Casaubon L, Sajan M P, Rivas J, Powe J L, Standaert M L, Farese R V
Research Service, James A Haley Veterans Administration Medical Center and Department of Internal Medicine, University of South Florida College of Medicine, Tampa, FL, USA.
Diabetologia. 2006 Dec;49(12):3000-8. doi: 10.1007/s00125-006-0471-5. Epub 2006 Oct 7.
AIMS/HYPOTHESIS: Insulin-stimulated glucose transport in muscle is impaired in obesity and type 2 diabetes, but alterations in levels of relevant signalling factors, i.e. atypical protein kinase C (aPKC) and protein kinase B (PKB/Akt), are still uncertain. Clamp studies using maximal insulin concentrations have revealed defects in activation of aPKC, but not PKB, in both obese non-diabetic and obese diabetic subjects. In contrast, clamp studies using submaximal insulin concentrations revealed defects in PKB activation/phosphorylation in obese non-diabetic and diabetic subjects, but changes in aPKC were not reported. The aim of this study was to test the hypothesis that dose-related effects of insulin may account for the reported differences in insulin signalling to PKB in diabetic muscle.
We compared enzymatic activation of aPKC and PKB, and PKB phosphorylation (threonine-308 and serine-473) during hyperinsulinaemic-euglycaemic clamp studies using both submaximal (400-500 pmol/l) and maximal (1400 pmol/l) insulin levels in non-diabetic control and obese diabetic subjects.
In lean control subjects, the submaximal insulin concentration increased aPKC activity and glucose disposal to approximately 50% of the maximal level and PKBbeta activity to 25% of the maximal level, but PKBalpha activity was not increased. In these subjects, phosphorylation of PKBalpha and PKBbeta was increased to near-maximal levels at submaximal insulin concentrations. In obese diabetic subjects, whereas aPKC activation was defective at submaximal and maximal insulin concentrations, PKBbeta activation and the phosphorylation of PKBbeta and PKBalpha were defective at submaximal, but not maximal, insulin concentrations.
CONCLUSIONS/INTERPRETATIONS: Defective PKBbeta activation/phosphorylation, seen on submaximal insulin stimulation in diabetic muscle, may largely reflect impaired activation of insulin signalling factors present in concentrations greater than those needed for full PKB activation/phosphorylation. Defective aPKC activation, seen at all insulin levels, appears to reflect, at least partly, an impaired action of distal factors needed for aPKC activation, or poor aPKC responsiveness.
目的/假设：肥胖和2型糖尿病患者肌肉中胰岛素刺激的葡萄糖转运受损，但相关信号因子，即非典型蛋白激酶C（aPKC）和蛋白激酶B（PKB/Akt）水平的变化仍不确定。使用最大胰岛素浓度的钳夹研究显示，肥胖非糖尿病和肥胖糖尿病患者中aPKC的激活存在缺陷，但PKB无缺陷。相比之下，使用次最大胰岛素浓度的钳夹研究显示，肥胖非糖尿病和糖尿病患者中PKB的激活/磷酸化存在缺陷，但未报道aPKC的变化。本研究的目的是检验以下假设：胰岛素的剂量相关效应可能解释了糖尿病肌肉中胰岛素信号传导至PKB的差异。
我们在非糖尿病对照和肥胖糖尿病受试者中，使用次最大（400 - 500 pmol/l）和最大（1400 pmol/l）胰岛素水平进行高胰岛素-正常血糖钳夹研究，比较aPKC和PKB的酶促激活以及PKB磷酸化（苏氨酸-308和丝氨酸-473）情况。
在瘦的对照受试者中，次最大胰岛素浓度使aPKC活性和葡萄糖处置增加至最大水平的约50%，PKBβ活性增加至最大水平的25%，但PKBα活性未增加。在这些受试者中，次最大胰岛素浓度下PKBα和PKBβ的磷酸化增加至接近最大水平。在肥胖糖尿病受试者中，次最大和最大胰岛素浓度下aPKC激活均存在缺陷，次最大胰岛素浓度下PKBβ激活以及PKBβ和PKBα的磷酸化存在缺陷，但最大胰岛素浓度下无缺陷。
结论/解读：糖尿病肌肉在次最大胰岛素刺激下出现的PKBβ激活/磷酸化缺陷，可能主要反映了浓度高于完全激活/磷酸化PKB所需浓度的胰岛素信号因子激活受损。在所有胰岛素水平下均出现的aPKC激活缺陷，似乎至少部分反映了aPKC激活所需的远端因子作用受损，或aPKC反应性较差。
