A role of insulin-like growth factor I for follicle-stimulating hormone receptor expression in rat granulosa cells

Molecular crosstalk between insulin-like growth factors and follicle-stimulating hormone in the regulation of granulosa cell function

Background

The last phase of folliculogenesis is driven by follicle-stimulating hormone (FSH) and locally produced insulin-like growth factors (IGFs), both essential for forming preovulatory follicles.

Methods

This review discusses the molecular crosstalk of the FSH and IGF signaling pathways in regulating follicular granulosa cells (GCs) during the antral-to-preovulatory phase.

Main findings

IGFs were considered co-gonadotropins since they amplify FSH actions in GCs. However, this view is not compatible with data showing that FSH requires IGFs to stimulate GCs, that FSH renders GCs sensitive to IGFs, and that FSH signaling interacts with factors downstream of AKT to stimulate GCs. New evidence suggests that FSH and IGF signaling pathways intersect at several levels to regulate gene expression and GC function.

Conclusion

FSH and locally produced IGFs form a positive feedback loop essential for preovulatory follicle formation in all species. Understanding the mechanisms by which FSH and IGFs interact to control GC function will help design new interventions to optimize follicle maturation, perfect treatment of ovulatory defects, improve in vitro fertilization, and develop new contraceptive approaches.

Plane of nutrition and FSH-induced superovulation affect the expression of steroid hormone receptors and growth factors in caruncular tissue of non-pregnant sheep

Implantation is a critical step in the establishment of pregnancy and an important part of embryo-maternal contact. Uterine receptivity can be affected by changes in body condition and the maternal endocrine milieu, including those caused by the use of exogenous gonadotropins in controlled ovarian hyperstimulation to induce the development of multiple follicles. This study demonstrates the effects of FSH-mediated ovarian hyperstimulation on the caruncles of ewes under various feeding regimes. Sheep were classified into 3 categories: control fed (CF), overfed (OF), or underfed (UF). In each group, animals were superovulated with FSH or injected with a saline solution (non-treated control). Uterine caruncles were collected at the early (d 5) and mid-luteal phase (d 10) of the estrous cycle. The transcript levels of steroid hormone receptors (ESR1, ESR2, PGR) and growth factors (IGF1, IGF2, VEGFA) were investigated and their expression localized by immunohistochemical staining. As for the main findings, day of the estrous cycle affected expression of ESR1, IGF1 and IGF2, but not of ESR2, PGR and VEGFA; both feeding and superovulation had modulatory effects, with feeding (UF/OF) stimulating expression of all genes studied, and superovulation altering expression of some genes, eg IGF1, PGR and ESR1 and ESR2, in CF animals. Similarly, feeding (UF/OF) altered responsiveness to superovulation for PGR on d 5 and ESR1/ESR2 on d 5 and/or 10. Our data emphasize possible effects of dietary and/or hormonal stimuli on uterine physiology, which may affect pregnancy outcomes by disrupting uterine functionality.

A polymorphism in the transcriptional regulatory region strongly influences ovine FSHR mRNA decay

Follicle-stimulating hormone receptor (FSHR) is an important G protein-coupled receptor, which is required for steroidogenesis, follicular development and female infertility. Here, we report a novel polymorphism in the 3'-UTR that strongly influences ovine FSHR mRNA decay. The partial 3'-UTR sequence of Hu sheep FSHR gene was isolated and characterized, and a polymorphism (c.2327A>G) was identified. Luciferase assay and qRT-PCR showed that c.2327A>G polymorphism in the 3'-UTR exerts a strong regulatory role in FSHR transcription. This regulatory role is achieved by affecting FSHR mRNA decay. Furthermore, the c.2327A>G mutation in the 3'-UTR influences ARE (AU-rich element, a cis-acting element promoting mRNA decay)-mediated mRNA decay of Hu sheep FSHR gene. Together, our study identified a novel polymorphism and elucidated a new mechanism underlying transcriptional regulation of FSHR in mammals.

Folliculogenic factors in photoregressed ovaries: Differences in mRNA expression in early compared to late follicle development

The early stages of ovarian folliculogenesis generally progress independent of gonadotropins, whereas later stages require signaling initiated by FSH. In Siberian hamsters, cycles of folliculogenesis are mediated by changes in photoperiod which depress the hypothalamic pituitary gonadal axis. Reduced gonadotropins lead to decreases in mature follicle development and ovulation; however, early stages of folliculogenesis have not been explored in regressed ovaries. We hypothesized that intraovarian factors that contribute predominantly to later stages of folliculogenesis would react to changes in photoperiod, whereas factors contributing to earlier stages would not change. To probe if the early stages of folliculogenesis continue in the photoinhibited ovary while late stages decline, we measured the mRNA abundance of factors that interact with FSH signaling (Fshr, Igf1, Cox2) and factors that can function independently of FSH (c-Kit, Kitl, Foxo3, Figla, Nobox, Sohlh1, Lhx8). While plasma FSH, antral follicles, and corpora lutea numbers declined with exposure to inhibitory photoperiod, the numbers of primordial, primary, and secondary follicles did not change. Expression of factors that interact with FSH signaling changed with changes in photoperiod; however, expression of factors that do not interact with FSH were not significantly altered. These results suggest that the photoinhibited ovary is not completely quiescent, as factors important for follicle selection and early follicle growth are still expressed in regressed ovaries. Instead, the lack of gonadotropin support that characterizes the non-breeding season appears to inhibit only final stages of folliculogenesis in Siberian hamsters.

Physiological Adaptations to Milk Production that Affect the Fertility of High Yielding Dairy Cows

The high yielding dairy cow is expected to produce a substantial milk output every year and at the same time to conceive and maintain a pregnancy to term. To fulfil lifetime production potential a balance between yield, fertility and other influential factors has to be achieved. Any inability on the part of the management system to identify and rectify problems or on the part of the cow to cope with metabolic demands invariably results in economic or welfare issues. Our studies of high yielding dairy cows have revealed that some animals are capable of normal reproductive function whilst others are classic repeat breeders (requiring 3+ services per conception) or simply fail to rebreed. It is well established that the somatotrophic axis (growth hormone and insulin-like growth factors) drives lactation in ruminants but it is also intimately involved in reproductive processes. An awareness of metabolic adaptations to lactation that impact on reproduction in dairy cows is needed for appropriate management.

The objective of our studies was to explore the metabolic profiles of high yielding dairy cows to identify factors influencing their ovarian function and fertility, hence to characterise the physiological adaptations involved. Our studies revealed different relationships between progesterone profile categories and metabolic status post partum. Delayed ovulation (DOV) or persistent corpora lutea (PCL) may be an appropriate response to a nutritional state or physiological situation and it may therefore be inaccurate to refer to these as ‘abnormal’. Whilst associated with high milk yields, not all profile categories detrimentally affected fertility parameters. Delayed ovulation postcalving (DOV1) was identified as the most prevalent abnormal profile encountered in first lactation high yielding cows. This may have occurred because the cows were not yet physically mature and unable to sustain both milk production and growth. The condition lasted long enough (71 ± 8.3 days from calving) to have a detrimental impact on their overall fertility parameters and was associated with significant physiological changes, representative of tissue mobilisation. Although the incidence of persistent luteal phases (PCL1 and PCL2) in dairy cows is increasing, this condition was not found to have any substantial detrimental effects on fertility or production parameters of the primiparous or multiparous cows in these studies. The main reproductive problems in our high yielding primiparous and multiparous cows appeared to be a failure to ovulate and conceive at the expected time or to maintain a pregnancy. These situations were associated predominantly with high milk yields and low concentrations of plasma IGF-I. A failure to ovulate appears to occur when body reserves are mobilised to maintain milk yield at the expense of reproduction and seems most likely to occur in primiparous high yielding cows or those experiencing GH-resistance (low IGF-I) due to excessive body condition loss, reduced feed intakes and factors such as stress and disease. More detailed investigations of dietary means of increasing IGF-I and optimising insulin concentrations, targeted at important reproductive times, are required in high yielding dairy cows, to aid in their management.

Expression of the gonadotropin receptors during follicular development

Background

Gonadotropins induce follicular development that leads to ovulation and luteinization. In women, the level of gonadotropins, along with the expression of their receptors, changes dynamically throughout the menstrual cycle. This study aimed to clarify the mechanisms underlying these phenomena.

