Retinoic acid and erythropoietin maintain alveolar development in mice treated with an angiogenesis inhibitor

Abnormal Fetal Lung of Hoxa1-/- Piglets Is Rescued by Maternal Feeding with All-Trans Retinoic Acid

Neonatal Hoxa1-/- piglets were characterized by dyspnea owing to the Hoxa1 mutation, and maternal administration with ATRA alleviated the dyspnea of neonatal Hoxa1-/- piglets. The purpose of this experiment was to explore how maternal ATRA administration rescued the abnormal fetal lungs of Hoxa1-/- piglets. Samples of the lungs were collected from neonatal Hoxa1-/- and non-Hoxa1-/- piglets delivered by sows in the control group, and from neonatal Hoxa1-/- piglets born by sows administered with ATRA at 4 mg/kg body weight on dpc 12, 13, or 14, respectively. These were used for the analysis of ELISA, histological morphology, immunofluorescence staining, immunohistochemistry staining, and quantitative real-time PCR. The results indicate that the Hoxa1 mutation had adverse impacts on the development of the alveoli and pulmonary microvessels of Hoxa1-/- piglets. Maternal administration with ATRA at 4 mg/kg body weight on dpc 14 rescued the abnormal lung development of Hoxa1-/- piglets by increasing the IFN-γ concentration (p < 0.05), airspace area (p < 0.01) and pulmonary microvessel density (p < 0.01); increasing the expression of VEGFD (p < 0.01), PDGFD (p < 0.01), KDR (p < 0.01), ID1 (p < 0.01), and NEDD4 (p < 0.01); and decreasing the septal wall thickness (p < 0.01) and the expression of SFTPC (p < 0.01) and FOXO3 (p < 0.01). Maternal administration with ATRA plays a vital role in rescuing the abnormal development of lung of Hoxa1-/- fetal piglets.

Retinoids stored locally in the lung are required to attenuate the severity of acute lung injury in male mice

Retinoids are potent transcriptional regulators that act in regulating cell proliferation, differentiation, and other cellular processes. We carried out studies in male mice to establish the importance of local cellular retinoid stores within the lung alveolus for maintaining its health in the face of an acute inflammatory challenge induced by intranasal instillation of lipopolysaccharide. We also undertook single cell RNA sequencing and bioinformatic analyses to identify roles for different alveolar cell populations involved in mediating these retinoid-dependent responses. Here we show that local retinoid stores and uncompromised metabolism and signaling within the lung are required to lessen the severity of an acute inflammatory challenge. Unexpectedly, our data also establish that alveolar cells other than lipofibroblasts, specifically microvascular endothelial and alveolar epithelial cells, are able to take up lipoprotein-transported retinoid and to accumulate cellular retinoid stores that are directly used to respond to an acute inflammatory challenge.

Capillary Changes Precede Disordered Alveolarization in a Mouse Model of Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD), the most common sequela of preterm birth, is a severe disorder of the lung that is often associated with long-lasting morbidity. A hallmark of BPD is the disruption of alveolarization, whose pathogenesis is incompletely understood. Here, we tested the vascular hypothesis that disordered vascular development precedes the decreased alveolarization associated with BPD. Neonatal mouse pups were exposed to 7, 14, or 21 days of normoxia (21% O₂) or hyperoxia (85% O₂) with n = 8-11 for each group. The right lungs were fixed by vascular perfusion and investigated by design-based stereology or three-dimensional reconstruction of data sets obtained by serial block-face scanning EM. The alveolar capillary network of hyperoxia-exposed mice was characterized by rarefaction, partially altered geometry, and widening of capillary segments as shown by three-dimensional reconstruction. Stereology revealed that the development of alveolar epithelium and capillary endothelium was decreased in hyperoxia-exposed mice; however, the time course of these effects was different. That the surface area of the alveolar epithelium was smaller in hyperoxia-exposed mice first became evident at Day 14. In contrast, the surface area of the endothelium was reduced in hyperoxia-exposed mouse pups at Day 7. The thickness of the air-blood barrier decreased during postnatal development in normoxic mice, whereas it increased in hyperoxic mice. The endothelium and the septal connective tissue made appreciable contributions to the thickened septa. In conclusion, the present study provides clear support for the idea that the stunted alveolarization follows the disordered microvascular development, thus supporting the vascular hypothesis of BPD.

