Prostaglandin E2 receptor subtype EP2 gene expression in the mouse uterus coincides with differentiation of the luminal epithelium for implantation

Maternal recognition of pregnancy in the pig: A servomechanism involving sex steroids, cytokines and prostaglandins

Maternal recognition of pregnancy (MRP) is a term utilized in mammals to describe pathways in which the conceptus alters the endometrial environment to prevent regression of corpora lutea to ensure continued production of progesterone (P4) required for establishment and maintenance of pregnancy. For nearly 40 years after publication of the endocrine/exocrine theory, conceptus estrogen (E2) was considered the primary maternal recognition signal in the pig. Conceptus production of prostaglandin E2 (PGE2) was also considered to be a major factor in preventing luteolysis. An addition to E2 and PGE2, pig conceptuses produce interleukin 1B2 (IL1B2) and interferons (IFN) delta (IFND) and gamma (IFNG). The present review provides brief history of the discovery of E2, PGs and IFNS which led to research investigating the role of these conceptus secreted factors in establishing and maintaining pregnancy in the pig. The recent utilization of gene editing technology allowed a more direct approach to investigate the in vivo roles of IL1B2, E2, PGE2, AND IFNG for establishment of pregnancy. These studies revealed unknown functions for IFNG and ILB2 in addition to PGE2 and E2. Thus, pregnancy recognition signal is via a servomechanism in requiring sequential effects of P4, E2, IL1B2, PGE2 and IFNG. Results indicate that the original established dogma for the role of conceptus E2 and PGs in MRP is a far too simplified model that involves the interplay of numerous mechanisms for inhibiting luteolysis, inducing critical elongation of the conceptuses and resolution of inflammation in pigs.

The endometrial transcriptome transition preceding receptivity to embryo implantation in mice

BACKGROUND

Receptivity of the uterus is essential for embryo implantation and progression of mammalian pregnancy. Acquisition of receptivity involves major molecular and cellular changes in the endometrial lining of the uterus from a non-receptive state at ovulation, to a receptive state several days later. The precise molecular mechanisms underlying this transition and their upstream regulators remain to be fully characterized. Here, we aimed to generate a comprehensive profile of the endometrial transcriptome in the peri-ovulatory and peri-implantation states, to define the genes and gene pathways that are different between these states, and to identify new candidate upstream regulators of this transition, in the mouse.

RESULTS

High throughput RNA-sequencing was utilized to identify genes and pathways expressed in the endometrium of female C57Bl/6 mice at estrus and on day 3.5 post-coitum (pc) after mating with BALB/c males (n = 3-4 biological replicates). Compared to the endometrium at estrus, 388 genes were considered differentially expressed in the endometrium on day 3.5 post-coitum. The transcriptional changes indicated substantial modulation of uterine immune and vascular systems during the pre-implantation phase, with the functional terms Angiogenesis, Chemotaxis, and Lymphangiogenesis predominating. Ingenuity Pathway Analysis software predicted the activation of several upstream regulators previously shown to be involved in the transition to receptivity including various cytokines, ovarian steroid hormones, prostaglandin E2, and vascular endothelial growth factor A. Our analysis also revealed four candidate upstream regulators that have not previously been implicated in the acquisition of uterine receptivity, with growth differentiation factor 2, lysine acetyltransferase 6 A, and N-6 adenine-specific DNA methyltransferase 1 predicted to be activated, and peptidylprolyl isomerase F predicted to be inhibited.

CONCLUSIONS

This study confirms that the transcriptome of a receptive uterus is vastly different to the non-receptive uterus and identifies several genes, regulatory pathways, and upstream drivers not previously associated with implantation. The findings will inform further research to investigate the molecular mechanisms of uterine receptivity.

Targeting EP2 Receptor for Drug Discovery: Strengths, Weaknesses, Opportunities, and Threats (SWOT) Analysis

Cyclooxygenase-1 and -2 (COX1 and COX2) derived endogenous ligand prostaglandin-E2 (PGE2) triggers several physiological and pathological conditions. It mediates signaling through four G-protein coupled receptors, EP1, EP2, EP3, and EP4. Among these, EP2 is expressed throughout the body including the brain and uterus. The functional role of EP2 has been extensively studied using EP2 gene knockout mice, cellular models, and selective small molecule agonists and antagonists for this receptor. The efficacy data from in vitro and in vivo animal models indicate that EP2 receptor is a major proinflammatory mediator with deleterious functions in a variety of diseases suggesting a path forward for EP2 inhibitors as the next generation of selective anti-inflammatory and antiproliferative agents. Interestingly in certain diseases, EP2 action is beneficial; therefore, EP2 agonists seem to be clinically useful. Here, we highlight the strengths, weaknesses, opportunities, and potential threats (SWOT analysis) for targeting EP2 receptor for therapeutic development for a variety of unmet clinical needs.

Embryo-derive TNF promotes decidualization via fibroblast activation

Decidualization is a process in which endometrial stromal fibroblasts differentiate into specialized secretory decidual cells and essential for the successful establishment of pregnancy. The underlying mechanism during decidualization still remains poorly defined. Because decidualization and fibroblast activation share similar characteristics, this study was to examine whether fibroblast activation is involved in decidualization. In our study, fibroblast activation-related markers are obviously detected in pregnant decidua and under in vitro decidualization. ACTIVIN A secreted under fibroblast activation promotes in vitro decidualization. We showed that arachidonic acid released from uterine luminal epithelium can induce fibroblast activation and decidualization through PGI₂ and its nuclear receptor PPARδ. Based on the significant difference of fibroblast activation-related markers between pregnant and pseudopregnant mice, we found that embryo-derived TNF promotes CPLA_2α phosphorylation and arachidonic acid release from luminal epithelium. Fibroblast activation is also detected under human in vitro decidualization. Similar arachidonic acid-PGI₂-PPARδ-ACTIVIN A pathway is conserved in human endometrium. Collectively, our data indicate that embryo-derived TNF promotes CPLA_2α phosphorylation and arachidonic acid release from luminal epithelium to induce fibroblast activation and decidualization.

Fractalkine Improves the Expression of Endometrium Receptivity-Related Genes and Proteins at Desferrioxamine-Induced Iron Deficiency in HEC-1A Cells

Fractalkine (CX3CL1/FKN) is a unique chemokine belonging to the CX3C chemokine subclass. FKN exists in two forms: a membrane-bound form expressed by both endometrium cells and trophoblasts thought to be implicated in maternal-fetal interaction and a soluble form expressed by endometrium cells. Endometrium receptivity is crucial in embryo implantation and a complex process regulated by large numbers of proteins, e.g., cytokines, progesterone receptor (PR), SOX-17, prostaglandin receptors (PTGER2), and tissue inhibitors of metalloproteinases (TIMPs). It has also been reported that iron is important in fertility and affects the iron status of the mother. Therefore, iron availability in the embryo contributes to fertilization and pregnancy. In this study, we focused on the effect of iron deficiency on the secreted cytokines (IL-6, IL-1β, leukocyte inhibitory factor, TGF-β), chemokines (IL-8, FKN), and other regulatory proteins (bone morphogenic protein 2, activin, follistatin, PR, SOX-17, prostaglandin E2 receptor, TIMP2), and the modifying effect of FKN on the expression of these proteins, which may improve endometrium receptivity. Endometrial iron deficiency was mediated by desferrioxamine (DFO) treatment of HEC-1A cells. FKN was added to the cells 24 h and 48 h after DFO with or without serum for modelling the possible iron dependence of the alterations. Our findings support the hypothesis that FKN ameliorates the effects of anemia on the receptivity-related genes and proteins in HEC-1A cells by increasing the secretion of the receptivity-related cytokines via the fractalkine receptor (CX3CR1). FKN may contribute to cell proliferation and differentiation by regulating activin, follistatin, and BMP2 expressions, and to implantation by altering the protein levels of PR, SOX-17, PTGER2, and TIMP2. FKN mitigates the negative effect of iron deficiency on the receptivity-related genes and proteins of HEC-1A endometrium cells, suggesting its important role in the regulation of endometrium receptivity.

