Thirty years of interferon-tau research; Past, present and future perspective

Exosomes: The role in mammalian reproductive regulation and pregnancy-related diseases

Exosomes are a kind of extracellular vesicles that are produced and secreted by different mammalian cells. They serve as cargo proteins and can transfer different kinds of biomolecules, including proteins, lipids, and nucleic acids, which consequently act on target cells to exert different biological effects. Recent years have witnessed a significant increase in the number of studies on exosomes due to the potential effects of exosomes in the diagnosis and treatment of cancers, neurodegenerative diseases, and immune disorders. Previous studies have demonstrated that exosomal contents, especially miRNAs, are implicated in numerous physiological processes such as reproduction, and are crucial regulators of mammalian reproduction and pregnancy-related diseases. Here, we describe the origin, composition, and intercellular communication of exosomes, and discuss their functions in follicular development, early embryonic development, embryonic implantation, male reproduction and development of pregnancy-related diseases in humans and animals. We believe this study will provide a foundation for revealing the mechanism of exosomes in regulating mammalian reproduction, and providing new approaches and ideas for the diagnosis and treatment of pregnancy-related diseases.

The Importance of Interferon-Tau in the Diagnosis of Pregnancy

Several decades of improving dairy cattle towards unilateral utilization of dairy cattle led to enormous progress in the field of milk yield; however, it resulted in a number of unfavorable features, such as reproductive disorders, increased calf mortality, and reduced health. Most cases of embryo loss and/or lost pregnancies occur during the first four to five weeks of gestation; accurate detection for pregnancy during this period is likely to contribute to an improvement in gestation rates. A specific protein, interferon-tau (IFNT), stimulates interferon-stimulated genes (ISGs), and their expression increases during gestation within 21 days after insemination. In bovines, the early conceptus undergoes a phase of rapid growth and elongation before implantation, the latter occurring 2–3 weeks after fertilization. IFNT acts mainly in the endometrium of the luminal epithelium. It is a new type I interferon that regulates several genes encoding uterine-derived factors. They are crucial in the processes of preparing the uterus for placenta attachment, modifying the uterine immune system, and regulating early fetal development. Because IFNT is expressed and induces ISGs in the endometrium during pregnancy recognition, it was reasoned that surrogate markers for pregnancy or IFNT might be present in the blood and provide an indicator of pregnancy status in cattle.

Early pregnancy affects expression of Toll-like receptor signaling members in ovine spleen

Toll-like receptors (TLRs) are involved to the maternal immune tolerance. The spleen is essential for adaptive immune reactions. However, it is unclear that early pregnancy regulates TLR-mediated signalings in the maternal spleen. The purpose of this study was to investigate the effects of early pregnancy on expression of TLR signaling members in the ovine spleen. Ovine spleens were collected at day 16 of the estrous cycle, and at days 13, 16 and 25 of pregnancy (n = 6 for each group). Real-time quantitative PCR, western blot and immunohistochemistry analysis were used to detect TLR signaling members, including TLR2, TLR3, TLR4, TLR5, TLR7, TLR9, myeloid differentiation primary-response protein 88 (MyD88), tumor necrosis factor receptor associated factor 6 (TRAF6) and interleukin-1-receptor-associated kinase 1 (IRAK1). The results showed that expression levels of TLR2, TLR4 and IRAK1 were downregulated, but expression levels of TLR3, TLR5, TLR7, TLR9, TRAF6 and MyD88 were increased during early pregnancy. In addition, MyD88 protein was located in the capsule, trabeculae and splenic cords of the maternal spleen. This paper reports for the first time that early pregnancy has effects on TLR signaling pathways in the ovine spleen, which is beneficial for understanding the maternal immune tolerance during early pregnancy.

Changes in mRNA and protein levels of gonadotropin releasing hormone and receptor in ovine thymus, lymph node, spleen, and liver during early pregnancy

There exists maternal immunological modification in maternal immune organs during early pregnancy in mammals. Gonadotropin releasing hormone (GnRH) is widely distributed in vertebrate tissues, including immune organs. However, it is unclear that early pregnancy induces expression of GnRH and GnRH receptor (GnRHR) in ovine immune organs. The objective of this study was to explore the expression of GnRH and GnRHR in main immune organs (thymus, lymph node, spleen, and liver) during early pregnancy in sheep. Ovine thymus, lymph node, spleen and liver were sampled at day 16 of estrous cycle, and days 13, 16, and 25 of pregnancy. The expression of GnRH and GnRHR was detected through real-time quantitative PCR, Western blot and immunohistochemistry analysis. The results indicated that early pregnancy induced upregulation of mRNA and protein levels of GnRH and GnRHR in the maternal lymph node, spleen and liver, and mRNA and protein of GnRH in the maternal thymus, but mRNA and protein of GnRHR decreased in the maternal thymus during early pregnancy. In summary, the mRNA and protein levels of GnRH and GnRHR were changed in maternal thymus, lymph node, spleen and liver in a tissue specific manner during early pregnancy in sheep.

