Regulation of luteinizing hormone receptor messenger ribonucleic acid levels by gonadotropins, growth factors, and gonadotropin-releasing hormone in cultured rat granulosa cells

Actions and Roles of FSH in Germinative Cells

Follicle stimulating hormone (FSH) is produced by the pituitary gland in a coordinated hypothalamic-pituitary-gonadal (HPG) axis event, plays important roles in reproduction and germ cell development during different phases of reproductive development (fetal, neonatal, puberty, and adult life), and is consequently essential for fertility. FSH is a heterodimeric glycoprotein hormone of two dissociable subunits, α and β. The FSH β-subunit (FSHβ) function starts upon coupling to its specific receptor: follicle-stimulating hormone receptor (FSHR). FSHRs are localized mainly on the surface of target cells on the testis and ovary (granulosa and Sertoli cells) and have recently been found in testicular stem cells and extra-gonadal tissue. Several reproduction disorders are associated with absent or low FSH secretion, with mutation of the FSH β-subunit or the FSH receptor, and/or its signaling pathways. However, the influence of FSH on germ cells is still poorly understood; some studies have suggested that this hormone also plays a determinant role in the self-renewal of germinative cells and acts to increase undifferentiated spermatogonia proliferation. In addition, in vitro, together with other factors, it assists the process of differentiation of primordial germ cells (PGCLCs) into gametes (oocyte-like and SSCLCs). In this review, we describe relevant research on the influence of FSH on spermatogenesis and folliculogenesis, mainly in the germ cell of humans and other species. The possible roles of FSH in germ cell generation in vitro are also presented.

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.

Prolactin Is a Strong Candidate for the Regulation of Luteal Steroidogenesis in Vizcachas (Lagostomus maximus)

Prolactin (PRL) is essential for the maintenance of the corpora lutea and the production of progesterone (P4) during gestation of mice and rats, which makes it a key factor for their successful reproduction. Unlike these rodents and the vast majority of mammals, female vizcachas (Lagostomus maximus) have a peculiar reproductive biology characterized by an ovulatory event during pregnancy that generates secondary corpora lutea with a consequent increment of the circulating P4. We found that, although the expression of pituitary PRL increased steadily during pregnancy, its ovarian receptor (PRLR) reached its maximum in midpregnancy and drastically decreased at term pregnancy. The luteinizing hormone receptor (LHR) exhibited a similar profile than PRLR. Maximum P4 and LH blood levels were recorded at midpregnancy as well. Remarkably, the P4-sinthesizing enzyme 3β-HSD accompanied the expression pattern of PRLR/LHR throughout gestation. Instead, the luteolytic enzyme 20α-HSD showed low expression at early and midpregnancy, but reached its maximum at the end of gestation, when PRLR/LHR/3ß-HSD expressions and circulating P4 were minimal. In conclusion, both the PRLR and LHR expressions in the ovary would define the success of gestation in vizcachas by modulating the levels of 20α-HSD and 3ß-HSD, which ultimately determine the level of serum P4 throughout gestation.

Effect of High-Fat Diet on Immature Female Mice and Messenger and Noncoding RNA Expression Profiling in Ovary and White Adipose Tissue

Obesity is a chronic multifactorial disease prevalent in many areas of the world and is a major cause of morbidity and mortality. In women, obesity increases the risks of both metabolic and reproductive diseases, such as diabetes and infertility. The mechanisms underlying these effects, especially in young women, are largely unknown. To explore these mechanisms, we established a high-fat diet (HFD) model of obesity in immature female mice. Microarray analysis of gene expression in ovaries and white adipose tissue identified a large number of differentially expressed genes (>1.3-fold change) in both tissues. In ovaries of the HFD group, there were 208 differentially expressed messenger RNAs (mRNAs), including 98 upregulated and 110 downregulated, and 295 differentially expressed lncRNAs (long non coding RNAs), including 63 upregulated and 232 downregulated. In white adipose tissue, there were 625 differentially expressed mRNAs, including 220 upregulated and 605 downregulated in the HFD group, and 1595 differentially expressed lncRNAs, including 1320 and 275 downregulated in the HFD group. Our results reveal significant differences between the transcriptomes of the HFD and control groups in both ovaries and white adipose tissue that provide clues to the molecular mechanisms of diet-induced female reproductive dysfunction and metabolic disorders, as well as biomarkers of risk for these disorders.

Apoptosis of bovine granulosa cells: Intracellular pathways and differentiation

Follicular atresia in granulosa and theca cells occurs by apoptosis through weak hormonal stimulation. We have previously proposed an in vitro model to study this process by inducing apoptosis in BGC-1, a bovine granulosa cell line, and in primary cultures from ovaries with or without corpus luteum (CPGB+ and CPGB-, respectively), with different doses of gonadotropin releasing hormone (GnRH) analogs (leuprolide acetate (LA) as agonist and antide as antagonist). BGC-1 represent immature granulosa cells, whereas CPGB represent different degrees of luteinization. Our aim was to evaluate the intracellular pathways involved in the GnRH regulation of apoptosis in BGC-1. Treatment with LA 100nM but not with antide led to an increase in BAX over BCL-2 expression, showing antagonism of antide. All treatments inhibited phospholipase-D (PLD) activity compared to control, implying agonist behavior of antide. Progesterone in vitro production and 3β-hydroxysteroid dehydrogenase (3β-HSD) expression revealed different degrees of luteinization: BGC-1 were immature, whereas CPGB+ were less differentiated than CPGB-. We concluded that LA-induced apoptosis in BGC-1 occurs by activation of the mitochondrial pathway and by inhibition of PLD activity and that antide might work both as an antagonist of the intrinsic pathway and as an agonist of the extrinsic protection pathway by inhibiting PLD activity.

The spatiotemporal hormonal orchestration of human folliculogenesis, early embryogenesis and blastocyst implantation

The early reproductive events starting with folliculogenesis and ending with blastocyst implantation into the uterine endometrium are regulated by a complex interplay among endocrine, paracrine and autocrine factors. This review examines the spatiotemporal integration of these maternal and embryonic signals that are required for successful reproduction. In coordination with hypothalamic-pituitary-gonadal (HPG) hormones, an intraovarian HPG-like axis regulates folliculogenesis, follicular quiescence, ovulation, follicular atresia, and corpus luteal functions. Upon conception and passage of the zygote through the fallopian tube, the contribution of maternal hormones in the form of paracrine secretions from the endosalpinx to embryonic development declines, with autocrine and paracrine signaling becoming increasingly important as instructional signals for the differentiation of the early zygote/morula into a blastocyst. These maternal and embryonic signals include activin and gonadotropin-releasing hormone 1 (GnRH1) that are crucial for the synthesis and secretion of the 'pregnancy' hormone human chorionic gonadotropin (hCG). hCG in turn signals pre-implantation embryonic cell division and sex steroid production required for stem cell differentiation, and subsequent blastulation, gastrulation, cavitation and blastocyst formation. Upon reaching the uterus, blastocyst hatching occurs under the influence of decreased activin signaling, while the attachment and invasion of the trophoblast into the endometrium appears to be driven by a decrease in activin signaling, and by increased GnRH1 and hCG signaling that allows for tissue remodeling and the controlled invasion of the blastocyst into the uterine endometrium. This review demonstrates the importance of integrative endocrine, paracrine, and autocrine signaling for successful human reproduction.

Control of Oocyte Growth and Development by Intercellular Communication Within the Follicular Niche

In the mammalian ovary, each oocyte grows and develops within its own structural and developmental niche-the follicle. Together with the female germ cell in the follicle are somatic granulosa cells, specialized companion cells that surround the oocyte and provide support to it, and an outer layer of thecal cells that serve crucial roles including steroid synthesis. These follicular compartments function as a single physiological unit whose purpose is to produce a healthy egg, which upon ovulation can be fertilized and give rise to a healthy embryo, thus enabling the female germ cell to fulfill its reproductive potential. Beginning from the initial stage of follicle formation and until terminal differentiation at ovulation, oocyte and follicle growth depend absolutely on cooperation between the different cellular compartments. This cooperation synchronizes the initiation of oocyte growth with follicle activation. During growth, it enables metabolic support for the follicle-enclosed oocyte and allows the follicle to fulfill its steroidogenic potential. Near the end of the growth period, intra-follicular interactions prevent the precocious meiotic resumption of the oocyte and ensure its nuclear differentiation. Finally, cooperation enables the events of ovulation, including meiotic maturation of the oocyte and expansion of the cumulus granulosa cells. In this chapter, we discuss the cellular interactions that enable the growing follicle to produce a healthy oocyte, focusing on the communication between the germ cell and the surrounding granulosa cells.

