Amphiregulin is much more abundantly expressed than transforming growth factor-alpha and epidermal growth factor in human follicular fluid obtained from patients undergoing in vitro fertilization-embryo transfer

Associations Between Follicular Fluid Biomarkers and IVF/ICSI Outcomes in Normo-Ovulatory Women-A Systematic Review

(1) Background: The follicular fluid (FF) comprises a large portion of ovarian follicles, and serves as both a communication and growth medium for oocytes, and thus should be representative of the metabolomic status of the follicle. This review aims to explore FF biomarkers as well as their effects on fertilization, oocyte, and embryo development, and later on implantation and maintenance of pregnancy. (2) Methods: This review was registered in the PROSPERO database with the ID: CRD42025633101. We parsed PubMed, Scopus, and Google Scholar for research on the effects of different FF biomarkers on IVF/ICSI outcomes in normo-ovulatory women. Included studies were assessed for risk of bias using the NOS scale. Data were extracted and tabulated by two independent researchers. (3) Results: 22 included articles, with a sample size range of 31 to 414 and a median of 60 participants, contained 61 biomarkers, including proteins, growth factors, steroid and polypeptide hormones, inflammation and oxidative stress markers, amino acids, vitamins, lipids of different types, and miRNAs. Most of the biomarkers studied had significant effects on IVF/ICSI outcomes, and seem to have roles in various cellular pathways responsible for oocyte and embryo growth, implantation, placental formation, and maintenance of pregnancy. The FF metabolome also seems to be interconnected, with its various components influencing the levels and activities of each other through feedback loops. (4) Conclusions: FF biomarkers can be utilized for diagnostic and therapeutic purposes in IVF; however, further studies are required for choosing the most promising ones due to heterogeneity of results. Widespread adoption of LC-MS and miRNA microarrays can help quantify a representative FF metabolome, and we see great potential for in vitro supplementation (IVS) of some FF biomarkers in improving IVF/ICSI outcomes.

Amphiregulin Downregulates E-cadherin Expression by Activating YAP/Egr-1/Slug Signaling in SKOV3 Human Ovarian Cancer Cells

Amphiregulin (AREG) stimulates human epithelial ovarian cancer (EOC) cell invasion by downregulating E-cadherin expression. YAP is a transcriptional cofactor that has been shown to regulate tumorigenesis. This study aimed to examine whether AREG activates YAP in EOC cells and explore the roles of YAP in AREG-induced downregulation of E-cadherin and cell invasion. Analysis of the Cancer Genome Atlas (TCGA) showed that upregulation of AREG and EGFR were associated with poor survival in human EOC. Treatment of SKOV3 human EOC cells with AREG induced the activation of YAP. In addition, AREG downregulated E-cadherin, upregulated Egr-1 and Slug, and stimulated cell invasion. Using gain- and loss-of-function approaches, we showed that YAP was required for the AREG-upregulated Egr-1 and Slug expression. Furthermore, YAP was also involved in AREG-induced downregulation of E-cadherin and cell invasion. This study provides evidence that AREG stimulates human EOC cell invasion by downregulating E-cadherin expression through the YAP/Egr-1/Slug signaling.

Impact of Amphiregulin on Oocyte Maturation and Embryo Quality: Insights from Clinical and Molecular Perspectives

Introduction

Identifying non-invasive biomarkers which can predict the outcome of intracytoplasmic sperm injection (ICSI) is crucial, particularly in Germany where the challenges are intensified by the Embryo Protection Act. Recent research has highlighted biomarkers within the epidermal growth factor (EGF) family as central to follicular processes, although their predictive utility remains a subject of debate in the literature. Therefore, the primary objective of this study was to investigate the significance of amphiregulin concentrations in follicular fluid and gene expression in mural granulosa cells on oocyte maturation, fertilization, and embryo quality.

Patients and Methods

A total of 33 women were recruited at the University Clinic of Saarland Fertility Center (Homburg, Germany). Follicular fluid aspiration consisted of single/individual aspiration of follicles, enabling a 1 : 1 correlation with retrieved oocytes. Follicular fluid and mural granulosa cell samples from 108 oocytes were analyzed. Amphiregulin levels were determined with enzyme-linked immunosorbent assay, while gene expression was analyzed with the StepOnePlus Real-Time PCR System using TaqMan Fast Advanced Master Mix assays.

Results

Results showed that amphiregulin concentrations affect oocyte maturation, fertilization, and embryo quality, while luteinizing hormone concentrations influence oocyte maturation, with significant differences identified between fertilized/unfertilized and good/poor embryo groups. Amphiregulin expression significantly impacts oocyte maturation, with downregulation observed in immature oocytes, while luteinizing hormone/chorionic gonadotropin receptor expression showed no significant differences between groups and did not influence maturation, fertilization, or embryo quality.

Conclusion

These findings are very important for advancing infertility treatment, especially in Germany. The results for amphiregulin may provide prognostic insights which could be useful when selecting viable oocytes and embryos. This research underscores the importance of non-invasive biomarkers for optimizing ICSI outcomes and potentially enhancing the success rates of assisted reproductive technology.

Epidermal growth factor receptor ligands enriched in follicular fluid exosomes promote oncogenesis of fallopian tube epithelial cells

BACKGROUND

Incessant ovulation is the main etiologic factor of ovarian high-grade serous carcinomas (HGSC), which mostly originate from the fallopian tube epithelium (FTE). Receptor tyrosine kinase (RTK) ligands essential for follicle development and ovulation wound repair were abundant in the follicular fluid (FF) and promoted the transformation of FTE cells. This study determined whether RTK ligands are present in FF exosomes and whether epidermal growth factor receptor (EGFR) signaling is essential for oncogenic activity.

METHODS

The FF of women undergoing in vitro fertilization was fractionated based on the richness of exosomes and tested for transformation toward FTE cells under different RTK inhibitors. EGFR ligands in FF exosomes were identified, and downstream signaling proteins in FTE cells were characterized.

RESULTS

The transforming activity of FF was almost exclusively enriched in exosomes, which possess a high capacity to induce anchorage-independent growth, clonogenicity, migration, invasion, and proliferation of FTE cells. EGFR inhibition abolished most of these activities. FF and FF exosome exposure markedly increased EGFR phosphorylation and the downstream signal proteins, including AKT, MAPK, and FAK. Multiple EGF family growth factors, such as amphiregulin, epiregulin, betacellulin, and transforming growth factor-alpha, were identified in FF exosomes.

CONCLUSIONS

Our results demonstrate that FF exosomes serve as carriers of EGFR ligands as well as ligands of other RTKs that mediate the transformation of FTE cells and underscore the need to further explore the content and roles of FF exosomes in HGSC development.

