Global analyses and potential effects of extracellular vesicles on the establishment of conceptus implantation during the peri-implantation period

Intrauterine extracellular vesicles (EVs) are involved in establishing proper conceptus-endometrial communication, which is essential for conceptus implantation and subsequent successful placentation. Despite several studies on intrauterine EVs, the composition and quantitative changes in conceptus and endometrial EVs, as well as the effects of intrauterine EVs on endometrial epithelial cells (EECs) during the peri-implantation period, have not been well characterized. To elucidate global changes in proteins in EVs extracted from uterine flushings (UFs) during the pre-implantation (P17), just-implantation (P20), and post-implantation (P22) periods, the datasets of the proteome iTRAQ analysis were compared among P17, P20, and P22 EVs. These analyses revealed that the composition and function of proteins in the EVs changed dramatically during peri-implantation in cattle. Notably, intrauterine P17 EVs affected the high expression of "Developmental Biology" and "morphogenesis of an endothelium" compared with those in P20 and P22 EVs. Furthermore, P20 EVs had the functions of the high expression of "mitochondrial calcium ion homeostasis" and "Viral mRNA Translation" compared with those in P17 EVs. Transcripts extracted from EECs treated with P17, P20, or P22 EVs were subjected to RNA-seq analysis. These analyses identified 60 transcripts in EECs commonly induced by intrauterine EVs recovered from P17, P20, and P22, a large number of which were associated with "type I interferon signaling pathway". Collectively, these findings reveal the presence and multiple functions of EVs that are potentially implicated in facilitating conceptus implantation into the uterine epithelium during the peri-implantation period.

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.

Expression of NFIL3 and CEBPA regulated by IFNT induced-PGE2 in bovine endometrial stromal cells during the pre-implantation period

Prostaglandin E2 (PGE2) is considered as a luteoprotective factor, influencing the corpus luteum during the early pregnant period in the bovine species. Cyclic AMP (cAMP) is activated in response to PGE2 and plays a role in many physiological processes. The maternal recognition signal, interferon τ (IFNT), induces PGE2 secretion from the endometrial epithelial cells, the function of which in stroma cells has not been completely understood. In this study, PGE2 was found to activate cAMP in the bovine endometrial stromal cells (STRs). STRs were then treated with forskolin to activate the cAMP signaling, from which RNA extracted was subjected to global expression analysis. Transcripts related to transcription regulatory region nucleic acid binding of molecular function, nucleus of cellular component, and mitotic spindle organization of biological processes were up-regulated in cAMP-activated bovine STRs. An increase in the transcription factors, NFIL3, CEBPA, and HIF1A via the cAMP/PKA/CREB signaling pathway in the bovine STRs was also found by qPCR. Knockdown of NFIL3, CEBPA, or HIF1A blocked forskolin-induced PTGS1/2 and IGFBP1/3 expression. Moreover, NFIL3 and CEBPA were localized in endometrial stroma on pregnant day 17 (day 0 = estrous cycle), but not on cyclic day 17. These observations indicated that uterine PGE2 induced by conceptus IFNT is involved in the early pregnancy-related gene expression in endometrial stromal cells, which could facilitate pregnancy establishment in the bovine.

Podocalyxin molecular characteristics and endometrial expression: high conservation between humans and macaques but divergence in mice†

Podocalyxin (PODXL) is a newly identified key negative regulator of human endometrial receptivity, specifically down-regulated in the luminal epithelium at receptivity to permit embryo implantation. Here, we bioinformatically compared the molecular characteristics of PODXL among the human, rhesus macaque and mouse, determined by immunohistochemistry and in situ hybridization (mouse tissues) whether endometrial PODXL expression is conserved across the three species, and examined if PODXL inhibits mouse embryo attachment in vitro. The PODXL gene, mRNA and protein sequences showed greater similarities between humans and macaques than with mice. In all species, PODXL was expressed in endometrial luminal/glandular epithelia and endothelia. In macaques (n = 9), luminal PODXL was significantly down-regulated when receptivity is developed, consistent with the pattern found in women. At receptivity PODXL was also reduced in shallow glands, whereas endothelial expression was unchanged across the menstrual cycle. In mice, endometrial PODXL did not vary considerably across the estrous cycle (n = 16); however, around embryo attachment on d4.5 of pregnancy (n = 4), luminal PODXL was greatly reduced especially near the site of embryo attachment. Mouse embryos failed to attach or thrive when co-cultured on a monolayer of Ishikawa cells overexpressing PODXL. Thus, endometrial luminal PODXL expression is down-regulated for embryo implantation in all species examined, and PODXL inhibits mouse embryo implantation. Rhesus macaques share greater conservations with humans than mice in PODXL molecular characteristics and regulation, thus represent a better animal model for functional studies of endometrial PODXL for treatment of human fertility.

