Down-regulation of thyroid transcription factor-1 gene expression in fetal lung hypoplasia is restored by glucocorticoids

Basic and translational science advances in congenital diaphragmatic hernia

Congenital Diaphragmatic Hernia (CDH) is a birth defect that is characterized by lung hypoplasia, pulmonary hypertension and a diaphragmatic defect that allows herniation of abdominal organs into the thoracic cavity. Although widely unknown to the public, it occurs as frequently as cystic fibrosis (1:2500). There is no monogenetic cause, but different animal models revealed various biological processes and epigenetic factors involved in the pathogenesis. However, the pathobiology of CDH is not sufficiently understood and its mortality still ranges between 30 and 50%. Future collaborative initiatives are required to improve our basic knowledge and advance novel strategies to (prenatally) treat the abnormal lung development. This review focusses on the genetic, epigenetic and protein background and the latest advances in basic and translational aspects of CDH research.

Assessment of the nitrofen model of congenital diaphragmatic hernia and of the dysregulated factors involved in pulmonary hypoplasia

PURPOSE

To study pulmonary hypoplasia (PH) associated with congenital diaphragmatic hernia (CDH), investigators have been employing a fetal rat model based on nitrofen administration to dams. Herein, we aimed to: (1) investigate the validity of the model, and (2) synthesize the main biological pathways implicated in the development of PH associated with CDH.

METHODS

Using a defined strategy, we conducted a systematic review of the literature searching for studies reporting the incidence of CDH or factors involved in PH development. We also searched for PH factor interactions, relevance to lung development and to human PH.

RESULTS

Of 335 full-text articles, 116 reported the incidence of CDH after nitrofen exposure or dysregulated factors in the lungs of nitrofen-exposed rat fetuses. CDH incidence: 54% (27-85%) fetuses developed a diaphragmatic defect, whereas the whole litter had PH in varying degrees. Downregulated signaling pathways included FGF/FGFR, BMP/BMPR, Sonic Hedgehog and retinoid acid signaling pathway, resulting in a delay in early epithelial differentiation, immature distal epithelium and dysfunctional mesenchyme.

CONCLUSIONS

The nitrofen model effectively reproduces PH as it disrupts pathways that are critical for lung branching morphogenesis and alveolar differentiation. The low CDH rate confirms that PH is an associated phenomenon rather than the result of mechanical compression alone.

Evolution, Development, and Function of the Pulmonary Surfactant System in Normal and Perturbed Environments

Surfactant lipids and proteins form a surface active film at the air-liquid interface of internal gas exchange organs, including swim bladders and lungs. The system is uniquely positioned to meet both the physical challenges associated with a dynamically changing internal air-liquid interface, and the environmental challenges associated with the foreign pathogens and particles to which the internal surface is exposed. Lungs range from simple, transparent, bag-like units to complex, multilobed, compartmentalized structures. Despite this anatomical variability, the surfactant system is remarkably conserved. Here, we discuss the evolutionary origin of the surfactant system, which likely predates lungs. We describe the evolution of surfactant structure and function in invertebrates and vertebrates. We focus on changes in lipid and protein composition and surfactant function from its antiadhesive and innate immune to its alveolar stability and structural integrity functions. We discuss the biochemical, hormonal, autonomic, and mechanical factors that regulate normal surfactant secretion in mature animals. We present an analysis of the ontogeny of surfactant development among the vertebrates and the contribution of different regulatory mechanisms that control this development. We also discuss environmental (oxygen), hormonal and biochemical (glucocorticoids and glucose) and pollutant (maternal smoking, alcohol, and common "recreational" drugs) effects that impact surfactant development. On the adult surfactant system, we focus on environmental variables including temperature, pressure, and hypoxia that have shaped its evolution and we discuss the resultant biochemical, biophysical, and cellular adaptations. Finally, we discuss the effect of major modern gaseous and particulate pollutants on the lung and surfactant system.

