Accumulation and regulation of elastin in the rat uterus

The relative levels of elastin-specific mRNA were used as a measure of tropoelastin expression in uteri from pregnant Sprague-Dawley rats. The levels of elastin-specific mRNA were also correlated with values for net tropoelastin production and net deposition of mature, crosslinked elastin. The total content of uterine elastin increased throughout gestation, reaching maximal levels at Day 19 of gestation, which were three times those of nongravid tissue. Following involution, the elastin content decreased rapidly to near baseline values by 5 days postpartum. The content of soluble elastin, estimated using an enzyme-linked immunosorbent assay, paralleled in part the increase in elastin deposition and elastin mRNA levels. Uterine elastin metabolism appears to be unlike that in other elastic tissues, e.g., lung and large blood vessels. In most elastin containing tissues, the protein is synthesized during discrete developmental periods and is not readily degraded. However, uterine elastin is continuously expressed, and appears to be in a continual cycle of degradation and replacement.     

Effects of glucose infusion on surfactant and glycogen regulation in fetal lamb lung

To investigate the increased incidence of respiratory distress syndrome (RDS) that occurs in infants of diabetic mothers (IDM) with poor maternal glucose homeostasis, we infused glucose intravenously at a rate of 14 +/- 2 (SD) mg.kg-1.min-1 into eight twin and four singleton chronically catheterized fetal lambs from 112 days (0.77) gestation onward. Twelve catheterized and seven uncatheterized fetuses served as controls, including the eight twins of the glucose-treated fetuses. Glucose infusion resulted in a twofold elevation in fetal serum glucose levels and a 2.2-fold elevation in fetal serum insulin levels. Before 113 days (0.9) gestation, pulmonary disaturated phosphatidylcholine (DSPC) content was 1.5-fold higher in the glucose-infused fetuses than in the controls. However, after 0.9 gestation, pulmonary DSPC content increased 2.2-fold in the controls but did not increase significantly in the glucose-infused fetuses. In addition, the DSPC content of lung lavage was 5.0-fold higher in the controls and lung stability to air inflation was 2.0-fold greater and to deflation was 2.2-fold greater than in the glucose-infused fetuses. Pulmonary adenosine 3',5'-cyclic monophosphate-dependent protein kinase activity was also 1.5-fold higher, and pulmonary protein kinase C activity was 1.3-fold higher in the controls than in the glucose-infused fetuses. In contrast, glucose infusion was associated with a 1.8-fold increase in pulmonary glycogen content and with increased activities of glycogen phosphorylase kinase and glycogen phosphorylase. We conclude that the effects of chronic glucose infusion on fetal lamb lung DSPC and lung stability are compatible with a predisposition of the fetus to develop RDS.(ABSTRACT TRUNCATED AT 250 WORDS)     

JNK suppresses pulmonary fibroblast elastogenesis during alveolar development

Background

The formation of discrete elastin bands at the tips of secondary alveolar septa is important for normal alveolar development, but the mechanisms regulating the lung elastogenic program are incompletely understood. JNK suppress elastin synthesis in the aorta and is important in a host of developmental processes. We sought to determine whether JNK suppresses pulmonary fibroblast elastogenesis during lung development.

Methods

Alveolar size, elastin content, and mRNA of elastin-associated genes were quantitated in wild type and JNK-deficient mouse lungs, and expression profiles were validated in primary lung fibroblasts. Tropoelastin protein was quantitated by Western blot. Changes in lung JNK activity throughout development were quantitated, and pJNK was localized by confocal imaging and lineage tracing.

Results

By morphometry, alveolar diameters were increased by 7% and lung elastin content increased 2-fold in JNK-deficient mouse lungs compared to wild type. By Western blot, tropoelastin protein was increased 5-fold in JNK-deficient lungs. Postnatal day 14 (PND14) lung JNK activity was 11-fold higher and pJNK:JNK ratio 6-fold higher compared to PN 8 week lung. Lung tropoelastin, emilin-1, fibrillin-1, fibulin-5, and lysyl oxidase mRNAs inversely correlated with lung JNK activity during alveolar development. Phosphorylated JNK localized to pulmonary lipofibroblasts. PND14 JNK-deficient mouse lungs contained 7-fold more tropoelastin, 2,000-fold more emilin-1, 800-fold more fibrillin-1, and 60-fold more fibulin-5 than PND14 wild type lungs. Primarily lung fibroblasts from wild type and JNK-deficient mice showed similar differences in elastogenic mRNAs.

