Transforming growth factor beta enhances basal and FSH-stimulated inhibin production by rat granulosa cells in vitro

Effects of miR-101-3p on goat granulosa cells in vitro and ovarian development in vivo via STC1

Background

MiRNAs act as pivotal post-transcriptional gene mediators in the regulation of diverse biological processes, including proliferation, development and apoptosis. Our previous study has showed that miR-101-3p is differentially expressed in dairy goat ovaries compared single with multiple litters. The objective of this research was to explore the potential function and molecular mechanism of miR-101-3p via its target STC1 in goat ovarian growth and development.

Results

cDNA libraries were constructed using goat granulosa cells transfected with miR-101-3p mimics and negative control by RNA-sequencing. In total, 142 differentially expressed unigenes (DEGs) were detected between two libraries, including 78 down-regulated and 64 up-regulated genes. GO and KEGG enrichment analysis showed the potential impacts of DEGs on ovarian development. STC1 was singled out from DEGs for further research owing to it regulates reproductive-related processes. In vitro, bioinformatics analysis and 3′-UTR assays confirmed that STC1 was a target of miR-101-3p. ELISA was performed to detect the estrogen (E2) and progesterone (P4) levels. CCK8, EdU and flow cytometry assays were performed to detect the proliferation and apoptosis of granulosa cells. Results showed that miR-101-3p regulated STAR, CYP19A1, CYP11A1 and 3β-HSD steroid hormone synthesis-associated genes by STC1 depletion, thus promoted E2 and P4 secretions. MiR-101-3p also affected the key protein PI3K, PTEN, AKT and mTOR in PI3K-AKT pathway by STC1, thereby suppressing proliferation and promoting apoptosis of granulosa cells. In vivo, the distribution and expression levels of miR-101-3p in mouse ovaries were determined through fluorescence in situ hybridisation (FISH). Immunohistochemistry results showed that STC1 expression was suppressed in mouse ovaries in miR-101-3p-agonist and siRNA-STC1 groups. Small and stunted ovarian fragments, decreased numbers of follicles at diverse stages were observed using Hematoxylin-eosin (HE) staining, thereby showing unusual ovarian development after miR-101-3p overexpression or STC1 depletion. Inhibition of miR-101-3p manifested opposite results.

Conclusions

Taken together, our results demonstrated a regulatory mechanism of miR-101-3p via STC1 in goat granulosa cells, and offered the first in vivo example of miR-101-3p and STC1 functions required for ovarian development.

Effects o follicular fluid oxidative status on human mural granulosa cells, oocyte competency and ICSI parameters

PURPOSE

The aim of the present study was to understand the molecular and genetic alterations involved in follicular fluid oxidative process by investigating human mural granulosa cells and to find possible biomarkers for oocyte competency and ICSI outcome measures.

METHODS

A total of 166 patients were included in the study. Total antioxidant and oxidant levels of follicular fluids were measured on the day of oocyte pick-up and oxidative status were calculated. Expression profiles of three potential target proteins in cases of oxidative stress (Hsp70, Tgf-β, Notch1), DNA status and chromatin integrity of mural granulosa cells were analyzed.

RESULTS

TAS levels were positively correlated with the Hsp70 and Tgf-β expression patterns of mural granulosa cells. Mature oocyte rate and fertilization rates were affected negatively by the presence of oxidative stress and a significant positive correlation was found with the oxidative status and the fertilization rate, whereas no correlation with the remaining ICSI parameters in the overall group.

CONCLUSIONS

Oxidative stress detected in follicular fluid adversely affects fertilization rates post-ICSI however no effect on the remaining parameters including embryo quality, pregnancy, and implantation rates. DNA damage, chromatin integrity were increased, whereas Hsp70 and Tgf-ß were decreased in mural granulosa cells in cases of oxidative stress which may indirectly reflect the oocyte competency and may be used as biomarkers for ICSI outcome measures.