In the mouse, prostaglandin D2 signalling protects the endometrium against adenomyosis

Adenomyosis is characterised by epithelial gland and mesenchymal stroma invasion of the uterine myometrium. Adenomyosis is an oestrogen-dependent gynaecological disease in which a number of factors, such as inflammatory molecules, prostaglandins (PGs), angiogenic factors, cell proliferation and extracellular matrix remodelling proteins, also play a role as key disease mediators. In this study, we used mice lacking both lipocalin and hematopoietic-PG D synthase (L- and H-Pgds) genes in which PGD2 is not produced to elucidate PGD2 roles in the uterus. Gene expression studied by real-time PCR and hormone dosages performed by ELISA or liquid chromatography tandem mass spectroscopy in mouse uterus samples showed that components of the PGD2 signalling pathway, both PGDS and PGD2-receptors, are expressed in the mouse endometrium throughout the oestrus cycle with some differences among uterine compartments. We showed that PGE2 production and the steroidogenic pathway are dysregulated in the absence of PGD2. Histological analysis of L/H-Pgds-/- uteri, and immunohistochemistry and immunofluorescence analyses of proliferation (Ki67), endothelial cell (CD31), epithelial cell (pan-cytokeratin), myofibroblast (α-SMA) and mesenchymal cell (vimentin) markers, identify that 6-month-old L/H-Pgds-/- animals developed adenomyotic lesions, and that disease severity increased with age. In conclusion, this study suggests that the PGD2 pathway has major roles in the uterus by protecting the endometrium against adenomyosis development. Additional experiments, using for instance transcriptomic approaches, are necessary to fully determine the molecular mechanisms that lead to adenomyosis in L/H-Pgds-/- mice and to confirm whether this strain is an appropriate model for studying the human disease.

Differential Signals From TNFα-Treated and Untreated Embryos in Uterine Tissues and Splenic CD4+ T Lymphocytes During Preimplantation Pregnancy in Mice

The main aim of this study was to examine if a female mouse body in preimplantation pregnancy can distinguish between embryos of normal and impaired biological quality in the local and peripheral compartments. Normal (control group) and TNFα (tumor necrosis factor-α)-treated embryos (experimental group) at the morula stage were non-surgically transferred into the uteri of CD-1 strain [Crl:CD1(Icr)] female murine recipients. Twenty-four hours after the embryo transfer, females were euthanised, and uteri and spleens were dissected. In uterine tissues (local compartment), we assessed the expression of 84 genes comprising nine signal transduction pathways, using a modified RT² Profiler PCR Array. In the spleen (peripheral compartment), we determined the proteome of splenic CD4⁺ lymphocytes using 2D protein electrophoresis with subsequent protein identification by mass spectrometry. Sample clustering and differential gene expression analyses within individual signal transduction pathways revealed differential expression of genes in the uteri of females after transplantation of normal vs. TNFα-treated embryos. The most affected signal transduction cascade was the NFKB (Nuclear factor NF-kappa-B) pathway, where 87.5% of the examined genes were significantly differentially expressed. Proteomic analysis of splenic CD4⁺ T lymphocytes revealed significant differential expression of 8 out of 132 protein spots. Identified proteins were classified as proteins influenced by cell stress, proteins engaged in the regulation of cytoskeleton stabilization and cell motility, and proteins having immunomodulatory function. These results support the hypothesis that even before embryo implantation, the body of pregnant female mice can sense the biological quality of an embryo both at the local and peripheral level.

Molecules and Prostaglandins Related to Embryo Tolerance

It is generally understood that the entry of semen into the female reproductive tract provokes molecular and cellular changes facilitating conception and pregnancy. We show a broader picture of the participation of prostaglandins in the fertilization, implantation and maintenance of the embryo. A large number of cells and molecules are related to signaling networks, which regulate tolerance to implantation and maintenance of the embryo and fetus. In this work, many of those cells and molecules are analyzed. We focus on platelets, polymorphonuclear leukocytes, and group 2 innate lymphoid cells involved in embryo tolerance in order to have a wider view of how prostaglandins participate. The combination of platelets and neutrophil extracellular traps (Nets), uterine innate lymphoid cells (uILC), Treg cells, NK cells, and sex hormones have an important function in immunological tolerance. In both animals and humans, the functions of these cells can be regulated by prostaglandins and soluble factors in seminal plasma to achieve an immunological balance, which maintains fetal-maternal tolerance. Prostaglandins, such as PGI2 and PGE2, play an important role in the suppression of the previously mentioned cells. PGI2 inhibits platelet aggregation, in addition to IL-5 and IL-13 expression in ILC2, and PGE2 inhibits some neutrophil functions, such as chemotaxis and migration processes, leukotriene B4 (LTB4) biosynthesis, ROS production, and the formation of extracellular traps, which could help prevent trophoblast injury and fetal loss. The implications are related to fertility in female when seminal fluid is deposited in the vagina or uterus.

A Review of Prostanoid Receptors: Expression, Characterization, Regulation, and Mechanism of Action

Prostaglandin signaling controls a wide range of biological processes from blood pressure homeostasis to inflammation and resolution thereof to the perception of pain to cell survival. Disruption of normal prostanoid signaling is implicated in numerous disease states. Prostaglandin signaling is facilitated by G-protein-coupled, prostanoid-specific receptors and the array of associated G-proteins. This review focuses on the expression, characterization, regulation, and mechanism of action of prostanoid receptors with particular emphasis on human isoforms.

Prostaglandin E Pathway in Uterine Tissue During Window of Preimplantation in Female Mice Mated With Intact and Seminal Vesicle-Excised Male

Prostaglandin E₂ (PGE₂) has been introduced as an important factor for embryo implantation. So the present study was carried out to evaluate the effect of seminal fluid (SF) on PGE₂ pathway in uterus tissues of mice during window of preimplantation. The messenger RNA (mRNA) expressions of microsomal PGE synthase (mPGES) and cytosolic PGE synthase (cPGES) as well as protein expression of PGE receptor 2 and 4 (EP2 and EP4) were determined in uterine tissue of control and seminal vesicle-excised (SVX)-mated female mice during days 1 to 5 of pregnancy using real-time polymerase chain reaction (qRT-PCR) and Western blotting, respectively. We found that mRNA expression of mPGES at day 1 and 2 of pregnancy was significantly higher in the control group than the SVX-mated group ( P < .05), but such result was not obtained for cPGES expression. The protein levels of EP2 at day 1 to 4 of pregnancy were significantly higher in the control group compared with the SVX-mated group ( P < .05), also the EP4 levels were significantly different between the control and SVX-mated groups at the first day of pregnancy ( P < .05). Implantation rate was higher in the control group and also there were positive correlations between mPGES and EP2 expressions in the fifth day of pregnancy with implantation rate. Our results demonstrated significant effect of SF on uterine expressions of the evaluated factors, especially mPGES and EP2. Regarding the correlations between levels of these factors and implantation rate, we suggest that possibly one of the important mechanisms of SF in affecting female pregnancy is through mPGES and EP2.

Prostaglandin receptors EP and FP are regulated by estradiol and progesterone in the uterus of ovariectomized rats

BACKGROUND

Prostaglandins are important for female reproduction. Prostaglandin-E2 acts via four different receptor subtypes, EP1, EP2, EP3 and EP4 whereas prostaglandin-F2alpha acts through FP. The functions of prostaglandins depend on the expression of their receptors in different uterine cell types. Our aim was to investigate the expression of EPs and FP in rat uterus and to identify the regulation by estradiol, progesterone and estrogen receptor (ER) selective agonists.

METHODS

We performed four different rat experiments involving treatments with estradiol, progesterone and ER agonists. Real-time PCR and immunohistochemistry were employed to evaluate receptor expression.

