In vitro culture methods of preantral follicles

In vitro production of meiotically competent oocytes from early antral follicles in sheep

The potential of using long in vitro culture (LIVC) of cumulus-oocyte complexes (COCs) from early antral follicles (EAFs) as an assisted reproductive technology in cattle has shown promising results. This study explored the feasibility of applying this technology to sheep as seasonal breeding animals. Ovaries from sheep were collected during both the breeding and non-breeding seasons. COCs were isolated from EAFs (350-450 μm) and cultured in TCM199 medium supplemented with 0.15 μg/mL Zn sulfate, 10-4IU/mL FSH, 10 ng/mL estradiol, 50 ng/mL testosterone, 50 ng/mL progesterone, and 5 μM Cilostamide. After five days of LIVC, the COCs were submitted to an in vitro maturation procedure. The results indicate successful in vitro development of COCs, evidenced by a significant increase in oocyte diameter (p < 0.000) and the preservation of gap junction communication between oocyte and cumulus cells. The gradual uncoupling was accompanied by a progressive chromatin transition from the non-surrounded nucleolus (NSN) to the surrounded nucleolus (SN) (p < 0.000), coupled with a gradual decrease in global transcriptional activity and an increase in oocyte meiotic competence (p < 0.000). Maintenance of oocyte-cumulus investment architecture, viability, and metaphase II capability was significantly higher in COCs collected during the breeding season (p < 0.000), suggesting higher quality than those obtained during the non-breeding season. In conclusion, our study confirms LIVC feasibility in sheep, emphasizing increased effectiveness during the breeding season in isolating higher-quality COCs from EAFs. These findings can influence improving the LIVC system in mammals with seasonal reproduction.

Age-associated increased stiffness of the ovarian microenvironment impairs follicle development and oocyte quality and rapidly alters follicle gene expression

In humans, aging triggers cellular and tissue deterioration, and the female reproductive system is the first to show signs of decline. Reproductive aging is associated with decreased ovarian reserve, decreased quality of the remaining oocytes, and decreased production of the ovarian hormones estrogen and progesterone. With aging, both mouse and human ovaries become pro-fibrotic and stiff. However, whether stiffness directly impairs ovarian function, folliculogenesis, and oocyte quality is unknown. To answer this question, we cultured mouse follicles in alginate gels that mimicked the stiffness of reproductively young and old ovaries. Follicles cultured in stiff hydrogels exhibited decreased survival and growth, decreased granulosa cell viability and estradiol synthesis, and decreased oocyte quality. We also observed a reduction in the number of granulosa cell-oocyte transzonal projections. RNA sequencing revealed early changes in the follicle transcriptome in response to stiffness. Follicles cultured in a stiff environment had lower expression of genes related to follicle development and greater expression of genes related to inflammation and extracellular matrix remodeling than follicles cultured in a soft environment. Altogether, our findings suggest that ovarian stiffness directly modulates folliculogenesis and contributes to the progressive decline in oocyte quantity and quality observed in women of advanced maternal age.

In Vitro Growth of Human Follicles: Current and Future Perspectives

Ovarian tissue cryopreservation is gaining importance as a successful method to restore fertility to girls and young women at high risk of sterility. However, there are concerns regarding the safety of transplantation after ovarian tissue cryopreservation due to the high risk of reintroducing cancer cells and causing disease recurrence. In these cases, the development of culture systems that support oocyte development from the primordial follicle stage is required. Notable achievements have been reached in human follicle in vitro growth in the past decade. Currently, systems for the in vitro culture of ovarian tissue are based on two-dimensional substrates that do not support the survival of follicles or recapitulate the mechanical heterogenicity in the mammalian ovary. Recognition of the importance of special arrangements between cells has spurred research in three-dimensional culture systems, and the provision of a precise culture system that maximizes the diffusion of nutrients and gases through the follicles has raised interest in advanced biomimetic models. The current review critically examines various culture systems employed for the in vitro development of follicles, with a particular focus on solutions utilizing Organ-on-a-Chip (OOC) technology. The emphasis on OOC technology underscores its role as a promising avenue in ensuring the successful cultivation and maintenance of follicular structures during the culture period.

A self-gelling hydrogel based on thiolated hyaluronic acid for three-dimensional culture of ovine preantral follicles

Three-dimensional (3D) ovarian follicle culture offers a promising option for fertility preservation in patients who cannot receive ovarian tissue transplantation. Our research evaluated the potential of a hydrogel composed of thiolated hyaluronic acid (HA-SH) for ovine preantral follicle development compared to routinely used alginate hydrogel (ALG). Synthesized via a carbodiimide reaction, HA-SH facilitated a self-crosslinking hydrogel through disulfide bond formation. Ovine preantral follicles (200-300 μm) retrieved through mechanical and enzymatic methods were encapsulated individually in either ALG or HA-SH hydrogels. Although both hydrogels adequately supported follicle survival, 3D integrity, and antrum formation over a 17-day in vitro culture, follicle growth was significantly higher within the HA-SH hydrogel. Gene expression analysis underscored that some folliculogenesis-related genes (ZP3, BMP7, and GJA1) and a steroidogenic gene (CYP19A1) demonstrated higher expression levels in HA-SH encapsulated follicles versus ALG. Collectively, our findings advocate for HA-SH hydrogel as a potent biomaterial for in vitro follicle cultures, attributing its efficacy to facile gelation, bio-responsiveness, and superior support for follicle growth.

