Synergistic effect of insulin and follicle-stimulating hormone on biochemical and morphological differentiation of porcine granulosa cells in vitro

Insulin regulates gap junction intercellular communication in porcine granulosa cells through modulation of connexin43 protein expression

Gap junction intercellular communication (GJIC) among granulosa cells plays an important role in folliculogenesis, and it is temporal-spatially regulated during follicular development. Connexin (Cx) proteins predominantly form the basal structure of gap junctions in granulosa cells. In our study, immunohistochemical analysis revealed that Cx43 is the most widely expressed connexin in porcine follicles, especially among the large antral follicles. With application of insulin on porcine granulosa cells, we found that insulin significantly facilitated the protein level of Cx43, not mRNA level. This process is dependent on the phosphorylated activities of AKT and Erk since selective AKT and Erk inhibitors, LY294002 and U0126, respectively, hampered the potential of insulin to up-regulate Cx43 protein expression. As a consequence, the insulin-enhanced Cx43-couple GJIC activity in porcine granulosa cells was corresponding attenuated by the administration of LY294002 and U0126. Our findings provide a new insight into the molecular mechanisms by which insulin mediates cell-cell communication in porcine granulosa cells and sheds light on nutrition-reproduction interactions.

CAPA-IVM improves the cytoplasmic quality of in vitro-matured oocytes from unstimulated mice

Ovarian tissue oocyte (OTO) in vitro maturation (IVM) is a strategy to improve fertility preservation efficiency. Here, the effects of capacitation IVM (CAPA-IVM) on OTO function were investigated. Immature cumulus-oocyte complexes (COCs) from unstimulated 28-day-old mouse ovaries (mimicking OTOs) underwent CAPA-IVM, standard IVM (S-IVM) or in vivo maturation following ovarian stimulation (OS; positive control), and oocyte meiotic maturation and cytoplasmic quality were assessed. CAPA-IVM resulted in improved oocyte meiotic maturation (P < 0.05) and cumulus expansion (P < 0.0001) compared to S-IVM, with expansion comparable to the OS group. MII OTO ROS was lower after CAPA-IVM than S-IVM (P < 0.0001) but not as low as in the OS group (P = 0.036). CAPA-IVM resulted in a better oocyte mitochondrial distribution than S-IVM (P < 0.05) and was similar to the OS group (P > 0.05). Mitochondrial membrane potential in MII OTOs was higher after CAPA-IVM than S-IVM and OS (P < 0.0001). Compared with S-IVM, CAPA-IVM resulted in lower rates of spindle/chromosome configuration and cortical granule distribution abnormalities (P < 0.05), which were similar to OS levels (P > 0.05). MII OTO intracellular Ca2+ levels were similar in the CAPA-IVM and OS groups (P > 0.05), while S-IVM decreased intracellular Ca2+ (P < 0.05). CAPA-IVM and S-IVM decreased mitochondrial Ca2+ levels (P < 0.05). CAPA-IVM increased expression of antioxidant genes (Sod2 and Sirt1) and Egfr (P < 0.05) but not apoptotic genes (Bcl2, Bax and Bcl2/Bax; P > 0.05). CAPA-IVM increased the OTO maturation rate and quality of oocytes from unstimulated mice to the extent that many features of oocyte cytoplasmic quality were comparable to superovulated in vivo matured oocytes.

Balance of insulin and FSH concentrations improves the in vitro development of isolated goat preantral follicles in medium containing GH

The aim of this study was to evaluate the effect of different combinations of insulin and FSH concentrations in culture media containing GH on the in vitro follicle morphology, antrum formation, growth rates, estradiol (E2) production, oocyte viability and maturation as well as gene expression for FSHR, GHR, INSR, CYP19A1, CYP17, 3ßHSD. Secondary follicles were individually cultured for 18 days in a basic medium containing 50ng/mL GH supplemented with low insulin concentration (INS-LW: 10ng/mL) or high insulin concentration (INS-HG: 10μg/mL) alone or with a fixed FSH concentration (FSH100: 100ng/mL) or with increasing FSH concentrations (FSH-SEQ: 100ng/mL, days 0-6; 500ng/mL, days 6-12; 1000ng/mL days 12-18). In the INS-LW treatment was observed a higher (P<0.05) incidence of normal follicles at day 18 of culture. However, overall higher (P<0.05) follicular growth, oocyte diameter and meiotic resumption rates were obtained using INS-HG+FSH 100. The INS-HG and INS-HG+FSH100 treatments showed higher E2 production and mRNA levels for CYP19A1, CYP17, 3βHSD when compared to INS-LW and INS-LW+FSH100. However, the addition of increasing FSH concentration, regardless of insulin concentration, did not improve the follicular growth, meotic resumption, E2 production or gene expression of steroidogenic enzymes when compared with INS-HG+FSH100. In conclusion, in presence of GH, a basic medium supplemented with 10μg/mL insulin and 100μg/mL FSH throughout the culture period, improves follicular and oocyte growth, oocyte meiotic resumption and E2 production from isolated preantral caprine follicles cultured in vitro.