Extracellular Vesicle Mediated Crosstalk Between the Gametes, Conceptus, and Female Reproductive Tract

Extracellular vesicles (EVs) mediated intracellular communication plays an imperative role in the proper completion of different physiological events. Most of the bio-fluids are enriched with several subpopulations of EVs including exosomes and microvesicles (MVs), with the capacity of transferring different functional molecules (lipids, proteins, and nucleic acids) to target cells. Recipient cells upon receiving the signal molecules undergo different changes that positively affect the structural and functional integrity of the cells. This article was aimed to highlight the role of EVs secreted by gametes, the female reproductive tract, and the growing conceptus in the successful completion of different reproductive events related to gestation. EVs associated with the reproductive system are actively involved in the regulation of different physiological events including gamete maturation, fertilization, and embryo and fetal development. In the reproductive system, EVs mediated intracellular communication is not unidirectional but is rather regulated through crosstalk between the reproductive tract and the growing conceptus. These vesicles are secreted from the ovary, oviductal epithelium, endometrium, developing embryo, and the placenta. The cargo inside these vesicles exerts pleiotropic effects on both maternal and embryonic environments. A better understanding of the EVs-mediated crosstalk will be helpful in the development of useful tools serving both the diagnostic as well as therapeutic needs related to female fertility.

Adhesion molecules in gamete transport, fertilization, early embryonic development, and implantation-role in establishing a pregnancy in cattle: A review

Cell-cell adhesion molecules have critically important roles in the early events of reproduction including gamete transport, sperm-oocyte interaction, embryonic development, and implantation. Major adhesion molecules involved in reproduction include cadherins, integrins, and disintegrin and metalloprotease domain-containing (ADAM) proteins. ADAMs on the surface of sperm adhere to integrins on the oocyte in the initial stages of sperm-oocyte interaction and fusion. Cadherins act in early embryos to organize the inner cell mass and trophectoderm. The trophoblast and uterine endometrial epithelium variously express cadherins, integrins, trophinin, and selectin, which achieve apposition and attachment between the elongating conceptus and uterine epithelium before implantation. An overview of the major cell-cell adhesion molecules is presented and this is followed by examples of how adhesion molecules help shape early reproductive events. The argument is made that a deeper understanding of adhesion molecules and reproduction will inform new strategies that improve embryo survival and increase the efficiency of natural mating and assisted breeding in cattle.

Effects of miR-98 in intrauterine extracellular vesicles on maternal immune regulation during the peri-implantation period in cattle

Evidence accumulated suggests that extracellular vesicles (EVs) present in uterine lumen play a role in conceptus-endometrial cell interactions during peri-implantation periods. However, how intrauterine EVs function on endometrium have not been well characterized. To study how intrauterine EVs affect endometrial milieu in cattle, bovine endometrial epithelial cells (EECs) were treated with EVs isolated from uterine flushing fluids (UFs) on day 17 or 20 pregnancy (P17, P20, respectively; conceptus implantation to endometrium begins on days 19–19.5). RNA extracted from EECs were then subjected to RNA sequence analysis. The analysis revealed that transcripts related to immune system were down-regulated in EECs treated with EVs on P20 compared with those on P17. To investigate whether microRNAs (miRNAs) in EVs regulate maternal immune system in the endometrium during the peri-implantation, microRNA sequence and in silico analyses were performed, identifying bta-miR-98 in EVs as a potential miRNA to regulate maternal immune system. Furthermore, the treatment of EECs with bta-miR-98 negatively regulated several immune system-related genes, CTSC, IL6, CASP4 and IKBKE, in EECs. These results suggest that EVs containing bta-miR-98 is a regulator of maternal immune system, possibly allowing the conceptus attachment to the endometrial epithelium during the peri-implantation period.

