Protein kinase B is obligatory for follicle-stimulating hormone-induced granulosa cell differentiation

Co-administration of insulin with a gonadotropin partly improves ovulatory responses of estrogen-deficient mice

Administration of 17-βestradiol (E2) with pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) can induce ovulation in estrogen-deficient (ArKO) mice; nevertheless, ovulatory efficiency and rate are low. In this study, effects of insulin on the ovulatory responses were investigated. In ArKO ovary, hCG signal was found to be transmitted in an uncoordinated manner when phosphorylation levels of signaling molecules are examined. Co-administration of insulin with hCG improved the transmission of hCG signal as well as the ovulatory efficiency in ArKO mice. It also improved the ovulatory rate but far below the wild-type rate. Gene expression analysis demonstrated that Cyp11a1 and Cyp17a1 mRNAs were significantly induced 4 h after PMSG administration in the wild-type ovary, but not in ArKO ovary. Collectively, these results suggest that insulin improves ovulatory responses of ArKO mice, but it fails to ameliorate follicular dysfunctions caused possibly by an inappropriate intraovarian milieu during follicular maturation.

Heat Stress Alters Ovarian Insulin-Mediated Phosphatidylinositol-3 Kinase and Steroidogenic Signaling in Gilt Ovaries

Heat stress (HS) compromises a variety of reproductive functions in several mammalian species. Inexplicably, HS animals are frequently hyperinsulinemic despite marked hyperthermia-induced hypophagia. Our objectives were to determine the effects of HS on insulin signaling and components essential to steroid biosynthesis in the pig ovary. Female pigs (35 ± 4 kg) were exposed to constant thermoneutral (20°C; 35%-50% humidity; n = 6) or HS conditions (35°C; 20%-35% humidity; n = 6) for either 7 (n = 10) or 35 days (n = 12). After 7 days, HS increased (P < 0.05) ovarian mRNA abundance of the insulin receptor (INSR), insulin receptor substrate 1 (IRS1), protein kinase B subunit 1 (AKT1), low-density lipoprotein receptor (LDLR), luteinizing hormone receptor (LHCGR), and aromatase (CYP19a). After 35 days, HS increased INSR, IRS1, AKT1, LDLR, LHCGR, CYP19a, and steroidogenic acute regulatory protein (STAR) ovarian mRNA abundance. In addition, after 35 days, HS increased ovarian phosphorylated IRS1 (pIRS1), phosphorylated AKT (pAKT), STAR, and CYP19a protein abundance. Immunostaining analysis revealed similar localization of INSR and pAKT1 in the cytoplasmic membrane and oocyte cytoplasm, respectively, of all stage follicles, and in theca and granulosa cells. Collectively, these results demonstrate that HS alters ovarian insulin-mediated PI3K signaling pathway members, which likely impacts follicle activation and viability. In summary, environmentally induced HS is an endocrine-disrupting exposure that modifies ovarian physiology and potentially compromises production of ovarian hormones essential for fertility and pregnancy maintenance.

Intraovarian control of early folliculogenesis

Although hormonal regulation of ovarian follicle development has been extensively investigated, most studies concentrate on the development of early antral follicles to the preovulatory stage, leading to the successful use of exogenous FSH for infertility treatment. Accumulating data indicate that preantral follicles are under stringent regulation by FSH and local intraovarian factors, thus providing the possibility to develop new therapeutic approaches. Granulosa cell-derived C-type natriuretic factor not only suppresses the final maturation of oocytes to undergo germinal vesicle breakdown before ovulation but also promotes preantral and antral follicle growth. In addition, several oocyte- and granulosa cell-derived factors stimulate preantral follicle growth by acting through wingless, receptor tyrosine kinase, receptor serine kinase, and other signaling pathways. In contrast, the ovarian Hippo signaling pathway constrains follicle growth and disruption of Hippo signaling promotes the secretion of downstream CCN growth factors capable of promoting follicle growth. Although the exact hormonal factors involved in primordial follicle activation has yet to be elucidated, the protein kinase B (AKT) and mammalian target of rapamycin signaling pathways are important for the activation of dormant primordial follicles. Hippo signaling disruption after ovarian fragmentation, combined with treating ovarian fragments with phosphatase and tensin homolog (PTEN) inhibitors and phosphoinositide-3-kinase stimulators to augment AKT signaling, promote the growth of preantral follicles in patients with primary ovarian insufficiency, leading to a new infertility intervention for such patients. Elucidation of intraovarian mechanisms underlying early folliculogenesis may allow the development of novel therapeutic strategies for patients diagnosed with primary ovarian insufficiency, polycystic ovary syndrome, and poor ovarian response to FSH stimulation, as well as for infertile women of advanced reproductive age.

IGF1R signaling is necessary for FSH-induced activation of AKT and differentiation of human Cumulus granulosa cells

CONTEXT

FSH is routinely administered to in vitro fertilization patients to induce follicle maturation. During this process, granulosa cells differentiate and acquire specific functional characteristics that are required to coordinate ovulation and oocyte maturation.

OBJECTIVE

The objective of the study was to gain insight into the molecular mechanisms regulating human granulosa cell differentiation. Design, Setting, Patients, and Interventions: Cumulus and mural granulosa cells were isolated from the follicular aspirates of in vitro fertilization patients and analyzed immediately or cultured in serum-free media in the presence of FSH, IGFs, or an inhibitor of type I IGF receptor (IGF1R) activity.

MAIN OUTCOME

We quantified the mRNA and protein levels of steroidogenic enzymes, components of the IGF system, and gonadotropin receptors; measured 17β-estradiol levels; and examined the activation of intracellular signaling pathways to assess the granulosa cell differentiation as well as the FSH and IGF actions in both cumulus and mural cells.

RESULTS

In freshly isolated cells, LH receptor (Lhr) and steroidogenic acute regulator (Star) were expressed at lower levels in cumulus than mural cells, whereas FSH receptor (Fshr) and anti-Müllerian hormone (Amh) were expressed at higher levels in cumulus than mural cells. In vitro, the expression of Igf2, the differentiation markers Lhr, Star, and Cyp19a1 (aromatase) as well as 17β-estradiol production remained low in untreated cumulus cells but increased significantly after FSH treatment. Strikingly, this stimulatory effect of FSH was abolished by the inhibition of IGF1R activity. FSH-induced activation of v-akt murine thymoma viral oncogene homolog 3 (AKT) required IGF1R activity, and overexpression of constitutively active AKT rescued the induction of differentiation markers and 17β-estradiol production by FSH in the presence of the IGF1R inhibitor.

CONCLUSIONS

The cumulus cell response to FSH resembles the differentiation of preantral to preovulatory granulosa cells. This differentiation program requires IGF1R activity and subsequent AKT activation.

Factors regulating the bovine, caprine, rat and human ovarian aromatase promoters in a bovine granulosa cell model

The ovarian promoter of the primate and rodent genes encoding cytochrome P450 aromatase (CYP19A1) are robustly responsive to forskolin in luteinized cell models, whereas the ruminant ovarian promoter is minimally active. We explored this discrepancy by investigating the activity of the bovine ovarian promoter in two bovine granulosa cell models, luteinizing and non-luteinizing cells in vitro. In non-luteinizing cells, both FSH and IGF1 increased abundance of transcripts derived from the ovarian promoter. Comparison of the activity of promoters of several species in response to transcription factors (forskolin, NR5A2, FOXL2) in luteinizing cells demonstrated that a rat ovarian promoter-luciferase reporter was regulated mainly by forskolin (18-fold increase over basal expression) and addition of NR5A2 or FOXL2 had no further effect. Activity of a human promoter was significantly increased by NR5A2 plus forskolin (153-fold) compared with forskolin alone (71-fold over basal); addition of FOXL2 did not significantly increase promoter activity. Forskolin alone provoked minor activation of caprine and bovine promoter reporters (3-fold over basal), and addition of NR5A2 increased activity (7- to 11-fold). When forskolin, NR5A2 and FOXL2 treatments were combined, the activity of the caprine and bovine promoters increased to 20- and 34-fold, respectively. These data suggest that a major reason why CYP19A1 is not expressed in luteinized cells (and the corpus luteum) of ruminants may be the stimulatory effect of FOXL2, which does not appear to be the case in the human and rat.