Revolutionizing the female reproductive system research using microfluidic chip platform

Comprehensively understanding the female reproductive system is crucial for safeguarding fertility and preventing diseases concerning women's health. With the capacity to simulate the intricate physio- and patho-conditions, and provide diagnostic platforms, microfluidic chips have fundamentally transformed the knowledge and management of female reproductive health, which will ultimately promote the development of more effective assisted reproductive technologies, treatments, and drug screening approaches. This review elucidates diverse microfluidic systems in mimicking the ovary, fallopian tube, uterus, placenta and cervix, and we delve into the culture of follicles and oocytes, gametes' manipulation, cryopreservation, and permeability especially. We investigate the role of microfluidics in endometriosis and hysteromyoma, and explore their applications in ovarian cancer, endometrial cancer and cervical cancer. At last, the current status of assisted reproductive technology and integrated microfluidic devices are introduced briefly. Through delineating the multifarious advantages and challenges of the microfluidic technology, we chart a definitive course for future research in the woman health field. As the microfluidic technology continues to evolve and advance, it holds great promise for revolutionizing the diagnosis and treatment of female reproductive health issues, thus propelling us into a future where we can ultimately optimize the overall wellbeing and health of women everywhere.

Regulation of follicular activation signaling pathways by in vitro inhibition of YAP/TAZ activity in mouse ovaries

The Hippo pathway plays a crucial role in the regulation of follicular activation, which constitutes the first step of the folliculogenesis process. Disruption of this pathway occurs in several non-physiological contexts, after fragmentation for ovarian tissue cryopreservation procedures or chemotherapy exposure, leading to massive follicular growth and depletion. This study aimed to investigate the effect of controlling the Hippo pathway using verteporfin (VERT) during in vitro ovarian culture and to evaluate its potential preventive effects on chemotherapy-induced follicle activation using a mouse model. After exposure of cut ovaries to different concentrations of VERT for 3 h, a dose-dependent effect of VERT was observed that reached significant inhibition of YAP activity at 3 µmol/L. To assess the potential effect of controlling chemotherapy-induced Hippo pathway disruption, whole mouse ovaries were exposed to VERT alone or as a co-treatment with 4-hydroperoxycylophosphamide (4HC). VERT co-treatment prevented chemotherapy-induced YAP activation but had a limited impact on downstream effector gene, Ccn2. Surprisingly, VERT co-treatment also prevented mTOR and survival signaling pathway alterations following chemotherapy exposure. These results suggest an interaction between the two main signaling pathways regulating follicle activation and a protective effect of VERT on 4HC-induced DNA damage.

Reducing 3D Hydrogel Stiffness, Addition of Oestradiol in a Physiological Concentration and Increasing FSH Concentration Improve In Vitro Growth of Murine Preantral Follicles

This study aimed to optimise culture conditions for murine preantral follicles to improve their growth and survival. Preantral follicles (diameter 100-130 µm) were isolated from prepubertal NMRI mice and individually cultured within alginate beads for 12 days. Three conditions were evaluated: (1) follicle re-encapsulation on day 6 of culture-reducing alginate concentration (0.5% to 0.25% w/v), (2) the presence of oestradiol (E2), and (3) increased follicle-stimulating hormone (FSH) concentration in the culture medium (from 10 to 100 mIU/mL FSH). Follicle morphology and growth, as well as anti-Müllerian hormone (AMH) production, were evaluated. From day 8, re-embedded follicles had a larger average diameter compared to follicles without alginate re-encapsulation (0.5% and 0.25% groups, p < 0.05). Oestradiol (1 µM) had a significantly positive effect on the mean follicular diameter and antrum formation (p < 0.001). Moreover, follicles cultured with 100 mIU/mL FSH showed faster growth (p < 0.05) and significantly higher antrum formation (p < 0.05) compared to the low FSH group. Nevertheless, AMH production was not affected by any of the culture conditions. In conclusion, the growth and survival of mouse preantral follicles during a 12-day period were improved by altering the alginate concentration midways during culture and adding E2 and FSH to the culture medium.

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.

The mechanisms that control the preantral to early antral follicle transition and the strategies to have efficient culture systems to promote their growth in vitro

Preantral to early antral follicles transition is a complex process regulated by endocrine and paracrine factors, as well as by a precise interaction among oocyte, granulosa cells and theca cells. Understanding the mechanisms that regulate this step of folliculogenesis is important to improve in vitro culture systems, and opens new perspectives to use oocytes from preantral follicles for assisted reproductive technologies. Therefore, this review aims to discuss the endocrine and paracrine mechanisms that control granulosa cell proliferation and differentiation, formation of the antral cavity, estradiol production, atresia, and follicular fluid production during the transition from preantral to early antral follicles. The strategies that promote in vitro growth of preantral follicles are also discussed.

Novel Approaches Used in Ovarian Tissue Transplantation for Fertility Preservation: Focus on Tissue Engineering Approaches and Angiogenesis Capacity

Due to the impact of the modern lifestyle, female infertility has been reduced because of different reasons. For example, in combined chemotherapeutic therapies, a small fraction of cancer survivors has faced different post-complications and side effects such as infertility. Besides, in modern society, delayed age of childbearing has also affected fertility. Nowadays, ovarian tissue cryopreservation and transplantation (OTC/T) is considered one of the appropriate strategies for the restoration of ovarian tissue and bioactivity in patients with the loss of reproductive function. In this regard, several procedures have been considered to improve the efficacy and safety of OTT. Among them, a surgical approach is used to transplant ovaries into the optimal sites, but the existence of ischemic changes and lack of appropriate revascularization can lead to bulk follicular atresia. Besides, the role of OTC/T is limited in women of advanced maternal age undergoing lifesaving chemo-radiation. As a correlate, the development of de novo approaches with efficacious regenerative outcomes is highly welcomed. Tissue engineering shows high therapeutic potentialities to restore fertility in males and females using the combination of biomaterials, cells, and growth factors. Unfortunately, most synthetic and natural materials are at the experimental stage and only the efficacy has been properly evaluated in limited cases. Along with these descriptions, strategies associated with the induction of angiogenesis in transplanted ovaries can diminish the injuries associated with ischemic changes. In this review, the authors tried to summarize recent techniques, especially tissue engineering approaches for improving ovarian function and fertility by focusing on angiogenesis and neovascularization.