Interaction between epidermal growth factor receptor and C-C motif chemokine receptor 2 in the ovulatory cascade

The epidermal growth factor receptor (EGFR) signaling pathway is one of the main pathways responsible for propagating the luteinizing hormone (LH) signal throughout the cumulus cells and the oocyte. Recently, we have proposed the C-C motif chemokine receptor 2 (CCR2) and its main ligand (monocyte chemoattractant protein-1, MCP1) as novel mediators of the ovulatory cascade. Our previous results demonstrate that the gonadotropins (GNT), amphiregulin (AREG), and prostaglandin E2 (PGE2) stimulation of periovulatory gene mRNA levels occurs, at least in part, through the CCR2/MCP1 pathway, proposing the CCR2 receptor as a novel mediator of the ovulatory cascade in a feline model. For that purpose, feline cumulus-oocyte complexes (COCs) were cultured in the presence or absence of an EGFR inhibitor, recombinant chemokine MCP1, and gonadotropins [as an inducer of cumulus-oocyte expansion (C-OE), and oocyte maturation] to further assess the mRNA expression of periovulatory key genes, C-OE, oocyte nuclear maturation, and steroid hormone production. We observed that MCP1 was able to revert the inhibition of AREG mRNA expression by an EGFR inhibitor within the feline COC. In accordance, the confocal analysis showed that the GNT-stimulated hyaluronic acid (HA) synthesis, blocked by the EGFR inhibitor, was recovered by the addition of recombinant MCP1 in the C-OE culture media. Also, MCP1 was able to revert the inhibition of progesterone (P4) production by EGFR inhibitor in the C-OE culture media. Regarding oocyte nuclear maturation, recombinant MCP1 could also revert the inhibition triggered by the EGFR inhibitor, leading to a recovery in the percentage of metaphase II (MII)-stage oocytes. In conclusion, our results confirm the chemokine receptor CCR2 as a novel intermediate in the ovulatory cascade and demonstrate that the EGFR/AREG and the CCR2/MCP1 signaling pathways play critical roles in regulating feline C-OE and oocyte nuclear maturation, with CCR2/MCP1 signaling pathway being downstream EGFR/AREG pathway within the ovulatory cascade.

The role of amphiregulin in ovarian function and disease

Amphiregulin (AREG) is an epidermal growth factor (EGF)-like growth factor that binds exclusively to the EGF receptor (EGFR). Treatment with luteinizing hormone (LH) and/or human chorionic gonadotropin dramatically induces the expression of AREG in the granulosa cells of the preovulatory follicle. In addition, AREG is the most abundant EGFR ligand in human follicular fluid. Therefore, AREG is considered a predominant propagator that mediates LH surge-regulated ovarian functions in an autocrine and/or paracrine manner. In addition to the well-characterized stimulatory effect of LH on AREG expression, recent studies discovered that several local factors and epigenetic modifications participate in the regulation of ovarian AREG expression. Moreover, aberrant expression of AREG has recently been reported to contribute to the pathogenesis of several ovarian diseases, such as ovarian hyperstimulation syndrome, polycystic ovary syndrome, and epithelial ovarian cancer. Furthermore, increasing evidence has elucidated new applications of AREG in assisted reproductive technology. Collectively, these studies highlight the importance of AREG in female reproductive health and disease. Understanding the normal and pathological roles of AREG and elucidating the molecular and cellular mechanisms of AREG regulation of ovarian functions will inform innovative approaches for fertility regulation and the prevention and treatment of ovarian diseases. Therefore, this review summarizes the functional roles of AREG in ovarian function and disease.

AREG upregulates secreted protein acidic and rich in cysteine expression in human granulosa cells

The secreted protein acidic and rich in cysteine (SPARC) is a secreted glycoprotein and the expression of ovarian SPARC peaks during ovulation and luteinization. Besides, SPARC expression was induced by human chorionic gonadotropin (hCG) in rat granulosa cells. Amphiregulin (AREG) is the most abundant epidermal growth factor receptor (EGFR) ligand expressed in human granulosa cells and follicular fluid. AREG mediates the physiological functions of luteinizing hormone (LH)/hCG in the ovary. However, to date, the biological function of SPARC in the human ovary remains undetermined, and whether AREG regulates SPARC expression in human granulosa cells is unknown. In this study, we show that AREG upregulated SPARC expression via EGFR in a human granulosa-like tumor cell line, KGN. Treatment of AREG activated ERK1/2, JNK, p38 MAPK, and PI3K/AKT signaling pathways and all of them were required for the AREG-induced SPARC expression. Using RNA-sequencing, we identified that steroidogenic acute regulatory protein (StAR) was a downstream target gene of SPARC. In addition, we demonstrated that SPARC mRNA levels were positively correlated with the levels of StAR mRNA in the primary culture of human granulosa cells. Moreover, SPARC protein levels were positively correlated with progesterone levels in follicular fluid of in vitro fertilization patients. This study provides the regulatory role of AREG on the expression of SPARC and reveals the novel function of SPARC in progesterone production in granulosa cells.

HB-EGF upregulates StAR expression and stimulates progesterone production through ERK1/2 signaling in human granulosa-lutein cells

Background

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) belongs to the epidermal growth factor (EGF) family of growth factors. HB-EGF and its receptors, epidermal growth factor receptor (EGFR) and HER4, are expressed in the human corpus luteum. HB-EGF has been shown to regulate luteal function by preventing cell apoptosis. Steroidogenesis is the primary function of the human corpus luteum. Steroidogenic acute regulatory protein (StAR) plays a critical role in steroidogenesis. StAR expression and progesterone (P4) production in human granulosa-lutein (hGL) cells have been shown to be upregulated by a ligand of EGFR, amphiregulin. However, whether HB-EGF can achieve the same effects remains unknown.

Methods

A steroidogenic human ovarian granulosa-like tumor cell line, KGN, and primary culture of hGL cells obtained from patients undergoing in vitro fertilization treatment were used as experimental models. The underlying molecular mechanisms mediating the effects of HB-EGF on StAR expression and P4 production were explored by a series of in vitro experiments.

Results

Western blot showed that EGFR, HER2, and HER4 were expressed in both KGN and hGL cells. Treatment with HB-EGF for 24 h induced StAR expression but did not affect the expression of steroidogenesis-related enzymes, P450 side chain cleavage enzyme, 3β-hydroxysteroid dehydrogenase, and aromatase. Using pharmacological inhibitors and a siRNA-mediated knockdown approach, we showed that EGFR, HER4, but not HER2, were required for HB-EGF-stimulated StAR expression and P4 production. In addition, HB-EGF-induced upregulations of StAR expression and P4 production were mediated by the activation of the ERK1/2 signaling pathway.

Conclusion

This study increases the understanding of the physiological role of HB-EGF in human luteal functions.