Increasing cell plating density mimics an early post-LH stage in cultured bovine granulosa cells

Cultured ovarian granulosa cells are essential models to study molecular mechanisms of gene regulation during folliculogenesis. Here, we characterize primary tissue culture models for bovine granulosa cells by morphological and physiological parameters and by novel molecular luteinization markers, as transcript abundance and DNA methylation levels. The data show that: (1) collagen substrate increased the number of attached, viable cells; (2) the expression of the key transcripts of estrogen synthesis, CYP19A1, could be induced and maintained in granulosa cells from small to medium but not from large follicles, whereas (3) only granulosa cells from large but not from smaller follicles were responsive to LH; (4) serum supplementation unfavorably transformed the cellular phenotype, induced proliferation and PCNA expression, reduced or abolished the transcript abundance of steroidogenic key genes and of gonadotropin receptor genes, CYP11A1, CYP19A1, FSHR and LHCGR but, however, did not increase the abundance of the luteinization-specific marker transcripts PTGS2, PTX3, RGS2 and VNN2; but (5) by increasing the plating density, estradiol production and the abundance of CYP19A1 transcripts, in particular those derived from the main ovarian promoter P2, were decreased concurrently leaving P2-specific DNA methylation levels unchanged, whereas progesterone secretion was stimulated and the expression of both luteinization-specific marker transcripts, RGS2 and VNN2, was significantly induced. From these data, we conclude that increasing the plating density induces a different, partly complementary, physiological and gene expression profile in cultured bovine granulosa cells and drives the cells towards an early post-LH stage of luteinization, even in the absence of luteinizing agents.

Estrogen biosynthesis in the gonad of the frog Rana rugosa

In certain species of amphibians gonadal differentiation is influenced by steroid hormones. In the case of the frog Rana rugosa testosterone given to tadpoles reverses sex from female to male, while the opposite reversal - male to female - can be achieved using estradiol-17β. In this study, we investigated whether CYP19 (P450 aromatase), the enzyme responsible for a production of estradiol-17β, was present in the differentiating gonad of R. rugosa. Initially, we immunized rabbits against frog CYP19 peptides and performed immunostaining using specific antibodies purified from that serum. CYP19-reactive signals were observed in gonadal somatic cells of the female, but not male tadpoles at stage (St.) I (the stage prior to phenotypic sex determination in tadpoles of R. rugosa). Immunopositive signals were also produced in ovarian somatic cells froglets at St. XXV (just after the completion of metamorphosis). We also examined the enzymatic activity of CYP19 in the differentiating gonad of R. rugosa. Reverse-phase HPLC (high performance liquid chromatography) analysis revealed that [(3)H]testosterone was converted to [(3)H]estradiol-17β in the gonad of tadpoles at St. I. Interestingly, the rate of conversion was much higher in females than in males. To the best of our knowledge, this is the first report on the biosynthesis of estradiol-17β in the gonad of amphibians, and the co-incident identification of active CYP19 enzyme in the differentiating gonad of R. rugosa. Based on our results, we conclude that estradiol-17β may be involved in ovarian differentiation in this species.

Expression of P450 aromatase protein in developing and in sex-reversed gonads of the XX/XY type of the frog Rana rugosa

Gonadal differentiation in some species of amphibians is sensitive to steroids. The phenotypic sex of XX/XY-type frogs such as Rana rugosa can be reversed from female to male by injection of testosterone into tadpoles, but little is known about the molecular mechanism of this sex reversal. To elucidate the mechanism of the sex differentiation, we examined the role of P450 aromatase (P450arom), an enzyme that converts testosterone to estrogen, during gonadal differentiation of amphibians. In this study, we first cloned a P450arom cDNA homolog of the frog R. rugosa and analyzed by RT-PCR its expression profile in developing and in female-to-male sex-reversed gonads. P450arom expression was observed in the gonad of tadpoles during ovarian differentiation and became much stronger in the developing ovary in which only immature oocytes were observed. However, its expression declined significantly in the ovary of frogs 2 months after metamorphosis, when oocytes were growing; and it was no longer seen in adult ovaries. By RT-PCR, we also examined the expression of P450arom and SF-1 (steroidogenic factor-1; the orphan nuclear receptor) in the female-to-male sex-reversed gonad. The level of P450arom mRNA was high in the ovary, but it declined rapidly after the injection of testosterone. In contrast, no change in the SF-1 (also known as Ad4BP) expression was observed. Moreover, to identify the type(s) of cells expressing P450arom protein, we performed immunostaining with an antibody against frog P450arom protein. Cells giving positive signals were observed around oocytes in the ovary of frogs 1 month after metamorphosis. They were identified as follicle cells by both light and electron microscopy. The results, taken together, indicate that P450arom protein is synthesized in follicle cells and that P450arom is very much involved in ovarian differentiation in R. rugosa.