RESULTS

Our results showed that all mRNAs and proteins of EPs and FP are expressed in the rat uterus. The expression pattern and intensity of immunostaining vary between different cell types and treatments. The mRNA expression of all EPs and FP are downregulated by estradiol and the ERalpha specific agonist PPT, whereas the ERbeta specific agonist DPN downregulates only EP2 and EP4. The protein expression however, showed an increase in EP2 and EP3 after estradiol treatment. When treated with estradiol and progesterone in combination, the expressions of EP1 and EP3 are upregulated.

CONCLUSIONS

Regulation of EPs and FP expression by estradiol appears to be mainly modulated via ERalpha for EP1, EP3 and FP, while EP2 and EP4 also are affected by the ERbeta selective ligand. Our immunohistochemical data shows a cell specific regulation of prostaglandin receptors under the influence of ovarian steroids, where EP2 is estrogen regulated in all uterine tissues examined. EP1 and EP3 are upregulated by the combination of estradiol and progesterone. Thus, our observations indicate that estradiol and progesterone regulate the mRNA and protein expression of EPs and FP in a receptor and tissue specific way.

Role of secretory protease inhibitor SPINK3 in mouse uterus during early pregnancy

Successful embryo implantation depends on intricate epithelial-stromal cross-talk. However, molecular modulators involved in this cellular communication remain poorly elucidated. Using multiple approaches, we have investigated the spatiotemporal expression and regulation of serine protease inhibitor Kazal type 3 (SPINK3) in mouse uterus during the estrous cycle and early pregnancy. In cycling mice, both SPINK3 mRNA and protein are only expressed during proestrus. In the pregnant mouse, the expression levels of both SPINK3 mRNA and protein increase on days 5-8 and then decline. Spink3 mRNA is expressed exclusively in the uterine glandular epithelium, whereas SPINK3 protein is localized on the surface of both luminal and glandular epithelium and in the decidua. Moreover, SPINK3 in the decidua has been observed in the primary decidual zone on day 6 and the secondary decidual zone on days 7-8; this is tightly associated with the progression of decidualization. SPINK3 has also been found in decidual cells of the artificially decidualized uterine horn but not control horn, whereas Spink3 mRNA localizes in the glands of both horns. The expression of endometrial Spink3 is not regulated by the blastocyst according to its expression pattern during pseudopregnancy and delayed implantation but is induced by progesterone and further augmented by a combination of progesterone and estrogen in ovariectomized mice. Thus, uterine-gland-derived SPINK3, as a new paracrine modulator, might play an important role in embryo implantation through its influence on stromal decidualization in mice.

Expression and regulation of lanosterol 14alpha-demethylase in mouse embryo and uterus during the peri-implantation period

Lanosterol 14alpha-demethylase (LDM) is expressed ubiquitously in all mammals and is important in cholesterol biosynthesis. However, whether LDM expression is involved in the interaction between uterus and embryo during implantation remains unknown. In the present study, the expression of LDM was investigated in mouse embryo and uterus during the peri-implantation period using confocal microscopy, immunohistochemistry and western blot methods. Further, regulation of LDM expression was investigated in pseudopregnancy, delayed implantation, artificial decidualisation and ovariectomisation using 17beta-oestradiol and progesterone treatment mouse models. The results showed that LDM was selectively expressed in preimplantation embryos and the uterine subluminal stroma surrounding the implanting blastocyst on Day 5 of pregnancy. No corresponding signal was detected in the uterus on Day 5 of pseudopregnancy. Most notably, once delayed implantation was terminated by oestrogen treatment and the embryo implanted, a high level of LDM expression was induced in the subluminal stroma surrounding the implanting blastocyst, whereas no corresponding signal was detected in the delayed implantation uterus. A high level of LDM expression was observed in the uterus decidua on Days 6-8 of pregnancy. Furthermore, LDM expression was induced in the uterine stroma under artificial decidualisation. Oestrogen, but not progesterone, treatment induced a high level of LDM expression in the uterus of ovariectomised mice. These results indicate that LDM is closely related to mouse embryo implantation and can be upregulated by oestrogen.

Progesterone regulation of glutathione S-transferase Mu2 expression in mouse uterine luminal epithelium during preimplantation period

OBJECTIVE

To investigate the differential expression and regulation of Gstm2 in mouse uterus during early pregnancy.

DESIGN

Experimental animal study.

SETTING

University research laboratory.

ANIMAL(S)

Sexually mature female Kunming white strain mice.

INTERVENTION(S)

Delayed and activated implantation, pseudopregnancy, hormonal treatment.

MAIN OUTCOME MEASURE(S)

The expression of Gstm2 mRNA was detected by in situ hybridization and reverse-transcription polymerase chain reaction (RT-PCR).

RESULT(S)

By in situ hybridization, there were a low level of Gstm2 expression in luminal epithelium on day 3 and a strong level in the luminal epithelium on day 4 during early pregnancy. The expression pattern of Gstm2 in the pseudopregnant uterus was similar to that during early pregnancy. By RT-PCR, Gstm2 was strongly detected in the uteri on days 3 and 4 of pregnancy and pseudopregnancy. Gstm2 expression was strongly detected in the luminal epithelium under delayed implantation, but not seen after delayed implantation was activated by estrogen. In the ovariectomized mouse uterus, Gstm2 expression was strongly up-regulated by progesterone via progesterone receptor.

CONCLUSION(S)

The results showed that Gstm2 was highly expressed in the uterine luminal epithelium during preimplantation period and up-regulated by progesterone.

Differential expression and regulation of prostaglandin transporter and metabolic enzymes in mouse uterus during blastocyst implantation

OBJECTIVE

To examine the spatiotemporal expression and regulation of prostaglandin transporter (PGT), 15-hydroxy-PG dehydrogenase (15-PGDH), and carbonyl reductase 1 (CBR1) messenger RNA (mRNA) and protein in the mouse uterus during embryo implantation and in related models.

DESIGN

Experimental animal study.

SETTING

University research laboratory.

ANIMAL(S)

Sexually mature female Kunming strain white mice.

INTERVENTION(S)

Delayed and activated implantation, artificial decidualization, and subcutaneous injection of progesterone (P) and E(2) in ovariectomized mouse.

MAIN OUTCOME MEASURE(S)

The expression of mRNA and protein were detected by in situ hybridization and immunohistochemistry in mouse uterus.

RESULT(S)

Prostaglandin transporter mRNA and protein were expressed in the subluminal stroma at implantation site on day 5 of pregnancy and then in decidua but were not detected at the interimplantation sites and in preimplantation or pseudopregnant uterus. The presence of an active blastocyst was required for PGT expression at the implantation site. Both 15-PGDH and CBR1 mRNA were detected in glandular epithelium on day 4 of pregnancies. The expression of 15-PGDH and CBR1 mRNA was also detected in postimplantation embryos.

CONCLUSION(S)

These data suggest that differentially expressed PGT and 15-PGDH may participate in PG signaling in mouse uterus during implantation and decidualization.

Expression of mouse membrane-associated prostaglandin E2 synthase-2 (mPGES-2) along the urogenital tract

Prostaglandin E(2) (PGE(2)) is the most common prostanoid and has a variety of bioactivities including a crucial role in urogenital function. Multiple enzymes are involved in its biosynthesis. Among 3 PGE(2) terminal synthetic enzymes, membrane-associated PGE(2) synthase-2 (mPGES-2) is the most recently identified, and its role remains uncharacterized. In previous studies, membrane-associated PGE(2) synthase-1 (mPGES-1) and cytosolic PGE(2) synthase (cPGES) were reported to be expressed along the urogenital tracts. Here we report the genomic structure and tissue distribution of mPGES-2 in the urogenital system. Analysis of several bioinformatic databases demonstrated that mouse mPGES-2 spans 7 kb and consists of 7 exons. The mPGES-2 promoter contains multiple Sp1 sites and a GC box without a TATA box motif. Real-time quantitative PCR revealed that constitutive mPGES-2 mRNA was most abundant in the heart, brain, kidney and small intestine. In the urogenital system, mPGES-2 was highly expressed in the renal cortex, followed by the renal medulla and ovary, with lower levels in the ureter, bladder and uterus. Immunohistochemistry studies indicated that mPGES-2 was ubiquitously expressed along the nephron, with much lower levels in the glomeruli. In the ureter and bladder, mPGES-2 was mainly localized to the urothelium. In the reproductive system, mPGES-2 was restricted to the epithelial cells of the testis, epididymis, vas deferens and seminal vesicle in males, and oocytes, stroma cells and corpus luteum of the ovary and epithelial cells of the oviduct and uterus in females. This expression pattern is consistent with an important role for mPGES-2-mediated PGE(2) in urogenital function.

