Surfactant Protein A Levels Research Articles

Surfactant protein-A reduces binding and phagocytosis of pneumocystis carinii by human alveolar macrophages in vitro.

Surfactant protein-A (SP-A) levels are increased in Pneumocystis carinii pneumonia, but the role of SP-A in the pathogenesis of P. carinii pneumonia is not completely understood. This study investigated the effect of SP-A on the in vitro binding and phagocytosis of P. carinii by normal human alveolar macrophages (AM). Determination of binding and phagocytosis was done with a fluorescence-based assay, utilizing fluorescein isothiocyanate (FITC)-labeled P. carinii. Binding and phagocytosis of P. carinii to AM correlated inversely with the levels of SP-A present on the surface of the organisms (r = -0.6323, P = 0.0086; and r = -0.9827, P < 0.0001, respectively). The addition of exogenous SP-A to organisms with low surface-associated SP-A reduced P. carinii binding by 30% (P < 0.05) and reduced phagocytosis by 20% (P < 0.05), whereas this effect was reversed with ethylenediamine tetraacetic acid (EDTA) or anti-SP-A antibody. Furthermore, binding and phagocytosis were enhanced after enzymatic removal of P. carinii surface-associated SP-A, and this effect was reversed with the addition of exogenous SP-A. The observed inhibitory effect of SP-A on P. carinii binding and phagocytosis reflected binding of SP-A to the organisms rather than a direct effect of SP-A on the macrophages. These data suggest that increased levels of SP-A may contribute to the pathogenesis of P. carinii pneumonia through binding to the surface of the organism and interfering with AM recognition of this opportunistic pulmonary pathogen.

Inhibition of tyrosine kinase activity decreases expression of surfactant protein A in a human lung adenocarcinoma cell line independent of epidermal growth factor receptor

Epidermal growth factor (EGF) enhances fetal lung development in vivo and in vitro. Ligand binding to the EGF receptor stimulates an intrinsic receptor tyrosine kinase initiating a signal transduction cascade. We hypothesized that blocking EGF receptor function with tyrosine kinase inhibitors would decrease the expression of surfactant protein A in human pulmonary epithelial cells. Human pulmonary adenocarcinoma cells (NCI-H441) were exposed to genistein (a broad range inhibitor of tyrosine kinases) and tyrphostin AG1478 (a specific inhibitor of EGF receptor tyrosine kinase). Genistein significantly decreased surfactant protein A (SP-A) and SP-A mRNA levels in H441 cells without affecting cell viability. The inhibitory effect of genistein on SP-A content was reversible. In contrast, tyrphostin AG1478 had no effect on SP-A levels despite a greater inhibitory effect than genistein on EGF receptor tyrosine autophosphorylation. Furthermore, treatment of H441 cells with exogenous EGF did not increase SP-A content or mRNA levels beyond baseline. We conclude that inhibition of tyrosine kinase activity other than the EGF receptor decreases the expression of surfactant protein A at a pretranslational level in human pulmonary adenocarcinoma cells. These results suggest the importance of tyrosine kinases in modulating human SP-A synthesis.

Effect of contact avoidance or treatment with oral prednisolone on bronchoalveolar lavage surfactant protein A levels in subjects with farmer's lung.

Surfactant protein A (SP-A) acts as an immune system modulator in the lungs and may therefore be involved in the pathogenesis of hypersensitivity pneumonitis. The levels of SP-A in bronchoalveolar lavage (BAL) fluid were measured in 20 subjects with acute farmer's lung, 16 asymptomatic dairy farmers, and 14 normal controls. Eight patients had a second evaluation after one month of treatment by either contact avoidance (n = 3) or oral prednisolone (20 or 25 mg/day, n = 5). Chest radiographs and lung function measurements were also obtained in all farmers, twice in those re-evaluated after treatment. Patients with acute farmer's lung had significantly higher levels of SP-A than asymptomatic farmers and normal controls (p = 0.005) with mean (SE) values of 1.43 (0.29) micrograms/ml, 0.62 (0.09) microgram/ml, and 0.68 (0.11) microgram/ml, respectively. In eight subjects tested after one month of treatment the level of SP-A was unchanged although all were clinically improved. No correlations were seen between levels of SP-A in BAL fluid and numbers of BAL cells, lung function measurements, or chest radiographic scores. Although the level of SP-A is increased in the BAL fluid of patients with acute farmer's lung, it is not correlated with clinical abnormalities of this disease.

