Post-implantation mouse conceptuses produce paracrine signals that regulate the uterine endometrium undergoing decidualization

A Single Trophoblast Layer Acts as the Gatekeeper at the Endothelial-Hematopoietic Crossroad in the Placenta

During embryonic development the placental vasculature acts as a major hematopoietic niche, where endothelial to hematopoietic transition ensures emergence of hematopoietic stem cells (HSCs). However, the molecular mechanisms that regulate the placental hematoendothelial niche are poorly understood. Using a parietal trophoblast giant cell (TGC)-specific knockout mouse model and single-cell RNA-sequencing, we show that the paracrine factors secreted by the TGCs are critical in the development of this niche. Disruptions in the TGC-specific paracrine signaling leads to the loss of HSC population and the concomitant expansion of a KDR+/DLL4+/PROM1+ hematoendothelial cell-population in the placenta. Combining single-cell transcriptomics and receptor-ligand pair analyses, we also define the parietal TGC-dependent paracrine signaling network and identify Integrin signaling as a fundamental regulator of this process. Our study elucidates novel mechanisms by which non-autonomous signaling from the primary parietal TGCs maintain the delicate placental hematopoietic-angiogenic balance and ensures embryonic and extraembryonic development.

Trophoblastic signals facilitate endometrial interferon response and lipid metabolism, ensuring normal decidualization

The decidua plays a crucial role in providing structural and trophic support to the developing conceptus before placentation. Following embryo attachment, embryonic components intimately interact with the decidual tissue. While evidence indicates the participation of embryo-derived factors in crosstalk with the uterus, the extent of their impact on post-implantation decidual development requires further investigation. Here, we utilize transgenic mouse models to selectively eliminate primary trophoblast giant cells (pTGCs), the embryonic cells that interface with maternal tissue at the forefront. pTGC ablation impairs decidualization and compromises decidual interferon response and lipid metabolism. Mechanistically, pTGCs release factors such as interferon kappa (IFNK) to strengthen the decidual interferon response and lipoprotein lipase (LPL) to enhance lipid accumulation within the decidua, thereby promoting decidualization. This study presents genetic and metabolomic evidence reinforcing the proactive role of pTGC-derived factors in mobilizing maternal resources to strengthen decidualization, facilitating the normal progression of early pregnancy.

Adgrg1 is a new transcriptional target of Hand1 during trophoblast giant cell differentiation

The placenta, forming the maternal-fetal interface, is essential for the survival and development of the fetus. It has been shown that the basic helix-loop-helix (bHLH) transcription factor Hand1 plays an important role in trophoblast giant cells (TGCs) differentiation during placental development in mice. However, the underlying molecular mechanism remains elusive. We hereby report that Adgrg1 (GPR56), a G protein coupled receptor, was a new transcriptional target of Hand1. Hand1 activated the expression of Adgrg1 by binding to its promoter region during TGCs differentiation. Double in situ hybridization revealed co-expression of Hand1 and Adgrg1 in Prl2c2⁺ TGCs located in the junctional zone of the placenta. Knockdown of Adgrg1 not only led to increased Prl2c2 expression, but also the improvement of cell migration and invasion during TGC differentiation. Moreover, the ligand of Adgrg1, Tgm2, was expressed in Prl2c2⁺ TGCs located in the placental junctional zone and Tgm2 Knockdown increased cell migration and invasion, suggesting Tgm2 is a potential ligand involved in the functions of Adgrg1 during TGC differentiation in the manners of autocrine. Collectively, these results demonstrate that Adgrg1 is a new transcriptional target of Hand1, affecting Prl2c2 expression as well as cell migration and invasion during TGCs differentiation. As a transmembrane receptor, Adgrg1 perhaps could act as a potential therapeutic target for placental-associated diseases caused by abnormal trophoblast migration and invasion, providing new insights for the preventions and therapies of placenta-related diseases.

Dynamic Changes of Gene Expression in Mouse Mural Trophectoderm Regulated by Cdx2 During Implantation

Implantation of the blastocyst into the uterus is a specific and essential process for mammalian embryonic development. In mice, implantation is initiated from the mural trophectoderm of the blastocyst and the mTE controls implantation progression by acquiring the ability to attach and invade into the endometrium while differentiating into primary trophoblast giant cells. Nevertheless, it remains largely unclear when and how the mTE differentiates and acquires this ability during implantation. Here, by RNA sequencing analysis with the pre- and peri-implantation mTE, we show that the mTE undergoes stage-specific and dynamic changes of gene expression during implantation. We also reveal that the mTE begins down-regulating Cdx2 and up-regulating differentiation marker genes during the peri-implantation stage. In addition, using trophectoderm (TE) -specific lentiviral vector-mediated gene transduction, we demonstrate that TE-specific Cdx2 overexpression represses differentiation of the mTE into the primary trophoblast giant cells. Moreover, we reveal that TE-specific Cdx2 overexpression also represses the up-regulation of cell adhesion- and migration-related genes, including Slc6a14, Slc16a3, Itga7, Itgav and Itgb3, which are known to regulate migration of trophectoderm cells. In particular, the expression of Itgb3, an integrin subunit gene, exhibits high inverse correlation with that of Cdx2 in the TE. Reflecting the down-regulation of the genes for TE migration, TE-specific Cdx2 overexpression causes suppression of the blastocyst outgrowth in vitro and abnormal progression of implantation in vivo. Thus, our results specify the time-course changes of global gene expression in the mTE during implantation and uncover the significance of Cdx2 down-regulation for implantation progression.

A decreased expression of interferon stimulated genes in peri-implantation endometrium of embryo transfer recipient sows could contribute to embryo death

Pig pregnancy succeeds thanks to a well-coordinated system ruling both maternal immune activation and embryonic antigen tolerance. In physiological pregnancies, the maternal immune system should tolerate the presence of hemi-allogeneic conceptuses from the pre-implantation phase to term, while maintaining maternal defence against pathogens. Allogeneic pregnancies, as after embryo transfer (ET), depict high embryo mortality during the attachment phase, calling for studies of the dynamic modifications in immune processes occurring at the maternal-foetal interface, for instance, of interferon (IFN)-stimulated genes (ISGs). These ISGs are generally activated by IFN secreted by the conceptus during the process of maternal recognition of pregnancy (MRP) and responsible for recruiting immune cells to the site of embryo attachment, thus facilitating cell-antigen presentation and angiogenesis. We performed RNA-Seq analysis in peri-implantation (days 18 and 24) endometrial samples retrieved from artificially inseminated sows (hemi-allogeneic embryos (HAL) group) or sows subjected to ET (allogeneic embryos (AL) group) to monitor alterations of gene expression that could be jeopardising early pregnancy. Our results showed that endometrial gene expression patterns related to immune responses differed between hemi- or allogeneic embryo presence, with allogeneic embryos apparently inducing conspicuous modifications of immune-related genes and pathways. A decreased expression (P < 0.05; FC < -2) of several interferon ISGs, such as CXCL8, CXCL10, IRF1, IRF9, STAT1, and B2M, among others was detected in the endometrium of sows carrying allogeneic embryos on day 24 of pregnancy. This severe downregulation of ISGs in allogeneic pregnancies could represent a failure of ET-embryos to signal IFN to the endometrium to warrant the development of adequate immunotolerance mechanisms to facilitate embryo development, thus contributing to elevated embryo death.

