Prokineticin 1 mediates fetal-maternal dialogue regulating endometrial leukemia inhibitory factor

Novel Insights into Prokineticin 1 Role in Pregnancy-related Diseases

Prokineticin 1 (PROK1) is a secreted protein involved in a range of physiological activities such as cell proliferation, migration, angiogenesis, and neuronal cell proliferation. Emerging evidences show that PROK1/PROK receptors (PROKRs) are expressed by trophoblasts, and decidual stroma cells at the maternal-fetal interface. PROK1 plays a critical role in successful pregnancy establishment by regulating the decidualization, implantation and placental development. Dysregulation of prokineticin signaling has been described in certain pathological states associated with pregnancy, including pre-eclampsia, recurrent miscarriage and fetal growth restriction. In this review, the expression and pleiotropic roles of PROK1 under physiological and pathological pregnancy conditions are discussed.

Impaired decidualization and relative increase of PROK1 expression in the decidua of patients with unexplained recurrent pregnancy loss showing insulin resistance

A recent meta-analysis revealed that patients with unexplained recurrent pregnancy loss (RPL) show higher insulin resistance compared to healthy controls. However, the etiology of RPL remains unknown. Prokineticin (PROK1), a pleiotropic uterine endometrial protein, is important for implantation and decidualization and is regulated by hypoxia and insulin. In this study, we investigated the decidualization status and the role of PROK1 in the decidua of patients with unexplained RPL showing insulin resistance. Thirty-two patients with unexplained RPL were included in this study. Following the diagnosis of a miscarriage, the decidua and villi of the patient were surgically collected. Fasting blood glucose and insulin levels were measured, and HOMA-β was calculated. Using IHC and ELISA, the expression of IGFBP-1, PRL and PROK1 in the decidua and IGF-2 in the villi were analyzed in patients with euploid miscarriage with a high HOMA-β index (n = 8) and compared to controls (euploid miscarriage with normal HOMA-β: n = 12, aneuploid miscarriage with normal HOMA-β: n = 12). The co-localization of PROK1 and IGFBP-1 was observed in the decidua by IHC. In the decidua of RPL patients with high HOMA-β, the expression levels of IGFBP-1 and PRL were significantly lower, whereas the PROK1/IGFBP-1 ratio was significantly higher compared to that of the controls. IGF-2 expression in villi was significantly lower in RPL patients with high HOMA-β. Impaired decidualization and excessive PROK1 production may have pathological implications in patients with unexplained RPL with insulin resistance, especially under the state of hyper insulin production.

Increased Demand of Obese Women for Protectins, Maresin, and Resolvin D1 in the Last Trimester of Pregnancy

BACKGROUND

Pregnancy is a physiological state during which inflammation occurs. This complex biological response is necessary for the implantation process as well as delivery. In turn, its suppression during gestation favors the normal course of the pregnancy. Therefore, the presence of pro-resolving mediators, EPA and DHA derivatives, The aim of this study was to investigate the changes in the levels of anti-inflammatory resolvins and their precursors in different trimesters of pregnancy with consideration of the women's weight, including overweight and obese women before pregnancy.

METHODS

A total of 78 women participated in this study; the mean age and BMI before pregnancy were 32.3 ± 5.52 and 27.73 ± 6.13, respectively. The patients were divided into two groups, considering their BMI before pregnancy. The extraction of eicosanoids was performed by high-performance liquid chromatography. The results obtained were subjected to statistical analysis. The levels of all studied parameters showed statistically significant differences between the study group (SG) and the control group (CG) in the different trimesters of pregnancy. Over the course of pregnancy, the levels of protection (PDX), maresin, resolvins (RvD1, RvE1), and their precursors differed in relation to the trimester of pregnancy and the division into groups considering the correct body weight before pregnancy.

RESULTS

Overweight or obese women had significantly lower levels of RvE1 in the third trimester and their precursors compared to normal-weight women. While the levels of PDX and RvD1 were significantly higher, this may be due to both a lower intake of products rich in omega-3 fatty acids by obese women and an increased need of obese women's bodies to quench chronic inflammatory processes associated with obesity.

CONCLUSIONS

Both EPA and DHA derivatives are involved in calming down inflammation during pregnancy, which was observed.

Immune Tolerance of Embryo Implantation and Pregnancy: The Role of Human Decidual Stromal Cell- and Embryonic-Derived Extracellular Vesicles

Embryo–endometrial communication plays a critical role in embryo implantation and the establishment of a successful pregnancy. Successful pregnancy outcomes involve maternal immune modulation during embryo implantation. The endometrium is usually primed and immunomodulated by steroid hormones and embryo signals for subsequent embryo implantation and the maintenance of pregnancy. The roles of extracellular vesicles (EVs) and microRNAs for the embryo–maternal interactions have been elucidated recently. New evidence shows that endometrial EVs and trophectoderm-originated EV cargo, including microRNAs, proteins, and lipids in the physiological microenvironment, regulate maternal immunomodulation for embryo implantation and subsequent pregnancy. On the other hand, trophoblast-derived EVs also control the cross-communication between the trophoblasts and immune cells. The exploration of EV functions and mechanisms in the processes of embryo implantation and pregnancy will shed light on a practical tool for the diagnostic or therapeutic approaches to reproductive medicine and infertility.

Molecular Mechanisms Underlying the Association between Endometriosis and Ectopic Pregnancy

Endometriosis is a common inflammatory disease characterized by the presence of endometrial cells outside the uterine cavity. It is estimated that it affects 10% of women of reproductive age. Its pathogenesis covers a wide range of abnormalities, including adhesion, proliferation, and cell signaling disturbances. It is associated with a significant deterioration in quality of life as a result of chronic pelvic pain and may also lead to infertility. One of the most serious complications of endometriosis is an ectopic pregnancy (EP). Currently, the exact mechanism explaining this phenomenon is unknown; therefore, there are no effective methods of prevention. It is assumed that the pathogenesis of EP is influenced by abnormalities in the contraction of the fallopian tube muscles, the mobility of the cilia, and in the fallopian microenvironment. Endometriosis can disrupt function on all three levels and thus contribute to the implantation of the embryo beyond the physiological site. This review takes into account aspects of the molecular mechanisms involved in the pathophysiology of endometriosis and EP, with particular emphasis on the similarities between them.

A microenvironment of high lactate and low pH created by the blastocyst promotes endometrial receptivity and implantation

RESEARCH QUESTION

Is the blastocyst's idiosyncratic metabolic production of lactate, and creation of a specialized microenvironment at the implatation site, an important mediator of maternal-fetal signalling to promote endometrial receptivity and implantation?

DESIGN

Hormonally primed ECC-1 and Ishikawa cells were used to assess functional changes to the endometrial epithelium after exposure to lactic acid (LA), LA with neutralized pH (nLA) or acidic pH (pH_L). Tight junction integrity (transepithelial resistance [TER]), cellular proliferation or changes to gene expression by RT-PCR were analysed. The effect of LA on Endometrial stromal cells decidualization and migratory capacity, and HUVEC endothelial tube formation and angiogenesis, were also assessed.

RESULTS

Treatment of ECC-1 cells with 2.5 mM (P = 0.0037), 5 mM (P = 0.0044), 7.5 mM and 10 mM (P = 0.003) (P = 0.0021) LA significantly decreased the rate of cellular proliferation while TER was decreased with exposure to 2.5 mM LA (P = 0.024), 5 mM LA (P = 0.021) and 7.5 mM LA (P = 0.033). Exposure to nLA or pH_L had no effect on proliferation or TER. Upregulation of GLUT4 (P = 0.002), GPR81 (P = 0.048), VEGF, SNAI1 (both P < 0.001) and RELA (P = 0.023) mRNA expression was observed after exposure of Ishikawa cells to combined LA plus pH_L. Lactic acid increased the migratory capacity of decidualized stromal cells (P = 0.047) without changing the extent of decidualization. HUVEC tube formation was significantly increased by 5 mM LA exposure (P = 0.009).

CONCLUSIONS

The identification of LA as an important mediator in the maternal-fetal dialogue underpinning implantation is supported. Further examination of the role of LA within the infertile or compromised endometrium could improve natural and assisted pregnancy success and needs further investigation.