Spatial organization of endometrial gene expression at the onset of embryo attachment in pigs

BACKGROUND

During the preimplantation phase in the pig, the conceptus trophoblast elongates into a filamentous form and secretes estrogens, interleukin 1 beta 2, interferons, and other signaling molecules before attaching to the uterine epithelium. The processes in the uterine endometrium in response to conceptus signaling are complex. Thus, the objective of this study was to characterize transcriptome changes in porcine endometrium during the time of conceptus attachment considering the specific localization in different endometrial cell types.

RESULTS

Low-input RNA-sequencing was conducted for the main endometrial compartments, luminal epithelium (LE), glandular epithelium (GE), blood vessels (BV), and stroma. Samples were isolated from endometria collected on Day 14 of pregnancy and the estrous cycle (each group n = 4) by laser capture microdissection. The expression of 12,000, 11,903, 11,094, and 11,933 genes was detectable in LE, GE, BV, and stroma, respectively. Differential expression analysis was performed between the pregnant and cyclic group for each cell type as well as for a corresponding dataset for complete endometrium tissue samples. The highest number of differentially expressed genes (DEGs) was found for LE (1410) compared to GE, BV, and stroma (800, 1216, and 384). For the complete tissue, 3262 DEGs were obtained. The DEGs were assigned to Gene Ontology (GO) terms to find overrepresented functional categories and pathways specific for the individual endometrial compartments. GO classification revealed that DEGs in LE were involved in 'biosynthetic processes', 'related to ion transport', and 'apoptotic processes', whereas 'cell migration', 'cell growth', 'signaling', and 'metabolic/biosynthetic processes' categories were enriched for GE. For blood vessels, categories such as 'focal adhesion', 'actin cytoskeleton', 'cell junction', 'cell differentiation and development' were found as overrepresented, while for stromal samples, most DEGs were assigned to 'extracellular matrix', 'gap junction', and 'ER to Golgi vesicles'.

CONCLUSIONS

The localization of differential gene expression to different endometrial cell types provided a significantly improved view on the regulation of biological processes involved in conceptus implantation, such as the control of uterine fluid secretion, trophoblast attachment, growth regulation by Wnt signaling and other signaling pathways, as well as the modulation of the maternal immune system.

Fucosyltransferase gene expression in goat endometrium during the estrous cycle and early pregnancy

Regulation of the expression of the alpha(1,2)fucosyltransferase (FUT) genes and their enzymatic products, including the H-type 1 antigen (HT1), on the luminal surface of the uterus is believed to be critical for establishment of pregnancy in mammals. The FUT1 gene is a marker for conception rates in dairy cows and HT1 is a marker for uterine receptivity in rodents. To determine the spatiotemporal expression patterns of FUT1 and FUT2 genes in goats, endometrial tissues were obtained on six days spanning the estrous cycle (Days 5, 11, 13, 15, 17 and 19) and seven days spanning early pregnancy (Days 5, 11, 13, 15, 17, 19 and 25). In all data, we found no effect of status (cyclic or pregnant; P > 0.1) and pooled data where appropriate. We cloned FUT1 cDNA from goat endometrium and made probes from it for Northern and slot blot analyses. The analyses indicated that FUT1 gene expression was high until Day 13, and then declined. In situ hybridization revealed a change in the cell-specificity of FUT1 gene expression over the estrous cycle and early pregnancy. In situ hybridization signal intensity scores indicated that FUT1 expression by uterine epithelium was high on Day 5, moderate on Day 11, and minimal on subsequent days. In situ hybridization signals in uterine glandular epithelial cells remained high from Day 5 to Day 13, with weaker signals thereafter. Quantitative reverse transcription-PCR (RT-qPCR) assays were used for quantitation of FUT1 and FUT2 mRNAs. Quantitative RT-qPCR data were generated from endometrium collected from cyclic and pregnant animals on Days 5, 11 and 17. Relative levels of FUT1 mRNA were high on Days 5 and 11, but then fell 5-fold by Day 17 (P < 0.01). FUT2 mRNA concentrations were below the accurate detectable limit of the assay. High levels of HT1 were observed on the apical surface of uterine luminal epithelia on Days 5, 15, 17 and 19, with much lower levels on Days 11 and 13. Thus, data suggests that FUT1 is the primary enzyme responsible for the high levels of HT1 antigen present on the uterine luminal epithelium between Days 5 and 11 of the estrous cycle and early pregnancy. But changes in the expression of the FUT1 gene does not directly correlate to HT1 staining, which increased from Day 13-15. Future studies are required to understand the regulation of the HT1 antigen on the luminal surface of endometrium.

