Effects of cell storage and passage on basal and oxytocin-regulated prostaglandin secretion by equine endometrial epithelial and stromal cells

Intrauterine devices influence prostaglandin secretion by equine uterus: in vitro and in vivo studies

BACKGROUND

Intrauterine devices (IUD) are used in the veterinary practice as the non-pharmacological method of oestrus suppression in mares. When placed in the uterus, IUD create a physical contact with the endometrium that mimics the presence of an equine embryo. However, the mechanism of their action has not been fully elucidated. The objective of the present study was to examine the effect of mechanical stimulation of IUD on mare`s endometrium in both in vitro and in vivo study. For this purpose, we demonstrated the effect of IUD on prostaglandin (PG) F2α and PGE2 secretion, and mRNA transcription of genes involved in PG synthesis pathway in equine endometrial cells in vitro. In the in vivo study, we aimed to compare short-term effect of IUD inserted on day 0 (oestrus) with day 5-6 post-ovulation (the specific time when embryo reaches uterus after fertilization) on PG secretion from equine endometrium. To determine the long-term effect on PG synthase mRNA transcription, a single endometrial biopsy was taken only once within each group of mares at certain time points of the estrous cycle from mares placement with IUD on days 0 or 5-6 post-ovualtion.

RESULTS

We showed for the first time that the incubation of the endometrial cells with the presence of IUD altered the pattern of PG synthase mRNA transcription in equine epithelial and stromal endometrial cells. In vivo, in mares placement with IUD on day 0, PGE2 concentrations in blood plasma were upregulated between 1 and 6, and at 10 h after the IUD insertion, compared with the control mares (P < 0.05). Moreover, the decrease of PTGFS mRNA transcription on day 16- 18, associated with an elevation in PTGES mRNA transcription on day 20 -21 of the estrous cycle in endometrial biopsies collected from mares placement with IUD on days 5-6 suggest an antiluteolytic action of IUD during the estrous cycle.

CONCLUSION

We conclude that the application of IUD may mimic the equine conceptus presence through the physical contact with the endometrium altering PG synthase transcription, and act as a potent modulator of endometrial PG secretion both in vitro and in vivo.

Transcriptomic profiling of mare endometrium at different stages of endometrosis

In the current study, transcriptome profiles of mare endometrium, classified into categories I, IIA, and IIB according to Kenney and Doig, were compared using RNA sequencing, analyzed, and functionally annotated using in silico analysis. In the mild stage (IIA) of endometrosis compared to category I endometrium, differentially expressed genes (DEGs) were annotated to inflammation, abnormal metabolism, wound healing, and quantity of connective tissue. In the moderate stage (IIB) of endometrosis compared to category I endometrium, DEGs were annotated to inflammation, fibrosis, cellular homeostasis, mitochondrial dysfunction, and pregnancy disorders. Ingenuity pathway analysis (IPA) identified cytokines such as transforming growth factor (TGF)-β1, interleukin (IL)-4, IL-13, and IL-17 as upstream regulators of DEGs associated with cellular homeostasis, metabolism, and fibrosis signaling pathways. In vitro studies showed the effect of these cytokines on DEGs such as ADAMTS1, -4, -5, -9, and HK2 in endometrial fibroblasts at different stages of endometrosis. The effect of cytokines on ADAMTS members' gene transcription in fibroblasts differs according to the severity of endometrosis. The identified transcriptomic changes associated with endometrosis suggest that inflammation and metabolic changes are features of mild and moderate stages of endometrosis. The changes of ADAMTS-1, -4, -5, -9, in fibrotic endometrium as well as in endometrial fibroblast in response to TGF-β1, IL-4, IL-13, and IL-17 suggest the important role of these factors in the development of endometrosis.

