Fatty acid-induced induction of Toll-like receptor-4/nuclear factor-kappaB pathway in adipocytes links nutritional signalling with innate immunity.
To study the effects of fatty acids and the involvement of the Toll-like receptor-4/nuclear factor-kappaB (TLR-4/NF-kappaB) 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-kappaB p65 nuclear translocation and TLR-4 expression were investigated by Western blot. The effects mediated by NF-kappaB were tested using a specific NF-kappaB-inhibitor and TLR-4-induced effects were analysed with a neutralizing TLR-4 antibody. Binding of (14)C-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-kappaB. 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.
Schaeffler
Andreas
A
Department of Internal Medicine I, Regensburg University Hospital, Regensburg, Germany. andreas.schaeffler@klinik.uni-regensburg.de
Gross
Philipp
P
Buettner
Roland
R
Bollheimer
Cornelius
C
Buechler
Christa
C
Neumeier
Markus
M
Kopp
Andrea
A
Schoelmerich
Juergen
J
Falk
Werner
W
D050153:Abdominal Fat / Q000378:metabolism; D017667:Adipocytes / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D052242:Adiponectin / Q000378:metabolism; D000824:Animal Nutritional Physiological Phenomena / Q000276:immunology*; D000818:Animals; D002454:Cell Differentiation; D002478:Cells, Cultured; D018932:Chemokine CCL2 / Q000378:metabolism; D004032:Diet; D004041:Dietary Fats / Q000008:administration & dosage; D005227:Fatty Acids / Q000378:metabolism / Q000494:pharmacology*; D007113:Immunity, Innate / Q000502:physiology; D008297:Male; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D051381:Rats; D017208:Rats, Wistar; D052243:Resistin / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D015398:Signal Transduction / Q000276:immunology; D051197:Toll-Like Receptor 4 / Q000037:antagonists & inhibitors / Q000096:biosynthesis*
D052242:Adiponectin; C491766:Ccl2 protein, rat; D018932:Chemokine CCL2; D004041:Dietary Fats; D005227:Fatty Acids; D016328:NF-kappa B; D052243:Resistin; C499622:Retn protein, rat; C495347:Tlr4 protein, rat; D051197:Toll-Like Receptor 4