In vitro maturation of cumulus-partially enclosed immature human oocytes by priming with gonadotropin

Developmental potential of non- and mono-pronuclear zygotes and associated clinical outcomes in IVF cycles

Purpose

This study aims to evaluate the developmental potential of 0PN, 1PN, and 2PN zygotes in IVF cycles and compare their clinical outcomes.

Methods

We conducted a retrospective cohort study involving IVF patients. Blastocyst formation rates were assessed with 0PN, 1PN, and 2PN zygotes. Subsequently, we collected clinical outcome data following the transfer of these zygotes.

Results

The overall blastulation rate was similar between 0PN (29.6%) and 2PN (32.1%) zygotes, but 1PN zygotes exhibited a significantly lower blastulation rate (17.0%) compared to both 0PN and 2PN zygotes. Similarly, the overall rate of good-quality blastulation was comparable between 0PN (15.3%) and 2PN (17.5%) zygotes, while 1PN zygotes showed a significantly lower rate (7.0%) compared to both 0PN and 2PN. Clinical pregnancy, ectopic pregnancy, implantation, and live birth rates were similar among single blastocyst frozen embryo transfers (FET) of 0PN, 1PN, and 2PN. Additionally, no significant differences were observed between single- and double-blastocyst FET of 0PN and 2PN.

Conclusions

Our findings suggest that 0PN and 2PN zygotes have comparable developmental potential, while 1PN embryos exhibit lower developmental potential. Blastocyst FET outcomes appear similar among 0PN, 1PN, and 2PN zygotes.

Future potential of in vitro maturation including fertility preservation

In several mammalian species, oocytes from small antral follicles after in vitro maturation (IVM) are successfully used for procreation. Humans are the exception, mainly because of limited access to immature oocytes and because oocyte maturation is uniquely regulated in women. With the introduction of cryopreservation of the ovarian cortex for fertility preservation, immature oocytes from small antral follicles in the medulla are now available for developing IVM on the basis of actual human studies. This review presents recent findings in favor of developing human IVM, including the oocyte diameter, follicle size from which the immature oocytes are collected, necessary level of follicle-stimulating hormone and luteinizing hormone to accelerate IVM, and secretion of factors from the cumulus-oocyte complex that affect the way oocyte maturation takes place. Furthermore, on the basis of studies in human granulosa cells and follicle fluid collected during the final maturation of follicles in vivo, a number of signal transduction pathways and hormone levels active during physiological conditions have been identified, providing new candidates and ways to improve the current IVM platform. Furthermore, it is suggested that the small droplet of culture medium in which IVM is performed mimics the hormonal milieu within a follicle created by the somatic cells and oocyte in vivo and may be used to advance oocyte nuclear and cytoplasmic maturation. Collectively, we envision that a continued research effort will develop a human IVM platform equally effective as for other mammalian species.

Potential Development of Vitrified Immature Human Oocytes: Influence of the Culture Medium and the Timing of Vitrification

How does the in vitro maturation (IVM) medium and the vitrification procedure affect the survival of germinal vesicle (GV) oocytes obtained from stimulated cycles and their development to the blastocyst stage? In total, 1085 GV human oocytes were obtained after women underwent a cycle of controlled ovarian stimulation, and these oocytes were subjected to IVM before or after their vitrification. IVM was carried out in two commercial culture media not specifically designed for maturation. MII oocytes were then activated and embryo development until day 6 was evaluated. According to the results, a higher percentage of oocytes reach the MII stage if they are vitrified before they undergo IVM. Nevertheless, the medium used and the sample size determine whether these differences become significant or not. Similar survival rates and development to blastocysts were observed in all the conditions studied.

A threshold concentration of FSH is needed during IVM of ex vivo collected human oocytes

PURPOSE

To investigate the effect of different FSH concentrations on human oocyte maturation in vitro and its impact on gene expression of key factors in the surrounding cumulus cells.

METHODS

The study included 32 patients who underwent unilateral oophorectomy for ovarian tissue cryopreservation (OTC) (aged 28 years on average). Immature oocytes were collected from surplus medulla tissue. A total of 587 immature oocytes were divided into three categories according to the size of the cumulus mass: large (L-COCs), small (S-COCs), and naked oocytes (NOs), and submitted to 44-h IVM with one of the following concentrations of recombinant FSH: 0 IU/L, 20 IU/L, 40 IU/L, 70 IU/L, or 250 IU/L. After IVM, oocyte nuclear maturation stage and diameter were recorded. The relative gene expression of FSHR, LHCGR, and CYP19A1 in cumulus cells before (day 0; D0) and after IVM were evaluated.

