PTEN inhibitor and kit ligand increase in vitro activation and survival of primordial follicles in alpaca

In mammals, activation of primordial follicles to primary follicle is a progressive and highly regulated process. There is evidence in mice that phosphatase and tensin homologue deleted on Chromosome 10 (PTEN) silencing is an important negative regulator of phosphatidylinositol 3-kinase (PI3K), which initiates activation of dormant follicles. The objective of the study was to evaluate the effect of the addition of PTEN inhibitor (bpV(HOpic)) (10 μM) and/or Kit Ligand (KL) (100 ng/mL) on the in vitro activation and survival of alpaca primordial follicles. Ovarian cortical fragments from 11 adult alpacas were cultured for 24 h in tissue culture medium (α-MEM+ ) supplemented with KL and bpV or the association of both. Subsequently, each sample was processed by classical histology and follicular counting and classification were performed. The results obtained show a reduction (p < 0.05) of primordial follicles in more than 50% in follicular tissue cultured in vitro in α-MEM+ or supplemented with bpV and/or KL versus the control (not cultured). Further, >25% increase in primary follicles in follicular tissue cultured in vitro in α-MEM+ or supplemented with KL and/or bpV versus control. However, the follicular survival rate showed a decrease of 20% in the cultured tissues, except for the α-MEM+ supplemented with KL and bpV. In conclusion, supplementation of bpV (HOpic) (10 μM) and KL (100 ng/mL) increased the activation in vitro of primordial follicles and survival after in vitro culture of alpaca ovarian tissue.

The ovaries of transgender men indicate effects of high dose testosterone on the primordial and early growing follicle pool

Androgens are essential in normal ovarian function and follicle health but hyperandrogenism, as seen in polycystic ovary syndrome, is associated with disordered follicle development. There are few data on the effect of long-term exposure to high levels of testosterone as found in transgender men receiving gender-affirming endocrine therapy. In this study, we investigate the effect of testosterone on the development, morphological health and DNA damage and repair capacity of human ovarian follicles in vivo and their survival in vitro. Whole ovaries were obtained from transgender men (mean age: 27.6 ± 1.7 years; range 20-34 years, n = 8) at oophorectomy taking pre-operative testosterone therapy. This was compared to cortical biopsies from age-matched healthy women obtained at caesarean section (mean age: 31.8±1.5 years; range= 25-35 years, n=8). Cortical tissues were dissected into fragments and either immediately fixed for histological analysis or cultured for 6 days and subsequently fixed. Follicle classification and morphological health were evaluated from histological sections stained with H&E and expression of γH2AX as a marker of DNA damage by IHC. In uncultured tissue, testosterone exposure was associated with reduced follicle growth activation, poor follicle health and increased DNA damage. After 6 days of culture, there was enhanced follicle activation compared to control with further deterioration in morphological health and increased DNA damage. These data indicate that high circulating concentrations of testosterone have effects on the primordial and small-growing follicles of the ovary. These results may have implications for transgender men receiving gender-affirming therapy prior to considering pregnancy or fertility preservation measures.

Why is there an "oversupply" of human ovarian follicles?

Women are born with hundreds of thousands to over a million primordial ovarian follicles (PFs) in their ovarian reserve. However, only a few hundred PFs will ever ovulate and produce a mature egg. Why are hundreds of thousands of PFs endowed around the time of birth when far fewer follicles are required for ongoing ovarian endocrine function and only a few hundred will survive to ovulate? Recent experimental, bioinformatics, and mathematical analyses support the hypothesis that PF growth activation (PFGA) is inherently stochastic. In this paper, we propose that the oversupply of PFs at birth enables a simple stochastic PFGA mechanism to yield a steady supply of growing follicles that lasts for several decades. Assuming stochastic PFGA, we apply extreme value theory to histological PF count data to show that the supply of growing follicles is remarkably robust to a variety of perturbations and that the timing of fertility cessation (age of natural menopause) is surprisingly tightly controlled. Though stochasticity is often viewed as an obstacle in physiology and PF oversupply has been called "wasteful," this analysis suggests that stochastic PFGA and PF oversupply function together to ensure robust and reliable female reproductive aging.

