Regulation Of Surfactant Protein Research Articles

Regulation of Surfactant Protein B Gene Expression in Bone Marrow-Derived Cells

While investigating the differentiation potential of bone marrow-derived cells, we previously demonstrated upregulated expression of the lung-related surfactant protein B (SP-B) gene in hematopoietic progenitor cells (HPCs) when they were cocultured with macerated lung tissue. During coculture, HPCs differentiated toward a dendritic-like myeloid cell phenotype (hematopoietic progenitor cell-derived dendritic-like cells [HPC-DCs]). However, immature dendritic cells (iDCs) cocultured under identical conditions did not express SP-B mRNA before or after coculture. We have now further examined the regulation of SP-B expression in HPC-DCs and iDCs. Of the transcription factors involved in SP-B gene expression, neither cell type expressed TTF-1, HNF3alpha, or HNF3beta, but both cell types expressed Sp1 and Sp3. Sp1 binding to the SP-B promoter was investigated in these cells. Three novel Sp1 binding motifs were identified in the mouse SP-B promoter. Using chromatin immunoprecipitation, it was demonstrated that Sp1 was bound to all three sites in HPC-DCs after coculture with lung tissue, but not in iDCs. We hypothesized that although genes from multiple lineages may be active in HPCs, gene silencing events, such as methylation, may subsequently occur to suppress expression of these genes in more mature myeloid cells, such as iDCs. Treatment with the demethylating agent 5-azacytidine resulted in expression of the SP-B gene in iDCs. These data indicate that tissue-specific transcription factors are not required to express the lung-related gene SP-B in hematopoietic progenitor cells. Furthermore, silencing events, such as methylation, may occur to suppress lung-related gene expression as progenitor cells become committed toward more mature hematopoietic cell phenotypes.

Glucocorticoid actions on airway epithelial responses in immunity: Functional outcomes and molecular targets

Research on the biology of airway epithelium in the last decades has progressively uncovered the many roles of this cell type during the immune response. Far from the early view of the epithelial layer simply as a passive barrier, the airway epithelium is now considered a central player in mucosal immunity, providing innate mechanisms of first-line host defense as well as facilitating adaptive immune responses. Alterations of the epithelial phenotype are primarily involved in the pathogenesis of allergic airways disease, particularly in severe asthma. Appreciation of the epithelium as target of glucocorticoid therapy has also grown, because of studies defining the pathways and mediators affected by glucocorticoids, and studies illustrating the relevance of the control of the response from epithelium in the overall efficacy of topical and systemic therapy with glucocorticoids. Studies of the mechanism of action of glucocorticoids within the biology of the immune response of the epithelium have uncovered mechanisms of gene regulation involving both transcriptional and posttranscriptional events. The view of epithelium as therapeutic target therefore has plenty of room to evolve, as new knowledge on the role of epithelium in immunity is established and novel pathways mediating glucocorticoid regulation are elucidated.

Regulation of surfactant protein D in the rodent prostate

BackgroundSurfactant protein D (SP-D) is an innate immune protein that is present in mucosal lined surfaces throughout the human body, including the male reproductive tract. In the present study, we characterized the regulation of SP-D expression in the mouse and rat prostate.MethodsReal time reverse transcriptase polymerase chain reaction (RT-PCR) and immunostaining were used to characterize SP-D mRNA and protein in the mouse male reproductive tract. In order to evaluate the effects of testosterone on SP-D gene expression, we measured SP-D mRNA levels via real time RT-PCR in prostates from sham-castrated mice and castrated mice. In addition, we used a rat prostatitis model in which Escherichia coli was injected into the prostate in vivo to determine if infection influences SP-D protein levels in the prostate.ResultsWe found that SP-D mRNA and protein are present throughout the mouse male reproductive tract, including in the prostate. We determined that castration increases prostate SP-D mRNA levels (~7 fold) when compared to levels in sham-castrated animals. Finally, we demonstrated that infection in the prostate results in a significant increase in SP-D content 24 and 48 hours post-infection.ConclusionOur results suggest that infection and androgens regulate SP-D in the prostate.

