Insulin improves in vitro survival of equine preantral follicles enclosed in ovarian tissue and reduces reactive oxygen species production after culture

Ethanol, Carnoy, and paraformaldehyde as fixative solutions for histological evaluation of preantral follicles in equine ovarian tissue

The most adequate fixative solution for equine ovarian tissue is still to be determined as a tool to evaluate the improvement of methodological studies in assisted reproductive techniques and fertility preservation. This study aimed to evaluate a short-time ethanol 70% (ST-EtOH, 45 min) exposure as an alternative fixative compared with two classically fixatives [Carnoy's (CAR) solution and paraformaldehyde 4% (PFA)] at different fixation times (6 h, 12 h). The end points evaluated were morphology and classes of preantral follicles, follicular and stromal cell densities, and follicular and oocyte nuclear diameters in equine ovarian tissue. Ovaries (n = 6) from ovariectomized young mares were fragmented (3 × 3 × 1 mm; 20 fragments/ovary) and fixed in the tested treatments. Overall, a total of 11,661 preantral follicles were evaluated in 1444 histological slides. The ST-EtOH similarly preserved the preantral follicle morphometry and stromal cell density compared to the PFA fixative, regardless of the exposure time. Nonetheless, the CAR fixative solution had the greatest percentage of normal preantral follicles and the highest stromal cell density among all treatments. In conclusion, Carnoy's solution must be preferred compared with ST-EtOH and PFA fixatives for studies concerning the cellular morphology of equine ovarian tissue. Moreover, ST-EtOH fixative is a good alternative for equine ovarian tissue when a quick histological evaluation is required instead of more time-consuming and expensive techniques. Additional studies concerning the impact of different fixatives on the ultrastructure of cellular populations and their compatibility with IHC and molecular techniques in equine ovarian tissue are warranted.

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

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

In Vitro Activation and Development of Goat Preantral Follicles Enclosed in Ovarian Tissue Co-cultured with Mesenchymal Stem Cells

The development of culture systems capable of maintaining follicular growth since the preantral stage has been the target of investigations. Mesenchymal stem cells (MSC) present potential for use in a wide range of applications, including research aimed at preserving fertility. Therefore, this study investigated the use of caprine Wharton's Jelly Mesenchymal Stem Cells (WJMSC) on the survival and in vitro development of goat preantral follicles enclosed in ovarian fragments cultured for 1 or 7 days. Fragments of the ovarian cortex were immediately fixed (non-cultured control) or distributed in four treatments: ovarian tissue cultured in control medium (α-MEM⁺); ovarian tissue cultured in α-MEM⁺ supplemented with FBS (α-MEM⁺ + FBS); ovarian tissue co-cultured with stem cells in α-MEM⁺ (α-MEM⁺ + SC); and ovarian tissue co-cultured with stem cell in α-MEM⁺ + FBS (α-MEM⁺ + SC + FBS). The rates of cell proliferation, follicular survival, and activation, as well as follicular diameter, were evaluated. After 7 days, the treatment co-cultured with stem cells showed a higher (P < 0.05) percentage of morphologically normal preantral follicles compared to the other treatments, as well as a higher (P < 0.05) activation rate compared to cultured control. Moreover, the follicular diameter was higher (P < 0.05) in the treatment co-cultured with stem cells compared to co-cultured with stem cells plus FBS. This study demonstrates for the first time that in vitro co-culture of caprine WJMSC with preantral follicles enclosed in goat ovarian tissue improves activation and early follicular development.

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.

Supportive techniques to investigate in vitro culture and cryopreservation efficiencies of equine ovarian tissue: A review

During the reproductive lifespan of a female, only a limited quantity of oocytes are naturally ovulated; therefore, the mammalian ovary possesses a substantial population of preantral follicles available to be handled and explored in vitro. Hence, the manipulation of preantral follicles enclosed in ovarian tissue aims to recover a considerable population of oocytes of high-value animals for potential application in profitable assisted reproductive technologies (ARTs). For this purpose, the technique of preantral follicle in vitro culture (IVC) has been the most common research tool, achieving extraordinary results with offspring production in the mouse model. Although promising outcomes have been generated in livestock animals after IVC of preantral follicles, the quantity and quality of embryo production with those oocytes are still poor. In recent years, the mare has become an additional model for IVC studies due to remarkable similarities with women and livestock animals regarding in vivo and in vitro ovarian folliculogenesis. For a successful IVC system, several factors should be carefully considered to provide an optimum culture environment able to support the viability and growth of preantral follicles enclosed in ovarian tissue. The cryopreservation of the ovarian tissue is another important in vitro manipulation technique that has been used to preserve the reproductive potential in humans and, in the future, may be used in highly valuable domestic animals or endangered species. Several improvements in cryopreservation protocols are necessary to support the utilization of ovarian tissue of different species in follow-up ARTs (e.g., ovarian fragment transplantation). This review aims to provide an update on the most current advances regarding supportive in vitro techniques used in equids to evaluate and manipulate preantral follicles and ovarian tissue, as well as methodological approaches used during IVC and cryopreservation techniques.