Preeclampsia is Associated With Reduced ISG15 Levels Impairing Extravillous Trophoblast Invasion

Among several interleukin (IL)-6 family members, only IL-6 and IL-11 require a gp130 protein homodimer for intracellular signaling due to lack of intracellular signaling domain in the IL-6 receptor (IL-6R) and IL-11R. We previously reported enhanced decidual IL-6 and IL-11 levels at the maternal-fetal interface with significantly higher peri-membranous IL-6 immunostaining in adjacent interstitial trophoblasts in preeclampsia (PE) vs. gestational age (GA)-matched controls. This led us to hypothesize that competitive binding of these cytokines to the gp130 impairs extravillous trophoblast (EVT) differentiation, proliferation and/or invasion. Using global microarray analysis, the current study identified inhibition of interferon-stimulated gene 15 (ISG15) as the only gene affected by both IL-6 plus IL-11 vs. control or IL-6 or IL-11 treatment of primary human cytotrophoblast cultures. ISG15 immunostaining was specific to EVTs among other trophoblast types in the first and third trimester placental specimens, and significantly lower ISG15 levels were observed in EVT from PE vs. GA-matched control placentae (p = 0.006). Induction of primary trophoblastic stem cell cultures toward EVT linage increased ISG15 mRNA levels by 7.8-fold (p = 0.004). ISG15 silencing in HTR8/SVneo cultures, a first trimester EVT cell line, inhibited invasion, proliferation, expression of ITGB1 (a cell migration receptor) and filamentous actin while increasing expression of ITGB4 (a receptor for hemi-desmosomal adhesion). Moreover, ISG15 silencing further enhanced levels of IL-1β-induced pro-inflammatory cytokines (CXCL8, IL-6 and CCL2) in HTR8/SVneo cells. Collectively, these results indicate that ISG15 acts as a critical regulator of EVT morphology and function and that diminished ISG15 expression is associated with PE, potentially mediating reduced interstitial trophoblast invasion and enhancing local inflammation at the maternal-fetal interface. Thus, agents inducing ISG15 expression may provide a novel therapeutic approach in PE.

Context is key: Maternal immune responses to pig allogeneic embryos

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

Antigestagens Mediate the Expression of Decidualization Markers, Extracellular Matrix Factors and Connexin 43 in Decidualized Dog Uterine Stromal (DUS) Cells

Simple Summary

Adequate embryo-maternal communication is essential for a successful pregnancy. In the dog, this interaction is intimately associated with maternal stroma-derived decidual cells, the only cell population in the canine placenta expressing the nuclear progesterone receptor (PGR) and, therefore, sensitive to the circulating progesterone levels. Prepartum decrease of progesterone or clinical application of PGR blockers (antigestagens, e.g., aglepristone and mifepristone) induce placental release of luteolytic factors and terminate pregnancy. However, the importance of progesterone for decidual cells functionality has not been fully elucidated. Therefore, we investigated the effects of PGR blockers on the expression of markers of decidualization and cellular viability, as well as on epithelial and mesenchymal factors in in vitro decidualized dog uterine stromal (DUS) cells. Decidualization increased the expression of the respective markers, including factors involved in cell growth and prostaglandin synthesis. Their expression was suppressed by the application of antigestagens. Additionally, the expression of factors involved in tissue remodeling and cell-cell communication was increased, and antiproliferative and proapoptotic effects were induced in decidualized cells. Altogether, progesterone signaling appears to be crucial for modulating decidual cells physiology and biological activity, and thus for the maintenance of pregnancy.

Abstract

Feto-maternal communication in the dog involves the differentiation of stromal cells into decidual cells. As the only placental cells expressing the nuclear progesterone (P4) receptor (PGR), decidual cells play crucial roles in the maintenance and termination of pregnancy. Accordingly, to investigate possible PGR-mediated mechanisms in canine decidual cells, in vitro decidualized dog uterine stromal (DUS) cells were treated with functional PGR-blockers, mifepristone and aglepristone. Effects on decidualization markers, epithelial and mesenchymal factors, and markers of cellular viability were assessed. Decidualization increased the expression of PTGES, PGR, IGF1, and PRLR, along with ECM1, COL4 and CX43, but downregulated IGF2. DUS cells retained their mesenchymal character, and the expression of COL4 indicated the mesenchymal-epithelial transformation. Antigestagen treatment decreased the availability of PTGES, PRLR, IGF1 and PGR. Furthermore, antigestagens decreased the mRNA and protein expression of CX43, and transcriptional levels of ECM1 and COL4. Additionally, antigestagens increased levels of activated-CASP3 (a proapoptotic factor), associated with lowered levels of PCNA (a proliferation marker). These data reveal important aspects of the functional involvement of PGR in canine decidual cells, regarding the expression of decidualization markers and acquisition of epithelial-like characteristics. Some of these mechanisms may be crucial for the maintenance and/or termination of canine pregnancy.

Effects of Aurora kinase A on mouse decidualization via Stat3-plk1-cdk1 pathway

BACKGROUND

Decidualization is essential to the successful pregnancy in mice. The molecular mechanisms and effects of Aurora kinase A (Aurora A) remain poorly understood during pregnancy. This study is the first to investigate the expression and role of Aurora A during mouse decidualization.

METHODS

Quantitative real time polymerase chain reaction, western blotting and in situ hybridization were used to determine the expression of Aurora A in mouse uteri. Aurora A activity was inhibited by Aurora A inhibitor to explore the role of Aurora A on decidualization via regulating the Aurora A/Stat3/Plk1/Cdk1 signaling pathway.

RESULTS

Aurora A was strongly expressed at implantation sites compared with inter-implantation sites. Furthermore, Aurora A was also significantly increased in oil-induced deciduoma compared with control. Both Aurora A mRNA and protein were significantly increased under in vitro decidualization. Under in vitro decidualization, Prl8a2, a marker of mouse decidualization, was significantly decreased by TC-S 7010, an Aurora A inhibitor. Additionally, Prl8a2 was reduced by Stat3 inhibitor, Plk1 inhibitor and Cdk1 inhibitor, respectively. Moreover, the protein levels of p-Stat3, p-Plk1 and p-Cdk1 were suppressed by TC-S 7010. The protein levels of p-Stat3, p-Plk1 and p-Cdk1 were also suppressed by S3I-201, a Stat3 inhibitor). SBE 13 HCl (Plk1 inhibitor) could reduce the protein levels of p-Plk1 and p-Cdk1. Collectively, Aurora A could regulate Stat3/Plk1/Cdk1 signaling pathway.

CONCLUSION

Our study shows that Aurora A is expressed in decidual cells and should be important for mouse decidualization. Aurora A/Stat3/Plk1/Cdk1 signaling pathway may be involved in mouse decidualization.

Angiopoietin-2 regulated by progesterone induces uterine vascular remodeling during pregnancy

During pregnancy, the uterus undergoes intense neovascularization and vascular remodeling to supply oxygen and nutrients to the embryo. During this period, progesterone secreted from the ovary has effects on vascular remodeling in the endometrium and interacts with angiogenic factors. However, the exact mechanism of uterine vascular remodeling during pregnancy is poorly understood. Therefore, the aim of the present study was to investigate the association between angiopoietin-2 (Ang-2), one of the angiopoietins, and intrauterine vessel remodeling during pregnancy, and to determine the effect of progesterone on Ang-2 levels. Changes in Ang-2 expression were observed according to quantitative modification of progesterone using pregnant mice and human uterine microvascular endothelial cells. As a result, Ang-2 was observed mainly in the mesometrial region (MR) of the uterus during the period between implantation and placentation. Furthermore, a substantial amount of Ang-2 also appeared in endothelial cells, particularly of the venous sinus region (VSR). Interestingly, Ang-2 expression was increased by progesterone, whereas estrogen had limited effects. To confirm the association between Ang-2 and progesterone, the function of the progesterone receptor (PR) was inhibited using RU486, a blocker of PR. Ang-2 expression and vascular remodeling of the VSR in the uterus were decreased when the functions of progesterone were inhibited. Overall, the regulation of Ang-2 by progesterone/PR was associated with vascular remodeling in the VSR during pregnancy. The present study proposed a solution to prevent pregnancy failure due to a lack of vascularity in the uterus in advance.

