Cryopreservation Competence of Chicken Oocytes as a Model of Endangered Wild Birds: Effects of Storage Time and Temperature on the Ovarian Follicle Survival

For the conservation of endangered avian species, developing gamete preservation technologies is essential. However, studies in oocytes have not been widely conducted. In this study, assuming that the ovaries are transported to a research facility after death, we investigated the effect of ovary storage on oocytes for the purpose of cryopreserving avian female gametes by using a chicken as a model of endangered avian species. After excision, the ovaries were stored at either a low temperature (4 °C) or room temperature for 1–3 days. Ovarian follicles stored under different conditions for each period were examined by neutral red staining, histology, and gene and protein expression analysis. In addition, the pH of the storage medium after preserving the ovaries was measured. Then, ovarian tissues were vitrified to determine the cryopreservation competence. Storing the ovarian tissues at 4 °C kept the follicles viable and morphologically normal for 3 days with slow decline. In contrast, although different storage temperature did not influence follicle viability and morphology after only 1 day of storage, ovarian tissues stored at room temperature rapidly declined in structurally normal follicles, and viable follicles were rarely seen after 3 days of storage. Gene and protein expression analysis showed that apoptosis had already started on the first day, as shown by the higher expression of CASP9 under room temperature conditions. Furthermore, high expression of SOD1 and a rapid decline of pH in the storage medium under room temperature storage suggested the influence of oxidative stress associated with low pH in this condition on the follicle survivability in hen ovarian tissues. Our cryopreservation study also showed that ovarian tissues stored at 4 °C could recover after cryopreservation even after 3 days of storage. The described storage conditions and cryopreservation methods, which preserve chicken follicle survival, will lay the foundation of ovarian tissue preservation to preserve the fertility of wild female birds.

Cellular and Molecular Events that Occur in the Oocyte during Prolonged Ovarian Storage in Sheep

Simple Summary

Establishing efficient in vitro embryo production (IVP) protocols in sheep usually requires prolonged transportation of post-mortem ovaries since adult animals are often slaughtered in abattoirs far from laboratories. In this study, different analyses were carried out to investigate important cellular and molecular aspects of hypoxic injury on excised ovaries over time in order to understand the factors jeopardizing the development of competent oocytes during prolonged transport times. We observed that, when ovaries were stored for more than 7 h, the quality and developmental potential of oocytes and cumulus cells were greatly reduced. Moreover, the use of medium TCM199 over saline solution also had deleterious effects. Beyond transport time, strategies aimed at reducing these damages may improve oocyte quality and developmental competence.

Abstract

For the past two decades, there has been a growing interest in the application of in vitro embryo production (IVP) in small ruminants such as sheep. To improve efficiency, a large number abattoir-derived ovaries must be used, and long distances from the laboratory are usually inevitable when adult animals are used. In that scenario, prolonged sheep ovary transportation may negatively affect oocyte developmental competence. Here, we evaluated the effect of ovary storage time (3, 5, 7, 9, 11 and 13 h) and the medium in which they were transported (TCM199 and saline solution) on oocyte quality. Thus, live/dead status, early apoptosis, DNA fragmentation, reduced glutathione (GSH) and reactive oxygen species (ROS) content, caspase-3 activity, mitochondrial membrane potential and distribution, and relative abundance of mRNA transcript levels were assessed in oocytes. After in vitro maturation (IVM), cumulus cell viability and quality, meiotic and fertilization competence, embryo rates and blastocyst quality were also evaluated. The results revealed that, after 7 h of storage, oocyte quality and developmental potential were significantly impaired since higher rates of dead oocytes and DNA fragmentation and lower rates of viable, matured and fertilized oocytes were observed. The percentage of cleavage, blastocyst rates and cumulus cell parameters (viability, active mitochondria and GSH/ROS ratio) were also decreased. Moreover, the preservation of ovaries in medium TCM199 had a detrimental effect on cumulus cells and oocyte competence. In conclusion, ovary transport times up to 5 h in saline solution are the most adequate storage conditions to maintain oocyte quality as well as developmental capacity in sheep. A strategy to rescue the poor developmental potential of stored oocytes will be necessary for successful production of high-quality embryos when longer ovarian preservation times are necessary.

Ovarian tissue transportation: a systematic review

In recent years, some countries and fertility preservation networks have started adopting 24 h transportation for ovarian tissue, a practice that has the potential to spread very quickly due to the high costs and bureaucracy involved in the establishment of ovarian tissue cryobanks. While pregnancies and live births have been reported after such long periods of transportation, this, however, remains an empirical procedure. This review aims to prompt reflection on ovarian tissue transport, highlighting the lack of knowledge in humans by providing a counterpoint looking into more than 40 studies published in different animal models. By discussing these studies in animals, the findings of various models can be deciphered, and light shed on the patterns identified. Like the development of different assisted reproductive technology procedures, this is an important step in creating guidelines for future studies on human ovarian tissue transportation.