All-trans retinoic acid enhances, and a pan-RAR antagonist counteracts, the stem cell promoting activity of EVI1 in acute myeloid leukemia

Ecotropic virus integration site 1 (EVI1), whose overexpression characterizes a particularly aggressive subtype of acute myeloid leukemia (AML), enhanced anti-leukemic activities of all-trans retinoic acid (atRA) in cell lines and patient samples. However, the drivers of leukemia formation, therapy resistance, and relapse are leukemic stem cells (LSCs), whose properties were hardly reflected in these experimental setups. The present study was designed to address the effects of, and interactions between, EVI1 and retinoids in AML LSCs. We report that Evi1 reduced the maturation of leukemic cells and promoted the abundance, quiescence, and activity of LSCs in an MLL-AF9-driven mouse model of AML. atRA further augmented these effects in an Evi1 dependent manner. EVI1 also strongly enhanced atRA regulated gene transcription in LSC enriched cells. One of their jointly regulated targets, Notch4, was an important mediator of their effects on leukemic stemness. In vitro exposure of leukemic cells to a pan-RAR antagonist caused effects opposite to those of atRA. In vivo antagonist treatment delayed leukemogenesis and reduced LSC abundance, quiescence, and activity in Evi1^high AML. Key results were confirmed in human myeloid cell lines retaining some stem cell characteristics as well as in primary human AML samples. In summary, our study is the first to report the importance of EVI1 for key properties of AML LSCs. Furthermore, it shows that atRA enhances, and a pan-RAR antagonist counteracts, the effects of EVI1 on AML stemness, thus raising the possibility of using RAR antagonists in the therapy of EVI1^high AML.

Retinoic acid signaling in vascular development

Formation of the vasculature is an essential developmental process, delivering oxygen and nutrients to support cellular processes needed for tissue growth and maturation. Retinoic acid (RA) and its downstream signaling pathway is vital for normal pre- and post-natal development, playing key roles in the specification and formation of many organs and tissues. Here, we review the role of RA in blood and lymph vascular development, beginning with embryonic yolk sac vasculogenesis and remodeling and discussing RA's organ-specific roles in angiogenesis and vessel maturation. In particular, we highlight the multi-faceted role of RA signaling in CNS vascular development and acquisition of blood-brain barrier properties.

Clostridium difficile toxins induce VEGF-A and vascular permeability to promote disease pathogenesis

Clostridium difficile infection (CDI) is mediated by two major exotoxins, toxin A (TcdA) and toxin B (TcdB), that damage the colonic epithelial barrier and induce inflammatory responses. The function of the colonic vascular barrier during CDI has been relatively understudied. Here we report increased colonic vascular permeability in CDI mice and elevated vascular endothelial growth factor A (VEGF-A), which was induced in vivo by infection with TcdA- and/or TcdB-producing C. difficile strains but not with a TcdA^-TcdB^- isogenic mutant. TcdA or TcdB also induced the expression of VEGF-A in human colonic mucosal biopsies. Hypoxia-inducible factor signalling appeared to mediate toxin-induced VEGF production in colonocytes, which can further stimulate human intestinal microvascular endothelial cells. Both neutralization of VEGF-A and inhibition of its signalling pathway attenuated CDI in vivo. Compared to healthy controls, CDI patients had significantly higher serum VEGF-A that subsequently decreased after treatment. Our findings indicate critical roles for toxin-induced VEGF-A and colonic vascular permeability in CDI pathogenesis and may also point to the pathophysiological significance of the gut vascular barrier in response to virulence factors of enteric pathogens. As an alternative to pathogen-targeted therapy, this study may enable new host-directed therapeutic approaches for severe, refractory CDI.

