Concerted stimulation of rat granulosa cell deoxyribonucleic acid synthesis by sex steroids and follicle-stimulating hormone

Arachidonic Acid in Follicular Fluid of PCOS Induces Oxidative Stress in a Human Ovarian Granulosa Tumor Cell Line (KGN) and Upregulates GDF15 Expression as a Response

Polycystic ovarian ovary syndrome (PCOS) is the main cause of ovulatory infertility and a common reproductive endocrine disease of women in reproductive age. In addition, nearly half of PCOS patients are associated with obesity, and their total free fatty acids tend to increase. Arachidonic acid (AA) is a polyunsaturated fatty acid. Oxidation products of AA reacting with various enzymes[cyclooxygenases (COX), lipoxygenases (LOX), cytochrome P450s (CYP)] can change cellular mitochondrial distribution and calcium ion concentration, and increase reactive oxygen species (ROS) production. In this study, we analyzed the follicular fluid fatty acids and found higher levels of C20:4n6 (AA) in PCOS patients than in normal control subjects. Also, to determine whether AA induces oxidative stress (OS) in the human ovarian granulosa tumor cell line (KGN) and affects its function, we treated KGN cells with or without reduced glutathione (GSH) and then stimulated them with AA. The results showed that AA significantly reduced the total antioxidant capacity (TAC) and activity of antioxidant enzymes and increased the malondialdehyde (MDA), ROS and superoxide anion(O_2-)levels in KGN cells. In addition, AA was also found to impair the secretory and mitochondrial functions of KGN cells and induce their apoptosis. We further investigated the downstream genes affected by AA in KGN cells and its mechanism of action. We found that AA upregulated the expression of growth differentiation factor 15 (GDF15), which had a protective effect on inflammation and tissue damage. Therefore, we investigated whether AA-induced OS in KGN cells upregulates GDF15 expression as an OS response.Through silencing of GDF15 and supplementation with recombinant GDF15 (rGDF15), we found that GDF15, expressed as an OS response, protected KGN cells against AA-induced OS effects, such as impairment of secretory and mitochondrial functions and apoptosis. Therefore, this study suggested that AA might induce OS in KGN cells and upregulate the expression of GDF15 as a response to OS.

Co-culture with peritoneum mesothelial stem cells supports the in vitro growth of mouse ovarian follicles

The important roles played by the ovarian microenvironment and cell interactions in folliculogenesis suggest promising approaches for in vivo growth of ovarian follicles using appropriate scaffolds containing suitable cell sources. In this study, we have investigated the growth of early preantral follicles in the presence of decellularized mesenteric peritoneal membrane (MPM), peritoneum mesothelial stem cells (PMSCs), and conditioned medium (CM) of PMSCs. MPM of mouse was first decellularized; PMSCs were isolated from MPM and cultured and their conditioned medium (CM) was collected. Mouse follicles were separated into four groups: (1) culture in base medium (control), (2) culture in decellularized MPM (DMPM), (3) co-culture with PMSCs (Co-PMSCs), and (4) culture in CM of PMSCs (CM-PMSCs). Qualitative and quantitative assessments were performed to evaluate intact mesenteric peritoneal membrane (IMPM) as well as decellularized ones. After culturing the ovarian follicles, follicular and oocyte diameter, viability, eccentric oocyte percentage, and estradiol hormone amounts were evaluated. Quantitative and qualitative evaluations confirmed removal of cells and retention of the essential fibers in MPM after the decellularization process. Follicular parameters showed that Co-PMSCs better support in vitro growth and development of ovarian follicles than the other groups. The eccentric rate and estradiol production were statistically higher for the Co-PMSCs group than for the CM-PMSCs and control groups. Although the culture of early preantral follicles on DMPM and CM-PMSCs could improve in vitro follicular growth, co-culture of follicles with PMSCs showed even greater improvements in terms of follicular growth and diameter.

