PKA and AMPK Signaling Pathways Differentially Regulate Luteal Steroidogenesis

Luteinizing hormone (LH) via protein kinase A (PKA) triggers ovulation and formation of the corpus luteum, which arises from the differentiation of follicular granulosa and theca cells into large and small luteal cells, respectively. The small and large luteal cells produce progesterone, a steroid hormone required for establishment and maintenance of pregnancy. We recently reported on the importance of hormone-sensitive lipase (HSL, also known as LIPE) and lipid droplets for appropriate secretory function of the corpus luteum. These lipid-rich intracellular organelles store cholesteryl esters, which can be hydrolyzed by HSL to provide cholesterol, the main substrate necessary for progesterone synthesis. In the present study, we analyzed dynamic posttranslational modifications of HSL mediated by PKA and AMP-activated protein kinase (AMPK) as well as their effects on steroidogenesis in luteal cells. Our results revealed that AMPK acutely inhibits the stimulatory effects of LH/PKA on progesterone production without reducing levels of STAR, CYP11A1, and HSD3B proteins. Exogenous cholesterol reversed the negative effects of AMPK on LH-stimulated steroidogenesis, suggesting that AMPK regulates cholesterol availability in luteal cells. AMPK evoked inhibitory phosphorylation of HSL (Ser565). In contrast, LH/PKA decreased phosphorylation of AMPK at Thr172, a residue required for its activation. Additionally, LH/PKA increased phosphorylation of HSL at Ser563, which is crucial for enzyme activation, and decreased inhibitory phosphorylation of HSL at Ser565. The findings indicate that LH and AMPK exert opposite posttranslational modifications of HSL, presumptively regulating cholesterol availability for steroidogenesis.

Granulosa-Lutein Cell Sirtuin Gene Expression Profiles Differ between Normal Donors and Infertile Women

Sirtuins are a family of deacetylases that modify structural proteins, metabolic enzymes, and histones to change cellular protein localization and function. In mammals, there are seven sirtuins involved in processes like oxidative stress or metabolic homeostasis associated with aging, degeneration or cancer. We studied gene expression of sirtuins by qRT-PCR in human mural granulosa-lutein cells (hGL) from IVF patients in different infertility diagnostic groups and in oocyte donors (OD; control group). Study 1: sirtuins genes’ expression levels and correlations with age and IVF parameters in women with no ovarian factor. We found significantly higher expression levels of SIRT1, SIRT2 and SIRT5 in patients ≥40 years old than in OD and in women between 27 and 39 years old with tubal or male factor, and no ovarian factor (NOF). Only SIRT2, SIRT5 and SIRT7 expression correlated with age. Study 2: sirtuin genes’ expression in women poor responders (PR), endometriosis (EM) and polycystic ovarian syndrome. Compared to NOF controls, we found higher SIRT2 gene expression in all diagnostic groups while SIRT3, SIRT5, SIRT6 and SIRT7 expression were higher only in PR. Related to clinical parameters SIRT1, SIRT6 and SIRT7 correlate positively with FSH and LH doses administered in EM patients. The number of mature oocytes retrieved in PR is positively correlated with the expression levels of SIRT3, SIRT4 and SIRT5. These data suggest that cellular physiopathology in PR’s follicle may be associated with cumulative DNA damage, indicating that further studies are necessary.

Inductions of granulosa cell luteinization and cumulus expansion are dependent on the fibronectin-integrin pathway during ovulation process in mice

It has been known that EGF-like factor secreted from LH-stimulated granuloma cells acts on granulosa cells and cumulus cells to induce ovulation process. Granulosa cells are changed the morphology with differentiating cell functions to produce progesterone. Cumulus cells are detached to make a space between the cells to accumulate hyaluronan rich matrix. LH also changes extracellular matrix (ECM) components including fibronectin in the follicular walls and granulosa cell layers. EGF like factor and fibronectin synergistically play important roles in numerous cell functions, especially cancer cell migration, estimating that fibronectin would impact on granulosa cells and cumulus cells. To clear this hypothesis, the localizations of fibronectin and its receptor integrin were observed by immunofluorescence technique. The functions were monitored by the detection of downstream signaling pathway, focal adhesion kinase (FAK). The pharmacological approach in both in vivo and in vitro were used for analyzing the physiological roles of FAK during ovulation process. The immunofluorescence staining revealed that fibronectin and integrin were observed in granulosa cells, cumulus cells and the space between cumulus cells and oocyte at 4 and 8 h after hCG injection. Concomitantly with the changes of fibronectin-integrin localization, FAK was phosphorylated in periovulatory follicles. The injection of FAK inhibitor suppressed not only ovulation but also luteinization of granulosa cells and cumulus expansion. In cultured-granulosa cells, fibronectin-integrin synergistically activated FAK with amphiregulin (AREG). Such cooperative stimulations induced a morphological change in granulosa cells, which resulted in the maximum level of progesterone production via the induction of Hsd3b. When cumulus-oocyte complexes (COCs) were cultured with AREG in the presence of serum, the maximum level of cumulus expansion was observed. The AREG-induced cumulus expansion was also suppressed by FAK inhibitor. Thus, it is concluded that fibronectin and AREG synergistically activate FAK not only in granulosa cells and cumulus cells to induce successful ovulation process.

Roles of prostaglandin F2alpha and hydrogen peroxide in the regulation of Copper/Zinc superoxide dismutase in bovine corpus luteum and luteal endothelial cells

BACKGROUND

Prostaglandin F2alpha (PGF) induces luteolysis in cow by inducing a rapid reduction in progesterone production (functional luteolysis) followed by tissue degeneration (structural luteolysis). However the mechanisms of action of PGF remain unclear. Reactive oxygen species (ROS) play important roles in regulating the luteolytic action of PGF. The local concentration of ROS is controlled by superoxide dismutase (SOD), the main enzyme involved in the control of intraluteal ROS. Thus SOD seems to be involved in luteolysis process induced by PGF in cow.

METHODS

To determine the dynamic relationship between PGF and ROS in bovine corpus luteum (CL) during luteolysis, we determined the time-dependent change of Copper/Zinc SOD (SOD1) in CL tissues after PGF treatment in vivo. We also investigated whether PGF and hydrogen peroxide (H2O2) modulates SOD1 expression and SOD activity in cultured bovine luteal endothelial cells (LECs) in vitro.

RESULTS

Following administration of a luteolytic dose of PGF analogue (0 h) to cows at the mid-luteal stage, the expression of SOD1 mRNA and protein, and total SOD activity in CL tissues increased between 0.5 and 2 h, but fell below the initial (0 h) level at 24 h post-treatment. In cultured LECs, the expression of SOD1 mRNA was stimulated by PGF (1-10 microM) and H2O2 (10-100 microM) at 2 h (P<0.05). PGF and H2O2 increased SOD1 protein expression and total SOD activity at 2 h (P<0.05), whereas PGF and H2O2 inhibited SOD1 protein expressions and total SOD activity at 24 h (P<0.05). In addition, H2O2 stimulated PGF biosynthesis at 2 and 24 h in bovine LECs. Overall results indicate that, SOD is regulated by PGF and ROS in bovine LECs. SOD may play a role in controlling intraluteal PGF and ROS action during functional and structural luteolysis in cows.

Activation of PI3K/mTOR signaling pathway contributes to induction of vascular endothelial growth factor by hCG in bovine developing luteal cells

We recently reported that HIF-1α plays a critical role in the regulation of vascular endothelial growth factor (VEGF) expression in the developing letual cells (LCs) and VEGF-dependent angiogenesis is essential for normal luteal development. Although it is believed that hypoxia is the primary inducer of VEGF, recent reports have also shown that human chorionic gonadotrophin (hCG) up-regulates VEGF expression in developing corpus luteum (CL). Therefore the present study was designed to test the induced effects of hCG on the expression of VEGF and HIF-1α in LCs under normoxic and hypoxic conditions. In addition, we also investigated whether the signaling pathways such as phosphatidylinositol 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) and mitogen-activated protein kinase (MAPK) are involved in hCG-induced VEGF in LCs. A significant increase of VEGF mRNA was found in LCs treated with hCG, which was consistent with the changes of HIF-1α protein, even under hypoxic conditions. However, there was no obvious changes of HIF-1α mRNA in hCG-treated LCs between normoxic and hypoxic conditions, indicating hCG induces VEGF expression by increasing transcription of HIF-1α, while hypoxia mainly increases HIF-1α protein stability. When LCs were pretreated with inhibitors, we found that the PI3K/mTOR signaling pathway is required for HIF-1α and VEGF expression induced by hCG, while the MAPK pathway is not required. Together, these results suggest that activation of IP3K/mTOR signaling pathway contributes to the induction of VEGF and HIF-1α in hCG-treated LCs. To our knowledge this will provide a new insight into the important mechanism of hCG/LH-induced VEGF-dependent angiogenesis in the bovine ovary.

Nitric oxide stimulates progesterone and prostaglandin E2 secretion as well as angiogenic activity in the equine corpus luteum

Cytokines and nitric oxide (NO) are potential mediators of luteal development and maintenance, angiogenesis, and blood flow. The aim of this study was to evaluate (i) the localization and protein expression of endothelial and inducible nitric oxide synthases (eNOS and iNOS) in equine corpora lutea (CL) throughout the luteal phase and (ii) the effect of a nitric oxide donor (spermine NONOate, NONOate) on the production of progesterone (P4) and prostaglandin (PG) E(2) and factor(s) that stimulate endothelial cell proliferation using equine luteal explants. Luteal tissue was classified as corpora hemorrhagica (CH; n = 5), midluteal phase CL (mid-CL; n = 5) or late luteal phase CL (late CL; n = 5). Both eNOS and iNOS were localized in large luteal cells and endothelial cells throughout the luteal phase. The expression of eNOS was the lowest in mid-CL (P < 0.05) and the highest in late CL (P < 0.05). However, no change was found for iNOS expression. Luteal explants were cultured with no hormone added or with NONOate (10(-5) M), tumor necrosis factor-α (TNFα; 10 ng/mL; positive control), or equine LH (100 ng/mL; positive control). Conditioned media by luteal tissues were assayed for P4 and PGE(2) and for their ability to stimulate proliferation of bovine aortic endothelial cells (BAEC). All treatments stimulated release of P4 in CH, but not in mid-CL. TNFα and NONOate treatments also increased PGE(2) levels and BAEC proliferation in CH (P < 0.05). However, in mid-CL, no changes were observed, regardless of the treatments used. These data suggest that NO and TNFα stimulate equine CH secretory functions and the production of angiogenic factor(s). Furthermore, in mares, NO may play a role in CL growth during early luteal development, when vascular development is more intense.

