Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK.
Institute of Molecular Cell and Systems Biology, University of Glasgow, Glasgow, UK.
Endocrinol Diabetes Metab. 2022 Sep;5(5):e361. doi: 10.1002/edm2.361. Epub 2022 Aug 14.
The regulated delivery of the glucose transporter GLUT4 from intracellular stores to the plasma membrane underpins insulin-stimulated glucose transport. Insulin-stimulated glucose transport is impaired in skeletal muscle of patients with type-2 diabetes, and this may arise because of impaired intracellular trafficking of GLUT4. However, molecular details of any such impairment have not been described. We hypothesized that GLUT4 and/or levels of proteins involved in intracellular GLUT4 trafficking may be impaired in skeletal muscle in type-2 diabetes and tested this in obese individuals without and without type-2 diabetes.
We recruited 12 participants with type-2 diabetes and 12 control participants. All were overweight or obese with BMI of 25-45 kg/m . Insulin sensitivity was measured using an insulin suppression test (IST), and vastus lateralis biopsies were taken in the fasted state. Cell extracts were immunoblotted to quantify levels of a range of proteins known to be involved in intracellular GLUT4 trafficking.
Obese participants with type-2 diabetes exhibited elevated fasting blood glucose and increased steady state glucose infusion rates in the IST compared with controls. Consistent with this, skeletal muscle from those with type-2 diabetes expressed lower levels of GLUT4 (30%, p = .014). Levels of Syntaxin4, a key protein involved in GLUT4 vesicle fusion with the plasma membrane, were similar between groups. By contrast, we observed reductions in levels of Syntaxin16 (33.7%, p = 0.05), Sortilin (44%, p = .006) and Sorting Nexin-1 (21.5%, p = .039) and -27 (60%, p = .001), key proteins involved in the intracellular sorting of GLUT4, in participants with type-2 diabetes.
We report significant reductions of proteins involved in the endosomal trafficking of GLUT4 in skeletal muscle in obese people with type 2 diabetes compared with age- and weight-matched controls. These abnormalities of intracellular GLUT4 trafficking may contribute to reduced whole body insulin sensitivity.
葡萄糖转运蛋白 GLUT4 从细胞内储存到质膜的调节释放是胰岛素刺激葡萄糖转运的基础。2 型糖尿病患者的骨骼肌胰岛素刺激葡萄糖转运受损，这可能是由于 GLUT4 的细胞内转运受损所致。然而，尚未描述任何此类损伤的分子细节。我们假设 2 型糖尿病患者的骨骼肌中 GLUT4 及其/或参与细胞内 GLUT4 转运的蛋白质水平可能受损，并在超重或肥胖且 BMI 为 25-45kg/m 的非 2 型糖尿病患者和 2 型糖尿病患者中对此进行了测试。
我们招募了 12 名 2 型糖尿病患者和 12 名对照参与者。所有参与者的 BMI 均在 25-45kg/m 之间，超重或肥胖。使用胰岛素抑制试验（IST）测量胰岛素敏感性，并在空腹状态下取股外侧肌活检。细胞提取物通过免疫印迹进行定量，以定量测定已知参与细胞内 GLUT4 转运的一系列蛋白质的水平。
与对照组相比，患有 2 型糖尿病的肥胖参与者的空腹血糖升高，IST 中的稳态葡萄糖输注率增加。与此一致的是，2 型糖尿病患者的骨骼肌中 GLUT4 表达水平较低（30%，p=0.014）。网格蛋白 4（一种参与 GLUT4 囊泡与质膜融合的关键蛋白）的水平在两组之间相似。相比之下，我们观察到Syntaxin16 的水平降低（33.7%，p=0.05），Sortilin（44%，p=0.006）和 Sorting Nexin-1（21.5%，p=0.039）和-27（60%，p=0.001），这些是参与 GLUT4 细胞内分拣的关键蛋白，在 2 型糖尿病患者中。
我们报告了与年龄和体重匹配的对照组相比，肥胖的 2 型糖尿病患者的骨骼肌中 GLUT4 内体转运所涉及的蛋白质显著减少。这些细胞内 GLUT4 转运异常可能导致全身胰岛素敏感性降低。
