Human chorionic gonadotropin-dependent up-regulation of epiregulin and amphiregulin in equine and bovine follicles during the ovulatory process

Assessment of Epiregulin Effect and its Combination with Gonadotropins on Proliferation, Apoptosis, and Secretory Activity by Human Ovarian Cells

The release of epidermal growth factor ligand epiregulin (EREG) by human ovarian granulosa cells, its direct action on basic ovarian cell functions, and interrelationships with gonadotropins were investigated. We examined (1) the ovarian production of EREG (the time-dependent accumulation of EREG in the medium incubated with human ovarian granulosa cells, and (2) the effect of the addition of EREG (0, 1, 10, and 100 ng.ml^-1) given alone or in combination with FSH or LH (100 ng.ml^-1) on basic granulosa cells functions. Viability, proliferation (accumulation of PCNA and cyclin B1) and apoptosis (accumulation of bax and caspase 3), the release of steroid hormones (progesterone, testosterone, and estradiol), and prostaglandin E2 (PGE2) were analyzed by using the Trypan blue exclusion test, quantitative immunocytochemistry, and ELISA. A significant time-dependent accumulation of EREG in a medium cultured with human granulosa cells with a peak at 3 and 4 days was observed. The addition of EREG alone increased cell viability, proliferation, progesterone, testosterone, and estradiol release, decreased apoptosis, bud did not affect PGE2 release. The addition of either FSH or LH alone increased cell viability, proliferation, progesterone, testosterone, estradiol, and PGE2 release and decreased apoptosis. Furthermore, both FSH and LH mostly promoted the stimulatory action of EREG on granulosa cell functions. These results demonstrated, that EREG produced by ovarian cells can be an autocrine/paracrine stimulator of human ovarian cell functions. Furthermore, they demonstrate the functional interrelationship between EREG and gonadotropins in the control of ovarian functions.

Luteinizing hormone stimulates the expression of amphiregulin in human theca cells

BACKGROUND

Luteinizing hormone (LH) can stimulate mural granulosa cells to produce Amphiregulin (AREG), which can induce the resumption of meiosis in oocytes. Theca cells are present in the outer layer of follicles, providing communication with the pituitary axis through the established vascular system around the follicle. As LH target cells, it is unknown whether theca cells can produce AREG after LH stimulation.

METHODS

Primary cultured human theca cells were treated with LH (with or without the inhibitor of PKA, H89), or agonists of adenylate cyclase (forskolin or db-cAMP). The mRNA and protein levels of AREG were evaluated by RT-qPCR, immunochemistry, immunofluorescence, western blotting, and ELISA.

RESULTS

Immunohistochemistry of normal ovarian tissue obtained in the early-mid follicle phase showed that AREG expression was absent in both the theca layer and the granulosa cell layer of antral follicles. Double immunofluorescent staining revealed colocalization of AREG and CYP17A1 in human theca cells and colocalization of FSHR and AREG in human granulosa cells isolated from follicular fluid collected during IVF/ICSI after hCG trigger. LH significantly increased the mRNA and protein levels of AREG in human theca cells and the concentration of AREG in the culture medium. Forskolin and db-cAMP, activators of the cAMP/PKA signalling pathway, also significantly increased the mRNA and protein levels of AREG in human theca cells and the concentration of AREG in the culture medium. H89 antagonized the stimulating effect of LH on AREG expression in human theca cells. In addition, the concentration of AREG was lower in polycystic ovarian syndrome (PCOS) follicular fluid than in normal follicular fluid. The mRNA levels of AREG were significantly lower in PCOS granulosa cells and theca cells than in normal granulosa cells and theca cells.

CONCLUSION

LH can stimulate the expression of AREG in human theca cells, and the adenylate cyclase/cAMP/PKA cascade may mediate this process. Expression of AREG is decreased in PCOS theca cells compared to normal theca cells, with or without LH stimulation.

A central role for cAMP/EPAC/RAP/PI3K/AKT/CREB signaling in LH-induced follicular Pgr expression at medaka ovulation†

Nuclear progestin receptor (PGR) is a ligand-activated transcription factor that has been identified as a pivotal mediator of many processes associated with ovarian and uterine function, and aberrant control of PGR activity causes infertility and disease including cancer. The essential role of PGR in vertebrate ovulation is well recognized, but the mechanisms by which PGR is rapidly and transiently induced in preovulatory follicles after the ovulatory LH surge are not known in lower vertebrates. To address this issue, we utilized the small freshwater teleost medaka Oryzias latipes, which serves as a good model system for studying vertebrate ovulation. In the in vitro ovulation system using preovulatory follicles dissected from the fish ovaries, we found that inhibitors of EPAC (brefeldin A), RAP (GGTI298), PI3K (Wortmannin), AKT (AKT inhibitor IV), and CREB (KG-501) inhibited LH-induced follicle ovulation, while the PKA inhibitor H-89 had no effect on follicle ovulation. The inhibitors capable of inhibiting follicle ovulation also inhibited follicular expression of Pgr and matrix metalloproteinase-15 (Mmp15), the latter of which was previously shown to not only be a downstream effector of Pgr but also a proteolytic enzyme indispensable for follicle rupture in medaka ovulation. Further detailed analysis revealed for the first time that the cAMP/EPAC/RAP/PI3K/AKT/CREB signaling pathway mediates the LH signal to induce Pgr expression in preovulatory follicles. Our data also showed that phosphorylated Creb1 is a transcription factor essential for pgr expression and that Creb1 phosphorylated by Akt1, rather than PKA, may be preferably used to induce pgr expression.

