Pig blastocyst–uterine interactions

Effect of gestational age and fetal sex on metabolism of creatine by uteri, placentae, and fetuses of pigs†

The creatine (Cr) biosynthesis pathway buffers adenosine triphosphate in metabolically active tissues. We investigated whether sex of fetus and day of gestation influence Cr in endometrial and conceptus tissues from gilts on days 60 and 90 (n = 6 gilts/day) of gestation. Uterine and conceptus tissues associated with one male and one female fetus from each gilt were analyzed for creatine, messenger RNAs (mRNAs), and proteins for Cr biosynthesis. Total Cr decreased in amniotic fluid but increased in allantoic fluid between days 60 and 90 of gestation for male (P < 0.05) but not for female fetuses (P > 0.05). Endometrial expression of creatine kinase, muscle (CKM), creatine kinase mitochondrial type 1 (CKMT1), and solute carrier family 6, member 8 (SLC6A8) mRNAs increased (P < 0.05) between days 60 and 90 only for female fetuses. On day 60, expression of creatine kinase, brain (CKB) and CKMT1 mRNAs was greater (P < 0.05) for placentae of female than male fetuses. Livers of male fetuses had greater expression of arginine:glycine amidinotransferase (AGAT) and CKB than for females on day 60, while kidneys of female fetuses had greater expression of guanidinoacetate-N-methyltransferase (GAMT) than male fetuses on day 90 (P < 0.05). Localization of GAMT, CKB, CKMT1, and SLC6A8 proteins to uterine and chorionic epithelium was not influenced by gestational age or fetal sex. Arginine-glycine amidinotransferase localized to fetal kidneys and appeared greater on day 90 than on day 60 in both sexes. Thus, expression of the creatine-creatine kinase-phosphocreatine system at the uterine-conceptus interface is affected by gestational age and fetal sex to influence energy homeostasis in pigs.

The parturition-relevant hormone profile in hyper-prolific sows under different housing conditions

Aim was to characterize birth-relevant hormone profiles of reproductively productive hybrid sows in the peripartum period. It was examined whether there are deviations in the hormone profile depending on the birth process (eutocia:dystocia) and the type of housing (box stall BS vs. farrowing pen FP vs. group housing GH).A total of 40 healthy, heavily pregnant hybrid sows (German Landrace x Large White) with a gestation number≥ 2 were available. The distribution between the housing types was: BS n=18, FP n=15, GH n=7. All births occurred after the biologically completed gestation period. Blood samples were taken via indwelling catheters (113th day ante partum to 4th day post partum). Progesterone (P4), oestradiol (E2), prostaglandin F2α and its metabolites (PGFM), relaxin, oxytocin, cortisol, adrenaline and noradrenaline were determined.The ratio of eutocia:dystocia was 15:25. Dystocia occurred regardless of type of housing. The only reason for dystocia was a weak labor (>60 min). The litter size was 17.73± 3.85 piglets. Differences in the hormone profiles between eutocia and dystocia were as follows: P4 tended to be higher in dystocia p=0.0776; oxytocin higher in eutocia (not significant), 12.5% of sows permanently with hypoxytocinemia; cortisol p=0.0503; noradrenaline p=0.0098. The type of housing had the following influence on the hormone profile: P4 p=0.046; E2 p=0.0009; PGFM p=0.0108; relaxin p=0.0022; noradrenaline p=0.0078.The parturition-relevant hormones are related to the parturition and to the type of housing during birth. The hormone profiles obtained could be of use in the discussion about the animal welfare-oriented housing system in the peripartum phase in pigs. The proportion of sows of the hyperproliferative line studied with permanent hypoxytocinaemia in stage II of parturition is remarkable. The ratio of eutocia:dystocia is unevenly distributed. Dystocia occurred regardless of the type of housing.

Effects of dietary supplementation of creatine on fetal development in gilts at d 60 and d 90 of gestation

BACKGROUND

The creatine-creatine kinase-phosphocreatine (Cr-CK-PCr) system maintains intracellular ratios of ATP/ADP for support of cellular functions and has been characterized at the placental-uterine interface of rodents, primates, swine and sheep, and thus may support fetal development. This study determined effects of dietary supplementation of creatine (Cr) to gestating gilts on fetal development, the number and ratio of primary and secondary muscle fibers, and on protein expression in endometrium and fetal biceps-femoris muscle, respectively in fetal pigs on d 60 and d 90 of gestation.

METHODS

Reproductively mature gilts were synchronized to estrus using Matrix, observed for estrus (d 0), and artificially inseminated 12 h and 36 h later. Gilts were individually housed and fed 0.86 kg of 14% crude protein diet twice daily that meets nutritional requirements for pregnant gilts. Gilts were assigned to either basal diet control (CON) group, or Cr supplemented group (provided 30 g Cr monohydrate daily) from d 10 to either d 60 or d 90 of gestation. Gilts were euthanized and hysterectomized on either d 60 or d 90 of gestation. These protocols were completed in two replicates, as gilts were bred in spring and euthanized in summer or bred in fall and euthanized in winter (n = 20 gilts/replicate). Litter size, crown-rump length, sex, and fetal weight was recorded. Three female and male fetuses closest to mean litter weight were selected to assess effects of treatment on weight of fetal brain, kidney, liver, spleen, and biceps-femoris muscle. Data were analyzed to determine effects of treatment, days of gestation, replicate, and sex on litter size, fetal measurements, and incidence of intrauterine growth restriction.

RESULTS

Dietary Cr supplementation increased fetal brain weight to body weight ratios on d 90 of gestation (P < 0.05) and fetal kidney weight to body weight ratios on d 60 of gestation (P < 0.01), while days of gestation had significant effect on expression of mitochondrial CK isoform in gilt endometria (P < 0.05).

CONCLUSIONS

Results suggest that dietary supplementation of Cr in gestating gilts enhanced development of select fetal organs and contribute to understanding roles of the Cr-CK-PCr system in pregnancy.

Analysis of differential transcriptome expression reveals that ISG15 provides support for embryo development by promoting angiogenesis in porcine mesometrium

Mesometrium is the "gateway" through which the endometrium exchanges nutrients and substances with the outside world due to blood vessels entering endometrium across mesometrium. Therefore, dissecting the transcription atlas of the mesometrium will be a great help in understanding the role of mesometrium during implantation. In this study, we collected samples from the mesometrium and adjacent endometrium on the 12th day of estrous cycle and pregnancy. Transcription atlas of mesometrium and adjacent endometrium revealed that genes such as ISG15, which are related to the pathway of response to Interferon α and γ, were significantly enriched. The result of immunohistochemistry demonstrated that the core genes within these pathways were mainly located in the vascular endothelial cells both the endometrium and mesometrium. ISG15 interferon assay revealed the down-regulation of ISG15 induced proliferation, migration and tube formation. Taken together, we concluded that down-regulation of genes related to response of interferons promoted angiogenesis in the mesometrium and adjacent endometrium, allowing mesometrium to play an essential supportive role in pregnancy.

The Role of Nutrition Across Production Stages to Improve Sow Longevity

Modern hyperprolific sows are increasingly susceptible to health challenges. Their rapid growth rates predispose them to locomotor disorders, while high metabolic demands, reduced backfat thickness, and increased protein accretion heighten their vulnerability to heat stress and dystocia. Additionally, prolonged farrowing negatively affects the oxidative and inflammatory status of these females. Additionally, prevalent conditions such as gastric ulcers and cystitis raise ethical, welfare, and economic concerns. Despite the several studies related to sow nutrition, there are no studies which compile and extrapolate nutrition approaches from the rearing period and their impact on sows' health and longevity. Also, the aim of our review was to shed light on gaps that require further investigation. Controlling body condition scores is crucial for maximizing productivity in sows. During gestation, high-fiber diets help maintain optimal body condition and prevent constipation, particularly during the peripartum period. Antioxidants offer a range of beneficial effects during this critical phase. Additionally, probiotics and acidifiers can enhance gut health and lower the risk of genitourinary infections. On the day of farrowing, energy supplementation emerges as a promising strategy to reduce farrowing duration. Collectively, these strategies address major health challenges, enhancing welfare and promoting sow's longevity.

Melatonin improves endometrial receptivity and embryo implantation via MT2/PI3K/LIF signaling pathway in sows

BACKGROUND

Increased backfat thickness of sows in early gestation is negative to reproductive performance. Endometrial receptivity is an important determinant of reproductive success, but it is unclear whether the effect of sow backfat thickness on litter size is associated with endometrial receptivity and whether melatonin treatment may have benefits. The present study seeks to answer these questions through in vitro and in vivo investigations.

