Alterations in gene expression and DNA methylation during murine and human lung alveolar septation

Epigenetic modifications in the development of bronchopulmonary dysplasia: a review

While perinatal medicine advancements have bolstered survival outcomes for premature infants, bronchopulmonary dysplasia (BPD) continues to threaten their long-term health. Gene-environment interactions, mediated by epigenetic modifications such as DNA methylation, histone modification, and non-coding RNA regulation, take center stage in BPD pathogenesis. Recent discoveries link methylation variations across biological pathways with BPD. Also, the potential reversibility of histone modifications fuels new treatment avenues. The review also highlights the promise of utilizing mesenchymal stem cells and their exosomes as BPD therapies, given their ability to modulate non-coding RNA, opening novel research and intervention possibilities. IMPACT: The complexity and universality of epigenetic modifications in the occurrence and development of bronchopulmonary dysplasia were thoroughly discussed. Both molecular and cellular mechanisms contribute to the diverse nature of epigenetic changes, suggesting the need for deeper biochemical techniques to explore these molecular alterations. The utilization of innovative cell-specific drug delivery methods like exosomes and extracellular vesicles holds promise in achieving precise epigenetic regulation.

Prospective epigenome and transcriptome analyses of cord and peripheral blood from preterm infants at risk of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a prevalent chronic lung disease of prematurity with limited treatment options. To uncover biomarkers of BPD risk, this study investigated epigenetic and transcriptomic signatures of prematurity at birth and during the neonatal period at day 14 and 28. Peripheral blood DNAs from preterm infants were applied to methylation arrays and cell-type composition was estimated by deconvolution. Covariate-adjusted robust linear regression elucidated BPD- and prolonged oxygen (≥ 14 days) exposure-associated CpGs. RNAs from cord and peripheral blood were sequenced, and differentially expressed genes (DEGs) for BPD or oxygen exposure were determined. Estimated neutrophil-lymphocyte ratios in peripheral blood at day 14 in BPD infants were significantly higher than nonBPD infants, suggesting an heightened inflammatory response in developing BPD. BPD-DEGs in cord blood indicated lymphopoiesis inhibition, altered Th1/Th2 responses, DNA damage, and organ degeneration. On day 14, BPD-associated CpGs were highly enriched in neutrophil activation, infection, and CD4 + T cell quantity, and BPD-DEGs were involved in DNA damage, cellular senescence, T cell homeostasis, and hyper-cytokinesis. On day 28, BPD-associated CpGs along with BPD-DEGs were enriched for phagocytosis, neurological disorder, and nucleotide metabolism. Oxygen supplementation markedly downregulated mitochondrial biogenesis genes and altered CpGs annotated to developmental genes. Prematurity-altered DNA methylation could cause abnormal lymphopoiesis, cellular assembly and cell cycle progression to increase BPD risk. Similar pathways between epigenome and transcriptome networks suggest coordination of the two in dysregulating leukopoiesis, adaptive immunity, and innate immunity. The results provide molecular insights into biomarkers for early detection and prevention of BPD.

Effects of DNA methylase inhibitors in a murine model of severe BPD

DNA methylation is necessary for developmental gene regulation, but adverse environments result in aberrant methylation and gene silencing. The current pilot study tested the hypothesis that treatment with DNA methylation inhibitors (decitabine; RG108) would improve alveolarization in a newborn murine model of severe bronchopulmonary dysplasia. Newborn mice exposed to maternal inflammation (LPS) and neonatal hyperoxia (85% O2) were treated with decitabine (p3, 0.1 mg/kg; p2, 4, 6, 0.1 mg/kg; or p2, 4, 6, 0.15 mg/kg) or RG108 (p3, 0.0013 mg/kg) delivered intranasally. Modest improvements in alveolarization were observed with decitabine, but no differences were observed with RG108. Attenuated phospho-SMAD2/3 levels and greater surfactant protein C protein levels compared to vehicle were observed with some tested doses. No detrimental side effects were observed with the doses used in this study. In summary, our pilot investigations identified a safe dose for intranasal administration of both methylation inhibitors and provides a foundation for further studies into methylation inhibitors in the context of neonatal lung injury.

Early Origins of Chronic Obstructive Pulmonary Disease: Prenatal and Early Life Risk Factors

The main risk factor for chronic obstructive pulmonary disease (COPD) is active smoking. However, a considerable amount of people with COPD never smoked, and increasing evidence suggests that adult lung disease can have its origins in prenatal and early life. This article reviews some of the factors that can potentially affect lung development and lung function trajectories throughout the lifespan from genetics and prematurity to respiratory tract infections and childhood asthma. Maternal smoking and air pollution exposure were also analyzed among the environmental factors. The adoption of preventive strategies to avoid these risk factors since the prenatal period may be crucial to prevent, delay the onset or modify the progression of COPD lung disease throughout life.

Investigation of PM2.5-induced carcinogenic effects through mediation of ErbB family based on DNA methylation and transcriptomics analysis by a lung-mimicking microfluidic platform

Fine particle (PM_2.5, less than 2.5 micrometers in diameter) is regarded as a harmful carcinogen. However, the molecular mechanisms of the carcinogenic effects of ambient fine particles have not been fully elucidated, and therapeutic options to address this major public health challenge are lacking. Here, we present global gene-specific DNA methylation and transcriptomic (RNA-Seq) analyses after HBE cells were exposed to fine particles on a portable, small, and all-in-one organ-level lung-mimicking air-liquid interface exposure (MALIE) microfluidic platform. A series of cancer-related signal transduction pathways were activated. ErbB1, ErbB2, and ErbB3 gene expression altered by fine particle exposure was the result of changes in the cellular DNA methylome. The protein expression of ErbB family was inhibited by drugs and could regulate downstream Grb2/Raf pathway and Akt/MDM2 pathway. All of the above results indicated that ErbB family may be promising drug targets for air pollution-related diseases and that inhibitor drugs can be used as therapeutic options to treat these diseases.

Pathogenesis of Bronchopulmonary Dysplasia: Role of Oxidative Stress from 'Omics' Studies

Bronchopulmonary dysplasia (BPD) remains the most common respiratory complication of prematurity as younger and smaller infants are surviving beyond the immediate neonatal period. The recognition that oxidative stress (OS) plays a key role in BPD pathogenesis has been widely accepted since at least the 1980s. In this article, we examine the interplay between OS and genetic regulation and review 'omics' data related to OS in BPD. Data from animal models (largely models of hyperoxic lung injury) and from human studies are presented. Epigenetic and transcriptomic analyses have demonstrated several genes related to OS to be differentially expressed in murine models that mimic BPD as well as in premature infants at risk of BPD development and infants with established lung disease. Alterations in the genetic regulation of antioxidant enzymes is a common theme in these studies. Data from metabolomics and proteomics have also demonstrated the potential involvement of OS-related pathways in BPD. A limitation of many studies includes the difficulty of obtaining timely and appropriate samples from human patients. Additional 'omics' studies could further our understanding of the role of OS in BPD pathogenesis, which may prove beneficial for prevention and timely diagnosis, and aid in the development of targeted therapies.

