Insufficient luteinizing hormone-induced intracellular signaling disrupts ovulation in preovulatory follicles lacking estrogen receptor-{beta}

LH/hCG Regulation of Circular RNA in Mural Granulosa Cells during the Periovulatory Period in Mice

Ovarian follicles undergo a series of dynamic changes following the ovulatory surge of luteinizing hormone including cumulus expansion, oocyte maturation, ovulation, and luteinization. Post-transcriptional gene regulatory events are critical for mediating LH follicular responses, and among all RNA isoforms, circular RNA (circRNA) is one of the most abundant forms present in cells, yet they remain the least studied. Functionally, circRNA can act as miRNA sponges, protein sponges/decoys, and regulators of transcription and translation. In the context of ovarian follicular development, the identity and roles of circRNA are relatively unknown. In the present study, high throughput RNA sequencing of granulosa cells immediately prior to and 4-h after the LH/hCG surge identified 42,381 circRNA originating from 7712 genes. A total of 54 circRNA were identified as differentially expressed between 0-h and 4-h time points (Fold Change ± 1.5, FDR ≤ 0.1), among them 42 circRNA were upregulated and 12 circRNA were downregulated. All differentially expressed circRNA between the 0-h and 4-h groups were subjected to circinteractome analysis and identified networks of circRNA-protein and circRNA-miRNA were further subjected to "micro-RNA target filter analysis" in Ingenuity Pathway Analyses, which resulted in the identification of miRNA targeted mRNAs. A comparison of these circRNA target mRNAs with LH-induced mRNAs identified Runx2, Egfr, Areg, Sult1el, Cyp19a1, Cyp11a1, and Hsd17b1 as targets of circKif2, circVcan, circMast4, and circMIIt10. These newly identified LH/hCG-induced circRNA, their target miRNA and protein networks provide new insights into the complex interactions associated with periovulatory follicular development.

Expression and regulation of estrogen receptor 2 and its coregulators in mouse granulosa cells

The cooperative effects of estrogen and oocyte-derived paracrine factors (ODPFs) play critical roles in the normal development of ovarian follicles; however, the mechanism underlying this cooperation has not been well studied. The present study aimed to determine whether ODPFs affect estrogen signaling by regulating the expression of estrogen receptor (ESR) and its coregulators in mouse granulosa cells. Some transcripts encoding ESR coregulators were differentially expressed between cumulus and mural granulosa cells (MGCs). The transcript levels of ESR coregulators, including nuclear receptor corepressor 1 and activator 2, in cumulus cells were significantly suppressed by ODPFs; however, they increased when cumulus cell-oocyte complexes were treated with the transforming growth factor beta receptor I inhibitor, SB431542. Moreover, MGCs exhibited significantly higher ESR2 protein and transcript levels than those in cumulus cells. ODPFs promoted Esr2 expression in cumulus cells but had no effect on that in MGCs. Overall, regulation of the expression of ESR2 and its coregulators in cumulus cells by oocytes seems to be one of the mechanisms underlying estrogen-oocyte cooperation in well-developed antral follicles in mice.

Nuclear receptors: Key regulators of somatic cell functions in the ovulatory process

The development of the ovarian follicle to its culmination by ovulation is an essential element of fertility. The final stages of ovarian follicular growth are characterized by granulosa cell proliferation and differentiation, and steroid synthesis under the influence of follicle-stimulating hormone (FSH). The result is a population of granulosa cells poised to respond to the ovulatory surge of luteinizing hormone (LH). Members of the nuclear receptor superfamily of transcription factors play indispensable roles in the regulation of these events. The key regulators of the final stages of follicular growth that precede ovulation from this family include the estrogen receptor beta (ESR2) and the androgen receptor (AR), with additional roles for others, including steroidogenic factor-1 (SF-1) and liver receptor homolog-1 (LRH-1). Following the LH surge, the mural and cumulus granulosa cells undergo rapid changes that result in expansion of the cumulus layer, and a shift in ovarian steroid hormone biosynthesis from estradiol to progesterone production. The nuclear receptor best associated with these events is LRH-1. Inadequate cumulus expansion is also observed in the absence of AR and ESR2, but not the progesterone receptor (PGR). The terminal stages of ovulation are regulated by PGR, which increases the abundance of the proteases that are directly responsible for rupture. It further regulates the prostaglandins and cytokines associated with the inflammatory-like characteristics of ovulation. LRH-1 regulates PGR, and is also a key regulator of steroidogenesis, cellular proliferation, and cellular migration, and cytoskeletal remodeling. In summary, nuclear receptors are among the panoply of transcriptional regulators with roles in ovulation, and several are necessary for normal ovarian function.

