Regulation of Expression of Fibroblast Growth Factor 7 in the Pig Uterus by Progesterone and Estradiol1

Stanniocalcin 1 is a luminal epithelial marker for implantation in pigs regulated by progesterone and estradiol

Stanniocalcin 1 (STC1) is a glycoprotein that decreases calcium and increases phosphate in cells/tissues. This investigation examined endocrine regulation of STC1 in endometria of pigs during the estrous cycle and pregnancy. STC1 mRNA was present exclusively in luminal epithelium (LE) between d 12 and 15 of the estrous cycle, increased between d 12 and d 20, and was not detectable by d 30 of pregnancy. STC1 protein was also detected in uterine flushings. To determine effects of estrogen and progesterone, pigs were ovariectomized and treated with these hormones alone or together. Progesterone, but not estrogen, induced STC1 in LE. Cotreatment with progesterone and estrogen further stimulated STC1 over progesterone alone. To determine effects of pseudopregnancy, nonpregnant gilts were given daily injections of estradiol benzoate from d 11 to d 14. STC1 was not expressed in LE on d 90 of pseudopregnancy, suggesting that the estradiol given to induce pseudopregnancy and/or long-term exposure to progesterone are required for down-regulation of STC1. To determine effects of long-term progesterone, without effects of estradiol, pigs were ovariectomized on d 12, given daily injections of progesterone through d 39, and hysterectomized on d 40 after estrus. STC1 was expressed in LE of progesterone-treated pigs, suggesting that estrogen is involved in down-regulation of STC1. We conclude that STC1 is induced in LE by progesterone and further stimulated by estrogen, and its down-regulation in LE by d 25 likely requires exposure of the progestinized uterus to estrogen. The temporal and cell type-specific expression of STC1 makes this gene a unique marker for implantation in pigs.

Analysis of lysophosphatidic acid (LPA) receptor and LPA-induced endometrial prostaglandin-endoperoxide synthase 2 expression in the porcine uterus

Lysophosphatidic acid (LPA), a simple phospholipid-derived mediator with diverse biological actions, acts through the specific G protein-coupled receptors endothelial differentiation gene (EDG) 2, EDG4, EDG7, and GPR23. Recent studies indicate a critical role for LPA receptor signaling in embryo implantation. To understand how LPA acts in the uterus during pregnancy in pigs, we evaluated: 1) spatial and temporal expression of LPA receptors in the uterine endometrium during the estrous cycle and pregnancy and in early-stage concepti, 2) LPA levels in uterine luminal fluids from d 12 of the estrous cycle and pregnancy, 3) effects of steroid hormones on EDG7 mRNA levels, and 4) effects of LPA on prostaglandin-endoperoxide synthase 2 (PTGS2) mRNA levels in the uterine endometrium using explant cultures. Of the four receptors, EDG7 was dominant, and its expression was regulated by pregnancy stage and status. EDG7 expression was highest on d 12 pregnancy, and localized to the luminal and glandular epithelium, and EDG7 mRNA levels were elevated by estrogen in the endometrium. EDG7 expression was also detected in concepti of d 12 and 15. LPA with various fatty acyl groups was present in the uterine lumen on d 12 of both the estrous cycle and pregnancy. LPA increased PTGS2 mRNA abundance in the uterine endometrium. These results indicate that LPA produced in the uterine endometrium may play a critical role in uterine endometrial function and conceptus development through EDG7-mediated PTGS2 expression during implantation and establishment of pregnancy in pigs.

Pig conceptuses secrete estrogen and interferons to differentially regulate uterine STAT1 in a temporal and cell type-specific manner

Conceptus trophectoderm and uterine luminal epithelial cells interact via endocrine, paracrine, and autocrine modulators to mediate pregnancy recognition and implantation. Pig conceptuses not only release estrogens for pregnancy recognition but also secrete interferons during implantation. Because interferon-stimulated genes are increased by interferons secreted for pregnancy recognition in ruminants, we asked whether the interferon-stimulated gene, STAT1, is up-regulated in pig endometrium by conceptus estrogens and/or interferons. STAT1 expression in response to day of pregnancy, estrogen injection, and intrauterine infusion of conceptus secretory proteins in pigs indicated 1) estrogen increases STAT1 in luminal epithelial cells, 2) conceptus secretory proteins that contain interferons increase STAT1 in stroma, 3) STAT1 increases in close proximity to the conceptus, and 4) early estrogen results in conceptus death and no STAT1 in stroma. The interactions of estrogen and interferons to regulate cell-type-specific expression of STAT1 highlight the complex interplay between endometrium and conceptus for pregnancy recognition and implantation.