Intestinal Flora Changes Induced by a High-Fat Diet Promote Activation of Primordial Follicles through Macrophage Infiltration and Inflammatory Factor Secretion in Mouse Ovaries

Obesity induced by a high-fat diet (HFD) leads to the excessive consumption of primordial follicles (PFs) in the ovaries. There is systemic chronic inflammation under HFD conditions, but no previous studies have explored whether there is a certain causal relationship between HFD-induced chronic inflammation and the overactivation of PFs. Here, we showed that HFD causes disorders of intestinal microflora in mice, with five Gram-negative bacteria showing the most profound increase at the genus level compared to the normal diet (ND) groups and contributes to the production of endotoxin. Endotoxin promotes M1 macrophage infiltration in the ovaries, where they exhibit proinflammatory actions by secreting cytokines IL-6, IL-8, and TNFα. These cytokines then boost the activation of PFs by activating Signal Transducer and Activator of Transcription 3 (STAT3) signaling in follicles. Interestingly, transplantation of the HFD intestinal microflora to the ND mice partly replicates ovarian macrophage infiltration, proinflammation, and the overactivation of PFs. Conversely, transplanting the ND fecal microbiota to the HFD mice can alleviate ovarian inflammation and rescue the excessive consumption of PFs. Our findings uncover a novel and critical function of gut microbes in the process of PF overactivation under HFD conditions, and may provide a new theoretical basis for the microbial treatment of patients with premature ovarian insufficiency caused by HFD.

PI3K/PTEN/AKT Signaling Pathways in Germ Cell Development and Their Involvement in Germ Cell Tumors and Ovarian Dysfunctions

Several studies indicate that the PI3K/PTEN/AKT signaling pathways are critical regulators of ovarian function including the formation of the germ cell precursors, termed primordial germ cells, and the follicular pool maintenance. This article reviews the current state of knowledge of the functional role of the PI3K/PTEN/AKT pathways during primordial germ cell development and the dynamics of the ovarian primordial follicle reserve and how dysregulation of these signaling pathways may contribute to the development of some types of germ cell tumors and ovarian dysfunctions.

The Crazy Ovary

From fetal life until senescence, the ovary is an extremely active tissue undergoing continuous structural and functional changes. These ever-changing events are best summarized by a quotation attributed to Plato when describing motion in space and time-'nothing ever is but is always becoming…'. With respect to the ovary, these changes include, at the beginning, the processes of follicular formation and thereafter those of follicular growth and atresia, steroidogenesis, oocyte maturation, and decisions relating to the number of mature oocytes that are ovulated for fertilization and the role of the corpus luteum. The aims of this review are to offer some examples of these complex and hitherto unknown processes. The ones herein have been elucidated from studies undertaken in vitro or from normal in vivo events, natural genetic mutations or after experimental inactivation of gene function. Specifically, this review offers insights concerning the initiation of follicular growth, pathologies relating to poly-ovular follicles, the consequences of premature loss of germ cells or oocytes loss, the roles of AMH (anti-Müllerian hormone) and BMP (bone morphogenetic protein) genes in regulating follicular growth and ovulation rate together with species differences in maintaining luteal function during pregnancy. Collectively, the evidence suggests that the oocyte is a key organizer of normal ovarian function. It has been shown to influence the phenotype of the adjacent somatic cells, the growth and maturation of the follicle, and to determine the ovulation rate. When germ cells or oocytes are lost prematurely, the ovary becomes disorganized and a wide range of pathologies may arise.

Activation of autophagy in early neonatal mice increases primordial follicle number and improves lifelong fertility†

The number of stockpiled primordial follicles is thought to be responsible for the fate of female fertility and reproductive lifetime. We previously reported that starvation in nonsuckling early neonatal mice increases the number of primordial follicles with concomitant autophagy activation, suggesting that autophagy may accelerate the formation of primordial follicles. In this study, we attempted to upregulate the numbers of primordial follicles by administering an autophagy inducer and evaluated the progress of primordial follicle formation and their fertility during the life of the mice. To induce autophagy, mice were intraperitoneally injected with the Tat-beclin1 D-11 peptide (0.02 mg/g body weight) at 6-54 h or 60-84 h after birth. In animals that received Tat-beclin 1 D-11 by 54 h after birth, the primordial follicle numbers were significantly increased compared with the control group at 60 h. The ratio of expressed LC3-II/LC3-I proteins was also significantly greater. The numbers of littermates from pregnant females that had been treated with Tat-beclin 1 D-11 were maintained at remarkably greater levels until 10 months old. These results were supported by an abundance of primordial follicles at even 13-15 months old.

