Downregulation of Follicle-Stimulating Hormone (FSH)-Receptor Messenger RNA Levels in the Hamster Ovary: Effect of the Endogenous and Exogenous FSH1

Regulation of antral follicular growth by an interplay between gonadotropins and their receptors

Knowledge of the growth and maturation of human antral follicles is based mainly on concepts and deductions from clinical observations and animal models. To date, new experimental approaches and in vitro data contributed to a deep comprehension of gonadotropin receptors' functioning and may provide new insights into the mechanisms regulating still unclear physiological events. Among these, the production of androgen in the absence of proper LH levels, the programming of follicular atresia and dominance are some of the most intriguing. Starting from evolutionary issues at the basis of the gonadotropin receptor signal specificity, we draw a new hypothesis explaining the molecular mechanisms of the antral follicular growth, based on the modulation of endocrine signals by receptor-receptor interactions. The "heteromer hypothesis" explains how opposite death and life signals are delivered by gonadotropin receptors and other membrane partners, mediating steroidogenesis, apoptotic events, and the maturation of the dominant follicle.

Interplay Between mTOR and Hippo Signaling in the Ovary: Clinical Choice Guidance Between Different Gonadotropin Preparations for Better IVF

One of the most widely used types of assisted reproduction technology is the in vitro fertilization (IVF), in which women undergo controlled ovarian stimulation through the administration of the appropriate hormones to produce as many mature follicles, as possible. The most common hormone combination is the co-administration of gonadotropin-releasing hormone (GnRH) analogues with recombinant or urinary-derived follicle-stimulating hormone (FSH). In the last few years, scientists have begun to explore the effect that different gonadotropin preparations have on granulosa cells' maturation and apoptosis, aiming to identify new predictive markers of oocyte quality and successful fertilization. Two major pathways that control the ovarian development, as well as the oocyte-granulosa cell communication and the follicular growth, are the PI3K/Akt/mTOR and the Hippo signaling. The purpose of this article is to briefly review the current knowledge about the effects that the different gonadotropins, used for ovulation induction, may exert in the biology of granulosa cells, focusing on the importance of these two pathways, which are crucial for follicular maturation. We believe that a better understanding of the influence that the various ovarian stimulation protocols have on these critical molecular cascades will be invaluable in choosing the best approach for a given patient, thereby avoiding cancelled cycles, reducing frustration and potential treatment-related complications, and increasing the pregnancy rate. Moreover, individualizing the treatment plan will help clinicians to better coordinate assisted reproductive technology (ART) programs, discuss the specific options with the couples undergoing IVF, and alleviate stress, thus making the IVF experience easier.

Eremomastax speciosa potentializes the PMSG-inducing effect on some physiological and biochemical parameters in PMSG-primed immature rats

The present study evaluated the effect of the aqueous extract from leaves of E. speciosa on some physiological and biochemical parameters of reproduction and the onset of puberty in pregnant mare serum gonadotropin (PMSG)-primed immature female rats. High pressure liquid chromatography (HPLC) was used to quantify the phenolic compounds in the methanol/methylene chloride (1:1) extract, the ethanolic and ethyl acetate fractions and the aqueous residue of E. speciosa. E. speciosa (0, 8, 32 or 64 mg/kg) were administered for 15 days to 24 non-PMSG-primed and 24 primed rats with 0.01 IU of PMSG. At the end of the treatment period, animal were sacrificed and their body, ovarian, uterine weight, ovarian protein or cholesterol level, as well as data on puberty onset were recorded. Of the 16 polyphenolic compounds quantitatively revealed in the extracts and fractions of E. speciosa after HPLC analysis, quercetin, rutin, apigenin and eugenol were the most abundant. Non-primed rats showed a significant increase (P < 0.05) in the uterine relative weight at the dose of 8 mg/kg when compared with the other treatments. The uterine proteins and the ovarian cholesterol (P < 0.05), respectively, showed a reduction at doses of 64 mg/kg and 32 mg/kg in non-primed rats. However in PMSG-primed rats, a significant decrease (P < 0.05) was observed in ovarian cholesterol at 64 mg/kg. In conclusion, E. speciosa potentializes the PMSG-inducing effect on folliculogenesis in PMSG-primed rats.