Progressive obesity alters ovarian folliculogenesis with impacts on pro-inflammatory and steroidogenic signaling in female mice

Diet-induced obesity induces immune cell infiltration and inflammation in peri-ovarian adipose tissue and mRNA expression of inflammatory markers in ovarian tissue. Whether these changes are associated with obesity-related ovarian dysfunction remains unknown. In the present study, qRT-PCR and Western blotting techniques were used to compare mRNA and protein abundance of ovarian immune cell and inflammation markers, along with NF-kappaB and steroidogenic pathway members in normal wild-type non-agouti (a/a; lean) and lethal yellow mice (KK.CG-A(y/)J; obese) at 6, 12, 18, or 24 wk of age. Our data revealed that, beginning at 12 wk of age, NF-kappaB inflammatory signaling members were elevated (P < 0.05) in obese females. Interestingly obesity had opposing and temporal effects on the steroidogenic enzyme pathway. Obesity decreased (P < 0.05) STAR protein at 12, 18, and 24 wk of age. CYP11A1 and CYP19A1 proteins were increased (P < 0.05) at 12 wk but were decreased (P < 0.05) at 18 and 24 wk. Interestingly, CYP19A1 was increased in lethal yellow mouse ovaries at 6 wk of age, potentially indicating early puberty onset. These data demonstrate that obesity alters expression of ovarian inflammatory and steroidogenic pathway genes in ways which could adversely affect ovarian function.

Prolactin signaling mechanisms in ovary

Prolactin is a hormone that is essential for normal reproduction and signals through two types of receptors. Not only is the classical long form of the prolactin receptor identified, but so are many short form receptors in rodents and human tissues. Mouse mutagenesis studies have offered insight into the biology of prolactin family, providing compelling evidence that the different isoforms have independent biological activity. The possibility that short forms mediate cell proliferation is important for a variety of tissues including mammary gland and ovarian follicles. This review summarizes our current knowledge about prolactin signaling and its role in reproduction through either long or short isoform receptors.

Effect of triptolide on estradiol release from cultured rat granulosa cells

Triptolide, a major active component of Tripterygium wilfordii Hook F (TWHF), is known to have multiple pharmacological activities. However, studies have also shown that triptolide is highly toxic to the reproductive system by disrupting normal androgen and estrogen signaling. In the present study, we investigated the effect of triptolide (5, 10, or 20 nM for 24 h) on estradiol production by rat granulosa cells. Triptolide inhibited basal and human chorionic gonadotropin (HCG)- or 8-bromo-cAMP-stimulated estradiol production as revealed by RIA assay. Furthermore, the HCG-evoked increase in cellular cAMP content was also inhibited by triptolide, indicating that disruption of the cAMP/PKA signaling pathway may mediate the deleterious effects of triptolide on steroid hormone regulation. In addition, (3)H(2)O tests showed that aromatase activity was significantly inhibited by triptolide in granulosa cells. Western blot and quantitative real-time PCR (qRT-PCR) assays further revealed that triptolide decreased protein and mRNA expression of aromatase in granulosa cells. Moreover, mRNA expression of luteinizing hormone receptor (LHR) was induced by triptolide also using qRT-PCR method. In contrast, cell viability tests using Cell Counting Kit-8 (CCK-8) and 3-(4,5-dimethyl-thiazol-2-yl)-2,5- diphenyl-tetrazolium bromide (MTT) method indicated that triptolide did not cause measurable cell death at doses that suppressed steroidogenesis. The reproductive toxicity of triptolide may be mainly caused by disruption of cAMP/PKA-mediated expression of estrogen synthesis enzymes, leading to reduced estradiol synthesis and reproductive dysfunction.

Differential regulation of gonadotropin receptors (fshr and lhcgr) by estradiol in the zebrafish ovary involves nuclear estrogen receptors that are likely located on the plasma membrane

FSH and LH are gonadotropins (GTH) that control all major events of gonadal function. FSH and LH signal through their cognate receptors, FSH receptor and LH/choriogonadotropin receptor, respectively, across vertebrates. Compared with the information in mammals, very little is known about these receptors in fish, especially the regulation of their expression. In female zebrafish, fshr and lhcgr exhibit significant temporal difference in expression, with fshr increasing first when the follicles are activated to enter the vitellogenic growth phase and lhcgr lagging behind. This raises an interesting question on the differential regulation of these two GTH receptors (GTHR) during folliculogenesis. Using a primary follicle cell culture, the present study demonstrated that 17β-estradiol (E2), but not testosterone, was a potent endocrine hormone that differentially regulated the expression of fshr and lhcgr. Although E2 stimulated both receptors, its effect on the steady-state level of lhcgr mRNA was much higher (>8-fold up-regulation) than that of fshr (∼0.5-fold increase). E2 likely acted at the transcription level via its nuclear estrogen receptors (ERα and ERβ), because ICI 182,780 could abolish its effects. However, our evidence suggested that these receptors might be localized on the plasma membrane, because β-estradiol 6-(O-carboxy methyl)oxime:BSA could fully mimic the effects of E2. Demonstrating that E2 is likely one of the differentiating factors for the distinct expression of the two GTHR in the zebrafish ovary, this study sheds important light on the functions of the two GTH and their receptors in fish as well as the conservation and diverse aspects of GTHR regulation across vertebrates.

Immunohistochemical localization of GnRH and RFamide-related peptide-3 in the ovaries of mice during the estrous cycle

Gonadotropin releasing hormone (GnRH) has now been suggested as an important intraovarian regulatory factor. Gonadotropin inhibitory hormone (GnIH) a hypothalamic dodecapeptide, acts opposite to GnRH. GnRH, GnIH and their receptors have been demonstrated in the gonads. In order to find out the physiological significance of these neuropeptides in the ovary, we aim to investigate changes in the abundance of GnRH I and GnIH in the ovary of mice during estrous cycle. The present study investigated the changes in GnRH I, GnRH I-receptor and RFRP-3 protein expression in the ovary of mice during estrous cycle by immunohistochemistry and immunoblot analysis. The immunoreactivity of GnRH I and its receptor and RFRP-3 were mainly localized in the granulosa cells of the healthy and antral follicles during proestrus and estrus and in the luteal cells during diestrus 1 and 2 phases. The relative abundance of immunoreactivity of GnRH I, GnRH I-receptor and RFRP-3 undergo significant variation during proestrus and thus may be responsible for selection of follicle for growth and atresia. A significant increase in the concentration of RFRP-3 during late diestrus 2 coincided with the decline in corpus luteum activity and initiation of follicular growth and selection. In general, immunolocalization of GnRH I, GnRH I-receptor and RFRP-3 were found in close vicinity suggesting functional interaction between these peptides. It is thus, hypothesized that interaction between GnRH I-RFRP-3 neuropeptides may be involved in the regulation of follicular development and atresia.

Identification of genes targeted by FSH and oocytes in porcine granulosa cells

In the mammalian ovarian follicle maturing oocytes are nurtured and supported by surrounding somatic cells, the mural granulosa cells and the cumulus cells. These cells are regulated by follicle-stimulating hormone (FSH), originating from the pituitary, and paracrine factors derived from the oocyte. To gain insight into the mechanisms involved in the regulation of granulosa cell function, this study aimed to identify genes in mural granulosa cells that are regulated by FSH and oocyte secreted factors using the pig as a model organism. Mural granulosa cells were collected from 3-6 mm follicles from sow ovaries and cultured in serum free medium in the presence or absence of FSH and/or isolated cumulus oocyte complexes (COCs). FSH significantly increased both the metabolic activity and progesterone production of granulosa cells, while the presence of COCs reversed these FSH effects. Expression levels of mRNA in the absence/presence of FSH and COCs were analyzed on porcine specific microarrays representing 11,300 genes. Both previously identified and novel FSH target genes as well as some oocyte affected genes were found. Expression of inhibitor of DNA binding protein 2 and 3, ID2 and ID3, was decreased by FSH but increased by COCs, as validated by quantitative PCR. These proteins function as dominant negative basic helix loop helix (bHLH) transcription factors and since all regulated genes contain the consensus E-box sequence that can bind bHLH factors, our data suggest that FSH and COCs may regulate granulosa cell function by tuning the activity of bHLH factors, through ID2 and ID3.

