Immunohistochemical Localization of Oestrogen Receptors α and β, Progesterone Receptor and Aromatase in the Equine Placenta

Abstract

The functions of placental oestrogens during equine pregnancy are still unclear. Yet, they may act predominantly as local regulators of growth and differentiation in the microplacentomes. Thus, expression patterns of oestrogen receptors (ERs) alpha and beta were investigated in the microcotyledonary placenta from pregnant mares at 110, 121, 179, 199 and 309 days of gestation by immunohistochemistry. In microplacentomes, both the ER isoforms were detected in trophoblast (T) cells, chorionic villous stroma (FS), microcaruncular epithelium (ME) and microcaruncular stroma (MS). Proportions of positive cells were 38-91% (T), 11-41% (FS), 55-89% (ME), 17-51% (MS) for ERalpha and 66-76% (T), 21-37% (FS), 41-68% (ME) and 24-55% (MS) for ERbeta. Between days 110 and 199, proportions of cells positive for progesterone receptor (PR) varied between 19% and 62% (T), 3% and 50% (CS), 15% and 46% (ME), and 4% and 33% (MS). At day 309, PR was virtually absent in T, CS and ME (percentages < 0.1), whereas in MS 14.3% of cells were still positive. The expression of ERs and PR in equine microplacentomes gives evidence for a role of placental steroids as regulators of placental growth, differentiation and function. The detection of ERalpha, ERbeta and PR in foetal and maternal vascular tissue suggests that placental steroids are also involved in the control of placental angiogenesis and /or vascular functions. The co-localization of ERs with aromatase in T suggests auto- or intracrine functions of oestrogens in this cell type.

New insights in equine steroidogenesis: an in-depth look at steroid signaling in the placenta

“…9A). This finding is in contrast with an earlier immunohistochemistrybased study which identified PGR in trophoblastic nuclei through mid-late gestation (Abd-Elnaeim et al 2009). The immediate cause for the discrepancy is not clear; however, Abd-Elnaeim et al used a human progesterone receptor antibody.…”

Concentrations of sulphated estrone, estradiol and dehydroepiandrosterone measured by mass spectrometry in pregnant mares

“…Thereafter however, the equine placenta has little ability to synthesise its own androgen substrate but, like the equine embryo, has considerable capacity to synthesise oestrogen if provided with androgen substrate . This is consistent with high levels of CYP19A1 transcript encoding aromatase and the immunohistochemical location of aromatase in the equine placenta . In fact, the capacity for aromatisation by the equine placenta is so high , it is surprising that any androgen escapes metabolism and is detectable in the maternal circulation, as DHEA is .…”

“…This suggests that the apparent detection of DHEAS in pregnant mares by immunoassay [60] and the increase observed in mares on letrozole reported previously [22], was likely due to cross-reactivity with another steroid, another sulphated androgen perhaps. As noted above, it is remarkable that enough unconjugated DHEA escapes metabolism by the placenta [40,61] to be detectable in maternal circulation as the fetal gonads grow. The placenta must first oxidise DHEA to androstenedione for aromatisation to be possible, which is consistent with the high levels of transcript encoding 3b-hydroxysteroid dehydrogenase (3bHSD) in the equine allantochorion [28], and the activity in tissue [37,61].…”

Expression of receptors for ovarian steroids and prostaglandin E2 in the endometrium and myometrium of mares during estrus, diestrus and early pregnancy

“…Protein localization of ER-␣, ER-␤, PR, EP2 and EP4 in uterine tissue was investigated by immunohistochemistry (IHC) using antibodies previously validated for the horse (Abd-Elnaeim et al, 2009;Alm et al, 2009;Ball et al, 2013;Parlevliet et al, 2006;Pearl et al, 2011). Endometrium and myometrium were fixed in 10% formalin for 24 h. After the 24 h fixation period, samples were dehydrated and embedded in paraffin.…”