Fetal origins of neonatal lung disease: understanding the pathogenesis of bronchopulmonary dysplasia

Maternal Body Mass Index and Risk of Bronchopulmonary Dysplasia in Extremely Preterm Infants

OBJECTIVE

We evaluated the relationship between maternal body mass index (BMI) and death or bronchopulmonary dysplasia (BPD). We hypothesized that in extremely low birth weight (ELBW; BW < 1,000 g) infants, the risk of death or BPD would be greater if the maternal BMI deviated further from the ideal BMI of 24.

STUDY DESIGN

ELBW infants admitted to AdventHealth Neonatal Intensive Care Unit (NICU) between calendar years 2012 and 2017 were included in this retrospective observational study. BPD was defined as continuous supplemental oxygen use at 36 weeks post-menstrual age.

RESULT

There was no association between the deviation of maternal BMI from the ideal of 24 and the composite outcome of death or BPD (6.9 ± 6.7 vs. 7.06 ± 6.6, pp = 0.966). However, there was a lower risk of death with a higher maternal BMI (p = 0.024). BPD was also associated with a higher maternal BMI (p = 0.045).

CONCLUSION

Maternal BMI was not associated with the composite variable of death or BPD in ELBW infants. The lack of association was due to the contrast between high BMI and a lower risk of death and a higher risk for BPD.

KEY POINTS

· Maternal BMI was not associated with the composite outcome of death or BPD.. · Elevated BMI was associated with a higher risk of BPD.. · Elevated BMI was associated with a lower risk of death..

Gestational Diabetes Mellitus Impedes Fetal Lung Development Through Exosome-Dependent Crosstalk Between Trophoblasts and Lung Epithelial Cells

Background

Fetal lung underdevelopment (FLUD) is associated with neonatal and childhood severe respiratory diseases, among which gestational diabetes mellitus (GDM) play crucial roles as revealed by recent prevalence studies, yet mechanism underlying GDM-induced FLUD, especially the role of trophoblasts, is not all known.

Methods

From the perspective of trophoblast-derived exosomes, we established in vitro, ex vivo, in vivo and GDM trophoblast models. Utilizing placenta-derived exosomes (NUB-exos and GDMUB-exos) isolated from normal and GDM umbilical cord blood plasma and trophoblast-derived exosomes (NC-exos and HG-exos) isolated from HTR8/SVneo trophoblasts medium with/without high glucose treatment, we examined their effects on fetal lung development and biological functions.

Results

We found that, compared with the NUB-exos group, the exosome concentration increased in GDMUB-exos group, and the content of exosomes also changed evidenced by 61 dysregulated miRNAs. After applying these exosomes to A549 alveolar type II epithelial cells, the proliferation and biological functions were suppressed while the proportion of apoptotic cells was increased as compared to the control. In ex vivo studies, we found that GDMUB-exos showed significant suppression on the growth of the fetal lung explants, where the number of terminal buds and the area of explant surface decreased and shrank. Besides, the expression of Fgf10, Vegfa, Flt-1, Kdr and surfactant proteins A, B, C, and D was downregulated in GDMUB-exos group, whilst Sox9 was upregulated. For in vivo studies, we found significant suppression of fetal lung development in GDMUB-exos group. Importantly, we found consistent alterations when we used NC-exos and HG-exos, suggesting a dominant role of trophoblasts in placenta-derived exosome-induced FLUD.

Conclusion

In conclusion, GDM can adversely affect trophoblasts and alter exosome contents, causing crosstalk disorder between trophoblasts and fetal lung epithelial cells and finally leading to FLUD. Findings of this study will shine insight into the theoretical explanation for the pathogenesis of FLUD.

Differential placental CpG methylation is associated with chronic lung disease of prematurity

BACKGROUND

Chronic lung disease (CLD) is the most common pulmonary morbidity in extremely preterm infants. It is unclear to what extent prenatal exposures influence the risk of CLD. Epigenetic variation in placenta DNA methylation may be associated with differential risk of CLD, and these associations may be dependent upon sex.

METHODS

Data were obtained from a multi-center cohort of infants born extremely preterm (<28 weeks' gestation) and an epigenome-wide approach was used to identify associations between placental DNA methylation and CLD (n = 423). Associations were evaluated using robust linear regression adjusting for covariates, with a false discovery rate of 0.05. Analyses stratified by sex were used to assess differences in methylation-CLD associations.

