Induction of Amnion Epithelial Apoptosis by Cortisol via tPA/Plasmin System

Rupture of fetal membranes (ROM) can initiate parturition at both term and preterm birth. Apoptosis of the amnion epithelium plays a key role in structural remodeling of the membranes preceding ROM. However, the causative factors for apoptosis remain unidentified. Toward the end of gestation, a feed-forward regeneration of cortisol via 11β-hydroxysteroid dehydrogenase 1 exists in the fetal membranes. Here, we have examined whether cortisol accumulation is a causative factor for amnion cells apoptosis. By using primary human amnion epithelial and fibroblast cells, we demonstrated cortisol induced apoptosis specifically in epithelial cells but not in fibroblasts via reciprocal regulation of tissue-type plasminogen activator (tPA)/plasmin system. Cortisol increased PLAT expression, the gene encoding tPA, via glucocorticoid receptor binding to a glucocorticoid response element in PLAT promoter, thereby increasing plasmin activity in epithelial cells. Further study revealed that a Fas-mediated extrinsic apoptotic pathway was involved in the induction of epithelial cells apoptosis by cortisol, which was blocked by inhibiting either tPA or plasmin. Consistently, cortisol increased cleaved-caspase-3 and tPA abundance in amnion tissue explants. Moreover, the abundance of cortisol, cleaved-caspase-3, and tPA was significantly increased in amnion tissue after labor-initiated spontaneous rupture of membranes. In conclusion, local accumulation of cortisol is a causative factor for amnion epithelial apoptosis via activation of tPA/plasmin system toward the end of gestation. This may contribute to the ROM at both term and preterm birth.