Epigenome-wide association study of bronchopulmonary dysplasia in preterm infants: results from the discovery-BPD program

BACKGROUND

Bronchopulmonary dysplasia (BPD) is a lung disease in premature infants caused by therapeutic oxygen supplemental and characterized by impaired pulmonary development which persists into later life. While advances in neonatal care have improved survival rates of premature infants, cases of BPD have been increasing with limited therapeutic options for prevention and treatment. This study was designed to explore the relationship between gestational age (GA), birth weight, and estimated blood cell-type composition in premature infants and to elucidate early epigenetic biomarkers associated with BPD.

METHODS

Cord blood DNA from preterm neonates that went on to develop BPD (n = 14) or not (non-BPD, n = 93) was applied to Illumina 450 K methylation arrays. Blood cell-type compositions were estimated using DNA methylation profiles. Multivariable robust regression analysis elucidated CpGs associated with BPD risk. cDNA microarray analysis of cord blood RNA identified differentially expressed genes in neonates who later developed BPD.

RESULTS

The development of BPD and the need for oxygen supplementation were strongly associated with GA (BPD, p < 1.0E-04; O2 supplementation, p < 1.0E-09) and birth weight (BPD, p < 1.0E-02; O2 supplementation, p < 1.0E-07). The estimated nucleated red blood cell (NRBC) percent was negatively associated with birth weight and GA, positively associated with hypomethylation of the tobacco smoke exposure biomarker cg05575921, and high-NRBC blood samples displayed a hypomethylation profile. Epigenome-wide association study (EWAS) identified 38 (Bonferroni) and 275 (false discovery rate 1%) differentially methylated CpGs associated with BPD. BPD-associated CpGs in cord blood were enriched for lung maturation and hematopoiesis pathways. Stochastic epigenetic mutation burden at birth was significantly elevated among those who developed BPD (adjusted p = 0.02). Transcriptome changes in cord blood cells reflected cell cycle, development, and pulmonary disorder events in BPD.

CONCLUSIONS

While results must be interpreted with caution because of the small size of this study, NRBC content strongly impacted DNA methylation profiles in preterm cord blood and EWAS analysis revealed potential insights into biological pathways involved in BPD pathogenesis.

Epigenetic regulation of pediatric and neonatal immune responses

Epigenetic regulation of transcription is a collective term that refers to mechanisms known to regulate gene transcription without changing the underlying DNA sequence. These mechanisms include DNA methylation and histone tail modifications which influence chromatin accessibility, and microRNAs that act through post-transcriptional gene silencing. Epigenetics is known to regulate a variety of biological processes, and the role of epigtenetics in immunity and immune-mediated diseases is becoming increasingly recognized. While DNA methylation is the most widely studied, each of these systems play an important role in the development and maintenance of appropriate immune responses. There is clear evidence that epigenetic mechanisms contribute to developmental stage-specific immune responses in a cell-specific manner. There is also mounting evidence that prenatal exposures alter epigenetic profiles and subsequent immune function in exposed offspring. Early life exposures that are associated with poor long-term health outcomes also appear to impact immune specific epigenetic patterning. Finally, each of these epigenetic mechanisms contribute to the pathogenesis of a wide variety of diseases that manifest during childhood. This review will discuss each of these areas in detail. IMPACT: Epigenetics, including DNA methylation, histone tail modifications, and microRNA expression, dictate immune cell phenotypes. Epigenetics influence immune development and subsequent immune health. Prenatal, perinatal, and postnatal exposures alter immune cell epigenetic profiles and subsequent immune function. Numerous pediatric-onset diseases have an epigenetic component. Several successful strategies for childhood diseases target epigenetic mechanisms.

Bronchopulmonary dysplasia as a determinant of respiratory outcomes in adult life

Respiratory disease is unfortunately common in preterm infants with the archetype being bronchopulmonary dysplasia (BPD). BPD affects approximately 50,000 preterm infants in the U.S. annually with substantial morbidity and mortality related to its pathology (alveolar, airway, and pulmonary vasculature maldevelopment). Predicting the likelihood and severity of chronic respiratory disease in these children as they age is difficult and compounded by the lack of consistent phenotyping. Barriers to understanding the actual scope of this problem include few longitudinal studies, information limited by small retrospective studies and the ever-changing landscape of therapies in the NICU that affect long-term respiratory outcomes. Thus, the true burden of adult respiratory disease caused by premature birth is currently unknown. Nevertheless, limited data suggest that a substantial percentage of children with a history of BPD have long-term respiratory symptoms and persistent airflow obstruction associated with altered lung function trajectories into adult life. Small airway disease with variable bronchodilator responsiveness, is the most common manifestation of lung dysfunction in adults with a history of BPD. The etiology of this is unclear however, developmental dysanapsis may underlie the airflow obstruction in some adults with a history of BPD. This type of flow limitation resembles that of aging adults with chronic obstructive lung disease with no history of smoking. It is also unclear whether lung function abnormalities in people with a history of BPD are static or if these individuals with BPD have a more accelerated decline in lung function as they age compared to controls. While some of the more significant mediators of lung function, such as tobacco smoke and respiratory infections have been identified, more work is necessary to identify the best means of preserving lung function for individuals born prematurely throughout their lifespan.

Oxygen Toxicity to the Immature Lung-Part II: The Unmet Clinical Need for Causal Therapy

Oxygen toxicity continues to be one of the inevitable injuries to the immature lung. Reactive oxygen species (ROS) production is the initial step leading to lung injury and, subsequently, the development of bronchopulmonary dysplasia (BPD). Today, BPD remains the most important disease burden following preterm delivery and results in life-long restrictions in lung function and further important health sequelae. Despite the tremendous progress in the pathomechanistic understanding derived from preclinical models, the clinical needs for preventive or curative therapies remain unmet. This review summarizes the clinical progress on guiding oxygen delivery to the preterm infant and elaborates future directions of research that need to take into account both hyperoxia and hypoxia as ROS sources and BPD drivers. Many strategies have been tested within clinical trials based on the mechanistic understanding of ROS actions, but most have failed to prove efficacy. The majority of these studies were tested in an era before the latest modes of non-invasive respiratory support and surfactant application were introduced or were not appropriately powered. A comprehensive re-evaluation of enzymatic, antioxidant, and anti-inflammatory therapies to prevent ROS injury is therefore indispensable. Strategies will only succeed if they are applied in a timely and vigorous manner and with the appropriate outcome measures.