RESULTS

CLD was associated with differential methylation at 49 CpG sites representing 46 genes in the placenta. CLD was associated with differential methylation of probes within genes related to pathways involved in fetal lung development, such as p53 signaling and myo-inositol biosynthesis. Associations between CpG methylation and CLD differed by sex.

CONCLUSIONS

Differential placental methylation within genes with key roles in fetal lung development may reflect complex cell signaling between the placenta and fetus which mediate CLD risk. These pathways appear to be distinct based on fetal sex.

IMPACT

In extremely preterm infants, differential methylation of CpG sites within placental genes involved in pathways related to cell signaling, oxidative stress, and trophoblast invasion is associated with chronic lung disease of prematurity. DNA methylation patterns associated with chronic lung disease were distinctly based on fetal sex, suggesting a potential mechanism underlying dimorphic phenotypes. Mechanisms related to fetal hypoxia and placental myo-inositol signaling may play a role in fetal lung programming and the developmental origins of chronic lung disease. Continued research of the relationship between the placental epigenome and chronic lung disease could inform efforts to ameliorate or prevent this condition.

A Preconception Paternal Fish Oil Diet Prevents Toxicant-Driven New Bronchopulmonary Dysplasia in Neonatal Mice

New bronchopulmonary dysplasia is a developmental lung disease associated with placental dysfunction and impaired alveolarization. Risk factors for new BPD include prematurity, delayed postnatal growth, the dysregulation of epithelial-to-mesenchymal transition (EMT), and parental exposure to toxicants. Our group previously reported that a history of paternal toxicant exposure increased the risk of prematurity and low birth weight in offspring. A history of paternal toxicant exposure also increased the offspring's risk of new BPD and disease severity was increased in offspring who additionally received a supplemental formula diet, which has also been linked to poor lung development. Risk factors associated with new BPD are well-defined, but it is unclear whether the disease can be prevented. Herein, we assessed whether a paternal fish oil diet could attenuate the development of new BPD in the offspring of toxicant exposed mice, with and without neonatal formula feeding. We investigated the impact of a paternal fish oil diet preconception because we previously reported that this intervention reduces the risk of TCDD associated placental dysfunction, prematurity, and low birth weight. We found that a paternal fish oil diet significantly reduced the risk of new BPD in neonatal mice with a history of paternal toxicant exposure regardless of neonatal diet. Furthermore, our evidence suggests that the protective effects of a paternal fish oil diet are mediated in part by the modulation of small molecules involved in EMT.

Patho-mechanisms of the origins of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) continues to be one of the most common complications of prematurity, despite significant advancement in neonatology over the last couple of decades. The new BPD is characterized histopathologically by impaired lung alveolarization and dysregulated vascularization. With the increased survival of extremely preterm infants, the risk for the development of BPD remains high, emphasizing the continued need to understand the patho-mechanisms that play a role in the development of this disease. This brief review summarizes recent advances in our understanding of the maldevelopment of the premature lung, highlighting recent research in pathways of oxidative stress-related lung injury, the role of placental insufficiency, growth factor signaling, the extracellular matrix, and microRNAs.

Cardiovascular Programming During and After Diabetic Pregnancy: Role of Placental Dysfunction and IUGR

Intrauterine growth restriction (IUGR) is a condition whereby a fetus is unable to achieve its genetically determined potential size. IUGR is a global health challenge due to high mortality and morbidity amongst affected neonates. It is a multifactorial condition caused by maternal, fetal, placental, and genetic confounders. Babies born of diabetic pregnancies are usually large for gestational age but under certain conditions whereby prolonged uncontrolled hyperglycemia leads to placental dysfunction, the outcome of the pregnancy is an intrauterine growth restricted fetus with clinical features of malnutrition. Placental dysfunction leads to undernutrition and hypoxia, which triggers gene modification in the developing fetus due to fetal adaptation to adverse utero environmental conditions. Thus, in utero gene modification results in future cardiovascular programming in postnatal and adult life. Ongoing research aims to broaden our understanding of the molecular mechanisms and pathological pathways involved in fetal programming due to IUGR. There is a need for the development of effective preventive and therapeutic strategies for the management of growth-restricted infants. Information on the mechanisms involved with in utero epigenetic modification leading to development of cardiovascular disease in adult life will increase our understanding and allow the identification of susceptible individuals as well as the design of targeted prevention strategies. This article aims to systematically review the latest molecular mechanisms involved in the pathogenesis of IUGR in cardiovascular programming. Animal models of IUGR that used nutrient restriction and hypoxia to mimic the clinical conditions in humans of reduced flow of nutrients and oxygen to the fetus will be discussed in terms of cardiac remodeling and epigenetic programming of cardiovascular disease. Experimental evidence of long-term fetal programming due to IUGR will also be included.

