Prostaglandin E 2 induced caspase-dependent apoptosis possibly through activation of EP2 receptors in cultured hippocampal neurons

Abstract

Cyclooxygenase-2 (COX-2) induction and prostaglandin E 2 elevation have been reported to occur after cerebral ischemic insult. To evaluate whether the cyclooxygenase-2 reaction product prostaglandin E 2 is directly related to induction of apoptosis in neuronal cells, the effect of prostaglandin E 2 on cell viability was examined in hippocampal cells. Prostaglandin E 2 (5–25 μM) induced apoptosis in a dose-dependent manner 48 h after addition to the cells, which was characterized by cell shrinkage, nuclear condensation or fragmentation and attenuated by a protein synthesis inhibitor, cycloheximide. Neither 17-phenyl trinor-prostaglandin E 2 (an EP1 agonist) nor sulprostone (an EP3 agonist) induced cell death, whereas butaprost (an EP2 agonist) induced apoptosis. Prostaglandin E 2 increased the intracellular concentration of cAMP, and the selective EP2 agonist butaprost also induced apoptosis accompanied by increasing cAMP levels in hippocampal cells. Moreover, a cell permeable cAMP analog, dibutyryl cAMP also induced apoptosis in hippocampal cells. These findings suggest that prostaglandin E 2-induced apoptosis was mediated through a mechanism involving the cAMP-dependent pathway. In addition, prostaglandin E 2 activated caspase-3 activity in a dose-dependent manner and a caspase-3 inhibitor prevented the prostaglandin E 2-induced apoptosis. We showed in this report that prostaglandin E 2 directly induced apoptosis in hippocampal neurons. Moreover, it is likely that the direct effects of prostaglandin E 2 on hippocampal neurons were mediated by activation of EP2 receptors followed by elevation of the intracellular cAMP levels.