolar air space enlargement and septal destruction, and bronchiolitis. However, pulmonary fibrosis was very limited and only seen in the subpleural, peribronchiolar, and perivascular regions. Physiological assessment showed an increase in lung volumes and a decrease in elastic recoil characteristic of emphysema; there was no evidence of restrictive lung disease characteristic of pulmonary fibrosis. In addition, the mice raised in ambient conditions in Denver developed pulmonary hypertension. Gelatinase activity was increased in the lavage fluid from these lungs. These results suggest that in these mice TNF-alpha contributed to the development of pulmonary emphysema through chronic lung inflammation and activation of the elastolytic enzymes but by itself was unable to produce significant pulmonary fibrosis.

Lung hypoplasia in the nitrofen model of congenital diaphragmatic hernia occurs early in development

The teratogen nitrofen produces a congenital diaphragmatic hernia (CDH) and pulmonary hypoplasia in rodent fetuses that closely parallel observations made in humans. We hypothesized that these changes may be due to primary pulmonary hypoplasia and not herniation of the abdominal contents. Timed-pregnant rats were given nitrofen on day 9, and fetuses were harvested on days 13 through 21. Initial evagination of lung buds on gestational day 11 was not delayed in nitrofen-treated fetuses. On gestational day 13, however, there was a significant decrease in the number of terminal end buds in the lungs of nitrofen-exposed fetuses vs. controls. Thymidine-labeled lung epithelial and mesenchymal cells were significantly decreased in nitrofen-treated lungs. Lungs from nitrofen-treated fetuses exhibited wide septae with disorganized, compacted tissue, particularly around the air spaces. Expression of surfactant protein B and C mRNAs was significantly decreased in the nitrofen litters. In situ hybridization of fetal lung tissue at all gestational ages showed no difference in the expression of vascular endothelial growth factor, Flk-1, or Flt-1 mRNAs. Because closure of the diaphragm is completed on gestational day 16 in the rat, our results suggest that lung hypoplasia in this model of CDH is due at least in part to a primary effect of nitrofen on the developing lung.

KGF regulates pulmonary epithelial proliferation and surfactant protein gene expression in adult rat lung

Keratinocyte growth factor (KGF, FGF-7) is a potent mitogen for epithelial cells. We instilled recombinant human KGF to determine the effects of KGF on alveolar epithelial cells. Left lungs of adult rats were instilled intrabronchially with KGF (5 mg/kg) or normal saline. KGF instillation resulted in epithelial cell hyperplasia, and the alveolar bromodeoxyuridine (BrdU) labeling index peaked at 35% on day 2 after instillation. The mRNA levels for the surfactant proteins (SPs) SP-A, SP-B, and SP-D were increased in whole lung tissue on days 1 and 2 after KGF treatment and then returned to control levels on days 3-7. SP-C mRNA levels were increased on days 2-5 after KGF instillation. However, all surfactant protein mRNAs were reduced in type II cells isolated from rats instilled with KGF 2 or 3 days before isolation. These observations were confirmed by in situ hybridization. Instillation of KGF also increased the amount of SP-A and SP-D in lavage fluid. Transcripts for CC10, the 10-kDa Clara cell protein, were decreased. KGF increases the mRNA for the surfactant proteins per lung because of type II cell hyperplasia, but the mRNA per cell is slightly diminished as measured in isolated cells or estimated by in situ hybridization.

A transitional stage in the commitment of mesoderm to hematopoiesis requiring the transcription factor SCL/tal-1

In this report, we describe the identification and characterization of an early embryoid body-derived colony, termed the transitional colony, which contains cell populations undergoing the commitment of mesoderm to the hematopoietic and endothelial lineages. Analysis of individual transitional colonies indicated that they express Brachyury as well as flk-1, SCL/tal-1, GATA-1, (beta)H1 and (beta)major reflecting the combination of mesodermal, hematopoietic and endothelial populations. This pattern differs from that found in the previously described hemangioblast-derived blast cell colonies in that they typically lacked Brachyury expression, consistent with their post-mesodermal stage of development (Kennedy, M., Firpo, M., Choi, K., Wall, C., Robertson, S., Kabrun, N. and Keller, G. (1997) Nature 386, 488–493). Replating studies demonstrated that transitional colonies contain low numbers of primitive erythroid precursors as well as a subset of precursors associated with early stage definitive hematopoiesis. Blast cell colonies contain higher numbers and a broader spectrum of definitive precursors than found in the transitional colonies. ES cells homozygous null for the SCL/tal-1 gene, a transcription factor known to be essential for development of the primitive and definitive hematopoietic systems, were not able to form blast colonies but did form transitional colonies. Together these findings suggest that the transitional colony represents a stage of development earlier than the blast cell colony and one that uniquely defines the requirement for a functional SCL/tal-1 gene for the progression to hematopoietic commitment.

Tissue interactions mediate early events in pulmonary vasculogenesis

Extensive study has provided considerable insight into the mechanisms governing branching morphogenesis and developmental maturation of the pulmonary epithelium. The process by which the vascular tree arises in the mesodermal mesenchyme of the developing lung, however, is not known. Because normal epithelial branching and differentiation have been shown to be dependent on interactions with the lung mesenchyme, we hypothesized that the developing pulmonary vasculature is dependent on a reciprocal interaction with pulmonary epithelium. In this study we have defined the temporal and spatial expression of flk-1 mRNA, which encodes an endothelial cell-specific vascular endothelial growth factor (VEGF) receptor, in fetal and neonatal rat lung. Flk-1-positive cells were observed in the lung at every prenatal stage from fetal day 11 through birth, demonstrating that vascularization has been initiated as soon as the lung evaginates from the foregut epithelium. The spatial distribution of vascular precursors was distinct and consistent in early lung (fetal days 11-16): clusters of flk-1-positive cells were localized in the mesenchyme closely apposed to the developing epithelium. This spatial relationship between vascular precursors and the developing epithelium suggested that vascular development in the lung may be dependent on interactions between the two tissue types. To investigate this possibility, day-13 distal lung mesenchyme was cultured in the presence and absence of lung epithelium. Lung mesenchyme cultured in the absence of epithelium degenerated significantly, and few flk-1-positive cells were maintained. In contrast, lung mesenchyme recombined with lung epithelium contained abundant flk-1-positive cells, and their spatial distribution mimicked that observed in vivo. These studies provide the first detailed information regarding the temporal and spatial pattern of pulmonary vascularization in early development and suggest that tissue interactions play an important role in growth and maintenance of the developing lung vasculature.

