Sustained activity of the EGF receptor is an absolute requisite for LH-induced oocyte maturation and cumulus expansion

EGF-like growth factors upregulate pentraxin 3 expression in human granulosa-lutein cells

The epidermal growth factor (EGF)-like factors, comprising amphiregulin (AREG), betacellulin (BTC), and epiregulin (EREG), play a critical role in regulating the ovulatory process. Pentraxin 3 (PTX3), an essential ovulatory protein, is necessary for maintaining extracellular matrix (ECM) stability during cumulus expansion. The aim of this study was to investigate the impact of EGF-like factors, AREG, BTC, and EREG on the expression and production of PTX3 in human granulosa-lutein (hGL) cells and the molecular mechanisms involved. Our results demonstrated that AREG, BTC, and EREG could regulate follicular function by upregulating the expression and increasing the production of PTX3 in both primary (obtained from 20 consenting patients undergoing IVF treatment) and immortalized hGL cells. The upregulation of PTX3 expression was primarily facilitated by the activation of the extracellular signal-regulated kinase 1 and 2 (ERK1/2) signaling pathway, induced by these EGF-like factors. In addition, we found that the upregulation of PTX3 expression triggered by the EGF-like factors was completely reversed by either pretreatment with the epidermal growth factor receptor (EGFR) inhibitor, AG1478, or knockdown of EGFR, suggesting that EGFR is crucial for activating the ERK1/2 signaling pathway in hGL cells. Overall, our findings indicate that AREG, BTC, and EREG may modulate human cumulus expansion during the periovulatory stage through the upregulation of PTX3.

Altered ovarian tissue level of lysophosphatidic acid and mRNA expressions of its metabolic enzymes and receptors in rats received gonadotropin-hyperstimulation

Lysophosphatidic acid (LPA), a well-studied member of the lysophospholipid family, is known to exert an important bio-effect on oocyte maturation and ovulation in mammals. We attempted to determine how follicle maturation in the rat ovary affects the levels of LPA and its precursor lysophospholipids, as well as mRNA levels of LPA-producing and -degrading enzymes and LPA receptors in rats that received gonadotropin-hyper-stimulation. Tissue levels of lysophospholipids were quantified by LC-MS/MS, and relative mRNA expression levels of LPA-producing and -degrading enzymes, and LPA receptors were measured by RT-PCR. Tissue levels of n-6 polyunsaturated LPAs and LPCs were higher in the ovaries of rats after receiving human chorionic gonadotropin, unlike the distinct profiles of n-3 polyunsaturated LPAs, which had lower levels, and LPCs which had higher levels, after the gonadotropin treatment. The effects of different levels of other polyunsaturated lysophospholipids were variable: decreased levels of lysophosphatidylglycerol, and unaltered levels of lysophosphatidylethanolamine, lysophosphatidylinositol, and lysophosphatidylserine. The results indicate that expression of mRNA levels of autotaxin and acylglycerol kinase were reduced and expression of lipid phosphate phosphatase 3 was elevated, whereas expressions of two membrane phosphatidic acid phosphatases (A1α and A1β) and lipid phosphate phosphatase 1 were essentially unaltered in rat ovary at several stages after ovary hyperstimulation. After the gonadotropin treatment, the expression levels of all LPA receptors except LPA3 were decreased at various times. These results are discussed with respect to the physiological processes of the ovarian environment and development in rats.

The molecular regulatory mechanisms of meiotic arrest and resumption in Oocyte development and maturation

In human female primordial germ cells, the transition from mitosis to meiosis begins from the fetal stage. In germ cells, meiosis is arrested at the diplotene stage of prophase in meiosis I (MI) after synapsis and recombination of homologous chromosomes, which cannot be segregated. Within the follicle, the maintenance of oocyte meiotic arrest is primarily attributed to high cytoplasmic concentrations of cyclic adenosine monophosphate (cAMP). Depending on the specific species, oocytes can remain arrested for extended periods of time, ranging from months to even years. During estrus phase in animals or the menstrual cycle in humans, the resumption of meiosis occurs in certain oocytes due to a surge of luteinizing hormone (LH) levels. Any factor interfering with this process may lead to impaired oocyte maturation, which in turn affects female reproductive function. Nevertheless, the precise molecular mechanisms underlying this phenomenon has not been systematically summarized yet. To provide a comprehensive understanding of the recently uncovered regulatory network involved in oocyte development and maturation, the progress of the cellular and molecular mechanisms of oocyte nuclear maturation including meiosis arrest and meiosis resumption is summarized. Additionally, the advancements in understanding the molecular cytoplasmic events occurring in oocytes, such as maternal mRNA degradation, posttranslational regulation, and organelle distribution associated with the quality of oocyte maturation, are reviewed. Therefore, understanding the pathways regulating oocyte meiotic arrest and resumption will provide detailed insight into female reproductive system and provide a theoretical basis for further research and potential approaches for novel disease treatments.

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.

Regulation of oocyte maturation: Role of conserved ERK signaling

During oogenesis, oocytes arrest at meiotic prophase I to acquire competencies for resuming meiosis, fertilization, and early embryonic development. Following this arrested period, oocytes resume meiosis in response to species-specific hormones, a process known as oocyte maturation, that precedes ovulation and fertilization. Involvement of endocrine and autocrine/paracrine factors and signaling events during maintenance of prophase I arrest, and resumption of meiosis is an area of active research. Studies in vertebrate and invertebrate model organisms have delineated the molecular determinants and signaling pathways that regulate oocyte maturation. Cell cycle regulators, such as cyclin-dependent kinase (CDK1), polo-like kinase (PLK1), Wee1/Myt1 kinase, and the phosphatase CDC25 play conserved roles during meiotic resumption. Extracellular signal-regulated kinase (ERK), on the other hand, while activated during oocyte maturation in all species, regulates both species-specific, as well as conserved events among different organisms. In this review, we synthesize the general signaling mechanisms and focus on conserved and distinct functions of ERK signaling pathway during oocyte maturation in mammals, non-mammalian vertebrates, and invertebrates such as Drosophila and Caenorhabditis elegans.

Aberrant activation of KRAS in mouse theca-interstitial cells results in female infertility

KRAS plays critical roles in regulating a range of normal cellular events as well as pathological processes in many tissues mediated through a variety of signaling pathways, including ERK1/2 and AKT signaling, in a cell-, context- and development-dependent manner. The in vivo function of KRAS and its downstream targets in gonadal steroidogenic cells for the development and homeostasis of reproductive functions remain to be determined. To understand the functions of KRAS signaling in gonadal theca and interstitial cells, we generated a Kras mutant (tKrasMT) mouse line that selectively expressed a constitutively active KrasG12D in these cells. KrasG12D expression in ovarian theca cells did not block follicle development to the preovulatory stage. However, tKrasMT females failed to ovulate and thus were infertile. The phosphorylated ERK1/2 and forkhead box O1 (FOXO1) and total FOXO1 protein levels were markedly reduced in tKrasMT theca cells. KrasG12D expression in theca cells also curtailed the phosphorylation of ERK1/2 and altered the expression of several ovulation-related genes in gonadotropin-primed granulosa cells. To uncover downstream targets of KRAS/FOXO1 signaling in theca cells, we found that the expression of bone morphogenic protein 7 (Bmp7), a theca-specific factor involved in ovulation, was significantly elevated in tKrasMT theca cells. Chromosome immunoprecipitation assays demonstrated that FOXO1 interacted with the Bmp7 promoter containing forkhead response elements and that the binding activity was attenuated in tKrasMT theca cells. Moreover, Foxo1 knockdown caused an elevation, whereas Foxo1 overexpression resulted in an inhibition of Bmp7 expression, suggesting that KRAS signaling regulates FOXO1 protein levels to control Bmp7 expression in theca cells. Thus, the anovulation phenotype observed in tKrasMT mice may be attributed to aberrant KRAS/FOXO1/BMP7 signaling in theca cells. Our work provides the first in vivo evidence that maintaining normal KRAS activity in ovarian theca cells is crucial for ovulation and female fertility.

