Role of protein kinase C in luteinizing hormone-releasing hormone (LHRH)-stimulated progesterone production in rat granulosa cells

Animal Models for Human Polycystic Ovary Syndrome (PCOS) Focused on the Use of Indirect Hormonal Perturbations: A Review of the Literature

Hormonal disturbances, such as hyperandrogenism, are considered important for developing polycystic ovary syndrome (PCOS) in humans. Accordingly, directly hormone-regulated animal models are widely used for studying PCOS, as they replicate several key PCOS features. However, the pathogenesis and treatment of PCOS are still unclear. In this review, we aimed to investigate animal PCOS models and PCOS-like phenotypes in animal experiments without direct hormonal interventions and determine the underlying mechanisms for a better understanding of PCOS. We summarized animal PCOS models that used indirect hormonal interventions and suggested or discussed pathogenesis of PCOS-like features in animals and PCOS-like phenotypes generated in other animals. We presented integrated physiological insights and shared cellular pathways underlying the pathogenesis of PCOS in reviewed animal models. Our review indicates that the hormonal and metabolic changes could be due to molecular dysregulations, such as upregulated PI3K-Akt and extracellular signal-regulated kinase (ERK) signalling, that potentially cause PCOS-like phenotypes in the animal models. This review will be helpful for considering alternative animal PCOS models to determine the cellular/molecular mechanisms underlying PCOS symptoms. The efforts to determine the specific cellular mechanisms of PCOS will contribute to novel treatments and control methods for this complex syndrome.

Transforming growth factor-alpha stimulates insulin-like growth factor binding protein-4 (IGFBP-4) expression and blocks follicle-stimulating hormone regulation of IGFBP-4 production in rat granulosa cells

The ability of TGF-alpha to regulate insulin-like growth factor binding protein-4 (IGFBP-4), was investigated. Primary cultures of rat granulosa cells (GC) were grown in serum-free medium with rat (r) TGF-alpha and/or rFSH, and secreted IGFBP-4 protein and its steady state mRNA levels were measured by Western immunoblotting and Northern blotting, respectively. Control (untreated) cells secreted IGFBP-4 spontaneously, and the levels were increased by rTGF-alpha in a dose- and time-dependent manner. rTGF-alpha abolished FSH-induced IGFBP-4 protease activity and suppressed FSH-dependent effects on IGFBP-4 production. IGFBP-4 mRNA levels were decreased and increased by FSH and TGF-alpha, respectively, and TGF-alpha blocked the FSH effects. These results demonstrate that TGF-alpha is a potent stimulator of IGFBP-4 expression in rat GC and can overcome the regulatory effects of FSH on IGFBP-4 production. The consequence of these TGF-alpha effects is a marked, sustained increase in the levels of IGFBP-4 in the microenvironment.

Regulation of follistatin messenger ribonucleic acid in cultured rat granulosa cells

The regulation of the follistatin mRNA by hormones and endocrine manipulations was examined in granulosa cell cultures. The follistatin mRNA accumulation was stimulated in a dose-dependent manner by follicle-stimulating hormone (FSH) with a maximal response twice as great as in control cultures at a dose of 100 ng/ml FSH. The time course of the FSH effect on follistatin mRNA had a biphasic effect in which FSH increased follistatin mRNA within 2 h, and subsequently reduced it to below the control level. 8-Br-8 brom-adenosine 3,5-cyclic monophosphate (cAMP) (2 mM) and phorbol 12-myristate 13-acetate (PMA) (10 nm) induced a time-dependent increase in follistatin mRNA levels, with the maximal response at 6 h and 2 h, respectively. Co-treatment of the granulosa cells with cAMP and PMA demonstrated that 0.2 mM of 8-Br-cAMP suppressed the follistatin mRNA of the control and the samples with a small amount of PMA in the granulosa cells. Follistatin expression is therefore regulated by protein kinase A and protein kinase C pathways in rat granulosa cells. A more dramatic stimulation of follistatin mRNA was observed when this culture was treated with activin, and follistatin also blocked the effect of activin on the follistatin mRNA.

Regulation of follicle-stimulating hormone receptor messenger ribonucleic acid levels in cultured rat granulosa cells

The acquisition of follicle-stimulating hormone (FSH) receptors during follicogenesis is believed to be a key event in the subsequent development of the follicle. We have examined the effect of FSH on FSH receptor mRNA in cultured rat granulosa cells by means of FSH receptor cRNA probe. Northern blot analysis indicated the existence of two predominant FSH receptor mRNA transcripts of approximately 5.5 and 2.4 kb in total RNA prepared from rat granulosa cells. Treatment of granulosa cell culture with FSH resulted in tentative suppression of FSH receptor mRNA level 2-6 h after treatment, with subsequent recovery at 24 h. Culture of granulosa cells for 6 h in the presence of increasing concentration of FSH resulted in a dose-dependent decrease in FSH receptor mRNA with a maximal suppression about 50% of control observed in response to 100 ng/ml FSH. We could not detect a similar effect on FSH receptor mRNA by 8-brom-adenosine 3,5-cyclic monophosphate (8-Br-cAMP; 0.2 mM) which showed continuous stimulation on FSH receptor mRNA during a similar time course. In this system, therefore, this transient down-regulation of FSH mRNA was not mediated by the cAMP pathway. Since the inhibitory effect of follistatin on activin-induced FSH binding to rat granulosa cells had been investigated, we studied the action of follistatin on the levels of activin-induced FSH receptor mRNA in rat granulosa cell culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Arachidonic acid and cell signalling in the ovary and placenta

