Kit ligand and the somatostatin receptor antagonist, BIM-23627, stimulate in vitro resting follicle growth in the neonatal mouse ovary

Prenatal cannabinoid exposure alters the ovarian reserve in adult offspring of rats

In animals, research in the past two decades has demonstrated the strong involvement of the endocannabinoid system (ECS) in numerous steps of the reproductive process, including ovarian physiology. Reproductive lifespan is closely related to the number of nongrowing ovarian follicles, called ovarian reserve (OR), which is definitively established during foetal life. Thus, OR damage may lead to poor reproductive outcomes and a shortened reproductive lifespan. We investigated whether prenatal ECS modulation had an effect on the OR at different ages in the rat offspring. Four groups of gestating female rats (F0) were exposed to the CB1-/CB2-receptor agonist WIN55212 (0.5 mg/kg), the CB1R inverse agonist SR141716 (3 mg/kg) or Δ9THC (5 mg/kg) and were compared to negative control groups. OR was histologically assessed at different postnatal timepoints (F1 individuals): postnatal day (PND) 6, PND40 and PND90. At PND6, prenatal exposure had no effect on OR. In the young adult group (PND90) exposed during gestation to WIN55212, we observed a CB1R-mediated delayed OR decrease, which was reversed by prenatal CB1R blockade by SR141716. Conversely, after prenatal SR141716 exposure, we observed higher OR counts at PND90. RT-PCR experiments also showed that prenatal ECS modulation perturbed the mRNA levels of ECS enzymes and OR regulation genes. Our findings support the role of the ECS in OR regulation during the foetal life of rats and highlight the need for further studies to elucidate its precise role in OR physiology.

Treatment of female rhesus macaques with a somatostatin receptor antagonist that increases oocyte fertilization rates without affecting post-fertilization development outcomes

PURPOSE

To determine the effects of PGL1001, a somatostatin receptor isoform-2 (SSTR-2) antagonist, on ovarian follicle development, oocyte fertilization, and subsequent embryo developmental potential in the rhesus macaque.

METHODS

Cycling female rhesus macaques (N = 8) received vehicle through one menstrual (control) cycle, followed by daily injections of PGL1001, a SSTR-2 antagonist, for three menstrual (treatment) cycles. Main endpoints include overall animal health and ovarian hormones (e.g., estradiol [E2], progesterone [P4], and anti-Müllerian hormone [AMH]), ovarian circumference, numbers of oocytes and their maturation status following controlled ovarian stimulation (COS), as well as oocyte fertilization and subsequent blastocyst rates that were assessed in control and PGL1001 treatment cycles. Circulating PGL1001 levels were assessed at baseline as well as 6, 60, and 90 days during treatment.

RESULTS

PGL1001 treatment did not impact overall animal health, menstrual cycle length, or circulating levels of ovarian hormones (E2, P4, and AMH) in comparison to vehicle treatment during natural cycles. PGL1001 treatment increased (p ˂ 0.05) ovarian circumference and the day 8 to day 1 ratio of AMH levels (p ˂ 0.05) during a COS protocol, as well as oocyte fertilization rates compared to the vehicle treatment interval. Blastocyst development rates were not significantly different between vehicle and PGL1001 treatment groups.

CONCLUSION

Prolonged treatment with PGL1001 appears to be safe and does not affect rhesus macaque general health, menstrual cycle length, or ovarian hormone production. Interestingly, PGL1001 treatment increased the fertilization rate of rhesus macaque oocytes collected following ovarian stimulation.

Basic fibroblast growth factor promotes macaque follicle development in vitro

Fertility preservation is an important type of frontier scientific research in the field of reproductive health. The culture of ovarian cortices to i) initiate primordial follicle growth and ii) procure developing follicles for later oocyte maturation is a promising fertility preservation strategy, especially for older women or cancer patients. At present, this goal remains largely unsubstantiated in primates because of the difficulty in attaining relatively large follicles via ovarian cortex culture. To overcome this hurdle, we cultured macaque monkey ovarian cortices with FSH, kit ligand (KL), basic fibroblast growth factor (bFGF), and/or epidermal growth factor (EGF). The various factors and factor combinations promoted primordial follicle development to different extents. Notably, both bFF (bFGF, 100 ng/ml and FSH, 50 ng/ml) and KF (KL, 100 ng/ml and FSH, 50 ng/ml) contributed to the activation of primordial follicles at day 12 (D12) of culture, whereas at D18, the proportions of developing follicles were significantly higher in the bFF and KF groups relative to the other treatment groups, particularly in the bFF group. Estradiol and progesterone production were also highest in the bFF group, and primary follicle diameters were the largest. Up until D24, the bFF group still exhibited the highest proportion of developing follicles. In conclusion, the bFGF–FSH combination promotes nonhuman primate primordial follicle developmentin vitro, with the optimal experimental window within 18 days. These results provide evidence for the future success of human ovarian cortex culture and the eventual acquisition of mature human follicles or oocytes for fertility restoration.