YAP signaling in preovulatory granulosa cells is critical for the functioning of the EGF network during ovulation

Failure to ovulate is a major cause of infertility. The critical pathway that induces ovulation involves the EGF and MAPK phosphorylation, but studies in rodents have suggested that the Hippo activator, YAP, is also involved. It is unknown whether YAP-dependent transcriptional activity is important for the LH- or EGF-induced ovulatory cascade in monovulatory species such as the cow. Using a well-defined preovulatory GC culture system, we employed pharmacological inhibitors to demonstrate that YAP signaling is critical for expression of EGFR and downstream target genes EREG, EGR1 and TNFAIP6. Most importantly, by using an ultrasound guided follicle injection system, we also showed that the classic Hippo signaling inhibitor Verteporfin inhibits GnRH-induced ovulation in vivo in cattle. In conclusion, YAP transcriptional activity is critical for EGF-like cascade induced by LH to promote ovulation in a monovulatory species.

The Hippo pathway effectors YAP and TAZ interact with EGF-like signaling to regulate expansion-related events in bovine cumulus cells in vitro

PURPOSE

To determine if the inhibition of the interaction between the Hippo effector YAP or its transcriptional co-activator TAZ with the TEAD family of transcription factors is critical for the cumulus expansion-related events induced by the EGF network in cumulus-oocyte complexes (COCs).

METHODS

We performed a series of experiments using immature bovine COCs subjected to an IVM protocol for up 24 h in which cumulus expansion was stimulated with EGF recombinant protein or FSH.

RESULTS

The main results indicated that EGFR activity stimulation in bovine cumulus cells (CC) increases mRNA levels encoding the classic YAP/TAZ-TEAD target gene CTGF. To determine if important genes for cumulus expansion are transcriptional targets of YAP/TAZ-TEAD interaction in CC, COCs were then subjected to IVM in the presence of FSH with or without distinct concentrations of Verteporfin (VP; a small molecule inhibitor that interferes with YAP/TAZ binding to TEADs). COCs were then collected at 6, 12, 18, and 24 h for total RNA extraction and RT-qPCR analyses. This experiment indicated that VP inhibits in a time- and concentration-dependent manner distinct cumulus expansion and oocyte maturation-related genes, by regulating EGFR and CTGF expression in CC.

CONCLUSIONS

Taken together, the results presented herein represent considerable insight into the functional relevance of a completely novel signaling pathway underlying cumulus expansion and oocyte maturation in monovulatory species. YAP/TAZ or CTGF may represent potential targets to improve the efficiency of IVM systems, not only for monovulatory species of agricultural importance as the cow, but for human embryo production.

Beneficial Effects of Neurotrophin-4 Supplementation During in vitro Maturation of Porcine Cumulus-Oocyte Complexes and Subsequent Embryonic Development After Parthenogenetic Activation

Neurotrophin-4 (NT-4) is a neurotrophic factor that plays an important role in follicular development and oocyte maturation. However, it is not yet known whether NT-4 is related to oocyte maturation and follicular development in pigs. This study aims to investigate the effects of NT-4 supplementation during in vitro maturation (IVM) of porcine oocytes and subsequent embryonic development after parthenogenetic activation (PA). First, NT-4 and its receptors (TrkB and p75^NTR) were identified through fluorescent immunohistochemistry in porcine ovaries. NT-4 was mainly expressed in theca and granulosa cells; phospho-TrkB and total TrkB were expressed in theca cells, granulosa cells, and oocytes; p75^NTR was expressed in all follicular cells. During IVM, the defined maturation medium was supplemented with various concentrations of NT-4 (0, 1, 10, and 100 ng/mL). After IVM, the nuclear maturation rate was significantly higher in the 10 and 100 ng/mL NT-4 treated groups than in the control. There was no significant difference in the intracellular reactive oxygen species levels in any group after IVM, but the 1 and 10 ng/mL NT-4 treatment groups showed a significant increase in the intracellular glutathione levels compared to the control. In matured cumulus cells, the 10 ng/mL NT-4 treatment group showed significantly increased cumulus expansion-related genes and epidermal growth factor (EGF) signaling pathway-related genes. In matured oocytes, the 10 ng/mL treatment group showed significantly increased expression of cell proliferation-related genes, antioxidant-related genes, and EGF signaling pathway-related genes. We also investigated the subsequent embryonic developmental competence of PA embryos. After PA, the cleavage rates significantly increased in the 10 and 100 ng/mL NT-4 treatment groups. Although there was no significant difference in the total cell number of blastocysts, only the 10 ng/mL NT-4 treatment group showed a higher blastocyst formation rate than the control group. Our findings suggest that supplementation with the 10 ng/mL NT-4 can enhance porcine oocyte maturation by interacting with the EGF receptor signaling pathway. In addition, we demonstrated for the first time that NT-4 is not only required for porcine follicular development, but also has beneficial effects on oocyte maturation and developmental competence of PA embryos.

The Role of MAPK3/1 and AKT in the Acquisition of High Meiotic and Developmental Competence of Porcine Oocytes Cultured In Vitro in FLI Medium

The developmental potential of porcine oocytes cultured in vitro was remarkably enhanced in a medium containing FGF2, LIF and IGF1 (FLI) when compared to a medium supplemented with gonadotropins and EGF (control). We analyzed the molecular background of the enhanced oocyte quality by comparing the time course of MAPK3/1 and AKT activation, and the expression of genes controlled by these kinases in cumulus-oocyte complexes (COCs) cultured in FLI and the control medium. The pattern of MAPK3/1 activation in COCs was very similar in both media, except for a robust increase in MAPK3/1 phosphorylation during the first hour of culture in the FLI medium. The COCs cultured in the FLI medium exhibited significantly higher activity of AKT than in the control medium from the beginning up to 16 h of culture; afterwards a deregulation of AKT activity occurred in the FLI medium, which was not observed in the control medium. The expression of cumulus cell genes controlled by both kinases was also modulated in the FLI medium, and in particular the genes related to cumulus-expansion, signaling, apoptosis, antioxidants, cell-to-cell communication, proliferation, and translation were significantly overexpressed. Collectively, these data indicate that both MAPK3/1 and AKT are implicated in the enhanced quality of oocytes cultured in FLI medium.

Glucocorticoids, Stress and Delta-9 Tetrahydrocannabinol (THC) during Early Embryonic Development

Elevated molecular stress in women is known to have negative impacts on the reproductive development of oocytes and the embryos prior to implantation. In recent years, the prevalence of cannabis use among women of reproductive age has risen due to its ability to relieve psychological stress and nausea, which are mediated by its psychoactive component, ∆-9-tetrahydrocannabinol (THC). Although cannabis is the most popular recreational drug of the 21st century, much is unknown about its influence on molecular stress in reproductive tissues. The current literature has demonstrated that THC causes dose- and time-dependent alterations in glucocorticoid signaling, which have the potential to compromise morphology, development, and quality of oocytes and embryos. However, there are inconsistencies across studies regarding the mechanisms for THC-dependent changes in stress hormones and how either compounds may drive or arrest development. Factors such as variability between animal models, physiologically relevant doses, and undiscovered downstream gene targets of both glucocorticoids and THC could account for such inconsistencies. This review evaluates the results of studies which have investigated the effects of glucocorticoids on reproductive development and how THC may alter stress signaling in relevant tissues.