Surfactant protein C expression in urethane-induced murine pulmonary tumors

Mice injected with urethane develop tumors with distinct histological patterns, which are classified as solid, papillary, or a mixture of these two patterns within the same tumor. Most investigators agree that solid tumors arise from alveolar type II cells, but the cellular origin of papillary tumors is less certain, being attributed to either type II cells or nonciliated bronchiolar epithelial (Clara) cells. To characterize the state of differentiation of these tumors more precisely and to provide additional information on gene expression, we used immunocytochemistry and/or in situ hybridization to determine the cellular localization of surfactant-associated proteins A (SP-A), SP-B, SP-C, and SP-D; Clara cell-associated protein CC-10; and thyroid transcription factor-1. In normal mouse lung, the messenger RNAs (mRNAs) for SP-A, SP-B, and SP-D were expressed in both type II cells and Clara cells. SP-C mRNA, however, was expressed only in type II cells, and CC-10 expression of mRNA was restricted to Clara cells. All tumors examined, both solid and papillary, expressed SP-A, SP-B, SP-C, SP-D, and thyroid transcription factor-1, but not CC-10. However, SP-C expression was slightly diminished in larger (older) papillary tumors. These results demonstrate that urethane-induced murine lung tumors express the type II cell phenotype.

Abnormal lung growth and the development of pulmonary hypertension in the Fawn-Hooded rat

The Fawn-Hooded rat (FHR) strain develops accelerated and severe pulmonary hypertension when exposed to slight decreases in alveolar PO(2). We recently observed that adult FHR lungs showed a striking pattern of disrupted alveolarization and hypothesized that abnormalities in lung growth in the perinatal period predisposes the FHR to the subsequent development of pulmonary hypertension. We found a reduction in lung weight in the fetus and 1-day- and 1-wk-old FHR compared with a normal rat strain (Sprague-Dawley). Alveolarization was reduced in infant and adult FHR lungs. In situ hybridization showed similar patterns of expression of two epithelial markers, surfactant protein C and 10-kDa Clara cell secretory protein, suggesting that the FHR lung is not characterized by global delays in epithelial maturation. Barium-gelatin angiograms demonstrated reduced background arterial filling and density in adult FHR lungs. Perinatal treatment of FHR with supplemental oxygen increased alveolarization and reduced the subsequent development of right ventricular hypertrophy in adult FHR. We conclude that the FHR strain is characterized by lung hypoplasia with reduced alveolarization and increased risk for developing pulmonary hypertension. We speculate that altered oxygen sensing may cause impaired lung alveolar and vascular growth in the FHR.

Keratinocyte growth factor-induced hyperplasia of rat alveolar type II cells in vivo is resolved by differentiation into type I cells and by apoptosis

Keratinocyte growth factor (KGF) is a potent mitogen of alveolar epithelial type II cells (AEII). AEII hyperplasia is resolved within several days following intratracheal instillation of KGF by unknown mechanism(s). AEII hyperplasia was induced in rat lungs by intrabronchial instillation of 5 mg recombinant human (rh)KGF x kg body weight(-1) or an equivalent amount of diluent. Epithelial architecture, cell proliferation, transformation of AEII into type I cells (AEI) and apoptosis were investigated by means of immunohistochemistry, stereology, double immunofluorescence microscopy, electron microscopy and the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labelling (TUNEL) technique in lungs fixed 1, 2, 3 and 7 days after treatment. After 1 day of rhKGF instillation, an increase was observed in the nuclear antigen Ki-67, a proliferation marker detected by the antibody MIB-5-expressing surfactant protein (SP)-B, -C, -D-positive AEII. The incidence of mitosis was increased by day 2, resulting in AEII micropapillae with intense basolateral expression of the exon 6 containing isoform (v6) of CD446 (CD44v6), a marker for AEII. By day 3, monolayers of AEII exhibiting lateral CD44v6 covered 45% of the alveolar surface. After 7 days, there were numerous intermediate AEII/AEI cells characterized by a flat elongated shape, staining for SP-D, apical appearance of AEI marker Lycopersicon esculentum lectin and lateral staining for AEII marker CD44v6. Increased numbers of TUNEL-positive epithelial cells were seen at days 2-7. In conclusion, restoration of normal alveolar epithelium after instillation of recombinant human keratinocyte growth factor is accomplished by terminal differentiation and apoptosis of hyperplastic alveolar epithelial type II cells in vivo.

Induction of alveolar type II cell differentiation in embryonic tracheal epithelium in mesenchyme-free culture

We have previously shown that fetal lung mesenchyme can reprogram embryonic rat tracheal epithelium to express a distal lung phenotype. We have also demonstrated that embryonic rat lung epithelium can be induced to proliferate and differentiate in the absence of lung mesenchyme. In the present study we used a complex growth medium to induce proliferation and distal lung epithelial differentiation in embryonic tracheal epithelium. Day-13 embryonic rat tracheal epithelium was separated from its mesenchyme, enrobed in growth factor-reduced Matrigel, and cultured for up to 7 days in medium containing charcoal-stripped serum, insulin, epidermal growth factor, hepatocyte growth factor, cholera toxin, fibroblast growth factor 1 (FGF1), and keratinocyte growth factor (FGF7). The tracheal epithelial cells proliferated extensively in this medium, forming lobulated structures within the extracellular matrix. Many of the cells differentiated to express a type II epithelial cell phenotype, as evidenced by expression of SP-C and osmiophilic lamellar bodies. Deletion studies showed that serum, insulin, cholera toxin, and FGF7 were necessary for maximum growth. While no single deletion abrogated expression of SP-C, deleting both FGF7 and FGF1 inhibited growth and prevented SP-C expression. FGF7 or FGF1 as single additions to the medium, however, were unable to induce SP-C expression, which required the additional presence of serum or cholera toxin. FGF10, which binds the same receptor as FGF7, did not support transdifferentiation when used in place of FGF7. These data indicate that FGF7 is necessary, but not sufficient by itself, to induce the distal rat lung epithelial phenotype, and that FGF7 and FGF10 play distinct roles in lung development.

A 50-kDa variant form of human surfactant protein D

The dominant form of human surfactant protein D (SP-D) is a multimeric collagenous glycoprotein composed of monomeric subunits that have a molecular mass of 43 kDa under reducing conditions. However, in evaluating monoclonal antibodies to human SP-D, an additional monomeric subunit was identified with a reduced molecular mass of 50 kDa. This 50-kDa variant was detected in approximately half of the samples evaluated and was found in lavage fluid from normal subjects, patients with alveolar proteinosis or idiopathic pulmonary fibrosis and in amniotic fluid. This 50-kDa variant had the same amino-terminal sequence, amino acid composition and apparent size of the carboxy-terminal collagenase-resistant fragment (20 kDa) as the 43-kDa subunit. The major difference was in the amino-terminal portion of the molecule and was due to altered glycosylation, as determined by carbohydrate staining, chemical deglycosylation, treatment with N-glycanase and neuraminidase and reduced signals for threonine at positions 5, 9 and 10 during amino-terminal sequencing. After gel filtration chromatography, the 50-kDa form was not present in the high molecular weight fraction, which is commonly used in purification of SP-D, but was found only in the smaller molecular weight fraction of monomers and trimers of SP-D. In conclusion, the 50 kDa-form of surfactant protein D is produced by post-translational glycosylation and does not form higher ordered oligomers, but its precise physiological function remains to be determined.