Decreased PECAM1-mediated TGF-β1 expression in the mid-secretory endometrium in women with recurrent implantation failure

STUDY QUESTION

Is recurrent implantation failure (RIF) associated with decreased expression of platelet and endothelial cell adhesion molecule 1 (PECAM1) and transforming growth factor β1 (TGF-β1) in the endometrium during the implantation window?

SUMMARY ANSWER

The present study demonstrates that the expression of PECAM1 and TGF-β1 is significantly decreased in the mid-secretory endometrium in women with RIF, which may account for embryo implantation failure.

WHAT IS KNOWN ALREADY

RIF has become a bottleneck issue that hampers the improvement of pregnancy rates in IVF-embryo transfer (IVF-ET). The causes of RIF are complex and may involve the dysregulation of various growth factors, metabolites, and inflammatory cytokines. At present, the precise pathogenesis of RIF has not been elucidated.

STUDY DESIGN, SIZE, DURATION

This was a prospective case-control study. Endometrial tissue samples were obtained from January 2014 to December 2016 from two groups of women who had undergone IVF (RIF group, 22 women who underwent ≥3 ETs including a total of ≥4 good-quality embryos without pregnancy, control group, 18 women who conceived in their first treatment cycle). At the same time, samples were obtained from 18 women with infertility secondary to tubal factor in the early proliferative, late proliferative and mid-secretory phases of the menstrual cycle (n = 6 per group). Samples used for isolation of primary human endometrial epithelial cells and stromal cells (HEECs and HESCs) were collected in December 2017 from six women with infertility secondary to tubal factor.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We investigated gene expression using integrative whole genome expression microarray analysis, including differentially expressed gene screening, principal component analysis, and functional enrichment analysis. RT-qPCR, western blotting, immunohistochemistry, immunofluorescence co-localization analysis and short hairpin RNA (shRNA) plasmid transfection in Ishikawa cell line, HEECs and HESCs were used to investigate the expression of PECAM1 and TGF-β1.

MAIN RESULTS AND THE ROLE OF CHANCE

Integrative data mining of whole-genome expression profiles identified cell adhesion as a key regulator in RIF. Database retrieval and literature review screened several novel cell adhesion-related genes that might participate in embryo implantation, which include PECAM1, intercellular adhesion molecule 2 (ICAM2), integrin subunit β2 (ITGB2), selectin P (SELP) and TEK receptor tyrosine kinase (TEK). Among these targets, the mRNA and protein levels of PECAM1 were significantly lower in the RIF group than those in the control group. During the menstrual cycles of women with secondary infertility, the protein expression level of PECAM1 was the lowest in early proliferative phase, slightly increased in late proliferative phase and was the highest in mid-secretory phase. While the expression level of HOXA10, an endometrial receptivity marker, kept at a low level in early proliferative phase and increased in late proliferative phase, then maintained at a high level in the mid-secretory phase. Furthermore, TGF-β1, mediated by PECAM1, was also decreased significantly in the RIF group. Using shRNA-based approach, we demonstrated that the depletion of PECAM1 significantly decreased the expression of TGF-β1 in Ishikawa cells, as well as in primary HEECs and HESCs. These results indicated that PECAM1 and TGF-β1 might play a pivotal role in modulating endometrial receptivity.

LIMITATIONS REASONS FOR CAUTION

Although we have shown that PECAM1 and TGF-β1 were down-regulated in the women with RIF, the molecular mechanism of the effect of the factors on the endometrial receptivity remain unclear.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings provide insight into the contribution of PECAM1 and TGF-β1 in regulating implantation, which could be used to develop potential therapeutic methods for RIF.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by grants from the National Natural Science Foundation of China (Nos. 81771656 and 81370763), Special fund for clinical research of the Chinese Medical Association (No. 16020480664), and the Merck Serono China Research Fund for Fertility Agreement. The authors have no competing interests.

