Inhibiting lung elastase activity enables lung growth in mechanically ventilated newborn mice

Complex roles of TGF-β signaling pathways in lung development and bronchopulmonary dysplasia

As survival of extremely preterm infants continues to improve, there is also an associated increase in bronchopulmonary dysplasia (BPD), one of the most significant complications of preterm birth. BPD development is multifactorial resulting from exposure to multiple antenatal and postnatal stressors. BPD has both short-term health implications and long-term sequelae including increased respiratory, cardiovascular, and neurological morbidity. Transforming growth factor β (TGF-β) is an important signaling pathway in lung development, organ injury, and fibrosis and is implicated in the development of BPD. This review provides a detailed account on the role of TGF-β in antenatal and postnatal lung development, the effect of known risk factors for BPD on the TGF-β signaling pathway, and how medications currently in use or under development, for the prevention or treatment of BPD, affect TGF-β signaling.

Relationship between impaired BMP signalling and clinical risk factors at early-stage vascular injury in the preterm infant

INTRODUCTION

Chronic lung disease, that is, bronchopulmonary dysplasia (BPD) is the most common complication in preterm infants and develops as a consequence of the misguided formation of the gas-exchange area undergoing prenatal and postnatal injury. Subsequent vascular disease and its progression into pulmonary arterial hypertension critically determines long-term outcome in the BPD infant but lacks identification of early, disease-defining changes.

METHODS

We link impaired bone morphogenetic protein (BMP) signalling to the earliest onset of vascular pathology in the human preterm lung and delineate the specific effects of the most prevalent prenatal and postnatal clinical risk factors for lung injury mimicking clinically relevant conditions in a multilayered animal model using wild-type and transgenic neonatal mice.

RESULTS

We demonstrate (1) the significant reduction in BMP receptor 2 (BMPR2) expression at the onset of vascular pathology in the lung of preterm infants, later mirrored by reduced plasma BMP protein levels in infants with developing BPD, (2) the rapid impairment (and persistent change) of BMPR2 signalling on postnatal exposure to hyperoxia and mechanical ventilation, aggravated by prenatal cigarette smoke in a preclinical mouse model and (3) a link to defective alveolar septation and matrix remodelling through platelet derived growth factor-receptor alpha deficiency. In a treatment approach, we partially reversed vascular pathology by BMPR2-targeted treatment with FK506 in vitro and in vivo.

CONCLUSION

We identified impaired BMP signalling as a hallmark of early vascular disease in the injured neonatal lung while outlining its promising potential as a future biomarker or therapeutic target in this growing, high-risk patient population.

Association of immune cell recruitment and BPD development

In the neonatal lung, exposure to both prenatal and early postnatal risk factors converge into the development of injury and ultimately chronic disease, also known as bronchopulmonary dysplasia (BPD). The focus of many studies has been the characteristic inflammatory responses provoked by these exposures. Here, we review the relationship between immaturity and prenatal conditions, as well as postnatal exposure to mechanical ventilation and oxygen toxicity, with the imbalance of pro- and anti-inflammatory regulatory networks. In these conditions, cytokine release, protease activity, and sustained presence of innate immune cells in the lung result in pathologic processes contributing to lung injury. We highlight the recruitment and function of myeloid innate immune cells, in particular, neutrophils and monocyte/macrophages in the BPD lung in human patients and animal models. We also discuss dissimilarities between the infant and adult immune system as a basis for the development of novel therapeutic strategies.

When inflammation meets lung development-an update on the pathogenesis of bronchopulmonary dysplasia

Even more than 50 years after its initial description, bronchopulmonary dysplasia (BPD) remains one of the most important and lifelong sequelae following premature birth. Tremendous efforts have been undertaken since then to reduce this ever-increasing disease burden but a therapeutic breakthrough preventing BPD is still not in sight. The inflammatory response provoked in the immature lung is a key driver of distorted lung development and impacts the formation of alveolar, mesenchymal, and vascular structures during a particularly vulnerable time-period. During the last 5 years, new scientific insights have led to an improved pathomechanistic understanding of BPD origins and disease drivers. Within the framework of current scientific progress, concepts involving disruption of the balance of key inflammatory and lung growth promoting pathways by various stimuli, take center stage. Still today, the number of efficient therapeutics available to prevent BPD is limited to a few, well-established pharmacological interventions including postnatal corticosteroids, early caffeine administration, and vitamin A. Recent advances in the clinical care of infants in the neonatal intensive care unit (NICU) have led to improvements in survival without a consistent reduction in the incidence of BPD. Our update provides latest insights from both preclinical models and clinical cohort studies and describes novel approaches to prevent BPD.

Lysyl oxidase regulation and protein aldehydes in the injured newborn lung

During newborn lung injury, excessive activity of lysyl oxidases (LOXs) disrupts extracellular matrix (ECM) formation. Previous studies indicate that TGFβ activation in the O₂-injured mouse pup lung increases lysyl oxidase (LOX) expression. But how TGFβ regulates this, and whether the LOXs generate excess pulmonary aldehydes are unknown. First, we determined that O₂-mediated lung injury increases LOX protein expression in TGFβ-stimulated pup lung interstitial fibroblasts. This regulation appeared to be direct; this is because TGFβ treatment also increased LOX protein expression in isolated pup lung fibroblasts. Then using a fibroblast cell line, we determined that TGFβ stimulates LOX expression at a transcriptional level via Smad2/3-dependent signaling. LOX is translated as a pro-protein that requires secretion and extracellular cleavage before assuming amine oxidase activity and, in some cells, reuptake with nuclear localization. We found that pro-LOX is processed in the newborn mouse pup lung. Also, O₂-mediated injury was determined to increase pro-LOX secretion and nuclear LOX immunoreactivity particularly in areas populated with interstitial fibroblasts and exhibiting malformed ECM. Then, using molecular probes, we detected increased aldehyde levels in vivo in O₂-injured pup lungs, which mapped to areas of increased pro-LOX secretion in lung sections. Increased activity of LOXs plays a critical role in the aldehyde generation; an inhibitor of LOXs prevented the elevation of aldehydes in the O₂-injured pup lung. These results reveal new mechanisms of TGFβ and LOX in newborn lung disease and suggest that aldehyde-reactive probes might have utility in sensing the activation of LOXs in vivo during lung injury.

Patho-mechanisms of the origins of bronchopulmonary dysplasia

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

Macrophage-derived IL-6 trans-signaling as a novel target in the pathogenesis of bronchopulmonary dysplasia

Rationale

Premature infants exposed to oxygen are at risk for bronchopulmonary dysplasia (BPD), which is characterised by lung growth arrest. Inflammation is important, but the mechanisms remain elusive. Here, we investigated inflammatory pathways and therapeutic targets in severe clinical and experimental BPD.

Methods and results

First, transcriptomic analysis with in silico cellular deconvolution identified a lung-intrinsic M1-like-driven cytokine pattern in newborn mice after hyperoxia. These findings were confirmed by gene expression of macrophage-regulating chemokines (Ccl2, Ccl7, Cxcl5) and markers (Il6, Il17A, Mmp12). Secondly, hyperoxia-activated interleukin 6 (IL-6)/signal transducer and activator of transcription 3 (STAT3) signalling was measured in vivo and related to loss of alveolar epithelial type II cells (ATII) as well as increased mesenchymal marker. Il6 null mice exhibited preserved ATII survival, reduced myofibroblasts and improved elastic fibre assembly, thus enabling lung growth and protecting lung function. Pharmacological inhibition of global IL-6 signalling and IL-6 trans-signalling promoted alveolarisation and ATII survival after hyperoxia. Third, hyperoxia triggered M1-like polarisation, possibly via Krüppel-like factor 4; hyperoxia-conditioned medium of macrophages and IL-6-impaired ATII proliferation. Finally, clinical data demonstrated elevated macrophage-related plasma cytokines as potential biomarkers that identify infants receiving oxygen at increased risk of developing BPD. Moreover, macrophage-derived IL6 and active STAT3 were related to loss of epithelial cells in BPD lungs.

