Supplementation of EGF, IGF-1, and Connexin 37 in IVM Medium Significantly Improved the Maturation of Bovine Oocytes and Vitrification of Their IVF Blastocysts

Cytokine-Supplemented Maturation Medium Enhances Cytoplasmic and Nuclear Maturation in Bovine Oocytes

Bovine in vitro oocyte maturation (IVM) is an easy way to obtain oocytes for subsequent assisted reproductive techniques but is inefficient compared to in vivo maturation. Supplementation of three cytokines, fibroblast growth factor 2 (FGF2), leukemia inhibitory factor (LIF), and insulin-like growth factor 1 (IGF1), or FLI, has increased oocyte maturation and embryo development in multiple species, but studies have not explored the oocyte differences caused by FLI IVM supplementation. This study aimed to assess important nuclear and cytoplasmic maturation events in high-quality oocytes. FLI-supplemented oocytes had a decreased GV (3.0% vs. 13.7%, p < 0.01) and increased telophase I incidence (34.6% vs. 17.6%, p < 0.05) after IVM, increased normal meiotic spindles (68.8% vs. 50.0%, p < 0.001), and an increased nuclear maturation rate (75.1% vs. 66.8%, p < 0.001). Moreover, in metaphase II oocytes, the percentage of FLI-treated oocytes with a diffuse mitochondrial distribution was higher (87.7% vs. 77.5%, p < 0.05) and with a cortical mitochondrial distribution was lower (11.6% vs. 17.4%, p < 0.05). Additionally, FLI-supplemented oocytes had more pattern I cortical granules (21.3% vs. 14.4%, p < 0.05). These data suggest that FLI supplementation in bovine in vitro maturation medium coordinates nuclear and cytoplasmic maturation to produce higher-quality oocytes.

Epigen enhances the developmental potential of in vitro fertilized embryos by improving cytoplasmic maturation

Numerous growth factors contribute to oocyte maturation and embryonic development in vivo; however, only a few are understood. One such factor is epigen, a new member of the epidermal growth factor (EGF) family that is secreted by the granulosa cells of immature oocytes. We hypothesized that epigen may play a role in oocyte maturation, specifically in the nuclear and cytoplasmic aspects. This study aimed to investigate the effects of epigen on porcine oocyte maturation and embryo development in vitro. In this study, three different concentrations of epigen (3, 6, and 30 ng/mL) were added to tissue culture medium-199 (TCM-199) during in vitro maturation of porcine oocytes. A control group that did not receive epigen supplementation was also included. Mature porcine oocytes were fertilized, and the resulting zygotes were cultured until day 7. The levels of intracellular glutathione (GSH) and reactive oxygen species (ROS) were measured in the in vitro matured oocytes. At the same time, the expression patterns of genes related to apoptosis were detected in day 7 blastocysts (BLs) using real-time quantitative PCR Apoptosis was detected by annexin-V assays in mature oocytes. Data were analyzed using ANOVA and Duncan's test on SPSS, and results are presented as mean ± SEM. The group that received 6 ng/mL epigen had a significantly lower rate of germinal vesicle breakdown (GVBD) than the control group without affecting the nuclear maturation among the experimental groups. Among the treatment groups, the 6 ng/mL epigen group showed significantly higher levels of intracellular GSH and lower ROS production. Supplementation with 6 ng/mL epigen significantly improved blastocyst (BL) formation rates compared to those in the control and 3 ng/mL groups. Additionally, the blastocyst expansion rate was significantly higher with epigen supplementation (6 ng/mL). In the fertilization experiment, the group supplemented with 6 ng/mL epigen exhibited significantly higher levels of monospermy and fertilization efficiency and lower levels of polyspermy than the control group. This study indicated that adding epigen at a concentration of 6 ng/mL can significantly enhance the developmental potential of porcine oocytes fertilized in vitro. Specifically, the study found that epigen improves cytoplasmic maturation, which helps prevent polyspermy and emulates monospermic penetration.

Gap junctions in polycystic ovary syndrome: Implications for follicular arrest

Gap junctions are specialized intercellular conduits that provide a direct pathway between neighboring cells, which are involved in numerous physiological processes, such as cellular differentiation, cell growth, and metabolic coordination. The effect of gap junctional hemichannels in folliculogenesis is particularly obvious, and the down-regulation of connexins is related to abnormal follicle growth. Polycystic ovary syndrome (PCOS) is a ubiquitous endocrine disorder of the reproductive system, affecting the fertility of adult women due to anovulation. Exciting evidence shows that gap junction is involved in the pathological process related to PCOS and affects the development of follicles in women with PCOS. In this review, we examine the expression of connexins in follicular cells of PCOS and figure out whether such communication could have consequences for PCOS women. While along with results from clinical and related animal studies, we summarize the mechanism of connexins involved in the pathogenesis of PCOS.