Novel functional role of GH/IGF-I in neonatal lung myofibroblasts and in rat lung growth after intrauterine growth restriction

Intrauterine growth restriction (IUGR) is a risk factor for neonatal chronic lung disease (CLD) characterized by reduced alveoli and perturbed matrix remodeling. Previously, our group showed an activation of myofibroblasts and matrix remodeling in rat lungs after IUGR. Because growth hormone (GH) and insulin-like growth factor I (IGF-I) regulate development and growth, we queried 1) whether GH/IGF-I signaling is dysregulated in lungs after IUGR and 2) whether GH/IGF-I signaling is linked to neonatal lung myofibroblast function. IUGR was induced in Wistar rats by isocaloric low-protein diet during gestation. Lungs were obtained at embryonic day (E) 21, postnatal day (P) 3, P12, and P23. Murine embryonic fibroblasts (MEF) or primary neonatal myofibroblasts from rat lungs of control (pnF^Co) and IUGR (pnF^IUGR) were used for cell culture studies. In the intrauterine phase (E21), we found a reduction in GH receptor (GH-R), Stat5 signaling and IGF-I expression in lungs after IUGR. In the postnatal phase (P3-P23), catchup growth after IUGR was linked to increased GH mRNA, GH-R protein, activation of proliferative Stat5/Akt signaling, cyclin D1 and PCNA in rat lungs. On P23, a thickening of the alveolar septae was related to increased vimentin and matrix deposition, indicating fibrosis. In cell culture studies, nutrient deprivation blocked GH-R/IGF-IR signaling and proliferation in MEFs; this was reversed by IGF-I. Proliferation and Stat5 activation were increased in pnF^IUGR. IGF-I and GH induced proliferation and migration of pnF^Co; only IGF-I had these effects on pnF^IUGR. Thus, we show a novel mechanism by which the GH/IGF-I axis in lung myofibroblasts could account for structural lung changes after IUGR.

Intra-Amniotic Soluble Endoglin Impairs Lung Development in Neonatal Rats

Soluble endoglin (sENG) is increased in the amniotic fluid of women with preeclampsia and chorioamnionitis. Preterm infants born to women with these disorders have an increased risk of aberrant lung development. Whether this increased risk is secondary to elevated sENG levels is unclear. The objective of this study was to determine whether intrauterine exposure to an adenovirus overexpressing sENG impairs neonatal lung angiogenesis by modulating lung endothelial nitric oxide synthase (eNOS) signaling. Pregnant Sprague-Dawley rats were randomly assigned to receive ultrasound-guided intra-amniotic injections of adenovirus overexpressing sENG (Ad-sENG) or control adenovirus (Ad-control) on embryonic day 17. After this exposure, rat pups were maintained in normoxia and evaluated on postnatal day 14. Intra-amniotic Ad-sENG decreased lung vascular endothelial growth factor receptor 2 and eNOS expression in rat pups. This was accompanied by a marked decrease in lung angiogenesis and alveolarization. Ad-sENG-exposed pups also had an increase in right ventricular systolic pressure, weight ratio of right ventricle to left ventricle plus septum, and pulmonary vascular remodeling. In addition, exposure of human pulmonary artery endothelial cells to recombinant sENG reduced endothelial tube formation and protein levels of eNOS, phosphorylated eNOS, and phosphorylated Smad1/5. Together, our findings demonstrate that intrauterine exposure to an adenovirus overexpressing sENG disrupts lung development by impairing Smad1/5-eNOS signaling. We speculate that sENG-mediated dysregulation of Smad1/5-eNOS signaling contributes to impaired lung development and potentially primes the developing lung for further postnatal insults. Further studies exploring the relationship between amniotic fluid sENG levels and preterm respiratory outcomes will be necessary.