Mesenchyme specifies epithelial differentiation in reciprocal recombinants of embryonic lung and trachea

Normal lung morphogenesis and cytodifferentiation require interactions between epithelium and mesenchyme. We have previously shown that distal lung mesenchyme (LgM) is capable of reprogramming tracheal epithelium (TrE) from day 13-14 rat fetuses to branch in a lung-like pattern and express a distal lung epithelial phenotype. In the present study, we have assessed the effects of tracheal mesenchyme (TrM) on branching and cytodifferentiation of distal lung epithelium (LgE). Tracheae and distal lung tips from day 13 rat fetuses were separated into purified epithelial and mesenchymal components, then recombined as homotypic (LgM + LgE or TrM + TrE) or heterotypic (LgM + TrE or TrM + LgE) recombinants and cultured for 5 days; unseparated lung tips and tracheae served as controls. Control lung tips, LgM + LgE, and LgM + TrE recombinants all branched in an identical pattern. Epithelial cells, including those from the induced TrE, contained abundant glycogen deposits and lamellar bodies, and expressed surfactant protein C (SP-C) mRNA. Trachea controls, and both TrM + TrE, and TrM + LgE recombinants did not branch, but instead formed cysts. The epithelium contained ciliated and mucous secretory cells; importantly, no cells containing lamellar bodies were observed, nor was SP-C mRNA detected. Mucin immunostaining showed copious production of mucous in both LgE and TrE when recombined with TrM. These results demonstrate that epithelial differentiation in the recombinants appears to be wholly dependent on the type of mesenchyme used, and that the entire respiratory epithelium has significant plasticity in eventual phenotype at this stage in development.

Effects of soluble factors and extracellular matrix on DNA synthesis and surfactant gene expression in primary cultures of rat alveolar type II cells

Proliferation and differentiation of epithelial cells are thought to be regulated by soluble factors in extracellular fluid and insoluble components of the extracellular matrix. We have examined the combined effects of soluble factors and an extracellular matrix (EHS matrix) on DNA synthesis, cell proliferation, and surfactant protein gene expression in primary cultures of alveolar type II epithelial cells. Cells on EHS matrix cultured in DMEM containing insulin, cholera toxin, EGF, aFGF, 5% rat serum, and 15-fold concentrated bronchoalveolar lavage fluid (D-GM) formed larger aggregates than cells cultured on the same substratum in DMEM containing 5% rat serum (D-5). Cells cultured in D-GM on EHS matrix incorporated more [3H]-thymidine than cells on the same substratum in D-5, with an eight-fold increase seen on day 4 of culture. This increase in [3H]-thymidine incorporation was accompanied by a labeling index of greater than 65% of the cells. Cell counts showed that exposure of type II cells on EHS matrix to D-GM resulted in increased cell number on day 4 of culture. [3H]-thymidine autoradiography combined with immunostaining with anti-cytokeratin, anti-SP-A, and anti-vimentin antibodies demonstrated that the proliferating cells were epithelial cells that contained SP-A. Type II cells cultured on plastic in D-GM also showed increased [3H]-thymidine incorporation compared to cells cultured in D-5. The level of [3H]-thymidine incorporation by cells on plastic, however, was significantly less than that seen in cells cultured in the same medium on EHS matrix. Type II cells cultured on EHS matrix in D-GM had a decreased abundance of mRNAs for SP-A and SP-C than cells cultured on EHS matrix in D-5 as determined by Northern analysis. This inhibition was reversed by switching from D-GM to D-5 on day 4 and culturing the cells for an additional 4 days. In contrast, SP-B mRNA was increased in response to D-GM. This increase was not reversed by switching from D-GM to D-5 on day 4. These results suggest that the interaction of soluble factors and extracellular matrix components has a strong influence on type II cell proliferation, which were partially associated with the reversible inhibition of lung tissue-specific protein mRNAs. Their dynamic interplay among the type II cell, the extracellular matrix, and growth factors may determine multicellular functions and play an important role in normal lung development and in the repair of the lung epithelium following injury.

Influence of the cytoskeleton on surfactant protein gene expression in cultured rat alveolar type II cells

We have investigated the role of the cytoskeleton in surfactant protein gene expression. Cytochalasin D (CD), colchicine (Col), or nocodazole (Noco) were tested on primary cultures of adult rat alveolar type II cells. Treatment with any of the drugs did not result in dramatic cell shape changes, but ultrastructural examination revealed that the cytoplasm of cells treated with CD was markedly disorganized; cells treated with Col did not exhibit such changes. Treatment with any of the three drugs resulted in a reduction in surfactant protein (SP) mRNAs. These decreases were not the result of cell toxicity, since overall protein synthesis was unimpaired by drug treatment. Washing the cells followed by an additional 2 days of culture resulted in a reaccumulation of SP mRNAs in CD-treated cells but not in Col-treated cells. Washing of Noco-treated cultures resulted in partial recovery. SP mRNA stability was estimated in the presence or absence of cytoskeleton-disrupting drugs. Disruption of either microfilaments or microtubules significantly affected the half-lives of mRNAs for SP-A, SP-B, and SP-C. These data support a role for the cytoskeleton in the maintenance of type II cell differentiation and suggest that the role of the cytoskeleton is at least in part to stabilize SP mRNAs.

Expression of a brain-type cannabinoid receptor (CB1) in alveolar Type II cells in the lung: regulation by hydrocortisone

Using the polymerase chain reaction with degenerate primers to identify novel G-protein-coupled receptors of the rat alveolar Type II cell, we identified sequences expressed by the Type II cell identical to the sequence of the rat brain cannabinoid receptor (CB1). The use of Northern blot analysis to examine expression of CB1 mRNA in rat tissues revealed differences between the brain and lung. While rat brain expressed a 6.0 kb mRNA as previously described, rat lung expressed mRNA of 4.5 and 6.0 kb. Isolated lung alveolar Type II cells also expressed mRNA of 4.5 and 6.0 kb as determined by Northern analysis. However, only freshly isolated Type II cells contained cannabinoid receptor mRNA. Reverse transcriptase-polymerase chain reaction (RT-PCR) failed to detect CB1 mRNA in Type II cells maintained in culture for 1 or 2 days. We next determined developmental changes in lung CB1 mRNA expression using semi-quantitative RT-PCR. CB1 expression was detected as early as gestational day 16 in rat lung and mRNA levels increased to fetal day 20 before birth, before declining to adult levels. Fetal rat lung explants were utilized to further examine the ontogeny and hormonal effects on CB1 mRNA expression. Hydrocortisone induced a dose-dependent expression in 15-day and 18-day explants, similar to previous results for surfactant-associated proteins. Our results demonstrate expression of CB1 mRNA in rat alveolar Type II cells and rat lung. This expression is ontogenically and hormonally regulated, with maximal expression noted just prior to birth in rat lung. Since CB1 mRNA is only expressed in freshly isolated Type II cells, CB1 may be useful as a Type II cell marker.

