Regulation of gonadotropin-releasing hormone and its receptor gene expression by 17beta-estradiol in cultured human granulosa-luteal cells

Cellular localization and seasonal variation of GnRH and Bradykinin in the ovary of Heteropneustes fossilis (Bloch.) during its reproductive cycle

The present study investigates the distribution and dynamics of gonadotropin-releasing hormone I (GnRH I) and bradykinin in the air-breathing catfish, Heteropneustes fossilis, in relation to the reproductive cycle. Changes in bradykinin, bradykinin B2-receptor, and ovarian GnRH I regulation were demonstrated during the reproductive cycle. The localization of GnRH I, bradykinin, and their respective receptors in the ovaries was investigated by immunohistochemistry, while their levels were quantified by slot/western blot followed by densitometry. GnRH I and its receptor were mainly localized in the cytoplasm of oocytes during the early previtellogenic phase. However, as the follicles grew larger, immunoreactivity was observed in the granulosa and theca cells of the late previtellogenic follicles. The ovaries showed significantly higher expression of GnRH I protein and its receptor during the early to mid-previtellogenic phase, suggesting their involvement in follicular development. Bradykinin and bradykinin B2-receptor showed a distribution pattern similar to that of GnRH I and its receptor. This study further suggested the possibility that bradykinin regulates GnRH I synthesis in the ovary. Thus, we show that the catfish ovary has a GnRH-bradykinin system and plays a role in follicular development and oocyte maturation in H. fossilis.

Mode of action exploration of reproductive toxicity induced by bisphenol S using human normal ovarian epithelial cells through ERβ-MAPK signaling pathway

BACKGROUND

In the plastics production sector, bisphenol S (BPS) has gained popularity as a replacement for bisphenol A (BPA). However, the mode of action (MOA) of female reproductive toxicity caused by BPS remains unclear and the safety of BPS is controversial.

METHODS

Human normal ovarian epithelial cell line, IOSE80, were exposed to BPS at human-relevant levels for short-term exposure at 24 h or 48 h, or for long-term exposure at 28 days, either alone or together with five signaling pathway inhibitors: ICI 18,2780 (estrogen receptor [ER] antagonist), G15 (GPR30 specific inhibitor), U0126 (extracellular regulated protein kinase [ERK] 1/2 inhibitor), SP600125 (c-Jun N-terminal kinase [JNK] inhibitor) or SB203580 (p38 mitogen‑activated protein kinase [p38MAPK] inhibitor). MOA through ERβ-MAPK signaling pathway interruption was explored, and potential thresholds were estimated by the benchmark dose method.

RESULTS

For short-term exposure, BPS exposure at human-relevant levels elevated the ESR2 and MAPK8 mRNA levels, along with the percentage of the G0/G1 phase. For long-term exposure, BPS raised the MAPK1 and EGFR mRNA levels, the ERβ, p-ERK, and p-JNK protein levels, and the percentage of the G0/G1 phase, which was partly suppressed by U0126. The benchmark dose lower confidence limit (BMDL) of the percentage of the S phase after 24 h exposure was the lowest among all the BMDLs of a good fit, with BMDL5 of 9.55 μM.

CONCLUSIONS

The MOA of female reproductive toxicity caused by BPS at human-relevant levels might involve: molecular initiating event (MIE)-BPS binding to ERβ receptor, key event (KE)1-the interrupted expression of GnRH, KE2-the activation of JNK (for short-term exposure) and ERK pathway (for long-term exposure), KE3-cell cycle arrest (the increased percentage of the G0/G1 phase), and KE4-interruption of cell proliferation (only for short-term exposure). The BMDL of the percentage of the S phase after 24 h exposure was the lowest among all the BMDLs of a good fit, with BMDL5 of 9.55 μM.

Interplay between nitric oxide and gonadotrophin-releasing hormone in the neuromodulation of the corpus luteum during late pregnancy in the rat

BACKGROUND

Nitric oxide and GnRH are biological factors that participate in the regulation of reproductive functions. To our knowledge, there are no studies that link NO and GnRH in the sympathetic ganglia. Thus, the aim of the present work was to investigate the influence of NO on GnRH release from the coeliac ganglion and its effect on luteal regression at the end of pregnancy in the rat.

METHODS

The ex vivo system composed by the coeliac ganglion, the superior ovarian nerve, and the ovary of rats on day 21 of pregnancy was incubated for 180 min with the addition, into the ganglionic compartment, of L-NG-nitro arginine methyl ester (L-NAME), a non-selective NO synthase inhibitor. The control group consisted in untreated organ systems.

RESULTS

The addition of L-NAME in the coeliac ganglion compartment decreased NO as well as GnRH release from the coeliac ganglion. In the ovarian compartment, and with respect to the control group, we observed a reduced release of GnRH, NO, and noradrenaline, but an increased production of progesterone, estradiol, and expression of their limiting biosynthetic enzymes, 3β-HSD and P450 aromatase, respectively. The inhibition of NO production by L-NAME in the coeliac ganglion compartment also reduced luteal apoptosis, lipid peroxidation, and nitrotyrosine, whereas it increased the total antioxidant capacity within the corpora lutea.

