Estrogen Receptors and Estrogen-Induced Uterine Vasodilation in Pregnancy.

Normal pregnancy is associated with dramatic increases in uterine blood flow to facilitate the bidirectional maternal-fetal exchanges of respiratory gases and to provide sole nutrient support for fetal growth and survival. The mechanism(s) underlying pregnancy-associated uterine vasodilation remain incompletely understood, but this is associated with elevated estrogens, which stimulate specific estrogen receptor (ER)-dependent vasodilator production in the uterine artery (UA). The classical ERs (ERα and ERß) and the plasma-bound G protein-coupled ER (GPR30/GPER) are expressed in UA endothelial cells and smooth muscle cells, mediating the vasodilatory effects of estrogens through genomic and/or nongenomic pathways that are likely epigenetically modified. The activation of these three ERs by estrogens enhances the endothelial production of nitric oxide (NO), which has been shown to play a key role in uterine vasodilation during pregnancy. However, the local blockade of NO biosynthesis only partially attenuates estrogen-induced and pregnancy-associated uterine vasodilation, suggesting that mechanisms other than NO exist to mediate uterine vasodilation. In this review, we summarize the literature on the role of NO in ER-mediated mechanisms controlling estrogen-induced and pregnancy-associated uterine vasodilation and our recent work on a "new" UA vasodilator hydrogen sulfide (H2S) that has dramatically changed our view of how estrogens regulate uterine vasodilation in pregnancy.

Estradiol-17ß stimulates H2 S biosynthesis by ER-dependent CBS and CSE transcription in uterine artery smooth muscle cells in vitro.

Endogenous hydrogen sulfide (H2 S), synthesized by cystathionine ß-synthase (CBS) and cystathionine γ-lyase (CSE), is a potent vasodilator that can be stimulated by estradiol-17ß (E 2 ß) in uterine artery (UA) smooth muscle (UASMC) in vivo; however, the underlying mechanisms are unknown. This study tested a hypothesis that E 2 ß stimulates H 2 S biosynthesis by upregulating CBS expression via specific estrogen receptor (ER). Treatment with E 2 ß stimulated time- and concentration- dependent CBS and CSE messenger RNA (mRNA) and protein expressions, and H 2 S production in cultured primary UASMC isolated from late pregnant ewes, which were blocked by ICI 182,780. Treatment with specific ERα or ERß agonist mimicked these E 2 ß-stimulated responses, which were blocked by specific ERα or ERß antagonist. Moreover, E 2 ß activated both CBS and CSE promoters and ICI 182,780 blocked the E 2 ß-stimulated responses. Thus, E 2 ß stimulates H 2 S production by upregulating CBS and CSE expression via specific ER-dependent transcription in UASMC in vitro.

Ovine uterine artery hydrogen sulfide biosynthesis in vivo: effects of ovarian cycle and pregnancy†.

Uterine vasodilation dramatically increases during the follicular phase of the estrous cycle and pregnancy, which are estrogen-dominant physiological states. Uterine vasodilation is believed to be mainly controlled by local uterine artery (UA) production of vasodilators and angiogenic factors. The extremely potent vasodilator and proangiogenic hydrogen sulfide (H2S) is synthesized via metabolizing L-cysteine by cystathionine ß-synthase (CBS) and cystathionine γ-lyase (CTH). This study was designed to determine if UA H2S production increases with augmented expression and/or activity of CBS and/or CTH during the ovarian cycle and pregnancy in sheep. Uterine arteries from intact nonpregnant (NP) luteal and follicular phase and late (130-135 days, term ≈ 145 days) pregnant (P) ewes were collected; endothelium-enriched proteins (UAendo) and endothelium-denuded smooth muscle (UAvsm) were mechanically prepared for accessing CBS and CTH proteins by immunoblotting; their cellular localization was determined by semi-quantitative immunofluorescence microscopy. H2S production was measured by the methylene blue assay. Immunoblotting revealed that CBS but not CTH protein was greater in P > > > NP follicular > luteal UAendo and UAvsm (P < 0.001). H2S production was greater in P > > > NP UAendo and UAvsm (P < 0.01). Pregnancy-augmented UAendo and UAvsm H2S production was inhibited by the specific CBS but not CTH inhibitor. CBS and CTH proteins were localized to both endothelium and smooth muscle; however, only CBS protein was significantly greater in P vs NP UA endothelium and smooth muscle. Thus, ovine UA H2S production is significantly augmented via selectively upregulating endothelium and smooth muscle CBS during the follicular phase and pregnancy in vivo.

