Pregnancy-dependent expression of leukaemia inhibitory factor (LIF), LIF receptor-beta and interleukin-6 (IL-6) messenger ribonucleic acids in the porcine female reproductive tract

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.

Changes in Immune Response during Pig Gestation with a Focus on Cytokines

Pigs have the highest percentage of embryonic death not associated with specific diseases of all livestock species, at 20-45%. During gestation processes, a series of complex alterations can arise, including embryonic migration and elongation, maternal immunological recognition of pregnancy, and embryonic competition for implantation sites and subsequent nutrition requirements and development. Immune cells and cytokines act as mediators between other molecules in highly complex interactions between various cell types. However, other non-immune cells, such as trophoblast cells, are important in immune pregnancy regulation. Numerous studies have shed light on the crucial roles of several cytokines that regulate the inflammatory processes that characterize the interface between the fetus and the mother throughout normal porcine gestation, but most of these reports are limited to the implantational and peri-implantational periods. Increase in some proinflammatory cytokines have been found in other gestational periods, such as placental remodeling. Porcine immune changes during delivery have not been studied as deeply as in other species. This review details some of the immune system cells actively involved in the fetomaternal interface during porcine gestation, as well as the principal cells, cytokines, and molecules, such as antibodies, that play crucial roles in sow pregnancy, both in early and mid-to-late gestation.

Local action of cytokines and immune cells in communication between the conceptus and uterus during the critical period of early embryo development, attachment and implantation - Implications for embryo survival in cattle: A review

Early embryo development, implantation and pregnancy involve a complex dialogue between the embryo and mother. In cattle this dialogue starts as early as days 3-4 when the embryo is still in the oviduct, and it continues to implantation. Immunological processes involving cytokines, mast cells and macrophages form an important part of this dialogue. Amongst the cytokines, interleukin-6 (Il-6) and leukemia inhibitory factor (LIF) are secreted by both the embryo and uterine endometrium and form part of an ongoing and reciprocating dialogue. Mast cells and macrophages populate the uterine endometrium during embryo development and are involved in achieving the correct balance between inflammatory and anti-inflammatory reactions at the uterus that are associated with embryo attachment and implantation. Embryo loss is the major cause of reproductive wastage in cattle, and livestock generally. A deeper understanding of immunological processes during early embryo development will help to achieve the next step change in the efficiency of natural and assisted breeding.

Allogeneic Embryos Disregulate Leukemia Inhibitory Factor (LIF) and Its Receptor in the Porcine Endometrium During Implantation

Despite its advantages for pig breeding, embryo transfer (ET) has a major handicap: high embryo mortality during the pre- and implantation period, probably caused by divergent phenomena of tolerance between the immunologically unrelated (i.e., allogeneic) embryos and the recipient sow. Thus, to reach a similar maternal tolerance as in conventional breeding by artificial insemination (AI) would be the key to ET-success. For this reason, we studied the expression of the leukemia inhibitory factor (LIF) cytokine and its receptor in the pig endometrium during the implantation period (days 18 and 24) in sows subjected to ET (AL group) vs. post-cervical-AI controls (Hemi-AL group). Quantification of expression was performed at both mRNA (rt-qPCR) and protein (WB) levels. The expression of endometrial LIF on day 24 was considerably lower in ET than in AI pregnancies. Correlations between endometrial mRNA levels of LIF and LIF-R showed that, contrary to early AI-pregnancies, ET-pregnancies lack an inverse relation between cytokine and receptor levels. In conclusion, ET-pregnancies lack sufficient endometrial levels of LIF to develop adequate immunotolerance mechanisms to prevent the rejection of allogeneic ET-embryos.

Pleiotropic role of prokineticin 1 in the porcine endometrium during pregnancy establishment and embryo implantation †

Acquisition of endometrial receptivity for embryo implantation is one of the crucial processes during pregnancy and is induced mainly by progesterone and enhanced by conceptus signals. Prokineticin 1 (PROK1) is characterized as a secretory protein with diverse functions in various tissues, including the reproductive tract. PROK1, with its receptor PROKR1, are up-regulated in the porcine endometrium during implantation and in women's receptive endometrium and decidua. However, the function of PROK1 in embryo-maternal communication has still not been fully elucidated. Hence, we hypothesize that PROK1 is involved in endometrial receptivity development and implantation in pigs. In this study, using the porcine in vivo model of intrauterine infusions of estradiol-17β (E2) and prostaglandin E2 (PGE2), we revealed that these hormones elevated endometrial expression of PROK1 and PROKR1 mRNA, respectively. Moreover, E2, acting synergistically with PGE2, increased PROKR1 protein expression. We also evidenced that PROK1-PROKR1 signaling induced expression of following genes and/or proteins CCN2, CDH13, FGF2, NFATC2, ANGPT1, ANGPT2, CDH1, MUC4, SPP1, IFNG, IL6, LIF, LIFR, TNF, TGFB3, and FGF9, as well as phosphorylation of PTK2 and secretion of IL6 and IL11 by endometrial explants in vitro. Ingenuity pathway analysis revealed that functions associated with the PROK1-regulated genes/proteins include cell-to-cell contact, cell attachment, migration and viability, differentiation of epithelial tissue, leukocyte migration, inflammatory response, angiogenesis, and vasculogenesis. Summarizing, our study suggests that PROK1 acts pleiotropically as an embryonic signal mediator that regulates endometrial receptivity by increasing the expression of the genes and proteins involved in implantation and pregnancy establishment in pigs.

