Effect of PGE2 on uterine contractility and tone in mares

Mapping the lipidomic secretome of the early equine embryo

The lipidomic secretions of embryos provide a unique opportunity to examine the cellular processes of the early conceptus. In this study we profiled lipids released by the early equine conceptus, using high-resolution mass spectrometry to detect individual lipid species. This study examined the lipidomic profile in embryo-conditioned media from in vivo-produced, 8-9 day-old equine embryos (n = 3) cultured in vitro for 36 h, analyzed over 3 timepoints. A total of 1,077 lipid IDs were recorded across all samples, containing predominantly glycerolipids. Seventy-nine of these were significantly altered in embryo conditioned-media versus media only control (p < 0.05, fold-change >2 or < 0.5). Fifty-five lipids were found to be released into the embryo-conditioned media, of which 54.5% were triacylglycerols and 23.6% were ceramides. The sterol lipid, cholesterol, was also identified and secreted in significant amounts as embryos developed. Further, 24 lipids were found to be depleted from the media during culture, of which 70.8% were diacylglycerols, 16.7% were triacylglycerols and 12.5% were ceramides. As lipid-free media contained consistently detectable lipid peaks, a further profile analysis of the various components of non-embryo-conditioned media consistently showed the presence of 137 lipids. Lipid peaks in non-embryo-conditioned media increased in response to incubation under mineral oil, and contained ceramides, diacylglycerols and triacylglycerols. These results emphasize the importance of a defined embryo culture medium and a need to identify the lipid requirements of the embryo precisely. This study sheds light on early embryo lipid metabolism and the transfer of lipids during in vitro culture.

Embryo-endometrial interaction associated with the location of the embryo during the mobility phase in mares

Embryo-maternal crosstalk is essential to establish pregnancy, with the equine embryo moving throughout the uterus on days 9-15 (ovulation = day 0) as part of this interaction. We hypothesized that the presence of a mobile embryo induces local changes in the gene expression of the endometrium. On Day 12, the endometrial transcripts were compared among three groups: uterine horn with an embryo (P+, n = 7), without an embryo (P-, n = 7) in pregnant mares, and both uterine horns of nonbred mares (NB, n = 6). We identified 1,101 differentially expressed genes (DEGs) between P+ vs. NB and 1,229 DEGs between P- vs. NB. The genes upregulated in both P+ and P- relative to NB were involved in growth factor pathway and fatty acid activation, while downregulated genes were associated with oxytocin signaling pathway and estrogen receptor signaling. Comparing the transcriptome of P+ to that of P-, we found 59 DEGs, of which 30 genes had a higher expression in P+. These genes are associated with regulating vascular growth factors and the immune system, all known to be essential in early pregnancy. Overall, this study suggests that the mobile embryo influences the endometrial gene expression locally.

Contributions to Mare Reproduction Research by the Ginther Team

Examples of research discoveries and first reports on mare reproduction by the O.J. Ginther team are (1) determined daily circulating concentrations of four hormones during the estrous cycle, (2) showed that mares can be induced to ovulate and superovulate by hormone treatment during both ovulatory and anovulatory seasons, (3) demonstrated that prostaglandin F2α was the luteolysin in mares, (4) described the mare's elaborate hormonal and biochemical mechanism for selecting the ovulatory follicle from a pool of like follicles, (5) developed the method for diagnosing fetal sex by Day 60 using location of the genital tubercle, (6) refuted the dogma that the primary corpus luteum regresses at about one month of pregnancy, (7) demonstrated that the uterus induces luteolysis in nonpregnant mares through a systemic pathway unlike the local uteroovarian venoarterial pathway in ruminants, (8) developed the method for greatly reducing the devastating twinning problem, and (9) discovered intrauterine embryo mobility and fixation and thereby solved several enigmas in mare reproduction. During 56 years on the University of Wisconsin faculty, Ginther was sole author of seven hard cover texts and reference books. He supervised 112 graduate-students, postdoctorates, and research trainees from 17 countries. His team published 680 full-length journal papers that were cited 43,034 times according to Google Scholar. The Institute for Scientific Information ranked him among the top 1% of the world's scientists in all fields. According to a survey in 2012-23 by Expertscape, he published more scientific manuscripts than anyone on ovarian follicles, corpora lutea, and luteolysis.

