Cyclooxygenase-2-derived prostaglandin E(2) directs oocyte maturation by differentially influencing multiple signaling pathways.
ABSTRACT The process of oocyte maturation, which impacts ovulation and fertilization, is complex and requires an integration of the endocrine, paracrine, juxtacrine, and autocrine signaling pathways. This process involves an intimate interaction between the oocyte and encircling cumulus cells within a follicle, a unique venue for somatic and germ cell communication. Cumulus cell expansion and resumption of meiosis with germinal vesicle breakdown are major events in oocyte maturation. Cyclooxygenase-2 (COX-2)-derived prostaglandin E(2) (PGE(2)) is a known critical mediator of oocyte maturation, but the diverse function of this lipid mediator in oocyte maturation, ovulation, and fertilization has not been fully appreciated. We show here that gonadotropins in coordination with PGE(2) signaling via its cell surface G-protein-coupled EP2 and EP4 receptor subtypes direct cumulus cell expansion and survival and oocyte meiotic maturation by differentially impacting cAMP-dependent protein kinase, MAPK, NF-kappaB, and phosphatidylinositol 3-kinase/Akt pathways. This study is unique in the sense that it provides evidence for new site- and event-specific involvement of these signaling pathways under the influence of COX-2-derived PGE(2) during the critical stages of this somatic-germ cell interaction, an absolute requirement for oocyte maturation.
- [Show abstract] [Hide abstract]
ABSTRACT: Cyclooxygenase-2 (COX-2) inhibitors reduce prostaglandin synthesis and disrupt essential reproductive processes. Ultrasound studies in women demonstrated that oral COX-2 inhibitors can delay or prevent follicle collapse associated with ovulation. The goal of this study was to determine if oral administration of a COX-2 inhibitor can inhibit reproductive function with sufficient efficacy to prevent pregnancy in primates. The COX-2 inhibitor meloxicam (or vehicle) was administered orally to proven fertile female cynomolgus macaques using one emergency contraceptive model and three monthly contraceptive models. In the emergency contraceptive model, females were bred with a proven fertile male once 2±1 days before ovulation, returned to the females' home cage, and then received 5 days of meloxicam treatment. In the monthly contraceptive models, females were cocaged for breeding with a proven fertile male for a total of 5 days beginning 2±1 days before ovulation. Animals received meloxicam treatment (1) cycle days 5-22, or (2) every day, or (3) each day of the 5-day breeding period. Female were then assessed for pregnancy. The pregnancy rate with meloxicam administration using the emergency contraception model was 6.5%, significantly lower than the pregnancy rate of 33.3% when vehicle without meloxicam was administered. Pregnancy rates with the three monthly contraceptive models (75%-100%) were not consistent with preventing pregnancy. Oral COX-2 inhibitor administration can prevent pregnancy after a single instance of breeding in primates. While meloxicam may be ineffective for regular contraception, pharmacological inhibition of COX-2 may be an effective method of emergency contraception for women. COX-2 inhibitors can interfere with ovulation, but the contraceptive efficacy of drugs of this class has not been directly tested. This study, conducted in nonhuman primates, is the first to suggest that a COX-2 inhibitor may be effective as an emergency contraceptive.Contraception 09/2013; · 3.09 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Prostaglandin E2 produced within the ovarian follicle is necessary for ovulation. Prostaglandin E2 is recognized by four distinct G-protein coupled receptors. Among them, PTGER3 (also known as EP3) is unique in that mRNA splicing generates multiple isoforms. Each isoform has a distinct amino acid composition in the C-terminal region, which is involved in G-protein coupling. To determine if monkey EP3 isoforms couple to different G-proteins, each EP3 isoform was expressed in Chinese hamster ovary (CHO) cells, and intracellular signals were examined after stimulation with the EP3 agonist sulprostone. Stimulation of EP3 isoform 5 (EP3-5) reduced cyclic adenosine monophosphate (cAMP) in a pertussis toxin-sensitive manner, indicating involvement of Gαi. Stimulation of EP3-9 increased cAMP, which was reduced by the general G-protein inhibitor GDP-β-S, and also increased intracellular calcium, which was reduced by pertussis toxin and GDP-β-S. So, EP3-9 likely couples to both Gαs and a pertussis toxin-sensitive G-protein to regulate intracellular signals. Stimulation of EP3-14 increased cAMP, which was further increased by pertussis toxin, so EP3-14 likely regulates cAMP via multiple G-proteins. Granulosa cell expression of all EP3 isoforms increased in response to an ovulatory dose of hCG. Two EP3 isoforms were differentially expressed in functional subpopulations of granulosa cells. EP3-5 was low in granulosa cells at the follicle apex while EP3-9 was high in cumulus granulosa cells. Differential expression of EP3 isoforms may yield different intracellular responses to prostaglandin E2 in granulosa cell subpopulations, contributing to the different roles played by granulosa cell subpopulations in the process of ovulation.Reproduction 09/2013; · 3.56 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: The aim of this study was to determine the effects of trans-10, cis-12 conjugated linoleic acid (t10c12 CLA) supplementation on oocyte maturation and embryo development in pigs. Compared with the control, supplementation of 50 µM t10c12 CLA to in vitro maturation (IVM) medium significantly increased the proportion of oocytes at the metaphase II (MII) stage and subsequent parthenogenetic embryo development in terms of cleavage rate, blastocyst formation rate, and cell numbers in blastocysts. The t10c12 CLA-treated oocytes resumed meiotic maturation and progressed to the MII stage significantly faster than those of control. The expression of phosphorylated mitogen-activated protein kinase 3/1 (p-MAPK3/1) and cyclooxygenase-2 (COX2) in cumulus oocyte complexes (COCs) at 5, 10, and 22 h of IVM were significantly increased in the t10c12 CLA-treatment group. The level of p-MAPK3/1 in t10c12 CLA-treated MII oocytes was also higher (P <0.05) than that of control. Moreover, t10c12 CLA supplementation partially overcame the negative effects of U0126 on cumulus expansion and nuclear maturation, and completely recovered COX2 protein levels in the presence of U0126. Treatment of COCs with NS398 also significantly suppressed cumulus expansion and nuclear maturation, which was overcome by t10c12 CLA. Yet, this simulatory effect of t10c12 CLA was blocked in the presence of both U0126 and NS398. The t10c12 CLA treatment significantly reduced reactive oxygen species level and increased glutathione concentrations in MII oocyte. In conclusion, supplementation of t10c12 CLA during porcine oocyte maturation exerts its beneficial effects on nuclear and cytoplasmic maturation, which contributes to enhancing subsequent embryo development. Mol. Reprod. Dev. © 2013 Wiley Periodicals, Inc.Molecular Reproduction and Development 10/2013; · 2.81 Impact Factor