Ovarian follicle culture: advances and challenges for human and nonhuman primates

Classification system of human ovarian follicle morphology: recommendations of the National Institute of Child Health and Human Development - sponsored ovarian nomenclature workshop

OBJECTIVE

To develop a consensus on histologic human ovarian follicle staging nomenclature, provide guidelines for follicle density calculation, and assess changes due to fixation to enhance communication among clinicians and ovarian biology researchers to gain a deeper understanding of human fertility.

SETTING

Beginning in March 2021, the Ovarian Nomenclature Workshop's Follicle Classification Working Subgroup was organized by the Pediatric and Adolescent Gynecology program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development.

METHODS

After the initial workshop held in May 2021, a Follicle Working Subgroup comprised of experts in reproductive endocrinology and ovarian biology held multiple meetings to develop the human follicle classification system and reported to the collective group during two follow up workshops.

RESULTS

The Follicle Working Subgroup recommends consolidation and expansion of the current classification systems to include six stages of normal preantral follicles, five stages of normal antral follicles, as well as categories of corpus lutea, abnormal preantral follicles, abnormal antral follicles, and other distinct follicle types. The new preantral staging added intermediate stages (primordial, transitional primordial, primary, transitional primary, secondary, and multilayer ovarian follicles). The antral follicle staging includes early, preselection, selection, dominance, and preovulatory follicles. Abnormal preantral follicles include those with an abnormal oocyte, granulosa cells, or both. We suggest a uniform way of calculating the mean follicle density in the number of follicles/mm2.

CONCLUSION

To establish a consensus in human ovarian follicle terminology, the Ovarian Follicle Working Subgroup of the National Institute of Child Health and Human Development Ovarian Nomenclature Workshop standardized follicle staging nomenclature and follicle density calculating systems so consistent common language can be used among ovarian biology researchers and clinicians.

Meeting proceedings: International Society for Fertility Preservation Tokyo, 15-17 November, 2024

The 8 th International Congress of the ISFP was held in Tokyo, Japan, from November 15 to 17, 2024. The theme of this year's Congress was "Rethinking Personalized Fertility Preservation and Cancer Survivors-Opening a New Frontier". The congress featured special lectures, keynote addresses, and 25 sessions-including a dedicated session on nursing and oral presentations by young doctors and researchers-making it one of the largest and most comprehensive events in the ISFP's history. Additionally, the program incorporated sessions featuring the Japanese, Korean, and Chinese Societies for Fertility Preservation, providing a convenient platform for international participants from across the globe to showcase their work and discuss the unique characteristics and challenges of these areas within Asia. Participants also had the opportunity to attend workshops on ovarian tissue cryopreservation and oocyte cryopreservation, conducted by leaders in their respective fields exploring the latest technological and clinical advances and translational prospects for the future.

Ovarian Stem Cells: Will the Dream of Neo-Folliculogenesis After Birth Become Real?

Importance

Ovarian stem cells (OSCs) represent a promising tool in reproductive medicine, particularly for the treatment of premature ovarian failure and fertility preservation.

Objectives

Herein, we summarize the main characteristics of adult stem cells, their status, needs, and new challenges in the application in reproductive medicine.

Evidence Acquisition

Clinical studies have shown that OSCs transplantation can restore ovarian function and stimulate neo-folliculogenesis in patients with premature ovarian failure, enabling them to conceive naturally or through in vitro fertilization techniques. Moreover, OSCs gained increasing interest as a chance to preserve fertility in cancer patients undergoing gonadotoxic treatments affecting their fertility, as chemotherapy or radiotherapy.

Results

The recruitment of OSCs from fresh or thawed ovarian fragments coupled with their capability to differentiate in vitro to mature oocytes could provide a novel opportunity to verify their suitability to be expanded in vitro as oocyte like cells.

Conclusions and Relevance

Research into OSCs and their applications in reproductive medicine is still in its infancy, but the results so far are promising and offer new possibilities for patients suffering from premature ovarian failure or cancer.

Combination of FSH and testosterone could enhance activation of primordial follicles and growth of activated follicles in 1-day-old mice ovaries in vitro cultured for 12 days

Treatment with follicle-stimulating hormone (FSH) and testosterone (T2) and their combination have been observed to be influential on ovarian follicles of 1-day-old mice ovaries cultured for 8 days. Given that extension of the culture period could positively impact the development of follicles in cultured ovaries, the present study was conducted to evaluate the main and interaction effects of FSH by T2 on the development of ovarian follicles in 1-day-old mice ovaries cultured for 12 days. One-day-old mice ovaries were initially cultured with base medium for 4 days; thereafter, different hormonal treatments were added to the culture media, and the culture was continued for 8 additional days until day 12. Ovaries were collected for histological and molecular assessments on day 12. The greatest activation of primordial follicles and progression of activated follicles to the preantral stage was detected in ovaries treated with the combination of FSH and T2 (P < 0.05). This positive effect on the morphology of ovarian follicles was accompanied by upregulation of Pi3k, Gdf9, Bmp15, Cx37 and Fshr in the ovaries cultured with the combination of FSH and T2 (P < 0.05). Nonetheless, treatment with FSH and T2 led to a diminished proportion of intact follicles (P < 0.05), even though Bax/Bcl2 gene expression ratio, as an apoptotic index, was less in hormone-treated ovaries (P < 0.05). In conclusion, the combination of FSH and T2 could improve the activation of primordial follicles and the growth of activated follicles towards the preantral stage. This positive effect of FSH plus T2 appeared to be at least partly mediated through the upregulation of Pi3k and oocyte-derived growth factors including Gdf9 and Bmp15.

A spotlight on factors influencing the in vitro folliculogenesis of isolated preantral follicles

Female fertility preservation via complete in vitro folliculogenesis is still chimerical. Due to many factors affecting the efficiency of isolation and culture of preantral follicles, the improvement of techniques geared to fertility preservation in higher mammals seems to be at an impasse. We need an objective view of the current stand to understand how to progress further. As such, a survey was conducted to analyze the relative distribution of studies performed in ten mammalian species on preantral follicle culture available on PubMed. Using the bovine as a reference model, we explore some factors influencing data variation that contribute to the difficulty in reproducing studies. While years of research have enabled the recapitulation of folliculogenesis from as modest as the early antral follicle stage ex vivo, in vitro preantral folliculogenesis remains elusive. Herein, we revisit the classical evidence that laid the foundations for understanding preantral folliculogenesis and review the length, breadth, and depth of information that the era of big data has currently levied. Moving forward, we recognize the urgency of synthesizing the multi-disciplinary approaches to mimic folliculogenesis in vitro to achieve a translational landscape of infertility at individual and large-scale conservation levels.