Prokineticin 1-prokineticin receptor 1 signaling in trophoblast promotes embryo implantation and placenta development

Successful pregnancy establishment in mammals depends on proper embryo-maternal communication. Prokineticin 1 (PROK1) is a secretory protein that exerts pleiotropic functions in various tissues. Despite the studies that have primarily been performed with human cell lines and mice, the function of PROK1 in trophoblasts has still not been fully elucidated. Hence, the aim of this study was to establish the role of PROK1 in trophoblasts during implantation and placentation. Prokineticin 1 mRNA was elevated in porcine trophoblasts during implantation and the early placentation period. Furthermore, we reveal that PROK1–PROKR1 signaling induces the expression of genes involved in the regulation of angiogenesis, immunological response, trophoblast cell adhesion, invasion, and proliferation, as well as stimulating phosphorylation of MAPK and PTK2. Ingenuity Pathway Analysis identified the aforementioned and also other functions associated with PROK1-regulated genes/proteins, such as cell-to-cell contact, epithelial tissue differentiation, Ca2+ release, lipid synthesis, and chemotaxis. We also showed evidence that PROK1 acting via PROKR1 increased trophoblast cell proliferation and adhesion. The PROK1-stimulated cell proliferation was mediated by PI3K/AKT/mTOR, MAPK, and cAMP, whereas adhesion was mediated by MAPK and/or PI3K/AKT signaling pathways. Concluding, our study suggests that PROK1 plays a pleiotropic role in trophoblast function during implantation and early placentation.

Pleiotropic role of prokineticin 1 in the porcine endometrium during pregnancy establishment and embryo implantation †

Acquisition of endometrial receptivity for embryo implantation is one of the crucial processes during pregnancy and is induced mainly by progesterone and enhanced by conceptus signals. Prokineticin 1 (PROK1) is characterized as a secretory protein with diverse functions in various tissues, including the reproductive tract. PROK1, with its receptor PROKR1, are up-regulated in the porcine endometrium during implantation and in women's receptive endometrium and decidua. However, the function of PROK1 in embryo-maternal communication has still not been fully elucidated. Hence, we hypothesize that PROK1 is involved in endometrial receptivity development and implantation in pigs. In this study, using the porcine in vivo model of intrauterine infusions of estradiol-17β (E2) and prostaglandin E2 (PGE2), we revealed that these hormones elevated endometrial expression of PROK1 and PROKR1 mRNA, respectively. Moreover, E2, acting synergistically with PGE2, increased PROKR1 protein expression. We also evidenced that PROK1-PROKR1 signaling induced expression of following genes and/or proteins CCN2, CDH13, FGF2, NFATC2, ANGPT1, ANGPT2, CDH1, MUC4, SPP1, IFNG, IL6, LIF, LIFR, TNF, TGFB3, and FGF9, as well as phosphorylation of PTK2 and secretion of IL6 and IL11 by endometrial explants in vitro. Ingenuity pathway analysis revealed that functions associated with the PROK1-regulated genes/proteins include cell-to-cell contact, cell attachment, migration and viability, differentiation of epithelial tissue, leukocyte migration, inflammatory response, angiogenesis, and vasculogenesis. Summarizing, our study suggests that PROK1 acts pleiotropically as an embryonic signal mediator that regulates endometrial receptivity by increasing the expression of the genes and proteins involved in implantation and pregnancy establishment in pigs.

Prokineticin 1 is a new biomarker of human oocyte competence: expression and hormonal regulation throughout late folliculogenesis

CONTEXT

Prokineticin 1 (PROK1) quantification in global follicular fluid (FF) has been recently reported as a predictive biomarker of in vitro fertilization (IVF) outcome. It is now necessary to evaluate its clinical usefulness in individual follicles.

OBJECTIVES

To evaluate the clinical value of PROK1 secretion in individual FF to predict oocyte competence. To determine the impact of follicular size, oocyte maturity, and gonadotropin treatments on PROK1 secretion.

DESIGN AND SETTING

Prospective cohort study from May 2015 to May 2017 at the University Hospital of Grenoble.

PATIENTS

A total of 69 infertile couples underwent IVF.

INTERVENTION(S)

Collection of 298 individual FF from 44 women undergoing IVF; 52 individual cumulus cell (CC) samples and 15 CC primary cultures from 25 women undergoing IVF-intracytoplasmic sperm injection (ICSI).

MAIN OUTCOME MEASURE(S)

Oocyte competence was defined as the ability to sustain embryo development to the blastocyst stage. Follicular size was measured by 2D-sonography. PROK1 concentration was quantified by ELISA assay.

RESULTS

PROK1 concentration was correlated to follicular size (r = 0.85, P = 2.2 × 10-16). Normalized PROK1 concentration in FF was predictive of subsequent oocyte competence (AUROC curve = 0.76 [95% CI, 0.69-0.83]; P = 1.7 × 10-9), irrespectively of day-2 embryo morphokinetic parameters. The expression and secretion of PROK1 were increased in FF and CC of mature oocytes (P < 0.01). Follicle Stimulating Hormone and hCG up-regulated PROK1 secretion in CC primary cultures (P < 0.01; P < 0.05), probably through the cAMP pathway (P < 0.01).

CONCLUSIONS

PROK1 quantification in individual FF could constitute a new predictive biomarker of oocyte competence in addition with embryo morphokinetic parameters.

TRIAL REGISTRATION NUMBER

none.

Endometrial receptivity and pregnancy outcome

Human implantation is a highly complex and multifactorial process. Successful implantation requires the presence of a healthy embryo, a receptive endometrium, and a synchronized molecular dialogue between the two, as well as immune tolerance/protection from the host. The endometrial receptivity refers to a hormonally limited period in which the endometrial tissue acquires a transient functional status allowing blastocyst implantation and pregnancy initiation. Global knowledge of endometrial receptivity grew up in recent years. Improvements in genetics, new biomarkers, noninvasive methods, new advanced techniques (Endometrial receptivity assay - the ERA system, proteomic analysis) offer the possibility to evaluate the endometrial status and to manage patients with infertility problems, especially women undergoing assisted reproductive treatment. This overview reports the most relevant knowledge and recent advances in the study of implantation processes from the perspective of the endometrium, often considered as being the main barrier for a successful pregnancy initiation. Endometrial receptivity is a topic of great interest and further studies are needed for the early identification of endometrial abnormalities and the discovery of new strategies for increasing the chance for the establishment of pregnancy.

The role of prokineticins in recurrent implantation failure

The aim of the present study was to investigate the expression patterns of prokineticins (PROK) and prokineticin receptors (PROKR) in the endometrium of women with recurrent implantation failure (RIF). Fifteen (15) women with RIF and 15 fertile controls were enrolled in this study. Endometrial samples were taken from study participants with an endometrial biopsy cannula during the implantation window. Real time polymerase chain reaction and immunohistochemistry were used to determine PROK/PROKR mRNA expression and protein localization, respectively. PROK1 mRNA levels were 6.09 times higher compared to endometrial samples obtained from women with RIF than in samples obtained from fertile controls, whereas PROKR1 mRNA levels were 2.46 times lower in endometrial samples obtained from women with RIF than in samples from fertile controls. In addition, decreased PROKR1 was supported by immunohistochemistry analysis at protein level. There was no statistically significant difference between women with RIF and fertile controls regarding PROK2 and PROKR2 levels. Altered expression of the PROK1/PROKR1 system could be one of the numerous abnormalities in the endometrium of women with RIF.

Prokineticin 1-prokineticin receptor 1 signaling promotes angiogenesis in the porcine endometrium during pregnancy†

Pregnancy establishment in mammals, including pigs, requires proper communication between embryos and the maternal reproductive tract. Prokineticin 1 (PROK1) has been described as a secretory protein with pleiotropic functions and as a novel tissue-specific angiogenic factor. However, despite the studies performed mainly on human cell lines and in mice, the function of PROK1 in the endometrium during early pregnancy is still not fully elucidated. We hypothesized that PROK1 contributes to pregnancy establishment in pigs. The present study is the first to report that the expression of PROK1 and its receptor (PROKR1) is elevated in the porcine endometrium during the implantation and early placentation period. PROK1 protein was detected mainly in luminal epithelial cells, glandular epithelial cells, and blood vessels in the endometrium. Using the porcine in vivo model of unilateral pregnancy, we revealed that conceptuses induced the endometrial expression of PROK1 and PROKR1. Moreover, the embryonic signal, estradiol-17β, as well as progesterone, stimulated the endometrial expression of PROK1 and PROKR1. We also evidenced that PROK1-PROKR1 signaling supports endometrial angiogenesis in pigs. The PROK1-stimulated proliferation of primary porcine endometrial endothelial (PEE) cells involved PI3K/AKT/mTOR, MAPK, cAMP, and NFKB signaling pathways. Furthermore, PROK1 via PROKR1 promoted the formation of capillary-like structures by PEE cells. PROK1 also stimulated VEGFA and PGF2α secretion, which in turn may indirectly support angiogenic changes within endometrial tissue. In summary, our study suggests that PROK1 acts as an embryonic signal mediator that regulates endometrial angiogenesis and secretory function during the implantation and early placentation period in pigs.