RESULTS

Excessive lipid deposition and lower melatonin levels in the uterus are detrimental to endometrial receptivity and embryo implantation in high backfat thickness sows. In cells treated with melatonin, the MT2/PI3K/LIF axis played a role in reducing lipid accumulation in porcine endometrial epithelium cells and improved endometrial receptivity. Furthermore, we found a reduction of lipids in the uterus after eight weeks of intraperitoneal administration of melatonin to HFD mice. Notably, melatonin treatment caused a significant reduction in the deposition of endometrial collagen, an increase in the number of glands, and repair of the pinopode structure, ultimately improving endometrial receptivity, promoting embryo implantation, and increasing the number of litter size of mice.

CONCLUSIONS

Collectively, the finding reveals the harmful effects of high backfat thickness sows on embryo implantation and highlight the role of melatonin and the MT2/PI3K/LIF axis in improving endometrial receptivity by enhancing metabolism and reducing the levels of uterine lipids in obese animals.

Extracellular Vesicles in Implantation: Cross-Talk Between the Embryo and Endometrium

Extracellular vesicles (EVs), including exosomes and microvesicles, have emerged as pivotal mediators of intercellular communication. Embryo implantation is a critical process in early pregnancy and requires communication between the embryo and maternal uterus. EVs are important in coordinating the communication between the embryo and maternal uterus. This review explores EV biogenesis, molecular composition, and functional roles during implantation. It emphasizes the dynamic role of EVs in modulating the maternal-embryo dialogue, which is critical for establishing a receptive endometrium and facilitating successful implantation. EVs secreted by the embryo and endometrial cells have been shown to carry a diverse cargo of proteins, lipids, and miRNAs, which collectively influence key physiological processes, including immune tolerance, endometrial receptivity, and trophoblast invasion. EVs can be potential candidates as non-invasive biomarkers to assess the quality of embryos and uterine receptivity to enhance reproductive success. By providing a comprehensive overview of the current understanding of EVs in implantation, this chapter aims to highlight the significance of EVs in reproductive biology and their potential applications in improving fertility rates.

Resmethrin induces implantation failure by disrupting calcium homeostasis and forcing mitochondrial defects in porcine trophectoderm and uterine luminal epithelial cells

Resmethrin, a type I pyrethroid insecticide, is frequently used globally in residential and farmland areas to control pests. Owing to the repeated administration of resmethrin, and particularly because of its lipophilic nature, residues have been detected in various environments, crops, and livestock. Previous studies have shown the adverse effects of resmethrin, including neurotoxicity and hepatotoxicity. However, the toxic effects of resmethrin on the female reproductive system have rarely been investigated. In the present study, we used two cell types, porcine trophectoderm (pTr) and porcine uterine luminal epithelial (pLE) cells, to examine the toxic effects of resmethrin on implantation and its mechanisms. Our study showed that resmethrin exposure induced apoptosis and inhibited cell cycle progression, thereby reducing the viability of both cell types. In addition, calcium homeostasis was disrupted following resmethrin treatment, and disrupted calcium homeostasis impaired the mitochondrial membrane potential and mitochondrial respiration. In addition to mitochondrial dysfunction, GRP75 and ER stress-related proteins were upregulated. Furthermore, the AKT and MAPK cascades were altered, and reactive oxygen species production and inflammation occurred after resmethrin treatment. Ultimately, through various mechanisms, resmethrin decreased the migratory abilities, and it could diminish the crosstalk between the two cell lines and lower the probability of successful implantation. Overall, we demonstrated that resmethrin interfered with the implantation process by triggering various toxic mechanisms. This study presents, for the first time, evidence regarding the mechanisms through which resmethrin exerts toxic effects on the female reproductive system, thereby raising awareness regarding the potential implications of its widespread use.

Cross-Species Insights into Trophoblast Invasion During Placentation Governed by Immune-Featured Trophoblast Cells

Proper development of the placenta, the transient support organ forms after embryo implantation, is essential for a successful pregnancy. However, the regulation of trophoblast invasion, which is most important during placentation, remains largely unknown. Here, rats, mice, and pigs are used as biomedical models, used scRNA-seq to comparatively elucidate the regulatory mechanism of placental trophoblast invasion, and verified it using a human preeclampsia disease model combined with scStereo-seq. A dual-featured type of immune-featured trophoblast (iTrophoblast) is unexpectedly discovered. Interestingly, iTrophoblast only exists in invasive placentas and regulates trophoblast invasion during placentation. In a normally developing placenta, iTrophoblast gradually transforms from an immature state into a functional mature state as it develops. Whereas in the developmentally abnormal preeclamptic placenta, disordered iTrophoblast transformation leads to the accumulation of immature iTrophoblasts, thereby disrupting trophoblast invasion and ultimately leading to the progression of preeclampsia.

Function of immune cells and effector molecules of the innate immune system in the establishment and maintenance of pregnancy in mammals - A review

In mammalian species, pregnancy is a complex process that involves the maternal recognition of pregnancy, implantation, decidualization, placentation, and parturition. The innate immune system is composed of cellular components, such as natural killer cells, neutrophils, monocytes, and macrophages, and effector molecules, such as cytokines, interferons, antimicrobial peptides, and complement components. The innate immune system plays a critical role as the first line of defense against infection or inflammation to maintain homeostasis and activate the adaptive immunity. During pregnancy, innate immune cells and effector molecules act on the regulation of innate immunity for host defense and processes such as embryo development, implantation, and placentation at the maternal-conceptus interface. In this review, we describe the components of the innate immune system and their functions at the maternal-conceptus interface to establish and maintain pregnancy in animal species that form hemochorial- or epitheliochorial-type placentas, including humans, rodents, ruminants, and pigs.

Fructose metabolism is unregulated in cancers and placentae

Fructose and lactate are present in high concentrations in uterine luminal fluid, fetal fluids and fetal blood of ungulates and cetaceans, but their roles have been ignored and they have been considered waste products of pregnancy. This review provides evidence for key roles of both fructose and lactate in support of key metabolic pathways required for growth and development of fetal-placental tissues, implantation and placentation. The uterus and placenta of ungulates convert glucose to fructose via the polyol pathway. Fructose is sequestered within the uterus and cannot be transported back into the maternal circulation. Fructose is phosphorylated by ketohexokinase to fructose-1-PO4 (F1P) by that is metabolized via the fructolysis pathway to yield dihydoxyacetone phosphate and glyceraldehyde-3-PO4 that are downstream of phosphofructokinase. Thus, there is no inhibition of the fructolysis pathway by low pH, citrate or ATP which allows F1P to continuously generate substrates for the pentose cycle, hexosamine biosynthesis pathway, one-carbon metabolism and tricarboxylic acid cycle, as well as lactate. Lactate sustains the activity of hypoxia-inducible factor alpha and its downstream targets such as vascular endothelial growth factor to increase utero-placental blood flow critical to growth and development of the fetal-placental tissues and a successful outcome of pregnancy. Pregnancy has been referred to as a controlled cancer and this review addresses similarities regarding metabolic aspects of tumors and the placenta.

Expression Profiles of Fatty Acid Transporters and the Role of n-3 and n-6 Polyunsaturated Fatty Acids in the Porcine Endometrium

Fatty acids (FAs) are important for cell membrane composition, eicosanoid synthesis, and metabolic processes. Membrane proteins that facilitate FA transport into cells include FA translocase (also known as CD36) and FA transporter proteins (encoded by SLC27A genes). The present study aimed to examine expression profiles of FA transporters in the endometrium of cyclic and early pregnant gilts on days 3 to 20 after estrus and the possible regulation by conceptus signals and polyunsaturated FAs (PUFAs). The effect of PUFAs on prostaglandin (PG) synthesis and transcript abundance of genes related to FA action and metabolism, angiogenesis, and immune response was also determined. Day after estrus and reproductive status of animals affected FA transporter expression, with greater levels of CD36, SLC27A1, and SLC27A4 observed in pregnant than in cyclic gilts. Conceptus-conditioned medium and/or estradiol-17β stimulated SLC27A1 and CD36 expression. Among PUFAs, linoleic acid decreased SLC27A1 and SLC27A6 mRNA expression, while arachidonic, docosahexaenoic, and eicosapentaenoic acids increased SLC27A4 transcript abundance. Moreover, arachidonic acid stimulated ACOX1, CPT1A, and IL1B expression and increased PGE2 and PGI2 secretion. In turn, α-linolenic acid up-regulated VEGFA, FGF2, FABP4, and PPARG mRNA expression. These results indicate the presence of an active transport of FAs in the porcine endometrium and the role of PUFAs as modulators of the uterine activity during conceptus implantation.

