KIT/KIT Ligand in Mammalian Oogenesis and Folliculogenesis: Roles in Rabbit and Murine Ovarian Follicle Activation and Oocyte Growth1

Parabens effects on female reproductive health - Review of evidence from epidemiological and rodent-based studies

Parabens have been used as antimicrobial preservatives since the 1920s. The prevalent use of parabens increases their detection in the environment and in women's biological samples including reproductive tissues. Recent studies suggest parabens may alter endocrine function and thus female reproductive health may be affected. In this literature review, we summarize findings on parabens and female reproduction while focusing on epidemiological and rodent-based studies. The topics reviewed include paraben effects on cyclicity, pregnancy, newborn and pubertal development, reproductive hormones, and ovarian and uterine specific outcomes. Overall, the scientific literature on paraben effects on female reproduction is limited and with some conflicting results. Yet, some epidemiological and/or rodent-based experimental studies report significant findings in relation to paraben effects on cyclicity, fertility, gestation length, birth weight, postnatal development and pubertal onset, hormone levels, and hormone signaling in reproductive tissues. Future epidemiological and experimental studies are needed to better understand paraben effects on female reproduction while focusing on human related exposures including mixtures, physiologic concentrations of parabens, and multi-generational studies.

Serum levels of stem cell factor for predicting embryo quality

We evaluated whether serum stem cell factor (s-SCF) levels just prior to ovulation induction could indicate the ability to develop a top-quality (TQ) blastocyst by day 5. We investigated patients with normal ovarian reserve (NOR), polycystic ovary syndrome (PCOS), diminished ovarian reserve (DOR), or mild endometriosis. Our pilot research suggests a correlation between s-SCF levels and the ability to form TQ blastocysts in patients with mild endometriosis. This significant statistical difference (p < 0.05) was noted between mild endometriosis patients for whom a TQ blastocyst was obtained and those for whom it was not possible, as measured on the 8th day of stimulation and the day of oocyte retrieval. The mean SCF levels in the serum of these women on the 8th day were at 28.07 (± 2.67) pg/ml for the TQ subgroup and 53.32 (± 16.02) pg/ml for the non-TQ subgroup (p < 0.05). On oocyte retrieval day it was 33.47 (± 3.93) pg/ml and 52.23 (± 9.72) pg/ml (p < 0.05), respectively.

Optimisation of hormonal treatment to improve follicular development in one-day-old mice ovaries cultured under in vitro condition

CONTEXT

Base medium containing knock-out serum replacement (KSR) has been found to support formation and maintenance of follicles in one-day-old mice ovaries, but has not been shown to properly support activation and growth of primordial follicles.

AIMS

The present study was conducted to tailor the hormonal content of base medium containing KSR to enhance development of primordial follicles in neonatal ovaries.

METHODS

One-day-old mice ovaries were initially cultured with base medium for four days, and then, different hormonal treatments were added to the culture media and the culture was proceeded for four additional days until day eight. Ovaries were collected for histological and molecular assessments on days four and eight.

KEY RESULTS

In experiment I, the main and interactive effects of FSH and testosterone were investigated and FSH promoted activation of primordial follicles and development of primary and preantral follicles, and upregulated genes of phosphoinositide 3-kinase (Pi3k ), KIT ligand (Kitl ), growth differentiation factor 9 (Gdf9 ) and follicle stimulating hormone receptor (Fshr ) (P Bmp15 ), Connexin-43 (Cx43 ) and luteinising hormone and choriogonadotropin receptor (Lhcgr ) (P P Lhcgr (P P >0.05).

CONCLUSIONS

Supplementation of culture medium containing KSR with gonadotropins, particularly hMG, could improve follicular growth and expression of factors regulating follicular development.

IMPLICATIONS

This study was a step forward in formulating an optimal medium for development of follicles in cultured one-day-old mice ovaries.

Making a good egg: human oocyte health, aging, and in vitro development

Mammalian eggs (oocytes) are formed during fetal life and establish associations with somatic cells to form primordial follicles that create a store of germ cells (the primordial pool). The size of this pool is influenced by key events during the formation of germ cells and by factors that influence the subsequent activation of follicle growth. These regulatory pathways must ensure that the reserve of oocytes within primordial follicles in humans lasts for up to 50 years, yet only approximately 0.1% will ever be ovulated with the rest undergoing degeneration. This review outlines the mechanisms and regulatory pathways that govern the processes of oocyte and follicle formation and later growth, within the ovarian stroma, through to ovulation with particular reference to human oocytes/follicles. In addition, the effects of aging on female reproductive capacity through changes in oocyte number and quality are emphasized, with both the cellular mechanisms and clinical implications discussed. Finally, the details of current developments in culture systems that support all stages of follicle growth to generate mature oocytes in vitro and emerging prospects for making new oocytes from stem cells are outlined.

The transcriptome reveals the molecular regulatory network of primordial follicle depletion in obese mice

OBJECTIVE

To explore the dynamic transcriptional regulatory network of primordial follicle fate in obese mice to elucidate the potential mechanism of primordial follicle depletion.

DESIGN

Experimental study and transcriptomic analysis.

ANIMALS

Healthy (n=15) and obese (n=15) female mice.

INTERVENTIONS

Six-week-old CD-1 mice were divided into healthy and high-fat diet groups and fed continuously for 12 weeks. The diet of healthy mice contained 10% fat. The diet of high-fat mice contained 60% fat.

MAIN OUTCOME MEASURES

Primordial to primary follicle transition rate, gene expression changes, enriched Kyoto Encyclopedia of Genes and Genomes pathways, and ferroptosis.

RESULTS

Primordial follicle depletion was increased in the ovaries of obese mice. We found that deposited fat around primordial and primary follicles of obese mice was higher than that for healthy mice. The proliferation of granulosa cells around primary follicles was increased in obese mice. In addition, we uncovered specific gene signatures associated with the primordial to primary follicle transition (PPT) in obese mice using laser capture microdissection RNA sequencing analysis. Gene set enrichment analysis indicated that ferroptosis, cell oxidation, vascular endothelial growth factor, and mammalian target of rapamycin signaling were increased significantly in the primordial follicles of obese mice. Notably, the ferritin, acyl CoA synthetase long-chain family member 4, and solid carrier family 7 member 11 associated proteins of the ferroptosis signaling pathway were significantly increased in the PPT phase of obese mice.

CONCLUSION

Our work suggests that ferroptosis is a key pathway activated within immature ovarian follicles in the context of obesity and that the process may be involved in the physiological regulation of the PPT as well.

From in vivo to in vitro: exploring the key molecular and cellular aspects of human female gametogenesis

Human oogenesis is a highly complex and not yet fully understood process due to ethical and technological barriers that limit studies in the field. In this context, replicating female gametogenesis in vitro would not only provide a solution for some infertility problems, but also be an excellent study model to better understand the biological mechanisms that determine the formation of the female germline. In this review, we explore the main cellular and molecular aspects involved in human oogenesis and folliculogenesis in vivo, from the specification of primordial germ cells (PGCs) to the formation of the mature oocyte. We also sought to describe the important bidirectional relationship between the germ cell and the follicular somatic cells. Finally, we address the main advances and different methodologies used in the search for obtaining cells of the female germline in vitro.

The protective effects of astaxanthin on pre-antral follicle degeneration in ovine vitrified/warmed ovarian tissue

This study assesses the protective effects of astaxanthin (AST) against vitrification/warming-induced cryoinjuries of ovarian tissue slices in sheep. Cortical slices of slaughterhouse acquired-ovine ovaries were randomly distributed in different groups: fresh, toxicity, and five vitrification groups including vitrification in presence of 0 (control group), 1, 10 and 100 μM astaxanthin or 100 μM vitamin E. After vitrification/warming and 24 h culturing, the samples were subjected to histological studies, antioxidant evaluation by TAC and TBAR assays, and assessment of relative expression of BMP4, BMP15, GDF9 and KITLG genes related to folliculogenesis and follicular growth regulation. According to the results, vitrification reduced the percentage of morphologically intact follicles compared to the fresh and toxicity groups (p < 0.05). In vitrification groups, vitamin E and all three concentrations of AST increased the percentage of intact pre-antral follicles and antioxidant activity relative to the vitrified control (p < 0.05). This enhancement significantly occurred in 10 μM AST group more than vitamin E (p < 0.05). Also, 10 μM concentration of AST enhanced the expression of all the examined genes compared to the control (p < 0.05), while the expression of BMP4, BMP15 and KITLG was higher in the AST than vitamin E (p < 0.05). The latter could increase only the expression of GDF9 compared to the control group (p = 0.011). In conclusion, AST is a highly effective antioxidant for maintaining the survival of pre-antral follicles, retaining cell density, increasing total antioxidant capacity, and increasing the expression of some genes related to follicular development after short-term culture of vitrified/warmed ovarian tissue slices.