Tissue Engineered Human Amniotic Membrane Application in Mouse Ovarian Follicular Culture

Since folliculogenesis requires a powerful cell-matrix interaction, natural scaffolds seem to be needed for follicular culture. Human amniotic membrane (HAM) offers promise as a support of in vitro ovarian follicular culture. HAM was decellularized with trypsin and EDTA. DNA and histology assays were performed to determine the elimination rate of genomic components. Cyto-biocompatibility of decellular AM (DAM) was verified by the cell viability (MTT) test. The small parts of intact amniotic membrane (IAM) and DAM were coated on the bottom of 96-well and each well was filled with 150 µL of base medium. Mouse primary-secondary (PS) follicles were separated to three groups: 1-culture in base medium (Control), 2-culture on IAM and 3-culture on DAM. Follicular size, morphology, viability, estradiol production and genes expression were evaluated and IAM group showed better growth and development in follicle culture. The viability rate and estradiol production in both experimental groups were statistically higher than the Control. Gdf9, Bmp15 and Cx37 were found to have higher expression levels in IAM group. Also, maximum apoptotic and survival indexes were determined in Control and IAM groups, respectively. Finally, IAM provides a better protective environment for mouse PS follicular culture that can reduce apoptosis level.

17β-Estradiol is critical for the preovulatory induction of prostaglandin E(2) synthesis in mice

Aromatase-deficient (ArKO) mice are totally anovulatory due to insufficient estrogen production. However, sequential administrations of high doses of 17β-estradiol (E2) and gonadotropins were found to induce ovulation in these mice. Here, we examined how the ovulatory stimulation for ArKO mice alters the expressions of genes related to prostaglandin (PG) E(2) metabolism and ovarian contents of PGE(2), as PGE(2) is one of the critical mediators of ovulatory induction. The ovulatory stimulation significantly increased mRNA expressions of prostaglandin-endoperoxide synthase 2, PGE(2) receptor type 4 and sulfotransferase family 1E, member 1, in preovulatory ArKO ovaries. In contrast, it suppressed the mRNA expression of 15-hydroxyprostaglandin dehydrogenase. Furthermore, significant elevation in the PGE(2) contents was detected in the preovulatory ovaries of ArKO mice after stimulation with E2 plus ovulatory doses of gonadotropins. Thus, these analyses demonstrate a requirement of E2 for the preovulatory enhancement of PGE(2) synthesis, leading to future success in ovulation.

Bovine oocytes in secondary follicles grow in medium containing bovine plasma after vitrification

There has been no culture system that supports the growth of bovine oocytes for more than 2 weeks. In the present study, bovine secondary follicles were cultured for 4 weeks, and the effects of supplemented protein components and FSH in the culture medium on the growth of the oocytes were examined. The effect of vitrification of secondary follicles on the subsequent oocyte growth was also examined. Secondary follicles (150 to 200 µm in diameter) containing growing oocytes (approximately 60 µm in diameter) were dissected from ovaries and cultured in a medium supplemented with FSH (0, 25 or 50 ng/ml) and one of the following four kinds of protein components: bovine serum albumin (BSA), bovine plasma (BPL), fetal calf serum (FCS) and bovine follicular fluid (BFF). In BSA- and BPL-supplemented media with 0 or 25 ng/ml FSH, more than 50% of follicles showed no degenerative signs during culture, and oocytes significantly increased in size after 4 weeks (P<0.05). Higher percentages of granulosa cell-enclosed oocytes were recovered from the follicles cultured in BPL-supplemented media with 0 and 25 ng/ml FSH, and the oocytes grew to 90 µm or more in diameter. In FCS- and BFF-supplemented media, FSH increased the numbers of degenerating follicles. Next, vitrified-warmed secondary follicles were cultured in BPL-supplemented medium. One third of the follicles showed no degenerative signs, and the oocytes increased in diameter to 88.8 ± 3.1 µm after 4 weeks of culture. These results suggest that a BPL-supplemented medium supports oocyte growth in bovine secondary follicles for 4 weeks, even after vitrification and warming of the follicles.

Exposing cultured mouse ovarian follicles under increased gonadotropin tonus to aromatizable androgens influences the steroid balance and reduces oocyte meiotic capacity

Acquisition of oocyte developmental competence relies on the well-controlled events accompanying antral follicular development. Elevated basal androgen levels, as in PCOS, potentially affect oocyte quality. Current experiments in an in vitro follicle bioassay studied dose-effects of androstenedione and testosterone on FSH and hCG stimulated antral follicle growth and meiotic maturation. The addition of either androgens altered follicle's endogenous production of androstenedione, testosterone, estradiol, and progesterone and affected the oocyte's capacity to resume meiosis. Exposure to 200 nM androstenedione induced an increased production of testosterone and estradiol. Exposure to a concentration of ≥200 nM testosterone induced elevated levels of estradiol and progesterone. Significant dose-dependent negative effects on polar body extrusion were seen at concentrations of ≥200 nM of either androgen. In addition, chromosome displacement on the metaphase plate was observed in oocytes obtained from androstenedione-treated follicles. Follicles exposed to a combination of 25 mIU/ml FSH and 3 mIU/ml hCG and elevated aromatizable androgens altered the steroid production profile, affected the follicular development and impaired oocyte meiotic competence.