Complement system molecules: Expression and regulation at the maternal-conceptus interface during pregnancy in pigs

The complement system, composed of complement components and complement control proteins, plays an essential role in innate immunity. Complement system molecules are expressed at the maternal-conceptus interface, and inappropriate activation of the complement system is associated with various adverse pregnancy outcomes in humans and rodents. However, the expression, regulation, and function of the complement system at the maternal-conceptus interface in pigs have not been studied. In this study, we investigated the expression, localization, and regulation of complement system molecules at the maternal-conceptus interface in pigs. Complement components and complement control proteins were expressed in the endometrium, early-stage conceptus, and chorioallantoic tissues during pregnancy. The expression of complement components acting on the early stage of complement activation increased in the endometrium on Day 15 of pregnancy, with greater levels on that day compared with the estrous cycle. Localization of several complement components and complement control proteins was cell-type specific in the endometrium. The expression of C1QC, C2, C3, C4A, CFI, ITGB2, MASP1, and SERPING1 was increased by IFNG in endometrial explant tissues. Furthermore, cleaved C3 fragments were detected in endometrial tissues and uterine flushings on Day 15 of the estrous cycle and Day 15 of pregnancy, with greater levels on Day 15 of pregnancy. These results suggest that complement system molecules in pigs expressed at the maternal-conceptus interface play important roles in the establishment and maintenance of pregnancy by regulating innate immunity and modulating the maternal immune environment during pregnancy.

Evidence for metabolism of creatine by the conceptus, placenta, and uterus for production of adenosine triphosphate during conceptus development in pigs†

In pigs, the majority of embryonic mortality occurs when free-floating conceptuses (embryos/fetuses and associated placental membranes) elongate, and the uterine-placental interface undergoes folding and develops areolae. Both periods involve proliferation, migration, and changes in morphology of cells that require adenosine triphosphate (ATP). We hypothesize that insufficient ATP in conceptus and uterine tissues contributes to conceptus loss in pigs. Creatine is stored in cells as phosphocreatine for ATP regeneration through the creatine-creatine kinase- phosphocreatine pathway. However, the expression of components of this pathway in pigs has not been examined throughout gestation. Results of qPCR analyses indicated increases in AGAT, GAMT, CKM, CKB, and SLC6A8 mRNAs in elongating porcine conceptuses, and immunofluorescence microscopy localized guanidinoacetate N-methyltransferase, creatine kinase M, and creatine kinase B proteins to the trophectoderm of elongating conceptuses, to the columnar chorionic epithelial cells at the bottom of chorioallantoic troughs, and to endometrial luminal epithelium at the tops of the endometrial ridges of uterine-placental folds on Days 40, 60, and 90 of gestation. Guanidinoacetate N-methyltransferase protein is expressed in endometrial luminal epithelium at the uterine-placental interface, but immunostaining is more intense in luminal epithelium at the bottoms of the endometrial ridges. Results of this study indicate that key elements of the pathway for creatine metabolism are expressed in cells of the conceptus, placenta, and uterus for potential production of ATP during two timepoints in pregnancy with a high demand for energy; elongation of the conceptus for implantation and development of uterine-placental folding during placentation.

Dynamic intrauterine crosstalk promotes porcine embryo implantation during early pregnancy

Dynamic crosstalk between the embryo and mother is crucial during implantation. Here, we comprehensively profile the single-cell transcriptome of pig peri-implantation embryos and corresponding maternal endometrium, identifying 4 different lineages in embryos and 13 cell types in the endometrium. Cell-specific gene expression characterizes 4 distinct trophectoderm subpopulations, showing development from undifferentiated trophectoderm to polar and mural trophectoderm. Dynamic expression of genes in different types of endometrial cells illustrates their molecular response to embryos during implantation. Then, we developed a novel tool, ExtraCellTalk, generating an overall dynamic map of maternal-foetal crosstalk using uterine luminal proteins as bridges. Through cross-species comparisons, we identified a conserved RBP4/STRA6 pathway in which embryonic-derived RBP4 could target the STRA6 receptor on stromal cells to regulate the interaction with other endometrial cells. These results provide insight into the maternal-foetal crosstalk during embryo implantation and represent a valuable resource for further studies to improve embryo implantation.

Evolutionary Patterns of Maternal Recognition of Pregnancy and Implantation in Eutherian Mammals

The implantation of the embryo into the maternal endometrium is a complex process associated with the evolution of viviparity and placentation in mammals. In this review, we provide an overview of maternal recognition of pregnancy signals and implantation modes in eutherians, focusing on their diverse mechanisms and evolutionary patterns. Different pregnancy recognition signals and implantation modes have evolved in eutherian mammals, reflecting the remarkable diversity of specializations in mammals following the evolution of viviparity. Superficial implantation is the ancestral implantation mode in Eutheria and its major clades. The other modes, secondary, partially, and primary interstitial implantation have each independently evolved multiple times in the evolutionary history of eutherians. Although significant progress has been made in understanding pregnancy recognition signals and implantation modes, there is still much to uncover. Rodents and chiropterans (especially Phyllostomidae) offer valuable opportunities for studying the transitions among implantation modes, but data is still scarce for these diverse orders. Further research should focus on unstudied taxa so we can establish robust patterns of evolutionary changes in pregnancy recognition signaling and implantation modes.

Beta-cyfluthrin impairs implantation process by inducing mitochondrial defects and changes in reactive oxygen species-mediated signaling pathways in porcine trophectoderm and uterine luminal epithelial cells

Pyrethroid insecticides, such as beta-cyfluthrin, are used extensively globally, including in households and agriculture, and have been detected in the milk and urine of humans and cattle. Beta-cyfluthrin exhibits toxic effects, including neurotoxicity and male reproductive toxicity; however, few studies have investigated female reproductive toxicity despite its wide environmental distribution. The present study investigates effects of beta-cyfluthrin on implantation in porcine cells (pTr from the trophectoderm and pLE from the endometrial luminal epithelium). To identify the various physiological changes induced by beta-cyfluthrin, such as apoptosis and lipid peroxidation, flow cytometry analysis and immunofluorescence were performed with various reagents. In addition, the expression of genes and proteins associated with intracellular changes was confirmed using qRT-PCR and western blotting. Beta-cyfluthrin induced cell-cycle arrest and altered intracellular calcium flux. It also disrupted the mitochondrial function and promoted reactive oxygen species (ROS) production, leading to lipid peroxidation. Moreover, ROS induced by beta-cyfluthrin altered mitogen-activated protein kinase (MAPK) pathways and decreased cell migration capability. The expression levels of genes that are significant during early pregnancy were altered by beta-cyfluthrin in both cell lines. The changes resulted in apoptosis and diminished cell proliferation of pTr and pLE. Collectively, the results imply that beta-cyfluthrin disrupts the implantation process by affecting the physiology of the trophectoderm and endometrial luminal epithelial cells. The present study is the first to reveal the cellular mechanisms of beta-cyfluthrin on the female reproductive system and highlights the need for further in-depth research into its hazards.

Pig conceptuses utilize extracellular vesicles for interferon-gamma-mediated paracrine communication with the endometrium†

Interferon-gamma (IFNG) is a pro-inflammatory cytokine secreted by the porcine conceptus (embryo and extra-embryonic membranes) during the peri-implantation period of pregnancy. IFNG modifies the endometrial inflammatory immune response and is required for the implantation and survival of the conceptus. It is not known how IFNG from the conceptus trophectoderm is transported across the endometrial luminal epithelium (LE). In the present study, immunofluorescence analyses detected immunoreactive IFNG protein in both the trophectoderm and endometrial LE on Day 15 of pregnancy, while our previous research localized IFNG mRNA only to conceptus trophectoderm. Using minced endometrial explants to disrupt the barrier posed by the intact endometrial LE, treatment with recombinant IFNG induced the expression of genes that were not induced when IFNG was infused into the uterine lumen in vivo by McLendon et al. (Biology of Reproduction. 2020;103(5):1018-1029). We hypothesized that during pregnancy extracellular vesicles (EVs) serve as intercellular signaling vehicles to transport conceptus-derived IFNG across the intact endometrial LE and into the stromal compartment of the uterus. Western blotting detected the presence of IFNG in EVs isolated from the uterine fluid of pregnant gilts, but not nonpregnant gilts. Real-time PCR demonstrated increased expression of IFNG-stimulated genes in EV-treated endometrial explants and EV-mediated IFNG transport was confirmed in whole uterine sections cultured with EVs from Day 15 of pregnancy. These results suggest that EVs are involved in IFNG transport across the endometrial LE to enable paracrine communication between the conceptus and cells within the endometrial stroma.