HucMSC-EVs Facilitate In Vitro Development of Maternally Aged Preantral Follicles and Oocytes

Follicle developmental capacity and oocyte quality decline with advanced maternal age. Extracellular vesicles from human umbilical cord mesenchymal stem cells (HucMSC-EVs) act as a potential therapeutic product in the treatment of age-related ovarian dysfunction. In vitro culture (IVC) of preantral follicles is a useful method for understanding the mechanism of follicle development and is a promising means for improving female fertility. However, whether HucMSC-EVs have beneficial effects on aged follicle development during IVC has not yet been reported. Our research demonstrated that follicular development with single-addition withdrawal of HucMSC-EVs was better than that with continuous treatment with HucMSC-EVs. HucMSC-EVs facilitated the survival and growth of follicles, promoted the proliferation of granulosa cells (GCs), and improved the steroid hormone secretion of GCs during IVC of aged follicles. Both GCs and oocytes could uptake HucMSC-EVs. Moreover, we observed elevated cellular transcription in GCs and oocytes after treatment with HucMSC-EVs. The RNA sequencing (RNA-seq) results further validated that the differentially expressed genes are related to the promotion of GC proliferation, cell communication, and oocyte spindle organization. Additionally, the aged oocytes displayed a higher maturation rate, presented less aberrant spindle morphology, and expressed a higher level of the antioxidant protein Sirtuin 1 (SIRT1) after treatment with HucMSC-EVs. Our findings suggested that HucMSC-EVs can improve the growth and quality of aged follicles and oocytes in vitro through the regulation of gene transcription, which provides evidence for HucMSC-EVs as potential therapeutic reagents to restore female fertility with advanced age.

Mechanisms of primordial follicle activation and new pregnancy opportunity for premature ovarian failure patients

Primordial follicles are the starting point of follicular development and the basic functional unit of female reproduction. Primordial follicles are formed around birth, and most of the primordial follicles then enter a dormant state. Since primordial follicles are limited in number and can't be renewed, dormant primordial follicles cannot be reversed once they enter the growing state. Thus, the orderly occurrence of primordial follicles selective activation directly affects the rate of follicle consumption and thus determines the length of female reproductive lifespan. Studies have found that appropriately inhibiting the activation rate of primordial follicles can effectively slow down the rate of follicle consumption, maintain fertility and delay ovarian aging. Based on the known mechanisms of primordial follicle activation, primordial follicle in vitro activation (IVA) technique has been clinically developed. IVA can help patients with premature ovarian failure, middle-aged infertile women, or infertile women due to gynecological surgery treatment to solve infertility problems. The study of the mechanism of selective activation of primordial follicles can contribute to the development of more efficient and safe IVA techniques. In this paper, recent mechanisms of primordial follicle activation and its clinical application are reviewed.

In vivo promotion of primordial follicle activation by stem cell factor treatment in mice with premature ovarian insufficiency and advanced age

Dormant primordial follicles (PFs) are the most abundant reproductive resource in mammalian ovaries. With advances in the mechanism of study of the regulation of PF activation, PFs have been used to improve fertility in clinical practice. As a central controlling element of follicle activation signaling, the pre-granulosa cell-secreted stem cell factor (SCF; also known as KIT ligand, KITL), which initiates the growth of dormant oocytes, is an ideal natural activator that stimulates follicle activation. However, no systematic study has been conducted to identify the activating effect of SCF in vivo and in vitro. In this study, by combining an in vitro whole ovary culture system and several mouse models, we provide a series of experimental evidence that SCF is an efficient activator for improving PF activation in mouse ovaries. Our in vitro study showed that SCF increased phosphatidylinositol 3-kinase (PI3K) signaling and PF activation ratio in neonatal ovaries. In vivo ovarian non-invasive topical administrations of SCF to the ovaries efficiently improved follicle activation and development, oocyte retrieval ratio and fertility in inducible premature ovarian insufficiency mouse models and aged mice. Our study suggests that SCF is an efficient growth factor that can be applied to improve PF activation.

Aberrant BMP15/HIF-1α/SCF signaling pathway in human granulosa cells is involved in the PCOS related abnormal follicular development

AIMS

To investigate the regulatory mechanism of SCF expression in human GCs of PCOS related follicles.

MATERIALS AND METHODS

SCF, BMP15 and HIF-1α were evaluated in human serums, follicular fluids (FFs) and GCs, which were collected from 69 PCOS patients and 74 normal ovulatory patients. KGN cell line was used in this study.

RESULTS

Our results showed that the rate of MII oocyte and 2PN fertilization was lower in PCOS group, though PCOS patients retrieved much more oocytes. The level of BMP15 in FF and the level of SCF in serum and FF were also lower in PCOS patients. We found a weakened expression of HIF-1α and SCF in GCs from PCOS patients when compared with the non-PCOS patients. The expression of HIF-1α and SCF was significantly increased in KGN cells after treating cells with rhBMP15, however, this promotion effects of BMP15 on HIF-1α and SCF expression were obviously abolished by co-treatment with BMP-I receptor inhibitor (DM). Moreover, knock down of HIF-1α expression in KGN cells significantly reduced the expression of SCF in human GCs, in spite of activating BMP15 signaling pathway.

CONCLUSIONS

The present study suggest that BMP15 could induce SCF expression by up-regulating HIF-1α expression in human GCs, the aberrance of this signaling pathway might be involved in the PCOS related abnormal follicular development.

Kelulut Honey Improves Folliculogenesis, Steroidogenic, and Aromatase Enzyme Profiles and Ovarian Histomorphology in Letrozole-Induced Polycystic Ovary Syndrome Rats

Polycystic ovary syndrome (PCOS) has been linked to aberrant folliculogenesis and abnormalities in the aromatase enzyme (Cyp19a1) and the steroidogenic enzyme, 17-alpha-hydroxylase (Cyp17a1) expression. It has been demonstrated that Kelulut honey (KH) improves both female and male reproductive system anomalies in animal studies. Here, we examined the effects of isolated and combined KH, metformin, and clomiphene in improving folliculogenesis, aromatase, and steroidogenic enzyme profiles and ovarian histomorphology in letrozole-induced PCOS rats. Letrozole (1 mg/kg/day) was administered to female Sprague-Dawley (SD) rats for 21 days to induce PCOS. PCOS rats were subsequently divided into six experimental groups: untreated, treatment with metformin (500 mg/kg/day), clomiphene (2 mg/kg/day), KH (1 g/kg/day), combined KH (1 g/kg/day) and metformin (500 mg/kg/day), and combined KH (1 g/kg/day) and clomiphene (2 mg/kg/day). All treatments were given orally for 35 days. We found that KH was comparable with clomiphene and metformin in improving the expression of Cyp17a1 and Cyp19a1, apart from enhancing folliculogenesis both histologically and through the expression of folliculogenesis-related genes. Besides, the combination of KH with clomiphene was the most effective treatment in improving the ovarian histomorphology of PCOS rats. The effectiveness of KH in restoring altered folliculogenesis, steroidogenic, and aromatase enzyme profiles in PCOS warrants a future clinical trial to validate its therapeutic effect clinically.

Systematic review of the receptor tyrosine kinase superfamily in neuroblastoma pathophysiology

BACKGROUND

Neuroblastoma is a devastating disease accounting for 15% of all childhood cancer deaths. Yet, our understanding of key molecular drivers such as receptor tyrosine kinases (RTKs) in this pathology remains poorly clarified. Here, we provide a systematic analysis of the RTK superfamily in the context of neuroblastoma pathogenesis.

METHODS

Statistical correlations for all RTK family members' expression to neuroblastoma patient survival across 10 independent patient cohorts were annotated, synthesized, and ranked using the R2: Genomics Analysis and Visualization Platform. Gene expression of selected members across different cancer cell lines was further analyzed in the Cancer Cell Line Encyclopedia, part of the Cancer Dependency Map portal (depmap portal ( http://depmap.org )). Finally, we provide a detailed literature review for highly ranked candidates.

RESULTS

Our analysis defined two subsets of RTKs showing robust associations with either better or worse survival, constituting potential novel players in neuroblastoma pathophysiology, diagnosis, and therapy. We review the available literature regarding the oncogenic functions of these RTKs, their roles in neuroblastoma pathophysiology, and potential utility as therapeutic targets.

CONCLUSIONS

Our systematic analysis and review of the RTK superfamily in neuroblastoma pathogenesis provides a new resource to guide the research community towards focused efforts investigating signaling pathways that contribute to neuroblastoma tumor establishment, growth, and/or aggressiveness and targeting these druggable molecules in novel therapeutic strategies.

