Engineering the ovarian cycle using in vitro follicle culture

A more natural follicle culture system: Detailed steps of In Vitro 3D follicle culture with alginate gel

Follicle culture is a process of dividing follicle unit structures from ovaries for continued culture in vitro in an incubator, which simulates the in vivo environment. Alginate gel is the most stable and most convenient 3D material currently used in follicle culture. We performed in vitro follicle culture following the standard operating procedure recommended by the Follicle Handbook and we have summarized our experience and skills in details. Through several experiments, we found only follicles tightly surrounded by theca cells can grow healthily until the preovulatory stage. In addition, the hardness of alginate gel is crucial for constructing the 3D culture system, and selecting appropriate tools can reduce damage to the alginate gel and shorten the time follicles are exposed to room temperature. Our detailed operation improves bioavailability and provides a more natural environment for the entire process of follicular growth.•Alginate gel is still the most suitable 3D material used for in vitro follicle culture.•Follicle integrity and the hardness of alginate gel are the keys for in vitro culture.•Detailed operation steps better protect the follicular microenvironment and improve bioavailability.

Transcriptome profiling reveals superovulation with the gonadotropin-releasing hormone agonist trigger impaired embryo implantation in mice

Introduction

Superovulation is a critical step in assisted reproductive technology, but the use of human chorionic gonadotropin (hCG) as a trigger for superovulation can result in ovarian hyperstimulation. Thus, the use of Gonadotropin-releasing hormone agonist (GnRHa) trigger has been increasingly adopted, although it has been associated with a higher rate of pregnancy failure compared to natural cycles. This study aimed to investigate the effect of GnRHa trigger on embryo implantation in a mouse model.

Methods

Mice in the superovulation (PG) group were administered 7.5 IU of PMSG, followed by the injection of 3.5 μg of GnRHa (Leuprorelin) 48 h later, while mice in the control group (CTR) mated naturally. We compared the number of oocytes, blastocysts, and corpus luteum between the two groups and the implantation sites after the transfer of natural blastocysts. Ovaries, uterus, and serum 2 and 4 days after mating were collected for qRT-PCR, transcriptome sequencing, and hormone assays.

Results

The PG group had more oocytes, blastocysts, and corpus luteum after superovulation than the CTR group. However, the mRNA expression of leukemia inhibitory factor (Lif) and the number of implantation sites were reduced in the PG group. The ELISA assay revealed that superovulation increased ovarian estrogen secretion. The transcriptome analysis showed that superphysiological estrogen led to a response of the uterus to a high estrogen signal, resulting in abnormal endometrium and extracellular matrix remodeling and up-regulation of ion transport and inflammation-related genes.

Conclusion

Our findings suggest that a combination of PMSG and GnRHa trigger impaired embryo implantation in mice, as the excessive uterine response to superphysiological estrogen levels can lead to the change of gene expression related to endometrial remodeling, abnormal expression of uterine ion transport genes and excessive immune-related genes.

Neurotrophin-4 promotes in vitro development and maturation of human secondary follicles yielding metaphase II oocytes and successful blastocyst formation

STUDY QUESTION

Does a matrix-free culture system supplemented with neurotrophic factor 4 (NT4) improve human in vitro follicular development and meiotic maturation, ultimately resulting in fertilizable oocytes?

SUMMARY ANSWER

NT4 supplementation of in vitro culture significantly enhances the growth, steroid hormone production, and maturity potential of human secondary follicles derived from fresh ovarian medulla (from post- and pre-pubertal patients), thereby yielding fertilizable oocytes.

WHAT IS KNOWN ALREADY

Reconstituting folliculogenesis in vitro is of paramount importance in the realms of fertility preservation, reproductive biology research, and reproductive toxicity assessments. However, the efficiency of in vitro culture systems remains suboptimal, as the attainment of fertilizable oocytes from in vitro growth (IVG) of human follicles remains unachieved, with the data being particularly scant regarding follicles from prepubertal girls. We have previously found that mouse oocytes from secondary follicles derived from IVG are deficient in neuroendocrine regulation. NT4 and its corresponding receptor have been identified in human follicles. Significantly, the addition of NT4 during the IVG process markedly enhances both follicle growth and oocyte maturation rates in mice.

STUDY DESIGN SIZE DURATION

Fresh medulla tissue obtained during tissue preparation for ovarian tissue cryopreservation (OTC) were collected from 10 patients aged from 6 to 21 years old, all of whom had undergone unilateral oophorectomy as a means of fertility preservation. Isolated secondary follicles were individually cultured in vitro with or without NT4 in a matrix-free system.

PARTICIPANTS/MATERIALS SETTING METHODS

Secondary follicles, extracted via enzymatic digestion and mechanical disruption from each patient, were randomly allocated to either a control group or an NT4-supplemented group (100 ng/ml), followed by individual culture on an ultra-low attachment plate. Follicle growth and viability were assessed by microscopy. Levels of anti-Müllerian hormone (AMH), estradiol, and progesterone in the medium were quantified. An oocyte-specific marker was identified using confocal fluorescence microscopy following DEAD box polypeptide 4 (DDX4) staining. The competence of individual oocytes for maturation and fertilization were assessed after IVM and ICSI with donated sperm samples.

MAIN RESULTS AND THE ROLE OF CHANCE

Overall, isolated follicles from both groups survived up to 6 weeks with increasing diameters over the duration (P < 0.05), reaching terminal diameters of almost 1 mm with confirmed steroidogenesis and expression of oocyte marker (DDX4), and producing morphologically normal MII oocytes. When compared with the control group, the NT4 group had a similar initial follicular diameter (206 ± 61.3 vs 184 ± 93.4 μm) but exhibited a significant increase in follicular diameter from the ninth day of culture onwards (P < 0.05). From Week 3, estradiol and progesterone production were significantly increased in the NT4 group, while no significant difference was observed in AMH production between groups. The proportion of 'fast-growth' follicles in the NT4 group was significantly higher than that in the control group (13/23 vs 6/24, P < 0.05). An increased efficiency of MII oocyte maturation per live follicle in the NT4 group was also observed (control group vs NT4 group, 4/24 vs 10/23, P < 0.05). It is noteworthy that an MII oocyte obtained from the control group exhibited abnormal fertilization after ICSI. In contrast, an MII oocyte acquired from the NT4 group progressed to the blastocyst stage and showed potential for transfer.

LARGE SCALE DATA

N/A.

LIMITATIONS REASONS FOR CAUTION

The cohort examined in this study was all patients diagnosed with beta-thalassemia major. Whether this culture system is effective for patients with other diseases remains unknown. Since the chosen dose of NT4 was established based on dose finding in mice, the optimal dose for use in a human IVG system needs further confirmation. The oocytes and embryos procured from this study have not been quantified for ploidy status or epigenetic signatures.

WIDER IMPLICATIONS OF THE FINDINGS

Fresh medulla tissue obtained during tissue preparation for OTC may serve as a precious source of fertilizable oocytes for female fertility preservation, even for pre-pubertal girls, without the threat of tumour reintroduction. After further characterization and optimization of the system, this culture system holds the potential to provide a powerful future research tool, for the comprehensive exploration of human follicular development mechanisms and for conducting reproductive toxicity evaluations.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by the National Key R&D Program of China (grant number 2022YFC2703000) and National Natural Science Foundation of China (grant numbers 82271651 and 81871214). The medium used in human follicle in vitro culture in this study has been applied for a national invention patent in China (No. 202211330660.7). The inventors of the patent, in order, are: Y.G., C.F., and X.L.

Thiol-yne click crosslink hyaluronic acid/chitosan hydrogel for three-dimensional in vitro follicle development

There is a great deal of potential for in vitro follicle growth to provide an alternative approach to fertility preservation. This strategy reduces the possibility of cancer cells re-exposure after transplantation, and it does not require hormone stimulation. Adopting a three-dimensional (3D) culture method helps preserve the architecture of the follicle and promotes the maturity of oocytes. In order to maintain follicle morphology, enhance the quality of mature oocytes, and facilitate meiotic spindle assembly, the current work aimed to develop the 3D in vitro preantral mouse follicle culture method. Thiolated chitosan-co-thiolated hyaluronic (CSHS) hydrogel was designed to evaluate the effects of biomaterials on ovarian follicle development. Isolated follicles from mouse ovaries were randomly divided into alginate (Alg) as a 3D control, thiolated hyaluronic acid (HASH), and CSHS groups. Single follicle was encapsulated in each hydrogel, and performed for 10 days and subsequently ovulated to retrieve mature oocytes on day 11. CSHS hydrogel promoted follicle survival and oocyte viability with maintained spherical morphology of follicle. Matured oocytes with normal appearance of meiotic spindle and chromosome alignment were higher in the CSHS group compared with those in the Alg and HASH groups. Furthermore, CSHS increased expression level of folliculogenesis genes (TGFβ-1, GDF-9) and endocrine-related genes (LHCGR, and FSHR). With various experimental setups and clinical applications, this platform could be applied as an alternative method to in vitro follicle culture with different experimental designs and clinical applications in the long-term period.

