mRNA/lncRNA expression patterns and the function of fibrinogen-like protein 2 in Meishan pig endometrium during the preimplantation phases

DIA-based quantitative proteomic analysis of porcine endometrium in the peri-implantation phase

The 12th day of gestation is a critical period for embryo loss and the beginning of imminent implantation in sows. Data independent acquisition (DIA) technology is one of the high-throughput, high-resolution and reproducible proteomics technologies for large-scale digital qualitative and quantitative research. The aim of this study was to identify and characterize the protein abundance landscape of Yorkshire pig endometrium on the 12th day of pregnancy (P12) and estrous cycle (C12) using DIA proteomics. A total of 1251 differentially abundant proteins (DAPs) were identified, of which 882 were up-regulated and 369 were down-regulated at P12. Functional enrichment analysis showed that the identified proteins were related to metabolism, biosynthesis and signaling pathways. Three proteins were selected for Western blot (WB) validation and the results were consistent with the DIA data. Further combined with transcriptome data, fibrinogen like 2 (FGL2) and S100 calcium binding protein A8 (S100A8) were verified to be highly abundant in the P12 endometrial epithelium. In summary, there were significantly different abundance of proteome profiles in C12 and P12 endometrium, suggesting that DAPs are associated with changes in endometrial receptivity, which laid the foundation for further research on related regulatory mechanisms. SIGNIFICANCE: The 12th day of gestation is an important point in the peri-implantation period of pigs, when the endometrium presents a receptive state under the stimulation of estrogen. DIA proteomics technology is an emerging protein identification technology in recent years, which can obtain protein information through comprehensive and unbiased scanning. In this study, DIA technology was used to characterize endometrial proteins in pigs during the peri-implantation period. The results showed that higher protein abundance was detected using the DIA technique, and some of these DAPs may be involved in regulating embryo implantation. This study will help to better reveal the related proteins involved in embryo implantation, and lay a foundation for further research on the mechanism of endometrial regulation of embryo implantation. SIGNIFICANCE OF THE STUDY: The 12th day of gestation is an important point in the peri-implantation period of pigs, when the endometrium presents a receptive state under the stimulation of estrogen. DIA proteomics technology is an emerging protein identification technology in recent years, which can obtain protein information through comprehensive and unbiased scanning. In this study, DIA technology was used to characterize endometrial proteins in pigs during the peri-implantation period. The results showed that higher protein abundance was detected using the DIA technique, and some of these DAPs may be involved in regulating embryo implantation. This study will help to better reveal the related proteins involved in embryo implantation, and lay a foundation for further research on the mechanism of endometrial regulation of embryo implantation.

Cuyun Recipe ameliorates pregnancy loss by regulating macrophage polarization and hypercoagulable state during the peri-implantation period in an ovarian hyperstimulation mouse model

BACKGROUND

The Chinese herbal prescription Cuyun Recipe (CYR) has been widely used to treat clinical infertility and has shown good efficacy. Animal experiments have shown that CYR can promote implantation in mice, however, the exact mechanism underlying the implantation has not been elucidated.

PURPOSE

To investigate the effect and mechanism of CYR on regulating macrophage polarization and hypercoagulability during the peri-implantation period in mice with ovarian hyperstimulation.

METHODS

An ovarian hyperstimulation mouse model was developed, followed by treatment with CYR. Mice were sacrificed on day (D)4.5, D6, or D8 of gestation. The number of implantation sites, the pathological changes of the uterus and ovaries were assessed. The polarization of monocytes/macrophages in the spleen and endometrium, the expression and localization of cytokines were further detected. Furthermore, analyses of hypercoagulable state of the blood were also performed.

RESULTS

Treatment with CYR increased the average number of implantation sites, promoted angiogenesis in endometrial, and regulated monocytes/macrophages and the cytokine levels. Moreover, CYR downregulated the overexpression of D-dimer and fgl2 after ovarian hyperstimulation.