Influences of environmental exposures on preterm lung disease

Introduction: Environmental factors play a critical role in the progression or resolution of chronic respiratory diseases. However, studies are limited on the impact of environmental risk factors on individuals born prematurely with lung disease after they leave the neonatal intensive care unit and are discharged into the home environment.Areas covered: In this review, we cover current knowledge of environmental exposures that impact outcomes of preterm respiratory disease, including air pollution, infections, and disparities. The limited data do suggest that certain exposures should be avoided and there are potential preventative strategies for other exposures. There is a need for additional research outside the neonatal intensive care unit that focuses on individual and community-level factors that affect long-term outcomes.Expert opinion: Preterm respiratory disease can impose a significant burden on infants, children, and young adults born prematurely, but may improve for many individuals over time. In this review, we outline the exposures that may potentially hasten, delay, or prevent resolution of lung injury in preterm children.

Intrauterine Hypoxia and Epigenetic Programming in Lung Development and Disease

Clinically, intrauterine hypoxia is the foremost cause of perinatal morbidity and developmental plasticity in the fetus and newborn infant. Under hypoxia, deviations occur in the lung cell epigenome. Epigenetic mechanisms (e.g., DNA methylation, histone modification, and miRNA expression) control phenotypic programming and are associated with physiological responses and the risk of developmental disorders, such as bronchopulmonary dysplasia. This developmental disorder is the most frequent chronic pulmonary complication in preterm labor. The pathogenesis of this disease involves many factors, including aberrant oxygen conditions and mechanical ventilation-mediated lung injury, infection/inflammation, and epigenetic/genetic risk factors. This review is focused on various aspects related to intrauterine hypoxia and epigenetic programming in lung development and disease, summarizes our current knowledge of hypoxia-induced epigenetic programming and discusses potential therapeutic interventions for lung disease.

Chronic Exposure to Cadmium Induces Differential Methylation in Mice Spermatozoa

Cadmium exposure is ubiquitous and has been linked to diseases including cancers and reproductive defects. Since cadmium is nonmutagenic, it is thought to exert its gene dysregulatory effects through epigenetic reprogramming. Several studies have implicated germline exposure to cadmium in developmental reprogramming. However, most of these studies have focused on maternal exposure, while the impact on sperm fertility and disease susceptibility has received less attention. In this study, we used reduced representation bisulfite sequencing to comprehensively investigate the impact of chronic cadmium exposure on mouse spermatozoa DNA methylation. Adult male C57BL/J6 mice were provided water with or without cadmium chloride for 9 weeks. Sperm, testes, liver, and kidney tissues were collected at the end of the treatment period. Cadmium exposure was confirmed through gene expression analysis of metallothionein-1 and 2, 2 well-known cadmium-induced genes. Analysis of sperm DNA methylation changes revealed 1788 differentially methylated sites present at regulatory regions in sperm of mice exposed to cadmium compared with vehicle (control) mice. Furthermore, most of these differential methylation changes positively correlated with changes in gene expression at both the transcription initiation stage as well as the splicing levels. Interestingly, the genes targeted by cadmium exposure are involved in several critical developmental processes. Our results present a comprehensive analysis of the sperm methylome in response to chronic cadmium exposure. These data, therefore, highlight a foundational framework to study gene expression patterns that may affect fertility in the exposed individual as well as their offspring, through paternal inheritance.

Clinical analysis and pluripotent stem cells-based model reveal possible impacts of ACE2 and lung progenitor cells on infants vulnerable to COVID-19

Introduction: An increasing number of children with severe coronavirus disease 2019 (COVID-19) is being reported, yet the spectrum of disease severity and expression patterns of angiotensin-converting enzyme 2 (ACE2) in children at different developmental stages are largely unknow.

Methods: We analysed clinical features in a cohort of 173 children with COVID-19 (0-15 yrs.-old) between January 22, 2020 and March 15, 2020. We systematically examined the expression and distribution of ACE2 in different developmental stages of children by using a combination of children's lung biopsies, pluripotent stem cell-derived lung cells, RNA-sequencing profiles, and ex vivo SARS-CoV-2 pseudoviral infections.

Results: It revealed that infants (< 1yrs.-old), with a weaker potency of immune response, are more vulnerable to develop pneumonia whereas older children (> 1 yrs.-old) are more resistant to lung injury. The expression levels of ACE2 however do not vary by age in children's lung. ACE2 is notably expressed not only in Alveolar Type II (AT II) cells, but also in SOX9 positive lung progenitor cells detected in both pluripotent stem cell derivatives and infants' lungs. The ACE2⁺SOX9⁺ cells are readily infected by SARS-CoV-2 pseudovirus and the numbers of the double positive cells are significantly decreased in older children.

Conclusions: Infants (< 1 yrs.-old) with SARS-CoV-2 infection are more vulnerable to lung injuries. ACE2 expression in multiple types of lung cells including SOX9 positive progenitor cells, in cooperation with an unestablished immune system, could be risk factors contributing to vulnerability of infants with COVID-19. There is a need to continue monitoring lung development in young children who have recovered from SARS-CoV-2 infection.

Predicting Long-Term Respiratory Outcomes in Premature Infants: Is It Time to Move beyond Bronchopulmonary Dysplasia?

Premature birth has been shown to be associated with adverse respiratory health in children and adults; children diagnosed with bronchopulmonary dysplasia (BPD) in infancy are at particularly high risk. Since its first description by Northway et al. about half a century ago, the definition of BPD has gone through several iterations reflecting the changes in the patient population, advancements in knowledge of lung development and injury, and improvements in perinatal care practices. One of the key benchmarks for optimally defining BPD has been the ability to predict long-term respiratory and health outcomes. This definition is needed by multiple stakeholders for hosts of reasons including: providing parents with some expectations for the future, to guide clinicians for developing longer term follow-up practices, to assist policy makers to allocate resources, and to support researchers involved in developing preventive or therapeutic strategies and designing studies with meaningful outcome measures. Long-term respiratory outcomes in preterm infants with BPD have shown variable results reflecting not only limitations of the current definition of BPD, but also potentially the impact of other prenatal, postnatal and childhood factors on the respiratory health. In this manuscript, we present an overview of the long-term respiratory outcomes in infants with BPD and discuss the role of other modifiable or non-modifiable factors affecting respiratory health in preterm infants. We will also discuss the limitations of using BPD as a predictor of respiratory morbidities and some of the recent advances in delineating the causes and severity of respiratory insufficiency in infants diagnosed with BPD.