Oocyte quality is enhanced by hypoglycosylated FSH through increased cell-to-cell interaction during mouse follicle development

Macroheterogeneity in follicle-stimulating hormone (FSH) β-subunit N-glycosylation results in distinct FSH glycoforms. Hypoglycosylated FSH21 is the abundant and more bioactive form in pituitaries of females under 35 years of age, whereas fully glycosylated FSH24 is less bioactive and increases with age. To investigate whether the shift in FSH glycoform abundance contributes to the age-dependent decline in oocyte quality, the direct effects of FSH glycoforms on folliculogenesis and oocyte quality were determined using an encapsulated in vitro mouse follicle growth system. Long-term culture (10-12 days) with FSH21 (10 ng/ml) enhanced follicle growth, estradiol secretion and oocyte quality compared with FSH24 (10 ng/ml) treatment. FSH21 enhanced establishment of transzonal projections, gap junctions and cell-to-cell communication within 24 h in culture. Transient inhibition of FSH21-mediated bidirectional communication abrogated the positive effects of FSH21 on follicle growth, estradiol secretion and oocyte quality. Our data indicate that FSH21 promotes folliculogenesis and oocyte quality in vitro by increasing cell-to-cell communication early in folliculogenesis, and that the shift in in vivo abundance from FSH21 to FSH24 with reproductive aging may contribute to the age-dependent decline in oocyte quality.

The chromatin remodeling protein BPTF mediates cell cycle, proliferation and apoptosis in porcine ovarian granulosa cells

Bromodomain PHD finger transcription factor (BPTF), a core subunit of nucleosome-remodeling factor (NURF) complex, plays an important role in chromatin remodeling. However, few information of BPTF is available in pig, especially in mammalian follicular granulosa cells (GCs). The present study firstly confirmed that BPTF in porcine was relative close to human and mouse. The expression of BPTF could be detected in ovary, testes, lung, kidney, large intestine, and small intestine. And a relative high expression of BPTF was observed in ovarian follicles and GCs. When BPTF was knocked down (BPTF-siRNA), the viability of GCs was affected. And the expression level of CDK1, cyclin B1, CDK4 and CDK2 was higher than the control, which might indicate that the cell cycle of GCs was inhibited from S to G2/M phase. Although the apoptosis level was induced in the BPTF-siRNA GCs, the reduced level of H3K4 methylation was detected with the down regulation of SMYD3, EHMT2 and DPY30. Thereby, results in the present might provide the primary knowledge of BPTF in GCs and the follicular development in pig.

Common mechanisms of physiological and pathological rupture events in biology: novel insights into mammalian ovulation and beyond

Ovulation is a cyclical biological rupture event fundamental to fertilisation and endocrine function. During this process, the somatic support cells that surround the germ cell undergo a remodelling process that culminates in breakdown of the follicle wall and release of a mature egg. Ovulation is driven by known proteolytic and inflammatory pathways as well as structural alterations to the follicle vasculature and the fluid-filled antral cavity. Ovulation is one of several types of systematic remodelling that occur in the human body that can be described as rupture. Although ovulation is a physiological form of rupture, other types of rupture occur in the human body which can be pathological, physiological, or both. In this review, we use intracranial aneurysms and chorioamniotic membrane rupture as examples of rupture events that are pathological or both pathological and physiological, respectively, and compare these to the rupture process central to ovulation. Specifically, we compared existing transcriptomic profiles, immune cell functions, vascular modifications, and biomechanical forces to identify common processes that are conserved between rupture events. In our transcriptomic analysis, we found 12 differentially expressed genes in common among two different ovulation data sets and one intracranial aneurysm data set. We also found three genes that were differentially expressed in common for both ovulation data sets and one chorioamniotic membrane rupture data set. Combining analysis of all three data sets identified two genes (Angptl4 and Pfkfb4) that were upregulated across rupture systems. Some of the identified genes, such as Rgs2, Adam8, and Lox, have been characterised in multiple rupture contexts, including ovulation. Others, such as Glul, Baz1a, and Ddx3x, have not yet been characterised in the context of ovulation and warrant further investigation as potential novel regulators. We also identified overlapping functions of mast cells, macrophages, and T cells in the process of rupture. Each of these rupture systems share local vasoconstriction around the rupture site, smooth muscle contractions away from the site of rupture, and fluid shear forces that initially increase and then decrease to predispose one specific region to rupture. Experimental techniques developed to study these structural and biomechanical changes that underlie rupture, such as patient-derived microfluidic models and spatiotemporal transcriptomic analyses, have not yet been comprehensively translated to the study of ovulation. Review of the existing knowledge, transcriptomic data, and experimental techniques from studies of rupture in other biological systems yields a better understanding of the physiology of ovulation and identifies avenues for novel studies of ovulation with techniques and targets from the study of vascular biology and parturition.

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

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

Bioengineered 3D Ovarian Models as Paramount Technology for Female Health Management and Reproduction

Ovarian dysfunction poses significant threats to the health of female individuals. Ovarian failure can lead to infertility due to the lack or inefficient production of fertilizable eggs. In addition, the ovary produces hormones, such as estrogen and progesterone, that play crucial roles not only during pregnancy, but also in maintaining cardiovascular, bone, and cognitive health. Decline in estrogen and progesterone production due to ovarian dysfunction can result in menopausal-associated syndromes and lead to conditions, such as osteoporosis, cardiovascular disease, and Alzheimer's disease. Recent advances in the design of bioengineered three-dimensional (3D) ovarian models, such as ovarian organoids or artificial ovaries, have made it possible to mimic aspects of the cellular heterogeneity and functional characteristics of the ovary in vitro. These novel technologies are emerging as valuable tools for studying ovarian physiology and pathology and may provide alternatives for fertility preservation. Moreover, they may have the potential to restore aspects of ovarian function, improving the quality of life of the (aging) female population. This review focuses on the state of the art of 3D ovarian platforms, including the latest advances modeling female reproduction, female physiology, ovarian cancer, and drug screening.

Current progress on in vitro differentiation of ovarian follicles from pluripotent stem cells

Mammalian female reproduction requires a functional ovary. Competence of the ovary is determined by the quality of its basic unit-ovarian follicles. A normal follicle consists of an oocyte enclosed within ovarian follicular cells. In humans and mice, the ovarian follicles are formed at the foetal and the early neonatal stage respectively, and their renewal at the adult stage is controversial. Extensive research emerges recently to produce ovarian follicles in-vitro from different species. Previous reports demonstrated the differentiation of mouse and human pluripotent stem cells into germline cells, termed primordial germ cell-like cells (PGCLCs). The germ cell-specific gene expressions and epigenetic features including global DNA demethylation and histone modifications of the pluripotent stem cells-derived PGCLCs were extensively characterized. The PGCLCs hold potential for forming ovarian follicles or organoids upon cocultured with ovarian somatic cells. Intriguingly, the oocytes isolated from the organoids could be fertilized in-vitro. Based on the knowledge of in-vivo derived pre-granulosa cells, the generation of these cells from pluripotent stem cells termed foetal ovarian somatic cell-like cells was also reported recently. Despite successful in-vitro folliculogenesis from pluripotent stem cells, the efficiency remains low, mainly due to the lack of information on the interaction between PGCLCs and pre-granulosa cells. The establishment of in-vitro pluripotent stem cell-based models paves the way for understanding the critical signalling pathways and molecules during folliculogenesis. This article aims to review the developmental events during in-vivo follicular development and discuss the current progress of generation of PGCLCs, pre-granulosa and theca cells in-vitro.

Impact of antioxidant supplementation during in vitro culture of ovarian preantral follicles: A review

The in vitro culture systems of ovarian preantral follicles have been developed for studying follicular and oocyte growth, for future use of immature oocytes as sources of fertilizable oocytes and for screening ovarian toxic substances. One of the key limitations of the in vitro culture of preantral follicles is the oxidative stress by accumulation of reactive oxygen species (ROS), which can impair follicular development and oocyte quality. Several factors are associated with oxidative stress in vitro, which implies the need for a rigorous control of the conditions as well as addition of antioxidant agents to the culture medium. Antioxidant supplementation can minimize or eliminate the damage caused by ROS, supporting follicular survival and development and producing mature oocytes competent for fertilization. This review focuses on the use of antioxidants and their role in preventing follicular damage caused by oxidative stress in the in vitro culture of preantral follicles.