Activin promotes oocyte development in ovine preantral follicles in vitro

Activins have been implicated as important regulating factors for many reproductive processes. The aim of this study was to determine the effect of activin A on the development of ovine preantral follicles in vitro. Mechanically isolated preantral follicles (161 +/- 2 microm) were cultured for 6 days in the presence of human recombinant activin A (0, 10 and 100 ng/ml). Half of the medium was replaced every second day and follicle diameters were measured. Conditioned medium was subsequently analysed for oestradiol content using a delayed enhancement lanthanide fluorometric immunoassay (DELFIA). At the end of the culture period, follicles were fixed and processed for histology, after which oocyte diameter and granulosa cell death were measured. There was significant follicle growth over 6 days in all groups (p < 0.001). Activin, at both concentrations, increased follicle growth over control levels by Day 6 (p < 0.05). Oocyte diameters were also significantly increased by Day 6 of culture in all groups (p < 0.05), with 100 ng/ml activin increasing oocyte diameter over control levels (p < 0.05). Activin, at both concentrations, increased oestradiol production on Day 2 of culture, but this increase was not sustained during the culture period. Moreover, activin did not have any effect on antrum formation or follicle survival. In conclusion, activin promoted ovine preantral follicle and oocyte growth in vitro, but did not accelerate follicle differentiation over a six-day culture period. These results support a paracrine role for activin A during early oocyte and follicular development.

Cellular target of weak magnetic fields: ionic conduction along actin filaments of microvilli

The interaction of weak electromagnetic fields (EMF) with living cells is a most important but still unresolved biophysical problem. For this interaction, thermal and other types of noise appear to cause severe restrictions in the action of weak signals on relevant components of the cell. A recently presented general concept of regulation of ion and substrate pathways through microvilli provides a possible theoretical basis for the comprehension of physiological effects of even extremely low magnetic fields. The actin-based core of microfilaments in microvilli is proposed to represent a cellular interaction site for magnetic fields. Both the central role of F-actin in Ca2+ signaling and its polyelectrolyte nature eliciting specific ion conduction properties render the microvillar actin filament bundle an ideal interaction site for magnetic and electric fields. Ion channels at the tip of microvilli are connected with the cytoplasm by a bundle of microfilaments forming a diffusion barrier system. Because of its polyelectrolyte nature, the microfilament core of microvilli allows Ca2+ entry into the cytoplasm via nonlinear cable-like cation conduction through arrays of condensed ion clouds. The interaction of ion clouds with periodically applied EMFs and field-induced cation pumping through the cascade of potential barriers on the F-actin polyelectrolyte follows well-known physical principles of ion-magnetic field (MF) interaction and signal discrimination as described by the stochastic resonance and Brownian motor hypotheses. The proposed interaction mechanism is in accord with our present knowledge about Ca2+ signaling as the biological main target of MFs and the postulated extreme sensitivity for coherent excitation by very low field energies within specific amplitude and frequency windows. Microvillar F-actin bundles shielded by a lipid membrane appear to function like electronic integration devices for signal-to-noise enhancement; the influence of coherent signals on cation transduction is amplified, whereas that of random noise is reduced.

Effects of propylene glycol drenching on energy balance, plasma glucose, plasma insulin, ovarian function and conception in dairy cows

We postulated that daily drenching of propylene glycol to cows in early lactation would increase plasma glucose and insulin concentrations and improve fertility in postpartum cows. Thirty-six Holstein cows were assigned to treatment or control groups. Each treatment cow was given 500 ml of propylene glycol by drenching daily from 7 to 42 days of lactation. Blood samples for glucose, insulin, nonesterified fatty acids (NEFA), and plasma urea N were collected at 0, 30, and 90 min postdrenching once weekly during 1-6 weeks. Blood samples were collected for progesterone analysis and cows were palpated three times per week until 11 weeks to assess ovarian status. Propylene glycol did not affect dry matter intake (DMI), milk yield or energy balance in treatment cows. After drenching, propylene glycol increased (P<0.01) plasma glucose and insulin and decreased (P<0.01) NEFA; plasma urea N of the treatment group tended (P=0.07) to be higher than that of the control group through 90 min. Days to first service, days open, and services per conception were not different between groups. Conception rates to first insemination were 33% in the control group and 57% in treated cows, but these were not significantly different. First ovulation of treatment cows occurred earlier than that of control cows (32.3 versus 44.5 days, P=0.06) and the length of the first luteal phase was longer in treated cows (13.1 versus 7.3 days, P<0.05). These data are consistent with the hypothesis that insulin is important for normal ovarian function. During negative energy balance, treatment with propylene glycol, which induced small increases in plasma concentrations of insulin, prevented the short luteal phase characteristic of the first estrous cycle in control cows.

