Lanosterol metabolic product(s) is involved in primordial folliculogenesis and establishment of primordial folliclepool in mouse fetal ovary

Effect of FSH on E2/GPR30-mediated mouse oocyte maturation in vitro

Mammalian oocyte restores meiosis can be stimulated by follicle-stimulating hormone (FSH) under normal physiological conditions. G-protein coupled receptor 30 (GPR30), an non-classical estrogen membrane receptor, has been widely reported in teleost oocyte maturation. However, it remains unknown whether GPR30 involves the role of FSH in mammalian cumulus expansion and oocyte maturation. Here, we used mouse cumulus-oocyte complexes (COCs) as a model to investigate how FSH affects the in vitro maturation of mouse oocytes mediated by 17β-estradiol (E₂)/GPR30signaling. Our study reveals that FSH starts regulating mouse cumulus expansion precisely at 8h in in vitro culture. ELISA measurement of E₂ levels in culture medium revealed that FSH activated aromatase to promote E₂ production in vitro in cultured mouse COCs. Moreover, the results of real-time quantitative PCR indicated that FSH-induced in vitro maturation of mouse oocytes was regulated by the estrogen-signaling pathway mediated by GPR30; FSH treatment markedly increased the mRNA expression of HAS2, PTGS2, and GREM1 in COCs. Exploration of the underlying mechanism suggested that E₂ produced by mouse COCs regulated the phosphorylation level of extracellular signal-regulated kinase 1/2 (ERK1/2) through GPR30 and thereby promoted mouse cumulus-cell expansion and oocyte maturation. In conclusion, our study reveals that FSH induced estrogen production in mouse COCs through aromatase, and that aromatase/GPR30/ERK1/2 signaling is involved in FSH-induced cumulus expansion.

Roles of different n-3/n-6 PUFA ratios in ovarian cell development and steroidogenesis in PCOS rats

Polycystic ovary syndrome (PCOS) is a complex and common endocrine disorder characterized by hyperandrogenism, which is accompanied by follicle growth arrest at the small antral stage, minimal granulosa cell proliferation, and chronic anovulation. Polyunsaturated fatty acids (PUFAs) are necessary for the body's metabolism, growth and development. Although PUFAs play an important role in the regulation of female reproduction, their role in ovarian development in PCOS is still unclear. The present study was conducted to investigate the effects of different ratios of n-3/n-6 PUFAs (omega-3/omega-6) on ovary development in PCOS rats. Serum levels of reproductive hormones and enzymes related to steroidogenesis were assessed. The results indicated that PUFAs (n-3/n-6: 1/15) significantly increased ovarian weight and improved the ovarian structure although they had no significant effect on body weight in PCOS rats. Meanwhile, apoptosis was attenuated accompanied by increased cell proliferation by PUFAs (n-3/n-6: 1/15). Moreover, serum levels of hormones (FSH and E₂) were also significantly increased by PUFAs (n-3/n-6: 1/15) accompanied by decreased T levels. To investigate whether PUFAs regulate the expression of enzymes related to hormone synthesis, western blotting was used to determine the protein levels of CYP51, CYP19, StAR and 3β-HSD. The results showed that PUFAs significantly increased the protein levels of all of these enzymes. These results indicate that PUFAs enhance the reproductive performance of PCOS by increasing the expression of steroidogenesis enzymes, which are related to hormone secretion and ovarian functions. These findings provide evidence that a balanced n-3/n-6 PUFA ratio is beneficial for PCOS reproduction.

Regulation by 3,5,3'-tri-iodothyronine and FSH of cytochrome P450 family 19 (CYP19) expression in mouse granulosa cells

