Nobiletin enhances the development and quality of bovine embryos in vitro during two key periods of embryonic genome activation

Inflammatory uterine microenvironment in long-term infertility repeat breeder cows compared with normal fertile cows

The reproductive performance of lactating dairy cows is gradually declining, and one of the causes of this problem is the presence of long-term infertility repeat breeder cows (RBCs). The causes of RBCs are largely thought to be maternal factors, including the uterine environment. This study aimed to accurately investigate the uterine environment of RBCs using uterine tissue and fluid. Next, we investigated the effect of nobiletin in bovine endometrial epithelial cells to explore the possibility of improving the uterine environment of RBCs. Uterine fluid was collected by flushing the uterus and endometrial tissues were collected by biopsy on day 7 of the estrous cycle from both normal fertile cows and RBCs (n = 5 in each group). A comprehensive analysis of the uterus revealed that gene expression and altered pathways differed between normal fertile cows and RBCs. Especially, pathways of natural killer cell-mediated cytotoxicity, cell cycle, and calcium signaling pathway were picked up in the uterine tissues of RBCs. In the uterine fluid, the levels of lipopolysaccharide were higher in the RBC than in normal group (P = 0.08). In in vitro experiment, treatment with the uterine fluid from RBCs upregulated inflammation-related pathways and molecules such as interleukin-8 (IL-8) in bovine endometrial epithelial cells. The treatment with nobiletin suppressed IL-8 induced by the treatment with uterine fluid. In conclusion, the uterine environment of RBCs was found to be in inflammatory condition, causing the lower reproductive performance. It is necessary to develop methods to improve to the anti-inflammatory state in the uterine environment of RBCs.

Nobiletin as a novel agent to enhance porcine in vitro embryo development and quality

In vitro embryo production (IVP) is of great importance to the porcine industry, as well as for basic research and biomedical applications. Despite the large efforts made in laboratories worldwide to address suboptimal culture conditions, porcine IVP remains inefficient. Nobiletin (Nob, 5,6,7,8,3',4' hexamethoxyflavone) supplementation to in vitro culture (IVC) medium, enhances in vitro embryo development in various species. However, its impact on the quality and developmental capacity of in vitro-produced pig embryos is yet to be established. This study evaluated the effects of different concentrations (2.5 and 5 μM) of Nob during the early culture of in vitro-produced pig embryos on embryo developmental competence, mitochondrial activity, lipid content, intracellular Reactive Oxygen Species (ROS) and Glutathione (GSH) content, Total Cell Number (TCN) per blastocyst, and expression of genes related to embryo development, quality and oxidative stress. Embryos cultured in medium without Nob supplementation and in medium supplemented with 0.01 % dimethyl sulfoxide (DMSO-vehicle for Nob) constituted the Control and DMSO groups, respectively. Embryo development rates were evaluated on Days 2, 6 and 7 of IVC. Additionally, a representative group of embryos was selected to assess mitochondrial activity, lipid, ROS and GSH content (on Days 2 and 6 of IVC), TCN assessment and gene expression analyses (on Day 6 of IVC). No significant differences were observed in any of the parameters evaluated on Day 2 of IVC. In contrast, embryos cultured under the presence of Nob 2.5 showed higher developmental rates on Days 6 and 7 of IVC. In addition, Day 6 embryos showed increased mitochondrial activity, with decreased levels of ROS and GSH in the Nob 2.5 group compared to the other groups. Both Nob 2.5 and Nob 5 embryos showed higher TCN compared to the Control and DMSO groups. Furthermore, Nob 2.5 and Nob 5 upregulated the expression of Superoxide dismutase type 1 (SOD1) and Glucose-6-phosphate dehydrogenase (G6PDH) genes, which could help to counteract oxidative stress during IVC. In conclusion, the addition of Nob during the first 48 h of IVC increased porcine embryo development rates and enhanced their quality, including the upregulation of relevant genes that potentially improved the overall efficiency of the IVP system.

miRNAs in Follicular and Oviductal Fluids Support Global DNA Demethylation in Early-Stage Embryos

Global methylation levels differ in in vitro- and in vivo-developed embryos. Follicular fluid (FF) contains extracellular vesicles (EVs) containing miRNAs that affect embryonic development. Here, we examined our hypothesis that components in FF affect global DNA methylation and embryonic development. Oocytes and FF were collected from bovine ovaries. Treatment of zygotes with a low concentration of FF induced global DNA demethylation, improved embryonic development, and reduced DNMT1/3A levels. We show that embryos take up EVs containing labeled miRNA secreted from granulosa cells and the treatment of zygotes with EVs derived from FF reduces global DNA methylation in embryos. Furthermore, the methylation levels of in vitro-developed blastocysts were higher than those of in their vivo counterparts. Based on small RNA-sequencing and in silico analysis, we predicted miR-29b, -199a-3p, and -148a to target DNMTs and to induce DNA demethylation, thereby improving embryonic development. Moreover, among FF from 30 cows, FF with a high content of these miRNAs demethylated more DNA in the embryos than FF with a lower miRNA content. Thus, miRNAs in FF play a role in early embryonic development.

