Heritability of bronchopulmonary dysplasia, defined according to the consensus statement of the national institutes of health

Exome sequencing identifies gene variants and networks associated with extreme respiratory outcomes following preterm birth

Background

Previous studies have identified genetic variants associated with bronchopulmonary dysplasia (BPD) in extremely preterm infants. However, findings with genome-wide significance have been rare, and not replicated. We hypothesized that whole exome sequencing (WES) of premature subjects with extremely divergent phenotypic outcomes could facilitate the identification of genetic variants or gene networks contributing disease risk.

Results

The Prematurity and Respiratory Outcomes Program (PROP) recruited a cohort of > 765 extremely preterm infants for the identification of markers of respiratory morbidity. We completed WES on 146 PROP subjects (85 affected, 61 unaffected) representing extreme phenotypes of early respiratory morbidity. We tested for association between disease status and individual common variants, screened for rare variants exclusive to either affected or unaffected subjects, and tested the combined association of variants across gene loci. Pathway analysis was performed and disease-related expression patterns were assessed. Marginal association with BPD was observed for numerous common and rare variants. We identified 345 genes with variants unique to BPD-affected preterm subjects, and 292 genes with variants unique to our unaffected preterm subjects. Of these unique variants, 28 (19 in the affected cohort and 9 in unaffected cohort) replicate a prior WES study of BPD-associated variants. Pathway analysis of sets of variants, informed by disease-related gene expression, implicated protein kinase A, MAPK and Neuregulin/epidermal growth factor receptor signaling.

Conclusions

We identified novel genes and associated pathways that may play an important role in susceptibility/resilience for the development of lung disease in preterm infants.

Electronic supplementary material

The online version of this article (10.1186/s12863-018-0679-7) contains supplementary material, which is available to authorized users.

Chronic lung disease in preterm infants receiving various modes of noninvasive ventilation at ≤30 weeks' postmenstrual age

Objective: To determine the incidence of chronic lung disease (CLD) in mechanically ventilated infants who were born at <29 weeks' gestational age (GA), extubated to continuous positive airway pressure (CPAP) or nasal intermittent positive pressure ventilation (NIPPV), and treated with CPAP/NIPPV alone, changed to heated humidified high flow nasal cannula (HHHFNC), or exposed to a combination of CPAP/NIPPV and HHHFNC at ≤30 weeks' postmenstrual age (PMA).Study design: Retrospective cohort study of infants born at <29 weeks' GA admitted to tertiary Canadian neonatal intensive care units between 2011 and 2015. Infants were grouped according to the type of noninvasive ventilation they received at ≤30 weeks' PMA: CPAP/NIPPV alone, HHHFNC alone, or a combination of both.Results: Of the 2378 eligible infants, 1091 (46%) were on CPAP/NIPPV alone, 173 (7.3%) were on HHHFNC alone, and 1114 (47%) were on a combination of CPAP/NIPPV and HHHFNC at ≤30 weeks' PMA until weaned to room air or low flow nasal cannula. After adjustment for confounders, infants in both the CPAP/NIPPV (odds ratio [95% confidence interval]; 2.37 [1.18, 4.79]) and Combination (3.47 [2.06, 5.86]) groups had higher odds of developing CLD than infants in the HHHFNC group.Conclusions: Our results demonstrate that infants transitioned to HHHFNC ≤30 weeks' PMA after extubation to CPAP/NIPPV were associated with a lower odds of CLD than infants maintained on CPAP/NIPPV or a combination of CPAP/NIPPV and HHHFNC.

Ancestry and genetic associations with bronchopulmonary dysplasia in preterm infants

Bronchopulmonary dysplasia in premature infants is a common and often severe lung disease with long-term sequelae. A genetic component is suspected but not fully defined. We performed an ancestry and genome-wide association study to identify variants, genes, and pathways associated with survival without bronchopulmonary dysplasia in 387 high-risk infants treated with inhaled nitric oxide in the Trial of Late Surfactant study. Global African genetic ancestry was associated with increased survival without bronchopulmonary dysplasia among infants of maternal self-reported Hispanic white race/ethnicity [odds ratio (OR) = 4.5, P = 0.01]. Admixture mapping found suggestive outcome associations with local African ancestry at chromosome bands 18q21 and 10q22 among infants of maternal self-reported African-American race/ethnicity. For all infants, the top individual variant identified was within the intron of NBL1, which is expressed in midtrimester lung and is an antagonist of bone morphogenetic proteins ( rs372271081 , OR = 0.17, P = 7.4 × 10^-7). The protective allele of this variant was significantly associated with lower nitric oxide metabolites in the urine of non-Hispanic white infants ( P = 0.006), supporting a role in the racial differential response to nitric oxide. Interrogating genes upregulated in bronchopulmonary dysplasia lungs indicated association with variants in CCL18, a cytokine associated with fibrosis and interstitial lung disease, and pathway analyses implicated variation in genes involved in immune/inflammatory processes in response to infection and mechanical ventilation. Our results suggest that genetic variation related to lung development, drug metabolism, and immune response contribute to individual and racial/ethnic differences in respiratory outcomes following inhaled nitric oxide treatment of high-risk premature infants.

Genetics of the patent ductus arteriosus (PDA) and pharmacogenetics of PDA treatment

Patent ductus arteriosus (PDA) is a frequent, complex, and difficult to treat clinical syndrome among preterm infants in the neonatal intensive care unit. In addition to known clinical risk factors, there are emerging data about genetic predisposition to PDA in both animal and human models. Clinical response and toxicity from drugs used to treat PDA are highly variable. Developmental and genetic aspects of pharmacokinetics and pharmacodynamics influence exposure and response to pharmacologic therapies. Given the variable efficacy and toxicity of known drug therapies, novel therapeutic targets for PDA treatment offer the promise of precision medicine. This review addresses the known genetic contributions to prolonged ductal patency, variability in response to drug therapy for PDA, and potential novel drug targets for future PDA treatment discovery.

The association between surfactant protein B gene variation and bronchopulmonary dysplasia in Chinese premature newborns

OBJECTIVE

This study aimed to correlate the pulmonary surfactant B (SP-B) gene variation with bronchopulmonary dysplasia (BPD) in ethnic Han, Chinese, premature newborns.

METHOD

47 newborns with BPD and 55 controls without BPD were included. Genomic DNA was extracted from cord or artery blood. Genotyping for the SP-B gene was performed by polymerase chain reaction or gene sequencing, and the clinical characteristics were also analyzed.

RESULTS

Two types of SP-B gene variations in Exon 2 or Exon 5 were discovered, including V1 (Exon 2: c.[5A > C] + [5A > C] or c.[5A > C] + [=]) and V2 (Exon 5: c.[428C > T] + [428C > T] or c.[428C > T] + [=]). In the BPD group, there were 33 newborns with gene variations, of which type V1 and V2 accounted for 18 and 15 respectively. In the control group, there were 19 newborns with gene variations, of which type V1 and V2 accounted for 7 and 12 respectively. There was a significant difference between the two groups in type V1 variation (X²=8.956, P < 0.05), and V1 variation was more likely associated with BPD occurrence. Logistic regression analysis showed that gene variation, premature rupture of membranes, birth weight, and the duration of mechanical ventilation were associated with BPD development. Among them, gene variation and premature rupture of the membranes were risk factors for BPD development.