Hydrogen-rich water ameliorates bronchopulmonary dysplasia (BPD) in newborn rats

Bronchopulmonary dysplasia (BPD) is characterized by developmental arrest of the alveolar tissue. Oxidative stress is causally associated with development of BPD. The effects of hydrogen have been reported in a wide range of disease models and human diseases especially caused by oxidative stress. We made a rat model of BPD by injecting lipopolysaccharide (LPS) into the amniotic fluid at E16.5. The mother started drinking hydrogen-rich water from E9.5 and also while feeding milk. Hydrogen normalized LPS-induced abnormal enlargement of alveoli at P7 and P14. LPS increased staining for nitrotyrosine and 8-OHdG of the lungs, and hydrogen attenuated the staining. At P1, LPS treatment decreased expressions of genes for FGFR4, VEGFR2, and HO-1 in the lungs, and hydrogen increased expressions of these genes. In contrast, LPS treatment and hydrogen treatment had no essential effect on the expression of SOD1. Inflammatory marker proteins of TNFα and IL-6 were increased by LPS treatment, and hydrogen suppressed them. Treatment of A549 human lung adenocarcinoma epithelial cells with 10% hydrogen gas for 24 hr decreased production of reactive oxygen species in both LPS-treated and untreated cells. Lack of any known adverse effects of hydrogen makes hydrogen a promising therapeutic modality for BPD. Pediatr Pulmonol. 2016; 51:928-935. © 2016 Wiley Periodicals, Inc.

Can the preterm lung recover from perinatal stress?

After birth, adequate lung function is necessary for the successful adaptation of a preterm baby. Both prenatal and postnatal insults and therapeutic interventions have an immediate effect on lung function and gas exchange but also interfere with fetal and neonatal lung development. Prenatal insults like chorioamnionitis and prenatal interventions like maternal glucocorticosteroids interact but might also determine the preterm baby's lung response to postnatal interventions ("second hit") like supplementation of oxygen and drug therapy. We review current experimental and clinical findings on the influence of different perinatal factors on preterm lung development and discuss how well-established interventions in neonatal care might be adapted to attenuate postnatal lung injury.

Maternal high-fat diet is associated with impaired fetal lung development

Maternal nutrition has a profound long-term impact on infant health. Poor maternal nutrition influences placental development and fetal growth, resulting in low birth weight, which is strongly associated with the risk of developing chronic diseases, including heart disease, hypertension, asthma, and type 2 diabetes, later in life. Few studies have delineated the mechanisms by which maternal nutrition affects fetal lung development. Here, we report that maternal exposure to a diet high in fat (HFD) causes placental inflammation, resulting in placental insufficiency, fetal growth restriction (FGR), and inhibition of fetal lung development. Notably, pre- and postnatal exposure to maternal HFD also results in persistent alveolar simplification in the postnatal period. Our novel findings provide a strong association between maternal diet and fetal lung development.

Change in practice after the Surfactant, Positive Pressure and Oxygenation Randomised Trial

OBJECTIVE

To test the hypothesis that the proportion of endotracheal intubation (ETI) in the delivery room (DR) decreased in Neonatal Research Network (NRN) centres after the National Institute of Child Health and Human Development NRN Surfactant, Positive Pressure, and Oxygenation Randomised Trial (SUPPORT).

DESIGN

Retrospective cohort study using the prospective NRN generic database.

SETTING

Eleven centres that participated in the SUPPORT trial and remained part of the NRN. Preterm neonates 24(0/7)-27(6/7) weeks' gestational age enrolled in the SUPPORT trial were randomised to: (1) DR continuous positive airway pressure or DR ETI with early surfactant administration; and (2) oxygen saturation targets of 85-89% or 91-95%. The prior NRN feasibility trial had assessed the feasibility of randomisation to continuous positive airway pressure versus ETI.

PATIENTS

Infants 24(0/7)-27(6/7) weeks' gestational age, excluding infants with syndromes or major malformations and those on comfort care only.

MAIN OUTCOME MEASURE

Proportion of DR ETI.

