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

WHAMM Inhibits Type II Alveolar Epithelial Cell EMT by Mediating Autophagic Degradation of TGF-β1 in Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is one of the most prevalent complication in preterm infants, primarily characterized by arrested alveolar growth. The involvement of epithelial-mesenchymal transition (EMT) of AECII cells is proposed to have a crucial role in the pathogenesis of BPD; however, the underlying mechanism remains unclear. The present study reveals a significant reduction of WHAMM (WASP homolog associated with actin, membranes, and microtubules) in hyperoxia-induced BPD mice, highlighting its crucial role in suppressing the progression of BPD through the inhibition of EMT in AECIIs. We demonstrated that hyperoxia-induced downregulation of WHAMM leads to the accumulation of TGF-β1 primarily through its mediation of the autophagic degradation pathway. Mechanistically, WHAMM enhanced the autophagosomal localization of TGF-β1 and concurrently promoted the process of autophagy, thereby comprehensively facilitating the autophagic degradation of TGF-β1. These findings reveal the important role of WHAMM in the development of BPD, and the proposed WHAMM/autophagy/TGF-β1/EMT pathway may represent a potential therapeutic strategy for BPD treatment.

Elevated visfatin levels illuminate the inflammatory path in bronchopulmonary dysplasia

BACKGROUND

Bronchopulmonary dysplasia (BPD) is a chronic lung disease in premature infants caused by an imbalance between lung injury and lung repair in the developing immature lungs of the newborn. Pulmonary inflammation is an important feature in the pathogenesis of BPD. The aim of this study was to evaluate the relationship between the inflammatory microenvironment and the levels of visfatin and nesfatin-1, which are among the new adipocytokines, in BPD patients.

METHODS

The groups consisted of 30 patients with BPD and 30 healthy children. Plasma levels of visfatin and nesfatin-1 and inflammation-related markers including interleukin-4 (IL-4), interleukin-10 (IL-10), nuclear factor kappa B (Nf-κB) and matrix metalloproteinase-9 (MMP-9) were determined by enzyme-linked immunosorbent assay (ELISA). RT-PCR was performed to evaluate the change in mRNA expression of visfatin and nesfatin-1 in the groups.

RESULTS

Visfatin levels were significantly higher in the BPD group compared to the healthy control (7.05±4.07 ng/ml vs. 2.13±1.66 ng/ml, p<0.0001). There was a 1.36±0.12 fold increase in visfatin mRNA expression (p<0.05) in the BPD group. There was no significant difference in plasma levels of nesfatin-1, IL-4, and IL-10 between the groups. Although MMP-9 and Nf-κB levels were significantly higher in the BPD group (p<0.0001), there was no correlation between visfatin levels and MMP-9 and Nf-κB levels in BPD patients.

CONCLUSIONS

This study showed that significant changes in visfatin levels in BPD patients might be associated with the risk of developing inflammation in BPD.

Maternal Lactobacillus johnsonii supplementation attenuates hyperoxia-induced lung injury in neonatal mice through microbiota regulation

BACKGROUND

Supplemental oxygen impairs lung development in premature infants with respiratory distress. This study investigated the effects of maternal Lactobacillus johnsonii supplementation on hyperoxia-induced lung injury in neonatal mice.

METHODS

Pregnant C57BL/6 mice received L. johnsonii in normal saline (NS) from gestational days 16-21. Control pregnant mice received an equal volume of NS. After birth, the pups were exposed to hyperoxia (O2) or room air (RA) for 1 week. Four groups were studied: NS + RA, probiotic + RA, NS + O2, and probiotic + O2. On postnatal day 7, the lung and intestinal microbiota were sampled, and the right lung was analyzed.

RESULTS

Compared to the NS + RA, probiotic + RA, and probiotic + O2 groups, the NS + O2 group exhibited significantly lower body weight, lung vascular density, and more significant mean linear intercept, IL-6, and 8-OHdG. In the genus level of gut microbiota, the NS + O2 group showed considerably more Staphylococcus and less Lactobacillus than the other three groups. The outcomes showed that in neonatal mice exposed to hyperoxia, maternal L. johnsonii supplementation improved lung development, decreased IL-6 and 8-OHdG levels, and restored gut microbiota.

CONCLUSIONS

Maternal L. johnsonii supplementation reduced lung inflammation and improved lung development in hyperoxia-exposed neonatal mice. The mechanism may be related to the gut microbiota, as L. johnsonii improved gut microbiota communities and regulated dysregulated metabolic pathways.

Fingolimod, a sphingosine-1-phosphate receptor modulator, prevents neonatal bronchopulmonary dysplasia and subsequent airway remodeling in a murine model

Neonatal bronchopulmonary dysplasia (BPD) is associated with alveolar simplification and airway remodeling. Airway remodeling leads to deformation of airways characterized by peribronchial collagen deposition and hypertrophy of airway smooth muscle, which contribute to the narrowing of airways. Poorly developed lungs contribute to reduced lung function that deteriorates with the passage of time. We have earlier shown that sphingosine kinase 1 (SPHK 1)/sphingosine-1-phosphate (S1P)/S1P receptor1 (S1PR1) signaling plays a role in the pathogenesis of BPD. In this study, we investigated the role of fingolimod or FTY720, a known S1PR1 modulator approved for the treatment of multiple sclerosis in the treatment of BPD. Fingolimod promotes the degradation of S1PR1 by preventing its recycling, thus serving as the equivalent of an inhibitor. Exposure of neonatal mice to hyperoxia enhanced the expression of S1PR1 in both airways and alveoli as compared with normoxia. This increased expression of S1PR1 in the airways persisted into adulthood, accompanied by airway remodeling and airway hyperreactivity (AHR) after neonatal hyperoxia. Intranasal fingolimod at a much lower dose compared with the intraperitoneal route of administration during neonatal hyperoxia improved alveolarization in neonates and reduced airway remodeling and AHR in adult mice associated with improved lung function. The intranasal route was not associated with the lymphopenia seen with the intraperitoneal route of administration of the drug. An increase in S1PR1 expression in the airways was associated with an increase in the expression of enzyme lysyl oxidase (LOX) in the airways following hyperoxia, which was suppressed by fingolimod. This association warrants further investigation.NEW & NOTEWORTHY The role of the S1P receptor1 modulator, fingolimod, as an FDA-approved drug in preventing the recurrence of multiple sclerosis is established. Fingolimod prevented bronchopulmonary dysplasia (BPD) and its sequela of airway remodeling in a neonatal murine model. This protection was associated with the downregulation of lysyl oxidase signaling pathway. Fingolimod could be repurposed for the therapy of BPD.

Lung epithelial-endothelial-mesenchymal signaling network with hepatocyte growth factor as a hub is involved in bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is fundamentally characterized by the arrest of lung development and abnormal repair mechanisms, which result in impaired development of the alveoli and microvasculature. Hepatocyte growth factor (HGF), secreted by pulmonary mesenchymal and endothelial cells, plays a pivotal role in the promotion of epithelial and endothelial cell proliferation, branching morphogenesis, angiogenesis, and alveolarization. HGF exerts its beneficial effects on pulmonary vascular development and alveolar simplification primarily through two pivotal pathways: the stimulation of neovascularization, thereby enriching the pulmonary microvascular network, and the inhibition of the epithelial-mesenchymal transition (EMT), which is crucial for maintaining the integrity of the alveolar structure. We discuss HGF and its receptor c-Met, interact with various growth factors throughout the process of lung development and BPD, and form a signaling network with HGF as a hub, which plays the pivotal role in orchestrating and integrating epithelial, endothelial and mesenchymal.

Cardiovascular Sequelae of Bronchopulmonary Dysplasia in Preterm Neonates Born before 32 Weeks of Gestational Age: Impact of Associated Pulmonary and Systemic Hypertension

Bronchopulmonary dysplasia (BPD) remains the most common respiratory disorder of prematurity for infants born before 32 weeks of gestational age (GA). Early and prolonged exposure to chronic hypoxia and inflammation induces pulmonary hypertension (PH) with the characteristic features of a reduced number and increased muscularisation of the pulmonary arteries resulting in an increase in the pulmonary vascular resistance (PVR) and a fall in their compliance. BPD and BPD-associated pulmonary hypertension (BPD-PH) together with systemic hypertension (sHTN) are chronic cardiopulmonary disorders which result in an increased mortality and long-term problems for these infants. Previous studies have predominantly focused on the pulmonary circulation (right ventricle and its function) and developing management strategies accordingly for BPD-PH. However, recent work has drawn attention to the importance of the left-sided cardiac function and its impact on BPD in a subset of infants arising from a unique pathophysiology termed postcapillary PH. BPD infants may have a mechanistic link arising from chronic inflammation, cytokines, oxidative stress, catecholamines, and renin-angiotensin system activation along with systemic arterial stiffness, all of which contribute to the development of BPD-sHTN. The focus for the treatment of BPD-PH has been improvement of the right heart function through pulmonary vasodilators. BPD-sHTN and a subset of postcapillary PH may benefit from afterload reducing agents such as angiotensin converting enzyme inhibitors. Preterm infants with BPD-PH are at risk of later cardiac and respiratory morbidities as young adults. This paper reviews the current knowledge of the pathophysiology, diagnosis, and treatment of BPD-PH and BPD-sHTN. Current knowledge gaps and emerging new therapies will also be discussed.

