title: TNF-alpha impairs insulin signaling and insulin stimulation of glucose uptake in C2C12 muscle cells.
abstract: Physiological stressors such as sepsis and tissue damage initiate an acute immune response and cause transient systemic insulin resistance. This study was conducted to determine whether tumor necrosis factor-alpha (TNF-alpha), a cytokine produced by immune cells during skeletal muscle damage, decreases insulin responsiveness at the cellular level. To examine the molecular mechanisms associated with TNF-alpha and insulin action, we measured insulin receptor substrate (IRS)-1- and IRS-2-mediated phosphatidylinositol 3-kinase (PI 3-kinase) activation, IRS-1-PI 3-kinase binding, IRS-1 tyrosine phosphorylation, and the phosphorylation of two mitogen-activated protein kinases (MAPK, known as p42(MAPK) and p44(MAPK)) in cultured C2C12 myotubes. Furthermore, we determined the effects of TNF-alpha on insulin-stimulated 2-deoxyglucose (2-DG) uptake. We observed that TNF-alpha impaired insulin stimulation of IRS-1- and IRS-2-mediated PI 3-kinase activation by 54 and 55% (P < 0.05), respectively. In addition, TNF-alpha decreased insulin-stimulated IRS-1 tyrosine phosphorylation by 40% (P < 0.05). Furthermore, TNF-alpha repressed insulin-induced p42(MAPK) and p44(MAPK) tyrosine phosphorylation by 81% (P < 0.01). TNF-alpha impairment of insulin signaling activation was accompanied by a decrease (P < 0.05) in 2-DG uptake in the muscle cells (60 +/- 4 vs. 44 +/- 6 pmol. min-1. mg-1). These data suggest that increases in TNF-alpha may cause insulin resistance in skeletal muscle by inhibiting IRS-1- and IRS-2-mediated PI 3-kinase activation as well as p42(MAPK) and p44(MAPK) tyrosine phosphorylation, leading to impaired insulin-stimulated glucose uptake.
mesh_terms: D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002460:Cell Line; D003847:Deoxyglucose / Q000378:metabolism; D004789:Enzyme Activation; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D009132:Muscles / Q000187:drug effects* / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism / Q000494:pharmacology; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*