Biased signalling in follicle stimulating hormone action

Follicle-stimulating hormone (FSH) plays a crucial role in the control of reproduction by specifically binding to and activating a membrane receptor (FSHR) that belongs to the G protein-coupled receptor (GPCR) family. Similar to all GPCRs, FSHR activation mechanisms have generally been viewed as a two-state process connecting a unique FSH-bound active receptor to the Gs/cAMP pathway. Over the last decade, paralleling the breakthroughs that were made in the GPCR field, our understanding of FSH actions at the molecular level has dramatically changed. There are numerous facts indicating that the active FSHR is connected to a complex signalling network rather than the sole Gs/cAMP pathway. Consistently, the FSHR probably exists in equilibrium between multiple conformers, a subset of them being stabilized upon ligand binding. Importantly, the nature of the stabilized conformers of the receptor directly depends on the chemical structure of the ligand bound. This implies that it is possible to selectively control the intracellular signalling pathways activated by using biased ligands. Such biased ligands can be of different nature: small chemical molecules, glycosylation variants of the hormone or antibody/hormone complexes. Likewise, mutations or polymorphisms affecting the FSHR can also lead to stabilization of preferential conformers, hence to selective modulation of signalling pathways. These emerging notions offer a new conceptual framework that could potentially lead to the development of more specific drugs while also improving the way FSHR mutants/variants are functionally characterized.

Constitutive activity in gonadotropin receptors

Constitutively active mutants (CAMs) of gonadotropin receptors are, in general, rare conditions. Luteinizing hormone-choriogonadotropin receptor (LHCGR) CAMs provoke the dramatic phenotype of familial gonadotropin-independent isosexual male-limited precocious puberty, whereas in females, there is not yet any identified phenotype. Only one isolated follicle-stimulating hormone receptor (FSHR) CAM (Asp567Gly) has so far been detected in a single male patient, besides other FSHR weak CAMs linked to pregnancy-associated ovarian hyperstimulation syndrome or to impaired desensitization and internalization. Several animal models have been developed for studying enhanced gonadotropin action; in addition to unraveling valuable new information about the possible phenotypes of isolated FSHR and LHCGR CAMs in women, the information obtained from these mouse models has served multiple translational goals, including the development of new diagnostic and therapeutic targets as well as the prediction of phenotypes for mutations not yet identified in humans. Mutagenesis and computational studies have shed important information on the physiopathogenic mechanisms leading to constitutive activity of gonadotropin receptors; a common feature in these receptor CAMs is the release of stabilizing interhelical interactions between transmembrane domains (TMDs) 3 and 6 leading to an increase, with respect to the wild-type receptor, in the solvent accessibility at the cytosolic extension of TMDs 3, 5, and 6, which involves the highly conserved Glu/Asp-Arg-Tyr/Trp sequence. In this chapter, we summarize the structural features, functional consequences, and mechanisms that lead to constitutive activation of gonadotropin receptor CAMs and provide information on pharmacological approaches that might potentially modulate gonadotropin receptor CAM function.

Integrating microRNAs into the complexity of gonadotropin signaling networks

Follicle-stimulating hormone (FSH) is a master endocrine regulator of mammalian reproductive functions. Hence, it is used to stimulate folliculogenesis in assisted reproductive technologies (ART), both in women and in breeding animals. However, the side effects that hormone administration induces in some instances jeopardize the success of ART. Similarly, the luteinizing hormone (LH) is also of paramount importance in the reproductive function because it regulates steroidogenesis and the LH surge is a pre-requisite to ovulation. Gaining knowledge as extensive as possible on gonadotropin-induced biological responses could certainly lead to precise selection of their effects in vivo by the use of selective agonists at the hormone receptors. Hence, over the years, numerous groups have contributed to decipher the cellular events induced by FSH and LH in their gonadal target cells. Although little is known on the effect of gonadotropins on microRNA expression so far, recent data have highlighted that a microRNA regulatory network is likely to superimpose on the signaling protein network. No doubt that this will dramatically alter our current understanding of the gonadotropin-induced signaling networks. This is the topic of this review to present this additional level of complexity within the gonadotropin signaling network, in the context of recent findings on the microRNA machinery in the gonad.

Identification of two novel, alternatively spliced mRNA transcripts of the human follicle-stimulating hormone receptor

Glycoprotein hormone receptors contain large extracellular domains encoded by multiple exons that can be alternatively spliced. Using human ovarian surface epithelium, we cloned two new splice variants of the human follicle-stimulating hormone receptor (FSH-R) gene, hFSH-R2 and hFSH-R3. The hFSH-R2 splice variant differed from the full-length FSH-R mRNA by the deletion of exon 10 and inclusion of two small exons after exon 9 whereas the hFSH-R3 splice variant retained only exons 1-6 of the full-length transcript. Both variants were expressed at low levels, but were detected in cells from follicular fluid derived from 30 different subjects. Transfection of these two variants individually into KGN cells, an ovarian cancer cell line that expresses wild-type FSH-R, reduced FSH-mediated phosphorylation of ERK(1/2), Akt, and p38/MAPK. Furthermore, in vitro co-expression of either hFSH-R2 or hFSH-R3 and full-length FSH-R in HEK293T cells reduced signal transduction through full-length FSH-R. Further studies are needed to fully elucidate the functions of these receptor isoforms.

The Interplay between Circadian System, Cholesterol Synthesis, and Steroidogenesis Affects Various Aspects of Female Reproduction

Circadian aspect of reproduction has gained much attention in recent years. In mammals, it is very important that the timing of greatest sexual motivation is in line with the highest fertility. Peripheral clocks have been found to reside also in reproductive organs, such as the uterus and ovary. The timing signal from the suprachiasmatic nucleus is suggested to be transmitted via hormonal and neural mechanisms, and could thus mediate circadian expression of target genes in these organs. In turn, estrogens from the ovary have been found to signal back to the hypothalamus, completing the feedback loop. In this review we will focus on the interplay between clock and estrogens. Estradiol has been directly linked with expression of Per1 and Per2 in the uterus. CLOCK, on the other hand, has been shown to alter estradiol signaling. We also present the idea that cholesterol could play a vital role in the regulation of reproduction. Cholesterol synthesis itself is circadially regulated and has been found to interfere with steroidogenesis in the ovary on the molecular level. This review presents a systems view on how the interplay between circadian clock, steroidogenesis, and cholesterol synthesis affect various aspects of mammalian reproduction.

Follicular stage-dependent regulation of apoptosis and steroidogenesis by prohibitin in rat granulosa cells

BACKGROUND

Follicular growth and atresia are tightly regulated processes, which involve the participation of endocrine, autocrine and paracrine factors at the cellular level. Prohibitin (PHB) is a multifunctional intracellular protein playing an important role in the regulation of proliferation, apoptosis and differentiation. Here we examined the expression of PHB and its regulation by FSH in vitro and studied the role of PHB in the regulation of apoptosis and steroidogenesis in response to the apoptosis inducer staurosporine (STS) and to FSH, respectively.

METHODS

Undifferentiated and differentiated granulosa cells were collected from diethylstilbestrol (DES)- and equine chronic gonadotropin (eCG)-primed immature rats, respectively and then cultured with various treatments (FSH, adenovirus infection, STS) according to experimental design. The apoptosis rate, the production of estradiol and progesterone, and the expression of distinct proteins (PHB, caspase-3, phospho- and total Akt) were assessed.

RESULTS

PHB is anti-apoptotic and its action is dependent on the differentiated state of the granulosa cells. Data from gain- and loss-of-function experiments demonstrate that PHB inhibited STS-induced caspase-3 cleavage and apoptosis in undifferentiated granulosa cells, but was ineffective in differentiated cells. In contrast, PHB suppresses FSH-induced steroidogenesis and this response is evident irrespective of the differentiated state of granulosa cells.

CONCLUSION

These findings suggest that PHB regulates granulosa cell apoptosis and steroidogenesis in a follicular stage-dependent manner and that the dysregulation of PHB expression and action may be relevant to ovarian dysfunction.

Resistin decreases insulin-like growth factor I-induced steroid production and insulin-like growth factor I receptor signaling in human granulosa cells

OBJECTIVE

To identify resistin in human ovarian follicles and investigate the effect and the molecular mechanisms associated with resistin on steroidogenesis in human granulosa cells (GCs).

DESIGN

The effects of recombinant human resistin on the secretion of progesterone (P) and estradiol (E2) by cultured human GCs were investigated.

SETTING

Academic institutions.

PATIENT(S)

Twenty infertile and healthy women undergoing IVF.

INTERVENTION(S)

Primary human GC cultures stimulated with recombinant human resistin (10 ng/mL).

MAIN OUTCOME MEASURE(S)

Determination of messenger RNA (mRNA) and protein expression of resistin in fresh human GCs by reverse transcriptase-polymerase chain reaction (RT-PCR), immunoblot and immunohistochemistry, respectively; measurement of P and E2 levels in the conditioned media by radioimmunoassay; determination of cell proliferation by tritiated thymidine incorporation; and analysis of signaling pathways activation by immunoblot analysis.