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.

GDF9-β promotes folliculogenesis in sheep ovarian transplantation onto the chick embryo chorioallantoic membrane (CAM) in cryopreservation programs

PURPOSE

Ovarian tissue (OT) cryopreservation is a treatment option for fertility preservation among young cancer patients. However, the procedure may involve a reduction in the GDF9-β expression and a delay in follicular growth after thawing and transplantation. The aim of this study was to evaluate whether supplementation of GDF9-β can compensate the reduction of this factor during the cryopresevation process and promote folliculogenesis after transplantation of thawed sheep ovarian tissue.

METHODS

Sheep OT was cryopreserved using two methods of vitrification and slow freezing. Fresh and thawed OTs were then transplanted onto chick embryo chorioallantoic membrane (CAM) and then divided into two groups based on the addition of GDF9-β to the grafted tissue. After 5 days of culture, both histological and immunohistological (Ki-67) assessments were performed to evaluate follicular structure, development, and proliferation. The fibrotic and necrotic areas were measured using MICROVISIBLE software.

RESULTS

Folliculogenesis took place in all culture groups, but was significantly improved only in the +GDF9-β cultured group. Also, better follicular structure was preserved in the aforementioned group (p < 0.05). When GDF9-β was supplemented to the culture medium, more neovascularization (p < 0.05) and better transplantation (p > 0.05) was observed. Furthermore, the areas of fibrosis and necrosis were lower in this group rather than the controls. Follicular proliferative activity was significantly higher only in the slow freezing +GDF9-β cultured group.

CONCLUSIONS

GDF9-β, as a stimulatory factor, not only promoted the folliculogenesis in the fresh ovarian transplant, but also compensated for its reduction during the cryopreservation process.

Reactive oxygen species level, mitochondrial transcription factor A gene expression and succinate dehydrogenase activity in metaphase II oocytes derived from in vitro cultured vitrified mouse ovaries

The aim of this study was to evaluate the effects of ovarian tissue vitrification and two-step in vitro culture on the metaphase II (MII) oocyte reactive oxygen species (ROS) level, mitochondrial transcription factor A (TFAM) expression and succinate dehydrogenase (SDH) activity. After collection of neonatal mouse ovaries, 45 ovaries were vitrified and the others (n = 45) were considered as control. All ovaries were cultured for seven days, and their isolated preantral follicles were cultured in three-dimensional culture system. After 12 days, the follicular development and oocyte maturation were evaluated and compared in vitrified and non-vitrified ovaries. The collected MII oocytes were inseminated with capacitated spermatozoa. Then, the fertilization, embryonic development, ROS level, TFAM gene expression and SDH activity of oocytes were assessed and compared. There was no significant difference between morphology and percentage of normal follicles between vitrified and non-vitrified ovaries at the beginning of culture. The follicular development and hormone level in the vitrified group was significantly lower than non-vitrified group and the ROS concentration in the vitrified group was significantly higher than non-vitrified group after one-week culture. After follicular culture, there was no significant difference in follicular development, oocyte maturation, fertilization rate, TFAM gene expression, ROS level and mitochondrial SDH activity between the groups. This study showed that ovarian tissue vitrification influences the follicular development through increase in ROS level during culture but these harmful effects may be recovered during the follicular culture period. Thus, vitrification and ovarian culture method should be improved.

Effects of FSH addition to an enriched medium containing insulin and EGF after long-term culture on functionality of equine ovarian biopsy tissue