Conclusion

We present a novel IL-6-mediated mechanism by which hyperoxia activates macrophages in immature lungs, impairs ATII homeostasis and disrupts elastic fibre formation, thereby inhibiting lung growth. The data provide evidence that IL-6 trans-signalling could offer an innovative pharmacological target to enable lung growth in severe neonatal chronic lung disease.

M1-like macrophage activation is linked to IL-6/STAT3 axis in clinical and experimental BPD. Inhibition of macrophage-related IL-6 trans-signalling promotes ATII survival and lung growth in experimental BPD as a new therapy for preterm infants.https://bit.ly/3AhF7GP

Reduced neutrophil elastase inhibitor elafin and elevated transforming growth factor-β1 are linked to inflammatory response in sputum of cystic fibrosis patients with Pseudomonas aeruginosa

Research question

Pulmonary disease progression in patients with cystic fibrosis (CF) is characterised by inflammation and fibrosis and aggravated by Pseudomonas aeruginosa (Pa). We investigated the impact of Pa specifically on: 1) protease/antiprotease balance; 2) inflammation; and 3) the link of both parameters to clinical parameters of CF patients.

Methods

Transforming growth factor-β₁ (TGF-β₁), interleukin (IL)-1β, IL-8, neutrophil elastase (NE) and elastase inhibitor elafin were measured (ELISA assays), and gene expression of the NF-κB pathway was assessed (reverse transcriptase PCR) in the sputum of 60 CF patients with a minimum age of 5 years. Spirometry was assessed according to American Thoracic Society guidelines.

Results

Our results demonstrated the following: 1) NE was markedly increased in Pa-positive sputum, whereas elafin was significantly decreased; 2) increased IL-1β/IL-8 levels were associated with both Pa infection and reduced forced expiratory volume in 1 s, and sputum TGF-β₁ was elevated in Pa-infected CF patients and linked to an impaired lung function; and 3) gene expression of NF-κB signalling components was increased in sputum of Pa-infected patients, and these findings were positively correlated with IL-8.

Conclusion

Our study links Pa infection to an imbalance of NE and NE inhibitor elafin and increased inflammatory mediators. Moreover, our data demonstrate an association between high TGF-β₁ sputum levels and a progress in chronic lung inflammation and pulmonary fibrosis in CF. Controlling the excessive airway inflammation by inhibition of NE and TGF-β₁ might be promising therapeutic strategies in future CF therapy and a possible complement to cystic fibrosis transmembrane conductance regulator (CFTR) modulators.

Early Changes and Indicators Characterizing Lung Aging in Neonatal Chronic Lung Disease

Infants suffering from neonatal chronic lung disease, i.e., bronchopulmonary dysplasia, are facing long-term consequences determined by individual genetic background, presence of infections, and postnatal treatment strategies such as mechanical ventilation and oxygen toxicity. The adverse effects provoked by these measures include inflammatory processes, oxidative stress, altered growth factor signaling, and remodeling of the extracellular matrix. Both, acute and long-term consequences are determined by the capacity of the immature lung to respond to the challenges outlined above. The subsequent impairment of lung growth translates into an altered trajectory of lung function later in life. Here, knowledge about second and third hit events provoked through environmental insults are of specific importance when advocating lifestyle recommendations to this patient population. A profound exchange between the different health care professionals involved is urgently needed and needs to consider disease origin while future monitoring and treatment strategies are developed.

LISA/MIST: Complex clinical problems almost never have easy solutions

Over the last 10 years, new techniques to administer surfactant have been promoted, based on their presumed lesser invasiveness and they have been generally called LISA (less invasive surfactant administration). We believe that the clinical potential of LISA techniques is currently overestimated. LISA lacks biological and pathophysiological background justifying its potential benefits. Moreover, LISA has been investigated in clinical trials without previous translational data and these trials are affected by significant flaws. The available data from these trials only allow to conclude that LISA is better than prolonged, unrestricted invasive ventilation with loosely described parameters, a mode of respiratory support that should be anyway avoided in preterm infants. We urge the conduction of high-quality studies to understand how to choose and titrate analgesia/sedation and optimize surfactant administration in preterm neonates. We offer a comprehensive, evidence-based review of the clinical data on LISA, their biases and the lack of physiopathology background.

Use of Nasoil® via intranasal to control the harmful effects of Covid-19

In the absence of vaccines and antiviral drugs available to prevent and treat COVID-19, it becomes imperative to find or use all those products with the potential to fight this virus. This article is an attempt to propose ways to prevent, treat and control the COVID-19 virus, using a product based on plant extracts with the potential to reduce the symptoms caused by the SARS-CoV-2 virus. Nasoil® counts as one of its main components, Asclepias curassavica extracts, and in the present study it has been shown that it is an effective adjuvant in the treatment of Covid-19, increasing the respiratory capacity of the patients (SpO2> 90%) and reducing the symptoms from the first application, improving the patients around the fifth to the eighth application. At a preventive level, the individuals in this study who have applied it (400 individuals) only a 3.15% of these presented symptoms, disappearing when increasing the weekly applications.

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Nasoil® protects from the appearance of symptoms by 96% due to Covid-19.

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Modifying lung microenvironments reduces Covid-19 symptoms.

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Promoting new interactions in the elastic protein decreases the elastase activity of neutrophils.

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The combination of plant extracts in Nasoil® help in respiratory problems.

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Nasoil® is an co-adjuvant for the control and prevention of the SARS-CoV-2 virus.

IL-33-induced neutrophil extracellular traps degrade fibronectin in a murine model of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is the leading cause of chronic lung disease in preterm neonates. Extracellular matrix (ECM) abnormalities reshape lung development, contributing to BPD progression. In the present study, we first discovered that the ECM component fibronectin was reduced in the pulmonary tissues of model mice with BPD induced by lipopolysaccharide (LPS) and hyper-oxygen. Meanwhile, interleukin-33 (IL-33) and other inflammatory cytokines were elevated in BPD lung tissues. LPS stimulated the production of IL-33 in alveolar epithelial cells via myeloid differentiation factor 88 (MyD88), protein 38 (p38), and nuclear factor-kappa B (NF-κB) protein 65 (p65). Following the knockout of either IL-33 or its receptor suppression of tumorigenicity 2 (ST2) in mice, BPD disease severity was improved, accompanied by elevated fibronectin. ST2 neutralization antibody also relieved BPD progression and restored the expression of fibronectin. IL-33 induced the formation of neutrophil extracellular traps (NETs), which degraded fibronectin in alveolar epithelial cells. Moreover, DNase-mediated degradation of NETs was protective against BPD. Finally, a fibronectin inhibitor directly decreased fibronectin and caused BPD-like disease in the mouse model. Our findings may shed light on the roles of IL-33-induced NETs and reduced fibronectin in the pathogenesis of BPD.

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.