Pathways and factors regulated by bone marrow-derived stem cells in human ovarian tissue

OBJECTIVE

To describe molecular and paracrine signaling changes produced by human bone marrow-derived stem cells (BMDSC) in human ovarian cortex.

DESIGN

Experimental study.

SETTING

University hospital research laboratories.

PATIENT(S)

Ovarian cortex from poor responder women (n = 7).

ANIMALS

Immunodeficient NOD/SCID female mice (n = 18).

INTERVENTION(S)

Human ovarian cortex strips were xenografted into ovariectomized NOD/SCID female mice. A week later, mice were infused with phosphate-buffered saline, 1 × 106 BMDSC, or 3 × 105 CD133+ cells via tail vein. Gene expression changes and enriched pathways were assessed by RT2 Profiler Arrays. Several upregulated genes were validated in individual samples by real-time quantitative PCR, and transcriptomic results were reinforced by a proteomic assessment.

MAIN OUTCOME MEASURE(S)

Gene expression changes, enriched Kyoto Encyclopedia of Genes and Genomes pathways, and paracrine factors.

RESULT(S)

Seventy-four Kyoto Encyclopedia of Genes and Genomes pathways were upregulated, with the PI3K-Akt signaling pathway the most enriched after BMDSC and CD133 treatments. The greatest transcriptomic changes were seen on day 14 in the BMDSC group, affecting the regulation of paracrine factors such as KITLG, THBS1, SERPINF1, and TIMP2. Proteomics data verified changes in FoxO signaling, actin cytoskeleton remodeling, and apoptosis by BMDSC.

CONCLUSION(S)

We identified paracrine factors and pathways regulated by BMDSC that may be future targets of treatment for the increasing number of poor responder women. Our findings suggest that BMDSC upregulated soluble factors such as KITLG, THBS1, SERPINF1, and TIMP2 as well as PI3K-Akt signaling and regulation of actin cytoskeleton pathways. The identification of these putative underlying mechanisms informs future experiments aiming to optimizing clinical application of BMDSC.

Effect of dietary supplementation with nettle or fenugreek on folliculogenesis and steroidogenesis in the rabbit ovary - An in vivo study

The objective of the study was to investigate the effect of dietary supplementation with nettle or fenugreek on folliculogenesis and steroidogenesis in the juvenile rabbit ovary. To gain insight into the mechanism of action of these herbs, we examined follicle formation, ovarian cell proliferation and apoptosis, steroidogenic enzyme abundance and steroid concentrations in ovarian tissue and plasma. Animals were fed with control, 1% nettle- or 1% fenugreek-supplemented pellets from 5 to 12 weeks of age (n = 10 per each group), when animals were slaughtered for ovary and blood collection. The addition of nettle decreased the numbers of primordial (P = 0.015) and early antral (P = 0.02) follicles and increased the number of primary (P = 0.04) ones when compared with the control group. Following fenugreek supplementation, the numbers of primary (P = 0.008) and antral (P = 0.027) follicles were greater, while the number of early antral (P = 0.003) follicles was lower in comparison with the control group. Nettle revealed apoptotic activity through activation of caspases 9 (P = 0.047), 8 (P = 0.022) and 3 (P = 0.004), whereas fenugreek increased (P = 0.042) follicular cell proliferation marked by PCNA protein abundance. Furthermore, only fenugreek targeted steroidogenic enzymes, decreasing CYP17A1 (P = 0.043) and increasing CYP19A1 (P = 0.048) protein abundances that resulted in enhanced estradiol biosynthesis and its elevated (P = 0.006) plasma concentration. In conclusion, both herbs affected follicle development in the rabbit ovary in a stage specific manner. Additionally, fenugreek altered ovarian steroidogenesis in a way that might affect sexual maturation in rabbits.

Where are the theca cells from: the mechanism of theca cells derivation and differentiation

Mammalian follicles are composed of oocytes, granulosa cells, and theca cells. Theca cells form in the secondary follicles, maintaining follicular structural integrity and secreting steroid hormones. Two main sources of theca cells exist: Wilms tumor 1 positive (Wt1⁺) cells native to the ovary and Gli1⁺ mesenchymal cells migrated from the mesonephros. Normal folliculogenesis is a process where oocytes, granulosa cells, and theca cells constantly interact with and support each other through autocrine and paracrine mechanisms. The proliferation and differentiation of theca cells are regulated by oocyte-derived factors, including growth development factor 9 and bone morphogenetic protein 15, and granulosa cell-derived factors, including desert hedgehog, Indian hedgehog, kit ligand, insulin-like growth factor 1, as well as hormones such as insulin and growth hormones. Current research on the origin of theca cells is limited. Identifying the origin of theca cells will help us to systematically elaborate the mechanisms of follicular formation and development.

The PARP inhibitor, olaparib, depletes the ovarian reserve in mice: implications for fertility preservation

STUDY QUESTION

What is the impact of the poly(ADP-ribose) polymerase (PARP) inhibitor, olaparib, alone or in combination with chemotherapy on the ovary in mice?

SUMMARY ANSWER

Olaparib treatment, when administered alone, depletes primordial follicle oocytes, but olaparib does not exacerbate chemotherapy-mediated ovarian follicle loss in mice.

WHAT IS KNOWN ALREADY

The ovary contains a finite number of oocytes stored within primordial follicles, which give rise to all mature ovulatory oocytes. Unfortunately, they are highly sensitive to exogenous DNA damaging insults, such as cytotoxic cancer treatments. Members of the PARP family of enzymes are central to the repair of single-strand DNA breaks. PARP inhibitors have shown promising clinical efficacy in reducing tumour burden, by blocking DNA repair capacity. Olaparib is a PARP1/2 inhibitor recently FDA-approved for treatment of BRCA1 and BRCA2 mutation carriers with metastatic breast cancer. It is currently being investigated as an adjunct to standard treatment at an earlier stage, potentially curable, BRCA1- and BRCA2-associated breast cancer which affects reproductive age women. Despite this, there is no preclinical or clinical information regarding the potential impacts of olaparib on the ovary or on female fertility. Unfortunately, it may be many years before clinical data on fertility outcomes for women treated with PARP inhibitors becomes available, highlighting the importance of rigorous preclinical research using animal models to establish the potential for new cancer therapies to affect the ovary in humans. We aimed to comprehensively determine the impact of olaparib alone, or following chemotherapy, on the ovary in mice.

STUDY DESIGN, SIZE, DURATION

On Day 0, mice (n = 5/treatment group) were administered a single intraperitoneal dose of cyclophosphamide (75 mg/kg/body weight), doxorubicin (10 mg/kg), carboplatin (80 mg/kg), paclitaxel (7.5 mg/kg) or vehicle control. From Days 1 to 28, mice were administered subcutaneous olaparib (50 mg/kg) or vehicle control. This regimen is proven to reduce tumour burden in preclinical mouse studies and is also physiologically relevant for women.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Adult female wild-type C57BL6/J mice at peak fertility (8 weeks) were administered a single intraperitoneal dose of chemotherapy, or vehicle, then either subcutaneous olaparib or vehicle for 28 days. Vaginal smears were performed on each animal for 14 consecutive days from Days 15 to 28 to monitor oestrous cycling. At 24 h after final treatment, ovaries were harvested for follicle enumeration and immunohistochemical analysis of primordial follicle remnants (FOXL2 expressing granulosa cells), DNA damage (γH2AX) and analysis of apoptosis by TUNEL assay. Serum was collected to measure circulating anti-Müllerian hormone (AMH) concentrations by ELISA.

MAIN RESULTS AND THE ROLE OF CHANCE

Olaparib significantly depleted primordial follicles by 36% compared to the control (P < 0.05) but had no impact on other follicle classes, serum AMH, corpora lutea number (indicative of ovulation) or oestrous cycling. Primordial follicle remnants were rarely detected in control ovaries but were significantly elevated in ovaries from mice treated with olaparib alone (P < 0.05). Similarly, DNA damage denoted by γH2AX foci was completely undetectable in primordial follicles of control animals but was observed in ∼10% of surviving primordial follicle oocytes in mice treated with olaparib alone. These observations suggest that functional PARPs are essential for primordial follicle oocyte maintenance and survival. Olaparib did not exacerbate chemotherapy-mediated follicle depletion in the wild-type mouse ovary.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

This study was performed in mice, so the findings may not translate to women and further studies utilizing human ovarian tissue and sera samples should be performed in the future. Only one long-term time point was analysed, therefore olaparib-mediated follicle damage should be assessed at more immediate time points in the future to support our mechanistic findings.