E2ß stimulates ovine uterine artery endothelial cell H2S production in vitro by estrogen receptor-dependent upregulation of cystathionine ß-synthase and cystathionine γ-lyase expression†.

Endogenous hydrogen sulfide (H2S) is a potent vasodilator and proangiogenic second messenger synthesized from L-cysteine by cystathionine ß-synthase (CBS) and cystathionine γ-lyase (CTH). Estrogens are potent vasodilators that stimulate H2S biosynthesis in uterine arteries (UA) in vivo; however, the underlying mechanisms are unknown. We hypothesized that estrogens stimulate H2S biosynthesis in UA endothelial cells (UAEC) via specific estrogen receptor (ER)-dependent mechanisms. In cultured primary UAEC, treatment with estradiol-17ß (E2ß) stimulated CBS and CTH mRNAs and proteins in a time- and concentration-dependent fashion. As little as 0.1 nM E2ß was effective in increasing CBS and CTH expressions and these stimulatory effects maximized with 10-100 nM E2ß at 48-72 h. E2ß also activated CBS and CTH promoters in UAEC, leading to CBS and CTH expression. Treatment with E2ß stimulated H2S production, which was blocked by specific inhibitors of either CBS or CTH and their combination and the ER antagonist ICI 182780. Treatment with either specific agonist of ERα or ERß stimulated both CBS and CTH mRNA and protein expressions and H2S production to levels similar to that of E2ß. Specific antagonist of either ERα or ERß blocked E2ß-stimulated CBS and CTH mRNA and protein expressions and H2S production. Combinations of either ERα or ERß agonists or their antagonists had no additive effects. Thus, E2ß stimulates H2S production by upregulating CBS and CTH mRNA and protein expressions through specific ERα or ERß-dependent CBS and CTH transcription in UAEC in vitro.

Role of osteopontin in decidualization and pregnancy success.

OPN is essential for blastocyst implantation and placentation. Previous study found that miR181a was increased while miR181b was downregulated in endometrium during decidualization. However, the information regarding their effects on decidualization in human endometrium is still limited. Here, we report a novel role of OPN and miR181b in uterine decidualization and pregnancy success in humans. The expression of OPN was high in endometrium in secretory phase and in vitro decidualized hESC, whereas miR181b expression was low in identical conditions. Further analysis confirmed that OPN expression was upregulated by cAMP and C/EBPß signal pathway, while downregulated by miR181b. Increased OPN expression could promote the expression of decidualization-related and angiogenesis-related genes. Conversely, the processes of decidualization and angiogenesis in hESC were compromised by inhibiting OPN expression in vitro OPN expression was repressed in implantation failure group when compared with successful pregnancy group in IVF/ICSI-ET cycles. These findings add a new line of evidence supporting the fact that OPN is involved in decidualization and pregnancy success.

Warburg-like Glycolysis and Lactate Shuttle in Mouse Decidua during Early Pregnancy.

Decidualization is an essential process of maternal endometrial stromal cells to support pregnancy. Although it is known that enhanced glucose influx is critical for decidualization, the underlying mechanism in regulating glucose metabolism in decidua remains insufficiently understood. Here, we demonstrate that aerobic glycolysis-related genes and factors are all substantially induced during decidualization, indicating the existence of Warburg-like glycolysis in decidua. In vitro, progesterone activates hypoxia-inducible factor 1α (Hif1α) and c-Myc through Pi3k-Akt signaling pathway to maintain aerobic glycolysis in decidualizing cells. Knocking down of pyruvate kinase M2 (Pkm2) attenuates the induction of decidual marker gene. Decidual formation in vivo is also impaired by glycolysis inhibitor 3-bromopyruvate. Besides, lactate exporter monocarboxylate transporter 4 (Mct4) is induced in newly formed decidual cells, whereas lactate importer Mct1 and proliferation marker Ki-67 are complementarily located in the surrounding undifferentiated cells, which are supposed to consume lactate for proliferation. Hif1α activation is required for lactate-dependent proliferation of the undifferentiated cells. Inhibition of lactate flux leads to compromised decidualization and decelerated lactate-dependent proliferation. In summary, we reveal that Warburg-like glycolysis and local lactate shuttle are activated in decidua and play important roles for supporting early pregnancy.

Progesterone and DNA damage encourage uterine cell proliferation and decidualization through up-regulating ribonucleotide reductase 2 expression during early pregnancy in mice.