Regulation of surfactant protein D in the mouse female reproductive tract in vivo

Surfactant protein D (SP-D) plays a role in innate immunity in the lung and is expressed at many other mucosal surfaces throughout the human body. In this study, we show that SP-D mRNA and protein are present in the murine female reproductive tract; i.e. in the vagina, cervix, uterus and oviduct. SP-D protein is primarily localized to epithelial cells lining the genital tract and is also present in secretory material within the lumen of the uterus and cervix. The levels of SP-D mRNA in the uterus vary by a factor of 10 during the estrous cycle with peak levels present at estrus and the lowest levels at diestrus. In contrast, SP-D mRNA levels in the lung do not change during the estrous cycle. Since SP-D is an innate host defense protein present in the mouse reproductive tract, we studied the influence of infection on SP-D levels in vivo. We found that Chlamydia muridarum infection caused an increase in the SP-D protein content of reproductive tract epithelial cells. These data are suggestive that SP-D may play a role in innate immunity in the female reproductive tract in vivo.

Regulation of surfactant protein and defensin mRNA expression in cultured ovine type II pneumocytes by all‐trans retinoic acid and VEGF

Beta-defensins and surfactant proteins are components of the pulmonary innate immune system. Their gene expression is regulated by development, hormones, growth and immunoregulatory factors. It was our hypothesis that growth and differentiation factors such as all-trans retinoic acid (RA) and vascular endothelial growth factor (VEGF) may affect expression of selected innate immune genes by respiratory epithelial cells. Ovine JS7 cells (alveolar type II pneumocytes) were incubated in serum-free Dulbecco's modified Eagle's medium (DMEM) complete media that contained: no treatment (negative control), RA (500 nM), or VEGF (100 ng/ml) for 6, 12 or 24 h incubation. Total RNA was isolated, cDNA synthesized, and relative mRNA levels of surfactant protein A (SP-A) and SP-D, and sheep beta-defensin-1 (SBD-1) were determined by real-time reverse transcriptase-polymerase chain reaction (RT-PCR). Cells had significantly increased expression of SP-D mRNA at 6 h and 24 h, decreased expression of SP-A mRNA at 12 h, and unchanged levels of SBD-1 mRNA after the treatment with RA compared with their respective negative controls. VEGF did not alter the expression of the three innate immune genes. These findings suggest that SP-A and SP-D have different transcription regulation pathways, and that expression of SBD-1 is not inducible by RA similar to its human homolog HBD-1. The lack of changes induced by VEGF treatment suggests that VEGF does not have a direct effect on epithelial cells, but may affect gene expression indirectly.

Gene Expression of Surfactant Protein A mRNA of the Lung in Endotoxin and Thiourea Treated Rats

Background : The surfactant protein A(SP-A) is important in the regulation of surfactant secretion, synthesis and recycling. Since the acute respiratory distress syndrome(ARDS) is usually viewed as the functional and morphological expression of a similar underlying lung injury caused by a variety of insults and since abnormalities in surfactant function have been described in ARDS, the authors investigated the different effects of endotoxin and thiourea on the accumulation of mRNA encoding SP-A. Methods : Sprague-Dawley rats were given 5 mg/kg intraperitoneal endotoxin from Salmonella enteritidis and 3.5 mg/kg intraperitoneal thiourea and sacrified at different time periods. Results : 1) SP-A mRNA was significantly increased 67.0% in 6 hours and 73.4% in 24 hours after 5 mg/kg endotoxin treatment respectively(P<0.005, P<0.005). 2) SP-A mRNA was significantly decreased 32.9% in 24 hours after 3.5 mg/kg thiourea treatment(P<0.05). Conclusions : These results indicate that the differential regulation of surfactant protein A in vivo is evident and suggest that surfactant protein A might be differentially regulated during different kind of insults of lung injury at different time periods without altering lung wet to dry ratios. (Tuberculosis and

Thyroid transcription factor-1 expression during normal human lung development and in patients with congenital diaphragmatic hernia

