Regulation of pulmonary surfactant apoprotein SP 28-36 gene in fetal human lung

The Yin and Yang of the oxytocin and stress systems: opposites, yet interdependent and intertwined determinants of lifelong health trajectories

During parturition and the immediate post-partum period there are two opposite, yet interdependent and intertwined systems that are highly active and play a role in determining lifelong health and behaviour in both the mother and her infant: the stress and the anti-stress (oxytocin) system. Before attempting to understand how the environment around birth determines long-term health trajectories, it is essential to understand how these two systems operate and how they interact. Here, we discuss together the hormonal and neuronal arms of both the hypothalamic-pituitary-adrenal (HPA) axis and the oxytocinergic systems and how they interact. Although the HPA axis and glucocorticoid stress axis are well studied, the role of oxytocin as an extremely powerful anti-stress hormone deserves more attention. It is clear that these anti-stress effects depend on oxytocinergic nerves emanating from the supraoptic nucleus (SON) and paraventricular nucleus (PVN), and project to multiple sites at which the stress system is regulated. These, include projections to corticotropin releasing hormone (CRH) neurons within the PVN, to the anterior pituitary, to areas involved in sympathetic and parasympathetic nervous control, to NA neurons in the locus coeruleus (LC), and to CRH neurons in the amygdala. In the context of the interaction between the HPA axis and the oxytocin system birth is a particularly interesting period as, for both the mother and the infant, both systems are very strongly activated within the same narrow time window. Data suggest that the HPA axis and the oxytocin system appear to interact in this early-life period, with effects lasting many years. If mother-child skin-to-skin contact occurs almost immediately postpartum, the effects of the anti-stress (oxytocin) system become more prominent, moderating lifelong health trajectories. There is clear evidence that HPA axis activity during this time is dependent on the balance between the HPA axis and the oxytocin system, the latter being reinforced by specific somatosensory inputs, and this has long-term consequences for stress reactivity.

Association between Thyroid Function and Respiratory Distress Syndrome in Preterm Infants

Thyroid hormones are known to influence the production and secretion of pulmonary surfactant. The objective of this study was to explore the relationship between respiratory distress syndrome (RDS) and thyroid hormones. This was a retrospective study of preterm infants at 24−33 weeks gestational age from April 2017 to February 2019. T3, free T4 (fT4), and thyroid-stimulating hormone (TSH) were measured 1, 3, and 6 weeks after birth. Multivariate logistic regression analyses were performed to determine the relationship between RDS and TSH. A total of 146 infants were enrolled. Of these, 60 had RDS, 72 had no RDS, and 14 were excluded. T3 and TSH were lower in the RDS groups (p < 0.05) on the day of birth. Multivariate logistic regression analysis indicated that lower serum TSH levels immediately after birth were associated with a higher incidence of RDS (OR, 0.89; 95% CI, 0.81−0.97). The TSH level was associated with the incidence of RDS. This suggests that suppression of the hypothalamus−pituitary axis function contributes to RDS, which is the result of surfactant deficiency.

Differential Regulation of Human Surfactant Protein A Genes, SFTPA1 and SFTPA2, and Their Corresponding Variants

The human SFTPA1 and SFTPA2 genes encode the surfactant protein A1 (SP-A1) and SP-A2, respectively, and they have been identified with significant genetic and epigenetic variability including sequence, deletion/insertions, and splice variants. The surfactant proteins, SP-A1 and SP-A2, and their corresponding variants play important roles in several processes of innate immunity as well in surfactant-related functions as reviewed elsewhere [1]. The levels of SP-A have been shown to differ among individuals both under baseline conditions and in response to various agents or disease states. Moreover, a number of agents have been shown to differentially regulate SFTPA1 and SFTPA2 transcripts. The focus in this review is on the differential regulation of SFTPA1 and SFTPA2 with primary focus on the role of 5′ and 3′ untranslated regions (UTRs) and flanking sequences on this differential regulation as well molecules that may mediate the differential regulation.

Role of collectins and complement protein C1q in pregnancy and parturition

Collectins such as surfactant proteins SP-A, SP-D, and mannan-binding lectin (MBL), as well as complement protein C1q are evolutionarily conserved innate immune molecules. They are known to opsonize a range of microbial pathogens (bacteria, fungi, virus, and parasites) and trigger effector clearance mechanisms involving phagocytosis and/or complement activation. Collectins and C1q have also attracted attention in studies involving pregnancy as they are expressed in the female reproductive tissues during pregnancy; a unique state of immune suppression with increased susceptibility to infectious diseases. Recent studies are beginning to unravel their functional significance in implantation, placentation, pregnancy maintenance and parturition in normal and adverse pregnancies. Collectins and C1q, expressed in gestational tissues during pregnancy, might alter the status of mother's immune response to the allogenic fetus and the microenvironment, thereby serving as important regulators of fetus-mother interaction. Here, we discuss the functional roles that have been assigned to SP-A, SP-D, MBL and C1q in pregnancy and parturition.

The critical importance of the fetal hypothalamus-pituitary-adrenal axis

The fetal hypothalamus-pituitary-adrenal (HPA) axis is at the center of mechanisms controlling fetal readiness for birth, survival after birth and, in several species, determination of the timing of birth. Stereotypical increases in fetal HPA axis activity at the end of gestation are critical for preparing the fetus for successful transition to postnatal life. The fundamental importance in fetal development of the endogenous activation of this endocrine axis at the end of gestation has led to the use of glucocorticoids for reducing neonatal morbidity in premature infants. However, the choice of dose and repetition of treatments has been controversial, raising the possibility that excess glucocorticoid might program an increased incidence of adult disease (e.g., coronary artery disease and diabetes). We make the argument that because of the critical importance of the fetal HPA axis and its interaction with the maternal HPA axis, dysregulation of cortisol plasma concentrations or inappropriate manipulation pharmacologically can have negative consequences at the beginning of extrauterine life and for decades thereafter.

Comparison of the effects of betamethasone and dexamethasone on surfactant protein A mRNA expression in human lung cells

OBJECTIVE

While prenatal administration of synthetic corticosteroids stimulates both fetal lung development and expression of pulmonary surfactant, the specific effects may depend on the corticosteroid formulation used. We compared the dose-dependent effects of various concentrations of two synthetic corticosteroids, betamethasone and dexamethasone, on steady state levels of surfactant protein A (SP-A) mRNA in human lung cells.

METHODS

Cultured human NCI-H441 bronchoalveolar epithelial cells were exposed to varying concentrations of betamethasone or dexamethasone (10^-7 to 10^-12 M) for 48 h alone or in combination with dibutyryl cAMP (1 mM), which augments surfactant protein gene expression. RNA was harvested and SP-A mRNA levels were quantified by real-time quantitative reverse transcriptase polymerase chain reaction analysis. Results were compared using the Kruskal-Wallis test.

RESULTS

A dose-dependent modification in SP-A mRNA levels was demonstrated with both dexamethasone and betamethasone. Cells treated with cAMP expressed higher levels of SP-A mRNA than untreated cells. A biphasic curve in the SP-A mRNA response to corticosteroids was elicited only in the presence of cAMP: at lower concentrations (10^-10 through 10^-12 M), SP-A mRNA levels were upregulated, whereas at higher concentrations (10^-7 and 10^-8 M), SP-A mRNA levels were reduced. Dexamethasone was more effective than betamethasone in inducing these changes.

CONCLUSIONS

Our results support a biphasic effect on SP-A mRNA levels after exposure to corticosteroids in combination with cAMP. At higher corticosteroid concentrations, betamethasone is less inhibitory than dexamethasone on SP-A mRNA.

