Prostaglandin Involvement in the Conventional Outflow Pathway

Abstract

Prostaglandins (PG) play a major role in many endogenous processes including inflammation, labor, reproduction, and blood clotting. In the last two decades, these lipid signaling molecules have shown great potential as ocular hypotensive agents. Intraocular pressure (IOP) is a major risk factor in primary open-angled glaucoma (POAG), the second leading cause of blindness world-wide. Currently, prostaglandin F(2α) analogues are the most widely prescribed medications used to treat ocular hypertension. Studies have identified that almost all prostaglandin analogues exhibit anti-hypertensive effects in the eye, although they are not clinically available. Initial studies attributed the decrease in IOP observed to changes in hydraulic conductivity across the pressure-independent or uveoscleral pathway. More recent studies have shown that prostaglandin F(2α) analogues also lower IOP by affecting the pressure-dependent or trabecular pathway--the diseased tissue in POAG. Little is currently known about PG endogenous function, or the etiology of POAG. However, these studies suggest prostaglandin involvement in the maintenance of IOP in humans and identify the potential of PG analogues to treatment ocular hypertension. The research and findings presented in this dissertation address three specific aims designed to test the hypothesis that Endogenous prostaglandins, prostaglandin enzymes and prostaglandin receptors are involved in regulating conventional outflow facility. Specific aim 1 characterizes the distribution and activity of prostamide/prostaglandin F synthase (PM/PGFS) in the mouse and human eye using immunohistochemistry, western blot analysis and thin layer chromatography. Using techniques in biochemistry, molecular biology and physiology, specific aim 2, identifies the presence of the PG-EP₄ receptor within the outflow pathways, and the efficacy of a selective PG-EP₄ agonist, 3,7-dithiPGE₁, is also determined. Finally, specific aim 3 identifies PG-EP4 receptor coupling and downstream signaling using in vitro assays of transfected and primary cell lines to measure cAMP accumulation after treatment with a PG-EP₄ agonist. Collectively, these studies reveal the importance of PGE₂ synthesis and signaling to the conventional outflow pathway. They identify the PG-EP₄ receptor as a regulator of aqueous outflow and provide more specific therapeutic targets for the treatment of POAG.