PGE2 in the regulation of programmed erythrocyte death

Hyperosmotic shock, energy depletion, or removal of extracellular Cl- activates Ca2+-permeable cation channels in erythrocyte membranes. Subsequent Ca2+ entry induces erythrocyte shrinkage and exposure of phosphatidylserine ( PS) at the erythrocyte surface. PS-exposing cells are engulfed by macrophages. The present study explored the signalling involved. Hyperosmotic shock and Cl- removal triggered the release of prostaglandin E-2 (PGE(2)). In whole-cell recording, activation of the cation channels by Cl- removal was abolished by the cyclooxygenase inhibitor diclophenac. In FACS analysis, phospholipase-A(2) inhibitors quinacrine and palmitoyltrifluoromethyl-ketone, and cyclooxygenase inhibitors acetylsalicylic acid and diclophenac, blunted the increase of PS exposure following Cl- removal. PGE(2) ( but not thromboxane) induced cation channel activation, increase in cytosolic Ca2+ concentration, cell shrinkage, PS exposure, calpain activation, and ankyrin-R degradation. The latter was attenuated by calpain inhibitors-I/II, while PGE(2)- induced PS exposure was not. In conclusion, hyperosmotic shock or Cl- removal stimulates erythrocyte PS exposure through PGE(2) formation and subsequent activation of Ca2+-permeable cation channels.