Oocyte mitochondrial bioenergy potential and oxidative stress: within-/between-subject, in vivo vs IVM and age-related variations in a sheep model.

Abstract: Mitochondrial activity in oocytes from hormonally-stimulated donor sheep shows within- and between-subject, maturation procedure- and age-related variations. ROS levels increases in aged oocytes. High mitochondria/ROS colocalization identifies in-vivo matured oocytes. Objective: To analyze within-/between-subject, in vivo vs IVM and age-related variations of mitochondrial (mt) bioenergy potential and oxidative status of metaphase II (MII) oocytes recovered from hormonally stimulated sheep. Design: Prospective study. Settings: Academic basic research laboratory. Subject(s): ten adult ewes. Intervention(s): Estrous synchronization, controlled ovarian hyperstimulation (COH), ovariohysterectomy. Follicular and oviductal oocyte retrieval. IVM of follicular oocytes. Main Outcome Measure(s): Mean±SD, within-subject (CVw) and between-subject (CVb) variation coefficients of mt activity, intracellular reactive oxygen species (ROS) levels and mt/ROS colocalization in sheep oocytes from young and aged donors and matured in vivo (in vivo-MIIs) or in vitro (IVM-MIIs). Results: Within- and between-subject, in vivo vs IVM and age-related variations of mt activity were observed in MII oocytes from hormonally stimulated donor sheep. ROS levels increased significantly in oocytes from aged donors. Mt/ROS colocalization was consistently higher in in vivo-MIIs compared with IVM-MIIs. Conclusions: Oocyte energy/oxidative status is affected by within-/between-subject, in vivo vs IVM and age-related variations. Mt/ROS colocalization is a reliable marker of in vivo-MII oocytes.