Morphological and ultrastructural evaluation of cultured frozen–thawed human fetal ovarian tissue

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.

Making human eggs in a dish: are we close?

In the space of 50 years, we have seen incredible achievements in human reproductive medicine. With these leaps forward, it is no wonder that there is a major interest in women's reproductive health research, including extension of reproductive lifespan. Substantial effort is currently being made to address this challenge, including from the commercial sector. In vitro gametogenesis (IVG) in mice is a spectacular breakthrough and has the potential to offer hope to women with intractable infertility. However, with such lofty goals, some reflection may be called for: mastering all of the techniques required for complete and safe IVG in women is likely to be extraordinarily difficult.

Ultrastructure of human ovarian tissues and risk of cancer cells re-implantation after transplantation to chick embryo chorioallantois membrane (CAM) following vitrification or slow freezing

Ovarian follicle depletion and premature ovarian failure are significant challenges in cancer patients subjected to radio- or chemotherapy. Ovarian tissue (OT) cryopreservation would be an option when other fertility preservation methods are not accessible. This study aimed to analyze the structure and ultrastructure of human OTs transplanted onto chick embryo chorioallantois membrane (CAM) after cryopreservation by vitrification or slow freezing. OTs from 10 cancer patients underwent cryopreservation. CAM transplantation was done on fresh and cryopreserved OTs, to assign samples to nine study groups as follows: 1) FI-FIII = fresh, 5- and 10-days post-CAM transplantation groups; 2) VI-VIII = vitrified, 5- and 10-days post-transplantation vitrified groups; 3) SFI-SFIII: slow frozen, 5- and 10-days post-transplantation slow freezing groups. Proliferation ability, folliculogenesis, and structural and ultrastructure were analyzed. The density of primordial follicles did not change after both freezing methods, but reduced after 5 (P ≥ 0.05) and 10 days (P ≤ 0.05) post-CAM transplantation. The follicular grade significantly decreased in all transplanted tissues (P ≤ 0.0). The proliferation marker increased after cryopreservation, but reduced after transplantation (P ≤ 0.05). TEM evaluation showed better follicular ultrastructure in the fresh group, after transplantation. Stromal ultrastructure appeared more preserved after vitrification compared with slow freezing. There was no sign of malignant cell contamination after transplantation. Some follicular TEM abnormalities were found in both methods of freezing, with a better transplantation rate after vitrification. Also, enhanced follicular activation resulted in faster follicular depletion in this method. The information regarding post grafting events would improve our knowledge for longer OTs' lifespans.

Role of apoptosis and autophagy in ovarian follicle pool decline in children and women diagnosed with benign or malignant extra-ovarian conditions

STUDY QUESTION

Which biological mechanisms are responsible for physiological ovarian reserve decline owing to aging, or pathological follicle depletion triggered by inflammation or a pro-oxidant environment throughout a woman's lifetime?

SUMMARY ANSWER

Ovarian follicle pool size is modulated by both apoptosis and autophagy, the first responsible for its physiological decline over time and increasing in the event of prior chemotherapy in children, and the latter playing a major role in physiological ovarian follicle pool diminution before puberty.

WHAT IS KNOWN ALREADY

Among the different pathways of controlled cell death, apoptosis and autophagy are implicated in follicle loss. Apoptosis participates in eliminating damaged follicles, such as those impaired by chemotherapy (CHT), but its involvement in physiological age-related follicle decline is less well understood. Autophagy has proved crucial in follicle quiescence maintenance in murine models, but its contribution to human follicle pool modulation is still unclear.

STUDY DESIGN, SIZE, DURATION

This retrospective study included 84 patients with benign or malignant extra-ovarian conditions aged between 1 and 35 years, with ovarian tissue stored for histological analyses at the time of cryopreservation (between 2012 and 2021) at a tertiary care center.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Ovarian fragments were used for the following analyses: hematoxylin and eosin staining for follicle count and classification; cleaved caspase-3 immunostaining to identify follicle apoptosis; and microtubule-associated proteins 1A/1B light chain 3B immunolabeling to detect follicle autophagy. Transmission electron microscopy was also carried out to investigate ultrastructural features of oocytes and granulosa cells. All analyses stratified patients by age, menarchal status (premenarchal = 32; postmenarchal = 52), potentially gonadotoxic CHT before cryopreservation (n = 14), presence of endometriosis and use of hormonal treatment.

MAIN RESULTS AND THE ROLE OF CHANCE

Premenarchal patients had a larger follicle pool in terms of total follicle density [mean, range 4979.98 (342.2-21789) versus 918.8 (26.18-3983), P < 0.001], but higher rates of morphologically abnormal [8.52 (0-25.37)% versus 3.54 (0-17.5)%, P < 0.001] and atretic [15.8 (0‒31.85)% versus 10.6 (0-33.33)%, P < 0.01] follicles than postmenarchal subjects. Apoptosis rates did not change with increasing age [27.94 (0-93.2)% in prepubertal subjects and 29.5 (0-100)% in postpubertal subjects], but autophagic follicles were around 10 times more common in premenarchal than postmenarchal subjects [10.21 (0-62.3)% versus 1.34 (0-25)%, P < 0.001], playing a crucial role in age-related follicle decline and elimination of 'abnormal' follicles, that are rarely seen after menarche. The impact of diagnosis and previous CHT varied according to age. In premenarchal patients with previous CHT, significantly more apoptotic [40.22 (0-100)% versus 26.79 (0-87)%, P < 0.05] and fewer abnormal [3.84 (0-10-76)% versus 9.83 (0-25.37)%, P < 0.01] follicles were detected than in subjects with no CHT prior to ovarian tissue cryopreservation, suggesting a direct effect on follicle elimination, especially of those with abnormalities. In postmenarchal subjects with previous CHT, quiescent follicle rates were lower than in patients with no CHT before tissue freezing [71.57 (0-100)% versus 85.89 (50-100)%, P < 0.05], suggesting accelerated follicle activation and growth. Moreover, increased autophagic activity was observed in the event of a cancer diagnosis compared to benign conditions after puberty [26.27 (0-100)% versus 9.48 (0-29.41)%, respectively, P < 0.05].