Individually Cultured Bovine Zygotes Successfully Develop to the Blastocyst Stage in an Extremely Confined Environment

The possibility of detecting the developmental competence of individually cultured embryos through analysis of spent media is a major current trend in an ART setting. However, individual embryo culture is detrimental compared with high-density group culture due to the reduced concentration of putative embryotropins. The main aim of this study was to identify an individual culture system that is not detrimental over high-density group culture in the bovine model. Blastocyst rates and competence were investigated in a conventional (GC) group, semi-confined group (MG), and individual culture (MS) in a commercial microwell device. Main findings showed that: (1) individual embryos can be continuously cultured for 7 days in ~70 nL microwells (MS) without detrimental effects compared with the GC and MG; (2) MS and MG blastocysts had a reduced number of TUNEL-positive cells compared to GC blastocysts; (3) though blastocyst mean cell numbers, mitochondrial activity, and lipid content were not different among the three culture conditions, MS blastocysts had a higher frequency of small-sized lipid droplets and a reduced mean droplet diameter compared with GC and MG blastocysts. Overall, findings open the way to optimize the development and competence of single embryos in an ART setting.

MicroRNA-148b secreted by bovine oviductal extracellular vesicles enhance embryo quality through BPM/TGF-beta pathway

BACKGROUND

Extracellular vesicles (EVs) and their cargoes, including MicroRNAs (miRNAs) play a crucial role in cell-to-cell communication. We previously demonstrated the upregulation of bta-mir-148b in EVs from oviductal fluid of cyclic cows. This miRNA is linked to the TGF-β pathway in the cell proliferation. Our aim was to verify whether miR-148b is taken up by embryos through gymnosis, validate its target genes, and investigate the effect of miR-148b supplementation on early embryo development and quality.

METHODS

Zygotes were cultured in SOF + 0.3% BSA (Control) or supplemented with: 1 µM miR-148b mimics during: D1-D7 (miR148b) or D1-D4 (miR148b-OV: representing miRNA effect in the oviduct) or D4-D7 (miR148b-UT: representing miRNA effect in the uterus) or 1 µM control mimics was used during: D1-D7 (CMimic). Embryos at ≥ 16-cells and D7 blastocysts (BD7) were collected to examine the mRNA abundance of transcripts linked to the TGF-β pathway (TGFBR2, SMAD1, SMAD2, SMAD3, SMAD5, BMPR2, RPS6KB1, POU5F1, NANOG), total cell number (TC), trophectoderm (TE), and inner cell mass (ICM) were also evaluated. One-way ANOVA was used for all analyses.

RESULTS

We demonstrated that miR-148b can be taken up in both 16-cell embryos and BD7 by gymnosis, and we observed a decrease in SMAD5 mRNA, suggesting it's a potential target of miR-148b. Cleavage and blastocysts rates were not affected in any groups; however, supplementation of miR-148b mimics had a positive effect on TC, TE and ICM, with values of 136.4 ± 1.6, 92.5 ± 0.9, 43.9 ± 1.3 for miR148b and 135.3 ± 1.5, 92.6 ± 1.2, 42.7 ± 0.8, for miR148b-OV group. Furthermore, mRNA transcripts of SMAD1 and SMAD5 were decreased (P ≤ 0.001) in 16-cell embryos and BD7 from miR148b and miR148b-OV groups, while POU5F1 and NANOG were upregulated (P ≤ 0.001) in BD7 and TGFBR2 was only downregulated in 16-cell embryos. pSMAD1/5 levels were higher in the miR148b and miR148b-OV groups.

CONCLUSIONS

Our findings suggest that supplementation of bta-miR-148b mimics during the entire culture period (D1 - D7) or from D1 - D4 improves embryo quality and influences the TGF-β signaling pathway by altering the transcription of genes associated with cellular differentiation and proliferation. This highlights the importance of miR-148b on embryo quality and development.