Conclusions

JNK suppresses fibroblast elastogenesis during the alveolar stage of lung development.     

Increased expansion of the lung stimulates calmodulin 2 expression in fetal sheep

Obstruction of the fetal trachea causes the lungs to expand with accumulated liquid. Although this is a potent stimulus for lung growth, the mechanisms involved are unknown. Our aim was to identify genes that are differentially expressed as a result of increased fetal lung expansion. Using differential display RT-PCR, we isolated a cDNA fragment partially encoding calmodulin 2 (CALM2) and identified the remainder of the coding region by 5'-rapid amplification of cDNA ends. Differential expression of CALM2 was confirmed by Northern blot analysis; CALM2 mRNA levels were increased to 161 +/- 5% of control at 2 days of increased lung expansion, induced by tracheal obstruction (TO), and had returned to control levels at days 4 and 10. Using in situ hybridization analysis, we found that the proportion of CALM2-labeled cells increased from 10.3 +/- 1.0% to 21.4 +/- 6.8% by 2 days of TO. This increase in CALM2 expression was reflected by a tendency for calmodulin protein levels to increase from 122.7 +/- 17.3 to 156.5 +/- 17.7 at 2 days of TO. Thus increases in fetal lung expansion result in time-dependent changes in CALM2 mRNA levels, which closely parallels the changes in lung DNA synthesis rates. As calmodulin is essential for cell proliferation, increased CALM2 mRNA levels may reflect an important role for calmodulin in expansion-induced fetal lung growth.     

Tropoelastin production and tropoelastin messenger RNA activity. Relationship to copper and elastin cross-linking in chick aorta.

The elastin content of the chick thoracic aorta increases 2--3-fold during the first 3 weeks post-hatching. The deposition of elastin requires the covalent cross-linking of tropoelastin by means of lysine-derived cross-links. This process is sensitive to dietary copper intake, since copper serves as cofactor for lysyl oxidase, the enzyme that catalyses the oxidative deamination of the lysine residues involved in cross-link formation. Disruption of cross-linking alters tissue concentrations of both elastin and tropoelastin and results in a net decrease in aortic elastin content. Autoregulation of tropoelastin synthesis by changes in the pool sizes of elastin or tropoelastin has been suggested as a possible mechanism for the diminished aortic elastin content. Consequently, dietary copper deficiency was induced to study the effect of impaired elastin cross-link formation on tropoelastin synthesis. Elastin in aortae from copper-deficient chicks was only two-thirds to one-half the amount measured in copper-supplemented chicks, whereas copper-deficient concentrations of tropoelastin in aorta were at least 5-fold higher than normal. In spite of these changes, however, increased amounts of tropoelastin, copper deficiency and decreased amounts of elastin did not influence the amounts of functional elastin mRNA in aorta. Likewise, the production of tropoelastin in aorta explants was the same whether the explants were taken from copper-sufficient or -deficient birds. The lower accumulation of elastin in aorta from copper-deficient chicks appeared to be due to extracellular proteolysis, rather than to a decrease in the rate of synthesis. Electrophoresis of aorta extracts, followed by immunological detection of tropoelastin-derived products, indicated degradation products in aortae from copper-deficient birds. In extracts of aortae from copper-sufficient chicks, tropoelastin was not degraded and appeared to be incorporated into elastin without further proteolytic processing.     

