Encapsulated three-dimensional culture supports development of nonhuman primate secondary follicles

Synergy of Paracrine Signaling During Early-Stage Mouse Ovarian Follicle Development In Vitro

Introduction

Paracrine signals, such as soluble cytokines and extracellular matrix cues, are essential for the survival and development of multicellular ovarian follicles. While it is well established that hydrogel-based culture systems successfully support the growth of late-stage follicles for fertility preservation, growing small, early-stage ovarian follicles still proves to be challenging. We hypothesized that paracrine factors secreted from neighboring follicles may be crucial for improving the survival of early-stage follicles in vitro.

Methods

To test our hypothesis, we investigated the bi-directional crosstalk of the paracrine signals, such as cell-secreted cytokines, sex hormones and transcription factors (TFs), in follicles encapsulated and cultured for 12 days in alginate in groups of five (5×) and ten (10×).

Results

The differential profiles of TF activity and secretome during folliculogenesis were analyzed using TRanscriptional Activity CEllular aRray (TRACER) and data-driven multivariate modeling approach. The mechano- and oxygen-responsive TFs, NF-κB and HIF1, exhibited a unique upregulation signature in 10× follicles. Consistently, levels of proangiogenic factors, such as VEGF-A and angiopoietin-2, were significantly higher in 10× follicles than those in 5× follicles, reaching 269.77 and 242.82 pg/mL on the last day of culture. The analysis of TRACER and secreted cytokines also revealed critical early interactions between cytokines and TFs, correlating with the observed phenotypical and functional differences between conditions.

Conclusions

We identified unique signatures of synergism during successful early-stage ovarian follicle development. These findings bring us closer to understanding of mechanisms underlying the downstream effects of interactions between the extracellular microenvironment and early-stage folliculogenesis in vitro.

Evaluation of an ovary-on-a-chip in large mammalian models: Species specificity and influence of follicle isolation status

The ability to grow oocytes from immature ovarian follicles in vitro has significant potential for fertility preservation; yet, it has proved challenging in large mammalian species due to the complex metabolic needs and long-term culture requirements. Currently, follicular incubations are based on a "static" system with manual exchange of medium. Despite the numerous advantages of conventional culturing approaches, recapitulating the native microenvironment and supporting the survival of ovarian follicles from large mammalian species still represent challenges. In this study, we utilized an innovative, dynamic microfluidic system to support the in vitro survival of domestic cat and dog follicles enclosed within the ovarian cortex or isolated from ovarian cortex. Results indicate both species-specific and tissue type-specific differences in response to microfluidic culture. Domestic cat but not dog ovarian cortical tissues maintained viability under flow similar to conventional agarose gel controls. Preantral stage isolated follicles from both species that grew most favourably in conventional alginate bead culture, but overall, there was no influence of culture system on expression of follicle development or oocyte health markers. This system represents an important exploration toward the development of an improved ovarian in vitro culture system of large mammalian species (e.g., cats and dogs), which has potential applications for fertility preservation, reproductive toxicology, and endangered mammal conservation efforts.

Improved BALB/c mice granulosa cell functions using purified alginate scaffold

Alginate, a non-toxic polysaccharide isolated from brown algae, is a widely used 3-dimensional (3D) porous scaffold for the granulosa cell and follicle encapsulation. However, impurities in commercial alginate can lead to alginate biocompatibility reduction. The aim of this study was to evaluate in vitro behavior of the granulosa cells seeded on the purified alginate in varying concentrations compared with matched non-purified ones. We produced a purified alginate using a simple and efficient method. Then, the granulosa cells from mice were isolated and seeded in various concentrations of (0.5%, 1% weight/volume) purified and non-purified alginate. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay was used on the 3rd, 5th and the 8th days of culture as an index of cell viability and proliferation. Furthermore, the secreted estradiol, progesterone and alkaline phosphatase enzyme (ALP) were measured in the granulosa cells culture media using radioimmunoassay kits. The cells cultured on purified and low concentration alginate showed a higher proliferation rate, sex hormone production and ALP activity. The results confirmed the impact of the alginate hydrogel properties on proliferative rate and function of granulosa cells in a 3D culture system.

Follicle dynamics: visualization and analysis of follicle growth and maturation using murine ovarian tissue culture

Purpose

To visualize and analyze follicle development in ovarian tissue culture using physiological concentrations of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in order to establish an ovarian tissue culture system that enables efficient in vitro growth of follicles.

Methods

Ovarian tissues from 4-week-old female ICR mice were sliced and cultured. Images of ovarian tissues in culture were obtained at 24-h or 30-min intervals by using a microscope. The area of each follicle observed in the ovarian tissue slices was tracked and analyzed in association with oocyte maturation.

Results

We were able to track the development of each follicle using this culture system. Follicle growth was associated with oocyte maturation. Meiotically matured oocytes (MII) were obtained from 33% of all follicles investigated. Approximately, a quarter of follicles (24%) did not grow and resulted in atresia.

Conclusion

Follicle dynamics were successfully visualized and analyzed in murine ovarian tissue culture. We were able to obtain mature oocytes from the fully grown follicles in vitro. This culture system would be helpful for efficient in vitro culturing of ovarian tissues.

Electronic supplementary material

The online version of this article (10.1007/s10815-017-1073-5) contains supplementary material, which is available to authorized users.

Development of macaque secondary follicles exposed to neutral red prior to 3-dimensional culture

PURPOSE

Neutral red (NR) may assist identification of preantral follicles in pieces of cortical tissue prior to cryopreservation in cancer patients requesting fertility preservation. This study is the first to analyze this effect by follicle growth rate after long-term culture in primates.

METHODS

Ovarian cortex was obtained from adult rhesus macaques, was cut into fragments, and was incubated with NR. Secondary follicles were readily visualized following NR staining and then were encapsulated into alginate beads and cultured individually for 4 weeks in αMEM media supplemented with 10 ng/ml FSH at 5% O2.

RESULTS

The survival rates of secondary follicles during culture were similar between those derived from control tissue (71 ± 13%) and those treated with NR (68 ± 9%). The proportion of surviving follicles that formed an antrum were also similar in both groups (70 ± 17% control; 48 ± 24% NR-treated). Follicle diameters were not different between control follicles (184 ± 5μm) and those stained with NR (181 ± 7 μm) on the day of isolation. The percentages of surviving follicles within three cohorts based on their diameters at week 4 of culture were similar between the control group and NR-stained tissue group, fast-grow follicles (24 ± 6% vs. 13 ± 10%), slow-grow follicles (66 ± 5% vs. 60 ± 9%), or no-grow (10 ± 9% vs. 27 ± 6%), respectively. There were no differences in follicle diameters between groups during the culture period. Pre-exposure of secondary follicles to NR diminished their capacity to produce both estradiol and androstenedione by week 4 of culture, when follicles are exhibiting an antrum. Inhibitory effects of NR on steroid production by slow-grow follicles was less pronounced.

CONCLUSIONS

NR does not affect secondary follicle survival, growth, and antrum formation during long-term culture, but steroid hormone production by fast-grow follicles is compromised. NR can be used as a non-invasive tool for in situ identification of viable secondary follicles in ovarian cortex before tissue cryopreservation without affecting follicle survival and growth in vitro. Whether maturation or developmental competence of oocytes derived from antral follicles in 3D culture that were previously isolated from NR-stained tissue is normal or compromised remains to be determined. Likewise, the functional consequences of pre-exposure to NR prior to ovarian cortical tissue cryopreservation and transplantation are unknown.

In vitro porcine blastocyst development in three-dimensional alginate hydrogels

Appropriate embryonic and fetal development significantly impact pregnancy success and, therefore, the efficiency of swine production. The pre-implantation period of porcine pregnancy is characterized by several developmental hallmarks, which are initiated by the dramatic morphological change that occurs as pig blastocysts elongate from spherical to filamentous blastocysts. Deficiencies in blastocyst elongation contribute to approximately 20% of embryonic loss, and have a direct influence on within-litter birth weight variation. Although factors identified within the uterine environment may play a role in blastocyst elongation, little is known about the exact mechanisms by which porcine (or other species') blastocysts initiate and progress through the elongation process. This is partly due to the difficulty of replicating elongation in vitro, which would allow for its study in a controlled environment and in real-time. We developed a three dimensional (3-D) culture system using alginate hydrogel matrices that can encapsulate pig blastocysts, maintain viability and blastocyst architecture, and facilitate reproducible morphological changes with corresponding expression of steroidogenic enzyme transcripts and estrogen production, consistent with the initiation of elongation in vivo. This review highlights key aspects of the pre-implantation period of porcine pregnancy and the difficulty of studying blastocyst elongation in vivo or by using in vitro systems. This review also provides insights on the utility of 3-D hydrogels to study blastocyst elongation continuously and in real-time as a complementary and confirmatory approach to in vivo analysis.