Impact of prolactin receptor isoforms on reproduction

Prolactin is a hormone involved in growth, development, reproduction, metabolism, water and electrolyte balance, brain and behavior, and immunoregulation. Its actions on reproductive processes represent the largest group of functions identified for this hormone. Besides the classic long form of the prolactin receptor, many short form receptors have been identified in rodents and human tissues. Mouse mutagenesis studies have offered insight into the biology of the prolactin family, providing compelling evidence that different isoforms have independent biological activity. The possibility that short forms mediate cell proliferation is important for a variety of tissues including mammary glands and ovarian follicles. This review summarizes the current knowledge about prolactin signaling and its role in reproduction through either long or short isoform receptors.

Prolactin independent rescue of mouse corpus luteum life span: identification of prolactin and luteinizing hormone target genes

The corpus luteum (CL) plays a central role in the maintenance of pregnancy in rodents, mainly by secreting progesterone. Female mice lacking prolactin (PRL) receptor (R) are sterile due to a failure of embryo implantation, which is a consequence of decreased luteinizing hormone (LH) receptor expression in the CL and inadequate levels of progesterone. We attempted to treat PRLR(-/-) females with human chorionic gonadotropin (hCG) and showed a de novo expression of LHR mRNA in the corpora lutea. Binding analysis confirmed that the LHR in hCG-treated PRLR(-/-) animals was functional. This was accompanied with increased expression of steroidogenic enzymes involved in progesterone synthesis. Despite these effects, no embryo implantation was observed because of high expression of 20alpha-hydroxysteroid dehydrogenase. To better appreciate the molecular mechanisms underlying maintenance of the CL, a series of mRNA expression-profiling experiments was performed on isolated corpora lutea of PRLR(-/-) and hCG-treated PRLR(-/-) mice. This approach revealed several novel candidate genes with potentially pivotal roles in ovarian function, among them, p27, VE-cadherin, Pten, and sFRP-4, a member of the Wnt/frizzled family. This study showed the differential role of PRL and LH in CL function and identified new targets of these hormones in luteal cells.

Differential expression and regulation of gonadotropins and their receptors in the Japanese eel, Anguilla japonica

Eel species have a striking life cycle with a blockade of puberty until the oceanic migration. We report the first molecular data on eel gonadotropin receptors. The partial sequences cloned covered two-third of the open reading frame and included most of the extracellular and transmembrane domains. Phylogenetic analysis partitioned the two eel gonadotropin receptors into the two teleost FSHR and LHR clusters, respectively. Real-time quantitative RT-PCR was used to quantify the expression of eel gonadotropins and their receptors. Similar levels of pituitary FSH-beta and LH-beta transcripts were found in the immature previtellogenic female eels. In contrast, ovarian FSHR mRNA level was at 100- to 185-fold higher than that of LHR. This revealed that FSHR rather LHR would mediate gonadotropin stimulation of the early stages of ovarian growth. Chronic treatment with fish pituitary homogenates, applied to induce eel sexual maturation, stimulated pituitary LH-beta but suppressed FSH-beta transcripts. In the ovaries, both FSHR and LHR mRNA were significantly increased in experimentally matured eels. Treatments with sexual steroids showed a stimulatory effect of estradiol-17beta (E(2)) on pituitary LH-beta mRNA levels, while FSH-beta transcripts were suppressed by E(2) or testosterone (T). In contrast, neither E(2) nor T-treatment had any significant effect on ovarian FSHR nor LHR transcripts. This suggests that steroid feedbacks may be responsible for the opposite regulation of pituitary gonadotropins in experimentally matured eels, but are not involved in the regulation of gonadotropin receptors. In conclusion, these are the first data on the sequence, expression and regulation of gonadotropin receptors in the eel. They provide new foundation for basic and applied research on eel reproduction.

Regulation of ovarian angiogenesis and apoptosis by GnRH-I analogs

An adequate vascular supply is important to provide endocrine and paracrine signals during follicular development. We evaluated the direct in vivo effects of both the GnRH-agonist Leuprolide acetate (LA) and the GnRH-antagonist Antide (Ant) on the expression of VEGF-A and ANPT-1 and their receptors in ovarian follicles from prepubertal eCG-treated rats. We also examined whether the changes observed in apoptosis by GnRH-I analogs have an effect on the caspase cascade. LA significantly decreased the levels of VEGF-A, its receptor Flk-1, and ANPT-1 when compared to controls, while the co-injection of Ant interfered with this effect. No changes were observed in the levels of Tie-2 after treatment with these analogs. When we measured the follicular content of caspase-3 protein, we observed that LA significantly increased the level of the active form. The co-injection of Ant interfered with this effect and Ant alone significantly decreased caspase-3 cleavage. IHC analyses corroborated these data. Notably, while LA increased caspase-3 activity levels, Ant decreased them when compared to controls. In follicles obtained from LA-treated rats, cleavage of PARP (a substrate of caspase-3) from the intact 113-kDa protein showed a significant enhancement in an 85-kDa fragment. The co-injection of Ant interfered with this effect. Ant alone significantly decreased PARP cleavage as compared to controls. We conclude that the decrease in VEGF-A, its receptor Flk-1/KDR, and ANPT-1 produced by the administration of GnRH-I agonist is one of the mechanisms involved in ovarian cell apoptosis. This suggests an intraovarian role of an endogenous GnRH-like peptide in gonadotropin-induced follicular development.

Inhibition of cytochrome P-450 C17 enzyme by a GnRH agonist in ovarian follicles from gonadotropin-stimulated rats

Our objective was to study the direct action of a GnRH-I agonist, leuprolide acetate (LA), on ovarian steroidogenesis in preovulatory follicles obtained from equine chorionic gonadotropin (eCG)-treated rats. Previously, we have demonstrated an inhibitory effect of LA on steroidogenesis and follicular development. In this study, we tested the hypothesis that gonadotropin-releasing hormone (GnRH) exerts its negative effect on follicular development by inhibiting thecal cytochrome P-450 C17 (P450C17) alpha-hydroxylase expression and, consequently, androgen synthesis. Studies were carried out in prepubertal female rats injected with either eCG (control) or eCG plus LA (LA) and killed at different time points. Immunohistochemical studies indicated that LA induced steroidogenic acute regulatory protein (StAR) expression mainly in theca cells of preantral and antral follicles. In addition, serum progesterone levels increased significantly (P < 0.05), whereas those of androsterone decreased (P < 0.05) after 8 h of LA treatment. This inhibition caused by LA seemed to be a consequence of the decreased expression of follicular P450C17 alpha-hydroxylase, as demonstrated by Western blot and RT-PCR techniques. In vitro studies using follicles isolated from 48-h-eCG-treated rats and cultured with LA showed a significant (P < 0.05) inhibition of FSH-induced androsterone follicular content as well as P450C17 alpha-hydroxylase protein levels, as determined by Western analysis. However, LA increased StAR protein expression in these follicles without significant changes in P450scc enzyme levels. Taking all these findings into account, we suggest that GnRH-I exerts a direct inhibitory action on gonadotropin-induced follicular development by decreasing the temporal expression of the P450C17 enzyme and, consequently, androgen production, thus reducing the supply of estrogens available to developing follicles.

The molecular control of corpus luteum formation, function, and regression

The corpus luteum (CL) is one of the few endocrine glands that forms from the remains of another organ and whose function and survival are limited in scope and time. The CL is the site of rapid remodeling, growth, differentiation, and death of cells originating from granulosa, theca, capillaries, and fibroblasts. The apparent raison d'etre of the CL is the production of progesterone, and all the structural and functional features of this gland are geared toward this end. Because of its unique importance for successful pregnancies, the mammals have evolved a complex series of checks and balances that maintains progesterone at appropriate levels throughout gestation. The formation, maintenance, regression, and steroidogenesis of the CL are among the most significant and closely regulated events in mammalian reproduction. During pregnancy, the fate of the CL depends on the interplay of ovarian, pituitary, and placental regulators. At the end of its life span, the CL undergoes a process of regression leading to its disappearance from the ovary and allowing the initiation of a new cycle. The generation of transgenic, knockout and knockin mice and the development of innovative technologies have revealed a novel role of several molecules in the reprogramming of granulosa cells into luteal cells and in the hormonal and molecular control of the function and demise of the CL. The current review highlights our knowledge on these key molecular events in rodents.

