Lung-specific inactivation of CCAAT/enhancer binding protein alpha causes a pathological pattern characteristic of COPD

TRβ activation confers AT2-to-AT1 cell differentiation and anti-fibrosis during lung repair via KLF2 and CEBPA

Aberrant repair underlies the pathogenesis of pulmonary fibrosis while effective strategies to convert fibrosis to normal regeneration are scarce. Here, we found that thyroid hormone is decreased in multiple models of lung injury but is essential for lung regeneration. Moreover, thyroid hormone receptor α (TRα) promotes cell proliferation, while TRβ fuels cell maturation in lung regeneration. Using a specific TRβ agonist, sobetirome, we demonstrate that the anti-fibrotic effects of thyroid hormone mainly rely on TRβ in mice. Cellularly, TRβ activation enhances alveolar type-2 (AT2) cell differentiation into AT1 cell and constrains AT2 cell hyperplasia. Molecularly, TRβ activation directly regulates the expression of KLF2 and CEBPA, both of which further synergistically drive the differentiation program of AT1 cells and benefit regeneration and anti-fibrosis. Our findings elucidate the modulation function of the TRβ-KLF2/CEBPA axis on AT2 cell fate and provide a potential treatment strategy to facilitate lung regeneration and anti-fibrosis.

Targeting CEBPA to restore cellular identity and tissue homeostasis in pulmonary fibrosis

Fibrosis in the lung is thought to be driven by epithelial cell dysfunction and aberrant cell-cell interactions. Unveiling the molecular mechanisms of cellular plasticity and cell-cell interactions is imperative to elucidating lung regenerative capacity and aberrant repair in pulmonary fibrosis. By mining publicly available RNA-Seq data sets, we identified loss of CCAAT enhancer-binding protein alpha (CEBPA) as a candidate contributor to idiopathic pulmonary fibrosis (IPF). We used conditional KO mice, scRNA-Seq, lung organoids, small-molecule inhibition, and potentially novel gene manipulation methods to investigate the role of CEBPA in lung fibrosis and repair. Long-term (6 months or more) of Cebpa loss in AT2 cells caused spontaneous fibrosis and increased susceptibility to bleomycin-induced fibrosis. Cebpa knockout (KO) in these mice significantly decreased AT2 cell numbers in the lung and reduced expression of surfactant homeostasis genes, while increasing inflammatory cell recruitment as well as upregulating S100a8/a9 in AT2 cells. In vivo treatment with an S100A8/A9 inhibitor alleviated experimental lung fibrosis. Restoring CEBPA expression in lung organoids ex vivo and during experimental lung fibrosis in vivo rescued CEBPA deficiency-mediated phenotypes. Our study establishes a direct mechanistic link between CEBPA repression, impaired AT2 cell identity, disrupted tissue homeostasis, and lung fibrosis.

Targeting the nuclear long noncoding transcript LSP1P5 abrogates extracellular matrix deposition by trans-upregulating CEBPA in keloids

Keloids are characterized by fibroblast hyperproliferation and excessive accumulation of extracellular matrix (ECM) and are a major global health care burden among cutaneous diseases. However, the function of long noncoding RNA (lncRNA)-mediated ECM remodeling during the pathogenesis of keloids is still unclear. Herein, we identified a long noncoding transcript, namely, lymphocyte-specific protein 1 pseudogene 5 (LSP1P5), that modulates ECM component deposition in keloids. First, high-throughput transcriptome analysis showed that LSP1P5 was selectively upregulated in keloids and correlated with more severe disease in a clinical keloid cohort. Therapeutically, the attenuation of LSP1P5 significantly decreased the expression of ECM markers (COL1, COL3, and FN1) both in vitro and in vivo. Intriguingly, an antifibrotic gene, CCAAT enhancer binding protein alpha (CEBPA), is a functional downstream candidate of LSP1P5. Mechanistically, LSP1P5 represses CEBPA expression by hijacking Suppressor of Zeste 12 to the promoter of CEBPA, thereby enhancing the polycomb repressive complex 2-mediated H3K27me3 and changing the chromosomal opening status of CEBPA. Taken together, these findings indicate that targeting LSP1P5 abrogates fibrosis in keloids through epigenetic regulation of CEBPA, revealing a novel antifibrotic therapeutic strategy that bridges our current understanding of lncRNA regulation, histone modification and ECM remodeling in keloids.

Epigenetic Reprogramming Drives Epithelial Disruption in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) remains a major public health challenge that contributes greatly to mortality and morbidity worldwide. Although it has long been recognized that the epithelium is altered in COPD, there has been little focus on targeting it to modify the disease course. Therefore, mechanisms that disrupt epithelial cell function in patients with COPD are poorly understood. In this study, we sought to determine whether epigenetic reprogramming of the cell-cell adhesion molecule E-cadherin, encoded by the CDH1 gene, disrupts epithelial integrity. By reducing these epigenetic marks, we can restore epithelial integrity and rescue alveolar airspace destruction. We used differentiated normal and COPD-derived primary human airway epithelial cells, genetically manipulated mouse tracheal epithelial cells, and mouse and human precision-cut lung slices to assess the effects of epigenetic reprogramming. We show that the loss of CDH1 in COPD is due to increased DNA methylation site at the CDH1 enhancer D through the downregulation of the ten-eleven translocase methylcytosine dioxygenase (TET) enzyme TET1. Increased DNA methylation at the enhancer D region decreases the enrichment of RNA polymerase II binding. Remarkably, treatment of human precision-cut slices derived from patients with COPD with the DNA demethylation agent 5-aza-2'-deoxycytidine decreased cell damage and reduced air space enlargement in the diseased tissue. Here, we present a novel mechanism that targets epigenetic modifications to reverse the tissue remodeling in human COPD lungs and serves as a proof of concept for developing a disease-modifying target.