Embryo implantation into the maternal uterus is a crucial step for the successful establishment of mammalian pregnancy. Following the attachment of embryo to the uterine luminal epithelium, uterine stromal cells undergo steroid hormone-dependent decidualization, which is characterized by stromal cell proliferation and differentiation. The mechanisms underlying steroid hormone-induced stromal cell proliferation and differentiation during decidualization are still poorly understood. Ribonucleotide reductase, consisting of two subunits (RRM1 and RRM2), is a rate-limiting enzyme in deoxynucleotide production for DNA synthesis and plays an important role in cell proliferation and tumorgenicity. Based on our microarray analysis, Rrm2 expression was significantly higher at implantation sites compared with interimplantation sites in mouse uterus. However, the expression, regulation, and function of RRM2 in mouse uterus during embryo implantation and decidualization are still unknown. Here we show that although both RRM1 and RRM2 expression are markedly induced in mouse uterine stromal cells undergoing decidualization, only RRM2 is regulated by progesterone, a key regulator of decidualization. Further studies showed that the induction of progesterone on RRM2 expression in stromal cells is mediated by the AKT/c-MYC pathway. RRM2 can also be induced by replication stress and DNA damage during decidualization through the ATR/ATM-CHK1-E2F1 pathway. The weight of implantation sites and deciduoma was effectively reduced by specific inhibitors for RRM2. The expression of decidual/trophoblast prolactin-related protein (Dtprp), a reliable marker for decidualization in mice, was significantly reduced in deciduoma and steroid-induced decidual cells after HU treatment. Therefore, RRM2 may be an important effector of progesterone signaling to induce cell proliferation and decidualization in mouse uterus.

Uterine micro-environment and estrogen-dependent regulation of osteopontin expression in mouse blastocyst.

Embryo implantation is a highly synchronized bioprocess between an activated blastocyst and a receptive uterus. In mice, successful implantation relies on the dynamic interplay of estrogen and progesterone; however, the key mediators downstream of these hormones that act on blastocyst competency and endometrium receptivity acquisition are largely unknown. In this study, we showed that the expression of osteopontin (OPN) in mouse blastocysts is regulated by ovarian estrogen and uterine micro-environment. OPN mRNA is up-regulated in mouse blastocyst on day 4 of pregnancy, which is associated with ovarian estrogen secretion peak. Hormone treatment in vivo demonstrated that OPN expression in a blastocyst is regulated by estrogen through an estrogen receptor (ER). Our results of the delayed and activated implantation model showed that OPN expression is induced after estrogen injection. While estrogen treatment during embryo culture in vitro showed less effect on OPN expression, the tubal ligation model on day 3 of pregnancy confirmed that the regulation of estrogen on OPN expression in blastocyst might, through some specific cytokines, have existed in a uterine micro-environment. Collectively, our study presents that estrogen regulates OPN expression and it may play an important role during embryo implantation by activating blastocyst competence and facilitating the endometrium acceptable for active blastocyst.

Enhanced Stromal Cell CBS-H2S Production Promotes Estrogen-Stimulated Human Endometrial Angiogenesis.

Angiogenesis is a physiological process for endometrial regeneration in the menstrual cycle and remodeling during pregnancy. Endogenous hydrogen sulfide (H2S), produced by cystathionine-ß synthase (CBS) and cystathionine-γ lyase (CSE), is a potent proangiogenic factor; yet, whether the H2S system is expressed in the endometrium and whether H2S plays a role in endometrial angiogenesis are unknown. This study was to test whether estrogens stimulate endometrial H2S biosynthesis to promote endometrial microvascular endothelial cell (EMEC) angiogenesis. CBS messenger RNA/protein and H2S production significantly differed among endometria from postmenopausal (POM), premenopausal secretory (sPRM), and proliferative (pPRM) nonpregnant (NP) and pregnant (Preg) women (P < .05) in a rank order of POM approximately equal to sPRM is less than pPRM is less than Preg, positively correlating with angiogenesis indices and endogenous estrogens and with no difference in CSE expression. CBS and CSE proteins were localized to stroma, glands, and vessels in endometrium, and greater stromal CBS protein was observed in the pPRM and Preg states. Estradiol-17ß (E2) (but not progesterone) stimulated CBS (but not CSE) expression and H2S production in pPRM endometrial stromal cells (ESCs) in vitro, which were attenuated by ICI 182 780. The H2S donor sodium hydrosulfide promoted in vitro EMEC angiogenesis. Co-culture with sPRM, pPRM, and Preg ESCs all stimulated EMEC migration with a rank order of sPRM less than pPRM approximately equal to Preg. CBS (but not CSE) inhibition attenuated ESC-stimulated EMEC migration. E2 did not affect EMEC migration but potentiated ESC-stimulated EMEC migration. Altogether, estrogens stimulate specific receptor-dependent stromal CBS-H2S production to promote endometrial EMEC angiogenesis in women.