Oxidative stress-inducible antioxidant adaptive response during prostaglandin F2α-induced luteal cell deathin vivo

Oxidative stress-induced antioxidant adaptive response would be particularly important to cells in high reactive oxygen species (ROS) environments. We aimed to determine the dynamic adaptive response of antioxidant enzymatic systems in sheep corpus luteum (CL) during PGF2alpha-induced luteal cell death. Activities of superoxide dismutase (SOD1 and SOD2), catalase (CAT), glutathione peroxidase (GPX) and glutathione reductase (GSR), and in situ DNA fragmentation were determined in CL at day 10 of the estrous cycle (0 h) and at 12, 24 or 48 h after PGF2alpha injection. A decrease in plasma progesterone concentration was first observed at 6 h after treatment (P < 0.05). Apoptotic cells were rarely observed in the CL at 0 h (less than 0.7%), and their incidence increased (P < 0.01) by 12 h post-PGF2alpha (11.7%) and remained thereafter elevated through 48 h. Activities of SOD1, SOD2, GPX and GSR were not changed at any time points after PGF2alpha treatment. CAT activity increased at 12 h (P < 0.01) and at 24 h (P < 0.05) after PGF2alpha treatment as compared to that at 0 h. These findings demonstrate that PGF2alpha induce luteal cell death without depressing the activity of antioxidant enzymes. It is suggested that transient increase in CAT activity is an adaptive response of the CL to oxidative stress induced by PGF2alpha.

Protein kinase C isoforms in the porcine corpus luteum: temporal and spatial expression patterns

Porcine corpora lutea (CL) fail to show a luteolytic response to prostaglandin-F-2alpha (PGF-2alpha) (ie, luteolytic sensitivity, or LS) until approximately day 13 of the estrous cycle. In view of the importance of protein kinase C (PRKC) in PGF-2alpha signal transduction, it was hypothesized that limiting levels of 1 or more PRKC isoforms may explain the lack of LS before day 13. This hypothesis was tested by examining expression of mRNA and protein, and the cellular localization patterns of the 11 PRKC isoforms throughout the porcine estrous cycle, to determine whether PRKC expression correlates with and thus may be associated with the control of the acquisition of LS in the pig. The expression patterns show that for most PRKC isoforms (ie, PRKC alpha, beta 1, beta 2, delta, epsilon, theta, iota, and zeta), mRNA was maximally expressed on day 7 or day 10 (protein kinase D1 only) of the cycle, whereas PRKCs gamma, eta, and lambda were unchanged. At the protein level, only PRKC epsilon (PRKCE) significantly changed during the estrous cycle and was elevated on day 13 (versus days 4, 7, and 15; P<0.05). By immunofluoresence, most PRKC isoforms, including PRKCE, were localized to steroidogenic large luteal cells (LLC) and small (nonendothelial cell) luteal cell subtypes (SLC). In conclusion, since the increase in PRKCE protein expression (day 13) occurred coincidentally with the onset of LS (> or =day 12), these results support a potential role for PRKCE in control of the acquisition of LS in the pig.

Atrazine-induced changes in aromatase activity in estrogen sensitive target tissues

Atrazine (ATR) is a pesticide used widely throughout North America. Although not directly estrogenic, ATR treatment has been shown to increase aromatase activity in tumor cell lines. Thus, it is suggested that ATR can increase local tissue estrogen levels in estrogen sensitive target tissues through increased aromatase activity. Therefore the effect of ATR on aromatase activity was measured in human granulosa-lutein cell cultures, cells that abundantly express aromatase, and endometrial stromal cell (ESC) cultures, cells that do not express aromatase. Aromatase activity was quantified by the tritiated water method and the specificity of the assay was confirmed by co-incubation with 4-hydroxyandrostenedione, an irreversible inhibitor of the catalytic activity of aromatase. Aromatase activity in ATR treated (1-10 microm) granulosa-lutein cells was increased more than 2-fold compared with control cultures. There were no treatment related changes in cellular protein and thus it is suggested that the ATR-induced change in aromatase activity was not due to an increase in cell number. ATR-treatment had no effect on ESC aromatase activity at any concentration tested. Similarly, there was no effect of ATR treatment on human recombinant aromatase activity in our cell-free test system. Therefore it is concluded that microm concentrations of ATR can increase aromatase activity of human granulosa cells but not ESC and this effect is not elicited at the enzyme level.

Müllerian-inhibiting substance inhibits cytochrome P450 aromatase activity in human granulosa lutein cell culture

OBJECTIVE

To investigate the effects of Müllerian-inhibiting substance (MIS) on cytochrome P450 aromatase (CYP19) gene expression in cultured human granulosa lutein cells (GLC).

DESIGN

In vitro primary cell culture study.

SETTING

Academic research laboratory and hospital-based fertility center.

PATIENT(S)

Eight normo-ovulatory patients undergoing IVF procedures due to male factor or tubal infertility.

INTERVENTION(S)

Serum and follicular fluid (FF) collected and stored at -80 degrees C until assayed. Granulosa lutein cells were harvested from follicular aspirates obtained during oocyte retrieval and cultured for 7 days with media in the presence or absence of MIS (10 ng/mL) or FSH 0.2 IU/mL.

MAIN OUTCOME MEASURE(S)

Serum and FF levels of E2 and MIS, and E2 production by GLC in culture. Levels of CYP19 mRNA in cultured GLC were determined by quantitative polymerase chain reaction (PCR) and CYP19 protein by Western blot. Statistical comparison used ANOVA and post hoc Tukey tests.

RESULT(S)

Follicle-stimulating hormone significantly increased E2 production in cultured GLC compared with control. The increase in E2 production is associated with higher levels of CYP19 mRNA and protein in GLC. The presence of MIS significantly inhibited FSH-induced E2 production, with concomitant reduction in CYP19mRNA and protein levels.

CONCLUSION(S)

Müllerian-inhibiting substance inhibits FSH augmentation of CYP19 enzyme activity and CYP19 gene expression in GLC. These findings may help to explain the association of high MIS levels and low FF E2 levels reported in women with polycystic ovary syndrome (PCOS).

Size distribution of dispersed luteal cells during oestrous cycle in Angora goats

The present study examines the size distribution of the goat steroidogenic luteal cells throughout the oestrous cycle. Corpora lutea (CL) were collected after laparatomy on days 5, 10 and 16 of the oestrous cycle. Luteal cells were isolated from CL by collagenase digestion. Steriodogenic luteal cells were identified by staining of the cells for 3beta-hydroxysteroid dehydrogenase activity, a marker for steroidogenic cells. Luteal cells having steroidogenic capacity covered a wide spectrum of sizes, ranging from 5 to 37.5 microm in diameter. There was a significant increase in mean cell diameters (p < 0.01) as CL aged. The mean cell diameter on day 5 was 11.55 +/- 0.12 microm, which was significantly increased and reached up to 19.18 +/- 0.24 mum by day 16 of the oestrous cycle. The ratio of large to small luteal cells was 0.06:1.0 on day 5 of the oestrous cycle. This ratio increased to 0.78:1.0 by day 16 of the oestrous cycle. Luteal cell size on days 5, 10 and 16 of the oestrous cycle reached its maximum at 7.5, 10 and 35 microm in diameter, respectively. Development of CL is associated with an increase in luteal cell size in goats. It is likely that small luteal cells could develop into large luteal cells as CL becomes older during oestrous cycle in goats.

11beta-Hydroxysteroid dehydrogenase expression and activities in bovine granulosa cells and corpora lutea implicate corticosteroids in bovine ovarian physiology

Cortisol-cortisone metabolism is catalysed by the bi-directional NADP(H)-dependent type 1 11beta-hydroxysteroid dehydrogenase (11betaHSD1) enzyme and the oxidative NAD(+)-dependent type 2 11betaHSD (11betaHSD2). This study related the expression of 11betaHSD1 and 11betaHSD2 enzymes (mRNA and protein) to net 11-ketosteroid reductase and 11beta-dehydrogenase (11beta-DH) activities in bovine follicular granulosa and luteal cells. Granulosa cells were isolated from follicles of < 4, 4-8, > 8 and > 12 mm in diameter in either the follicular or luteal phase of the ovarian cycle. Luteal cells were obtained from corpora lutea (CL) in the early non-pregnant luteal phase. Enzyme expression was assessed by reverse transcription-PCR and western blotting, while enzyme activities were measured over 1 h in cell homogenates using radiometric conversion assays with 100 nM [(3)H]cortisone or [(3)H]cortisol and pyridine dinucleotide cofactors. Irrespective of follicle diameter, the expression of 11betaHSD2 and NAD(+)-dependent oxidation of cortisol predominated in granulosa cells harvested in the follicular phase. In contrast, in granulosa cells obtained from luteal phase follicles and in bovine luteal cells, expression of 11betaHSD1 exceeded that of 11betaHSD2 and the major enzyme activity was NADP(+)-dependent cortisol oxidation. Increasing follicular diameter was associated with progressive increases in expression and activities of 11betaHSD2 and 11betaHSD1 in follicular and luteal phase granulosa cells respectively. In follicular phase granulosa cells from antral follicles < 12 mm, 11betaHSD1 migrated with a molecular mass of 34 kDa, whereas in the dominant follicle, CL and all luteal phase granulosa cells, a second protein band of 68 kDa was consistently detected. In all samples, 11betaHSD2 had a molecular mass of 48 kDa, but in large antral follicles (> 8 mm), there was an additional immunoreactive band at 50 kDa. We conclude that 11betaHSD2 is the predominant functional 11betaHSD enzyme expressed in follicular phase granulosa cells from growing bovine antral follicles. In contrast, in bovine granulosa cells from dominant or luteal phase follicles, and in bovine luteal cells from early non-pregnant CL, 11betaHSD1 is the major glucocorticoid-metabolising enzyme. The increasing levels of cortisol inactivation by the combined NADP(+)- and NAD(+)-dependent 11beta-DH activities suggest a need to restrict cortisol access to corticosteroid receptors in the final stages of follicle development.

