Agnieszka Waclawik

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

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.

Mechanisms for the Establishment of Pregnancy in the Pig

Establishment of pregnancy in pigs requires continuous function of corpora lutea and endometrial preparation for embryo implantation. Progesterone regulates expression of many proteins necessary for endometrial remodelling and embryo-maternal communications. Attaining the uterine receptivity involves progesterone priming and loss of progesterone receptors in the uterine epithelium before days 10-12 after oestrus. Spermatozoa and oocytes in oviduct alter secretion of specific proteins that exert beneficial effect on gametes and embryos. Moreover, an appropriate leucocyte activation and maintenance of delicate cytokine balance within the oviduct and uterus are important for early pregnancy. This early local immune response is rather mediated by seminal plasma components. These components also influence prostaglandin (PG) synthesis in the oviduct that is important for gamete and embryo transport. Pregnancy establishment requires the biphasic pattern of oestrogen secretion by conceptuses on days 11-12 and 15-30. Conceptus affects lipid signalling system consisting of prostaglandins and lysophosphatic acid. PG synthesis is changed by conceptus signals in favour of luteoprotective PGE(2) . Additionally, existence of PGE(2) positive feedback loop in the endometrium contributes to increased PGE(2) /PGF(2α) ratio during the peri-implantation period. PGE(2) through endometrial PGE(2) receptor (PTGER2) elevates the expression of enzymes involved in PGE(2) synthesis. Higher PGE(2) secretion in uterine lumen coincides with the elevated expression of HOXA10 transcription factor critical for implantation. A stable adhesion between conceptus and endometrium requires reduction in mucin-1 on the apical surface of epithelium and integrin activation by extracellular matrix proteins. Furthermore, growth factors, cytokines and its receptors are involved in embryo-maternal interactions.

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

Ovarian progesterone induces essential changes leading to a temporary state of uterine receptivity for conceptus implantation. Estrogens secreted by the porcine conceptus on days 11 and 12 of pregnancy provide the initial signal for maternal recognition of pregnancy and maintenance of a functional corpus luteum (CL) for continued production of progesterone. As prostaglandins F(2)(α) (PGF(2)(α)) and E(2) (PGE(2)) exert opposing actions on the CL, a tight control over their synthesis and secretion is critical either for the initiation of luteolysis or maintenance of pregnancy. One of the supportive mechanisms by which conceptus inhibits luteolysis is changing PG synthesis in favor of luteoprotective PGE(2). Conceptus PGE(2) could be amplified by PGE(2) feedback loop in the endometrium. In pigs, as in other species, implantation and establishment of pregnancy is associated with upregulation of expression of proinflammatory factors, which include cytokines, growth factors, and lipid mediators. The conceptus produces inflammatory mediators: interferon γ and interferon δ, interleukins IL1B and IL6, and PGs, which probably activate inflammatory pathways in the endometrium. The endometrium responds to these embryonic signals by enhancing further progesterone-induced uterine receptivity. Understanding the mechanisms of pregnancy establishment is required for translational research to increase reproductive efficiencies and fertility in humans and animals.

Differential expression of prostaglandin (PG) synthesis enzymes in conceptus during peri-implantation period and endometrial expression of carbonyl reductase/PG 9-ketoreductase in the pig

Prostaglandins (PGs) play a pivotal role in luteolysis, maternal recognition of pregnancy, and implantation. In many species, including pigs, both conceptus (embryo and associated membranes) and endometrium synthesize PGE(2), which may antagonize PGF(2alpha) by playing a luteotropic/antiluteolytic role. Previously, we have reported expression profiles of PG G/H synthases (PGHS-1 and PGHS-2), PGE synthase (mPGES-1), and PGF synthase (PGFS) in the endometrium of cyclic and pregnant pigs. In the present study, expression of above-mentioned PG synthesis enzymes and PG 9-ketoreductase (CBR1), which converts PGE(2) into PGF(2alpha), and the PGE(2)/PGF(2alpha) ratios were investigated in porcine peri- and post-implantation conceptuses. Furthermore, expression of CBR1 was examined in the endometrium. PGHS-2 and mPGES-1 were upregulated, and PGHS-1, PGFS, and CBR1 were downregulated in conceptuses during trophoblastic elongation. A second increase of mPGES-1 mRNA occurred after days 20-21 of pregnancy. After initiation of implantation, expression of PGHS-1, PGFS, and CBR1 in conceptuses increased and remained higher until days 24-25 of pregnancy. Comparison of the endometrial CBR1 protein expression in cyclic and pregnant gilts revealed upregulation on days 16-17 of the cycle and downregulation on days 10-11 of pregnancy. In conclusion, reciprocal expression of PGHS-2, mPGES-1, PGFS, and CBR1 in day 10-13 conceptuses and decrease of endometrial CBR1 may be important in increasing the PGE(2)/PGF(2alpha) ratio during maternal recognition of pregnancy. This study indicates that PGE(2) produced via PGHS-2 and mPGES-1 in conceptus may be involved in corpus luteum control. Moreover, high expression of conceptus PGHS-1, mPGES-1, PGFS, and CBR1 after initiation of implantation suggests their significant role in placentation.