CONCLUSIONS

The exon 2 or 5 of SP-B gene variations were associated with the BPD in Chinese premature newborns, and the type V1: Exon 2: c.[5A > C] + [5A > C] or c.[5A > C] + [=] was a risk factor for the development of BPD.

The Potentials and Caveats of Mesenchymal Stromal Cell-Based Therapies in the Preterm Infant

Preponderance of proinflammatory signals is a characteristic feature of all acute and resulting long-term morbidities of the preterm infant. The proinflammatory actions are best characterized for bronchopulmonary dysplasia (BPD) which is the chronic lung disease of the preterm infant with lifelong restrictions of pulmonary function and severe consequences for psychomotor development and quality of life. Besides BPD, the immature brain, eye, and gut are also exposed to inflammatory injuries provoked by infection, mechanical ventilation, and oxygen toxicity. Despite the tremendous progress in the understanding of disease pathologies, therapeutic interventions with proven efficiency remain restricted to a few drug therapies with restricted therapeutic benefit, partially considerable side effects, and missing option of applicability to the inflamed brain. The therapeutic potential of mesenchymal stromal cells (MSCs)—also known as mesenchymal stem cells—has attracted much attention during the recent years due to their anti-inflammatory activities and their secretion of growth and development-promoting factors. Based on a molecular understanding, this review summarizes the positive actions of exogenous umbilical cord-derived MSCs on the immature lung and brain and the therapeutic potential of reprogramming resident MSCs. The pathomechanistic understanding of MSC actions from the animal model is complemented by the promising results from the first phase I clinical trials testing allogenic MSC transplantation from umbilical cord blood. Despite all the enthusiasm towards this new therapeutic option, the caveats and outstanding issues have to be critically evaluated before a broad introduction of MSC-based therapies.

Recent Advances in Bronchopulmonary Dysplasia: Pathophysiology, Prevention, and Treatment

Bronchopulmonary dysplasia (BPD) is potentially one of the most devastating conditions in premature infants with longstanding consequences involving multiple organ systems including adverse effects on pulmonary function and neurodevelopmental outcome. Here we review recent studies in the field to summarize the progress made in understanding in the pathophysiology, prognosis, prevention, and treatment of BPD in the last decade. The work reviewed includes the progress in understanding its pathobiology, genomic studies, ventilatory strategies, outcomes, and therapeutic interventions. We expect that this review will help guide clinicians to treat premature infants at risk for BPD better and lead researchers to initiate further studies in the field.

Association of cytokine gene polymorphisms with bronchopulmonary dysplasia in Han Chinese newborns

OBJECTIVE

To investigate the association of 14 cytokine gene polymorphisms with bronchopulmonary dysplasia (BPD) among Han Chinese newborns. The 14 polymorphisms investigated were IL18 rs1946519, rs1946518, rs187238, rs360718, and rs360717 polymorphisms, IL10 rs3024493 polymorphism, IL6 rs1800795, rs1800796, and rs1800797 polymorphisms, TNF rs361525 and rs1800629 polymorphisms, and TGFB1 rs1800469, rs1800468, and rs1800471 polymorphisms.

WORKING HYPOTHESIS

The polymorphisms could be associated with the risk of BPD among Han Chinese newborns.

STUDY DESIGN, PATIENT-SUBJECT SELECTION, AND METHODOLOGY

This is a retrospective study. Genotyping of these polymorphisms were performed on BPD cases (N = 1022) and non-BPD controls (N = 1039) who were ascertained using the established Jobe and Bancalari criteria. The odds ratios (ORs) of polymorphisms whose genotype distribution in the controls fulfilled the Hardy-Weinberg equilibrium (HWE) were calculated to evaluate the strengths of genetic association.

RESULTS

Genotype distributions of IL6 rs1800795 and rs1800797 polymorphisms deviated significantly from HWE and were omitted from the analysis. Among the 12 remaining polymorphisms, only TNF rs361525 polymorphism demonstrated a statistically significant association with BPD risk. The heterozygous GA genotype of TNF rs361525 polymorphism showed an OR of 1.932 (1.512-2.470), while the homozygous AA variant genotype showed an OR of 2.927 (1.216-7.048) (P = 0.000 and P = 0.017, respectively). Besides, the allelic OR was also analyzed, and it was found that the variant A allele of TNF rs361525 polymorphism showed an OR of 2.146 (1.718-2.680) (P = 0.000).

CONCLUSION

TNF rs361525 polymorphism could influence BPD risk among Han Chinese newborns.

A Time-Based Analysis of Inflammation in Infants at Risk of Bronchopulmonary Dysplasia

OBJECTIVE

To precisely delineate the timing and contribution of inflammation to bronchopulmonary dysplasia (BPD) in preterm infants during the neonatal period.

STUDY DESIGN

Longitudinal study of blood inflammatory biomarkers (interleukin [IL]-6, IL-8, and granulocyte colony-stimulating factor) measured between birth and 42 days of age, at high temporal (daily) resolution, in infants born at or below 30 weeks of gestation. Cytokine predictors of BPD at 36 weeks postmenstrual age were adjusted for infant-specific and time-dependent factors, using hierarchical mixed effects regressions models.

RESULTS

A total of 1518 data points were obtained in 62 infants (mean gestational age of 27 weeks). Infants who developed BPD later on presented increased inflammation after birth compared with infants without BPD. Inflammation was sustained, with gradual attenuation over 2 weeks (IL-8: OR: 6.5 [95% CI: 1.8-24]; granulocyte colony-stimulating factor: 3.3 [1.5-7.6]) and was higher in boys and in infants of lower birth weight. This inflammation preceded the clinical increased requirement in supplemental oxygen characteristic of BPD, and preceded the peak occurrence of neonatal sepsis or necrotizing enterocolitis.

CONCLUSIONS

Systemic inflammation occurs early in the neonatal period and precedes clinical symptoms in infants with BPD. These data provide a discrete vulnerability window period, supporting a role for targeted intensive care interventions during the early phase of BPD.

Bronchopulmonary dysplasia: A review of pathogenesis and pathophysiology

Bronchopulmonary dysplasia (BPD) is a chronic lung disease of primarily premature infants that results from an imbalance between lung injury and repair in the developing lung. BPD is the most common respiratory morbidity in preterm infants, which affects nearly 10, 000 neonates each year in the United States. Over the last two decades, the incidence of BPD has largely been unchanged; however, the pathophysiology has changed with the substantial improvement in the respiratory management of extremely low birth weight (ELBW) infants. Here we have attempted to comprehensively review and summarize the current literature on the pathogenesis and pathophysiology of BPD. Our goal is to provide insight to help further progress in preventing and managing severe BPD in the ELBW infants.