Methods

The literature was reviewed, including that published by the authors.

Main findings (Results)

Follicle‐stimulating hormone receptor expression in the granulosa cells was induced by androgens that were derived from growth differentiation factor‐9‐stimulated theca cells. In the theca cells, luteinizing hormone receptor (LHR) expression was noted from their appearance. In the granulosa cells, follicle‐stimulating hormone (FSH) stimulation was essential for LHR expression. However, FSH alone was not sufficient to respond to the luteinizing hormone (LH) surge for oocyte maturation, ovulation, and subsequent luteinization. To achieve these stages, various local factors that were derived from the granulosa and theca cells in response to FSH and LH stimulation had to work synergistically in an autocrine/paracrine manner to strongly induce LHR expression. Following the LH surge, the LHR expression decreased markedly; miRNAs were involved in this transient LHR downregulation. Following ovulation, LHR expression drastically increased again toward luteinization.

Conclusion

The expression of gonadotropin receptors is controlled by sophisticated and complicated systems; a breakdown of this system could lead to ovulation disorders.

Reproductive endocrinology of vitamin D

Vitamin D is a versatile hormone with several functions beyond its well-established role in maintenance of skeletal health and calcium homeostasis. The effects of vitamin D are mediated by the vitamin D receptor, which is expressed together with the vitamin D metabolizing enzymes in the reproductive tissues. The reproductive organs are therefore responsive to and able to metabolize vitamin D locally. The exact role remains to be clarified but several studies have suggested a link between vitamin D and production/release of reproductive hormones into circulation, which will be the main focus of this review. Current evidence is primarily based on small human association studies and rodent models. This highlights the need for randomized clinical trials, but also functional animal and human in vitro studies, and larger, prospective cohort studies are warranted. Given the high number of men and women suffering from reproductive problems and abnormal endocrinology research addressing the role of vitamin D in reproductive endocrinology may be of clinical importance.

RNA-seq based gene expression analysis of ovarian granulosa cells exposed to zearalenone in vitro: significance to steroidogenesis

Zearalenone (ZEA) is a natural contaminant of various food and feed products representing a significant problem worldwide. Since the occurrence of ZEA in grains and feeds is frequent, the present study was carried out to evaluate the possible effects of ZEA on steroid production and gene expression of porcine granulosa cells, using RNA-seq analysis. Porcine granulosa cells were administered 10 μM and 30 μM ZEA during 72 h of culture in vitro. Following ZEA treatment the gene expression profile of control and exposed granulosa cells was compared using RNA-seq analysis. The results showed that in the exposed granulosa cells ZEA significantly altered the transcript levels, particularly steroidogenesis associated genes. Compared with the control group, 10 μM and 30 μM ZEA treatment significantly increased the mRNA expression of EDN1, IER3, TGFβ and BDNF genes and significantly reduced the mRNA expression of IGF-1 and SFRP2 genes. In particular, ZEA significantly decreased the expression of genes essential for estrogen synthesis including FSHR, CYP19A1 and HSD17β in granulosa cells. Furthermore, Q-PCR and Western-blot analysis also confirmed reduced expression of these genes in ZEA exposed granulosa cells. These effects were associated with a significant reduction of 17β-estradiol concentrations in the culture medium of granulosa cells. Collectively, these results demonstrated a concretely deleterious effect of ZEA exposure on the mRNA expression of steroidogenesis related genes and the production of steroid hormones in porcine ovarian granulosa cells in vitro.

The emerging role of insulin-like growth factors in testis development and function

The insulin-like family of growth factors (IGFs) - composed of insulin, and insulin-like growth factors I (IGF1) and II (IGF2) - provides essential signals for the control of testis development and function. In the testis, IGFs act in an autocrine-paracrine manner but the extent of their actions has been underestimated due to redundancies at both the ligand and receptor levels, and the perinatal lethality of constitutive knockout mice. This review synthesizes the current understanding of how the IGF system regulates biological processes such as primary sex determination, testis development, spermatogenesis and steroidogenesis, and highlights the questions that remain to be explored.

On the origin of information in epigenetic structures in metazoans

Epigenetic inheritance implies the existence of epigenetic information. Great progress has been made in recent years in understanding the role of the changes in epigenetic structures (methylated DNA, histone acetylation/deacetylation and chromatin remodelling) as well as the role of miRNA (MIR) expression patterns in epigenetic processes. However, as of yet, we do not have a satisfactory understanding of the origin of epigenetic information stored in, and conveyed by, these structures. We do not know whether these structures are the ultimate source of the information or whether they are simply media for storing and transmitting epigenetic information for gene expression from upstream sources to the phenotype. Herein an attempt is made to ascertain the ultimate sources of the epigenetic information they contain and transmit by tracing back the causal chain leading to the changes in epigenetic structures.

Insulin influences developmental competence of bovine oocytes cultured in α-MEM plus follicle-simulating hormone

The aim of this study was to evaluate the dose-response effect of insulin, plus follicle-simulating hormone (FSH) at a fixed concentration, in a serum-free defined culture medium (DCM) on the in vitro maturation of bovine cumulus-oocyte complexes (COCs). For oocyte nuclear maturation, the expression levels of GDF9, GLUT1, PRDX1 and HSP70.1 transcripts related to oocyte and embryo developmental competence were analysed. For in vitro maturation (IVM), cumulus-oocyte complexes from slaughterhouse ovaries were distributed into four groups based on insulin concentration added to serum-free DCM, which was composed of alpha minimum essential medium (α-MEM), as basal medium: (1) DCM control: 0 ng/ml; (2) DCM1: 1 ng/ml; (3) DCM10: 10 ng/ml; and (4) DCM100: 100 ng/ml. After IVM, the nuclear status of a sample of oocytes was analysed and the other oocytes were submitted for in vitro fertilization (IVF) and in vitro culture (IVC). Different concentrations of insulin did not affect significantly the nuclear maturation and cleavage rate (72 h post-insemination) across all groups. Blastocyst rate (192 h post-insemination) did not differ in DCM control (24.3%), DCM1 (27.0%) and DCM10 (26.3%) groups, but the DCM100 (36.1%) group showed a greater blastocyst rate (P 0.05) was observed at the different insulin concentrations. The results indicated that insulin added to DCM influenced levels of transcripts related to cellular stress (HSP70-1 and PRDX1) and oocyte competence (GDF9) in bovine oocytes and at higher concentrations enhanced blastocyst production.

Computational modelling of bovine ovarian follicle development

Background

The development of ovarian follicles hinges on the timely exposure to the appropriate combination of hormones. Follicle stimulating hormone (FSH) and luteinizing hormone (LH) are both produced in the pituitary gland and are transported via the blood circulation to the thecal layer surrounding the follicle. From there both hormones are transported into the follicle by diffusion. FSH-receptors are expressed mainly in the granulosa while LH-receptors are expressed in a gradient with highest expression in the theca. How this spatial organization is achieved is not known. Equally it is not understood whether LH and FSH trigger distinct signalling programs or whether the distinct spatial localization of their G-protein coupled receptors is sufficient to convey their distinct biological function.

Results

We have developed a data-based computational model of the spatio-temporal signalling processes within the follicle and (i) predict that FSH and LH form a gradient inside the follicle, (ii) show that the spatial distribution of FSH- and LH-receptors can arise from the well known regulatory interactions, and (iii) find that the differential activity of FSH and LH may well result from the distinct spatial localisation of their receptors, even when both receptors respond with the same intracellular signalling cascade to their ligand.

Conclusion

The model integrates the large amount of published data into a consistent framework that can now be used to better understand how observed defects translate into failed follicle maturation.

An essential role for insulin and IGF1 receptors in regulating sertoli cell proliferation, testis size, and FSH action in mice

Testis size and sperm production are directly correlated to the total number of adult Sertoli cells (SCs). Although the establishment of an adequate number of SCs is crucial for future male fertility, the identification and characterization of the factors regulating SC survival, proliferation, and maturation remain incomplete. To investigate whether the IGF system is required for germ cell (GC) and SC development and function, we inactivated the insulin receptor (Insr), the IGF1 receptor (Igf1r), or both receptors specifically in the GC lineage or in SCs. Whereas ablation of insulin/IGF signaling appears dispensable for GCs and spermatogenesis, adult testes of mice lacking both Insr and Igf1r in SCs (SC-Insr;Igf1r) displayed a 75% reduction in testis size and daily sperm production as a result of a reduced proliferation rate of immature SCs during the late fetal and early neonatal testicular period. In addition, in vivo analyses revealed that FSH requires the insulin/IGF signaling pathway to mediate its proliferative effects on immature SCs. Collectively, these results emphasize the essential role played by growth factors of the insulin family in regulating the final number of SCs, testis size, and daily sperm output. They also indicate that the insulin/IGF signaling pathway is required for FSH-mediated SC proliferation.