Surfactant protein-A enhances ureaplasmacidal activity in vitro

BACKGROUND

Persistent respiratory tract colonization with Ureaplasma spp. in preterm infants is a significant risk factor for the development of the chronic lung disorder, bronchopulmonary dysplasia (BPD). Surfactant protein-A (SP-A), a lung collectin critical for bacterial clearance and regulating inflammation, is deficient in the preterm lung. In an experimental Ureaplasma-pneumonia model, infected SP-A deficient mice exhibited delayed bacterial clearance and an exaggerated inflammatory response compared to infected wild-type mice. The objective was to analyze the role of SP-A in Ureaplasma clearance in vitro.

SUBJECTS AND METHODS

We analyzed SP-A binding to Ureaplasma isolates and SP-A-mediated ureaplasmal phagocytosis and killing by cultured RAW 264.7 macrophages.

RESULTS

Calcium-dependent SP-A binding was similar among Ureaplasma isolates tested. Pre-incubation of RAW 264.7 cells with SP-A (10-50 μg/ml) enhanced phagocytosis of fluorescein-isothiocyanate (FITC)-labeled Ureaplasma. Surfactant protein-A also increased ureaplasmacidal activity of RAW 264.7 cells by 2.1-fold over 4 h. Pre-incubation of RAW 264.7 cells with 10 μg/ml SP-A reduced lipopolysaccharide (LPS) (100 ng/ml) and Ureaplasma (10(6) color changing units/ml)-stimulated release of tumor necrosis factor-α (TNF-α) by 46% and 43%, respectively, but did not affect transforming growth factor β(1) (TGFβ(1)) release.

CONCLUSIONS

These in vitro data confirm that SP-A is important in host defense to perinatally-acquired Ureaplasma infection.

Surfactant protein-A limits Ureaplasma-mediated lung inflammation in a murine pneumonia model

Ureaplasma respiratory tract colonization stimulates prolonged, dysregulated inflammation in the lungs of preterm infants, contributing to bronchopulmonary dysplasia (BPD) pathogenesis. Surfactant protein-A (SP-A), a lung collectin critical for bacterial clearance and regulating inflammation, is deficient in the preterm lung. To analyze the role of SP-A in modulating Ureaplasma-mediated lung inflammation, SP-A deficient (SP-A-/-) and WT mice were inoculated intratracheally with a mouse-adapted U. parvum isolate and indices of inflammation were sequentially assessed up to 28 d postinoculation. Compared with infected WT and noninfected controls, Ureaplasma-infected SP-A-/- mice exhibited an exaggerated inflammatory response evidenced by rapid influx of neutrophils and macrophages into the lung, and higher bronchoalveolar lavage TNF-alpha, mouse analogue of human growth-related protein alpha (KC), and monocyte chemotactic factor (MCP-1) concentrations. However, nitrite generation in response to Ureaplasma infection was blunted at 24 h and Ureaplasma clearance was delayed in SP-A-/- mice compared with WT mice. Coadministration of human SP-A with the Ureaplasma inoculum to SP-A-/- mice reduced the inflammatory response, but did not improve the bacterial clearance rate. SP-A deficiency may contribute to the prolonged inflammatory response in the Ureaplasma-infected preterm lung, but other factors may contribute to the impaired Ureaplasma clearance.

Effects of Growth Factors on the Differentiation of Murine ESC into Type II Pneumocytes

We have previously shown that embryonic stem cells (ESC) can be directed to differentiate into alveolar type II cells by provision of a serum-free medium designed for in vitro maintenance of mature alveolar epithelial cells (small airway growth medium: SAGM), although the target cell yield was low. SAGM comprises a basal serum-free medium (SABM) plus a series of defined supplements. In order to try increase the proportion of pneumocytes in differentiated cultures, we aimed in this study to determine the effects on murine ESC of each of the individual growth factors in SAGM. In accordance with our previous reports, expression of surfactant protein C (SPC) and its mRNA was used to monitor differentiation of type II pneumocytes. Surprisingly, we found that addition of each factor separately to SABM decreased the expression of SPC mRNA when compared with the effect of SABM alone. Thus, it seems that the observed enhancement by SAGM of pneumocyte differentiation from murine ESC can, in fact, be attributed to the provision of a serum-free environment.

The effect of repeated umbilical cord occlusions on pulmonary surfactant protein mRNA levels in the ovine fetus

OBJECTIVES

In this study we sought to determine the effect of brief repeated umbilical cord occlusions (rUCO) on surfactant protein (SP) mRNA levels in the fetal sheep lung at two different gestational ages.

METHODS

Fourteen fetuses at 112 to 115 days' gestation (control n = 7, rUCO n = 7) and 15 fetuses at 130 to 133 days' gestation (control n = 7, rUCO n = 8) were studied over 4 successive days with rUCO of 90 seconds duration performed every 30 minutes for 3 to 5 hours each day in the rUCO animals. Blood samples were collected for corticotrophin (ACTH) and cortisol measurements. Animals were killed within 1 hour of the final cord occlusion. SP-A, -B, -C, and -D mRNA levels were determined in lung tissue using a ribonuclease protection assay.

RESULTS

Cord occlusions resulted in temporary increases in circulating ACTH on day 1 with both gestational ages, but the elevations were blunted by day 4. Plasma cortisol levels increased transiently with the larger effect being observed on day 4, in particular with the near-term group. With advancing gestational age there was a significant (P < .05) increase in the level of SP-A (control 112-115 days: 0.01 +/- 0.01 vs control 130-133 days: 0.07 +/- 0.02 fmol/mg RNA), SP -B (control 112-115 days: 0.02 +/- 0.01 vs control 130-133 days: 0.07 +/- 0.01 fmol/mg RNA) and SP-C (control 112-115 days: 0.13 +/- 0.09 vs control 130-133 days: 0.51 +/- 0.10 fmol/mg RNA), but not SP-D mRNA levels (control 112-115 days: 0.002 +/- 0.002 vs control 130-133 days: 0.01 +/- 0.002 fmol/mg RNA). At 112 to 115 days, there was no significant change in any of the SP mRNA levels following rUCO compared to controls. However, the same regime of rUCO at 130 to 133 days resulted in an 85% reduction in SP-A and SP-B mRNA content and a 66% reduction in SP-C mRNA levels compared to controls.

CONCLUSION

The surprising decrease in SP-A and SP-B mRNA levels, which contrasts with other studies, suggests intermittent asphyxial episodes impact differently on surfactant apoprotein mRNA expression than does prolonged hypoxia.

Current concepts on the pulmonary surfactant in infants

Surfactant has been a main topic of neonatology in the last 20 years. Many studies have been conducted since the discovery of its role in the pathogenesis of respiratory distress syndrome and the knowledge on its composition and metabolism has become complex. In this article we review the current concepts of its metabolism, ways of acting, properties of its proteins and activities other than the ability of reducing surface tension within the lung as a basis to understand the development of disease in case of its deficiency.

Human SP-A 3'-UTR variants mediate differential gene expression in basal levels and in response to dexamethasone

Human surfactant protein A (SP-A) is encoded by two genes (SP-A1, SP-A2), and each is identified with several alleles. SP-A is involved in normal lung function, innate immunity, inflammatory processes, and is regulated by glucocorticoids. We investigated the role of 3'-untranslated region (UTR) of 10 SP-A variants on gene expression using transient transfection of 3'-UTR constructs in the human lung adenocarcinoma cell line NCI-H441. We found: 1) both basal mRNA and protein levels of the reporter gene of SP-A 3'-UTR constructs are significantly (P < 0.01) reduced compared with controls (vector pGL3 and surfactant protein B pGL3) and that differences exist among alleles; and 2) after dexamethasone (Dex) treatment (100 nM for 16 h), mRNA was reduced (31-51%). Seven alleles showed a significant decrease (P < 0.05) in mRNA, and three did not. Reporter activity was also decreased, from 17% (1A(1)) to 38% (1A), with six alleles showing a significant decrease. The data indicate that the 3'-UTR of SP-As play a differential role in SP-A basal expression and in response to Dex. Therefore, a careful consideration of individual use of steroid treatment may be considered.