CONCLUSION

Collectively, the results indicate that NO production by the coeliac ganglion modulates the physiology of the ovary and luteal regression during late pregnancy in rats.

Post-Transcriptional Regulation of Gnrhr: A Checkpoint for Metabolic Control of Female Reproduction

The proper expression of gonadotropin-releasing hormone receptors (GnRHRs) by pituitary gonadotropes is critical for maintaining maximum reproductive capacity. GnRH receptor expression must be tightly regulated in order to maintain the normal pattern of expression through the estrous cycle in rodents, which is believed to be important for interpreting the finely tuned pulses of GnRH from the hypothalamus. Much work has shown that Gnrhr expression is heavily regulated at the level of transcription. However, researchers have also discovered that Gnrhr is regulated post-transcriptionally. This review will discuss how RNA-binding proteins and microRNAs may play critical roles in the regulation of GnRHR expression. We will also discuss how these post-transcriptional regulators may themselves be affected by metabolic cues, specifically with regards to the adipokine leptin. All together, we present evidence that Gnrhr is regulated post-transcriptionally, and that this concept must be further explored in order to fully understand the complex nature of this receptor.

Genome-wide identification of estrogen receptor binding sites reveals novel estrogen-responsive pathways in adult male germ cells

Spermatogenesis occurs in the seminiferous epithelium that shows the presence of estrogen receptors alpha (ERα) and beta (ERβ), both of which regulate gene transcription by binding to the DNA. Estrogen responsive phases of spermatogenesis are well documented; however, the genes regulated remain inexplicit. To study the regulation of genes by estrogen in male germ cells, we performed chromatin immunoprecipitation (ChIP) sequencing for ERα and ERβ under normal physiological conditions. A total of 27 221 DNA binding regions were enriched with ERα and 20 926 binding sites with ERβ. Majority of the peaks were present in the intronic regions and located 20 kb upstream or downstream from the transcription start site (TSS). Pathway analysis of the genes enriched by ChIP-Seq showed involvement in several biological pathways. Genes involved in pathways whose role in spermatogenesis is unexplored were validated; these included prolactin, GnRH, and oxytocin signaling. All the selected genes showed the presence of estrogen response elements (EREs) in their binding region and were also found to be significantly enriched by ChIP-qPCR. Functional validation using seminiferous tubule culture after treatment with estrogen receptor subtype-specific agonist and antagonist confirmed the regulation of these genes by estrogen through its receptors. The genes involved in these pathways were also found to be regulated by the respective receptor subtypes at the testicular level in our in vivo estrogen receptor agonist rat models. Our study provides a genome-wide map of ERα and ERβ binding sites and identifies the genes regulated by them in the male germ cells under normal physiological conditions.

Gonadotropin regulation by pulsatile GnRH: Signaling and gene expression

The precise orchestration of hormonal regulation at all levels of the hypothalamic-pituitary-gonadal axis is essential for normal reproductive function and fertility. The pulsatile secretion of hypothalamic gonadotropin-releasing hormone (GnRH) stimulates the synthesis and release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) by pituitary gonadotropes. GnRH acts by binding to its high affinity seven-transmembrane receptor (GnRHR) on the cell surface of anterior pituitary gonadotropes. Different signaling cascades and transcriptional mechanisms are activated, depending on the variation in GnRH pulse frequency, to stimulate the synthesis and release of FSH and LH. While changes in GnRH pulse frequency may explain some of the differential regulation of FSH and LH, other factors, such as activin, inhibin and sex steroids, also contribute to gonadotropin production. In this review, we focus on the transcriptional regulation of the gonadotropin subunit genes and the signaling pathways activated by pulsatile GnRH.

Estrus cyclicity of spinogenesis: underlying mechanisms

Hippocampal spine density varies with the estrus cycle. The cyclic change in estradiol levels in serum was hypothesized to underlie this phenomenon, since treatment of ovariectomized animals with estradiol induced an increase in spine density in hippocampal dendrites of rats, as compared to ovariectomized controls. In contrast, application of estradiol to hippocampal slice cultures did not promote spinogenesis. In addressing this discrepancy, we found that hippocampal neurons themselves are capable of synthesizing estradiol de novo. Estradiol synthesis can be suppressed by aromatase inhibitors and by knock-down of Steroid Acute Regulatory Protein (StAR) and enhanced by substrates of steroidogenesis. Expression of estrogen receptors (ERs) and synaptic proteins, synaptogenesis, and long-term potentiation (LTP) correlated positively with aromatase activity in hippocampal cultures without any difference between genders. All effects due to inhibition of aromatase activity were rescued by application of estradiol to the cultures. Most importantly, gonadotropin-releasing hormone (GnRH) increased estradiol synthesis dose-dependently via an aromatase-mediated mechanism and consistently increased spine synapse density and spinophilin expression. As a consequence, our data suggest that cyclic fluctuations in spine synapse density result from pulsative release of GnRH from the hypothalamus and its effect on hippocampal estradiol synthesis, rather than from varying levels of serum estradiol. This hypothesis is further supported by higher GnRH receptor (GnRH-R) density in the hippocampus than in the cortex and hypothalamus and the specificity of estrus cyclicity of spinogenesis in the hippocampus, as compared to the cortex.