LIMITATIONS, REASONS FOR CAUTION

The impact of specific CHT protocols could not be investigated since the group of patients with previous CHT was highly heterogeneous.

WIDER IMPLICATIONS OF THE FINDINGS

This study yields a deeper understanding of regulation of the follicle pool decline, showing for the first time that both apoptosis and autophagy pathways are involved in physiological follicle depletion, the latter being crucial before puberty. Moreover, our data showed a different response to non-physiological damage according to age, with higher apoptosis rates only in premenarchal subjects with previous CHT, confirming that this pathway is activated by drugs known to induce DNA damage in oocytes, such as alkylating agents, but not by cancer itself.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by grants from the Fonds National de la Recherche Scientifique de Belgique (F.R.S.-FNRS/FRIA FC29657 awarded to L.C., CDR J.0063.20 and grant 5/4/150/5 awarded to M.M.D.), grants from the Fondation contre le Cancer (grant 2018-042 awarded to A.Ca.), the Fondazione Comunitaria del Varesotto and Provincia di Varese ('Amalia Griffini' Fellowship in Gynecology and Obstetrics awarded to A.Ce.), Fonds Spéciaux de Recherche, Fondation St Luc and donations from the Ferrero family. The authors have no competing interests to declare.

TRIAL REGISTRAION NUMBER

N/A.

Proliferating cell nuclear antigen presentation, as a marker of folliculogenesis, in the transplanted ovarian tissue

AIM

One of the most important ways to understand the ovarian biology is studding the initiation of primordial follicle development and subsequent folliculogenesis control. In this study, proliferating cell nuclear antigen (PCNA) presentation was used as a marker of follicular development in the thawed ovarian tissue (OT) following transplantation onto chick embryo chorioallantoic membrane (CAM) using two methods of freezing of slow freezing and vitrification.

METHODS

Samples of OT from 10 patients were subjected to slow freezing and vitrification. After warming, CAM transplantation was done and PCNA proliferation index (PI; percent of PCNA-positive granulosa cells) was calculated for each follicle stage. Image J software was used to determine the mean staining intensity.

RESULTS

PCNA was positive for granulosa cells and oocytes nuclei, but negative for ooplasm. There were no remarkable PCNA staining in the granulosa cells of primordial follicles, but increased significantly as follicle progression (p < 0.05). Proliferation rate was also insignificantly higher in the vitrified than slow freezing group, before and after transplantation (p < 0.05). Lower PCNA presentation index was observed after CAM transplantation (p < 0.05). The earliest stage of follicular recruitment took place in the transitional follicles, before squamous cells transform to cuboidal cells.

CONCLUSION

PCNA showed that follicles had proliferation power after cryopreservation. Higher presentation after vitrification may indicate accelerated folliculogenesis in the thawed OT.

Effects of epidermal growth factor and progesterone on development, ultrastructure and gene expression of bovine secondary follicles cultured in vitro

The aims of this study were to investigate the effects of epidermal growth factor (EGF) and progesterone on the development, viability and the gene expression of bovine secondary follicle culture in vitro for 18 days. Secondary follicles (∼0.2 mm) were isolated from ovarian cortex and individually cultured at 38.5 °C, with 5% CO₂ in air, for 18 days, in TCM-199⁺ (n = 63) alone (control medium) or supplemented with 10 ng/mL progesterone (n = 64), 10 ng/mL EGF (n = 61) or both EGF and progesterone (n = 66). The effects of these treatments on growth, antrum formation, viability, ultrastructure and mRNA levels for GDF-9, c-MOS, H1foo and cyclin B1 were evaluated, significantly different (p < 0.05). The results showed that there was a progressive increase in follicular diameter in all treatments, but only follicles cultured in medium supplemented with EGF had increased significantly in diameter when compared to follicles cultured in the control medium at the end of the culture period, significantly different (p < 0.05). A positive interaction between EGF and progesterone was not observed. In addition, the presence of EGF, progesterone or both in culture medium did not influence the rate of follicle survival and antrum formation. However, the presence of only progesterone in cultured medium increased the expression of mRNAs for GDF9 and cyclin B1 in oocytes. EGF also significantly increased the levels of mRNAs for cMOS and GDF9 when compared to follicles cultured in control medium. Ultrastructural analyzes showed that cultured follicles in all treatments maintained the integrity of granulosa cells. In conclusion, the EGF promotes the development of secondary follicles cultured in vitro for 18 days and increases the expression of cMOS and GDF9, while progesterone alone or in association with EGF have not a positive effect on follicular growth. However, progesterone increases the expression of GDF9 and cyclin B1 in oocytes.

Fertility Preservation in Cancer Patients: In Vivo and In Vitro Options

Oocyte, embryo and ovarian tissue cryopreservation are being increasingly proposed for fertility preservation among cancer patients undergoing therapy to enable them to have babies after the cancer is cured. Embryo cryopreservation is not appropriate for single girls without any sperm partner and also because oocyte retrieval is an extended procedure, it is impossible in cases requiring immediate cancer cure. Thus ovarian tissue cryopreservation has been suggested for fertility preservation especial in cancer patients. The main goal of ovarian cryopreservation is re-implanting the tissue into the body to restore fertility and the hormonal cycle. Different cryopreservation protocols have been examined and established for vitrification of biological samples. We have used Cryopin to plunge ovarian tissue into the liquid nitrogen and promising results have been observed. Ovarian tissue re-implantation after cancer cure has one problem- the possibility of recurrence of malignancy in the reimplanted tissue is high. Xenografting-implantation of the preserved tissue in another species- also has its drawbacks such as molecular signaling from the recipient. In vitro follicle culturing is a safer method to obtain mature oocytes for fertilization and the various studies that have been carried out in this area are reviewed in this paper.