A Case-Control Study of Follicular Fluid Cytokine Profiles in Women with Diminished Ovarian Reserve

Ovarian reserve is an important determinant of a woman's reproductive potential, and women with diminished ovarian reserve (DOR) often seek in vitro fertilization (IVF). The underlying etiology of DOR is unknown, but follicular fluid cytokine concentrations likely play a role in follicular development and maturation. The present study seeks to investigate the expression of cytokines in follicular fluid (FF) of women with DOR undergoing IVF and explore correlated functional pathways. One hundred ninety-four women undergoing ovarian stimulation were recruited at the time of oocyte retrieval. Women were classified as having DOR if they met one or more of the following criteria: AMH < 1 ng/ml, FSH > 10 mIU/ml, and/or AFC < 10. Controls included women undergoing IVF for male factor, tubal factor due to tubal ligation, or planned oocyte cryopreservation (non-oncologic). The concentrations of 480 cytokines and related growth factors in follicular fluid were determined using a multiplex immunoassay. Fifty-nine cytokines had significantly different concentrations (53 higher and 6 lower) in the DOR relative to the control group after adjusting for age and body mass index (BMI) (false discovery rate; FDR < 0.1). Using the most informative 44 biomarkers as indicated by a random forest (RF) model, an area under the curve (AUC) of 0.78 was obtained. Thus, follicular microenvironment differs between women with DOR and normal ovarian reserve. The differentially expressed cytokines belong to diverse processes that are primarily involved in follicular maturation and ovulation. These changes may play an important role in treatment outcomes in women with DOR.

Amphiregulin Supplementation During Pig Oocyte In Vitro Maturation Enhances Subsequent Development of Cloned Embryos by Promoting Cumulus Cell Proliferation

The oocyte in vitro maturation (IVM) technique is important in animal husbandry, biomedicine, and human-assisted reproduction. However, the developmental potential of in vitro matured oocytes is usually lower than that of in vivo matured (IVVM) oocytes. Amphiregulin (AREG) is an EGF-like growth factor that plays critical roles in the maturation and development of mammalian oocytes. This study investigated the effects of AREG supplementation during pig oocyte IVM on the subsequent development of cloned embryos. The addition of AREG to pig oocyte IVM medium improved the developmental competence of treated oocyte-derived cloned embryos by enhancing the expansion and proliferation of cumulus cells (CCs) during IVM. The positive effect of AREG on enhancing the quality of IVVM pig oocytes might be due to the activation of proliferation-related pathways in CCs by acting on the AREG receptor. The present study provides an AREG treatment-based method to improve the developmental competence of cloned pig embryos.

Positive effects of amphiregulin on human oocyte maturation and its molecular drivers in patients with polycystic ovary syndrome

STUDY QUESTION

Does use of medium containing amphiregulin improve meiotic maturation efficiency in oocytes of women with polycystic ovary syndrome (PCOS) undergoing in vitro maturation (IVM) preceded by a capacitation culture step capacitation IVM (CAPA-IVM)?

SUMMARY ANSWER

Use of medium containing amphiregulin significantly increased the maturation rate from oocytes retrieved from follicles with diameters <6 or ≥6 mm pre-cultured in capacitation medium.

WHAT IS KNOWN ALREADY

Amphiregulin concentration in follicular fluid is correlated with human oocyte developmental competence. Amphiregulin added to the meiotic trigger has been shown to improve outcomes of IVM in a range of mammalian species.

STUDY DESIGN, SIZE, DURATION

This prospective, randomized cohort study included 30 patients and was conducted at an academic infertility centre in Vietnam from April to December 2019. Patients with PCOS were included.

PARTICIPANTS/MATERIALS, SETTING, METHODS

In the first stage, sibling oocytes from each patient (671 in total) were allocated in equal numbers to maturation in medium with (CAPA-AREG) or without (CAPA-Control) amphiregulin 100 ng/ml. After a maturation check and fertilization using intracytoplasmic sperm injection (ICSI), all good quality Day 3 embryos were vitrified. Cumulus cells (CCs) from both groups were collected at the moment of ICSI denudation and underwent a molecular analysis to quantify key transcripts of oocyte maturation and to relate these to early embryo development. On return for frozen embryo transfer (second stage), patients were randomized to have either CAPA-AREG or CAPA-Control embryo(s) implanted. Where no embryo(s) from the randomized group were available, embryo(s) from the other group were transferred. The primary endpoint of the study was meiotic maturation efficiency (proportion of metaphase II [MII] oocytes; maturation rate).

MAIN RESULTS AND THE ROLE OF CHANCE

In the per-patient analysis, the number of MII oocytes was significantly higher in the CAPA-AREG group versus the CAPA-Control group (median [interquartile range] 7.0 [5.3, 8.0] versus 6.0 [4.0, 7.0]; P = 0.01). When each oocyte was evaluated, the maturation rate was also significantly higher in the CAPA-AREG group versus the CAPA-Control group (67.6% versus 55.2%; relative risk [RR] 1.22 [95% confidence interval (CI) 1.08-1.38]; P = 0.001). No other IVM or embryology outcomes differed significantly between the two groups. Rates of clinical pregnancy (66.7% versus 42.9%; RR 1.56 [95% CI 0.77-3.14]), ongoing pregnancy (53.3% versus 28.6%; RR 1.87 [95% CI 0.72-4.85]) and live birth (46.7% versus 28.6%; RR 1.63 [95% CI 0.61-4.39]) were numerically higher in the patients who had CAPA-AREG versus CAPA-Control embryos implanted, but each fertility and obstetric outcome did not differ significantly between the groups. In the CAPA-AREG group, there were significant shifts in CC expression of genes involved in steroidogenesis (STAR, 3BHSD), the ovulatory cascade (DUSP16, EGFR, HAS2, PTGR2, PTGS2, RPS6KA2), redox and glucose metabolism (CAT, GPX1, SOD2, SLC2A1, LDHA) and transcription (NRF2). The expression of three genes (TRPM7, VCAN and JUN) in CCs showed a significant correlation with embryo quality.

LIMITATIONS, REASONS FOR CAUTION

This study included only Vietnamese women with PCOS, limiting the generalizability. Although 100 ng/ml amphiregulin addition to the maturation culture step significantly improved the MII rate, the sample size in this study was small, meaning that these findings should be considered as exploratory. Therefore, a larger patient cohort is needed to confirm whether the positive effects of amphiregulin translate into improved fertility outcomes in patients undergoing IVM.

WIDER IMPLICATIONS OF THE FINDINGS

Data from this study confirm the beneficial effects of amphiregulin during IVM with respect to the trigger of oocyte maturation. The gene expression findings in cumulus indicate that multiple pathways might contribute to these beneficial effects and confirm the key role of the epidermal growth factor system in the stepwise acquisition of human oocyte competence.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED; grant number FWO.106-YS.2017.02) and by the Fund for Research Flanders (FWO; grant number G.OD97.18N). L.N.V. has received speaker and conference fees from Merck, grants, speaker and conference fees from Merck Sharpe and Dohme, and speaker, conference and scientific board fees from Ferring. T.M.H. has received speaker fees from Merck, Merck Sharp and Dohme and Ferring. J.S. reports speaker fees from Ferring Pharmaceuticals and Biomérieux Diagnostics and grants from FWO Flanders, is co-inventor on granted patents on CAPA-IVM methodologies in USA (US10392601B2), Europe (EP3234112B1) and Japan (JP 6806683 registered 08-12-2020) and is a co-shareholder of Lavima Fertility Inc., a spin-off company of the Vrije Universiteit Brussel (VUB, Brussels, Belgium). NA, TDP, AHL, MNHN, SR, FS, EA and UDTH report no financial relationships with any organizations that might have an interest in the submitted work in the previous three years, and no other relationships or activities that could appear to have influenced the submitted work.