Intratracheal administration of glucocorticoids using surfactant as a vehicle

1. Glucocorticoids are an effective treatment in the amelioration of chronic lung disease in neonates. However, systemic administration of glucocorticoids to neonates is associated with significant side-effects that preclude them as an early intervention to prevent onset of the condition. Conversely, local intratracheal administration of glucocorticoids may prevent inflammatory insult to the lungs without the development of systemic side-effects. We therefore investigated whether local intratracheal delivery of corticosteroids could be facilitated using surfactant as a vehicle. 2. Addition of dexamethasone to either diluted or commercial artificial surfactant, Survanta (Abbott Industries, Sydney, NSW, Australia), did not alter the surface properties of the surfactant. 3. After intratracheal instillation to rats, radiolabelled dexamethasone in Survanta was well distributed throughout all four lobes of the lungs. A concentration gradient of the steroid was observed between the root and the peripheral sections of all lobes. 4. Our results suggest that surfactant is an effective vehicle for intratracheal delivery of glucocorticoids. Moreover, we propose that prophylactic intratracheal administration of glucocorticoids administered shortly after birth may prevent inflammatory insult to the lungs and thereby reduce the likelihood of chronic lung disease developing.

Members of the C/EBP transcription factor family stimulate expression of the human and rat surfactant protein A (SP-A) genes

Members of the CCAAT enhancer binding protein (C/EBP) transcription factor family were detected in fetal lung of both human and rat. In rat lung, the level of C/EBPs increased with time of gestation, peaking around birth. In adult rat lung, C/EBPs were localized to the alveolar type II cells. The effect of C/EBPs on pulmonary surfactant protein A (SP-A), which is also expressed late in gestation, was investigated. In contrast to control plasmids, C/EBP delta expressing plasmids reversed the action of a transcriptional silencer just upstream of the rat SP-A promoter. In order to test the effect of C/EBPs on endogenous SP-A gene expression, cells that express SP-A were exposed to a phosphorothioate-substituted, double-stranded oligonucleotide matching the consensus C/EBP binding site (decoy oligonucleotide) at concentrations from 0.5 to 10 microM for 72 h. A mutant oligonucleotide with an 8-base pair (bp) substitution served as a control. The decoy oligonucleotide reduced SP-A mRNA as much as 75% compared to a mutant oligonucleotide both in the human lung cell line, NCI-H441, and in primary human fetal alveolar type II cells. The data indicate that C/EBPs facilitate SP-A gene expression, possibly by overcoming transcriptional silencing.

Could a combined administration of dexamethasone and 3,5-dimethyl-3'-isopropyl-L-thyronine (DIMIT) be a more effective alternative to dexamethasone alone in the prevention of RDS?

OBJECTIVE

To test whether the combined application of dexamethasone (DEXA) and 3,5-dimethyl-3'-isopropyl-L-thyronine (DIMIT) induces the synthesis of surfactant protein A (SP-A) mRNA at a higher rate than both substances given alone?

STUDY DESIGN

Organoid culture of fetal rat lungs (Wistar rats; day 19 of gestation) was prepared. After 48h of incubation we added DEXA (10(-5), 10(-7), 10(-8) and 10(-9)mol/l), DIMIT (10(-5), 10(-7) and 10(-9)mol/l) and the combination of DEXA in 10(-8)mol/l with various concentrations of DIMIT. After another 48h of incubation, northern blot and hybridization with a 32P-labeled SP-A cDNA probe was performed. One-way-variance-analysis with a Scheffé-test, Levene-test and one-sample-t-test were used for statistical analysis.

RESULTS

DEXA alone above 10(-8)mol/l resulted in a significant increase, DIMIT resulted in a decrease of SP-A mRNA induction. Combined application of DIMIT and DEXA resulted in a significant increase compared to the controls. Compared to DEXA alone in 10(-8)mol/l, we found an increased induction, but the data were not significant.

CONCLUSIONS

The combined application of DEXA and DIMIT shows a higher induction of SP-A mRNA than both drugs given alone.

Primary lung tumors in mice as an aid for understanding, preventing, and treating human adenocarcinoma of the lung

Primary lung tumors in mice have morphologic, histogenic, and molecular features similar to human lung adenocarcinoma, and in particular, the bronchiolo-alveolar carcinoma subtype. Because of this, and because of the genetic homology between man and mouse and the ease of genetic manipulations in mice, this model system is receiving intense research attention. This review is intended to be informative to clinical investigators, and describes features of this model, how it is being used for translational research, and points out additional avenues of study that could have practical benefits, such as application for identifying novel therapeutic strategies.

Surfactant protein A (SP-A): the alveolus and beyond

Surfactant protein A (SP-A) is the major protein component of pulmonary surfactant, a material secreted by the alveolar type II cell that reduces surface tension at the alveolar air-liquid interface. The function of SP-A in the alveolus is to facilitate the surface tension-lowering properties of surfactant phospholipids, regulate surfactant phospholipid synthesis, secretion, and recycling, and counteract the inhibitory effects of plasma proteins released during lung injury on surfactant function. It has also been shown that SP-A modulates host response to microbes and particulates at the level of the alveolus. More recently, several investigators have reported that pulmonary surfactant phospholipids and SP-A are present in nonalveolar pulmonary sites as well as in other organs of the body. We describe the structure and possible functions of alveolar SP-A as well as the sites of extra-alveolar SP-A expression and the possible functions of SP-A in these sites.

Role of transcription factors in fetal lung development and surfactant protein gene expression

Branching morphogenesis of the lung and differentiation of specialized cell populations is dependent upon reciprocal interactions between epithelial cells derived from endoderm of embryonic foregut and surrounding mesenchymal cells. These interactions are mediated by elaboration and concerted actions of a variety of growth and differentiation factors binding to specific receptors. Such factors include members of the fibroblast growth factor family, sonic hedgehog, members of the transforming growth factor-beta family, epidermal growth factor, and members of the platelet-derived growth factor family. Hormones that increase cyclic AMP formation, glucocorticoids, and retinoids also play important roles in branching morphogenesis, alveolar development, and cellular differentiation. Expression of the genes encoding these morphogens and their receptors is controlled by a variety of transcription factors that also are highly regulated. Several of these transcription factors serve dual roles as regulators of genes involved in early lung development and in specialized functions of differentiated cells. Targeted null mutations of genes encoding many of these morphogens and transcription factors have provided important insight into their function during lung development. In this chapter, the cellular and molecular mechanisms that control lung development are considered, as well as those that regulate expression of the genes encoding the surfactant proteins.

Development of the pulmonary surfactant system in two oviparous vertebrates

In birds and oviparous reptiles, hatching is often a lengthy and exhausting process, which commences with pipping followed by lung clearance and pulmonary ventilation. We examined the composition of pulmonary surfactant in the developing lungs of the chicken, Gallus gallus, and of the bearded dragon, Pogona vitticeps. Lung tissue was collected from chicken embryos at days 14, 16, 18 (prepipped), and 20 (postpipped) of incubation and from 1 day and 3 wk posthatch and adult animals. In chickens, surfactant protein A mRNA was detected using Northern blot analysis in lung tissue at all stages sampled, appearing relatively earlier in development compared with placental mammals. Chickens were lavaged at days 16, 18, and 20 of incubation and 1 day posthatch, whereas bearded dragons were lavaged at day 55, days 57-60 (postpipped), and days 58-61 (posthatched). In both species, total phospholipid (PL) from the lavage increased throughout incubation. Disaturated PL (DSP) was not measurable before 16 days of incubation in the chick embryo nor before 55 days in bearded dragons. However, the percentage of DSP/PL increased markedly throughout late development in both species. Because cholesterol (Chol) remained unchanged, the Chol/PL and Chol/DSP ratios decreased in both species. Thus the Chol and PL components are differentially regulated. The lizard surfactant system develops and matures over a relatively shorter time than that of birds and mammals. This probably reflects the highly precocial nature of hatchling reptiles.