Feed restriction as a biostimulant of the production of oocyte, their quality and GDF-9 gene expression in rabbit oocytes

The use of short-term feed restriction (R) without or with subsequent refeeding (F) as biostimulant of rabbit fertility was examined in this study. A total of 40 mature, non-pregnant, non-lactating New Zealand white female rabbits were allocated to five treatments. The rabbits were individually caged and fed a complete pelleted diet (16.7% CP; 13.1 CF; 2490kcalDE/kg). Rabbits on the control (C) treatment received 150g/d of the diet. Two groups of 8 rabbits received 70% of the control daily feed intake (105g/d; moderate restriction; M) and the other two groups received 50% of the control feed intake (75g/d; severe restriction; S) for 21d. At the end of this period, one group each of M and S fed rabbits were slaughtered for oocyte recovery. Rabbits in the remaining three groups (C, MF and SF) were retained for a further 8d before slaughter and fed the control level of the diet during this period. The effects on body weight, oocyte number and quality, GDF-9 gene expression in oocytes, and changes in serum levels of leptin and IGF-1 were recorded. Initial mean body weights were not significantly different ranging from 2.50±0.33kg (S) to 2.58±0.24kg (C). After 3wk on treatment the C rabbits were significantly heavier (2.65±0.32kg; P<0.05) than rabbits on the M (2.26±0.33kg) or S (2.10±0.33kg) treatments. Following 8d of refeeding, the remaining group of S treated rabbits (SF) were still significantly lighter (2.40±0.21kg; P<0.05) than C (2.71±0.31kg) with MF rabbits having an intermediate weight (2.50±0.20kg). The number of mature grade A oocytes recovered per ovary was significantly lower for control (3.3±0.35) than the refed treatments (MF 4.0±0.30; SF 4.5±0.39; P<0.05). Semi-quantitative PCR analysis of GDF-9 expression showed that control mature grade A oocytes had significantly lower levels of expression (1.27±0.20; P<0.05) than those of refed rabbits (MF 1.60±0.10; SF 1.39±0.01). Leptin and IGF-1 values for refed rabbits were significantly higher (P<0.05) than at the end of feed restriction and the start point. It was concluded that this biostimulant method has the potential to improve the fertility of rabbits.

cAMP-dependent regulation of ovulatory response genes is amplified by IGF1 due to synergistic effects on Akt phosphorylation and NF-κB transcription factors

Granulosa cells play a crucial role as mediator of the LH-dependent ovulatory response. The intraovarian factor IGF1 is produced by ovarian somatic cells of healthy follicles during the ovulatory response. The objective of this study was to identify mechanisms by which IGF1, alone or in combination with LH, regulates the expression of genes in granulosa cells, which are crucial for ovulation. To achieve this objective, short-term, primary murine granulosa cell cultures were treated for 2-8  h with 1 mM 8-bromoadenosine 3',5'-cAMP to mimic the LH surge and/or 100  ng/ml IGF1. While cAMP induced significant increases in the expression of important ovulatory response genes including amphiregulin (Areg), epiregulin (Ereg), betacellulin (Btc), or interleukin 6 (Il6), IGF1 alone had no effect. However, co-treatment of cells with IGF1 and cAMP had a synergistic effect on Areg, Ereg, Btc, and Il6 mRNA abundance. Pretreatment of granulosa cells with the MEK1/2 inhibitor U0126 demonstrated that cAMP-dependent increases in Areg, Ereg, Btc, and Il6 were mediated by extracellular regulated kinase 1/2 phosphorylation. However, western blot analyses coupled with pretreatment of cells with the PI3K inhibitor LY294002 indicated that the synergistic effect of cAMP and IGF1 on transcript levels was due in part to cooperative increases in Akt phosphorylation. Western blot analyses also demonstrated that IGF1 and the combined treatment of cAMP and IGF1 decreased NF-κB p65 phosphorylation and increased NF-κB p52 levels. Together, these data indicate that IGF1 may amplify cAMP-dependent regulation of ovulatory response gene expression above an important threshold level and therefore represents a novel role for IGF1 during ovulation.

Hematopoietic-Prostaglandin D2 synthase through PGD2 production is involved in the adult ovarian physiology

Background

The prostaglandin D2 (PGD2) pathway is involved in numerous biological processes and while it has been identified as a partner of the embryonic sex determining male cascade, the roles it plays in ovarian function remain largely unknown. PGD2 is secreted by two prostaglandin D synthases (Pgds); the male-specific lipocalin (L)-Pgds and the hematopoietic (H)-Pgds.

Methods

To study the expression of the Pgds in the adult ovary, in situ hybridization were performed. Then, to evaluate the role of H-Pgds produced PGD2 in the ovarian physiology, adult female mice were treated with HQL-79, a specific inhibitor of H-Pgds enzymatic activity. The effects on expression of the gonadotrophin receptors FshR and LhR, steroidogenic genes Cyp11A1, StAR and on circulating progesterone and estradiol, were observed.

Results

We report the localization of H-Pgds mRNA in the granulosa cells from the primary to pre-ovulatory follicles. We provide evidence of the role of H-Pgds-produced PGD2 signaling in the FSH signaling through increased FshR and LhR receptor expression. This leads to the activation of steroidogenic Cyp11A1 and StAR gene expression leading to progesterone secretion, independently on other prostanoid-synthetizing mechanisms. We also identify a role whereby H-Pgds-produced PGD2 is involved in the regulation of follicular growth through inhibition of granulosa cell proliferation in the growing follicles.

Conclusions

Together, these results show PGD2 signaling to interfere with FSH action within granulosa cells, thus identifying an important and unappreciated role for PGD2 signaling in modulating the balance of proliferation, differentiation and steroidogenic activity of granulosa cells.

IGF1 induces up-regulation of steroidogenic and apoptotic regulatory genes via activation of phosphatidylinositol-dependent kinase/AKT in bovine granulosa cells

IGF1, a potent stimulator of cellular proliferation, differentiation and development, regulates granulosa cell steroidogenesis and apoptosis during follicular development. Depending upon species and stage of follicular growth, IGF1 acts on granulosa cell steroidogenesis either alone or together with FSH. We examined the mechanism of action of IGF1 in bovine granulosa cells in serum-free culture without insulin to determine its potential role in the regulation of steroidogenic and apoptotic regulatory gene expression and to investigate the interaction of FSH with IGF1 on this mechanism. Bovine granulosa cells treated with IGF1 demonstrated a significant increase in 17beta-oestradiol (OE(2)) production, cell number and in mRNA expression of CYP11A1, HSD3B1, CYP19A1, BAX, type 1 IGF receptor (IGF1R) and FSHR, while FSH alone had no significant effects. IGF1 or FSH alone or both together had no effect on BCL2 expression. IGF1 with FSH resulted in a synergistic increase in granulosa cell number and in mRNA expression of CYP19A1 and IGF1R without altering OE(2) production. IGF1 stimulated the phosphoinositide 3'-OH kinase (PI3K) but not the MAPK pathway in granulosa cells, as evidenced by increased phosphorylation of AKT but not extracellular-regulated kinase 1/2. Addition of the PI3K pathway inhibitor LY294002 (but not the MAPK pathway inhibitor PD98059) abrogated the increased expression of genes induced by IGF1. IGF1 therefore up-regulates the steroidogenic and apoptotic regulatory genes via activation of PI3K/AKT in bovine granulosa cells. The synergistic action of IGF1 with FSH is of likely key importance for the development of small antral follicles before selection; subsequently, other factors such as LH may also become necessary for continued cell survival.