Polymorphisms in CYP2C9 are associated with response to indomethacin among neonates with patent ductus arteriosus

BackgroundPatent ductus arteriosus (PDA) is a common complication seen in preterm infants. Indomethacin is routinely used to treat PDA. Evidence suggests that the response of indomethacin is highly heritable. This study investigated the association between single-nucleotide polymorphisms (SNPs) in CYP2C9 and the closure of PDA in response to indomethacin.MethodsSix SNPs in CYP2C9 were analyzed for association with indomethacin response. A case-control analysis was performed among neonates who responded to indomethacin (responders) and among those who required surgical ligation (non-responders). Independent transmission disequilibrium tests were performed among parent-child trios of responders and non-responders.ResultsThe G allele of rs2153628 was associated with increased odds of response to indomethacin in the case-control analysis (odds ratios (OR): 1.918, 95% confidence interval (CI): 1.056, 3.483). Among indomethacin responders, the G allele of rs2153628 and the T allele of rs1799853 were overtransmitted from the parents to their child (OR: 2.667, 95% CI: 1.374, 5.177 and OR: 2.375, 95% CI: 1.040, 5.425, respectively), consistent with the case-control analysis.ConclusionWe identified an association between two SNPs in CYP2C9, rs2153628 and rs1799853, and indomethacin response for the treatment of PDA. These findings suggest that response to indomethacin in the closure of PDA may be influenced by polymorphisms associated with altered indomethacin metabolism.

Pulmonary hypertension associated with bronchopulmonary dysplasia in preterm infants

Bronchopulmonary dysplasia (BPD) and BPD-associated pulmonary hypertension (BPD-PH) are chronic inflammatory cardiopulmonary diseases with devastating short- and long-term consequences for infants born prematurely. The immature lungs of preterm infants are ill-prepared to achieve sufficient gas exchange, thus usually necessitating immediate commencement of respiratory support and oxygen supplementation. These therapies are life-saving, but they exacerbate the tissue damage that is inevitably inflicted on a preterm lung forced to perform gas exchange. Together, air-breathing and necessary therapeutic interventions disrupt normal lung development by aggravating pulmonary inflammation and vascular remodelling, thus frequently precipitating BPD and PH via an incompletely understood pathogenic cascade. BPD and BPD-PH share common risk factors, such as low gestational age at birth, fetal growth restriction and perinatal maternal inflammation; however, these risk factors are not unique to BPD or BPD-PH. Occurring in 17-24% of BPD patients, BPD-PH substantially worsens the morbidity and mortality attributable to BPD alone, thus darkening their outlook; for example, BPD-PH entails a mortality of up to 50%. The absence of a safe and effective therapy for BPD and BPD-PH renders neonatal cardiopulmonary disease an area of urgent unmet medical need. Besides the need to develop new therapeutic strategies, a major challenge for clinicians is the lack of a reliable method for identifying babies at risk of developing BPD and BPD-PH. In addition to discussing current knowledge on pathophysiology, diagnosis and treatment of BPD-PH, we highlight emerging biomarkers that could enable clinicians to predict disease-risk and also optimise treatment of BPD-PH in our tiniest patients.

Genome-wide association study of bronchopulmonary dysplasia: a potential role for variants near the CRP gene

Bronchopulmonary dysplasia (BPD), the main consequence of prematurity, has a significant heritability, but little is known about predisposing genes. The aim of this study was to identify gene loci predisposing infants to BPD. The initial genome-wide association study (GWAS) included 174 Finnish preterm infants of gestational age 24–30 weeks. Thereafter, the most promising single-nucleotide polymorphisms (SNPs) associated with BPD were genotyped in both Finnish (n = 555) and non-Finnish (n = 388) replication cohorts. Finally, plasma CRP levels from the first week of life and the risk of BPD were assessed. SNP rs11265269, flanking the CRP gene, showed the strongest signal in GWAS (odds ratio [OR] 3.2, p = 3.4 × 10⁻⁶). This association was nominally replicated in Finnish and French African populations. A number of other SNPs in the CRP region, including rs3093059, had nominal associations with BPD. During the first week of life the elevated plasma levels of CRP predicted the risk of BPD (OR 3.4, p = 2.9 × 10^–4) and the SNP rs3093059 associated nominally with plasma CRP levels. Finally, SNP rs11265269 was identified as a risk factor of BPD (OR 1.8, p = 5.3 × 10⁻⁵), independently of the robust antenatal risk factors. As such, in BPD, a potential role for variants near CRP gene is proposed.

Examining the role of unmeasured confounding in mediation analysis with genetic and genomic applications

Background

In mediation analysis if unmeasured confounding is present, the estimates for the direct and mediated effects may be over or under estimated. Most methods for the sensitivity analysis of unmeasured confounding in mediation have focused on the mediator-outcome relationship.

Results

The Umediation R package enables the user to simulate unmeasured confounding of the exposure-mediator, exposure-outcome, and mediator-outcome relationships in order to see how the results of the mediation analysis would change in the presence of unmeasured confounding. We apply the Umediation package to the Genetic Epidemiology of Chronic Obstructive Pulmonary Disease (COPDGene) study to examine the role of unmeasured confounding due to population stratification on the effect of a single nucleotide polymorphism (SNP) in the CHRNA5/3/B4 locus on pulmonary function decline as mediated by cigarette smoking.

Conclusions

Umediation is a flexible R package that examines the role of unmeasured confounding in mediation analysis allowing for normally distributed or Bernoulli distributed exposures, outcomes, mediators, measured confounders, and unmeasured confounders. Umediation also accommodates multiple measured confounders, multiple unmeasured confounders, and allows for a mediator-exposure interaction on the outcome. Umediation is available as an R package at https://github.com/SharonLutz/Umediation A tutorial on how to install and use the Umediation package is available in the Additional file 1.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-017-1749-y) contains supplementary material, which is available to authorized users.

Airway Remodeling and Hyperreactivity in a Model of Bronchopulmonary Dysplasia and Their Modulation by IL-1 Receptor Antagonist

Bronchopulmonary dysplasia (BPD) is a chronic disease of extreme prematurity that has serious long-term consequences including increased asthma risk. We earlier identified IL-1 receptor antagonist (IL-1Ra) as a potent inhibitor of murine BPD induced by combining perinatal inflammation (intraperitoneal LPS to pregnant dams) and exposure of pups to hyperoxia (fraction of inspired oxygen = 0.65). In this study, we determined whether airway remodeling and hyperresponsiveness similar to asthma are evident in this model, and whether IL-1Ra is protective. During 28-day exposure to air or hyperoxia, pups received vehicle or 10 mg/kg IL-1Ra by daily subcutaneous injection. Lungs were then prepared for histology and morphometry of alveoli and airways, or for real-time PCR, or inflated with agarose to prepare precision-cut lung slices to visualize ex vivo intrapulmonary airway contraction and relaxation by phase-contrast microscopy. In pups reared under normoxic conditions, IL-1Ra treatment did not affect alveolar or airway structure or airway responses. Pups reared in hyperoxia developed a severe BPD-like lung disease, with fewer, larger alveoli, increased subepithelial collagen, and increased expression of α-smooth muscle actin and cyclin D1. After hyperoxia, methacholine elicited contraction with similar potency but with an increased maximum reduction in lumen area (air, 44%; hyperoxia, 89%), whereas dilator responses to salbutamol were maintained. IL-1Ra treatment prevented hyperoxia-induced alveolar disruption and airway fibrosis but, surprisingly, not the increase in methacholine-induced airway contraction. The current study is the first to demonstrate ex vivo airway hyperreactivity caused by systemic maternal inflammation and postnatal hyperoxia, and it reveals further preclinical mechanistic insights into IL-1Ra as a treatment targeting key pathophysiological features of BPD.

