Gene analysis of major signaling pathways regulated by gonadotropins in human ovarian granulosa tumor cells (KGN)†.

The female reproductive function largely depends on timing and coordination between follicle-stimulating hormone (FSH) and luteinizing hormone. Even though it was suggested that these hormones act on granulosa cells via shared signaling pathways, mainly protein kinases A, B, and C (PKA, PKB, and PKC), there is still very little information available on how these signaling pathways are regulated by each hormone to provide such differences in gene expression throughout folliculogenesis. To obtain a global picture of the principal upstream factors involved in PKA, PKB, and PKC signaling in granulosa cells, human granulosa-like tumor cells (KGN) were treated with FSH or specific activators (forskolin, SC79, and phorbol 12-myristate 13-acetate) for each pathway to analyze gene expression with RNA-seq technology. Normalization and cutoffs (FC 1.5, P ≤ 0.05) revealed 3864 differentially expressed genes between treatments. Analysis of major upstream regulators showed that PKA is a master kinase of early cell differentiation as its activation resulted in the gene expression profile that accompanies granulosa cell differentiation. Our data also revealed that the activation of PKC in granulosa cells is also a strong differentiation signal that could control "advanced" differentiation in granulosa cells and the inflammatory cascade that occurs in the dominant follicle. According to our results, PKB activation provides support for PKA-stimulated gene expression and is also involved in granulosa cell survival throughout follicular development. Taken together, our results provide new information on PKA, PKB, and PKC signaling pathways and their roles in stimulating a follicle at the crossroad between maturation/ovulation and atresia.

Clock control of mammalian reproductive cycles: Looking beyond the pre-ovulatory surge of gonadotropins.

Several aspects of the physiology and behavior of organisms are expressed rhythmically with a 24-h periodicity and hence called circadian rhythms. Such rhythms are thought to be an adaptive response that allows to anticipate cyclic events in the environment. In mammals, the circadian system is a hierarchically organized net of endogenous oscillators driven by the hypothalamic suprachiasmatic nucleus (SCN). This system is synchronized by the environment throughout afferent pathways and in turn it organizes the activity of tissues by means of humoral secretions and neuronal projections. It has been shown that reproductive cycles are regulated by the circadian system. In rodents, the lesion of the SCN results on alterations of the estrous cycle, sexual behavior, tonic and phasic secretion of gonadotropin releasing hormone (GnRH)/gonadotropins and in the failure of ovulation. Most of the studies regarding the circadian control of reproduction, in particular of ovulation, have only focused on the participation of the SCN in the triggering of the proestrus surge of gonadotropins. Here we review aspects of the evolution and organization of the circadian system with particular focus on its relationship with the reproductive cycle of laboratory rodents. Experimental evidence of circadian control of neuroendocrine events indispensable for ovulation that occur prior to proestrus are discussed. In order to offer a working model of the circadian regulation of reproduction, its participation on aspects ranging from gamete production, neuroendocrine regulation, sexual behavior, mating coordination, pregnancy and deliver of the product should be assessed experimentally.

Evolution of gonadotropin signaling on gonad development: insights from gene knockout studies in zebrafish.

Gonadal development is precisely regulated by the two gonadotropins luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Much progress on understanding the functions of LH and FSH signaling on gonad development has been achieved in the past decades, mostly from studies in mammals, especially genetic studies in both mouse and human. The functions of both LH and FSH signaling in nonmammalian species are still largely unknown. In recent years, using zebrafish, a teleost phylogenetically distant from mammals, we and others have genetically analyzed the functions of gonadotropins and their receptors through gene knockout studies. In this review, we will summarize the pertinent findings and discuss how the actions of gonadotropin signaling on gonad development have evolved during evolution from fish to mammals.

Isolation of an insulin-like peptide from the Asian malaria mosquito, Anopheles stephensi, that acts as a steroidogenic gonadotropin across diverse mosquito taxa.

