Mitochondrial characteristics in oocytes of the domestic cat (Felis catus ) after in vitro maturation and vitrification

Microenvironment factors promoting the quality of vitrified cat oocytes

In oocyte cryopreservation programs, vitrification has overthrown conventional slow freezing both in veterinary and human medicine. In animals, its feasibility in field conditions makes it the preferred technique for the safeguard of genetic resources from zoo or wild animals, including threatened felids, for which the domestic cat is an excellent model. However, many cellular injuries, such as cytoskeleton, mitochondria and meiotic spindle alterations, DNA damage, zona pellucida hardening and cumulus cell loss, might occur following vitrification. After warming, although the exact mechanisms are still unclear, degeneration is a frequent outcome for cat vitrified oocytes. For immature (germinal vesicle) gametes, in vitro maturation after warming is a challenge, and cleavage after fertilization barely reaches 15-30%, while for mature (metaphase II) cryopreserved gametes it can get to 30-50%. Anyway, the progression to late embryos stages is often impaired, and improvements are needed. Standard cryopreservation protocol and the use of conventional in vitro culture systems after warming may not be enough for vitrified oocytes to recover and demonstrate their full developmental potential. Physical or chemical factors applied to oocytes undergoing vitrification, as an enrichment to the vitrification step, or to the culture microenvironment, could create more favorable conditions and promote vitrified oocyte survival and development. From the use of three-dimensional culture systems to the regulation of metabolic activities and cellular pathways, this review aims to explore all the possibilities employed so far, including the studies performed by our own lab, and the future perspectives, to present the most effective strategies for cat oocyte vitrification and the best time for their application (i.e., before, during, or after vitrification-warming).

The reaggregation of normal granulosa-cumulus cells and mouse oocytes with polycystic ovarian syndrome in vitro: An experimental study

Background

The dialogue between oocytes and their surrounding cells plays a major role in the progress of oocyte meiosis and their developmental potential.

Objective

This study aimed to evaluate the effect of co-culture of normal granulosa-cumulus cells (GCCs) with oocytes from polycystic ovarian syndrome (PCOS) mice.

Materials and Methods

Normal GCCs were collected from 10 virgin adult Naval Medical Research Institute female mice (30-35 gr, 7-8 wk old), and were cultured in an alpha-minimum essential medium supplemented with 5% fetal calf serum for 24-48 hr (1×106 cells/well). Then, germinal-vesicle oocytes from PCOS mice were cultured in the presence of cultured normal GCCs (experimental group) and without GCCs (control group). The maturation rate and quality of the PCOS oocytes were examined by evaluating TFAM and Cx43 gene expression (real-time PCR) and the connection among PCOS oocytes and normal GCCs after 24 hr of culture.

Results

The co-culture of normal GCCs and PCOS oocytes in the experimental group led to the formation of a complex called a PCOS oocyte-normal GCCs complex. The maturation rate of these complexes was significantly increased compared to that of the control group (p ≤ 0.001). A significant difference was also found in the expression of Cx43 (p ≤ 0.001) and TFAM (p < 0.05) genes in the experimental group compared with the control group. The connection between PCOS oocytes and normal GCCs was observed in the scanning electron microscope images.

Conclusion

Co-culture with normal GCCs improves the capacity of PCOS oocytes to enter meiosis, which may result in the promotion of assisted reproduction techniques.

Inhibition of Apoptotic Pathways Improves DNA Integrity but Not Developmental Competence of Domestic Cat Immature Vitrified Oocytes