Identification of a stage-specific permissive in vitro culture environment for follicle growth and oocyte development

The availability of viable oocytes is the limiting factor in the development of new reproductive techniques. Many attempts have been made to grow immature oocytes in vitro during recent decades. Recently, a modified alginate-based three-dimensional culture system was designed to support the growth and maturation of multilayered secondary follicles. This system was able to produce oocytes that successfully completed meiosis, fertilization, and development to the blastocyst stage. Subsequent attempts to culture two-layered secondary follicles were unsuccessful under the original conditions. Herein, we investigated the effect of alginate consistency on two-layered follicle growth and oocyte developmental competence by encapsulating follicles into alginate scaffolds of various concentrations. Although there were no significant differences in survival rates, 0.25% and 0.5% alginate supported more rapid growth of follicles and antrum formation compared with 1.5% and 1.0% alginate after 8 days of culture. Alginate scaffold concentration also affected the proliferation and differentiation of somatic cells (theca and granulosa cells), measured in terms of morphological changes, steroid profiles (androstenedione, estradiol, and progesterone), and specific molecular markers (Fshr, Lhcgr, and Gja1). Theca cell proliferation and steroid production were hindered in follicles cultured in 1.5% alginate. In vitro fertilization and embryo culture revealed that oocytes obtained from 0.25% alginate retained the highest developmental competence. Overall, the present study showed that the alginate scaffold consistency affects folliculogenesis and oocyte development in vitro and that the alginate culture system can and should be tailored to maximally support follicle growth depending on the size and stage of the follicles selected for culture.

Ovarian steroids: the good, the bad, and the signals that raise them

Ovarian steroid production and subsequent local steroid-mediated signaling are critical for normal ovarian processes, including follicle growth, oocyte maturation, and ovulation. In contrast, elevated steroidogenesis and/or increased steroid signaling in the ovary can lead to profound ovarian pathology, such as polycystic ovarian syndrome, the leading cause of infertility in reproductive age women. Through the use of several in vitro and animal models, great strides have been made toward characterizing the mechanisms regulating local steroid production and action in the ovary. Examples of this progress include insights into luteinizing hormone (LH)- and growth factor-mediated signaling, steroidogenic acute regulatory protein (StAR) activation, and both genomic and nongenomic steroid-mediated signaling in somatic and germ cells, respectively. The following review will address these advances, focusing on how this rapidly expanding knowledge base can be used to better understand female reproduction, and to further improve treatments for common diseases of infertility.

GnRH in non-hypothalamic reproductive tissues

Gonadotropin releasing hormone (GnRH) is a hypothalamic neuronal secretory decapeptide that plays a pivotal role in mammalian reproduction. GnRH and its analogues are used extensively in the treatment of hormone dependent diseases and assisted reproductive technology. Fourteen structural variants and three different forms of GnRH, named as hypothalamic GnRH or GnRH-I, mid brain GnRH or GnRH-II and GnRH-III across various species of protochordates and vertebrates have been recognised. The hormone acts by binding to cell surface transmembrane G protein coupled receptors (GPCRs) and activates Gq/11 subfamily of G proteins. Although hypothalamus and pituitary are the principal source and target sites for GnRH, several reports have recently suggested extra-hypothalamic GnRH and GnRH receptors in various reproductive tissues such as ovaries, placenta, endometrium, oviducts, testes, prostrate, and mammary glands. GnRH-II appears to be predominantly expressed in extra pituitary reproductive tissues where it produces its effect by PLC, PKA2, PLD, and AC cell signalling pathways. In these tissues, GnRH is considered to act by autocrine or paracrine manner and regulate ovarian steroidogenesis by having stimulatory as well as inhibitory effect on the production of steroid hormones and apoptosis in ovarian follicle and corpus luteum. In male gonads, GnRH has been shown to cause a direct stimulatory effect on basal steroidogenesis and an inhibitory effect on gonadotropin-stimulated androgen biosynthesis. Recent studies have shown that GnRH is more abundantly present in ovarian, endometrial and prostrate carcinomas. The presence of type-II GnRH receptors in reproductive tissues (e.g. gonads, prostrate, endometrium, oviduct, placenta, and mammary glands) suggests existence of distinct role(s) for type-II GnRH molecule in these tissues. The existence of different GnRH forms indicates the presence of distinctive cognate receptors types in vertebrates and is a productive area of research and may contribute to the development of new generation of GnRH analogues with highly selective and controlled action on different reproductive tissues and the target-specific GnRH analogues could be developed.

The differential effects of the gonadotropin receptors on aromatase expression in primary cultures of immature rat granulosa cells are highly dependent on the density of receptors expressed and the activation of the inositol phosphate cascade

Signaling pathways mediating the divergent effects of FSH and LH on aromatase in immature rat granulosa cells were studied by infecting cells with increasing amounts of adenoviral vectors for the human LH receptor (hLHR) or FSH receptor (hFSHR). Increasing amounts of Ad-hLHR, used at a multiplicity of infection (MOI) of 20 or 200 viable viral particles/cell, increased human chorionic gonadotropin (hCG) binding and hCG-induced cAMP and Akt phosphorylation, but inositol phosphates only increased in response to hCG in cells infected with 200 MOI Ad-hLHR. In contrast, hCG increased aromatase expression in cells infected with 20, but not in cells infected with 200, MOI Ad-hLHR. Cells infected with 20 or 200 MOI Ad-hFSHR showed increased hFSH binding and hFSH-induced Akt phosphorylation, but the hFSH-induced cAMP response was unchanged relative to control cells. However, hFSH was able to stimulate the inositol phosphate cascade in the Ad-hFSHR-infected cells, and the hFSH induction of aromatase was abolished. We also found that activation of C kinase or expression of a constitutively active form of Galphaq inhibited the induction of aromatase by hFSH or 8Br-cAMP. We conclude that the differential effects of FSH and LH on aromatase in immature granulosa cells are highly dependent on gonadotropin receptor density and on the signaling pathways activated. We propose that aromatase is induced by common signals generated by activation of the FSHR and LHR (possibly cAMP and Akt) and that the activation of the inositol phosphate cascade in cells expressing a high density of LHR or FSHR antagonizes this induction.

Zebrafish gonadotropins and their receptors: II. Cloning and characterization of zebrafish follicle-stimulating hormone and luteinizing hormone subunits--their spatial-temporal expression patterns and receptor specificity

Gonadotropins, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) play critical roles in vertebrate reproduction. In the present study, we cloned and characterized zebrafish FSHbeta (fshb), LHbeta (lhb), and GTHalpha (cga) subunits. Compared with the molecules of other teleosts, the cysteine residues and potential glycosylation sites are fully conserved in zebrafish Lhb and Cga but not in Fshb, whose cysteines exhibit unique distribution. Interestingly, in addition to the pituitary, fshbeta, lhbeta, and cga were also expressed in some extrapituitary tissues, particularly the gonads and brain. In situ hybridization showed that zebrafish fshbeta and lhbeta were expressed in two distinct populations of gonadotrophs in the pituitary. Real-time reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed that all the three subunits increased expression before ovulation (0100-0400) when the germinal vesicles in the full-grown follicles were migrating toward the periphery, but the levels dropped at 0700, when ovulation occurred. Recombinant zebrafish FSH (zfFSH) and LH (zfLH) were produced in the Chinese hamster ovary (CHO) cells and their effects on the cognate receptors (zebrafish Fshr and Lhr) tested. Interestingly, zfFSH specifically activated zebrafish Fshr expressed together with a cAMP-responsive reporter gene in the CHO cells, whereas zfLH could stimulate both Fshr and Lhr. In conclusion, the present study systematically investigated gonadotropins in the zebrafish in terms of their structure, spatial-temporal expression patterns, and receptor specificity. These results, together with the availability of recombinant zfFSH and zfLH, provide a solid foundation for further studies on the physiological relevance of FSH and LH in the zebrafish, one of the top biological models in vertebrates.

Follicle-stimulating hormone activation of hypoxia-inducible factor-1 by the phosphatidylinositol 3-kinase/AKT/Ras homolog enriched in brain (Rheb)/mammalian target of rapamycin (mTOR) pathway is necessary for induction of select protein markers of follicular differentiation

We sought to elucidate the role of AKT in follicle-stimulating hormone (FSH)-mediated granulosa cell (GC) differentiation. Our results define a signaling pathway in GCs whereby the inactivating phosphorylation of tuberin downstream of phosphatidylinositol (PI) 3-kinase/AKT activity leads to Rheb (Ras homolog enriched in brain) and subsequent mTOR (mammalian target of rapamycin) activation. mTOR then stimulates translation by phosphorylating p70 S6 kinase and, consequently, the 40 S ribosomal protein S6. Activation of this pathway is required for FSH-mediated induction of several follicular differentiation markers, including luteinizing-hormone receptor (LHR), inhibin-alpha, microtubule-associated protein 2D, and the PKA type IIbeta regulatory subunit. FSH also promotes activation of the transcription factor hypoxia-inducible factor-1 (HIF-1). FSH-stimulated HIF-1 activity is inhibited by the PI 3-kinase inhibitor LY294002, the Rheb inhibitor FTI-277 (farnesyltransferase inhibitor-277), and the mTOR inhibitor rapamycin. Finally, we find that the FSH-mediated up-regulation of reporter activities for LHR, inhibin-alpha, and vascular endothelial growth factor is dependent upon HIF-1 activity, because a dominant negative form of HIF-1alpha interferes with the up-regulation of these genes. These results show that FSH enhances HIF-1 activity downstream of the PI 3-kinase/AKT/Rheb/mTOR pathway in GCs and that HIF-1 activity is necessary for FSH to induce multiple follicular differentiation markers.

