Pattern and tissue distribution of catechol estrogen forming activity by pig conceptuses during the peri-implantation period

New perspective on conceptus estrogens in maternal recognition and pregnancy establishment in the pig†

The proposed signal for maternal recognition of pregnancy in pigs is estrogen (E2), produced by the elongating conceptuses between days 11 to 12 of pregnancy with a more sustained increase during conceptus attachment and placental development on days 15 to 30. To understand the role of E2 in porcine conceptus elongation and pregnancy establishment, a loss-of-function study was conducted by editing aromatase (CYP19A1) using CRISPR/Cas9 technology. Wild-type (CYP19A1+/+) and (CYP19A1-/-) fibroblast cells were used to create embryos through somatic cell nuclear transfer, which were transferred into recipient gilts. Elongated and attaching conceptuses were recovered from gilts containing CYP19A1+/+ or CYP19A1-/- embryos on day 14 and 17 of pregnancy. Total E2 in the uterine flushings of gilts with CYP19A1-/- embryos was lower than recipients containing CYP19A1+/+ embryos with no difference in testosterone, PGF2α, or PGE2 on either day 14 or 17. Despite the loss of conceptus E2 production, CYP19A1-/- conceptuses were capable of maintaining the corpora lutea. However, gilts gestating CYP19A1-/- embryos aborted between days 27 and 31 of gestation. Attempts to rescue the pregnancy of CYP19A1-/- gestating gilts with exogenous E2 failed to maintain pregnancy. However, CYP19A1-/- embryos could be rescued when co-transferred with embryos derived by in vitro fertilization. Endometrial transcriptome analysis revealed that ablation of conceptus E2 resulted in disruption of a number biological pathways. Results demonstrate that intrinsic E2 conceptus production is not essential for pre-implantation development, conceptus elongation, and early CL maintenance, but is essential for maintenance of pregnancy beyond 30 days .

Endometrial response to conceptus-derived estrogen and interleukin-1β at the time of implantation in pigs

The establishment of pregnancy is a complex process that requires a well-coordinated interaction between the implanting conceptus and the maternal uterus. In pigs, the conceptus undergoes dramatic morphological and functional changes at the time of implantation and introduces various factors, including estrogens and cytokines, interleukin-1β2 (IL1B2), interferon-γ (IFNG), and IFN-δ (IFND), into the uterine lumen. In response to ovarian steroid hormones and conceptus-derived factors, the uterine endometrium becomes receptive to the implanting conceptus by changing its expression of cell adhesion molecules, secretory activity, and immune response. Conceptus-derived estrogens act as a signal for maternal recognition of pregnancy by changing the direction of prostaglandin (PG) F_2α from the uterine vasculature to the uterine lumen. Estrogens also induce the expression of many endometrial genes, including genes related to growth factors, the synthesis and transport of PGs, and immunity. IL1B2, a pro-inflammatory cytokine, is produced by the elongating conceptus. The direct effect of IL1B2 on endometrial function is not fully understood. IL1B activates the expression of endometrial genes, including the genes involved in IL1B signaling and PG synthesis and transport. In addition, estrogen or IL1B stimulates endometrial expression of IFN signaling molecules, suggesting that estrogen and IL1B act cooperatively in priming the endometrial function of conceptus-produced IFNG and IFND that, in turn, modulate endometrial immune response during early pregnancy. This review addresses information about maternal-conceptus interactions with respect to endometrial gene expression in response to conceptus-derived factors, focusing on the roles of estrogen and IL1B during early pregnancy in pigs.

Preimplantation mouse blastocysts fail to express CYP genes required for estrogen biosynthesis

Implantation is initiated on day 4 in the mouse and on day 13 in the pig. The preimplantation pig blastocyst synthesizes steroid hormones, but whether preimplantation rodent embryos also have this ability has remained unresolved for the last two decades. In this study, the mRNAs encoding NADPH-cytochrome P450 reductase (P450-reductase), adrenodoxin, lanosterol 14-demethylase P450 (CYP51), 17 alpha-hydroxylase P450 (CYP17), cholesterol side-chain cleavage P450 (CYP11A1), sterol 27-hydroxylase P450 (CYP27), and aromatase P450 (CYP19) were examined in day 4 mouse blastocysts (day 1 = vaginal plug) and in day 13 and 16 pig blastocysts using reverse transcription-polymerase chain reaction (RT-PCR). In mouse blastocysts, mRNAs of P450-reductase, adrenodoxin, and CYP51, but not CYP17, CYP11A1, CYP27, and CYP19, were detected. In agreement with this finding, no aromatase protein could be detected by immunohistochemistry. By contrast, all these mRNAs were detected in the pig blastocyst. Furthermore, both the ovarian and placental types of aromatase (CYP19) mRNAs were detected in the pig blastocyst on days 13 and 16 of pregnancy, although the ovarian form was more abundant. Both forms of aromatase were much higher in day 13 than in day 16 pig blastocysts. The results provide definitive evidence that the preimplantation mouse blastocyst, as opposed to the pig blastocyst, has no ability to synthesize estrogen and no steroidogenic capacity. Maternal estrogen synthesis is essential for implantation of the mouse blastocyst.