Bone Morphogenetic Protein 15 (BMP-15) Improves In Vitro Mouse Folliculogenesis

Multilayered secondary follicles were encapsulated in a 0.5% alginate matrix and cultured in a 3D culture system supplemented with bone morphogenetic protein 15 (BMP-15; 15 ng/mL) for 12 days. The in vitro development of ovarian follicles was evaluated. On day 12, the follicle diameter, follicle survival rate, and antrum formation rate were significantly higher for follicles cultured in BMP-15-supplemented medium than those cultured in regular medium. The percentage of ovulated metaphase II oocytes retrieved from follicles cultured in BMP-15-supplemented medium was greater than that of oocytes retrieved from follicles cultured in regular medium. The secretion of P4 was significantly higher on days 6, 8, and 10 in follicles cultured in BMP-15-supplemented medium. The result for E2 tended toward significance on day 12. Intracellular reactive oxygen species levels were higher and glutathione levels were lower in mature oocytes from the in vitro culture than in mature oocytes from an in vivo control. A 3D culture system using an alginate matrix and supplemented with BMP-15 effectively improves the outcomes of in vitro ovarian follicle culture.

Simulated microgravity reduces quality of ovarian follicles and oocytes by disrupting communications of follicle cells

Ovarian follicles are the fundamental structures that support oocyte development, and communications between oocytes and follicle somatic cells are crucial for oogenesis. However, it is unknown that whether exposure to microgravity influences cellular communications and ovarian follicle development, which might be harmful for female fertility. By 3D culturing of ovarian follicles under simulated microgravity (SMG) conditions in a rotating cell culture system, we found that SMG treatment did not affect the survival or general growth of follicles but decreased the quality of cultured follicles released oocytes. Ultrastructure detections by high-resolution imaging showed that the development of cellular communicating structures, including granulosa cell transzonal projections and oocyte microvilli, were markedly disrupted. These abnormalities caused chaotic polarity of granulosa cells (GCs) and a decrease in oocyte-secreted factors, such as Growth Differentiation Factor 9 (GDF9), which led to decreased quality of oocytes in these follicles. Therefore, the quality of oocytes was dramatically improved by the supplementations of GDF9 and NADPH-oxidase inhibitor apocynin. Together, our results suggest that exposure to simulated microgravity impairs the ultrastructure of ovarian follicles. Such impairment may affect female fertility in space environment.

Effects and potential mechanism of Ca2+/calmodulin‑dependent protein kinase II pathway inhibitor KN93 on the development of ovarian follicle

Adequate regulation of the speed of follicular development has been reported to prolong the reproductive life of the ovary. The aim of the present study was to assess the potential effects and mechanism of the Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) pathway on the development of ovarian follicle. In the present study, the expression of CaMKII was measured in the ovary of mice at different developmental stages by immunofluorescence, confirming that CaMKII has a role in follicular development. Subsequently, the 17.5 days post-coitus (dpc) embryonic ovaries were collected and cultured with KN93 for 4 days in vitro. It was revealed that KN93 inhibited the development of follicles, where it reduced the expression levels of oocyte and granulosa cell markers DEAD-box helicase 4 (DDX4) and forkhead box L2 (FOXL2). These results suggested that KN93 could delay follicular development. Proteomics technology was then used to find that 262 proteins of KN93 treated 17.5 dpc embryonic ovaries were significantly altered after in vitro culture. Bioinformatics analysis was used to analyze these altered proteins. In total, four important Kyoto Encyclopedia of Genes and Genome pathways, namely steroid biosynthesis, p53 signaling pathway and retinol metabolism and metabolic pathways, were particularly enriched. Further analysis revealed that the upregulated proteins NADP-dependent steroid dehydrogenase-like (Nsdhl), lanosterol synthase (Lss), farnesyl-diphosphate farnesyltransferase 1 (Fdft1), cytochrome P450 family 51 family A member 1 (Cyp51a1), hydroxymethylglutaryl-CoA synthase 1 (Hmgcs1), fatty acid synthase (Fasn) and dimethylallyltranstransferase (Fdps) were directly interacting with each other in the four enriched pathways. In summary, the potential mechanism of KN93 in slowing down follicular development most likely lies in its inhibitory effects on CaMKII, which upregulated the expression of Nsdhl, Lss, Fdft1, Cyp51a1, Hmgcs1, Fasn and Fdps. This downregulated the expression of oocyte and granulosa cell markers DDX4 and FOXL2 in the follicles, thereby delaying follicular development. Overall, these results provide novel insight into the potential mechanism by which KN93 and CaMKII can delay follicular development.

IL-6 of follicular fluid and outcome of in vitro fertilization

The quality of an oocyte is influenced by its microenvironment, which includes cumulus cells and follicular fluid, as well as cells of the immune system and their products. The ovarian interleukins, which are secreted by the granulosa cells and other immune cells within the ovaries and follicles, regulate various functions between the cells. IL-6 is a cytokine that is present in the follicular fluid and may affect the quality of oocytes. There are some inconsistencies in the literature regarding the concentration of interleukin 6 in the follicular fluid. The main objective of this study was to examine whether the concentration of interleukin 6 in the follicular fluid affects the outcome of IVF. This study involved 83 patients who underwent IVF. Follicular fluid was used as the biological material for the analysis. Examination of the obtained follicular fluid and collection of oocytes under a stereomicroscope was performed in the embryological laboratory. The concentration of IL-6 in the follicular fluid was analyzed. IVF and ICSI methods were used as the fertilization methods. Pregnancy was confirmed by the positive serum β-hCG level. The software package SPSS 20 was used for statistical data processing. Analysis of the follicular fluid samples showed a correlation between the concentration of IL-6 in the follicular fluid and the outcome of IVF. The concentration of IL-6 in the follicular fluid was higher in patients with confirmed pregnancy (9.55 ± 7.47 ng/ml). Based on our results, we conclude that the concentration of IL-6 affects the outcome of IVF. If the range of IL-6 concentration is between 3,67 ng/ml and 10 ng/ml, we can expect good IVF outcome with vital pregnancy.

