Folic acid supplementation during oocytes maturation influences in vitro production and gene expression of bovine embryos

Folic acids promote in vitro maturation of bovine oocytes by inhibition of ferroptosis via upregulated glutathione and downregulated Fe2+ accumulation

Bovine embryos by in vitro fertilization have become the primary source of commercial embryo transfers globally. However, the developmental capacity of in vitro maturation (IVM) oocytes is considerably lower than that of in vivo maturation (IVO) oocytes, owing to the production of reactive oxygen species (ROS) via mitochondrial metabolism, which was higher in IVM oocytes than in IVO oocytes. To avoid the negative effects of ROS on embryo quality, folic acid (FA) was supplemented directly into the IVM medium to antagonize ROS production, however, the mechanisms remain unknown. In the present study, five levels of FA (0, 25, 50, 100, and 200 µM) were supplemented into the bovine oocyte culture medium. The maturation, cleavage, and blastocyst formation rates increased by 8.95 %, 6.94 %, and 4.36 %, respectively, in the 50 µM group compared to the 0 µM group. Moreover, 7904 differential genes were identified between 0 µM and 50 µM groups by transcriptome sequencing, and they were mainly enriched in 8 pathways. The glutathione, ROS, and Fe2+ levels in oocytes were found to be associated with ferroptosis. Our results revealed that 50 µM FA promoted the IVM of bovine oocytes and affected the expression of genes involved in the ferroptosis pathway. The downregulation of TFR1 and STEAP3 led to a decrease in intracellular Fe2+ accumulation, and the upregulation of GCL increased oocyte GSH levels, thereby reducing the production of ROS in the ferroptosis pathway. Our study provides a new insight into the molecular mechanisms by which FA promotes bovine oocyte development in vitro.

The Role of One-Carbon Metabolism and Methyl Donors in Medically Assisted Reproduction: A Narrative Review of the Literature

One-carbon (1-C) metabolic deficiency impairs homeostasis, driving disease development, including infertility. It is of importance to summarize the current evidence regarding the clinical utility of 1-C metabolism-related biomolecules and methyl donors, namely, folate, betaine, choline, vitamin B12, homocysteine (Hcy), and zinc, as potential biomarkers, dietary supplements, and culture media supplements in the context of medically assisted reproduction (MAR). A narrative review of the literature was conducted in the PubMed/Medline database. Diet, ageing, and the endocrine milieu of individuals affect both 1-C metabolism and fertility status. In vitro fertilization (IVF) techniques, and culture conditions in particular, have a direct impact on 1-C metabolic activity in gametes and embryos. Critical analysis indicated that zinc supplementation in cryopreservation media may be a promising approach to reducing oxidative damage, while female serum homocysteine levels may be employed as a possible biomarker for predicting IVF outcomes. Nonetheless, the level of evidence is low, and future studies are needed to verify these data. One-carbon metabolism-related processes, including redox defense and epigenetic regulation, may be compromised in IVF-derived embryos. The study of 1-C metabolism may lead the way towards improving MAR efficiency and safety and ensuring the lifelong health of MAR infants.

Dynamic methylation pattern of H19DMR and KvDMR1 in bovine oocytes and preimplantation embryos

PURPOSE

This study aimed to evaluate the epigenetic reprogramming of ICR1 (KvDMR1) and ICR2 (H19DMR) and expression of genes controlled by them as well as those involved in methylation, demethylation, and pluripotency.

METHODS

We collected germinal vesicle (GV) and metaphase II (MII) oocytes, and preimplantation embryos at five stages [zygote, 4-8 cells, 8-16 cells, morula, and expanded blastocysts (ExB)]. DNA methylation was assessed by BiSeq, and the gene expression was evaluated using qPCR.

RESULTS

H19DMR showed an increased DNA methylation from GV to MII oocytes (68.04% and 98.05%, respectively), decreasing in zygotes (85.83%) until morula (61.65%), and ExB (63.63%). H19 and IGF2 showed increased expression in zygotes, which decreased in further stages. KvDMR1 was hypermethylated in both GV (71.82%) and MII (69.43%) and in zygotes (73.70%) up to morula (77.84%), with a loss of methylation at the ExB (36.64%). The zygote had higher expression of most genes, except for CDKN1C and PHLDA2, which were highly expressed in MII and GV oocytes, respectively. DNMTs showed increased expression in oocytes, followed by a reduction in the earliest stages of embryo development. TET1 was downregulated until 4-8-cell and upregulated in 8-16-cell embryos. TET2 and TET3 showed higher expression in oocytes, and a downregulation in MII oocytes and 4-8-cell embryo.

CONCLUSION

We highlighted the heterogeneity in the DNA methylation of H19DMR and KvDMR1 and a dynamic expression pattern of genes controlled by them. The expression of DNMTs and TETs genes was also dynamic owing to epigenetic reprogramming.

