Retinoids in Lung Development and Regeneration

Genetics of diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a life-threatening malformation characterised by failure of diaphragmatic development with lung hypoplasia and persistent pulmonary hypertension of the newborn (PPHN). The incidence is 1:2000 corresponding to 8% of all major congenital malformations. Morbidity and mortality in affected newborns are very high and at present, there is no precise prenatal or early postnatal prognostication parameter to predict clinical outcome in CDH patients. Most cases occur sporadically, however, genetic causes have long been discussed to explain a proportion of cases. These range from aneuploidy to complex chromosomal aberrations and specific mutations often causing a complex phenotype exhibiting multiple malformations along with CDH. This review summarises the genetic variations which have been observed in syndromic and isolated cases of congenital diaphragmatic hernia.

Vitamin A Update: Forms, Sources, Kinetics, Detection, Function, Deficiency, Therapeutic Use and Toxicity

Vitamin A is a group of vital micronutrients widely present in the human diet. Animal-based products are a rich source of the retinyl ester form of the vitamin, while vegetables and fruits contain carotenoids, most of which are provitamin A. Vitamin A plays a key role in the correct functioning of multiple physiological functions. The human organism can metabolize natural forms of vitamin A and provitamin A into biologically active forms (retinol, retinal, retinoic acid), which interact with multiple molecular targets, including nuclear receptors, opsin in the retina and, according to the latest research, also some enzymes. In this review, we aim to provide a complex view on the present knowledge about vitamin A ranging from its sources through its physiological functions to consequences of its deficiency and metabolic fate up to possible pharmacological administration and potential toxicity. Current analytical methods used for its detection in real samples are included as well.

Transcriptome profiling of mouse brain and lung under Dip2a regulation using RNA-sequencing

Disconnected interacting protein 2 homolog A (DIP2A) is highly expressed in nervous system and respiratory system of developing embryos. However, genes regulated by Dip2a in developing brain and lung have not been systematically studied. Transcriptome of brain and lung in embryonic 19.5 day (E19.5) were compared between wild type and Dip2a^-/- mice. An average of 50 million reads per sample was mapped to the reference sequence. A total of 214 DEGs were detected in brain (82 up and 132 down) and 1900 DEGs in lung (1259 up and 641 down). GO enrichment analysis indicated that DEGs in both Brain and Lung were mainly enriched in biological processes ‘DNA-templated transcription and Transcription from RNA polymerase II promoter’, ‘multicellular organism development’, ‘cell differentiation’ and ‘apoptotic process’. In addition, COG classification showed that both were mostly involved in ‘Replication, Recombination, and Repair’, ‘Signal transduction and mechanism’, ‘Translation, Ribosomal structure and Biogenesis’ and ‘Transcription’. KEGG enrichment analysis showed that brain was mainly enriched in ‘Thyroid cancer’ pathway whereas lung in ‘Complement and Coagulation Cascades’ pathway. Transcription factor (TF) annotation analysis identified Zinc finger domain containing (ZF) proteins were mostly regulated in lung and brain. Interestingly, study identified genes Skor2, Gpr3711, Runx1, Erbb3, Frmd7, Fut10, Sox11, Hapln1, Tfap2c and Plxnb3 from brain that play important roles in neuronal cell maturation, differentiation, and survival; genes Hoxa5, Eya1, Errfi1, Sox11, Shh, Igf1, Ccbe1, Crh, Fgf9, Lama5, Pdgfra, Ptn, Rbp4 and Wnt7a from lung are important in lung development. Expression levels of the candidate genes were validated by qRT-PCR. Genome wide transcriptional analysis using wild type and Dip2a knockout mice in brain and lung at embryonic day 19.5 (E19.5) provided a genetic basis of molecular function of these genes.

Vitamin A Deficiency and the Lung

Vitamin A (all-trans-retinol) is a fat-soluble micronutrient which together with its natural derivatives and synthetic analogues constitutes the group of retinoids. They are involved in a wide range of physiological processes such as embryonic development, vision, immunity and cellular differentiation and proliferation. Retinoic acid (RA) is the main active form of vitamin A and multiple genes respond to RA signalling through transcriptional and non-transcriptional mechanisms. Vitamin A deficiency (VAD) is a remarkable public health problem. An adequate vitamin A intake is required in early lung development, alveolar formation, tissue maintenance and regeneration. In fact, chronic VAD has been associated with histopathological changes in the pulmonary epithelial lining that disrupt the normal lung physiology predisposing to severe tissue dysfunction and respiratory diseases. In addition, there are important alterations of the structure and composition of extracellular matrix with thickening of the alveolar basement membrane and ectopic deposition of collagen I. In this review, we show our recent findings on the modification of cell-junction proteins in VAD lungs, summarize up-to-date information related to the effects of chronic VAD in the impairment of lung physiology and pulmonary disease which represent a major global health problem and provide an overview of possible pathways involved.

Stem cell therapies for chronic obstructive pulmonary disease: current status of pre-clinical studies and clinical trials

Chronic obstructive pulmonary disease (COPD) is a respiratory disease that has a major impact worldwide. The currently-available drugs mainly focus on relieving the symptoms of COPD patients. Novel regenerative therapeutic approaches have been investigated with the aim of repairing or replacing the injured functional structures of the respiratory system. We summarized the progress made by regenerative therapies for COPD by analyzing results from both pre-clinical studies and completed clinical trials. These approaches include the application of exogenous stem cells or small molecules to stimulate the regeneration by endogenous lung stem/progenitor cells. Exogenous mesenchymal stem cells (MSCs) have been reported to repair the structure and improve the function of the injured respiratory system in COPD models. However, the studies that used MSCs in patients with moderate-to-severe COPD patients did not lead to clear respiratory functional improvements. Exogenous human lung stem cells applied to cryo-injured (CI) lungs of mice have been shown to organize into human-like pulmonary structures, indicating a new property of stem cells that is potentially capable of curing COPD patients. Small molecules like retinoic acid has been shown to lead to regeneration and repair of the damaged lung structures in COPD mouse models probably by activation of endogenous lung stem/progenitor cells. However, retinoic acid or agonists of retinoic acid receptor administered to moderate or severe COPD patients did not improve the density and function of the damaged lung. These novel regenerative approaches have failed in preliminary clinical trials, possibly due to the advanced severity of the disease. Further work should be done to develop the current regenerative approaches for curing patients at different stages of COPD. We suggest that some modifications of the approach in the clinical studies may lead to more successful outcomes of regenerative therapy for COPD.