Medical interventions to reverse pulmonary hypoplasia in the animal model of congenital diaphragmatic hernia: A systematic review

We aimed to systematically review all published pre-clinical research on prenatal medical treatment of pulmonary hypoplasia in congenital diaphragmatic hernia (CDH). Background The neonatal mortality due to isolated CDH remains high. Whether fetal endoscopic tracheal occlusion (FETO) reduces mortality is still to be demonstrated. Therefore more potent preferentially medical therapy would be welcomed. Methods We searched MEDLINE (Pubmed), Embase and the Web of Science including all studies from the earliest date (1951) to December 2013. Article quality was assessed using the modified CAMRADES checklist. Inclusion criteria were those animal studies addressing prenatal medical interventions and principal variables were confirmation of a diaphragmatic defect, lung to body weight ratio (LBWR), formal airway morphometry or DNA/protein content. Results In total 983 articles were identified. Following abstract review, 96 articles were assessed by two authors in agreement with a third for eligibility. Of these, 43 were included in the final analysis. The median number of study quality checklist items (maximum 10) scored was 4 (IQ range: 2-5). Thirty (69.8%) of studies were in the nitrofen rat. The majority were treated with vitamins or glucocorticoids. Single studies reported some improvement in lung morphology with alternative therapies. It was impossible to identify a pattern in animal model selection or creation, mode, time point or duration of treatment and readouts. Only one study reported a sample size calculation. Conclusion Comparison in pre-clinical studies in CDH is challenging due to methodological variation. Agreed standardized methods need to be applied in future investigation of new medical therapies.

Novel non-surgical prenatal approaches to treating congenital diaphragmatic hernia

This review focuses on the emerging field of non-surgical in-utero therapies in the management of fetal pulmonary hypoplasia and pulmonary hypertension associated with congenital diaphragmatic hernia (CDH). These experimental approaches include pharmacologic as well as stem-cell-based strategies. Current barriers of non-surgical therapies toward clinical translation are emphasized. As the severity of CDH will likely influence the efficacy of any in-utero therapy, the current status of prenatal imaging and the role of novel biomarkers, especially those related to fetal inflammation, are also reviewed.

Pulmonary GLP-1 receptor increases at birth and exogenous GLP-1 receptor agonists augmented surfactant-protein levels in litters from normal and nitrofen-treated pregnant rats

The glucagon-like peptide-1 receptor (GLP-1R) is found in a variety of tissues outside of the pancreas. For example, GLP-1R is expressed in the lung, where it has been implicated in the regulation of the lipid fraction of surfactants, suggesting it fulfills an important role in lung function. Here, we show that GLP-1R expression is strongly up-regulated immediately after birth in neonatal rats, particular in male offspring. Moreover, administering long half-life GLP-1R agonists to the mother from gestational day 14 to birth (exendin-4 or liraglutide) increased surfactant protein (SP)-A and SP-B mRNA expression and the amount of SPs in the amniotic fluid at the end of pregnancy. These effects were similar or more potent to those induced by the glucocorticoid dexamethasone, which also increased GLP-1R expression in fetuses just before delivery. Lir increased fetal SP-A and GLP-1R expression in control rats and in a nitrofen-induced model of lung hypoplasia. Moreover, lung size increased in controls after Lir administration, which also prevented the decrease in lung weight and the poor neonatal survival of the offspring from nitrofen-treated dams, effects that were not produced by dexamethasone. Taken together, our results demonstrate the importance of the GLP-1 system in regulating SP production and lung development.

Synergistic effect of caffeine and glucocorticoids on expression of surfactant protein B (SP-B) mRNA

Administration of glucocorticoids and caffeine is a common therapeutic intervention in the neonatal period, but possible interactions between these substances are still unclear. The present study investigated the effect of caffeine and different glucocorticoids on expression of surfactant protein (SP)-B, crucial for the physiological function of pulmonary surfactant. We measured expression levels of SP-B, various SP-B transcription factors including erythroblastic leukemia viral oncogene homolog 4 (ErbB4) and thyroid transcription factor-1 (TTF-1), as well as the glucocorticoid receptor (GR) after administering different doses of glucocorticoids, caffeine, cAMP, or the phosphodiesterase-4 inhibitor rolipram in the human airway epithelial cell line NCI-H441. Administration of dexamethasone (1 µM) or caffeine (5 mM) stimulated SP-B mRNA expression with a maximal of 38.8±11.1-fold and 5.2±1.4-fold increase, respectively. Synergistic induction was achieved after co-administration of dexamethasone (1 mM) in combination with caffeine (10 mM) (206±59.7-fold increase, p<0.0001) or cAMP (1 mM) (213±111-fold increase, p = 0.0108). SP-B mRNA was synergistically induced also by administration of caffeine with hydrocortisone (87.9±39.0), prednisolone (154±66.8), and betamethasone (123±6.4). Rolipram also induced SP-B mRNA (64.9±21.0-fold increase). We detected a higher expression of ErbB4 and GR mRNA (7.0- and 1.7-fold increase, respectively), whereas TTF-1, Jun B, c-Jun, SP1, SP3, and HNF-3α mRNA expression was predominantly unchanged. In accordance with mRNA data, mature SP-B was induced significantly by dexamethasone with caffeine (13.8±9.0-fold increase, p = 0.0134). We found a synergistic upregulation of SP-B mRNA expression induced by co-administration of various glucocorticoids and caffeine, achieved by accumulation of intracellular cAMP. This effect was mediated by a caffeine-dependent phosphodiesterase inhibition and by upregulation of both ErbB4 and the GR. These results suggested that caffeine is able to induce the expression of SP-transcription factors and affects the signaling pathways of glucocorticoids, amplifying their effects. Co-administration of caffeine and corticosteroids may therefore be of benefit in surfactant homeostasis.

