IGF2 reduces meiotic defects in oocytes from obese mice and improves embryonic developmental competency

BACKGROUND

Maternal obesity is a global issue that has devastating effects across the reproductive spectrum such as meiotic defects in oocytes, consequently worsening pregnancy outcomes. Different studies have shown that such types of meiotic defects originated from the oocytes of obese mothers. Thus, there is an urgent need to develop strategies to reduce the incidence of obesity-related oocyte defects that adversely affect pregnancy outcomes. Multiple growth factors have been identified as directly associated with female reproduction; however, the impact of various growth factors on female fertility in response to obesity remains poorly understood.

METHODS

The immature GV-stage oocytes from HFD female mice were collected and cultured in vitro in two different groups (HFD oocytes with and without 50 nM IGF2), however; the oocytes from ND mice were used as a positive control. HFD oocytes treated with or without IGF2 were further used to observe the meiotic structure using different analysis including, the spindle and chromosomal analysis, reactive oxygen species levels, mitochondrial functional activities, and early apoptotic index using immunofluorescence. Additionally, the embryonic developmental competency and embryos quality of IGF2-treated zygotes were also determined.

RESULTS

In our findings, we observed significantly reduced contents of insulin-like growth factor 2 (IGF2) in the serum and oocytes of obese mice. Our data indicated supplementation of IGF2 in a culture medium improves the blastocyst formation: from 46% in the HFD group to 61% in the HFD + IGF2-treatment group (50 nM IGF2). Moreover, adding IGF2 to the culture medium reduces the reactive oxygen species index and alleviates the frequency of spindle/chromosome defects. We found increased mitochondrial functional activity in oocytes from obese mice after treating the oocytes with IGF2: observed elevated level of adenosine triphosphate, increased mitochondrial distribution, higher mitochondrial membrane potentials, and reduced mitochondrial ultrastructure defects. Furthermore, IGF2 administration also increases the overall protein synthesis and decreases the apoptotic index in oocytes from obese mice.

CONCLUSIONS

Collectively, our findings are strongly in favor of adding IGF2 in culture medium to overcome obesity-related meiotic structural-developmental defects by helping ameliorate the known sub-optimal culturing conditions that are currently standard with assisted reproduction technologies.

IGF2 improves the developmental competency and meiotic structure of oocytes from aged mice

Advanced maternal-age is a major factor adversely affecting oocyte quality, consequently worsening pregnancy outcomes. Thus, developing strategies to reduce the developmental defects associated with advanced maternal-age would benefit older mothers. Multiple growth factors involved in female fertility have been extensively studied; however, the age-related impacts of various growth factors remain poorly studied. In the present study, we identified that levels of insulin-like growth factor 2 (IGF2) are significantly reduced in the serum and oocytes of aged mice. We found that adding IGF2 in culture medium promotes oocyte maturation and significantly increases the proportion of blastocysts: from 41% in the untreated control group to 64% (50 nM IGF2) in aged mice (p < 0.05). Additionally, IGF2 supplementation of the culture medium reduced reactive oxygen species production and the incidence of spindle/chromosome defects. IGF2 increases mitochondrial functional activity in oocytes from aged mice: we detected increased ATP levels, elevated fluorescence intensity of mitochondria, higher mitochondrial membrane potentials, and increased overall protein synthesis, as well as increased autophagy activity and decreased apoptosis. Collectively, our findings demonstrate that IGF2 supplementation in culture media improves oocyte developmental competence and reduces meiotic structure defects in oocytes from aged mice.

Extracellular vesicles derived from endometrial human mesenchymal stem cells enhance embryo yield and quality in an aged murine model†

Advanced age is a risk factor undermining women's fertility. Hence, the optimization of assisted reproduction techniques is an interdisciplinary challenge that requires the improvement of in vitro culture systems. Here, we hypothesize that supplementation of embryo culture medium with extracellular vesicles from endometrial-derived mesenchymal stem cells (EV-endMSCs) may have a positive impact on the embryo competence of aged oocytes. In this work, 24 weeks old B6D2 female mice were used as egg donors and in vitro fertilization assays were performed using males from the same strain (8-12 weeks); the presumptive zygotes were incubated in the presence of 0, 10, 20, 40, or 80 μg/ml of EV-endMSCs. The results from the proteomic analysis of EV-endMSCs and the classification by Reactome pathways allowed us to identify proteins closely related with the fertilization process. Moreover, in our aged murine model, the supplementation of the embryo culture medium with EV-endMSCs improved the developmental competence of the embryos as well as the total blastomere count. Finally, gene expression analysis of murine blastocysts showed significant changes on core genes related to cellular response to oxidative stress, metabolism, placentation, and trophectoderm/inner cell mass formation. In summary, we demonstrate that EV-endMSCs increase the quality of the embryos, and according to proteomic and genomic analysis, presumably by modulating the expression of antioxidant enzymes and promoting pluripotent activity. Therefore, EV-endMSCs could be a valuable tool in human assisted reproduction improving the developmental competence of aged oocytes and increasing the odds of implantation and subsequent delivery.

