Novel concepts on the role of prostaglandins on luteal maintenance and maternal recognition and establishment of pregnancy in ruminants.

In ruminants, the corpus luteum (CL) of early pregnancy is resistant to luteolysis. Prostaglandin (PG)E2 is considered a luteoprotective mediator. Early studies indicate that during maternal recognition of pregnancy (MRP) in ruminants, a factor(s) from the conceptus or gravid uterus reaches the ovary locally through the utero-ovarian plexus (UOP) and protects the CL from luteolysis. The local nature of the embryonic antiluteolytic or luteoprotective effect precludes any direct effect of a protein transported or acting between the gravid uterus and CL in ruminants. During MRP, interferon tau (IFNT) secreted by the trophoblast of the conceptus inhibits endometrial pulsatile release of PGF2α and increases endometrial PGE2. Our recent studies indicate that (1) luteal PG biosynthesis is selectively directed toward PGF2α at the time of luteolysis and toward PGE2 at the time of establishment of pregnancy (ESP); (2) the ability of the CL of early pregnancy to resist luteolysis is likely due to increased intraluteal biosynthesis and signaling of PGE2; and (3) endometrial PGE2 is transported from the uterus to the CL through the UOP vascular route during ESP in sheep. Intrauterine co-administration of IFNT and prostaglandin E2 synthase 1 (PGES-1) inhibitor reestablishes endometrial PGF2α pulses and regresses the CL. In contrast, intrauterine co-administration of IFNT and PGES-1 inhibitor along with intraovarian administration of PGE2 rescues the CL. Together, the accumulating information provides compelling evidence that PGE2 produced by the CL in response to endometrial PGE2 induced by pregnancy may counteract the luteolytic effect of PGF2α as an additional luteoprotective mechanism during MRP or ESP in ruminants. Targeting PGE2 biosynthesis and signaling selectively in the endometrium or CL may provide luteoprotective therapy to improve reproductive efficiency in ruminants.

Arosh JA ，Banu SK ，McCracken JA 《-》

Intraluteal prostaglandin biosynthesis and signaling are selectively directed towards PGF2alpha during luteolysis but towards PGE2 during the establishment of pregnancy in sheep.

Lee J ，McCracken JA ，Stanley JA ，Nithy TK ，Banu SK ，Arosh JA ... -  《-》

Implantation and Establishment of Pregnancy in Ruminants.

Spencer TE ，Hansen TR 《Advances in Anatomy Embryology and Cell Biology》

Intrauterine coadministration of ERK1/2 inhibitor U0126 inhibits interferon TAU action in the endometrium and restores luteolytic PGF2alpha pulses in sheep.

In ruminants, prostaglandin F2 alpha (PGF2alpha) is synthesized and released in a pulsatile pattern from the endometrial luminal epithelial (LE) cells during the process of luteolysis. Interferon tau (IFNT) is a Type 1 IFN secreted by the trophoblast cells of the developing conceptus. IFNT acts locally on endometrial LE cells to inhibit pulsatile releases of PGF2alpha and thus establish an endocrine environment for recognition of pregnancy. Cell signaling pathways through which IFNT stimulates expression of multiple genes or proteins in endometrial LE are largely unknown. Results of the present investigation indicate that intrauterine administration of IFNT inhibits pulsatile release of PGF2alpha, while coadministration IFNT and ERK 1/2 inhibitor U0126 restores luteolytic PGF2alpha pulses in sheep. IFNT increases phosphorylation of ERK1/2 proteins and increases its interaction with PGT proteins in endometrial LE. Blockade of ERK1/2 pathways inhibits IFNT action, decreases pERK1/2 and PGT protein interactions, and re-establishes the spatial expression of the oxytocin receptor protein completely and the estrogen receptor protein partially without modulating the expression of interferon regulatory factor-2 (IRF-2) protein in endometrial LE. IFNT does not decrease expression of COX-2, PGDH, or PGT protein in endometrial LE. Our results provide important new insights into IFNT signaling and the molecular endocrine control of PGF2alpha release at the time of establishment of pregnancy in ruminants. This novel IFNT-ERK1/2 signaling module needs to be explored in future studies to understand molecular and cellular mechanisms of IFNT action in endometrial LE in ruminants.

Lee J ，Stanley JA ，McCracken JA ，Banu SK ，Arosh JA ... -  《-》

The role of progesterone and conceptus-derived factors in uterine biology during early pregnancy in ruminants.

This review integrates established and new information on the role of progesterone, interferon tau (IFNT), and prostaglandins in uterine biology of ruminants. Establishment of pregnancy in ruminants encompasses growth of the posthatching blastocyst, elongation of the conceptus (embryo and extraembryonic membranes), and suppression of the endometrial luteolytic mechanism to maintain progesterone production by the ovary. Conceptus elongation involves exponential increases in length of the trophectoderm for pregnancy recognition signaling, implantation, and establishment of pregnancy. Pregnancy recognition signaling is accomplished by IFNT from the trophectoderm that has a paracrine antiluteolytic effect to inhibit upregulation of oxytocin receptors in the endometrial epithelia, thereby inhibiting production of luteolytic PGF2α pulses by the uterus. Survival and growth of the preimplantation blastocyst and elongating conceptus clearly requires embryotrophic factors (AA, carbohydrates, proteins, lipids, and other substances) in the uterine lumen. Individual, interactive, and coordinated actions of progesterone, IFNT, and prostaglandins regulate expression of elongation- and implantation-related genes in the endometrial epithelia that, in turn alter the uterine luminal histotroph and govern conceptus survival and growth. An increased knowledge of progesterone biology and conceptus-endometrial interactions is necessary to understand and elucidate the causes of pregnancy loss and provide a basis for new strategies to improve pregnancy outcome and reproductive efficiency in ruminants.

Spencer TE ，Forde N ，Lonergan P 《-》