Application of fibrin-based biomaterial for human ovarian tissue encapsulation and cryopreservation as alternative approach for fertility preservation

This study aimed to investigate the effects of fibrin-based hydrogel encapsulation, with or without vascular endothelial growth factor (VEGF), on follicle quality and cell survival signaling pathways after ovarian tissue cryopreservation. Ovarian cortex donated by seven patients (ages 44-47 years old) was divided into four groups: I) fresh control, II) ovarian tissue without encapsulation (non-FT), III) fibrin (10 mg/mL fibrinogen plus 50 IU/mL thrombin; 10FT) encapsulated tissue without VEGF, and IV) encapsulated tissue with 0.1 μg/mL VEGF (10FT-VEGF), followed by a slow freezing process. Evaluation criteria included normal follicle morphology, density, cell proliferation, apoptosis, and metabolism signaling pathways (BAX/BCL-2 ratio, CASPASE-3 and 9, ATP-6 genes, VEGF-A, and ERK-1/2 protein expression levels). Major outcomes revealed that the percentages of morphologically normal follicles and density were significantly decreased by cryopreservation. Ovarian tissue encapsulation using the 10FT formulation (with or without VEGF) could maintain the ERK-signaling cascade, which was comparable to the fresh control. Among the frozen-thawed cohorts, the BAX/BCL-2 ratio, CASPASE-3, CASPASE-9, and ATP-6 expression levels were unfavorable in the non-FT group. However, statistically different results, including VEGF-A expression levels, were not detected. Collectively, our present data demonstrated the first applicable biomaterial matrix for human ovarian tissue encapsulation which might create an optimal intra-ovarian cortex environment during cryopreservation. Further studies to optimize hydrogel polymerization should be expanded, given the potential benefits for cancer patients who wish to preserve fertility through ovarian tissue cryopreservation.

In vitro culture of mechanically isolated murine primary follicles in the presence of human platelet lysate PLTMax

OBJECTIVE

To develop a system for the culture of murine preantral ovarian follicles using Human Serum Albumin (HSA) and Human Platelet Lysate (PLTMax).

METHODS

Mechanically isolated preantral follicles (N=146) were obtained from Swiss mice and cultured in DMEM:F12 medium for ten days in a 96-well plate with conical bottom. The medium was supplemented with penicillin, streptomycin, and equine chorionic gonadotropin. Additional proteins were tested in 4 test groups: G1: human serum albumin (HSA), G2: human platelet lysate (PLTM), and G3 and G4: HSA + PLTMax at lower and higher concentrations, respectively. Cellular vitality and oocyte morphology were evaluated on day 11 of culture.

RESULTS

The highest follicular growth (3.4 fold) was achieved in HSA (G1), while a significantly lower (1.8 fold) growth was achieved in the presence of PLTM (G2, G4) and even further reduced (1.2 fold) when HSA and PLTM were combined (G3). Cellular vitality was close to 70-80% among the four groups, and the highest number of intact oocytes were found in G1.

CONCLUSIONS

PLTM did not improve follicular development and oocyte maturation compared to HSA but preserved cell vitality.

Generation of Tailored Extracellular Matrix Hydrogels for the Study of In Vitro Folliculogenesis in Response to Matrisome-Dependent Biochemical Cues

While ovarian tissue cryopreservation (OTC) is an important fertility preservation option, it has its limitations. Improving OTC and ovarian tissue transplantation (OTT) must include extending the function of reimplanted tissue by reducing the extensive activation of primordial follicles (PMFs) and eliminating the risk of reimplanting malignant cells. To develop a more effective OTT, we must understand the effects of the ovarian microenvironment on folliculogenesis. Here, we describe a method for producing decellularized extracellular matrix (dECM) hydrogels that reflect the protein composition of the ovary. These ovarian dECM hydrogels were engineered to assess the effects of ECM on in vitro follicle growth, and we developed a novel method for selectively removing proteins of interest from dECM hydrogels. Finally, we validated the depletion of these proteins and successfully cultured murine follicles encapsulated in the compartment-specific ovarian dECM hydrogels and these same hydrogels depleted of EMILIN1. These are the first, optically clear, tailored tissue-specific hydrogels that support follicle survival and growth comparable to the "gold standard" alginate hydrogels. Furthermore, depleted hydrogels can serve as a novel tool for many tissue types to evaluate the impact of specific ECM proteins on cellular and molecular behavior.

In vitro culture of sheep early-antral follicles: Milestones, challenges and future perspectives

Early antral follicles (EAFs) represent the transitional stage between pre-antral and antral follicles, containing oocytes that have completed most of their growth phase. Therefore, they offer an easily exploitable reserve for producing mature oocytes and preserving genetic resources, given their higher abundance compared to antral follicles (AFs) and shorter culture period than other pre-antral follicles (PAFs). Despite these advantages, the culture of EAFs remains challenging, and the success rates of in vitro embryo production (IVEP) from EAF-derived oocytes are still far below the standard achieved with fully grown oocytes in ruminant species. The difficulty is related to developing suitable in vitro culture systems tailored with nutrients, growth factors, and other signaling molecules to support oocyte growth. In this review, we focus on the in vitro development of sheep EAFs to provide an informative reference to current research progress. We also summarize the basic aspect of folliculogenesis in sheep and the main achievements and limitations of the current methods for EAF isolation, in vitro culture systems, and medium supplementation. Finally, we highlight future perspectives and challenges for improving EAF culture outcomes.

Melatonin acts through different mechanisms to control oxidative stress and primordial follicle activation and survival during in vitro culture of bovine ovarian tissue

This study aims to evaluate the effects of melatonin and its mechanisms of action on preantral follicle activation and survival, stromal cell density and collagen distribution in extracellular matrix (ECM). The involvement of melatonin receptors and mTORC1 pathway in these procedures were also investigated. To this end, ovarian fragments were cultured for six days in α-MEM+ alone or supplemented with 1000 pM melatonin, 1000 pM melatonin with 1000 pM luzindole (inhibitor of melatonin receptors), or 1000 pM melatonin with 0.16 µg/ml rapamycin (mTORC1 inhibitor). At the end of culture period, tissues were processed for classical histology, and the follicles were classified as normal or degenerated, as well as in primordial or growing follicles. The ovarian stromal cell density and ECM collagen distribution were also evaluated. Samples of ovarian tissues were also destined to measure the levels of thiol and mRNA for CAT, SOD, GPX1 and PRDX1, as well as the activity of antioxidant enzymes CAT, SOD, and GPX1. The results demonstrated that ovarian tissues cultured with melatonin, melatonin with luzindole or melatonin with rapamycin had significantly higher percentage of morphologically normal follicles than those cultured in control medium (α-MEM+). However, the presence of either luzindole or rapamycin, did not block the positive effects of melatonin on follicle survival (P > 0.05). Although the presence of melatonin in culture medium reduced the percentage of primordial follicles and increased the percentage of development follicles, these positive effects of melatonin were blocked by either luzindole or rapamycin (P < 0.05). Melatonin, melatonin with luzindole or melatonin with rapamycin did not influence the number of ovarian stromal cells. In contrast, melatonin significantly increased the percentages of collagen in ovarian tissues, but the positive effects of melatonin were blocked by either luzindole or rapamycin. Tissues cultured with melatonin and rapamycin had higher levels of mRNA for CAT and lower GPx activity when compared to those cultured in control medium. In conclusion, melatonin promotes primordial follicle activation, increases collagen fiber in ECM of in vitro cultured bovine ovarian tissue through its membrane-coupled receptors and mTORC1. Oppositely, melatonin increase follicles survival by acting through other pathways, since it can pass through cell membranes and directly regulate oxidative stress.