Elafin Treatment Rescues EGFR-Klf4 Signaling and Lung Cell Survival in Ventilated Newborn Mice

Mechanical ventilation with O₂-rich gas (MV-O₂) inhibits alveologenesis and lung growth. We previously showed that MV-O₂ increased elastase activity and apoptosis in lungs of newborn mice, whereas elastase inhibition by elafin suppressed apoptosis and enabled lung growth. Pilot studies suggested that MV-O₂ reduces lung expression of prosurvival factors phosphorylated epidermal growth factor receptor (pEGFR) and Krüppel-like factor 4 (Klf4). Here, we sought to determine whether apoptosis and lung growth arrest evoked by MV-O₂ reflect disrupted pEGFR-Klf4 signaling, which elafin treatment preserves, and to assess potential biomarkers of bronchopulmonary dysplasia (BPD). Five-day-old mice underwent MV with air or 40% O₂ for 8-24 hours with or without elafin treatment. Unventilated pups served as controls. Immunoblots were used to assess lung pEGFR and Klf4 proteins. Cultured MLE-12 cells were exposed to AG1478 (EGFR inhibitor), Klf4 siRNA, or vehicle to assess effects on proliferation, apoptosis, and EGFR regulation of Klf4. Plasma elastase and elafin levels were measured in extremely premature infants. In newborn mice, MV with air or 40% O₂ inhibited EGFR phosphorylation and suppressed Klf4 protein content in lungs (vs. unventilated controls), yielding increased apoptosis. Elafin treatment inhibited elastase, preserved lung pEGFR and Klf4, and attenuated the apoptosis observed in lungs of vehicle-treated mice. In MLE-12 studies, pharmacological inhibition of EGFR and siRNA suppression of Klf4 increased apoptosis and reduced proliferation, and EGFR inhibition decreased Klf4. Plasma elastase levels were more than twofold higher, without a compensating increase of plasma elafin, in infants with BPD, compared to infants without BPD. These findings indicate that pEGFR-Klf4 is a novel prosurvival signaling pathway in lung epithelium that MV disrupts. Elafin preserves pEGFR-Klf4 signaling and inhibits apoptosis, thereby enabling lung growth during MV. Together, our animal and human data raise the question: would elastase inhibition prevent BPD in high-risk infants exposed to MV-O₂?

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.

Targeting transglutaminase 2 partially restores extracellular matrix structure but not alveolar architecture in experimental bronchopulmonary dysplasia

The generation, maturation and remodelling of the extracellular matrix (ECM) are essential for the formation of alveoli during lung development. Alveoli formation is disturbed in preterm infants that develop bronchopulmonary dysplasia (BPD), where collagen fibres are malformed, and perturbations to lung ECM structures may underlie BPD pathogenesis. Malformed ECM structures might result from abnormal protein cross-linking, in part attributable to the increased expression and activity of transglutaminase 2 (TGM2) that have been noted in affected patient lungs, as well as in hyperoxia-based BPD animal models. The objective of the present study was to assess whether TGM2 plays a causal role in normal and aberrant lung alveolarization. Targeted deletion of Tgm2 in C57BL/6J mice increased septal thickness and reduced gas-exchange surface area in otherwise normally developing lungs. During aberrant lung alveolarization that occurred under hyperoxic conditions, collagen structures in Tgm2^-/- mice were partially protected from the impact of hyperoxia, where normal dihydroxylysinonorleucine and hydroxylysylpiridinoline collagen cross-link abundance was restored; however, the lung alveolar architecture remained abnormal. Inhibition of transglutaminases (including TGM2) with cysteamine appreciably reduced transglutaminase activity in vivo, as assessed by N^ε -(γ-l-glutamyl)-l-lysine abundance and TGM catalytic activity, and restored normal dihydroxylysinonorleucine and hydroxylysylpiridinoline collagen cross-link abundance under pathological conditions. Furthermore, a moderate improvement in alveoli size and gas-exchange surface density was noted in cysteamine-treated mouse lungs in which BPD was modelled. These data indicate that TGM2 plays a role in normal lung alveolarization, and contributes to the formation of aberrant ECM structures during disordered lung alveolarization.

Attenuated PDGF signaling drives alveolar and microvascular defects in neonatal chronic lung disease

Neonatal chronic lung disease (nCLD) affects a significant number of neonates receiving mechanical ventilation with oxygen-rich gas (MV-O₂). Regardless, the primary molecular driver of the disease remains elusive. We discover significant enrichment for SNPs in the PDGF-Rα gene in preterms with nCLD and directly test the effect of PDGF-Rα haploinsufficiency on the development of nCLD using a preclinical mouse model of MV-O₂ In the context of MV-O₂, attenuated PDGF signaling independently contributes to defective septation and endothelial cell apoptosis stemming from a PDGF-Rα-dependent reduction in lung VEGF-A. TGF-β contributes to the PDGF-Rα-dependent decrease in myofibroblast function. Remarkably, endotracheal treatment with exogenous PDGF-A rescues both the lung defects in haploinsufficient mice undergoing MV-O₂ Overall, our results establish attenuated PDGF signaling as an important driver of nCLD pathology with provision of PDGF-A as a protective strategy for newborns undergoing MV-O₂.

An Official American Thoracic Society Workshop Report 2015. Stem Cells and Cell Therapies in Lung Biology and Diseases

The University of Vermont College of Medicine, in collaboration with the NHLBI, Alpha-1 Foundation, American Thoracic Society, Cystic Fibrosis Foundation, European Respiratory Society, International Society for Cellular Therapy, and the Pulmonary Fibrosis Foundation, convened a workshop, "Stem Cells and Cell Therapies in Lung Biology and Lung Diseases," held July 27 to 30, 2015, at the University of Vermont. The conference objectives were to review the current understanding of the role of stem and progenitor cells in lung repair after injury and to review the current status of cell therapy and ex vivo bioengineering approaches for lung diseases. These are all rapidly expanding areas of study that both provide further insight into and challenge traditional views of mechanisms of lung repair after injury and pathogenesis of several lung diseases. The goals of the conference were to summarize the current state of the field, discuss and debate current controversies, and identify future research directions and opportunities for both basic and translational research in cell-based therapies for lung diseases. This 10th anniversary conference was a follow up to five previous biennial conferences held at the University of Vermont in 2005, 2007, 2009, 2011, and 2013. Each of those conferences, also sponsored by the National Institutes of Health, American Thoracic Society, and respiratory disease foundations, has been important in helping guide research and funding priorities. The major conference recommendations are summarized at the end of the report and highlight both the significant progress and major challenges in these rapidly progressing fields.

The BPD trio? Interaction of dysregulated PDGF, VEGF, and TGF signaling in neonatal chronic lung disease

The development of neonatal chronic lung disease (nCLD), i.e., bronchopulmonary dysplasia (BPD) in preterm infants, significantly determines long-term outcome in this patient population. Risk factors include mechanical ventilation and oxygen toxicity impacting on the immature lung resulting in impaired alveolarization and vascularization. Disease development is characterized by inflammation, extracellular matrix remodeling, and apoptosis, closely intertwined with the dysregulation of growth factor signaling. This review focuses on the causes and consequences of altered signaling in central pathways like transforming growth factor (TGF), platelet-derived growth factor (PDGF), and vascular endothelial growth factor (VEGF) driving these above indicated processes, i.e., inflammation, matrix remodeling, and vascular development. We emphasize the shared and distinct role of these pathways as well as their interconnection in disease initiation and progression, generating important knowledge for the development of future treatment strategies.

Facilitated Diagnosis of Pneumothoraces in Newborn Mice Using X-ray Dark-Field Radiography

OBJECTIVE

The aim of this study was to evaluate the diagnostic value of x-ray dark-field imaging in projection radiography-based depiction of pneumothoraces in the neonatal murine lung, a potentially life-threatening medical condition that requires a timely and correct diagnosis.

MATERIALS AND METHODS

By the use of a unique preclinical model, 7-day-old C57Bl/6N mice received mechanical ventilation for 2 or 8 hours with oxygen-rich gas (FIO2 = 0.4; n = 24). Unventilated mice either spontaneously breathed oxygen-rich gas (FIO2 = 0.4) for 2 or 8 hours or room air (n = 22). At the end of the experiment, lungs were inflated with a standardized volume of air after a lethal dose of pentobarbital was administered to the pups. All lungs were imaged with a prototype grating-based small-animal scanner to acquire x-ray transmission and dark-field radiographs. Image contrast between the air-filled pleural space and lung tissue was quantified for both transmission and dark-field radiograms. After the independent expert's assessment, 2 blinded readers evaluated all dark-field and transmission images for the presence or absence of pneumothoraces. Contrast ratios, diagnostic accuracy, as well as reader's confidence and interreader agreement were recorded for both imaging modalities.

