Epithelial-mesenchymal transition induced by cigarette smoke in lung epithelial cells is associated with metabolic reprogramming and senescence

A dysregulated epithelial–mesenchymal transition (EMT) contributes to tumor progression, fibrosis and lung tissue remodeling in Chronic Obstructive Pulmonary Disease (COPD). Cigarette smoke, a risk factor for all these processes, induces oxidative stress, mitochondrial damage and drives cell senescence by reducing FoxO3, an anti-aging factor. Mitochondrial dysfunction is involved in aging and increases lactate generation, which is correlated with EMT induction. Here, we investigated the cigarette smoke extract (CSE) effects on mitochondrial status and cell metabolism and on the expression of EMT markers in lung epithelial cells, focusing on the role of FoxO3 in this process. A549 cells were exposed to CSE and TGF-β1. Reactive oxygen species (ROS), mitochondrial superoxide, intracellular ATP, E-cadherin and FoxO3 expression were assessed. Extracellular lactate was measured as readout of the glycolytic flux. FoxO3 expression was silenced using siRNA and E-cadherin gene expression was evaluated. Some key results were confirmed in primary bronchial epithelial cells (PBEC). Our results showed that CSE and TGF-β1 reduced E-cadherin and FoxO3 expression in A549 and this was confirmed in PBEC. FoxO3 silencing decreased E-cadherin in A549. EMT induced by CSE in A549 was associated with ROS and mitochondrial superoxide increase, lactate release and intracellular ATP decrease. These data suggest that cigarette smoke-induced EMT is mediated in part by a decrease of FoxO3, in lung epithelial cells. This is accompanied metabolic reprogramming where mitochondrial damage is associated with an increase of glycolysis, most likely as a compensatory mechanism.