CRTC2 and Nedd4 ligase involvement in FSH and TGFβ1 upregulation of connexin43 gap junction

The major mission of the ovarian follicle is the timely production of the mature fertilizable oocyte, and this is achieved by gonadotropin-regulated, gap junction-mediated cell-cell communication between the oocyte and surrounding nurturing granulosa cells. We have demonstrated that FSH and transforming growth factor beta 1 (TGFβ1) stimulate Gja1 gene-encoded connexin43 (Cx43) gap junction formation/function in rat ovarian granulosa cells is important for their induction of steroidogenesis; additionally, cAMP-protein kinase A (PKA)- and calcium-calcineurin-sensitive cAMP response element-binding (CREB) coactivator CRTC2 plays a crucial role during steroidogenesis. This study was to explore the potential molecular mechanism whereby FSH and TGFβ1 regulate Cx43 synthesis and degradation, particularly the involvement of CRTC2 and ubiquitin ligase Nedd4. Primary culture of granulosa cells from ovarian antral follicles of gonadotropin-primed immature rats was used. At 48 h post-treatment, FSH plus TGFβ1 increased Cx43 level and gap junction function in a PKA- and calcineurin-dependent manner, and TGFβ1 acting through its type I receptor modulated FSH action. Chromatin-immunoprecipitation analysis reveals FSH induced an early-phase (45 min) and FSH+TGFβ1 further elicited a late-phase (24 h) increase in CRTC2, CREB and CBP binding to the Gja1 promoter. Additionally, FSH+TGFβ1 increased the half-life of hyper-phosphorylated Cx43 (Cx43-P2). Also, the proteasome inhibitor MG132 prevented the brefeldin A (blocker of protein transport through Golgi)-reduced Cx43-P2 level and membrane Cx43 gap junction plaque. This is associated with FSH+TGFβ1-attenuated Cx43 interaction with Nedd4 and Cx43 ubiquitination. In all, this study uncovers that FSH and TGFβ1 upregulation of Cx43 gap junctions in ovarian granulosa cells critically involves enhancing CRTC2/CREB/CBP-mediated Cx43 expression and attenuating ubiquitin ligase Nedd4-mediated proteosomal degradation of Cx43 protein.

CREB coactivator CRTC2/TORC2 and its regulator calcineurin crucially mediate follicle-stimulating hormone and transforming growth factor β1 upregulation of steroidogenesis

In vitro and in vivo studies implicate that follicle-stimulating hormone (FSH) and transforming growth factor β1 (TGFβ1) play crucial physiological roles in regulating ovarian granulosa cell function essential to fertility control in females. FSH induces cAMP and calcium signaling, thereby activating transcription factor CREB to upregulate steroidogenic gene expression, and TGFβ1 greatly enhances FSH-stimulated steroidogenesis. A CREB coactivator CRTC2/TORC2 was identified to function as a cAMP and calcium-sensitive coincidence sensor. This led us to explore the role of CRTC2 and its regulator calcineurin in FSH and TGFβ1-stimulated steroidogenesis. Primary culture of granulosa cells from gonadotropin-primed immature rats was used. Immunoblotting analysis shows that FSH rapidly and transiently induced dephosphorylation/activation of CRTC2, and FSH + TGFβ1 additionally induced late-phase CRTC2 dephosphorylation. Immunofluorescence analysis further confirms FSH ± TGFβ1 promoted CRTC2 nuclear translocation. Using selective inhibitors, we demonstrate that FSH activated CRTC2 in a PKA- and calcineurin-dependent manner, and TGFβ1 acting through its type I receptor (TGFβRI)-modulated FSH action in a calcineurin-mediated and PKA-independent fashion. Next, we investigated the involvement of calcineurin and CRTC2 in FSH and TGFβ1-stimulated steroidogenesis. Calcineurin and TGFβRI inhibitor dramatically reduced the FSH ± TGFβ1-increased progesterone synthesis and protein levels of StAR, P450scc, and 3β-HSD enzyme. Furthermore, chromatin-immunoprecipitation and immunoprecipitation analyses demonstrate that FSH ± TGFβ1 differentially increased CRTC2, CREB, and CBP binding to these steroidogenic genes, and CREB nuclear association with CRTC2 and CBP. In all, this study reveals for the first time that CRTC2 and calcineurin are critical signaling mediators in FSH and TGFβ1-stimulated steroidogenesis in ovarian granulosa cells.

A single early postnatal estradiol injection affects morphology and gene expression of the ovary and parametrial adipose tissue in adult female rats