Exploring optimal folic acid supplementation levels for lactating-pregnant rabbit does with different litter size

The lactation-pregnancy overlap in the industrialized 49-d breeding model increases nutritional demands for lactating-pregnant rabbit does. This study examined the effects of folic acid (FA) on the production performance and intestinal microflora of does with different litter sizes (LS, or number of kits). A total of 144 third-parity Hyplus does, aged 11 mo and weighing approximately 5.00 ± 0.07 kg, were divided into 4 treatment groups: control group (basal diet) and FA groups (basal diet + 15, 30, and 45 mg/kg FA). Does with LS of 5, 7, and 9 were selected after weaning. Our findings revealed that 1) Increased FA supplementation initially increased and then decreased the pre-lactation body weight of 21-d-old kits and prolactin (PRL) level of lactating does, while showing an inverse trend for estrogen (E) level of does. Increased LS significantly (P < 0.05) correlated with reduced milk yield of does. There was a significant (P < 0.05) interaction between FA and LS affecting PRL, E, growth hormone levels of does, and the pre-lactation body weight of 21-d-old kits; 2) Increased FA supplementation initially increased and then decreased the post-lactation body weight of 21-d-old and 35-d-old kits, elevated plasma FA (PFA) level of lactating-pregnant does, and significantly (P < 0.05) impacted the pregnancy rate of does. Increased LS was associated with reduced post-lactation body weight in 21-d-old and 35-d-old kits (P < 0.05). There was a significant (P < 0.05) interaction between FA and LS affecting plasma insulin-like growth factor-1 (IGF-1), homocysteine (HCY), PFA levels of does, the post-lactation body weight of 21-d-old kits, and weaning body weight of 35-d-old kits; and 3) FA supplementation promoted the growth of Ruminococcaceae and Rikenellaceae_RC9_gut_group in the feces of lactating-pregnant does, as well as the proliferation of Lachnospiraceae_NK4A136_group in the feces of pregnant does, suggesting enhanced anti-inflammatory properties and improved crude fiber breakdown. In summary, FA supplementation improved conception rates, regulated lactation-related hormone synthesis and secretion, increased body weight of 21-d-old kits, and enhanced intestinal anti-inflammatory functions.

In vivo and in vitro matured bovine oocytes present a distinct pattern of single-cell gene expression

Oocyte gene expression is a well controlled event that promotes gamete competence to undergo maturation, fertilization, and to support early embryo development, directly affecting reproductive outcomes. Considering that in vivo controlled ovarian stimulation or in vitro maturation (IVM) for the acquisition of mature oocytes has distinct implications for gene expression, we sought to evaluate the effects of these procedures on the expression of competence-related genes in single-cell oocytes. Healthy Nelore cows of reproductive age were synchronized to harvest in vivo matured oocytes; ovaries from slaughtered animals were used to obtain cumulus-oocyte complexes that were in vitro matured. Single-cell gene expression was performed using TaqMan Low-Density Arrays and 42 genes were evaluated. In silico analysis of protein interactions and Gene Ontology (GO) analysis was performed. Reduced gene expression was observed for 24 targets in IVM oocytes when compared with those of in vivo matured oocytes (P < 0.05). Differences ranged from 1.5-fold to 4.8-fold higher in in vivo oocytes and the BMP15 (5.28), GDF9 (6.23), NOBOX (7.25), HSPA8 (7.85) and MSX1 (11.00) showed the greatest fold increases. The strongest score of functional interactions was observed between the CDC20 and CKS2, with the differentially expressed gene CDC20 being the main marker behind GO enrichment. IVM negatively affected the expression of important genes related to oocyte competency, and showed higher expression levels in in vivo matured oocytes. In vivo controlled ovarian stimulation may be a better strategy to achieve proper oocyte competence and increase the success of assisted reproductive technologies.

Status of maternal serum B vitamins and pregnancy outcomes: New insights from in vitro fertilization and embryo transfer (IVF-ET) treatment

The influence of B vitamins on human fertility and infertility treatments remains elusive. Therefore, this study investigated the association of most B vitamins with IVF-ET outcomes. A total of 216 subjects aged <35 year in their first oocyte retrieval cycle were recruited. Blood samples from the participants were collected before the oocyte pick-up procedure, and serum levels of riboflavin, niacin, pantothenic acid, vitamin B6 (including PA and PLP), folate, and methylmalonic acid (MMA) were detected using high-performance liquid chromatography–tandem mass spectrometry (HPLC-MS/MS). Endpoints were classified into three groups according to tertiles (lower, middle, and upper) of each vitamin index, and the association of the serum vitamin status with intermediate and clinical outcomes was analyzed using a generalized estimating equation model. Higher riboflavin levels were associated with elevated probabilities of high-quality embryos, as well as clinical pregnancy after embryo transfer. A greater likelihood of transferable embryos was found in the middle tertile of serum folate. Similarly, a negative correlation of serum MMA, a marker of vitamin B12 deficiency, with high-quality embryos was identified. No significance was observed for other vitamins in terms of all endpoints. Therefore, sufficient levels of pre-conception riboflavin, folate, and vitamin B12 are recommended for successful infertility treatment and pregnancy planning; further evidence is needed to confirm our conclusion.