Many insulin-like peptides (ILPs) have been identified in insects, yet only a few were isolated in their native form for structural and functional studies. Antiserum produced to ILP3 in Aedes aegypti was used in a radioimmunoassay to monitor the purification of an ILP from heads of adult An. stephensi and recognized the ILP in other immunoassays. The structure of the purified peptide matched that predicted for the ILP3 in this species. The native form stimulated ecdysteroid production by ovaries isolated from non-blood fed females. Synthetic forms of An. stephensi ILP3 and ILP4 similarly activated this process in a dose responsive manner. This function was first established for ILP3 and ILP4 homologs in Aedes aegypti, thus suggesting their structural and functional conservation in mosquitoes. We tested the extent of conservation by treating ovaries of An. gambiae, Ae. aegypti, and Culex quinquefasciatus with the An. stephensi ILPs, and both the native and synthetic ILP3 were stimulatory, as was the ILP4. Taken together, these results offer the first evidence for ILP functional conservation across the Anophelinae and Culicinae subfamilies.

The roles of kisspeptin and gonadotropin inhibitory hormone in stress-induced reproductive disorders.

Several kinds of stress suppress the hypothalamic-pituitary-gonadal (HPG) axis and reproductive behavior in humans and animals. These changes can eventually cause diseases and disorders, such as amenorrhea and infertility. In previous studies, it has been shown that stress-related factors, e.g., corticotropin-releasing hormone, cortisol, and pro-inflammatory cytokines, promote the stress-induced suppression of the HPG axis. However, these mechanisms are not sufficient to explain how stress suppresses HPG axis activity, and it has been suggested that some other factors might also be involved. In the early 21st century, novel neuroendocrine peptides, kisspeptin and gonadotropin inhibitory hormone (GnIH)/RFamide-related peptide 3 (RFRP-3), which directly regulate GnRH/gonadotropin synthesis and secretion, were newly discovered. Growing evidence indicates that kisspeptin and GnIH/RFRP-3 play pivotal roles in the stress-induced disruption of the HPG axis and reproductive behavior in addition to their physiological functions. This review summarizes what is currently known about the roles of kisspeptin and GnIH/RFRP-3 in stress-induced reproductive disorders.

The gonadotropin-inhibitory hormone (Lpxrfa) system's regulation of reproduction in the brain-pituitary axis of the zebrafish (Danio rerio).

Gonadotropin-inhibitory hormone (GNIH) was discovered in quail with the ability to reduce gonadotropin expression/secretion in the pituitary. There have been few studies on GNIH orthologs in teleosts (LPXRFamide (Lpxrfa) peptides), which have provided inconsistent results. Therefore, the goal of this study was to determine the roles and modes of action by which Lpxrfa exerts its functions in the brain-pituitary axis of zebrafish (Danio rerio). We localized Lpxrfa soma to the ventral hypothalamus, with fibers extending throughout the brain and to the pituitary. In the preoptic area, Lpxrfa fibers interact with gonadotropin-releasing hormone 3 (Gnrh3) soma. In pituitary explants, zebrafish peptide Lpxrfa-3 downregulated luteinizing hormone beta subunit and common alpha subunit expression. In addition, Lpxrfa-3 reduced gnrh3 expression in brain slices, offering another pathway for Lpxrfa to exert its effects on reproduction. Receptor activation studies, in a heterologous cell-based system, revealed that all three zebrafish Lpxrfa peptides activate Lpxrf-R2 and Lpxrf-R3 via the PKA/cAMP pathway. Receptor activation studies demonstrated that, in addition to activating Lpxrf receptors, zebrafish Lpxrfa-2 and Lpxrfa-3 antagonize Kisspeptin-2 (Kiss2) activation of Kisspeptin receptor-1a (Kiss1ra). The fact that kiss1ra-expressing neurons in the preoptic area are innervated by Lpxrfa-ir fibers suggests an additional pathway for Lpxrfa action. Therefore, our results suggest that Lpxrfa may act as a reproductive inhibitory neuropeptide in the zebrafish that interacts with Gnrh3 neurons in the brain and with gonadotropes in the pituitary, while also potentially utilizing the Kiss2/Kiss1ra pathway.

Influence of gonadotropins on ovarian follicle growth and development in vivo and in vitro.

Gonadotropins are the key regulators of ovarian follicles development. They are applied in therapeutic practice in assisted reproductive technology clinics. In the present review we discuss the basic gonadotropic hormones - recombinant human follicle-stimulating hormone, its derivatives, luteinizing hormone and gonadotropin serum of pregnant mares, their origin, and application in ovarian follicle systems in in vitro culture systems.

