Toll-like receptor ligands cause proinflammatory and prodiabetic activation of adipocytes via phosphorylation of extracellular signal-regulated kinase and c-Jun N-terminal kinase but not interferon regulatory factor-3.
Here, we aim to investigate the mechanisms of Toll-like receptor (TLR)-induced prodiabetic and proinflammatory activation of adipocytes and to detect differences in the responsiveness of TLRs to their respective ligands between adipocytes isolated from inflamed vs. noninflamed adipose tissue. Experiments using specific ligands for all known TLRs were performed in murine 3T3-L1 adipocytes and in human adipocytes isolated from noninflamed and inflamed adipose tissue. IL-6 and monocyte chemoattractant protein-1 (MCP-1) release were measured by ELISA. The expression of the signal transduction proteins phospho-extracellular signal-regulated kinase (P-Erk), P-c-Jun N-terminal kinase (JNK), and P-interferon regulatory factor-3 was investigated by Western blot analysis. Additionally, functional inhibitors of MAPK kinase-1/-2 and JNK-1/-2 were used in the stimulation experiments. Activation of TRL4 by lipopolysaccharide (LPS) and TLR1/2 by Pam(3)Cys up-regulates IL-6 and MCP-1 release in adipocytes via specific activation of Erk. Stimulation of adipocytes by macrophage activating lipopeptide-2 (MALP-2) induces MCP-1 but has no effect on IL-6 release. This stimulatory effect on MCP-1 release is antagonized by inhibition of both mitogen-activated protein kinase-1/-2 and JNK-1/-2. Phosphorylation of Erk and JNK is up-regulated after stimulation by MALP-2. In human adipocytes isolated from noninflamed adipose tissue, LPS and Pam(3)Cys, but not MALP-2, are potent inducers of IL-6 and MCP-1. MALP-2 is able to induce IL-6 and MCP-1 release in adipocytes isolated from inflamed adipose tissue, whereas these adipocytes lost their ability to respond to LPS. The present results point to a role of the adipose tissue in innate immunity. TLR-ligand-induced proinflammatory and prodiabetic activation of adipocytes might couple visceral adipose tissue dysfunction with insulin resistance and type 2 diabetes mellitus.
Department of Internal Medicine I, University of Regensburg, D-93042 Regensburg, Germany.
Andrea
A
Kopp
Christa
C
Buechler
Margarita
M
Bala
Markus
M
Neumeier
Juergen
J
Schölmerich
Andreas
A
Schäffler
D041721:3T3-L1 Cells; D017667:Adipocytes / Q000378:metabolism*; D000273:Adipose Tissue / Q000276:immunology / Q000378:metabolism; D000328:Adult; D000818:Animals; D000873:Anthracenes; D002070:Butadienes; D018932:Chemokine CCL2 / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D006801:Humans; D007249:Inflammation / Q000378:metabolism; D007328:Insulin / Q000378:metabolism; D050838:Interferon Regulatory Factor-3 / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism*; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D008070:Lipopolysaccharides; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048370:MAP Kinase Kinase 2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D020935:MAP Kinase Signaling System; D008297:Male; D051379:Mice; D053594:Myeloid Differentiation Factor 88; D009570:Nitriles; D010766:Phosphorylation; D012333:RNA, Messenger / Q000378:metabolism; D051193:Toll-Like Receptors / Q000378:metabolism*
D000873:Anthracenes; D002070:Butadienes; C491768:Ccl2 protein, mouse; D018932:Chemokine CCL2; D007328:Insulin; D050838:Interferon Regulatory Factor-3; D015850:Interleukin-6; C494233:Irf3 protein, mouse; D008070:Lipopolysaccharides; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D009570:Nitriles; D012333:RNA, Messenger; D051193:Toll-Like Receptors; C113580:U 0126; C432165:pyrazolanthrone; D048049:Extracellular Signal-Regulated MAP Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2