Overexpression of follicle-stimulating hormone receptor facilitates the development of ovarian epithelial cancer

We previously showed that the expressing level of FSH receptor (FSHR) increased from ovarian epithelial inclusions (OEIs) to benign ovarian epithelial tumors (OETs) and to borderline OETs, whereas FSHR levels decreased with an increase in carcinoma grade. The aim of this study was to investigate the role of FSHR in OET development. MCV152 cells with FSHR overexpression showed an increased cellular proliferation and invasive capacity, which was associated with reduced levels of prohibitin and RII-beta expression and increased levels of HER-2/neu, c-Myc, and EGFR expression. Overexpression of FSHR may be associated with an elevated level of OET cell proliferation via an enhanced activity of potential oncogenic pathways. Therefore, the findings in this study suggest that overexpression of FSHR may play a role in OET development.

Inhibin A inhibits follicle-stimulating hormone (FSH) action by suppressing its receptor expression in cultured rat granulosa cells

Inhibin has long been considered as a suppresser of follicle-stimulating hormone (FSH) secretion from anterior pituitary through pituitary-gonad negative feedback to regulate follicle development. We demonstrated that addition of inhibin A could significantly suppress FSH-induced FSHR mRNA level in cultured rat granulosa cells (GCs) measured by real-time PCR. The inhibin A exerted its action mainly by inhibiting FSHR promoter activity. Furthermore, exogenous inhibin A could dramatically decrease FSH-induced P450arom and P450scc level and suppress progesterone and estradiol production in the cultured GCs, but it did not decrease forskolin-induced steroidogenesis, indicating that the inhibitory effect of inhibin A on FSH action may be upstream of cAMP signaling. Inhibin A was also capable of suppressing FSH-induced expression of steroidogenic factor 1 (SF-1) and androgen receptor, but stimulating DAX-1 expression in the culture. Our study has provided new evidence to show that inhibin A is capable of feedback antagonizing FSH action on GCs by reducing FSHR expression at ovarian level via a short feedback loop. Transcriptional factor receptors, such as SF-1, AR and DAX-1 were involved in this regulation.

Crucial role of estrogen receptor-alpha interaction with transcription coregulators in follicle-stimulating hormone and transforming growth factor beta1 up-regulation of steroidogenesis in rat ovarian granulosa cells

This study was to explore estrogen receptor (ER) involvement in FSH and TGFbeta1-stimulated steroidogenesis in rat ovarian granulosa cells. We first determined the specific involvement of ERalpha and ERbeta in the process, and then investigated the molecular interaction of ERalpha and transcription coregulators in FSH and TGFbeta1 up-regulation of steroidogenic gene expression. Primary culture of ovarian granulosa cells from antral follicles of gonadotropin-primed immature rats was used. Interestingly, a selective ERalpha antagonist methyl-piperidino-pyrazole (MPP) [like ER antagonist ICI-182,780 (ICI)] decreased FSH +/- TGFbeta1-stimulated progesterone production, whereas an androgen receptor antagonist hydroxyflutamide and particularly a selective ERbeta antagonist 4-[2-Phenyl-5,7-bis(trifluoromethyl) pyrazolo [1,5-a] pyrimidin-3-yl] phenol had no significant effect. Consistent with this, a selective ERbeta agonist diarylpropionitrile (unlike 17beta-estradiol) also had no effect on FSH +/- TGFbeta1-stimulated progesterone production. Furthermore, a selective ERalpha agonist 4,4',4''-(4-Propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (like 17beta-estradiol) enhanced FSH-stimulated progesterone production, and this was abolished by pretreatment with MPP. Immunoblotting and chromatin immunoprecipitation analyses indicate that MPP/ICI suppression of FSH +/- TGFbeta1 action is partly attributed to the reduced ERalpha-mediated expression of Hsd3b and Cyp11a1 genes, but not steroidogenic acute regulatory protein. Furthermore, FSH +/- TGFbeta1 increased ERalpha association with histone acetylases (CBP and SRC-1) and coactivator of peroxisome proliferator-activated receptor gamma (PGC-1alpha), and MPP/ICI dramatically reduced these interactions. In addition, FSH +/- TGFbeta1 increased CBP, SRC-1, and PGC-1alpha binding to Hsd3b and Cyp11a1 genes. Together, we demonstrate for the first time that ERalpha interaction with transcription coregulators, histone acetylases (CBP/SRC-1), and PGC-1alpha is crucial to FSH and TGFbeta1-up-regulated expression of Hsd3b and Cyp11a1, and, thus, progesterone production in rat ovarian granulosa cells.

Effects of bushen tiaochong recipe containing serum on ovarian granulosa cell proliferation, steroidogenesis and associated gene expression in rats

OBJECTIVE

To observe the effect of bushen tiaochong recipe (BSTCR) on rats' ovarian granulosa cell (GC) proliferation, steroidogenesis and follicle-stimulating hormone receptor (FSHR), and insulin-like growth factor-1 (IGF-1) mRNA expression using serum pharmacological method.

METHODS

Rats' GCs were incubated with 10% blank serum (as negative control group), follicle-stimulating hormone (FSH)-containing serum (S-FSH, as positive control group), or BSTCR (in different dosages) containing serum (S-BSTCR, as the BSTCR groups) for 48 h. 3H-TdR incorporation was then performed; DNA was measured to analyze the distribution of GCs in the cell cycle and their proliferation index (PI) using a flow cytometer; estradiol (E2) and progesterone (P) content in the culture fluid were examined by radioimmunoassay; and levels of FSHR and IGF-1 mRNA expression in GCs were measured by real-time RT-PCR.

RESULTS

A dose-dependent increase of 3H-TdR incorporation in GC was shown in the BSTCR groups. Cells in G0/G1 phase had markedly less, while those in S phase had a significantly higher increase in the BSTCR groups compared with the negative control group. A high value of PI was also shown in the BSTCR groups, especially in the high dose group where the influence of cell proliferation was stronger than that in the positive control group. The levels of E2 and P in the BSTCR groups of all dosages were significantly higher than those in the negative control group, and did not show any significant difference compared with those in the positive control group. Levels of FSHR and IGF-1 mRNA expression in the BSTCR groups increased in a dose-dependent manner at levels higher than those in the negative control group.

CONCLUSION

S-BSTCR can obviously stimulate the proliferation and steroidogenesis of ovarian GCs. It is speculated that BSTCR could play a regulatory action on ovarian function through two different pathways of endocrine and autocrine by promoting FSHR and IGF-1 mRNA expression.

Effects of Fusarium mycotoxins on steroid production by porcine granulosa cells

Fusarium mycotoxins, such as trichothecenes and zearalenone, are common grain and foodstuffs contaminants. Some of these like deoxynivalenol (DON) can negatively impact pregnancy success in swine, but evidence for direct ovarian effects of DON, zearalenone, and its major metabolite, alpha-zearalenol (ZEA) is meager. To evaluate the effects of two mycotoxins, DON and ZEA on porcine granulosa cell(s) (GC) proliferation, steroidogenesis and gene expression, pig GC from small follicles (1-5mm) were cultured for 2 days in 5% fetal bovine serum and 5% porcine serum-containing medium followed by 2 days in serum-free medium containing control (no mycotoxins) or mycotoxins (at various doses/combinations). Both DON and ZEA had biphasic effects on IGF-I-induced estradiol production, increasing estradiol production at smaller doses and inhibiting at larger doses. ZEA at 3,000 ng/mL (9.37 microM) increased IGF-I-induced progesterone production and at 30 ng/mL (0.0937 microM) and 300 ng/mL (0.937 microM) were without effect, but these doses of ZEA increased FSH-induced progesterone production. ZEA at 3,000 ng/mL inhibited FSH plus IGF-I-induced CYP19A1 and CYP11A1 mRNA abundance. DON inhibited progesterone production at 100 ng/mL (0.337 microM) and 1,000 ng/mL (3.37 microM) but at 10 ng/mL (0.0337 microM) was without effect. DON at 1,000 ng/mL (but not at 10 ng/mL) completely inhibited FSH plus IGF-I-induced CYP19A1 and CYP11A1 mRNA abundance. The concomitant treatment of ZEA had little effect on the dose response to DON. DON increased IGF-I-induced cell numbers at 10 and 100 ng/mL and inhibited cell numbers at 1,000 ng/mL, whereas ZEA had no effect on GC numbers. Only a combined treatment of DON and ZEA increased serum-induced cell proliferation. In conclusion, mycotoxins have direct dose-dependent effects on GC proliferation, steroidogenesis and gene expression. These direct ovarian effects could be one mechanism whereby contaminating Fusarium mycotoxins in feedstuffs could impact reproductive performance in swine.

