Quercetin supports bovine preimplantation embryo development under oxidative stress condition via activation of the Nrf2 signalling pathway.

Nrf2 is a master regulator for antioxidant machinery against oxidative stress in bovine preimplantation embryos. The endogenous or exogenous modulation of Nrf2-KEAP1 system in bovine embryos may contribute to the understanding of the mechanisms behind the response of embryos to stress conditions. Therefore, here we aimed to investigate the protective effect of quercetin on bovine preimplantation embryos exposed to higher atmospheric oxygen concentration. For that, blastocysts, which were developed from zygotes cultured in media supplemented with or without quercetin under high oxygen level (20%), were subjected intracellular ROS level and mitochondrial analysis, and determining blastocyst formation rate and total cell number. Moreover, mRNA and protein expression level of Nrf2 and selected downstream antioxidant genes were investigated in the resulting blastocysts. Quercetin supplementation in vitro culture did not affect cleavage and blastocyst rate until day 7. However, quercetin supplementation resulted in higher blastocyst total cell number and reduction of intracellular ROS level accompanied by increasing mitochondrial activity compared with control group in both day 7 and day 8 blastocysts. Moreover, quercetin supplementation induced mRNA and protein of Nrf2 with subsequent increase in the expression of downstream antioxidants namely: NQO1, PRDX1, CAT and SOD1 antioxidants. In conclusion, quercetin protects preimplantation embryos against oxidative stress and improves embryo viability through modulation of the Nrf2 signalling pathway.