HUMAN FOLLICLE STIMULATING HORMONE (hFSH) AND THYROXINE (T4) IN SURVIVAL MAINTENANCE AND IN VITRO GROWTH PROMOTION OF CAPRINE PREANTRAL FOLLICLES

The aim of this study was to investigate the interaction of human FSH (10ng/ml) with T4 (20ng/mL) on survival, activation and growth of preantral follicles cultured in vitro for 28 days. Fragments of non-cultured and cultured ovarian tissue were processed for classic histology and transmission electron microscopy. The results showed a reduction in the survival rate in all the media tested (one to 28 days) when compared to the fresh control. However the treatment with T4/hFSH for seven days of culture maintained the rate similar to the control. The media tested by one and 28 days reduced the percentage of primordial follicles in all periods of culture. However, T4/hFSH on day one of culture remained similar to the fresh control. None of the media were able to keep the percentage of the developing follicles. It was observed that the follicular diameter in the medium with T4/hFSH remained similar to the fresh control. The ultrastructural analysis confirmed the integrity of follicles cultured for seven days in a medium supplemented with T4/hFSH. In conclusion, the medium with T4/hFSH is able to maintain the survival, promote the activation, and the ultrastructural integrity of caprine preantral follicles for until seven days.

Involvement of doublesex and mab-3-related transcription factors in human female germ cell development demonstrated by xenograft and interference RNA strategies

We identified three doublesex and mab-3-related transcription factors (DMRT) that were sexually differentially expressed in human fetal gonads and present in the ovaries at the time of meiotic initiation. These were also identified in murine embryonic female germ cells. Among these, we focused on DMRTA2 (DMRT5), whose function is unknown in the developing gonads, and clarified its role in human female fetal germ cells, using an original xenograft model. Early human fetal ovaries (8-11 weeks post-fertilization) were grafted into nude mice. Grafted ovaries developed normally, with no apparent overt changes, when compared with ungrafted ovaries at equivalent developmental stages. Appropriate germ cell density, mitotic/meiotic transition, markers of meiotic progression and follicle formation were evident. Four weeks after grafting, mice were treated with siRNA, specifically targeting human DMRTA2 mRNA. DMRTA2 inhibition triggered an increase in undifferentiated FUT4-positive germ cells and a decrease in the percentage of meiotic γH2AX-positive germ cells, when compared with mice that were injected with control siRNA. Interestingly, the expression of markers associated with pre-meiotic germ cell differentiation was also impaired, as was the expression of DMRTB1 (DMRT6) and DMRTC2 (DMRT7). This study reveals, for the first time, the requirement of DMRTA2 for normal human female embryonic germ cell development. DMRTA2 appears to be necessary for proper differentiation of oogonia, prior to entry into meiosis, in the human species. Additionally, we developed a new model of organ xenografting, coupled with RNA interference, which provides a useful tool for genetic investigations of human germline development.

Isolation of ovarian components essential for growth and development of mammalian oocytes in vitro

Mammalian ovaries contain a large number of oocytes, most of which degenerate either before or at various stages of growth. Dynamic and precise regulation in the ovary involves many factors, each with a unique role. Identifying the single most important factor is impossible; however, it may be possible to identify factors essential for oocyte growth. It is evident that oocytes can grow into competent ova in vitro; however, how faithfully the follicle should mimic the in vivo conditions remains unclear. In the culture system discussed in this review, bovine and mouse oocyte-granulosa cell complexes, at approximately the late mid-growth stage, spread on a substratum without the involvement of theca cells. The structural simplicity of this system is advantageous because it reduces the basic conditions essential for regulation of oocyte growth. Apart from biological factors, high concentrations of polyvinylpyrrolidone (molecular weight: 360000) improved oocyte growth. Among ovarian factors, androstenedione was used to compensate for the absence of theca cells, and it promoted both follicular growth and acquisition of oocyte meiotic competence. Most oocytes cultured in a group were viable after long-term culture, suggesting that unlike ovarian events, there was no exhaustive follicle selection. Collectively, oocytes and their associated granulosa cells can establish independent units capable of supporting oocyte growth in appropriately modified culture media.

Optimizing cryoprotectant perfusion conditions for intact ovary: a bovine model

PURPOSE

The aim of this study was to detect the effects of different perfusion pressure and different length of perfusion period on whole ovarian cryopreservation

METHODS

Bovine whole ovaries were vitrified-warmed. The ovaries were divided into the experimental groups according to different perfusion pressure and different length of perfusion period. Follicular viability was assessed using the trypan blue test; the percentage of morphologically normal primordial follicles and the 17-β estradiol level in the culture supernatants were measured.

RESULTS

When perfusion pressure was 100 mmHg, and the length of perfusion period was 40 min, the viability of ovarian tissues in bovine whole ovarian cryopreservation were higher than other protocols.

CONCLUSION

Protocol IIb (the perfusion pressure was 100 mmHg, and the length of perfusion period was 40 min) was appropriate for bovine whole ovarian cryopreservation.

