Saturated fatty acid activates but polyunsaturated fatty acid inhibits Toll-like receptor 2 dimerized with Toll-like receptor 6 or 1
Department of Medicine, Division of Infectious Diseases and Immunology
Animals; Bone Marrow; Cell Line; Cyclooxygenase 2; Dimerization; Fatty Acids; Fatty Acids, Unsaturated; Genes, Dominant; Humans; Immunoblotting; Isoenzymes; Lauric Acids; Ligands; Luciferases; Macrophages; Membrane Glycoproteins; Membrane Proteins; Mice; Mice, Inbred C3H; NF-kappa B; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Plasmids; Precipitin Tests; Prostaglandin-Endoperoxide Synthases; Receptors, Cell Surface; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction; Toll-Like Receptor 1; Toll-Like Receptor 2; Toll-Like Receptor 4; Toll-Like Receptor 6; Toll-Like Receptors; Transfection
Toll-like receptor 4 (TLR4) and TLR2 agonists from bacterial origin require acylated saturated fatty acids in their molecules. Previously, we reported that TLR4 activation is reciprocally modulated by saturated and polyunsaturated fatty acids in macrophages. However, it is not known whether fatty acids can modulate the activation of TLR2 or other TLRs for which respective ligands do not require acylated fatty acids. A saturated fatty acid, lauric acid, induced NFkappaB activation when TLR2 was co-transfected with TLR1 or TLR6 in 293T cells, but not when TLR1, 2, 3, 5, 6, or 9 was transfected individually. An n-3 polyunsaturated fatty acid (docosahexaenoic acid (DHA)) suppressed NFkappaB activation and cyclooxygenase-2 expression induced by the agonist for TLR2, 3, 4, 5, or 9 in a macrophage cell line (RAW264.7). Because dimerization is considered one of the potential mechanisms for the activation of TLR2 and TLR4, we determined whether the fatty acids modulate the dimerization. However, neither lauric acid nor DHA affected the heterodimerization of TLR2 with TLR6 as well as the homodimerization of TLR4 as determined by co-immunoprecipitation assays in 293T cells in which these TLRs were transiently overexpressed. Together, these results demonstrate that lauric acid activates TLR2 dimers as well as TLR4 for which respective bacterial agonists require acylated fatty acids, whereas DHA inhibits the activation of all TLRs tested. Thus, responsiveness of different cell types and tissues to saturated fatty acids would depend on the expression of TLR4 or TLR2 with either TLR1 or TLR6. These results also suggest that inflammatory responses induced by the activation of TLRs can be differentially modulated by types of dietary fatty acids.
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Citation: J Biol Chem. 2004 Apr 23;279(17):16971-9. Epub 2004 Feb 13. Link to article on publisher's site