A novel "embryo-endometrial" adhesion model can potentially predict "receptive" or "non-receptive" endometrium

OBJECTIVE

To establish a model of human implantation that responds to hormonal stimuli and can differentiate between endometrium from fertile women and those with idiopathic infertility.

DESIGN

A trophoblast stem cell (trophectodermal) line (TSC; derived from human pre-implantation embryo) was used to form trophectodermal spheroids (TS). TS attachment to monolayers of endometrial epithelial cell lines or primary endometrial epithelial cells (pHEECs) was determined.

SETTING

Independent Medical Research Institute with close clinical linkages INTERVENTIONS: Spheroid attachment and outgrowth was determined with added hormones (estradiol 17β (E), E + medroxyprogesterone acetate (MPA) or E + MPA + human chorionic gonadotropin (hCG)). Spheroid attachment to E/MPA treated pHEEC prepared from fertile women or those with idiopathic infertility tested.

MAIN OUTCOME MEASURE

Firmly attached spheroids counted after co-culture for 6 h. Outgrowth was determined by quantitation of area covered by spheroid after firm adhesion.

RESULTS

Functional adhesion of TS to two endometrial epithelial cell lines, Ishikawa and ECC-1 cells, was hormonally responsive, with adhesion/outgrowth increased by E/MPA (ECC-1; p < 0.01, Ishikawa; p < 0.01) and E/MPA/hCG (ECC-1; p < 0.001, Ishikawa p < 0.01) versus E alone. The same pattern of hormone responsiveness was observed in pHEEC obtained from fertile women (E vs, E/MPA; p < 0.01, E vs. E/MPA/hCG; p < 0.001). TS adhered to 85% of pHEEC obtained from fertile women (11/13) and 11% of pHEEC obtained from women with unexplained infertility (2/18, p < 0.001).

CONCLUSION

This new model of "embryo" implantation largely discriminates between endometrial epithelial cells obtained from fertile vs. infertile women based on adhesion; this holds potential as an in vitro "diagnostic" tool of endometrial infertility.

Human Endometrial Extracellular Vesicles Functionally Prepare Human Trophectoderm Model for Implantation: Understanding Bidirectional Maternal-Embryo Communication

Embryo implantation into maternal endometrium is critical for initiation and establishment of pregnancy, requiring developmental synchrony between endometrium and blastocyst. However, factors regulating human endometrial-embryo cross talk and facilitate implantation remain largely unknown. Extracellular vesicles (EVs) are emerging as important mediators of this process. Here, a trophectoderm spheroid-based in vitro model mimicking the pre-implantation human embryo is used to recapitulate important functional aspects of blastocyst implantation. Functionally, human endometrial EVs, derived from hormonally treated cells synchronous with implantation, are readily internalized by trophectoderm cells, regulating adhesive and invasive capacity of human trophectoderm spheroids. To gain molecular insights into mechanisms underpinning endometrial EV-mediated enhancement of implantation, quantitative proteomics reveal critical alterations in trophectoderm cellular adhesion networks (cell adhesion molecule binding, cell-cell adhesion mediator activity, and cell adherens junctions) and metabolic and gene expression networks, and the soluble secretome from human trophectodermal spheroids. Importantly, transfer of endometrial EV cargo proteins to trophectoderm to mediate changes in trophectoderm function is demonstrated. This is highlighted by correlation among endometrial EVs, the trophectodermal proteome following EV uptake, and EV-mediated trophectodermal cellular proteome, important for implantation. This work provides an understanding into molecular mechanisms of endometrial EV-mediated regulation of human trophectoderm functions-fundamental in understanding human endometrium-embryo signaling during implantation.

Obstetric and perinatal outcomes of pregnancies according to initial maternal serum HCG concentrations after vitrified-warmed single blastocyst transfer

RESEARCH QUESTION

Do pregnancy, obstetric and perinatal outcomes differ according to initial maternal serum human chorionic gonadotrophin (HCG) level measured on day 11 after single blastocyst transfer?

DESIGN

Vitrified-warmed single blastocyst transfer cycles (n = 640) were collected between 1 January 2013 and 30 April 2017 with positive HCG values and retrospectively analysed by receiver operating characteristic curves to predict clinical pregnancy, ongoing pregnancy and delivery. Cycles were divided into a low HCG group (n = 155) and high HCG group (n = 485) based on cut-off value of live birth prediction. Cycles in the HCG group were subdivided into a low-high subgroup (n = 162), medium-high subgroup (n = 162) and high-high subgroup (n = 161) based on tertile points. Pregnancy rates and obstetric and perinatal outcomes were compared.

RESULTS

The area under curves for clinical pregnancy, ongoing pregnancy and live birth prediction were 0.95, 0.81 and 0.79, respectively; corresponding cut-off values were 152.2 IU/l, 211.9 IU/l and 211.9 IU/l; HCG less than 211.9 IU/l indicated an extremely low clinical pregnancy rate (34.84%), a high early miscarriage rate (61.11%) and a low live birth rate (12.26%). Rates of gestational diabetes mellitus (GDM) (P = 0.007) and female neonates (P = 0.001) were significantly higher in the LHG group compared with the HHG group; no significant differences were observed in the low versus high HCG group overall.

CONCLUSIONS

Lower initial maternal serum HCG levels indicated poorer clinical outcomes. Within the high HCG group, a lower initial maternal HCG level was found to be associated with GDM occurrence and proportion of female neonates.

Prokineticins and their G protein-coupled receptors in health and disease

Prokineticins are two conserved small proteins (~8kDa), prokineticin 1 (PROK1; also called EG-VEGF) and prokineticin 2 (PROK2; also called Bv8), with an N-terminal AVITGA sequence and 10 cysteines forming 5 disulfide bridges. PROK1 and PROK2 bind to two highly related G protein-coupled receptors (GPCRs), prokineticin receptor 1 (PROKR1) and prokineticin receptor 2 (PROKR2). Prokineticins and their receptors are widely expressed. PROK1 is predominantly expressed in peripheral tissues, especially steroidogenic organs, whereas PROK2 is mainly expressed in the central nervous system and nonsteroidogenic cells of the testes. Prokineticins signaling has been implicated in several important physiological functions, including gastrointestinal smooth muscle contraction, circadian rhythm regulation, neurogenesis, angiogenesis, pain perception, mood regulation, and reproduction. Dysregulation of prokineticins signaling has been observed in a variety of diseases, such as cancer, ischemia, and neurodegeneration, in which prokineticins signaling seems to be a promising therapeutic target. Based on the phenotypes of knockout mice, PROKR2 and PROK2 have recently been identified as causative genes for idiopathic hypogonadotropic hypogonadism, a developmental disorder characterized by impaired development of gonadotropin-releasing hormone neurons and infertility. In vitro functional studies with these disease-associated PROKR2 mutations uncovered some novel features for this receptor, such as biased signaling, which may be used to understand GPCR signaling regulation in general.

Decidualization of the human endometrium

BACKGROUND

Decidualization of the human endometrium, which involves a dramatic morphological and functional differentiation of human endometrial stromal cells (ESCs), is essential for the establishment of a successful pregnancy. Decidualization results from a complex interplay of transcription factors, morphogens, cytokines, cell cycle regulators, and signaling pathways.

METHODS

Based on a literature review, the regulation of, and the molecular mechanisms involved in, the decidualization of the endometrium are described.

MAIN FINDINGS

Progesterone, together with proteins that are regulated by progesterone and/or cyclic adenosine monophosphate, including homeobox A10, forkhead box O1, signal transducers and activators of transcription, and heart and neural crest derivatives expressed transcript 2, forms a critical network for ESC decidualization and is a prerequisite to successful implantation. Decidualized ESCs contribute to the microenvironment at the feto-maternal interface and its direct or indirect influence on extracellular matrix remodeling, regulation of the local immune response, anti-oxidative stress, and angiogenesis (vascular maturation). Impairment of this process is associated with a variety of pregnancy disorders, including infertility, recurrent miscarriages, and uteroplacental disorders.

