Calcium Oscillatory Patterns and Oocyte Activation During Fertilization: a Possible Mechanism for Total Fertilization Failure (TFF) in Human In Vitro Fertilization?

Identification of Differentially Expressed mRNAs and miRNAs and Related Regulatory Networks in Cumulus Oophorus Complexes Associated with Fertilization

Cumulus oophorus complexes (COCs) are the first extracellular barriers that sperm must pass through to fuse with oocytes, which have an important role in oocyte maturation and fertilization. However, little is known about the molecular mechanisms of COCs involved in fertilization. In this study, COCs were collected and then randomly divided into a test group that interacted with sperm and a control group that did not interact with sperm. Then, the total RNA was extracted; RNA transcriptome and small RNA libraries were prepared, sequenced, and analyzed. The results showed that 1283 differentially expressed genes (DEGs), including 560 upregulated and 723 downregulated genes. In addition, 57 differentially expressed miRNAs (DEMIs) with 35 upregulated and 22 downregulated were also detected. After the RNA-seq results were verified by RT-qPCR, 86 effective DEGs and 40 DEMIs were finally screened and a DEMI-DEG regulatory network was constructed. From this, the top ten hub target genes were HNF4A, SPN, WSCD1, TMEM239, SLC2A4, E2F2, SIAH3, ADORA3, PIK3R2, and GDNF, and they were all downregulated. The top ten hub DEMIs were miR-6876-5p, miR-877-3p, miR-6818-5p, miR-4690-3p, miR-6789-3p, miR-6837-5p, miR-6861-5p, miR-4421, miR-6501-5p, and miR-6875-3p, all of which were upregulated. The KEGG signaling pathway enrichment analysis showed that the effective DEGs were significantly enriched in the calcium, AMPK, and phospholipase D signaling pathways. Our study identified several DEGs and DEMIs and potential miRNA-mRNA regulatory pathways in COCs and these may contribute to fertilization. This study may provide novel insights into potential biomarkers for fertilization failure.

Artificial oocyte activation with Ca2+ ionophore improves reproductive outcomes in patients with fertilization failure and poor embryo development in previous ICSI cycles

Research question

Does artificial oocyte activation (AOA) by a calcium ionophore (ionomycin) improve the previous fertilization failure or poor embryo development of intracytoplasmic sperm injection (ICSI) account for male factor infertility or other infertility causes?

Design

This retrospective study involved 114 patients receiving ICSI-AOA in Shanghai First Maternity and Infant Hospital with previous ICSI fertilization failure or poor embryo development. The previous ICSI cycles of the same patients without AOA served as the control group. The fertilization rates, cleavage rates, transferable embryo rates and blastocyst formation rates of the two groups were compared. Additionally, the clinical pregnancy, implantation rate and live birth rates were also compared to assess the efficiency and safety of AOA. Furthermore, two subgroup analyses were performed in this study based on the cause of infertility and the reason for AOA. The fertilization rate, embryonic development potential and clinical outcome were compared among groups.

Results

Among 114 ICSI-AOA cycles, the fertilization rate, top-quality embryo rate, implantation rate, clinical pregnancy per patient and live birth rate per patient were improved significantly compared with previous ICSI cycles (p<0.05 to P< 0.001), and the miscarriage rate in the AOA group was significantly lower than that of the control group (p<0.001). In the AOA subgroups based on the cause of infertility, the fertilization rates of each subgroup were significantly improved compared with previous control cycles except for the mixed factor infertility subgroup (p<0.05 to p<0.001). In the AOA subgroups based on the reason for AOA, the fertilization rates of each subgroup were significantly increased compared with those in their previous ICSI cycle without AOA (p<0.001); however, there was no significant difference in the top-quality embryo rate. No significant improvement was found in the implantation rates and the clinical pregnancy rate in each subgroup except for the poor embryo development subgroup. In the 114 AOA cycles, 35 healthy infants (21 singletons and 7 twins) were delivered without major congenital birth defects or malformations.

Conclusion

This study showed that AOA with the calcium ionophore ionomycin can improve the reproductive outcomes of patients with previous fertilization failure and poor embryo development after ICSI.