Current Understandings of Core Pathways for the Activation of Mammalian Primordial Follicles

The mammalian ovary has two main functions-producing mature oocytes for fertilization and secreting hormones for maintaining the ovarian endocrine functions. Both functions are vital for female reproduction. Primordial follicles are composed of flattened pre-granulosa cells and a primary oocyte, and activation of primordial follicles is the first step in follicular development and is the key factor in determining the reproductive capacity of females. The recent identification of the phosphatidylinositol 3 kinase (PI3K)/phosphatase and tensin homolog deleted on chromosome 10 (PTEN) signaling pathway as the key controller for follicular activation has made the study of primordial follicle activation a hot research topic in the field of reproduction. This review systematically summarizes the roles of the PI3K/PTEN signaling pathway in primordial follicle activation and discusses how the pathway interacts with various other molecular networks to control follicular activation. Studies on the activation of primordial follicles have led to the development of methods for the in vitro activation of primordial follicles as a treatment for infertility in women with premature ovarian insufficiency or poor ovarian response, and these are also discussed along with some practical applications of our current knowledge of follicular activation.

Activation of goat primordial follicles in vitro: Influence of alginate and ovarian tissue

The present study aimed to evaluate the effect of three culture systems on caprine primordial follicle activation in vitro: follicles cultured either in the isolated form within alginate (Isolated follicles + Alginate treatment), or enclosed in ovarian tissue (in situ), with or without alginate (Fragment + Alginate, and Fragment alone treatments, respectively). After culture, the Isolated follicles + Alginate treatment presented a percentage of morphologically normal follicles (MNF) similar to both the non-cultured control and the Fragment Alone treatments. Nevertheless, Fragment + Alginate treatment showed a significant reduction in the number of MNF when compared to the other treatments. Regarding follicle development, our results showed that regardless of the alginate, the presence of ovarian tissue limited primordial follicle activation during in vitro culture. Remarkably, the Isolated primordial follicle + Alginate treatment was the only one that significantly promoted follicle activation and increased both follicle and oocyte diameters during IVFC, pointing out a higher cell proliferation. In conclusion, the presence of ovarian tissue with or without alginate limited follicle development (activation) after culture. Nevertheless, when primordial follicles were isolated and encapsulated in alginate they presented suitable survival rates, higher rates of follicle activation and continued to grow throughout the culture period.

ELAVL2-directed RNA regulatory network drives the formation of quiescent primordial follicles

Formation of primordial follicles is a fundamental, early process in mammalian oogenesis. However, little is known about the underlying mechanisms. We herein report that the RNA-binding proteins ELAVL2 and DDX6 are indispensable for the formation of quiescent primordial follicles in mouse ovaries. We show that Elavl2 knockout females are infertile due to defective primordial follicle formation. ELAVL2 associates with mRNAs encoding components of P-bodies (cytoplasmic RNP granules involved in the decay and storage of RNA) and directs the assembly of P-body-like granules by promoting the translation of DDX6 in oocytes prior to the formation of primordial follicles. Deletion of Ddx6 disturbs the assembly of P-body-like granules and severely impairs the formation of primordial follicles, indicating the potential importance of P-body-like granules in the formation of primordial follicles. Furthermore, Ddx6-deficient oocytes are abnormally enlarged due to misregulated PI3K-AKT signaling. Our data reveal that an ELAVL2-directed post-transcriptional network is essential for the formation of quiescent primordial follicles.

Neoadjuvant Treatment With Müllerian-Inhibiting Substance Synchronizes Follicles and Enhances Superovulation Yield

Müllerian-inhibiting substance (MIS), also known as anti-Müllerian hormone, is thought to be a negative regulator of primordial follicle activation. We have previously reported that treatment with exogenous MIS can induce complete ovarian suppression within 5 weeks of treatment in mice. To investigate the kinetics of the return of folliculogenesis following the reversal of suppression, we treated animals with recombinant human MIS (rhMIS) protein for 40 days in adult female Nu/Nu mice and monitored the recovery of each follicle type over time. Following cessation of MIS therapy, secondary, and antral follicles returned within 30 days, along with the normalization of reproductive hormones, including LH, FSH, MIS, and Inhibin B. Furthermore, 30 days following MIS pretreatment, the number of antral follicles were significantly higher than controls, and superovulation with timed pregnant mare serum gonadotropin and human chorionic gonadotropin stimulation at this time point resulted in an approximately threefold increased yield of eggs. Use of the combined rhMIS-gonadotropin superovulation regimen in a diminished ovarian reserve (DOR) mouse model, created by 4-vinylcyclohexene dioxide treatment, also resulted in a twofold improvement in the yield of eggs. In conclusion, treatment with rhMIS can induce a reversible ovarian suppression, following which a rapid and synchronized large initial wave of growing follicles can be harnessed to enhance the response to superovulation. Therapies modulating MIS signaling may therefore augment the response to current ovarian stimulation protocols and could be particularly useful to women with DOR or poor responders to controlled ovarian hyperstimulation during in vitro fertilization.