A Prolactin Family Paralog Regulates Placental Adaptations to a Physiological Stressor.

The prolactin (PRL) family of hormones and cytokines participates in the regulation of optimal reproductive performance in the mouse and rat. Members of the PRL family are expressed in the anterior pituitary, uterus, and/or placenta. In the present study, we investigated the ontogeny of PRL family 7, subfamily b, member 1 (PRL7B1; also called PRL-like protein-N, PLP-N) expression in the developing mouse placenta and established a mouse model for investigating the biological function of PRL7B1. Transcripts for Prl7b1 were first detected on Gestation Day (d) 8.5. From gestation d8.5 through d14.5, Prl7b1 was expressed in trophoblast cells residing at the interface between maternal mesometrial decidua and the developing placenta. On gestation d17.5, the predominant cellular source of Prl7b1 mRNA was migratory trophoblast cells invading into the uterine mesometrial decidua. The Prl7b1 null mutant allele was generated via replacement of the endogenous Prl7b1 coding sequence with beta-galactosidase (LacZ) reporter and neomycin cassettes. The mutant Prl7b1 allele was successfully passed through the germline. Homozygous Prl7b1 mutant mice were viable and fertile. Under standard animal housing conditions, Prl7b1 had undetectable effects on placentation and pregnancy. Hypoxia exposure during pregnancy evoked adaptations in the organization of the wild-type placenta that were not observed in Prl7b1 null placentation sites. In summary, PRL7B1 is viewed as a part of a pathway regulating placental adaptations to physiological stressors.

The differentiation of mammalian ovarian granulosa cells – living in the shadow of cellular developmental capacity.

The mammalian cumulus-oocyte complex (COCs) promotes oocyte growth and development during long stages of folliculogenesis and oogenesis. Before ovulation, the follicle is formed by a variety of fully differentiated cell populations; cumulus cells (CCs) that tightly surround the female gamete, granulosa cells (GCs) and theca cells (TCs) which build the internal and external mass of the follicular wall. It is well documented that CCs surrounding the oocyte are necessary for resumption of meiosis and full maturation of the gamete. However, the role of the granulosa cells in acquisition of MII stage and/or full fertilization ability is not yet entirely known. In this article, we present an overview of mammalian oocytes and their relationship to the surrounding cumulus and granulosa cells. We also describe the processes of GCs differentiation and developmental capacity. Finally, we describe several markers of mammalian GCs, which could be used for positive identification of isolated cells. The developmental capacity of oocytes and surrounding somatic cells – a “fingerprint” of folliculogenesis and oogenesis.

Live birth rates after modified natural cycle compared with high-dose FSH stimulation using GnRH antagonists in poor responders.