Neutrophil elastase-initiated EGFR/MEK/ERK signaling counteracts stabilizing effect of autocrine TGF-beta on tropoelastin mRNA in lung fibroblasts

Neutrophil elastase (NE) plays an important role in emphysema, a pulmonary disease associated with excessive elastolysis and ineffective repair of interstitial elastin. Besides its direct elastolytic activity, NE releases soluble epidermal growth factor receptor (EGFR) ligands and initiates EGFR/MEK/ERK signaling to downregulate tropoelastin mRNA in neonatal rat lung fibroblasts (DiCamillo SJ, Carreras I, Panchenko MV, Stone PJ, Nugent MA, Foster JA, and Panchenko MP. J Biol Chem 277: 18938-18946, 2002). We now report that NE downregulates tropoelastin mRNA in the rat fetal lung fibroblast line RFL-6. The tropoelastin mRNA downregulation is preceded by release of EGF-like and TGF-alpha-like polypeptides and requires EGFR/MEK/ERK signaling, because it is prevented by the EGFR inhibitor AG1478 and the MEK/ERK uncoupler U0126. Tropoelastin expression in RFL-6 fibroblasts is governed by autocrine TGF-beta signaling, because TGF-beta type I receptor kinase inhibitor or TGF-beta neutralizing antibody dramatically decreases tropoelastin mRNA and protein levels. Half-life of tropoelastin mRNA in RFL-6 cells is >24 h, but it is decreased to approximately 8 h by addition of TGF-beta neutralizing antibody, EGF, TGF-alpha, or NE. Tropoelastin mRNA destabilization by NE, EGF, or TGF-alpha is abolished by AG1478 or U0126. EGF-dependent tropoelastin mRNA downregulation is reversed upon ligand withdrawal, whereas chronic EGF treatment leads to persistent downregulation of tropoelastin mRNA and protein levels and decreases insoluble elastin deposition. We conclude that NE-initiated EGFR/MEK/ERK signaling cascade overrides the autocrine TGF-beta signaling on tropoelastin mRNA stability and, therefore, decreases the elastogenic response in RFL-6 fibroblasts. We hypothesize that persistent EGFR/MEK/ERK signaling could impede the TGF-beta-induced elastogenesis/elastin repair in the chronically inflamed, elastase/anti-elastase imbalanced lung in emphysema.     

Pattern of accumulation of elastin and the level of mRNA for elastin in aortic tissue of growing chickens

Synthesis and accumulation of elastin in many elastic tissues begins in the last third of fetal development, reaches a maximum shortly after birth, and then declines rapidly. For the aorta of the chick and the pig and the ligamentum nuchae and lung of the sheep, it has been shown that increased levels of elastin production with fetal development are correlated with increased levels of elastin mRNA in the tissue, measured both by cell-free translation and by hybridization to cDNA probes. In this study we examine the relationship between insoluble elastin accumulation and message levels for tropoelastin in aortic tissue of chickens during posthatching development and growth. Whether evaluated by cell-free translation or by dot blot hybridization, steady state levels of tropoelastin message increase to a maximum at 2 weeks after hatching, and then fall rapidly with further development and growth. This pattern correlates well with production of insoluble elastin by the aorta, determined either by direct measurements of synthesis or by rate of accumulation of insoluble elastin. The data indicate that the major site of regulation of elastin production is pretranslational throughout the entire period of development and growth of the chicken aorta.     

Insulin-like growth factor I stimulates elastin synthesis by bovine pulmonary arterial smooth muscle cells

Insulin-like growth factor I stimulates mitogenesis in smooth muscle cells, and upregulates elastin synthesis in embryonic aortic tissue. Increased smooth muscle elastin synthesis may play an important role in vascular remodeling in chronic pulmonary hypertension. Therefore, we studied the effect of IGF-I on elastin and total protein synthesis by pulmonary arterial smooth muscle cells in vitro. Tropoelastin synthesis was measured by enzyme immunoassay, and total protein synthesis was measured by [3H]-leucine incorporation. In addition, the steady-state levels of tropoelastin mRNA were determined by slot blot hybridization. Incubation of confluent cultures with various concentrations of IGF-I resulted in a dose-dependent stimulation of elastin synthesis, with a 2.4-fold increase over control levels at 1000 ng/ml of IGF. The increase in elastin synthesis was reflected by a stimulation of the steady-state levels of tropoelastin mRNA. We conclude that IGF-I has potent elastogenic effects on vascular smooth muscle cells, and speculate that it may contribute to vascular wall remodeling in chronic hypertension.     