Events during early life can affect reproductive and metabolic functions in adulthood. We evaluated the programming effects of a single early postnatal estradiol injection (within 3h after birth) in female rats. We assessed ovarian and parametrial adipose tissue morphology, evaluated gene expression related to follicular development and adipose tissue metabolism, and developed a non-invasive volumetric estimation of parametrial adipose tissue by magnetic resonance imaging. Estradiol reduced ovarian weight, increased antral follicle size and number of atretic antral follicles, and decreased theca interna thickness in atretic antral follicles. Adult estradiol-injected rats also had malformed vaginal openings and lacked corpora lutea, confirming anovulation. Estradiol markedly reduced parametrial adipose tissue mass. Adipocyte size was unchanged, suggesting reduced adipocyte number. Parametrial adipose tissue lipoprotein lipase activity was increased. In ovaries, estradiol increased mRNA expression of adiponectin, complement component 3, estrogen receptor α, and glucose transporter 3 and 4; in parametrial adipose tissue, expression of complement component 3 was increased, expression of estrogen receptor α was decreased, and expression of leptin, lipoprotein lipase, and hormone-sensitive lipase was unaffected. These findings suggest that early postnatal estradiol exposure of female rats result in long-lasting effects on the ovary and parametrial adipose tissue at adult age.

Oestrogen, telomerase, ovarian ageing and cancer

1. Oestrogen plays an important role in ageing and ageing-related development. Lack of oestrogen prompts endocrine cell ageing of the ovary, whereas oestrogen overflow impacts on epithelial cell neoplastic development. 2. Recent studies indicate that oestrogen regulates cell proliferative fates by a mechanism of reprogramming the size of telomeres (ends of chromosomes) in the oestrogen target cells. This is achieved by upregulating the telomerase reverse transcriptase (TERT) gene in a temporal and spatial manner. 3. Currently, the relationship between oestrogen and telomerase activity in regulating productive cell development and function remains elusive. A number of lines of evidence suggest that telomerase is a downstream target of oestrogen in oestrogen-dependent reproductive ageing and neoplastic development. 4. The present minireview discusses our current understanding of the mechanisms by which telomerase maintenance of telomere homeostasis mediates oestrogen-induced ageing and tumourigenesis in the ovary under physiological and pathological conditions.

Crucial role of estrogen receptor-alpha interaction with transcription coregulators in follicle-stimulating hormone and transforming growth factor beta1 up-regulation of steroidogenesis in rat ovarian granulosa cells

This study was to explore estrogen receptor (ER) involvement in FSH and TGFbeta1-stimulated steroidogenesis in rat ovarian granulosa cells. We first determined the specific involvement of ERalpha and ERbeta in the process, and then investigated the molecular interaction of ERalpha and transcription coregulators in FSH and TGFbeta1 up-regulation of steroidogenic gene expression. Primary culture of ovarian granulosa cells from antral follicles of gonadotropin-primed immature rats was used. Interestingly, a selective ERalpha antagonist methyl-piperidino-pyrazole (MPP) [like ER antagonist ICI-182,780 (ICI)] decreased FSH +/- TGFbeta1-stimulated progesterone production, whereas an androgen receptor antagonist hydroxyflutamide and particularly a selective ERbeta antagonist 4-[2-Phenyl-5,7-bis(trifluoromethyl) pyrazolo [1,5-a] pyrimidin-3-yl] phenol had no significant effect. Consistent with this, a selective ERbeta agonist diarylpropionitrile (unlike 17beta-estradiol) also had no effect on FSH +/- TGFbeta1-stimulated progesterone production. Furthermore, a selective ERalpha agonist 4,4',4''-(4-Propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (like 17beta-estradiol) enhanced FSH-stimulated progesterone production, and this was abolished by pretreatment with MPP. Immunoblotting and chromatin immunoprecipitation analyses indicate that MPP/ICI suppression of FSH +/- TGFbeta1 action is partly attributed to the reduced ERalpha-mediated expression of Hsd3b and Cyp11a1 genes, but not steroidogenic acute regulatory protein. Furthermore, FSH +/- TGFbeta1 increased ERalpha association with histone acetylases (CBP and SRC-1) and coactivator of peroxisome proliferator-activated receptor gamma (PGC-1alpha), and MPP/ICI dramatically reduced these interactions. In addition, FSH +/- TGFbeta1 increased CBP, SRC-1, and PGC-1alpha binding to Hsd3b and Cyp11a1 genes. Together, we demonstrate for the first time that ERalpha interaction with transcription coregulators, histone acetylases (CBP/SRC-1), and PGC-1alpha is crucial to FSH and TGFbeta1-up-regulated expression of Hsd3b and Cyp11a1, and, thus, progesterone production in rat ovarian granulosa cells.