The Steroid Metabolome in the Isolated Ovarian Follicle and Its Response to Androgen Exposure and Antagonism

The ovarian follicle is a major site of steroidogenesis, crucially required for normal ovarian function and female reproduction. Our understanding of androgen synthesis and metabolism in the developing follicle has been limited by the sensitivity and specificity issues of previously used assays. Here we used liquid chromatography-tandem mass spectrometry to map the stage-dependent endogenous steroid metabolome in an encapsulated in vitro follicle growth system, from murine secondary through antral follicles. Furthermore, follicles were cultured in the presence of androgen precursors, nonaromatizable active androgen, and androgen receptor (AR) antagonists to assess effects on steroidogenesis and follicle development. Cultured follicles showed a stage-dependent increase in endogenous androgen, estrogen, and progesterone production, and incubations with the sex steroid precursor dehydroepiandrosterone revealed the follicle as capable of active androgen synthesis at early developmental stages. Androgen exposure and antagonism demonstrated AR-mediated effects on follicle growth and antrum formation that followed a biphasic pattern, with low levels of androgens inducing more rapid follicle maturation and high doses inhibiting oocyte maturation and follicle growth. Crucially, our study provides evidence for an intrafollicular feedback circuit regulating steroidogenesis, with decreased follicle androgen synthesis after exogenous androgen exposure and increased androgen output after additional AR antagonist treatment. We propose that this feedback circuit helps maintain an equilibrium of androgen exposure in the developing follicle. The observed biphasic response of follicle growth and function in increasing androgen supplementations has implications for our understanding of polycystic ovary syndrome pathophysiology and the dose-dependent utility of androgens in in vitro fertilization settings.

Microfluidic Encapsulation of Ovarian Follicles for 3D Culture

The ovarian follicle that contains one single oocyte is the fundamental functional tissue unit of mammalian ovary. Therefore, isolation and in vitro culture of ovarian follicles to obtain fertilizable oocytes are regarded as a promising strategy for women to combat infertility. In this communication, we performed a brief survey of studies on microfluidic encapsulation of ovarian follicles in core-shell hydrogel microcapsules for biomimetic 3D culture. These studies highlighted that recapitulation of the mechanical heterogeneity of the extracellular matrix in ovary is crucial for in vitro culture to develop early pre-antral follicles to the antral stage, and for the release of cumulus-oocyte complex (COC) from antral follicles in vitro. The hydrogel encapsulation-based biomimetic culture system and the microfluidic technology may be invaluable to facilitate follicle culture as a viable option for restoring women's fertility in the clinic.

Short-term hypertonic exposure enhances in vitro follicle growth and meiotic competence of enclosed oocytes while modestly affecting mRNA expression of aquaporin and steroidogenic genes in the domestic cat model

Using the domestic cat as a non-rodent, larger animal model, the objective was to determine the impact of a brief incubation in a hypertonic microenvironment on (1) ovarian follicle and oocyte growth in vitro, (2) developmental capacity of the resident oocyte, and (3) expression of aquaporin (AQP) genes in parallel with genes involved in regulation of folliculogenesis. In Study 1: Secondary or early antral follicles encapsulated in 0.5% alginate were allocated to one of three treatment groups: 1) culture in standard medium at 290 mOsm for 15 d (Control); 2) incubation in 350 mOsm medium for 1 h followed by culture in standard medium for 15 d (Hypertonic-1h); or 3) incubation in 350 mOsm medium for 24 h followed by incubation in standard medium for additional 14 d (Hypertonic-24h). After measuring follicle and oocyte diameters on Day 15, in vitro-grown oocytes were incubated for 24 h before assessing nuclear status. In Study 2: secondary or early antral follicles were subjected to one of the three treatments: 1) culture in standard medium at 290 mOsm for 48 h; 2) incubation in 350 mOsm medium for 1 h followed by culture in standard medium for additional 47 h; or 3) incubation in 350 mOsm medium for 24 h followed by culture in standard medium for additional 24 h. At the end of the culture period, all follicles were assessed for mRNA level of Cyp17a1, Cyp19a1, Star, Aqp1, 3, 5, 7 and 8 as well as Fshr using qPCR. Freshly collected follicles also were subjected to gene expression analysis and served as the 'Non-cultured control'. Hypertonic-24h follicles grew larger (P < 0.05) than the control, whereas those in Hypertonic-1h group exhibited intermediate growth, especially when the culture started at the early antral stage. Oocytes in the Hypertonic-24h group were larger and resumed meiosis at a higher rate than in the other treatments. In vitro culture affected (P < 0.05) mRNA expression of Cyp19a1, Star, Aqp1, and Aqp7 in both the secondary and early antral stage while Fshr was only affected in the former compared to the non-cultured control. Pre-incubating follicles in 350 mOsm medium for 24 h enhanced (P < 0.05) Star and Aqp7 while decreasing (P < 0.05) Aqp1 expression compared to the control in secondary follicles, but not in the early antral stage. In summary, short-term hypertonic exposure promoted cat follicle development in vitro (including the meiotic competence of the enclosed oocyte) possibly through a mechanism that does not involve water transport genes.

Toward precision medicine for preserving fertility in cancer patients: existing and emerging fertility preservation options for women

As the number of young cancer survivors increases, quality of life after cancer treatment is becoming an ever more important consideration. According to a report from the American Cancer Society, approximately 810,170 women were diagnosed with cancer in 2015 in the United States. Among female cancer survivors, 1 in 250 are of reproductive age. Anticancer therapies can result in infertility or sterility and can have long-term negative effects on bone health, cardiovascular health as a result of reproductive endocrine function. Fertility preservation has been identified by many young patients diagnosed with cancer as second only to survival in terms of importance. The development of fertility preservation technologies aims to help patients diagnosed with cancer to preserve or protect their fertility prior to exposure to chemo- or radiation therapy, thus improving their chances of having a family and enhancing their quality of life as a cancer survivor. Currently, sperm, egg, and embryo banking are standard of care for preserving fertility for reproductive-age cancer patients; ovarian tissue cryopreservation is still considered experimental. Adoption and surrogate may also need to be considered. All patients should receive information about the fertility risks associated with their cancer treatment and the fertility preservation options available in a timely manner, whether or not they decide to ultimately pursue fertility preservation. Because of the ever expanding number of options for treating cancer and preserving fertility, there is now an opportunity to take a precision medicine approach to informing patients about the fertility risks associated with their cancer treatment and the fertility preservation options that are available to them.

Efficient biomaterials for tissue engineering of female reproductive organs

Current investigations on the bioengineering of female reproductive tissues have created new hopes for the women suffering from reproductive organ failure including congenital anomaly of the female reproductive tract or serious injuries. There are many surgically restore forms that constitute congenital anomaly, however, to date, there is no treatment except surgical treatment of transplantation for patients who are suffering from anomaly or dysfunction organs like vagina and uterus. Restoring and maintaining the normal function of ovary and uterus require the establishment of biological substitutes that can cover the roles of structural support for cells and passage of secreting molecules. As in the case of constructing other functional organs, reproductive organ manufacturing also needs biological matrices which can provide an appropriate condition for attachment, growth, proliferation and signaling of various kinds of grafted cells. Among the organs, uterus needs special features such as plasticity due to their amazing changes in volume when they are in the state of pregnancy. Although numerous natural and synthetic biomaterials are still at the experimental stage, some biomaterials have already been evaluated their efficacy for the reconstruction of female reproductive tissues. In this review, all the biomaterials cited in recent literature that have ever been used and that have a potential for the tissue engineering of female reproductive organs were reviewed, especially focused on bioengineered ovary and uterus.