Developmental changes in endothelin expression and activity in the ovine fetal lung

Mechanisms that regulate endothelin (ET) in the perinatal lung are complex and poorly understood, especially with regard to the role of ET before and after birth. We hypothesized that the ET system is developmentally regulated and that the balance of ET(A) and ET(B) receptor activity favors vasoconstriction. To test this hypothesis, we performed a series of molecular and physiological studies in the fetal lamb, newborn lamb, and adult sheep. Lung preproET-1 mRNA levels, tissue ET peptide levels, and cellular localization of ET-1 expression were determined by Northern blot analysis, peptide assay, and immunohistochemistry in distal lung tissue from fetal lambs between 70 and 140 days (term = 145 days), newborn lambs, and ewes. Lung mRNA expression for the ET(A) and ET(B) receptors was also measured at these ages. We found that preproET-1 mRNA expression increased from 113 to 130 days gestation. Whole lung ET protein content was highest at 130 days gestation but decreased before birth in the fetal lamb lung. Immunolocalization of ET-1 protein showed expression of ET-1 in the vasculature and bronchial epithelium at all gestational ages. ET(A) receptor mRNA expression and ET(B) receptor mRNA increased from 90 to 125 and 135 days gestation. To determine changes in activity of the ET(A) and ET(B) receptors, we studied the effect of selective antagonists to the ET(A) or ET(B) receptors at 120, 130, and 140 days of fetal gestation. ET(A) receptor-mediated vasoconstriction increased from 120 to 140 days, whereas blockade of the ET(B) receptor did not change basal fetal pulmonary vascular tone at any age examined. We conclude that the ET system is developmentally regulated and that the increase in ET(A) receptor gene expression correlates with the onset of the vasodilator response to ET(A) receptor blockade. Although ET(B) receptor gene expression increases during late gestation, the balance of ET receptor activity favors vasoconstriction under basal conditions. We speculate that changes in ET receptor activity play important roles in regulation of pulmonary vascular tone in the ovine fetus.     

Pro-inflammatory phenotype of COPD fibroblasts not compatible with repair in COPD lung

Chronic obstructive pulmonary disease (COPD) is characterized by loss of elastic fibres from small airways and alveolar walls, with the decrease in elastin increasing with disease severity. It is unclear why there is a lack of repair of elastic fibres. We have examined fibroblasts cultured from lung tissue from subjects with or without COPD to determine if the secretory profile explains lack of tissue repair. In this study, fibroblasts were cultured from lung parenchyma of patients with mild COPD [Global initiative for chronic Obstructive Lung Disease (GOLD) 1, n= 5], moderate to severe COPD (GOLD 2-3, n= 12) and controls (non-COPD, n= 5). Measurements were made of proliferation, senescence-associated β-galactosidase-1, mRNA expression of IL-6, IL-8, MMP-1, tropoelastin and versican, and protein levels for IL-6, IL-8, PGE(2,) tropoelastin, insoluble elastin, and versican. GOLD 2-3 fibroblasts proliferated more slowly (P < 0.01), had higher levels of senescence-associated β-galactosidase-1 (P < 0.001) than controls and showed significant increases in mRNA and/or protein for IL-6 (P < 0.05), IL-8 (P < 0.01), MMP-1 (P < 0.05), PGE(2) (P < 0.05), versican (P < 0.05) and tropoelastin (P < 0.05). mRNA expression and/or protein levels of tropoelastin (P < 0.01), versican (P < 0.05), IL-6 (P < 0.05) and IL-8 (P < 0.05) were negatively correlated with FEV1% of predicted. Insoluble elastin was not increased. In summary, fibroblasts from moderate to severe COPD subjects display a secretory phenotype with up-regulation of inflammatory molecules including the matrix proteoglycan versican, and increased soluble, but not insoluble, elastin. Versican inhibits assembly of tropoelastin into insoluble elastin and we conclude that the pro-inflammatory phenotype of COPD fibroblasts is not compatible with repair of elastic fibres.     