Evidence of metabolic activity during low-temperature ovarian tissue preservation in different media

PURPOSE

Although ovarian tissue transportation has been validated for up to 24 h, there is no standard protocol to date. We aimed to elucidate how existing media currently used for ovarian tissue transportation affect ovarian tissue metabolism and cell viability.

METHODS

Cow ovarian fragments were immersed in 0.9% NaCl solution, IVF medium, Leibovitz 15 medium (L-15), or PBS for 1, 4, or 24 h at 4 °C. Media were analyzed for pH, lactate dehydrogenase (LDH) activity, and glucose, pyruvate, and lactate concentrations, while apoptosis was assessed by TUNEL assays in fixed fragments. Viability rates were assessed by flow cytometry (FACS).

RESULTS

There were lower pH levels in NaCl at all time points compared with other media. LDH activity increased with time and was lowest in NaCl at 1 and 4 h. There was no significant difference in glucose levels, but a significant pyruvate decrease in L-15 and a significant lactate increase in all media. TUNEL showed apoptosis rates ranging from 0 to 5%. FACS showed a mean of 4% necrotic cells and 15-19% apoptotic cells after 1 h of incubation, but less than 1% necrotic cells and 2-6% apoptotic cells after 24 h in all media.

CONCLUSION

Our results indicate marked metabolic activity in ovarian tissue at 4 °C and suggest that cells use internal sources of energy, which may influence transplantation outcomes. This highlights the importance of better understanding whole tissue dynamics to develop a standard protocol for ovarian tissue transportation. Graphical abstract.

Impact of oxidative stress on oocyte competence for in vitro embryo production programs

Producing high-competent oocytes during the in vitro maturation (IVM) is considered a key step for the success of the in vitro production (IVP) of embryos. One of the known disruptors of oocyte developmental competence on IVP is oxidative stress (OS), which appears due to the imbalance between the production and neutralization of reactive oxygen species (ROS). The in vitro conditions induce supraphysiological ROS levels due to the exposure to an oxidative environment and the isolation of the oocyte from the follicle protective antioxidant milieu. In juvenile in vitro embryo transfer (JIVET), which aims to produce embryos from prepubertal females, the oocytes are more sensitive to OS as they have inherent lower quality. Therefore, the IVM strategies that aim to prevent OS have great interest for both IVP and JIVET programs. The focus of this review is on the effects of ROS on oocyte IVM and the main antioxidants that have been tested for protecting the oocyte from OS. Considering the importance that OS has on oocyte competence, it is crucial to create standardized antioxidant IVM systems for improving the overall IVP success.

Beneficial Effects of Melatonin in the Ovarian Transport Medium on In Vitro Embryo Production of Iberian Red Deer (Cervus elaphus hispanicus)

Simple Summary

The development of in vitro embryo production (IVP) in wild species, such as Iberian red deer, can become a daunting challenge since prolonged ovary transport times to the laboratory are often unavoidable. This may have detrimental effects on the quality and developmental capacity of oocytes. We evaluated the effect of supplementing the ovary transport medium with the antioxidant melatonin and observed an increased level of oocyte intracellular reduced glutathione content. Moreover, melatonin enhanced cleavage and blastocyst rates and had a positive effect on embryo quality in terms of the expression of essential embryo development-related genes. In conclusion, the addition of melatonin to the ovary storage medium could mitigate the negative impacts that long transport times may have on oocyte developmental competence and quality of the resulting blastocysts in Iberian red deer.

Abstract

A major limiting factor for the development of in vitro embryo production (IVP) in wild species, such as Iberian red deer, compared to livestock animals is the poor availability and limited access to biological material. Thus, the use of post-mortem ovaries from slaughtered animals represent a source of oocytes for the large scale production of embryos needed for research and to improve the efficiency of IVP. However, these oocytes are not as developmentally competent as their in vivo counterparts. Moreover, oocytes are usually obtained from ovaries that have been transported for long distances, which may also affect their quality. In order to overcome the issues associated with prolonged storage times of post-mortem material, in this study we examined the effect of melatonin supplementation to the ovary transport medium on oocyte quality, embryo yield, and blastocyst quality in Iberian red deer. When necessary, sheep was used as an experimental model due to the large number of samples required for analysis of oocyte quality parameters. Oocytes were in vitro matured and assessed for early apoptosis; DNA fragmentation; reactive oxygen species (ROS); reduced glutathione (GSH) content, mitochondrial membrane potential, and distribution; and relative abundance of mRNA transcript levels. After in vitro fertilization, embryo rates and blastocyst quality were also investigated. The results revealed that melatonin treatment significantly increased intracellular level of GSH in sheep oocytes. Moreover, the percentage of cleavage and blastocyst yield in red deer was greater compared to the Control group and there was lower abundance of oxidative stress- and apoptosis-related SHC1, TP53, and AKR1B1 mRNA transcripts in blastocysts for the Melatonin group. In conclusion, the supplementation of melatonin to the ovary storage medium had a positive effect on the developmental competence and quality of resulting blastocysts in Iberian red deer.

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.