Follicle-stimulating hormone and luteinizing hormone increase Ca2+ in the granulosa cells of mouse ovarian follicles†

In mammalian ovarian follicles, follicle stimulating hormone (FSH) and luteinizing hormone (LH) signal primarily through the G-protein Gs to elevate cAMP, but both of these hormones can also elevate Ca2+ under some conditions. Here, we investigate FSH- and LH-induced Ca2+ signaling in intact follicles of mice expressing genetically encoded Ca2+ sensors, Twitch-2B and GCaMP6s. At a physiological concentration (1 nM), FSH elevates Ca2+ within the granulosa cells of preantral and antral follicles. The Ca2+ rise begins several minutes after FSH application, peaks at ∼10 min, remains above baseline for another ∼10 min, and depends on extracellular Ca2+. However, suppression of the FSH-induced Ca2+ increase by reducing extracellular Ca2+ does not inhibit FSH-induced phosphorylation of MAP kinase, estradiol production, or the acquisition of LH responsiveness. Like FSH, LH also increases Ca2+, when applied to preovulatory follicles. At a physiological concentration (10 nM), LH elicits Ca2+ oscillations in a subset of cells in the outer mural granulosa layer. These oscillations continue for at least 6 h and depend on the activity of Gq family G-proteins. Suppression of the oscillations by Gq inhibition does not inhibit meiotic resumption, but does delay the time to 50% ovulation by about 3 h. In summary, both FSH and LH increase Ca2+ in the granulosa cells of intact follicles, but the functions of these Ca2+ rises are only starting to be identified.

MiR-126-3p inhibits apoptosis and promotes proliferation by targeting phosphatidylinositol 3-kinase regulatory subunit 2 in porcine ovarian granulosa cells

Objective

Numerous studies have indicated that the apoptosis and proliferation of granulosa cells (GCs) are closely related to the normal growth and development of follicles and ovaries. Previous evidence has suggested that miR-126-3p might get involved in the apoptosis and proliferation of GCs, and phosphatidylinositol 3-kinase regulatory subunit 2 (PIK3R2) gene has been predicted as one target of miR-126-3p. However, the molecular regulation of miR-126-3p on PIK3R2 and the effects of PIK3R2 on porcine GCs apoptosis and proliferation remain virtually unexplored.

Methods

In this study, using porcine GCs as a cellular model, luciferase report assay, mutation and deletion were applied to verify the targeting relationship between miR-126-3p and PIK3R2. Annexin-V/PI staining and 5-ethynyl-2′-deoxyuridine assay were applied to explore the effect of PIK3R2 on GCs apoptosis and proliferation, respectively. Real-time quantitative polymerase chain reaction and Western Blot were applied to explore the regulation of miR-126-3p on PIK3R2 expression.

Results

We found that miR-126-3p targeted at PIK3R2 and inhibited its mRNA and protein expression. Knockdown of PIK3R2 significantly inhibited the apoptosis and promoted the proliferation of porcine GCs, and significantly down-regulated the mRNA expression of several key genes of PI3K pathway such as insulin-like growth factor 1 receptor (IGF1R), insulin receptor (INSR), pyruvate dehydrogenase kinase 1 (PDK1), and serine/threonine kinase 1 (AKT1).

Conclusion

MiR-126-3p might target and inhibit the mRNA and protein expressions of PIK3R2, thereby inhibiting GC apoptosis and promoting GC proliferation by down-regulating several key genes of the PI3K pathway, IGF1R, INSR, PDK1, and AKT1. These findings would provide great insight into further exploring the molecular regulation of miR-126-3p and PIK3R2 on the functions of GCs during the folliculogenesis in female mammals.