Intraovarian injection of platelet-rich plasma in assisted reproduction: too much too soon?

The prospect of ovarian rejuvenation offers the tantalising prospect of treating age-related declines in fertility or in pathological conditions such as premature ovarian failure. The concept of ovarian rejuvenation was invigorated by the indication of the existence of oogonial stem cells (OSCs), which have been shown experimentally to have the ability to differentiate into functional follicles and generate oocytes; however, their clinical potential remains unknown. Furthermore, there is now growing interest in performing ovarian rejuvenation in situ. One proposed approach involves injecting the ovary with platelet rich plasma (PRP).

PRP is a component of blood that remains after the in vitro removal of red and white blood cells. It contains blood platelets, tiny anucleate cells of the blood, which are responsible for forming athrombus to prevent bleeding. In addition, PRP contains an array of cytokines and growth factors, as well as a number of small molecules.The utility ofPRP has been investigatedin a range of regenerative medicine approaches and has been shown to induce differentiation of a range of cell types, presumably through the action of cytokines.

A handful ofcasereports have described the use of PRP injections into the ovaryin the human, and while these clinical data report promising results, knowledge on the mechanisms and safety of PRP injections into the ovary remain limited.In this article, we summarise some of the physiological detail of platelets and PRP, before reviewing the existing emerging literature in this area. We then propose potential mechanisms by which PRP may be eliciting any effects before reflecting on some considerations for future studies in the area. Importantly, on the basis of our existing knowledge, we suggest that immediate use of PRP in clinical applications is perhaps premature and further fundamental and clinical research on the nature of ovarian insufficiency, as well as the mechanism by which PRP may act on the ovary, is needed to fully understand this promising development.

Mechanisms of Oocyte Maturation and Related Epigenetic Regulation

Meiosis is the basis of sexual reproduction. In female mammals, meiosis of oocytes starts before birth and sustains at the dictyate stage of meiotic prophase I before gonadotropins-induced ovulation happens. Once meiosis gets started, the oocytes undergo the leptotene, zygotene, and pachytene stages, and then arrest at the dictyate stage. During each estrus cycle in mammals, or menstrual cycle in humans, a small portion of oocytes within preovulatory follicles may resume meiosis. It is crucial for females to supply high quality mature oocytes for sustaining fertility, which is generally achieved by fine-tuning oocyte meiotic arrest and resumption progression. Anything that disturbs the process may result in failure of oogenesis and seriously affect both the fertility and the health of females. Therefore, uncovering the regulatory network of oocyte meiosis progression illuminates not only how the foundations of mammalian reproduction are laid, but how mis-regulation of these steps result in infertility. In order to provide an overview of the recently uncovered cellular and molecular mechanism during oocyte maturation, especially epigenetic modification, the progress of the regulatory network of oocyte meiosis progression including meiosis arrest and meiosis resumption induced by gonadotropins is summarized. Then, advances in the epigenetic aspects, such as histone acetylation, phosphorylation, methylation, glycosylation, ubiquitination, and SUMOylation related to the quality of oocyte maturation are reviewed.

Synergistic effect between LH and estrogen in the acceleration of cumulus expansion via GPR30 and EGFR pathways

The estrogen membrane receptor GPR30 (also known as G-protein coupled receptor 30) has recently been shown to be involved in the regulation of oocyte maturation and cumulus expansion. However, whether GPR30 expression is regulated by gonadotropin stimulation and how it participates in the regulation of the maturation process is still not clear. In this study, we explored the mechanism underlying the synergy between luteinizing hormone and 17β-estradiol (17β-E₂) to improve the epidermal growth factor (EGF) response in cumulus oocyte complexes (COCs) during oocyte maturation in mice. The expression and distribution of GPR30, EGFR, and EGF-like growth factors were examined by real-time quantitative PCR, western blot, and immunofluorescence staining. Lyso-Tracker Red labeling was performed to detect the lysosomal activity in follicle granular cells (FGCs). Cumulus expansion of COCs was evaluated after in vitro maturation for 16 h. We found that EGF-like growth factors transmit LH signals to increase GRP30 levels by inhibiting protein degradation in lysosomes. Meanwhile, 17β-E₂ stimulates the GPR30 signaling pathway to increase EGF receptor levels, enhancing the response ability of EGF signaling in COCs and thus promoting cumulus expansion. In conclusion, our study reveals the synergistic mechanism between LH and estrogen in the regulation of cumulus expansion during oocyte maturation process.

A multilevel analysis identifies the different relationships between amino acids and the competence of oocytes matured individually or in groups

High-protein diets contribute to an increase in urea follicular concentrations associated with decreased fertility. Urea has been shown to interfere with the epidermal growth factor (EGF)/EGFR system, which has been shown to have a beneficial effect during in vitro maturation (IVM) of oocytes. Of note, the number of cumulus-oocyte complexes (COCs) in the maturation medium can change the maturation and the developmental competence of COCs. Therefore, it was hypothesized that, the presence of urea and EGF may have a differential effect on the depletion/appearance of AAs and competence of COCs matured individually (I-IVM system) or in groups (G-IVM system). In the G-IVM system, COCs increased consumption (depletion) of AAs compared with other groups in the presence of high-level urea (40 mg/dl) + EGF (10 ng/ml). In the I-IVM system, the non-cleaved COCs depleted more AAs than the cleaved COCs, in particular in the presence of urea. The combination of urea and EGF increased the depletion of AAs in the G-IVM system. However, the EGF abrogated the urea-induced depletion of AAs by the I-IVM COCs. The use of N-acetyl-L-cysteine as an EGFR inhibitor canceled urea-induced depletion of AAs. This shows the inhibiting effect of urea over the EGF/EGFR system. In the presence of urea + EGF, COCs had a lower degree of developmental competence than control in both I- and G-IVM systems. Arginine had the best predictive power to identify highly competent COCs in the G-IVM system, while glutamine was the best predictor of the cleavage in the I-IVM system. In conclusion, this multi-level study shows that COCs matured individually or in groups may have different association with AAs metabolism. These findings provide new insights into the relationships between AA metabolism and the subsequent developmental competence of COCs.

Follicle-stimulating hormone and luteinizing hormone increase Ca2+ in the granulosa cells of mouse ovarian follicles†

In mammalian ovarian follicles, follicle stimulating hormone (FSH) and luteinizing hormone (LH) signal primarily through the G-protein Gs to elevate cAMP, but both of these hormones can also elevate Ca2+ under some conditions. Here, we investigate FSH- and LH-induced Ca2+ signaling in intact follicles of mice expressing genetically encoded Ca2+ sensors, Twitch-2B and GCaMP6s. At a physiological concentration (1 nM), FSH elevates Ca2+ within the granulosa cells of preantral and antral follicles. The Ca2+ rise begins several minutes after FSH application, peaks at ∼10 min, remains above baseline for another ∼10 min, and depends on extracellular Ca2+. However, suppression of the FSH-induced Ca2+ increase by reducing extracellular Ca2+ does not inhibit FSH-induced phosphorylation of MAP kinase, estradiol production, or the acquisition of LH responsiveness. Like FSH, LH also increases Ca2+, when applied to preovulatory follicles. At a physiological concentration (10 nM), LH elicits Ca2+ oscillations in a subset of cells in the outer mural granulosa layer. These oscillations continue for at least 6 h and depend on the activity of Gq family G-proteins. Suppression of the oscillations by Gq inhibition does not inhibit meiotic resumption, but does delay the time to 50% ovulation by about 3 h. In summary, both FSH and LH increase Ca2+ in the granulosa cells of intact follicles, but the functions of these Ca2+ rises are only starting to be identified.

