Searching for better animal models of BPD: a perspective

Pharmacotherapy of BPD: Current status & future perspectives

Bronchopulmonary dysplasia (BPD) is a disease exclusive to prematurity and has changed in its definition since Northway first described it in 1967. There have been countless clinical trials evaluating the efficacy of drugs in the treatment and prevention of BPD in human subjects, and an even larger number of animal studies. Despite these, only a handful of drugs are used at the bedside today, primarily due to the lack of consistent efficacy seen in clinical trials or due to reports of adverse effects. This review summarizes the list of the most commonly used drugs and emerging new therapies which target BPD and BPD-related pulmonary hypertension (BPD-PH), including those which have shown promise in human trials but are not yet used routinely.

Endothelial to mesenchymal transition in neonatal hyperoxic lung injury: role of sex as a biological variable

Bronchopulmonary dysplasia (BPD) is characterized by an arrest in alveolarization, abnormal vascular development, and variable interstitial fibroproliferation in the premature lung. Endothelial to mesenchymal transition (EndoMT) may be a source of pathological fibrosis in many organ systems. Whether EndoMT contributes to the pathogenesis of BPD is not known. We tested the hypothesis that pulmonary endothelial cells will show increased expression of EndoMT markers upon exposure to hyperoxia and that sex as a biological variable will modulate differences in expression. Wild-type (WT) and Cdh5-PAC CreERT2 (endothelial reporter) neonatal male and female mice (C57BL6) were exposed to hyperoxia (0.95 [Formula: see text]) either during the saccular stage of lung development (95% [Formula: see text]; postnatal day 1-5 [PND1-5]) or through the saccular and early alveolar stages of lung development (75% [Formula: see text]; PND1-14). Expression of EndoMT markers was measured in whole lung and endothelial cell mRNA. Sorted lung endothelial cells (from room air- and hyperoxia-exposed lungs) were subjected to bulk RNA-Seq. We show that exposure of the neonatal lung to hyperoxia leads to upregulation of key markers of EndoMT. Furthermore, using lung sc-RNA-Seq data from neonatal lung we were able to show that all endothelial cell subpopulations including the lung capillary endothelial cells show upregulation of EndoMT-related genes. Markers related to EndoMT are upregulated in the neonatal lung upon exposure to hyperoxia and show sex-specific differences. Mechanisms mediating EndoMT in the injured neonatal lung can modulate the response of the neonatal lung to hyperoxic injury and need further investigation.NEW & NOTEWORTHY We show that neonatal hyperoxia exposure increased EndoMT markers in the lung endothelial cells and this biological process exhibits sex-specific differences.

Oxygen and mechanical stretch in the developing lung: risk factors for neonatal and pediatric lung disease

Chronic airway diseases, such as wheezing and asthma, remain significant sources of morbidity and mortality in the pediatric population. This is especially true for preterm infants who are impacted both by immature pulmonary development as well as disproportionate exposure to perinatal insults that may increase the risk of developing airway disease. Chronic pediatric airway disease is characterized by alterations in airway structure (remodeling) and function (increased airway hyperresponsiveness), similar to adult asthma. One of the most common perinatal risk factors for development of airway disease is respiratory support in the form of supplemental oxygen, mechanical ventilation, and/or CPAP. While clinical practice currently seeks to minimize oxygen exposure to decrease the risk of bronchopulmonary dysplasia (BPD), there is mounting evidence that lower levels of oxygen may carry risk for development of chronic airway, rather than alveolar disease. In addition, stretch exposure due to mechanical ventilation or CPAP may also play a role in development of chronic airway disease. Here, we summarize the current knowledge of the impact of perinatal oxygen and mechanical respiratory support on the development of chronic pediatric lung disease, with particular focus on pediatric airway disease. We further highlight mechanisms that could be explored as potential targets for novel therapies in the pediatric population.

Neonatal hyperoxia induces activated pulmonary cellular states and sex-dependent transcriptomic changes in a model of experimental bronchopulmonary dysplasia

Hyperoxia disrupts lung development in mice and causes bronchopulmonary dysplasia (BPD) in neonates. To investigate sex-dependent molecular and cellular programming involved in hyperoxia, we surveyed the mouse lung using single cell RNA sequencing (scRNA-seq), and validated our findings in human neonatal lung cells in vitro. Hyperoxia-induced inflammation in alveolar type (AT) 2 cells gave rise to damage-associated transient progenitors (DATPs). It also induced a new subpopulation of AT1 cells with reduced expression of growth factors normally secreted by AT1 cells, but increased mitochondrial gene expression. Female alveolar epithelial cells had less EMT and pulmonary fibrosis signaling in hyperoxia. In the endothelium, expansion of Car4+ EC (Cap2) was seen in hyperoxia along with an emergent subpopulation of Cap2 with repressed VEGF signaling. This regenerative response was increased in females exposed to hyperoxia. Mesenchymal cells had inflammatory signatures in hyperoxia, with a new distal interstitial fibroblast subcluster characterized by repressed lipid biosynthesis and a transcriptomic signature resembling myofibroblasts. Hyperoxia-induced gene expression signatures in human neonatal fibroblasts and alveolar epithelial cells in vitro resembled mouse scRNA-seq data. These findings suggest that neonatal exposure to hyperoxia programs distinct sex-specific stem cell progenitor and cellular reparative responses that underpin lung remodeling in BPD.

Lung Development in a Dish: Models to Interrogate the Cellular Niche and the Role of Mechanical Forces in Development

Over the past decade, emphasis has been placed on recapitulating in vitro the architecture and multicellular interactions found in organs in vivo [1, 2]. Whereas traditional reductionist approaches to in vitro models enable teasing apart the precise signaling pathways, cellular interactions, and response to biochemical and biophysical cues, model systems that incorporate higher complexity are needed to ask questions about physiology and morphogenesis at the tissue scale. Significant advancements have been made in establishing in vitro models of lung development to understand cell-fate specification, gene regulatory networks, sexual dimorphism, three-dimensional organization, and how mechanical forces interact to drive lung organogenesis [3-5]. In this chapter, we highlight recent advances in the rapid development of various lung organoids, organ-on-a-chip models, and whole lung ex vivo explant models currently used to dissect the roles of these cellular signals and mechanical cues in lung development and potential avenues for future investigation (Fig. 3.1).

