C/EBP{alpha} is required for pulmonary cytoprotection during hyperoxia

GCN5L1 regulates pulmonary surfactant production by modulating lamellar body biogenesis and trafficking in mouse alveolar epithelial cells

BACKGROUND

The pulmonary surfactant that lines the air-liquid surface within alveoli is a protein-lipid mixture essential for gas exchange. Surfactant lipids and proteins are synthesized and stored in the lamellar body (LB) before being secreted from alveolar type II (AT2) cells. The molecular and cellular mechanisms that regulate these processes are incompletely understood. We previously identified an essential role of general control of amino acid synthesis 5 like 1 (GCN5L1) and the biogenesis of lysosome-related organelle complex 1 subunit 1 (BLOS1) in surfactant system development in zebrafish. Here, we explored the role of GCN5L1 in pulmonary surfactant regulation.

METHOD

GCN5L1 knockout cell lines were generated with the CRISPR/Cas9 system. Cell viability was analyzed by MTT assay. Released surfactant proteins were measured by ELISA. Released surfactant lipids were measured based on coupled enzymatic reactions. Gene overexpression was mediated through lentivirus. The RNA levels were detected through RNA-sequencing (RNA-seq) and quantitative reverse transcription (qRT)- polymerase chain reaction (PCR). The protein levels were detected through western blotting. The cellular localization was analyzed by immunofluorescence. Morphology of the lamellar body was analyzed through transmission electron microscopy (TEM), Lysotracker staining, and BODIPY phosphatidylcholine labeling.

RESULTS

Knocking out GCN5L1 in MLE-12 significantly decreased the release of surfactant proteins and lipids. We detected the downregulation of some surfactant-related genes and misregulation of the ROS-Erk-Foxo1-Cebpα axis in mutant cells. Modulating the activity of the axis or reconstructing the mitochondrial expression of GCN5L1 could partially restore the expression of these surfactant-related genes. We further showed that MLE-12 cells contained many LB-like organelles that were lipid enriched and positive for multiple LB markers. These organelles were smaller in size and accumulated in the absence of GCN5L1, indicating both biogenesis and trafficking defects. Accumulated endogenous surfactant protein (SP)-B or exogenously expressed SP-B/SP-C in adenosine triphosphate-binding cassette transporterA3 (ABCA3)-positive organelles was detected in mutant cells. GCN5L1 localized to the mitochondria and LBs. Reconstruction of mitochondrial GCN5L1 expression rescued the organelle morphology but failed to restore the trafficking defect and surfactant release, indicating specific roles associated with different subcellular localizations.

CONCLUSIONS

In summary, our study identified GCN5L1 as a new regulator of pulmonary surfactant that plays a role in the biogenesis and positioning/trafficking of surfactant-containing LBs.

Harnessing the therapeutic potential of the stem cell secretome in neonatal diseases

Preterm birth and intrapartum related complications account for a substantial amount of mortality and morbidity in the neonatal period despite significant advancements in neonatal-perinatal care. Currently, there is a noticeable lack of curative or preventative therapies available for any of the most common complications of prematurity including bronchopulmonary dysplasia, necrotizing enterocolitis, intraventricular hemorrhage, periventricular leukomalacia and retinopathy of prematurity or hypoxic-ischemic encephalopathy, the main cause of perinatal brain injury in term infants. Mesenchymal stem/stromal cell-derived therapy has been an active area of investigation for the past decade and has demonstrated encouraging results in multiple experimental models of neonatal disease. It is now widely acknowledged that mesenchymal stem/stromal cells exert their therapeutic effects via their secretome, with the principal vector identified as extracellular vesicles. This review will focus on summarizing the current literature and investigations on mesenchymal stem/stromal cell-derived extracellular vesicles as a treatment for neonatal diseases and examine the considerations to their application in the clinical setting.

Mesenchymal Stromal Cell-Derived Extracellular Vesicles for Neonatal Lung Disease: Tiny Particles, Major Promise, Rigorous Requirements for Clinical Translation

Extreme preterm birth disrupts late lung development and puts newborns at risk of developing chronic lung disease, known as bronchopulmonary dysplasia (BPD). BPD can be associated with life-long complications, and currently no effective treatment is available. Cell therapies are entering the clinics to curb complications of extreme preterm birth with several clinical trials testing the feasibility, safety and efficacy of mesenchymal stromal cells (MSCs). The therapeutic effect of MSCs is contained in their secretome, and nanosized membranous structures released by the MSCs, known as extracellular vesicles (EVs), have been shown to be the therapeutic vectors. Driven by this discovery, the efficacy of EV-based therapy is currently being explored in models of BPD. EVs derived from MSCs, contain a rich cargo of anti-inflammatory and pro-angiogenic molecules, making them suitable candidates to treat multifactorial diseases such as BPD. Here, we review the state-of-the-art of preclinical studies involving MSC-derived EVs in models of BPD and highlight technical and regulatory challenges that need to be addressed before clinical translation. In addition, we aim at increasing awareness regarding the importance of rigorous reporting of experimental details of EV experiments and to increase the outreach of the current established guidelines amongst researchers in the BPD field.