Differential actions of FSH and LH during folliculogenesis

In the gonadotrophin-dependent stage of follicular development, FSH- and LH-signalling pathways play an obligatory role in follicle differentiation, selection and survival. Under the effect of LH the theca-interstitial cell layer acts as an androgen producer. Thus, androgen diffusing into the mural granulosa cell layer represents the substrate for FSH-induced aromatase for follicular oestradiol synthesis. This is the landmark 'two cell-two gonadotrophin' concept in the physiology of ovarian function in mammals. The increase in plasma FSH during luteo-follicular transition is the basis for follicle selection. The rise of FSH to the threshold concentration represents a critical condition for the growth of the most sensitive follicle in a given time frame of the last 14 days of the dominant follicle odyssey. The gonadotrophin-induced follicular oestradiol secretion inhibits pituitary secretion of FSH, which in turn causes the concentration of FSH in the developing cohort follicles to drop below threshold concentrations and the arrest of the development of the less FSH-sensitive follicle (FSH threshold and window concept). In the gonadotrophin-dependent phase of follicular development, LH also seems to acts within a critical window of the hormone concentration framed between the minimal threshold and a ceiling for the normal functions of the follicle unit.

TGF-β superfamily members and ovarian follicle development

In recent years, exciting progress has been made towards unravelling the complex intraovarian control mechanisms that, in concert with systemic signals, coordinate the recruitment, selection and growth of follicles from the primordial stage through to ovulation and corpus luteum formation. A plethora of growth factors, many belonging to the transforming growth factor-β (TGF-β ) superfamily, are expressed by ovarian somatic cells and oocytes in a developmental, stage-related manner and function as intraovarian regulators of folliculogenesis. Two such factors, bone morphogenetic proteins, BMP-4 and BMP-7, are expressed by ovarian stromal cells and/or theca cells and have recently been implicated as positive regulators of the primordial-to-primary follicle transition. In contrast, evidence indicates a negative role for anti-Mullerian hormone (AMH, also known as Mullerian-inhibiting substance) of pre-granulosa/granulosa cell origin in this key event and subsequent progression to the antral stage. Two other TGF-β superfamily members, growth and differentiation factor-9 (GDF-9) and BMP-15 (also known as GDF-9B) are expressed in an oocyte-specific manner from a very early stage and play key roles in promoting follicle growth beyond the primary stage; mice with null mutations in the gdf-9 gene or ewes with inactivating mutations in gdf-9 or bmp-15 genes are infertile with follicle development arrested at the primary stage. Studies on later stages of follicle development indicate positive roles for granulosa cell-derived activin, BMP-2, -5 and -6, theca cell-derived BMP-2, -4 and -7 and oocyte-derived BMP-6 in promoting granulosa cell proliferation, follicle survival and prevention of premature luteinization and/or atresia. Concomitantly, activin, TGF-β and several BMPs may exert paracrine actions on theca cells to attenuate LH-dependent androgen production in small to medium-size antral follicles. Dominant follicle selection in monovular species may depend on differential FSH sensitivity amongst a growing cohort of small antral follicles. Changes in intrafollicular activins, GDF-9, AMH and several BMPs may contribute to this selection process by modulating both FSH- and IGF-dependent signalling pathways in granulosa cells. Activin may also play a positive role in oocyte maturation and acquisition of developmental competence. In addition to its endocrine role to suppress FSH secretion, increased output of inhibin by the selected dominant follicle(s) may upregulate LH-induced androgen secretion that is required to sustain a high level of oestradiol secretion during the pre-ovulatory phase. Advances in our understanding of intraovarian regulatory mechanisms should facilitate the development of new approaches for monitoring and manipulating ovarian function and improving fertility in domesticated livestock, endangered species and man.

Local roles of TGF-beta superfamily members in the control of ovarian follicle development