Remarkable sex-specific differences at single-cell resolution in neonatal hyperoxic lung injury

Exposure to supraphysiological concentrations of oxygen (hyperoxia) predisposes to bronchopulmonary dysplasia (BPD), which is characterized by abnormal alveolarization and pulmonary vascular development, in preterm neonates. Neonatal hyperoxia exposure is used to recapitulate the phenotype of human BPD in murine models. Male sex is considered an independent predictor for the development of BPD, but the main mechanisms underlying sexually dimorphic outcomes are unknown. Our objective was to investigate sex-specific and cell-type specific transcriptional changes that drive injury in the neonatal lung exposed to hyperoxia at single-cell resolution and delineate the changes in cell-cell communication networks in the developing lung. We used single-cell RNA sequencing (scRNAseq) to generate transcriptional profiles of >35,000 cells isolated from the lungs of neonatal male and female C57BL/6 mice exposed to 95% [Formula: see text] between PND1-5 (saccular stage of lung development) or normoxia and euthanized at PND7 (alveolar stage of lung development). ScRNAseq identified 22 cell clusters with distinct populations of endothelial, epithelial, mesenchymal, and immune cells. Our data identified that the distal lung vascular endothelium (composed of aerocytes and general capillary endothelial cells) is exquisitely sensitive to hyperoxia exposure with the emergence of an intermediate capillary endothelial population with both general capillaries (gCap) and aerocytes or alveolar capillaries (aCap) markers. We also identified a myeloid-derived suppressor cell population from the lung neutrophils. Sex-specific differences were evident in all lung cell subpopulations but were striking among the lung immune cells. Finally, we identified that the specific intercellular communication networks and the ligand-receptor pairs that are impacted by neonatal hyperoxia exposure.

Headway and the remaining hurdles of mesenchymal stem cells therapy for bronchopulmonary dysplasia

Objective

Preterm infants are at a high risk of developing BPD. Although progression in neonatal care has improved, BPD still causes significant morbidity and mortality, which can be attributed to the limited therapeutic choices for BPD. This review discusses the potential of MSC in treating BPD as well as their hurdles and possible solutions.

Data Sources

The search for data was not limited to any sites but was mostly performed on all clinical trials available in ClinicalTrials.gov as well as on PubMed by applying the following keywords: lung injury, preterm, inflammation, neonatal, bronchopulmonary dysplasia and mesenchymal stem cells.

Study Selections

The articles chosen for this review were collectively determined to be relevant and appropriate in discussing MSC not only as a potential treatment strategy for curbing the incidence of BPD but also including insights on problems regarding MSC treatment for BPD.

Results

Clinical trials regarding the use of MSC for BPD had good results but also illustrated insights on problems to be addressed in the future regarding the treatment strategy. Despite that, the clinical trials had mostly favourable reviews.

Conclusion

With BPD existing as a constant threat and there being no permanent solutions, the idea of regenerative medicine such as MSC may prove to be a breakthrough strategy when it comes to treating BPD. The success in clinical trials led to the formulation of prospective MSC‐derived products such as PNEUMOSTEM®, and there is the possibility of a stem cell medication and permanent treatment for BPD in the near future.

Group 3 Pulmonary Hypertension: From Bench to Bedside

Pulmonary hypertension (PH) because of chronic lung disease is categorized as Group 3 PH in the most recent classification system. Prevalence of these diseases is increasing over time, creating a growing need for effective therapeutic options. Recent approval of the first pulmonary arterial hypertension therapy for the treatment of Group 3 PH related to interstitial lung disease represents an encouraging advancement. This review focuses on molecular mechanisms contributing to pulmonary vasculopathy in chronic hypoxia, the pathology and epidemiology of Group 3 PH, the right ventricular dysfunction observed in this population and clinical trial data that inform the use of pulmonary vasodilators in Group 3 PH.

Sphingosine kinase 1 regulates lysyl oxidase through STAT3 in hyperoxia-mediated neonatal lung injury

INTRODUCTION

Neonatal lung injury as a consequence of hyperoxia (HO) therapy and ventilator care contribute to the development of bronchopulmonary dysplasia (BPD). Increased expression and activity of lysyl oxidase (LOX), a key enzyme that cross-links collagen, was associated with increased sphingosine kinase 1 (SPHK1) in human BPD. We, therefore, examined closely the link between LOX and SPHK1 in BPD.

METHOD

The enzyme expression of SPHK1 and LOX were assessed in lung tissues of human BPD using immunohistochemistry and quantified (Halo). In vivo studies were based on Sphk1^-/- and matched wild type (WT) neonatal mice exposed to HO while treated with PF543, an inhibitor of SPHK1. In vitro mechanistic studies used human lung microvascular endothelial cells (HLMVECs).

RESULTS

Both SPHK1 and LOX expressions were increased in lungs of patients with BPD. Tracheal aspirates from patients with BPD had increased LOX, correlating with sphingosine-1-phosphate (S1P) levels. HO-induced increase of LOX in lungs were attenuated in both Sphk1^-/- and PF543-treated WT mice, accompanied by reduced collagen staining (sirius red). PF543 reduced LOX activity in both bronchoalveolar lavage fluid and supernatant of HLMVECs following HO. In silico analysis revealed STAT3 as a potential transcriptional regulator of LOX. In HLMVECs, following HO, ChIP assay confirmed increased STAT3 binding to LOX promoter. SPHK1 inhibition reduced phosphorylation of STAT3. Antibody to S1P and siRNA against SPNS2, S1P receptor 1 (S1P₁) and STAT3 reduced LOX expression.

CONCLUSION

HO-induced SPHK1/S1P signalling axis plays a critical role in transcriptional regulation of LOX expression via SPNS2, S1P₁ and STAT3 in lung endothelium.

Does Duration Off Respiratory Support Prior to Discharge from NICU Predict Hospital Readmission among Extremely Low Gestational Age Neonates?

OBJECTIVE

Our objective was to determine if the duration off respiratory support prior to discharge home from the neonatal intensive care unit (NICU) would impact hospital readmission rates among extremely low gestational age neonates (ELGAN).

STUDY DESIGN

In this retrospective chart review, we examined readmission rates for ELGAN admitted to the Montefiore-Weiler NICU between 2013 and 2015.

RESULTS

Of 140 infants born at <29 weeks' gestational age, 30 (21%) of these infants were subsequently readmitted within 90 days, primarily for respiratory complaints. Readmitted infants were born at an earlier gestational age (median = 26 weeks; interquartile range [IQR]: 24-27 weeks) compared to infants who did not require readmission (median = 27 weeks; IQR: 25-28 weeks), p = 0.03. Birth weights were smaller among infants who required readmission, 800 ± 248 g compared to 910 ± 214 g (p = 0.02). Infants with Hispanic ethnicity and those discharged during the spring season were likely to be readmitted. Duration off respiratory support prior to discharge did not predict 90-day readmission rates. Lower gestational age and birth weight were associated with higher rates of readmissions after NICU discharge.

CONCLUSION

Duration off and invasiveness of respiratory support prior to discharge did not predict risk of 90-day readmission nor did discharge during months with traditionally higher prevalence of respiratory viruses.