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.

Profiles of progesterone and bovine interferon-τ in repeat breeding and non-repeat breeding Aceh cows

AIM

This study aimed at determining the profiles of progesterone and bovine interferon-τ (bIFN-τ) and the correlation between the two in repeat breeding (RB) Aceh cattle and non-RB Aceh cattle.

MATERIALS AND METHODS

The study was performed on five RB and five non-RB Aceh cows. These cows were subjected to estrous synchronization using the prostaglandin F2 alpha hormone, which was followed by artificial insemination (AI). Serum samples were collected on days 5, 6, 7, 15, 16, and 17 after AI to measure the concentration of progesterone at the beginning and end of the luteal phase and from days 14 to 18 after AI to measure the concentration of bIFN-τ. The concentrations of progesterone and bIFN-τ were determined using enzyme-linked immunosorbent assay. Pregnancy examinations were performed by ultrasonography on days 25, 35, 45, and 55 after AI. Data for progesterone and bIFN-τ concentrations were analyzed using the Mann-Whitney and t-tests, and the correlation between progesterone and bIFN-τ was analyzed using the Spearman correlation test.

RESULTS

The average concentration of progesterone in RB Aceh cows tended to be lower than non-RB Aceh cows, but it was not significantly different (p>0.05). Similar results also found in the concentration of bIFN-τ which RB Aceh cows tended to have lower bIFN-τ concentrations compared to non-RB Aceh cows, but it was also not significantly different (p>0.05). Moreover, the concentrations of progesterone and bIFN-τ in RB and non-RB Aceh cows did not show a significant correlation (p>0.05). These results of the ultrasonography showed that non-RB Aceh cows were pregnant from day 25 to day 55 after AI, whereas RB Aceh cows were not pregnant and had early embryonic death.

CONCLUSION

The concentrations of progesterone and bIFN-τ in non-RB Aceh cows tended to be higher than those in RB Aceh cows, although, it was not significantly different. Non-RB Aceh cows were able to maintain pregnancy until day 55, whereas RB Aceh cows were diagnosed with early embryonic death before day 25 after AI.

Profiles of prostaglandin F2α metabolite in dairy cattle during luteal regression and pregnancy: implications for corpus luteum maintenance†

Mechanisms of bovine corpus luteum (CL) maintenance during the second month of pregnancy have not been adequately investigated, despite significant reproductive losses. In the first month, interferon-tau is believed to suppress oxytocin-stimulated prostaglandin F2α (PGF) production, yet there are conflicting reports of circulating PGF metabolite (PGFM). In this study, characterization of PGFM and P4 occurred through continuous bihourly blood sampling in cows undergoing CL regression (day 18-21, n = 5), and during the first (day 18-21, n = 5) and second month (day 47-61; n = 16) of pregnancy. Cattle in the second month were assigned to control (n = 8) or oxytocin treatment (n = 8; three pulses to mimic luteolysis) to evaluate if oxytocin receptors were active. All cows but one (which had elevated PGFM prior to oxytocin treatment) maintained the pregnancy. Basal PGFM concentrations were low (11.6 ± 0.7 pg/mL) in the first month but increased 2.54-fold in the second month. Few (0.26 ± 0.12 pulses/day) PGFM pulses with low peak concentrations (28.8 ± 3.1 pg/mL) were observed during the first month of pregnancy, similar to cows not undergoing regression. However, in the second month, frequency (1.10 ± 0.26 pulses/day) and peak concentration (67.2 ± 5.0 pg/mL) of PGFM pulses increased, displaying similar frequency but lower peak PGFM than seen in regression (1.44 ± 0.14 pulses/day; 134.5 ± 18.9 pg/mL). Oxytocin treatment increased likelihood of PGFM pulses post-treatment and increased peak concentration (89.7 ± 10.1 pg/mL) in cows during the second month. Thus, cows have more PGFM pulses during second than first month of pregnancy, possibly induced by endogenous oxytocin, indicating suppression of PGF production is an important mechanism for CL maintenance during first but not second month of pregnancy.