RESULTS

Evaluation of both x-ray transmission and dark-field radiographs by independent experts revealed the development of a total of 10 pneumothoraces in 8 mice. Here, the contrast ratio between the air-filled pleural space of the pneumothoraces and the lung tissue was significantly higher in the dark field (8.4 ± 3.5) when compared with the transmission images (5.1 ± 2.8; P < 0.05). Accordingly, the readers' diagnostic confidence for the diagnosis of pneumothoraces was significantly higher for dark-field compared with transmission images (P = 0.001). Interreader agreement improved from moderate for the analysis of transmission images alone (κ = 0.41) to very good when analyzing dark-field images alone (κ = 0.90) or in combination with transmission images (κ = 0.88). Diagnostic accuracy significantly improved for the analysis of dark-field images alone (P = 0.04) or in combination with transmission images (P = 0.02), compared with the analysis of transmission radiographs only.

CONCLUSIONS

The significant improvement in contrast ratios between lung parenchyma and free air in the dark-field images allows the facilitated detection of pneumothoraces in the newborn mouse. These preclinical experiments indicate the potential of the technique for future clinical applications.

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

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

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

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

Visualization of neonatal lung injury associated with mechanical ventilation using x-ray dark-field radiography

Mechanical ventilation (MV) and supplementation of oxygen-enriched gas, often needed in postnatal resuscitation procedures, are known to be main risk factors for impaired pulmonary development in the preterm and term neonates. Unfortunately, current imaging modalities lack in sensitivity for the detection of early stage lung injury. The present study reports a new imaging approach for diagnosis and staging of early lung injury induced by MV and hyperoxia in neonatal mice. The imaging method is based on the Talbot-Lau x-ray grating interferometry that makes it possible to quantify the x-ray small-angle scattering on the air-tissue interfaces. This so-called dark-field signal revealed increasing loss of x-ray small-angle scattering when comparing images of neonatal mice undergoing hyperoxia and MV-O₂ with animals kept at room air. The changes in the dark field correlated well with histologic findings and provided superior differentiation than conventional x-ray imaging and lung function testing. The results suggest that x-ray dark-field radiography is a sensitive tool for assessing structural changes in the developing lung. In the future, with further technical developments x-ray dark-field imaging could be an important tool for earlier diagnosis and sensitive monitoring of lung injury in neonates requiring postnatal oxygen or ventilator therapy.

Absence of TNF-α enhances inflammatory response in the newborn lung undergoing mechanical ventilation

Bronchopulmonary dysplasia (BPD), characterized by impaired alveolarization and vascularization in association with lung inflammation and apoptosis, often occurs after mechanical ventilation with oxygen-rich gas (MV-O2). As heightened expression of the proinflammatory cytokine TNF-α has been described in infants with BPD, we hypothesized that absence of TNF-α would reduce pulmonary inflammation, and attenuate structural changes in newborn mice undergoing MV-O2 Neonatal TNF-α null (TNF-α(-/-)) and wild type (TNF-α(+/+)) mice received MV-O2 for 8 h; controls spontaneously breathed 40% O2 Histologic, mRNA, and protein analysis in vivo were complemented by in vitro studies subjecting primary pulmonary myofibroblasts to mechanical stretch. Finally, TNF-α level in tracheal aspirates from preterm infants were determined by ELISA. Although MV-O2 induced larger and fewer alveoli in both, TNF-α(-/-) and TNF-α(+/+) mice, it caused enhanced lung apoptosis (TUNEL, caspase-3/-6/-8), infiltration of macrophages and neutrophils, and proinflammatory mediator expression (IL-1β, CXCL-1, MCP-1) in TNF-α(-/-) mice. These differences were associated with increased pulmonary transforming growth factor-β (TGF-β) signaling, decreased TGF-β inhibitor SMAD-7 expression, and reduced pulmonary NF-κB activity in ventilated TNF-α(-/-) mice. Preterm infants who went on to develop BPD showed significantly lower TNF-α levels at birth. Our results suggest a critical balance between TNF-α and TGF-β signaling in the developing lung, and underscore the critical importance of these key pathways in the pathogenesis of BPD. Future treatment strategies need to weigh the potential benefits of inhibiting pathologic cytokine expression against the potential of altering key developmental pathways.

High-Mobility Group Box-1 Protein Disrupts Alveolar Elastogenesis of Hyperoxia-Injured Newborn Lungs

Although high-mobility group box-1 (HMGB1) levels in tracheal aspirates are associated with the pathological features of bronchopulmonary dysplasia (BPD), the role of HMGB1 in the terminal stage of abnormal alveologenesis has not yet been understood. In this study, we addressed the role of HMGB1 in the elastogenesis disruption in the lungs of newborn mice with BPD. We found that elevations of whole lung HMGB1 level were associated with impaired alveolar development and aberrant elastin production in 85% O2-exposed lungs. HMGB1 neutralizing antibody attenuated the structural disintegration developed in hyperoxia-damaged lungs. Furthermore, HMGB1 inhibition rescued the neutrophil influx in hyperoxia-injured lung and partially abolished the mRNA level of the proinflammatory mediators, interleukin (IL)-1β and transforming growth factor (TGF)-β1. These data suggested that pulmonary HMGB1 plays an important role in the disruption of elastogenesis in the terminal stage of lung development through reduced pulmonary inflammatory response.

The Extracellular Matrix in Bronchopulmonary Dysplasia: Target and Source

Bronchopulmonary dysplasia (BPD) is a common complication of preterm birth that contributes significantly to morbidity and mortality in neonatal intensive care units. BPD results from life-saving interventions, such as mechanical ventilation and oxygen supplementation used to manage preterm infants with acute respiratory failure, which may be complicated by pulmonary infection. The pathogenic pathways driving BPD are not well-delineated but include disturbances to the coordinated action of gene expression, cell-cell communication, physical forces, and cell interactions with the extracellular matrix (ECM), which together guide normal lung development. Efforts to further delineate these pathways have been assisted by the use of animal models of BPD, which rely on infection, injurious mechanical ventilation, or oxygen supplementation, where histopathological features of BPD can be mimicked. Notable among these are perturbations to ECM structures, namely, the organization of the elastin and collagen networks in the developing lung. Dysregulated collagen deposition and disturbed elastin fiber organization are pathological hallmarks of clinical and experimental BPD. Strides have been made in understanding the disturbances to ECM production in the developing lung, but much still remains to be discovered about how ECM maturation and turnover are dysregulated in aberrantly developing lungs. This review aims to inform the reader about the state-of-the-art concerning the ECM in BPD, to highlight the gaps in our knowledge and current controversies, and to suggest directions for future work in this exciting and complex area of lung development (patho)biology.

Understanding the Impact of Infection, Inflammation, and Their Persistence in the Pathogenesis of Bronchopulmonary Dysplasia

The concerted interaction of genetic and environmental factors acts on the preterm human immature lung with inflammation being the common denominator leading to the multifactorial origin of the most common chronic lung disease in infants – ­bronchopulmonary dysplasia (BPD). Adverse perinatal exposure to infection/inflammation with added insults like invasive mecha nical ventilation, exposure to hyperoxia, and sepsis causes persistent immune dysregulation. In this review article, we have attempted to analyze and consolidate current knowledge about the role played by persistent prenatal and postnatal inflammation in the pathogenesis of BPD. While some parameters of the early inflammatory response (neutrophils, cytokines, etc.) may not be detectable after days to weeks of exposure to noxious stimuli, they have already initiated the signaling pathways of the inflammatory process/immune cascade and have affected permanent defects structurally and functionally in the BPD lungs. Hence, translational research aimed at prevention/amelioration of BPD needs to focus on dampening the inflammatory response at an early stage to prevent the cascade of events leading to lung injury with impaired healing resulting in the pathologic pulmonary phenotype of alveolar simplification and dysregulated vascularization characteristic of BPD.