Regulation of the aryl hydrocarbon receptor activity in bovine cumulus-oocyte complexes during in vitro maturation: The role of EGFR and post-EGFR ERK1/2 signaling cascade

The aryl hydrocarbon receptor (AhR) has been extensively characterized as an environmental sensor with major roles in xenobiotic-induced toxicity. Evidence is accumulating that these functions serve as adaptive mechanisms overlapping its physiological roles. We previously described a critical role of constitutive AhR activation for the correct progress of mammalian oocyte maturation but the signaling pathway through which AhR controls maturation remains unclear. The aim of this study was to investigate whether the AhR interacts with the epidermal growth factor receptor (EGFR) and p42/44 extracellular regulated kinases (ERK1/2), both key factors in the signaling network that finely regulates the oocyte maturation. As experimental model we used bovine cumulus-oocyte complexes (COCs) during in vitro maturation (IVM). Blocking ERK1/2 signaling in COCs during IVM with the specific EGFR inhibitor AG1478 or the mitogen-activated protein kinase kinase (MEK) inhibitor PD98059 downregulated the expression of the AhR-target gene Cyp1a1. Inhibition of AhR activity was associated with a reduction in the oocytes' ability to progress in meiosis resumption. In contrast, exposure to the AhR antagonist resveratrol reduced both CYP1A1 expression and the oocytes' maturation competence, without affecting ERK1/2 signaling. These findings strongly indicate the EGFR/ERKs signaling network as an upstream regulator of the AhR activation in COCs, offering a new understanding of the finely tuned physiological mechanism leading to oocyte maturation. This information may provide fresh opportunities for improving oocyte in vitro maturation, and therefore boosting the efficiency of assisted reproduction techniques in mammals.

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.

Reporting on the Role of miRNAs and Affected Pathways on the Molecular Backbone of Ovarian Insufficiency: A Systematic Review and Critical Analysis Mapping of Future Research

Ovarian insufficiency is identified as a perplexing entity in the long list of pathologies impairing fertility dynamics. The three distinct classifications of ovarian insufficiency are poor ovarian response, premature ovarian insufficiency/failure, and advanced maternal age, sharing the common denominator of deteriorated ovarian reserve. Despite efforts to define clear lines among the three, the vast heterogeneity and overlap of clinical characteristics renders their diagnosis and management challenging. Lack of a consensus has prompted an empirically based management coupled by uncertainty from the clinicians' perspective. Profiling of patients in the era of precision medicine seems to be the way forward, while the necessity for a novel approach is underlined. Implicating miRNAs in the quest for patient profiling is promising in light of their fundamental role in cellular and gene expression regulation. To this end, the current study sets out to explore and compare the three pathophysiologies-from a molecular point of view-in order to enable profiling of patients in the context of in vitro fertilization treatment and enrich the data required to practice individualized medicine. Following a systematic investigation of literature, data referring to miRNAs were collected for each patient category based on five included studies. miRNA-target pairs were retrieved from the DIANA-TarBase repository and microT-CDS. Gene and miRNA annotations were derived from Ensembl and miRbase. A subsequent gene-set enrichment analysis of miRNA targets was performed for each category separately. A literature review on the most crucial of the detected pathways was performed to reveal their relevance to fertility deterioration. Results supported that all three pathophysiologies share a common ground regarding the affected pathways, naturally attributed to the common denominator of ovarian insufficiency. As evidenced, miRNAs could be employed to explore the fine lines and diverse nature of pathophysiology since they constitute invaluable biomarkers. Interestingly, it is the differentiation through miRNAs and not through the molecular affected pathways that corresponds to the three distinctive categories. Alarming discrepancies among publications were revealed, pertaining to employment of empirical and arbitrary criteria in categorizing the patients. Following bioinformatic analysis, the final step of the current study consisted of a critical analysis of the molecular data sourced, providing a clear and unique insight into the physiological mechanisms involved. It is our intention to contribute to mapping future research dedicated to ovarian insufficiency and to help researchers navigate the overwhelming information published in molecular studies.

Mitogen-activated protein kinase kinase kinase 8 (MAP3K8) mediates the LH-induced stimulation of progesterone synthesis in the porcine corpus luteum

Progesterone (P4) synthesized by the corpus luteum (CL) plays a key role in the establishment and maintenance of pregnancy. The LH signal is important for luteinisation and P4 synthesis in pigs. In a previous study, we demonstrated that mitogen-activated protein kinase kinase kinase 8 (MAP3K8) regulates P4 synthesis in mouse CL, but whether the function and mechanism of MAP3K8 in the pig is similar to that in the mouse is not known. Thus, in the present study we investigated the effects of MAP3K8 on porcine CL. Abundant expression of MAP3K8 was detected in porcine CL, and, in pigs, MAP3K8 expression was higher in mature CLs (or those of the mid-luteal phase) than in regressing CLs (late luteal phase). Further functional studies in cultured porcine luteal cells showed that P4 synthesis and the expression of genes encoding the key enzymes in P4 synthesis are significantly reduced when MAP3K8 is inhibited with the MAP3K8 inhibitor Tpl2 kinase inhibitor (MAP3K8i, 10μM). After 12-24h treatment of luteal cells with 100ngmL-1 LH, MAP3K8 expression and P4 secretion were significantly upregulated. In addition, the 10μM MAP3K8 inhibitor blocked the stimulatory effect of LH on P4 synthesis and extracellular signal-regulated kinase (ERK) 1/2 phosphorylation in porcine luteal cells. The LH-induced increases in MAP3K8 phosphorylation and expression, ERK1/2 phosphorylation and P4 synthesis were all blocked when protein kinase A was inhibited by its inhibitor H89 (20 μM) in porcine luteal cells. In conclusion, MAP3K8 mediates the LH-induced stimulation of P4 synthesis through the PKA/mitogen-activated protein kinase signalling pathway in porcine CL.

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.

Interaction of the EGFR signaling pathway with porcine cumulus oocyte complexes and oviduct cells in a coculture system

It has become increasingly recognized that coculture has a beneficial effect on the in vitro maturation (IVM) of oocytes and embryo development in many species. However, these effects of coculture on IVM have been documented only for their positive conditioning roles without any evidence on the precise mechanisms underlying the action of coculture systems on the development of cumulus oocyte complexes (COCs). It has been suggested that the epidermal growth factor receptor (EGFR) signaling pathway is important for development of COCs, mediated by several epidermal growth factor (EGF)-like proteins with downstream mitogen-activated protein kinase 1/3 signaling. Therefore, we hypothesized that canine oviduct cells (OCs) in a coculture system, which shows improvement of oocyte quality in several species, are associated with EGFR signaling by exposure to progesterone (P4; imitating its production before ovulation and its continuous increase while oocytes reside in the oviduct to complete maturation in dogs). We designed three experimental groups: control, OCs coculture exposed to P4, and OCs coculture without exposure to P4. The result showed that the OCs coculture exposed to P4 strongly expressed EGF-like proteins and significantly improved COCs and subsequent embryo development. Furthermore, the expression of EGFR-related genes in cumulus cells and GDF9 and BMP15 in oocytes was upregulated in the P4-treated group. This study provides the first evidence that OCs exposed to P4 can induce strong expression of EGF-like proteins, and OCs effectively mediate improved porcine COCs development and subsequent embryo development by altering EGFR signaling related mRNA expression.