Fine-tuned adaptation of embryo-endometrium pairs at implantation revealed by transcriptome analyses in Bos taurus

Interactions between embryo and endometrium at implantation are critical for the progression of pregnancy. These reciprocal actions involve exchange of paracrine signals that govern implantation and placentation. However, it remains unknown how these interactions between the conceptus and the endometrium are coordinated at the level of an individual pregnancy. Under the hypothesis that gene expression in endometrium is dependent on gene expression of extraembryonic tissues and genes expressed in extraembryonic tissues are dependent of genes expressed in the endometrium, we performed an integrative analysis of transcriptome profiles of paired extraembryonic tissue and endometria obtained from cattle (Bos taurus) pregnancies initiated by artificial insemination. We quantified strong dependence (|r| > 0.95, empirical false discovery rate [eFDR] < 0.01) in transcript abundance of genes expressed in the extraembryonic tissues and genes expressed in the endometrium. The profiles of connectivity revealed distinct coexpression patterns of extraembryonic tissues with caruncular and intercaruncular areas of the endometrium. Notably, a subset of highly coexpressed genes between extraembryonic tissue (n = 229) and caruncular areas of the endometrium (n = 218, r > 0.9999, eFDR < 0.001) revealed a blueprint of gene expression specific to each pregnancy. Gene ontology analyses of genes coexpressed between extraembryonic tissue and endometrium revealed significantly enriched modules with critical contribution for implantation and placentation, including “in utero embryonic development,” “placenta development,” and “regulation of transcription.” Coexpressing modules were remarkably specific to caruncular or intercaruncular areas of the endometrium. The quantitative association between genes expressed in extraembryonic tissue and endometrium emphasize a coordinated communication between these two entities in mammals. We provide evidence that implantation in mammalian pregnancy relies on the ability of the extraembryonic tissue and the endometrium to develop a fine-tuned adaptive response characteristic of each pregnancy.

An integrative analysis of interactions between conceptus and endometrium, in cattle, reveals complex regulatory networks operating at the time of implantation, highlighting the unique transcriptional blueprint of conceptus-maternal communication

Implantation in mammals requires a complex crosstalk between the conceptus (the embryo and associated membranes) and the uterus. An imbalanced regulation of the factors contributing to these interactions has negative impacts on the attachment of the fetus, the progression of the pregnancy, and the progeny. Focusing on paired conceptus–endometrium analyses of individual pregnancies in cows, we have determined that communication at implantation encompasses synchronized genome-wide coregulation of genes. Gene regulatory interactions between one conceptus and the surrounding maternal tissue vary between endometrial regions containing or lacking glands. Our data reveal new insights, to our knowledge, on the coordination of molecular mechanisms that contribute to implantation and pregnancy establishment in mammals. We conclude that the biological response of the endometrium is embryo-specific, a phenomenon that deserves further investigation in the context of assisted reproductive technologies.

Intrauterine exosomes are required for bovine conceptus implantation

Exosomes, extracellular vesicles, are present in uterine flushing fluids (UFs), which are involved in conceptus-endometrial interactions during peri-implantation periods. Despite several studies on intrauterine exosomes conducted, the roles conceptus and endometrial exosomes play during peri-implantation periods have not been well characterized. To investigate the effect of bovine intrauterine exosomes on conceptus implantation, exosomes isolated from bovine UFs during peri-implantation periods were subjected to global protein analysis. The analysis detected 596 exosomal proteins, including ruminants' pregnancy recognition factor IFNT, and 172 differentially expressed proteins with more than 1.5-fold changes in UFs on days 17, 20 and 22 pregnancy (day of conceptus implantation is initiated on days 19-19.5). Treatment of primary bovine endometrial epithelial cells with exosomes from day 17 UFs up-regulated the expression of apoptosis-related genes, and treatment with exosomes from day 20 and 22 UFs up-regulated the expression of adhesion molecule. Based on these findings, intrauterine exosomes should be considered as an essential constituent for successful implantation.

Interferon-tau and fertility in ruminants

Establishment of pregnancy in domestic ruminants includes pregnancy recognition signalling by the conceptus, implantation and placentation. Despite the high fertilisation success rate in ruminants, a significant amount of embryo loss occurs, primarily during early gestation. Interferon-tau (IFNT), a type I interferon that is exclusively secreted by the cells of the trophectoderm of the ruminant conceptus, has been recognised as the primary agent for maternal recognition of pregnancy in ruminants. It produces its antiluteolytic effect on the corpus luteum by inhibiting the expression of oxytocin receptors in the uterine epithelial cells, which prevents pulsatile, luteolytic secretion of prostaglandin F2α by the uterine endometrium. While the importance of IFNT in maternal recognition of pregnancy and prevention of luteolysis in ruminants is unequivocal, important questions, for example, relating to the threshold level of IFNT required for pregnancy maintenance, remain unanswered. This paper reviews data linking IFNT with measures of fertility in ruminants.