Background/Purpose: Thyroid transcription factor-1 (TTF-1) was detected in human respiratory epithelial cells from 11 weeks of gestation. TTF-1 is involved in both lung morphogenesis and in the regulation of surfactant proteins. Recently, low expression of TTF-1 in the nitrofen rat model of congenital diaphragmatic hernia (CDH) was shown and restoration of this downregulation by antenatal glucocorticolds (CS) was reported. The aim of this study was to investigate the expression of TTF-1 as a marker of lung morphogenesis in normal human lung development and in age-matched controls of human lung specimen in hypoplastic lungs of human CDH and other forms of lung hypoplasia. Methods: Immunohistochemistry by a monoclonal TTF-1 antibody was performed on paraffin sections of human fetal and neonatal lung tissues. The so-called developmental group (12 weeks' gestation to full term) included 47 lung specimens. The congenital hypoplasia group included 8 full-term CDH patients who died within 12 hours after birth, 3 full-term CDH patients who had antenatal CS therapy, and 4 full-term CDH patients after extracorporeal membrane oxygenation (ECMO) therapy. For comparison, 6 full-term born patients, who died of other forms of pulmonary hypoplasia, were used as comparative specimen. Immunohistochemical localization of TTF-1 was evaluated by light microscopy for 3 different areas of the airways including intrapulmonary bronchi, intermediate airways so-called terminal bronchioles, distal airways, and later sacculi and alveoli. Results: Nuclear TTF-1 staining was observed in the progenitor cells of the developing bronchiolar cells early in the human lung developmental series. At full term, TTF-1 was expressed in both type II epithelial cells and in subsets of respiratory nonciliated bronchiolar epithelial cells in a pattern similar in all studied groups. No TTF-1 expression was detected at the level of the intrapulmonary bronchi. Conclusions: No difference in TTF-1 expression was observed in the developing early fetal and full-term neither in hypoplastic human lungs. This expression did not change with antenatal CS and postnatal ECMO treatment. Although TTF-1 appears to play an important role in lung morphogenesis, a pivotal role in human lung development is not likely. J Pediatr Surg 37:1258-1262. Copyright 2002, Elsevier Science (USA). All rights reserved.

Regulation of surfactant proteins by LPS and proinflammatory cytokines in fetal and newborn lung.

Intra-amniotic lipopolysaccharide (LPS) and cytokines may decrease respiratory distress syndrome (RDS) and increase chronic lung disease in the newborn. The aim was to identify the primary inflammatory mediators regulating the expression of surfactant proteins (SP) in explants from immature (22-day-old fetus) and mature (30-day term fetus and 2-day-old newborn) rabbits. In immature lung, interleukin (IL)-1alpha and IL-1beta upregulated the expression of SP-A and SP-B. These effects of IL-1 were diminished, and SP-C mRNA was suppressed additively in the presence of tumor necrosis factor (TNF)-alpha and either LPS or interferon (IFN)-gamma. LPS, TNF-alpha, or IFN-gamma had no effect alone. In explants from the term fetus and the newborn, LPS, IL-1alpha, and TNF-alpha additively suppressed the SPs. LPS acutely induced IL-1alpha in alveolar macrophages in mature lung but not in the immature lung. IFN-gamma that generally has low expression in intrauterine infection decreased the age dependence of the other agonists' effects on SPs. The present study serves to explain the variation of the pulmonary outcome after an inflammatory insult. We propose that IL-1 from extrapulmonary sources induces the SPs in premature lung and is responsible for the decreased risk of RDS in intra-amniotic infection.

Regulation of SP-B and SP-C secretion in rat type II cells in primary culture.