Constitutive steroidogenesis in ovine large luteal cells may be mediated by tonically active protein kinase A

The mechanisms responsible for the increased basal rates of progesterone secretion from large steroidogenic luteal cells (LLC) relative to small steroidogenic luteal cells (SLC) have not been clearly defined. To determine if protein kinase A (PKA) is tonically active in LLC, the adenylate cyclase activator forskolin and a specific PKA inhibitor (PKI) were utilized in a 2 x 2 factorial treatment with each steroidogenic cell type. Progesterone and cAMP production were quantified after the different treatments. In addition, the effects of the treatments on the concentrations and relative phosphorylation status of the steroidogenic acute regulatory (STAR) protein in the two cell types were determined as a measure of PKA activity. Treatment with PKI blocked forskolin-induced increases in progesterone secretion by SLC without affecting the production of cAMP. The treatment of LLC with PKI significantly decreased basal progesterone secretion in the presence or absence of forskolin, indicating that the high level of steroidogenesis in this cell type requires PKA activity. There were no differences in the steady-state concentrations of STAR protein in either cell type after treatment. However, the percentage of relative STAR phosphorylation was higher in the LLC than in SLC, and PKI treatment significantly decreased the phosphorylation of STAR in the LLC. The relative phosphorylation status of STAR and the concentrations of progesterone in the media were significantly correlated with the treatments in both cell types. The amount of progesterone secreted per picogram of cAMP was higher in the LLC than in the SLC, and this was accompanied by a significant increase in the ratio of relative STAR phosphorylation to the steady-state concentration of STAR protein. These data are compatible with the theory that LLC are constitutively steroidogenic, partly because they have tonically active PKA. In addition, the phosphorylation of STAR appears to be a primary activity of PKA in both types of ovine steroidogenic luteal cells.

Role for prostaglandins in the regulation of type 1 11beta-hydroxysteroid dehydrogenase in human granulosa-lutein cells

11beta-hydroxysteroid dehydrogenase (11betaHSD) enzymes regulate glucocorticoid availability in target tissues. 11betaHSD1 is the predominant isoenzyme expressed and active in human granulosa-lutein (hGL) cells. This study investigated the effects of pharmacological inhibitors of prostaglandin (PG) synthesis on 11betaHSD1 activities and expression in hGL cells. The consequences for 11betaHSD1 of increasing exposure of hGL cells to PGs, either by treatment with exogenous PGs or by challenging cells with IL-1beta, were also assessed. Suppression of basal PG synthesis using four different inhibitors of PG H synthase enzymes [indomethacin, niflumic acid, meclofenamic acid (MA) and N-(2-cyclohexyloxy-4-nitorophenyl) methane sulfonamide (NS-398)] each resulted in significant decreases in both cortisol oxidation and cortisone reduction. Both activities of 11betaHSD1 were suppressed by up to 64+/-6% (P<0.05). Over 4 and 24 h, neither MA nor NS-398 affected the expression of 11betaHSD1 protein, suggesting enzyme regulation by PGs at the posttranslational level. When cells were cotreated for 4 h with PGHS inhibitors plus 30 nm PGD2, PGF2alpha, or PGE2, each PG overcame the suppression of cortisol oxidation by indomethacin or MA. Treatment of hGL cells with IL-1beta increased the concentrations of both PGE2 and PGF2alpha, accompanied by a 70+/-25% increase in net cortisol oxidation. All three responses to IL-1beta were abolished when cells were cotreated with MA. These findings suggest a role for PGs in the posttranslational regulation of 11betaHSD1 activities in hGL cells.

Phytoestrogens and their low dose combinations inhibit mRNA expression and activity of aromatase in human granulosa-luteal cells

There is evidence that certain phytoestrogens inhibit aromatase, the enzyme that converts androgens to oestrogens. Kinetic studies in cell-free preparations show that they may inhibit aromatase by competitive binding to the enzyme, but there is a paucity of studies investigating longer-term effects of phytoestrogens on the expression of steroidogenic enzymes. This study tested the hypothesis that phytoestrogens could reduce aromatase activity by down-regulation of its expression. Experiments were carried out on primary cultures of human granulosa-luteal (GL) cells after they had been exposed to phytoestrogens for 48 h. Aromatase activity was measured by the ability of cells to convert testosterone to estradiol over a 4h period and aromatase mRNA expression (mRNA(arom)) was subsequently measured from the same cells using quantitative real-time PCR. The compounds investigated were the flavones, apigenin and quercetin, and the isoflavones, genistein, biochanin A and daidzein at doses of 10 microM and 100 nM. Combinations of these compounds at the lower dose were also investigated. All compounds tested dose-dependently reduced mean mRNA(arom) compared with controls. Apigenin was the most potent inhibitor with significant inhibition of mRNA(arom) seen at both 10 microM and 100 nM, whilst other flavonoids (except biochanin A) only induced significant inhibition (p<or=0.05) at the higher dose. Low dose (100 nM) mixtures of the compounds were ineffective except for a combination of the three isoflavones that induced a significant inhibition of mRNA(arom). The changes in aromatase activity paralleled the mRNA(arom) results and additional studies showed that the reduction in aromatase activity was significantly delayed in time compared with the reduction in mRNA(arom.) This is the first study to compare the action of various phytoestrogens, either singly or in low-dose combination, on the expression and activity of aromatase in human cells and it suggests that chronic dietary exposure and tissue accumulation of low-dose mixtures of phytoestrogens could have important consequences for aromatase activity and the production of oestrogens.

Participation of specific PKC isozymes in the inhibitory effect of ET-1 on progesterone accumulation in cells isolated from early- and mid-phase corpora lutea

Expression of PKC alpha, beta I, beta II, epsilon and micro has been demonstrated in the whole bovine CL with PKC epsilon being differentially expressed as a function of development. In experiment 1 we have investigated the amount of mRNA encoding PKC epsilon at different stages of luteal development (days 1, 4, 10 and 17). In experiment 2, the cellular source of luteal PKC isozymes was determined. Enriched steroidogenic (SC) and endothelial (EC) cells from day-10 CL were used to examine this question by Western blot analysis and immuno-histochemistry. In experiment 3, Western blot analysis was used to examine the ability of ET-1 to activate luteal PKC isozymes in day-10 CL. In experiment 4, the role of luteal PKC isozymes in the ET-1 mediated inhibition of P(4) accumulation in steroidogenic cell cultures from day-4 and day-10 CL was examined. Abundance of PKC epsilon mRNA gradually increased from day-1 to -10 with no further increase on day-17. In experiment 2, PKC epsilon was exclusively detected in SC (LLC and SLC). In contrast, PKC alpha, beta I and beta II were detected in both SC and EC, with EC expressing higher amounts of PKC isozymes. In day-10 CL, ET-1 induced cellular redistribution of PKC alpha, beta I, epsilon but not beta II. Inhibitors specific for conventional PKC isozymes as well as PKC epsilon were able to negate the inhibitory effects of ET-1 on P4 accumulation in the day 10 CL. In the day-4 CL, the inhibitory effect of ET-1 might be mediated via conventional PKC. Thus, an exclusive presence of PKC epsilon in luteal steroidogenic cells, its higher expression along with the ability of ET-1 to stimulate its activation in day-10 CL strongly suggests that this PKC isoform may play an important regulatory role in decreasing P(4) during luteal regression. Inhibition of P(4) by ET-1 in the early CL may be mediated via conventional PKC isozymes.

Canine corpus luteum regression: Apoptosis and caspase-3 activity

The present study evaluated the occurrence of apoptosis and caspase-3 activity in the canine corpus luteum during the period of luteal regression in eight pregnant and nine nonpregnant diestrus bitches. Intact luteal cells were obtained from corpora lutea in both peripartum pregnant bitches and nonpregnant diestrus bitches at approximately 65 d (range 63-68) after estrus, but not at days 75 and 85 in nonpregnant bitches. In all bitches, apoptotic cells were rarely detected and when present, those cells were more easily detected using the hematoxylin and eosin technique than using the critical electrolyte concentration technique. The luteal structures at 75 and 85 d of diestrus had histological characteristics similar to a corpus albicans. Caspase-3 activity was detected in morphologically normal corpora lutea from both pregnant and diestrus bitches around day 65, and also in the later structures considered corpus albicans tissue. These results suggested that apoptosis may not be the major mechanism involved in canine functional luteal regression, and that caspase-3 participated in both functional and morphological luteolysis and in the tissue reorganization involved in corpus albicans formation.

Indoleamine 2,3-Dioxygenase Participates in the Interferon-gamma-Induced Cell Death Process in Cultured Bovine Luteal Cells1

Interferon-gamma (IFNG) induces apoptotic cell death in bovine luteal cells, but the pathway(s) involved in this process are not well defined. Evidence supporting the involvement of an IFNG-inducible enzymatic pathway that degrades tryptophan in IFNG-induced death of bovine luteal cells is presented in this study. The IFNG-inducible enzyme indoleamine 2,3-dioxygenase (INDO) catalyzes the first step in a metabolic pathway that degrades tryptophan. In the first experiment, RT-PCR revealed the presence of INDO mRNA in luteal cells treated with IFNG, but not in untreated cells. To determine whether INDO participates in IFNG-induced death of bovine luteal cells, an experiment was performed to test the effect of 1-methyl-D-tryptophan (1-MT), an inhibitor of INDO, on IFNG-induced DNA fragmentation in luteal cells. Single-cell gel electrophoresis and microscopic image analysis revealed that 1-MT inhibited DNA fragmentation induced by IFNG. To determine whether supplementation of cell cultures with additional tryptophan could also protect luteal cells from IFNG-induced DNA fragmentation, luteal cells were cultured in the presence of IFNG, and L-tryptophan was added to cultures to achieve final concentrations that were 5-, 10-, or 25-fold higher than the concentration of L-tryptophan found in nonsupplemented culture medium. Supplementation of IFNG-treated luteal cell cultures with elevated concentrations of tryptophan also prevented IFNG-induced DNA fragmentation. We conclude that INDO participates in IFNG-induced death of bovine luteal cells, through a mechanism that involves degradation of tryptophan, thereby reducing tryptophan concentrations to a point insufficient to meet luteal cells needs.

Dose-response effects of phytoestrogens on the activity and expression of 3beta-hydroxysteroid dehydrogenase and aromatase in human granulosa-luteal cells

There is evidence that certain phytoestrogens can inhibit key steroidogenic enzymes although most studies have been carried out on microsomal or purified enzyme preparations, some using cell lines. This study was designed to test the hypothesis that low doses of phytoestrogens, at concentrations that would be attained through the diet, could inhibit 3beta-hydroxysteroid dehydrogenase (HSD) and/or aromatase in primary cultures of human granulosa-luteal (GL) cells and that this effect was due to a decrease in the expression of these proteins. Based on published evidence, eight compounds were selected for investigation and these included the flavones apigenin and quercetin, the isoflavones genistein, biochanin A and daidzein, the lignans, enterodiol and enterolactone, and the mycotoxin zearalenone. Human GL cells were cultured for 48 h in the presence of these phytoestrogens at concentrations ranging from 0.01 to 100 microM and after addition of fresh media the conversion of pregnenolone to progesterone or androstenedione to oestradiol over a 4h period was measured. Biochanin A was the only phytoestrogen that displayed any dose-dependent inhibition of 3beta-HSD, others showing inhibition at doses >/=10 microM. Apigenin and quercetin only inhibited aromatase/17beta-HSD at high doses as did genistein, biochanin A and daidzein. The lignans had weak inhibitory effects on aromatase/17beta-HSD, whilst zearalenone showed potent inhibition at 0.1 microM. Phytoestrogens did not exert any significant effects on protein expression of 3beta-HSD or aromatase as determined by Western blots. It is concluded that steroidogenic enzymes are inhibited by phytoestrogens in primary cultures of human GL cells but these cells are less sensitive to the effects of phytoestrogens than cell-free systems. This may be due to poor lipid solubility or cellular metabolism. We have also shown for the first time that phytoestrogens do not act by inhibiting the cellular concentration of 3beta-HSD and aromatase even though exposure time would have allowed for changes in gene expression.