Simultaneous Determination of Prostaglandin and Hormones in Excreta of Trogopterus xanthipes

The excreta of Trogopterus xanthipes (also called Wulingzhi in Chinese, WLZ) is a well-known traditional Chinese medicine used for the treatment of irregular menstruation in clinic. Few reports are available on the chemical profiling of WLZ. In this work, qualitative and quantitative analyses of endogenous prostaglandin and hormones in WLZ were performed using UHPLC-orbitrap-MSn. In total, 48 compounds were identified in urine of T. xanthipes. Furthermore, the contents of four target compounds were simultaneously quantitated in 20 batches of samples by UPLC-MS/MS. The quantitative method showed a good linear correlation (R > 0.995) in a wide range for each compound. The method had a high sensitivity with LOD (0.5-1.0 ng/mL) and LOQ (1.0-2.5 ng/mL). The intra- and inter-day precisions were < 9.17 (RSD %), and repeatability and stability were < 6.14 (RSD %). The recovery of the analytes varied between 85.8% and 97.3% at three different concentrations. The present integrated qualitative and quantitative assessment of WLZ provides an evaluation strategy to assess the constituent in traditional Chinese medicine.

A Preliminary Study on the Characteristics of microRNAs in Ovarian Stroma and Follicles of Chuanzhong Black Goat during Estrus

microRNAs (miRNAs) play a significant role in ovarian follicular maturity, but miRNA expression patterns in ovarian stroma (OS), large follicles (LF), and small follicles (SF) have been rarely explored. We herein aimed to identify miRNAs, their target genes and signaling pathways, as well as their interaction networks in OS, LF, and SF of Chuanzhong black goats at the estrus phase using small RNA-sequencing. We found that the miRNA expression profiles of LF and SF were more similar than those of OS—32, 16, and 29 differentially expressed miRNAs were identified in OS vs. LF, OS vs. SF, and LF vs. SF, respectively. Analyses of functional enrichment and the miRNA-targeted gene interaction network suggested that miR-182 (SMC3), miR-122 (SGO1), and miR-206 (AURKA) were involved in ovarian organogenesis and hormone secretion by oocyte meiosis. Furthermore, miR-202-5p (EREG) and miR-485-3p (FLT3) were involved in follicular maturation through the MAPK signaling pathway, and miR-2404 (BMP7 and CDKN1C) played a key role in follicular development through the TGF-β signaling pathway and cell cycle; nevertheless, further research is warranted. To our knowledge, this is the first study to investigate miRNA expression patterns in OS, LF, and SF of Chuanzhong black goats during estrus. Our findings provide a theoretical basis to elucidate the role of miRNAs in follicular maturation. These key miRNAs might provide candidate biomarkers for the diagnosis of follicular maturation and will assist in developing new therapeutic targets for female goat infertility.

Ovulation: Parallels With Inflammatory Processes

The midcycle surge of LH sets in motion interconnected networks of signaling cascades to bring about rupture of the follicle and release of the oocyte during ovulation. Many mediators of these LH-induced signaling cascades are associated with inflammation, leading to the postulate that ovulation is similar to an inflammatory response. First responders to the LH surge are granulosa and theca cells, which produce steroids, prostaglandins, chemokines, and cytokines, which are also mediators of inflammatory processes. These mediators, in turn, activate both nonimmune ovarian cells as well as resident immune cells within the ovary; additional immune cells are also attracted to the ovary. Collectively, these cells regulate proteolytic pathways to reorganize the follicular stroma, disrupt the granulosa cell basal lamina, and facilitate invasion of vascular endothelial cells. LH-induced mediators initiate cumulus expansion and cumulus oocyte complex detachment, whereas the follicular apex undergoes extensive extracellular matrix remodeling and a loss of the surface epithelium. The remainder of the follicle undergoes rapid angiogenesis and functional differentiation of granulosa and theca cells. Ultimately, these functional and structural changes culminate in follicular rupture and oocyte release. Throughout the ovulatory process, the importance of inflammatory responses is highlighted by the commonalities and similarities between many of these events associated with ovulation and inflammation. However, ovulation includes processes that are distinct from inflammation, such as regulation of steroid action, oocyte maturation, and the eventual release of the oocyte. This review focuses on the commonalities between inflammatory responses and the process of ovulation.

Cellular and molecular mechanisms of the preovulatory follicle differenciation and ovulation: What do we know in the mare relative to other species

Terminal follicular differentiation and ovulation are essential steps of reproduction. They are induced by the increase in circulating LH, and lead to the expulsion from the ovary of oocytes ready to be fertilized. This review summarizes our current understanding of cellular and molecular pathways that control ovulation using a broad mammalian literature, with a specific focus to the mare, which is unique in some aspects of ovarian function in some cases. Essential steps and key factors are approached. The first part of this review concerns LH, receptors and signaling, addressing the description of the equine gonadotropin and cloning, signaling pathways that are activated following the binding of LH to its receptors, and implication of transcription factors which better known are CCAAT-enhancer-binding proteins (CEBP) and cAMP response element-binding protein (CREB). The second and major part is devoted to the cellular and molecular actors within follicular cells during preovulatory maturation. We relate to 1) molecules involved in vascular permeability and vasoconstriction, 2) involvement of neuropeptides, such as kisspeptin, neurotrophins and neuronal growth factor, neuropeptide Y (NPY), 3) the modification of steroidogenesis, steroids intrafollicular levels and enzymes activity, 4) the local inflammation, with the increase in prostaglandins synthesis, and implication of leukotrienes, cytokines and glucocorticoids, 5) extracellular matrix remodelling with involvement of proteases, antiproteases and inhibitors, as well as relaxin, and finaly 6) the implication of oxytocine, osteopontin, growth factors and reactive oxygen species. The third part describes our current knowledge on molecular aspect of in vivo cumulus-oocyte-complexe maturation, with a specific focus on signaling pathways, paracrine factors, and intracellular regulations that occur in cumulus cells during expansion, and in the oocyte during nuclear and cytoplasmic meiosis resumption. Our aim was to give an overall and comprehensive map of the regulatory mechanisms that intervene within the preovulatory follicle during differentiation and ovulation.

