Insulin inhibits surfactant protein A and B gene expression in the H441 cell line

Fetuses of mothers with uncontrolled gestational diabetes have an increased risk of developing neonatal respiratory distress syndrome and are frequently hyperinsulinemic, thus it has been proposed that high levels of insulin delay fetal lung maturation. We have shown previously that insulin inhibits the accumulation of mRNA for the surfactant-associated proteins A and B (SP-A and SP-B) in human fetal lung explants maintained in vitro. To test the hypothesis that the inhibitory effects of insulin on the surfactant proteins are the result of a direct action of insulin on the lung epithelial cell, we evaluated the effects of insulin in the H441 cell line, a human pulmonary adenocarcinoma cell line that expresses SP-A and SP-B mRNA. We observed that insulin treatment for 48 h decreased SP-A mRNA and protein levels in a concentration-dependent manner when compared to controls. The inhibitory effect of insulin on SP-A mRNA levels was apparent as early as after 4 h of exposure. SP-B mRNA levels were also significantly decreased by insulin in a concentration-dependent manner. Insulin, at 2.5 microg/ml, inhibited SP-A gene transcription by approx. 67%, and inhibited SP-B gene transcription by about 32%. There was no significant effect of insulin on SP-A or SP-B mRNA stability. Thus, we have observed a pattern of insulin inhibition of SP-A and SP-B gene expression in the H441 lung epithelial cell line similar to that previously observed in human fetal lung explants, which are comprised of both epithelial and mesenchymal cells. Our findings provide further evidence that insulin may delay fetal lung maturation by inhibiting SP-A and SP-B gene expression. Furthermore, our findings suggest that the inhibitory effects of insulin are, at least partially, the result of a direct action on the lung epithelial cell.

SP-A2 gene expression in human fetal lung airways

In the present study, we characterized surfactant protein (SP)-A messenger RNA (mRNA) in mid-trimester human fetal trachea and bronchi. SP-A protein was localized by immunocytochemistry to scattered epithelial cells in the airway surface epithelium and in submucosal glands of the fetal trachea and bronchi. SP-A mRNA (2.2 kb) was detected by Northern blot analysis in human fetal trachea, as well as in primary and more distal bronchi. The levels of detectable SP-A mRNA were highest in the upper airways and were decreased in smaller bronchi in comparison. SP-A mRNA was barely detectable in the distal fetal lung tissue. In contrast, SP-A mRNA was abundant in cultured explants of distal human fetal lung tissue. SP-A1 and SP-A2 mRNA were detected by primer extension analysis in adult human lung tissue and in cultured human fetal lung explants. Only SP-A2 mRNA was detected in RNA isolated from human fetal trachea and bronchi. SP-A mRNA was localized by in situ hybridization in the fetal trachea and bronchi in scattered cells in the surface epithelium and, most prominently, in submucosal glands. Our results suggest that SP-A2, and not SP-A1, is produced in the human fetal tracheal and bronchial epithelium and in submucosal glands.

Surfactant protein-A: new insights into an old protein--Part I

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.

Mechanism of all trans-retinoic acid and glucocorticoid regulation of surfactant protein mRNA

The surfactant proteins (SPs) are required for the normal function of pulmonary surfactant, a lipoprotein substance that prevents alveolar collapse at end expiration. We characterized the effects of cortisol and all trans-retinoic acid (RA) on SP-A and SP-B gene expression in H441 cells, a human pulmonary adenocarcinoma cell line. Cortisol, at 10(-6) M, caused a significant inhibition of SP-A mRNA to levels that were 60-70% of controls and a five- to sixfold increase in the levels of SP-B mRNA. RA alone (10(-6) M) had no effect on SP-A mRNA levels and modestly reduced the inhibitory effect of cortisol. RA alone and the combination of cortisol and RA both significantly increased SP-B mRNA levels. RA had no effect on the rate of SP-A gene transcription or on SP-A mRNA stability. Cortisol alone and the combination of cortisol and RA significantly inhibited the rate of SP-A gene transcription but had no effect on SP-A mRNA half-life. RA at 10(-6) M had no effect on the rate of SP-B gene transcription but prolonged SP-B mRNA half-life. Cortisol alone and the combination of cortisol and RA caused a significant increase in the rate of SP-B gene transcription and also caused a significant increase in SP-B mRNA stability. We conclude that RA has no effect on SP-A gene expression and increases SP-B mRNA levels by an effect on SP-B mRNA stability and not on the rate of SP-B gene transcription. In addition, the effects of the combination of RA and cortisol were generally similar to those of cortisol alone.