Feed restriction and insulin treatment affect subsequent luteal function in the immediate postovulatory period in pigs: progesterone production in vitro and messenger ribonucleic acid expression for key steroidogenic enzymes

Progesterone production and release in vitro, and mRNA expression for key steroidogenic enzymes, were studied in luteal tissue recovered in the immediate postovulatory period from cyclic gilts allocated to one of three treatments: moderate feed restriction during the first (RH) or second week of the estrous cycle, with (HR+I) or without (HR) concomitant injections of long-acting insulin. Time of feed restriction affected neither progesterone production or release, nor mRNA expression for several key steroidogenic enzymes. However, luteal tissue from RH but not from HR gilts responded to LH stimulation by increasing progesterone production and release (P: < 0.05). Insulin treatment increased progesterone production and release, restored luteal tissue responsiveness to LH, up-regulated steroidogenic enzyme mRNA expression, and down-regulated the tissue inhibitor of metalloproteinase-I mRNA expression in HR+I compared with HR gilts (P: < 0.05). In vitro progesterone production and gene expression were affected by time of tissue collection after ovulation in RH and HR gilts but not in HR+I gilts, and were correlated with temporal changes in oviductal and peripheral plasma progesterone concentrations. Inherent differences in luteal function therefore appear to mediate latent effects of nutrition and insulin treatment on circulating progesterone concentrations in the critical postovulatory period in gilts.

Establishment and characterization of steroidogenic granulosa cells expressing beta(2)-adrenergic receptor: regulation of adrenodoxin and steroidogenic acute regulatory protein by adrenergic agents

Primary granulosa cells obtained from PMSG primed immature rats were triple transfected with SV40 DNA, Ha-ras oncogene and an expression vector containing human beta(2)-adrenergic receptors resulting in granulosa cell lines constitutively expressing the beta(2)-adrenergic receptors. Isoproterenol, a potent adrenergic agent, stimulated both cAMP accumulation and progesterone production in these cells in a dose dependent manner. Responsiveness of these cells was specific only to isoproterenol, while hCG (2.4 nM) and hFSH (2.4 nM) had no effect on steroid production. ED(50) for stimulation of cAMP and progesterone in these cells by isoproterenol was 2x10(-6) M and 7x10(-6) M, respectively. Forskolin also showed a dose dependent stimulation of cAMP and progesterone with ED(50) of 1.5 and 0.35 microg/ml, respectively. Epinephrine at a dose of 10(-5) M elicited maximum response to produce cAMP and progesterone. Isoproterenol induced accumulation of cAMP and progesterone in these cells were inhibited by beta(2)-adrenergic blocker, propranolol with an ED(50) of 6x10(-8) and 7x10(-9) M, respectively, whereas the beta(1)-adrenergic blocker, metoprolol was effective only at a very high concentration (ED(50)>10(-4) and 1.9x10(-5) M for inhibiting isoproterenol induced cAMP and progesterone production, respectively). Induction of steroidogenesis by isoproterenol or forskolin involved de novo synthesis of the cytochrome P450 side chain cleavage (SCC) enzyme complex, as assessed by indirect immunofluorescence staining for adrenodoxin. Western analysis indicate that expression of adrenodoxin is upregulated by forskolin, isoproterenol and adrenalin by 7.8-, 6.9- and 10.8-fold, respectively. The presence of StAR protein was identified by Western blotting. StAR expression was elevated by 8.3-, 2.5- and 4.7-fold upon stimulation with forskolin, isoproterenol and adrenalin, respectively. Thus, this cell line could serve as a good model system to study catecholamine mediated regulation of growth and differentiation of granulosa cells and the role of oncogenes in this process.

Conditions that affect acquisition of developmental competence by mouse oocytes in vitro: FSH, insulin, glucose and ascorbic acid

The simplest unit required for the support of oocyte growth and development is the oocyte-granulosa cell complex. Therefore, a culture system was established that utilizes these complexes to assess mechanisms promoting nuclear, cytoplasmic and genomic maturation in mammalian oocytes. Deletion of serum from the culture, results in increased apoptosis in oocyte-associated granulosa cells (OAGCs), however, addition of ascorbic acid (0.5 mM) significantly reduced the level of apoptosis in the OAGCs, although no improvement of oocyte developmental competence was detected. The effects of reducing glucose during oocyte growth were studied since, under some culture conditions, glucose has deleterious effects on early preimplantation development. Reducing the glucose concentration to 1 mM resulted in the production of oocytes with greatly reduced developmental competence. Deleterious effects of FSH plus insulin during oocyte growth in vitro on preimplantation development are reviewed and discussed in terms of the communication of oocytes with inappropriately developing granulosa cells. Evidence that oocytes promote the appropriate differentiation of OAGCs in intact follicles in vivo is also discussed. It is hypothesized that oocytes control the differentiation of these cells, in order to promote intercellular signaling essential for the acquisition of competence to undergo normal embryogenesis.