Sonomechanobiology: Vibrational stimulation of cells and its therapeutic implications

All cells possess an innate ability to respond to a range of mechanical stimuli through their complex internal machinery. This comprises various mechanosensory elements that detect these mechanical cues and diverse cytoskeletal structures that transmit the force to different parts of the cell, where they are transcribed into complex transcriptomic and signaling events that determine their response and fate. In contrast to static (or steady) mechanostimuli primarily involving constant-force loading such as compression, tension, and shear (or forces applied at very low oscillatory frequencies (≤ 1 Hz) that essentially render their effects quasi-static), dynamic mechanostimuli comprising more complex vibrational forms (e.g., time-dependent, i.e., periodic, forcing) at higher frequencies are less well understood in comparison. We review the mechanotransductive processes associated with such acoustic forcing, typically at ultrasonic frequencies (> 20 kHz), and discuss the various applications that arise from the cellular responses that are generated, particularly for regenerative therapeutics, such as exosome biogenesis, stem cell differentiation, and endothelial barrier modulation. Finally, we offer perspectives on the possible existence of a universal mechanism that is common across all forms of acoustically driven mechanostimuli that underscores the central role of the cell membrane as the key effector, and calcium as the dominant second messenger, in the mechanotransduction process.

Acid-Base, Gas, Ions, and Glucose Analysis in Follicular Fluid in Holstein-Friesian Dairy Cows Is Associated with the Follicle Size in Poland

The lack of fertilization and early pregnancy loss is seen in the quality and maturation of the oocytes. The environment of the first divisions and maturation of the oogonia, which is also a reflection of the quality of the oocyte, is the follicular fluid (FF). Thus, the purpose of this study was to investigate the variations in parameters such as pH, pCO₂, pO₂, standard HCO₃^-, actual HCO₃^-, base excess (BE), base excess of extracellular fluid (BE ecf), ctCO₂, ions: Na⁺, K⁺, actual ionized calcium Ca²⁺, adjusted ionized calcium (at pH 7.4) Ca²⁺ (7.4), Cl^-, anion gap (AnGap), and glucose in FF collected from different size follicles in dairy cattle. The most apparent differences were related to pH, K⁺, and Ca²⁺ 7.4 concentration in comparison to changes in follicle size (p < 0.05). Several trends were also evaluated as an increase in follicular size was followed by an increase in pH, BE, and Ca²⁺ 7.4 value and a decrease in the K⁺ concentration (p < 0.05). In conclusion, there are changes in FF formularies associated with the size of follicles. However, more research is necessary to establish the reference value, which then could be one of the factors describing the quality of the follicle and the developmental potential of the associated oocyte.

The Therapeutic and Diagnostic Potential of Phospholipase C Zeta, Oocyte Activation, and Calcium in Treating Human Infertility

Oocyte activation, a fundamental event during mammalian fertilisation, is initiated by concerted intracellular patterns of calcium (Ca2+) release, termed Ca2+ oscillations, predominantly driven by testis-specific phospholipase C zeta (PLCζ). Ca2+ exerts a pivotal role in not just regulating oocyte activation and driving fertilisation, but also in influencing the quality of embryogenesis. In humans, a failure of Ca2+ release, or defects in related mechanisms, have been reported to result in infertility. Furthermore, mutations in the PLCζ gene and abnormalities in sperm PLCζ protein and RNA, have been strongly associated with forms of male infertility where oocyte activation is deficient. Concurrently, specific patterns and profiles of PLCζ in human sperm have been linked to parameters of semen quality, suggesting the potential for PLCζ as a powerful target for both therapeutics and diagnostics of human fertility. However, further to PLCζ and given the strong role played by Ca2+ in fertilisation, targets down- and up-stream of this process may also present a significantly similar level of promise. Herein, we systematically summarise recent advancements and controversies in the field to update expanding clinical associations between Ca2+-release, PLCζ, oocyte activation and human fertility. We discuss how such associations may potentially underlie defective embryogenesis and recurrent implantation failure following fertility treatments, alongside potential diagnostic and therapeutic avenues presented by oocyte activation for the diagnosis and treatment of human infertility.