Temporal expression profiling of the uterine luminal epithelium of the pseudo-pregnant mouse suggests receptivity to the fertilized egg is associated with complex transcriptional changes

BACKGROUND

The molecular basis of changes underlying the altered sensitivity of the uterine luminal epithelium (LE) to the embryo over the peri-implantation period is not fully understood.

METHODS

Microarray analysis was performed on purified LE isolated from the pseudo-pregnant mouse uterus at 12-h intervals from pre-receptivity through the implantation window to refractoriness. The aim was to identify genes whose expression changes in the LE during this period.

RESULTS

A total of 447 transcripts were identified whose abundance changed more than 2-fold in the LE but which did not change in the underlying stroma (S) and glands. Six major patterns of changing expression were noted. Of the 447 genes, 140 were expressed in LE at least 15-fold higher than in S and glandular epithelium (GE) (101 of these more than 20-fold). Detailed spatiotemporal expression profiles were derived for several genes previously implicated in implantation (including Edg7, Ptgs1, Pla2g4a and Alox15).

CONCLUSIONS

Functional changes in LE receptivity are characterized by changing constellations of gene expression. Pre-receptivity has a different molecular footprint to refractoriness. Because we have used the pseudo-pregnant mouse model, these changes are driven solely by endocrine signals rather than events downstream of embryo attachment. Some of these genes have been described in previous microarray studies on endometrium, but for the majority, this is the first time they have been implicated in implantation. The 140 genes enriched in the LE greatly expand the list of epithelial markers and provide many novel candidates for further studies to identify genes playing important roles in receptivity and embryo attachment.

Coupling of COX-1 to mPGES1 for prostaglandin E2 biosynthesis in the murine mammary gland

The mammary gland, like most tissues, produces measurable amounts of prostaglandin E2 (PGE2), a metabolite of arachidonic acid produced by sequential actions of two cyclooxygenases (COX-1 and COX-2) and three terminal PGE synthases: microsomal prostaglandin E2 synthase-1 (mPGES1), mPGES2, and cytosolic prostaglandin E2 synthase (cPGES). High PGE2 levels and COX-2 overexpression are frequently detected in mammary tumors and cell lines. However, less is known about PGE2 metabolic enzymes in the context of normal mammary development. Additionally, the primary COX partnerships of terminal PGE synthases and their contribution to normal mammary PGE2 biosynthesis are poorly understood. We demonstrate that expression of COX-1, generally considered constitutive, increases dramatically with lactogenic differentiation of the murine mammary gland. Concordantly, total PGE2 levels increase throughout mammary development, with highest levels measured in lactating tissue and breast milk. In contrast, COX-2 expression is extremely low, with only a modest increase detected during mammary involution. Expression of the G(s)-coupled PGE2 receptors, EP2 and EP4, is also temporally regulated, with highest levels detected at stages of maximal proliferation. PGE2 production is dependent on COX-1, as PGE2 levels are nearly undetectable in COX-1-deficient mammary glands. Interestingly, PGE2 levels are similarly reduced in lactating glands of mPGES1-deficient mice, indicating that PGE2 biosynthesis results from the coordinated activity of COX-1 and mPGES1. We thus provide evidence for the first time of functional coupling between COX-1 and mPGES1 in the murine mammary gland in vivo.

Expression of prostaglandin transporter in the bovine uterus and fetal membranes during pregnancy

Uteroplacental prostaglandins (PGs) play pivotal roles in the maintenance and termination of pregnancy in mammals. In the present study, we have characterized the expression of prostaglandin transporter (PGT) in placentome caruncles, intercaruncular tissues, fetal membranes, and utero-ovarian plexus during pregnancy in cattle. Pregnant bovine uteri were collected and classified into six groups covering the entire gestational length. In caruncles and intercaruncular tissues, PGT mRNA (also known as SLC02A1) and PGT protein were highly expressed at the late stage of pregnancy compared to the early and mid stages, whereas the level of expression is constant and low in fetal membranes throughout pregnancy. PGT mRNA and PGT protein were expressed at a constant level in the utero-ovarian plexus both ipsilateral and contralateral to corpus luteum throughout the course of pregnancy. Overall, the relative expression of PGT mRNA and PGT protein were higher in caruncles than in intercaruncular tissue and fetal membranes, whereas no differences were detected between intercaruncular tissues and fetal membranes at any stage of gestation. Immunohistochemistry indicated that PGT was preferentially expressed in caruncular epithelial cells of placentomes and endometrial luminal epithelial and myometrial smooth muscle cells of the intercaruncular regions. The level of PGT expression was comparatively higher in maternal components than in fetal components. In conclusion, differential spatiotemporal tissue-specific expression of PGT in uterine and intrauterine tissues suggests a role for this transporter in the exchange of PGs between the maternal and the fetal compartments, as well as for intrauterine metabolism of PGs during pregnancy.

Effect of interferon-tau on prostaglandin biosynthesis, transport, and signaling at the time of maternal recognition of pregnancy in cattle: evidence of polycrine actions of prostaglandin E2

Recognition and establishment of pregnancy involve several molecular and cellular interactions among the conceptus, uterus, and corpus luteum (CL). In ruminants, interferon-tau (IFNtau) of embryonic origin is recognized as the pregnancy recognition signal. Endometrial prostaglandin F(2alpha) (PGF(2alpha)) is the luteolysin, whereas PGE(2) is considered a luteoprotective or luteotrophic mediator at the time of establishment of pregnancy. The interplay between IFNtau and endometrial PGs production, transport, and signaling at the time of maternal recognition of pregnancy (MRP) is not well understood. We have studied the expression of enzymes involved in metabolism of PGE(2) and PGF(2alpha), cyclooxygenase-1 (COX-1) and COX-2, PG synthases (PGES and PGFS), PG 15-dehydrogenase, and PG transporter as well as PGE(2) (EP2 and EP3) and PGF(2alpha) receptors. IFNtau influences cell-specific expression of COX-2, PGFS, EP2, and EP3 in endometrium, myometrium, and CL in a spatio-temporal and tissue-specific manner, whereas it does not alter COX-1, PGES, PG 15-dehydrogenase, PG transporter, or PGF(2alpha) receptor expression in any of these tissues. In endometrium, IFNtau decreases PGFS in epithelial cells and increases EP2 in stroma. In myometrium, IFNtau decreases PGFS and increases EP2 in smooth muscle cells. In CL, IFNtau increases PGES and decreases EP3. Together, our results show that IFNtau directly or indirectly increases PGE(2) biosynthesis and EP2-associated signaling in endometrium, myometrium, and CL during MRP. Thus, PGE(2) may play pivotal roles in endometrial receptivity, myometrial quiescence, and luteal maintenance, indicating polycrine (endocrine, exocrine, paracrine, and autocrine) actions of PGE(2) at the time of MRP. Therefore, the establishment of pregnancy may depend not only on inhibition of endometrial PGF(2alpha), but also on increased PGE(2) production in cattle.