Dysregulation of pulmonary elastin synthesis and assembly in preterm lambs with chronic lung disease

Failed alveolar formation and excess, disordered elastin are key features of neonatal chronic lung disease (CLD). We previously found fewer alveoli and more elastin in lungs of preterm compared with term lambs that had mechanical ventilation (MV) with O(2)-rich gas for 3 wk (MV-3 wk). We hypothesized that, in preterm more than in term lambs, MV-3 wk would reduce lung expression of growth factors that regulate alveolarization (VEGF, PDGF-A) and increase lung expression of growth factors [transforming growth factor (TGF)-alpha, TGF-beta(1)] and matrix molecules (tropoelastin, fibrillin-1, fibulin-5, lysyl oxidases) that regulate elastin synthesis and assembly. We measured lung expression of these genes in preterm and term lambs after MV for 1 day, 3 days, or 3 wk, and in fetal controls. Lung mRNA for VEGF, PDGF-A, and their receptors (VEGF-R2, PDGF-Ralpha) decreased in preterm and term lambs after MV-3 wk, with reduced lung content of the relevant proteins in preterm lambs with CLD. TGF-alpha and TGF-beta(1) expression increased only in lungs of preterm lambs. Tropoelastin mRNA increased more with MV of preterm than term lambs, and expression levels remained high in lambs with CLD. In contrast, fibrillin-1 and lysyl oxidase-like-1 mRNA increased transiently, and lung abundance of other elastin-assembly genes/proteins was unchanged (fibulin-5) or reduced (lysyl oxidase) in preterm lambs with CLD. Thus MV-3 wk reduces lung expression of growth factors that regulate alveolarization and differentially alters expression of growth factors and matrix proteins that regulate elastin assembly. These changes, coupled with increased lung elastase activity measured in preterm lambs after MV for 1-3 days, likely contribute to CLD.     

Elastase-released epidermal growth factor recruits epidermal growth factor receptor and extracellular signal-regulated kinases to down-regulate tropoelastin mRNA in lung fibroblasts

Elastase/anti-elastase imbalance is a hallmark of emphysema, a chronic obstructive pulmonary disease associated with the rupture and inefficient repair of interstitial elastin. We report that neutrophil elastase (NE) at low physiologic concentrations, ranging from 35 nm to 1 microm, invokes transient, peaking at 15 min, activation of extracellular signal-regulated kinases 1 and 2 (ERK) in elastogenic lung fibroblasts. ERK activation is preceded by the release of soluble 25-26-kDa forms of epidermal growth factor (EGF) and transactivation of EGF receptor (EGFR) in NE-exposed cells. The stimulatory effect of NE on ERK is abrogated in the presence of anti-EGF-neutralizing antibodies, EGFR tyrosine kinase inhibitor (AG1478), and ERK kinase inhibitor (PD98059), as well as abolished in both EGFR-desensitized and endocytosis-arrested fibroblasts. Nuclear accumulation of activated ERK is associated with transient, peaking at 30 min, induction of c-Fos and sustained, observed at 24-48 h, decrease of tropoelastin mRNA levels in NE-challenged cells. Pretreatment of fibroblasts with AG1478 or PD98059 abrogates the NE-initiated tropoelastin mRNA suppression. We conclude that proteolytically released EGF signals directly via EGFR and ERK to down-regulate tropoelastin mRNA in NE-challenged lung fibroblasts.     

Elastin mRNA levels during foetal development of sheep nuchal ligament and lung. Hybridization to complementary and cloned DNA

