Application of Omni-ATAC to Profile Chromatin Accessibility Before and After Ovarian Tissue Cryopreservation

Ovarian tissue cryopreservation and subsequent autologous transplantation has allowed resumption of endocrine function as well as fertility in certain populations. However, graft function is short-lived due to ischemia and aberrant follicular activation post-transplantation. While many studies have focused on gene expression, we wanted to determine whether cryopreservation itself had a deleterious effect on regulatory elements that might influence transcriptional integrity and graft performance. In this study, we used Omni-ATAC to assess genome-wide chromatin accessibility in primary human follicles before and after cryopreservation. Omni-ATAC from fresh ovarian follicles identified active regulatory elements expected to be functional in oocytes and granulosa cells, and gene ontology was consistent with RNA translation/processing and DNA repair. While promoter accessibility was largely maintained in cryopreserved ovarian follicles, we observed a widespread increase in the number of accessible enhancers. Transcription factor motif analysis and gene ontology suggested that this dysregulation was focused around the epithelial-mesenchymal transition. Indeed, transcription factor binding was noted in major pathways involved in this transition: TGF-{beta} and Wnt signaling. Overall, our work provides the first genomic analysis of active regulatory elements in matched fresh and cryopreserved ovarian follicles as they undergo the process of ovarian tissue cryopreservation. Our data suggest that the process of cryopreservation activates an epithelial-mesenchymal transition state, which may lead to graft burn-out post-transplantation. Optimizing this technique in relation to this transition may therefore be an important step towards improving graft longevity and patient outcomes in fertility preservation. Summary sentenceCryopreservation of ovarian cortical tissue results in activation of differentiation and EMT pathways in follicles, which may explain graft burnout after autotransplantation.