Embryonic signals direct the formation of tight junctional permeability barrier in the decidualizing stroma during embryo implantation

The protection of the embryo from the maternal adverse environment during early pregnancy is considered to be achieved by the establishment of a transitory permeability barrier created by decidual cells immediately surrounding the implanting embryo. Normally, the polarized epithelium acts as a barrier by regulating paracellular passage of substances through tight junctions. The expression of tight junction proteins in the uterine luminal epithelium prior to implantation is consistent with this idea. However, limited information is available regarding the nature and regulation of the permeability barrier that is created by decidualizing stromal cells during implantation. We show here that the tight junction proteins, occludin, claudin-1, zonula occludens-1 and zonula occludens-2, are all expressed and physically associated in decidualizing stromal cells of the primary decidual zone forming a barrier surrounding the embryo with the loss of adjacent luminal epithelium. The blastocyst trophectoderm appears to be the stimulus for the creation of this barrier, since isolated inner cell mass or artificial stimuli failed to induce such a barrier. Furthermore, the primary decidual zone induced by the normal blastocyst is impermeable to immunoglobulin molecules. These findings suggest that trophoblast-induced expression of tight junctions forms a temporary barrier in cells of the primary decidual zone that restricts the passage of injurious stimuli such as maternal immunoglobulins to the embryo.

Expression and regulation of the rat prostaglandin E2 receptor type 4 (EP4) in pregnant cervical tissue

OBJECTIVE

Prostaglandins play an important role in the regulation of parturition and cervical ripening. Prostaglandin E(2) (PGE(2))-induced tissue remodeling is mediated through activation of prostaglandin E(2) receptor type 4 (EP4). EP4 is known to regulate matrix metalloproteinase secretion and expression and therefore may play a role in cervical ripening. We hypothesized that EP4 expression is regulated in the rat cervix to coincide with cervical ripening. In addition, we analyzed transcriptional regulation of the rat EP4 gene.

STUDY DESIGN

EP4 expression was evaluated in the cervix in timed pregnancy Sprague-Dawley rats by real-time reverse transcriptase polymerase chain reaction and Western blot. The genomic structure of the rat EP4 gene was determined by sequencing rat genomic clones obtained by plaque hybridization. Northern blots were performed to identify the number of different transcripts. The transcriptional start site was identified on the basis of sequence comparison to the human and mouse EP4 gene. The minimal promoter was identified by using reporter constructs containing portions of the 5' flanking region. Reporter activity was evaluated in vitro. Identified regulatory regions were mutated to determine their role in transcription.

RESULTS

Cervical EP4 expression (messenger RNA and protein) peaks on the day of parturition. The rat EP4 gene is structurally similar to other prostaglandin receptors as well as the human EP4 gene and contains three exons separated by two introns. The coding regions are located in the second and third exons separated in the sixth transmembrane spanning region. Northern blot identified a single EP4 transcript with an estimated size of 4 kb, indicating a single transcription initiation site. The first 80 bases of the 5' flanking region were required for constitutive expression of EP4. Expression was lost after mutation of the GC/Sp1 binding site located at position -78 to -66 downstream from the transcription initiation site. Three Sp1 binding sites were identified and appear to cooperate to enhance EP4 transcription.

CONCLUSION

EP4 expression is regulated in the cervix and peaks on the day of parturition. The genomic structure of the human and rat EP4 gene is conserved between these two species. A GC rich/Sp1 binding site located within the first 80 bases of the transcription start site is important in transcription initiation of the EP4 gene.

Peroxisome proliferator-activated receptor delta expression and regulation in mouse uterus during embryo implantation and decidualization

The aim of this study was to examine the expression and regulation of peroxisome proliferator-activated receptor (PPAR) PPARdelta gene in mouse uterus during early pregnancy by in situ hybridization and immunohistochemistry. PPARdelta expression under pseudopregnancy, delayed implantation, hormonal treatment, and artificial decidualization was also investigated. There was a very low level of PPARdelta expression on days 1-4 of pregnancy. On day 5 when embryo implanted, PPARdelta expression was exclusively observed in the subluminal stroma surrounding the implanting blastocyst. No corresponding signals were seen in the uterus on day 5 of pregnancy. There was no detectable PPARdelta signal under delayed implantation. Once delayed implantation was terminated by estrogen treatment and embryo implanted, a strong level of PPARdelta expression was induced in the subluminal stroma surrounding the implanting blastocyst. Estrogen treatment induced a moderate level of PPARdelta expression in the glandular epithelium, while progesterone treatment had no effects in the ovariectomized mice. A strong level of PPARdelta expression was seen in the decidua on days 6-8 of pregnancy. PPARdelta expression was also induced under artificial decidualization. These data suggest that PPARdelta expression at implantation sites require the presence of an active blastocyst and may play an essential role for blastocyst implantation.

Identification and characterization of a novel progesterone receptor-binding element in the mouse prostaglandin E receptor subtype EP2 gene

BACKGROUND

Gene expression of prostaglandin E receptor EP2 is induced in the luminal epithelium of the mouse uterus during peri-implantation period (day-5 of pseudopregnancy), suggesting the involvement of progesterone and its receptor (PR) in this expression. However it remains unclear whether PR affects EP2 gene expression through its binding.

RESULTS

We investigated transcriptional regulation of EP2 gene expression with reporter gene analysis using HeLa cells with or without expression of the PR. The 5'-flanking region (-3260 to -27, upstream of the translation initiation site) exhibited progesterone-induced promoter activation and basal promoter activity in the presence of PR. Using successive deletion analysis, we determined the six regulatory regions in the EP2 gene. Three regions were found to be involved in progesterone-induced promoter activation, whereas the other three regions were involved in basal promoter activity in the presence of PR. We identified a novel PR-binding sequence, 5'-G(G/A)CCGGA-3', in the two basal promoter regions and Sp1- and Sp3-binding in the other basal promoter region.

CONCLUSIONS

We identified a novel PR-binding sequence, which may be involved in the regulation of basal promoter activity in the EP2 gene.

Molecular cloning and characterization of bovine prostaglandin E2 receptors EP2 and EP4: expression and regulation in endometrium and myometrium during the estrous cycle and early pregnancy

Prostaglandins (PGs) play important functions in the reproductive system, and PGE(2) appears necessary for recognition of pregnancy. We have found that PGE(2) is able to increase cAMP generation in the bovine endometrium. There are two PGE(2) receptors (EP), EP2 and EP4, that are coupled to adenylate cyclase to generate cAMP, but these receptors have not been studied in the bovine. We have cloned and characterized bovine EP2 and EP4 receptors and studied their expression in the uterus. The amino acid sequences of bovine EP2 and EP4 possess a high degree (>80%) of identity with the other mammalian homologs. EP2 is expressed in most tissues, and EP4 is expressed only in intestine and testis. EP2 mRNA and protein are expressed in endometrium and myometrium during the estrous cycle, whereas EP4 is undetectable. The Western analysis indicates that EP2 is maximally expressed in both endometrium and myometrium between d 10 and 18 of the estrous cycle. Immunohistochemical localization reveals that EP2 protein is expressed in all cell types of endometrium and myometrium. On d 18, pregnancy up-regulates EP2 protein, primarily in endometrial stroma and myometrial smooth muscle cells. In conclusion, EP2 is the major cAMP-generating PGE(2) receptor expressed and regulated in the bovine uterus during the estrous cycle and early pregnancy.

Expression and regulation of cytosolic prostaglandin E synthase in mouse uterus during the peri-implantation period

Prostaglandin E(2) (PGE(2)) is considered important for blastocyst spacing, implantation, and decidualization in rodent uteri. PGE synthase (PGES) catalyzes the isomerization of PGH(2) to PGE(2). Two isoforms of PGES exist: microsomal PGES (mPGES) and cytosolic PGES (cPGES); however, the expression and regulation of cPGES in the mammalian uterus during early pregnancy are still unknown. The aim of this study was to investigate the differential expression of cPGES in mouse uterus during early pregnancy and its regulation under different conditions using in situ hybridization and immunohistochemistry. A strong level of cPGES mRNA signal was exhibited in the stromal cells at the implantation site on Day 5 of pregnancy, whereas cPGES immunostaining was strongly detected in the luminal epithelium. The signals for both cPGES mRNA and immunostaining were strongly detected in the decidualized cells from Days 6-8 of pregnancy. A basal level of cPGES mRNA signal and immunostaining was exhibited in the uterus in delayed implantation. After delayed implantation was terminated by estrogen treatment and embryo implantation was initiated, cPGES mRNA signal was strongly detected in the stroma underlying the luminal epithelium at the implantation site, and cPGES immunostaining was strongly observed in the luminal epithelium surrounding the implanting blastocyst. A strong cPGES mRNA signal and immunostaining were detected in decidualized cells under artificial decidualization, whereas only a basal level of cPGES mRNA signal and immunostaining were observed in the control horn. Our data suggest that cPGES may play an important role during implantation and decidualization.

