Effects of Insulin and Transgenic Overexpression of UDP-glucose Pyrophosphorylase on UDP-glucose and Glycogen Accumulation in Skeletal Muscle Fibers

Thomas H. Reynolds; Yunbae Pak; Thurl E. Harris; Jill Manchester; Eugene J. Barrett; John C. Lawrence

doi:10.1074/jbc.M413614200

Effects of Insulin and Transgenic Overexpression of UDP-glucose Pyrophosphorylase on UDP-glucose and Glycogen Accumulation in Skeletal Muscle Fibers*

Departments of ^‡Pharmacology and ^**Medicine, University of Virginia School of Medicine, Charlottesville, Virginia 22908, the ^§Department of Exercise and Sport Sciences, Ithaca College, Ithaca, New York 14850, the ^¶Department of Biochemistry, Gyeongsang National University, Jinju 666-701, Korea, and the ^∥Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110

↵‡‡ To whom correspondence should be addressed: Dept. of Pharmacology, P. O. Box 800735, 1300 Jefferson Park Ave., Charlottesville, VA 22908-0735. Tel.: 434-924-1584; Fax: 434-982-3575; E-mail: jcl3p{at}virginia.edu.

Abstract

UDP-glucose (UDP-Glc) and glycogen levels in skeletal muscle fibers of defined fiber type were measured using microanalytical methods. Infusing rats with insulin increased glycogen in both Type I and Type II fibers. Insulin was without effect on UDP-Glc in Type I fibers but decreased UDP-Glc by 35–40% in Type IIA/D and Type IIB fibers. The reduction in UDP-Glc suggested that UDP-Glc pyrophosphorylase (PPL) activity might limit glycogen synthesis in response to insulin. To explore this possibility, we generated mice overexpressing a UDP-Glc PPL transgene in skeletal muscle. The transgene increased both UDP-Glc PPL activity and levels of UDP-Glc in skeletal muscles by ∼3-fold. However, overexpression of UDP-Glc PPL was without effect on either the levels of skeletal muscle glycogen or glucose tolerance in vivo. The transgene was also without effect on either control or insulin-stimulated rates of ¹⁴C-glucose incorporation into glycogen in muscles incubated in vitro. The results indicate that UDP-Glc PPL activity is not limiting for glycogen synthesis.