53 The effect of dexamethasone and platelet-rich plasma on the equine post-breeding endometrial transcriptome

Endometritis remains one of the leading causes of sub-/infertility in mares, having a significant economic impact on the equine industry. Mares develop an acute inflammatory reaction in utero after breeding in response to exposure to allogenic semen, referred to as breeding-induced endometritis, which is necessary to prepare the uterine lumen for embryo arrival and pregnancy. However, in some mares, the inflammation is prolonged (beyond 36–48 h post-breeding), leading to the pathological condition of persistent breeding-induced endometritis (PBIE). Anti-inflammatory products are one of the treatment strategies for PBIE. A single dose of dexamethasone (IV, 50 mg) at the time of breeding has been proposed as an effective treatment strategy for PBIE. Also, platelet-rich plasma (PRP) has been practiced for its immunomodulatory properties. However, there is significant variation in the outcome of these treatment methods. Hence, understanding the mechanism of action of dexamethasone and PRP therapy at the molecular level will further optimise these treatment strategies. Our study aimed to elucidate the endometrial response to dexamethasone and PRP therapy using a whole transcriptomic approach. In a randomised crossover study, 14 mares were assigned to receive an intrauterine infusion of Ringer’s lactate solution (Control), autologous PRP intrauterine treatment 24 h before breeding (PRP; 20 mL, 250 000 platelets mL⁻¹), or 50 mg dexamethasone IV at the time of breeding (DEX). Those 14 mares were selected based on a preliminary trial, consisting of infusion of dead frozen-thawed sperm (to mimic breeding irritation) followed by fluid measurement 6, 24, and 36 h post-breeding. Mares that accumulated >2 cm fluid 24 h post-breeding and/or any fluid 36 h post-breeding were selected and considered susceptible for PBIE. All mares were bred with a mixture of two stallions’ fresh semen. Total RNA was extracted and sequenced from the endometrial biopsy samples taken 24h after artificial insemination. Differentially expressed genes (DEGs) were evaluated using DESEqn 2, using paired comparison, followed by gene ontology (GO) analysis. Endometrial samples from mares treated with dexamethasone exhibited 768 DEGs (FDR < 0.05, fold-change >2) and those treated with PRP exhibited 5370 DEGs (FDR < 0.05, fold-change >2) relative to the control cycles. As expected, the functional annotation of DEGs in the DEX group showed genes mainly involved in immune and inflammatory responses. However, the most enriched pathways in the PRP group were involved in tissue development, blood vessel formation, and cell migration. Our data suggest that PRP might have its effects based on tissue regeneration while, as expected, DEX modulates the immune system by altering the expression of several cytokines. This study demonstrated significant differences in the endometrial response to the two proposed anti-inflammatory treatments for PBIE and provided fundamental information on the mechanism of action of these treatment strategies.