CONCLUSION

CYR facilitates embryo implantation by alleviating ovarian hyperstimulation, promoting endometrial decidualization and angiogenesis, regulating macrophage polarization, and reversing the hypercoagulable state of the blood.

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.

Extracellular vesicles derived from endometrial epithelial cells deliver exogenous miR-92b-3p to affect the function of embryonic trophoblast cells via targeting TSC1 and DKK3

BACKGROUND

Extracellular vesicles (EVs) could mediate embryo-maternal communication to affect embryo implantation by delivering biology information, including microRNA (miRNA), protein, lipid. Our previous research shows that miR-92b-3p was differentially expressed in EVs of uterine flushing fluids during the embryo implantation period. However, the role of miR-92b-3p from EVs in embryo implantation remains elusive.

MATERIALS AND METHODS

EVs were isolated from porcine endometrial epithelial cells (EECs) by ultracentrifugation. MiR-92b-3p mimics and EVs were used to regulate the expression of miR-92b-3p in porcine trophoblast cells (PTr2 cells). Cell proliferation, migration and adhesion analyses were used to observe the phenotype. RT-qPCR, western blot and dual-luciferase reporter assay were used to assess the targets of miR-92b-3p.

RESULTS

In this study, EVs derived from porcine EECs were identified and could be taken up by PTr2 cells. We found that the EVs derived from EECs transfected with miR-92b-3p mimic (EVs-miR-92b-3p) significantly promoted the proliferation, migration and adhesion of PTr2 cells. We verified that Tuberous sclerosis complex subunit (TSC1) and Dickkopf 3 (DKK3) were the target genes of miR-92b-3p. Moreover, our study showed that miR-92b-3p plays a vital role in PTr2 cells via targeting TSC1 and DKK3. Furthermore, the 3'UTR vectors of TSC1 and DKK3 can rescue the effect of miR-92b-3p on PTr2 cells.

CONCLUSIONS

Taken together, this study reveals a novel mechanism that EVs derived from porcine EECs treated with miR-92b-3p crosstalk with trophoblasts by targeting TSC1 and DKK3, leading to an enhanced ability for implantation.

New Roles for EVs, miRNA and lncRNA in Bovine Embryo Implantation

The sine qua non of new life is fertilization. However, approximately 50% of fertilized eggs/blastocysts in cattle and up to 75% of those from human assisted reproductive procedures fail during the first 3 to 4 weeks of pregnancy, including peri-implantation periods. In these periods, blastocyst hatching and implantation to the maternal endometrium proceeds, during which physiological events such as epithelial-mesenchymal transition (EMT) and trophoblast cell fusion occur. Quite recently, extracellular vesicles (EVs) with micro RNAs (miRNAs) and long non-coding RNAs (lncRNAs) have been found to play a pivotal role for the establishment of the proper uterine environment required for peri-implantation processes to proceed. New findings of EVs, miRNA, and lncRNAs will be described and discussed to elucidate their connections with conceptus implantation to the maternal endometrium.

Heat Stress Impairs Maternal Endometrial Integrity and Results in Embryo Implantation Failure by Regulating Transport-Related Gene Expression in Tongcheng Pigs

Heat stress (HS) poses a significant threat to production and survival in the global swine industry. However, the molecular regulatory effects of heat stress on maternal endometrial cells are poorly understood in pigs during early embryo implantation. In this study, we systematically examined morphological changes in the endometrium and the corresponding regulation mechanism in response to HS by combining scanning electron microscopy (SEM), hematoxylin/eosin (H&E) staining, western blot, and RNA-seq analyses. Our results showed that HS led to porcine endometrium damage and endometrial thinness during embryo implantation. The expression levels of cell adhesion-related proteins, including N-cadherin and E-cadherin, in the uterus were significantly lower in the heat stress group (39 ± 1 °C, n = 3) than in the control group (28 ± 1 °C, n = 3). A total of 338 up-regulated genes and 378 down-regulated genes were identified in porcine endometrium under HS. The down-regulated genes were found to be mainly enriched in the pathways related to the microtubule complex, immune system process, and metalloendopeptidase activity, whereas the up-regulated genes were mainly involved in calcium ion binding, the extracellular region, and molecular function regulation. S100A9 was found to be one of the most significant differentially expressed genes (DEGs) in the endometrium under HS, and this gene could promote proliferation of endometrial cells and inhibit their apoptosis. Meanwhile, HS caused endometrial epithelial cell (EEC) damage and inhibited its proliferation. Overall, our results demonstrated that HS induced uterine morphological change and tissue damage by regulating the expression of genes associated with calcium ions and amino acid transport. These findings may provide novel molecular insights into endometrial damage under HS during embryo implantation.