Association of cord blood Ang-1 and sCD105 levels with bronchopulmonary dysplasia in preterm infants

BACKGROUND

To investigate the relationship between cord blood levels of Angiopoietin-1 (Ang-1) and S-endoglin (sCD105) and bronchopulmonary dysplasia (BPD) in preterm infants.

METHODS

Sixty-one preterm infants admitted to the neonatal intensive care unit of the study hospital between July 2021 and September 2022 were included. Cord blood was collected after the birth of premature infants. Ang-1 and sCD105 levels were quantified using the vascular endothelial growth factor enzyme-linked immunosorbent assay. Preterm infants were divided into BPD and non-BPD groups, and differences in Ang-1 and sCD105 levels between the two groups were compared. A binary logistic model was used to assess the association between low and high levels Ang-1 and BPD in preterm infants.

RESULTS

In the study, there were 20 preterm infants with BPD (32.8%) and 41 preterm infants with non-BPD (67.2%). Ang-1 concentration levels were lower in the BPD group than in the non-BPD group (7105.43 (5617.01-8523.00) pg/ml vs. 10488.03 (7946.19-15962.77) pg/ml, P = 0.027). However, the sCD105 concentration levels were not significantly different between the BPD and non-BPD groups (P = 0.246). A median Ang-1 concentration of 8800.40 pg/ml was calculated. Logistic regression analysis showed that after adjusting for gestational age, birth weight, and maternal prenatal steroid hormone application, the odds ratio (OR) was 8.577 for the risk of BPD in preterm infants with Ang-1 concentrations of ≤ 8800.40 pg/ml compared to those with Ang-1 concentrations of > 8800.40 pg/ml (OR: 8.577, 95% confidence interval: 1.265-58.155, P = 0.028).

CONCLUSION

Our study indicated that Ang-1 levels in the cord blood of preterm infants may be associated the risk of BPD. In the future, we will continue to conduct study with large samples.

Conditional knockout of ITGB4 in bronchial epithelial cells directs bronchopulmonary dysplasia

Neonatal respiratory system disease is closely associated with embryonic lung development. Our group found that integrin β4 (ITGB4) is downregulated in the airway epithelium of asthma patients. Asthma is the most common chronic respiratory illness in childhood. Therefore, we suspect whether the deletion of ITGB4 would affect fetal lung development. In this study, we characterized the role of ITGB4 deficiency in bronchopulmonary dysplasia (BPD). ITGB4 was conditionally knocked out in CCSP-rtTA, Tet-O-Cre and ITGB4f/f triple transgenic mice. Lung tissues at different developmental stages were collected for experimental detection and transcriptome sequencing. The effects of ITGB4 deficiency on lung branching morphogenesis were observed by fetal mouse lung explant culture. Deleting ITGB4 from the airway epithelial cells results in enlargement of alveolar airspaces, inhibition of branching, the abnormal structure of epithelium cells and the impairment of cilia growth during lung development. Scanning electron microscopy showed that the airway epithelial cilia of the β4ccsp.cre group appear to be sparse, shortened and lodging. Lung-development-relevant factors such as SftpC and SOX2 significantly decreased both mRNA and protein levels. KEGG pathway analysis indicated that multiple ontogenesis-regulating-relevant pathways converge to FAK. Accordingly, ITGB4 deletion decreased phospho-FAK, phospho-GSK3β and SOX2 levels, and the correspondingly contrary consequence was detected after treatment with GSK3β agonist (wortmannin). Airway branching defect of β4ccsp.cre mice lung explants was also partly recovered after wortmannin treatment. Airway epithelial-specific deletion of ITGB4 contributes to lung developmental defect, which could be achieved through the FAK/GSK3β/SOX2 signal pathway.

Type 2 innate lymphoid cell-derived amphiregulin regulates type II alveolar epithelial cell transdifferentiation in a mouse model of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a common complication in preterm infants characterized by alveolar growth arrest. Interleukin (IL)-33 and type 2 innate lymphoid cell (ILC2) affect type II alveolar epithelial cell (AECII) differentiation in BPD mice and may cause increased lung epithelial-mesenchymal transition (EMT). Amphiregulin (AREG) can be produced by ILC2 and is associated with tissue repair. However, the action mechanism of AREG produced by ILC2 to alveolar development in BPD is unclear. In this study, we aimed to demonstrate the role and mechanism of AREG in influencing AECII transdifferentiation in the lung tissue of BPD mice. The effects of ILC2-derived AREG on AECII transdifferentiation were verified in vivo and in vitro, and the role of IL-33 on ILC2-derived AREG in AECII transdifferentiation in BPD mice and a preliminary investigation of the role of AREG's receptor-epidermal growth factor receptor (EGFR) on AECII transdifferentiation. The results showed that neonatal mice developed severe lung injury after hyperoxia, and IL-33 induced AREG production via ILC2 affected normal AECII differentiation and promoted EMT. In addition, the blockade of EGFR was found to alleviate the impaired AECII differentiation under hyperoxia in an in vitro study. In summary, our study demonstrates that AREG secreted by ILC2 affects AECII transdifferentiation in BPD mice, which provides a new idea for the clinical treatment of BPD.

Intranasal administration of Lactobacillus johnsonii attenuates hyperoxia-induced lung injury by modulating gut microbiota in neonatal mice

BACKGROUND

Supplemental oxygen impairs lung development in newborn infants with respiratory distress. Lactobacillus johnsonii supplementation attenuates respiratory viral infection in mice and exhibits anti-inflammatory effects. This study investigated the protective effects of intranasal administration of L. johnsonii on lung development in hyperoxia-exposed neonatal mice.

METHODS

Neonatal C57BL/6N mice were reared in either room air (RA) or hyperoxia condition (85% O₂). From postnatal days 0 to 6, they were administered intranasal 10 μL L. johnsonii at a dose of 1 × 10⁵ colony-forming units. Control mice received an equal volume of normal saline (NS). We evaluated the following four study groups: RA + NS, RA + probiotic, O₂ + NS, and O₂ + probiotic. On postnatal day 7, lung and intestinal microbiota were sampled from the left lung and lower gastrointestinal tract, respectively. The right lung of each mouse was harvested for Western blot, cytokine, and histology analyses.

RESULTS

The O₂ + NS group exhibited significantly lower body weight and vascular density and significantly higher mean linear intercept (MLI) and lung cytokine levels compared with the RA + NS and RA + probiotic groups. At the genus level of the gut microbiota, the O₂ + NS group exhibited significantly higher Staphylococcus and Enterobacter abundance and significantly lower Lactobacillus abundance compared with the RA + NS and RA + probiotic groups. Intranasal L. johnsonii treatment increased the vascular density, decreased the MLI and cytokine levels, and restored the gut microbiota in hyperoxia-exposed neonatal mice.

CONCLUSIONS

Intranasal administration of L. johnsonii protects against hyperoxia-induced lung injury and modulates the gut microbiota.

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.

