del Aguila L F, Claffey K P, Kirwan J P
Noll Physiological Research Center, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Am J Physiol. 1999 May;276(5):E849-55. doi: 10.1152/ajpendo.1999.276.5.E849.
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.
诸如脓毒症和组织损伤等生理应激源会引发急性免疫反应，并导致短暂的全身性胰岛素抵抗。本研究旨在确定肿瘤坏死因子-α（TNF-α），一种在骨骼肌损伤期间由免疫细胞产生的细胞因子，是否会在细胞水平上降低胰岛素反应性。为了研究与TNF-α和胰岛素作用相关的分子机制，我们在培养的C2C12肌管中测量了胰岛素受体底物（IRS）-1和IRS-2介导的磷脂酰肌醇3-激酶（PI 3-激酶）激活、IRS-1与PI 3-激酶的结合、IRS-1酪氨酸磷酸化以及两种丝裂原活化蛋白激酶（MAPK，即p42(MAPK)和p44(MAPK)）的磷酸化。此外，我们还确定了TNF-α对胰岛素刺激的2-脱氧葡萄糖（2-DG）摄取的影响。我们观察到，TNF-α分别使IRS-1和IRS-2介导的PI 3-激酶激活的胰岛素刺激受损54%和55%（P < 0.05）。此外，TNF-α使胰岛素刺激的IRS-1酪氨酸磷酸化降低了40%（P < 0.05）。此外，TNF-α使胰岛素诱导的p42(MAPK)和p44(MAPK)酪氨酸磷酸化抑制了81%（P < 0.01）。TNF-α对胰岛素信号激活的损害伴随着肌肉细胞中2-DG摄取的减少（P < 0.05）（60±4对44±6 pmol·min-1·mg-1）。这些数据表明，TNF-α的增加可能通过抑制IRS-1和IRS-2介导的PI 3-激酶激活以及p42(MAPK)和p44(MAPK)酪氨酸磷酸化，导致骨骼肌中的胰岛素抵抗，从而损害胰岛素刺激的葡萄糖摄取。
