77 Nobiletin supplementation affects gene expression profiles of the Akt pathway in bovine embryos invitro

Abstract

Embryonic genome activation (EGA) is a critical event in early embryonic development and occurs in 8-16-cell stage embryos in bovine. Invitro embryo production increases reactive oxygen species (ROS), leading to low yield and cell death. Nobiletin is an antioxidant that inhibits ROS production and affects cell cycle regulation. The aim of this study was to evaluate the effect of nobiletin supplementation in two key periods of early embryo development on blastocyst yield and expression of candidate genes of the Akt pathway. Invitro-produced zygotes were cultured in synthetic oviductal fluid supplemented with 5% FCS (control; C); C with 5 or 10 µM nobiletin (MedChemExpress; N5, N10) or C with 0.03% dimethyl sulfoxide (CD vehicle for nobiletin dilution) during the minor (2-8-cell stage; MNEGA) or major (8-16-cell stage; MJEGA) phase of EGA, considered as two separate experiments. For all groups, the speed of development was considered, and normally developing embryos that reach ≥8 cells at 54h post-insemination and ≥16 cells at 96h post-insemination were selected and cultured in control medium until Day 8, respectively. Embryos at ≥8-cell stage (N5/N10 MNEGA), 16-cell stage (N5/N10MJEGA), and Day 7 blastocysts of both periods were snap-frozen in LN2 for gene expression analysis. Cleavage rate and blastocyst yield (Day 7-8) were evaluated. The mRNA abundance of candidate genes related to the Akt pathway (CDK2, PGC1A, PPARG, RPS6KB1) and oxidative stress (GPX1) was measured by quantitative PCR. The H2AFZ and ACTB genes were used as housekeeping genes. Statistical analysis was assessed by one-way ANOVA. Nobiletin supplementation during MNEGA showed no differences in cleavage rate, whereas the blastocyst yield at Day 8 was higher (P<0.001) for N5 (42.9±1.4%) and N10 (45.3±2.1%) compared with C (32.9±1.1%) and CD (32.6±1.4%) groups. When nobiletin was supplemented during MJEGA, no differences were found in cleavage rate; however, Day 8 blastocyst yield was higher (P<0.001) for N10 (61.8±0.7%) compared with C (45.2±1.7%), CD (43.6±1.4%), and N5 (52.1±2.1%) groups, whereas N5 was higher (P<0.05) compared with both control groups. The mRNA abundance of CDK2 significantly increases in 8-cell stage embryos from N5 and N10 groups during MNEGA, whereas 16-cell stage embryos from N10 group during MJEGA showed a significant increase compared with both controls (P<0.05). The expression of PGC1A was significantly higher in blastocysts from N5, N10 during MNEGA, and N10 during MJEGA groups compared with both controls (P<0.05). No differences were observed for PPARG and RPS6KB1 in any group from both phases. GPX1, an oxidative indicator gene, was up-regulated in all nobiletin-supplemented groups from both phases compared with controls (P<0.05). In conclusion, supplementation of embryo culture during MNEGA or MJEGA with nobiletin improves embryo development and induces changes in the transcriptional genes related to cell cycle regulation and oxidative stress. This suggests that nobiletin acts through the Akt pathway during the first stages of embryonic development. Funding was provided by MINECO-Spain AGL2015-70140-R&RTI2018-093548-B-I00; Y. N. Cajas, SENESCYT-Ecuador; C. L. V. Leal, FAPESP-Brasil 2017/20339-3.