ESR2 regulates granulosa cell genes essential for follicle maturation and ovulation

Estrogen receptor 2 (ESR2) plays a critical role in folliculogenesis and ovulation. Disruption of ESR2-function in the rats results in female infertility due to failure of ovulation. Ovulation failure occurred in two distinct rat models, a null mutant and a DNA binding domain (DBD) mutant of ESR2, indicating that transcriptional regulation by ESR2 is indispensable for ovulation. To define the regulatory role of ESR2 in preovulatory follicular maturation and ovulation, we investigated ovarian responsiveness to exogenous gonadotropins in prepubertal females. Granulosa cells (GCs) play a vital role in follicle maturation and ovulation, and ESR2-dependent estrogen signaling is predominant in GCs, therefore, we examined the differential expression of gonadotropin-induced genes in GCs. Of 32,623 genes detected by RNA-sequencing, 1696 were differentially expressed in Esr2-mutant rats (789 downregulated, and 907 upregulated, absolute fold change 2, FDR p < 0.05). Molecular pathway analyses indicated that these differentially expressed genes are involved in steroidogenesis, follicle maturation, and ovulation. Many of these genes are known regulators of ovarian function and a subset were also disrupted in Esr2-mutant mice. Interestingly, Kiss1 was identified as one of the differentially expressed genes implicating a potential role within the follicle and its regulation by ESR2. Our findings indicate that ESR2 regulates key genes in GCs that are essential for follicle maturation and ovulation in the rat.

Multiple cAMP Phosphodiesterases Act Together to Prevent Premature Oocyte Meiosis and Ovulation

Luteinizing hormone (LH) acts on the granulosa cells that surround the oocyte in mammalian preovulatory follicles to cause meiotic resumption and ovulation. Both of these responses are mediated primarily by an increase in cyclic adenosine monophosphate (cAMP) in the granulosa cells, and the activity of cAMP phosphodiesterases (PDEs), including PDE4, contributes to preventing premature responses. However, two other cAMP-specific PDEs, PDE7 and PDE8, are also expressed at high levels in the granulosa cells, raising the question of whether these PDEs also contribute to preventing uncontrolled activation of meiotic resumption and ovulation. With the use of selective inhibitors, we show that inhibition of PDE7 or PDE8 alone has no effect on the cAMP content of follicles, and inhibition of PDE4 alone has only a small and variable effect. In contrast, a mixture of the three inhibitors elevates cAMP to a level comparable with that seen with LH. Correspondingly, inhibition of PDE7 or PDE8 alone has no effect on meiotic resumption or ovulation, and inhibition of PDE4 alone has only a partial and slow effect. However, the fraction of oocytes resuming meiosis and undergoing ovulation is increased when PDE4, PDE7, and PDE8 are simultaneously inhibited. PDE4, PDE7, and PDE8 also function together to suppress the premature synthesis of progesterone and progesterone receptors, which are required for ovulation. Our results indicate that three cAMP PDEs act in concert to suppress premature responses in preovulatory follicles.

Defining the Role of Estrogen Receptor β in the Regulation of Female Fertility

Estrogens are essential hormones for the regulation of fertility. Cellular responses to estrogens are mediated by estrogen receptor α (ESR1) and estrogen receptor β (ESR2). In mouse and rat models, disruption of Esr1 causes infertility in both males and females. However, the role of ESR2 in reproductive function remains undecided because of a wide variation in phenotypic observations among Esr2-mutant mouse strains. Regulatory pathways independent of ESR2 binding to its cognate DNA response element have also been implicated in ESR2 signaling. To clarify the regulatory roles of ESR2, we generated two mutant rat models: one with a null mutation (exon 3 deletion, Esr2ΔE3) and the other with an inframe deletion selectively disrupting the DNA binding domain (exon 4 deletion, Esr2ΔE4). In both models, we observed that ESR2-mutant males were fertile. ESR2-mutant females exhibited regular estrous cycles and could be inseminated by wild-type (WT) males but did not become pregnant or pseudopregnant. Esr2-mutant ovaries were small and differed from WT ovaries by their absence of corpora lutea, despite the presence of follicles at various stages of development. Esr2ΔE3- and Esr2ΔE4-mutant females exhibited attenuated preovulatory gonadotropin surges and did not ovulate in response to a gonadotropin regimen effective in WT rats. Similarities of reproductive deficits in Esr2ΔE3 and Esr2ΔE4 mutants suggest that DNA binding-dependent transcriptional function of ESR2 is critical for preovulatory follicle maturation and ovulation. Overall, the findings indicate that neuroendocrine and ovarian deficits are linked to infertility observed in Esr2-mutant rats.