The effect of FSH supplementation on an enriched cultured medium containing insulin (10 ng/mL) and EGF (50 ng/mL) was investigated on in vitro culture of equine ovarian biopsy tissue. Ovarian tissue fragments were collected from mares (n = 10) and distributed in the following treatments: noncultured control, cultured control, and cultured + FSH. Both treated groups were cultured for 7 or 15 days. The end points evaluated were: follicular morphology, estradiol levels in the culture medium, fluorescence intensity for TUNEL, EGFR and Ki-67 detection, and gene expression of GDF-9, BMP-15, and Cyclin-D2 in the ovarian tissue. After seven days of culture, medium supplemented with FSH had a similar (P > 0.05) percentage of morphologically normal follicles compared to the noncultured control group. Estradiol levels increased (P < 0.05) from Day 7 to Day 15 of culture for both treated groups. No difference (P > 0.05) was observed for TUNEL and EGFR intensity between the noncultured control group and the treated groups after 15 days of culture. Ki-67 intensity did not differ (P > 0.05) between treated groups after 15 days of culture, but decreased (P < 0.05) when compared with the noncultured control group. Similar (P > 0.05) mRNA expression for GDF-9, BMP-15, and Cyclin-D2 was observed among all treatments after 15 days of culture. In conclusion, an enriched medium supplemented or not with FSH was able to maintain the functionality of equine ovarian biopsy tissue after a long-term in vitro culture.

Ovarian fragment sizes affect viability and morphology of preantral follicles during storage at 4°C

The method of transportation and the conditions imposed on the ovarian tissue are pivotal aspects for the success of ovarian tissue cryopreservation (OTC). The aim of this study was to evaluate the effect of the size of the ovarian tissue (e.g. whole ovary, biopsy size and transplant size) during different times of storage (0, 6, 12 and 24 h) on the structural integrity of equine ovarian tissue transported at 4°C. Eighteen pairs of ovaries from young mares (<10 years old) were harvested in a slaughterhouse and processed to simulate the fragment sizes (biopsy and transplant size groups) or kept intact (whole ovary group) and stored at 4°C for up to 24 h in α-MEM-enriched solution. The effect of the size of the ovarian tissue was observed on the morphology of preantral follicles, stromal cell density, DNA fragmentation and mitochondrial membrane potential. The results showed that (i) biopsy size fragments had more morphologically normal preantral follicles after 24 h of storage at 4°C; (ii) mitochondrial membrane potential was the lowest during each storage time when the whole ovary was used; (iii) DNA fragmentation rate in the ovarian cells of all sizes of fragments increased as storage was prolonged and (iv) transplant size fragments had increased stromal cell density during storage at cool temperature. In conclusion, the biopsy size fragment was the best to preserve follicle morphology for long storage (24 h); however, transportation/storage should be prior determined according to the distance (time of transportation) between patient and reproduction centers/clinics.

Carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP) pre-exposure ensures follicle integrity during in vitro culture of ovarian tissue but not during cryopreservation in the domestic cat model

PURPOSE

Temporary and reversible downregulation of metabolism may improve the survival of tissues exposed to non-physiological conditions during transport, in vitro culture, and cryopreservation. The objectives of the study were to (1) optimize the concentration and duration of carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP-a mitochondrial uncoupling agent) exposures for biopsies of domestic cat ovarian tissue and (2) examine the effects of FCCP pre-exposures on follicle integrity after tissue culture and/or cryopreservation.

METHODS

Biopsies of cat ovarian tissue were first treated with various concentrations of FCCP (0, 10, 40, or 200 nM) for 10 or 120 min to determine the most suitable pre-exposure conditions. Based on these results, tissues were pre-exposed to 200 nM FCCP for 120 min for the subsequent studies on culture and cryopreservation. In all experiments and for each treatment group, tissue activity and integrity were measured by mitochondrial membrane potential (relative optical density of rhodamine 123 fluorescence), follicular viability (calcein assay), follicular morphology (histology), granulosa cell proliferation (Ki-67 immunostaining), and follicular density.

RESULTS

Ovarian tissues incubated with 200 nM FCCP for 120 min led to the lowest mitochondrial activity (1.17 ± 0.09; P < 0.05) compared to control group (0 nM; 1.30 ± 0.12) while maintaining a constant percentage of viable follicles (75.3 ± 7.8 %) similar to the control group (71.8 ± 11.7 %; P > 0.05). After 2 days of in vitro culture, percentage of viable follicles (78.8 ± 8.9 %) in similar pre-exposure conditions was higher (P < 0.05) than in the absence of FCCP (61.2 ± 12.0 %) with percentages of morphologically normal follicles (57.6 ± 17.3 %) not different from the fresh tissue (70.2 ± 7.1 %; P > 0.05). Interestingly, percentages of cellular proliferation and follicular density were unaltered by the FCCP exposures. Based on the indicators mentioned above, the FCCP-treated tissue fragments did not have a better follicle integrity after freezing and thawing.

CONCLUSIONS

Pre-exposure to 200 nM FCCP during 120 min protects and enhances the follicle integrity in cat ovarian tissue during short-term in vitro culture. However, FCCP does not appear to exert a beneficial or detrimental effect during ovarian tissue cryopreservation.