Integration of molecules to construct the processes of conceptus implantation to the maternal endometrium

During the peri-implantation period, ruminant conceptuses go through rapid elongation, followed by their attachment to the uterine endometrial epithelial cells, during which interferon-tau (IFNT), a trophectodermal cytokine required for the process of maternal recognition of pregnancy, is expressed in a temporal and spatial manner. On day 22 (day 0 = day of estrus), 2 to 3 d after the initiation of bovine conceptus attachment to the uterine epithelium, when IFNT production begins to subside, the expression of molecules related to epithelial-mesenchymal transition, zinc finger E-box binding homeobox 1, snail family transcriptional repressor 2, N-cadherin, and vimentin was found in the trophectoderm. Through the use of in vitro coculture system with bovine trophoblast CT-1 and endometrial epithelial cells, a series of experiments have been conducted to elucidate mechanisms associated with the regulation of IFNT gene transcription and conceptus implantation, including epithelial-mesenchymal transition processes. Expression of IFNT, both up- and downregulation, during the peri-implantation period is tightly controlled. Cytokines and cell adhesion molecules such as epidermal growth factor, basic fibroblast growth factor, transforming growth factor beta, activin A, L-selectin-podocalyxin, and vascular cell adhesion molecule 1-integrin α4 expressed in utero all contribute to the initiation of epithelial-mesenchymal transition in the trophectoderm. These results indicate that conceptus implantation to the uterine endometrium proceeds while elongated conceptuses and endometria express cell adhesion molecules and their receptors, and the trophectoderm experiences epithelial-mesenchymal transition. Data accumulated suggest that while the conceptus and the endometrial epithelium adhere, trophectodermal cells must gain more flexibility for binucleate and possibly trinucleate cell formation during the peri-implantation period, and that understanding and constructing the conditions throughout implantation processes is key to improving ruminants' fertility.

Endometrial pinopode biomarkers: Molecules and microRNAs

Ultrastructural changes on the apical surface of the luminal epithelium of the uterus are known as pinopodes. Their morphology in species and in special species is associated with different results about size, duration, and percentage of surface area covered by pinopodes. The content of pinopodes is different in rodents and humans. In mice and rats pinopodes have many vacuoles and no organelle that extends to the actin stalk above the microvilli. Human pinopodes do not have a large vacuole and contain the golgi complex, a rough endoplasmic reticulum, secretory vesicles, and mitochondria that extend from the entire cell surface. It has been suggested that pinopodes are good markers of endometrial receptivity and implantation window. There are several molecular markers related to the presence of pinopodes, including integrins, leukemia inhibiting factor (LIF), l-selectin, HOXA10, glutaredoxin, glycodelinA, heparin-binding epidermal growth factor, mucins, and microRNAs (miRNAs). Multiple lines of evidence have indicated that miRNAs could affect the expression of LIF and pinopodes in the endometrium and these molecules play key roles in implantation window processes. Here, we have summarized the morphology and function of pinopodes. Moreover, we have highlighted several molecules in relation to pinopodes that could be used as biomarkers.

The study of blood transcriptome profiles in Holstein cows with miscarriage during peri-implantation

Objective

In this study, the transcriptome profile of cow experiencing miscarriage during peri-implantation was investigated.

Methods

Total transcriptomes were checked by RNA sequencing, and the analyzed by bioinformatics methods, the differentially expressed genes (DEGs) were analysed with hierarchical clustering and Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis.

Results

The results suggested that serum progesterone levels were significantly decreased in cows that miscarried as compared to the pregnant cows at 18, 21, 33, 39, and 51 days after artificial insemination. The RNA sequencing results suggested that 32, 176, 5, 10, and 2 DEGs were identified in the pregnant cows and miscarried cows at 18, 21, 33, 39, and 51 d after artificial insemination. And 15, 101, 1, 2, and 2 DEGs were upregulated, and 17, 74, 4, and 8 DEGs were downregulated in the cows in the pregnant and miscarriage groups, respectively at 18, 21, 33, and 39, but no gene was downregulated at 51 d after artificial insemination. These DEGs were distributed to 13, 20, 3, 6, and 20 pathways, and some pathway essential for pregnancy, such as cell adhesion molecules, tumor necrosis factor signaling pathway and PI3K-Akt signaling pathway.

Conclusion

This analysis has identified several genes and related pathways crucial for pregnancy and miscarriage in cows, as well as these genes supply molecular markers to predict the miscarriage in cows.

The newly established bovine endometrial gland cell line (BEGC) forms gland acini in vitro and is only IFNτ-responsive (MAPK42/44 activation) after E2 and P4-pre-incubation

INTRODUCTION

Uterine glands (UG) are crucial for the establishment of ruminant pregnancy and influenced (orchestrated manner) by estrogen (E₂), progesterone (P₄) and interferon tau (IFNτ). In the study we established a bovine endometrial glandular cell line (BGEC) and tested its functional reactivity (signaling) to IFNτ.