Advances of xenogeneic ovarian extracellular matrix hydrogels for in vitro follicle development and oocyte maturation

Research aimed at preserving female fertility is increasingly using bioengineering techniques to develop new platforms capable of supporting ovarian cell function in vitro and in vivo. Natural hydrogels (alginate, collagen, and fibrin) have been the most exploited approaches; however they are biologically inert and/or biochemically simple. Thus, establishing a suitable biomimetic hydrogel from decellularized ovarian cortex (OC) extracellular matrix (OvaECM) could provide a complex native biomaterial for follicle development and oocyte maturation. The objectives of this work were (i) to establish an optimal protocol to decellularize and solubilize bovine OC, (ii) to characterize the histological, molecular, ultrastructural, and proteomic properties of the resulting tissue and hydrogel, and (iii) to assess its biocompatibility and adequacy for murine in vitro follicle growth (IVFG). Sodium dodecyl sulfate was identified as the best detergent to develop bovine OvaECM hydrogels. Hydrogels added into standard media or used as plate coatings were employed for IVFG and oocyte maturation. Follicle growth, survival, hormone production, and oocyte maturation and developmental competence were evaluated. OvaECM hydrogel-supplemented media best supported follicle survival, expansion, and hormone production, while the coatings provided more mature and competent oocytes. Overall, the findings support the xenogeneic use of OvaECM hydrogels for future human female reproductive bioengineering.

Prospects for fertility preservation: the ovarian organ function reconstruction techniques for oogenesis, growth and maturation in vitro

Today, fertility preservation is receiving more attention than ever. Cryopreservation, which preserves ovarian tissue to preserve fertility in young women and reduce the risk of infertility, is currently the most widely practiced. Transplantation, however, is less feasible for women with blood-borne leukemia or cancers with a high risk of ovarian metastasis because of the risk of cancer recurrence. In addition to cryopreservation and re-implantation of embryos, in vitro ovarian organ reconstruction techniques have been considered as an alternative strategy for fertility preservation. In vitro culture of oocytes in vitro Culture, female germ cells induction from pluripotent stem cells (PSC) in vitro, artificial ovary construction, and ovaria-related organoids construction have provided new solutions for fertility preservation, which will therefore maximize the potential for all patients undergoing fertility preservation. In this review, we discussed and thought about the latest ovarian organ function reconstruction techniques in vitro to provide new ideas for future ovarian disease research and fertility preservation of patients with cancer and premature ovarian failure.

Current Trends on Bioengineering Approaches for Ovarian Microenvironment Reconstruction

Ovarian tissue has a unique microarchitecture and a complex cellular and molecular dynamics that are essential for follicular survival and development. Due to this great complexity, several factors may lead to ovarian insufficiency, and therefore to systemic metabolic disorders and female infertility. Techniques currently used in the reproductive clinic such as oocyte cryopreservation or even ovarian tissue transplant, although effective, have several limitations, which impair their wide application. In this scenario, mimetic ovarian tissue reconstruction comes as an innovative alternative to develop new methodologies for germ cells preservation and ovarian functions restoration. The ovarian extracellular matrix (ECM) is crucial for oocyte viability maintenance, once it acts actively in folliculogenesis. One of the key components of ovarian bioengineering is biomaterials application that mimics ECM and provides conditions for cell anchorage, proliferation, and differentiation. Therefore, this review aims at describing ovarian tissue engineering approaches and listing the main limitations of current methods for preservation and reestablishment of ovarian fertility. In addition, we describe the main elements that structure this study field, highlighting the main advances and the challenges to overcome to develop innovative methodologies to be applied in reproductive medicine. Impact Statement This review presents the main advances in the application of tissue bioengineering in the ovarian tissue reconstruction to develop innovative solutions for ovarian fertility reestablishment.

Determination of the appropriate concentration of sodium alginate used for in vitro culture of cat preantral follicles in a serum-free medium containing FSH, EGF and IGF-I

Culture of domestic cat preantral follicles can be a suitable technology to assist oocyte conservation strategies in the family Felidae. This research was aimed to comparatively analyse cat preantral follicular development of follicles directly seeded on growth surface or encapsulated in 0.5 or 1% of sodium alginate in a serum-free medium containing FSH, EGF and IGF-I. Preantral follicles were isolated from cat ovarian cortical tissue after ovariectomy. Alginate was dissolved at 0.5 or 1% in PBS. Follicles, 4 per well, with 0% (G-0%), 0.5% (G-0.5%) or 1% (G-1%) of sodium alginate were cultured in M199 with FSH (100 ng/mL), EGF (100 ng/mL) and IGF-I (100 ng/mL) for 7 days at 37°C, 5% CO₂ and 99% humidity. Culture medium was replaced every 48 h and samples were stored at -20°C until ELISA of steroid hormones. Morphometric evaluation of follicles was performed every 24 h. G-0% follicles showed granulosa cell migration away from the oocyte and disrupted morphology, whereby they reached apparently larger diameters (203.70 ± 5.82 μm; p < .05) than G-0.5% and G-1% follicles (157.89 ± 8.47 μm and 95.23 ± 1.67 μm, respectively) which maintained three-dimensional organization, being larger in G-0.5% than in G-1% (p < .05). G-0.5% follicles attained the multi-layer preantral follicle stage on day 7 of culture, whereas G-1% follicles underwent progressive atresia. On day 6, steroid concentrations were higher (p < .05) in G-0% than in G-1%: 60 ± 19 vs 0.88 ± 0.32 pg/mL oestradiol; 2.6 ± 0.84 vs 0.04 ± 0.02 ng/mL progesterone; 1.3 ± 0.22 vs 0.61 ± 0.04 ng/mL testosterone and 1.6 ± 0.54 vs 0.22 ± 0.07 ng/mL androstenedione respectively. Steroid concentrations in G-0.5% were comprised between those of G-0% and G-1% (p > .05). In conclusion, two-layer cat preantral follicles encapsulated in 0.5% alginate cultured in medium containing FSH, EGF and IGF-I can develop up to the multi-layer preantral stage in 7 days of culture, whereas follicles directly seeded on growth surface or encapsulated in 1% alginate lost their three-dimensional organization, and experienced regression with compromised steroidogenesis, respectively.

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

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

Recapitulating folliculogenesis and oogenesis outside the body: encapsulated in vitro follicle growth†

Folliculogenesis is a tightly coordinated process essential for generating a fertilization-competent gamete while also producing gonadal hormones that sustain endocrine function. In vitro follicle growth systems have been critical to our understanding of key events in folliculogenesis, such as gonadotropin-independent and dependent growth, steroid hormone production, and oocyte growth and maturation (cytoplasmic and meiotic). Although there are several successful follicle culture strategies, the following protocol details an encapsulated in vitro follicle growth (eIVFG) system for use with mouse ovarian follicles. Encapsulated IVFG is performed with alginate hydrogels, which are biologically inert, maintains cell-to-cell interactions between granulosa cells and the oocyte, and preserves follicle architecture as found in the ovary. The system supports follicle growth, development, and differentiation from the early primary follicle to the antral follicle stage. Moreover, post-folliculogenesis events including meiotic maturation, ovulation, and luteinization are also supported. Importantly, the culture of secondary follicles has successfully resulted in viable pups after blastocyst transfer. This alginate-based eIVFG system is versatile and has broad applications as a tool for interrogating the fundamental biology of the ovarian follicle in a controlled manner, a screening platform for toxicity and bioactivity, and a potential fertility preservation method for endangered species as well as humans.

Advanced bioengineering of female germ cells to preserve fertility

Oogenesis and folliculogenesis are considered as complex and species-specific cellular differentiation processes, which depend on the in vivo ovarian follicular environment and endocrine cues. Considerable efforts have been devoted to driving the differentiation of female primordial germ cells toward mature oocytes outside of the body. The recent experimental attempts have laid stress on offering a suitable microenvironment to assist the in vitro folliculogenesis and oogenesis. Despite developing a variety of bioengineering techniques and generating functional mature gametes through in vitro oogenesis in earlier studies, we still lack knowledge of appropriate microenvironment conditions for building biomimetic culture systems for female fertility preservation. Therefore, this review paper can provide a source for a large body of scientists developing cutting-edge in vitro culture systems for female germ cells or setting up the next generation of reproductive medicine as feasible options for female infertility treatment. The focal point of this review outlines advanced bioengineering technologies such as 3D biofabricated hydrogels/scaffolds and microfluidic systems utilized with female germlines for fertility preservation through in vitro folliculogenesis and oogenesis.

New hyaluronan-based biomatrix for 3-D follicle culture yields functionally competent oocytes

BACKGROUND

Encapsulation of follicles within a biomatrix is one approach to maintaining 3-D follicle architecture during culture. Hyaluronan is one component of the natural extracellular matrix (ECM) that provides support to cells in vivo. This report describes the application of a novel tyramine-linked hyaluronan for 3-D in vitro follicle culture and the production of developmentally competent metaphase II oocytes.