Akt and Erk signal transduction pathways are early markers of differentiation in dominant and subordinate ovarian follicles in cattle

Dominant follicles are those that continue to develop and have the potential to ovulate while subordinate follicles regress. Characteristics of dominant follicles include a larger diameter, higher intrafollicular estradiol, and lower IGF-binding protein (IGFBP)-4 concentrations compared with other cohort follicles. Follicle development is regulated by endocrine hormones that act via intracellular signaling pathways. Here, we show the differences in Akt, Erk, c-Jun N-terminal protein kinase, and p-38 signaling pathways between dominant and subordinate follicles at the dominance stage of the follicle wave. However, earlier in the follicle wave (dominant follicle selection), there were only differences in the levels of Akt and Erk signal transduction proteins among dominant and subordinate follicles. Using this profile of Akt and Erk protein expression in granulosa and theca cells of selected dominant follicles compared with subordinate follicles, we suggest a predictive model to identify future dominant and subordinate follicles from the pool of otherwise similar cohort follicles at the time of follicle wave emergence. We conclude that the Erk and Akt signal transduction pathways are important for dominant follicle selection and development and, furthermore, that the observed differences in these pathways mark the future dominant follicle from subordinate follicles before differences in follicular diameter, follicular fluid estradiol, and IGFBP-4 concentrations are apparent.

Influence of short-term fasting during the luteal phase of the estrous cycle on ovarian follicular development during the ensuing proestrus of ewes

Short-term fasting of mature ewes during diestrus results in increased serum concentrations of progesterone and a delayed pre-ovulatory surge release of LH. To determine if these changes in reproductive hormones influence subsequent follicular development, mature ewes observed in estrus were assigned randomly to control (n=10) or fasted (n=15) groups. Control ewes had ad libitum access to feed, whereas fasted ewes were not fed from day 7 through 11 of their estrous cycle. Daily blood samples were collected from control and fasted ewes throughout the fasting period. Fasting increased (P<0.001) serum concentrations of progesterone (4.4 ng/mL versus 2.7 ng/mL [+/-0.3]). On day 12, all ewes were treated with 10mg of PGF(2alpha) and fasted ewes were returned to ad libitum feed. Ovaries were collected from ewes (n=5 each group) at 0 and 72 h following PGF(2alpha) in control and 0, 72 and 96 h in fasted ewes. Ovaries were weighed and small (< or =2mm), medium (3-4mm), and large (> or =5mm) follicles were enumerated. Total numbers of follicles were less (P<0.001) in fasted than fed ewes (14.6 versus 30.2 [+/-2.2]) at 0 h, but did not differ (P=0.9) when numbers of follicles were compared at similar times before the anticipated LH surge (i.e., at 72 h versus 96 h in control and fasted ewes, respectively). Within follicular size class, numbers of small and medium follicles were decreased (P=0.04) at 0 h in fasted ewes. Numbers of large follicles did not differ (P=1.0) between groups. Although numbers of small and medium ovarian follicles in fasted ewes recovered by 96 h to values comparable to fed ewes at 72 h following PGF(2alpha), serum concentrations of estradiol 17beta (P=0.08) and FSH (P=0.06) tended to be decreased in fasted ewes before the anticipated surge release of LH. Pituitary content of LH and FSH also tended to be lower (P< or =0.09) at 96 h in fasted ewes than at 72 h in control ewes, but did not differ (P> or =0.4) at hour 0 following PGF(2alpha). Hypothalamic and stalk median eminence contents of GnRH were not influenced (P> or =0.2) by fasting at any time period. Fasting during the luteal phase perturbs gonadotropin secretion and may influence fertility by causing a delay in ovarian follicle development.

Distinct Regulation by Steroids of Messenger RNAs for FSHR and CYP19A1 in Bovine Granulosa Cells

Steroidal regulation of gene expression in follicular cells is not completely defined. Granulosa cells from 5 mm bovine follicles were cultured and treated and steady-state mRNA levels determined for FSHR (follicle-stimulating hormone receptor) and CYP19A1 (aromatase). Cells were treated for 5 days with (0.1-300 ng/ml) 17beta-estradiol (E2), testosterone (T), or 5alpha-dihydrotestosterone (DHT). FSHR mRNA was increased by T and DHT but not E2. In contrast, CYP19A1 mRNA was induced by all doses of E2 but only high doses of T and DHT. Similarly, varying treatment duration (1-5 days) showed that FSHR was increased by T and DHT and CYP19A1 mRNA increased by E2 and T at all times. Synergism between steroid hormones and FSH or forskolin was also evaluated. FSH or E2 did not alter FSHR mRNA and did not enhance DHT stimulation of FSHR mRNA. In contrast, DHT alone had no effect on CYP19A1 mRNA but synergized with FSH plus E2 to increase CYP19A1 mRNA, probably due to induction of FSHR by DHT. Effects of E2 and T on CYP19A1 were blocked by ICI 182,780, indicating mediation by estrogen receptors. However, the specific androgen receptor antagonist bicalutamide did not block E2 or T effects on CYP19A1 but did block T and DHT stimulation of FSHR. Thus, FSHR is specifically regulated through androgen receptor, whereas CYP19A1 is regulated by multiple pathways, including estrogen receptors and cAMP/protein kinase A induced by FSHR activation in granulosa cells. These inter- and intracellular regulatory mechanisms may be critical for normal follicle growth and dominant follicle selection.

Evidence of a local negative role for cocaine and amphetamine regulated transcript (CART), inhibins and low molecular weight insulin like growth factor binding proteins in regulation of granulosa cell estradiol production during follicular waves in cattle

The ability of ovarian follicles to produce large amounts of estradiol is a hallmark of follicle health status. Estradiol producing capacity is lost in ovarian follicles before morphological signs of atresia. A prominent wave like pattern of growth of antral follicles is characteristic of monotocous species such as cattle, horses and humans. While our knowledge of the role of pituitary gonadotropins in support of antral follicle growth and development is well established, the intrinsic factors that suppress estradiol production and may help promote atresia during follicular waves are not well understood. Numerous growth factors and cytokines have been reported to suppress granulosa cell estradiol production in vitro, but the association of expression of many such factors in vivo with follicle health status and their physiological significance are not clear. The purpose of this review is to discuss the in vivo and in vitro evidence supporting a local physiological role for cocaine and amphetamine regulated transcript, inhibins and low molecular weight insulin like growth factor binding proteins in negative regulation of granulosa cell estradiol production, with emphasis on evidence from the bovine model system.

Does hormone replacement therapy prevent epithelial ovarian cancer?

Two much-debated hypotheses regarding the aetiology of epithelial ovarian cancer (EOC) are incessant ovulation and gonadotrophin stimulation. A significant inverse correlation is found between the risk of EOC and number of pregnancies, duration of oral contraceptive use (about 10% risk reduction per year) and duration of breastfeeding. Whereas ovulation in the 20-29 year age group was associated with a 20% increase in risk for each year of ovulation, maximum protective effect was noticed in late childbirth (>35 years). Although both in-vitro and in-vivo studies showed that gonadotrophins may initiate and stimulate the growth of EOC, it is not known whether gonadotrophins promote EOC. FSH and LH receptors have been detected by ligand-binding assay and by reverse transcriptase polymerase chain reaction in ovarian surface epithelium (OSE) and in malignant epithelial ovarian tissue. Key aetiological events for this cancer may occur in the premenopausal period. Although hormone replacement therapy (HRT) can lower FSH and LH concentrations substantially, it cannot reduce EOC. The ideal time of ovulation and/or gonadotrophin suppression for prevention of EOC, and why oral contraceptives (OC) can but HRT cannot reduce EOC effectively, are unknown. Various growth-related genes, factors, adhesion molecules and angiogenic factors are present in OSE. Pituitary ovarian axis hormones seem to maintain a delicate balance towards growth control whilst the resultant chain of abnormal growth-promoting events occur at cellular level. Reports regarding the relation of exogenous and endogenous hormones, especially oestrogen, and post-menopausal EOC are reviewed.