Members of the transforming growth factor-beta (TGF-beta) superfamily have wide-ranging influences on many tissue and organ systems including the ovary. Two recently discovered TGF-beta superfamily members, growth/differentiation factor-9 (GDF-9) and bone morphogenetic protein-15 (BMP-15; also designated as GDF-9B) are expressed in an oocyte-specific manner from a very early stage and play a key role in promoting follicle growth beyond the primary stage. Follicle growth to the small antral stage does not require gonadotrophins but appears to be driven by local autocrine/paracrine signals from both somatic cell types (granulosa and theca) and from the oocyte. TGF-beta superfamily members expressed by follicular cells and implicated in this phase of follicle development include TGF-beta, activin, GDF-9/9B and several BMPs. Acquisition of follicle-stimulating hormone (FSH) responsiveness is a pre-requisite for growth beyond the small antral stage and evidence indicates an autocrine role for granulosa-derived activin in promoting granulosa cell proliferation, FSH receptor expression and aromatase activity. Indeed, some of the effects of FSH on granulosa cells may be mediated by endogenous activin. At the same time, activin may act on theca cells to attenuate luteinizing hormone (LH)-dependent androgen production in small to medium-size antral follicles. Dominant follicle selection appears to depend on differential FSH sensitivity amongst a growing cohort of small antral follicles. Activin may contribute to this selection process by sensitizing those follicles with the highest "activin tone" to FSH. Production of inhibin, like oestradiol, increases in selected dominant follicles, in an FSH- and insulin-like growth factor-dependent manner and may exert a paracrine action on theca cells to upregulate LH-induced secretion of androgen, an essential requirement for further oestradiol secretion by the pre-ovulatory follicle. Like activin, BMP-4 and -7 (mostly from theca), and BMP-6 (mostly from oocyte), can enhance oestradiol and inhibin secretion by bovine granulosa cells while suppressing progesterone secretion; this suggests a functional role in delaying follicle luteinization and/or atresia. Follistatin, on the other hand, may favor luteinization and/or atresia by bio-neutralizing intrafollicular activin and BMPs. Activin receptors are expressed by the oocyte and activin may have a further intrafollicular role in the terminal stages of follicle differentiation to promote oocyte maturation and developmental competence. In a reciprocal manner, oocyte-derived GDF-9/9B may act on the surrounding cumulus granulosa cells to attenuate oestradiol output and promote progesterone and hyaluronic acid production, mucification and cumulus expansion.

Expression of Bambi is widespread in juvenile and adult rat tissues and is regulated in male germ cells

Members of the TGF beta superfamily may compete for receptor occupancy and intracellular signaling molecules in specific developmental circumstances. We explored the potential importance of the TGF beta family inhibitor, Bambi (Bmp and activin membrane-bound inhibitor) by examining its pattern of mRNA expression in juvenile and adult rat tissues, with a focus on reproductive organs. The 1.8-kb transcript was ubiquitous, whereas a 3-kb transcript was unique to enriched spermatocyte and spermatid cell fractions and adult testis. The full-length rat cDNA is 89% (nucleic acid) and 95% (amino acid) identical to its human homolog, hnma. Using in situ hybridization, Bambi mRNA was detected in granulosa and thecal cells of adult ovaries and in spermatogonia, spermatocytes, round spermatids, and Sertoli cells of adult testes. In addition to a persistent signal in Sertoli cells in juvenile testes, this mRNA within germ cells appeared dramatically increased as gonocytes matured into spermatogonia immediately after birth. These data indicate that TGF beta superfamily signaling within male germ cells is down-regulated at the onset of spermatogenesis. The addition of exogenous activin A to 24-h cultures of newborn rat testis fragments decreased the Bambi mRNA level. Regulated Bambi mRNA synthesis may contribute to TGF beta superfamily signaling modulation in several organs, as suggested by its discrete expression switch in male germ cells.

Regulation of inhibin alpha- and beta(A)-subunit messenger ribonucleic acid levels by gonadotropins and IGF-I in cultured chicken granulosa cells

A quantitative competitive reverse transcription polymerase chain reaction assay (QC RT-PCR) for quantifying the absolute levels of the expression of inhibin alpha- and beta(A)-subunits in chicken granulosa cells showed that these subunits are expressed in different amounts depending on follicular maturation. The present study determined the regulation of the expression of these subunits. The individual effect of different doses of IGF-I, LH or FSH (1-100 ng/ml) or the combination of IGF-I with either LH or FSH at different concentrations, on the expression of inhibin alpha- and beta(A)-subunit was determined on cultured granulosa cells of F(1) and the combined F(4)+F(5) follicle. Cells were cultured for 48 h in 6-well plates with or without added hormones. Culture medium was discarded, cells were washed and total RNA was extracted from the cells. Five hundred nanograms of total RNA was reverse transcribed using specific primers and coamplified with an internal standard, as described previously, to determine expression level in the cells. IGF-I, LH, and FSH enhanced the inhibin alpha-subunit mRNA levels in a dose dependent manner in both F(1) and the combined F(4)+F(5) whereas inhibin beta(A)-subunit was not affected. The effects of FSH, LH were more expressed in F(1) follicles compared to F(4)+F(5) on the alpha-subunit. The addition of IGF-I and either LH or FSH during the culture period significantly increased the stimulatory effects of both LH and FSH on the expression of inhibin alpha-subunit in F(1) follicles but had no significant effect on the inhibin beta(A)-subunit. The results suggest that the changing expression levels of inhibin alpha-subunit during follicular development are the result of the regulatory effect of the interaction between IGF-I and the gonadotropins and that the regulation of this subunit may be the main factor for the regulation of the protein inhibin levels. Other factors may be also implicated in the changing expression levels of the beta(A)-subunit.