Association of Polymorphisms in Candidate Genes with the Litter Size in Two Sheep Breeds

Hu sheep and Small-tailed Han sheep are the most widely raised and most famous maternal sheep breeds in China, which are known for precocious puberty, perennial oestrus and high fecundity (1-6 lambs each parity). Therefore, it is crucial to increase litter size of these two breeds for intensive sheep industry. The objective of this study was to identify potential genetic markers linked with sheep litter size located at ten genes. This study collected blood sample of 537 Hu sheep and 420 Small-tailed Han sheep with litter size of first parity. The average litter sizes in Hu sheep and Small-tailed Han sheep were 2.21 and 1.93. DNA-pooling sequencing method was used for detecting the potential single nucleotide polymorphisms (SNPs) in ten genes related to follicle development and female reproduction. SNPscan® was used for individually genotyping. As a result, a total of 78 putative SNPs in nine out of ten candidate genes (except NOG) were identified. In total, 50 SNPs were successfully genotyped in Hu sheep and Small-tailed Han sheep. After quality control, a total of 42 SNPs in Hu sheep and 44 SNPs in Small-tailed Han sheep were finally used for further analysis. Association analysis revealed that nine SNPs within six genes (KIT: g.70199073A>G, KITLG: g.124520653G>C, ADAMTS1: g.127753565T>C, ADAMTS1: g.127754640G>T, NCOA1: g.31928165C>T, NCOA1: g.32140565G>A, LIFR: g.35862868C>T, LIFR: g.35862947G>T and NGF: g.91795933T>C) were significantly associated with litter size in Hu sheep or Small-tailed Han sheep. A combined haplotypes analysis of the two loci (LIFR: g.35862868C>T and LIFR: g.35862947G>T) revealed that H2H3 (CTTT) combined haplotypes had the largest litter size than the rest combined haplotypes and more than those with either mutation alone in Small-tailed Han sheep. Taken together, our study suggests that nine significant SNPs in six genes can be served as useful genetic markers for MAS in sheep.

Leukemia inhibitory factor and its receptor: expression and regulation in the porcine endometrium throughout the estrous cycle and pregnancy

Objective

Leukemia inhibitory factor (LIF) binds to a heterodimeric receptor composed of LIF receptor (LIFR) and glycoprotein 130 (GP130) to transmit signals into the cell. LIF plays an important role in reproduction by regulating immune response, decidualization, and implantation in several species. However, the expression of LIF and LIFR in the endometrium throughout the estrous cycle and pregnancy in pigs is not fully understood.

Methods

We analyzed the expression of LIF and LIFR in the endometrium on days 0 (estrus), 3, 6, 9, 12, 15, and 18 of the estrous cycle, and days 12, 15, 30, 60, 90, and 114 of pregnancy, in conceptuses on days 12 and 15, and in chorioallantoic tissues on days 30, 60, 90, and 114 of pregnancy in pigs. We also determined the effects of estrogen and progesterone on the expression of LIF and LIFR in endometrial tissues.

Results

The expression of LIF increased in the endometrium during the late diestrus phase of the estrous cycle and during mid- to late- pregnancy, while the expression of LIFR increased during early pregnancy. The expression of LIF was induced by increasing doses of estrogen, whereas the expression of LIFR was induced by increasing doses of progesterone.

Conclusion

These results indicate that the expression of LIF and its receptor LIFR in the endometrium is regulated in a stage-specific manner during the estrous cycle and pregnancy, suggesting that LIF and its receptor signaling system may play critical roles in regulating endometrial function in pigs.

Integrated transcriptomes throughout swine oestrous cycle reveal dynamic changes in reproductive tissues interacting networks

Female fertility is a highly regulated process involving the synchronized activities of multiple tissues. The underlying genomic regulation of the tissue synchronization is poorly understood. To understand this better we investigated the transcriptomes of the porcine ovary, endometrium, and oviduct at days 0, 3, 6, 9, 12, 15, or 18 of the oestrous cycle. We analysed the transcriptome profiles of the individual tissues and focus on the bridging genes shared by two or more tissues. The three tissue-networks were connected forming a triangular shape. We identified 65 bridging genes with a high level of connectivity to all other genes in the network. The expression levels showed negative correlations between the ovary and the other two tissues, and low correlations between endometrium and oviduct. The main functional annotations involved biosynthesis of steroid hormones, cell-to-cell adhesion, and cell apoptosis, suggesting that regulation of steroid hormone synthesis and tissue viability are major regulatory mechanisms.

Differences in mRNA populations of short and long bovine conceptuses on Day 15 of gestation

The majority of pregnancy loss in cattle occurs between Days 8 and 16 of gestation, coincident with the initiation of conceptus elongation and the onset of maternal recognition of pregnancy. Differences in conceptus length on the same day of gestation may be related to an inherent lack of developmental competency or may simply be a consequence of asynchrony with the maternal environment. The objective of this work was to characterize differential patterns of mRNA expression between short and long bovine conceptuses recovered on Day 15 of gestation. Embryos were produced from super-ovulated Holstein donor cows, and groups of Grade-1 and Grade-3 compact morulas were transferred into recipient heifers at Day 6.5 of their cycle. Conceptuses were recovered at Day 15 of gestation, and measured to assess overall length and area. Total RNA was extracted and analyzed on individual GeneChip Bovine Genome Arrays (Affymetrix, Santa Clara, CA). Gene expression was compared between conceptuses derived from the transfer of Grade-1 versus Grade-3 embryos; no differences were identified in the profiles of Day-15 conceptuses of these different embryo grades. When gene expression was compared between conceptuses classified as either short (mean length of 4.2 ± 0.1 mm [standard error]) or long (24.7 ± 1.9 mm) upon recovery at Day 15 of gestation, a total of 348 genes were differentially expressed. Of these, 221 genes were up-regulated and 127 were down-regulated in long compared to short conceptuses. In summary, differences in gene expression were identified between conceptuses recovered on Day 15 of gestation, based on their length. These data may be used to identify genes and cellular pathways involved in enhanced conceptus elongation that could serve as markers of successful pregnancy. Mol. Reprod. Dev. 83: 424-441, 2016. © 2016 Wiley Periodicals, Inc.