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.

RGD-modified dextran hydrogel promotes follicle growth in three-dimensional ovarian tissue culture in mice

In vitro follicle growth is a promising technology to preserve fertility for cancer patients. We previously developed a three-dimensional (3-D) ovarian tissue culture system supported by mouse tumor cell-derived Matrigel. When murine ovarian tissues at 14 days old were cultured in Matrigel drops, antrum formation and oocyte competence were significantly enhanced compared with those cultured without Matrigel. In this study, we tested whether nonanimal-derived dextran hydrogels can support a 3-D ovarian tissue culture. We employed chemically defined dextran hydrogels consisting of dextran polymers crosslinked with polyethylene glycol (PEG)-based cell-degradable crosslinker. To determine the optimal gel elasticity for the 3-D tissue culture, we measured Young's modulus of dextran hydrogels at four concentrations (1.75, 2.25, 2.75, and 3.25 mmol/L), and cultured ovarian tissues in these gels for 7 days. As a result, 2.25 mmol/L dextran hydrogel with Young's modulus of 224 Pa was appropriate to provide physical support as well as to promote follicle expansion in the 3-D system. To mimic the natural extracellular matrix (ECM) environment, we modified the dextran hydrogels with two bioactive factors: ECM-derived Arg-Gly-Asp (RGD) peptides as a cell-adhesive factor, and activin A. The ovarian tissues were cultured in 2.25 mmol/L dextran hydrogels under four different conditions: Activin-/RGD- (A-R-), A + R-, A-R+, and A + R+. On Day 7 of culture, follicle and oocyte sizes were significantly increased in the RGD-modified conditions compared with those without RGD. The RGD-modified hydrogels also promoted mRNA levels of steroidogenic-related genes and estradiol production in the 3-D ovarian tissue culture. In vitro maturation and developmental competence of follicular oocytes were remarkably improved in the presence of RGD. In particular, blastocyst embryos were obtained only from A-R+ or A+R+ conditions after in vitro fertilization. We also determined synergistic effects of the RGD peptides and activin A on follicle growth and oocyte development in the 3-D tissue culture. In conclusion, our results suggest that RGD-modified dextran hydrogels provide an ECM-mimetic bioactive environment to support folliculogenesis in a 3-D ovarian tissue culture system.

Imaging and tracing the pattern of adult ovarian angiogenesis implies a strategy against female reproductive aging

Robust angiogenesis is continuously active in ovaries to remodel the ovary-body connections in mammals, but understanding of this unique process remains elusive. Here, we performed high-resolution, three-dimensional ovarian vascular imaging and traced the pattern of ovarian angiogenesis and vascular development in the long term. We found that angiogenesis was mainly active on ovarian follicles and corpus luteum and that robust angiogenesis constructs independent but temporary vascular networks for each follicle. Based on the pattern of ovarian angiogenesis, we designed an angiogenesis-blocking strategy by axitinib administration to young females, and we found that the temporary suppression of angiogenesis paused ovarian development and kept the ovarian reserve in the long term, leading to postponed ovarian senescence and an extension of the female reproductive life span. Together, by uncovering the detailed model of physiological ovarian angiogenesis, our experiments suggest a potential approach to delay female reproductive aging through the manipulation of angiogenesis.

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.

Synergistic Promoting Effects of X-Linked Inhibitor of Apoptosis Protein and Matrix on the In Vitro Follicular Maturation of Marmoset Follicles

BACKGROUND

In vitro follicular maturation (IVFM) of ovarian follicles is an emerging option for fertility preservation. Many paracrine factors and two-dimensional or three-dimensional (3D) environments have been used for optimization. However, since most studies were conducted using the murine model, the physiological differences between mice and humans limit the interpretation and adaptation of the results. Marmoset monkey is a non-human primate (NHPs) with more similar reproductive physiology to humans. In this study, we attempted to establish a 3D matrix (Matrtigel)-based IVFM condition for marmoset ovarian follicles in combination with anti-apoptotic factor, X-linked inhibitor of apoptosis protein (XIAP).

METHODS

Marmoset follicles were isolated as individual follicles and cultured in a single drop with the addition of 0, 10, and 100 μg/mL of XIAP molecules. Matured oocytes and granulosa cells from mature follicles were collected and analyzed. The average number of isolated follicles was less than 100, and primordial and antral follicles were abundant in the ovaries.

RESULTS

IVFM of marmoset follicles in 3D matrix conditions with XIAP increased the rates of survival and in vitro follicle development. Furthermore, oocytes from the 3D cultures were successfully fertilized and developed in vitro. The addition of XIAP increased the secretion of estradiol and aromatase. Furthermore, expression of granulosa-specific genes, such as bone morphogenetic protein 15, Oct4, and follicle-stimulating hormone receptor were upregulated in the in vitro-matured follicles than in normal, well-grown, and atretic follicles. Apoptosis-related B-cell lymphoma-2 was highly expressed in the atretic follicles than in the XIAP-treated follicles, and higher caspase-3 was localized in the XIAP-treated follicles.

CONCLUSION

In this study, we attempted to establish a 3D-matrix-based marmoset IVFM condition and demonstrated the synergistic effects of XIAP. The use of a 3D matrix may be applied as an optimal culture condition for marmoset ovarian follicles.

