TLR signalling and adapter utilization in primary human in vitro differentiated adipocytes.
Toll-like receptors (TLRs) are central to innate immunity and yet their expression is widespread and not restricted to professional inflammatory cells. TLRs have been reported on adipocytes and have been implicated in obesity-associated pathologies such as diabetes. Why TLRs are found on adipocytes is not clear although one hypothesis is that they may coordinate energy utilization for the energy intensive process of an immune response. We have explored TLR signalling in primary human in vitro differentiated adipocytes and investigated the specific adapter molecules that are involved. Only lipopolysaccharide (LPS), poly(I:C), Pam3CSK4 and MALP-2 could induce the production of IL-6, IL-8 and MCP-1 by adipocytes. Poly(I:C) alone caused a strong induction of type I interferons, as assessed by IP-10 production. Using siRNA, it was confirmed that LPS-dependent signalling in adipocytes occurs via TLR4 utilizing the adapter molecules MyD88, Mal and TRIF and caused rapid degradation of IκBα. Pam3CSK4 signalling utilized TLR2, MyD88 and Mal (but not TRIF). However, the response to poly(I:C) observed in these cells appeared not to require TRIF, but MyD88 was required for induction of NFκB-dependent cytokines by Poly(I:C). Despite this, IκBα degradation could not be detected in poly(I:C) stimulated adipocytes at any time-point up to 4 h. Indeed, IL-6 transcription was not induced until 8-16 h after exposure. These data suggest that Pam3CSK4 and LPS signal via the expected routes in human adipocytes, whereas poly(I:C)/TLR3 signalling may act via a TRIF-independent, MyD88-dependent route.
Kennedy Institute of Rheumatology, Nuffield Department of Orthopaedics Rheumatology and Musculoskeletal Sciences, University of Oxford, London, UK.
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Brenner
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Simmonds
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Feldmann
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D033942:Adaptor Proteins, Vesicular Transport / Q000235:genetics / Q000378:metabolism; D017667:Adipocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects; D018932:Chemokine CCL2 / Q000096:biosynthesis; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D020672:I-kappa B Proteins / Q000235:genetics / Q000378:metabolism; D015850:Interleukin-6 / Q000096:biosynthesis; D016209:Interleukin-8 / Q000096:biosynthesis; D055666:Lipopeptides / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D053594:Myeloid Differentiation Factor 88 / Q000494:pharmacology; D000072000:NF-KappaB Inhibitor alpha; D011070:Poly I-C / Q000494:pharmacology; D061251:Primary Cell Culture; D020033:Protein Isoforms / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics*; D051193:Toll-Like Receptors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
D033942:Adaptor Proteins, Vesicular Transport; C111835:CCL2 protein, human; D018932:Chemokine CCL2; D020672:I-kappa B Proteins; C508600:IL6 protein, human; D015850:Interleukin-6; D016209:Interleukin-8; D055666:Lipopeptides; D008070:Lipopolysaccharides; C507779:MYD88 protein, human; D053594:Myeloid Differentiation Factor 88; C000606204:NFKBIA protein, human; C508075:Pam(3)CSK(4) peptide; D020033:Protein Isoforms; D034741:RNA, Small Interfering; C470409:TICAM1 protein, human; D051193:Toll-Like Receptors; D000072000:NF-KappaB Inhibitor alpha; C106335:macrophage stimulatory lipopeptide 2; D011070:Poly I-C