Identification of differentially expressed mRNAs and miRNAs and related regulatory networks in cumulus oophorus complexes associated with fertilization

Background and aims: Failure of in vitro fertilization (IVF) is still a major challenge in our clinics. COCs are the first extracellular barriers that sperm must pass through to fuse with oocytes, which have an important role in oocyte maturation and fertilization. However, little is known about the molecular mechanisms of COCs involved in fertilization. Therefore, the present study aimed to identify the key miRNAs and mRNAs in COCs that contribute to fertilization, which may provide novel insights into potential biomarkers for fertilization failure.Methods: COCs were collected during oocytes retrieval and then randomly divided into a test and a control group. In the test group, COCs were cultured with sperm, while in the control group, COCs were cultured alone. After culture, the total RNA was extracted, RNA transcriptome and small RNA libraries were prepared and sequenced. Then, differentially expressed genes (DEGs) and miRNAs (DEMIs) were compared and further downstream bioinformatics analysis were performed.Results: 1283 DEGs, including 560 up-regulated and 723 down-regulated genes, and 57 DEMIs with 35 up-regulated and 22 down-regulated, were detected. After the RNA-seq results were verified by RT-qPCR, 86 effective DEGs and 40 DEMIs were finally screened and a DEMI-DEG regulatory network were constructed. From the regulation network, the top ten hub target genes were HNF4A, SPN, WSCD1, TMEM239, SLC2A4, E2F2, SIAH3, ADORA3, PIK3R2 and GDNF, all of which were down-regulated. The top ten hub DEMIs were miR-6876-5p, miR-877-3p, miR-6818-5p, miR-4690-3p, miR-6789-3p, miR-6837-5p, miR-6861-5p, miR-4421, miR-6501-5p and miR-6875-3p, all of which were up-regulated. The KEGG signaling pathway enrichment analysis showed that the effective DEGs were significantly enriched in the calcium, AMPK and phospholipase D signaling pathways. In the PPI network, there were 60 nodes, including 15 up-regulated DEGs and 45 down-regulated DEGs. The top ten hub nodes of the PPI network were NTRK3, SLC2A4, GDNF, SLC6A7, WNT2, ADCY1, HNF4A, SIX2, PLEK and KCNJ10, all of which were down-regulated except for PLEK which was up-regulated.Conclusions: Our study identified several DEGs and DEMIs and potential miRNA-mRNA regulatory pathways in COCs that may contributing to fertilization.