The preservation of vital functions in cat ovarian tissues during vitrification depends more on the temperature of the cryoprotectant exposure than on the sucrose supplementation

The objective of this study was to better characterize the impact of cryoprotectant exposure (temperature and sucrose supplementation) on the health and function of preantral follicles in ovarian tissues during vitrification using the domestic cat model. Ovarian cortical pieces from peri-pubertal individuals were exposed to cryoprotectants at 4 °C or room temperature and supplemented with 0 or 0.5 M of sucrose, followed by vitrification. After rapid warming, cortical pieces were cultured in vitro and assessed for normal follicular morphology, viability and resumption of transcriptional activities for up to 7 days. Throughout the culture period, follicular morphology (up to 67.5% normal follicles) and global RNA transcription (up to 50.9% follicles with transcriptional activity) in warmed tissues were improved by cryoprotectant exposure at 4 °C compared to room temperature, but viability (up to 84.6% viable follicles) did not seem to be affected by exposure temperature. Sucrose supplementation did not have a consistent effect as it increased RNA transcription but decreased normal follicular morphology. For the first time, the study demonstrated that the preservation of critical tissue functions, such as the transcriptional activities, highly depends on the temperature of the cryoprotectant exposure and not necessarily on the presence of sucrose.