Chorionic gonadotropin regulates prostaglandin E synthase via a phosphatidylinositol 3-kinase-extracellular regulatory kinase pathway in a human endometrial epithelial cell line: implications for endometrial responses for embryo implantation

Expression and function of the luteinizing hormone choriogonadotropin receptor in human endometrial stromal cells

The human luteinising hormone choriogonadotropin receptor (LHCGR) is a G-protein coupled receptor activated by both human chorionic gonadotropin (hCG) and luteinizing hormone (LH), two structurally related gonadotropins with essential roles in ovulation and maintenance of the corpus luteum. LHCGR expression predominates in ovarian tissues where it elicits functional responses through cyclic adenosine mononucleotide (cAMP), Ca²⁺ and extracellular signal-regulated kinase (ERK) signalling. LHCGR expression has also been localized to the human endometrium, with purported roles in decidualization and implantation. However, these observations are contentious. In this investigation, transcripts encoding LHCGR were undetectable in bulk RNA sequencing datasets from whole cycling endometrial tissue and cultured human endometrial stromal cells (EnSC). However, analysis of single-cell RNA sequencing data revealed cell-to-cell transcriptional heterogeneity, and we identified a small subpopulation of stromal cells with detectable LHCGR transcripts. In HEK-293 cells expressing recombinant LHCGR, both hCG and LH elicited robust cAMP, Ca²⁺ and ERK signals that were absent in wild-type HEK-293 cells. However, none of these responses were recapitulated in primary EnSC cultures. In addition, proliferation, viability and decidual transformation of EnSC were refractory to both hCG and LH, irrespective of treatment to induce differentiation. Although we challenge the assertion that LHCGR is expressed at a functionally active level in the human endometrium, the discovery of a discrete subpopulation of EnSC that express LHCGR transcripts may plausibly account for the conflicting evidence in the literature.

Transcriptomic analysis shows that surgical treatment is likely to influence the endometrial receptivity of patients with stage III/IV endometriosis

BACKGROUND

Endometriosis negatively affects fertility, and it is a common disease in assisted reproductive practice. Surgical removal of endometriotic lesions is widely carried out to relieve symptoms and promote fertility. But it is not intensively investigated what changes in the secretory eutopic endometrium of patients with endometriosis after surgery.

METHODS

Eighteen patients with stage III/IV endometriosis were included in the study, and they were divided into the untreated group and the treated group (6 vs. 12). Basic clinical data were compared, and transcriptomic data of the secretory eutopic endometrium were analyzed with DESeq2, Cytoscape, ClueGO, CluePedia, and Gene Set Enrichment Analysis (GSEA). CIBERSORT was used to calculate the relative abundance of 22 immune cells in the samples.

RESULTS

We determined 346 differentially expressed genes (DEGs) using DESeq2. These DEGs were used to enrich seven Gene Ontology terms including three associated with immune processes and one correlated to prostaglandin using ClueGO and CluePedia. GSEA enriched 28 Gene Ontology terms in the treated group mainly associated with immune and blood pressure regulation process. Compared to the untreated group, the relative abundance of resting CD4+ memory T cells [0.218 (0.069, 0.334) vs. 0.332 (0.181, 0.429), P = 0.022] and the even less abundant memory B cells [0.001 (0.000, 0.083) vs. 0.033 (0.007, 0.057), P = 0.049] are significantly decreased in the treated group.

CONCLUSION

Surgical treatment of stage III/IV endometriosis influences some genes and biological processes related to endometrial receptivity, but more evidence is needed.

Main actors behind the endometrial receptivity and successful implantation

Embryo implantation occurs during a short period of time, the implantation window, in the mid-secretory phase of the menstrual cycle. The cross-talk between the endometrium and the embryo, at the stage of blastocyst, is a necessary condition for successful implantation. Till now, no single molecule or receptor has been identified to play an essential role on embryo implantation but a huge number of mediators, including cytokines, lipids, adhesion molecules, growth factors, and others, are reported to support the establishment of pregnancy. Therefore, the aim of this review is not only to describe the different actors involved in the implantation process, but also to try to characterize the relationships between these factors as well as their time-regulated activation. Moreover, the availability of in vitro culture systems to study the interactions between embryo and endometrium as well as the paracrine communication regulated by exosomal vesicles will be investigated, as an innovative approach for a more precise characterization of the interactions between the different molecules involved in this process. The in-depth knowledge of all these complex mechanisms will allow to address the reasons of implantation failure and infertility, thus providing new avenues for promoting the successful establishment of a pregnancy.

CXCL12 enhances pregnancy outcome via improvement of endometrial receptivity in mice

Successful pregnancy inevitably depends on the implantation of a competent embryo into a receptive endometrium. Although many substances have been suggested to improve the rate of embryo implantation targeting enhancement of endometrial receptivity, currently there rarely are effective evidence-based treatments to prevent or cure this condition. Here we strongly suggest minimally-invasive intra-uterine administration of embryo-secreted chemokine CXCL12 as an effective therapeutic intervention. Chemokine CXCL12 derived from pre- and peri-implanting embryos significantly enhances the rates of embryo attachment and promoted endothelial vessel formation and sprouting in vitro. Consistently, intra-uterine CXCL12 administration in C57BL/6 mice improved endometrial receptivity showing increased integrin β3 and its ligand osteopontin, and induced endometrial angiogenesis displaying increased numbers of vessel formation near the lining of endometrial epithelial layer with higher CD31 and CD34 expression. Furthermore, intra-uterine CXCL12 application dramatically promoted the rates of embryo implantation with no morphologically retarded embryos. Thus, our present study provides a novel evidence that improved uterine endometrial receptivity and enhanced angiogenesis induced by embryo-derived chemokine CXCL12 may aid to develop a minimally-invasive therapeutic strategy for clinical treatment or supplement for the patients with repeated implantation failure with less risk.