Pulmonary Hypoplasia Induced by Oligohydramnios: Findings from Animal Models and a Population-Based Study

Pulmonary hypoplasia is a substantial cause of death in newborn infants, and oligohydramnios is one of the most commonly associated abnormalities. Lung growth is influenced by physical factors such as the intrauterine space, lung liquid volume and pressure, and fetal breathing movements. During lung development, the main physical force experienced by the lungs is stretching induced by breathing movements and the lung fluid in the airspaces. Oligohydramnios reduces the intrathoracic cavity size, thus disrupting fetal lung growth and leading to pulmonary hypoplasia. The exact mechanism by which oligohydramnios alters the respiratory system structure and the effect of oligohydramnios on long-term respiratory outcomes remain unknown. In this review, we summarize the effects of oligohydramnios on lung development, discuss the mechanisms of oligohydramnios-induced pulmonary hypoplasia identified in various animal studies, and describe the long-term respiratory outcomes in childhood of oligohydramnios-exposed fetuses reported by a population-based study.

Glucocorticoids and erythropoietin in chronic lung disease of prematurity: Proliferative potential in lung fibroblast and epithelial cells exposed to tracheal aspirates

BACKGROUND

We investigated the effects of glucocorticoids, erythropoietin (EPO) and spironolactone (SPL) n human fetal lung fibroblasts and human alveolar epithelial cells exposed to tracheal aspirate fluid (TAF) from extremely premature infants with chronic lung disease (CLD), characterized by fibrosis and changes in the alveolar epithelium.

METHODS

Fibroblasts and epithelial cells (FHs 738Lu and A549, respectively) were treated with different concentrations of hydrocortisone (HDC), dexamethasone (DEX), betamethasone (BET), SPL, and EPO in the absence or presence of TAF from infants with CLD (gestational age, 25.3 ± 0.8 weeks; birthweight, 658 ± 77 g; postnatal age, 0-28 days) and assayed for proliferation.

RESULTS

Exposure to TAF resulted in a concentration-dependent proliferation of fibroblasts and epithelial cells. Proliferation of TAF-exposed fibroblasts was suppressed most significantly by 100 μmol/L DEX (21%, P = 0.046) and 300 mIU/mL EPO (18%, P = 0.02) and promoted most significantly by 0.4 μmol/L HDC (10%, P = 0.04). Epithelial proliferation was promoted by 4 μmol/L HDC (15%, P = 0.04), 10 μmol/L DEX (53%, P < 0.01), 0.2 μmol/L BET (56%, P < 0.01), and 300 mIU/mL EPO (35%, P < 0.01) in the presence of TAF. Treatment with glucocorticoids alone did not significantly affect fibroblast proliferation.

CONCLUSIONS

Glucocorticoids and EPO reduced fibroproliferation while promoting epithelial cell growth in vitro within certain dose ranges. Appropriate doses of glucocorticoids and EPO may be useful in the prevention and resolution of CLD in extremely premature infants.

VEGF and endothelium-derived retinoic acid regulate lung vascular and alveolar development