Prevention of bleomycin-induced lung injury in rats by keratinocyte growth factor

Intratracheal instillation of bleomycin produces pulmonary fibrosis in rats. Alveolar type II cell proliferation is thought to minimize the fibrotic response after lung injury. Because keratinocyte growth factor (KGF) stimulates type II cell proliferation in the rat, we designed experiments to evaluate whether intratracheal KGF before or after intratracheal bleomycin would prevent pulmonary fibrosis. Intratracheal bleomycin without KGF resulted in moderate to severe lung injury and subsequent fibrosis. Conversely, intratracheal KGF pretreatment at 48 or 72 hr before bleomycin resulted in minimal to no visible lung injury. Rats pretreated with phosphate buffered saline before bleomycin had significantly more neutrophils and protein in bronchoalveolar lavage fluid at 4 and 6 days and higher hydroxyproline levels after bleomycin as compared to KGF-pretreated rats. Pretreatment with KGF at 48 hr protected against bleomycin-induced alterations in pulmonary physiology and increased surfactant protein C-positive (SP-C)-positive cells and SP-A, SP-B, SP-C, and SP-D mRNA levels after bleomycin instillation when compared to saline pretreated rats on day 1 or day 7. KGF posttreatment protocols did not prevent bleomycin lung injury and fibrosis. We conclude that KGF pretreatment attenuates bleomycin lung injury and increases type II cell proliferation and surfactant protein gene expression after bleomycin instillation in the rat.

Heparin-binding EGF-like growth factor is a mitogen for rat alveolar type II cells

Alveolar type II cells proliferate and differentiate into type I epithelial cells to restore the alveolar epithelium after lung injury. Since mitogens that bind the epidermal growth factor (EGF), EGF, receptor and transforming growth factor alpha (TGF alpha) have been shown to stimulate type II cell proliferation, studies were undertaken to determine whether the recently described protein, heparin-binding EGF-like growth factor (HB-EGF), was a mitogen for rat alveolar type II cells in primary culture. In addition, since HB-EGF is produced by macrophages, it was of interest to determine whether mitogenic activity for type II cells present in macrophage conditioned medium was due to HB-EGF. Rat and human recombinant HB-EGF stimulated thymidine incorporation into rat type II cells in a concentration-dependent manner up to 10-50 ng/ml then became inhibitory. The nuclear labeling index of type II cells increased from 2% to 16% with 10 ng/ml HB-EGF. However, HB-EGF induced only a small increase in cell number after 48 h and did not support low-density proliferation of alveolar type II cells. Conditioned medium from the human monocytic cell line, U937, stimulated type II cell DNA synthesis, and stimulatory activity could be partially purified by S-sepharose and heparin-sepharose chromatography. The growth-promoting activity from U937 cells that bound to heparin-sepharose was inhibited by a neutralizing antibody to human HB-EGF. Immunoblot analysis of active fractions also verified the presence of HB-EGF. However, the neutralizing antibody to rat HB-EGF did not inhibit mitogenic activity for type II cells found in rat bronchoalveolar lavage fluid. HB-EGF mRNA was found to be expressed in human alveolar macrophages to similar levels as differentiated U937 cells but was not detected in rat alveolar macrophages by Northern analysis of total mRNA. There was no difference in the level of HB-EGF mRNA expression in human alveolar macrophages from patients with interstitial lung disease compared with macrophages from normal subjects. The results demonstrate that HB-EGF is a mitogen for rat alveolar type II cells but appears to show species-specific differences with regard to its production by macrophages. Leslie, C. C., K. McCormick-Shannon, J. M. Shannon, B. Garrick, D. Damm, J. A. Abraham, and R. J. Mason. 1997. Heparin-binding EGF-like growth factor is a mitogen for rat alveolar type II cells. Am. J. Respir. Cell Mol. Biol. 16:379-387.

Developmental changes of fetal rat lung Na-K-ATPase after maternal treatment with dexamethasone

Late in gestation, the prenatal fetal alveolar epithelium switches from fluid secretion to resorption of salt and water via apical sodium channels and basal Na-K-ATPase. The amounts of lung sodium pump activity protein and mRNA increase in the lung just before birth. Because maternal glucocorticoids (GC) may promote maturation of the alveolar epithelium and augment fetal surfactant apoprotein levels, we hypothesized that GC increase the fetal lung Na-K-ATPase alpha- and beta-subunit gene expression in development. Timed-pregnant Sprague-Dawley rats were injected daily with intraperitoneal dexamethasone (1 mg/kg) or saline for 1, 3, or 5 days before death at fetal day (FD) 17 or 19. Maternal GC treatment altered the fetal lung wet to dry weight, decreasing it at FD17 and increasing it at FD19. Northern analysis of total lung RNA for the alpha1- and beta1-pump subunits demonstrated differential regulation of the mRNA in response to GC. At FD17, beta1-mRNA increased after 1 (FD16) or 3 days (FD14-FD16) of GC treatment, whereas alpha1-mRNA was not altered. There were accompanying increases in beta1-, but not alpha1-, protein. At FD19, GC treatment for 5 days (FD14-FD18) increased beta1- and decreased alpha1-mRNA levels, but treatment for 1 (FD18) or 3 days (FD16-FD18) had no effect. In all groups, the alpha1-Na-K-ATPase protein was predominantly on the basolateral surface of airspace epithelium by immunofluorescence. In summary, maternal dexamethasone differentially affected the fetal lung mRNA levels of the two sodium pump subunits in a complex manner, with increased beta1-mRNA levels dependent on duration of treatment and fetal age.