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.

Effects of Fullerenol Nanoparticles on Rat Oocyte Meiosis Resumption

The excellent biocompatibility and biological effects of fullerenol and its derivatives make their biomedical application promising. The potential effects of fullerenol in mammals have been extensively studied, but little is known about its effects on female reproduction. Using canonical oocyte-granulosa cell complexes (OGCs) in vitro maturation culture model, we investigated the effect of fullerenol on the first oocyte meiotic resumption. In the surrounding granulosa cells, fullerenol nanoparticles occluded the extracellular domain of the epidermal growth factor receptor (EGFR) to reduce EGFR-ligand binding and subsequent extracellular signal-regulated kinase 1 and 2 (ERK1/2) activation, which involved the regulation of connexin 43 (CX43) expression and internalization. Downregulation of CX43 expression and the retraction of transzonal projections (TZPs) interrupted the gap junction channel and TZPs based mass transportation. This effect decreased cyclic adenosine monophosphate (cAMP) levels in the oocyte and thereby accelerated rat oocyte meiosis resumption. Moreover, perinuclear distribution of CX43 and EGFR was observed in granulosa cells, which could further exacerbate the effects. Fullerenol nanoparticles interfered with the strict process of oocyte meiosis resumption, which likely reduced the oocyte quality.

The Biological Role of Hyaluronan-Rich Oocyte-Cumulus Extracellular Matrix in Female Reproduction

Fertilization of the mammalian oocyte requires interactions between spermatozoa and expanded cumulus extracellular matrix (ECM) that surrounds the oocyte. This review focuses on key molecules that play an important role in the formation of the cumulus ECM, generated by the oocyte-cumulus complex. In particular, the specific inhibitors (AG1478, lapatinib, indomethacin and MG132) and progesterone receptor antagonist (RU486) exerting their effects through the remodeling of the ECM of the cumulus cells surrounding the oocyte have been described. After gonadotropin stimulus, cumulus cells expand and form hyaluronan (HA)-rich cumulus ECM. In pigs, the proper structure of the cumulus ECM depends on the interaction between HA and serum-derived proteins of the inter-alpha-trypsin inhibitor (IαI) protein family. We have demonstrated the synthesis of HA by cumulus cells, and the presence of the IαI, tumor necrosis factor-alpha-induced protein 6 and pentraxin 3 in expanding oocyte-cumulus complexes (OCC). We have evaluated the covalent linkage of heavy chains of IαI proteins to HA, as the principal component of the expanded HA-rich cumulus ECM, in porcine OCC cultured in medium with specific inhibitors: AG1478 and lapatinib (both inhibitors of epidermal growth factor receptor tyrosine kinase activity); MG132 (a specific proteasomal inhibitor), indomethacin (cyclooxygenase inhibitor); and progesterone receptor antagonist (RU486). We have found that both RU486 and indomethacin does not disrupt the formation of the covalent linkage between the heavy chains of IαI to HA in the expanded OCC. In contrast, the inhibitors AG1478 and lapatinib prevent gonadotropin-induced cumulus expansion. Finally, the formation of oocyte-cumulus ECM relying on the covalent transfer of heavy chains of IαI molecules to HA has been inhibited in the presence of MG132.

Dieldrin-induced neurotoxicity involves impaired mitochondrial bioenergetics and an endoplasmic reticulum stress response in rat dopaminergic cells

Mitochondria are sensitive targets of environmental chemicals. Dieldrin (DLD) is an organochlorine pesticide that remains a human health concern due to high lipid bioaccumulation, and it has been epidemiologically associated to an increased risk for Parkinson's disease (PD). As mitochondrial dysfunction is involved in the etiology of PD, this study aimed to determine whether DLD impaired mitochondrial bioenergetics in dopaminergic cells. Rat immortalized dopaminergic N27 cells were treated for 24 or 48h with one dose of either a solvent control, 2.5, 25, or 250μM DLD. Dopaminergic cells treated with 250μM DLD showed increased Casp3/7 activity at 24 and 48h. DLD also caused a dose dependent reduction in cell viability of ∼25-30% over 24h. No significant effects on cell viability, apoptosis, nor cytotoxicity were detected at 24 or 48h with 2.5μM DLD. Following a 24h exposure to 2.5 and 25μM DLD, viable cells were subjected to a mitochondrial stress test using the Seahorse XFe24 Extracellular Flux Analyzer. Following three independent experiments conducted for rigor, dopaminergic cells that were treated with 2.5 and 25μM DLD consistently showed a reduction in maximum respiration and spare capacity compared to the control group. Molecular responses were measured to determine mechanisms of DLD-induced mitochondrial dysfunction. There were no changes in transcripts associated with mitochondrial membrane potential and permeability (e.g. Ant, Hk1, Tspo, Vdac), nor PI3 K/Akt/mTor signaling or mitochondrial-associated apoptotic factors (Bax, Bcl2, Casp3). However, transcript levels for Chop/Gadd153 (DNA Damage Inducible Transcript 3), an apoptotic gene activated following endoplasmic reticulum (ER) stress, were 3-fold higher in N27 cells treated with DLD, suggesting that DLD-induced mitochondrial dysfunction is related to ER stress. Dopamine cells were also assessed for changes in tyrosine hydroxylase (TH) protein, which did not differ among treatments. This study demonstrates that DLD impairs oxidative respiration in dopamine cells, and ER stress is hypothesized to be associated with the DLD-induced mitochondrial dysfunction. This is important as ER stress is also linked to PD. This study presents mechanistic insight into pesticide-induced mitochondrial dysfunction using a chemical that is reported to be associated to a higher risk for neurodegenerative disease.

Reversible meiotic arrest of bovine oocytes by EGFR inhibition and follicular hemisections

The objective of this study was to investigate the effects of inhibiting the epidermal growth factor receptor (EGFR) pathway on meiosis blockage and resumption, mRNA expression of genes involved in oocyte maturation and cumulus expansion, and embryo development. Bovine cumulus-oocyte complexes (COCs) were cultured for 15 h in the presence of the EGFR inhibitor (AG1478) and follicular hemisections (FHS). Most of the oocytes (89.3%) remained at the germinal vesicle (GV) stage when cultured in the presence of FHS and 5 μM AG1478. The inhibitory effect was reversible as most oocytes (83.8%) completed meiosis after additional 20 h maturation. Embryo development to the blastocyst stage was similar (P > 0.05) between FHS and 5 μM AG1478 treated (39.3%) and control (41.1%) groups. In cumulus cells, mRNA abundance of early growth response protein 1 (EGR1), tumor necrosis factor alpha-induced protein 6 (TNFAIP6) and hyaluronan synthase 2 (HAS2) genes, and phosphorylated extracellular regulated kinase (p-ERK1/2) protein were lower in COCs treated with AG1478 plus FHS compared with FHS alone (P < 0.05). In granulosa cells of FHS, AG1478 treatment reduced transcript levels of PGR and ADAMTS1 (P < 0.05). The inhibitory effect of AG1478 on meiotic progression was not reverted by treatment with angiotensin II (ANG II) or prostaglandins (PGF_2α or PGE₂). This study demonstrates that inhibition of EGFR in the presence of FHS is a reliable approach to promote reversible arrest of bovine oocytes at the GV stage.