METHODS

BGEC was characterized by light microscopy (LM), epithelial markers (ezrin, CK18) [immunofluorescence (IF)/immunohistochemistry (IHC)] and ultrastructure (TEM/SEM) (apical microvilli). In vitro formation of gland acini and transepithelial-electric-resistance (TEER) measurements (EVOM) were done. The expression of mRNA-transcripts (RT-PCR) of steroid receptors (PR, PGRMC1/2, ESR1/2) and the IFNτ-system (IFNAR1/2, IRF1, 2, 9) was checked. BEGC was stimulated with IFNτ (10 ng/ml;1000 ng/ml) (15 min) after steroid pre-treatment [10 pg/ml E₂ (two days)/20 ng/ml P₄ (two days)]. Activation of MAPK42/44;STAT1 was evaluated (densitometrical Western Blot).

RESULTS

BGEC cells expressed epithelial markers and possessed apical microvilli. High TEER-values could be measured (2320-2620 ohm/cm²). The assembled BEGC acini (25 days) were similar to UG in vivo (markers/ultrastructure). All transcripts (steroid receptors/IFNτ-system) could be detected in BEGC (mRNA). MAPK42/44 were significantly activated after E₂/P₄ pre-treatment and IFNτ stimulation (10 ng/ml) (p < 0.05), whilst 1000 ng/ml IFNτ did not activate MAPK42/44. Neither a STAT1 (by IFNτ) nor an activation (MAPK42/44;STAT1) by IFNτ-only was observed.

DISCUSSION

BGEC retains its epithelial phenotype in culture and forms gland acini in vitro thereby confirming its glandular character. Cells were only reactive to (low) IFNτ concentrations when pre-treated with steroids thereby closely resembling implantation physiology in vivo. BEGC can be used as a bovine implantation model to study embryo-maternal communication during early pregnancy in cattle.

Down-regulation of transcription factor OVOL2 contributes to epithelial-mesenchymal transition in a noninvasive type of trophoblast implantation to the maternal endometrium

Embryo implantation into the uterine endometrium is required for pregnancy establishment in most mammals. By using global expression analysis, we investigated the molecules that are related to epithelial-mesenchymal transition (EMT) in noninvasive bovine trophoblasts and found that the transcription factor, ovo-like zinc finger 2 ( OVOL2), which is essential for mesenchymal-epithelial transition in various cancers, was down-regulated after trophoblast attachment to the endometrial epithelium in utero. In cultured bovine trophoblast cells, OVOL2 down-regulation occurred only when cells were allowed to attach to bovine endometrial epithelial cells via the TEAD3/YAP signaling pathway. This resulted in the up-regulation of the EMT-associated transcription factors, ZEB1 and SNAI2, and the mesenchymal cell markers, N-cadherin ( CDH2) and vimentin ( VIM), whereas epithelial cell marker, E-cadherin ( CDH1), was down-regulated. In contrast, OVOL2 overexpression in bovine trophoblast cells exhibited a decrease in ZEB1 transcripts and an increase in E-cadherin. These observations revealed that ovo-like protein (OVOL)2 down-regulation occurred concurrently with conceptus implantation into the uterine endometrium via the YAP/TEAD3 signaling pathway, and suggest that the down-regulation of OVOL2 expression contributes to the up-regulation of EMT-related transcription factor expression, which enables EMT progression in the noninvasive bovine trophectoderm postimplantation.-Bai, R., Kusama, K., Nakamura, K., Sakurai, T., Kimura, K., Ideta, A., Aoyagi, Y., Imakawa, K. Down-regulation of transcription factor OVOL2 contributes to epithelial-mesenchymal transition in a noninvasive type of trophoblast implantation to the maternal endometrium.

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.

Fibroblast growth factor 2 induces proliferation and distribution of G2 /M phase of bovine endometrial cells involving activation of PI3K/AKT and MAPK cell signaling and prevention of effects of ER stress