The potential role of miRNAs and regulation of their expression in the development of mare endometrial fibrosis

Mare endometrial fibrosis (endometrosis), is one of the main causes of equine infertility. Despite the high prevalence, both ethology, pathogenesis and the nature of its progression remain poorly understood. Recent studies have shown that microRNAs (miRNAs) are important regulators in multiple cellular processes and functions under physiological and pathological circumstances. In this article, we reported changes in miRNA expression at different stages of endometrosis and the effect of transforming growth factor (TGF)-β1 on the expression of the most dysregulated miRNAs. We identified 1, 26, and 5 differentially expressed miRNAs (DEmiRs), in categories IIA (mild fibrosis), IIB (moderate fibrosis), and III (severe fibrosis) groups compared to category I (no fibrosis) endometria group, respectively (Padjusted < 0.05, log2FC ≥ 1.0/log2FC ≤  - 1.0). This study indicated the potential involvement of miRNAs in the regulation of the process associated to the development and progression of endometrosis. The functional enrichment analysis revealed, that DEmiRs target genes involved in the mitogen-activated protein kinases, Hippo, and phosphoinositide-3-kinase (PI3K)-Akt signalling pathways, focal adhesion, and extracellular matrix-receptor interaction. Moreover, we demonstrated that the most potent profibrotic cytokine-TGF-β1-downregulated novel-eca-miR-42 (P < 0.05) expression in fibroblasts derived from endometria at early-stage endometrosis (category IIA).

The Roles of Extracellular Vesicles and Organoid Models in Female Reproductive Physiology

Culture model systems that can recapitulate the anatomy and physiology of reproductive organs, such as three-dimensional (3D) organoid culture systems, limit the cost and welfare concerns associated with a research animal colony and provide alternative approaches to study specific processes in humans and animals. These 3D models facilitate a greater understanding of the physiological role of individual cell types and their interactions than can be accomplished with traditional monolayer culture systems. Furthermore, 3D culture systems allow for the examination of specific cellular, molecular, or hormonal interactions, without confounding factors that occur with in vivo models, and provide a powerful approach to study physiological and pathological reproductive conditions. The goal of this paper is to review and compare organoid culture systems to other in vitro cell culture models, currently used to study female reproductive physiology, with an emphasis on the role of extracellular vesicle interactions. The critical role of extracellular vesicles for intercellular communication in physiological processes, including reproduction, has been well documented, and an overview of the roles of extracellular vesicles in organoid systems will be provided. Finally, we will propose future directions for understanding the role of extracellular vesicles in normal and pathological conditions of reproductive organs, utilizing 3D organoid culture systems.

Evaluation of growth, viability, and structural integrity of equine endometrial organoids following cryopreservation

Reproductive diseases in mares are a significant cause of subfertility and profound economic loss in the equine industry. Utilizing a 3D in vitro cell culture system that recapitulates the in vivo physiology will reduce time, cost, and welfare concerns associated with in vivo reproductive research in mares. If this 3D model is combined with effective cryopreservation, reproductive research on mares can occur year-round, which is not currently possible in this seasonal species. Endometrial organoids, 3D in vitro cell clusters that exhibit in vivo uterine physiology, have been established in mice, women, and mares. Here we report the first comprehensive assessment of cryopreservation of endometrial organoids in the domestic mare. Organoid growth rate was not affected by the type of freezing media. However, growth rate varied among non-cryopreserved controls, organoids cryopreserved at passage 0 (P0), and organoids cryopreserved at passage 3 (P3). Additionally, there was no difference in organoid viability among freezing media or freezing timepoint (passages). Furthermore, fresh and frozen-thawed organoids displayed positive immunohistochemical staining for ZO-1, which is a marker for intercellular tight junctions, and for periodic acid-Schiff staining as marker for organoid function through mucin production. Results demonstrate that equine endometrial organoids can be cryopreserved with 10% dimethyl sulfoxide with minimal detrimental effects while maintaining intercellular tight junctions (ZO-1) and secretory function. Availability of cryopreserved endometrial organoids may permit expanded research on uterine pathologies that negatively affect mare fertility and improve efficiency, reduce cost, and minimize animal welfare concerns associated with in vivo research in the domestic mare.

Seasonal and Nutritional Fluctuations in the mRNA Levels of the Short Form of the Leptin Receptor (LRa) in the Hypothalamus and Anterior Pituitary in Resistin-Treated Sheep

Simple Summary

Research since the discovery of leptin has mainly focused on the long form of the leptin receptor. Currently, experiments on the short form of the leptin receptor have confirmed that not only is short form of leptin receptor present in the hypothalamus, but also expanded knowledge with information documenting the specific expression of that form of leptin receptor in selected areas of the hypothalamus and in the pituitary gland. In addition, we have shown that short form of leptin receptor expression levels are affected by day length, adiposity and resistin in sheep.