Fibrin-alginate hydrogel supports steroidogenesis, in vitro maturation of oocytes and parthenotes production from caprine preantral follicles cultured in group

This study aimed to establish a culture system that improves the in vitro development of caprine preantral follicles. In a first experiment, follicles were encapsulated as a single unit per bead and cultured singly or in groups or with five follicles in the same alginate (ALG) bead for 18 days. In a subsequent experiment, the "five follicles per bead" design was chosen to culture in ALG, fibrin-alginate (FA) or hyaluronate (HA) for 18 days. In a third experiment, we chose the five follicles per bead in FA to culture for 30 days. The culture set-up of five follicles per ALG bead increased antrum formation and follicle diameter compared to the other culture designs (p < .05). Moreover, under this condition, 44.44% of the oocytes from in vitro cultured preantral follicles reached meiotic resumption. A significant increase of follicle diameter occurred in attachment system and FA (p < .05), but the ALG condition reached the highest among all groups on day 18 (p < .05). Follicles encapsulated in matrix produced more estradiol and progesterone than attachment system (p < .05). The expression of MMP-9 mRNA was higher in FA than in other groups (p < .05) and similar to antral follicles from in vivo control (p > .05). Only FA group resulted in oocytes matured. After 30 days, oocytes from preantral follicles in vitro grown in FA developed to eight-cell parthenotes. In conclusion, a culture system using FA supported the development of caprine preantral follicles cultured in group and included in the same bead of hydrogel, improving the oocyte maturation and producing parthenotes.

Anti-Müllerian hormone is produced heterogeneously in primate preantral follicles and is a potential biomarker for follicle growth and oocyte maturation in vitro

PURPOSE

The main goals of this study were to investigate the expression of anti-Müllerian hormone (AMH) and its receptor (AMHR2) during follicular development in primates, and to evaluate the potential of AMH as a biomarker for follicle growth and oocyte maturation in vitro.

METHODS

The mRNA and protein expression of AMH and AMHR2 were determined using isolated follicles and ovarian sections from rhesus macaques (n = 4) by real-time PCR and immunohistochemistry, respectively. Isolated secondary follicles were cultured individually. Follicle growth and media AMH concentrations were assessed by ELISA. The mRNA expression profiles, obtained from RNA sequencing, of in vitro- and in vivo-developed antral follicles were compared. Secondary follicles from additional animals (n = 35) were cultured. Follicle growth, oocyte maturation, and media AMH concentrations were evaluated for forecasting follicular development in vitro by AMH levels.

RESULTS

AMH immunostaining was heterogeneous in the population of preantral follicles that were also stained for AMHR2. The mRNA expression profiles were comparable between in vivo- and in vitro-developed follicles. AMH levels produced by growing follicles were higher than those of nongrowing follicles in culture. With a cutoff value of 1.40 ng/ml, 85 % of nongrowing follicles could be identified while eliminating only 5 % of growing follicles. Growing follicles that generated metaphase II-stage oocytes secreted greater amounts of AMH than did those yielding immature germinal vesicle-stage oocytes.

CONCLUSIONS

AMH, co-expressed with AMHR2, was produced heterogeneously by preantral follicles in macaques with levels correlated positively with follicle growth and oocyte maturation. AMH may serve as a biomarker for primate follicular development in vitro.

In vitro culture of ovarian follicles from Peromyscus

The ovarian follicle is the fundamental functional tissue unit of mammalian ovary. Each ovarian follicle contains one single oocyte. Isolation and in vitro culture of ovarian follicles to obtain fertilizable oocytes have been regarded as a promising strategy for women to combat infertility. The follicles from Peromyscus are considered as a better model than that from inbred mice for studying follicle culture. This is because Peromyscus mice are outbred (as with humans) with an increased life span. In this article, we reviewed studies on this subject conducted using Peromyscus follicles. These studies show that the conventional 2D micro-drop and 3D hanging-drop approaches established for in vitro culture of early preantral follicles from inbred mice are not directly applicable for cultivating the follicles from Peromyscus. However, the efficiency could be significantly improved by culturing multiple early preantral follicles in one hanging drop of Peromyscus ovarian cell-conditioned medium. It is further revealed that the mechanical heterogeneity in the extracellular matrix of ovary is crucial for developing early preantral follicles to the antral stage and for the subsequent ovulation to release cumulus-oocyte complex. These findings may provide valuable guidance for furthering the technology of in vitro follicle culture to restore fertility in the clinic.

Where are oncofertility and fertility preservation treatments heading in 2016?

An improvement in the survival rates of cancer patients and recent advancements in assisted reproductive technologies have led to remarkable progress in oncofertility and fertility preservation treatments. Although there are several available or emerging approaches for fertility preservation, the limited evidence for each strategy is the greatest concern. In this review, we discuss the concerns on currently available options, and propose new approaches for fertility preservation that may be available in the future.

Growth and differentiation factor 9 promotes oocyte growth at the primary but not the early secondary stage in three-dimensional follicle culture

PURPOSE

Factors that differentially regulate oocyte and granulosa cell growth within the early preantral follicle and how these factors differ at each stage of follicle growth remain poorly understood. The aim of this study was to isolate and evaluate the effect of recombinant growth and differentiation factor 9 (GDF9) on oocyte and granulosa cell growth at the primary and early secondary stages of preantral follicle growth during in vitro culture.

METHODS

Primary stage follicles (diameters of 50-89 μm) and early secondary stage follicles (diameters of 90-120 μm) were isolated from immature mice, and individual, intact follicles were cultured in vitro in the presence and absence of recombinant GDF9. The effects of GDF9 on follicle growth were determined by the assessment of changes in the follicle volume during culture. The growth of the granulosa cell and oocyte compartments of the follicles was evaluated separately at each stage.

RESULTS

GDF9 significantly increased the growth of isolated follicles at both the primary and early secondary follicle stages. Independent evaluation of the granulosa cell and oocyte compartments revealed that, while GDF9 promoted granulosa cell growth at both stages of folliculogenesis, oocyte growth was stage specific. GDF9 promoted growth of the oocyte at the primary, but not the early secondary, follicle stage.

CONCLUSIONS

These findings demonstrate a stage-specific role for GDF9 in the regulation of oocyte and granulosa cell growth at the primary and early secondary stages of preantral follicle development.

Impact of insulin concentration and mode of FSH addition on the in vitro survival and development of isolated bovine preantral follicles

The insulin and FSH are two important substances in the folliculogenesis process. Thus, the hypothesis of this experiment is that insulin concentration and the form of FSH addition affect the in vitro survival, growth, and estradiol production after culture of isolated bovine preantral follicles. The effects of insulin concentration (experiment 1) and the influence of both fixed and sequential concentrations of FSH (experiment 2) on the in vitro survival and development of bovine preantral follicles were investigated in this study by IVC for 18 days. In experiment 1, on Day 18 of culture, the addition of insulin at all concentrations promoted follicular survival rates significantly higher than that of the control, with the 10-ng/mL insulin treatment showing values significantly higher than the other treatments. The addition of 5- and 10-ng/mL insulin promoted higher follicular growth than the control and other treatments. In experiment 2, FSH 100 had a higher percentage of follicular viability compared with the control. FSH 100 produced follicle diameters significantly higher than those of the control and FSH seq.

TREATMENT

Estradiol levels in the presence of FSH (fixed concentration) were significantly higher than the other treatments. In conclusion, the association of insulin (10 ng/mL) and fixed concentration FSH (100 ng/mL) provides high rates of survival, growth, and estradiol production in bovine preantral follicles.

The effect of FSH and activin A on Akt and MAPK1/3 phosphorylation in cultured bovine ovarian cortical strips

Background

rhFSH and rhActA have been used in mammalian ovarian follicle culture systems for activation of follicular growth in vitro and suggested to be responsible for primordial follicle survival through MAPK and Akt pathways. The aim of our study was to determine the effects of rhFSH and rhActA on Akt, pAkt, MAPK1/3 and pMAPK1/3 protein levels in bovine ovarian cortical strips cultured in vitro.

