Prostaglandin E₂ protects human lung fibroblasts from cigarette smoke extract-induced apoptosis via EP₂ receptor activation

Prostaglandin E₂ (PGE₂) has been shown to have a strong cytoprotective effect, inhibiting apoptosis. In the present study, we evaluated whether PGE₂ has a protective effect on cigarette smoke extract (CSE)-induced apoptosis in human lung fibroblasts. Apoptosis was assessed by various methods, including DNA content analysis. CSE (15%-20%) led to apoptosis and induced imbalance in favor of pro- over anti-apoptotic protein expression and activated caspases. PGE₂ blocked CSE-induced apoptosis and modulated the balance of pro- and anti-apoptotic proteins and decreased the activation of caspases. This anti-apoptotic effect was mediated via EP ₂ receptor activation as the EP₂ agonist butaprost mimicked PGE₂ activity and siRNA for the EP₂ receptor blocked it. An adenylyl cyclase inhibitor was found to abolish the PGE ₂-mediated cytoprotective effect. Correspondingly, c-AMP analogs blocked CSE-induced apoptosis. Consistently, the protein kinase A (PKA) inhibitor KT-5720 abolished PGE₂-mediated protection. PGE₂ and butaprost phosphorylated Bad and KT-5720 blocked phosphorylation. These results suggest that PGE₂ inhibits CSE-induced apoptosis via EP ₂ receptor activation and activation of PKA, which leads to an alteration in the balance between pro-and anti-apoptotic factors. Through such a mechanism, PGE₂ may alter survival of cells in the smoke-exposed lungs, thus affecting the pathogenesis of cigarette smoke-induced disease.