Being a model for endangered wild felids, cryopreservation protocols for domestic cat oocytes are under continuous development. Immature vitrified oocytes (VOs) are a valuable resource for fertility preservation programs, but they often degenerate after warming and their in vitro development is poor. Since the exact mechanisms are not clear, this study assessed whether vitrification might trigger two apoptotic markers (DNA fragmentation and caspase activity, Experiment I) and the effects of a chemical inhibitor (i.e., the pan-caspase inhibitor Z-VAD-FMK) on the same markers (Experiment II) and on VOs in vitro development (Experiment III). The overarching aim was to check whether apoptosis inhibition might be a strategy to improve cat oocytes cryotolerance. In Experiment I, vitrification induced DNA fragmentation and increased caspase activity in VOs incubated for 24 h after warming (DNA fragmentation: 59.38%; caspase activity: 414.6 ± 326.8) compared to a fresh control (9.68%; 199.6 ± 178.3; p = 0.02). In Experiment II, the addition of Z-VAD-FMK to vitrification-warming and incubation media decreased DNA fragmentation and caspase activity (8.82%; 243.7 ± 106.9) compared to control (untreated) VOs (69.44%; 434.5 ± 248.3; p < 0.001). In Experiment III, Z-VAD-FMK brought maturation rates of treated VOs close to those of fresh oocytes (53.13 and 65.38%, respectively, p = 0.057), but there were no differences in VOs embryo development (cleavage rates; Z-VAD-FMK-treated VOs: 34.38%; control VOs: 31.78%; p = 0.69). In summary, vitrification increased apoptotic markers in cat VOs, and while Z-VAD-FMK was able to hinder DNA damage and caspase activity, its addition was not determinant for embryo development. To make the best use of VOs, other oocyte in vitro maturation and embryo culture strategies, such as the addition of other inhibitors or their prolonged use, should be investigated.

Association between outdoor air pollution during in vitro culture and the outcomes of frozen-thawed embryo transfer

STUDY QUESTION

Does outdoor air pollution differentially affect the outcomes of frozen-thawed embryo transfer (FET) and fresh transfer in IVF treatment?

SUMMARY ANSWER

Increased SO2 and O3 levels at the site of IVF unit were significantly associated with lower live birth rates following FET but did not affect the contemporary fresh transfer outcomes.

WHAT IS KNOWN ALREADY

Ambient air pollution has been associated with human infertility and IVF outcomes. However, most of the studies excluded FET cycles.

STUDY DESIGN, SIZE, DURATION

A retrospective cohort study of 11148 patients contributing to 16290 transfer cycles between January 2013 and December 2016 was carried out.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The average age of the cohort was 31.51 ± 4.48 years and the average BMI was 21.14 ± 2.37 kg/cm2. Inverse distance weighting interpolation was used to estimate the daily ambient exposures to six pollutants (PM2.5, PM10, SO2, NO2, CO, O3) at an IVF clinical site, according to the data from fixed air quality monitoring stations in the city. The exposures of each cycle were presented as average daily concentrations of pollutants from oocyte retrieval to embryo transfer/cryopreservation. Exposures were analyzed in quartiles. A generalized estimating equation was used to evaluate the association between pollutants and IVF outcomes, adjusted for important confounding factors including maternal age, infertility diagnosis, BMI, endometrial status and embryo transfer policy.

MAIN RESULTS AND THE ROLE OF CHANCE

The clinical pregnancy rate and live birth rate of the cycles was 55.1% (8981/16290) and 47.1% (7672/16290), respectively. Among the included cycles, 4013 patients received 5299 FET cycles, resulting in 2263 live births (42.7% per ET), whereas 9553 patients received 10991 fresh transfer cycles, resulting in 5409 live births (49.2% per ET). SO2 and O3 levels were significantly associated with live birth rates in FET cycles, whereas none of the pollutants were significantly associated with IVF outcomes in contemporary fresh transfer cycles. The FET cycles in the highest quartile of SO2 and O3 exposure had significantly lower live birth rates (adjusted odds ratio (OR) 0.63, 95%CI 0.53-0.74; 0.69, 95% CI 0.58-0.82, respectively) in comparison with those in the lowest quartile. Models involving all transfer cycles and interaction terms (FET×exposures) suggested that FET significantly enhanced the effects of SO2 and O3 exposure on IVF outcomes (P < 0.001). Multi-pollutant models gave consistent results for the association between SO2 and live birth in FET cycles. Accounting for all six pollutants, women in the highest quartile of SO2 still had the lowest live birth rates (OR 0.61, 95%CI 0.47-0.80).

LIMITATIONS, REASONS FOR CAUTION

The study was limited by its retrospective nature. The exposure data were estimated according to monitoring data rather than measured directly from the IVF unit. Unknown confounding factors may skew the results.