Effects of Intrauterine Air Bubbles on Embryonic Development in Mice

During murine embryo transfer, air bubbles frequently are loaded with embryos into the transfer catheter, but the role of air bubbles on embryonic development is unclear. This study shows that intrauterine air disrupted embryo spacing, induced deciduoma, and impaired postimplantation development. RNA sequencing showed that the gene expression profile of air-induced deciduoma differed significantly from that of embryo-induced decidua but is similar to tetraploid-induced deciduoma. A subset of 33 common genes was upregulated in the embryo-induced decidua compared with air- or tetraploid-induced deciduoma. These data suggest that the inner cell mass (ICM) plays a key role in regulating decidualization and that the trophectoderm is an intermediate that relays ICM-derived signals to other target cells. Our results may provide an innovative approach for detecting the developmental status of embryos in human reproductive medicine.

Differentiating mouse embryonic stem cells express markers of human endometrium

BACKGROUND

Modeling early endometrial differentiation is a crucial step towards understanding the divergent pathways between normal and ectopic endometrial development as seen in endometriosis.

METHODS

To investigate these pathways, mouse embryonic stem cells (mESCs) and embryoid bodies (EBs) were differentiated in standard EB medium (EBM). Immunofluorescence (IF) staining and reverse-transcription polymerase chain reaction (RT-PCR) were used to detect expression of human endometrial cell markers on differentiating cells, which were sorted into distinct populations using fluorescence-activated cell sorting (FACS).

RESULTS

A subpopulation (50%) of early differentiating mESCs expressed both glandular (CD9) and stromal (CD13) markers of human endometrium, suggestive of a novel endometrial precursor cell population. We further isolated a small population of endometrial mesenchymal stem cells, CD45-/CD146+/PDGFR-β+, from differentiating EBs, representing 0.7% of total cells. Finally, quantitative PCR demonstrated significantly amplified expression of transcription factors Hoxa10 and Foxa2 in CD13+ EBs isolated by FACS (p = 0.03).

CONCLUSIONS

These findings demonstrate that mESCs have the capacity to express human endometrial cell markers and demonstrate potential differentiation pathways of endometrial precursor and mesenchymal stem cells, providing an in vitro system to model early endometrial tissue development. This model represents a key step in elucidating the mechanisms of ectopic endometrial tissue growth. Such a system could enable the development of strategies to prevent endometriosis and identify approaches for non-invasive monitoring of disease progression.

A novel homologous model for noninvasive monitoring of endometriosis progression

To date, several groups have generated homologous models of endometriosis through the implantation of endometrial tissue fluorescently labeled by green fluorescent protein (GFP) or tissue from luciferase-expressing transgenic mice into recipient animals, enabling noninvasive monitoring of lesion signal. These models present an advantage over endpoint models, but some limitations persist; use of transgenic mice is laborious and expensive, and GFP presents poor tissue penetration due to the relatively short emission wavelength. For this reason, a homologous mouse model of endometriosis that allows in vivo monitoring of generated lesions over time and mimics human lesions in recipient mice would be most desirable. In this regard, using C57BL/6 and B6N-Tyrc-Brd/BrdCrCrl mice, we optimized a decidualization protocol to obtain large volumes of decidual endometrium and mimic human lesions. Subsequently, to obtain a more robust and reliable noninvasive monitoring of lesions, we used the fluorescent reporter mCherry, which presents deeper tissue penetration and higher photostability, showing that endometrial tissue was properly labeled with 1 × 108 PFU/mL mCherry adenoviral vectors. mCherry-labeled endometriotic tissue was implanted in recipient mice, generating lesions that displayed characteristics typical of human endometriotic lesions, such as epithelial cells forming glands, local inflammation, collagen deposits, and new vessel formation. In vivo monitoring demonstrated that subcutaneous implantation on ventral abdomen of recipient mice provided the most intense and reliable signal for noninvasive lesion monitoring over a period of at least 20 days. This homologous model improves upon previously reported models of endometriosis and provides opportunities to study mechanism underlying endometriotic lesion growth and progression. We created a cost-effective but accurate homologous mouse model of endometriosis that allows the study of growth and progression of endometriotic lesions over early time points in lesion development through noninvasive monitoring.

Polycomb repressive complex 1 controls uterine decidualization

Uterine stromal cell decidualization is an essential part of the reproductive process. Decidual tissue development requires a highly regulated control of the extracellular tissue remodeling; however the mechanism of this regulation remains unknown. Through systematic expression studies, we detected that Cbx4/2, Rybp, and Ring1B [components of polycomb repressive complex 1 (PRC1)] are predominantly utilized in antimesometrial decidualization with polyploidy. Immunofluorescence analyses revealed that PRC1 members are co-localized with its functional histone modifier H2AK119ub1 (mono ubiquitination of histone-H2A at lysine-119) in polyploid cell. A potent small-molecule inhibitor of Ring1A/B E3-ubiquitin ligase or siRNA-mediated suppression of Cbx4 caused inhibition of H2AK119ub1, in conjunction with perturbation of decidualization and polyploidy development, suggesting a role for Cbx4/Ring1B-containing PRC1 in these processes. Analyses of genetic signatures by RNA-seq studies showed that the inhibition of PRC1 function affects 238 genes (154 up and 84 down) during decidualization. Functional enrichment analyses identified that about 38% genes primarily involved in extracellular processes are specifically targeted by PRC1. Furthermore, ~15% of upregulated genes exhibited a significant overlap with the upregulated Bmp2 null-induced genes in mice. Overall, Cbx4/Ring1B-containing PRC1 controls decidualization via regulation of extracellular gene remodeling functions and sheds new insights into underlying molecular mechanism(s) through transcriptional repression regulation.

Identification of target genes for a prolactin family paralog in mouse decidua

Prolactin family 8, subfamily a, member 2 (PRL8A2; also called decidual prolactin-related protein; dPRP) is a member of the expanded prolactin family. PRL8A2 is expressed in the uterine decidua and contributes to pregnancy-dependent adaptations to hypoxia. The purpose of this study was to identify gene targets for PRL8A2 action within the uteroplacental compartment. Affymetrix DNA microarray analysis was performed for RNA samples from WT and Prl8a2 null tissues. Validation of the DNA microarray was performed using quantitative RT-PCR. Nine genes were confirmed with decreased expression in Prl8a2 null tissues (e.g., Klk7, Rimklb, Arhgef6, Calm4, Sprr2h, Prl4a1, Ccl27, Lipg, and Htra3). These include potential decidual, endothelial and trophoblast cell targets positively regulated by PRL8A2. A significant upregulation of Derl3, Herpud1, Creld2, Hsp90b1, Ddit3 and Hspa5 was identified in Prl8a2 null tissues, reflecting an increased endoplasmic reticulum (ER) stress response. ER stress genes were prominently expressed in the uterine decidua. We propose that PRL8A2 is a mediator of progesterone-dependent modulation of intrauterine responses to physiological stressors.

Developmental plasticity, cell fate specification and morphogenesis in the early mouse embryo

A critical point in mammalian development is when the early embryo implants into its mother's uterus. This event has historically been difficult to study due to the fact that it occurs within the maternal tissue and therefore is hidden from view. In this review, we discuss how the mouse embryo is prepared for implantation and the molecular mechanisms involved in directing and coordinating this crucial event. Prior to implantation, the cells of the embryo are specified as precursors of future embryonic and extra-embryonic lineages. These preimplantation cell fate decisions rely on a combination of factors including cell polarity, position and cell–cell signalling and are influenced by the heterogeneity between early embryo cells. At the point of implantation, signalling events between the embryo and mother, and between the embryonic and extraembryonic compartments of the embryo itself, orchestrate a total reorganization of the embryo, coupled with a burst of cell proliferation. New developments in embryo culture and imaging techniques have recently revealed the growth and morphogenesis of the embryo at the time of implantation, leading to a new model for the blastocyst to egg cylinder transition. In this model, pluripotent cells that will give rise to the fetus self-organize into a polarized three-dimensional rosette-like structure that initiates egg cylinder formation.