Microbial-induced Redox Imbalance in the Neonatal Lung Is Ameliorated by Live Biotherapeutics

Bronchopulmonary dysplasia (BPD) is a common lung disease of premature infants. Hyperoxia exposure and microbial dysbiosis are contributors to BPD development. However, the mechanisms linking pulmonary microbial dysbiosis to worsening lung injury are unknown. Nrf2 (nuclear factor erythroid 2-related factor 2) is a transcription factor that regulates oxidative stress responses and modulates hyperoxia-induced lung injury. We hypothesized that airway dysbiosis would attenuate Nrf2-dependent antioxidant function, resulting in a more severe phenotype of BPD. Here, we show that preterm infants with a Gammaproteobacteria-predominant dysbiosis have increased endotoxin in tracheal aspirates, and mice monocolonized with the representative Gammaproteobacteria Escherichia coli show increased tissue damage compared with germ-free (GF) control mice. Furthermore, we show Nrf2-deficient mice have worse lung structure and function after exposure to hyperoxia when the airway microbiome is augmented with E. coli. To confirm the disease-initiating potential of airway dysbiosis, we developed a novel humanized mouse model by colonizing GF mice with tracheal aspirates from human infants with or without severe BPD, producing gnotobiotic mice with BPD-associated and non-BPD-associated lung microbiomes. After hyperoxia exposure, BPD-associated mice demonstrated a more severe BPD phenotype and increased expression of Nrf2-regulated genes, compared with GF and non-BPD-associated mice. Furthermore, augmenting Nrf2-mediated antioxidant activity by supporting colonization with Lactobacillus species improved dysbiotic-augmented lung injury. Our results demonstrate that a lack of protective pulmonary microbiome signature attenuates an Nrf2-mediated antioxidant response, which is augmented by a respiratory probiotic blend. We anticipate antioxidant pathways will be major targets of future microbiome-based therapeutics for respiratory disease.

Metabolome and microbiome multi-omics integration from a murine lung inflammation model of bronchopulmonary dysplasia

BACKGROUND

Respiratory tract microbial dysbiosis can exacerbate inflammation and conversely inflammation may cause dysbiosis. Dysbiotic microbiome metabolites may lead to bronchopulmonary dysplasia (BPD). Hyperoxia and lipopolysaccharide (LPS) interaction alters lung microbiome and metabolome, mediating BPD lung injury sequence.

METHODS

C57BL6/J mice were exposed to 21% (normoxia) or 70% (hyperoxia) oxygen during postnatal days (PND) 1-14. Pups were injected with LPS (6 mg/kg) or equal PBS volume, intraperitoneally on PND 3, 5, and 7. At PND14, the lungs were collected for microbiome and metabolomic analyses (n = 5/group).

RESULTS

Microbiome alpha and beta diversity were similar between groups. Metabolic changes included hyperoxia 31 up/18 down, LPS 7 up/4 down, exposure interaction 8. Hyperoxia increased Intestinimonas abundance, whereas LPS decreased Clostridiales, Dorea, and Intestinimonas; exposure interaction affected Blautia. Differential co-expression analysis on multi-omics data identified exposure-altered modules. Hyperoxia metabolomics response was integrated with a published matching transcriptome, identifying four induced genes (ALDOA, GAA, NEU1, RENBP), which positively correlated with BPD severity in a published human newborn cohort.

CONCLUSIONS

We report hyperoxia and LPS lung microbiome and metabolome signatures in a clinically relevant BPD model. We identified four genes correlating with BPD status in preterm infants that are promising targets for therapy and prevention.

IMPACT

Using multi-omics, we identified and correlated key biomarkers of hyperoxia and LPS on murine lung micro-landscape and examined their potential clinical implication, which shows strong clinical relevance for future research. Using a double-hit model of clinical relevance to bronchopulmonary dysplasia, we are the first to report integrated metabolomic/microbiome landscape changes and identify novel disease biomarker candidates.

Extracellular Signal-Regulated Kinase 1 Alone Is Dispensable for Hyperoxia-Mediated Alveolar and Pulmonary Vascular Simplification in Neonatal Mice

Bronchopulmonary dysplasia (BPD) is a morbid lung disease distinguished by lung alveolar and vascular simplification. Hyperoxia, an important BPD causative factor, increases extracellular signal-regulated kinases (ERK)-1/2 expression, whereas decreased lung endothelial cell ERK2 expression reduces angiogenesis and potentiates hyperoxia-mediated BPD in mice. However, ERK1′s role in experimental BPD is unclear. Thus, we hypothesized that hyperoxia-induced experimental BPD would be more severe in global ERK1-knockout (ERK1^-/-) mice than their wild-type (ERK1^+/+ mice) littermates. We determined the extent of lung development, ERK1/2 expression, inflammation, and oxidative stress in ERK1^-/- and ERK1^+/+ mice exposed to normoxia (FiO₂ 21%) or hyperoxia (FiO₂ 70%). We also quantified the extent of angiogenesis and hydrogen peroxide (H₂O₂) production in hyperoxia-exposed neonatal human pulmonary microvascular endothelial cells (HPMECs) with normal and decreased ERK1 signaling. Compared with ERK1^+/+ mice, ERK1^-/- mice displayed increased pulmonary ERK2 activation upon hyperoxia exposure. However, the extent of hyperoxia-induced inflammation, oxidative stress, and interrupted lung development was similar in ERK1^-/- and ERK1^+/+ mice. ERK1 knockdown in HPMECs increased ERK2 activation at baseline, but did not affect in vitro angiogenesis and hyperoxia-induced H₂O₂ production. Thus, we conclude ERK1 is dispensable for hyperoxia-induced experimental BPD due to compensatory ERK2 activation.

Effect of First Mother's Own Milk Feeding Time on the Risk of Moderate and Severe Bronchopulmonary Dysplasia in Infants With Very Low Birth Weight

OBJECTIVE

To explore the effect of mother's own milk (MOM) feeding time on the risk of moderate and severe bronchopulmonary dysplasia (BPD) in infants with very low birth weight (VLBW).

METHODS

Clinical data from 630 infants with VLBW were retrospectively analyzed. Participants were divided into the early mother's own milk (EMOM) feeding group (first mother's own milk feeding time ≤72 h after birth, n = 397) and the late mother's own milk (LMOM) feeding group (first mother's own milk feeding time >72 h after birth, n = 233). Differences in the incidence of moderate and severe BPD among the two groups were analyzed using the chi-square test. Effects of MOM feeding time on the incidence of moderate and severe BPD were evaluated using univariate and multivariate logistic regression analysis.

RESULTS

The incidences of moderate and severe BPD in the EMOM feeding group and the LMOM feeding group were 13.9% (55/397) and 21.0% (49/233), respectively (P = 0.019). Variate logistic regression analysis showed that the LMOM feeding group had an increased risk of moderate and severe BPD compared with the EMOM feeding group (OR = 1.656, 95% CI:1.083-2.532). The results of multivariate logistic regression analysis showed that the LMOM feeding group had an increased risk of moderate and severe BPD compared with the EMOM feeding group (OR = 1.894, 95% CI:1.127-3.185).

CONCLUSION

The first time of MOM feeding within 72 h after birth and the persistence of mother's own milk feeding during hospitalization can reduce the incidence of moderate and severe BPD in infants with VLBW.

Targeting the Toll-like receptor pathway as a therapeutic strategy for neonatal infection

Toll-like receptors (TLRs) are crucial transmembrane receptors that form part of the innate immune response. They play a role in the recognition of various microorganisms and their elimination from the host. TLRs have been proposed as vital immunomodulators in the regulation of multiple neonatal stressors that extend beyond infection such as oxidative stress and pain. The immune system is immature at birth and takes some time to become fully established. As such, babies are especially vulnerable to sepsis at this early stage of life. Findings suggest a gestational age-dependent increase in TLR expression. TLRs engage with accessory and adaptor proteins to facilitate recognition of pathogens and their activation of the receptor. TLRs are generally upregulated during infection and promote the transcription and release of proinflammatory cytokines. Several studies report that TLRs are epigenetically modulated by chromatin changes and promoter methylation upon bacterial infection that have long-term influences on immune responses. TLR activation is reported to modulate cardiorespiratory responses during infection and may play a key role in driving homeostatic instability observed during sepsis. Although complex, TLR signaling and downstream pathways are potential therapeutic targets in the treatment of neonatal diseases. By reviewing the expression and function of key Toll-like receptors, we aim to provide an important framework to understand the functional role of these receptors in response to stress and infection in premature infants.

Developmental Pathways Underlying Lung Development and Congenital Lung Disorders

Lung organogenesis is a highly coordinated process governed by a network of conserved signaling pathways that ultimately control patterning, growth, and differentiation. This rigorously regulated developmental process culminates with the formation of a fully functional organ. Conversely, failure to correctly regulate this intricate series of events results in severe abnormalities that may compromise postnatal survival or affect/disrupt lung function through early life and adulthood. Conditions like congenital pulmonary airway malformation, bronchopulmonary sequestration, bronchogenic cysts, and congenital diaphragmatic hernia display unique forms of lung abnormalities. The etiology of these disorders is not yet completely understood; however, specific developmental pathways have already been reported as deregulated. In this sense, this review focuses on the molecular mechanisms that contribute to normal/abnormal lung growth and development and their impact on postnatal survival.