Disruptions in the reproductive system of female rats after prenatal lipopolysaccharide-induced immunological stress: role of sex steroids

Stress signals during fetal or early postnatal periods may disorganize reproductive axis development at different levels. This study was aimed to test the hypothesis that prenatal immunological stress induced by bacterial endotoxin, lipopolysaccharide (LPS), has impact on structure and function of the reproductive system in female offspring. Adult female Wistar rats were divided into two groups, a control group (n = 5) and a LPS group (n = 12). Rats were injected with LPS 50 μg/kg body or 0.9% saline intraperitoneally on the 12th day of pregnancy. After birth the female pups (n = 20 in each group) were divided into four groups: (group 1) 0.9% saline prenatally, sesame oil (vehicle) postnatally; (group 2) LPS prenatally, sesame oil postnatally; (group 3) LPS prenatally, fulvestrant postnatally; (group 4) LPS prenatally, flutamide postnatally. Pups were injected subcutaneously into the neck with fulvestrant (estrogen receptor antagonist), 1.5 mg/kg in sesame oil, from postnatal day (PND) 5 to PND14; or flutamide (androgen receptor antagonist), 20 mg/kg in sesame oil, from PND14 to PND30. Rats of the control group were injected with sesame oil during the same time period. Parameters were evaluated by ELISA (serum estradiol and testosterone) and ovarian histology. The main findings were: (1) prenatal stress during the critical period resulted in delayed vaginal opening, decreased body weight and serum concentrations of sex steroids, and significant disorders in ovarian development; (2) postnatal estradiol and testosterone antagonist treatments decreased follicular atresia through increasing the number of healthy follicles and restored endogenous steroid production. Lay summaryImmunological stress, caused by simulating infection through exposure to a bacterial toxin (LPS), during a critical period of fetal development in laboratory rats results in delayed reproductive maturity, decreased body weight and decreased secretion of sex steroids in female offspring, and abnormalities in the ovaries like those in polycystic ovarian syndrome. These prenatally toxin-induced sexual disorders in females could be corrected by estradiol/testosterone antagonists during the postnatal period.

Differentially Expressed lncRNAs After the Activation of Primordial Follicles in Mouse

The activation of primordial follicles is critical to ovarian follicle development, which directly influences female fertility and reproductive life span. Several studies have suggested a role for long noncoding RNAs (lncRNAs) in ovarian function. However, the precise involvement of lncRNAs in the initiation of primordial follicles is still unknown. Here, an in vitro culture model was used to investigate the roles of lncRNAs in primordial follicle activation. We found that primordial follicles in day 3 mouse ovaries were activated after culturing for 8 days in vitro, as indicated by ovarian morphology changes, increases in primary follicle number, and downregulation of mammalian Sterile 20-like kinase messenger RNA (mRNA) and upregulation of growth differentiation factor 9 mRNA. We next examined lncRNA expression profiles by RNA sequencing at the transcriptome level and found that among 60 078 lncRNAs, 6541 lncRNA were upregulated and 2135 lncRNA were downregulated in 3-day ovaries cultured for 8 days in vitro compared with ovaries from day 3 mice. We also found that 4171 mRNAs were upregulated and 1795 were downregulated in the cultured ovaries. Gene ontology and pathway analyses showed that the functions of differentially expressed lncRNA targets and mRNAs were closely linked with many processes and pathways related to ovary development, including cell proliferation and differentiation, developmental processes, and other signaling transduction pathways. Additionally, many novel identified lncRNAs showed inducible expression, suggesting that these lncRNAs may be good candidates for investigating mouse primordial follicle activation. This study provides a foundation for further exploring lncRNA-related mechanisms in the initiation of mouse primordial follicles.

Dormancy and activation of human oocytes from primordial and primary follicles: molecular clues to oocyte regulation

STUDY QUESTION

Do specific transcriptome dynamics in human oocytes from primordial and primary follicles identify novel pathways in oocyte activation?

SUMMARY ANSWER

The transcriptomic profiles in oocytes from primordial and primary follicles, respectively, revealed several new canonical pathways as putative mediators of oocyte dormancy and activation.