Epigenetic response to hyperoxia in the neonatal lung is sexually dimorphic

Sex as a biological variable plays a critical role both during lung development and in modulating postnatal hyperoxic lung injury and repair. The molecular mechanisms behind these sex-specific differences need to be elucidated. Our objective was to determine if the neonatal lung epigenomic landscape reconfiguration has profound effects on gene expression and could underlie sex-biased differences in protection from or susceptibility to diseases. Neonatal male and female mice (C57BL/6) were exposed to hyperoxia (95% FiO, PND 1-5: saccular stage) or room air and euthanized on PND 7 and 21. Pulmonary gene expression was studied using RNA-seq on Illumina HiSeq 2500 platform and quantified. Epigenomic landscape was assessed using Chromatin Immunoprecipitation (ChIP-Seq) of the H3K27ac histone modification mark, associated with active genes, enhancers, and super-enhancers. These data were then integrated, pathways identified and validated. Sex-biased epigenetic modulation of gene expression leads to differential regulation of biological processes in the developing lung at baseline and after exposure to hyperoxia. The female lung exhibits a more robust epigenomic response for the H3K27ac mark in response to hyperoxia. Epigenomic changes distribute over genomic and epigenomic domains in a sex-specific manner. The differential epigenomic responses also enrich for key transcription regulators crucial for lung development. In addition, by utilizing H3K27ac as the target epigenomic change we were also able to identify new epigenomic reprogramming at super-enhancers. Finally, we report for the first time that the upregulation of p21 (Cdkn1a) in the injured neonatal lung could be mediated through gain of H3K27ac. These data demonstrate that modulation of transcription via epigenomic landscape alterations may contribute to the sex-specific differences in preterm neonatal hyperoxic lung injury and repair.

Changes in the Composition of the Gut Microbiota and the Blood Transcriptome in Preterm Infants at Less than 29 Weeks Gestation Diagnosed with Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is a common chronic lung condition in preterm infants that results in abnormal lung development and leads to considerable morbidity and mortality, making BPD one of the most common complications of preterm birth. We employed RNA sequencing and 16S rRNA gene sequencing to profile gene expression in blood and the composition of the fecal microbiota in infants born at <29 weeks gestational age and diagnosed with BPD in comparison to those of preterm infants that were not diagnosed with BPD. 16S rRNA gene sequencing, performed longitudinally on 255 fecal samples collected from 50 infants in the first months of life, identified significant differences in the relative levels of abundance of Klebsiella, Salmonella, Escherichia/Shigella, and Bifidobacterium in the BPD infants in a manner that was birth mode dependent. Transcriptome sequencing (RNA-Seq) analysis revealed that more than 400 genes were upregulated in infants with BPD. Genes upregulated in BPD infants were significantly enriched for functions related to red blood cell development and oxygen transport, while several immune-related pathways were downregulated. We also identified a gene expression signature consistent with an enrichment of immunosuppressive CD71+ early erythroid cells in infants with BPD. Intriguingly, genes that were correlated in their expression with the relative abundances of specific taxa in the microbiota were significantly enriched for roles in the immune system, suggesting that changes in the microbiota might influence immune gene expression systemically.IMPORTANCE Bronchopulmonary dysplasia (BPD) is a serious inflammatory condition of the lung and is the most common complication associated with preterm birth. A large body of evidence now suggests that the gut microbiota can influence immunity and inflammation systemically; however, the role of the gut microbiota in BPD has not been evaluated to date. Here, we report that there are significant differences in the gut microbiota of infants born at <29 weeks gestation and subsequently diagnosed with BPD, which are particularly pronounced when infants are stratified by birth mode. We also show that erythroid and immune gene expression levels are significantly altered in BPD infants. Interestingly, we identified an association between the composition of the microbiota and immune gene expression in blood in early life. Together, these findings suggest that the composition of the microbiota may influence the risk of developing BPD and, more generally, may shape systemic immune gene expression.

Respiratory Phenotypes for Preterm Infants, Children, and Adults: Bronchopulmonary Dysplasia and More

Ongoing advancements in neonatal care since the late 1980s have led to increased numbers of premature infants surviving well beyond the neonatal period. As a result of increased survival, many individuals born preterm manifest chronic respiratory symptoms throughout infancy, childhood, and adult life. The archetypical respiratory disease of prematurity, bronchopulmonary dysplasia, is the second most common chronic pediatric respiratory disease after asthma. However, there are several commonly held misconceptions. These misconceptions include that bronchopulmonary dysplasia is rare, that bronchopulmonary dysplasia resolves within the first few years of life, and that bronchopulmonary dysplasia does not impact respiratory health in adult life. This focused review describes a spectrum of respiratory conditions that individuals born prematurely may experience throughout their lifespan. Specifically, this review provides quantitative estimates of the number of individuals with alveolar, airway, and vascular phenotypes associated with bronchopulmonary dysplasia, as well as non-bronchopulmonary dysplasia respiratory phenotypes such as airway malacia, obstructive sleep apnea, and control of breathing issues. Furthermore, this review illustrates what is known about the potential for progression and/or lack of resolution of these respiratory phenotypes in childhood and adult life. Recognizing the spectrum of respiratory phenotypes associated with individuals born preterm and providing comprehensive and personalized care to these individuals may help to modulate adverse respiratory outcomes in later life.

Oxygen radical disease in the newborn, revisited: Oxidative stress and disease in the newborn period

Thirty years ago, there was an emerging appreciation for the significance of oxidative stress in newborn disease. This prompted a renewed interest in the impact of oxygen therapy for the newborn in the delivery room and beyond, especially in premature infants. Today, the complexity of oxidative stress both in normal regulation and pathology is better understood, especially as it relates to neonatal mitochondrial oxidative stress responses to hyperoxia. Mitochondria are recipients of oxidative damage and have a propensity for oxidative self-injury that has been implicated in the pathogenesis of neonatal lung diseases. Similarly, both intrauterine growth restriction (IUGR) and macrosomia are associated with mitochondrial dysfunction and oxidative stress. Additionally, reoxygenation with 100% O₂ in a hypoxic-ischemic newborn lamb model increased the production of pro-inflammatory cytokines in the brain. Moreover, the interplay between inflammation and oxidative stress in the newborn is better understood because of animal studies. Transcriptomic analyses have found a number of genes to be differentially expressed in murine models of bronchopulmonary dysplasia (BPD). Epigenetic changes have also been detected both in animal models of BPD and premature infants exposed to oxygen. Antioxidant therapy to prevent newborn disease has not been very successful; however, new therapeutic principles, like melatonin, are under investigation.