Abstract

The short form of the leptin receptor (LRa) plays a key role in the transport of leptin to the central nervous system (CNS). Here, the resistin (RSTN)-mediated expression of LRa in the preoptic area (POA), ventromedial and dorsomedial nuclei (VMH/DMH),arcuate nucleus (ARC) and the anterior pituitary gland (AP)was analyzed considering the photoperiodic (experiment 1) and nutritional status (experiment 2) of ewes. In experiment 1, 30 sheep were fed normally and received one injection of saline or two doses of RSTN one hour prior to euthanasia. RSTN increased LRa expression mainly in the ARC and AP during long days (LD) and only in the AP during short days (SD). In experiment 2, an altered diet for 5 months created lean or fat sheep. Twenty sheep were divided into four groups: the lean and fat groups were given saline, while the lean-R and fat-R groups received RSTN one hour prior to euthanasia. Changes in adiposity influenced the effect of RSTN on LRa mRNA transcript levels in the POA, ARC and AP and without detection of LRa in the VMH/DMH. Overall, both photoperiodic and nutritional signals influence the effects of RSTN on leptin transport to the CNS and are involved in the adaptive/pathological phenomenon of leptin resistance in sheep.

Effects of cortisol on prostaglandin F2α secretion and expression of genes involved in the arachidonic acid metabolic pathway in equine endometrium - In vitro study

Glucocorticoids (GCs) are known to play an important role in maintaining basal and stress-related homeostasis by interacting with endocrine mediators and prostaglandins (PGs). Although a growing body of evidence shows that GCs exert their regulatory action at a multitude of sites in the reproductive axis through corticosteroid receptors, little is known about the direct role of cortisol, an active form of GCs, in the equine endometrium. Thus, the study aimed to determine the effect of cortisol on PGF_2α synthesis in the endometrial tissue and cells in vitro. In Exp.1, the immunolocalization and the expression of the glucocorticoid receptor (GCR) in the endometrium throughout the estrous cycle were established. In Exp. 2 and 3, the effects of cortisol on PGF_2α secretion and transcripts associated with the arachidonic acid (AA) cascade in endometrial tissues, and cells were defined. Endometrial tissues obtained from the early, mid, and late luteal phases and the follicular phase of the estrous cycle were exposed to cortisol (100, 200, and 400 nM) for 24 h. Endometrial epithelial and stromal cells (early phase of estrous cycle) were exposed to cortisol (100 nM) for 24 h. Then, PGF_2α secretion and transcripts associated with the AA cascade (PLA2G2A, PLA2G4A, PTGS2, and PGFS) were assessed. GCR was expressed in the cytoplasm and the nucleus in the luminal and glandular epithelium as well as in the stroma. Endometrial GCR protein abundance was up-regulated at the late luteal phase compared to the mid-luteal phase of the estrous cycle. Cortisol dose-dependently decreased PGF_2α secretion, PLA2G2A and PLA2G4A transcripts in endometrial tissues. Additionally, cortisol treatment decreased PGF_2α secretion from endometrial epithelial and stromal cells. Moreover, it affected PLA2G2A, PLA2G4A, and PTGS2 transcripts in endometrial stromal cells. These findings suggest that cortisol suppresses the synthesis of PGF_2α by affecting the AA cascade in the equine endometrium during the estrous cycle.

Fibrinogen in equine pregnancy as a mediator of cell adhesion, an epigenetic and functional investigation

Preimplantation equine embryos synthesize and secrete fibrinogen, which is a peculiar finding as fibrinogen synthesis almost exclusively occurs in the liver. This study investigated the hypothesis that conceptus-derived fibrinogen mediates cell adhesion during fixation. On day 21 of pregnancy, five integrin subunits, including ITGA5, ITGB1, ITGAV, and ITGB1, displayed significantly higher transcript abundance than on day 16 of pregnancy. Endometrial epithelial cells adhered to fibrinogen in an integrin-dependent manner in an in vitro cell adhesion assay. Bilaminar trophoblast and allantochorion expressed fibrinogen transcript, indicating that fibrinogen expression persists past fixation. Preimplantation-phase endometrium, conceptuses, and microcotyledonary tissue expressed components of the clotting cascade regulating fibrin homeostasis, leaving open the possibility that fibrinogen is converted to fibrin. Fibrinogen is likely to have functions beyond mediating cell adhesion, such trapping growth factors and triggering signaling cascades, and has remarkable parallels to the expression of fibrinogen by some tumors. The deposition of fibrinogen within tumor stroma is characteristic of breast carcinoma, and tumor-derived fibrinogen has been implicated in the metastatic potential of circulating tumor cells. DNA methylation of the fibrinogen locus in equine conceptuses was examined in comparison to liver and endometrium, and across the full gene cluster, was significantly higher for endometrium than liver and conceptus. DNA methylation of regulatory regions did not differ between liver and conceptus, and was significantly lower than in endometrium. These results, therefore, support the hypothesis of DNA methylation being a regulator of fibrinogen expression in the conceptus.