GDF-9 and bFGF enhance the effect of FSH on the survival, activation, and growth of cattle primordial follicles

This study aims to investigate the effects of follicle stimulating hormone (FSH) in combination with growth and differentiation factor-9 (GDF-9) or basic fibroblast growth factor (bFGF) on the activation, survival and growth of cattle primordial follicles. Ovarian tissues were cultured for 3, 7, 14, 22 days in α minimum essential medium (α-MEM) supplemented with FSH, FSH+GDF-9 or FSH+bFGF. Non-cultured and cultured ovarian fragments were processed for histological and TUNEL analysis. Compared to the FSH medium, the results showed FSH+GDF-9 medium increased the percentage of primary follicles in all culture periods and secondary follicles after 14 days of culture (P<0.05), meanwhile the diameter of primary and secondary follicles were also observed to increase in this medium after 7 days of cultures (P<0.05). FSH+bFGF medium appeared to increase the percentage of primary follicles after 14 days of culture and secondary follicles at day 14 of culture than FSH medium (P<0.05). Furthermore, the FSH+GDF-9 and FSH+bFGF mediums had a greater percentage of normal follicles, and lesser apoptotic cell rates than FSH medium. The results first indicated that FSH in combination with GDF-9 or bFGF can improve the survival, activation, and growth of cattle primordial follicles after the long-term culture of ovarian cortex.

Optimization of oxygen concentration for growing bovine oocytes in vitro: constant low and high oxygen concentrations compromise the yield of fully grown oocytes

The oxygen environment in cell culture has a significant impact on the health and performance of cells. Here, we compared the effects of reduced (5%) and ambient (20%) oxygen concentrations on bovine oocyte-granulosa cell complexes, each containing a growing oocyte 90-102 µm in diameter, cultured for 14 days. Both oxygen concentrations showed some advantages and disadvantages; in 5% oxygen, the survival rate of oocytes was significantly higher than in 20% oxygen, but the resulting oocytes were significantly smaller, which was a serious disadvantage. During the first 4 days of culture, the growth and viability of oocytes were satisfactory using 5% oxygen. This observation led us to examine the effect of changing the oxygen concentration from 5% to 20% on Day 4 in order to minimize the expected disadvantages of constant 5% and 20% oxygen. The largest population of fully grown oocytes was obtained from cultures in which the oxygen concentration was changed in this way, which also led to higher oocyte viability than in constant 20% oxygen. A similar tendency was found in the frequency of oocytes becoming blastocysts after in vitro fertilization. Surviving oocytes eventually became located within an enlarged dome-like structure, and although the 5% oxygen environment may have been appropriate for oocyte growth in the early stages, 20% oxygen may have been necessary for the growth of oocytes in the dome-like structure. These results indicate an effective way of modulating oxygen concentration according to the growth of oocyte-granulosa cell complexes in vitro.

Effects of cooling rates and ice-seeding temperatures on the cryopreservation of whole ovaries

PURPOSE

The aim of this study was to detect the effects of different cooling rates and different ice-seeding temperatures on the cryopreservation of whole ovaries.

METHODS

Cow whole ovaries were slowly frozen using different protocols with different cooling rates and different ice-seeding temperatures. Follicular viability was assessed using the trypan blue test; the percentage of morphologically normal primordial follicles and the follicular densities of grafts were measured.

RESULTS

Protocol IIb was most effective protocol. Protocol Ib was more effective than protocol Ia and protocol Ic, and protocol IIIb was more effective than protocol IIIa and protocol IIIc.

CONCLUSIONS

Protocol IIb (the cooling rate was 0.2°C/min, and the ice-seeding temperature was -5°C) was appropriate for slow freezing of cow whole ovaries.

Leukemia inhibitory factor stimulates the transition of primordial to primary follicle and supports the goat primordial follicle viability in vitro

The aim of this study was to evaluate the effect of leukemia inhibitory factor (LIF) on the activation and survival of preantral follicles cultured in vitro enclosed in ovarian fragments (in situ). Goat ovarian cortex was divided into fragments to be used in this study. One fragment was immediately fixed (fresh control - FC) and the remaining fragments were cultured in supplemented minimum essential medium (MEM) without (cultured control - CC) or with different concentrations of LIF (1, 10, 50, 100 or 200 ng/ml) for 1 or 7 days, at 39°C in air with 5% CO2. Fresh control, CC and treated ovarian fragments were processed for histological and fluorescence analysis. The percentage of histological normal preantral follicles cultured for 7 days with 1 ng/ml (49.3%), 10 ng/ml (58.6%) and 50 ng/ml (58%) of LIF was higher than in the CC (32.6%; p < 0.05). After 7 days of culture, the percentage of primordial follicles in situ cultured with LIF decreased and primary follicles increased in all LIF concentrations compared with FC and CC (p < 0.05). In conclusion, LIF induced primordial follicle activation and supported preantral follicle viability of goat ovarian tissues cultured for 7 days.

Meiosis in a bottle: new approaches to overcome Mammalian meiocyte study limitations

The study of meiosis is limited because of the intrinsic nature of gametogenesis in mammals. One way to overcome these limitations would be the use of culture systems that would allow meiotic progression in vitro. There have been some attempts to culture mammalian meiocytes in recent years. In this review we will summarize all the efforts to-date in order to culture mammalian sperm and oocyte precursor cells.

Cryopreservation of whole ovaries with vascular pedicles: vitrification or conventional freezing?

PURPOSE

To compare the efficacy of vitrification and conventional freezing of whole ovaries.

METHODS

Ovaries obtained from 5-year-old female bovines were cryopreserved by conventional freezing, rapid freezing and vitrification. The ovarian cortical strips were cryopreserved by conventional freezing. Follicular viability was assessed using the trypan blue test; the percentage of morphologically normal primordial follicles, hormones concentrations in the culture supernatants, and lactate dehyrogenase levels were measured.

RESULTS

The efficacy of cryopreservation of whole ovaries by vitrification was higher than those by conventional freezing and rapid freezing. Conventional freezing of ovarian cortical strips was more effective than cryopreservation of whole ovaries by conventional freezing, rapid freezing, and vitrification.

CONCLUSIONS

Vitrification seems to be more suitable than conventional freezing for cryopreservation of whole ovaries. However, further studies are required to improve the efficacy of vitrifying whole ovaries.