Arachidonic acid (AA) and its metabolites make up a diverse group of signalling molecules important to mediation of metabolic and endocrine function of ovarian and placental cell membranes. This paper reviews recent literature examining AA and eicosanoid involvement in the functional dynamics of follicular development, ovulation and corpus luteum function. The putative roles of AA metabolites in establishment and maintenance of pregnancy are reviewed with reference to decidualization, trophoblast invasion and implantation, maintenance of perfusion of the feto-placental unit and lipid transfer. Finally, recent evidence implicating AA metabolism in mediation of enzyme activity following hormone-receptor coupling within various cells types comprising the placental membranes is reviewed.

Steroidogenesis in Fundulus heteroclitus. IV. Dichotomous effects of a phorbol ester on ovarian steroid production and oocyte maturation

The possible role of protein kinase C (PKC) activation in mediating the stimulatory actions of a Fundulus pituitary extract (FPE) on ovarian steroidogenesis and oocyte maturation was investigated. The phorbol ester, phorbol 12-myristate 13-acetate (PMA), alone slightly increased basal 17 alpha-hydroxy,20 beta-dihydroprogesterone (DHP) and 17 beta-estradiol (E2) synthesis and significantly stimulated germinal vesicle breakdown (GVBD). Addition of FPE promoted synthesis of DHP, testosterone (T), and E2, and initiated GVBD. Phorbol ester inhibited FPE-induced steroidogenesis but increased the number of oocytes that underwent GVBD. Phorbol ester also markedly impeded induction of steroidogenesis by dibutyryl cAMP and differentially affected the conversion of 25-hydroxycholesterol, pregnenolone, or progesterone to DHP, T, and E2: DHP production was not affected; T production diminished; and E2 synthesis increased (T aromatization also increased). These results suggest an inhibitory role for the PKC pathway on FPE-induced ovarian steroid production, with PMA appearing to affect various steroidogenic steps. The stimulatory action of PMA on oocyte maturation seems to be independent of follicular steroid production since aminoglutethimide, an inhibitor of steroidogenesis, did not block PMA-induced GVBD. Moreover, PMA had a marked stimulatory effect on GVBD in denuded oocytes. Thus, in contrast to the inhibitory role found for the PKC pathway on ovarian follicular steroidogenesis, activation of PKC in the oocyte may serve as a signal-transducing mechanism leading to GVBD.

Intragonadal signalling mechanisms in the control of steroid hormone production

In the gonads, there are two recognized signal transduction mechanisms which operate in the processing of hormonal stimuli. The gonadotropins, follicle stimulating hormone and luteinizing hormone, act primarily through the generation of cyclic AMP. Several other hormonal regulators in the ovary and the testis, such as gonadotropin releasing hormone and prostaglandin F2 alpha stimulate inositol lipid metabolism following receptor binding. This triggers a cascading mechanism which ultimately results in the generation of increased cytosolic free calcium levels, enhanced protein kinase C activity, and liberation of arachidonic acid. There is also evidence that luteinizing hormone shares in the activation of this pathway. In this review, the significance of these signal transduction pathways is discussed in relation to the effects of various hormones on steroid biosynthesis in the gonads.

Evidence for modulation of progesterone secretion by calcium and protein kinase C activators in ovine chorionic cells

The hypothesis that calcium-dependent mechanisms may be involved in regulating ovine placental steroidogenesis was investigated using chorionic cells isolated by enzymatic digestion. Treatment of the cells with the calmodulin antagonist trifluoperazine (TFP) or pimozide caused a dose-related inhibition of progesterone (P4) production by 80 percent (P less than 0.001) at 40 microM TFP and 56 per cent (P less than 0.001) at 10 microM pimozide. Moreover, the conversion of 25 hydroxycholesterol (25 OH Chol.) to P4 was impaired in the presence of these compounds. These experiments suggest the involvement of a calcium-calmodulin system in the regulation of ovine placental P4 synthesis. Interestingly, calcium ionophore A23187 caused a gradual decline in P4 secretion and completely blocked it at 1 microM (P less than 0.001) and remains absent even in the presence of 25 OH Chol. In contrast, EGTA increased P4 secretion (P less than 0.01). Further, in the presence of 3 mM EGTA the inhibitory effect of 1 microM A23187 was fully reversed. Taken together these results suggest that extracellular calcium could play a role of negative modulation of P4 secretion in these cells. The possible involvement of protein kinase C (PKC) was tested using tumor-promoting phorbol ester (PMA) or permeant diacylglycerols (OAG or DOG). These compounds were unable to modify basal P4 secretion but reduced 25 OH Chol stimulated secretion to basal level. The phorbol ester that was unable to activate PKC had no effect on the metabolism of 25 OH chol. Thus, PMA and diacylglycerol effects are probably mediated by PKC. These data support the hypothesis that PKC activation plays a role in the modulation of cholesterol side-chain cleavage activity in ovine chorionic cells. These results show that calcium-dependent processes are involved in both positive and negative control of P4 secretion by ovine placenta. Our results also suggest a role for calmodulin and PKC pathways in modulating this secretion.