Fibroblast growth factor 2 (FGF2) is abundantly expressed in conceptuses and endometria during pregnancy in diverse animal models including domestic animals. However, its intracellular mechanism of action has not been reported for bovine endometrial cells. Therefore, the aim of this study was to identify functional roles of FGF2 in bovine endometrial (BEND) cell line which has served as a good model system for investigating regulation of signal transduction following treatment with interferon-tau (IFNT) in vitro. Results of present study demonstrated that administration of FGF2 to BEND cells increased their proliferation and regulated the cell cycle through DNA replication by an increase of PCNA and Cyclin D1. FGF2 also increased phosphorylation of AKT, P70S6K, S6, ERK1/2, JNK, and P38 in BEND cells in a dose-dependent manner, and expression of each of those transcription factors was inhibited by their respective pharmacological inhibitor including Wormannin, U0126, and SP600125. In addition, the increase in proliferation of BEND cells and activation of the protein kinases in response to FGF2 was suppressed by BGJ398, a FGFR inhibitor. Furthermore, proliferation of BEND cells was inhibited by tunicamycin, but treatment of BEND cells with FGF2 restored proliferation of BEND cells. Consistent with this result, the stimulated unfolded protein response (UPR) regulatory proteins induced by tunicamycin were down-regulated by FGF2. Results of this study suggest that FGF2 promotes proliferation of BEND cells and likely enhances uterine capacity and maintenance of pregnancy by activating cell signaling via the PI3K and MAPK pathways and by restoring ER stress through the FGFR.

Polymorphisms in the selectin gene cluster are associated with fertility and survival time in a population of Holstein Friesian cows

Selectins are adhesion molecules, which mediate attachment between leucocytes and endothelium. They aid extravasation of leucocytes from blood into inflamed tissue during the mammary gland’s response to infection. Selectins are also involved in attachment of the conceptus to the endometrium and subsequent placental development. Poor fertility and udder health are major causes for culling dairy cows. The three identified bovine selectin genes SELP, SELL and SELE are located in a gene cluster. SELP is the most polymorphic of these genes. Several SNP in SELP and SELE are associated with human vascular disease, while SELP SNP rs6127 has been associated with recurrent pregnancy loss in women. This study describes the results of a gene association study for SNP in SELP (n = 5), SELL (n = 2) and SELE (n = 1) with fertility, milk production and longevity traits in a population of 337 Holstein Friesian dairy cows. Blood samples for PCR-RFLP were collected at 6 months of age and animals were monitored until either culling or 2,340 days from birth. Three SNP in SELP_Ex4-6 formed a haplotype block containing a Glu/Ala substitution at rs42312260. This region was associated with poor fertility and reduced survival times. SELP_Ex8 (rs378218397) coded for a Val475Met variant locus in the linking region between consensus repeats 4 and 5, which may influence glycosylation. The synonymous SNP rs110045112 in SELE_Ex14 deviated from Hardy Weinberg equilibrium. For both this SNP and rs378218397 there were too few AA homozygotes present in the population and AG heterozygotes had significantly worse fertility than GG homozygotes. Small changes in milk production associated with some SNP could not account for the reduced fertility and only SELP_Ex6 showed any association with somatic cell count. These results suggest that polymorphisms in SELP and SELE are associated with the likelihood of successful pregnancy, potentially through compromised implantation and placental development.

Continuous model of conceptus implantation to the maternal endometrium

As placental morphology as well as trophoblast characteristics exhibit wide diversity across mammalian species, underling molecules were also thought to vary greatly. In the majority of cases, however, regardless of the mode of implantation, physiological and biochemical processes in conceptus implantation to the maternal endometrium including the kinds of gene expression and their products are now considered to share many similarities. In fact, recent progress has identified that in addition to the hormones, cytokines, proteases and cell adhesion molecules classically characterized, molecules related to lymphocyte homing and epithelial-mesenchymal transition (EMT) are all required for the progression of conceptus implantation to placentation. In this review, therefore, the newest findings are all incorporated into the molecular and cellular events related to conceptus implantation to the maternal endometrium; primarily from non-invasive bovine placentation and also from invasive human implantation.

Bovine P-selectin mediates leukocyte adhesion and is highly polymorphic in dairy breeds