Enhanced epithelial sodium channel activity in neonatal Scnn1b mouse lung attenuates high oxygen-induced lung injury

Prolonged oxygen therapy leads to oxidative stress, epithelial dysfunction, and acute lung injury in preterm infants and adults. Heterozygous Scnn1b mice, which overexpress lung epithelial sodium channels (ENaC), and their wild-type (WT) C57Bl6 littermates were utilized to study the pathogenesis of high fraction inspired oxygen ([Formula: see text])-induced lung injury. Exposure to high [Formula: see text] from birth to postnatal (PN) day 11 was used to model oxidative stress. Chronic exposure of newborn pups to 85% O2 increased glutathione disulfide (GSSG) and elevated the GSH/GSSG redox potential (Eh) of bronchoalveolar lavage fluid (BALF). Longitudinal X-ray imaging and Evans blue-labeled-albumin assays showed that chronic 85% O2 and acute GSSG (400 µM) exposures decreased alveolar fluid clearance (AFC) in the WT lung. Morphometric analysis of WT pups insufflated with GSSG (400 µM) or amiloride (1 µM) showed a reduction in alveologenesis and increased lung injury compared with age-matched control pups. The Scnn1b mouse lung phenotype was not further aggravated by chronic 85% O2 exposure. These outcomes support the hypothesis that exposure to hyperoxia increases GSSG, resulting in reduced lung fluid reabsorption due to inhibition of amiloride-sensitive ENaC. Flavin adenine dinucleotide (FADH2; 10 µM) was effective in recycling GSSG in vivo and promoted alveologenesis, but did not impact AFC nor attenuate fibrosis following high [Formula: see text] exposure. In conclusion, the data indicate that FADH2 may be pivotal for normal lung development, and show that ENaC is a key factor in promoting alveologenesis, sustaining AFC, and attenuating fibrotic lung injury caused by prolonged oxygen therapy in WT mice.

Red cell distribution width as a predictor for bronchopulmonary dysplasia in premature infants

Bronchopulmonary dysplasia (BPD) is the most common morbidity complicating preterm birth. Red blood cell distribution width (RDW), a measure of the variation of red blood cell size, could reflect oxidative stress and chronic inflammation in many diseases such as cardiovascular, pulmonary, and other diseases. The objectives of the present study were to evaluate perinatal factors affecting RDW and to validate whether RDW could be a potential biomarker for BPD. A total of 176 preterm infants born at < 30 weeks were included in this study. They were categorized into BPD (n = 85) and non-BPD (n = 91) infants. RDW at birth and 14 days and 28 days of life (DOL 14, DOL 28) were measured. Clinical data were obtained from all subjects at Fukushima Medical University (Fukushima, Japan). The mean RDW at birth, DOL 14 and DOL 28 were 16.1%, 18.6%, 20.1%, respectively. Small for gestational age (SGA), chorioamnionitis (CAM), hypertensive disorders of pregnancy (HDP), gestational age and birth weight were significantly associated with RDW at birth. SGA, BPD and red blood cell (RBC) transfusion before DOL 14 were associated with RDW at DOL 14. BPD and RBC transfusion before DOL 14 were associated with RDW at DOL 28. Compared with non-BPD infants, mean RDW at DOL 14 (21.1% vs. 17.6%, P < 0.001) and DOL 28 (22.2% vs. 18.2%, P < 0.001) were significantly higher in BPD infants. Multivariate analysis revealed that RDW at DOL 28 was significantly higher in BPD infants (P = 0.001, odds ratio 1.63; 95% CI 1.22–2.19). Receiver operating characteristic analysis for RDW at DOL 28 in infants with and without BPD yielded an area under the curve of 0.87 (95% CI 0.78–0.91, P < 0.001). RDW at DOL 28 with mild BPD (18.1% vs. 21.3%, P < 0.001), moderate BPD (18.1% vs. 21.2%, P < 0.001), and severe BPD (18.1% vs. 24.0%, P < 0.001) were significantly higher than those with non-BPD, respectively. Furthermore, there are significant differences of RDW at DOL 28 among mild, moderate, and severe BPD. In summary, we conclude that RDW at DOL 28 could serve as a biomarker for predicting BPD and its severity. The mechanism by which RDW at DOL 28 is associated with the pathogenesis of BPD needs further elucidation.

Hyperoxia and Lungs: What We Have Learned From Animal Models

Although oxygen (O₂) is essential for aerobic life, it can also be an important source of cellular damage. Supra-physiological levels of O₂ determine toxicity due to exacerbated reactive oxygen species (ROS) production, impairing the homeostatic balance of several cellular processes. Furthermore, injured cells activate inflammation cascades, amplifying the tissue damage. The lung is the first (but not the only) organ affected by this condition. Critically ill patients are often exposed to several insults, such as mechanical ventilation, infections, hypo-perfusion, systemic inflammation, and drug toxicity. In this scenario, it is not easy to dissect the effect of oxygen toxicity. Translational investigations with animal models are essential to explore injuring stimuli in controlled experimental conditions, and are milestones in understanding pathological mechanisms and developing therapeutic strategies. Animal models can resemble what happens in critical care or anesthesia patients under mechanical ventilation and hyperoxia, but are also critical to explore the effect of O₂ on lung development and the role of hyperoxic damage on bronchopulmonary dysplasia. Here, we set out to review the hyperoxia effects on lung pathology, contributing to the field by describing and analyzing animal experimentation's main aspects and its implications on human lung diseases.

The H2S-generating enzyme 3-mercaptopyruvate sulfurtransferase regulates pulmonary vascular smooth muscle cell migration and proliferation but does not impact normal or aberrant lung development

Along with nitric oxide (NO), the gasotransmitters carbon monoxide (CO) and hydrogen sulfide (H2S) are emerging as potentially important players in newborn physiology, as mediators of newborn disease, and as new therapeutic modalities. Several recent studies have addressed H2S in particular in animal models of bronchopulmonary dysplasia (BPD), a common complication of preterm birth where oxygen toxicity stunts lung development. In those studies, exogenous H2S attenuated the impact of oxygen toxicity on lung development, and two H2S-generating enzymes were documented to affect pulmonary vascular development. H2S is directly generated endogenously by three enzymes, one of which, 3-mercaptopyruvate sulfurtransferase (MPST), has not been studied in the lung. In a hyperoxia-based animal model of BPD, oxygen exposure deregulated MPST expression during post-natal lung development, where MPST was localized to the smooth muscle layer of the pulmonary vessels in developing lungs. siRNA-mediated abrogation of MPST expression in human pulmonary artery smooth muscle cells in vitro limited baseline cell migration and cell proliferation, without affecting apoptosis or cell viability. In vivo, MPST was dispensable for normal lung development in Mpst-/-mice, and MPST did not contribute to stunted lung development driven by hyperoxia exposure, assessed by design-based stereology. These data demonstrate novel roles for MPST in pulmonary vascular smooth muscle cell physiology. The potential caveats of using Mpst-/- mice to study normal and aberrant lung development are also discussed, highlighting the possible confounding, compensatory effects of other H2S-generating enzymes that are present alongside MPST in the smooth muscle compartment of developing pulmonary vessels.

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.

Management of Rare Causes of Pediatric Chronic Respiratory Failure

The need for long-term noninvasive positive pressure ventilation (NiPPV) in children with chronic respiratory failure is rapidly growing. This article reviews pediatric-specific considerations of NiPPV therapy. Indications for NiPPV therapy can be categorized by the cause of the respiratory failure: (1) upper airway obstruction, (2) musculoskeletal and/or neuromuscular disease, (3) lower respiratory tract diseases, and (4) control of breathing abnormalities. The role of NiPPV therapy in select rare conditions (spinal muscular atrophy, congenital central hypoventilation syndrome, cerebral palsy, scoliosis, and Chiari malformations) is also reviewed.