Retinoic acid regulates avian lung branching through a molecular network

Retinoic acid (RA) is of major importance during vertebrate embryonic development and its levels need to be strictly regulated otherwise congenital malformations will develop. Through the action of specific nuclear receptors, named RAR/RXR, RA regulates the expression of genes that eventually influence proliferation and tissue patterning. RA has been described as crucial for different stages of mammalian lung morphogenesis, and as part of a complex molecular network that contributes to precise organogenesis; nonetheless, nothing is known about its role in avian lung development. The current report characterizes, for the first time, the expression pattern of RA signaling members (stra6, raldh2, raldh3, cyp26a1, rarα, and rarβ) and potential RA downstream targets (sox2, sox9, meis1, meis2, tgfβ2, and id2) by in situ hybridization. In the attempt of unveiling the role of RA in chick lung branching, in vitro lung explants were performed. Supplementation studies revealed that RA stimulates lung branching in a dose-dependent manner. Moreover, the expression levels of cyp26a1, sox2, sox9, rarβ, meis2, hoxb5, tgfβ2, id2, fgf10, fgfr2, and shh were evaluated after RA treatment to disclose a putative molecular network underlying RA effect. In situ hybridization analysis showed that RA is able to alter cyp26a1, sox9, tgfβ2, and id2 spatial distribution; to increase rarβ, meis2, and hoxb5 expression levels; and has a very modest effect on sox2, fgf10, fgfr2, and shh expression levels. Overall, these findings support a role for RA in the proximal-distal patterning and branching morphogenesis of the avian lung and reveal intricate molecular interactions that ultimately orchestrate branching morphogenesis.

Inhibition of pulmonary β-carotene 15, 15'-oxygenase expression by glucocorticoid involves PPARα

β-carotene 15,15'-oxygenase (BCO1) catalyzes the first step in the conversion of dietary provitamin A carotenoids to vitamin A. This enzyme is expressed in a variety of developing and adult tissues, suggesting that its activity may regulate local retinoid synthesis. Vitamin A and related compounds (retinoids) are critical regulators of lung epithelial development, integrity, and injury repair. A balance between the actions of retinoids and glucocorticoids (GCs) promotes normal lung development and, in particular, alveolarization. Alterations in this balance, including vitamin A deficiency and GC excess, contribute to the development of chronic lung disorders. Consequently, we investigated if GCs counteract retinoid effects in alveolar epithelial cells by mechanisms involving BCO1-dependent local vitamin A metabolism. We demonstrate that BCO1 is expressed in human fetal lung tissue and human alveolar epithelial-like A549 cells. Our results indicate A549 cells metabolize β-carotene to retinal and retinoic acid (RA). GCs exposure using dexamethasone (DEX) decreases BCO1 mRNA and protein levels in A549 cells and reduces BCO1 promoter activity via inhibiting peroxisome proliferator-activated receptor γ (PPARγ) DNA binding. DEX also induces expression of PPARα, which in turn most likely causes a decrease in PPARγ/RXRα heterodimer binding to the bco1 gene promoter and consequent inhibition of bco1 gene expression. PPARα knockdown with siRNA abolishes DEX-induced suppression of BCO1 expression, confirming the requirement for PPARα in this DEX-mediated BCO1 mechanism. Taken together, these findings provide the first evidence that GCs regulate vitamin A (retinoid) signaling via inhibition of bco1 gene expression in a PPARα-dependent manner. These results explicate novel aspects of local GC:retinoid interactions that may contribute to alveolar tissue remodeling in chronic lung diseases that affect children and, possibly, adults.

Retinoid Homeostatic Gene Expression in Liver, Lung and Kidney: Ontogeny and Response to Vitamin A-Retinoic Acid (VARA) Supplementation from Birth to Adult Age

Vitamin A (VA, retinol) metabolism is homeostatically controlled, but little is known of its regulation in the postnatal period. Here, we determined the postnatal trajectory of VA storage and metabolism in major compartments of VA metabolism-plasma, liver, lung, and kidney from postnatal (P) day 1 to adulthood. We also investigated the response to supplementation with VARA, a combination of VA and 10% all-trans-retinoic acid that previously was shown to synergistically increase retinol uptake and storage in lung. Nursling pups of dams fed a VA-marginal diet received an oral dose of oil (placebo) or VARA on each of four neonatal days: P1, P4, P7, and P10; and again as adults. Tissues were collected 6 h after the final dosing on P1, P4, P10, and at adult age. Gene transcripts for Lrat and Rbp4 in liver and Raldh-1 and Raldh-3 in lung, did not differ in the neonatal period but were higher, P<0.05, in adults, while Cyp26B1, Stra6, megalin, and Raldh-2 in lung did not differ from perinatal to adult ages. VARA supplementation increased total retinol in plasma, liver and lung, with a dose-by-dose accumulation in neonatal liver and lung, while transcripts for Lrat in liver, megalin in kidney, Cyp26A1/B1 in liver and lung, respectively, and Stra6 in lung, were all increased, suggesting pathways of VA uptake, storage and RA oxidation were each augmented after VARA. VARA decreased hepatic expression of Rbp4, responsible for VA trafficking from liver to plasma, and, in lung, of Raldh-1 and Raldh-2, which function in RA production. Our results define retinoid homeostatic gene expression from neonatal and adult age and show that while supplementation with VARA acutely alters retinol content and retinoid homeostatic gene expression in neonatal and adult lung, liver and kidney, VARA supplementation of neonates increased adult-age VA content only in the liver.