A review of in vivo and in vitro studies of the mare endometrium

The inner layer of the uterus, the endometrium, is responsible and necessary for many reproductive functions. Normal reproductive cyclicity, maternal recognition of pregnancy, maternal interaction with the embryo, and interaction of the reproductive tract with pathogens are dependent on the endometrium. Although most studies have been conducted in vivo using live animals, recent advances in in vitro approaches could facilitate future research in a laboratory setting with minimal effect on animals. Many reproductive studies have been performed in vivo and in vitro in equids, but new in vitro methods to study the endometrium of mares remain unexplored. In this review, there is a description of the normal anatomy and physiology of the mare endometrium in vivo, in vitro endometrial cell culture techniques that have been previously described for the mare, and opportunities for future reproductive research using in vitro methods.

Prostaglandins effect on matrix metallopeptidases and collagen in mare endometrial fibroblasts

An increasing number of studies have shown that prostaglandins (PGs) exert multiple regulatory actions in the processes associated to tissue remodeling and fibrosis. Extracellular matrix (ECM) turnover is mediated by matrix metallopeptidases (MMPs). The knowledge about the regulation of their expression in mare endometrium is still limited. Thus, the aim of this study was to investigate whether: (i) profibrotic transforming growth factor (TGF)-β1 modulates PG production in equine endometrium; and (ii) PGE₂ and PGF_2α modulate MMPs, their tissue inhibitors (TIMPs), and collagen 1 (COL1) expression. In experiment 1, the effect of TGF-β1 (5 ng/mL) on PG secretion and PG synthases mRNA transcription, after 24 and 48 h treatment of mare endometrial fibroblast and epithelial cells was investigated using ELISA and qPCR. In experiment 2, the effects of PGE₂ and PGF_2α in doses 10^_-7M and 10^-8M on secretion and MMP1, 2, 9, 13, TIMP1, 2, and COL1A1 mRNA transcription in mare endometrial fibroblasts were assessed. Transforming growth factor-β1 treatment decreased secretion of PGF_2α by endometrial fibroblasts (P < 0.05) and PGF_2α and PGE₂ by endometrial epithelial cells (P < 0.05). Prostaglandin E₂ increased MMP-2 and MMP-9, and decreased MMP-13 secretion by endometrial fibroblasts (P < 0.05). Additionally, PGF_2α treatment increased MMP-2, MMP-13 and COL1, but decreased MMP-1 secretion by endometrial fibroblasts (P < 0.05). Prostaglandins may be involved in the processes associated to pathological endometrial remodeling by their effect on MMP expression. The effect of PGF_2α on COL1 secretion from fibroblasts suggests its profibrotic role in pathological endometrial remodeling.

Persian onager (Equus hemionus onager) endometrial explant cryopreservation and in vitro culture

Assisted reproduction of endangered equids, such as Persian onagers (Equus hemionus onager), is vital for species conservation. Little is known about Persian onager reproductive functions, including functions of the uterine endometrium. Recently, successful cryopreservation of the domestic mare endometrium was reported, but there is no information on cryo-sensitivity or in vitro culture of endometrial tissues of any non-domestic equid. In the present study, endometrial explants from Persian onagers were cryopreserved and cultured in vitro for 5 days. There was no difference between endometrial explants when 10% and 20% dimethyl sulfoxide (DMSO) was used for cryopreservation. Cell viability and structural integrity were comparable to fresh tissue. Abundance of estrogen receptor-α (ESR1) and progesterone receptor (PGR) mRNA transcript in endometrial explants was less in most treatment groups compared to the fresh tissue control. There was variation in E-cadherin mRNA abundance in endometrial explants among treatment groups with some treatment groups having a lesser abundance compared to the control group. The abundance of Ki67 mRNA transcript of endometrial explants was not different among treatment groups compared to the control group. Results indicate that DMSO is a suitable cryoprotectant for the Persian onager endometrium, and in vitro culture in a liquid-gas interface can maintain Persian onager endometrial explants for as long as 5 days. Findings allow for a greater understanding of reproductive mechanisms in vitro for this endangered species and other domestic equids including donkeys.