Developmental and glucocorticoid regulation of surfactant protein mRNAs in preterm lambs

Glucocorticoid treatment increases content of surfactant protein (SP) A and SP-B in lung tissue and lavage fluid of preterm lambs. To investigate this process, we determined the ontogeny and glucocorticoid induction of SP mRNAs. In separate treatment protocols, each with its own controls, sheep were injected with betamethasone 15 h, 48 h, or weekly for 1-4 doses before preterm delivery. Using ovine SP cDNAs, we found an increase equal to or more than threefold in basal levels of all three SP mRNAs between 125 days and term. After betamethasone treatment, SP-B and SP-C mRNA levels increased by 15 h and all SP mRNAs were elevated after 24 h (>/=2-fold); mRNA levels in fetuses delivered 1-3 wk after betamethasone were not different from control. We conclude that in vivo betamethasone rapidly induces a coordinated increase in SP mRNAs, which is fully reversible within 7 days despite repetitive doses of betamethasone. Similar increases in mRNA and protein contents for SP-A and SP-B suggest that glucocorticoid regulation of these SPs in vivo is primarily pretranslational.

Hormonal regulation and cellular localization of fatty acid synthase in human fetal lung

Fatty acid synthase (FAS; EC 2.3.1.85) supplies de novo fatty acids for pulmonary surfactant synthesis, and FAS gene expression is both developmentally and hormonally regulated in the fetal lung. To further examine hormonal regulation of FAS mRNA and to determine the cellular localization of FAS gene expression, we cultured human fetal lungs (18-22 wk gestation) as explants for 1-4 days in the absence (control) or presence of glucocorticoid [dexamethasone (Dex), 10 nM] and/or cAMP agents (8-bromo-cAMP, 0.1 mM and IBMX, 0.1 mM). FAS protein content and activity increased similarly in the presence of Dex (109 and 83%, respectively) or cAMP (87 and 111%, respectively), and responses were additive in the presence of both hormones (230 and 203%, respectively). With a rabbit anti-rat FAS antibody, FAS immunoreactivity was not detected in preculture lung specimens but appeared in epithelial cells lining the tubules with time in culture. Dex and/or cAMP markedly increased staining of epithelial cells, identified as type II cells, whereas staining of mesenchymal fibroblasts was very low under all conditions. With in situ hybridization, FAS mRNA was found to be enriched in epithelial cells lining the alveolar spaces, and the reaction product increased in these cells when the explants were cultured with the hormones. The increased FAS mRNA content in the presence of Dex and/or cAMP is primarily due to increased stabilization of mRNA, although Dex alone increased the transcription rate by approximately 30%. We conclude that hormonal treatment of cultured human fetal lungs increases FAS gene expression primarily by increasing stability of the message. The induction of FAS during explant culture and by hormones occurs selectively in type II epithelial cells, consistent with the regulatory role of this enzyme in de novo synthesis of fatty acid substrate for surfactant synthesis in perinatal lungs.

Transcriptional activation and protein binding by two regions of the rat surfactant protein A promoter

Surfactant protein A (SP-A) is expressed in lung alveolar type II cells and bronchiolar Clara cells. We have identified two active regions in the promoter of the rat SP-A gene by deletion analysis of a plasmid containing 163 bp before the start of transcription (-163 bp), linked to a reporter gene. Constructs were transfected into lung cell lines derived from each of the cell types that produces SP-A. We found a novel region of promoter activity at approximately 90 bp before the transcriptional start (SP-A(-90)). Mutation of four nucleotides in SP-A(-90) that are highly conserved among species (-92 to -89 bp) decreased expression of the SP-A construct by approximately 50% in both cell lines. Electrophoretic mobility shift analysis showed specific binding to SP-A(-90) by nuclear proteins from the cell lines, as well as from rat lung and liver. The electrophoretic mobility of the bands shifted by lung nuclear proteins changed late in fetal development. Although in the Clara cell line no reduction of promoter activity was seen on deletion of the region upstream of SP-A(-90), in the type II cell line, deletion of residues -163 to -133 did reduce activity by approximately 50%. This region contains a recognition element for thyroid transcription factor-1 (TTF-1). Endogenous TTF-1 binding activity was substantially higher in the type II cell line than in the Clara cell line, but cotransfection of a TTF-1 expression plasmid enhanced expression of the SP-A construct better in the Clara cell line than in the type II cell line. These results suggest that the recognition element for TTF-1 has varying activity in the lung cell lines of different origin due to the availability of TTF-1.

SP-A 3'-UTR is involved in the glucocorticoid inhibition of human SP-A gene expression

The synthetic glucocorticoid dexamethasone has a major inhibitory effect on human surfactant protein A1 (SP-A1) and SP-A2 gene expression that occurs at both the transcriptional and posttranscriptional levels. Toward the identification of cis-acting elements that may be involved in the dexamethasone regulation of SP-A mRNA stability, chimeric chloramphenicol acetyltransferase (CAT) constructs that contained various portions of SP-A1 or SP-A2 cDNA in place of the native CAT 3'-untranslated region (UTR) were transiently transfected into the lung adenocarcinoma cell line NCI-H441. CAT activity was reduced in NCI-H441 cells by exposure to 100 nM dexamethasone only for the chimeric CAT constructs that contained the SP-A 3'-UTR. Moreover, the inhibitory response seen with dexamethasone was greater for the 3'-UTR derived from the SP-A1 allele 6A3 than with the 3'-UTR derived from either the SP-A1 allele 6A2 or SP-A2 allele 1A0, indicating differential regulation between SP-A genes and/or alleles.

Glucocorticoid inhibition of human SP-A1 promoter activity in NCI-H441 cells

Glucocorticoids have complex effects on human surfactant protein (SP) SP-A1 and SP-A2 gene expression that occur at both transcriptional and post-transcriptional levels. In the lung adenocarcinoma cell line NCI-H441, dexamethasone causes a dose-dependent decrease in total SP-A mRNA levels and inhibits SP-A gene transcription. In this study, a deletional analysis of the SP-A1 promoter was performed in order to identify cis-acting elements that mediate dexamethasone responsiveness in NCI-H441 cells. The region -32/+63 relative to the start of SP-A1 transcription mediated both basal promoter activity and dexamethasone repression of transcription. Removal of the region +18/+63 abolished dexamethasone responsiveness, indicating that sequences within this region are necessary for the inhibitory effect. Furthermore, the region -32/+63 formed a sequence-specific DNA-protein complex with NCI-H441 nuclear extract. This DNA-protein complex was induced by dexamethasone exposure and its formation was mediated partially by sequences within the region +26/+63.

Animal models of CRH deficiency

Corticotropin-releasing hormone (CRH), the major regulator of hypothalamic-pituitary-adrenal (HPA) axis, was first isolated due to its ability to stimulate the release of adrenocorticotropic hormone from the anterior pituitary. Later, it was also found to have also a wide spectrum of actions within the central nervous system and the periphery. Studies with pharmacological administration of this peptide and/or antagonists and antibody neutralization techniques have yielded important information concerning the physiological relevance of CRH. The development of CRH knockout mice (CRH KO) has been an important tool for addressing the physiologic and pathologic roles of CRH. This review describes the phenotype of CRH-deficient mice, as well as the use of this model to study the roles of CRH on fetal development and postnatal life. The role of CRH in prenatal development and postnatal regulation of the HPA axis, in activation of the reproductive system during stress, and in modulation of the immune function will be discussed. The review concludes with a comparison of CRH KO mice with other models of CRH deficiency.