Expression of Oxytocin/Neurophysin I and Oxytocinase in the Equine Conceptus from Day 8 to Day 21 Post-Ovulation

Leucyl and cystinyl aminopeptidase (LNPEP/oxytocinase) is an enzyme that metabolizes oxytocin in serum and tissues. The presence of oxytocin/neurophysin I (OXT), oxytocin and LNPEP and their relationship to other genes is unknown in the equine conceptus. Our objective was to characterize gene expression of LNPEP and OXT on D8, 10, 12, 14, 15, 16 and 21 conceptuses in relationship to other genes. Immunohistochemistry, western blot and liquid chromatography with tandem mass spectrometry (LC-MS/MS) were used for identification of oxytocin and LNPEP in D15, 16 and 18 conceptuses. LNPEP was increased at D15 compared to D10, was immunolocalized in the equine trophectoderm and endoderm, and protein was confirmed by LC-MS/MS. Maximal abundance of OXT was at D21, and lowest on D12 and D14, but no protein was identified. OXTR abundance was highest on D14 and D21. LNPEP was correlated with PTGFR and PTGES on D12 and D14-D15, and high expression of PTGES, PTGS2 was found on D14, D15 and D21; PTGFR was found on D8 and D12-21. LNPEP may have a role in prostaglandin regulation and conceptus fixation by decreasing the availability of oxytocin. Further investigation on the role embryonic LNPEP during pregnancy is warranted.

The Effects of Prostaglandin E2 Treatment on the Secretory Function of Mare Corpus Luteum Depends on the Site of Application: An in vivo Study

We examined the effect of prostaglandin (PG) E₂ on the secretory function of equine corpus luteum (CL), according to the application site: intra-CL injection vs. an intrauterine (intra-U) administration. Moreover, the effect of intra-CL injection vs. intra-U administration of both luteotropic factors: PGE₂ and human chorionic gonadotropin (hCG) as a positive control, on CL function was additionally compared. Mares were assigned to the groups (n = 6 per group): (1) an intra-CL saline injection (control); (2) an intra-CL injection of PGE₂ (5 mg/ml); (3) an intra-CL injection of hCG (1,500 IU/ml); (4) an intra-U saline administration (control); (5) an intra-U administration of PGE₂ (5 mg/5 ml); (6) an intra-U administration of hCG (1,500 IU/5 ml). Progesterone (P₄) and PGE₂ concentrations were measured in blood plasma samples collected at −2, −1, and 0 (pre-treatment), and at 1, 2, 3, 4, 6, 8, 10, 12, and 24 h after treatments. Moreover, effects of different doses of PGE₂ application on the concentration of total PGF_2α (PGF_2α and its main metabolite 13,14-dihydro-15-keto-prostaglandin F_2α– PGFM) was determined. The time point of PGE₂, hCG, or saline administration was defined as hour “0” of the experiment. An intra-CL injection of PGE₂ increased P₄ and PGE₂ concentrations between 3 and 4 h or at 3 and 12 h, respectively (p < 0.05). While intra-U administration of PGE₂ elevated P₄ concentrations between 8 and 24 h, PGE₂ was upregulated at 1 h and between 3 and 4 h (p < 0.05). An intra-CL injection of hCG increased P₄ concentrations at 1, 6, and 12 h (p < 0.05), while its intra-U administration enhanced P₄ and PGE₂ concentrations between 1 and 12 h or at 3 h and between 6 and 10 h, respectively (p < 0.05). An application of PGE₂, dependently on the dose, supports equine CL function, regardless of the application site, consequently leading to differences in both P₄ and PGE₂ concentrations in blood plasma.

Equine Embryo Mobility. A Friend of Theriogenologists

Equine embryo mobility and cessation of mobility (fixation) provide explanations to several enigmas in reproductive biology of the pregnant mare and provide an efficient solution to the twinning problem, the bane of brood-mare owners. Embryo mobility is maximum on Days 12 to 15 (Day 0 = ovulation) while the spherical embryo is growing from 9 to 23 mm in diameter. During mobility, the embryo can be anywhere in the uterine lumen regardless of side of ovulation. Mobility solved the enigmas of how a small embryo can block luteolysis in a relatively massive uterus and why the side of ovulation does not determine the side of the initial placental attachment. Fixation occurs on ∼ Day 16 at a bend or flexure in a uterine horn that has a cross sectional diameter of the endometrium that is similar to diameter of the embryo. The occurrence of fixation in the horn with smaller diameter solved several enigmas involving side of fixation such as (1) greater frequency of postpartum fixation in the formerly nongravid horn and (2) later fixation in a horse than in a pony; horses and ponies have a similar embryo diameter but horses have a larger uterus. Unilateral fixation of twins is associated with a high frequency (e.g., 85%) of natural embryo reduction (elimination of one member of a twin set) whereas bilateral fixation precludes natural embryo reduction. The theriogenologist can efficiently solve the twinning problem by compressing one mobile or bilaterally fixed embryo with finger/thumb or with the ultrasound probe.