A polymorphism in the transcriptional regulatory region strongly influences ovine FSHR mRNA decay

Follicle-stimulating hormone receptor (FSHR) is an important G protein-coupled receptor, which is required for steroidogenesis, follicular development and female infertility. Here, we report a novel polymorphism in the 3'-UTR that strongly influences ovine FSHR mRNA decay. The partial 3'-UTR sequence of Hu sheep FSHR gene was isolated and characterized, and a polymorphism (c.2327A>G) was identified. Luciferase assay and qRT-PCR showed that c.2327A>G polymorphism in the 3'-UTR exerts a strong regulatory role in FSHR transcription. This regulatory role is achieved by affecting FSHR mRNA decay. Furthermore, the c.2327A>G mutation in the 3'-UTR influences ARE (AU-rich element, a cis-acting element promoting mRNA decay)-mediated mRNA decay of Hu sheep FSHR gene. Together, our study identified a novel polymorphism and elucidated a new mechanism underlying transcriptional regulation of FSHR in mammals.

The cAMP/PKA pathway: steroidogenesis of the antral follicular stage

Pituitary gonadotropins, follicle-stimulating (FSH) and luteinizing hormone (LH) promote follicular recruitment and support antral follicle growth, maturation and selection, resulting in ovulation of the dominant follicle. FSH and LH biological functions are mediated by G protein-coupled receptors, FSHR and LHCGR, resulting in the activation of a number of signaling cascades, such as the cyclic AMP/protein kinase A (cAMP/PKA) pathway. Some in-vitro data are consistent with the dual, proliferative and pro-apoptotic role of cAMP, leaving unanswered questions on how cAMP/PKA signaling is linked to the follicle fate. Progression of the antral stage is characterized by the presence of dynamic serum gonadotropin and estrogen levels, accompanying proliferation and steroidogenesis of growing as well as apoptosis of atretic follicles. These events are parallel to changes of FSHR and LHCGR density at the cell surface occurring throughout the antral stage, reasonably modulating the cAMP/PKA activation pattern, cell metabolism and functions. Understanding whether gonadotropins and receptor expression levels impact on the steroidogenic pathway and play a role in determining the follicular fate, may put new light on molecular mechanisms regulating human reproduction. The aim of the present review is to update the role of major players modulating the cAMP/PKA pathway and regulating the balance between proliferative, differentiating and pro-apoptotic signals.

Involvement of Bone Morphogenetic Proteins (BMP) in the Regulation of Ovarian Function

Primordial germ cells migrate to the fetal gonads and proliferate during gestation to generate a fixed complement of primordial follicles, the so-called ovarian reserve. Primordial follicles comprise an oocyte arrested at the diplotene stage of meiosis, surrounded by a layer of pregranulosa cells. Activation of primordial follicles to grow beyond this arrested stage is of particular interest because, once activated, they are subjected to regulatory mechanisms involved in growth, selection, maturation, and ultimately, ovulation or atresia. The vast majority of follicles succumb to atresia and are permanently lost from the quiescent or growing pool of follicles. The bone morphogenetic proteins (BMPs), together with other intraovarian growth factors, are intimately involved in regulation of follicle recruitment, dominant follicle selection, ovulation, and atresia. Activation of primordial follicles appears to be a continuous process, and the number of small antral follicles at the beginning of the menstrual cycle provides an indirect indication of ovarian reserve. Continued antral follicle development during the follicular phase of the menstrual cycle is driven by follicle stimulating hormone (FSH) and luteinizing hormone (LH) in conjunction with many intraovarian growth factors and inhibitors interrelated in a complex web of regulatory balance. The BMP signaling system has a major intraovarian role in many species, including the human, in the generation of transcription factors that influence proliferation, steroidogenesis, cell differentiation, and maturation prior to ovulation, as well as formation of corpora lutea after ovulation. At the anterior pituitary level, BMPs also contribute to the regulation of gonadotrophin production.

