Wang Hong, Wang Aileen X, Barrett Eugene J
Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Virginia Health System, Charlottesville, Virginia 22908, USA.
Mol Endocrinol. 2012 Aug;26(8):1327-38. doi: 10.1210/me.2012-1003. Epub 2012 Jun 25.
Insulin's trans-endothelial transport (TET) is critical for its metabolic action on muscle and involves trafficking of insulin bound to its receptor (or at high insulin concentrations, the IGF-I receptor) via caveolae. However, whether caveolae-mediated insulin TET involves actin cytoskeleton organization is unknown. Here we address whether insulin regulates actin filament organization in bovine aortic endothelial cells (bAEC) and whether this affects insulin uptake and TET. We found that insulin induced extensive cortical actin filament remodeling within 5 min. This remodeling was inhibited not only by disruption of actin microfilament organization but also by inhibition of phosphatidylinositol 3-kinase (PI3K) or by disruption of lipid rafts using respective specific inhibitors. Knockdown of either caveolin-1 or Akt using specific small interfering RNA also eliminated the insulin-induced cortical actin filament remodeling. Blocking either actin microfilament organization or PI3K pathway signaling inhibited both insulin uptake and TET. Disruption of actin microfilament organization also reduced the caveolin-1, insulin receptor, and IGF-I receptor located at the plasma membrane. Exposing bAEC for 6 h to either TNFα or IL-6 blocked insulin-induced cortical actin remodeling. Extended exposure (24 h) also inhibited actin expression at both mRNA and protein levels. We conclude that insulin-induced cortical actin filament remodeling in bAEC is required for insulin's TET in a PI3K/Akt and plasma membrane lipid rafts/caveolae-dependent fashion, and proinflammatory cytokines TNFα and IL-6 block this process.
胰岛素的跨内皮转运（TET）对其在肌肉上的代谢作用至关重要，且涉及胰岛素与其受体（或在高胰岛素浓度下，胰岛素样生长因子-I受体）结合后通过小窝进行的转运。然而，小窝介导的胰岛素TET是否涉及肌动蛋白细胞骨架组织尚不清楚。在此，我们探讨胰岛素是否调节牛主动脉内皮细胞（bAEC）中的肌动蛋白丝组织，以及这是否影响胰岛素摄取和TET。我们发现胰岛素在5分钟内诱导广泛的皮质肌动蛋白丝重塑。这种重塑不仅受到肌动蛋白微丝组织破坏的抑制，还受到磷脂酰肌醇3激酶（PI3K）抑制或使用各自特异性抑制剂破坏脂筏的抑制。使用特异性小干扰RNA敲低小窝蛋白-1或Akt也消除了胰岛素诱导的皮质肌动蛋白丝重塑。阻断肌动蛋白微丝组织或PI3K途径信号传导均抑制胰岛素摄取和TET。肌动蛋白微丝组织的破坏也减少了位于质膜的小窝蛋白-1、胰岛素受体和胰岛素样生长因子-I受体。将bAEC暴露于肿瘤坏死因子α（TNFα）或白细胞介素-6（IL-6）6小时可阻断胰岛素诱导的皮质肌动蛋白重塑。延长暴露（24小时）也在mRNA和蛋白质水平上抑制肌动蛋白表达。我们得出结论，bAEC中胰岛素诱导的皮质肌动蛋白丝重塑以PI3K/Akt和质膜脂筏/小窝依赖性方式是胰岛素TET所必需的，且促炎细胞因子TNFα和IL-6阻断这一过程。
