Lysophosphatidic acid as a regulator of endometrial connective tissue growth factor and prostaglandin secretion during estrous cycle and endometrosis in the mare.

Background: Equine endometrosis is a chronic degenerative condition, described as endometrial fibrosis that forms in the stroma, under the basement membrane and around the endometrial glands. The role of lysophosphatidic acid (LPA) in the development of tissue fibrosis varies depending on the organ, and its profibrotic role in mare endometrosis remains unclear. The study aimed to establish the endometrial presence of LPA and its receptors (LPAR1-4), together with its effects on connective tissue growth factor (CTGF) and prostaglandins (PG) secretion from equine endometrium under physiological (estrous cycle), or pathological conditions (endometrosis). Mare endometria in the mid-luteal phase (n = 5 for each category I, IIA, IIB, III of Kenney and Doig) and in the follicular phase (n = 5 for each category I, IIA, III and n = 4 for IIB) were used. In experiment 1, the levels of LPA, LPAR1-4 mRNA level and protein abundance were investigated in endometria at different stages of endometrosis. In experiment 2, the in vitro effect of LPA (10 ^- 9  M) on the secretion of CTGF and PGs from endometrial tissue explants at different stages of endometrosis were determined.
Results: Endometrial LPA concentration was higher in the mid-luteal phase compared to the follicular phase in category I endometrium (P < 0.01). There was an alteration in endometrial concentrations of LPA and LPAR1-4 protein abundance in the follicular phase at different stages of endometrosis (P < 0.05). Additionally, LPA increased the secretion of PGE ₂ from category I endometrium in both phases of the estrous cycle (P < 0.05). The effect of LPA on the secretion of CTGF and PGF _2α from endometrial tissue was altered depending on different stages of endometrosis (P < 0.05).
Conclusion: Our data indicate that endometrosis disturbs proper endometrial function and is associated with altered endometrial LPA concentration, its receptor expression and protein abundance, PGE ₂ /PGF _2α ratio, and CTGF secretion in response to LPA. These changes could influence several physiological events occurring in endometrium in mare during estrous cycle and early pregnancy.