Ultrastructure of isolated mouse ovarian follicles cultured in vitro

BACKGROUND

In vitro maturation of ovarian follicles, in combination with cryopreservation, might be a valuable method for preserving and/or restoring fertility in mammals with impaired reproductive function. Several culture systems capable of sustaining mammalian follicle growth in vitro have been developed and many studies exist on factors influencing the development of in vitro grown oocytes. However, a very few reports concern the ultrastructural morphology of in vitro grown follicles.

METHODS

The present study was designed to evaluate, by transmission and scanning electron microscopy, the ultrastructural features of isolated mouse preantral follicles cultured in vitro for 6 days in a standard medium containing fetal calf serum (FCS). The culture was supplemented or not with FSH.

RESULTS

The follicles cultured in FCS alone, without FSH supplementation (FCS follicles), did not form the antral cavity. They displayed low differentiation (juxta-nuclear aggregates of organelles in the ooplasm, a variable amount of microvilli on the oolemma, numerous granulosa cell-oolemma contacts, signs of degeneration in granulosa cell compartment). Eighty (80)% of FSH-treated follicles formed the antral cavity (FSH antral follicles). These follicles showed various ultrastructural markers of maturity (spreading of organelles in ooplasm, abundant microvilli on the oolemma, scarce granulosa cell-oolemma contacts, granulosa cell proliferation). Areas of detachment of the innermost granulosa cell layer from the oocyte were also found, along with a diffuse granulosa cell loosening compatible with the antral formation. Theca cells showed an immature morphology for the stage reached. Twenty (20)% of FSH-treated follicles did not develop the antral cavity (FSH non-antral follicles) and displayed morphological differentiation features intermediate between those shown by FCS and FSH antral follicles (spreading of organelles in the ooplasm, variable amount of microvilli, scattered granulosa cell-oolemma contacts, signs of degeneration in granulosa cell compartment).

CONCLUSIONS

It is concluded that FSH supports the in vitro growth of follicles, but the presence of a diffuse structural granulosa cell-oocyte uncoupling and the absence of theca development unveil the incomplete efficiency of the system. The present study contributes to explain, from a morphological point of view, the effects of culture conditions on the development of mouse in vitro grown follicles and to highlight the necessity of maintaining efficient intercellular communications to obtain large numbers of fully-grown mature germ cells.

Cryopreservation time does not decrease follicular viability in ovarian tissue frozen for fertility preservation

OBJECTIVE

To determine the effect of storage duration on cryopreserved ovarian tissue using fresh and frozen-thawed samples.

METHODS

Seventeen fertile patients underwent an ovarian biopsy during elective laparoscopic tubal ligation. The tissue sample was divided into three parts: one part was processed fresh (FG), and two were slowly frozen, cryopreserved for 30 (G30) or 180 days (G180), thawed and analyzed. Follicular density, follicular viability, and steroidogenic capacity were assessed.

RESULTS

We observed no differences between the groups in follicular density, which was assessed in hematoxylin and eosin-stained tissue sections. A heterogeneous follicular distribution was observed in the parenchyma, with a mean density of 361.3±255.4, 454.9±676.3, and 296.8±269.0 follicles/mm(3) for FG, G30 and G180, respectively (p = 0.46). Follicular viability was greater in FG (93.4%) when compared with the cryopreserved tissues (70.8% for G30 (p<0.001) and 78.4% for G180 (p<0.001)), with no difference in viability between the frozen samples (p>0.05). The steroidogenic capacity of the tissue was not significantly reduced following cryopreservation.

CONCLUSION

The slow freezing procedures used for ovarian cryopreservation are capable of preserving follicular viability and maintaining the steroidogenic capacity of the tissue despite a roughly 30% decrease in follicular viability. Furthermore, short-term storage of ovarian tissue does not appear to compromise follicle integrity.

Current achievements and future research directions in ovarian tissue culture, in vitro follicle development and transplantation: implications for fertility preservation

BACKGROUND Female cancer patients are offered 'banking' of gametes before starting fertility-threatening cancer therapy. Transplants of fresh and frozen ovarian tissue between healthy fertile and infertile women have demonstrated the utility of the tissue banked for restoration of endocrine and fertility function. Additional methods, like follicle culture and isolated follicle transplantation, are in development. METHODS Specialist reproductive medicine scientists and clinicians with complementary expertise in ovarian tissue culture and transplantation presented relevant published literature in their field of expertise and also unpublished promising data for discussion. As the major aims were to identify the current gaps prohibiting advancement, to share technical experience and to orient new research, contributors were allowed to provide their opinioned expert views on future research. RESULTS Normal healthy children have been born in cancer survivors after orthotopic transplantation of their cryopreserved ovarian tissue. Longevity of the graft might be optimized by using new vitrification techniques and by promoting rapid revascularization of the graft. For the in vitro culture of follicles, a successive battery of culture methods including the use of defined media, growth factors and three-dimensional extracellular matrix support might overcome growth arrest of the follicles. Molecular methods and immunoassay can evaluate stage of maturation and guide adequate differentiation. Large animals, including non-human primates, are essential working models. CONCLUSIONS Experiments on ovarian tissue from non-human primate models and from consenting fertile and infertile patients benefit from a multidisciplinary approach. The new discipline of oncofertility requires professionalization, multidisciplinarity and mobilization of funding for basic and translational research.

Duration of fertility after fresh and frozen ovary transplantation

OBJECTIVE

To evaluate the function of human ovarian transplants.

DESIGN

Follow a series of fresh ovarian transplants for up to 5 years, and compare fresh and frozen ovarian tissue transplantation.

SETTING

Tertiary referral community hospital.

PATIENT(S)

Nine women with premature ovarian failure who received an ovary donated from a monozygotic twin sibling, and 16 young cancer patients undergoing ovarian cryopreservation. Two of the transplant recipients were cancer survivors rendered sterile by their therapy.