Interactive and independent effects of early lipopolysaccharide and hyperoxia exposure on developing murine lungs

Bronchopulmonary dysplasia (BPD)-associated pulmonary hypertension (PH) is a chronic infantile lung disease that lacks curative therapies. Infants with BPD-associated PH are often exposed to hyperoxia and additional insults such as sepsis that contribute to disease pathogenesis. Animal models that simulate these scenarios are necessary to develop effective therapies; therefore, we investigated whether lipopolysaccharide (LPS) and hyperoxia exposure during saccular lung development cooperatively induce experimental BPD-PH in mice. C57BL/6J mice were exposed to normoxia or 70% O₂ (hyperoxia) during postnatal days (PNDs) 1-5 and intraperitoneally injected with varying LPS doses or a vehicle on PNDs 3-5. On PND 14, we performed morphometry, echocardiography, and gene and protein expression studies to determine the effects of hyperoxia and LPS on lung development, vascular remodeling and function, inflammation, oxidative stress, cell proliferation, and apoptosis. LPS and hyperoxia independently and cooperatively affected lung development, inflammation, and apoptosis. Growth rate and antioxidant enzyme expression were predominantly affected by LPS and hyperoxia, respectively, while cell proliferation and vascular remodeling and function were mainly affected by combined exposure to LPS and hyperoxia. Mice treated with lower LPS doses developed adaptive responses and hyperoxia exposure did not worsen their BPD phenotype, whereas those mice treated with higher LPS doses displayed the most severe BPD phenotype when exposed to hyperoxia and were the only group that developed PH. Collectively, our data suggest that an additional insult such as LPS may be necessary for models utilizing short-term exposure to moderate hyperoxia to recapitulate human BPD-PH.

FOSL1 is a novel mediator of endotoxin/lipopolysaccharide-induced pulmonary angiogenic signaling

Systemic sepsis is a known risk factor for bronchopulmonary dysplasia (BPD) in premature infants, a disease characterized by dysregulated angiogenesis and impaired vascular and alveolar development. We have previoulsy reported that systemic endotoxin dysregulates pulmonary angiogenesis resulting in alveolar simplification mimicking BPD in neonatal mice, but the underlying mechanisms remain unclear. We undertook an unbiased discovery approach to identify novel signaling pathways programming sepsis-induced deviant lung angiogenesis. Pulmonary endothelial cells (EC) were isolated for RNA-Seq from newborn C57BL/6 mice treated with intraperitoneal lipopolysaccharide (LPS) to mimic systemic sepsis. LPS significantly differentially-regulated 269 genes after 6 h, and 1,934 genes after 24 h. Using bioinformatics, we linked 6 h genes previously unknown to be modulated by LPS to 24 h genes known to regulate angiogenesis/vasculogenesis to identify pathways programming deviant angiogenesis. An immortalized primary human lung EC (HPMEC-im) line was generated by SV40 transduction to facilitate mechanistic studies. RT-PCR and transcription factor binding analysis identified FOSL1 (FOS like 1) as a transcriptional regulator of LPS-induced downstream angiogenic or vasculogenic genes. Over-expression and silencing studies of FOSL1 in immortalized and primary HPMEC demonstrated that baseline and LPS-induced expression of ADAM8, CXCR2, HPX, LRG1, PROK2, and RNF213 was regulated by FOSL1. FOSL1 silencing impaired LPS-induced in vitro HPMEC angiogenesis. In conclusion, we identified FOSL1 as a novel regulator of sepsis-induced deviant angiogenic signaling in mouse lung EC and human fetal HPMEC.

EPO enhances the protective effects of MSCs in experimental hyperoxia-induced neonatal mice by promoting angiogenesis

Bronchopulmonary dysplasia (BPD) is the most common type of chronic lung disease in infancy; however, there is no effective treatment for it. In the present study, a neonatal mouse BPD model was established by continuous exposure to high oxygen (HO) levels. Mice were divided randomly into 5 groups: control, BPD, EPO, MSCs, and MSCs+EPO. At 2 weeks post-treatment, vessel density and the expression levels of endothelial growth factor (VEGF), stromal cell-derived factor-1 (SDF-1), and its receptor C-X-C chemokine receptor type 4 (CXCR4) were significantly increased in the MSC+EPO group compared with the EPO or MSCs group alone; moreover, EPO significantly enhanced MSCs proliferation, migration, and anti-apoptosis ability in vitro. Furthermore, the MSCs could differentiate into cells that were positive for the type II alveolar epithelial cell (AECII)-specific marker surfactant protein-C, but not positive for the AECI-specific marker aquaporin 5. Our present results suggested that MSCs in combination with EPO could significantly attenuate lung injury in a neonatal mouse model of BPD. The mechanism may be by the indirect promotion of angiogenesis, which may involve the SDF-1/CXCR4 axis.

Sex difference in bronchopulmonary dysplasia of offspring in response to maternal PM2.5 exposure

The adverse effects of fine particulate matters (PM_2.5) on respiratory diseases start in utero. In order to investigate whether maternal PM_2.5 exposure could lead to bronchopulmonary dysplasia (BPD) in offspring, PM_2.5 was collected in Taiyuan, Shanxi, China during the annual heating period. Mice were mated and gestation day 0 (GD0) was considered the day on which a vaginal plug was observed. The plug-positive mice received 3 mg/kg b.w. PM_2.5 by oropharyngeal aspiration every other day starting on GD0 and throughout the gestation period. Offspring were sacrificed at postnatal days (PNDs) 1, 7, 14 and 21. We assessed some typical BPD-like symptoms in offspring. The results showed that maternal PM_2.5 exposure caused low birth weight, hypoalveolarization, decreased angiogenesis, suppressed production of secretory and surfactant proteins, and increased inflammation in the lungs of male offspring. However, maternal PM_2.5 exposure induced only hypoalveolarization and inflammation in the lungs of female offspring. Furthermore, these alterations were reversed during postnatal development. Our results demonstrated that maternal exposure to PM_2.5 caused reversible BPD-related consequences in offspring, and male offspring were more sensitive than females. However, these alterations were reversed during postnatal development.

Tie-2 Cre-Mediated Deficiency of Extracellular Signal-Regulated Kinase 2 Potentiates Experimental Bronchopulmonary Dysplasia-Associated Pulmonary Hypertension in Neonatal Mice

Bronchopulmonary dysplasia (BPD)-associated pulmonary hypertension (PH) is a significant lung morbidity of infants, and disrupted lung angiogenesis is a hallmark of this disease. We observed that extracellular signal-regulated kinases (ERK) 1/2 support angiogenesis in vitro, and hyperoxia activates ERK1/2 in fetal human pulmonary microvascular endothelial cells (HPMECs) and in neonatal murine lungs; however, their role in experimental BPD and PH is unknown. Therefore, we hypothesized that Tie2 Cre-mediated deficiency of ERK2 in the endothelial cells of neonatal murine lungs would potentiate hyperoxia-induced BPD and PH. We initially determined the role of ERK2 in in vitro angiogenesis using fetal HPMECs. To disrupt endothelial ERK2 signaling in the lungs, we decreased ERK2 expression by breeding ERK2^flox/flox mice with Tie-Cre mice. One-day-old endothelial ERK2-sufficient (eERK2^+/+) or –deficient (eERK2^+/−) mice were exposed to normoxia or hyperoxia (FiO₂ 70%) for 14 d. We then performed lung morphometry, gene and protein expression studies, and echocardiography to determine the extent of inflammation, oxidative stress, and development of lungs and PH. The knockdown of ERK2 in HPMECs decreased in vitro angiogenesis. Hyperoxia increased lung inflammation and oxidative stress, decreased lung angiogenesis and alveolarization, and induced PH in neonatal mice; however, these effects were augmented in the presence of Tie2-Cre mediated endothelial ERK2 deficiency. Therefore, we conclude that endothelial ERK2 signaling is necessary to mitigate hyperoxia-induced experimental BPD and PH in neonatal mice. Our results indicate that endothelial ERK2 is a potential therapeutic target for the management of BPD and PH in infants.

S-endoglin expression is induced in hyperoxia and contributes to altered pulmonary angiogenesis in bronchopulmonary dysplasia development

Altered pulmonary angiogenesis contributes to disrupted alveolarization, which is the main characteristic of bronchopulmonary dysplasia (BPD). Transforming growth factor β (TGFβ) plays an important role during lung vascular development, and recent studies have demonstrated that endoglin is engaged in the modulation of TGFβ downstream signalling. Although there are two different isoforms of endoglin, L- and S-endoglin, little is known about the effect of S-endoglin in developing lungs. We analysed the expression of both L- and S-endoglin in the lung vasculature and its contribution to TGFβ-activin-like kinase (ALK)-Smad signalling with respect to BPD development. Hyperoxia impaired pulmonary angiogenesis accompanied by alveolar simplification in neonatal mouse lungs. S-endoglin, phosphorylated Smad2/3 and connective tissue growth factor levels were significantly increased in hyperoxia-exposed mice, while L-endoglin, phosphor-Smad1/5 and platelet-endothelial cell adhesion molecule-1 levels were significantly decreased. Hyperoxia suppressed the tubular growth of human pulmonary microvascular endothelial cells (ECs), and the selective inhibition of ALK5 signalling restored tubular growth. These results indicate that hyperoxia alters the balance in two isoforms of endoglin towards increased S-endoglin and that S-endoglin attenuates TGFβ-ALK1-Smad1/5 signalling but stimulates TGFβ-ALK5-Smad2/3 signalling in pulmonary ECs, which may lead to impaired pulmonary angiogenesis in developing lungs.