Keratinocyte growth factor reduces lung damage due to acid instillation in rats

Acid aspiration is a serious complication of anesthesia and other forms of unconsciousness that can result in the adult respiratory distress syndrome (ARDS), which continues to have a very high mortality despite our current therapeutic interventions. This type of injury damages the alveolar epithelium, principally alveolar type I cells, and requires proliferation of alveolar type II cells to restore gas exchange units. Since keratinocyte growth factor (KGF) has been shown to be a potent mitogen for alveolar type II cells, we evaluated whether intrabronchial administration of KGF would minimize lung injury due to the unilateral instillation of 0.1 N hydrochloric acid (HCl). Rats were pretreated or post-treated by intrabronchial instillation of KGF (5 mg/kg) into the left lung before HCl instillation. All rats receiving KGF at 48 or 72 h before HCl instillation survived for the 7-day observation period, whereas the mortality rate for those receiving HCl alone or saline followed by HCl was 31% and 33%, respectively. Pretreatment with KGF at 72 h but not at 24 or 48 h considerably ameliorated morphologic damage produced by HCl. Inflammatory cells in bronchoalveolar lavage were markedly decreased 3 and 7 days after HCl instillation by the 72-h KGF pretreatment. Pretreatment with KGF at 72 h also attenuated the reduction of total lung capacity, decreased the alpha 1(I) procollagen mRNA levels, and diminished hydroxyproline accumulation due to HCl instillation. Saline pretreatment at 72 h had no significant effect on the HCl injury and subsequent physiologic abnormalities. Our attempts to improve outcome with post-treatment instillation of KGF were unsuccessful. We conclude that KGF pretreatment reduces lung injury due to acid instillation and can prevent subsequent pulmonary fibrosis.

Acidic fibroblast growth factor and keratinocyte growth factor stimulate fetal rat pulmonary epithelial growth

We have shown that pulmonary epithelial growth and differentiation can occur if pulmonary mesenchyme is replaced with a mixture of growth factors [total growth medium (TGM)] that consists of adult rat bronchoalveolar lavage fluid, insulin, epidermal growth factor (EGF), cholera toxin (CT), acidic fibroblast growth factor (aFGF), and fetal bovine serum. In the present study, we have defined the importance of specific components of TGM. Day 14 fetal rat distal lung epithelium, devoid of mesenchyme, was enrobed in growth factor-depleted Matrigel and cultured for 5 days in various soluble factors. We found that deleting aFGF or CT from TGM significantly reduced DNA synthesis. Epithelial proliferation was not significantly different when keratinocyte growth factor (KGF) replaced aFGF in TGM. KGF, however, required the presence of a basal medium containing CT, insulin, and serum for optimal proliferation. We then added specific growth factors to the basal medium and showed that aFGF and KGF were more potent mitogens than EGF, transforming growth factor-alpha, and hepatocyte growth factor. Additionally, basal medium + KGF also allowed progression to a distal alveolar phenotype. We conclude that aFGF and KGF may be important mediators in epithelial-mesenchymal interactions.

Keratinocyte growth factor increases mRNAs for SP-A and SP-B in adult rat alveolar type II cells in culture

The production of pulmonary surfactant, a complex of phospholipids and lung-specific surfactant proteins, is a primary function of alveolar type II cells. Although previous studies have demonstrated a role for cell-extracellular matrix interactions and normal cell shape in the maintenance of differentiated function in primary cultures of adult rat type II cells, a positive role for growth factors in surfactant protein gene expression in isolated normal adult type II cells has not been reported. In the present study, we have examined the effects of a panel of hormones, growth factors, and cytokines on the expression of mRNAs for surfactant proteins A, B, and C (SP-A, SP-B, and SP-C). Our results show that keratinocyte growth factor (KGF) induced a two- to threefold increase in steady-state levels of mRNAs for SP-A and SP-B, but had no effect on or decreased SP-C mRNA. The increase in SP-A mRNA was accompanied by an increase in SP-A protein. The effects of KGF were both dose and time dependent, and they could be neutralized by a monoclonal antibody against KGF. The effects of KGF were mimicked by acidic fibroblast growth factor, which will bind the KGF receptor. We conclude that KGF can support differentiation of alveolar type II cells as well as act as a mitogen, thus suggesting an important role for KGF in maintenance of the alveolar epithelium.

Proliferation and differentiation of fetal rat pulmonary epithelium in the absence of mesenchyme

Previous studies have shown that pulmonary mesenchyme is required to maintain epithelial viability and to support branching morphogenesis and cytodifferentiation. We have examined whether pulmonary mesenchyme can be replaced by a medium containing a combination of soluble factors. Day 13-14 fetal rat distal lung epithelium was enzymatically separated from its mesenchyme, enrobed in EHS tumor matrix, and cultured for 5 d in medium containing concentrated bronchoalveolar lavage, EGF, acidic fibroblast growth factor, cholera toxin, insulin, and FBS (TGM), or in control medium containing only FBS. After 5 d in culture, marked growth and morphological changes occurred in epithelial rudiments cultured in TGM, whereas no changes were seen in controls. [3H]Thymidine incorporation and nuclear labeling indices during the last 24 h of culture confirmed that epithelial rudiments cultured in TGM had significant proliferative capacities. Evaluation of surfactant protein gene expression by Northern analysis, in situ hybridization, and immunocytochemistry demonstrated that distal lung epithelial differentiation progressed in TGM. Ultrastructural analysis demonstrated that fetal distal lung epithelium cultured in TGM contained lamellar bodies and deposited a basal lamina. These results are the first demonstration that sustained proliferation and differentiation of glandular stage distal pulmonary epithelium can proceed in the absence of mesenchyme.

Reversible transdifferentiation of alveolar epithelial cells

Alveolar epithelial type II (AT2) cells have been thought to be the progenitors of terminally differentiated type I (AT1) cells in the adult animal in vivo. In this study, we used an AT1 cell-specific monoclonal antibody (mAb VIII B2) to investigate expression of the AT1 cell phenotype accompanying reversible changes in expression of the AT2 cell phenotype. AT2 cells were isolated and cultured either on attached collagen gels or on gels detached 1 or 4 days after plating and maintained thereafter as floating gels. Monolayers on both attached and floating gels were harvested on days 4 and 8 and analyzed by electron microscopy for changes in morphology and binding of mAb VIII B2. Results indicate that: (1) alveolar epithelial cells (AEC) on attached gels develop characteristics of the AT1 cell phenotype, (2) AEC on gels detached on day 1 maintain features of the AT2 cell phenotype (and do not react with mAb VIII B2), and (3) the expression of AT1 cell phenotypic traits seen by day 4 on attached gels is reversed after detachment. We conclude that commitment to the AT1 and AT2 cell lineages requires continuous regulatory input to maintain the differentiated states, and that transdifferentiation between AT2 and AT1 cells may be reversible.