Alterations in surfactant protein A after acute exposure to ozone

The surfactant layer covering the gas-exchange region of the lung serves as the initial site of interaction with inhaled oxidant gases. Among the endogenous compounds potentially vulnerable to oxidative injury are surfactant proteins. This study focused on the effect of ozone on surfactant protein A (SP-A) function, content, and gene expression. To determine the time course of response to ozone, guinea pigs were exposed to 0.2-0.8 parts/million (ppm) ozone for 6 h and were killed up to 120 h postexposure. To determine the effect of repeated exposure, animals were exposed to 0.8 ppm ozone for 6 h/day and were killed on days 3 and 5. A significant increase in surfactant's ability to modulate the respiratory burst induced by phorbol 12-myristate 13-acetate in naive macrophages was observed at 24 h after a single 0.8 ppm ozone exposure. Because neutralizing antibodies to SP-A blunted this stimulatory effect, we hypothesized that ozone enhanced the modulatory role of SP-A in macrophage function. This alteration in function was accompanied by an influx of inflammatory cells and only marginal changes in SP-A levels as determined by an enzyme-linked immunosorbent assay. No significant changes in steady-state levels of SP-A mRNA were observed after single or repeated exposure to ozone. Thus the inflammation that accompanies in vivo ozone exposure may result in a change in the structure and thus functional role of SP-A in modulating macrophage activity.

Decreased Contents of Surfactant Proteins A and D in BAL Fluids of Healthy Smokers

Hydrophilic surfactant proteins, surfactant protein A (SP-A) and surfactant protein D (SP-D), have important roles in modulating the host defense functions in the peripheral airways. It has been reported that cigarette smoke may alter the component and function of pulmonary surfactant. In this study, we determined the contents of SP-A and SP-D in BAL fluids of healthy smokers and nonsmokers by enzyme-linked immunosorbent assay using monoclonal antibodies against each protein. The contents of SP-A and SP-D in BAL fluids were significantly (p<0.05) decreased in smokers compared to those in nonsmokers, although there was no significant difference of total phospholipid content between smokers and nonsmokers. These results suggest that the decreased levels of SP-A and SP-D in smokers may impair the host defense functions of surfactant in the peripheral airways and might have a crucial roles in the development of chronic obstructive lung disease.

Surfactant protein-A levels increase during Pneumocystis carinii pneumonia in the rat.

In bronchoalveolar lavage (BAL) of human immunodeficiency virus (HIV)-infected patients with Pneumocystis carinii pneumonia and in lungs of glucocorticoid-immunosuppressed rats infected with P. carinii, surfactant phospholipid levels are reduced. However, levels of the surfactant-associated protein-A (SP-A) in BAL are 4-5 times higher than normal in patients with P. carinii pneumonia. In this study, we examined the effects of glucocorticoid immunosuppression and P. carinii infection on SP-A messenger ribonucleic acid (mRNA) and protein levels in rat lungs. Rats were immunosuppressed by adding dexamethasone to their drinking water and were infected with P. carinii by intratracheal instillation of the organism. SP-A was measured by enzyme-linked immunosorbent assay (ELISA) and SP-A mRNA by hybridization of Northern blots with an SP-A complementary deoxyribonucleic acid (cDNA) probe. There was a severalfold increase in SP-A protein and mRNA levels in uninfected glucocorticoid-treated rats. However, contrary to what has been reported with the surfactant-associated lipids, SP-A mRNA and protein levels in P. carinii-infected animals were significantly higher than those found in the uninfected, immunosuppressed animals. Our results demonstrate that SP-A increases, probably as a result of elevated mRNA levels, in immunosuppressed rats with P. carinii infection and are consistent with our findings in HIV-positive patients with P. carinii pneumonia.

Surfactant protein A in bronchoalveolar lavage fluid from patients with idiopathic interstitial pneumonia

We measured the levels of surfactant protein A (SP-A) in bronchoalveolar lavage fluid from patients with idiopathic interstitial pneumonia and from healthy volunteers. The SP-A levels in the patients who were smokers (1.4 +/- 0.2 micrograms/ml) were significantly (p < 0.05) lower than those in the patients who were nonsmokers (3.0 +/- 0.5 micrograms/ml). However, SP-A levels did not differ significantly between patients and volunteers who were smokers, or between patients and volunteers who were nonsmokers. The ratios of SP-A to phospholipid in patients who were smokers and in those who were non-smokers did not differ significantly from those in volunteers who were smokers and volunteers who were non smokers. The total number of alveolar macrophages in bronchoalveolar lavage fluid did not significantly correlate with the level of SP-A, although the percentage of alveolar macrophages correlated negatively (p < 0.05) with the level of SP-A. The low level of SP-A in patients with idiopathic interstitial pneumonia who are smokers may weaken the host defense functions in peripheral airways and may contribute to the poor outcomes in these patients.