Oxytocin and tumor necrosis factor α stimulate expression of prostaglandin E2 synthase and secretion of prostaglandin E2 by luminal epithelial cells of the porcine endometrium during early pregnancy

Oxytocin (OXT) and tumor necrosis factor α (TNF) have been implicated in the control of luteolysis by stimulating endometrial secretion of luteolytic prostaglandin F(2α) (PGF(2α)). Nevertheless, OXT concentration in porcine uterine lumen increases markedly on days 11-12 of pregnancy, and TNF is expressed in endometrium during pregnancy. The objective of the study was to determine the effect of OXT and TNF on expression of the enzymes involved in PG synthesis: PG-endoperoxide synthase 2 (PTGS2), PGE(2) synthase (mPGES-1) and PGF synthase, and PGE(2) receptor (PTGER2), as well as on PG secretion by endometrial luminal epithelial cells (LECs) on days 11-12 of the estrous cycle and pregnancy. LECs isolated from gilts on days 11-12 of the estrous cycle (n=8) and pregnancy (n=7) were treated with OXT (100  nmol/l) and TNF (0.6  nmol/l) for 24  h. OXT increased PTGS2 mRNA and mPGES-1 protein contents, as well as PGE(2) secretion but only on days 11-12 of pregnancy. TNF stimulated PTGS2 and mPGES-1 mRNA, as well as mPGES-1 protein expression and PGE(2) release on days 11-12 of pregnancy and the estrous cycle. In addition, expressions of PTGER2 and PTGER4 were determined in corpus luteum (CL). Abundance of PTGER2 mRNA and PTGER4 protein in CL was upregulated on day 14 of pregnancy versus day 14 of the estrous cycle. This study indicates that TNF and OXT regulate PGE(2) synthesis in LECs during early pregnancy. PGE(2) secreted by LECs, after reaching ovaries, could have a luteoprotective effect through luteal PTGER2 and PTGER4, or may directly promote uterine function and conceptus development.

Conceptus Signals for Establishment and Maintenance of Pregnancy in Pigs : Lipid Signaling System

Establishment of pregnancy in pigs requires estrogen secretion by the conceptus. The developmental changes of embryo before implantation and embryo-uterine cross talk are dependent on various biological molecules secreted by the endometrium and conceptus. An integral part of maternal recognition of pregnancy seems to be also the lipid signaling system consisting of prostaglandin (PG) F2 alpha and E2 and/or lysophosphatic acid (LPA). The downstream enzymes in PG synthesis pathway are: microsomal PGE synthase-1 (mPGES-1), PGF synthase (PGFS) and prostaglandin 9-ketoreductase/carbonyl reductase (CBR1) which catalyzes conversion of PGE 2 into PGF2 alpha. In contrast to mPGES-1, endometrial PGFS is highly increased on days 13-15 similarly as CBR1 on days 16-17 of the estrous cycle. Potential mechanism by which a conceptus inhibits luteolysis is changing the PGE2/PGF2 alpha ratio in favor of PGE2. It may be result of high expression of mPGES-1 in trophoblast and endometrium on days 10-13 of pregnancy and simultaneously the down-regulation of PGFS and CBR1 in conceptuses during this period. The conceptus can alter expression of endometrial CBR1 to modulate the PGE2/PGF2 alpha ratio in the uterus during the maternal recognition of pregnancy. High expression of conceptus and endometrial terminal PG synthases and CBR1 after initiation of blastocyst attachment suggest their involvement in early placentation. The higher LPA3 receptor mRNA expression during the early pregnancy compared to corresponding period of estrous cycle could indicate an important role of LPA and its receptor during the peri-implantation stage of pregnancy in pigs. Above results suggest that the lipid signaling system is an integral part of establishment and maintenance of pregnancy in the pig.

Expression of prostaglandin synthesis pathway enzymes in the porcine corpus luteum during the oestrous cycle and early pregnancy

Prostaglandins (PGs) of luteal origin may have paracrine and/or autocrine actions on the functions of the corpus luteum (CL). Previously, we have shown that enzymes of PG synthesis pathway such as prostaglandin E synthase (mPGES-1), prostaglandin F synthase (PGFS) and prostaglandin 9-ketoreductase (CBR1) are important in regulation of PG production in the conceptuses and endometrium of cyclic and pregnant pigs. Therefore, localization and expression patterns of these enzymes were determinated in porcine CL. The PGFS protein content was lower in metestrus and higher around luteolysis, and then decreased in late regressing CL. PGFS protein levels were lower on days 5-8 of pregnancy and did not differ between days 10 and 25. Elevated expression of mPGES-1 mRNA was found in early luteal phase. The mPGES-1 protein content, similarly to PGFS, was higher during luteolysis. mPGES-1 mRNA and protein levels were constant between days 5 and 25 of pregnancy. PGFS and mPGES-1 expression was down-regulated on days 16-17 of the oestrous cycle when compared to the corresponding days of pregnancy. Enhanced mPGES-1/PGFS ratio occurred during early luteal phase and days 5-8 of pregnancy. Expression of CBR1 mRNA and protein was constant during the cycle and pregnancy. Our studies revealed higher mPGES-1/PGFS ratios in the CL during early luteal phase and corresponding days of pregnancy that could favor PGE(2) synthesis and may be important in the control of luteal development. However, PG synthesis in the endometrium/conceptus rather than in the CL could be involved in luteolysis and maternal recognition of pregnancy in pigs.