Functional AR signaling is evident in an in vitro mouse follicle culture bioassay that encompasses most stages of folliculogenesis

Androgens have distinct physiological functions within the ovary. The biological action of androgens is primarily exerted through transcriptional regulation by the nuclear androgen receptor (AR), but the molecular cascades governed by AR remain largely unknown. At present, there is imminent concern that environmental man-made chemicals with antiandrogenic properties, among others, are capable of modulating hormonal responses, thereby interfering with normal physiological processes that are critical to fertility. In the present study, we aimed to further characterize a standardized and reproducible follicle culture system in terms of AR expression during in vitro folliculogenesis to be able to use it as a bioassay to study effects of antiandrogens on follicular and oocyte growth, steroid secretion profile, and oocyte meiotic maturation capacity. Immunohistochemical analysis revealed that cytoplasmic AR protein was translocated to the nucleus of granulosa and theca cells in response to endogenous androgen production in theca cells during preantral follicular development. During the antral phase in vitro, AR was differentially expressed in mural and cumulus cells, implying an oocyte-mediated regulation. Treatment of follicles with hydroxyflutamide or bicalutamide, two model antiandrogenic compounds, resulted in reduced follicular growth during the preantral phase, altered steroidogenic environment, and arrest in oocyte meiotic maturation in response to human chorionic gonadotropin. Androgen receptor expression in the culture model corresponded well to what is described in vivo, and this system revealed several ovarian functions targeted by AR antagonists that can be further investigated using more in-depth molecular techniques.

Interaction between the aryl hydrocarbon receptor and transforming growth factor-beta signaling pathways: evidence of an asymmetrical relationship in rat granulosa cells

The aryl hydrocarbon receptor (AHR) mediates toxic responses to environmental contaminants and plays pivotal physiological roles in various biological processes as well, particularly in ovarian function. It is well documented that expression and function of the AHR is negatively regulated by transforming growth factor-beta (TGF-beta) in many cell types. In addition, several studies indicate that AHR activity inhibits TGF-beta expression and function in some systems. However, the interplay between these two signals is highly dependent upon the cell type being studied, precluding a generalization about the outcome of such interaction. Therefore, the goal of the present study was to determine the effect of TGF-beta on AHR expression and activation in granulosa cells, an ovarian cell type where the growth factor is mitogenic and AHR activation has been associated with promotion of proliferation as well. In addition, we conducted experiments aimed at evaluating the effect of AHR ligands on TGF-beta action in our system. Results presented herein demonstrate that AHR expression is not regulated by TGF-beta in rat granulosa cells, neither at the mRNA level nor at the protein level. Moreover, we find that the growth factor does not alter the transcriptional function of the AHR. Conversely, we show that activation of AHR by an agonist deregulates TGF-beta function in granulosa cells, inhibiting its transcriptional activity and its mitogenic action. The described one-sided interplay between TGF-beta and AHR signaling pathway may help provide a mechanistic explanation to some of the physiological outcomes of AHR or TGF-beta activation in granulosa cells.

Regulation of Aryl Hydrocarbon Receptor Expression in Rat Granulosa Cells1

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates most of the toxic and endocrine-disruptive actions of aromatic compounds in the ovary. Paradoxically, this receptor has been shown to play important roles in normal female reproductive function as well. Although knowledge of AHR expression regulation in the ovary is of crucial significance to understand the receptor biology and its function in reproductive physiology, there are only limited data in this area. The purpose of the present study was to establish the possible regulation that AHR might undergo in ovarian cells. Here we show that the hormones FSH and estradiol are able to reduce AHR protein and transcript levels in granulosa cells in a way that parallels the changes observed in ovarian tissue across the rat estrous cycle. These findings suggest that estradiol and FSH would be cycle-associated endogenous modulators of AHR expression. In addition, we show that in granulosa cells the receptor is rapidly downregulated via proteasomal degradation following treatment with AHR ligands. However, prolonged treatment with an agonist caused an increase in Ahr mRNA levels. These actions would constitute a regulatory mechanism that both attenuates AHR signal rapidly and replenishes the cellular receptor pool in the long term. In conclusion, our results indicate that AHR expression is regulated by classical hormones and by its own ligands in granulosa cells.