N- and O-glycosylation patterns and functional testing of CGB7 versus CGB3/5/8 variants of the human chorionic gonadotropin (hCG) beta subunit

The classical function of human chorionic gonadotropin (hCG) is its role in supporting pregnancy. hCG is a dimer consisting of two highly glycosylated subunits, alpha (CGA) and beta (CGB). The beta-hCG protein is encoded by CGB3, CGB5, CGB7 and CGB8 genes. CGB3, 5 and 8 code for an identical protein, CGB3/5/8, whereas CGB7 differs in three amino acids from CGB3/5/8. We had observed earlier that CGB7 and CGB3/5/8 display very distinct tissue expression patterns and that the tumor suppressor and transcription factor p53 can activate expression of CGB7 but not of CGB3/5/8 genes. Here, we investigate the glycan structures and possible functional differences of the two CGB variants. To this end, we established a system to produce and isolate recombinant CGA, CGB7 and CGB3/5/8 proteins. We found that N- and O-glycosylation patterns of CGB7 and CGB3/5/8 are quite similar. Functional assays were performed by testing activation of the ERK1/2 pathway and demonstrated that CGB7 and CGB5/5/8 appear to be functionally redundant isoforms, although a slight difference in the kinetics of ERK1/2 pathway activation was observed. This is the first time that biological activity of CGB7 is shown. In summary, the results lead to the hypothesis that CGB7 and CGB3/5/8 do not hold significant functional differences but that timing and cell type of their expression is the key for understanding their divergent evolution.

Molecular Signaling Regulating Endometrium-Blastocyst Crosstalk

Implantation of the embryo into the uterine endometrium is one of the most finely-regulated processes that leads to the establishment of a successful pregnancy. A plethora of factors are released in a time-specific fashion to synchronize the differentiation program of both the embryo and the endometrium. Indeed, blastocyst implantation in the uterus occurs in a limited time frame called the "window of implantation" (WOI), during which the maternal endometrium undergoes dramatic changes, collectively called "decidualization". Decidualization is guided not just by maternal factors (e.g., estrogen, progesterone, thyroid hormone), but also by molecules secreted by the embryo, such as chorionic gonadotropin (CG) and interleukin-1β (IL-1 β), just to cite few. Once reached the uterine cavity, the embryo orients correctly toward the uterine epithelium, interacts with specialized structures, called pinopodes, and begins the process of adhesion and invasion. All these events are guided by factors secreted by both the endometrium and the embryo, such as leukemia inhibitory factor (LIF), integrins and their ligands, adhesion molecules, Notch family members, and metalloproteinases and their inhibitors. The aim of this review is to give an overview of the factors and mechanisms regulating implantation, with a focus on those involved in the complex crosstalk between the blastocyst and the endometrium.

Transcriptome Changes in the Mink Uterus during Blastocyst Dormancy and Reactivation

Embryo implantation in the mink follows the pattern of many carnivores, in that preimplantation embryo diapause occurs in every gestation. Details of the gene expression and regulatory networks that terminate embryo diapause remain poorly understood. Illumina RNA-Seq was used to analyze global gene expression changes in the mink uterus during embryo diapause and activation leading to implantation. More than 50 million high quality reads were generated, and assembled into 170,984 unigenes. A total of 1684 differential expressed genes (DEGs) in uteri with blastocysts in diapause were compared to the activated embryo group (p < 0.05). Among these transcripts, 1527 were annotated as known genes, including 963 up-regulated and 564 down-regulated genes. The gene ontology terms for the observed DEGs, included cellular communication, phosphatase activity, extracellular matrix and G-protein couple receptor activity. The KEGG pathways, including PI3K-Akt signaling pathway, focal adhesion and extracellular matrix (ECM)-receptor interactions were the most enriched. A protein-protein interaction (PPI) network was constructed, and hub nodes such as VEGFA, EGF, AKT, IGF1, PIK3C and CCND1 with high degrees of connectivity represent gene clusters expected to play an important role in embryo activation. These results provide novel information for understanding the molecular mechanisms of maternal regulation of embryo activation in mink.

Prostaglandin E2 involvement in mammalian female fertility: ovulation, fertilization, embryo development and early implantation

BACKGROUND

Infertility in mammalian females has been a challenge in reproductive medicine. The causes of female infertility include anovulation, ovulated oocyte defects, abnormal fertilization, and insufficient luteal support for embryo development, as well as early implantation. Ovulation induction, in vitro fertilization and luteal support regimens have been performed for decades to increase fertility rates. The identification of proteins and biochemical factors involved in female reproduction is essential to further increase female fertility rates. Evidence has shown that prostaglandins (PGs) might be involved in the female reproductive process, mainly ovulation, fertilization, and implantation. However, only a few studies on individual PGs in female reproduction have been done so far. This review aimed to identify the pivotal role of prostaglandin E2 (PGE2), a predominant PG, in female reproduction to improve fertility, specifically ovulation, fertilization, embryo development and early implantation.

RESULTS

Prostaglandin E2 (PGE2) was shown to play a relevant role in the ovulatory cascade, including meiotic maturation, cumulus expansion and follicle rupture, through inducing ovulatory genes, such as Areg, Ereg, Has2 and Tnfaip6, as well as increasing intracellular cAMP levels. PGE2 reduces extracellular matrix viscosity and thereby optimizes the conditions for sperm penetration. PGE2 reduces the phagocytic activity of polymorphonuclear neutrophils (PMNs) against sperm. In the presence of PGE2, sperm function and binding capacity to oocytes are enhanced. PGE2 maintains luteal function for embryo development and early implantation. In addition, it induces chemokine expression for trophoblast apposition and adhesion to the decidua for implantation.