Methods

Ovarian cortical strips from heifers were cultured in the presence of rhFSH (50 ng/mL), rhActA (100 ng/mL) or combination of these factors for 6 days. The strips were embedded in paraffin for histological observations and homogenized for western blot to determine Akt, pAkt, MAPK1/3 and pMAPK1/3 protein levels after the culture. Determination of primordial, primary and secondary follicle proportions at the end of culture as well as comparison of healthy follicle for each developmental stage after the culture was performed to quantify follicle survival and activation.

Results

pAkt protein levels were significantly lower in rhFSH + rhActA group among the other groups, whereas pMAPK1/3 levels were not significantly changed. Follicular activation and survival was measured to be significantly lower in rhFSH + rhActA group. Percentage of healthy primordial follicles was higher in control group whereas healthy secondary follicle proportion was higher in both rhActA and rhFSH groups. rhActA alone had a better impact on follicular activation, since the percentage of the secondary follicles was significantly higher than other treatment groups.

Conclusions

The use of rhActA and rhFSH alone or in the combined form results in differential levels of Akt and MAPK proteins. Both rhActA and rhFSH alone has a remarkable contribution in survival and activation of the follicles in accordance with higher levels of these proteins. Thus, the manipulation of Akt and MAPK pathways with appropriate activators might contribute to proper activation and development of ovarian follicles in vitro.

Human single follicle growth in vitro from cryopreserved ovarian tissue after slow freezing or vitrification

STUDY QUESTION

What is the effect of human ovarian tissue cryopreservation on single follicular development in vitro?

SUMMARY ANSWER

Vitrification had a greater negative effect on growth and gene expression of human ovarian follicles when compared with fresh follicles.

WHAT IS KNOWN ALREADY

For human ovarian cortex cryopreservation, the conventional option is slow freezing while more recently vitrification has been demonstrated to maintain good quality and function of ovarian tissues.

STUDY DESIGN, SIZE, DURATION

Ovarian tissues were collected from 11 patients. For every patient, the ovarian cortex was divided into three samples: Fresh, slow-rate freezing (Slow) and vitrification (Vit). Tissue histology was performed and follicles were isolated for single-cell mRNA analysis and in vitro culture (IVC) in 1% alginate for 8 days.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Follicle morphology was assessed with hematoxylin-eosin analysis. Follicles were individually embedded in alginate (1% w/v) and cultured in vitro for 8 days. Follicle survival and growth were assessed by microscopy. Follicle viability was observed after Calcein-AM and ethidium homodimer-I (Ca-AM/EthD-I) staining. Expression of genes, including GDF9 (growth differentiation factor 9), BMP15 (bone morphogenetic protein 15) and ZP3 (zona pellucida glycoprotein 3) in oocytes and AMH (anti-Mullerian hormone), FSHR (FSH receptor), CYP11A (cholesterol side-chain cleavage cytochrome P450) and STAR (steroidogenic acute regulatory protein) in GCs, was evaluated by single-cell mRNA analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 129 follicles were separated from ovarian cortex (Fresh n = 44; Slow n = 40; Vit n = 45). The percentage of damaged oocytes and granulosa cells was significantly higher in both the Slow and Vit groups, as compared with Fresh control (P< 0.05). The growth of follicles in vitro was significantly delayed in the Vit group compared with the Fresh group (P< 0.05). Both slow freezing (P< 0.05) and vitrification (P< 0.05) down-regulated the mRNA levels of ZP3 and CYP11A compared with Fresh group, while there was no significant difference between the Slow and Vit groups (P> 0.05). Vitrification also down-regulates AMH mRNA levels compared with Fresh group (P< 0.05).

LIMITATIONS, REASONS FOR CAUTION

Only short-term IVC studies (8 days) are reported. Further study should be performed to examine and improve follicular development in a long-term culture system after cryopreservation.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first comparison of gene expression and growth of single human ovarian follicles in vitro after either slow freezing or vitrification. With the decreased gene expression and growth during IVC, damage by cryopreservation still exists and needs to be minimized during the long-term IVC of follicles in the future for eventual clinical application.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by the National Natural Science Foundation of China (31230047, 81571386, 81471508, 31429004 and 81501247), National Natural Science Foundation of Beijing (7142166) and Mega-projects of Science Research for the 12th five-year plan (2012ba132b05). There are no conflicts of interest to declare.

Three dimensional in vitro culture of preantral follicles following slow-freezing and vitrification of mouse ovarian tissue

To evaluate the effects slow-freezing and vitrification on three dimensional in vitro culture of preantral follicles, ovaries of 12-14 days old female NMRI mice were isolated and randomly assigned to fresh control, slow-freezing and vitrification groups. Slow-freezing was performed using programmable freezer. Vitrification was carried out in a medium consisting of ethylene glycol (EG) and dimethyl sulphoxide (Me2SO) by needle immersion method. middle sized preantral follicles were mechanically isolated and cultured for 12 days in 0.7% sodium alginate gel. The follicles development and quantitative expression of oocyte specific genes (Bmp15, Gdf9, Fgf8) and the growth related genes (Igf1, Kit, Kit-l) were assessed after 1, 8 and 12 days of culture. Both cryopreserved groups showed reduction of follicular survival rates compared to the control group on days 8 and 12 of culture (P < 0.05). Antrum formation rates reduced in slow-freezing after 12 days of culture (P < 0.05). Evaluation of gene expression showed reduction of Bmp15, Gdf9, Fgf8, Kit and Kit-l during 12 days of culture (P < 0.05). Kit and Kit-l expression in slow-freezing group significantly reduced on day 8 of culture (p < 0.05). Igf1 expression was lower in slow-freezing group on 1st day of culture than vitrification and control groups (P < 0.05). Finally, intergroup comparison showed same expression pattern of genes after 12 days of culture. Thus, cryopreservation of mouse ovaries by both methods can preserve most developmental parameters and expression of maturation genes. However, vitrification is a better method for cryopreservation of mouse ovaries due to greater antrum formation and expression of growth related markers.

Oncofertility: a grand collaboration between reproductive medicine and oncology

In 2007, I was asked by the University of Calgary to participate in a symposium called 'Pushing the Boundaries--Advances that Will Change the World in 20 Years'. My topic was oncofertility, a word I had just coined to describe the intersection of two disciplines--oncology and fertility--and I was thrilled to share my passion for this new field and help young women with cancer protect their future reproductive health. Fertility preservation in the cancer setting lacked a concerted effort to bridge the disciplines in an organized manner. In early 2015, I was delighted to deliver a presentation for the Society for Reproduction and Fertility titled 'Sex in Three Cities', where I gave an update on the oncofertility movement, a remarkable cross-disciplinary, global collaboration created to address the fertility preservation needs of young cancer patients. During my tour of the UK, I was impressed by the interest among the society and its members to engage colleagues outside the discipline as well as the public in a dialogue about cutting-edge reproductive science. In this invited review, I will describe the work of the Oncofertility Consortium to provide fertility preservation options in the cancer setting and accelerate the acceptance of this critical topic on a global scale. I hope that one day this word and field it created will change the world for women who had been left out of the equation for far too long.

Size-specific follicle selection improves mouse oocyte reproductive outcomes

Encapsulated in vitro follicle growth (eIVFG) has great potential to provide an additional fertility preservation option for young women and girls with cancer or other reproductive health threatening diseases. Currently, follicles are cultured for a defined period of time and analyzed as a cohort. However, follicle growth is not synchronous, and culturing follicles for insufficient or excessive times can result in compromised gamete quality. Our objective is to determine whether the selection of follicles based on size, rather than absolute culture time, better predict follicle maturity and oocyte quality. Multilayer secondary mouse follicles were isolated and encapsulated in 0.25% alginate. Follicles were cultured individually either for defined time periods or up to specific follicle diameter ranges, at which point several reproductive endpoints were analyzed. The metaphase II (MII) percentage after oocyte maturation on day 6 was the highest (85%) when follicles were cultured for specific days. However, if follicles were cultured to a terminal diameter of 300-350 μm irrespective of absolute time in culture, 93% of the oocytes reached MII. More than 90% of MII oocytes matured from follicles with diameters of 300-350 μm showed normal spindle morphology and chromosome alignment, 85% of oocytes showed two pronuclei after IVF, 81% developed into the two-cell embryo stage and 38% developed to the blastocyst stage, all significantly higher than the percentages in the other follicle size groups. Our study demonstrates that size-specific follicle selection can be used as a non-invasive marker to identify high-quality oocytes and improve reproductive outcomes during eIVFG.