Control of the growth and development of murine preantral follicles in a biomimetic ovary using a decellularized porcine scaffold

This study aimed to derive mature oocytes from murine preantral follicles cultured in a biomimetic ovary with a porcine scaffold using decellularization technology. We evaluated the DNA content and the presence of cell and extracellular matrix (ECM) components, including collagen, elastin, and glycosaminoglycans (GAGs), in decellularized (decell) porcine ovaries. The DNA content inthe decell ovarian tissues was approximately 94 % less than that in native tissues (66 ± 9.8 ng/mg vs. 1139 ± 269 ng/mg). Furthermore, the ECM component integrity was maintained in the decell ovarian tissue. The soluble collagen concentration of native ovarian tissue (native) was 195.34 ± 15.13 μg/mg (dry wt.), which was less than 878.6 ± 8.24 μg/mg for the decell ovarian tissue due to the loss of cellular mass. Hydrogels derived from decell porcine ovaries were prepared to develop an in vitro biomimetic ovary with appropriate ECM concentration (2-6 mg/mL). Scanning electron microscope (SEM) imagining revealed that the complex fiber network and porous structure were maintained in all groups treated with varying ECM concentration (2-6 mg/mL). Furthermore, rheometer analysis indicated that mechanical strength increased with ECM concentration in a dose-dependently. The preantral follicles cultured with 4 mg/mL ECM showed high rates of antral follicle (66 %) and mature oocyte (metaphase II) development (47 %). The preantral follicles cultured in a biomimetic ovary with a decell porcine scaffold showed a higher rate of antral follicle and mature oocytes than those cultured in other biomaterials such as collagen and Matrigel. In mature oocytes derived from antral follicles, meiotic spindles and nuclei were stained using a tubulin antibody and Hoechst, respectively. Two-cell embryos were developed from MII oocytes following parthenogenetic activation. Preantral follicles were cultured in a biomimetic ovary derived from the ECM of a decell porcine ovary, and embryos were generated from MII oocytes. This biomimetic ovary could contribute to restoring fertility in infertile women with reduced ovarian function, benefit mating efforts for endangered species, and maintain animals with valuable genetic traits.

Innovative Strategies for Fertility Preservation in Female Cancer Survivors: New Hope from Artificial Ovary Construction and Stem Cell-Derived Neo-Folliculogenesis

Recent advances in anticancer treatment have significantly improved the survival rate of young females; unfortunately, in about one third of cancer survivors the risk of ovarian insufficiency and infertility is still quite relevant. As the possibility of becoming a mother after recovery from a juvenile cancer is an important part of the quality of life, several procedures to preserve fertility have been developed: ovarian surgical transposition, induction of ovarian quiescence by gonadotropin-releasing hormone agonists (GnRH-a) treatment, and oocyte and/or ovarian cortical tissue cryopreservation. Ovarian tissue cryostorage and allografting is a valuable technique that applies even to prepubertal girls; however, some patients cannot benefit from it due to the high risk of reintroducing cancer cells during allograft in cases of ovary-metastasizing neoplasias, such as leukemias or NH lymphomas. Innovative techniques are now under investigation, as in the construction of an artificial ovary made of isolated follicles inserted into an artificial matrix scaffold, and the use of stem cells, including ovarian stem cells (OSCs), to obtain neo-folliculogenesis and the development of fertilizable oocytes from the exhausted ovarian tissue. This review synthesizes and discusses these innovative techniques, which potentially represent interesting strategies in oncofertility programs and a new hope for young female cancer survivors.

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.

Micromechanical characterizations and viscoelastic modeling reveal elastic and viscoelastic heterogeneities in ovarian tissue and the significant viscoelastic contribution to the apparent elastic modulus determined by AFM indentation

Ovarian follicles develop in a highly regulated mechanical microenvironment and disruptions to the microenvironment may cause infertility. However, the viscoelastic properties of the ovarian tissue are not well studied. Here, we characterize both the elastic and viscoelastic properties of ovarian tissue from both reproductively older and younger domestic cats using atomic force microscopy (AFM) indentation and viscoelastic models of stress relaxation. Importantly, our analyses reveal the apparent elastic modulus obtained from the conventional AFM indentation measurement is significantly higher than the intrinsic elastic modulus and insignificantly different from the equivalent elastic modulus that is the summation of the intrinsic elastic modulus and the viscoelastic contribution to modulus at time 0. Interestingly, the ovarian cortex of both reproductive age groups has a higher apparent/intrinsic modulus than that of the medulla. Furthermore, two different kinetics of stress relaxation are identified with rate constants of ∼1 s and ∼20-40 s, respectively. Moreover, the rate constant of the slow kinetics is significantly different between the cortex and medulla in the reproductively older ovaries. Finally, these mechanical heterogeneities appear to follow the heterogeneous distribution of hyaluronic acid (HA) in the ovary. These findings may be invaluable to the development of biomimetic follicle culture for treating infertility. STATEMENT OF SIGNIFICANCE: This study investigates not only elastic but also the viscoelastic heterogeneity in both reproductively younger and older ovarian tissues for the first time. Further, by combining AFM indentation measurement and viscoelastic modeling, we show the apparent elastic modulus conventionally reported in the literature for AFM indentation measurement is the summation of the intrinsic elastic modulus and a significant viscoelastic contribution to the modulus at time 0. This is an important consideration for others who use this method to quantify biomaterial properties. In addition, the possible connection between the mechanical and compositional heterogeneities is explored. These findings may be invaluable for designing biomaterials to recapitulate the mechanical environment of the ovary and possibly many other organs for biomimetic tissue engineering.

Ovarian tissue cryopreservation and transplantation: a review on reactive oxygen species generation and antioxidant therapy

Cancer is the leading cause of death worldwide. Fortunately, the survival rate of cancer continues to rise, owing to advances in cancer treatments. However, these treatments are gonadotoxic and cause infertility. Ovarian tissue cryopreservation and transplantation (OTCT) is the most flexible option to preserve fertility in women and children with cancer. However, OTCT is associated with significant follicle loss and an accompanying short lifespan of the grafts. There has been a decade of research in cryopreservation-induced oxidative stress in single cells with significant successes in mitigating this major source of loss of viability. However, despite its success elsewhere and beyond a few promising experiments, little attention has been paid to this key aspect of OTCT-induced damage. As more and more clinical practices adopt OTCT for fertility preservation, it is a critical time to review oxidative stress as a cause of damage and to outline potential ameliorative interventions. Here we give an overview of the application of OTCT for female fertility preservation and existing challenges; clarify the potential contribution of oxidative stress in ovarian follicle loss; and highlight potential ability of antioxidant treatments to mitigate the OTCT-induced injuries that might be of interest to cryobiologists and reproductive clinicians.

JAK/STAT3 pathway promotes proliferation of ovarian aggregate-derived stem cells in vitro

BACKGROUND

The accurate identification and isolation of ovarian stem cells from mammalian ovaries remain a major challenge because of the lack of specific surface markers and suitable in vitro culture systems. Optimized culture conditions for in vitro expansion of ovarian stem cells would allow for identifying requirements of these stem cells for proliferation and differentiation that would pave the way to uncover role of ovarian stem cells in ovarian pathophysiology. Here, we used three-dimensional (3D) aggregate culture system for enrichment of ovarian stem cells and named them aggregate-derived stem cells (ASCs). We hypothesized that mimicking the ovarian microenvironment in vitro by using an aggregate model of the ovary would provide a suitable niche for the isolation of ovarian stem cells from adult mouse and human ovaries and wanted to find out the main cellular pathway governing the proliferation of these stem cells.

RESULTS

We showed that ovarian aggregates take an example from ovary microenvironment in terms of expression of ovarian markers, hormone secretion and supporting the viability of the cells. We found that aggregates-derived stem cells proliferate in vitro as long-term while remained expression of germline markers. These ovarian stem cells differentiated to oocyte like cells in vitro spontaneously. Transplantation of these stem cells in to chemotherapy mouse ovary could restore ovarian structure. RNA-sequencing analysis revealed that interleukin6 is upregulated pathway in ovarian aggregate-derived stem cells. Our data showed that JAK/Stat3 signaling pathway which is activated downstream of IL6 is critical for ovarian stem cells proliferation.

