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

Cytokine profile in peripheral blood mononuclear cells differs between embryo donor and potential recipient sows

Introduction

Pregnancy success relies on the establishment of a delicate immune balance that requires the early activation of a series of local and systemic immune mechanisms. The changes in the immunological profile that are normally occurring in the pregnant uterus does not take place in cyclic (non-pregnant) uterus, a fact that has been widely explored in pigs at the tissue local level. Such differences would be especially important in the context of embryo transfer (ET), where a growing body of literature indicates that immunological differences at the uterine level between donors and recipients may significantly impact embryonic mortality. However, whether components of peripheral immunity also play a role in this context remains unknown. Accordingly, our hypothesis is that the immune status of donor sows differs from potential recipients, not only at the tissue local level but also at the systemic level. These differences could contribute to the high embryonic mortality rates occurring in ET programs.

Methods

In this study differences in systemic immunity, based on cytokine gene expression profile in peripheral blood mononuclear cells (PBMCs), between embryo-bearing donor (DO group; N = 10) and potential recipient sows (RE group; N = 10) at Day 6 after the onset of the estrus were explored. Gene expression analysis was conducted for 6 proinflammatory (IL-1α, IL-1β, IL-2, GM-CSF, IFN-γ, and TNF-α) and 6 anti-inflammatory (IL-4, IL-6, IL-10, IL-13, TGF-β1, and LIF) cytokines.

Results and discussion

All cytokines were overexpressed in the DO group except for IL-4, suggesting that stimuli derived from the insemination and/or the resultant embryos modify the systemic immune profile in DO sows compared to RE (lacking these stimuli). Our results also suggest that certain cytokines (e.g., IL-1α and IL-1β) might have a predictive value for the pregnancy status.

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.

LIF regulates the expression of miR-27a-3p and HOXA10 in bovine endometrial epithelial cells via STAT3 pathway

LIF is crucial in regulating embryo implantation, while HOXA10 is a marker gene for uterine receptivity. However, the specific mechanism of LIF regulating HOXA10 during cow embryo implantation has not been fully understood. To address this knowledge gap, the experiment involved treating bovine endometrial epithelial cells (BEECs) with LIF to investigate the relationship between LIF, miRNA, and HOXA10. The experimental findings revealed that applying LIF resulted in a substantial increase in the proliferation of endometrial epithelial cells. Moreover, the expressions of PI3K, AKT, HOXA10, CDK4, cyclinD1, and cyclinE1 were significantly elevated. Conversely, the expression of p21Cipl was significantly reduced. In the group that received a combination of LIF and a STAT3 inhibitor, the expression of PI3K/AKT remained significantly increased, but there was no significant change in the expression of HOXA10. When miRNA-27a-3p was overexpressed, it resulted in a decrease in both the RNA and protein expression of HOXA10. Conversely, inhibiting miRNA-27a-3p increased the RNA and protein expression of HOXA10. In the presence of LIF treatment, the expression of miRNA-27a-3p was reduced, while the expression of HOXA10 was increased. However, when LIF and a STAT3 inhibitor were combined, there was no significant change in the expression of miRNA-27a-3p or HOXA10. Consequently, LIF facilitated cell proliferation by activating the PI3K/AKT pathway. LIF controlled the expression of miRNA-27a-3p and HOXA10 in endometrial epithelial cells through STAT3, with miRNA-27a-3p negatively regulating the expression of HOXA10.

Growth hormone inhibits the JAK/STAT3 pathway by regulating SOCS1 in endometrial cells in vitro: a clue to enhance endometrial receptivity in recurrent implantation failure

Recurrent implantation failure (RIF) is defined as failure to achieve clinical pregnancy after at least 3 transfers of good-quality embryos by natural or artificial means. RIF is often a complex problem with a wide variety of etiologies and mechanisms as well as treatment options. In this study, using immunohistochemistry and Western blot, we demonstrated that the expression of leukemia inhibitory factor (LIF), Janus kinase 1 (JAK1), and signal transducer and activator of transcription 3 (STAT3) was increased, while that of suppressor of cytokine signaling 1 (SOCS1) was decreased in RIF patients. Growth hormone (GH) administration proved to have positive effects on embryo implantation in RIF patients, but the action mechanism of GH has not been elucidated yet. To this aim, we studied the effects of GH on the proliferation in vitro of endometrial adenocarcinoma Ishikawa cells. GH stimulated the expression of LIF and SOCS1, and through SOCS1 inhibits the expression of phosphorylated STAT3, and finally inhibits the occurrence of RIF. Excessive phosphorylation of STAT can lead to decreased endometrial receptivity and abnormal embryo implantation. We also examined the effects of LIF overexpression and an LIF inhibitor (EC330) on the JAK/STAT pathway. LIF promoted cell proliferation, and the up-regulation of LIF increased the expression of SOCS1 and JAK1/STAT3 pathway-related genes in Ishikawa cells. As GH can inhibit the JAK1/STAT3 pathway through LIF, we hypothesize that upregulating SOCS1 may be a potential approach to treat RIF at the molecular level. GH can inhibit the JAK1/STAT3 pathway through LIF, up-regulating SOCS1 to treat RIF at the molecular level.

Immunological uterine response to pig embryos before and during implantation

The establishment of a successful pregnancy can only occur through a concerted functioning of the entire female reproductive system, allowing for fertilization, subsequent embryo development and implantation of the conceptus. In this context, the uterine immunological responses responsible for rejection or tolerance of the conceptus are of critical importance. The aim of the present review is to summarize our current knowledge about those cellular and molecular immunological events occurring at the uterine level during pre-implantation and implantation stages of pregnancy in the pig. Advancing our understanding of the immune mechanisms involved in the success or failure of pregnancy will provide cues to develop novel strategies augmenting endometrial receptivity, finally increasing the efficiency of assisted reproductive technologies in pigs.

Context is key: Maternal immune responses to pig allogeneic embryos

Successful establishment of pregnancy includes the achievement of a state of immune tolerance toward the embryos (and placenta), where the well‐coordinated maternal immune system is capable of recognizing conceptus antigens while maintaining maternal defense against pathogens. In physiological pregnancies, following natural mating or artificial insemination (AI), the maternal immune system is exposed to the presence of hemi‐allogeneic embryos, that is, embryos containing maternal self‐antigens and foreign antigens from the paternal side. In this scenario, the hemi‐allogeneic embryo is recognized by the mother, but the immune system is locally modified to facilitate embryo implantation and pregnancy progression. Pig allogeneic pregnancies (with embryos containing both paternal and maternal material foreign to the recipient female), occur during embryo transfer (ET), with conspicuously high rates of embryonic death. Mortality mainly occurs during the peri‐attachment phase, suggesting that immune responses to allogeneic embryos are more complex and less efficient, hindering the conceptuses to survive to term. Reaching a similar maternal tolerance as in conventional breeding would render ET successful. The present review critically summarizes mechanisms of maternal immune recognition of pregnancy and factors associated with impaired maternal immune response to the presence of allogeneic embryos in the porcine species.