Goat DNMT3B: An indel mutation detection, association analysis with litter size and mRNA expression in gonads

DNA methyltransferase 3β (DNMT3B) is a gene encoding a de novo methylation enzyme that is required for DNA methylation during mammalian embryo development. Previous genome-wide association analysis suggested DNMT3B is a candidate gene for goat fertility, but there is no study on the effect of DNMT3B on litter size in goat. The aim of this study was to identify possible insertion/deletion (indel) mutations associated with litter size. Seven putative indels were designed to study their association with litter size, but just one 11-bp insertion variant of intron 22 (the last intron) was found in healthy female Shaanbei white cashmere goats (SBWC goats) (n = 1534). Statistical analysis showed that the 11-bp insertion was related to the first-born litter size (P < 0.01) and the goats with the deletion/deletion genotype had a higher average first-born litter size (P < 0.01). In addition, the expression profile of the DNMT3B mRNA in goat was detected, which revealed significant differences in DNMT3B mRNA expression in the gonads. Additionally, the results of western blotting revealed that the ovaries of mothers of multi-lamb (MML) had a higher level of DNMT3B protein than the ovaries of mothers of single-lamb (MSL). Furthermore, the mRNA of DNMT3B was widely expressed in male goats. Differences in mRNA expression levels were observed in the ovaries of MSL and MML. These findings indicated that the 11-bp indel in DNMT3B was significantly associated with first-born litter size, which can be used for marker-assisted selection (MAS) of goats for breeding.

Roles of insulin-like growth factor II in regulating female reproductive physiology

The number of growth factors involved in female fertility has been extensively studied, but reluctance to add essential growth factors in culture media has limited progress in optimizing embryonic growth and implantation outcomes, a situation that has ultimately led to reduced pregnancy outcomes. Insulin-like growth factor II (IGF-II) is the most intricately regulated of all known reproduction-related growth factors characterized to date, and is perhaps the predominant growth factor in human ovarian follicles. This review aims to concisely summarize what is known about the role of IGF-II in follicular development, oocyte maturation, embryonic development, implantation success, placentation, fetal growth, and in reducing placental cell apoptosis, as well as present strategies that use growth factors in culture systems to improve the developmental potential of oocytes and embryos in different species. Synthesizing the present knowledge about the physiological roles of IGF-II in follicular development, oocyte maturation, and early embryonic development should, on the one hand, deepen our overall understanding of the potential beneficial effects of growth factors in female reproduction and on the other hand support development (optimization) of improved outcomes for assisted reproductive technologies.

Extracellular vesicles derived from endometrial human mesenchymal stem cells improve IVF outcome in an aged murine model

Advanced age reduces the success of in vitro fertilization (IVF) being this effect partly mediated by an overproduction of reactive oxygen species (ROS) that trigger apoptosis. It has been demonstrated that extracellular vesicles derived from endometrial mesenchymal stem cells (EV-endMSCs) exert an antioxidant effect and can be used as IVF coadjutants. In this work, endMSCs were isolated from human menstrual blood (n = 4) and characterized according to multipotentiality and surface marker expression prior EV-endMSCs isolation. Oocytes were obtained from 21 B6D2 mice (24 weeks) and coincubated with sperm from young males (8-12 weeks). Presumptive zygotes were incubated in the presence of 0, 10, 20, 40 or 80 μg/ml of EV-endMSCs in KSOM medium. Blastocyst yield was evaluated, and 25 blastocysts per group were used for qPCR. Blastocyst rate was 29.4% in control; 45.2% for 10 μg/ml, 62.9% for 20 μg/ml, 55.5% for 40 μg/ml and 53.8% in the 80 μg/ml (n = 124-130 oocytes) being all the increases significantly different when compared against control (p < 0.05). The 20-80 μg/ml treatments decreased the expression of glutathione peroxidase (Gpx1), and the 10-40 μg/ml treatments reduced the expression of superoxide dismutase (Sod1; p < 0.05) compared to control; Bax mRNA expression did not vary. Our results suggest that the increased developmental competence of the embryos could be partly mediated by the EV-endMSCs' ROS scavenger activity.

Exogenous growth factors do not affect the development of individually cultured murine embryos

PURPOSE

The objective of this study was to evaluate the effects of multiple growth factors on the development of individually cultured murine embryos.

METHODS

Embryos produced by in vitro fertilization using in vitro (IVM) or in vivo (IVO) matured oocytes from three strains of mice (CF1, Swiss Webster, B6D2F1) were cultured individually (10 μl) in the absence (control) or presence of growth factors (paf, epidermal growth factor [EGF], insulin-like growth factor 1 [IGF-1], and granulocyte-macrophage colony-stimulating factor [GM-CSF]). Blastocyst formation, hatching, and blastocyst cell numbers (trophectoderm, inner cell mass, and total) were evaluated on days 4 and 5 of culture. Post-hatching development of CF1 IVO embryos was also evaluated in vitro and in vivo.

RESULTS

The presence of growth factors did not improve the proportion of embryos forming blastocysts or initiating hatching for any of the types of embryos tested. The only significant (P < 0.05) effect of growth factors was a decrease in the proportion of embryos that formed blastocysts by day 5 in CF1 IVM embryos. The presence of growth factors also did not affect blastocyst cell numbers. For CF1 IVO embryos, the presence of growth factors during culture did not affect the proportion of embryos that attached to fibronectin-coated dishes, the size of the resulting outgrowths, or in vivo development following transfer.

CONCLUSION

Combinations of paf, EGF, GM-CSF, and IGF-1 did not improve development of murine embryos cultured individually in a sequential medium containing a defined protein source.