O2 regulates surfactant protein A mRNA transcription and stability in human fetal lung in vitro

The effect of O2 on surfactant protein (SP) A mRNA transcription and half-life was determined in midtrimester human fetal lung tissue cultured in either 20 (control) or 70% O2. Incubation of tissues in 70% O2 resulted in a 133% increase in SP-A mRNA transcription rate compared with control tissues. The SP-A mRNA half-life was increased by 54% in lung tissues cultured in 70% O2 vs. control tissues. Western blot analysis indicated a threefold increase in SP-A in the 70% O2 condition, demonstrating that O2 regulation of SP-A mRNA levels results in corresponding changes in SP-A levels. Primer extension assays were performed to determine whether the observed increase in SP-A mRNA levels is secondary to the preferential expression of one of the human SP-A genes, SP-A1 or SP-A2. Transcripts of both the SP-A1 and SP-A2 genes were increased approximately 100% in tissues maintained in 70% O2 compared with control tissues. These data demonstrate that O2 regulates human SP-A mRNA levels by both transcriptional and posttranscriptional mechanisms. Furthermore, because there is no differential effect of O2 on the expression of SP-A1 vs. SP-A2 mRNA, the properties of these genes that mediate regulation by O2 must be conserved between the two genes.

Transient surfactant protein B deficiency in a term infant with severe respiratory failure

A 38-day-old male infant with persistent pulmonary hypertension and respiratory failure since birth was found to have a complete absence of surfactant protein B (SP-B) along with an aberrant form of SP-C in his tracheal aspirate fluid, findings consistent with the diagnosis of hereditary SP-B deficiency. Surprisingly, SP-B and SP-B messenger ribonucleic acid were present in lung biopsy tissue. However, DNA sequence analysis demonstrated a point mutation in exon 5 of one of the SP-B gene alleles. The infant's mother was found to be a carrier of this mutation. The infant's other SP-B allele did not differ from the published DNA sequence for the SP-B gene. We conclude that this patient had a transient deficiency of SP-B, in contrast to that of previously described infants with irreversible respiratory failure caused by hereditary SP-B deficiency. We recommend that infants with suspected SP-B deficiency have serial analysis of tracheal fluid samples for both SP-B and SP-C before lung biopsy, along with genetic analysis for the known SP-B mutations. We speculate that the new mutation found in one of this patient's SP-B genes was in part responsible for the transient deficiency of SP-B.

Differential regulation of SP-A1 and SP-A2 genes by cAMP, glucocorticoids, and insulin

In the human fetal lung, surfactant protein A (SP-A) is encoded by two highly similar genes, SP-A1 and SP-A2, which are developmentally and hormonally regulated. Using primer extension analysis, we evaluated the levels of SP-A1 and SP-A2 mRNA transcripts in human fetal lung explants and in a human adult lung adenocarcinoma cell line (H441 cells) cultured in the absence or presence of either dibutyryladenosine 3',5'-cyclic monophosphate (DBcAMP, 1 mM), dexamethasone (10(-7) M), or insulin (2.5 micrograms/ml). In the human fetal lung explants, the content of SP-A1 mRNA was approximately four times that of SP-A2 mRNA. DBcAMP increased SP-A1 mRNA levels by 100% and SP-A2 mRNA levels by 500%, thus reducing the ratio of SP-A1 mRNA to SP-A2 mRNA to approximately 1:1. Dexamethasone inhibited all of the SP-A1 and SP-A2 mRNA transcripts to the same extent, by approximately 70%, whereas insulin inhibited all SP-A mRNA transcripts by approximately 60%. The ratio of SP-A1 to SP-A2 mRNA in dexamethasone- or insulin-treated explants was the same as the ratio observed in controls. In the H441 cells, SP-A1 mRNA levels were approximately 1.5 times that of SP-A2 mRNA levels. DBcAMP increased both SP-A1 and SP-A2 mRNA levels by 100%. Dexamethasone inhibited SP-A1 mRNA levels in the cell line by 60%, whereas SP-A2 mRNA levels were not significantly affected. Insulin inhibited SP-A1 mRNA levels in the cell line by 40% without affecting SP-A2 mRNA levels. These findings suggest that the two human SP-A genes are regulated differently in the two model systems.