Gene expression profile in newborn rat lungs after two days of recovery of mechanical ventilation

BACKGROUND

Preterm infants having immature lungs often require respiratory support, potentially leading to bronchopulmonary dysplasia (BPD). Conventional BPD rodent models based on mechanical ventilation (MV) present outcome measured at the end of the ventilation period. A reversible intubation and ventilation model in newborn rats recently allowed discovering that different sets of genes modified their expression related to time after MV. In a newborn rat model, the expression profile 48 h after MV was analyzed with gene arrays to detect potentially interesting candidates with an impact on BPD development.

METHODS

Rat pups were injected P4-5 with 2 mg/kg lipopolysaccharide (LPS). One day later, MV with 21 or 60% oxygen was applied during 6 h. Animals were sacrified 48 h after end of ventilation. Affymetrix gene arrays assessed the total gene expression profile in lung tissue.

RESULTS

In fully treated animals (LPS + MV + 60% O(2)) vs. controls, 271 genes changed expression significantly. All modified genes could be classified in six pathways: tissue remodeling/wound repair, immune system and inflammatory response, hematopoiesis, vasodilatation, and oxidative stress. Major alterations were found in the MMP and complement system.

CONCLUSION

MMPs and complement factors play a central role in several of the pathways identified and may represent interesting targets for BPD treatment/prevention.Bronchopulmonary dysplasia (BPD) is a chronic lung disease occurring in ~30% of preterm infants born less than 30 wk of gestation (1). Its main risk factors include lung immaturity due to preterm delivery, mechanical ventilation (MV), oxygen toxicity, chorioamnionitis, and sepsis. The main feature is an arrest of alveolar and capillary formation (2). Models trying to decipher genes involved in the pathophysiology of BPD are mainly based on MV and oxygen application to young mammals with immature lungs of different species (3). In newborn rodent models, analyses of lung structure and gene and protein expression are performed for practical reasons directly at the end of MV (4,5,6). However, later appearing changes of gene expression might also have an impact on lung development and the evolution towards BPD and cannot be discovered by such models. Recently, we developed a newborn rat model of MV using an atraumatic (orotracheal) intubation technique that allows the weaning of the newborn animal off anesthesia and MV, the extubation to spontaneous breathing, and therefore allows the evaluation of effects of MV after a ventilation-free period of recovery (7). Indeed, applying this concept of atraumatic intubation by direct laryngoscopy, we recently were able to show significant differences between gene expression changes appearing directly after MV compared to those measured after a ventilation-free interval of 48 h. Immediately after MV, inflammation-related genes showed a transitory modified expression, while another set of more structurally related genes changed their expression only after a delay of 2 d (7). Lung structure, analyzed by conventional 2D histology and also by 3D reconstruction using synchrotron x-ray tomographic microscopy revealed, 48 h after end of MV, a reduced complexity of lung architecture compared to the nonventilated rat lungs, similar to the typical findings in BPD. To extend these observations about late gene expression modifications, we performed with a similar model a full gene expression profile of lung tissue 48 h after the end of MV with either room air or 60% oxygen. Essentially, we measured changes in the expression of genes related to the MMPs and complement system which played a role in many of the six identified mostly affected pathways.

Animal Models, Learning Lessons to Prevent and Treat Neonatal Chronic Lung Disease

Bronchopulmonary dysplasia (BPD) is a unique injury syndrome caused by prolonged injury and repair imposed on an immature and developing lung. The decreased septation and decreased microvascular development phenotype of BPD can be reproduced in newborn rodents with increased chronic oxygen exposure and in premature primates and sheep with oxygen and/or mechanical ventilation. The inflammation caused by oxidants, inflammatory agonists, and/or stretch injury from mechanical ventilation seems to promote the anatomic abnormalities. Multiple interventions targeted to specific inflammatory cells or pathways or targeted to decreasing ventilation-mediated injury can substantially prevent the anatomic changes associated with BPD in term rodents and in preterm sheep or primate models. Most of the anti-inflammatory therapies with benefit in animal models have not been tested clinically. None of the interventions that have been tested clinically are as effective as anticipated from the animal models. These inconsistencies in responses likely are explained by the antenatal differences in lung exposures of the developing animals relative to very preterm humans. The animals generally have normal lungs while the lungs of preterm infants are exposed variably to intrauterine inflammation, growth abnormalities, antenatal corticosteroids, and poorly understood effects from the causes of preterm delivery. The animal models have been essential for the definition of the mediators that can cause a BPD phenotype. These models will be necessary to develop and test future-targeted interventions to prevent and treat BPD.

Neutrophil elastase-induced elastin degradation mediates macrophage influx and lung injury in 60% O2-exposed neonatal rats

Neutrophil (PMNL) influx precedes lung macrophage (LM) influx into the lung following exposure of newborn pups to 60% O2. We hypothesized that PMNL were responsible for the signals leading to LM influx. This was confirmed when inhibition of PMNL influx with a CXC chemokine receptor-2 antagonist, SB-265610, also prevented the 60% O2-dependent LM influx, LM-derived nitrotyrosine formation, and pruning of small arterioles. Exposure to 60% O2was associated with increased lung contents of neutrophil elastase and α-elastin, a marker of denatured elastin, and a decrease in elastin fiber density. This led us to speculate that neutrophil elastase-induced elastin fragments were the chemokines that led to a LM influx into the 60% O2-exposed lung. Inhibition of neutrophil elastase with sivelestat or elafin attenuated the LM influx. Sivelestat also attenuated the 60% O2-induced decrease in elastin fiber density. Daily injections of pups with an antibody to α-elastin prevented the 60% O2-dependent LM influx, impaired alveologenesis, and impaired small vessel formation. This suggests that neutrophil elastase inhibitors may protect against neonatal lung injury not only by preventing structural elastin degradation, but also by blocking elastin fragment-induced LM influx, thus preventing tissue injury from LM-derived peroxynitrite formation.

Collagen and elastin cross-linking is altered during aberrant late lung development associated with hyperoxia

Maturation of the lung extracellular matrix (ECM) plays an important role in the formation of alveolar gas exchange units. A key step in ECM maturation is cross-linking of collagen and elastin, which imparts stability and functionality to the ECM. During aberrant late lung development in bronchopulmonary dysplasia (BPD) patients and animal models of BPD, alveolarization is blocked, and the function of ECM cross-linking enzymes is deregulated, suggesting that perturbed ECM cross-linking may impact alveolarization. In a hyperoxia (85% O2)-based mouse model of BPD, blunted alveolarization was accompanied by alterations to lung collagen and elastin levels and cross-linking. Total collagen levels were increased (by 63%). The abundance of dihydroxylysinonorleucine collagen cross-links and the dihydroxylysinonorleucine-to-hydroxylysinonorleucine ratio were increased by 11 and 18%, respectively, suggestive of a profibrotic state. In contrast, insoluble elastin levels and the abundance of the elastin cross-links desmosine and isodesmosine in insoluble elastin were decreased by 35, 30, and 21%, respectively. The lung collagen-to-elastin ratio was threefold increased. Treatment of hyperoxia-exposed newborn mice with the lysyl oxidase inhibitor β-aminopropionitrile partially restored normal collagen levels, normalized the dihydroxylysinonorleucine-to-hydroxylysinonorleucine ratio, partially normalized desmosine and isodesmosine cross-links in insoluble elastin, and partially restored elastin foci structure in the developing septa. However, β-aminopropionitrile administration concomitant with hyperoxia exposure did not improve alveolarization, evident from unchanged alveolar surface area and alveoli number, and worsened septal thickening (increased by 12%). These data demonstrate that collagen and elastin cross-linking are perturbed during the arrested alveolarization of developing mouse lungs exposed to hyperoxia.