CONCLUSION

A deeper understanding of the process of decidualization is expected to provide new insights into the fields of reproductive biology and reproductive medicine.

The Endometrial Polarity Paradox: Differential Regulation of Polarity Within Secretory-Phase Human Endometrium

A major cause of infertility in normal and assisted reproduction cycles is failure of the endometrium to undergo appropriate changes during the secretory phase of the menstrual cycle as it acquires receptivity for an implanting blastocyst. Current dogma states that loss of epithelial polarity in the luminal epithelial cells, the point of first contact between maternal endometrium and blastocyst, may facilitate embryo implantation. Loss of polarity is likely an important change during the secretory phase to overcome mutual repulsion between otherwise polarized epithelial surfaces. Although "plasma membrane transformation" describes morphological/molecular alterations associated with loss of polarity, direct measures of polarity have not been investigated. Transepithelial resistance, a proxy measure of polarity, was downregulated in endometrial epithelial (ECC-1) cells by combined estrogen/progestin, mimicking the hormonal milieu of the secretory phase. Examination of defined polarity markers within human endometrium throughout the menstrual cycle identified downregulation of atypical protein kinase C, Stardust, Crumbs, and Scribble within the luminal-epithelial layer, with upregulation of Scribble within the stromal compartment as the menstrual cycle progressed from the estrogen-dominated proliferative to progesterone-dominated secretory phase. Epithelial (ECC-1) Scribble expression was downregulated in vitro by combined estrogen/progestin and estrogen/progestin/human chorionic gonadotropin treatment, whereas knockdown of Scribble in these cells enhanced "embryo" (trophectodermal spheroid) adhesion. In contrast, Scribble was upregulated within decidualized primary human endometrial stromal cells, with decidualization downregulated upon Scribble knockdown. These data highlight an important contribution of polarity modulation within the human endometrium, likely important for receptivity. Clinical investigations examining how polarity may be modulated in the infertile endometrium may facilitate fertility.

hCG: Biological Functions and Clinical Applications

Human chorionic gonadotropin (hCG) is produced primarily by differentiated syncytiotrophoblasts, and represents a key embryonic signal that is essential for the maintenance of pregnancy. hCG can activate various signaling cascades including mothers against decapentaplegic homolog 2 (Smad2), protein kinase C (PKC), and/or protein kinase A (PKA) in several cells types by binding to luteinizing hormone/chorionic gonadotropin receptor (LHCGR) or potentially by direct/indirect interaction with transforming growth factor beta receptor (TGFβR). The molecule displays specialized roles in promoting angiogenesis in the uterine endothelium, maintaining myometrial quiescence, as well as fostering immunomodulation at the maternal-fetal interface. It is a member of the glycoprotein hormone family that includes luteinizing hormone (LH), thyroid-stimulating hormone (TSH), and follicle-stimulating hormone (FSH). The α-subunit of hCG displays homologies with TSH, LH, and FSH, whereas the β subunit is 80–85% homologous to LH. The hCG molecule is produced by a variety of organs, exists in various forms, exerts vital biological functions, and has various clinical roles ranging from diagnosis and monitoring of pregnancy and pregnancy-related disorders to cancer surveillance. This review presents a detailed examination of hCG and its various clinical applications.

Targeting lysyl oxidase reduces peritoneal fibrosis

Background

Abdominal surgery and disease cause persistent abdominal adhesions, pelvic pain, infertility and occasionally, bowel obstruction. Current treatments are ineffective and the aetiology is unclear, although excessive collagen deposition is a consistent feature. Lysyl oxidase (Lox) is a key enzyme required for crosslinking and deposition of insoluble collagen, so we investigated whether targeting Lox might be an approach to reduce abdominal adhesions.

Methods

Female C57Bl/6 mice were treated intraperitoneally with multiwalled carbon nanotubes (NT) to induce fibrosis, together with chemical (ß-aminoproprionitrile–BAPN) or miRNA Lox inhibitors, progesterone or dexamethasone. Fibrotic lesions on the diaphragm, and expression of fibrosis-related genes in abdominal wall peritoneal mesothelial cells (PMC) were measured. Effects of BAPN and dexamethasone on collagen fibre alignment were observed by TEM. Isolated PMC were cultured with interleukin-1 alpha (IL-1α) and progesterone to determine effects on Lox mRNA in vitro.

Results

NT-induced fibrosis and collagen deposition on the diaphragm was ameliorated by BAPN, Lox miRNA, or steroids. BAPN and dexamethasone disrupted collagen fibres. NT increased PMC Lox, Col1a1, Col3a1 and Bmp1 mRNA, which was inhibited by steroids. Progesterone significantly inhibited IL-1α induced Lox expression by PMC in vitro.

Conclusion

Our results provide proof-of-concept that targeting peritoneal Lox could be an effective approach in ameliorating fibrosis and adhesion development.

Prokineticin 1 is up-regulated by insulin in decidualizing human endometrial stromal cells

Prokineticin 1 (PROK1), a hypoxia‐regulated angiogenic factor, has emerged as a crucial regulator of embryo implantation and placentation. Dysregulation of PROK1 has been linked to recurrent pregnancy loss, pre‐eclampsia, foetal growth restriction and preterm birth. These pregnancy complications are common in women with obesity and polycystic ovary syndrome, i.e. conditions associated with insulin resistance and compensatory hyperinsulinaemia. We investigated the effect of insulin on PROK1 expression during in vitro decidualization. Endometrial stromal cells were isolated from six healthy, regularly menstruating women and decidualized in vitro. Insulin induced a significant dose‐dependent up‐regulation of PROK1 on both mRNA and protein level in decidualizing endometrial stromal cells. This up‐regulation was mediated by hypoxia‐inducible factor 1‐alpha (HIF1α) via the phosphatidylinositol 3‐kinase (PI3K) pathway. Furthermore, we demonstrated that PROK1 did not affect the viability, but significantly inhibited the migration of endometrial stromal cells and the migratory and invasive capacity of trophoblast cell lines. This in vitro study provides new insights into the regulation of PROK1 by insulin in human decidualizing endometrial stromal cells, the action of PROK1 on migration of endometrial stromal cells, as well as migration and invasion of trophoblasts. We speculate that hyperinsulinaemia may be involved in the mechanisms by which PROK1 is linked to placenta‐related pregnancy complications.

Fertile ground: human endometrial programming and lessons in health and disease

The human endometrium is a highly dynamic tissue that is cyclically shed, repaired, regenerated and remodelled, primarily under the orchestration of oestrogen and progesterone, in preparation for embryo implantation. Humans are among the very few species that menstruate and that, consequently, are equipped with unique cellular and molecular mechanisms controlling these cyclic processes. Many reproductive pathologies are specific to menstruating species, and studies in animal models rarely translate to humans. Abnormal remodelling and regeneration of the human endometrium leads to a range of reproductive complications. Furthermore, the processes regulating endometrial remodelling and implantation, including those controlling hormonal impact, breakdown and repair, stem/progenitor cell activation, inflammation and cell invasion have broad applications to other fields. This Review presents current knowledge regarding the normal and abnormal function of the human endometrium. The development of biomarkers for prediction of uterine diseases and pregnancy disorders and future avenues of investigation to improve fertility and enhance endometrial function are also discussed.

Prokineticins in central and peripheral control of human reproduction

Prokineticin 1 (PROK1) and (PROK2), are two closely related proteins that were identified as the mammalian homologs of their two amphibian homologs, mamba intestinal toxin (MIT-1) and Bv8. PROKs activate two G-protein linked receptors (prokineticin receptor 1 and 2, PROKR1 and PROKR2). Both PROK1 and PROK2 have been found to regulate a stunning array of biological functions. In particular, PROKs stimulate gastrointestinal motility, thus accounting for their family name "prokineticins". PROK1 acts as a potent angiogenic mitogen, thus earning its other name, endocrine gland-derived vascular endothelial factor. In contrast, PROK2 signaling pathway has been shown to be a critical regulator of olfactory bulb morphogenesis and sexual maturation. During the last decade, strong evidences established the key roles of prokineticins in the control of human central and peripheral reproductive processes. PROKs act as main regulators of the physiological functions of the ovary, uterus, placenta, and testis, with marked dysfunctions in various pathological conditions such as recurrent pregnancy loss, and preeclampsia. PROKs have also been associated to the tumor development of some of these organs. In the central system, prokineticins control the migration of GnRH neurons, a key process that controls reproductive functions. Importantly, mutations in PROK2 and PROKR2 are associated to the development of Kallmann syndrome, with direct consequences on the reproductive system. This review describes the finely tuned actions of prokineticins in the control of the central and peripheral reproductive processes. Also, it discusses future research directions for the use of these cytokines as diagnostic markers for several reproductive diseases.

