185 PGI2 ANALOG INDUCES HIGH-QUALITY PORCINE BLASTOCYSTS IN VITRO

Abstract

Prostaglandin I2 (PGI2) exists in oviductal fluid and is synthesized from arachidonic acid by prostacyclin synthetase. In hatched embryos, prostaglandin I2 (PGI2) is related to implantation improvement, but its role during oocyte maturation and early embryo development remains controversial. Therefore, in this study, the effect of addition of a PGI2 analog during early porcine oocyte maturation on nuclear maturation, blastocyst formation, and pre-implantation embryonic quality was investigated. Porcine oocytes were matured in NCSU-23 medium supplemented with 10% (v/v) porcine follicular fluid, 10 ng mL-1 epidermal growth factor, 25 �M �-mercaptoethanol, 0.57 mM cysteine, 10 IU mL-1 pregnant mare serum gonadotropin, 10 IU mL-1 hCG, and 1 �M PGI2 analog for 22 h, and then further cultured in maturation medium without PGI2 analog and hormones for 22 h. After fertilization in Tris-buffered (mTBM) medium for 6 h, presumptive porcine zygotes were cultured in the NCSU-23 medium supplemented with 4% BSA for 6 days. All data were analyzed by using the Duncan test of ANOVA by the Statistical Analysis System (SAS Institute, Inc., Cary, NC, USA). First, we confirmed that PGI2 analog-treated (90.0 � 2.6%) oocytes showed a higher proportion of the metaphase II stage than non-treated (65.7 � 1.4%) ones (P < 0.05). Thus, to confirm the activities of maturation promoting factor (MPF) and mitogen-activated protein kinase (MAPK), Western blots were performed in matured oocytes by using specific antibodies such as anti-cdc2 and anti-ERK1/2. The activities of MPF and MAPK were increased in porcine oocytes treated with PGI2 analog. In the PGI2 analog-treated group, polyspermic rate (17.9 � 13.3%) was reduced as compared with that of the non-treated group (35.8 � 9.4%). Furthermore, the rate (25.3%, 40/158) of blastocyst formation in the PGI2 analog-treated group was higher than in the non-treated group (19.7%, 27/137; P < 0.05). Also, cell numbers of blastocysts were increased (29 � 2.5% vs. 39.6 � 1.4%) in the treated vs. the non-treated group. The numbers of fragmented DNA nuclei detected in the blastocyst stage by the TUNEL assay were decreased in the PGI2-treated group compared with the non-treated group (2.1% vs. 5.2%). In conclusion, direct roles of PGI2 during porcine oocyte maturation may involve reducing apoptosis and enhancing blastocyst quality.