Interleukins, interferons, and establishment of pregnancy in pigs

Early pregnancy in mammals requires complex and highly orchestrated cellular and molecular interactions between specialized cells within the endometrium and the conceptus. Proinflammatory cytokines are small signaling proteins released by leukocytes that augment innate and adaptive immune responses. They are also released by the mammalian trophectoderm as the conceptus apposes the uterine surface for implantation. On approximately day 12 of development in pigs, the conceptus undergoes a rapid morphological transformation referred to as elongation while simultaneously releasing estrogens and a novel conceptus form of interleukin-1 beta (IL1β). Following elongation, pig conceptuses express interferon gamma (IFNγ) and, in lesser amounts, interferon delta (IFNδ). Significant IFN signaling takes place within the endometrium between day 14 and 18 of pregnancy as the conceptus intimately associates with the uterine epithelium. Based on studies carried out in pigs and other mammals, the combined spacio-temporal activities of conceptus estrogens, IL1β, and IFN set in motion a series of coordinated events that promote establishment of pregnancy. This is achieved through enhancement of conceptus development, uterine receptivity, maternal-fetal hemotropic exchange, and endometrial leukocyte function. These events require activation of specific signaling pathways within the uterine luminal epithelium, glandular epithelium, and stroma. Here, we review proinflammatory cytokine expression by pig conceptuses and the hypothesized actions of these molecules during establishment of pregnancy.

In vitro morphology, viability and cytokine secretion of uterine telocyte-activated mouse peritoneal macrophages

Telocytes (TCs), a distinct interstitial cell population, have been identified in the uterus, oviduct and placenta, with multiple proposed potential biological functions. Their unique structure allows them to form intercellular junctions with various immunocytes, both in normal and diseased tissues, suggesting a potential functional relationship with the local immune response. It has been hypothesized that through direct heterocellular junctions or indirect paracrine effects, TCs influence the activity of local immunocytes that are involved in the inflammatory process and in immune-mediated reproductive abnormalities. However, no reliable cytological evidence for this hypothesis is currently available. In this study, we cultured primary murine uterine TCs and collected TC conditioned media (TCM). Mouse peritoneal macrophages (pMACs) were co-cultured for 48 hrs with TCM or with DMEM/F12 or lipopolysaccharide (LPS) as negative and positive controls, respectively. Normal uterine TCs with a typical structure and a CD-34-positive/vimentin-positive/c-kit-negative immunophenotype were observed during culture. Morphologically, TCM-treated pMACs displayed an obvious activation/immunoresponse, in contrast to over-stimulation and cell death after LPS treatment and no sign of activation in the presence of DMEM/F12. Accordingly, a cell counting kit 8 (CCK-8) assay indicated significant activation of pMACs by TCM and LPS compared to DMEM/F12, thus supporting the marked morphological differences among these groups of cells. Furthermore, within a panel of macrophage-derived cytokines/enzymes, interleukin-6 (IL-6) and inducible nitric oxide synthase were significantly elevated in TCM-treated pMACs; tumour necrosis factor α, IL1-R1, and IL-10 were slightly, but significantly, up-regulated; and no changes were observed for transforming growth factor-β1, IL-1β, IL-23α and IL-18. Our results indicate that TCs are not simply innocent bystanders but are rather functional players in the activation of pMACs; they trigger and maintain the immune response, likely through indirect paracrine effects. Thus, we provide preliminary in vitro evidence of immunoregulatory and immunosurveillance roles for TCs.

Expression of leukaemia inhibitory factor at the conceptus?maternal interface during preimplantation development and in the endometrium during the oestrous cycle in the mare

Leukaemia inhibitory factor (LIF) plays a critical role in blastocyst development and implantation in several species. The present study investigated mRNA and protein expression for LIF, as well as the low-affinity LIF receptor (LIFR) and interleukin-6 signal transducer (IL6ST), in equine endometrium, trophoblast and histotroph during early pregnancy and in the endometrium during the oestrous cycle. Endometrial LIF mRNA expression was upregulated after Day 21 of pregnancy, whereas LIF immunoreactivity increased in the endometrium on Day 28. Expression of LIF mRNA in the yolk sac membrane increased from Day 21 of pregnancy, whereas LIF immunoreactivity increased from Day 28 in the trophoblast. LIFR and IL6ST mRNA was expressed in the endometrium during both the oestrous cycle and early pregnancy and, although LIFR and IL6ST protein were localised to the glandular epithelium during the cycle and first 14 days of pregnancy, from Day 21 they were located in the luminal epithelium. Trophoblast expression of LIFR and IL6ST increased as pregnancy proceeded. In conclusion, LIF expression increased at the conceptus-maternal interface during capsule attenuation. Because contemporaneous upregulation of both LIFR and IL6ST was also observed in the trophoblast, we propose that LIF plays an important role in the development of endometrial receptivity for trophoblast growth, apposition and adhesion in mares.