The Immune System and the Role of Inflammation in Perinatal Depression

Major depression during pregnancy is a common psychiatric disorder that arises from a complex and multifactorial etiology. Psychosocial stress, sex, hormones, and genetic vulnerability increase the risk for triggering mood disorders. Microglia and toll-like receptor 4 play a crucial role in triggering wide and varied stress-induced responses mediated through activation of the inflammasome; this leads to the secretion of inflammatory cytokines, increased serotonin metabolism, and reduction of neurotransmitter availability along with hypothalamic-pituitary-adrenal axis hyperactivity. Dysregulation of this intricate neuroimmune communication network during pregnancy modifies the maternal milieu, enhancing the emergence of depressive symptoms and negative obstetric and neuropsychiatric outcomes. Although several studies have clearly demonstrated the role of the innate immune system in major depression, it is still unclear how the placenta, the brain, and the monoaminergic and neuroendocrine systems interact during perinatal depression. Thus, in the present review we describe the cellular and molecular interactions between these systems in major depression during pregnancy, proposing that the same stress-related mechanisms involved in the activation of the NLRP3 inflammasome in microglia and peripheral myeloid cells in depressed patients operate in a similar fashion in the neuroimmune placenta during perinatal depression. Thus, activation of Toll-like receptor 2 and 4 signaling and the NLRP3 inflammasome in placental immune cells may promote a shift of the Th1/Th2 bias towards a predominant Th1/Th17 inflammatory response, associated with increased secretion of pro-inflammatory cytokines, among other secreted autocrine and paracrine mediators, which play a crucial role in triggering and/or exacerbating depressive symptoms during pregnancy.

Prokineticin1 and pregnancy

Prokineticin 1 (PROK1), also called EG-VEGF, is a peptide of 86 amino acids with multiple biological functions. PROK1 acts via two G-protein coupled receptors: PROKR1 PROKR2. PROK1 is highly expressed in the placenta. This article reports the expression and the role of PROK1 during normal and pathological pregnancies: (i) during early pregnancy, PROK1 exhibits a peak of placental expression shortly before the establishment of the feto-maternal circulation; (ii) its receptors, PROKR1 PROKR2 are highly expressed in human placenta; (iii) its expression is increased by hypoxia; (iv) PROK1 inhibits extravillous trophoblasts migration and invasion and increases their proliferation and survival; (v) PROK1 is also a pro-angiogenic placental factor that increases microvascular placental endothelial cells proliferation, migration, invasion, and permeability. Circulating PROK1 levels are five times higher in pregnant women during the first trimester compared to the second and third trimesters. Also, its serum levels are higher in patients with preeclampsia (PE) and in patients with isolated intra-uterine growth restriction (IUGR). In mice, maintaining high level of PROK1 beyond its normal period of production (>10.5dpc) reproduces symptoms of PE. To date, our results demonstrated that PROK1 is a central factor of human placentation with direct roles both in the control of trophoblast invasion and villous growth. Thus, a failure in the expression of PROK1 and/or its receptor during pregnancy may contribute to the development of PE and/or IUGR. Besides theses original findings, we also report a direct role of this factor in parturition.

Human Decidual Stromal Cells as a Component of the Implantation Niche and a Modulator of Maternal Immunity

The human decidua is a specialized tissue characterized by embryo-receptive properties. It is formed during the secretory phase of menstrual cycle from uterine mucosa termed endometrium. The decidua is composed of glands, immune cells, blood and lymph vessels, and decidual stromal cells (DSCs). In the process of decidualization, which is controlled by oestrogen and progesterone, DSCs acquire specific functions related to recognition, selection, and acceptance of the allogeneic embryo, as well as to development of maternal immune tolerance. In this review we discuss the relationship between the decidualization of DSCs and pathological obstetrical and gynaecological conditions. Moreover, the critical influence of DSCs on local immune cells populations as well as their relationship to the onset and maintenance of immune tolerance is described.

Association between polymorphisms of prokineticin receptor (PKR1 rs4627609 and PKR2 rs6053283) and recurrent pregnancy loss

Recurrent pregnancy loss (RPL) is a condition with complex etiologies, to which both genetic and environmental factors may contribute. During the last decade, studies indicated that the expression patterns of the prokineticin receptor (PKR1 and PKR2) are closely related to early pregnancy. However, there are few studies on the role of PKR1 and PKR2 in RPL. In this study, we purpose to investigate the association between polymorphisms of the prokineticin receptor (PKR1 rs4627609 and PKR2 rs6053283) and RPL on a group of 93 RPL cases and 169 healthy controls. Genotyping of the single nucleotide polymorphisms (SNPs) was performed using a Sequenom MassARRAY iPLEX system. The results revealed a significant association between PKR2 rs6053283 polymorphism and RPL (P=0.003), whereas no association was observed between PKR1 rs4627609 polymorphism and RPL (P=0.929) in the Chinese Han population.

Effect of high ovarian response on the expression of endocrine gland-derived vascular endothelial growth factor (EG-VEGF) in peri-implantation endometrium in IVF women

OBJECTIVE

To investigate the effect of ovarian stimulation on the expression of EG-VEGF mRNA and protein in peri-implantation endometrium in women undergoing IVF and its relation with endometrial receptivity (ER).

DESIGN

Prospective laboratory study.

SETTING

University hospital.

PATIENTS

Eighteen women in stimulated cycles (SC) as study subjects and 18 women in natural cycles (NC) as controls. Women in SC group were classified with two subgroups, high ovarian response (SC1, n=9) with peak serum E2>5,000 pg/mL and moderate ovarian response (SC2, n=9) with peak serum E2 1,000-5,000 pg/mL.

INTERVENTION(S)

Endometrial biopsies were collected 6 days after ovulation in NC or after oocyte retrieval in SC.

MAIN OUTCOME MEASURE(S)

Endometrium histological dating was observed with HE staining. EG-VEGF mRNA expression levels determined by real-time polymerase chain reaction analysis, and protein levels by immunohistochemistry.

RESULTS

All endometrial samples were in the secretory phase. The endometrial development in SC1 was 1 to 2 days advanced to NC, and with dyssynchrony between glandular and stromal tissue. Immunohistochemistry analysis showed that EG-VEGF protein was predominantly expressed in the glandular epithelial cells and endothelial cells of vessels, and also presented in the stroma. The image analysis confirmed that both the gland and stroma of endometrium in SC1 had a significantly lower EG-VEGF protein expression than that in SC2 and NC endometrium. Moreover, EG-VEGF mRNA levels were significantly lower in SC1 than in NC. Both EG-VEGF protein and mRNA levels had no significant difference between SC2 and NC.

CONCLUSION

Decreased expression of EG-VEGF in the peri-implantation is associated with high ovarian response, which may account for the impaired ER and lower implantation rate in IVF cycles.

