Regulation of steroidogenic genes by insulin-like growth factor-1 and follicle-stimulating hormone: differential responses of cytochrome P450 side-chain cleavage, steroidogenic acute regulatory protein, and 3beta-hydroxysteroid dehydrogenase/isomerase 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.

Growth factors and female reproduction in vertebrates

Female reproductive efficiency is influenced by the outcomes of various processes, including folliculogenesis, apoptosis, response to gonadotropin signaling, oocyte maturation, and ovulation. The role of hormones in regulating these processes and other reproductive activities has been well established. It is becoming increasingly evident that in addition to well-characterized hormones, growth factors play vital roles in regulating some of these reproductive activities. Growth factors and their receptors are widely distributed in vertebrate ovaries at different stages of ovarian development, indicating their involvement in intraovarian reproductive functions. In the ovary, cell surface receptors allow growth factors to regulate intraovarian reproductive activities. Understanding these actions in the reproductive axis would provide a tool to target growth factors and/or their receptors to yield desirable reproductive outcomes. These include enrichment of in vitro maturation and fertilization culture media, and management of infertility. This review discusses some widely characterized growth factors belonging to the TGF, EGF, IGF, FGF, and BDNF family of peptides and their role in female reproduction in vertebrates, with a focus on mammals.

Effect of IGF1 and FSH on the function of granulosa cells from prehierarchal follicles in chickens†

Insulin-like growth factor 1 (IGF1) is an essential regulator of mammalian follicle development and synergizes with follicle-stimulating hormone (FSH) to amplify its effects. In avian preovulatory follicles, IGF1 increases the expression of genes involved in steroidogenesis and progesterone and inhibin A production. The role of IGF1 in prehierarchal follicles has not been well studied in chickens. The aim of this study was to investigate the role of IGF1 in granulosa cells from prehierarchal follicles and to determine whether IGF1 and FSH synergize to promote follicle development. Granulosa cells of 3-5 and 6-8 mm prehierarchal follicles were cultured with IGF1 (0, 10, 100 ng/mL) in the presence or absence of FSH (0, 10 ng/mL). Cell proliferation, expression of genes important in follicle development (FSHR, IGF1R, AMH, STAR, CYP11A1, INHA, and INHBA), and progesterone production were evaluated following treatment. IGF1 treatment alone significantly increased STAR, CYP11A1, and INHBA mRNA expression and cell proliferation in granulosa cells of 6-8 mm follicles. IGF1 and FSH synergized to increase STAR mRNA expression in 6-8 mm follicles. IGF1 and FSH co-treatment were necessary to increase INHA mRNA expression in 6-8 mm follicles. Although IGF1 significantly increased the expression of genes involved in steroidogenesis, progesterone production in granulosa cells of 6-8 mm follicles was not affected. IGF1 did not affect AMH mRNA expression, although FSH significantly decreased AMH expression in granulosa cells of 3-5 mm follicles. These results suggest that IGF1 may act with FSH to promote follicle selection at the prehierarchal follicle stage.

Rat Ovarian Function Is Impaired during Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) is an autoimmune disease affecting the CNS and occurring far more prevalently in women than in men. In both MS and its animal models, sex hormones play important immunomodulatory roles. We have previously shown that experimental autoimmune encephalomyelitis (EAE) affects the hypothalamic-pituitary-gonadal axis in rats of both sexes and induces an arrest in the estrous cycle in females. To investigate the gonadal status in female rats with EAE, we explored ovarian morphometric parameters, circulating and intraovarian sex steroid levels, and the expression of steroidogenic machinery components in the ovarian tissue. A prolonged state of diestrus was recorded during the peak of EAE, with maintenance of the corpora lutea, elevated intraovarian progesterone levels, and increased gene and protein expression of StAR, similar to the state of pseudopregnancy. The decrease in CYP17A1 protein expression was followed by a decrease in ovarian testosterone and estradiol levels. On the contrary, serum testosterone levels were slightly increased. With unchanged serum estradiol levels, these results point at extra-gonadal sites of sex steroid biosynthesis and catabolism as important regulators of their circulating levels. Our study suggests alterations in the function of the female reproductive system during central autoimmunity and highlights the bidirectional relationships between hormonal status and EAE.

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

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

Ad Libitum Feeding in Broiler Breeder Hens Alters the Transcriptome of Granulosa Cells of Pre-Hierarchal Follicles

Intense selective breeding of chickens has resulted in suboptimal egg production in broiler breeder hens. This reproductive phenotype is exacerbated by ad libitum feeding, which leads to excessive and disorganized follicular growth. One strategy used to improve broiler breeder hens' reproductive efficiency is restricted feeding. In this study, we sought to identify transcriptional changes, which translate the level of dietary intake into increased follicle selection. Broiler breeder hens (n = 16 per group) were raised according to commercial guidelines until 28 weeks of age and then randomly assigned to an ad libitum diet (FF) or continued on a restricted diet (RF) for 6 weeks. Following dietary treatment, FF hens (n = 2) with excessive follicle selection and RF hens (n = 3) with normal follicle selection were selected for RNA-sequencing. Transcriptomes of granulosa cells from 6-8-mm follicles were sequenced to identify transcriptional differences in the follicle population from which selection was made for the preovulatory stage. Differential expression analysis identified several genes known to play a role in follicle development (CYP11A1, STAR, INHA, and INHBB) that are upregulated in FF hens. These changes in gene expression suggest earlier granulosa cell differentiation and steroidogenic competency in the granulosa layer from FF hens.

Altered redox homeostasis in steroid-depleted follicles attenuates hCG regulation of follicular events: Cross-talk between endocrine and IGF axis in maturing oocytes

Steroids and insulin-like growth factors (Igfs) are indispensable for folliculogenesis and reproductive fitness in the vertebrate ovary. The intrafollicular redox balance is also of immense importance for ovarian follicles wherein low levels of ROS are being utilized for cell signalling and regulation of gene expression; its excess may interfere with normal physiological processes leading to ovotoxicity. However, the functional relevance of ovarian steroidogenesis in maintaining the follicular microenvironment with coordinated redox homeostasis and intra-ovarian growth factors axis is relatively less understood. Using zebrafish full-grown (FG) ovarian follicles in vitro, our study shows that blocking steroid biosynthesis with anti-steroidal drugs, DL-aminoglutethimide (AG) or Trilostane (Trilo), prevents hCG (LH analogue)-induced StAR expression concomitant with a robust increase in intrafollicular ROS levels. Congruent with heightened intracellular levels of superoxide anions (O₂^•-) and hydrogen peroxide (H₂O₂), priming with AG or Trilo abrogates the transcript abundance of major antioxidant enzyme genes (SOD1, SOD2, and CAT) in hCG-stimulated follicles. Significantly, blocking steroidogenesis attenuates transcript abundance of HSP70 but elevates NOX4 expression potentially through ERα-mediated pathway. Importantly, disrupted redox balance in AG/Trilo pre-incubated FG follicles negatively impacts hCG-mediated activation of PKA/CREB signaling and transcriptional activation of igf ligands. Elevated ROS attenuation of antioxidant defense parameters and impaired endocrine and autocrine/paracrine homeostasis converge upon reduced p34cdc2 (Thr-161) phosphorylation, a reliable marker for MPF activation, and resumption of meiotic G2-M1 transition in hCG-treated follicles. Collectively, altered redox homeostasis in steroid-depleted follicles has a significant negative influence on GTH (LH) regulation of follicular events, specifically Igf synthesis, meiotic maturational competence and ovarian fitness.

Arachidonic Acid Regulation of Intracellular Signaling Pathways and Target Gene Expression in Bovine Ovarian Granulosa Cells

Simple Summary

Arachidonic acid (AA) is one of the polyunsaturated fatty acids that presents in a very high proportion in the mammalian follicular fluid. However, the mechanism of its effects on bovine ovarian granulosa cells is not clear. In the present study, we found that arachidonic acid plays an important role in regulating cell proliferation, lipid accumulation and steroidogenesis of granulosa cells. In this sense, arachidonic acid can directly affect the functionality of granulosa cells and therefore follicular development and ovulation, which could provide useful information for future studies relating to increasing fecundity of bovine.