Regulation of Mammalian Oocyte Meiosis by Intercellular Communication Within the Ovarian Follicle

Meiotic progression in mammalian preovulatory follicles is controlled by the granulosa cells around the oocyte. Cyclic GMP (cGMP) generated in the granulosa cells diffuses through gap junctions into the oocyte, maintaining meiotic prophase arrest. Luteinizing hormone then acts on receptors in outer granulosa cells to rapidly decrease cGMP. This occurs by two complementary pathways: cGMP production is decreased by dephosphorylation and inactivation of the NPR2 guanylyl cyclase, and cGMP hydrolysis is increased by activation of the PDE5 phosphodiesterase. The cGMP decrease in the granulosa cells results in rapid cGMP diffusion out of the oocyte, initiating meiotic resumption. Additional, more slowly developing mechanisms involving paracrine signaling by extracellular peptides (C-type natriuretic peptide and EGF receptor ligands) maintain the low level of cGMP in the oocyte. These coordinated signaling pathways ensure a fail-safe system to prepare the oocyte for fertilization and reproductive success.

Effect of kit ligand on natriuretic peptide precursor C and oocyte maturation in cattle

In vitro maturation (IVM) of oocytes in cattle is inefficient, and there is great interest in the development of approaches to improve maturation and fertilization rates. Intraovarian signalling molecules are being explored as potential additives to IVM media. One such factor is kit ligand (KITL), which stimulates the growth of oocytes. We determined if KITL enhances oocyte maturation in cattle. The two main isoforms of KITL (KITL1 and KITL2) were expressed in bovine cumulus–oocyte complexes (COC), and levels of mRNA increased during FSH-stimulated IVM. The addition of KITL to the culture medium increased the percentage of oocytes that reached meiosis II but did not affect cumulus expansion after 22 h of IVM. Addition of KITL reduced the levels of mRNA encoding natriuretic peptide precursor C (NPPC), a protein that holds oocytes in meiotic arrest, and increased the levels of mRNA encoding YBX2, an oocyte-specific factor involved in meiosis. Removal of the oocyte from the COC resulted in increased KITL mRNA levels and decreased NPPC mRNA levels in cumulus cells, and addition of denuded oocytes reversed these effects. Taken together, our results suggest that KITL enhances bovine oocyte nuclear maturation through a mechanism that involves NPPC, and that the oocyte regulates cumulus expression of KITL mRNA.

FSH stimulation of anestrous cats improves oocyte quality and development of parthenogenetic embryos

In the domestic cat, the efficiency of in vitro embryo production systems is negatively affected during the nonbreeding season. The objective of this research was to evaluate the effect of FSH stimulation in anestrous cats, on quality of cumulus-oocyte complexes (COCs) and in vitro developmental competence after parthenogenetic activation. To accomplish this purpose, anestrous cats were grouped into: (1) FSH treated (serial doses of 5 mg of porcine FSH each, every 24 hours, for 4 days) and (2) untreated control. The COCs were classified morphologically and a proportion of grade I and II COCs was used for expression analysis of FSHR, LHCGR, EGFR, PTGS2, EGR1, GDF9, and GATM by RT-qPCR. In addition, another proportion of grade I and II COCs was matured in vitro and used for parthenogenetic activation. After 8 days in culture, blastocyst and hatching blastocyst rates were assessed, and the expression of OCT4, SOX2, NANOG, CDX2, and GATA6 was evaluated. The COCs in the FSH group had an enhanced quality, a higher expression of LHCGR and a lower expression of GATM than did COCs from the control group (P < 0.05). Furthermore, embryos in the FSH group had increased blastocyst and hatching blastocyst rates, and those embryos had a higher expression of OCT4 and GATA than their counterparts from the control group (P < 0.05). In conclusion, ovarian stimulation of anestrous cats with FSH improved quality and increased the expression of LHCGR in COCs. The enhanced in vitro developmental competence, after parthenogenetic activation of oocytes from FSH-treated cats, coincided with an increased expression of OCT4 and GATA6 in blastocysts and hatching blastocysts.

Embryonic Poly(A)-Binding Protein (EPAB) Is Required for Granulosa Cell EGF Signaling and Cumulus Expansion in Female Mice

Embryonic poly(A)-binding protein (EPAB) is the predominant poly(A)-binding protein in Xenopus, mouse, and human oocytes and early embryos before zygotic genome activation. EPAB is required for translational activation of maternally stored mRNAs in the oocyte and Epab(-/-) female mice are infertile due to impaired oocyte maturation, cumulus expansion, and ovulation. The aim of this study was to characterize the mechanism of follicular somatic cell dysfunction in Epab(-/-) mice. Using a coculture system of oocytectomized cumulus oophorus complexes (OOXs) with denuded oocytes, we found that when wild-type OOXs were cocultured with Epab(-/-) oocytes, or when Epab(-/-) OOXs were cocultured with WT oocytes, cumulus expansion failed to occur in response to epidermal growth factor (EGF). This finding suggests that oocytes and cumulus cells (CCs) from Epab(-/-) mice fail to send and receive the necessary signals required for cumulus expansion. The abnormalities in Epab(-/-) CCs are not due to lower expression of the oocyte-derived factors growth differentiation factor 9 or bone morphogenetic protein 15, because Epab(-/-) oocytes express these proteins at comparable levels with WT. Epab(-/-) granulosa cells (GCs) exhibit decreased levels of phosphorylated MEK1/2, ERK1/2, and p90 ribosomal S6 kinase in response to lutenizing hormone and EGF treatment, as well as decreased phosphorylation of the EGF receptor. In conclusion, EPAB, which is oocyte specific, is required for the ability of CCs and GCs to become responsive to LH and EGF signaling. These results emphasize the importance of oocyte-somatic communication for GC and CC function.

MAPK3/1 is conducive to luteinizing hormone-mediated C-type natriuretic peptide decrease in bovine granulosa cells

C-type natriuretic peptide (CNP) plays a role as an oocyte maturation inhibitor (OMI) in many species, including the bovine. However, the effects of luteinizing hormone (LH) on CNP expression and its potential mechanisms have not reported in the bovine. In the present study, we aimed to study the effects of LH on CNP expression and to illuminate the potential molecular mechanism in this process. Our results showed that LH induced epidermal growth factor receptor (EGFR) phosphorylation, mitogen-activated protein kinase3/1 (MAPK3/1) activation and CNP mRNA decrease in cultured bovine granulosa cells. Further study revealed that LH suppressed CNP expression via the MAPK3/1 signaling pathway, which was activated by the EGFR pathway. In conclusion, our research suggested that MAPK3/1 is involved in LH-mediated decrease of CNP and that this process is related to the EGFR and MAPK3/1 signal pathways.

Mitogen-Activated Protein Kinase 8 (MAP3K8) Mediates the Signaling Pathway of Estradiol Stimulating Progesterone Production Through G Protein-Coupled Receptor 30 (GPR30) in Mouse Corpus Luteum

The corpus luteum (CL) is a transient endocrine gland developed from the ovulated follicles, and the most important function is to synthesize and secrete progesterone (P(4)), a key hormone to maintain normal pregnancy and estrous cycle in most mammals. It is known that estrogen has a vital role in stimulating P(4) synthesis in CL, but it still remains unclear about the mechanism of estradiol (E(2)) regulating P(4) production in CL. Our results here first show that all of the CL cells express MAPK 8 (MAP3K8), and the MAP3K8 level is much higher at the midstage than at the early and late stages during CL development. The further functional studies show that the forced inhibition of endogenous MAP3K8 by using MAP3K8 small interfering RNA and MAP3K8 signaling inhibitor (MAP3K8i) in the luteal cells significantly block the P(4) synthesis and neutralize the enhancing effect of E(2) on P(4) production in the CL. In addition, our results here demonstrate that the stimulating effect of E(2) on P(4) synthesis relies on the estrogen no-classical protein-coupled receptor 30, and MAP3K8 is involved in mediating the protein-coupled receptor 30signaling of E(2) affecting P(4) synthesis via stimulating ERK phosphorylation. These novel findings are critical for our understanding the ovary physiology and pathological mechanism.