Metabolic disturbances of the vitamin A pathway in human diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a common life-threatening congenital anomaly resulting in high rates of perinatal death and neonatal respiratory distress. Some of the nonisolated forms are related to single-gene mutations or genomic rearrangements, but the genetics of the isolated forms (60% of cases) still remains a challenging issue. Retinoid signaling (RA) is critical for both diaphragm and lung development, and it has been hypothesized that subtle disruptions of this pathway could contribute to isolated CDH etiology. Here we used time series of normal and CDH lungs in humans, in nitrofen-exposed rats, and in surgically induced hernia in rabbits to perform a systematic transcriptional analysis of the RA pathway key components. The results point to CRPBP2, CY26B1, and ALDH1A2 as deregulated RA signaling genes in human CDH. Furthermore, the expression profile comparisons suggest that ALDH1A2 overexpression is not a primary event, but rather a consequence of the CDH-induced lung injury. Taken together, these data show that RA signaling disruption is part of CDH pathogenesis, and also that dysregulation of this pathway should be considered organ specifically.

Unilateral pulmonary agenesis: a report of four cases, two diagnosed antenatally and literature review

Pulmonary agenesis is a rare congenital malformation of lung development defined as complete absence of lung tissues, bronchi, and pulmonary vessels; it may be uni- or bilateral. The right-sided form carries the poorest prognosis due to severity of co-existent anomalies. Its diagnostic circumstances are variables: first reported cases were diagnosed at autopsy, but early postnatal as well as fortuitous discovery have been reported. In recent years, progress in obstetrical imaging has made antenatal diagnosis possible so that fetal ultrasound and MRI allow early diagnosis and refinement by permitting the elimination of differential diagnoses (diaphragmatic hernia, cystic adenomatoid malformation of the lung, giant lobar emphysema, and situs inversus). This anomaly is compatible with normal life provided co-existent malformations are thoroughly investigated and managed in a multidisciplinary setting. We report four cases of lung agenesis two of which were diagnosed antenatally at 23rd and 30th weeks of gestation respectively. Our aim is to describe the circumstances having led to diagnosis and report both follow-up and outcome of our patients.

Pediatric cardiothoracic surgery in patients with unilateral pulmonary agenesis or aplasia

BACKGROUND

Unilateral pulmonary agenesis or aplasia (UPA), a rare developmental defect of the lung, is sometimes associated with congenital heart and tracheal diseases. The purpose of this study was to assess our experience of pediatric cardiothoracic surgery in UPA patients.

METHODS

Cardiothoracic surgery for congenital heart defect or tracheal stenosis performed between 1981 and 2010 in 8 UPA patients (agenesis in 5 and aplasia in 3) was reviewed retrospectively. Associated cardiac anomalies included ventricular septal defect, double outlet right ventricle with pulmonary atresia, total anomalous pulmonary venous connection, and interrupted aortic arch complex.

RESULTS

For 7 patients with right UPA and 1 patient with left UPA, 12 cardiothoracic operations were performed, including 8 cardiac procedures in 4 patients and 4 tracheal procedures in 4 patients. Cardiac palliative repairs included Blalock-Park anastomosis, systemic-to-pulmonary artery shunt, and pulmonary artery banding. Cardiac definitive repairs included ventricular septal defect closure, subaortic membrane resection, modified Konno procedure, total anomalous pulmonary venous connection repair, and Rastelli-type operation. Tracheal repairs were costal cartilage tracheoplasty and slide tracheoplasty. The median age at surgery was 8 months and median body weight was 6.2 kg; the median operative time was 6.5 hours. There were 3 hospital deaths and 1 late death, with the 1-year mortality rate of 25%. Cardiopulmonary bypass-induced acute lung injury has occurred in 3 cases, 2 of which required extracorporeal membrane oxygenation support. Younger age of less than 1 month and prolonged cardiopulmonary bypass time of more than 200 minutes were related to operative risk factors for hospital mortality and morbidity.

CONCLUSIONS

Most of the pediatric cardiothoracic operations in UPA patients were successfully performed through an optimal surgical approach and procedure, but they still presented surgical risks of high mortality and morbidity. Perioperative management of UPA patients should be provided with a precise understanding of anatomic configuration and a careful consideration of underlying risk factors.

VARA attenuates hyperoxia-induced impaired alveolar development and lung function in newborn mice

We have recently shown that a combination of vitamin A (VA) and retinoic acid (RA) in a 10:1 molar ratio (VARA) synergistically increases lung retinoid content in newborn rodents, more than either VA or RA alone in equimolar amounts. We hypothesized that the increase in lung retinoids would reduce oxidative stress and proinflammatory cytokines, resulting in attenuation of alveolar simplification and abnormal lung function in hyperoxia-exposed newborn mice. Newborn C57BL/6 mice were exposed to 85% O₂ (hyperoxia) or air (normoxia) for 7 or 14 days from birth and given vehicle or VARA every other day. Lung retinol content was measured by HPLC, function was assessed by flexiVent, and development was evaluated by radial alveolar counts, mean linear intercept, and secondary septal crest density. Mediators of oxidative stress, inflammation, and alveolar development were evaluated in lung homogenates. We observed that VARA increased lung retinol stores and attenuated hyperoxia-induced alveolar simplification while increasing lung compliance and lowering resistance. VARA attenuated hyperoxia-induced increases in DNA damage and protein oxidation accompanied with a reduction in nuclear factor (erythroid-derived 2)-like 2 protein but did not alter malondialdehyde adducts, nitrotyrosine, or myeloperoxidase concentrations. Interferon-γ and macrophage inflammatory protein-2α mRNA and protein increased with hyperoxia, and this increase was attenuated by VARA. Our study suggests that the VARA combination may be a potential therapeutic strategy in conditions characterized by VA deficiency and hyperoxia-induced lung injury during lung development, such as bronchopulmonary dysplasia in preterm infants.