RESULT(S)

Human GCs and theca cells express resistin. In primary human GCs, resistin decreases P and E2 secretion in response to insulin-like growth factor I (IGF-I). This was associated with a reduction in the P450 aromatase and P450scc (cholesterol side-chain cleavage cytochromes P450) (P450scc) protein levels but not those of 3β-hydroxysteroid dehydrogenase (3β-HSD) or steroidogenic acute regulatory protein (StAR) and with a decrease in IGF-I-induced IGF-I receptor and mitogen-activated protein kinase (MAPK) extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation. Resistin treatment does not affect IGF-I-induced cell proliferation and basal steroidogenesis (there is no IGF-I or follicle-stimulating hormone stimulation). In the basal state, resistin rapidly stimulates Akt and MAPK ERK1/2 and p38 phosphorylation in primary human GCs.

CONCLUSION(S)

Resistin is present in human GCs and theca cells. It decreases P and E2 secretion, P450scc and P450 aromatase protein levels, and IGF-IR signaling in response to IGF-I in primary human GCs.

Inhibitory roles of prohibitin and chemerin in FSH-induced rat granulosa cell steroidogenesis

Follicular differentiation is a tightly regulated process involving various endocrine, autocrine, and paracrine factors. The biosynthesis of progesterone and estradiol in response to FSH involves the regulation of multiple steroidogenic enzymes, such as p450 cholesterol side-chain cleavage enzyme and aromatase. Here we demonstrated that prohibitin (PHB), a multifunctional protein, inhibits FSH-induced progesterone and estradiol secretion in rat granulosa cells. The mRNA abundances of cyp11a (coding p450 cholesterol side-chain cleavage enzyme) and cyp19 (coding aromatase) were also suppressed by PHB in a time-dependent manner. It is known that a novel adipokine chemerin suppresses FSH-induced steroidogenesis in granulosa cells. Chemerin up-regulates the content of PHB, and PHB knockdown attenuates the suppressive role of chemerin on steroidogenesis. In addition, inhibition of phosphatidylinositol 3-kinase/Akt pathway enhances the suppressive action of PHB, whereas expression of constitutively active Akt attenuates this response. These findings suggest that PHB is a novel negative regulator of FSH-induced steroidogenesis, and its action with chemerin may contribute to the dysregulation of steroidogenesis in the pathogenesis of polycystic ovarian syndrome.

IGF-I signaling is essential for FSH stimulation of AKT and steroidogenic genes in granulosa cells

FSH and IGF-I synergistically stimulate gonadal steroid production; conversely, silencing the FSH or the IGF-I genes leads to infertility and hypogonadism. To determine the molecular link between these hormones, we examined the signaling cross talk downstream of their receptors. In human and rodent granulosa cells (GCs), IGF-I potentiated the stimulatory effects of FSH and cAMP on the expression of steroidogenic genes. In contrast, inhibition of IGF-I receptor (IGF-IR) activity or expression using pharmacological, genetic, or biochemical approaches prevented the FSH- and cAMP-induced expression of steroidogenic genes and estradiol production. In vivo experiments demonstrated that IGF-IR inactivation reduces the stimulation of steroidogenic genes and follicle growth by gonadotropins. FSH or IGF-I alone stimulated protein kinase B (PKB), which is also known as AKT and in combination synergistically increased AKT phosphorylation. Remarkably, blocking IGF-IR expression or activity decreased AKT basal activity and abolished AKT activation by FSH. In GCs lacking IGF-IR activity, FSH stimulation of Cyp19 expression was rescued by overexpression of constitutively active AKT. Our findings demonstrate, for the first time, that in human, mouse, and rat GCs, the well-known stimulatory effect of FSH on Cyp19 and AKT depends on IGF-I and on the expression and activation of the IGF-IR.

Role of the inositol polyphosphate-4-phosphatase type II Inpp4b in the generation of ovarian teratomas

Teratomas are a unique class of tumors composed of ecto-, meso- and endodermal tissues, all foreign to the site of origin. In humans, the most common teratoma is the ovarian teratoma. Not much is known about the molecular and genetic etiologies of these tumors. Female carriers of the Tgkd transgene are highly susceptible to developing teratomas. Ovaries of Tgkd/+ hemizygous female mice exhibit defects in luteinization, with numerous corpora lutea, some of which contain central trapped, fully-grown oocytes. Genetically, Tgkd teratomas originate from mature oocytes that have completed meiosis I, suggesting that Tgkd teratomas originate from these trapped oocytes. The insertion of Tgkd 3' of the Inpp4b gene is associated with decreased expression of Inpp4b and changes in intracellular PI3 Kinase/AKT signaling in follicular granulosa cells. Because Inpp4b is not expressed in fully-grown wild-type or Tgkd oocytes, these findings suggest that hyperactivation of the PI3K/AKT pathway caused by the decrease in INPP4B in granulosa cells promotes an ovarian environment defective in folliculogenesis and conducive to teratoma formation.

PKA and GAB2 play central roles in the FSH signaling pathway to PI3K and AKT in ovarian granulosa cells

Controlled maturation of ovarian follicles is necessary for fertility. Follicles are restrained at an immature stage until stimulated by FSH secreted by pituitary gonadotropes. FSH acts on granulosa cells within the immature follicle to inhibit apoptosis, promote proliferation, stimulate production of steroid and protein hormones, and induce ligand receptors and signaling intermediates. The phosphoinositide 3-kinase (PI3K)/AKT (protein kinase B) pathway is a pivotal signaling corridor necessary for transducing the FSH signal. We report that protein kinase A (PKA) mediates the actions of FSH by signaling through multiple targets to activate PI3K/AKT. PKA uses a route that promotes phosphorylation of insulin receptor substrate-1 (IRS-1) on Tyr(989), a canonical binding site for the 85-kDa regulatory subunit of PI3K that allosterically activates the catalytic subunit. PI3K activation leads to activation of AKT through phosphorylation of AKT on Thr(308) and Ser(473). The adaptor growth factor receptor bound protein 2-associated binding protein 2 (GAB2) is present in a preformed complex with PI3K heterodimer and IRS-1, it is an A-kinase anchoring protein that binds the type I regulatory subunit of PKA, and it is phosphorylated by PKA on Ser(159). Overexpression of GAB2 enhances FSH-stimulated AKT phosphorylation. GAB2, thus, seems to coordinate signals from the FSH-stimulated rise in cAMP that leads to activation of PI3K/AKT. The ability of PKA to commandeer IRS-1 and GAB2, adaptors that normally integrate receptor/nonreceptor tyrosine kinase signaling into PI3K/AKT, reveals a previously unrecognized route for PKA to activate a pathway that promotes proliferation, inhibits apoptosis, enhances translation, and initiates differentiation of granulosa cells.

Human antral follicles <6 mm: a comparison between in vivo maturation and in vitro maturation in non-hCG primed cycles using cumulus cell gene expression

Within the context of an oocyte in vitro maturation (IVM) program for reproductive treatment, oocyte cumulus complexes (COCs) derived from follicles <6 mm in patients with PCOS were matured in vitro. Key transcripts related to meiotic maturation (FSHR, LHCGR, EGFR, PGR) and oocyte competence (AREG, ADAMTS, HAS2, PTGS2) were quantified in cumulus cells (CCs) before and after maturation. Control CC samples were collected from PCOS and normo-ovulatory patients who had undergone conventional gonadotrophin stimulation for IVF/ICSI. Additional control samples from a non-stimulated condition were obtained ex vivo from patients undergoing ovariectomy for fertility preservation. Expression data from CCs from follicles with a diameter of <6 mm before (IVM-CCs) and after in vitro maturation (IVM-CCs) were obtained after pooling CCs into four groups in relation to the percentage of matured (MII) oocytes obtained after 40 h of IVM (0; 40-60; 61-80; 100% MII) and values were compared with in vivo matured controls (IVO-CCs). Genes encoding key receptors mediating meiotic resumption are expressed in human antral follicles of <6 mm before and after IVM. The expression levels of FSHR, EGFR and PGR in CCs were significantly down-regulated in the IVO-CCs groups and in the 100% MII IVM group compared with the BM groups; all the receptors studied in the 100% MII IVM group reached an expression profile similar to that of IVO-CCs. However, after maturation in a conventional IVF/ICSI cycle, IVO-CCs from large follicles contained significantly increased levels of ADAMTS1, AREG, HAS2 and PTGS2 compared with IVM-CCs and IVM-CCs; the expression patterns for these genes in all IVM-CCs were unchanged compared with IVM-CCs. In conclusion, genes encoding receptors involved in oocyte meiotic resumption appeared to be expressed in CCs of small human antral follicles. Expression levels of genes-encoding factors reflecting oocyte competence were significantly altered in IVM-CCs compared with in vivo matured oocytes from large follicles. Observed differences might be explained by the different stimulation protocols, doses of gonadotrophin or by the intrinsic differences between in vivo and in vitro maturation.

