Expression of Sex Steroid Receptors in Ovine Placental Tissues During Early Pregnancy: Effects of Assisted Reproductive Technologies (ART).

Abstract

Placental development can be compromised by genetic, epigenetic, environmental, or other factors, leading to poor fetal growth as well as poor pregnancy and postnatal outcomes. Pregnancies established with ART generate especially poor pregnancies (for example, only approximately 40 to 50% of IVF and less than 10% of cloned embryos survive to birth) that are associated with altered vascularization of the placenta. We have shown recently that these placental vascular defects in pregnancies from ART occur within the first few weeks of pregnancy in sheep, at approximately the same time at which substantial embryonic loss begins. Sex steroids and their receptors are important regulators of angiogenesis and growth in reproductive tissues, including the placenta. However, little is known about the expression of sex steroid receptors in placental tissues during early pregnancy or how ART affects their expression. We hypothesized that ART would affect the expression of estrogen receptor alpha and beta, nuclear progesterone receptor, and membrane progesterone receptors alpha, beta, and gamma in utero-placental tissues during early pregnancy in sheep. Pregnancies (n = 7 per group) were achieved through natural breeding (NAT, control), or transfer of embryos generated through natural breeding (NAT-ET), in vitro fertilization (IVF), or in vitro activation (IVA; parthenogenetic clones). On day 22 of pregnancy, samples of caruncle (CAR; maternal utero-placenta) and fetal membranes (FM; fetal placenta [chorioallantois]) were snap-frozen separately for RNA extraction followed by quantitative real-time RT-PCR. In CAR, mRNA expression of estrogen receptor alpha and nuclear progesterone receptor was decreased (P < 0.001) by 64 to 86% in NAT-ET, IVF, and IVA groups compared with NAT. In contrast, in FM mRNA expression of estrogen receptor alpha tended (P = 0.1) to be 2.5- to 6.4-fold greater in the IVA group compared with NAT and NAT-ET, which were similar; expression of estrogen receptor alpha was intermediate in the IVF group. Expression of mRNA for nuclear progesterone receptor in FM, and for estrogen receptor beta and membrane progesterone receptors alpha, beta, and gamma in CAR and FM, did not differ among the pregnancy-type groups. Because sex steroids are critical regulators of utero-placental vascularization, growth, and function, these data suggest that altered expression of placental sex steroid receptors may be an early event leading to poor placental vascularization and growth after ART. These data also provide a basis for understanding the mechanisms by which sex steroids regulate placental growth and vascular development in normal and compromised pregnancies. Supported by USDA 2007-01215 to LPR and ATGB, and NIH HL64141 to LPR and DAR.