2,3,7,8-Tetrachlorodibenzo-p-dioxin induces CYP1B1 expression in human luteinized granulosa cells

The environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a reproductive toxicant in multiple species; however, mechanisms and direct ovarian effects are poorly understood. DNA microarrays were used to characterize gene expression profiles of human luteinized granulosa cells (HLGCs) exposed to TCDD in primary cultures. Exposure to 10 nM TCDD for 24 h induced a significant increase in CYP1B1, while few other genes responded. TaqMan PCR and Western immunoblotting demonstrated that induction was dose-dependent. Additionally, the microsomal form of catechol-O-methyltransferase (COMT) was highly expressed in HLGCs, along with only fractional amounts of the soluble form. This is the first report of CYP1B1 and COMT expression, and CYP1B1 induction, in cells from the human ovary. The role of CYP1B1 in the oxidative metabolism of estrogens and potential generation of DNA adducts in the ovary may have significant consequences for oocyte quality, corpus luteum function, and ovarian carcinogenesis.

Adenosine triphosphate induces activation of caspase-3 in apoptosis of human granulosa-luteal cells

Adenosine triphosphate (ATP) has been shown to induce programmed cell death in various systems. However, little is known about the effect of ATP on human granulosa-luteal cells (hGLCs). The present study was designed to examine the effect of ATP on the activation of the caspase signaling pathway and its role in inducing programmed cell death. Human GLCs were collected from patients undergoing in vitro fertilization programs, and then were cultured in FBS-supplemented DMEM for 3 days prior to our studies. To examine the dose-response relationship, hGLCs were treated with increasing concentrations of ATP (10 microM, 100 microM, 1 mM or 10 mM) for 24 hours. For time-course experiments, hGLCs were treated with 10 mM ATP for 6, 12, or 24 hours. Western blot analysis was performed using antibodies against the pro- and active forms of caspase-3, -9, or PARP. To quantify the induction of apoptosis, DNA fragmentation was measured using the cell death detection enzyme-linked immunosorbent assay. To examine the effect of human chorionic gonadotropin (hCG) in protecting cells from apoptosis, hGLCs were treated with 10 IU hCG in the presence of 10 mM ATP for 12 hours. It was demonstrated that ATP was capable of inducing DNA fragmentation in a dose- and time-dependent manner. Furthermore, Western blot analysis, which detected the pro- and active forms of caspase-3, or PARP, demonstrated that ATP activated the caspase-signaling pathway, leading to the proteolytic conversion of pro-caspase-3 to active caspase-3, and the subsequent cleavage of the caspase substrate PARP. Based on our observation, caspase-9 was not triggered by ATP. Interestingly, hCG attenuated the effect of ATP in activating the caspase signaling pathway. To our knowledge, this is the first demonstration of the ATP-induced activation of the caspase signaling pathway in the human ovary. These results support the notion that the caspase-signaling pathway is involved in mediating ATP actions in the human ovary.

Ovarian and placental production of progesterone and oestradiol during pregnancy in reindeer

We obtained uterine and peripheral venous plasma, and samples of luteal and placental tissues from 2- to 7-year-old, Eurasian mountain reindeer (Rangifer tarandus tarandus) from a free-living, semi-domesticated herd in northern Norway in November 1995, and February and March 1996. In November, ovarian venous blood was also collected from four animals. Plasma samples were assayed for progesterone and oestradiol. The tissue samples were examined by light and electron microscopy, steroid dehydrogenase histochemistry, and northern blot analysis for RNAs for 3beta-hydroxy-steroid dehydrogenase (3beta-HSD) and P450 (side chain cleavage (scc)). Peripheral blood was taken from non-pregnant females in the same herd on the same dates. Peripheral progesterone concentrations in pregnant reindeer (3.4 +/- 0.5 ng/ml, n = 8) clearly exceeded those in non-pregnant animals (0.40 +/- 0.14 ng/ml; P < 0.0004 , n = 10) but oestradiol levels were only marginally higher in pregnant (6.0 +/- 0.7 pg/ml) than in non-pregnant (4.8 +/- 0.5 pg/ml; P = 0.35) reindeer at the stages examined. In pregnant animals, peripheral progesterone and oestradiol concentrations rose slightly between November and March but the differences did not reach significance (progesterone, P = 0.083; oestradiol, P = 0.061). In November, progesterone concentrations in the ovarian vein (79 +/- 15 ng/ml) greatly exceeded (P < 0.03) those in the uterine vein ( 10 +/- 4 ng/ml) which in turn exceeded the levels in the peripheral blood (2.8 +/- 0.4 ng/ml; P < 0.29). Oestradiol concentrations were slightly but significantly (P < 0.05) higher in the ovarian (20 +/- 3 pg/ml) than the uterine vein (13 +/- 1 pg/ml) and, in turn, greater (P < 0.03) than in peripheral blood (4.6 +/- 0.4 pg/ml). All samples of luteal tissue consisted exclusively of normal fully-differentiated cells and stained intensely for 3beta-HSD. Isolated groups of placental cells also stained strongly for 3beta-HSD. RNA for P450 (scc) and 3beta-HSD was abundant in all corpora lutea and lower concentrations of P450 (scc) were present in the placenta. 3beta-HSD RNA in the placenta was below the limit of detection. We conclude that the corpus luteum remains an important source of progesterone throughout pregnancy in reindeer but that the placenta is also steroidogenic.

[Effect of L-tyrosine on 3beta-HSD activity of rat luteal cells in vitro]

AIM

To study the effects of L-tyrosine on 3beta-HSD activity of rat luteal cells in vitro.

METHODS

Luteal cells were isolated from ovary tissues of female rats pretreated with PMSG and hCG. Luteal cells were cultured with 95% oxygen and 5% carbon dioxide in 37 degrees C. 3beta-HSD activity was measured by radioimmunoassay (RIA).

RESULTS

(1) 0.2 mmol x L(-1) and 2.0 mmol x L(-1) L-tyrosine significantly inhibited 3beta-HSD activity. (2) 0.2 mmol x L(-1) L-tyrosine exerted different effects on 3beta-HSD activity at different concentrations of pregnenolone (Ph). It increased 3beta-HSD activity at 0.1 micromol x L(-1) and 1 micromol x L(-1) of Pn concentration. With further increase in the concentration of Pn to 100 micromol x L(-1), the stimulating effect of L-tyrosine was switched to suppression effect. (3) L-tyrosine and L-tyrosine hydrazide both inhibited 3beta-HSD activity induced by hCG.

CONCLUSION

L-tyrosine affects 3beta-HSD activity of rat luteal cells in vitro. L-tyrosine and tyrosine hydrazide inhibits hCG induced 3beta-HSD activity.

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.

Activation of the cAMP-dependent protein kinase signaling pathway by luteinizing hormone in trout theca layers

In the fish ovary, LH is the main factor regulating the production of steroids during the periovulatory period and its effects are believed to be mediated, at least partially, through the cAMP-dependent protein kinase (PKA) signaling pathway. However, there is no direct evidence for the presence of PKA in the fish ovary nor on the regulation of its activity by fish LH. Here, we show the identification of regulatory (R) and catalytic (C) subunits of PKA in trout theca cells by immunoblotting. DEAE-cellulose chromatography of theca cell extracts indicated the presence of PKA type I and II and showed that trout theca cells display PKA-specific phosphotransferase and cAMP-binding activities. Salmon LH (sLH) stimulated PKA activity and increased the levels of immunoreactive RIIalpha, RIIbeta and C subunits in trout theca layers. These observations, coupled with the sLH-dependent decrease in the half-life of the C subunit, as shown by pulse-chase experiments, strongly suggest that sLH activates PKA in trout theca cells. Furthermore, our results suggest that ovarian PKA activity and its regulation by LH has been well conserved from fish to humans.

Expression of 11beta-hydroxysteroid dehydrogenase (11betaHSD) proteins in luteinizing human granulosa-lutein cells

In a range of tIssues, cortisol is inter-converted with cortisone by 11beta-hydroxysteroid dehydrogenase (11betaHSD). To date, two isoforms of 11betaHSD have been cloned. Previous studies have shown that human granulosa cells express type 2 11betaHSD mRNA during the follicular phase of the ovarian cycle, switching to type 1 11betaHSD mRNA expression as luteinization occurs. However, it is not known whether protein expression, and 11betaHSD enzyme activities reflect this reported pattern of mRNA expression. Hence, the aims of the current study were to investigate the expression and activities of 11betaHSD proteins in luteinizing human granulosa-lutein (hGL) cells. Luteinizing hGL cells were cultured for up to 3 days with enzyme activities (11beta-dehydrogenase (11betaDH) and 11-ketosteroid reductase (11 KSR)) and protein expression (type 1 and type 2 11betaHSD) assessed on each day of culture. In Western blots, an immunopurified type 1 11betaHSD antibody recognized a band of 38 kDa in hGL cells and in human embryonic kidney (HEK) cells stably transfected with human type 1 11betaHSD. The type 2 11betaHSD antibody recognized a band of 48 kDa in HEK cells transfected with human type 2 11betaHSD cDNA but the type 2 protein was not expressed in hGL cells throughout the 3 days of culture. While the expression of type 1 11betaHSD protein increased progressively by 2.7-fold over 3 days as hGL cells luteinized, both 11betaDH and reductase activities declined (by 52.9% and 34.2%; P<0.05) over this same period. Changes in enzyme expression and activity were unaffected by the suppression of ovarian steroid synthesis.