Luteinizing hormone/human chorionic gonadotropin-mediated activation of mTORC1 signaling is required for androgen synthesis by theca-interstitial cells

LH triggers the biosynthesis of androgens in the theca-interstitial (T-I) cells of ovary through the activation of a cAMP-dependent pathway. We have previously shown that LH/human chorionic gonadotropin (hCG) activates mammalian target of rapamycin complex 1 (mTORC1) signaling network, leading to cell proliferation. In the present study, we provide evidence that the LH/hCG-mediated activation of the mTORC1 signaling cascade is involved in the regulation of steroidogenic enzymes in androgen biosynthesis. Treatment with LH/hCG increased the expression of downstream targets of mTORC1, ribosomal protein S6 kinase 1, and eukaryotic initiation factor 4E as well as steroidogenic enzymes. LH/hCG-mediated stimulation of the steroidogenic enzyme mRNA was blocked by the mTORC1 inhibitor, rapamycin. This inhibitory effect was selective because rapamycin failed to block hCG-mediated increase in the expression of Star mRNA levels. Furthermore, pharmacological targeting of mTORC1 with rapamycin also blocked LH/hCG- or forskolin-induced expression of cAMP response element-binding protein (CREB) and steroidogenic enzymes (P450 side-chain cleavage enzyme, 3β-hydroxysteroid dehydrogenase type 1, and 17α-hydroxylase/17,20 lyase) but produced no effect on steroidogenic acute regulatory protein levels. These results were further confirmed by demonstrating that the knockdown of mTOR using small interfering RNA selectively abrogated the LH/hCG-induced increase in steroidogenic enzyme expression, without affecting steroidogenic acute regulatory protein expression. LH/hCG-stimulated androgen production was also blocked by rapamycin. Furthermore, the pharmacological inhibition of mTORC1 or ribosomal protein S6 kinase 1 signaling prevented the LH/hCG-induced phosphorylation of CREB. Chromatin immunoprecipitation assays revealed the association of CREB with the proximal promoter of the Cyp17a1 gene in response to hCG, and this association was reduced by rapamycin treatment. Taken together, our findings show for the first time that LH/hCG-mediated activation of androgen biosynthesis is regulated by the mTORC1 signaling pathway in T-I cells.

Follicle-stimulating hormone regulation of estradiol production: possible involvement of WNT2 and β-catenin in bovine granulosa cells

Follicle-stimulating hormone regulation of estrogen biosynthesis in the adult rodent ovary requires β-catenin (CTNNB1), but whether CTNNB1 is involved in FSH-induced estrogen production in cattle is unknown. To elucidate the effect of FSH in regulating specific wingless-type mouse mammary tumor virus integration site (WNT)/CTNNB1 pathway components in bovine folliculogenesis and steroidogenesis, granulosa cells and follicular fluid were collected from large antral follicles (8 to 22 mm) from ovaries containing stage-III corpora lutea (d 11 to 17 of an estrous cycle). Follicles were categorized as high estradiol (n = 3; ≥ 25 ng/mL) or low estradiol (n = 3; ≤ 14 ng/mL) based on intra-follicular estradiol concentrations. Protein fractions were collected from granulosa cells and CTNNB1 abundance was analyzed by Western blot. Follicles with increased estradiol concentrations had 6-fold greater (P < 0.001) abundances of CTNNB1 compared with those classified as low-estradiol follicles, indicating that the hormonal milieu responsible for increased estradiol content could result in CTNNB1 accumulation. To ascertain specific contributions of FSH to increases in CTNNB1 protein abundances, granulosa cells were isolated from small ovarian follicles (1 to 5 mm) and cultured in the presence or absence of 100 ng/mL FSH for 24 or 48 h. Real-time PCR quantification of aromatase (CYP19A1) and select WNT family members were evaluated in response to FSH treatment. Successful stimulation of granulosa cells with FSH was confirmed by induction of CYP19A1 mRNA and parallel temporal increases of medium estradiol concentrations. Additionally, protein kinase b (AKT), a known FSH target, increased 1.7-fold (P = 0.07). Of the WNT family members analyzed, only WNT2 mRNA was induced after 24 h of FSH treatment compared with controls (0.12-fold and 3.7-fold for control and FSH-treated, respectively; P < 0.05), and WNT2 expression tended (P = 0.11) to remain increased at 48 h in FSH-treated cells compared with controls (1.0- and 3.14-fold, respectively). Furthermore, FSH-treated granulosa cells had greater abundances of total CTNNB1 (P = 0.04) protein. These data demonstrate for the first time that FSH regulates CTNNB1 protein and WNT2 mRNA expressions in bovine granulosa cells, suggesting a potential role of canonical WNT signaling in ovarian steroidogenesis and follicular growth of cattle. Future studies are necessary to determine if FSH directly regulates CTNNB1 through modulation of AKT or indirectly by up regulating WNT2, which subsequently activates the canonical WNT pathway.

Functional roles of the phosphatidylinositol 3-kinases (PI3Ks) signaling in the mammalian ovary

Phosphatidylinositol 3-kinase (PI3K) signaling is a fundamental pathway for the regulation of cell proliferation, survival, migration, and metabolism in a variety of physiological and pathological processes. In recent years information provided by genetically modified mouse models has revealed that PI3K signaling plays vital roles in oogenesis, folliculogenesis, ovulation, and carcinogenesis in mouse ovary. In this review, we summarize (1) the physiological function of intra-oocyte PI3K signaling in regulation of primordial follicle survival and activation; (2) intra-granulosa cell PI3K signaling in regulation of cyclic follicular recruitment and ovulation; (3) intra-oocyte PI3K signaling in regulation of meiosis resumption and early embryogenesis; and also (4) the pathological function of PI3K signaling in ovarian diseases such as premature ovarian failure, granulosa cell tumors, and ovarian surface epithelium carcinomas. This updated info hopefully will lead to a better understanding of the human ovary and provide potential therapies for treating human infertility.

CREB coactivator CRTC2/TORC2 and its regulator calcineurin crucially mediate follicle-stimulating hormone and transforming growth factor β1 upregulation of steroidogenesis

In vitro and in vivo studies implicate that follicle-stimulating hormone (FSH) and transforming growth factor β1 (TGFβ1) play crucial physiological roles in regulating ovarian granulosa cell function essential to fertility control in females. FSH induces cAMP and calcium signaling, thereby activating transcription factor CREB to upregulate steroidogenic gene expression, and TGFβ1 greatly enhances FSH-stimulated steroidogenesis. A CREB coactivator CRTC2/TORC2 was identified to function as a cAMP and calcium-sensitive coincidence sensor. This led us to explore the role of CRTC2 and its regulator calcineurin in FSH and TGFβ1-stimulated steroidogenesis. Primary culture of granulosa cells from gonadotropin-primed immature rats was used. Immunoblotting analysis shows that FSH rapidly and transiently induced dephosphorylation/activation of CRTC2, and FSH + TGFβ1 additionally induced late-phase CRTC2 dephosphorylation. Immunofluorescence analysis further confirms FSH ± TGFβ1 promoted CRTC2 nuclear translocation. Using selective inhibitors, we demonstrate that FSH activated CRTC2 in a PKA- and calcineurin-dependent manner, and TGFβ1 acting through its type I receptor (TGFβRI)-modulated FSH action in a calcineurin-mediated and PKA-independent fashion. Next, we investigated the involvement of calcineurin and CRTC2 in FSH and TGFβ1-stimulated steroidogenesis. Calcineurin and TGFβRI inhibitor dramatically reduced the FSH ± TGFβ1-increased progesterone synthesis and protein levels of StAR, P450scc, and 3β-HSD enzyme. Furthermore, chromatin-immunoprecipitation and immunoprecipitation analyses demonstrate that FSH ± TGFβ1 differentially increased CRTC2, CREB, and CBP binding to these steroidogenic genes, and CREB nuclear association with CRTC2 and CBP. In all, this study reveals for the first time that CRTC2 and calcineurin are critical signaling mediators in FSH and TGFβ1-stimulated steroidogenesis in ovarian granulosa cells.

Novel pathways in gonadotropin receptor signaling and biased agonism

Gonadotropins play a central role in the control of male and female reproduction. Selective agonists and antagonists of gonadotropin receptors would be of great interest for the treatment of infertility or as non steroidal contraceptive. However, to date, only native hormones are being used in assisted reproduction technologies as there is no pharmacological agent available to manipulate gonadotropin receptors. Over the last decade, there has been a growing perception of the complexity associated with gonadotropin receptors' cellular signaling. It is now clear that the Gs/cAMP/PKA pathway is not the sole mechanism that must be taken into account in order to understand these hormones' biological actions. In parallel, consistent with the emerging paradigm of biased agonism, several examples of ligand-mediated selective signaling pathway activation by gonadotropin receptors have been reported. Small molecule ligands, modulating antibodies interacting with the hormones and glycosylation variants of the native glycoproteins have all demonstrated their potential to trigger such selective signaling. Altogether, the available data and emerging concepts give rise to intriguing opportunities towards a more efficient control of reproductive function and associated disorders.

