Vitrification of feline ovarian tissue: Comparison of protocols based on equilibration time and temperature

Global contraction of biodiversity pushed most members of Felidae into threatened or endangered list except the domestic cat (Felis catus) thence preferred as the best model for conservation studies. One of the emerging conservation strategies is vitrification of ovarian tissue which is field-friendly but not yet standardized. Thus, our main goal was to establish a suitable vitrification protocol for feline ovarian tissue in field condition. Feline ovarian tissue fragments were punched with biopsy punch (1.5 mm diameter) and divided into 4 groups. Group 1 was fresh control (Fr), while the other three were exposed to 3 vitrification protocols (VIT_CT, VIT_RT1 and VIT_RT2). VIT_CT involved two step equilibrations in solutions containing dimethyl sulfoxide (DMSO) and ethylene glycol (EG) for 10 min each at 4 °C. VIT_RT1 involved three step equilibration in solutions containing DMSO, EG, polyvinylpyrrolidone and sucrose for 14 min in total at room temperature, while in VIT_RT2 all conditions remained the same as in VIT_RT1 except equilibration timing which was reduced by half. After vitrification and warming, fragments were morphologically evaluated and then cultured for six days. Subsequently, follicular morphology, cellular proliferation (expression of Ki-67, MCM-7) and apoptosis (expression of caspase-3) were evaluated, and data obtained were analysed using generalised linear mixed model and chi square tests. Proportions of intact follicles were higher in Fr (P = 0.0001) and VIT_RT2 (P = 0.0383) in comparison to the other protocols both post warming and after the six-day culture. Generally, most follicles remained at primordial state which was confirmed by the low expression of Ki-67, MCM-7 markers. In conclusion, VIT_RT2 protocol, which has lower equilibration time at room temperature has proven superior thus recommended for vitrification of feline ovarian tissue.

First report on successful delivery after retransplantation of vitrified, rapid warmed ovarian tissue in Europe

RESEARCH QUESTION

Cryopreservation of ovarian tissue is one feasible option to preserve female fertility prior to cancer treatment. The slow freezing protocol represents the current standard approach, while vitrification has been suggested as a promising alternative. This paper reports the follow-up and first successful delivery after retransplantation of vitrified, rapid warmed ovarian tissue in Europe.

DESIGN

After the patient received a diagnosis of breast cancer, ovarian tissue was removed laparoscopically and sent via overnight transportation to University Hospital Bonn for vitrification on site. The patient was treated with chemotherapy, leading to ovarian failure. After 2 years, retransplantation of the vitrified, rapid warmed tissue was conducted on site.

RESULTS

Two months after grafting, the patient reported regular menstrual cycles. After 1 further month a clinical pregnancy occurred, which ended in a spontaneous abortion at the 8th week of pregnancy. Six months after grafting, another naturally conceived pregnancy was determined, resulting in the birth of a healthy boy 14 months after retransplantation of the ovarian tissue.

CONCLUSIONS

Complementing the successful deliveries reported by the groups of Suzuki (Japan) and Silber (USA) regarding vitrified tissue, the current results confirm the high potential of this cryopreservation method in a clinical routine setting as an alternative approach to the widespread slow freezing method.

Comparison of angiogenic potential in vitrified vs. slow frozen human ovarian tissue

Vitrification of ovarian tissue is a promising alternative approach to the traditional slow freezing method. Few empirical investigations have been conducted to determine the angiogenic profiles of these two freezing methods. In this study we aimed to answer the question whether one of the cryopreservation methods should be preferred based on the secretion of angiogenic factors. Tissue culture with reduced oxygen (5%) was conducted for 48 h with samples of fresh, slow frozen/thawed and vitrified/rapid warmed ovarian cortex tissue from 20 patients. From each patient, tissue was used in all three treatment groups. Tissue culture supernatants were determined regarding cytokine expression profiles of angiogenin, angiopoietin-2, epidermal growth factor, basic fibroblast growth factor, heparin binding epidermal growth factor, hepatocyte growth factor, Leptin, Platelet-derived growth factor B, placental growth factor and vascular endothelial growth factor A via fluoroimmunoassay. Apoptotic changes were assessed by TUNEL staining of cryosections and supplemented by hematoxylin and eosin and proliferating cell nuclear antigen staining. Comparing the angiogenic expression profiles of vitrified/rapid warmed tissue with slow frozen/thawed tissue samples, no significant differences were observed. Detection of apoptotic DNA fragmentation via TUNEL indicated minor apoptotic profiles that were not significantly different comparing both cryopreservation methods. Vitrification of ovarian cortical tissue does not appear to impact negatively on the expression profile of angiogenic factors and may be regarded as an effective alternative approach to the traditional slow freezing method.

Importance of oxygen tension in human ovarian tissue in vitro culture

STUDY QUESTION

Is there any difference between 20% and 5% oxygen (O2) tension in vitro culture (IVC) on the viability and quality of human follicles contained in cultured ovarian cortex?