Antenatal steroids and the IUGR fetus: are exposure and physiological effects on the lung and cardiovascular system the same as in normally grown fetuses?

Glucocorticoids are administered to pregnant women at risk of preterm labour to promote fetal lung surfactant maturation. Intrauterine growth restriction (IUGR) is associated with an increased risk of preterm labour. Hence, IUGR babies may be exposed to antenatal glucocorticoids. The ability of the placenta or blood brain barrier to remove glucocorticoids from the fetal compartment or the brain is compromised in the IUGR fetus, which may have implications for lung, brain, and heart development. There is conflicting evidence on the effect of exogenous glucocorticoids on surfactant protein expression in different animal models of IUGR. Furthermore, the IUGR fetus undergoes significant cardiovascular adaptations, including altered blood pressure regulation, which is in conflict with glucocorticoid-induced alterations in blood pressure and flow. Hence, antenatal glucocorticoid therapy in the IUGR fetus may compromise regulation of cardiovascular development. The role of cortisol in cardiomyocyte development is not clear with conflicting evidence in different species and models of IUGR. Further studies are required to study the effects of antenatal glucocorticoids on lung, brain, and heart development in the IUGR fetus. Of specific interest are the aetiology of IUGR and the resultant degree, duration, and severity of hypoxemia.

Lung hypoplasia in rats with esophageal atresia and tracheo-esophageal fistula

INTRODUCTION

Survivors of esophageal atresia and tracheo-esophageal fistula (EA-TEF) often suffer chronic respiratory tract disease. EA-TEF results from abnormal emergence of the trachea from the foregut. This study in a rat model tests the hypothesis that primary lung maldevelopment might be a downstream consequence of this defect.

RESULTS

The lung was hypoplastic in rats with EA-TEF although the histological pattern was normal. Maturation and arteriolar wall thickness were unchanged, but mesenchymal control of airway branching was weakened. This branching was deficient from embryonal day (E13) on in adriamycin-treated explants.

DISCUSSION

In conclusion, the lungs were hypoplastic in rats with experimental EA-TEF due to defective embryonal airway branching. However, arteriolar wall and respiratory epithelial patterns remained normal. These findings suggest that similarly defective lung development might contribute to chronic respiratory disease in EA-TEF patients.

METHODS

Pregnant rats received either 1.75 mg/kg i.p. adriamycin or vehicle on E7, E8, and E9. Lungs were recovered at E15, E18, and E2. Lung weight/body weight ratio, total DNA and protein, radial alveolar count, arteriolar wall thickness, lung maturity, and mesenchymal control of airway branching were assessed. E13 lungs were cultured for 72 h and explant airway branching was measured daily. For comparisons, nonparametric tests (*P < 0.05) were used.

