Bronchopulmonary dysplasia and emphysema: in search of common therapeutic targets

Regulating NLRP3 Inflammasome-Induced Pyroptosis via Nrf2: TBHQ Limits Hyperoxia-Induced Lung Injury in a Mouse Model of Bronchopulmonary Dysplasia

Nuclear factor e2-related factor 2 (Nrf2) plays a key role in cellular resistance to oxidative stress injury. Oxidative stress injury, caused by Nrf2 imbalance, results in increased pyroptosis, DNA damage, and inflammatory activation, which may lead to the arrest of alveolar development and bronchopulmonary dysplasia (BPD) in premature infants under hyperoxic conditions. We established a BPD mouse model to investigate the effects of tert-butylhydroquinone (TBHQ), an Nrf2 activator, on oxidative stress injury, pyroptosis, NLRP3 inflammasome activation, and alveolar development. TBHQ reduced abnormal cell death in the lung tissue of BPD mice and restored the number and normal structure of the alveoli. TBHQ administration activated the Nrf2/heme oxygenase-1 (HO-1) signaling pathway, resulting in the decrease in the following: reactive oxygen species (ROS), activation of the NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome, and IL-18 and IL-1β expression and activation, as well as inhibition of pyroptosis. In contrast, after Nrf2 gene knockout in BPD mice, there was more severe oxidative stress injury and cell death in the lungs, there were TUNEL + and NLRP3 + co-positive cells in the alveoli, the pyroptosis was significantly increased, and the development of alveoli was significantly blocked. We demonstrated that TBHQ may promote alveolar development by enhancing Nrf2-induced antioxidation in the lung tissue of BPD mice and that the decrease in the NLRP3 inflammasome and pyroptosis caused by Nrf2 activation may be the underlying mechanism. These results suggest that TBHQ is a promising treatment for lung injury in premature infants with hyperoxia.

Self-assembled miR-134-5p inhibitor nanoparticles ameliorate experimental bronchopulmonary dysplasia (BPD) via suppressing ferroptosis

Bronchopulmonary dysplasia (BPD) is a chronic lung disease in premature infants with increased levels of reactive oxygen species (ROS) and ferroptosis. Herein, we designed a peptide-based nanoparticle to deliver therapeutic molecules to pulmonary, thereby ameliorating BPD. The BPD-induced damages of lung tissues were detected by H&E and immunohistochemistry staining. Inflammatory cytokines, Fe2+, and ROS levels were quantified by the indicated kits, respectively. The targeting relationship was verified by luciferase reporter assay and pull-down assay. Subsequently, self-assembled miR-134-5p inhibitor nanoparticles with pulmonary epithelial cell-targeting were synthesized. The characteristics were detected by transmission electron microscopy, luminescence imaging, and dynamic light scattering. A significant ferroptosis was observed in the BPD mice. The protein level of GPX4 was decreased significantly compared to the control group. Constantly, miR-134-5p showed positive regulation on ferroptosis by targeting GPX4. The designed nanoparticles were mainly accumulated in the lung region. Besides, it ameliorated experimental bronchopulmonary dysplasia via suppressing ferroptosis, in vivo and in vitro. Our findings provided a miR-134-5p/GPX4 axis in regulating ferroptosis of BPD and prompted the potential of applying the peptide-based nanoparticle to BPD treatment.

Magnetic resonance imaging-based scoring of the diseased lung in the preterm infant with bronchopulmonary dysplasia: UNiforme Scoring of the disEAsed Lung in BPD (UNSEAL BPD)

Neonatal chronic lung disease lacks standardized assessment of lung structural changes. We addressed this clinical need by the development of a novel scoring system [UNSEAL BPD (UNiforme Scoring of the disEAsed Lung in BPD)] using T2-weighted single-shot fast-spin-echo sequences from 3 T MRI in very premature infants with and without bronchopulmonary dysplasia (BPD). Quantification of interstitial and airway remodeling, emphysematous changes, and ventilation inhomogeneity was achieved by consensus scoring on a five-point Likert scale. We successfully identified moderate and severe disease by logistic regression [area under the curve (AUC), 0.89] complemented by classification tree analysis revealing gestational age-specific structural changes. We demonstrated substantial interreader reproducibility (weighted Cohen's κ 0.69) and disease specificity (AUC = 0.91). Our novel MRI score enables the standardized assessment of disease-characteristic structural changes in the preterm lung exhibiting significant potential as a quantifiable endpoint in early intervention clinical trials and long-term disease monitoring.

Endotypes of Prematurity and Phenotypes of Bronchopulmonary Dysplasia: Toward Personalized Neonatology

Bronchopulmonary dysplasia (BPD), the chronic lung disease of prematurity, is increasingly recognized as the consequence of a pathological reparative response of the developing lung to both antenatal and postnatal injury. According to this view, the pathogenesis of BPD is multifactorial and heterogeneous with different patterns of antenatal stress (endotypes) that combine with varying postnatal insults and might distinctively damage the development of airways, lung parenchyma, interstitium, lymphatic system, and pulmonary vasculature. This results in different clinical phenotypes of BPD. There is no clear consensus on which are the endotypes of prematurity but the combination of clinical information with placental and bacteriological data enables the identification of two main pathways leading to birth before 32 weeks of gestation: (1) infection/inflammation and (2) dysfunctional placentation. Regarding BPD phenotypes, the following have been proposed: parenchymal, peripheral airway, central airway, interstitial, congestive, vascular, and mixed phenotype. In line with the approach of personalized medicine, endotyping prematurity and phenotyping BPD will facilitate the design of more targeted therapeutic and prognostic approaches.

Can red cell distribution width in very low birth weight infants predict bronchopulmonary dysplasia?

Red cell distribution width (RDW) is a useful marker for assessing the severity and prognosis of various diseases in adults. However, whether it is applicable to children, especially in newborns, has not been determined.This study aimed to investigate the RDW values of preterm infants and evaluate whether RDW values in the early days of life can predict bronchopulmonary dysplasia (BPD) development.One hundred and eight infants born at <30 weeks of gestation with a birth weight of <1500 g participated in this retrospective study. RDW values measured at birth, 7 days (D7), and 28 days (D28) after birth were reviewed. The changes in RDW values in the first month of life were analyzed, and we evaluated the relationship between RDW and BPD.The mean RDW values at birth, D7, D28 and the change from birth to D7 were 16.2 ± 0.1%, 17.5 ± 0.2%, 17.6 ± 0.2% and 1.3 ± 1.8%, respectively. RDW at birth was lower in the infants born at <28 weeks' gestational age than in those born at ≥28 weeks' gestational age (15.7 ± 0.3 vs 16.4 ± 0.2, P = .024). RDW values of both groups increased during the first week after birth and did not differ significantly at D7. The levels remained similar at 1 month of age. RDW at birth, D7, and D28 and the changes in RDW from birth to D7 were not correlated with the development of BPD independent of its severity.The usefulness of RDW as a predictor of BPD development remains questionable and requires further study.

