Gonadotropin regulation of RIP140 messenger ribonucleic acid expression in the rat ovary

Female mice null for receptor-interacting protein 140 (RIP140) are infertile because of the failure of follicle rupture. The present study examined gonadotropin regulation of RIP140 expression in immature rat ovary. Treatment with PMSG increased ovarian RIP140 mRNA and protein levels. In contrast, hCG treatment rapidly inhibited RIP140 mRNA and protein levels within 1-3 h. RIP140 mRNA was detected in theca cells of growing follicles in untreated ovary and in granulosa cells in PMSG-treated ovary. Interestingly, hCG treatment reduced RIP140 mRNA levels in granulosa cells of preovulatory follicles, but not of growing follicles. Neither treatment of immature rats with diethylstilbestrol in vivo nor of immature granulosa cells with FSH in vitro affected RIP140 mRNA levels. Treatment of immature granulosa cells with 17beta-estradiol in vitro, however, stimulated RIP140 mRNA levels. In cultured preovulatory granulosa cells, RIP140 mRNA levels were stimulated at 1 h and then declined to below control levels by 3 h after LH treatment. Treatment with MDL-12,330A, an inhibitor of adenylate cyclase, or chelerythrine chloride, an inhibitor of protein kinase C (PKC), inhibited LH-stimulated RIP140 gene expression. Furthermore, forskolin or TPA treatment for 1 h mimicked the stimulatory action of LH, indicating the involvement of both adenylate cyclase and PKC pathways. These results demonstrate the stimulation by PMSG and inhibition by hCG of RIP140 expression in granulosa cells of preovulatory follicles in the rat ovary.     

Distribution of ganglioside GM3 in the rat ovary after gonadotropin stimulation.

Gangliosides are ubiquitous membrane components in mammalian cells and are suggested to play important roles in various cell functions, such as cell-cell recognition, differentiation and transmembrane signalling. Ovaries have been shown to contain GM3 as a major ganglioside. To study GM3 distribution during gonadotropin stimulation in the hypophysectomized rat ovary, ovarian sections and cultured granulosa cells were stained with specific monoclonal antibody against GM3. Interstitial cells of follicles of immature hypophysectomized rat ovary expressed ganglioside GM3. Theca cells of early antral follicles but not primary follicles expressed GM3. No granulosa cells of these follicles expressed GM3. When a surge dose of FSH/LH was injected, Graafian follicles were formed and GM3 expression was detected in granulosa cells of these follicles. After ovulation, cumulus cells kept expressing GM3 in the ampulla region of ovulated oviduct. The follicles did not show GM3 expression in their granulosa cells after an ovulatory dose of FSH/LH. At 48 h after in vitro culture with FSH/LH of granulosa cells from preantral follicles, GM3 was expressed to a detectable extent on the outer part of the granulosa layer. Finally, at 72 h after culture, all granulosa cells became positive to anti-GM3 antibody. These data suggest that the expression of ganglioside GM3 in the hypophysectomized rat ovary is spatiotemporally regulated by FSH/LH during follicular development and ovulation.     

Inhibitory activity of a low molecular weight substance extracted from porcine small follicular fluid on estradiol and progesterone secretions by rat granulosa cells in vitro and by rat ovaries in vivo

Follicular fluid from small porcine follicles was filtrated through an Amicon XM-50 membrane to obtain a filtrate less than 50,000 MW. The filtrate was eluted through a Sephadex G-25 column (1.5 X 70 cm) using 0.01 N CH3COOH, pH 4.0, as elution buffer, and divided to five fractions. To test the inhibitory activity of these fractions on the in vitro estradiol and progesterone secretion, each fraction was added into a rat granulosa cell culture with FSH and testosterone in the medium. Two of five fractions exerted a significant inhibitory activity on the estradiol and progesterone secretions by the granulosa cells. They were in a range of low molecular weight fractions (MW 1,000-3,000) on the elution profile. Whether the in vitro active fractions are capable of inhibiting the in vivo estradiol and progesterone secretions by the ovary was assessed using the hypophysectomized DES-treated immature rat with hMG stimulation and the testosterone-treated immature rat with PMSG stimulation. The administration of the fractions to the former animal significantly suppressed the increases due to gonadotropin in the ovarian and serum estradiol concentrations. The administration of the fractions to the latter animal significantly suppressed the increases due to gonadotropin in the estradiol and progesterone concentrations of the ovary and serum. These results suggest that a low molecular weight substance from porcine small follicular fluid is capable of inhibiting the estradiol and progesterone biosyntheses in the follicle of the rat ovary.     

