Peroxisome-proliferator-activated receptors and the control of levels of prostaglandin-endoperoxide synthase 2 by arachidonic acid in the bovine uterus

Arachidonic acid is a potential paracrine agent released by the uterine endometrial epithelium to induce PTGS2 [PG (prostagland in)-endoperoxide synthase 2] in the stroma. In the present study, bovine endometrial stromal cells were used to determine whether PTGS2 is induced by arachidonic acid in stromal cells, and to investigate the potential role of PPARs (peroxisome-pro liferator-activated receptors) in this effect. Arachidonic acid increased PTGS2 levels up to 7.5-fold within 6 h. The cells expressed PPARa and PPAR delta (also known as PPAR beta) (but not PPAR gamma). PTGS2 protein level was increased by PPAR agonists, including polyunsaturated fatty acids, synthetic PPAR ligands, PGA, and NSAtDs (non-steroidal anti-inflammatory drugs) with a time course resembling that of arachidonic acid. Use of agonists and antagonists indicated PPARa (but not PPAR delta or PPAR gamma) was responsible for PTGS2 induction. PTGS2 induction by arachidonic acid did not require PG synthesis. PTGS2 levels were increased by the PKC (protein kinase C) activators 4 beta-PMA and PGF(2 alpha), and the effects of arachidonic acid, NSAIDs, synthetic PPAR ligands and 4 beta-PMA were blocked by PKC inhibitors. This is consistent with PPAR phosphorylation by PKC. Induction of PTGS2 protein by 4 beta-PMA in the absence of a PPAR ligand was decreased by the NF-kappa B (nuclear factor kappa B) inhibitors MG 132 and parthenolide, suggesting that PKC acted through NF-kappa B in addition to PPAR phosphorylation. Use of NF-kappa B inhibitors allowed the action of arachidonic acid as a PPAR agonist to be dissociated from an effect through PKC. The results are consistent with the hypothesis that arachidonic acid acts via PPAR alpha to increase PTGS2 levels in bovine endometrial stromal cells.