Differential Activation of a Mouse Estrogen Receptor β Isoform (mERβ2) with Endocrine-Disrupting Chemicals (EDCs)

BACKGROUND

Endocrine-disrupting chemicals (EDCs) are suspected of altering estrogenic signaling through estrogen receptor (ER) α or β (mERβ1 in mice). Several EDC effects have been reported in animal studies and extrapolated to human studies. Unlike humans, rodents express a novel isoform of ERβ (mERβ2) with a modified ligand-binding domain sequence. EDC activity through this isoform remains uncharacterized.

OBJECTIVES

We identified the expression pattern of mERβ2 in mouse tissues and assessed the estrogenic activity of EDCs through mERβ2.

METHODS

mERβ2 mRNA expression was measured in mouse tissues. HepG2 cells were used to assess the transactivation activity of mERβ isoforms with EDCs and ER co-activators. 293A cells transiently transfected with mER isoforms were used to detect EDC-mediated changes in endogenous ER target gene expression.

RESULTS

Expression of mERβ2 mRNA was detected in mouse reproductive tissues (ovary, testis, and prostate) and lung and colon tissues from both female and male mice. Five (E2, DES, DPN, BPAF, Coum, 1-BP) of 16 compounds tested by reporter assay had estrogenic activity through mERβ2. mERβ2 had a compound-specific negative effect on ERβ/ligand-mediated activity and ER target genes when co-expressed with mERβ1. mERβ2 recruited coactivators SRC2 or SRC3 in the presence of EDCs, but showed less recruitment than mERβ1.

CONCLUSION

mERβ2 showed weaker estrogenic activity than mERβ1 in our in vitro system, and can dampen mERβ1 activity. In vivo models of EDC activity and ER-mediated toxicity should consider the role of mERβ2, as rodent tissue responses involving mERβ2 may not be reproduced in human biology.

Regulation of Mammalian Oocyte Meiosis by Intercellular Communication Within the Ovarian Follicle

Meiotic progression in mammalian preovulatory follicles is controlled by the granulosa cells around the oocyte. Cyclic GMP (cGMP) generated in the granulosa cells diffuses through gap junctions into the oocyte, maintaining meiotic prophase arrest. Luteinizing hormone then acts on receptors in outer granulosa cells to rapidly decrease cGMP. This occurs by two complementary pathways: cGMP production is decreased by dephosphorylation and inactivation of the NPR2 guanylyl cyclase, and cGMP hydrolysis is increased by activation of the PDE5 phosphodiesterase. The cGMP decrease in the granulosa cells results in rapid cGMP diffusion out of the oocyte, initiating meiotic resumption. Additional, more slowly developing mechanisms involving paracrine signaling by extracellular peptides (C-type natriuretic peptide and EGF receptor ligands) maintain the low level of cGMP in the oocyte. These coordinated signaling pathways ensure a fail-safe system to prepare the oocyte for fertilization and reproductive success.

Estrogen Hormone Biology

The hormone estrogen is involved in both female and male reproduction, as well as numerous other biological systems including the neuroendocrine, vascular, skeletal, and immune systems. Therefore, it is also implicated in many different diseases and conditions such as infertility, obesity, osteoporosis, endometriosis, and a variety of cancers. Estrogen works through its two distinct nuclear receptors, estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ). Various transcriptional regulation mechanisms have been identified as the mode of action for estrogen, mainly the classical mechanism with direct DNA binding but also a nongenomic mode of action and one using tethered or indirect binding. The expression profiles of ERα and ERβ are unique with the primary sites of ERα expression being the uterus and pituitary gland and the main site of ERβ expression being the granulosa cells of the ovary. Mouse models with knockout or mutation of Esr1 and Esr2 have furthered our understanding of the role of each individual receptor plays in physiology. From these studies, it is known that the primary roles for ERα are in the uterus and neuroendocrine system, as female mice lacking ERα are infertile due to impaired ovarian and uterine function, whereas female mice lacking ERβ are subfertile due to ovarian defects. The development of effective therapies for estrogen-related diseases has relied on an understanding of the physiological roles and mechanistic functionalities of ERα and ERβ in human health and disease.

