Annexin I and dexamethasone effects on phospholipase and cyclooxygenase activity in human synoviocytes

[摘要] Annexin I is a glucocorticoid-induced mediator with anti-inflammatory activity in animal models of arthritis. We studied the effects of a bioactive annexin I peptide, ac 2–26, dexamethasone (DEX), and interleukin-1β (IL-1β) on phospholipase A2(PLA2) and cyclooxygenase (COX) activities and prostaglandin E2(PGE2) release in cultured human fibroblast-like synoviocytes (FLS). Annexin I binding sites on human osteoarthritic (OA) FLS were detected by ligand binding flow cytometry. PLA2activity was measured using3H-arachidonic acid release, PGE2release and COX activity by ELISA, and COX2 content by flow cytometry. Annexin I binding sites were present on human OA FLS. Annexin I peptide ac 2–26 exerted a significant concentration-dependent inhibition of FLS constitutive PLA2activity, which was reversed by IL-1β. In contrast, DEX inhibited IL-1β-induced PLA2activity but not constitutive activity. DEX but not annexin I peptide inhibited IL-1β-induced PGE2release. COX activity and COX2 expression were significantly increased by IL-1β. Annexin I peptide demonstrated no inhibition of constitutive or IL-1β-induced COX activity. DEX exerted a concentration-dependent inhibition of IL-1β-induced but not constitutive COX activity. Uncoupling of inhibition of PLA2and COX by annexin I and DEX support the hypothesis that COX is rate-limiting for PGE2synthesis in FLS. The effect of annexin I but not DEX on constitutive PLA2activity suggests a glucocorticoid-independent role for annexin I in autoregulation of arachidonic acid production. The lack of effect of annexin I on cytokine-induced PGE2production suggests PGE2-independent mechanisms for the anti-inflammatory effects of annexin Iin vivo.

[学科分类] 生理学与病理学