Cycle Characteristics and Pregnancy Outcomes of Early Rescue Intracytoplasmic Sperm Injection Cycles in Normal and Hyper-Ovarian Response Women: A Six-Year Retrospective Study

This study aims to analyze the cycle characteristics, pregnancy, and neonatal outcomes in early rescue intracytoplasmic sperm injection (r-ICSI) cycles in normal and hyper-ovarian response women in their first IVF/ICSI attempts. Data from short-term in vitro fertilization (IVF, N = 7148), early r-ICSI (N = 618), and ICSI (N = 1744) cycles were retrospectively analyzed from normal and hyper-ovarian women who underwent their first IVF/ICSI cycles at our center from October 2015 to October 2021. The r-ICSI group was subdivided into partial r-ICSI (N = 451) and total r-ICSI (N = 167) based on the number of fertilized oocytes in the IVF part. Cyclic characteristics, pregnancy, delivery and neonatal outcomes in the fresh cycle were compared among the four groups; pregnancy, delivery and neonatal outcomes in frozen-thawed cycles were compared regarding cleavage and blastocyst transfers derived from r-ICSI cycles. Partial r-ICSI cycles showed different cyclic characteristics compared to total r-ICSI cycles, presenting as elevated AMH and estradiol levels on trigger day and an increased number of oocytes retrieved. Early r-ICSI delayed blastocyst development as seen by the increase in the number of day 6 blastocysts. There was no significant difference among the groups in clinical pregnancy, pregnancy loss, and live birth in fresh cleavage-stage embryo transfer cycles. However, early r-ICSI groups showed a reduction in clinical pregnancy and live birth rates in fresh blastocyst transfer cycles but not in the frozen-thawed cycles. For pregnant women, early r-ICSI did not show a negative effect on the risk of preterm birth, Cesarean section, neonatal birth weight, and sex ratio. In conclusion, early r-ICSI had comparable pregnancy, delivery, and neonatal outcomes when compared with short-term IVF and ICSI groups in fresh cleavage-stage embryo transfer cycles, but early r-ICSI did result in reduced pregnancy outcomes in fresh blastocyst embryo cycles, possibly due to delayed blastocyst development and asynchronization with the endometrium.

ATP Induces Interleukin-8, Intracellular Calcium Release, and ERK1/2 Phosphorylation in Bovine Endometrial Cells, Partially through P2Y Receptors

The bovine endometrium has an important defensive role in the postpartum period that acts when an inflammatory process associated with tissue damage or infection by bacteria is produced. Endometrial cells release cytokines and chemokines that recruit inflammatory cells, which release danger-associated molecular patterns (DAMPs), such as adenosine triphosphate (ATP), and initiate and regulate the inflammatory response. However, the role of ATP in bovine endometrial cells is unclear. The aim of this study was to determine the effect of ATP on interleukin-8 (IL-8) release, intracellular calcium mobilization, ERK1/2 phosphorylation, and the role of P2Y receptors, in bovine endometrial cells. Bovine endometrial (BEND) cells were incubated with ATP and the IL-8 release was determined by the ELISA assay. ATP of 50 and 100 μM significantly increased IL-8 released in BEND cells (50 μM: 23.16 ± 3.82 pg/mL, p = 0.0018; 100 μM: 30.14 ± 7.43 pg/mL, p = 0.0004). ATP (50 μM) also induced rapid intracellular calcium mobilization in Fura-2AM-loaded BEND cells, as well as ERK1/2 phosphorylation (ratio 1.1 ± 0.04, p = 0.0049). Suramin (50 μM), a pan-antagonist of P2Y receptors, partially reduced the intracellular calcium mobilization, ERK1/2 phosphorylation (ratio 0.83 ± 0.08, p = 0.045), and IL-8 release (9.67 ± 0.02 pg/mL, p = 0.014) induced by ATP. Finally, BEND cells expressed higher mRNA levels of P2Y1 and P2Y2 purinergic subtype receptors, and lower levels of P2Y11 and P2Y12 receptors, as determined by RT-qPCR. In conclusion, these results showed that ATP activates pro-inflammatory responses in BEND cells, which are partially mediated via P2Y receptors, and BEND cells express the mRNA of subtypes of P2Y receptors, which could have a key role in bovine endometrial inflammation.