Comparison of protein synthesis patterns in mouse cumulus cells and mural granulosa cells: effects of follicle-stimulating hormone and insulin on granulosa cell differentiation in vitro

Successful development of mammalian oocytes requires correct interactions between developing oocytes and associated granulosa cells. Development of oocyte-granulosa cell complexes from preantral follicles in vitro does not produce oocytes competent to develop to blastocysts at the same frequency as for oocytes that develop in vivo. Addition of either FSH or insulin to cultures of oocyte-granulosa cell complexes does not improve the frequency of blastocyst development, and the combination of both insulin and FSH is deleterious. Here, high-resolution 2-dimensional PAGE (2D-PAGE) and computerized gel image analysis were used to compare patterns of protein synthesis in cumulus cells and mural granulosa cells of small antral follicles, and then to assess effects of FSH and insulin on the differentiation of oocyte-associated granulosa cells (OAGCs) in vitro. Culture of OAGCs without FSH or insulin resulted in failure to synthesize many proteins at rates characteristic of cumulus cells. Either hormone used alone caused many cumulus cell proteins that were decreased in control cultures to be synthesized at nearly normal cumulus cell rates, and also caused the synthesis of other proteins to be increased or decreased. The two hormones added together produced the greatest change in protein synthetic pattern, including overexpression or underexpression of many proteins not affected by either hormone alone. Addition of these hormones to culture media thus appeared insufficient to elicit a normal cumulus cell phenotype in OAGCs and could lead to complex changes in protein synthesis that may be deleterious to oocyte development. The high-resolution 2D-PAGE approach described here should be a valuable tool in studies on oocyte and granulosa cell development in vitro, since phenotype can be evaluated globally through the display of over 1000 newly synthesized proteins rather than relying upon the expression of just a few genes.

Relaxin secretion and gene expression in porcine granulosa and theca cells are stimulated during in vitro luteinization

During formation of the corpus luteum, the primary source of relaxin switches from theca cells (TC) to granulosa-derived, large luteal cells. What controls this shift in relaxin production is poorly understood. The objective of this study was to observe the effect of luteinization on relaxin gene expression and secretion by porcine granulosa (GC) and TC using an in vitro model. TC and GC from medium-sized porcine follicles (4-6 mm) were treated for up to 8 days with LH (250 ng/ml) and/or insulin-like growth factor-I (IGF-I; 10 ng/ml). Media were assayed for relaxin and progesterone by RIA, changes in cell morphology were recorded, and total RNA was subjected to reverse transciption-polymerase chain reaction to monitor relaxin gene expression. In vitro luteinization, induced with LH + IGF-I treatment, was confirmed in both GC and TC by a change in morphology and a sustained, significant rise in progesterone secretion. In luteinizing GC, relaxin secretion was first detected after 5 treatment days, and steadily rose until it became significantly higher (p < 0.001) by treatment Days 7-8. In contrast, relaxin release from luteinizing TC was significant after only 2 days of treatment (p < 0.05) and increased consistently over the 8-day culture period (p < 0.001). In GC, relaxin mRNA was not detected until treatment Day 4 and became significantly higher (p < 0.001) by Day 8, the final treatment day. Relaxin transcript in luteinizing TC was low on treatment Days 2-4 and significantly higher (p < 0.01) by treatment Days 6 and 8. In summary, the present study demonstrates that hormones important in the control of luteinization are essential for regulating relaxin gene expression and secretion by GC and TC in the porcine follicle.

Factors affecting the developmental competence of mouse oocytes grown in vitro: follicle-stimulating hormone and insulin