Abstract

In the present study, AA was used to challenge bovine ovarian granulosa cells in vitro and the related parameters of cellular and molecular biology were measured. The results indicated that lower doses of AA increased survival of bovine granulosa cells whereas higher doses of AA suppressed survival. While lower doses of AA induced accumulation of lipid droplet in granulosa cells, the higher dose of AA inhibited lipid accumulation, and AA increased abundance of FABP3, CD36 and SLC27A1 mRNA. Higher doses of AA decreased the secretion of E2 and increased the secretion of P4 accompanied by down-regulation of the mRNA abundance of CYP19A1, FSHR, HSD3B1 and STAR in granulosa cells. The signaling pathways employed by AA in the stimulation of genes expression included both ERK1/2 and Akt. Together, AA specifically affects physiological features, gene expression levels and steroid hormone secretion, and thus altering the functionality of granulosa cells of cattle.

In silico predicted transcriptional regulatory control of steroidogenesis in spawning female fathead minnows (Pimephales promelas)

Oocyte development and maturation (or oogenesis) in spawning female fish is mediated by interrelated transcriptional regulatory and steroidogenesis networks. This study integrates a transcriptional regulatory network (TRN) model of steroidogenic enzyme gene expressions with a flux balance analysis (FBA) model of steroidogenesis. The two models were functionally related. Output from the TRN model (as magnitude gene expression simulated using extreme pathway (ExPa) analysis) was used to re-constrain linear inequality bounds for reactions in the FBA model. This allowed TRN model predictions to impact the steroidogenesis FBA model. These two interrelated models were tested as follows: First, in silico targeted steroidogenic enzyme gene activations in the TRN model showed high co-regulation (67-83%) for genes involved with oocyte growth and development (cyp11a1, cyp17-17,20-lyase, 3β-HSD and cyp19a1a). Whereas, no or low co-regulation corresponded with genes concertedly involved with oocyte final maturation prior to spawning (cyp17-17α-hydroxylase (0%) and 20β-HSD (33%)). Analysis (using FBA) of accompanying steroidogenesis fluxes showed high overlap for enzymes involved with oocyte growth and development versus those involved with final maturation and spawning. Second, the TRN model was parameterized with in vivo changes in the presence/absence of transcription factors (TFs) during oogenesis in female fathead minnows (Pimephales promelas). Oogenesis stages studied included: PreVitellogenic-Vitellogenic, Vitellogenic-Mature, Mature-Ovulated and Ovulated-Atretic stages. Predictions of TRN genes active during oogenesis showed overall elevated expressions for most genes during early oocyte development (PreVitellogenic-Vitellogenic, Vitellogenic-Mature) and post-ovulation (Ovulated-Atretic). Whereas ovulation (Mature-Ovulated) showed highest expression for cyp17-17α-hydroxylase only. FBA showed steroid hormone productions to also follow trends concomitant with steroidogenic enzyme gene expressions. General trends predicted by in silico modeling were similar to those observed in vivo. The integrated computational framework presented was capable of mechanistically representing aspects of reproductive function in fish. This approach can be extended to study reproductive effects under exposure to adverse environmental or anthropogenic stressors.

An intracrine view of sex steroids, immunity, and metabolic regulation

Background

Over the past two decades, parallel recognition has grown of the importance of both sex steroids and immune activity in metabolic regulation. More recently, these discrete areas have been integrated in studies examining the metabolic effects of sex steroid immunomodulation. Implicit in these studies has been a traditional, endocrine model of sex steroid delivery from the gonads to target cells, including immune cells. Thus, research to date has focused on the metabolic effects of sex steroid receptor signaling in immune cells. This endocrine model, however, overlooks the extensive capacity of immune cells to generate and metabolize sex steroids, enabling the production of sex steroids for intracrine signaling – that is, sex steroid production for signaling within the cell of origin. Intracrine function allows highly cell-autonomous regulation of sex steroid exposure, and sex steroid secretion by immune cells could confer paracrine signaling effects in neighboring cells within metabolic tissues. In this review, immune cell intracrinology will denote sex steroid production within immune cells for either intracrine or paracrine signaling. This intracrine capacity of immune cells has been well established, and prior work has supported its importance in autoimmune disorders, trauma, and cancer. The potential relevance of immune cell intracrine function to the regulation of energy balance, body weight, body composition, and insulin sensitivity has yet to be explored.

Scope of review

The following review will detail findings to date regarding the steroidogenic and steroid metabolizing capacity of immune cells, the regulation of immune cell intracrine function, and the biological effects of immune-derived sex steroids, including the clinical relevance of immune cell intracrinology in fields other than metabolism. These findings will serve as the basis for a proposed model of immune cell intracrinology constituting a new frontier in metabolism research.

Major conclusions

The development of highly sensitive mass spectrometric methods for sex steroid measurement and quantitation of metabolic flux now allows unprecedented ability to interrogate sex steroid production, metabolism and secretion by immune cells. Immune cell intracrinology could reveal key mechanisms underlying immune cell-mediated metabolic regulation.

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Sex steroids exert immunomodulatory effects that may influence metabolic health.

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Immune cells can synthesize, modify, and metabolize sex steroids.

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Immune cell-derived sex steroids may play intracrine, autocrine, paracrine, and possibly even endocrine roles.

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Immune cell steroidogenesis is a largely unexplored area of metabolism research.

Interference of Steroidogenesis by Gold Nanorod Core/Silver Shell Nanostructures: Implications for Reproductive Toxicity of Silver Nanomaterials

As a widely used nanomaterial in daily life, silver nanomaterials may cause great concern to female reproductive system as they are found to penetrate the blood-placental barrier and gain access to the ovary. However, it is largely unknown about how silver nanomaterials influence ovarian physiology and functions such as hormone production. This study performs in vitro toxicology study of silver nanomaterials, focusing especially on cytotoxicity and steroidogenesis and explores their underlying mechanisms. This study exposes primary rat granulosa cells to gold nanorod core/silver shell nanostructures (Au@Ag NRs), and compares outcomes with cells exposed to gold nanorods. The Au@Ag NRs generate more reactive oxygen species and reduce mitochondrial membrane potential and less production of adenosine triphosphate. Au@Ag NRs promote steroidogenesis, including progesterone and estradiol, in a time- and dose-dependent manner. Chemical reactivity and transformation of Au@Ag NRs are then studied by electron spin resonance spectroscopy and X-ray absorption near edge structure, which analyze the generation of free radical and intracellular silver species. Results suggest that both particle-specific activity and intracellular silver ion release of Au@Ag NR contribute to the toxic response of granulosa cells.

Forkhead box O member FOXO1 regulates the majority of follicle-stimulating hormone responsive genes in ovarian granulosa cells

FSH promotes maturation of ovarian follicles. One pathway activated by FSH in granulosa cells (GCs) is phosphatidylinositol-3 kinase/AKT. The AKT target FOXO1 is reported to function primarily as a repressor of FSH genes, including Ccnd2 and Inha. Based on its broad functions in other tissues, we hypothesized that FOXO1 may regulate many more GC genes. We transduced GCs with empty adenovirus or constitutively active FOXO1 followed by treatment with FSH for 24 h, and conducted RNA deep sequencing. Results show that FSH regulates 3772 genes ≥2.0-fold; 60% of these genes are activated or repressed by FOXO1. Pathway Studio Analysis revealed enrichment of genes repressed by FOXO1 in metabolism, signaling, transport, development, and activated by FOXO1 in signaling, cytoskeletal functions, and apoptosis. Gene regulation was verified by q-PCR (eight genes) and ChIP analysis (two genes). We conclude that FOXO1 regulates the majority of FSH target genes in GCs.

Oleic acid induces specific alterations in the morphology, gene expression and steroid hormone production of cultured bovine granulosa cells

After parturition, one of the major problems related to nutritional management that is faced by the majority of dairy cows is negative energy balance (NEB). During NEB, excessive lipid mobilization takes place and hence the levels of free fatty acids, among them oleic acid, increase in the blood, but also in the follicular fluid. This accumulation can be associated with serious metabolic and reproductive disorders. In the present study, we analyzed the effects of physiological concentrations of oleic acid on cell morphology, apoptosis, necrosis, proliferation and steroid production, and on the abundance of selected transcripts in cultured bovine granulosa cells. Increasing oleic acid concentrations induced intracellular lipid droplet accumulation, thus resulting in a foam cell-like morphology, but had no effects on apoptosis, necrosis or proliferation. Oleic acid also significantly reduced the transcript abundance of the gonadotropin hormone receptors, FSHR and LHCGR, steroidogenic genes STAR, CYP11A1, HSD3B1 and CYP19A1, the cell cycle regulator CCND2, but not of the proliferation marker PCNA. In addition, treatment increased the transcript levels of the fatty acid transporters CD36 and SLC27A1, and decreased the production of 17-beta-estradiol and progesterone. From these data it can be concluded that oleic acid specifically affects morphological and physiological features and gene expression levels thus altering the functionality of granulosa cells. Suggestively, these effects might be partly due to the reduced expression of FSHR and thus the reduced responsiveness to FSH stimulation.