LKB1 drives stasis and C/EBP-mediated reprogramming to an alveolar type II fate in lung cancer

LKB1 is among the most frequently altered tumor suppressors in lung adenocarcinoma. Inactivation of Lkb1 accelerates the growth and progression of oncogenic KRAS-driven lung tumors in mouse models. However, the molecular mechanisms by which LKB1 constrains lung tumorigenesis and whether the cancer state that stems from Lkb1 deficiency can be reverted remains unknown. To identify the processes governed by LKB1 in vivo, we generated an allele which enables Lkb1 inactivation at tumor initiation and subsequent Lkb1 restoration in established tumors. Restoration of Lkb1 in oncogenic KRAS-driven lung tumors suppressed proliferation and led to tumor stasis. Lkb1 restoration activated targets of C/EBP transcription factors and drove neoplastic cells from a progenitor-like state to a less proliferative alveolar type II cell-like state. We show that C/EBP transcription factors govern a subset of genes that are induced by LKB1 and depend upon NKX2-1. We also demonstrate that a defining factor of the alveolar type II lineage, C/EBPα, constrains oncogenic KRAS-driven lung tumor growth in vivo. Thus, this key tumor suppressor regulates lineage-specific transcription factors, thereby constraining lung tumor development through enforced differentiation.

Mechanism of Adipose-Derived Mesenchymal Stem Cell-Derived Extracellular Vesicles Carrying miR-21-5p in Hyperoxia-Induced Lung Injury

Hyperoxia-induced lung injury (HILI) tends to develop bronchopulmonary dysplasia. Adipose-derived mesenchymal stem cell (ADMSC)-derived extracellular vesicles (EVs) hold great promise in alleviating lung injury. This study explored the mechanism of ADMSC-EVs in HILI. ADMSC-EVs were isolated and identified. The murine and cell models of HILI were established. HILI mice and cells were pre-treated with ADMSC-EVs. The lung dry/wet ratio, pathological structure, apoptosis, and inflammation of HILI mice were measured. The viability, apoptosis, and oxidative stress of HILI cells were measured. The internalization of EVs in lung and cells was observed by fluorescence labeling. The binding relationships between miR-21-5p and SKP2, and Nr2f2 and C/EBPα were analyzed. The binding of SKP2 and Nr2f2 and the Nr2f2 ubiquitination level were detected. ADMSC-EVs exerted preventive effects on HILI mice, evidenced by reduced lung dry/wet ratio, inflammation, and apoptosis in HILI mice. In vitro, EVs enhanced HILI cell viability and reduced apoptosis, inflammation, and oxidative stress. EVs carried miR-21-5p into lung cells to upregulate miR-21-5p expression and thereby target SKP2. SKP2 bound to Nr2f2 and promoted its ubiquitination degradation. EVs inhibited the binding of Nr2f2 and C/EBPα and further suppressed C/EBPα transcription. Collectively, ADMSC-EVs carrying miR-21-5p alleviated HILI via the SKP2/Nr2f2/C/EBPα axis. Role and mechanism of adipose-derived mesenchymal stem cell-derived extracellular vesicles in hyperoxia-induced lung injury. ADMSC-EVs upregulated miR-21-5p expression in cells by carrying miR-21-5p into lung cells, thereby promoting the binding of miR-21-5p and SKP2 mRNA, inhibiting the expression of SKP2, reducing the ubiquitination level of Nr2f2, increasing the expression of Nr2f2, promoting the binding of Nr2f2 and the C/EBPα promoter, upregulating C/EBPα mRNA level, and eventually alleviating HILI.

Role of NRF2 in immune modulator expression in developing lung

After birth, the alveolar epithelium is exposed to environmental pathogens and high O₂ tensions. The alveolar type II cells may protect this epithelium through surfactant production. Surfactant protein, SP-A, an immune modulator, is developmentally upregulated in fetal lung with surfactant phospholipid synthesis. Herein, we observed that the redox-regulated transcription factor, NRF2, and co-regulated C/EBPβ and PPARγ, were markedly induced during cAMP-mediated differentiation of cultured human fetal lung (HFL) epithelial cells. This occurred with enhanced expression of immune modulators, SP-A, TDO2, AhR, and NQO1. Like SP-A, cAMP induction of NRF2 was prevented when cells were exposed to hypoxia. NRF2 knockdown inhibited induction of C/EBPβ, PPARγ, and immune modulators. Binding of endogenous NRF2 to promoters of SP-A and other immune modulator genes increased during HFL cell differentiation. In mouse fetal lung (MFL), a developmental increase in Nrf2, SP-A, Tdo2, Ahr, and Nqo1 and decrease in Keap1 occurred from 14.5 to 18.5 dpc. Developmental induction of Nrf2 in MFL was associated with increased nuclear localization of NF-κB p65, a decline in p38 MAPK phosphorylation, increase in the MAPK phosphatase, DUSP1, induction of the histone acetylase, CBP, and decline in the histone deacetylase, HDAC4. Thus, together with surfactant production, type II cells protect the alveolar epithelium through increased expression of NRF2 and immune modulators to prevent inflammation and oxidative stress. Our findings further suggest that lung cancer cells have usurped this developmental pathway to promote immune tolerance and enhance survival.