TRIAL REGISTRATION NUMBER

NCT03915054.

In Vitro Maturation of Oocytes Retrieved from Ovarian Tissue: Outcomes from Current Approaches and Future Perspectives

In vitro maturation (IVM) of transvaginally aspirated immature oocytes is an effective and safe assisted reproductive treatment for predicted or high responder patients. Currently, immature oocytes are also being collected from the contralateral ovary during laparoscopy/laparotomy and even ex vivo from the excised ovary or the spent media during ovarian tissue preparation prior to ovarian cortex cryopreservation. The first live births from in vitro-matured ovarian tissue oocytes (OTO-IVM) were reported after monophasic OTO-IVM, showing the ability to achieve mature OTO-IVM oocytes. However, fertilisations rates and further embryological developmental capacity appeared impaired. The introduction of a biphasic IVM, also called capacitation (CAPA)-IVM, has been a significant improvement of the oocytes maturation protocol. However, evidence on OTO-IVM is still scarce and validation of the first results is of utmost importance to confirm reproducibility, including the follow-up of OTO-IVM children. Differences between IVM and OTO-IVM should be well understood to provide realistic expectations to patients.

Human chorionic gonadotropin-induced amphiregulin stimulates aromatase expression in human granulosa-lutein cells: a mechanism for estradiol production in the luteal phase

STUDY QUESTION

Does amphiregulin (AREG), the most abundant and important epidermal growth factor receptor (EGFR) ligand in the follicular fluid, regulate aromatase expression in human granulosa-lutein (hGL) cells?

SUMMARY ANSWER

AREG mediates the hCG-induced up-regulation of aromatase expression and estradiol (E2) production in hGL cells.

WHAT IS KNOWN ALREADY

AREG expression and secretion are rapidly induced by hCG in hGL cells and mediate physiological functions of LH/hCG in the ovary. EGFR protein is expressed in follicles not only in the pre-ovulatory phase but also throughout the luteal phase of the menstrual cycle. After the LH surge, the human corpus luteum secretes high levels of E2, which regulates various luteal cell functions. Aromatase is an enzyme responsible for a key step in the biosynthesis of E2. However, whether AREG regulates aromatase expression and E2 production in hGL cells remains unexplored.

STUDY DESIGN, SIZE, DURATION

This study is an experimental study performed over a 1-year period. In vitro investigations examined the role of AREG in the regulation of aromatase expression and E2 production in primary hGL cells.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Primary hGL cells were obtained from women undergoing IVF treatment in an academic research center. Aromatase mRNA and protein levels were examined after exposure of hGL cells to recombinant human AREG, hCG or LH. The EGFR tyrosine kinase inhibitor AG1478, PI3K inhibitor LY294002 and siRNAs targeting EGFR, LH receptor, StAR and AREG were used to verify the specificity of the effects and to investigate the underlying molecular mechanisms. Reverse transcription quantitative real-time PCR (RT-qPCR) and western blot were used to measure the specific mRNA and protein levels, respectively. Follicular fluid and serum were collected from 65 infertile women during IVF treatment. Pearson's correlation analysis was performed to examine the correlation coefficient between two values.

MAIN RESULTS AND THE ROLE OF CHANCE

Treatment of hGL cells with AREG-stimulated aromatase expression and E2 production. Using pharmacological inhibitors and specific siRNAs, we revealed that AREG-stimulated aromatase expression and E2 production via EGFR-mediated activation of the protein kinase B (AKT) signaling pathway. In addition, inhibition of EGFR activity and AREG knockdown attenuated hCG-induced up-regulation of aromatase expression and E2 production. Importantly, the protein levels of AREG in the follicular fluid were positively correlated with the E2 levels in serum after 2 days of oocyte pick-up and in the follicular fluid of IVF patients.

LARGE-SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

The in vitro setting of this study is a limitation that may not reflect the real intra-ovarian microenvironment. Clinical data were obtained from a small sample size.

WIDER IMPLICATIONS OF THE FINDINGS

Our results provide the first evidence that hCG-induced AREG contributes to aromatase expression and E2 production in the luteal phase of the menstrual cycle. A better understanding of the hormonal regulation of female reproductive function may help to develop new strategies for the treatment of clinical infertility.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Natural Science Foundation of China for Young Scientists (81601253), the specific fund of clinical medical research of Chinese Medical Association (16020160632) and the Foundation from the First Affiliated Hospital of Zhengzhou University for Young Scientists to Lanlan Fang. This work was also supported by an operating grant from the National Natural Science Foundation of China (81820108016) to Ying-Pu Sun. All authors declare no conflict of interest.

GnRH triggering may improve euploidy and live birth rate in hyper-responders: a retrospective cohort study

PURPOSE

Despite the increasing use of GnRHa to trigger final oocyte maturation in segmented IVF cycles, the effects of trigger modality on chromosomal competence and embryo quality remain controversial. Hence, the purpose of this study was to compare euploidy rates and pregnancy outcomes among hyper-responding women using hCG versus GnRHa trigger.

METHODS

This retrospective study included 333 hyper-responders, defined as >15 oocytes retrieved, who underwent preimplantation genetic testing (PGT-A) in segmented IVF cycles using either GnRHa or urinary hCG trigger. Live birth rate (LBR) was the primary outcome of interest. Implantation rate (IR), clinical pregnancy rate (CPR), and euploidy rate were secondary outcomes.

RESULTS

GnRH triggering was associated with improved IR (70.5 vs. 53.2%, p = 0.0475), LBR (51.3 vs. 33.8%, p = 0.0170) compared to hCG. A greater number of oocytes were retrieved (21.9 vs 18.4%, p < 0.001) and euploid embryos produced (2.8 vs. 2.1, p = 0.0109) after GnRHa triggering, while higher euploidy rates were only observed among women <35-years-old (62.0 vs. 51.7%, p = 0.0307) using GnRHa trigger. Higher OHSS rates were observed after hCG triggering (10.6 vs. 2.1%, p = 0.0009).

CONCLUSION

Hyper-responders who received GnRHa trigger experienced improved pregnancy outcomes and lower rates of OHSS compared to hCG triggering. The higher number of oocytes retrieved and euploid embryos produced may reflect an improved developmental competence using GnRHa triggering due to physiologic induction of both LH and FSH surge or other undefined mechanisms that improve embryo development. However, higher overall euploid rates were only observed among women <35-years-old using the GnRHa trigger. Further prospective studies are required to validate this observation and evaluate the specific influence of different ovulation triggers on gamete developmental competence among hyper-responder women.