CONCLUSIONS

We developed a platform that is highly reproducible for in vitro propagation of ovarian stem cells. Our study provides a primary insight into cellular pathway governing the proliferation of ovarian stem cells.

Recent trends and advances in type 1 diabetes therapeutics: A comprehensive review

Type 1 diabetes (T1D) is a chronic autoimmune disease characterized by the destruction of pancreatic β-cells, leading to insulin deficiency. Insulin replacement therapy is the current standard of care for T1D, but it has significant limitations. However, stem cell-based replacement therapy has the potential to restore β-cell function and achieve glycaemic control eradicating the necessity for drugs or injecting insulin externally. While significant progress has been made in preclinical studies, the clinical translation of stem cell therapy for T1D is still in its early stages. In continuation, further research is essentially required to determine the safety and efficacy of stem cell therapies and to develop strategies to prevent immune rejection of stem cell-derived β-cells. The current review highlights the current state of cellular therapies for T1D including, different types of stem cell therapies, gene therapy, immunotherapy, artificial pancreas, and cell encapsulation being investigated, and their potential for clinical translation.

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.

IVM Advances for Early Antral Follicle-Enclosed Oocytes Coupling Reproductive Tissue Engineering to Inductive Influences of Human Chorionic Gonadotropin and Ovarian Surface Epithelium Coculture

In vitro maturation (IVM) is not a routine assisted reproductive technology (ART) for oocytes collected from early antral (EA) follicles, a large source of potentially available gametes. Despite substantial improvements in IVM in the past decade, the outcomes remain low for EA-derived oocytes due to their reduced developmental competences. To optimize IVM for ovine EA-derived oocytes, a three-dimensional (3D) scaffold-mediated follicle-enclosed oocytes (FEO) system was compared with a validated cumulus-oocyte complex (COC) protocol. Gonadotropin stimulation (eCG and/or hCG) and/or somatic cell coculture (ovarian vs. extraovarian-cell source) were supplied to both systems. The maturation rate and parthenogenetic activation were significantly improved by combining hCG stimulation with ovarian surface epithelium (OSE) cells coculture exclusively on the FEO system. Based on the data, the paracrine factors released specifically from OSE enhanced the hCG-triggering of oocyte maturation mechanisms by acting through the mural compartment (positive effect on FEO and not on COC) by stimulating the EGFR signaling. Overall, the FEO system performed on a developed reproductive scaffold proved feasible and reliable in promoting a synergic cytoplasmatic and nuclear maturation, offering a novel cultural strategy to widen the availability of mature gametes for ART.

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.

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

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

Ex vivo purging of cancer cells from ovarian tissue using photodynamic therapy: a novel strategy to restore fertility in leukemia patients

STUDY QUESTION

Is it possible to purge leukemia cells from ovarian tissue (OT) fragments before transplantation?

SUMMARY ANSWER

Our photodynamic therapy (PDT) approach has been shown to efficiently destroy leukemia cells from tumor-infiltration mimicking models (TIMs), indicating the feasibility of this technique to purge OT samples.

WHAT IS KNOWN ALREADY

Autotransplantation of cryopreserved OT is the most suitable option to preserve fertility for prepubertal girls and women who require immediate cancer treatment. Up until now, more than 200 live births have already been reported after OT cryopreservation and transplantation. Leukemia is the 12th most common cancer in Europe among prepubertal girls and women of reproductive age and in 2020, the estimated number of new leukemia cases was higher than 33 000 in girls between 0 and 19 years old. Unfortunately, once their health has been restored, autotransplantation of cryopreserved OT for leukemia patients is not advised due to the high risk of transferring malignant cells back to the patient leading to leukemia recurrence.

STUDY DESIGN SIZE DURATION

To safely transplant the OT from leukemia patients and restore their fertility, our goal was to develop a PDT strategy to eliminate leukemia ex vivo. To this end, we designed OR141-loaded niosomes (ORN) to create the most effective formulation for ex vivo purging of acute myelogenous leukemia cells from OT fragments (n = 4). Moreover, to ensure that such treatments are not harmful to follicle survival and development so they can be deemed a potential fertility restoration alternative, the effect of the ORN-based PDT purging procedure on follicles was assessed after xenografting the photodynamic-treated OT in SCID mice (n = 5). The work was carried out between September 2020 and April 2022 at the Catholic University of Louvain.

PARTICIPANTS/MATERIALS SETTING METHODS

After establishing the best ORN formulation, our PDT approach was used to eradicate HL60 cells from ex vivo TIMs prepared by microinjection of a cancer cell suspension into OT fragments. The purging efficiency was analyzed by droplet digital polymerase chain reaction and immunohistochemical analyses. Additionally, we evaluated the effect of ORN-based PDT on follicle density, survival and development, and tissue quality in terms of fibrotic areas and vascularization after 7-day xenotransplantation to immunodeficient mice.

MAIN RESULTS AND THE ROLE OF CHANCE

The ex vivo purging of TIMs demonstrated that our PDT strategy could selectively eradicate the malignant cells from tissue fragments without affecting OT normal cells, as evidenced by PCR and immunohistochemical analysis. Regarding the effect of our PDT approach on follicle population and OT quality, our results after xenotransplantation revealed no significant difference between the follicle density of control (non-treated, grafted OT) and PDT-treated groups (2.38 ± 0.63 and 3.21 ± 1.94 morphologically normal follicles/mm², respectively). In addition, our findings showed that the control and PDT-treated OT could be equally vascularized (7.65 ± 1.45% and 9.89 ± 2.21%, respectively). Similarly, the proportions of fibrotic area did not differ between the control (15.96 ± 5.94%) and PDT-treated groups (13.32 ± 3.05%).

LARGE SCALE DATA

N/A.

LIMITATIONS REASONS FOR CAUTION

This study did not use OT fragments from leukemia patients, but TIMs created after injection of HL60 cells into OT from healthy patients. Therefore, while the results are promising, whether our PDT approach will be equally successful in eliminating malignant cells from leukemia patients remains to be assessed.

WIDER IMPLICATIONS OF THE FINDINGS

Our results showed that the purging procedure causes no significant impairment effect on follicle development and tissue quality, suggesting that our novel PDT procedure could be a promising strategy to destroy leukemia cells in fragments of OT, allowing safe transplantation in cancer survivors.

STUDY FUNDING/COMPETING INTERESTS

This study was supported by grants from the Fonds National de la Recherche Scientifique de Belgique (FNRS-PDR Convention grant number T.0004.20 awarded to C.A.A.); Fondation Louvain (awarded to C.A.A.; a Ph.D. scholarship awarded to S.M., as part of a legacy from Mr Frans Heyes, and a Ph.D. scholarship awarded to A.D. as part of a legacy from Mrs. Ilse Schirmer); and Foundation Against Cancer (grant number 2018-042 awarded to A.C.). The authors declare no competing interests.