WIDER IMPLICATIONS OF THE FINDINGS

Olaparib dramatically depleted primordial follicles and this could be attributed to loss of intrinsic PARP-mediated DNA repair mechanisms. Importantly, diminished ovarian reserve can result in premature ovarian insufficiency and infertility. Notably, the extent of follicle depletion might be enhanced in BRCA1 and BRCA2 mutation carriers, and this is the subject of current investigations. Together, our data suggest that fertility preservation options should be considered for young women prior to olaparib treatment, and that human studies of this issue should be prioritized.

STUDY FUNDING/COMPETING INTEREST(S)

This work was made possible through Victorian State Government Operational Infrastructure Support and Australian Government NHMRC IRIISS. This work was supported by funding from the National Health and Medical Research Council (NHMRC); (K.J.H. #1050130) (A.L.W. #1120300). K.A.P. is a National Breast Cancer Foundation Fellow (Australia-PRAC-17-004). K.A.P. is the Breast Cancer Trials (Australia) Study Chair for the OlympiA clinical trial sponsored by AstraZeneca, the manufacturer of olaparib. All other authors declare no competing financial or other interests.

Establishing and maintaining fertility: the importance of cell cycle arrest

In this review, Frost et al. summarize the current knowledge on the Cip/Kip family of cyclin-dependent kinase inhibitors in mouse gonad development and highlight new roles for cell cycle inhibitors in controlling and maintaining female fertility.

Development of the ovary or testis is required to establish reproductive competence. Gonad development relies on key cell fate decisions that occur early in embryonic development and are actively maintained. During gonad development, both germ cells and somatic cells proliferate extensively, a process facilitated by cell cycle regulation. This review focuses on the Cip/Kip family of cyclin-dependent kinase inhibitors (CKIs) in mouse gonad development. We particularly highlight recent single-cell RNA sequencing studies that show the heterogeneity of cyclin-dependent kinase inhibitors. This diversity highlights new roles for cell cycle inhibitors in controlling and maintaining female fertility.

Differential expression and prediction of function of lncRNAs in the ovaries of low and high fecundity Hanper sheep

Litter size is an important trait that determines the production efficiency of sheep bred for meat. Its detailed investigation can reveal the molecular mechanisms that control the fecundity of sheep and possibly accelerate the breeding process of new varieties of sheep that have high prolificacy. Long non-coding RNAs (lncRNAs) have proven to be an important factor in the regulation of follicular development. However, the mechanisms by which lncRNAs regulate litter size in sheep remain unclear. In the present study, ovarian tissues from the follicular (F) or luteal phase (L) of Hanper sheep that were either monotocous (M) or polytocous (P; FM, FP, LM and LP groups) were collected and sequenced to identify differentially expressed lncRNAs and predict their function. The results indicate that the number of up- and down-regulated lncRNAs in the follicular phase (FM vs. FP) was 95 and 111 and 109 and 49, respectively, in the luteal phase (LM vs. LP). The functional enrichment of the different lncRNAs coexpressed with mRNA was analysed. The results demonstrated that the KISS1-GnRH-LH/FSH-E2 and EGF-EGFR-RAS-PI3K signalling pathways promoted the initiation of the primordial period, follicular development and ovulation in the follicular phase (FM vs. FP). During the luteal phase (LM vs. LP), the production and development of the corpus luteum in ewes was influenced by the KITLG-KIT/FGF-FGFR/HGF-MET-RAS-ERK signalling pathway. STEM clustering functional enrichment analysis of the differentially expressed lncRNAs indicated that profile11 was principally enriched in the Cytokine-Jak-STAT, PDGF-PDGFR-PI3K and KITLG-KIT-RAS-ERK signalling pathways. By analysis of the differential expression of the lncRNAs and their expression in each group, lncRNAs Xist (loc101112291) and Gtl2 (loc101123329) were found to be highly expressed, suggesting that regulation of follicular development was mediated through methylation processes.

Human placenta-derived mesenchymal stem cells stimulate ovarian function via miR-145 and bone morphogenetic protein signaling in aged rats

Background

Aging has detrimental effects on the ovary, such as a progressive reduction in fertility and decreased hormone production, that greatly reduce the quality of life of women. Thus, the current study was undertaken to investigate whether human placenta-derived mesenchymal stem cell (hPD-MSC) treatment can restore the decreases in folliculogenesis and ovarian function that occur with aging.

Methods

Acclimatized 52-week-old female SD rats were randomly divided into four groups: single hPD-MSC (5 × 10⁵) therapy, multiple (three times, 10-day intervals) hPD-MSC therapy, control (PBS), and non-treated groups. hPD-MSC therapy was conducted by tail vein injection into aged rats. The rats were sacrificed 1, 2, 3, and 5 weeks after the last injection. hPD-MSC tracking and follicle numbers were histologically confirmed. The serum levels of sex hormones and circulating miRNAs were detected by ELISA and qRT-PCR, respectively. TGF-β superfamily proteins and SMAD proteins in the ovary were detected by Western blot analysis.

Results

We observed that multiple transplantations of hPD-MSCs more effectively promoted primordial follicle activation and ovarian hormone (E₂ and AMH) production than a single injection. After hPD-MSC therapy, the levels of miR-21-5p, miR-132-3p, and miR-212-3p, miRNAs associated with the ovarian reserve, were increased in the serum. Moreover, miRNAs (miR-16-5p, miR-34a-5p, and miR-191-5p) with known adverse effects on folliculogenesis were markedly suppressed. Importantly, the level of miR-145-5p was reduced after single- or multiple-injection hPD-MSC therapy, and we confirmed that miR-145-5p targets Bmpr2 but not Tgfbr2. Interestingly, downregulation of miR-145-5p led to an increase in BMPR2, and activation of SMAD signaling concurrently increased primordial follicle development and the number of primary and antral follicles.

Conclusions

Our study verified that multiple intravenous injections of hPD-MSCs led to improved ovarian function via miR-145-5p and BMP-SMAD signaling and proposed the future therapeutic potential of hPD-MSCs to promote ovarian function in women at advanced age to improve their quality of life during climacterium.

Comparison of methods for quantifying primordial follicles in the mouse ovary

Background

Accurate evaluation of primordial follicle numbers in mouse ovaries is an essential endpoint for studies investigating how endogenous and exogenous insults, such as maternal aging and chemotherapy, impact the ovarian reserve. In this study, we compared and contrasted two methods for counting healthy primordial follicles following exposure to cyclophosphamide (75 mg/kg), a well-established model of follicle depletion. The first was the fractionator/optical dissector technique, an unbiased, assumption-free stereological approach for quantification of primordial follicle numbers. While accurate, highly reproducible and sensitive, this method relies on specialist microscopy equipment and software, requires specific fixation, embedding and sectioning parameters to be followed, and is largely a manual process that is tedious and time-consuming. The second method was the more widely used serial section and direct count approach, which is relatively quick and easy. We also compared the impacts of different fixatives, embedding material and section thickness on the overall results for each method.

Results

Direct counts resulted in primordial follicle numbers that were significantly lower than those obtained by stereology, irrespective of fixation and embedding material. When applied to formalin fixed tissue, the direct count method did not detect differences in follicle numbers between saline and cyclophosphamide treated groups to the same degree of sensitivity as the gold standard stereology method (referred to as the Reference standard). However, when Bouin’s fixative was used, direct counts and stereology were comparable in their ability to detect follicle depletion caused by cyclophosphamide.

Conclusions

This work indicates that the direct count method can produce similar results to stereology when Bouin’s fixative is used instead of formalin. The findings presented here will assist others to select the most appropriate experimental approach for accurate follicle enumeration, depending on whether the primary objective of the study is to determine absolute primordial follicle numbers or relative differences between groups.

Effects of dietary supplementation with algae, sunflower oil or soybean oil on folliculogenesis in the rabbit ovary during sexual maturation

This study aimed to examine the effects of algae (rich in omega-3 fatty acids), sunflower oil (rich in omega-6 fatty acids) and soybean oil (rich in omega-6 fatty acids) on the entire folliculogenesis in juvenile and sexually mature rabbits. After weaning, rabbits were randomly divided into four experimental groups of 14 animals each. Control animals received non-supplemented pellets, while in the other groups, the pellets contained 1% marine algae, 3% sunflower oil or 3% soybean oil. Animals from each group were slaughtered at 12 weeks of age (n = 7 per group) or at 18 weeks of age (n = 7 per group). The ovaries were harvested and fixed for hematoxylin-eosin staining, immunohistochemical localization of PCNA and TUNEL assay. Algae-enriched diet markedly decreased the number of primordial and primary follicles, while addition of sunflower oil reduced the number of primary follicles in 12-week-old rabbits. The number of antral follicles was higher following algae supplementation, but lower after addition of soybean oil in that age group. Proliferating index was decreased following supplementation with algae and soybean oil in juvenile rabbits, whereas it was increased after addition of algae and decreased following vegetable oils in mature ones. Dietary PUFAs did not impact apoptosis in the rabbit ovary of both age groups. The obtained results suggest that PUFA-enriched diet regulate either early folliculogenesis or antral follicle development in rabbits that might influence reproductive performance as a consequence. It appears that observed effects are attributed to sexual maturity.