Bronchopulmonary dysplasia early changes leading to long-term consequences

Neonatal chronic lung disease, i.e., bronchopulmonary dysplasia, is characterized by impaired pulmonary development resulting from the impact of different risk factors including infections, hyperoxia, and mechanical ventilation on the immature lung. Remodeling of the extracellular matrix, apoptosis as well as altered growth factor signaling characterize the disease. The immediate consequences of these early insults have been studied in different animal models supported by results from in vitro approaches leading to the successful application of some findings to the clinical setting in the past. Nonetheless, existing information about long-term consequences of the identified early and most likely sustained changes to the developing lung is limited. Interesting results point towards a tremendous impact of these early injuries on the pulmonary repair capacity as well as aging related processes in the adult lung.

Cathepsin K overexpression modifies lung development in newborn mice

Cathepsin K (CatK), contributes to the development of chronic lung disease in newborn infants, but the impact of CatK for the lungs may be multifaceted. We have previously demonstrated that low level of CatK is associated with newborn lung injury and CatK deficiency aggravates lung injury in hyperoxia-exposed newborn mice. Thus, we hypothesized that sustained/higher expression of CatK could ameliorate hyperoxia-induced injury and restrain the development of pulmonary fibrosis. We studied the lungs of newborn wild-type (WT) and CatK overexpressing transgenic mice (TG) that were exposed to hyperoxia or room air for 7 or 14 days after birth. Fourfold pulmonary overexpression of CatK did not affect the growth or lung weight in room-air bred TG mice. The distal airspaces in TG mice were, however, enlarged on postnatal days (PN) 7 and 14, the latter together with increased apoptosis, compared with WT controls. Survival rate was normal and no respiratory distress was observed in air-bred TG mice. Hyperoxia inhibited alveolarization and increased collagen accumulation in WT mice. In TG mice, hyperoxia for 1 week did not aggravate the lung injury, and the lung morphology and already enlarged alveoli remained unchanged in TG mice at PN7. Prolonged hyperoxic exposure caused significant lung injury and mortality similarly in both group of mice, and only few mice survived until PN14. In summary, CatK overexpression slightly enlarges distal airways in infant mice, but hyperoxic environment is initially better tolerated when compared to WT mice. These findings suggest multifaceted role for CatK in lung development and newborn lung injury.

Alterations in expression of elastogenic and angiogenic genes by different conditions of mechanical ventilation in newborn rat lung

Mechanical ventilation is an important risk factor for development of bronchopulmonary dysplasia. Here we investigated the effects of different tidal volumes (VT) and duration of ventilation on expression of genes involved in alveolarization [tropoelastin (Eln), lysyloxidase-like 1 (Loxl1), fibulin5 (Fbln5), and tenascin-C (Tnc)] and angiogenesis [platelet derived growth factors (Pdgf) and vascular endothelial growth factors (Vegf) and their receptors] in 8-day-old rats. First, pups were ventilated for 8 h with low (LVT: 3.5 ml/kg), moderate (MVT: 8.5 ml/kg), or high (HVT: 25 ml/kg) tidal volumes. LVT and MVT decreased Tnc expression, whereas HVT increased expression of all three elastogenic genes and Tnc. PDGF α-receptor mRNA was increased in all ventilation groups, while Pdgfb expression was decreased after MVT and HVT ventilation. Only HVT ventilation upregulated Vegf expression. Independent of VT, ventilation upregulated Vegfr1 expression, while MVT and HVT downregulated Vegfr2 expression. Next, we evaluated duration (0-24 h) of MVT ventilation on gene expression. Although expression of all elastogenic genes peaked at 12 h of ventilation, only Fbln5 was negatively affected at 24 h. Tnc expression decreased with duration of ventilation. Changes in expression of Pdgfr and Vegfr were maximal at 8 h of ventilation. Disturbed elastin fiber deposition and decrease in small vessel density was only observed after 24 h. Thus, an imbalance between Fbln5 and Eln expression may trigger dysregulated elastin fiber deposition during the first 24 h of mechanical ventilation. Furthermore, ventilation-induced alterations in Pdgf and Vegf receptor expression are tidal volume dependent and may affect pulmonary vessel formation.

Conditional overexpression of TGFβ1 promotes pulmonary inflammation, apoptosis and mortality via TGFβR2 in the developing mouse lung

Background

Earlier studies have reported that transforming growth factor beta 1(TGFβ1) is a critical mediator of hyperoxia-induced acute lung injury (HALI) in developing lungs, leading to impaired alveolarization and a pulmonary phenotype of bronchopulmonary dysplasia (BPD). However, the mechanisms responsible for the TGFβ1-induced inflammatory signals that lead to cell death and abnormal alveolarization are poorly understood. We hypothesized that TGFβ1 signaling via TGFβR2 is necessary for the pathogenesis of the BPD pulmonary phenotype resulting from HALI.

Methods

We utilized lung epithelial cell-specific TGFβ1 overexpressing transgenic and TGFβR2 null mutant mice to evaluate the effects on neonatal mortality as well as pulmonary inflammation and apoptosis in developing lungs. Lung morphometry was performed to determine the impaired alveolarization and multicolor flow cytometry studies were performed to detect inflammatory macrophages and monocytes in lungs. Apoptotic cell death was measured with TUNEL assay, immunohistochemistry and western blotting and protein expression of angiogenic mediators were also analyzed.

Results

Our data reveals that increased TGFβ1 expression in newborn mice lungs leads to increased mortality, macrophage and immature monocyte infiltration, apoptotic cell death specifically in Type II alveolar epithelial cells (AECs), impaired alveolarization, and dysregulated angiogenic molecular markers.

Conclusions

Our study has demonstrated the potential role of inhibition of TGFβ1 signaling via TGFβR2 for improved survival, reduced inflammation and apoptosis that may provide insights for the development of potential therapeutic strategies targeted against HALI and BPD.

Lung matrix and vascular remodeling in mechanically ventilated elastin haploinsufficient newborn mice

Elastin plays a pivotal role in lung development. We therefore queried if elastin haploinsufficient newborn mice (Eln(+/-)) would exhibit abnormal lung structure and function related to modified extracellular matrix (ECM) composition. Because mechanical ventilation (MV) has been linked to dysregulated elastic fiber formation in the newborn lung, we also asked if elastin haploinsufficiency would accentuate lung growth arrest seen after prolonged MV of neonatal mice. We studied 5-day-old wild-type (Eln(+/+)) and Eln(+/-) littermates at baseline and after MV with air for 8-24 h. Lungs of unventilated Eln(+/-) mice contained ∼50% less elastin and ∼100% more collagen-1 and lysyl oxidase compared with Eln(+/+) pups. Eln(+/-) lungs contained fewer capillaries than Eln(+/+) lungs, without discernible differences in alveolar structure. In response to MV, lung tropoelastin and elastase activity increased in Eln(+/+) neonates, whereas tropoelastin decreased and elastase activity was unchanged in Eln(+/-) mice. Fibrillin-1 protein increased in lungs of both groups during MV, more in Eln(+/-) than in Eln(+/+) pups. In both groups, MV caused capillary loss, with larger and fewer alveoli compared with unventilated controls. Respiratory system elastance, which was less in unventilated Eln(+/-) compared with Eln(+/+) mice, was similar in both groups after MV. These results suggest that elastin haploinsufficiency adversely impacts pulmonary angiogenesis and that MV dysregulates elastic fiber integrity, with further loss of lung capillaries, lung growth arrest, and impaired respiratory function in both Eln(+/+) and Eln(+/-) mice. Paucity of lung capillaries in Eln(+/-) newborns might help explain subsequent development of pulmonary hypertension previously reported in adult Eln(+/-) mice.