The cAMP-EPAC Pathway Mediates PGE2-Induced FGF2 in Bovine Granulosa Cells

During the periovulatory period, the profile of fibroblast growth factor 2 (FGF2) coincides with elevated prostaglandin E2 (PGE2) levels. We investigated whether PGE2 can directly stimulate FGF2 production in bovine granulosa cells and, if so, which prostaglandin E2 receptor (PTGER) type and signaling cascades are involved. PGE2 temporally stimulated FGF2. Accordingly, endoperoxide-synthase2-silenced cells, exhibiting low endogenous PGE2 levels, had reduced FGF2. Furthermore, elevation of viable granulosa cell numbers by PGE2 was abolished with FGF2 receptor 1 inhibitor, suggesting that FGF2 mediates this action of PGE2. Epiregulin (EREG), a known PGE2-inducible gene, was studied alongside FGF2. PTGER2 agonist elevated cAMP as well as FGF2 and EREG levels. However, a marked difference between cAMP-induced downstream signaling was observed for FGF2 and EREG. Whereas FGF2 upregulated by PGE2, PTGER2 agonist, or forskolin was unaffected by the protein kinase A (PKA) inhibitor H89, EREG was significantly inhibited. FGF2 was dose-dependently stimulated by the exchange protein directly activated by cAMP (EPAC) activator; a similar induction was observed for EREG. However, forskolin-stimulated FGF2, but not EREG, was inhibited in EPAC1-silenced cells. These findings ascribe a novel autocrine role for PGE2, namely, elevating FGF2 production in granulosa cells. This study also reveals that cAMP-activated EPAC1, rather than PKA, mediates the effect of PGE2/PTGER2 on the expression of FGF2. Stimulation of EREG by PGE2 is also mediated by PTGER2 but, in contrast to FGF2, EREG was found to be PKA sensitive. PGE2-stimulated FGF2 can act to maintain granulosa cell survival; it can also act on ovarian endothelial cells to promote angiogenesis.

Expanded equine cumulus-oocyte complexes exhibit higher meiotic competence and lower glucose consumption than compact cumulus-oocyte complexes

Equine cumulus-oocyte complexes (COCs) are classified as compact (cCOC) or expanded (eCOC) and vary in their meiotic competence. This difference could be related to divergent glucose metabolism. To test this hypothesis in the present study, eCOCs, cCOCs and expanded or compact mural granulosa cells (EC and CC respectively) were matured in vitro for 30h, at which time maturation rate, glucose metabolism and the expression of genes involved in glucose transport, glycolysis, apoptosis and meiotic competence were determined. There were significant differences between eCOCs and cCOCs in maturation rate (50% vs 21.7% (n=192 and 46) respectively; P<0.001), as well as mean (±s.e.m.) glucose consumption (1.8±0.5 vs 27.9±5.9 nmol per COC respectively) and pyruvate (0.09±0.01 vs 2.4±0.8 nmol per COC respectively) and lactate (4.7±1.3 vs 64.1±20.6 nmol per COC respectively; P<0.05 for all) production. Glucose consumption in EC and CC did not differ significantly. Expression of hyaluronan-binding protein (tumour necrosis factor alpha induced protein 6; TNFAIP6) was increased in eCOCs and EC, and solute carrier family 2 member 1 (SLC2A1) expression was increased in eCOCs, but there were no differences in the expression of glycolysis-related enzymes and solute carrier family 2 member 3 (SLC2A3) between the COC or mural granulosa cell types. The findings of the present study demonstrate that metabolic and genomic differences exist between eCOCs and cCOCs and mural granulosa cells in the horse.

Impact of Equine and Bovine Oocyte Maturation in Follicular Fluid From Young and Old Mares on Embryo Production in Vitro

Equine follicular fluid (FF) provides autocrine and paracrine factors from theca, granulosa, and cumulus cells, both reflecting and impacting oocyte and follicle maturation. We hypothesized that maturation of oocytes in FF from old versus young mares has a deleterious effect on oocyte maturation and their subsequent developmental potential. Follicular fluid was collected from the large, dominant follicle from young mares (4-13 years) or old mares (21-26 years) and classified as: (1) Noninduced follicular fluid (NFF), FF from noninduced follicle 33 ± 3 mm, or (2) Induced follicular fluid (IFF), FF collected ∼24 hours after administration of ovulation-inducing drugs when a follicle 33 ± 3 mm was observed. In experiment 1, immature equine oocytes were collected, matured in vitro for 30 ± 2 hours in 100% IFF, collected from young or old mares, with the addition of follicle stimulating hormone (5 mU/mL), then fertilized by intracytoplasmic sperm injection. In experiment 2, immature bovine oocytes were collected, matured in 100% IFF or NFF, collected from young mares or old mares, then fertilized via in vitro fertilization. In experiment 1, more blastocysts tended (P = .08) to be produced from equine oocytes that were matured in old versus young mare FF. In experiment 2, when IFF and NFF groups were combined, cleavage rates were higher (P = .001) when bovine oocytes were matured in FF from young than old mares. In contrast to our hypothesis, we observed no conclusive evidence that FF from old mares has a deleterious impact on oocytes and their early developmental potential.