Multi-factorial role of GnRH-I and GnRH-II in the human ovary

Normal ovarian functions are regulated by a wide variety of endocrine hormones, local paracrine and autocrine factors, which functionally interact with each other in a highly coordinated fashion. Recent findings have demonstrated that both forms of gonadotropin-releasing hormone (GnRH-I and GnRH-II) are expressed in various compartments of the human ovary including the granulosa-luteal cells, ovarian surface epithelial cells and ovarian tumors, and their expressions have been shown to be tightly regulated by gonadal steroids and gonadotropins. Functionally, these neuropeptides exert diverse biological effects in the ovary via binding to their cognate receptors, supporting the notion that these peptides act as paracrine and autocrine factors in modulating local ovarian functions. In this review, we will summarize recent literatures regarding the regulation of GnRH-I and GnRH-II gene expressions in the human ovary, and discuss the possible signal transduction mechanisms by which these hormones exert their actions in the gonad. Recent cloning of the second form of the GnRH receptor (GnRH-II receptor) in primates and other vertebrates demonstrated that it was structurally, and thus, functionally distinct from the GnRH-I receptor. Cell proliferation studies showed that GnRH-II inhibited the growth of human ovarian cancer cells that express GnRH-II but not GnRH-I receptor, indicating that the GnRH-II binding sites are functional in these cells. However, it remains unknown if GnRH-II receptor is expressed as a full-length, properly processed and functional gene transcript in humans, and its potential physiological roles such as differential regulation of gonadotropin secretion, neuroendocrine modulation and female sexual behavior await further investigation.

Roles of cyclic GMP in modulating ovarian functions

The production of a viable oocyte is dependent upon the critical influences of gonadotrophins on follicular development, granulosa cell maturation, ovulation, and luteinization. While the effects of LH and FSH are due in large part to cyclic AMP-dependent signalling mechanisms, it is clear that a number of other factors modulate the actions of gonadotrophins on the ovary via activation of alternative signalling pathways. In this regard, recent studies indicate that the second messenger guanosine 3',5'-cyclic monophosphate (cGMP) mediates a wide range of influences on the ovary. Nitric oxide (NO) is a major regulator of cGMP production via its action on soluble guanylyl cyclase, while natriuretic peptides activate receptors with intrinsic guanylyl cyclase activities. In addition, other factors known to influence ovarian functions are now recognized to act via NO/cGMP pathways. This report will review these previous findings and present new data demonstrating the inhibitory influence of cGMP on cAMP-stimulated LH receptor expression in cultured granulosa cells.

Apoptosis of granulosa cells and female infertility in achondroplastic mice expressing mutant fibroblast growth factor receptor 3G374R

Fibroblast growth factors play an important role in the control of ovarian folliculogenesis, but the complete repertoire of ovarian receptors which can transduce the fibroblast growth factor signals and their precise localization in the ovary have not yet been characterized. The most common form of inherited human dwarfism results from a point mutation in the transmembrane region of fibroblast growth factor receptor 3. A mouse model for achondroplasia was generated by introducing the human mutation (glycine 380-arginine) into the mouse fibroblast growth factor receptor 3 (G374R) by a "knock-in" approach using gene targeting leading to a constitutively active receptor. This resulted in the development of dwarf mice that share many features with human achondroplasia. Here we report that female (fibroblast growth factor receptor 3 G374R) dwarf mice become infertile. While no significant changes were observed in the anatomical and histological appearance of ovaries of 3-wk-old dwarf mice, a dramatic difference was observed in ovaries of 3-month-old mice. The normal ovary consists mainly of healthy corpora lutea and follicles at different stages of development, whereas the ovaries of the dwarf mice remain small and contain mainly follicles with a progressive apoptosis in the granulosa cells, and no corpora lutea could be observed. The levels of LH, FSH, and progesterone were lower by 72.3%, 38.0%, and 40.0%, respectively, in the blood of the dwarf mice compared with normal mice, and the total bioactivity of pituitary FSH and LH was lower by 65.6% and 79.6%, respectively, in the dwarf mice compared with normal mice. However treatment with PMSG and human CG of the dwarf mice led to rapid follicular development and formation of corpora lutea. Interestingly, the expression of the tumor suppressor gene p53 was increased dramatically in ovaries of the dwarf mice. The presence of the fibroblast growth factor receptor 3 cellular receptors in both normal and dwarf animals was demonstrated by Western blot and immunostaining. However, the distribution of the fibroblast growth factor receptors in the two strains shows significant differences. In the normal ovaries fibroblast growth factor receptor 3 was homogeneously distributed on the cell membrane of the granulosa cells and was absent in theca as well as corpora lutea cells, whereas in dwarf mice ovaries it was highly clustered on granulosa cells and very often appears in endocytic vesicles. Aged oocytes were more frequently observed in preantral follicles of ovaries of the dwarf mice. Nevertheless, oocytes isolated from antral follicles resume their meiotic division at a high percentage, similar to oocytes obtained from normal ovaries. The results imply fibroblast growth factor receptor 3 involvement in the control of follicular development through regulation of granulosa cell growth and differentiation, and that unovulation in the dwarf mice could be overcome in part by administration of exogenous gonadotropins. Moreover, it is suggested that the infertile phenotype is partially due to defects in the pituitary-gonadal axis.

Gonadotropic control of ovarian follicular growth and development

Development-related paracrine cues that sensitize follicles to follicle stimulating hormone (FSH) and luteinizing hormone (LH) are crucial to the emergence of a single dominant follicle in each ovulatory menstrual cycle. Sex steroids, insulin-like growth factors and members of the transforming growth factor-beta superfamily are key players in the follicular paracrine system. FSH acts through membrane-associated granulosa cell receptors (FSHR) to stimulate granulosa cell proliferation and differentiation. The most responsive follicle at the beginning of the cycle is the first to produce estrogen and express granulosa cell LHR. Paracrine signalling activated by FSH and LH sustains growth and oestrogen secretion until an ovulation-inducing LH surge is discharged by the pituitary gland. LH then reprograms granulosa cell function, leading to terminal differentiation (luteinization) rupture of the follicle wall, and release of the fertilizable egg. The genes regulated by the LH surge orchestrate profound changes in sex steroid production, metabolism and action which are necessary for ovulation. Preovulatory granulosa cells also increase their ability to metabolise cortisone to cortisol, which may be part of a local anti-inflammatory mechanism to promote rapid healing of the ruptured ovarian surface.

Chicken Granulosa Cells Show Differential Expression of Epidermal Growth Factor (EGF) and Luteinizing Hormone (LH) Receptor Messenger RNA and Differential Responsiveness to EGF and LH Dependent upon Location of Granulosa Cells to the Germinal Disc1

Granulosa cells in the chicken follicle exhibit different phenotypes according to their location relative to the germinal disc (GD). Granulosa cells proximal to the GD (referred to as proximal granulosa cells) are more proliferative, whereas granulosa cells distal to the GD (referred to as distal granulosa cells) are more differentiated. We have shown that epidermal growth factor (EGF) derived from the GD stimulated proliferation of granulosa cells proximal to the GD, whereas extraovarian LH promoted differentiation. We tested the hypothesis that phenotypic differences of granulosa cells are the result of differential responsiveness of granulosa cells to EGF and LH. We found that both granulosa and theca layers of chicken preovulatory follicles expressed mRNA for EGF receptor (EGFr) by polymerase chain reaction (PCR) analysis. However, only the granulosa layer showed differential expression of EGFr and LH receptor (LHr) mRNA. Competitive reverse transcription-PCR revealed that proximal granulosa cells expressed more EGFr mRNA but less LHr mRNA than distal granulosa cells. In addition, proximal granulosa cells proliferated more in response to EGF than their distal counterparts. We further demonstrated that EGF decreased LHr mRNA expression by granulosa cells in a dose-dependent manner, whereas EGF and LH had no effect on EGFr mRNA expression except at one dose of LH (15 ng/ml) that stimulated EGFr mRNA expression. Our findings suggest that EGF derived from the GD influences the phenotypes of granulosa cells. Granulosa cells proximal to the GD exhibit a proliferative phenotype possibly because they are exposed to and are more responsive to GD-derived EGF. Furthermore, GD-derived EGF decreases LHr mRNA expression by proximal granulosa cells and therefore results in less differentiated granulosa cell phenotype. In contrast, granulosa cells distal to the GD are not under the influence of EGF and exhibit a more differentiated phenotype.

