Estradiol-17β, Prostaglandin E2 (PGE2), and the PGE2 Receptor Are Involved in PGE2 Positive Feedback Loop in the Porcine Endometrium

Abstract

Before implantation, the porcine endometrium and trophoblast synthesize elevated amounts of luteoprotective prostaglandin estradiol-17beta (E(2)) (PGE(2)). We hypothesized that embryo signal, E(2), and PGE(2) modulate expression of key enzymes in PG synthesis: PG-endoperoxide synthase-2 (PTGS2), microsomal PGE synthase (mPGES-1), PGF synthase (PGFS), and PG 9-ketoreductase (CBR1) as well as PGE(2) receptor (PTGER2 and -4) expression and signaling within the endometrium. We determined the site of action of PGE(2) in endometrium during the estrous cycle and pregnancy. Endometrial tissue explants obtained from gilts (n = 6) on d 11-12 of the estrous cycle were treated with vehicle (control), PGE(2) (100 nM), E(2) (1-100 nm), or phorbol 12-myristate 13-acetate (100 nm, positive control). E(2) increased PGE(2) secretion through elevating expression of mPGES-1 mRNA and PTGS2 and mPGES-1 protein in endometrial explants. By contrast, E(2) decreased PGFS and CBR1 protein expression. E(2) also stimulated PTGER2 but not PTGER4 protein content. PGE(2) enhanced mPGES-1 and PTGER2 mRNA as well as PTGS2, mPGES-1, and PTGER2 protein expression. PGE(2) had no effect on PGFS, CBR1, and PTGER4 expression and PGF(2alpha) release. Treatment of endometrial tissue with PGE(2) increased cAMP production. Cotreatment with PTGER2 antagonist (AH6809) but not PTGER4 antagonist (GW 627368X) inhibited significantly PGE(2)-mediated cAMP production. PTGER2 protein was localized in luminal and glandular epithelium and blood vessels of endometrium and was significantly up-regulated on d 11-12 of pregnancy. Our results suggest that E(2) prevents luteolysis through enzymatic modification of PG synthesis and that E(2), PGE(2), and endometrial PTGER2 are involved in a PGE(2) positive feedback loop in porcine endometrium.

Novel insights into the mechanisms of pregnancy establishment: regulation of prostaglandin synthesis and signaling in the pig

“…This PGE 2 probably originates from the conceptus and endometrium but not from the CL (Waclawik et al 2008a). The conceptus PGE 2 signal could be amplified by PGE 2 feedback loop only in the gravid horn because of its local regulation (Waclawik et al 2009a).…”

“…It stimulates luteal progesterone secretion directly (Conley & Ford 1989). Indirect action of estrogen involves increasing luteal LH receptor concentration (Garverick et al 1982), decreasing PGF 2a release from uterus into the peripherial circulation , and regulating PG synthesis and signaling in the endometrium (Waclawik et al 2009a) and conceptus (A Waclawik, unpublished observations). Estrogen receptor (ESR) expression in LE and glandular epithelium (GE) of the endometrium (Geisert et al 1993) and in the conceptus (Kowalski et al 2002) coincides with estrogen secretion from the conceptus, suggesting both autocrine and paracrine actions.…”

“…During pregnancy, the endometrium rapidly metabolizes E 2 to estrone sulfate, which is the biologically inactive form and is present in greater amounts in the uterine lumen of pregnant pigs (Flood 1974). Sulfatase enzyme activity of the trophectoderm restores the biological activity of estrogen that results in a localized effect of estrogen to regulate expression of some endometrial genes (Johnson et al 2009, Waclawik et al 2009a.…”

“…Prostaglandins (PGs) play a pivotal role in luteolysis as well as in establishment of pregnancy , McCracken et al 1999, Waclawik et al 2009a. Corpus luteum (CL) regression on days 15-16 of the estrous cycle results from an increase in pulsatile endometrial secretion of prostaglandin F 2a (PGF 2a ) in pigs (Moeljono et al 1977).…”

Expression of the orexin system in the porcine uterus, conceptus and trophoblast during early pregnancy

“…Oestrogens and ovarian progesterone make up the specific hormonal microenvironment (Bazer and Johnson, 2014). The first oestrogens peak (days 10 to 12 of gestation) stimulates prostaglandin E2 (PGE2) synthesis and increases the PGE2/ prostaglandin F2α (PGF2α) ratio (Waclawik et al, 2009), boosts endometrial production of fibroblast growth factor 7 (FGF7), transforming growth factor beta (TGFβ), interleukin-1β, tumour necrosis factor alpha (TNFα), interferon delta (IFND) and interferon gamma (IFNG) (Harney and Bazer, 1989;Ka et al, 2001;Ross et al, 2003;White et al, 2009;Waclawik et al, 2010). The discussed growth factors and cytokines directly influence various genes whose products deliver luteoprotective effects and support conceptus development (Bazer and Johnson, 2014).…”