RESULTS

The proportion of DR ETI decreased significantly in the group of infants from centres that had not participated in the feasibility trial (91% before vs 75% after SUPPORT, adjusted relative risk 0.86, 95% CI 0.83-0.89, p<0.0001) but not in the group of infants from the other centres, where the proportion of ETI was already lower prior to initiation of the SUPPORT trial (61% before vs 58% after SUPPORT, adjusted relative risk 0.96, 95% CI 0.89 to 1.05, p=0.40).

CONCLUSION

This study shows that DR ETI changed after SUPPORT only in NRN centres that had not participated in a similar trial.

TRIAL REGISTRATION NUMBER

NCT00063063 (GDB) and NCT00233324 (SUPPORT).

Postnatal weight gain in preterm infants with severe bronchopulmonary dysplasia

OBJECTIVES

To characterize postnatal growth failure (PGF), defined as weight < 10th percentile for postmenstrual age (PMA) in preterm (≤ 27 weeks' gestation) infants with severe bronchopulmonary dysplasia (sBPD) at specified time points during hospitalization, and to compare these in subgroups of infants who died/underwent tracheostomy and others.

STUDY DESIGN

Retrospective review of data from the multicenter Children's Hospital Neonatal Database (CHND).

RESULTS

Our cohort (n = 375) had a mean ± standard deviation gestation of 25 ± 1.2 weeks and birth weight of 744 ± 196 g. At birth, 20% of infants were small for gestational age (SGA); age at referral to the CHND neonatal intensive care unit (NICU) was 46 ± 50 days. PGF rates at admission and at 36, 40, 44, and 48 weeks' PMA were 33, 53, 67, 66, and 79% of infants, respectively. Tube feedings were administered to > 70% and parenteral nutrition to a third of infants between 36 and 44 weeks' PMA. At discharge, 34% of infants required tube feedings and 50% had PGF. A significantly greater (38 versus 17%) proportion of infants who died/underwent tracheostomy (n = 69) were SGA, compared with those who did not (n = 306; p < 0.01).

CONCLUSIONS

Infants with sBPD commonly had progressive PGF during their NICU hospitalization. Fetal growth restriction may be a marker of adverse outcomes in this population.

Recent advances in late lung development and the pathogenesis of bronchopulmonary dysplasia

In contrast to early lung development, a process exemplified by the branching of the developing airways, the later development of the immature lung remains very poorly understood. A key event in late lung development is secondary septation, in which secondary septa arise from primary septa, creating a greater number of alveoli of a smaller size, which dramatically expands the surface area over which gas exchange can take place. Secondary septation, together with architectural changes to the vascular structure of the lung that minimize the distance between the inspired air and the blood, are the objectives of late lung development. The process of late lung development is disturbed in bronchopulmonary dysplasia (BPD), a disease of prematurely born infants in which the structural development of the alveoli is blunted as a consequence of inflammation, volutrauma, and oxygen toxicity. This review aims to highlight notable recent developments in our understanding of late lung development and the pathogenesis of BPD.

Gpr177 regulates pulmonary vasculature development

Establishment of the functional pulmonary vasculature requires intimate interaction between the epithelium and mesenchyme. Previous genetic studies have led to inconsistent conclusions about the contribution of epithelial Wnts to pulmonary vasculature development. This discrepancy is possibly due to the functional redundancy among different Wnts. Here, we use Shh-Cre to conditionally delete Gpr177 (the mouse ortholog of Drosophila Wntless, Wls), a chaperon protein important for the sorting and secretion of Wnt proteins. Deletion of epithelial Gpr177 reduces Wnt signaling activity in both the epithelium and mesenchyme, resulting in severe hemorrhage and abnormal vasculature, accompanied by branching defects and abnormal epithelial differentiation. We then used multiple mouse models to demonstrate that Wnt/β-catenin signaling is not only required for the proliferation and differentiation of mesenchyme, but also is important for the maintenance of smooth muscle cells through the regulation of the transcription factor Kruppel-like factor 2 (Klf2). Together, our studies define a novel mechanism by which epithelial Wnts regulate the normal development and maintenance of pulmonary vasculature. These findings provide insight into the pathobiology of congenital lung diseases, such as alveolar capillary dysplasia (ACD), that have abnormal alveolar development and dysmorphic pulmonary vasculature.