Study on Potential Differentially Expressed Genes in Idiopathic Pulmonary Fibrosis by Bioinformatics and Next-Generation Sequencing Data Analysis

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive lung disease with reduced quality of life and earlier mortality, but its pathogenesis and key genes are still unclear. In this investigation, bioinformatics was used to deeply analyze the pathogenesis of IPF and related key genes, so as to investigate the potential molecular pathogenesis of IPF and provide guidance for clinical treatment. Next-generation sequencing dataset GSE213001 was obtained from Gene Expression Omnibus (GEO), and the differentially expressed genes (DEGs) were identified between IPF and normal control group. The DEGs between IPF and normal control group were screened with the DESeq2 package of R language. The Gene Ontology (GO) and REACTOME pathway enrichment analyses of the DEGs were performed. Using the g:Profiler, the function and pathway enrichment analyses of DEGs were performed. Then, a protein-protein interaction (PPI) network was constructed via the Integrated Interactions Database (IID) database. Cytoscape with Network Analyzer was used to identify the hub genes. miRNet and NetworkAnalyst databaseswereused to construct the targeted microRNAs (miRNAs), transcription factors (TFs), and small drug molecules. Finally, receiver operating characteristic (ROC) curve analysis was used to validate the hub genes. A total of 958 DEGs were screened out in this study, including 479 up regulated genes and 479 down regulated genes. Most of the DEGs were significantly enriched in response to stimulus, GPCR ligand binding, microtubule-based process, and defective GALNT3 causes HFTC. In combination with the results of the PPI network, miRNA-hub gene regulatory network and TF-hub gene regulatory network, hub genes including LRRK2, BMI1, EBP, MNDA, KBTBD7, KRT15, OTX1, TEKT4, SPAG8, and EFHC2 were selected. Cyclothiazide and rotigotinethe are predicted small drug molecules for IPF treatment. Our findings will contribute to identification of potential biomarkers and novel strategies for the treatment of IPF, and provide a novel strategy for clinical therapy.

Associations of prenatal exposure to NO2 and near roadway residence with placental gene expression

INTRODUCTION

Traffic-related air pollution (TRAP), a common exposure, potentially impacts pregnancy through altered placental function. We investigated associations between prenatal TRAP exposure and placental gene expression.

METHODS

Whole transcriptome sequencing was performed on placental samples from CANDLE (Memphis, TN) (n = 776) and GAPPS (Seattle and Yakima, WA) (n = 205), cohorts of the ECHO-PATHWAYS Consortium. Residential NO2 exposures were computed via spatiotemporal models for full-pregnancy, each trimester, and the first/last months of pregnancy. Individual cohort-specific, covariate-adjusted linear models were fit for 10,855 genes and respective exposures (NO2 or roadway proximity [≤150 m]). Infant-sex/exposure interactions on placental gene expression were tested with interaction terms in separate models. Significance was based on false discovery rate (FDR<0.10).

RESULTS

In GAPPS, final-month NO2 exposure was positively associated with MAP1LC3C expression (FDR p-value = 0.094). Infant-sex interacted with second-trimester NO2 on STRIP2 expression (FDR interaction p-value = 0.011, inverse and positive associations among male and female infants, respectively) and roadway proximity on CEBPA expression (FDR interaction p-value = 0.045, inverse among females). In CANDLE, infant-sex interacted with first-trimester and full-pregnancy NO2 on RASSF7 expression (FDR interaction p-values = 0.067 and 0.013, respectively, positive among male infants and inverse among female infants).

DISCUSSION

Overall, pregnancy NO2 exposure and placental gene expression associations were primarily null, with exception of final month NO2 exposure and placental MAP1LC3C association. We found several interactions of infant sex and TRAP exposures on placental expression of STRIP2, CEBPA, and RASSF7. These highlighted genes suggest influence of TRAP on placental cell proliferation, autophagy, and growth, though additional replication and functional studies are required for validation.

Potential Mechanisms Between HF and COPD: New Insights From Bioinformatics

Heart failure (HF) and chronic obstructive pulmonary disease (COPD) are closely related in clinical practice. This study aimed to investigate the co-genetic characteristics and potential molecular mechanisms of HF and COPD. HF and COPD datasets were downloaded from gene expression omnibus database. After identifying common differentially expressed genes (DEGs), the functional analysis highlighted the critical role of extracellular matrix and ribosomal signaling pathways in both diseases. In addition, GeneMANIA's results suggested that the 2 diseases were related to immune infiltration, and CIBERSORT suggested the role of macrophages. We also discovered 4 TFs and 1408 miRNAs linked to both diseases, and salbutamol may positively affect them.

CCAAT/Enhancer-Binding Proteins in Fibrosis: Complex Roles Beyond Conventional Understanding

CCAAT/enhancer-binding proteins (C/EBPs) are a family of at least six identified transcription factors that contain a highly conserved basic leucine zipper domain and interact selectively with duplex DNA to regulate target gene expression. C/EBPs play important roles in various physiological processes, and their abnormal function can lead to various diseases. Recently, accumulating evidence has demonstrated that aberrant C/EBP expression or activity is closely associated with the onset and progression of fibrosis in several organs and tissues. During fibrosis, various C/EBPs can exert distinct functions in the same organ, while the same C/EBP can exert distinct functions in different organs. Modulating C/EBP expression or activity could regulate various molecular processes to alleviate fibrosis in multiple organs; therefore, novel C/EBPs-based therapeutic methods for treating fibrosis have attracted considerable attention. In this review, we will explore the features of C/EBPs and their critical functions in fibrosis in order to highlight new avenues for the development of novel therapies targeting C/EBPs.

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.

The Role of Heme Oxygenase-1 Promoter Polymorphisms in Perinatal Disease

Heme oxygenase (HO) is the rate-limiting enzyme in the heme catabolic pathway, which degrades heme into equimolar amounts of carbon monoxide, free iron, and biliverdin. Its inducible isoform, HO-1, has multiple protective functions, including immune modulation and pregnancy maintenance, showing dynamic alteration during perinatal periods. As its contribution to the development of perinatal complications is speculated, two functional polymorphisms of the HMOX1 gene, (GT)_n repeat polymorphism (rs3074372) and A(-413)T single nucleotide polymorphism (SNP) (rs2071746), were studied for their association with perinatal diseases. We systematically reviewed published evidence on HMOX1 polymorphisms in perinatal diseases and clarified their possible significant contribution to neonatal jaundice development, presumably due to their direct effect of inducing HO enzymatic activity in the bilirubin-producing pathway. However, the role of these polymorphisms seems limited for other perinatal complications such as bronchopulmonary dysplasia. We speculate that this is because the antioxidant or anti-inflammatory effect is not directly mediated by HO but by its byproducts, resulting in a milder effect. For better understanding, subtyping each morbidity by the level of exposure to causative environmental factors, simultaneous analysis of both polymorphisms, and the unified definition of short and long alleles in (GT)_n repeats based on transcriptional capacity should be further investigated.