WHAT IS KNOWN ALREADY

Cellular signaling pathways including PI3K/AKT and AKT/mTOR as well as TGF-β and IGF signaling are known to regulate the primordial-to-primary transition in mammalian follicle development.

STUDY DESIGN, SIZE, DURATION

We performed a class comparison study on human oocytes from primordial (n = 436) and primary (n = 182) follicles donated by three women having ovarian tissue cryopreserved before chemotherapy.

PARTICIPANTS/MATERIALS, SETTING, METHODS

RNA was extracted from oocytes from primordial and primary follicles isolated by Laser Capture Microdissection, and submitted to the HiSeq Illumina platform. Data mapping, quality control, filtering and expression analysis were performed using Tophat (2.0.4), Cufflinks (2.0.2), BWA (0.6.2) and software R. Modeling of complex biological systems was performed using the IPA® software. Finally, qPCR and immunohistochemistry were employed to explore expression and localization of selected genes and products in human ovarian tissue.

MAIN RESULTS AND THE ROLE OF CHANCE

We found 223 and 268 genes down-regulated and up-regulated, respectively, in the oocytes during the human primordial-to-primary follicle transition (P < 0.05 and/or FPKM fold-change >2). IPA® enrichment analysis revealed known pathways ('mTOR Signaling', 'PI3K/AKT Signaling' and 'PTEN Signaling') as well as enriched canonical pathways not previously associated with human ovarian follicle development such as 'ErB Signaling' and 'NGF Signaling' in the down-regulated category and 'Regulation of eIF4 and P70S6K Signaling' and 'HER-2 Signaling in Breast Cancer' in the up-regulated group. Additionally, immunohistochemistry on human ovarian tissue explored the intraovarian localization of VASA, FOXO1 and eIF4E.

LARGE SCALE DATA

http://users-birc.au.dk/biopv/published_data/ernst_2017/.

LIMITATIONS, REASONS FOR CAUTION

This is a descriptive analysis and no functional studies were performed. The study was based on a limited number of patients and the experimental design could not take into account the natural biological variance in human samples. Therefore, qPCR was used to confirm selected genes alongside immunohistochemical stainings.

WIDER IMPLICATIONS OF THE FINDINGS

This study shows, for the first time, a detailed molecular description of global gene transcription activities in oocytes from primordial and primary follicles, respectively. Knowing the global transcription profiles of human oocyte dormancy and activation are important in developing new clinical applications.

STUDY FUNDING/COMPETING INTEREST(S)

E.H.E. was supported by Health Faculty, Aarhus University and Kong Christian Den Tiendes Fond. K.H. and S.F. were supported by an MRC (UK) project grant MR/M012638/1. K.L.H. was supported by grants from Fonden til Lægevidenskabens Fremme, Kong Christian Den Tiendes Fond. K.L.H. and L.S. were supported by the IDEAS grant from Aarhus University Research Foundation (AUFF). There are no conflicts of interest.

Ovarian reserve testing: a user's guide

Ovarian reserve is a complex clinical phenomenon influenced by age, genetics, and environmental variables. Although it is challenging to predict the rate of an individual's ovarian reserve decline, clinicians are often asked for advice about fertility potential and/or recommendations regarding the pursuit of fertility treatment options. The purpose of this review is to summarize the state-of-the-art of ovarian reserve testing, providing a guide for the obstetrician/gynecologist generalist and reproductive endocrinologist. The ideal ovarian reserve test should be convenient, be reproducible, display little if any intracycle and intercycle variability, and demonstrate high specificity to minimize the risk of wrongly diagnosing women as having diminished ovarian reserve and accurately identify those at greatest risk of developing ovarian hyperstimulation prior to fertility treatment. Evaluation of ovarian reserve can help to identify patients who will have poor response or hyperresponse to ovarian stimulation for assisted reproductive technology. Ovarian reserve testing should allow individualization of treatment protocols to achieve optimal response while minimizing safety risks. Ovarian reserve testing may inform patients regarding their reproductive lifespan and menopausal timing as well as aid in the counselling and selection of treatment for female cancer patients of reproductive age who receive gonadotoxic therapy. In addition, it may aid in establishing the diagnosis of polycystic ovary syndrome and provide insight into its severity. While there is currently no perfect ovarian reserve test, both antral follicular count and antimüllerian hormone have good predictive value and are superior to day-3 follicle-stimulating hormone. The convenience of untimed sampling, age-specific values, availability of an automated platform, and potential standardization of antimüllerian hormone assay make this test the preferred biomarker for the evaluation of ovarian reserve in women.