Hormonal regulation of ovarian cellular proliferation

The steroid hormone estradiol, and the glycoprotein hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH), are known to be essential for the growth and differentiation of follicles in the ovary. The present study was conducted to determine quantitatively the effects of estradiol, FSH and LH on proliferation of different ovarian cell types (granulosa and theca cells). The immature female hypophysectomized rate sequentially primed with estradiol, FSH and LH was used as the experimental model. Proliferation was assessed by examining changes in total DNA, incorporation of 3H-thymidine into DNA and labeling index in specific cell types. Estradiol and FSH each acted on follicles at different stages of development to stimulate proliferative activity of both granulosa and theca cells. Continued administration of either hormone caused a decrease in the proliferative activity of both cell types. These observations have been interpreted to indicate that estradiol and FSH can each alter the length of the specific phases of the cell cycle. A luteinizing dose of LH caused a cessation of proliferation in luteinizing granulosa cells while stimulating a limited proliferation of theca cells. Absence of the appropriate hormonal stimulus caused both granulosa and theca cells to stop proliferating and the follicles to undergo atresia. These results indicate that, depending upon the state of differentiation of granulosa and theca cells, estradiol, FSH and LH can stimulate or inhibit the ability of these cells to proliferate.     

The effect of follicle-stimulating hormone (FSH) on the expression of FSH receptor in cultured rat granulosa cells

The acquisition of FSH receptors during folliculogenesis is believed to be a key event in the subsequent development of the follicle. The regulation by FSH of FSH receptor expression and function were further studied using cultured granulosa cells of diethylstilbestrol (DES)-primed immature rats. Incubation of rat granulosa cells with FSH led to a reduction in FSH receptor levels for a short time (6 h), followed by an increase in FSH receptor levels that reached maximum of around 150% of the initial level within 3 days after the addition of FSH. FSH stimulation caused a reduced cAMP response to subsequent FSH treatment and a time course experiment demonstrated that this response was detectable within 30 min of exposure to FSH and reached a plateau after 4 h to 24 h. The recovery of FSH responsiveness in cAMP production of granulosa cells was seen after 48 h of FSH-free interval. Treatment with forskolin (FSK) enhanced the effect of subsequent FSH on the production of intracellular cAMP. Treatment with PMA did not affect the response to subsequent FSH treatment. These data showed that the FSH is essential for the suppression of the FSH receptor function in the adenylyl cyclase pathway. Desensitization of cellular response to continuous agonist stimulation may occur because of changes in the numbers of FSH receptor, as well as changes in the functional properties of the effector system.     

Effect of follicle size on in vitro production of steroids and insulin-like growth factor (IGF)-I,IGF-II,and the IGF-binding proteins by equine ovarian granulosa cells

Little is known regarding the hormonal regulation of granulosa cell steroidogenesis and the ovarian insulin-like growth factor (IGF) system in the mare. The objectives of this study were to determine, first, if estradiol, insulin, and/or FSH affect steroid production by equine granulosa cells (experiment 1) and, second, if the components of the IGF system are produced by equine granulosa cells in culture as well as whether estradiol, insulin, and/or FSH affects IGF and/or IGF-binding protein (IGFBP) production by equine granulosa cells (experiment 2). Granulosa cells from small (6-15 mm), medium (16-25 mm), and large (25-48 mm) follicles were collected from cyclic mares (n = 14), cultured for 2 days in medium containing 10% fetal calf serum, washed, and then treated for an additional 2 days in serum-free medium with or without added hormones. In experiment 1, large-follicle granulosa cells produced less progesterone and more estradiol than did medium- and/or small-follicle granulosa cells (P < 0.05). Progesterone production was inhibited (P < 0.05) by FSH and insulin in small- and medium- but not in large-follicle granulosa cells; estradiol was without effect. Insulin increased (P < 0.05) estradiol production in small- and medium-follicle granulosa cells but had no effect in large-follicle granulosa cells. In experiment 2, IGF-I production was inhibited (P < 0.05) by insulin across all follicle sizes but was not affected by estradiol or FSH. Granulosa cells of medium and large follicles produced more IGF-II than did granulosa cells of small follicles (P < 0.05). Insulin and FSH inhibited (P < 0.05) IGF-II production by granulosa cells of large and medium but not of small follicles; estradiol was without effect. Only IGFBP-2 and -5 were produced by equine granulosa cells. Production of IGFBP-2 was less (P < 0.10) in granulosa cells of large versus those of small and medium follicles, whereas medium-follicle granulosa cells produced more (P < 0.05) IGFBP-5 than did small- or large-follicle granulosa cells. Averaged across follicle sizes, estradiol increased (P < 0.05) IGFBP-2 production, FSH increased (P < 0.10) IGFBP-2 and -5 production, and insulin was without effect. These results indicate that IGF-I, IGF-II, IGFBP-2, and IGFBP-5 are produced by equine granulosa cells and that insulin, FSH, and estradiol play a role in the regulation of steroidogenesis and the IGF system of equine granulosa cells.     