Development and Characterization of Novel Rat Anti-mERβ Sera

Estrogens regulate normal sexual and reproductive development in females. Their actions are mediated mainly by estrogen receptor (ER)α and ERβ. Understanding the function of ERs necessitates knowing their cellular location and protein partners, which, in turn, requires reliable and specific antibodies. Several antibodies are available for ERα; however, discrepancies in immunoreactivity have been reported for ERβ. Here, we have developed antisera for mouse ERβ (mERβ) using a specific C-terminal 18-amino acid peptide conjugated to mariculture keyhole limpet hemocyanin. Sprague Dawley rats were immunized, and the resulting antisera were characterized by Western blot analysis of nuclear extracts from tissues of wild-type (WT) mice, and mice genetically modified to lack either ERα (CERαKO) or ERβ (CERβKO). An approximately 56-kDa protein was detected in the hypothalamus, uterus, ovary, mammary gland, testes, and epididymis of WT mice, consistent with the predicted molecular size of ERβ. In addition, the same protein band was identified in in vitro synthesized mERβ protein and in the mammary glands of CERαKO mice. The approximately 56-kDa protein was not observed in in vitro synthesized mERα protein or in any tissue examined in the CERβKO mice. Immunohistochemistry using the antisera revealed ERβ staining in the granulosa cells of WT ovaries and in the mediobasal hypothalamus, paraventricular nucleus, and cerebral cortex in the WT adult mouse brain. These data suggest that the novel rat anti-mERβ sera are specific to ERβ to allow investigators to explore to cellular and physiological role of ERβ in the brain and other mouse tissues.

De Novo-Synthesized Retinoic Acid in Ovarian Antral Follicles Enhances FSH-Mediated Ovarian Follicular Cell Differentiation and Female Fertility

Retinoic acid (RA) is the active form of vitamin A and is synthesized from retinol by two key enzymes, alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH). As the physiological precursor of RA, retinol impacts female reproductive functions and fertility. The expression of Adh1 and Adh5 as well as Aldh1a1 and Aldh1a7 are significantly increased in the ovaries of mice treated with equine chorionic gonadotropin/FSH. The RA receptor is expressed and localized in granulosa cells and is activated by endogenous RA as indicated by LacZ expression in granulosa cells of RA-responsive transgene-LacZ transgenic mice (RA reporter mice). Coinjection of the ADH inhibitor, 4-methylpyrazole, with equine chorionic gonadotropin significantly decreases the number and developmental competence of oocytes ovulated in response to human chorionic gonadotropin/LH as compared with controls. Injections of RA completely reverse the effects of the inhibitor of ovulation and oocyte development. When mice were fed a retinol-free, vitamin A-deficient diet that significantly reduced the serum levels of retinol, the expression of the LH receptor (Lhcgr) was significantly lower in the ovaries of the vitamin A-deficient mice, and injections of human chorionic gonadotropin failed to induce genes controlling ovulation. These results indicate that ovarian de novo biosynthesis of RA is required for the follicular expression of Lhcgr in granulosa cells and their ability to respond to the ovulatory LH surge.