Factors associated with development of early and late pulmonary hypertension in preterm infants with bronchopulmonary dysplasia

OBJECTIVE

To investigate factors associated with development of early and late pulmonary hypertension (E/LPH) in preterm infants with bronchopulmonary dysplasia (BPD).

STUDY DESIGN

A retrospective case-control observational study of preterm infants with BPD admitted to a level IV referral neonatal intensive care unit over 5 years. We compared pre- and postnatal characteristics between infants with or without BPD-associated EPH and LPH.

RESULTS

Fifty-nine out of 220 infants (26.8%) had LPH, while 85 out of 193 neonates (44%) had EPH. On multiple logistic regression, novel factors associated with development of BPD-LPH included presence of maternal diabetes, EPH, tracheostomy, tracheitis, intraventricular hemorrhage (IVH, grade ≥3) and systemic steroid use. For EPH, these were maternal diabetes, IVH grade ≥3, high frequency ventilator use, and absence of maternal antibiotics use.

CONCLUSION

We identified novel factors and confirmed previously established factors with development of LPH and EPH, which can help develop a screening strategy in BPD patients.

Severe but not moderate hyperoxia of newborn mice causes an emphysematous lung phenotype in adulthood without persisting oxidative stress and inflammation

Background

Preterm newborns typically require supplemental oxygen but hyperoxic conditions also damage the premature lung. Oxygen-induced lung damages are mainly studied in newborn mouse models using oxygen concentrations above 75% and looking at short-term effects. Therefore, we aimed at the investigation of long-term effects and their dependency on different oxygen concentrations.

Methods

Newborn mice were exposed to moderate vs. severe hyperoxic air conditions (50 vs. 75% O₂) for 14 days followed by a longer period of normoxic conditions. Lung-related parameters were collected at an age of 60 or 120 days.

Results

Severe hyperoxia caused lower alveolar density, enlargement of parenchymal air spaces and fragmented elastic fibers as well as higher lung compliance with peak airflow limitations and higher sensitivity to ventilation-mediated damages in later life. However, these long-term lung structural and functional changes did not restrict the voluntary physical activity. Also, they were not accompanied by ongoing inflammatory processes, increased formation of reactive oxygen species (ROS) or altered expressions of antioxidant enzymes (superoxide dismutases, catalase) and lung elasticity-relevant proteins (elastin, pro-surfactant proteins) in adulthood. In contrast to severe hyperoxia, moderate hyperoxia was less lung damaging but also not free of long-term effects (higher lung compliance without peak airflow limitations, increased ROS formation).

Conclusions

Severe but not moderate neonatal hyperoxia causes emphysematous lungs without persisting oxidative stress and inflammation in adulthood. As the existing fragmentation of the elastic fibers seems to play a pivotal role, it indicates the usefulness of elastin-protecting compounds in the reduction of long-term oxygen-related lung damages.

Time-lapse Imaging of Alveologenesis in Mouse Precision-cut Lung Slices

Alveoli are the gas-exchange units of lung. The process of alveolar development, alveologenesis, is regulated by a complex network of signaling pathways that act on various cell types including alveolar type I and II epithelial cells, fibroblasts and the vascular endothelium. Dysregulated alveologenesis results in bronchopulmonary dysplasia in neonates and in adults, disrupted alveolar regeneration is associated with chronic lung diseases including COPD and pulmonary fibrosis. Therefore, visualizing alveologenesis is critical to understand lung homeostasis and for the development of effective therapies for incurable lung diseases. We have developed a technique to visualize alveologenesis in real-time using a combination of widefield microscopy and image deconvolution of precision-cut lung slices. Here, we describe this live imaging technique in step-by-step detail. This time-lapse imaging technique can be used to capture the dynamics of individual cells within tissue slices over a long time period (up to 16 h), with minimal loss of fluorescence or cell toxicity.

Host Components Contributing to Respiratory Syncytial Virus Pathogenesis

Respiratory syncytial virus (RSV) is the most prevalent viral etiological agent of acute respiratory tract infection. Although RSV affects people of all ages, the disease is more severe in infants and causes significant morbidity and hospitalization in young children and in the elderly. Host factors, including an immature immune system in infants, low lymphocyte levels in patients under 5 years old, and low levels of RSV-specific neutralizing antibodies in the blood of adults over 65 years of age, can explain the high susceptibility to RSV infection in these populations. Other host factors that correlate with severe RSV disease include high concentrations of proinflammatory cytokines such as interleukins (IL)-6, IL-8, tumor necrosis factor (TNF)-α, and thymic stromal lymphopoitein (TSLP), which are produced in the respiratory tract of RSV-infected individuals, accompanied by a strong neutrophil response. In addition, data from studies of RSV infections in humans and in animal models revealed that this virus suppresses adaptive immune responses that could eliminate it from the respiratory tract. Here, we examine host factors that contribute to RSV pathogenesis based on an exhaustive review of in vitro infection in humans and in animal models to provide insights into the design of vaccines and therapeutic tools that could prevent diseases caused by RSV.

Effect of Intranasal Instillation of Lipopolysaccharide on Lung Development and Its Related Mechanism in Newborn Mice

Premature infants are prone to repeated lung infections after birth, which can disrupt the development of lung structure and function. However, the effects of postnatal pulmonary inflammation on lung development in newborn mice have not been reported and may play an important role in the development of bronchopulmonary dysplasia (BPD). This study aimed to establish a BPD model of postnatal pulmonary inflammation in premature infants and to explore its role and possible mechanisms in the pathogenesis of BPD. We exposed postnatal day 1 mice to lipopolysaccharide (LPS) and normal saline for 14 days. Pulmonary inflammation and alveolar microvascular development were assessed by histology. In addition, we also examined the expression of vascular endothelial growth factor (VEGF), VEGFR2, nuclear factor-kappa-B (NF-κB) and related inflammatory mediators [interleukin-1β (IL-1β), tumor necrosis factor-alpha (TNF-α), macrophage inflammatory protein-1α (MIP-1α), monocyte chemoattractant protein-1 (MCP-1)] in the lungs. Lung histology revealed inflammatory cell infiltration, alveolar simplification, and decreased microvascular density in LPS-exposed lungs. VEGF and VEGFR2 expression was decreased in the lungs of LPS-exposed neonatal mice. Furthermore, we detected elevated levels of the inflammatory mediators IL-1β, TNF-α, MIP-1α, and MCP-1 in the lungs, which are associated with the activation of NF-κB. Intranasal instillation of LPS inhibits lung development in newborn mice, and postnatal pulmonary inflammation may participate in the pathogenesis of BPD. The mechanism is related to the inhibition of VEGF and VEGFR2 and the upregulation of inflammatory mediators through activation of NF-κB.

Exosomes secreted by endothelial progenitor cells improve the bioactivity of pulmonary microvascular endothelial cells exposed to hyperoxia in vitro

Background

Paracrine factors secreted by endothelial progenitor cells (EPCs) are suggested to be responsible, in part, for the improved microvascular development in bronchopulmonary dysplasia (BPD) models. This study aims to investigate the potential role of exosomes derived from EPCs (EPC-EXOs), a component of paracrine secretion, in angiogenesis by mediating the activity of PMVECs exposed to hyperoxia.

Methods

EPCs were isolated from bone marrow of rats. EPC-EXOs were isolated by ExoQuick-TC kits from the conditioned media of EPCs. The PMVECs were divided into three groups, including the normal group, the hyperoxia group (exposed to 85% O₂) and the EPC-EXOs treatment group (exposed to 85% O₂ and EPC-EXOs with the concentration of 100 µg/mL). The activities of proliferation, migration and tube formation of PMVECs were detected at the endpoint. The mRNA and protein expression levels of VEGF, VEGFR2 and eNOS in different groups were detected by real-time quantitative PCR and western blot.