STUDY QUESTION: Do live birth rates differ between modified natural cycles (MNCs) and cycles using high-dose follicle stimulating hormone (HDFSH) with gonadotrophin-releasing hormone (GnRH) antagonist in poor responder patients? SUMMARY ANSWER: Live birth rates are significantly higher in MNC compared with HDFSH GnRH antagonist cycles in poor responder patients. WHAT IS KNOWN ALREADY: Previous data on the efficiency of MNC in poor responders are very limited and suggest that MNC in vitro fertilization (IVF) does not offer a realistic solution for parenthood in these patients, since live birth rates are disappointingly low. To date, no studies exist comparing MNC with HDFSH stimulation protocols in poor responders. STUDY DESIGN, SIZE, DURATION: The present retrospective study included 161 MNCs (106 women in the MNC group) and 164 HDFSH antagonist cycles (136 women in the HDFSH group) performed between January 2008 and December 2013 at Eugonia Assisted Reproduction Unit. The patients included in the study had to fulfill the Bologna criteria for the definition of poor ovarian response. PARTICIPANTS/MATERIALS, SETTING, METHODS: Irrespective of their age, poor responder patients should have a diminished ovarian reserve as shown by low antral follicle count (≤5) and increased basal FSH (>12 IU/l), and one or more previous failed IVF cycles in which ≤3 oocytes were retrieved using a high gonadotrophin dose. Analysis was performed by adjusting for the non-independence of the data. MAIN RESULTS AND THE ROLE OF CHANCE: The probability of live birth was significantly higher in the MNC when compared with the HDFSH group (OR: 4.01, 95% CI: 1.14-14.09), after adjusting for basal FSH, female age and cause of infertility, variables which were shown to be associated with the probability of live birth in univariable analysis. MNCs were characterized by significantly lower total gonadotrophin dose (490.0 ± 35.2 IU versus 2826.1 ± 93.4 IU, P < 0.001), lower estradiol concentrations (237.5 ± 12.3 pg/ml versus 487.3 ± 29.8 pg/ml, P < 0.001), fewer follicles present on the day of hCG (1.9 ± 0.1 versus 3.2 ± 0.2, P < 0.001), fewer oocytes retrieved (1.1 ± 0.01 versus 2.4 ± 0.1, P < 0.001), fewer oocytes fertilized (0.7 ± 0.1 versus 1.4 ± 0.1, P < 0.001), fewer embryos transferred (0.7 ± 0.1 versus 1.4 ± 0.1, P < 0.001), fewer good-quality embryos available (0.5 ± 0.1 versus 0.8 ± 0.1, P < 0.001) and fewer good-quality embryos transferred (0.5 ± 0.05 versus 0.8 ± 0.1, P < 0.001) compared with the HDFSH group. However, the proportion of cycles with at least one good-quality embryo transferred per started cycle was similar between the two groups compared (62.5, 95% CI: 52.7-72.3 versus 62.7, 95% CI: 53.0-72.5, respectively). LIMITATIONS, REASONS FOR CAUTION: This is a retrospective comparison between MNC and HDFSH GnRH antagonist protocols in a large group of poor responder patients according to the Bologna criteria. Although the two groups compared were not imbalanced for all basic characteristics and multivariate analysis were performed to adjust for all known confounders, it cannot be excluded that non-apparent sources of bias might still be present. Future randomized controlled trials are necessary to verify the present findings. WIDER IMPLICATIONS OF THE FINDINGS: Both MNC and HDFSH antagonist protocols offer very low chances of live birth in poor responder patients who fulfill the Bologna criteria. However, MNC-IVF is a more patient-friendly approach, with a higher probability of live birth compared with the HDFSH antagonist protocol. In this respect, the current data might be of help in counseling such patients, who do not wish to undergo oocyte donation, prior to abandoning treatment altogether and/or proceeding to adoption. STUDY FUNDING/COMPETING INTERESTS: No funding was obtained. C.A.V. reports personal fees and non-financial support from Merck, Sharp and Dome, personal fees and non-financial support from Merck Serono, personal fees and non-financial support from IPSEN Hellas S.A. outside the submitted work. B.C.T. reports grants from Merck Serono, grants from Merck Sharp & Dohme, personal fees from IBSA, personal fees from Merck Sharp & Dohme and personal fees from Ovascience outside the submitted work .

The involvement of gonadotropins and gonadal steroids in the ovulatory dysfunction of the potamodromous Salminus hilarii (Teleostei: Characidae) in captivity.

Potamodromous teleosts that require migration to reproduce show dysfunctions that block ovulation and spawning while in captivity. To understand the physiological basis of these reproductive dysfunctions, follicle-stimulating hormone b subunit (fshb) and luteinizing hormone b subunit (lhb) gene expression analyses by real-time quantitative PCR, together with measurements of estradiol (E 2), 17α-hydroxyprogesterone (17α-OHP) and 17α,20ß-dihydroxy-4-pregnen-3-one (17α,20ß-DHP) levels, were carried out throughout the reproductive cycle of the potamodromous Salminus hilarii. The following reproductive stages were evaluated in captive and wild females: previtellogenic (PV), advanced maturation/mature (AM) and regression/spent (REG/SPENT). In the wild females, fshb expression decreased from the PV to the AM stage, and the opposite pattern was detected for E 2, which increased from the PV to the AM stage. fshb was expressed at lower levels in captive than in wild females, and this difference did not change during the reproductive cycle. lhb expression also increased from the PV to the AM stage in both groups, but the wild females at the AM and REG/SPENT stages showed higher lhb expression levels than the captive females. The concentrations of 17α-OHP did not change during the reproductive cycle, and the levels were higher in the captive than in the wild females at all reproductive stages. 17α,20ß-DHP levels did not change between wild and captive females. However, in captive females, the transition from PV to AM stage was followed by an increase in 17α,20ß-DHP levels. These data indicate that dysfunctions in the gonadotropins and steroids synthesis pathways cause the ovulation failure in captive S. hilarii.