Induction of alveolar type II cell differentiation in fetal tracheal epithelium by grafted distal lung mesenchyme

Normal branching morphogenesis and cytodifferention of the lung require a specific interaction between the epithelial rudiment and pulmonary mesenchyme. Previous studies in the mouse have shown glandular stage pulmonary mesenchyme can elicit a lung-like pattern of branching morphogenesis when grafted onto tracheal epithelium of the same age that has been denuded of its own mesenchyme. We have examined whether are not this pattern of branching is accompanied by changes in epithelial cytodifferentiation. Purified pulmonary mesenchyme was isolated from the distal tips of day 13-14 fetal rat lungs and grafted onto a stretch of tracheal epithelium from which the mesenchyme had been removed. The grafts were cultured on semisolid 0.5% agarose in Waymouth's medium containing 10% serum for 5 days and then for an additional 2 days in the same medium containing 10(-6) M cortisol. Unoperated or operated-ungrafted tracheae and intact lung explants served as controls. Grafting distal tip pulmonary mesenchyme onto the tracheal epithelium induced a pattern of branching identical to that seen in control lung explant cultures, while ungrafted control tracheal cultures formed cystic structures. Light microscopy of the induced tracheal epithelium showed that the constituent cells exhibited a morphology virtually identical to cells in control lung explants. Ultrastructural analysis demonstrated that the induced tracheal epithelial cells contained lamellar inclusion bodies, and the lumina of the induced acinar structures contained tubular myelin figures. Reverse transcription polymerase chain reaction analysis of the induced tracheae revealed the presence of mRNAs for surfactant protein A (SP-A) and SP-B, as well as SP-C, which is a specific marker for type II cell differentiation in the adult rat. Control tracheal cultures contained mRNAs only for SP-A and SP-B. Immunocytochemistry demonstrated that many cells within the induced tracheal epithelium were positive for SP-A and SP-C proteins. Further studies demonstrated that the ability of mesenchyme to induce tracheal epithelium varied within the pulmonary tree, and that the competence of the tracheal epithelium to respond to the influence of distal tip mesenchyme was temporally restricted. Our results demonstrate that pulmonary mesenchyme can act instructively on the tracheal epithelium to induce a program of type II cell differentiation.

Hepatocyte growth factor is a growth factor for rat alveolar type II cells

Proliferation of alveolar type II cells is thought to be critical for restoration of gas exchange units after diffuse alveolar damage. However, the factors that regulate type II cell proliferation are not well understood. Hepatocyte growth factor (HGF) is a potentially important mitogen because it causes epithelial cells but not fibroblasts to proliferate and is found in the lung. We used rat alveolar type II cells in primary culture to demonstrate that HGF stimulates DNA synthesis in a concentration-dependent manner. The half maximal effect on stimulation of thymidine incorporation was less than 1 ng/ml. By autoradiography, HGF increased nuclear labeling from 1.3% of type II cells with medium alone to 9.4% with 5 ng/ml HGF. During this time, HGF modestly increased cell number in comparison to control media. However, in an assay of colony formation in low-density cultures, HGF did not consistently increase colony formation by alveolar type II cells and was less effective than acidic fibroblast growth factor or bronchoalveolar lavage fluid in this assay. The receptor for HGF (c-met proto-oncogene) was expressed in rat type II cells and whole lung but not in macrophages. In contrast, the mRNA for HGF was detected in rat macrophages and lung but not in type II cells. However, HGF message was not detected in human alveolar macrophages under conditions in which the HGF message was detected in rat alveolar macrophages and in human fibroblasts. Hence, HGF is a potential paracrine growth factor for alveolar type II cells, but there may be important species differences in the relative level of expression.

Regulation of surfactant protein D expression by glucocorticoids in vitro and in vivo

SP-D is a recently described lung-associated protein that is produced by alveolar type II cells and may function in pulmonary host defenses. Since little is known regarding the hormonal regulation of SP-D, and since the other surfactant proteins (SP-A, SP-B, and SP-C) are known to be regulated by glucocorticoids, we sought to determine the effects of glucocorticoids on SP-D mRNA and protein expression, both in vitro and in vivo, in the fetal rat lung. In vitro experiments were performed on lung explants from fetuses on gestational day 15 or 18. Explants were cultured in serum-free conditions with or without hydrocortisone for 3 days. SP-D mRNA expression was evaluated by Northern blot analysis. SP-D protein expression was analyzed using a polyclonal antibody against SP-D and standard immunohistochemical techniques. The expression of SP-D mRNA increased in fetal day 15 explants but remained unchanged in fetal day 18 explants cultured without the addition of hydrocortisone, compared with in vivo controls. The addition of hydrocortisone resulted in increases in SP-D mRNA expression at both gestational ages. This pattern of SP-D mRNA expression was compared with the expression of the other surfactant proteins and found to be most similar to that of SP-B. In vivo experiments were performed using maternal administration of dexamethasone (1 mg/kg) or an equal volume of saline on fetal days 15, 16, and 17 or on fetal day 17 with sacrifice on fetal day 18.(ABSTRACT TRUNCATED AT 250 WORDS)

Proliferation of rat alveolar epithelial cells in low density primary culture

Alveolar type II cells proliferate to restore the alveolar epithelium after lung injury and differentiate into type I epithelial cells. A variety of factors promote rat type II cell DNA synthesis in vitro; however, only low levels of proliferation occur when type II cells are cultured at high density. We plated type II cells at low density to determine if those growth factors that stimulate thymidine incorporation also stimulate low density proliferation. Type II cells were plated at 1 x 10(3) cells/cm2 in Dulbecco's modified Eagle's medium containing 2% fetal bovine serum, cholera toxin, insulin, epidermal growth factor, acidic fibroblast growth factor (aFGF), and concentrated bronchoalveolar lavage fluid from normal rats. By 7 days, numerous colonies had grown out that exhibited an epithelial morphology and stained positively for cytokeratin. The cell number at day 7 in the presence of the combined factors was 5.9 x 10(3) (+/- 0.6 x 10(3)) cells/cm2 (n = 4). There was no colony formation in the absence of fetal bovine serum. The addition of linoleic acid to serum-free medium containing all the growth supplements was found to partially restore colony formation. When aFGF or lavage fluid was omitted from the culture medium, colony formation was dramatically reduced. The colonies lacked characteristics of differentiated type II cells, which was anticipated since these cells were cultured on tissue culture plastic. To see if these cells could express differentiated functions, we maintained the colonies under growth conditions, removed them from the plastic substratum, and then replated them on EHS matrix.(ABSTRACT TRUNCATED AT 250 WORDS)

Surfactant protein C is expressed in alveolar type II cells but not in Clara cells of rat lung

The expression of the surfactant-associated proteins in bronchiolar cells remains to be defined. We used in situ hybridization to identify sites of message expression of the surfactant-associated proteins A, B, and C (SP-A, SP-B, and SP-C) in adult and fetal rat lung. The expression of these messages by in situ hybridization was also compared with the localization of SP-A by immunocytochemistry. The localization of SP-A was used to identify type II cells and nonciliated bronchiolar epithelial (Clara) cells in these sections. The cRNA antisense probes for SP-A, SP-B, and SP-C appeared to hybridize over type II cells. Sense probes showed no localization or apparent specific hybridization. Messages for both SP-A and SP-B were also found in nonciliated bronchiolar epithelial (Clara) cells. However, no message for SP-C was observed in these cells. Clara cells from terminal to large bronchioles lacked detectable mRNA for SP-C. Expression of surfactant protein mRNAs was not detectable in type I cells, alveolar macrophages, interstitial cells, or vascular cells. Similarly, in fetal rat lung the messages for SP-A and SP-B but not SP-C were detected in bronchiolar cells. We conclude that rat Clara cells do not express SP-C mRNA, and thus SP-C can be regarded as a specific marker for rat type II cells.