Levels of pulmonary surfactant protein A in fetal lung and amniotic fluid from protein-malnourished pregnant rats.

Surfactant protein A (SP-A) is a major apo-protein of pulmonary surfactant, which lines the alveolar walls, lowering the surface tension to prevent lung collapse. Pregnant rats were divided into two groups which received a diet with either 5% or 20% protein from gestational day 9. By a sensitive immunoassay, SP-A levels in the fetal lungs and the amniotic fluid showed a dramatic increase with advancing gestation after the initial appearance on gestational day 18 in both diet groups. Significantly lower levels of SP-A in pregnant rats fed 5% protein diet than those in pregnant rats fed 20% protein diet were observed in the fetal lungs on gestational day 21 and in the amniotic fluid on gestational days 20 and 21. The profiles of increased SP-A levels in the amniotic fluid reflected those in the fetal lungs during gestation. Immunohistochemical examination with anti-rat SP-A antibody at 21 days of gestation showed that the immunoreactive staining of bronchiolar epithelial Clara cells and alveolar type II cells were weaker in the fetal lung sections from pregnant rats fed 5% protein diet than in those from pregnant rats fed 20% protein diet. It is concluded that protein malnutrition in pregnant rats affects the biosynthesis of SP-A in the fetal lungs, which may have important consequences for prematurity and decreased respiratory functions in the neonatal lungs at birth.

Surfactant protein a promotes attachment of Mycobacterium tuberculosis to alveolar macrophages during infection with human immunodeficiency virus.

The incidence of tuberculosis is increasing on a global scale, in part due to its strong association with human immunodeficiency virus (HIV) infection. Attachment of Mycobacterium tuberculosis to its host cell, the alveolar macrophage (AM), is an important early step in the pathogenesis of infection. Bronchoalveolar lavage of HIV-infected individuals demonstrated the presence of a factor which significantly enhances the attachment of tubercle bacilli to AMs 3-fold relative to a normal control population. This factor is surfactant protein A (SP-A). SP-A levels are increased in the lungs of HIV-infected individuals. SP-A levels and attachment of M. tuberculosis to AMs inversely correlate with peripheral blood CD4 lymphocyte counts. Elevated concentrations of SP-A during the progression of HIV infection may represent an important nonimmune risk factor for acquiring tuberculosis, even before significant depletion of CD4 lymphocytes in the peripheral blood occurs.

Alveolar-to-Vascular Leakage of Surfactant Protein A in Ventilated Immature Newborn Rabbits

We measured alveolar-to-vascular leakage of surfactant protein A (SP-A) in immature newborn rabbits delivered at a gestational age of 27 days. Experimental animals received, via a tracheal cannula, 2 ml/kg of a mixture of modified porcine surfactant (Curosurf, 80 mg/ml) and human recombinant SP-A (4 mg/ml). Littermate controls received the same volume of human SP-A in saline (4 mg/ml). After 30 min of artificial ventilation with a frequency of 40/min and an inspiration time of either 0.75 or 0.45 s, blood was sampled from the right ventricle and the lungs were lavaged. The content of human SP-A in serum and lung lavage fluid was determined with ELISA kits, and the alveolar-to-vascular leak expressed as the quotient of total SP-A in serum and lavage fluid. The leak in control animals amounted to about 2% of SP-A in lung wash and was several times higher in these animals than in those receiving surfactant. The leak was of the same order irrespective of whether the animals were ventilated with long or short inspiration time. We speculate that serum levels of SP-A may reflect the degree of lung injury in various forms of respiratory failure.

Aberrant appearance of lung surfactant protein A in sera of patients with idiopathic pulmonary fibrosis and its clinical significance.