Dephosphorylation and inactivation of NPR2 guanylyl cyclase in granulosa cells contributes to the LH-induced decrease in cGMP that causes resumption of meiosis in rat oocytes

In mammals, the meiotic cell cycle of oocytes starts during embryogenesis and then pauses. Much later, in preparation for fertilization, oocytes within preovulatory follicles resume meiosis in response to luteinizing hormone (LH). Before LH stimulation, the arrest is maintained by diffusion of cyclic (c)GMP into the oocyte from the surrounding granulosa cells, where it is produced by the guanylyl cyclase natriuretic peptide receptor 2 (NPR2). LH rapidly reduces the production of cGMP, but how this occurs is unknown. Here, using rat follicles, we show that within 10 min, LH signaling causes dephosphorylation and inactivation of NPR2 through a process that requires the activity of phosphoprotein phosphatase (PPP)-family members. The rapid dephosphorylation of NPR2 is accompanied by a rapid phosphorylation of the cGMP phosphodiesterase PDE5, an enzyme whose activity is increased upon phosphorylation. Later, levels of the NPR2 agonist C-type natriuretic peptide decrease in the follicle, and these sequential events contribute to the decrease in cGMP that causes meiosis to resume in the oocyte.

Ovarian dendritic cells act as a double-edged pro-ovulatory and anti-inflammatory sword

Ovulation and inflammation share common attributes, including immune cell invasion into the ovary. The present study aims at deciphering the role of dendritic cells (DCs) in ovulation and corpus luteum formation. Using a CD11c-EYFP transgenic mouse model, ovarian transplantation experiments, and fluorescence-activated cell sorting analyses, we demonstrate that CD11c-positive, F4/80-negative cells, representing DCs, are recruited to the ovary under gonadotropin regulation. By conditional ablation of these cells in CD11c-DTR transgenic mice, we revealed that they are essential for expansion of the cumulus-oocyte complex, release of the ovum from the ovarian follicle, formation of a functional corpus luteum, and enhanced lymphangiogenesis. These experiments were complemented by allogeneic DC transplantation after conditional ablation of CD11c-positive cells that rescued ovulation. The pro-ovulatory effects of these cells were mediated by up-regulation of ovulation-essential genes. Interestingly, we detected a remarkable anti-inflammatory capacity of ovarian DCs, which seemingly serves to restrict the ovulatory-associated inflammation. In addition to discovering the role of DCs in ovulation, this study implies the extended capabilities of these cells, beyond their classic immunologic role, which is relevant also to other biological systems.

Luteinizing hormone and human chorionic gonadotropin: origins of difference

Luteinizing hormone (LH) and human chorionic gonadotropin (hCG) are widely recognized for their roles in ovulation and the support of early pregnancy. Aside from the timing of expression, however, the differences between LH and hCG have largely been overlooked in the clinical realm because of their similar molecular structures and shared receptor. With technologic advancements, including the development of highly purified and recombinant gonadotropins, researchers now appreciate that these hormones are not as interchangeable as once believed. Although they bind to a common receptor, emerging evidence suggests that LH and hCG have disparate effects on downstream signaling cascades. Increased understanding of the inherent differences between LH and hCG will foster more effective diagnostic and prognostic assays for use in a variety of clinical contexts and support the individualization of treatment strategies for conditions such as infertility.

Knockdown of TrkA in cumulus oocyte complexes (COCs) inhibits EGF-induced cumulus expansion by down-regulation of IL-6

Tyrosine kinase receptor A (TrkA), the high-affinity receptor of nerve growth factor (NGF), is known to play key roles in ovarian follicular development, such as assembly of early follicles and follicular ovulation. However, little is known about the roles of TrkA in cumulus oocyte complex (COC) expansion. In this study, we found that TrkA was abundant in large antral follicles and knockdown of TrkA in COCs attenuated epidermal growth factor (EGF)-induced COC expansion and further decreased the ovulation rate. The effect of TrkA on COC expansion was not mediated through downstream EGF effectors, phosphorylation of extracellular regulated protein kinases 1/2 (ERK1/2) or drosophila mothers against decapentaplegic protein (SMAD), or through up-regulation of COC expansion-related transcripts such as prostaglandin-endoperoxide synthase 2 (Ptgs2), hyaluronan synthase 2 (Has2), TNF-induced protein 6 (Tnfaip6) or pentraxin 3 (Ptx3). However, pharmacological blockade of TrkA transducing activity (K252α) in COCs decreased the mRNA expression and protein secretion of interleukin-6 (IL-6), identified from mRNA microarray of K252α-treated COCs. Meanwhile, knockdown of IL-6 attenuated EGF-induced COC expansion. In addition, IL-6 rescued the inhibitory effect of K252α on EGF-induced cumulus expansion. Therefore, IL-6 may act as a new potential cumulus expansion-related transcript, which may be involved in the integration of TrkA and EGF signaling in affecting COC expansion. Here, we provide mechanistic insights into the roles of TrkA in EGF-induced cumulus expansion. Understanding potential cross-points between TrkA and EGF affecting cumulus expansion will help in the discovery of new therapeutic targets in ovulation-related diseases.

FSH in vitro versus LH in vivo: similar genomic effects on the cumulus

The use of gonadotropins to trigger oocyte maturation both in vivo and in vitro has provided precious and powerful knowledge that has significantly increased our understanding of the ovarian function. Moreover, the efficacy of most assisted reproductive technologies (ART) used in both humans and livestock species relies on gonadotropin input, mainly FSH and LH. Despite the significant progress achieved and the huge impact of gonadotropins, the exact molecular pathways of the two pituitary hormones, FSH and LH, still remain poorly understood. Moreover, these pathways may not be the same when moving from the in vivo to the in vitro context. This misunderstanding of the intricate synergy between these two hormones leads to a lack of consensus about their use mainly in vitro or in ovulation induction schedules in vivo. In order to optimize their use, additional work is thus required with a special focus on comparing the in vitro versus the in vivo effects. In this context, this overview will briefly summarize the downstream gene expression pathways induced by both FSH in vitro and LH in vivo in the cumulus compartment. Based on recent microarray comparative analysis, we are reporting that in vitro FSH stimulation on cumulus cells appears to achieve at least part of the gene expression activity after in vivo LH stimulation. We are then proposing that the in vitro FSH-response of cumulus cells have similitudes with the in vivo LH-response.

Human chorionic gonadotropin (hCG) induces MAPK3/1 phosphorylation in the zebrafish ovarian follicle cells independent of EGF/EGFR pathway

In mammals, human chorionic gonadotropin (hCG), a luteinizing hormone (LH) analogue, induces MAPK3/1 phosphorylation in the granulosa cells and this event is largely dependent on epidermal growth factor receptor (EGFR) activity. However, whether this mechanism also works in other vertebrates such as fish remains unknown. Here, we showed that treatment of cultured zebrafish ovarian follicle cells with hCG also resulted in MAPK3/1 phosphorylation without affecting the total protein level of MAPK3/1. The phosphorylation level peaked at 5 min and then declined to the basal level after 40 min of hCG treatment. Further experiment showed that H89 (a PKA inhibitor) could abolish hCG-stimulated MAPK3/1 phosphorylation, but had no effect on EGF-induced phosphorylation, suggesting a mediating role for cAMP/PKA in hCG activation of MAPK3/1. On the other hand, AG1478 (an EGFR inhibitor) completely blocked EGF-stimulated MAPK3/1 phosphorylation, but had no effect on the hCG-induced MAPK3/1 phosphorylation. These data indicate that similar to its action in mammals, hCG/LH also stimulated MAPK3/1 phosphorylation in the zebrafish ovarian follicle cells; however, unlike the situation in the mammalian ovary, the hCG-stimulated MAPK3/1 phosphorylation in cultured zebrafish ovarian follicle cells was independent of EGFR.