Ovarian incision enhances folliculogenesis: A rat model

AIM

To determine whether performing incision on the surface of the ovarian cortex in rats advances follicular development.

METHODS

Five to seven separate superficial incisions were performed on the surface of right ovaries of 6-7-month-old albino Wistar rats. Daily 40 IU of gonadotropins were administered for 14 days. On the 15th day, both ovaries of the rats were removed. The right (incised) ovaries were compared with the contralateral ovaries in terms of ovary's weight, numbers of primordial, primary, secondary and antral follicles, their mean percentages and mean Ki-67 proliferation indices.

RESULTS

A total of 22 ovaries were evaluated, with 11 right ovaries (incised) and 11 left ovaries (non-incised). The mean weight of ovaries was greater in the right ovaries than in the left ovaries; however, no statistical difference was found between them (0.77 ± 1.22 vs. 0.22 ± 0.08 gr, P = 0.159). The numbers of secondary and antral follicle were statistically higher in the right ovaries than in the left ovaries (4.4 ± 1.5 vs. 2.1 ± 1.6, P = 0.003 and 18.6 ± 8.7 vs. 11.3 ± 7.5, P = 0.046, respectively). The right ovaries also significantly differed from the left ovaries in terms of mean percentages of primordial and antral follicles (P < 0.05 for both). The mean Ki-67 proliferation index had a marginal difference between the groups (P = 0.064).

CONCLUSION

Performing incisions on the surface of the ovarian cortex in rats may advance the ovarian follicular development. Future animal studies may provide more evidence regarding potential benefits of mechanical stimulation to the ovaries.

Effect of the neuropeptide phoenixin and its receptor GPR173 during folliculogenesis

Folliculogenesis is a complex process, defined by the growth and development of follicles from the primordial population. Granulosa cells (GCs) play a vital role in every stage of follicular growth through proliferation, acquisition of gonadotropic responsiveness, steroidogenesis and production of autocrine/paracrine factors. A recently discovered hypothalamic neuropeptide phoenixin is involved in the regulation of the reproductive system. Phoenixin acts through its receptor, G protein-coupled receptor 173 (GPR173), to activate the cAMP/PKA pathway leading to the phosphorylation of CREB (pCREB). Here, we demonstrated the expression patterns of phoenixin and GPR173 in human ovary and explored its role in folliculogenesis. Phoenixin and GPR173 were both expressed in the human ovarian follicle, with increased expression in GCs as the follicle grows. Phoenixin treatment at 100 nM for 24 h induced the proliferation of human non-luteinized granulosa cell line, HGrC1 and significantly increased the expression levels of CYP19A1, FSHR, LHR and KITL, but decreased NPPC expression levels. These effects were suppressed by GPR173 siRNA. The expression level of CREB1, pCREB and estradiol (E2) production in the culture medium was significantly enhanced by phoenixin treatment in a concentration-dependent manner. Phoenixin also significantly increased the follicular area in a murine ovarian tissue culture model, leading to an increased number of ovulated oocytes with a higher level of maturation. Taken together, our data demonstrate that phoenixin is an intraovarian factor that promotes follicular growth through its receptor GPR173 by accelerating proliferation of GCs, inducing E2 production and increasing the expression of genes related to follicle development.

CREB activity is required for mTORC1 signaling-induced primordial follicle activation in mice

In mammals, progressive activation of primordial follicles is essential for maintenance of the reproductive lifespan. Several reports have demonstrated that mitogen-activated protein kinases 3 and 1 (MAPK3/1)-mammalian target of rapamycin complex 1 (mTORC1) signaling in pre-granulosa cells promotes primordial follicle activation by increasing KIT ligand (KITL) expression and then stimulating phosphatidylinositol 3 kinase signaling in oocytes. However, the mechanism of mTORC1 signaling in the promotion of KITL expression is unclear. Immunofluorescence staining results showed that phosphorylated cyclic AMP response element-binding protein (CREB) was mainly expressed in pre-granulosa cells. The CREB inhibitor KG-501 and CREB knockdown by Creb siRNA significantly suppressed primordial follicle activation, reduced pre-granulosa cell proliferation and dramatically increased oocyte apoptosis. Western blotting results demonstrated that both the MAPK3/1 inhibitor U0126 and mTORC1 inhibitor rapamycin significantly decreased the levels of phosphorylated CREB, indicating that MAPK3/1-mTORC1 signaling is required for CREB activation. Furthermore, CREB could bind to the Kitl promoter region, and KG-501 significantly decreased the expression levels of KITL. In addition, KG-501 and CREB knockdown significantly decreased the levels of phosphorylated Akt, leading to a reduced number of oocytes with Foxo3a nuclear export. KG-501 also inhibited bpV (HOpic)-stimulated primordial follicle activation. Taken together, the results show that CREB is required for MAPK3/1-mTORC1 signaling-promoted KITL expression followed by the activation of primordial follicles.

Dissecting Cell Lineage Specification and Sex Fate Determination in Gonadal Somatic Cells Using Single-Cell Transcriptomics

Sex determination is a unique process that allows the study of multipotent progenitors and their acquisition of sex-specific fates during differentiation of the gonad into a testis or an ovary. Using time series single-cell RNA sequencing (scRNA-seq) on ovarian Nr5a1-GFP⁺ somatic cells during sex determination, we identified a single population of early progenitors giving rise to both pre-granulosa cells and potential steroidogenic precursor cells. By comparing time series single-cell RNA sequencing of XX and XY somatic cells, we provide evidence that gonadal supporting cells are specified from these early progenitors by a non-sex-specific transcriptomic program before pre-granulosa and Sertoli cells acquire their sex-specific identity. In XX and XY steroidogenic precursors, similar transcriptomic profiles underlie the acquisition of cell fate but with XX cells exhibiting a relative delay. Our data provide an important resource, at single-cell resolution, for further interrogation of the molecular and cellular basis of mammalian sex determination.

Phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) and Janus kinase/signal transducer and activator of transcription (JAK/STAT) follicular signalling is conserved in the mare ovary

The mare ovary is unique in its anatomical structure; however, the signalling pathways responsible for physiological processes, such as follicular activation, remain uncharacterised. This provided us with the impetus to explore whether signalling molecules from important folliculogenesis pathways, phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) and Janus kinase/signal transducer and activator of transcription (JAK/STAT), are conserved in the mare ovary. Messenger RNA expression of six genes important in follicle development was measured using quantitative polymerase chain reaction and protein localisation of key pathway members (PI3K, AKT1, phosphatase and tensin homologue (PTEN), JAK1, STAT3 and suppressor of cytokine signalling 4 (SOCS4)) was compared in tissue from fetal and adult mare ovaries. Tissue from adult ovaries exhibited significantly increased levels of mRNA expression of PI3K, AKT1, PTEN, JAK1, STAT3 and SOCS4 compared with tissue from fetal ovaries. PI3K, AKT1, JAK1 and STAT3 demonstrated redistributed localisation, from pregranulosa cells in fetal development, to both the oocyte and granulosa cells of follicles in the adult ovary, whilst negative feedback molecules PTEN and SOCS4 were only localised to the granulosa cells in the adult ovary. These findings suggest that the PI3K/AKT and JAK/STAT signalling pathways are utilised during folliculogenesis in the mare, similarly to previously studied mammalian species, and may serve as useful biomarkers for assessment of ovary development in the horse.

Janus kinase JAK1 maintains the ovarian reserve of primordial follicles in the mouse ovary

STUDY QUESTION

Is the Janus kinase and signal transducer and activator of transcription (JAK-STAT) signalling pathway involved in ovarian follicle development and primordial follicle activation?

SUMMARY ANSWER

JAK1 is a key factor involved in the regulation of primordial follicle activation and maintenance of the ovarian reserve.

WHAT IS KNOWN ALREADY

A series of integrated, intrinsic signalling pathways (including PI3K/AKT, mTOR and KITL) are responsible for regulating the ovarian reserve of non-growing primordial follicles and ultimately female fertility. The JAK-STAT signal transduction pathway is highly conserved with established roles in cell division and differentiation. Key pathway members (specifically JAK1, STAT3 and SOCS4) have been previously implicated in early follicle development.