Photodynamic therapy using OR141-loaded nanovesicles for eradication of leukemic cells from ovarian tissue

In 2020, the estimated number of new leukemia cases was higher than 30,000 in girls between 0 and 19 years old. Due to cancer treatment, some of these patients may lose both endocrine and reproductive functions. Transplantation of cryopreserved ovarian tissue is not advised after cancer remission because it has a high risk of reintroducing malignant cells in the patient, potentially leading to leukemia recurrence. To safely transplant the ovarian tissue from these patients and restore their fertility, our goal was to develop a photodynamic therapy (PDT) strategy to eliminate leukemia ex vivo. To this end, we designed, optimized, and characterized OR141-loaded niosomes (ORN) to develop the most effective formulation for ex vivo purging ovarian fragments from chronic myelogenous leukemia cells. After establishing the best ORN formulation, the PDT efficiency of optimized ORN was determined for human ovarian stromal cells and acute myeloid leukemia cell line (HL60). Blank niosomes treatment on ovarian stromal cells causes no significant toxicity, showing that the composition of the nanoparticle is not toxic. On the other hand, the in vitro studies showed that while ovarian stromal cells were still viable (82.04 ± 2.79%) after the treatment by 0.5 µM ORN, the same treatment yielded 95.43 ± 3.89% toxicity and cell death in the cancer cells. In conclusion, our results showed that our novel PDT procedure could be a promising strategy to destroy leukemia cells in ovarian tissue fragments allowing safe transplantation in cancer survivors.

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.

Does the ovarian surface epithelium differentiate into primordial follicle and primary follicle precursor structures?

Purpose: The aim of this study is to investigate the differentiation capacity of ovarian surface epithelial cells both in cell culture conditions and in ovarian tissue sections. Materials and Methods: The ovaries of two prepubertal (4 weeks old) female rats were divided into small pieces and explant cell culture was created. Ovarian surface epithelium proliferating together with ovarian stromal cells in mixed cell culture was isolated and reproduced. In addition, ovarian surface epithelium was examined in histological sections of ovarian tissue and images were taken under the microscope. Results: The morphological appearance of the ovarian surface epithelium was found to be cobblestone. In the count performed under phase contrast microscopy, it was observed that 2x106 and 3x106 cells were grown in the culture dishes, respectively. Primordial follicle-like structures were observed in some areas of the petri dishes. On the histological sections, primordial and primary follicle precursor structures were observed on the basement membrane. Conclusion: Showing oocyte markers (Gdf-9, C-Mos, Zpc, Stella) and germ cell markers (Dazl, Vasa, Blimp1, Fragilis) both in cell cultures and in histological sections can give us valuable information in terms of monitoring the differentiation capacity of these cells.

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.

Immunolocalization of melatonin receptor type 1 in the sheep ovary and involvement of the PI3K/Akt/FOXO3a signaling pathway in the effects of melatonin on survival and in vitro activation of primordial follicles

This study characterized the expression of melatonin receptor type 1 (MT₁ ) protein in sheep ovaries, evaluated melatonin effects on primordial follicle survival and development after in vitro culture of ovarian tissue and verified the possible involvement of the phosphatidylinositol-3-kinase/protein kinase B/forkhead box O3a (PI3K/Akt/FOXO3a) pathway in the melatonin actions. Ovine ovarian fragments were cultured in α-modified minimum essential medium alone (α-MEM⁺ ) or supplemented with 100, 500, or 1000 pg/ml melatonin for 7 days. PI3K inhibition was performed through pretreatment of ovarian fragments with LY294002. Thereafter, immunohistochemistry was performed to evaluate the expression of cleaved caspase-3, Akt, phosphorylated-Akt, and phosphorylated-FOXO3a (p-FOXO3a). The immunohistochemical localization of the MT₁ receptor protein was documented in sheep preantral and antral follicles. After in vitro culture, 100 pg/ml melatonin showed higher follicular survival and activation than α-MEM⁺ and other melatonin concentrations. After PI3K inhibition, there was an increase in cleaved caspase-3-positive follicles, and a decrease in the primordial follicle activation, Akt phosphorylation, and nuclear exclusion of p-FOXO3a. In conclusion, MT₁ receptor protein is present in the sheep ovary. Furthermore, 100 pg/ml melatonin maintains survival and stimulates activation of primordial follicles through the PI3K/Akt/FOXO3a signaling pathway after in vitro culture of sheep ovarian tissue.

History of fertility preservation

Background: Fertility preservation refers to a procedure performed to maintain the ability to become pregnant before receiving treatment with a risk of fertility loss, such as chemo- or radiation therapy. Examples of fertility-preserving procedures include freezing, sperm freezing, embryo freezing through in vitro fertilization, and ovarian tissue freezing.Current Concepts: Until the late 1990s, awareness of fertility preservation among clinicians and patients was relatively low, and the only way to preserve and restore fertility in women with cancer was the cryopreservation of embryos. However, as the survival rate of cancer patients increased and the treatment results of various diseases improved, interest in quality of life such as pregnancy and childbirth after treatment gradually increased, and became a driving force for the development of fertility preservation. In the 2000s, several centers began cryopreserving ovarian tissue, including primordial follicles from young patients before chemotherapy. Currently, ovarian tissue cryopreservation can be used in combination with in vitro maturation and egg vitrification techniques. Novel methods to improve follicle survival after transplantation are currently being investigated. Methods to improve follicle survival after transplantation and new ovarian protective agents to protect the ovaries from cytotoxic agents are currently being studied.Discussion and Conclusion: Advances in fertility-preserving technologies in the future will contribute to the delivery of healthy children by providing tailored treatments and more individualized fertility-preserving strategies to patients whose fertility is at risk.

MYO10 promotes transzonal projection (TZP)-dependent germ line-somatic contact during mammalian folliculogenesis

Granulosa cells of growing ovarian follicles elaborate filopodia-like structures termed transzonal projections (TZPs) that supply the enclosed oocyte with factors essential for its development. Little is known, however, of the mechanisms underlying the generation of TZPs. We show in mouse and human that filopodia, defined by an actin backbone, emerge from granulosa cells in early-stage primary follicles and that actin-rich TZPs become detectable as soon as a space corresponding to the zona pellucida appears. mRNA encoding Myosin10 (MYO10), a motor protein that accumulates at the base and tips of filopodia and has been implicated in their initiation and elongation, is present in granulosa cells and oocytes of growing follicles. MYO10 protein accumulates in foci located mainly between the oocyte and innermost layer of granulosa cells, where it co-localizes with actin. In both mouse and human, the number of MYO10 foci increases as oocytes grow, corresponding to the increase in the number of actin-TZPs. RNAi-mediated depletion of MYO10 in cultured mouse granulosa cell-oocyte complexes is associated with a 52% reduction in the number of MYO10 foci and a 28% reduction in the number of actin-TZPs. Moreover, incubation of cumulus-oocyte complexes in the presence of epidermal growth factor, which triggers a 93% reduction in the number of actin-TZPs, is associated with a 55% reduction in the number of MYO10 foci. These results suggest that granulosa cells possess an ability to elaborate filopodia, which when directed towards the oocyte become actin-TZPs, and that MYO10 increases the efficiency of formation or maintenance of actin-TZPs.

Therapeutic Potential of In Vitro-Derived Oocytes for the Restoration and Treatment of Female Fertility

Considerable progress has been made with the development of culture systems for the in vitro growth and maturation (IVGM) of oocytes from the earliest-staged primordial follicles and from the more advanced secondary follicles in rodents, ruminants, nonhuman primates, and humans. Successful oocyte production in vitro depends on the development of a dynamic culture strategy that replicates the follicular microenvironment required for oocyte activation and to support oocyte growth and maturation in vivo while enabling the coordinated and timely acquisition of oocyte developmental competence. Significant heterogeneity exists between the culture protocols used for different stages of follicle development and for different species. To date, the fertile potential of IVGM oocytes derived from primordial follicles has been realized only in mice. Although many technical challenges remain, significant advances have been made, and there is an increasing consensus that complete IVGM will require a dynamic, multiphase culture approach. The production of healthy offspring from in vitro-produced oocytes in a secondary large animal species is a vital next step before IVGM can be tested for therapeutic use in humans.