SUMMARY ANSWER

An O2 tension of 5% yields higher follicle viability and quality than does 20% O2 tension after 6 days of IVC.

WHAT IS KNOWN ALREADY

The primordial follicle (PMF) pool resides within the ovarian cortex, where the in vivo O2 tension ranges between 2% and 8%. Some studies suggest that lowering O2 tension to physiological levels may improve in vitro follicle quality rates.

STUDY DESIGN, SIZE, DURATION

This prospective experimental study included frozen-thawed ovarian cortex from six adult patients (mean age: 28.5 years; age range: 26-31 years) who were undergoing laparoscopic surgery for non-ovarian diseases. Ovarian cortical fragments were cultured for 6 days at (i) 20% O2 with 5% CO2 and (ii) 5% O2 with 5% CO2. Non-cultured fragments served as controls.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Cortical fragments were used for the following analyses: hematoxylin and eosin staining for follicle count and classification; Ki67 staining to evaluate PMF proliferation; cleaved caspase-3 immunostaining to identify follicle apoptosis; 8-hydroxy-2-deoxyguanosine and gamma-H2AX (γH2AX) immunolabeling to detect oxidative stress damage and DNA double-strand breaks (DSBs) in oocytes and granulosa cells (GCs); and β-galactosidase staining to assess follicle senescence. Droplet digital PCR was also performed to further explore the gene expression of superoxide dismutase 2 (SOD2) and glutathione peroxidase 4 (GPX4) from the antioxidant defense system and cyclin-dependent kinase inhibitors (p21 and p16) as tissue senescence-related genes.

MAIN RESULTS AND THE ROLE OF CHANCE

Apoptosis (P = 0.002) and follicle senescence (P < 0.001) rates were significantly lower in the 5% O2 group than in the 20% O2 group. Moreover, GCs in follicles in the 20% O2 group exhibited significantly (P < 0.001) higher oxidative stress damage rates than those in the 5% O2 group. DNA DSB damage rates in GCs of follicles were also significantly higher (P = 0.001) in the 20% O2 group than in the 5% O2 group. SOD2 expression was significantly greater in the 5% O2 group compared to the 20% O2 group (P = 0.04) and the non-cultured group (P = 0.002). Expression of p21 was significantly increased in both the 20% O2 (P = 0.03) and 5% O2 (P = 0.008) groups compared to the non-cultured group. Moreover, the 20% O2 group showed significantly greater p16 expression (P = 0.04) than the non-cultured group, while no significant variation was observed between the 5% O2 and no culture groups.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

This study focuses on improving follicle outcomes during the first step of ovarian tissue IVC, where follicles remain in situ within the tissue. The impact of O2 tension in further steps, such as secondary follicle isolation and maturation, was not investigated here.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings suggest that 5% O2 tension culture is a promising step toward potentially solving the problem of poor follicle viability after IVC.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by grants from the Fonds National de la Recherche Scientifique de Belgique (FNRS-PDR T.0064.22, CDR J.0063.20 and grant 5/4/150/5 awarded to M.M.D.). The authors have nothing to disclose.

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.

Follicle outcomes in human ovarian tissue: effect of freezing, culture, and grafting

OBJECTIVE

To study the effect of freezing, in vitro culture (IVC) and grafting to chorioallantoic membrane (CAM) on follicle outcomes in human ovarian tissue.

DESIGN

An experimental study.

SETTING

University-based research laboratory.

PATIENTS

Fresh and cryopreserved ovarian tissue from 10 patients was donated to research with their consent and institutional review board approval.

INTERVENTIONS

Fresh and frozen-thawed ovarian cortical pieces were in vitro-cultured and compared (fresh-IVC vs FT-IVC). The FT-IVC fragments were then examined against fragments grafted to CAM (FT-CAM). After both IVC and CAM grafting, ovarian cortical pieces (4×2×1 mm³) were analyzed on days 0, 1, and 6.

MAIN OUTCOME MEASURES

Follicle analyses included histology (count and classification) and immunohistochemistry (Ki67 [proliferation], caspase-3 [apoptosis], 1A and 1B light chain 3B [autophagy], p-Akt, FOXO1, and p-rpS6 [PI3K activation]). Droplet digital polymerase chain reaction further explored expression of PI3K pathway- and oocyte-related genes in tissue sections.

RESULTS

No major differences were detected between fresh-IVC and FT-IVC tissues in any conducted analyses. Although a significant drop was observed in primordial follicle (PF) proportions in the fresh-IVC and FT-IVC groups (d0 vs. d6, P<.002), they held steady in the FT-CAM group (d0 vs. d6, P>.05). The PF rates were also significantly higher in the FT-CAM group than the FT-IVC group on d6 (P=.02). Importantly, avian erythrocytes were already present in 30% of implants from d1. Apoptotic and autophagic follicle rates increased during IVC (P<.008), but remained significantly lower in the FT-CAM group (P<.01), confirming superior follicle preservation in CAM-grafted tissue. Upregulation of the PI3K/FOXO pathway was established in the IVC groups, demonstrating PF activation, whereas significant pathway downregulation was detected in the FT-CAM group (P<.03). The droplet digital polymerase chain reaction tests confirmed oocyte growth during IVC and follicle autophagy in all groups; however, the PI3K pathway appeared to be differentially modulated in tissues and follicles.