INTERVENTION(S)

Fresh ovary transplantation between monozygotic twin sisters, as well as transplantation of previously frozen ovarian tissue, and study of cryopreserved tissue in cancer patients.

MAIN OUTCOME MEASURE(S)

Return of normal menstrual cycling, hormone levels, pregnancy, healthy babies, duration of transplant function, and ovarian tissue evaluation.

RESULT(S)

Normal serum FSH and regular menstrual cycles returned by 5 months after surgery in all cases, both fresh and frozen. Fourteen spontaneous pregnancies were established leading to eight healthy live births and two healthy ongoing conceptions. All three frozen tissue transplants conceived spontaneously, one delivered, and two were ongoing. Oocyte survival with slow freezing was 42% and after vitrification 89%.

CONCLUSION(S)

Ovarian transplantation in humans is a robust procedure, even after cryopreservation, and vitrification might prove to be more effective than slow freezing.

Interaction between ascorbic acid and follicle-stimulating hormone maintains follicular viability after long-term in vitro culture of caprine preantral follicles

This study evaluates the effects of ascorbic acid and its interaction with follicle-stimulating hormone (FSH) on the morphology, activation, and in vitro growth of caprine preantral follicles. Ovarian fragments were cultured for 1, 7, or 14 d in minimum essential medium (MEM) containing ascorbic acid (50 or 100microg/mL), FSH (50ng/mL), or both of these substances. Ovarian tissue that was either fresh (control) or cultured for 1, 7, or 14 d was processed for histological and ultrastructural evaluation. The results showed that after 14 d of culture, medium supplemented with 50microg/mL of ascorbic acid alone or combined with FSH showed higher rates of follicular survival compared with MEM. After 7 d of culture, FSH, ascorbic acid at 50microg/mL with or without FSH, and ascorbic acid at 100microg/mL increased the percentage of follicular activation compared to fresh control. In addition, FSH alone significantly increased the percentage of growing follicles after 14 d. The combination of 50microg/mL of ascorbic acid and FSH promoted a significant increase in oocyte and follicular diameter after 7 d of culture. Ultrastructural and fluorescent analysis confirmed the integrity of follicles cultured with 50microg/mL of ascorbic acid and FSH after 14 d. In conclusion, the combination of 50microg/mL of ascorbic acid and FSH maintained follicular integrity and promoted follicular activation and growth after long-term in vitro culture of caprine preantral follicles.

Healthy Early Preantral Follicle Can Be Obtained in a Culture of Frozen–Thawed Human Ovarian Tissue of 32 Weeks

The objective of this study was to report morphological and functional evidence of a well-preserved preantral follicle recovered from human frozen-thawed ovarian tissue in a long-term culture. The tissue was originally obtained from a 26-year-old woman with breast cancer. The ovarian cortex was collected by laparoscopy and frozen/thawed and cultured for 32 weeks in minimum essential medium alpha-MEM, supplemented with insulin transferrine selenite (ITS), human serum (HS), antibiotics, follicle-stimulating hormone (FSH). and N-acetyl cysteine (NAC). Thawed tissue samples were examined by light microscopy (LM), transmission electron microscopy (TEM), and real-time RT-PCR. LM examination of cortical pieces after 32 weeks of culture showed a healthy early preantral follicle; TEM and real-time PCR confirmed its good state of preservation. The synergy in action of NAC and FSH plays an important role in follicle growth of ovarian tissue cultures. For the first time a well-preserved preantral follicle was found in a culture of frozen-thawed human ovarian tissue.

Oogenesis and cell death in human prenatal ovaries: what are the criteria for oocyte selection?

Prenatal oogenesis produces hundreds of thousands of oocytes, most of which are discarded through apoptosis before birth. Despite this large-scale selection, the survivors do not constitute a perfect population, and the factors at the cellular level that result in apoptosis or survival of any individual oocyte are largely unknown. What then are the selection criteria that determine the size and quality of the ovarian reserve in women? This review focuses on new data at the cellular level, on human prenatal oogenesis, offering clues about the importance of the timing of entry to meiotic prophase I by linking the stages and progress through MPI with the presence or absence of apoptotic markers. The characteristics and responsiveness of cultured human fetal ovarian tissue at different gestational ages to growth factor supplementation and the impact of meiotic abnormalities upon apoptotic markers are discussed. Future work will require the use of a tissue culture model of prenatal oogenesis in order to investigate the fate of individual live oocytes at different stages of development.

Growth differentiation factor-9 and anti-Müllerian hormone expression in cultured human follicles from frozen-thawed ovarian tissue

In-vitro growth of frozen-thawed human follicles is perceived as a potential option for restoring women's fertility. The aims of this study were: (i) to test the usefulness of a defined serum-free medium for growth of frozen-thawed human follicles; and (ii) to evaluate the expression of growth differentiation factor-9 (GDF-9) and anti-Müllerian hormone (AMH) in cultured follicles. Frozen-thawed ovarian cortical pieces from 7-, 12-, 25- and 27-year-old women were cultured for 0, 7, 14, 21 and 28 days. Follicle developmental quality was evaluated and expression of proliferating cell nuclear antigen (PCNA) (day 21), GDF-9 (days 14 and 28) and AMH (day 21) was assessed by immunohistochemistry. Primary follicles and enclosed oocytes underwent significant growth at the end of culture (P < 0.05). Cultured follicles from all patients studied reached the early secondary stage and a few follicles from two patients developed up to the secondary stage. The rate of atresia was variable throughout the culture periods. PCNA was expressed in the granulosa cells at all the different follicular stages. AMH and GDF-9 immunostaining were found respectively in the granulosa cells and oocytes after several weeks of culture. The transition from resting to growing follicles leading to the development of secondary follicles showed the normal expression patterns of GDF-9 and AMH.