Luteinizing Hormone Action in Human Oocyte Maturation and Quality: Signaling Pathways, Regulation, and Clinical Impact

The ovarian follicle luteinizing hormone (LH) signaling molecules that regulate oocyte meiotic maturation have recently been identified. The LH signal reduces preovulatory follicle cyclic nucleotide levels which releases oocytes from the first meiotic arrest. In the ovarian follicle, the LH signal reduces cyclic nucleotide levels via the CNP/NPR2 system, the EGF/EGF receptor network, and follicle/oocyte gap junctions. In the oocyte, reduced cyclic nucleotide levels activate the maturation promoting factor (MPF). The activated MPF induces chromosome segregation and completion of the first and second meiotic divisions. The purpose of this paper is to present an overview of the current understanding of human LH signaling regulation of oocyte meiotic maturation by identifying and integrating the human studies on this topic. We found 89 human studies in the literature that identified 24 LH follicle/oocyte signaling proteins. These studies show that human oocyte meiotic maturation is regulated by the same proteins that regulate animal oocyte meiotic maturation. We also found that these LH signaling pathway molecules regulate human oocyte quality and subsequent embryo quality. Remarkably, in vitro maturation (IVM) prematuration culture (PMC) protocols that manipulate the LH signaling pathway improve human oocyte quality of cultured human oocytes. This knowledge has improved clinical human IVM efficiency which may become a routine alternative ART for some infertile patients.

Novel Concepts for Inducing Final Oocyte Maturation in In Vitro Fertilization Treatment

Infertility affects one in six of the population and increasingly couples require treatment with assisted reproductive techniques. In vitro fertilization (IVF) treatment is most commonly conducted using exogenous FSH to induce follicular growth and human chorionic gonadotropin (hCG) to induce final oocyte maturation. However, hCG may cause the potentially life-threatening iatrogenic complication "ovarian hyperstimulation syndrome" (OHSS), which can cause considerable morbidity and, rarely, even mortality in otherwise healthy women. The use of GnRH agonists (GnRHas) has been pioneered during the last two decades to provide a safer option to induce final oocyte maturation. More recently, the neuropeptide kisspeptin, a hypothalamic regulator of GnRH release, has been investigated as a novel inductor of oocyte maturation. The hormonal stimulus used to induce oocyte maturation has a major impact on the success (retrieval of oocytes and chance of implantation) and safety (risk of OHSS) of IVF treatment. This review aims to appraise experimental and clinical data of hormonal approaches used to induce final oocyte maturation by hCG, GnRHa, both GnRHa and hCG administered in combination, recombinant LH, or kisspeptin. We also examine evidence for the timing of administration of the inductor of final oocyte maturation in relationship to parameters of follicular growth and the subsequent interval to oocyte retrieval. In summary, we review data on the efficacy and safety of the major hormonal approaches used to induce final oocyte maturation in clinical practice, as well as some novel approaches that may offer fresh alternatives in future.

The epidermal growth factor network: role in oocyte growth, maturation and developmental competence

BACKGROUND

The LH surge induces great physiological changes within the preovulatory follicle, which culminate in the ovulation of a mature oocyte that is capable of supporting embryo and foetal development. However, unlike mural granulosa cells, the oocyte and its surrounding cumulus cells are not directly responsive to LH, indicating that the LH signal is mediated by secondary factors produced by the granulosa cells. The mechanisms by which the oocyte senses the ovulatory LH signal and hence prepares for ovulation has been a subject of considerable controversy for the past four decades. Within the last 15 years several significant insights have been made into the molecular mechanisms orchestrating oocyte development, maturation and ovulation. These findings centre on the epidermal growth factor (EGF) pathway and the role it plays in the complex signalling network that finely regulates oocyte maturation and ovulation.

OBJECTIVE AND RATIONALE

This review outlines the role of the EGF network during oocyte development and regulation of the ovulatory cascade, and in particular focuses on the effect of the EGF network on oocyte developmental competence. Application of this new knowledge to advances in ART is examined.

SEARCH METHODS

The PubMed database was used to search for peer-reviewed original and review articles concerning the EGF network. Publications offering a comprehensive description of the role of the EGF network in follicle and oocyte development were used.

OUTCOMES

It is now clear that acute upregulation of the EGF network is an essential component of the ovulatory cascade as it transmits the LH signal from the periphery of the follicle to the cumulus-oocyte complex (COC). More recent findings have elucidated new roles for the EGF network in the regulation of oocyte development. EGF signalling downregulates the somatic signal 3'5'-cyclic guanine monophosphate that suppresses oocyte meiotic maturation and simultaneously provides meiotic inducing signals. The EGF network also controls translation of maternal transcripts in the quiescent oocyte, a process that is integral to oocyte competence. As a means of restricting the ovulatory signal to the Graffian follicle, most COCs in the ovary are unresponsive to EGF-ligands. Recent studies have revealed that development of a functional EGF signalling network in cumulus cells requires dual endocrine (FSH) and oocyte paracrine cues (growth differentiation factor 9 and bone morphogenetic protein 15), and this occurs progressively in COCs during the last stages of folliculogenesis. Hence, a new concept to emerge is that cumulus cell acquisition of EGF receptor responsiveness represents a developmental hallmark in folliculogenesis, analogous to FSH-induction of LH receptor signalling in mural granulosa cells. Likewise, this event represents a major milestone in the oocyte's developmental progression and acquisition of developmental competence. It is now clear that EGF signalling is perturbed in COCs matured in vitro. This has inspired novel concepts in IVM systems to ameliorate this perturbation, resulting in improved oocyte developmental competence.

WIDER IMPLICATIONS

An oocyte of high quality is imperative for fertility. Elucidating the fundamental molecular and cellular mechanims by which the EGF network regulates oocyte maturation and ovulation can be expected to open new opportunities in ART. This knowledge has already led to advances in oocyte IVM in animal models. Translation of such advances into a clinical setting should increase the efficacy of IVM, making it a viable treatment option for a wide range of patients, thereby simplifying fertility treatment and bringing substantial cost and health benefits.

Sprouty2 inhibits amphiregulin-induced down-regulation of E-cadherin and cell invasion in human ovarian cancer cells

Similar to Drosophila Sprouty (SPRY), mammalian SPRY proteins inhibit the receptor tyrosine kinase-mediated activation of cellular signaling pathways. SPRY2 expression levels have been shown to be down-regulated in human ovarian cancer, and patients with low SPRY2 expression have significantly poorer survival than those with high SPRY2 expression. In addition, epidermal growth factor receptor (EGFR) is overexpressed in human ovarian cancer and is associated with more aggressive clinical behavior and a poor prognosis. Amphiregulin (AREG), the most abundant EGFR ligand in ovarian cancer, binds exclusively to EGFR and stimulates ovarian cancer cell invasion by down-regulating E-cadherin expression. However, thus far, the roles of SPRY2 in AREG-regulated E-cadherin expression and cell invasion remain unclear. In the present study, we show that treatment with AREG up-regulated SPRY2 expression by activating the EGFR-mediated ERK1/2 signaling pathway in two human ovarian cancer cell lines, SKOV3 and OVCAR5. In addition, overexpression of SPRY2 attenuated the AREG-induced down-regulation of E-cadherin by inhibiting the induction of the E-cadherin transcriptional repressor, Snail. Moreover, SPRY2 overexpression attenuated AREG-stimulated cell invasion and proliferation. This study reveals that SPRY2 acts as a tumor suppressor in human ovarian cancer and illustrates the underlying mechanisms that can be used as possible targets for the development of novel therapeutics.