Characterization of lncRNA functioning in ovine conceptuses and endometria during the peri-implantation period

In ruminants, RNA-sequence analyses have revealed many characteristics of transcripts expressed in conceptuses (embryo and extraembryonic membrane) during peri-implantation periods; however, lncRNA profiles are yet characterized. In this study, we aimed to characterize the lncRNA expression profile in conceptuses during peri-implantation periods in sheep. We analyzed the RNA-sequence data of ovine conceptuses and endometria obtained from pregnant animals on days 15, 17, 19 and 21 (day 0 = day of estrus, n = 3 or 4/day). We predicted the protein coding ability of the assembled transcripts to identify the lncRNA candidates. This analysis identified 8808 lncRNAs, 3423 of which were novel lncRNAs. Gene ontology analysis revealed that lncRNA target genes were enriched for biological processes involved in the respiratory electron transport chain (RETC). qPCR analysis demonstrated that the expression levels on transcripts encoding RETC such as mitochondrially encoded cytochrome c oxidase II (MTCO2) and mitochondria DNA copy number in conceptuses were not increased on P21, although western blotting analysis and immunohistochemistry demonstrated that MTCO2 protein in conceptuses was increased on P21. NAD/NADH assay revealed that NADH level in conceptuses was increased on P21. These results indicate that lncRNAs could regulate the RETC through post-transcriptional levels in the conceptuses. Therefore, lncRNA is a potential new regulator in ovine conceptus development during peri-implantation periods.

Global Transcriptomic Analyses Reveal Genes Involved in Conceptus Development During the Implantation Stages in Pigs

Prenatal mortality remains a significant concern to the pig farming industry around the world. Spontaneous fetal loss ranging from 20 to 45% by term occur after fertilization, with most of the loss happening during the implantation period. Since the factors regulating the high mortality rates of early conceptus during implantation phases are poorly understood, we sought to analyze the overall gene expression changes during this period, and identify the molecular mechanisms involved in conceptus development. This work employed Illumina's next-generation sequencing (RNA-Seq) and quantitative real-time PCR to analyze differentially expressed genes (DEGs). Soft clustering was subsequently used for the cluster analysis of gene expression. We identified 8236 DEGs in porcine conceptus at day 9, 12, and 15 of pregnancy. Annotation analysis of these genes revealed rRNA processing (GO:0006364), cell adhesion (GO:1904874), and heart development (GO:0007507), as the most significantly enriched biological processes at day 9, 12, and 15 of pregnancy, respectively. In addition, we found various genes, such as T-complex 1, RuvB-like AAA ATPase 2, connective tissue growth factor, integrins, interferon gamma, SLA-1, chemokine ligand 9, PAG-2, transforming growth factor beta receptor 1, and Annexin A2, that play essential roles in conceptus morphological development and implantation in pigs. Furthermore, we investigated the function of PAG-2 in vitro and found that PAG-2 can inhibit trophoblast cell proliferation and migration. Our analysis provides a valuable resource for understanding the mechanisms of conceptus development and implantation in pigs.