Thyroid transcription factor-1 (TTF-1/Nkx2.1/TITF1) gene regulation in the lung

TTF-1 [thyroid transcription factor-1; also known as Nkx2.1, T/EBP (thyroid-specific-enhancer-binding protein) or TITF1] is a homeodomain-containing transcription factor essential for the morphogenesis and differentiation of the thyroid, lung and ventral forebrain. TTF-1 controls the expression of select genes in the thyroid, lung and the central nervous system. In the lung, TTF-1 controls the expression of surfactant proteins that are essential for lung stability and lung host defence. Human TTF-1 is encoded by a single gene located on chromosome 14 and is organized into two/three exons and one/two introns. Multiple transcription start sites and alternative splicing produce mRNAs with heterogeneity at the 5' end. The 3' end of the TTF-1 mRNA is characterized by a rather long untranslated region. The amino acid sequences of TTF-1 from human, rat, mouse and other species are very similar, indicating a high degree of sequence conservation. TTF-1 promoter activity is maintained by the combinatorial or co-operative actions of HNF-3 [hepatocyte nuclear factor-3; also known as FOXA (forkhead box A)], Sp (specificity protein) 1, Sp3, GATA-6 and HOXB3 (homeobox B3) transcription factors. There is limited information on the regulation of TTF-1 gene expression by hormones, cytokines and other biological agents. Glucocorticoids, cAMP and TGF-beta (transforming growth factor-beta) have stimulatory effects on TTF-1 expression, whereas TNF-alpha (tumour necrosis factor-alpha) and ceramide have inhibitory effects on TTF-1 DNA-binding activity in lung cells. Haplo-insufficiency of TTF-1 in humans causes hypothyroidism, respiratory dysfunction and recurring pulmonary infections, underlining the importance of optimal TTF-1 levels for the maintenance of thyroid and lung function. Recent studies have implicated TTF-1 as a lineage-specific proto-oncogene for lung cancer.

Surfactant maturation is not delayed in human fetuses with diaphragmatic hernia

BACKGROUND

Pulmonary hypoplasia and persistent pulmonary hypertension account for significant mortality and morbidity in neonates with congenital diaphragmatic hernia (CDH). Global lung immaturity and studies in animal models suggest the presence of surfactant deficiency that may further complicate the pathophysiology of CDH. However, data about surfactant status in human fetuses with CDH at birth are contradictory. The lack of a chronological study of surfactant content in late pregnancy has been a significant limitation. The appropriateness of administering surfactant supplements to neonates with CDH is therefore a debated question.

METHODS AND FINDINGS

We investigated surfactant content in human fetuses with CDH compared to age-matched fetuses with nonpulmonary diseases used as controls. Concentrations of disaturated phosphatidylcholine and surfactant proteins were found to be similar at a given stage of pregnancy, with both components showing a similar pattern of increase with progressing pregnancy in fetuses with CDH and in control fetuses. Thyroid transcription factor 1, a critical regulator of surfactant protein transcription, similarly displayed no difference in abundance. Finally, we examined the expression of three glucocorticoid-regulated diffusible mediators involved in lung epithelial maturation, namely: keratinocyte growth factor (KGF), leptin, and neuregulin 1 beta 1 (NRG1-beta1). KGF expression decreased slightly with time in control fetuses, but remained unchanged in fetuses with CDH. Leptin and NRG1-beta1 similarly increased in late pregnancy in control and CDH lungs. These maturation factors were also determined in the sheep fetus with surgical diaphragmatic hernia, in which surfactant deficiency has been reported previously. In contrast to the findings in humans, surgical diaphragmatic hernia in the sheep fetus was associated with decreased KGF and neuregulin expression. Fetoscopic endoluminal tracheal occlusion performed in the sheep model to correct lung hypoplasia increased leptin expression, partially restored KGF expression, and fully restored neuregulin expression.

CONCLUSIONS

Our results indicate that CDH does not impair surfactant storage in human fetuses. CDH lungs exhibited no trend toward a decrease in contents, or a delay in developmental changes for any of the studied surfactant components and surfactant maturation factors. Surfactant amounts are likely to be appropriate to lung size. These findings therefore do not support the use of surfactant therapy for infants with CDH. Moreover, they raise the question of the relevance of CDH animal models to explore lung biochemical maturity.

Thyroid transcription factor in differentiating type II cells: regulation, isoforms, and target genes

Thyroid transcription factor-1 (TTF-1, product of the Nkx2.1 gene) is essential for branching morphogenesis of the lung and enhances expression of surfactant proteins by alveolar type II cells. We investigated expression of two TTF-1 mRNA transcripts, generated by alternative start sites and coding for 42- and 46-kD protein isoforms in the mouse, during hormone-induced differentiation of human fetal lung type II cells in culture. Transcript for 42-kD TTF-1 was 20-fold more abundant than TTF-1(46) mRNA by RT-PCR. Only 42-kD protein was detected in lung cells, and its content increased during in vivo development and in response to in vitro glucocorticoid plus cAMP treatment. To examine TTF-1 target proteins, recombinant, phosphorylated TTF-1(42) was expressed in nuclei of cells by adenovirus transduction. By microarray analysis, 14 genes were comparably induced by recombinant TTF-1 (rTTF-1) and hormone treatment, and 9 additional hormone-responsive genes, including surfactant proteins-A/B/C, were partially induced by rTTF-1. The most highly (approximately 10-fold) TTF-1-induced genes were DC-LAMP (LAMP3) and CEACAM6 with induction confirmed by Western analysis and immunostaining. Treatment of cells with hormones plus small inhibitory RNA directed toward TTF-1 reduced TTF-1 content by approximately 50% and inhibited hormone induction of the 23 genes induced by rTTF-1. In addition, knockdown of TTF-1 inhibited 72 of 274 other genes induced by hormones. We conclude that 42-kD TTF-1 is required for induction of a subset of regulated genes during type II cell differentiation.