Tissue culture before transplantation of frozen-thawed human fetal ovarian tissue into immunodeficient mice

OBJECTIVE

To evaluate the effects of tissue culture on the viability and development of follicles in frozen-thawed human fetal ovarian tissue before transplantation into severe combined immunodeficient (SCID) mice and to determine the optimal duration of pretransplant tissue culture.

DESIGN

Experimental prospective study.

SETTING

Animal center and reproductive laboratories in university hospitals.

INTERVENTION(S)

Frozen-thawed human fetal ovarian tissue samples from 20-week-old abortuses were randomly divided into four groups and cultured in vitro for 0, 3, 6, or 9 days before being xenografted into kidney capsules of bilaterally oophorectomized severe combined immunodeficient (SCID) mice. Grafts were removed 16 weeks after transplantation. Histological analysis and assessment of proliferative cell nuclear antigen (PCNA) expression levels were used to evaluate the survival and development of follicles.

RESULT(S)

The proportion of growing follicles was significantly increased in groups cultured before transplantation as compared with the noncultured group. Sixteen weeks after transplantation, the number of follicles in the cultured grafts was higher than that in the noncultured grafts. Grafts cultured for 6 or 9 days showed higher proportions of preantral and antral follicles than grafts cultured for 0 or 3 days. PCNA immunohistochemical analysis indicated that follicle cells were in a proliferative state after culture and transplantation.

CONCLUSION(S)

The viability and development of human fetal follicles may be improved by pretransplant tissue culture. The optimal culture duration before transplantation of fetal ovarian tissue is 6 days.

Preservation of fertility in young cancer patients: contribution of transmission electron microscopy

During the last decade, new technologies in reproductive medicine have emerged to preserve the fertility of women whose gonadal function is threatened by premature menopause or gonadotoxic treatments. To offer an individualized approach to these patients, different experimental procedures are under investigation, including oocyte cryopreservation and cryopreservation and transplantation of ovarian tissue in the form of cortical fragments, whole ovary or isolated follicles. This review shows that transmission electron microscopy (TEM), combined with other in-vivo and in-vitro analysis techniques, is a valuable tool in the establishment of new experimental protocols to preserve female fertility. Ultrastructural studies allow in-depth evaluation of the oocyte's unique morpho-functional characteristics, which explain its low cryotolerance, and provide essential information on follicular, stromal and endothelial cell integrity, as well as cellular interactions crucial for normal folliculogenesis. In order to be able to offer appropriate and efficient options in every clinical situation, oocyte in-vitro maturation and ovarian tissue transplantation need to be optimized. Further development of new approaches, such as follicular isolation and whole ovary transplantation, should be encouraged. Fine ultrastructural details highlighted by TEM studies will be useful for the further optimization of these emerging technologies.

Cryopreservation and xenotransplantation of human ovarian tissue: an ultrastructural study

OBJECTIVE

To analyze the ultrastructure of human ovarian follicles after cryopreservation and short-term xenografting.

DESIGN

Prospective experimental study.

SETTING

Academic gynecology and anatomy research units.

PATIENT(S)

Ovarian cortical biopsy specimens were obtained from 13 patients.

INTERVENTION(S)

Each ovarian biopsy specimen was dissected into pieces of 1 mm(3) and divided into three groups: [1] fresh tissue, [2] frozen-thawed tissue, and [3] frozen-thawed tissue xenografted onto the peritoneum of nude mice for 3 weeks.

MAIN OUTCOME MEASURE(S)

Follicular ultrastructure was assessed by light and transmission electron microscopy in [1] fresh, [2] frozen, and [3] frozen-grafted tissue.

RESULT(S)

Thirty-five ovarian follicles were analyzed by light and transmission electron microscopy. Twenty-five primordial and primary ovarian follicles were found. Most of them exhibited ultrastructurally well preserved features (fresh [N = 8/10], frozen [N = 7/10], and frozen-grafted [N = 4/5] tissue). Ten secondary follicles were present in xenografts. By transmission electron microscopy, all the healthy-looking secondary follicles (70%) were shown to contain intact oocytes, with features typical of earlier developmental stages, surrounded by several layers of follicular cells.

CONCLUSION(S)

The present study demonstrates, for the first time, that cryopreservation and xenotransplantation do not appear to greatly affect human primordial/primary follicle ultrastructure. Interestingly, in frozen-thawed xenografts, secondary human ovarian follicles presented a well preserved ultrastructure, but asynchrony between oocyte and granulosa cell development was detected. The possible causes for this asynchrony are discussed.

Expression of growth differentiation factor 9, bone morphogenetic protein 15, and anti-Müllerian hormone in cultured mouse primary follicles

Growth differentiation factor 9 (GDF9), bone morphogenetic protein 15 (BMP15), and anti-Müllerian hormone (AMH) play an important role in the primary to secondary follicle transition and follicle activation in vivo. In organ culture of neonatal mouse ovaries, it was observed that significantly fewer primary follicles develop to the secondary stage. The objectives of this study were: (1) to compare ovarian follicular populations between organ-cultured neonatal mouse ovaries and freshly isolated age-matched control ovaries; (2) to quantify RNA levels of Gdf9, Bmp15, and Amh in cultured primary follicles; and (3) to immunolocalize GDF9 and AMH in cultured ovaries. Ovaries from 3-day-old (PND 3) mice were cultured for 7 or 10 days in the absence or presence of FSH. Follicular populations were counted in freshly isolated 13-day-old (PND 13) ovaries and organ-cultured ovaries. Transcripts were quantified in isolated primary follicles using real-time RT-PCR, and protein expressions were localized using immunohistochemistry. The number of secondary follicles in organ-cultured ovaries was significantly lower than in vivo controls. Gdf9 and Bmp15 mRNA expression levels were similar as in controls. Amh mRNA levels were significantly (P<0.05) lower after day 10 of culture in the absence of FSH. GDF9 and AMH proteins were respectively detected in the oocytes and the granulosa cells (GC) beginning at the primary and primordial stages onward. GDF9 and BMP15 production in cultured primary follicles are not different from in vivo controls; hence abnormal early follicular growth was not related to a deficient transcription of these factors.

