Mechanical Stretch Induces Senescence of Lung Epithelial Cells and Drives Fibroblast Activation by Paracrine Mechanisms

Severe lung injury requiring mechanical ventilation may lead to secondary fibrosis. Senescence, a cell response characterized by cell cycle arrest and a shift toward a proinflammatory/profibrotic phenotype, is one of the involved mechanisms. In this study, we explore the contribution of mechanical stretch as a trigger of senescence of the respiratory epithelium and its link with fibrosis. Human lung epithelial cells and fibroblasts were exposed <i>in vitro</i> to mechanical stretch, and senescence was assessed. In addition, fibroblasts were exposed to culture media preconditioned by senescent epithelial cells, and their activation was studied. Transcriptomic profiles from stretched, senescent epithelial cells and activated fibroblasts were combined to identify potential activated pathways. Finally, the senolytic effects of digoxin were tested in these models. Mechanical stretch induced senescence in lung epithelial cells, but not in fibroblasts. This stretch-induced senescence has specific features compared with senescence induced by doxorubicin. Fibroblasts were activated after exposure to supernatants conditioned by epithelial senescent cells. Transcriptomic analyses revealed Notch signaling as potentially responsible for the epithelial-mesenchymal cross-talk, because blockade of this pathway inhibits fibroblast activation. Treatment with digoxin reduced the percentage of senescent cells after stretch and ameliorated the fibroblast response to preconditioned media. These results suggest that lung fibrosis in response to mechanical stretch may be caused by the paracrine effects of senescent cells. This pathogenetic mechanism can be pharmacologically manipulated to improve lung repair.