The role of steroids in follicular growth

The steroidogenic pathway within the ovary gives rise to progestins, androgens and oestrogens, all of which act via specific nuclear receptors to regulate reproductive function and maintain fertility. The role of progestins in follicular growth and development is limited, its action confined largely to ovulation, although direct effects on granulosa cell function have been reported. Consistent with these findings, progesterone receptor knockout mice are infertile because they cannot ovulate. Androgens have been shown to promote early follicular growth, but also to impede follicular development by stimulating atresia and apoptosis. The inability of androgens to transduce a signal in mice lacking androgen receptors culminates in reduced fertility. Oestrogens are known to exert effects on granulosa cell growth and differentiation in association with gonadotrophins. Studies with oestrogen receptor knockouts and oestrogen depleted mice have shown us that oestrogen is essential for folliculogenesis beyond the antral stage and is necessary to maintain the female phenotype of ovarian somatic cells. In summary, the action of steroids within the ovary is based on the developmental status of the follicle. In the absence of any single sex steroid, ovarian function and subsequently fertility, are compromised.

An aryl hydrocarbon receptor agonist amplifies the mitogenic actions of estradiol in granulosa cells: evidence of involvement of the cognate receptors

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that, besides mediating toxic responses, may have a central role in ovarian physiology. Studying the actions of AHR ligands on granulosa cells function, we have found that beta-naphthoflavone amplifies the comitogenic actions of FSH and 17beta-estradiol in a dose-dependent manner. This amplification was even greater in cells that overexpress the AHR and was reversed by cotreatment with the AHR antagonist alpha-naphthoflavone, suggesting that this effect is mediated by the AHR. The estrogen receptor is likewise implicated in this phenomenon, because a pure antiestrogen abolished the described synergism. However, the more traditional inhibitory AHR-estrogen receptor interaction was observed on the estrogen response element-driven transcriptional activity. On the other hand, alpha-naphthoflavone inhibited dose-dependently the mitogenic actions of FSH and 17beta-estradiol. Beta-naphthoflavone induced the expression of Cyp1a1 and Cyp1b1 transcripts, two well-characterized AHR-inducible genes that code for hydroxylases that metabolize estradiol to catecholestrogens. Nevertheless, the positive effect of beta-naphthoflavone on proliferation was not caused by increased metabolism of estradiol to catecholestrogens, because these compounds inhibited the hormonally stimulated DNA synthesis. This latter inhibition exerted by catecholestrogens suggests that these hydroxylases would play a regulatory point in granulosa cell proliferation. Our study indicates that AHR ligands modulate the proliferation of rat granulosa cells, and demonstrates for the first time that an agonist of this receptor is able to amplify the comitogenic action of classical hormones through a mechanism that might implicate a positive cross-talk between the AHR and the estrogen receptor pathways.

Androgens Augment the Mitogenic Effects of Oocyte-Secreted Factors and Growth Differentiation Factor 9 on Porcine Granulosa Cells1

In this study, we test the hypothesis that the growth-promoting action of androgens on granulosa cells requires paracrine signaling from the oocyte. Mural granulosa cells (MGCs) from small antral (1-3 mm) prepubertal pig follicles were cultured in the presence or absence of denuded oocytes (DO) from the same follicles to determine whether mitogenic and/or steroidogenic responses, to combinations of FSH, insulin-like growth factor 1 (IGF1), and dihydrotestosterone (DHT) were influenced by oocyte-secreted factors (OSFs). To further explore the identity of such factors we performed the same experiments, substituting growth differentiation factor 9 (GDF9), a known OSF, for the DO. OSFs and GDF9 both potently enhanced IGF1-stimulated proliferation, and inhibited FSH-stimulated progesterone secretion. Alone, DHT had little effect on DNA synthesis, but significantly enhanced the mitogenic effects of OSFs or GDF9 in the presence of IGF1. Denuded oocytes, GDF9, and DHT independently inhibited FSH-stimulated progesterone secretion, and androgen, together with DO or GDF9, caused the most potent steroidogenic inhibition. Focusing on mitogenic effects, we demonstrate that both natural androgen receptor (AR) agonists, testosterone and DHT, dose-dependently augmented the mitogenic activity of DO or GDF9. Antiandrogen (hydroxyflutamide) treatment, which is used to block androgen receptor activity, opposed the interaction between androgen and GDF9. In conclusion, androgens stimulate porcine MGC proliferation in vitro by potentiating the growth-promoting effects of oocytes or GDF9, via a mechanism that involves the AR. These signaling pathways are likely to be important regulators of folliculogenesis in vivo, and may contribute to the excess follicle growth that is observed in androgen-treated female animals.