MicroRNAome of porcine conceptuses and trophoblasts: expression profile of micrornas and their potential to regulate genes crucial for establishment of pregnancy

Tightly coordinated, reciprocal embryo-maternal interactions affect gene expression during early pregnancy. Recently, microRNAs (miRNAs) have emerged as new players in the fine tuning of embryo development and implantation in mammals via posttranscriptional gene regulation mechanisms. Here, we integrated transcriptomic and computational approaches to profile miRNAs and miRNA synthesis and transport-related genes at different developmental stages of porcine conceptuses and trophoblast during early pregnancy in the pig. Using semiquantitative RT-PCR, we examined mRNA levels of 10 genes encoding proteins involved in miRNA synthesis and transport: DROSHA, DGCR8, XPO5, DICER1, TARBP2, TNRC6A, AGO1, AGO2, AGO3, and AGO4. Custom, multispecies microarrays were used to profile miRNAs. Prediction algorithms of miRNA-mRNA interactions allowed identification of target transcripts for the analyzed miRNAs. These included VEGF, LIF, PTGS2, and IL-6R, known to be crucial components of embryo-maternal interactions in the pig. Two selected miRNAs, miR-26a and miR-125b, were tested for the presence in the extracellular vesicles isolated from uterine luminal flushings during pregnancy. Results of in vitro study demonstrated that miRNAs, such as miR-125b, can regulate expression of genes crucial for embryo development and implantation in porcine endometrial luminal epithelial cells. For the first time, expression profiles of miRNAs and related genes in porcine conceptuses and trophoblast during maternal recognition of pregnancy and embryo implantation in the pig were described. Altogether, our results indicate potential roles of these small, noncoding RNAs in the early development of embryos and embryo-maternal cross-talk during early pregnancy in the pig.

Cytokines from the pig conceptus: roles in conceptus development in pigs

Establishment of pregnancy in pigs involves maintaining progesterone secretion from the corpora lutea in addition to regulating a sensitive interplay between the maternal immune system and attachment of the rapidly expanding trophoblast for nutrient absorption. The peri-implantation period of rapid trophoblastic elongation followed by attachment to the maternal uterine endometrium is critical for establishing a sufficient placental-uterine interface for subsequent nutrient transport for fetal survival to term, but is also marked by the required conceptus release of factors involved with stimulating uterine secretion of histotroph and modulation of the maternal immune system. Many endometrial genes activated by the conceptus secretory factors stimulate a tightly controlled proinflammatory response within the uterus. A number of the cytokines released by the elongating conceptuses stimulate inducible transcription factors such as nuclear factor kappa B (NFKB) potentially regulating the maternal uterine proinflammatory and immune response. This review will establish the current knowledge for the role of conceptus cytokine production and release in early development and establishment of pregnancy in the pig.

Global gene expression profiling of porcine endometria on Days 12 and 16 of the estrous cycle and pregnancy

The objective of the study was to investigate transcriptomic profile of pig endometrium on Days 12 and 16 of pregnancy in comparison with the respective days of the estrous cycle. Labeled complementary DNA was hybridized to Porcine Long Oligo microarray containing 13,297 oligonucleotide probes, which represented complementary DNA and expressed sequence tags. Statistical analysis revealed 110 differentially expressed genes (DEGs) on Day 12 of pregnancy and 179 DEGs on Day 16 of pregnancy. In silico analysis of gene function and functionality networks revealed links between genes implicated in cell death and survival, protein synthesis, lipid metabolism, cellular movement, tissue development, and cell-to-cell signaling. On Day 12 of pregnancy, estrogen, transforming growth factor (TGF) β1, and fibroblast growth factor (FGF) 2, and on Day 16 of pregnancy, epidermal growth factor (EGF), insulin, interleukin 11 (IL-11), and FGF family members were indicated as possible upstream regulators of several DEGs. Obtained results showed changes in global endometrial gene expression at the time of maternal recognition of pregnancy and embryo implantation. Additionally, these data revealed signaling molecules, which together with E2, may evoke molecular changes in the uterus, leading to successful pregnancy establishment.

The contribution of leukemia inhibitory factor (LIF) for embryo implantation differs among strains of mice

Despite of the claim that maternal leukemia inhibitory factor (LIF) - a member of interleukin 6 (IL6) family of cytokines - plays indispensable roles for murine embryo implantation, these roles remain undefined in humans because the potency of LIF on implantation appears to vary among individuals. Here, we showed that the contribution of LIF for murine implantation was dependent on the strains of mice (ICR, C57BL/6J (B6), ddY, BALB/c, DBA/2Cr and MF1 strains). Inhibition of LIF during the implantation period caused severe disruption of embryo implantation in B6 and MF1 strains. Implantation was partly disrupted in other strains, but some embryos were implanted successfully. We speculated that other IL6 family members compensate for LIF actions on implantation in ICR, ddY, BALB/c, and DBA/2Cr strains. Indeed, the expression level of Ctf1 was upregulated by blockage of LIF function. CT-1 (encoded by Ctf1) treatment induced successful implantation without LIF in delayed implantation mice (ICR and B6) via phosphorylation of the signal transducer and activator of transcription 3 (STAT3) in the uterine luminal epithelium. Simultaneous inhibition of LIF and CT-1 did not block implantation completely in ICR mice, indicating that embryo implantation in this strain was robustly protected by LIF, CT-1 and other potential STAT3 activators. The present study might provide an explanation for the individual variation in the potency of LIF for embryo implantation in humans.

Regulation of expression and role of leukemia inhibitory factor and interleukin-6 in the uterus of early pregnant pigs

Cytokines, which are generally involved in the process of inflammation, may also play a critical role in conceptus implantation. We examined: (1) the expression profiles of leukemia inhibitory factor (LIF) and interleukin (IL)-6 mRNA and their protein content in the endometrium of cyclic and pregnant gilts on Days 10 to 18 after estrus; (2) the effect of conceptus-exposed medium on LIF and IL-6 synthesis in the endometrium; (3) the profiles of IL6R and LIFR mRNA expression in pig conceptuses collected on Days 10 to 18 of pregnancy; and (4) the effect of LIF and IL-6 on the attachment and proliferation of porcine trophoblast cells. The expression of LIF mRNA in the endometrium increased between Days 10 and 12 in both cyclic and pregnant gilts, and tended to be higher in Day 12 pregnant animals compared with nonpregnant ones. The LIF protein content in the uterine lumen peaked on Day 12 of pregnancy, and was higher than on Day 12 of the estrous cycle. Endometrial IL-6 mRNA expression was upregulated on Day 12 in pregnant gilts compared with nonpregnant animals. Moreover, a higher content of IL-6 protein was observed in pregnant than in cyclic gilts. The addition of conceptus-exposed medium resulted in up-regulation of LIF and IL6 mRNA expression, and increased IL-6 content in endometrial slices. In conceptuses, increased mRNA expression was detected on Days 10 to 14 for IL6R and on Day 14 for LIFR, when compared with other days studied. LIF and IL-6 stimulated the attachment and proliferation of trophoblast cells in vitro. In summary, LIF and IL-6 are important components of embryo-uterine interactions during early pregnancy in the pig, and may contribute to successful conceptus implantation.

