Expression, localization, and signaling of PGE(2) and EP2/EP4 receptors inhuman nonpregnant endometrium across the menstrual cycle

This study was designed to elucidate the sites of synthesis and action of P GE(2) in the nonpregnant human uterus across the menstrual cycle. The sites of expression of PGE synthase and synthesis of PGE(2) were investigated by immunohistochemistry using full thickness uterine biopsies. Expression of PGE synthase and synthesis of PGE(2) were localized to glandular epithelial and endothelial cells in both basalis and functionalis regions of the huma n endometrium. By contrast, stromal. staining was predominantly localized i n the functionalis layer. Some cyclical variation in expression of PGE synt hase and PGE(2) synthesis was observed, with reduced expression/synthesis d etected in the stromal compartment of the functionalis during the late secr etory phase of the menstrual cycle. Subsequently, we assessed the site of a ction of PGE(2) by investigating the expression of two PGE(2) receptor isof orms, namely EP2 and EP4. Cyclical variation in endometrial EP2 and EP4 rec eptor mRNA expression was quantified by Taq-Man quantitative RT-PCR using R NA isolated from endometrial tissue collected across the menstrual cycle. N o differences in EP2 receptor mRNA expression were detected; however, EP4 r eceptor mRNA expression was significantly higher in late proliferative stag e (P < 0.05) than in early, mid, and late secretory stage endometrium. Expr ession patterns of EP2 and EP4 receptors were localized by nonradioactive i n situ hybridization using fluorescein isothiocyanate end-labeled oligonucl eotide probes. Expression of both receptors was observed in endometrial gla ndular epithelial and vascular cells, with no notable spatial or temporal v ariation. Finally, signaling of EP2/EP4 receptors was assessed by investiga ting cAMP generation in vitro after stimulation with PGE(2). Endometrial cA MP generation in response to PGE(2) was significantly greater in proliferat ive tissue compared with early and midsecretory stage tissue (3.77 +/- 0.85 vs. 1.96 +/- 0.28 and 1.38 +/- 0.23, respectively; P < 0.05). In conclusio n, this study demonstrates glandular and vascular coexpression of PGE synth ase, PGE(2), EP2, and EP4 receptors and suggests an autocrine/paracrine rol e for PGE(2) in epithelial/endothelial cell function in the human endometri um.