Luteinizing hormone upregulates NPPC and downregulates NPR3 mRNA abundance in bovine granulosa cells through activation of the EGF receptor

During folliculogenesis, the luteinizing hormone (LH) surge triggers dynamic events in granulosa cells that culminate with ovulation. The aim of this study was to evaluate if the epidermal growth factor receptor (EGFR) is required for ovulation in cattle, and if it regulates the expression of the natriuretic peptide (NP) system in granulosa cells after gonadotropin-releasing hormone (GnRH)/LH stimulation. It was observed that GnRH induces amphiregulin (AREG) and epiregulin (EREG) mRNA at 3 and 6 h after in vivo treatment, but the expression of these genes was not regulated by atrial (ANP) and C-type (CNP) NPs in granulosa cells cultured in vitro. The abundance of mRNA encoding the NP receptors (NPR1, 2 and 3) was not altered by LH supplementation and/or EGFR inhibition (AG1478; AG) in granulosa cells after 6 h of in vitro culture. However, in the same conditions, mRNA encoding the natriuretic peptide precursor C (NPPC) was upregulated by LH, whereas AG (0.5 and 5 μM) inhibited the LH effect. In order to confirm those results, 5 μM AG or saline were intrafollicularly injected in preovulatory follicles and cows were simultaneously treated with GnRH intramuscularly. Granulosa cells harvested at 6 h after GnRH injection revealed higher NPR3 and lower NPPC mRNA levels in AG-treated, compared to control cows. However, intrafollicular injection of AG did not inhibit GnRH-induced ovulation. In granulosa cells cultured in vitro, ANP associated with LH increased prostaglandin-endoperoxide synthase 2 (PTGS2) mRNA abundance. In conclusion, we inferred that LH modulated NPPC and NPR3 mRNA abundance through EGFR in bovine granulosa cells, but ovulation in cattle did not seem to depend on EGFR activation.

Gene expression profiling of upregulated mRNAs in granulosa cells of bovine ovulatory follicles following stimulation with hCG

BACKGROUND

Ovulation and luteinization of follicles are complex biological processes initiated by the preovulatory luteinizing hormone surge. The objective of this study was to identify genes that are differentially expressed in bovine granulosa cells (GC) of ovulatory follicles.

METHODS

Granulosa cells were collected during the first follicular wave of the bovine estrous cycle from dominant follicles (DF) and from ovulatory follicles (OF) obtained 24 h following injection of human chorionic gonadotropin (hCG). A granulosa cell subtracted cDNA library (OF-DF) was generated using suppression subtractive hybridization and screened.

RESULTS

Detection of genes known to be upregulated in bovine GC during ovulation, such as ADAMTS1, CAV1, EGR1, MMP1, PLAT, PLA2G4A, PTGES, PTGS2, RGS2, TIMP1, TNFAIP6 and VNN2 validated the physiological model and analytical techniques used. For a subset of genes that were identified for the first time, gene expression profiles were further compared by semiquantitative RT-PCR in follicles obtained at different developmental stages. Results confirmed an induction or upregulation of the respective mRNAs in GC of OF 24 h after hCG-injection compared with those of DF for the following genes: ADAMTS9, ARAF, CAPN2, CRISPLD2, FKBP5, GFPT2, KIT, KITLG, L3MBLT3, MRO, NUDT10, NUDT11, P4HA3, POSTN, PSAP, RBP1, SAT1, SDC4, TIMP2, TNC and USP53. In bovine GC, CRISPLD2 and POSTN mRNA were found as full-length transcript whereas L3MBLT3 mRNA was alternatively spliced resulting in a truncated protein missing the carboxy-terminal end amino acids, ⁷⁷⁴KNSHNEL⁷⁸⁰. Conversely, L3MBLT3 is expressed as a full-length mRNA in a bovine endometrial cell line. The ⁷⁷⁴KNSHNEL⁷⁸⁰ sequence is well conserved in all mammalian species and follows a SAM domain known to confer protein/protein interactions, which suggest a key function for these amino acids in the epigenetic control of gene expression.

CONCLUSIONS

We conclude that we have identified novel genes that are upregulated by hCG in bovine GC of OF, thereby providing novel insight into peri-ovulatory regulation of genes that contribute to ovulation and/or luteinization processes.

Coordinated Regulation Among Progesterone, Prostaglandins, and EGF-Like Factors in Human Ovulatory Follicles

CONTEXT

In animal models, the luteinizing hormone surge increases progesterone (P4) and progesterone receptor (PGR), prostaglandins (PTGs), and epidermal growth factor (EGF)-like factors that play essential roles in ovulation. However, little is known about the expression, regulation, and function of these key ovulatory mediators in humans.

OBJECTIVE

To determine when and how these key ovulatory mediators are induced after the luteinizing hormone surge in human ovaries.

DESIGN AND PARTICIPANTS

Timed periovulatory follicles were obtained from cycling women. Granulosa/lutein cells were collected from in vitro fertilization patients.

MAIN OUTCOME MEASURES

The in vivo and in vitro expression of PGR, PTG synthases and transporters, and EGF-like factors were examined at the level of messenger RNA and protein. PGR binding to specific genes was assessed. P4 and PTGs in conditioned media were measured.

RESULTS

PGR, PTGS2, and AREG expressions dramatically increased in ovulatory follicles at 12 to 18 hours after human chorionic gonadotropin (hCG). In human granulosa/lutein cell cultures, hCG increased P4 and PTG production and the expression of PGR, specific PTG synthases and transporters, and EGF-like factors, mimicking in vivo expression patterns. Inhibitors for P4/PGR and EGF-signaling pathways reduced hCG-induced increases in PTG production and the expression of EGF-like factors. PGR bound to the PTGS2, PTGES, and SLCO2A1 genes.

CONCLUSIONS

This report demonstrated the time-dependent induction of PGR, AREG, and PTGS2 in human periovulatory follicles. In vitro studies indicated that collaborative actions of P4/PGR and EGF signaling are required for hCG-induced increases in PTG production and potentiation of EGF signaling in human periovulatory granulosa cells.