The influence of embryo presence on prostaglandins synthesis and prostaglandin E2 and F2α content in corpora lutea during periimplantation period in the pig

We determined the expression of PGE2 synthase (mPGES‐1), PGF synthase (PGFS), carbonyl reductase/prostaglandin 9‐ketoreductase (CBR1) genes and the content of PGE2, PGF2α in porcine corpora lutea on Days 12–14 of pregnancy and Days 12–14 of the estrous cycle. For this study we used a surgically‐generated model in which one of the uterine horns was cut transversely and a part of this horn was detached from the uterine corpus. The expression of mPGES‐1, PGFS, and CBR1 genes and mPGES‐1/PGFS ratio were significantly higher in corpora lutea of the pregnant gilts compared to the corpora lutea from the parallel ovaries of the cyclic gilts. There was no difference in mPGES‐1, PGFS, CBR1 genes expression and mPGES‐1/PGFS ratio between corpora lutea ipsi‐(CL1) and contralateral (CL2) to the uterine horn with the developing embryos. The highest content of PGE2 was found in CL1 of the pregnant gilts. The PGE2/PGF2α ratio was significantly higher in CL1 of the pregnant gilts compared to corpora lutea from parallel ovary of the cyclic gilts. We suggest that the activity of the investigated genes is induced by compounds of embryonic origin which are not distributed only to the ipsilateral ovary but are transported within the mesometrium to both ovaries in a more systemic manner. Mol. Reprod. Dev. 75: 1208–1216, 2008.

Targeted Ablation of Prostate Carcinoma Cells Through LH Receptor Using Hecate-CGβ Conjugate: Functional Characteristic and Molecular Mechanism of Cell Death Pathway

A Hecate-CGβ conjugate (lytic peptide and β-chorionic gonadotropin) selectively destroyed cells possessing LH receptors. This study described functional characteristics of the conjugate and the molecular mechanism of the cell death pathway in prostate cancer cells. Based on in vitro studies, we conclude that the conjugate kills cells possessing luteinizing hormone receptors (LHR) faster than Hecate alone. Competitive studies have shown that blocking of LHR by preincubation with chorionic gonadotropin (100 ng/ml) reduced toxicity of the conjugate in low concentrations. Further studies have also shown that the conjugate in treated cells both did not induce internucleosomal DNA fragmentation and did not induce morphological changes in cells characterized as having apoptotic features. These results proved that cells died by necrosis rather than apoptosis after the conjugate treatment.

Effect of estrus induction on prostaglandin content and prostaglandin synthesis enzyme expression in the uterus of early pregnant pigs.

Prostaglandins (PGs) play a pivotal role in maternal recognition of pregnancy and implantation in pigs. In the present study, PGE(2), PGF(2alpha), and PGFM (PGF(2alpha) metabolite) content, as well as PGE(2) synthase (mPGES-1) and PGF(2alpha) synthase (PGFS) expression was investigated in early pregnant gilts with natural (n=21) and PMSG/hCG-stimulated (n=19) estrus. Endometrial tissue samples, uterine luminal flushings (ULFs), and blood serum were collected on days 10-11, 12, and 15 after insemination. Additionally, day 15 conceptuses were collected for mPGES-1 and PGFS protein expression. Effect of estrus induction was observed on day 15 of pregnancy, when the content of PGE(2) in the uterine lumen was fourfold lower in gonadotropin-stimulated gilts in comparison to controls (P<0.001). Decreased PGE(2) content in ULFs of gonadotropin-treated pigs was preceded by lower endometrial mPGES-1 gene expression in hormonally-stimulated animals in comparison to control gilts (P<0.01). On the other hand, estrus induction with PMSG/hCG resulted in higher PGE(2) accumulation in the endometrial tissue on day 15 of pregnancy (P<0.01). Furthermore, PGF(2alpha) content in the endometrium and PGFM levels in blood serum were lower in gonadotropin-treated gilts, especially on day 12 after insemination when compared to control gilts (P<0.01). Finally, PGFS expression in day 15 conceptuses was decreased in animals with hormonally-induced estrus. We conclude that PMSG/hCG stimulation of prepubertal gilts to induce estrus results in changes of PG production and secretion during early pregnancy, which, in turn, may affect conceptus development, implantation, and the course of pregnancy.