Modulation of alveolar type II cell differentiated function in vitro

We have investigated whether the loss of differentiated function observed in adult rat alveolar type II cells cultured on a substratum that promotes cell spreading and flattening represents a reversible phenotypic change. Cells were cultured for 4 and 8 days in association with fetal rat lung fibroblast feeder layers on either attached collagen gels, which promote the loss of differentiated function, or on floating collagen gels, which support differentiation. A fifth group of cultures were maintained as attached gels for 4 days, then detached and cultured as floating gels for the remaining 4 days. Expression of mRNAs for surfactant proteins A, B, and C, patterns of phospholipid biosynthesis, rates and patterns of protein synthesis, and cell morphology were evaluated as markers of differentiation. Without exception, detaching the gels after 4 days in culture resulted in significant recovery of differentiated characteristics, demonstrating that type II cells modulate differentiated function in response to the culture environment. The results are discussed in relation to the importance of normal cell architecture to normal cell function and to the possible in vitro progression of type II cells to type I cells.

In vivo regulation of surfactant proteins by glucocorticoids

Surfactant proteins have key roles in regulating surfactant secretion, in recycling, and in the assembly of the surfactant monolayer but little is known about their regulation in vivo. Surfactant proteins SP-A, SP-B, and SP-C have been shown to be upregulated by glucocorticoids in vitro, but the role of glucocorticoids in the physiologic regulation of surfactant protein synthesis remains unknown. We have studied the effects of exogenously administered glucocorticoids on the regulation of steady-state surfactant protein mRNA accumulation. We have also studied the effects of adrenalectomy on the accumulation of the surfactant protein mRNAs. Surfactant protein genes appear to have quantitatively different responses to exogenously administered glucocorticoids, with SP-C mRNA increasing at the lowest dose, SP-A and SP-B mRNA increasing in response to similar glucocorticoids doses but with SP-B yielding the highest maximum response. Adrenalectomy, however, does not alter surfactant protein mRNA levels. These observations support a minor role for glucocorticoids in maintaining the steady-state accumulation of surfactant protein mRNA. Adrenalectomy decreases total pulmonary SP-A when compared to sham-operated animals in the absence of changes in its mRNA. Therefore, glucocorticoids may have translational or post-translational effects that regulate total pulmonary SP-A accumulation, but the effects appear to be minor. These findings support a potential role for the adrenal in the pulmonary response to stress and demonstrate for the first time differential accumulation of the surfactant protein mRNAs to glucocorticoids in vivo.

Effects of maternal dexamethasone on expression of SP-A, SP-B, and SP-C in the fetal rat lung

Prenatal administration of glucocorticoids has been shown to enhance surfactant production in the fetus. Since the surfactant proteins play an important role in surfactant function and secretion, we wished to determine the effects of maternal glucocorticoid administration on their fetal expression and appearance. Daily dexamethasone (DEX) (1 mg/kg/day) or 0.9% saline was administered to timed-pregnant rats on gestational days 14 through 16 or on day 16 with sacrifice on day 17 (term day 22), and on gestational days 14 through 18, or days 16 through 18, or day 18 with sacrifice on day 19. SP-A content was determined in lung homogenates from treated and control male and female fetal rats by an enzyme-linked in lung homogenates from treated and control male and female fetal rats by an enzyme-linked immunosorbent assay. The abundance of mRNAs for SP-A, SP-B, and SP-C per fixed amount of total cellular RNA was also determined in lungs from treated and control male and female fetal rats by Northern blot analysis. In litters sacrificed on day 17, DEX administered on days 14 through 16 and on day 16 resulted in significant increases in SP-A content. Expression of SP-A mRNA, which was not detectable in control fetuses on day 17, became clearly apparent after either 1 or 3 d of DEX treatment. The abundance of mRNAs for SP-B and SP-C also increased in day-17 fetuses after either 1 or 3 d of DEX treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression and characterization of rat surfactant protein A synthesized in Chinese hamster ovary cells

Rat surfactant protein A (SP-A) was expressed in a Chinese hamster ovary (CHO-K1) cell line and characterized for biologic activity using assays for receptor binding and modulation of phospholipid secretion from isolated type II cells. The CHO-K1 cell line was cotransfected with separate plasmids encoding for the rat SP-A, dihydrofolate reductase and neomycin phosphotransferase, respectively. Antibiotic (Geneticin-G418)-resistant transformants were screened by ELISA for the secretion of recombinant SP-A into the media. Northern analysis of the transfected cell lines demonstrated the expression of both 1.6 kb and 0.9 kb mRNA species for SP-A, consistent with the proposed differential polyadenylation of the primary transcript. Amplification with methotrexate resulted in a dose-dependent increase in mRNA for SP-A and a 20-fold increase in the production of recombinant SP-A relative to untreated cells. Maximum production of SP-A was 370 micrograms of SP-A/l of media in a 4-day incubation. Recombinant SP-A was purified from the serum-free media of large scale cultures of transfected, amplified CHO cells by affinity chromatography on mannose-Sepharose. The recombinant SP-A migrated similarly to native SP-A by NaDodSO4-PAGE analysis under reducing and nonreducing conditions and under reducing conditions after digestion with N-glycanase. Recombinant SP-A effectively competed with 125I-native SP-A for binding to the high affinity receptor for SP-A on isolated plasma membranes from rat alveolar type II cells. The recombinant SP-A was as effective as native SP-A in the inhibition of secretion of phospholipid from isolated type II cells. We conclude that recombinant rat SP-A produced in Chinese hamster ovary cells is physically and functionally similar to native rat SP-A.

