Pro-cumulin addition in a biphasic in vitro oocyte maturation system modulates human oocyte and cumulus cell transcriptomes.

Abstract

Biphasic in vitro oocyte maturation (IVM) can be offered as a patient-friendly alternative to conventional ovarian stimulation in in vitro fertilization (IVF) patients predicted to be hyper-responsive to ovarian stimulation. However, cumulative live birth rates after IVM per cycle are lower than after conventional ovarian stimulation for IVF. In different animal species, supplementation of IVM media with oocyte-secreted factors (OSFs) improves oocyte developmental competence through the expression of pro-ovulatory genes in cumulus cells. Whether the addition of OSFs in human biphasic IVM culture impacts the transcriptome of oocytes and cumulus cells retrieved from small antral follicles in minimally stimulated non-hCG-triggered IVM cycles remains to be elucidated. To answer this, human cumulus oocyte complexes (COCs) that were fully surrounded by cumulus cells or partially denuded at the time of retrieval were cultured in a biphasic IVM system either without or with the addition of pro-cumulin, a GDF9: BMP15 heterodimer. Oocytes and their accompanying cumulus cells were collected separately, and single-cell RNA-seq libraries were generated. The transcriptomic profile of cumulus cells revealed that pro-cumulin upregulated the expression of genes involved in cumulus cell expansion and proliferation while downregulating steroidogenesis, luteinization and apoptosis pathways. Moreover, pro-cumulin modulated the immature oocyte transcriptome during the prematuration step, including regulating translation, apoptosis and mitochondria remodeling pathways in the growing germinal vesicle (GV) oocytes. The addition of pro-cumulin also restored the transcriptomic profile of matured metaphase II (MII) oocytes that were partially denuded at collection. These results suggest that cumulus cell and oocyte transcriptome regulation by pro-cumulin may increase the number of developmentally competent oocytes after biphasic IVM treatment. Future studies should assess the effects of pro-cumulin addition in human biphasic IVM at the proteomic level and the embryological outcomes, particularly its potential to enhance outcomes of oocytes that are partially denuded at COC collection.