Tenascin-C Deficiency Is Associated With Reduced Bacterial Outgrowth During Klebsiella pneumoniae-Evoked Pneumosepsis in Mice

Tenascin C (TNC) is an extracellular matrix glycoprotein that recently emerged as an immunomodulator. TNC-deficient (TNC^−/−) mice were reported to have a reduced inflammatory response upon systemic administration of lipopolysaccharide, the toxic component of gram-negative bacteria. Here, we investigated the role of TNC during gram-negative pneumonia derived sepsis. TNC^+/+ and TNC^−/− mice were infected with Klebsiella pneumoniae via the airways and sacrificed 24 and 42 h thereafter for further analysis. Pulmonary TNC protein levels were elevated 42 h after infection in TNC^+/+ mice and remained undetectable in TNC^−/− mice. TNC^−/− mice showed modestly lower bacterial loads in lungs and blood, and a somewhat reduced local—but not systemic—inflammatory response. Moreover, TNC^−/− and TNC^+/+ mice did not differ with regard to neutrophil recruitment, lung pathology or plasma markers of distal organ injury. These results suggest that while TNC shapes the immune response during lipopolysaccharide-induced inflammation, this role may be superseded during pneumosepsis caused by a common gram-negative pathogen.

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.

Sumoylation of CCAAT-enhancer-binding protein α inhibits lung differentiation in Bronchopulmonary Dysplasia model rats

Bronchopulmonary dysplasia (BPD) is a major cause of mortality and morbidity in premature infants, characterized by alveolar simplification, surfactant deficiency, and respiratory distress. In the present study, we have investigated the functional roles of sumoylated CCAAT/enhancer binding protein alpha (C/EBPα) in the BPD rat model. A significant increase in small ubiquitin‐like modifier 1 (SUMO1) and sumoylated C/EBPα protein levels were observed in BPD rats, and the levels of the sumoylated C/EBPα were associated with the pulmonary surfactant proteins (SPs). In order to confirm the role of sumoylated C/EBPα in BPD rats, SUMO1 was knocked down by lentiviral transfection of neonatal rat lungs with SUMO1‐RNAi‐LV. We found that the expression of C/EBPα and surfactant proteins increased following SUMO1 knockdown. Furthermore, the relatively low decrease in the levels of C/EBPα sumoylation was correlated with reduced glycogen consumption. Besides, co‐immunoprecipitation assays revealed that sumoylation is involved in the regulation of the interaction between C/EBPα and TGFβ2 in the lung. In conclusion, our findings indicate that sumoylation may act as a negative regulator of the C/EBPα‐mediated transactivation in BPD rats.

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.

Cancer Stem Cells: Emergent Nature of Tumor Emergency

A functional analysis of 167 genes overexpressed in Krebs-2 tumor initiating cells was performed. In the first part of the study, the genes were analyzed for their belonging to one or more of the three groups, which represent the three major phenotypic manifestation of malignancy of cancer cells, namely (1) proliferative self-sufficiency, (2) invasive growth and metastasis, and (3) multiple drug resistance. 96 genes out of 167 were identified as possible contributors to at least one of these fundamental properties. It was also found that substantial part of these genes are also known as genes responsible for formation and/or maintenance of the stemness of normal pluri-/multipotent stem cells. These results suggest that the malignancy is simply the ability to maintain the stem cell specific genes expression profile, and, as a consequence, the stemness itself regardless of the controlling effect of stem niches. In the second part of the study, three stress factors combined into the single concept of "generalized cellular stress," which are assumed to activate the expression of these genes, were defined. In addition, possible mechanisms for such activation were identified. The data obtained suggest the existence of a mechanism for the de novo formation of a pluripotent/stem phenotype in the subpopulation of "committed" tumor cells.

[Dynamic expression and role of SUMO-modified C/EBP&alpha; in preterm rats with bronchopulmonary dysplasisa induced by hyperoxia exposure]

OBJECTIVE

To study the expression of SUMO-modified CCAAT enhancer binding protein &alpha; (C/EBP&alpha;) in preterm rat model of bronchopulmonary dysplasisa (BPD) induced by hyperoxia exposure and its role.

METHODS

Eighteen preterm rats were randomly divided into an air group and a hyperoxia group (n=9 each). The model of BPD was prepared in preterm rats exposed to hyperoxia. The rats from the two groups were sacrificed on postnatal days 4, 7 and 14 respectively (3 rats at each time) and lung tissues were harvested. Periodic acid-Schiff (PAS) staining was used to observe the differentiation of rat lung tissues. Ki67 expression was detected by immunohistochemistry. Western blot was used to measure the protein expression of small ubiquitin-related modifier-1(SUMO1) and C/EBP&alpha;. A co-immunoprecipitation assay was performed to measure the protein expression of SUMO-modified C/EBP&alpha;.