Binding sites for gonadotropins in the ovary of immature and adult mice

Binding sites for gonadotropins in the mouse ovary were studied using the immunohistochemical technique. Binding sites for LH were localized in the interstitial cells and theca as well as granulosa cells of large follicles. Binding sites for FSH were demonstrated in the interstitial cells and granulosa cells of small follicles. In immature mice very few binding sites for both the gonadotropins were observed until day 21 of age. An intense staining reaction for peroxidase was observed in the ovary of 24-day old mouse. In adult mice, maximum number of binding sites for FSH were demonstrated in the ovary in estrus and metestrus stage of the cycle, respectively. A good correlation between the circulating levels of gonadotropins and binding sites for them in the ovary could be noted in the cycling but not in the prepubertal mice.     

Ultrastructural evidence for estradiol synthesis in the ovary of persistent-estrous rats exposed to continuous illumination

The relation between sex hormone levels in blood and ultrastructural changes of ovarian follicles was examined in persistent-estrous rats exposed to continuous illumination (LL) for 100 days. Plasma LH showed a tonic level secretory pattern, and circulating estradiol and estrone concentrations were relatively high, while both levels of FSH and progesterone were low. Various stages of growing and degenerating follicles were observed in the ovary of the LL-exposed rats. The early stage of antral follicle did not seem to possess the ability of steroidogenesis. Theca cells around mature antral follicles contained prominent Golgi apparatuses, plenty of smooth endoplasmic reticulum (ER), abundant free ribosomes and many round-mitochondria. A few newly formed lipid droplets were seen in some of theca cells. Granulosa cells contained much distended rough ER, well-developed mitochondria, several lipid droplets and microfilaments. The theca cells of abnormal follicles with hyperplastic and infolded layers of granulosa cells contained many lipid droplets. However, the development of the smooth ER became hindered with increasing lipid droplets in the theca cell. On the other hand, granulosa cells of abnormal follicles contained greater numbers of lipid droplets than those of antral mature follicles, and were equipped with well-developed cytoplasmic organelles as were those of mature antral follicles. Theca interna cells of abnormal follicles may be more involved in the secretion of androgen, which has already been accumulated in the lipid droplets, than the cells involved in the active synthesis of the hormone, while the granulosa cells may convert its androgen to estrogen. The present findings suggest that both follicles of mature and abnormal types in the LL-exposed rat retain enough capacity of estradiol production and participate in the continued elevation of circulating estradiol, probably resulting in the stimulation of the theca cells by the tonic level of LH and of the granulosa cells by the levels of FSH, which are lower than the basal values during the normal 4-day estrous cycle.     

Immunocytochemical localization and enzymatic distribution of rat ovarian aromatase