Infertility and ovarian follicle reserve depletion are associated with dysregulation of the FSH and LH receptor density in human antral follicles

The low take-home baby rate in older women in Australia (5.8%) undergoing IVF (5.8%) is linked to the depletion of the ovarian reserve of primordial follicles. Oocyte depletion causes an irreversible change to ovarian function. We found that the young patient FSH receptor and LH receptor expression profile on the granulosa cells collected from different size follicles were similar to the expression profile reported in natural cycles in women and sheep. This was reversed in the older patients with poor ovarian reserve. The strong correlation of BMPR1B and FSH receptor density in the young was not present in the older women; whereas, the LH receptor and BMPR1B correlation was weak in the young but was strongly correlated in the older women. The reduced fertilisation and pregnancy rate was associated with a lower LH receptor density and a lack of essential down-regulation of the FSH and LH receptor. The mechanism regulating FSH and LH receptor expression appears to function independently, in vivo, from the dose of FSH gonadotrophin, rather than in response to it. Restoring an optimum receptor density may improve oocyte quality and the pregnancy rate in older women.

Compensatory Increase in Ovarian Aromatase in Older Regularly Cycling Women

CONTEXT

Serum estradiol (E2) levels are preserved in older reproductive-aged women with regular menstrual cycles despite declining ovarian function.

OBJECTIVE

The objective of the study was to determine whether increased granulosa cell aromatase expression and activity account for preservation of E2 levels in older, regularly cycling women.

DESIGN

The protocol included daily blood sampling and dominant follicle aspirations at an academic medical center during a natural menstrual cycle.

SUBJECTS

Healthy, regularly cycling older (36-45 y; n = 13) and younger (22-34 y; n = 14) women participated in the study.

MAIN OUTCOME MEASURES

Hormone levels were measured in peripheral blood and follicular fluid aspirates and granulosa cell CYP19A1 (aromatase) and FSH-R mRNA expression were determined.

RESULTS

Older women had higher FSH levels than younger women during the early follicular phase with similar E2 but lower inhibin B and antimullerian hormone levels. Late follicular phase serum E2 did not differ between the two groups. Follicular fluid E2 [older (O) = 960.0 [interquartile range (IQR) 765.0-1419.0]; younger (Y) = 994.5 [647.3-1426.5] ng/mL, P = 1.0], estrone (O = 39.6 [29.5-54.1]; Y = 28.8 [22.5-42.1] ng/mL, P = 0.3), and the E2 to testosterone (T) ratio (O = 109.0 ± 41.9; Y = 83.0 ± 18.6, P = .50) were preserved in older women. Granulosa cell CYP19A1 expression was increased 3-fold in older compared with younger women (P < .001), with no difference in FSH-R expression.

CONCLUSIONS

Ovarian aromatase expression increases with age in regularly cycling women. Thus, up-regulation of aromatase activity appears to compensate for the known age-related decrease in granulosa cell number in the dominant follicle to maintain ovarian estrogen production in older premenopausal women.

Expression of FSH receptor in the hamster ovary during perinatal development

FSH plays an important role in ovarian follicular development, and it functions via the G-protein coupled FSH receptor. The objectives of the present study were to determine if full-length FSHR mRNA and corresponding protein were expressed in fetal through postnatal hamster ovaries to explain the FSH-induced primordial follicle formation, and if FSH or estrogen (E) would affect the expression. A full-length and two alternately spliced FSHR transcripts were expressed from E14 through P20. The level of the full-length FSHR mRNA increased markedly through P7 before stabilizing at a lower level with the formation and activation of primordial follicles. A predicted 87 kDa FSHR protein band was detected in fetal through P4 ovaries, but additional bands appeared as ovary developed. FSHR immunosignal was present in undifferentiated somatic cells and oocytes in early postnatal ovaries, but was granulosa cells specific after follicles formed. Both eCG and E significantly up-regulated full-length FSHR mRNA levels. Therefore, FSHR is expressed in the hamster ovary from the fetal life to account for FSH-induced primordial follicle formation and cAMP production. Further, FSH or E regulates the receptor expression.

