ABCC4 is a PGE2 Efflux Transporter in The Ovarian Follicle: A Mediator of Ovulation and A Potential Non-Hormonal Contraceptive Target

The role of Prostaglandins (PGs) in the ovulatory process is known. However, the role of the ATP binding cassette subfamily C member 4 (ABCC4), transmembrane PG carrier protein, in ovulation remains unknown. We report herein that ABCC4 expression is significantly upregulated in preovulatory human granulosa cells (GCs). We found that PGE2 efflux in cultured human GCs is mediated by ABCC4 thus regulating its extracellular concentration. The ABCC4 inhibitor Probenecid demonstrated effective blocking of ovulation and affects key ovulatory genes in female mice in vivo. We postulate that the reduction of PGE2 efflux caused by the inhibition of ABCC4 activity in GCs decreases the extracellular concentration of PGE2 and its ovulatory effect. Treatment of female mice with low dose of Probenecid as well as with the PTGS inhibitor Indomethacin or Meloxicam synergistically blocks ovulation. These results support the hypothesis that ABCC4 has an important role in ovulation and might be a potential target for non-hormonal contraception, especially in combination with PGE2 synthesis inhibitors. These findings may fill the gap in understanding the role of ABCC4 in PGE2 signaling, enhance the understanding of ovulatory disorders, and facilitate the treatment and control of fertility.

Dissection of the Ovulatory Process Using ex vivo Approaches

Ovulation is a unique physiological phenomenon that is essential for sexual reproduction. It refers to the entire process of ovarian follicle responses to hormonal stimulation resulting in the release of mature fertilization-competent oocytes from the follicles and ovaries. Remarkably, ovulation in different species can be reproduced out-of-body with high fidelity. Moreover, most of the molecular mechanisms and signaling pathways engaged in this process have been delineated using in vitro ovulation models. Here, we provide an overview of the major molecular and cytological events of ovulation observed in frogs, primarily in the African clawed frog Xenopus laevis, using mainly ex vivo approaches, with the focus on meiotic oocyte maturation and follicle rupture. For the purpose of comparison and generalization, we also refer extensively to ovulation in other biological species, most notoriously, in mammals.

DUOX2 is a Generator of ROS in the Ovary and a Potential Mediator of Ovulation

Background: Ovulation is triggered by the preovulatory surge of the pituitary luteinizing hormone (LH). LH/hCG induction of reactive oxygen species (ROS) is required for successful ovulation. H2O2, one of ROS species, was shown to fully mimic the effect of LH/hCG in mice ovulation. However, the molecular process that generates H2O2 in the ovary during ovulation remains largely unknown. DUOX2, a member of the NOX/DUOX family of NADPH oxidase, is capable of generating H2O2. Results: Using global transcriptome RNAseq, we identified that DUOX2 is one of the transcripts that was markedly upregulated in granulosa cells during ovulation. Treatment with human chorionic gonadotropin (hCG), an ovulatory trigger, significantly increases the expression of DUOX2 mRNA and protein in human GCs both in vivo and in vitro. hCG-induced up-regulation of DUOX2 is mediated by the cAMP-PKA and the PKC pathway. A functional test reveals that DUOX2 chemical inhibitor, Diphenyleneiodonium (DPI), an NADPH oxidase inhibitor, decreased H2O2 levels in MGCs (Mural Granulosa Cells) treated with hCG. The inhibition of H2O2 by DPI suggests that DUOX2 activity is required for hCG-induced elevation of extracellular H2O2 in MGCs. In vivo treatment of mice with DPI significantly decreases the number of ovulated oocytes and markedly attenuates the expression of key ovulatory genes. These results support the putative role of DUOX2 in ovulation. Conclusions: DUOX2 is a ROS generator during the ovulatory process and is involved in the LH/hCG-induced signaling cascades leading to ovulation. Treatment with DUOX2 inhibitors may affect late folliculogenesis and ovulation and thus may serve for fertility control.

