Differential expression of prostaglandin (PG) synthesis enzymes in conceptus during peri-implantation period and endometrial expression of carbonyl reductase/PG 9-ketoreductase in the pig

Abstract

Prostaglandins (PGs) play a pivotal role in luteolysis, maternal recognition of pregnancy, and implantation. In many species, including pigs, both conceptus (embryo and associated membranes) and endometrium synthesize PGE₂, which may antagonize PGF_2α by playing a luteotropic/antiluteolytic role. Previously, we have reported expression profiles of PG G/H synthases (PGHS-1 and PGHS-2), PGE synthase (mPGES-1), and PGF synthase (PGFS) in the endometrium of cyclic and pregnant pigs. In the present study, expression of above-mentioned PG synthesis enzymes and PG 9-ketoreductase (CBR1), which converts PGE₂ into PGF_2α, and the PGE₂/PGF_2α ratios were investigated in porcine peri- and post-implantation conceptuses. Furthermore, expression of CBR1 was examined in the endometrium. PGHS-2 and mPGES-1 were upregulated, and PGHS-1, PGFS, and CBR1 were downregulated in conceptuses during trophoblastic elongation. A second increase of mPGES-1 mRNA occurred after days 20–21 of pregnancy. After initiation of implantation, expression of PGHS-1, PGFS, and CBR1 in conceptuses increased and remained higher until days 24–25 of pregnancy. Comparison of the endometrial CBR1 protein expression in cyclic and pregnant gilts revealed upregulation on days 16–17 of the cycle and downregulation on days 10–11 of pregnancy. In conclusion, reciprocal expression of PGHS-2, mPGES-1, PGFS, and CBR1 in day 10–13 conceptuses and decrease of endometrial CBR1 may be important in increasing the PGE₂/PGF_2α ratio during maternal recognition of pregnancy. This study indicates that PGE₂ produced via PGHS-2 and mPGES-1 in conceptus may be involved in corpus luteum control. Moreover, high expression of conceptus PGHS-1, mPGES-1, PGFS, and CBR1 after initiation of implantation suggests their significant role in placentation.