Estrogen Receptor-ß Mediates Estradiol-Induced Pregnancy-Specific Uterine Artery Endothelial Cell Angiotensin Type-2 Receptor Expression.

The pregnancy-augmented uterine vasodilation is linked to increased AT2R (angiotensin type-2 receptor) that mediates the vasodilatory effects of angiotensin II. However, the mechanisms controlling AT2R expression during pregnancy remain unclear. Estrogens are known to play a role in vascular adaptations during pregnancy. We hypothesized that estrogen stimulates uterine artery AT2R expression via ER (estrogen receptor)-ß-dependent transcription in a pregnancy-specific endothelium-dependent manner. Plasma estradiol levels increased and peaked in late pregnancy and returned to prepregnant levels post-partum, correlating with uterine artery AT2R and ERß upregulation. Estradiol stimulated AT2R mRNA expression in endothelium-intact but not endothelium-denuded late pregnant and nonpregnant rat uterine artery ex vivo. Consistently, estradiol stimulated AT2R mRNA expression in late pregnant but not nonpregnant primary human uterine artery endothelial cells in vitro, which was abolished by ER antagonist ICI 182,780. Higher ERα protein bound to ER-responsive elements in AT2R promoter in the nonpregnant arteries whereas higher ERß bound in the pregnant state. ERα protein levels were similar but higher ERß protein levels were expressed in pregnant versus nonpregnant human uterine artery endothelial cells. Estradiol stimulation recruited ERα to the AT2R promoter in the nonpregnant state and ERß to the AT2R promoter in pregnancy; however, only ERß recruitment mediated transactivation of the AT2R reporter gene in pregnant human uterine artery endothelial cells. Estradiol-induced AT2R expression was abolished by the specific ERß (not ERα) antagonist 4-[2-Phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl]phenol (PHTPP) and mimicked by the specific ERß (not ERα) agonist 2,3-bis(4-Hydroxyphenyl)-propionitrile (DPN) in pregnant human uterine artery endothelial cells in vitro. This study demonstrates a novel role of pregnancy-augmented ERß in AT2R upregulation in the uterine artery and provides new insights into the mechanisms underlying uterine vascular adaptation to pregnancy.

Effect of Progestin-primed Ovarian Stimulation Protocol on Outcomes of Aged Infertile Women Who Failed to Get Pregnant in the First IVF/ ICSI Cycle: A Self-controlled Study.

This study aimed to explore the outcomes of progestin-primed ovarian stimulation protocol (PPOS) in aged infertile women who failed to get pregnant in the first IVF/ICSI-ET cycles with GnRH-a long protocol. A self-controlled study was conducted to retrospectively investigate the clinical outcomes of 104 aged infertile patients who didn't get pregnant in the first IVF/ICSI-ET treatment by stimulating with GnRH-a long protocol (non-PPOS group), and underwent PPOS protocol (PPOS group) in the second cycle between January 2016 and December 2016 in the Center for Reproductive Medicine, Renmin Hospital of Wuhan University. The primary outcomes included clinical pregnancy rate of frozen-thawed embryos transfer (FET) in PPOS group, and good-quality embryo rate in both groups. The secondary outcomes were fertilization rate, egg utilization rate and cycle cancellation rate. The results showed that there were no significant differences in basal follicle stimulating hormone (bFSH), antral follicle count (AFC), duration and total dosage of gonadotropin (Gn), number of oocytes retrieved, intracytoplasmic sperm injection (ICSI) rate, fertilization rate, and cycle cancellation rate between the two groups (P>0.05). However, the oocyte utilization rate and good-quality embryo rate in PPOS group were significantly higher than those in non-PPOS group (P<0.05). By the end of April 2017,62 FET cycles were conducted in PPOS group. The clinical pregnancy rate and embryo implantation rate were 22.58% and 12.70%, respectively. In conclusion, PPOS protocol may provide better clinical outcomes by improving the oocyte utilization rate and good-quality embryo rate for aged infertile patients who failed to get pregnant in the first IVF/ICSI-ET cycles.