In vitro development of preimplantation porcine embryos using alginate hydrogels as a three-dimensional extracellular matrix

Between Days 10 and 12 of gestation, porcine embryos undergo a dramatic morphological change, known as elongation, with a corresponding increase in oestrogen production that triggers maternal recognition of pregnancy. Elongation deficiencies contribute to embryonic loss, but exact mechanisms of elongation are poorly understood due to the lack of an effective in vitro culture system. Our objective was to use alginate hydrogels as three-dimensional scaffolds that can mechanically support the in vitro development of preimplantation porcine embryos. White cross-bred gilts were bred at oestrus (Day 0) to Duroc boars and embryos were recovered on Days 9, 10 or 11 of gestation. Spherical embryos were randomly assigned to be encapsulated within double-layered 0.7% alginate beads or remain as non-encapsulated controls (ENC and CONT treatment groups, respectively) and were cultured for 96h. Every 24h, half the medium was replaced with fresh medium and an image of each embryo was recorded. At the termination of culture, embryo images were used to assess morphological changes and cell survival. 17β-Oestradiol levels were measured in the removed media by radioimmunoassay. Real-time polymerase chain reaction was used to analyse steroidogenic transcript expression at 96h in ENC and CONT embryos, as well as in vivo-developed control embryos (i.e. spherical, ovoid and tubular). Although no differences in cell survival were observed, 32% (P<0.001) of the surviving ENC embryos underwent morphological changes characterised by tubal formation with subsequent flattening, whereas none of the CONT embryos exhibited morphological changes. Expression of steroidogenic transcripts STAR, CYP11A1 and CYP19A1 was greater (P<0.07) in ENC embryos with morphological changes (ENC+) compared with CONT embryos and ENC embryos with no morphological changes (ENC-), and was more similar to expression of later-stage in vivo-developed controls. Furthermore, a time-dependent increase (P<0.001) in 17β-oestradiol was observed in culture media from ENC+ compared with ENC- and CONT embryos. These results illustrate that preimplantation pig embryos encapsulated in alginate hydrogels can undergo morphological changes with increased expression of steroidogenic transcripts and oestrogen production, consistent with in vivo-developed embryos. This alginate culture system can serve as a tool for evaluating specific mechanisms of embryo elongation that could be targeted to improve pregnancy outcomes.

Hypoxia limits mouse follicle growth in vitro

Ovarian follicle culture is useful for elucidation of factors involved in the regulation of follicular function. We examined the effects of gas phase oxygen concentration, an oil overlay, serum type and medium supplementation with FSH, insulin-transferrin-selenium (ITS) and l-ascorbic acid on cultured preantral mouse follicle growth in a spherical, non-attached follicle culture system. Follicle growth in 5% oxygen was significantly (P < 0.01) inferior to growth in 20% oxygen in terms of follicle diameter. This was likely due to hypoxia, as evidenced by significantly (P < 0.05) increased follicle secretion of vascular endothelial growth factor (VEGF), a marker of cell hypoxia. Follicular growth was not (P > 0.05) affected by an oil overlay, ITS supplementation or serum type. Culture in medium with 5% mouse serum, 1 IU mL-1 FSH, 25 μg mL-1 l-ascorbic acid and 20% oxygen without an oil overlay supported the growth of follicles to a maximum diameter of 380 μm in 6 days. Compared with mature preovulatory mouse follicles in vivo that often have diameters >500 μm within the same time frame, in vitro-grown follicles clearly exhibit limited growth. Thus, adequate oxygenation is an essential factor in the process of optimising follicle growth.

Mesenchymal Stem Cells Facilitate In Vitro Development of Human Preantral Follicle

Biological folliculogenesis is a lengthy and complicated process, and follicle growth microenvironment is poorly understood. Mesenchymal stem cells (MSCs) have been shown to establish a supportive microenvironment for wound repair, autoimmune diseases amelioration, and tumor development. Therefore, this study is aimed to investigate whether MSCs could help to reconstruct a microenvironment to facilitate the in vitro follicle development. Here we show human MSCs significantly promote the survival rates, increase the growth velocity, and improve the viability of preantral follicles in a dose-dependent manner. Further analyses reveal that growth differentiation factor 9 and bone morphogenetic protein 15 in oocytes and inhibin βA and transforming growth factor β1 in granulose cells within the follicles cocultured with MSCs express notably higher than those in the follicles cultured without MSCs. In summary, our findings demonstrate a previously unrecognized function of MSCs in promoting preantral follicle development and provide a useful strategy to optimize fertility preservation and restoration by facilitating in vitro follicle growth.

Engineering the ovarian cycle using in vitro follicle culture

STUDY QUESTION

Can cultured follicles model the ovarian cycle, including follicular- and luteal-phase hormone synthesis patterns and ovulation?

SUMMARY ANSWER

Under gonadotrophin stimulation, murine follicles grown in an encapsulated three-dimensional system ovulate in vitro and murine and human follicle hormone synthesis mimics follicular and luteal phases expected in vivo.

WHAT IS KNOWN ALREADY

Studies of the human ovary and follicle function are limited by the availability of human tissue and lack of in vitro models. We developed an encapsulated in vitro follicle growth (eIVFG) culture system, which preserves 3D follicular structure. Thus far, the alginate system has supported the culture of follicles from mice, dog, rhesus macaque, baboon and human. These studies have shown that cultured follicles synthesize steroid hormones similar to those observed during the follicular phase in vivo.

STUDY DESIGN, SIZE, DURATION

Cultured murine follicles were treated with human chorionic gonadotrophin (hCG) and epidermal growth factor (EGF) and either assayed for luteinization or removed from alginate beads and assayed for ovulation. Human follicles were also cultured, treated with follicle-stimulating hormone (FSH), hCG and EGF to mimic gonadotrophin changes throughout the ovarian cycle, and culture medium was assayed for hormone production.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Murine and human follicles were cultured in alginate hydrogel and hormone production [17β-estradiol, progesterone, inhibin A, inhibin B, activin A and anti-Müllerian hormone (AMH)] was quantified in medium by enzyme-linked immuno assay (ELISA). Human ovarian tissue was acquired from females between 6 and 34 years of age with a cancer diagnosis. These participants were undergoing ovarian tissue cryopreservation at National Physicians Cooperative sites as part of the Oncofertility Consortium.

MAIN RESULTS AND THE ROLE OF CHANCE

When grown in this system, 96% of mouse follicles ovulated in response to hCG and released meiotically competent eggs. Ovulated follicles recapitulated transcriptional, morphologic and hormone synthesis patterns post-luteinizing hormone (LH/hCG). In addition to rodent follicles, individual human follicles secreted steroid and peptide hormones that mimicked the patterns of serum hormones observed during the menstrual cycle.

LIMITATIONS, REASONS FOR CAUTION

This was a descriptive study of an in vitro model of ovulation and the ovarian hormone cycle. The ovulation studies were limited to murine tissue and further studies are needed to optimize conditions using other species.

WIDER IMPLICATIONS OF THE FINDINGS

The eIVFG system reliably phenocopies the in vivo ovarian cycle and provides a new tool to study human follicle biology and the influence of cycling female hormones on other tissue systems in vitro.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by NIH U54 HD041857, NIH U54 HD076188, NIH UH2 E5022920, NIH UH3 TR001207 and F30 AG040916 (R.M.S.). The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH. The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript.

Expression of the beta-2 adrenergic receptor (ADRB-2) in human and monkey ovarian follicles: a marker of growing follicles?

Background

ADRB-2 was implicated in rodent ovarian functions, including initial follicular growth. In contrast, ADRB-2 expression and function in nonhuman primate and human ovary were not fully known but innervation and significant levels of norepinephrine (NE), which is a ligand at the ADRB-2, were reported in the ovary.

Methods

We studied expression of ADRB-2 in human and rhesus monkey ovary (RT-PCR, immunohistochemistry; laser micro dissection) and measured levels of norepinephrine (NE; ELISA) in monkey follicular fluid (FF). 3D cultures of monkey follicles (4 animals) were exposed to NE or the ADRB-2 agonist isoproterenol (ISO), and follicular development (size) was monitored. Upon termination expression of ADRB-2, FSH receptor and aromatase genes were examined.