Constitutive and follicle-stimulating hormone-induced action of somatostatin receptor-2 on regulation of apoptosis and steroidogenesis in bovine granulosa cells

In the present study, we employed primary bovine culture of granulosa cells (GCs) as a cellular model to study the potential involvement of somatostatin receptor 2 (SSTR2) in ovarian function. The results showed that bovine GCs expressed SST2 receptor and further found that SSTR2 was possibly regulated by follicle-stimulating hormone (FSH), as a significant increase in protein level of SSTR2 was observed in FSH-treated GCs. For further analysis, endogenous SSTR2 expression was disrupted using small inhibitory RNA (siRNA) and the efficacy of differential silencing of endogenous SSTR2 expression was measured both at transcriptional and translational levels. Transient blockage of SSTR2 evidenced its constitutive action on GCs, as it significantly increased level of cAMP (2.4-folds) and basal progesterone production (∼2-fold, P<0.05) with significant increase (P<0.05) in mRNA levels of StAR and P450ssc without altering estradiol concentration and aromatase mRNA expression. Furthermore, silencing of SSTR2 reduced GCs apoptosis (52.5%, P<0.05) and increased cell proliferation, which was further corroborated by up-regulation in protein expressions of B-cell leukemia/lymphoma 2 (Bcl-2), inhibition of caspase3 and mRNA level of bcl2-associated-X protein (Bax). These results provide evidence that SSTR2 subtype controls GCs apoptosis, proliferation and hormonal secretions through selective constitutive action, independently of somatostatin (SST). Given the local inhibitory actions of SSTR2 on the gonads, we further found that apoptosis in ssRNAi-2 transfected cells decreased (6.8% vs 1.9%, P<0.05) more strongly on FSH treatment. Apoptotic protein expressions and steroid hormone mRNA levels were correlated with a relative decrease in apoptosis and increase in progesterone production. Our results suggest that SSTR2 may play a crucial role as a local inhibitor of FSH action on GCs apoptosis and steroidogenesis.

Development of a serum-free defined system employing growth factors for preantral follicle culture

This study was conducted to evaluate if mouse preantral follicles can yield developmentally competent oocytes following culture in serum-free, defined medium. Donor follicles were obtained from 14-day-old B6CBAF1 mice, and cultured in α-MEM-Glutamax medium. The replacement of fetal bovine serum with knockout serum replacement (KSR) did not significantly reduce follicle growth or oocyte maturation in vitro, although it significantly reduced the development of oocytes after activation. Regardless of the replacement medium, follicle growth was not influenced by the addition of leukemia inhibitory factor (LIF). The addition of 100 ng/ml stem cell factor (SCF) to the KSR-supplemented serum-free medium significantly stimulated follicle development, which further improved blastocyst formation after oocyte activation. On Day 3 of culture, a significant increase in Bmp7 expression was detected in the SCF-containing medium compared with the serum-containing medium, whereas Gdf9 and Amh were increased in the serum-containing medium. A significant increase in estradiol production was detected under serum-free conditions, but minimal progesterone secretion was detected throughout the culture period. In conclusion, serum-free media can be used to optimize ovarian follicle cultures, and the addition of SCF is beneficial for deriving developmentally competent oocytes through follicle culture.