Formation of mammalian oocytes and their growth, differentiation and maturation within ovarian follicles

The limited knowledge on the regulation of oocyte formation, the different steps of folliculogenesis and the required conditions for oocytes to undergo proper growth, differentiation and maturation are major causes of the failure in obtaining viable offspring from in vitro cultured early oocytes from domestic animals and humans. This review highlights the factors that at present are known to be involved in the formation of mammalian oocytes and their growth, differentiation and maturation within ovarian follicles.

Effects of feed restriction on reproductive and metabolic hormones in ewes

The goal of this study was to determine the effects of short-term feed withdrawal on reproductive and metabolic hormones during the luteal phase of the estrous cycle in mature ewes. Mature ewes observed in estrus were assigned randomly to control and fasted groups (n = 10 per group Trials 1 and 2). For Trials 1 and 2, control ewes had ad libitum access to feed, whereas fasted ewes were not fed from d 7 through 11 of their estrous cycle; on d 12, all ewes were treated with 10 mg of PGF2alpha, and fasted ewes were gvien ad libitum access to feed. For Trial 1, blood samples were collected daily through fasting and at 2-h intervals following PGF2alpha for 72 h. Serum concentrations of insulin (P < or = 0.002) and IGF-I (P < or = 0.01), but not GH (P > or = 0.60), were decreased during fasting compared with fed ewes. Serum concentrations of 29 (P = 0.02) and 34 kDa (P = 0.04) IGFBP were greater in fasted ewes at 96 h after initiation of fasting than in control ewes. Two control and four fasted ewes in Trial 1 did not exhibit a preovulatory surge release of LH by 72 h. Therefore, Trial 2 was conducted so that the timing of the LH surge could be predicted following the collection of blood samples at 2-h intervals for 112 h and then at 6-h intervals until 178 h following PGF2alpha administration and realimentation. The magnitude of the preovulatory LH surge in Trial 2 was decreased (P = 0.009) and delayed (P = 0.04), and serum concentrations of estradiol were diminished (P < or = 0.03) 12 h before the LH surge in fasted ewes. Ovulation rates were not influenced (P > or = 0.32) by fasting in Trials 1 and 2. Serum concentrations of progesterone in both Trials 1 and 2 were, however, greater (P < 0.001) in fasted than in control ewes. A third trial with ovariectomized ewes was conducted to determine whether the increased serum concentrations of progesterone observed in fasted ewes during Trials 1 and 2 were ovarian-derived. Ovariectomized ewes were implanted with progesterone-containing intravaginal implants and allotted to control (n = 5) or fasted (n = 5) treatment groups and fed as described for Trials 1 and 2. Similar to intact ewes, serum concentrations of progesterone were approximately twofold greater (P < 0.001) in fasted than in control implanted ovariectomized ewes. In summary, feed withdrawal for 5 d during the luteal phase of the estrous cycle increased serum concentrations of progesterone and evoked endocrine changes that could perturb the subsequent estrous cycle.

Regulation of Follicle-Stimulating Hormone-Receptor Messenger RNA in Hen Granulosa Cells Relative to Follicle Selection1

Both the viability of hen prehierarchal follicles and subsequent differentiation associated with the selection of a single follicle per day into the preovulatory hierarchy depend on circulating FSH and the expression of FSH receptor (FSH-R) in granulosa cells. The present study addresses mechanisms that mediate both basal expression plus selective up-regulation of FSH-R mRNA in granulosa cells from prehierarchal follicles. Results demonstrate that FSH-R mRNA is both expressed and functional in granulosa cells collected from growing prehierarchal follicles as small as those of 1-2 mm in diameter, as indicated by rapid induction of steroidogenic acute regulatory (StAR) protein expression by FSH in vitro. Real-time polymerase chain reaction determined that relative FSH-R expression within the granulosa layer from individual prehierarchal follicles of 6-8 mm in diameter was similar among the 8-13 follicles within this cohort, with the notable exception that the granulosa layer from a single follicle (presumably the selected follicle) showed elevated expression. Levels of FSH-R mRNA expression were enhanced by both recombinant human (rh) transforming growth factor (TGF) beta1 and, to a lesser extent, rh-activin A after 20 h of culture. This stimulatory effect was effectively blocked by mitogen-activated protein (MAP) kinase signaling induced by TGF alpha treatment. Finally, inhibition of MAP kinase signaling, using the selective inhibitor U0126, promoted FSH-R expression and further enhanced TGF beta1-induced FSH-R expression in vitro. Collectively, results suggest that premature granulosa cell differentiation normally is suppressed by tonic MAP kinase signaling. At the time of follicle selection, a release from inhibitory MAP kinase signaling is proposed to occur, which enables the full potentiation of FSH-R expression mediated by intrafollicular factors.

Zebrafish gonadotropins and their receptors: I. Cloning and characterization of zebrafish follicle-stimulating hormone and luteinizing hormone receptors--evidence for their distinct functions in follicle development

In the present study, we cloned and characterized zebrafish FSH receptor (Fshr) and LH receptor (Lhr). Both fshr and lhr were abundantly expressed in the zebrafish gonads; however, they could also be detected in the kidney and liver, respectively. When overexpressed in mammalian cell lines together with a cAMP-responsive reporter gene, zebrafish Fshr responded to goldfish pituitary extract but not hCG, whereas Lhr could be activated by both. It was further demonstrated that Fshr was specific to bFSH, while Lhr could be stimulated by both bovine FSH and LH. Low level of fshr expression could be detected in the immature ovary, but the level steadily increased during vitellogenesis of the first cohort of developing follicles. In contrast, the expression of lhr could barely be detected in the immature ovary, but it became detectable at the beginning of vitellogenesis and steadily increased afterward with the peak level reached at the full-grown stage. At the follicle level, the expression of fshr was very weak in the follicles of primary growth stage but significantly increased with the follicles entering vitellogenesis. However, after reaching the maximal level in the midvitellogenic follicles, the level of fshr expression dropped slightly but significantly at the full-grown stage. In comparison, the expression of lhr obviously lagged behind that of fshr. Its expression became detectable only when the follicles started to accumulate yolk granules, but the level rose steadily afterward and reached the peak at the full-grown stage before oocyte maturation. These results suggest differential roles for Fshr and Lhr in zebrafish ovarian follicle development.

The effect of follicle-stimulating hormone on follicular development, granulosa cell apoptosis and steroidogenesis and its mediation by insulin-like growth factor-I in the goat ovary

The effect of FSH on goat follicular development, granulosa cell apoptosis and steroidogenesis and its mediation by insulin-like growth factor (IGF)-I were studied through both in vivo and in vitro experiments. The FSH treatment was begun on Day 9 after estrus and consisted of injections twice a day for 3 days in decreasing doses (7.5-7.5-5.0-5.0-2.5-2.5 mg). Does in both treatment and control groups were slaughtered for ovaries on Day 12. Granulosa cell apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL). Expression of IGF-I and IGF-II mRNA was determined by RT-PCR, while concentrations of progesterone (P4), estradiol (E2), IGF-I and IGF-II were measured by radioimmunoassay (RIA). Following parameters increased significantly (P<0.05) after the FSH treatment: follicle number (5.0+/-1.5 versus 9.0+/-2.0 per ovary), the level of E2 (0.1+/-0.1 ng/ml versus 0.7+/-0.2 ng/ml), the E2/P4 ratio (0.7+/-0.4 versus 4.7+/-3.0) and the concentrations of IGF-I (0.5+/-0.2 ng/ml versus 119.4+/-15.1 ng/ml) and IGF-II (0.12+/-0.03 ng/ml versus 40.9+/-18.7 ng/ml) in follicular fluid of the medium sized (3-5 mm) follicles and in the ovarian cortex the relative quantity of IGF-I mRNA (0.37+/-0.17 versus 0.90+/-0.12 Max OD). In contrast, the ratio of apoptotic granulosa cells in these follicles was reduced significantly (0.53+/-0.1 versus 0.10+/-0.01, P<0.05). In large (>5 mm) follicles, however, only the follicle number (2.3+/-0.7 versus 7.0+/-1.5 per ovary) and the level of IGF-I (38.4+/-11.0 ng/ml versus 87.3+/-13.9 ng/ml) increased significantly (P<0.05), whereas other values did not change. In vitro culture of granulosa cells showed that FSH significantly (P<0.05) enhanced IGF-I production (12.7+/-2.1 ng/ml versus 26.+/-21.9 ng/ml) by these cells, and both FSH and IGF-I reduced the ratios of apoptotic cells (from 0.7+/-0.07 to 0.3+/-0.1 and 0.2+/-0.04, respectively) and the effect was additive when both were used together. H89, the PKA pathway inhibitor, blocked the effect of FSH on granulosa cell apoptosis and IGF-I production in vitro. These results indicated that FSH mainly enhanced the development of medium sized follicles in the goat by suppressing the apoptosis of granulosa cells via increasing production of IGF-I and steroids, possibly through the PKA pathway.

