Long chain n-3 polyunsaturated fatty acid inhibition of mast cell activation

Allergic diseases are a major medical concern with increasing prevalence in the world. Inflammation is one of the hallmarks of allergic diseases. Long chain n-3 polyunsaturated fatty acids (PUFAs) have been shown to inhibit allergic inflammation, but their direct effect on activation of the mast cell, a major effector cell in allergic inflammation, is poorly understood. We hypothesized that long chain n-3 PUFAs inhibit mast cell activation through alteration of the expression of some signaling molecules and modification of Fc epsilon receptor I (FcepsilonRI) association with lipid rafts, membrane microdomains containing high levels of cholesterol, sphingolipid, transmembrane proteins, acylated proteins, and glycosylphosphatidylinisotol (GPI)-anchored proteins. Bone marrow-derived mast cells (BMMC) were cultivated from C57BL/6 wild type (WT) and fat-1 transgenic mice which express fatty acid n-3 desaturase and produce endogenous n-3 PUFAs. Exogenously, long chain n-3 PUFAs were supplemented to BMMC and human mast cell line laboratory of allergic diseases 2 (LAD2) cells. Mast cell degranulation, lipid-derived mediator release, and cytokine/chemokine production were evaluated following cell activation through FcepsilonRI. FcepsilonRI expression and signal transduction was determined by flow cytometry and western blot analysis.;GC-MS analysis showed increased long chain n-3 PUFAs levels in whole cell and lipid rafts of fat-1 BMMC, compared to WT, and in whole cell long chain n-3 PUFA-treated BMMC. Fat-1 BMMC produced less tumor necrosis factor (TNF) and CC chemokine ligand 2 (CCL2), and cysteinyl leukotrienes (cys-LTs), and showed reduced degranulation compared to WT BMMC after cell stimulation with immunoglobulin E (IgE)/antigen. Long chain n-3 PUFA exogenous supplementation caused decreased degranulation, cys-LT synthesis and cytokine/chemokine production in activated BMMC and LAD2 cells. Western blot analysis showed that the expression of Lyn and linker for activation of T cells (LAT) and phosphorylation of Lyn and spleen tyrosine kinase (Syk) and LAT was inhibited in fat-1 BMMC compared to WT. In both BMMC and LAD2 cells, long chain n-3 PUFAs did not alter cell surface and whole cell FcepsilonRI expression. However, FcepsilonRI was excluded from lipid rafts by long chain n-3 PUFAs in resting mast cells. Furthermore, the shuttling of FcepsilonRI to rafts of activated mast cells was inhibited by long chain n-3 PUFAs. After lipid raft disruption by depleting cholesterol, mast cell degranulation, cys-LT release and cytokine/chemokine production were reduced in both WT and fat-1 BMMC. In addition, FcepsilonRI and Lyn localization to lipid rafts were suppressed by MBCD treatment. This study clearly indicates that long chain n-3 PUFAs inhibit FcepsilonRI-mediated signal transduction and mediator release from mast cells by disrupting FcepsilonRI localization and partitioning to lipid rafts, and supressing the expression of Lyn and LAT. Cholesterol is required for the inhibitory effect of long chain n-3 PUFAs on mast cell activation.