Production and actions of inhibin and activin during folliculogenesis in the rat

Evidence to enhance the premise that inhibin and activin are local regulators of ovarian folliculogenesis is presented in this review. Granulosa cells (GC) have been identified as the source of inhibin/activin in the ovary on the basis of mRNA and protein localisation and the measurement of the inhibin forms in GC conditioned media. Expression of the subunit mRNAs changed with follicular development, being maximal in the ovaries of 8-day-old rats, where secondary follicles predominate. The expression of beta subunit mRNAs by GC isolated from diethylstilboestrol (DES)-treated immature rats, was reduced in the absence of any change in alpha subunit mRNA expression. Dimeric inhibin-A, -B and free alpha subunit were produced by ovarian cell cultures prepared from 4- to 12-day-old rats. Inhibin-A production by these cultures was responsive to FSH and TGF-beta, with preantral follicles of day 8 ovaries exerting effects so profound that the inhibin A/alpha subunit ratio increased, most likely due to a stimulation of beta(A) subunit production. In contrast, inhibin-B was not stimulated by TGF-beta until day 8 and FSH until day 12. Fractionation of GC conditioned media revealed a prominence of free alpha subunit and inhibin-A, but little inhibin-B, suggesting that inhibin-B production declines with follicular development. Activin receptor types I and II, Smads 1-8 and betaglycan (beta-glycan) mRNAs were present in the rat ovary and showed distinct patterns of expression between postnatal days 4 and 12. Oocytes and GC localised activin receptor, Smad and beta-glycan proteins, with beta-glycan also present in theca cells (TC). These data indicate that activin/TGF-beta signalling machinery and factors which influence these pathways, are present in the postnatal rat ovary. Our hypothesis that inhibin and activin play important and changing autocrine/paracrine roles in the growth and differentiation of follicles, including the oocyte, has been supported by these studies.

Dimeric inhibin A and B production are differentially regulated by hormones and local factors in rat granulosa cells

In the present study, we have examined the role of hormones and growth factors in regulating dimeric inhibin production in immature rat granulosa cells. Purified granulosa cells from estrogen-primed immature rats were cultured under defined conditions. Inhibins A and B in the culture media were measured using a two-site enzyme-linked immunosorbent assay specific for each dimer. Under basal conditions, granulosa cells produced 14-fold more inhibin A than inhibin B (inhibin A, 2.0; inhibin B, 0.14 ng/ml, measured against human standards; average A/B apparent ratio, 14). Addition of increasing doses of FSH elicited dose-dependent increases in both inhibins, the effects being more pronounced on inhibin A than on inhibin B (9.4- and 4.1-fold increases, respectively; average A/B ratio, 34). Estradiol, when added alone, stimulated inhibin A production 3- to 6-fold, whereas minor changes were observed in inhibin B production. Insulin-like growth factor-I produced a similar stimulation of both inhibins (3-fold stimulation over control). This growth factor, however, induced a marked dissociation in the sensitivity of inhibins A and B to FSH stimulation, with maximal stimulation of inhibin B observed at comparatively lower concentrations of the gonadotropin. Transforming growth factor-beta (TGF-beta, 5 ng/ml) had a more marked stimulatory effect on inhibin B than on inhibin A production (7- to 14-fold vs. 2- to 5-fold for inhibin B and A, respectively). A more pronounced differential stimulation of inhibin B was also exerted by another member of the TGF-beta superfamily, activin A (A/B ratio, 0.66). This preferential stimulation of inhibin B by TGF-beta and activin A was amplified in the presence of FSH. Coculture of rat granulosa cells with freshly isolated bovine oocytes was also associated with a marked stimulation of inhibin B production (100-fold increase) and a comparatively lower stimulation of inhibin A (10-fold increase; A/B ratio, 1). The discrepancy between the proportion of inhibin dimers in serum (A/B ratio, 0.13) and those produced by untreated granulosa cells may suggest that intraovarian factors, such as TGF-beta, activin A, or oocyte-derived factor(s), are responsible for the shift of the ratio toward the predominance of inhibin B.