MATERIALS AND METHODS

Enzymatically isolated mouse preantral follicles or follicle clusters (FL-C) from fresh or vitrified ovaries were encapsulated in 3 mg/ml of hyaluronan gel (HA). Follicle growth, antrum formation and meiotic maturation to metaphase II oocytes was monitored. Chromatin staining was used to assess GV oocyte progression towards meiotic competence. Functional competence of in vitro matured (IVM) oocytes was evaluated by in vitro fertilization and ability to develop to blastocyst. Modifying the HA gel by inclusion of laminin (HA-LM), mouse sarcoma extracellular matrix (Matrigel;HA-MG) or placental extracellular matrix (HA-PM) was also tested to see if this might further enhance IVM outcomes.

RESULTS

A total of 402 preantral follicles were cultured in HA gel. After hCG trigger, 314 oocyte-cumulus complexes ovulated from the embedded follicles. Meiotic maturation rate to the metaphase II stage was 73% (228/314). After insemination 83% (188/228) of IVM oocytes fertilized with a subsequent blastulation rate of 46% (87/188). A pilot transfer study with 3 recipient mice resulted in the birth of a single pup. HA gel supported individually isolated follicles as well ovarian tissue fragments containing clusters of 6-8 preantral follicles. Meiotic maturation was lower with FL-clusters from vitrified versus fresh ovaries (34% and 55%, respectively; p < 0.007). Modification of the HA gel with ECMs or laminin affected antrum formation and follicle retention. Maturation rates to the metaphase II stage were however not significantly different: 74% for HA gel alone as compared to HA-LM (67%), HA-MG (56%) and HA-PM (58%).

CONCLUSION

Hyaluronan gel is an effective and versatile extracellular matrix based biomaterial for 3-D culture of ovarian follicles. This culture model allowed ovulation of functionally competent metaphase II oocytes, capable of fertilization, genomic activation and blastulation. Future testing with human follicles that require longer in vitro culture times should be considered.

Follicle isolation methods reveal plasticity of granulosa cell steroidogenic capacity during mouse in vitro follicle growth

Follicles are the functional unit of the ovary and several methods have been developed to grow follicles ex vivo, which recapitulate key events of oogenesis and folliculogenesis. Enzymatic digestion protocols are often used to increase the yield of follicles from the ovary. However, the impact of these protocols on the outermost theca and granulosa cells, and thereby follicle function, is not well defined. To investigate the impact of enzymatic digestion on follicle function, we collected preantral follicles from CD1 mice either by enzymatic digestion (Enzy-FL) or mechanical isolation (Mech-FL) and compared follicle growth, steroidogenesis and cell differentiation within an encapsulated in vitro follicle growth system which maintains the 3D architecture of the oocyte and its surrounding somatic cells. Follicles were encapsulated in 0.5% alginate and cultured for 8 days. Compared with Enzy-FL, Mech-FL grew more rapidly and produced significantly higher levels of androstenedione, estradiol and progesterone. The expression of theca-interstitial cell marker genes, Cyp17a1, which encodes 17-hydroxylase/17, 20-lyase and catalyzes the hydroxylation of pregnenolone and progesterone to 17-hydroxypregnenolone and 17-hydroxyprogesterone, and the conversion of these products into dehydroepiandrosterone and androstenedione, and Star, which encodes a transport protein essential for cholesterol entry into mitochondria, were also higher in Mech-FL than in Enzy-FL. Mech-FL maintained an intact theca-interstitial layer on the outer edge of the follicle that phenocopied in vivo patterns as confirmed by alkaline phosphatase staining, whereas theca-interstitial cells were absent from Enzy-FL from the onset of culture. Therefore, preservation of the theca cell layer at the onset of culture better supports follicle growth and function. Interestingly, granulosa cells in the outermost layers of Enzy-FL expressed CYP17A1 by Day 4 of culture while maintaining inhibin α-subunit expression and a cuboidal nucleus. Thus, in the absence of theca-interstitial cells, granulosa cells have the potential to differentiate into androgen-producing cells. This work may have implications for human follicle culture, where enzymatic isolation is required owing to the density of the ovarian cortex.

UC-MSCs promote frozen-thawed ovaries angiogenesis via activation of the Wnt/β-catenin pathway in vitro ovarian culture system

Background

Ovarian tissue cryopreservation and transplantation are novel therapeutic approaches for fertility preservation. However, follicle loss caused by ischemic and hypoxic damage is one of the issues after frozen-thawed ovarian tissue transplantation. Promoting angiogenesis in grafts is the key to restore cryopreserved ovarian function. Mesenchymal stem cells (MSCs) have been reported to facilitate angiogenesis in the cryopreserved ovarian tissue transplantation. However, the risk of embolization, immunogenic effect and tumorigenesis hinders the clinical application of MSCs to human organ transplantation. In this study, we established an in vitro ovarian culture system to restore frozen-thawed ovarian function before transplantation with the application of umbilical cord mesenchymal stem cells (UC-MSCs), and explored the effects of UC-MSCs on frozen-thawed ovaries in vitro ovarian culture system and the mechanisms of UC-MSCs on the angiogenesis of frozen-thawed ovaries.

Methods

A simple in vitro three dimensional (3D) ovarian culture system using Matrigel was established to support to an ideal niche, and ovary was alone cultured in the 24-well plate as a control. We also evaluated the effects of UC-MSCs treatment on ovarian function with or without Matrigel support. All thawed ovaries were randomly divided into control group (Matrigel−/UC-MSCs−), Matrigel group (Matrigel+/UC-MSCs−), UC-MSCs group (Matrigel−/UC-MSCs+) and UC-MSCs + Matrigel group (Matrigel+/UC-MSCs+). HE staining was used to detect the histological structure of follicles and TUNEL staining was used to detect cell apoptosis. The number of microvessels was counted to evaluate neovascularization. The mRNA expression of VEGFA, IGF1 and ANGPT2 were detected by RT-PCR. Western blotting was used to measure the expression of GSK-3β, β-catenin and p-β-catenin.

Results

In the absence of UC-MSCs, 3D culture system supported by Matrigel showed significantly improved follicular development and microvascular number. Additionally, UC-MSCs were also found to effectively improve follicular development and microvascular number regardless of the culture condition used. However, alleviated follicular apoptosis, increased mRNA expression of angiogenesis-related gene and activated Wnt/β-catenin pathway occurred only in the UC-MSCs + Matrigel group. Besides, with the application of IWP-2 in UC-MSCs + Matrigel group, Wnt//β-catenin pathway could be blocked by IWP-2 serving as one of Wnt/β-catenin pathway inhibitors.

Conclusions

This in vitro study showed the beneficial effects of UC-MSCs on thawed ovaries and explored a potential mechanism inducing angiogenesis. In particular, 3D ovarian culture system supported by Matrigel further improved UC-MSCs treatment. The in vitro culture system using Matrigel and UC-MSCs may provide a potential treatment strategy for improving the success rate of thawed ovaries transplantation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02989-8.

An Ovarian Steroid Metabolomic Pathway Analysis in Basal and Polycystic Ovary Syndrome (PCOS)-like Gonadotropin Conditions Reveals a Hyperandrogenic Phenotype Measured by Mass Spectrometry

Prior work has demonstrated that murine ovarian explants and isolated ovarian follicles can recapitulate human-like 28-day cycles in vitro with normal patterns of estradiol and progesterone secretion in response to gonadotropin stimulation. The objective of this study was to manipulate the gonadotropin stimulation protocol to mimic polycystic ovary syndrome (PCOS) and assess the resulting changes in ovarian steroidogenesis. A secondary aim of the study was to develop a high-throughput, sensitive, and specific liquid chromatography with tandem mass spectrometry (LC-MS/MS) assay to measure seven steroid hormones (estrone, estradiol, progesterone, testosterone, androstenedione, dehydroepiandrosterone, and dihydrotestosterone) in conditioned culture media. Ovaries were harvested from 12-day-old CD-1 mice and cultured for 28 days, with ovulation induction on culture day 14. Media were supplemented human chorionic gonadotropin (hCG, a luteinizing hormone analog) and follicle stimulating hormone (FSH) at ratios of 1:0 (standard media), 1:1 (physiologic ratio), and 3:1 (PCOS-like ratio). Ovaries cultured in PCOS-like media displayed hyperandrogenism and impaired ovulation, two key features of a PCOS-like phenotype. Taken together, this first-of-its-kind presentation of hormone levels from single tissues creates a map of the enzymatic steps most acutely affected by gonadotropin dysregulation and may provide opportunities for assessing other potential insults in PCOS pathogenesis.

