Changes in the interactions between mural granulosa cells and cumulus cells during ovulation after the LH surge based on transcriptome analyses.

BACKGROUND: The luteinizing hormone (LH) surge during ovulation induces dynamic changes in cellular functions of mural granulosa cells (MGCs) and cumulus cells (CCs). However, the mechanisms by which the two cell types interact with each other and regulate their cellular functions remain unclear. In this study, we investigated transcriptomic changes in both cell types in order to reveal the cell-cell interactions between MGCs and CCs during the ovulatory process. METHODS: MGCs and CCs were collected from mice treated with equine chorionic gonadotropin (eCG), at 0 h (before), and 4 and 12 h after human chorionic gonadotropin (hCG) injection. Transcriptomes of both cell types were obtained by RNA sequencing. The changes in cellular functions and cell-cell interactions were investigated by gene ontology (GO) analysis and interactome analysis, respectively. To validate the predicted interactions, MGCs and COCs collected 48 h after eCG injection were cocultured for 12 h, after which gene expression and COC expansion were assessed. RESULTS: From 0 to 4 h after hCG injection, many cellular functions, including steroidogenesis, angiogenesis, follicle rupture, inflammatory response and cumulus-oocyte complex (COC) expansion were activated by cell-cell interactions, most of which were bidirectional interactions between MGCs and CCs. From 4 h to 12 h, cell-cell interactions regulating angiogenesis, follicle rupture, and inflammatory response remained activated, while those regulating steroidogenesis and COC expansion were attenuated. The coculture model revealed that COC expansion was induced in the presence of MGCs. Furthermore, the expressions of genes related to steroidogenesis, angiogenesis, and COC expansion in CCs increased in the presence of MGCs while their expressions in MGCs increased in the presence of CCs. CONCLUSIONS: Interactions between MGCs and CCs regulate the dynamic and time-dependent changes in their cellular functions during the ovulatory process, highlighting their essential regulatory roles.