CONCLUSION

It has been shown that PGE2 positively affects different stages of female fertility. Therefore, PGE2 should be taken into consideration when optimizing reproduction in infertile females. We suggest that in clinical practice, the administration of non-steroidal anti-inflammatory drugs, which are PGE2 synthesis inhibitors, should be reasonable and limited in infertile women. Additionally, assessments of PGE2 protein and receptor expression levels should be taken into consideration.

hCG activates Epac-Erk1/2 signaling regulating Progesterone Receptor expression and function in human endometrial stromal cells

STUDY QUESTION

How does hCG signal in human endometrial stromal cells (ESCs) and what is its role in regulating ESC function?

SUMMARY ANSWER

hCG signaling in ESCs activates the extracellular signal-regulated protein kinases 1 and 2 (Erk1/2) pathway through exchange protein activated by cyclic AMP (cAMP) (Epac) and transiently increases progesterone receptor (PR) transcript and protein expression and its transcriptional function.

WHAT IS KNOWN ALREADY

hCG is one of the earliest embryo-derived secreted signals in the endometrium, which abundantly expresses LH/hCG receptors. hCG signals through cAMP/protein kinase A (PKA) in gonadal cells, but in endometrial epithelial cells, hCG induces Erk1/2 activation independent of the cAMP/PKA pathway. Few data exist concerning the signal transduction pathways triggered by hCG in ESCs and their role in regulation of ESC function.

STUDY DESIGN, SIZE, DURATION

This is an in vitro study comprising patients undergoing benign gynecological surgery (n = 46).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Endometrial samples were collected from normal cycling women during the mid-secretory phase for ESCs isolation. The study conducted in an academic research laboratory within a tertiary-care hospital. The activation of the Erk1/2 signal transduction pathway elicited by hCG was evaluated in ESC. Signaling pathway inhibitors were used to examine the roles of PKA, PI3K, PKC, adenylyl cyclase and Epac on the hCG-stimulated up-regulation of phospho-Erk1/2 (pErk1/2). Erk1/2 phosphorylation was determined by immunoblot. siRNA targeting Epac was used to investigate the molecular mechanisms. To assess the role of Erk1/2 signaling induced by hCG on ESC function, gene expression regulation was examined by immunofluorescence and real-time quantitative PCR. The role of PR on the regulation of transcript levels was studied using progesterone and the PR antagonist RU486. All experiments were conducted using at least three different cell culture preparations in triplicate.

MAIN RESULTS AND THE ROLE OF CHANCE

Addition of hCG to ESCs in vitro induced the phosphorylation of Erk1/2 through cAMP accumulation. Such induction could not be blocked by inhibitors for PKA, PKC and PI3K. Epac inhibition and knockdown with siRNA prevented pErk1/2 induction by hCG. ESCs stimulated with hCG for up to 72 h showed a significant increase in PR mRNA and immunofluorescent label at 48 h only; an effect that was abrogated with the mitogen-activated protein kinase kinase inhibitor UO126. In addition, the hCG-activated Erk1/2 pathway significantly decreased the mRNA levels for secreted frizzled-related protein 4 (SFRP4) at 24 h, whereas it increased those for homeobox A10 (HOXA10) at 48 h (P = 0.041 and P = 0.022 versus control, respectively). Prolactin mRNA levels were not significantly modified. HOXA10 mRNA up-regulation by hCG was not enhanced by co-stimulation with progesterone; however, it was completely abolished in the presence of RU486 (P = 0.036 hCG versus hCG + RU486).

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

This is an in vitro study utilizing stromal cell cultures from human endometrial tissues. Furthermore, results obtained should also be confirmed in vivo in the context of the whole human endometrial tissue and hormonal milieu. The in vitro experiments using hCG have been conducted without other hormones/factors that may also modulate the ESCs response to hCG.

WIDER IMPLICATIONS OF THE FINDINGS

We have determined that hCG induces the PR through the Erk1/2 pathway in ESCs which may render them more sensitive to progesterone, increasing our understanding about the effects of hCG at the embryo-maternal interface. The activation of such a pathway in the context of the hormonal milieu during the window of implantation might contribute to a successful dialog between the embryo and the uterus, leading to appropriate endometrial function. Defective hCG signaling in the endometrial stromal tissue may lead to an incomplete uterine response, compromising embryo implantation and early pregnancy.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Fund for Scientific and Technological Development, Government of Chile (FONDECYT) grants 11100443 and 1140614 (A.T.-P.). The authors have no conflicts of interest to declare.

Ovarian-like differentiation in eutopic and ectopic endometrioses with aberrant FSH receptor, INSL3 and GATA4/6 expression

Endometriosis, the hormone-dependent extrauterine dissemination of endometrial tissue outside the uterus, affects 5–15% of women of reproductive age. Pathogenesis remains poorly understood as well as the estrogen production by endometriotic tissue yielding autocrine growth. Estrogens (E2) are normally produced by the ovaries. We investigated whether aberrant “ovarian-like” differentiation occurred in endometriosis.

69 women, with (n = 38) and without (n = 31) histologically proven endometriosis were recruited. Comparative RT-qPCR was performed on 20 genes in paired eutopic and ectopic lesions, together with immunohistochemistry. Functional studies were performed in primary cultures of epithelial endometriotic cells (EEC).