Effects of N-Acetyl-L-Cystein Antioxidant on Ex Vivo Culture of Vitrified Premature Mouse Ovarian Tissue

Optimization of practical ways to obtain mature follicles from cryopreserved ovarian tissues, especially in patients suffering from ovarian dysfunction, is very important. In vitro ovarian tissue culture allows faster screening of follicle development and reduces follicle isolation damage. During ovarian tissue culture, controlling oxidative stress is critical to support better follicular development and less damage. Immature Naval Medical Research Institute (NMRI) mouse ovaries (8-days-old) were randomly distributed into four cultured groups; non-vitrified, vitrified, non-vitrified N-acetyl-L-cysteine (NAC)⁺, and vitrified NAC⁺. Ovaries of vitrified groups along with non-vitrified ovaries were cultured on agar gel in the presence or absence of NAC for 5 days. Afterward, morphological evaluations, mRNA expressions of Gdf9, Bmp6, Lif, Amh, Bax, and Bcl2 genes, malondialdehyde, and total antioxidant capacities were compared between four groups at the first and last day of culture. Good preservation of tissue integrity and an increase of follicular development were observed in all groups. In addition, the expression of Gdf9, Lif, Bax, and Bcl2 genes were increased and Amh was decreased in groups cultured in the presence of NAC compared to groups cultured without NAC. Although total antioxidant capacity was not significantly different between the experimental groups, the lipid peroxidation and apoptotic index were significantly reduced in the presence of NAC. Thus, it appears that NAC antioxidant acts as a contributory factor for the ex vivo culture of ovarian tissue and reduces oxidative stress, apoptotic index, and improves follicular development, especially in non-vitrified groups.

Effects of Androgen Excess-Related Metabolic Disturbances on Granulosa Cell Function and Follicular Development

Polycystic ovary syndrome (PCOS) is a common reproductive endocrine disease in women of reproductive age. Ovarian dysfunction including abnormal steroid hormone synthesis and follicular arrest play a vital role in PCOS pathogenesis. Hyperandrogenemia is one of the important characteristics of PCOS. However, the mechanism of regulation and interaction between hyperandrogenism and ovulation abnormalities are not clear. To investigate androgen-related metabolic state in granulosa cells of PCOS patients, we identified the transcriptome characteristics of PCOS granulosa cells by RNA-seq. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of differentially expressed genes (DEGs) revealed that genes enriched in lipid metabolism pathway, fatty acid biosynthetic process and ovarian steroidogenesis pathway were abnormally expressed in PCOS granulosa cells in comparison with that in control. There are close interactions among these three pathways as identified by analysis of the protein-protein interaction (PPI) network of DEGs. Furthermore, in vitro mouse follicle culture system was established to explore the effect of high androgen and its related metabolic dysfunction on follicular growth and ovulation. RT-qPCR results showed that follicles cultured with dehydroepiandrosterone (DHEA) exhibited decreased expression levels of cumulus expansion-related genes (Has2, Ptx3, Tnfaip6 and Adamts1) and oocyte maturation-related genes (Gdf9 and Bmp15), which may be caused by impaired steroid hormone synthesis and lipid metabolism, thus inhibited follicular development and ovulation. Furthermore, the inhibition effect of DHEA on follicle development and ovulation was ameliorated by flutamide, an androgen receptor (AR) antagonist, suggesting the involvement of AR signaling. In summary, our study offers new insights into understanding the role of androgen excess induced granulosa cell metabolic disorder in ovarian dysfunction of PCOS patients.

OUP accepted manuscript

BACKGROUND

To provide the optimal milieu for implantation and fetal development, the female reproductive system must orchestrate uterine dynamics with the appropriate hormones produced by the ovaries. Mature oocytes may be fertilized in the fallopian tubes, and the resulting zygote is transported toward the uterus, where it can implant and continue developing. The cervix acts as a physical barrier to protect the fetus throughout pregnancy, and the vagina acts as a birth canal (involving uterine and cervix mechanisms) and facilitates copulation. Fertility can be compromised by pathologies that affect any of these organs or processes, and therefore, being able to accurately model them or restore their function is of paramount importance in applied and translational research. However, innate differences in human and animal model reproductive tracts, and the static nature of 2D cell/tissue culture techniques, necessitate continued research and development of dynamic and more complex in vitro platforms, ex vivo approaches and in vivo therapies to study and support reproductive biology. To meet this need, bioengineering is propelling the research on female reproduction into a new dimension through a wide range of potential applications and preclinical models, and the burgeoning number and variety of studies makes for a rapidly changing state of the field.

OBJECTIVE AND RATIONALE

This review aims to summarize the mounting evidence on bioengineering strategies, platforms and therapies currently available and under development in the context of female reproductive medicine, in order to further understand female reproductive biology and provide new options for fertility restoration. Specifically, techniques used in, or for, the uterus (endometrium and myometrium), ovary, fallopian tubes, cervix and vagina will be discussed.

SEARCH METHODS

A systematic search of full-text articles available in PubMed and Embase databases was conducted to identify relevant studies published between January 2000 and September 2021. The search terms included: bioengineering, reproduction, artificial, biomaterial, microfluidic, bioprinting, organoid, hydrogel, scaffold, uterus, endometrium, ovary, fallopian tubes, oviduct, cervix, vagina, endometriosis, adenomyosis, uterine fibroids, chlamydia, Asherman’s syndrome, intrauterine adhesions, uterine polyps, polycystic ovary syndrome and primary ovarian insufficiency. Additional studies were identified by manually searching the references of the selected articles and of complementary reviews. Eligibility criteria included original, rigorous and accessible peer-reviewed work, published in English, on female reproductive bioengineering techniques in preclinical (in vitro/in vivo/ex vivo) and/or clinical testing phases.

OUTCOMES

Out of the 10 390 records identified, 312 studies were included for systematic review. Owing to inconsistencies in the study measurements and designs, the findings were assessed qualitatively rather than by meta-analysis. Hydrogels and scaffolds were commonly applied in various bioengineering-related studies of the female reproductive tract. Emerging technologies, such as organoids and bioprinting, offered personalized diagnoses and alternative treatment options, respectively. Promising microfluidic systems combining various bioengineering approaches have also shown translational value.

WIDER IMPLICATIONS

The complexity of the molecular, endocrine and tissue-level interactions regulating female reproduction present challenges for bioengineering approaches to replace female reproductive organs. However, interdisciplinary work is providing valuable insight into the physicochemical properties necessary for reproductive biological processes to occur. Defining the landscape of reproductive bioengineering technologies currently available and under development for women can provide alternative models for toxicology/drug testing, ex vivo fertility options, clinical therapies and a basis for future organ regeneration studies.

Dynamic in vitro culture of cryopreserved-thawed human ovarian cortical tissue using a microfluidics platform does not improve early folliculogenesis

Current strategies for fertility preservation include the cryopreservation of embryos, mature oocytes or ovarian cortical tissue for autologous transplantation. However, not all patients that could benefit from fertility preservation can use the currently available technology. In this regard, obtaining functional mature oocytes from ovarian cortical tissue in vitro would represent a major breakthrough in fertility preservation as well as in human medically assisted reproduction. In this study, we have used a microfluidics platform to culture cryopreserved-thawed human cortical tissue for a period of 8 days and evaluated the effect of two different flow rates in follicular activation and growth. The results showed that this dynamic system supported follicular development up to the secondary stage within 8 days, albeit with low efficiency. Surprisingly, the stromal cells in the ovarian cortical tissue were highly sensitive to flow and showed high levels of apoptosis when cultured under high flow rate. Moreover, after 8 days in culture, the stromal compartment showed increase levels of collagen deposition, in particular in static culture. Although microfluidics dynamic platforms have great potential to simulate tissue-level physiology, this system still needs optimization to meet the requirements for an efficient in vitro early follicular growth.

Advancements in Microfluidic Systems for the Study of Female Reproductive Biology

The female reproductive tract is a highly complex physiological system that consists of the ovaries, fallopian tubes, uterus, cervix, and vagina. An enhanced understanding of the molecular, cellular, and genetic mechanisms of the tract will allow for the development of more effective assisted reproductive technologies, therapeutics, and screening strategies for female specific disorders. Traditional 2-dimensional and 3-dimensional static culture systems may not always reflect the cellular and physical contexts or physicochemical microenvironment necessary to understand the dynamic exchange that is crucial for the functioning of the reproductive system. Microfluidic systems present a unique opportunity to study the female reproductive tract, as these systems recapitulate the multicellular architecture, contacts between different tissues, and microenvironmental cues that largely influence cell structure, function, behavior, and growth. This review discusses examples, challenges, and benefits of using microfluidic systems to model ovaries, fallopian tubes, endometrium, and placenta. Additionally, this review also briefly discusses the use of these systems in studying the effects of endocrine disrupting chemicals and diseases such as ovarian cancer, preeclampsia, and polycystic ovarian syndrome.