Arachidonic acid stimulates steroidogenesis in goldfish preovulatory ovarian follicles

The possibility that arachidonic acid (AA) plays a role in the regulation of steroidogenesis in goldfish was investigated using preovulatory ovarian follicles incubated in vitro. AA was shown to act in a time- and dose-dependent manner to stimulate testosterone production. AA in the range of 10(-5) to 10(-4) M increased testosterone production within 2 hr and had a maximal effect by 9 hr. The magnitude of the testosterone response to AA was similar to that observed when ovarian follicles were incubated with human chorionic gonadotropin (hCG). Ovarian follicles incubated with AA and either hCG or forskolin (adenylate cyclase activator) produced more testosterone than follicles incubated with either of these compounds alone. The actions of AA on testosterone production were completely blocked by cyclooxygenase inhibitors (indomethacin or ibuprofen) and were reduced by 50% by the lipoxygenase inhibitor nordihydroguaiaretic acid. Phospholipase C was far more effective than phospholipase A2 in the stimulation of testosterone production. Taken together, these results suggest that AA formed subsequent to the action of phospholipase C on membrane phospholipids has a role in the regulation of steroidogenesis in preovulatory goldfish ovarian follicles.

Differential role of protein kinase C in the action of luteinizing hormone-releasing hormone on hormone production in rat ovarian cells

This study was undertaken to determine the involvement of arachidonic acid and protein kinase C in the actions of luteinizing hormone-releasing hormone on steroid and prostaglandin formation in the ovary. In primary culture of rat granulosa cells, treatment with 3 x 10(-7) mol/L melittin stimulates progesterone and prostaglandin E2 accumulation after a 5-hour culture period. Concomitant treatment of the cells with melittin and luteinizing hormone-releasing hormone or 12-0-tetradecanoylphorbol 13-acetate further enhances the stimulatory action of either luteinizing hormone-releasing hormone or 12-0-tetradecanoylphorbol 13-acetate by itself on prostaglandin E2 production. In contrast, no synergistic effects are observed on progesterone production by the same treatments. Treatment with luteinizing hormone-releasing hormone for 24 hours significantly decreases follicle-stimulating hormone-induced progesterone production by approximately 50%. Treatment of the cells with either follicle-stimulating hormone or luteinizing hormone-releasing hormone stimulates prostaglandin E2 production at least tenfold in the same cultures. When follicle-stimulating hormone and luteinizing hormone-releasing hormone are present concomitantly, they synergistically enhance prostaglandin E2 formation (p less than 0.01). Similar effects are observed with the phorbol ester, 12-0-tetradecanoylphorbol 13-acetate, which causes a dose-dependent inhibition of progesterone production by follicle-stimulating hormone whereas follicle-stimulating hormone-stimulated prostaglandin E2 formation is enhanced. Thus luteinizing hormone-releasing hormone-induced activation of protein kinase C may play multiple roles (stimulatory or inhibitory) in hormone production in the ovary.

Inhibition of follicle-stimulating hormone- and adenosine-3',5'-cyclic monophosphate-induced progesterone production by calcium and protein kinase C in the rat ovary

In this study we examined the effects of A23187 (a calcium ionophore) and 12-O-tetradecanoyl phorbol-13-acetate, a known activator of protein kinase C, on progesterone production. Granulosa cells obtained from pregnant mare serum gonadotropin-primed rats were maintained in primary culture. Treatment with follicle-stimulating hormone (0.5 microgram/ml), 8-bromo-adenosine-3',5'-cyclic monophosphate (2 mmol/L), or cholera toxin (0.1 microgram/ml) for 5 hours or 24 hours markedly stimulated progesterone production. The concomitant presence of A23187 attenuated the elevated levels of progesterone induced by follicle-stimulating hormone, 8-bromo-adenosine-3',5'-cyclic monophosphate, or cholera toxin, with or without the presence of a phosphodiesterase inhibitor, 1-methyl-3-isobutylxanthine (0.2 mmol/L). Likewise, treatment of the cells with 12-O-tetradecanoyl phorbol-13-acetate suppressed follicle-stimulating hormone-induced progesterone production, whether or not 1-methyl-3-isobutylxanthine was present in the cultures. The effect of 12-O-tetradecanoyl phorbol-13-acetate was not mimicked by phorbol-13-monoacetate or 4 alpha-phorbol-12, 13-didecanoate. These results indicate that both A23187 and 12-O-tetradecanoyl phorbol-13-acetate inhibit follicle-stimulating hormone-induced progesterone production, in part at a step or steps beyond adenosine-3',5'-cyclic monophosphate generation and degradation. They further support a role of calcium and protein kinase C in the intraovarian action of luteinizing hormone-releasing hormone.