Matrix metallopeptidase expression and modulation by transforming growth factor-β1 in equine endometrosis

Equine endometrial fibrosis (endometrosis) is described as a degenerative chronic condition in the uterus. Its characteristic feature is excessive deposition of extracellular matrix (ECM) components around the endometrial glands and stroma. Although matrix metallopeptidases (MMPs) that mediate ECM turnover are important factors in the process of fibrosis, knowledge of their expression and regulation in endometrosis is limited. In other species, one of the important regulators of MMPs and tissue inhibitors of MMPs (TIMPs) is transforming growth factor (TGF)-β1. The goal of this study was to determine (i) endometrial expression of MMPs and TIMPs during endometrosis and (ii) the effect of TGF-β1 on expression of MMPs and TIMPs in equine endometrial fibroblasts and epithelial cells. In the follicular phase of the estrous cycle, MMP-1, -2, -9, and TIMP concentrations were higher during endometrosis than in healthy endometrium (P < 0.05). In the midluteal phase, MMP-3 concentration was lower in severe endometrosis compared to healthy endometrium (P < 0.05). In fibroblasts, TGF-β1 upregulated MMP-1, -9, -13, and TIMP1, but downregulated MMP-3 secretion (P < 0.05). In epithelial cells, TGF-β1 upregulated MMP-1, -9, -13, and TIMP secretion (P < 0.05). Endometrial expression of MMPs and TIMPs is altered during endometrosis. TGF-β1 is a regulator of endometrial ECM remodeling via its effect on MMPs and TIMPs in equine endometrial fibroblasts and epithelial cells.

Dimethyl sulfoxide maintains structure and function of cryopreserved equine endometrial explants

Availability of viable frozen-thawed endometrial tissues could facilitate detailed studies into physiologic and disease processes influencing the endometrium. This study was designed to investigate the cryosurvival of equine endometrial tissue. Previous studies in the human and horse have focused on cryopreservation of dissociated endometrial cells. To our knowledge, there are no studies on cryopreservation of endometrial explants. Our objectives were to 1) determine the influence of differing concentrations of the permeating cryoprotectant dimethyl sulfoxide (Me₂SO) on viability, structural integrity, and gene expression of cryopreserved equine endometrial tissues prior to and following a 5-day explant culture in vitro and 2) examine the influence of low (1000 mg/L dextrose) vs high (4500 mg/L dextrose) glucose medium during in vitro culture. Both 10% and 20% (v/v) concentrations of Me₂SO maintained viability following cryopreservation and in vitro culture. In addition, gene expression remained unaltered following cryopreservation with either 10% or 20% Me₂SO. However, tissue structural integrity was slightly reduced compared to the fresh control. Furthermore, there was no difference in structural integrity, cell viability, or gene expression between low and high glucose medium during in vitro culture. Although E-cadherin and Ki67 gene expression was not different among fresh, 10% Me₂SO, and 20% Me₂SO treatments prior to or following tissue culture, estrogen receptor-α and progesterone receptor gene expression were reduced in all groups after explant culture. This is the first report of successful cryopreservation of equine endometrial explants.

Expression profiling of selected miRNAs in equine endometrium in response to LPS challenge in vitro: A new understanding of the inflammatory immune response

