Genes coding for transcription factors involved in stem cell maintenance are repressed by TGF-ß and downstream of Slug/Snail2 in COPD bronchial epithelial progenitors.

BACKGROUND: Basal stem/progenitor cells of airway epithelium from chronic obstructive pulmonary disease (COPD) patients have a decrease in differentiation and self-renewal potential. Our study aimed at identifying deregulations in the genetic program of these cells that could account for their exhaustion, focusing on genes downstream of the epithelial-mesenchymal transition-inducing transcription factor Slug/Snail2 and responding to transforming growth factor (TGF)-ß. TGF-ß is at higher levels in COPD patient lungs, plays a role in stem/progenitor cell fate and regulates the expression of Slug/Snail2 that is highly expressed in airway basal stem/progenitors. METHODS AND RESULTS: We reanalyzed a gene expression dataset that we generated from COPD and normal primary bronchial basal progenitor cells knocked down for Slug/Snail2 gene. Among the genes that we identified to be repressed downstream of Slug/Snail2 in COPD, we selected those responding to differentiation and TGF-ß. The large majority of these genes are upregulated with differentiation but repressed by TGF-ß. Pathway and ontology enrichment analysis revealed a set of genes coding for transcription factors involved in stem cell maintenance that are repressed downstream of Slug/Snail2 and by TGF-ß in COPD but not normal basal progenitor cells. We also reveal a link between Slug/Snail2 expression and the repressive effect of TGF-ß on these stem cell maintenance genes. CONCLUSION: Our work brings a new insight and molecular perspective to the exhaustion of basal stem/progenitor cells observed in the airway epithelium of COPD patients, revealing that stem cell maintenance genes are repressed in these cells, with TGF-ß and Slug/Snail2 being involved in this deregulation.

Proliferation Genes Repressed by TGF-ß Are Downstream of Slug/Snail2 in Normal Bronchial Epithelial Progenitors and Are Deregulated in COPD.

Slug/Snail2 belongs to the Epithelial-Mesenchymal Transition (EMT)-inducing transcription factors involved in development and diseases. Slug is expressed in adult stem/progenitor cells of several epithelia, making it unique among these transcription factors. To investigate Slug role in human bronchial epithelium progenitors, we studied primary bronchial basal/progenitor cells in an air-liquid interface culture system that allows regenerating a bronchial epithelium. To identify Slug downstream genes we knocked down Slug in basal/progenitor cells from normal subjects and subjects with COPD, a respiratory disease presenting anomalies in the bronchial epithelium and high levels of TGF-ß in the lungs. We show that normal and COPD bronchial basal/progenitors, even when treated with TGF-ß, express both epithelial and mesenchymal markers, and that the epithelial marker E-cadherin is not a target of Slug and, moreover, positively correlates with Slug. We reveal that Slug downstream genes responding to both differentiation and TGF-ß are different in normal and COPD progenitors, with in particular a set of proliferation-related genes that are among the genes repressed downstream of Slug in normal but not COPD. In COPD progenitors at the onset of differentiation in presence of TGF-ß,we show that there is positive correlations between the effect of differentiation and TGF-ß on proliferation-related genes and on Slug protein, and that their expression levels are higher than in normal cells. As well, the expression of Smad3 and ß-Catenin, two molecules from TGF-ßsignaling pathways, are higher in COPD progenitors, and our results indicate that proliferation-related genes and Slug protein are increased by different TGF-ß-induced mechanisms.