Autocrine regulation of corneal endothelium by prostaglandin E2

Previous studies have shown that prostaglandin E2 is synthesized by rabbit corneal endothelial cells in culture and that PGE2 acts to increase synthesis of adenosine 3'-5'-monophosphate (cyclic AMP) and to inhibit endothelial migration in response to experimental wounds. The present study was undertaken to identify endogenously produced prostanoids, to evaluate the effect of PGE2 on corneal endothelial cell cycle parameters, to examine PGE2 receptor effector coupling, and to examine the distribution of cyclooxygenase, a key enzyme regulating PGE2 synthesis, in cultured rabbit corneal endothelial cells.

Prostaglandin biosynthesis was evaluated by thin layer chromatographic analysis of metabolically labeled arachidonic acid products and by radioimmunoassay of PGE2. Corneal endothelial mitosis was examined by flow cytometric analysis of cycling cells and by direct cell counts. PGE2 receptor-mediated cyclic AMP synthesis was quantified by a protein binding assay, and cyclooxygenase was localized by immunohistochemistry.

PGE2 is the major prostanoid produced by rabbit corneal endothelial cells, and its synthesis is enhanced by mitogenic stimulation and is blocked by the cyclooxygenase inhibitor, indomethacin. Inhibition of PGE2 synthesis results in a larger percentage of cycling cells and agonists selective for EP2 receptors reverse indomethacin-induced increases in cell density. Inhibition of endogenous PGE2 synthesis also results in upregulation of receptor-stimulated cyclic AMP synthesis. Cyclooxygenase is present in confluent endothelial cells and is particularly abundant in subconfluent cultures and in cells migrating to close an experimental wound.

The synthesis of PGE2 is regulated in corneal endothelial cells, and this autocoid acts to inhibit endothelial mitosis and activity of prostaglandin receptors of the EP2 subtype.