The Anti-Müllerian Hormone as Endocrine and Molecular Marker Associated with Reproductive Performance in Holstein Dairy Cows Exposed to Heat Stress

Anti-Müllerian hormone (AMH) is proposed as a biomarker for fertility in cattle, yet this associative relationship appears to be influenced by heat stress (HS). The objective was to test serum AMH and AMH-related single nucleotide polymorphisms (SNPs) as markers potentially predictive of reproductive traits in dairy cows experiencing HS. The study included 300 Holstein cows that were genotyped using BovineSNP50 (54,000 SNP). A genome-wide association study was then executed. Nine intragenic SNPs within the pathways that influence the AMH gene were found important with multiple comparisons adjustment tests (p < 1.09 × 10-6). A further validation study was performed in an independent Holstein cattle population, which was divided into moderate (MH; n = 152) and severe heat-stressed (SH; n = 128) groups and then subjected to a summer reproductive management program. Serum AMH was confirmed as a predictor of fertility measures (p < 0.05) in MH but not in the SH group. Cows were genotyped, which revealed four SNPs as predictive markers for serum AMH (p < 0.01), reproductive traits (p < 0.01), and additional physiological variables (p < 0.05). These SNPs were in the genes AMH, IGFBP1, LGR5, and TLR4. In conclusion, serum AMH concentrations and AMH polymorphisms are proposed as predictive markers that can be used in conjunction with genomic breeding value approaches to improve reproductive performance in Holstein cows exposed to summer HS conditions.

Developmental, cytogenetic and epigenetic consequences of removing complex proteins and adding melatonin during in vitro maturation of bovine oocytes

Background

In vitro maturation (IVM) of germinal vesicle intact oocytes prior to in vitro fertilization (IVF) is practiced widely in animals. In human assisted reproduction it is generally reserved for fertility preservation or where ovarian stimulation is contraindicated. Standard practice incorporates complex proteins (CP), in the form of serum and/or albumin, into IVM media to mimic the ovarian follicle environment. However, the undefined nature of CP, together with batch variation and ethical concerns regarding their origin, necessitate the development of more defined formulations. A known component of follicular fluid, melatonin, has multifaceted roles including that of a metabolic regulator and antioxidant. In certain circumstances it can enhance oocyte maturation. At this stage in development, the germinal-vesicle intact oocyte is prone to aneuploidy and epigenetic dysregulation.

Objectives

To determine the developmental, cytogenetic and epigenetic consequences of removing CP and including melatonin during bovine IVM.

Materials and methods

The study comprised a 2 x 2 factorial arrangement comparing (i) the inclusion or exclusion of CP, and (ii) the addition (100 nM) or omission of melatonin, during IVM. Cumulus-oocyte complexes (COCs) were retrieved from stimulated cycles. Following IVM and IVF, putative zygotes were cultured to Day 8 in standard media. RNAseq was performed on isolated cumulus cells, cytogenetic analyses (SNP-based algorithms) on isolated trophectoderm cells, and DNA methylation analysis (reduced representation bisulfite sequencing) on isolated cells of the inner-cell mass.

Results

Removal of CP during IVM led to modest reductions in blastocyst development, whilst added melatonin was beneficial in the presence but detrimental in the absence of CP. The composition of IVM media did not affect the nature or incidence of chromosomal abnormalities but cumulus-cell transcript expression indicated altered metabolism (primarily lipid) in COCs. These effects preceded the establishment of distinct metabolic and epigenetic signatures several days later in expanded and hatching blastocysts.

Conclusions

These findings highlight the importance of lipid, particularly sterol, metabolism by the COC during IVM. They lay the foundation for future studies that seek to develop chemically defined systems of IVM for the generation of transferrable embryos that are both cytogenetically and epigenetically normal.

Insulin-like growth factor (IGF) performance in ovarian function and applications in reproductive biotechnologies

The role of the insulin-like growth factor (IGF) system has attracted close attention. The activity of IGF binding proteins (IGFBPs) within the ovary has not been fully elucidated to date. These proteins bind to IGF with an equal, or greater, affinity than to the IGF1 receptor, thus being in the main position to regulate IGF signalling, in addition to extending the half-life of IGFs within the bloodstream and promoting IGF storage in specific tissue niches. IGF1 has an important part in cell proliferation, differentiation and apoptosis. Considering the importance of IGFs in oocyte maturation, this review sought to elucidate aspects including: IGF production mechanisms; constituent members of their family and their respective functions; the role that these factors play during folliculogenesis, together with their functions during oocyte maturation and apoptosis, and their performance during luteal development. This review also explores the role of IGFs in biotechnological applications, focusing specifically on animal genetic gain.