Regulatory Action of Calcium Ion on Cyclic AMP-Enhanced Expression of Implantation-Related Factors in Human Endometrial Cells

Decidualization of human endometrial stroma and gland development is mediated through cyclic AMP (cAMP), but the role of intracellular calcium ion (Ca2+) on cAMP mediated-signaling in human endometrial stroma and glandular epithelia has not been well-characterized. The present study was designed to investigate the role of intracellular Ca2+ on cAMP mediated-decidualization and gland maturation events, which can be identified by the up-regulation of prolactin and IGF-binding protein (IGFBP)1 in human endometrial stromal cells (ESCs), and cyclooxygenase 2 (COX2) and prostaglandin E2 (PGE2) and glandular epithelial EM-1 cells. Increases in decidual prolactin and IGFBP-1 transcript levels, induced by cAMP-elevating agents forskolin or dibutyryl cyclic AMP, were inhibited by Ca2+ influx into ESCs with Ca2+ ionophores (alamethicin, ionomycin) in a dose-dependent manner. Conversely, inhibitors of Ca2+ influx through L-type voltage-dependent Ca2+ channel (VDCC), nifedipine and verapamil, enhanced the decidual gene expression. Furthermore, dantrolene, an inhibitor of Ca2+ release from the intracellular Ca2+ store, up-regulated prolactin and IGFBP-1 expression. Ca2+ ionophores decreased intracellular cAMP concentrations, whereas nifedipine, verapamil or dantrolene increased cAMP concentrations in ESCs. In glandular epithelial cells, similar responses in COX2 expression and PGE2 production were found when intracellular cAMP levels were up-regulated by decreases in Ca2+ concentrations. Thus, a marked decrease in cytosolic Ca2+ levels caused the elevation of cAMP concentrations, resulting in enhanced expression of implantation-related factors including decidual markers. These findings suggest that fluctuation in cytosolic Ca2+ concentrations alters intracellular cAMP levels, which then regulate differentiation of endometrial stromal and glandular epithelial cells.

HCG induces β1,4-GalT I expression and promotes embryo implantation

Embryo implantation is regarded as a critical physiological process for the success of pregnancy. There are so many reports on the research of human chorionic gonadotropin (HCG) in artificial insemination, but the impact of HCG on endometrial receptivity has not been elucidated. Beta1, 4-Galactosyltransferase-I (β1,4-GalT-I) is ubiquitously expresses in human tissues with the exception of the brain. It not only transfers galactose from UDP-galactoside to GlcNAc to form Galβl,4-GlcNAc, but plays crucial role as cell adhesion molecule by recognizing and adhering other extracellular matrix and galactose of cell surface glycoprotein and glycolipid in cancer cells invasion and migration. The process of the embryos implantation is very similar to tumor invasion, so many biological factors participate in the tumor invasion also play a role in embryo implantation. We hypothesize that β1,4-GalT-I may take part in embryo implantation. In this study, we demonstrated that the over expression of β1,4-GalT-I was induced by HCG in RL95-2 cells. Moreover, the expression of some molecules, such as TIMP-1, LN and MMPs could be regulated by engineered expression of β1,4-GalT-I and therefore lead to the significantly alteration of adhesion capability of RL95-2 cells, even result in reduced adhesive ability between JAR cells and RL95-2 cells. Furthermore, our results indicated that HCG can obviously increase the EGFR signaling pathways-dependent molecular expression through β1,4-GalT-I, HCG also improved the adhesive ability between JAR cells and RL95-2 cells (P<0.01). Taken together, our data suggested that HCG provides a mechanism to bridge embryo to endometrium through β1,4-GalT.

Endometrial CRISP3 is regulated throughout the mouse estrous and human menstrual cycle and facilitates adhesion and proliferation of endometrial epithelial cells

The endometrium (the mucosal lining of the uterus) is a dynamic tissue that undergoes extensive remodeling, secretory transformation in preparation for implantation of an embryo, inflammatory and proteolytic activity during menstruation, and rapid postmenstrual repair. A plethora of local factors influence these processes. Recently, a cysteine-rich protein, CRISP3, a clade of the CRISP, antigen 5, pathogenesis-related (CAP) protein superfamily, has been implicated in uterine function. The localization, regulation, and potential function of CRISP3 in both the human and mouse endometrium is described. CRISP3 localizes to the luminal and glandular epithelium of the endometrium within both species, with increased immunoreactivity during the proliferative phase of the human cycle. CRISP3 also localizes to neutrophils, particularly within the premenstrual human endometrium and during the postbreakdown repair phase of a mouse model of endometrial breakdown and repair. Endometrial CRISP3 is produced by primary human endometrial epithelial cells and secreted in vivo to accumulate in the uterine cavity. Secreted CRISP3 is more abundant in uterine lavage fluid during the proliferative phase of the menstrual cycle. Human endometrial epithelial CRISP3 is present in both a glycosylated and a nonglycosylated form in vitro and in vivo. Treatment of endometrial epithelial cells in vitro with recombinant CRISP3 enhances both adhesion and proliferation. These data suggest roles for epithelial and neutrophil-derived CRISP3 in postmenstrual endometrial repair and regeneration.

Synthetic glucocorticoid reduces human placental system a transport in women treated with antenatal therapy

CONTEXT

Synthetic glucocorticoids (sGCs) are routinely given to women with threatened preterm labor and have been linked to fetal growth restriction and developmental programming. Reductions in fetal growth are likely to be mediated by placental dysfunction, including altered nutrient transport. sGCs modify the system A neutral amino acid transporter in vitro, but there are no in vivo comparable data in human placenta.

OBJECTIVE

Because ∼ 30% of women who receive sGCs carry to term, our objective was to examine the short- and longer-term consequences of antenatal sGCs on placental system A transport.

METHODS AND PATIENTS

Placental tissue was collected from women treated with sGCs between 24 hours and 14 days before delivery (24h-14d), 14 days after treatment but before term (14d-term), or at term, compared with healthy term (control) deliveries to measure system A-mediated activity (Na(+)-dependent [(14)C]methylaminoisobutyric acid uptake per gram placenta) and mRNA expression.

RESULTS

After sGC treatment, system A activity was significantly reduced at term compared with both sGC placentas delivered 24h-14d and compared with controls. Placentae from women treated with sGCs who delivered between 14d-term also had significantly reduced system A activity compared with 24h-14d placentas. SLC38A1 and SLC38A2 mRNA expression was unaffected. However, SLC38A4 was significantly reduced by sGCs at term compared with placentas delivered between 14d-term.

CONCLUSION

We conclude that women who are at risk of preterm labor and receive sGCs but deliver at term have significantly reduced placental system A amino acid transporter activity. Altered placental transporter function could affect fetal growth and may contribute to developmental programming reported in both animal and clinical studies.

Inflammation and endometrial bleeding

Most of the key physiological processes in the human reproductive tract involve a significant inflammatory component. These processes include follicle development, ovulation, implantation, pregnancy, labor, postpartum, remodeling and menstruation. In this context, the term 'inflammation' usually means an influx of leukocytes ('immune cells'), often of different types, into a reproductive tract tissue. These examples of inflammation are not overtly associated with any infective process. There may also be evidence that these invading leukocytes have altered their functions to take on specific and relevant local regulatory roles. Specific sequential changes in different leukocytes can be demonstrated within human endometrium during the different phases of the normal menstrual cycle. Leukocytes are fairly sparse in numbers through the proliferative phase, but increase substantially into and through the secretory phase, so much so that around 40% of all stromal cells in the premenstrual phase are leukocytes, mainly uterine natural killer cells, a large granulated lymphocyte. Other leukocytes which play key roles in menstruation appear to be macrophages, mast cells, dendritic cells, neutrophils, eosinophils and regulatory T cells. Premenstrual withdrawal of progesterone increases the endometrial expression of inflammatory mediators, including IL-8 and MCP-1, which are believed to drive endometrial leukocyte recruitment at this time. Macrophages and neutrophils are rich sources of defensins and whey acid protein motif proteins, which play important roles in ensuring microbial protection while the epithelial barrier is disrupted. Mast cells are increasingly activated as the menstrual phase approaches, and leukocyte proteases trigger a cascade of matrix metalloproteinases and degradation of extracellular matrix. Dendritic cells and other antigen-presenting cells (e.g. macrophages) almost certainly facilitate clearance of cellular debris from the uterine cavity, and reduce the amount of viable cellular material transiting the Fallopian tubes. All of these processes are influenced or controlled by regulatory T cells. Many of these leukocytes also have the potential to release regulatory molecules which stimulate endometrial repair mechanisms. Increasing recent evidence also implicates disturbances of immune cells and their cytokine mediators in contributing to symptoms of abnormal uterine bleeding and pelvic pain. These recent findings all point towards the importance of the 'inflammatory process' in both normal and abnormal endometrial bleeding.

Prokineticin 1 and leukemia inhibitory factor mRNA expression in the endometrium of women with idiopathic recurrent pregnancy loss

OBJECTIVE

To determine the expression patterns of prokineticin 1 (PROK1) and leukemia inhibitory factor (LIF) mRNA differ in peri-implantation endometrial tissue of women with idiopathic recurrent pregnancy loss (RPL) from normal fertile women.

DESIGN

A case-control study.

SETTING

University-based tertiary care center.