IGF1R controls mechanosignaling in myofibroblasts required for pulmonary alveologenesis

Ventilation throughout life is dependent on the formation of pulmonary alveoli, which create an extensive surface area in which the close apposition of respiratory epithelium and endothelial cells of the pulmonary microvascular enables efficient gas exchange. Morphogenesis of the alveoli initiates at late gestation in humans and the early postnatal period in the mouse. Alveolar septation is directed by complex signaling interactions among multiple cell types. Here, we demonstrate that IGF1 receptor gene (Igf1r) expression by a subset of pulmonary fibroblasts is required for normal alveologenesis in mice. Postnatal deletion of Igf1r caused alveolar simplification, disrupting alveolar elastin networks and extracellular matrix without altering myofibroblast differentiation or proliferation. Moreover, loss of Igf1r impaired contractile properties of lung myofibroblasts and inhibited myosin light chain (MLC) phosphorylation and mechanotransductive nuclear YAP activity. Activation of p-AKT, p-MLC, and nuclear YAP in myofibroblasts was dependent on Igf1r. Pharmacologic activation of AKT enhanced MLC phosphorylation, increased YAP activation, and ameliorated alveolar simplification in vivo. IGF1R controls mechanosignaling in myofibroblasts required for lung alveologenesis.

Global Long Noncoding RNA and mRNA Expression Changes between Prenatal and Neonatal Lung Tissue in Pigs

Lung tissue plays an important role in the respiratory system of mammals after birth. Early lung development includes six key stages, of which the saccular stage spans the pre- and neonatal periods and prepares the distal lung for alveolarization and gas-exchange. However, little is known about the changes in gene expression between fetal and neonatal lungs. In this study, we performed transcriptomic analysis of messenger RNA (mRNA) and long noncoding RNA (lncRNA) expressed in the lung tissue of fetal and neonatal piglets. A total of 19,310 lncRNAs and 14,579 mRNAs were identified and substantially expressed. Furthermore, 3248 mRNAs were significantly (FDR-adjusted p value ≤ 0.05, FDR: False Discovery Rate) differentially expressed and were mainly enriched in categories related to cell proliferation, immune response, hypoxia response, and mitochondrial activation. For example, CCNA2, an important gene involved in the cell cycle and DNA replication, was upregulated in neonatal lungs. We also identified 452 significantly (FDR-adjusted p value ≤ 0.05) differentially expressed lncRNAs, which might function in cell proliferation, mitochondrial activation, and immune response, similar to the differentially expressed mRNAs. These results suggest that differentially expressed mRNAs and lncRNAs might co-regulate lung development in early postnatal pigs. Notably, the TU64359 lncRNA might promote distal lung development by up-regulating the heparin-binding epidermal growth factor-like (HB-EGF) expression. Our research provides basic lung development datasets and will accelerate clinical researches of newborn lung diseases with pig models.

Expansion of hedgehog disrupts mesenchymal identity and induces emphysema phenotype

GWAS have repeatedly mapped susceptibility loci for emphysema to genes that modify hedgehog signaling, but the functional relevance of hedgehog signaling to this morbid disease remains unclear. In the current study, we identified a broad population of mesenchymal cells in the adult murine lung receptive to hedgehog signaling, characterized by higher activation of hedgehog surrounding the proximal airway relative to the distal alveoli. Single-cell RNA-sequencing showed that the hedgehog-receptive mesenchyme is composed of mostly fibroblasts with distinct proximal and distal subsets with discrete identities. Ectopic hedgehog activation in the distal fibroblasts promoted expression of proximal fibroblast markers and loss of distal alveoli and airspace enlargement of over 20% compared with controls. We found that hedgehog suppressed mesenchymal-derived mitogens enriched in distal fibroblasts that regulate alveolar stem cell regeneration and airspace size. Finally, single-cell analysis of the human lung mesenchyme showed that segregated proximal-distal identity with preferential hedgehog activation in the proximal fibroblasts was conserved between mice and humans. In conclusion, we showed that differential hedgehog activation segregates mesenchymal identities of distinct fibroblast subsets and that disruption of fibroblast identity can alter the alveolar stem cell niche, leading to emphysematous changes in the murine lung.

Experimental animal models for COPD: a methodological review

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) is a progressive disorder that makes the breathing difficult and is characterized by pathological conditions ranging from chronic inflammation to tissue proteolysis. With regard to ethical issues related to the studies on patients with COPD, the use of animal models of COPD is inevitable. Animal models improve our knowledge about the basic mechanisms underlying COPD physiology, pathophysiology and treatment. Although these models are only able to mimic some of the features of the disease, they are valuable for further investigation of mechanisms involved in human COPD.

METHODS

We searched the literature available in Google Scholar, PubMed and ScienceDirect databases for English articles published until November 2015. For this purpose, we used 5 keywords for COPD, 3 for animal models, 4 for exposure methods, 3 for pathophysiological changes and 3 for biomarkers. One hundred and fifty-one studies were considered eligible for inclusion in this review.

RESULTS

According to the reviewed articles, animal models of COPD are mainly induced in mice, guinea pigs and rats. In most of the studies, this model was induced by exposure to cigarette smoke (CS), intra-tracheal lipopolysaccharide (LPS) and intranasal elastase. There were variations in time course and dose of inducers used in different studies. The main measured parameters were lung pathological data and lung inflammation (both inflammatory cells and inflammatory mediators) in most of the studies and tracheal responsiveness (TR) in only few studies.

CONCLUSION

The present review provides various methods used for induction of animal models of COPD, different animals used (mainly mice, guinea pigs and rats) and measured parameters. The information provided in this review is valuable for choosing appropriate animal, method of induction and selecting parameters to be measured in studies concerning COPD.