Elastin mRNA levels were quantified in sheep nuchal ligament and lung during the latter half of foetal development with elastin-specific cDNA (complementary DNA) probes using both hybridization in solution (saturation analysis) and hybridization on a fixed support (Northern analysis). For the solution-hybridization studies, cDNA prepared from nuchal-ligament mRNA was enriched to 65% for elastin sequences by hybridizing it to its template at a R0t (mol X s X litre-1) value that included only the abundant class of mRNA sequences. Hybridization of this probe to RNA extracted from nuchal ligament between 70 and 138 days after conception demonstrated elastin sequences increased about 10-fold (from 0.047 to 0.438% of total RNA). In contrast, lung elastin mRNA levels increased only 3-fold (from 0.009 to 0.022% of total RNA) during the same period. Over this development period these values correspond to increases in the average number of elastin mRNA molecules from 950 to 20 000 molecules/ligament cell and from 130 to 330 molecules/lung cell. For Northern analysis, elastin mRNA was purified from near-term-sheep nuchal ligament on sucrose density gradients. Analysis of the translation products of this elastin mRNA showed that relative elastin precursor synthesis was at least 80% of total [3H]valine incorporation. The Mr of this elastin mRNA, determined by methylmercury-agarose-gel electrophoresis, was approx. 1.25 X 10(6). Northern hybridization of nuchal ligament and lung RNA to a [32P]cDNA probe, transcribed from this sucrose-gradient-purified elastin mRNA, confirmed the developmental changes in elastin mRNA levels detected by solution-hybridization techniques. The specificity of this method was confirmed by using a cloned elastin gene fragment. These studies demonstrate that elastin mRNA levels in organs such as nuchal ligament and lung increase with foetal development, but that there are significant differences in the average cellular elastin mRNA content of these two organs.     

Developmental changes in endothelial nitric oxide synthase expression and activity in ovine fetal lung

Endothelial nitric oxide (NO) synthase (eNOS) produces NO, which contributes to vascular reactivity in the fetal lung. Pulmonary vasoreactivity develops during late gestation in the ovine fetal lung, during the period of rapid capillary and alveolar growth. Although eNOS expression peaks near birth in the fetal rat, lung capillary and distal air space development occur much later than in the fetal lamb. To determine whether lung eNOS expression in the lamb differs from the timing and pattern reported in the rat, we measured eNOS mRNA and protein by Northern and Western blot analyses and NOS activity by the arginine-to-citrulline conversion assay in lung tissue from fetal, newborn, and maternal sheep. Cellular localization of eNOS expression was determined by immunohistochemistry. eNOS mRNA, protein, and activity were detected in samples from all ages, and eNOS was expressed predominantly in the vascular endothelium. Lung eNOS mRNA expression increases from low levels at 70 days gestation to peak at 113 days and remains high for the rest of fetal life. Newborn eNOS mRNA expression does not change from fetal levels but is lower in the adult ewe. Lung eNOS protein expression in the fetus rises and peaks at 118 days gestation but decreases before birth. eNOS protein expression rises in the newborn period but is lower in the adult. Lung NOS activity also peaks at 118 days gestation in the fetus before falling in late gestation and remaining low in the newborn and adult. We conclude that the pattern of lung eNOS expression in the sheep differs from that in the rat and may reflect species-related differences in lung development. We speculate that the rise in fetal lung eNOS may contribute to the marked lung growth and angiogenesis that occurs during the same period of time.     

Studies on pulmonary surfactant. Effects of cortisol administration to fetal rabbits on lung phospholipid content, composition and biosynthesis.

Corticosteroids are known to accelerate maturation of the fetal lung and production of surfactant. We examined the effect of cortisol administration to fetal rabbits on the phospholipid content and composition of lung lavage and lung tissue, as well as on the activities of enzymes involved in the synthesis of phosphatidylcholine and phosphatidylglycerol, the major surface-active components of surfactant. Cortisol was administered by intrauterine injection at 25 days' gestation and the fetuses were delivered at 27 days (full term, 31 days). Saline-injected fetuses, littermates of the cortisol-treated as well as non-littermates, were used as controls. The amount of phospholipid in lung lavage from the hormone-treated fetuses was almost double that of the saline-injected controls and was similar to that of an untreated fetus of more than 30 days' gestation. Similarly, the phospholipid composition of lung lavage from the hormone-treated fetuses was similar to that of an untreated fetus at a greater gestational age. These data, therefore, suggest that cortisol acts by accelerating physiological development. Cortisol administratration stimulated the activity of cholinephosphate cytidylyltransferase and lysolecithin acyltransferase to a small, but statistically significant extent. This is also consistent with an acceleration of normal development. The stimulation of lysolecithin acyltransferase is of interest, since this enzyme is believed to be involved in the synthesis of dipalmitoylglycerophosphocholine, the major surface-active species of phosphatidylcholine. Cortisol administration had no effect on the activities of pulmonary choline kinase, cholinephosphotransferase, lysophosphatidic acid acyltransferase and glycerolphosphate phosphatidyltranferase, although we have previously shown the latter enzyme to be stimulated following a longer period of exposure to the hormone. Saline injection produced some maturational effects presumably as a result of stress, which may be mediated by corticosteroids or other hormones.     