In vitro effects of diethylstilbestrol, genistein, 4-tert-butylphenol, and 4-tert-octylphenol on steroidogenic activity of isolated immature rat ovarian follicles

Isolated rat ovarian follicles grow and produce steroid hormones in vitro and so provide a good model for studying the effects of hormonally active compounds on follicular steroidogenesis. We have evaluated the effects of diethylstilbestrol (DES), genistein (GEN) and two alkylphenols, 4-tert-butylphenol (BP) and 4-tert-octylphenol (OP) on the growth, survival, and steroid hormone and cAMP production by isolated 14-day-old rat (Sprague-Dawley) ovarian follicles. During a 5-day culture, FSH was obligatory for follicle growth and increased estradiol and testosterone secretion in a dose-dependent manner. DES (10(-6) M) caused the strongest decline in estradiol and testosterone levels but did not have detectable effects on either cAMP production or aromatase enzyme activity. GEN caused a prominent decrease in cAMP and testosterone levels without significant changes in secreted estradiol. The latter, apparently, was due to a dose-dependent stimulation of aromatase enzyme activity in the presence of genistein. Both BP and OP decreased estradiol and testosterone secretion in a dose-dependent manner while no effect on aromatase activity was observed. OP, unlike BP, decreased forskolin-induced cAMP levels. Xenoestrogens at the used concentrations did not interfere with the growth and survival of the follicles. The results indicate that isolated ovarian follicles representing intact morphological and functional units offer a sensitive model system for elucidating the female-specific reproductive effects of environmental chemicals.

Interactions Between Androgen and Growth Factors in Granulosa Cell Subtypes of Porcine Antral Follicles1

Androgens acting via the androgen receptor (AR) have been implicated in regulation of folliculogenesis in many animal species. These effects are possibly mediated via enhancement of FSH and/or insulin-like growth factor (IGF)-I activity in granulosa cells, which contain high levels of AR protein. We examined the in vitro effect of dihydrotestosterone (DHT) on DNA synthesis and progesterone secretion by follicular cells in response to FSH and IGF-I, alone or in combination. Cells from separate pools of 1- to 3-mm and 3- to 5-mm antral follicles were aspirated from gilt ovaries and fractioned into mural granulosa cells (MGCs) and cumulus-oocyte complexes (COCs) for subsequent cell culture. Androgen alone or with any combination of mitogen had minimal effect on proliferative and no effect on steroidogenic responses of MGCs from 3- to 5-mm antral follicles. Conversely, in MGCs from 1- to 3-mm follicles, DHT significantly enhanced IFG-I-stimulated proliferation and had variable influence on progesterone secretion. The effects of DHT on proliferative responses of COCs were also dependent on follicle size: DHT significantly augmented either IGF-I-stimulated proliferation (1- to 3-mm follicles) or FSH-stimulated proliferation (3- to 5-mm follicles). However, the steroidogenic responses of all COCs were identical, whereby DHT significantly suppressed progesterone secretion, predominantly in the presence of FSH. Addition of an AR antagonist, hydroxyflutamide, generally reversed the proliferative responses invoked by DHT but not the steroidogenic responses. We conclude that androgen-receptor-mediated activity in granulosa cells of antral follicles is dependent on follicle size, is influenced by proximity of cells to the oocyte, and possibly involves both classic and nonclassic steroid mechanisms.