Proteasome dysfunction inhibits surfactant protein gene expression in lung epithelial cells: mechanism of inhibition of SP-B gene expression

Surfactant proteins maintain lung function through their actions to reduce alveolar surface tension and control of innate immune responses in the lung. The ubiquitin proteasome pathway is responsible for the degradation of majority of intracellular proteins in eukaryotic cells, and proteasome dysfunction has been linked to the development of neurodegenerative, cardiac, and other diseases. Proteasome function is impaired in interstitial lung diseases associated with surfactant protein C (SP-C) mutation mapping to the BRICHOS domain located in the proSP-C protein. In this study we determined the effects of proteasome inhibition on surfactant protein expression in H441 and MLE-12 lung epithelial cells to understand the relationship between proteasome dysfunction and surfactant protein gene expression. Proteasome inhibitors lactacystin and MG132 reduced the levels of SP-A, SP-B, and SP-C mRNAs in a concentration-dependent manner in H441 and MLE-12 cells. In H441 cells, lactacystin and MG132 inhibition of SP-B mRNA was associated with similar decreases in SP-B protein, and the inhibition was due to inhibition of gene transcription. Proteasome inhibitors decreased thyroid transcription factor-1 (TTF-1)/Nkx2.1 DNA binding activity, and the reduced TTF-1 DNA binding activity was due to reduced expression levels of TTF-1 protein. These data indicated that the ubiquitin proteasome pathway is essential for the maintenance of surfactant protein gene expression and that disruption of this pathway inhibits surfactant protein gene expression via reduced expression of TTF-1 protein.

Retinoic acid rescues lung hypoplasia in nitrofen-induced hypoplastic foetal rat lung explants

There is increasing evidence to suggest that the retinoid pathway is involved in the pathogenesis of congenital diaphragmatic hernia (CDH). We hypothesised that retinoids are involved in the pathogenesis of associated pulmonary hypoplasia in CDH and therefore designed this study to investigate the effects of retinoid acid on nitrofen-induced hypoplastic lungs. Pregnant rats were exposed to either olive oil or 100 mg nitrofen on day 9.5 of gestation. Foetal lungs were harvested on embryonic day 13.5 and were cultured for 96 h with or without exogenous retinoic acid (RA) (1 muM) added daily to the culture medium. Lungs were divided into four study groups: control (n=31); control + RA (n=19); nitrofen (n=19); and nitrofen + RA (n=12). Lung growth was assessed in each group by measuring branching morphogenesis, total DNA content and the proportion of proliferating cells stained by immunohistochemistry. One-way ANOVA test was used for statistical analysis. Retinoic acid significantly increased the growth of nitrofen-induced hypoplastic lungs, whilst growth of control lungs did not change. The number of lung buds and lung area of nitrofen-exposed hypoplastic lungs after 96 h of culture significantly increased after the addition of RA compared to the non-treated hypoplastic lungs (25.75+/-6.47 vs 15.11+/-3.29 and 0.98+/-0.18 mm(2) vs 0.65+/-0.13 mm(2), respectively; P<0.0001). Lung perimeter was also higher when RA was added to hypoplastic lungs compared to the non-treated ones, although it did not reach significance (12.51+/-2.53 mm vs 11.19+/-2.56 mm; P=0.17). Conversely, the addition of RA to control lungs did not affect the number of lung buds, lung area or lung perimeter after 96 h in culture compared to the non-treated ones (31.28+/-4.66 vs 31.81+/-6.67; 1.29+/-0.18(2) vs 1.29+/-0.23 mm(2) and 18.47+/-3.47 mm vs 17.89+/-2.94 mm, respectively; P=NS). Retinoic acid also increased the total DNA content and the proportion of proliferating cells in hypoplastic lungs compared to the non-treated ones (2.59+/-0.58 mug vs 1.96+/-0.31 mug and 57.89+/-9.46% vs 36.76+/-8.15%, respectively; P<0.001). The addition of RA did not affect either total DNA content or the proportion of proliferating cells in control lungs compared to the non-treated ones (4.04+/-0.64 mug vs 3.79+/-0.85 mug and 58.67+/-11.23% vs 56.03+/-10.36%, respectively; P=NS). This study demonstrates for the first time that RA rescues lung hypoplasia in nitrofen-induced hypoplastic lungs. These results suggest that retinoid pathway may be involved in the pathogenesis of associated pulmonary hypoplasia in CDH.