Equine embryo mobility. A game changer

The equine embryo or embryonic vesicle on Days 11-15 postovulation travels with profound physiologic purpose throughout the lumen of the two uterine horns and uterine body making 12 to 22 trips between the two uterine horns per day. This phenomenon is termed embryo mobility and is unique in equids among domestic species. Apparently, the embryo first reaches the uterine body on Days 8 or 9. Mobility increases to maximum by Days 11 or 12 and continues until an abrupt cessation of mobility (fixation) on Days 15 (ponies) or 16 (horses and donkeys). The embryo is propelled by uterine contractions in response to the production of apparently both PGF2α and PGE2 by both the embryo and uterus. An increase in endometrial vascular perfusion accompanies the mobile embryo as it moves from horn to horn. Restricting the embryo to one uterine horn by a ligature has indicated that specific roles of the traveling embryo include the stimulation of uterine contractions, tone, vascularity, and edema and to curtail the production of the luteolysin (PGF2α) by the uterus. The increase in uterine tone, decrease in diameter of the uterine horns, and a flexure in the caudal portion of each horn collaborate in the selection of a horn of fixation. Embryo mobility is a game changer that has solved several long-time enigmas in mare reproduction and has provided a needed and effective finger/thumb compression method for eliminating one member of a twin set.

Expression of Enzymes Associated with Prostaglandin Synthesis in Equine Conceptuses

Simple Summary

The mobile preimplantative phase of equine gestation, taking place between day 9 and 16 after ovulation, is characterized by peristaltic contractions of the uterus caused by secretion of prostaglandins by the spheric equine conceptus. This mobility is necessary for maternal recognition of pregnancy in equids, taking place around day 14 after ovulation. The presented study investigated the spatial and temporal abundance of prostaglandin synthesis enzymes of the equine conceptus, elucidating a basal and an inducible system for prostaglandin E2. Prostaglandin F2α synthesis is restricted to the “periembryonic”pole area and relies on enzymatic conversion of prostaglandin E2. This scenario led to a model able to explain the embryonic forward motion driven by the peristaltic contractions of the uterus. In vitro incubation of primary trophoblast cell cultures with oxytocin showed no influence of this hormone on prostaglandin synthesis.

Abstract

In the horse, mobility of the conceptus is required for maternal recognition of pregnancy depending on secretion of prostaglandins by the conceptus. The aim of this study was to determine the expression and localization of key enzymes of the different pathways leading to synthesis of prostaglandin E2 and F2α in the equine conceptus during the mobility phase. Enzyme expression was analyzed via quantitative RT-PCR in total RNA samples of equine conceptuses collected on days 10 (n = 5), 12 (n = 12), 14 (n = 5) and 16 (n = 7) from healthy mares. Relative abundance of cyclooxygenase (COX)-2 mRNA was higher (p < 0.05) than of COX-1 irrespective of conceptus age and for phospholipase A2 on day 16 in comparison to all other days (p < 0.01). Abundance of mRNA of cytosolic and microsomal prostaglandin E synthase (PGES) and of carbonyl reductase (CBR) 1 was not influenced by conceptus age. Immunohistochemically, COX-1, COX-2, as well as cytosolic and microsomal PGES were present in both the ectodermal and endodermal layer of the yolk sac wall. CBR-1 was restricted to periembryonic disc area. The localisation of the key enzymes explains the mechanism of embryo mobility. In vitro incubation of primary trophoblast cell cultures with oxytocin had no effect on key enzyme synthesis.

Impairment of the antifibrotic prostaglandin E2 pathway may influence neutrophil extracellular traps-induced fibrosis in the mare endometrium