Cellular and humoral biomarkers of Bronchopulmonary Dysplasia

The pathogenesis of Bronchopulmonary Dysplasia (BPD) is multifactorial and the clinical phenotype of BPD is extremely variable. Predicting BPD is difficult, as it is a disease with a clinical operational definition but many clinical phenotypes and endotypes. Most biomarkers studied over the years have low predictive accuracy, and none are currently used in routine clinical care or shown to be useful for predicting longer-term respiratory outcome. Targeted cellular and humoral biomarkers and novel systems biology 'omic' based approaches including genomic and microbiomic analyses are described in this review.

Bronchopulmonary Dysplasia: Chronic Lung Disease of Infancy and Long-Term Pulmonary Outcomes

Bronchopulmonary dysplasia (BPD) is a chronic lung disease most commonly seen in premature infants who required mechanical ventilation and oxygen therapy for acute respiratory distress. While advances in neonatal care have resulted in improved survival rates of premature infants, limited progress has been made in reducing rates of BPD. Lack of progress may in part be attributed to the limited therapeutic options available for prevention and treatment of BPD. Several lung-protective strategies have been shown to reduce risks, including use of non-invasive support, as well as early extubation and volume ventilation when intubation is required. These approaches, along with optimal nutrition and medical therapy, decrease risk of BPD; however, impacts on long-term outcomes are poorly defined. Characterization of late outcomes remain a challenge as rapid advances in medical management result in current adult BPD survivors representing outdated neonatal care. While pulmonary disease improves with growth, long-term follow-up studies raise concerns for persistent pulmonary dysfunction; asthma-like symptoms and exercise intolerance in young adults after BPD. Abnormal ventilatory responses and pulmonary hypertension can further complicate disease. These pulmonary morbidities, combined with environmental and infectious exposures, may result in significant long-term pulmonary sequalae and represent a growing burden on health systems. Additional longitudinal studies are needed to determine outcomes beyond the second decade, and define risk factors and optimal treatment for late sequalae of disease.

Lung Function and Bronchial Hyperresponsiveness in Adults Born Prematurely. A Cohort Study

RATIONALE

Bronchopulmonary dysplasia and the long-term consequences of prematurity are underrecognized entities, unfamiliar to adult clinicians. Well described by the pediatric community, these young adults are joining the ranks of a growing population of adults with chronic lung disease.

OBJECTIVES

To describe the quality of life, pulmonary lung function, bronchial hyperresponsiveness, body composition, and trends in physical activity of adults born prematurely, with or without respiratory complications.

METHODS

Four groups of young adults born in Canada between 1987 and 1993 were enrolled in a cohort study: (1) preterm subjects with no neonatal respiratory complications, (2) preterm subjects with neonatal respiratory distress syndrome, (3) preterm subjects with bronchopulmonary dysplasia, and (4) subjects born at term. The following measurements were compared across the four groups: health-related quality of life, respiratory health, pulmonary function, methacholine challenge test results, and sedentary behavior and physical activity level.

MEASUREMENTS AND MAIN RESULTS

Adult subjects who had bronchopulmonary dysplasia in infancy had mild airflow obstruction (FEV1, 80% predicted; FEV1/FCV ratio, 70) and gas trapping compared with others. They also had less total active energy expenditure and more time spent in sedentary behavior compared with subjects born at term. All preterm groups had a high prevalence of bronchial hyperresponsiveness compared with term subjects.

CONCLUSIONS

In a population-derived, cross-sectional study, we confirmed previous reports that adults 21 or 22 years of age who were born prematurely with neonatal bronchopulmonary dysplasia are more likely to have airflow obstruction, bronchial hyperresponsiveness, and pulmonary gas trapping than subjects born prematurely without bronchopulmonary dysplasia or at term. Clinicians who care for adults need to be better informed of the long-term respiratory consequences of premature birth to assist young patients in maintaining lung function and health.

Searching for better animal models of BPD: a perspective

There have been many efforts to develop good animal models of bronchopulmonary dysplasia (BPD) to better understand the pathophysiology and mechanisms underlying development of BPD as well as to test potential strategies for its prevention and treatment. This Perspectives summarizes the features of common animal models of BPD and the strengths and limitations of such models. Potential optimal approaches to development of animal models are indicated, with the underlying concepts that require emphasis.

Association of TLR polymorphisms with bronchopulmonary dysplasia

BACKGROUND

Bronchopulmonary dysplasia (BPD) remains a leading cause of morbidity and mortality during infancy. Evidence suggests that the Toll-like receptor (TLR) signaling pathway plays an integral role in lung inflammation and injury. This study aimed to detect single nucleotide polymorphisms (SNPs) in TLR pathway genes [TLR5 and Toll-interleukin 1 receptor domain-containing adaptor protein (TIRAP)] among preterm neonates and to determine their association with the development and severity of bronchopulmonary dysplasia.

Epidemiology, presentation and population genetics of patent ductus arteriosus (PDA) in the Dutch Stabyhoun dog

Background

Patent ductus arteriosus (PDA) is one of the most common congenital heart defects in dogs and is considered to be a complex, polygenic threshold trait for which a female sex predisposition has been described. Histological studies in dogs suggest that smooth muscle hypoplasia and asymmetry of the ductus tissue is the major cause of PDA. The Stabyhoun population is small and a predisposition for PDA has been suggested. The aims of this study were to describe the incidence, presentation from a clinical and histopathological perspective, and the population genetics of PDA in the Dutch Stabyhoun population.

Results

Forty-six cases were identified between 2000 and 2013. Between 2009 and 2012 the birth incidence of PDA in the Stabyhoun breed was 1.05 %. We estimated this to be 7–13 times higher than expected in the general dog population. Twelve of the 46 cases were part of a litter in which more than one sibling was affected. There was no sex predilection in our case cohort. Dogs diagnosed in adulthood showed severe cardiomegaly. The mean inbreeding coefficient of the reference population of Stabyhoun dogs was 31.4 % and the actual and effective numbers of founders were 14 and 6.5, respectively. The heritability of PDA was 0.51 (±0.09) for the reference population and 0.41 (±0.10) for the phenotyped population. Histopathology of sections of the PDA from two dogs showed findings similar to those described in other breeds although the smooth muscle of the ductus adjacent to the pulmonary artery appeared more hypoplastic than that in the ductus adjacent to the aorta.