Comparative Analysis of Porcine Follicular Fluid Proteomes of Small and Large Ovarian Follicles

Ovarian follicular fluid is widely used for in vitro oocyte maturation, but its in-depth characterization to extract full beneficial effects remains unclear. Here, we performed both shotgun (nanoscale liquid chromatography coupled to tandem mass spectrometry or nanoLC-MS/MS) and gel-based (two dimension-differential in-gel electrophoresis or 2D-DIGE) proteomics, followed by functional bioinformatics to compare the proteomes of follicular fluids collected from small (<4 mm) and large (>6–12 mm) follicles of pig ovaries. A total of 2321 unique spots were detected with the 2D-DIGE across small and large follicles, while 2876 proteins with 88% successful annotations were detected with the shotgun approach. The shotgun and 2D-DIGE approaches revealed about 426 and 300 proteins that were respectively common across samples. Six proteins detected with both technical approaches were significantly differently expressed between small and large follicles. Pathways such as estrogen and PI3K-Akt signaling were significantly enriched in small follicles while the complement and coagulation cascades pathways were significantly represented in large follicles. Up-regulated proteins in small follicles were in favor of oocyte maturation, while those in large follicles were involved in the ovulatory process preparation. Few proteins with potential roles during sperm–oocyte interactions were especially detected in FF of large follicles and supporting the potential role of the ovarian FF on the intrafallopian sperm migration and interaction with the oocyte.

Kisspeptin induces LH release and ovulation in an induced ovulator†

Kisspeptin has been implicated in the ovulatory process of several species of spontaneous ovulators but in only one induced ovulator. In contrast, NGF in semen is the principal trigger of ovulation in other species of induced ovulators—camelids. We tested the hypotheses that kisspeptin induces luteinizing hormone (LH) secretion in llamas through a hypothalamic mechanism, and kisspeptin neurons are the target of NGF in its ovulation-inducing pathway. In Experiment 1, llamas were given either NGF, kisspeptin, or saline intravenously, and LH secretion and ovulation were compared among groups. All llamas treated with NGF (5/5) or kisspeptin (5/5) had an elevation of LH blood concentrations after treatment and ovulated, whereas none of the saline group did (0/5). In Experiment 2, llamas were either pretreated with a gonadotropin-releasing hormone (GnRH) receptor antagonist or saline and treated 2 h later with kisspeptin. Llamas pretreated with saline had elevated plasma LH concentrations and ovulated (6/6) whereas llamas pretreated with cetrorelix did not (0/6). In Experiment 3, we evaluated the hypothalamic kisspeptin-GnRH neuronal network by immunohistochemistry. Kisspeptin neurons were detected in the arcuate nucleus, the preoptic area, and the anterior hypothalamus, establishing synaptic contacts with GnRH neurons. We found no colocalization between kisspeptin and NGF receptors by double immunofluorescence. Functional and morphological findings support the concept that kisspeptin is a mediator of the LH secretory pathway in llamas; however, the role of kisspeptins in the NGF ovulation-inducing pathway in camelids remains unclear since NGF receptors were not detected in kisspeptin neurons in the hypothalamus.

Involvement of peroxiredoxin 2 in cumulus expansion and oocyte maturation in mice

Peroxiredoxin 2 (Prdx2), an antioxidant enzyme, is expressed in the ovary during the ovulatory process. The aim of the present study was to examine the physiological role of Prdx2 during ovulation using Prdx2-knockout mice and mouse cumulus–oocyte complex (COC) from WT mice. Two days of treatment of immature mice (21–23 days old) with equine chorionic gonadotrophin and followed by treatment with human chorionic gonadotrophin greatly impaired cumulus expansion and oocyte maturation in Prdx2-knockout but not wild-type mice. Treatment of COCs in culture with conoidin A (50µM), a 2-cys Prdx inhibitor, abolished epiregulin (EPI)-induced cumulus expansion. Conoidin A treatment also inhibited EPI-stimulated signal molecules, including signal transducer and activator of transcription-3, AKT and mitogen-activated protein kinase 1/2. Conoidin A treatment also reduced the gene expression of EPI-stimulated expansion-inducing factors (hyaluronan synthase 2 (Has2), pentraxin 3 (Ptx3), TNF-α induced protein 6 (Tnfaip6) and prostaglandin-endoperoxide synthase 2 (Ptgs2)) and oocyte-derived factors (growth differentiation factor 9 (Gdf9) and bone morphogenetic protein 15 (Bmp15)). Furthermore, conoidin A inhibited EPI-induced oocyte maturation and the activity of connexins 43 and 37. Together, these results demonstrate that Prdx2 plays a role in regulating cumulus expansion and oocyte maturation during the ovulatory process in mice, probably by modulating epidermal growth factor receptor signalling.