Culture of preantral ovarian follicles of Bos taurus indicus with alpha-lipoic acid

The aim of this study was to evaluate follicular development, morphological integrity, and antioxidant potential of preantral ovarian follicles from Bos taurus indicus females grown in vitro with alpha-lipoic acid. Ovaries (n = 24) of Bos taurus indicus (n = 12) females were collected during slaughter and fragmented. A randomly obtained fragment from each pair of ovaries was fixed in Bouin (non-cultivated control; D0). These fragments were intended for classical histology (morphology and evaluation of follicular growth), and a fragment from each pair of ovaries was frozen at -80°C (non-cultivated control; D0), and assigned for analysis of oxidative stress [thiobarbituric acid reactive substances (TBARS), nitroblue tetrazolium (NBT), and ferric reducing antioxidant power (FRAP)]. The remaining fragments were cultured in vitro for 6 (D6) or 12 (D12) days, containing only minimum essential medium (MEM) or MEM supplemented with alpha-lipoic acid (50, 100, or 250 ng/ml), on an extracellular matrix of agarose gel, in an oven at 38.5ºC. Every 2 days, 100% of the culture medium was replaced. Supplementation with 100 ng/ml was effective for maintaining follicular integrity after 6 days of culture (primordial: 51.28%; development: 36.88%; P < 0.0001). There was no difference (P > 0.05) between treatments compared with the non-cultivated control treatment (D0), using the NBT and TBARS assays. Therefore, supplementation of the in vitro culture medium of bovine preantral ovarian follicles with a concentration of 100 ng/ml of alpha-lipoic acid at 6 days of culture was effective for maintaining follicular integrity and, after 6 days, maintaining stable levels of reactive oxygen species.

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.

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.

Oocyte-derived microvilli control female fertility by optimizing ovarian follicle selection in mice

Crosstalk between oocytes and surrounding somatic cells is crucial for mammalian oogenesis, but the structural mechanisms on oocytes to control female reproduction remain unknown. Here we combine endogenous-fluorescent tracing mouse models with a high-resolution live-cell imaging system to characterize oocyte-derived mushroom-like microvilli (Oo-Mvi), which mediate germ-somatic communication in mice. We perform 3D live-cell imaging to show that Oo-Mvi exhibit cellular characteristics that fit an exocrine function for signaling communication. We find that deletion of the microvilli-forming gene Radixin in oocytes leads to the loss of Oo-Mvi in ovaries, and causes a series of abnormalities in ovarian development, resulting in shortened reproductive lifespan in females. Mechanistically, we find that Oo-Mvi enrich oocyte-secreted factors and control their release, resulting in optimal selection of ovarian follicles. Taken together, our data show that the Oo-Mvi system controls the female reproductive lifespan by governing the fate of follicles.

How structural features on oocytes regulate mammalian female reproduction is unclear. Here, the authors provide imaging and physiological evidence (for example on Radixin knockout) to identify oocyte-derived mushroom-like microvilli that control the female reproductive lifespan by governing the fate of follicles.

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.

Effect of animal-sourced bioactive peptides on the in vitro development of mouse preantral follicles

The aim of this study was to investigate the effect of bioactive peptides (BAPT) from animal sources on the development of mouse preantral follicles in vitro. Preantral follicles were isolated and randomly divided into the following groups: an untreated group (control) and three groups supplemented with 20, 40 and 60 μg/mL BAPT, respectively. After establishing the in vitro follicle culture, the gene expression levels and hormone levels were quantified. After in vitro maturation, the developmental rates, reactive oxygen species (ROS) production levels and mitochondrial distributions of MII oocytes were investigated, followed by the analyses of embryonic developmental rates after in vitro fertilization.The results showed that BAPT promoted the growth of mouse preantral follicles. Notably, after 14 d of in vitro culture, the levels of 17 β-estradiol and progesterone were up-regulated with BAPT treatments. Moreover, the expression levels of Oct4, Bmp15, GDF9, FOXO3, Zp3, FOXL2, Inhibin alpha, SOD2, Catalase, GPx and Bcl-2 in the developing follicles were significantly up-regulated after BAPT treatments (P < 0.05), while BAPT significantly inhibited the expression levels of BAX (P < 0.05). Following BAPT treatments, the ROS production levels of MII oocytes were decreased while the mitochondrial distributions were significantly enhanced. Furthermore, increased maturation rates, fertilization and embryonic developmental rates were found in these BAPT-treated groups (P < 0.05).These results demonstrated that BAPT significantly improved the development of preantral follicles in vitro by reducing ROS-dependent cellular damages and by enhancing mitochondrial distributions, thereby promoting the further applications of animal-derived BAPT in biomedical research.

Harvesting, processing, and evaluation of in vitro-manipulated equine preantral follicles: A review

The mammalian ovary is responsible for essential stages of folliculogenesis and hormonal production, regulating the female physiological functions during the menstrual/estrous cycles. The mare has been considered an attractive model for comparative studies due to the striking similarities shared with women regarding in vivo and in vitro folliculogenesis. The ovarian follicular population in horses contains a large number of oocytes enclosed in preantral follicles that are yet to be explored. Therefore, the in vitro manipulation of equine preantral follicles aims to avoid the process of atresia and promote the development of follicles with competent oocytes. In this regard, after ovarian tissue harvesting, the use of appropriate processing techniques, as well as suitable approaches to evaluating equine preantral follicles and ovarian tissue, are necessary. Although high-quality equine ovarian tissue can be obtained from several sources, some critical aspects, such as the age of the animals, ovarian cyclicity, reproductive phase, and the types of ovarian structures, should be considered. Therefore, this review will focus on providing an update on the most current advances concerning the critical factors able to influence equine preantral follicle quality and quantity. Also, the in vivo strategies used to harvest equine ovarian tissue, the approaches to manipulating ovarian tissue post-harvesting, the techniques for processing ovarian tissue, and the classical approaches used to evaluate preantral follicles will be discussed.