Prostaglandin E₂ (PGE₂) has contradictory effects in many organs. It may have proinflammatory, anti-inflammatory, or anti-fibrotic roles, depending on the type of receptors to which it binds. By signaling through its receptors EP2 and EP4, PGE₂ mediates anti-inflammatory and anti-fibrotic actions. In spite of chronic endometrial fibrosis (endometrosis) being a major cause of mare infertility, its pathogenesis is not fully understood. We have shown that contact of mare endometrium in vitro with neutrophil extracellular traps (NETs) proteases favors endometrial collagen type I production. Therefore, we investigated the involvement of the PGE₂ pathway in collagen deposition in mare endometrium, challenged in vitro with proteases present in NETs. Mare endometria (Kenney and Doig categories I/IIA and IIB/III), obtained in the follicular phase (FLP) and mid-luteal phase (MLP), were incubated for 24 h with components found in NETs (elastase, cathepsin-G, and myeloperoxidase). Secretion of PGE₂ and transcripts for specific PGE synthase (PGES) and PGE₂ receptors (EP2 and EP4) were evaluated. Impaired PGE₂ production and low EP2 transcript abundance depended on the endometrial category and estrous cycle phase. Impairment of PGE₂ and/or EP2 might play a role in FLP (category IIB/III) and MLP (I/IIA) endometrial fibrogenesis because of the reduction in its antifibrotic capacity. In conclusion, priming of the endometrium with endogenous ovarian steroids might inhibit the antifibrotic PGE₂ pathway either in healthy or pathologic tissues with collagen formation after NETs proteases action.

Early pregnancy in the mare: old concepts revisited

"Maternal recognition of pregnancy" (MRP) is commonly used to describe the ongoing embryo-maternal communication during early pregnancy that culminates in prevention of luteolysis and ensures ongoing progestin support. The conceptus-derived pregnancy recognition signal has not yet been identified in the mare. Although equine conceptuses produce substantial amounts of estrogens, there is a lack of evidence that estrogens are the pregnancy recognition signal in mares. Conceptus mobility is integral to MRP and is driven by conceptus-derived prostaglandin production. Cessation of conceptus mobility, referred to as fixation, is caused by increases in conceptus size and uterine tone and reduction in sialic acid content of the embryonic capsule. Gene expression profiling of equine preimplantation conceptuses revealed expression of neuraminidase 2 (NEU2), an enzyme that cleaves sialic acid from polysaccharide chains. Furthermore, secretion of NEU2 by conceptuses in vitro was functionally active; it appears therefore, that the conceptus itself regulates sialic acid content through expression of NEU2. Based on gene expression profiling, equine conceptuses express increasing amounts of fibrinogen during early development. Western blot analysis confirmed secretion of fibrinogen into culture medium when conceptuses were cultured in vitro and with immunohistochemistry, the acellular glycoprotein capsule of the conceptus had particularly intense staining for fibrinogen. Therefore, we hypothesize that conceptus-derived fibrinogen interacts with endometrial integrins to promote cessation of conceptus mobility and fixation. Indeed, next generation sequencing analysis of conceptus and endometrial samples 16 d after ovulation revealed that the integrin signaling pathway is significantly enriched in both sample types. Real-time reverse transcription polymerase chain reaction (RT-PCR) confirmed ITGAVB1 as the most abundant integrin receptor in endometrium; fibrinogen has the highest affinity for ITGAVB1 among integrins receptors to which it binds. Finally, the equine conceptus expresses increasing quantities of relaxin during preimplantation development, with the endometrium expressing relaxin receptors. In the pig, mouse, and human, relaxin is produced by the corpus luteum and is known to promote angiogenesis during early pregnancy. In summary, substantial advances in understanding MRP in the horse are underway.

How ultrasound technologies have expanded and revolutionized research in reproduction in large animals

Gray-scale ultrasonic imaging (UI) was introduced in 1980 and initially was used to examine clinically the reproductive tract of mares. By 1983 in mares and 1984 in heifers/cows, UI had become a tool for basic research. In each species, transrectal gray-scale UI has been used extensively to characterize follicle dynamics and investigate the gonadotropic control and hormonal role of the follicles. However, the use of transrectal UI has also disclosed and characterized many other aspects of reproduction in each species, including (1) endometrial echotexture as a biological indicator of circulating estradiol concentrations, (2) relative location of the genital tubercle for fetal gender diagnosis by Days 50 to 60, and (3) timing of follicle evacuation during ovulation. Discoveries in mares include (1) embryo mobility wherein the spherical conceptus (6-16 mm) travels to all parts of the uterus on Days 11 to 15, (2) how one embryo of a twin set eliminates the other without self-inflicted damage, and (3) serration of the granulosum of the preovulatory follicle opposite to the future rupture site as an indicator of imminent ovulation. Studies with color-Doppler UI have shown that vascular perfusion of the endometrium follows the equine embryo back and forth between uterine horns and follows the expansion of the bovine allantochorion throughout each horn. In heifers, blood flow in the CL increases during the ascending portion of an individual pulse of PGF2α metabolite and then decreases. These examples highlight the power of UI in reproduction research. Without UI, it is likely that these and many other findings would still be unknown.