Effects of aging on gene expression and mitochondrial DNA in the equine oocyte and follicle cells

We hypothesised that advanced mare age is associated with follicle and oocyte gene alterations. The aims of the study were to examine quantitative and temporal differences in mRNA for LH receptor (LHR), amphiregulin (AREG) and epiregulin (EREG) in granulosa cells, phosphodiesterase (PDE) 4D in cumulus cells and PDE3A, G-protein-coupled receptor 3 (GPR3), growth differentiation factor 9 (GDF9), bone morphogenetic protein 15 (BMP15) and mitochondrial (mt) DNA in oocytes. Samples were collected from dominant follicles of Young (3-12 years) and Old (≥20 years) mares at 0, 6, 9 and 12h after administration of equine recombinant LH. LHR mRNA declined after 0h in Young mares, with no time effect in Old mares. For both ages, gene expression of AREG was elevated at 6 and 9h and EREG was expression was elevated at 9h, with higher expression in Old than Young mares. Cumulus cell PDE4D expression increased by 6h (Old) and 12h (Young). Oocyte GPR3 expression peaked at 9 and 12h in Young and Old mares, respectively. Expression of PDE3A increased at 6h, with the increase greater in oocytes from Old than Young mares at 6 and 9h. Mean GDF9 and BMP15 transcripts were higher in Young than Old, with a peak at 6h. Copy numbers of mtDNA did not vary over time in oocytes from Young mares, but a temporal decrease was observed in oocytes from Old mares. The results support an age-associated asynchrony in the expression of genes that are essential for follicular and oocyte maturation before ovulation.

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.

Effects of intramuscular administration of folic acid and vitamin B12 on granulosa cells gene expression in postpartum dairy cows

The fertility of dairy cows is challenged during early lactation, and better nutritional strategies need to be developed to address this issue. Combined supplementation of folic acid and vitamin B12 improve energy metabolism in the dairy cow during early lactation. Therefore, the present study was undertaken to explore the effects of this supplement on gene expression in granulosa cells from the dominant follicle during the postpartum period. Multiparous Holstein cows received weekly intramuscular injection of 320 mg of folic acid and 10 mg of vitamin B12 (treated group) beginning 24 (standard deviation=4) d before calving until 56 d after calving, whereas the control group received saline. The urea plasma concentration was significantly decreased during the precalving period, and the concentration of both folate and vitamin B12 were increased in treated animals. Milk production and dry matter intake were not significantly different between the 2 groups. Plasma concentrations of folates and vitamin B12 were increased in treated animals. Daily dry matter intake was not significantly different between the 2 groups before [13.5 kg; standard error (SE)=0.5] and after (23.6 kg; SE=0.9) calving. Average energy-corrected milk tended to be greater in vitamin-treated cows, 39.7 (SE=1.4) and 38.1 (SE=1.3) kg/d for treated and control cows, respectively. After calving, average plasma concentration of β-hydroxybutyrate tended to be lower in cows injected with the vitamin supplement, 0.47 (SE=0.04) versus 0.55 (SE=0.03) for treated and control cows, respectively. The ovarian follicle ≥12 mm in diameter was collected by ovum pick-up after estrus synchronization. Recovered follicular fluid volumes were greater in the vitamin-treated group. A microarray platform was used to investigate the effect of treatment on gene expression of granulosa cells. Lower expression of genes involved in the cell cycle and higher expression of genes associated with granulosa cell differentiation before ovulation were observed. Selected candidate genes were analyzed by reverse transcription quantitative PCR. Although the effects of intramuscular injections of folic acid and vitamin B12 on lactational performance and metabolic status of animals were limited, ingenuity pathway analysis of gene expression in granulosa cells suggests a stimulation of cell differentiation in vitamin-treated cows, which may be the result of an increase in LH secretion.

Molecular characterization of a disintegrin and metalloprotease-17 (ADAM17) in granulosa cells of bovine preovulatory follicles

A disintegrin and metalloprotease-17 (ADAM17) is thought to play a key role in the release of soluble and active epiregulin (EREG) and amphiregulin (AREG) in ovarian follicles but its transcriptional regulation in follicular cells remains largely unknown. The objectives of this study were to characterize the regulation of ADAM17 transcripts in bovine follicles prior to ovulation and to investigate its transcriptional control in bovine granulosa cells. To study the regulation of ADAM17 transcripts, RT-PCR analyses were performed using total RNA extracted from bovine follicles collected between 0 h and 24 h post-hCG. Results showed that levels of ADAM17 mRNA were low prior to hCG (0 h), markedly and transiently increased 6-12 h post-hCG (P <0.05), and returned to low baseline levels at 24 h post-hCG in granulosa and theca interna cells of preovulatory follicles. To determine the transcriptional control of ADAM17 expression, primary cultures of bovine granulosa cells were used. Forskolin (FSK) stimulation induced a pattern of ADAM17 mRNA up-regulation in vitro similar to that observed by hCG in vivo. 5'-Deletion mutagenesis studies identified a minimal region of the bovine ADAM17 promoter containing basal and FSK-inducible activities, which were dependent on the presence of a consensus AP1 cis-element. Electrophoretic mobility shift assays revealed an interaction between AP1 and the trans-acting factor Fra2. Chromatin immunoprecipitation assays confirmed an endogenous interaction between Fra2 and the ADAM17 promoter in granulosa cell cultures. FSK-inducible ADAM17 promoter activity and mRNA expression were suppressed by PKA and ERK1/2 inhibitors but not by a p38MAPK inhibitor, pointing to the importance of PKA and ERK1/2 signaling pathways in the up-regulation of bovine ADAM17 mRNA. Collectively, these findings describe the gonadotropin/FSK-dependent up-regulation of ADAM17 transcripts in bovine preovulatory follicles and unravel for the first time some of the molecular mechanisms involved in ADAM17 gene expression in granulosa cells of a monoovulatory species.