Epidermal growth factor induces c-fos and c-jun mRNA via Raf-1/MEK1/ERK-dependent and -independent pathways in bovine luteal cells

Epidermal growth factor (EGF) modulates the actions of gonadotropins in the corpus luteum. The membrane-associated EGF receptors undergo rapid tyrosine phosphorylation and internalization upon ligand binding in ovarian cells, including luteal cells. However, little is known about the post-receptor signaling events induced by EGF that lead to the transcriptional regulation of EGF-responsive genes in the ovary. The present study was designed to examine in bovine luteal cells (1) activation of the extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) signaling cascade (Raf/MEK/ERK) by EGF; (2) mRNA expression of AP-1 transcription factors, i.e. c-fos and c-jun, in response to EGF; and (3) the role of ERK in EGF-induced expression of c-fos and c-jun mRNA. Raf-1 and B-Raf, but not A-Raf, were activated by EGF (10 ng/ml) and the pharmacological protein kinase C (PKC) activator phorbol myristate acetate (PMA, 20 nM). Activation of Raf resulted in the phosphorylation and activation of MAPK kinase (MEK1) which subsequently activated ERKs. Treatment with EGF-induced the phosphorylation of both ERK2 and ERK1 in a time and concentration dependent manner. Additionally, activated ERK was found in the nucleus of the cells following treatment with EGF (10 ng/ml) and PMA (PMA, 20 nM) for 5 min. Depletion of PKC by chronic PMA treatment (2.5 microM, 24 h) only partially inhibited the stimulatory effects of EGF on Raf-1, ERK2 and ERK1. These data demonstrate that PKC-dependent and independent-mechanisms are involved in EGF activation of the Raf/MEK/ERK signaling cascade in bovine luteal cells. EGF rapidly and transiently stimulated the expression of c-fos and c-jun mRNA in bovine luteal cells. Maximal induction of c-fos and c-jun mRNA by EGF occurred within 30 min of treatment with 10 ng/ml EGF. Treatment with the MEK1 inhibitor PD098059 (50 microM) abolished EGF-induced ERK activation. However, blocking EGF-induced ERK activation by pretreatment with PD098059 only partially attenuated EGF-induced c-fos and c-jun mRNA expression. Thus, additional pathways are implicated in the regulation of c-fos and c-jun mRNA expression by EGF in bovine luteal cells.

Progesterone attenuates the inhibitory effects of cardiotonic digitalis on pregnenolone production in rat luteal cells

Previous studies have shown that digoxin decreases testosterone secretion in testicular interstitial cells. However, the effect of digoxin on progesterone secretion in luteal cells is unclear. Progesterone is known as an endogenous digoxin-like hormone (EDLH). This study investigates how digitalis affected progesterone production and whether progesterone antagonized the effects of digitalis. Digoxin or digitoxin, but not ouabain, decreased the basal and human chorionic gonadotropin (hCG)-stimulated progesterone secretion as well as the activity of cytochrome P450 side chain cleavage enzyme (P450scc) in luteal cells. 8-Br-cAMP and forskolin did not affect the reduction. Neither the amount of P450scc, the amount of steroidogenic acute regulatory (StAR) protein, nor the activity of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) was affected by digoxin or digitoxin. Moreover, in testicular interstitial and luteal cells, progesterone partially attenuated the reduction of pregnenolone by digoxin or digitoxin and the progesterone antagonist, RU486, blocked this attenuation. These new findings indicated that (1) digoxin or digitoxin inhibited pregnenolone production by decreasing the activity of P450scc enzyme, but not Na(+)-K(+)-ATPase, resulting in a decrease on progesterone secretion in rat luteal cells, and (2) the inhibitory effect on pregnenolone production by digoxin or digitoxin was reversed partially by progesterone. In conclusion, digoxin or digitoxin decreased progesterone production via the inhibition of pregnenolone by decreasing P450scc activity. Progesterone, an EDLH, could antagonize the effects of digoxin or digitoxin in luteal cells.

Requirement for ERK1/2 activation in the regulation of progesterone production in human granulosa-lutein cells is stimulus specific

This study was conducted to determine whether the ERK1/2 family of MAPKs can be modulated by physiological regulators of the human corpus luteum, and whether this activation is important for progesterone secretion in human granulosa-lutein (hGL) cells. Human LH (hLH), hCG, and agents that indirectly elevate cAMP [cholera toxin, forskolin, (Bu)(2)cAMP], time- and dose-dependently activated ERK1/2 in hGL cells. ERK1/2 activation was reduced by preincubation with PKA inhibitors, including myristoylated PKI, suggesting that cAMP mediates ERK1/2 activation. Two structurally distinct inhibitors of MAPK kinase (MEK), PD 98059 and U 0126, abrogated hLH/hCG-induced ERK1/2 activation, but had no effect on hLH-, hCG-, or 22R-hydroxycholesterol-stimulated progesterone secretion. In contrast, both inhibitors blocked cholera toxin-, forskolin-, and (Bu)(2)cAMP-induced ERK1/2 phosphorylation concomitant with a reduction in progesterone secretion. The known luteotropin, PGE(2), promoted MEK- and cAMP-dependent activation of ERK1/2, and inhibitors of either MEK or PKA decreased PGE(2)-induced progesterone synthesis. Our findings demonstrate that the requirement for ERK1/2 activation as a regulator of progesterone synthesis in hGL cells is stimulus dependent, and that the MEK inhibitor-sensitive step is distal to cAMP generation, but proximal to the conversion of cholesterol to pregnenolone.

Alteration of glutathione reductase expression in the female reproductive organs during the estrous cycle

The enzyme glutathione reductase (GR) recycles oxidized glutathione (GSSG) by converting it to the reduced form (GSH) in an NADPH-dependent manner. A specific antibody raised against recombinant rat GR was used to localize the protein in the female reproductive organs during the estrous cycle in the rat. In the ovary, the strongest reactivity to the antibody was observed in oocytes, followed by granulosa cells, corpus luteum, and interstitial cells. A strongly positive reaction was also observed mainly in the oviduct epithelia, uterine epithelia, and endometrial gland in the reproductive tract. Oviducts contained the highest GR activity. The GR activity of uterus during metestrus was about twice as high as that for other stages of the cycle. The levels of GR proteins in the tissues roughly matched the activities. The expression of the GR mRNA was highest during metestrus. Because GSH is known to increase gamete viability and the efficiency of fertility, GR, which is expressed in these tissues, is predicted to play a pivotal role in the reproduction process as a source of GSH.

Transcriptional regulation of cyclooxygenase-2 gene in ovine large luteal cells

There is positive feedback pathway in the ovine large luteal cell, such that prostaglandin (PG) F(2 alpha) stimulation induces intraluteal PGF(2 alpha) production as the result of induction of one of the rate-limiting enzymes in PG production, cyclooxygenase-2 (Cox-2). The objective of the present study was to evaluate the intracellular effector systems and important DNA transcriptional element(s) involved in regulating the Cox-2 gene in ovine large luteal cells. In transient transfection assays, Cox-2 promoter was rapidly induced (4 h) by phorbol didecanoate (a protein kinase [PK] C activator), ionomycin, and cloprostenol (PGF(2 alpha) analogue), with a peak induction at 12 h. Cloprostenol-mediated promoter activation was not blocked by inhibition of various second messenger systems, including PKA, calcium calmodulin kinase II, or mitogen-activated protein kinases. However, myristoylated PKC pseudosubstrate peptide inhibited cloprostenol stimulation of Cox-2 promoter, indicating the critical role of PKC in this stimulation. The Cox-2 promoter could be reduced to 282 base pairs (bp) of the 5' flanking sequence with retention of full inducibility by cloprostenol. Mutation of three critical cis-responsive elements within this 282-bp region (C/EBP, cAMP responsive element [CRE], and E-box) indicated that E-box was critical in both basal and cloprostenol-induced promoter activity. However, there was also significant but less dramatic inhibition of cloprostenol stimulation by mutation of C/EBP and CRE in the Cox-2 promoter, and mutation of all three elements eliminated cloprostenol induction of this promoter. Electrophoretic mobility shift assays of nuclear extracts from large luteal cells revealed that upstream stimulatory factor (USF)-1 and USF-2 bound to the E-box in Cox-2. Thus, PKC directly regulates transcription of the Cox-2 gene in large luteal cells by acting through DNA elements close to the putative transcriptional start point, particularly an E-box region at -50 bp.

The androgen-conjugating uridine diphosphoglucuronosyltransferase-2B enzymes are differentially expressed temporally and spatially in the monkey follicle throughout the menstrual cycle

UDP-glucuronosyltransferase (UGT) enzymes enhance the polarity of steroid hormones by catalyzing their conjugation with the sugar group from UDP-glucuronic acid. Previous results have shown that the monkey is a suitable animal model to study steroid glucuronidation in steroid target tissues. In humans, as in the monkey, the main androgen metabolites found in the circulation are 5alpha-androstane-3alpha,17beta-diol-glucuronide and androsterone glucuronide, and high levels of androsterone glucuronide were also measured in human follicular fluid. Ovarian androgens play a significant role as precursors for estrogens and may modulate the recruitment and growth of follicles. To analyze the expression pattern of UGT2B enzymes involved in androgen metabolism throughout the menstrual cycle, cynomolgus monkey ovaries were collected during the mid and late follicular and luteal phases. Microsomal proteins and total RNA were analyzed for UGT2B expression in the whole ovary. Western blot and specific RT-PCR analyses demonstrated no significant changes in the expression of UGT2B protein or transcripts during the menstrual cycle. Immunocytochemistry analysis showed that UGT2B proteins are expressed in the cytoplasm of thecal and granulosa cells of growing follicles. Interestingly, the thecal cells of secondary follicles and of corpus luteum were extensively stained, whereas luteal granulosa cells were not labeled. These results suggest an important regulation of cell type-specific UGT2B expression during follicular development. Previous results demonstrated similar changes in the expression of the androgen receptor. The colocalization of the androgen receptor and UGT2B enzymes in the same cell types of the ovary provide evidence for a potential role of glucuronidation as a modulator of the intracellular androgen response during follicular development.

Differential regulation of prostaglandin endoperoxide synthase-2 transcription in ovine granulosa and large luteal cells

The objective of the present study was to evaluate second messenger regulation of prostaglandin synthase-2 (PGS-2) mRNA and PGS-2 promoter in ovine granulosa cells and large luteal cells. In granulosa cells, PGS-2 mRNA was induced by forskolin (PKA activator) but not by phorbol didecanoate (PDD; PKC activator) with maximal stimulation at 24 h. In contrast, PDD was the more potent inducer in large luteal cells with the most dramatic effect by 4 h. Similarly, forskolin but not PDD increased media PGF2 alpha in granulosa cells at 24 h; whereas, PDD but not forskolin increased PGF2 alpha at 4 h and 24 h in large luteal cells. To evaluate if these effects were due to activation of transcription, a plasmid was constructed containing 1500 bp of PGS-2 promoter linked to a luciferase gene. Forskolin stimulated transcription from this construct in granulosa cells (5-fold); whereas, PDD but not forskolin stimulated transcription in large luteal cells (40-fold). Taking these findings together, we propose that transcriptional regulation of the PGS-2 gene changes from PKA-dependence in granulosa cells to PKC-dependence in large luteal cells after luteinization.

