Luteal fibroblasts produce prostaglandins in response to IL1β in a MAPK-mediated manner

The corpus luteum is a temporary endocrine gland that is crucial for pregnancy, as it produces the progesterone needed to maintain optimal uterine conditions for implantation. In the absence of a conceptus, the corpus luteum becomes non-functional and undergoes rapid tissue remodeling to regress into a fibrotic corpus albicans. Early luteal regression is characterized by increased cytokine release. Because the role of fibroblasts in the bovine corpus luteum remains to be elucidated, the aim of this study was to elucidate the response of bovine luteal fibroblasts to inflammatory cytokines, tumor necrosis factor α (TNFα), and interleukin 1β (IL1β). Both cytokines induced canonical mitogen activated protein kinase (MAPK) signaling in luteal fibroblasts by phosphorylation of ERK1/2, p38 MAPK, and JNK. IL1β elevated expression and phosphorylation of cytosolic phospholipase A2 (cPLA₂), an enzyme that mobilizes arachidonic acid for prostanoid synthesis. IL1β also elevated expression of prostaglandin-endoperoxide synthase 2 (PTGS2), another enzyme needed to synthesize prostanoids. IL1β increased PGF2α and PGE₂ levels in the culture medium over 20-fold. Inhibition of MAPKs with small-molecule inhibitors abrogated the stimulatory effects of IL1β. IL1β also induced prostaglandin production in steroidogenic cells; however, there was no elevation in cPLA₂. Therefore, actions of IL1β differ based on ovarian cell type. All together, we have identified luteal fibroblasts as potential inflammatory mediators during luteal regression.