[State of the art on in vitro folliculogenesis in mouse]

Follicle culture systems have been developed so as to achieve in vitro fertilization of oocytes coming from immature follicles. The in vitro folliculogenesis methods would be especially useful in reproductive medicine to restore fertility in women having undergone ovarian cryopreservation. Several culture systems allowing in vitro growth of small follicles have been developed in mouse. These have proven to be successful by the birth of healthy offsprings. Some elements determine the outcome of culture: follicle isolations at a defined stage of development, follicular morphology preservation, and supplementation of growth factors or hormones. Development of follicle culture in the mouse model led to a better understanding of ovarian physiology, in particular the relation between endocrine and paracrine factors on follicle development. The in vitro techniques in mouse became a valuable tool for improving reproductive technics improvement, and for toxicology studies.

[What are at present the real hopes of pregnancy after ovarian cryopreservation?]

Survival rates for cancers that occur in childhood and adolescence have improved over the last decades, and preservation of future fertility in these patients has become a relevant issue. Premature ovarian failure is a consequence of exposing women to chemotherapeutic drugs and ionizing radiation. Ovarian cryopreservation is an alternative to cryopreservation of embryos or oocytes for theses patients. Ovarian cryopreservation aims to reimplant ovarian tissue after complete remission into the pelvic cavity (orthotopique site) or a heterotopic site like the abdominal wall or the forearm. In vitro folliculogenesis, that aims at the maturation of ovarian cortex primordial follicles cryopreserved for a FIV, is still in an experimental research stage. In this review, the objective was to evaluate the real hopes of pregnancy after ovarian cryopreservation. Indeed, many teams offer ovarian cryopreservation at present time, although only two pregnancies have been achieved to date. In both cases, it can be discussed whether the fertilized oocyte originated from the transplant or from the native ovary. Furthermore, the potential for reintroduction of cancerous cells may limit this technique in cancers that are known to have a risk of ovarian dissemination. The hopes engendered by ovarian cryopreservation, but also its limits, must be explained to the patients before an ovarian surgery for cryopreservation.

Ovarian tissue preservation, present and clinical perspectives

Ovarian tissue preservation and transplantation are intended for women undergoing aggressive regimens of chemical and/or radiological therapy, bone marrow transplantation or stem cell transplantation. Main indications for the procedure are neoplastic diseases and autoimmune disorders. The first live human birth after ovarian tissue autotransplantation was successfully done in 2002. Cryopreserved ovarian tissue can be autografted either orthotopically or heterotopically. Neovascularization of the implanted tissue is essential for the procedure. Vascular transplantation seems to be the best approach for avoiding follicular loss and extending the lifespan of the ovarian grafts. The procedure, regardless of whether ortho- or heterotopic, is connected with a risk of reimplantation of neoplastic cells. This can be minimized by multiple ovary biopsies, thorough histological examination and molecular genetic techniques. Introducing ovarian tissue transplantation into clinical practice requires many problems to be solved. Standardization of the freeze-thaw protocol is one of the most important issues. Solving the problem of transient graft ischemia is also essential. Eventually, the future safety of the method requires the development of efficient tests to detect the presence of neoplastic cells in the transplanted tissue.

Follicle stimulating hormone and fibroblast growth factor-2 interact and promote goat primordial follicle development in vitro

The aims of the present study were to investigate the effects of the interaction between follicle stimulating hormone (FSH) and fibroblast growth factor-2 (FGF-2) on survival, follicular growth initiation and further growth of caprine preantral follicles. Pieces of caprine ovarian cortex were cultured for 1 or 7 days in minimum essential medium (MEM) supplemented with FSH, FGF-2 or FSH + FGF-2. Small fragments from non-cultured ovarian tissue and from those cultured for 1 or 7 days were processed for classical histology and transmission electron microscopy (TEM) to verify follicular morphology and growth. The results showed that, after 7 days culture, the highest percentages of normal follicles were observed in medium supplemented with FSH. After 7 days culture, the interaction between FSH and FGF-2 was most effective to promote the initiation of primordial follicles growth and oocyte growth. TEM showed ultrastructural integrity of follicles after 1 day of culture in MEM and after 7 days in all treatments, except in those follicles cultured for 7 days in MEM. In conclusion, this study demonstrated that the interaction between FSH and FGF-2 stimulates the initiation of primordial follicles growth and the subsequent growth of developing follicles. Furthermore, these data showed that FSH is important to maintain follicular integrity after 7 days culture.

Human fetal ovarian culture permits meiotic progression and chromosome pairing process

BACKGROUND

The female meiotic process seems to be crucial for aneuploidy in humans. The first stages of mammalian female meiosis take place during the fetal period. Therefore, only little is known about female meiosis. The goal of this study was to develop a culture technique that permits human oocytes to progress through meiotic prophase, to provide a system to study human female meiosis.

METHOD

Fetal ovaries from four cases were cultured up to 35 days in alpha-minimal essential medium, 2% human serum albumin, 5 microg/ml insulin, 5 microg/ml transferrin, 5 ng/ml selenium and 100 IU/ml penicillin-100 microg/ml streptomycin.

RESULTS AND CONCLUSIONS

Although ovarian response to culture conditions varied, human oocytes survived in vitro up to 5 weeks. In three cases, we observed significant variation in stages of meiosis among the cultures. The homologous chromosome pairing process was studied for the first time in cultured oocytes, and the results suggested that the pairing process was completed following the same features described previously for euploid oocytes, as followed by the chromosome-13 pairing process and synaptonemal complex formation. Although a higher proportion of degenerated oocytes were observed as culture time increased, we also observed oogonial entrance to meiotic prophase.