Advances in in vitro folliculogenesis in domestic ruminants

The in vitro follicle culture (IVFC) represents an outstanding tool to enhance our understanding of the control of folliculogenesis and to allow the future use of a large number of immature oocytes enclosed in preantral follicles (PFs) in assisted reproductive techniques in humans as well as in others mammalian species including the ruminants. So far, the best results of IVFC were reported from mice with the production of live offspring from primordial follicles cultured in vitro. Live birth has been obtained after the in vitro culture of bovine early antral follicles. However, in other ruminant species, these results have been limited to the production of a variable number of mature oocytes and low percentages of embryos after in vitro culture of goat, buffalo and sheep isolated secondary preantral follicles. The present review presents and discusses the main findings, limitations, and prospects of in vitro folliculogenesis in ruminants focusing on bovine, caprine, and ovine species.

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.

Improvement of in situ Follicular Activation and Early Development in Cryopreserved Human Ovarian Cortical Tissue by Co-Culturing with Mesenchymal Stem Cells

Follicular loss and tissue degeneration are great challenges in ovarian tissue culture systems. Mesenchymal stem cells (MSC) secrete a cocktail of growth factors and cytokines which supports adjacent cells and tissues. The aim of the current study was to investigate the impact of human bone marrow (hBM)-MSC, as co-culture cells, on human follicular development in ovarian cortical tissue (OCT) culture. For this purpose, warmed OCT fragments were co-cultured with hBM-MSC for 8 days and compared to monocultured OCT. During the culture period, ovarian follicle survival and development in the OCT were evaluated using histological observation, follicular developmental-related genes expression, and estradiol production. Furthermore, cell proliferation and apoptosis were assessed. The results showed that there were no significant differences in conserved ovarian follicles with a normal morphology between the two groups. However, the percentage of developing follicles, as well as follicular developmental gene expression, significantly increased in the co-culture group compared to the monoculture group. On the other hand, compared with the monoculture group, the co-culture group demonstrated a significant increase in cell proliferation, indicated by Ki67 gene expression, as well as a dramatic decrease in apoptotic cell percentage, revealed by TUNEL assay. These findings indicated that co-culturing of hBM-MSC with OCT could improve follicular activation and early follicular development in human ovarian tissue culture systems.

Xanthan gum and Locust bean gum gel supports in vitro development of porcine oocytes derived from early antral follicles

Early antral follicle (EAF)-derived porcine oocytes develop more readily on polyacrylamide-gel (PAG) than on plastic plates. Xanthan gum (XG) and locust bean gum (LBG) are edible polysaccharides. We investigated XG-LBG gel supports in the development of EAF-derived porcine oocytes. XG and LBG were mixed in a 1:1 ratio to form a substrate. We cultured oocyte granulosa cell complexes (OGCs) from the EAFs on XG-LBG gels of various concentrations. The oocyte diameters were comparable among the 0.3, 0.5, and 1.0% gels; granulosa cell proliferation was greater on the 1.0% gel. The proliferation and survival rates of the granulosa cells, and the histone H4 at lysine 12 acetylation levels were higher in OGCs cultured on 1.0% XG-LBG than those grown on 0.3% PAG. Development to the blastocyst stage was 13.8% for the XG-LBG gels and 9.4% for PAG. In conclusion, XG-LBG are safe and efficient substrates for in vitro culture of oocytes.

Is the pre-antral ovarian follicle the 'holy grail'for female fertility preservation?

Fertility preservation is not only a concern for humans with compromised fertility after cancer treatment. The preservation of genetic material from endangered animal species or animals with important genetic traits will also greatly benefit from the development of alternative fertility preservation strategies. In humans, embryo cryopreservation and mature-oocyte cryopreservation are currently the only approved methods for fertility preservation. Ovarian tissue cryopreservation is specifically indicated for prepubertal girls and women whose cancer treatment cannot be postponed. The cryopreservation of pre-antral follicles (PAFs) is a safer alternative for cancer patients who are at risk of the reintroduction of malignant cells. As PAFs account for the vast majority of follicles in the ovarian cortex, they represent an untapped potential, which could be cultivated for reproduction, preservation, or research purposes. Vitrification is being used more and more as it seems to yield better results compared to slow freezing, although protocols still need to be optimized for each specific cell type and species. Several methods can be used to assess follicle quality, ranging from simple viability stains to more complex xenografting procedures. In vitro development of PAFs to the pre-ovulatory stage has not yet been achieved in humans and larger animals. However, in vitro culture systems for PAFs are under development and are expected to become available in the near future. This review will focus on recent developments in (human) fertility preservation strategies, which are often accomplished by the use of in vitro animal models due to ethical considerations and the scarcity of human research material.

Melatonin improves developmental competence of oocyte-granulosa cell complexes from porcine preantral follicles

Melatonin has been reported to improve the survival rate of mouse and goat preantral follicles cultured in vitro. However, the role of melatonin in the development of oocyte-granulosa cell complexes (OGCs) isolated from preantral follicles remains unclear. Cumulus-oocyte complexes were isolated from OGCs cultured in vitro for 18.5 days and were then maturated in vitro for 42 h. The matured oocytes were parthenogenetically activated and were further cultured up to the blastocyst stage. We found that the developmental capacity of oocytes from in vitro cultured OGCs was significantly inferior to that from in vivo grown counterparts. Additionally, a 10^-5 M dose of melatonin added to the medium during in vitro culture of OGCs did not improve oocyte meiotic maturation but enhanced blastocyst rate of parthenogenetically activated embryos. Besides, these beneficial effects could be reversed by luzindole treatment, a melatonin membrane receptor antagonist. mRNA sequencing analysis further revealed that melatonin caused differential expression of 76 genes of which 75 were upregulated and 1 was downregulated in OGCs. Twelve of the 76 genes were identified as potential regulators of metabolic pathways by functional analysis. Taken together, these results indicate that melatonin improves developmental competence of porcine oocyte-granulosa cell complexes.