Factors associated with recurrent wheezing in the first year of life among premature newborns from Neonatal Intensive Care Units

Abstract Objectives: to determine the prevalence and factors associated with recurrent wheezing in the first year of life among premature newborns from Neonatal Intensive Care Units, in the city of Montes Claros, northern Minas Gerais. Methods: cross-sectional study, with data collection from medical records of a follow-up clinic, interviews with mothers and, eventually, search in hospital records. Bivariate analyzes were carried out between sociodemographic and clinical characteristics and recurrent wheezing. Variables associated up to the level of 20% were analyzed by binary logistic regression, and associations defined by the Odds Ratio and respective 95% confidence intervals. Only variables associated with a 5% significance level were maintained in the final model of logistic regression. Results: among 277 infants studied, about one fifth (21.3%) were extremely low birth weight preterm and more than half (60.7%) had birth weight below 1500 grams. The prevalence of recurrent wheezing was 14.4% (CI95% = 10.3-18.4). Mechanical ventilation (OR = 2.12; CI95% = 1.09-4.76; p = 0.030) and oxygen therapy time ≥ 15 days (OR = 2.49; CI95%= 1.12-5.00; p = 0.010) were the risk factors for the event. Conclusions: there is a high prevalence of recurrent wheezing in the evaluated group and the associated variables reiterate the risk of prolonged oxygen therapy and mechanical ventilation for premature newborns.

Characterization of the innate immune response in a novel murine model mimicking bronchopulmonary dysplasia

BACKGROUND

Bronchopulmonary dysplasia (BPD), the most common complication of prematurity, arises from various factors that compromise lung development, including oxygen and inflammation. Hyperoxia has been used to mimic the disease in newborn rodents. The use of a second hit to induce systemic inflammation has been suggested as an added strategy to better mimic the inflammatory aspect of BPD. Here we report a novel 2 hit (2HIT) BPD model with in-depth characterization of the innate immune response, enabling mechanistic studies of therapies with an immunomodulatory component.

METHODS

C57BL/6N mice were exposed to 85% O₂ from postnatal day (P)1 to P7, and received postnatally (P3) Escherichia coli LPS. At various timepoints, immune activation in the lung and at the systemic level was analyzed by fluorescence-activated cell sorting (FACS), and gene and protein expressions.

RESULTS

2HIT mice showed fewer alveoli, increased lung compliance, and right ventricular hypertrophy. A transient proinflammatory cytokine response was observed locally and systemically. Type 2 anti-inflammatory cytokine expression was decreased in the lung together with the number of mature alveolar macrophages. Simultaneously, a Siglec-F intermediate macrophage population emerged.

CONCLUSION

This study provides long-term analysis of the 2HIT model, suggesting impairment of type 2 cytokine environment and altered alveolar macrophage profile in the lung.

IMPACT

We have developed a novel 2HIT mouse BPD model with postnatal LPS and hyperoxia exposure, which enables mechanistic studies of potential therapeutic strategies with an immunomodulatory component. This is the first report of in-depth characterization of the lung injury and recovery describing the evolution of the innate immune response in a standardized mouse model for experimental BPD with postnatal LPS and hyperoxia exposure. The 2HIT model has the potential to help understand the link between inflammation and impaired lung development, and will enable testing of new therapies in a short and more robust manner.

Hyperoxia-induced bronchopulmonary dysplasia: better models for better therapies

Bronchopulmonary dysplasia (BPD) is a chronic lung disease caused by exposure to high levels of oxygen (hyperoxia) and is the most common complication that affects preterm newborns. At present, there is no cure for BPD. Infants can recover from BPD; however, they will suffer from significant morbidity into adulthood in the form of neurodevelopmental impairment, asthma and emphysematous changes of the lung. The development of hyperoxia-induced lung injury models in small and large animals to test potential treatments for BPD has shown some success, yet a lack of standardization in approaches and methods makes clinical translation difficult. In vitro models have also been developed to investigate the molecular pathways altered during BPD and to address the pitfalls associated with animal models. Preclinical studies have investigated the efficacy of stem cell-based therapies to improve lung morphology after damage. However, variability regarding the type of animal model and duration of hyperoxia to elicit damage exists in the literature. These models should be further developed and standardized, to cover the degree and duration of hyperoxia, type of animal model, and lung injury endpoint, to improve their translational relevance. The purpose of this Review is to highlight concerns associated with current animal models of hyperoxia-induced BPD and to show the potential of in vitro models to complement in vivo studies in the significant improvement to our understanding of BPD pathogenesis and treatment. The status of current stem cell therapies for treatment of BPD is also discussed. We offer suggestions to optimize models and therapeutic modalities for treatment of hyperoxia-induced lung damage in order to advance the standardization of procedures for clinical translation.

Intratracheal administration of mesenchymal stem cell-derived extracellular vesicles reduces lung injuries in a chronic rat model of bronchopulmonary dysplasia

Early therapeutic effect of intratracheally (IT)-administered extracellular vesicles secreted by mesenchymal stem cells (MSC-EVs) has been demonstrated in a rat model of bronchopulmonary dysplasia (BPD) involving hyperoxia exposure in the first 2 postnatal weeks. The aim of this study was to evaluate the protective effects of IT-administered MSC-EVs in the long term. EVs were produced from MSCs following GMP standards. At birth, rats were distributed in three groups: (a) animals raised in ambient air for 6 weeks (n = 10); and animals exposed to 60% hyperoxia for 2 weeks and to room air for additional 4 weeks and treated with (b) IT-administered saline solution (n = 10), or (c) MSC-EVs (n = 10) on postnatal days 3, 7, 10, and 21. Hyperoxia exposure produced significant decreases in total number of alveoli, total surface area of alveolar air spaces, and proliferation index, together with increases in mean alveolar volume, mean linear intercept and fibrosis percentage; all these morphometric changes were prevented by MSC-EVs treatment. The medial thickness index for <100 µm vessels was higher for hyperoxia-exposed/sham-treated than for normoxia-exposed rats; MSC-EV treatment significantly reduced this index. There were no significant differences in interstitial/alveolar and perivascular F4/8-positive and CD86-positive macrophages. Conversely, hyperoxia exposure reduced CD163-positive macrophages both in interstitial/alveolar and perivascular populations and MSC-EV prevented these hyperoxia-induced reductions. These findings further support that IT-administered EVs could be an effective approach to prevent/treat BPD, ameliorating the impaired alveolarization and pulmonary artery remodeling also in a long-term model. M2 macrophage polarization could play a role through anti-inflammatory and proliferative mechanisms.

Pulmonary immune cell transcriptome changes in double-hit model of BPD induced by chorioamnionitis and postnatal hyperoxia

BACKGROUND

Preterm infants with bronchopulmonary dysplasia (BPD) have lifelong increased risk of respiratory morbidities associated with environmental pathogen exposure and underlying mechanisms are poorly understood. The resident immune cells of the lung play vital roles in host defense. However, the effect of perinatal events associated with BPD on pulmonary-specific immune cells is not well understood.

METHODS

We used a double-hit model of BPD induced by prenatal chorioamnionitis followed by postnatal hyperoxia, and performed a global transcriptome analysis of all resident pulmonary immune cells.

RESULTS

We show significant up-regulation of genes involved in chemokine-mediated signaling and immune cell chemotaxis, and down-regulation of genes involved in multiple T lymphocyte functions. Multiple genes involved in T cell receptor signaling are downregulated and Cd8a gene expression remains downregulated at 2 months of age in spite of recovery in normoxia for 6 weeks. Furthermore, the proportion of CD8a+CD3+ pulmonary immune cells is decreased.