Surfactant protein-A: new insights into an old protein--II

Pulmonary surfactant is a lipoprotein substance that lines the lungs and helps reduce surface tension. Surfactant associated protein-A (SP-A) is the most abundant non-serum protein in pulmonary surfactant. This complex glycoprotein aids in the synthesis, secretion and recycling of surfactant phospholipids, and facilitates the reduction of surface tension by surfactant phospholipids. Recent evidence has highlighted the role of SP-A in the innate immune system present in the lung. SP-A may play a major role in defense against pathogens by interacting with both infectious agents and the immune system. Factors that affect fetal lung maturation, e.g. gestational age and hormones regulate SP-A gene expression. Mediators of immune function also regulate SP-A levels. A number of lung disorders, including infectious diseases and respiratory distress syndrome are associated with abnormal alveolar SP-A levels. SP-A can no longer be called a lung-specific protein, since it has recently been detected in other tissues. In most species, SP-A is encoded by a single gene, however in humans it is encoded by two, very similar genes. Models for the structure of the human SP-A protein molecule have been proposed, suggesting that the mature alveolar SP-A molecule is composed of both gene products. The study of SP-A may provide information helpful in understanding disease processes and formulating new treatment modalities.

Human surfactant proteins A1 and A2 are differentially regulated during development and by soluble factors

An RT-PCR method for the relative quantitation of the mRNAs for human surfactant protein (SP) A1 and SP-A2 was developed, verified, and then utilized to determine the relative levels of these mRNAs in fetal and adult lung samples in vivo, as well as in cultured human fetal lung explants and H441 cells. For the cultured tissue and cells, we assessed the effects of a variety of soluble factors known to modulate total SP-A. Comprehensive analysis revealed many significant findings, including the following: both mRNAs were expressed as early as 15 wk of gestation; throughout midgestation, SP-A1 was present at higher levels than SP-A2, with an average ratio of 30:1. In the adult lung, SP-A1 mRNA was present at lower levels than SP-A2, with a ratio of 0.4:1, whereas in H441 cells, the ratio was 0.85:1. In fetal lung cultured for 4 days, both mRNAs increased, with a greater increase in SP-A2 (97-fold) than in SP-A1 (15-fold), resulting in a final ratio of 4:1. Differential regulation was demonstrated for 8-(4-chlorophenylthio)-cAMP, interferon (IFN)-gamma, tumor necrosis factor-alpha, and transforming growth factor (TGF)-beta in the human fetal lung explant system, with SP-A2 being more affected, and for IFN-gamma and TGF-beta in the H441 cells, where SP-A1 showed greater regulation. Of the soluble factors tested, IFN-gamma and TGF-beta had the most potent and consistent effects in both systems.

Collectins and pulmonary host defense

The surfactant-associated proteins SP-A and SP-D are members of a family of collagenous host defense lectins, designated collectins. There is increasing evidence that these pulmonary epithelial-derived proteins are important components of the innate immune response to microbial challenge, and that they participate in other aspects of immune and inflammatory regulation within the lung. The collectins bind to glycoconjugates and/or lipid moieties expressed by a wide variety of microorganisms and certain other organic particles in vitro. Although binding may facilitate microbial clearance through aggregation or other direct effects on the organism, SP-A and SP-D also have the capacity to modulate leukocyte function and, in some circumstances, to enhance their killing of microorganisms. The biologic activity of cell wall components, such as gram-negative bacterial polysaccharides, may be altered by interactions with collectins. Complementary or cooperative interactions between SP-A and SP-D could contribute to the efficiency of this defense system. Collectins may play particularly important roles in settings of inadequate or impaired specific immunity. Acquired or genetic alterations in the levels of active proteins within the airspaces and distal airways may increase susceptibility to infection.

Glucocorticoid receptor mRNA and protein in fetal rat lung in vivo: modulation by glucocorticoid and androgen

Pulmonary glucocorticoid receptor (GR) is essential to timely preparation for the onset of breathing air at birth. We have previously used primary culture of late-gestation fetal rat lung cells to demonstrate differential regulation of GR by glucocorticoid depending on cell type. In this study, we hypothesized that the action of glucocorticoid on GR mRNA expression and protein elaboration in lung cells might be modulated by interactions present in vivo but not in primary culture. Given that male sex hormone (androgen) has an inhibitory effect on antenatal lung development, we also postulated that androgen would decrease antenatal lung GR. We report that antenatal maternal injection of the glucocorticoid dexamethasone (1 mg/kg) enhanced fetal lung cellular levels of GR mRNA and protein as assessed by in situ hybridization and immunocytochemistry (ICC), respectively. ICC was performed using polyclonal rabbit anti-human antibody that reacts with rat GR whether bound to ligand or not and does not interfere with GR binding to DNA. Levels of GR mRNA and protein were enhanced in cells throughout all areas of the lung tissue, suggesting that interactions occurring in intact tissue may override the previously reported direct inhibition by glucocorticoid of GR protein elaboration in isolated fetal rat lung epithelial cells. Furthermore, antenatal administration of the androgen 5alpha-dihydrotestosterone (0.2 mg/kg) reduced tissue levels of GR mRNA and protein, consistent with androgenic inhibition of antenatal lung development by decreasing GR. We conclude that glucocorticoids and androgens exert opposite effects on fetal lung GR.

Regulation of expression of human SP-A1 and SP-A2 genes in fetal lung explant culture

Human pulmonary surfactant protein A (SP-A) is genetically complex and its regulation may also be complex, reflecting genotypic variability. Fetal lung explants were used to study the regulation of the SP-A genes, SP-A1 and SP-A2, by dexamethasone, interferon, gamma (IFN gamma), cyclic 3',-5' adenosine monophosphate (cAMP), and tumor necrosis factor alpha (TNF alpha). For comparison, the mRNA levels of surfactant protein B (SP-B) and its response to test substances were also examined. Results showed: (a) In control culture total SP-A mRNA varied widely among explants (C.V. = 0.70) compared with SP-B (C.V. = 0.26) (b) IFN gamma significantly increased total SP-A mRNA but there were marked differences among fetal lungs in response to all treatments. (c) SP-A1 mRNA concentration is higher than SP-A2 in both control and treated explants. (d) SP-A1 alleles are inhibited to a greater degree by dexamethasone than SP-A2 alleles. The relative effect of cAMP and IFN gamma on SP-A1 and SP-A2 mRNA varied widely among explants. We conclude that SP-A genotype may account in part for the marked differences in SP-A mRNA concentration among fetal lungs and that the SP-A genes and/or alleles may be differentially regulated.

Organization of the human SP-A and SP-D loci at 10q22-q23. Physical and radiation hybrid mapping reveal gene order and orientation

The human surfactant protein (SP) A locus has been assigned to chromosome 10q22-q23 and consists of two very similar genes, SP-A1 and SP-A2, as well as a truncated pseudogene. SP-A belongs to the family of collagenous C-type lectins along with mannose binding protein (MBP) and SP-D, both of which have also been mapped to the long arm of chromosome 10. In this article we report the relative location and orientation of each of the SP-A and SP-D genomic sequences. Characterization of two overlapping genomic clones revealed that the SP-A pseudogene lies in a reverse orientation 15 kb away from the 5' side of SP-A1. This finding was verified by the amplification of the entire SP-A pseudogene/SP-A1 intergenic region using long-range polymerase chain reaction. The relative location of SP-A2 and SP-D was then ascertained by testing a number of sequence tagged sites against the Stanford TNG3 and G3 radiation hybrid panels. The radiation hybrid mapping data showed that both SP-A2 and SP-D are on the 5' side of SP-A1 at approximate distances of 40 kb and 120 kb, respectively. The SP-A and SP-D loci were also oriented relative to the centromere, with the overall order being: centromere-SP-D-SP-A2-pseudogene-SP-A1- telomere.