Uterine glands: biological roles in conceptus implantation, uterine receptivity and decidualization

All mammalian uteri contain glands in the endometrium that synthesize or transport and secrete substances essential for survival and development of the conceptus (embryo/fetus and associated extraembryonic membranes). This review summarizes information related to the biological roles of uterine glands and their secretions in uterine receptivity, blastocyst/conceptus survival and implantation, and stromal cell decidualization. Studies with the ovine uterine gland knockout (UGKO) model support a primary role for uterine glands and, by inference, their secretions present in uterine luminal fluid histrotroph for conceptus survival and development. In rodents, studies with mutant and progesterone-induced UGKO mice found that uterine glands and their secretions are unequivocally required for establishment of uterine receptivity and blastocyst implantation and also may influence blastocyst trophectoderm activation and stromal cell decidualization in the uterus. Similarly in humans, histotroph from uterine glands appears critical for blastocyst implantation, uterine receptivity, and conceptus nutrition during the first trimester and uterine glands likely have a role in stromal cell decidualization. An increased understanding of uterine gland biology is important for diagnosis, prevention and treatment of fertility problems, particularly infertility and recurrent pregnancy loss, in domestic animals and humans.

Sirh7/Ldoc1 knockout mice exhibit placental P4 overproduction and delayed parturition

Sirh7/Ldoc1 [sushi-ichi retrotransposon homolog 7/leucine zipper, downregulated in cancer 1, also called mammalian retrotransposon-derived 7 (Mart7)] is one of the newly acquired genes from LTR retrotransposons in eutherian mammals. Interestingly, Sirh7/Ldoc1 knockout (KO) mice exhibited abnormal placental cell differentiation/maturation, leading to an overproduction of placental progesterone (P4) and placental lactogen 1 (PL1) from trophoblast giant cells (TGCs). The placenta is an organ that is essential for mammalian viviparity and plays a major endocrinological role during pregnancy in addition to providing nutrients and oxygen to the fetus. P4 is an essential hormone in the preparation and maintenance of pregnancy and the determination of the timing of parturition in mammals; however, the biological significance of placental P4 in rodents is not properly recognized. Here, we demonstrate that mouse placentas do produce P4 in mid-gestation, coincident with a temporal reduction in ovarian P4, suggesting that it plays a role in the protection of the conceptuses specifically in this period. Pregnant Sirh7/Ldoc1 knockout females also displayed delayed parturition associated with a low pup weaning rate. All these results suggest that Sirh7/Ldoc1 has undergone positive selection during eutherian evolution as a eutherian-specific acquired gene because it impacts reproductive fitness via the regulation of placental endocrine function.

Embryo mortality in Isg15-/- mice is exacerbated by environmental stress

The interferon-stimulated gene 15 (Isg15) encodes a ubiquitin-like protein that is induced in the endometrium by pregnancy in mice, humans, and ruminants. Because ISG15 is a component of the innate immune system, we hypothesized that development of the embryo, fetus, and postnatal pup may be impaired in mice lacking Isg15 (Isg15(-/-)) and that this development would be further impaired in response to environmental insults such as hypoxia. The number of implantation sites, resorption sites, dead embryos, and the changes in overall gross morphology of the uterus were evaluated in Isg15(-/-) mice on Days 7.5 and 12.5 postcoitum (dpc). Postnatal development also was monitored from birth to 12 wk of age. On 7.5 dpc, the number of implantation sites and serum progesterone concentrations were similar. However, embryo mortality increased (P < 0.05) in Isg15(-/-) dams by 12.5 dpc, resulting in smaller litter sizes (4.26 ± 0.21 embryos; n = 83 litters) compared to Isg15(+/+) females (7.78 ± 0.29 pups; n = 47 litters). Embryo mortality in Isg15(-/-) mice was further exacerbated to 70% when dams were stressed through housing under hypoxic conditions (PB = 445 mmHg; 6.5-12.5 dpc). Transmission electron microscopy revealed lesions in antimesometrial decidua as well as trophoblast cells adjacent to decidual cells on 7.5 dpc. ISG15 was localized to mesometrial decidua on 7.5 dpc. By 12.5 dpc, ISG15 was intensely localized to the labyrinth of the placenta. By 7.5 dpc, uterine natural killer cell migration into the mesometrial pole was diminished by 65% and was less prevalent in Isg15(-/-) compared to Isg15(+/+) deciduum. Postnatal growth rate of offspring that survived to birth from Isg15(-/-) and Isg15(+/+) dams was not different. Embryo mortality occurs in pregnant Isg15(-/-) mice, is exacerbated by environmental insults like maternal hypoxia, and might result from impaired early decidualization, vascular development, and formation of the labyrinth.

p28, a truncated form of TRα1 regulates mitochondrial physiology

We have previously identified in mitochondria two truncated forms of the T3 nuclear receptor TRα1, with molecular weights of 43kDa (p43) and 28kDa (p28) respectively located in the matrix and in the inner membrane. Previously, we have demonstrated that p43 stimulates mitochondrial transcription and protein synthesis in the presence of T3. Here we report that p28 is targeted into the organelle in a T3-dependent manner and displays an affinity for T3 higher than the nuclear receptor. We tried to generate mice overexpressing p28 using the human α-skeletal actin promoter, however we found an early embryonic lethality that was probably linked to a transient expression of p28 in trophoblast giant cells. This could be partly explained by the observation that overexpression of p28 in human fibroblasts induced alterations of mitochondrial physiology.

Differential expression and anti-oxidant function of glutathione peroxidase 3 in mouse uterus during decidualization

Glutathione peroxidase 3 (GPX3) is an important member of antioxidant enzymes for reducing reactive oxygen species and maintaining the oxygen balance. Gpx3 mRNA is strongly expressed in decidual cells from days 5 to 8 of pregnancy. After pregnant mice are treated with GPX inhibitor for 3 days, pregnancy rate is significantly reduced. Progesterone stimulates Gpx3 expression through PR/HIF1α in mouse endometrial stromal cells. In the decidua, the high level of GPX3 expression is closely associated with the reduction of hydrogen peroxide (H2O2). Based on our data, GPX3 may play a major role in reducing H2O2 during decidualization.

Development of the hemochorial maternal vascular spaces in the placenta through endothelial and vasculogenic mimicry

The maternal vasculature within the placenta in primates and rodents is unique because it is lined by fetal cells of the trophoblast lineage and not by maternal endothelial cells. In addition to trophoblast cells that invade the uterine spiral arteries that bring blood into the placenta, other trophoblast subtypes sit at different levels of the vascular space. In mice, at least five distinct subtypes of trophoblast cells have been identified which engage maternal endothelial cells on the arterial and venous frontiers of the placenta, but which also form the channel-like spaces within it through a process analogous to formation of blood vessels (vasculogenic mimicry). These cells are all large, post-mitotic trophoblast giant cells. In addition to assuming endothelial cell-like characteristics (endothelial mimicry), they produce dozens of different hormones that are thought to regulate local and systemic maternal adaptations to pregnancy. Recent work has identified distinct molecular pathways in mice that regulate the morphogenesis of trophoblast cells on the arterial and venous sides of the vascular circuit that may be analogous to specification of arterial and venous endothelial cells.