Integrating multiomics longitudinal data to reconstruct networks underlying lung development

A comprehensive understanding of the dynamic regulatory networks that govern postnatal alveolar lung development is still lacking. To construct such a model, we profiled mRNA, microRNA, DNA methylation, and proteomics of developing murine alveoli isolated by laser capture microdissection at 14 predetermined time points. We developed a detailed comprehensive and interactive model that provides information about the major expression trajectories, the regulators of specific key events, and the impact of epigenetic changes. Intersecting the model with single-cell RNA-Seq data led to the identification of active pathways in multiple or individual cell types. We then constructed a similar model for human lung development by profiling time-series human omics data sets. Several key pathways and regulators are shared between the reconstructed models. We experimentally validated the activity of a number of predicted regulators, leading to new insights about the regulation of innate immunity during lung development.

Secondary crest myofibroblast PDGFRα controls the elastogenesis pathway via a secondary tier of signaling networks during alveologenesis

Postnatal alveolar formation is the most important and the least understood phase of lung development. Alveolar pathologies are prominent in neonatal and adult lung diseases. The mechanisms of alveologenesis remain largely unknown. We inactivated Pdgfra postnatally in secondary crest myofibroblasts (SCMF), a subpopulation of lung mesenchymal cells. Lack of Pdgfra arrested alveologenesis akin to bronchopulmonary dysplasia (BPD), a neonatal chronic lung disease. The transcriptome of mutant SCMF revealed 1808 altered genes encoding transcription factors, signaling and extracellular matrix molecules. Elastin mRNA was reduced, and its distribution was abnormal. Absence of Pdgfra disrupted expression of elastogenic genes, including members of the Lox, Fbn and Fbln families. Expression of EGF family members increased when Tgfb1 was repressed in mouse. Similar, but not identical, results were found in human BPD lung samples. In vitro, blocking PDGF signaling decreased elastogenic gene expression associated with increased Egf and decreased Tgfb family mRNAs. The effect was reversible by inhibiting EGF or activating TGFβ signaling. These observations demonstrate the previously unappreciated postnatal role of PDGFA/PDGFRα in controlling elastogenic gene expression via a secondary tier of signaling networks composed of EGF and TGFβ.

Preventing bronchopulmonary dysplasia: new tools for an old challenge

Bronchopulmonary dysplasia (BPD) is the most prevalent chronic lung disease in infants and presents as a consequence of preterm birth. Due to the lack of effective preventive and treatment strategies, BPD currently represents a major therapeutic challenge that requires continued research efforts at the basic, translational, and clinical levels. However, not all very low birth weight premature babies develop BPD, which suggests that in addition to known gestational age and intrauterine and extrauterine risk factors, other unknown factors must be involved in this disease's development. One of the main goals in BPD research is the early prediction of very low birth weight infants who are at risk of developing BPD in order to initiate the adequate preventive strategies. Other benefits of determining the risk of BPD include providing prognostic information and stratifying infants for clinical trial enrollment. In this article, we describe new opportunities to address BPD's complex pathophysiology by identifying prognostic biomarkers and develop novel, complex in vitro human lung models in order to develop effective therapies. These therapies for protecting the immature lung from injury can be developed by taking advantage of recent scientific progress in -omics, 3D organoids, and regenerative medicine.

Genome-wide association study of lung lesions and pleurisy in New Zealand lambs

Pneumonia is an important issue for sheep production, leading to reduced growth rate and a predisposition to pleurisy. The objective of this study was to identify loci associated with pneumonic lesions and pleurisy in New Zealand progeny test lambs. The lungs from 3,572 progeny-test lambs were scored for presence and severity of pneumonic lesions and pleurisy at slaughter. Animals were genotyped using the Illumina Ovine Infinium HD SNP BeadChip (606,006 markers). The heritability of lung lesion score and pleurisy were calculated using the genomic relationship matrix, and genome-wide association analyses were conducted using EMMAX and haplotype trend regression. At slaughter, 35% of lambs had pneumonic lesions, with 9% showing lesions on more than half of any individual lobe. The number of lambs recorded as having pleurisy by the processing plants was 9%. Heritability estimates for pneumonic lesions and pleurisy scores adjusted for heteroscedasticity (CPSa and PLEURa) were 0.16 (± 0.03) and 0.05 (± 0.02), respectively. Five single-nucleotide polymorphisms (SNPs) were significantly associated with pneumonic lesions at the genome-wide level, and additional 37 SNPs were suggestively significant. Four SNPs were significantly associated with pleurisy, with an additional 11 SNPs reaching the suggestive level of significance. There were no regions that overlapped between the 2 traits. Multiple SNPs were in regions that contained genes involved in either the DNA damage response or the innate immune response, including several that had previously been reported to have associations with respiratory disease. Both EMMAX and HTR analyses of pleurisy data showed a significant peak on chromosome 2, located downstream from the transcription factor SP3. SP3 activates or suppresses the expression of numerous genes, including several genes with known functions in the immune system. This study identified several SNPs associated with genes involved in both the innate immune response and the response to DNA damage that are associated with pneumonic lesions and pleurisy in lambs at slaughter. Additionally, the identification in sheep of several SNPs within genes that have previously been associated with the respiratory system in cattle, pigs, rats, and mice indicates that there may be common pathways that underlie the response to invasion by respiratory pathogens in multiple species.

Bronchopulmonary dysplasia: what are its links to COPD?

Emerging evidence suggests that adverse early life events can affect long-term health trajectories throughout life. Preterm birth, in particular, is a significant early life event that affects approximately 10% of live births. Worldwide, prematurity is the number one cause of death in children less than 5 years of age and has been shown to disrupt normal lung development with lasting effects into adult life. Along with impaired lung development, interventions used to support gas exchange and other sequelae of prematurity can lead to the development of bronchopulmonary dysplasia (BPD). BPD is a chronic respiratory disease of infancy characterized by alveolar simplification, small airways disease, and pulmonary vascular changes. Although many survivors of BPD improve with age, survivors of BPD often have chronic lung disease characterized by airflow obstruction and intermittent pulmonary exacerbations. Long-term lung function trajectories as measured by FEV1 can be lower in children and adults with a history BPD. In this review, we discuss the epidemiology and manifestations of BPD and its long-term consequences throughout childhood and into adulthood. Available evidence suggests that disrupted lung development, genetic susceptibility and subsequent environment and infectious events that occur in prenatal and postnatal life likely increase the predisposition of children with BPD to develop early onset chronic obstructive pulmonary disease (COPD). The reviews of this paper are available via the supplemental material section.