Changes in GnRH I, bradykinin and their receptors and GnIH in the ovary of Calotes versicolor during reproductive cycle

The aim of this study was to investigate changes in the abundance of gonadotrophin releasing hormone I (GnRH I) and GnRH I receptor in the ovary of Calotes versicolor during the reproductive cycle and correlate them with the changes in gonadotrophin inhibitory hormone (GnIH), bradykinin and bradykinin B(2) receptor in order to understand their interaction during ovarian cycle. GnRH I, bradykinin and their receptors and GnIH, were localized immunohistochemically in the ovary. Relative intensity of these peptides was estimated from the contralateral ovary using slot/Western blot followed by densitometry. The immunostaining of GnRH I, bradykinin and their receptors and GnIH were localized in the granulosa cells of previtellogenic follicles and stroma cells, whereas in the peripheral part of the cytoplasm in oocytes of vitellogenic and ovulatory follicles. The GnRH I immunostaining was relatively higher in inactive phase, but was low during active preovulatory phase suggesting inverse correlation with circulating estradiol level. The study showed a positive correlation between the expression pattern of GnRH I and GnIH, but showed a negative correlation between GnIH with GnRH I receptor in the ovary. This study further suggests a possibility for bradykinin regulating GnRH I synthesis in the ovary. An increase in the immunostaining of both GnRH I and GnIH in the oocyte prior to ovulation suggests their involvement in the oocyte maturation. It is thus concluded that the ovary of C. versicolor possesses GnRH I-GnIH-bradykinin system and interaction between these neuropeptides may be involved in the regulation of follicular development and oocyte maturation.

Epigenetic repression of the estrogen-regulated Homeobox B13 gene in breast cancer

Several studies have reported that a high expression ratio of HOXB13 to IL17BR predicts tumor recurrence in node-negative, estrogen receptor (ER) alpha-positive breast cancer patients treated with tamoxifen. The molecular mechanisms underlying this dysregulation of gene expression remain to be explored. Our epigenetic analysis has found that increased promoter methylation of one of these genes, HOXB13, correlate with the decreased expression of its transcript in breast cancer cell lines (P < 0.005). Transcriptional silencing of this gene can be reversed by a demethylation treatment. HOXB13 is suppressed by the activation of estrogen signaling in ERalpha-positive breast cancer cells. However, treatment with 4-hydroxytamoxifen (4-OHT), an antiestrogen, abrogates the ERalpha-mediated suppression in cancer cells. The notion that this transcriptional induction of HOXB13 occurs in vitro with simultaneous exposure to both estrogen and 4-OHT may provide a biological explanation for its aberrant expression in many node-negative patients undergoing tamoxifen therapy. Interestingly, promoter hypermethylation of HOXB13 is more frequently observed in ERalpha-positive patients with increased lymph node metastasis (P = 0.031) and large tumor sizes (>5 cm) (P = 0.008). In addition, this aberrant epigenetic event is associated with shorter disease-free survival (P = 0.029) in cancer patients. These results suggest that hypermethylation of HOXB13 is a late event of breast tumorigenesis and a poor prognostic indicator of node-positive cancer patients.

Gonadotropin-releasing hormone regulates spine density via its regulatory role in hippocampal estrogen synthesis

Spine density in the hippocampus changes during the estrus cycle and is dependent on the activity of local aromatase, the final enzyme in estrogen synthesis. In view of the abundant gonadotropin-releasing hormone receptor (GnRH-R) messenger RNA expression in the hippocampus and the direct effect of GnRH on estradiol (E2) synthesis in gonadal cells, we asked whether GnRH serves as a regulator of hippocampal E2 synthesis. In hippocampal cultures, E2 synthesis, spine synapse density, and immunoreactivity of spinophilin, a reliable spine marker, are consistently up-regulated in a dose-dependent manner at low doses of GnRH but decrease at higher doses. GnRH is ineffective in the presence of GnRH antagonists or aromatase inhibitors. Conversely, GnRH-R expression increases after inhibition of hippocampal aromatase. As we found estrus cyclicity of spine density in the hippocampus but not in the neocortex and GnRH-R expression to be fivefold higher in the hippocampus compared with the neocortex, our data strongly suggest that estrus cycle–dependent synaptogenesis in the female hippocampus results from cyclic release of GnRH.

Triggering ovulation with gonadotropin-releasing hormone agonists does not compromise embryo implantation rates

OBJECTIVE

To evaluate the implant capacity of embryos derived from oocytes matured with a bolus of GnRH agonist.

DESIGN

Donors were randomly assigned to a protocol using either GnRH agonist or recombinant (r) hCG to trigger ovulation. Analysis of variance, Student t test, and Fisher exact test were used where appropriate.

SETTING

Private clinical setting.

PATIENT(S)

Young voluntary donors receiving GnRH agonist (n = 30) or rhCG (n = 30). Eighty-nine patients received oocytes.

