Saturated fatty acids activate TLR-mediated proinflammatory signaling pathways

Shurong Huang,Kikumi D Ono-Moore,Dina A Schneider,Ryan G Snodgrass,Jennifer M Rutkowsky,John W Newman,Daniel H Hwang,Sean H Adams

doi:10.1194/jlr.d029546

Abstract

Toll-like receptor 4 (TLR4) and TLR2 were shown to be activated by saturated fatty acids (SFAs) but inhibited by docosahexaenoic acid (DHA). However, one report suggested that SFA-induced TLR activation in cell culture systems is due to contaminants in BSA used for solubilizing fatty acids. This report raised doubt about proinflammatory effects of SFAs. Our studies herein demonstrate that sodium palmitate (C16:0) or laurate (C12:0) without BSA solubilization induced phosphorylation of inhibitor of nuclear factor-κB α, c-Jun N-terminal kinase (JNK), p44/42 mitogen-activated-kinase (ERK), and nuclear factor-κB subunit p65, and TLR target gene expression in THP1 monocytes or RAW264.7 macrophages, respectively, when cultured in low FBS (0.25%) medium. C12:0 induced NFκB activation through TLR2 dimerized with TLR1 or TLR6, and through TLR4. Because BSA was not used in these experiments, contaminants in BSA have no relevance. Unlike in suspension cells (THP-1), BSA-solubilized C16:0 instead of sodium C16:0 is required to induce TLR target gene expression in adherent cells (RAW264.7). C16:0-BSA transactivated TLR2 dimerized with TLR1 or TLR6 and through TLR4 as seen with C12:0. These results and additional studies with the LPS sequester polymixin B and in MyD88(-/-) macrophages indicated that SFA-induced activation of TLR2 or TLR4 is a fatty acid-specific effect, but not due to contaminants in BSA or fatty acid preparations.

Highlights

Toll-like receptor 4 (TLR4) and TLR2 were shown to be activated by saturated fatty acids (SFAs) but inhibited by docosahexaenoic acid (DHA)
Our previous studies demonstrated that water-soluble sodium laurate (C12:0) activates pattern recognition receptor (PRR) (TLR2, TLR4, nucleotide-binding oligomerization domain family (NOD)) [7, 25]
We determined whether C12:0 or C16:0-BSA-induced expression of COX-2 or tumor necrosis factor (TNF)-␣ is due to contamination of LPS in BSA or fatty acid preparations

Summary

Introduction

Toll-like receptor 4 (TLR4) and TLR2 were shown to be activated by saturated fatty acids (SFAs) but inhibited by docosahexaenoic acid (DHA). One report suggested that SFA-induced TLR activation in cell culture systems is due to contaminants in BSA used for solubilizing fatty acids. Emerging evidence suggests that PRRs can sense metabolic disturbance and link immune responses to metabolic homeostasis [1, 2] Such a functional diversity of PRRs may be achieved by their ability to recognize a wide variety of structurally unrelated molecules. High saturated fat diets have been used for diet-induced obesity and insulin resistance in many animal studies Both in vitro and in vivo studies suggest that saturated fatty acids (SFAs) can activate proinflammatory signaling pathways leading to insulin resistance [5].

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