Alpha/Beta Hydrolase Domain-Containing Protein 2 Regulates the Rhythm of Follicular Maturation and Estrous Stages of the Female Reproductive Cycle

Mammalian female fertility is defined by a successful and strictly periodic ovarian cycle, which is under the control of gonadotropins and steroid hormones, particularly progesterone and estrogen. The latter two are produced by the ovaries that are engaged in controlled follicular growth, maturation, and release of the eggs, i.e., ovulation. The steroid hormones regulate ovarian cycles via genomic signaling, by altering gene transcription and protein synthesis. However, despite this well-studied mechanism, steroid hormones can also signal via direct, non-genomic action, by binding to their membrane receptors. Here we show, that the recently discovered membrane progesterone receptor α/β hydrolase domain-containing protein 2 (ABHD2) is highly expressed in mammalian ovaries where the protein plays a novel regulatory role in follicle maturation and the sexual cycle of females. Ablation of Abhd2 caused a dysregulation of the estrous cycle rhythm with females showing shortened luteal stages while remaining in the estrus stage for a longer time. Interestingly, the ovaries of Abhd2 knockout (KO) females resemble polycystic ovary morphology (PCOM) with a high number of atretic antral follicles that could be rescued with injection of gonadotropins. Such a procedure also allowed Abhd2 KO females to ovulate a significantly increased number of mature and fertile eggs in comparison with their wild-type littermates. These results suggest a novel regulatory role of ABHD2 as an important factor in non-genomic steroid regulation of the female reproductive cycle.

Single-cell transcriptome and cell-specific network analysis reveal the reparative effect of neurotrophin-4 in preantral follicles grown in vitro

BACKGROUND

In-vitro-grow (IVG) of preantral follicles is essential for female fertility preservation, while practical approach for improvement is far from being explored. Studies have indicated that neurotrophin-4 (NT-4) is preferentially expressed in human preantral follicles and may be crucial to preantral follicle growth.

METHODS

We observed the location and expression of Tropomyosin-related kinase B (TRKB) in human and mouse ovaries with immunofluorescence and Western blot, and the relation between oocyte maturation and NT-4 level in follicular fluid (FF). Mice model was applied to investigate the effect of NT-4 on preantral follicle IVG. Single-cell RNA sequencing of oocyte combined with cell-specific network analysis was conducted to uncover the underlying mechanism of effect.

RESULTS

We reported the dynamic location of TRKB in human and mouse ovaries, and a positive relationship between human oocyte maturation and NT-4 level in FF. Improving effect of NT-4 was observed on mice preantral follicle IVG, including follicle development and oocyte maturation. Transcriptome analysis showed that the reparative effect of NT-4 on oocyte maturation might be mediated by regulation of PI3K-Akt signaling and subsequent organization of F-actin. Suppression of advanced stimulated complement system in granulosa cells might contribute to the improvement. Cell-specific network analysis revealed NT-4 may recover the inflammation damage induced by abnormal lipid metabolism in IVG.

CONCLUSIONS

Our data suggest that NT-4 is involved in ovarian physiology and may improve the efficiency of preantral follicle IVG for fertility preservation.

A platform utilizing Drosophila ovulation for nonhormonal contraceptive screening

A significant unmet need for new contraceptive options for both women and men remains due to side-effect profiles, medical concerns, and the inconvenience of many currently available contraceptive products. Unfortunately, the development of novel nonsteroidal female contraceptive medicine has been stalled in the last couple of decades due to the lack of effective screening platforms. Drosophila utilizes conserved signaling pathways for follicle rupture, a final step in ovulation that is essential for female reproduction. Therefore, we explored the potential to use Drosophila as a model to screen compounds that could inhibit follicle rupture and be nonsteroidal contraceptive candidates. Using our ex vivo follicle rupture assay, we screened 1,172 Food and Drug Administration (FDA)-approved drugs and identified six drugs that could inhibit Drosophila follicle rupture in a dose-dependent manner. In addition, we characterized the molecular actions of these drugs in the inhibition of adrenergic signaling and follicle rupture. Furthermore, we validated that three of the four drugs consistently inhibited mouse follicle rupture in vitro and that two of them did not affect progesterone production. Finally, we showed that chlorpromazine, one of the candidate drugs, can significantly inhibit mouse follicle rupture in vivo. Our work suggests that Drosophila ovulation is a valuable platform for identifying lead compounds for nonsteroidal contraceptive development and highlights the potential of these FDA-approved drugs as novel nonsteroidal contraceptive agents.

Effects of Three-Dimensional Sodium Alginate Scaffold on Maturation and Developmental Gene Expressions in Fresh and Vitrified Preantral Follicles of Mice

BACKGROUND

Prior to chemotherapy interventions, n vitroi maturation (IVM) of folliclesthrough vitrification can be used to help young people conserve their fertility. The aim of s tudy was to inves tigate effect of sodium alginat scaffold on follicles development and improvement of the culture medium.

MATERIALS AND METHODS

This experimental study was conducted on immature female BALB/c mice (12-14 days). Follicles were gathered mechanically and placed in α-Minimal Essential Medium (α-MEM) containing 5% fetal bovine serum (FBS). Some pre-antral follicles were frozen. The fresh and vitrified follicles were cultured in different concentrations of sodium alginate (0.25%, 0.5%, and 1%) and two dimensional (2D) medium for 12 days. The samples were evaluated for viability percentage, the number of MII-phase oocytes and reactive oxygen specious (ROS) level. Additionally, Gdf9, Bmp15, Bmp7, Bmp4, Gpx, mnSOD and Gcs gene expressions were assessed in the samples.

RESULTS

The highest and lowest percentages of follicle viability and maturation in the fresh and vitrified groups were respectively 0.5% concentration and 2D culture. There was no significant difference among the concentrations of 0.25% and 1%. Viability and maturation of follicles showed a significant increase in the fresh groups in comparison with the vitrified groups. ROS levels in the both fresh and vitrified groups with different concentrations of alginate showed a significant decrease compared to the control group. ROS levels in follicles showed a significant decrease in the fresh groups in comparison with the vitrified groups (P≤0.0001). The highest gene expression levels were observed in the 0.5% alginate (P≤0.0001). Moreover, the viability percentage, follicle maturation, and gene expression levels were higher in the fresh groupsthan the vitrified groups (P≤0.0001).

CONCLUSION

Alginate hydrogel at a proper concentration of 5%, not only helps follicle get mature, but also promotes the expression of developmental genes and reducesthe level of intracellular ROS. Follicular vitrification decreases quality of the follicles, which are partially compensated using a three dimensional (3D) cell culture medium.

Advances in the applications of polymer biomaterials for in vitro follicle culture

The ovarian reserve (OR) indicates ovarian function by representing the quantity and quality of ovarian follicles, and it gradually decreases with increasing age. With the prolongation of women's lives, the protection provided by estrogen is lost for decades in postmenopausal women, and the related cardiovascular and cerebrovascular diseases, osteoporosis, and decreased immunity are the main risk factors affecting women's quality of life and longevity. Pharmacologic hormone replacement therapy (PHRT) has been controversial, and the construction of artificial ovary (AO) has attracted increasing attention. The most critical step of AO generation is the establishment of an in vitro culture (IVC) system to support the development of isolated follicles. This article mainly compares the advantages and disadvantages of different polymer biomaterials for use in follicle IVC, provides theoretical support for the development and construction of the follicle IVC system using natural biological materials, and provides a theoretical basis for establishing mature AO technology.

In vitro growth and maturation of primordial follicles and immature oocytes

Cryopreservation of ovarian tissue to preserve the fertility of girls and young women at high risk of sterility is now widely practiced. Pieces of cryopreserved ovarian cortex can be thawed and autografted to restore fertility, but because of the risks of reintroduction of the cancer, transplantation may not be possible for girls and women with blood-borne leukemias or cancers with a high risk of ovarian metastasis. Cryopreserved ovarian tissue contains mainly primordial follicles but also provides access to immature oocytes from small antral follicles, which may be matured in vitro to provide an additional source of mature oocytes. So in cases in which transplantation is contraindicated, fertility restoration could be safely achieved in the laboratory either by in vitro maturation (IVM) of oocytes aspirated from growing follicles or by the complete in vitro growth (IVG) and maturation (IVM) of primordial follicles to produce fertile metaphase II (MII) oocytes. The development of IVM and IVG methods to support all stages of oocytes available within ovarian tissue will maximize the potential for all patients undergoing fertility preservation.