A broaden ovarian-like differentiation was found in half eutopic and all ectopic endometriosis with aberrant expression of transcripts and protein for the transcription factors GATA4 and GATA6 triggering ovarian differentiation, for the FSH receptor (FSHR) and the ovarian hormone INSL3. Like in ovaries the FSHR induced aromatase, the key enzyme in E2 production, and vascular factors in EEC. The LH receptor (LHR) was also aberrantly expressed in a subset of ectopic endometriosis (21%) and induced strongly androgen-synthesizing enzymes and INSL3 in EEC, as in ovaries, as well as endometriotic cell growth. The ERK pathway mediates signaling by both hormones. A positive feedback loop occurred through FSHR and LHR-dependent induction of GATA4/6 in EEC, as in ovaries, enhancing the production of the steroidogenic cascade.

This work highlights a novel pathophysiological mechanism with a broadly ovarian pattern of differentiation in half eutopic and all ectopic endometriosis. This study provides new tools that might improve the diagnosis of endometriosis in the future.

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In endometriosis aberrant E2 production raises questions on ovarian differentiation.

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FSHR and INSL3 upregulation in eutopic/ectopic, and LHR in ectopic lesions are found.

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Ovarian GATA4/6 are upregulated in eutopic/ectopic lesions and induced by FSHR and LHR.

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FSHR and LHR induce steroidogenic enzymes and the ERK pathway in endometriotic cells.

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New pathophysiological mechanism of endometriosis with tools for diagnosis is shown.

Intrauterine human chorionic gonadotropin infusion in oocyte donors promotes endometrial synchrony and induction of early decidual markers for stromal survival: a randomized clinical trial

STUDY QUESTION

Does a single intrauterine infusion of human chorionic gonadotropin (hCG) at the time corresponding to a Day 3 embryo transfer in oocyte donors induce favorable molecular changes in the endometrium for embryo implantation?

SUMMARY ANSWER

Intrauterine hCG was associated with endometrial synchronization between endometrial glands and stroma following ovarian stimulation and the induction of early decidual markers associated with stromal cell survival.

WHAT IS KNOWN ALREADY

The clinical potential for increasing IVF success rates using an intrauterine hCG infusion prior to embryo transfer remains unclear based on previously reported positive and non-significant findings. However, infusion of CG in the non-human primate increases the expression of pro-survival early decidual markers important for endometrial receptivity, including α-smooth muscle actin (α-SMA) and NOTCH1.

STUDY DESIGN, SIZE, DURATION

Oocyte donors (n=15) were randomly assigned to receive an intrauterine infusion of 500 IU hCG (n=7) or embryo culture media vehicle (n=8) 3 days following oocyte retrieval during their donor stimulation cycle. Endometrial biopsies were performed 2 days later, followed by either RNA isolation or tissue fixation in formalin and paraffin embedding.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Reverse transcription of total RNA from endometrial biopsies generated cDNA, which was used for analysis in the endometrial receptivity array (ERA; n = 5/group) or quantitative RT-PCR to determine relative expression of ESR1, PGR, C3 and NOTCH1. Tissue sections were stained with hematoxylin and eosin followed by blinded staging analysis for dating of endometrial glands and stroma. Immunostaining for ESR1, PGR, α-SMA, C3 and NOTCH1 was performed to determine their tissue localization.

MAIN RESULTS AND THE ROLE OF CHANCE

Intrauterine hCG infusion was associated with endometrial synchrony and reprograming of stromal development following ovarian stimulation. ESR1 and PGR were significantly elevated in the endometrium of hCG-treated patients, consistent with earlier staging. The ERA did not predict an overall positive impact of intrauterine hCG on endometrial receptivity. However, ACTA2, encoding α-SMA was significantly increased in response to intrauterine hCG. Similar to the hCG-treated non-human primate, sub-epithelial and peri-vascular α-SMA expression was induced in women following hCG infusion. Other known targets of hCG in the baboon were also found to be increased, including C3 and NOTCH1, which have known roles in endometrial receptivity.

LIMITATIONS, REASONS FOR CAUTION

This study differs from our previous work in the hCG-treated non-human primate along with clinical studies in infertile patients. Specifically, we performed a single intrauterine infusion in oocyte donors instead of either continuous hCG via an osmotic mini-pump in the baboon or infusion followed by blastocyst-derived hCG in infertile women undergoing embryo transfer. Therefore, the full impact of intrauterine hCG in promoting endometrial receptivity may not have been evident.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings suggest a potential clinical benefit for intrauterine hCG prior to embryo transfer on Day 3 in counteracting endometrial dyssynchrony from ovarian stimulation and promoting expression of markers important for stromal survival. Finally, there were no obvious negative effects of intrauterine hCG treatment.

STUDY FUNDING/COMPETING INTERESTS

Funding for this work was provided by NICHD R01 HD042280 (A.T.F.) and NICHD F30 HD082951 (M.R.S.). C.S. and P.D.-G are co-inventors of the patented ERA, which is owned by IGENOMIX SL and was used in this study, and C.S. is a shareholder in IGENOMIX SL. M.R.-A. is employed by IGENOMIX SL. No other authors have any conflicts of interest to report.

TRIAL REGISTRATION NUMBER

This study was registered with ClinicalTrials.gov (NCT01786252).

TRIAL REGISTRATION DATE

5 February 2013.

DATE OF FIRST PATIENT'S ENROLLMENT

10 May 2013.

Therapeutic Potential of Human Chorionic Gonadotropin Against Painful Bladder Syndrome/Interstitial Cystitis

Painful bladder syndrome/interstitial cystitis is a debilitating chronic bladder disease that primarily affects women. The disease is due to a damage of urothelial cell lining. As a result, potassium particles and other toxic substances in urine can leak into bladder mucosa, causing the symptoms of lower abdominal/pelvic discomfort, pain, increased urination frequency, urgency, nocturia, and so on, all of which can substantially reduce the quality of daily life. There are multiple symptom reliving therapies. Among them, only pentosan polysulfate sodium, sold under the brand name of Elmiron, has been approved for oral use by US Food and Drug Administration. It provides the relief after several months of use. Based on the scientific leads presented in this article, we propose that human chorionic gonadotropin has a therapeutic potential that is worth investigating for the treatment of this disease.