RESULTS

Compared with the air group, the hyperoxia group showed a decreased glycogen content in the lung tissue on postnatal day 4, and an increased content on postnatal days 7 and 14. Over the time of hyperoxia exposure, the hyperoxia group showed an increased expression of Ki67 in the lung tissue compared with the air group at all time points. Compared with the air group, the protein expression of C/EBP&alpha; increased on postnatal day 4 and decreased on postnatal days 7 and 14 in the hyperoxia group (P&lt;0.05). The hyperoxia group had significantly upregulated expression of SUMO1 and SUMO-modified C/EBP&alpha; compared with the air group at all time points (P&lt;0.05). In the hyperoxia group, the protein expression of SUMO-modified C/EBP&alpha; was positively correlated with the glycogen content (r=0.529, P&lt;0.05) and the expression of Ki67 (r=0.671, P&lt;0.05).

CONCLUSIONS

Hyperoxia may induce over-proliferation and differentiation disorders of alveolar epithelial cells in preterm rat model of BPD, possibly through an increased expression of SUMO-modified C/EBP&alpha.

Single-cell mRNA quantification and differential analysis with Census

Single-cell gene expression studies promise to unveil rare cell types and cryptic states in development and disease through a stunningly high-resolution view of gene regulation. However, measurements from single-cell RNA-Seq are highly variable, frustrating efforts to assay how expression differs between cells. We introduce Census, an algorithm available through our single-cell analysis toolkit Monocle 2, which converts relative RNA-Seq expression levels into relative transcript counts without the need for experimental spike-in controls. We show that analyzing changes in relative transcript counts leads to dramatic improvements in accuracy compared to normalized read counts and enables new statistical tests for identifying developmentally regulated genes. We explore the power of Census through reanalysis of single-cell studies in several developmental and disease contexts. Census counts can be analyzed with widely used regression techniques to reveal changes in cell fate-dependent gene expression, splicing patterns, and allelic imbalances, demonstrating that Census enables robust single-cell analysis at multiple layers of gene regulation.

Oxygen differentially affects the hox proteins Hoxb5 and Hoxa5 altering airway branching and lung vascular formation

Hoxb5 and Hoxa5 transcription factor proteins uniquely impact lung morphogenesis at the developmental time point when extremely preterm infants are born. The effect of O2 exposure (0.4 FiO2) used in preterm infant care on these Hox proteins is unknown. We used ex vivo fetal mouse lung organ cultures to explore the effects of 0.4 FiO2 on lung airway and vascular formation in the context of Hoxb5 and Hoxa5 expression and regulation. Compared to room air, 48 h (h) 0.4 FiO2 adversely attenuated airway and microvasculature formation while reducing lung growth and epithelial cell volume, and increasing mesenchymal volume. 0.4 FiO2 decreased pro-angiogenic Hoxb5 and VEGFR2 while not altering protein levels of angiostatic Hoxa5. Lungs returned to RA after 24 h 0.4FiO2 had partial structural recovery but remained smaller and less developed. Mesenchymal cell apoptosis increased and proliferation decreased with time in O2 while epithelial cell proliferation significantly increased. Hoxb5 overexpression led to prominent peri-airway VEGFR2 expression and promoted lung vascular and airway patterning. Hoxa5 overexpression had the opposite effects. We conclude that 0.4 FiO2 exposure causes a profound loss of airway and lung microvascular development that occurs partially via reduction in pro-angiogenic Hoxb5 while angiostatic Hoxa5 expression is maintained.

Abca3 haploinsufficiency is a risk factor for lung injury induced by hyperoxia or mechanical ventilation in a murine model

BACKGROUND

Heterozygous ATP-binding-cassette subfamily A member 3 (ABCA3) mutations are associated with neonatal respiratory complications. In an adult murine model, we investigated whether Abca3 haploinsufficiency is a predisposing factor for lung injury induced by hyperoxia or mechanical ventilation.

METHODS

Abca3 haploinsufficient (Abca3(+/-)) and wild-type (WT) mice were prospectively randomized to 25 min of ventilation or 72 h of hyperoxia or left unchallenged in air.

RESULTS

As compared with WT mice, unchallenged Abca3(+/-) mice had significantly decreased lung phosphatidylcholine (PC) and phosphatidylglycerol (PG) levels (P < 0.02) and decreased lung compliance (P < 0.05). When ventilated for 25 min, Abca3(+/-) mice demonstrated a significantly greater increase in bronchoalveolar lavage (BAL) interleukins (P ≤ 0.01) and lung wet to dry ratio (P < 0.005). Hyperoxia resulted in increased compliance (P < 0.05) and total lung capacity (TLC) (P = 0.01) only in the Abca3(+/-) mice, consistent with enlarged alveolar spaces. The ratio of PC to PG in BAL-relevant for surfactant dysfunction-was significantly elevated by oxygen exposure, with the greatest increase in Abca3(+/-) mice.

CONCLUSION

In a murine model, Abca3 haploinsufficiency results in an altered biochemical and lung mechanical phenotype, as well as a greater lung injury induced by hyperoxia or mechanical ventilation. The inability to maintain a normal PC/PG ratio appears to play a key role.