Conclusions

The Stabyhoun breed shows a strong predisposition for PDA. Apart from the absence of a higher incidence in females, no other significant features distinguish PDA in Stabyhouns from the condition in other dog breeds. Heritability and the mean inbreeding coefficient are both very high making the Dutch Stabyhoun breed particularly suited to the study of inherited risk factors for PDA.

The genetic predisposition to bronchopulmonary dysplasia

PURPOSE OF REVIEW

Bronchopulmonary dysplasia (BPD) is a prevalent chronic lung disease in premature infants. Twin studies have shown strong heritability underlying this disease; however, the genetic architecture of BPD remains unclear.

RECENT FINDINGS

A number of studies employed different approaches to characterize the genetic aberrations associated with BPD, including candidate gene studies, genome-wide association studies, exome sequencing, integrative omics analysis, and pathway analysis. Candidate gene studies identified a number of genes potentially involved with the development of BPD, but the etiological contribution from each gene is not substantial. Copy number variation studies and three independent genome-wide association studies did not identify genetic variations significantly and consistently associated with BPD. A recent exome-sequencing study pointed to rare variants implicated in the disease. In this review, we summarize these studies' methodology and findings, and suggest future research directions to better understand the genetic underpinnings of this potentially life-long lung disease.

SUMMARY

Genetic factors play a significant role in the development of BPD. Recent studies suggested that rare variants in genes participating in lung development pathways could contribute to BPD susceptibility.

Complex genetics of pulmonary diseases: lessons from genome-wide association studies and next-generation sequencing

The advent of high-throughput technologies has provided exceptional assistance for lung scientists to discover novel genetic variants underlying the development and progression of complex lung diseases. However, the discovered variants thus far do not explain much of the estimated heritability of complex lung diseases. Here, we review the literature of successfully used genome-wide association studies (GWASs) and identified the polymorphisms that reproducibly underpin the susceptibility to various noncancerous complex lung diseases or affect therapeutic responses. We also discuss the inherent limitations of GWAS approaches and how the use of next-generation sequencing technologies has furthered our understanding about the genetic determinants of these diseases. Next, we describe the contribution of the metagenomics to understand the interactions of the airways microbiome with lung diseases. We then highlight the urgent need for new integrative genomics-phenomics methods to more effectively interrogate and understand multiple downstream "omics" (eg, chromatin modification patterns). Finally, we address the scarcity of genetic studies addressing under-represented populations such as African Americans and Hispanics.

BPD Following Preterm Birth: A Model for Chronic Lung Disease and a Substrate for ARDS in Childhood

It has been suggested that pediatric acute respiratory distress syndrome (PARDS) may be a different entity, vis-à-vis adult acute respiratory distress syndrome (ARDS), based on its epidemiology and outcomes. A more pediatric-specific definition of PARDS to include the subgroup of patients with underlying lung (and heart) disease has been proposed. Epidemiological data suggest that up to 13% of the children with ARDS have a history of prematurity and/or underlying chronic lung disease. However, the specific contribution of bronchopulmonary dysplasia (BPD), the most common chronic lung disease in infants, to the development of PARDS is not known. BPD leads to damaged lungs with long-term consequences secondary to disordered growth and immune function. These damaged lungs could potentially act as a substrate, which given the appropriate noxious stimuli, can predispose a child to PARDS. Interestingly, similar biomarkers [KL-6, interleukin (IL)-6, IL-8, sICAM-1, angiopoietin-2, and matrix metalloproteinase-8 and -9] of pulmonary injury have been associated both with BPD and ARDS. Recognition of a unique pattern of clinical symptomatology and/or outcomes of PARDS, if present, could potentially be useful for investigating targeted therapeutic interventions.

What is the basis for a genetic approach in neonatal disorders?

Gene-environment interactions likely account for some degree of the variance in response rates that are clinically observed with antenatal corticosteroids, breast milk prophylaxis, surfactant administration, early recognition and treatment of sepsis, utility of non-invasive ventilation, and judicious exposure to supplemental oxygen. While these therapies and practice guidelines have significantly decreased overall neonatal mortality in the NICU, they have not made a marked impact on the frequency and severity of conditions such as bronchopulmonary dysplasia (BPD), necrotizing enterocolitis, and periventricular leukomalacia. One possible explanation is that genetic factors in the neonate modulate response to external intervention or preventative agents, culminating in variable levels of injury and different degrees of resolution and repair. Gene-environment explanations are supported by the observed heritability of BPD in twin studies, but they do not differentiate the interactions between neonate and offending toxin or pathogen, from interactions between neonate and intervention or therapeutic agent. Likely, both kinds of interactions are important in determining outcome.

Genetic predisposition to bronchopulmonary dysplasia

The objective of this study is to review the candidate gene and genome-wide association studies relevant to bronchopulmonary dysplasia, and to discuss the emerging understanding of the complexities involved in genetic predisposition to bronchopulmonary dysplasia and its outcomes. Genetic factors contribute much of the variance in risk for BPD. Studies to date evaluating single or a few candidate genes have not been successful in yielding results that are replicated in GWAS, perhaps due to more stringent p-value thresholds. GWAS studies have identified only a single gene (SPOCK2) at genome-wide significance in a European White and African cohort, which was not replicated in two North American studies. Pathway gene-set analysis in a North American cohort confirmed involvement of known pathways of lung development and repair (e.g., CD44 and phosphorus oxygen lyase activity) and indicated novel molecules and pathways (e.g., adenosine deaminase and targets of miR-219) involved in genetic predisposition to BPD. The genetic basis of severe BPD is different from that of mild/moderate BPD, and the variants/pathways associated with BPD vary by race/ethnicity. A pilot study of whole exome sequencing identified hundreds of genes of interest, and indicated the overall feasibility as well as complexity of this approach. Better phenotyping of BPD by severity and pathophysiology, and careful analysis of race/ethnicity is required to gain a better understanding of the genetic basis of BPD. Future translational studies are required for the identification of potential genetic predispositions (rare variants and dysregulated pathways) by next-generation sequencing methods in individual infants (personalized genomics).

Biomarkers, Early Diagnosis, and Clinical Predictors of Bronchopulmonary Dysplasia

The pathogenesis of bronchopulmonary dysplasia (BPD) is multifactorial, and the clinical phenotype of BPD is extremely variable. Several clinical and laboratory biomarkers have been proposed for the early identification of infants at higher risk of BPD and for determination of prognosis of infants with a diagnosis of BPD. The authors review available literature on prediction tools and biomarkers of BPD, using clinical variables and biomarkers based on imaging, lung function measures, and measurements of various analytes in different body fluids that have been determined to be associated with BPD either in a targeted manner or by unbiased omic profiling.

Exome Sequencing of Neonatal Blood Spots and the Identification of Genes Implicated in Bronchopulmonary Dysplasia

RATIONALE

Bronchopulmonary dysplasia (BPD), a prevalent severe lung disease of premature infants, has a strong genetic component. Large-scale genome-wide association studies for common variants have not revealed its genetic basis.