De novo synthesis of sphingolipids is essential for decidualization in mice.

Sphingolipids play multiple roles in membrane structure, signal transduction, stress responses, neural development and immune reaction. The rate of de novo synthesis pathway of sphingolipids is regulated by two key enzymes, serine palmitoyltransferase (SPT), and ketoreductase (Kds). Here, we find that the mRNA levels of three subunits of the SPT holoenzyme (Sptlc1, Sptlc2, and Ssspta) are significantly up-regulated in mouse uterine stromal cells during decidualization. The expression of Kds, which reduces 3-keto-dihydrosphingosine to dihydrosphingosine, is co-localized with Sptlc1 in mouse uteri during early pregnancy. Moreover, l-Cycloserine, a specific inhibitor of SPT, can significantly decrease the weight and number of implantation sites, and impede the decidualization process in mouse uterine stromal cells, suggesting that blockage of de novo sphingolipid synthesis may cause defective decidualization and early pregnancy loss in mice. In addition, this study also shows progesterone (P4) can stimulate the expression of both Sptlc2 and Ssspta in mouse uterus. Therefore, our study shows that de novo synthesis of sphingolipids is necessary in implantation and plays a key role in decidualization of mouse.

Reproductive outcomes in women with prior cesarean section undergoing in vitro fertilization: A retrospective case-control study.

The impact of prior cesarean section (CS) on the pregnancy and neonatal outcomes of in vitro fertilization and embryo transfer (IVF-ET) was investigated. A retrospective analysis was performed on 144 patients with prior CS between January 2013 and December 2015. The pregnancy, delivery, and neonatal outcomes of patients who had previous CS delivery and received IVF-ET were analyzed. The control group comprised 166 patients who had only previous vaginal delivery (VD) and received IVF-ET during the same period. The results showed that the basal follicle stimulating hormone level, estradiol level on human chorionic gonadotropin (hCG) day, gonadotrophin dosage, duration of stimulation, retrieved oocytes, fertilization rate, high-quality embryo rate, multiple birth rate, abortion rate and ectopic pregnancy rate had no significant difference between the two groups (P>0.05). The pregnancy rate (40.28% vs. 54.22%) and implantation rate (24.01% vs. 34.67%) were significantly lower (P<0.05), and the ratio of embryo difficulty transfer (9/144 vs. 0/166) was significantly higher in CS group than in VD group. The risk of pernicious placenta previa and postpartum hemorrhage in twin deliveries was significantly increased in CS group as compared with that in VD group (P<0.05), and gestational age and neonatal birth weight were significantly reduced in twin deliveries as compared with singleton deliveries in both groups (P<0.05). It was suggested that the existence of CS scar may impact embryo implantation and clinical pregnancy outcome, and increase the difficulty of ET. We should limit the number of transfer embryos to avoid multiple pregnancies and strengthen gestational supervision in patients with cesarean scar.

Patients with cervical Ureaplasma Urealyticum and Chlamydia Trachomatis infection undergoing IVF/ICSI-ET: The need for new paradigm.

Genital tract infections with ureaplasma urealyticum (UU) and chlamydia trachomatis (CT) are the most frequent sexually-transmitted disease worldwide. UU and CT infections are considered to be the leading cause for infertility and adverse pregnancy outcomes. However, little is known about the specific effect of cervical UU and CT infections on the etiology of female infertility, as well as the pregnancy outcomes of the patients undergoing in vitro fertilization/intracytoplasmic sperm injection-embryo transfer (IVF/ICSI-ET). In order to find the association between cervical UU and/or CT infection and pregnancy outcomes, we conducted a retrospective case-control study on the patients undergoing IVF/ICSI-ET with cervical UU and/or CT infection. A total of 2208 patients who received IVF/ICSI-ET were enrolled in this study. Data on the general conditions, pregnancy history and clinical pregnant outcomes were analyzed in terms of the cervical UU and CT detection. Our results revealed that cervical UU and CT infections were the risk factors for ectopic pregnancy and tubal factor-induced infertility. Moreover, the pregnancy rate, abortion rate, ectopic pregnancy rate and premature birth rate in patients with UU and/or CT infections showed no significant difference when compared with the control group. We recommend that cervical UU and CT detection should be an optional item for infertility patients and clinical UU detection should differentiate the subtypes of cervical UU. Positive cervical UU and CT infections should not be taken as strict contraindications for IVF/ICSI-ET.