WIDER IMPLICATIONS OF THE FINDINGS

Our data implied that embryos undergoing FET may be more vulnerable to a suboptimal environment than those undergoing fresh transfer. In heavily polluted sites or seasons, fluctuation in FET outcomes may be partially explained by the dynamic changes of ambient gaseous air pollutant.

STUDY FUNDING/COMPETING INTEREST(S)

National Natural Science Foundation (81302454). The authors have no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Cold case: Small animal gametes cryobanking

Germplasm preservation of animals, whether they are valuable domestic breeds or rare species, is the main goal of gamete cryobanking. Dogs and cats act as models for this purpose thanks to the wide availability of biological material which can be employed to experiment protocols that can then be applied to wild animals. This review is focused on spermatozoa, oocytes and gonadal tissues cryobanking in small domestic animals, which is still an unsolved case. Like in a courtroom, evidences of cryoinjuries affecting cellular structures will be presented, penalties as loss of functionality due to cellular alterations will be described, and appeal as strategies to protect gametes from damages or rescue their functionality will be discussed. Differences and similarities between single cell or tissue cryopreservation will be highlighted, together with the rationale for the choice of one type of preservation or another and the fundamental principles which they are based on. The deep analysis of different aspects that still hamper the success of cryopreservation in small animals can help clarify where research is most needed. Therefore, as in a cold case, investigation should remain open in order to hopefully find the solution and make these procedures more and more efficient in the future.

Influence of interleukin 1 beta and tumour necrosis factor alpha on the in vitro growth, maturation and mitochondrial distribution of bovine oocytes from small antral follicles

SummaryThis study aimed to investigate the effects of IL1β and TNFα on growth and maturation of oocytes from small follicles (1-3 mm) during in vitro culture. To this end, cumulus-oocyte complexes (COCs) with diameters of ~110 µm were cultured in TCM-199 medium alone or supplemented with IL1β (10 ng/ml), TNFα (10 ng/ml) or both for 48 h. The oocytes were measured at the beginning and at the end of the culture period. COCs were cultured for 20 h in pre-maturation medium and then half of the COCs of each group was destined for in vitro maturation and the remaining COCs were used to evaluate meiotic progression, mitochondrial distribution and the expression of mRNAs for GDF-9, c-Mos, Cyclin-B1 and H1foo. The results showed that COCs cultured with TNFα alone or together with IL1β had higher diameters than those cultured in control medium alone or supplemented with IL1β. Control oocytes isolated from large antral follicles (>5 mm) had heterogeneous distribution of mitochondria. Oocytes isolated from small antral follicles, that had been grown in vitro in TCM-199 alone or supplemented with TNFα had similar heterogeneous mitochondrial distribution before in vitro maturation (IVM). After IVM, mitochondria were heterogeneously distribution when cultured in TCM-199. However, when cultured with TNFα and/or IL1β, mitochondria were homogeneously distributed. Presence of TNFα and/or IL1β in TCM-199 culture medium did not influence the expression of mRNAs for GDF-9, c-Mos, Cyclin-B1 and H1foo. In conclusion, TNFα and a mixture of TNFα and IL1β both stimulated the growth of bovine oocytes during their in vitro culture, but do not influence gene expression in grown oocytes.

Human oocyte maturation in vitro is improved by co-culture with cumulus cells from mature oocytes

The conventional method of human oocyte maturation in vitro in the presence of gonadotrophins continues to be a relatively low-success procedure in the assisted conception programme owing to suboptimal maturation conditions in the absence of an ovarian 'niche' and poor understanding of this procedure at the molecular level in oocytes. In this study, the gene expression profiles of human oocytes were analysed according to their manner of maturation: in vivo (in the ovaries) or in vitro (matured either by the conventional method or by a new approach - co-cultured with cumulus cells of mature oocytes from the same patient). Our results show that the in-vitro maturation procedure strongly affects the gene expression profile of human oocytes, including several genes involved in transcriptional regulation, embryogenesis, epigenetics, development, and the cell cycle. The in-vitro maturation of oocytes co-cultured with cumulus cells from mature oocytes provides an ovarian 'niche' to some degree, which improves oocyte maturation rates and their gene expression profile to the extent that they are more comparable to oocytes that naturally mature in the ovarian follicle.