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.

Oocyte maturation: gamete-somatic cells interactions, meiotic resumption, cytoskeletal dynamics and cytoplasmic reorganization

BACKGROUND

In a growth phase occurring during most of folliculogenesis, the oocyte produces and accumulates molecules and organelles that are fundamental for the development of the preimplantation embryo. At ovulation, growth is followed by a phase of maturation that, although confined within a short temporal window, encompasses modifications of the oocyte chromosome complement and rearrangements of cytoplasmic components that are crucial for the achievement of developmental competence. Cumulus cells (CCs) are central to the process of maturation, providing the oocyte with metabolic support and regulatory cues.

METHODS

PubMed was used to search the MEDLINE database for peer-reviewed original articles and reviews concerning oocyte maturation in mammals. Searches were performed adopting 'oocyte' and 'maturation' as main terms, in association with other keywords expressing concepts relevant to the subject. The most relevant publications, i.e. those concerning major phenomena occurring during oocyte maturation in established experimental models and the human species, were assessed and discussed critically to offer a comprehensive description of the process of oocyte maturation.

RESULTS

By applying the above described search criteria, 6165 publications were identified, of which 543 were review articles. The number of publications increased steadily from 1974 (n = 7) to 2013 (n = 293). In 2014, from January to the time of submission of this manuscript, 140 original manuscripts and reviews were published. The studies selected for this review extend previous knowledge and shed new and astounding knowledge on oocyte maturation. It has long been known that resumption of meiosis and progression to the metaphase II stage is intrinsic to oocyte maturation, but novel findings have revealed that specific chromatin configurations are indicative of a propensity of the oocyte to resume the meiotic process and acquire developmental competence. Recently, genetic integrity has also been characterized as a factor with important implications for oocyte maturation and quality. Changes occurring in the cytoplasmic compartment are equally fundamental. Microtubules, actin filaments and chromatin not only interact to finalize chromosome segregation, but also crucially co-operate to establish cell asymmetry. This allows polar body extrusion to be accomplished with minimal loss of cytoplasm. The cytoskeleton also orchestrates the rearrangement of organelles in preparation for fertilization. For example, during maturation the distribution of the endoplasmic reticulum undergoes major modifications guided by microtubules and microfilaments to make the oocyte more competent in the generation of intracellular Ca(2+) oscillations that are pivotal for triggering egg activation. Cumulus cells are inherent to the process of oocyte maturation, emitting regulatory signals via direct cell-to-cell contacts and paracrine factors. In addition to nurturing the oocyte with key metabolites, CCs regulate meiotic resumption and modulate the function of the oocyte cytoskeleton.

CONCLUSIONS

Although the importance of oocyte maturation for the achievement of female meiosis has long been recognized, until recently much less was known of the significance of this process in relation to other fundamental developmental events. Studies on chromatin dynamics and integrity have extended our understanding of female meiosis. Concomitantly, cytoskeletal and organelle changes and the ancillary role of CCs have been better appreciated. This is expected to inspire novel concepts and advances in assisted reproduction technologies, such as the development of novel in vitro maturation systems and the identification of biomarkers of oocyte quality.

Regulation of ovulatory genes in bovine granulosa cells: lessons from siRNA silencing of PTGS2

Prostaglandin endoperoxide synthase-2 (PTGS2), tumour necrosis factor-alpha-induced protein-6 (TNFAIP6), pentraxin-3 (PTX3), epidermal growth factor-like factors: amphiregulin (AREG) and epiregulin (EREG) are essential for successful ovulation. In this study, we compared the induction of these ovulatory genes in bovine granulosa cells (GCs) in vivo (after LH surge) and in vitro (forskolin (FRS) treatment). These genes were markedly stimulated in GCs isolated from cows 21 h after LH-surge. In isolated GCs, FRS induced a distinct temporal profile for each gene. Generally, there was a good agreement between the in vivo and in vitro inductions of these genes except for PTX3. Lack of PTX3 induction in isolated GCs culture suggests that other follicular compartments may mediate its induction by LH. Next, to study the role of PTGS2 and prostaglandins (PGs) in the cascade of ovulatory genes, PTGS2 was silenced with siRNA. PTGS2 siRNA caused a marked and specific knockdown of PTGS2 mRNA and PGE2 production (70% compared with scrambled siRNA) in bovine GCs. Importantly, PTGS2 silencing also reduced AREG, EREG and TNFAIP6 mRNA levels but not PTX3. Exogenous PGE2 increased AREG, EREG and TNFAIP6 mRNA levels, further confirming that these genes are prostanoid dependent. A successful and specific knockdown of PTGS2 was also achieved in endometrial cells (EndoCs) expressing PTGS2. Then, cholesterol-conjugated PTGS2 (chol-PTGS2) siRNA that facilitates cells' entry was investigated. In EndoCs, but not in GCs, chol-PTGS2 siRNA succeeded to reduce PTGS2 and PGE2 levels even without transfection reagent. PTGS2 knockdown is a promising tool to critically examine the functions of PTGS2 in the reproductive tract.

