TNF-alpha impairs insulin signaling and insulin stimulation of glucose uptake in C2C12 muscle cells

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, decrea ses insulin responsiveness at the cellular level. To examine the molecular mechanisms associated with TNF-alpha and insulin action, we measured insuli n receptor substrate (IRS)-1- and IRS-2-mediated phosphatidylinositol 3-kin ase (PI 3-kinase) activation, IRS-1-PI 3-kinase binding, IRS-1 tyrosine pho sphorylation, and the phosphorylation of two mitogen-activated protein kina ses (MAPK, known as p42(MAPK) and p44(MAPK)) in cultured C2C12 myotubes. Fu rthermore, we determined the effects of TNF-alpha on insulin-stimulated a-d eoxyglucose (2-DG) uptake. We observed that TNF-alpha impaired insulin stim ulation of IRS-1- and IRS-alpha-mediated PI S-kinase activation by 54 and 5 5% (P < 0.05), respectively. In addition, TNF-alpha decreased insulin-stimu lated IRS-I tyrosine phosphorylation by 40% (P < 0.05). Furthermore, TNF-al pha repressed insulin-induced p42(MAPK) and p44(MAPK) tyrosine phosphorylat ion 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 cell s (60 +/- 4 vs. 44 +/- 6 pmol min(-1) mg(-1)). These data suggest that incr eases in TNF-alpha may cause insulin resistance in skeletal muscle by inhib iting IRS-1- and IRS-2-mediated PI 3-kinase activation as well as p42MAPK a nd p44MAPK tyrosine phosphorylation, leading to impaired insulin-stimulated glucose uptake.