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

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

Effects of aromatase inhibition on in vitro follicle and oocyte development analyzed by early preantral mouse follicle culture

In vivo studies on folliculogenesis have documented a relation among intrafollicular steroid content, follicle growth, and oocyte development. This study examined how profound changes in androgen/estrogen ratio would affect mouse in vitro follicular development. Arimidex, a potent follicular aromatase inhibitor was used for this purpose. Early preantral follicles were cultured for 12 days up to the preovulatory stage. Oocyte's meiotic maturation, spindle and chromosome configurations, in vitro fertilization and preimplantation embryo development were evaluated. Compared to controls, Arimidex reduced E2 concentration in follicle culture medium by a factor 1000, and an expected simultaneous accumulation of testosterone was measured in the conditioned medium. Arimidex treatment provoked a dose-dependent earlier differentiation of the granulosa cells as judged by an earlier antrallike cavity formation and slightly elevated basal progesterone secretion. Follicle survival exceeded 98% in all groups and all follicles responded normally to HCG/EGF addition on day 12 by cumulus mucification. By the HCG ovulatory challenge, progesterone output was reduced in Arimidex supplemented groups suggesting preovulatory luteinization. These results indicate that in vitro mouse follicles can develop normally under very low levels of estrogens and that a local androgen increase by a factor 3 is not atretogenic. Oocyte growth did not differ among culture conditions. Arimidex treatment induced a dose dependent enhancement of GVBD and polar body formation rate in response to HCG at the end of culture. Spindle and chromosome analyses demonstrated that in all groups, 90% of the oocytes which extruded a polar body had also reached the MII stage. While most of the cultured MII oocytes had a normal spindle and well aligned chromosomes, significantly less oocytes were fertilized in the groups cultured in the presence of Arimidex. Once fertilized, however, there was found to be no difference for preimplantation embryo development between controls and Arimidex treatment. These data suggest that in mice a pronounced estrogenic environment is not essential for in vitro folliculogenesis. Drastic changes in the intrafollicular steroid concentrations do not disrupt meiotic maturation nor compromise early preimplantation development, but adversely affect fertilization of in vitro grown oocytes.

Activation of extracellular-regulated kinase pathways in ovarian granulosa cells by the novel growth factor type 1 follicle-stimulating hormone receptor. Role in hormone signaling and cell proliferation

Follicle-stimulating hormone (FSH) regulated growth and function of the ovarian follicle was previously thought to be mediated solely through activation of G(s)-coupled receptors. In this study, we show for the first time that this function is predominantly mediated through the alternatively spliced and novel growth factor type 1 receptor (oFSH-R3) that is also present in the ovary. Immortalized granulosa cells lacking endogenous FSH receptors, when transfected with either oFSH-R3 cDNA (JC-R3) or the G(s)-coupled oFSH-R1 (JC-R1), expressed the corresponding glycosylated receptor. In JC-R3 or JC-R1 cells labeled with bromodeoxyuridine or [(3)H]thymidine, FSH stimulated the cells to progress through S-phase and divide. The growth promoting effect of recombinant FSH in JC-R3 cells was preceded by the rapid activation of ERK1 and ERK2. This effect was hormone-specific and transient. In JC-R3 cells inhibitors like calphostin C, PD98059, Ag 18, or calcium chelators EGTA or 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid/AM inhibited both mitogen-activated protein kinase activation and bromodeoxyuridine incorporation. FSH induced phosphorylation of the FSH-R3 receptor was blocked by pretreating cells with calphostin C. There was no cAMP induction by FSH in JC-R3 cells. The cAMP independent growth promoting effect of FSH is mediated by activation of Ca(2+) and mitogen-activated protein kinase-dependent pathways. Thus, alternative splicing of a G-protein coupled receptor creates the expression of a novel receptor motif that can mediate a widely recognized function of the glycoprotein hormone.

Estrogen receptor transcription and transactivation: Estrogen receptor knockout mice: what their phenotypes reveal about mechanisms of estrogen action

Natural, synthetic and environmental estrogens have numerous effects on the development and physiology of mammals. Estrogen is primarily known for its role in the development and functioning of the female reproductive system. However, roles for estrogen in male fertility, bone, the circulatory system and immune system have been established by clinical observations regarding sex differences in pathologies, as well as observations following menopause or castration. The primary mechanism of estrogen action is via binding and modulation of activity of the estrogen receptors (ERs), which are ligand-dependent nuclear transcription factors. ERs are found in highest levels in female tissues critical to reproduction, including the ovaries, uterus, cervix, mammary glands and pituitary gland. Since other affected tissues have extremely low levels of ER, indirect effects of estrogen, for example induction of pituitary hormones that affect the bone, have been proposed. The development of transgenic mouse models that lack either estrogen or ER have proven to be valuable tools in defining the mechanisms by which estrogen exerts its effects in various systems. The aim of this article is to review the mouse models with disrupted estrogen signaling and describe the associated phenotypes.