Cytochrome P450 family 19 (CYP19) plays an important role in follicular development, which is regulated by FSH. Although 3,5,3'-tri-iodothyronine (T3) combines with FSH to induce preantral follicle growth and granulosa cell development, the mechanism involved remains unclear. The aim of the present study was to determine the cellular and molecular mechanisms by which thyroid hormone (TH) and FSH regulate CYP19 expression and sterol biosynthesis during preantral follicle growth. Mice were injected subcutaneously (s.c.) with eCG (Equine chorionic gonadotropin). The results showed that eCG increased CYP19 expression in ovarian cells. CYP19 expression in granulosa cells was increased after FSH treatment, and this response was enhanced by T3. Knockdown of CYP19 significantly decreased granulosa cell viability and hormone-stimulated proliferation. In addition, CYP19 knockdown also blocked T3- and FSH-induced oestradiol (E2) synthesis in granulosa cells. Furthermore, activation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway was required for T3 and FSH regulation of CYP19 expression. In conclusion, the results of the present study indicate that CYP19 is important for T3- and FSH-induced granulosa cell development in the early stages. CYP19 could be a downstream effector of the PI3K/Akt pathway in regulating TH and FSH during follicular development and sterol biosynthesis. The findings suggest that CYP19 is a novel mediator of T3- and FSH-induced follicular development.

Effect of hypothyroidism on CYP51 and FSHR expression in rat ovary

Although thyroid hormone (TH) plays important roles in regulating ovarian development, the mechanism are still unclear. Cytochrome P450 lanosterol 14α-demethylase (CYP51) is a key enzyme in sterols and steroids biosynthesis that involved in folliculogenesis and oocyte maturation, which is regulated by follicle stimulating hormone (FSH). However, the effect of TH on CYP51 expression in ovarian cells is unclear. The objective of this study was to determine the effects of TH on CYP51 in rat ovary. Hypothyroidism rats were induced by 6-propyl-2-thiouracil (PTU), genes expressions in ovary were analyzed by Western blot or qRT-PCR. The data showed that CYP51 was significantly decreased in hypothyroidism, which was accompanied by the down-regulation of mRNA level. Meanwhile, similar tendency was also showed in FSHR expression in hypothyroidism. To evaluate the effect of the gonadotropin on CYP51 and FSHR expression in ovarian cells in vivo, hypo rats were injected subcutaneously with equine chorionic gonadotropin (eCG) respectively. The results showed that eCG reversed CYP51 and FSHR expression in hypo group. Moreover, FSH-induced CYP51 expression was meditated by FSHR. In addition, serum concentration of FSH and E₂ were also decreased in hypothyroidism, and E₂ was up-regulated by eCG treatment. These results indicate that hypothyroidism changes CYP51 and FSHR expression in ovary, which are regulated by gonadotropin. Moreover, genes changes in ovary are at least partially attributed to steroids biosynthesis.

Effects of omega-3 polyunsaturated fatty acids on steroidogenesis and cellular development in PCOS rats

Polycystic ovary syndrome (PCOS) is a common endocrine disorder, which is characterized by hyperandrogenism.

Retinoic acid-induced CYP51 nuclear translocation promotes meiosis prophase I process and is correlated to the expression of REC8 and STAG3 in mice

Lanosterol 14 α-demethylase (CYP51) plays a crucial role in cholesterol biosynthesis. In gamete development, CYP51 is involved in initiating meiosis resumption in oocytes through its product, meiosis activating sterol (MAS). In this study, CYP51 was observed to localize within the nucleus of germ cells undergoing meiotic prophase I. Following the addition of retinoic acid (RA) to induce meiosis or the RA receptor pan-antagonist AGN193109 to block meiosis in fetal ovaries, the translocation of CYP51 into the nucleus of oocytes was advanced or delayed, respectively. In addition, treatment with Cyp51-siRNA or RS21745, a specific CYP51 inhibitor, significantly delayed the meiotic progression of oocytes in the ovary, with most oocytes arresting at the zygotene stage, and likewise, significantly reduced perinatal primordial follicle formation. Furthermore, inhibition of CYP51 is correlated to significantly decreased expression of REC8 and STAG3, both of which are meiosis-specific cohesin subunits. To sum up, RA-induced CYP51 nuclear translocation is critical for oocytes meiotic progression, and consequently folliculogenesis, which might act through impacting the expression of meiosis-specific cohesins REC8 and STAG3.

Summary: CYP51 displays cytoplasm-to-nucleus translocation in germ cells in mice. CYP51 participates in germ cell meiotic progression and folliculogenesis via regulating the expression of cohesin REC8 and STAG3.