Co-administration of insulin with a gonadotropin partly improves ovulatory responses of estrogen-deficient mice

Administration of 17-βestradiol (E2) with pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) can induce ovulation in estrogen-deficient (ArKO) mice; nevertheless, ovulatory efficiency and rate are low. In this study, effects of insulin on the ovulatory responses were investigated. In ArKO ovary, hCG signal was found to be transmitted in an uncoordinated manner when phosphorylation levels of signaling molecules are examined. Co-administration of insulin with hCG improved the transmission of hCG signal as well as the ovulatory efficiency in ArKO mice. It also improved the ovulatory rate but far below the wild-type rate. Gene expression analysis demonstrated that Cyp11a1 and Cyp17a1 mRNAs were significantly induced 4 h after PMSG administration in the wild-type ovary, but not in ArKO ovary. Collectively, these results suggest that insulin improves ovulatory responses of ArKO mice, but it fails to ameliorate follicular dysfunctions caused possibly by an inappropriate intraovarian milieu during follicular maturation.

The naturally occurring luteinizing hormone surge is diminished in mice lacking estrogen receptor Beta in the ovary

Female ESR2-null mice (betaERKO) display defects in ovarian function and are subfertile. Follicular maturation is impaired and explains smaller litters, but betaERKO also produce fewer litters, which may be partially due to inadequate ovulatory signals. To test this, the amplitude and timing of the naturally occurring luteinizing hormone (LH) surge was measured in individual intact betaERKO and wild-type (WT) mice. Vaginal cytology was evaluated daily, and blood samples were taken from mice in proestrus. The amplitude of the LH surge was severely blunted in betaERKO mice compared to WT, but pituitary LH levels revealed no differences. The betaERKO mice did not produce a preovulatory estradiol surge. To determine if the smaller LH surges and the reduced number of litters in betaERKO were due to the lack of ESR2 in the hypothalamic-pituitary axis or due to the absence of ESR2 in the ovary, ovaries were transplanted from WT into betaERKO mice and vice versa. The size of the LH surge was reduced only in mice lacking ESR2 within the ovary, and these mice had fewer litters. Fertility and size of the LH surge were rescued in betaERKO mice receiving a WT ovary. These data provide the first experimental evidence that the LH surge is impaired in betaERKO females and may contribute to their reduced fertility. ESR2 is not necessary within the pituitary and hypothalamus for the generation of a normal LH surge and for normal fertility, but ESR2 is essential within the ovary to provide proper signals.

The absence of ER-β results in altered gene expression in ovarian granulosa cells isolated from in vivo preovulatory follicles

Determining the spatial and temporal expression of genes involved in the ovulatory pathway is critical for the understanding of the role of each estrogen receptor in the modulation of folliculogenesis and ovulation. Estrogen receptor (ER)-β is highly expressed in ovarian granulosa cells, and mice lacking ER-β are subfertile due to inefficient ovulation. Previous work has focused on isolated granulosa cells or cultured follicles and, although informative, provides confounding results due to the heterogeneous cell types present including granulosa and theca cells and oocytes and exposure to in vitro conditions. Herein we isolated preovulatory granulosa cells from wild-type (WT) and ERβ-null mice using laser capture microdissection to examine the genomic transcriptional response downstream of pregnant mare serum gonadotropin (mimicking FSH) and pregnant mare serum gonadotropin/human chorionic gonadotropin (mimicking LH) stimulation. This allows for a direct comparison of in vivo granulosa cells at the same stage of development from both WT and ERβ-null ovaries. ERβ-null granulosa cells showed altered expression of genes known to be regulated by FSH (Akap12 and Runx2) as well as not previously reported (Arnt2 and Pou5f1) in WT granulosa cells. Our analysis also identified 304 genes not previously associated with ERβ in granulosa cells. LH-responsive genes including Abcb1b and Fam110c show reduced expression in ERβ-null granulosa cells; however, novel genes including Rassf2 and Megf10 were also identified as being downstream of LH signaling in granulosa cells. Collectively, our data suggest that granulosa cells from ERβ-null ovaries may not be appropriately differentiated and are unable to respond properly to gonadotropin stimulation.

