Expression of progesterone receptor in the porcine uterus and placenta throughout gestation: correlation with expression of uteroferrin and osteopontin.
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Progesterone (P4) stimulates production and secretion of histotroph, a mixture of hormones, growth factors, nutrients, and other substances required for growth and development of the conceptus (embryo or fetus and placental membranes). Progesterone acts through the progesterone receptor (PGR); however, there is a gap in our understanding of P4 during pregnancy because PGR have not been localized in the uteri and placentae of pigs beyond day 18. Therefore, we determined endometrial expression of PGR messenger RNA (mRNA) and localized PGR protein in uterine and placental tissues throughout the estrous cycle and through day 85 of pregnancy in pigs. Further, 2 components of histotroph, tartrate-resistant acid phosphatase 5 (ACP5; uteroferrin) and secreted phosphoprotein 1 (SPP1; osteopontin) proteins, were localized in relation to PGR during pregnancy. Endometrial expression of PGR mRNA was highest at day 5 of the estrous cycle, decreased between days 5 and 11 of both the estrous cycle and pregnancy, and then increased between days 11 and 17 of the estrous cycle (P < 0.01), but decreased from days 13 to 40 of pregnancy (P < 0.01). Progesterone receptor protein localized to uterine stroma and myometrium throughout all days of the estrous cycle and pregnancy. PGR were expressed by uterine luminal epithelium (LE) between days 5 and 11 of the estrous cycle and pregnancy, then PGR became undetectable in LE through day 85 of pregnancy. During the estrous cycle, PGR were downregulated in LE between days 11 and 15, but expression returned to LE on day 17. All uterine glandular epithelial (GE) cells expressed PGR from days 5 to 11 of the estrous cycle and pregnancy, but expression decreased in the superficial GE by day 12. Expression of PGR in GE continued to decrease between days 25 and 85 of pregnancy; however, a few glands near the myometrium and in close proximity to areolae maintained expression of PGR protein. Acid phosphatase 5 protein was detected in the GE from days 12 to 85 of gestation and in areolae. Secreted phosphoprotein 1 protein was detected in uterine LE in apposition to interareolar, but not areolar areas of the chorioallantois on all days examined, and in uterine GE between days 35 and 85 of gestation. Interestingly, uterine GE cells adjacent to areolae expressed PGR, but not ACP5 or SPP1, suggesting these are excretory ducts involved in the passage, but not secretion, of histotroph into the areolar lumen and highlighting that P4 does not stimulate histotroph production in epithelial cells that express PGR.