Prohibitin regulates the FSH signaling pathway in rat granulosa cell differentiation

Published results from our laboratory identified prohibitin (PHB), a gene product expressed in granulosa cells (GCs) that progressively increases during follicle maturation. Our current in vitro studies demonstrate that follicle-stimulating hormone (FSH) stimulates Phb expression in rat primary GCs. The FSH-dependent expression of PHB was primarily localized within mitochondria, and positively correlates with the morphological changes in GCs organelles, and synthesis and secretions of estradiol (E2) and progesterone (P4). In order to confirm that PHB plays a regulatory role in rat GC differentiation, endogenous PHB-knockdown studies were carried out in undifferentiated GCs using adenoviral (Ad)-mediated RNA interference methodology. Knockdown of PHB in GCs resulted in the suppression of the key steroidogenic enzymes including steroidogenic acute regulatory protein (StAR), p450 cholesterol side-chain cleavage enzyme (p450scc), 3β-hydroxysteroid dehydrogenase (3β-HSD), and aromatase (Cyp19a1); and decreased E2 and P4 synthesis and secretions in the presence of FSH stimulation. Furthermore, these experimental studies also provided direct evidence that PHB within the mitochondrial fraction in GCs is phosphorylated at residues Y249, T258, and Y259 in response to FSH stimulation. The observed levels of phosphorylation of PHB at Y249, T258, and Y259 were significantly low in GCs in the absence of FSH stimulation. In addition, during GC differentiation FSH-induced expression of phospho-PHB (pPHB) requires the activation of MEK1-ERK1/2 signaling pathway. Taken together, these studies provide new evidence supporting FSH-dependent PHB/pPHB upregulation in GCs is required to sustain the differentiated state of GCs.

The proteolytic activity of pregnancy-associated plasma protein-A is potentially regulated by stanniocalcin-1 and -2 during human ovarian follicle development

STUDY QUESTION

Is the proteolytic activity of pregnancy-associated plasma protein-A (PAPP-A) regulated by the stanniocalcins (STC1 and STC2) during human follicle maturation?

SUMMARY ANSWER

The STCs and PAPP-A show similar expression by immunohistochemistry in developing follicles, and regulation of PAPP-A proteolytic activity is suggested by the identification of inhibited protein complexes between PAPP-A and STC1 or STC2 in human follicular fluid (FF).

WHAT IS KNOWN ALREADY

The insulin-like growth factor (IGF)-regulating proteinase PAPP-A is secreted by the granulosa cells of estrogen-dominant follicles and is involved in follicle growth. STC1 and STC2 have recently been identified as novel PAPP-A inhibitors, and their expression in non-human mammalian ovaries has previously been observed.

STUDY DESIGN, SIZE, DURATION

The proteolytic activity of PAPP-A in human follicular fluid was assessed, and the interaction between PAPP-A and the STCs in human ovarian tissues and follicular fluid was analyzed using immunoassays. From 21 women, matched pairs of follicular fluid were obtained from one follicle just prior to final maturation of follicles with human chorionic gonadotrophin (hCG), and from another follicle in connection with oocyte aspiration after hCG treatment. Ovarian tissues were obtained from women having one ovary removed for fertility preservation by cryopreservation prior to gonadotoxic treatment.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The concentration and activity of PAPP-A were determined in all samples of follicular fluid. Furthermore, to investigate PAPP-A regulation during follicle development, immunohistochemical staining of PAPP-A, STC1, and STC2 was performed on pre-antral and antral human follicles. To attempt the demonstration of native complexes between PAPP-A and the STCs, immunoprecipitation from a pool of human follicular fluid was performed.

MAIN RESULTS AND THE ROLE OF CHANCE

The concentration of PAPP-A antigen in follicular fluid increased upon stimulation of ovulation with hCG (P < 0.02), but at the same time, PAPP-A activity was decreased. PAPP-A, STC1, and STC2 were localized together in primordial, late primary, and antral follicles, indicating that complex formation is possible in ovarian tissue. Covalent PAPP-A:STC2 and non-covalent PAPP-A:STC1 complexes were immunoprecipitated from follicular fluid, documenting for the first time native inhibited complexes between PAPP-A and the STCs.

LIMITATIONS, REASONS FOR CAUTION

We have demonstrated the presence of native complexes between PAPP-A and the STCs in the human ovary, indicating STC-mediated PAPP-A proteolytic inhibition. Further investigation is required to extend this principle to other tissues.

WIDER IMPLICATIONS OF THE FINDINGS

Our data suggest that the STCs contribute to PAPP-A regulation during folliculogenesis and support a general model in which STC1 and STC2 are regulators of mammalian IGF activity through inhibition of PAPP-A. We suggest that future functional studies take both PAPP-A and the STCs into consideration.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by grants from the Novo Nordisk Foundation, and the Danish Council for Independent Research. No competing interests declared.

Insulin Receptor Substrate 1, the Hub Linking Follicle-stimulating Hormone to Phosphatidylinositol 3-Kinase Activation

The ubiquitous phosphatidylinositol 3-kinase (PI3K) signaling pathway regulates many cellular functions. However, the mechanism by which G protein-coupled receptors (GPCRs) signal to activate PI3K is poorly understood. We have used ovarian granulosa cells as a model to investigate this pathway, based on evidence that the GPCR agonist follicle-stimulating hormone (FSH) promotes the protein kinase A (PKA)-dependent phosphorylation of insulin receptor substrate 1 (IRS1) on tyrosine residues that activate PI3K. We report that in the absence of FSH, granulosa cells secrete a subthreshold concentration of insulin-like growth factor-1 (IGF-1) that primes the IGF-1 receptor (IGF-1R) but fails to promote tyrosine phosphorylation of IRS1. FSH via PKA acts to sensitize IRS1 to the tyrosine kinase activity of the IGF-1R by activating protein phosphatase 1 (PP1) to promote dephosphorylation of inhibitory Ser/Thr residues on IRS1, including Ser(789). Knockdown of PP1β blocks the ability of FSH to activate PI3K in the presence of endogenous IGF-1. Activation of PI3K thus requires both PKA-mediated relief of IRS1 inhibition and IGF-1R-dependent tyrosine phosphorylation of IRS1. Treatment with FSH and increasing concentrations of exogenous IGF-1 triggers synergistic IRS1 tyrosine phosphorylation at PI3K-activating residues that persists downstream through protein kinase B (AKT) and FOXO1 (forkhead box protein O1) to drive synergistic expression of genes that underlies follicle maturation. Based on the ability of GPCR agonists to synergize with IGFs to enhance gene expression in other cell types, PP1 activation to relieve IRS1 inhibition may be a more general mechanism by which GPCRs act with the IGF-1R to activate PI3K/AKT.

Human steroidogenesis: implications for controlled ovarian stimulation with exogenous gonadotropins

In the menstrual cycle, the mid-cycle surge of gonadotropins (both luteinising hormone [LH] and follicle-stimulating hormone [FSH]) signals the initiation of the periovulatory interval, during which the follicle augments progesterone production and begins to luteinise, ultimately leading to the rupture of the follicle wall and the release of an oocyte. The administration of gonadotropins in controlled ovarian stimulation (COS) leads to supraphysiological steroid concentrations of a very different profile compared with those seen during natural cycles. It has been suggested that these high steroid concentrations cause alterations in endometrial development, affecting oocyte viability in assisted reproductive technology. Furthermore, it has been proposed that elevated progesterone levels have a negative effect on the reproductive outcome of COS. This may arise from an asynchrony between embryo stage and endometrium status at the window of implantation. The regulation of progesterone production by the developing follicles during COS is a complicated interplay of hormonal systems involving the theca and granulosa cells, and the effect of the actions of both LH and FSH. The present paper reviews current knowledge of the regulation of progesterone in the human ovary during the follicular phase and highlights areas where knowledge remains limited. In this review, we provide in-depth information outlining the regulation and function of gonadotropins in the complicated area of steroidogenesis. Based on current evidence, it is not clear whether the high levels of progesterone produced during COS have detrimental effects on fertility.