Expression of ErbB3-binding protein-1 (EBP1) during primordial follicle formation: role of estradiol-17ß

The formation of primordial follicles involves the interaction between the oocytes and surrounding somatic cells, which differentiate into granulosa cells. Estradiol-17ß (E) promotes primordial follicle formation in vivo and in vitro; however, the underlying mechanisms are poorly understood. The expression of an ERBB3-binding protein 1 (EBP1) is downregulated in 8-day old hamster ovaries concurrent with the increase in serum estradiol levels and the formation of primordial follicles. The objectives of the present study were to determine the spatio-temporal expression and putative E regulation of EBP1 in ovarian cells during perinatal development with respect to primordial follicle formation. Hamster EBP1 nucleic acid and amino acid sequences were more than 93% and 98% similar, respectively, to those of mouse and human, and contained nucleolar localization signal, RNA-binding domain and several phosphorylation sites. EBP1 protein was present in somatic cells and oocytes from E15, and declined in oocytes by P1 and in somatic cells by P5. Thereafter, EBP1 expression increased through P7 with a transient decline on P8 primarily in interstitial cells. EBP1 mRNA levels mirrored protein expression pattern. E treatment on P1 and P4 upregulated EBP1 expression by P8 whereas E treatment on P4 downregulated it by 72 h suggesting a compensatory upregulation due to E pretreatment. Treatment with an FSH-antiserum, which suppressed primordial follicle formation, prevented the decline in EBP1 levels, and the effect was reversed by E treatment. Therefore, the results provide the first evidence that EBP1 may play an important role in mediating the effect of E in the differentiation of somatic cells into granulosa cells during primordial follicle formation.

Follicle-stimulating hormone responsiveness in antral follicles from aryl hydrocarbon receptor knockout mice

BACKGROUND

Previous studies have demonstrated that pre-pubertal aryl hydrocarbon receptor knockout (AHRKO) mice have slow antral follicle growth and reduced capacity to produce estradiol compared to wild-type (WT) mice. Although previous studies have suggested that this is likely due to a reduced ability of the AHRKO follicles to respond to follicle-stimulating hormone (FSH), this possibility was not directly tested. Thus, the goal of these studies was to test the hypothesis that low FSH responsiveness is responsible for the slow growth and reduced estradiol production observed in pre-pubertal AHRKO versus WT antral follicles.

METHODS

Antral follicles from WT and AHRKO mice were cultured with varying amounts of FSH (0-15 IU/mL) for up to 7 days, and subjected to measurements of growth, FSH receptor and steroidogenic regulator expression, sex steroid hormone levels, and inhibin beta-A expression. General linear models (GLM) for repeated measures were used to compare follicle diameters over time among treatments. If the global tests from GLM were significant, Tukey's tests were used for pairwise comparisons. Remaining comparisons among groups were performed using one-way analysis of variance followed by Tukey's post hoc test.

RESULTS

The results indicate that FSH stimulated growth in both WT and AHRKO follicles, but that high levels of FSH (10-15 IU/mL) were required for AHRKO follicles to reach maximal growth, whereas lower levels of FSH (5 IU/mL) were required for WT follicles to reach maximal growth. Further, FSH stimulated expression of FSH receptor, steroidogenic factors, and inhibin beta-A as well as production of steroid hormones in both WT and AHRKO follicles, but the degree of stimulation differed between WT and AHRKO follicles. Interestingly, FSH treatment increased expression of FSH receptor, some steroidogenic regulators, inhibin beta-A, and steroid hormone production more in AHRKO follicles compared to WT follicles.

CONCLUSIONS

Collectively, these data suggest that the slow growth, but not reduced steroidogenesis in AHRKO follicles, is due to their reduced ability to respond to FSH compared to WT follicles. These data also suggest that the AHR may contribute to the ability of FSH to stimulate proper follicle growth, but it may not contribute to FSH-induced steroidogenesis.