This study was undertaken to test the hypothesis that FSH treatment of cultured oocyte-granulosa cell complexes promotes acquisition of competence to complete preimplantation embryo development. Oocyte-granulosa cell complexes were isolated from the preantral follicles of 12-day-old mice and cultured for 10 days in serum-free medium, supplemented with insulin (5 microgram/ml), transferrin (5 microgram/ml), and selenium (5 ng/ml) and containing a highly potent preparation of FSH (0-5 ng/ml). Oocytes were matured and fertilized in vitro and embryos cultured to determine the frequency of development to the blastocyst stage. There was no effect of FSH on oocyte size, general morphology, or competence to resume meiosis. However, addition of FSH to medium containing insulin had a deleterious effect on the percentage of mature oocytes competent to develop to the blastocyst stage. Deletion of insulin from the medium for culture of oocyte-granulosa cell complexes prevented the deleterious effect of FSH, but FSH still did not promote acquisition of competence to complete preimplantation development. Culture of oocyte-granulosa cell complexes with FSH resulted in elevated expression of LH receptor (LHR) mRNA by granulosa cells and stimulated the production of functional LHRs, whether or not insulin was present. However, FSH-induced expression of LHR mRNA reached a maximum steady-state level by 4 days of culture in the presence of insulin, but this level was not reached until 10 days of culture without insulin. Granulosa cells encompassing growing mouse oocytes in vivo do not express LHR mRNA. Thus, expression of LHR mRNA by granulosa cells closely associated with growing oocytes in vitro indicates inappropriate or ambiguous development. In conclusion, conditions occurring during oocyte growth can have profound detrimental effects on oocyte developmental competence to complete preimplantation development, even when oocyte growth, general morphology, and competence to resume meiosis appear unaffected.

Effect of insulin-like growth factor I and its interaction with gonadotropins on in vitro maturation and embryonic development, cell proliferation, and biosynthetic activity of cumulus-oocyte complexes and granulosa cells in buffalo

In this study we have examined the effect of insulin like growth factor I (IGF-I) and its interaction with gonadotropins in the presence or absence of granulosa cell coculture on in vitro oocyte maturation (IVM) and their subsequent embryonic development in buffalo. We also have examined the role of IGF-I alone or in combination with gonadotropins on DNA synthesis, steroidogenesis, and protein synthesis of cumulus-oocytes complexes (COCs) and granulosa cells. Results showed that IGF-I stimulates oocytes maturation in a dose-dependent manner, with maximal effect at a dose of 100 ng/ml (P < 0.05). IGF-I showed positive interaction with follicle-stimulating hormone (FSH) in the presence or absence of granulosa cells on meiotic maturation and synergistically enhanced DNA synthesis, protein synthesis, and steroidogenesis in the presence of granulosa cells. This synergistic effect is mainly caused by the increase of IGF-I receptors in granulosa cells by FSH, as evident by [125I]IGF-I binding study. Luteinizing hormone (LH), however, was found to suppress IGF-I and IGF-I + FSH stimulated oocyte maturation. Addition of LH to cultures containing IGF-I + FSH, on the contrary, caused a significant increase in oocyte maturation when cocultured with granulosa cells. Addition of IGF-I during IVM significantly improve cleavage and blastocyst development rate over the control group. However, there was no cumulative effect when IGF-I and gonadotropins were present together. Addition of granulosa cells during IVM, however, enhanced blastocyst development in the IGF-I + FSH and IGF-I + FSH + LH groups. Our results demonstrated that IGF-I is a major follicular factor responsible for stimulating oocyte maturation in the buffalo. Interaction between IGF-I and FSH suggests that they seem to act synergistically as an autocrine and paracrine regulator of granulosa cells and therefore together promote mitosis, steroidogenesis, and protein synthesis.

A first catalog of genes involved in pig ovarian follicular differentiation

As a first step toward the characterization of genetic expression in pig ovaries, we have selected 238 clones by differential hybridization from a pig granulosa cell cDNA library, using probes prepared from RNA extracted from either untreated or FSH-treated cells and, in order to generate expressed sequence tags (ESTs), we have performed 3' and 5' single-pass sequencing of these clones. Sequences of the 3' end of the 167 clones that produced informative sequence data were first compared with each other, revealing a redundancy level of 21%. Sequences from the 136 unique clones were analyzed for similarities with sequence data included in Genbank and EMBL databases. Among these unique clones, 54 (40%) matched significantly with sequences from either Genbank of EMBL: 4 with known genes in pig, 35 matched with previously reported human genes, and 15 with other mammalian genes. Eighty-two clones (60%) showed no significant match with any gene or DNA sequence in the Genbank and EMBL databases and thus may represent new pig transcripts.

Cross-talk between cAMP and p53-generated signals in induction of differentiation and apoptosis in steroidogenic granulosa cells

