Characterization of Nuclear Progesterone Receptor Isoforms in the Term Equine Placenta.
Authors: Nagy Ahmed M, Sathe Swanand R, Atta Attia H, Hammam Abdel Mohsen M, Hsu Walter H
Journal: Frontiers in veterinary science
Summary
# Editorial Summary: Nuclear Progesterone Receptor Isoforms in the Term Equine Placenta Progesterone's role in maintaining pregnancy and triggering parturition in mares remains incompletely understood, particularly regarding how its signalling mechanisms operate within placental tissue. Nagy Ahmed and colleagues characterised two isoforms of the nuclear progesterone receptor (PRA and PRB) in term equine placentas using reverse transcription polymerase chain reaction to measure mRNA expression and Western blotting to quantify protein levels across six samples. Counter to established knowledge from other species where PRB typically predominates, the equine placenta expressed significantly higher levels of the PRA isoform at both gene and protein levels (P < 0.0001), suggesting the receptor profile differs meaningfully from human and rodent models. Given that progesterone withdrawal is critical for myometrial activation and expulsion of fetal membranes, the authors propose that PRA—rather than the more transcriptionally active PRB—may orchestrate the transition from pregnancy maintenance to labour and placental expulsion in mares. Understanding this isoform-specific expression could refine our interpretation of progesterone dynamics in late gestation and inform management strategies for mares approaching parturition, though further functional studies are needed to clarify precisely how PRA mediates these reproductive events.
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Practical Takeaways
- •The dominance of PRA over PRB in the equine placenta suggests PRA may be the primary mediator of placental expulsion during parturition—relevant for understanding dystocia and retained placenta cases
- •This molecular characterization provides a foundation for future research into progesterone-related reproductive complications in mares, though clinical applications require further investigation
- •Understanding placental progesterone signaling may eventually inform targeted interventions for parturition disorders, but more translational research is needed before clinical recommendations can be made
Key Findings
- •PRA (progesterone receptor alpha) mRNA and protein expression was significantly higher than PRB (progesterone receptor beta) in term equine placental tissue (P < 0.0001)
- •Nuclear progesterone receptors are detectable in the term equine placenta
- •PRA is the dominant nPR isoform expressed in the equine placenta at parturition