Role of CYP51 in the Regulation of T3 and FSH-Induced Steroidogenesis in Female Mice

Cytochrome P450 lanosterol 14α-demethylase (CYP51) is a key enzyme in sterol and steroid biosynthesis that is involved in folliculogenesis and oocyte maturation, which is regulated by follicle-stimulating hormone (FSH), as a key reproductive hormone during follicular development. Thyroid hormone (TH) is also important for normal reproductive function. Although 3,5,3'-triiodothyronine (T3) enhances FSH-induced preantral follicle growth, whether and how TH combines with FSH to regulate CYP51 expression during the preantral to early antral transition stage is unclear. The objective of this study was to determine the cellular and molecular mechanisms by which T3 and FSH regulate CYP51 expression and steroid biosynthesis during preantral follicle growth. Our results indicated that CYP51 expression was upregulated in granulosa cells by FSH, and this response was enhanced by T3. Moreover, knockdown CYP51 decreased cell viability. Meanwhile, gene knockdown also blocked T3 and FSH-induced estradiol (E2) and progesterone (P4) synthesis. These changes were accompanied by upregulation of phospho-GATA-4 content. Results of small interfering RNA analysis showed that knockdown of GATA-4 significantly diminished CYP51 gene expression as well as E2/P4 levels. Furthermore, thyroid hormone receptor β was necessary to the activation of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt), which was required for the regulation of CYP51 expression; activated GATA-4 was also involved these processes. Our data demonstrate that T3 and FSH cotreatment potentiates cellular development and steroid biosynthesis via CYP51 upregulation, which is mediated through the activation of the PI3K/Akt pathway. Meanwhile, activated GATA-4 is also involved in this regulatory system. These findings suggest that CYP51 is a mediator of T3 and FSH-induced follicular development.

Progesterone Receptor Membrane Component 1 Mediates Progesterone-Induced Suppression of Oocyte Meiotic Prophase I and Primordial Folliculogenesis

Well-timed progression of primordial folliculogenesis is essential for mammalian female fertility. Progesterone (P4) inhibits primordial follicle formation under physiological conditions; however, P4 receptor that mediates this effect and its underlying mechanisms are unclear. In this study, we used an in vitro organ culture system to show that progesterone receptor membrane component 1 (PGRMC1) mediated P4-induced inhibition of oocyte meiotic prophase I and primordial follicle formation. We found that membrane-impermeable BSA-conjugated P4 inhibited primordial follicle formation similar to that by P4. Interestingly, PGRMC1 and its partner serpine1 mRNA-binding protein 1 were highly expressed in oocytes in perinatal ovaries. Inhibition or RNA interference of PGRMC1 abolished the suppressive effect of P4 on follicle formation. Furthermore, P4-PGRMC1 interaction blocked oocyte meiotic progression and decreased intra-oocyte cyclic AMP (cAMP) levels in perinatal ovaries. cAMP analog dibutyryl cAMP reversed P4–PGRMC1 interaction-induced inhibition of meiotic progression and follicle formation. Thus, our results indicated that PGRMC1 mediated P4-induced suppression of oocyte meiotic progression and primordial folliculogenesis by decreasing intra-oocyte cAMP levels.

Characterization of a piRNA binding protein Miwi in mouse oocytes

Argonaute proteins and Piwi proteins bind with microRNA (mRNA) and Piwi-interacting RNA (piRNA), respectively, to form functional complexes. Piwi proteins are mostly restricted to germ cells and stem cells, and the Piwi-piRNA pathway is required for normal spermatogenesis. Although piRNAs were also recently identified in mammalian oocytes, expression of Piwi proteins in the ovary has not been well characterized. Previous studies did not detect mRNA of Miwi, a murine homologue of Piwi proteins, in total RNA of mouse ovary tissue. We demonstrated herein the presence of Miwi in murine oocytes. Reverse transcription polymerase chain reaction (RT-PCR), Western blot, and immunofluorescence based on quantum dots immune labeling technique were used to investigate the expression profile of Miwi in oocytes of adult and neonatal females at 0, 1, 2, 3, and 4 weeks postpartum. Although RT-PCR was negative in total RNA of the adult ovary, both RT-PCR and Western blot detected Miwi in oocytes of adult mice, and ovaries of neonatal females. Miwi transcript and protein peaked at 1 and 2 weeks postpartum, respectively. Miwi mRNA was detectable in newborn mouse ovaries, implying its transcription was initiated at least in the primordial follicle. Its protein was strong in late primary and secondary follicles, but appeared to decrease as maturation proceeded. The exclusion of anti-Miwi immunofluorescence from some cytoplasmic granules was observed. Given that diverse biologic and molecular functions have been revealed for the Piwi-piRNA pathway in germline cells of many species, Miwi might be an important functional protein in murine folliculogenesis.