In each menstrual cycle only very few follicles in the mammalian ovary undergo maturation and ovulation while most of the follicles degenerate in the process of atresia. Moreover, in the absence of pregnancy, the newly formed corpora lutea will degenerate and disappear in the process of luteolysis. Recent studies suggest that ovarian follicular atresia is associated with DNA fragmentation and degeneration of follicular cells, characteristics of programmed cell death (apoptosis). Apoptosis can be induced in vitro, in primary granulosa cell culture, by serum deprivation and by induction of a high intracellular level of cAMP. This induction of apoptosis can be blocked by fibroblast growth factor, suggesting that receptor-medicated activation of a tyrosine kinase can serve as a survival signal. Apoptosis can also be induced in immortalized steroidogenic granulosa cells, transformed by SV40 DNA and Ha-ras oncogene, by overexpression of the wild-type p53 tumor suppressor gene in cAMP-stimulated cells. Omitting the cAMP stimulus prevents the p53-induced apoptosis in these cells, suggesting cross-talk between p53 and c-AMP-generated signals in the induction of apoptosis. Steroidogenic activity in these cells, as well as in nontransformed granulosa cells, does not decline during apoptosis but is rather significantly elevated before total cell collapse occurs. Cytochemical studies using confocal laser microscopy, electron microscopy, and three-dimensional reconstruction reveal a specific reorganization pattern of proteasomes, the most abundant nonlysosomal protease, and of the steroidogenic organelles, such as mitochondria and lipid droplets, in the apoptotic cell. Our results suggest that compartmentalization of intracellular organelles during apoptosis permits proteolysis without interfering with steroidogenesis, characteristic of the differentiated phenotype of the granulosa cell. Moreover, cytoskeletal rearrangement may serve as a barrier between these cellular activities.

Protein kinase C inhibition of in vitro FSH-induced differentiation in pig granulosa cells

In granulosa cells, growth factor IGF I plays a major role in both growth and differentiation, acting through an autocrine/paracrine mechanism, and its production is regulated by FSH, via cyclic AMP (cAMP). As protein kinase C is also involved in granulosa cell function, we investigated the possibility that its activation could balance the positive effects of FSH. Using pig granulosa cells cultured in vitro, we studied the effects of protein kinase C activation by tetradecanoylphorbol acetate (TPA) on IGF I mRNA level. We also checked morphological modifications, cAMP production and steroidogenesis at the P450 side chain cleavage mRNA and progesterone levels. Our data demonstrate that protein kinase C activation antagonizes the in vitro FSH-induced differentiation, particularly morphological modifications and accumulation of IGF I mRNA. These inhibitory effects on FSH responses suggest that there could be a balance between protein kinase A and protein kinase C pathways in regulating differentiation in pig granulosa cells.

Increased insulin secretion in patients with multifollicular and polycystic ovaries and its impact on ovulation induction

OBJECTIVE

To assess the oral glucose tolerance test (OGTT)-stimulated insulin secretion and its relation to pulsatile GnRH ovulation induction outcome in patients with multifollicular or polycystic ovaries (PCOs).

DESIGN

Prospective study.

SETTING

Reproductive Endocrinology Center, University of Bologna, Bologna, Italy.

PATIENTS

Eight normal and 29 anovulatory women (8 with multifollicular ovaries and 21 with PCOs).

INTERVENTION

A standard OGTT was performed in all subjects. In all anovulatory patients, ovulation was induced with pulsatile GnRH (5 micrograms i.v. every 60 minutes). In multifollicular ovary patients, pulsatile GnRH was administered alone, whereas in PCOs it was preceded by GnRH agonist (GnRH-a) suppression.

MAIN OUTCOME MEASURES

Glucose, insulin, and C-peptide response to the OGTT, expressed as area under the curve (AUC). Ovulatory rates in response to pulsatile GnRH.

RESULTS

Insulin and C-peptide AUC were greater than controls in both multifollicular ovary and PCO patients. Insulin AUC was positively correlated to ovarian volume. Ovulation was achieved in 88% and 57% of multifollicular ovary and PCO patients, respectively. Body mass index and glucose AUC but not insulin and C-peptide AUC were significantly greater in the anovulatory PCO.

CONCLUSIONS

[1] Insulin AUC was increased in both multifollicular ovary and PCO patients; [2] derangements of insulin secretion may be present in a greater variety of anovulatory patients than previously thought; [3] insulin levels during the OGTT did not predict a response to pulsatile GnRH in PCOs, suggesting complex insulin interactions at the ovarian level; [4] given the in vitro stimulatory properties of insulin on granulosa cells synergistic with FSH, we propose that excessive insulin levels may contribute to the ovarian enlargement often found in multifollicular ovary and PCO patients.

Plasticity of cell organization during differentiation of normal and oncogene transformed granulosa cells

Granulosa cells, which nurse the oocyte and serve as a major source for estradiol and progesterone production, undergo major morphological changes which correlate very well with modulation of their steroidogenic capacity. These include changes in intercellular contacts and communication, in cell membrane receptors, and in the development and organization of organelles associated with steroidogenesis (i.e., mitochondria, smooth endoplasmic reticulum, lipid droplets, and lysosomes). These biochemical and morphological changes can also be obtained in primary cultures as well as in oncogene transformed granulosa cell lines established recently in our laboratory. A growing body of evidence suggests that plasticity of the cytoskeleton plays a major role in the biochemical and morphological differentiation of granulosa cells as well as in other steroidogenic cells.