Effects of Nobiletin supplementation on the freezing diluent on porcine sperm cryo-survival and subsequent in vitro embryo development

Nobiletin (NOB) is a bioflavonoid compound isolated from citrus fruit peels. The present study aimed to elucidate whether NOB facilitates the porcine sperm cryosurvival and embryo development after in vitro fertilization (IVF). To this end, spermatozoa were diluted and cryopreserved in a freezing extender supplemented with 0 (control), 50, 100, 150, and 200 μM Nobiletin. The kinematic patterns of frozen-thawed (FT) sperm were assessed after 30 and 90 min incubation using a Sperm Class Analyzer (SCA). Viability, acrosome integrity, and mitochondrial membrane potential (MMP) were measured by fluorescence microscopy 30 min after thawing using SYBR-14/PI, PSA/FITC, and R123/PI, respectively. Lipid peroxidation was determined using MDA assay after incubation for 90 min. The addition of 100 μM and 150 μM NOB to the extender significantly improved sperm progressive motility, and acrosome integrity compared to the control group (P < 0.05). The proportion of viable spermatozoa was significantly higher in the 150 μM NOB group. MDA levels were less in 50 μM and 150 μM NOB treated groups compared to the control. In addition, IVF with FT sperm was used to assess the embryo developmental competence. Treatment with 150 μM NOB before cryopreservation increased the cleavage and blastocyst formation rates compared to the control group. Furthermore, the relative expression of POU5F1 and AMPK, genes related to pluripotency and cell differentiation were significantly upregulated in embryos resulting from NOB-treated sperm compared to the control group. These results suggest that Nobiletin is a functionally novel phytochemical to mitigate oxidative stress during the freezing-thawing of porcine spermatozoa as reflected by improved FT sperm quality and IVF outcome.

Serum supplementation during in vitro fertilization of sheep oocytes influences blastocyst quality through the differential abundance of mRNA transcripts

Incubation with estrous sheep serum (ESS) is required to induce in vitro capacitation of spermatozoa during in vitro fertilization of small ruminants. However, the effect of adding different serum concentrations in the fertilization media on the quality of resulting blastocysts has not yet been studied. Here, 298 sheep oocytes were co-incubated with capacitated spermatozoa with either 10% or 2% ESS. There were no differences between treatments in cleavage (10% ESS: 63.81 ± 5.87% and 2% ESS: 45.31 ± 5.87%) and blastocyst rates (10% ESS: 20.83 ± 2.12% and 2% ESS: 15.93 ± 2.12%). Nonetheless, in vitro-produced blastocysts from the 10% ESS treatment showed a higher transcript abundance of mRNAs involved in apoptosis (ITM2B and BCL2), antioxidant defence (GPX1) and growth-related imprinting (IGF2R). Our data suggest that ESS supplementation during in vitro fertilization can influence the quality of sheep embryos at later stages of development by increasing the transcription of developmentally important genes.

miR-17-5p in bovine oviductal fluid affects embryo development

This study identified microRNAs (miRNAs) in bovine oviductal fluids (OFs) and examined the effect of miR-17-5p in OFs on embryonic development to the blastocyst stage. Small RNA-seq of extracellular vesicles of OFs revealed 242 miRNAs. Additionally, analyzing expressions of randomly selected OF-miRNAs with RT-qPCR in the culture medium of oviductal epithelial cells indicated that the abundance of miRNAs in OFs increased during the luteal phase. miR-17-5p mimic-treated eight-cell-stage zona pellucida-free embryos showed improved embryonic development to the blastocyst stage. The effect of the miR-17-5p mimic was confirmed using a dual-luciferase assay and immunostaining. In addition, RNA-seq of the miR-17-5p mimic- or control-treated embryos revealed differentially expressed genes (DEGs), suggesting possible pathways that overlapped with the in silico-predicted pathways for miR-17-5p targeting genes. Furthermore, ingenuity pathway analysis of DEG predicted miR-17 to be a significant upstream regulator. Our results suggest that miR-17-5p in OFs regulates embryonic development in bovines.

Nobiletin-induced partial abrogation of deleterious effects of AKT inhibition on preimplantation bovine embryo development in vitro

During preimplantational embryo development, PI3K/AKT regulates cell proliferation and differentiation and nobiletin modulates this pathway to promote cell survival. Therefore, we aimed to establish whether, when the AKT cascade is inhibited using inhibitors III and IV, nobiletin supplementation to in vitro culture media during the minor (2 to 8-cell stage, MNEGA) or major (8 to 16-cell stage, MJEGA) phases of EGA is able to modulate the development and quality of bovine embryos. In vitro zygotes were cultured during MNEGA or MJEGA phase in SOF + 5% FCS or supplemented with: 15 μM AKT-InhIII; 10 μM AKT-InhIV; 10 μM nobiletin; nobiletin+AKT-InhIII; nobiletin+AKT-InhIV; 0.03% DMSO. Embryo development was lower in treatments with AKT inhibitors, while combination of nobiletin with AKT inhibitors was able to recover their adverse developmental effect and also increase blastocyst cell number. The mRNA abundance of GPX1, NFE2L2, and POU5F1 was partially increased in 8- and 16-cell embryos from nobiletin with AKT inhibitors. Besides, nobiletin increased the p-rpS6 level whether or not AKT inhibitors were present. In conclusion, nobiletin promotes bovine embryo development and quality and partially recovers the adverse developmental effect of AKT inhibitors which infers that nobiletin probably uses another signalling cascade that PI3K/AKT during early embryo development in bovine.