INTERVENTION(S)

Controlled ovarian stimulation was carried out with GnRH antagonist and FSH/LH in a step-down protocol. Donors received a single bolus of GnRH agonist (0.2 mg) or rhCG (250 microg). The endometrial tissue of recipient patients was prepared with oral E(2) and P.

MAIN OUTCOME MEASURE(S)

Pregnancy and implantation rates and ovarian hyperstimulation syndrome (OHSS) in an IVF donor program.

RESULT(S)

No significant differences in the number of retrieved oocytes (327 vs. 288), MII oocytes (70% vs. 76%), fertilization (80% vs. 65%,), pregnancy/transfer (55% vs. 59%), and implantation rates (29% vs. 32%) were found between recipients whose embryos originated from donors in whom final oocyte maturation was triggered with GnRH agonist and those whose donors received hCG. Significant differences in luteal phase length (4.16 + 0.70 days vs. 13.63 + 2.12 days) and in OHSS (0/30 vs. 5/30) were seen between donors ovulated with the agonist and the donors in whom ovulation was triggered with hCG.

CONCLUSION(S)

In controlled ovarian stimulation IVF donor cycles, GnRH agonists trigger ovulation and induce luteolysis but do not compromise embryo implantation capacity.

Molecular biology of gonadotropin-releasing hormone (GnRH)-I, GnRH-II, and their receptors in humans

In human beings, two forms of GnRH, termed GnRH-I and GnRH-II, encoded by separate genes have been identified. Although these hormones share comparable cDNA and genomic structures, their tissue distribution and regulation of gene expression are significantly dissimilar. The actions of GnRH are mediated by the GnRH receptor, which belongs to a member of the rhodopsin-like G protein-coupled receptor superfamily. However, to date, only one conventional GnRH receptor subtype (type I GnRH receptor) uniquely lacking a carboxyl-terminal tail has been found in the human body. Studies on the transcriptional regulation of the human GnRH receptor gene have indicated that tissue-specific gene expression is mediated by differential promoter usage in various cell types. Functionally, there is growing evidence showing that both GnRH-I and GnRH-II are potentially important autocrine and/or paracrine regulators in some extrapituitary compartments. Recent cloning of a second GnRH receptor subtype (type II GnRH receptor) in nonhuman primates revealed that it is structurally and functionally distinct from the mammalian type I receptor. However, the human type II receptor gene homolog carries a frameshift and a premature stop codon, suggesting that a full-length type II receptor does not exist in humans.

Differential role of progesterone receptor isoforms in the transcriptional regulation of human gonadotropin-releasing hormone I (GnRH I) receptor, GnRH I, and GnRH II

Hypothalamic GnRH is a decapeptide that plays a pivotal role in mammalian reproduction by stimulating the synthesis and secretion of gonadotropins via binding to the GnRH receptor on the pituitary gonadotropins. It is hypothesized that sex steroids may regulate GnRH I (a classical form of GnRH), GnRH II (a second form of GnRH), and GnRH I receptor (GnRHRI) at the transcriptional level in target tissues. Thus, in the present study a role for progesterone (P4) in the regulation of GnRH I, GnRH II, and GnRHRI was investigated using a human neuronal medulloblastoma cell line (TE671) as an in vitro model. The cells were transfected with human GnRHRI promoter-luciferase constructs, and promoter activities were analyzed after P4 treatment by luciferase and beta-galactosidase assay. The mRNA levels of GnRH I and GnRH II were analyzed by RT-PCR. Treatment of TE671 cells with P4 resulted in a decrease in GnRHRI promoter activity compared with the control level in a dose- and time-dependent manner. Cotreatment of these cells with RU486, an antagonist of P4, reversed P4-induced inhibition of GnRHRI promoter activity, suggesting that the P4 effect is mediated by P4 receptor (PR). In the cells transfected with a full-length of PR A- or PR B-expressing vector, overexpression of PR A increased the sensitivity toward P4 in an inhibition of GnRHRI promoter, whereas PR B increased transcriptional activity of GnRHRI promoter in the presence of P4. However, PR B itself did not act as a transcriptional activator of GnRHRI promoter. Because TE671 cells have been recently demonstrated to express and synthesize two forms of GnRHs, we also investigated the regulation of GnRH mRNAs by P4. In the present study, P4 increased GnRH I mRNA levels in a time- and dose-dependent manner. This stimulatory effect of P4 in the regulation of GnRH I mRNAs was significantly attenuated by RU486, whereas no significant difference in the expression level of GnRH II was observed with P4 or RU496. Interestingly, although the expression level of PR B was low compared with that of PR A, P4 action on the GnRH I gene was mediated by PR B. In conclusion, these results indicate that P4 is a potent regulator of GnRHRI at the transcriptional level as well as GnRH I mRNA. This distinct effect of P4 on the GnRH system may be derived from different pathways through PR A or PR B.