OBJECTIVES

Given the historical high mortality rate of extremely preterm infants who now survive and develop BPD, we hypothesized that risk loci underlying this disease are under severe purifying selection during evolution; thus, rare variants likely explain greater risk of the disease.

METHODS

We performed exome sequencing on 50 BPD-affected and unaffected twin pairs using DNA isolated from neonatal blood spots and identified genes affected by extremely rare nonsynonymous mutations. Functional genomic approaches were then used to systematically compare these affected genes.

MEASUREMENTS AND MAIN RESULTS

We identified 258 genes with rare nonsynonymous mutations in patients with BPD. These genes were highly enriched for processes involved in pulmonary structure and function including collagen fibril organization, morphogenesis of embryonic epithelium, and regulation of Wnt signaling pathway; displayed significantly elevated expression in fetal and adult lungs; and were substantially up-regulated in a murine model of BPD. Analyses of mouse mutants revealed their phenotypic enrichment for embryonic development and the cyanosis phenotype, a clinical manifestation of BPD.

CONCLUSIONS

Our study supports the role of rare variants in BPD, in contrast with the role of common variants targeted by genome-wide association studies. Overall, our study is the first to sequence BPD exomes from newborn blood spot samples and identify with high confidence genes implicated in BPD, thereby providing important insights into its biology and molecular etiology.

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.

Genetic and Environmental Influences on Retinopathy of Prematurity

OBJECTIVE

The goals were to isolate and study the genetic susceptibility to retinopathy of prematurity (ROP), as well as the gene-environment interaction established in this disease.

METHODS

A retrospective study (2000-2014) was performed about the heritability of retinopathy of prematurity in 257 infants who were born at a gestational age of ≤ 32 weeks. The ROP was studied and treated by a single pediatric ophthalmologist. A binary logistic regression analysis was completed between the presence or absence of ROP and the predictor variables.

RESULTS

Data obtained from 38 monozygotic twins, 66 dizygotic twins, and 153 of simple birth were analyzed. The clinical features of the cohorts of monozygotic and dizygotic twins were not significantly different. Genetic factors represented 72.8% of the variability in the stage of ROP, environmental factors 23.08%, and random factors 4.12%. The environmental variables representing the highest risk of ROP were the number of days of tracheal intubation (p < 0.001), postnatal weight gain (p = 0.001), and development of sepsis (p = 0.0014).

CONCLUSION

The heritability of ROP was found to be 0.73. The environmental factors regulate and modify the expression of the genetic code.

Two cases of bronchopulmonary dysplasia of similar appearance in adult monozygotic twin: pathology and computed tomographic findings

Bronchopulmonary dysplasia (BPD) is related to decreased lung function throughout life. However, the pathology and radiology pattern of BPD of adults are not documented well yet. In this case report, we present BPD case of an adult monozygotic twin showing nearly identical lesions on chest computed tomography (CT). CT images showed mixed areas of ground-glass and reticular opacities in both lungs. They had common histories of pneumonias requiring mechanical ventilations in period of infants. Pulmonary function test of one patient showed a pulmonary insufficiency with airway obstruction. Pathologic findings showed bronchiolar hyperplasia and peribronchiolar fibrosis which was similar to classic BPD patients. Our twin case report might help provide distinguishing pathology and radiology pattern of an adult pulmonary sequelaes of BPD. It might be reasonable to make close follow-up for BPD patients to evaluate the long-term outcomes of BPD survivors.

Polymorphisms of the gene encoding Kit ligand are associated with bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic inflammatory lung disease that affects infants born preterm. Family studies indicate that BPD has a significant genetic component.

RATIONALE

We assessed the gene encoding Kit ligand (KITLG) as a candidate for genetic predisposition to moderate-to-severe BPD (controls were infants with no or mild BPD).

STUDY DESIGN

Eight KITLG-tagging single nucleotide polymorphisms (SNPs) were analyzed in cohorts of very preterm infants originating from northern Finland (56 cases and 197 controls), southern Finland (n = 59 + 52), and Canada (n = 58 + 68). Additional replication populations included infants born in Finland (n = 41 + 241) and Hungary (n = 29 + 40). All infants were of European origin. Results were controlled for risk factors of BPD. Kit ligand concentration in umbilical cord blood, collected from very preterm infants (n = 120), was studied.

RESULTS

Six SNPs of KITLG and a haplotype including all eight genotyped SNPs were associated with moderate-to-severe BPD in the northern Finnish population. When all the populations were combined, SNP rs11104948 was significantly associated with BPD. Kit ligand concentration in umbilical cord blood of infants born very preterm was an independent risk factor of BPD.

CONCLUSIONS

We show that KITLG polymorphisms are associated with susceptibility to moderate-to-severe BPD. In addition, higher Kit ligand concentrations were observed in infants that subsequently developed BPD. These results support the possibility that KITLG gene is involved in predisposition to BPD. Pediatr Pulmonol. 2015; 50:260-270. © 2014 Wiley Periodicals, Inc.

Antioxidant response genes sequence variants and BPD susceptibility in VLBW infants

BACKGROUND

Lung injury resulting from oxidative stress contributes to bronchopulmonary dysplasia (BPD) pathogenesis. Nuclear factor erythroid-2 related factor-2 (NFE2L2) regulates cytoprotective responses to oxidative stress by inducing enzymes containing antioxidant response elements (ARE). We hypothesized that ARE genetic variants will modulate susceptibility or severity of BPD in very-low-birth-weight (VLBW) infants.

METHODS

Blood samples obtained from VLBW infants were used for genotyping variants in the SOD2, NFE2L2, GCLC, GSTP1, HMOX1, and NQO1 genes. SNPs were genotyped utilizing TaqMan probes (Applied Biosystems (ABI), Grand Island, NY), and data were analyzed using the ABI HT7900. Genetic dominance and recessive models were tested to determine associations between SNPs and BPD.

RESULTS

In our cohort (n = 659), 284 infants had BPD; 135 of whom developed severe BPD. Presence of the hypomorphic NQO1 SNP (rs1800566) in a homozygous state was associated with increased BPD, while presence of the NFE2L2 SNP (rs6721961) was associated with decreased severe BPD in the entire cohort and in Caucasian infants. In regression models that adjusted for epidemiological confounders, the NQO1 and the NFE2L2 SNPs were associated with BPD and severe BPD, respectively.

CONCLUSION

Genetic variants in NFE2L2-ARE axis may contribute to the variance in liability to BPD observed in preterm infants. These results require confirmation in independent cohorts.

Surfactant protein B gene polymorphisms is associated with risk of bronchopulmonary dysplasia in Chinese Han population

OBJECTIVE

To investigate the relationship between Surfactant protein B (SP-B) gene polymorphisms and bronchopulmonary dysplasia (BPD) development in preterm infants of China Han ethnic population.

METHODS

SP-B gene polymorphisms were studied in 134 neonates who were born at <32 weeks of gestation, with the diagnosis of BPD and in a control group of 168 preterm infants without BPD. Genotyping for SP-B was performed by polymerase chain reaction (PCR) and gene sequencing.