The Bromodomain Containing 8 (BRD8) transcriptional network in human lung epithelial cells

Mechanisms regulating gene expression in the airway epithelium underlie its response to the environment. A network of transcription factors (TFs) and architectural proteins, modulate chromatin accessibility and recruit activating or repressive signals. Bromodomain-containing proteins function as TFs or by engaging methyltransferase or acetyltransferase activity to induce chromatin modifications. Here we investigate the role of Bromodomain Containing 8 (BRD8) in coordinating lung epithelial function. Sites of BRD8 occupancy genome-wide were mapped in human lung epithelial cell lines (Calu-3 and 16HBE14o^-). CCCTC-Binding Factor (CTCF) was identified as a predicted co-factor of BRD8, based upon motif over-representation under BRD8 ChIP-seq peaks. Following siRNA-mediated depletion of BRD8, differentially expressed genes with nearby peaks of BRD8 occupancy were subject to gene ontology process enrichment analysis. BRD8 targets are enriched for genes involved in the innate immune response and the cell cycle. Depletion of BRD8 increased the secretion of the antimicrobial peptide beta-defensin 1 and multiple chemokines, and reduced cell proliferation.

Serine Protease Imbalance in the Small Airways and Development of Centrilobular Emphysema in Chronic Obstructive Pulmonary Disease

Epithelial dysfunction in the small airways may cause the development of emphysema in chronic obstructive pulmonary disease. C/EBPα (CCAAT/enhancer binding protein-α), a transcription factor, is required for lung maturation during development, and is also important for lung homeostasis after birth, including the maintenance of serine protease/antiprotease balance in the bronchiolar epithelium. This study aimed to show the roles of C/EBPα in the distal airway during chronic cigarette smoke exposure in mice and in the small airways in smokers. In a model of chronic smoke exposure using epithelial cell-specific C/EBPα-knockout mice, significant pathological phenotypes, such as higher protease activity, impaired ciliated cell regeneration, epithelial cell barrier dysfunction via reduced zonula occludens-1 (Zo-1), and decreased alveolar attachments, were found in C/EBPα-knockout mice compared with control mice. We found that Spink5 (serine protease inhibitor kazal-type 5) gene (encoding lymphoepithelial Kazal-type-related inhibitor [LEKTI], an anti-serine protease) expression in the small airways is a key regulator of protease activity in this model. Finally, we showed that daily antiprotease treatment counteracted the phenotypes of C/EBPα-knockout mice. In human studies, CEBPA (CCAAT/enhancer binding protein-α) gene expression in the lung was downregulated in patients with emphysema, and six smokers with centrilobular emphysema (CLE) showed a significant reduction in LEKTI in the small airways compared with 22 smokers without CLE. LEKTI downregulation in the small airways was associated with disease development during murine small airway injury and CLE in humans, suggesting that LEKTI might be a key factor linking small airway injury to the development of emphysema.

Developing small activating RNA as a therapeutic: current challenges and promises

RNA activation (RNAa) allows specific gene upregulation mediated by a small activating RNA (saRNA). Harnessing this process would help in developing novel therapeutics for undruggable diseases. Since its discovery in mid 2000s, improvements of saRNA design, synthetic chemistry and understanding of the biology have matured the way to apply RNAa. Indeed, MiNA therapeutics Ltd has conducted the first RNAa clinical trial for advanced hepatocellular carcinoma patients with promising outcomes. However, to fully realize the RNAa potential better saRNA delivery strategies are needed to target other diseases. Currently, saRNA can be delivered in vivo by lipid nanoparticles, dendrimers, lipid and polymer hybrids and aptamers. Further developing these delivery technologies and novel application of RNAa will prove to be invaluable for new treatment development.

Targeted regulation of fibroblast state by CRISPR-mediated CEBPA expression

Background

Fibroblasts regulate tissue homeostasis and the balance between tissue repair and fibrosis. CCAAT/enhancer-binding protein alpha (CEBPA) is a key transcription factor that regulates adipogenesis. CEBPA has been shown to be essential for lung maturation, and deficiency of CEBPA expression leads to abnormal lung architecture. However, its specific role in lung fibroblast regulation and fibrosis has not yet been elucidated.

Methods

Lung fibroblast CEBPA expression, pro-fibrotic and lipofibroblast gene expression were assessed by qRT-PCR. CEBPA gain and loss of function experiments were carried out to evaluate the role of CEBPA in human lung fibroblast activation with and without TGF-β1 treatment. Adipogenesis assay was used to measure the adiopogenic potential of lung fibroblasts. Finally, CRISPR activation system was used to enhance endogenous CEBPA expression.

Results

We found that CEBPA gene expression is significantly decreased in IPF-derived fibroblasts compared to normal lung fibroblasts. CEBPA knockdown in normal human lung fibroblasts enhanced fibroblast pro-fibrotic activation and ECM production. CEBPA over-expression by transient transfection in IPF-derived fibroblasts significantly reduced pro-fibrotic gene expression, ECM deposition and αSMA expression and promoted the formation of lipid droplets measured by Oil Red O staining and increased lipofibroblast gene expression. Inhibition of the histone methyl transferase G9a enhanced CEBPA expression, and the anti-fibrotic effects of G9a inhibition were partially mediated by CEBPA expression. Finally, targeted CRISPR-mediated activation of CEBPA resulted in fibroblasts switching from fibrogenic to lipofibroblast states.

Conclusions

CEBPA expression is reduced in human IPF fibroblasts and its deficiency reduces adipogenic potential and promotes fibrogenic activation. CEBPA expression can be rescued via an inhibitor of epigenetic repression or by targeted CRISPR activation, leading to reduced fibrogenic activation.