Gonadotropin-releasing hormone (GnRH) antagonists promote proapoptotic signaling in peripheral reproductive tumor cells by activating a Galphai-coupling state of the type I GnRH receptor

Gonadotropin-releasing hormone (GnRH) receptor agonists are extensively used in the treatment of sex hormone-dependent cancers via the desensitization of pituitary gonadotropes and consequent decrease in steroid sex hormone secretion. However, evidence now points to a direct inhibitory effect of GnRH analogs on cancer cells. These effects appear to be mediated via the Galpha(i)-type G protein, in contrast to the predominant Galpha(q) coupling in gonadotropes. Unlike Galpha(q) coupling, Galpha(i) coupling of the GnRH receptor can be activated by both agonists and antagonists. This unusual pharmacology suggested that the receptor involved in the cancer cells may not be the classical gonadotrope type I GnRH receptor. However, we have previously shown that a functional type II GnRH receptor is not present in man. In the present study, we show that GnRH agonists and selective GnRH antagonists exert potent antiproliferative effects on JEG-3 choriocarcinoma, benign prostate hyperplasia (BPH-1), and HEK293 cells stably expressing the type I GnRH receptor. This antiproliferative action occurs through a Galpha(i)-mediated activation of stress-activated protein kinase pathways, resulting in caspase activation and transmembrane transfer of phosphatidlyserine to the outer membrane envelope. Structurally related antagonistic GnRH analogs displayed divergent antiproliferative efficacies but demonstrated equal efficacies in inhibiting GnRH-induced Galpha(q)-based signaling. Therefore the ability of GnRH receptor antagonists to exert an antiproliferative effect on reproductive tumors may be dependent on ligand-selective activation of the Galpha(i)-coupled form of the type I GnRH receptor.

An activator protein 1-like motif mediates 17beta-estradiol repression of gonadotropin-releasing hormone receptor promoter via an estrogen receptor alpha-dependent mechanism in ovarian and breast cancer cells

Although it is recognized that estrogen is one of the most important regulators of GnRH receptor (GnRHR) gene expression, the mechanism underlying the regulation at the transcriptional level is unknown. In the present study, we demonstrated that 17beta-estradiol (E2) repressed human GnRHR promoter via an activator protein 1-like motif and estrogen receptor-alpha, of which the DNA-binding domain and the ligand-binding domain were indispensable for the repression. Interestingly, the same cis-acting motif was also found to be important for both the basal activity and phorbol 12-myristate 13-acetate responsiveness of the GnRHR promoter. EMSAs indicated that multiple transcription factors including c-Jun and c-Fos bound to the activator protein 1-like site and that their DNA binding activity was not significantly affected by E2 treatment. In addition, we demonstrated that the E2 repression could be antagonized by phorbol 12-myristate 13-acetate, which stimulated c-Jun phosphorylation on serine 63, a process that is a prerequisite for recruitment of the transcriptional coactivator cAMP response element binding protein (CREB)-binding protein (CBP). Concomitantly, we found that overexpression of CBP could reverse the suppression in a dose-dependent manner. Taken together, our data indicate that E2-activated estrogen receptor-alpha represses human GnRHR gene transcription via an indirect mechanism involving CBP and possibly other transcriptional regulators.

Gonadotropin and steroid regulation of matrix metalloproteinases and their endogenous tissue inhibitors in the developed corpus luteum of the rhesus monkey during the menstrual cycle

The factors regulating the dynamic expression of matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) in the primate corpus luteum (CL) during the menstrual cycle are unknown. We hypothesized that LH or progesterone (P) regulate interstitial-collagenase (MMP-1), the gelatinases (MMP-2 and -9), TIMP-1, and TIMP-2 in the CL. Hormone ablation/replacement was performed in rhesus monkeys on Days 9-11 of the luteal phase in five treatment groups (n = 4/group): control (no treatment), antide (GnRH antagonist), antide + LH; antide + LH + trilostane (TRL; 3beta-hydroxysteroid dehydrogenase inhibitor), and antide + LH + TRL + R5020 (nonmetabolizable progestin). On Day 12, the CL was removed and the RNA and protein isolated for real-time polymerase chain reaction and immunoassays, respectively. The MMP-1 mRNA increased 20-fold with antide, whereas LH replacement maintained MMP-1 mRNA at control levels. Likewise, TRL increased MMP-1 mRNA 54-fold, and R5020 prevented this effect. Immunodetectable MMP-1 protein also increased with antide or TRL; these increases were abated with LH or R5020. Gelatinase mRNA and/or protein levels increased with antide (e.g., 3-fold, MMP-2 mRNA), and LH replacement reduced protein levels (e.g., 11-fold, MMP-2). The TRL increased MMP-9, but not MMP-2, expression; however, R5020 replacement had no effect on mRNA or protein levels. The LH treatment increased TIMP-1 and -2 mRNA and TIMP-1 protein expression compared to controls and antide groups, whereas R5020 enhanced only immunodetectable TIMP-1. These data strongly suggest that LH suppresses MMP-1 in the primate CL via P and that it also suppresses gelatinases, either at the mRNA (MMP-2) or protein (MMP-2 and -9) levels, perhaps in part via steroids, including P. In contrast, LH promotes TIMP expression, perhaps via steroids, including P.

