Impairment of the antifibrotic prostaglandin E2 pathway may influence neutrophil extracellular traps-induced fibrosis in the mare endometrium

Abstract

Prostaglandin E₂ (PGE₂) has contradictory effects in many organs. It may have proinflammatory, anti-inflammatory, or anti-fibrotic roles, depending on the type of receptors to which it binds. By signaling through its receptors EP2 and EP4, PGE₂ mediates anti-inflammatory and anti-fibrotic actions. In spite of chronic endometrial fibrosis (endometrosis) being a major cause of mare infertility, its pathogenesis is not fully understood. We have shown that contact of mare endometrium in vitro with neutrophil extracellular traps (NETs) proteases favors endometrial collagen type I production. Therefore, we investigated the involvement of the PGE₂ pathway in collagen deposition in mare endometrium, challenged in vitro with proteases present in NETs. Mare endometria (Kenney and Doig categories I/IIA and IIB/III), obtained in the follicular phase (FLP) and mid-luteal phase (MLP), were incubated for 24 h with components found in NETs (elastase, cathepsin-G, and myeloperoxidase). Secretion of PGE₂ and transcripts for specific PGE synthase (PGES) and PGE₂ receptors (EP2 and EP4) were evaluated. Impaired PGE₂ production and low EP2 transcript abundance depended on the endometrial category and estrous cycle phase. Impairment of PGE₂ and/or EP2 might play a role in FLP (category IIB/III) and MLP (I/IIA) endometrial fibrogenesis because of the reduction in its antifibrotic capacity. In conclusion, priming of the endometrium with endogenous ovarian steroids might inhibit the antifibrotic PGE₂ pathway either in healthy or pathologic tissues with collagen formation after NETs proteases action.

Keywords: Endometrium; Fibrosis; Mare; Neutrophil extracellular traps; PGE(2) receptors; Prostaglandin E(2).