Expression of estrogen receptor α 36 (ESR36) in the hamster ovary throughout the estrous cycle: effects of gonadotropins

Estradiol-17β (E) plays an important role in ovarian follicular development. Evidence indicates that some of the effect of E is mediated by the transmembrane estrogen receptor. In this study, we examined the spatio-temporal expression of recently discovered ERα36 (ESR36), a splice variant of Esr1 and a receptor for non-genomic E signaling, in the hamster ovary during the estrous cycle and the role of gonadotropins and ovarian steroid hormones in ESR36 expression. ESR36 expression was high on estrus (D1:0900 h) and declined precipitously by proestrus (D4:0900 h) and remained low up to D4:1600 h. Immunofluorescence findings corroborated immunoblot findings and revealed that ESR36 was expressed only in the cell membrane of both follicular and non-follicular cells, except the oocytes. Ovarian ESR36 was capable of binding to the E-affinity matrix, and have different molecular weight than that of the ESR1 or GPER. Hypophysectomy (Hx) resulted in a marked decline in ESR36 protein levels. FSH and LH, alone or combined, markedly upregulated ESR36 protein in Hx hamsters to the levels observed in D1 hamsters, but neither E nor P had any effect. Inhibition of the gonadotropin surge by phenobarbital treatment on D4:1100 h attenuated ESR36 expression in D1:0900 h ovaries, but the decline was restored by either FSH or LH replacement on D4 afternoon. This is the first report to show that ESR36, which is distinct from ESR1 or GPER is expressed in the plasma membrane of ovarian follicular and non-follicular cells, binds to E and its expression is regulated directly by the gonadotropins. In light of our previous findings, the results suggest that ovarian cells contain at least two distinct membrane estrogen receptors, such as GPER and ESR36, and strongly suggest for a non-genomic action of E regulating ovarian follicular functions.

LH-receptor gene expression in human granulosa and cumulus cells from antral and preovulatory follicles

CONTEXT

Human granulosa cells (GC) acquire LH receptor (LHR) expression during the follicular phase of the menstrual cycle. Currently, the precise follicular stage is unknown, and specific roles of LH in the follicular development are not fully understood.

OBJECTIVE

Our objective was to measure LHR gene expression on GC and cumulus cells (CC) from normal human follicles with diameters form 3-20 mm.

DESIGN, SETTING, AND PATIENTS

At a university hospital, GC, CC, and the corresponding follicular fluid (FF) were collected from patients undergoing fertility preservation by having one ovary frozen and patients undergoing infertility treatment.

INTERVENTIONS

Cells and fluids were isolated from surgically excised ovaries or from aspirated preovulatory follicles.

MAIN OUTCOME MEASURES

We evaluated gene expression of LHR, FSHR, androgen receptor (AR), aromatase (CYP19a1), and AMHR2 normalized to the GAPDH expression and associated with FF levels of anti-Mullerian hormone, inhibin-B, and steroids.

RESULTS

LHR expression was maximal in GC from preovulatory follicles before ovulation induction. A majority of 150 antral follicles (3-10 mm in diameter) showed LHR expression at approximately 10% of the maximum, and LHR expression showed significant associations with FSHR, AR, CYP19a1, and AMHR2 and with FF estradiol and progesterone. Levels of FSHR continued to decline in GC as the follicular diameter increased.

CONCLUSIONS

The LHR gene is expressed in GC of human antral follicles throughout the follicular phase and is significantly associated with expression of the CYP19a1 gene and with the corresponding FF concentrations of estradiol and progesterone. LH appears to affect human follicular development during most the follicular phase in normal women.

