Prostaglandin E2 induces fibroblast apoptosis by modulating multiple survival pathways.

Although the lipid mediator prostaglandin E2 (PGE2) exerts antifibrotic effects by inhibiting multiple fibroblast functions, its ability to regulate fibroblast survival is unknown. Here, we examined the effects of this prostanoid on apoptosis and apoptosis pathways in normal and fibrotic lung fibroblasts. As compared to medium alone, 24 h of treatment with PGE2 increased apoptosis of normal lung fibroblasts in a dose-dependent manner (EC50 ~ 50 nM), as measured by annexin V staining, caspase 3 activity, cleavage of poly-ADP-ribose polymerase, and single-stranded DNA levels. PGE also potentiated apoptosis elicited by Fas ligand plus cycloheximide. These proapoptotic actions were dependent on signaling through the EP2/EP4 receptors and by downstream activation of both caspases 8 and 9. Silencing and gene deletion of PTEN demonstrated that the effects of PGE involved decreased activity of the prosurvival molecule Akt. PGE2 also down-regulated expression of survivin, an inhibitor of apoptosis, and increased expression of Fas. Fibroblasts from patients with pulmonary fibrosis exhibited resistance to the apoptotic effects of PGE2. These findings show for the first time that, in contrast to its effects on many other cell types, PGE promotes apoptosis in lung fibroblasts through diverse pathways. They provide another dimension by which PGE2 may inhibit, and perhaps even reverse, fibrogenesis in patients with interstitial lung disease. [ABSTRACT FROM AUTHOR]