Site specificity of surfactant protein expression in airways of baboons during gestation

BACKGROUND

There are disparate reports concerning the presence of surfactant proteins in the airways of lung. The recent finding of SP-A in tracheobronchial epithelium and submucosal glands in lungs from second trimester humans has renewed interest in potential new functions of surfactant in lung biology.

METHODS

In situ hybridization studies were done to determine the distribution of SP-A, SP-B, and SP-C in baboon lung specimens from 60, 90, 120, 140, 160, and 180 (term) days of gestation and adults. Lungs from gestation controls were obtained at the time of hysterotomy and adult lungs at necropsy. Riboprobes used for in situ hybridization contained the entire coding regions for human SP-A, SP-B, and SP-C.

RESULTS

At 60 days, SP-C mRNA expression was evident in focal portions of primitive tubular epithelium but not bronchi. This distal pattern of SP-C mRNA expression persisted and was present in some epithelial cells of respiratory bronchioles at term. At 90 days, SP-A mRNA expression was present in the epithelium of trachea and large bronchi. SP-B mRNA expression was found in small bronchi, bronchioles, and distal tubular epithelium at 120 days of gestation. SP-A mRNA bronchiolar localization became evident at 140 days of gestation and alveolar type 2 cellular expression at 160 days of gestation. Abrupt transitions of surfactant protein expression were identified (e.g., SP-A mRNA-positive cells in the epithelium of large bronchi with adjoining SP-B mRNA expression in small bronchi and bronchioles).

CONCLUSIONS

Findings in the baboon indicate that there are well-delineated sites of surfactant protein mRNA expression in bronchial and bronchiolar epithelia. mRNA expressions of SP-A and SP-B are present in both bronchial and bronchiolar epithelium but at different sites, whereas SP-C expression is seen in loci of epithelial cells in respiratory bronchioles.

Primary cell culture of human type II pneumonocytes: maintenance of a differentiated phenotype and transfection with recombinant adenoviruses

Studies of the regulation of surfactant lipoprotein metabolism and secretion and surfactant protein gene expression have been hampered by the lack of a cell culture system in which the phenotypic properties of type II cells are maintained. We have developed a primary culture system that facilitates the maintenance of a number of morphologic and biochemical properties of type II pneumonocytes for up to 2 wk. Cells were isolated by collagenase digestion of midgestation human fetal lung tissue that had been maintained in organ culture in the presence of dibutyryl cyclic AMP (Bt2cAMP) for 5 days. The isolated cells were enriched for epithelial components by treatment with DEAE-dextran, plated on an extracellular matrix (ECM) derived from Madin-Darby canine kidney (MDCK) cells, and incubated at an air/liquid interface in a minimal amount of culture medium containing Bt2cAMP. The cell cultures were comprised of islands of round epithelial-like cells containing numerous dense osmiophilic granules, surrounded by sparse spindle-shaped cells with the appearance of fibroblasts. Ultrastructural examination revealed that the osmiophilic granules had the appearance of lamellar bodies, the distinguishing feature of type II pneumonocytes. Additionally, the cultures maintained elevated levels of SP-A gene expression for up to 2 wk. The expression of mRNAs encoding SP-A, SP-B, and SP-C were regulated in the cultured cells by glucocorticoids and cyclic AMP in a manner similar to that observed in fetal lung tissue in organ culture. The differentiated phenotype was most apparent when the cells were cultured at an air/liquid interface. In order to utilize the cultured type II cells for study of the effects of overexpression of various proteins and for promoter analysis, it is of essence to transfect DNA constructs into these cells with high efficiency. Unfortunately, we found the cells to be refractory to efficient transfer of DNA using conventional methods (i.e., lipofection, electroporation, or calcium phosphate-mediated transfection). However, replication-defective recombinant human adenoviruses were found to provide a highly efficient means of introducing DNA into the type II pneumonocytes. Furthermore, we observed in type II cell-enriched cultures infected with recombinant adenoviruses containing the lacZ gene under control of a cytomegalovirus promoter, that beta-galactosidase was expressed uniformly in the islands of type II cells and surrounding fibroblasts. By contrast, in cultures infected with recombinant adenoviruses containing the human growth hormone (hGH) gene under control of the SP-A gene promoter and 5'-flanking region, hGH was expressed only in the type II cells. Thus, this culture system provides an excellent means for identifying genomic elements that mediate type II cell-specific gene expression.

Transcriptional regulation of surfactant proteins SP-A and SP-B by phorbol ester

Phorbol esters such as 12-O-tetradecanoylphorbol-13-acetate (TPA) activate protein kinase C and have been previously shown to down-regulate surfactant proteins SP-A and SP-B in H441 adenocarcinoma cells. We used H441 cells and human fetal lung to further study the mechanism of TPA action and to examine physiologic relevance. In H441 cells, TPA (10 nM) treatment for 24 h decreased SP-A mRNA content to approximately 5% of control cells, with half-maximal effect at approximately 0.5 nM, and reduced SP-A gene transcription rate to 28% of control after 8 h exposure. In cells cultured in the presence of dexamethasone, which increases the low basal level of SP-B expression, TPA decreased both SP-B mRNA content (approximately 8% of control) and rate of transcription (7% of control). In cultured human fetal lung explants, TPA decreased SP-A and SP-B protein and mRNA in a time- and dose-dependent fashion, with half-maximal effect on mRNAs at approximately 3 nM and approximately 50% inhibition after 24 h of exposure, and similarly reduced SP-A and SP-B gene transcription (approximately 55% of control at 8-24 h). We conclude that TPA acts primarily at the level of gene transcription to down-regulate both SP-A and SP-B in H441 and fetal lung cells, and we speculate that inflammatory and other agents that act through PKC may modulate expression of the surfactant proteins and alter surfactant function in vivo.

Collectins: collectors of microorganisms for the innate immune system

Collectins are a group of multimeric proteins mostly consisting of 9-18 polypeptides organised into either 'bundle-of-tulips' or 'X-like' overall structures. Each polypeptide contains a short N-terminal segment followed by a collagen-like sequence and then by a C-terminal lectin domain. A collectin molecule is assembled from identical or very similar polypeptides by disulphide bonds at the N-terminal segment, formation of triple helices in the collagen-like region and clusters of three lectin domains at the peripheral ends of triple helices. These proteins can bind to sugar residues on microorganisms via the peripheral lectin domains and subsequently interact, via the collagen-like triple-helices, with receptor(s) on phagocytes and/or the complement system to bring about the killing and clearance of the targets without the involvement of antibodies. The collectins can also bind to phagocyte receptor(s) to enhance phagocytosis mediated by other phagocytic receptors. Lack, or low levels, of collectin expression can lead to higher susceptibility to infections, especially during childhood when specific immunity has not fully developed. Therefore, the collectins play important roles in the enhancement of innate immunity.

Effect of genotype on the levels of surfactant protein A mRNA and on the SP-A2 splice variants in adult humans

Human pulmonary surfactant protein A (SP-A) is encoded by two genes, SP-A1 and SP-A2, that exhibit coding sequence (allelic) and 5' splicing variability. In this report we determine the effect of the genetic variability within the SP-A1 and SP-A2 genes on the level of SP-A mRNAs and on the SP-A2 splicing variants in different individuals. We analysed mRNA specimens from 23 unrelated adults using genotype analysis, Northern analysis and primer extension, and made the following observations. (1) The level of SP-A mRNA varies among individuals (coefficient of variation = 0.49). One SP-A genotype (6A(2)6A(2)1A(0)1A0) appears to be associated with a low to moderate level of SP-A mRNA. (2) The SP-A1/SP-A2 mRNA ratio varies among individuals, from 0.94 (lowest) to 6.80 (highest) within the study population. One genotype appears to be associated with a moderate to high SP-A1/SP-A2 mRNA ratio and another with a low to moderate ratio. (3) There is no correlation between the level of SP-A mRNA and the SP-A1/SP-A2 mRNA ratio. (4) Variability in the ratio of the major SP-A2 splice variants among individuals results from nucleotide differences in the splice-recognition sequence of specific SP-A2 alleles. The SP-A mRNA levels, the SP-A1/SP-A2 mRNA ratio, and the ratio of the major SP-A2 splice variants have a genetic basis in that they vary depending upon the specific SP-A alleles present.