CCAAT/enhancer-binding protein-α suppresses lung tumor development in mice through the p38α MAP kinase pathway

The transcription factor CCAAT/enhancer-binding protein α (C/EBPα) is a basic leucine zipper transcription factor and is expressed in alveolar type II cells, alveolar macrophages and Clara cells in the lung. Although decrease or absence of C/EBPα expression in human non-small cell lung cancer suggests a possible role of C/EBPα as a lung tumor suppressor, there is no direct proof for this hypothesis. In this study, we investigated, for the first time, the role of C/EBPα in lung tumors in vivo using transgenic mice with lung epithelial specific conditional deletion of Cebpa (Cebpα(Δ/Δ) mice) and a urethane-induced lung tumor model. C/EBPα expression in the lung was dispensable, and its deletion was not oncogenic under unstressed conditions. However, at 28 wk after urethane injection, the number and size of tumors and the tumor burden were significantly higher in Cebpα(Δ/Δ) mice than in littermate control mice. Urethane-injected Cebpα(Δ/Δ) mice showed highly proliferative adenomas and adenocarcinomas in the lung, and survival time after urethane-injection was significantly shorter than that in control mice. In control mice, C/EBPα was strongly induced in the tumor tissues at 28 weeks after urethane-injection, but became weakened or absent as tumors progressed after long-term observation for over 1 year. Using intraperitoneal injection of p38 inhibitor (SB203580), we demonstrated that the induction of C/EBPα is strongly regulated by the p38 MAP kinase in murine alveolar epithelial cells. A high correlation was demonstrated between the expression of C/EBPα and p38α MAP kinase in tumor cells, suggesting that C/EBPα silencing in tumor cells is caused by down-regulation of p38α MAP kinase. In conclusion, the role of C/EBPα as a lung tumor suppressor was demonstrated for the first time in the present study, and the extinguished C/EBPα expression through p38α inactivation leads tumor promotion and progression.

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.

Kruppel-like factor 5 controls villus formation and initiation of cytodifferentiation in the embryonic intestinal epithelium

Kruppel-like factor 5 (Klf5) is a transcription factor expressed by embryonic endodermal progenitors that form the lining of the gastrointestinal tract. A Klf5 floxed allele was efficiently deleted from the intestinal epithelium by a Cre transgene under control of the Shh promoter resulting in the inhibition of villus morphogenesis and epithelial differentiation. Although proliferation of the intestinal epithelium was maintained, the expression of Elf3, Pparγ, Atoh1, Ascl2, Neurog3, Hnf4α, Cdx1, and other genes associated with epithelial cell differentiation was inhibited in the Klf5-deficient intestines. At E18.5, Klf5(Δ/Δ) fetuses lacked the apical brush border characteristic of enterocytes, and a loss of goblet and enteroendocrine cells was observed. The failure to form villi was not attributable to the absence of HH or PDGF signaling, known mediators of this developmental process. Klf5-deletion blocked the decrease in FoxA1 and Sox9 expression that accompanies normal villus morphogenesis. KLF5 directly inhibited activity of the FoxA1 promoter, and in turn FOXA1 inhibited Elf3 gene expression in vitro, linking the observed loss of Elf3 with the persistent expression of FoxA1 observed in Klf5-deficient mice. Genetic network analysis identified KLF5 as a key transcription factor regulating intestinal cell differentiation and cell adhesion. These studies indicate a novel requirement for KLF5 to initiate morphogenesis of the early endoderm into a compartmentalized intestinal epithelium comprised of villi and terminally differentiated cells.

FOXM1 promotes allergen-induced goblet cell metaplasia and pulmonary inflammation

Chronic airway disorders, including chronic obstructive pulmonary disease (COPD), cystic fibrosis, and asthma, are associated with persistent pulmonary inflammation and goblet cell metaplasia and contribute to significant morbidity and mortality worldwide. While the molecular pathogenesis of these disorders is actively studied, little is known regarding the transcriptional control of goblet cell differentiation and mucus hyperproduction. Herein, we demonstrated that pulmonary allergen sensitization induces expression of FOXM1 transcription factor in airway epithelial and inflammatory cells. Conditional deletion of the Foxm1 gene from either airway epithelium or myeloid inflammatory cells decreased goblet cell metaplasia, reduced lung inflammation, and decreased airway resistance in response to house dust mite allergen (HDM). FOXM1 induced goblet cell metaplasia and Muc5AC expression through the transcriptional activation of Spdef. FOXM1 deletion reduced expression of CCL11, CCL24, and the chemokine receptors CCR2 and CX3CR1, resulting in decreased recruitment of eosinophils and macrophages to the lung. Deletion of FOXM1 from dendritic cells impaired the uptake of HDM antigens and decreased cell surface expression of major histocompatibility complex II (MHC II) and costimulatory molecule CD86, decreasing production of Th2 cytokines by activated T cells. Finally, pharmacological inhibition of FOXM1 by ARF peptide prevented HDM-mediated pulmonary responses. FOXM1 regulates genes critical for allergen-induced lung inflammation and goblet cell metaplasia.