Action of gonadotropin-releasing hormone II on the baboon ovary

The content, binding affinity, and bioactivity of chicken II GnRH (GnRH II) and a stable analogue of GnRH II (GnRH II analogue) in the baboon ovary were studied. Although mammalian GnRH is rapidly degraded by baboon ovarian extracts, we designed a GnRH II analogue that is stable to ovarian enzymatic degradation. This analogue binds to the ovarian membranes with high affinity (41 +/- 3 nM), having 20-fold the affinity of a potent mammalian GnRH analogue. The bioactivity of GnRH II and this GnRH II analogue on the regulation of ovarian progesterone release was compared with that for a potent mammalian GnRH analogue using a baboon granulosa cell culture system. Both GnRH II and GnRH II analogue produced significant inhibition of progesterone release from the granulosa cells (P < 0.03 and P < 0.005, respectively), with a greater reduction observed using the GnRH II analogue. After 24 h in culture, this GnRH II analogue produced a 59% +/- 5% inhibition of progesterone with a concentration as low as 1 nM. Maximal inhibition of 75% +/- 1% was attained with 10 nM GnRH II analogue. The endogenous GnRH II content in the baboon ovary was 5-14 pmoles/g protein. The release of endogenous GnRH II from granulosa cells was observed throughout the 48 h in culture. These studies demonstrated the presence of high enzymatic activity for the degradation of mammalian GnRH in the ovary, whereas this GnRH II analogue was stable. High-affinity binding sites for this GnRH II analogue were also found. GnRH II and this GnRH II analogue can regulate progesterone production from baboon granulosa cells, suggesting that GnRH II is a potent regulator of ovarian function.

Evolutionary aspects of cellular communication in the vertebrate hypothalamo-hypophysio-gonadal axis

This review emphasizes the comparative approach for developing insight into knowledge related to cellular communications occurring in the hypothalamus-pituitary-gonadal axis. Indeed, research on adaptive phenomena leads to evolutionary tracks. Thus, going through recent results, we suggest that pheromonal communication precedes local communication which, in turn, precedes communication via the blood stream. Furthermore, the use of different routes of communication by a certain mediator leads to a conceptual change related to what hormones are. Nevertheless, endocrine communication should leave out of consideration the source (glandular or not) of mediator. Finally, we point out that the use of lower vertebrate animal models is fundamental to understanding general physiological mechanisms. In fact, different anatomical organization permits access to tissues not readily approachable in mammals.

Differential regulation of gonadotropin-releasing hormone (GnRH)I and GnRHII messenger ribonucleic acid by gonadal steroids in human granulosa luteal cells

In humans, reproduction was generally believed to be controlled by only one form of GnRH (called mammalian GnRH or GnRHI). However, recently, a second form of GnRH, analogous to chicken GnRHII, was discovered in several tissues, including the human ovary. The regulation and function of GnRHI in the hypothalamus has been well studied. However, the function and regulation of GnRHI, and particularly GnRHII in the ovary, is less well understood. Because gonadal sex steroids are one of the main regulators of reproduction, we investigated, in the present study, the regulation of GnRHI and GnRHII mRNA expression by 17beta-estradiol (E2) and RU486 (a progesterone antagonist) in human granulosa luteal cells (hGLCs). The levels of the mRNA transcripts encoding the two GnRH forms were examined using semiquantitative RT-PCR followed by Southern blot analysis. With time in culture, GnRHI and GnRHII mRNA levels significantly increased, by 120% and 210%, at d 8 and d 1, respectively. The levels remained elevated until the termination of these experiments at d 10. A 24-h treatment of hGLCs with E2 (10(-9) to 10(-7) M) resulted in a dose-dependent decrease and increase in mRNA expression of GnRHI and GnRHII, respectively. E2 (10(-9) M) significantly decreased GnRHI mRNA levels (by 55%) and increased GnRHII mRNA levels (by 294%). Time-course studies demonstrated that E2 (10(-9) M) significantly decreased GnRHI mRNA levels in a time-dependent manner, with maximal inhibition of 77% at 48 h. In contrast, GnRHII mRNA levels significantly increased in a time-dependent fashion, reaching a maximum level of 280% at 24 h. Cotreatment of hGLCs with E2 and tamoxifen (an E2 antagonist) reversed the inhibitory and stimulatory effects of E2 on the mRNA expression of GnRHI and GnRHII, respectively. Time- and dose-dependent treatment with RU486 did not affect GnRHI mRNA levels in hGLCs. In contrast, RU486 treatment significantly increased GnRHII mRNA levels in hGLCs in a time- and dose-dependent fashion, with a maximum increase being observed at 24 h (with 10(-5)M RU486). In summary, the present study demonstrated that the expression of GnRHI and GnRHII at the transcriptional level is differently regulated by E2 and P4 in hGLCs.