Successful Live Birth Outcome Following Assisted Activation of Failed Fertilized Oocytes

Here, we report on a rare case of a live birth following assisted oocyte activation of failed fertilized oocytes. A 34-year-old nulliparous woman presenting at a university-based assisted reproductive technology center with multi-factor infertility underwent an IVF cycle using intracytoplasmic sperm injection (ICSI) of frozen/thawed testicular sperm aspiration (TESA) sample and preimplantation genetic testing for aneuploidy (PGT-A). All oocytes displayed failed fertilization at assessment 18 h post-ICSI. Rescue of this cycle was achieved with the use of an assisted oocyte activation (AOA) protocol, whereby oocytes were subjected to AOA with calcium ionophore at 19 h post-ICSI and assessed for blastocyst development. Blastocyst-stage embryos were biopsied for PGT-A analysis with one of the three embryos reporting as genetically normal. This embryo was transferred in a frozen embryo transfer cycle and resulted in a normal pregnancy and term live birth. In conclusion, application of AOA protocols following failed fertilization outcomes can lead to viable, genetically normal embryos capable of resulting in a live birth.

Vitrification of bovine germinal vesicle oocytes significantly decreased the methylation level of their in vitro derived MII oocytes

CONTEXT

The vitrification of oocytes is important for the conservation of animals, and the effect of vitrification on methylation patterns of bovine oocytes remains unclear.

AIMS

This article aims to investigate the effect of vitrification on the DNA methylation patterns on vitrified GV oocytes and their in vitro derived MII oocytes.

METHODS

5-MeC staining and single-cell whole genome bisulphite sequencing (SC-WGBS) were utilised to analyse fresh GV oocytes (F_GV group), MII oocytes (F_MII group), vitrified GV oocytes (V_GV group) and their in vitro derived MII oocytes (V_MII group).

KEY RESULTS

Results of both 5-MeC staining and SC-WGBS showed that no significant difference was found between the F_GV group and the V_GV group, while the methylation level of the V_MII group was significantly lower than that of the F_MII group. Moreover, supplementation of 2μM resveratrol (Res) in IVM medium significantly improved maturation and development ability of vitrified GV oocytes by restoring their DNA methylation levels.

CONCLUSION

In conclusion, vitrification of bovine GV oocytes significantly decreased the DNA methylation level of their in vitro derived MII oocytes, and 2μM Res improved their development ability by restoring DNA methylation level.

IMPLICATIONS

Our results provide an efficient approach to improve the maturation and fertilisation ability of vitrified GV oocytes.

Reproductive Consequences of Electrolyte Disturbances in Domestic Animals

Electrolyte balance is essential to maintain homeostasis in the body. The most crucial electrolytes are sodium (Na+), potassium (K+), magnesium (Mg2+), chloride (Cl−), and calcium (Ca2+). These ions maintain the volume of body fluids, and blood pressure, participate in muscle contractions, and nerve conduction, and are important in enzymatic reactions. The balance is mainly ensured by the kidneys, which are an important organ that regulates the volume and composition of urine, together with which excess electrolytes are excreted. They are also important in the reproductive system, where they play a key role. In the male reproductive system, electrolytes are important in acrosomal reaction and sperm motility. Sodium, calcium, magnesium, and chloride are related to sperm capacitation. Moreover, Mg2+, Ca2+, and Na+ play a key role in spermatogenesis and the maintenance of morphologically normal spermatozoa. Infertility problems are becoming more common. It is known that disturbances in the electrolyte balance lead to reproductive dysfunction. In men, there is a decrease in sperm motility, loss of sperm capacitation, and male infertility. In the female reproductive system, sodium is associated with estrogen synthesis. In the contraction and relaxation of the uterus, there is sodium, potassium, and calcium. Calcium is associated with oocyte activation. In turn, in women, changes in the composition of the follicular fluid are observed, leading to a restriction of follicular growth. Imbalance of oocyte electrolytes, resulting in a lack of oocyte activation and, consequently, infertility.

