The regulation of glycogen metabolism is deranged in both Type I and Type II diabetes mellitus. Glycogen metabolism is impaired in insulin- sensitive tissues, primarily in skeletal muscle and liver, so that the synthesis of this glucose storage compound is inadequate to meet the demands of hyperglycemia. Glycogenin is a self-glycosylating enzyme which has recently been shown to serve as the core protein for glycogen synthesis by transferring glucose to itself to form a protein-linked oligosaccharide chain which serves as a primer for glycogen synthase to assemble the glycogen molecule. We have recently demonstrated that several alkylglycosides serve as acceptors for glucose transfer mediated by enzyme preparations of both glycogenin and glycogen synthase and have shown that these compounds increase glucose incorporation in liver and diaphragm of mice. They therefore have the potential to serve as artificial primers for the synthesis of glycogen. The principal objective of this proposal is to demonstrate that alkylglucosides and alkylmaltosides can initiate the synthesis of alpha 1 greater than 4 linked maltooligosaccharide chains in cultured skeletal muscle (L6) and liver (HEP-G2) cells and thereby modulate the synthesis of glycogen in these cells.We propose to determine the activities of glycogenin and glycogen synthesis in cell-free extracts of these cells and demonstrate that the alkylglycosides will serve as substrates for glucose transfer by these enzymes. We will then establish that the alkylglycosides will serve as acceptor substrates for glucose addition in intact cells and characterize the alkylmaltooligosaccharide products produced as a result of such addition. The effects of alkylglycosides on glycogenin and glycogen synthase activities and on glycogen synthesis will also be determined as will the effects on glucose transport and the influence of ambient glucose concentrations and insulin on the glucosylation of alkylglycosides and on glycogen synthesis in these cells. Any effects of the alkylglycosides on the molecular size and structure of glycogen synthesized will also be investigated. Significant findings in cultured cells will be correlated with the effects of the compounds in vivo in the ob/ob mouse model of NIDDM. The goal of these studies will be to elucidate how the alkylglycosides serve as exogenous acceptors for glucose transfer mediated by glycogenin and glycogen synthase in intact cells and therefore initiate and/or modulate the biosynthesis of glycogen. These studies may have therapeutic implications for modulating the disposal of glucose in diabetes.
| Gundlach, M; Oluwole, S F; D'Agati, V et al. (1992) Differential effects of pretreatment with ultraviolet-B modified or unmodified donor-specific leukocyte transfusions on intestinal and cardiac allograft survival in the rat. Transplantation 53:613-9 |