An integrative overview of the role of gonadotropin-inhibitory hormone in behavior: applying Tinbergen's four questions.

The integration of various fields of investigation is of key importance to fully comprehending endocrine function. Here, I enact the theoretical framework of Nikolaas Tinbergen's four questions for understanding behavior to help bridge the wide gap that exists between our relatively reductionist molecular knowledge of a particular neurohormone, gonadotropin-inhibitory hormone (GnIH), and its place in animal behavior. Hypothalamic GnIH, upon its discovery in 2000, was so named because of its inhibitory effect on the release of the gonadotropins, luteinizing hormone (LH) and follicle stimulating hormone (FSH), from the pituitary. Because gonadotropins are necessary for reproduction, this finding stimulated questions about the functional significance of GnIH in reproduction and sexual behavior. After over a decade of research, invaluable knowledge has been gained regarding the mechanistic attributes of GnIH (mammalian homolog, RFamide-related peptide (RFRP)) in a variety of vertebrate species. However, many questions remain regarding the effect of the environment on GnIH and the subsequent effects of GnIH on behavior. I review the role of GnIH in shaping behavior using the framework of Tinbergen's four questions of mechanism, ontogeny, function and phylogeny. The studies I review were conducted in various species of mammals, birds, and in one species of fish. Because GnIH can play a role in mediating behaviors such as those important for reproduction, sociality, feeding, and the stress response in a variety of species, an integrative approach to the study of GnIH will help provide a multipronged schema for answering questions of GnIH function. By using the framework highlighted by Tinbergen's four questions, we will deepen and enhance our knowledge of the role of hormones in behavior from the point of view of the mechanisms involved.

In vitro induction of oocyte maturation and steroidogenesis by gonadotropins, insulin, calcitonin and growth factor in an estuarine flat head grey mullet, Mugil cephalus L.

In this article, an in vitro investigation was carried out to ascertain the roles of hormones and growth factor in the inductions of oocyte maturation and steroidogenesis of the postvitellogenic follicles in an Indian estuarine grey mullet, Mugil cephalus L. Oocyte maturation was evaluated by scoring the germinal vesicle breakdown (GVBD) percent of the postvitellogenic follicles. All the sex [17α,20ß-dihydroxy-4-pregnane-3-one (DHP), estradiol 17ß (E2), progesterone (P), 17α-OH progesterone (17-OH-P) and testosterone] and other [bovine-insulin and salmon-calcitonin, human chorionic gonadotropin (hCG), luteinizing hormone (LH) or hCG+DHP] hormones and insulin-like growth factor-I (IGF-I) significantly increased GVBD% in 9 h culture. DHP had a maximum effect (75 %) compared to other effectors. Some effectors (hCG: 82.14 %, LH: 78.94 %, hCG plus DHP: 81.81 %, E2: 80 % and IGF-I: 74.19 %) including DHP (79 %) further increased GVBD% in 15-h culture. All the hormones (except DHP) and IGF-I increased DHP, E2 and testosterone productions by the postvitellogenic ovarian follicles in vitro. DHP and testosterone productions were increased with the increase of incubation time from 9 h through 15 h. E2 production was not further increased beyond 12 h. DHP production was highest by hCG compared to other effectors. The hCG of all the test compounds was most effective in both the induction of GVBD% and steroid production. DHP is the most potent inducer of oocyte maturation in Indian estuarine flat head grey mullet. Involvement of estrogen in mullet oocyte maturation is indicated. hCG, like DHP, is equally potent and induces oocyte maturation via DHP production in vitro. hCG with DHP has synergistic action on oocyte maturation in mullet ovary. Interplay of several hormones (hCG, LH, and probably E2 and testosterone) and IGF-I on oocyte maturation is suggested in the mullet.