Ovulation is Inhibited by an Environmentally Relevant Phthalate Mixture in Mouse Antral Follicles In Vitro

Phthalates are solvents and plasticizers found in consumer products including cosmetics, food/beverage containers, housing materials, etc. Phthalates are known endocrine-disrupting chemicals that can directly target the ovary, potentially causing defects in ovulation and fertility. Women are exposed to multiple different phthalates daily, therefore this study investigated the effects of an environmentally relevant phthalate mixture (PHTmix) on ovulation. Ovulation is initiated by the luteinizing hormone (LH) surge, which induces prostaglandin (PG) production, progesterone (P4)/progesterone receptor (PGR) signaling, and extracellular matrix (ECM) remodeling. We hypothesized that the PHTmix would directly inhibit ovulation by altering the levels of PGs, P4/PGR, and enzymes involved in ECM remodeling. Antral follicles from CD-1 mice were treated with vehicle control alone (dimethylsulfoxide, DMSO), hCG alone (LH analog), and hCG+PHTmix (1-500μg/ml), and samples were collected across the ovulatory period. The PHTmix decreased ovulation rates at all doses tested in a dose-dependent manner when compared to hCG. PG levels were decreased by the PHTmix when compared to hCG, which was potentially mediated by altered levels of PG synthesis (Ptgs2) and transport (Slco2a1) genes. The PHTmix altered P4 and Pgr levels when compared to hCG, leading to decreases in downstream PGR-mediated genes (Edn2, Il6, Adamts1). ECM remodeling was potentially dysregulated by altered levels of ovulatory mediators belonging to the matrix metalloproteases and plasminogen activator families. These data suggest that phthalate exposure inhibits ovulation by altering PG levels, P4/PGR action, and ECM remodeling.

Decellularization Methods of Ovary in Tissue Engineering

The ovaries or female gonads are situated in the ovarian fossa of the abdominal cavity. These are paired, almond-shaped organs measuring about 3.5 cm long and 1.5 cm thick and exist out of a central medullary zone and a peripheral cortex that are enclosed in a fibrous capsule called the tunica albuginea. The ovaries serve 2 main functions, the first one being the production of female gametes called oocytes (oogenesis). Interestingly, the number of primary oocytes that reside in the ovary is determined at birth. About 400 oocyte-containing follicles successfully go through all the developmental stages from this limited pool during folliculogenesis throughout the female reproductive life. In this process, primordial follicles grow and advance until forming a mature or Graafian follicle; during ovulation, secondary oocytes are released and the remaining follicular wall collapses and forms the highly vascularized corpus luteum or luteal gland. This ovarian cycle is regulated by several hormones secreted from the adenohypophysis and lasts about 28 days. During this cycle, the ovaries also serve as endocrine glands and produce female sex hormones such as estrogens and progesterone (steroidogenesis), influencing the growth and development of tissues sensitive to these hormones such as the endometrium. Hence, the endometrial cycle goes synchronized with the ovarian cycle.

Artificially produced gametes in mice, humans and other species

The production of gametes from pluripotent stem cells in culture, also known as invitro gametogenesis, will make an important contribution to reproductive biology and regenerative medicine, both as a unique tool for understanding germ cell development and as an alternative source of gametes for reproduction. Invitro gametogenesis was developed using mouse pluripotent stem cells but is increasingly being applied in other mammalian species, including humans. In principle, the entire process of germ cell development is nearly reconstitutable in culture using mouse pluripotent stem cells, although the fidelity of differentiation processes and the quality of resultant gametes remain to be refined. The methodology in the mouse system is only partially applicable to other species, and thus it must be optimised for each species. In this review, we update the current status of invitro gametogenesis in mice, humans and other animals, and discuss challenges for further development of this technology.

Dissection of the Ovulatory Process Using ex vivo Approaches

Ovulation is a unique physiological phenomenon that is essential for sexual reproduction. It refers to the entire process of ovarian follicle responses to hormonal stimulation resulting in the release of mature fertilization-competent oocytes from the follicles and ovaries. Remarkably, ovulation in different species can be reproduced out-of-body with high fidelity. Moreover, most of the molecular mechanisms and signaling pathways engaged in this process have been delineated using in vitro ovulation models. Here, we provide an overview of the major molecular and cytological events of ovulation observed in frogs, primarily in the African clawed frog Xenopus laevis, using mainly ex vivo approaches, with the focus on meiotic oocyte maturation and follicle rupture. For the purpose of comparison and generalization, we also refer extensively to ovulation in other biological species, most notoriously, in mammals.

Microfluidic Systems for Assisted Reproductive Technologies: Advantages and Potential Applications

Microfluidic technologies have emerged as a powerful tool that can closely replicate the in-vivo physiological conditions of organ systems. Assisted reproductive technology (ART), while being able to achieve successful outcomes, still faces challenges related to technical error, efficiency, cost, and monitoring/assessment. In this review, we provide a brief overview of the uses of microfluidic devices in the culture, maintenance and study of ovarian follicle development for experimental and therapeutic applications. We discuss existing microfluidic platforms for oocyte and sperm selection and maintenance, facilitation of fertilization by in-vitro fertilization/intracytoplastimc sperm injection, and monitoring, selection and maintenance of resulting embryos. Furthermore, we discuss the possibility of future integration of these technologies onto a single platform and the limitations facing the development of these systems. In spite of these challenges, we envision that microfluidic systems will likely evolve and inevitably revolutionize both fundamental, reproductive physiology/toxicology research as well as clinically applicable ART.

In vitro reconstitution of germ cell development†

Germ cell development is a series of highly specialized processes through which diploid pluripotent cells differentiate into haploid gametes. The processes include biologically important events such as epigenetic reprogramming, sex determination, and meiosis. The mechanisms underlying these events are key issues in reproductive and developmental biology, yet they still remain elusive. As a tool to elucidate these mechanisms, in vitro gametogenesis, which reproduces germ cell development in culture, has long been sought for decades. Recently, methods of in vitro gametogenesis have undergone rapid development in association with stem cell biology, opening many possibilities in this field. This new technology is considered an alternative source of gametes for the reproduction of animals and perhaps humans. This review summarizes current advances and problems in in vitro gametogenesis.

Evaluating the Effects of Different Concentrations of Human Follicular Fluid on Growth, Development, and PCNA Gene Expression of Mouse Ovarian Follicles

Follicle culture in vitro provides a method for investigating stages of folliculogenesis that can lead to preserving fertility through cryopreservation techniques. This study aims to assess the effects of various concentrations of human follicular fluid (hFF) on growth, development, and expression of the proliferating cell nuclear antigen (PCNA) gene in mouse ovarian follicles in vitro. Preantral follicles were isolated from 14-day NMRI mouse ovaries. The follicles were cultured in basic media enriched with FBS, FSH, and insulin-transferrin-selenium, and supplemented with different concentrations of hFF (10, 20, and 30%) for 12 days. During the culture period, survival rate and follicular maturation, follicular diameter, levels of estrogen and progesterone secretion, and PCNA gene expression rate were evaluated. Survival rate, maturation, and antrum formation were significantly higher in the 10% hFF group than in the 20 and 30% hFF groups. On day 4, follicle diameter in the 10% hFF group was also higher than in the 20 and the 30% hFF group. In comparison with other groups, significantly higher estrogen and progesterone production levels were measured in the 10% hFF group. PCNA gene expression was also higher with 10 than 20 and 30% hFF concentrations. The present study suggests that addition of 10% hFF to mice ovarian preantral follicle culture media enhances follicle growth and oocyte maturation.

Lessons from bioengineering the ovarian follicle: a personal perspective

The ovarian follicle and its maturation captivated my imagination and inspired my scientific journey - what we know now about this remarkable structure is captured in this invited review. In the past decade, our knowledge of the ovarian follicle expanded dramatically as cross-disciplinary collaborations brought new perspectives to bear, ultimately leading to the development of extragonadal follicles as model systems with significant clinical implications. Follicle maturation in vitro in an 'artificial' ovary became possible by learning what the follicle is fundamentally and autonomously capable of - which turns out to be quite a lot. Progress in understanding and harnessing follicle biology has been aided by engineers and materials scientists who created hardware that enables tissue function for extended periods of time. The EVATAR system supports extracorporeal ovarian function in an engineered environment that mimics the endocrine environment of the reproductive tract. Finally, applying the tools of inorganic chemistry, we discovered that oocytes require zinc to mature over time - a truly new aspect of follicle biology with no antecedent other than the presence of zinc in sperm. Drawing on the tools and ideas from the fields of bioengineering, materials science and chemistry unlocked follicle biology in ways that we could not have known or even predicted. Similarly, how today's basic science discoveries regarding ovarian follicle maturation are translated to improve the experience of tomorrow's patients is yet to be determined.

