Departments of Internal Medicine and Cellular and Molecular Physiology and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06536, USA.
Proc Natl Acad Sci U S A. 2011 Apr 5;108(14):5748-52. doi: 10.1073/pnas.1103451108. Epub 2011 Mar 21.
Mice overexpressing acylCoA:diacylglycerol (DAG) acyltransferase 2 in the liver (Liv-DGAT2) have been shown to have normal hepatic insulin responsiveness despite severe hepatic steatosis and increased hepatic triglyceride, diacylglycerol, and ceramide content, demonstrating a dissociation between hepatic steatosis and hepatic insulin resistance. This led us to reevaluate the role of DAG in causing hepatic insulin resistance in this mouse model of severe hepatic steatosis. Using hyperinsulinemic-euglycemic clamps, we studied insulin action in Liv-DGAT2 mice and their wild-type (WT) littermate controls. Here, we show that Liv-DGAT2 mice manifest severe hepatic insulin resistance as reflected by decreased suppression of endogenous glucose production (0.8 ± 41.8 vs. 87.7 ± 34.3% in WT mice, P < 0.01) during the clamps. Hepatic insulin resistance could be attributed to an almost 12-fold increase in hepatic DAG content (P < 0.01) resulting in a 3.6-fold increase in protein kinase Cε (PKCε) activation (P < 0.01) and a subsequent 52% decrease in insulin-stimulated insulin receptor substrate 2 (IRS-2) tyrosine phosphorylation (P < 0.05), as well as a 64% decrease in fold increase pAkt/Akt ratio from basal conditions (P < 0.01). In contrast, hepatic insulin resistance in these mice was not associated with increased endoplasmic reticulum (ER) stress or inflammation. Importantly, hepatic insulin resistance in Liv-DGAT2 mice was independent of differences in body composition, energy expenditure, or food intake. In conclusion, these findings strengthen the link between hepatic steatosis and hepatic insulin resistance and support the hypothesis that DAG-induced PKCε activation plays a major role in nonalcoholic fatty liver disease (NAFLD)-associated hepatic insulin resistance.
肝脏过表达酰基辅酶 A：二酰基甘油（DAG）酰基转移酶 2 的小鼠（Liv-DGAT2）尽管存在严重的肝脂肪变性和肝甘油三酯、二酰基甘油和神经酰胺含量增加，但仍具有正常的肝胰岛素反应性，表明肝脂肪变性和肝胰岛素抵抗之间存在分离。这促使我们重新评估 DAG 在严重肝脂肪变性的这种小鼠模型中引起肝胰岛素抵抗的作用。我们使用高胰岛素-正葡萄糖钳夹技术研究了 Liv-DGAT2 小鼠及其野生型（WT）同窝对照小鼠的胰岛素作用。在这里，我们表明 Liv-DGAT2 小鼠表现出严重的肝胰岛素抵抗，表现在钳夹期间内源性葡萄糖产生的抑制作用降低（0.8±41.8%比 WT 小鼠的 87.7±34.3%，P<0.01）。肝胰岛素抵抗可归因于肝 DAG 含量增加近 12 倍（P<0.01），导致蛋白激酶 Cε（PKCε）激活增加 3.6 倍（P<0.01），随后胰岛素刺激的胰岛素受体底物 2（IRS-2）酪氨酸磷酸化降低 52%（P<0.05），以及基础条件下 pAkt/Akt 比值的增加倍数降低 64%（P<0.01）。相比之下，这些小鼠的肝胰岛素抵抗与内质网（ER）应激或炎症无关。重要的是，Liv-DGAT2 小鼠的肝胰岛素抵抗与身体成分、能量消耗或食物摄入的差异无关。总之，这些发现加强了肝脂肪变性和肝胰岛素抵抗之间的联系，并支持 DAG 诱导的 PKCε 激活在非酒精性脂肪性肝病（NAFLD）相关肝胰岛素抵抗中起主要作用的假说。