Prevention or treatment of lung diseases caused by the failure to form, or destruction of, existing alveoli, as observed in infants with bronchopulmonary dysplasia and adults with emphysema, requires understanding of the molecular mechanisms of alveolar development. In addition to its critical role in gas exchange, the pulmonary circulation also contributes to alveolar morphogenesis and maintenance by the production of paracrine factors, termed "angiocrines," that impact the development of surrounding tissue. To identify lung angiocrines that contribute to alveolar formation, we disrupted pulmonary vascular development by conditional inactivation of the Vegf-A gene during alveologenesis. This resulted in decreased pulmonary capillary and alveolar development and altered lung elastin and retinoic acid (RA) expression. We determined that RA is produced by pulmonary endothelial cells and regulates pulmonary angiogenesis and elastin synthesis by induction of VEGF-A and fibroblast growth factor (FGF)-18, respectively. Inhibition of RA synthesis in newborn mice decreased FGF-18 and elastin expression and impaired alveolarization. Treatment with RA and vitamin A partially reversed the impaired vascular and alveolar development induced by VEGF inhibition. Thus we identified RA as a lung angiocrine that regulates alveolarization through autocrine regulation of endothelial development and paracrine regulation of elastin synthesis via induction of FGF-18 in mesenchymal cells.

Effects of maternal retinoic acid administration on lung angiogenesis in oligohydramnios-exposed fetal rats

BACKGROUND

All-trans retinoic acid (ATRA) induces in vitro angiogenesis and vascular endothelial growth factor (VEGF) secretion. Prenatal administration of vitamin A tends to increase the pulmonary and plasma levels of VEGF in the developing mouse. The aims of this study were to examine the effects of maternal retinoic acid treatment on lung VEGF expression and angiogenesis in oligohydramnios-exposed fetal rats.

METHODS

On day 16 of gestation, pregnant Sprague-Dawley rats were randomly assigned to either the retinoic acid group (intragastric ATRA at 10 mg/kg body weight) or the vehicle group. We punctured each uterine sac to produce oligohydramnios, and fetuses in the opposite uterine horn served as controls. On day 21 of gestation, the fetuses were delivered by cesarean section.

RESULTS

Rats exposed to oligohydramnios exhibited lower lung weights and lung/body weight ratios, and ATRA exhibited no effects on the body or lung weights of oligohydramnios-exposed rats. Lung microvessel density decreased in oligohydramnios-exposed rats of maternal vehicle-treated dams. Microvessel density was comparable between the oligohydramnios + retinoic acid group and the control + retinoic acid group. VEGF expression was comparable among control and oligohydramnios-exposed rats of maternal vehicle- or retinoic acid-treated dams.

CONCLUSION

Maternal retinoic acid treatment did not increase lung VEGF expression or enhance lung development in oligohydramnios-exposed fetal rats. These results do not support the use of maternal retinoic acid to prevent oligohydramnios-induced pulmonary hypoplasia in the pseudoglandular stage.

Timing of umbilical cord blood derived mesenchymal stem cells transplantation determines therapeutic efficacy in the neonatal hyperoxic lung injury

Intratracheal transplantation of human umbilical cord blood (UCB)-derived mesenchymal stem cells (MSCs) attenuates the hyperoxia-induced neonatal lung injury. The aim of this study was to optimize the timing of MSCs transplantation. Newborn Sprague-Dawley rats were randomly exposed to hyperoxia (90% for 2 weeks and 60% for 1 week) or normoxia after birth for 21 days. Human UCB-derived MSCs (5×10(5) cells) were delivered intratracheally early at postnatal day (P) 3 (HT3), late at P10 (HT10) or combined early+late at P3+10 (HT3+10). Hyperoxia-induced increase in mortality, TUNEL positive cells, ED1 positive alveolar macrophages, myeloperoxidase activity and collagen levels, retarded growth and reduced alveolarization as evidenced by increased mean linear intercept and mean alveolar volume were significantly better attenuated in both HT3 and HT3+10 than in HT10. Hyperoxia-induced up-regulation of both cytosolic and membrane p47(phox) indicative of oxidative stress, and increased inflammatory markers such as tumor necrosis factor-α, interleukin (IL) -1α, IL-1β, IL-6, and transforming growth factor-β measured by ELISA, and tissue inhibitor of metalloproteinase-1, CXCL7, RANTES, L-selectin and soluble intercellular adhesion molecule-1 measured by protein array were consistently more attenuated in both HT3 and HT3+10 than in HT10. Hyperoxia-induced decrease in hepatocyte growth factor and vascular endothelial growth factor was significantly up-regulated in both HT3 and HT3+10, but not in HT10. In summary, intratracheal transplantation of human UCB derived MSCs time-dependently attenuated hyperoxia-induced lung injury in neonatal rats, showing significant protection only in the early but not in the late phase of inflammation. There were no synergies with combined early+late MSCs transplantation.

