BackgroundThe small airway epithelium (SAE), the cell population that covers the human airway surface from the 6th generation of airway branching to the alveoli, is the major site of lung disease caused by smoking. The focus of this study is to provide quantitative assessment of the SAE transcriptome in the resting state and in response to chronic cigarette smoking using massive parallel mRNA sequencing (RNA-Seq).ResultsThe data demonstrate that 48% of SAE expressed genes are ubiquitous, shared with many tissues, with 52% enriched in this cell population. The most highly expressed gene, SCGB1A1, is characteristic of Clara cells, the cell type unique to the human SAE. Among other genes expressed by the SAE are those related to Clara cell differentiation, secretory mucosal defense, and mucociliary differentiation. The high sensitivity of RNA-Seq permitted quantification of gene expression related to infrequent cell populations such as neuroendocrine cells and epithelial stem/progenitor cells. Quantification of the absolute smoking-induced changes in SAE gene expression revealed that, compared to ubiquitous genes, more SAE-enriched genes responded to smoking with up-regulation, and those with the highest basal expression levels showed most dramatic changes. Smoking had no effect on SAE gene splicing, but was associated with a shift in molecular pattern from Clara cell-associated towards the mucus-secreting cell differentiation pathway with multiple features of cancer-associated molecular phenotype.ConclusionsThese observations provide insights into the unique biology of human SAE by providing quantit-ative assessment of the global transcriptome under physiological conditions and in response to the stress of chronic cigarette smoking.
BackgroundCiliated cells play a central role in cleansing the airways of inhaled contaminants. They are derived from basal cells that include the airway stem/progenitor cells. In animal models, the transcription factor FOXJ1 has been shown to induce differentiation to the ciliated cell lineage, and the RFX transcription factor-family has been shown to be necessary for, but not sufficient to induce, correct cilia development.MethodsTo test the hypothesis that FOXJ1 and RFX3 cooperatively induce expression of ciliated genes in the differentiation process of basal progenitor cells toward a ciliated cell linage in the human airway epithelium, primary human airway basal cells were assessed under conditions of in vitro differentiation induced by plasmid-mediated gene transfer of FOXJ1 and/or RFX3. TaqMan PCR was used to quantify mRNA levels of basal, secretory, and cilia-associated genes.ResultsBasal cells, when cultured in air-liquid interface, differentiated into a ciliated epithelium, expressing FOXJ1 and RFX3. Transfection of FOXJ1 into resting basal cells activated promoters and induced expression of ciliated cell genes as well as both FOXJ1 and RFX3, but not basal cell genes. Transfection of RFX3 induced expression of RFX3 but not FOXJ1, nor the expression of cilia-related genes. The combination of FOXJ1 + RFX3 enhanced ciliated gene promoter activity and mRNA expression beyond that due to FOXJ1 alone. Corroborating immunoprecipitation studies demonstrated an interaction between FOXJ1 and RFX3.ConclusionFOXJ1 is an important regulator of cilia gene expression during ciliated cell differentiation, with RFX3 as a transcriptional co-activator to FOXJ1, helping to induce the expression of cilia genes in the process of ciliated cell differentiation of basal/progenitor cells.
The link between respiratory complications in prematurely born infants and susceptibility for developing chronic obstructive pulmonary disease (COPD) is receiving increasing attention. We have previously found that CCAAT/enhancer binding protein (C/EBP) activity in airway epithelial cells of COPD patients is decreased compared to healthy smokers, suggesting a previously unknown role for C/EBPs in COPD pathogenesis.To investigate the role of the transcription factor C/EBPa in lung development and its potential role in COPD, mice with a lung epithelial-specific disruption of the C/EBPa gene (Cebpa DLE ) were generated using Cre-mediated excision, and the resulting pathology was studied during development and into adulthood. Cebpa DLE mice exhibit impaired lung development and epithelial differentiation, as well as affected vascularity. Furthermore, Cebpa DLE mice that survive until adulthood develop a severe pathological picture with irregular emphysema; bronchiolitis, including goblet cell hyperplasia, bronchiolar metaplasia, fibrosis and mucus plugging; and an inflammatory cell and gene expression profile similar to COPD. Cebpa DLE mice display lung immaturity during development, and adult Cebpa DLE mice develop a majority of the histopathological and inflammatory characteristics of COPD. Cebpa DLE mice could thus provide new valuable insights into understanding the long-term consequences of lung immaturity and the link to susceptibility of developing COPD.
Our data suggest a previously unknown role for C/EBPβ and the airway epithelium in mediating inflammatory and innate immune responses to cigarette smoke.
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 (CebpaΔLE), C/EBPβ (CebpbΔLE), or both genes (CebpaΔLE; CebpbΔLE). Results: Both CebpaΔLE mice and CebpaΔLE; CebpbΔLE mice demonstrated severe pulmonary immaturity compared to wild‐type littermates, while no differences in lung histology or epithelial differentiation were observed in CebpbΔLE mice. In contrast to CebpaΔLE mice, CebpaΔLE; CebpbΔLE 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 CebpaΔLE; CebpbΔLE 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. Developmental Dynamics 241:911–923, 2012. © 2012 Wiley Periodicals, Inc.
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