Gene regulatory network analysis supports inflammation as a key neurodegeneration process in prion disease

Background

The activation of immune cells in the brain is believed to be one of the earliest events in prion disease development, where misfolded PrionSc protein deposits are thought to act as irritants leading to a series of events that culminate in neuronal cell dysfunction and death. The role of these events in prion disease though is still a matter of debate. To elucidate the mechanisms leading from abnormal protein deposition to neuronal injury, we have performed a detailed network analysis of genes differentially expressed in several mouse prion models.

Results

We found a master regulatory core of genes related to immune response controlling other genes involved in prion protein replication and accumulation, and neuronal cell death. This regulatory core determines the existence of two stable states that are consistent with the transcriptome analysis comparing prion infected versus uninfected mouse brain. An in silico perturbation analysis demonstrates that core genes are individually capable of triggering the transition and that the network remains locked once the diseased state is reached.

Conclusions

We hypothesize that this locking may be the cause of the sustained immune response observed in prion disease. Our analysis supports the hypothesis that sustained brain inflammation is the main pathogenic process leading to neuronal dysfunction and loss, which, in turn, leads to clinical symptoms in prion disease.

Foxm1 transcription factor is critical for proliferation and differentiation of Clara cells during development of conducting airways

Respiratory epithelial cells are derived from cell progenitors in the foregut endoderm that subsequently differentiate into the distinct cell types lining the conducting and alveolar regions of the lung. To identify transcriptional mechanisms regulating differentiation and maintenance of respiratory epithelial cells, we conditionally deleted Foxm1 transcription factor from the conducting airways of the developing mouse lung. Conditional deletion of Foxm1 from Clara cells, controlled by the Scgb1a1 promoter, dramatically altered airway structure and caused peribronchial fibrosis, resulting in airway hyperreactivity in adult mice. Deletion of Foxm1 inhibited proliferation of Clara cells and disrupted the normal patterning of epithelial cell differentiation in the bronchioles, causing squamous and goblet cell metaplasia, and the loss of Clara and ciliated cells. Surprisingly, conducting airways of Foxm1-deficient mice contained highly differentiated cuboidal type II epithelial cells that are normally restricted to the alveoli. Lineage tracing studies showed that the ectopic alveolar type II cells in Foxm1-deficient airways were derived from Clara cells. Deletion of Foxm1 inhibited Sox2 and Scgb1a1, both of which are critical for differentiation and function of Clara cells. In co-transfection experiments, Foxm1 directly bound to and induced transcriptional activity of Scgb1a1 and Sox2 promoters. Foxm1 is required for differentiation and maintenance of epithelial cells lining conducting airways.

CCAAT/enhancer binding protein-α regulates the protease/antiprotease balance required for bronchiolar epithelium regeneration

Many transcription factors that regulate lung morphogenesis during development are reactivated to mediate repairs of the injured adult lung. We hypothesized that CCAAT/enhancer binding protein-α (C/EBPα), a transcription factor critical for perinatal lung maturation, regulates genes required for the normal repair of the bronchiolar epithelium after injury. Transgenic Cebpα(Δ/Δ) mice, in which Cebpa was conditionally deleted from Clara cells and Type II cells after birth, were used in this study. Airway injury was induced in mice by the intraperitoneal administration of naphthalene to ablate bronchiolar epithelial cells. Although the deletion of C/EBPα did not influence lung structure and function under unstressed conditions, C/EBPα was required for the normal repair of terminal bronchiolar epithelium after naphthalene injury. To identify cellular processes that are influenced by C/EBPα during repair, mRNA microarray was performed on terminal bronchiolar epithelial cells isolated by laser-capture microdissection. Normal repair of the terminal bronchiolar epithelium was highly associated with the mRNAs regulating antiprotease activities, and their induction required C/EBPα. The defective deposition of fibronectin in Cebpα(Δ/Δ) mice was associated with increased protease activity and delayed differentiation of FoxJ1-expressing ciliated cells. The fibronectin and ciliated cells were restored by the intratracheal treatment of Cebpα(Δ/Δ) mice with the serine protease inhibitor. In conclusion, C/EBPα regulates the expression of serine protease inhibitors that are required for the normal increase of fibronectin and the restoration of ciliated cells after injury. Treatment with serine protease inhibitor may aid in the recovery of injured bronchiolar epithelial cells, and prevent common chronic lung diseases.