BMP signaling regulates the differentiation of mouse embryonic stem cells into lung epithelial cell lineages

Somatic stem/progenitor cells are known to be present in most adult tissues. However, those in the lung have limited abilities for tissue regeneration after serious damage as a result of chronic disease. Therefore, regenerative medicine using exogenous stem cells has been suggested for the treatment of progressive lung diseases such as chronic obstructive pulmonary disease and pulmonary fibrosis. Embryonic stem (ES) cells and induced pluripotent stem cells, with their potent differentiation abilities, are promising sources for the generation of various tissue cells. In this study, we investigated the effects of various differentiation-inducing growth factors on the differentiation of lung cells from ES cells in vitro. Several factors, including activin, nodal, and noggin, significantly promoted the induction of Nkx2.1-positive lung progenitor cells when cells were cultured as embryoid bodies. Bone morphogenetic protein (BMP) 4 signaling controls the lineage commitment of lung cells along the proximal-distal axis. BMP4 promotes the induction of distal cell lineages of alveolar bud, such as Clara cells and mucus-producing goblet cells. These results suggest that several developmentally essential factors, including nodal/activin and BMP signaling, are important in the control of the differentiation of lung epithelial cells from mouse ES cells in vitro.

Prenatal retinoic acid upregulates connexin 43 (Cx43) gene expression in pulmonary hypoplasia in the nitrofen-induced congenital diaphragmatic hernia rat model

PURPOSE

Connexin 43 (Cx43), a major gap junction protein, is necessary for alveologenesis and plays an important role in the differentiation of type II to type I alveolar epithelial cells. Knockout mice of Cx43 display severe pulmonary hypoplasia (PH). Prenatal administration of retinoic acid (RA) is known to stimulate alveologenesis in nitrofen-induced PH. Recent studies revealed that retinoids upregulate Cx43 expression. We hypothesized that gene expression of Cx43 is downregulated during alveologenesis and that administration of RA upregulates Cx43 expression in the nitrofen-induced PH.

METHODS

Pregnant rats were exposed to olive oil or nitrofen on day 9 (D9) of gestation. Retinoic acid was given intraperitoneally on D18, D19, and D20. Fetal lungs were harvested on D18 and D21 and divided into control, nitrofen, control+RA (D21), and nitrofen+RA (D21). The Cx43 expression levels were determined using reverse transcription polymerase chain reaction and immunohistochemistry.

RESULTS

On D18 and D21, Cx43 relative messenger RNA expression levels were significantly downregulated in nitrofen compared with those in the control group. On D21, expression levels of Cx43 were significantly upregulated in nitrofen+RA and control+RA compared with those in nitrofen group. Immunohistochemical studies confirmed these results.

CONCLUSION

Downregulation of Cx43 expression may interfere with normal alveologenesis. Upregulation of Cx43 pulmonary gene expression after RA treatment may promote lung growth by stimulating alveologenesis in nitrofen-induced PH.

Prenatal administration of retinoic acid upregulates insulin-like growth factor receptors in the nitrofen-induced hypoplastic lung

BACKGROUND

Pulmonary hypoplasia (PH) is the main cause of mortality in newborns with congenital diaphragmatic hernia (CDH). Prenatal administration of retinoic acid (RA) stimulates alveologenesis in the nitrofen-induced pulmonary hypoplasia. Insulin-like growth factor receptors (IGFRs) play a crucial role in alveologenesis during lung development. We recently demonstrated that IGFRs were downregulated in later stages of lung development in the nitrofen CDH model. Several studies suggest the ability of RA to regulate insulin-like growth factor signaling. We hypothesized that IGFRs pulmonary gene expression is upregulated after the administration of RA in the nitrofen-induced CDH model.

METHODS

Pregnant rats were exposed to either olive oil or nitrofen on day 9 (D9) of gestation. RA was given intraperitoneally on days D18, D19, and D20. Fetal lungs were dissected on D21 and divided into control, control + RA, CDH, and CDH + RA group. IGFRs gene and protein expression were determined using RT-PCR and immunohistochemistry.

RESULTS

mRNA expression levels of IGFRs were significantly increased in control + RA and CDH + RA compared with CDH group. Immunoreactivity of IGFRs was markedly increased in control + RA and CDH + RA compared with CDH lungs.

CONCLUSIONS

Upregulation of pulmonary gene and protein expression of IGFRs after prenatal RA treatment in the nitrofen model suggests that RA may promote lung growth by stimulating IGFRs mediated alveologenesis.

Downregulation of Midkine gene expression and its response to retinoic acid treatment in the nitrofen-induced hypoplastic lung

PURPOSE

Nitrofen-induced congenital diaphragmatic hernia (CDH) model has been widely used to investigate the pathogenesis of pulmonary hypoplasia (PH) in CDH. Recent studies have suggested that retinoids may be involved in the molecular mechanisms of PH in CDH. Prenatal treatment with retinoic acid (RA) has been reported to improve the growth of hypoplastic lung in the nitrofen CDH model. Midkine (MK), a RA-responsive growth factor, plays key roles in various organogenesis including lung development. In fetal lung, MK mRNA expression has its peak at E13.5-E16.5 and is markedly decreased during mid-to-late gestation, indicating its important role in early lung morphogenesis. We designed this study to investigate the hypothesis that the pulmonary MK gene expression is downregulated in the early lung morphogenesis in the nitrofen-induced PH, and to evaluate the effect of prenatal RA treatment on pulmonary MK gene expression in the nitrofen-induced CDH model.