A rabbit antiserum directed against purified human placental aromatase was used for immunohistochemical localization of the enzyme in rat ovaries. Immunostaining was conducted on tissue from animals at various ages and in different reproductive states: immature; immature, eCG-treated; immature pseudopregnant; adult cycling; and adult pregnant. Various labeling protocols were employed (e.g. horseradish peroxidase-conjugated secondary antibody, peroxidase-antiperoxidase, and avidin-biotin-peroxidase on fresh frozen and Bouin's fixed paraffin-embedded sections), but the avidin-biotin-peroxidase method on paraffin sections proved to be superior to the others. In immature rats, most of the immunostaining, which was quite weak, was limited to the stroma. After stimulation with eCG, some of the granulosa cells of antral follicles exhibited immunostaining; in pseudopregnant rats, most staining occurred in the luteal cells. In mature animals, the corpora lutea of pregnant and cycling rats demonstrated the greatest degree of immunostaining. No significant immunoreactivity was detected in pre-antral follicles, but in early antral follicles and preovulatory follicles, both theca and granulosa cells exhibited immunostaining. Aromatase enzymatic activity was also determined on ovarian microsomal fractions of eCG-treated immature animals, pregnant animals at term, and cycling animals. Furthermore, enzyme activity and estradiol concentrations were examined after ovaries from proestrous rats were dissected into follicular, luteal, and residual components. Activity was found in all regions and correlated with immunostaining and estrogen production. These results argue against a model in which all the immunoreactive/enzymatically active protein is localized in granulosa cells of Graafian follicles and suggest that corpora lutea may be involved in estrogen synthesis during the rat estrous cycle as well as during pregnancy.     

Comparison of granulosa cell proliferation in small follicles of hypophysectomized, prepubertal, and mature rats

The factors that control the rate of granulosa cell proliferation during follicular development are unknown. The object of this study was to test the hypothesis that growth rates of small and medium follicles may be modulated by cyclic alterations in endogenous hormone concentrations. Follicular growth in adult cycling rats was compared with hypophysectomized rats, untreated prepubertal rats, and prepubertal rats treated with exogenous gonadotropins. Cell kinetics was studied using a metaphase arrest technique and by long-term infusion of [3H]thymidine. Many follicles of hypophysectomized rats showed evidence of continued cell proliferation despite the absence of gonadotropins. In hypophysectomized rats, follicular growth was able to proceed to the size of the largest healthy non-preovulatory follicles in the proestrous rat ovary. Follicular growth in prepubertal rats progressed little beyond this same size range. Granulosa cell proliferation rates differed in immature rats and cycling rats. Granulosa cells in small follicles (80-180 cells in the largest cross-section) of cycling rats grew slowly. However, granulosa cells in small follicles of immature rats were among the fastest growing in the ovary. These results suggest that, although gonadotropins are not absolutely required to maintain granulosa cell proliferation in small follicles, the rate at which these follicles grow varies under different hormonal conditions.     

Follicle stimulating hormone-induced DNA synthesis in the granulosa cells of hamster preantral follicles involves activation of cyclin-dependent kinase-4 rather than cyclin d2 synthesis

Although cyclin D2 mRNA synthesis precedes gonadotropin-induced DNA synthesis in quiescent granulosa cells in culture, it is unclear whether a similar mechanism exists for the granulosa cells of growing preantral follicles in cyclic animals. The objective was to evaluate whether the synthesis of cyclin D2 protein was a prerequisite for FSH-induced DNA synthesis in the granulosa cells of intact preantral follicles of cyclic hamsters. Preantral follicles from cyclic hamsters were cultured in the presence or absence of FSH, and cell cycle parameters were examined. FSH stimulated cyclin-dependent kinase (CDK)-4 activity by 2 h and DNA synthesis by 4 h without altering the levels of cyclin D2 in the granulosa cells. The FSH effect was mimicked by epidermal growth factor administered in vivo. Although FSH increased the levels of cyclin D2 mRNA, it also stimulated the degradation of cyclin D2 as well as p27(Kip1) and p19(INK4) proteins. FSH activation of CDK4 was mediated by cAMP and ERK-1/2. In contrast to granulosa cells in intact follicles, FSH or cAMP significantly increased cyclin D2 protein levels in cultured granulosa cells but failed to induce DNA synthesis. Collectively, these data suggest that granulosa cells of preantral follicles, which are destined to enter the S phase during the estrous cycle, contain necessary amounts of cyclin D2 and other G1 phase components. FSH stimulation results in the formation and activation of the cyclin D2/CDK4 complex leading to DNA synthesis. This mechanism may be necessary for rapid movement of follicles from preantral to antral stages during the short duration of the murine estrous cycle.     