Selective inhibition of steroidogenic enzymes by ketoconazole in rat ovary cells

OBJECTIVE

Ketoconazole (KCZ) is an anti-fungal agent extensively used for clinical applications related to its inhibitory effects on adrenal and testicular steroidogenesis. Much less information is available on the effects of KCZ on synthesis of steroid hormones in the ovary. The present study aimed to characterize the in situ effects of KCZ on steroidogenic enzymes in primary rat ovary cells.

METHODS

Following the induction of folliculogenesis in gonadotropin treated rats, freshly prepared ovarian cells were incubated in suspension for up to four hours while radiolabeled steroid substrates were added and time dependent generation of their metabolic products was analyzed by thin layer chromatography (TLC).

RESULTS

KCZ inhibits the P450 steroidogenic enzymes in a selective and dose dependent manner, including cholesterol side-chain cleavage cytochrome P450 (CYP11A1/P450scc), the 17α-hydroxylase activity of CYP17A1/P450c17, and CYP19A1/P450arom, with IC₅₀ values of 0.3, 1.8, and 0.3 μg/mL (0.56, 3.36, and 0.56 μM), respectively. Unaffected by KCZ, at 10 μg/mL, were the 17,20 lyase activity of CYP17A1, as well as five non-cytochrome steroidogenic enzymes including 3β-hydroxysteroid dehydrogenase-Δ^5–4 isomerase type 1 (3βHSD1), 5α-reductase, 20α-hydroxysteroid dehydrogenase (20α-HSD), 3α-hydroxysteroid dehydrogenase (3α-HSD), and 17β-hydroxysteroid dehydrogenase type 1 (17HSD1).

CONCLUSION

These findings map the effects of KCZ on the ovarian pathways of progestin, androgen, and estrogen synthesis. Hence, the drug may have a potential use as an acute and reversible modulator of ovarian steroidogenesis in pathological circumstances.

The impact of antiandrogen 2-hydroxyflutamide on the expression of steroidogenic enzymes in cultured porcine ovarian follicles

We used our model system for agonism and antagonism of the androgen receptor (AR), in which the porcine ovarian follicles were exposed on the excessive concentration of an AR agonist- testosterone (T) or an AR antagonist- 2-hydroxyflutamide (2-Hf) to: (1) analyze the spatiotemporal expression of ovarian 3β-hydroxysteroid dehydrogenase (3β-HSD), cytochrome P450 17α-hydroxylase/c17,20-lyase (P450c17) and cytochrome P450 aromatase (P450arom); (2) to determine the contribution of AR-mediated action during steroidogenesis and (3) to establish some correlations between the onset and expression pattern of the investigated proteins. Whole follicles (6–8 mm in diameter) isolated from mature porcine ovaries have been incubated (for 24 h) in an organ culture system in the presence of T (10⁻⁷ M), 2-Hf (1.7 × 10⁻⁴ M) or both T and 2-hydroxyflutamide (T+2-Hf, at the same concentrations as when added separately). Thereafter, sections obtained from cultured follicles were processed for main steroidogenic enzymes detection by immunohistochemistry. Moreover, expression of their mRNA and protein was determined by real-time PCR and Western blot analysis. Progesterone, androgens and estradiol concentrations in the culture media were measured by radioimmunoassays (RIA). Our results demonstrated that 2-Hf can influence the steroidogenic activity of porcine follicles in vitro through the blockade of AR. It was shown that follicular 2-Hf treatment brought about dramatic decline in the production of the investigated steroids. What is more the addition of 2-Hf separately caused a negative effect on 3β-HSD and P450c17 mRNA and protein expression by ovarian follicles, while it was without effect on P450arom mRNA level. Quite opposite effect was observed in case of the simultaneous addition of 2-Hf and T. It caused high increase, in both P450arom mRNA and its protein. What was interesting, addition T+2-Hf evoked 3β-HSD and P450c17 increase on mRNA level, but decreased their protein expression. This was against our expectations but the reason for that finding remains undiscovered, intriguing and worth reporting. These results suggest that alike, steroidogenic enzymes activity and their expression is associated with the presence of androgens and AR in the porcine ovary.

The glycan structure in recombinant human FSH affects endocrine activity and global gene expression in human granulosa cells

The aim of this study was to analyse the biological response to different recombinant human FSH (rhFSH) glycosylation variants on the endocrine activity and gene expression at whole-genome scale in human granulosa-like tumor cell line, KGN. The effects of differences in rhFSH sialylation and oligosaccharide complexity were determined on steroid hormone and inhibin production. A microarray approach was used to explore gene expression patterns induced by rhFSH glycosylation variants. Set enrichment analysis revealed that hormone sialylation and oligosaccharide complexity in rhFSH differentially affected the expression of genes involved in essential biological processes and molecular functions of KGN cells. The relevance of rhFSH oligosaccharide structure on steroidogenesis was confirmed assessing gene expression by real time-PCR. The results demonstrate that FSH oligosaccharide structure affects expression of genes encoding proteins, growth factors and hormones essential for granulosa cells function.

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.

Expression profiles of key candidate genes involved in steroidogenesis during follicular atresia in the pig ovary

More than 99 % of follicles in mammalian ovaries undergo a degenerative process known as atresia, and thus only a limited number of ovarian follicles actually ovulate after full growth and development. The endocrinological regulatory mechanisms involved in follicular development have been studied extensively, but the precise and systematic molecular mechanisms of steroidogenesis enzymes involved in atresia are unclear. In the present study, we examined whether and how the steroidogenesis enzymes are involved in porcine ovary follicular atresia. Expression of steroidogenic acute regulatory protein, CYP11, CYP17, 3β-hydroxysteroid dehydrogenase (3β-HSD), CYP19, as well as related pituitary and ovarian hormone receptors were quantified in ovaries. During porcine follicular atresia, expressions of P450 cholesterol side chain cleavage enzyme, progesterone and androgen receptors increased significantly during the late atretic stage, while the expression of aromatase and follicle-stimulating hormone receptors decreased significantly in the early stage. These data suggested that the regulation of aromatase by follicle-stimulating hormone might induce follicular atresia, and that progesterone and androgen production further promoted follicular atresia. Additionally, a correlation analysis indicated a large and complex interactive network among these genes and the endocrinological microenvironment of the follicles. Significant correlations were observed between expression of steroidogenic enzymes and their receptors, and also between progesterone and 17β-estradiol (E2) levels in follicular fluid. Taken together, these results suggest that CYP19 plays a role during early atresia by regulating the production of E2, whereas CYP11 and 3β-HSD increase atresia progression by increasing progesterone levels.

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.

Follicle-stimulating hormone regulation of ovarian transcripts for steroidogenesis-related proteins and cell survival, growth and differentiation factors in vitro during early secondary oocyte growth in coho salmon

Little is known about follicle-stimulating hormone (FSH) function during oocyte growth in fishes. The goal of this study was to gain a fundamental understanding of FSH action on ovarian follicles during early secondary oocyte growth by examining changes in ovarian gene expression and steroidogenesis in response to FSH. Coho salmon (Oncorhynchus kisutch) mid to late cortical alveolus stage follicles were incubated with or without salmon FSH in time-course and concentration-response experiments. Steroid levels were determined in the culture medium by immunoassay and levels of target ovarian mRNAs were determined by quantitative RT-PCR. Medium estradiol-17β (E2) levels increased in response to FSH and plateaued by 36h, while testosterone levels increased similarly but were lower and more variable than E2. Gonadotropin receptor transcripts were differentially regulated, with fshr and lhcgr being down- and up- regulated, respectively. Transcripts encoding proteins involved in steroidogenesis, such as star and hsd3b were significantly upregulated by FSH, whereas aromatase (cyp19a1a) mRNA was unaffected by FSH and declined over time in culture. A recently identified teleost gene, bmp16, was suppressed by FSH and an anti-apoptotic factor, clusterin 1 (clu1), was upregulated by FSH. Lesser FSH effects were observed on igf2, cyp11a1 and cyp17a1, which were stimulated, and igf1ra, inhbb, amh and apoe, which were suppressed. As evident by the significant increases in steroid production and transcripts for specific steroidogenesis-related proteins, FSH influences steroidogenesis during early secondary growth and may be a critical signal for puberty onset. Effects of FSH on ovarian anti-apoptotic and growth factor genes suggest roles for FSH in cell survival, growth and differentiation in teleosts.