Estrous Cycle of Induced Ovulators: Lesson From The Camel — A Review

Camel, rabbit, cat, ferrets, minks, koala and meadow moles are induced ovulators requiring copulation to trigger the ovulatory process and the estrous cycle differs from that of other domestic animals. The estrous cycle in these animals composed of follicular recruitment, follicular growth, follicular maturity and follicular regression phase. These animals are variously reared as companion, fur-bearing and meat animals. Among these, the camel is the most valuable and classical induced ovulator which is rear not only for milk and meat, but as work animal and contributes effectively to the welfare of people in harsh and difficult environments. As a classical induced ovulatory, camelid has cycling receptivity with distinctive estrus but requires mating in order to ovulate. The other classes of induced ovulators like cats and ferrets require both the presence of male to achieve behavioral estrus and actual copulation to ovulate. The camel has good prospects of survival as a suitable livestock for projects of sustainable agriculture and animal production under harsh desert or arid conditions. However the reproductive nature of camels presents a huge challenge to camel husbandry. The natural constraints include the long period of attaining puberty, limited breeding season, difficulties in induced ovulation, long gestation period and inter-calving intervals. Efforts to improve the reproductive efficiency of the female camel are closely related to a better understanding of the folliculogenesis or follicular wave pattern. Many investigators might not be aware of the peculiar reproductive information available about this animal species. A working knowledge of ovarian function or estrous cycle will be of immense importance to the application of assisted reproductive technologies (ARTs) and enhancements of reproduction in camelids. This work presents the overview of estrous cycle in camel as a classical example of induced ovulators with the aim of providing current knowledge to the reader and to stimulate wider research interest in camel research and reproduction.

Chemokine Ligand 20: A Signal for Leukocyte Recruitment During Human Ovulation?

Ovulation is one of the cornerstones of female fertility. Disruption of the ovulatory process results in infertility, which affects approximately 10% of couples. Using a unique model in which the dominant follicle is collected across the periovulatory period in women, we have identified a leukocyte chemoattractant, chemokine ligand 20 (CCL20), in the human ovary. CCL20 mRNA is massively induced after an in vivo human chorionic gonadotropin (hCG) stimulus in granulosa (&gt;10 000-fold) and theca (&gt;4000-fold) cells collected during the early ovulatory (12–18 h) and late ovulatory (18–34 h) periods after hCG administration. Because the LH surge sets in motion an inflammatory reaction characterized by an influx of leukocytes and CCL20 is known to recruit leukocytes in other systems, the composition of ovarian leukocytes (CD45+) containing the CCL20 receptor CCR6 was determined immediately prior to ovulation. CD45+/CCR6+ cells were primarily natural killer cells (41%) along with B cells (12%), T cells (11%), neutrophils (10%), and monocytes (9%). Importantly, exogenous CCL20 stimulated ovarian leukocyte migration 59% within 90 minutes. Due to the difficulties in obtaining human follicles, an in vitro model was developed using granulosa-lutein cells to explore CCL20 regulation. CCL20 expression increased 40-fold within 6 hours after hCG, was regulated partially by the epithelial growth factor pathway, and was positively correlated with progesterone production. These results demonstrate that hCG dramatically increases CCL20 expression in the human ovary, that ovarian leukocytes contain the CCL20 receptor, and that CCL20 stimulates leukocyte migration. Our findings raise the prospect that CCL20 may aid in the final ovulatory events and contribute to fertility in women.