Elevated p66Shc is associated with intracellular redox imbalance in developmentally compromised bovine embryos

The in vitro production of mammalian embryos suffers from low efficiency, with 50-70% of all fertilized oocytes failing to develop to the blastocyst stage. This high rate of developmental failure is due, in part, to the effects of oxidative stress generated by reactive oxygen species (ROS). The p66Shc adaptor protein controls oxidative stress response by regulating intracellular ROS levels through multiple pathways, including mitochondrial ROS generation and the repression of antioxidants. This study explored the relationship between p66Shc levels, redox state, and developmental potential in early bovine embryos. Embryo developmental potential was established based on observing their time of first cleavage. P66Shc, catalase, and mitochondrial-specific, manganese-superoxide dismutate (MnSOD) levels were compared between embryos with high and low developmental potentials. Additionally, p66Shc, catalase, and MnSOD content were assayed following a variety of oxidative stress-inducing and-alleviating conditions. Increased developmental potential correlated with significantly lower p66Shc content, significantly higher levels of catalase and MnSOD, and significantly lower intracellular ROS levels (MitoSOX staining) and reduced DNA damage (γ-H2A.X(phospho S139) immunostaining). p66Shc content was increased by either high (20%) O(2) culture or H(2)O(2) treatment, and significantly decreased by supplementing culture media with the antioxidant polyethylene glycol-conjugated catalase. While the abundance of p66Shc varied according to pro/anti-oxidant culture conditions, antioxidant content varied only according to developmental potential. This discrepancy has important implications regarding ongoing efforts towards maximizing in vitro embryo production.