Results

Immunohistochemistry and RT-PCR of either human follicular granulosa cells (GCs) obtained by laser micro dissection or isolated monkey follicles revealed ADRB-2 in GCs of primordial, primary, secondary and tertiary follicles. Staining of GCs in primordial and primary follicles was intense. In large preantral and antral follicles the staining was heterogeneous, with positive and negative GCs present but GCs lining the antrum of large follicles were generally strongly immunopositive. Theca, interstitial, and ovarian surface epithelial cells were also positive. NE was detected in FF of preovulatory antral monkey follicles (0.37 + 0.05 ng/ml; n = 7; ELISA) but not in serum. We examined preantral follicles ranging from 152 to 366 μm in diameter in a 3D culture in media supplemented with follicle stimulating hormone (FSH). Under these conditions, neither NE, nor ISO, influenced growth rate in a period lasting up to one month. Upon termination of the cultures, all surviving follicles expressed aromatase and FSH receptors, but only about half of them also co-expressed ADRB-2. The ADRB-2 expression was not correlated with the treatment but was positively correlated with the follicular size at the beginning and at the end of the culture period. Hence, expression of ADRB-2 was found in the largest and fastest-in vitro growing follicles.

Conclusions

The results imply ADRB-2-mediated actions in the development of primate follicles. Drugs interfering with ADRB-2 are used to treat medical conditions and may have unexplored effects in the human ovary.

Exposure of female macaques to Western-style diet with or without chronic T in vivo alters secondary follicle function during encapsulated 3-dimensional culture

Increased adiposity and hyperandrogenemia alter reproductive parameters in both animal models and women, but their effects on preantral follicles in the ovary remain unknown. We recently reported that Western-style diet (WSD) consumption over 1 year, with or without chronic exposure to elevated circulating T, increased the body fat percentage, elicited insulin resistance, suppressed estradiol and progesterone production, as well as altered the numbers, size, and dynamics of antral follicles in the ovary during the menstrual cycle in female macaques. Therefore, experiments were designed to compare the WSD and WSD+T effects to age-matched controls on the survival, growth, and function of isolated secondary follicles during 5 weeks of encapsulated 3-dimensional culture. Follicle survival significantly declined in the WSD and WSD+T groups compared with the control (CTRL) group. Although media progesterone levels were comparable among groups, androstenedione and estradiol levels were markedly reduced in the WSD and WSD+T groups compared with the CTRL group at week 5. Anti-Müllerian hormone levels peaked at week 3 and were lower in the WSD+T group compared with the WSD or CTRL group. Vascular endothelial growth factor levels also decreased at week 5 in the WSD+T group compared with the WSD or CTRL group. After human chorionic gonadotropin exposure, only antral follicles developed from the CTRL group yielded metaphase II oocytes. Thus, WSD with or without T exposure affects the cohort of secondary follicles in vivo, suppressing their subsequent survival, production of steroid hormones and local factors, as well as oocyte maturation in vitro.

Use of an organotypic mammalian in vitro follicle growth assay to facilitate female reproductive toxicity screening

Screening of pharmaceutical, chemical and environmental compounds for their effects on reproductive health relies on in vivo studies. More robust and efficient methods to assess these effects are needed. Herein we adapted and validated an organotypic in vitro follicle growth (IVFG) assay to determine the impact of compounds on markers of ovarian function. We isolated mammalian follicles and cultured them in the presence of compounds with: (1) known fertotoxicity (i.e. toxicity to the reproductive system; cyclophosphamide and cisplatin); (2) no known fertotoxicity (nalbuphine); and (3) unknown fertotoxicity (Corexit EC 9500 A; CE, Nalco, Chicago, IL, USA). For each compound, we assayed follicle growth, hormone production and the ability of follicle-enclosed oocytes to resume meiosis and produce a mature egg. Cyclophosphamide and cisplatin caused dose-dependent disruption of follicle dynamics, whereas nalbuphine did not. The reproductive toxicity of CE, an oil dispersant used heavily during the 2010 Deepwater Horizon oil spill, has never been examined in a mammalian system. In the present study, CE compromised follicle morphology and functional parameters. Our findings demonstrate that this IVFG assay system can be used to distinguish fertotoxic from non-toxic compounds, providing an in vitro tool to assess the effects of chemical compounds on reproductive function and health.

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.

Direct actions of androgens on the survival, growth and secretion of steroids and anti-Müllerian hormone by individual macaque follicles during three-dimensional culture

STUDY QUESTION

What are the direct effects of androgens on primate follicular development and function at specific stages of folliculogenesis?

SUMMARY ANSWER

Androgen addition altered primate follicle survival, growth, steroid and anti-Müllerian hormone (AMH) production, and oocyte quality in vitro, in a dose- and stage-dependent manner.

WHAT IS KNOWN ALREADY

Androgens have local actions in the ovary, particularly in the developing follicles. It is hypothesized that androgen promotes early follicular growth, but becomes detrimental to the antral follicles in primates.

STUDY DESIGN, SIZE, DURATION

In vitro follicle maturation was performed using rhesus macaques. Secondary (125-225 µm) follicles were mechanically isolated from 14 pairs of ovaries, encapsulated into alginate (0.25% w/v), and cultured for 40 days.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Individual follicles were cultured in a 5% O2 environment, in alpha minimum essential medium supplemented with recombinant human FSH. Follicles were randomly assigned to experiments of steroid ablation by trilostane (TRL), testosterone (T) replacement and dihydrotestosterone (DHT) replacement. Follicle survival and growth were assessed. Follicles with diameters ≥500 μm at Week 5 were categorized as fast-grow follicles. Pregnenolone (P5), progesterone (P4), estradiol (E2) and AMH concentrations in media were measured. Meiotic maturation and fertilization of oocytes from recombinant human chorionic gonadotrophin-treated follicles were assessed at the end of culture.

MAIN RESULTS AND THE ROLE OF CHANCE

Compared with controls, TRL exposure reduced (P < 0.05) follicle survival, antrum formation rate and follicle diameters at Week 5. While P5 concentrations increased (P < 0.05) following TRL treatment, P4 levels decreased (P < 0.05) in fast-grow follicles at Week 5. Few healthy oocytes were retrieved from antral follicles developed in the presence of TRL. T replacement with TRL increased (P < 0.05) follicle survival and antrum formation at Week 5, compared with TRL alone, to levels comparable to controls. However, high-dose T with TRL decreased (P < 0.05) diameters of fast-grow follicles. Although P4 concentrations produced by fast-grow follicles were not altered by T in the presence of TRL, there was a dose-dependent increase (P < 0.05) in E2 levels at Week 5. High-dose T with TRL decreased (P < 0.05) AMH production by fast-grow follicles at Week 3. More healthy oocytes were retrieved from antral follicles developed in TRL+T compared with TRL alone. DHT had the similar effects to those of high-dose T, except that DHT replacement decreased (P < 0.05) E2 concentrations produced by fast-grow follicles at Week 5 regardless of TRL treatment.

LIMITATION, REASONS FOR CAUTION

This study reports T and DHT actions on in vitro-developed individual primate (macaque) follicles, which are limited to the interval from the secondary to small antral stage.

WIDER IMPLICATION OF THE FINDINGS

The above findings provide novel information on the role(s) of androgens in primate follicular development and oocyte maturation. We hypothesize that androgens promote pre-antral follicle development, but inhibit antral follicle growth and function in primates. While androgens can act positively, excess levels of androgens may have negative impacts on primate folliculogenesis.

STUDY FUNDING/COMPETING INTERESTS

NIH U54 RR024347/RL1HD058294/PL1EB008542 (Oncofertility Consortium), NIH U54 HD071836 (SCCPIR), NIH ORWH/NICHD 2K12HD043488 (BIRCWH), NIH FIC TW/HD-00668, ONPRC 8P51OD011092. There are no conflicts of interest.