Consequences of early postnatal lipopolysaccharide exposure on developing lungs in mice

Bronchopulmonary dysplasia (BPD) is a chronic lung disease of infants that is characterized by interrupted lung development. Postnatal sepsis causes BPD, yet the contributory mechanisms are unclear. To address this gap, studies have used lipopolysaccharide (LPS) during the alveolar phase of lung development. However, the lungs of infants who develop BPD are still in the saccular phase of development, and the effects of LPS during this phase are poorly characterized. We hypothesized that chronic LPS exposure during the saccular phase disrupts lung development by mechanisms that promote inflammation and prevent optimal lung development and repair. Wild-type C57BL6J mice were intraperitoneally administered 3, 6, or 10 mg/kg of LPS or a vehicle once daily on postnatal days (PNDs) 3-5. The lungs were collected for proteomic and genomic analyses and flow cytometric detection on PND6. The impact of LPS on lung development, cell proliferation, and apoptosis was determined on PND7. Finally, we determined differences in the LPS effects between the saccular and alveolar lungs. LPS decreased the survival and growth rate and lung development in a dose-dependent manner. These effects were associated with a decreased expression of proteins regulating cell proliferation and differentiation and increased expression of those mediating inflammation. While the lung macrophage population of LPS-treated mice increased, the T-regulatory cell population decreased. Furthermore, LPS-induced inflammatory and apoptotic response and interruption of cell proliferation and alveolarization was greater in alveolar than in saccular lungs. Collectively, the data support our hypothesis and reveal several potential therapeutic targets for sepsis-mediated BPD in infants.

Lung omics signatures in a bronchopulmonary dysplasia and pulmonary hypertension-like murine model

Bronchopulmonary dysplasia (BPD), the most common chronic lung disease in infants, is associated with long-term morbidities, including pulmonary hypertension (PH). Importantly, hyperoxia causes BPD and PH; however, the underlying mechanisms remain unclear. Herein, we performed high-throughput transcriptomic and proteomic studies using a clinically relevant murine model of BPD with PH. Neonatal wild-type C57BL6J mice were exposed to 21% oxygen (normoxia) or 70% oxygen (hyperoxia) during postnatal days (PNDs) 1-7. Lung tissues were collected for proteomic and genomic analyses on PND 7, and selected genes and proteins were validated by real-time quantitative PCR and immunoblotting analysis, respectively. Hyperoxia exposure dysregulated the expression of 344 genes and 21 proteins. Interestingly, hyperoxia downregulated genes involved in neuronal development and maturation in lung tissues. Gene set enrichment and gene ontology analyses identified apoptosis, oxidoreductase activity, plasma membrane integrity, organ development, angiogenesis, cell proliferation, and mitophagy as the predominant processes affected by hyperoxia. Furthermore, selected deregulated proteins strongly correlated with the expression of specific genes. Collectively, our results identified several potential therapeutic targets for hyperoxia-mediated BPD and PH in infants.

5-aza-2'-deoxycytidine, a DNA methylation inhibitor, attenuates hyperoxia-induced lung fibrosis via re-expression of P16 in neonatal rats

BackgroundP16 methylation plays an important role in the pathogenesis of hyperoxia-induced lung fibrosis. 5-aza-2'-deoxycytidine (5-aza-CdR) is a major methyltransferase-specific inhibitor. In this study, the effects of 5-aza-CdR on a hyperoxia-induced lung fibrosis in neonatal rats were investigated.MethodsRat pups were exposed to 85% O₂ for 21 days of and received intraperitoneal injections of 5-aza-CdR or normal saline (NS) once every other day. Survival rates and lung coefficients were calculated. Hematoxylin-eosin staining was performed to analyze the degree of lung fibrosis. Collagen content and TGF-β1 levels were determined. A methylation-specific polymerase chain reaction and western blotting were performed to determine P16 methylation status and P16, cyclin D1, and E2F1 protein expression.Results5-aza-CdR treatment during hyperoxia significantly improved the survival rate and weight gain, while it decreases the degree of lung fibrosis and levels of hydroxyproline and TGF-β1. Hyperoxia induced abnormal P16 methylation and 5-aza-CdR effectively reversed the hypermethylation of P16. Expression of the P16 protein in lung tissues was enhanced, while cyclin D1 and E2F1 protein were reduced by 5-aza-CdR treatment during hyperoxia.ConclusionThese data show that 5-aza-CdR attenuated lung fibrosis in neonatal rats exposed to hyperoxia by lowering hydroxyproline and TGF-β1 expression and via re-expression of P16 in neonatal rats.

Recent advances in our understanding of the mechanisms of late lung development and bronchopulmonary dysplasia

The objective of lung development is to generate an organ of gas exchange that provides both a thin gas diffusion barrier and a large gas diffusion surface area, which concomitantly generates a steep gas diffusion concentration gradient. As such, the lung is perfectly structured to undertake the function of gas exchange: a large number of small alveoli provide extensive surface area within the limited volume of the lung, and a delicate alveolo-capillary barrier brings circulating blood into close proximity to the inspired air. Efficient movement of inspired air and circulating blood through the conducting airways and conducting vessels, respectively, generates steep oxygen and carbon dioxide concentration gradients across the alveolo-capillary barrier, providing ideal conditions for effective diffusion of both gases during breathing. The development of the gas exchange apparatus of the lung occurs during the second phase of lung development-namely, late lung development-which includes the canalicular, saccular, and alveolar stages of lung development. It is during these stages of lung development that preterm-born infants are delivered, when the lung is not yet competent for effective gas exchange. These infants may develop bronchopulmonary dysplasia (BPD), a syndrome complicated by disturbances to the development of the alveoli and the pulmonary vasculature. It is the objective of this review to update the reader about recent developments that further our understanding of the mechanisms of lung alveolarization and vascularization and the pathogenesis of BPD and other neonatal lung diseases that feature lung hypoplasia.

