title: JNK and tumor necrosis factor-alpha mediate free fatty acid-induced insulin resistance in 3T3-L1 adipocytes.
abstract: Lipid infusion and high fat feeding are established causes of systemic and adipose tissue insulin resistance. In this study, we treated 3T3-L1 adipocytes with a mixture of free fatty acids (FFAs) to investigate the molecular mechanisms underlying fat-induced insulin resistance. FFA treatment impaired insulin receptor-mediated signal transduction and decreased insulin-stimulated GLUT4 translocation and glucose transport. FFAs activated the stress/inflammatory kinases c-Jun N-terminal kinase (JNK) and IKKbeta, and the suppressor of cytokine signaling protein 3, increased secretion of the inflammatory cytokine tumor necrosis factor (TNF)-alpha, and decreased secretion of adiponectin into the medium. RNA interference-mediated down-regulation of JNK blocked JNK activation and prevented most of the FFA-induced defects in insulin action. Blockade of TNF-alpha signaling with neutralizing antibodies to TNF-alpha or its receptors or with a dominant negative TNF-alpha peptide had a partial effect to inhibit FFA-induced cellular insulin resistance. We found that JNK activation by FFAs was not inhibited by blocking TNF-alpha signaling, whereas the FFA-induced increase in TNF-alpha secretion was inhibited by RNA interference-mediated JNK knockdown. Together, these results indicate that 1) JNK can be activated by FFAs through TNF-alpha-independent mechanisms, 2) activated JNK is a major contributor to FFA-induced cellular insulin resistance, and 3) TNF-alpha is an autocrine/paracrine downstream effector of activated JNK that can also mediate insulin resistance.
authors.affiliation: Division of Endocrinology-Metabolism, University of California, San Diego, La Jolla, California 92093-0673, USA.
authors.forename: M T Audrey
authors.initials: MT
authors.lastname: Nguyen
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Satoh
authors.forename: Svetlana
authors.initials: S
authors.lastname: Favelyukis
authors.forename: Jennie L
authors.initials: JL
authors.lastname: Babendure
authors.forename: Takeshi
authors.initials: T
authors.lastname: Imamura
authors.forename: Juan I
authors.initials: JI
authors.lastname: Sbodio
authors.forename: Jonathan
authors.initials: J
authors.lastname: Zalevsky
authors.forename: Bassil I
authors.initials: BI
authors.lastname: Dahiyat
authors.forename: Nai-Wen
authors.initials: NW
authors.lastname: Chi
authors.forename: Jerrold M
authors.initials: JM
authors.lastname: Olefsky
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000378:metabolism; D052242:Adiponectin / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D015153:Blotting, Western; D002454:Cell Differentiation; D003847:Deoxyglucose / Q000378:metabolism; D015536:Down-Regulation; D004789:Enzyme Activation; D004797:Enzyme-Linked Immunosorbent Assay; D005230:Fatty Acids, Nonesterified / Q000378:metabolism*; D005799:Genes, Dominant; D005947:Glucose / Q000378:metabolism; D051275:Glucose Transporter Type 4; D051550:I-kappa B Kinase / Q000378:metabolism; D007249:Inflammation; D007328:Insulin / Q000378:metabolism; D007333:Insulin Resistance; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008055:Lipids / Q000737:chemistry; D048670:MAP Kinase Kinase 4 / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D021381:Protein Transport; D034622:RNA Interference; D015398:Signal Transduction; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000378:metabolism; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism / Q000502:physiology*
chemical_list: D052242:Adiponectin; D005230:Fatty Acids, Nonesterified; D051275:Glucose Transporter Type 4; D007328:Insulin; D008055:Lipids; C495693:Slc2a4 protein, mouse; C491411:Socs3 protein, mouse; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D014409:Tumor Necrosis Factor-alpha; D003847:Deoxyglucose; D051550:I-kappa B Kinase; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D005947:Glucose