Kruppel-like factor 5 is required for formation and differentiation of the bladder urothelium

Kruppel-like transcription factor 5 (Klf5) was detected in the developing and mature murine bladder urothelium. Herein we report a critical role of KLF5 in the formation and terminal differentiation of the urothelium. The Shh(GfpCre) transgene was used to delete the Klf5(floxed) alleles from bladder epithelial cells causing prenatal hydronephrosis, hydroureter, and vesicoureteric reflux. The bladder urothelium failed to stratify and did not express terminal differentiation markers characteristic of basal, intermediate, and umbrella cells including keratins 20, 14, and 5, and the uroplakins. The effects of Klf5 deletion were unique to the developing bladder epithelium since maturation of the epithelium comprising the bladder neck and urethra was unaffected by the lack of KLF5. mRNA analysis identified reductions in Pparγ, Grhl3, Elf3, and Ovol1expression in Klf5 deficient fetal bladders supporting their participation in a transcriptional network regulating bladder urothelial differentiation. KLF5 regulated expression of the mGrhl3 promoter in transient transfection assays. The absence of urothelial Klf5 altered epithelial-mesenchymal signaling leading to the formation of an ectopic alpha smooth muscle actin positive layer of cells subjacent to the epithelium and a thinner detrusor muscle that was not attributable to disruption of SHH signaling, a known mediator of detrusor morphogenesis. Deletion of Klf5 from the developing bladder urothelium blocked epithelial cell differentiation, impaired bladder morphogenesis and function causing hydroureter and hydronephrosis at birth.

Conditional deletion of Nrf2 in airway epithelium exacerbates acute lung injury and impairs the resolution of inflammation

Oxidant stress, resulting from an excess of reactive electrophiles produced in the lung by both resident (epithelial and endothelial) and infiltrated leukocytes, is thought to play an obligatory role in tissue injury and abnormal repair. Previously, using a conventional (whole-body) knockout model, we showed that antioxidative gene induction regulated by the transcription factor Nrf2 is critical for mitigating oxidant-induced (hyperoxic) stress, as well as for preventing and resolving tissue injury and inflammation in vivo. However, the contribution to pathogenic acute lung injury (ALI) of the cellular stress produced by resident versus infiltrated leukocytes remains largely undefined in vivo. To address this critical gap in our knowledge, we generated mice with a conditional deletion of Nrf2 specifically in Clara cells, subjected these mice to hyperoxic insult, and allowed them to recover. We report that a deficiency of Nrf2 in airway epithelia alone is sufficient to contribute to the development and progression of ALI. When exposed to hyperoxia, mice lacking Nrf2 in Clara cells showed exacerbated lung injury, accompanied by greater levels of cell death and epithelial sloughing than in their wild-type littermates. In addition, we found that an Nrf2 deficiency in Clara cells is associated with a persistent inflammatory response and epithelial sloughing in the lungs during recovery from sublethal hyperoxic insult. Our results demonstrate (for the first time, to the best of our knowledge) that Nrf2 signaling in Clara cells is critical for conferring protection from hyperoxic lung injury and for resolving inflammation during the repair process.

Silencing hyperoxia-induced C/EBPα in neonatal mice improves lung architecture via enhanced proliferation of alveolar epithelial cells

Postnatal lung development requires proliferation and differentiation of specific cell types at precise times to promote proper alveolar formation. Hyperoxic exposure can disrupt alveolarization by inhibiting cell growth; however, it is not fully understood how this is mediated. The transcription factor CCAAT/enhancer binding protein-α (C/EBPα) is highly expressed in the lung and plays a role in cell proliferation and differentiation in many tissues. After 72 h of hyperoxia, C/EBPα expression was significantly enhanced in the lungs of newborn mice. The increased C/EBPα protein was predominantly located in alveolar type II cells. Silencing of C/EBPα with a transpulmonary injection of C/EBPα small interfering RNA (siRNA) prior to hyperoxic exposure reduced expression of markers of type I cell and differentiation typically observed after hyperoxia but did not rescue the altered lung morphology at 72 h. Nevertheless, when C/EBPα hyperoxia-exposed siRNA-injected mice were allowed to recover for 2 wk in room air, lung epithelial cell proliferation was increased and lung morphology was restored compared with hyperoxia-exposed control siRNA-injected mice. These data suggest that C/EBPα is an important regulator of postnatal alveolar epithelial cell proliferation and differentiation during injury and repair.

Comparative proteomic analysis of lung lamellar bodies and lysosome-related organelles

Pulmonary surfactant is a complex mixture of lipids and proteins that is essential for postnatal function. Surfactant is synthesized in alveolar type II cells and stored as multi-bilayer membranes in a specialized secretory lysosome-related organelle (LRO), known as the lamellar body (LB), prior to secretion into the alveolar airspaces. Few LB proteins have been identified and the mechanisms regulating formation and trafficking of this organelle are poorly understood. Lamellar bodies were isolated from rat lungs, separated into limiting membrane and core populations, fractionated by SDS-PAGE and proteins identified by nanoLC-tandem mass spectrometry. In total 562 proteins were identified, significantly extending a previous study that identified 44 proteins in rat lung LB. The lung LB proteome reflects the dynamic interaction of this organelle with the biosynthetic, secretory and endocytic pathways of the type II epithelial cell. Comparison with other LRO proteomes indicated that 60% of LB proteins were detected in one or more of 8 other proteomes, confirming classification of the LB as a LRO. Remarkably the LB shared 37.8% of its proteins with the melanosome but only 9.9% with lamellar bodies from the skin. Of the 229 proteins not detected in other LRO proteomes, a subset of 34 proteins was enriched in lung relative to other tissues. Proteins with lipid-related functions comprised a significant proportion of the LB unique subset, consistent with the major function of this organelle in the organization, storage and secretion of surfactant lipid. The lung LB proteome will facilitate identification of molecular pathways involved in LB biogenesis, surfactant homeostasis and disease pathogenesis.

