Bovine embryo survival under oxidative‐stress conditions is associated with activity of the NRF2‐mediated oxidative‐stress‐response pathway

Abstract

In present study, we sought to examine the ability of preimplantation bovine embryos to activate the NF-E2-related factor 2 (NRF2)-mediated oxidative-stress response under an oxidative stress environment. In vitro 2-, 4-, 8-, 16-cell-, and blastocyst-stage embryos were cultured under low (5%) or high (20%) oxygen levels. The expression of NRF2, KEAP1 (NRF2 inhibitor), antioxidants downstream of NRF2, and genes associated with embryo metabolism were analyzed between the embryo groups using real-time quantitative PCR. NRF2 and KEAP1 protein abundance, mitochondrial activity, and accumulation of reactive oxygen species (ROS) were also investigated in blastocysts of varying competence that were derived from high- or low-oxygen levels. The expression levels of NRF2 and its downstream antioxidant genes were higher in 8-cell, 16-cell, and blastocyst stages under high oxygen tension, whereas KEAP1 expression was down-regulated under the same conditions. Higher expression of NRF2 and lower ROS levels were detected in early (competent) blastocysts compared to their late (noncompetent) counterparts in both oxygen-tension groups. Similarly, higher levels of active nuclear NRF2 protein were detected in competent blastocysts compared to their noncompetent counterparts. Thus, the survival and developmental competence of embryos cultured under oxidative stress are associated with activity of the NRF2-mediated oxidative stress response pathway during bovine pre-implantation embryo development.

Sexual dimorphic expression and release of transcription factors in bovine embryos exposed to oxidative stress

“…Accordingly, the maturation and fertilization were done at high oxygen tension in the current study. Furthermore, here we showed that irrespective of the sex of embryo, those embryos cultured under 5% oxygen level showed higher development rate of blastocyst than those under 20% oxygen level, as it has been reported before (Amin et al, ; Leite et al, ). Differences in metabolism (Gómez et al, ) and genetics (Bermejo‐Alvarez et al, ) between male and female bovine embryo could contribute to skewness in sex ratio of the resulted embryos (Oliveira et al, ; Xu, Yadav, King, & Betteridge, ).…”

“…Similarly, our results showed that the blastocyst rate at Days 7 and 8 (Figure ) were skewed toward the male embryos when cultured under either 5 or 20% oxygen levels. As it was been reported previously (Amin et al, ; Leite et al, ; Yoon et al, ), embryos cultured under higher oxygen tension (20%) revealed elevated intracellular ROS accumulation irrespective of the sex of the embryos (Figure ). However, male embryos exhibited higher ROS accumulation than female embryos at lower oxygen level, which may be attributed to higher metabolism rate of male embryo compared with female counterparts (Tiffin, Rieger, Betteridge, Yadav, & King, ).…”

“…The suboptimal culture conditions of the in vitro production system are partly responsible for the reduction in number and quality of blastocysts (Farin & Farin, ; Gad et al, ). In addition to the culture media, the higher oxygen level in in vitro system is responsible for contributing to the suboptimal environment (Amin et al, ; Kelley & Gardner, ; Leite et al, ). However, previous evidence indicated that there was no significant difference observed in terms of embryo development between maturation followed by fertilization at high oxygen tension and maturation at low oxygen followed by fertilization at high oxygen level, but a dramatic effect was observed in case of fertilization at low oxygen level (Bermejo‐Alvarez, Lonergan, Rizos, & Gutiérrez‐Adan, ).…”

“…OS is triggered by an imbalance between reactive oxygen species (ROS) and its scavenger of antioxidant molecules (Martindale & Holbrook, ), due to culture media, temperature, pH, and oxygen tension (Cagnone & Sirard, ; Wale & Gardner, ). For instance, the oxygen levels in oviduct and uterus of most mammalian species (1.5–8.7%) are less than half of atmospheric oxygen level (20%; Fischer & Bavister, ), which is widely used in In vitro fertilization (IVF) laboratories and consequently lead to elevation of ROS (Amin et al, ; Leite et al, ; Yoon et al, ). Excess accumulation of ROS damages cellular bioactive molecules such as DNA, protein, and lipid (Martindale & Holbrook, ), subsequently compromising the mitochondrial integrity and activity (Amin et al, ; Kadenbach, Arnold, Lee, & Hüttemann, ) as well as cell number (Amin et al, ; Kelley & Gardner, ; Leite et al, ), resulting in abnormal embryonic development or apoptosis (Amin et al, ; Kadenbach et al, ; Leite et al, ).…”

Effects of Pterostilbene on the Activation of Nuclear Factor Erythroid 2-Related Factor 2 Pathway During in vitro Maturation of Mouse Oocytes

“…The role of NFE2L2 has been investigated in a different cultural environment in bovine embryos that reached blastocyst stage (Gad et al, 2012). However, under suboptimal culture condition in early bovine embryos, NFE2L2-KEAP1 signaling pathway protects the embryo from oxidative stress (Amin et al, 2014). But also, the development of rabbit embryo was promoted by activation of NFE2L2 during induced oxidative stress condition (Mehaisen et al, 2015).…”