METHODS

Pregnant rats were exposed to either olive oil or nitrofen on day 9 of gestation (D9). Fetal lungs were harvested on D15, D18, and D21 and divided into control, nitrofen with or without CDH [CDH(+) or CDH(-)]. In addition, RA was given on days D18, D19, and D20 and fetal lungs were harvested on D21, and then divided into control + RA and nitrofen + RA. The pulmonary gene expression levels of MK were evaluated by real-time RT-PCR and statistically analyzed. Immunohistochemistry was also performed to examine protein expression/distribution of MK in fetal lung.

RESULTS

The relative mRNA expression levels of MK were significantly downregulated in nitrofen group compared to controls at D15 ((§)p < 0.01), whereas there were no significant differences at D18 and D21. MK gene expression levels were significantly upregulated in nitrofen + RA (0.71 ± 0.17) compared to the control (0.35 ± 0.16), CDH(-) (0.24 ± 0.15), CDH(+) (0.39 ± 0.19) and control + RA (0.47 ± 0.13) (*p < 0.05). Immunoreactivity of MK was also markedly decreased in nitrofen lungs compared to controls on D15, and increased in nitrofen + RA lungs compared to the other lungs on D21.

CONCLUSION

Downregulation of MK gene on D15 may contribute to primary PH in the nitrofen CDH model by disrupting early lung morphogenesis. Upregulation of MK gene after RA treatment in the nitrofen-induced hypoplastic lung suggests that RA may have a therapeutic potential to rescue PH in CDH through RA-responsive growth factor signaling.

Prenatal treatment with retinoic acid activates parathyroid hormone-related protein signaling in the nitrofen-induced hypoplastic lung

PURPOSE

Prenatal treatment with retinoic acid (RA) has been reported to stimulate alveologenesis in hypoplastic lungs (HL) in the nitrofen model of congenital diaphragmatic hernia (CDH). Parathyroid hormone-related protein (PTHrP) promotes alveolar maturation by stimulating surfactant production, regulated by PTHrP receptor (PTHrP-R). PTHrP knockout and PTHrP-R null mice both exhibit pulmonary hypoplasia. We have recently reported that nitrofen inhibits PTHrP signaling in the nitrofen-induced HL. Because both PTHrP and PTHrP-R genes have RA-inducible element, we hypothesized that prenatal administration of RA upregulates pulmonary gene expression of PTHrP and PTHrP-R in the nitrofen-induced HL.

METHODS

Pregnant rats were exposed to either olive oil or nitrofen on day 9 of gestation (D9). RA was given on days D18, D19 and D20. Fetal lungs were obtained on D21 and divided into four groups: control, control + RA, nitrofen, nitrofen + RA. RT-PCR and Immunohistochemistry were performed to investigate the pulmonary PTHrP and PTHrP-R gene and protein expression in each group, respectively.

RESULTS

The pulmonary gene expression levels of PTHrP and PTHrP-R were significantly increased in nitrofen + RA group compared to nitrofen group (p < 0.05). Immunoreactivity of PTHrP and PTHrP-R was also remarkably increased in nitrofen + RA group compared to nitrofen group.

CONCLUSIONS

Upregulation of PTHrP and PTHrP-R genes after prenatal treatment with RA in the nitrofen-induced HL suggests that RA may have a therapeutic potential in reverting lung hypoplasia in CDH, by stimulating surfactant production and alveolar maturation.

Prenatal retinoic acid upregulates pulmonary gene expression of PI3K and AKT in nitrofen-induced pulmonary hypoplasia

BACKGROUND

The precise mechanism of pulmonary hypoplasia associated with congenital diaphragmatic hernia (CDH) still remains unclear. Recently, prenatal treatment with retinoic acid (RA) has been reported to stimulate alveologenesis in hypoplastic lungs in the nitrofen model of CDH. The serine/threonine protein kinase B (AKT) plays a key role in lung morphogenesis through epithelial-mesenchymal interaction in phosphatidylinositide 3-kinase (PI3K)-dependent manner. It has been reported that the lung morphogenesis in explants in mice is interfered by inhibitors of PI3K-AKT signaling pathway. Furthermore, we have recently shown that nitrofen inhibits PI3K-AKT signaling during mid-to-late lung morphogenesis in the nitrofen-induced hypoplastic lung. We hypothesized that prenatal administration of RA upregulates pulmonary gene expression of PI3K and AKT in the nitrofen-induced hypoplastic lung.

METHODS

Pregnant rats were exposed to either olive oil or nitrofen on day 9 of gestation (D9). 5 mg/kg of RA was given on D18, D19 and D20. The fetuses were harvested on D21, and fetal lungs were obtained and divided into four groups: control, control + RA, nitrofen, nitrofen + RA. The mRNA expression levels of PI3K and AKT were analyzed in each lung by real-time RT-PCR and statistically analyzed. Immunohistochemistry was also performed to evaluate protein expression of PI3K and AKT in the fetal lungs at D21.

RESULTS

The pulmonary gene expression levels of PI3K and AKT were significantly upregulated in nitrofen + RA group compared to nitrofen group and control + RA group (p < 0.05), whereas there were no significant differences between controls and control + RA group. Immunoreactivity of PI3K and AKT was markedly increased in nitrofen + RA lungs compared to nitrofen-induced hypoplastic lungs.