Histochemical analyses of altered fetal lung development following single vs multiple courses of antenatal steroids

A single course of antenatal steroids is widely used during preterm labor to promote fetal lung maturation. However, little is known regarding efficacy and safety of multiple courses of antenatal steroids. In animal models and clinical trials, treatment with glucocorticoids can inhibit growth. The present study of single- vs multiple-course steroids in pregnant ewes analyzes the effects of steroids vs placebo on fetal lung histopathology. Single-course groups received dexamethasone (Dex) 6 mg or normal saline every 12 hr for 48 hr at 104-106 days of gestation (term = 150 days). Multiple-course groups received the first course at 76-78 days; this was repeated weekly for 5 weeks. At 108 days, lungs were analyzed using immunohistochemistry for alpha-smooth muscle actin, a myofibroblast marker and proliferating cell nuclear antigen. Cell injury/death was evaluated using TdT-mediated dUTP digoxigenin nick end labeling (TUNEL) analysis. Although fetal growth was restricted by either single or multiple courses of Dex, alveolar development was accelerated as measured by mean linear intercepts. Alveolar walls were thinner, developing septa were longer, and septal myofibroblasts were increased for both Dex groups compared with controls. Cell proliferation increased following multiple steroid courses, especially in the distal parenchyma, with a corresponding decrease in apoptosis. These observations suggest that Dex promotes alveolarization, whether given in single or multiple courses.

Congenital diaphragmatic hernia, tracheal occlusion, thyroid transcription factor-1, and fetal pulmonary epithelial maturation

Congenital diaphragmatic hernia (CDH) occurs in ∼1:2,500 human births and has high morbidity and mortality rates, primarily due to pulmonary hypoplasia and pulmonary hypertension. Tracheal occlusion (TO), in experimental animals, distends lungs and increases lung growth and alveolar type I cell maturation but decreases surfactant components and reduces alveolar type II cell density. We examined effects of CDH and CDH+TO on lung growth and maturation in fetal rats. To induce CDH, we administered nitrofen (100 mg) to dams at 9.5 days of gestation. We compared lungs from fetuses with CDH, CDH+TO, and those exposed to nitrofen without CDH. CDH decreased lung wet weight bilaterally ( P < 0.0001) and DNA content in lung ipsilateral to CDH ( P < 0.05). CDH+TO significantly increased lung wet weights bilaterally; DNA content was intermediate between CDH and NC. To evaluate effects on the distal pulmonary epithelium, we examined surfactant mRNA and protein levels, type I and II cell-specific markers (RTI40 and RTII70, respectively), and transcriptional regulator thyroid transcription factor-1 (TTF-1). Decreased lung distension (due to CDH) increased SP-C mRNA and TTF-1 protein expression and reduced RTI40 ( P < 0.05 for all). Increased lung distension (due to CDH+TO) reduced expression of SP mRNAs and pro-SP-C and TTF-1 proteins and enhanced expression of RTI40 (mRNA and protein; P < 0.05 for all). We conclude that CDH+TO partially reverses effects of CDH; it corrects the pulmonary hypoplasia and restores type I cell differentiation but adversely affects SP expression in type II cells. These effects may be mediated through changes in TTF-1 expression.