Follicle development as an orchestrated signaling network in a 3D organoid

The ovarian follicle is the structural and functional unit of the ovary, composed of the female gamete (the oocyte) and supportive somatic cells. Follicles are not only the source of a female's germ cell supply, but also secrete important hormones necessary for proper endocrine function. Folliculogenesis, the growth and maturation of the follicular unit, is a complex process governed by both intrafollicular crosstalk and pituitary-secreted hormones. While the later stages of this process are gonadotropin-dependent, early folliculogenesis appears to be controlled by the ovarian microenvironment and intrafollicular paracrine and autocrine signaling. In vitro follicle culture remains challenging because of the limited knowledge of growth factors and other cytokines influencing early follicle growth. Here we discuss the current state of knowledge on paracrine and autocrine signaling influencing primary follicles as they develop into the antral stage. Given the importance of intrafollicular signaling and the ovarian microenvironment, we reviewed the current engineering approaches for in vitro follicle culture, including 3D systems using natural hydrogels such as alginate and synthetic hydrogels such as poly(ethylene glycol). Our discussion is focused on what drives the proliferation of granulosa cells, development of the thecal layer, and antrum formation-three processes integral to follicle growth up to the antral stage. Further research in this area may reveal the mechanisms behind these complex signaling relationships within the follicle, leading to more successful and physiologically-relevant in vitro culture methods that will translate well to clinical applications.

Three-dimensional levitation culture improves in-vitro growth of secondary follicles in bovine model

RESEARCH QUESTION

Does a three-dimensional culture system based on magnetic levitation with nanoparticles assembly maintain the follicular structure and viability with adequate growth rates leading to oocyte maturation after long-term culture?

DESIGN

Randomized-controlled trial of treatments in a bovine model. Secondary follicles (n = 213) isolated from bovine ovaries were cultured in a two-dimensional system (two-dimensional control) or three-dimensional levitation system with different concentrations (three-dimensional 50 µl/ml, 100 µl/ml and 200 µl/ml) of magnetic nanoparticles. Follicular growth (diameter, daily growth and growth patterns), morphology (normal, degenerated and extruded follicles), antrum formation, oocyte viability and chromatin configuration were assessed.

RESULTS

Secondary follicles of three-dimensional 200-µl/ml treatment showed higher viability, antrum formation and lower degeneration rates than two-dimensional control. Also, follicles cultured in the three-dimensional 200-µl/ml treatment presented a most homogenous daily growth rate as shown by the lowest variance and standard deviation. Compared with the two-dimensional control, the proportion of non-growing and slow-growing follicles were 3.8-fold lower and 1.6-fold higher, respectively, in the three-dimensional 200-µl/ml treatment. After in-vitro maturation, the three-dimensional 200-µl/ml had a greater proportion of viable oocytes (1.7-fold) and meiotic resumption rates (2.4-fold) than the two-dimensional control treatment.

CONCLUSION

The three-dimensional levitation culture system improves the viability of in-vitro development of bovine secondary follicles, antrum formation and lower extrusion and degeneration rates and adequate growth rate leading to relevant oocyte viability and meiotic resumption after in-vitro maturation. This approach does not require a specific medium, and has the potential as an alternative method to in-vitro follicle culture in several species, including humans.

Conditioned medium of ovine Wharton's jelly-derived mesenchymal stem cells improves growth and reduces ROS generation of isolated secondary follicles after short-term in vitro culture

The aim of this study was to evaluate the effect of the conditioned medium of ovine Wharton's jelly-derived mesenchymal stem cells (oWJ-MSCs) on the morphology, growth, reactive oxygen species (ROS) and glutathione (GSH) intracellular levels, active mitochondria, and meiotic resumption of isolated ovine secondary follicles in vitro. The oWJ-MSCs were isolated and the medium where they were cultured was recovered (conditioned medium). Isolated ovine secondary follicles were cultured for 6 days in 1) supplemented α-MEM⁺ (control); 2) 50% α-MEM⁺ + 50% conditioned medium (α-MEM + CM group) or 3) conditioned medium only (CM group). The parameters analyzed were morphology, antrum formation, follicle and oocyte growth, ROS and GSH levels, mitochondrial activity and meiotic resumption. The percentage of normal follicles, antrum formation, and fully grown oocytes did not differ (P > 0.05) among treatments. Follicles cultured in α-MEM + CM group had greater (P < 0.05) diameter than other treatments after culture. Moreover, the diameter of the follicles cultured in CM alone was higher (P < 0.05) than in the α-MEM⁺. In addition, α-MEM + CM and CM treatments increased the growth rate compared to the α-MEM⁺. Treatments containing conditioned medium (α-MEM + CM or CM) significantly reduced ROS levels compared to the control medium. Moreover, mitochondrial activity was higher in α-MEM⁺ and α-MEM + CM than in CM alone. All treatments showed oocytes in GV, GVBD and MI. In conclusion, oWJ-MSCs conditioned medium, especially when associated with α-MEM, improves the growth of secondary follicles and reduces ROS generation after short-term culture.

Structure of preantral follicles, oxidative status and developmental competence of in vitro matured oocytes after ovary storage at 4 °C in the domestic cat model

BACKGROUND

Storage conditions during transportation of explanted ovaries are a critical step in setting up fertility preservation protocols in both animal and human fields. Here, we evaluated the effects of ovary storage at 4 °C on the preservation of preantral follicles and oocytes retrieved from antral follicles using the domestic cat as model.