CONCLUSIONS

Upregulation of PI3K and AKT genes after prenatal treatment with RA in the nitrofen-induced hypoplastic lung suggests that RA may have a therapeutic potential in modulating lung alveologenesis by stimulating epithelial-mesenchymal interaction via PI3K-AKT signaling.

Retinol status of newborn infants is associated with congenital diaphragmatic hernia

OBJECTIVE

Genetic analyses in humans suggest a role for retinoid-related genes in the pathogenesis of congenital diaphragmatic hernia (CDH). The goal of this study was to investigate the vitamin A status of mothers and their newborns in association with CDH.

METHODS

We conducted a hospital-based, case-control study with 22 case and 34 control mothers and their newborns. In maternal and cord blood samples, retinol and retinol-binding protein (RBP) levels were measured with high-performance liquid chromatography and an enzyme-linked immunosorbent assay, respectively. Univariate and multivariate logistic regression analyses were performed to determine crude and adjusted risk estimates.

RESULTS

Case newborns had significantly lower levels of retinol (0.60 vs 0.76 μmol/L; P=.003) and RBP (5.42 vs 7.11 mg/L; P=.02) than did control newborns. The multivariate logistic regression analysis showed lower levels of retinol and RBP in association with CDH risk; the odds ratio for retinol levels of <15th percentile (<0.61 μmol/L) was 11.11 (95% confidence interval: 2.54-48.66; P=.001), and that for RBP levels of <15th percentile (<4.54 mg/L) was 4.00 (95% confidence interval: 1.00-15.99; P=.05). Retinol and RBP levels were not different between case and control mothers.

CONCLUSIONS

CDH is strongly associated with low retinol and RBP levels in newborns, independent of maternal retinol status. This is an important finding supporting the idea that human CDH is linked with abnormal retinoid homeostasis.

The role of pleiotrophin and beta-catenin in fetal lung development

Mammalian lung development is a complex biological process, which is temporally and spatially regulated by growth factors, hormones, and extracellular matrix proteins. Abnormal changes of these molecules often lead to impaired lung development, and thus pulmonary diseases. Epithelial-mesenchymal interactions are crucial for fetal lung development. This paper reviews two interconnected pathways, pleiotrophin and Wnt/β-catenin, which are involved in fibroblast and epithelial cell communication during fetal lung development.

Prenatal retinoic acid up-regulates pulmonary gene expression of COUP-TFII, FOG2, and GATA4 in pulmonary hypoplasia

PURPOSE

Retinoids play an important role in lung development. Recently, prenatal treatment with retinoic acid (RA) has been reported to stimulate alveologenesis in hypoplastic lungs in the nitrofen model of congenital diaphragmatic hernia (CDH). Chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) is a transcription factor in the steroid/thyroid hormone receptor superfamily, and targeted ablation of COUP-TFII causes CDH and associated lung hypoplasia in mice. Friend of GATA 2 (FOG2) is a zinc finger-containing protein that modulates the transcriptional activity of GATA proteins. GATA4 is a member of a family of DNA-binding proteins, which is found in the promoter regions of many genes. The COUP-TFII, FOG2, and GATA4 genes, regulated by the retinoid signaling pathway, are located on chromosomes 15q26, 8q23, and 8p23.1 respectively, regions reported to be deleted in individuals with CDH. The aim of this study was to examine the pulmonary gene expression of COUP-TFII, FOG2, and GATA4 in the nitrofen model of CDH.

MATERIALS AND METHODS

Pregnant rats were exposed to either olive oil or 100 mg nitrofen on day 9 of gestation (D9). 5 mg/kg of RA was given intraperitoneally on days D18, D19, and D20. The fetuses were recovered by caesarean section on D21, and the diaphragm was carefully examined for the presence of a hernia under a microscope. Left lungs were obtained from CDH fetuses and controls and divided into four groups: control (n = 9), control + RA (n = 9), CDH (n = 9), and CDH + RA (n = 9). The relative mRNA expression levels of COUP-TFII, FOG2, and GATA4 were analyzed in each lung by real-time reverse transcriptase-polymerase chain reaction from cDNA generated by mRNA from pulmonary total RNA.

RESULTS

The relative mRNA expression levels of COUP-TFII, FOG2, and GATA4 were significantly increased in CDH + RA lungs compared to control, control + RA, and CDH (P < .05).

CONCLUSIONS

Up-regulation of pulmonary gene expression of COUP-TFII, FOG2, and GATA4 after prenatal treatment with retinoic acid in the nitrofen model of CDH suggests that RA may have a therapeutic potential in modulating lung growth. Furthermore, these results support the concept that these proteins work together to regulate downstream target genes that play an important role in the development of lung.

Developmental expression of retinoic acid receptors (RARs)

Here, I review the developmental expression features of genes encoding the retinoic acid receptors (RARs) and the 'retinoid X' or rexinoid receptors (RXRs). The first detailed expression studies were performed in the mouse over two decades ago, following the cloning of the murine Rar genes. These studies revealed complex expression features at all stages of post-implantation development, one receptor gene (Rara) showing widespread expression, the two others (Rarb and Rarg) with highly regionalized and/or cell type-specific expression in both neural and non-neural tissues. Rxr genes also have either widespread (Rxra, Rxrb), or highly-restricted (Rxrg) expression patterns. Studies performed in zebrafish and Xenopus demonstrated expression of Rar and Rxr genes (both maternal and zygotic), at early pre-gastrulation stages. The eventual characterization of specific enzymes involved in the synthesis of retinoic acid (retinol/retinaldehyde dehydrogenases), or the triggering of its catabolism (CYP26 cytochrome P450s), all of them showing differential expression patterns, led to a clearer understanding of the phenomenons regulated by retinoic acid signaling during development. Functional studies involving targeted gene disruptions in the mouse, and additional approaches such as dominant negative receptor expression in other models, have pinpointed the specific, versus partly redundant, roles of the RARs and RXRs in many developing organ systems. These pleiotropic roles are summarized hereafter in relationship to the receptors' expression patterns.