Endotoxin inhalation alters lung development in neonatal mice

BACKGROUND

Childhood asthma is a significant public health problem. Epidemiologic evidence suggests an association between childhood asthma exacerbations and early life exposure to environmental endotoxin. Although the pathogenesis of endotoxin-induced adult asthma is well studied, questions remain about the impact of environmental endotoxin on pulmonary responsiveness in early life.

METHODS

We developed a murine model of neonatal/juvenile endotoxin exposures approximating those in young children and evaluated the lungs inflammatory and remodeling responses.

RESULTS

Persistent lung inflammation induced by the inhalation of endotoxin in early life was demonstrated by the influx of inflammatory cells and pro-inflammatory mediators to the airways and resulted in abnormal alveolarization.

CONCLUSIONS

Results of this study advance the understanding of the impact early life endotoxin inhalation has on the lower airways, and demonstrates the importance of an experimental design that approximates environmental exposures as they occur in young children.

Intratracheal Transplantation of Human Umbilical Cord Blood-Derived Mesenchymal Stem Cells Dose-Dependently Attenuates Hyperoxia-Induced Lung Injury in Neonatal Rats

Intratracheal transplantation of human umbilical cord blood (UCB)-derived mesenchymal stem cells (MSCs) attenuates the hyperoxia-induced neonatal lung injury. The aim of this preclinical translation study was to optimize the dose of human UCB-derived MSCs in attenuating hyperoxia-induced lung injury in newborn rats. Newborn Sprague-Dawley rats were randomly exposed to hyperoxia (95% oxygen) or normoxia after birth for 14 days. Three different doses of human UCB-derived MSCs, 5 × 103 (HT1), 5 × 104 (HT2), and 5 × 105 (HT3), were delivered intratracheally at postnatal day (P) 5. At P14, lungs were harvested for analyses including morphometry for alveolarization, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) staining, myeoloperoxidase activity, mRNA level of tumor necross factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, and transforming growth factor-β (TGF-β), human glyceradehyde-3-phosphate dehydrogenase (GAPDH), and p47 phox, and collagen levels. Increases in TUNEL-positive cells were attenuated in all transplantation groups. However, hyperoxia-induced lung injuries, such as reduced alveolarization, as evidenced by increased mean linear intercept and mean alveolar volume, and increased collagen levels were significantly attenuated in both HT2 and HT3, but not in HT1, with better attenuation in HT3 than in HT2. Dose-dependent human GAPDH expression, indicative of the presence of human RNA in lung tissue, was observed only in the transplantation groups, with higher expression in HT3 than in HT2, and higher expression in HT2 than in HT1. Hyperoxia-induced inflammatory responses such as increased myeloperoxidase acitivity, mRNA levels of TNF-α, IL-1β, IL-6, and TGF-β of the lung tissue, and upregulation of both cytosolic and membrane p47 phox, indicative of oxidative stress, were significantly attenuated in both HT2 and HT3 but not in HT1. These results demonstrate that intratracheal transplantation of human UCB-derived MSCs with appropriate doses may attenuate hyperoxia-induced lung injury through active involvement of these cells in modulating host inflammatory responses and oxidative stress in neonatal rats.