Bacterial infections of the genital tract are the major cause of reproductive failure in the mares. MiRNAs are important regulators of gene expression, mostly through transcriptional and translational regression. We hypothesized that LPS induced aberrant expression of miRNAs and their targets, which are involved in regulation of uterine homeostasis. Three groups of primary endometrial epithelial and stromal cells, and endometrial tissue explants were cultured. The 1^st group was kept as control, while the 2^nd and 3^rd groups were challenged with low (0.5 μg/mL) or high (3.0 μg/mL) doses of Lipopolysaccharides (LPS). Cell pellets and tissue explants were collected after 24 and 48 h, for total RNA isolation and qRT-PCR of the selected miRNAs and their targets. Culture media and cell lysates were collected after 24 and 48 h, for cytokines (IL6 and TNF_α) and prostaglandins (PGE₂ & PGF_α2) measurement. Both endometrial cells expressed TLR4 and its accessory molecules (MyD88 & CD14) that are required for triggering inflammatory immune response after LPS, via up-regulation of TRAF6, TNF_α, IL6 and IL8, compared to the respective control. After both doses of LPS challenge, miR-155, miR-223 and miR-17 were significantly increased; miR-181b, miR-21 and let-7a were significantly decreased compared to respective controls. Interestingly, miR-24 and miR-532-5p were clearly up-regulated after only the low LPS dose. TNF_α, IL6 and PGs in culture media and from cell lysates revealed dose- and time-dependent patterns, after LPS. Results indicated that both epithelial and stromal cells have a primary role in innate immune response after LPS challenge, while this recognition occurred via TLR4 and its accessory molecules. Dysregulation of miRNAs and their targets expression after LPS might affect normal uterine function through perturbation of PG and cytokine secretion.

Effect of transforming growth factor -β1 on α-smooth muscle actin and collagen expression in equine endometrial fibroblasts

Transforming growth factor (TGF)-β1 not only regulates cell growth, development, and tissue remodeling, but it also participates in the pathogenesis of tissue fibrosis. In the equine endometrium, the concentration of TGF-β1 is correlated with endometrosis (equine endometrial fibrosis). In other tissues, TGF-β1 induces differentiation of many cell types into myofibroblasts. These cells are characterized by α-smooth muscle actin (α-SMA) expression and an ability to deposit excessive amounts of extracellular matrix (ECM) components. The aim of the study was to determine whether TGF-β1 plays a role in the development of equine endometrosis. In Exp. 1, endometrial expression of α-SMA in different stages of endometrosis was determined. In endometrial tissues from the mid luteal phase (n = 6 for each stages of endometrosis) and the follicular phase of the estrous cycle (n = 5 for each stages of endometrosis), mRNA transcription and protein expression of α-Sma were evaluated by Real-time PCR and Western-blot, respectively. The α-Sma mRNA transcription and protein expression levels were correlated with the severity of endometrosis (P < 0.05). In both phases of the estrous cycle, α-SMA protein expression was up-regulated in final stage of endometrosis compared to initial stage (P < 0.05). In Exp. 2, the dose- and time-dependent effects of TGF-β1 on expression of α-SMA and ECM components were determined, as well as cell proliferation of equine fibroblasts. Equine endometrial fibroblasts (n = 6, Kenney and Doig category I) were stimulated with vehicle or TGF-β1 (1, 5, 10 ng/ml) for 24, 48 or 72 h. Then, mRNA transcription of α-Sma, collagen type I (Col1a1), collagen type III (Col3a1) and fibronectin 1 (Fn1) were determined by Real-time PCR. The production of ECM components was determined by ELISA. Transforming growth factor-β1 increased the mRNA transcription of α-Sma and ECM components in a dose- and time-dependent manner in cultured endometrial fibroblasts (P < 0.05). Additionally, TGF-β1 at a dose of 10 ng/ml increased α-SMA protein expression and COL1, COL3, FN production after 72 h of stimulation (P < 0.05). The data showed a positive linkage between the presence of myofibroblasts and severity of endometrosis. We conclude that TGF-β1 may participate in pathological fibrotic changes in equine endometrial tissue by induction of myofibroblast differentiation, increased production of ECM components and fibroblast proliferation.

Equine Endometrial Explants Undergo Significant Degenerative Changes in Culture

This study evaluated equine endometrial explants following 12, 24, and 48 hr in culture. Measurement of an indicator of cell death in explant supernatant, light microscopy, and gene expression of biomarkers of endometrial function and cellular stress were used to compare the effect of six different media on explant viability and morphology. Viability of explants was assessed indirectly through measuring LDH activity in the culture supernatant. Regardless of culture medium composition, a significant increase in LDH activity was observed within 12 hr of culture, indicating occurrence of cell damage. Morphological analysis through light microscopy revealed degenerative changes occurring within 12 hr and, after 48 hr, there is nearly complete loss of luminal and superficial glandular epithelium and diffuse detachment of deep glandular epithelium. Transcript abundance of prostaglandin-endoperoxide synthase 2 (PTGS2), estrogen receptor 1 (ESR1), and vascular endothelial growth factor (VEGF) was assessed as biomarkers of endometrial function. A marked increase in PTGS2 and VEGF expression occurred; ESR1 displayed more or less steady expression levels. Above-described changes were seen irrespective of cell culture medium used. The marked increase in expression in PTGS2 expression presents a limitation to using endometrial explants in the current culture system to study aspects of endometrial function such as the inflammatory response to insemination. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 301:148-153, 2018. © 2017 Wiley Periodicals, Inc.