Role of C/EBPα hypermethylation in diesel engine exhaust exposure-induced lung inflammation

Exposure to diesel engine exhaust (DEE) impairs lung function. But the underlying mechanisms are still not fully understood. The aim of this study was to investigate the effects of long-term DEE exposure on lung inflammation and the underlying mechanisms. Sprague-Dawley male rats were exposed to DEE with 3 mg/m³ of diesel exhaust particles (DEP) for 12 weeks. Then urine, blood, bronchoalveolar lavage fluid (BALF), and lung tissue were collected for the determination of biochemistry indexes, DNA methylation status, and histological changes in the lung. The results showed that the metabolites of polycyclic aromatic hydrocarbons (PAHs) 2-hydroxyphenanthrene (2-OHPh) and 9-OHPh, and 8-hydroxy-2'-deoxyguanosine (8-OHdG), and malondialdehyde (MDA) level were higher in urine of DEE-exposed rats than control group. The level of proinflammatory cytokines IL-8, IL-6, and TNF-α was significantly higher in serum (1.8, 3.5, and nearly 1.0-fold increase, respectively), BALF (2.2, 3.8, and 2.0-fold increase, respectively) and lung tissues (3.5, 4.3, and 2.4-fold increase, respectively) of DEE-exposed rats than control group. While the level of clara cell secretory protein (CC16) and pulmonary surfactant protein D (SP-D) with anti-inflammatory property was obviously lower in serum (reduction of 29% and 38%, respectively), BALF (reduction of 50% and 46%, respectively) and lung tissues (reduction of 50% and 55%, respectively) of DEE-exposed rats than control group. Exposure to DEE also resulted in significant increases in total white blood cell (WBC), neutrophil, eosinophil, and lymphocyte number in BALF. Airway inflammation and remolding were apparent in DEE group. The methylation level of CCAAT/enhancer-binding protein alpha (C/EBPα) promoter was markedly increased (about 3.2-fold increase), and its mRNA and protein expression were significantly decreased (about 62% and 68% decrease, respectively) in the lungs of DEE-exposed rats compared with the group. Further, cell experiments were performed to investigate the relationship between C/EBPα and CC16, and CC16 function under DEP conditions. The results showed that DEP inhibited CC16 expression via methylation of C/EBPα promoter, and the increase of CC16 level significantly relieved the proinflammatory effects caused by DEP exposure. In conclusion, our data indicated that long-term exposure to DEE can cause lung inflammation, at least in part via methylation of C/EBPα promoter, and inhibition of CC16 expression.

Effects of C/EBPα overexpression on alveolar epithelial type II cell proliferation, apoptosis and surfactant protein-C expression after exposure to hyperoxia

Background

This study aims to investigate the effects of CCAAT/enhancer binding protein alpha (C/EBPα) overexpression on cell proliferation, apoptosis and surfactant protein-C(SP-C) in alveolar epithelial type II (AEC II) cells after exposure to hyperoxia.

Methods

pcDNA3.1(+)-C/EBPα plasmid or air-empty vector were transfected into AEC II cells with or without hyperoxia. AEC II cells were divided into air group, air+pcDNA3.1-C/EBPα group, air-empty vector group, hyperoxia group, hyperoxia+pcDNA3.1-C/EBPα group, and hyperoxia-empty vector group. Cell proliferation was analyzed using Cell Counting Kit-8. The mRNA level and protein expression were measured using PCR and Western blot techniques, respectively. The cell cycle and apoptosis were analyzed using flow cytometry.

Results

After 48 h of post-transfection, significantly higher protein expression of C/EBPα was observed in the C/EBPα transfection group with or without hyperoxia compared to the others (P < 0.05). Compared to the air group, hyperoxia decreased cell proliferation, increased apoptosis, decreased SP-C expression, decreased percentage of cells in G1 phase, and increased percentage of cells in the S and G2 phases (P < 0.05); however, reversed by C/EBPα transfection (P < 0.05). No significant changes were observed in cell proliferation, SP-C expression, and apoptosis rates in the C/EBPα transfection group as compared to the controls air-empty vector group.

Conclusion

C/EBPα overexpression significantly upregulates the expression of SP-C, promotes cell proliferation, and inhibits apoptosis in AEC II cells after exposure to hyperoxia. Hence, this data suggests that C/EBPα overexpression may reverse the damage and exert a protective role in hyperoxia-induced lung injury.

Electronic supplementary material

The online version of this article (10.1186/s12890-019-0911-x) contains supplementary material, which is available to authorized users.

Endothelial-to-mesenchymal transition: Pathogenesis and therapeutic targets for chronic pulmonary and vascular diseases

Endothelial-to-mesenchymal transition (EndoMT) is a process of transdifferentiation where endothelial cells gradually adopt the phenotypic characteristics of mesenchymal cells. This phenomenon was first discovered in embryonic heart development. The mechanisms underlying EndoMT are due to the activation of transforming growth factor-β, bone morphogenetic protein, Wingless/Integrated, or Notch signaling pathways. The EndoMT can be modulated by pathological processes, including inflammation, disturbed shear stress, vascular stiffness, and metabolic dysregulation. Recent studies have shown that EndoMT is implicated in the pathogenesis of chronic lung diseases, including pulmonary hypertension and lung fibrosis. Lung pathology of bronchopulmonary dysplasia can be mimicked in rodents exposed to hyperoxia as neonates. Although hyperoxic exposure reduces an endothelial cell marker platelet and endothelial cell adhesion molecule but increases a mesenchymal cell biomarker α-smooth muscle actin in vitro in human pulmonary endothelial cells, there is no direct evidence showing EndoMT in the development of bronchopulmonary dysplasia. Both pulmonary hypertension and lung fibrosis occur in long-term survivors with bronchopulmonary dysplasia. In this review, we discuss the EndoMT and its modulation by pathological processes. We then focus on the role of EndoMT in the pathogenesis of these chronic lung diseases, and discuss therapeutic approaches targeting the EndoMT using its negative regulators.

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

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

Lung function trajectories throughout childhood in survivors of very preterm birth: a longitudinal cohort study

BACKGROUND

Data on longitudinal respiratory follow-up after preterm birth in the surfactant era are scarce and of increasing importance, with concerns that preterm survivors are destined for early onset chronic obstructive airway disease. We aimed to comprehensively assess lung function longitudinally from early childhood to mid-childhood in very preterm children (≤32 weeks gestation), and to explore factors negatively impacting on lung function trajectories.