RESULTS

Addition of 70 or 250 IU/L FSH to the IVM medium improved oocyte nuclear maturation compared to 0, 20, and 40 IU/L FSH by upregulating LHCGR and downregulating FSHR in the cumulus cells.

CONCLUSION

FSH improved oocyte nuclear maturation at concentrations above 70 IU/L suggesting a threshold for FSH during IVM of ex vivo collected human oocytes from small antral follicles. Moreover, current results for the first time highlight that FSH function in vitro is mediated via cumulus cells by downregulating FSHR and upregulating LHCGR, which was also observed when the immature oocytes progressed in meiosis from the GV to the MII stage.

The Effect of Human Chorionic Gonadotropin on the In vitro Development of Immature to Mature Human Oocytes: A Randomized Controlled Study

Context

In controlled ovarian hyperstimulation cycles, 15% of oocytes have been proven to be immature. Key factors include failure in signal transmission from the cumulus cell to the oocyte, insufficient level of luteinizing hormone, and internal conditions of the oocyte itself.

Aims

The aim of the present study was to investigate the effect of human chorionic gonadotropin (hCG) on the in vitro maturity of partially cumulus-denuded immature oocytes collected after controlled ovarian stimulation for in vitro fertilization (IVF).

Settings and Design

This was a prospective, randomized controlled design at the department of obstetrics and gynaecology, university hospital.

Subjects and Methods

Infertile women underwent gonadotropin-releasing hormone antagonist stimulated protocol for IVF with final maturation triggered by hCG, partially cumulus-denuded immature human oocytes were allocated to two groups: the first was treated with fertilization medium and the second was treated with fertilization medium and hCG. They were cultured for 24 h. Outcomes measured were the oocyte maturation rates to metaphase II (MII) and glucose-6-phosphate dehydrogenase (G6PD) activity of in vitro maturation (IVM) mature oocytes which represent the oocyte quality.

Statistical Analysis Used

The Mann-Whitney U-test and One-way ANOVA were used to compare continuous variables, and Chi-square was used for categorical data.

Results

In all, 250 immature stimulated oocytes were allocated (125 per group). The maturation rate was higher in the hCG supplement group (48% vs. 39.2%) without significance. The positive brilliant cresyl blue results among the MII oocytes developed from the metaphase I (MI) were significantly higher in the hCG group (P = 0.001).

Conclusions

Rescue IVM in fertilization culture medium plus hCG was slightly better than that in the only fertilization culture. MII oocytes developed from MI in hCG supplemented medium had a higher quality based on the measured G6PD activity.

Blastocysts Derived From 0PN Oocytes: Genetic And Clinical Results

Objective

To analyze the genetic and clinical outcomes of blastocysts derived from 0PN oocytes after IVF/ICSI.

Methods

This retrospective observational study included patients aged 40 years or younger submitted to IVF/ICSI with their own oocytes and with blastocysts derived from 0PN oocytes between January 2015 and April 2018. The clinical outcomes of 0PN blastocyst transfers were analyzed. Genetic tests were performed on biopsied 0PN blastocysts with Next Generation Sequencing.

Results

A total of 27 0PN blastocysts were transferred, yielding an implantation rate of 48.0% and an ongoing pregnancy rate of 50.0%. The transfers resulted in 13 live births (59.0% live birth rate). Genetic test results revealed that four of the 17 0PN blastocysts biopsied were 46XX; three were 46XY; and 10 were aneuploid embryos, awarding a diploid rate to 76.4% (13/17).

Conclusion

Almost half of the 0PN blastocysts implanted (48.0%) and 13 healthy babies were born. More than three quarters (76.4%) of the 0PN blastocysts were diploid, thus ruling out the possibility of parthenogenetic activation. Our study indicated that the transfer of 0PN blastocysts is a safe, worthy option when the number of normal 2PN embryos is insufficient.

Role of Sirt3 in mitochondrial biogenesis and developmental competence of human in vitro matured oocytes

STUDY QUESTION

Does Sirt3 dysfunction result in poor developmental outcomes for human oocytes after in vitro maturation (IVM)?

SUMMARY ANSWER

Inefficient Sirt3 expression induced decreased mitochondrial DNA copy number and biogenesis, and therefore impaired the developmental competence of human IVM oocytes.

WHAT IS KNOWN ALREADY

Cytoplasmic immaturity in IVM oocytes may lead to reduced developmental competence. Mitochondrial dysfunction results in the accumulation of free radicals and leads to DNA mutations, protein damage, telomere shortening and apoptosis. SIRT3 (in the Sirtuin protein family) has emerged as a mitochondrial fidelity protein that directs energy generation and regulates reactive oxygen species scavenging proteins.