Amphiregulin mediates hCG-induced StAR expression and progesterone production in human granulosa cells

Progesterone plays critical roles in maintaining a successful pregnancy at the early embryonic stage. Human chorionic gonadotropin (hCG) rapidly induces amphiregulin (AREG) expression. However, it remains unknown whether AREG mediates hCG-induced progesterone production. Thus, the objective of this study was to investigate the role of AREG in hCG-induced progesterone production and the underlying molecular mechanism in human granulosa cells; primary cells were used as the experimental model. We demonstrated that the inhibition of EGFR and the knockdown of AREG abolished hCG-induced steroidogenic acute regulatory protein (StAR) expression and progesterone production. Importantly, follicular fluid AREG levels were positively correlated with progesterone levels in the follicular fluid and serum. Treatment with AREG increased StAR expression and progesterone production, and these stimulatory effects were abolished by EGFR inhibition. Moreover, activation of ERK1/2, but not PI3K/Akt, signaling was required for the AREG-induced up-regulation of StAR expression and progesterone production. Our results demonstrate that AREG mediates hCG-induced StAR expression and progesterone production in human granulosa cells, providing novel evidence for the role of AREG in the regulation of steroidogenesis.

Altered amphiregulin expression induced by diverse luteinizing hormone receptor reactivity in granulosa cells affects IVF outcomes

The expression of specific genes (LHR, AREG, EREG, EGFR, NPPC and NPR2) involved in peri-ovulatory signalling pathways induced by LH surge in granulosa cells was investigated, and their relationships with IVF outcomes analysed. mRNA levels of the genes of 147 infertile women undergoing IVF and intracytoplasmic sperm injection (ICSI) with embryo transfer were evaluated. Compared with non-pregnant women, amphiregulin (AREG) mRNA levels in mural and cumulus graunulosa cells were significantly higher (P < 0.05) in pregnant women, and were positively correlated with number of oocytes retrieved and good-quality embryos. No significant differences were found between the two groups in the remaining detected genes. To investigate the reason for the differences in AREG expression, mural granulosa cells were cultured and stimulated with human chorionic gonadotrophin (HCG) for 2-24 h. At 4 h after HCG stimulation, AREG and epiregulin mRNA expression peaked, with much greater increases in the pregnant group. The fold-change of AREG expression was positively correlated with number of good-quality embryos. No obvious correlation, however, was found between NPPC/Npr2 expression levels in granulosa cells and IVF outcomes. Altered AREG expression induced by diverse luteinizing hormone receptor reactivity in granulosa cells may provide a useful marker for oocyte developmental competency.

Amphiregulin induces human ovarian cancer cell invasion by down-regulating E-cadherin expression

Aberrant epidermal growth factor receptor (EGFR) activation is associated with ovarian cancer progression. In this study, we report that the EGFR ligand amphiregulin (AREG) stimulates cell invasion and down-regulates E-cadherin expression in two human ovarian cancer cell lines, SKOV3 and OVCAR5. In addition, AREG increases the expression of transcriptional repressors of E-cadherin including SNAIL, SLUG and ZEB1. siRNA targeting SNAIL or SLUG abolishes AREG-induced cell invasion. Moreover, ERK1/2 and AKT pathways are involved in AREG-induced E-cadherin down-regulation and cell invasion. Finally, we show that three EGFR ligands, AREG, epidermal growth factor (EGF) and transforming growth factor-α (TGF-α), exhibit comparable effects in down-regulating E-cadherin and promoting cell invasion. This study demonstrates that AREG induces ovarian cancer cell invasion by down-regulating E-cadherin expression.

GnRH agonist vs. hCG for triggering of ovulation--differential effects on gene expression in human granulosa cells

OBJECTIVE

To investigate the mRNA expression of genes related to steroidogenesis and OHSS in granulosa cells (GCs) of patients triggered with GnRH agonist compared to patients triggered with hCG.

DESIGN

Mural GCs were obtained at the time of oocyte retrieval and gene expression was analyzed using quantitative real time RT-PCR.

SETTINGS

Single center, case control study.

PATIENT(S)

24 women who were treated with GnRH agonist or hCG for triggering of ovulation.

INTERVENTIONS

GC collection.

MAIN OUTCOME MEASURE(S)

The expression of genes related to steroidogenesis and OHSS in mural GCs.

RESULTS

The fertilization rate was similar in the two groups. The mRNA expression of CYP19A1 (0.50 vs 1, arbitrary unit), CYP11A1 (0.6 vs. 1) and 3 beta hydroxysteroid-dehydrogenase (0.39 vs 1) was significantly lower in the GnRH group. The expression of VEGF (0.74 vs. 1) and inhibin β B (0.38 vs 1) was lower in the GnRH analog triggered group.

CONCLUSION

Expression of genes related to steroidogenesis is lower at the time of oocyte retrieval in patients triggered with GnRH agonist. The decreased expression of VEGF and inhibin β B in the GnRH agonist group can explain the mechanism of early OHSS prevention.

EGF-like ligands mediate progesterone's anti-apoptotic action on macaque granulosa cells

A local autocrine/paracrine role for progesterone is an absolute requirement for corpus luteum formation in primates. Despite this, the mechanism(s) remain obscure, although existing data suggest an anti-apoptotic action to be central. There are a limited number of progestin-regulated gene targets identified in the luteinizing primate follicle, suggesting that a small number of important genes may mediate progesterone action. Possible gene targets could be the epidermal growth factor (EGF) family members amphiregulin (AREG) and epiregulin (EREG). Using macaques undergoing controlled ovarian stimulation cycles, we show that the phosphorylation of EGF receptor (EGFR), ERK 1/2, and AKT increases 6 h after an ovulatory human chorionic gonadotropin (hCG) stimulus and remains activate through 24 h. Immunoreactive EREG and AREG ligands in the follicular fluid both increased in a time frame commensurate with EGFR phosphorylation. The mRNA expression of AREG and EREG in nonluteinized granulosa cells (NLGC) was induced in culture with hCG, an effect blocked by progesterone receptor (PGR) antagonists. Overexpression of PGR B in NLGC and treatment with a nonmetabolizable progestin did not increase either gene, indicating both progesterone and luteinizing hormone/CG are necessary. Addition of EGF and EGF-like ligands did not promote steroidogenesis in vitro by granulosa cells in the presence of gonadotropin, but were able to partially reverse RU486-induced cell death. These data suggest that progesterone promotes the expression of AREG and EREG, which in turn maintain viability of luteinizing granulosa cells, representing one possible mechanism whereby progesterone promotes corpus luteum formation in the primate.