Secretion of lung surfactant phospholipids is a highly regulated process. A variety of physiological and pharmacological agents stimulate surfactant phospholipid secretion in isolated type II cells. Although the lipid and hydrophobic protein components of surfactant are believed to be secreted together by exocytosis of lamellar body contents, regulation of surfactant protein (SP) B and SP-C secretion has not previously been examined. To address the question of whether secretion of SP-B and SP-C is stimulated by the same agonists that stimulate phospholipid secretion, we measured secretion of all four SPs under the same conditions used to measure phosphatidylcholine secretion. Freshly isolated rat type II cells were cultured overnight and exposed to known surfactant phospholipid secretagogues for 2.5 h, after which the amounts of SP-A, SP-B, SP-C, and SP-D in the medium were measured with immunoblotting. Secretion of SP-B and SP-C was stimulated three- to fivefold by terbutaline, 5'-(N-ethylcarboxyamido)adenosine, ATP, 12-O-tetradecanoylphorbol 13-acetate, and ionomycin. Similar to their effects on phospholipid secretion, the stimulatory effects of the agonists were abolished by Ro 31-8220. Secretion of SP-A and SP-D was not stimulated by the secretagogues tested. We conclude that secretion of the phospholipid and hydrophobic protein components of surfactant is similarly regulated, whereas secretion of the hydrophilic proteins is regulated differently.

Mice lacking CCAAt/enhancer-binding protein-alpha show hyperproliferation of alveolar type II cells and increased surfactant protein mRNAs.

The lung-specific surfactant proteins (SP) are essential for normal respiratory function. Transcription factors may play an important role in the regulation of surfactant proteins. The CCAAT/enhancer-binding protein (C/EBP) family consists of transcription factors that can stimulate expression of genes in lipid-metabolizing epithelial cells. C/EBPalpha-deficient mice have been shown to exhibit abnormal pulmonary histopathology. Recently, we demonstrated that C/EBP family members are differentially expressed in alveolar type II cell proliferation and in pulmonary fibrosis. In the present study, to investigate whether the C/EBP family would be involved in the regulation of surfactant proteins, we examined the protein expression of SP-A, and SP-C, and mRNA expression of SP-A, SP-B, and SP-C in the lungs from newborn C/EBPalpha-deficient mice. Using immunohistochemistry, we demonstrated that positive cells for SP-C, specific to alveolar type II cells, in the lungs were more abundant in the newborn C/EBPalpha-deficient mice than in control mice, which suggests the hyperproliferation of alveolar type II cells in the lungs of the C/EBPalpha-deficient mice. In situ hybridization analysis revealed that expression of SP-A, SP-B, and SP-C mRNAs were increased in the lungs of newborn C/EBPalpha-deficient mice. Northern blot analysis revealed that surfactant protein mRNAs were also increased. Thus, these results suggest that C/EBPalpha may play a key role in the proliferation of alveolar type II cells and the regulation of genes of surfactant protein.

Transforming growth factor-β 1 regulation of surfactant protein B gene expression is mediated by protein kinase-dependent intracellular translocation of thyroid transcription factor-1 and hepatocyte nuclear factor 3

The transforming growth factor-β (TGFβ) polypeptides control a variety of cellular processes including organogenesis and cellular proliferation and differentiation. In the developing lung, TGFβ 1 treatment inhibits airway branching and expression of the genes for surfactant proteins (SP). Many effects of TGFβ are mediated at the level of gene transcription but there is limited information regarding signaling pathways and target transcription factors. In this study with human pulmonary adenocarcinoma H441 cells, we investigated TGFβ 1 effects on SP-B, a protein which is essential for normal function of pulmonary surfactant. TGFβ 1 (10 ng/ml) reduced SP-B mRNA content in a time-dependent fashion, and transient transfection studies localized responsiveness to the region of the SP-B promoter (−112/−72 bp) containing binding sites for thyroid transcription factor-1 (TTF-1) and hepatocyte nuclear factor 3 (HNF3), transcription factors that are important enhancers of SP gene expression. Using electrophoretic mobility shift assay and immunofluorescence, we demonstrated rapid accumulation of these transcription factors in the cytoplasm and subsequent loss from the nucleus on TGFβ 1 treatment of both adenocarcinoma cells and cultured human fetal lung. TGFβ 1 treatment caused intracellular translocation of protein kinase C and effects of TGFβ 1 were mostly abrogated in the presence of the protein kinase inhibitor calphostin C. We conclude that TGFβ 1, acting via protein phosphorylation, blocks nuclear translocation of TTF-1 and HNF3 which results in down-regulation of the SP-B gene and presumably other pulmonary genes which are transactivated by these factors.