Expression of antiapoptosis gene survivin in luteinized ovarian granulosa cells of women undergoing IVF or ICSI and embryo transfer: clinical correlations

BACKGROUND

The purpose of the study was to determine the incidence of survivin gene expression in human granulosa cells during ovarian stimulation in Greek women with normal FSH levels, undergoing IVF or ICSI and to discover any correlation between levels of gene expression and clinical parameters, efficacy of ovulation or outcomes of assisted reproduction.

METHODS

Twenty nine women underwent ovulation induction for IVF or ICSI and ET with standard GnRH analogue-recombinant FSH protocol. Infertility causes were male and tubal factor. Cumulus-mature oocyte complexes were denuded and the granulosa cells were analyzed for each patient separately using quantitative reverse transcription polymerase chain reaction analysis for survivin gene expression with internal standard the ABL gene.

RESULTS

The ABL and survivin mRNA were detected in granulosa cells in 93.1%. The expression levels of survivin were significantly lower in normal women (male infertility factor) compared to women with tubal infertility factor (p = 0.007). There was no additional statistically significant correlation between levels of survivin expression and estradiol levels or dosage of FSH for ovulation induction or number of dominant follicles aspirated or number of retrieved oocytes or embryo grade or clinical pregnancy rates respectively.

CONCLUSIONS

High levels of survivin mRNA expression in luteinized granulosa cells in cases with tubal infertility seem to protect ovaries from follicular apoptosis. A subpopulation of patients with low levels of survivin mRNA in granulosa cells might benefit with ICSI treatment to bypass possible natural barriers of sperm-oocyte interactions.

Obesity does not aggravate vitrification injury in mouse embryos: a prospective study

BACKGROUND

Obesity is associated with poor reproductive outcomes, but few reports have examined thawed embryo transfer in obese women. Many studies have shown that increased lipid accumulation aggravates vitrification injury in porcine and bovine embryos, but oocytes of these species have high lipid contents (63 ng and 161 ng, respectively). Almost nothing is known about lipids in human oocytes except that these cells are anecdotally known to be relatively lipid poor. In this regard, human oocytes are considered to be similar to those of the mouse, which contain approximately 4 ng total lipids/oocyte. To date, no available data show the impact of obesity on vitrification in mouse embryos. The aim of this study was to establish a murine model of maternal diet-induced obesity and to characterize the effect of obesity on vitrification by investigating the survival rate and embryo developmental competence after thawing.

METHODS

Prospective comparisons were performed between six-eight-cell embryos from obese and normal-weight mice and between fresh and vitrified embryos. Female C57BL/6 mice were fed standard rodent chow (normal-weight group) or a high-fat diet (obese group) for 6 weeks. The mice were mated, zygotes were collected from oviducts and cultured for 3 days, and six-eight-cell embryos were then selected to assess lipid content in fresh embryos and to evaluate differences in apoptosis, survival, and development rates in response to vitrification.

RESULTS

In fresh embryos from obese mice, the lipid content (0.044 vs 0.030, P<0.01) and apoptosis rate (15.1% vs.9.3%, P<0.05)were significantly higher, the survival rate (83.1% vs. 93.1%, P<0.01) on day 5 was significantly lower, and embryo development was notably delayed on days 3-5 compared with the normal-weight group. After vitrification, no significant difference was found between thawed embryos from obese and normal-weight mice in apoptosis, survival, and development rates on days 4 and 5. In both groups, pre- and post-vitrification embryo apoptosis, survival, and development rates were similar.