Implantation and Establishment of Pregnancy in Human and Nonhuman Primates

Implantation and the establishment of pregnancy are critical for the propagation of the species, but yet remain the limiting steps in human and primate reproduction. Successful implantation requires a competent blastocyst and a receptive endometrium during a specific window of time during the menstrual cycle to initiate the bilateral communication required for the establishment of a successful pregnancy. This chapter provides an overview of these processes and discusses the molecular mechanisms associated with implantation of the blastocyst and decidualization of the uterus in primates.

The PI3K/Akt signaling pathway exerts effects on the implantation of mouse embryos by regulating the expression of RhoA

The aim of this study was to investigate whether the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway affects the implantation of mouse embryos by regulating the expression of RhoA. The expression of PI3K, Akt, phosphorylated (p-)Akt, phosphatase and tensin homolog (PTEN) and RhoA in the uterus of mice on day 5 of pregnancy (D5) and in pseudopregnant mice was examined by quantitative reverse transcription polymerase chain reaction (qRT-PCR), immunohistochemistry and western blot analysis. A functional analysis of these genes was also performed by the intrauterine injection with the PI3K inhibitor, LY294002, on day 2 of pregnancy (D2). The expression levels of PI3K, p-Akt, RhoA at the implantation site were higher than those at the inter-implantation site in the endometrium; however, opposite effects were observed for PTEN expression. The expression levels of the above genes in the pseudopregnant group and in the group injected with the PI3K/Akt inhibitor, LY294002, were markedly lower than those in the pregnant group. Functional experiments revealed that the number of implantation sites had been significantly decreased (P<0.05) following the intrauterine injection of the PI3K inhibitor, LY294002, on day 2 of gestation compared with the contralateral injection of phosphate-buffered saline (PBS). These results suggest that the PI3K/Akt signaling pathway affects embryo implantation by regulating the expression of RhoA.

Diverse roles of prostaglandins in blastocyst implantation

Prostaglandins (PGs), derivatives of arachidonic acid, play an indispensable role in embryo implantation. PGs have been reported to participate in the increase in vascular permeability, stromal decidualization, blastocyst growth and development, leukocyte recruitment, embryo transport, trophoblast invasion, and extracellular matrix remodeling during implantation. Deranged PGs syntheses and actions will result in implantation failure. This review summarizes up-to-date literatures on the role of PGs in blastocyst implantation which could provide a broad perspective to guide further research in this field.

Extracellular signal-regulated kinase 1/2 signaling pathway is required for endometrial decidualization in mice and human

Decidualization is a crucial change required for successful embryo implantation and the maintenance of pregnancy. During this process, endometrial stromal cells differentiate into decidual cells in response to the ovarian steroid hormones of early pregnancy. Extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) are known to regulate cell proliferation and apoptosis in multiple cell types, including uterine endometrial cells. Aberrant activation of ERK1/2 has recently been implicated in the pathological processes of endometriosis and endometrial cancer. However, the function of ERK1/2 signaling during implantation and decidualization is still unknown. To determine the role and regulation of ERK1/2 signaling during implantation and decidualization, we examine ERK1/2 signaling in the mouse uterus during early pregnancy using immunostaining and qPCR. Interestingly, levels of phospho-ERK1/2 were highest within decidual cells located at the implantation sites. Expression levels of ERK1/2 target genes were also significantly higher at implantation sites, when compared to either inter-implantation sites. To determine if ERK1/2 signaling is also important during human endometrial decidualization, we examined levels of phospho-ERK1/2 in cultured human endometrial stromal cells during in vitro decidualization. Following treatment with a well-established decidualization-inducing steroidogenic cocktail, levels of phospho-ERK1/2 were markedly increased. Treatment with the ERK1/2 inhibitor, U0126, significantly decreased the expression of the known decidualization marker genes, IGFBP1 and PRL as well as inhibited the induction of known ERK1/2 target genes; FOS, MSK1, STAT1, and STAT3. Interestingly, the phosphorylation level of CCAAT/ enhancer binding protein β (C/EBPβ), a protein previously shown to be critical for decidualization, was significantly reduced in this model. These results suggest that ERK1/2 signaling is required for successful decidualization in mice as well as human endometrial stromal cells and implicates C/EBPβ as a downstream target of ERK1/2.

Too much of a good thing? Experimental evidence suggests prolonged exposure to hCG is detrimental to endometrial receptivity

STUDY QUESTION

Does prolonged exposure of the endometrium to hCG, as experienced after ovulation induction in an assisted reproduction technology (ART) cycle, affect functional measures of endometrial receptivity?

SUMMARY ANSWER

Prolonged endometrial hCG exposure detrimentally affects the manner in which the endometrium can respond to hCG secreted by the blastocyst.

WHAT IS KNOWN ALREADY

Prolonged hCG exposure down-regulates endometrial LH-CG receptor (LHCGR) expression in a baboon model. HCG exposure during the proliferative phase of oocyte-donation cycles and frozen embryo transfer cycles is associated with a lower pregnancy rate.