Expression of messenger RNA for gonadotropin receptor in the granulosa layer during the ovulatory cycle of hens

The present experiments were conducted to evaluate the mRNA levels of luteinizing hormone receptor (LHR) and follicle-stimulating hormone receptor (FSHR) in granulosa layers during the ovulatory cycle of hens, in relation to the release of LH and steroid hormones. After the release of LH, progesterone (P4) and estradiol-17beta (E2), found 4-5 h before ovulation, LHR and FSHR mRNA levels were observed to decrease in the granulosa layers of the largest (F1) and second largest (F2) preovulatory follicles, with the greatest in the LHR mRNA level of F1. P4 concentrations in the granulosa layers of F1 and F2 increased 4-5 h before ovulation, with greater in F1 than in F2. F2 concentrations in the theca layers were greater in F2 than in F1 throughout the ovulatory cycle. Also, the injection of ovine LH caused decreases in the mRNA levels of LHR and FSHR in the granulosa layers. However, these decreases were abolished by the injection of aminoglutethimide, an inhibitor of steroid synthesis. These results suggest that in hen granulosa cells, the mRNA levels of not only LHR but also FSHR are down-regulated by LH and the down-regulation may be mediated steroid hormones.

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.

The expression, regulation and signal transduction pathways of the mammalian gonadotropin-releasing hormone receptor

Normal mammalian sexual maturation and reproductive functions require the integration and precise coordination of hormones at the hypothalamic, pituitary, and gonadal levels. Hypothalamic gonadotropin-releasing hormone (GnRH) is a key regulator in this system; after binding to its receptor (GnRHR), it stimulates de novo synthesis and release of gonadotropins in anterior pituitary gonadotropes. Since the isolation of the GnRHR cDNA, the expression of GnRHR mRNA has been detected not only in the pituitary, but also in extrapituitary tissues, including the ovary and placenta. It has been shown that change in GnRHR mRNA is one of the mechanisms for regulating the expression of the GnRHR. To help understand the molecular mechanism(s) involved in transcriptional regulation of the GnRHR gene, the 5' flanking region of the GnRHR gene has recently been isolated. Initial characterization studies have identified several DNA regions in the GnRHR 5' flanking region which are responsible for both basal expression and GnRH-mediated homologous regulation of this gene in pituitary cells. The mammalian GnRHR lacks a C-terminus and possesses a relatively short third intracellular loop; both features are important in desensitization of many others G-protein coupled receptors (GPCRs), Homologous desensitization of GnRHR has been shown to be regulated by various serine-threonine protein kinases including protein kinase A (PKA) and protein kinase C (PKC), as well as by G-protein coupled receptor kinases (GRKs). Furthermore, GnRHR was demonstrated to couple with multiple G proteins (Gq/11, Gs, and Gi), and to activate cascades that involved the PKC, PKA, and mitogen-activator protein kinases. These results suggest the diversity of GnRHR-G protein coupling and signal transduction systems. The identification of second form of GnRH (GnRH-II) in mammals adds to the complexity of the GnRH-GnRHR system. This review summaries our recent progress in understanding the regulation of GnRHR gene expression and the GnRHR signal transduction pathways.Key words: gonadotropin-releasing hormone receptor, transcriptional regulation, desensitization, signal transduction.

Three different turkey luteinizing hormone receptor (tLH-R) isoforms II: characterization of differentially regulated tLH-R messenger ribonucleic acid isoforms in the ovary

We have recently characterized three different, alternatively spliced, partial turkey LH receptor (tLH-R) cDNA isoforms by the combination of reverse transcription-polymerase chain reaction (RT-PCR) and 5'- and 3'-rapid amplification of cDNA ends. The first cDNA (intact form: tLH-R(intact)) showed 98% and 72-75% similarity with chicken and mammalian LH receptor sequences, respectively. The other two cloned cDNA isoforms (insertion and truncated forms: tLH-R(insert) and tLH-R(trunc)) could encode truncated soluble protein isoforms that lack the transmembrane region. Northern blot analysis detected two transcripts of 3.0 kilobases (kb) (tLH-R(intact)) and 1.5 kb (tLH-R(trunc)) in the turkey ovary but could not discriminate a third alternatively spliced transcript (tLH-R(insert)) due to the small 86-base pair difference in the size range of approximately 3.0-kb mRNAs. But with the combination of RNase protection assay, RT-PCR, and Northern blot analysis, three different alternatively spliced tLH-R mRNA isoforms were quantified. Differential expression of the tLH-R mRNA isoforms was demonstrated in ovarian stromal tissue during various reproductive stages and in the theca and granulosa layer through follicular development. To gain a better understanding of the physiological significance of the three different tLH-R isoforms, total RNA from the theca layer through follicular development after prolactin (PRL) treatment was analyzed by RT-PCR. PRL treatment for 8-14 days significantly increased the steady-state levels of total tLH-R mRNAs, including tLH-R(insert) and tLH-R(trunc) mRNAs, compared to those in nontreated controls. In contrast, the steady-state levels of tLH-R(intact) mRNA during the same period was not significantly changed when compared to that in nontreated controls. The present study shows that tLH-R transcripts are alternatively spliced in a tissue-specific manner in the turkey and that the mechanism may, in part, be controlled hormonally.

Effect of prolactin on follicle-stimulating hormone receptor binding and progesterone production in cultured porcine granulosa cells

OBJECTIVE

To determine the effect of prolactin (PRL) on follicle-stimulating hormone receptor (FSH-R) binding and progesterone (P) production in cultured porcine granulosa cells.

DESIGN

Controlled experiment.

SETTING

Academic research laboratory.

INTERVENTION(S)

Immature granulosa cells were cultured in a serum-free medium. All cell populations were supplemented with porcine (p) FSH and cultured in the absence or presence of ovine (o) PRL.

MAIN OUTCOME MEASURE(S)

Specific pFSH-R binding and P in medium.

RESULT(S)

In the control cells, FSH-R binding increased 31-fold and P production increased 700-fold by day 4. Physiologic levels of oPRL potentiated the action of pFSH and resulted in a further 50% increase in pFSH-R binding and P production by day 4 over that in controls. In contrast, higher concentrations of oPRL blocked the rise in both pFSH-R binding and P production. The alteration in pFSH-R binding was associated with a change in FSH-R number.

CONCLUSION(S)

Physiologic levels of PRL amplify the stimulatory effects of FSH on the acquisition of the FSH-R and P production in cultured granulosa cells. Higher concentrations of PRL cause a decrease in FSH-R binding and P production. Prolactin may act as a "co-gonadotropin" and fine-tune the process of folliculogenesis by altering the acquisition of granulosa FSH receptors.