CONCLUSIONS

This study demonstrated that differences in survival and developmental rates between embryos from obese and normal-weight mice were eliminated after vitrification. Thus, maternal obesity does not aggravate vitrification injury, but obesity alone greatly impairs pre-implantation embryo survival and development.

Ovarian reaction and estrus manifestation in delayed puberty gilts after treatment with equine chorionic gonadotropin

BACKGROUND

Prolonged pre-insemination anestrus (i.e. delayed puberty) is a major contributing factor for culling up to 30% of the replacement gilts at large breeding farm units in Vojvodina. It is imperative to determine if these gilts are acyclic (prepubertal) or cyclic, but just fail to exhibit behavioural estrus. Recent investigations demonstrate that treatment with equine chorionic gonadotropin (eCG) can increase the diestrous phase duration in sexually mature gilts. Based on these finding, the aim of the present studies was to determine the reproductive status of delayed puberty gilts following injection with eCG.

METHODS

Two experiments were conducted on a swine breeding farm in Vojvodina. In Exp. 1, 20 prepubertal (acyclic) gilts, and 120 sexually mature (cyclic) gilts were injected with a single injection of 400  IU eCG + 200 IU human chorionic gonadotropin (hCG) or with 1000  IU eCG (cyclic gilts), at d5, d11 or d17 after spontaneous estrus detection, to determine their ovarian reaction and induced estrus manifestation. In Exp. 2, sixty delayed puberty gilts (estrus not detected until 8 month of age, av. 258 days) were culled from breeding herd and slaughtered to determine their reproductive status based on ovarian anatomical features. The second group of gilts (n = 60) was treated with a single 1000  IU eCG injection to determine their reproductive status, based on the interval between eCG injection to estrus detection and duration. The data were analyzed by descriptive statistics, t-test, analysis of variance and Duncan's test in the software package Statistics 10th.

RESULTS

Ovulations were induced in 90% of acyclic (sexually immature) and, on average, 93.3% of cyclic (sexually mature) gilts after the eCG injection. On average, 4 days after the eCG injection, estrus was detected in 85% of the treated acyclic (sexually immature) gilts and in 95% (19/20) of the cyclic (sexually mature) gilts, treated with eCG on day 17 after spontaneous estrus detection. The interval from eCG to induced estrus detection was prolonged (av. 25 days) in 95% (19/20) of the sexually mature gilts treated with eCG on day 5 and in 90% (18/20) of gilts treated on day 11 after spontaneous estrus detection (Exp. 1). Forty anestrous gilts reached cyclic pubertal ovarian activity. Estrus manifestation was detected in 56 gilts (93.3% of the total 60 treated prolonged anestrous gilts, av. 259 days of age), after a single 1000  IU eCG injection. Thirty-four gilts (60.7% of the total gilts in estrus) with prolonged eCG to estrus interval (av. 24.7 days) were considered spontaneously cyclic (sexually mature), but behaviourally anestrous before treatment. The remaining 22 (39.3% of the total gilts in estrus) were considered truly sexually immature (acyclic) before the treatment or were eCG injected in the late luteal or proestrous phase of spontaneous estrous cycle (Exp. 2).

CONCLUSIONS

In 66.7% of the delayed puberty gilts, pre-ovulatory follicles (PoF), corpora hemorrhagica (CH), corpora lutea (CL), or corpora albicantia (CA) were found on the ovaries upon post mortem examination. These gilts were considered as sexually mature before slaughtering. In 60.7% of the delayed puberty gilts, behavioural estrus was detected an average of 24.7 days following eCG injections. These gilts were considered as eCG treated during the luteal phase (diestrus) of the spontaneous estrus cycle. Both findings suggest that delayed puberty gilts actually reached cyclic pubertal ovarian activity (sexual maturity) before culling from the breeding herd.