Combination of CNP, MT and FLI during IVM Significantly Improved the Quality and Development Abilities of Bovine Oocytes and IVF-Derived Embryos

Oocyte maturation is a critical step in the completion of female gametogenesis in the ovary; thus, for subsequent fertilization and embryogenesis. Vitrification of embryo also has been shown to be closely associated with oocyte maturation. To improve the quality and developmental potential of bovine oocytes derived from in vitro maturation (IVM), Pre-IVM with C-type natriuretic peptide (CNP), melatonin (MT) and in combination, IGF1, FGF2, LIF (FLI) were supplemented in the IVM medium. In this current study, we cultured bovine oocytes in Pre-IVM with CNP for 6 h before transferring them to the IVM medium supplemented with MT and FLI. The developmental potential of bovine oocytes was then investigated by measuring the reactive oxygen species (ROS), the intracellular glutathione (GSH) and ATP levels, the transzonal projections (TZP), the mitochondrial membrane potential (ΔΨm), cacline-AM, and the expression of related genes (cumulus cells (CCs), oocytes, blastocysts). The results revealed that oocytes treated with a combination of CNP, MT, and FLI had dramatically improved the percentage of oocytes developed to blastocyst, ATP content, GSH levels, TZP intensity, the ΔΨm, cacline-AM fluorescence intensity, and considerably reduced ROS levels of oocytes. Furthermore, the survival rate and the hatched rate after vitrification of the CNP+MT+FLI group were significantly higher than those other groups. Thus, we speculated that CNP+MT+FLI increases the IVM of bovine oocytes. In conclusion, our findings deepen our understanding and provide new perspectives on targeting the combination of CNP, MT and FLI to enhance the quality and developmental potential of bovine oocytes.

IVM Advances for Early Antral Follicle-Enclosed Oocytes Coupling Reproductive Tissue Engineering to Inductive Influences of Human Chorionic Gonadotropin and Ovarian Surface Epithelium Coculture

In vitro maturation (IVM) is not a routine assisted reproductive technology (ART) for oocytes collected from early antral (EA) follicles, a large source of potentially available gametes. Despite substantial improvements in IVM in the past decade, the outcomes remain low for EA-derived oocytes due to their reduced developmental competences. To optimize IVM for ovine EA-derived oocytes, a three-dimensional (3D) scaffold-mediated follicle-enclosed oocytes (FEO) system was compared with a validated cumulus-oocyte complex (COC) protocol. Gonadotropin stimulation (eCG and/or hCG) and/or somatic cell coculture (ovarian vs. extraovarian-cell source) were supplied to both systems. The maturation rate and parthenogenetic activation were significantly improved by combining hCG stimulation with ovarian surface epithelium (OSE) cells coculture exclusively on the FEO system. Based on the data, the paracrine factors released specifically from OSE enhanced the hCG-triggering of oocyte maturation mechanisms by acting through the mural compartment (positive effect on FEO and not on COC) by stimulating the EGFR signaling. Overall, the FEO system performed on a developed reproductive scaffold proved feasible and reliable in promoting a synergic cytoplasmatic and nuclear maturation, offering a novel cultural strategy to widen the availability of mature gametes for ART.

The transcription factor RUNX1 affects the maturation of porcine oocytes via the BMP15/TGF-β signaling pathway

Bone morphogenetic protein 15 (BMP15) is specifically expressed in oocytes in pigs at all stages from early stages to ovulation and has an important role in oocyte maturation. However, there are few reports on the molecular mechanisms by which BMP15 affects oocyte maturation. In this study, we identified the core promoter region of BMP15 using a dual luciferase activity assay and successfully predicted the DNA binding motif of the transcription factor RUNX1. The effect of BMP15 and RUNX1 on oocyte maturation was examined using the first polar body extrusion rate, a reactive oxygen species (ROS) assay and total glutathione (GSH) content at three time points of 12, 24 and 48 h of in vitro culture of porcine isolated oocytes. Subsequently, the effect of the transcription factor RUNX1 on the TGF-β signaling pathway (BMPR1B and ALK5) was further verified using RT-qPCR and Western blotting. We found that the overexpression of BMP15 significantly increased the first polar body extrusion rate (P < 0.01) and total glutathione content of oocytes cultured in vitro for 24 h and decreased reactive oxygen levels (P < 0.01), whereas interference with BMP15 decreased the first polar body extrusion rate (P < 0.01), increased reactive oxygen levels in oocytes cultured in vitro for 24 h (P < 0.01), and decreased glutathione content (P < 0.01). The dual luciferase activity assay and online software prediction showed that RUNX1 is a potential transcription factor binding to the core promoter region (-1203/-1423 bp) of BMP15. Overexpression of RUNX1 significantly increased the expression of BMP15 and oocyte maturation rate, while inhibition of RUNX1 decreased the expression of BMP15 and the oocyte maturation rate. Moreover, the expression of BMPR1B and ALK5 in the TGF-β signaling pathway increased significantly after overexpression of RUNX1, whereas their expression decreased after inhibition of RUNX1. Overall, our results suggest that the transcription factor RUNX1 positively regulates the expression of BMP15 and influences oocyte maturation through the TGF-β signaling pathway. This study provides a theoretical basis for further complementing the BMP15/TGF-β signaling pathway to regulate mammalian oocyte maturation.