Early Embryonic Development in Agriculturally Important Species

The fertilization of oocytes ovulated by pigs, sheep, cows, and horses is not considered a limiting factor in successful establishment of pregnancy. Pig, sheep, and cow embryos undergo cleavage to the blastocyst stage, hatch from the zona pellucida, and undergo central-type implantation. Hatched blastocysts of pigs, sheep, and cows transition from tubular to long filamentous forms to establish surface area for exchange of nutrients and gases with the uterus. The equine blastocyst, surrounded by external membranes, does not elongate but migrates throughout the uterine lumen before attaching to the uterine luminal epithelium (LE) to begin implantation. Pregnancy recognition signaling in pigs requires the trophectoderm to express interleukin 1 beta, estrogens, prostaglandin E2, and interferon gamma. Sheep and cow conceptus trophectoderm expresses interferon tau that induces interferon regulatory factor 2 that inhibits transcription of estrogen and oxytocin receptors by uterine epithelia. This prevents oxytocin-induced luteolytic pulses of prostaglandin F2-alpha from regressing the corpora lutea, as well as ensuring the secretion of progesterone required for maintenance of pregnancy. The pregnancy recognition signal produced by equine blastocysts is not known. Implantation in these species requires interactions between extracellular matrix (ECM) proteins and integrins as the conceptus undergoes apposition and firm attachment to the uterine LE. This review provides details with respect to early embryonic development and the transition from spherical to filamentous conceptuses in pigs, sheep, and cows, as well as pre-implantation development of equine blastocysts and implantation of the conceptuses.

Visfatin impact on the proteome of porcine luteal cells during implantation

Visfatin (VIS) is a hormone belonging to the adipokines' group secreted mainly by the adipose tissue. VIS plays a crucial role in the control of energy homeostasis, inflammation, cell differentiation, and angiogenesis. VIS expression was confirmed in the hypothalamic-pituitary-gonadal (HPG) axis structures, as well as in the uterus, placenta, and conceptuses. We hypothesised that VIS may affect the abundance of proteins involved in the regulation of key processes occurring in the corpus luteum (CL) during the implantation process in pigs. In the present study, we performed the high-throughput proteomic analysis (liquid chromatography with tandem mass spectrometry, LC-MS/MS) to examine the in vitro influence of VIS (100 ng/mL) on differentially regulated proteins (DRPs) in the porcine luteal cells (LCs) on days 15-16 of pregnancy (implantation period). We have identified 511 DRPs, 276 of them were up-regulated, and 235 down-regulated in the presence of VIS. Revealed DRPs were assigned to 162 gene ontology terms. Western blot analysis of five chosen DRPs, ADAM metallopeptidase with thrombospondin type 1 motif 1 (ADAMTS1), lanosterol 14-α demethylase (CYP51A1), inhibin subunit beta A (INHBA), notch receptor 3 (NOTCH3), and prostaglandin E synthase 2 (mPGES2) confirmed the veracity and accuracy of LC-MS/MS method. We indicated that VIS modulates the expression of proteins connected with the regulation of lipogenesis and cholesterologenesis, and, in consequence, may be involved in the synthesis of steroid hormones, as well as prostaglandins' metabolism. Moreover, we revealed that VIS affects the abundance of protein associated with ovarian cell proliferation, differentiation, and apoptosis, as well as CL new vessel formation and tissue remodelling. Our results suggest important roles for VIS in the regulation of ovarian functions during the peri-implantation period.

The Extremely-Low-Frequency Electromagnetic Field Affects Apoptosis and Oxidative-Stress-Related Genes and Proteins in the Porcine Endometrium-An In Vitro Study

Nowadays, the extremely-low-frequency electromagnetic field (ELF-EMF) is recognized as environmental pollution. The data indicate that the ELF-EMF may affect factors related to epigenetic regulation and alter important biological processes in the uterus. The impact of the ELF-EMF on apoptosis and oxidative-stress-related genes has not been documented in porcine endometrium. This raises the question of whether the exposure to the ELF-EMF can induce apoptosis and/or oxidative stress in the endometrium of pigs during the peri-implantation period. Porcine endometrial slices (100 ± 5 mg) collected (n = 5) during the peri-implantation period were treated in vitro with ELF-EMF at a frequency of 50 Hz and flux density of 8 × 104 mG for 2 h. To determine the effect of ELF-EMF on apoptosis and oxidative stress in the endometrium, CASP3, CASP7, CIDEB, GADD45G, NOS1, NOS2, NOS3, and TP53I3 mRNA transcript were analyzed using real-time PCR, and protein abundance of CASP3, CASP7 using Western blot, and eNOS using ELISA were determined. Moreover, CASP3/7 and NOS activity was analyzed using flow cytometry and colorimetry, respectively. The decreased CASP7 and increased NOS3 mRNA transcript and protein abundance in ELF-EMF-treated endometrium were observed. Moreover, CIDEB, GADD45G, and TP53I3 mRNA transcript abundance was increased. Only p ≤ 0.05 was considered a statistically significant difference. The documented alterations indicate the potential of the ELF-EMF to affect apoptosis and generate oxidative stress in the endometrium. The insight into observed consequences documents for the first time the fact that the ELF-EMF may influence endometrial cell proliferation, angiogenesis, and/or tissue receptivity during peri-implantation.

Placental Transcriptome Analysis in Connection with Low Litter Birth Weight Phenotype (LBWP) Sows

It is possible to identify sub-populations of sows in every pig herd that consistently give birth to low birth weight (BW) piglets, irrespective of the litter size. A previous study from our group demonstrated that placental development is a main factor affecting the litter birth weight phenotype (LBWP) in sows, thereby impacting the BW of entire litters, but the biological and molecular pathways behind this phenomenon are largely unknown. The aim of this study was to investigate the differential gene expression in placental tissues at day 30 of gestation between low LBWP (LLBWP) vs. high LBWP (HLBWP) sows from a purebred Large White maternal line. Using mRNA sequencing, we found 45 differentially expressed genes (DEGs) in placental tissues of LLBWP and HLBWP sows. Furthermore, (GO) enrichment of upregulated DEGs predicted that there were two biological processes significantly related to cornification and regulation of cell population proliferation. To better understand the molecular interaction between cell proliferation and cornification, we conducted transcriptional factor binding site (TFBS) prediction analysis. The results indicated that a highly significant TFBS was located at the 5' upstream of all four upregulated genes (CDSN, DSG3, KLK14, KRT17), recognized by transcription factors EGR4 and FOSL1. Our findings provide novel insight into how transcriptional regulation of two different biological processes interact in placental tissues of LLBWP sows.

Mechanisms of female reproductive toxicity in pigs induced by exposure to environmental pollutants

Environmental pollutants, including endocrine disruptors, heavy metals, nanomaterials, and pesticides, have been detected in various ecosystems and are of growing global concern. The potential for toxicity to non-target organisms has consistently been raised and is being studied using various animal models. In this review, we focus on pesticides frequently detected in the environment and investigate their potential exposure to livestock. Owing to the reproductive similarities between humans and pigs, various in vitro porcine models, such as porcine oocytes, trophectoderm cells, and luminal epithelial cells, are used to verify reproductive toxicity. These cell lines are being used to study the toxic mechanisms induced by various environmental toxicants, including organophosphate insecticides, pyrethroid insecticides, dinitroaniline herbicides, and diphenyl ether herbicides, which persist in the environment and threaten livestock health. Collectively, these results indicate that these pesticides can induce female reproductive toxicity in pigs and suggest the possibility of adverse effects on other livestock species. These results also indicate possible reproductive toxicity in humans, which requires further investigation.

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.

Sex and fetal genome influence gene expression in pig endometrium at the end of gestation

BACKGROUND

A fine balance of feto-maternal resource allocation is required to support pregnancy, which depends on interactions between maternal and fetal genetic potential, maternal nutrition and environment, endometrial and placental functions. In particular, some imprinted genes have a role in regulating maternal-fetal nutrient exchange, but few have been documented in the endometrium. The aim of this study is to describe the expression of 42 genes, with parental expression, in the endometrium comparing two extreme breeds: Large White (LW); Meishan (MS) with contrasting neonatal mortality and maturity at two days of gestation (D90-D110). We investigated their potential contribution to fetal maturation exploring genes-fetal phenotypes relationships. Last, we hypothesized that the fetal genome and sex influence their endometrial expression. For this purpose, pure and reciprocally crossbred fetuses were produced using LW and MS breeds. Thus, in the same uterus, endometrial samples were associated with its purebred or crossbred fetuses.