Changes in surfactant protein A mRNA levels in a rat model of insulin-treated diabetic pregnancy

Maternal diabetes during pregnancy is associated with increased risk of neonatal respiratory distress syndrome (RDS). Previous studies using rat models for the diabetic pregnancy have documented decreased amounts of surfactant protein mRNA in the lungs of fetuses. In this study, we measured fetal lung surfactant-associated protein A (SP-A) mRNA from diabetic rats treated with insulin by daily injection or osmotic pump. Lungs were taken from fetuses on gestational d 20, and RNA was isolated and subjected to Northern blotting and densitometry to quantify SP-A mRNA. Fetal lung SP-A mRNA from untreated diabetic pregnancies was 34 +/- 2.9% of control. Insulin treatment increased levels to 55 +/- 4.2% of control values. Fetal lung SP-A mRNA levels were affected by the timing, length, and effectiveness of insulin treatment. Although levels from all treatment groups were still less than control values, insulin treatment during the last 5 or 10 d of pregnancy resulted in a substantial increase in SP-A mRNA levels over those of from untreated diabetic pregnancies. However, fetuses from the group with insulin treatment for the entire pregnancy showed decreases in fetal SP-A mRNA levels. Although the mechanism(s) responsible for the effects of diabetes and its treatment on fetal SP-A expression remain unclear, it appears unlikely that hyperglycemia is the principal cause.

Marker proteins in the particulate fraction of third-trimester amniotic fluid

The present clinical evaluation of fetal lung maturity relies largely on the determination of the amniotic surfactant phospholipids phosphotidylglycerol, lecithin, and sphingomyelin, but there are many false negatives as well as false positives among diabetics. The use of other components of lung surfactant, namely, the hydrophobic surfactant proteins (SPs) has long been suggested as an alternative to the classical assay, but tests based on the detection of immunoreactive SP-A have not proved superior or supplanted phospholipid ratios as an index. This report investigates the proteins in a fraction of third-trimester human amniotic fluid (the particulate fraction) enriched in the SP complexes that form the surfactant monolayer. The proteins were analyzed by two-dimensional polyacrylamide gel electrophoresis and visualized by silver staining and immunoblotting. Eight proteins are of particular interest. Three novel proteins (termed AFPP-1, AFPP-4, and AFPP-8) and the alpha-fetoprotein/human serum albumin complex (AFPP-7) can be detected throughout the 28- to 38-week gestational window. The protein that is referred to as AFPP-2 could be identified as SP-A on the basis of immunologic cross-reactivity as well as size and charge characteristics. The time course of appearance of AFPP-2 was also followed in patients with Rh isoimmunization syndrome and was found to be the same as that seen for SP-A. The SP-A was detected as at least five major charged isoforms with multiple subisoforms of different molecular weight and can be distinguished from a related set of proteins (AFPP-5) that appear with a different time course but are possible precursors. Two other proteins (AFPP-3, AFPP-6), which are detectable inconsistently bear some similarity to others reported previously but not extensively characterized. These results define both constant and variable proteins of the particulate fraction of the amniotic fluid and indicate that certain protein isoforms are changing throughout the third trimester. These data enhance the possibility of the utilization of these proteins as markers of lung maturity in conditions such as maternal diabetes.

Surfactant protein A-directed toxin gene kills lung cancer cells in vitro

Human surfactant protein A (SPA) expression is considered a marker of respiratory epithelial differentiation. Non-small cell lung cancers (NSCLC) are respiratory epithelial derivatives, and it was previously shown that a minority of these cancers expressed SPA, presumably a consequence of their respiratory epithelial origin. In the studies reported here, SPA-I gene transcriptional regulatory sequences were localized to a 2.75-kb genomic 5'-flanking region fragment obtained by screening a human genomic library. The 2.75-kb fragment was used to direct a luciferase coding sequence transcriptionally within a plasmid construct. In plasmid transduction experiments, the SPA-directed luciferase plasmid produced significant luciferase activity in the SPA-expressing NSCLC cell line, H441, but only background levels in the non-SPA-expressing A549 cells. Because Northern blot analysis of resected NSCLC showed that the majority expressed SPA, an SPA-transcriptional targeting strategy was investigated using chimeric toxin genes comprising the coding sequence for herpes simplex virus thymidine kinase (HSV-TK) under transcriptional control of SPA or SV40 regulatory sequences. As expected, transduction of the constitutive, SV40-directed plasmid followed by ganciclovir treatment reduced numbers of both the A549 and H441 cells. In contrast, the SPA-directed plasmid reduced only the SPA-expressing H441 cells and had no significant effect on the A549 cells. The results of these in vivo experiments suggest the concept of transcriptionally directing toxin genes with SPA can produce targeted toxicity in NSCLC.

Conservation analysis of rat and human SP-A gene identifies 5' flanking sequences of rat SP-A that bind rat lung nuclear proteins

As an initial step toward understanding regulation of tissue-specific expression of SP-A, 5' flanking sequences of the rat SP-A gene and human SP-A I gene were cloned, sequenced, and compared using dot matrix analysis. Two regions were identified, each with a considerable degree of homology between the two species. One region was proximal to the TATAA box, at position -225/-17 in rats and -226/-36 in humans, and the other at position -1115/-1026 in rats and -938/-851 in humans. Studies in rats revealed the specific binding of rat lung nuclear proteins to each of the conserved 5' flanking regions identified in rat SP-A. Binding studies using the rat proximal (rPPS) or distal (rDPS) promoter segments, or overlapping fragments of these segments, with rat nuclear extracts detected the presence of a number (1-4) of lung-specific DNA/protein complexes. When nuclear proteins from liver, a nonexpressing tissue, were used the binding profile of certain nuclear proteins differed from that of the lung. These studies, taken together, suggest that sequences within identified conserved DNA segments in the 5' flanking region of the rat SP-A gene contribute to its tissue-specific expression in rats.

Secretion of surfactant protein A and phosphatidylcholine from type II cells of human fetal lung

Surfactant protein A (SP-A) appears to have a role in lung immune defense as well as generation and metabolism of the alveolar surface-active film. Previous studies indicated that lamellar bodies isolated from lung tissue had a relatively low content of SP-A and that exogenous SP-A was needed for rapid formation of a surface-active film in vitro. We therefore tested the hypothesis that SP-A was secreted from type II cells primarily by a pathway separate from lamellar bodies. Cells were isolated from explants of human fetal lung that had been cultured with hormones to promote differentiation of type II cells, and secretion of surfactant lipid and SP-A were compared. Cultured cells secreted labeled phosphatidylcholine in a nearly linear fashion for 48 h. Basal secretion of SP-A, assayed by enzyme-linked immunosorbent assay, was linear for only 12 h after plating of cells; during this time, there was no accumulation of intracellular SP-A. Addition of secretagogues (phorbol ester, calcium ionophore, and beta-adrenergic agonist) stimulated phosphatidylcholine secretion approximately 4-fold. In contrast, the secretion rate of SP-A was not significantly affected by secretagogues. These findings indicate that a relatively small amount of secreted SP-A (approximately 10%) is released with lamellar bodies. Most SP-A is released by constitutive secretion and may be important for both surfactant- and nonsurfactant-related functions.