Thermoprotective molecules: Effect of insulin-like growth factor type I (IGF-1) in cattle oocytes exposed to high temperatures

The adverse effects of heat stress (HS) on the welfare and productivity of cattle are the result of the associated hyperthermia and the physiological and behavioral mechanisms performed by the animal to regulate body temperature. The negative effects of HS on in vitro oocyte maturation and in vitro bovine embryo production have been reported; being one of the major concerns due to economic and productive losses, and several mechanisms have been implemented to reduce its impact. These mechanisms include supplementation of the medium with hormones, adjuvants, identification of protective genes, among others. This review aims to explore the cellular and molecular mechanisms of insulin-like growth factor-1 (IGF-1) during in vitro and in vivo maturation of bovine oocytes and its thermoprotective effect under HS. Although the supplementation of the culture medium during oocyte maturation with IGF-1 has been implemented during the last years, there are still controversial results, however, supplementation with low concentration showed a positive effect on maturation and thermoprotection of oocytes exposed to higher temperatures. Additionally, IGF-1 is involved in multiple cellular pathways, and it may regulate cell apoptosis in cases of HS and protect oocyte competence under in vitro conditions.

Simple and Efficient Chemically Defined In Vitro Maturation and Embryo Culture System for Bovine Embryos

Supplementation of the culture media for in vitro production (IVP) of bovine embryos with fetal bovine serum (FBS) is associated with inconsistent outcomes. The present study sought to replace FBS and BSA by insulin-like growth factor 1 (IGF1), fibroblast growth factor 2 (FGF2) and epidermal growth factor (EGF). In Experiment 1, absence of FBS from maturation medium (MM) did not affect the rate of in vitro maturation, as assessed by the extrusion of the first polar body. However, when gonadotropins and FBS were removed from the MM, the maturation rate was significantly reduced even in the presence of growth factors. Therefore, gonadotropin-supplemented MM medium was established as the base medium for the defined maturation condition. In Experiment 2, the addition of growth factors to gonadotropin-supplemented MM medium supported similar maturation (~90%) compared to the undefined condition (FBS-carrying). In Experiment 3, the addition of growth factors to embryo culture medium showed similar in vitro competence compared to the undefined (FBS) control. In Experiment 4, completely defined conditions (absence of FBS and BSA during in vitro maturation and embryo culture) were tested. A higher cleavage was observed with FGF2 (86%) compared to EGF (77%) and the FBS control (77%), but similar blastocyst rates were observed for FGF2 (24%), EGF (19%) and the FBS control (25%). Embryo quality was similar among groups. Finally, post-thawing survival was higher for FGF2 (94%) compared to the FBS control (77%). Thus, we report a simple defined IVP system for bovine species that generates developmental outcomes and embryos of similar quality than those produced under conditions containing FBS.

The role of oxidative stress in ovarian aging: a review

Ovarian aging refers to the process by which ovarian function declines until eventual failure. The pathogenesis of ovarian aging is complex and diverse; oxidative stress (OS) is considered to be a key factor. This review focuses on the fact that OS status accelerates the ovarian aging process by promoting apoptosis, inflammation, mitochondrial damage, telomere shortening and biomacromolecular damage. Current evidence suggests that aging, smoking, high-sugar diets, pressure, superovulation, chemotherapeutic agents and industrial pollutants can be factors that accelerate ovarian aging by exacerbating OS status. In addition, we review the role of nuclear factor E2-related factor 2 (Nrf2), Sirtuin (Sirt), mitogen-activated protein kinase (MAPK), protein kinase B (AKT), Forkhead box O (FoxO) and Klotho signaling pathways during the process of ovarian aging. We also explore the role of antioxidant therapies such as melatonin, vitamins, stem cell therapies, antioxidant monomers and Traditional Chinese Medicine (TCM), and investigate the roles of these supplements with respect to the reduction of OS and the improvement of ovarian function. This review provides a rationale for antioxidant therapy to improve ovarian aging.