The Effect of Tumor Necrosis Factor (TNF) on Gene Expression of Surfactant Protein A, B, and C

BACKGROUND: TNF may play an important role (central mediator) in the development of an acute respiratory distress syndrome. Since TNF induced lung injury in the actute respiratory distress syndrome and abnormalities in surfactant function have been dexcribed in acute respiratory distress syndrome, the authors investigated the effects of TNF on the regulation of surfactant protein A, B, and C mRNA accumulation. METHODS: The effects of TNF on gene expression of surfactant protein A, B, and C were analyzed using filter hybridiztion, 12 and 24 hours after intravenous injection of TNF in rats. RESULTS: 1. The accumulation of SP-A mRNA in the TNF treated group (12 and 24 hours after TNF injection) was significantly decreased by 22.9% and 27.4%, respectively, compared to the control group (P < .025, P < .025). 2. The accumulation of SP-B mRNA in 24 hours after TNF treated group was significantly decreased by 20.5% compared to that of the control group (P<.01). 3. The accumulation of SP-C mRNA in 12 hours after treated group was significantly decreased by 31% the compared to that of the control group(P<.01). CONCLUSION: These findings indicate the marked inhibitory effects of tumor necrosis factor on surfactant proteins expression in vivo. This finding, in turn, supports the idea of inhibitory effects of tumor necrosis factor on surfactant proteins expression as it relates to pathogenesis of acute respiratory distress syndrome.

Regulation and Function of Pulmonary Surfactant Protein B

Pulmonary surfactant, a complex mixture of phospholipids and specific associated proteins, reduces the surface tension at the air-liquid interface of the distal conducting airways and gas exchanging alveoli of the lung. Lipids, primarily neutral and phospholipids, compose approximately 90% of the surfactant complex. The remaining 10% of surfactant is composed of at least three surfactant-specific proteins, designated surfactant protein A (SP-A), SP-B, and SP-C. These proteins contribute to the formation, stabilization, and function of organized surfactant structures. This article briefly reviews the normal composition and function of pulmonary surfactant and specifically reviews the structure, function, and regulation of surfactant protein B (SP-B). The recent identification of neonates with refractory respiratory failure due to a genetic absence of SP-B and the study of transgenic mice in which SP-B gene expression has been ablated highlight the importance of the protein to surfactant function, synthesis, and metabolism and to the maintenance of lung function. Gene reconstitution experimentsin vitroand in SP-B-deficient transgenic mice suggest specific functions for the amino and carboxyl terminal domains of the protein. SP-B deficiency is a potential target for gene therapy in human patients.

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Pulmonary surfactant, a complex mixture of phospholipids and specific associated proteins, reduces the surface tension at the air-liquid interface of the distal conducting airways and gas exchanging alveoli of the lung. Lipids, primarily neutral and phospholipids, compose approximately 90% of the surfactant complex. The remaining 10% of surfactant is composed of at least three surfactant-specific proteins, designated surfactant protein A (SP-A), SP-B, and SP-C. These proteins contribute to the formation, stabilization, and function of organized surfactant structures. This article briefly reviews the normal composition and function of pulmonary surfactant and specifically reviews the structure, function, and regulation of surfactant protein B (SP-B). The recent identification of neonates with refractory respiratory failure due to a genetic absence of SP-B and the study of transgenic mice in which SP-B gene expression has been ablated highlight the importance of the protein to surfactant function, synthesis, and metabolism and to the maintenance of lung function. Gene reconstitution experimentsin vitroand in SP-B-deficient transgenic mice suggest specific functions for the amino and carboxyl terminal domains of the protein. SP-B deficiency is a potential target for gene therapy in human patients.

Regulation of surfactant proteins A and B by TNF-alpha and phorbol ester independent of NF-kappa B.