Estradiol, progesterone, testosterone profiles in human follicular fluid and cultured granulosa cells from luteinized pre-ovulatory follicles

BACKGROUND

The production of sex steroids by follicular cells is proposed to be influenced by the maturity of the incumbent oocyte. Thus steroid levels may reflect suitability of an oocyte for IVF. We examined follicular fluids and granulosa cell production of steroid from IVF patients in order to test the relationship between steroid levels and fertilization.

METHODS

Follicular fluid and granulosa cells were extracted from 206 follicles of 35 women undergoing controlled ovarian stimulation. Follicular fluid was assayed for estradiol, progesterone and testosterone. Granulosa cells were cultured from individual follicles and their culture media assayed for production of these hormones after 24 hrs in vitro. Levels of steroids were correlated with follicular diameter, oocyte recovery and subsequent fertilization.

RESULTS

Follicular fluid levels of progesterone were 6100 times higher than that of estradiol, and 16,900 times higher that of testosterone. Despite the size of follicle triggered after controlled luteinization, the levels of progesterone and testosterone were maintained at relatively constant levels (median 98.1 micromoles/L for progesterone, and 5.8 nanomoles/L for testosterone). However, estradiol levels were slightly lower in the larger follicles (follicular diameter 10-15 mm, median 25.3 nanomoles/L; follicles > = 15 mm, median 15.1 nanomoles/L; linear correlation r = -0.47, p < 0.0001). With respect to oocyte recovery, no steroid showed a significant association in follicular fluid levels. Similarly no difference in follicular fluid steroid levels was found for those oocytes that did or did not fertilize. Significant quantities of progesterone were produced by the granulosa cells but production was constant regardless of the size of follicle from which the cells originated. Estradiol levels were only detectable in 10 of 121 cultures examined, and testosterone in none. Interestingly, when an oocyte was present follicular estradiol levels correlated with progesterone levels. However, when absent, follicular estradiol levels correlated with testosterone levels but not with progesterone.

CONCLUSIONS

The principle steroid product of luteinized pre-ovulatory granulosa is progesterone, a differentiation triggered by the gonadotropin surge. However, absolute steroid levels are associated with follicular size, not oocyte maturation/ability to fertilize.

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.

Transcriptional regulation of steroidogenic genes: STARD1, CYP11A1 and HSD3B

Expression of the genes that mediate the first steps in steroidogenesis, the steroidogenic acute regulatory protein (STARD1), the cholesterol side-chain cleavage enzyme, cytochrome P450scc (CYP11A1) and 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase (HSD3B), is tightly controlled by a battery of transcription factors in the adrenal cortex, the gonads and the placenta. These genes generally respond to the same hormones that stimulate steroid production through common pathways such as cAMP signaling and common actions on their promoters by proteins such as NR5A and GATA family members. However, there are distinct temporal, tissue and species-specific differences in expression between the genes that are defined by combinatorial regulation and unique promoter elements. This review will provide an overview of the hormonal and transcriptional regulation of the STARD1, CYP11A1 and specific steroidogenic HSD3B genes in the adrenal, testis, ovary and placenta and discuss the current knowledge regarding the key transcriptional factors involved.

Growth differentiation factor 9 promotes rat preantral follicle growth by up-regulating follicular androgen biosynthesis

The transition from preantral to early antral stage is the penultimate stage of ovarian follicular development in terms of gonadotropin dependence and follicle destiny. Although oocyte-somatic cell communication is important in early follicular development, our knowledge of the precise role of the oocyte-derived growth differentiation factor (GDF)-9 during preantral follicle growth is incomplete. We examined whether and by what means oocyte-derived GDF-9 controls follicular development and steroidogenesis during the preantral to early antral transition, by a combination of in vitro gene manipulation (i.e. intraoocyte injection of GDF-9 antisense oligos) and preantral follicle culture. Intraoocyte injection of GDF-9 antisense suppressed rat preantral follicle growth in vitro, whereas GDF-9 enhanced follicular development. GDF-9 augmented testosterone production in preantral follicles. GDF-9 antisense suppressed androgen production and CYP17A1 mRNA expression in cultured follicles, a response attenuated by exogenous GDF-9. The nonaromatizable androgen 5alpha-dihydrotestosterone rescued the follicular growth arrest caused by GDF-9 down-regulation. The specific androgen receptor antagonist flutamide suppressed GDF-9-induced preantral follicle growth in vitro. The data suggest that GDF-9 plays an important role in promoting preantral follicle growth by up-regulating follicular androgen biosynthesis. GDF-9 is essential for CYP17A1 expression during follicular development from the preantral to the early antral stage.

Transcription of steroidogenic acute regulatory protein in the rodent ovary and placenta: alternative modes of cyclic adenosine 3', 5'-monophosphate dependent and independent regulation

Steroid hormone synthesis is a vital function of the adrenal cortex, serves a critical role in gonadal function, and maintains pregnancy if normally executed in the placenta. The substrate for the synthesis of all steroid hormones is cholesterol, and its conversion to the first steroid, pregnenolone, by the cholesterol side-chain cleavage cytochrome P450 (CYP11A1) enzyme complex takes place in the inner mitochondrial membranes. Steroidogenic acute regulatory protein (STAR) facilitates the rate-limiting transfer of cholesterol from the outer mitochondrial membrane to CYP11A1 located in the inner organelle membranes. The current study explored the mechanisms controlling transcription of the Star gene in primary cell cultures of mouse placental trophoblast giant cells and rat ovarian granulosa cells examined throughout the course of their functional differentiation. Our findings show that the cis-elements required for Star transcription in the rodent placenta and the ovary are centered in a relatively small proximal region of the promoter. In placental trophoblast giant cells, cAMP is required for activation of the Star promoter, and the cis-elements mediating a maximal response were defined as cAMP response element 2 and GATA. EMSA studies show that placental cAMP-responsive element binding protein (CREB)-1 and activating transcription factor-2 (ATF2) bind to a -81/-78 sequence, whereas GATA-2 binds to a -66/-61 sequence. In comparison, patterns of Star regulation in the ovary suggested tissue-specific and developmental controlled modes of Star transcription. During the follicular phase, FSH/cAMP induced CREB-1 dependent activity, whereas upon luteinization STAR expression becomes cAMP and CREB independent, a functional shift conferred by FOS-related antigen-2 displacement of CREB-1 binding, and the appearance of a new requirement for CCAAT enhancer-binding protein beta and steroidogenic factor 1 that bind to upstream elements (-117/-95). These findings suggest that during evolution, the promoters of the Star gene acquired nonconsensus sequence elements enabling expression of a single gene in different organs, or allowing dynamic temporal changes corresponding to progressing phases of differentiation in a given cell type.

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.

Effects of high levels of glucose on the steroidogenesis and the expression of adiponectin receptors in rat ovarian cells

BACKGROUND

Reproductive dysfunction in the diabetic female rat is associated with altered folliculogenesis and steroidogenesis. However, the molecular mechanisms involved in the reduction of steroid production have not been described. Adiponectin is an adipocytokine that has insulin-sensitizing actions including stimulation of glucose uptake in muscle and suppression of glucose production in liver. Adiponectin acts via two receptor isoforms - AdipoR1 and AdipoR2 - that are regulated by hyperglycaemia and hyperinsulinaemia in liver and muscle. We have recently identified AdipoR1 and AdipoR2 in rat ovary. However, their regulation in ovaries of diabetic female rat remains to be elucidated.

METHODS

We incubated rat primary granulosa cells in vitro with high concentrations of glucose (5 or 10 g/l) + or - FSH (10-8 M) or IGF-1 (10-8 M), and we studied the ovaries of streptozotocin-induced diabetic rats (STZ) in vivo. The levels of oestradiol and progesterone in culture medium and serum were measured by RIA. We used immunoblotting to assay key steroidogenesis factors (3beta HSD, p450scc, p450 aromatase, StAR), and adiponectin receptors and various elements of signalling pathways (MAPK ERK1/2 and AMPK) in vivo and in vitro. We also determined cell proliferation by [3H] thymidine incorporation.

RESULTS

Glucose (5 or 10 g/l) impaired the in vitro production in rat granulosa cells of both progesterone and oestradiol in the basal state and in response to FSH and IGF-1 without affecting cell proliferation and viability. This was associated with substantial reductions in the amounts of 3beta HSD, p450scc, p450 aromatase and StAR proteins and MAPK ERK1/2 phosphorylation. In contrast, glucose did not affect the abundance of AdipoR1 or AdipoR2 proteins. In vivo, as expected, STZ treatment of rats caused hyperglycaemia and insulin, adiponectin and resistin deficiencies. Plasma progesterone and oestradiol levels were also reduced in STZ rats. However, the amounts of 3beta HSD and p450 aromatase were the same in STZ rat ovary and controls, and the amounts of StAR and p450scc were higher. Streptozotocin treatment did not affect adiponectin receptors in rat ovary but it increased AMPK phosphorylation without affecting MAPK ERK1/2 phosphorylation.