Estradiol-17 beta and androgen secretion by isolated porcine ovarian follicular cells in vitro

The cellular sources and gonadotropic regulation of porcine ovarian estrogen and androgen were assessed by culturing isolated granulosa cells and thecal cells from medium size follicles (4-6 mm diameter) separately for 24 h in a chemically defined medium containing gonadotropins and (or) testosterone. At the end of the culture period, estradiol-17 beta (estradiol) and androgens in the media were determined by radioimmunoassays. Production of estradiol by granulosa cells without an exogenous aromatizable androgen was low in the absence or presence of a highly purified preparation of either follicle-stimulating hormone (FSH. 0.25 microgram/mL) or luteinizing hormone (LH. 1 microgram/mL). Addition of testosterone or androstenedione (0.5 microM), but not dihydrotestosterone or pregnenolone, significantly increased estradiol secretion. Additional increases were observed when FSH, LH, prostaglandin E2, or dibutyryl cyclic 3'.5'-adenosine monophosphate was present. Production of estradiol by thecal cells was low in the presence or absence of exogenous testosterone, and was essentially unaffected by the presence of gonadotropins. Thecal cells, however, released large amounts of androstenedione and smaller amounts of testosterone and other androgens during 24-h culture and the production of these androgens was stimulated by LH but not by FSH. Androgen secretion by granulosa cells was negligible when compared with the theca and was unaffected by gonadotropins. It is concluded that the theca is the prime site for follicular androgen biosynthesis by the porcine ovarian follicle, and, upon LH stimulation, may provide androgen precursors for estradiol production by granulosa cells.     

Gonadotropin-releasing hormone analogs inhibit primate granulosa cell steroidogenesis via a mechanism distinct from that in the rat

Gonadotropin-releasing hormone (GnRH) and related peptides are implicated in the local control of rat ovarian function, but evidence to date for direct effects of such peptides on primate ovarian cells is equivocal. In contrast to rat ovaries, where GnRH action is mediated through specific, high-affinity GnRH receptors, no such binding sites have been identified in primate tissue. Using undifferentiated granulosa cells from immature follicles in cyclic (luteal phase) marmoset ovaries, we have observed direct suppression of human (h) FSH-induced steroidogenesis by GnRH analogs in vitro. Granulosa cells from immature (less than 1 mm diameter) follicles were incubated for 4 days in the presence of hFSH and testosterone (aromatase substrate) to stimulate cyclic AMP (cAMP) production and steroidogenesis. The additional presence of GnRH alone (up to 10 microM) had no effect on FSH action. However, the GnRH agonist, [D-Ser(But)6]GnRH 1-9)-ethylamide (Buserelin, 0.1 microM-10 microM), caused time- and dose-dependent inhibition of estradiol (maximum inhibition = 79%; ED50 = 0.55 microM) and progesterone production (maximum inhibition = 93%; ED50 = 0.1 microM). Accumulation of cAMP was also inhibited by up to 54%. Paradoxically, a GnRH antagonist [( N-Ac-D-Nal(2)1,D-pCl-Phe2, D-Trp3, D-hArg(Et2)6, D-Ala10]-GnRH; 10 microM) alone also inhibited hFSH-stimulated cAMP and steroid production by 40% and 70%, respectively. Moreover, the suppressive effects of the GnRH agonist on granulosa cell functions were augmented by the presence of the GnRH antagonist (10 microM).(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of phosphodiesterase in cyclic AMP signaling in cultured rat granulosa cells

Inactivation of the cyclic nucleotide signal in granulosa cells depends on a complex array of cyclic nucleotide phosphodiesterases (PDE). In order to examine the role of PDE in cyclic AMP (cAMP) signaling in granulosa cells, the present study examined the expression of PDE4D proteins and regulation of cAMP-PDE activities in cultured rat granulosa cells. The results of immunoblot analyses showed that two predominant PDE4D subtypes of approximately 80 and 70 kDa appeared when immature rat granulosa cells were treated with FSH. However, these two new subtypes presumed to be PDE4D proteins were not influenced by treatments of DETA/NO, cGMP and PKB inhibitor, LY294002. Immature rat granulosa cells treated with medium alone displayed low cAMP-PDE activity throughout 48 h of culture while those treated with FSH (2 ng.mL-1) showed a marked increase in cAMP-PDE activity between 6 and 12 h of culture, followed by a decline. The findings from the present study indicate that the increased cAMP-PDE activity by FSH is mainly related to the changes of PDE4D protein levels. However, the inhibitory effects of NO on cAMP accumulation in rat granulosa cells are not via the increased cAMP-PDE activity.