Three-dimensional systems for in vitro follicular culture: overview of alginate-based matrices

The in vitro culture of ovarian follicles has provided critical insight into the biology of the follicle and its enclosed oocyte and the physical interaction and communication between the theca and granulosa cells and the oocyte that is necessary to produce meiotically competent oocytes. Various two-dimensional (2D) and three-dimensional (3D) culture systems have been developed to evaluate the effect of growth factors, hormones, extracellular matrix components and culture conditions on follicle development and oocyte growth and maturation. Among these culture systems, 3D systems make it possible to maintain follicle structure and support communication between the various cell compartments within the follicle. In this review article, we will discuss the three main approaches to ovarian follicle culture: 2D attachment systems, 3D floating systems and 3D encapsulated systems. We will specifically emphasise the development of and advances in alginate-based encapsulated systems for in vitro follicle culture.

Alginate encapsulation supports the growth and differentiation of human primordial follicles within ovarian cortical tissue

PURPOSE

In vitro follicle growth (IVFG) is an investigational fertility preservation technique in which immature follicles are grown in culture to produce mature eggs that can ultimately be fertilized. Although progress has been made in growing primate primary and secondary follicles in vitro, it has been a relatively greater challenge to isolate and culture primordial follicles. The purpose of this study was to develop methods to grow human primordial follicles in vitro using alginate hydrogels.

METHODS

We obtained human ovarian tissue for research purposes through the National Physicians Cooperative from nationwide sites and used it to test two methods for culturing primordial follicles. First, primordial follicles were isolated from the ovarian cortex and encapsulated in alginate hydrogels. Second, 1 mm × 1 mm pieces of 500 μm-thick human ovarian cortex containing primordial follicles were encapsulated in alginate hydrogels, and survival and follicle development within the tissue was assessed for up to 6 weeks.

RESULTS

We found that human ovarian tissue could be kept at 4 °C for up to 24 h while still maintaining follicle viability. Primordial follicles isolated from ovarian tissue did not survive culture. However, encapsulation and culture of ovarian cortical pieces supported the survival, differentiation, and growth of primordial and primary follicles. Within several weeks of culture, many of the ovarian tissue pieces had formed a defined surface epithelium and contained growing preantral and antral follicles.

CONCLUSIONS

The early stages of in vitro human follicle development require the support of the native ovarian cortex.

Characterization of freshly retrieved preantral follicles using a low-invasive, mechanical isolation method extended to different ruminant species

Due to the increased interest in preantral follicular physiology, non-invasive retrieval and morphological classification are crucial. Therefore, this study aimed: (1) to standardize a minimally invasive isolation protocol, applicable to three ruminant species; (2) to morphologically classify preantral follicles upon retrieval; and (3) to describe morphological features of freshly retrieved follicles compared with follicle characteristics using invasive methods. Bovine, caprine and ovine ovarian cortex strips were retrieved from slaughterhouse ovaries and dispersed. This suspension was filtered, centrifuged, re-suspended and transferred to a Petri dish, to which 0.025 mg/ml neutral red (NR) was added to assess the viability of the isolated follicles. Between 59 and 191 follicles per follicle class and per species were collected and classified by light microscopy, based on follicular cell morphology. Subsequently, follicle diameters were measured. The proposed isolation protocol was applicable to all three species and showed a significant, expected increase in diameter with developmental stage. With an average diameter of 37 ± 5 μm for primordial follicles, 47 ± 6.3 μm for primary follicles and 67.1 ± 13.1 μm for secondary follicles, no significant difference in diameter among the three species was observed. Bovine, caprine and ovine follicles (63, 59 and 50% respectively) were graded as viable upon retrieval. Using the same morphological characteristics as determined by invasive techniques [e.g. haematoxylin–eosin (HE) sections], cumulus cell morphology and follicle diameter could be used routinely to classify freshly retrieved follicles. Finally, we applied a mechanical, minimally invasive, follicle isolation protocol and extended it to three ruminant species, yielding viable preantral follicles without compromising further in vitro processing and allowing routine follicle characterization upon retrieval.

Bioengineering the ovarian follicle microenvironment

Chemo- and radiation therapies used to treat cancer can have the unintended effect of making patients infertile. Clinically established fertility preservation methods, such as egg and embryo cryopreservation, are not applicable to all patients, which has motivated the development of strategies that involve ovarian tissue removal and cryopreservation before the first sterilizing treatment. To restore fertility at a later date, the early-stage follicles present in the tissue must be matured to produce functional oocytes, a process that is not possible using existing cell culture technologies. This review describes the application of tissue engineering principles to promote ovarian follicle maturation and produce mature oocytes through either in vitro culture or transplantation. The design principles for these engineered systems are presented, along with identification of emerging opportunities in reproductive biology.

Alginate hydrogel matrix stiffness influences the in vitro development of caprine preantral follicles

This study examined caprine follicular development in different concentrations of alginate matrix to determine the optimal conditions for culture. Caprine preantral follicles were cultured in a two-dimensional system (control) or a three-dimensional encapsulated system in 0.25%, 0.5%, or 1% alginate (ALG 0.25, ALG 0.5, and ALG 1, respectively). A higher percentage of morphologically normal follicles developed in ALG 0.5 and ALG 1 than in ALG 0.25 or the control (P < 0.05). The rate of antrum formation, however, was higher in ALG 0.25 than in ALG 0.5 and ALG 1 conditions (P < 0.05), but similar to the control. Follicles cultured in ALG 0.25 had higher growth rates and meiotic resumption than those cultured in ALG 0.5, ALG 1, or the control (P < 0.05). Moreover, follicles cultured in ALG 0.25 had higher levels of estradiol and progesterone than those cultured in ALG 0.5, ALG 1, or the control, as well as higher levels of CYP19A1 and HSD3B mRNA. In conclusion, a three-dimensional system that uses ALG 0.25 fosters the in vitro development of caprine preantral follicles and increases the rate of meiotic resumption.

Hypoxia-mediated carbohydrate metabolism and transport promote early-stage murine follicle growth and survival

Oxygen tension is critical for follicle growth and metabolism, especially for early-stage follicles, where vascularity is limited. Its role and underlying mechanism in the in vitro activation and maturation of immature to ovulatory follicles is largely unknown. In this study, early secondary (110 μm) murine follicles were isolated and encapsulated in alginate hydrogels to replicate the in vivo environment of the growing/maturing follicle. Encapsulated follicles were cultured for 8 days at either 2.5 or 20% O2. Survival (2.6-fold) and growth (1.2-fold) were significantly higher for follicles cultured at 2.5% compared with 20% O2. Using a mouse hypoxia-signaling pathway qRT-PCR array and GeneGo Metacore analysis, we found that direct target genes of the hypoxia-activated HIF1-complex were significantly upregulated in follicles cultured for 8 days at 2.5% compared with 20% O2, including the carbohydrate transport and metabolism genes Slc2a3, Vegfa, Slc2a1, Edn1, Pgk1, Ldha, and Hmox1. Other upregulated genes included carbohydrate transporters (Slc2a1, Slc2a3, and Slc16a3) and enzymes essential for glycolysis (Pgk1, Hmox1, Hk2, Gpi1, Pfkl, Pfkp, Aldoa, Gapdh, Pgam1, Eno1, Pkm2, and Ldha). For follicles cultured at 2.5% O2, a 7.2-fold upregulation of Vegfa correlated to an 18-fold increase in VEGFA levels, and a 3.2-fold upregulation of Ldha correlated to a 4.8-fold increase in lactate levels. Both VEGFA and lactate levels were significantly higher in follicles cultured at 2.5% compared with 20% O2. Therefore, enhanced hypoxia-mediated glycolysis is essential for growth and survival of early secondary follicles and provides vital insights into improving in vitro culture conditions.