Prevention of the polycystic ovarian phenotype and characterization of ovulatory capacity in the estrogen receptor-alpha knockout mouse

Ovarian-derived estradiol plays a critical endocrine role in the regulation of gonadotropin synthesis and secretion from the hypothalamic-pituitary axis. In turn, several para/autocrine effects of estrogen within the ovary are known, including increased ovarian weight, stimulation of granulosa cell growth, augmentation of FSH action, and attenuation of apoptosis. The estrogen receptor-alpha (ERalpha) is present in all three components of the hypothalamic-pituitary-ovarian axis of the mouse. In contrast, estrogen receptor-beta (ERbeta) is easily detectable in ovarian granulosa cells but is low to absent in the pituitary of the adult mouse. This distinct expression pattern for the two ERs suggests the presence of separate roles for each in the regulation of ovarian function. Herein, we definitively show that a lack of ERalpha in the hypothalamic-pituitary axis of the ERalpha-knockout (alphaERKO) mouse results in chronic elevation of serum LH and is the primary cause of the ovarian phenotype of polycystic follicles and anovulation. Prolonged treatment with a GnRH antagonist reduced serum LH levels and prevented the alphaERKO cystic ovarian phenotype. To investigate a direct role for ERalpha within the ovary, immature alphaERKO females were stimulated to ovulate with exogenous gonadotropins. Ovulatory capacity in the immature alphaERKO female was reduced compared with age-matched wild-type (14.5+/-2.9 vs. 40.6+/-2.6 oocytes/animal, respectively); however, oocytes collected from the alphaERKO were able to undergo successful in vitro fertilization. A similar discrepancy in oocyte yield was observed after superovulation of peripubertal (42 days) wild-type and alphaERKO females. In addition, ovaries from immature superovulated alphaERKO females possessed several ovulatory but unruptured follicles. Investigations of the possible reasons for the reduced number of ovulations in the alphaERKO included ribonuclease protection assays to assess the mRNA levels of several markers of follicular maturation and ovulation, including ERbeta, LH-receptor, cyclin-D2, P450-side chain cleavage enzyme, prostaglandin synthase-2, and progesterone receptor. No marked differences in the expression pattern for these mRNAs during the superovulation regimen were observed in the immature alphaERKO ovary compared with that of the wild-type. Serum progesterone levels just before ovulation were slightly lower in the alphaERKO compared with wild-type. These studies indicate that treatment of alphaERKO females with a GnRH antagonist decreased the serum LH levels to within the wild-type range and concurrently prevented development of the characteristic ovarian phenotype of cystic and hemorrhagic follicles. Furthermore, a lack of functional ERalpha within the ovary had no effect on the regulation of several genes required for follicular maturation and ovulation. However, the reduced numbers of ovulations following the administration of exogenous gonadotropins in the alphaERKO suggests an intraovarian role for ERalpha in follicular development and ovulation.

Cloning, functional characterization, and expression of a gonadotropin receptor cDNA in the ovary and testis of amago salmon (Oncorhynchus rhodurus)

A gonadotropin receptor was cloned from amago salmon (Oncorhynchus rhodurus) ovarian follicles. This receptor (sGTH-R) belongs to the glycoprotein hormone receptor family with a large extracellular and seven-transmembrane domains. Its sequence homology is highest with mammalian LH receptors. Phylogenetic analysis reveals that sGTH-R is grouped with mammalian and chicken FSH and LH receptors, but not with mammalian TSH receptors. sGTH-R is expressed dominantly in the ovary and testis. Functional characterization examined with transiently transfected mammalian cells revealed increased intracellular cAMP level when exposed to mammalian and fish gonadotropins; the most potent hormone was salmon GTH II. These results indicate that the cloned cDNA encodes a functional amago salmon GTH receptor protein.

Control of the expression of luteinizing hormone receptor by local factors in rat granulosa cells

To identify the mechanisms underlying the hormone-dependent induction and maintenance of luteinizing hormone receptor (LH-R) in rat granulosa cells, the effect of follicle-stimulating hormone (FSH) and local factors on the LH-R mRNA levels were studied. LH-R mRNA levels of the cells incubated with FSH decreased rapidly after medium removal, and readdition of FSH with the fresh medium did not restore these levels. On the other hand, 8-bromoadenosine 3,5-cyclic monophosphate significantly enhanced the expression of LH-R mRNA after medium removal, while the level of LH-R mRNA was lower than that of the cells replaced by original medium including FSH. In addition, the incubation with 8-Br-cAMP produced dose-dependent responses for LH-R mRNAs and enhanced the activity of 1379 bp of the LH-R 5'-flanking region, while the level of LH-R mRNA decreased 3 days after medium removal. Further studies were undertaken to assess the role of factors in maintaining the LH receptor once induced by FSH. Since FSH and cAMP increase follistatin production in granulosa cells, we examined the effect of follistatin on LH-R induction in the presence of activin and FSH. Activin induced LH-R in the presence of FSH significantly, and follistatin antagonized this effect in a dose-dependent manner. However, insulinlike growth factor-I (IGF-I) induced LH-R mRNA in the presence of FSH even after medium change. IGF-I might be one of the important factors that act in the medium to maintain LH-R levels in granulosa cells.

Targeted disruption of the estrogen receptor-alpha gene in female mice: characterization of ovarian responses and phenotype in the adult

Targeted disruption of the mouse estrogen receptor-alpha gene (estrogen receptor-alpha knockout; ERKO) results in a highly novel ovarian phenotype in the adult. The ERKO mouse model was used to characterize ER alpha-dependent processes in the ovary. Visualization of the ovaries of 10-, 20-, and 50-day-old wild-type (WT) and ERKO mice showed that the ERKO phenotype developed between 20 and 50 days of age. Developmental progression through the primordial, primary, and antral follicle stages appeared normal, but functional maturation of preovulatory follicles was arrested resulting in atresia or in anovulatory follicles, which in many cases formed large, hemorrhagic cysts. Corpora lutea were absent, which also indicates that the normal biochemical and mechanical processes that accomplish ovulation were compromised. Northern and ribonuclease protection analyses indicated that ERKO ovary FSH receptor (FSHR) messenger RNA (mRNA) expression was approximately 4-fold greater than in WT controls. Ovarian LH receptor (LHR) mRNA expression was also higher in the ERKO animals. Cellular localization studies by in situ hybridization analysis of ERKO ovaries showed a high level of LHR mRNA expression in the granulosa and thecal layers of virtually all the antral follicles. Ribonuclease protection analyses showed that ovarian progesterone receptor and androgen receptor mRNA expression were similar in the two groups. These results indicated that ER alpha action was not a prerequisite for LHR mRNA expression by thecal or granulosa cells or for ovarian expression of progesterone receptor mRNA. Ovarian estrogen receptor beta (ER beta) was detected immunohistochemically, was sharply compartmentalized to the granulosa cells, and was expressed approximately equally in the ERKO animals and the WT controls. In contrast, ER alpha staining was present in the thecal cells but not the granulosa cells of the WT animals. The summary findings indicate that in the adult the major cause of the ERKO phenotype is high circulating LH interacting with functional LHR of the theca and granulosa cells. These features result in a failure of the normal maturational events leading to successful ovulation and luteinization and presumably involve both hypothalamic-pituitary and intraovarian mechanisms dependent upon ER alpha action. The presence of ER beta in the granulosa cells did not rescue the phenotype of the ovary.

Progesterone can participate in down-regulation of the luteinizing hormone receptor gene expression and function in cultured murine Leydig cells

The intratesticular concentration of progesterone (P) rises up to the micromolar range during high-dose luteinizing hormone (LH)/hCG stimulation. The aim of this study was to examine whether P is involved in the concomitant down-regulation of the LH receptor (R) function. The effects were tested in a mouse Leydig tumor cell line (mLTC-1) and in Percoll-purified adult mouse Leydig cells. Pre-incubation of the mLTC-1 cells for 48 h with P (1-10 micromol/l) decreased in dose-dependent fashion their specific binding of [125I]iodo-hCG as well as the hCG-induced cAMP production (down to 65 and 40% respectively, of controls, P < 0.01). Similar effect of P on hCG-induced cAMP production was observed in adult mouse Leydig cells following a 24 h incubation in the presence of P (0.3-10 micromol/l). In addition, P treatment significantly inhibited the expression of a transiently transfected murine LHR promoter (715 or 950 bp of the 5' untranslated region)-luciferase fusion constructs in mLTC-1 cells (down to 50% of control, P < 0.01). In accordance, a 6-12 h culture in the presence of 5-10 micromol/l of P showed significant down-regulatory effects on the steady state levels of LHR-mRNA in mLTC-1 cells. These inhibitory effects of P on the LHR expression and function were mimicked by similar concentrations of cortisol, but not by testosterone or estradiol. Blocking the steroid synthesis of mLTC-1 cells with 86 micromol/l of aminoglutethimide (AMG) partially reversed the down-regulating effect of hCG on the LHR-mRNA. Moreover, a 24 h culture in the presence of AMG showed an up-regulating effect on expression of the LHR promoter-luciferase constructs, and including hCG (50 microg/l) in the culture medium enhanced this effect. Hence, in the absence of steroidogenesis, hCG up-regulates the LHR promoter expression. In conclusion, we present here a novel short-loop regulatory mechanism in murine Leydig cells where P exerts a negative effect on LHR expression and function. Since Leydig cell P production is dramatically increased during high-dose stimulation with LH/hCG, due to blockade of C21 steroid side chain cleavage, the present findings offer a function for this steroid in the LHR down-regulation.