STUDY DESIGN, SIZE, DURATION

LHCGR was examined in endometria of women undergoing ART cycles (GnRH agonist/antagonist) and across the menstrual cycle in normally cycling fertile women. To determine whether prolonged hCG exposure affects the subsequent endometrial response to hCG, endometrial epithelial cells (HES cell line and primary cultures of human endometrial epithelial cells) were exposed to a low dose of hCG (0.5-5 IU) for up to 5 days, to mimic the chronic exposure during an ART cycle, and subsequently exposed to an acute 'blastocyst mimic' dose of hCG (20 IU).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Endometrial tissues were collected at hCG + 2 (n = 37) from women undergoing ART between August 2006 and August 2008, and across the cycle from women with known fertility (n = 40). LHCGR localization and staining intensity were determined by immunohistochemistry and semi-quantitative scoring. HES cells were treated with hCG as above and analyzed for LHCGR localization (immunocytochemistry), phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 (western immunoblotting), adhesion to trophoblast-like matrices (adhesion assays) and tight junction integrity (trans-epithelial resistance assessment).

MAIN RESULTS AND THE ROLE OF CHANCE

Endometrial epithelial LHCGR staining was significantly lower in women stimulated with a GnRH agonist protocol who did not become pregnant in that cycle versus the natural menstrual cycle (P < 0.05). Chronic low-dose hCG exposure in vitro mediated a down-regulation and internalization of the LHCGR in endometrial epithelial cells. Prolonged exposure to chronic low-dose hCG (3-5 days) abrogated ERK 1/2 phosphorylation, adhesion to extracellular matrices and changes in tight junction integrity in response to a subsequent acute high dose (20 IU) of hCG.

LIMITATIONS, REASONS FOR CAUTION

Studies using cell lines and primary cultures of cells in vitro are not fully representative of the complex endometrial milieu in vivo.

WIDER IMPLICATIONS OF THE FINDINGS

These data reinforce the clinical observations that precocious or prolonged hCG exposure may detrimentally affect endometrial receptivity and provide a mechanistic basis for these clinical findings. The data appear to support the notion that in women for whom ART has not succeeded, a different, minimally stimulated approach without exposure to exogenous hCG may improve outcomes.

The role of FOXO1 in the decidual transformation of the endometrium and early pregnancy

Successful pregnancy requires coordination of embryo development, decidualization of endometrium, and placenta formation. Decidualization denotes the transformation of endometrial stromal cells into specialized secretory cells, a process further characterized with influx of specialized immune cells into stroma, predominantly uterine natural killer cells and macrophages, and vascular remodeling. This differentiation process depends on the convergence of the cyclic adenosine monophosphate and progesterone signaling pathways. The decidual process is indispensable for the formation of a functional feto-maternal interface as it controls tissue homeostasis during endovascular trophoblast invasion and bestows tissue resistance to environmental stress signals, including protection against oxidative cell death. FOXO proteins have emerged as key mediators of cell fate because of their ability to regulate either pro-apoptotic genes or genes involved in differentiation, cell cycle arrest, oxidative defenses, and DNA repair. In the endometrium, FOXO1 is of particular importance as a critical regulator of progesterone-dependent differentiation, menstrual shedding, and protection of the feto-maternal against oxidative damage during pregnancy.

EMMPRIN is secreted by human uterine epithelial cells in microvesicles and stimulates metalloproteinase production by human uterine fibroblast cells

Endometrial remodeling is a physiological process involved in the gynecological disease, endometriosis. Tissue remodeling is directed by uterine fibroblast production of matrix metalloproteinases (MMPs). Several MMPs are regulated directly by the protein extracellular matrix metalloproteinase inducer (EMMPRIN) and also by proinflammatory cytokines such as interleukin (IL)1-α/β. We hypothesized that human uterine epithelial cells (HESs) secrete intact EMMPRIN to stimulate MMPs. Microvesicles from HES cell-conditioned medium (CM) expressed intact EMMPRIN protein. Treatment of HES cells with estradiol or phorbyl 12-myristate-13-acetate increased the release of EMMPRIN-containing microvesicles. The HES CM stimulated MMP-1, -2, and -3 messenger RNA levels in human uterine fibroblasts (HUFs) and EMMPRIN immunodepletion from HES-cell concentrated CM reduced MMP stimulation (P < .05). Treatment of HUF cells with low concentrations of IL-1β/α stimulated MMP production (P < .05). These results indicate that HES cells regulate MMP production by HUF cells by secretion of EMMPRIN, in response to ovarian hormones, proinflammatory cytokines as well as activation of protein kinase C.

DNA profiling analysis of endometrial and ovarian cell lines reveals misidentification, redundancy and contamination

OBJECTIVES

Cell lines derived from human ovarian and endometrial cancers, and their immortalized non-malignant counterparts, are critical tools to investigate and characterize molecular mechanisms underlying gynecologic tumorigenesis, and facilitate development of novel therapeutics. To determine the extent of misidentification, contamination and redundancy, with evident consequences for the validity of research based upon these models, we undertook a systematic analysis and cataloging of endometrial and ovarian cell lines.

METHODS

Profiling of cell lines by analysis of DNA microsatellite short tandem repeats (STR), p53 nucleotide polymorphisms and microsatellite instability was performed.

RESULTS

Fifty-one ovarian cancer lines were profiled with ten found to be redundant and five (A2008, OV2008, C13, SK-OV-4 and SK-OV-6) identified as cervical cancer cells. Ten endometrial cell lines were analyzed, with RL-92, HEC-1A, HEC-1B, HEC-50, KLE, and AN3CA all exhibiting unique, uncontaminated STR profiles. Multiple variants of Ishikawa and ECC-1 endometrial cancer cell lines were genotyped and analyzed by sequencing of mutations in the p53 gene. The profile of ECC-1 cells did not match the EnCa-101 tumor, from which it was reportedly derived, and all ECC-1 isolates were genotyped as Ishikawa cells, MCF-7 breast cancer cells, or a combination thereof. Two normal, immortalized endometrial epithelial cell lines, HES cells and the hTERT-EEC line, were identified as HeLa cervical carcinoma and MCF-7 breast cancer cells, respectively.