METHODS

Preterm children (with and without bronchopulmonary dysplasia) and healthy term children as controls were studied. All preterm participants were born at 32 weeks' gestation or earlier at King Edward Memorial Hospital, Perth, WA, Australia, between 1997 and 2003. Bronchopulmonary dysplasia was defined as at least 28 days of supplemental oxygen requirement as assessed at 36 weeks' post-menstrual age. Spirometry, oscillatory mechanics, gas exchange, lung volumes, and respiratory symptoms were assessed at three visits, two in early childhood (4-8 years) and one in mid-childhood (9-12 years). CT of the chest was done in preterm children in mid-childhood. Respiratory symptoms were documented via questionnaire at each visit. Data were analysed longitudinally using linear mixed models.

FINDINGS

200 very preterm children (126 with bronchopulmonary dysplasia and 74 without bronchopulmonary dysplasia) and 67 healthy term control children attended 458 visits between age 4 and 12 years. Chest CT was done on 133 preterm children at a mean age of 10·9 (SD 0·6) years. Preterm children, with and without bronchopulmonary dysplasia, had declines in spirometry z-scores over time compared with controls: forced expiratory volume in 1 s (FEV₁), forced expiratory flow at 25-75% of the pulmonary volume, and FEV₁/forced vital capacity all declined by at least 0·1 z-score per year in children with bronchopulmonary dysplasia (all p<0·001). Respiratory mechanics and gas exchange also deteriorated over time in children with bronchopulmonary dysplasia (relative to term controls, respiratory system reactance at 8 Hz decreased by -0·05 z-score per year [95% CI -0·08 to -0·01; p=0·006] and diffusing capacity of the lungs for carbon monoxide decreased by -0·03 z-score per year [95% CI -0·06 to -0·01; p=0·048]). Preterm children with bronchial wall thickening on chest CT (suggestive of inflammation) had bigger decreases in spirometry outcomes through childhood. For example, children with bronchial wall thickening on chest CT had an FEV₁ z-score decline of -0·61 (95% CI -1·03 to-0·19; p=0·005) more than those without. Similarly, children exposed to tobacco smoke, those with earlier gestation, or those requiring more neonatal supplemental oxygen declined at a faster rate.

INTERPRETATION

Lung function trajectories are impaired in survivors of very preterm birth. Survivors with bronchopulmonary dysplasia, ongoing respiratory symptoms, or CT changes reflecting inflammation have the poorest trajectories and might be at increased risk of lung disease in later life. Close targeted pulmonary follow-up of these individuals is necessary.

FUNDING

National Health and Medical Research Council grants APP634519, APP1073301 (to SJS), APP1077691 (to JJP), and APP1025550 (to GLH), Princess Margret Hospital Foundation, and Raine Medical Foundation.

RNAseq analysis of bronchial epithelial cells to identify COPD-associated genes and SNPs

Background

There is a need for more powerful methods to identify low-effect SNPs that contribute to hereditary COPD pathogenesis. We hypothesized that SNPs contributing to COPD risk through cis-regulatory effects are enriched in genes comprised by bronchial epithelial cell (BEC) expression patterns associated with COPD.

Methods

To test this hypothesis, normal BEC specimens were obtained by bronchoscopy from 60 subjects: 30 subjects with COPD defined by spirometry (FEV1/FVC < 0.7, FEV1% < 80%), and 30 non-COPD controls. Targeted next generation sequencing was used to measure total and allele-specific expression of 35 genes in genome maintenance (GM) genes pathways linked to COPD pathogenesis, including seven TP53 and CEBP transcription factor family members. Shrinkage linear discriminant analysis (SLDA) was used to identify COPD-classification models. COPD GWAS were queried for putative cis-regulatory SNPs in the targeted genes.

Results

On a network basis, TP53 and CEBP transcription factor pathway gene pair network connections, including key DNA repair gene ERCC5, were significantly different in COPD subjects (e.g., Wilcoxon rank sum test for closeness, p-value = 5.0E-11). ERCC5 SNP rs4150275 association with chronic bronchitis was identified in a set of Lung Health Study (LHS) COPD GWAS SNPs restricted to those in putative regulatory regions within the targeted genes, and this association was validated in the COPDgene non-hispanic white (NHW) GWAS. ERCC5 SNP rs4150275 is linked (D’ = 1) to ERCC5 SNP rs17655 which displayed differential allelic expression (DAE) in BEC and is an expression quantitative trait locus (eQTL) in lung tissue (p = 3.2E-7). SNPs in linkage (D’ = 1) with rs17655 were predicted to alter miRNA binding (rs873601). A classifier model that comprised gene features CAT, CEBPG, GPX1, KEAP1, TP73, and XPA had pooled 10-fold cross-validation receiver operator characteristic area under the curve of 75.4% (95% CI: 66.3%–89.3%). The prevalence of DAE was higher than expected (p = 0.0023) in the classifier genes.

Conclusions

GM genes comprised by COPD-associated BEC expression patterns were enriched for SNPs with cis-regulatory function, including a putative cis-rSNP in ERCC5 that was associated with COPD risk. These findings support additional total and allele-specific expression analysis of gene pathways with high prior likelihood for involvement in COPD pathogenesis.

Electronic supplementary material

The online version of this article (10.1186/s12890-018-0603-y) contains supplementary material, which is available to authorized users.

Functional roles of C/EBPα and SUMO‑modification in lung development

CCAAT enhancer binding protein alpha (C/EBPα) is a transcription factor regulating the core aspects of cell growth and differentiation. The present study investigated the level and functional role of C/EBPα during the development of the rat lung. C/EBPα protein exhibits a dynamic expression pattern. The correlation between the expression of C/EBPα protein and the content of glycogen during lung maturation was analyzed to understand the function of C/EBPα in lung differentiation. The high expression of C/EBPα coincides with the reduction of glycogen in the fetal lung. In addition, the authors identified that changes in the level of C/EBPα are associated with the secretion of pulmonary surfactant. C/EBPα is modified by small ubiquitin-related modifier (SUMO) post-translationally. The results of double immunofluorescence staining and immunoprecipitation demonstrated that SUMO-modified C/EBPα was present in the lung. The sumoylated C/EBPα gradually decreased during lung differentiation and was negatively correlated with pulmonary surfactant secretion, thereby suggesting that the SUMO modification may participate in C/EBPα-mediated lung growth and differentiation. These results indicated that C/EBPα played a role in lung development and provided the insight into the mechanism underlying SUMO-modification.