Testicular dmrt1 is involved in the sexual fate of the ovotestis in the protandrous black porgy.

In hermaphroditic fish, the ovotestis can respond to external stimuli so that only one type of gonadal tissue (either ovarian or testicular tissue) will remain reproductively active and the other will recede to a rudimentary stage. However, the molecular mechanism for sexual fate determination is still poorly understood in hermaphroditic fish. In the present study, we examined whether sexual fate determination with respect to testis development is due to differential expression of dmrt1. Expression of dmrt1 was limited to the spermatogonia-surrounding cells (Sertoli cells) throughout testis development. Testicular dmrt1 was differentially expressed in fish (black porgy [Acanthopagrus schlegeli Bleeker]) depending on if fish were destined to be female or male. Expression of dmrt1 in Sertoli cells did not require germ cell factors with busulfan treatment. To examine the role of dmrt1, we used virus-based RNA interference. Deficiency of dmrt1 resulted in a reduced number of germ cells in the testis and stimulated a male-to-female sex change. Higher serum luteinizing hormone levels were detected in 2(+)- to 3-yr-old male fish as compared to sex-changing female fish. Furthermore, we showed that fish treated in vivo with gonadotropin-releasing hormone (Gnrh) and fish treated in vitro with gonadotropin (Gth) had higher dmrt1 expression in the testis, suggesting that these endocrine factors may affect the male-to-female sex change. Therefore, our data suggest that dmrt1 plays a key role in initial testis differentiation and in later maintenance of male development. We show, to our knowledge for the first time, the functions of dmrt1 in hermaphroditic fish, which indicate that male-phase maintenance may be regulated by the brain-pituitary-gonadal axis via the Gnrh-Gth-Dmrt1 axis.

Inhibition of follicular development induced by chronic unpredictable stress is associated with growth and differentiation factor 9 and gonadotropin in mice.

Chronic psychosocial stress negatively affects ovarian function. Ovarian follicular development is regulated by both pituitary-derived gonadotropins and intraovarian regulatory factors. To date, the suppressive effects of chronic stress on the ovary have been observed to be manifested mainly as an inhibition of gonadotropin release. It is not clear whether there are any other intraovarian regulatory mechanisms involved in this process. Growth and differentiation factor 9 (GDF9) is an important, oocyte-specific paracrine regulator required for follicular development. In this study, the chronic unpredictable mild stress model was used to produce psychosocial stress in mice. The number of different developmental stages of follicles was counted on ovarian sections stained with hematoxylin and eosin. Real-time PCR and Western blotting were used to detect the mRNA and protein levels, respectively, of GDF9. The results show that chronic unpredictable stress inhibits follicular development, increases follicular atresia, and suppresses GDF9 expression. Exogenous gonadotropin treatment partly restores the repressed antral follicular development, but has no effect on the repressed secondary follicular development associated with chronic stress. Treatment with recombinant GDF9 restores secondary follicular development. Cotreatments with GDF9 and gonadotropins restore both secondary and antral follicular development in stressed mice. These findings demonstrate that inhibition of follicular development induced by chronic unpredictable stress is associated with GDF9 and gonadotropin.

Photoperiod-gonadotropin mismatches induced by treatment with acyline or FSH in Siberian hamsters: impacts on ovarian structure and function.

Many seasonal breeders time their reproductive efforts to specific times of the year to ensure adequate resources for the production and care of young. For long-day (LD) breeders, females born before the summer solstice (LDs) reach sexual maturity quickly and often breed that same year, whereas females born after the summer solstice (short days (SDs)) may delay reproductive development to the following spring when environmental conditions are favorable for reproduction. In Siberian hamsters, development in SD is associated with structural and functional differences in the ovary compared with females held in LD, including a greater number of primordial follicles and an abundance of hypertrophied granulosa cells (HGCs), which are immunoreactive for anti-Müllerian hormone. The goal of this study was to determine whether SD-induced gonadotropin suppression is responsible for these phenotypic differences. Gonadotropin levels were suppressed in LD hamsters using the GNRH antagonist acyline. Conversely, to determine whether the SD ovarian phenotype is completely reversed by gonadotropin stimulation, recombinant human FSH (rhFSH) was administered. Our treatments were successful in mimicking FSH concentrations of the opposite photoperiod, but they did not produce a comparable change in the ovarian phenotype. Most notable was the lack of HGCs in the ovaries of acyline-treated LD females. Similarly, HGCs were maintained in the ovaries of SD females treated with rhFSH. Our data suggest that gonadotropins alone do not account for the SD ovarian phenotype. Future studies will determine whether SD-induced changes in other factors underlie these phenotypic changes.