Pharmacological Inhibition of the DNA Damage Checkpoint Prevents Radiation-Induced Oocyte Death

Ovarian function is directly correlated with survival of the primordial follicle reserve. Women diagnosed with cancer have a primary imperative of treating the cancer, but since the resting oocytes are hypersensitive to the DNA-damaging modalities of certain chemo- and radiotherapeutic regimens, such patients face the collateral outcome of premature loss of fertility and ovarian endocrine function. Current options for fertility preservation primarily include the collection and cryopreservation of oocytes or in vitro-fertilized oocytes, but this necessitates a delay in cancer treatment and additional assisted reproductive technology procedures. Here, we evaluated the potential of pharmacological preservation of ovarian function by inhibiting a key element of the oocyte DNA damage checkpoint response, checkpoint kinase 2 (CHK2; CHEK2). Whereas nonlethal doses of ionizing radiation (IR) eradicate immature oocytes in wild-type mice, irradiated Chk2^-/- mice retain their oocytes and, thus, fertility. Using an ovarian culture system, we show that transient administration of the CHK2 inhibitor 2-(4-(4-chlorophenoxy)phenyl)-¹H-benzimidazole-5-carboxamide-hydrate ("CHK2iII") blocked activation of the CHK2 targets TRP53 and TRP63 in response to sterilizing doses of IR, and preserved oocyte viability. After transfer into sterilized host females, these ovaries proved functional and readily yielded normal offspring. These results provide experimental evidence that chemical inhibition of CHK2 is a potentially effective treatment for preserving the fertility and ovarian endocrine function of women exposed to DNA-damaging cancer therapies such as IR.

Lifestyle factors associated with histologically derived human ovarian non-growing follicle count in reproductive age women

STUDY QUESTION

Are lifestyle factors (smoking, BMI, alcohol use and oral contraceptive pill use) associated with the human ovarian reserve as determined by the total ovarian non-growing follicle number?

SUMMARY ANSWER

Light to moderate alcohol use was significantly associated with greater ovarian non-growing follicle (NGF) count, whereas other lifestyle factors were not significantly related.

WHAT IS KNOWN ALREADY

A single previous investigation has suggested that smoking and alcohol use are associated with lower ovarian follicle density. However, this investigation utilized follicle density as the outcome of interest rather than the estimated total ovarian NGF count.

STUDY DESIGN, SIZE, DURATION

This cross-sectional investigation included a convenience sample of premenopausal women from two different academic sites, the University of Washington (n = 37, from 1999-2004) and the University of Oklahoma (n = 73, from 2004-2013), undergoing incidental oophorectomy at the time of hysterectomy (total n = 110, age range 21-52 years).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Prior to undergoing oophorectomy, participants completed detailed questionnaires regarding lifestyle exposures. Following surgery, total ovarian NGF counts were determined with systematic random sampling rules and a validated fractionator/optical dissector technique. Associations between lifestyle factors and log-transformed ovarian follicle counts were determined using multivariable linear regression.

MAIN RESULTS AND THE ROLE OF CHANCE

After controlling for age, BMI, oral contraceptive pill (OCP) use, tobacco use and site of collection, cumulative alcohol use (measured in alcoholic drinks per day multiplied by years of drinking) was associated with ovarian NGF count. Women reporting light (>0 to <1 drink-years) and moderate (1-3 drink-years) alcohol use had greater NGF counts (β = 0.75, P = 0.04, and β = 1.00, P = 0.03; light and moderate use, respectively) as compared with non-users. Neither heavier alcohol use (>3 drink-years), BMI, OCP use, nor tobacco use were significantly associated with the ovarian NGF count. Similar patterns of association with moderate cumulative alcohol use were observed when evaluating associations with pre-antral follicles and total follicle counts.

LIMITATIONS, REASONS FOR CAUTION

All participants in this convenience sample had a benign indication for hysterectomy, and therefore may not be broadly representative of the population without such an indication. Additionally, lifestyle factors were self-reported, and the sample size of the present investigation limits our ability to detect associations of smaller magnitude.

WIDER IMPLICATIONS OF THE FINDINGS

While our findings are in disagreement with a single investigation that utilized human follicle density as the outcome of interest, they are consistent with many studies investigating the relationship between lifestyle factors and the age of spontaneous menopause. Furthermore, they suggest a mechanism that does not involve accelerated follicular atresia to explain the association between smoking and an earlier age of menopause.

