Activation of the hexosamine pathway by glucosamine in vivo induces insulin resistance of early postreceptor insulin signaling events in skeletal muscle

To explore potential cellular mechanisms by which activation of the hexosam ine pathway induces insulin resistance, we have evaluated insulin signaling in conscious fasted rats infused for 2-6 h with saline, insulin (18 mU.kg( -1).min(-1)), or insulin and glucosamine (30 mu mol.kg(-1).min(-1)) under e uglycemic conditions. Glucosamine infusion increased muscle UDP-N-acetyl-gl ucosamine concentrations 3.9- and 4.3-fold over saline- or insulin-infused animals, respectively (P < 0.001), Glucosamine induced significant insulin resistance to glucose uptake both at the level of the whole body and in rec tus abdominis muscle, and it blunted the insulin-induced increase in muscle glycogen content, At a cellular level, these metabolic effects were parall eled by inhibition of postreceptor insulin signaling critical for glucose t ransport and glycogen storage, including a 45% reduction in insulin-stimula ted insulin receptor substrate (IRS)-1 tyrosine phosphorylation (P = 0.02), a 44% decrease in IRS-1 association with the p85 regulatory subunit of pho sphatidylinositol (PI) 3-kinase (P = 0.03), a 34% reduction in IRS-1-associ ated PI 3-kinase activity (P = 0.03), and a 51% reduction in insulin-stimul ated glycogen synthase activity (P = 0.03). These alterations in postrecept or insulin signaling were time-dependent and paralleled closely the progres sive inhibition of systemic glucose disposal from 2 to 6 h of glucosamine i nfusion. We also demonstrated that glucosamine infusion results in O-linked N-acetyl-glucosamine modification of IRS-1 and IRS-2. These data indicate that activation of the hexosamine pathway may directly modulate early postr eceptor insulin signal transduction, perhaps via posttranslation modificati on of IRS proteins, and thus contribute to the insulin resistance induced b y chronic hyperglycemia.