Dexamethasone induces senescence of lung epithelial cells and augments TGF-β1-mediated production of the fibrosis mediator serpin E1 (plasminogen activator inhibitor-1)

Background Idiopathic pulmonary fibrosis (IPF) is a progressive, incurable scarring disease of the lungs with a prognosis worse than most cancers. Pathologically, IPF is characterised by upregulation of the pro-fibrotic cytokine transforming growth factor-β1 (TGF-β1), activation of fibroblasts, and deposition of collagen in the alveolar interstitium. Recent evidence has highlighted the role of senescent type 2 alveolar epithelial cells in the pathogenesis of IPF. In a clinical trial, a treatment regimen containing a corticosteroid drug accelerated pulmonary fibrosis leading to more hospitalizations and deaths, particularly in patients with telomere shortening which drives cellular senescence.

Aim To investigate the potential pro-fibrotic actions of corticosteroids on lung epithelial cells in vitro, including effects on cellular senescence and interactions with TGF-β1.

Methods The synthetic glucocorticoid dexamethasone (DEX) was incubated with A549 and BEAS-2B human lung epithelial cells in the presence or absence of TGF-β1. Cellular senescence was assessed by morphology, senescence-associated beta-galactosidase (SA β-Gal) expression, and qPCR for transcription of senescence-associated molecular markers. Conditioned media were screened for growth factors and cytokines and cultured with human lung fibroblasts. An IPF lung tissue RNA array dataset was re-analysed with a focus on senescence markers.

Results DEX induced senescence in lung epithelial cells associated with increased p21 (CDKN1A) expression independently of p16 (CDKN2A) or p53 (TP53). DEX amplified upregulation of the pro-fibrotic mediator serpin E1/plasminogen activator inhibitor-1 (PAI-1) in the presence of TGF-β1. The senescence-associated secretory phenotype from lung epithelial cells treated with DEX plus TGF-β1-treated contained increased concentrations of GM-CSF and IL-6 and when incubated with primary human lung fibroblasts there were trends to increased senescence and production of fibrosis markers. Upregulation of senescence markers was demonstrated by analysis of an IPF transcriptomic dataset.

Discussion DEX induces senescence in lung epithelial cell lines in vitro and interacts with TGF-β1 to amplify production of the pro-fibrotic mediator serpin E1 (PAI-1). This may be a mechanism by which corticosteroids promote pulmonary fibrosis in susceptible individuals. Serpin E1/PAI-1 is a potential druggable target in pulmonary fibrosis.