Human single follicle growth in vitro from cryopreserved ovarian tissue after slow freezing or vitrification

STUDY QUESTION: What is the effect of human ovarian tissue cryopreservation on single follicular development in vitro? SUMMARY ANSWER: Vitrification had a greater negative effect on growth and gene expression of human ovarian follicles when compared with fresh follicles. WHAT IS KNOWN ALREADY: For human ovarian cortex cryopreservation, the conventional option is slow freezing while more recently vitrification has been demonstrated to maintain good quality and function of ovarian tissues. STUDY DESIGN, SIZE, DURATION: Ovarian tissues were collected from 11 patients. For every patient, the ovarian cortex was divided into three samples: Fresh, slow-rate freezing (Slow) and vitrification (Vit). Tissue histology was performed and follicles were isolated for single-cell mRNA analysis and in vitro culture (IVC) in 1% alginate for 8 days. PARTICIPANTS/MATERIALS, SETTING, METHODS: Follicle morphology was assessed with hematoxylin-eosin analysis. Follicles were individually embedded in alginate (1% w/v) and cultured in vitro for 8 days. Follicle survival and growth were assessed by microscopy. Follicle viability was observed after Calcein-AM and ethidium homodimer-I (Ca-AM/EthD-I) staining. Expression of genes, including GDF9 (growth differentiation factor 9), BMP15 (bone morphogenetic protein 15) and ZP3 (zona pellucida glycoprotein 3) in oocytes and AMH (anti-Mullerian hormone), FSHR (FSH receptor), CYP11A (cholesterol side-chain cleavage cytochrome P450) and STAR (steroidogenic acute regulatory protein) in GCs, was evaluated by single-cell mRNA analysis. MAIN RESULTS AND THE ROLE OF CHANCE: A total of 129 follicles were separated from ovarian cortex (Fresh n = 44; Slow n = 40; Vit n = 45). The percentage of damaged oocytes and granulosa cells was significantly higher in both the Slow and Vit groups, as compared with Fresh control (P < 0.05). The growth of follicles in vitro was significantly delayed in the Vit group compared with the Fresh group (P < 0.05). Both slow freezing (P < 0.05) and vitrification (P < 0.05) down-regulated themRNAlevels of ZP3 and CYP11A compared with Fresh group, while there was no significant difference between the Slow and Vit groups (P > 0.05). Vitrification also down-regulates AMH mRNA levels compared with Fresh group (P < 0.05). LIMITATIONS, REASONS FOR CAUTION: Only short-term IVC studies (8 days) are reported. Further study should be performed to examine and improve follicular development in a long-term culture system after cryopreservation. WIDER IMPLICATIONS OF THE FINDINGS: This is the first comparison of gene expression and growth of single human ovarian follicles in vitro after either slow freezing or vitrification. With the decreased gene expression and growth during IVC, damage by cryopreservation still exists and needs to be minimized during the long-term IVC of follicles in the future for eventual clinical application.