Effect of genistein, tyrphostin and herbimycin on prolactin-stimulated progesterone production by porcine theca and luteal cells

The potential involvement of protein tyrosine kinases (PTK) in the mechanism of prolactin (Prl) action on ovarian cell steroidogenesis has not been elucidated and information about research on this subject is scarce. In this preliminary study pharmacological intervention was used to provide support for a possible involvement of tyrosine kinases in prolactin induction of progesterone secretion by porcine thecal and luteal cells. Material used in this experiment were cultures of porcine follicular theca interna and early corpus luteum cells. The former were isolated from, proestrous preovulatory follicles and the latter were obtained by enzymatic dispersion of luteal tissue. Three of tyrosine kinase inhibitors, genistein, herbimycin and tyrphostin, were applied. They act through different mechanisms, partially blocking Prl-stimulated progesterone secretion. Herbimycin at a dose of 3 microM inhibited Prl-stimulated progesterone secretion beneath the control level in theca and by 70% in luteal cells. Genistein at a dose of 45 microM inhibited Prl-stimulated progesterone secretion beneath the control level in theca and down to the control in luteal cells. On the other hand, tyrphostin at a dose of 100 microM only slightly suppressed Prl-stimulated progesterone secretion by thecal and luteal cells (33% and 40% respectively). This investigation is the first search for evidence of involvement of tyrosine kinases in Prl-stimulated progesterone production by ovarian cells in the pig.

Functional and subcellular changes in the A-kinase-signaling pathway: relation to aromatase and Sgk expression during the transition of granulosa cells to luteal cells

The responsiveness of granulosa cells to FSH (cAMP) changes as these cells switch from the proliferative stage in growing follicles to the terminally differentiated, nonproliferating stage after LH-induced luteinization. To analyze this transition, two well characterized culture systems were used. 1) Granulosa cells isolated from immature rats were cultured in serum-free medium, a system that permits analysis of dynamic, short-term responses to hormones/cAMP. 2) Granulosa cells from preovulatory (PO) follicles that have been exposed in vivo to surge concentrations of hCG (PO/ hCG) were cultured in medium containing 1% FBS, a system that permits analyses of cells that have undergo irreversible, long-term changes associated with luteinization. To analyze the biochemical basis for the switch in cAMP responsiveness, the localization of A-kinase pathway components was related to the expression of two cAMP target genes, aromatase (CYP19) and serum-and glucocorticoid-induced kinase (Sgk). Components of the A-kinase pathway were analyzed by Western blotting and indirect immunofluorescence using specific antibodies to the C subunit, RIIalpha/beta subunits, CREB (cAMP-regulatory element binding protein), phospho-CREB, CBP (CREB binding protein), and Sgk. Cellular levels of C subunit and CREB were similar in all cell types and hormone treatments. CREB and CBP were nuclear; RIIalpha/beta was restricted to a cytoplasmic basket-like structure. Addition of FSH to immature granulosa cells caused rapid nuclear import of C subunit within 1 h. Nuclear C subunit decreased by 6 h after FSH but could be rapidly reimported to the nucleus by the addition of forskolin at 6, 24, or 48 h. Nuclear C subunit was associated with the rapid but transient increases in phospho-CREB. FSH induced Sgk in a biphasic manner in which the protein was nuclear at 1 h and cytoplasmic at 48 h. Aromatase mRNA was only expressed at 24-48 h after FSH, a pattern that was not altered by phosphodiesterases or phosphatases. In the luteinized (PO/hCG) granulosa cells, immunoreactive C subunit was localized in a punctate pattern in the nucleus as well as to a cytoplasmic basket-like structure, a distribution pattern not altered by forskolin. Aromatase, Sgk, and phospho-CREB were expressed at elevated levels in a non-forskolin-responsive manner. Most notable, both phospho-CREB and Sgk were preferentially localized in a punctate pattern within the cytoplasm and not altered by forskolin. Collectively, these data indicate that when granulosa cells differentiate to luteal cells the subcellular localization (nuclear vs. cytoplasmic) of A-kinase pathway components changes markedly. Thus, either the mechanisms of nuclear import and export or the presence of distinct docking sites (and functions ?) dictate where A-kinase, phospho-CREB and Sgk are localized in granulosa cells compared with the terminally differentiated luteal cells.

Molecular mechanism for cooperation between Sp1 and steroidogenic factor-1 (SF-1) to regulate bovine CYP11A gene expression

Bovine cholesterol side-chain cleavage cytochrome P450 (P450scc; product of the CYP11A gene) gene expression is regulated by gonadotropins via cAMP in the ovary, and by ACTH via cAMP in adrenal cortical cells. Previously, we characterized response elements located at -57/-32 and at -111/-101 bp in the 5'-flanking region of the bovine CYP11A gene required for cAMP-stimulated transcription in both mouse Y-1 adrenal tumor cells and bovine ovarian cells in primary culture, which bind SF-1 (or Ad4-BP) and Sp1, respectively. The role of these transcription factors in CYP11A transcription was further confirmed by deletion and mutation analyses. In addition, results obtained employing a double mutation of the Sp1- and SF-1-binding sites and a mammalian two-hybrid system indicate that Sp1 and SF-1 function cooperatively in the transactivation of the bovine CYP11A promoter in both bovine luteal cells and Y-1 cells. Here we report that SF-1 and Sp1 are able to associate with one another in vitro and in vivo. The NH2-terminal region of SF-1, especially the DNA-binding domain, is the binding site for Sp1. In addition, as CBP is a common coactivator required for the transcriptional activity of numerous transcription factors including nuclear receptors, we investigated whether CBP functions as a cofactor for the regulation of bovine CYP11A promoter activity. We show here that CBP enhanced the PKA-induced CYP11A promoter activity, while a double mutation of both Sp1 and SF-1 sites within the CYP11A promoter region abolished CBP-induced activity. Furthermore, CBP stimulated Sp1-dependent transactivation, and a CBP/Sp1 complex in vivo was demonstrated by a co-immunoprecipitation assay. Also, CBP potentiated the transcriptional activity of GAL4-SF-1 in the presence of PKA. Thus, the cooperation between SF-1 and Sp1, required for the regulation of bovine CYP11A gene expression, is mediated by a direct protein-protein interaction and/or the common coactivator CBP.

Expression of glutathione transferase isoenzymes in the porcine ovary in relationship to follicular maturation and luteinization

The expression of different isoenzymes of glutathione transferase (GST), i.e. the cytosolic subunits GSTA1/A2, A3, A4, A5, M1/2, M2 and P1, T2, and the microsomal GST in follicles of different sizes and in corpora lutea from porcine ovary, was investigated by Western blotting. No immunoreactivity was obtained with anti-rat GSTT2 or anti-rat microsomal GST polyclonal antibodies. In contrast, GSTA1/A2, A3, A4, A5, M1/2, M2 and P1 are all expressed in the cytosol from porcine ovaries. In general, the highest levels of these GST isoenzymes were present in the cytosol from corpora lutea, in agreement with measurements of activity towards 1-chloro-2,4-dinitrobenzene. Immunoreactivity with anti-rat GSTP1 was only obtained with follicles. The cytosolic GSTs from follicles and corpora lutea were affinity purified on glutathione-Sepharose and separated by reversed-phase high-performance liquid chromatography in order to quantitate the different subunits. A peak corresponding to the class pi subunit was present in follicles. This peak was also seen with corpora lutea, although at very low level. There were four peaks containing class mu subunits. The remaining peaks were concluded to contain the class alpha subunits, except for two peaks which are suggested to contain proteins other than GSTs. The levels of the different subunits were quantitated on the basis of the areas under the peaks and the relative amounts in follicles of different sizes and in corpora lutea corresponded well with the Western blot analysis.

Corticosteroid metabolism in human granulosa-lutein cells

OBJECTIVE

The aims of this study were to determine the type and level of 11 beta-hydroxysteroid dehydrogenase (11 beta HSD) in human granulosa-leutein cells (GLE) shortly before ovulation and to correlate activity with the outcome of treatment in patients undergoing in vitro fertilization and embryo transfer (IVF/ET).

DESIGN

GLC from 32 patients undergoing IVF/ET were tested for type and level of 11 beta HSD activity in relation to treatment outcome.

PATIENTS

Periovulatory follicles were aspirated by ultrasound guided transvaginal puncture following a standard controlled ovarian stimulation protocol, approximately 36 h after administering an ovulation-inducing dose of human chorionic gonadotrophin (HCG). GLC were separated from follicular fluid by density-gradient centrifugation and taken for measurement of 11 beta HSD activity in vitro; oocytes were used for IVF/ET.

MEASUREMENTS

Interconversion of cortisol (F) and cortisone (E), and dexamethasone (D) and 11-dehydrodexamethasone (DHD) was measured in standardized assays comprising incubation of GLC with 3H-labelled substrate, with separation of substrate and product by thin-layer radiochromatography.

RESULTS

Conversion of F to E varied from 10.5 to 30.9% while that of E to F was between 2.4 and 44.6%. In the GLC of 25 patients in whom both activities were measured, dehydrogenase (F to E) activity predominated in 13 and reductase (E to F) in 12. By contrast, D (substrate for 11 beta HSD2 but not 11 beta HSD1) showed less than 1% metabolism in this system while DHD (substrate for 11 beta HSD1 and 11 beta HSD2) was converted significantly (65.6-90.5%) to D in the four patients tested. There was no significant difference in the interconversion of F and E between patients who became pregnant and those who did not.

CONCLUSIONS

The dehydrogenase and oxoreductase reactions catalysed by 11 beta HSD both occur in granulosa-lutein cells at the time of follicular rupture, probably due to 11 beta HSD1. A lack of measurable conversion of dexamethasone to 11-dehydrodexamethasone suggests that dehydrogenation due to 11 beta HSD2 is low or absent. Neither type nor level of 11 beta HSD activity measured under the present assay conditions correlates with IVF outcome.