Results

We found EPC-EXOs exhibited a cup or biconcave morphology, with the size ranging from 30 to 150 nm, and positive for the characteristic exosomal surface marker proteins, CD63 and TSG101. Comparing to the control group, Hyperoxic stress impaired the proliferation, migration, and tubule formation of PMVECs, and decreased the expression of endothelial nitric oxide synthase (eNOS), vascular endothelial growth factor (VEGF), and vascular endothelial growth factor receptor 2 (VEGFR-2) of PMVECs. Comparing to the hyperoxia group, EPC-EXOs treatment enhanced the bioactivity of PMVECs in vitro, and increased the expression of eNOS, VEGF and VEGFR2.

Conclusions

Our data demonstrate EPCs secrete exosomes that have independent angiogenic activity in vitro. This may help explain in part the protective effects of EPCs on hyperoxic injury in the developing lung vasculature and may represent a promising therapeutic strategy for BPD.

Live imaging of alveologenesis in precision-cut lung slices reveals dynamic epithelial cell behaviour

Damage to alveoli, the gas-exchanging region of the lungs, is a component of many chronic and acute lung diseases. In addition, insufficient generation of alveoli results in bronchopulmonary dysplasia, a disease of prematurity. Therefore visualising the process of alveolar development (alveologenesis) is critical for our understanding of lung homeostasis and for the development of treatments to repair and regenerate lung tissue. Here we show live alveologenesis, using long-term, time-lapse imaging of precision-cut lung slices. We reveal that during this process, epithelial cells are highly mobile and we identify specific cell behaviours that contribute to alveologenesis: cell clustering, hollowing and cell extension. Using the cytoskeleton inhibitors blebbistatin and cytochalasin D, we show that cell migration is a key driver of alveologenesis. This study reveals important novel information about lung biology and provides a new system in which to manipulate alveologenesis genetically and pharmacologically.

The process of alveologenesis is incompletely understood, partly due to the lack of applicable real-time imaging methods. Here the authors describe the process of alveologenesis and the behaviour of epithelial cells in real-time, using widefield microscopy and image deconvolution in precision-cut lung slices, revealing the dominant role of epithelial cell migration.

Consequences of early postnatal lipopolysaccharide exposure on developing lungs in mice

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

Control Interventions Can Impact Alveolarization and the Transcriptome in Developing Mouse Lungs

There is currently much interest in understanding the mechanisms of normal and aberrant lung alveolarization, particularly in the context of bronchopulmonary dysplasia, a common complication of preterm birth where alveolarization is impeded. To this end, the parenteral administration of pharmacological agents that modulate biochemical pathways, or facilitate modulation of gene expression in transgenic animals, has facilitated the discovery and validation of mechanisms that direct lung development. Such studies include control interventions, where the solvent vehicle, perhaps containing an inactive form of the agent applied, is administered; thereby providing a well-controlled point of reference for the analysis of the partner experiment. In the present study, the impact of several widely used control interventions in developing C57Bl/6J mouse pups was examined for effects on lung structure and the lung transcriptome. Parenteral administration of scrambled microRNA inhibitors (called antagomiRs) that are used to control in vivo microRNA neutralization studies, impacted lung volume, septal thickness, and the transcriptome of developing mouse lungs; with some effects dependent upon nucleotide sequence. Repeated intraperitoneal isotonic saline injections altered lung volume, with limited impact on the transcriptome. Parenteral administration of the tamoxifen solvent Miglyol accelerated mouse pup growth, and changed the abundance of 73 mRNA transcripts in the lung. Tamoxifen applied in Miglyol-in the absence of Cre recombinase-decreased pup growth, lung volume, and lung alveolarization and changed the abundance of 298 mRNA transcripts in the lung. These data demonstrate that widely used control interventions can directly impact lung alveolarization and the lung transcriptome in studies on lung development. Anat Rec, 302:346-363, 2019. © 2018 Wiley Periodicals, Inc.

Understanding alveolarization to induce lung regeneration

Background

Gas exchange represents the key physiological function of the lung, and is dependent upon proper formation of the delicate alveolar structure. Malformation or destruction of the alveolar gas-exchange regions are key histopathological hallmarks of diseases such as bronchopulmonary dysplasia (BPD), chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis; all of which are characterized by perturbations to the alveolo-capillary barrier structure. Impaired gas-exchange is the primary initial consequence of these perturbations, resulting in severe clinical symptoms, reduced quality of life, and death. The pronounced morbidity and mortality associated with malformation or destruction of alveoli underscores a pressing need for new therapeutic concepts. The re-induction of alveolarization in diseased lungs is a new and exciting concept in a regenerative medicine approach to manage pulmonary diseases that are characterized by an absence of alveoli.

Main text

Mechanisms of alveolarization first need to be understood, to identify pathways and mediators that may be exploited to drive the induction of alveolarization in the diseased lung. With this in mind, a variety of candidate cell-types, pathways, and molecular mediators have recently been identified. Using lineage tracing approaches and lung injury models, new progenitor cells for epithelial and mesenchymal cell types – as well as cell lineages which are able to acquire stem cell properties – have been discovered. However, the underlying mechanisms that orchestrate the complex process of lung alveolar septation remain largely unknown.

Conclusion

While important progress has been made, further characterization of the contributing cell-types, the cell type-specific molecular signatures, and the time-dependent chemical and mechanical processes in the developing, adult and diseased lung is needed in order to implement a regenerative therapeutic approach for pulmonary diseases.

Leflunomide attenuates oxidative stress in fetal human lung endothelial cells via superoxide dismutase 2 and catalase

Hyperoxia-induced oxidative stress contributes to the pathogenesis of bronchopulmonary dysplasia (BPD), the most common respiratory morbidity of preterm infants. Importantly, the disease lack specific therapies and is associated with long-term cardio-pulmonary and neurodevelopmental morbidities, signifying the need to discover novel therapies and decrease the disease burden. We and others have demonstrated that leflunomide, a food and drug administration approved drug to treat humans with rheumatoid arthritis, increases the expression of the anti-oxidant enzymes, NAD(P)H quinone dehydrogenase 1 (NQO1), catalase, and superoxide dismutase (SOD). However, whether this drug can decrease oxidative stress in fetal human pulmonary arterial endothelial cells (HPAECs) is unknown. Therefore, we tested the hypothesis that leflunomide will decrease hyperoxia-induced oxidative stress by upregulating these anti-oxidant enzymes in HPAECs. Leflunomide decreased hydrogen peroxide (H₂O₂) levels and increased the mRNA and protein levels of catalase, NQO1, and SOD2 in HPAECs at basal conditions. Further, leflunomide-treated cells continued to have decreased H₂O₂ and increased SOD2 levels upon hyperoxia exposure. Leflunomide did not affect the expression of other anti-oxidant enzymes, including hemoxygenase-1 and SOD1. AhR-knockdown experiments suggested that leflunomide regulated NQO1 levels via AhR-dependent mechanisms and H₂O₂, catalase, and SOD2 levels via AhR-independent mechanisms. Collectively, the results support the hypothesis that leflunomide decreases oxidative stress in HPAECs via SOD2-and catalase-dependent, but AhR- and NQO1-independent mechanisms. Our findings indicate that leflunomide is a potential drug for the management of BPD in preterm infants.

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

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

Hyperoxia Disrupts Extracellular Signal-Regulated Kinases 1/2-Induced Angiogenesis in the Developing Lungs

Hyperoxia contributes to the pathogenesis of bronchopulmonary dysplasia (BPD), a chronic lung disease of infants that is characterized by interrupted alveologenesis. Disrupted angiogenesis inhibits alveologenesis, but the mechanisms of disrupted angiogenesis in the developing lungs are poorly understood. In pre-clinical BPD models, hyperoxia increases the expression of extracellular signal-regulated kinases (ERK) 1/2; however, its effects on the lung endothelial ERK1/2 signaling are unclear. Further, whether ERK1/2 activation promotes lung angiogenesis in infants is unknown. Hence, we tested the following hypotheses: (1) hyperoxia exposure will increase lung endothelial ERK1/2 signaling in neonatal C57BL/6J (WT) mice and in fetal human pulmonary artery endothelial cells (HPAECs); (2) ERK1/2 inhibition will disrupt angiogenesis in vitro by repressing cell cycle progression. In mice, hyperoxia exposure transiently increased lung endothelial ERK1/2 activation at one week of life, before inhibiting it at two weeks of life. Interestingly, hyperoxia-mediated decrease in ERK1/2 activation in mice was associated with decreased angiogenesis and increased endothelial cell apoptosis. Hyperoxia also transiently activated ERK1/2 in HPAECs. ERK1/2 inhibition disrupted angiogenesis in vitro, and these effects were associated with altered levels of proteins that modulate cell cycle progression. Collectively, these findings support our hypotheses, emphasizing that the ERK1/2 pathway is a potential therapeutic target for BPD infants with decreased lung vascularization.