PATIENT(S)

30 women with idiopathic RPL and 30 fertile controls.

INTERVENTION(S)

Endometrial biopsies.

MAIN OUTCOME MEASURE(S)

Real-time polymerase chain reaction analysis for expression of PROK1 and LIF mRNA.

RESULT(S)

The expression of PROK1 and LIF was statistically significantly increased in the endometrium of the women with idiopathic RPL compared with the controls. Furthermore, increased LIF expression was observed in the endometrium of women with idiopathic RPL compared with controls.

CONCLUSION(S)

An increased mRNA expression of PROK1 and LIF could be one of the several abnormalities characterizing the endometrium in women with RPL.

Fresh versus frozen embryo transfer: backing clinical decisions with scientific and clinical evidence

BACKGROUND

Improvements in vitrification now make frozen embryo transfers (FETs) a viable alternative to fresh embryo transfer, with reports from observational studies and randomized controlled trials suggesting that: (i) the endometrium in stimulated cycles is not optimally prepared for implantation; (ii) pregnancy rates are increased following FET and (iii) perinatal outcomes are less affected after FET.

METHODS

This review integrates and discusses the available clinical and scientific evidence supporting embryo transfer in a natural cycle.

RESULTS

Laboratory-based studies demonstrate morphological and molecular changes to the endometrium and reduced responsiveness of the endometrium to hCG, resulting from controlled ovarian stimulation. The literature demonstrates reduced endometrial receptivity in controlled ovarian stimulation cycles and supports the clinical observations that FET reduces the risk of ovarian hyperstimulation syndrome and improves outcomes for both the mother and baby.

CONCLUSIONS

This review provides the basis for an evidence-based approach towards changes in routine IVF, which may ultimately result in higher delivery rates of healthier term babies.

Prokineticin 1 induces a pro-inflammatory response in murine fetal membranes but does not induce preterm delivery

The mechanisms that regulate the induction of term or preterm delivery (PTD) are not fully understood. Infection is known to play a role in the induction of pro-inflammatory cascades in uteroplacental tissues associated with preterm pathological parturition. Similar but not identical cascades are evident in term labour. In the current study, we used a mouse model to evaluate the role of prokineticins in term and preterm parturition. Prokineticins are multi-functioning secreted proteins that signal through G-protein-coupled receptors to induce gene expression, including genes important in inflammatory responses. Expression of prokineticins (Prok1 and Prok2) was quantified in murine uteroplacental tissues by QPCR in the days preceding labour (days 16-19). Prok1 mRNA expression increased significantly on D18 in fetal membranes (compared with D16) but not in uterus or placenta. Intrauterine injection of PROK1 on D17 induced fetal membrane mRNA expression of the pro-inflammatory mediators Il6, Il1b, Tnf, Cxcl2 and Cxcl5, which are not normally up-regulated until D19 of pregnancy. However, intrauterine injection of PROK1 did not result in PTD. As expected, injection of lipopolysaccharide (LPS) induced PTD, but this was not associated with changes in expression of Prok1 or its receptor (Prokr1) in fetal membranes. These results suggest that although Prok1 exhibits dynamic mRNA regulation in fetal membranes preceding labour and induces a pro-inflammatory response when injected into the uterus on D17, it is insufficient to induce PTD. Additionally, prokineticin up-regulation appears not to be part of the LPS-induced inflammatory response in mouse fetal membranes.

The expression of IL-6Rα and Gp130 in fallopian tubes bearing an ectopic pregnancy

Women with tubal ectopic pregnancies have high levels of circulating interleukin 6 (IL-6). IL-6 treatment in vitro significantly reduces the ciliary activity of tubal epithelium. The effects of IL-6 on target cells occur via the formation of a high-affinity complex with its receptors IL-6Rα and glycoprotein 130 (Gp130). IL-6Rα is specifically expressed in the cilia of the epithelial cells. In this study, we performed a quantitative reverse transcriptase polymerase chain reaction to determine the mRNA expression of IL-6Rα and Gp130 in the fallopian tubes obtained from 12 women with ectopic pregnancies, 12 women with normal pregnancies, and 12 healthy nonpregnant women in the luteal phase of their menstrual cycle. Fallopian tubes were evaluated from specimens taken during tubal ligation in normal pregnancies and nonpregnant fertile women or during tubal surgery in ectopic pregnancies. We observed that IL-6Rα mRNA expression in fallopian tubes was increased in ectopic pregnancy compared with that in the midluteal phase. We also found that the Gp130 mRNA expression was significantly lower in fallopian tubes from ectopic pregnancies than in those from nonpregnant women during the midluteal phase of their menstrual cycle, although its expression was noticeably high in fallopian tubes in the midluteal phase, which suggests that high Gp130 levels may possibly contribute to embryo transport into the uterus.

Prokineticin receptor variants (PKR1-I379V and PKR2-V331M) are protective genotypes in human early pregnancy

Endocrine gland-derived vascular endothelial growth factor (EG-VEGF) and its receptor genes (PROKR1(PKR1) andPROKR2(PKR2)) play an important role in human early pregnancy. We have previously shown thatPROKR1andPROKR2are associated with recurrent miscarriage (RM) using the tag-SNP method. In this study, we aimed to identifyPROKR1andPROKR2variants in idiopathic RM patients by genotyping of the entire coding regions. Peripheral blood DNA samples of 100 RM women and 100 controls were subjected to sequence the entire exons ofPROKR1andPROKR2. Significant non-synonymous variant genotypes present in the original 200 samples were further confirmed in the extended samples of 144 RM patients and 153 controls. Genetic variants that were over- or under-represented in the patients were ectopically expressed in HEK293 and JAR cells to investigate their effects on intracellular calcium influx, cell proliferation, cell invasion, cell–cell adhesion, and tube organization. We found that the allele and genotype frequencies ofPROKR1(I379V) andPROKR2(V331M) were significantly increased in the normal control groups compared with idiopathic RM women (P<0.05).PROKR1(I379V) andPROKR2(V331M) decreased intracellular calcium influx but increased cell invasiveness (P<0.05), whereas cell proliferation, cell–cell adhesion, and tube organization were not significantly affected. In conclusion,PROKR1(I379V) andPROKR2(V331M) variants conferred lower risk for RM and may play protective roles in early pregnancy by altering calcium signaling and facilitating cell invasiveness.

Transcriptome analysis reveals new insights into the modulation of endometrial stromal cell receptive phenotype by embryo-derived signals interleukin-1 and human chorionic gonadotropin: possible involvement in early embryo implantation

The presence of the conceptus in uterine cavity necessitates an elaborate network of interactions between the implanting embryo and a receptive endometrial tissue. We believe that embryo-derived signals play an important role in the remodeling and the extension of endometrial receptivity period. Our previous studies provided original evidence that human Chorionic Gonadotropin (hCG) modulates and potentiates endometrial epithelial as well as stromal cell responsiveness to interleukin 1 (IL1), one of the earliest embryonic signals, which may represent a novel pathway by which the embryo favors its own implantation and growth within the maternal endometrial host. The present study was designed to gain a broader understanding of hCG impact on the modulation of endometrial cell receptivity, and in particular, cell responsiveness to IL1 and the acquisition of growth-promoting phenotype capable of receiving, sustaining, and promoting early and crucial steps of embryonic development. Our results showed significant changes in the expression of genes involved in cell proliferation, immune modulation, tissue remodeling, apoptotic and angiogenic processes. This points to a relevant impact of these embryonic signals on the receptivity of the maternal endometrium, its adaptation to the implanting embryo and the creation of an environment that is favorable for the implantation and the growth of this latter within a new and likely hostile host tissue. Interestingly our data further identified a complex interaction between IL1 and hCG, which, despite a synergistic action on several significant endometrial target genes, may encompass a tight control of endogenous IL1 and extends to other IL1 family members.

Human chorionic gonadotropin (hCG) modulation of TIMP1 secretion by human endometrial stromal cells facilitates extravillous trophoblast invasion in vitro

STUDY QUESTION

Are secreted extracellular matrix (ECM) remodelling elements, relevant to embryo implantation and placentation, modified by hCG in endometrial stromal cells (ESCs)?

SUMMARY ANSWER

hCG decreases tissue inhibitor of metalloproteinase 1 (TIMP-1) secretion in ESCs, thereby facilitating extravillous trophoblast invasion in vitro.