Effects of systemic administration or intrabursal injection of serotonin on puberty, first ovulation and follicular development in rats

To elucidate the role of serotonin in the onset of puberty, the effects of both systemic and in-ovarian bursa administration of serotonin on the neuroendocrine mechanism that modulates the onset of puberty, follicular development and first ovulation were evaluated. Two experiments were carried out. For the first, 25 or 37.5 mg kg–1 of bodyweight of serotonin creatinine sulfate was administered by a subcutaneous route to 30-day-old female rats. In the second experiment, serotonin creatinine sulfate was administered directly into the ovarian bursa of 34-day-old female rats. Systemic administration of 25 or 37.5 mg kg–1 of serotonin creatinine sulfate induced a delay in the ages of vaginal opening and first vaginal oestrus, a decrease in the number of ovulating animals, and serum concentrations of FSH, LH, oestradiol and progesterone. An increase in the number of Class 3 (>500 μm) and atretic follicles was observed in the ovaries of these animals. The administration of serotonin creatinine sulfate in the ovarian bursa did not modify the onset of puberty and ovulation, but a reduced serum concentration of oestradiol was observed. Our results suggest that serotonin acts on the components of the hypothalamus–hypophysis–ovary axis by modulating follicular development, ovarian functions and the onset of puberty.

Role of estrogen receptor signaling required for endometriosis-like lesion establishment in a mouse model

Endometriosis results from ectopic invasion of endometrial tissue within the peritoneal cavity. Aberrant levels of the estrogen receptor (ER), ERα and ERβ, and higher incidence of autoimmune disorders are observed in women with endometriosis. An immunocompetent mouse model of endometriosis was used in which minced uterine tissue from a donor was dispersed into the peritoneal cavity of a recipient. Wild-type (WT), ERα-knockout (αERKO), and βERKO mice were donors or recipients to investigate the roles of ERα, ERβ, and estradiol-mediated signaling on endometriosis-like disease. Mice were treated with vehicle or estradiol, and resulting location, number, and size of endometriosis-like lesions were assessed. In comparison with WT lesions in WT hosts, αERKO lesions in WT hosts were smaller and fewer in number. The effect of ER status and estradiol treatment on nuclear receptor status, proliferation, organization, and inflammation within lesions were examined. αERKO lesions in WT hosts did not form distal to the incision site, respond to estradiol, or proliferate but did have increased inflammation. WT lesions in αERKO hosts did respond to estradiol, proliferate, and show decreased inflammation with treatment, but surprisingly, progesterone receptor expression and localization remained unchanged. Only minor differences were observed between WT lesions in βERKO hosts and βERKO lesions in WT hosts, demonstrating the estradiol-mediated signaling responses are predominately through ERα. In sum, these results suggest ER in both endometriosis-like lesions and their environment influence lesion characteristics, and understanding these interactions may play a critical role in elucidating this enigmatic disease.

Amounts of an estrogen receptor β isoform increased in the theca of preovulatory follicles of sheep

Determination of the specific roles of the estrogen receptor (ER) forms in reproductive processes of different species remains incomplete. In the present experiment, cellular localization and changes in relative amounts of the ERα and ERβ in late developing ovarian follicles, oviduct, and uterus were determined during the follicular phase of the estrous cycle in sheep. Ewes in mid-luteal phase were treated with prostaglandin F(2α) (PG) to induce luteolysis and control the onset of the follicular phase. The oviducts, uterus, and the ovaries were collected at 0 (ewes not treated with PG), 4, 18, and 36 h after PG treatment (early, mid, and late follicular phase, respectively) and processed to evaluate the ERs using immunohistochemical (IHC) procedures. The ERα was localized to nuclei of granulosa cells of late developing follicles and most cells of the oviduct and uterus. The ERβ was detected only in ovarian follicles using two antibodies directed to different regions of the ERβ. Western immunoblotting demonstrated that the antibody directed against the N-terminal region of the ERβ detected one isoform (approximately 53 kDa) whereas the antibody directed against the C-terminus detected two ERβ isoforms (approximately 53 kDa and 59 kDa). Western and IHC results combined indicated presence of the 59 kDa ERβ in granulosa cells and the 53 kDa ERβ in both granulosa and theca cells. Relative amounts (immunostaining intensity) of the ERα increased (P<.05) in granulosa cells of preovulatory follicles and in the isthmian muscularis of the oviduct at the late follicular phase. Amounts of the ERα in the mucosal epithelium of the oviductal regions (isthmus, ampulla, and infundibulum), and in various uterine cell types (glandular and luminal epithelia, endometrial stromal cells, and myometrium) did not change (P>.05) throughout the follicular phase. A major increase (four-fold) in expression of the 53 kDa ERβ in the theca and a less pronounced increase in the granulosa occurred at the late follicular phase. The ERα is broadly expressed in reproductive organs of sheep and is upregulated only in few cell types during the late follicular phase. Immunoreactive ERβ was detected only in the ovary. Important estrogen actions in theca cells during preovulatory follicular development likely occur in association with a major increase in expression of an ERβ isoform.