Perturbations to lysyl oxidase expression broadly influence the transcriptome of lung fibroblasts

Lysyl oxidases are credited with pathogenic roles in lung diseases, including cancer, fibrosis, pulmonary hypertension, congenital diaphragmatic hernia, and bronchopulmonary dysplasia (BPD). Lysyl oxidases facilitate the covalent intra- and intermolecular cross-linking of collagen and elastin fibers, thereby imparting tensile strength to the extracellular matrix (ECM). Alternative ECM-independent roles have recently been proposed for lysyl oxidases, including regulation of growth factor signaling, chromatin remodeling, and transcriptional regulation, all of which impact cell phenotype. We demonstrate here that three of the five lysyl oxidase family members, Lox, Loxl1, and Loxl2, are highly expressed in primary mouse lung fibroblasts compared with other constituent cell types of the lung. Microarray analyses revealed that small interfering RNA knockdown of Lox, Loxl1, and Loxl2 was associated with apparent changes in the expression of 134, 3,761, and 3,554 genes, respectively, in primary mouse lung fibroblasts. The impact of lysyl oxidase expression on steady-state Mmp3, Mmp9, Eln, Rarres1, Gdf10, Ifnb1, Csf2, and Cxcl9 mRNA levels was validated, which is interesting, since the corresponding gene products are relevant to lung development and BPD, where lysyl oxidases play a functional role. In vivo, the expression of these genes broadly correlated with Lox, Loxl1, and Loxl2 expression in a mouse model of BPD. Furthermore, β-aminopropionitrile (BAPN), a selective lysyl oxidase inhibitor, did not affect the steady-state mRNA levels of lysyl oxidase target genes, in vitro in lung fibroblasts or in vivo in BAPN-treated mice. This study is the first to report that lysyl oxidases broadly influence the cell transcriptome.

Selecting the most appropriate time points to profile in high-throughput studies

Biological systems are increasingly being studied by high throughput profiling of molecular data over time. Determining the set of time points to sample in studies that profile several different types of molecular data is still challenging. Here we present the Time Point Selection (TPS) method that solves this combinatorial problem in a principled and practical way. TPS utilizes expression data from a small set of genes sampled at a high rate. As we show by applying TPS to study mouse lung development, the points selected by TPS can be used to reconstruct an accurate representation for the expression values of the non selected points. Further, even though the selection is only based on gene expression, these points are also appropriate for representing a much larger set of protein, miRNA and DNA methylation changes over time. TPS can thus serve as a key design strategy for high throughput time series experiments. Supporting Website: www.sb.cs.cmu.edu/TPS.

Linking bronchopulmonary dysplasia to adult chronic lung diseases: role of WNT signaling

Bronchopulmonary dysplasia (BPD) is one of the most common chronic lung diseases in infants caused by pre- and/or postnatal lung injury. BPD is characterized by arrested alveolarization and vascularization due to extracellular matrix remodeling, inflammation, and impaired growth factor signaling. WNT signaling is a critical pathway for normal lung development, and its altered signaling has been shown to be involved in the onset and progression of incurable chronic lung diseases in adulthood, such as chronic obstructive pulmonary disease (COPD) or idiopathic pulmonary fibrosis (IPF). In this review, we summarize the impact of WNT signaling on different stages of lung development and its potential contribution to developmental lung diseases, especially BPD, and chronic lung diseases in adulthood.

Should we still use vitamin A to prevent bronchopulmonary dysplasia?

Bronchopulmonary dysplasia (BPD) is associated with significant short- and long-term morbidity in preterm infants, and it can be prevented in some infants with vitamin A prophylaxis. Vitamin A, once widely used in neonatal intensive care, was scarce for the last few years, but has become available again at a much higher price, leading to dilemmas about its routine use. In this review we discuss experimental, clinical and socioeconomic evidence related to BPD, and provide a framework for clinicians and policy-makers to evaluate the value of vitamin A treatment and make decisions about its use for prevention of BPD.

Attenuation of miR-17∼92 Cluster in Bronchopulmonary Dysplasia

RATIONALE

Bronchopulmonary dysplasia remains a significant cause of neonatal morbidity; however, the identification of novel targets to predict or prevent the development of bronchopulmonary dysplasia remains elusive. Proper microRNA (miR)-17∼92 cluster is necessary for normal lung development, and alterations in expression are reported in other pulmonary diseases. The overall hypothesis for our work is that altered miR-17∼92 cluster expression contributes to the molecular pathogenesis of bronchopulmonary dysplasia.

OBJECTIVES

The current studies tested the hypothesis that alterations in miR-17∼92 cluster and DNA methyltransferase expression are present in bronchopulmonary dysplasia.

METHODS

miR-17∼92 cluster expression, promoter methylation, and DNA methyltransferase expression were determined in autopsy lung samples obtained from premature infants who died with bronchopulmonary dysplasia, or from term/near-term infants who died from nonrespiratory causes. Expression of miR-17∼92 cluster members miR-17 and -19b was measured in plasma samples collected in the first week of life from a separate cohort of preterm infants at a second institution in whom bronchopulmonary dysplasia was diagnosed subsequently.

MEASUREMENTS AND MAIN RESULTS

Autopsy tissue data indicated that miR-17∼92 expression is significantly lower in bronchopulmonary dysplasia lungs and is inversely correlated with promoter methylation and DNA methyltransferase expression when compared with that of control subjects without bronchopulmonary dysplasia. Plasma sample analyses indicated that miR-17 and -19b expression was decreased in infants who subsequently developed bronchopulmonary dysplasia.

CONCLUSIONS

Our data are the first to demonstrate altered expression of the miR-17∼92 cluster in bronchopulmonary dysplasia. The consistency between our autopsy and plasma findings further support our working hypothesis that the miR-17∼92 cluster contributes to the molecular pathogenesis of bronchopulmonary dysplasia.

Early injury of the neonatal lung contributes to premature lung aging: a hypothesis

Chronic lung disease of the newborn, also known as bronchopulmonary dysplasia (BPD), is the most common chronic lung disease in early infancy and results in an increased risk for long-lasting pulmonary impairment in the adult. BPD develops upon injury of the immature lung by oxygen toxicity, mechanical ventilation, and infections which trigger sustained inflammatory immune responses and extensive remodeling of the extracellular matrix together with dysregulated growth factor signaling. Histopathologically, BPD is characterized by impaired alveolarization, disrupted vascular development, and saccular wall fibrosis. Here, we explore the hypothesis that development of BPD involves disturbance of conserved pathways of molecular aging that may contribute to premature aging of the lung and an increased susceptibility to chronic lung diseases in adulthood.