Congenital diaphragmatic hernia and retinoids: searching for an etiology

Congenital diaphragmatic hernia (CDH) is a major life-threatening cause of respiratory failure in the newborn. Recent data reveal the role of a retinoid-signaling pathway disruption in the pathogenesis of CDH. We describe the epidemiology and pathophysiology of human CDH, the metabolism of retinoids and the implications of retinoids in the development of the diaphragm and lung. Finally, we describe the existing evidence of a disruption of the retinoid-signaling pathway in CDH.

Effects of maternal retinoic acid administration in a congenital diaphragmatic hernia rabbit model

Maternal retinoid administration has beneficial effects on lung development in the nitrofen rodent toxic model of congenital diaphragmatic hernia (DH). We wanted to investigate the effects in a surgical model, where the retinoid signaling pathway is not primarily disrupted by the toxic agent. We created DH in fetal rabbits at day 23 of gestation, administrated to the does all trans-retinoic acid (ATRA) or vehicle (VHC) intramuscularly for 8 consecutive days and harvested normal and operated (DH) fetuses at 31 d (n = 7 in each group). Normal lungs exposed to ATRA had increased surfactant protein mRNA levels without change in type II pneumocyte density. There was no measurable effect on lung-to-body weight ratio and airway morphometry by ATRA. In DH lungs (DH/VHC) surfactant protein mRNA levels were increased, as well as the density of type II pneumocytes. When supplemented with ATRA (DH/ATRA) these parameters returned to normal (VHC). Cell proliferation or apoptosis were not influenced by ATRA supplementation. In conclusion, maternal ATRA supplementation does not affect gross anatomic, morphologic or proliferation indices in hypoplastic lungs related to surgically induced DH in rabbit. However, ATRA lowers surfactant protein expression and normalizes type I/II pneumocyte ratio to what is observed in normal lungs.

Prenatal treatment with retinoic acid promotes pulmonary alveologenesis in the nitrofen model of congenital diaphragmatic hernia

BACKGROUND/PURPOSE

Severe pulmonary hypoplasia remains the main cause of the high mortality in newborn infants with congenital diaphragmatic hernia (CDH). Retinoids are a family of molecules derived from vitamin A, which play an important role in lung development. We hypothesized that retinoids promote alveologenesis at the end of gestation and therefore designed this study to investigate the effects of retinoid acid on nitrofen-induced hypoplastic lungs in CDH.

METHODS

Pregnant rats were exposed to either olive oil or 100 mg nitrofen on day 9 of gestation. Retinoic acid 5 mg/kg was given intraperitoneally on days 18, 19, and 20 of gestation and fetuses were recovered on day 21. We had 4 study groups: control (n = 24), control + retinoic acid (n = 22), CDH (n = 24), and CDH + retinoic acid (n = 19). Lungs from the 4 study groups were fixed, and the following stereological measurements were performed on vertical random sections: total lung volume, volume density of airspaces, volume density of air walls, gas exchange surface area, alveolar volume, and total number of alveoli per lung. Total DNA content of each lung was measured using a spectrophotometer.

RESULTS

Total lung volume increased in CDH lungs after the addition of retinoic acid but remained the same in the control group. Gas exchange surface area was larger in CDH lungs after the addition of retinoic acid but remained unchanged in the control group. The total number of alveoli per lung was higher after the addition of retinoic acid. Total DNA content as well as total DNA content-lung weight ratio of the left lung increased significantly in the CDH group after the addition of retinoic acid compared with CDH without retinoic acid.

CONCLUSIONS

Our results demonstrate that prenatal treatment with retinoic acid stimulates alveologenesis in hypoplastic lungs in CDH.

Prenatal treatment with retinoic acid accelerates type 1 alveolar cell proliferation of the hypoplastic lung in the nitrofen model of congenital diaphragmatic hernia

PURPOSE

Retinoids play an important role in lung development. A recent study has demonstrated that prenatal treatment with retinoic acid (RA) stimulates alveologenesis in hypoplastic lungs in the nitrofen model of congenital diaphragmatic hernia (CDH). Furthermore, it has also been demonstrated that the differentiation from alveolar epithelial cells type II (AECs-II) into alveolar epithelial cells type I (AECs-I), which is the key process in lung development, is disturbed in this model. We hypothesized that retinoids promote alveologenesis by stimulating differentiation of AECs-II to AECs-I at the end of gestation; and therefore, we investigated the effect of RA on the pulmonary expression of intercellular adhesion molecule 1 (ICAM-1), a marker for AECs-I, and thyroid transcription factor 1 (Ttf-1), a marker for AECs-II, in nitrofen-induced hypoplastic lungs.

MATERIALS AND METHODS

Pregnant rats were exposed to either olive oil or 100 mg nitrofen on day of gestation (D) 9. Five milligrams per kilogram of RA was given intraperitoneally on D18, D19, and D20; and fetuses were recovered on D21. We had 4 study groups: control (n = 7), control + RA (n = 7), CDH (n = 6), and CDH + RA (n = 6). The expression of ICAM-1 and Ttf-1 was analysed in each lung by real-time reverse transcription polymerase chain reaction and immunohistochemistry. One-way analysis of variance test was used for statistical analysis.

RESULTS

Expression levels of ICAM-1 were significantly reduced in CDH lungs compared with normal controls, whereas levels increased significantly in CDH group after the addition of RA (P < .05). Expression levels of Ttf-1 were significantly decreased in lungs from RA-treated CDH animals compared with CDH without RA (P < .05). The ICAM-1 and Ttf-1 immunoreactivity demonstrated similar pattern of expression in various groups.

