O-173 Cellular and developmental damage from oocyte cryopreservation

Abstract

Abstract Compared to somatic or sperm cells, mammalian oocytes are much more sensitive to cryopreservation mainly because of the large volume, cytoskeleton, and presence of the zona pellucida. Connections with the surrounding cumulus cells also are challenging to preserve in immature oocytes. Besides the genetic and epigenetic information enclosed in the nucleus, oocytes contain organelles and cytoplasmic factors that are necessary for the early embryo development. Therefore, exposure to cryoprotectant and freezing temperatures can easily damage the oocyte’s complex cellular structure and developmental competence, which leads to poor success in fertilization, lower embryo quality, and reduced pregnancy rates. Using the domestic cat as a model, our laboratory has studied damages in cumulus-oocyte complexes (immature oocytes) occurring at each step of the cryopreservation process. Specifically, this included the impact of cryoprotectants on microtubules, the effect of osmotic changes on the overall structures, as well as sensitivity of the nuclear chromatin and epigenetic patterns to freezing temperatures. Based on those findings, it has been possible to design mitigating solutions like customized ultra-rapid freezing or vitrification protocols, Laser-warming methods, or post-warming reanimations. New horizons have also been explored to move away from issues and limitations related to cryopreservation. Approaches like storage of oocytes for the long-term at non-freezing temperatures are currently being developed based on encouraging data generated in preliminary studies. For instance, incorporation of trehalose into the oocyte followed by microwave-assisted dehydration can allow to remove enough water while creating a protective trehalose glass compatible with survival and storage at non-freezing temperatures. Interestingly, transcriptomic and proteomic studies have already shown that stresses and damages induced by dehydration versus cryopreservation are different and may be easier to overcome.