STUDY DESIGN, SIZE, DURATION

In vivo matured metaphase II (IVO-MII) oocytes and IVM-MII oocytes were donated by 324 infertile patients undergoing assisted reproductive technology cycles (12 patients for 60 IVO oocytes, and 312 patients for 403 IVM oocytes). Five oocytes each in the germinal vesicle (GV), IVM and IVO groups were compared with respect to mRNA levels for Sirt1-7 mRNA, and five samples at each developmental stage were analysed for Sirt3 mRNA. IVM-MII oocytes were injected with in vitro transcribed mRNA (n = 59) or small interfering RNA (siRNA) (n = 78). In human and mouse, IVM, mRNA-injection IVM, and siRNA-injection IVM groups (n = 5 each) were analysed for mitochondrial DNA copy number and abundance of Sirt3 and Pgc1α (an inducer of mitochondrial biogenesis) mRNAs. Human blastocysts in the IVO (n = 12), IVM (n = 9), mRNA-injection IVM (n = 13) and siRNA-injection IVM (n = 6) groups were used to generate embryonic stem cells (ESCs). In addition, 587 IVO-MII and 1737 IVM-MII oocytes from 83 mice were collected to compare the preliminary human oocyte data with another species.

PARTICIPANTS/MATERIALS, SETTING, METHODS

mRNA abundance was analysed by single-cell real-time PCR. Karyotyping of human embryos was performed with an array comparative genomic hybridization method, and that of ESCs by cytogenetic analysis. The function of the Sirt3 gene was investigated using siRNA and in vitro transcribed mRNA injection. Markers of ESCs were identified using immunofluorescence.

MAIN RESULTS AND THE ROLE OF CHANCE

A retrospective analysis revealed a higher spontaneous abortion rate (P < 0.01) and decrease in high quality embryo rate (P < 0.01) in patients with IVM versus controlled ovarian stimulation (COS) cycles. A decrease in abundance of Sirt3 mRNA (P < 0.01) and mitochondrial biogenesis (P < 0.05) were identified in human IVM compared with IVO oocytes. The developmental potential of human IVM-MII oocytes to the blastocyst stage was significantly reduced when Sirt3 mRNA was inhibited by siRNA (P < 0.05 versus IVM-MII group) but could be up-regulated by injection of Sirt3 mRNAs. Compared with IVO-MII group, comparable generation efficiency of human ESCs can be obtained using blastocysts from IVM-MII oocytes with Sirt3 mRNA injection. Sirt3 mRNA was significantly increased in mouse zygotes after IVF (P < 0.001 versus MII oocytes) but gradually declined until the blastocyst stage. In mice, lower Sirt3 mRNA levels were observed IVM-MII oocytes and preimplantation embryos compared with in vivo controls, and mitochondrial biogenesis and the developmental efficiency from oocytes to blastocyst were affected by the abundance of Sirt3 mRNA in accordance with human. Therefore a similar role for Sirt3 mRNA in IVM-MII oocytes was observed in mouse and human.

LIMITATIONS, REASONS FOR CAUTION

The couples in the study had a variety of different simple and complex factors causing infertility. Additional studies with a larger number of oocytes are required to confirm the present results owing to the limited number of human oocytes in the present study.

WIDER IMPLICATIONS OF THE FINDINGS

To our knowledge, this is the first study investigating a role of the Sirt3 gene in mitochondrial biogenesis and the developmental competence of human IVM-MII oocytes. The observation may help to improve clinical application of the IVM procedure.

STUDY FUNDING/COMPETING INTERESTS

This work was supported in part by the National Natural Science Foundation of Key Program (31230047), Ministry of Science and Technology of China Grants (973 program; 2014CB943203), the National Natural Science Foundation of General Program (31371521 and 81571400), Beijing Nova Program (xxjh2015011), and Specialized Research Fund for the Doctoral Program of Higher Education (20120001130008) and the National Natural Science Foundation of Young Scholar (31501201). The authors have declared that no conflict of interest exists.