STUDY DESIGN, SIZE, DURATION

A laboratory animal study was undertaken using the C57Bl/6 inbred mouse strain as a model for human ovarian follicle development. To determine which Jak genes were most abundantly expressed during primordial follicle activation, mRNA expression was analysed across a developmental time-course, with ovaries collected from female mice at post-natal days 1 (PND1), 4 (PND4), 8 (PND8), as well as at 6 weeks (6WK) and 7 months (7MTH) (n ≥ 4). Functional analysis of JAK1 was performed on PND2 mouse ovaries subjected to in vitro explant culture treated with 12.5 μM Ruxolitinib (JAK inhibitor) or vehicle control (DMSO) for 48 h prior to histological assessment (n ≥ 4).

PARTICIPANTS/MATERIALS, SETTING, METHODS

The expression and localization of the JAK family during ovarian follicle development in the C57Bl/6 inbred mouse strain were evaluated using quantitative PCR, immunoblotting and immunolocalisation. Functional studies were undertaken using the JAK inhibitor Ruxolitinib to investigate the underpinning cellular mechanisms via biochemical in vitro inhibition and histological assessment of intact neonate ovaries. All experiments were replicated at least three times using tissue from different mice unless otherwise stated.

MAIN RESULTS AND THE ROLE OF CHANCE

Jak1 is the predominant Jak mRNA expressed in the C57Bl/6 mouse ovary across all developmental time-points assessed (P ≤ 0.05). Forty-eight hour inhibition of JAK1 with Ruxolitinib of PND2 ovaries in vitro demonstrated concomitant acceleration of primordial follicle activation and apoptosis (P ≤ 0.001) and upregulation of downstream JAK-STAT pathway members STAT3 and suppressors of cytokine signalling 4 (SOCS4).

LARGE-SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Results are shown in one species, the C57Bl/6 mouse strain as an established model of human ovary development. Ruxolitinib also inhibits JAK2, with decreased efficacy. However, Jak2 mRNA had limited expression in the mouse ovary, particularly at the neonatal stages of follicle development, thus any effect of Ruxolitinib on primordial follicle activation was unlikely to be mediated via this isoform.

WIDER IMPLICATIONS OF THE FINDINGS

This study supports a key role for JAK1 in the maintenance and activation of primordial follicles, with potential for targeting the JAK-STAT pathway as a method of regulating the ovarian reserve and female fertility.

STUDY FUNDING AND COMPETING INTEREST(S)

This project has been funded by the Australian National Health and Medical Research Council (G1600095) and The Hunter Medical Research Institute Bob and Terry Kennedy Children's Research Project Grant in Pregnancy & Reproduction (G1501433). All authors declare no conflict of interests.

Serum and follicular fluid Stem Cell Factor assay in IVF poor responder and normal responder patients: a predictive biomarker of oocyte retrieval

OBJECTIVE

The aim of the study is to investigate serum stem cell factor (SCF) concentrations as potential biomarker for oocyte retrieval efficiency in IVF patients with poor prognosis.

METHODS

A pilot case-control study was performed on 30 poor and 30 normal responders that were stimulated with antagonist protocol. SCF concentrations were evaluated in samples of serum and follicular fluid obtained by all patients on the day of oocyte retrieval. At the time of oocyte retrieval, follicular fluid from at least two follicles ≥ 14 mm and two follicles < 14 mm was collected for SCF determination.

RESULTS

We did not find any statistical difference when comparing serum and follicular fluid levels of SCF in both poor- and normal-responder patients, the same results were achieved when poor-responder patients were stratified according to the number of MII oocytes retrieved. Moreover, levels of SCF (OR 1.000, 0.994-1.006) or in follicular fluid from ovarian follicles ≥ 14 mm (OR 0.995, CI 0.989-1.001) or from ovarian follicles < 14 mm (OR 1.003, CI 0.999-1.0069), were not significantly associated with the chances of ongoing pregnancies in poor-responder patients.

CONCLUSION

SCF was unable to predict oocyte retrieval efficiency or the chances of reaching embryo transfer.

A way for in vitro/ex vivo egg production in mammals

Eggs are female germ cells that are required for producing offspring through sexual reproduction. In mammals, eggs are produced in the ovary and ovulated into the oviduct. It is well known that over 99% of eggs are degenerated without ovulation, so that many studies have attempted in vitro folliculogenesis to produce many eggs in different species for a few decades. Although many methods have been developed, a success of in vitro egg production with the resultant live birth of offspring has been limited, especially in livestock animals. More recently, we have succeeded in producing live pups derived from in vitro/ex vivo egg production in mice. This review aims to introduce our recent findings with a brief history of in vitro/ex vivo culture systems for follicles and ovaries.

KIT as a therapeutic target for non-oncological diseases

KIT is a receptor tyrosine kinase that after binding to its ligand stem cell factor activates signaling cascades linked to biological processes such as proliferation, differentiation, migration and cell survival. Based on studies performed on SCF and/or KIT mutant animals that presented anemia, sterility, and/or pigmentation disorders, KIT signaling was mainly considered to be involved in the regulation of hematopoiesis, gametogenesis, and melanogenesis. More recently, novel animal models and ameliorated cellular and molecular techniques have led to the discovery of a widen repertoire of tissue compartments and functions that are being modulated by KIT. This is the case for the lung, heart, nervous system, gastrointestinal tract, pancreas, kidney, liver, and bone. For this reason, the tyrosine kinase inhibitors that were originally developed for the treatment of hemato-oncological diseases are being currently investigated for the treatment of non-oncological disorders such as asthma, rheumatoid arthritis, and alzheimer's disease, among others. The beneficial effects of some of these tyrosine kinase inhibitors have been proven to depend on KIT inhibition. This review will focus on KIT expression and regulation in healthy and pathologic conditions other than cancer. Moreover, advances in the development of anti-KIT therapies, including tyrosine kinase inhibitors, and their application will be discussed.

Nuclear exclusion of SMAD2/3 in granulosa cells is associated with primordial follicle activation in the mouse ovary

Maintenance and activation of the limited supply of primordial follicles in the ovary are important determinants of reproductive lifespan. Currently, the molecular programme that maintains the primordial phenotype and the early events associated with follicle activation are not well defined. Here, we have systematically analysed these events using microscopy and detailed image analysis. Using the immature mouse ovary as a model, we demonstrate that the onset of granulosa cell (GC) proliferation results in increased packing density on the oocyte surface and consequent GC cuboidalization. These events precede oocyte growth and nuclear translocation of FOXO3a, a transcription factor important in follicle activation. Immunolabelling of the TGFβ signalling mediators and transcription factors SMAD2/3 revealed a striking expression pattern specific to GCs of small follicles. SMAD2/3 were expressed in the nuclei of primordial GCs but were mostly excluded in early growing follicles. In activated follicles, GC nuclei lacking SMAD2/3 generally expressed Ki67. These findings suggest that the first phenotypic changes during follicle activation are observed in GCs, and that TGFβ signalling is fundamental for regulating GC arrest and the onset of proliferation.

Cadmium exposure in newborn rats ovary induces developmental disorders of primordial follicles and the differential expression of SCF/c-kit gene

Since the 1990s, the rising problem that gonad reproductive toxicity on adult female after exposing to cadmium (Cd), an environmental endocrine disruptor, has attracted high attention at home and abroad,and was systematically studied. Our research focuses on a further problem is that early cadmium exposure (during birth to before puberty) impact on development and function of ovarian cells and its possible mechanism. Our research focuses on the changes of ovarian cells growth and development after the newborn rat ovaries with cadmium exposure in vitro, and different expression of ovarian cells development-related factors, SCF/c-kit and changes of their DNA methylation status. We obtained ovaries from 4-day-old SD rats and cultured them in DMEM/F12 mixed with α-MEM media in vitro. Different doses of cadmium were designed as control, 0.5, 5, 10 and 50μM, and then the constituent ratio of ovarian follicle and follicular oocytes diameter were observed with microscope after 4-h exposure. We found that the increased constituent ratio of original follicle and decreased diameter of all levels of follicular oocytes(compared with control, with statistically significant differences, P<0.01).After the measurement of expression of SCF/c-kit by qRT-PCR and Western Blotting, the mRNA and protein expression of SCF/c-kit in ovarian were both decreased. We further found that the increased constituent ratio of growth follicle and increased diameter of oocytes under the treatment of adding SCF in cell culture media. Finally, MALDI-TOF-MS method showed DNA-low methylation status of SCF/c-kit promoter region after Cd exposure. Overall, we concluded that the exposure of cadimium (5-50μM) on newborn rats ovaries could inhibit follicle development.SCF/c-kit system might mediate follicle development damage caused by cadmium, which is associated with DNA hypomethylation of SCF/c-kit promoter region may be worthy of further study.