Establishment of steroidogenic granulosa cell lines expressing follicle stimulating hormone receptors

Follicle stimulating hormone (FSH) plays an important role in the regulation of oogenesis, spermatogenesis and production of steroid hormones. Receptors to FSH, which are uniquely expressed in ovarian granulosa and testicular Sertoli cells, are rapidly lost in tissue culture conditions and upon cell transformation. We have succeeded, by triple transfection of primary rat granulosa cells with SV40 DNA, Ha-ras oncogene and an FSH receptor expression plasmid, to establish stable steroidogenic cell lines expressing FSH receptors. The cell lines respond to rat, ovine and bovine FSH, which stimulate progesterone production at levels comparable to primary granulosa cells obtained from preovulatory follicles. No steroidogenic response is detected upon stimulation with ovine luteinizing hormone or human chorionic gonadotropin. The steroidogenic response is accompanied by de novo appearance of adrenodoxin which serves as a marker for the mitochondrial steroidogenic enzyme system. These cells express approximately 27,000 receptors per cell with a Kd of 100-115 pM. This Kd is close to the value calculated for the native receptor. The ED50 for the steroidogenic response to ovine FSH is 200 pM, suggesting a tight coupling between receptor activation and the steroidogenic response. FSH induces pronounced morphological changes in the established cell lines, which are also characteristic of primary granulosa cells. These FSH responsive cell lines can serve as a useful model for the study of the structure and function of the FSH receptor and the effect of oncogenes on its expression.

Diabetes prevents the normal responses of the ovary to FSH

FSH in vitro stimulates increased oxygen uptake by isolated follicular granulosa cells from immature rats treated with diethylstilbestrol (DES) when substrates are present (glucose, glutamate, pyruvate or fumerate) or are completely absent. However, when glucose is the only substrate or when any single substrate is omitted from the buffer, FSH has no effect. FSH in vitro also increases the uptake of glucose and the formation of 14CO2 from [1-6 14C]-glucose. Granulosa cells from diabetic immature rats treated with DES did not show increased oxygen uptake with in vitro FSH. Diabetic cells had similar receptor binding of FSH to that of control non-diabetic cells. The addition of both insulin and FSH in vitro to buffer with diabetic granulosa cells gave increased oxygen uptake over that of control cells from diabetic rats. The insulin stimulation of oxygen uptake by FSH in cells from diabetic rats was not duplicated by either epidermal growth factor (EGF) or insulin-like growth factor I (IGF-1). Follicle counts of ovaries from diabetic and control immature rats treated with DES showed increased atresia in the diabetic ovaries after only 44 hr. of diabetes. Follicle counts of ovaries from adult diabetic rats showed increased atresia in 24 hours after induction of diabetes at proestrus. Follicle counts of pseudopregnant rats showed increased atresia by 3 days after diabetes was induced. We conclude that diabetes prevents normal follicle growth stimulated either by exogenous DES or by endogenous hormones secreted during proestrus.

Culture of bovine granulosa cells in a chemically defined serum-free medium: the effect of insulin and fibronectin on the response to FSH

Granulosa cells from fully differentiated bovine follicles were cultured in serum-free medium for 4 days. At the end of culture, the number of viable cells was low (10-15% of cells plated on day one) and only progesterone secretion responded to FSH. Insulin increased the number of viable cells at the end of culture (ED50 # 70 ng/ml) and stimulated progesterone secretion (ED50 # 50 ng/ml); the secretion of oestradiol-17 beta over basal value was evident only for concentrations of 1000 and 10,000 ng/ml. FSH acted synergistically with insulin to modify steroid secretion. In the presence of 50 ng/ml of insulin, dose-response studies indicated that secretion of progesterone was maximal at 10 ng/ml of FSH and plateaud thereafter, while oestradiol output peaked at 2 ng/ml of FSH, decreasing at higher concentrations. When cells were seeded in wells precoated with fibronectin, a comparison with cells cultured on plastic showed an increase (30-40%) in the number of viable cells at the end of culture and in oestradiol secretion but a decrease in progesterone output. These results indicate that granulosa cells from large bovine follicles, cultured in a serum-free medium containing insulin, maintain their steroidogenic potency for at least 4 days. Moreover, they show that oestradiol and progesterone synthesis are differentially sensitive to FSH concentrations and that fibronectin increases oestradiol secretion in response to FSH.

Coordinated regulation of morphological and biochemical differentiation in a steroidogenic cell: the granulosa cell model

Studies on the dynamic biochemical and morphological events occurring during steroidogenesis in granulosa cells suggest that the organization and expression of the actin-cytoskeleton may play a major role in the transduction of endocrine and paracrine steroidogenic signals, and in the coordination between the organelles involved in this process. Since steroid hormones are not stored intracellularly, regulation of their production is dependent mainly on the expression of genes coding for membrane-bound steroidogenic enzymes. Recently, the expression of oncogenes of the ras family was also implicated in the regulation of steroidogenesis.