Phenotypic assessment of pulmonary hypertension using high-resolution echocardiography is feasible in neonatal mice with experimental bronchopulmonary dysplasia and pulmonary hypertension: a step toward preventing chronic obstructive pulmonary disease

Bronchopulmonary dysplasia (BPD) and chronic obstructive pulmonary disease (COPD) are chronic lung diseases of human infants and adults, respectively, that are characterized by alveolar simplification. One-third of the infants with severe BPD develop pulmonary hypertension (PH). More importantly, PH increases morbidity and mortality in BPD patients. Additionally, COPD is a common respiratory morbidity in former BPD patients. The lack of an appropriate small animal model wherein echocardiography (Echo) can demonstrate PH is one of the major barriers to understand the molecular mechanisms of the disease and, thereby, develop rational therapies to prevent and/or treat PH in BPD patients. Thus, the goal of this study was to establish a model of experimental BPD and PH and investigate the feasibility of Echo to diagnose PH in neonatal mice. Since hyperoxia-induced oxidative stress and inflammation contributes to the development of BPD with PH, we tested the hypothesis that exposure of newborn C57BL/6J mice to 70% O2 (hyperoxia) for 14 days leads to lung oxidative stress, inflammation, alveolar and pulmonary vascular simplification, pulmonary vascular remodeling, and Echo evidence of PH. Hyperoxia exposure caused lung oxidative stress and inflammation as evident by increased malondialdehyde adducts and inducible nitric oxide synthase, respectively. Additionally, hyperoxia exposure caused growth restriction, alveolar and pulmonary vascular simplification, and pulmonary vascular remodeling. At 14 days of age, Echo of these mice demonstrated that hyperoxia exposure decreased pulmonary acceleration time (PAT) and PAT/ejection time ratio and increased right ventricular free wall thickness, which are indicators of significant PH. Thus, we have demonstrated the feasibility of Echo to phenotype PH in neonatal mice with experimental BPD with PH, which can aid in discovery of therapies to prevent and/or treat BPD with PH and its sequelae such as COPD in humans.

Bridging Lung Development with Chronic Obstructive Pulmonary Disease. Relevance of Developmental Pathways in Chronic Obstructive Pulmonary Disease Pathogenesis

Chronic obstructive pulmonary disease (COPD) is characterized by chronic airflow limitation. This generic term encompasses emphysema and chronic bronchitis, two common conditions, each having distinct but also overlapping features. Recent epidemiological and experimental studies have challenged the traditional view that COPD is exclusively an adult disease occurring after years of inhalational insults to the lungs, pinpointing abnormalities or disruption of the pathways that control lung development as an important susceptibility factor for adult COPD. In addition, there is growing evidence that emphysema is not solely a destructive process because it is also characterized by a failure in cell and molecular maintenance programs necessary for proper lung development. This leads to the concept that tissue regeneration required stimulation of signaling pathways that normally operate during development. We undertook a review of the literature to outline the contribution of developmental insults and genes in the occurrence and pathogenesis of COPD, respectively.

A Role for the Liver in Parturition and Preterm Birth

Neither the mechanisms of parturition nor the pathogenesis of preterm birth are well understood. Poor nutritional status has been suspected as a major causal factor, since vitamin A concentrations are low in preterm infants. However, even large enteral doses of vitamin A from birth fail to increase plasma concentrations of vitamin A or improve outcomes in preterm and/or extremely low birthweight infants. These findings suggest an underlying impairment in the secretion of vitamin A from the liver, where about 80% of the vitamin is stored. Vitamin A accumulates in the liver and breast during pregnancy in preparation for lactation. While essential in low concentration for multiple biological functions, vitamin A in higher concentration can be pro-oxidant, mutagenic, teratogenic and cytotoxic, acting as a highly surface-active, membrane-seeking and destabilizing compound. Regarding the mechanism of parturition, it is conjectured that by nine months of gestation the hepatic accumulation of vitamin A (retinol) from the liver is such that mobilization and secretion are impaired to the point where stored vitamin A compounds in the form of retinyl esters and retinoic acid begin to spill or leak into the circulation, resulting in amniotic membrane destabilization and the initiation of parturition. If, however, the accumulation and spillage of stored retinoids reaches a critical threshold prior to nine months, e.g., due to cholestatic liver disease, which is common in mothers of preterm infants, the increased retinyl esters and/or retinoic acid rupture the fetal membranes, inducing preterm birth and its complications, including retinopathy, necrotizing enterocolitis and bronchopulmonary dysplasia. Subject to testing, the model suggests that measures taken prior to and during pregnancy to improve liver function could reduce the risk of adverse birth outcomes, including preterm birth.

Glucocorticoid receptors in lung cancer: new perspectives

Proper expression of the glucocorticoid receptor (GR) plays an essential role in the development of the lung. GR expression and signalling in the lung is manipulated by administration of synthetic glucocorticoids (Gcs) for the treatment of neonatal, childhood and adult lung diseases. In lung cancers, Gcs are also commonly used as co-treatment during chemotherapy. This review summarises the effect of Gc monotherapy and co-therapy on lung cancers in vitro, in mouse models of lung cancer, in xenograft, ex vivo and in vivo The disparity between the effects of pre-clinical and in vivo Gc therapy is commented on in light of the recent discovery of GR as a novel tumour suppressor gene.

Affect of Early Life Oxygen Exposure on Proper Lung Development and Response to Respiratory Viral Infections

Children born preterm often exhibit reduced lung function and increased severity of response to respiratory viruses, suggesting that premature birth has compromised proper development of the respiratory epithelium and innate immune defenses. Increasing evidence suggests that premature birth promotes aberrant lung development likely due to the neonatal oxygen transition occurring before pulmonary development has matured. Given that preterm infants are born at a point of time where their immune system is also still developing, early life oxygen exposure may also be disrupting proper development of innate immunity. Here, we review current literature in hopes of stimulating research that enhances understanding of how the oxygen environment at birth influences lung development and host defense. This knowledge may help identify those children at risk for disease and ideally culminate in the development of novel therapies that improve their health.

Epithelial-mesenchymal co-culture model for studying alveolar morphogenesis

Division of large, immature alveolar structures into smaller, more numerous alveoli increases the surface area available for gas exchange. Alveolar division requires precise epithelial-mesenchymal interactions. However, few experimental models exist for studying how these cell-cell interactions produce changes in 3-dimensional structure. Here we report an epithelial-mesenchymal cell co-culture model where 3-dimensional peaks form with similar cellular orientation as alveolar structures in vivo. Co-culturing fetal mouse lung mesenchyme with A549 epithelial cells produced tall peaks of cells covered by epithelia with cores of mesenchymal cells. These structures did not form when using adult lung fibroblasts. Peak formation did not require localized areas of cell proliferation or apoptosis. Mesenchymal cells co-cultured with epithelia adopted an elongated cell morphology closely resembling myofibroblasts within alveolar septa in vivo. Because inflammation inhibits alveolar formation, we tested the effects of E. coli lipopolysaccharide on 3-dimensional peak formation. Confocal and time-lapse imaging demonstrated that lipopolysaccharide reduced mesenchymal cell migration, resulting in fewer, shorter peaks with mesenchymal cells present predominantly at the base. This epithelial-mesenchymal co-culture model may therefore prove useful in future studies of mechanisms regulating alveolar morphogenesis.