Comparison of follicular fluid amphiregulin and EGF concentrations in patients undergoing IVF with different stimulation protocols

Epidermal growth factor (EGF)-like growth factors, such as amphiregulin (AR) and EGF, have emerged as mediators to propagate Luteinizing hormone (LH) stimulus for the oocyte maturation throughout the preovulatory follicle, because cumulus cells and oocytes express few or no LH receptors. This study was to compare AR and EGF concentrations in follicular fluid (FF) among four controlled ovary stimulation (COS) protocols and to investigate the relationship between FF EGF-like growth factors and COS outcomes. Ninety-five patients who underwent in vitro fertilization-embryo transfer (IVF-ET) were treated by four different COS protocols, including gonadotropin-releasing hormone agonist (GnRH-a) long protocol, GnRH-a ultra-long protocol, GnRH-a short protocol, and GnRH antagonist protocol. FF was taken on oocyte retrieval day. FF AR and EGF concentrations were measured and their correlations with COS outcomes were analyzed. FF AR concentration was significantly different from each other among four COS protocol groups (GnRH-a ultra-long protocol group, 186.12 ng/ml; GnRH-a long protocol group, 128.35 ng/ml; GnRH antagonist protocol group, 108.23 ng/ml; GnRH-a short protocol group, 77.13 ng/ml, p < 0.05). FF AR concentrations were higher in GnRH-a ultra-long and long protocol groups, while number of oocytes retrieval, available embryos, and good quality embryos in these two groups were also significantly higher than GnRH-a short protocol group and GnRH antagonist protocol group. FF AR concentration was positively correlated with available embryos, but negatively correlated with serum LH level on hCG day. FF EGF concentration had no relationship with COS parameters. Different COS protocols might have variable effects on AR synthesis. FF AR might be a good indicator to predict the number of oocytes and embryos. FF AR elevation may result in increasing the number of oocyte retrieval and embryo generation, consequently increased cumulative pregnancy rate.

Decorin is a part of the ovarian extracellular matrix in primates and may act as a signaling molecule

STUDY QUESTION

Is decorin (DCN), a putative modulator of growth factor (GF) signaling, expressed in the primate ovary and does it play a role in ovarian biology?

SUMMARY ANSWER

DCN expression in the theca, the corpus luteum (CL), its presence in the follicular fluid (FF) and its actions revealed in human IVF-derived granulosa cells (GCs), suggest that it plays multiple roles in the ovary including folliculogenesis, ovulation and survival of the CL.

WHAT IS KNOWN ALREADY

DCN is a secreted proteoglycan, which has a structural role in the extracellular matrix (ECM) and also interferes with the signaling of multiple GF/GF receptors (GFRs). However, DCN expression and action in the primate ovary has yet to be determined.

STUDY DESIGN, SIZE, DURATION

Archival human and monkey ovarian samples were analyzed. Studies were conducted using FF and GC samples collected from IVF patients.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Immunohistochemistry, western blotting, RT-PCR, quantitative RT-PCR (qPCR) and enzyme-linked immunosorbent assay (ELISA) studies were complemented by cellular studies, including the measurements of intracellular Ca²⁺, reactive oxygen species (ROS), epidermal GF receptor (EGFR) phosphorylation by DCN and caspase activity.

MAIN RESULTS AND THE ROLE OF CHANCE

Immunohistochemistry revealed strong DCN staining in the connective tissue and follicular thecal compartments, but not in GCs of pre-antral and antral follicles. Pre-ovulatory follicles could not be studied, but DCN was associated with connective tissue of CL samples and the cytoplasm of luteal cells. DCN expression in monkey CL doubled (P < 0.05) towards the end of the luteal lifespan. DCN was found in human FF obtained from IVF patients (mean: 12.9 ng/ml; n = 20) as determined by ELISA. DCN mRNA and/or protein were detected in freshly isolated and cultured, luteinized human GCs. In the latter, exogenous human recombinant DCN increased intracellular Ca²⁺ levels and induced the production of ROS in a concentration-dependent manner. DCN, like epidermal GF, phosphorylated EGFR significantly (P < 0.05) and reduced the activity of caspase 3/7 in cultured GCs. The data indicate the expression of DCN in the theca of growing follicles, in FF of ovulatory follicles and in the CL. Therefore, DCN may exert paracrine actions via GF/GFR systems in multiple ovarian compartments.

LIMITATIONS, REASONS FOR CAUTION

Functional studies were performed in cultures of human luteinized GCs, which are an apt model but may not fully mirror the pre-ovulatory GC compartment or the CL. Other human ovarian cells, including the thecal cells, were not available.

WIDER IMPLICATIONS OF THE FINDINGS

In accordance with its evolving roles in other organs, ovarian DCN is an ECM-associated component, which acts as a multifunctional regulator of GF signaling in the primate ovary. DCN may thus be involved in folliculogenesis, ovulation and the regulation of the CL survival in primates.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by Deutsche Forschungsgemeinschaft (DFG) MA1080/17-3 and in part DFG MA1080/21-1 (to AM), NIH grants HD24870 (S.R.O. and R.L.S.), the Eunice Kennedy Shriver NICHD/NIH through cooperative agreement HD18185 as part of the Specialized Cooperative Centers Program in Reproduction and Infertility Research (S.R.O.) and 8P51OD011092-53 for the operation of the Oregon National Primate Research Center (G.A.D., J.D.H., S.R.O. and R.L.S).

Novel signaling mechanisms in the ovary during oocyte maturation and ovulation

During the peri-ovulatory period, the gonadotropin LH triggers major changes in both the somatic and germ cell compartments of the ovarian follicle. The oocyte completes the meiotic cell cycle to become a fertilizable egg, and dramatic changes in gene expression and secretion take place in the somatic compartment of the follicle in preparation for follicular rupture and oocyte release. The concerted changes are regulated by activation of intracellular signaling pathways as well as paracrine and autocrine regulatory loops. This review will provide a summary of the current knowledge of the molecular events triggered by LH focusing mostly on the signaling pathways required for oocyte maturation.

Amphiregulin promotes the maturation of oocytes isolated from the small antral follicles of the rhesus macaque

BACKGROUND

In non-primates, the epidermal growth factor (EGF) and EGF-related ligands such as amphiregulin (AREG) serve as critical intermediates between the theca/mural cells and the cumulus-oocyte-complex (COC) following the mid-cycle LH surge. Studies were designed in primates (1) to analyze AREG levels in follicular fluid (follicular fluid) obtained from pre-ovulatory follicles, as well as (2) to assess dose-dependent effects of AREG on oocytes from small antral follicles (SAFs) during culture, including meiotic and cytoplasmic maturation.

METHODS

Controlled ovulation protocols were performed on rhesus monkeys (n=12) to determine AREG content within the single, naturally selected dominant follicle after an ovulatory stimulus. Using healthy COCs (n=271) obtained from SAFs during spontaneous cycles (n=27), in vitro maturation (IVM) was performed in the absence or presence of physiological concentrations of AREG (10 or 100 ng/ml) with or without gonadotrophins (FSH, 75 mIU/ml; LH, 75 mIU/ml). At the end of the culture period, oocyte meiotic maturation was evaluated and ICSI was performed (n=111), from which fertilization and early embryo development was followed in vitro.