RESULTS

In this study, three of the SNP genotypes, -18C/A, 1580C/T and 4564T/C were common identified in SP-B gene. The -18C/A genotype was found to be significantly associated with BPD (χ2=10.741, P<0.01), with P<0.01 for the dominant model (OR=1.712, 95% CI=1.228-2.3894) and the allelic model (OR=1.787, 95% CI=1.276-2.502). The 1580C/T genotype was found to be associated with BPD (χ2=7.014, P<0.05), with P<0.05 for the dominant model (OR=0.752, 95% CI=0.593-0.954) and P<0.01 for the allelic model (OR=0.706, 95% CI=0.548-0.909). The 4564T/C genotypes and alleles were found not to be associated with BPD (χ2=3.399 and 3.227, P>0.05).

CONCLUSION

SP-B -18C/A and 1580C/T polymorphisms are associated with BPD. The 1580C/T polymorphism was protective while the -18C/A polymorphism increased the risk for BPD. SP-B 4564T/C polymorphism is not associated with BPD.

Secreted phosphoprotein 1 is a determinant of lung function development in mice

Secreted phosphoprotein 1 (Spp1) is located within quantitative trait loci associated with lung function that was previously identified by contrasting C3H/HeJ and JF1/Msf mouse strains that have extremely divergent lung function. JF1/Msf mice with diminished lung function had reduced lung SPP1 transcript and protein during the peak stage of alveologenesis (postnatal day [P]14-P28) as compared with C3H/HeJ mice. In addition to a previously identified genetic variant that altered runt-related transcription factor 2 (RUNX2) binding in the Spp1 promoter, we identified another promoter variant in a putative RUNX2 binding site that increased the DNA protein binding. SPP1 induced dose-dependent mouse lung epithelial-15 cell proliferation. Spp1((-/-)) mice have decreased specific total lung capacity/body weight, higher specific compliance, and increased mean airspace chord length (Lm) compared with Spp1((+/+)) mice. Microarray analysis revealed enriched gene ontogeny categories, with numerous genes associated with lung development and/or respiratory disease. Insulin-like growth factor 1, Hedgehog-interacting protein, wingless-related mouse mammary tumor virus integration site 5A, and NOTCH1 transcripts decreased in the lung of P14 Spp1((-/-)) mice as determined by quantitative RT-PCR analysis. SPP1 promotes pneumocyte growth, and mice lacking SPP1 have smaller, more compliant lungs with enlarged airspace (i.e., increased Lm). Microarray analysis suggests a dysregulation of key lung developmental transcripts in gene-targeted Spp1((-/-)) mice, particularly during the peak phase of alveologenesis. In addition to its known roles in lung disease, this study supports SPP1 as a determinant of lung development in mice.

Genes Encoding Vascular Endothelial Growth Factor A (VEGF-A) and VEGF Receptor 2 (VEGFR-2) and Risk for Bronchopulmonary Dysplasia

BACKGROUND

Bronchopulmonary dysplasia (BPD) is one of the main consequences of prematurity, with notably high heritability. Vascular endothelial growth factor A (VEGF-A) and its main receptor, vascular endothelial growth factor receptor 2 (VEGFR-2), have been implicated in the pathogenesis of BPD.

OBJECTIVE

To study whether common polymorphisms of the genes encoding VEGF-A and VEGFR-2 are associated with BPD.

METHODS

In this association study, six tagging single nucleotide polymorphism (tSNPs) for VEGFA and 25 tSNPs for VEGFR2 were genotyped in a prospectively collected, genetically homogeneous discovery population of 160 infants (44 infants with grade 2-3 BPD) born before 30 completed gestational weeks. The replication population of 328 infants included 120 cases of BPD.

RESULTS

VEGFR2 SNP rs4576072 was associated with BPD grade 2-3 with a minor allele frequency in 23.9% of the cases compared to 9.1% in controls (p = 0.0005, odds ratio 3.15, 95% CI: 1.62-6.12) in the discovery population. This association was not observed in the more heterogeneous replication population.

CONCLUSIONS

In line with the results of recent large-scale genetic studies, our findings indicate that common polymorphisms of the genes encoding VEGF-A and VEGFR-2 are not consistently associated with BPD. This finding does not rule out the involvement of VEGFA and VEGFR2 in BPD pathogenesis since, in addition to common variations within the gene region, other mechanisms also play important roles in the regulation of gene function.

A study of genes encoding cytokines (IL6, IL10, TNF), cytokine receptors (IL6R, IL6ST), and glucocorticoid receptor (NR3C1) and susceptibility to bronchopulmonary dysplasia

Background

Bronchopulmonary dysplasia (BPD) is a common chronic lung disease associated with very preterm birth. The major risk factors include lung inflammation and lung immaturity. In addition, genetic factors play an important role in susceptibility to moderate-to-severe BPD. In this study, the aim was to investigate whether common polymorphisms of specific genes that are involved in inflammation or differentiation of the lung have influence on BPD susceptibility.

Methods

Genes encoding interleukin-6 (IL6) and its receptors (IL6R and IL6ST), IL-10 (IL10), tumor necrosis factor (TNF), and glucocorticoid receptor (NR3C1) were assessed for associations with moderate-to-severe BPD susceptibility. Five IL6, nine IL6R, four IL6ST, one IL10, two TNF, and 23 NR3C1 single nucleotide polymorphisms (SNPs) were analyzed in very preterm infants born in northern Finland (56 cases and 197 controls) and Canada (58 cases and 68 controls). IL-6, TNF and gp130 contents in umbilical cord blood, collected from very preterm infants, were studied for associations with the polymorphisms. Epistasis (i.e., interactions between SNPs in BPD susceptibility) was also examined. SNPs showing suggestive associations were analyzed in additional replication populations from Finland (39 cases and 188 controls) and Hungary (29 cases and 40 controls).

Results

None of the studied SNPs were associated with BPD nor were the IL6, TNF or IL6ST SNPs associated with cord blood IL-6, TNF and gp130, respectively. However, epistasis analysis suggested that SNPs in IL6ST and IL10 were associated interactively with risk of BPD in the northern Finnish population; however, this finding did not remain significant after correction for multiple testing and the finding was not replicated in the other populations.

Conclusions

We conclude that the analyzed SNPs within IL6, IL6R, IL6ST, IL10, TNF, and NR3C1 were not associated with BPD. Furthermore, there was no evidence that the studied SNPs directly contribute to the cord blood protein contents.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-014-0120-7) contains supplementary material, which is available to authorized users.

