Transcriptional profiling of equine endometrium before, during and after capsule disintegration during normal pregnancy and after oxytocin-induced luteostasis in non-pregnant mares.
Authors: Klein Claudia, Bruce Phoebe, Hammermueller Jutta, Hayes Tony, Lillie Brandon, Betteridge Keith
Journal: PloS one
Summary
# Editorial Summary The equine endometrium undergoes dramatic transcriptional remodelling during early pregnancy, particularly in response to conceptus signals rather than progesterone alone. Klein and colleagues used RNA sequencing to profile endometrial gene expression at days 14, 22, and 28 post-ovulation in pregnant mares, alongside samples from non-pregnant mares given oxytocin to artificially extend luteal function, allowing them to distinguish conceptus-dependent changes from those driven by elevated progesterone. Between days 22 and 28 of pregnancy, remarkably few genes (only 55 transcripts) showed differential expression, suggesting the endometrium reaches a relatively stable state under sustained progesterone exposure; however, the transition from day 14 to day 22/28 revealed substantial remodelling, with complement cascade components significantly upregulated and complement inhibitors (SERPING1) induced—a pattern consistent with immune tolerance of the conceptus. Critically, prostaglandin synthase 1 (PTGS1) expression increased markedly from day 14 onwards in pregnant mares and was significantly higher in pregnant versus artificially lutealised non-pregnant mares, indicating the conceptus actively enhances prostaglandin production capacity independent of progesterone signalling alone. These findings clarify which endometrial changes are pregnancy-specific and have implications for understanding implantation failure, early pregnancy loss, and potentially for managing mares with subfertility linked to aberrant endometrial responses.
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Practical Takeaways
- •Understanding conceptus-endometrial molecular interactions during early pregnancy may inform strategies for improving fertility and early pregnancy loss prevention
- •The complement system and prostaglandin pathways appear critical to early pregnancy maintenance in mares, offering potential diagnostic or therapeutic targets
- •Conceptus presence directly influences endometrial gene expression patterns distinct from progesterone effects alone, relevant to understanding pregnancy establishment
Key Findings
- •Only 55 transcripts were differentially expressed between Day 22 and Day 28 of pregnancy, indicating stable progesterone-dominated environment in late early pregnancy
- •Complement system pathway was significantly enriched in transcripts differentially expressed between Day 14 and Day 22/28 of pregnancy
- •Prostaglandin G/H synthase 1 expression was significantly higher at Days 22-28 compared to Day 14, with conceptus presence enhancing this upregulation
- •SERPING1 (complement system inhibitor) and complement components 7 and 8 showed pregnancy-stage-specific expression patterns in endometrium