Evidence for a PGF2α auto-amplification system in the endometrium in mares

In mares, prostaglandin F2α (PGF2α) secreted from the endometrium is a major luteolysin. Some domestic animals have an auto-amplification system in which PGF2α can stimulate its own production. Here, we investigated whether this is also the case in mares. In an in vivo study, mares at the mid-luteal phase (days 6-8 of estrous cycle) were injected i.m. with cloprostenol (250 µg) and blood samples were collected at fixed intervals until 72 h after treatment. Progesterone (P4) concentrations started decreasing 45 min after the injection and continued to decrease up to 24 h (P < 0.05). In turn, 13,14-dihydro-15-keto-PGF2α (PGFM) metabolite started to increase 4h after an injection and continued to increase up to 72 h (P < 0.05). PGF receptor (PTGFR) mRNA expression in the endometrium was significantly higher in the late luteal phase than in the early and regressed luteal phases (P < 0.05). In vitro, PGF2α significantly stimulated (P < 0.05) PGF2α production by endometrial tissues and endometrial epithelial and stromal cells and significantly increased (P < 0.05) the mRNA expression of prostaglandin-endoperoxide synthase-2 (PTGS2), an enzyme involved in PGF2α synthesis in endometrial cell. These findings strongly suggest the existence of an endometrial PGF2α auto-amplification system in mares.

Ovarian steroids affect prostaglandin production in equine endometrial cells in vitro

This study aimed to evaluate the influence of ovarian steroids on equine endometrial epithelial and stromal cells, specifically i) prostaglandin (PG) production in a time-dependent manner, ii) specific PG synthases mRNA transcription and protein expression, and iii) cell proliferation. After passage I, cells were exposed to vehicle, oxytocin (OT, positive control, 10(-7) M), progesterone (P4, 10(-7) M), 17β estradiol (E2, 10(-9) M), or P4+E2 for 12, 24, 48, or 72 h. Following treatment, PG concentration was determined using the direct enzyme immunoassay (EIA) method. Alterations in PG synthases mRNA transcriptions, PG synthases protein expression, and cell proliferation in response to the treatments were determined after 24 h using real-time PCR, western blot, or 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide respectively. After 24 h, E2 and P4+E2 increased PGE2 and PGF2α secretion as well as specific prostaglandin-endoperoxide synthase-2 (PTGS2), PGE2 synthases (PGES), and PGF2α synthases (PGFS) expression in the epithelial cells (P<0.05). Additionally, E2 and P4+E2 increased PTGS2 expression in stromal cells after 24 h (P<0.05). In stromal cells, P4+E2 increased PGE2 production as well as PGES expression after 24 h (P<0.05). Both E2 and P4+E2 increased PGF2α production by stromal cells after 24 h (P<0.05). Ovarian steroids affected proliferation of stromal and epithelial cells during the 24-h incubation period (P<0.05). We provide evidence that ovarian steroids affect PG production in equine endometrial cells, upregulating PTGS2, PGES, and PGFS expression. Ovarian steroid-stimulated PG production could be an important mechanism occurring in the equine endometrium that is involved in the regulation of the estrous cycle and early pregnancy.