Improved maintenance of adult rat alveolar type II cell differentiation in vitro: effect of serum-free, hormonally defined medium and a reconstituted basement membrane

We have developed a serum-free, hormonally defined medium for maintenance of differentiation of adult type II cells cultured on Engelbreth-Holm-Swarm (EHS) tumor basement membrane gels. This defined medium consists of 1:1 (vol/vol) mixture of Ham's F12 and Dulbecco's modified Eagle's media supplemented with insulin, dibutyryl cyclic AMP, hydrocortisone, epidermal growth factor, selenium, and albumin/linoleic acid complex. Compared to cells cultured on EHS gels in serum-supplemented medium, type II cells cultured on EHS gels in this defined medium showed increased acetate incorporation into total lipids (10-fold) and an increase in the relative percentage of acetate incorporated into phosphatidylcholine (PC) (87.8 +/- 0.4% versus 78.5 +/- 1.0% [mean +/- SE]; P less than 0.01), saturated phosphatidylcholine (SPC) (61.4 +/- 0.5% versus 55.2 +/- 0.9%; P less than 0.01), and phosphatidylglycerol (PG) (5.3 +/- 0.3% versus 0.8 +/- 0.1%; P less than 0.01) and decreased acetate incorporation into neutral lipids (9.7 +/- 0.8% versus 62.6 +/- 1.9%; P less than 0.01). No response to this defined medium was seen when type II cells were cultured on tissue culture plastic. Type II cells cultured on EHS gels in serum-supplemented medium for 4 d had numerous neutral lipid droplets in their cytoplasm. In contrast, neutral lipid droplets were not commonly observed within the cytoplasm of the cells cultured in serum-free, hormonally defined medium on EHS gels. This morphologic finding was consistent with the result that cells cultured in serum-supplemented medium significantly increased the relative percentage of acetate incorporated into neutral lipids. These data indicate that adult type II cells cultured on a reconstituted basement membrane (EHS gels) can be maintained in synthetic culture medium without serum. These culture conditions permit the expression of a pattern of differentiated phospholipid biosynthesis and cell morphology more similar to normal type II cell differentiation.

Protection of rat spermatogenic epithelium from damage induced by procarbazine chemotherapy

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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)

Effects of two extracellular matrices on morphologic and biochemical properties of human type II cells in vitro

Previous observations have suggested that differentiated functions of adult rat type II alveolar cells are affected in part by cell-matrix interactions. We examined several aspects of differentiated adult human type II cells cultured on either bovine corneal endothelial cell extracellular matrix (BCECM) or matrix derived from the Englebreth-Holm-Swarm tumor (EHS). Compared to cells cultured on BCECM, adult human type II cells grown on EHS assumed a more cuboidal shape, had a more defined apical-basal polarity, and appeared to contain a greater number of lamellar bodies and neutral lipid inclusions. These cells also incorporated a greater percentage of [14C]acetate into saturated phosphatidylcholine (SPC) than did their counterparts grown on BCECM. In contrast, the relative incorporation of [14C]acetate into phosphatidylglycerol (PG) was lower in cells grown on EHS than cells cultured on BCECM. The histochemical stain for alkaline phosphatase was useful in identification of human type II cells. Alkaline phosphatase expression was elevated in cells cultured on EHS compared to those cultured on BCECM. These results suggest that maintenance of a differentiated morphology, lipid synthesis, and expression of alkaline phosphatase activity by primary cultures of adult human type II cells are also influenced by cell-matrix interactions. All markers of differentiated function of type II cells except synthesis of PG are better maintained on EHS than on BCECM. Under the conditions of these experiments, synthesis of SPC and PG appears to be independently regulated.

Ontogeny of surfactant apoproteins in the rat

Content of the 26-38-kD surfactant apoprotein (SP-A) was determined in lung homogenates from fetal (17-21 d gestation), postnatal (1-28 d of life), and adult male and female rats by a double sandwich ELISA. Expression of mRNA for SP-A as well as the hydrophobic apoproteins, SP-B and SP-C, were also determined in lung homogenates from fetal and adult rats of both sexes by Northern blot analysis. SP-A was undetectable in fetal lungs on d 17 (day of birth = d 22) and barely detectable on d 18. On d 19 there was a 3- to 4-fold increase in SP-A content above d 18 levels. Between d 19 and 21 SP-A content significantly increased another 6- to 9-fold. SP-A content on the day of birth was not significantly different from that seen on gestational d 21. SP-A content decreased 35-40% between the day of birth and postnatal d 7. After the second postnatal week SP-A content gradually increased, reaching adult levels after d 28. No sex differences in SP-A content were observed during fetal or postnatal lung maturation. SP-A mRNA was first detected in fetal lungs on d 18 and increased in relative abundance until d 21, but remained below adult levels. Developmental changes in fetal lung SP-A content closely paralleled changes in fetal expression of SP-A mRNA. SP-B mRNA was also first detected on d 18, then increased in relative abundance to adult levels by d 20. SP-C mRNA was clearly detectable on d 17, then increased in relative abundance to adult levels by d 20-21. Unlike surfactant phospholipids, there are no apparent sex differences in the expression of any of the surfactant apoproteins during late gestation. The differences observed during fetal lung maturation in the time of onset and changes in relative abundance among the three apoprotein mRNA imply that their genes may be differentially regulated in the developing rat lung.

Alveolar type II cells, surfactant protein A (SP-A), and the phospholipid components of surfactant in acute silicosis in the rat

Silica instillation causes a massive accumulation of surfactant phospholipids and the appearance of hypertrophic type II cells in the rat. We have examined the metabolic consequences of silica instillation with a special emphasis on surfactant protein A (SP-A), the major glycoprotein of surfactant. Fourteen days after instillation of 10 mg of silica, the amount of phospholipids in lavage increased 14-fold and the amount of SP-A increased 10-fold. The phospholipid composition of lavage material from silica-treated animals was altered by a reduction in the percentage of phosphatidylglycerol and an increase in phosphatidylinositol. The percentage of saturated phosphatidylcholine did not change. Type II cells isolated from rats treated with silica could be separated into cells of normal size and of increased size by centrifugal elutriation. There was an increase in phospholipid and SP-A content in the larger type II cells isolated from silica-treated rats relative to type II cells from control rats (by 45% and 70%, respectively, when expressed per micrograms protein; p less than 0.01). Activities of the phospholipid biosynthetic enzymes cholinephosphate cytidyltransferase, lysophosphatidylcholine acyltransferase, and phosphatidylglycerol phosphate synthetase increased (nmol/min/mg cell protein) in the hypertrophic type II cells relative to type II cells from control rats (by 40%, 112%, and 95%, respectively, p less than 0.05). Incorporation of (1-14C)-acetate was also increased in hypertrophic type II cells relative to type II cells from control rats (by 43%, p less than 0.05). The only difference in the distribution of acetate incorporated into individual lipids was a slight increase in the percentage incorporated into phosphatidylinositol. Although the increase in phosphatidylcholine found in the lavage could be due to increased synthesis as reflected by the changes in enzymatic activity and rate of acetate incorporation, the reduction in phosphatidylglycerol in lavage and in type II cells could not be explained simply by a reduction in synthesis on the basis of available data. There was a marked increase in SP-A content in lavage and in type II cells isolated from silica-treated rats without a significant change in the relative abundance of SP-A mRNA. This dissociation of SP-A mRNA abundance and apoprotein content suggests that factors other than transcription may be important for the observed accumulation of SP-A in silica-treated rats. We conclude that the phospholipidosis and proteinosis that occur subsequent to silica instillation in the rat lung are not solely attributable to increase in the rates of synthesis of these components.