METHODS

Ovaries were harvested from fifty-five healthy domestic queens during ovariectomy and stored at 4 °C for 0 (control), 24, 48, 72 and 96 h. In Experiment 1, the effects of the storage period at 4 °C on the morphology, cytoskeleton (α/β tubulin) and DNA integrity (phosphorylation of histone H2AX) of preantral follicles were investigated. In Experiment 2, oocytes recovered from antral follicles were matured and fertilized in vitro to evaluate their meiotic and developmental competence. Reactive oxygen species (ROS), glutathione (GSH) and lipid peroxidation were measured in matured oocytes.

RESULTS

The results showed that: a) storage up to 24 h did not affect the morphology and the DNA integrity of preantral follicles; b) extended storage times caused progressive morphological abnormalities, disassembling of microtubules and DNA damage; c) storage up to 48 h did not influence in vitro meiotic maturation of oocytes nor cleavage after in vitro fertilization. However, only oocytes stored within the ovary for 24 h produced blastocysts in a percentage similar to control oocytes; d) GSH levels of in vitro matured oocytes did not change at any time during ovary storage; a progressive increase in ROS levels was detected from 48 h associated with elevated lipid peroxidation at 72 and 96 h of storage.

CONCLUSIONS

Storage of cat ovaries for up to 24 h caused minimal alteration of preantral follicles and oocytes. The extension of the storage period beyond 24 h progressively impaired the structure of follicles, and modified the oxidative status of in vitro matured oocytes and their developmental competence after in vitro fertilization. This information may help when setting up programs for fertility conservation, especially for wild feline species which die in geographic areas located far away from ARTs centers.

Female fertility preservation: past, present and future

Anti-cancer therapy, particularly chemotherapy, damages ovarian follicles and promotes ovarian failure. The only pharmacological means for protecting the ovaries from chemotherapy-induced injury is gonadotrophin-releasing hormone agonist, but its efficiency remains controversial; ovarian transposition is used to shield the ovary from radiation when indicated. Until the late 1990s, the only option for fertility preservation and restoration in women with cancer was embryo cryopreservation. The development of other assisted reproductive technologies such as mature oocyte cryopreservation andin vitromaturation of oocytes has contributed to fertility preservation. Treatment regimens to obtain mature oocytes/embryos have been modified to overcome various limitations of conventional ovarian stimulation protocols. In the last decades, several centres have begun cryopreserving ovarian samples containing primordial follicles from young patients before anti-cancer therapy. The first live birth following implantation of cryopreserved-thawed ovarian tissue was reported in 2004; since then, the number has risen to more than 130. Nowadays, ovarian tissue cryopreservation can be combined within vitromaturation and vitrification of oocytes. The use of cryopreserved oocytes eliminates the risk posed by ovarian implantation of reseeding the cancer. Novel methods for enhancing follicular survival after implantation are presently being studied. In addition, researchers are currently investigating agents for ovarian protection. It is expected that the risk of reimplantation of malignant cells with ovarian grafts will be overcome with the putative development of an artificial ovary and an efficient follicle class- and species-dependentin vitrosystem for culturing primordial follicles.

Effects of vitrification on the viability of alginate encapsulated isolated bovine pre-antral follicles

PURPOSE

Individual follicle cryopreservation techniques, without hydrogel support, are labor-intensive and a substantial proportion of isolated follicles are lost during handling and after warming. Therefore, the viability and morphology of isolated bovine (as a model for human) pre-antral follicles after vitrification and warming, when encapsulated in alginate beads, were investigated.

METHODS

Bovine pre-antral follicles were mechanically isolated and divided into four different groups: (1) culture in 2% alginate beads (3D system) and vitrification in beads using mesh cups (3DVIT), (2) culture in 2% alginate beads (3DCUL), (3) culture in 96-well plates (2D system) and vitrification using High Security Vitrification straws® (2DVIT), (4) culture in a 2D system (2DCUL). The same vitrification and warming protocols were used for embedded (3DVIT) and non-embedded follicles (2DVIT).

RESULTS

No differences were observed in follicle viability between group 2DCUL and 3DCUL. Group 3DVIT showed the lowest viability (45.9%) according to calcein and neutral red staining among all groups. Group 2DVIT displayed the highest viability (87.5%) and largest percentage of follicles with a well-preserved morphology.

CONCLUSIONS

Our results show that, using a vitification protocol optimized for non-embedded follicles, 2D culture is more effective in vitrifying isolated follicles. However, embedding in alginate allow to handle follicles more efficiently, i.e., without excessive manipulation and thus less labor-intensive in combination with a reduced loss of follicles during the procedure. Based on the increased work efficiency, but lower viability and higher proportion of follicles showing impaired morphology, we consider it advantageous to optimize the protocol for the vitrification of embedded follicles to increase survival and maintain morphology after vitrification.

Uterine Tissue Engineering and the Future of Uterus Transplantation

The recent successful births following live donor uterus transplantation are proof-of-concept that absolute uterine factor infertility is a treatable condition which affects several hundred thousand infertile women world-wide due to a dysfunctional uterus. This strategy also provides an alternative to gestational surrogate motherhood which is not practiced in most countries due to ethical, religious or legal reasons. The live donor surgery involved in uterus transplantation takes more than 10 h and is then followed by years of immunosuppressive medication to prevent uterine rejection. Immunosuppression is associated with significant adverse side effects, including nephrotoxicity, increased risk of serious infections, and diabetes. Thus, the development of alternative approaches to treat absolute uterine factor infertility would be desirable. This review discusses tissue engineering principles in general, but also details strategies on how to create a bioengineered uterus that could be used for transplantation, without risky donor surgery and any need for immunosuppression. We discuss scaffolds derived from decellularized organs/tissues which may be recellularized using various types of autologous somatic/stem cells, in particular for uterine tissue engineering. It further highlights the hurdles that lay ahead in developing an alternative to an allogeneic source for uterus transplantation.