Cyclooxygenase‐2 is expressed by cumulus cells during oocyte maturation in cattle

Abstract

Prostaglandins could be involved in various aspects of final differentiation of ovarian follicles. Prostaglandins are generated by the cyclooxygenase (cox) pathway. Until now, the expression pattern of isoforms cox-1 and cox-2 of cyclooxygenase in bovine cumulus-oocyte complexes (COCs) was unknown. Using immunodetection procedure, we demonstrated in the present study that cox-2 was expressed by cumulus cells during in vivo and in vitro maturation. Time course induction of cox-2 expression was investigated during in vitro maturation using Western blot analysis. Specific signal of cox-2 was markedly evidenced from 6 hr of culture and increased to reach a maximal level at 24 hr of culture. In vitro, cox-2 expression in COCs was associated with increased concentrations of PGE(2) and PGF(2alpha) in the maturation medium. In addition, the effects of culture conditions on cox-2 expression was considered using RT-PCR and Western-blot analysis. We demonstrated that the addition of 10 ng/ml of EGF to TCM199 clearly increased the expression level of cox-2 mRNA and protein. Higher levels of in vitro cox-2 expression was associated with greater rates of cumulus expansion and oocytes at metaphase II at 24 hr of culture. In conclusion, our present results suggest that cox-2 expression in cumulus cells may be involved in differentiation of COCs that occurs during oocyte maturation.

Role of PTGS2-generated PGE2 during gonadotrophin-induced bovine oocyte maturation and cumulus cell expansion

“…24 h (Nuttinck et al, 2002). Notwithstanding the differences in the pattern of PTGS2 expression during the later stages of culture (after 6 h), the increase in PTGS2 expression at 6 h, which occurs just before the time for GVBD (Sirard et al, 1989), supports the idea that prostaglandin production may be important in regulating oocyte maturation and cumulus cell expansion.…”

“…Basal expression of PTGS2 increased significantly between 0-6 h, declined between 6-12 h and was unchanged from 12-24 h. The presence of PTGS2 mRNA and protein has previously been measured in cultured bovine COC during maturation, although their expression pattern was somewhat different to what is reported here. It was reported that PTGS2 increased at 6 h to reach maximum concentrations at 12 h after incubation in maturation media containing Gn (Calder et al, 2001;Nuttinck et al, 2002), then decreased at 18 and 24 h (Calder et al, 2001) or continued to increase until …”

“…In cattle, PTGS2 is found in granulosa cells of preovulatory follicles (Liu and Sirois, 1998;Sirois, 1994) and cumulus cells (Nuttinck et al, 2002). PTGS1 is not observed in isolated bovine cumulus-oocyte complexes (COC) before or after in-vivo and in-vitro maturation and, with the exception of some sparse theca cells, no PTGS1-specific immunostaining is detectable in any compartment of 3-6 mm ovarian antral follicles (Nuttinck et al, 2002).…”

“…PTGS1 is not observed in isolated bovine cumulus-oocyte complexes (COC) before or after in-vivo and in-vitro maturation and, with the exception of some sparse theca cells, no PTGS1-specific immunostaining is detectable in any compartment of 3-6 mm ovarian antral follicles (Nuttinck et al, 2002). With respect to the PGE 2 receptors, PTGER2 and PTGER3 mRNA are detectable in COC while PTGER4 mRNA concentrations are very low and PTGER1 is not detected (Calder et al, 2001).…”

Evidence that the effect of angiotensin II on bovine oocyte nuclear maturation is mediated by prostaglandins E2 and F2α

“…Recently, our group demonstrated that AngII stimulates the expression of PTGS2 mRNA in cultured bovine granulosa cells, which was potentiated by LH (Portela et al 2008). The involvement of the PTGS2 pathway in oocyte nuclear maturation has been previously demonstrated in sheep (Murdoch 1988(Murdoch , 1996, cattle (Nuttinck et al 2002, Calder et al 2005, mice (Takahashi et al 2006), humans (Ben-Ami et al 2006), and horses (Dell'Aquila et al 2004). In sheep, the systemic administration of indomethacin (nonselective PTGS inhibitor) resulted in suppression of the cumulus cell expansion and oocyte nuclear maturation, which were reversed by PGE 2 intrafollicular injection (Murdoch 1988(Murdoch , 1996.…”