Differential glucocorticoid regulation of the pulmonary hydrophobic surfactant proteins SP-B and SP-C

Glucocorticoids increase expression of the genes for the pulmonary surfactant-associated proteins SP-B and SP-C in fetal lung both in vivo and in vitro. To examine the mechanism of these effects, we studied induction of SP-B and SP-C mRNAs in human fetal lung cultured as explants. Both mRNA levels rose rapidly in response to 100 nM dexamethasone (Dex), with a faster response for SP-B: maximal levels of induction were achieved in < or = 12 h for SP-B (3.5-fold versus control) versus approximately 24 h for SP-C mRNA (35-fold versus control). Cycloheximide (2.5 micrograms/ml) did not affect glucocorticoid induction of SP-B mRNA but markedly decreased induction of SP-C mRNA. In control cultures, cycloheximide did not significantly reduce levels of either transcript. In nuclear run-on assays, Dex increased the rate of gene transcription for both SP-B (2.8 +/- 0.3-fold versus control, n = 4) and SP-C (10- to 30-fold). Using actinomycin D to assess mRNA stability, the t1/2 of SP-B mRNA was increased from 7.5 +/- 0.4 h to 18.8 +/- 2.9 h by Dex treatment (P < 0.05), whereas the t1/2 of SP-C mRNA was not affected (9.3 +/- 1.7 h versus 8.1 +/- 1.2 h; NS). A similar increase in SP-B mRNA t1/2 with Dex (from 6 h to 19 h) was observed in label-chase studies with [3H]uridine. We conclude that glucocorticoids regulate the hydrophobic surfactant proteins of alveolar type II cells by different mechanisms: induction of SP-B is a primary response and includes an increase in both transcription rate and mRNA stability, whereas induction of SP-C is a secondary process, requiring ongoing protein synthesis, involving increased transcription rate without a change in mRNA stability.

Developmental regulation of surfactant-associated proteins in rabbit fetal lung in vivo

The developmental regulation of the rabbit surfactant-associated proteins, SP-A, SP-B, and SP-C, was investigated using Northern blot analysis. These proteins comprise approximately 10% by weight of pulmonary surfactant, a lipoprotein secreted by type II cells that reduces surface tension at the air-alveolar interface. SP-A mRNA and SP-B mRNA were first detected in rabbit fetal lung at day 24 of gestation (term = 31 days), i.e., approximately two days prior to the appearance of lamellar bodies within differentiated alveolar type II cells. The relative abundance of SP-B mRNA detected on day 24 of gestation was greater than that of SP-A mRNA. Fetal lung SP-A mRNA and SP-B mRNA levels increased rapidly during the remainder of gestation, reaching a maximum at day 31 of gestation. The relative concentrations of SP-A mRNA and SP-B mRNA were decreased in day 2 neonatal and adult lung tissues when compared to the levels present in fetal lung tissue late in gestation. A 0.5-kb rabbit SP-C cDNA was generated using the reverse transcriptase-polymerase chain reaction and was found to have high sequence homology to the human and rat SP-C cDNA nucleotide sequences. The predicted amino acid sequence for the rabbit SP-C cDNA revealed strong conservation of a hydrophobic region close to the amino terminus of the SP-C protein. Fetal lung SP-C mRNA was detected at day 19 of gestation, the earliest time point examined in this study. SP-C mRNA levels gradually increased in fetal lung tissue until day 28 of gestation and then remained level throughout the remainder of gestation and in the day 2 neonatal and adult rabbit lung tissue. These results suggest that the developmental pattern of induction of mRNA for the surfactant-associated proteins, SP-A, SP-B, and SP-C, differ from each other and are different in several respects from the developmental patterns observed in fetal lung tissue of the rat and human species.

Localization of surfactant-associated proteins SP-A and SP-B mRNA in rabbit fetal lung tissue by in situ hybridization

Pulmonary surfactant is a lipoprotein substance, comprised of approximately 80% phospholipid and approximately 10% protein, that lowers surface tension at the air-alveolar aqueous interface. Surfactant is synthesized and secreted by alveolar type II epithelial cells where it is stored intracellularly in lamellar bodies. In the present study, we used the technique of in situ hybridization to localize the mRNA for two surfactant-associated proteins, SP-A and SP-B, in developing rabbit fetal lung tissue. We found that SP-A mRNA was first localized in rabbit fetal lung alveolar type II cells on day 26 of gestation, the time at which lamellar bodies are first observed within fetal lung type II cells. On day 28 of gestation, a very small amount of SP-A mRNA was also detectable in the epithelial cells of some bronchioles. In neonatal and adult rabbit lung tissue, SP-A mRNA was primarily restricted to alveolar type II cells; however, the epithelial cells of some bronchioles contained small amounts of SP-A mRNA. SP-B mRNA was first detected in cuboidal epithelial cells in the prealveolar region of the rabbit fetal lung tissue on day 24 of gestation, i.e., at least 2 days before the appearance of SP-A mRNA and lamellar bodies within differentiated alveolar type II cells. SP-B mRNA was detected in most bronchiolar epithelial cells of the rabbit fetal lung tissue at day 28 of gestation.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of surfactant-associated protein C (SP-C) mRNA in fetal rabbit lung tissue by in situ hybridization

Surfactant is a lipoprotein substance that is synthesized and secreted by alveolar type II epithelial cells and acts to reduce surface tension at the air-alveolar interface. SP-C is a 5,000-D molecular weight, hydrophobic, surfactant-associated protein. In the present study, we used a ribonuclease protection assay to show that SP-C mRNA is induced in rabbit fetal lung tissue early in development, increases in relative concentration as development proceeds, and is present in maximal concentration at term (31 days of gestation). We also used the technique of in situ hybridization to localize SP-C mRNA in fetal, neonatal, and adult rabbit lung tissue. SP-C mRNA was present in all of the epithelial cells of the prealveolar region of day 19 gestational age rabbit fetal lung tissue, i.e., about 7 days before the appearance of differentiated alveolar type II cells in the fetal lung tissue. By day 27 of gestation, SP-C mRNA was restricted to epithelial cells with the morphologic characteristics of alveolar type II cells. SP-C mRNA was not detected in bronchiolar epithelium at any stage of lung development. The intensity of SP-C mRNA hybridization in the prealveolar and alveolar type II epithelial cells increased as a function of gestational age and was maximal at term. The pattern of SP-C mRNA localization in neonatal and adult rabbit lung tissue was consistent with the restriction of SP-C gene expression to differentiated alveolar type II cells. Our data are suggestive that SP-C may serve some as yet unknown function early in lung development because it is present in fetal lung prealveolar epithelial cells much earlier in gestation than are differentiated, surfactant-producing alveolar type II cells.

Hormonal effects on the surfactant protein B (SP-B) mRNA in cultured fetal rat lung

Glucocorticoids, triiodothyronine (T3), and cyclic adenosine monophosphate (cAMP) have been shown previously to modulate phosphatidylcholine and surfactant protein A (SP-A) synthesis in fetal rat lung explant cultures. In this report, we have examined the hormonal regulation of the rat surfactant protein B (SP-B) mRNA to determine whether SP-B expression is coordinately regulated with the surfactant phospholipids or with SP-A. Dexamethasone (1 to 200 nM) and cAMP (200 microM) had a stimulatory effect on SP-B mRNA levels, whereas T3 tended to inhibit the accumulation of SP-B mRNA. In combination experiments, treatment with dibutyryl-cAMP (200 microM) and dexamethasone (100 nM) resulted in about a 22-fold increase, whereas dexamethasone or dibutyryl-cAMP alone produced 18- and 2-fold increases, respectively. When the cAMP analogue 8-bromo-cAMP (200 microM) was used in combination with dexamethasone, there was no significant difference between the combined effect and that of dexamethasone alone. T3 treatment, however, resulted in a significant reduction of the dexamethasone-induced stimulation from about a 22-fold to a 14-fold increase. Tissue in situ hybridization showed that dexamethasone stimulated the levels of SP-B mRNA in cells from both the alveolar and bronchiolar epithelium. These data indicate that there are differences in the hormonal regulation of the components of surfactant, suggesting that they are independently regulated.