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.

Estrogen receptor null mice: what have we learned and where will they lead us?

All scientific investigations begin with distinct objectives: first is the hypothesis upon which studies are undertaken to disprove, and second is the overall aim of obtaining further information, from which future and more precise hypotheses may be drawn. Studies focusing on the generation and use of gene-targeted animal models also apply these goals and may be loosely categorized into sequential phases that become apparent as the use of the model progresses. Initial studies of knockout models often focus on the plausibility of the model based on prior knowledge and whether the generation of an animal lacking the particular gene will prove lethal or not. Upon the successful generation of a knockout, confirmatory studies are undertaken to corroborate previously established hypotheses of the function of the disrupted gene product. As these studies continue, observations of unpredicted phenotypes or, more likely, the lack of a phenotype that was expected based on models put forth from past investigations are noted. Often the surprising phenotype is due to the loss of a gene product that is downstream from the functions of the disrupted gene, whereas the lack of an expected phenotype may be due to compensatory roles filled by alternate mechanisms. As the descriptive studies of the knockout continue, use of the model is often shifted to the role as a unique research reagent, to be used in studies that 1) were not previously possible in a wild-type model; 2) aimed at finding related proteins or pathways whose existence or functions were previously masked; or 3) the subsequent effects of the gene disruption on related physiological and biochemical systems. The alpha ERKO mice continue to satisfy the confirmatory role of a knockout quite well. As summarized in Table 4, the phenotypes observed in the alpha ERKO due to estrogen insensitivity have definitively illustrated several roles that were previously believed to be dependent on functional ER alpha, including 1) the proliferative and differentiative actions critical to the function of the adult female reproductive tract and mammary gland; 2) as an obligatory component in growth factor signaling in the uterus and mammary gland; 3) as the principal steroid involved in negative regulation of gonadotropin gene transcription and LH levels in the hypothalamic-pituitary axis; 4) as a positive regulator of PR expression in several tissues; 5) in the positive regulation of PRL synthesis and secretion from the pituitary; 6) as a promotional factor in oncogene-induced mammary neoplasia; and 7) as a crucial component in the differentiation and activation of several behaviors in both the female and male. The list of unpredictable phenotypes in the alpha ERKO must begin with the observation that generation of an animal lacking a functional ER alpha gene was successful and produced animals of both sexes that exhibit a life span comparable to wild-type. The successful generation of beta ERKO mice suggests that this receptor is also not essential to survival and was most likely not a compensatory factor in the survival of the alpha ERKO. In support of this is our recent successful generation of double knockout, or alpha beta ERKO mice of both sexes. The precise defects in certain components of male reproduction, including the production of abnormal sperm and the loss of intromission and ejaculatory responses that were observed in the alpha ERKO, were quite surprising. In turn, certain estrogen pathways in the alpha ERKO female appear intact or unaffected, such as the ability of the uterus to successfully exhibit a progesterone-induced decidualization response, and the possible maintenance of an LH surge system in the hypothalamus. [ABSTRACT TRUNCATED]

Dimeric inhibin A and B production are differentially regulated by hormones and local factors in rat granulosa cells