Involvement of atypical transcription factor E2F8 in the polyploidization during mouse and human decidualization.

Polyploid decidual cells are specifically differentiated cells during mouse uterine decidualization. However, little is known about the regulatory mechanism and physiological significance of polyploidization in pregnancy. Here we report a novel role of E2F8 in the polyploidization of decidual cells in mice. E2F8 is highly expressed in decidual cells and regulated by progesterone through HB-EGF/EGFR/ERK/STAT3 signaling pathway. E2F8 transcriptionally suppresses CDK1, thus triggering the polyploidization of decidual cells. E2F8-mediated polyploidization is a response to stresses which are accompanied by decidualization. Interestingly, polyploidization is not detected during human decidualization with the down-regulation of E2F8, indicating differential expression of E2F8 may lead to the difference of decidual cell polyploidization between mice and humans.

Dysregulated LIF-STAT3 pathway is responsible for impaired embryo implantation in a Streptozotocin-induced diabetic mouse model.

The prevalence of diabetes is increasing worldwide with the trend of patients being young and creating a significant burden on health systems, including reproductive problems, but the effects of diabetes on embryo implantation are still poorly understood. Our study was to examine effects of diabetes on mouse embryo implantation, providing experimental basis for treating diabetes and its complications. Streptozotocin (STZ) was applied to induce type 1 diabetes from day 2 of pregnancy or pseudopregnancy in mice. Embryo transfer was used to analyze effects of uterine environment on embryo implantation. Our results revealed that the implantation rate is significantly reduced in diabetic mice compared to controls, and the change of uterine environment is the main reason leading to the decreased implantation rate. Compared to control, the levels of LIF and p-STAT3 are significantly decreased in diabetic mice on day 4 of pregnancy, and serum estrogen level is significantly higher. Estrogen stimulates LIF expression under physiological level, but the excessive estrogen inhibits LIF expression. LIF, progesterone or insulin supplement can rescue embryo implantation in diabetic mice. Our data indicated that the dysregulated LIF-STAT3 pathway caused by the high level of estrogen results in the impaired implantation in diabetic mice, which can be rescued by LIF, progesterone or insulin supplement.

Regulation and function of signal transducer and activator of transcription 3.

Signal transducer and activator of transcription 3 (STAT3), a member of the STAT family, is a key regulator of many physiological and pathological processes. Significant progress has been made in understanding the transcriptional control, posttranslational modification, cellular localization and functional regulation of STAT3. STAT3 can translocate into the nucleus and bind to specific promoter sequences, thereby exerting transcriptional regulation. Recent studies have shown that STAT3 can also translocate into mitochondria, participating in aerobic respiration and apoptosis. In addition, STAT3 plays an important role in inflammation and tumorigenesis by regulating cell proliferation, differentiation and metabolism. Conditional knockout mouse models make it possible to study the physiological function of STAT3 in specific tissues and organs. This review summarizes the latest advances in the understanding of the expression, regulation and function of STAT3 in physiological and tumorigenic processes.

Osteopontin is expressed in the mouse uterus during early pregnancy and promotes mouse blastocyst attachment and invasion in vitro.

Embryo implantation into the maternal uterus is a decisive step for successful mammalian pregnancy. Osteopontin (OPN) is a member of the small integrin-binding ligand N-linked glycoprotein family and participates in cell adhesion and invasion. In this study, we showed that Opn mRNA levels are up-regulated in the mouse uterus on day 4 and at the implantation sites on days 5 and 8 of pregnancy. Immunohistochemistry localized the OPN protein to the glandular epithelium on day 4 and to the decidual zone on day 8 of pregnancy. OPN mRNA and proteins are induced by in vivo and in vitro decidualization. OPN expression in the endometrial stromal cells is regulated by progesterone, a key regulator during decidualization. As a secreted protein, the protein level of OPN in the uterine cavity is enriched on day 4, and in vitro embryo culturing has indicated that OPN can facilitate blastocyst hatching and adhesion. Knockdown of OPN attenuates the adhesion and invasion of blastocysts in mouse endometrial stromal cells by suppressing the expression and enzymatic activity of matrix metalloproteinase-9 in the trophoblast. Our data indicated that OPN expression in the mouse uterus during early pregnancy is essential for blastocyst hatching and adhesion and that the knockdown of OPN in mouse endometrial stroma cells could lead to a restrained in vitro trophoblast invasion.

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.

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.