Characterization of a new upstream GnRH receptor promoter in human ovarian granulosa-luteal cells

GnRH has been implicated as an important local autocrine and paracrine factor in regulating ovarian function. However, to date, the transcriptional regulation of GnRH receptor (GnRHR) gene in human ovary remains poorly understood. Here we report the characterization of a new upstream promoter for the GnRHR gene in human granulosa-luteal cells. Using progressive deletion analysis, a region between nucleotide -1300 and -1018 (relative to the translation start site) was shown to exhibit the highest promoter activities in two immortalized human granulosa-luteal cell lines, SVOG-4o and SVOG-4m. Two putative CCAAT/enhancer binding protein (C/EBP) motifs and one GATA motif were identified within this region. Mutational studies showed that these three motifs cooperated synergistically to regulate GnRHR gene transcription in the granulosa cells but not in other cell types including human ovarian carcinoma OVCAR-3, human embryonic kidney-293 (HEK-293) and mouse pituitary gonadotrope-derived alphaT3-1 cells. Surprisingly, by competitive EMSAs, we found that an Oct-1 consensus sequence was able to inhibit protein complex formation with the distal C/EBP motif, suggesting a possible cross-talk between the Oct-1 transcription factor and this C/EBP motif. Taken together, our results strongly indicate a role of the C/EBP and GATA motifs in regulating GnRHR gene transcription in human granulosa-luteal cells and further suggest that tissue-specific expression of human GnRHR gene is mediated by differential promoter usage.

Expression of prepro-GnRH and GnRH receptor messengers in rainbow trout ovary depends on the stage of ovarian follicular development

Gonadotropin-Releasing Hormones (GnRHs) are decapeptides well known to regulate the reproductive cycle. They are expressed not only in the brain, but also in other tissues including the gonads. It is believed that they may be involved in the endocrine and paracrine regulation of the reproductive cycle. To date, two forms of GnRH have been identified in salmonids: salmon (sGnRH) and chicken II (cGnRH-II). In the present study, the temporal expression of sGnRH-1, sGnRH-2, cGnRH-II, and rtGnRH receptor genes was studied in rainbow trout ovary during the reproductive cycle according to the stages of follicular development. Using RT-PCR coupled with Southern-blot hybridization, sGnRH-1, sGnRH-2, cGnRH-II, and rtGnRH-R transcripts were detected in morphologically nondifferentiated ovaries as early as 55-65 days post-fertilization and throughout all stages of vitellogenesis. Using Northern blot analysis, cGnRH-II mRNA was detected only in immature previtellogenic ovary, whereas sGnRH mRNA was detected also during early and mid-exogenous vitellogenesis. No sGnRH mRNA was detected at the end of vitellogenesis. In maturing pre-ovulated ovary, sGnRH transiently reappeared before germinal vesicle breakdown (GVBD) and decreased thereafter. A few days after ovulation, a strong sGnRH mRNA expression was found in ovarian tissue as the eggs were kept in the body cavity of females. However, in females stripped just after ovulation, sGnRH mRNA levels remained low in ovary during several weeks. Fully spliced sGnRH-1 and sGnRH-2 messengers were mostly expressed during the reproductive cycle; however different sGnRH-1 and sGnRH-2 splicing variants containing intronic sequences were also detected. Some of these messengers may encode prepro-GnRH precursors with truncated GnRH-associated peptides. The stage-dependent expression and different cell localization of sGnRH, cGnRH-II, and rtGnRH-R transcripts suggest that GnRH-like peptides may have different roles in the paracrine regulation of ovarian follicular development.

Promoter sequences targeting tissue-specific gene expression of hypothalamic and ovarian gonadotropin-releasing hormone in vivo

Molecular mechanisms directing tissue-specific expression of gonadotropin-releasing hormone (GnRH) are difficult to study due to the paucity and scattered distribution of GnRH neurons. To identify regions of the mouse GnRH (mGnRH) promoter that are critical for appropriate tissue-specific gene expression, we generated transgenic mice with fragments (-3446/+23 bp, -2078/+23 bp, and -1005/+28 bp) of mGnRH promoter fused to the luciferase reporter gene. The pattern of mGnRH promoter activity was assessed by measuring luciferase activity in tissue homogenates. All three 5'-fragments of mGnRH promoter targeted hypothalamic expression of the luciferase transgene, but with the exception of the ovary, luciferase expression was absent in non-neural tissues. High levels of ovarian luciferase activity were observed in mice generated with both -2078 and -1005 bp of promoter. Our study is the first to define a region of the GnRH gene promoter that directs expression to both neural and non-neural tissues in vivo. We demonstrate that DNA sequences contained within the proximal -1005 bp of the mGnRH promoter are sufficient to direct mGnRH gene expression to both the ovary and hypothalamus. Our results also suggest that DNA sequences distal to -2078 bp mediate the repression of ovarian GnRH.

Are estrogens of import to primate/human ovarian folliculogenesis?

The notion that estrogens play a meaningful role in ovarian folliculogenesis stems from a large body of in vitro and in vivo experiments carried out in certain rodent models, (e.g., rats) wherein the stimulatory role of estrogen on granulosa cell growth and differentiation is undisputed. However, evidence derived from these polyovulatory species may not be readily generalizable to the monoovulatory subhuman primates, let alone the human. Only recently, significant observations on the ovarian role(s) of estrogen have been reported for the primate/human. It is thus the objective of this communication to review the evidence for and against a role for estrogens in primate/human ovarian follicular development with an emphasis toward the application of the concepts so developed to contemporary reproductive physiology and to the practice of reproductive medicine. The role(s) of estrogens will be examined not only by analyzing the physiological evidence to the effect that these hormones control ovarian function and follicular growth, but also by summarizing the molecular evidence for the existence and distribution of the cognate receptors.

