Glucose Regulates in Vivo Glucose-6-phosphatase Gene Expression in the Liver of Diabetic Rats

Abstract

Overproduction of glucose by the liver is the major cause of fasting hyperglycemia in both insulin-dependent and non-insulin-dependent diabetes mellitus. The distal enzymatic step in the process of glucose output is catalyzed by the glucose-6-phosphatase complex. We show here that 90% partially pancreatectomized diabetic rats have a >5-fold increase in the messenger RNA and a 3-4-fold increase in the protein level of the catalytic subunit of glucose-6-phosphatase in the liver. Normalization of the plasma glucose concentration in diabetic rats with either insulin or the glycosuric agent phlorizin normalized the hepatic glucose-6-phosphatase messenger RNA and protein within ∼8 h. Conversely, phlorizin failed to decrease hepatic glucose-6-phosphatase gene expression in diabetic rats when the fall in the plasma glucose concentration was prevented by glucose infusion. These data indicate that in vivo gene expression of glucose-6-phosphatase in the diabetic liver is regulated by glucose independently from insulin, and thus prolonged hyperglycemia may result in overproduction of glucose via increased expression of this protein. Overproduction of glucose by the liver is the major cause of fasting hyperglycemia in both insulin-dependent and non-insulin-dependent diabetes mellitus. The distal enzymatic step in the process of glucose output is catalyzed by the glucose-6-phosphatase complex. We show here that 90% partially pancreatectomized diabetic rats have a >5-fold increase in the messenger RNA and a 3-4-fold increase in the protein level of the catalytic subunit of glucose-6-phosphatase in the liver. Normalization of the plasma glucose concentration in diabetic rats with either insulin or the glycosuric agent phlorizin normalized the hepatic glucose-6-phosphatase messenger RNA and protein within ∼8 h. Conversely, phlorizin failed to decrease hepatic glucose-6-phosphatase gene expression in diabetic rats when the fall in the plasma glucose concentration was prevented by glucose infusion. These data indicate that in vivo gene expression of glucose-6-phosphatase in the diabetic liver is regulated by glucose independently from insulin, and thus prolonged hyperglycemia may result in overproduction of glucose via increased expression of this protein.