In vitro development of secondary follicles from pre-pubertal and adult goats cultured in two-dimensional or three-dimensional systems

The aim of this study was to evaluate the influence of two-dimensional (2D) and three-dimensional (3D) alginate culture systems on in vitro development of pre-antral caprine follicles. In addition, the influence of the reproductive age of the ovary donor on the in vitro culture success was investigated. Pre-antral follicles from pre-pubertal or adult goats were isolated and cultured directly on a plastic surface (2D) or encapsulated in an alginate-based matrix (3D). After 18 days, the oocytes underwent in vitro maturation (IVM) and in vitro fertilization (IVF) to produce embryos. The 3D system showed higher rates of follicle survival, lower rates of oocyte extrusion, and a greater number of recovered oocytes for IVM and IVF (P < 0.05). Only pre-antral follicles from adult animals produced MII oocytes and embryos. The estradiol concentrations increased from day 2 to day 12 of culture in all groups tested (P < 0.05). Conversely, progesterone concentrations were lower in 3D-cultured follicles than in 2D-cultured follicles, with differences on days 2 and 6 of culture (P < 0.05). We provide compelling evidence that a 2D or 3D alginate in vitro culture system offers a promising approach to achieving full in vitro development of caprine pre-antral follicles to produce mature oocytes that are capable of fertilization and viable embryos.

Wnt/β-catenin signaling regulates follicular development by modulating the expression of Foxo3a signaling components

Wnt signaling is an evolutionarily conserved pathway that regulates cell proliferation, differentiation and apoptosis. To investigate the possible role of Wnt signaling in the regulation of ovarian follicular development, secondary follicles were isolated and cultured in vitro in the presence or absence of its activator (LiCl or Wnt3a) or inhibitor (IWR-1). We have demonstrated that activation of β-catenin signals by activators dramatically suppressed follicular development by increasing granulosa cell apoptosis and inhibiting follicle steroidogenesis. In contrast, inhibition of Wnt signaling by IWR-1 was observed with better developed follicles and increased steroidogenesis. Further studies have shown that the transcription factor Forkhead box O3a (Foxo3a) and its downstream target molecules were modulated by the activators or the inhibitor. These findings provide evidence that Wnt signaling might negatively regulate follicular development potentially through Foxo3a signaling components.

High insulin concentrations promote the in vitro growth and viability of canine preantral follicles

To determine whether the effects of different concentrations of insulin on the development of canine preantral follicles in vitro were associated or not with FSH, secondary follicles were isolated and cultured. In Experiment 1, follicles were cultured in the following media: modified minimum essential medium (CtrlMEM) alone; CtrlMEM plus 5 ng mL⁻¹ insulin (Ins5ng); CtrlMEM plus 10 ng mL⁻¹ insulin (Ins10ng); and CtrlMEM plus 10 μg mL⁻¹ insulin. In Experiment 2, follicles were cultured in the same media but in the presence of sequential FSH (i.e. CtrlFSH, Ins5ngF, Ins10ngF and 10μgF, respectively). Increasing concentrations of FSH (100, 500 and 1000 ng mL⁻¹) were added sequentially to the culture medium on Days 0, 6 and 12 of culture. Viability were assessed at the end of culture and follicular diameter and the antrum formation rate at four time points (Days 0, 6, 12 and 18). In Experiment 1, the high insulin concentration significantly increased follicular viability (P<0.05). In contrast, in Experiment 2, viability was not affected by the inclusion of insulin. In addition, viability was significantly better in follicles cultured in CtrlFSH (P<0.05). The diameter of follicles in the high-insulin group in Experiment 1 and high-insulin plus FSH group in Experiment 2 was superior to other groups tested. In experiment 2, the Ins10μg and Ins10μgF groups exhibited significantly higher antrum formation rates than the other groups. In conclusion, in the absence of FSH, high concentrations of insulin have beneficial effects on follicular viability. However, to promote the growth of canine preantral follicles in vitro, it is recommended that a combination of insulin and FSH be added to the medium.

Promoting extracellular matrix remodeling via ascorbic acid enhances the survival of primary ovarian follicles encapsulated in alginate hydrogels

The in vitro growth of ovarian follicles is an emerging technology for fertility preservation. Various strategies support the culture of secondary and multilayer follicles from various species including mice, non-human primate, and human; however, the culture of early stage (primary and primordial) follicles, which are more abundant in the ovary and survive cryopreservation, has been limited. Hydrogel-encapsulating follicle culture systems that employed feeder cells, such as mouse embryonic fibroblasts (MEFs), stimulated the growth of primary follicles (70-80 µm); yet, survival was low and smaller follicles (<70 µm) rapidly lost structure and degenerated. These morphologic changes were associated with a breakdown of the follicular basement membrane; hence, this study investigated ascorbic acid based on its role in extracellular matrix (ECM) deposition/remodeling for other applications. The selection of ascorbic acid was further supported by a microarray analysis that suggested a decrease in mRNA levels of enzymes within the ascorbate pathway between primordial, primary, and secondary follicles. The supplementation of ascorbic acid (50 µg/mL) significantly enhanced the survival of primary follicles (<80 µm) cultured in alginate hydrogels, which coincided with improved structural integrity. Follicles developed antral cavities and increased to diameters exceeding 250 µm. Consistent with improved structural integrity, the gene/protein expression of ECM and cell adhesion molecules was significantly changed. This research supports the notion that modifying the culture environment (medium components) can substantially enhance the survival and growth of early stage follicles.

Basic fibroblast growth factor promotes the development of human ovarian early follicles during growth in vitro

STUDY QUESTION

What is the effect of basic fibroblast growth factor (bFGF) on the growth of individual early human follicles in a three-dimensional (3D) culture system in vitro?

SUMMARY ANSWER

The addition of 200 ng bFGF/ml improves human early follicle growth, survival and viability during growth in vitro.

WHAT IS KNOWN ALREADY

It has been demonstrated that bFGF enhances primordial follicle development in human ovarian tissue culture. However, the growth and survival of individual early follicles in encapsulated 3D culture have not been reported.

STUDY DESIGN, SIZE, DURATION

The maturation in vitro of human ovarian follicles was investigated. Ovarian tissue (n= 11) was obtained from 11 women during laparoscopic surgery for gynecological disease, after obtaining written informed consent. One hundred and fifty-four early follicles were isolated by enzymic digestion and mechanical disruption. They were individually encapsulated into alginate (1% w/v) and randomly assigned to be cultured with 0, 100, 200 or 300 ng bFGF/ml for 8 days.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Individual follicles were cultured in minimum essential medium α (αMEM) supplemented with bFGF. Follicle survival and growth were assessed by microscopy. Follicle viability was evaluated under confocal laser scanning microscope following Calcein-AM and Ethidium homodimer-I (Ca-AM/EthD-I) staining.

MAIN RESULTS AND THE ROLE OF CHANCE

After 8 days in culture, all 154 follicles had increased in size. The diameter and survival rate of the follicles and the percentage with good viability were significantly higher in the group cultured with 200 ng bFGF/ml than in the group without bFGF (P < 0.05). The percentage of follicles in the pre-antral stage was significantly higher in the 200 ng bFGF/ml group than in the group without bFGF (P < 0.05), while the percentages of primordial and primary follicles were significantly lower (P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

The study focuses on the effect of bFGF on the development of individual human early follicles in 3D culture in vitro and has limited ability to reveal the specific effect of bFGF at each different stage. The findings highlight the need to improve the acquisition and isolation of human ovarian follicles.

WIDER IMPLICATIONS OF THE FINDINGS

The in vitro 3D culture of human follicles with appropriate dosage of bFGF offers an effective method to investigate their development. Moreover, it allows early follicles to be cultured to an advanced stage and therefore has the potential to become an important source of mature oocytes for assisted reproductive technology; particularly as an option for fertility preservation in women, including patients with cancer.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Basic Research Program of China (2011|CB944504, 2011CB944503) and the National Natural Science Foundation of China (81200470, 81000275, 31230047, 8110197). There are no conflicts of interest to declare.

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The female reproductive tract produces hormones for reproductive function and cardiovascular, bone and sexual health; the tract supplies a finite number of gametes, and it supports fetal development. Diseases that affect each of the female reproductive tract organs, along with treatments that have direct, deleterious effects on the reproductive tract (for example, chemotherapeutics), are understudied due to the lack of model systems that phenocopy in vivo function. This review describes a path toward developing female reproductive tract mimics. The models use isolated primary support cells cultured onto a biological scaffold and within a microfluidic system to create a niche and support the desired differentiation of epithelia, germ and somatic cells from patient-derived induced pluripotent stem cells. Improving our fund of knowledge about reproductive tract biology and creating reproductive organs for patients who have lost gonadal, uterine or vaginal/ cervical function is a major step forward in women's health and an important advancement in personalized medicine.