Regulation of prostacyclin synthase expression and prostacyclin content in the pig endometrium

Prostaglandins (PGs) are critical regulators of a number of reproductive processes, including embryo development and implantation. In the present study, prostacyclin (PGI(2)) synthase (PGIS) mRNA and protein expression, as well as 6-keto PGF(1α) (a PGI(2) metabolite) concentration, were investigated in the pig uterus. Endometrial tissue and uterine luminal flushings were obtained on Days 4 to 18 of the estrous cycle and pregnancy. Additionally, conceptuses were collected and examined for PGIS mRNA expression and 6-keto PGF(1α) concentration. Regulation of PGI(2) synthesis in the porcine endometrium by steroids, conceptus products, and cytokines was studied in vitro and/or in vivo. Endometrial PGIS protein level increased on Days 12 and 16 in pregnant but not in cyclic gilts. Moreover, higher PGIS protein expression on Day 12 of pregnancy was accompanied by a greater content of 6-keto PGF(1α) in the endometrium. The concentration of 6-keto PGF(1α) in uterine luminal flushings increased substantially on Days 16 and 18 in pregnant gilts and was higher than in cyclic animals. Greater PGIS mRNA expression and PGI(2) metabolite concentration were detected in Day 12 and 14 conceptuses, respectively. Incubation of endometrial explants with conceptus-conditioned medium resulted in upregulation of PGIS protein expression and increased PGI(2) secretion. Moreover, PGIS mRNA and protein expression were upregulated in the endometrium collected from gravid uterine horn on Day 14 of pregnancy. In summary, PGIS is differentially expressed in the endometrium of cyclic and pregnant gilts resulting in higher PGI(2) synthesis in pregnant animals. Porcine conceptuses are important regulators of endometrial PGIS expression and PGI(2) release during the implantation period.

Interaction of the conceptus and endometrium to establish pregnancy in mammals: role of interleukin 1β

Implantation and the establishment of pregnancy in mammals involves an intricate interplay of hormones, cytokines, growth factors, proteins, lipids, ions and the extracellular matrix between the uterine epithelium, stroma, immune cells and the conceptus trophectoderm. The divergent nature of implantation in the mouse, human and pig provides not only an interesting contrast in the establishment of pregnancy and early embryonic development but also intriguing similarities with regard to early endometrial-conceptus signaling. An interesting pro-inflammatory cytokine expressed in a number of mammalian species during the period of implantation is interleukin-1β (IL1B). The presence of IL1B might be involved with immunotolerance at the maternal-placental interface and has been proposed as one of the mediators in placental viviparity. The production of IL1B and other proinflammatory cytokines might play a role in establishing pregnancy through modulation of the nuclear factor kappa-B (NFKB) system in a number of species. A model for the regulation of cellular progesterone receptor expression and NFKB activation for endometrial receptivity and conceptus attachment is continuing to evolve and is discussed in the present review.

Mechanisms for the establishment of pregnancy in the pig

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

Endometrial and conceptus expression of HoxA10, transforming growth factor beta1, leukemia inhibitory factor, and prostaglandin H synthase-2 in early pregnant pigs with gonadotropin-induced estrus

This study was conducted to evaluate the effect of estrus induction with gonadotropins on endometrial and conceptus expression of HoxA10, transforming growth factor (TGF) beta1, leukemia inhibitory factor (LIF), and prostaglandin H synthase-2 (PGHS-2) during early pregnancy in pigs. Twenty-four prepubertal gilts received 750 IU of pregnant mare serum gonadotropin (PMSG) and 500 IU of human chorionic gonadotropin (hCG) 72h later. Gilts in the control group (n=23) were observed daily for estrus behavior. Endometrial tissue samples, conceptuses, blood serum, and uterine luminal flushings (ULFs) were collected on days 10, 11, 12, and 15 after insemination. There was no effect of estrus induction on estradiol content in ULFs, or on ovulation and fertilization rates in studied gilts. However, the content of progesterone in the blood serum was greater in naturally ovulated gilts in comparison to gonadotropin-treated animals on day 12 of pregnancy (P<0.05). HoxA10 expression was up-regulated in the endometrium of pregnant gilts, with natural ovulation on days 12 (P<0.05) and 15 (P<0.001) in comparison to days 10 and 11. When compared to control gilts, administration of PMSG/hCG resulted in decreased expression of endometrial HoxA10, TGFbeta, LIF, and PGHS-2 on day 12 of pregnancy (P<0.05). Conceptus expression of studied factors was not affected by gonadotropin treatment. Overall, these results suggest improper endometrial preparation for implantation in prepubertal gilts induced to ovulate with PMSG/hCG.

