Muscle Biology Laboratory, School of Kinesiology, University of Michigan, Ann Arbor, MI, USA.
Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, USA.
Sci Rep. 2016 Dec 14;6:39230. doi: 10.1038/srep39230.
AKT1 and AKT2, the AKT isoforms that are highly expressed in skeletal muscle, have distinct and overlapping functions, with AKT2 more important for insulin-stimulated glucose metabolism. In adipocytes, AKT2 versus AKT1 has greater susceptibility for insulin-mediated redistribution from cytosolic to membrane localization, and insulin also causes subcellular redistribution of AKT Substrate of 160 kDa (AS160), an AKT2 substrate and crucial mediator of insulin-stimulated glucose transport. Although skeletal muscle is the major tissue for insulin-mediated glucose disposal, little is known about AKT1, AKT2 or AS160 subcellular localization in skeletal muscle. The major aim of this study was to determine insulin's effects on the subcellular localization and phosphorylation of AKT1, AKT2 and AS160 in skeletal muscle. Rat skeletal muscles were incubated ex vivo ± insulin, and differential centrifugation was used to isolate cytosolic and membrane fractions. The results revealed that: 1) insulin increased muscle membrane localization of AKT2, but not AKT1; 2) insulin increased AKT2 phosphorylation in the cytosol and membrane fractions; 3) insulin increased AS160 localization to the cytosol and membranes; and 4) insulin increased AS160 phosphorylation in the cytosol, but not membranes. These results demonstrate distinctive insulin effects on the subcellular redistribution of AKT2 and its substrate AS160 in skeletal muscle.
AKT1 和 AKT2 是在骨骼肌中高度表达的 AKT 同工型，具有不同但重叠的功能，AKT2 对胰岛素刺激的葡萄糖代谢更为重要。在脂肪细胞中，AKT2 比 AKT1 更容易受到胰岛素介导的从细胞质到膜定位的重新分布的影响，胰岛素还导致 AKT 底物 160kDa (AS160) 的亚细胞重新分布，AS160 是 AKT2 的底物，也是胰岛素刺激葡萄糖转运的关键介质。虽然骨骼肌是胰岛素介导的葡萄糖消耗的主要组织，但对骨骼肌中 AKT1、AKT2 或 AS160 的亚细胞定位知之甚少。本研究的主要目的是确定胰岛素对骨骼肌中 AKT1、AKT2 和 AS160 的亚细胞定位和磷酸化的影响。离体培养大鼠骨骼肌，进行差速离心以分离细胞质和膜部分。结果表明：1）胰岛素增加了肌肉膜定位的 AKT2，但不增加 AKT1；2）胰岛素增加了细胞质和膜部分 AKT2 的磷酸化；3）胰岛素增加了 AS160 向细胞质和膜的定位；4）胰岛素增加了细胞质中，但不是膜中的 AS160 磷酸化。这些结果表明胰岛素对骨骼肌中 AKT2 及其底物 AS160 的亚细胞再分布具有独特的影响。