Ovulation and ovarian wound healing are impaired with advanced reproductive age

Aging is associated with reduced tissue remodeling efficiency and increased fibrosis, characterized by excess collagen accumulation and altered matrix degradation. Ovulation, the process by which an egg is released from the ovary, is one of the most dynamic cycles of tissue wounding and repair. Because the ovary is one of the first organs to age, ovulation and ovarian wound healing is impaired with advanced reproductive age. To test this hypothesis, we induced superovulation in reproductively young and old mice and determined the numbers of eggs ovulated and corpora lutea (CLs), the progesterone producing glands formed post-ovulation. Reproductively old mice ovulated fewer eggs and had fewer CLs relative to young controls. Moreover, reproductively old mice exhibited a greater number of oocytes trapped within CLs and expanded cumulus oocyte complexes within unruptured antral follicles, indicative of failed ovulation. In addition, post-ovulatory tissue remodeling was compromised with age as evidenced by reduced CL vasculature, increased collagen, decreased hyaluronan, decreased cell proliferation and apoptosis, impaired wound healing capacity, and aberrant morphology of the ovarian surface epithelium (OSE). These findings demonstrate that ovulatory dysfunction is an additional mechanism underlying the age-related loss of fertility beyond the reduction of egg quantity and quality.

In vitro ovarian follicle growth: a comprehensive analysis of key protocol variables†

Folliculogenesis is a complex process that requires integration of autocrine, paracrine, and endocrine factors together with tightly regulated interactions between granulosa cells and oocytes for the growth and survival of healthy follicles. Culture of ovarian follicles is a powerful approach for investigating folliculogenesis and oogenesis in a tightly controlled environment. This method has not only enabled unprecedented insight into the fundamental biology of follicle development but also has far-reaching translational applications, including in fertility preservation for women whose ovarian follicles may be damaged by disease or its treatment or in wildlife conservation. Two- and three-dimensional follicle culture systems have been developed and are rapidly evolving. It is clear from a review of the literature on isolated follicle culture methods published over the past two decades (1980-2018) that protocols vary with respect to species examined, follicle isolation methods, culture techniques, culture media and nutrient and hormone supplementation, and experimental endpoints. Here we review the heterogeneity among these major variables of follicle culture protocols.

Toward the understanding of biology of oocyte life cycle in Xenopus Laevis: No oocytes left behind

BACKGROUND

For the past more than 25 years, we have been focusing on the developmental and reproductive biology of the female gametes, oocytes, and eggs, of the African clawed frog Xenopus laevis.

METHODS

The events associated with the life cycle of these cells can be classified into the four main categories: first, oogenesis and cell growth in the ovary during the first meiotic arrest; second, maturation and ovulation that occur simultaneously and result in the acquisition of fertilization competence and the second meiotic arrest; third, fertilization, that is sperm-induced transition from egg to zygote; and fourth, egg death after spontaneous activation in the absence of fertilizing sperm.

MAIN FINDINGS

Our studies have demonstrated that signal transduction system involving tyrosine kinase Src and other oocyte/egg membrane-associated molecules such as uroplakin III and some other cytoplasmic proteins such as mitogen-activated protein kinase (MAPK) play important roles for successful ovulation, maturation, fertilization, and initiation of embryonic development.

CONCLUSION

We summarize recent advances in understanding cellular and molecular mechanisms underlying life cycle events of the oocytes and eggs. Our further intention is to discuss and predict potentially promising impact of the recent findings on the challenges facing reproductive biology and medicine, as well as societal contexts.

Engineered reproductive tissues

Engineered male and female biomimetic reproductive tissues are being developed as autonomous in vitro units or as integrated multi-organ in vitro systems to support germ cell and embryo function, and to display characteristic endocrine phenotypic patterns, such as the 28-day human ovulatory cycle. In this Review, we summarize how engineered reproductive tissues facilitate research in reproductive biology, and overview strategies for making engineered reproductive tissues that might eventually allow the restoration of reproductive capacity in patients.

Engineering a bioprosthetic ovary for fertility and hormone restoration

There has been an increase in childhood cancer survivors over the past few decades, and with this, an increased awareness of the co-morbidities of the treatment or disease that affect the survivor's quality-of-life. The increased rate of infertility among this patient group and the desire to have biological children voiced by childhood cancer survivors underscores the urgent need for fertility preservation and development of techniques to restore fertility and gonadal hormone function for this population. The ovarian tissue contains a finite source of female gametes that can be transplanted to restore ovarian function and has resulted in over one hundred reported live births. However, the success of biological offspring per ovarian tissue transplant, the reduced lifespan of these transplants, and the potential for these tissues to contain cancer cells from patients with metastatic diseases supports the need for improved options. One innovation that could improve ovarian transplantation is the development of a bioprosthetic ovary comprised of a 3D printed scaffold with isolated ovarian follicles. A murine bioprosthetic ovary restored ovarian hormones in ovariectomized mice, which also gave birth to healthy offspring. Research is ongoing to create the next iteration of the scaffold that would support ovarian follicles from large animal models and humans with the hopes of translating this technology for patients.

Human Follicle in vitro Culture Including Activation, Growth, and Maturation: A Review of Research Progress

Fertility preservation has received unprecedented attention nowadays. In addition to cryopreservation and re-implantation of embryos, oocytes, and ovarian tissue pieces, in vitro culture system for follicles/oocytes has been considered as an alternative strategy for fertility preservation. Since the metabolic dynamics and required nutrients are not entirely the same in different stages of follicular development, optimization of each culture step is needed. In this paper, literature regarding culture conditions in three steps were analyzed. Known additives in activation stage included 740Y-P, bpV(HOpic), follicle stimulating hormone (FSH), human serum albumin (HSA), ITS, growth differentiation factor 9 (GDF9), bone morphogenetic protein 15 (BMP15), and cyclic adenosine monophosphate (cAMP), with different degrees of activation promotion and potential detrimental effect on DNA integrity. For isolated follicles growth stage, actin A, FSH, basic fibroblast growth factor (bFGF), estradiol were proved to improve development or proliferation. As for maturation, addition of growth hormone, melatonin, C-type natriuretic peptide (CNP), GDF9, cilostamide, or forskolin helped to regulate maturation rate or improve oocyte quality. Based on previous sequential culture system for human follicles, optimization is needed to achieve higher maturation rate and better oocyte quality, pursuant to current review, which demonstrated the effects of various additives on different stages.

Roles of vitamin D and its receptor in the proliferation and apoptosis of luteinised granulosa cells in the goat

The objective of this study was to investigate the dose-dependent effect of 1α,25-(OH)2VD3 (Vit D3) on invitro proliferation of goat luteinised granulosa cells (LGCs) and to determine the underlying mechanisms of its action by overexpressing and silencing vitamin D receptor (VDR) in LGCs. Results showed that VDR was prominently localised in GCs and theca cells (TCs) and its expression increased with follicle diameter, but was lower in atretic follicles than in healthy follicles. The proliferation rate of LGCs was significantly higher in the Vit D3-treated groups than in the control group, with the highest proliferation rate observed in the 10nM group; this was accompanied by changes in the expression of cell cycle-related genes. These data indicate that Vit D3 affects LGC proliferation in a dose-dependent manner. Contrary to the VDR knockdown effects, its overexpression upregulated and downregulated cell cycle- and apoptosis-related genes respectively; moreover, supplementation with 10nM of Vit D3 significantly enhanced these effects. These results suggest that changes in VDR expression patterns in LGCs may be associated with follicular development by regulation of cell proliferation and apoptosis. These findings will enhance the understanding of the roles of Vit D3 and VDR in goat ovarian follicular development.

Proteomic analyses of decellularized porcine ovaries identified new matrisome proteins and spatial differences across and within ovarian compartments

Premature ovarian insufficiency (POI) affects approximately 1% of women. We aim to understand the ovarian microenvironment, including the extracellular matrix (ECM) and associated proteins (matrisome), and its role in controlling folliculogenesis. We mapped the composition of the matrisome of porcine ovaries through the cortical compartment, where quiescent follicles reside and the medullary compartment, where the larger follicles grow and mature. To do this we sliced the ovaries, uniformly in two anatomical planes, enriched for matrisome proteins and performed bottom-up shotgun proteomic analyses. We identified 42 matrisome proteins that were significantly differentially expressed across depths, and 11 matrisome proteins that have not been identified in previous ovarian protein analyses. We validated these data for nine proteins and confirmed compartmental differences with a second processing method. Here we describe a processing and proteomic analysis pipeline that revealed spatial differences and matrisome protein candidates that may influence folliculogenesis.

Insights into the Pathophysiology of Infertility in Females with Classical Galactosaemia

Classical galactosaemia (CG) (OMIM 230400) is a rare inborn error of galactose metabolism caused by the deficiency of the enzyme galactose-1-phosphate uridylyltransferase (GALT, EC 2.7.7.12). Primary ovarian insufficiency (POI) is the most common long-term complication experienced by females with CG, presenting with hypergonadotrophic hypoestrogenic infertility affecting at least 80% of females despite new-born screening and lifelong galactose dietary restriction. In this review, we describe the hypothesized pathophysiology of POI from CG, implications of timing of the ovarian dysfunction, and the new horizons and future prospects for treatments and fertility preservation.