Uterine progesterone receptor and leukaemia inhibitory factor mRNA expression in canine pregnancy

The study investigated the expression of genes for progesterone receptor (PR) and for the cytokine leukaemia inhibitory factor (LIF) in the uterine tube and uterine horn tissues from pregnant and non-pregnant bitches. The aim was to study whether a relation existed between the likely biological effectiveness of progesterone (P(4)) and the change in the uterine expression of LIF mRNA during pregnancy, as has been described in primates. For this purpose, 20 pregnant bitches were ovariohysterectomized after being allotted to three groups according to gestational age (pre-implantation: days 10 to 12, n = 7; peri-implantation: days 18 to 25, n = 7; post-placentation: days 28 to 45, n = 7). Tissue samples were obtained from the uterine tubes, one uterine horn (including placentation sites and interplacental sites in bitches that had already implanted) and the corpus uteri, stored at -80 degrees C, and then analysed by qualitative and quantitative PCR for PR and LIF mRNA expression. From the pre-implantation to the placentation stage, a decrease in the relative expression of PR mRNA in uterine tissue was obvious and significant when expressed relative to beta-actin (11.2 +/- 6.8 vs 2.7 +/- 1.9; p < 0.05). However, over the same period, the relative expression of LIF mRNA increased (10.1 +/- 16.1 vs 50.0 +/- 32.3; p < 0.05). In addition, PR mRNA went from being detectable to no longer detectable in the uterine tube, and no longer detectable in interplacental-site uterine tissue. We conclude that LIF is important for the establishment of canine pregnancy; that decreased uterine PR mRNA expression may contribute to the increase in uterine LIF mRNA; and, that the ability of the embryo to preserve PR mRNA expression at implantation and placentation sites while expression is lost in the remainder of the uterus represent an effect important to the establishment and maintenance of pregnancy. We additionally propose that canine embryo secretory proteins have a regulatory effect on both PR and LIF before as well as at and after implantation.

Effect of polymorphism in the leukemia inhibitory factor gene on litter size in Large White pigs

DNA polymorphism of the porcine leukemia inhibitory factory (LIF) was investigated and used to study the effects on litter size in Large White pigs. A total of 2,167 litter records from 420 sows genotyped at two SNP loci (LIF1 and LIF2) within LIF gene were analyzed to determine whether LIF influenced total number born (TNB) and number born alive (NBA). The results indicated that B allele at LIF1 locus and A allele at LIF2 locus seem to have advantageous effects on litter size. However, the combined analyzed results demonstrated that genotype AAAA, ABBB, and BBBB are better than genotype AAAB, AABB, and ABAB for TNB and NBA in either third to eighth parity or all parities. In all parities, the sows with AAAA genotype had an advantage of 1.76 piglets (P < 0.001) for TNB and 1.44 piglets (P < 0.01) for NBA per litter over the AAAB sows, respectively. The results in this study demonstrated that LIF gene was significantly associated with litter size in pigs.

Effect of polymorphisms in the genes for LIF and RBP4 on litter size in two German pig lines

The association of two diallelic polymorphisms in the porcine genes for leukaemia inhibitory factor (LIF) and retinol-binding protein 4 (RBP4) with number of piglets born alive (NBA) in two German pig lines was studied. The investigated single nucleotide polymorphism (SNP) in the porcine LIF gene has been located in the 3'-untranslated region of its third exon, whereas the SNP in the RBP4 gene genotyped in this study is intronic. At the LIF locus the allele frequencies were 0.613 for the A allele and 0.387 for the B allele in German Landrace (GL) and 0.276 for A and 0.724 for B in German Large White (GW). At the RBP4 locus, the allele frequencies were 0.586 for the A allele and 0.414 for the B allele in GL and 0.733 for A and 0.267 for B in GW. There was a significant additive effect of the LIF B allele on NBA in GW over all parities (p <or= 0.05) and a significant positive dominance effect of 0.69 +/- 0.22 (p = 0.002) was observed for first parity on NBA in GL. For RBP4, no association of genotypes and NBA was detected in GW but a significant additive effect of the A allele of 0.24 +/- 0.11 (p = 0.027) and a significant dominance effect of 0.31 +/- 0.13 (p = 0.020) were found in GL over all parities and confirmed through the evaluations by parity.

Evidence of a new leukemia inhibitory factor-associated genetic marker for litter size in a synthetic pig line

The association of a diallelic polymorphism in the leukemia inhibitory factor (LIF) gene with reproductive, growth, and carcass traits was studied in a German synthetic pig line. The diallelic SNP has been located in the 3'-untranslated region of the third exon of the porcine LIF gene. Information on 955 litter records from 273 genotyped sows was used in the analyses with respect to the number of piglets born alive. To identify possible pleiotropic marker effects, the growth and carcass traits ADG and backfat thickness were tested for associations with the SNP within the LIF gene in this population. At the LIF locus, the allele frequencies were 0.27 for the A allele and 0.73 for the B allele. There was an indication of an additive effect on the number of piglets born alive, and a significant dominance effect of the B allele was observed for first, second, and third to 10th parities (P = 0.044). The dominance effect for the first parity amounted to -0.73 +/- 0.36 (P = 0.047). No associations were detected between the marker alleles and the growth and carcass traits.

Immunosuppression by placental indoleamine 2,3-dioxygenase: a role for mesenchymal stem cells

BACKGROUND/OBJECTIVES

Mesenchymal stem cells (MSC) can be isolated from human placenta and have the potential to contribute to the immunosuppressive properties of placental tissue. The objectives of this study were to investigate the phenotype and differentiation characteristics of MSC derived from human placenta and evaluate the role of the tryptophan degrading enzyme, indoleamine 2,3 dioxygenase (IDO), in mediating their immunosuppressive affect.

METHODS

MSC obtained from placental tissue (pMSC) were characterised using flow cytometry and tested for multipotency by determining differentiation into all mesenchymal lineages. The immunosuppressive properties of pMSC were tested in allogeneic mixed lymphocyte reactions and IDO expression and activity were measured by semi-quantitative real-time PCR and HPLC respectively.