Interleukins affect equine endometrial cell function: modulatory action of ovarian steroids

The aim of the present study was to investigate the interaction between ovarian steroids, interleukins and prostaglandins (PG) in equine epithelial and stromal cells in vitro. In Experiment 1, cells were exposed to IL-1α (10 ng/mL), IL-1β (10 ng/mL) or IL-6 (10 ng/mL) for 24 h and cell proliferation was determined using MTT. In Experiment 2, cells were exposed to progesterone (P₄; 10⁻⁷ M); 17-β estradiol (E₂; 10⁻⁹ M) or P₄+E₂ for 24 h and later medium was replaced with a fresh one treated with IL-1α, IL-1β or IL-6 (10 ng/mL, each) for 24 h. The oxytocin (OT; 10⁻⁷ M) was used as a positive control. In Experiment 3, cells were exposed to P₄ (10⁻⁷ M), E₂ (10⁻⁹ M) or P₄+E₂ for 24 h and the IL receptor mRNAs transcription was determined using Real-time PCR. Prostaglandins concentration was determined using the direct enzyme immunoassay (EIA) method. Our findings reveal a functional linking between ovarian steroids and IL-stimulated PG secretion by equine endometrial cells. This interaction could be one of the mechanisms responsible for endometrial local orchestrating events during the estrous cycle and early pregnancy.

Effect of cytokines and ovarian steroids on equine endometrial function: an in vitro study

Regulation of immune–endocrine interactions in the equine endometrium is not fully understood. The aims of the present study were to: (1) investigate the presence of tumour necrosis factor alpha (TNF), interferon gamma (IFNG), Fas ligand (FASLG) and their receptors in the mare endometrium throughout the oestrous cycle; and (2) assess endometrial secretory function (prostaglandins), angiogenic activity and cell viability in response to TNF, oestradiol (E2), progesterone (P4) and oxytocin (OXT). Transcription of TNF and FASLG mRNA increased during the early and late luteal phase (LP), whereas IFNG mRNA increased in late LP. Transcription of the mRNA of both TNF receptors was highest in the mid-LP. All cytokines and receptors were expressed in surface and glandular epithelium, as well as in the stroma. Expression of TNF and its receptor TNFRSF1A increased during the follicular phase (FP) and mid-LP. IFNG was expressed in the mid-LP, whereas its receptor IFNR1 was expressed in the in mid- and late LP. The highest expression of FASLG and FAS occurred during the late LP. OXT increased the secretion of prostaglandin (PG) E2 and PGF2α in the FP and mid-LP. In the mid-LP, E2 and P4+E2 stimulated PGF2α secretion, whereas TNF and P4 increased cell viability. All treatments, with the exception of P4, increased nitric oxide and angiogenic activity in both phases. The coordinated action of cytokines and ovarian hormones may regulate secretory, angiogenic and proliferative functions in the equine endometrium.

Effects of oxytocin, lipopolysaccharide (LPS), and polyunsaturated fatty acids on prostaglandin secretion and gene expression in equine endometrial explant cultures

Increased secretion of prostaglandin F(2)α (PGF(2)α) within the uterus because of uterine inflammation can cause luteolysis and result in early embryonic loss. Supplementation with polyunsaturated fatty acids (PUFAs) has been shown to influence PG production in many species, although the effects on the mare remain unknown. The present study aimed to determine fatty acid uptake in equine endometrial explants and evaluate their influence on PG secretion and expression of enzymes involved in PG synthesis in vitro. Equine endometrial explants were treated with 100 μM arachidonic acid, eicosapentaenoic acid, or docosahexaenoic acid and then challenged with oxytocin (250 nM) or lipopolysaccharide (LPS; 1 μg/mL). Production of PGF(2)α and PG E(2) (PGE(2)) was measured, and mRNA expression of enzymes involved in PG synthesis was determined with quantitative real-time PCR. Media concentrations of PGF(2)α and PGE(2) were higher (P < 0.0001) from endometrial explants challenged with oxytocin or LPS compared with controls despite which fatty acid was added. Only DHA lowered (P < 0.0001) media concentrations of PGF(2)α and PGE(2) from explants. Endometrial explants stimulated with oxytocin had increased expression of PG-endoperoxide synthase 1 (PTGS1; P < 0.02), PG-endoperoxide synthase 2 (PTGS2; P < 0.001), PG F(2)α synthase (PGFS; P < 0.01), PG E(2) synthase (PGES; P < 0.01), and phospholipase A(2) (PLA(2); P < 0.005) compared with controls and regardless of fatty acid treatment; whereas stimulation with LPS increased expression of PTGS2 (P < 0.004), PGFS (P < 0.03), PGES (P < 0.01), and PLA(2) (P < 0.01) compared with controls and regardless of fatty acid treatment. Treatment with PUFAs, specifically DHA, can influence PG secretion in vitro through mechanisms other than enzyme expression.