Ssc-miR-21-5p regulates endometrial epithelial cell proliferation, apoptosis and migration via the PDCD4/AKT pathway

Endometrial receptivity plays a vital role in successful embryo implantation in pigs. MicroRNAs (miRNAs), known as regulators of gene expression, have been implicated in the regulation of embryo implantation. However, the role of miRNAs in endometrial receptivity during the pre-implantation period remains elusive. In this study, we report that the expression level of Sus scrofa (ssc)-miR-21-5p in porcine endometrium tissues was significantly increased from day 9 to day 12 of pregnancy. Knockdown of ssc-miR-21-5p inhibited proliferation and migration of endometrial epithelial cells (EECs), and induced their apoptosis. We verified that programmed cell death 4 (PDCD4) was a target gene of ssc-miR-21-5p. Inhibition of PDCD4 rescued the effect of ssc-miR-21-5p repression on EECs. Our results also revealed that knockdown of ssc-miR-21-5p impeded the phosphorylation of AKT (herein referring to AKT1) by targeting PDCD4, which further upregulated the expression of Bax, and downregulated the levels of Bcl2 and Mmp9. Furthermore, loss of function of Mus musculus (mmu)-miR-21-5p in vivo resulted in a decreased number of implanted mouse embryos. Taken together, knockdown of ssc-miR-21-5p hampers endometrial receptivity by modulating the PDCD4/AKT pathway.

The Interaction of lncRNA XLOC-2222497, AKR1C1, and Progesterone in Porcine Endometrium and Pregnancy

The endometrium is an important tissue for pregnancy and plays an important role in reproduction. In this study, high-throughput transcriptome sequencing was performed in endometrium samples of Meishan and Yorkshire pigs on days 18 and 32 of pregnancy. Aldo-keto reductase family 1 member C1 (AKR1C1) was found to be a differentially expressed gene, and was identified by quantitative real-time PCR (qRT-PCR) and Western blot. Immunohistochemistry results revealed the cellular localization of the AKR1C1 protein in the endometrium. Luciferase activity assay demonstrated that the AKR1C1 core promoter region was located in the region from -706 to -564, containing two nuclear factor erythroid 2-related factor 2 (NRF2) binding sites (antioxidant response elements, AREs). XLOC-2222497 was identified as a nuclear long non-coding RNA (lncRNA) highly expressed in the endometrium. XLOC-2222497 overexpression and knockdown have an effect on the expression of AKR1C1. Endocrinologic measurement showed the difference in progesterone levels between Meishan and Yorkshire pigs. Progesterone treatment upregulated AKR1C1 and XLOC-2222497 expression in porcine endometrial epithelial cells. In conclusion, transcriptome analysis revealed differentially expressed transcripts during the early pregnancy process. Further experiments demonstrated the interaction of XLOC-2222497/AKR1C1/progesterone in the endometrium and provided new potential targets for pregnancy maintenance and its control.

Spatial Transcriptomic and miRNA Analyses Revealed Genes Involved in the Mesometrial-Biased Implantation in Pigs

Implantation failure is a major cause of early embryonic loss. Normally, the conceptus attachment is initiated at mesometrial side of the uterus and then spread to the anti-mesometrial side in pigs, however, the mechanisms that direct the mesometrial-biased attachment are largely unknown. In this study, the histological features of the entire uterine cross-section from gestational days 12 (pre-attachment stage) and 15 (post-attachment stage) were investigated and the differences in histological features between the mesometrial and anti-mesometrial side of the uterus were observed. Then, transcriptomic and miRNA analyses were performed on mesometrial and anti-mesometrial endometrium obtained from gestational days 12 and 15, respectively. Differentially expressed genes (DEGs) and miRNAs (DE-miRs) that were common to both or unique to either of the two anatomical locations of uterus were identified, respectively, indicating that differences in molecular response to the implanting conceptus exist between the two anatomical locations. In addition, we detected DEGs and DE-miRs between the two anatomical locations on the two gestational days, respectively. Of these DEGs, a number of genes, such as chemokine and T cell surface marker genes, were found to be significantly up-regulated mesometrially. Furthermore, we detected the interaction of CXCR4, CXCL11 and miR-9 using dual luciferase reporter assay. Taken together, this study revealed genes and pathways that might play the role of creating a receptive microenvironment at the mesometrial side, which is required to guide a proper positioning of conceptus in the uterus in pigs.