Novel WEE2 compound heterozygous mutations identified in patients with fertilization failure or poor fertilization

Purpose

To study associations between novel WEE2 mutations and patients with fertilization failure or poor fertilization.

Methods

Thirty-one Chinese patients who underwent treatment with assisted reproductive technology and suffered from repeated (at least two times) total fertilization failure (TFF) or a low fertilization rate were enrolled. Genomic DNA was extracted from patients for whole-exome sequencing. Suspicious mutations were validated by Sanger sequencing. WEE2 protein levels in oocytes from affected patients were examined by immunofluorescence. Disruptive effects of mutations on WEE2 protein stability, subcellular localization, and kinase function were analyzed through western blotting, immunofluorescence, and flow cytometry in HeLa cells.

Results

Three of thirty-one (9.6%) enrolled patients had six compound heterozygous mutations of the WEE2 gene, and three of them were reported here for the first time (c.115_116insT, c.756_758delTGA, and c.C1459T). Oocytes from affected patients showed decreased WEE2 immunofluorescence signals. In vitro experiments showed that the mutant WEE2 gene caused reduced WEE2 protein levels or cellular compartment translocation in HeLa cells, leading to decreased levels of the phosphorylated Cdc2 protein. Compared with the wild-type WEE2 protein, the mutant WEE2 proteins were also found to have different effects on the cell cycle.

Conclusion

Three novel compound heterozygous WEE2 variants were found in patients with pronucleus formation failure. This study provides new evidence that WEE2 mutations result in loss of function, which could result in fertilization failure.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10815-021-02285-z.

Sperm-oocyte interplay: an overview of spermatozoon's role in oocyte activation and current perspectives in diagnosis and fertility treatment

The fertilizing spermatozoon is a highly specialized cell that selects from millions along the female tract until the oocyte. The paternal components influence the oocyte activation during fertilization and are fundamental for normal embryo development; however, the sperm-oocyte interplay is in a continuous debate. This review aims to analyze the available scientific information related to the role of the male gamete in the oocyte activation during fertilization, the process of the interaction of sperm factors with oocyte machinery, and the implications of any alterations in this interplay, as well as the advances and limitations of the reproductive techniques and diagnostic tests. At present, both PLCζ and PAWP are the main candidates as oocyte activated factors during fertilization. While PLCζ mechanism is via IP₃, how PAWP activates the oocyte still no clear, and these findings are important to study and treat fertilization failure due to oocyte activation, especially when one of the causes is the deficiency of PLCζ in the sperm. However, no diagnostic test has been developed to establish the amount of PLCζ, the protocol to treat this type of pathologies is broad, including treatment with ionophores, sperm selection improvement, and microinjection with PLCζ protein or RNA.

Diagnosis and Treatment of Male Infertility-Related Fertilization Failure

Infertility affects approximately 15% of reproductive-aged couples worldwide, of which up to 30% of the cases are caused by male factors alone. The origin of male infertility is mostly attributed to sperm abnormalities, of which many are caused by genetic defects. The development of intracytoplasmic sperm injection (ICSI) has helped to circumvent most male infertility conditions. However, there is still a challenging group of infertile males whose sperm, although having normal sperm parameters, are unable to activate the oocyte, even after ICSI treatment. While ICSI generally allows fertilization rates of 70 to 80%, total fertilization failure (FF) still occurs in 1 to 3% of ICSI cycles. Phospholipase C zeta (PLCζ) has been demonstrated to be a critical sperm oocyte activating factor (SOAF) and the absence, reduced, or altered forms of PLCζ have been shown to cause male infertility-related FF. The purpose of this review is to (i) summarize the current knowledge on PLCζ as the critical sperm factor for successful fertilization, as well as to discuss the existence of alternative sperm-induced oocyte activation mechanisms, (ii) describe the diagnostic tests available to determine the cause of FF, and (iii) summarize the beneficial effect of assisted oocyte activation (AOA) to overcome FF.