Activities of glucose metabolic enzymes in human preantral follicles: in vitro modulation by follicle-stimulating hormone, luteinizing hormone, epidermal growth factor, insulin-like growth factor I, and transforming growth factor beta1

Modulation of glucose metabolic capacity of human preantral follicles in vitro by gonadotropins and intraovarian growth factors was evaluated by monitoring the activities of phosphofructokinase (PFK) and pyruvate kinase (PK), two regulatory enzymes of the glycolytic pathway, and malate dehydrogenase (MDH), a key mitochondrial enzyme of the Krebs cycle. Preantral follicles in classes 1 and 2 from premenopausal women were cultured separately in vitro in the absence or presence of FSH, LH, epidermal growth factor (EGF), insulin-like growth factor (IGF-I), or transforming growth factor beta1 (TGFbeta1) for 24 h. Mitochondrial fraction was separated from the cytosolic fraction, and both fractions were used for enzyme assays. FSH and LH significantly stimulated PFK and PK activities in class 1 and 2 follicles; however, a 170-fold increase in MDH activity was noted for class 2 follicles that were exposed to FSH. Although both EGF and TGFbeta1 stimulated glycolytic and Krebs cycle enzymes for class 1 preantral follicles, TGFbeta1 consistently stimulated the activities of both glycolytic enzymes more than that of EGF. IGF-I induced PK and MDH activities in class 1 follicles but negatively influenced PFK activity for class 1 follicles. In general, only gonadotropins consistently stimulated both glycolytic and Krebs cycle enzyme activities several-fold in class 2 follicles. These results suggest that gonadotropins and ovarian growth factors differentially influence follicular energy-producing capacity from glucose. Moreover, gonadotropins may either directly influence glucose metabolism in class 2 preantral follicles or do so indirectly through factors other than the well-known intraovarian growth factors. Because growth factors modulate granulosa cell mitosis and functionality, their role on energy production may be related to specific cellular activities.

Characterization of immortalized mouse granulosa cell lines

Cell cultures of primary mouse granulosa cells were transfected with a v-myc-containing plasmid, and the resulting stable cell lines were tested for their steroidogenic properties and physiologic status. Granulosa cells were obtained from 22-day-old NMRI mice injected with 8 IU pregnant mare serum gonadotropin i.p. 2 days earlier. In Passage 1 the cells were transfected with pSVv-myc using calcium phosphate precipitation or lipofectin. The 3 beta- and 17 beta-hydroxy steroid dehydrogenase activity was visualized in control cultures. The three cell lines obtained have been in culture for over 1 yr and have been subcultured for more than 90 passages. The cell line GRM01, with a doubling time of 37 +/- 3 h and a diploid modal chromosome number, produced progesterone, estradiol, as well as inhibinlike and activinlike material under basal conditions. A combination of follicle-stimulating hormone and luteinizing hormone was able to increase the secretion of progesterone. GRM01L, a fast growing clone of the GRM01 line with a doubling time of 10 +/- 1 h, retained only the capacity to produce activinlike material and transforming growth factor-beta, and it was the only one with a tumorigenic capacity. Epidermal growth factor, insulin, and interleukin-6 were able to induce the [3H]thymidine incorporation into DNA in these two cell lines. GRM02, with a doubling time of 36 +/- 2 h and a hypertriploid modal chromosome number, produced progesterone and activinlike and inhibinlike material. Follicle-stimulating hormone and luteinizing hormone were able to enhance the secretion of progesterone. For this cell line, only insulin was shown to induce [3H]thymidine incorporation into DNA.

Production of immunoactive inhibin by bovine granulosa cells in serum-free culture: effects of exogenous steroids and FSH