Glucocorticoids stimulate elastin production in differentiated bovine ligament fibroblasts but do not induce elastin synthesis in undifferentiated cells

Glucocorticoid treatment of fibroblasts from late gestation fetal bovine ligamentum nuchae resulted in a time- and dose-dependent selective increase in elastin production. Tropoelastin levels increased 2-3-fold in the presence of 10 nM dexamethasone while total protein synthesis and the rate of cell division decreased with glucocorticoid exposure. Two tropoelastin bands of molecular weights 64,500 and 61,000 were identified by immunoprecipitation and sodium dodecyl sulfate gradient-gel electrophoresis and both bands increased to an equal extent in the presence of dexamethasone. Undifferentiated cells from early-gestation animals did not synthesize elastin after hormone exposure, even though glucocorticoid receptors were demonstrated by nuclear-translocation experiments. These results indicate that glucocorticoids stimulate elastin production in elastin-producing ligament cells but do not induce elastin synthesis (differentiation) in undifferentiated cells.     

Regulation of alveolar epithelial cell phenotypes in fetal sheep: roles of cortisol and lung expansion

Our aim was to determine whether cortisol's effect on alveolar epithelial cell (AEC) phenotypes in the fetus is mediated via a sustained alteration in lung expansion. Chronically catheterized fetal sheep were exposed to 1) saline infusion, 2) cortisol infusion (122-131 days' gestation, 1.5-4.0 mg/day), 3) saline infusion plus reduced lung expansion, or 4) cortisol infusion plus reduced lung expansion. The proportions of type I and II AECs were determined by electron microscopy, and surfactant protein (SP)-A, -B, and -C mRNA levels were determined by Northern blot analysis. Cortisol infusions significantly increased type II AEC proportions (to 38.2 +/- 2.2%), compared with saline-infused fetuses (23.8 +/- 2.4%), and reduced type I AEC proportions (to 59.0 +/- 2.2%), compared with saline-infused fetuses (70.4 +/- 2.4%). Reduced lung expansion also increased type II AEC proportions (to 52.9 +/- 3.5%) and decreased type I AEC proportions (to 34.2 +/- 3.7%), compared with control, saline-infused fetuses. The infusion of cortisol into fetuses exposed to reduced lung expansion tended to further increase type II (to 60.3 +/- 2.1%, P = 0.066) and reduce type I AEC (to 26.6 +/- 2.3%, P = 0.07) proportions. SP-A, -B, and -C mRNA levels changed in parallel with the changes in type II AEC proportions. These results indicate that cortisol alters the proportion of type I and type II AECs via a mechanism unrelated to the degree of fetal lung expansion. However, reductions in fetal lung expansion appear to have a greater impact on the proportion of AECs than cortisol.     

Stimualtion of glycerolphosphate phosphatidyltransferase activity in fetal rabbit lung by cortisol administration.

Phosphatidylglycerol is an important component of pulmonary surfactant. Previous studies have shown that direct administration of corticosteroids of thyroxine to the fetus during the latter part of gestation results in accelerated lung maturation with increased surfactant production. We have shown that administration of cortisol to fetal rabbits at 24 days' gestation results 3 days later in a significant increase in the activity of pulmonary glycerolphosphate phosphatidyltransferase, an enzyme involved in the synthesis of phosphatidylglycerol. The activity of the liver enzyme was not affected. Choline phosphotransferase, CDPdiglyceride-inositol phosphatidyltransferase, lysophosphatidic acid acyltransferase and lysolecithin acyltransferase activities were not altered significantly by cortisol treatment. Thyroxine treatment had no effect on any of the enzymes of phospholipid or fatty acid biosynthesis studied.