RESULTS

Among the 22 differentially expressed genes (DEGs), 14 DEGs were differentially regulated between the two days of gestation. More gestational changes were described in LW (11 DEGs) than in MS (2 DEGs). Nine DEGs were differentially regulated between the two extreme breeds, highlighting differences in the regulation of endometrial angiogenesis, nutrient transport and energy metabolism. We identified DEGs that showed high correlations with indicators of fetal maturation, such as ponderal index at D90 and fetal blood fructose level and placental weight at D110. We pointed out for the first time the influence of fetal sex and genome on endometrial expression at D90, highlighting AMPD3, CITED1 and H19 genes. We demonstrated that fetal sex affects the expression of five imprinted genes in LW endometrium. Fetal genome influenced the expression of four genes in LW endometrium but not in MS endometrium. Interestingly, both fetal sex and fetal genome interact to influence endometrial gene expression.

CONCLUSIONS

These data provide evidence for some sexual dimorphism in the pregnant endometrium and for the contribution of the fetal genome to feto-maternal interactions at the end of gestation. They suggest that the paternal genome may contribute significantly to piglet survival, especially in crossbreeding production systems.

Protein Dynamic Landscape of Pig Embryos during Peri-Implantation Development

Properly developed embryos are critical for successful embryo implantation. The dynamic landscape of proteins as executors of biological processes in pig peri-implantation embryos has not been reported so far. In this study, we collected pig embryos from days 9, 12, and 15 of pregnancy during the peri-implantation stage for a PASEF-based quantitative proteomic analysis. In total, approximately 8000 proteins were identified. These proteins were classified as stage-exclusive proteins and stage-specific proteins, respectively, based on their presence and dynamic abundance changes at each stage. Functional analysis showed that their roles are consistent with the physiological processes of corresponding stages, such as the biosynthesis of amino acids and peptides at P09, the regulation of actin cytoskeletal organization and complement activation at P12, and the vesicular transport at P15. Correlation analysis between mRNAs and proteins showed a general positive correlation between pig peri-implantation embryonic mRNAs and proteins. Cross-species comparisons with human early embryos identified some conserved proteins that may be important in regulating embryonic development, such as STAT3, AP2A1, and PFAS. Our study provides a comprehensive overview of the pig embryo proteome during implantation, fills gaps in relevant developmental studies, and identifies some important proteins that may serve as potential targets for future research.

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.

The importance of optimal body condition to maximise reproductive health and perinatal outcomes in pigs

Overnutrition or undernutrition during all or part of the reproductive cycle predisposes sows to metabolic consequences and poor reproductive health which contributes to a decrease in sow longevity and an increase in perinatal mortality. This represents not only an economic problem for the pig industry but also results in poor animal welfare. To maximise profitability and increase sustainability in pig production, it is pivotal to provide researchers and practitioners with synthesised information about the repercussions of maternal obesity or malnutrition on reproductive health and perinatal outcomes, and to pinpoint currently available nutritional managements to keep sows' body condition in an optimal range. Thus, the present review summarises recent work on the consequences of maternal malnutrition and highlights new findings.

Role of Endometrial Extracellular Vesicles in Mediating Cell-to-Cell Communication in the Uterus: A Review

There are several critical events that occur in the uterus during early pregnancy which are necessary for the establishment and maintenance of pregnancy. These events include blastocyst implantation, uterine decidualization, uterine neoangiogenesis, differentiation of trophoblast stem cells into different trophoblast cell lineages, and formation of a placenta. These processes involve several different cell types within the pregnant uterus. Communication between these cell types must be intricately coordinated for successful embryo implantation and the formation of a functional maternal-fetal interface in the placenta. Understanding how this intricate coordination transpires has been a focus of researchers in the field for many years. It has long been understood that maternal endometrial tissue plays a key role in intercellular signaling during early pregnancy, sending signals to nearby tissues in a paracrine manner. Recently, insights have been obtained into the mechanisms by which these signaling events occur. Notably, the endometrium has been shown to secrete extracellular vesicles (EVs) that contain crucial cargo (proteins, lipids, RNA, miRNA) that are taken up by recipient cells to initiate a response leading to the occurrence of critical events during implantation and placentation. In this review, we aim to summarize the role that endometrium-derived EVs play in mediating cell-to-cell communications within the pregnant uterus to orchestrate the events that must occur to establish and maintain pregnancy. We will also discuss how aberrant endometrial EV signaling may lead to pathophysiological conditions, such as endometriosis and infertility.

CYP24A1 is associated with fetal mummification in pigs

Mummified piglets are among the leading causes of fertility loss and severely hamper reproductive performance in pigs. However, the contributions of genomic variation to the emergence of mummified piglets (MUM) have rarely been studied. This study aims to (1) elucidate the genetic architecture of MUM in sows of parity 1 - 3 using a single-step genome-wide association study (ssGWAS). The ssGWAS involved genotyping-by-sequencing of Large White and Landrace pig breeds. (2) Explore the biological role of the candidate genes at the cellular level. A total of 185 and 48 genome-wide significant SNPs are associated with MUM in Large White and Landrace pigs, explaining 0.01-36.52% genetic variance for different significant loci, respectively. All the significant SNPs are parity-specific, and the numerous, consecutive significant loci likely generated the nine significant peaks in different parities. Multiple candidate genes (including CYP24A1, FBXO30, and ARHGEF28) are associated with fetal congenital and maternal diseases. Collectively, CYP24A1 regulation contributes to steady-state levels of embryo development genes. CYP24A1 is involved in reproduction and, immune and gestational disorders. Thus, it is associated with known newborn death traits and MUM in Large White sows. Altogether, these results improve the current understanding of the genetic architecture of MUM and expand the knowledge on genetic variations for selecting against mummified piglets in pig breeding.

Bifenox compromises porcine trophectoderm and luminal epithelial cells in early pregnancy by arresting cell cycle progression and impairing mitochondrial and calcium homeostasis

Bifenox is a widely used herbicide that contains a diphenyl ether group. However its global usage, the cell physiological effects that induce toxicity have not been elucidated. In this study, the effect of bifenox was examined in porcine trophectoderm and uterine epithelial cells to investigate the potential toxicity of the implantation process. To uncover the toxic effects of bifenox, cell viability and apoptosis following treatment with bifenox were evaluated. To investigate the underlying cellular mechanisms, mitochondrial and calcium homeostasis were investigated in both cell lines. In addition, the dysregulation of cell signal transduction and transcriptional alterations were also demonstrated. Bifenox reduced cell viability and significantly increased the number of cells arrested at the sub-G1 stage. Moreover, bifenox depolarized the mitochondrial membrane and upregulated the calcium flux into the mitochondria in both cell lines. Cytosolic calcium flux increased in porcine trophectoderm (pTr) cells and decreased in porcine luminal epithelium (pLE) cells. In addition, bifenox activated the mitogen-activated protein kinase and phosphoinositide 3-kinase signaling pathways. Furthermore, bifenox inhibited the expression of retinoid receptor genes, such as RXRA, RXRB, and RXRG. Chemokine CCL8 was also downregulated at the mRNA level, whereas CCL5 expression remained unchanged. Overall, the results of this study suggest that bifenox deteriorates cell viability by arresting cell cycle progression, damaging mitochondria, and controlling calcium levels in pTr and pLE cells. The present study indicates the toxic potential of bifenox in the trophectoderm and luminal epithelial cells, which can lead to implantation disorders in early pregnancy.

Different seminal ejaculated fractions in artificial insemination condition the protein cargo of oviductal and uterine extracellular vesicles in pig

The seminal plasma (SP) is the liquid component of semen that facilitates sperm transport through the female genital tract. SP modulates the activity of the ovary, oviductal environment and uterine function during the periovulatory and early pregnancy period. Extracellular vesicles (EVs) secreted in the oviduct (oEVs) and uterus (uEVs) have been shown to influence the expression of endometrial genes that regulate fertilization and early embryo development. In some species, semen is composed of well-separated fractions that vary in concentration of spermatozoa and SP composition and volume. This study aimed to investigate the impact of different accumulative fractions of the porcine ejaculate (F1, composed of the sperm-rich fraction, SRF; F2, composed of F1 plus the intermediate fraction; F3, composed of F2 plus the post-SRF) on oEVs and uEVs protein cargo. Six days after the onset of estrus, we determined the oEVs and uEVs size and protein concentration in pregnant sows by artificial insemination (AI-sows) and in non-inseminated sows as control (C-sows). We also identified the main proteins in oEVs and uEVs, in AI-F1, AI-F2, AI-F3, and C-sows. Our results indicated that although the size of EVs is similar between AI- and C-sows, the protein concentration of both oEVs and uEVs was significantly lower in AI-sows (p < 0.05). Proteomic analysis identified 38 unique proteins in oEVs from AI-sows, mainly involved in protein stabilization, glycolytic and carbohydrate processes. The uEVs from AI-sows showed the presence of 43 unique proteins, including already-known fertility-related proteins (EZR, HSPAA901, PDS). We also demonstrated that the protein composition of oEVs and uEVs differed depending on the seminal fraction(s) inseminated (F1, F2, or F3). In conclusion, we found specific protein cargo in oEVs and uEVs according to the type of semen fraction the sow was inseminated with and whose functions these specific EVs proteins are closely associated with reproductive processes.