Oocyte quality following in vitro follicle development†

In vitro follicle development (IVFD) is an adequate model to obtain basic knowledge of folliculogenesis and provides a tool for ovarian toxicity screening. IVFD yielding competent oocytes may also offer an option for fertility and species preservation. To promote follicle growth and oocyte maturation in vitro, various culture systems are utilized for IVFD in rodents, domestic animals, wild animals, nonhuman primates, and humans. Follicle culture conditions have been improved by optimizing gonadotropin levels, regulatory factors, nutrient supplements, oxygen concentration, and culture matrices. This review summarizes quality assessment of oocytes generated from in vitro-developed antral follicles from the preantral stage, including oocyte epigenetic and genetic profile, cytoplasmic and nuclear maturation, preimplantation embryonic development following in vitro fertilization, as well as pregnancy and live offspring after embryo transfer. The limitations of oocyte quality evaluation following IVFD and the gaps in our knowledge of IVFD to support proper oocyte development are also discussed. The information may advance our understanding of the requirements for IVFD, with a goal of producing competent oocytes with genetic integrity to sustain embryonic development resulting in healthy offspring.

Aloe vera increases collagen fibres in extracellular matrix and mRNA expression of peroxiredoxin-6 in bovine ovarian cortical tissues cultured in vitro

In vitro culture of ovarian tissue containing primordial follicles is an important tool to study the initiation of follicular populations and to develop efficient culture systems to support in vitro follicle growth. Considering that in vitro culture favours oxidative stress, it is very important to supplement culture medium with antioxidant substances such as Aloe vera extract. This study aims to evaluate the effects of different concentrations of Aloe vera on the distribution of collagen fibres in the extracellular matrix, follicular activation, development and survival in bovine ovarian cortical tissues cultured in vitro, as well as on expression of mRNAs for antioxidant enzymes [superoxide dismutase (SOD), catalase (CAT), peroxiredoxin 6 (PRDX6) and glutathione peroxidase 1 (GPX1)]. To this end, ovarian cortical tissues were cultured for 6 days in α-MEM alone or supplemented with different concentrations of Aloe vera extract (1.0, 5.0, 10.0 or 50.0%). After culture, fragments were fixed and processed histologically to evaluate follicular morphology and activation, as well as the extracellular matrix by staining with picrosirius red. The levels of mRNA for SOD, CAT, PRDX6 and GPX1 in cultured ovarian tissues were evaluated by real-time polymerase chain reaction (PCR). Ovarian tissues cultured with 10.0 or 50.0% Aloe vera had higher percentages of collagen fibres than tissues cultured in control medium. A significant increase in developing follicles was observed in ovarian tissues cultured in α-MEM alone or supplemented with 10% Aloe vera when compared with fresh control or tissues cultured with 1.0% Aloe vera. Presence of Aloe vera did not influence the percentage of morphologically normal follicles when compared with control medium. Ovarian tissues cultured with 50.0% Aloe vera had higher percentages of morphologically normal follicles than those cultured with 10.0% Aloe vera. Furthermore, 10% Aloe vera significantly increased mRNA levels for PRDX6. In conclusion, 10.0% Aloe vera improves extracellular matrix distribution in cultured tissues and increases the expression of mRNA for PRDX6 after 6 days in vitro.

Ovarian extracellular matrix-based hydrogel for human ovarian follicle survival in vivo: A pilot work

To successfully assemble a bio-engineered ovary, we need to create a three-dimensional matrix able to accommodate isolated follicles and cells. The goal of this study was to develop an extracellular matrix hydrogel (oECM) derived from decellularized bovine ovaries able to support, in combination with alginate, human ovarian follicle survival and growth in vitro. Two different hydrogels (oECM1, oECM2) were produced and compared in terms of decellularization efficiency (dsDNA), ECM preservation (collagen and glycosaminoglycan levels), ultrastructure, rigidity, and cytotoxicity. oECM2 showed significantly less dsDNA, greater retention of glycosaminoglycans and better rigidity than oECM1. Isolated human ovarian follicles were then encapsulated in four selected hydrogel combinations: (1) 100% oECM2, (2) 90% oECM2 + 10% alginate, (3) 75% oECM2 + 25% alginate, and (4) 100% alginate. After 1 week of in vitro culture, follicle recovery rate, viability, and growth were analyzed. On day 7 of in vitro culture, follicle recovery rates were 0%, 23%, 65%, 82% in groups 1-4, respectively, rising proportionally with increased alginate content. However, there was no difference in follicle viability or growth between groups 2 and 3 and controls (group 4). In conclusion, since pure alginate cannot be used to graft preantral follicles due to its poor revascularization and degradation after grafting, oECM2 hydrogel combined with alginate may provide a new and promising alternative to graft isolated human follicles in a bio-engineered ovary.

In Vitro Folliculogenesis in Mammalian Models: A Computational Biology Study

In vitro folliculogenesis (ivF) has been proposed as an emerging technology to support follicle growth and oocyte development. It holds a great deal of attraction from preserving human fertility to improving animal reproductive biotechnology. Despite the mice model, where live offspring have been achieved,in medium-sized mammals, ivF has not been validated yet. Thus, the employment of a network theory approach has been proposed for interpreting the large amount of ivF information collected to date in different mammalian models in order to identify the controllers of the in vitro system. The WoS-derived data generated a scale-free network, easily navigable including 641 nodes and 2089 links. A limited number of controllers (7.2%) are responsible for network robustness by preserving it against random damage. The network nodes were stratified in a coherent biological manner on three layers: the input was composed of systemic hormones and somatic-oocyte paracrine factors; the intermediate one recognized mainly key signaling molecules such as PI3K, KL, JAK-STAT, SMAD4, and cAMP; and the output layer molecules were related to functional ivF endpoints such as the FSH receptor and steroidogenesis. Notably, the phenotypes of knock-out mice previously developed for hub.BN indirectly corroborate their biological relevance in early folliculogenesis. Finally, taking advantage of the STRING analysis approach, further controllers belonging to the metabolic axis backbone were identified, such as mTOR/FOXO, FOXO3/SIRT1, and VEGF, which have been poorly considered in ivF to date. Overall, this in silico study identifies new metabolic sensor molecules controlling ivF serving as a basis for designing innovative diagnostic and treatment methods to preserve female fertility.

Disparities in Female Pediatric, Adolescent and Young Adult Oncofertility: A Needs Assessment

Advancements in cancer screening and implementation of targeted treatments have significantly improved survival rates to 85% for pediatric and AYA survivors. Greater than 75% of survivors will live to experience the long-term adverse outcomes of cancer therapies, termed late effects (LE), that disrupt quality of life (QoL). Infertility and poor reproductive outcomes are significant disruptors of QoL in survivorship, affecting 12-88% of survivors who receive at-risk therapies. To mitigate risk, fertility preservation (FP) counseling is recommended as standard of care prior to gonadotoxic therapy. However, disparities in FP counseling, implementation of FP interventions, and screening for gynecologic late effects in survivorship persist. Barriers to care include a lack of provider and patient knowledge of the safety and breadth of current FP options, misconceptions about the duration of time required to implement FP therapies, cost, and health care team bias. Developing strategies to address barriers and implement established guidelines are necessary to ensure equity and improve quality of care across populations.