Self-oocyte activation and parthenogenesis: an unusual outcome of a misconducted IVF cycle

A rare cause of infertility is the lack of fertilisation with the spontaneous activation of oocytes, leading to parthenogenesis. We present such a case. The patient was a G1P0 38-year-old woman of African ethnicity, who requested an in vitro fertilisation (IVF) with donor sperm. She received a stimulation protocol of 75 IU of FSH/LH from day 3 of the cycle, which she interrupted after 2 d, and restarted with the same dosage for another 3 d from day 7, plus one administration of GnRH antagonist in day 10 of the cycle. With a follicle reaching 19 mm on day 11, estradiol of 325 ng/ml, ovulation was induced with hMG 5000 UI, and oocyte pick-up performed at 30 h. One oocyte was retrieved, and good-quality sperms were added to the insemination procedure. No fecundation occurred at 20 h, with the extruded oocyte separated from the granulosa wall. At 40 h and 64 h the aspect was of three cells, one cell with one nucleus, the others with high granulation and no visible nuclei. This case shows an unusual self-activation oocyte in a poorly managed IVF cycle. The patient will be further evaluated, to decide if a better managed stimulation protocol would prevent recurrence.

Chromosomal aberrations in in-vitro matured oocytes influence implantation and ongoing pregnancy rates in a mouse model undergoing intracytoplasmic sperm injection

Implantation failure and early pregnancy loss have been reported to be closely related to the quality of mammalian oocytes; however, the pregnant outcome of embryos from in-vitro matured (IVM) oocytes remains unknown. In this study we examined spindle assembly and chromosome segregation during differentiation, and the duration of IVM of mouse oocytes. The resulting implantation and pregnancy outcomes were analyzed to clarify the relationship between the spindle and chromosomes of IVM oocytes and implantation and early pregnancy. Cumulus-enclosed germinal vesicle oocytes were collected and randomly cultured in IVM medium with different IVM durations. One part of IVM oocytes were analyzed the spindle and chromosome morphology by immunofluorescence method, and the other part of them were fertilized by intracytoplasmic sperm injection. The resulting embryos were transferred into pseudo-pregnant female mice, and the post-implantation and full term development was observed. The chromosome aberrations and incorrect spindle assembly seems not affect the early development and blastocyst cell number derived from IVM oocytes, however the development potential of the resulting embryos after implantation were significant decreased with the ratio increasing of chromosome aberrations and incorrect spindle assembly. Accordingly, the full-term development was also decreased. In conclusion, the present study showed the spindle assembly of in vitro-matured oocytes was one of the most important factors that affected the implantation and ongoing pregnancy rates of IVM oocytes, and the improvement by an appropriate duration of maturation in vitro will enhance the post-implantation development potential of the resulting embryos, and decrease implantation failure and early pregnancy loss.

FSH in vitro versus LH in vivo: similar genomic effects on the cumulus

The use of gonadotropins to trigger oocyte maturation both in vivo and in vitro has provided precious and powerful knowledge that has significantly increased our understanding of the ovarian function. Moreover, the efficacy of most assisted reproductive technologies (ART) used in both humans and livestock species relies on gonadotropin input, mainly FSH and LH. Despite the significant progress achieved and the huge impact of gonadotropins, the exact molecular pathways of the two pituitary hormones, FSH and LH, still remain poorly understood. Moreover, these pathways may not be the same when moving from the in vivo to the in vitro context. This misunderstanding of the intricate synergy between these two hormones leads to a lack of consensus about their use mainly in vitro or in ovulation induction schedules in vivo. In order to optimize their use, additional work is thus required with a special focus on comparing the in vitro versus the in vivo effects. In this context, this overview will briefly summarize the downstream gene expression pathways induced by both FSH in vitro and LH in vivo in the cumulus compartment. Based on recent microarray comparative analysis, we are reporting that in vitro FSH stimulation on cumulus cells appears to achieve at least part of the gene expression activity after in vivo LH stimulation. We are then proposing that the in vitro FSH-response of cumulus cells have similitudes with the in vivo LH-response.

Morphological and molecular markers are correlated with maturation-competence of human oocytes

STUDY QUESTION

Does the position of the germinal vesicle (GV) in human oocytes correlate with molecular and morphological parameters as well as with maturation-competence?

SUMMARY ANSWER

The position of GV in human oocytes correlates with density of microtubule (MT) filaments, concentration of Fyn, nucleolus localization and the ability of the oocytes to complete maturation following GV breakdown (GVBD).

WHAT IS KNOWN ALREADY

Our knowledge is confined to oocytes of young mice where maturation-competence is correlated with a central GV and regulated by MTs and the presence of a chromatin ring. Fyn kinase is localized at the spindle and cortex of mouse oocytes and plays a role in both maturation and MT stabilization.

STUDY DESIGN, SIZE, DURATION

Spatial localization of the GV and nucleolus (central or peripheral), the presence of a chromatin ring, the localization of Fyn, MT density and oocyte maturation were assessed in 153 human oocytes, 335 oocytes from young mice (2-month-old) and 146 oocytes from old mice (12-month-old).

