n-3 polyunsaturated fatty acids suppress CD4+ T cell proliferation by altering phosphatidylinositol-(4,5)-bisphosphate [PI(4,5)P2] organization

The mechanisms by which n-3 polyunsaturated fatty acids (n-3 PUFA), abundant in fish oil, exert their anti-inflammatory effects have not been rigorously defined. We have previously demonstrated that n-3 PUFA decrease the amount of phosphatidylinositol-(4,5)-bisphosphate, [PI(4,5)P-2], in CD4(+) T cells, leading to suppressed actin remodeling upon activation. Since discrete pools of PI(4,5)P-2 exist in the plasma membrane, we determined whether n-3 PUFA modulate spatial organization of PI(4,5)P-2 relative to raft and non-raft domains. We used Forster resonance energy transfer (FRET) to demonstrate that lipid raft mesodomains in the plasma membrane of CD4(+) T cells enriched in n-3 PUFA display increased co-clustering of Lck(N10) and LAT(Delta CP), markers of lipid rafts. CD4(+) T cells enriched in n-3 PUFA also exhibited a depleted plasma membrane non-raft PI(4,5)P-2 pool as detected by decreased co-clustering of Src(N15), a non-raft marker, and PH(PLC-6), a P1(4,5)P-2 reporter. Incubation with exogenous P1(4,5)1,2 rescued the effects on the non-raft P1(4,5)P-2 pool, and reversed the suppression of T cell proliferation in CD4(+) T cells enriched with n-3 PUFA. Furthermore, CD4(+) T cells isolated from mice fed a 4% docosahexaenoic add (DHA)-enriched diet exhibited a decrease in the non-raft pool of P1(4,5)P-2, and exogenous PI(4,5)P-2 reversed the suppression of T cell proliferation. Finally, these effects were not due to changes to post-translational lipidation, since n-3 PUFA did not alter the palmitoylation status of signaling proteins. These data demonstrate that n-3 PUFA suppress T cell proliferation by altering plasma membrane topography and the spatial organization of PI(4,5)P-2. (C) 2015 Elsevier B.V. All rights reserved.