ISGylation: a conserved pathway in mammalian pregnancy

Successful pregnancy includes remodeling and differentiation of the endometrium in response to sex steroid hormones, development of maternal immunotolerance to the implanting embryo, and modification of the local uterine environment by the embryo to suit its own needs. The major signal released by the ruminant conceptus during establishment of pregnancy is interferon-tau (IFNT) that stimulates the expression of many genes in the endometrium and ovary. One of these genes is called interferon stimulated gene 15 (ISG15), which encodes a ubiquitin homolog with a C-terminal Gly that becomes covalently attached to Lys residues on targeted proteins through an ATP-dependent multi-step enzymatic reaction called ISGylation. The conceptus-derived induction of endometrial ISGs also occurs in mouse and human deciduas and placenta, in response to pregnancy presumably through action of cytokines such as interleukins and type I IFN. Described herein is evidence to support the concept that ISGylation is a maternal response to the developing conceptus, implantation and placentation that is conserved across mammalian pregnancy. Although the precise role for ISG15 remains elusive during pregnancy, it is clear that up-regulation in response to pregnancy may impart a pre-emptive defense to infection or other environmental insults, and protection of the conceptus against inflammatory insults across species.

Progesterone regulates secretin expression in mouse uterus during early pregnancy

Secretin, a classical gastrointestinal and neuroendocrine peptide, plays an important role in maintaining the body fluid balance. However, the expression and regulation of secretin in the reproductive system are still unknown. In our study, secretin is specifically expressed in the decidua on days 5 to 8 of pregnancy. Secretin expression is not detected under delayed implantation but is stimulated after estrogen activation and under artificial decidualization. Progesterone induces secretin expression in ovariectomized mice and cultured stromal cells, which is abrogated by specific LY294002. Because secretin is mainly localized in the decidua and also strongly expressed during in vitro decidualization, secretin may play a role during mouse decidualization through regulating cyclic adenosine monophosphate level.

Differential gene expression profiling of mouse uterine luminal epithelium during periimplantation

Uterine luminal epithelium (LE) is critical for establishing uterine receptivity. Microarray analysis of gestation day 3.5 (D3.5, preimplantation) and D4.5 (postimplantation) LE from natural pregnant mice identified 382 upregulated and 245 downregulated genes in the D4.5 LE. Gene Ontology annotation grouped 186 upregulated and 103 downregulated genes into 22 and 15 enriched subcategories, respectively, in regulating DNA-dependent transcription, metabolism, cell morphology, ion transport, immune response, apoptosis, signal transduction, and so on. Signaling pathway analysis revealed 99 genes in 21 significantly changed signaling pathways, with 14 of these pathways involved in metabolism. In situ hybridization confirmed the temporal expression of 12 previously uncharacterized genes, including Atp6v0a4, Atp6v0d2, F3, Ggh, Tmprss11d, Tmprss13, Anpep, Fxyd4, Naip5, Npl, Nudt19, and Tpm1 in the periimplantation uterus. This study provides a comprehensive picture of the differentially expressed genes in the periimplantation LE to help understand the molecular mechanism of LE transformation upon establishment of uterine receptivity.

Progesterone receptor-mediated regulation of N-acetylneuraminate pyruvate lyase (NPL) in mouse uterine luminal epithelium and nonessential role of NPL in uterine function

N-acetylneuraminate pyruvate lyase (NPL) catalyzes N-acetylneuraminic acid, the predominant sialic acid. Microarray analysis of the periimplantation mouse uterine luminal epithelium (LE) revealed Npl being the most downregulated (35×) gene in the LE upon embryo implantation. In natural pregnant mouse uterus, Npl expression increased 56× from gestation day 0.5 (D0.5) to D2.5. In ovariectomized mouse uterus, Npl was significantly upregulated by progesterone (P4) but downregulated by 17β-estradiol (E2). Progesterone receptor (PR) antagonist RU486 blocked the upregulation of Npl in both preimplantation uterus and P4-treated ovariectomized uterus. Npl was specifically localized in the preimplantation D2.5 and D3.5 uterine LE. Since LE is essential for establishing uterine receptivity, it was hypothesized that NPL might play a critical role in uterine function, especially during embryo implantation. This hypothesis was tested in the Npl^(−/−) mice. No significant differences were observed in the numbers of implantation sites on D4.5, gestation periods, litter sizes, and postnatal offspring growth between wild type (WT) and Npl^(−/−) females from mating with WT males. Npl^(−/−)xNpl^(−/−) crosses produced comparable little sizes as that from WTxWT crosses. Comparable mRNA expression levels of several genes involved in sialic acid metabolism were observed in D3.5 uterus and uterine LE between WT and Npl^(−/−), indicating no compensatory upregulation in the D3.5 Npl^(−/−) uterus and LE. This study demonstrates PR-mediated dynamic expression of Npl in the periimplantation uterus and dispensable role of Npl in uterine function and embryo development.

Widespread but tissue-specific patterns of interferon-induced transmembrane protein 3 (IFITM3, FRAGILIS, MIL-1) in the mouse gastrula

Interferon-induced transmembrane protein 3 (IFITM3; FRAGILIS; MIL-1) is part of a larger family of important small interferon-induced transmembrane genes and proteins involved in early development, cell adhesion, and cell proliferation, and which also play a major role in response to bacterial and viral infections and, more recently, in pronounced malignancies. IFITM3, together with tissue-nonspecific alkaline phosphatase (TNAP), PRDM1, and STELLA, has been claimed to be a hallmark of segregated primordial germ cells (PGCs) (Saitou et al., 2002). However, whether IFITM3, like STELLA, is part of a broader stem/progenitor pool that builds the posterior region of the mouse conceptus (Mikedis and Downs, 2012) is obscure. To discover the whereabouts of IFITM3 during mouse gastrulation (~E6.5-9.0), systematic immunohistochemical analysis was carried out at closely spaced 2-4-h intervals. Results revealed diverse, yet consistent, profiles of IFITM3 localization throughout the gastrula. Within the putative PGC trajectory and surrounding posterior tissues, IFITM3 localized as a large cytoplasmic spot with or without staining in the plasma membrane. IFITM3, like STELLA, was also found in the ventral ectodermal ridge (VER), a posterior progenitor pool that builds the tailbud. The large cytoplasmic spot with plasma membrane staining was exclusive to the posterior region; the visceral yolk sac, non-posterior tissues, and epithelial tissues exhibited spots of IFITM3 without cell surface staining. Colocalization of the intracellular IFITM3 spot with the endoplasmic reticulum, Golgi apparatus, or endolysosomes was not observed. That relatively high levels of IFITM3 were found throughout the posterior primitive streak and its derivatives is consistent with evidence that IFITM3, like STELLA, is part of a larger stem/progenitor cell pool at the posterior end of the primitive streak that forms the base of the allantois and builds the fetal-umbilical connection, thus further obfuscating practical phenotypic distinctions between so-called PGCs and surrounding soma.