Regulation of surfactant protein gene expression by retinoic acid metabolites

Surfactant-associated proteins (SP) play an important role in the function of pulmonary surfactant. We have previously shown that SP-B mRNA is increased whereas SP-A and SP-C mRNA are decreased by all-trans-retinoic acid (RA) in a dose-dependent manner in human fetal lung explants. All-trans-RA binds primarily to the retinoic acid receptors (RARs) and 9-cis-RA binds primarily to the retinoid X receptors (RXRs). Because the fetal lung contains RXRs, we hypothesized that 9-cis-RA regulates surfactant protein gene expression in lung epithelial cells. H441 human lung adenocarcinoma cells, which synthesize SP-A and SP-B mRNA and protein, were treated with either all-trans-RA or 9-cis-RA (10(-10) to 10(-6) M) for 24 h. Neither all-trans-RA nor 9-cis-RA had an effect on SP-A mRNA levels in the H441 cells. All-trans-RA (10(-6) M) significantly increased SP-B mRNA levels in the H441 cells and 9-cis-RA had a smaller, not statistically significant effect. Human fetal lung explants were treated with 9-cis-RA for 6 d. 9-cis-RA did not significantly increase SP-B mRNA levels, significantly inhibited SP-A mRNA levels at all concentrations tested, and significantly inhibited SP-C mRNA levels at 10(-6) M in the human fetal lung explants. Both all-trans-RA (10(-6) M) and 9-cis-RA (10(-6) M) significantly increased SP-B protein levels in the human fetal lung explants. Together, these results are suggestive that all-trans-RA directly regulates SP-B gene expression in human pulmonary epithelial cells. In addition, the inhibitory effect of all-trans-RA and 9-cis-RA on SP-A mRNA levels in pulmonary epithelial cells is probably an indirect effect mediated by other cell types present in fetal lung tissue.

Fat content for nutritional labeling by supercritical fluid extraction and an on-line lipase catalyzed reaction

A method using sequential supercritical fluid extraction (SFE) and enzymatic transesterification has been developed for the rapid determination of total nutritional fat content in meat samples. SFE conditions of 12.16 MPa and 50 degrees C were utilized to extract lipid species from the sample matrix. The enzymatic transesterification of the lipids by methanol was catalyzed by an immobilized lipase isolated from Candida antarctica. Conversion of the triglycerides to fatty acid methyl esters was monitored by supercritical fluid chromatography, while the fatty acid content of the extract was determined by capillary gas chromatography (GC). Total fat, saturated fat and monounsaturated fat contents were calculated from the GC data and compared to values from traditional extraction and lipid determination methods. Both off-line SFE and automated SFE followed by on-line GC analysis using two different instruments were utilized in this study. The enzymatic-based SFE method gave comparable results to the organic solvent extraction-based method followed by conventional BF3-catalyzed esterification.

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

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

Localization of epidermal growth factor receptor in alveolar epithelium during human fetal lung development in vitro

Epidermal growth factor (EGF) enhances alveolar type II cell differentiation. In human fetal lung explants, EGF stimulates surfactant protein A (SP-A) synthesis. This effect may occur through a direct interaction of the ligand on EGF receptors located within distal pulmonary epithelium during alveolar type II cell differentiation. To determine if EGF receptor is present in alveolar epithelium, immunostaining for EGF receptor and in situ hybridization for EGF receptor mRNA were performed in human fetal lung explants undergoing alveolar type II cell differentiation in vitro. After 4 days in culture, EGF receptor immunostaining was present in alveolar epithelium from human fetal lung explants compared to minimal immunostaining in undifferentiated human fetal lung epithelium prior to culture. In situ hybridization revealed increased EGF receptor mRNA in differentiated type II cells from cultured explants, with minimal EGF receptor mRNA detected in undifferentiated epithelium from tissue prior to culture. Immunogold staining revealed EGF receptors on the cytoplasmic membranes of epithelial cells lining the prealveolar ducts in human fetal lung explants after 2 days in culture. Alveolar type II cell differentiation in vitro was confirmed ultrastructurally by the presence of lamellar bodies and biochemically by an increase in SP-A content. Thus, EGF receptor is found in alveolar epithelium during differentiation, which suggests an important role for EGF during human fetal lung development.