Expression of kit ligand and insulin-like growth factor binding protein 3 during in vivo or in vitro development of ovarian follicles in sheep

Expression of Kit ligand (KL) and insulin-like growth factor binding protein (IGFBP3) genes was studied at different in vivo and corresponding in vitro stages of development of the ovarian follicles in sheep. The expression of both KL and IGFBP3 was significantly higher in the primordial follicles relative to any other stage of development. Compared to the other stages, the KL expression in the cumulus cells from in vivo grown large antral follicles and that of IGFBP3 in COCs' isolated from large antral follicles matured in vitro for 24 hr were significantly higher. In the oocytes from in vivo grown ovarian follicles, the expression of KL was the same at all the stages of development. Insulin-like growth factor binding protein 3 expression was also the same in the oocytes at all the stages of the development except for a significantly lower expression in those from antral follicles. The expression of KL in the cumulus cells decreased significantly in the in vitro grown early antral follicles but did not change further as the development progressed. The expression of IGFBP3 in the cumulus cells from in vitro grown ovarian follicles appeared to increase as the development progressed although the increase was not significant between any two consecutive stages of development. In the oocytes in in vitro grown ovarian follicles, the expression levels of KL and IGFBP3 genes did not change with development. It is concluded that (i) KL and IGFBP3 genes follow specific patterns of expression during ovarian folliculogenesis and (ii) in vitro culture of preantral follicles compromises the development potential through alterations in the stage-specific patterns of expression of these and other developmentally important genes.

MAPK3/1 participates in the activation of primordial follicles through mTORC1-KITL signaling

The majority of ovarian primordial follicles are preserved in a dormant state to maintain the female reproductive lifespan, and only a few primordial follicles are activated to enter the growing follicle pool in each wave. Recent studies have shown that primordial follicular activation depends on mammalian target of rapamycin complex 1 (mTORC1)-KIT ligand (KITL) signaling in pre-granulosa cells and its receptor (KIT)-phosphoinositol 3 kinase (PI3K) signaling in oocytes. However, the upstream regulator of mTORC1 signaling is unclear. The results of the present study showed that the phosphorylated mitogen-activated protein kinase3/1 (MAPK3/1) protein is expressed in some primordial follicles and all growing follicles. Culture of 3 days post-parturition (dpp) ovaries with the MAPK3/1 signaling inhibitor U0126 significantly reduced the number of activated follicles and was accompanied by dramatically reduced granulosa cell proliferation and increased oocyte apoptosis. Western blot and immunofluorescence analyses showed that U0126 significantly decreased the phosphorylation levels of Tsc2, S6K1, and rpS6 and the expression of KITL, indicating that U0126 inhibits mTORC1-KITL signaling. Furthermore, U0126 decreased the phosphorylation levels of Akt, resulting in a decreased number of oocytes with Foxo3 nuclear export. To further investigate MAPK3/1 signaling in primordial follicle activation, we used phosphatase and tensin homolog deleted on chromosome 10 (PTEN) inhibitor bpV(HOpic) to promote primordial follicle activation. In this model, U0126 also inhibited the activation of primordial follicles and mTORC1 signaling. Thus, these results suggest that MAPK3/1 participates in primordial follicle activation through mTORC1-KITL signaling.

Increased SCF in Follicular Fluid and Granulosa Cells Positively Correlates With Oocyte Maturation, Fertilization, and Embryo Quality in Humans

Stem cell factor (SCF), which is derived from granulosa cells (GCs), plays a key role in the process of follicular development and oocyte maturation. The present study aimed to explore whether the levels of SCF in follicular fluid (FF) and GCs can be used as a potential marker for predicting oocyte developmental potential. Follicular fluid and GC samples from 150 female patients undergoing intracytoplasmic sperm injection were collected in this study. The SCF concentrations in FFs and SCF messenger RNA (mRNA) in GCs were evaluated by using enzyme-linked immunosorbent assay and real-time polymerase chain reaction, respectively. The results showed that the levels of SCF protein and mRNA were significantly associated with oocyte maturation, normal fertilization, cleavage, and embryo quality. Moreover, the levels of SCF protein and mRNA in pregnancy group were also higher than those in the nonpregnancy group. The cutoff value of SCF in FF for predicting high-quality embryo was 1.346, with a sensitivity of 57.8% and a specificity of 72.4%, and the cutoff value of SCF in GCs for predicting high-quality embryo was 6.650, with a sensitivity of 64.4% and a specificity of 78.1%. In conclusion, our results showed a positive and statistically significant relationship between SCF level and oocyte maturation, normal fertilization, cleavage, embryo quality, and clinical pregnancy. Therefore, the levels of SCF in FF and GCs might be considered as a new marker for predicting oocyte developmental potential.

The role of Notch signaling in the mammalian ovary

The Notch pathway is a contact-dependent, or juxtacrine, signaling system that is conserved in metazoan organisms and is important in many developmental processes. Recent investigations have demonstrated that the Notch pathway is active in both the embryonic and postnatal ovary and plays important roles in events including follicle assembly and growth, meiotic maturation, ovarian vasculogenesis and steroid hormone production. In mice, disruption of the Notch pathway results in ovarian pathologies affecting meiotic spindle assembly, follicle histogenesis, granulosa cell proliferation and survival, corpora luteal function and ovarian neovascularization. These aberrations result in abnormal folliculogenesis and reduced fertility. The knowledge of the cellular interactions facilitated by the Notch pathway is an important area for continuing research, and future studies are expected to enhance our understanding of ovarian function and provide critical insights for improving reproductive health. This review focuses on the expression of Notch pathway components in the ovary, and on the multiple functions of Notch signaling in follicle assembly, maturation and development. We focus on the mouse, where genetic investigations are possible, and relate this information to the human ovary.

Stem cell factor promotes in vitro ovarian follicle development in the domestic cat by upregulating c-kit mRNA expression and stimulating the phosphatidylinositol 3-kinase/AKT pathway

In the present study we examined the effects of stem cell factor (SCF; 50 vs 100 ng mL–1) alone or in combination with epidermal growth factor (EGF; 100 ng mL–1) on: (1) the in vitro viability and growth of cat follicles within ovarian cortices; (2) phosphatidylinositol 3-kinase (PI3K)/AKT and mitogen-activated protein kinase (MAPK) phosphorylation; and (3) c-kit and FSH receptor (FSHr) mRNA expression. At 100 ng mL–1, SCF increased (P ≤ 0.05) the percentage and size of secondary follicles after 14 days of in vitro culture and sustained AKT phosphorylation after 3 days incubation. EGF suppressed this beneficial effect and reduced (P ≤ 0.05) the percentage of structurally normal follicles and FSHr expression when combined with 100 ng mL–1 SCF. Expression of c-kit mRNA was higher (P ≤ 0.05) in the presence of 100 ng mL–1 SCF compared with fresh follicles and cohorts cultured under other conditions. A c-kit inhibitor suppressed follicle growth and reduced AKT phosphorylation. Collectively, the results demonstrate that SCF promotes cat follicle development by upregulating c-kit mRNA expression and AKT phosphorylation. EGF suppresses the stimulating effect of SCF, leading to downregulation of FSHr expression.

The spatiotemporal hormonal orchestration of human folliculogenesis, early embryogenesis and blastocyst implantation

The early reproductive events starting with folliculogenesis and ending with blastocyst implantation into the uterine endometrium are regulated by a complex interplay among endocrine, paracrine and autocrine factors. This review examines the spatiotemporal integration of these maternal and embryonic signals that are required for successful reproduction. In coordination with hypothalamic-pituitary-gonadal (HPG) hormones, an intraovarian HPG-like axis regulates folliculogenesis, follicular quiescence, ovulation, follicular atresia, and corpus luteal functions. Upon conception and passage of the zygote through the fallopian tube, the contribution of maternal hormones in the form of paracrine secretions from the endosalpinx to embryonic development declines, with autocrine and paracrine signaling becoming increasingly important as instructional signals for the differentiation of the early zygote/morula into a blastocyst. These maternal and embryonic signals include activin and gonadotropin-releasing hormone 1 (GnRH1) that are crucial for the synthesis and secretion of the 'pregnancy' hormone human chorionic gonadotropin (hCG). hCG in turn signals pre-implantation embryonic cell division and sex steroid production required for stem cell differentiation, and subsequent blastulation, gastrulation, cavitation and blastocyst formation. Upon reaching the uterus, blastocyst hatching occurs under the influence of decreased activin signaling, while the attachment and invasion of the trophoblast into the endometrium appears to be driven by a decrease in activin signaling, and by increased GnRH1 and hCG signaling that allows for tissue remodeling and the controlled invasion of the blastocyst into the uterine endometrium. This review demonstrates the importance of integrative endocrine, paracrine, and autocrine signaling for successful human reproduction.