CONCLUSIONS

Results demonstrate significant misidentification, duplication, and loss of integrity of endometrial and ovarian cancer cell lines. Authentication by STR DNA profiling is a simple and economical method to verify and validate studies undertaken with these models.

The evolution of menstruation: a new model for genetic assimilation: explaining molecular origins of maternal responses to fetal invasiveness

Why do humans menstruate while most mammals do not? Here, we present our answer to this long-debated question, arguing that (i) menstruation occurs as a mechanistic consequence of hormone-induced differentiation of the endometrium (referred to as spontaneous decidualization, or SD); (ii) SD evolved because of maternal-fetal conflict; and (iii) SD evolved by genetic assimilation of the decidualization reaction, which is induced by the fetus in non-menstruating species. The idea that menstruation occurs as a consequence of SD has been proposed in the past, but here we present a novel hypothesis on how SD evolved. We argue that decidualization became genetically stabilized in menstruating lineages, allowing females to prepare for pregnancy without any signal from the fetus. We present three models for the evolution of SD by genetic assimilation, based on recent advances in our understanding of the mechanisms of endometrial differentiation and implantation. Testing these models will ultimately shed light on the evolutionary significance of menstruation, as well as on the etiology of human reproductive disorders like endometriosis and recurrent pregnancy loss.

Extragonadal actions of chorionic gonadotropin

The primary embryonic signal in primates is chorionic gonadotropin (CG, designated hCG in humans), that is classically associated with corpus luteum rescue and progesterone production. However, research over the past decade has revealed the presence of the hCG receptor in a variety of extragonadal tissues. Additionally, discoveries of the multiple variants of hCG, namely, native hCG, hyperglycosylated hCG (hyp-hCG) and the β- subunit of the hyperglycosylated hCG (hCG-free β) has established a role for extragonadal actions of hCG. For the initiation and maintenance of pregnancy, hCG mediates multiple placental, uterine and fetal functions. Some of these include development of syncytiotrophoblast cells, mitotic growth and differentiation of the endometrium, localized suppression of the maternal immune system, modulation of uterine morphology and gene expression and coordination of intricate signal transduction between the endometrium. Recurrent pregnancy loss, pre-eclampsia and endometriosis are associated with altered responses of hCG, all of which have a detrimental effect on pregnancy. A role for hyp-hCG in mediating the development of both trophoblastic and non-trophoblastic tumors has also been suggested. Other significant non-gonadal applications of hCG include predicting preeclampsia, determining the risk of Down's syndrome and gestational trophoblastic disease, along with relaxing myometrial contractility and preventing recurrent miscarriages. Presence of hCG free-β in serum of cancer patients enables its usage as a diagnostic tumor marker. Thus, the extragonadal functions of hCG encompasses a wide spectrum of applications and is an open area for continued investigation.

Novel insights into the mechanisms of pregnancy establishment: regulation of prostaglandin synthesis and signaling in the pig

Ovarian progesterone induces essential changes leading to a temporary state of uterine receptivity for conceptus implantation. Estrogens secreted by the porcine conceptus on days 11 and 12 of pregnancy provide the initial signal for maternal recognition of pregnancy and maintenance of a functional corpus luteum (CL) for continued production of progesterone. As prostaglandins F(2)(α) (PGF(2)(α)) and E(2) (PGE(2)) exert opposing actions on the CL, a tight control over their synthesis and secretion is critical either for the initiation of luteolysis or maintenance of pregnancy. One of the supportive mechanisms by which conceptus inhibits luteolysis is changing PG synthesis in favor of luteoprotective PGE(2). Conceptus PGE(2) could be amplified by PGE(2) feedback loop in the endometrium. In pigs, as in other species, implantation and establishment of pregnancy is associated with upregulation of expression of proinflammatory factors, which include cytokines, growth factors, and lipid mediators. The conceptus produces inflammatory mediators: interferon γ and interferon δ, interleukins IL1B and IL6, and PGs, which probably activate inflammatory pathways in the endometrium. The endometrium responds to these embryonic signals by enhancing further progesterone-induced uterine receptivity. Understanding the mechanisms of pregnancy establishment is required for translational research to increase reproductive efficiencies and fertility in humans and animals.

The endometrial response to chorionic gonadotropin is blunted in a baboon model of endometriosis

Endometriosis-associated infertility has a multifactorial etiology. We tested the hypothesis that the endometrial response to the early embryonic signal, human chorionic gonadotropin (hCG), alters over time in a nonhuman primate model of endometriosis. Animals with experimental or spontaneous endometriosis were treated with hCG (30 IU/d), from d 6 after ovulation for 5 d, via an oviductal cannula. Microarray analysis of endometrial transcripts from baboons treated with hCG at 3 and 6 months of disease (n=6) identified 22 and 165 genes, respectively, whose levels differed more than 2-fold compared with disease-free (DF) animals treated with hCG (P<0.01). Quantitative RT-PCR confirmed abnormal responses of known hCG-regulated genes. APOA1, SFRP4, and PAPPA, which are normally down-regulated by hCG were up-regulated by hCG in animals with endometriosis. In contrast, the ability of hCG to induce SERPINA3 was lost. Immunohistochemistry demonstrated dysregulation of C3 and superoxide dismutase 2 proteins. We demonstrate that this abnormal response to hCG persists for up to 15 months after disease induction and that the nature of the abnormal response changes as the disease progresses. Immunohistochemistry showed that this aberrant gene expression was not a consequence of altered LH/choriogonadotropin receptor distribution in the endometrium of animals with endometriosis. We have shown that endometriosis induces complex changes in the response of eutopic endometrium to hCG, which may prevent the acquisition of the full endometrial molecular repertoire necessary for decidualization and tolerance of the fetal allograft. This may in part explain endometriosis-associated implantation failure.