Growth factor receptor-bound protein 14: a potential new gene associated with oocyte competence

The Grb14 protein is a member of the Grb7 protein family. This protein family acts by binding to tyrosine kinase receptors, promoting cell proliferation and differentiation. There is evidence of the involvement of tyrosine kinase factors in the bovine oocyte maturation process. However, Grb14 has not been studied for bovine cumulus–oocyte complexes (COCs). The aim of the present study was to characterize Grb14 mRNA expression in bovine COCs during follicular development. Furthermore, we demonstrated that the expression of Grb14 mRNA is not regulated by estradiol. mRNA expression of Grb14 was assessed in 480 COCs from follicles of different sizes (1–3, 4–6, 6–8 or >8 mm) by quantitative reverse transcription polymerase chain reaction (qRT-PCR). Grb14 mRNA expression decreased in COCs throughout follicular growth (P < 0.05). The role of estradiol in the expression of Grb14 mRNA in COCs was studied. Grb14 mRNA abundance did not differ in COCs cultured in the presence or absence of 17β-estradiol or fulvestrant. In conclusion, we showed that Grb14 mRNA is downregulated in COCs during antral follicle development, a finding that suggests a role for Grb14 in oocyte competence.

Lapatinib inhibits meiotic maturation of porcine oocyte-cumulus complexes cultured in vitro in gonadotropin-supplemented medium

OBJECTIVE

To determine whether inhibition of epidermal growth factor (EGF) receptor tyrosine kinase with lapatinib affects oocyte maturation, expression of the cumulus expansion-associated genes such as tumor necrosis factor alpha-induced protein 6 (TNFAIP6) and prostaglandin-endoperoxide synthase 2 (PTGS2), and synthesis of hyaluronan (HA) and progesterone (P) by porcine oocyte cumulus complexes (OCC).

DESIGN

Our work focuses on lapatinib, an orally active small molecule that selectively inhibits the tyrosine kinase domain of both EGF receptor and human EGF receptor 2, and downstream signaling.

SETTING

A reproductive biology laboratory.

PATIENT(S)

Not applicable.

INTERVENTION(S)

Porcine OCC were cultured in vitro in a medium with FSH/LH in the presence/absence of lapatinib.

MAIN OUTCOME MEASURE(S)

Methods performed: real-time reverse transcriptase-polymerase chain reaction (PCR), immunofluorescence, RIA.

RESULT(S)

In FSH/LH-stimulated and expanded cumulus oophorus extracellular matrix, HA was detected with biotinylated HA-binding proteins. However, weaker HA- and weaker cytoplasmic TNFAIP6 were detected were detected in lapatinib-pretreated OCC. The expression of the two cumulus expansion-associated gene transcripts was significantly decreased and synthesis of HA by cumulus cells was reduced. Lapatinib (10 μM) inhibited FSH/LH-induced oocyte meiotic maturation. Progesterone production increased after OCC stimulation with FSH/LH and was significantly decreased by lapatinib (10 μM).

CONCLUSION(S)

Lapatinib inhibits oocyte maturation and reduces expression of cumulus expansion-associated transcripts, and synthesis of HA and P in OCC cultured in vitro in FSH/LH-supplemented medium.

Effect of varying glucose and glucosamine concentration in vitro on mouse oocyte maturation and developmental competence

The effects of hyper- and hypo-glycaemic conditions during the in vitro maturation of mouse cumulus–oocyte complexes on developmental competence were examined, with an emphasis on the role of the hexosamine biosynthesis pathway. A low (1 mM) glucose concentration achieved optimal oocyte competence (3-fold higher blastocyst development rate compared with high (30 mM) glucose, P < 0.05). In addition, glucose supplementation during only the first hour after release from the follicle was necessary and sufficient to support oocyte maturation and embryo development to the blastocyst stage. Glucosamine (a known hyperglycaemic mimetic and specific activator of the hexosamine pathway) was able to substitute for glucose during this first hour, indicating that flux through the hexosamine pathway is essential for oocyte competence. In the absence of glucose throughout the maturation period, glucosamine was not able to increase developmental competence, and at higher concentrations (2.5 and 5 mM) had a detrimental effect on MII and blastocyst development rates, compared with controls (P < 0.05). These experiments underscore the importance of glucose metabolic pathways during in vitro maturation and support the concept that excess flux through the hexosamine pathway has detrimental consequences.

Effect of superstimulatory treatments on the expression of genes related to ovulatory capacity, oocyte competence and embryo development in cattle

Multiple ovulation (superovulation) and embryo transfer has been used extensively in cattle. In the past decade, superstimulatory treatment protocols that synchronise follicle growth and ovulation, allowing for improved donor management and fixed-time AI (FTAI), have been developed for zebu (Bos indicus) and European (Bos taurus) breeds of cattle. There is evidence that additional stimulus with LH (through the administration of exogenous LH or equine chorionic gonadotrophin (eCG)) on the last day of the superstimulatory treatment protocol, called the ‘P-36 protocol’ for FTAI, can increase embryo yield compared with conventional protocols that are based on the detection of oestrus. However, inconsistent results with the use of hormones that stimulate LH receptors (LHR) have prompted further studies on the roles of LH and its receptors in ovulatory capacity (acquisition of LHR in granulosa cells), oocyte competence and embryo quality in superstimulated cattle. Recent experiments have shown that superstimulation with FSH increases mRNA expression of LHR and angiotensin AT2 receptors in granulosa cells of follicles >8 mm in diameter. In addition, FSH decreases mRNA expression of growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) in oocytes, but increases the expression of both in cumulus cells, without diminishing the capacity of cumulus–oocyte complexes to generate blastocysts. Although these results indicate that superstimulation with FSH is not detrimental to oocyte competence, supplementary studies are warranted to investigate the effects of superstimulation on embryo quality and viability. In addition, experiments comparing the cellular and/or molecular effects of adding eCG to the P-36 treatment protocol are being conducted to elucidate the effects of superstimulatory protocols on the yield of viable embryos.

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.

Epidermal growth factor differentially regulates activin subunits in the zebrafish ovarian follicle cells via diverse signaling pathways

Epidermal growth factor (EGF) promotes oocyte maturation in the zebrafish and its effect is mediated via the activin system. However, the mechanisms by which EGF regulates activin subunits in the follicle cells remain unknown. The present study demonstrated that EGF controlled expression of three activin subunits (inhbaa, inhbab and inhbb) in the follicle cells via diverse signaling pathways. The expression of inhbaa and inhbb was often co-regulated via similar pathways. Suppression of MAPK3/1, p38 MAPK, PKC and PKA each blocked or partially reduced the stimulatory effects of EGF on the expression of inhbaa and inhbb while up-regulated that of inhbab. Conversely, inhibition of PI3K did not have any effect on the expression of inhbaa and inhbb but significantly suppressed the stimulatory effect of EGF on inhbab. In summary, EGF action in the zebrafish ovary involves activin system and its regulation of activin subunits is mediated by diverse signaling pathways downstream of EGFR.