The infusion of glucose in ewes during the luteal phase increases the number of follicles but reduces oestradiol production and some correlates of metabolic function in the large follicles

Short-term nutritional supplementation stimulates folliculogenesis in ewes probably by insulin-mediated actions of glucose in the follicle. The aim of this study was to determine the effect of glucose on follicle number and granulosa levels of Aromatase P450 and phosphorylated Akt and AMPK. Twelve Ile-de-France ewes were allocated to two groups; one (n=7) infused with saline and the other (n=5) with glucose (10mM/h) for 72h in the luteal phase. At the end of infusion, ovaries were collected and all follicles >1mm in diameter were dissected to recover granulosa cells. Aromatase P450 and phosphorylated Akt and AMPK were analysed by Western blotting of granulosa cell lysates. Blood plasmas collected before and during the infusions were analysed for progesterone, oestradiol, LH, FSH, glucose, insulin and IGF-I. The infusion of glucose significantly increased follicle number but, significantly reduced Aromatase P450 and phosphorylated Akt and AMPK in granulosa cells. The circulating concentration of glucose rose significantly 3h after the start of the glucose infusion and remained elevated until 27h then fell; the circulating concentration of insulin rose significantly by 3h and remained elevated. The circulating concentration of oestradiol fell significantly by 32h and remained low; the circulating concentrations of LH and FSH were unaffected. These data show that short-term infusion of glucose stimulated follicular growth but decreased Aromatase P450 in granulosa cells. The reduced levels of phosphorylated Akt and AMPK suggest that the phosphatidylinositol 3-kinase pathway has been inhibited by high concentrations of glucose. These data also suggest that there may be functional cross-talk between FSH and insulin signalling in granulosa cells.

Effects of the FSH receptor gene polymorphism p.N680S on cAMP and steroid production in cultured primary human granulosa cells

The study was designed to evaluate in vitro the cellular mechanisms of the single nucleotide polymorphism (SNP) p.N680S of the FSH receptor gene (FSHR) in human granulosa cells (GC) and included patients homozygous for the FSHR SNP (NN/SS) undergoing ovarian stimulation. GC were isolated during oocyte retrieval and cultured for 1–7 days. Basal oestradiol and progesterone concentrations were measured after short-term culture. The kinetics of cAMP, oestradiol and progesterone concentrations in response to various amounts of FSH were analysed in a 6–7 day culture. Basal oestradiol, but not progesterone, concentrations on day 1 of GC culture, were significantly higher in NN compared with SS (P = 0.045), but non-responsive to FSH stimulation. Immunofluorescence microscopy demonstrated the re-appearance of FSHR expression with increasing days in culture. Upon stimulation with FSH, GC cultured for 6–7 days displayed a dose-dependent increase of cAMP, oestradiol and progesterone but no difference in the EC50 values between both variants. Primary long-term GC cultures are a suitable system to study the effects of FSH in vitro. However, the experiments suggest that factors down-stream of progesterone production or external to GC might be involved in the clinically observed differences in an FSHR variant-mediated response to FSH.

The adapter protein APPL1 links FSH receptor to inositol 1,4,5-trisphosphate production and is implicated in intracellular Ca(2+) mobilization

FSH binds to its receptor (FSHR) on target cells in the ovary and testis, to regulate oogenesis and spermatogenesis, respectively. The signaling cascades activated after ligand binding are extremely complex and have been shown to include protein kinase A, mitogen-activated protein kinase, phosphatidylinositol 3-kinase/protein kinase B, and inositol 1,4,5-trisphosphate-mediated calcium signaling pathways. The adapter protein APPL1 (Adapter protein containing Pleckstrin homology domain, Phosphotyrosine binding domain and Leucine zipper motif), which has been linked to an assortment of other signaling proteins, was previously identified as an interacting protein with FSHR. Thus, alanine substitution mutations in the first intracellular loop of FSHR were generated to determine which residues are essential for FSHR-APPL1 interaction. Three amino acids were essential; when any one of them was altered, APPL1 association with FSHR mutants was abrogated. Two of the mutants (L377A and F382A) that displayed poor cell-surface expression were not studied further. Substitution of FSHR-K376A did not affect FSH binding or agonist-stimulated cAMP production in either transiently transfected human embryonic kidney cells or virally transduced human granulosa cells (KGN). In the KGN line, as well as primary cultures of rat granulosa cells transduced with wild type or mutant receptor, FSH-mediated progesterone or estradiol production was not affected by the mutation. However, in human embryonic kidney cells inositol 1,4,5-trisphosphate production was curtailed and KGN cells transduced with FSHR-K376A evidenced reduced Ca(2+) mobilization from intracellular stores after FSH treatment.

A negative allosteric modulator demonstrates biased antagonism of the follicle stimulating hormone receptor

High quality gamete production in males and females requires the pituitary gonadotropin follicle stimulating hormone (FSH). In this report a novel chemical class of small molecule inhibitors of FSH receptor (FSHR) is described. ADX61623, a negative allosteric modulator (NAM), increased the affinity of interaction between (125)I-hFSH and human FSHR (hFSHR) five fold. This form of FSHR occupied simultaneously by FSH and ADX61623 was inactive for cAMP and progesterone production in primary cultures of rat granulosa cells. In contrast, ADX61623 did not block estrogen production. This demonstrates for the first time, biased antagonism at the FSHR. To determine if ADX61623 blocked FSH induction of follicle development in vivo, a bioassay to measure follicular development and oocyte production in immature female rats was validated. ADX61623 was not completely effective in blocking FSH induced follicular development in vivo at doses up to 100mg/kg as oocyte production and ovarian weight gain were only moderately reduced. These data illustrate that FSHR couples to multiple signaling pathways in vivo. Suppression of one pool of FSHR uncouples Gαs and cAMP production, and decreases progesterone production. Occupancy of another pool of FSHR sensitizes granulosa cells to FSH induced estradiol production. Therefore, ADX61623 is a useful tool to investigate further the mechanism of the FSHR signaling dichotomy. This may lead to a greater understanding of the signaling infrastructure which enables estrogen biosynthesis and may prove useful in treating estrogen dependent disease.

Decreased degradation of internalized follicle-stimulating hormone caused by mutation of aspartic acid 6.30(550) in a protein kinase-CK2 consensus sequence in the third intracellular loop of human follicle-stimulating hormone receptor

A naturally occurring mutation in follicle-stimulating hormone receptor (FSHR) gene has been reported: an amino acid change to glycine occurs at a conserved aspartic acid 550 (D550, D567, D6.30(567)). This residue is contained in a protein kinase-CK2 consensus site present in human FSHR (hFSHR) intracellular loop 3 (iL3). Because CK2 has been reported to play a role in trafficking of some receptors, the potential roles for CK2 and D550 in FSHR function were evaluated by generating a D550A mutation in the hFSHR. The hFSHR-D550A binds hormone similarly to WT-hFSHR when expressed in HEK293T cells. Western blot analyses showed lower levels of mature hFSHR-D550A. Maximal cAMP production of both hFSHR-D550A as well as the naturally occurring mutation hFSHR-D550G was diminished, but constitutive activity was not observed. Unexpectedly, when (125)I-hFSH bound to hFSHR-D550A or hFSHR-D550G, intracellular accumulation of radiolabeled FSH was observed. Both sucrose and dominant-negative dynamin blocked internalization of radiolabeled FSH and its commensurate intracellular accumulation. Accumulation of radiolabeled FSH in cells transfected with hFSHR-D550A is due to a defect in degradation of hFSH as measured in pulse chase studies, and confocal microscopy imaging revealed that FSH accumulated in large intracellular structures. CK2 kinase activity is not required for proper degradation of internalized FSH because inhibition of CK2 kinase activity in cells expressing hFSHR did not uncouple degradation of internalized radiolabeled FSH. Additionally, the CK2 consensus site in FSHR iL3 is not required for binding because CK2alpha coimmunoprecipitated with hFSHR-D550A. Thus, mutation of D550 uncouples the link between internalization and degradation of hFSH.

Mapping the follicle-stimulating hormone-induced signaling networks

Follicle-stimulating hormone (FSH) is a central regulator of male and female reproductive function. Over the last decade, there has been a growing perception of the complexity associated with FSH-induced cellular signaling. It is now clear that the canonical Gs/cAMP/PKA pathway is not the sole mechanism that must be considered in FSH biological actions. In parallel, consistent with the emerging concept of biased agonism, several examples of ligand-mediated selective signaling pathway activation by gonadotropin receptors have been reported. In this context, it is important to gain an integrative view of the signaling pathways induced by FSH and how they interconnect to form a network. In this review, we propose a first attempt at building topological maps of various pathways known to be involved in the FSH-induced signaling network. We discuss the multiple facets of FSH-induced signaling and how they converge to the hormone integrated biological response. Despite of their incompleteness, these maps of the FSH-induced signaling network represent a first step toward gaining a system-level comprehension of this hormone's actions, which may ultimately facilitate the discovery of novel regulatory processes and therapeutic strategies for infertility and non-steroidal contraception.