RESULTS

Multipotent stem cells were isolated from placenta and displayed chondrogenic, osteogenic and limited adipogenic differentiation. Cell surface antigen expression of pMSC was similar to bone marrow MSC (bMSC) with lack of the haematopoietic and common leukocyte markers (CD34, CD45), and expression of adhesion (CD29, CD166, CD44) and stem cell (CD 90, CD105, CD73) markers. Placental MSC were suppressive of allogeneic T-cell proliferation, an effect which was intensified following IDO induction by IFN-gamma. Replenishment of tryptophan or treatment with the IDO-blocker, 1-methyl-tryptophan (1-MT), attenuated the immunosuppressive action of pMSC.

CONCLUSIONS

These results suggest that placental tissue contains MSC, which are phenotypically and functionally similar to bMSC, and that IDO is a key mediator of their immunosuppressive effect. Further investigation is needed to determine if pMSC function effects pregnancy outcome.

Leukaemia inhibitory factor receptor and gp130 in the human Fallopian tube and endometrium before and after mifepristone treatment and in the human preimplantation embryo

Leukaemia inhibitory factor (LIF) is a cytokine, which is associated with reproductive processes such as embryo development and implantation. The objectives of this study were to detect the presence of LIF receptor (LIFR) and glycoprotein 130 (gp 130) in the human Fallopian tube, endometrium and preimplantation embryo and to study the effect of mifepristone on the expression of LIFR and gp130 in the Fallopian tube. Twenty-two healthy fertile women received a single dose of 200 mg mifepristone or placebo immediately after ovulation (LH + 2). Biopsies were obtained from the Fallopian tubes during laparoscopic sterilization once between days LH + 4 and LH + 6 and from endometrium once between days LH + 6 and LH + 8. Preimplantation embryos were received from couples undergoing in vitro fertilization treatment. Immunohistochemistry was used to detect the presence of LIFR and gp130 in the Fallopian tube, endometrium and preimplantation embryo. Real-time PCR was used to study LIFR and gp130 expression in the Fallopian tube and endometrium. LIFR and gp130 were localized in the Fallopian tube, preimplantation embryo and endometrium. LIFR was more abundant in the Fallopian tube than in the endometrium. In the blastocyst, the staining of gp130 was mainly localized in the inner cell mass, whereas LIFR was expressed in all cells. The presence of LIFR and gp130 in the Fallopian tube and preimplantation embryo indicates a role for LIF in communication between the embryo and the Fallopian tube. Mifepristone did not affect the expression of LIFR and gp130 in the Fallopian tube, nor in the endometrium suggesting that progesterone might not be directly involved in the regulation of LIFR or gp130.

Genetic approaches to the improvement of fertility traits in the pig

One of the major determinants for litter size in pigs is prenatal mortality. It occurs most frequently during the first few weeks of gestation and can be attributed to abnormalities in developmental processes during embryogenesis including trophoblastic elongation and blastocyst implantation. Improvement of litter size has been attempted by means of phenotypic selection. However, another promising approach in pursuit of this aim has been the use of genotypic information. Reproductive traits in general are well-suited for application of marker-assisted selection (MAS). The possibility of exerting selection criteria at the molecular level shortens the generation interval as the selection decision can take place early in the life of an animal. Moreover, in consideration of the sex-limited nature of reproductive traits, genotypic information allows for selection in the gender in which the trait cannot be directly observed. Accordingly, there has been considerable interest in mapping and identifying genes involved in the regulation of reproductive traits and in elucidating their expression patterns. This review offers a comprehensive, if not exhaustive, account of the efforts being made and the approaches currently used in this field. One approach has been to choose candidate genes a priori because of the physiological importance of the proteins they encode and their role in the reproduction of other mammals. The usefulness of candidate genes is then examined by association studies between genetic polymorphisms identified in the respective candidate genes and the phenotypic reproductive traits. The other approach discussed uses pre-existing or designed families for linkage analyses in order to map the location of quantitative trait loci (QTL) for the reproductive trait of interest. The results reported were not consistent among different studies but the QTL regions detected may be useful for identification of positional candidate genes in further molecular genetic studies. However, a better understanding of porcine reproduction requires that these functional genomic approaches are merged and integrated with detailed analyses of the proteome to establish linkages between predisposition and physiology.

Stage-specific expression of leukaemia inhibitory factor and its receptor in rabbit pre-implantation embryo and uterine epithelium during early pregnancy

Leukaemia inhibitory factor (LIF) has been shown to play an important role in the development and implantation of blastocysts in mice. In the current study, the reverse transcription-polymerase chain reaction (RT-PCR) was employed to examine the expression patterns of LIF and its receptor (LIFR) genes in rabbit embryos during pre-implantation development, and the uterine expression of LIF and LIFR was also evaluated by Western blotting. Transcripts for LIFR were detected within morula and blastocyst-stage embryos, while the LIF mRNA was only found in blastocysts (from early to fully expanded blastocoel cavities), indicating that embryo-derived LIF can act in an autocrine manner on the process of blastocyst formation. The expression levels of LIF and LIFR in uterine epithelium were gradually increased during pre-implantation period and reached their highest levels on days 6.5 of pregnancy, just before the time of blastocyst implantation, suggest that paracrine LIF circuit should exist between the endometrium and the early embryos, which may be involved in the embryo-maternal dialogue and important for the blastocyst implantation. The data present here show the stage-specific and dynamic expression patterns of LIF and LIFR, both in embryos and endometrium, during early pregnancy in rabbits, which indicated that LIF might play an important role in the pre-implantation development and subsequent implantation of rabbit embryos.

