Expression profiling and function analysis identified new microRNAs regulating cumulus expansion and apoptosis in cumulus cells

Abstract

Although microRNAs (miRNAs) expressed in cumulus cells (CCs) may be used to select competent oocytes/embryos, only a limited number of such miRNAs has been reported. To identify more miRNAs that regulate cumulus expansion (CE) and CC apoptosis, we first established that mouse cumulus-oocyte complexes (COCs) cultured in expansion-supporting medium supported full CE while undergoing mild apoptosis, whereas mouse oocytectomized COCs (OOXs) cultured in apoptosis-triggering medium underwent severe apoptosis while supporting no CE. RNA- and miRNA-sequencing and bioinformatics using CCs from these cultured COCs/OOXs identified candidate apoptosis- and/or CE-regulating miRNAs. Transfection of COCs/OOXs with miRNA mimic or inhibitor validated that miR-212-5p and 149-5p promoted CE by facilitating Has2 expression; miR-31-5p and 27a-3p promoted CE by increasing both Has2 and Ptx3 expression; and miR-351-5p and 503-5p inhibited CE by suppressing Ptx3 expression. Furthermore, miR-212-5p, 149-5p and Nov798 inhibited CC apoptosis, involving both Bcl2/Bax and Fas signaling. Analysis using in vivo matured COCs further verified the above apoptosis- and/or CE-regulating miRNAs, except for miR-149-5p. In conclusion, this study identified and validated new CE- and apoptosis-regulating miRNAs in CCs, which could be used as biomarkers to select competent oocytes/embryos and for elucidating how the oocyte-derived factors regulate CE and CC apoptosis.