The enzyme glucokinase (GK) plays a central role in glucose homeostasis. Hepatic GK activity is acutely controlled by the action of the GK regulatory protein (GKRP). In vitro evidence suggests that GKRP reversibly binds to GK and inhibits its activity; however, less is known about the in vivo function of GKRP. To further explore the physiological role of GKRP in vivo, we used an E1/E2a/E3-deficient adenoviral vector containing the cDNA encoding human GKRP (Av3hGKRP). High fat diet–induced diabetic mice were administered Av3hGKRP or a control vector lacking a transgene (Av3Null). Surprisingly, the Av3hGKRP-treated mice showed a significant improvement in glucose tolerance and had lower fasting blood glucose levels than Av3Null-treated mice. A coincident decrease in insulin levels indicated that the Av3hGKRP-treated mice had sharply improved insulin sensitivity. These mice also exhibited lower leptin levels, reduced body weight, and decreased liver GK activity. In vitro experiments indicated that GKRP was able to increase both GK protein and enzymatic activity levels, suggesting that another role for GKRP is to stabilize and/or protect GK. These data are the first to indicate the ability of GKRP to treat type 2 diabetes and therefore have significant implications for future therapies of this disease.
Address correspondence and reprint requests to Eric D. Slosberg, Novartis Institute for Biomedical Research, Metabolic and Cardiovascular Diseases, 556 Morris Avenue, Summit, NJ 07901. E-mail:.
Received for publication 22 December 2000 and accepted in revised form 13 April 2001.
B.F. is an employee of Novartis Pharmaceutical Corporation, and E.D.S., I.S.T., S.L.C., and B.R.B. are paid employees and stockholders of Novartis Pharmaceutical. U.J.D., S.C., and M.K. are employees of Genetic Therapy, a Novartis Company. Novartis Pharmaceutical and Genetic Therapy manufacture and market pharmaceuticals related to the treatment of diabetes and its complications.
ALT, alanine aminotransferase; AUC, area under the curve; GK, glucokinase; GKRP, glucokinase regulatory protein; HBSS, Hanks’ balanced salt solution; HF, high-fat diet; LF, control diet; OGTT, oral glucose tolerance test; PTG, protein targeting to glycogen; RSV, Rous sarcoma virus.