Development of glucose-induced insulin resistance in muscle requires protein synthesis

Muscles and fat cells develop insulin resistance when exposed to high conce ntrations of glucose and insulin. We used an isolated muscle preparation in cubated with high levels of glucose and insulin to further evaluate how glu cose-induced insulin resistance (GIIR) is mediated. Incubation with 2 milli units/ml insulin and 36 mM glucose for 5 h resulted in an similar to 50% de crease in insulin-stimulated muscle glucose transport. The decrease in insu lin responsiveness of glucose transport induced by glucose was not due to i mpaired insulin signaling, as insulin-stimulated phosphatidylinositol 3-kin ase activity and protein kinase B phosphorylation were not reduced, It has been hypothesized that entry of glucose into the hexosamine biosynthetic pa thway with accumulation of UDP-N-acetylhexosamines (UDP-HexNAcs) mediates G IIR. However, inhibition of the rate-limiting enzyme GFAT (glutamine:fructo se-g-phosphate amido-transferase) did not protect against GIIR despite a ma rked reduction of UDP-HexNAcs, The mRNA synthesis inhibitor actinomycin D a nd the protein synthesis inhibitor cycloheximide both completely protected against GIIR despite the massive increases in UDP-HexNAcs and glycogen that resulted from increased glucose entry. Activation of AMP-activated protein kinase also protected against GIIR, These results provide evidence that GI IR can occur in muscle without increased accumulation of hexosamine pathway end products, that neither high glycogen concentration nor impaired insuli n signaling is responsible for GIIR, and that synthesis of a protein with a short half-life mediates GIIR, They also suggest that dephosphorylation of a transcription factor may be involved in the induction of GIIR.