Single-nucleotide polymorphisms in the FSH receptor gene and ovarian performance: future role in IVF

The ovarian response to follicle stimulating hormone (FSH) stimulation in assisted conception cycles is variable. Although it would be beneficial to predict accurately the response of patients to FSH, to date no absolute predictors of ovarian performance have been identified. Recently, there have been a number of studies on the effect of single-nucleotide polymorphisms (SNPs) in the FSH receptor gene and its predictability in ovarian response to FSH stimulation. Several reports have shown that two very common SNPs at positions 307 and 680 in exon 10 of the FSH receptor gene are associated with ovarian response in IVF. The SNPs in exon 10 result in four discrete allelic variants characterised by the amino acid combinations Thr(307)-Asn(680), Ala(307)-Ser(680), Ala(307)-Asn(680) and Thr(307)-Ser(680). Because Thr(307) is almost always in linkage disequilibrium with Asn(680), and Ala(307) almost always with Ser(680), most studies are focussed solely on position 680. Some authors have shown predictability of ovarian response to FSH stimulation in patients with different alleles, while others have refuted this finding. In vitro models have not shown any difference in response among various alleles. Most of the available studies are retrospective, observational. Until now, there is no clear clinical benefit in the screening for SNP before IVF treatment. However, there is the prospect of devising mathematical models using a group of polymorphisms to provide an important tool for improving ovulation induction, especially in poor responders.

Emerging roles for the FSH receptor adapter protein APPL1 and overlap of a putative 14-3-3τ interaction domain with a canonical G-protein interaction site

The interaction of cytoplasmic proteins with intracellular domains of membrane receptors can occur at several opportunities, including: during biosynthesis, while in membrane residency and during internalization and recycling following ligand binding. Since the initial discovery that it interacts with the FSH receptor (FSHR) together with additional members of a potential signaling complex, APPL1 has been shown to interact with a variety of membrane receptors. Recent subcellular localizations of APPL1 place it in dynamic and varied venues in the cell, including at the cell membrane, the nucleus and the early endosomes. Another adapter protein family the 14-3-3 proteins, are largely recognized as binding to phosphorylation sites but recent work demonstrated that in the case of FSHR, the 14-3-3 site overlaps with the canonical G-protein binding site. G-proteins appear to sample the environment and exchange between the membrane and intracellular locales and this binding could be mediated by or modulated by receptor interactions at the 14-3-3 binding site. Observations that multiple proteins can interact with cytoplasmic domains of GPCRs leads to the inescapable conclusion that either the interactions occur via orderly replacement or exchange, or that receptors are simultaneously occupied by a variety of adapters and effectors or even that oligomers of dimeric GPCRs provide for platforms that can simultaneously interact with effectors and adaptors.

Human chorionic gonadotropin stimulates theca-interstitial cell proliferation and cell cycle regulatory proteins by a cAMP-dependent activation of AKT/mTORC1 signaling pathway

In addition to playing a cardinal role in androgen production, LH also regulates growth and proliferation of theca-interstitial (T-I) cells. Here, we show for the first time that LH/human chorionic gonadotropin (hCG) regulates T-I cell proliferation via the mammalian target of rapamycin complex 1 (mTORC1) signaling network. LH/hCG treatment showed a time-dependent stimulation of T-I cell proliferation and phosphorylation of protein kinase B (AKT), ERK1/2, and ribosomal protein (rp)S6 kinase 1 (S6K1), and its downstream effector, rpS6. Pharmacological inhibition of ERK1/2 signaling did not block the hCG-induced phosphorylation of tuberin, the upstream regulator of mTORC1 or S6K1, the downstream target of mTORC1. However, inhibition of AKT signaling completely blocked the hCG response. Furthermore, the AKT-specific inhibitor abolished forskolin (FSK)-stimulated phosphorylation of AKT, tuberin, S6K1, and rpS6. Human CG and FSK-mediated phosphorylation of AKT and downstream targets of mTORC1 were attenuated by inhibition of adenylyl cyclase. Pharmacologic targeting of mTORC1 with rapamycin also abrogated hCG or FSK-induced phosphorylation of S6K1, rpS6, and eukaryotic initiation factor 4E binding protein 1. In addition, hCG or FSK-mediated up-regulation of the cell cycle regulatory proteins cyclin-dependent kinase 4, cyclin D3, and proliferating cell nuclear antigen was blocked by rapamycin. These results were further confirmed by demonstrating that knockdown of mTORC1 using small interfering RNA abolished hCG-mediated increases in cell proliferation and the expression of cyclin D3 and proliferating cell nuclear antigen. Taken together, the present studies show a novel intracellular signaling pathway for T-I cell proliferation involving LH/hCG-mediated activation of the AKT/mTORC1 signaling cascade.

Beta-catenin (CTNNB1) promotes preovulatory follicular development but represses LH-mediated ovulation and luteinization

Wingless-type mouse mammary tumor virus integration site family (WNT)/beta-catenin (CTNNB1) pathway components are expressed in ovarian granulosa cells, direct female gonad development, and are regulated by the pituitary gonadotropins. However, the in vivo functions of CTNNB1 during preovulatory follicular development, ovulation, and luteinization remain unclear. Using a mouse model Ctnnb1((Ex3)fl/fl);Cyp19-Cre (Ctnnb1((Ex3)gc-/-)), expressing dominant stable CTNNB1 in granulosa cells of small antral and preovulatory follicles, we show that CTNNB1 facilitates FSH-induced follicular growth and decreases the follicle atresia (granulosa cell apoptosis). At the molecular level, WNT signaling and FSH synergistically promote the expression of genes required for cell proliferation and estrogen biosynthesis, but decrease FOXO1, which negatively regulates proliferation and steroidogenesis. Conversely, dominant stable CTNNB1 represses LH-induced oocyte maturation, ovulation, luteinization, and progesterone biosynthesis. Specifically, granulosa cells in the Ctnnb1((Ex3)gc)(-/-) mice showed compromised responses to the LH surge and decreased levels of the epidermal growth factor-like factors (Areg and Ereg) that in vivo and in vitro mediate LH action. One underlying mechanism by which CTNNB1 prevents LH responses is by reducing phosphorylation of cAMP-responsive element-binding protein, which is essential for the expression of Areg and Ereg. By contrast, depletion of Ctnnb1 using the Ctnnb1(fl/fl);Cyp19-Cre mice did not alter FSH regulation of preovulatory follicular development or female fertility but dramatically enhanced LH induction of genes in granulosa cells in culture. Thus, CTNNB1 can enhance FSH and LH actions in antral follicles but overactivation of CTNNB1 negatively effects LH-induced ovulation and luteinization, highlighting the cell context-dependent and developmental stage-specific interactions of WNT/CTNNB1 pathway and G protein-coupled gonadotropin receptors in female fertility.

Transactivation of the epidermal growth factor receptor is involved in the lutropin receptor-mediated down-regulation of ovarian aromatase expression in vivo

Ovarian follicular development and differentiation is characterized by dramatic changes in aromatase (Cyp19a1) expression. In preovulatory follicles, activation of the FSH receptor increases aromatase expression until the surge of LH decreases it. Here we provide in vivo evidence that down-regulation of Cyp19a1 by the LH surge requires efficient signaling through the epidermal growth factor receptor (EGFR). The human chorionic gonadotropin (hCG)-induced down-regulation of Cyp19a1 expression in the two different mouse models with inactivating mutations of the EGFR (wa2 and velvet) is impaired but not abolished. The hCG-induced phosphorylation of ovarian ERK1/2, expression of C/EBPbeta, and the phosphorylation of Connexin43 (two downstream targets of ERK1/2 action) are also decreased in these two mouse models. In contrast, disruption of EGFR signaling does not have any affect on the hCG-induced phosphorylation of cAMP response element-binding protein or AKT. This study provides the first in vivo evidence linking the LH receptor, the EGFR, and ERK1/2 as sequential components of a pathway that regulates ovarian Cyp19a1 expression.