Stem cell therapy for neonatal diseases associated with preterm birth

In the last decades, the prevention and treatment of neonatal respiratory distress syndrome with antenatal steroids and surfactant replacement allowed the survival of infants born at extremely low gestational ages. These extremely preterm infants are highly vulnerable to the detrimental effects of oxidative stress and infection, and are prone to develop lung and brain diseases that eventually evolve in severe sequelae: The so-called new bronchopulmonary dysplasia (BPD) and the noncystic, diffuse form of periventricular leukomalacia (PVL). Tissue simplification and developmental arrest (larger and fewer alveoli and hypomyelination in the lungs and brain, respectively) appears to be the hallmark of these emerging sequelae, while fibrosis is usually mild and contributes to a lesser extent to their pathogenesis. New data suggest that loss of stem/progenitor cell populations in the developing brain and lungs may underlie tissue simplification. These observations constitute the basis for the application of stem cell-based protocols following extremely preterm birth. Transplantation of different cell types (including, but not limited to, mesenchymal stromal cells, endothelial progenitor cells, human amnion epithelial cells) could be beneficial in preterm infants for the prevention and/or treatment of BPD, PVL and other major sequelae of prematurity. However, before this new knowledge can be translated into clinical practice, several issues still need to be addressed in preclinical in vitro and in vivo models.

Disrupted lung development and bronchopulmonary dysplasia: opportunities for lung repair and regeneration

PURPOSE OF REVIEW

Advances in medical therapy have increased survival of extremely premature infants and changed the pathology of bronchopulmonary dysplasia (BPD) from one of acute lung injury to a disease of disrupted lung development. With this evolution, new questions emerge regarding the molecular mechanisms that control postnatal lung development, the effect of early disruptions of postnatal lung development on long-term lung function, and the existence of endogenous mechanisms that permit lung regeneration after injury.

RECENT FINDINGS

Recent data demonstrate that a significant component of alveolarization, the final stage of lung development, occurs postnatally. Further, clinical and experimental studies demonstrate that premature birth disrupts alveolarization, decreasing the gas exchange surface area of the lung and causing BPD. BPD is associated with significant short-term morbidity, and new longitudinal, clinical data demonstrate that survivors of BPD have long-standing deficits in lung function and may be at risk for the development of additional lung disease as adults. Unfortunately, current care is mainly supportive with few effective therapies that prevent or treat established BPD. These studies underscore the need to further elucidate the mechanisms that direct postnatal lung growth and develop innovative strategies to stimulate lung regeneration.

SUMMARY

Despite significant improvements in the care and survival of extremely premature infants, BPD remains a major clinical problem. Although efforts should remain focused on the prevention of preterm labor and BPD, novel research aimed at promoting postnatal alveolarization offers a unique opportunity to develop effective strategies to treat established BPD.

Association of a vascular endothelial growth factor polymorphism with the development of bronchopulmonary dysplasia in Japanese premature newborns

Our objective was to correlate vascular endothelial growth factor (VEGF) genetic polymorphisms with the risk of bronchopulmonary dysplasia (BPD) development in premature newborns. Fifty-five newborns with BPD (BPD: median gestational age [GA]: 27 weeks, birthweight [BW]: 786 g) and 42 newborns without BPD (non-BPD: median GA: 29 weeks, BW: 1,165 g), who were born at <32 weeks gestational age and were admitted to Kobe University Hospital, were included. BPD was defined as oxygen dependency at 36 weeks postmenstrual age. Genomic DNA was extracted from the umbilical cord, cord blood, or buccal mucosa. Six VEGF genotypes (-1498T > C, -1154G > A, -634C > G, -7C > T, 936C > T, and 1612G > A) were determined by DNA sequencing. Clinical characteristics, and allele and genotype frequencies of VEGF in the BPD and non-BPD groups were analyzed. G allele frequencies in -634C > G of the BPD group were significantly higher than in the non-BPD group (66.4% vs. 50%, P = 0.02). -634C > G genotype distributions differed significantly between the BPD and non-BPD groups (BPD: CC 7%/CG 53%/GG 40%; non-BPD: CC 24%/CG 52%/GG 24%; P = 0.04). Multivariate logistic regression showed that duration of ventilation, VEGF-634G > C G alleles, and male gender were independent risk factors for BPD. In conclusion, polymorphism VEGF -634C > G may influence the risk of BPD.

Altered lung development in bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is the main respiratory sequela of extreme prematurity. Its pathophysiology is complex, involving interactions between host and environment, likely to be significantly influenced by genetic factors. Thus, the clinical presentation and histological lesions have evolved over time, along with the reduction in neonatal injuries, and the care of more immature children. Impaired alveolar growth, however, is a lesion consistently observed in BPD, such that it is a key feature in BPD, and is even the dominant characteristic of the so-called "new" forms of BPD. This review describes the key molecular pathways that are believed to be involved in the genesis of BPD. Much of our understanding is based on animal models, but this is increasingly being enriched by genetic approaches, and long-term respiratory functional studies.

Genome-wide association mapping of acute lung injury in neonatal inbred mice

Reactive oxygen species (ROS) contribute to the pathogenesis of many acute and chronic pulmonary disorders, including bronchopulmonary dysplasia (BPD), a respiratory condition that affects preterm infants. However, the mechanisms of susceptibility to oxidant stress in neonatal lungs are not completely understood. We evaluated the role of genetic background in response to oxidant stress in the neonatal lung by exposing mice from 36 inbred strains to hyperoxia (95% O2) for 72 h after birth. Hyperoxia-induced lung injury was evaluated by using bronchoalveolar lavage fluid (BALF) analysis and pathology. Statistically significant interstrain variation was found for BALF inflammatory cells and protein (heritability estimates range: 33.6-55.7%). Genome-wide association mapping using injury phenotypes identified quantitative trait loci (QTLs) on chromosomes 1, 2, 4, 6, and 7. Comparative mapping of the chromosome 6 QTLs identified Chrm2 (cholinergic receptor, muscarinic 2, cardiac) as a candidate susceptibility gene, and mouse strains with a nonsynonymous coding single-nucleotide polymorphism (SNP) in Chrm2 that causes an amino acid substitution (P265L) had significantly reduced hyperoxia-induced inflammation compared to strains without the SNP. Further, hyperoxia-induced lung injury was significantly reduced in neonatal mice with targeted deletion of Chrm2, relative to wild-type controls. This study has important implications for understanding the mechanisms of oxidative lung injury in neonates.

Bronchopulmonary dysplasia - trends over three decades

OBJECTIVES

To describe the characteristics of bronchopulmonary dysplasia (BPD) and respiratory distress syndrome subjects, along with the trends in severity and mortality associated with BPD over the past three decades.

METHODS

Retrospective study of BPD and respiratory distress syndrome subjects born between 1980 and 2008, and admitted to Montreal Children's Hospital (Montreal, Quebec). Data were abstracted from hospital records.

RESULTS

Gestational age and birth weight were correlated with the occurrence of BPD with each additional week of gestation and 100 g in birth weight being associated with an OR of developing BPD of 0.77 and 0.89, respectively. BPD severity was associated with male sex, Apgar score and the occurrence of neonatal pneumonia. Significant trends were observed for lower mortality despite lower gestational age and birth weight, greater maternal age and multiple gestations.

CONCLUSION

Mortality from BPD has improved over the past three decades despite significant trends toward more pronounced prematurity and lower birth weights.