Cell-type specific responses in prostaglandin secretion by glandular and stromal cells from pig endometrium treated with catecholestrogens, methoxyestrogens and progesterone

The pig conceptus and endometrium possess the ability to convert estrogens into catecholestrogens and catecholestrogens into methoxyestrogens. Experiments were carried out to evaluate the effect of catecholestrogens, methoxyestrogens and progesterone on the secretion of prostaglandin (PG) E and F2 alpha by porcine endometrial glandular and stromal cells in vitro. Both 2-hydroxyestradiol (2-OH-E2, 0-20 microM) and 4-hydroxyestradiol (4-OH-E2, 0-20 microM) increased (P less than .05) PGE and PGF2 alpha secretion by stromal cells in a dose response manner. Two-hydroxyestradiol tended (P less than .1) to decrease PGF2 alpha production by glandular cells. Two-methoxyestradiol (20 microM) suppressed (P less than .05) PGF2 alpha secretion by glandular and stromal cells. Four-methoxyestradiol (20 microM) stimulated (P less than .05) PGE production and PGE:PGF2 alpha ratio. Progesterone (.1 microM) suppressed (P less than .05) PG secretion in both cell types. We conclude that catecholestrogens, methoxyestrogens, and progesterone may participate in the establishment of pregnancy by modulating PG production in the endometrium.

Characterization of the epidermal growth factor receptor in preimplantation pig conceptuses

Embryos recovered from sows on Days 9-13 of pregnancy (Day 0 = first day of estrus) exhibited saturable and time-dependent specific binding of 125I-epidermal growth factor (EGF). The specific binding (pg/mg protein) was greater (P less than 0.001) for Day 13 elongated conceptuses than for conceptuses of earlier stages. Scatchard analyses showed two classes of binding sites (Kd = 7.0 +/- 2.6 x 10(-11) M, Bmax = 6.2 +/- 1.4 fmol/mg protein and Kd = 3.4 +/- 0.2 x 10(-8) M, Bmax = 420 +/- 80 fmol/mg protein). The EGF receptor in Day 13 conceptus membranes is a 170-kDa protein and was phosphorylated in the presence of EGF and adenosine triphosphate. EGF stimulated protein tyrosine kinase activity about 1.6-fold over basal levels. The results show that the preimplantation pig conceptus possesses EGF-binding sites with the properties of functional EGF-receptors.

Estradiol-15 alpha-hydroxylation: a new avenue of estrogen metabolism in peri-implantation pig blastocysts

Pig blastocysts have the capacity to convert estradiol into catechol estrogens. Our present study shows that they also have the capacity to hydroxylate estradiol in cycloaliphatic C-atom 15, and this aliphatic hydroxylation reaction is more predominate than the aromatic hydroxylations. The conversion of [4-14C]estradiol to [4-14C]15 alpha-hydroxyestradiol by mitochondrial-rich/microsomal fractions was examined by isolation of this product using reversed phase high-performance liquid chromatography (HPLC) attached to a radiometric flow detector, and its identification by gas chromatography-mass spectrometry. The enzyme kinetics for estrogen 15 alpha-hydroxylase were performed in the pig blastocyst obtained on Day 13 of pregnancy (Day 0 = first acceptance of the male). The enzyme follows classical Michaelis-Menten kinetics. The apparent Kms for estradiol were 2.47 and 1.85 microM, and the apparent Vmaxs were 0.25 and 0.197 nmol/mg/min in the mitochondrial-rich and microsomal fractions, respectively. The enzyme activity was inhibited by different steroidal compounds and non-steroidal estrogens, as well as by CO, SKF-525A, piperonyl butoxide and antibody to cytochrome P450 reductase. Ontogenesis of the blastocyst's estrogen 15 alpha-hydroxylase follows a similar pattern to that of estrogen-2/4-hydroxylase. Thus, highest activity was observed on Days 12 and 13 and lowest was on Day 15 of pregnancy. Furthermore, the enzyme is abundant primarily in the extraembryonic tissues rather than in the embryo proper. The abundance of the enzyme in the extraembryonic tissues, and its surge at a critical time of pregnancy recognition and just prior to implantation suggest that 15 alpha-hydroxylated estradiol could be involved in these processes.