Expression and regulation of regulator of G-protein signaling protein-2 (RGS2) in equine and bovine follicles prior to ovulation: molecular characterization of RGS2 transactivation in bovine granulosa cells

The luteinizing hormone preovulatory surge stimulates several signal pathways essential for ovulation, and the regulator of G-protein signaling protein-2 (RGS2) is thought to be involved in this process. The objectives of this study were to characterize the regulation of RGS2 transcripts in equine and bovine follicles prior to ovulation and to determine its transcriptional control in bovine granulosa cells. To assess the regulation of equine RGS2 prior to ovulation, RT-PCR was performed using total RNA extracted from equine follicles collected at various times after human chorionic gonadotropin (hCG) injection. Results showed that RGS2 mRNA levels were very low at 0 h but markedly increased 12-39 h post-hCG (P < 0.05). In the bovine species, results revealed that RGS2 mRNA levels were low in small and dominant follicles and in ovulatory follicles obtained at 0 h, but markedly increased in ovulatory follicles 6-24 h post-hCG (P < 0.05). To study the molecular control of RGS2 expression, primary cultures of bovine granulosa cells were used. Stimulation with forskolin induced an up-regulation of RGS2 mRNA in vitro. Studies using 5'-deletion mutants identified a minimal region containing full-length basal and forskolin-inducible RGS2 promoter activities. Site-directed mutagenesis indicated that these activities were dependent on CRE and ETS1 cis-elements. Electrophoretic mobility shift assays confirmed the involvement of these elements and revealed their interactions with CREB1 and ETS1 proteins. Chromatin immunoprecipitation assays confirmed endogenous interactions of these proteins with the RGS2 promoter in granulosa cells. Forskolin-inducible RGS2 promoter activity and mRNA expression were markedly decreased by PKA and ERK1/2 inhibitors, and treatment with an antagonist of PGR (RU486) and inhibitors of PTGS2 (NS398) and EGFR (PD153035) blocked the forskolin-dependent RGS2 transcript expression, suggesting the importance of RGS2 in ovulation. Collectively, this study reports for the first time the gonadotropin-dependent up-regulation of RGS2 in equine and bovine preovulatory follicles and presents some of the regulatory controls involved in RGS2 gene expression in granulosa cells.

Transcriptome profiling of granulosa and theca cells during dominant follicle development in the horse

Several aspects of equine ovarian physiology are unique among domestic species. Moreover, follicular growth patterns are very similar between horses and humans. This study aimed to characterize, for the first time, global gene expression profiles associated with growth and preovulatory (PO) maturation of equine dominant follicles. Granulosa cells (GCs) and theca interna cells (TCs) were harvested from follicles (n = 5) at different stages of an ovulatory wave in mares corresponding to early dominance (ED; diameter ≥22 mm), late dominance (LD; ≥33 mm) and PO stage (34 h after administration of crude equine gonadotropins at LD stage), and separately analyzed on a horse gene expression microarray, followed by validation using quantitative PCR and immunoblotting/immunohistochemistry. Numbers of differentially expressed transcripts (DETs; ≥2-fold; P < 0.05) during the ED-LD and LD-PO transitions were 546 and 2419 in GCs and 5 and 582 in TCs. The most prominent change in GCs was the down-regulation of transcripts associated with cell division during both ED-LD and LD-PO. In addition, DET sets during LD-PO in GCs were enriched for genes involved in cell communication/adhesion, antioxidation/detoxification, immunity/inflammation, and cholesterol biosynthesis. In contrast, the largest change in TCs during the LD-PO transition was an up-regulation of genes involved in immune activation, with other DET sets mapping to GPCR/cAMP signaling, lipid/amino acid metabolism, and cell proliferation/survival and differentiation. In conclusion, distinct expression profiles were identified between growing and PO follicles and, particularly, between GCs and TCs within each stage. Several DETs were identified that have not been associated with follicle development in other species.

Nitric oxide synthase activity is critical for the preovulatory epidermal growth factor-like cascade induced by luteinizing hormone in bovine granulosa cells

In rabbits and rodents, nitric oxide (NO) is generally considered to be critical for ovulation. In monovulatory species, however, the importance of NO has not been determined, nor is it clear where in the preovulatory cascade NO may act. The objectives of this study were (1) to determine if nitric oxide synthase (NOS) enzymes are regulated by luteinizing hormone (LH) and (2) to determine if and where endogenous NO is critical for expression of genes essential for the ovulatory cascade in bovine granulosa cells in serum-free culture. Time- and dose-response experiments demonstrated that LH had a significant stimulatory effect on endothelial NOS (NOS3) mRNA abundance, but in a prostaglandin-dependent manner. NO production was stimulated by LH before a detectable increase in NOS3 mRNA levels was observed. Pretreatment of cells with the NOS inhibitor L-NAME blocked the effect of LH on the epidermal growth factor (EGF)-like ligands epiregulin and amphiregulin, as well as prostaglandin-endoperoxide synthase-2 mRNA abundance and protein levels. Similarly, EGF treatment increased mRNA encoding epiregulin, amphiregulin, and the early response gene EGR1, and this was inhibited by pretreatment with L-NAME. Interestingly, pretreatment with L-NAME had no effect on either ERK1/2 or AKT activation. Taken together, these results suggest that endogenous NOS activity is critical for the LH-induced ovulatory cascade in granulosa cells of a monotocous species and acts downstream of EGF receptor activation but upstream of the EGF-like ligands.