Chorionic gonadotrophin regulates CXCR4 expression in human endometrium via E-series prostanoid receptor 2 signalling to PI3K-ERK1/2: implications for fetal-maternal crosstalk for embryo implantation

Murine knock-out models and blastocyst co-culture studies have identified prostaglandin-endoperoxide synthase (PTGS) 2, prostaglandin (PG) E receptor 2 (PTGER2) and the chemokine receptor CXCR4 as important regulators of early pregnancy events. In vitro studies and studies in non-human primates have shown that these proteins are regulated in the endometrium by the early embryonic signal, chorionic gonadotrophin (CG). Here we show that expressions of PTGER2 and CXCR4 are elevated during the mid-secretory phase of the menstrual cycle and decidua of early pregnancy in humans. Using first trimester decidua explants, we show that CG induces expression of PTGS2 and biosynthesis of PGE₂, and expression of PTGER2. Subsequently, PGE₂via PTGER2 induces expression of CXCR4. Using an in vitro model system of Ishikawa endometrial epithelial cells stably expressing PTGER2 and human first trimester decidua explants, we demonstrate that CXCR4 expression is regulated by PTGER2 via the epidermal growth factor receptor (EGFR)-phosphatidylinositol-3-kinase (PI3K)-extracellular signal-regulated kinase (ERK1/2) pathway.Taken together, our data suggest that early embryonic signals may regulate fetal–maternal crosstalk in the human endometrium by inducing CXCR4 expression via the PGE₂–PTGER2-mediated induction of the EGFR, PI3K and ERK1/2 pathways.

Epidermal growth factor receptor is an obligatory intermediate for oxytocin-induced cyclooxygenase 2 expression and prostaglandin F2 alpha production in bovine endometrial epithelial cells

Oxytocin (OT) triggers the luteolytic pulses of prostaglandin F(2 alpha) (PGF(2 alpha)) from the endometrial epithelial cells in ruminants. We have proposed that the embryonic signal interferon-tau exerts its antiluteolytic effect by disrupting the OT signaling axis. Accordingly, we have attempted to define the signaling pathway of OT-induced PGF(2 alpha) production in the bovine endometrium using our newly characterized epithelial cell line (bEEL). OT receptor was coupled to the classical G alpha(q) pathway as evidenced by calcium release and activation of phospholipase C. Similarly, OT-induced PGF(2 alpha) production was mediated through the canonical ERK1/2 pathway. Because of the importance of receptor and nonreceptor tyrosine kinases in G protein-coupled receptor signaling, we studied the role of epidermal growth factor receptor (EGFR), c-Src, and phosphoinositide 3-kinase (PI3K) on OT-induced PGF(2 alpha) production in association with cyclooxygenase 2 (COX2) expression and ERK1/2 and Akt phosphorylation. The EGFR inhibitor AG1478 (10 microm) nearly abolished basal and OT-induced PGF(2 alpha) production and down-regulated COX2 expression and ERK1/2 phosphorylation. Because the transactivated EGFR can serve as a ligand for the signaling proteins with Src homology 2 (SH2) domain, we hypothesized a role for c-Src and PI3K in OT-induced PGF(2 alpha) production. Inhibitors of c-Src (PP2, 10 microm) and PI3K (LY294002, 25 microm) produced a significant decrease in OT-induced PGF(2 alpha) production and reduced COX2 expression. Also, PP2, but not LY294002, decreased OT-induced ERK1/2 phosphorylation. Because LY294002 did not affect ERK1/2 phosphorylation, but inhibited PGF(2 alpha) production and down-regulated COX2 expression, it is likely that the Akt pathway is also involved in PGF(2 alpha) production. Thus, EGFR may simultaneously activate c-Src and PI3K to amplify the OT signaling to increase the output of PGF(2 alpha) in bEEL cells.

Endometrial responses to embryonic signals in the primate

The delicate interaction between an embryo and the uterus to initiate implantation and maintain pregnancy is one of the most elegant and fascinating interactions in human biology. Understanding the molecular events of embryo-maternal interaction is of interest to reproductive biologists, clinicians and couples affected by infertility. We have established the baboon as the non-human primate model for studying embryo implantation. Infusion of chorionic gonadotropin (CG), the major embryonic signal of primates, into the uterine cavity of normal cycling baboons during the window of receptivity induces a myriad of morphological, biochemical and molecular changes in the estrogen and progesterone primed endometrium. The luminal epithelium responds by forming plaques, the overall secretory function of the glandular epithelium increases and the stromal response is characterized by induction of alpha-smooth muscle actin (alphaSMA). Cross talk between ovarian and embryonic hormones is evidenced by the fact that these responses are inhibited upon treatment with a progesterone receptor antagonist. CG signals principally through the seven transmembrane LH/CG G-protein coupled receptor, and activates a mitogen activated protein kinase pathway in the endometrial epithelium that is unique and independent of all the classical signaling pathways. In the stromal compartment, CG both rescues stromal fibroblasts from their apoptotic demise and also differentiates them into the decidualized phenotype. We propose that stromal cell survival and differentiation is mediated by a critical modulator of cell fate, Notch-1. Thus, CG is an important embryonic signal which modulates communication between the embryo and the endometrium and induces changes that are critical to successful implantation.