The combined effects of insulin and cortisol on surfactant protein mRNA levels

Infants of diabetic mothers are frequently hyperinsulinemic and have an increased incidence of neonatal respiratory distress syndrome, a disease caused by a deficiency in the production of pulmonary surfactant by alveolar type II cells. It has been hypothesized that insulin inhibits fetal lung type II cell differentiation. We have shown previously that insulin inhibits the accumulation of surfactant protein (SP)-A and SP-B mRNA and has no effect on SP-C mRNA levels in human fetal lung tissue maintained in vitro. We hypothesized that treatment with glucocorticoids, which are used clinically to accelerate human fetal lung maturation, would overcome the inhibitory effects of insulin on human fetal lung development. In the present study, human fetal lung explants were maintained in the presence or absence of cortisol added alone, or in insulin plus cortisol added together. Cortisol significantly decreased SP-A mRNA levels by approximately 50% at the 100 nM concentration and significantly increased levels by approximately 20% at the 1 nM concentration. Cortisol increased SP-B and SP-C mRNA levels in a dose-dependent fashion (5- and 45-fold at 100 nM cortisol, respectively). The combination of 1 nM cortisol and insulin resulted in inhibition of mRNA levels for SP-A, SP-B, and SP-C at the high insulin concentrations (approximately 50% inhibition for SP-A and SP-B and approximately 25% inhibition of SP-C mRNA levels, in the presence of 40 pmol/L x 10(-3) insulin). Surprisingly, 100 nM cortisol plus inhibitory concentrations of insulin increased SP-A mRNA levels (2-fold at 40 pmol/L x 10(-3).(ABSTRACT TRUNCATED AT 250 WORDS)

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

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

Retinoic acid differentially regulates expression of surfactant-associated proteins in human fetal lung

Retinoic acid is known to play an essential role in maintaining the differentiation of a wide variety of epithelial cell types. However, its effects on the differentiation of lung alveolar epithelium have not been described. In the present study, we examined the effects of retinoic acid on the differentiation of human fetal lung tissue maintained in vitro. Human fetal lung explants were cultured in serum-free medium for 6 days in the absence or presence of all-trans retinoic acid at concentrations from 0.3 nM to 3 microM. Explant content of the surfactant-associated protein SP-A was measured using a specific enzyme-linked immunosorbent assay. Retinoic acid reduced SP-A protein levels in a concentration-dependent manner [analysis of variance (ANOVA), P < 0.01]. To evaluate possible cytotoxic effects of retinoic acid, culture media were assayed for lactate dehydrogenase (LDH), a cytoplasmic enzyme. LDH levels in media from retinoic acid-treated explants were not significantly different than LDH levels in media from control explants, indicating that retinoic acid is not cytotoxic in human fetal lung explants. Changes in messenger RNA (mRNA) levels for surfactant-associated proteins SP-A, SP-B, and SP-C were measured by Northern blot analysis. Retinoic acid reduced SP-A mRNA levels in a concentration-dependent manner (ANOVA, P < 0.02) and reduced SP-C mRNA levels at 3 microM. In contrast, retinoic acid increased SP-B mRNA levels in a concentration-dependent manner (ANOVA, P < 0.03). Morphometric analysis showed that retinoic acid decreased epithelial volume density in the explants by approximately 17% and increased connective tissue volume density by approximately 20% when compared to dimethyl sulfoxide vehicle controls. These data indicate that retinoic acid regulates type II cell surfactant protein gene expression in human fetal lung tissue.