Maternal recognition of pregnancy in the horse: a mystery still to be solved

Maternal recognition of pregnancy in the horse is the sum of events leading to maintenance of pregnancy; in a narrow sense, maternal recognition of pregnancy refers to the physiological process by which the lifespan of the corpus luteum is prolonged. The horse is one of the few domestic species in which the conceptus-derived pregnancy recognition signal has not been identified. The presence of the conceptus reduces pulsatile prostaglandin F2α secretion by the endometrium during early gestation in the mare, partly attributed to the reduced expression of cyclooxygenase-2. Cyclooxygenase-2 has therefore been suggested as one of the regulators of endometrial prostaglandin F2α release modified by the antiluteolytic factor secreted by the conceptus. In addition, altered oxytocin responsiveness has been implicated in the adjustment of prostaglandin release in pregnant mares. While conceptus mobility has proven to be essential for establishment of pregnancy, conceptus-derived oestrogens and prostaglandins, principally prostaglandin E2, have not been confirmed as the critical antiluteolytic factor. Various ways to induce prolonged luteal function in the non-pregnant mare will be highlighted in the current review, specifically, how they may pertain to the process of maternal recognition of pregnancy. Furthermore, recently published microarray experiments comparing the transcriptome of pregnant and non-pregnant endometria and different stages of conceptus development will be reviewed. Findings include the prevention of conceptus adhesion, the provision of nutrients to the conceptus and the avoidance of immunological rejection, among others.

Effect of seminal plasma on uterine inflammation, contractility and pregnancy rates in mares

REASONS FOR PERFORMING STUDY

There is conflicting evidence over the role seminal plasma plays in sperm transport and inflammation within the uterus of mares. In in vitro studies, seminal plasma has been shown to reduce polymorphonuclear neutrophil (PMN) function, but the opposite effect on uterine inflammation has been reported in vivo.

OBJECTIVES

To study the effect of seminal plasma on uterine contractility, inflammation and pregnancy rates by inseminating mares with low doses of sperm free from seminal plasma (Group 1) and containing seminal plasma (Group 2).

METHODS

Synchronised mares were inseminated with 50 x 10(6) sperm in either skim milk extender or seminal plasma. Uterine lavage was performed 6 h after insemination to assess the inflammatory response. The contraction frequency of the uterus was measured over a 4 min period 10 mins and 6 h after insemination, using B-mode ultrasonography. Pregnancy rates were assessed 16 days after insemination.

RESULTS

Uterine contractions were less frequent in Group 1 mares inseminated with seminal plasma and significantly more PMNs were found in the lavage fluid of those mares. Pregnancy rates were identical in both groups (62%).

CONCLUSIONS

This study provides evidence that seminal plasma decreases uterine contractility and increases the inflammatory response of the uterus to semen. No effect of seminal plasma on pregnancy rates was demonstrated.

POTENTIAL RELEVANCE

Mares that develop persistent mating-induced endometritis may have inherently poor uterine contractility and impaired uterine clearance. The presence of seminal plasma during breeding may not be desirable in these mares. The role of seminal plasma in problem mares warrants additional study.

In vitro response of prostaglandin E2 receptor (EP3) in the term pregnant rat uterus and cervix to misoprostol

We examined and compared the in vitro effects of misoprostol (synthetic prostaglandin E1 (PGE1) analogue) on prostaglandin E2 (PGE2) secretion and EP3 receptor mRNA expression in the pregnant rat myometrium and cervix at 19 days gestation. Myometrial and cervical tissue samples were exposed to media with or without misoprostol (50 or 100 pg/ml) and incubated for 15 and 30 min, and 1, 3, 6, 12, and 24 h. Media and tissue samples were collected for quantification of PGE2 and mRNA expression of rEP3alpha and rEP3beta receptor, respectively. PGE2 secretion increased (P < or = 0.05) in the myometrium exposed to 50 and 100 pg/ml misoprostol. Cervical PGE2 secretion increased following exposure to the 100 pg/ml dose only. In the myometrium, 50 and 100 pg/ml misoprostol induced elevations in rEP3alpha and rEP3beta receptor mRNA expression. rEP3alpha and rEP3beta receptor mRNA expression in the cervix was not different from controls. These data demonstrate that the EP3 receptor is differentially expressed in the myometrium and cervix in response to misoprostol. This may account for the ability of misoprostol to stimulate the myometrium when administered for cervical ripening.