CONCLUSIONS

In vitro culture induces PF depletion with no additional impact of freezing. Grafting to CAM preserves the PF pool by curbing follicle activation, apoptosis, and autophagy, probably thanks to rapid graft revascularization and/or the circulating embryonic antimüllerian hormone. These findings highlight the importance of enhancing neoangiogenesis in ovarian grafts and investigating the potential benefits of administering antimüllerian hormone to prevent PF burnout.

Adipose tissue-derived stem cells protect the primordial follicle pool from both direct follicle death and abnormal activation after ovarian tissue transplantation

PURPOSE

To investigate whether adipose tissue-derived stem cells (ASCs) protect the primordial follicle pool, not only by decreasing direct follicle loss but also by modulating follicle activation pathways.

METHODS

Twenty nude mice were grafted with frozen-thawed human ovarian tissue from 5 patients. Ten mice underwent standard ovarian tissue transplantation (OT group), while the remaining ten were transplanted with ASCs and ovarian tissue (2-step/ASCs+OT group). Ovarian grafts were retrieved on days 3 (n = 5) and 10 (n = 5). Analyses included histology (follicle count and classification), immunohistochemistry (c-caspase-3 for apoptosis and LC3B for autophagy), and immunofluorescence (FOXO1 for PI3K/Akt activation and YAP for Hippo pathway disruption). Subcellular localization was determined in primordial follicles on high-resolution images using structured illumination microscopy.

RESULTS

The ASCs+OT group showed significantly higher follicle density than the OT group (p = 0.01). Significantly increased follicle atresia (p < 0.001) and apoptosis (p = 0.001) were observed only in the OT group. In primordial follicles, there was a significant shift in FOXO1 to a cytoplasmic localization in the OT group on days 3 (p = 0.01) and 10 (p = 0.03), indicating follicle activation, while the ASCs+OT group and non-grafted controls maintained nuclear localization, indicating quiescence. Hippo pathway disruption was encountered in primordial follicles irrespective of transplantation, with nuclear YAP localized in their granulosa cells.

CONCLUSION

We demonstrate that ASCs exert positive effects on the ovarian reserve, not only by protecting primordial follicles from direct death but also by maintaining their quiescence through modulation of the PI3K/Akt pathway.

Long-Term Advantages of Ovarian Reserve Maintenance and Follicle Development Using Adipose Tissue-Derived Stem Cells in Ovarian Tissue Transplantation

(1) Background: Ovarian tissue transplantation with adipose tissue-derived stem cells (ASCs) has been shown to enhance graft vascularization and increase follicle survival after a short interval of 7 days. The aim of the present study was to investigate their long-term effects on primordial follicle pool maintenance and follicle development. (2) Methods: A total of 14 severe combined immunodeficient (SCID) mice were grafted with frozen-thawed human ovarian tissue with or without ASCs. Blood was taken monthly in order to quantify the anti-Müllerian hormone (AMH) and estradiol. After 6 months, all the grafts were retrieved and sent for histology and immunolabeling (AMH, AMH receptor II, estrogen receptors α and β, and c-kit/kit ligand). (3) Results: A significant upturn was observed in AMH and estradiol plasma levels 4 months after transplantation in both grafted groups. The primordial follicle pool was better preserved in the ASC group (41.86 ± 28.35) than in the standard transplantation group (9.65 ± 17.6, p < 0.05) compared to non-grafted controls (124.7 ± 140). (4) Conclusions: The use of ASCs prior to ovarian tissue transplantation yielded a larger primordial follicle pool and more physiological follicle distribution after long-term grafting. These findings suggested that ASC use might extend the ovarian tissue lifespan.

Fertility preservation in women for medical and social reasons: Oocytes vs ovarian tissue

Approximately 10% of cancers occur in women under 45 years of age. Chemotherapy, radiotherapy, and bone marrow transplantation cure more than 90% of cancer in women, but can result in premature ovarian insufficiency depending on follicular reserve, age, and drugs used. Some benign diseases are also indications for fertility preservation, particularly those requiring chemotherapy (like thalassemia and lupus), recurrent endometriosis, and family history of premature menopause. Social reasons also account for a large proportion of women who wish to postpone pregnancy. This article discusses the two main strategies for fertility preservation, namely oocyte vitrification and ovarian tissue cryopreservation, examining the indications and results of these options. Oocyte cryopreservation is an effective approach, but further studies are needed in cancer patients to ensure the excellent outcomes obtained in women without cancer or in egg donation programs. For prepubertal girls or cases where immediate therapy is required, cryopreservation of ovarian tissue is the only available option.