Involvement of bone morphogenetic protein activity in somatostatin actions on ovarian steroidogenesis

Somatostatin is expressed in the hypothalamus, pancreas and gastrointestinal tracts and it inhibits the secretion of various hormones in vivo. In the rodent ovary, somatostatin receptor (SSTR) subtypes 2 and 5 are expressed in granulosa cells and oocytes. Somatostatin analogs have been clinically used for treatment of endocrine tumors. For this purpose, relatively high-dose or long-term treatments of somatostatin analogs are necessary; however, the direct and continuous impact of somatostatin analogs on gonadal functions has yet to be elucidated. In the present study, we investigated the effects of somatostatin analogs (octreotide and pasireotide) on ovarian steroidogenesis by rat primary granulosa cell culture. The expression levels of SSTR2 and SSTR5 in granulosa cells were upregulated by FSH treatment. Treatment with somatostatin analogs decreased FSH-induced estradiol production with reduction in aromatase mRNA expression, while the treatment also suppressed FSH-induced progesterone production with reduction of mRNAs levels of StAR, P450scc and 3βHSD2 in granulosa cells. This trend was also observed in a granulosa/oocyte co-culture condition. The effect of pasireotide was more potent than that of octreotide. FSH-induced synthesis of steroids and cAMP was also suppressed by somatostatin analog treatment. Notably, pretreatment with a BMP-binding protein, noggin reversed the suppressive effects of somatostatin analogs on progesterone and cAMP production, suggesting that the endogenous BMP system is functionally involved in the SSTR effects in granulosa cells. Treatment with BMP-2, -4, -6 and -7 decreased the mRNA expression of inhibitory Smads6 and 7, leading to enhancement of BMP actions detected by Id-1 transcription in granulosa cells. Collectively, the results revealed that SSTR activation modulates ovarian steroidogenesis by upregulating endogenous BMP activity in growing follicles.

[Present and future strategies for women at risk, or suffering from premature ovarian failure (POF)]

The purpose of this review is to present the strategies for fertility preservation that are currently proposed to patients at risk from premature ovarian failure (POF) due to chemotherapy as well as some future solutions that could allow patients already affected by an IOP to recover their fertility. Today, cryo-preservation of pieces of ovarian cortex followed by orthotopic transplantation as well as in vitro maturation of oocytes (IVM) allow preservation of fertility in patients being to undergo an antitumor treatment. However, although promising results have been obtained, the pregnancy rate remains very low. Improvement of these techniques, but also stimulation of resting follicle activation, in vitro folliculogenesis, and culture of putative oogonia that may be present in the adult ovary, are all future opportunities for patients suffering from an IOP, and are currently the subject of intensive researches.

The ovarian reserve in mammals: a functional and evolutionary perspective

The constitution and the control of the ovarian reserve is of importance in mammals and women. In particular, the number of primordial follicles at puberty is positively correlated with the number of growing follicles and their response to gonadotropin treatments. The size of this ovarian reserve depends on genes involved in germ cell proliferation and differentiation, sexual differentiation, meiosis, germ cell degeneration, formation of primordial follicles, and on a potential mechanism of self-renewal of germ stem cells. In this review, we present the state of the art of the knowledge of genes and factors involved in all these processes. We first focus on the almost 70 genes identified mainly by mouse invalidation models, then we discuss the most plausible hypothesis concerning the possibility of the existence of germ cell self-renewal by neo-oogenesis in animal species and human, with a special interest for the role of corresponding genes in evolutionary distinct model species. All of the genes pointed out here are candidates susceptible to explain fertility defects such as the premature ovarian failure in human.

Human ovarian follicular development: from activation of resting follicles to preovulatory maturation

By integrating morphometrical and endocrinological data, as well as biological effects of various molecules synthesized by the human follicle, we propose a dynamic view of the follicle growth within the human ovary. Folliculogenesis starts with entry of resting follicles into the growth phase, a process where the kit system plays a key role. Several months are required for a new growing follicle to reach the preantral stage (0.15mm), then 70 additional days to reach the size of 2mm. Early growing follicle growth is regulated by subtle interactions between follicle-stimulating hormone (FSH) and local factors produced by theca and granulosa cells (GCs), as well as the oocyte. From the time they enter the selectable stage during the late luteal phase, follicles become sensitive to cyclic changes of FSH in terms of granulosa cell proliferation. During the early follicular phase, the early selected follicle grows very quickly and estradiol is present in the follicular fluid. However, the total steroid production remains moderate. From the mid-follicular phase, the preovulatory follicle synthesizes high quantities of estradiol, then after the mid-cycle gonadotropin surge, very large amounts of progesterone. At this stage of development, the responsiveness of the follicle to gonadotropins is maximum, especially to luteinizing hormone (LH) that triggers granulosa wall dissociation and cumulus expansion as well as oocyte nuclear maturation. Thus, as the follicle develops, its responsiveness to gonadotropins progressively increases under the control of local factors acting in an autocrine/paracrine fashion.