A rapid method for the measurement of the oxoreductase activity of 11beta-hydroxysteroid dehydrogenase in granulosa-lutein cells from patients undergoing in-vitro fertilization

The presence of 11beta-hydroxysteroid dehydrogenase (11beta-HSD; EC1.1.1.146), the enzyme responsible for the interconversion of cortisol and cortisone, in granulosa-lutein (GL) cells is associated with a poor outcome in in-vitro fertilization (IVF). We have developed a simple method of assessing the reductase component of 11beta-HSD in these cells which is sufficiently rapid to provide data on the enzyme's activity prior to embryo replacement. Cells were pooled from follicular aspirates and challenged with cortisone within 2 h of aspiration. Cortisol secretion was then measured by radioimmunoassay. Conversion of cortisone to cortisol was linear for up to 3 h and was completely inhibited by glycyrrhetinic acid, a specific 11beta-HSD inhibitor. Initial velocity rates were determined for eight cortisone concentrations (range 0.1-8 micromol/l), and the apparent Km calculated (1.6 +/- 0.4 micromol/l). There was no evidence of substrate/product inhibition and conversion of cortisone to cortisol was <2% in all experiments. In subsequent work, cells were challenged with cortisone (6 micromol/l) for 2 h. Cells challenged for 2 h immediately following purification from follicular aspirates produced varying amounts of cortisol (range 25-150 nmol/pooled follicles from each patient, n = 10 patients), while basal outputs were <6 nmol/l. Enzyme activity was also examined in cells on a per follicle basis from individual patients and found to vary considerably (e.g. 19, 53 and 36 nmol/l cortisol/1000 cells, three follicles). Having established the method for assessing 11beta-reductase activity within GL cells, we performed a small prospective study on a series of 20 patients examining the enzyme activity within 110 individual follicles. 11Beta-reductase activity varied greatly from patient to patient and from follicle to follicle ranging from <0.024-0.57 nmol cortisol/microg DNA but at present low patient numbers preclude a meaningful correlation between enzyme activity and pregnancy rate. In summary, we have developed a simple, rapid (<8 h) assay for detecting the reductase activity of 11beta-HSD in GL cells isolated from pooled or individual follicles. This procedure is sufficiently quick to aid in the choice of embryo for replacement.

Leukocytes modulate 11beta-hydroxysteroid dehydrogenase (11beta-HSD) activity in human granulosa-lutein cell cultures

It is well established that there are interactions between the immune and reproductive systems. The ovary contains indigenous macrophages, as well as other classes of leukocytes in smaller numbers. Cytokines secreted by these cells have been shown to have the ability to regulate ovarian steroidogenesis. In the present study, the effect of leukocytes on 11beta-hydroxysteroid dehydrogenase (11beta-HSD) in human granulosa-lutein cells was examined. In addition, individual cytokines were also tested for their ability to regulate this enzyme. The follicular aspirates of patients undergoing IVF treatment were used as a source of granulosa cells. Cells isolated from these aspirates were found to contain between 15 and 60% leukocytes as assessed by flow cytometry (FACS). Leukocytes were removed from the sample preparations by the use of immunomagnetic beads coated with CD45 antibody, which recognises a surface antigen on all classes of leukocyte. Removal of leukocytes significantly decreased the 11beta-HSD activity in the granulosa cells, assayed after 3 days of culture, from 7.3 (2-20) to 3.5 (1-10) pmol cortisone formed/50000 cells/4 h (medians and ranges, n = 15). Addition of IL-5 and IL-6 significantly increased the 11beta-HSD activity in granulosa cell cultures both in the presence and absence of leukocytes. Addition of IL-4 and IFN-gamma increased 11beta-HSD activity only in the leukocyte-depleted granulosa cell cultures, whereas IL-2 had no effect on either of the cultures. The data suggests that leukocytes interact with the ovarian cells through cytokine secretion and/or cell-cell contact to increase the 11beta-HSD activity in human granulosa cells.

Further evidence of increased aromatase activity in granulosa luteal cells from polycystic ovary

This study evaluated the effect of atamestane (a competitive inhibitor of P-450 aromatase) on granulosa luteal cells from polycystic and normal ovaries. Treatment with atamestane (10 micromol/l) determined a strong inhibition of basal aromatase activity in both types of cells; however, its effect was markedly more pronounced in granulosa cells from normal ovary than in granulosa cells from polycystic ovaries (PCO; P < 0.01). Concomitant treatment with insulin (25 microg/ml) and increasing doses of atamestane (0.01-10 micromol/l) caused a dose-dependent inhibition of insulin-stimulated aromatase activity, but again with marked differences between the two types of cells. In granulosa cells from PCO, the minimal effective dose of atamestane was 1 micromol/l and it had an EC50 of 2.23 +/- 0.4 micromol/l and a maximal inhibitory effect of 75%; in granulosa cells from normal ovary, the minimal effective dose of atamestane was 0.01 micromol/l, the EC50 was 0.4 +/- 0.07 micromol/l, and the maximal inhibitory effect was 94%. Significant differences were observed between the different cells at all the studied dose points. Reversibility studies showed that resumption of aromatase activity in granulosa cells from PCO is basally greater and more inducible with insulin treatment. This study provides further evidence of an increased in-vitro function of the aromatase complex in granulosa cells from PCO, that could be induced by an altered cellular autoregulation.

The 5'-flanking region of the ovarian promoter of the bovine CYP19 gene contains a deletion in a cyclic adenosine 3',5'-monophosphate-like responsive sequence

Conversion of C19 steroids to estrogens is catalyzed by aromatase P450 (P450arom; the product of the CYP19 gene). In the ovary, P450arom is expressed in granulosa cells of both human (h) and bovine (b) follicles. After the ovulatory surge of gonadotropins, however, P450arom expression is maintained only in the luteinized granulosa cells of the human ovary and is absent from the bovine corpus luteum. We compared the regulation of expression of the ovary-specific human CYP19 (hCYP19ov) and the bovine CYP19 (bCYP19ov) gene by cAMP (forskolin) and sought to determine whether the divergence in the expression of P450arom with the onset of luteinization could be explained by specific cis-acting elements present uniquely in the 5'-flanking DNA of the hCYP19ov or bCYP19ov gene. We, therefore, subcloned DNA encompassing the promoters and 5'-flanking regions of the hCYP19ov or bCYP19ov gene into a promoterless luciferase vector. These constructs were transfected into luteinized bovine granulosa cells or bovine luteal cells in primary culture. Neither cell type exhibits endogenous expression of bovine P450arom. After transfection, cells were treated with either vehicle or 25 microM forskolin. There was little or no increase in luciferase activity after forskolin treatment in cells transfected with any of the bCYP19ov constructs, whereas all of the corresponding hCYP19ov constructs (-693/-16 to -214/-16 bp) expressed reporter activity in the presence of forskolin. This dramatic difference between the activities of the constructs of the two species occurred despite the fact that there is an 88% sequence identity between the bovine and human promoters in the region between -214 to -16 bp. One possible explanation for this variability may be that the bCYP19ov gene has a 1-bp deletion in a cAMP-response element-like sequence (CLS) present at -208 to -201 bp in the hCYP19ov gene that we have shown to be critical for cAMP-stimulated transcription of hCYP19ov in the ovary. When this region of the bCYP19ov promoter was mutated to the hCLS, a partial restoration in luciferase activity was observed after forskolin treatment. Therefore, these results suggest that another sequence in this -214 bp region of the bCYP19ov gene is also contributing to the lack of expression of P450arom after luteinization in the bovine ovary. This lack of expression of the bCYP19ov gene may be due to the presence of a repressive trans-acting factor expressed with the onset of luteinization of the bovine granulosa cell. These results further suggest that in the cow, elements upstream of those employed by the hCYP19ov gene may have been recruited to facilitate regulated expression of the bCYP19ov gene in the absence of a functional CLS.

The detection and confirmation of 11 beta-hydroxysteroid dehydrogenase type 1 transcripts in human luteinized granulosa cells using RT-PCR and plasmid pUC18

The activity of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) in human granulosa cells has been shown to be associated with the outcome of treatment following in-vitro fertilization and embryo transfer. There are two known isoforms of 11 beta-HSD which differ significantly in their actions and co-factor requirements. The net activity of 11 beta-HSD which differ significantly in their actions and co-factor requirements. The net activity of 11 beta-HSD within the human ovary is unclear, but may be of particular importance within the ovarian follicle in regulating possible glucocorticoid influences on the oocyte. This study presents preliminary information regarding establishment of techniques to identify transcripts of the 11 beta-HSD isoforms within human granulosa cells and human cumulus cells using reverse transcription-polymerase chain reaction. In view of the high expression of the type 1 11 beta-HSD isoform and the possibility of other 11 beta-HSD isoforms in the ovary, plasmid technology was used to confirm the technique specifically identifying the known isoforms.

Triiodothyronine and follicle-stimulating hormone, alone and additively together, stimulate production of the tissue inhibitor of metalloproteinases-1 in cultured human luteinized granulosa cells

Thyroid disorders have been frequently associated with menstrual disturbances and impaired fertility. To characterize the nature of thyroid hormone action in the ovary, the direct effects of T3-gonadotropin interactions were investigated in vitro using a culture system of human luteinized granulosa cells in serum-free medium. Although FSH alone was devoid of any significant effect on cell proliferation, it inhibited T3-stimulated cell growth. The electrophoretic profiles of the radiolabeled proteins induced by the different hormonal treatments revealed similarity in overall protein patterns but differences in intensity of labeling. Human CG, alone or combined with T3, had no major influence on the total intensity of labeling compared with control, whereas T3 or FSH alone reduced total labeling intensity but a 30,000 Da protein band was increased. FSH combined with T3 augmented the total intensity of labeling, including the 30,000-Da protein band. Western blot analysis revealed the presence of the tissue inhibitor of metalloproteinases-1 (TIMP-1), mol wt 30,000, known to play a key role in ovarian function. TIMP-1 was dose dependently stimulated by T3 and FSH, and an additive effect was obtained when both hormones were combined. This is the first report of TIMP-1 modulation by FSH in ovarian cells and of an effect by thyroid hormone on TIMP-1 levels. The study shows TIMP-1 induction in human ovarian cells not only by FSH, i.e. via a probable protein kinase A mechanism, but also demonstrates an additional mode of TIMP-1 hormonal induction: via thyroid hormone stimulation, acting by modulation of gene transcription. The present study provides novel data on TIMP-1 hormonal modulation and of direct T3 in vitro ovarian effects that may account for the in vivo indications of a thyroid-ovarian connection.

A putative binding site for Sp1 is involved in transcriptional regulation of CYP17 gene expression in bovine ovary

In the bovine ovary, thecal cells are the only cell type capable of expressing the CYP17 gene in response to LH. With the onset of ovulation and luteinization in the cow, there is complete loss of P450c17alpha expression. To characterize the molecular mechanisms involved in tissue-specific regulation of the CYP17 gene in the bovine ovary, deletion mutations of the bovine CYP17 promoter were ligated into a promoterless luciferase expression vector, and reporter constructs were transiently transfected into primary cultures of bovine thecal and luteal cells. Deletion of the promoter sequences between -191 and 101 bp dramatically decreased the levels of reporter gene activity in both thecal and luteal cells. Computer-assisted analysis revealed the presence of a putative inverted Sp1-like binding site at -188/-180 bp. Deletion or mutation of this sequence caused a decrease in both basal and forskolin-stimulated reporter gene activity. In addition, mutation or deletion of this sequence also decreased reporter gene expression induced by overexpression of the protein kinase A catalytic subunit. Electrophoretic mobility shift assays showed that this sequence binds to a nuclear protein(s) from both thecal and luteal cells that is related to Sp1, as suggested by the results of gel mobility supershift assay employing an antibody raised against Sp1. DNA-binding activity was not increased by the addition of forskolin to thecal or luteal cells. We conclude that this inverted Sp1-like binding sequence is involved in constitutive as well as cAMP-dependent expression of the CYP17 gene in the bovine ovary.