Follicle-stimulating hormone and estradiol interact to stimulate glutathione synthesis in rat ovarian follicles and granulosa cells

Glutathione (GSH), the most abundant intracellular nonprotein thiol, is critical for many cellular functions. The rate-limiting step in GSH synthesis is catalyzed by glutamate cysteine ligase (GCL), a heterodimer composed of a catalytic (GCLC) and a modifier (GCLM) subunit. The tissue-specific regulation of GSH synthesis is poorly understood. We showed previously that gonadotropin hormones regulate ovarian GSH synthesis. In the present study, we sought to clarify the ovarian cell type-specific effects of follicle-stimulating hormone (FSH) and estradiol on GSH synthesis. Immature female rats were treated with estradiol to stimulate development of small antral follicles. Granulosa cells (GCs) from these follicles or whole follicles were cultured in serum-free media, with or without FSH and 17beta-estradiol. The GSH and GCLC protein and mRNA levels increased in GCs treated with FSH alone. The effects of FSH on GCLC and GCLM protein and mRNA levels, GCL enzymatic activity, and GSH concentrations in GCs were significantly enhanced by the addition of estradiol. Estradiol alone had no effects on GSH. Dibromo-cAMP mimicked and protein kinase A (PKA) inhibitors prevented FSH stimulation of GCL subunit protein levels. In cultured small antral follicles, FSH stimulated estradiol synthesis and robustly increased GCL subunit mRNA and protein levels and GSH concentrations. The GCL subunit mRNA expression increased in both the granulosa cells and theca cells of follicles with FSH stimulation. These data demonstrate that maximal stimulation of GSH synthesis by FSH in granulosa cells and follicles requires estradiol. Without estradiol, FSH causes lesser increases in GCL subunit expression via a PKA-dependent pathway.

FSH and FOXO1 regulate genes in the sterol/steroid and lipid biosynthetic pathways in granulosa cells

The forkhead box transcription factor FOXO1 is highly expressed in granulosa cells of growing follicles but is down-regulated by FSH in culture or by LH-induced luteinization in vivo. To analyze the function of FOXO1, we infected rat and mouse granulosa cells with adenoviral vectors expressing two FOXO1 mutants: a gain-of-function mutant FOXOA3 that has two serine residues and one threonine residue mutated to alanines rendering this protein constitutively active and nuclear and FOXOA3-mutant DNA-binding domain (mDBD) in which the DBD is mutated. The infected cells were then treated with vehicle or FSH for specific time intervals. Infection of the granulosa cells was highly efficient, caused only minimal apoptosis, and maintained FOXO1 protein at levels of the endogenous protein observed in cells before exposure to FSH. RNA was prepared from control and adenoviral infected cells exposed to vehicle or FSH for 12 and 24 h. Affymetrix microarray and database analyses identified, and real time RT-PCR verified, that genes within the lipid, sterol, and steroidogenic biosynthetic pathways (Hmgcs1, Hmgcr, Mvk, Sqle, Lss, Cyp51, Tm7sf2, Dhcr24 and Star, Cyp11a1, and Cyp19), including two key transcriptional regulators Srebf1 and Srebf2 of cholesterol biosynthesis and steroidogenesis (Nr5a1, Nr5a2), were major targets induced by FSH and suppressed by FOXOA3 and FOXOA3-mDBD in the cultured granulosa cells. By contrast, FOXOA3 and FOXOA3-mDBD induced expression of Cyp27a1 mRNA that encodes an enzyme involved in cholesterol catabolism to oxysterols. The genes up-regulated by FSH in cultured granulosa cells were also induced in granulosa cells of preovulatory follicles and corpora lutea collected from immature mice primed with FSH (equine choriogonadotropin) and LH (human choriogonadotropin), respectively. Conversely, Foxo1 and Cyp27a1 mRNAs were reduced by these same treatments. Collectively, these data provide novel evidence that FOXO1 may play a key role in granulosa cells to modulate lipid and sterol biosynthesis, thereby preventing elevated steroidogenesis during early stages of follicle development.

Role of the phosphatidylinositol-3-kinase and extracellular regulated kinase pathways in the induction of hypoxia-inducible factor (HIF)-1 activity and the HIF-1 target vascular endothelial growth factor in ovarian granulosa cells in response to follicle-stimulating hormone

FSH stimulation of granulosa cells (GCs) results in increased hypoxia-inducible factor (HIF)-1alpha protein levels and HIF-1 activity that is necessary for up-regulation of certain FSH target genes including vascular endothelial growth factor. We report that the role of the phosphatidylinositol (PI)-3-kinase/AKT pathway in increasing HIF-1alpha protein in FSH-stimulated GCs extends beyond an increase in mammalian target of rapamycin-stimulated translation. FSH increases phosphorylation of the AKT target mouse double-minute 2 (MDM2); a phosphomimetic mutation of MDM2 is sufficient to induce HIF-1 activity. The PI3-kinase/AKT target forkhead box-containing protein O subfamily 1 (FOXO1) also effects the accumulation of HIF-1alpha as evidenced by the ability of a constitutively active FOXO1 mutant to inhibit the induction by FSH of HIF-1alpha protein and HIF-1 activity. Activation of the PI3-kinase/AKT pathway in GCs by IGF-I is sufficient to induce HIF-1alpha protein but surprisingly not HIF-1 activity. HIF-1 activity also appears to require a PD98059-sensitive protein (kinase) activity stimulated by FSH that is both distinct from mitogen-activated ERK kinase1/2 or 5 and independent of the PI3-kinase/AKT pathway. These results indicate that FSH-stimulated HIF-1 activation leading to up-regulation of targets such as vascular endothelial growth factor requires not only PI3-kinase/AKT-mediated activation of mammalian target of rapamycin as well as phosphorylation of FOXO1 and possibly MDM2 but also a protein (kinase) activity that is inhibited by the classic ERK kinase inhibitor PD98059 but not ERK1/2 or 5. Thus, regulation of HIF-1 activity in GCs by FSH under normoxic conditions is complex and requires input from multiple signaling pathways.

First evidence of genetic association between AKT2 and polycystic ovary syndrome

OBJECTIVE

Insulin resistance has been reported in up to 70% of women with polycystic ovary syndrome (PCOS). Physiologic and genetic data currently implicate post-insulin receptor signaling defects in substrates such as glycogen synthase kinase 3beta (GSK3beta). The AKT2 gene was chosen as a candidate for PCOS because its product affects glucose metabolism and mitogenic signaling, interacts with GSK3beta, and mediates cell survival in the ovary.

RESEARCH DESIGN AND METHODS

Subjects were recruited from the reproductive endocrinology clinic at the University of Alabama at Birmingham, and control subjects were recruited from the surrounding community; 287 white women with PCOS and 187 white control subjects were genotyped for four single nucleotide polymorphisms (SNPs) in AKT2. Genotyping took place at Cedars-Sinai Medical Center in Los Angeles. SNPs and haplotypes were tested for association with PCOS risk and phenotypic markers of PCOS.

RESULTS

Minor allele carriers of SNPs rs3730051 and rs8100018 had increased odds of PCOS (odds ratio [OR] 2.2, P = 0.004, and 2.4, P = 0.001, respectively). The haplotype T-G-C-T was significantly associated with PCOS (OR 2.0, P = 0.01). Carriers of the risk haplotypes for both AKT2 and GSK3B had a further increased odds of PCOS (OR 3.1, P = 0.005).

CONCLUSIONS

These data suggest that polymorphisms in two components of the insulin signaling pathway, AKT2 and GSK3B, are associated with PCOS. The presence of multiple lesions in a single pathway may confer increased risk.

The luteinizing hormone receptor-activated extracellularly regulated kinase-1/2 cascade stimulates epiregulin release from granulosa cells

We examine the pathways involved in the luteinizing hormone receptor (LHR)-dependent activation of the epidermal growth factor (EGF) network using cocultures of LHR-positive granulosa cells and LHR-negative test cells expressing an EGF receptor (EGFR)-green fluorescent protein fusion protein. Activation of the LHR in granulosa cells results in the release of EGF-like growth factors that are detected by measuring the phosphorylation of the EGFR-green fluorescent protein expressed only in the LHR-negative test cells. Using neutralizing antibodies and real-time PCR, we identified epiregulin as the main EGF-like growth factor produced upon activation of the LHR expressed in immature rat granulosa cells, and we show that exclusive inhibition or activation of the ERK1/2 cascade in granulosa cells prevents or enhances epiregulin release, respectively, with little or no effect on epiregulin expression. These results show that the LHR-stimulated ERK1/2 pathway stimulates epiregulin release.

Functional significance of the signal transduction pathways Akt and Erk in ovarian follicles: in vitro and in vivo studies in cattle and sheep

Background

The intracellular signalling mechanisms that regulate ovarian follicle development are unclear; however, we have recently shown differences in the Akt and Erk signalling pathways in dominant compared to subordinate follicles. The aim of this study was to investigate the effects of inhibiting Akt and Erk phosphorylation on IGF- and gonadotropin- stimulated granulosa and theca cell function in vitro, and on follicle development in vivo.

Methods

Bovine granulosa and theca cells were cultured for six days and stimulated with FSH and/or IGF, or LH in combination with PD98059 (Erk inhibitor) and/or LY294002 (Akt inhibitor) and their effect on cell number and hormone secretion (estradiol, activin-A, inhibin-A, follistatin, progesterone and androstenedione) determined. In addition, ovarian follicles were treated in vivo with PD98059 and/or LY294002 in ewes on Day 3 of the cycle and follicles were recovered 48 hours later.

