n-3 Polyunsaturated fatty acids reduce Th17 polarization by decreasing responsiveness to interleukin-6
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CD4^(+) effector T cell subsets (e.g., Th1, Th17) are implicated in autoimmune and inflammatory disorders such as multiple sclerosis, psoriasis and rheumatoid arthritis. For optimal activation, IL-6 induces Th17 polarization and signals through the membrane-bound signal transducer, gp130. Previously, we have demonstrated that n-3 polyunsaturated fatty acids (PUFA), when supplied in the diet or in fat-1 transgenic mice which generate n-3 PUFA de novo, suppress CD4^(+) T cell activation and differentiation into pathogenic Th17 cells. Here we report that n-3 PUFA alter the response of CD4^(+) T cells to IL-6 in a lipid raft membrane-dependent fashion. Nave splenic CD4^(+) T cells from fat-1 mice exhibited significantly lower surface expression of the IL-6 receptor (IL-6R). This membrane bound receptor is known to be shed upon cellular activation in response to antigen; however, the release of soluble IL-6R after treatment with anti-CD3 and anti-CD28 was not changed in fat-1 mice suggesting that the decrease in surface expression is not due to ectodomain release. We observed a significant decrease in the association of gp130 with lipid rafts in activated fat-1 CD4^(+) T cells and a 35% reduction in gp130 homodimerization, an obligate requirement for downstream signaling. The phosphorylation of STAT3, a downstream target of IL-6-dependent signaling, was also decreased in response to exogenous IL-6 in fat-1 CD4^(+) T cells. Our results suggest that n-3 PUFA suppress Th17 cell differentiation, in part, by reducing membrane raft-dependent responsiveness to IL-6, an essential polarizing cytokine.