Role of serine proteases in the regulation of interleukin-877 during the development of bronchopulmonary dysplasia in preterm ventilated infants

RATIONALE

The chemokine interleukin-8 is implicated in the development of bronchopulmonary dysplasia in preterm infants. The 77-amino acid isoform of interleukin-8 (interleukin-877) is a less potent chemoattractant than other shorter isoforms. Although interleukin-877 is abundant in the preterm circulation, its regulation in the preterm lung is unknown.

OBJECTIVES

To study expression and processing of pulmonary interleukin-877 in preterm infants who did and did not develop bronchopulmonary dysplasia.

METHODS

Total interleukin-8 and interleukin-877 were measured in bronchoalveolar lavage fluid from preterm infants by immunoassay. Neutrophil serine proteases were used to assess processing. Neutrophil chemotaxis assays and degranulation of neutrophil matrix metalloproteinase-9 were used to assess interleukin-8 function.

MAIN RESULTS

Peak total interleukin-8 and interleukin-877 concentrations were increased in infants who developed bronchopulmonary dysplasia compared to those who did not. Shorter forms of interleukin-8 predominated in the preterm lung (96.3% No-bronchopulmonary dysplasia vs 97.1% bronchopulmonary dysplasia, p>0.05). Preterm bronchoalveolar lavage fluid significantly converted exogenously added interleukin-877 to shorter isoforms (p<0.001). Conversion was greater in bronchopulmonary dysplasia infants (p<0.05). This conversion was inhibited by α-1 antitrypsin and antithrombin III (p<0.01). Purified neutrophil serine proteases efficiently converted interleukin-877 to shorter isoforms in a time- and dose-dependent fashion; shorter interleukin-8 isoforms were primarily responsible for neutrophil chemotaxis (p<0.001). Conversion by proteinase-3 resulted in significantly increased interleukin-8 activity in vitro (p<0.01).

CONCLUSIONS

Shorter, potent, isoforms interleukin-8 predominate in the preterm lung, and are increased in infants developing bronchopulmonary dysplasia, due to conversion of interleukin-877 by neutrophil serine proteases and thrombin. Processing of interleukin-8 provides an attractive therapeutic target to prevent development of bronchopulmonary dysplasia.

Intrapulmonary instillation of perflurooctylbromide improves lung growth, alveolarization, and lung mechanics in a fetal rabbit model of diaphragmatic hernia

OBJECTIVES

Fetal tracheal occlusion of hypoplastic rabbit lungs results in lung growth and alveolarization although the surfactant protein messenger RNA expression is decreased and the transforming growth factor-β pathway induced. The prenatal filling of healthy rabbit lungs with perfluorooctylbromide augments lung growth without suppression of surfactant protein synthesis. We hypothesizes that Intratracheal perfluorooctylbromide instillation improves lung growth, mechanics, and extracellular matrix synthesis in a fetal rabbit model of lung hypoplasia induced by diaphragmatic hernia.

SETTING AND INTERVENTIONS

On day 23 of gestation, DH was induced by fetal surgery in healthy rabbit fetuses. Five days later, 0.8ml of perfluorooctylbromide (diaphragmatic hernia-perfluorooctylbromide) or saline (diaphragmatic hernia-saline) was randomly administered into the lungs of previously operated fetuses. After term delivery (day 31), lung mechanics, lung to body weight ratio, messenger RNA levels of target genes, assessment of lung histology, and morphological distribution of elastin and collagen were determined. Nonoperated fetuses served as controls.

MEASUREMENTS AND MAIN RESULTS

Fetal instillation of perfluorooctylbromide in hypoplastic lungs resulted in an improvement of lung-to-body weight ratio (0.016 vs 0.013 g/g; p = 0.05), total lung capacity (23.4 vs 15.4 μL/g; p = 0.03), and compliance (2.4 vs 1.2 mL/cm H2O; p = 0.007) as compared to diaphragmatic hernia-saline. In accordance with the results from lung function analysis, elastin staining of pulmonary tissue revealed a physiological distribution of elastic fiber to the tips of the secondary crests in the diaphragmatic hernia-perfluorooctylbromide group. Likewise, messenger RNA expression was induced in genes associated with extracellular matrix remodeling (matrix metalloproteinase-2, tissue inhibitor of metalloproteinase-1, and tissue inhibitor of metalloproteinase-2). Surfactant protein expression was similar in the diaphragmatic hernia-perfluorooctylbromide and diaphragmatic hernia-saline groups. Distal airway size, mean linear intercept, as well as airspace and tissue fractions were similar in diaphragmatic hernia-perfluorooctylbromide, diaphragmatic hernia-saline, and control groups.

CONCLUSIONS

Fetal perfluorooctylbromide treatment improves lung growth, lung mechanics, and extracellular matrix remodeling in hypoplastic lungs, most probably due to transient pulmonary stretch, preserved fetal breathing movements, and its physical characteristics. Perfluorooctylbromide instillation is a promising approach for prenatal therapy of lung hypoplasia.

Respiratory outcomes of the surfactant positive pressure and oximetry randomized trial (SUPPORT)

OBJECTIVE

To explore the early childhood pulmonary outcomes of infants who participated in the National Institute of Child Health and Human Development's Surfactant Positive Airway Pressure and Pulse Oximetry Randomized Trial (SUPPORT), using a factorial design that randomized extremely preterm infants to lower vs higher oxygen saturation targets and delivery room continuous positive airway pressure (CPAP) vs intubation/surfactant.

STUDY DESIGN

The Breathing Outcomes Study, a prospective secondary study to the Surfactant Positive Airway Pressure and Pulse Oximetry Randomized Trial, assessed respiratory morbidity at 6-month intervals from hospital discharge to 18-22 months corrected age (CA). Two prespecified primary outcomes-wheezing more than twice per week during the worst 2-week period and cough longer than 3 days without a cold-were compared for each randomized intervention.

RESULTS

One or more interviews were completed for 918 of the 922 eligible infants. The incidences of wheezing and cough were 47.9% and 31.0%, respectively, and did not differ between the study arms of either randomized intervention. Infants randomized to lower vs higher oxygen saturation targets had a similar risk of death or respiratory morbidity (except for croup and treatment with oxygen or diuretics at home). Infants randomized to CPAP vs intubation/surfactant had fewer episodes of wheezing without a cold (28.9% vs 36.5%; P<.05), respiratory illnesses diagnosed by a doctor (47.7% vs 55.2%; P<.05), and physician or emergency room visits for breathing problems (68.0% vs 72.9%; P<.05) by 18-22 months CA.

CONCLUSION

Treatment with early CPAP rather than intubation/surfactant is associated with less respiratory morbidity by 18-22 months CA. Longitudinal assessment of pulmonary morbidity is necessary to fully evaluate the potential benefits of respiratory interventions for neonates.