SH3GLB2/endophilin B2 regulates lung homeostasis and recovery from severe influenza A virus infection

New influenza A viruses that emerge frequently elicit composite inflammatory responses to both infection and structural damage of alveolar-capillary barrier cells that hinders regeneration of respiratory function. The host factors that relinquish restoration of lung health to enduring lung injury are insufficiently understood. Here, we investigated the role of endophilin B2 (B2) in susceptibility to severe influenza infection. WT and B2-deficient mice were infected with H1N1 PR8 by intranasal administration and course of influenza pneumonia, inflammatory, and tissue responses were monitored over time. Disruption of B2 enhanced recovery from severe influenza infection as indicated by swift body weight recovery and significantly better survival of endophilin B2-deficient mice compared to WT mice. Compared to WT mice, the B2-deficient lungs exhibited induction of genes that express surfactant proteins, ABCA3, GM-CSF, podoplanin, and caveolin mRNA after 7 days, temporal induction of CCAAT/enhancer binding protein CEBPα, β, and δ mRNAs 3-14 days after infection, and differences in alveolar extracellular matrix integrity and respiratory mechanics. Flow cytometry and gene expression studies demonstrated robust recovery of alveolar macrophages and recruitment of CD4+ lymphocytes in B2-deficient lungs. Targeting of endophilin B2 alleviates adverse effects of IAV infection on respiratory and immune cells enabling restoration of alveolar homeostasis.

Longitudinal impairment of lung function in school-age children with extremely low birth weights

OBJECTIVES

To assess lung function and long-term respiratory outcomes in extremely low birth weight (ELBW) survivors.

WORKING HYPOTHESIS

ELBW, especially with respiratory complications in the neonatal period, affects lung function at a later age.

STUDY DESIGN

Longitudinal retrospective study.

PATIENT-SUBJECT SELECTION

Lung function was evaluated in 89 ELBW survivors (at ages 8 and 12) with or without a history of bronchopulmonary dysplasia (BPD) or a bubbly/cystic lung appearance in the neonatal period.

METHODOLOGY

FVC, FEV₁ , FEF₅₀ , and FEF₇₅ were measured using spirometry. Two-way repeated-measures ANOVA was used to compare lung function and deterioration time course from 8 to 12 years of age.

RESULTS

Lung function variables were significantly and positively correlated between 8 and 12 years: %FVC (R²  = 0.558), %FEV₁ (R²  = 0.539), %FEF₅₀ (R²  = 0.412), and %FEF₇₅ (R²  = 0.429). Lung function values were lower than Japanese reference values, especially in children with a history of severe BPD or a bubbly/cystic appearance. %FEV₁ and FEV₁ /FVC ratio worsened from 8 to 12 years of age: 83.0 ± 17.0% versus 76.6 ± 17.8% (mean difference, 95%CI: -6.43, -9.10 to -3.75) and 84.0 ± 10.1% versus 78.2 ± 13.4% (mean difference, 95%CI: -5.82, -8.56 to -3.08), regardless of whether or not there was a history of neonatal respiratory disease.

CONCLUSIONS

In ELBW survivors, the obstructive pattern of lung function impairment deteriorated from 8 to 12 years of age, independent of the presence of severe BPD or bubbly/cystic appearance in the neonatal period.

Cigarette smoke extract promotes proliferation of airway smooth muscle cells through suppressing C/EBP-α expression

Cigarette smoke has been considered a major contributor to the pathogenesis of chronic obstructive pulmonary disease (COPD). In COPD patients, the airway smooth muscle layer has been observed to be markedly thickened and the proliferation of airway smooth muscle cells (ASMCs) was therefore used by the present study as a model to assess the impact of cigarette smoke extract (CSE). ASMCs were exposed to various concentrations of CSE and the proliferation of the cells was analyzed by an MTT assay. Furthermore, the expression levels of calreticulin and CCAAT/enhancer-binding protein alpha (C/EBP-α) in CSE-stimulated ASMCs were determined by polymerase chain reaction and western blot analyses. In addition, the effects of RNA interference (RNAi) to knockdown calreticulin and/or C/EBP-α on ASMC proliferation were studied. CSE was found to promote the proliferation of ASMCs, which was associated with increased expression of calreticulin and decreased expression of C/EBP-α. Knockdown of calreticulin resulted in the upregulation of C/EBP-α and inhibition of cell proliferation, while simultaneous knockdown of C/EBP-α promoted cell proliferation. The present study revealed that CSE promoted the proliferation of ASMCs, which was mediated by inhibition of C/EBP-α. These findings shed new light on airway remodeling in COPD and may provide novel approaches for therapies.

Pathogenesis of bronchopulmonary dysplasia: when inflammation meets organ development

Bronchopulmonary dysplasia is a chronic lung disease of preterm infants. It is caused by the disturbance of physiologic lung development mainly in the saccular stage with lifelong restrictions of pulmonary function and an increased risk of abnormal somatic and psychomotor development. The contributors to this disease’s entity are multifactorial with pre- and postnatal origin. Central to the pathogenesis of bronchopulmonary is the induction of a massive pulmonary inflammatory response due to mechanical ventilation and oxygen toxicity. The extent of the pro-inflammatory reaction and the disturbance of further alveolar growth and vasculogenesis vary largely and can be modified by prenatal infections, antenatal steroids, and surfactant application.

This minireview summarizes the important recent research findings on the pulmonary inflammatory reaction obtained in patient cohorts and in experimental models. Unfortunately, recent changes in clinical practice based on these findings had only limited impact on the incidence of bronchopulmonary dysplasia.

Mitochondrial dysfunction in inflammatory responses and cellular senescence: pathogenesis and pharmacological targets for chronic lung diseases

Mitochondria are dynamic organelles, which couple the various cellular processes that regulate metabolism, cell proliferation and survival. Environmental stress can cause mitochondrial dysfunction and dynamic changes including reduced mitochondrial biogenesis, oxidative phosphorylation and ATP production, as well as mitophagy impairment, which leads to increased ROS, inflammatory responses and cellular senescence. Oxidative stress, inflammation and cellular senescence all have important roles in the pathogenesis of chronic lung diseases, such as chronic obstructive pulmonary disease, pulmonary fibrosis and bronchopulmonary dysplasia. In this review, we discuss the current state on how mitochondrial dysfunction affects inflammatory responses and cellular senescence, the mechanisms of mitochondrial dysfunction underlying the pathogenesis of chronic lung diseases and the potential of mitochondrial transfer and replacement as treatments for these diseases.