CONCLUSIONS

Our study has highlighted that perinatal lung inflammation in a double-hit model of BPD results in short- and long-term dysregulation of genes associated with the pulmonary T cell receptor signaling pathway, which may contribute to increased environmental pathogen-associated respiratory morbidities seen in children and adults with BPD.

IMPACT

In a translationally relevant double-hit model of BPD induced by chorioamnionitis and postnatal hyperoxia, we identified pulmonary immune cell-specific transcriptomic changes and showed that T cell receptor signaling genes are downregulated in short term and long term. This is the first comprehensive report delineating transcriptomic changes in resident immune cells of the lung in a translationally relevant double-hit model of BPD. Our study identifies novel resident pulmonary immune cell-specific targets for potential therapeutic modulation to improve short- and long-term respiratory health of preterm infants with BPD.

A Review of Placenta and Umbilical Cord-Derived Stem Cells and the Immunomodulatory Basis of Their Therapeutic Potential in Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is a devastating lung disorder of preterm infants as a result of an aberrant reparative response following exposures to various antenatal and postnatal insults. Despite sophisticated medical treatment in this modern era, the incidence of BPD remains unabated. The current strategies to prevent and treat BPD have met with limited success. The emergence of stem cell therapy may be a potential breakthrough in mitigating this complex chronic lung disorder. Over the last two decades, the human placenta and umbilical cord have gained increasing attention as a highly potential source of stem cells. Placenta-derived stem cells (PDSCs) and umbilical cord-derived stem cells (UCDSCs) display several advantages such as immune tolerance and are generally devoid of ethical constraints, in addition to their stemness qualities. They possess the characteristics of both embryonic and mesenchymal stromal/stem cells. Recently, there are many preclinical studies investigating the use of these cells as therapeutic agents in neonatal disease models for clinical applications. In this review, we describe the preclinical and clinical studies using PDSCs and UCDSCs as treatment in animal models of BPD. The source of these stem cells, routes of administration, and effects on immunomodulation, inflammation and regeneration in the injured lung are also discussed. Lastly, a brief description summarized the completed and ongoing clinical trials using PDSCs and UCDSCs as therapeutic agents in preventing or treating BPD. Due to the complexity of BPD, the development of a safe and efficient therapeutic agent remains a major challenge to both clinicians and researchers.

Impact of litter size on survival, growth and lung alveolarization of newborn mouse pups

BACKGROUND

Lung alveolarization, the development of the alveoli, is disturbed in preterm infants with bronchopulmonary dysplasia (BPD), the most common complication of preterm birth. Animal models based on oxygen toxicity to the developing mouse lung are used to understand the mechanisms of stunted alveolarization in BPD, and to develop new medical management strategies for affected infants. The toxicity of genetic and pharmacological interventions, together with maternal cannibalism, reduce mouse litter sizes in experimental studies. The impact of litter size on normal and stunted lung alveolarization is unknown, but may influence data interpretation. The aim of the study was to assess the impact of litter size on normal and oxygen-stunted lung alveolarization in mice.

METHODS

BPD was experimentally modelled in newborn C57BL/6J mice by exposure to 85% O₂ in the inspired air for the first 14 days of post-natal life. Perturbations to mouse lung architecture were assessed by design-based stereology, in which the alveolar density, total number of alveoli, gas-exchange surface area, and the septal thickness were estimated.

RESULTS

Litter sizes of a single mouse were not viable to post-natal day 14. Normal lung alveolarization was comparable in mouse pups in litters of 2, 4, 6, and 8 pups per litter. Hyperoxia was equally effective at stunting lung alveolarization in mouse pups in litters of 2, 4, 6, and 8 pups per litter.

CONCLUSIONS

Studies on normal lung alveolarization as well as alveolarization stunted by oxygen toxicity can be undertaken in mouse litters as small as two pups, and as large as eight pups. There is no evidence to suggest that data cannot be compared within and between litters of two to eight mouse pups.

Early angiogenic proteins associated with high risk for bronchopulmonary dysplasia and pulmonary hypertension in preterm infants

Early pulmonary vascular disease in preterm infants is associated with the subsequent development of bronchopulmonary dysplasia (BPD) and pulmonary hypertension (PH); however, mechanisms that contribute to or identify infants with increased susceptibility for BPD and/or PH are incompletely understood. Therefore, we tested if changes in circulating angiogenic peptides during the first week of life are associated with the later development of BPD and/or PH. We further sought to determine alternate peptides and related signaling pathways with the risk for BPD or PH. We prospectively enrolled infants with gestational age <34 wk and collected blood samples during their first week of life. BPD and PH were assessed at 36 wk postmenstrual age. Samples were assayed for each of the 1,121 peptides included in the SOMAscan scan technology, with subsequent pathway analysis. Of 102 infants in the study, 82 had BPD, and 13 had PH. Multiple angiogenic proteins (PF-4, VEGF121, ANG-1, bone morphogenetic protein 10 [BMP10], hepatocyte growth factor (HGF), ANG-2) were associated with the subsequent diagnosis of BPD; and FGF-19, PF-4, connective tissue activating peptide (CTAP)-III, and PDGF-AA levels were associated with BPD severity. Early increases in BMP10 was strongly associated with the late risk for BPD and PH. We found that early alterations of circulating angiogenic peptides and others were associated with the subsequent development of BPD. We further identified peptides that were associated with BPD severity and BPD-associated PH, including BMP10. We speculate that proteomic biomarkers during the first week of life may identify infants at risk for BPD and/or PH to enhance care and research.

Using Experimental Models to Identify Pathogenic Pathways and Putative Disease Management Targets in Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is a common and serious complication of preterm birth. Limited pharmacological and other medical interventions are currently available for the management of severely affected, very preterm infants. BPD can be modelled in preclinical studies using experimental animals, and experimental animal models have been extremely valuable in the development of hallmark clinical management strategies for BPD, including pulmonary surfactant replacement and single-course antenatal corticosteroids. A gradual move away from large animal models of BPD in favor of term-born rodents has facilitated the identification of a multitude of new mechanisms of normal and stunted lung development, but this has also potentially limited the utility of experimental animal models for the identification of pathogenic pathways and putative disease management targets in BPD. Indeed, more recent pharmacological interventions for the management of BPD that have been validated in randomized controlled trials have relied very little on preclinical data generated in experimental animal models. While rodent-based models of BPD have tremendous advantages in terms of the availability of genetic tools, they also have considerable drawbacks, including limited utility for studying breathing mechanics, gas exchange, and pulmonary hemodynamics; and they have a less relevant clinical context where lung prematurity and a background of infection are now rarely present in the pathophysiology under study. There is a pressing need to refine existing models to better recapitulate pathological processes at play in affected infants, in order to better evaluate new candidate pharmacological and other interventions for the management of BPD.