Maternal micronutrient deficiency, fetal development, and the risk of chronic disease

Early life nutritional exposures, combined with changes in lifestyle in adult life, can result in increased risk of chronic diseases. Although much of the focus on the developmental origins of disease has been on birth size and growth in postnatal life and the availability of energy and protein during these critical developmental periods, micronutrient deficiencies may also play an important role in fetal growth and development. Micronutrient status in fetal and early life may alter metabolism, vasculature, and organ growth and function, leading to increased risk of cardiometabolic disorders, adiposity, altered kidney function, and, ultimately, to type 2 diabetes and cardiovascular diseases. This review elucidates pathways through which micronutrient deficiencies lead to developmental impairment and describes the research to date on the evidence that micronutrient deficiencies in utero influence the development of chronic disease risk. Animal studies, observational human studies examining maternal diet or micronutrient status, and limited data from intervention studies are reviewed. Where data are lacking, plausible mechanisms and pathways of action have been derived from the existing animal and in vitro models. This review fills a critical gap in the literature related to the seminal role of micronutrients in early life and extends the discussion on the developmental origins of health and disease beyond birth size and energy and protein deficiency.

Interactions of alpha1-proteinase inhibitor with small ligands of therapeutic potential: binding with retinoic acid

Human alpha(1)-proteinase inhibitor (alpha(1)-PI), also known as alpha(1)-antitrypsin, is the most abundant plasma serine protease inhibitor (serpin). It is best recognized for inhibition of neutrophil elastase. The alpha(1)-PI interactions with non-protease ligands were investigated mainly in regards to those molecules that may block the aggregation of alpha(1)-PI Z mutant. The objective of this study was to evaluate the potential of alpha(1)-PI to bind small non-peptide ligands of pharmaceutical interest that may attain additional properties to currently available alpha(1)-PI therapeutic preparations. Among putative ligands of bio-medical interest examined in this study, all-trans retinoic acid (RA) was selected due to its recently proposed roles in the lungs, and as an efficient optical probe. The results of this study, including absorption spectroscopy data, fluorescence quenching and the protein-induced chirality of the visible circular dichroism strongly suggest that alpha(1)-PI does bind RA in vitro to non-covalent complexes of up to two moles of RA per one mole of the protein. To our knowledge, this is the first report that provides experimental evidence of the alpha(1)-PI potential towards bi-functional drugs via a combination with RA, or potentially other molecules of pharmaceutical interest, that ultimately, may enhance currently available alpha(1)-PI therapies.

Human umbilical cord blood-derived mesenchymal stem cells attenuate hyperoxia-induced lung injury in neonatal rats

Recent evidence suggests mesenchymal stem cells (MSCs) can downmodulate bleomycin-induced lung injury, and umbilical cord blood (UCB) is a promising source for human MSCs. This study examined whether intratracheal or intraperitoneal transplantation of human UCB-derived MSCs can attenuate hyperoxia-induced lung injury in immunocompetent newborn rats. Wild-type Sprague-Dawley rats were randomly exposed to 95% oxygen or air from birth. In the transplantation groups, a single dose of PKH26-labeled human UCB-derived MSCs was administered either intratracheally (2 x 10(6) cells) or intraperitoneally (5 x 10(5) cells) at postnatal day (P) 5. At P14, the harvested lungs were examined for morphometric analyses of alveolarization and TUNEL staining, as well as the myeoloperoxidase activity, the level of tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, and transforming growth factor (TGF)-beta mRNA, alpha-smooth muscle actin (SMA) protein, and collagen levels. Differentiation of MSCs to the respiratory epithelium was also evaluated both in vitro before transplantation and in vivo after transplantation. Despite one fourth dosage of MSCs, significantly more PKH26-labeled donor cells were recovered with intratracheal administration than with intraperitoneal administration both during normoxia and hyperoxia. The hyperoxia-induced increase in the number of TUNEL-positive cells, myeloperoixdase activity, and the level of IL-6 mRNA were significantly attenuated with both intratracheal and intraperitoneal MSCs transplantation. However, the hyperoxia-induced impaired alveolarization and increased the level of TNF-alpha and TGF-beta mRNA, alpha-SMA protein, and collagen were significantly attenuated only with intratracheal MSCs transplantation. MSCs differentiated into respiratory epithelium in vitro and a few PKH26-positive donor cells were colocalized with pro surfactant protein C in the damaged lungs. In conclusion, intratracheal transplantation of human UCB-derived MSCs is more effective than intraperitoneal transplantation in attenuating the hyperoxia-induced lung injury in neonatal rats.