Granulosa cells from pooled bovine follicles were cultured under chemically-defined (serum-free) conditions to study the effects of exogenous steroids and FSH on production of immunoactive (ia) inhibin, oestradiol and progesterone. Levels of ia-inhibin in media samples and cell lysates were measured by radioimmunoassay (RIA) using an antiserum raised against a synthetic fragment of human inhibin alpha-subunit [hI alpha (1-32)]. Cells secreted measurable amounts of ia-inhibin, oestradiol and progesterone for at least 7 d of culture, although intracellular levels of inhibin were very low, indicating that newly-synthesized ia-inhibin is rapidly released from the cells. Treatment with androstenedione (0.2 mumol/l) or testosterone (0.2 mumol/l) increased ia-inhibin secretion markedly; levels on Day 5 of culture were approximately 6-fold (P < 0.005) higher than control values. In contrast, treatment with the non-aromatizable androgen dihydrotestosterone (DHT; 0.2 mumol/l) resulted in only a one- to two-fold increase (P < 0.05) over control values (Day 5). Addition of exogenous oestradiol (8 nmol/l) markedly increased ia-inhibin secretion (8-9 fold on Day 5; P < 0.05) compared with basal levels, whereas progesterone had no effect. Secretion of oestradiol, undetectable in the absence of exogenous androgens, rose daily in the presence of either androstenedione or testosterone, levels rising approximately 6-fold and 9-fold respectively over a 4-d treatment period. Progesterone secretion increased approximately 2-fold over the culture period and was unaffected by any steroid treatment. Treatment with ovine FSH (10ng/ml) alone stimulated secretion of progesterone over basal levels (3-fold higher on Day 6; P < 0.005), but did not affect output of either ia-inhibin or oestradiol. However, exposure to FSH in the presence of androstenedione not only promoted a further 4-fold increase in progesterone output but also led to a dose-dependent suppression of both ia-inhibin (approximately 90% lower on Day 6; P < 0.001) and oestradiol (approximately 80% lower on Day 6; P < 0.001) secretion compared to cells treated with androstenedione alone. These observations indicate that the secretion of ia-inhibin by bovine granulosa cells in culture is positively regulated by oestradiol, implying an autocrine/paracrine role for this hormone in control of ovarian inhibin production. The ability of aromatizable androgens to stimulate secretion of inhibin, coupled with the inability of the non-aromatizable androgen DHT to elicit such an effect, suggests that inhibin output is largely unaffected by androgens prior to their conversion to oestradiol.(ABSTRACT TRUNCATED AT 400 WORDS)

The potential relevance of cytokines to ovarian physiology

Elucidating the secrets of intraovarian intercellular communication constitutes a central area of investigation. While most attention has been directed thus far at the somatic cellular components of the ovary, the potential role(s) and relative importance of the resident ovarian white blood cell have received relatively limited attention. Efforts are currently under way to reconcile traditional ovarian physiology with observations relevant to intraovarian components of the white blood cell series. In this connection, it is important to note that unlike some gonadal compartments, the ovary does not constitute an immunologically privileged site. Thus, resident ovarian representatives of the white blood cell series can be observed at various stages of the ovarian life cycle. Current concepts suggest that regulatory cellular networks formerly viewed in immune terms now fall within the broad domain of endocrinology. Viewed in this light, resident ovarian representatives of the white blood cell series may constitute potential in situ modulators of ovarian function acting in all likelihood through the local secretion of regulatory cytokines. As the flow of information is probably multi directional, the very same cells are probably targeted for steroidal and peptidergic input in keeping with the existence of multiple autocrine and paracrine loops.

Regulation by growth factors of Leydig cell differentiated functions

In this paper the effects of growth factors on the differentiated function of pig Leydig cells and other steroidogenic cells are reviewed. Two types of action have been observed, i.e. positive or negative acute effects on testosterone secretion, and long-term trophic effects of hCG receptor and responsiveness to hCG. Among the growth factors, insulin-like growth factor I (IGF-I) and transforming growth factor beta (TGF beta-1) are of particular interest. IGF-I is required for the maintenance and probably the expression of differentiated functions of several steroidogenic cells, including the Leydig cells. TGF beta-1 has effects opposite to IGF-I on Leydig cell functions. When considering effects of growth factors on Leydig cells, caution should be taken in extrapolating results obtained in one species to another.

The effect of bovine activin and follicle-stimulating hormone (FSH) suppressing protein/follistatin on FSH-induced differentiation of rat granulosa cells in vitro

The time- and dose-dependent effects of bovine activin A and bovine follicle stimulating hormone (FSH) suppressing protein (FSP) or follistatin on basal and FSH-induced steroidogenesis and inhibin production were studied in granulosa cells from immature, diethylstilbestrol (DES)-treated rats. In the presence of rat FSH (20 ng/ml) which stimulates aromatase activity and the production of progesterone and inhibin, activin (0.3-100 ng/ml) augmented all three parameters, whereas FSP (0.3-100 ng/ml) enhanced progesterone production and attenuated the other two parameters. In the absence of FSH, the basal parameters were unaffected by treatment with either activin or FSP alone, except for a statistically significant increase in basal inhibin in the presence of activin alone (P less than 0.05, at doses of 30 and 100 ng/ml). Neither activin nor FSP influenced the timing of the maxima of FSH-induced activities over 5 days. These findings suggest that activin and FSP, both present in follicular fluid, may play an important role in the local regulation of granulosa cell differentiation.