The expression of miR-125b in Nrf2-silenced A549 cells exposed to hyperoxia and its relationship with apoptosis

Bronchopulmonary dysplasia (BPD) is a chronic lung disease that affects the quality of life of infants. At present, premature exposure to hyperoxia for extended periods of time is believed to affect the development of lung tissue and vascularity, resulting in BPD. The oxidative stress caused by hyperoxia exposure is an important risk factor for BPD in premature infants. Nuclear factor E2‐related factor 2 (Nrf2) is an important regulator of antioxidant mechanisms. As a microRNA, microRNA‐125b (miR‐125b) plays an important role in cell proliferation, differentiation and apoptosis. Although the Nrf2/ARE pathway has been extensively studied, little is known about the regulatory role of microRNAs in Nrf2 expression. In this study, the expression levels of Nrf2 and miR‐125b in the lung tissues of premature Sprague Dawley (SD) rats and A549 cells exposed to hyperoxia were detected by quantitative real‐time polymerase chain reaction (qRT‐PCR), and the apoptosis of A549 cells was detected by flow cytometry. The results showed that Nrf2 and miRNA‐125b in the lung tissues of premature rats increased significantly upon exposure to hyperoxia and played a protective role. Nrf2 was suppressed by small interfering RNA (siRNA) in A549 cells, miR‐125b was similarly inhibited, and apoptosis was significantly increased. These results suggest that miR‐125b helps protect against BPD as a downstream target of Nrf2.

Non-invasive measurements of respiratory system mechanical properties by the forced oscillation technique in spontaneously breathing, mixed-breed, normal term lambs from birth to five months of age

OBJECTIVE

To provide a non-invasive approach to monitoring lung function in spontaneously breathing lambs, from birth to five months of life, by the forced oscillation technique (FOT). This report describes the experimental set-up, data processing, and identification of normal predicted values of resistance (Rrs) and reactance (Xrs) of the respiratory system, along with normal bronchodilator response for bronchial reversibility testing.

APPROACH

Rrs and Xrs at 5, 11, and 19 Hz were measured monthly for five months in 20 normal term lambs that breathed spontaneously. In seven lambs, repeated measurements also were made within the first month of life (at 3, 7, 14, and 21 d of life). We determined the repeatability and reproducibility of the measurements and characterized the relationship between lung mechanics and age, sex, and body dimensions, using regression analysis, and measured changes in lung mechanics in response to inhaled bronchodilator.

MAIN RESULTS

The measurements provided repeatable and reproducible data. Rrs decreased, whereas Xrs increased, with growth from birth through the first two months of life, after which no statistically significant differences were detected. We identified normal value equations for Rrs and Xrs and for each of the measured anthropometric variables. Respiratory system mechanics were not affected by the bronchodilator.

SIGNIFICANCE

The FOT provides reliable non-invasive measurement of respiratory system mechanics in spontaneously breathing term lambs from birth to five months of age. The methods and normal reference values defined in this study will facilitate testing of the pathophysiological consequences of preterm birth and prolonged respiratory support on respiratory system mechanics.

Effects of hyperoxia on alveolar and pulmonary vascular development in germ-free mice

Airway microbial dysbiosis is associated with subsequent bronchopulmonary dysplasia (BPD) development in very preterm infants. However, the relationship of airway microbiome in normal pulmonary development has not been defined. To better understand the role of the airway microbiome, we compared normal and abnormal alveolar and pulmonary vascular development in mice with or without a microbiome. We hypothesized that the lungs of germ-free (GF) mice would have an exaggerated phenotypic response to hyperoxia compared with non-germ-free (NGF) mice. With the use of a novel gnotobiotic hyperoxia chamber, GF and NGF mice were exposed to either normoxia or hyperoxia. Alveolar morphometry, pulmonary mechanics, echocardiograms, inflammatory markers, and measures of pulmonary hypertension were studied. GF and NGF mice in normoxia showed no difference, whereas GF mice in hyperoxia showed protected lung structure and mechanics and decreased markers of inflammation compared with NGF mice. We speculate that an increase in abundance of pathogenic bacteria in NGF mice may play a role in BPD pathogenesis by regulating the proinflammatory signaling and neutrophilic inflammation in lungs. Manipulation of the airway microbiome may be a potential therapeutic intervention in BPD and other lung diseases.

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

Bronchopulmonary dysplasia (BPD) is the most common cause of morbidity and mortality in preterm infants. A key histopathological feature of BPD is stunted late lung development, where the process of alveolarization-the generation of alveolar gas exchange units-is impeded, through mechanisms that remain largely unclear. As such, there is interest in the clarification both of the pathomechanisms at play in affected lungs, and the mechanisms of de novo alveoli generation in healthy, developing lungs. A better understanding of normal and pathological alveolarization might reveal opportunities for improved medical management of affected infants. Furthermore, disturbances to the alveolar architecture are a key histopathological feature of several adult chronic lung diseases, including emphysema and fibrosis, and it is envisaged that knowledge about the mechanisms of alveologenesis might facilitate regeneration of healthy lung parenchyma in affected patients. To this end, recent efforts have interrogated clinical data, developed new-and refined existing-in vivo and in vitro models of BPD, have applied new microscopic and radiographic approaches, and have developed advanced cell-culture approaches, including organoid generation. Advances have also been made in the development of other methodologies, including single-cell analysis, metabolomics, lipidomics, and proteomics, as well as the generation and use of complex mouse genetics tools. The objective of this review is to present advances made in our understanding of the mechanisms of lung alveolarization and BPD over the period 1 January 2017-30 June 2019, a period that spans the 50th anniversary of the original clinical description of BPD in preterm infants.

Anti-sFlt-1 Therapy Preserves Lung Alveolar and Vascular Growth in Antenatal Models of Bronchopulmonary Dysplasia

RATIONALE

Pregnancies complicated by antenatal stress, including preeclampsia (PE) and chorioamnionitis (CA), increase the risk for bronchopulmonary dysplasia (BPD) in preterm infants, but biologic mechanisms linking prenatal factors with BPD are uncertain. Levels of sFlt-1 (soluble fms-like tyrosine kinase 1), an endogenous antagonist to VEGF (vascular endothelial growth factor), are increased in amniotic fluid and maternal blood in PE and associated with CA.

OBJECTIVES

Because impaired VEGF signaling has been implicated in the pathogenesis of BPD, we hypothesized that fetal exposure to sFlt-1 decreases lung growth and causes abnormal lung structure and pulmonary hypertension during infancy.

METHODS

To test this hypothesis, we studied the effects of anti-sFlt-1 monoclonal antibody (mAb) treatment on lung growth in two established antenatal models of BPD that mimic PE and CA induced by intraamniotic (i.a.) injections of sFlt-1 or endotoxin, respectively. In experimental PE, mAb was administered by three different approaches, including antenatal treatment by either i.a. instillation or maternal uterine artery infusion, or by postnatal intraperitoneal injections.

RESULTS

With each strategy, mAb therapy improved infant lung structure as assessed by radial alveolar count, vessel density, right ventricular hypertrophy, and lung function. As found in the PE model, the adverse lung effects of i.a. endotoxin were also reduced by antenatal or postnatal mAb therapy.

