P-651 Oocyte secreted factors supress the expression of prostaglandin synthase-2 (PTGS2), a key maturation promoter in cumulus cells: the oocyte is not in a hurry

Abstract Study question Does the oocyte control the expression of genes regulating the ovulatory cascade and the formation of the extracellular matrix in cumulus cells? Summary answer Oocyte secreted factors (OSFs) suppress the expression of prostaglandin synthase-2 (PTGS2) in cumulus cells, a key mediator of the maturation cascade. What is known already Oocyte quality depends on cytoplasmic and nuclear maturation synchrony. OSFs modulate maturation dynamics by inhibiting the expression of AREG (amphiregulin) and EREG (epiregulin), key mediators of the ovulatory cascade. AREG and EREG stimulate PTGS2 expression in cumulus cells, which catalyses the synthesis of prostaglandins, that amplify and translate AREG/EREG signals leading to meiotic completion and expression of genes required for cumulus expansion, among which HAS2 (hyaluronan synthase-2), essential for the synthesis of hyaluronan, the backbone of cumulus extracellular matrix, as well as PTX3 (pentraxin 3) and TNFAIP6 (tumor necrosis factor alpha-induced protein 6), genes encoding for matrix structural proteins. Study design, size, duration Relative mRNA levels of PTGS2, HAS2, PTX3 and TNFAIP6 were compared in cumulus cells from 3 treatment-groups: 1-COC: Intact cumulus-oocyte complexes subjected to in vitro maturation (IVM); 2-OOX: oocytectomized COC subjected to IVM; 3-OOX+DO: OOX subjected to IVM with the addition of denuded oocytes (1 DO/µL). Four experimental replicates including all three treatment-groups were performed. The inclusion of OOX+DO aimed to assess whether the effects of the oocyte on gene expression are mediated by OSFs. Participants/materials, setting, methods COC were aspirated from 3-8mm follicles of bovine ovaries. Oocytectomy was achieved by ooplasm aspiration with a micromanipulator. Pools of 20 COCs/OOX/OOX+DO were cultured for 22 hours in TCM199 with 100ng/mL AREG and 0.4% BSA. Subsequently, cumulus cells were separated, total RNA extracted, and mRNA abundance assessed by real-time RT-PCR with oligo-dT primers and two internal controls for relative quantification. Treatment effects were tested by ANOVA and groups were compared with the Tukey test. Main results and the role of chance Oocyctectomy drastically increased PTGS2 mRNA abundance, which was reversed by the addition of denuded oocytes (DO) to culture. Relative PTGS2 mRNA levels (mean ± EPM) were 1.02 ± 0.12, 10.40 ± 1.65 and 0.88 ± 0.08 for COC, OOX and OOX+DO, respectively (P = 0.02). Consistently, although in a lo