Gonadotropins and ovarian cancer.

Ovarian epithelial cancer (OEC) accounts for 90% of all ovarian cancers and is the leading cause of death from gynecological cancers in North America and Europe. Despite its clinical significance, the factors that regulate the development and progression of ovarian cancer are among the least understood of all major human malignancies. The two gonadotropins, FSH and LH, are key regulators of ovarian cell functions, and the potential role of gonadotropins in the pathogenesis of ovarian cancer is suggested. Ovarian carcinomas have been found to express specific receptors for gonadotropins. The presence of gonadotropins in ovarian tumor fluid suggests the importance of these factors in the transformation and progression of ovarian cancers as well as being prognostic indicators. Functionally, there is evidence showing a direct action of gonadotropins on ovarian tumor cell growth. This review summarizes the key findings and recent advances in our understanding of these peptide hormones in ovarian cancer development and progression and their role in potential future cancer therapy. We will first discuss the supporting evidence and controversies in the "gonadotropin theory" and the use of animal models for exploring the involvement of gonadotropins in the etiology of ovarian cancer. The role of gonadotropins in regulating the proliferation, survival, and metastasis of OEC is next summarized. Relevant data from ovarian surface epithelium, which is widely believed to be the precursor of OEC, are also described. Finally, we will discuss the clinical applications of gonadotropins in ovarian cancer and the recent progress in drug development.

Synthesis and secretion of gonadotropins including structure-function correlates.

The synthesis and secretion of the gonadotropic hormones involves coordination of signal transduction, gene expression, protein translation, post-translational folding and modification and finally secretion. The production of biologically active gonadotropin thus requires appropriately folded and glycosylated subunits that assemble to form the heterodimeric hormone. Here we overview recent literature on regulation of gonadotropin subunit gene expression and current understanding of the assembly and secretion of biologically active gonadotropic hormones. Finally, we discuss the therapeutic potential of understanding glycosylation function towards designing new forms of gonadotropins based on observations of physiologically relevant parameters such as age related glycosylation changes.

Animal models for aberrations of gonadotropin action.

During the last two decades a large number of genetically modified mouse lines with altered gonadotropin action have been generated. These mouse lines fall into three categories: the lack-of-function mice, gain-of-function mice, and the mice generated by breeding the abovementioned lines with other disease model lines. The mouse strains lacking gonadotropin action have elucidated the necessity of the pituitary hormones in pubertal development and function of gonads, and revealed the processes from the original genetic defect to the pathological phenotype such as hypo- or hypergonadotropic hypogonadism. Conversely, the strains of the second group depict consequences of chronic gonadotropin action. The lines vary from those expressing constitutively active receptors and those secreting follicle-stimulating hormone (FSH) with slowly increasing amounts to those producing human choriogonadotropin (hCG), amount of which corresponds to 2000-fold luteinizing hormone (LH)/hCG biological activity. Accordingly, the phenotypes diverge from mild anomalies and enhanced fertility to disrupted gametogenesis, but eventually chronic, enhanced and non-pulsatile action of both FSH and LH leads to female and male infertility and/or hyper- and neoplasias in most of the gonadotropin gain-of-function mice. Elevated gonadotropin levels also alter the function of several extra-gonadal tissues either directly or indirectly via increased sex steroid production. These effects include promotion of tumorigenesis in tissues such as the pituitary, mammary and adrenal glands. Finally, the crossbreedings of the current mouse strains with other disease models are likely to uncover the contribution of gonadotropins in novel biological systems, as exemplified by the recent crossbreed of LHCG receptor deficient mice with Alzheimer disease mice.