Effects of hepatocyte growth factor on cyclic nucleotide-dependent signaling and steroidogenesis in rat ovarian granulosa cells in vitro

Hepatocyte growth factor (HGF) down-modulates FSH-dependent estradiol-17beta (E(2)) production in ovarian granulosa cells in vitro. The mechanisms of action underlying the antiestrogenic effects of HGF are vague, although evidence indicates that HGF may affect cAMP signal transduction in rat granulosa cells. The present study investigated the effects of HGF on FSH-induced steroidogenesis in the presence and absence of insulin-like growth factor I (IGF-I), as well as the actions of HGF within cyclic nucleotide-dependent signal transduction cascades in granulosa cells. Immature rat granulosa cells were incubated with FSH, IGF-I, and HGF. HGF impaired the production of FSH-stimulated and FSH + IGF-I-stimulated E(2) synthesis, as well as FSH + IGF-I-dependent estrone production. Progesterone synthesis was not altered by HGF. HGF suppressed FSH-dependent cAMP content at 24 h, but not at 36 h; cGMP content was stimulated by HGF with and without FSH at 24 h. In the presence of the cyclic nucleotide phosphodiesterase (PDE) inhibitor, 3-isobutyl-1-methylxanthine (IBMX), FSH-dependent cAMP accumulation was not affected by HGF. The suppressive effect of HGF on FSH-dependent E(2) production was alleviated by IBMX, whereas the HGF-dependent block in FSH + IGF-I-supported E(2) production was not prevented by IBMX. The effects of HGF on cyclic nucleotide PDE activities were manifested in a time-dependent and hormone-dependent manner. FSH-induced cAMP PDE was suppressed by HGF at 24 h but not at 36 h, whereas FSH-dependent cGMP PDE was impaired at 36 h, but not at 24 h. HGF prevented the IGF-I-dependent reduction in FSH-stimulated cAMP-PDE activity at 24 and 36 h, and lowered FSH + IGF-I-stimulated cGMP-PDE activity at 36 h, concomitant with an HGF-dependent increase in cGMP content at 24 h. These data indicate that HGF affects cAMP-directed and cGMP-directed signaling pathways at multiple sites in granulosa cells. These HGF-dependent effects may provide insight for mechanisms of action whereby HGF reduces E(2) secretion by granulosa cells.

Influence of gonadotropins on insulin- and insulin-like growth factor-I (IGF-I)-induced steroid production by bovine granulosa cells

To determine the effect of gonadotropins on insulin- and insulin-like growth factor (IGF-I)-induced bovine granulosa cell functions, granulosa cells from bovine ovarian follicles were cultured for 2 days in the presence of 10% fetal calf serum (FCS), and then cultured for an additional 2 days in serum-free medium with added hormones. In the presence of 0 or 1 ng/mL of insulin or IGF-I, FSH had little or no effect (P > 0.05) on estradiol production by granulosa cells from both small (1-5mm) and large (> or = 8mm) follicles. However, in the presence of > or = 3 ng/mL of insulin, FSH increased (P < 0.05) estradiol production by granulosa cells from small and large follicles such that the estimated dose (ED(50)) of insulin necessary to stimulate 50% of the maximum estradiol production was decreased by 2- to 3-fold from 22 to 28 ng/mL in the absence of FSH to 7-14 ng/mL in the presence of FSH. Similarly, in the presence of > or = 3 ng/mL of IGF-I, FSH increased (P< 0.05) estradiol production by granulosa cells from small and large follicles such that the ED(50) of IGF-I for estradiol production was decreased by 4- to 5-fold from 25 to 36 ng/mL in the absence of FSH to 5-6 ng/mL in the presence of FSH. In the presence of FSH, the maximal effect of insulin on estradiol production was much greater than that of IGF-I (137- versus 12-fold increase) and were not additive; when combined, 100 ng/mL of IGF-I completely blocked the stimulatory effect of 100 ng/mL of insulin. In the absence of FSH, the maximal effect of insulin and IGF-I on estradiol production was similar. Concomitant treatment with 30 ng/mL of LH reduced (P<0.05) insulin-stimulated estradiol production by 52% on day 1 and 19% on day 2 of treatment. Insulin, IGF-I and FSH also increased (P<0.05) granulosa cell numbers and progesterone production but their maximal effects were less (i.e., < 4-fold increase) than their effects on estradiol production. In conclusion, insulin and IGF-I synergize with FSH to directly regulate ovarian follicular function in cattle, particularly granulosa cell aromatase activity.

A role for the androgen receptor in follicular atresia of estrogen receptor beta knockout mouse ovary

Estrogen receptor beta (ERbeta) is highly expressed, but ERalpha is not detectable in granulosa cells in the mouse ovary. In ERbeta knockout (BERKO) mice, there is abnormal follicular development and very reduced fertility. At 3 wk of age, no significant morphologic differences were discernable between wild type (WT) and BERKO mouse ovaries, but by 5 mo of age, atretic follicles were abundant in BERKO mice and there were very few healthy late antral follicles or corpora lutea. At 2 yr of age, unlike the ovaries of their WT littermates, BERKO mouse ovaries were devoid of healthy follicles but had numerous large, foamy lipid-filled stromal cells. The late antral and atretic follicles in BERKO mice were characterized by a high level of expression of the androgen receptor (AR) and IGF-1 receptor. These proteins were abundantly expressed in granulosa cells of preantral and early antral follicles in both genotypes, but their expression was extinguished in late antral follicles of WT mice. Healthy late antral follicles and corpora lutea were restored in BERKO ovaries after 15 days of treatment of mice with the antiandrogen flutamide. The results suggest that in the absence of ERbeta there was a loss of regulation of AR. Because androgens enhance recruitment of primordial follicles into the growth pool and cause atresia of late antral follicles, the inappropriately high level of AR probably is related to the follicular atresia and to the early exhaustion of follicles in BERKO mice.

Effects of growth hormone on in vitro maturation of germinal vesicle of human oocytes retrieved from small antral follicles

PURPOSE

Evaluation of the effect of GH, administered in vivo, on in vitro maturation of human GV oocytes obtained from small follicles.

METHODS

The study included 88 ICSI women stimulated with long agonist protocol. They were randomly allocated to two groups (Group 1, 44 women with 86 GV oocytes), were cotreated with GH (Group 2, no GH: 44 women with 67 GV oocytes). GV oocytes from small follicles were matured in vitro, injected, and their development observed.

RESULTS

Resumption of meiosis was significantly higher in Group 1 compared to Group 2 (60 and 37.3% respectively). Significantly more M2 oocytes were obtained in Group 1 than in Group 2 (45.5 and 23.9% respectively). Fertilization rates were also significantly higher (51.9 and 18.8% respectively). No embryos were obtained in Group 2, whereas 21.1% of fertilized oocytes in Group 1 cleaved into class A embryos.

CONCLUSION

In vivo administration of GH enhanced in vitro maturation and fertilization of human GV oocytes retrieved from small antral follicles.