Results

We have shown that gonadotropin- and IGF-stimulated hormone production by granulosa and theca cells is reduced by treatment with PD98059 and LY294002 in vitro. Furthermore, treatment with PD98059 and LY294002 reduced follicle growth and oestradiol production in vivo.

Conclusion

These results demonstrate an important functional role for the Akt and Erk signalling pathways in follicle function, growth and development.

Selective expression of KrasG12D in granulosa cells of the mouse ovary causes defects in follicle development and ovulation

Activation of the RAS family of small G-proteins is essential for follicle stimulating hormone-induced signaling events and the regulation of target genes in cultured granulosa cells. To analyze the functions of RAS protein in granulosa cells during ovarian follicular development in vivo, we generated conditional knock-in mouse models in which the granulosa cells express a constitutively active KrasG12D. The KrasG12D mutant mice were subfertile and exhibited signs of premature ovarian failure. The mutant ovaries contained numerous abnormal follicle-like structures that were devoid of mitotic and apoptotic cells and cells expressing granulosa cell-specific marker genes. Follicles that proceeded to the antral stage failed to ovulate and expressed reduced levels of ovulation-related genes. The human chorionic gonadotropin-stimulated phosphorylation of ERK1/2 was markedly reduced in mutant cells. Reduced ERK1/2 phosphorylation was due, in part, to increased expression of MKP3, an ERK1/2-specific phosphatase. By contrast, elevated levels of phospho-AKT were evident in granulosa cells of immature KrasG12D mice, even in the absence of hormone treatments, and were associated with the progressive decline of FOXO1 in the abnormal follicle-like structures. Thus, inappropriate activation of KRAS in granulosa cells blocks the granulosa cell differentiation pathway, leading to the persistence of abnormal non-mitotic, non-apoptotic cells rather than tumorigenic cells. Moreover, those follicles that reach the antral stage exhibit impaired responses to hormones, leading to ovulation failure. Transient but not sustained activation of RAS in granulosa cells is therefore crucial for directing normal follicle development and initiating the ovulation process.

Targeted disruption of Pten in ovarian granulosa cells enhances ovulation and extends the life span of luteal cells

FSH activates the phosphatidylinositol-3 kinase (PI3K)/acute transforming retrovirus thymoma protein kinase pathway and thereby enhances granulosa cell differentiation in culture. To identify the physiological role of the PI3K pathway in vivo we disrupted the PI3K suppressor, Pten, in developing ovarian follicles. To selectively disrupt Pten expression in granulosa cells, Ptenfl/fl mice were mated with transgenic mice expressing cAMP response element recombinase driven by Cyp19 promoter (Cyp19-Cre). The resultant Pten mutant mice were fertile, ovulated more oocytes, and produced moderately more pups than control mice. These physiological differences in the Pten mutant mice were associated with hyperactivation of the PI3K/acute transforming retrovirus thymoma protein kinase pathway, decreased susceptibility to apoptosis, and increased proliferation of mutant granulosa cells. Strikingly, corpora lutea of the Pten mutant mice persisted longer than those of control mice. Although the follicular and luteal cell steroidogenesis in Ptenfl/fl;Cyp19-Cre mice was similar to controls, viable nonsteroidogenic luteal cells escaped structural luteolysis. These findings provide the novel evidence that Pten impacts the survival/life span of granulosa/luteal cells and that its loss not only results in the facilitated ovulation but also in the persistence of nonsteroidogenic luteal structures in the adult mouse ovary.

Constitutively active protein kinase A qualitatively mimics the effects of follicle-stimulating hormone on granulosa cell differentiation

Activation of the protein kinase A (PKA) signaling system is necessary for FSH-induced granulosa cell differentiation, but it is not known whether activation of PKA is sufficient to account for the complex pattern of gene expression that occurs during this process. We addressed this question by infecting granulosa cells with a lentiviral vector that directs the expression of a constitutively active mutant of PKA (PKA-CQR) and compared the cellular responses to PKA-CQR with cells stimulated by FSH. Expression of PKA-CQR in undifferentiated granulosa cells resulted in the induction of both estrogen and progesterone production in the absence of cAMP. The stimulatory effects of both PKA-CQR and FSH on estrogen and progesterone production were suppressed by the PKA inhibitor H-89 and were mimicked by PKA-selective cAMP agonists. mRNA levels for P450scc and 3beta-HSD were induced to a similar extent by FSH and PKA-CQR, whereas mRNA levels for P450arom and the LHr were induced to a greater extent by FSH. Microarray analysis of gene expression profiles revealed that the majority of genes appeared to be comparably regulated by FSH and PKA-CQR but that some genes appear to be induced to a greater extent by FSH than by PKA-CQR. These results indicate that the PKA signaling pathway is sufficient to account for the induction of most genes (as identified by microarray analysis), including those of the progesterone biosynthetic pathway during granulosa cell differentiation. However, optimal induction of aromatase, the LHr, and other genes by FSH appears to require activation of additional signaling pathways.

Mutations of the lutropin/choriogonadotropin receptor that do not activate the phosphoinositide cascade allow hCG to induce aromatase expression in immature rat granulosa cells

Using primary cultures of immature rat granulosa cells and adenoviral infections we expressed two mutants of the human lutropin receptor (hLHR) that do not activate the phosphoinositide cascade. One mutant (hLFF) has the extracellular domain of the hLHR and the transmembrane and intracellular domains of the hFSHR. The other (hLHR-L457D) has a leucine to aspartate mutation in residue 457 of transmembrane helix 3. When expressed in immature rat granulosa cells the hLHR stimulates cAMP and inositol phosphate accumulation, transactivates the epidermal growth factor receptor (EGFR), elicits a transient increase in Akt phosphorylation, and a sustained increase in ERK1/2 phosphorylation but aromatase expression is not enhanced. When expressed at comparable densities, hLFF and hLHR-L457D support cAMP accumulation and transient Akt phosphorylation but do not support inositol phosphate accumulation, EGFR transactivation or a sustained phosphorylation of ERK1/2. Cells expressing either of these two mutants respond to hCG with increased aromatase expression. We also show that addition of hCG to cells expressing the hLHR antagonizes the effects of hFSH on aromatase expression whereas addition of hCG to cells expressing the hLHR-L457D mutant does not. These results show that activation of the phosphoinositide cascade is upstream of EGFR transactivation and ERK1/2 phosphorylation and that this pathway is a negative regulator of aromatase expression in granulosa cells.

Inhibition of rat granulosa cell differentiation by overexpression of Galphaq

Activation of FSH and LH receptors in undifferentiated granulosa cells (i.e., no prior exposure to FSH) results in comparable induction of progesterone production, but activation of the LH receptor is less effective than FSH in inducing aromatase and the native LH receptor. Because the LH receptor can also activate the Galphaq signaling pathway, we investigated whether activation of this pathway could be responsible for these differences. Overexpression of Galphaq inhibited FSH induction of both the estradiol and progesterone biosynthetic pathways as well as mRNA levels for cholesterol side-chain cleavage enzyme (P450scc), 3beta-hydroxysteroid dehydrogenase (3beta-HSD), LH receptor (LHr), and P450aromatase (aromatase). This suppression was associated with a reduction (P < 0.05) in FSH-stimulated cAMP production. Lower cAMP levels were not due to reduced FSH receptor (FSHr) mRNA levels or reduced levels of Galphas. Phosphodiesterase (PDE) activity and regulator of G-protein signaling 2 (RGS2) mRNA levels were significantly (P < 0.05) increased by Galphaq, both of which could account for diminished cAMP levels. We conclude that Galphaq signaling pathway inhibits both estradiol and progesterone production comparably and thus activation of this pathway does not seem to account for differences between FSH and LH in the regulation of aromatase and the LH receptor.

Aromatase expression in the ovary: hormonal and molecular regulation

Estrogens are synthesized by the aromatase enzyme encoded by the Cyp19a1 gene, which contains an unusually large regulatory region. In most mammals, aromatase expression is under the control of two distinct promoters a gonad- and a brain-specific promoter. In humans, this gene contains 10 tissue-specific promoters that are alternatively used in various cell types and tumors. Each promoter is regulated by a distinct set of regulatory sequences and transcription factors that bind to these specific sequences. The cAMP/PKA/CREB pathway is considered to be the primary signaling cascade through which the gonad Cyp19 promoter is regulated. Very interestingly, in rat luteal cells, the proximal promoter is not controlled in a cAMP dependent manner. Strikingly, these cells express aromatase at high levels similar to those found in preovulatory follicles, suggesting that alternative and powerful mechanisms control aromatase expression in luteal cells and that the rat corpus luteum represents an important paradigm for understanding alternative controls of the aromatase gene. Here, the molecular and cellular mechanisms controlling the expression of the aromatase gene in granulosa and luteal cells are discussed.