Pulmonary surfactant protein A (SP-A) is known to be a major phospholipid-associated glycoprotein in pulmonary surfactant, which is specific to the lung. In this study, the SP-A concentrations in sera of patients with various lung diseases were determined using an enzyme-linked immunosorbent assay. Patients with idiopathic pulmonary fibrosis (IPF) and pulmonary alveolar proteinosis (PAP) exhibited prominently high concentrations of serum SP-A compared to those of other lung diseases and healthy volunteers, although there were significant increases in serum SP-A concentrations in patients with pulmonary tuberculosis, chronic pulmonary emphysema, diffuse panbronchiolitis and bacterial pneumonia compared to those of healthy volunteers. Successive measurement in 2 patients with IPF showed that serum SP-A levels reflect the disease activity of IPF. In patients with IPF, serum SP-A concentrations were significantly correlated with those of serum lactate dehydrogenase, whereas there were no significant correlations of serum SP-A concentrations with erythrocyte sedimentation rate, arterial oxygen saturation, vital capacity and carbon monoxide diffusing capacity. Determination of serum SP-A will contribute to diagnosing IPF and PAP, and may reflect the disease activity of IPF.

Differential expressions of surfactant protein SP-A, SP-B, and SP-C mRNAs in rats with streptozotocin-induced diabetes demonstrated by in situ hybridization.

We have previously demonstrated by in situ hybridization and Northern blot analysis that alveolar type II cells and nonciliated bronchiolar epithelial (Clara) cells in lungs of rats with diabetes have decreased surfactant protein A (SP-A) but increased mRNA. In the present study, we have examined the mRNA expression and localization of two hydrophobic surfactant proteins, SP-B and SP-C, and have compared them with SP-A mRNA levels and cellular localization in streptozotocin-induced diabetic lungs. Localization and level of expression were analyzed by in situ hybridization using type-specific, surfactant cDNA probes. Diabetes was induced in adult rats by an intraperitoneal injection of 60 mg/kg streptozotocin. Ten weeks after injection, higher numbers of silver grains representing SP-A and SP-B mRNAs were observed in alveolar type II cells of diabetic lungs, compared with control lungs. Moreover, the number of silver grains representing SP-C mRNA decreased in alveolar type II cells from diabetic lungs compared with controls, and no silver grains for SP-C mRNA were present in bronchiolar epithelial cells from either control or diabetic groups. In contrast, in bronchiolar epithelial cells of diabetic lungs, the relative abundance of silver grains for SP-A mRNA increased approximately 2-fold above controls, while SP-B mRNA decreased slightly. Taken together, there is differential expression in the level of SP-A, SP-B, and SP-C mRNAs in both alveolar and bronchiolar epithelial cells from diabetic lungs when compared with control lungs.(ABSTRACT TRUNCATED AT 250 WORDS)

Butyrate modulates surfactant protein mRNA in fetal rat lung by altering mRNA transcription and stability.

We examined the effects of Na butyrate, a known regulator of gene expression, on surfactant protein mRNA concentration, transcription, and degradation. Exposure of explants of 18-day fetal rat lung to Na butyrate resulted in a decrease in surfactant protein A (SP-A) mRNA concentration to 7% of control after 6 h and to 18% of control after 24 h. The reduction in SP-A mRNA concentration was associated with decreased mRNA transcription and stability at both these times. The effects on SP-B mRNA were similar to those on SP-A, but quantitatively less. In contrast, butyrate had a biphasic effect on SP-C mRNA concentration. There was an initial decrease to 30% of control at 6 h, followed by an increase to control levels by 24 h. Transcription of SP-C was increased at both these times, whereas degradation was enhanced at 6 h, but not at 24 h. The level of surfactant protein mRNA after butyrate treatment therefore depends on the balance between induced changes in transcription and degradation. Butyrate had no effect on gamma-actin mRNA concentration in this system. Circulating levels of butyric acid analogues are elevated in the mothers and fetuses in diabetic pregnancies. Some of these fetuses have delayed lung maturation and decreased amniotic fluid SP-A levels. We speculate that butyric acid analogues partially mediate the changes in pulmonary maturation induced by maternal diabetes.

Oxygen modulates the differentiation of human fetal lung in vitro and its responsiveness to cAMP.