Neonatal hyperoxia depletes pulmonary vein cardiomyocytes in adult mice via mitochondrial oxidation

Supplemental oxygen given to preterm infants has been associated with permanently altering postnatal lung development. Now that these individuals are reaching adulthood, there is growing concern that early life oxygen exposure may also promote cardiovascular disease through poorly understood mechanisms. We previously reported that adult mice exposed to 100% oxygen between postnatal days 0 and 4 develop pulmonary hypertension, defined pathologically by capillary rarefaction, dilation of arterioles and veins, cardiac failure, and a reduced lifespan. Here, Affymetrix Gene Arrays are used to identify early transcriptional changes that take place in the lung before pulmonary capillary rarefaction. We discovered neonatal hyperoxia reduced expression of cardiac muscle genes, including those involved in contraction, calcium signaling, mitochondrial respiration, and vasodilation. Quantitative RT-PCR, immunohistochemistry, and genetic lineage mapping using Myh6^CreER; Rosa26^RmT/mG mice revealed this reflected loss of pulmonary vein cardiomyocytes. The greatest loss of cadiomyocytes was seen within the lung followed by a graded loss beginning at the hilum and extending into the left atrium. Loss of these cells was seen by 2 wk of age in mice exposed to ≥80% oxygen and was attributed, in part, to reduced proliferation. Administering mitoTEMPO, a scavenger of mitochondrial superoxide during neonatal hyperoxia prevented loss of these cells. Since pulmonary vein cardiomyocytes help pump oxygen-rich blood out of the lung, their early loss following neonatal hyperoxia may contribute to cardiovascular disease seen in these mice, and perhaps in people who were born preterm.

Early Acquisition of Pneumocystis jirovecii Colonization and Potential Association With Respiratory Distress Syndrome in Preterm Newborn Infants

Background

Pneumocystis pneumonia is a well-recognized lung disease of premature and malnourished babies. Even though serologic studies have shown that children are exposed to Pneumocystis jirovecii early in life, the epidemiology of human P. jirovecii infection and the host-microorganism relationship in infancy remain poorly understood. The aim of the present study was to investigate the prevalence of P. jirovecii colonization in preterm infants and its possible association with medical complications.

Methods

A prospective observational study of preterm infants (birth weight <1500 g and/or gestational age <32 weeks) was carried out. Identification of P. jirovecii colonization was performed by means of molecular techniques in nasal aspirated samples at birth.

Results

A total of 128 preterm infants were included during the study period. Pneumocystis DNA was identified in 25.7% (95% confidence interval [CI], 17.8%-33.7%) of newborns studied. A significant increase of respiratory distress syndrome in colonized group, even after adjusting for confounding factors (odds ratio, 2.7 [95% CI, 1.0-7.5]; P = .04), was observed. No differences were observed in other medical conditions between the 2 groups.

Conclusions

Pneumocystis jirovecii colonization is frequent in preterm births and could be a risk factor to develop respiratory distress syndrome among preterm infants.

Factors Affecting the Immunity to Respiratory Syncytial Virus: From Epigenetics to Microbiome

Respiratory syncytial virus (RSV) is a common pathogen that infects virtually all children by 2 years of age and is the leading cause of hospitalization of infants worldwide. While most children experience mild symptoms, some children progress to severe lower respiratory tract infection. Those children with severe disease have a much higher risk of developing childhood wheezing later in life. Many risk factors are known to result in exacerbated disease, including premature birth and early age of RSV infection, when the immune system is relatively immature. The development of the immune system before and after birth may be altered by several extrinsic and intrinsic factors that could lead to severe disease predisposition in children who do not exhibit any currently known risk factors. Recently, the role of the microbiome and the resulting metabolite profile has been an area of intense study in the development of lung disease, including viral infection and asthma. This review explores both known risk factors that can lead to severe RSV-induced disease as well as emerging topics in the development of immunity to RSV and the long-term consequences of severe infection.

Thioredoxin-1 Protects Bone Marrow-Derived Mesenchymal Stromal Cells from Hyperoxia-Induced Injury In Vitro

Background

The poor survival rate of mesenchymal stromal cells (MSC) transplanted into recipient lungs greatly limits their therapeutic efficacy for diseases like bronchopulmonary dysplasia (BPD). The aim of this study is to evaluate the effect of thioredoxin-1 (Trx-1) overexpression on improving the potential for bone marrow-derived mesenchymal stromal cells (BMSCs) to confer resistance against hyperoxia-induced cell injury.

Methods

80% O₂ was used to imitate the microenvironment surrounding-transplanted cells in the hyperoxia-induced lung injury in vitro. BMSC proliferation and apoptotic rates and the levels of reactive oxygen species (ROS) were measured. The effects of Trx-1 overexpression on the level of antioxidants and growth factors were investigated. We also investigated the activation of apoptosis-regulating kinase-1 (ASK1) and p38 mitogen-activated protein kinases (MAPK).

Result

Trx-1 overexpression significantly reduced hyperoxia-induced BMSC apoptosis and increased cell proliferation. We demonstrated that Trx-1 overexpression upregulated the levels of superoxide dismutase and glutathione peroxidase as well as downregulated the production of ROS. Furthermore, we illustrated that Trx-1 protected BMSCs against hyperoxic injury via decreasing the ASK1/P38 MAPK activation rate.

Conclusion

These results demonstrate that Trx-1 overexpression improved the ability of BMSCs to counteract hyperoxia-induced injury, thus increasing their potential to treat hyperoxia-induced lung diseases such as BPD.

Mesenchymal stem cells in combination with erythropoietin repair hyperoxia-induced alveoli dysplasia injury in neonatal mice via inhibition of TGF-β1 signaling

The aim of the present study is to investigate the protection effects of bone marrow mesenchymal stem cells (MSCs) in combination with EPO against hyperoxia-induced bronchopulmonary dysplasia (BPD) injury in neonatal mice. BPD model was prepared by continuous high oxygen exposure, 1×106 bone marrow MSCs and 5000U/kg recombinant human erythropoietin (EPO) were injected respectively. Results showed that administration of MSCs, EPO especially MSCs+EPO significant attenuated hyperoxia-induced lung damage with a decrease of fibrosis, radical alveolar counts and inhibition of the occurrence of epithelial-mesenchymal transition (EMT). Furthermore, MSCs+EPO co-treatment more significantly suppressed the levels of transforming growth factor-β1(TGF-β1) than MSCs or EPO alone. Collectively, these results suggested that MSCs, EPO in particular MSCs+EPO co-treatment could promote lung repair in hyperoxia-induced alveoli dysplasia injury via inhibition of TGF-β1 signaling pathway to further suppress EMT process and may be a promising therapeutic strategy.

Long-term pulmonary and cardiovascular morbidities of neonatal hyperoxia exposure in mice

Pulmonary hypertension (PH) frequently occurs in infants with bronchopulmonary dysplasia (BPD), causing increased mortality and right ventricular (RV) dysfunction that persists into adulthood. A first step in developing better therapeutic options is identifying and characterizing an appropriate animal model. Previously, we characterized the short-term morbidities of a model in which C57BL/6J wild-type (WT) mice were exposed to 70% O2 (hyperoxia) during the neonatal period. Here, we aimed to determine the long-term morbidities using lung morphometry, echocardiography (Echo), and cardiac magnetic resonance imaging (cMRI). The major highlight of this study is the use of the state-of-the art imaging technique, cMRI, in mice to characterize the long-term cardiac effects of neonatal hyperoxia exposure. To this end, WT mice were exposed to 21% O2 (normoxia) or hyperoxia for two weeks of life, followed by recovery in normoxia for six weeks. Alveolarization, pulmonary vascularization, pulmonary hypertension, and RV function were quantified at eight weeks. We found that hyperoxia exposure resulted in persistent alveolar and pulmonary vascular simplification. Furthermore, the Echo and cMRI studies demonstrated that hyperoxia-exposed mice had signs of PH and RV dysfunction as indicated by increased RV pressure, mass, and end-systolic and -diastolic volumes, and decreased RV stroke volume and ejection fractions. Taken together, our results demonstrate that neonatal hyperoxia exposure in mice cause cardiopulmonary morbidities that persists into adulthood and provides evidence for the use of this model to develop novel therapies for BPD infants with PH.