Maintenance of the bronchial alveolar stem cells in an undifferentiated state by secreted frizzled-related protein 1

Bronchoalveolar stem cells (BASCs) are mobilized during injury and identified as lung progenitor cells, but the molecular regulation of this population of cells has not been elucidated. Secreted frizzled-related protein 1 (SFRP1) is a critical molecule involved in alveolar duct formation in the lung and here we demonstrate its importance in controlling cell differentiation during lung injury. Mice lacking SFRP1 exhibited a rapid repair response leading to aberrant proliferation of differentiated cells. Furthermore, SFRP1 treatment of BASCs maintained these cells in a quiescent state. In vivo overexpression of SFRP1 after injury suppressed differentiation and resulted in the accumulation of BASCs correlating with in vitro studies. These findings suggest that SFRP1 expression in the adult maintains progenitor cells within their undifferentiated state and suggests that manipulation of this pathway is a potential target to augment the lung repair process during disease.

Developmental programs of lung epithelial progenitors: a balanced progenitor model

The daunting task of lung epithelium development is to transform a cluster of foregut progenitors into a three-dimensional (3D) tubular network with distinct cell types distributed at their appropriate locations. A complete understanding of lung development needs to address not only how, but also where, different cell types form. We propose that the lung epithelium forms through regulated deployment of three developmental programs: branching morphogenesis to expand progenitors and build a tree-like tubular network, airway differentiation to specify cells for the proximal conducting airways, and alveolar differentiation to specify cells for the peripheral gas exchange region. Each developmental program has its unique morphological features and molecular control mechanisms; their spatiotemporal coordination can be accounted for in a balanced progenitor model where progenitors balance between alternative developmental programs in response to spatiotemporal cues. This model integrates progenitor morphogenesis and differentiation, and provides new insights to lung immaturity in preterm birth and lung evolution. Advanced gene targeting and 3D imaging tools are needed to achieve a comprehensive understanding of lung epithelial progenitors on molecular, cellular, and morphological levels. For further resources related to this article, please visit the WIREs website.

CONFLICT OF INTEREST

The authors have declared no conflicts of interest for this article.

Intravenous and intratracheal mesenchymal stromal cell injection in a mouse model of pulmonary emphysema

The aim of this study was to characterize the evolution of lung function and -structure in elastase-induced emphysema in adult mice and the effect of mesenchymal stromal cell (MSC) administration on these parameters. Adult mice were treated with intratracheal (4.8 units/100 g bodyweight) elastase to induce emphysema. MSCs were administered intratracheally or intravenously, before or after elastase injection. Lung function measurements, histological and morphometric analysis of lung tissue were performed at 3 weeks, 5 and 10 months after elastase and at 19, 20 and 21 days following MSC administration. Elastase-treated mice showed increased dynamic compliance and total lung capacity, and reduced tissue-specific elastance and forced expiratory flows at 3 weeks after elastase, which persisted during 10 months follow-up. Histology showed heterogeneous alveolar destruction which also persisted during long-term follow-up. Jugular vein injection of MSCs before elastase inhibited deterioration of lung function but had no effects on histology. Intratracheal MSC treatment did not modify lung function or histology. In conclusion, elastase-treated mice displayed persistent characteristics of pulmonary emphysema. Jugular vein injection of MSCs prior to elastase reduced deterioration of lung function. Intratracheal MSC treatment had no effect on lung function or histology.

Hypoxia-inducible factors promote alveolar development and regeneration

Understanding how alveoli and the underlying capillary network develop and how these mechanisms are disrupted in disease states is critical for developing effective therapies for lung regeneration. Recent evidence suggests that lung angiogenesis promotes lung development and repair. Vascular endothelial growth factor (VEGF) preserves lung angiogenesis and alveolarization in experimental O2-induced arrested alveolar growth in newborn rats, but combined VEGF+angiopoietin 1 treatment is necessary to correct VEGF-induced vessel leakiness. Hypoxia-inducible factors (HIFs) are transcription factors that activate multiple O2-sensitive genes, including those encoding for angiogenic growth factors, but their role during postnatal lung growth is incompletely understood. By inducing the expression of a range of angiogenic factors in a coordinated fashion, HIF may orchestrate efficient and safe angiogenesis superior to VEGF. We hypothesized that HIF inhibition impairs alveolarization and that HIF activation regenerates irreversible O2-induced arrested alveolar growth. HIF inhibition by intratracheal dominant-negative adenovirus (dnHIF-1α)-mediated gene transfer or chetomin decreased lung HIF-1α, HIF-2α, and VEGF expression and led to air space enlargement and arrested lung vascular growth. In experimental O2-induced arrested alveolar growth in newborn rats, the characteristic features of air space enlargement and loss of lung capillaries were associated with decreased lung HIF-1α and HIF-2α expression. Intratracheal administration of Ad.HIF-1α restored HIF-1α, endothelial nitric oxide synthase, VEGF, VEGFR2, and Tie2 expression and preserved and rescued alveolar growth and lung capillary formation in this model. HIFs promote normal alveolar development and may be useful targets for alveolar regeneration.

Lung function outcome at school age in very low birth weight children

OBJECTIVE

The aim of this study was to assess pulmonary function and its predictors in very low birth weight (birth weight ≤1,500 g) children (VLBWc) with or without bronchopulmonary dysplasia (BPD), born at gestational age ≤32 weeks at a single tertiary center during 1996-1999, after the introduction of surfactant therapy.

METHODS

Of the 120 surviving VLBW children, 48 (40%) VLBWc (22 with prior-BPD) at age 8.5 ± 1.0 years and 46 age-matched controls (8.8 ± 1.4 years) born at term, underwent lung function study.