Integrins and their potential roles in mammalian pregnancy

Integrins are a highly complex family of receptors that, when expressed on the surface of cells, can mediate reciprocal cell-to-cell and cell-to-extracellular matrix (ECM) interactions leading to assembly of integrin adhesion complexes (IACs) that initiate many signaling functions both at the membrane and deeper within the cytoplasm to coordinate processes including cell adhesion, migration, proliferation, survival, differentiation, and metabolism. All metazoan organisms possess integrins, and it is generally agreed that integrins were associated with the evolution of multicellularity, being essential for the association of cells with their neighbors and surroundings, during embryonic development and many aspects of cellular and molecular biology. Integrins have important roles in many aspects of embryonic development, normal physiology, and disease processes with a multitude of functions discovered and elucidated for integrins that directly influence many areas of biology and medicine, including mammalian pregnancy, in particular implantation of the blastocyst to the uterine wall, subsequent placentation and conceptus (embryo/fetus and associated placental membranes) development. This review provides a succinct overview of integrin structure, ligand binding, and signaling followed with a concise overview of embryonic development, implantation, and early placentation in pigs, sheep, humans, and mice as an example for rodents. A brief timeline of the initial localization of integrin subunits to the uterine luminal epithelium (LE) and conceptus trophoblast is then presented, followed by sequential summaries of integrin expression and function during gestation in pigs, sheep, humans, and rodents. As appropriate for this journal, summaries of integrin expression and function during gestation in pigs and sheep are in depth, whereas summaries for humans and rodents are brief. Because similar models to those illustrated in Fig. 1, 2, 3, 4, 5 and 6 are present throughout the scientific literature, the illustrations in this manuscript are drafted as Viking imagery for entertainment purposes.

Single-cell transcriptomic characterization of sheep conceptus elongation and implantation

Bidirectional communication between the developing conceptus and endometrium is essential for pregnancy recognition and establishment in ruminants. We dissect the transcriptomic dynamics of sheep conceptus and corresponding endometrium at pre- and peri-implantation stages using single-cell RNA sequencing. Spherical blastocysts contain five cell types, with 68.62% trophectoderm cells. Strikingly, elongated conceptuses differentiate into 17 cell types, indicating dramatic cell fate specifications. Cell-type-specific gene expression delineates the features of distinctive trophectoderm lineages and indicates that the transition from polar trophectoderm to trophoblast increases interferon-tau expression and likely drives elongation initiation. We identify 13 endometrium-derived cell types and elucidate their molecular responses to conceptus development. Integrated analyses uncover multiple paired transcripts mediating the dialogues between extraembryonic membrane and endometrium, including IGF2-IGF1R, FGF19-FGFR1, NPY-NPY1R, PROS1-AXL, and ADGRE5-CD55. These data provide insight into the molecular regulation of conceptus elongation and represent a valuable resource for functional investigations of pre- and peri-implantation ruminant development.

Metabolic pathways utilized by the porcine conceptus, uterus, and placenta

Conceptus elongation and early placentation involve growth and remodeling that requires proliferation and migration of cells. This demands conceptuses expend energy before establishment of a placenta connection and when they are dependent upon components of histotroph secreted or transported into the uterine lumen from the uterus. Glucose and fructose, as well as many amino acids (including arginine, aspartate, glutamine, glutamate, glycine, methionine, and serine), increase in the uterine lumen during the peri-implantation period. Glucose and fructose enter cells via their transporters, SLC2A, SLC2A3, and SLC2A8, and amino acids enter the cells via specific transporters that are expressed by the conceptus trophectoderm. However, porcine conceptuses develop rapidly through extensive cellular proliferation and migration as they elongate and attach to the uterine wall resulting in increased metabolic demands. Therefore, coordination of multiple metabolic biosynthetic pathways is an essential aspect of conceptus development. Oxidative metabolism primarily occurs through the tricarboxylic acid (TCA) cycle and the electron transport chain, but proliferating and migrating cells, like the trophectoderm of pigs, enhance aerobic glycolysis. The glycolytic intermediates from glucose can then be shunted into the pentose phosphate pathway and one-carbon metabolism for the de novo synthesis of nucleotides. A result of aerobic glycolysis is limited availability of pyruvate for maintaining the TCA cycle, and trophectoderm cells likely replenish TCA cycle metabolites primarily through glutaminolysis to convert glutamine into TCA cycle intermediates. The synthesis of ATP, nucleotides, amino acids, and fatty acids through these biosynthetic pathways is essential to support elongation, migration, hormone synthesis, implantation, and early placental development of conceptuses.

Gene editing provides a tool to investigate genes involved in reproduction of pigs

CRISPR-Cas9 gene editing technology provides a method to generate loss-of-function studies to investigate, in vivo, the specific role of specific genes in regulation of reproduction. With proper design and selection of guide RNAs (gRNA) designed to specifically target genes, CRISPR-Cas9 gene editing allows investigation of factors proposed to regulate biological pathways involved with establishment and maintenance of pregnancy. The advantages and disadvantages of using the current gene editing technology in a large farm species is discussed. CRISPR-Cas9 gene editing of porcine conceptuses has generated new perspectives for the regulation of endometrial function during the establishment of pregnancy. The delicate orchestration of conceptus factors facilitates an endometrial proinflammatory response while regulating maternal immune cell migration and expansion at the implantation site is essential for establishment and maintenance of pregnancy. Recent developments and use of endometrial epithelial "organoids" to study endometrial function in vitro provides a future method to screen and target specific endometrial genes as an alternative to generating a gene edited animal model. With continuing improvements in gene editing technology, future researchers will be able to design studies to enhance our knowledge of mechanisms essential for early development and survival of the conceptus.

Sexual dimorphism in placental development and function: Comparative physiology with an emphasis on the pig

Across mammalian species, it has been demonstrated that sex influences birth weight, with males being heavier than females; a characteristic that can be observed from early gestation. Male piglets are more likely to be stillborn and have greater preweaning mortality than their female littermates, despite the additional maternal investment into male fetal growth. Given the conserved nature of the genome between the sexes, it is hypothesized that these developmental differences between males and females are most likely orchestrated by differential placental adaptation. This review summarizes the current understanding of fetal sex-specific differences in placental and endometrial structure and function, with an emphasis on pathways found to be differentially regulated in the pig including angiogenesis, apoptosis, and proliferation. Given the importance of piglet sex in agricultural enterprises, and the potential for skewed litter sex ratios, it is imperative to improve understanding of the relationship between fetal sex and molecular signaling in both the placenta and endometria across gestation.

Expression and localization of vascular endothelial growth factor and its receptors in the pig uterus during peri-implantation and determination of the in vitro effect of the angiogenesis inhibitor SU5416 on VEGF system expression

The aim of this work was to determine endometrial mRNA expression and uterine protein localization of vascular endothelial growth factor (VEGF) and its receptors VEGFR1 and VEGFR2 during the estrous cycle and peri-implantation period in sows. Uterine tissues were collected from pregnant sows on days 12, 14, 16, and 18 after artificial insemination and from non-pregnant animals on days 2 and 12 of the estrous cycle (day 0 = day of estrus). Using immunohistochemistry, a positive signal for VEGF and its receptor VEGFR2 was found in uterine luminal epithelial cells, endometrial glands, stroma, blood vessels, and myometrium. A VEGFR1 signal was only found in endometrial and myometrial blood vessels and stroma. By day 18 of gestation, the mRNA expression levels of VEGF, VEGFR1, and VEGFR2 were higher than those observed on days 2 and 12 of the estrous cycle and on days 12, 14, and 16 of gestation. Then, a primary culture of sow endometrial epithelial cells was established to define the potential of the selective inhibition of VEGFR2 after treatment with inhibitor SU5416 and determine its effects on the expression pattern of the VEGF system. The endometrial epithelial cells treated with SU5416 showed a dose-dependent decrease in VEGFR1 and VEGFR2 mRNA expression. The present study provides additional evidence on the importance of the VEGF system during peri-implantation, as well as on the specific inhibitory activity of SU5416 in epithelial cells, which, as demonstrated, express the protein and mRNA of VEGF and its receptors VEGFR1 and VEGFR2.