Haplotype and diplotype analyses of variation in ERCC5 transcription cis-regulation in normal bronchial epithelial cells

Excision repair cross-complementation group 5 (ERCC5) gene plays an important role in nucleotide excision repair, and dysregulation of ERCC5 is associated with increased lung cancer risk. Haplotype and diplotype analyses were conducted in normal bronchial epithelial cells (NBEC) to better understand mechanisms responsible for interindividual variation in transcript abundance regulation of ERCC5 We determined genotypes at putative ERCC5 cis-regulatory SNPs (cis-rSNP) rs751402 and rs2296147, and marker SNPs rs1047768 and rs17655. ERCC5 allele-specific transcript abundance was assessed by a recently developed targeted sequencing method. Syntenic relationships among alleles at rs751402, rs2296147, and rs1047768 were assessed by allele-specific PCR followed by Sanger sequencing. We then assessed association of ERCC5 allele-specific expression at rs1047768 with haplotype and diplotype structure at cis-rSNPs rs751402 and rs2296147. Genotype analysis revealed significantly (P < 0.005) higher interindividual variation in allelic ratios in cDNA samples relative to matched gDNA samples at both rs1047768 and rs17655. By diplotype analysis, mean expression was higher at the rs1047768 alleles syntenic with rs2296147 T allele compared with rs2296147 C allele. Furthermore, mean expression was lower at rs17655 C allele, which is syntenic with G allele at a linked SNP rs873601 (D' = 0.95). These data support the conclusions that in NBEC, T allele at SNP rs2296147 upregulates ERCC5, variation at rs751402 does not alter ERCC5 regulation, and that C allele at SNP rs17655 downregulates ERCC5 Variation in ERCC5 transcript abundance associated with allelic variation at these SNPs could result in variation in NER function in NBEC and lung cancer risk.

Ventilatory and sensory responses in adult survivors of preterm birth and bronchopulmonary dysplasia with reduced exercise capacity

RATIONALE

Adults born very to extremely preterm, with or without bronchopulmonary dysplasia (BPD), have obstructive lung disease, but it is unknown whether this results in respiratory limitations, such as mechanical constraints to Vt expansion during exercise leading to intolerable dyspnea and reduced exercise tolerance, as it does in patients with chronic obstructive pulmonary disease.

OBJECTIVES

To test the hypothesis that adult survivors of preterm birth (≤32 wk gestational age) with (n = 20) and without BPD (n = 15) with reduced exercise capacity demonstrate clinically important respiratory limitations at near-maximal exercise compared with full-term control subjects (n = 20).

METHODS

Detailed ventilatory and sensory measurements were made before and during exercise on all patients in the three study groups.

MEASUREMENTS AND MAIN RESULTS

During exercise at 90% of peak [Formula: see text]o2 ([Formula: see text]o2peak), inspiratory reserve volume decreased to ∼0.5 L in all groups, but this occurred at significantly lower absolute workloads and [Formula: see text]e in ex-preterm subjects with and without BPD compared with full-term control subjects. Severe dyspnea was present and similar at comparable [Formula: see text]e between all groups, but leg discomfort at comparable workloads was greater in ex-preterm subjects with and without BPD compared with control subjects. At 50 to 90% of [Formula: see text]o2peak, exercise-induced expiratory flow limitation was significantly greater in ex-preterm subjects with BPD compared with ex-preterm subjects without BPD and control subjects. The degree of expiratory flow limitation in ex-preterm subjects with and without BPD was significantly related to neonatal O2 therapy duration.

CONCLUSIONS

Severe dyspnea and leg discomfort associated with critical constraints on Vt expansion may lead to reduced exercise tolerance in adults born very or extremely preterm, whether or not their birth was complicated by BPD and despite differences in expiratory flow limitation. In this regard, adults born very or extremely preterm have respiratory limitations to exercise similar to patients with chronic obstructive pulmonary disease.

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.

Bronchopulmonary dysplasia: the earliest and perhaps the longest lasting obstructive lung disease in humans

Bronchopulmonary dysplasia (BPD) is one of the most important sequelae of premature birth and the most common form of chronic lung disease of infancy. From a clinical standpoint BPD subjects are characterized by recurrent respiratory symptoms, which are very frequent during the first years of life and, although becoming less severe as children grow up, they remain more common than in term-born controls throughout childhood, adolescence and into adulthood. From a functional point of view BPD subjects show a significant airflow limitation that persists during adolescence and adulthood and they may experience an earlier and steeper decline in lung function during adulthood. Interestingly, patients born prematurely but not developing BPD usually fare better, but they too have airflow limitations during childhood and later on, suggesting that also prematurity per se has life-long detrimental effects on pulmonary function. For the time being, little is known about the presence and nature of pathological mechanisms underlying the clinical and functional picture presented by BPD survivors. Nonetheless, recent data suggest the presence of persistent neutrophilic airway inflammation and oxidative stress and it has been suggested that BPD may be sustained in the long term by inflammatory pathogenic mechanisms similar to those underlying COPD. This hypothesis is intriguing but more pathological data are needed. A better understanding of these pathogenetic mechanisms, in fact, may be able to orient the development of novel targeted therapies or prevention strategies to improve the overall respiratory health of BPD patients.

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.

Hacking cell differentiation: transcriptional rerouting in reprogramming, lineage infidelity and metaplasia

Initiating neoplastic cell transformation events are of paramount importance for the comprehension of regeneration and vanguard oncogenic processes but are difficult to characterize and frequently clinically overlooked. In epithelia, pre-neoplastic transformation stages are often distinguished by the appearance of phenotypic features of another differentiated tissue, termed metaplasia. In haemato/lymphopoietic malignancies, cell lineage ambiguity is increasingly recorded. Both, metaplasia and biphenotypic leukaemia/lymphoma represent examples of dysregulated cell differentiation that reflect a history of trans-differentiation and/or epigenetic reprogramming. Here we compare the similarity between molecular events of experimental cell trans-differentiation as an emerging therapeutic concept, with lineage confusion, as in metaplasia and dysplasia forecasting tumour development.