RESULTS

Adjusted values (z-score) of forced vital capacity (z-FVC), forced expiratory volume in 1 sec (z-FEV1), forced expiratory flow 25-75% (z-FEF25-75), carbon monoxide lung diffusion capacity (z-DLCO), and DLCO/alveolar volume (z-DLCO/VA) were significantly lower than controls (mean difference, 95% CI: -1.35, -1.81 to -0.90, P < 0.001; -1.31, -1.73 to -0.90, P < 0.001; -0.87, -1.29 to -0.46, P < 0.001; -0.98, -1.72 to -0.23, P < 0.001; -0.70, -1.22 to -0.18, P < 0.05; respectively). Residual volume (z-RV) and RV/total lung capacity (RV/TLC) ratio (%) were significantly higher in VLBWc than controls (mean difference, 95% CI: 1.06, 0.44 to 1.68, P < 0.001; 9.54%, 5.73 to 13.3%, P < 0.001; respectively). No differences were found in lung function between VLBWc (no-BPD vs. BPD) with the exception of a significant higher RV/TLC ratio in the BPD-subgroup (mean difference, 95% CI: 7.0%, 0.4 to 13%, P = 0.03). Lung function abnormalities were found in 30 (63%) VLBWc with evidence of airway obstruction and diffusing capacity impairment. A weak relationship was observed between gestational age with z-FVC (r = 0.30, P = 0.04), birth weight with z-FEV1 (r = 0.30, P = 0.04) and RV/TLC ratio (r = -0.49, P = 0.001). The duration of oxygen treatment correlated negatively with the z-DLCO/Va (r = -0.5, P = 0.02). No differences were found in FeNO levels between VLBWc and controls.

CONCLUSION

VLBWc at school age showed lung function abnormalities characterized by airway obstruction, hyperinflation, and diffusion impairment. Neonatal lung damage together with preterm birth may play a role in worsening the functional respiratory outcome.

The axonal guidance cue semaphorin 3C contributes to alveolar growth and repair

Lung diseases characterized by alveolar damage such as bronchopulmonary dysplasia (BPD) in premature infants and emphysema lack efficient treatments. Understanding the mechanisms contributing to normal and impaired alveolar growth and repair may identify new therapeutic targets for these lung diseases. Axonal guidance cues are molecules that guide the outgrowth of axons. Amongst these axonal guidance cues, members of the Semaphorin family, in particular Semaphorin 3C (Sema3C), contribute to early lung branching morphogenesis. The role of Sema3C during alveolar growth and repair is unknown. We hypothesized that Sema3C promotes alveolar development and repair. In vivo Sema3C knock down using intranasal siRNA during the postnatal stage of alveolar development in rats caused significant air space enlargement reminiscent of BPD. Sema3C knock down was associated with increased TLR3 expression and lung inflammatory cells influx. In a model of O2-induced arrested alveolar growth in newborn rats mimicking BPD, air space enlargement was associated with decreased lung Sema3C mRNA expression. In vitro, Sema3C treatment preserved alveolar epithelial cell viability in hyperoxia and accelerated alveolar epithelial cell wound healing. Sema3C preserved lung microvascular endothelial cell vascular network formation in vitro under hyperoxic conditions. In vivo, Sema3C treatment of hyperoxic rats decreased lung neutrophil influx and preserved alveolar and lung vascular growth. Sema3C also preserved lung plexinA2 and Sema3C expression, alveolar epithelial cell proliferation and decreased lung apoptosis. In conclusion, the axonal guidance cue Sema3C promotes normal alveolar growth and may be worthwhile further investigating as a potential therapeutic target for lung repair.

Bronchopulmonary dysplasia in a double-hit mouse model induced by intrauterine hypoxia and postnatal hyperoxia: closer to clinical features?

Despite increased survival of very preterm newborns, bronchopulmonary dysplasia (BPD) remains a major threat, as it affects long-term pulmonary function and neurodevelopmental outcome. Recent research focused on mechanisms of lung repair. Animal models of BPD in term rodents use postnatal hyperoxia in order to mimic features observed in very preterm human neonates: reduced alveolarization and impaired septal architecture without profound inflammatory changes. In contrast, BPD in very preterm human neonates involves prenatal hits e.g. infections and growth restriction plus postnatal ventilation. BPD induced in rodents by postnatal hyperoxia also exhibits reduced alveolarization however without septal pathology but with marked inflammation. We therefore aimed to establish an animal model combining prenatal growth restriction (FiO₂ 0.1 for 4 days) with postnatal hyperoxia (FiO₂ 0.7 for 2 weeks). In double-hit mice the development was retarded: body weight and length, lung and brain weight were significantly reduced by day P14 compared with normoxic controls. Histomorphometric analysis revealed reduced alveolarization and increased septal thickness without pronounced inflammatory lesions. A down-regulation of SftpB and SftpC genes was observed in double-hit animals compared with controls. Thus, we established a new model of BPD using pre- and postnatal hits.

Dlg5 maintains apical aPKC and regulates progenitor differentiation during lung morphogenesis

Cell polarity plays an important role in tissue morphogenesis; however, the mechanisms of polarity and their role in mammalian development are still poorly understood. We show here that membrane-associated guanylate kinase protein Dlg5 is required for proper branching morphogenesis and progenitor differentiation in mammalian lung. We found that during lung development Dlg5 functions as an apical-basal polarity protein, which is necessary for the apical maintenance of atypical protein kinase C (aPKC). These results identify Dlg5 as a regulator of apical polarity complexes and uncover the critical function of Dlg5 in branching morphogenesis and differentiation of lung progenitor cells.

Receptor for advanced glycation end products contributes to postnatal pulmonary development and adult lung maintenance program in mice

The role of the receptor for advanced glycation end products (RAGE) in promoting the inflammatory response through activation of NF-κB pathway is well established. Recent findings indicate that RAGE may also have a regulative function in apoptosis, as well as in cellular proliferation, differentiation, and adhesion. Unlike other organs, lung tissue in adulthood and during organ development shows relatively high levels of RAGE expression. Thus a role for the receptor in lung organogenesis and homeostasis may be proposed. To evaluate the role of RAGE in lung development and adult lung homeostasis, we generated hemizygous and homozygous transgenic mice overexpressing human RAGE, and analyzed their lungs from the fourth postnatal day to adulthood. Moderate RAGE hyperexpression during lung development influenced secondary septation, resulting in an impairment of alveolar morphogenesis and leading to significant changes in morphometric parameters such as airspace number and the size of alveolar ducts. An increase in alveolar cell apoptosis and a decrease in cell proliferation were demonstrated by the terminal deoxy-nucleotidyltransferase-mediated dUTP nick end labeling reaction, active caspase-3, and Ki-67 immunohistochemistry. Alterations in elastin organization and deposition and in TGF-β expression were observed. In homozygous mice, the hyperexpression of RAGE resulted in histological changes resembling those changes characterizing human bronchopulmonary dysplasia (BPD). RAGE hyperexpression in the adult lung is associated with an increase of the alveolar destructive index and persistent inflammatory status leading to "destructive" emphysema. These results suggest an important role for RAGE in both alveolar development and lung homeostasis, and open new doors to working hypotheses on the pathogenesis of BPD and chronic obstructive pulmonary disease.