Molecular cloning and functional analysis of the FSH receptor gene promoter from the volcano mouse (Neotomodon alstoni alstoni)

To gain further insights on the genetic divergence and the species-specific characteristics of the follicle-stimulating hormone receptor (FSHR), we cloned 946 bp of the 5'-flanking region of the FSHR gene from the volcano mouse (Neotomodon alstoni alstoni), and compared its features with those from other mammalian species. The sequence of neotomodon FSHR (nFSHR) gene from the translation initiation site to -946 is 74, 71, 64, and 59% homologous to rat, mouse (129/J), human, and sheep, respectively. The nFSHR 5'-flanking region exhibits new interesting putative cis-regulatory elements including those for the SRY transcription factor, which had not been previously related to the FSHR gene. The transcriptional regulation properties of nFSHR gene were studied in mouse Sertoli (MSC-1) and non-Sertoli (H441) cell lines, and compared with those obtained with similar 129/J constructs. All constructs tested were more active in H441 than in MSC-1 cells. The low transcription levels detected in MSC-1 cells probably reflect the recruitment of Sertoli cells-specific nuclear factors that repress transcription of the FSHR gene. In H441 cells, 129/J constructs were more active than their neotomodon counterparts, indicating important species-specific differences in their transcription pattern. Functional analysis of a series of progressive 5'-deletion mutants identified regions involved in positive and negative transcriptional regulation as well as the strongest minimal promoter spanning 260 bp upstream the translation initiation site. The identification of inhibitory nuclear transcription factors, which are apparently expressed in MSC-1 cells, may contribute to a better understanding of the transcriptional regulation of the FSHR gene.

The gonadotropin receptors FSH-R and LH-R of Atlantic halibut (Hippoglossus hippoglossus)--2. Differential follicle expression and asynchronous oogenesis

The biological activity and spatio-temporal expression patterns of the gonadotropin receptors FSH-R and LH-R were examined in the repetitive spawner Atlantic halibut to elucidate the gonadotropic regulation of the asynchronous follicle development. The cloned receptors were expressed in mammalian COS-7 cells, and stimulation with sea bass FSH and LH increased the cAMP production. The halibut FSH-R and LH-R genes were shown to be highly expressed in the gonads of sexually mature fish, but the transcripts were also found in extra-gonadal tissues such as pituitary and brain. Different expression patterns of FSH-R and LH-R in the developing follicles were documented by semi-quantitative RT-PCR. Abundant FSH-R mRNA was found in the small follicles during primary growth and vitellogenesis, and the signals were localized to the granulosa cells by in situ hybridization. In contrast, follicular LH-R mRNA was hardly detectable during the early stages. Conversely, in follicles during final maturation FSH-R mRNA levels tended to decrease, while the expression of LH-R was highly upregulated. Whereas the pituitary FSH and LH are asynchronously expressed in annual spawners, both gonadotropins were expressed in the female halibut pituitary throughout the reproductive cycle, except in the prespawning females. Hence, the sequential gonadotropic activation of ovarian follicle growth and maturation in repetitive spawners is probably regulated by modulating the temporal expression of FSH-R and LH-R in the follicle membrane.

Proliferation of rat granulosa cells during the periovulatory interval

Granulosa cell proliferation during luteinization and terminal differentiation has historically been assumed to decline rapidly after an ovulatory stimulus. In contrast, terminal differentiation in other cell types has recently been associated with a transient increase in proliferation, suggesting that this may occur in the ovarian follicle. The goal of the current study was to test the hypothesis that an ovulatory stimulus to rats results in additional granulosa cell proliferation before cell cycle arrest. Immature rats were given a single injection of pregnant mare serum gonadotropin (PMSG) followed by human chorionic gonadotropin (hCG) to initiate periovulatory events. The proportion of granulosa cells in S phase did not change until 12 h after hCG, although the majority of the post-hCG proliferation was localized to cumulus granulosa cells for up to 10 h after hCG. The expression of cyclin D2 mRNA did not decline until 12 h after hCG, although both cyclin-dependent kinase (Cdk)4 and Cdk6 mRNA increased at 6 h. Protein levels of cyclin D2 and Cdk4 did not change as a result of hCG, whereas cyclin E increased 6 h after hCG. Kinase activity of Cdk2 dropped markedly by 4 h after hCG, but a slight increase in activity was evident 6-8 h after hCG. These data suggest that cumulus granulosa cells continue to proliferate for up to 10 h after an ovulatory stimulus, possibly via cyclin E/Cdk2. It is concluded that proliferation is maintained in granulosa cells in the proximity of the oocyte during luteinization of the rat follicle.