A systems approach to mapping transcriptional networks controlling surfactant homeostasis

Background

Pulmonary surfactant is required for lung function at birth and throughout life. Lung lipid and surfactant homeostasis requires regulation among multi-tiered processes, coordinating the synthesis of surfactant proteins and lipids, their assembly, trafficking, and storage in type II cells of the lung. The mechanisms regulating these interrelated processes are largely unknown.

Results

We integrated mRNA microarray data with array independent knowledge using Gene Ontology (GO) similarity analysis, promoter motif searching, protein interaction and literature mining to elucidate genetic networks regulating lipid related biological processes in lung. A Transcription factor (TF) - target gene (TG) similarity matrix was generated by integrating data from different analytic methods. A scoring function was built to rank the likely TF-TG pairs. Using this strategy, we identified and verified critical components of a transcriptional network directing lipogenesis, lipid trafficking and surfactant homeostasis in the mouse lung.

Conclusions

Within the transcriptional network, SREBP, CEBPA, FOXA2, ETSF, GATA6 and IRF1 were identified as regulatory hubs displaying high connectivity. SREBP, FOXA2 and CEBPA together form a common core regulatory module that controls surfactant lipid homeostasis. The core module cooperates with other factors to regulate lipid metabolism and transport, cell growth and development, cell death and cell mediated immune response. Coordinated interactions of the TFs influence surfactant homeostasis and regulate lung function at birth.

Conditional deletion of Abca3 in alveolar type II cells alters surfactant homeostasis in newborn and adult mice

ATP-binding cassette A3 (ABCA3) is a lipid transport protein required for synthesis and storage of pulmonary surfactant in type II cells in the alveoli. Abca3 was conditionally deleted in respiratory epithelial cells (Abca3(Δ/Δ)) in vivo. The majority of mice in which Abca3 was deleted in alveolar type II cells died shortly after birth from respiratory distress related to surfactant deficiency. Approximately 30% of the Abca3(Δ/Δ) mice survived after birth. Surviving Abca3(Δ/Δ) mice developed emphysema in the absence of significant pulmonary inflammation. Staining of lung tissue and mRNA isolated from alveolar type II cells demonstrated that ∼50% of alveolar type II cells lacked ABCA3. Phospholipid content and composition were altered in lung tissue, lamellar bodies, and bronchoalveolar lavage fluid from adult Abca3(Δ/Δ) mice. In adult Abca3(Δ/Δ) mice, cells lacking ABCA3 had decreased expression of mRNAs associated with lipid synthesis and transport. FOXA2 and CCAAT enhancer-binding protein-α, transcription factors known to regulate genes regulating lung lipid metabolism, were markedly decreased in cells lacking ABCA3. Deletion of Abca3 disrupted surfactant lipid synthesis in a cell-autonomous manner. Compensatory surfactant synthesis was initiated in ABCA3-sufficient type II cells, indicating that surfactant homeostasis is a highly regulated process that includes sensing and coregulation among alveolar type II cells.

Pulmonary effects of keratinocyte growth factor in newborn rats exposed to hyperoxia

Acute lung injury and compromised alveolar development characterize bronchopulmonary dysplasia (BPD) of the premature neonate. High levels of keratinocyte growth factor (KGF), a cell-cell mediator with pleiotrophic lung effects, are associated with low BPD risk. KGF decreases mortality in hyperoxia-exposed newborn rodents, a classic model of injury-induced impaired alveolarization, although the pulmonary mechanisms of this protection are poorly defined. These were explored through in vitro and in vivo approaches in the rat. Hyperoxia decreased by 30% the rate of wound closure of a monolayer of fetal alveolar epithelial cells, due to cell death, which was overcome by recombinant human KGF (100 ng/ml). In rat pups exposed to >95% O2 from birth, increased viability induced by intraperitoneal injection of KGF (2 microg/g body wt) every other day was associated with prevention of neutrophil influx in bronchoalveolar lavage (BAL), prevention of decreases in whole lung DNA content and cell proliferation rate, partial prevention of apoptosis increase, and a markedly increased proportion of surfactant protein B-immunoreactive cells in lung parenchyma. Increased lung antioxidant capacity is likely to be due in part to enhanced CAAT/enhancer binding protein alpha expression. By contrast, KGF neither corrected changes induced by hyperoxia in parameters of lung morphometry that clearly indicated impaired alveolarization nor had any significant effect on tissue or BAL surfactant phospholipids. These findings evidence KGF alveolar epithelial cell protection, enhancing effects on alveolar repair capacity, and anti-inflammatory effects in the injured neonatal lung that may account, at least in part, for its ability to reduce mortality. They argue in favor of a therapeutic potential of KGF in the injured neonatal lung.