Effects of long-term progesterone exposure on porcine uterine gene expression: progesterone alone does not induce secreted phosphoprotein 1 (osteopontin) in glandular epithelium

Abstract

Pigs experience significant conceptus loss near mid-gestation, correlating with increasing glandular epithelial (GE) development and secretory activity. Secreted phosphoprotein 1 (SPP1, osteopontin) increases in GE between days 30 and 40 of pregnancy and is expressed in the GE of day 90 pseudopregnant pigs, suggesting that progesterone (P 4 ) from corpora lutea is responsible for induction of SPP1 in GE. In this study, pigs were ovariectomized and treated daily with P 4 to assess effects of 40 days of P 4 exposure on SPP1, P 4 receptor (PGR), uteroferrin (ACP5), and fibroblast growth factor 7 (FGF7) expression in porcine endometria. PGR mRNA decreased in pigs injected with P 4 compared with pigs injected with corn oil (CO), and PGRs were downregulated in the luminal epithelium (LE) and GE. ACP5 mRNA increased in pigs injected with P 4 compared with pigs injected with CO, and ACP5 was induced in the GE of P 4 -treated pigs. FGF7 mRNA increased in pigs injected with P 4 compared with pigs injected with CO, and FGF7 was induced in the LE and GE of P 4 -treated pigs. SPP1 mRNA was not different between pigs injected with P 4 compared with pigs injected with CO, and SPP1 was not present in the GE of P 4 -treated pigs. Therefore, long-term P 4 , in the absence of ovarian and/or conceptus factors, does not induce SPP1 expression in GE. We hypothesize that a servomechanism involving sequential effects of multiple hormones and cytokines, similar to those for sheep and humans, is required for GE differentiation and function, including the synthesis and secretion of SPP1.

Implantation and Establishment of Pregnancy in the Pig

“…Based on current evidence, long-term treatment with progesterone is required in order to downregulate PGR in uterine epithelia as a prerequisite to epithelial cell proliferation, gene expression, and differentiated functions. Similar to all species studied, progesterone downregulates expression of PGR in the uterine epithelia of pigs after day 10 of pregnancy, immediately prior to the time when the endometrium becomes receptive to implantation (Geisert et al 1994 ;Bazer et al 2008 ;Bailey et al 2010 ). As previously indicated, uterine stromal cells express PGR throughout gestation, suggesting that effects of progesterone on PGR-negative uterine epithelia may be Fig.…”

Select Nutrients in the Uterine Lumen of Sheep and Pigs Affect Conceptus Development

“…From about Day 20 of pregnancy, FGF7 is expressed by uterine GE in response to P4 and is presumed to continue to affect uterine epithelia and conceptus development in pigs [63,64]. Indeed, P4 has profound effects on the expression of genes in pig uterine epithelia, particularly in the GE.…”

“…Notably, FGF7 has a similar pattern of GE expression to SPP1 during pig pregnancy, but diverges from SPP1 in its endocrine regulation in that it is induced in GE by long-term progesterone whereas SPP1 is not increased in GE by P4 alone. Collectively, these results suggest that the hormonal milieu necessary for the production of histotroph from GE varies for its individual components, and that genes that delay expression in GE until after the peri-implantation period may require specific servomechanisms of sequential exposure of the pregnant endometrium to ovarian, conceptus/placental and/ or uterine factors that may include progesterone, estrogens, IFNs and prolactin [64,65].Glucose present in the intrauterine environment of pigs and sheep can be metabolized, activate cell signaling pathways or be converted to a "storage" form. Total recoverable Gluc in uterine fluid of pregnant, but not cyclic pigs increases from Day 12 after onset of estrus in concert with conceptus elongation [63].…”

“…Although FGF7 is a unique SC-derived paracrine mediator of hormone-regulated epithelial growth and differentiation, the uterine luminal epithelium of the pig is unique in its expression of FGF7 in response to E2 with P4 being permissive to effects of E2 [62]. FGF7 binds to and activates FGFR2IIIb expressed by uterine epithelia and conceptus trophectoderm to increase cell proliferation, phosphorylated FGFR2IIIb, the MAPK cascade and expression of urokinase-typeplasminogen activator (PLAU), a marker for trophectoderm cell differentiation.From about Day 20 of pregnancy, FGF7 is expressed by uterine GE in response to P4 and is presumed to continue to affect uterine epithelia and conceptus development in pigs [63,64]. Indeed, P4 has profound effects on the expression of genes in pig uterine epithelia, particularly in the GE.…”

“…3) leads to synthesis of hyaluronic acid in increasing amounts over a 5 day period of culture of pTr2 cells. There is also evidence that Gluc is converted to glucosamine-6-PO4 and then to UDP-N acetyl-glucosamine that phosphorylated TSC2 to remove inhibition from MTOR cell signaling that results in affects growth and development of trophoblast [64]. …”