STUDY FUNDING/COMPETING INTERESTS

This investigation was funded by NIA R29-HD37360-04 (N.A.K.) and OCAST HR04-115 (K.R.H.) and by the National Institute of General Medical Sciences, Grant 1 U54GM104938 (J.D.P.). There is no conflict of interest.

Changes in the transcriptome of bovine ovarian cortex during follicle activation in vitro

The signals that regulate activation, a key transition in ovarian follicular development, are still not well understood, especially in nonrodent species. To gain insight into the regulation of this transition in cattle, we combined a microarray approach with an in vitro system in which ovarian cortical pieces cultured in control medium are enriched for primordial follicles, whereas pieces cultured with insulin are enriched for primary follicles. Total RNA was extracted from cultured cortical pieces, and then transcripts were identified and analyzed using the Affymetrix Bovine Genome GeneChip array. Around 65% of the transcripts in the bovine GeneChip were detected in cultured cortical pieces. Comparison between pieces cultured with or without insulin generated 158 differentially expressed transcripts. Compared with controls, 90 transcripts were upregulated and 68 were downregulated by insulin. These transcripts are involved in many biological processes and functions, but most are associated with cellular growth or cell cycle/cell death. The transcript encoding ubiquitin-conjugating enzyme E2C (UBE2C) was significantly upregulated during follicle activation, and Ingenuity Pathways Analysis revealed that UBE2C can interact with the tumor suppressor phosphatase and tensin homolog (PTEN). Both PTEN mRNA and protein were lower in cortical pieces cultured with insulin than in controls. In addition, FOXO3a, a downstream effector of PTEN signaling, underwent nuclear-cytoplasmic shuttling during primordial to primary follicle development in bovine fetal ovaries, further suggesting the involvement of the PTEN pathway in follicle activation in cattle. Genes and pathways identified in this study provide interesting candidates for further investigation of mechanisms underlying follicle activation.

How Is the Number of Primordial Follicles in the Ovarian Reserve Established?

The number of primordial follicles in the ovarian reserve is an important determinant of the length of the ovarian lifespan, and therefore the fertility of an individual. This reserve contains all of the oocytes potentially available for fertilization throughout the fertile lifespan. The maximum number is set during pregnancy or just after birth in most mammalian species; current evidence does not support neofolliculogenesis after the ovarian reserve is established, although this is increasingly being reexamined. Under physiological circumstances, this number will be influenced by the number of primordial germ cells initially specified in the epiblast of the developing embryo, their proliferation during and after migration to the developing gonads, and their death during oogenesis and formation of primordial follicles at nest breakdown. Death of germ cells during the establishment of the ovarian reserve occurs principally by autophagy or apoptosis, although the triggers that initiate these remain elusive. This review outlines the regulatory steps that determine the number of primordial follicles and thus the number of oocytes in the ovarian reserve at birth, using the mouse as the model, interspersed with human data where available. This information has application for understanding the variability in duration of fertility that occurs between normal individuals and with age, in premature ovarian insufficiency, and after chemotherapy or radiotherapy.

Comparative proteomic analysis of primordial follicles from ovaries of immature and aged rats

Age related decline in reproductive performance in women is well documented and apoptosis has been considered as one of the reasons for the decline of primordial follicle reserve. Recently we observed a decline in the efficiency of DNA repair ability in aged rat primordial follicles as demonstrated by decreased mRNA levels of DNA repair genes BRCA1 and H2AX. In the present study, a two-dimensional electrophoresis (2DE) proteomic approach was employed to identify differentially expressed proteins in primordial follicles isolated from ovaries of immature (∼20 days) and aged (∼400-450 days) rats. Using MALDI-TOF/TOF MS, we identified 13 differentially expressed proteins (p < 0.05) which included seven up-regulated and six down-regulated proteins in aged primordial follicles. These proteins are involved in a wide range of biological functions including apoptosis, DNA repair, and the immune system. Interestingly, the differentially expressed proteins such as FIGNL1 (DNA repair) and BOK (apoptotic protein) have not been previously reported in the rat primordial follicles and these proteins can be related to some common features of ovarian aging such as loss of follicle reserve and genome integrity. The quantitative differences of two important proteins BOK and FIGNL1 observed by the proteomic analysis were correlated with the transcript levels, as determined by semi-quantitative RT-PCR. Our results improve the current knowledge about protein factors associated with molecular changes in rat primordial follicles as a function of aging and our understanding of the proteomic processes involved in degenerative changes observed in aging primordial follicles.