Bovine P-selectin (SELP) mediates leukocyte rolling and primes leukocyte adhesion to endothelium, both essential for leukocyte recruitment to an infection site. We investigated SELP-mediated adhesion between bovine peripheral blood leukocytes (PBLs) and cultured bovine aortic endothelial cells pre-activated with lipopolysaccharide (LPS). We examined gene polymorphism for bovine selectins SELP, l-selectin (SELL) and E-selectin (SELE) and compared their SNP frequency between five dairy breeds (Holstein, Friesian, Jersey, Ayrshire and Brown Swiss). LPS treatment caused a rapid (10min) and slower (4h) enhancement of PBL adhesion (P<0.01). Antibody blocking of SELP inhibited LPS induced cell adhesion. SELP was highly polymorphic, with 9 of the 13 SNPs in its exons, whereas only three synonymous SNPs in SELL and one in SELE. The resulting amino acid changes for the three missense SELP SNP were located in the lectin domain and in two consensus repeat (CR) regions, CR2 and CR5. The Val475Met variant locus in the CR4 and CR5 linking region was very close to a predicted N-acetyl-d-glucosamine glycosylation site, which is likely to influence SELP function. The AA genotype was under-represented, only being found in 1% of 373 heifers genotyped from the 5 breeds (P=0.056), suggesting that AA homozygous animals carrying the Val475Met substitution for SELP may have compromised development. Our study thus confirmed that SELP mediates the attachment of PBL to endothelium and provides novel evidence that its high polymorphism is likely to affect biological function. This may potentially influence leukocyte migration and fertility, both key to successful performance in dairy cows.

Induction of IFNT-Stimulated Genes by Conceptus-Derived Exosomes during the Attachment Period

Biochemical and/or physical communication between the conceptus and the uterine endometrium is required for conceptus implantation to the maternal endometrium, leading to placentation and the establishment of pregnancy. We previously reported that in vitro co-culture system with bovine trophoblast CT-1 cells, primary uterine endometrial epithelial cells (EECs), and uterine flushings (UFs) mimics in vivo conceptus attachment process. To identify molecules in UFs responsible for this change, we first characterized protein contents of UFs from day 17 cyclic (C17) and pregnant (P17) ewes through the use of two dimensional-Polyacrylamide Gel Electrophoresis (2D-PAGE), followed by Liquid Chromatography-tandem Mass Spectrometry (LC-MS/MS) analysis. These analyses identified 266 proteins specific for P17 UFs, from which 172 proteins were identified as exosomal proteins. Among 172 exosomal proteins, 8 proteins that had been identified as exosomal proteins were chosen for further analysis, including macrophage-capping protein (CAPG), aldo-keto reductase family 1, member B1 protein (AKR1B1), bcl-2-like protein 15 (BCL2L15), carbonic anhydrase 2 (CA2), isocitrate dehydrogenase 2 (IDH2), eukaryotic translation elongation factor 2 (EEF2), moesin (MSN), and ezrin (EZR). CAPG and AKR1B1 were again confirmed in P15 and P17 UFs, and more importantly CAPG and AKR1B1, mRNA and protein, were found only in P15 and P17 conceptuses. Moreover, exosomes were isolated from C15, C17, P15, or P17 UFs. Only P15 and P17 exosomes, originated from the conceptus, contained interferon tau (IFNT) as well as CAPG and AKR1B1, and up-regulated STAT1, STAT2, MX1, MX2, BST2, and ISG15 transcripts in EECs. These observations indicate that in addition to endometrial derived exosomes previously described, conceptus-derived exosomes are present in UFs and could function to modify endometrial response. These results suggest that exosomes secreted from conceptuses as well as endometria are involved in cell to cell interactions for conceptus implantation to the maternal endometrium.

The bovine placenta in vivo and in vitro

The gross anatomic features (cotyledonary type) and histologic classification (synepitheliochorial) of the bovine placenta have been known for many years. Thorough ultrastructural analysis as well as a variety of descriptive studies dealing with the localization of cytoskeletal filaments, extracellular matrix, growth factor systems, steroid hormone receptors, and major histocompatibility complex have contributed further significant knowledge. However, this knowledge was not sufficient to solve clinical placenta-based problems, such as retained fetal membranes. Owing to the complexity of the fetomaternal interface in vitro, culture systems have been developed. As trophoblast giant cells (TGC) are thought to be key players in the cattle placenta, most cell culture models attempt to overcome the pitfall of losing the entire TGC population in vitro. Nevertheless, distinct cell line-based in vitro systems such as cell monolayers or 3-dimensional (co-culture) spheroids were generated for the fetal (trophoblast) and maternal (uterine epithelium) placental compartments. Monolayers have been used to study for example, growth factor or hormonal signaling and TGC formation, whereas spheroids served as models for, for example, trophoblast attachment, uterine epithelium depolarization, and also TGC formation. In the future, the use of more improved culture models might lead to better treatments of retained fetal membranes and increased prevention of embryonic loss. In addition, the in vitro models could shed more light on the mechanisms of the differentiation of uninucleate trophoblast into TGC.