Using Cell-Based Strategies to Break the Link between Bronchopulmonary Dysplasia and the Development of Chronic Lung Disease in Later Life

Bronchopulmonary dysplasia (BPD) is the chronic lung disease of prematurity that affects very preterm infants. Although advances in perinatal care have changed the course of lung injury and enabled the survival of infants born as early as 23-24 weeks of gestation, BPD still remains a common complication of extreme prematurity, and there is no specific treatment for it. Furthermore, children, adolescents, and adults who were born very preterm and developed BPD have an increased risk of persistent lung dysfunction, including early-onset emphysema. Therefore, it is possible that early-life pulmonary insults, such as extreme prematurity and BPD, may increase the risk of COPD later in life, especially if exposed to secondary challenges such as respiratory infections and/or smoking. Recent advances in our understanding of stem/progenitor cells and their potential to repair damaged organs offer the possibility of cell-based treatments for neonatal and adult lung injuries. This paper summarizes the long-term pulmonary outcomes of preterm birth and BPD and discusses the recent advances of cell-based therapies for lung diseases, with a particular focus on BPD and COPD.

Claudin-3 and Clara cell 10 kDa protein as early signals of cigarette smoke-induced epithelial injury along alveolar ducts

Smoking-associated chronic obstructive pulmonary disease is characterized by inflammation, changes affecting small airways, and development of emphysema. Various short- and long-term models have been introduced to investigate these processes. The aim of the present study was to identify markers of early epithelial injury/adaptation in a short-term animal model of cigarette smoke exposure. Initially, male BALB/c mice were exposed to smoke from one to five cigarettes and lung changes were assessed 4 and 24 hr after smoking cessation. Subsequently, animals were exposed to smoke from five cigarettes for 2 consecutive days and lungs investigated daily until the seventh postexposure day. Lung homogenates cytokines were determined, bronchioloalveolar fluid cells were counted, and lung tissue was analyzed by immunohistochemistry. Exposure to smoke from a single cigarette induced slight pulmonary neutrophilia. Smoke from two cigarettes additionally induced de novo expression of tight junction protein, claudin-3, by alveolar duct (AD) epithelial cells. Further increases in smoke exposure induced epithelial changes in airway progenitor regions. During the recovery period, the severity/frequency of epithelial reactions slowly decreased, coinciding with the switch from acute to a chronic inflammatory reaction. Claudin-3 and Clara cell 10 kDa protein were identified as possible markers of early tobacco smoke-induced epithelial injury along ADs.

RAGE and tobacco smoke: insights into modeling chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a progressive condition characterized by chronic airway inflammation and airspace remodeling, leading to airflow limitation that is not completely reversible. Smoking is the leading risk factor for compromised lung function stemming from COPD pathogenesis. First- and second-hand cigarette smoke contain thousands of constituents, including several carcinogens and cytotoxic chemicals that orchestrate chronic lung inflammation and destructive alveolar remodeling. Receptors for advanced glycation end-products (RAGE) are multi-ligand cell surface receptors primarily expressed by diverse lung cells. RAGE expression increases following cigarette smoke exposure and expression is elevated in the lungs of patients with COPD. RAGE is responsible in part for inducing pro-inflammatory signaling pathways that culminate in expression and secretion of several cytokines, chemokines, enzymes, and other mediators. In the current review, new transgenic mouse models that conditionally over-express RAGE in pulmonary epithelium are discussed. When RAGE is over-expressed throughout embryogenesis, apoptosis in the peripheral lung causes severe lung hypoplasia. Interestingly, apoptosis in RAGE transgenic mice occurs via conserved apoptotic pathways also known to function in advanced stages of COPD. RAGE over-expression in the adult lung models features of COPD including pronounced inflammation and loss of parenchymal tissue. Understanding the biological contributions of RAGE during cigarette smoke-induced inflammation may provide critically important insight into the pathology of COPD.

Genetic, host, and environmental interactions in a 19 year old with severe chronic obstructive lung disease; observations regarding the pathophysiology of airflow obstruction

A case of a 19-year-old with severe chronic obstructive pulmonary disease is presented. This case illustrates genetic (severe alpha-1 antitrypsin deficiency) and host factors (such as developmental diaphragmatic hernia and the innate response to injury), and environmental (high oxidative stress and lung injury) interactions that lead to severe chronic obstructive lung disease. The development of chronic lung disease was caused by lung injury under high oxidative and inflammatory conditions in the setting of a diaphragmatic hernia. In the absence of normal alpha-1 antitrypsin levels, a pro-elastolytic environment in the early period of lung growth enhanced the development of severe hyperinflation and precocious airflow obstruction.

Lipopolysaccharide disrupts the directional persistence of alveolar myofibroblast migration through EGF receptor

Bronchopulmonary dysplasia (BPD) is characterized by alveolar simplification with decreased alveolar number and increased airspace size. Formation of alveoli involves a process known as secondary septation triggered by myofibroblasts. This study investigated the underlying mechanisms of altered lung morphogenesis in a rat model of BPD induced by intra-amniotic injection of lipopolysaccharide (LPS). Results showed that LPS disrupted alveolar morphology and led to abnormal localization of myofibroblasts in the lung of newborn rats, mostly in primary septa with few in secondary septa. To identify potential mechanisms, in vitro experiments were carried out to observe the migration behavior of myofibroblasts. The migration speed of lung myofibroblasts increased with LPS treatment, whereas the directional persistence decreased. We found that LPS induced activation of EGFR and overexpression of its ligand, TGF-α in myofibroblasts. AG1478, an EGFR inhibitor, abrogated the enhanced locomotivity of myofibroblasts by LPS and also increased the directional persistence of myofibroblast migration. Myofibroblasts showed a high asymmetry of phospho-EGFR localization, which was absent after LPS treatment. Application of rhTGF-α to myofibroblasts decreased the directional persistence. Our findings indicated that asymmetry of phospho-EGFR localization in myofibroblasts was important for cell migration and its directional persistence. We speculate that LPS exposure disrupts the asymmetric localization of phospho-EGFR, leading to decreased stability of cell polarity and final abnormal location of myofibroblasts in vivo, which is critical to secondary septation and may contribute to the arrested alveolar development in BPD.