CONCLUSION

High levels of glucose decrease progesterone and oestradiol production in primary rat granulosa cells and in STZ-treated rats. However, the mechanism that leads to reduced ovarian steroid production seems to be different. Furthermore, adiponectin receptors in ovarian cells are not regulated by glucose.

Turnover of mitochondrial steroidogenic acute regulatory (StAR) protein by Lon protease: the unexpected effect of proteasome inhibitors

Steroidogenic acute regulatory protein (StAR) is a vital mitochondrial protein promoting transfer of cholesterol into steroid making mitochondria in specialized cells of the adrenal cortex and gonads. Our previous work has demonstrated that StAR is rapidly degraded upon import into the mitochondrial matrix. To identify the protease(s) responsible for this rapid turnover, murine StAR was expressed in wild-type Escherichia coli or in mutant strains lacking one of the four ATP-dependent proteolytic systems, three of which are conserved in mammalian mitochondria-ClpP, FtsH, and Lon. StAR was rapidly degraded in wild-type bacteria and stabilized only in lon (-)mutants; in such cells, StAR turnover was fully restored upon coexpression of human mitochondrial Lon. In mammalian cells, the rate of StAR turnover was proportional to the cell content of Lon protease after expression of a Lon-targeted small interfering RNA, or overexpression of the protein. In vitro assays using purified proteins showed that Lon-mediated degradation of StAR was ATP-dependent and blocked by the proteasome inhibitors MG132 (IC(50) = 20 microm) and clasto-lactacystin beta-lactone (cLbetaL, IC(50) = 3 microm); by contrast, epoxomicin, representing a different class of proteasome inhibitors, had no effect. Such inhibition is consistent with results in cultured rat ovarian granulosa cells demonstrating that degradation of StAR in the mitochondrial matrix is blocked by MG132 and cLbetaL but not by epoxomicin. Both inhibitors also blocked Lon-mediated cleavage of the model substrate fluorescein isothiocyanate-casein. Taken together, our former studies and the present results suggest that Lon is the primary ATP-dependent protease responsible for StAR turnover in mitochondria of steroidogenic cells.

Interactions among peroxisome proliferator activated receptor-gamma, insulin signaling pathways, and steroidogenic acute regulatory protein in human ovarian cells

CONTEXT AND OBJECTIVE

Peroxisome proliferator activated receptor-gamma (PPAR-gamma) agonists thiazolidinediones (TZDs) are thought to ameliorate hyperandrogenism in polycystic ovary syndrome by reducing hyperinsulinemia. However, TZDs also exhibit direct effects in the human ovary. We examined interactions among PPAR-gamma, insulin signaling pathways, and steroidogenic acute regulatory (StAR) protein in human ovarian cells.

MATERIALS AND METHODS

Mixed human ovarian tissue culture that contained granulosa, theca, and stromal cells, and a culture of purified granulosa cells obtained during in vitro fertilization, were established as previously described. Cells were cultured in the presence or absence of insulin, with or without 25 or 50 microm rosiglitazone or pioglitazone. Expression of PPAR-gamma, insulin receptor, or insulin receptor substrate (IRS)-1 in both cell systems and of the StAR protein in granulosa cells was measured using immunoprecipitation and immunoblotting.

RESULTS

Rosiglitazone stimulated expression of PPAR-gamma, insulin receptor alpha- and beta-subunits, and IRS-1 up to 168% (P < 0.05), 679% (P < 0.006), 290% (P < 0.037), and 323% (P < 0.01) of baseline, respectively. Pioglitazone stimulated expression of PPAR-gamma, insulin receptor alpha- and beta-subunits, and IRS-1 up to 222% (P < 0.01), 362% (P < 0.001), 402% (P < 0.029), and 492% (P < 0.03), respectively. Insulin alone stimulated expression of PPAR-gamma, alpha-subunit and beta-subunit of insulin receptor, and IRS-1 up to 174% (P < 0.001), 692% (P < 0.014), 275% (P < 0.024), and 431% (P < 0.01), respectively. In purified granulosa cell culture, rosiglitazone stimulated expression of StAR protein up to 540% (P < 0.007), and pioglitazone stimulated expression of StAR protein up to 670% (P < 0.007). Insulin alone stimulated expression of StAR protein up to 600% (P < 0.012).

CONCLUSIONS

Insulin and TZDs independently stimulate expression of PPAR-gamma, insulin receptor, IRS-1, and StAR protein in human ovarian cells. Thus, PPAR-gamma, insulin receptor with its signaling pathways, and StAR protein constitute a novel human ovarian regulatory system with complex interactions among its components.

Elaboration of a working model for the involvement of inhibin A as a mediator of the preovulatory rise of progesterone levels

During the final days of follicular development, exogenously administered follicle-stimulating hormone (FSH) produces a rise in serum progesterone level. The aim of the present study was to investigate the possible source and regulation of this preovulatory progesterone surge. Four sets of matching treatments with gonadotropins for in vitro fertilization and intracytoplasmic sperm injection were selected from a cohort of 953 treatments in 244 couples. Half of these four sets of treatments were selected based on the unusual course of the progesterone concentration during follicular development. The first set of 11 cycles with early termination of gonadotropin administration for prolonged coasting were compared with a set of 12 cycles with similar estradiol levels but with uninterrupted ovarian stimulation. Another set of 12 cycles with low preovulatory progesterone levels (<2 nmol/l) were matched with ten cycles with normal preovulatory progesterone levels (>2 nmol/l). The sera of these four selected sets of treatments were stored for subsequent measurement of the concentrations of inhibin A, inhibin B, activin A and leptin. During ovarian hyperstimulation serum levels of inhibin A correlated significantly with those of progesterone (p < 0.001), whereas this correlation disappeared after the withdrawal of FSH administration. The rapid fall of progesterone levels during prolonged coasting contrasts with the continuing rise of estradiol concentration and indicates that the theca interna, not the granulosa, is the major source of preovulatory progesterone. Women failing to produce any increment of progesterone levels at the end of follicular development had significantly lower levels of inhibin A (p < 0.05), indicating that inhibin A may well be involved in mediating the signal of FSH from the granulosa to the theca interna.

Regulation of serine protease inhibitor-E2 and plasminogen activator expression and secretion by follicle stimulating hormone and growth factors in non-luteinizing bovine granulosa cells in vitro

During ovarian follicle growth, there is expansion of the basal lamina and changes in the follicular extracellular matrix (ECM) that are mediated in part by proteolytic enzyme cascades regulated by tissue-type plasminogen activator (tPA) and urokinase plasminogen activator (uPA). One PA inhibitor, serine protease inhibitor-E2 (SERPINE2) is expressed in granulosa but not theca cells, and expression changes with follicle development. In this study, we hypothesized that PA and SERPINE2 expression/secretion by granulosa cells are regulated by FSH and growth factors. SERPINE2 mRNA and protein levels, tPA gene expression and uPA secretion were stimulated by FSH. Insulin-like growth factor-I stimulated SERPINE2 secretion and uPA activity, and decreased secreted tPA activity and gene expression. Bone morphogenetic protein-7 increased SERPINE2 secretion and expression and tPA secretion. In contrast, fibroblast growth factor-2 inhibited tPA secretion and SERPINE2 secretion and expression. Epidermal growth factor inhibited SERPINE2 secretion and expression, but increased secreted tPA activity. Estradiol and SERPINE2 secretion were highly positively correlated, but estradiol did not alter SERPINE2 expression. These data demonstrate that SERPINE2 expression and protein secretion are regulated by FSH and growth factors in non-luteinizing bovine granulosa cells. As estradiol is a known marker of follicle health, and SERPINE2 is an anti-apoptotic factor, we propose that SERPINE2 is involved in the regulation of atresia in bovine follicles.