Uterine sensitization-associated gene-1: a novel gene induced within the rat endometrium at the time of uterine receptivity/sensitization for the decidual cell reaction

For successful implantation, the embryo must develop to the blastocyst stage and the endometrium must attain a state that is receptive to the implanting blastocyst. In rodents, the timing, duration, and hormonal regulation of this receptive state has been well defined. However, the molecular cascade of events involved in the onset of the receptive phase remains unclear. In the present study, we sought to identify genes involved in the onset of the receptivity using the technique of suppressive subtraction hybridization. Herein we report the isolation, cloning, and characterization of a novel gene, uterine sensitization-associated gene-1 (UASG-1), that is preferentially expressed within the maximally sensitized/receptive rat endometrium. USAG-1 mRNA encodes a putative protein of 206 amino acids that contains a possible N-terminal secretion signal and a C-terminal cystine knotlike motif. Northern blot analysis revealed that induction of USAG-1 mRNA was restricted to the Day 5 pregnant or pseudopregnant uterus. In situ hybridization experiments demonstrated that this induction was restricted to the uterine glandular epithelial cells. Given the remarkably tight restriction of its expression, USAG-1 may be involved in the onset of endometrial receptivity for implantation/sensitization for the decidual cell reaction.

Expression of leukemia inhibitory factor receptor and gp130 in mouse uterus during early pregnancy

Leukemia inhibitory factor (LIF) is essential for implantation of mouse embryos. The aim of this study was to assess the expression and regulation of LIF receptor (LIFR) and gp130 mRNA in mouse uterus during early pregnancy using in situ hybridization and reverse transcription-polymerase chain reaction (RT-PCR). A strong level of LIFR mRNA signal was detected in the luminal epithelium on day 5 of pregnancy. On day 6-8 of pregnancy, LIFR signal was mainly localized in the decidua. LIFR signal in the luminal epithelium of ovariectomized mouse was slightly stimulated by a combination of progesterone and estrogen. By RT-PCR, LIFR mRNA signal was detected in all of the uteri from day 1-8 of pregnancy, being at the highest level on day 5. A low level of gp130 mRNA signal was seen in the glandular epithelium on day 3 of pregnancy and reached a high level on day 4 of pregnancy. gp130 signal in the decidua appeared on day 6 of pregnancy and reached a high level on day 7 and 8 of pregnancy. After the ovariectomized mouse was treated with a combination of progesterone and estrogen, a strong gp130 signal was observed in the glandular epithelium, while no signal was detected after progesterone or estrogen treatment alone. By RT-PCR analysis, gp130 mRNA was detected in all of the uteri from day 1-8 of pregnancy, being at the highest level on day 4 of pregnancy. Additionally, a high level of LIFR and gp130 mRNA signal was detected in the decidua under artificial decidualization compared to the control uninjected horn. The co-expression of a high level of LIFR and gp130 mRNA in the decidua may play a key role during the decidualization and placentation.

Function of prostanoid receptors: studies on knockout mice

Prostanoids consisting of the prostaglandins (PGs) and the thromboxanes (TXs) are the cyclooxygenase metabolites of arachidonic acid. They exert a range of actions mediated by their respective receptors expressed in the target cells. The receptors include the DP, EP, FP, IP and TP receptors for PGD, PGE, PGF, PGI and TXA, respectively. Furthermore, EP is subdivided into four subtypes, EP1, EP2, EP3 and EP4, which are encoded by different genes and differ in their responses to various agonists and antagonists. Recent developments in the molecular biology of the prostanoid receptors have enabled the investigation of physiological roles of each receptor by disruption of the respective gene. At this point, all the eight types and subtypes of the prostanoid receptors have been individually knocked out in mice, and various phenotypes have been reported for each strain. Here, we review the findings obtained in these studies. The results from these knockout mice studies may be useful in the development of novel therapeutics that can selectively manipulate actions mediated by each receptor.

Differential expression of microsomal prostaglandin e synthase at implantation sites and in decidual cells of mouse uterus

Prostaglandin E(2) (PGE(2)) is considered important for blastocyst spacing, implantation, and decidualization in the rodent uterus. PGE synthase (PGES) catalyzes the isomerization of PGH(2) to PGE(2). There are two isoforms of PGES, microsomal PGES (mPGES) and cytosolic PGES (cPGES). However, the expression and regulation of mPGES in the mammalian uterus during early pregnancy are still unknown. The aim of this study was to investigate the differential expression of mPGES in mouse uterus during early pregnancy and its regulation under different conditions by in situ hybridization and immunohistochemistry. Microsomal PGES expression in the preimplantation mouse embryos was also performed by reverse transcription polymerase chain reaction (RT-PCR). Expression of mPGES mRNA and protein was at a basal level in the luminal epithelium from Day 1 to Day 4 of pregnancy. However, mPGES mRNA and protein were highly expressed in the stroma immediately surrounding the blastocyst but not in the luminal epithelium on Day 5 of pregnancy. Microsomal PGES mRNA and protein were not detected in the pseudopregnant uterus from Day 1 to Day 5. During delayed implantation, mPGES mRNA and protein were also not detected in the uterus. Once delayed implantation was terminated by estrogen treatment and embryo implantation initiated, both mPGES mRNA and protein were induced to express in the stroma immediately surrounding the blastocyst, which was similar to the expression pattern on Day 5 of pregnancy. From Day 6 to Day 8 of pregnancy, the signals for mPGES mRNA and protein were strongly detected in the decidualized cells. Microsomal PGES mRNA and protein were also highly expressed in the artificially decidualized cells but not in the control horn. Microsomal PGES mRNA was detected in the oocytes and all the stages of preimplantation embryos. The strong mPGES expression in the implantation site and decidual cells suggests that mPGES might play an important role during implantation and more importantly in decidualization.

Cloning and expression of the rabbit prostaglandin EP2 receptor

BACKGROUND

Prostaglandin E2 (PGE2) has multiple physiologic roles mediated by G protein coupled receptors designated E-prostanoid, or "EP" receptors. Evidence supports an important role for the EP2 receptor in regulating fertility, vascular tone and renal function.

RESULTS

The full-length rabbit EP2 receptor cDNA was cloned. The encoded polypeptide contains 361 amino acid residues with seven hydrophobic domains. COS-1 cells expressing the cloned rabbit EP2 exhibited specific [3H]PGE2 binding with a Kd of 19.1 +/- 1.7 nM. [3H]PGE2 was displaced by unlabeled ligands in the following order: PGE2>>PGD2=PGF2alpha=iloprost. Binding of [3H]PGE2 was also displaced by EP receptor subtype selective agonists with a rank order of affinity consistent with the EP2 receptor (butaprost>AH13205>misoprostol>sulprostone). Butaprost free acid produced a concentration-dependent increase in cAMP accumulation in rabbit EP2 transfected COS-1 cells with a half-maximal effective concentration of 480 nM. RNase protection assay revealed high expression in the ileum, spleen, and liver with lower expression in the kidney, lung, heart, uterus, adrenal gland and skeletal muscle. In situ hybridization localized EP2 mRNA to the uterine endometrium, but showed no distinct localization in the kidney. EP2 mRNA expression along the nephron was determined by RT-PCR and its expression was present in glomeruli, MCD, tDL and CCD. In cultured cells EP2 receptor was not detected in collecting ducts but was detected in renal interstitial cells and vascular smooth muscle cells. EP2 mRNA was also detected in arteries, veins, and preglomerular vessels of the kidney.