Previously, it was found that lung explants from mid-trimester human abortuses differentiate spontaneously in organ culture in serum-free defined medium in an atmosphere of 95% air-5% CO2. Dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP) treatment of human fetal lung in culture increases the rate of morphological differentiation and enhances expression of the surfactant protein A (SP-A) gene. To begin to define the factors responsible for this accelerated in vitro differentiation, we analyzed the effects of atmospheric oxygen on the morphological and biochemical development of human fetal lung in culture and on responsiveness of the cultured tissue to DBcAMP. We found that when lung explants were maintained in an atmosphere containing 1% oxygen they failed to differentiate spontaneously and no induction of SP-A gene expression was apparent. Furthermore, at 1% oxygen, DBcAMP had no effect to stimulate morphological differentiation or SP-A gene expression. When lung tissues that had been maintained for 5 days in 1% oxygen were transferred to an environment containing 20% oxygen, there was rapid morphological development and induction of SP-A gene expression. The effects on morphological development were manifest within 24 h of transfer to the 20% oxygen environment; within 72 h, a marked stimulatory effect of DBcAMP on SP-A gene expression also was observed. Our findings further suggest that the effects of oxygen on the levels of SP-A and SP-A mRNA are concentration dependent. Interestingly, the inductive effects of DBcAMP on SP-A gene expression were apparent only at oxygen concentrations > or = 10%. Morphological differentiation of the cultured human fetal lung tissue also was influenced by oxygen in a concentration-dependent manner. These findings suggest that oxygen plays an important permissive role in the spontaneous differentiation of human fetal lung in vitro.

Elevated Levels of Lung Surfactant Protein A in Sera from Patients with Idiopathic Pulmonary Fibrosis and Pulmonary Alveolar Proteinosis

An enzyme-linked immunosorbent assay using monoclonal antibodies to human lung surfactant protein A (SP-A) was applied to sera from patients with lung diseases. We examined whether SP-A appears in the sera of patients with diseases that are known to cause alterations in surfactant composition in bronchoalveolar lavage fluids, and we characterized the SP-A that was found. The level of SP-A in sera from 57 healthy volunteers was 45 +/- 3 ng/ml (mean +/- SEM). The levels in patients with idiopathic pulmonary fibrosis (IPF) (205 +/- 23 ng/ml, n = 32) and pulmonary alveolar proteinosis (PAP) (285 +/- 23 ng/ml, n = 6) were significantly higher than those in healthy control subjects (p < 0.01), whereas those of sarcoidosis (n = 16), pneumonia (n = 14), and tuberculosis (n = 14) were 52 +/- 27 ng/ml, 65 +/- 11 ng/ml, and 49 +/- 23 ng/ml, respectively. Electrophoresis and immunoblotting analysis demonstrated that the fraction isolated from serum of a patient with PAP or IPF by anti-SP-A immunoaffinity column chromatography consisted chiefly of human IgG and IgM, and that it also contained SP-A. Furthermore, IgG was found in preparation of purified human SP-A. SP-A was demonstrated to bind to nonimmune IgG coated onto microtiter wells. Gel filtration analysis revealed that serum SP-A was eluted at fractions of larger molecular size than was the purified SP-A. These findings suggest that SP-A appears in the bloodstream as a complex with immunoglobulin in IPF and in PAP.

Pulmonary surfactant protein a in pleural effusions

Pulmonary surfactant protein A (SP-A) is known to be a major phospholipid-associated glycoprotein in pulmonary surfactant, which is specific to the lung. Immunohistochemically, expression of SP-A in tumor tissues is found in approximately 50% of patients with lung adenocarcinoma but not in the other histologic types of lung cancer of metastatic lung tumors. In this study, the SP-A content of pleural effusions was determined using an enzyme-linked immunosorbent assay. These results showed that approximately 40% of patients with lung adenocarcinomas (27 of 67) had high levels of SP-A (greater than 500 ng/ml) in their pleural effusions. By contrast, patients with other histologic types of lung cancers, adenocarcinomas of different primary sites, and tuberculosis had low levels of SP-A in their pleural effusions. The determination of SP-A in malignant effusions will contribute to distinguishing primary lung adenocarcinoma from adenocarcinomas of miscellaneous origin.

Ontogeny of surfactant apoprotein D, SP-D, in the rat lung

Surfactant protein D (SP-D) is a collagenous surfactant-associated glycoprotein synthesized by alveolar type II cells. Antiserum against rat SP-D was raised in rabbits and an enzyme-linked immunosorbant assay (ELISA) has been developed using anti-rat SP-D IgG. In the present study we examined the developmental profile of SP-D in the rat lung compared with that of surfactant protein A (SP-A). SP-A content in the lungs increased during late gestation and reached its maximum on day 1 of neonate, and then gradually decreased until at least day 5. SP-D content during early gestation was less than 10 ng/mg protein until day 18, but on day 19 there was a 4-fold increase in SP-D (compared to that on day 18). It increased twice between day 21 and the day of birth, when it reached the adult level of 250 ng/mg protein, which is about one fourth that of the adult level of SP-A. Unlike SP-A there seemed to be no decrease in SP-D content after birth. These results demonstrate that SP-D is regulated developmentally as are the other components of surfactant, but the inconsistency in the developmental profiles of SP-A and SP-D suggests that these proteins may play different roles in lung maturation.