CONCLUSIONS

We conclude that treatment with anti-sFlt-1 mAb preserves lung structure and function and prevents right ventricular hypertrophy in two rat models of BPD of antenatal stress and speculate that early mAb therapy may provide a novel strategy for the prevention of BPD.

Mouse genetic background impacts susceptibility to hyperoxia-driven perturbations to lung maturation

BACKGROUND

The laboratory mouse is widely used in preclinical models of bronchopulmonary dysplasia, where lung alveolarization is stunted by exposure of pups to hyperoxia. Whether the diverse genetic backgrounds of different inbred mouse strains impacts lung development in newborn mice exposed to hyperoxia has not been systematically assessed.

METHODS

Hyperoxia (85% O₂ , 14 days)-induced perturbations to lung alveolarization were assessed by design-based stereology in C57BL/6J, BALB/cJ, FVB/NJ, C3H/HeJ, and DBA/2J inbred mouse strains. The expression of components of the lung antioxidant machinery was assessed by real-time reverse transcriptase polymerase chain reaction and immunoblot.

RESULTS

Hyperoxia-reduced lung alveolar density in all five mouse strains to different degrees (C57BL/6J, 64.8%; FVB/NJ, 47.4%; BALB/cJ, 46.4%; DBA/2J, 45.9%; and C3H/HeJ, 35.9%). Hyperoxia caused a 94.5% increase in mean linear intercept in the C57BL/6J strain, whilst the C3H/HeJ strain was the least affected (31.6% increase). In contrast, hyperoxia caused a 65.4% increase in septal thickness in the FVB/NJ strain, where the C57BL/6J strain was the least affected (30.3% increase). The expression of components of the lung antioxidant machinery in response to hyperoxia was strain dependent, with the C57BL/6J strain exhibiting the most dramatic engagement. Baseline expression levels of components of the lung antioxidant systems were different in the five mouse strains studied, under both normoxic and hyperoxic conditions.

CONCLUSION

The genetic background of laboratory mouse strains dramatically influenced the response of the developing lung to hyperoxic insult. This might be explained, at least in part, by differences in how antioxidant systems are engaged by different mouse strains after hyperoxia exposure.

Hyperoxia-induced lung structure-function relation, vessel rarefaction, and cardiac hypertrophy in an infant rat model

BACKGROUND

Hyperoxia-induced bronchopulmonary dysplasia (BPD) models are essential for better understanding and impacting on long-term pulmonary, cardiovascular, and neurological sequelae of this chronic disease. Only few experimental studies have systematically compared structural alterations with lung function measurements.

METHODS

In three separate and consecutive series, Sprague-Dawley infant rats were exposed from day of life (DOL) 1 to 19 to either room air (0.21; controls) or to fractions of inspired oxygen (FiO2) of 0.6, 0.8, and 1.0. Our primary outcome parameters were histopathologic analyses of heart, lungs, and respiratory system mechanics, assessed via image analysis tools and the forced oscillation technique, respectively.

RESULTS

Exposure to FiO2 of 0.8 and 1.0 resulted in significantly lower body weights and elevated coefficients of lung tissue damping (G) and elastance (H) when compared with controls. Hysteresivity (η) was lower due to a more pronounced increase of H when compared with G. A positive structure-function relation was demonstrated between H and the lung parenchymal content of α-smooth muscle actin (α-SMA) under hyperoxic conditions. Moreover, histology and morphometric analyses revealed alveolar simplification, fewer pulmonary arterioles, increased α-SMA content in pulmonary vessels, and right heart hypertrophy following hyperoxia. Also, in comparison to controls, hyperoxia resulted in significantly lower plasma levels of vascular endothelial growth factor (VEGF). Lastly, rats in hyperoxia showed hyperactive and a more explorative behaviour.

CONCLUSIONS

Our in vivo infant rat model mimics clinical key features of BPD. To the best of our knowledge, this is the first BPD rat model demonstrating an association between lung structure and function. Moreover, we provide additional evidence that infant rats subjected to hyperoxia develop rarefaction of pulmonary vessels, augmented vascular α-SMA, and adaptive cardiac hypertrophy. Thus, our model provides a clinically relevant tool to further investigate diseases related to O2 toxicity and to evaluate novel pharmacological treatment strategies.

Bronchopulmonary Dysplasia: An Update on Experimental Therapeutics

Bronchopulmonary dysplasia (BPD) is a chronic inflammatory lung disease that affects thousands of newborns and infants every year. Although it is accepted that BPD results from lung damage and inflammation triggered by mechanical ventilation and hyperoxia, the causes and molecular events leading to lung damage and arrested development remain unknown. While recent advances in neonatal care have improved the survival of very low-weight infants, the rates of BPD have not improved accordingly. This is mainly due to our limited understanding of the disease’s pathogenesis and the effective therapeutic options available. Current therapeutics for BPD involve ventilation management, steroid treatment, and administration of various agents, such as pulmonary surfactant, caffeine, vitamin A, nitric oxide, and stem cells. However, the efficacy of these agents in preventing and ameliorating BPD symptoms varies depending on the populations studied and the disease stage. As the field moves towards personalised therapeutic approaches, this review summarises clinical and experimental studies conducted in various models, aiming to increase understanding of the cellular and molecular mechanisms by which these agents can prevent or treat BPD. Due to the increasing number of extremely premature infants, it is imperative that we continue to work towards understanding the mechanisms of BPD pathogenesis and generating more effective therapeutic options.

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.

Acute and chronic changes in the control of breathing in a rat model of bronchopulmonary dysplasia

Infants born very prematurely (<28 wk gestation) have immature lungs and often require supplemental oxygen. However, long-term hyperoxia exposure can arrest lung development, leading to bronchopulmonary dysplasia (BPD), which increases acute and long-term respiratory morbidity and mortality. The neural mechanisms controlling breathing are highly plastic during development. Whether the ventilatory control system adapts to pulmonary disease associated with hyperoxia exposure in infancy remains unclear. Here, we assessed potential age-dependent adaptations in the control of breathing in an established rat model of BPD associated with hyperoxia. Hyperoxia exposure ( FI O 2 ; 0.9 from 0 to 10 days of life) led to a BPD-like lung phenotype, including sustained reductions in alveolar surface area and counts, and modest increases in airway resistance. Hyperoxia exposure also led to chronic increases in room air and acute hypoxic minute ventilation (V̇e) and age-dependent changes in breath-to-breath variability. Hyperoxia-exposed rats had normal oxygen saturation ( S p O 2 ) in room air but greater reductions in S p O 2 during acute hypoxia (12% O2) that were likely due to lung injury. Moreover, acute ventilatory sensitivity was reduced at P12 to P14. Perinatal hyperoxia led to greater glial fibrillary acidic protein expression and an increase in neuron counts within six of eight or one of eight key brainstem regions, respectively, controlling breathing, suggesting astrocytic expansion. In conclusion, perinatal hyperoxia in rats induced a BPD-like phenotype and age-dependent adaptations in V̇e that may be mediated through changes to the neural architecture of the ventilatory control system. Our results suggest chronically altered ventilatory control in BPD.

