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

• Published in: Endocrinology (Philadelphia) 2010-03, Vol.151 (3), p.1097-1108
• Main Authors: Kopp, Andrea, Buechler, Christa, Bala, Margarita, Neumeier, Markus, Schölmerich, Juergen, Schäffler, Andreas
• Format: Article
• Language: English
• Subjects: 3T3-L1 Cells; Activation analysis; Adipocytes; Adipocytes - metabolism; Adipose tissue; Adipose Tissue - immunology; Adipose Tissue - metabolism; Adult; Animals; Anthracenes; Biological and medical sciences; Body fat; Butadienes; c-Jun protein; Cell activation; Chemokine CCL2 - metabolism; Diabetes mellitus; Diabetes mellitus (non-insulin dependent); Extracellular signal-regulated kinase; Extracellular Signal-Regulated MAP Kinases - metabolism; Female; Fundamental and applied biological sciences. Psychology; Humans; Immune system; Inflammation; Inflammation - metabolism; Innate immunity; Insulin - metabolism; Insulin resistance; Interferon; Interferon regulatory factor; Interferon Regulatory Factor-3 - metabolism; Interleukin 6; Interleukin-6 - metabolism; JNK Mitogen-Activated Protein Kinases - antagonists & inhibitors; JNK Mitogen-Activated Protein Kinases - metabolism; JNK protein; Kinases; Ligands; Lipopolysaccharides; Macrophages; Male; MALP2 protein; MAP kinase; MAP Kinase Kinase 1 - antagonists & inhibitors; MAP Kinase Kinase 1 - metabolism; MAP Kinase Kinase 2 - antagonists & inhibitors; MAP Kinase Kinase 2 - metabolism; MAP Kinase Signaling System; Mice; Monocyte chemoattractant protein; Monocyte chemoattractant protein 1; Monocytes; Myeloid Differentiation Factor 88; Nitriles; Phosphorylation; Proteins; RNA, Messenger - metabolism; Signal transduction; Stimulation; Toll-like receptors; Toll-Like Receptors - metabolism; Transcription factors; Vertebrates: endocrinology
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/en.2009-1140

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 Pam3Cys 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 Pam3Cys, 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. Stimulation of adipocytes by multiple Toll-like receptor ligands causes a characteristic pro-inflammatory and pro-diabetic activation that couples visceral adipose tissue dysfunction with insulin resistance.