Acute lung inflammation is complicated by altered pulmonary surfactant phospholipid and protein composition. The proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) and the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA) inhibit expression of surfactant-associated proteins A and B (SP-A and SP-B), both important for normal surfactant function. The transcription factor nuclear factor-kappa B (NF-kappa B) frequently mediates regulation of gene expression by TPA and TNF-alpha. In the present study, electrophoretic mobility shift assays (EM-SAs) and pyrrolidine dithiocarbamate (PDTC), an inhibitor of NF-kappa B activation, were utilized to determine the role of NF-kappa B activation in TPA and TNF-alpha inhibition of the surfactant proteins in NCI-H441 cells. Pentoxifylline (PTX), which inhibits TNF-alpha cellular effects without preventing NF-kappa B activation, was also tested. By EMSA, TPA and TNF-alpha increased nuclear NF-kappa B binding activity in temporally distinct patterns. PDTC decreased TPA- and TNF-alpha-induced NF-kappa B binding activity but did not limit their inhibition of SP-A and SP-B mRNAs. PDTC independently decreased both SP-A and SP-B mRNAs. PTX partially reversed TNF-alpha-but not TPA-mediated inhibition of SP-A and SP-B mRNAs without altering NF-kappa B binding. The effects of PDTC and PTX on NF-kappa B and the surfactant proteins suggest that NF-kappa B activation does not mediate TPA or TNF-alpha inhibition of SP-A and SP-B mRNA accumulation.

Regulation of surfactant protein D in human fetal lung.

Surfactant protein D (SP-D) is a collagenous glycoprotein, produced by lung type II cells, that has structural and functional similarities with SP-A. In this study we postulated that SP-D and SP-A gene expression are regulated in a similar fashion to provide a coordinated local immune defense response to pulmonary infection. We determined content of SP-D protein and mRNA in second-trimester fetal lung and in postnatal tissue by protein blotting and hybridization analyses. Low levels of SP-D mRNA and protein were detected at 16 wk gestation, before appearance of SP-A, and levels increased during gestation. The content of SP-D did not change during 5 days of explant culture, whereas SP-A increased manyfold. Dexamethasone treatment during culture increased SP-D mRNA and protein about 2-fold with maximal response after 1 to 3 days' exposure to 100 nM steroid; under the same conditions SP-A mRNA content is inhibited. There was no significant change in SP-D mRNA after treatment of explants with adenosine 3',5'-monophosphate (cAMP) analog or interferon-gamma, agents which increase SP-A gene expression, nor after exposure to phorbol ester, tumor necrosis factor-alpha, or lipopolysaccharide at concentrations that reduced levels of SP-A mRNA by approximately 50%. We conclude that SP-D in the human lung is under developmental and glucocorticoid regulation occurring at a pretranslational level. SP-D is not influenced by inflammatory mediators that regulate SP-A, suggesting that these two proteins are not coordinately regulated in response to lung infection.

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)

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.

Regulation of surfactant protein A mRNA by hormones and butyrate in cultured fetal rat lung

We have previously shown that dexamethasone, triiodothyronine (T3) and dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP) stimulate phosphatidylcholine (PC) synthesis in fetal rat lung explants in culture. There are also additive interactions between these agents with regard to PC synthesis. In this study we examined the regulation of surfactant protein A (SP-A) mRNA in fetal rat lung in culture. Dexamethasone increased SP-A mRNA in the explants in a dose-dependent fashion (1-200 nM), but T3 did not. Whereas 8-bromo-cAMP increased SP-A mRNA, a decrease was observed with dibutyryl cAMP. These findings support the view that at least some of the genes involved in the synthesis of the various components of surfactant are independently regulated. Since we observed differences in the effects of a cAMP analogue which contained butyrate and one that did not, explants were then cultured with Na butyrate, a known regulator of gene expression. A significant decrease in SP-A mRNA was observed at mM concentrations. Exposure of the explants to alpha-aminobutyric acid, a butyric acid analogue which is elevated in the blood of infants of diabetic mothers, resulted in a significant decrease in SP-A mRNA at a concentration 1/25 of that required for Na butyrate. This observation raises the question of whether the decreased SP-A levels reported in fetuses of diabetic mothers may, at least in part, be related to this metabolite.