Review: Embryonic diapause in the European roe deer - slowed, but not stopped

Embryonic diapause in mammals describes a transient reduction of proliferation and developmental progression occurring at the blastocyst stage. It was first described in the European roe deer (Capreolus capreolus) in the 19th century, and later found to occur in at least over 130 mammalian species across several taxa. Diapause is often displayed as an interruption, a halt, or an arrest of embryonic development. In this review, we explore reduced, but not stopped pace of growth, proliferation and developmental progression during embryonic diapause and revisit early embryonic proliferation and continued slow development as peculiar phenomenon in the roe deer.

Proteomic profiles and the function of RBP4 in endometrium during embryo implantation phases in pigs

BACKGROUND

Endometrial receptivity plays a vital role in the success of embryo implantation. However, the temporal proteomic profile of porcine endometrium during embryo implantation is still unclear.

RESULTS

In this study, the abundance of proteins in endometrium on days 9, 10, 11, 12, 13, 14, 15 and 18 of pregnancy (D9, 10, 11, 12, 13, 14, 15 and 18) was profiled via iTRAQ technology. The results showed that 25, 55, 103, 91, 100, 120, 149 proteins were up-regulated, and 24, 70, 169, 159, 164, 161, 198 proteins were down-regulated in porcine endometrium on D10, 11, 12, 13, 14, 15 and 18 compared with that on D9, respectively. Among these differentially abundance proteins (DAPs), Multiple Reaction Monitoring (MRM) results indicated that S100A9, S100A12, HRG and IFI6 were differentially abundance in endometrial during embryo implantation period. Bioinformatics analysis showed that the proteins differentially expressed in the 7 comparisons were involved in important processes and pathways related to immunization, endometrial remodeling, which have a vital effect on embryonic implantation.

CONCLUSION

Our results reveal that retinol binding protein 4 (RBP4) could regulate the cell proliferation, migration and apoptosis of endometrial epithelial cells and endometrial stromal cells to affect embryo implantation. This research also provides resources for studies of proteins in endometrium during early pregnancy.

IGF2 May Enhance Placental Fatty Acid Metabolism by Regulating Expression of Fatty Acid Carriers in the Growth of Fetus and Placenta during Late Pregnancy in Pigs

Fatty acids (FAs) are essential substances for the growth and development of the fetus and placenta. The growing fetus and placenta must obtain adequate FAs received from the maternal circulation and facilitated by various placental FA carriers, including FA transport proteins (FATPs), FA translocase (FAT/CD36), and cytoplasmic FA binding proteins (FABPs). Placental nutrition transport was regulated by imprinted genes H19 and insulin-like growth factor 2 (IGF2). Nevertheless, the relationship between the expression patterns of H19/IGF2 and placental fatty acid metabolism throughout pig pregnancy remains poorly studied and unclear. We investigated the placental fatty acid profile, expression patterns of FA carriers, and H19/IGF2 in the placentae on Days 40 (D40), 65 (D65), and 95 (D95) of pregnancy. The results showed that the width of the placental folds and the number of trophoblast cells of D65 placentae were significantly increased than those of D40 placentae. Several important long-chain FAs (LCFAs), including oleic acid, linoleic acid, arachidonatic acid, eicosapentaenoic acid, and docosatetraenoic acid, in the pig placenta showed dramatically increased levels throughout pregnancy. The pig placenta possessed higher expression levels of CD36, FATP4, and FABP5 compared with other FA carriers, and their expression levels had significantly upregulated 2.8-, 5.6-, and 12.0-fold from D40 to D95, respectively. The transcription level of IGF2 was dramatically upregulated and there were corresponding lower DNA methylation levels in the IGF2 DMR2 in D95 placentae relative to D65 placentae. Moreover, in vitro experimentation revealed that the overexpression of IGF2 resulted in a significant increase in fatty acid uptake and expression levels of CD36, FATP4, and FABP5 in PTr2 cells. In conclusion, our results indicate that CD36, FATP4, and FABP5 may be important regulators that enhance the transport of LCFAs in the pig placenta and that IGF2 may be involved in FA metabolism by affecting the FA carriers expression to support the growth of the fetus and placenta during late pregnancy in pigs.

RACK1 may participate in placental development at mid-gestation via regulating trophoblast cell proliferation and migration in pigs

Intrauterine growth restriction (IUGR) is a severe complication in swine production. Placental insufficiency is responsible for inadequate fetal growth, but the specific etiology of placental dysfunction-induced IUGR in pigs remains poorly understood. In this work, placenta samples supplying the lightest weight (LW) and mean weight (MW) pig fetuses in the litter at Day 65 (D65) of gestation were collected, and the relationship between fetal growth and placental morphologies and functions was investigated using histomorphological analysis, RNA sequencing, quantitative polymerase chain reaction, and in vitro experiment in LW and MW placentas. Results showed that the folded structure of the epithelial bilayer of LW placentas followed a poor and incomplete development compared with that of MW placentas. A total of 654 differentially expressed genes (DEGs) were screened out between the LW and MW placentas, and the gene encodes receptor for activated C kinase 1 (RACK1) was found to be downregulated in LW placentas. The DEGs were mainly enriched in translation, ribosome, protein synthesis, and mammalian target of rapamycin (mTOR) signaling pathway according to gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses. In vitro experiments indicated that the decreased RACK1 in LW placentas may be involved in abnormal development of placental folds (PFs) by inhibiting the proliferation and migration of porcine trophoblast cells. Taken together, these results revealed that RACK1 may be a vital regulator in the development of PFs via regulating trophoblast cell proliferation and migration in pigs.

Uterine luminal-derived extracellular vesicles: potential nanomaterials to improve embryo implantation

Most pregnancy losses worldwide are caused by implantation failure for which there is a lack of effective therapeutics. Extracellular vesicles are considered potential endogenous nanomedicines because of their unique biological functions. However, the limited supply of ULF-EVs prevents their development and application in infertility diseases such as implantation failure. In this study, pigs were used as a human biomedical model, and ULF-EVs were isolated from the uterine luminal. We comprehensively characterized the proteins enriched in ULF-EVs and revealed their biological functions in promoting embryo implantation. By exogenously supplying ULF-EVs, we demonstrated that ULF-EVs improve embryo implantation, suggesting that ULF-EVs are a potential nanomaterial to treat implantation failure. Furthermore, we identified that MEP1B is important in improving embryo implantation by promoting trophoblast cell proliferation and migration. These results indicated that ULF-EVs can be a potential nanomaterial to improve embryo implantation.

Secreted metabolome of porcine blastocysts encapsulated within in vitro 3D alginate hydrogel culture systems undergoing morphological changes provides insights into specific mechanisms involved in the initiation of porcine conceptus elongation

CONTEXT

The exact mechanisms regulating the initiation of porcine conceptus elongation are not known due to the complexity of the uterine environment.

AIMS

To identify contributing factors for initiation of conceptus elongation in vitro , this study evaluated differential metabolite abundance within media following culture of blastocysts within unmodified alginate (ALG) or Arg-Gly-Asp (RGD)-modified alginate hydrogel culture systems.

METHODS

Blastocysts were harvested from pregnant gilts, encapsulated within ALG or RGD or as non-encapsulated control blastocysts (CONT), and cultured. At the termination of 96h culture, media were separated into blastocyst media groups: non-encapsulated control blastocysts (CONT); ALG and RGD blastocysts with no morphological change (ALG- and RGD-); ALG and RGD blastocysts with morphological changes (ALG+ and RGD+) and evaluated for non-targeted metabolomic profiling by liquid chromatography (LC)-mass spectrometry (MS) techniques and gas chromatography-(GC-MS).

KEY RESULTS

Analysis of variance identified 280 (LC-MS) and 1 (GC-MS) compounds that differed (P <0.05), of which 134 (LC-MS) and 1 (GC-MS) were annotated. Metabolites abundance between ALG+ vs ALG-, RGD+ vs RGD-, and RGD+ vs ALG+ were further investigated to identify potential differences in metabolic processes during the initiation of elongation.