Hyperoxia arrests alveolar development through suppression of histone deacetylases in neonatal rats

Bronchopulmonary dysplasia (BPD) poses a significant global health problem. It mainly occurs in preterm infants. It is histopathologically characterized by fewer and larger alveoli and less secondary septa, suggesting an arrested or disordered lung development. To date, the mechanisms that lead to the pathophysiological changes in BPD have still not been totally understood. In embryonic development, histone deacetylase (HDAC) plays an important role by regulating gene transcription. Here, we hypothesize that a decreased HDAC expression and activity, caused by preterm birth or environmental stresses, contribute to a disorder in alveolar development in BPD. To this end, newborn Sprague-Dawley rats subjected to hyperoxia (85% O(2) ) were used to investigate the gene expression and protein activity of HDAC and alveolar development in lungs. Our results showed that hyperoxia exposure led to a suppression of the HDAC1/HDAC2 expression and activity, and the overall HDAC activity, as well as arrest of alveolarization, and an elevated expression of the cytokine-induced neutrophil chemoattractant-1 (CINC-1) in the lungs of newborn rats. However, preservation of HDAC activity by theophylline significantly improved alveolar development and attenuated CINC-1 release, all of which were blocked by a specific HDAC inhibitor, trichostatin A (TSA). TSA alone can disturb the alveolar development in neonatal rats. Our findings indicate that a persistent exposure to hyperoxia leads to a suppressed HDAC activity, which causes disorders in pulmonary development. This effect may be mediated by CINC-1. Attenuation of CINC-1-mediated inflammation by activating HDAC may have a protective effect in BPD.

[Adult respiratory sequelae of premature birth]

INTRODUCTION

Between 5 and 7% of babies are born prematurely. In the paediatric age group, the respiratory morbidity of these patients is well known, particularly in cases of bronchopulmonary dysplasia (BPD). On the other hand, very few data are available concerning their adult respiratory status.

BACKGROUND

There are currently three different groups of ex-premature babies: (1) those with no BPD who are usually not considered as respiratory high-risk adults but have not been well studied; (2) ex-premature babies with BPD who have an increased risk of asthma, respiratory infections, bronchial obstruction aggravated by smoking, and non-atopic bronchial hyperreactivity; this group has been well studied but not beyond 30 years of age; (3) the babies born very prematurely and affected with a new form of BPD due to neonatal intensive care at a very immature stage of pulmonary development, and for whom the future in adult life is unknown but worrying because of reduced lung volumes since birth.

VIEWPOINTS AND CONCLUSIONS

The respiratory physician must be aware of these groups of adults who he may encounter and who may develop, sooner or later, a certain type of chronic obstructive pulmonary disease.

Profiling target genes of FGF18 in the postnatal mouse lung: possible relevance for alveolar development

Better understanding alveolarization mechanisms could help improve prevention and treatment of diseases characterized by reduced alveolar number. Although signaling through fibroblast growth factor (FGF) receptors is essential for alveolarization, involved ligands are unidentified. FGF18, the expression of which peaks coincidentally with alveolar septation, is likely to be involved. Herein, a mouse model with inducible, lung-targeted FGF18 transgene was used to advance the onset of FGF18 expression peak, and genome-wide expression changes were determined by comparison with littermate controls. Quantitative RT-PCR was used to confirm expression changes of selected up- and downregulated genes and to determine their expression profiles in the course of lung postnatal development. This allowed identifying so-far unknown target genes of the factor, among which a number are known to be involved in alveolarization. The major target was adrenomedullin, a promoter of lung angiogenesis and alveolar development, whose transcript was increased 6.9-fold. Other genes involved in angiogenesis presented marked expression increases, including Wnt2 and cullin2. Although it appeared to favor cell migration notably through enhanced expression of Snai1/2, FGF18 also induced various changes consistent with prevention of epithelial-mesenchymal transition. Together with antifibrotic effects driven by induction of E prostanoid receptor 2 and repression of numerous myofibroblast markers, this could prevent alveolar septation-driving mechanisms from becoming excessive and deleterious. Last, FGF18 up- or downregulated genes of extracellular matrix components and epithelial cell markers previously shown to be up- or downregulated during alveolarization. These findings therefore argue for an involvement of FGF18 in the control of various developmental events during the alveolar stage.

Up-regulation of receptors for advanced glycation end-products by alveolar epithelium influences cytodifferentiation and causes severe lung hypoplasia

Receptors for advanced glycation end-products (RAGE) are cell-surface receptors expressed by pulmonary tissue that influence alveolar type (AT) II-ATI transition required for normal alveolar formation. However, the precise contribution of RAGE in interactions between pulmonary epithelium and splanchnic mesenchyme during lung organogenesis remains uncertain. To test the hypothesis that RAGE misexpression adversely affects lung morphogenesis, conditional transgenic mice were generated that overexpress RAGE. Mice that overexpress RAGE throughout embryogenesis experienced 100% mortality and significant lung hypoplasia coincident with large, vacuous areas in the periphery when compared with normal airway and alveolar architecture observed in control mouse lungs. Flow cytometry and immunohistochemistry employing cell-specific markers for distal (forkhead box protein A2) and respiratory (thyroid transcription factor-1) epithelium, ATII cells (pro-surfactant protein-C), and ATI cells (T1-α) demonstrated anomalies in key epithelial cell populations resulting from RAGE up-regulation. These results reveal that precise regulation of RAGE expression is required during lung formation. Furthermore, abundant RAGE results in profound alterations in epithelial cell differentiation that culminate in severe respiratory distress and perinatal lethality.

Exposure to neonatal cigarette smoke causes durable lung changes but does not potentiate cigarette smoke-induced chronic obstructive pulmonary disease in adult mice

The impact of early childhood cigarette smoke (CS) exposure on CS-induced chronic obstructive pulmonary disease (COPD) is unknown. This study was performed to evaluate the individual and combined effects of neonatal and adult CS exposure on lung structure, function, and gene expression in adult mice. To model a childhood CS exposure, neonatal C57/B6 mice were exposed to 14 days of CS (Neo CS). At 10 weeks of age, Neo CS and control mice were exposed to 4 months of CS. Pulmonary function tests, bronchoalveolar lavage, and lung morphometry were measured and gene expression profiling was performed on lung tissue. Mean chord lengths and lung volumes were increased in neonatal and/or adult CS-exposed mice. Differences in immune, cornified envelope protein, muscle, and erythrocyte genes were found in CS-exposed lung. Neonatal CS exposure caused durable structural and functional changes in the adult lung but did not potentiate CS-induced COPD changes. Cornified envelope protein gene expression was decreased in all CS-exposed mice, whereas myosin and erythrocyte gene expression was increased in mice exposed to both neonatal and adult CS, suggesting an adaptive response. Additional studies may be warranted to determine the utility of these genes as biomarkers of respiratory outcomes.