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

The effects of a maternally administered synthetic glucocorticoid, betamethasone, on the levels of mRNA for the surfactant proteins SP-A, SP-B, and SP-C and on the levels of SP-A protein were investigated in day 27 gestational age rabbit fetal lung tissue. Betamethasone administration to the pregnant rabbit caused approximately a twofold increase in the fetal lung level of SP-A protein and a threefold increase in fetal lung SP-A mRNA levels when compared to levels in fetuses obtained from saline-treated or uninjected animals. SP-B mRNA was increased fourfold in fetal lung tissue obtained from glucocorticoid-treated pregnant does when compared to levels in fetuses of uninjected pregnant does. However, SP-B mRNA levels in fetal lung tissue from saline-injected controls were also significantly elevated, approximately twofold, when compared to fetal lung SP-B mRNA levels in the uninjected control condition. SP-C mRNA levels in lung tissue of fetuses from both saline-injected and betamethasone-injected pregnant does were increased similarly, approximately twofold, over SP-C mRNA levels in fetal lung tissue obtained from uninjected control does. These data are suggestive that betamethasone treatment increases fetal lung SP-A and SP-B mRNA levels and that maternal stress alone can increase the expression of SP-B and SP-C mRNA in rabbit fetal lung tissue. Using in situ hybridization, SP-A mRNA was shown to be present primarily in alveolar type II cells in fetuses of control and saline-injected does. However, SP-A mRNA was easily detected in both alveolar type II cells and bronchiolar epithelial cells of rabbit fetal lung tissue following maternal betamethasone treatment. In contrast, SP-B and SP-C mRNA were present only in alveolar type II cells of lung tissue obtained from fetuses of control, saline, or betamethasone-treated does. Thus maternal administration of glucocorticoids increased SP-A protein as well as SP-A and SP-B mRNA levels in rabbit fetal lung tissue. SP-A mRNA was localized to both alveolar type II cells and in smaller amounts in bronchiolar epithelial cells of rabbit fetal lung tissue. However, SP-B and SP-C mRNA were detected only in alveolar type II cells.

Diuretic and diet effect on Menière's disease evaluated by the 1985 Committee on Hearing and Equilibrium guidelines

Fifty-four patients, diagnosed with Menière's disease and treated with diuretics and a low-salt diet, were evaluated retrospectively with the 1985 AAO/HNS Committee on Hearing and Equilibrium (CHE) guidelines for vertigo and hearing changes. The patient data base was also evaluated with other methods that helped determine the effectiveness of the 1985 AAO/HNS CHE guidelines. After 24 months of therapy, vertigo control was complete or substantial in 79% of the patients, limited or insignificant in 19%, and worse in 2% as evaluated by the CHE 1985 guidelines. Hearing improved in 35% of the patients, was unchanged in 29%, was worse in 22%, and could not be classified by CHE guidelines in 14%. Hearing was also evaluated by comparison of individual thresholds before medical therapy, and at 22 and 74 months after the start of medical therapy. We found a stabilization of low- and mid-threshold frequencies, with an average rate of hearing loss approximating 0 dB/yr with 74 months of followup. The results of this preliminary study suggest that diuretics and a low-salt diet may decrease the natural progression of sensorineural hearing loss in patients with Menière's disease. Compared with other methods of data analysis, the 1985 CHE guidelines lacked sensitivity to evaluate the hearing changes observed.

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.

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 cystic fibrosis transmembrane conductance regulator mRNA in human fetal lung tissue by in situ hybridization

The fetal pulmonary epithelium secretes fluid. Cl transport is presumed to provide the driving force for net fluid secretion, although the cellular mechanisms have not been well identified in the fetus. The cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP- and nucleoside triphosphate-regulated Cl channel; mutations in CFTR cause cystic fibrosis. We hypothesized that if CFTR is involved in fetal lung fluid transport, the fetal pulmonary epithelium should express CFTR mRNA. We used the technique of in situ hybridization with 3H-anti-sense and, as a control, 3H-sense CFTR cRNA probes to localize CFTR mRNA in human fetal lung tissue and cultured lung explants and determine when in gestation it is expressed. Epithelial cells of both first and second trimester lung tissues expressed CFTR mRNA. A decreasing gradient of CFTR mRNA expression was present from the proximal to the distal pulmonary epithelium. Cultured second trimester lung tissue explants expressed more CFTR mRNA than the uncultured starting tissue, suggesting CFTR gene expression increased during the five days in culture. Furthermore, alveolar type II cells in cultured explants expressed CFTR mRNA, suggesting that these cells are Cl-secretory and may be involved in lung fluid transport. These data confirm that CFTR mRNA is expressed in the human fetal pulmonary epithelium, consistent with the Cl-secretory properties of the fetal lung.

