Trinh K Y, O'Doherty R M, Anderson P, Lange A J, Newgard C B
Gifford Laboratories for Diabetes Research and Departments of Biochemistry and Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75235, USA.
J Biol Chem. 1998 Nov 20;273(47):31615-20. doi: 10.1074/jbc.273.47.31615.
The terminal step in hepatic gluconeogenesis is catalyzed by glucose-6-phosphatase, an enzyme activity residing in the endoplasmic reticulum and consisting of a catalytic subunit (glucose-6-phosphatase (G6Pase)) and putative accessory transport proteins. We show that Zucker diabetic fatty rats (fa/fa), which are known to exhibit impaired suppression of hepatic glucose output, have 2.4-fold more glucose-6-phosphatase activity in liver than lean controls. To define the potential contribution of increased hepatic G6Pase to development of diabetes, we infused recombinant adenoviruses containing the G6Pase cDNA (AdCMV-G6Pase) or the beta-galactosidase gene into normal rats. Animals were studied by one of three protocols as follows: protocol 1, fed ad libitum for 7 days; protocol 2, fed ad libitum for 5 days, fasted overnight, and subjected to an oral glucose tolerance test; protocol 3, fed ad libitum for 4 days, fasted for 48 h, subjected to oral glucose tolerance test, and then allowed to refeed overnight. Hepatic glucose-6-phosphatase enzymatic activity was increased by 1.6-3-fold in microsomes isolated from AdCMV-G6Pase-treated animals in all three protocols, and the resultant metabolic profile was similar in each case. AdCMV-G6Pase-treated animals exhibited several of the abnormalities associated with early stage non-insulin-dependent diabetes mellitus, including glucose intolerance, hyperinsulinemia, decreased hepatic glycogen content, and increased peripheral (muscle) triglyceride stores. These animals also exhibited significant decreases in circulating free fatty acids and triglycerides, changes not normally associated with the disease. Our studies show that overexpression of G6Pase in liver is sufficient to perturb whole animal glucose and lipid homeostasis, possibly contributing to the development of metabolic abnormalities associated with diabetes.
肝糖异生的终末步骤由葡萄糖-6-磷酸酶催化，该酶活性存在于内质网中，由一个催化亚基（葡萄糖-6-磷酸酶（G6Pase））和假定的辅助转运蛋白组成。我们发现，已知表现出肝葡萄糖输出抑制受损的Zucker糖尿病脂肪大鼠（fa/fa）肝脏中的葡萄糖-6-磷酸酶活性比瘦对照高2.4倍。为了确定肝脏G6Pase增加对糖尿病发展的潜在贡献，我们将含有G6Pase cDNA（AdCMV-G6Pase）或β-半乳糖苷酶基因的重组腺病毒注入正常大鼠体内。通过以下三种方案之一对动物进行研究：方案1，随意进食7天；方案2，随意进食5天，禁食过夜，并进行口服葡萄糖耐量试验；方案3，随意进食4天，禁食48小时，进行口服葡萄糖耐量试验，然后允许过夜再喂养。在所有三种方案中，从AdCMV-G6Pase处理的动物中分离的微粒体中，肝葡萄糖-6-磷酸酶的酶活性增加了1.6至3倍，并且每种情况下产生的代谢谱相似。AdCMV-G6Pase处理的动物表现出与早期非胰岛素依赖型糖尿病相关的几种异常，包括葡萄糖不耐受、高胰岛素血症、肝糖原含量降低和外周（肌肉）甘油三酯储存增加。这些动物的循环游离脂肪酸和甘油三酯也显著降低，这些变化通常与该疾病无关。我们的研究表明，肝脏中G6Pase的过表达足以扰乱整个动物的葡萄糖和脂质稳态，可能导致与糖尿病相关的代谢异常的发展。