Distinct spatiotemporal expression of serine proteases Prss23 and Prss35 in periimplantation mouse uterus and dispensable function of Prss35 in fertility

PRSS23 and PRSS35 are homologous proteases originally identified in mouse ovaries. In the periimplantation mouse uterus, Prss23 was highly expressed in the preimplantation gestation day 3.5 (D3.5) uterine luminal epithelium (LE). It disappeared from the postimplantation LE and reappeared in the stromal compartment next to the myometrium on D6.5. It was undetectable in the embryo from D4.5 to D6.5 but highly expressed in the embryo on D7.5. Prss35 became detectable in the uterine stromal compartment surrounding the embryo on D4.5 and shifted towards the mesometrial side of the stromal compartment next to the embryo from D5.5 to D7.5. In the ovariectomized uterus, Prss23 was moderately and Prss35 was dramatically downregulated by progesterone and 17β-estradiol. Based on the expression of Prss35 in granulosa cells and corpus luteum of the ovary and the early pregnant uterus, we hypothesized that PRSS35 might play a role in female reproduction, especially in oocyte development, ovulation, implantation, and decidualization. This hypothesis was tested in Prss35((-/-)) mice, which proved otherwise. Between wild type (WT) and Prss35((-/-)) mice, superovulation of immature females produced comparable numbers of cumulus-oocyte complexes; there were comparable numbers of implantation sites detected on D4.5 and D7.5; there were no obvious differences in the expression of implantation and decidualization marker genes in D4.5 or D7.5 uteri. Comparable mRNA expression levels of a few known protease-related genes in the WT and Prss35((-/-)) D4.5 uteri indicated no compensatory upregulation. Comparable litter sizes from WT × WT and Prss35((-/-))× Prss35((-/-)) crosses suggested that Prss35 gene was unessential for fertility and embryo development. Prss35 gene has been linked to cleft lip/palate in humans. However, no obvious such defects were observed in Prss35((-/-)) mice. This study demonstrates the distinct expression of Prss23 and Prss35 in the periimplantation uterus and the dispensable role of Prss35 in fertility and embryo development.

Immunology of the maternal-fetal interface

The immune cells that reside at the interface between the placenta and uterus are thought to play many important roles in pregnancy. Recent work has revealed that the composition and function of these cells are locally controlled by the specialized uterine stroma (the decidua) that surrounds the implanted conceptus. Here, I discuss how key immune cell types (natural killer cells, macrophages, dendritic cells, and T cells) are either enriched or excluded from the decidua, how their function is regulated within the decidua, and how they variously contribute to pregnancy success or failure. The discussion emphasizes the relationship between human and mouse studies. Deeper understanding of the immunology of the maternal-fetal interface promises to yield significant insight into the pathogenesis of many human pregnancy complications, including preeclampsia, intrauterine growth restriction, spontaneous abortion, preterm birth, and congenital infection.

The mesenchymal-epithelial transition during in vitro decidualization

The epithelial-mesenchymal transition plays a critical role in embryonic development, cancer progression, and metastasis. Decidualization is the process by which the fibroblast-like endometrial stromal cells differentiate into polygonal epithelial-like cells. However, it is still unclear whether mesenchymal-epithelial transition (MET) occurs during decidualization. The aim of this study was to examine whether decidualization causes the downregulation of some mesenchymal markers and upregulation of some epithelial markers in cultured uterine stromal cells. We showed that decidualization causes the downregulation of snail and vimentin expression, and upregulation of E-cadherin and cytokeratin expression. During in vitro decidualization, cultured stromal cells lose elongated shape and show epithelium-like characteristics. Our data suggest that the process of MET may exist during decidualization.

Physiological and molecular determinants of embryo implantation

Embryo implantation involves the intimate interaction between an implantation-competent blastocyst and a receptive uterus, which occurs in a limited time period known as the window of implantation. Emerging evidence shows that defects originating during embryo implantation induce ripple effects with adverse consequences on later gestation events, highlighting the significance of this event for pregnancy success. Although a multitude of cellular events and molecular pathways involved in embryo-uterine crosstalk during implantation have been identified through gene expression studies and genetically engineered mouse models, a comprehensive understanding of the nature of embryo implantation is still missing. This review focuses on recent progress with particular attention to physiological and molecular determinants of blastocyst activation, uterine receptivity, blastocyst attachment and uterine decidualization. A better understanding of underlying mechanisms governing embryo implantation should generate new strategies to rectify implantation failure and improve pregnancy rates in women.

Epigenetic changes through DNA methylation contribute to uterine stromal cell decidualization

Embryo-uterine interaction during early pregnancy critically depends on the coordinated expression of numerous genes at the site of implantation. The epigenetic mechanism through DNA methylation (DNM) plays a major role in the control of gene expression, although this regulatory event remains unknown in uterine implantation sites. Our analysis revealed the presence of DNA methyltransferase 1 (Dnmt1) in mouse endometrial cells on the receptive d 4 of pregnancy and early postattachment (d 5) phase, whereas Dnmt3a had lower abundant expression. Both Dnmt1 and Dnmt3a were coordinately expressed in decidual cells on d 6-8. 5-Methycytosine showed a similar expression pattern to that of Dnmt1. The preimplantation inhibition of DNM by 5-aza-2'-deoxycytodine was not antagonistic for embryonic attachment, although endometrial stromal cell proliferation at the site of implantation was down-regulated, indicating a disturbance with the postattachment decidualization event. Indeed, the peri- or postimplantation inhibition of DNM caused significant abrogation of decidualization, with concomitant loss of embryos. We next identified decidual genes undergoing alteration of DNM using methylation-sensitive restriction fingerprinting. One such gene, Chromobox homolog 4, an epigenetic regulator in the polycomb group protein family, exhibited hypomethylation in promoter DNA and increased expression with the onset of decidualization. Furthermore, inhibition of DNM resulted in enhanced expression of hypermethylated genes (Bcl3 and Slc16a3) in the decidual bed as compared with control, indicating aberration of gene expression may be associated with DNM-inhibition-induced decidual perturbation. Overall, these results suggest that uterine DNM plays a major role for successful decidualization and embryo development during early pregnancy.

Uterine NK cells are critical in shaping DC immunogenic functions compatible with pregnancy progression

Dendritic cell (DC) and natural killer (NK) cell interactions are important for the regulation of innate and adaptive immunity, but their relevance during early pregnancy remains elusive. Using two different strategies to manipulate the frequency of NK cells and DC during gestation, we investigated their relative impact on the decidualization process and on angiogenic responses that characterize murine implantation. Manipulation of the frequency of NK cells, DC or both lead to a defective decidual response characterized by decreased proliferation and differentiation of stromal cells. Whereas no detrimental effects were evident upon expansion of DC, NK cell ablation in such expanded DC mice severely compromised decidual development and led to early pregnancy loss. Pregnancy failure in these mice was associated with an unbalanced production of anti-angiogenic signals and most notably, with increased expression of genes related to inflammation and immunogenic activation of DC. Thus, NK cells appear to play an important role counteracting potential anomalies raised by DC expansion and overactivity in the decidua, becoming critical for normal pregnancy progression.

Progestin-induced heart and neural crest derivatives expressed transcript 2 is associated with fibulin-1 expression in human endometrial stromal cells

OBJECTIVE

To investigate whether heart and neural crest derivatives expressed transcript 2 (HAND2) regulates fibulin-1 (FBLN1) expression during decidualization of human endometrial stromal cells (ESCs).

DESIGN

In vitro experiment.

SETTING

Research laboratory.

PATIENT(S)

Twenty-four patients undergoing hysterectomy for benign reasons.

INTERVENTION(S)

ESCs were cultured with various progestins (medroxyprogesterone acetate [MPA], norethisterone, levonorgestrel, dienogest, and P), E(2), dexamethasone, and/or 8-bromoadenosine 3', 5'-cyclic monophosphate (8-Br-cAMP). HAND2 and FBLN1 were silenced by small interfering RNA technology.

MAIN OUTCOME MEASURE(S)

HAND2 and FBLN1 expression levels were assessed by real-time polymerase chain reaction and Western blot analysis.

RESULT(S)

MPA or E(2) + MPA increased HAND2 mRNA levels in ESCs in a time- and dose-dependent manner, and this stimulatory effect was blocked by RU-486 (P receptor antagonist). HAND2 was increased by E(2) + MPA earlier than FBLN1. Simultaneous MPA and 8-Br-cAMP treatment synergistically enhanced HAND2 mRNA levels. P and all the progestins significantly increased HAND2 mRNA levels, whereas E(2), 8-Br-cAMP, or dexamethasone alone had no effect. Silencing of HAND2 expression significantly reduced FBLN1 expression, whereas FBLN1 silencing had no effect on HAND2 expression.