Insulin regulation of messenger ribonucleic acid for the surfactant-associated proteins in human fetal lung in vitro

Respiratory distress syndrome (RDS) is primarily caused by an immaturity in the synthesis and secretion of surfactant by the fetal lung type II cell. Fetal hyperinsulinemia associated with maternal diabetes places the newborn at an increased risk of developing RDS, and therefore, it has been hypothesized that insulin inhibits type II cell differentiation. We have previously shown that insulin inhibits the accumulation of surfactant-associated protein A (SP-A), the major surfactant-associated protein, in human fetal lung explants maintained in vitro. In the present study, we used Northern blot analysis to evaluate the effects of insulin on the content of SP-A messenger RNA (mRNA) as well as on the content of mRNA for the hydrophobic surfactant-associated proteins SP-B and SP-C in human fetal lung explants maintained in vitro. Lung explants were maintained in serum-free medium with or without added insulin (0.25-2500 ng/ml) for up to 6 days. We observed that insulin, at concentrations of 25-2500 ng/ml, significantly inhibited the accumulation of SP-A mRNA when compared to controls (P less than 0.01). The inhibitory effect of insulin on SP-A mRNA accumulation was dose dependent with an approximately 75% inhibition observed at 2500 ng/ml. Insulin, at the concentration of 2500 ng/ml, significantly inhibited the accumulation of SP-B mRNA by approximately 30% when compared to control levels (P less than 0.01) but had no effect at lower concentrations. Insulin had no significant effect on SP-C mRNA levels at any concentration tested. Our findings provide evidence that insulin may delay fetal lung development by inhibiting SP-A and SP-B gene expression. A deficiency of these proteins in pulmonary surfactant may account for the increased incidence of RDS in infants of diabetic mothers.

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.

Glucocorticoid effects on rabbit fetal lung maturation in vivo: an ultrastructural morphometric study

Maternal administration of glucocorticoids is known to stimulate fetal lung maturation. In the present study, we used microscopy and stereology to evaluate the morphological effects of maternal glucocorticoid treatment on rabbit fetal lung tissue. Betamethasone was administered to pregnant rabbits on days 25 and 26 of gestation at a dose of 0.2 mg/kg body weight. The animals were sacrificed on day 27 of gestation. Glucocorticoid treatment significantly increased the presumptive airspace in the fetal lung tissue but did not alter the relative proportion of epithelium, connective tissue, or vasculature in the tissue. In addition, glucocorticoid treatment significantly increased the proportion of type II cells in the prealveolar epithelium, increased the rate of phosphatidylcholine synthesis, and increased the content of the major surfactant-associated protein, SP-A, in the fetal lung tissue. We could detect no effect of betamethasone on lamellar body cross-sectional area, numerical density, or volume density within fetal lung type II cells. Glucocorticoid treatment of the pregnant doe caused a decrease in the volume density of intracellular glycogen and an increase in the volume density of mitochondria in fetal lung type II cells. Betamethasone treatment did not alter the distance between fetal lung epithelial cells and subadjacent connective tissue cells. However, glucocorticoid treatment increased the number of connective tissue foot processes that pierced the epithelial basal lamina. Thus, glucocorticoid treatment of the pregnant doe results in structural changes in the fetal lung tissue, an acceleration of some aspects of type II cell differentiation, and a concomitant increase in epithelial-mesenchymal interactions.

An ultrastructural, morphometric analysis of rabbit fetal lung type II cell differentiation in vivo

Rabbit lung type II cell differentiation was evaluated by use of ultrastructural, morphometric techniques. Fetal lung epithelial cells decreased in size dramatically from day 19 to day 21 of gestation. Thereafter, the cell and cytoplasmic cross-sectional area declined gradually until the neonatal time point. The tall columnar cell shape characteristic of fetal lung epithelial cells at early stages of development became cuboidal by day 24 of gestation. The number of mitochondria per micron2 cytoplasmic area in presumptive alveolar epithelial cells and the mitochondrial volume density increased toward the end of gestation. The volume density of glycogen pools within fetal lung epithelial cells reached a plateau on day 21 of gestation and then declined sharply on day 26 of gestation in lamellar body-containing, type II epithelial cells. Lamellar bodies increased in number and volume density in epithelial cells starting on day 26 of gestation and peaked with respect to these parameters in the neonatal lung tissue. Multivesicular bodies, which are thought to be a precursor to the lamellar body, became more prominent in differentiated type II cells on day 26 of gestation and increased in volume density from day 28 of gestation to the adult time point. The distance between mesenchymal and epithelial cells in fetal lung tissue declined sharply between days 24 and 26 of gestation but remained relatively constant thereafter. Foot processes extending from connective tissue cells contiguous to the epithelium were generally more numerous than those extending from the basal plasma membrane of epithelial cells at every stage of development examined. These data quantitate for the first time key ultrastructural events that occur during the differentiation of fetal lung epithelial cells in vivo.