CONCLUSION

EP2 expression pattern is consistent with the known functional roles for cAMP coupled PGE2 effects in reproductive and vascular tissues and renal interstitial cells. It remains uncertain whether it is also expressed in renal tubules.

Global gene expression analysis to identify molecular markers of uterine receptivity and embryo implantation

Infertility and spontaneous pregnancy losses are an enduring problem to women's health. The establishment of pregnancy depends on successful implantation, where a complex series of interactions occurs between the heterogeneous cell types of the uterus and blastocyst. Although a number of genes are implicated in embryo-uterine interactions during implantation, genetic evidence suggests that only a small number of them are critical to this process. To obtain a global view and identify novel pathways of implantation, we used a dual screening strategy to analyze the expression of nearly 10,000 mouse genes by microarray analysis. Comparison of implantation and interimplantation sites by a conservative statistical approach revealed 36 up-regulated genes and 27 down-regulated genes at the implantation site. We also compared the uterine gene expression profile of progesterone-treated, delayed implanting mice to that of mice in which delayed implantation was terminated by estrogen. The results show up-regulation of 128 genes and down-regulation of 101 genes after termination of the delayed implantation. A combined analysis of these experiments showed specific up-regulation of 27 genes both at the implantation site and during uterine activation, representing a broad diversity of molecular functions. In contrast, the majority of genes that were decreased in the combined analysis were related to host immunity or the immune response, suggesting the importance of these genes in regulating the uterine environment for the implanting blastocyst. Collectively, we identified genes with recognized roles in implantation, genes with potential roles in this process, and genes whose functions have yet to be defined in this event. The identification of unique genetic markers for the onset of implantation signifies that genome-wide analysis coupled with functional assays is a promising approach to resolve the molecular pathways required for successful implantation.

Dual control of LIF expression and LIF receptor function regulate Stat3 activation at the onset of uterine receptivity and embryo implantation

Leukemia inhibitory factor (LIF) expression in the uterus is essential for embryo implantation in mice. Here we describe the spatial and temporal regulation of LIF signaling in vivo by using tissues isolated from uteri on different days over the implantation period. During this time, LIF receptors are expressed predominantly in the luminal epithelium (LE) of the uterus. Isolated epithelium responds to LIF by phosphorylation and nuclear translocation of signal transducer and activator of transcription (Stat) 3, but not by an increase in mitogen-activated protein kinase levels. The related cytokines Il-6, ciliary neurotrophic factor, as well as epidermal growth factor, do not activate Stat3, although epidermal growth factor stimulates mitogen-activated protein kinase. In vivo Stat3 activation is induced by LIF alone, resulting in the localization of Stat3 specifically to the nuclei of the LE coinciding with the onset of uterine receptivity. The responsiveness of the LE to LIF is regulated temporally, with Stat activation being restricted to day 4 of pregnancy despite the presence of constant levels of LIF receptor throughout the preimplantation period. Uterine receptivity is therefore under dual control and is regulated by both the onset of LIF expression in the endometrial glands and the release from inhibition of receptor function in the LE.

Diversification of cyclooxygenase-2-derived prostaglandins in ovulation and implantation

Previous observations of ovulation and fertilization defects in cyclooxygenase-2 (COX-2)-deficient mice suggested that COX-2-derived ovarian prostaglandins (PGs) participate in these events. However, the specific PG and its mode of action were unknown. Subsequent studies revealed that mice deficient in EP(2), a PGE(2)-receptor subtype, have reduced litter size, apparently resulting from poor ovulation but more dramatically from impaired fertilization. Using a superovulation regimen and in vitro culture system, we demonstrate herein that the ovulatory process, not follicular growth, oocyte maturation, or fertilization, is primarily affected in adult COX-2- or EP(2)-deficient mice. Furthermore, our results show that in vitro-matured and -fertilized eggs are capable of subsequent preimplantation development. However, severely compromised ovulation in adult COX-2- or EP(2)-deficient mice is not manifested in immature (3-wk-old) COX-2- or EP(2)-deficient mice, suggesting that the process of ovulation is more dependent on PGs in adult mice. Although the processes of implantation and decidualization are defective in COX-2(-/-) mice, our present results demonstrate that these events are normal in EP(2)-deficient mice, as determined by embryo transfer and experimentally induced decidualization. Collectively, previous and present results suggest that whereas COX-2-derived PGE(2) is essential for ovulation via activation of EP(2), COX-2-derived prostacyclin is involved in implantation and decidualization via activation of peroxisome proliferator-activated receptor delta.

Expression of cyclooxygenase 2 by prostaglandin E(2) in human endometrial adenocarcinoma cell line HEC-1B

The regulation of expression of cyclooxygenase 2 (COX-2) was investigated by treatment with PGE(2) in human endometrial adenocarcinoma cell line HEC-1B. One microM PGE(2) could stimulate the expression of COX-2 approximately twofold in this cell line. The same concentration of PGE(2) also stimulated activation of mitogen-activated protein kinase (MAP kinase) and protein kinase B (PKB). PGE(2)-induced MAP kinase activation was sensitive to a MAP kinase kinase (MEK) inhibitor, PD098059, and a protein kinase A inhibitor, H-89. PD098059 and H-89 also partially inhibited the expression of COX-2 stimulated by PGE(2). PGE(2) could stimulate the activation of PKB, which was sensitive to phosphatidylinositol-3-OH kinase (PI3K) inhibitor, wortmannin. Whereas wortmannin alone partially inhibited the expression of COX-2, a combination of wortmannin and PD098059 totally inhibited PGE(2)-mediated COX-2 expression. These results suggest that MAP kinase and PI3K pathways are stimulated with PGE(2), and that both of these pathways are involved in the expression of COX-2. In addition, they also suggest that protein kinase A remains upstream of PGE(2)-induced activation of MAP kinase in HEC-1B cells.

Prostaglandin E receptors and the kidney

Prostaglandin E(2) is a major renal cyclooxygenase metabolite of arachidonate and interacts with four G protein-coupled E-prostanoid receptors designated EP(1), EP(2), EP(3), and EP(4). Through these receptors, PGE(2) modulates renal hemodynamics and salt and water excretion. The intrarenal distribution and function of EP receptors have been partially characterized, and each receptor has a distinct role. EP(1) expression predominates in the collecting duct where it inhibits Na(+) absorption, contributing to natriuresis. The EP(2) receptor regulates vascular reactivity, and EP(2) receptor-knockout mice have salt-sensitive hypertension. The EP(3) receptor is also expressed in vessels as well as in the thick ascending limb and collecting duct, where it antagonizes vasopressin-stimulated salt and water transport. EP(4) mRNA is expressed in the glomerulus and collecting duct and may regulate glomerular tone and renal renin release. The capacity of PGE(2) to bidirectionally modulate vascular tone and epithelial transport via constrictor EP(1) and EP(3) receptors vs. dilator EP(2) and EP(4) receptors allows PGE(2) to serve as a buffer, preventing excessive responses to physiological perturbations.

Characterization of temporal and cell-specific changes in transcripts for prostaglandin E(2) receptors in pseudopregnant rat endometrium

In the rodent uterus, prostaglandin E(2) (PGE(2)) is believed to have a major role in implantation and decidualization. The present study investigated the temporal and hormonal control of mRNA expression for the four E-prostanoid (EP(1-4)) receptors in the rat endometrium. For Northern blot analysis and in situ hybridization, samples were obtained from rats on Days 1-10 of pseudopregnancy or from rats differentially sensitized for the decidual cell reaction with estradiol. No EP(1) mRNA signal was detected. Endometrial EP(2) and EP(3) mRNA levels increased to a maximum on Day 5, and the mRNAs were localized to the luminal epithelium at the antimesometrial pole, and in the endometrial stroma and glandular epithelium, respectively. Endometrial EP(4) mRNA levels were unchanged on Days 1-5, but the mRNA was concentrated in the antimesometrial endometrial stroma on Day 5. Cell-specific expression of EP(2), EP(3), and EP(4) on Day 5 was dependent upon a dose of estradiol given on Day 4 that induced differential uterine sensitization on Day 5. After the application of a deciduogenic stimulus on Day 5, mRNA levels for these receptors decreased significantly, while in nonstimulated horns they remained elevated. Overall, these results support a role for PGE(2) in the onset of receptivity and initiation of decidualization in the rat.