Real-time monitoring of cAMP response element binding protein signaling in porcine granulosa cells modulated by ovarian factors

The present study was performed to establish a real-time monitoring of the cAMP response element binding protein (CREB) signalling using granulosa cells, and to assess the modulation of CREB activity by potential ovarian autocrine/paracrine and oocyte-derived factors. Granulosa cells were isolated from porcine follicles and cultured for 2 days, and then transfected with CRE-containing pGL3. The cells were directly stimulated or cultured with FSH, LH, forskolin, or a permeable cAMP analog, and/or IGF-I, EGF, bFGF, TGF-beta2 or TNF-alpha, or cumulus-oocyte complex (COCs) for the real-time monitoring of CREB signaling. The activation pattern of CREB signaling consisted of three distinct phases, i.e., burst, attenuation and refractory. In contrast to FSH, LH, and forskolin, a cAMP analog induced the prolonged activation, although three distinct phases were observed at its high concentration. Of all the autocrine/paracrine factors, only IGF-I slightly induced CREB activity. On the other hand, TGF-beta2 and TNF-alpha significantly repressed FSH-stimulated transcriptional activation of CREB by 30% (P < 0.05) and 45% (P < 0.05), respectively. Additionally, coculture with COCs caused a significant suppression of transcriptional activation of CREB signaling stimulated by FSH. These results indicate that ovarian autocrine/paracrine factors such as IGF-I, TGF-beta2, TNF-alpha and oocyte-derived factors modulate the CREB signaling. The present study provides a new approach for direct signaling study on transcription factors under the influences of potential factors.

FSH signaling pathways in immature granulosa cells that regulate target gene expression: branching out from protein kinase A

Follicle-stimulating hormone (FSH) is necessary and sufficient to induce maturation of ovarian follicles to a mature, preovulatory phenotype in the intact animal, resulting in the generation of mature eggs and production of estrogen. FSH accomplishes these actions by inducing a complex pattern of gene expression in target granulosa cells that is regulated by input from many different signaling cascades, including those for the extracellular regulated kinases (ERKs), p38 mitogen-activated protein kinases (MAPKs), and phosphatidylinositol-3 kinase (PI3K). The upstream kinase that appears to be responsible for initiating all of the signaling that regulates gene expression in these epithelial cells is protein kinase A (PKA). PKA not only signals to directly phosphorylate transcription factors like cAMP response element binding protein and to promote chromatin remodeling by phosphorylating histone H3, this versatile kinase also enhances the activity of the p38 MAPK, ERK, and PI3K pathways. Additionally, accumulating evidence suggests that activation of a single signaling cascade downstream of PKA is not sufficient to activate target gene expression. Rather, cross-talk between and among signaling cascades is required. We will review the signaling cascades activated by FSH in granulosa cells and how these cascades contribute to the regulation of select target gene expression.

Steroidogenic activities of follicle-stimulating hormone in the ovary of Japanese eel, Anguilla japonica

To clarify the physiological functions of follicle-stimulating hormone (FSH) during oogenesis in Japanese eel, Anguilla japonica, the steroidogenic activities of recombinant Japanese eel FSH (rjeFSH) were assessed in the eel ovary. Female eel were injected with salmon pituitary homogenate to enhance the ovarian development, and the ovaries at different developmental stages were subjected to steroidogenic bioassay. These ovaries could be classified into three types according to oocyte growth and development of ovarian follicular cells. The type-A ovary possessed poorly developed follicular cells around pre- or early vitellogenic oocytes, and rjeFSH did not induce sex steroid secretion. Testosterone (T) secretion was stimulated by rjeFSH in the type-B ovary with developed theca cells and undeveloped granulosa cells around early to mid-vitellogenic oocytes, whereas estradiol-17beta (E2) secretion was not enhanced. The rjeFSH stimulated both T and E2 secretion in a dose-dependent manner from the type-C ovary with fully developed theca and granulosa cells around mid-vitellogenic oocytes. Salmon GTH fraction (sGTH) and a membrane permeable cAMP analogue, 8-bromo-cAMP (8-Br-cAMP) also enhanced T and E2 secretion from the type-C ovary. Human chorionic gonadotropin (hCG) similarly enhanced T secretion, but failed to stimulate E2 secretion from the type-C ovary, suggesting different effects on steroidogenic activities between eel FSH and hCG in eel ovary. There was a positive correlation between the oocyte diameter and E2 secretion from eel ovaries stimulated by rjeFSH. These results suggest that aromatase activity is accelerated by eel FSH in the granulosa cells, which develop following theca cell development in this species.

Adenosine 5'-monophosphate-activated protein kinase regulates progesterone secretion in rat granulosa cells

The AMP-activated protein kinase (AMPK) is a major regulator of energy metabolism involved in fatty acid and cholesterol synthesis. In the ovary, cholesterol plays a key role in steroid production. We report the presence of AMPK in rat ovaries, and we have investigated its role in granulosa cells. We show using RT-PCR and Western blot that the mRNAs for the alpha1/2 and beta1/2 subunits and the proteins are found in the ovaries. Immunohistochemistry localized the alpha1 AMPK subunit in granulosa cells, corpus luteum, and oocyte and less abundantly in theca cells. Treatment with 1 mm 5-amino-imidazole-4-carboxyamide-1-beta-D-ribofuranoside (AICAR), an activator of AMPK, increased dose-dependent and time-dependent phosphorylation of AMPKalpha1 on Thr172 in primary granulosa cells. Simultaneously, phosphorylation of acetyl-coenzyme A carboxylase at Ser79 was also increased. AICAR treatment for 48 h halved progesterone secretion, 3beta-HSD protein and mRNA levels, and phosphorylation of both basal MAPK ERK1/2 and p38 and in response to IGF-I and/or FSH in granulosa cells. AICAR treatment (1 mM) had no detectable effect on basal and FSH- and/or IGF-I-induced estradiol production and on granulosa cell proliferation or viability. Adenovirus-mediated expression of dominant negative AMPK totally abolished the effects of AICAR on progesterone secretion, 3beta-HSD protein production, and MAPK ERK1/2 and p38 phosphorylation. Moreover, we showed using specific in- hibitors of ERK1/2 and p38 MAPK that the MAPK ERK1/2 and not p38 is involved in progesterone secretion and 3beta-HSD expression, strongly suggesting that the activation of AMPK in response to AICAR reduces progesterone production through the MAPK ERK1/2 signaling pathway in rat granulosa cells.

Intracellular protein phosphorylation in adherent U937 monocytes mediated by various culture conditions and fibronectin-derived surface ligands

Macrophages play a central role in the normal healing process after tissue injury and the host response to foreign objects such as biomaterials. The process leading to macrophage adhesion and activation on protein-adsorbed substrates is complex and unresolved. While the use of primary cells offers clinical relevancy, macrophage cell lines offer unique advantages such as availability and relatively homogeneous phenotype as models to probe the molecular mechanism of cell-surface interaction. Our goal was to better characterize the effect of the culture condition and surface-associated ligands on the extent of U937 adhesion. Tyrosine phosphorylation of intracellular proteins was surveyed as a basis to seek a greater understanding of the molecular mechanism involved in mediating U937 adhesion on various ligand-adsorbed surfaces. U937 viability and adhesion on tissue culture polystyrene (TCPS) increased with (i) increasing serum level, (ii) decreasing tyrosine phosphorylation inhibitor AG18 concentration, or (iii) increasing culture time. The adsorption of various adhesion proteins such as fibronectin and peptide ligands (i.e., RGD, PHSRN) on TCPS did not significantly increase the adherent density of U937 when compared with albumin and PBS ligand controls. However, ligand identity and the presence of phorbol myristate acetate dramatically affected the extent (i.e., increase or decrease) and the identity (i.e., molecular weight) of phosphotyrosine proteins in adherent U937 in a time-dependent manner. The extent and identity of phosphotyrosine proteins did not exhibit a clear AG18 dose dependency, rather the level of tyrosine phosphorylation for a distinct group of proteins was either increased or decreased for a given AG18 concentration.

Overview of steroidogenic enzymes in the pathway from cholesterol to active steroid hormones

Significant advances have taken place in our knowledge of the enzymes involved in steroid hormone biosynthesis since the last comprehensive review in 1988. Major developments include the cloning, identification, and characterization of multiple isoforms of 3beta-hydroxysteroid dehydrogenase, which play a critical role in the biosynthesis of all steroid hormones and 17beta-hydroxysteroid dehydrogenase where specific isoforms are essential for the final step in active steroid hormone biosynthesis. Advances have taken place in our understanding of the unique manner that determines tissue-specific expression of P450aromatase through the utilization of alternative promoters. In recent years, evidence has been obtained for the expression of steroidogenic enzymes in the nervous system and in cardiac tissue, indicating that these tissues may be involved in the biosynthesis of steroid hormones acting in an autocrine or paracrine manner. This review presents a detailed description of the enzymes involved in the biosynthesis of active steroid hormones, with emphasis on the human and mouse enzymes and their expression in gonads, adrenal glands, and placenta.