Effect of oestrous cycle and early pregnancy on uterine production and expression of immune regulatory factors in gilts

This study was undertaken to characterize uterine immune factors involved in the establishment of pregnancy in gilts. Thirty crossbred Yorkshire-Landrace gilts of similar age and weight were observed twice a day for oestrous behaviour with intact boars. On the day of first standing oestrus (Day 0) and 12h later, 15 gilts were inseminated with pooled semen from Duroc boars of proven fertility. Pregnant gilts were slaughtered either on Days 10, 15 or 25 of gestation (n=5 per day). The other 15 gilts were not inseminated and were slaughtered on either Days 0, 10 or 15 of the oestrous cycle (n=5 per day). Immediately after slaughter, endometrial tissue samples from the mesometrial side were removed for gene expression using RNase protection assay and in situ hybridization methodologies. The other uterine horn was flushed with 20 ml of PBS to collect the uterine fluid. In pregnant gilts, endometrial interleukin (IL)-6 mRNA expression was higher on Day 15 than on Days 10 and 25 (P<0.01 and P<0.1, respectively). On Day 15, IL-6 expression was also significantly higher (P<0.01) in pregnant gilts than in cyclic gilts. In both pregnant and cyclic gilts, transforming growth factor (TGF)-beta2 in uterine fluid was significantly higher (P<0.0001) on Day 15 than on Day 10. At the gene expression level, TGF-beta2 also increased between Days 10 and 15 in both cyclic and pregnant gilts but differences were not significant. On Day 15, concentrations of interferon-gamma and prostaglandin E(2) (PGE(2)) in uterine fluid were markedly higher (P<0.001) in pregnant gilts than in cyclic gilts, whereas the total amount of TGF-beta2 in uterine fluid and its endometrial expression were approximately 70% higher although this increase was not significant. Finally, tumour-necrosis factor-alpha and granulocyte-macrophage/colony-stimulating factor mRNA expressions were undetectable in all endometrial samples. In conclusion, production and/or expression of uterine TGF-beta2, IL-6 and PGE(2) increased during the embryonic attachment period and are coincidental with embryonic interferon-gamma production.

Isolation of differentially expressed genes in conceptuses and endometrial tissue of sows in early gestation

The implantation period is a critical time for embryonic survival in pigs. During this period, numerous growth factors are secreted by the conceptuses and the uterine endometrium in order to establish pregnancy and to provide a proper environment for embryonic development. It is well known that the Chinese Meishan sows have a larger litter size when compared with occidental sows mainly because of a superior embryonic survival rate. As a further step toward understanding the mechanisms involved in embryonic survival, we used a suppression subtractive hybridization technique to identify genes that were differentially expressed in Meishan-Landrace conceptuses and endometrial tissue at Day 15 of gestation when compared with conventional Landrace sows. Of the 1000 subtractive clones isolated from each library, 137 endometrial and 166 conceptus-enriched cDNAs were single-pass sequenced and examined by BLAST analysis for identification. Sixty-two percent of the clones found in the endometrial library and 78% of the clones found in the conceptus library showed homology with known genes. Among these genes, the 20 most relevant to embryonic survival based on the available literature were validated through real-time reverse-transcriptase polymerase chain reaction (RT-PCR) analysis. Our results show that suppression subtractive hybridization is a powerful method applicable in identifying putative candidate genes that might be used for selection of high litter-size breeds.

Characterization of the interleukin-1beta system during porcine trophoblastic elongation and early placental attachment

Conceptus-uterine communication is established during trophoblastic elongation when the conceptus synthesizes and releases estrogen, the maternal recognition signal in the pig. Interleukin-1beta (IL-1beta) is a differentially expressed gene during rapid trophoblastic elongation in the pig. The current investigation determined conceptus and endometrial changes in gene expression for IL-1beta, IL-1 receptor antagonist (IL-1Rant), IL-1 receptor type 1 (IL-1RT1), and IL-1 receptor accessory protein (IL-1RAP) in developing peri- and postimplantation conceptuses as well as uterine endometrium collected from cyclic and pregnant gilts. Conceptus IL-1beta gene expression was enhanced during the period of rapid trophoblastic elongation compared with earlier spherical conceptuses, followed by a dramatic decrease in elongated Day 15 conceptuses. IL-1RT1 and IL-1RAP gene expression was greater in Day 12 and 15 filamentous conceptuses compared with earlier morphologies while IL-1Rant gene expression was unchanged by conceptus development. The uterine lumenal content of IL-1beta increased during the process of trophoblastic elongation on Day 12. Uterine IL-1beta content declined on Day 15, reaching a nadir by Day 18 of pregnancy. IL-1beta gene expression in porcine conceptuses was temporally associated with an increase in endometrial IL-1RT1 and IL-1RAP gene expression in pregnant gilts. Endometrial IL-1beta and IL-1Rant gene expression were lowest during Days 10-15 of the estrous cycle and pregnancy. The temporal expression of IL-1beta during conceptus development and the initiation of conceptus-uterine communication suggests conceptus IL-1beta synthesis plays an important role in porcine conceptus elongation and the establishment of pregnancy in the pig.

Mapping and microsatellite marker development for the porcine leukemia inhibitory factor receptor (LIFR) and epidermal growth factor receptor (EGFR) genes

Leukemia inhibitory factor receptor (LIFR), epidermal growth factor receptor (EGFR), and their respective ligands have been implicated in regulating growth and development of the early pig conceptus. We isolated a PAC clone containing the porcine gene for LIFR and a BAC clone with the porcine EGFR gene, respectively. On each of these clones one microsatellite marker was identified by sequencing a collection of subclones. These gene-associated markers were evaluated by genotyping of 202 unrelated boars of four different breeds. Based on fluorescence in situ hybridization and radiation hybrid mapping, the porcine LIFR gene was assigned to SSC16q13-->q14. The EGFR gene mapped to SSC9q26.

Cytokines during early pregnancy of mammals: a review

This article reviews the function of cytokines during early pregnancy of mammals including the human species. Investigations concerning conceptus and other secretory proteins, their meaning for maternal recognition and maintenance of pregnancy, fetal and placental growth and differentiation, adhesion, invasion and implantation are discussed, and differences between laboratory rodents, carnivores, artiodactyls, horses and human beings elucidated and summarized. Finally topics that might be of interest for further research are emphasized.