Control of lung development by latent TGF-β binding proteins

The latent TGF-β binding proteins (LTBP-1 -3, and -4) assist in the secretion and localization of latent TGF-β molecules. Ltbp3(-/-) and Ltbp4S(-/-) mice have distinct phenotypes and only in the lungs does deficiency of either Ltbp-3 or Ltbp-4 cause developmental abnormalities. To determine if these two LTBPs have additional common functions, we generated mice deficient for both Ltbp-3 and Ltbp-4S. The only novel defect in Ltbp3(-/-);Ltbp4S(-/-) mice was an early lethality compared to mice with single mutations. In addition lung abnormalities were exacerbated and the terminal air sac septation defect was more severe in Ltbp3(-/-);Ltbp4S(-/-) mice than in Ltbp4S(-/-) mice. Decreased cellularity of Ltbp3(-/-);Ltbp4S(-/-) lungs was correlated with higher rate of apoptosis in newborn lungs of Ltbp3(-/-);Ltbp4S(-/-) animals compared to WT, Ltbp3(-/-), and Ltbp4S(-/-) mice. No differences in the maturation of the major lung cell types were discerned between the single and double mutant mice. However, the distribution of type 2 cells and myofibroblasts was abnormal, and myofibroblast segregation in some areas might be an indication of early fibrosis. We also observed differences in ECM composition between Ltbp3(-/-);Ltbp4S(-/-) and Ltbp4S(-/-) lungs after birth, reflected in decreased incorporation of fibrillin-1 and -2 in Ltbp3(-/-);Ltbp4S(-/-) matrix. The function of the lungs of Ltbp3(-/-);Ltbp4S(-/-) mice after the first week of life was potentially further compromised by macrophage infiltration, as proteases secreted from macrophages might exacerbate developmental emphysema. Together these data indicate that LTBP-3 and -4 perform partially overlapping functions only in the lungs.

A role for matrix metalloproteinase 9 in IFNγ-mediated injury in developing lungs: relevance to bronchopulmonary dysplasia

We noted a marked increase in IFNγ mRNA in newborn (NB) murine lungs after exposure to hyperoxia. We sought to evaluate the role of IFNγ in lung injury in newborns. Using a unique triple-transgenic (TTG), IFNγ-overexpressing, lung-targeted, externally regulatable NB murine model, we describe a lung phenotype of impaired alveolarization, resembling human bronchopulmonary dysplasia (BPD). IFNγ-mediated abnormal lung architecture was associated with increased cell death and the upregulation of cell death pathway mediators caspases 3, 6, 8, and 9, and angiopoietin 2. Moreover, an increase was evident in cathepsins B, H, K, L, and S, and in matrix metalloproteinases (MMPs) 2, 9, 12, and 14. The IFNγ-mediated abnormal lung architecture was found to be MMP9-dependent, as indicated by the rescue of the IFNγ-induced pulmonary phenotype and survival during hyperoxia with a concomitant partial deficiency of MMP9. This result was concomitant with a decrease in caspases 3, 6, 8, and 9 and angiopoietin 2, but an increase in the expression of angiopoietin 1. In addition, NB IFNγ TTG mice exhibited significantly decreased survival during hyperoxia, compared with littermate controls. Furthermore, as evidence of clinical relevance, we show increased concentrations of the downstream targets of IFNγ chemokine (C-X-C motif) ligands (CXCL10 and CXCL11) in baboon and human lungs with BPD. IFNγ and its downstream targets may contribute significantly to the final common pathway of hyperoxia-induced injury in the developing lung and in human BPD.

Preparing for the first breath: genetic and cellular mechanisms in lung development

The mammalian respiratory system--the trachea and the lungs--arises from the anterior foregut through a sequence of morphogenetic events involving reciprocal endodermal-mesodermal interactions. The lung itself consists of two highly branched, tree-like systems--the airways and the vasculature--that develop in a coordinated way from the primary bud stage to the generation of millions of alveolar gas exchange units. We are beginning to understand some of the molecular and cellular mechanisms that underlie critical processes such as branching morphogenesis, vascular development, and the differentiation of multipotent progenitor populations. Nevertheless, many gaps remain in our knowledge, the filling of which is essential for understanding respiratory disorders, congenital defects in human neonates, and how the disruption of morphogenetic programs early in lung development can lead to deficiencies that persist throughout life.

Palifermin induces alveolar maintenance programs in emphysematous mice

RATIONALE

Emphysema is characterized by destruction of alveoli with ensuing airspace enlargement and loss of alveoli. Induction of alveolar regeneration is still a major challenge in emphysema therapy.

OBJECTIVES

To investigate whether therapeutic application of palifermin (DeltaN23-KGF) is able to induce a regenerative response in distal lung parenchyma after induction of pulmonary emphysema.

METHODS

Mice were therapeutically treated at three occasions by oropharyngeal aspiration of 10 mg DeltaN23-KGF per kg body weight after induction of emphysema by porcine pancreatic elastase.

MEASUREMENTS AND MAIN RESULTS

Airflow limitation associated with emphysema was largely reversed as assessed by noninvasive head-out body plethysmography. Porcine pancreatic elastase-induced airspace enlargement and loss of alveoli were partially reversed as assessed by design-based stereology. DeltaN23-KGF induced proliferation of epithelium, endothelium, and fibroblasts being associated with enhanced differentiation as well as increased expression of vascular endothelial growth factor, vascular endothelial growth factor receptors, transforming growth factor (TGF)-beta1, TGF-beta2, (phospho-) Smad2, plasminogen activator inhibitor-1, and elastin as assessed by quantitative reverse transcriptase-polymerase chain reaction, Western blotting, and immunohistochemistry. DeltaN23-KGF induced the expression of TGF-beta1 in and release of active TGF-beta1 from primary mouse alveolar epithelial type 2 (AE2) cells, murine AE2-like cells LA-4, and cocultures of LA-4 and murine lung fibroblasts (MLF), but not in MLF cultured alone. Recombinant TGF-beta1 but not DeltaN23-KGF induced elastin gene expression in MLF. Blockade of TGF-signaling by neutralizing antibody abolished these effects of DeltaN23-KGF in LA-4/MLF cocultures.

CONCLUSIONS

Our data demonstrate that therapeutic application of DeltaN23-KGF has the potential to induce alveolar maintenance programs in emphysematous lungs and suggest that the regenerative effect on interstitial tissue is linked to AE2 cell-derived TGF-beta1.