Prostaglandin-related genes are differentially expressed in equine endometrium with different biopsy grade, degrees of inflammation, and fibrosis.

Overview

• This study investigated how genes related to prostaglandin production and inflammation are differently expressed in the uterine lining of mares with various degrees of tissue changes and inflammation.
• The aim was to understand how these molecular changes might impact uterine function and fertility in horses.

Background and Importance

• Prostaglandins are lipid compounds that play vital roles in reproductive processes such as:
• Luteolysis (breakdown of the corpus luteum)
• Luteal support (maintenance of the corpus luteum)
• Ovulation
• Uterine tube transport
• Uterine contractions
• Embryonic mobility within the uterus
• Inflammation and fibrosis in the uterus
• In the uterus, an imbalance in inflammatory and prostaglandin signaling can disrupt normal function and reduce fertility.

Research Objective and Hypothesis

• The study aimed to evaluate the expression levels of several prostaglandin- and inflammatory-related genes in mares with different severity of uterine lining (endometrial) histological changes, such as inflammation and fibrosis.
• The hypothesis was that mares with higher inflammation or fibrosis would show altered levels of prostaglandin E2 (PGE2) and F2α (PGF2α), as well as differences in gene expression related to prostaglandins and inflammation, compared to mares with normal or minimal uterine changes.

Study Design and Methods

• Forty-five mares in estrus were biopsied to assess their endometrial health by a reproductive pathologist using the Kenney-Doig grading system:
• Grades ranged from I (normal) to IIB (more severe changes)
• Histological evaluation focused on:
• Neutrophilic inflammation (presence of neutrophils)
• Lymphocytic and plasmocytic inflammation (chronic inflammatory cells)
• Fibrosis (degree of tissue scarring)
• In 26 mares, uterine lavage fluid was collected to measure PGE2 and PGF2α concentrations using ELISA assays.
• Total RNA was extracted from endometrial biopsies to measure mRNA expression of 25 genes involved in prostaglandin synthesis and inflammation pathways.
• Statistical analysis used a linear model with restricted maximum likelihood to compare gene expression differences; significance was defined as P < 0.05.

Key Findings

• No significant differences were found in the concentrations of prostaglandin E2 or F2α in lavage fluid between any groups defined by inflammation, fibrosis, or biopsy grade.
• Mares with the lowest biopsy grade (Grade I) exhibited lower expression of several genes compared to mares with moderate biopsy grades (IIA or IIB), specifically:
• NF-kB (a key inflammatory transcription factor)
• PTGS1 (prostaglandin-endoperoxide synthase 1, also known as COX-1)
• HPGD (hydroxyprostaglandin dehydrogenase, involved in prostaglandin degradation)
• Mares with neutrophilic inflammation showed decreased expression of important inflammation and prostaglandin-related genes versus mares without inflammation, including:
• NF-kB
• PTGS1 (COX-1)
• PTGER4 (prostaglandin E receptor 4)
• CBR1 (carbonyl reductase 1, involved in prostaglandin metabolism)
• mPGES2 (microsomal prostaglandin E synthase 2)
• PTGIS (prostacyclin synthase)
• Mares with mild or minimal fibrosis had higher expression of mPGES2 and PTGIS compared to those with moderate fibrosis, suggesting changes in prostaglandin synthesis enzymes associated with tissue remodeling.

Conclusions and Implications

• The study identified that specific prostaglandin- and inflammation-related genes are differentially expressed in the equine endometrium depending on the severity of histological findings such as inflammation and fibrosis.
• The presence of inflammation and fibrosis appears to influence the gene expression involved in prostaglandin pathways, potentially altering the balance of prostaglandins in the uterine tissue, though this might not directly change measurable prostaglandin concentrations in lavage fluid.
• Since prostaglandins impact many uterine functions necessary for successful reproduction, these changes in gene expression might impair uterine environment quality during estrus, possibly affecting early embryo survival and hence fertility in mares.
• This work enhances understanding of molecular changes in diseased equine endometrium and may help guide future fertility treatments or diagnostic approaches based on molecular markers.