Expression and regulation of stromal cell-derived factor-1 (SDF1) and chemokine CXC motif receptor 4 (CXCR4) in equine and bovine preovulatory follicles

The interaction between stromal cell-derived factor-1 (SDF1) and chemokine CXC motif receptor 4 (CXCR4) has been implicated in leukocyte attraction, tissue remodeling and angiogenesis. The objective of the present study was to characterize the expression and regulation of SDF1 and CXCR4 in equine follicles during the ovulatory process. Equine preovulatory follicles were isolated during estrus 0-39h after hCG treatment. Follicle wall preparations (theca interna with attached granulosa cells) and isolated preparations of granulosa cells and theca interna were obtained, and total RNA extracts were analyzed by RT-PCR/Southern blot. Results showed that levels of CXCR4 transcripts were induced by hCG in follicles at 36 h post-hCG (P<0.05 vs 0 h), with the induction observed in both granulosa and theca cells. Immunoblotting and immunohistochemical analyses confirmed an increase in CXCR4 protein in follicles after hCG treatment. In contrast, levels of SDF1 transcripts were very low in granulosa cells but high in theca interna cells throughout most of the ovulatory period. Studies in vivo performed with bovine preovulatory follicles collected 0-24h post-hCG revealed a marked and significant up-regulation of CXCR4 transcripts after hCG (P<0.05), as observed in equine follicles. A similar pattern of CXCR4 mRNA up-regulation was observed in cultures of bovine granulosa cells treated with forskolin (P<0.05). This forskolin-dependent induction of CXCR4 mRNA was suppressed by co-treatment with inhibitors of PKA, ERK1/2 and EGFR, and by the progesterone receptor antagonist RU486 (P<0.05), underscoring the contribution of multiple signaling pathways. In complementary studies, treatment of bovine granulosa cells with EGF or the hypoxia mimetic cobalt chloride significantly increased CXCR4 transcript levels, whereas co-treatment with forskolin and a CXCR4 antagonist repressed the expression of several ovulation-related genes. Collectively, this study describes for the first time the gonadotropin-dependent up-regulation of CXCR4 transcript in ovarian follicles of large monoovulatory species, provides some insights into the regulation of CXCR4 gene expression in granulosa cells, and identifies a potential link between follicular SDF1/CXCR4 activation and the regulation of ovulation-related genes.

Expression, regulation, and promoter activation of vanin-2 (VNN2) in bovine follicles prior to ovulation

Vanin-2 (VNN2) is known to be involved in inflammation and leukocyte migration, but its regulation in follicles remains unknown. The objectives of this work were to study the regulation of VNN2 transcripts in bovine follicles prior to ovulation and to characterize the control of its expression in bovine granulosa cells. VNN2 expression was studied using total RNA extracted from granulosa cells of small follicles (2-4 mm in diameter), dominant follicles obtained on Day 5 of the estrous cycle, ovulatory follicles obtained 0-24 h after human chorionic gonadotropin (hCG), and corpora lutea on Day 5 of the cycle. The results from RT-PCR analyses showed that levels of VNN2 mRNA were high in ovulatory follicles 24 h post-hCG but low in the other tissues. In ovulatory follicles, levels of VNN2 mRNA were low at 0 h but significantly up-regulated 12-24 h post-hCG. To determine factors controlling VNN2 gene expression, established primary cultures of granulosa cells isolated from bovine dominant follicles were used. Treatment with forskolin elevated VNN2 mRNA expression as observed in vivo. Mutation studies identified the minimal region conferring basal and forskolin-stimulated VNN2 promoter activities, which were dependent on chicken ovalbumin upstream promoter-transcription factor (COUP-TF), GATA, and Ebox cis-elements. Electrophoretic mobility shift assays identified COUP-TF, GATA4, and upstream stimulating factor proteins as key factors interacting with these elements. Chromatin immunoprecipitation assays confirmed basal and forskolin-induced interactions between these proteins and the VNN2 promoter in bovine granulosa cell cultures. VNN2 promoter activity and mRNA expression were markedly stimulated by forskolin and overexpression of the catalytic subunit of PKA, but inhibited by PKA and ERK1/2 inhibitors. Collectively, the findings from this study describe for the first time the gonadotropin/forskolin-dependent up-regulation of VNN2 transcripts in granulosa cells of preovulatory follicles and provide insights into some of the molecular bases of VNN2 gene expression in follicular cells.

Molecular characterization and transcriptional regulation of a disintegrin and metalloproteinase with thrombospondin motif 1 (ADAMTS1) in bovine preovulatory follicles

The ovulatory process involves a complex remodeling of the extracellular matrix during which a desintegrin and metalloproteinase with thrombospondin motif 1 (ADAMTS1) is thought to play a key role, but its transcriptional regulation in bovine follicles remains largely unknown. The objectives of this study were to characterize the regulation of ADAMTS1 in bovine follicles before ovulation and to determine its transcriptional control in bovine granulosa cells. Regulation of ADAMTS1 was assessed using total RNA isolated from bovine preovulatory follicles obtained at various times after human chorionic gonadotropin treatment. Results from RT-PCR analyses showed that levels of ADAMTS1 mRNA were very low at 0 hours but increased at 6 to 24 hours after human chorionic gonadotropin in granulosa cells. To determine the regulatory mechanisms controlling ADAMTS1 gene expression in vitro, primary cultures of bovine granulosa cells were established, and treatment with forskolin up-regulated ADAMTS1 mRNA levels. Promoter activity assays, 5'-deletion, and site-directed mutagenesis identified a minimal region conferring full-length basal and forskolin-stimulated ADAMTS1 promoter activities, with both being dependent on Ebox cis-acting elements. EMSAs revealed upstream stimulating factor (USF) proteins as key trans-activating factors interacting with Ebox. Chromatin immunoprecipitation assays confirmed such interactions between USF and Ebox in vivo, and USF binding to Ebox elements was increased by forskolin treatment. ADAMTS1 promoter activity and mRNA expression were increased by forskolin and overexpression of the catalytic subunit of protein kinase A, but not by cotreatment with inhibitors of protein kinase A, ERK1/2, and epidermal growth factor receptor signaling pathways. Furthermore, treatment with a soluble epidermal growth factor induced ADAMTS1 mRNA expression in granulosa cells. Collectively, results from this study describe the gonadotropin/forskolin-dependent up-regulation of ADAMTS1 mRNA in granulosa cells of bovine preovulatory follicles in vivo and in vitro and identify for the first time some of the molecular mechanisms responsible for ADAMTS1 promoter activation in follicular cells of a large monoovulatory species.