CONCLUSIONS

This study identified changes in phospholipid, glycosphingolipid, lipid signalling, and amino acid metabolic processes as potential RGD-independent mechanisms of elongation and identified changes in lysophosphatidylcholine and sphingolipid secretions during RGD-mediated elongation.

IMPLICATIONS

These results illustrate changes in phospholipid and sphingolipid metabolic processes and secretions may act as mediators of the RGD-integrin adhesion that promotes porcine conceptus elongation.

Conceptus-derived cytokines interleukin-1β and interferon-γ induce the expression of acute phase protein serum amyloid A3 in endometrial epithelia at the time of conceptus implantation in pigs

OBJECTIVE

Serum amyloid A3 (SAA3), an acute phase response protein, plays important roles in opsonization, antimicrobial activity, chemotactic activity, and immunomodulation, but its expression, regulation, and function at the maternal-conceptus interface in pigs are not fully understood. Therefore, we determined the expression of SAA3 in the endometrium throughout the estrous cycle and at the maternal-conceptus interface during pregnancy.

METHODS

Endometrial tissues from pigs at various stages of the estrous cycle and pregnancy and with conceptuses derived from somatic cell nuclear transfer (SCNT), conceptus tissues during early pregnancy, and chorioallantoic tissues during mid- to late pregnancy were obtained and the expression of SAA3 was analyzed. The effects of the steroid hormones, interleukin-1β (IL1B), and interferon-γ (IFNG) on the expression of SAA3 were determined in endometrial explant cultures.

RESULTS

SAA3 was expressed in the endometrium during the estrous cycle and pregnancy, with the highest level on day 12 of pregnancy. The expression of SAA3 in the endometrium was significantly higher on day 12 of pregnancy than during the estrous cycle. Early-stage conceptuses and chorioallantoic tissues during mid to late pregnancy also expressed SAA3. The expression of SAA3 was primarily localized to luminal epithelial cells in the endometrium. In endometrial explant cultures, the expression of SAA3 was induced by increasing doses of IL1B and IFNG. Furthermore, the expression of SAA3 decreased significantly in the endometria of pigs carrying conceptuses derived from SCNT on day 12 of pregnancy.

CONCLUSION

These results suggest that the expression of SAA3 in the endometrium during the implantation period increases in response to conceptus-derived IL1B and IFNG. The failure of those appropriate interactions between the implanting conceptus and the endometrium leads to dysregulation of endometrial SAA3 expression, which could result in pregnancy failure. In addition, SAA3 could be a specific endometrial epithelial marker for conceptus implantation in pigs.

Lewis x-carrying O-glycans are candidate modulators for conceptus attachment in pigs†

Successful attachment of conceptus to the uterine luminal epithelium (LE) is crucial for establishing a functional placenta in pigs. However, the underlying mechanisms are yet to be elucidated. The uterine LE-conceptus interface is enriched in various glycoconjugates essential to implantation. Using MALDI-MS profiling, we identified for the first time the O-glycan repertoire of pig endometrium during the conceptus attachment stage. The expression pattern of blood group A, O(H), Lewis x, y, a, b (Lex, Ley, Lea, and Leb), the sialylated and sulfated Lex antigens in the uterine LE-conceptus interface was assessed using immunofluorescence assays. Notably, the Lex-carrying O-glycans exhibited a temporal-spatial expression pattern. They were absent in the endometrium on estrous cycle days but strongly and spatially presented in the conceptus and uterine LE to which the conceptus apposes during the early conceptus attachment stage. In addition, Lex-carrying O-glycans were co-localized with secreted phosphoprotein 1 (SPP1), a well-characterized factor that plays a role in promoting conceptus attachment through interacting with integrin αVβ3 and integrin αVβ6. Meanwhile, the immunoprecipitation assays revealed an interaction between the Lex-carrying O-glycans and SPP1, integrin αV, and integrin β6. Furthermore, we provided evidence that the β1,4-galactosyltransferase 1 (B4GALT1) gene is a potential regulator for Lex antigen expression in the uterine LE-conceptus interface during the early conceptus attachment stage. In conclusion, our findings show that Lex-carrying O-glycans, presumably dependent on B4GALT1 gene expression, might modulate conceptus attachment by interacting with the SPP1-integrin receptor complex in pigs.

Sex bias in utero alters ovarian reserve but not uterine capacity in female offspring†

Environmental stressors to which a fetus is exposed affect a range of physiological functions in postnatal offspring. We aimed to determine the in utero effect of steroid hormones on the reproductive potential of female offspring using a porcine model. Reproductive tracts of pigs from female-biased (>65% female, n = 15), non-biased (45-54.9% female, n = 15), and male-biased litters (<35% females, n = 9) were collected at slaughter (95-115 kg). Ovaries and uterine horns were processed for H&E or immunohistochemistry. Variability of data within groups was analyzed with a Levene's test, while data were analyzed using mixed linear models in R. In the ovarian reserve, there was a significant birth weight by sex ratio interaction (P = 0.015), with low birth weight pigs from male-biased litters having higher numbers of primordial follicles with opposite trends seen in pigs from female-biased litters. Sex bias held no effect on endometrial gland development. A lower birth weight decreased the proportion of glands found in the endometrium (P = 0.045) and was more variable in both male-biased and female-biased litters (P = 0.026). The variability of primordial follicles from male-biased litters was greater than non- and female-biased litters (P = 0.014). Similarly, endometrial stromal nuclei had a greater range in male- and female-biased litters than non-biased litters (P = 0.028). A crucial finding was the greater variability in primordial follicles in the ovaries from females derived from male-biased litters and stromal cell count in the endometrium of females from male- and female-biased litters. This could be inflating the variability of reproductive success seen in females from male-biased litters.

Placental Malfunction, Fetal Survival and Development Caused by Sow Metabolic Disorder: The Impact of Maternal Oxidative Stress

The energy and metabolic state of sows will alter considerably over different phases of gestation. Maternal metabolism increases dramatically, particularly in late pregnancy. This is accompanied by the development of an increase in oxidative stress, which has a considerable negative effect on the maternal and the placenta. As the only link between the maternal and the fetus, the placenta is critical for the maternal to deliver nutrients to the fetus and for the fetus' survival and development. This review aimed to clarify the changes in energy and metabolism in sows during different pregnancy periods, as well as the impact of maternal oxidative stress on the placenta, which affects the fetus' survival and development.

Transcriptome profile of the anterior pituitary gland in pigs during maternal recognition of pregnancy

The activity of the pituitary gland determines the success of female reproduction. The knowledge regarding the reproductive-status-related changes in the transcriptome of the porcine pituitary is limited. This study aimed to determine and compare the transcriptome profile of the pituitary gland collected from pigs during maternal recognition of pregnancy, i.e. on days 12-13 of pregnancy and during the respective days of the estrous cycle. Analysis indicated 482 differentially expressed genes (DEGs) with an FC > 1.5 (P < 0.05) in the pituitary of pregnant vs. estrous-cyclic pigs. Among them, 68 were up-regulated and 414 were down-regulated. The evaluated DEGs were annotated into 39 gene ontology (GO) biological process terms, 13 GO cellular component terms, and 10 GO molecular function terms. Among the evaluated DEGs were selected genes coding for proteins potentially involved in the regulation of early pregnancy in pigs and used for gene interaction analysis and validation of microarray results. An analysis of the relationships among DEGs in pituitaries collected during maternal recognition of pregnancy showed that some of them are connected with, for example, TGFβ signaling pathway, PRL synthesis, adipocytokines pathway and immune response during maternal recognition of pregnancy. These findings expand the knowledge regarding the molecular mechanisms appearing in the porcine pituitary during the maternal recognition period of pregnancy.

Antimicrobial peptides β-defensin family: Expression and regulation in the endometrium during the estrous cycle and pregnancy in pigs

Members of the β-defensin (DEFB) family, which are antimicrobial peptides and humoral components of the innate immune system, protect the surfaces of various host tissues by killing a broad range of microorganisms and are involved in immunomodulatory actions. The expression of these DEFB members changed during the estrous cycle and pregnancy in a stage-specific manner. The expression of DEFBs was also detected in conceptus and chorioallantoic tissues during pregnancy. DEFB1 and DEFB3 proteins and DEFB2 mRNA were localized primarily to endometrial epithelial cells during early pregnancy. Increasing doses of progesterone upregulated DEFB2 and EP2C expression in endometrial explant tissues. These results showed that members of the DEFB family were expressed stage-specifically at the maternal-conceptus interface in pigs, suggesting that the DEFB family plays important roles at the maternal-conceptus interface in regulation of innate immunity by protection of the maternal endometrial and conceptus tissues from pathogens to preserve fertility in pigs.