Nitric oxide inhibits aromatase activity: mechanisms of action

NO synthase is present in human ovarian granulosa-luteal cells and NO inhibits estradiol secretion by granulosa cells in culture. These findings suggest that NO is an autocrine regulator of ovarian steroidogenesis. The purpose of this investigation was to explore the mechanisms through which NO exerts an inhibitory effect on cytochrome P450 aromatase activity. To examine the effect of NO on aromatase mRNA levels, human granulosa-luteal cells were cultured in the presence or absence of the NO donor SNAP for 16 h. Using a probe for human aromatase, Northern blots revealed a 26% decrease in aromatase mRNA in cells exposed to SNAP. Because this modest decrease in mRNA is unlikely to explain a rapid and profound reduction in estradiol secretion that we have observed, we looked for direct effects of NO on cytochrome P450 aromatase activity. Aromatase activity was assayed in placental microsomes and granulosa-luteal cells by measuring the release of 3H2O from [1 beta-3H] androstenedione. NO (10(-4)-10(-3)M), added as a saturated saline solution, reduced aromatase activity by as much as 90% in a concentration-dependent, non-competitive manner. In contrast, carbon monoxide (CO), a gas known to bind to the heme iron in aromatase, had no effect on aromatase activity when added alone nor could CO reverse the NO-induced inhibition of aromatase. These data suggest that NO binding to the heme is insufficient to inhibit aromatase activity. NO has been reported to alter protein function by reacting with the sulfhydryl group of cysteines, forming a nitrosothiol group. Because a cysteine sulfhydryl group is thought to participate in the catalytic mechanism of all P450 enzymes, experiments were designed to test whether NO might inhibit aromatase via such a mechanism. Addition of increasing amounts of mercaptoethanol, a chemical with free sulfhydryl groups, blocked the NO-induced inhibition of aromatase in microsomes. N-Ethylmaleimide, a chemical which covalently modifies sulfhydryl groups, reduced aromatase activity in a concentration-dependent manner. We conclude that NO inhibits aromatase both by decreasing mRNA for the enzyme and by an acute, direct inhibition of enzyme activity. We hypothesize that the direct inhibition occurs as a result of the formation of a nitrosothiol on the cysteine residue adjacent to the heme in aromatase.

Follicular variation in ovarian 11 beta-hydroxysteroid dehydrogenase (11 beta HSD) activities: evidence for the paracrine inhibition of 11 beta HSD in human granulosa-lutein cells

We have previously shown that detectable metabolism of cortisol to cortisone by 11 beta-hydroxysteroid dehydrogenase (11 beta HSD) in human granulosa-lutein cells, pooled for each patient from all aspirated ovarian follicles, is associated with failure to conceive by in vitro fertilization and embryo transfer. The aims of the present study were to assess: (1) the variation in the 11 beta HSD activities of granulosa-lutein cells obtained from individual follicles in relation to oocyte maturity and (2) whether the 11 beta HSD activity of pooled granulosa-lutein cells reflects the 11 beta HSD activities of the individual follicles for a given patient. 11 beta HSD activities were measured in intact cells in serum-free medium by a radiometric conversion assay (100 nmol/l [3H]cortisol to [3H]cortisone). Follicular 11 beta HSD activities ranged from < 10 (undetectable) to 514 pmol/mg protein per 4 h (n = 105 follicles from 12 patients) and did not correlate with oocyte maturity. In three separate patients, the follicular 11 beta HSD activities ranged from < 10 to 117 pmol/mg protein per 4 h (n = 8 follicles), 19 to 514 pmol/mg per 4 h (n = 9) and 60 to 390 pmol/mg per 4 h (n = 8). The 11 beta HSD activities of the corresponding multi-follicular pools of cells were < 10, < 10 and 44 pmol/mg per 4 h respectively, all of which were significantly lower (P < 0.05) than the arithmetic means for the activities in the individual follicles (52, 132 and 215 pmol/mg per 4 h respectively). Likewise, the 11 beta HSD activities of two independent multi-patient pools of cells were significantly lower than the mean values of the 11 beta HSD activities of the appropriate individual patients. We conclude that ovarian 11 beta HSD activity varies between follicles and that co-culture of granulosa-lutein cells with low enzyme activity can suppress the ovarian 11 beta HSD activity in cells from different follicles (or patients) with high rates of cortisol metabolism. Hence, these data indicate the potential for paracrine inhibition of ovarian 11 beta HSD activity in human granulosa-lutein cells.

Activation of phospholipase D by prostaglandin F2 alpha in rat luteal cells and effects of inhibitors of arachidonic acid metabolism

In rat luteal cells labeled with [3H]oleic acid, PGF2 alpha-stimulated phospholipase D (PLD) activation was investigated. The PLD activity was detected by measuring the accumulation of [3H]phosphatidylethanol (PtdEt) in the presence of ethanol. PGF2 alpha stimulated PtdEt accumulation at concentrations of more than 100 nM in the presence of ethanol. However, PtdEt accumulation did not change in the absence of ethanol. PGF2 alpha (1 microM) increased PtdEt accumulation after 1 min, and the accumulation reached a plateau by 2-3 min. These results indicate that PGF2 alpha activates PLD in rat luteal cells. U-73122, a phospholipase C (PLC) inhibitor, and staurosporine, a protein kinase C (PKC) inhibitor, did not inhibit PGF2 alpha-stimulated [3H]PtdEt accumulation. These results suggest that PGF2 alpha-induced PLD activation is different from PLC-PKC systems. We reported previously that PGF2 alpha stimulated the release of arachidonic acid. The effects of indomethacin, nordihydroguaiaretic acid (NDGA), and 5,8,11,14-eicosatetraynoic acid (ETYA), inhibitors of arachidonic acid metabolism, on PGF2 alpha-stimulated PtdEt accumulation were examined. Pretreatment with indomethacin enhanced PGF2 alpha-induced PtdEt accumulation. In contrast, pretreatment with NDGA and ETYA inhibited PGF2 alpha-induced PtdEt accumulation. It is suggested that PGF2 alpha-stimulated PLD activation is mediated via lipoxygenase products.

[The effects of synthetic oligopeptides on progesterone production in corpus luteum cell of rat and their mechanism of action]

The effects of a series of synthetic oligopeptides on progesterone production by rat CL cells were compared and their mechanism of actions was studied in vitro. The ones with inhibitory actions were characterized by carrying positive charge in the medium of pH 7.3-7.5 and with intermolecular linkage. A preliminary survey of the effect of the active oligopeptides on signal systems showed: (1)GY and YG inhibited PLC system; (2)GY and GSK reduced hCG-induced progesterone production in CL cells probably by regulating cellular Ca2+ concentration; (3) GSK decreased TPK activity and GYK increased it in hCG treated CL cell though both of them were inhibitory on progesterone production. GSK also stimulated PKC and supressed PKA activity in CL cells. The anti-progesterone effect of oligopeptides so far synthesized may influence either PKA or PKC or TPK systems. The mechanism of action at the molecular level is quite complicated.

Gonadotropin-releasing hormone antagonist versus agonist administration in women undergoing controlled ovarian hyperstimulation: cycle performance and in vitro steroidogenesis of granulosa-lutein cells

OBJECTIVES

We sought to determine the effectiveness of a gonadotropin-releasing hormone antagonist compared with an agonist in suppressing a spontaneous luteinizing hormone surge in women undergoing controlled ovarian hyperstimulation for in vitro fertilization and gamete intrafallopian transfer and to examine whether in vivo administration of these analogs effects granulosa-lutein cells steroidogenesis in vitro.

STUDY DESIGN

This prospective case-control study included 30 healthy women undergoing ovarian hyperstimulation with human menopausal gonadotropins. Fifteen women received the Nal-Glu antagonist, 5 mg intramuscularly daily, when the lead follicle was > or = 15 mm or serum estradiol level was > or = 500 pg/ml. The control group included 15 women who underwent oocyte retrieval on the same day as the study subjects and were given the agonist leuprolide acetate, 250 micrograms subcutaneously daily, starting on cycle day 1. Granulosa-lutein cells were purified from follicular aspirates from six subjects and six controls and cultured in parallel, evaluating basal progesterone production, progesterone response to follicle-stimulating hormone or luteinizing hormone and aromatase activity.

RESULTS

No difference was demonstrated in the total amount of gonadotropins received by the two groups. Overall, the gonadotropin-releasing hormone antagonist was given for only 2.5 +/- 0.2 (mean +/- SEM) days before human chorionic gonadotropin administration. The antagonist group showed significantly lower levels of serum luteinizing hormone than did the agonist group, 1.0 +/- 0.2 versus 4.2 +/- 0.5 mIU/ml (p = 0.0001) on the day of human chorionic gonadotropin administration. Serum estradiol levels were significantly lower in the antagonist than the agonist group, 820 +/- 120 versus 1361 +/- 110 pg/ml (p = 0.003) on the day of human chorionic gonadotropin administration. There was no difference in the number of retrieved oocytes, but the antagonist group had a higher proportion of mature oocytes, 82% +/- 4% versus 62.4% (p = 0.02), and a higher proportion of embryos of good quality, 69.8% +/- 9.8% versus 44.3% +/- 7.2% (p = 0.03) in the agonist group. Granulosa-lutein cells from antagonist-treated women showed significantly lower aromatase activity the first 6 hours after retrieval, 17.6 +/- 1.6 versus 31.3 +/- 7.4 ng/ml per 6 hours estradiol (p = 0.03), whereas basal and gonadotropin-stimulated with progesterone responses were similar.

CONCLUSION

Gonadotropin-releasing hormone antagonist administration during the late follicular phase resulted in lower serum luteinizing hormone and estradiol levels and more mature oocytes and embryos of better quality compared with gonadotropin-releasing hormone agonist administration. These results suggest that gonadotropin-releasing hormone antagonist administration in ovarian hyperstimulation has practical advantages over the agonist regimen. Gonadotropin-releasing hormone analogs may have direct action on ovarian function with differential effects on granulosa-lutein cell aromatase activity. This could explain the lower serum estradiol levels routinely observed in women given gonadotropin-releasing hormone antagonist.