Bronchopulmonary Dysplasia: An Update on Experimental Therapeutics

Bronchopulmonary dysplasia (BPD) is a chronic inflammatory lung disease that affects thousands of newborns and infants every year. Although it is accepted that BPD results from lung damage and inflammation triggered by mechanical ventilation and hyperoxia, the causes and molecular events leading to lung damage and arrested development remain unknown. While recent advances in neonatal care have improved the survival of very low-weight infants, the rates of BPD have not improved accordingly. This is mainly due to our limited understanding of the disease's pathogenesis and the effective therapeutic options available. Current therapeutics for BPD involve ventilation management, steroid treatment, and administration of various agents, such as pulmonary surfactant, caffeine, vitamin A, nitric oxide, and stem cells. However, the efficacy of these agents in preventing and ameliorating BPD symptoms varies depending on the populations studied and the disease stage. As the field moves towards personalised therapeutic approaches, this review summarises clinical and experimental studies conducted in various models, aiming to increase understanding of the cellular and molecular mechanisms by which these agents can prevent or treat BPD. Due to the increasing number of extremely premature infants, it is imperative that we continue to work towards understanding the mechanisms of BPD pathogenesis and generating more effective therapeutic options.

Iloprost attenuates hyperoxia-mediated impairment of lung development in newborn mice

Cyclooxygenase-2 (COX-2/PTGS2) mediates hyperoxia-induced impairment of lung development in newborn animals and is increased in the lungs of human infants with bronchopulmonary dysplasia (BPD). COX-2 catalyzes the production of cytoprotective prostaglandins, such as prostacyclin (PGI2), as well as proinflammatory mediators, such as thromboxane A2. Our objective was to determine whether iloprost, a synthetic analog of PGI2, would attenuate hyperoxia effects in the newborn mouse lung. To test this hypothesis, newborn C57BL/6 mice along with their dams were exposed to normoxia (21% O2) or hyperoxia (85% O2) from 4 to 14 days of age in combination with daily intraperitoneal injections of either iloprost 200 µg·kg-1·day-1, nimesulide (selective COX-2 antagonist) 100 mg·kg-1·day-1, or vehicle. Alveolar development was estimated by radial alveolar counts and mean linear intercepts. Lung function was determined on a flexiVent, and multiple cytokines and myeloperoxidase (MPO) were quantitated in lung homogenates. Lung vascular and microvascular morphometry was performed, and right ventricle/left ventricle ratios were determined. We determined that iloprost (but not nimesulide) administration attenuated hyperoxia-induced inhibition of alveolar development and microvascular density in newborn mice. Iloprost and nimesulide both attenuated hyperoxia-induced, increased lung resistance but did not improve lung compliance that was reduced by hyperoxia. Iloprost and nimesulide reduced hyperoxia-induced increases in MPO and some cytokines (IL-1β and TNF-α) but not others (IL-6 and KC/Gro). There were no changes in pulmonary arterial wall thickness or right ventricle/left ventricle ratios. We conclude that iloprost improves lung development and reduces lung inflammation in a newborn mouse model of BPD.

Interleukin-33 (IL-33) Increases Hyperoxia-Induced Bronchopulmonary Dysplasia in Newborn Mice by Regulation of Inflammatory Mediators

Background

Interleukin-33 (IL-33) has been reported to affect chronic inflammation of the lungs, but its impact on hyperoxia-injured lungs in newborns remains obscure. This study aimed to investigate the role of IL-33 in the lungs of neonatal mice with hyperoxia-induced bronchopulmonary dysplasia (BPD).

Material/Methods

Twenty-four C57BL/6 baby mice were randomly separated into three groups: the on-air group (N=16); the O₂ group (N=8); and the O₂ + anti-IL-33 group (N=8). Forced mechanical ventilation with oxygen-rich air (MV-O₂) was used in 16 mouse pups. The mouse pups were incubated in containers with either air or 85% O₂ for 1, 3, 7, 14, 21, and 28 days after birth. At the end of the treatment period, the mouse lungs were studied by histology, Western blot, and quantitative real-time polymerase chain reaction (qRT-PCR) to examine the expression of the pro-inflammatory mediators, including interleukin (IL)-1β, chemokine (CC motif) ligand 1 (CXCL-1), and monocyte chemoattractant protein-1 (MCP-1).

Results

Following forced MV-O₂, increased levels of IL-33 in whole mouse lungs were associated with impaired alveolar growth and with changes consistent with BPD, including reduced numbers of enlarged alveoli, increased apoptosis, and increased expression of IL-1β, CXCL-1, and MCP-1. IL-33 inhibition improved alveolar development in hyperoxia-impaired lungs and suppressed IL-1β and MCP-1 expression and was associated with increased transforming growth factor-β (TGF-β) signaling, reduced pulmonary NF-κB activity and decreased expression of the TGF-β inhibitor SMAD-7 in forced MV-O₂ exposed mouse pups.

Conclusions

IL-33 increased hyperoxia-induced BPD in newborn mice by regulation of the expression of inflammatory mediators.

Evaluating the use of corticosteroids in preventing and treating bronchopulmonary dysplasia in preterm neonates

Approximately 15 million babies worldwide are born premature, and complications of prematurity are one of the leading causes of death in neonates. Neonatal respiratory distress syndrome (NRDS) and bronchopulmonary dysplasia (BPD) are two of the most common and serious consequences of prematurity. Synthetic corticosteroids, including dexamethasone, have been central in efforts to treat and prevent BPD. There is strong evidence to show that prenatal corticosteroids reduce infant mortality and the incidence of NRDS, leading to their widespread use in obstetric units. However, data suggest that they are not as effective in reducing the incidence of BPD as NRDS, which may be due to the multifactorial pathogenesis of BPD. On the other hand, the use of postnatal corticosteroids in preterm infants is much more controversial. They have been shown to improve lung function and help in reducing the need for mechanical ventilation. These benefits, however, are associated with a range of adverse short- and long-term effects. This review will discuss the benefits and consequences of corticosteroids in treating BPD and will examine alternative treatments and future research that may improve the understanding of BPD and inform clinical practice.