Mechanobiology of the female reproductive system

BACKGROUND

Mechanobiology in the field of human female reproduction has been extremely challenging technically and ethically.

METHODS

The present review provides the current knowledge on mechanobiology of the female reproductive system. This review focuses on the early phases of reproduction from oocyte development to early embryonic development, with an emphasis on current progress.

MAIN FINDINGS RESULTS

Optimal, well-controlled mechanical cues are required for female reproductive system physiology. Many important questions remain unanswered; whether and how mechanical imbalances among the embryo, decidua, and uterine muscle contractions affect early human embryonic development, whether the biomechanical properties of oocytes/embryos are potential biomarkers for selecting high-quality oocytes/embryos, whether mechanical properties differ between the two major compartments of the ovary (cortex and medulla) in normally ovulating human ovaries, whether durotaxis is involved in several processes in addition to embryonic development. Progress in mechanobiology is dependent on development of technologies that enable precise physical measurements.

CONCLUSION

More studies are needed to understand the roles of forces and changes in the mechanical properties of female reproductive system physiology. Recent and future technological advancements in mechanobiology research will help us understand the role of mechanical forces in female reproductive system disorders/diseases.

How will our understanding of human development evolve over the next 10 years

In the next 10 years, the continued exploration of human embryology holds promise to revolutionize regenerative and reproductive medicine with important societal consequences. In this Comment we speculate on the evolution of recent advances made and describe emerging technologies for basic research, their potential clinical applications, and, importantly, the ethical frameworks in which they must be considered.

Assessment of cGMP level in medium during in vitro growth period of murine preantral follicles with and without supplementation of C-type natriuretic peptide

To enhance the developmental competency of murine ovarian follicles cultured in vitro, C-type natriuretic peptide (CNP) was supplemented in the culture system. Although the mechanism is not fully elucidated, it was reported that the effect of CNP supplementation was mediated by increased cyclic guanosine monophosphate (cGMP). In the present study, cGMP levels in media for murine preantral follicle culture were compared both between a control group without CNP supplementation and an experimental group with CNP supplementation and between days in each group. In addition, follicle growth patterns and oocyte maturity were assessed and compared between the two groups. Results demonstrated that along with in vitro culture, cGMP levels increased (P < 0.05) both in the control group and the experimental group, whereas cGMP levels were not significantly different between the two groups on the same day of in vitro culture (P > 0.05). The oocyte's maturity was superior in the experimental group compared with the control group (P < 0.05). As ovarian follicles grew three-dimensionally in the experimental group but were flattened in the control group, CNP might improve oocyte maturity through maintaining the three-dimensional architecture of the ovarian follicle because of increased transzonal projections (TZP) and functional gap junctions between oocyte and surrounding granulosa cells.

Recent advances: fertility preservation and fertility restoration options for males and females

Fertility preservation is the process of saving gametes, embryos, gonadal tissues and/or gonadal cells for individuals who are at risk of infertility due to disease, medical treatments, age, genetics, or other circumstances. Adult patients have the options to preserve eggs, sperm, or embryos that can be used in the future to produce biologically related offspring with assisted reproductive technologies. These options are not available to all adults or to children who are not yet producing mature eggs or sperm. Gonadal cells/tissues have been frozen for several thousands of those patients worldwide with anticipation that new reproductive technologies will be available in the future. Therefore, the fertility preservation medical and research communities are obligated to responsibly develop next-generation reproductive technologies and translate them into clinical practice. We briefly describe standard options to preserve and restore fertility, but the emphasis of this review is on experimental options, including an assessment of readiness for translation to the human fertility clinic.

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.

In Vitro Activation Early Follicles: From the Basic Science to the Clinical Perspectives

Development of early follicles, especially the activation of primordial follicles, is strictly modulated by a network of signaling pathways. Recent advance in ovarian physiology has been allowed the development of several therapies to improve reproductive outcomes by manipulating early folliculogenesis. Among these, in vitro activation (IVA) has been recently developed to extend the possibility of achieving genetically related offspring for patients with premature ovarian insufficiency and ovarian dysfunction. This method was established based on basic science studies of the intraovarian signaling pathways: the phosphoinositide 3-kinase (PI3K)/Akt and the Hippo signaling pathways. These two pathways were found to play crucial roles in folliculogenesis from the primordial follicle to the early antral follicle. Following the results of rodent experiments, IVA was implemented in clinical practice. There have been multiple recorded live births and ongoing pregnancies. Further investigations are essential to confirm the efficacy and safety of IVA before used widely in clinics. This review aimed to summarize the published literature on IVA and provide future perspectives for its improvement.

Epidermal growth factor receptor signaling uncouples germ cells from the somatic follicular compartment at ovulation

Germ cells are physically coupled to somatic support cells of the gonad during differentiation, but this coupling must be disrupted when they are mature, freeing them to participate in fertilization. In mammalian females, coupling occurs via specialized filopodia that project from the ovarian follicular granulosa cells to the oocyte. Here, we show that signaling through the epidermal growth factor receptor (EGFR) in the granulosa, which becomes activated at ovulation, uncouples the germ and somatic cells by triggering a massive and temporally synchronized retraction of the filopodia. Although EGFR signaling triggers meiotic maturation of the oocyte, filopodial retraction is independent of the germ cell state, being regulated solely within the somatic compartment, where it requires ERK-dependent calpain-mediated loss of filopodia-oocyte adhesion followed by Arp2/3-mediated filopodial shortening. By uncovering the mechanism regulating germ-soma uncoupling at ovulation, our results open a path to improving oocyte quality in human and animal reproduction.

Preservation of connexin 43 and transzonal projections in isolated bovine pre-antral follicles before and following vitrification

PURPOSE

Gap junctions and transzonal projections play a crucial role in intercellular communication between different follicular components and are necessary for follicle development. We aimed to demonstrate gap junction protein connexin 43 (Cx43) and transzonal projections (TZPs) in viable, category 1, isolated bovine pre-antral follicles (PAFs) during short-term culture and after vitrification and warming.

METHODS

This study involved four experimental groups: fresh control, 2-day culture, 4-day culture, and vitrified secondary PAFs. Isolated PAFs were vitrified using a simple and efficient cryopreservation method by means of mini cell strainers.

RESULTS

Cx43 and TZPs were detected in pre-antral follicles of all stages, as well as in every experimental group. The group fresh follicles showed a higher percentage of follicles that were positive for Cx43 (91.7%) than the follicles that were vitrified (77.4%). All follicles that were cultured for 2 days were Cx43-positive (100%). Follicles cultured for 4 days (65.8%) (P = 0.002) showed the lowest percentage of follicles that were Cx43-positive. The percentages of the presence or (partial) absence of the TZP network were shown to be very heterogeneous between follicles in different treatment groups.

CONCLUSIONS

These results suggest the maintenance of communication between the oocyte and the somatic companion cells after vitrification and warming. The varying percentages of the expression of the TZP network within groups suggests that it will be of interest to investigate whether this is truly due to variability in TZP integrity and follicle quality or due to methodological limitations.

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.

