PERTURBATION OF FUEL HOMEOSTASIS CAUSED BY OVEREXPRESSION OF THE GLUCOSE-6-PHOSPHATASE CATALYTIC SUBUNIT IN LIVER OF NORMAL RATS

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 diabe tic fatty rats (fa/fa), which are known to exhibit impaired suppressio n of hepatic glucose output, have 2.4-fold more glucose-6-phosphatase activity in liver than lean controls. To define the potential contribu tion of increased hepatic G6Pase to development of diabetes, we infuse d recombinant adenoviruses containing the G6Pase cDNA (AdCMV-G6Pase) o r the beta-galactosidase gene into normal rats. Animals were studied b y one of three protocols as follows: protocol I, fed ad libitum for 7 days; protocol 2, fed ad libitum for 5 days, fasted overnight, and sub jected to an oral glucose tolerance test; protocol 3, fed ad libitum f or 4 days, fasted for 48 h, subjected to oral glucose tolerance test, and then allowed to refeed overnight. Hepatic glucose-6-phosphatase en zymatic activity was increased by 1.6-3-fold in microsomes isolated fr om AdCMV-G6Pase-treated animals in all three protocols, and the result ant metabolic profile was similar in each case. AdCMV-GGPase-treated a nimals exhibited several of the abnormalities associated with early st age non-insulin-dependent diabetes mellitus, including glucose intoler ance, hyperinsulinemia, decreased hepatic glycogen content, and increa sed peripheral (muscle) triglyceride stores, These animals also exhibi ted significant decreases in circulating free fatty acids and triglyce rides, changes not normally associated with the disease. Our studies s how that overexpression of G6Pase in liver is sufficient to perturb wh ole animal glucose and lipid homeostasis, possibly contributing to the development of metabolic abnormalities associated with diabetes.