Exosomal microRNA predicts and protects against severe bronchopulmonary dysplasia in extremely premature infants

Premature infants are at high risk for developing bronchopulmonary dysplasia (BPD), characterized by chronic inflammation and inhibition of lung development, which we have recently identified as being modulated by microRNAs (miRNAs) and alterations in the airway microbiome. Exosomes and exosomal miRNAs may regulate cell differentiation and tissue and organ development. We discovered that tracheal aspirates from infants with severe BPD had increased numbers of, but smaller, exosomes compared with term controls. Similarly, bronchoalveolar lavage fluid from hyperoxia-exposed mice (an animal model of BPD) and supernatants from hyperoxia-exposed human bronchial epithelial cells (in vitro model of BPD) had increased exosomes compared with air controls. Next, in a prospective cohort study of tracheal aspirates obtained at birth from extremely preterm infants, utilizing independent discovery and validation cohorts, we identified unbiased exosomal miRNA signatures predictive of severe BPD. The strongest signal of reduced miR-876-3p in BPD-susceptible compared with BPD-resistant infants was confirmed in the animal model and in vitro models of BPD. In addition, based on our recent discovery of increased Proteobacteria in the airway microbiome being associated with BPD, we developed potentially novel in vivo and in vitro models for BPD combining Proteobacterial LPS and hyperoxia exposure. Addition of LPS led to a larger reduction in exosomal miR 876-3p in both hyperoxia and normoxia compared with hyperoxia alone, thus indicating a potential mechanism by which alterations in microbiota can suppress miR 876-3p. Gain of function of miR 876-3p improved the alveolar architecture in the in vivo BPD model, demonstrating a causal link between miR 876-3p and BPD. In summary, we provide evidence for the strong predictive biomarker potential of miR 876-3p in severe BPD. We also provide insights on the pathogenesis of neonatal lung disease, as modulated by hyperoxia and microbial product-induced changes in exosomal miRNA 876-3p, which could be targeted for future therapeutic development.

Accepting the challenge: maintaining AJP-Lung as the best place to publish basic and translational studies in lung biology and pathophysiology

Rory E. Morty takes over from Sadis Matalon as Editor in Chief of the American Journal of Physiology-Lung Cellular and Molecular Physiology in January 2018. Here, key achievements and new and noteworthy additions to the editorial portfolio of the journal will be reviewed. Additionally, selected recent reports will be highlighted and used to illustrate how the broad spectrum of the journal's editorial content promotes methodological innovation and scientific advances in lung biology and pathophysiology.

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.

Sexual dimorphism of the pulmonary transcriptome in neonatal hyperoxic lung injury: identification of angiogenesis as a key pathway

Bronchopulmonary dysplasia (BPD) is characterized by impaired alveolar secondary septation and vascular growth. Exposure to high concentrations of oxygen (hyperoxia) contributes to the development of BPD. The male sex is considered an independent risk factor for the development of BPD. The reasons underlying sexually dimorphic outcomes in premature neonates are not known. We hypothesized that sex-specific modulation of biological processes in the lung under hyperoxic conditions contributes to sex-based differences. Neonatal male and female mice (C57BL/6) were exposed to hyperoxia [95% [Formula: see text], postnatal day (PND) 1-5: saccular stage of lung development] and euthanized on PND 7 or 21. Pulmonary gene expression was studied using RNA-Seq on the Illumina HiSeq 2500 platform. Analysis of the pulmonary transcriptome revealed differential sex-specific modulation of crucial pathways such as angiogenesis, response to hypoxia, inflammatory response, and p53 pathway. Candidate genes from these pathways were validated at the mRNA level by qPCR. Analysis also revealed sex-specific differences in the modulation of crucial transcription factors. Focusing on the differential modulation of the angiogenesis pathway, we also showed sex-specific differential activation of Hif-1α-regulated genes using ChIP-qPCR and differences in expression of crucial genes (Vegf, VegfR2, and Phd2) modulating angiogenesis. We demonstrate the translational relevance of our findings by showing that our murine sex-specific differences in gene expression correlate with those from a preexisting human BPD data set. In conclusion, we provide novel molecular insights into differential sex-specific modulation of the pulmonary transcriptome in neonatal hyperoxic lung injury and highlight angiogenesis as one of the crucial differentially modulated pathways.

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.

Posttranslational modification of β-catenin is associated with pathogenic fibroblastic changes in bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a common complication of premature birth. The histopathology of BPD is characterized by an arrest of alveolarization with fibroblast activation. The Wnt/β-catenin signaling pathway is important in early lung development. When Wnt signaling is active, phosphorylation of β-catenin by tyrosine kinases at activating sites, specifically at tyrosine 489 (Y489), correlates with nuclear localization of β-catenin. We examined fetal lung tissue, lung tissue from term newborns, and lung tissue from infants who died with BPD; we found nuclear β-catenin phosphorylation at Y489 in epithelial and mesenchymal cells in fetal tissue and BPD tissue, but not in the lungs of term infants. Using a 3D human organoid model, we found increased nuclear localization of β-catenin phosphorylated at Y489 (p-β-catenin^Y489) after exposure to alternating hypoxia and hyperoxia compared with organoids cultured in normoxia. Exogenous stimulation of the canonical Wnt pathway in organoids was sufficient to cause nuclear localization of p-β-catenin^Y489 in normoxia and mimicked the pattern of α-smooth muscle actin (α-SMA) expression seen with fibroblastic activation from oxidative stress. Treatment of organoids with a tyrosine kinase inhibitor prior to cyclic hypoxia-hyperoxia inhibited nuclear localization of p-β-catenin^Y489 and prevented α-SMA expression by fibroblasts. Posttranslational phosphorylation of β-catenin is a transient feature of normal lung development. Moreover, the persistence of p-β-catenin^Y489 is a durable marker of fibroblast activation in BPD and may play an important role in BPD disease pathobiology.

Intermittent hypoxia during recovery from neonatal hyperoxic lung injury causes long-term impairment of alveolar development: A new rat model of BPD

Bronchopulmonary dysplasia (BPD) is a chronic lung injury characterized by impaired alveologenesis that may persist into adulthood. Rat models of BPD using varying degrees of hyperoxia to produce injury either cause early mortality or spontaneously recover following removal of the inciting stimulus, thus limiting clinical relevance. We sought to refine an established rat model induced by exposure to 60% O₂ from birth by following hyperoxia with intermittent hypoxia (IH). Rats exposed from birth to air or 60% O₂ until day 14 were recovered in air with or without IH (FI_O2 = 0.10 for 10 min every 6 h) until day 28 Animals exposed to 60% O₂ and recovered in air had no evidence of abnormal lung morphology on day 28 or at 10-12 wk. In contrast, 60% O₂-exposed animals recovered in IH had persistently increased mean chord length, more dysmorphic septal crests, and fewer peripheral arteries. Recovery in IH also increased pulmonary vascular resistance, Fulton index, and arterial wall thickness. IH-mediated abnormalities in lung structure (but not pulmonary hypertension) persisted when reexamined at 10-12 wk, accompanied by increased pulmonary vascular reactivity and decreased exercise tolerance. Increased mean chord length secondary to IH was prevented by treatment with a peroxynitrite decomposition catalyst [5,10,15,20-Tetrakis(4-sulfonatophenyl)-21H,23H-porphyrin iron (III) chloride, 30 mg/kg/day, days 14-28], an effect accompanied by fewer inflammatory cells. We conclude that IH during recovery from hyperoxia-induced injury prevents recovery of alveologenesis and leads to changes in lung and pulmonary vascular function lasting into adulthood, thus more closely mimicking contemporary BPD.