WHAT IS KNOWN ALREADY

Successful embryo implantation and placentation depend on the appropriate invasion of the trophoblast into the maternal endometrial stroma. hCG is one of the earliest embryo-derived secreted signals in the endometrium which abundantly expresses hCG receptors. However, there is little data concerning the effects of hCG on endometrial ECM remodelling with respect to embryo implantation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

This study was conducted in an academic research laboratory within a tertiary-care hospital. Samples were collected from 36 women undergoing benign gynaecological surgery during the mid-secretory phase. ESCs were isolated and stimulated with hCG (10 UI/ml) or vehicle. Conditioned media (CM) were analysed to determine changes in the secreted profile of nine matrix metalloproteinases (MMPs) and three tissue-specific inhibitors of MMPs (TIMPs) using an ELISA array. Data were confirmed by gelatine zymography, western blot and ELISA. The HTR8/SVneo cell line served as a model for trophoblast cells. The invasive potential of trophoblast cells was assessed using Transwell invasion assays under CM or co-culture conditions with ECS and the role of regulated molecules was examined by using immunoprecipitation in CM prior to the assessment of invasive potential.

MAIN RESULTS AND THE ROLE OF CHANCE

MMP-2 levels increased 30%, whereas TIMP-1 levels decreased 20% in CM from ESCs stimulated with hCG (P < 0.05). Gelatine zymography confirmed an increase in MMP-2 activity (P < 0.05). ELISA and western blotting also confirmed the reduction in TIMP-1 upon hCG treatment (P < 0.05). Invasion assays revealed a ∼50% increase in invading HTR8/SVneo cells in chambers with hCG-stimulated ESCs compared with the control (P < 0.05). Immunodepletion of TIMP-1 from control ESC-CM partially resembled the effect of CM from hCG-stimulated ESCs in the trophoblast invasion assays.

LIMITATIONS, REASONS FOR CAUTION

The assays were performed in vitro and ESCs were not decidualized, therefore they reflected the very early stages of embryo implantation or the advanced stages when decidualization fails.

WIDER IMPLICATIONS OF THE FINDINGS

Our data suggest that hCG induces endometrial stromal extracellular remodelling by modulating secreted MMP-2 and TIMP-1. This regulation may be physiologically relevant because it increases the invasive potential of trophoblast-derived cells. At present, few data exist concerning the implications of hCG and endometrial ECM remodelling in embryo implantation. Hence, our results should be confirmed by further in vivo studies.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by FONDECYT 11100443, PBCT-PSD51 (IDIMI) and FONDAP 15010006. None of the authors have any conflicts of interest to declare.

The differential expression of Kiss1, MMP9 and angiogenic regulators across the feto-maternal interface of healthy human pregnancies: implications for trophoblast invasion and vessel development

Genes involved in invasion of trophoblast cells and angiogenesis are crucial in determining pregnancy outcome. We therefore studied expression profiles of these genes in both fetal and maternal tissues to enhance our understanding of feto-maternal dialogue. We investigated the expression of genes involved in trophoblast invasion, namely Kiss1, Kiss1 Receptor (Kiss1R) and MMP9 as well as the expression of angiogenic ligands Vascular Endothelial Growth Factor-A (VEGF-A) and Prokineticin-1 (PROK1) and their respective receptors (VEGFR1, VEGFR2 and PROK1R) across the feto-maternal interface of healthy human pregnancies. The placenta, placental bed and decidua parietalis were sampled at elective caesarean delivery. Real-time RT-PCR was used to investigate transcription, while immunohistochemistry and western blot analyses were utilized to study protein expression. We found that the expression of Kiss1 (p<0.001), Kiss1R (p<0.05) and MMP9 (p<0.01) were higher in the placenta compared to the placental bed and decidua parietalis. In contrast, the expression of VEGF-A was highest in the placental bed (p<0.001). While VEGFR1 expression was highest in the placenta (p<0.01), the expression of VEGFR2 was highest in the placental bed (p<0.001). Lastly, both PROK1 (p<0.001) and its receptor PROK1R (p<0.001) had highest expression in the placenta. Genes associated with trophoblast invasion were highly expressed in the placenta which could suggest that the influence on invasion capacity may largely be exercised at the fetal level. Furthermore, our findings on angiogenic gene expression profiles suggest that angiogenesis may be regulated by two distinct pathways with the PROK1/PROK1R system specifically mediating angiogenesis in the fetus and VEGFA/VEGFR2 ligand-receptor pair predominantly mediating maternal angiogenesis.

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.

Regulation of expression and role of leukemia inhibitory factor and interleukin-6 in the uterus of early pregnant pigs

Cytokines, which are generally involved in the process of inflammation, may also play a critical role in conceptus implantation. We examined: (1) the expression profiles of leukemia inhibitory factor (LIF) and interleukin (IL)-6 mRNA and their protein content in the endometrium of cyclic and pregnant gilts on Days 10 to 18 after estrus; (2) the effect of conceptus-exposed medium on LIF and IL-6 synthesis in the endometrium; (3) the profiles of IL6R and LIFR mRNA expression in pig conceptuses collected on Days 10 to 18 of pregnancy; and (4) the effect of LIF and IL-6 on the attachment and proliferation of porcine trophoblast cells. The expression of LIF mRNA in the endometrium increased between Days 10 and 12 in both cyclic and pregnant gilts, and tended to be higher in Day 12 pregnant animals compared with nonpregnant ones. The LIF protein content in the uterine lumen peaked on Day 12 of pregnancy, and was higher than on Day 12 of the estrous cycle. Endometrial IL-6 mRNA expression was upregulated on Day 12 in pregnant gilts compared with nonpregnant animals. Moreover, a higher content of IL-6 protein was observed in pregnant than in cyclic gilts. The addition of conceptus-exposed medium resulted in up-regulation of LIF and IL6 mRNA expression, and increased IL-6 content in endometrial slices. In conceptuses, increased mRNA expression was detected on Days 10 to 14 for IL6R and on Day 14 for LIFR, when compared with other days studied. LIF and IL-6 stimulated the attachment and proliferation of trophoblast cells in vitro. In summary, LIF and IL-6 are important components of embryo-uterine interactions during early pregnancy in the pig, and may contribute to successful conceptus implantation.

Implantation failure in mice with a disruption in Phospholipase C beta 1 gene: lack of embryonic attachment, aberrant steroid hormone signalling and defective endocannabinoid metabolism

Phospholipase C beta 1 (PLCβ1) is a downstream effector of G-protein-coupled receptor signalling and holds central roles in reproductive physiology. Mice with a disruption in the Plcβ1 gene are infertile with pleiotropic reproductive defects, the major reproductive block in females being implantation failure. Here, PLCβ1 was demonstrated at the luminal and glandular epithelia throughout the pre- and peri-implantation period, with transient stromal expression during 0.5-1.5 days post coitum (dpc). Examination of implantation sites at 4.5 dpc showed that in females lacking functional PLCβ1 (knock-out (KO) females), embryos failed to establish proper contact with the uterine epithelium. Proliferating luminal epithelial cells were evident in KO implantation sites, indicating failure to establish a receptive uterus. Real-time PCR demonstrated that KO implantation sites had aberrant ovarian steroid signalling, with high levels of estrogen receptor α, lactoferrin and amphiregulin mRNA, while immunohistochemistry revealed very low levels of estrogen receptor α protein, possibly due to rapid receptor turnover. KO implantation sites expressed markedly less fatty acid amide hydrolase and monoacylglycerol lipase, indicating that endocannabinoid metabolism was also affected. Collectively, our results show that PLCβ1 is essential for uterine preparation for implantation, and that defective PLCβ1-mediated signalling during implantation is associated with aberrant ovarian steroid signalling and endocannabinoid metabolism.

EG-VEGF: a key endocrine factor in placental development

Endocrine gland-derived vascular endothelial growth factor (EG-VEGF), also named prokineticin 1, is the canonical member of the prokineticin family. Numerous reports suggest a direct involvement of this peptide in normal and pathological reproductive processes. Recent advances propose EG-VEGF as a key endocrine factor that controls many aspects of placental development and suggest its involvement in the development of preeclampsia (PE), the most threatening pathology of human pregnancy. This review describes the finely tuned action and regulation of EG-VEGF throughout human pregnancy, argues for its clinical relevance as a potential diagnostic marker of the onset of PE, and discusses future research directions for therapeutic targeting of EG-VEGF.