Fatty acid-induced induction of Toll-like receptor-4/nuclear factor-κB pathway in adipocytes links nutritional signalling with innate immunity

Authors


Dr A. Schäffler, Department of Internal Medicine I, University of Regensburg, D-93042 Regensburg, Germany. Email: andreas.schaeffler@klinik.uni-regensburg.de
Senior author: Werner Falk, email: werner.falk@klinik.uni-regensburg.de

Summary

To study the effects of fatty acids and the involvement of the Toll-like receptor-4/nuclear factor-κB (TLR-4/NF-κB) pathway with respect to the secretion of adipokines from adipocytes 3T3-L1 adipocytes were stimulated with increasing doses of fatty acids. The secretion of adiponectin, resistin and monocyte chemoattractant protein-1 (MCP-1) was measured by enzyme-linked immunosorbent assay. The NF-κB p65 nuclear translocation and TLR-4 expression were investigated by Western blot. The effects mediated by NF-κB were tested using a specific NF-κB-inhibitor and TLR-4-induced effects were analysed with a neutralizing TLR-4 antibody. Binding of 14C-labelled fatty acids to TLR-4/MD-2 was investigated using a FLAG-tagged extracellular part of TLR-4 fused to full-length MD-2 via a linker (lipopolysaccharide-Trap). The messenger RNA (mRNA) expression of adipokines in abdominal adipose tissue of rats fed a standard chow or a high-fat diet was investigated by reverse transcription–polymerase chain reaction. The TLR-4 is induced during adipocyte differentiation and its expression is enhanced following fatty acid stimulation. The stimulatory effects of stearic and palmitic acids on MCP-1 secretion and of palmitoleic acid on resistin secretion are mediated via NF-κB. The stimulatory effects of stearic, palmitic and palmitoleic acids on resistin secretion and the stimulatory effect of stearic acid on MCP-1 secretion are mediated via TLR-4. Fatty acid-mediated effects are caused by an endogenous ligand because fatty acids were shown not to bind directly to TLR-4/MD-2. Adipose tissue mRNA expression and serum levels of adipokines did not differ in rats fed a high-fat diet. These data provide a new molecular mechanism by which fatty acids can link nutrition with innate immunity.

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