Effect of Insulin-Like Growth Factor-I During Preantral Follicular Culture on Steroidogenesis, In Vitro Oocyte Maturation, and Embryo Development in Mice1

Insulin-like growth factor-I (IGF-I) is involved in the regulation of ovarian follicular development and has been shown to potentiate the FSH responsiveness of granulosa cells from preantral follicles. The aim of the present study was to investigate the effect of IGF-I during preantral follicular culture on steroidogenesis, subsequent oocyte maturation, fertilization, and embryo development in mice. Preantral follicles were isolated mechanically and cultured for 12 days in a simplified culture medium supplemented with 1% fetal calf serum, recombinant human FSH, transferrin, and selenium. In these conditions, follicles were able to grow and produce oocytes that could be matured and fertilized. The first experiment analyzed the effect of different concentrations of IGF-I (0, 10, 50, or 100 ng/ml) added to the culture medium on the follicular survival, steroidogenesis, and the oocyte maturation process. The presence of IGF-I during follicular growth increased the secretion of estradiol but had no effect on the subsequent oocyte survival and maturation rates. In the second experiment, IGF-I (0 or 50 ng/ml) was added to the culture medium during follicular growth, oocyte maturation, or both, and subsequent oocyte fertilization and embryo development rates were evaluated. Oocyte fertilization rates were comparable in the presence or absence of IGF-I. However, the blastocyst development rate was enhanced after follicular culture in the presence of IGF-I. Moreover, the total cell number of the blastocysts observed after differential labeling staining was also higher when follicles were cultured or matured in the presence of IGF-I.

Cloning and characterization of granulosa cell high-mobility group (HMG)-box protein-1, a novel HMG-box transcriptional regulator strongly expressed in rat ovarian granulosa cells

Specific events in the ovary are dependent on gene expression in the tissue. By screening a rat ovarian granulosa cell cDNA library, a cDNA clone encoding a novel transcription factor-like protein containing a high-mobility group-box, referred to as granulosa cell high-mobility group-box protein-1 (GCX-1), was identified. The expression of GCX-1 is restricted to the hypothalamus, pituitary, testis, uterus, and ovary but was not detected in the adrenal gland. An in situ hybridization study revealed that the expression of GCX-1 was restricted to granulosa cell layers in early-stage follicles, and the expression was very low in large antral follicles and the corpus luteum, but localized expression in the testis or pituitary was not clear. Endogenous GCX-1 protein in the granulosa cells was identified by a Western blot analysis, and an analysis using the green fluorescence protein-GCX-1 fusion protein revealed that the GCX-1 protein was localized in the cell nucleus. GAL4 fusion protein-based assays demonstrated that GCX-1 is a potent transcriptional activator, and its putative transactivation domain was mapped to the region between amino acid residues 25 and 63 from the N terminus. These data strongly suggest that GCX-1 is likely a novel transcriptional activator that is exclusively expressed in reproductive tissues involving the hypothalamo-pituitary-gonadal axis, and functions as a specific regulator of follicular development, and may also participate in other specific events related to reproduction, particularly in the female.

Di(n-butyl) phthalate impairs cholesterol transport and steroidogenesis in the fetal rat testis through a rapid and reversible mechanism

In utero exposure to di(n-butyl) phthalate (DBP) leads to a variety of male reproductive abnormalities similar to those caused by androgen receptor antagonists. DBP demonstrates no affinity for the androgen receptor, but rather leads to diminished testosterone production by the fetal testis. The purpose of this study was to determine the onset and reversibility of DBP effects on the fetal testis and to determine at a functional level the points in the cholesterol transport and steroidogenesis pathways affected by DBP. Starting at gestational day (gd) 12, pregnant rats were gavaged daily with 500 mg/kg DBP or corn oil control. Significant decreases in testosterone production and mRNA expression of scavenger receptor B1, P450(SCC), steroidogenic acute regulatory protein, and cytochrome p450c17 were observed as early as gd 17. Testosterone, mRNA, and protein levels remained low 24 h after withdrawal of DBP treatment but increased 48 h after cessation of DBP exposure. In another experiment, pregnant dams were treated with DBP until gd 19, with the start of DBP treatment moved 1 d later into gestation for each treatment group, with the final group dosed only on gd 19. Significant decreases in testosterone, mRNA expression, and protein expression were evident as early as 3 h after treatment with DBP, with full repression apparent 24 h after treatment. Using a testis explant system, we determined that DBP treatment led to diminished transport of cholesterol across the mitochondrial membrane as well as diminished function at each point in the testosterone biosynthesis pathway except 17 beta-hydroxysteroid dehydrogenase. The transcriptional repression caused by DBP does not appear to be mediated via interference with steroidogenic factor-1 as determined by reporter assays. We conclude that high-dose DBP exposure leads to rapid and reversible diminution of the expression of several proteins required for cholesterol transport and steroidogenesis in the fetal testis, resulting in decreased testosterone synthesis and consequent male reproductive maldevelopment.

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

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

Upregulation of steroidogenic enzymes and ovarian 17beta-estradiol in human granulosa-lutein cells by Cordyceps sinensis mycelium

There is increasing evidence that 17beta-estradiol (E2) directly influences the quality of maturing oocytes and thus the outcome of assisted reproduction treatment. Although Cordyceps sinensis (CS) mycelium, a Chinese herbal medicine, is believed to enhance libido and fertility in both sexes, the mechanism of its effect in women has not been determined. The aim of the present study was to evaluate the effects of CS on steroidogenic enzyme expression and E2 biosynthesis in human granulosa-lutein cells (GLC). We found that CS induced E2 production by GLC in a dose- and time-dependent manner and that a 3-h treatment with CS induced increased levels of mRNAs coding for the P450 side chain cleavage enzyme (P450scc), 3beta-hydroxysteroid dehydrogenase (3beta-HSD), and aromatase. Western blot analysis demonstrated that, after treatment with CS for 3 h, protein levels of steroidogenic acute regulatory protein (StAR) and aromatase were upregulated while P450scc and 3beta-HSD levels showed no substantial change. New protein synthesis was required for CS-induced E2 production because it was abrogated by cycloheximide pretreatment. Addition of 22(R)-hydroxycholesterol, thus bypassing the need for StAR protein, did not induce as much E2 production as CS treatment, indicating that upregulation of StAR protein was not the only factor contributing to CS-induced steroidogenesis. Cotreatment of GLCs with CS and aminoglutethimide, an aromatase inhibitor, completely abolished CS-induced E2 production. In conclusion, treatment of GLCs with CS results in increased E2 production due, at least in part, to increased StAR and aromatase expression. These data may help in the development of treatment regimens to improve the success rate of in vitro fertilization.

Mechanism of follicle deviation in monovular farm species

Diameter deviation is a distinctive change in growth rates among the follicles of a wave, heralding the formation of a dominant follicle and subordinate follicles. When the follicles are about 5mm in cattle and 13 mm in horses, the wave-stimulating FSH surge reaches peak concentrations. Follicle and FSH manipulation studies in both species have shown that the declining portion of the surge before the beginning of deviation is a function of multiple growing follicles that require the decreasing FSH. During this time, all follicles of the wave have the potential for future dominance. Deviation begins when the two largest follicles on average are 8.5 and 7.7 mm in cattle and 22.5 and 19.0 mm in horses or about 3 days after the FSH peak in both species. The FSH/follicle relationship is close so that a change in one event soon causes a detectable change in the other. Thus, the difference in diameter between the two largest follicles at the beginning of deviation is compatible with rapid establishment of the destiny of the two follicles before the second-largest follicle can also show dominance. The deviation mechanism is initiated when FSH concentrations are low and the most advanced follicle reaches a specific developmental stage. In cattle, the future dominant follicle develops greater LH-receptor expression than the other follicles about 8 h before the beginning of diameter deviation. Estradiol and free IGF-1 begin to establish higher concentrations in the future dominant follicle than in other follicles and activin-A is transiently elevated in both follicles a few hours before the beginning of diameter deviation. In horses, estradiol, free IGF-1, activin-A, and inhibin-A begin to increase differentially in the future dominant follicle about 1 day before deviation. These changes underlie a greater responsiveness to LH and FSH by the developing dominant follicle than for other follicles, thereby accounting for deviation. Results of in vitro studies, although frequently done in other species, support this conclusion.