Dynamic expression of chymotrypsin-like elastase 1 over the course of murine lung development

Postnatal lung development requires coordination of three processes (surface area expansion, microvascular growth, and matrix remodeling). Because normal elastin structure is important for lung morphogenesis, because physiological remodeling of lung elastin has never been defined, and because elastin remodeling is angiogenic, we sought to test the hypothesis that, during lung development, elastin is remodeled in a defined temporal-spatial pattern, that a novel protease is associated with this remodeling, and that angiogenesis is associated with elastin remodeling. By elastin in situ zymography, lung elastin remodeling increased 24-fold between embryonic day (E) 15.5 and postnatal day (PND) 14. Remodeling was restricted to major vessels and airways on PND1 with a sevenfold increase in alveolar wall elastin remodeling from PND1 to PND14. By inhibition assays and literature review, we identified chymotrypsin-like elastase 1 (CELA1) as a potential mediator of elastin remodeling. CELA1 mRNA levels increased 12-fold from E15.5 to PND9, and protein levels increased 3.4-fold from E18.5 to PND9. By costaining experiments, the temporal-spatial pattern of CELA1 expression matched that of elastin remodeling, and 58-85% of CELA1(+) cells were <10 μm from an elastase signal. An association between elastin remodeling and angiogenesis was tested by similar methods. At PND7 and PND14, 60-95% of angiogenin(+) cells were associated with elastin remodeling. Both elastase inhibition and CELA1 silencing impaired angiogenesis in vitro. Our data defines the temporal-spatial pattern of elastin remodeling during lung development, demonstrates an association of this remodeling with CELA1, and supports a role for elastin remodeling in regulating angiogenesis.

Lung development alterations in newborn mice after recovery from exposure to sublethal hyperoxia

Exposure of newborn mice to hyperoxia arrests lung development, with resultant pathological characteristics similar to bronchopulmonary dysplasia in infants born prematurely. We tested the hypothesis that aberrations in lung development caused by 14 days of sublethal hyperoxia would be reversed during 14 days of recovery to room air (RA) when the concentration of oxygen exposure was weaned gradually. Newborn FVB mice were exposed to 85% oxygen or RA for 14 days. Weaning from hyperoxia was by either transfer directly into RA or a decrease in the concentration of oxygen by 10% per days. At 28 days, pups were euthanized, and the lungs were inflation fixed and assessed. At postnatal day 28, lungs of mice weaned abruptly from hyperoxia had fewer (6 ± 0.6 versus 10 ± 0.7; P < 0.001) alveoli per high-powered field and larger alveoli (4050 ± 207 versus 2305 ± 182 μm(2)) than animals weaned gradually; both hyperoxia-exposed groups were different from lungs obtained from air-breathing controls (20 ± 0.5 alveoli per high-powered field; P < 0.001). The results are consistent with the absence of catch-up alveolarization in this model and indicate that the long-term consequences of early exposures to hyperoxia merit closer examination. The effects of abrupt weaning to RA observed further suggest that weaning should be considered in experimental models of newborn exposure to hyperoxia.

JNK suppresses pulmonary fibroblast elastogenesis during alveolar development

Background

The formation of discrete elastin bands at the tips of secondary alveolar septa is important for normal alveolar development, but the mechanisms regulating the lung elastogenic program are incompletely understood. JNK suppress elastin synthesis in the aorta and is important in a host of developmental processes. We sought to determine whether JNK suppresses pulmonary fibroblast elastogenesis during lung development.

Methods

Alveolar size, elastin content, and mRNA of elastin-associated genes were quantitated in wild type and JNK-deficient mouse lungs, and expression profiles were validated in primary lung fibroblasts. Tropoelastin protein was quantitated by Western blot. Changes in lung JNK activity throughout development were quantitated, and pJNK was localized by confocal imaging and lineage tracing.

Results

By morphometry, alveolar diameters were increased by 7% and lung elastin content increased 2-fold in JNK-deficient mouse lungs compared to wild type. By Western blot, tropoelastin protein was increased 5-fold in JNK-deficient lungs. Postnatal day 14 (PND14) lung JNK activity was 11-fold higher and pJNK:JNK ratio 6-fold higher compared to PN 8 week lung. Lung tropoelastin, emilin-1, fibrillin-1, fibulin-5, and lysyl oxidase mRNAs inversely correlated with lung JNK activity during alveolar development. Phosphorylated JNK localized to pulmonary lipofibroblasts. PND14 JNK-deficient mouse lungs contained 7-fold more tropoelastin, 2,000-fold more emilin-1, 800-fold more fibrillin-1, and 60-fold more fibulin-5 than PND14 wild type lungs. Primarily lung fibroblasts from wild type and JNK-deficient mice showed similar differences in elastogenic mRNAs.

Conclusions

JNK suppresses fibroblast elastogenesis during the alveolar stage of lung development.

Postnatal inflammation in the pathogenesis of bronchopulmonary dysplasia

Exposure to hyperoxia, invasive mechanical ventilation, and systemic/local sepsis are important antecedents of postnatal inflammation in the pathogenesis of bronchopulmonary dysplasia (BPD). This review will summarize information obtained from animal (baboon, lamb/sheep, rat and mouse) models that pertain to the specific inflammatory agents and signaling molecules that predispose a premature infant to BPD.

Extracellular matrix structure and tissue stiffness control postnatal lung development through the lipoprotein receptor-related protein 5/Tie2 signaling system

Physical properties of the tissues and remodeling of extracellular matrix (ECM) play an important role in organ development. Recently, we have reported that low-density lipoprotein receptor-related protein (LRP) 5/Tie2 signaling controls postnatal lung development by modulating angiogenesis. Here we show that tissue stiffness modulated by the ECM cross-linking enzyme, lysyl oxidase (LOX), regulates postnatal lung development through LRP5-Tie2 signaling. The expression of LRP5 and Tie2 is up-regulated twofold in lung microvascular endothelial cells when cultured on stiff matrix compared to those cultured on soft matrix in vitro. LOX inhibitor, β-aminopropionitrile, disrupts lung ECM (collagen I, III, and VI, and elastin) structures, softens neonatal mouse lung tissue by 20%, and down-regulates the expression of LRP5 and Tie2 by 20 and 60%, respectively, which leads to the inhibition of postnatal lung development (30% increase in mean linear intercept, 1.5-fold increase in air space area). Importantly, hyperoxia treatment (Postnatal Days 1-10) disrupts ECM structure and stiffens mouse lung tissue by up-regulating LOX activity, thereby increasing LRP5 and Tie2 expression and deregulating alveolar morphogenesis in neonatal mice, which is attenuated by inhibiting LOX activity. These findings suggest that appropriate physical properties of lung tissue are necessary for physiological postnatal lung development, and deregulation of this mechanism contributes to postnatal lung developmental disorders, such as bronchopulmonary dysplasia.

Deregulation of the lysyl hydroxylase matrix cross-linking system in experimental and clinical bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a common and serious complication of premature birth, characterized by a pronounced arrest of alveolar development. The underlying pathophysiological mechanisms are poorly understood although perturbations to the maturation and remodeling of the extracellular matrix (ECM) are emerging as candidate disease pathomechanisms. In this study, the expression and regulation of three members of the lysyl hydroxylase family of ECM remodeling enzymes (Plod1, Plod2, and Plod3) in clinical BPD, as well as in an experimental animal model of BPD, were addressed. All three enzymes were localized to the septal walls in developing mouse lungs, with Plod1 also expressed in the vessel walls of the developing lung and Plod3 expressed uniquely at the base of developing septa. The expression of plod1, plod2, and plod3 was upregulated in the lungs of mouse pups exposed to 85% O2, an experimental animal model of BPD. Transforming growth factor (TGF)-β increased plod2 mRNA levels and activated the plod2 promoter in vitro in lung epithelial cells and in lung fibroblasts. Using in vivo neutralization of TGF-β signaling in the experimental animal model of BPD, TGF-β was identified as the regulator of aberrant plod2 expression. PLOD2 mRNA expression was also elevated in human neonates who died with BPD or at risk for BPD, compared with neonates matched for gestational age at birth or chronological age at death. These data point to potential roles for lysyl hydroxylases in normal lung development, as well as in perturbed late lung development associated with BPD.