Pregnancy and exogenous steroid treatments modulate the expression of relaxant EP(2) and contractile FP receptors in the rat uterus

Prostaglandins (PGs) interact with specific receptors on plasma membranes to regulate myometrial activity in many species. The present study examined whether the expression of relaxant prostaglandin E receptor subtype two (EP(2)) and contractile prostaglandin F receptor (FP) mRNA in the rat uterus is changed during various states of pregnancy and regulated by steroid hormones. Expression of mRNA for EP(2) and FP receptors in the full-thickness uteri was analyzed by reverse transcription-polymerase chain reaction using specific primers. Abundance of receptor mRNA was expressed relative to beta-actin mRNA. Results showed that 1) mRNA for EP(2) receptors in the rat uterus was substantially increased during pregnancy (320%) compared with the nonpregnant state (100%, P < 0.01), and declined during labor at term (36% vs. 100% in control, P < 0.01); 2) mRNA expression for FP receptors in rat uterus was increased during pregnancy (333% vs. 100% in nonpregnant rats, P < 0. 01) and reached maximal levels during labor (515% vs. 100% in control, P < 0.01); 3) upon RU-486 treatment on Day 19 of pregnancy, uterine EP(2) receptor mRNA levels were decreased (18% vs. 100% in control, P < 0.01), and FP mRNA levels were increased (357% vs. 100% in control, P < 0.01); 4) with ICI 164384 (an antiestrogen) treatment on Day 19 of gestation, uterine FP receptor mRNA levels were decreased without effects on EP(2) receptors; 5) in ovariectomized (ovx) rats, progesterone increased EP(2) (163% vs. 100% in control, P < 0.01) and had no effects on FP receptor mRNA expression in the rat uterus; 6) estradiol increased FP receptor mRNA levels (358% vs. 100% in control, P < 0.01) and had no effects on EP(2) mRNA in the ovx rat uterus. Therefore, we conclude that steroid hormones modulate the mRNA for relaxant EP(2) and contractile FP receptors for PGs in the uterus and thus regulate uterine activity during pregnancy and labor.

Prostanoid receptors: structures, properties, and functions

Prostanoids are the cyclooxygenase metabolites of arachidonic acid and include prostaglandin (PG) D(2), PGE(2), PGF(2alpha), PGI(2), and thromboxne A(2). They are synthesized and released upon cell stimulation and act on cells in the vicinity of their synthesis to exert their actions. Receptors mediating the actions of prostanoids were recently identified and cloned. They are G protein-coupled receptors with seven transmembrane domains. There are eight types and subtypes of prostanoid receptors that are encoded by different genes but as a whole constitute a subfamily in the superfamily of the rhodopsin-type receptors. Each of the receptors was expressed in cultured cells, and its ligand-binding properties and signal transduction pathways were characterized. Moreover, domains and amino acid residues conferring the specificities of ligand binding and signal transduction are being clarified. Information also is accumulating as to the distribution of these receptors in the body. It is also becoming clear for some types of receptors how expression of their genes is regulated. Furthermore, the gene for each of the eight types of prostanoid receptor has been disrupted, and mice deficient in each type of receptor are being examined to identify and assess the roles played by each receptor under various physiological and pathophysiological conditions. In this article, we summarize these findings and attempt to give an overview of the current status of research on the prostanoid receptors.

Cyclo-oxygenase-2-derived prostacyclin mediates embryo implantation in the mouse via PPARdelta

We have demonstrated previously that cyclo-oxygenase-2 (COX2), the rate-limiting enzyme in the biosynthesis of prostaglandins (PGs), is essential for blastocyst implantation and decidualization. However, the candidate PG(s) that participates in these processes and the mechanism of its action remain undefined. Using COX2-deficient mice and multiple approaches, we demonstrate herein that COX2-derived prostacyclin (PGI2) is the primary PG that is essential for implantation and decidualization. Several lines of evidence suggest that the effects of PGI2 are mediated by its activation of the nuclear hormone receptor PPARdelta, demonstrating the first reported biologic function of this receptor signaling pathway.

Zonula occludens-1 and E-cadherin are coordinately expressed in the mouse uterus with the initiation of implantation and decidualization

Two-way interactions between the blastocyst trophectoderm and the uterine luminal epithelium are essential for implantation. The key events of this process are cell-cell contact of trophectoderm cells with uterine luminal epithelial cells, controlled invasion of trophoblast cells through the luminal epithelium and the basement membrane, transformation of uterine stromal cells surrounding the blastocyst into decidual cells, and protection of the "semiallogenic" embryo from the mother's immunological responses. Because cell-cell contact between the trophectoderm epithelium and the luminal epithelium is essential for implantation, we investigated the expression of zonula occludens-1 (ZO-1) and E-cadherin, two molecules associated with epithelial cell junctions, in the mouse uterus during the periimplantation period. Preimplantation uterine epithelial cells express both ZO-1 and E-cadherin. With the initiation and progression of implantation, ZO-1 and E-cadherin are expressed in stromal cells of the primary decidual zone (PDZ). As trophoblast invasion progresses, these two molecules are expressed in stroma in advance of the invading trophoblast cells. These results suggest that expression of these adherence and tight junctions molecules in the PDZ serves to function as a permeability barrier to regulate access of immunologically competent maternal cells and/or molecules to the embryo and provide homotypic guidance of trophoblast cells in the endometrium.

The induction of cyclooxygenase-2 in IL-1beta-treated endothelial cells is inhibited by prostaglandin E2 through cAMP

Prostaglandins (PGs) have numerous cardiovascular and inflammatory effects. Cyclooxygenase (COX), which exists as COX-1 and COX-2 isoforms, is the first enzyme in the pathway in which arachidonic acid is converted to PGs. Prostaglandin E2 (PGE2) exerts a variety of biological activities for the maintenance of local homeostasis in the body. Elucidation of PGE2 involvement in the signalling molecules such as COX could lead to potential therapeutic interventions. Here, we have investigated the effects of PGE2 on the induction of COX-2 in human umbilical vein endothelial cells (HUVEC) treated with interleukin-1beta (IL-1beta 1 ng/ml). COX activity was measured by the production of 6-keto-PGF1alpha, PGE2, PGF2alpha and thromboxane B2 (TXB2) in the presence of exogenous arachidonic acids (10 microM for 10 min) using enzyme immunoassay (EIA). COX-1 and COX-2 protein was measured by immunoblotting using specific antibody. Untreated HUVEC contained only COX-1 protein while IL-1beta treated HUVEC contained COX-1 and COX-2 protein. PGE2 (3 microM for 24h) did not affect on COX activity and protein in untreated HUVEC. Interestingly, PGE2 (3 microM for 24h) can inhibit COX-2 protein, but not COX-1 protein, expressed in HUVEC treated with IL-1beta. This inhibition was reversed by coincubation with forskolin (100 microM). The increased COX activity in HUVEC treated with IL-1beta was also inhibited by PGE2 (0.03, 0.3 and 3 microM for 24h) in a dose-dependent manner. Similarly, forskolin (10, 50 or 100 microM) can also reverse the inhibition of PGE2 on increased COX activity in IL-1beta treated HUVEC. The results suggested that (i) PGE2 can initiate negative feedback regulation in the induction of COX-2 elicited by IL-1beta in endothelial cells, (ii) the inhibition of PGE2 on COX-2 protein and activity in IL-1beta treated HUVEC is mediated by cAMP and (iii) the therapeutic use of PGE2 in the condition which COX-2 has been involved may have different roles.