Expression of sGnRH mRNA in gonads during rainbow trout gametogenesis

The salmon gonadotropin-releasing hormone (sGnRH) is the major form of GnRH decapeptide expressed in the salmonid brain and it acts as a gonadotropin releaser. In rainbow trout, sGnRH-1 and sGnRH-2 mRNA forms were found in brain and gonads. We analyzed the expression of both forms in trout gonads at different stages of gametogenesis. Northern blot demonstrated that sGnRH-2 mRNA was the major sGnRH form in testis and ovary. In testis but not in ovary, brain or pituitary, alternatively spliced sGnRH-2 transcripts which coded for prepro-sGnRH with a truncated GnRH-associated peptide due to a premature stop codon in retained intron 2 were detected. In testis, sGnRH mRNA was highly expressed before the onset of spermatogenesis, it disappeared at stage II and then increased progressively up to stage VI. In ovary, the expression of sGnRH was high in immature pre-vitellogenic fish and progressively decreased throughout vitellogenesis. At ovulation it reached its maximum and came down again after stripping. The decrease of sGnRH mRNA expression during the period of active spermatogonial proliferation in testis and increase during meiosis occurrence in testis and ovary suggest an anti-proliferative and meiosis-stimulating effect of sGnRH during rainbow trout gametogenesis.

Embryo implantation and GnRH antagonists: ovarian actions of GnRH antagonists

The gonadotrophin-releasing hormone (GnRH) antagonists, cetrorelix and ganirelix, have both been approved for ovarian stimulation to prevent a premature LH surge. Since GnRH receptors and their gene expression have been detected in human ovary, concern has risen over whether GnRH antagonists might affect ovarian function. Three large trials which compared GnRH agonists (used in the standard protocol worldwide), with the new antagonist treatment found no significant differences concerning the most important goals, e.g. pregnancy rate, fertilization and quality of oocytes. However, the concentration of oestradiol, and the pregnancy and implantation rates were lower in GnRH antagonist-treated patients. These findings again fuelled the debate about the possible extrapituitary effects of GnRH antagonists. Here, we review the conflicting data in the literature on the ovarian effects of GnRH antagonists and discuss our own results. In our view, it is unlikely that GnRH antagonists have a relevant impact on ovarian steroidogenesis and function; however, GnRH antagonists may exert other effects on the ovary.

Differential regulation of two forms of gonadotropin-releasing hormone messenger ribonucleic acid in human granulosa-luteal cells

Until recently, the primate brain was thought to contain only one form of GnRH known as mammalian GnRH (GnRH-I). The recent cloning of a second form of GnRH (GnRH-II) with characteristics of chicken GnRH-II in the primate brain has prompted a reevaluation of the role of GnRH in reproductive functions. In the present study, we investigated the hormonal regulation of GnRH-II messenger RNA (mRNA) and its functional role in the human granulosa-luteal cells (hGLCs), and we provided novel evidence for differential hormonal regulation of GnRH-II vs. GnRH-I mRNA expression. Human GLCs were treated with various concentrations of GnRH-II, GnRH-II agonist (GnRH-II-a), or GnRH-I agonist (GnRH-I-a; leuprolide) in the absence or presence of FSH or human CG (hCG). The expression levels of GnRH-II, GnRH-I, and GnRH receptor (GnRHR) mRNA were investigated using semiquantitative or competitive RT-PCR. A significant decrease in GnRH-II and GnRHR mRNA levels was observed in cells treated with GnRH-II or GnRH-II-a. In contrast, GnRH-I-a revealed a biphasic effect (up- and down-regulation) of GnRH-I and GnRHR mRNA, suggesting that GnRH-I and GnRH-II may differentially regulate GnRHR and their ligands (GnRH-I and GnRH-II). Treatment with FSH or hCG increased GnRH-II mRNA levels but decreased GnRH-I mRNA levels, further indicating that GnRH-I and GnRH-II mRNA levels are differentially regulated. To investigate the physiological role of GnRH-II, hGLCs were treated with GnRH-II or GnRH-II-a in the presence or absence of hCG, for 24 h, and progesterone secretion was measured by RIA. Both GnRH-II and GnRH-II-a inhibited basal and hCG-stimulated progesterone secretion, effects which were similar to the effects of GnRH-I treatment on ovarian steroidogenesis. Next, hGLCs were treated with various concentrations of GnRH-II, GnRH-II-a, or GnRH-I-a; and the expression levels of FSH receptor and LH receptor were investigated using semiquantitative RT-PCR. A significant down-regulation of FSH receptor and LH receptor was observed in cells treated with GnRH-II, GnRH-II-a, and GnRH-I-a, demonstrating that GnRH-II and GnRH-I may exert their antigonadotropic effect by down-regulating gonadotropin receptors. Interestingly, GnRH-II and GnRH-II-a did not affect basal and hCG-stimulated intracellular cAMP accumulation, suggesting that the antigonadotropic effect of GnRH-II may be independent of modulation of cAMP levels. Taken together, these results suggest that GnRH-II may have biological effects similar to those of GnRH-I but is under differential hormonal regulation in the human ovary.