Estrogen-dependent gene expression in the mouse ovary

Estrogen (E) plays a pivotal role in regulating the female reproductive system, particularly the ovary. However, the number and type of ovarian genes influenced by estrogen remain to be fully elucidated. In this study, we have utilized wild-type (WT) and aromatase knockout (ArKO; estrogen free) mouse ovaries as an in vivo model to profile estrogen dependent genes. RNA from each individual ovary (n = 3) was analyzed by a microarray-based screen using Illumina Sentrix Mouse WG-6 BeadChip (45,281 transcripts). Comparative analysis (GeneSpring) showed differential expression profiles of 450 genes influenced by E, with 291 genes up-regulated and 159 down-regulated by 2-fold or greater in the ArKO ovary compared to WT. Genes previously reported to be E regulated in ArKO ovaries were confirmed, in addition to novel genes not previously reported to be expressed or regulated by E in the ovary. Of genes involved in 5 diverse functional processes (hormonal processes, reproduction, sex differentiation and determination, apoptosis and cellular processes) 78 had estrogen-responsive elements (ERE). These analyses define the transcriptome regulated by E in the mouse ovary. Further analysis and investigation will increase our knowledge pertaining to how E influences follicular development and other ovarian functions.

Tumor and reproductive traits are linked by RNA metabolism genes in the mouse ovary: a transcriptome-phenotype association analysis

BACKGROUND

The link between reproductive life history and incidence of ovarian tumors is well known. Periods of reduced ovulations may confer protection against ovarian cancer. Using phenotypic data available for mouse, a possible association between the ovarian transcriptome, reproductive records and spontaneous ovarian tumor rates was investigated in four mouse inbred strains. NIA15k-DNA microarrays were employed to obtain expression profiles of BalbC, C57BL6, FVB and SWR adult ovaries.

RESULTS

Linear regression analysis with multiple-test control (adjusted p ≤ 0.05) resulted in ovarian tumor frequency (OTF) and number of litters (NL) as the top-correlated among five tested phenotypes. Moreover, nearly one-hundred genes were coincident between these two traits and were decomposed in 76 OTF(-) NL(+) and 20 OTF(+) NL(-) genes, where the plus/minus signs indicate the direction of correlation. Enriched functional categories were RNA-binding/mRNA-processing and protein folding in the OTF(-) NL(+) and the OTF(+) NL(-) subsets, respectively. In contrast, no associations were detected between OTF and litter size (LS), the latter a measure of ovulation events in a single estrous cycle.

CONCLUSION

Literature text-mining pointed to post-transcriptional control of ovarian processes including oocyte maturation, folliculogenesis and angiogenesis as possible causal relationships of observed tumor and reproductive phenotypes. We speculate that repetitive cycling instead of repetitive ovulations represent the actual link between ovarian tumorigenesis and reproductive records.

Reducing CYP51 inhibits follicle-stimulating hormone induced resumption of mouse oocyte meiosis in vitro

Meiosis activating sterol, produced directly by lanosterol 14-alpha-demethylase (CYP51) during cholesterol biosynthesis, has been shown to promote the initiation of oocyte meiosis. However, the physiological significance of CYP51 action on oocyte meiosis in response to gonadotrophins' induction remained to be further explored. Herein, we analyzed the role of CYP51 in gonadotrophin-induced in vitro oocyte maturation via RNA interference (RNAi). We showed that although both luteinizing hormone (LH) and follicle-stimulating hormone (FSH) significantly induced meiotic resumption in follicle-enclosed oocytes (FEOs), the effect of LH on oocyte meiosis resumption in FEOs was weaker than FSH. Moreover, both FSH and LH were able to upregulate CYP51 expression in cultured follicular granulosa cells when examined at 8 h or 12 h posttreatments, respectively. Interestingly, whereas knockdown of CYP51 expression via small interference RNA (siRNA) moderately blocked (23% reduction at 24 h) FSH-induced oocyte maturation [43% germinal vesicle breakdown (GVBD) rate in RNAi vs. 66% in control, P < 0.05] in FEOs, similar treatments showed no apparent effects on LH-induced FEO meiotic maturation (58% GVBD rate in RNAi vs. 63% in control, P > 0.05). Moreover, the results in a cumulus-enclosed oocytes (CEOs) model showed that approximately 30% of FSH-induced CEOs' meiotic resumption was blocked upon CYP51 knockdown by siRNAs. These findings suggest that FSH, partially at least, employs CYP51, and therefore the MAS pathway, to initiate oocyte meiosis.