Immunohistochemical localization of basic fibroblast growth factor (bFGF) during folliculogenesis in the human ovary

Basic fibroblast growth factor (bFGF) has been suggested to be one of the intraovarian regulators of ovarian folliculogenesis, but its localization in the human ovary remains to be determined. We examined the immunohistochemical reactivity for bFGF in the course of follicular development and corpora lutea formation in the human ovary. Pregranulosa cells in the primordial follicle were negative, but at the preantral stage both granulosa and theca cells showed weakly positive immunostaining for bFGF. In the antral follicles, both granulosa and theca interna cells showed stronger staining for bFGF with the increase in follicular diameter. In atretic follicles at various stages, granulosa cells were negative or weakly positive for bFGF, whereas luteinized theca cells showed strong immunoreactivity. In the corpora lutea during the early luteal phase, granulosa lutein cells were strongly positive for bFGF but in the late luteal phase became immunonegative. On the other hand, bFGF staining in theca lutein cells was strong throughout the course of corpora lutea formation and regression. These findings suggest that bFGF is localized not only in granulosa cells but also in theca cells, and in the latter, bFGF immunoreactivity is associated with luteinization.

GnRH receptors and GnRH endocrine effects on luteoma cells

An ovary implanted into the spleen of an ovariectomized rat develops into a luteinized tumor, growing in response to gonadotrophins. Previously, it was shown that in vivo Buserelin, a gonadotrophin-releasing hormone (GnRH) analog, inhibited tumor growth. To determine if GnRH had a direct effect on tumor cells, the presence of GnRH receptors as well as the endocrine effects of buserelin were studied on tumoral tissue. GnRH receptors were present in luteoma in similar concentrations and dissociation constant (Kd) to control estrous ovaries. In vivo treatment with buserelin did not modify luteoma GnRH receptors. In organ incubations, luteoma secreted significantly higher estradiol and lower progesterone than estrous ovaries; addition of buserelin did not modify steroid secretion. The same difference in basal steroid secretion between luteoma cells and luteal cells superovulated prepubertal ovaries was observed in cell cultures. Although luteinizing-hormone (LH)-stimulated progesterone in both kinds of cells, buserelin significantly inhibited LH-stimulated progesterone only in luteoma cells. These results describe clear differences in basal steroid secretion between tumoral and normal tissue. Furthermore, they show that luteoma possess GnRH receptors similar to those in normal ovarian tissue, and that GnRH analogs have endocrine effects on these cells. Therefore, a direct effect of buserelin on luteoma cells can be postulated.

The regulation of follicle growth: some clinical implications in reproductive endocrinology

OBJECTIVE

To review the literature concerning the regulation of follicle growth, to describe a model for unifollicular ovulation based upon the information gleaned, and to discuss some clinical implications in reproductive endocrinology underscored by this expanding knowledge.

DESIGN

Studies relating to follicular growth in lower animals and primates were reviewed. From the most pertinent articles the individual agents playing a significant role in the regulation of follicle growth were identified along with their mechanisms of action. A model for unifollicular development was proposed based upon the results of the review of these studies. Refinements in the management of some clinical problems in reproductive endocrinology were discussed based upon this model.

RESULTS

From a review of these studies it appears that in the human and primate menstrual cycle one follicle is selected because it has adequate FSH receptors when plasma FSH levels are high. This follicle becomes dominant despite falling FSH levels because of increased sensitivity of the follicle to FSH brought about by intraovarian growth regulators.

CONCLUSIONS

Improved care of patients requiring ovulation induction for differing indications should be possible with this more comprehensive knowledge of natural follicle growth.

Gonadotropin-releasing hormone overcomes follicle-stimulating hormone's inhibition of insulin-like growth factor-5 synthesis and promotion of its degradation in rat granulosa cells

The effect of a gonadotropin-releasing hormone-agonist (GnRH-a) on the synthesis of insulin-like growth factor-binding protein-5 (IGFBP-5), a physiological marker for atresia, was investigated. Granulosa cells obtained from diethylstilbestrol (DES)-treated immature female rats were cultured in serum-free medium for 72 h with GnRH-a and the conditioned media were subjected to immunoblot analysis using rat IGFBP-5 specific antibody. GnRH-a caused a dose-dependent (ED50 = 8.6 x 10(-11) M) accumulation of IGFBP-5, which migrated as 35 (non-glycosylated) and 36 kDa (glycosylated) bands under reducing conditions. A maximally effective dose of GnRH-a (10(-9) M) caused a 4-fold increase in IGFBP-5 accumulation. In contrast, increasing doses of porcine follicle-stimulating hormone (pFSH) caused a biphasic effect on IGFBP-5 accumulation. A low dose of pFSH (0.25 ng/ml) increased and higher doses of pFSH (22.5 ng/ml) decreased the 35 and 36 kDa IGFBP-5 bands. In the presence of high doses of pFSH (20.75 ng/ml), a 22 kDa band corresponding to a cleaved IGFBP-5 fragment appeared in the media. When the granulosa cells were cultured with a saturating dose of pFSH, co-addition of GnRH-a dose dependently inhibited the FSH effects (ED50 = (2.3-3.7) x 10(-10) M). The GnRH-a effects were completely blocked by co-incubation with GnRH-antagonist. IGFBP-5 mRNA accumulation levels were increased by GnRH-a in a dose dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Transcription and post-transcriptional regulation of luteotropin/chorionic gonadotropin receptor by the agonist in Leydig cells

Porcine Leydig, cultured in a chemically defined medium, express luteotropin/human chorionic gonadotropin (LH/hCG) receptor and mRNA transcripts of several sizes (7.6, 6.7, 5.6, 4.7, 4, 2.6 and 1.4 kb). Incubation of these cells with hCG results in a concentration-dependent decrease of both LH/hCG receptor number and of all mRNA transcripts with a half-maximal at 0.01 nM. Time-course analysis of the effects of maximal (1 nM) concentration of hCG on both receptor number and mRNA levels results in a lag period of about 6-8 h. Thereafter, the receptor number progressively declines to reach a low point (20% of control) at 36 h, whereas more than 80% of receptor mRNA were lost between 8-12 h after addition of the hormone. By nuclear run-on assays, we showed that hCG caused a slight reduction (13 +/- 2%) in LH/hCG receptor gene transcription, which could not explain the rapid and pronounced mRNA decline observed between 8-12 h. In fact, we estimated that hCG reduced 10-fold (from < 22 h to 2 h) the half-life of LH/hCG receptor mRNA. Both actinomycin D and cycloheximide blocked the hCG-induced decrease in both receptor number and mRNA levels. These results indicate that the main mechanism by which hCG regulates its own receptor is by inducing a decrease in the stability of its own receptor mRNA and this effect requires induction of transcription and translation, presumably leading to synthesis of a labile factor(s) which favors the degradation of LH/hCG mRNA. Most of the effects of hCG are mediated by cAMP since treatment of cells with its 8-bromo derivative leads to a similar reduction in the level of LH/hCG receptor and mRNA. Finally, the effects of hCG are reversible, since after withdrawal of the hormone there was a recovery of receptor mRNA followed by receptor number.

Epidermal growth factor enhances oocyte maturation in pigs

Epidermal Growth Factor (EGF) has been reported to stimulate nuclear maturation in porcine oocytes (Sommer et al., 1992). The objective of this experiment was to test the effect of EGF alone or in combination with gonadotropins and follicular shell coculture, on cytoplasmic maturation of oocytes in vitro. A preliminary experiment tested the effective dose of EGF for stimulation of oocyte nuclear maturation in our culture system. Nuclear maturation rates (MII%) of 67.2 +/- 4.6, 81.1 +/- 8.6, and 80.7 +/- 5.1 for oocyte complexes cultured in the presence of 0.1, 1, and 10 ng/ml EGF, respectively, were significantly higher (P < 0.05) than for oocytes cultured in the absence of EGF (18.1 +/- 9.4%). In the main experiment a 2 x 2 x 2 factorial random complete block design was used to examine the effect of EGF (1.0 ng/ml) alone or in combination with gonadotropins and follicular shell coculture on cytoplasmic maturation. Cytoplasmic maturation was evaluated by the ability of oocytes to decondense sperm nuclei after sperm penetration. EGF alone did not stimulate cytoplasmic maturation in oocytes in vitro (P > 0.05). However, EGF showed a positive interaction (P < 0.05) with gonadotropin treatment on male pronuclear formation. We conclude that EGF alone can stimulate nuclear maturation in pig oocytes, and EGF can interact with gonadotropins to enhance cytoplasmic maturation. A high level of cytoplasmic maturation of in vitro matured pig oocytes could be achieved using a combination of EGF, gonadotropin, and follicular shell supplementation to the culture environment.