In the present study, we have examined the role of hormones and growth factors in regulating dimeric inhibin production in immature rat granulosa cells. Purified granulosa cells from estrogen-primed immature rats were cultured under defined conditions. Inhibins A and B in the culture media were measured using a two-site enzyme-linked immunosorbent assay specific for each dimer. Under basal conditions, granulosa cells produced 14-fold more inhibin A than inhibin B (inhibin A, 2.0; inhibin B, 0.14 ng/ml, measured against human standards; average A/B apparent ratio, 14). Addition of increasing doses of FSH elicited dose-dependent increases in both inhibins, the effects being more pronounced on inhibin A than on inhibin B (9.4- and 4.1-fold increases, respectively; average A/B ratio, 34). Estradiol, when added alone, stimulated inhibin A production 3- to 6-fold, whereas minor changes were observed in inhibin B production. Insulin-like growth factor-I produced a similar stimulation of both inhibins (3-fold stimulation over control). This growth factor, however, induced a marked dissociation in the sensitivity of inhibins A and B to FSH stimulation, with maximal stimulation of inhibin B observed at comparatively lower concentrations of the gonadotropin. Transforming growth factor-beta (TGF-beta, 5 ng/ml) had a more marked stimulatory effect on inhibin B than on inhibin A production (7- to 14-fold vs. 2- to 5-fold for inhibin B and A, respectively). A more pronounced differential stimulation of inhibin B was also exerted by another member of the TGF-beta superfamily, activin A (A/B ratio, 0.66). This preferential stimulation of inhibin B by TGF-beta and activin A was amplified in the presence of FSH. Coculture of rat granulosa cells with freshly isolated bovine oocytes was also associated with a marked stimulation of inhibin B production (100-fold increase) and a comparatively lower stimulation of inhibin A (10-fold increase; A/B ratio, 1). The discrepancy between the proportion of inhibin dimers in serum (A/B ratio, 0.13) and those produced by untreated granulosa cells may suggest that intraovarian factors, such as TGF-beta, activin A, or oocyte-derived factor(s), are responsible for the shift of the ratio toward the predominance of inhibin B.

The role of estrogen in folliculogenesis

Gonadotrophins are fundamental to the mechanisms regulating follicle status and development. Follicles in the ovary are either quiescent or committed to one of two pathways: growth or atresia. The requirement for gonadotrophins by the follicles varies with development: committed follicles grow independently of gonadotrophins (primarily FSH) until the late preantral stage when antrum formation is contingent upon FSH. The involvement of estrogen in regulating gonadotrophin secretion is well documented and while evidence for a local regulatory role of estrogen in the ovary mounts, an obligatory role for estrogen in the folliculogenic process has not been established. The availability of a wide range of gene-disrupted mice termed 'knockouts', is providing information relevant to the study of folliculogenesis. Mice deficient in either estrogen or estrogen receptors, are infertile primarily due to either a block in folliculogenesis prior to antrum formation or as a consequence of failing to ovulate. Blocking estrogen stimulated, post-receptor molecules such as cyclin D2, severely retards granulosa cell proliferation and leads to infertility, although the contribution of estrogen in this model is not so clear given that FSH also stimulates cyclin D2. Similar problems dissociating the roles of FSH and estrogen are evident with the FSH deficient animal models. Nevertheless, estrogen is clearly an important and probably obligatory regulator of folliculogenesis, especially in the post antral stage. The exact points in the folliculogenic process where estrogen exerts its principal effects remains to be elucidated.

Growth promoting activity of oocytes on granulosa cells is decreased upon meiotic maturation

An increasing body of evidence indicates that the oocyte plays an active role in the control of ovarian follicle development in mammals. In the present study, we have examined the role of oocytes in regulating granulosa cell proliferation. Rat and bovine oocytes cocultured with rat granulosa cells stimulated granulosa cell DNA synthesis and DNA content in the cultures. FSH or cAMP further amplified this effect. Poor-quality oocytes showed a marked decrease in their stimulatory effect. Stimulation of DNA synthesis by bovine oocytes seems to be cell-type specific, since Swiss 3T3 fibroblasts and CCL-64 mink lung epithelial cells were not responsive, while primary cultures of rat and bovine granulosa cells and the bovine granulosa cell line BGC-1 showed significant responses. Oocyte-conditioned medium produced only a slight stimulation of rat granulosa cell DNA synthesis. However, the effect of oocyte coculture was dependent on the total incubation volume, suggesting that the growth promoting activity was mediated by a soluble factor. The stimulation elicited by bovine oocytes was evident even in the presence of maximally effective doses of transforming growth factor-beta or tumor necrosis factor-alpha, indicating that neither of these growth factors was responsible for this effect. In vitro maturation of bovine oocytes was associated with a marked decrease in the stimulatory activity. This decrease was partially prevented when maturation was blocked by addition of cycloheximide. Comparison of the developmental pattern of the secretion of the growth promoting activity with that of the cumulus expansion-enabling factor indicated that both activities can be dissociated. Our data suggest the existence of a very labile factor produced by the oocyte before completion of the first meiotic division that promotes granulosa cell proliferation.