Synergistic upregulation of erythropoietin receptor (EPO-R) expression by sense and antisense EPO-R transcripts in the canine lung

We previously found increased erythropoietin receptor (EPO-R) protein levels in vigorously growing canine lungs after pneumonectomy (PNX), suggesting a role for paracrine EPO signaling in lung growth and remodeling. Now we find that sense and antisense EPO-R transcripts (sEPO-R and asEPO-R, respectively) are concordantly up-regulated in the post-PNX remaining lung, leading to the hypothesis that sEPO-R and asEPO-R interactions enhance EPO signaling during lung growth. We cloned a canine asEPO-R cDNA, which is fully complementary to the sense strand of the EPO-R gene from 2.5kb 3' to the sense stop codon, and extends into the 5' UTR of the sEPO-R transcript. Both asEPO-R and sEPO-R transcripts colocalize with EPO-R protein in the same lung cells. In cultured human embryonic kidney (HEK293) cells, transfection with sEPO-R (+FLAG tag) cDNA alone increased EPO-R protein expression (anti-EPO-R and anti-FLAG). At constant sEPO-R cDNA levels, cotransfection with escalating asEPO-R cDNA further increased recombinant EPO-R protein expression. The asEPO-R transcript harbors two putative opening reading frames (ORFs). Separate transfection of each asEPO-R ORF cDNA resulted in differential stimulatory effects on EPO-R protein expression. We conclude that both sEPO-R and asEPO-R transcripts contribute to in vivo up-regulation of EPO-R protein expression in the post-PNX remaining lung. This demonstrates synergism between sense-antisense EPO-R transcripts in response to physiological stimulation in a robust model of induced lung growth.

Prenatal administration of vitamin A alters pulmonary and plasma levels of vascular endothelial growth factor in the developing mouse

Vitamin A and the retinoids play a unique role in mammalian embryonic and foetal development and are essential for both cellular differentiation and the establishment of normal morphogenesis. Vascular endothelial growth factor (VEGF) is a known potent mitogenic factor that plays a key role in lung development and function maintenance. In order to contribute to a better knowledge of the modulating effects of vitamin A in lung development, we investigated the effects of the antenatal administration of vitamin A on VEGF expression in lungs and plasma from foetuses and neonates. Pregnant mice were subjected to subcutaneous administration of vitamin A on the 12th gestational day. The lungs and plasma from foetuses and neonates were collected daily from the 15th gestational day till the day of birth. Our results show that vitamin A modulates VEGF concentrations both in lungs and plasma. Statistically significant differences were observed at gestational days 15 (P = 0.004 for lungs; P < 0.0001 for plasma), 16 (P < 0.0001 for lungs and plasma) and 18 (P < 0.0001 for lungs; P < 0.05 for plasma). Vitamin A tends to increase the expression of this factor in the lung, particularly during the critical period of perinatal adaptation to postnatal life. These effects seem to be spatial and temporally regulated, and point out to the important role of vitamin A during lung development.