Expression of extracellular matrix components is disrupted in the immature and adult estrogen receptor β-null mouse ovary

Within the ovary, Estrogen Receptor β (ERβ) is localized to the granulosa cells of growing follicles. 17β-estradiol (E2) acting via ERβ augments the actions of follicle stimulating hormone in granulosa cells, leading to granulosa cell differentiation and formation of a preovulatory follicle. Adult ERβ-null females are subfertile and possess ovaries with reduced numbers of growing follicles and corpora lutea. Because the majority of E2 production by granulosa cells occurs once puberty is reached, a role for ERβ in the ovary prior to puberty has not been well examined. We now provide evidence that lack of ERβ disrupts gene expression as early as post-natal day (PND) 13, and in particular, we identify a number of genes of the extracellular matrix (ECM) that are significantly higher in ERβ-null follicles than in wildtype (WT) follicles. Considerable changes occur to the ECM occur during normal folliculogenesis to allow for the dramatic growth, cellular differentiation, and reorganization of the follicle from the primary to preovulatory stage. Using quantitative PCR and immunofluorescence, we now show that several ECM genes are aberrantly overexpressed in ERβ-null follicles. We find that Collagen11a1, a protein highly expressed in cartilage, is significantly higher in ERβ-null follicles than WT follicles as early as PND 13, and this heightened expression continues through PND 23–29 into adulthood. Similarly, Nidogen 2, a highly conserved basement membrane glycoprotein, is elevated in ERβ-null follicles at PND 13 into adulthood, and is elevated specifically in the ERβ-null focimatrix, a basal lamina-like matrix located between granulosa cells. Focimatrix laminin and Collagen IV expression were also higher in ERβ-null ovaries than in WT ovaries at various ages. Our findings suggest two novel observations: a) that ERβ regulates granulosa cell gene expression ovary prior to puberty, and b) that ERβ regulates expression of ECM components in the mouse ovary.

Estrogen promotes the development of mouse cumulus cells in coordination with oocyte-derived GDF9 and BMP15

The differentiation and function of cumulus cells depend upon oocyte-derived paracrine factors, but studies on the estrogen receptor knockout mice suggested that estrogen also participates in these processes. This study investigates the possible coordination of estrogen and oocytes in the development and function of cumulus cells using cumulus expansion and the expression of transcripts required for expansion as functional endpoints. Preantral granulosa cell-oocyte complexes developed in vitro with 17β-estradiol (E2) exhibited increased levels of cumulus expansion and Has2 transcripts, encoding hyaluronan synthase 2, compared with those developed without E2. Moreover, cumulus cell-oocyte complexes (COCs) isolated from antral follicles and maintained in culture without E2 exhibited reduced cumulus expansion and Has2 mRNA levels compared with freshly isolated COCs. Exogenous E2, provided during the maintenance culture, alleviated these deficiencies. However, when oocytes were removed from COCs, E2 supplementation did not maintain competence to undergo expansion; the presence in culture of either fully grown oocytes or recombinant growth differentiation factor 9 (GDF9) was required. Recombinant bone morphogenetic protein 15, but not fibroblast growth factor 8, augmented the GDF9 effect. Oocytes or GDF9 suppressed cumulus cell levels of Nrip1 transcripts encoding nuclear receptor-interacting protein 1, a potential inhibitor of estrogen receptor signals. Therefore, E2 and oocyte-derived paracrine factors GDF9 and bone morphogenetic protein 15 coordinate to promote the development of cumulus cells and maintain their competence to undergo expansion. Furthermore, suppression of Nrip1 expression in cumulus cells by oocyte may be one mechanism mediating cross talk between oocyte and E2 signals that promotes follicular development.