Increased Recovery of Surfactant Protein A in AIDS-related Pneumonia

Respiratory infection with Pneumocystis carinii (PC) is the most frequent serious opportunistic infection in the clinical setting of acquired immunodeficiency syndrome (AIDS). The factors responsible for the predisposition of human immunodeficiency virus (HIV)-infected patients for PC infection are not fully understood. We postulated that changes in the alveolar lining material (ALM) could play a role in the pathogenesis of PC infection in AIDS. We have compared constituents of ALM in bronchoalveolar lavage fluid from normal, nonsmoking volunteers with that of HIV-infected patients with pneumonia. Using an ELISA, we found that surfactant protein A (SP-A) was markedly elevated in the pneumonia patients. Mean SP-A values for the normal nonsmoking individuals (n = 21) were 1.50 +/- 0.25 micrograms/ml (mean +/- SEM). SP-A levels in the HIV-infected patients (n = 22) were significantly elevated (p less than 0.01) with a mean of 5.23 +/- 0.54 micrograms/ml. This increase was greatest in the patients with more clinically severe pneumonia. The increase in SP-A did not appear to be pathogen-specific as it was also observed in cases of non-PC pneumonia. We also found that total protein levels were nearly five times higher in the HIV-infected pneumonia patients. These studies indicate that the protein component of the ALM is markedly different from normal in cases of HIV-associated PC and non-PC infection. Further investigation is needed to determine the mechanism of these alterations and their role, if any, in AIDS-related pneumonia.

Posttranscriptional regulation of surfactant protein-A messenger RNA in human fetal lung in vitro by glucocorticoids.

Surfactant protein-A (SP-A), the major pulmonary surfactant-associated protein, is a developmentally and hormonally regulated sialoglycoprotein of about 35,000 mol wt. In previous studies we observed that dexamethasone has dose-dependent biphasic effects on the levels of SP-A and its mRNA in human fetal lung in vitro. At concentrations of 10(-10)-10(-9) M, dexamethasone increased the levels of SP-A and its mRNA over those of control tissues, whereas at concentrations greater than or equal to 10(-8) M, the steroid was markedly inhibitory. Our findings suggest that the inhibitory action of dexamethasone (greater than 10(-8) M) on SP-A mRNA levels was mediated by an effect to reduce SP-A mRNA stability, since the steroid caused a dose-dependent increase in the rate of transcription; however, an effect to increase transcription with premature termination leading to instability of mRNA transcripts could not be ruled out. In the present investigation we have studied in detail the mechanisms underlying the biphasic effects of glucocorticoids on SP-A mRNA levels in human fetal lung tissues in vitro. Our findings indicate that dexamethasone (10(-7) M) has no adverse effect on the elongation of nascent mRNA transcripts throughout the SP-A gene; elongation of SP-A mRNA transcripts in dexamethasone-treated tissue explants was similar to that observed in tissues incubated in control medium or medium containing (Bu)2cAMP. Therefore, premature termination of SP-A mRNA transcription leading to the instability of SP-A mRNA can be ruled out. On the other hand, we found that dexamethasone (10(-7) M) had a pronounced effect to reduce the apparent half-life of SP-A mRNA; in control explants maintained in the presence of actinomycin-D to block gene transcription, the SP-A mRNA half-life was estimated to be 11.4 h, whereas in tissues also treated with dexamethasone, the SP-A mRNA half-life was reduced by more than 60% to 5.0 h. Dexamethasone also was found to have dose-dependent effects on the degradation of SP-A mRNA. After 12 h of incubation in the presence of actinomycin-D and dexamethasone at 10(-9) and 10(-7) M, the levels of SP-A mRNA were reduced by 50% and 80%, respectively, compared to those in tissue incubated with actinomycin-D alone. The inhibitory effects of glucocorticoids on SP-A mRNA levels were completely reversible and were blocked by the glucocorticoid antagonist RU486.(ABSTRACT TRUNCATED AT 400 WORDS)

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.