Anti-Müllerian hormone as an ovarian reserve marker in young cancer women who undergo ovarian tissue cryopreservation

AIM

To evaluate if anti-Müllerian hormone (AMH) is a reliable marker of ovarian reserve in young women undergoing ovarian tissue cryopreservation.

PATIENTS & METHODS

Relationships of serum AMH levels with primordial follicle density, age and reproductive hormones were investigated using the Pearson or Spearman correlation coefficient in 86 women with cancer (12-38 years) undergoing ovarian tissue cryopreservation. AMH variations through the menstrual cycle were assessed by the Kruskal-Wallis test. p < 0.05 was accepted as significant.

RESULTS

AMH positively correlated with primordial follicle density (p = 0.03), showed great interindividual variability at all ages and negatively correlated with estradiol (p = 0.007) in the early follicular phase. AMH did not vary across the menstrual cycle (p = 0.415).

CONCLUSION

AMH appears a valid ovarian reserve marker in young cancer women.

Loss of the proapoptotic BH3-only protein BCL-2 modifying factor prolongs the fertile life span in female mice

The duration of the female fertile life span is influenced by the number of oocytes stored in the ovary as primordial follicles. Cell death, both during ovarian development in the embryo and in the postnatal ovary, plays a critical role in determining how many primordial follicles are established and maintained within the ovary. However, the roles of individual apoptotic regulators in mediating cell death within the ovary have not yet been characterized. In this study, gene targeted mice were used to investigate the role of BCL-2-modifying factor (BMF), a proapoptotic protein belonging to the BH3-only subgroup of the BCL-2 family, in determining the number of primordial follicles maintained in the adult ovary and the length of the fertile life span. Stereological analysis of ovaries showed that Bmf(-/-) mice had significantly more primordial follicles than wild-type (WT) control animals at Postnatal Days 100, 200, 300, and 400 but not at Day 20. No differences were observed between WT and Bmf(-/-) mice in the number of ova shed following ovulatory stimulation with exogenous gonadotropins. Bmf(-/-) females were fertile and produced the same number pups/litter as WT females, but Bmf(-/-) females produced litters more frequently and consequently more offspring than WT females over a 6-mo period. Furthermore, the fertile life span of Bmf(-/-) females was significantly extended compared to WT females. Our findings support an important role for BMF in determining the number of primordial follicles maintained in the ovary throughout adult reproductive life and thus indicate that the length of female fertility may be extended by increasing the number of primordial follicles maintained within the ovary through inhibition of BMF.

Possible direct cytoxicity effects of cyclophosphamide on cultured human follicles: an electron microscopy study

PURPOSE

To evaluate the direct effect of cyclophosphamide on cultured human ovarian follicles.

METHODS

Human ovarian cortical slices from premenopausal women were incubated with medium containing cyclophosphamide (0.0005-0.5 mg/mL) for 2-48 h and assessed by transmission electron microscopy. Noncultured specimens and samples cultured without cyclophosphamide were used as controls.

RESULTS

There were significantly more damaged granulosa cell nuclei after incubation with 0.5 mg/mL cyclophosphamide for at least 4 h. There were also more changes in the basement membrane after incubation with cyclophosphamide at concentrations of 0.05 and 0.5 mg/mL.

CONCLUSIONS

Although the cyclophosphamide dose that caused damage to the granulosa cell nuclei was above the pharmacological level, our results suggest that cyclophosphamide, and not only its active metabolite phospharamide mustard, might have a destructive effect on human follicles, as it remains in the circulation longer. This effect could be mediated by damage to the granulosa cells and perhaps the basement membrane.

Preservation of fertility in women undergoing chemotherapy: current approach and future prospects

PURPOSE

Anticancer treatment causes ovarian failure.

METHODS

Some hormones may have a protective effect on the ovary. Cryopreservation (freezing) of oocytes has had very limited success, and therefore, currently its use before chemotherapy is not a feasible option. However, cryopreservation of embryos is possible. Another solution is oocyte donation followed by in vitro fertilization (IVF).

RESULTS

Ovarian cortical slices containing primordial follicles have been cryopreserved successfully. To restore fertility, cryopreserved-thawed tissue taken from cancer patients before therapy could be replanted after recovery. The possible risk of malignancy restoration could be eliminated by obtaining unilaminar follicles from cryopreserved-thawed tissue and growing them in vitro, followed by routine IVF.

CONCLUSIONS

Although women who undergo chemotherapy face limited options for fertility preservation, intensive studies in cryopreservation and in vitro maturation of follicles harbor hope for brighter prospects in the future.