Neonatal thyrotoxicosis and persistent pulmonary hypertension necessitating extracorporeal life support

We report a case of neonatal Graves' disease involving an infant with severe persistent pulmonary hypertension (PPHN) associated with neonatal thyrotoxicosis that necessitated extracorporeal membrane oxygenation. Hyperthyroidism, although uncommon in the newborn period, has been associated with pulmonary hypertension among adults. The exact mechanisms responsible for this effect on pulmonary vascular pressure are not well understood. Recent studies have provided evidence that thyrotoxicosis has direct and indirect effects on pulmonary vascular maturation, metabolism of endogenous pulmonary vasodilators, oxygen economy, vascular smooth muscle reactivity, and surfactant production, all of which may contribute to the pathophysiologic development of PPHN. Therefore, because PPHN is a significant clinical entity among term newborns and the symptoms of hyperthyroidism may be confused initially with those of other underlying disorders associated with PPHN (eg, sepsis), it would be prudent to perform screening for hyperthyroidism among affected newborns.

Pituitary hypoplasia and respiratory distress syndrome in Prop1 knockout mice

Mutations in Prophet of PIT1 (Prop1), one of several homeodomain transcription factors that are required for the development of the anterior pituitary gland, are the predominant cause of MPHD (multiple pituitary hormone deficiency) in humans. We show that deletion of Prop1 in mice causes severe pituitary hypoplasia with failure of the entire Pit1 lineage and delayed gonadotrope development. The pituitary hormone deficiencies cause secondary endocrine problems and a high rate of perinatal mortality due to respiratory distress. Lung atelectasis in mutants correlates with reduced levels of NKX2.1 and surfactant. Lethality of mice homozygous for either the null allele or a spontaneous hypomorphic allele is strongly influenced by genetic background. Prop1-null mice are an excellent model for MPHD and may be useful for testing the efficacy of pharmaceutical intervention for neonatal respiratory distress.

Developmental cooperation of leukemia inhibitory factor and insulin-like growth factor I in mice is tissue-specific and essential for lung maturation involving the transcription factors Sp3 and TTF-1

The multifunctional proteins leukemia inhibitory factor (LIF) and insulin-like growth factor I (IGF-I) are expressed in overlapping patterns during development and, therefore, may act cooperatively. We show that mice doubly deficient in LIF and IGF-I all died at birth of apparent respiratory failure. Growth retardation, muscle hypoplasia and delayed ossification in IGF-I-deficient E18.5 mice were exacerbated by the absence of LIF. The transcription factor Sp3 was decreased in the skeleton of the double null mice. Pronounced depletion of olfactory bulb neurons, in contrast, was only IGF-I-dependent. The lungs displayed reduced air space in the IGF-I-deficient embryos and neonates, phenotype exacerbated in the double nulls, which showed abnormal epithelial cells and decreased Sp3 expression. In addition, the transcription factor TTF-1 and the surfactant protein B were lower in the lung of the double null neonates than in all other genotypes. LIF and IGF-I, thus, have cooperative and distinct tissue functions during development. Their essential role in bone ossification apparently involves Sp3, and in lung maturation Sp3 together with TTF-1.

Immunoreactivity for thyroid transcription factor-1 in stage I non-small cell carcinomas of the lung

Thyroid transcription factor-1 (TTF-1) is a nuclear protein regulating the transcriptional activity of lung-specific genes in the normal and neoplastic bronchioloalveolar cells. It has been implicated in the normal growth and development of the lung, and the disruption of the TTF-1 locus leads to neonatal death with pulmonary hypoplasia. We evaluated retrospectively the prevalence and clinical significance of TTF-1 immunoreactivity in 222 patients with stage I non-small cell lung carcinoma (NSCLC) with a follow-up time of at least 5 years, and we investigated its relationship with other markers of tumor growth, namely cell proliferation and angiogenesis. TTF-1 immunoreactivity was documented by using the commercially available monoclonal antibody 8G7G3/1 in 72% of 97 adenocarcinomas, 5% of 119 squamous cell carcinomas, and in the glandular component of two adenosquamous carcinomas. Four large cell carcinomas were completely unreactive. In adenocarcinomas, but not squamous cell carcinomas, TTF-1 immunoreactivity correlated significantly with microvessel density (p = 0.04) and inversely with the tumor proliferation fraction assessed by Ki-67 immunostaining (p = 0.03). Also, TTF-1-immunoreactive adenocarcinomas showed a trend for a size less than 3 cm (p = 0.08). TTF-1 expression was not related to specific growth patterns, tumor grade, or tumor cell typing. TTF-1 immunoreactivity did not significantly affect patient survival, although patients with more than 75% immunoreactive neoplastic cells showed a trend for longer overall and disease-free survival. Our findings suggest that TTF-1 could be involved in the development of small pulmonary adenocarcinomas, but it has not prognostic implications in patients with stage I NSCLC.