Fertility Preservation: The Challenge of Freezing and Transplanting Ovarian Tissue

Cancer treatments are increasingly effective, but can result in iatrogenic premature ovarian insufficiency. Ovarian tissue cryopreservation is the only option available to preserve fertility in prepubertal girls and young women who require immediate chemotherapy. Ovarian tissue transplantation has been shown to restore hormonal cycles and fertility, but a large proportion of the follicle reserve is lost as a consequence of exposure to hypoxia. Another crucial concern is the risk of reimplanting malignant cells together with the grafted tissue. In this review, the authors advance some challenging propositions, from prevention of chemotherapy-related gonadotoxicity to ovarian tissue cryopreservation and transplantation, including the artificial ovary approach.

Ovarian tissue cryopreservation and novel bioengineering approaches for fertility preservation

PURPOSE OF REVIEW

Breast cancer patients who cannot delay treatment or for whom hormone stimulation and egg retrieval are contraindicated require alternative methods of fertility preservation prior to gonadotoxic treatment. Ovarian tissue cryopreservation is an alternative approach that may offer patients the opportunity to preserve fertility and carry biologically-related children later in life. Various experimental approaches are being explored to obtain mature gametes from cryopreserved and thawed ovarian tissue for fertilization and implantation using biomimetic tissue culture in vitro. Here we review the most recent developments in ovarian tissue cryopreservation and exciting advances in bioengineering approaches to in vitro tissue and ovarian follicle culture.

RECENT FINDINGS

Slow freezing is the most widely accepted method for ovarian tissue cryopreservation, but efforts have been made to modify vitrification for this application as well. Numerous approaches to in vitro tissue and follicle culture are in development, most prominently two-step culture systems for ovarian cortical tissue and encapsulation of ovarian follicles in biomimetic matrices for in vitro culture.

SUMMARY

Refinements to slow freeze and vitrification protocols continue to address challenges associated with cryopreservation, such as ice crystal formation and damage to the stroma. Similarly, improvements to in vitro tissue and follicle culture show promise for utilizing patients' cryopreserved tissues to obtain mature gametes after disease treatment and remission. Development of an effective and reproducible culture system for human ovarian follicles will serve as a broad assisted reproductive technology for cancer survivors who cryopreserved tissue prior to treatment.

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.

Supplementation of c-type natriuretic peptide during in vitro growth period benefits the development of murine preantral follicles

The present study investigated the effects of c-type natriuretic peptide (CNP) on the development of murine preantral follicles during in vitro growth (IVG). Preantral follicles isolated from ovaries of Kunming mice were cultured in vitro. In the culture system, CNP was supplemented in the experimental groups and omitted in the control groups. In Experiment 1, CNP was only supplemented at the early stage and follicle development was evaluated. In Experiments 2 and 3, CNP was supplemented during the whole period of in vitro culture. In Experiment 2, follicle development and oocyte maturity were evaluated. In Experiment 3, follicle development and embryo cleavage after in vitro fertilization (IVF) were assessed. The results showed that in the control groups in all three experiments, granulosa cells migrated from within the follicle and the follicles could not reach the antral stage. In the experimental groups in all three experiments, no migration of granulosa cells was observed and follicle development was assessed as attaining the antral stage, which was significantly superior to that of the control group (P < 0.0001). Oocyte meiotic arrest was effectively maintained, hence giving good developmental competence. In conclusion, CNP supplementation in the culture system during IVG benefited the development of murine preantral follicles.

In-vitro fragmentation of ovarian tissue activates primordial follicles through the Hippo pathway

STUDY QUESTION

What is the role of the Hippo and PI3K/Akt pathway in follicles during ovarian tissue culture in tissue derived from oncological patients and transgender men?

SUMMARY ANSWER

Results highlight a Hippo pathway driven primordial follicle activation in vitro, predominantly from Day 0 to Day 4.

WHAT IS KNOWN ALREADY

In-vitro ovarian tissue culture aims at activating and maturing primordial follicles for fertility restoration in patients with a threatened ovarian reserve. Not all patients are eligible for ovarian cortex transplantation and therefore several groups are attempting to culture ovarian tissue in-vitro. Cortex fragmentation disrupts the Hippo pathway, leading to increased expression of downstream growth factors and follicle growth. The PI3K/Akt pathway is considered the intracellular pathway to where different extracellular factors involved in primordial follicle activation in-vivo converge. In order to optimise current ovarian tissue culture models, information on progression of these pathways during tissue culture is mandatory.

STUDY DESIGN SIZE DURATION

The first step of a multistep cortex culture system was performed using 144 ovarian cortex pieces from a total of six patients. Per patient, 24 cortical strips were cultured for 6 days and six pieces per patient were collected for downstream analysis of follicle development and Hippo and PI3K/Akt pathway targets every second day.

PARTICIPANTS/MATERIALS SETTING METHODS

Ovarian tissue was obtained from oncological (N = 3; 28.67 ± 4.51 years) and transgender (N = 3; 23.33 ± 1.53 years) patients. Follicles were analysed using haematoxylin-eosin staining and pathways were studied using immunohistochemistry and precise follicle excision by laser capture micro-dissection for RT-qPCR analysis. MIQE guidelines for RT-qPCR were pursued. Reference gene selection (GAPDH, RPL3A, 18s rRNA) was performed using GeNorm Reference Gene Selection Kit. Statistical analysis was conducted with IBM SPSS Statistics 23 (Poisson regression, negative binomial regression, ANOVA and paired t-test).

MAIN RESULTS AND THE ROLE OF CHANCE

Immunohistochemical analysis confirmed a Hippo pathway driven primordial follicle activation due to mechanical manipulation of the cortical strips. Ovarian tissue preparation and culture induced the inhibitory phosphorylated Yes-associated protein (pYAP) to disappear in granulosa cells of primordial follicles on Day 2. The stimulatory YAP on the contrary appeared in primordial granulosa cells over increasing culture days. Looking at the YAP target connective tissue growth factor (CTGF), a significantly up-regulated CTGF was noted in primordial follicles when comparing Day 2 and Day 4 (ratio Day 2/4 = 0.082; P < 0.05), clearly showing an effect on the Hippo pathway in primordial follicles during tissue culture. Follicle classification showed a significant drop in estimated primordial follicle counts in the oncological cohort (-78%; P = 0.021) on Day 2 and in the transgender cohort on Day 4 (-634%; P = 0.008). Intermediate follicle counts showed a non-significant increasing trend to during culture and this follicle recruitment and growth resulted in a significant rise in estimated primary follicle counts on Day 6 in oncological patients (170%; P = 0.025) and, although limited in absolute numbers, a significant increase in secondary follicles on Day 4 (367%; P = 0.021) in the transgender cohort. Subsequent antral follicle development could not be observed.

LIMITATIONS REASONS FOR CAUTION

A limitation is the small sample size, inherent to this study subject, especially as a large amount of tissue was needed per patient to reduce inter-patient variation in different downstream analysis techniques. A particular and specific weakness of this study is the inability to include an age-matched control group.

WIDER IMPLICATIONS OF THE FINDINGS

These findings support an adapted tissue preparation for Hippo pathway disruption and a shorter first phase of tissue culture. This work may also have implications for transplantation of cryopreserved tissue as larger strips (and thus slower burnout due to less Hippo pathway disruption) could be a benefit.

STUDY FUNDING/COMPETING INTERESTS

This research was financially supported by the Foundation Against Cancer (Stichting tegen Kanker, TBMT001816N), the Flemish Foundation of Scientific Research (FWO Vlaanderen, FWO G0.065.11N10) and the Gender Identity Research and Education Society (GIRES) foundation. The authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.