A Relationship between Epithelial Maturation, Bronchopulmonary Dysplasia, and Chronic Obstructive Pulmonary Disease

Premature infants frequently develop bronchopulmonary dysplasia (BPD). Lung immaturity and impaired epithelial differentiation contribute together with invasive oxygen treatment to BPD onset and disease progression. Substantial evidence suggests that prematurity is associated with long term pulmonary consequences. Moreover, there is increasing concern that lung immaturity at birth may increase the risk of developing chronic obstructive pulmonary disease (COPD). The mechanisms contributing to this phenomenon remains unknown, largely as a consequence of inadequate experimental models and clinical follow-up studies. Recent evidence suggests that defective transcriptional regulation of epithelial differentiation and maturation may contribute to BPD pathogenesis as well as early onset of COPD. The transcriptional regulators CCAAT/enhancer-binding protein (C/EBP)α and C/EBPβ, SMAD family member (Smad)3, GATA binding protein (GATA)6, and NK2 homeobox (NKX)2-1 are reported to be involved in processes contributing to pathogenesis of both BPD and COPD. Increased knowledge of the mechanisms contributing to early onset COPD among BPD survivors could translate into improved treatment strategies and reduced frequency of respiratory disorders among adult survivors of BPD. In this paper, we introduce critical transcriptional regulators in epithelial differentiation and summarize the current knowledge on the contribution of impaired epithelial maturation to the pathogenesis of inflammatory lung disorders.

Airway epithelial cell differentiation during lung organogenesis requires C/EBPα and C/EBPβ

BACKGROUND

CCAAT/enhancer-binding protein (C/EBP)α is crucial for lung development and differentiation of the pulmonary epithelium. Conversely, no lung defects have been observed in C/EBPβ-deficient mice, although C/EBPβ trans-activate pulmonary genes by binding to virtually identical DNA-sequences as C/EBPα. Thus, the pulmonary phenotype of mice lacking C/EBPβ could be explained by functional replacement with C/EBPα. We investigated whether C/EBPα and C/EBPβ have overlapping functions in regulating lung epithelial differentiation during organogenesis. Epithelial differentiation was assessed in mice with a lung epithelial-specific (SFTPC-Cre-mediated) deletion of C/EBPα (Cebpa(ΔLE) ), C/EBPβ (Cebpb(ΔLE) ), or both genes (Cebpa(ΔLE) ; Cebpb(ΔLE) ).

RESULTS

Both Cebpa(ΔLE) mice and Cebpa(ΔLE) ; Cebpb(ΔLE) mice demonstrated severe pulmonary immaturity compared to wild-type littermates, while no differences in lung histology or epithelial differentiation were observed in Cebpb(ΔLE) mice. In contrast to Cebpa(ΔLE) mice, Cebpa(ΔLE) ; Cebpb(ΔLE) mice also displayed undifferentiated Clara cells with markedly impaired protein and mRNA expression of Clara cell secretory protein (SCGB1A1), compared to wild-type littermates. In addition, ectopic mucus-producing cells were observed in the conducting airways of Cebpa(ΔLE) ; Cebpb(ΔLE) mice.

CONCLUSIONS

Our findings demonstrate that C/EBPα and C/EBPβ play pivotal, and partly overlapping roles in determining airway epithelial differentiation, with possible implications for tissue regeneration in lung homeostasis and disease.

The emerging role of C/EBPs in glucocorticoid signaling: lessons from the lung

Glucocorticoids (GCs) have been successfully used in the treatment of inflammatory diseases for decades. However, there is a relative GC resistance in several inflammatory lung disorders, such as chronic obstructive pulmonary disease (COPD), but still the mechanism(s) behind this unresponsiveness remains unknown. Interaction between transcription factors and the GC receptor contribute to GC effects but may also provide mechanisms explaining steroid resistance. CCAAT/enhancer-binding protein (C/EBP) transcription factors are important regulators of pulmonary gene expression and have been implicated in inflammatory lung diseases such as asthma, pulmonary fibrosis, cystic fibrosis, sarcoidosis, and COPD. In addition, several studies have indicated a role for C/EBPs in mediating GC effects. In this review, we discuss the different mechanisms of GC action as well as the function of the lung-enriched members of the C/EBP transcription factor family. We also summarize the current knowledge of the role of C/EBP transcription factors in mediating the effects of GCs, with emphasis on pulmonary effects, and their potential role in mediating GC resistance.

c-Kit is essential for alveolar maintenance and protection from emphysema-like disease in mice

RATIONALE

Previously, we demonstrated a candidate region for susceptibility to airspace enlargement on mouse chromosome 5. However, the specific candidate genes within this region accounting for emphysema-like changes remain unrecognized. c-Kit is a receptor tyrosine kinase within this candidate gene region that has previously been recognized to contribute to the survival, proliferation, and differentiation of hematopoietic stem cells. Increases in the percentage of cells expressing c-Kit have previously been associated with protection against injury-induced emphysema.

OBJECTIVES

Determine whether genetic variants of c-Kit are associated with spontaneous airspace enlargement.

METHODS

Perform single-nucleotide polymorphism association studies in the mouse strains at the extremes of airspace enlargement phenotype for variants in c-Kit tyrosine kinase. Characterize mice bearing functional variants of c-Kit compared with wild-type controls for the development of spontaneous airspace enlargement. Epithelial cell proliferation was measured in culture.

MEASUREMENTS AND MAIN RESULTS

Upstream regulatory single-nucleotide polymorphisms in the divergent mouse strains were associated with the lung compliance difference observed between the extreme strains. c-Kit mutant mice (Kit(W-sh)/(W-sh)), when compared with genetic controls, developed altered lung histology, increased total lung capacity, increased residual volume, and increased lung compliance that persist into adulthood. c-Kit inhibition with imatinib attenuated in vitro proliferation of cells expressing epithelial cell adhesion molecule.

CONCLUSIONS

Our findings indicate that c-Kit sustains and/or maintains normal alveolar architecture in the lungs of mice. In vitro data suggest that c-Kit can regulate epithelial cell clonal expansion. The precise mechanisms that c-Kit contributes to the development of airspace enlargement and increased lung compliance remain unclear and warrants further investigation.