Analysis of ovarian gene expression in follicle-stimulating hormone beta knockout mice

FSH is a heterodimeric glycoprotein hormone that is produced in the gonadotroph cells of the anterior pituitary. It acts on Sertoli cells of the testis and granulosa cells of the ovary. We previously demonstrated that FSHbeta knockout female mice are infertile due to a block in folliculogenesis preceding antral stage development. To investigate aberrations of ovarian gene regulation in the absence of FSH, we analyzed the expression of several important marker genes using Northern blot and in situ hybridization techniques. Key findings are as follows: 1) Follicles of FSHbeta knockout mice develop a well organized thecal layer, which is positive for P450 17alpha-hydroxylase and LH receptor messenger RNAs (mRNAs). This indicates that theca recruitment is completed autonomously with respect to FSH. 2) Granulosa cells in FSH-deficient mice demonstrate an increase in FSH receptor mRNA, and decreases in P450 aromatase, serum/glucocorticoid-induced kinase, and inhibin/activin subunit mRNAs. These data support studies that implicate FSH signaling cascades in the expression of these genes. 3) In contrast to the thecal layer, granulosa cell populations in FSHbeta knockout mice do not accumulate LH receptor mRNA. This suggests that although the granulosa cells have a block in proliferation at the antral follicle stage in the absence of FSH, they do not initiate programs of terminal differentiation as seen in luteinizing cells of wild-type ovaries. 4) Ovaries of FSH-deficient mice demonstrate a modest decrease in cyclin D2 mRNA, without up-regulation of cell cycle inhibitor mRNAs associated with luteinization (i.e. p15, p27, and p21). Although components of the FSH null phenotype may be caused by partial cyclin D2 loss of function, these findings indicate that the mechanisms of granulosa cell cycle arrest in FSHbeta knockout mice are distinct from those of cycle withdrawal at luteinization. Underscoring the usefulness of the FSH-deficient mouse model, this study clarifies aspects of gonadotropin-dependent folliculogenesis, thecal layer development, cycle control in granulosa cells, and luteinization.

Bone morphogenetic protein-15 inhibits follicle-stimulating hormone (FSH) action by suppressing FSH receptor expression

We have recently reported that oocyte-derived bone morphogenetic protein-15 (BMP-15) can directly modulate follicle-stimulating hormone (FSH) action in rat granulosa cells. Here, we investigate underlying mechanisms of this BMP-15 effect. Treatment with BMP-15 alone exerted no significant effect on the basal expression of mRNAs encoding steroidogenic acute regulatory protein, P450 side chain cleavage enzyme, P450 aromatase, 3beta-hydroxysteroid dehydrogenase, luteinization hormone receptor, and inhibin/activin subunits. However, BMP-15 markedly inhibited the FSH-induced increases in these messages. In striking contrast, BMP-15 did not change the forskolin-induced levels of these transcripts. Thus, the inhibitory effect of BMP-15 on FSH action must be upstream of cAMP signaling. We next examined changes in FSH receptor mRNA expression. Interestingly, BMP-15 severely reduced the levels of FSH receptor mRNA in both basal and FSH-stimulated cells. To determine whether this effect was at the level of FSH function, we investigated the effect of BMP-15 on FSH bioactivity. Consistent with the mRNA data, BMP-15 inhibited the biological response of FSH, but not that of forskolin. Based on these results, we propose that BMP-15 is an important determinant of FSH action through its ability to inhibit FSH receptor expression. Because FSH plays an essential role in follicle growth and development, our findings could have new implications for understanding how oocyte growth factors contribute to folliculogenesis.

Insulin-like growth factor-I (IGF-I) stimulates the development of cultured rat pre-antral follicles

The aim of the present study is to investigate the effect of insulin-like growth factor (IGF-I) on the development of cultured rat pre-antral follicles. Pre-antral follicles with a diameter between 140 and 160 microm are mechanically isolated from ovaries of 10-day-old rats and cultured in groups for 6 days in FSH and insulin-containing serum-free medium in the absence or presence of IGF-I at concentrations of 1, 10, and 100 ng/ml, respectively. DNA content of the follicles before and after culture is measured to evaluate whether a possible growth is due to proliferation of follicular cells and the ultrastructure of the cultured follicles is studied with transmission electron microscopy to evaluate the quality of follicles cultured under different conditions. Furthermore, reverse transcriptase polymerase chain reaction (RT-PCR) is used to assess the gene expression of IGF-I and type I IGF receptor in pre-antral follicles. When follicles were cultured in medium containing IGF-I at a concentration of 1 and 10 ng/ml, the increase in follicle diameter after a 6-day culture differs significantly from that in the absence of IGF-I. The ultrastructure of follicles cultured in IGF-I-containing medium is better sustained when compared to that of follicles cultured in the absence of IGF-I. Especially, theca cells, which are undergoing degeneration under controlled culture condition, demonstrate normal cellular ultrastructure with some characteristics of steroid-secreting cells in the presence of IGF-I. Moreover, in oocytes of follicles cultured in the presence of IGF-I, cortical granules are observed distributed along the ooplasma membrane whereas cortical granules are hardly present in follicles cultured without IGF-I. With RT-PCR, the presence of the mRNA of IGF-I and type I IGF receptor is demonstrated in both the somatic follicular cells and the oocytes. Taken together, these results suggest that IGF-I, in the presence of follicle-stimulating hormone (FSH), enhances rat pre-antral follicle development in vitro and supports the morphology of cultured pre-antral follicles. The stimulatory effect of exogenous IGF-I on the development of pre-antral follicle together with the gene expression of both IGF-I and type I IGF receptor in pre-antral follicles suggests the involvement of IGF-I in early folliculogenesis and its actions are likely mediated by the putative type I IGF receptor, via both endocrine and paracrine/autocrine pathways.

Characterization of regulatory elements of ovine follicle-stimulating hormone (FSH) receptor gene: the role of E-box in the regulation of ovine FSHreceptor expression

Expression and activation of follicle-stimulating hormone receptor (FSHR) in the granulosa and Sertoli cells are required for normal development of the ovarian follicles and germ cells. However, little is known regarding the mechanisms by which FSHR expression is regulated. We fused an ovine FSHR promoter to a luciferase gene to understand the promoter regulation in two gonadal cell lines. Deletion studies revealed that the strongest promoter was at -200 to +163 relative to the transcription start site. One of cis-elements protected from DNase I digestion was mapped to between +32 and +54 of the 174-base pair (bp) minimal promoter. Electrophoretic mobility shift assay with a 26-bp probe (+32 to +57) and nuclear extracts from Sertoli (15P1) and granulosa (JC-410) cell lines demonstrated a sequence-specific DNA-protein complex. Southwestern analysis detected a 43-kDa protein bound to the 26-bp probe. Gel supershift with upstream stimulatory factor 1 and 2 (USF-1/2) antibodies revealed that the DNA-protein complex contained these two transcription factors. Mutation within the E-box of the promoter abolished the sequence-specific binding and the minimal promoter activity but also greatly reduced the transcription of the proximal promoters by 49%-70%. These data suggest that the USF-1/2 binding to the promoter is required for the expression of the ovine FSHR in the gonadal cells.

Investigation of three doses of oral insulin-like growth factor-I on jejunal lactase phlorizin hydrolase activity and gene expression and enterocyte proliferation and migration in piglets

In a previous study, oral IGF-I at 65 nM increased lactase phlorizin hydrolase (LPH) activity and villus height in piglets, however, the mechanisms were unknown. Herein, the response to a range of doses of IGF-I was investigated and we hypothesized that LPH and villus height would respond to oral IGF-I in a dose-dependent manner. Two 14-d experiments were conducted using cesarean-derived piglets. In experiment 1, piglets (n = 28) were fed formula containing 0, 33, 65, or 131 nmol/L (0, 0.25, 0.5, or 1.0 mg/L) recombinant human IGF-I. In experiment 2, 5'-bromodeoxyuridine was administered to piglets fed formula alone (n = 4) or containing 131 nmol/L IGF-I (n = 4). IGF-I did not affect body weight gain or intestinal weight or length. Jejunal villus height and LPH activity were significantly greater in piglets fed 131 nmol IGF-I/L than control piglets. Villus height and lactase activity in piglets fed the 33 and 65 nmol/L IGF-I doses were similar and intermediate between control and 131 nmol IGF-I/L. Jejunal mRNA expression and LPH polypeptide abundance were investigated in piglets receiving 0 or 131 nmol/L IGF-I. Steady state LPH mRNA abundance was significantly higher (p < 0.05) in IGF-I-treated piglets. The relative abundance of proLPH(h) was not significantly increased (p = 0.06) by IGF-I treatment. Mucosal DNA content and DNA synthesis were greater in piglets receiving 131 nmol IGF-I/L than control, however, enterocyte migration and mucosal protein content were unaffected. Thus, oral IGF-I increased jejunal LPH activity and LPH mRNA abundance and stimulated intestinal cell hyperplasia in normal piglets.