CONCLUSION(S)

These results suggest that progestin-induced HAND2 contributes to FBLN1 expression in human ESCs.

Angiopoietin-like gene expression in the mouse uterus during implantation and in response to steroids

The purpose of this work was to determine if and where Angiopoietin-like genes are expressed in the mouse uterus during the implantation period of pregnancy and to determine if uterine expression of such genes is controlled by estrogen or progesterone. We found that all six known murine angiopoietin-like genes were expressed in the mouse uterus during implantation. The expression of four genes was controlled by either estrogen or progesterone. Only the levels of angiopoietin-like 4 (Angptl4) mRNA dramatically increased in implantation segments of the uterus during decidualization and was conceptus-independent. Due to this increased expression and the fact that angiopoietin-like 4 protein plays a role in lipid metabolism and angiogenesis in other tissues, only the expression of Angptl4 was further examined in the uterus and developing placenta. Angptl4 mRNA was localized to subpopulations of the endometrial stromal fibroblast and endothelial cell populations during decidualization. It was also localized to the ectoplacental cone, trophoblast giant cells and parietal endoderm of the conceptus at this time. By mid-pregnancy, Angptl4 mRNA was localized mainly to the mesometrial lymphoid aggregate region plus mesometrial endothelial cells of the uterus, as well as in various cell types of the conceptus. Additional work showed that Angptl4 expression increases in mouse endometrial stromal cells as they undergo decidualization in vitro. As in other cell types, the expression of Angptl4 in endometrial stromal cells was increased in response to an agonist of the peroxisome proliferator activated receptors. Taken together, the results of this work support the hypothesis that locally expressed Angptl4 might play a role in local uterine/placental lipid metabolism and vascular changes during implantation and thus provide a basis for future research.

Analysis of uterine gene expression in interleukin-15 knockout mice reveals uterine natural killer cells do not play a major role in decidualization and associated angiogenesis

During decidualization, uterine natural killer (uNK) cells are the most abundant immune cell types found in the uterus. Although it is well known that they play key roles in spiral arteriole modification and the maintenance of decidual integrity seen after mid-pregnancy, their roles in the differentiation of decidual cells and accompanying angiogenesis during the process of decidualization is less well characterized. To address this, we used whole-genome Illumina BeadChip analysis to compare the gene expression profiles in implantation segments of the uterus during decidualization on day 7.5 of pregnancy between wild-type and uNK cell-deficient (interleukin-15-knockout) mice. We found almost 300 differentially expressed genes and verified the differential expression of ~60 using quantitative RT-PCR. Notably, there was a lack of differential expression of genes involved in decidualization and angiogenesis and this was also verified by quantitative RT-PCR. Similar endothelial cell densities and proliferation indices were also found in the endometrium between the implantation site tissues of wild-type and knockout mice undergoing decidualization. Overall, the results of this study reveal that uNK cells likely do not play a major role in decidualization and accompanying angiogenesis during implantation. In addition, the study identifies a large number of genes whose expression in implantation-site uterine tissue during decidualization depends on interleukin-15 expression in mice.

Differential expression and regulation of angiopoietin-2 in mouse uterus during preimplantation period

Angiogenesis is crucial to successful implantation and decidualization, however, as an important angiogenic growth factor, the effect of Ang-2 in the process of implantation and decidualization is still unknown. This study is to investigate the differential expression of Ang-2 in mouse uterus during early pregnancy and its regulation by steroid hormones using in situ hybridization and RT-PCR. There is no detectable Ang-2 mRNA signal on days 1-5 of pregnancy by in situ hybridization. On days 6-8, Ang-2 mRNA is mainly expressed in the primary decidua of mesometrial side, and the expression gradually increases. By RT-PCR, a significantly higher level of Ang-2 expression is observed on day 8 of pregnancy, although Ang-2 expression can be found through days 1-8. Similarly, Ang-2 is highly expressed in decidualized cells under artificial decidualization. In the ovariectomized mouse uterus, Ang-2 expression gradually increases after estrogen injection and with peak levels at 12 hr, while progesterone injection can cause a decline in uterine Ang-2 mRNA level, which reaches a nadir at 12 hr. These results suggest that Ang-2 may play a key role in the process of mouse decidualization. Estrogen can induce the expression of Ang-2 while progesterone can inhibit its expression in the ovariectomized mouse uterus.

Expression and function of fatty acid-binding protein 4 during mouse decidualization

Fatty acid-binding protein 4 (Fabp4) is highly expressed in the secondary decidual zone of mouse decidua and deciduoma and stromal cells under in vitro decidualization. Dtprp, a well-known marker of in vitro decidualization, is diminished by small interfering RNA against Fabp4 and FABP4 inhibitor and stimulated through Fabp4 overexpression.

Placental vasculogenesis is regulated by keratin-mediated hyperoxia in murine decidual tissues

The mammalian placenta represents the interface between maternal and embryonic tissues and provides nutrients and gas exchange during embryo growth. Recently, keratin intermediate filament proteins were found to regulate embryo growth upstream of the mammalian target of rapamycin pathway through glucose transporter relocalization and to contribute to yolk sac vasculogenesis through altered bone morphogenetic protein 4 signaling. Whether keratins have vital functions in extraembryonic tissues is not well understood. Here, we report that keratins are essential for placental function. In the absence of keratins, we find hyperoxia in the decidual tissue directly adjacent to the placenta, because of an increased maternal vasculature. Hyperoxia causes impaired vasculogenesis through defective hypoxia-inducible factor 1α and vascular endothelial growth factor signaling, resulting in invagination defects of fetal blood vessels into the chorion. In turn, the reduced labyrinth, together with impaired gas exchange between maternal and embryonic blood, led to increased hypoxia in keratin-deficient embryos. We provide evidence that keratin-positive trophoblast secretion of prolactin-like protein a (Prlpa) and placental growth factor (PlGF) during decidualization are altered in the absence of keratins, leading to increased infiltration of uterine natural killer cells into placental vicinity and increased vascularization of the maternal decidua. Our findings suggest that keratin mutations might mediate conditions leading to early pregnancy loss due to hyperoxia in the decidua.

Tumor necrosis factor receptor subfamily 9 (Tnfrsf9) gene is expressed in distinct cell populations in mouse uterus and conceptus during implantation period of pregnancy

Tumor necrosis factor receptor subfamily 9 (TNFRSF9) plays a potentially important general role in immune function. Tnfrsf9 gene expression has previously been characterized in late pregnant mouse uterus and placenta. However, little is known about its expression in the uterus during the implantation phase of early pregnancy. We have assessed the levels and localization of Tnfrsf9 expression in the mouse uterus and conceptus during implantation. Relative Tnfrsf9 mRNA levels were significantly higher in implantation than in non-implantation site tissue on days 6.5-8.5 of pregnancy. This increase did not depend on the presence of the conceptus, as mRNA levels were not significantly different between pregnant implantation sites and artificially induced deciduomas. Localization by in situ hybridization revealed a subpopulation of endothelial and uterine natural killer cells expressing Tnfrsf9 in the endometrium during implantation. In the developing conceptus, primary trophoblast giant and ectoplacental cells expressed Tnfrsf9 on days 6.5-8.5, followed by expression in the trophoblast giant cell layers surrounding the conceptus on day 9.5 of pregnancy. Two main splice forms of Tnfrsf9 mRNA exist and encode proteins with distinct biological functions; both mRNA splice forms were present in uterine and conceptus tissues as determined by reverse transcription with the polymerase chain reaction. Thus, both membrane and soluble forms of Tnfrsf9 are expressed in specific cell types of the uterus and conceptus during the progression of implantation in mice and possibly have an important function in this process.