Oocyte-dependent activation of MTOR in cumulus cells controls the development and survival of cumulus-oocyte complexes

Communication between oocytes and their companion somatic cells promotes the healthy development of ovarian follicles, which is crucial for producing oocytes that can be fertilized and are competent to support embryogenesis. However, how oocyte-derived signaling regulates these essential processes remains largely undefined. Here, we demonstrate that oocyte-derived paracrine factors, particularly GDF9 and GDF9-BMP15 heterodimer, promote the development and survival of cumulus-cell-oocyte complexes (COCs), partly by suppressing the expression of Ddit4l, a negative regulator of MTOR, and enabling the activation of MTOR signaling in cumulus cells. Cumulus cells expressed less Ddit4l mRNA and protein than mural granulosa cells, which is in striking contrast to the expression of phosphorylated RPS6 (a major downstream effector of MTOR). Knockdown of Ddit4l activated MTOR signaling in cumulus cells, whereas inhibition of MTOR in COCs compromised oocyte developmental competence and cumulus cell survival, with the latter likely to be attributable to specific changes in a subset of transcripts in the transcriptome of COCs. Therefore, oocyte suppression of Ddit4l expression allows for MTOR activation in cumulus cells, and this oocyte-dependent activation of MTOR signaling in cumulus cells controls the development and survival of COCs.

Physiologic Course of Female Reproductive Function: A Molecular Look into the Prologue of Life

The genetic, endocrine, and metabolic mechanisms underlying female reproduction are numerous and sophisticated, displaying complex functional evolution throughout a woman's lifetime. This vital course may be systematized in three subsequent stages: prenatal development of ovaries and germ cells up until in utero arrest of follicular growth and the ensuing interim suspension of gonadal function; onset of reproductive maturity through puberty, with reinitiation of both gonadal and adrenal activity; and adult functionality of the ovarian cycle which permits ovulation, a key event in female fertility, and dictates concurrent modifications in the endometrium and other ovarian hormone-sensitive tissues. Indeed, the ultimate goal of this physiologic progression is to achieve ovulation and offer an adequate environment for the installation of gestation, the consummation of female fertility. Strict regulation of these processes is important, as disruptions at any point in this evolution may equate a myriad of endocrine-metabolic disturbances for women and adverse consequences on offspring both during pregnancy and postpartum. This review offers a summary of pivotal aspects concerning the physiologic course of female reproductive function.

Regulation of FOXO3 subcellular localization by Kit ligand in the neonatal mouse ovary

PURPOSE

Foxo3 protein is required in the oocyte nucleus for the maintenance of primordial follicles in a dormant state. PI3K/AKT-dependent phosphorylation of Foxo3 leads to its relocalization to the cytoplasm and subsequent follicular activation. However, the nature of the upstream signals controlling Foxo3 activity and subcellular localization remains unknown. We aimed to study the in vitro effects of Kit ligand (stem cell factor) on the subcellular localization of Foxo3 in primordial follicles within the postnatal mouse ovary.

METHODS

This was an in vitro study using explants of intact neonatal mouse ovaries. The study was performed in laboratory animal facility and basic science research laboratory at a University Hospital. The animals used for this study were FVB mice. Neonatal FVB mice ovaries at postnatal day 7 (PD7) were harvested and incubated in culture medium (DMEM) at 37 °C and 5 % CO(2) for 60-90 min with (n = 3) or without (n = 3) Kit ligand at 150 ng/mL (8 nM). Similar experimental conditions were used to establish a dose-response curve for the effects of Kit ligand and assess the effects of imatinib (small molecule inhibitor of the Kit receptor). Immunofluorescence was used to identify the subcellular location of Foxo3 in oocytes. Proportions of cytoplasmic versus nuclear Foxo3 in primordial follicles were determined.

RESULTS

Kit ligand treatment increased the cytoplasmic localization of Foxo3 from 40 % in the untreated ovaries to 74 % in the treated group (p = 0.007 in paired samples and p = 0.03 in unpaired samples). Furthermore, this effect was reversible with imatinib (p = 0.005). A dose-response curve for Kit ligand treatment showed that maximum effect was seen at 150 ng/mL.

CONCLUSION

Kit ligand treatment in vitro increases the proportion of cytoplasmic Foxo3 in primordial follicles at PD7, lending support to the idea that Kit receptor/ligand controls Foxo3 activity in the context of primordial follicle activation.

Kit ligand promotes the transition from primordial to primary follicles afterin vitroculture of ovine ovarian tissue

This study evaluated the effects of kit ligand (KL) on the morphology and development of ovine preantral follicles (fresh control) and after 7 days ofin vitroculture in α-Minimal Essential Medium (α-MEM; control medium) or the presence of KL (1, 10, 50, 100 or 200 ng/ml). There was an increase in the percentage of primary follicles at the concentration of 100 ng/ml KL, compared with the fresh control, control medium (α-MEM) and the other KL concentrations. Follicle diameter was significantly higher than the control medium only at concentrations of 50 and 100 ng/ml KL. In conclusion, 100 ng/ml KL promoted the transition from primordial to primary follicles (follicular activation) afterin vitroculture of ovine ovarian tissue.

Expression and localisation of c-kit and KITL in the adult human ovary

BACKGROUND

The c-kit/kit ligand (KITL) signalling axis is an essential component of ovarian folliculogenesis in mammals, but little is known about expression and localisation of its key components in the ovaries of reproductive age women. This study aimed to characterise mRNA expression of c-kit and KITL isoforms and the localisation of c-kit and KITL proteins in adult human premenopausal ovaries.

METHODS

This study utilised granulosa cells obtained from the preovulatory follicles of women undergoing assisted reproduction, pieces of ovarian tissue obtained from premenopausal women undergoing gynaecological surgeries and archival paraffin-embedded premenopausal ovarian tissues. Methodology included PCR for gene expression and Western blot or immunohistochemistry for protein expression.

RESULTS

Both c-kit mRNA isoforms, known as GNNK+ and GNNK-, were detected in human ovarian cortex, while KITL protein isoforms (KITL1 and KITL2) were present in ovarian cortex and human granulosa cells. Immunohistochemistry showed expression of KITL and c-kit protein in multiple cell types within follicles throughout development, from primordial follicles to large antral follicles, in addition to atretic follicles. Oocytes of all follicle stages expressed c-kit protein exclusively. Interestingly, unlike animal models, expression of both proteins displayed a less cell-type specific distribution with immunostaining present in granulosa, theca and stromal cells, suggesting that autocrine signalling occurs within the human ovary.

CONCLUSION

The results of this study indicate that c-kit/KITL signalling also occurs in the human ovary, as established in various animal models, and may involve previously unknown autocrine signalling.

Intraovarian control of early folliculogenesis

Although hormonal regulation of ovarian follicle development has been extensively investigated, most studies concentrate on the development of early antral follicles to the preovulatory stage, leading to the successful use of exogenous FSH for infertility treatment. Accumulating data indicate that preantral follicles are under stringent regulation by FSH and local intraovarian factors, thus providing the possibility to develop new therapeutic approaches. Granulosa cell-derived C-type natriuretic factor not only suppresses the final maturation of oocytes to undergo germinal vesicle breakdown before ovulation but also promotes preantral and antral follicle growth. In addition, several oocyte- and granulosa cell-derived factors stimulate preantral follicle growth by acting through wingless, receptor tyrosine kinase, receptor serine kinase, and other signaling pathways. In contrast, the ovarian Hippo signaling pathway constrains follicle growth and disruption of Hippo signaling promotes the secretion of downstream CCN growth factors capable of promoting follicle growth. Although the exact hormonal factors involved in primordial follicle activation has yet to be elucidated, the protein kinase B (AKT) and mammalian target of rapamycin signaling pathways are important for the activation of dormant primordial follicles. Hippo signaling disruption after ovarian fragmentation, combined with treating ovarian fragments with phosphatase and tensin homolog (PTEN) inhibitors and phosphoinositide-3-kinase stimulators to augment AKT signaling, promote the growth of preantral follicles in patients with primary ovarian insufficiency, leading to a new infertility intervention for such patients. Elucidation of intraovarian mechanisms underlying early folliculogenesis may allow the development of novel therapeutic strategies for patients diagnosed with primary ovarian insufficiency, polycystic ovary syndrome, and poor ovarian response to FSH stimulation, as well as for infertile women of advanced reproductive age.