CONCLUSIONS

Our results demonstrate that prenatal treatment with RA accelerates AEC-I proliferation in the hypoplastic lung in CDH.

Overview of retinoid metabolism and function

Retinoids (vitamin A) are crucial for most forms of life. In chordates, they have important roles in the developing nervous system and notochord and many other embryonic structures, as well as in maintenance of epithelial surfaces, immune competence, and reproduction. The ability of all-trans retinoic acid to regulate expression of several hundred genes through binding to nuclear transcription factors is believed to mediate most of these functions. The role of all-trans retinoic may extend beyond the regulation of gene transcription because a large number of noncoding RNAs also are regulated by retinoic acid. Additionally, extra-nuclear mechanisms of action of retinoids are also being identified. In organisms ranging from prokaryotes to humans, retinal is covalently linked to G protein-coupled transmembrane receptors called opsins. These receptors function as light-driven ion pumps, mediators of phototaxis, or photosensory pigments. In vertebrates phototransduction is initiated by a photochemical reaction where opsin-bound 11-cis-retinal is isomerized to all-trans-retinal. The photosensitive receptor is restored via the retinoid visual cycle. Multiple genes encoding components of this cycle have been identified and linked to many human retinal diseases. Central aspects of vitamin A absorption, enzymatic oxidation of all-trans retinol to all-trans retinal and all-trans retinoic acid, and esterification of all-trans retinol have been clarified. Furthermore, specific binding proteins are involved in several of these enzymatic processes as well as in delivery of all-trans retinoic acid to nuclear receptors. Thus, substantial progress has been made in our understanding of retinoid metabolism and function. This insight has improved our view of retinoids as critical molecules in vision, normal embryonic development, and in control of cellular growth, differentiation, and death throughout life.

Pulmonary agenesis--vascular airway compression and gastroesophageal reflux influence outcome

Pulmonary agenesis (PA) is a rare malformation that can be isolated or associated with other anomalies. We report 3 cases of left-sided PA having ipsilateral renal agenesis, facial, and radial ray anomalies. Patients presented in infancy with nonspecific respiratory symptoms and were diagnosed to have PA on chest radiograph and computed tomographic scan. Bronchial compression, by dilated pulmonary artery and associated severe gastroesophageal reflux, aggravated respiratory symptoms and required surgical intervention. The relevant literature is briefly reviewed.

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.

Congenital diaphragmatic hernia: a retinoid-signaling pathway disruption during lung development?

Congenital diaphragmatic hernia (CDH) usually occurs sporadically. The prognosis remains poor, with a 50% perinatal mortality rate. Most deaths result from hypoxemia due to lung hypoplasia and abnormal development of pulmonary vasculature that results in persistent pulmonary hypertension. Our current understanding of the pathogenesis of CDH is based on an assumption linking herniation of abdominal viscera into the thorax with compression of the developing lung. Pulmonary hypoplasia, however, can also result from reduced distension of the developing lung secondary to impaired fetal breathing movements. Moreover, a nitrofen-induced CDH model shows that lung hypoplasia precedes the diaphragmatic defect, leading to a "dual-hit hypothesis." Recent data reveal the role of a retinoid-signaling pathway disruption in the pathogenesis of CDH. We describe the clinical and epidemiological aspects of human CDH, the metabolic and molecular aspects of the retinoid-signaling pathway, and the implications of retinoids in the development of the diaphragm and the lung. Finally, we highlight the existing links between CDH and disruption of the retinoid-signaling pathway, which may suggest an eventual use of retinoids in the treatment of CDH.

Immunolocalization of retinoic acid biosynthesis systems in selected sites in rat

Vitamin A deficiency leads to focal metaplasia of numerous epithelial tissues with altered differentiation from columnar (in general) to stratified squamous cells. This process can be reversed with vitamin A repletion. Previously, we described a system of retinoic acid (RA) synthesis in the cycling rat uterus consisting of cellular retinol binding protein (Crbp), epithelial retinol dehydrogenase (eRoldh), retinal dehydrogenase 2 (Aldh1a2), and cellular retinoic acid binding protein type II (Crabp2). Western blot analysis, RT-PCR, and immunohistochemistry were performed to test whether this retinoic acid synthesis system was also present in other vitamin A sensitive tissues. We found that combinations of Crbp, eRoldh, Aldh1a2 or Aldh1a3, and Crabp2 were present in all vitamin A sensitive tissues examined. In the ureter, while eRoldh was present, another short chain alcohol dehydrogenase reductase (possibly Roldh 1, 2, or 3) was in higher concentration in the transitional epithelia. In several tissues, Crbp, Aldh1a2, and/or Aldh1a3 localized to mesenchyme and/or epithelial cells, while eRoldh and Crabp2 were expressed only in epithelial cells. This suggests that mesenchymal-epithelial interactions may be as important in the adult as they are during development and that local synthesis of RA is important in maintenance of these tissues.

Fetal lung and diaphragm development in congenital diaphragmatic hernia

Congenital Diaphragmatic Hernia (CDH) is a congenital disorder with an incidence of 1 in 2500 live births. Respiratory distress of newborns with CDH is the result of pulmonary hypoplasia and pulmonary hypertension. Hypoplastic lungs are characterized by a decreased number of airways with smaller airspaces, whereas the combination of a decreased number of vascular branches and an increased adventitia and medial thickness of the pulmonary arterial walls result in pulmonary hypertension. The appearance of the CDH lungs suggests that its complete formation is stalled during development. Understanding the basic mechanisms of lung development is mandatory to unravel the origin of CDH. Although the histological abnormalities in CDH lungs have been well described, less is known about the underlying molecular mechanisms. In this review we will discuss the current molecular and genetic background of lung formation, as well as a reflection of this knowledge towards CDH.