PARTICIPANTS/MATERIALS, SETTING, METHODS

GV human oocytes were donated by consenting female patients (n = 57), 21-45-year-old undergoing IVF/ICSI. As a control, GV mouse oocytes were collected from female mice after injection of pregnant mares' serum gonadotrophin. Human and mouse GV oocytes allocated for immunocytochemistry were fixed on day of retrieval, stained with specific antibodies and imaged using a confocal laser-scanning microscope. Human and mouse oocytes allocated for maturation were incubated for 48 and 24 h, respectively. GVBD and extrusion of the first polar body (PBI) were assessed using differential interference contrast optics.

MAIN RESULTS AND THE ROLE OF CHANCE

GV location was peripheral and independent of age in 69.9% of the human oocytes, but GV location did vary with age in mice oocytes; it was central in 89.9% of the oocytes retrieved from young-mice and peripheral in 52.1% of the oocytes retrieved from old mice (P < 0.05). A central GV, whether in human or mouse oocytes, was highly correlated with a central nucleolus, absence of Fyn at the GV and a dense MT network (P < 0.05), whereas a peripheral GV correlated with peripheral nucleolus, presence of Fyn at the GV and a flimsy MT network. After 48 h in culture, no degeneration was observed in human central-GV oocytes, however, 12/95 (12.6%) of the peripheral-GV oocytes degenerated (P < 0.05). No correlation was observed between GV position and presence of a chromatin ring. The percentage of human oocytes that extruded the PBI after completing GVBD was significantly higher (73.7%) in central than in peripheral-GV oocytes (45.8%; P < 0.05). In mice oocytes, central location of the GV correlated with maturation competence in young (P < 0.05) but not old mice.

LIMITATIONS, REASONS FOR CAUTION

The fact that the human GV oocytes used in this study were exposed to gonadotrophic stimulation but failed to mature in vivo might be a sign of their low quality and this should be considered when drawing conclusions from the data. Furthermore, our observation that only peripheral-GV human oocytes were degraded may indicate that they are of a lower quality than central-GV human oocytes.

WIDER IMPLICATIONS OF THE FINDINGS

We suggest that the central location of GV within the oocytes, which is associated with an absence of Fyn at the GV and the presence of thick filamentous MTs in the ooplasm, may serve as a predictor of successful maturation and provide new insights for the use of IVM.

Recombinant human phospholipase C zeta 1 induces intracellular calcium oscillations and oocyte activation in mouse and human oocytes

BACKGROUND

Oocyte activation is a crucial step that comprises the release of the oocyte from meiotic arrest, pronuclear formation and subsequent embryo development. Oocytes are activated by repetitive increases in the intracellular concentration of free Ca(2+), [Ca(2+)](i) oscillations, which are triggered during fertilization by the introduction of the sperm-specific phospholipase C zeta 1 (PLCZ1). Recent studies have shown that sperm from patients lacking expression of PLCZ1 or expressing mutant forms of PLCZ1 fail to induce [Ca(2+)](i) oscillations or oocyte activation. We first purified recombinant human PLCZ1 (hPLCZ1) protein and evaluated its [Ca(2+)](i) oscillation activity in mouse and human oocytes with the view to investigate its application in the clinic for assisted oocytes activation in lieu of chemical agents.

METHODS

Recombinant hPLCZ1 was synthesized using the Escherichia coli system, and subjected to immunoblot analysis with anti-PLCZ1 and anti-His tag antibodies. [Ca(2+)](i) oscillations by microinjection of recombinant hPLCZ1 into mouse or human oocytes were examined by [Ca(2+)](i) monitoring with Fluo 4. Ploidy of the oocytes with recombinant hPLCZ1 injection was confirmed with fluorescence in situ hybridization.

RESULTS

A band of 68 kDa on recombinant protein was detected with both antibodies. Injection of recombinant hPLCZ1 induced [Ca(2+)](i) oscillations in a dose-dependent manner in both mouse and human oocytes. These oscillations, which closely resembled those initiated by the sperm upon fertilization, triggered activation and cleavage in oocytes of both species, although further development of the mice embryos was low. U73122, a PLC inhibitor, blocked the ability of hPLCZ1 to initiate oscillations. Microinjection of recombinant hPLCZ1 into ICSI-failed human oocytes rescued fertilization failure in five of eight attempts.

CONCLUSIONS

Repeated [Ca(2+)](i) oscillations and oocyte activation were induced in mouse and human oocytes by microinjection of recombinant hPLCZ1 synthesized in E. Coli. Injection of recombinant protein could thus provide a biological solution for inducing artificial activation of oocytes.