Evidence for a conserved function of heart and neural crest derivatives expressed transcript 2 in mouse and human decidualization

Previously, we showed that heart and neural crest derivatives expressed transcript 2 (Hand2) mRNA levels dramatically increase in mouse uterine endometrial stromal cells (ESCs) as they undergo decidualization in vivo. However, to date, little is known about the expression and function of this transcription factor in mouse or human uterus decidualization. Therefore, this study was conducted to provide a more detailed assessment of Hand2 gene expression and function in the mouse uterus during the peri-implantation period and also in mouse plus human ESCs during decidualization in vitro. The results show that Hand2 mRNA and protein levels increase in the mouse uterus during decidualization and this does not depend on the presence of a conceptus. Interestingly, Hand2 mRNA and protein are present in ESCs adjacent to the luminal epithelium in the uterus prior to the onset of implantation. We find that progesterone is likely a regulator of Hand2 expression during uterine sensitization of the mouse uterus. Finally, Hand2 expression increases in mouse and human fibroblast cells as they undergo decidualization in vitro. This expression is significantly increased in response to prostaglandin E(2). In particular, reduction of Hand2 expression in these cells using small hairpin RNA or small interfering RNA approaches results in the reduced extent of decidualization as shown by the reduced expression of a subset of decidualization markers. The results of this study support the hypothesis that Hand2 expression not only plays an important role in decidualization but may also play a role in obtaining proper progesterone-dependent uterine sensitization required for implantation to begin.

Microarray assessment of the influence of the conceptus on gene expression in the mouse uterus during decidualization

During pregnancy in several species including humans and rodents, the endometrium undergoes decidualization. This process of differentiation from endometrial to decidual tissue occurs only after the onset of implantation in mice. It can also be artificially induced causing the formation of deciduomal tissue. The purpose of this study was to compare the gene expression profile of the developing decidua in pregnant mice with the deciduoma formed after artificial induction in an effort to identify conceptus-influenced changes in uterine gene expression during decidualization. We induced decidualization artificially by transferring blastocyst-sized ConA-coated agarose beads into the uterus on day 2.5 of pseudopregnancy. Recently published work has found this model to be more 'physiological' than other methods. Total RNA was isolated from blastocyst and bead-induced 'implantation' sites of the uteri of day 7.5 pregnant (decidua) and pseudopregnant (deciduoma) mice respectively. This RNA was then used for microarray analysis using Mouse Illumina BeadArray chips. This analysis revealed potential differential mRNA levels of only 45 genes between the decidua and bead-induced deciduoma tissues. We confirmed the differential mRNA levels of 31 of these genes using quantitative RT-PCR. Finally, the level and localization of some of the mRNAs for select genes (Aldh3a1, Bcmo1, Guca2b, and Inhbb) identified by our microarray analysis were examined in more detail. This study provides the identity of a small set of genes whose expression in the uterus during decidualization may be influenced by molecular signals from the conceptus.

Natural killer cell-triggered vascular transformation: maternal care before birth?

Natural killer (NK) cells are found in lymphoid and non-lymphoid organs. In addition to important roles in immune surveillance, some NK cells contribute to angiogenesis and circulatory regulation. The uterus of early pregnancy is a non-lymphoid organ enriched in NK cells that are specifically recruited to placental attachment sites. In species with invasive hemochorial placentation, these uterine natural killer (uNK) cells, via secretion of cytokines, chemokines, mucins, enzymes and angiogenic growth factors, contribute to the physiological change of mesometrial endometrium into the unique stromal environment called decidua basalis. In humans, uNK cells have the phenotype CD56(bright)CD16(dim) and they appear in great abundance in the late secretory phase of the menstrual cycle and early pregnancy. Gene expression studies indicate that CD56(bright)CD16(dim) uterine and circulating cells are functionally distinct. In humans but not mice or other species with post-implantation decidualization, uNK cells may contribute to blastocyst implantation and are of interest as therapeutic targets in female infertility. Histological and genetic studies in mice first identified triggering of the process of gestation spiral arterial modification as a major uNK cell function, achieved via interferon (IFN)-γ secretion. During spiral arterial modification, branches from the uterine artery that traverse the endometrium/decidua transiently lose their muscular coat and ability to vasoconstrict. The expression of vascular markers changes from arterial to venous as these vessels dilate and become low-resistance, high-volume channels. Full understanding of the vascular interactions of human uNK cells is difficult to obtain because endometrial time-course studies are not possible in pregnant women. Here we briefly review key information concerning uNK cell functions from studies in rodents, summarize highlights concerning human uNK cells and describe our preliminary studies on development of a humanized, pregnant mouse model for in vivo investigations of human uNK cell functions.

Estrogen regulates amiloride-binding protein 1 through CCAAT/enhancer-binding protein-beta in mouse uterus during embryo implantation and decidualization

Embryo implantation is an intricate interaction between receptive uterus and active blastocyst. The mechanism underlying embryo implantation is still unknown. Although histamine and putrescine are important for embryo implantation and decidualization, excess amount of histamine and putrescine is harmful. Amiloride binding protein 1 (Abp1) is a membrane-associated amine oxidase and mainly metabolizes histamine and putrescine. In this study, we first showed that Abp1 is strongly expressed in the decidua on d 5-8 of pregnancy. Abp1 expression is not detected during pseudopregnancy and under delayed implantation but is detected after estrogen activation. Because Abp1 is mainly localized in the decidua and also strongly expressed during in vitro decidualization, Abp1 might play a role during mouse decidualization. The regulation of estrogen on Abp1 is mediated by transcription factor CCAAT/enhancer-binding protein-β. Abp1 expression is also regulated by cAMP, bone morphogenetic protein 2, and ERK1/2. Abp1 may be essential for mouse embryo implantation and decidualization.

Deletion of the Isg15 gene results in up-regulation of decidual cell survival genes and down-regulation of adhesion genes: implication for regulation by IL-1beta

The ubiquitin homolog interferon stimulated gene 15 (ISG15) is up-regulated in the endometrium in response to pregnancy in primates, ruminants, pigs, and mice. ISG15 covalently attaches to intracellular proteins (isgylation) and regulates numerous intracellular responses. We hypothesized that ISG15 depletion (Isg15(-/-)) alters decidual tissue gene expression and that IL-1beta induces ISG15 expression and isgylation in cultured murine decidual explants and human uterine fibroblasts (HuFs). After studying the reproductive phenotype, contrary to earlier reports, up to 50% of the fetuses die between 7.5 and 12.5 d post coitum (dpc) in Isg15(-/-) mothers when mated to Isg15(-/-) fathers. Using microarray analysis, over 500 genes are differentially regulated in 7.5 dpc deciduas from Isg15(-/-) compared with Isg15(+/+) mice. The gene for interferon-inducible protein 202b, which functions in cell-survival mechanisms, was up-regulated (mRNA and protein) in deciduas from Isg15(-/-) mice. Culture of Isg15(+/+) mouse decidual explants (7.5 dpc) with IL-1beta decreased Isg15 mRNA but increased free and conjugated ISG15. In predecidual HuF cells, IL-1beta treatment increased ISG15 mRNA and isgylation. Additionally, IL-1beta up-regulated expression of enzymes (HERC5, UBCH8) that coordinate the covalent conjugation of ISG15 to target proteins, as well as the gene that encodes the deisglyation enzyme UBP43 in HuF cells. In conclusion, deletion of Isg15 gene results in 50% fetal loss after 7.5 dpc, which can be explained through differential decidual gene expression that is functionally tied to cell survival and adhesion pathways. This fetal death also might relate to impaired IL-1beta signaling, because ISG15 and isgylation are induced by IL-1beta in human and murine endometrial stromal cells.