Regulation of 17-Beta Hydroxysteroid Dehydrogenase Type 2 in Human Placental Endothelial Cells1

17-beta hydroxysteroid dehydrogenase type 2 (HSD17B2) oxidizes estradiol to estrone, testosterone to androstenedione, and 20 alpha-dihydroprogesterone to progesterone. HSD17B2 is highly expressed in human placental tissue where it is localized to placental endothelial cells lining the fetal compartment. The aim of this study was to investigate the effects of potential regulatory factors including progesterone, estradiol, and retinoic acid (RA) onHSD17B2 expression in primary human placental endothelial cells in culture.HSD17B2 mRNA expression was not regulated by progesterone, the progesterone agonist R5020, or estradiol treatment. RA significantly induced HSD17B2 mRNA levels and enzyme activity in a dose- and time-dependent manner. Maximal stimulation occurred at Hour 48 at an RA concentration of 10(-6) M. Both retinoic acid receptor alpha (RARA) and retinoid X receptor alpha (RXRA) were readily detected by immunoblotting in isolated placental endothelial cells. RNA interference directed against RARA or RXRA led to reduced basal levels of HSD17B2 mRNA levels and significantly abolished RA-stimulated HSD17B2 expression. Together, these data indicate that regulation of HSD17B2 mRNA levels and enzymatic activity by RA in the placenta is mediated by RARA and RXRA.

Retinoids increase lung elastin expression but fail to alter morphology or angiogenesis genes in premature ventilated baboons

Retinoids regulate elastin synthesis by alveolar myofibroblasts and affect angiogenesis pathways, both of which are processes critical for alveolar development. Retinoids accelerate alveolarization in rodents and are now used therapeutically in premature infants at risk of bronchopulmonary dysplasia (BPD). This study examined the effects of retinoid supplementation on alveolar elastin expression and deposition and angiogenesis-related signaling in a primate model of BPD. Premature baboons delivered at 125 d of gestation after maternal steroid treatment were given surfactant and ventilated with minimal supplemental oxygen for 14 d with (n = 5) and without (n = 5) supplemental vitamin A (5000 U/kg/d) and compared with 140-d unventilated controls. Ventilatory efficiency index (VEI) and oxygenation index (OI) were not statistically different between ventilated treatment groups. Expression of vascular endothelial growth factor A (VEGF-A), fms-related tyrosine kinase 1 (Flt-1), and tyrosine kinase with immunoglobulin-like and EGF-like domains 1 (TIE-1) was repressed by premature delivery and mechanical ventilation and was not altered by retinoid supplementation. Retinoid supplementation did not enhance alveolar angiogenesis. Elastin expression was repressed by premature delivery and extended ventilation, and retinoid supplementation increased elastin expression specifically in alveolar myofibroblasts within alveolar walls. These results suggest that the small decrease in mortality among premature infants receiving retinoid supplementation may not be mediated through enhanced alveolar development.

Lung function in infants and young children with chronic lung disease of infancy: the next steps?

Over the past year, a series of papers have reviewed the literature concerning assessment and interpretation of lung function in infants and young children with chronic lung disease of infancy. This manuscript, which represents the final paper in that series, summarizes the findings to date and highlights key areas for future research. Despite the huge literature in this field, interpretation of results and their use in guiding clinical management are still limited by difficulties in 'normalizing data' according to body size and maturation and selection of appropriate control groups. Furthermore, sensitive tests that more closely reflect the underlying pathophysiology of 'new' bronchopulmonary dysplasia, together with simple and reliable methods of assessing lung maturity at birth and true oxygen requirements at specified time points are urgently required. Research in this field is also challenged by the need to separate the independent effects of genetic predisposition, gene-environment interactions, preterm delivery, neonatal respiratory disorders and various treatment strategies on the growing lung. The extent to which disruption of lung growth following premature exposure to the extra-uterine environment leads to an earlier or more aggravated decline in respiratory function in later adult life remains to be elucidated. Whatever its origin, given the increasing survival of smaller and more immature infants, the long term sequelae of neonatal lung disease, are likely to continue to change, requiring ongoing, carefully designed longitudinal studies. Future research strategies need to encompass a multicenter, multi-disciplinary, collaborative approach with closer links between clinicians and basic scientists, to ensure that the most relevant research questions are addressed using appropriate methodology and that findings are implemented into clinical practice in a more timely fashion.