RESULTS

AREG levels in follicular fluid from pre-ovulatory follicles increased (P<0.05) following an ovulatory bolus of hCG at 12, 24 and 36 h post-treatment. At 12 h post-hCG, AREG levels in follicular fluid ranged from 4.8 to 121.4 ng/ml. Rhesus macaque COCs incubated with 10 ng/ml AREG in the presence of gonadotrophins displayed an increased percentage of oocytes that progressed to the metaphase II (MII) stage of meiosis (82 versus 56%, P<0.05) and a decreased percentage of metaphase I (MI) oocytes (2 versus 23%, P<0.05) relative to controls, respectively. The percentage of either MI or MII oocytes at the end of the culture period was not different between oocytes cultured with 100 ng/ml AREG or in media alone. Fertilization and first cleavage rates obtained by ICSI of all IVM MII oocytes were 93 and 98%, respectively, and did not vary among treatment groups. Of the MII oocytes that fertilized (n=103), 37 were randomly selected and maintained in culture to assess developmental potential. A total of 13 early blastocysts were obtained, with four embryos developing to expanded blastocysts.

CONCLUSIONS

These data indicate that AREG levels increase in rhesus macaque pre-ovulatory follicles after an ovulatory stimulus, and a specific concentration of AREG (10 ng/ml) enhances rhesus macaque oocyte nuclear maturation but not cytoplasmic maturation from SAFs obtained during the natural menstrual cycle. However, owing to the small number of samples in some treatment groups, further studies are now required.

Human oocyte maturation is dependent on LH-stimulated accumulation of the epidermal growth factor-like growth factor, amphiregulin

BACKGROUND

The LH surge promotes ovulation via activation of multiple signaling networks in the ovarian follicle. Studies in animal models have shown the importance of LH-induced activation of the epidermal growth factor (EGF)signaling network in critical peri-ovulatory events. We investigated the biological significance of regulatory mechanisms mediated by EGF-like growth factors during LH stimulation in humans.

METHODS

We characterized the EGF signaling network in mature human ovarian follicles using in vivo and in vitro approaches. Amphiregulin (AREG) levels were measured in 119 follicular fluid (FF) samples from IVF/ICSI patients. Biological activity of human FF was assessed using in vitro oocyte maturation, cumulus expansion and cell mitogenic assays.

RESULTS

AREG is the most abundant EGF-like growth factor accumulating in the FF of mature follicles of hCG-stimulated patients. No AREG was detected before the LH surge or before hCG stimulation of granulosa cells in vitro, demonstrating that the accumulation of AREG requires gonadotrophin stimulation. Epiregulin and betacellulin mRNA were detected in both human mural and cumulus granulosa cells, although at significantly lower levels than AREG. FF from stimulated follicles causes cumulus expansion and oocyte maturation in a reconstitution assay. Immunodepletion of AREG abolishes the ability of FF to stimulate expansion (P < 0.0001) and oocyte maturation (P < 0.05), confirming the biological activity of AREG. Conversely, mitogenic activity of FF remained after depletion of AREG, indicating that other mitogens accumulate in FF. FF from follicles yielding an immature germinal vesicle oocyte or from an oocyte that develops into an aberrant embryo contains lower AREG levels than that from follicles yielding a healthy oocyte (P = 0.008).

CONCLUSIONS

EGF-like growth factors play a role in critical peri-ovulatory events in humans, and AREG accumulation is a useful marker of gonadotrophin stimulation and oocyte competence.

The mammalian ovary from genesis to revelation

Two major functions of the mammalian ovary are the production of germ cells (oocytes), which allow continuation of the species, and the generation of bioactive molecules, primarily steroids (mainly estrogens and progestins) and peptide growth factors, which are critical for ovarian function, regulation of the hypothalamic-pituitary-ovarian axis, and development of secondary sex characteristics. The female germline is created during embryogenesis when the precursors of primordial germ cells differentiate from somatic lineages of the embryo and take a unique route to reach the urogenital ridge. This undifferentiated gonad will differentiate along a female pathway, and the newly formed oocytes will proliferate and subsequently enter meiosis. At this point, the oocyte has two alternative fates: die, a common destiny of millions of oocytes, or be fertilized, a fate of at most approximately 100 oocytes, depending on the species. At every step from germline development and ovary formation to oogenesis and ovarian development and differentiation, there are coordinated interactions of hundreds of proteins and small RNAs. These studies have helped reproductive biologists to understand not only the normal functioning of the ovary but also the pathophysiology and genetics of diseases such as infertility and ovarian cancer. Over the last two decades, parallel progress has been made in the assisted reproductive technology clinic including better hormonal preparations, prenatal genetic testing, and optimal oocyte and embryo analysis and cryopreservation. Clearly, we have learned much about the mammalian ovary and manipulating its most important cargo, the oocyte, since the birth of Louise Brown over 30 yr ago.

Follicular fluid content and oocyte quality: from single biochemical markers to metabolomics

The assessment of oocyte quality in human in vitro fertilization (IVF) is getting increasing attention from embryologists. Oocyte selection and the identification of the best oocytes, in fact, would help to limit embryo overproduction and to improve the results of oocyte cryostorage programs. Follicular fluid (FF) is easily available during oocyte pick-up and theorically represents an optimal source on non-invasive biochemical predictors of oocyte quality. Unfortunately, however, the studies aiming to find a good molecular predictor of oocyte quality in FF were not able to identify substances that could be used as reliable markers of oocyte competence to fertilization, embryo development and pregnancy. In the last years, a well definite trend toward passing from the research of single molecular markers to more complex techniques that study all metabolites of FF has been observed. The metabolomic approach is a powerful tool to study biochemical predictors of oocyte quality in FF, but its application in this area is still at the beginning. This review provides an overview of the current knowledge about the biochemical predictors of oocyte quality in FF, describing both the results coming from studies on single biochemical markers and those deriving from the most recent studies of metabolomics.

Epidermal growth factor-like growth factors in the follicular fluid: role in oocyte development and maturation

The growth and maturation of the ovarian follicle requires the coordinate function of somatic cells and the oocyte. Over the past three decades, numerous growth factors involved in the bidirectional signals between the somatic and germ cells have been identified. A possible function of epidermal growth factor (EGF) signaling at selected stages of follicle maturation had been proposed early on and is supported by many observations of in vitro effects of this growth factor on steroidogenesis, oocyte maturation, and cumulus expansion. However, attempts to link EGF levels in the follicular fluid with the state of follicle and oocyte maturation have been inconclusive. More recently, data generated using mouse genetic models perturbing ovulation and fertility indicate that EGF-like growth factors, rather than EGF itself, accumulate in the follicle at the time of ovulation. EGF-like growth factor mRNA is regulated by the luteinizing hormone surge, and corresponding proteins are detected in the follicle. The EGF-like growth factors amphiregulin, epiregulin, and betacellulin are potent stimulators of oocyte maturation and cumulus expansion, and perturbation of this EGF network in vivo impairs ovulation. Similar findings in species other than the mouse confirm an important physiological role for this network at the time of ovulation. Whether this network also plays a critical role in humans and whether it can be used as a biological marker of follicle development or for the improvement of fertility remains to be determined. This review summarizes the most recent findings on the EGF network during ovulation and the potential clinical applications of manipulating this intercellular communication pathway in the control of fertility.