Mitochondrial dysfunction in inflammatory responses and cellular senescence: pathogenesis and pharmacological targets for chronic lung diseases

Mitochondria are dynamic organelles, which couple the various cellular processes that regulate metabolism, cell proliferation and survival. Environmental stress can cause mitochondrial dysfunction and dynamic changes including reduced mitochondrial biogenesis, oxidative phosphorylation and ATP production, as well as mitophagy impairment, which leads to increased ROS, inflammatory responses and cellular senescence. Oxidative stress, inflammation and cellular senescence all have important roles in the pathogenesis of chronic lung diseases, such as chronic obstructive pulmonary disease, pulmonary fibrosis and bronchopulmonary dysplasia. In this review, we discuss the current state on how mitochondrial dysfunction affects inflammatory responses and cellular senescence, the mechanisms of mitochondrial dysfunction underlying the pathogenesis of chronic lung diseases and the potential of mitochondrial transfer and replacement as treatments for these diseases.

A three-dimensional human model of the fibroblast activation that accompanies bronchopulmonary dysplasia identifies Notch-mediated pathophysiology

Bronchopulmonary dysplasia (BPD) is a leading complication of premature birth and occurs primarily in infants delivered during the saccular stage of lung development. Histopathology shows decreased alveolarization and a pattern of fibroblast proliferation and differentiation to the myofibroblast phenotype. Little is known about the molecular pathways and cellular mechanisms that define BPD pathophysiology and progression. We have developed a novel three-dimensional human model of the fibroblast activation associated with BPD, and using this model we have identified the Notch pathway as a key driver of fibroblast activation and proliferation in response to changes in oxygen. Fetal lung fibroblasts were cultured on sodium alginate beads to generate lung organoids. After exposure to alternating hypoxia and hyperoxia, the organoids developed a phenotypic response characterized by increased α-smooth muscle actin (α-SMA) expression and other genes known to be upregulated in BPD and also demonstrated increased expression of downstream effectors of the Notch pathway. Inhibition of Notch with a γ-secretase inhibitor prevented the development of the pattern of cellular proliferation and α-SMA expression in our model. Analysis of human autopsy tissue from the lungs of infants who expired with BPD demonstrated evidence of Notch activation within fibrotic areas of the alveolar septae, suggesting that Notch may be a key driver of BPD pathophysiology.

Regulation of alveolar septation by microRNA-489

MicroRNAs (miRs) are small conserved RNA that regulate gene expression. Bioinformatic analysis of miRNA profiles during mouse lung development indicated a role for multiple miRNA, including miRNA-489. miR-489 increased on completion of alveolar septation [postnatal day 42 (P42)], associated with decreases in its conserved target genes insulin-like growth factor-1 (Igf1) and tenascin C (Tnc). We hypothesized that dysregulation of miR-489 and its target genes Igf1 and Tnc contribute to hyperoxia-induced abnormal lung development. C57BL/6 mice were exposed to normoxia (21%) or hyperoxia (85% O2) from P4 to P14, in combination with intranasal locked nucleic acid against miR-489 to inhibit miR-489, cytomegalovirus promoter (pCMV)-miR-489 to overexpress miR-489, or empty vector. Hyperoxia reduced miR-489 and increased Igf1 and Tnc. Locked nucleic acid against miR-489 improved lung development during hyperoxia and did not alter it during normoxia, whereas miR-489 overexpression inhibited lung development during normoxia. The 3' untranslated region in vitro reporter studies confirmed Igf1 and Tnc as targets of miR-489. While miR-489 was of epithelial origin and present in exosomes, its targets Igf1 and Tnc were produced by fibroblasts. Infants with bronchopulmonary dysplasia (BPD) had reduced lung miR-489 and increased Igf1 and Tnc compared with normal preterm or term infants. These results suggest increased miR-489 is an inhibitor of alveolar septation. During hyperoxia or BPD, reduced miR-489 and increased Igf1 and Tnc may be inadequate attempts at compensation. Further inhibition of miR-489 may permit alveolar septation to proceed. The use of specific miRNA antagonists or agonists may be a therapeutic strategy for inhibited alveolarization, such as in BPD.

Update on Molecular Biology of Lung Development--Transcriptomics

This article highlights some of the significant advances in our understanding of lung developmental biology made over the last few years, which challenge existing paradigms and are relevant to a fundamental understanding of this process. Additional comments address how these new insights may be informative for chronic lung diseases that occur, or initiate, in the neonatal period. This is not meant to be an exhaustive review of the molecular biology of lung development. For a more comprehensive, contemporary review of the cellular and molecular aspects of lung development, readers can refer to recent reviews by others.

Recent advances in the mechanisms of lung alveolarization and the pathogenesis of bronchopulmonary dysplasia

Alveolarization is the process by which the alveoli, the principal gas exchange units of the lung, are formed. Along with the maturation of the pulmonary vasculature, alveolarization is the objective of late lung development. The terminal airspaces that were formed during early lung development are divided by the process of secondary septation, progressively generating an increasing number of alveoli that are of smaller size, which substantially increases the surface area over which gas exchange can take place. Disturbances to alveolarization occur in bronchopulmonary dysplasia (BPD), which can be complicated by perturbations to the pulmonary vasculature that are associated with the development of pulmonary hypertension. Disturbances to lung development may also occur in persistent pulmonary hypertension of the newborn in term newborn infants, as well as in patients with congenital diaphragmatic hernia. These disturbances can lead to the formation of lungs with fewer and larger alveoli and a dysmorphic pulmonary vasculature. Consequently, affected lungs exhibit a reduced capacity for gas exchange, with important implications for morbidity and mortality in the immediate postnatal period and respiratory health consequences that may persist into adulthood. It is the objective of this Perspectives article to update the reader about recent developments in our understanding of the molecular mechanisms of alveolarization and the pathogenesis of BPD.

Impaired pulmonary vascular development in bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD), the chronic lung disease associated with preterm birth, results from the disruption of normal pulmonary vascular and alveolar growth. Though BPD was once described as primarily due to postnatal injury from mechanical ventilation and oxygen therapy after preterm birth, it is increasingly appreciated that BPD results from antenatal and perinatal factors that interrupt lung development in infants born at the extremes of prematurity. The lung in BPD consists of a simplified parenchymal architecture that limits gas exchange and leads to increased cardiopulmonary morbidity and mortality. This review outlines recent advances in the understanding of pulmonary vascular development and describes how the disruption of these mechanisms results in BPD. We point to future therapies that may augment postnatal vascular growth to prevent and treat this severe chronic lung disease.