title: In vivo administration of glucosamine inhibited phosphatidylinositol 3-kinase activity without affecting tyrosine phosphorylation of the insulin receptor or insulin receptor substrate in rat adipocytes.
abstract: We examined insulin signaling in rat epididymal adipocytes which developed insulin resistance by the in vivo infusion of glucosamine. Insulin-stimulated 2-deoxyglucose uptake into the adipocytes isolated from rats which were infused glucosamine for 4 hours was diminished by 26%. To analyze insulin signaling in adipocytes, the epididymal fat tissues were harvested 5 minutes after insulin administration (10U/kg), which was administered immediately after glucosamine infusion. Glucosamine had no effect on the insulin-stimulated tyrosine phosphorylation of the insulin receptor and insulin receptor substrate (IRS)-1. Glucosamine infusion decreased insulin-stimulated phosphatidylinositol (PI) 3-kinase activity by 66%. Glucosamine infusion also inhibited insulin-stimulated PI 3-kinase activity associated with IRS-1, 2, 3 by 30%, 43%, and 44%, respectively. There was no difference in the association of the 85kDa subunit of PI 3-kinase with the IRS-1 and IRS-2 protein. PI 3-kinase activity in adipocytes from rats treated with glucosamine that were administered platelet derived growth factor (3microg/kg) for 5 minutes was also reduced by 39%. When we measured the kinase activity of protein kinase C (PKC) lamda, which is the downstream effector of PI 3-kinase in isolated adipocytes, we found that glucosamine inhibited insulin stimulated PKClamda kinase activity by 33%. These results suggest that glucosamine infusion contributes to the development of insulin resistance by mainly modulating the PI 3-kinase molecules.
authors.affiliation: Division of Diabetes, Digestive and Kidney Diseases, Department of Clinical Molecular Medicine, Kobe University Graduate School of Medicine.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Miki
authors.forename: Motoyoshi
authors.initials: M
authors.lastname: Sakaue
authors.forename: Masato
authors.initials: M
authors.lastname: Kasuga
mesh_terms: D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D005944:Glucosamine / Q000008:administration & dosage / Q000494:pharmacology*; D007262:Infusions, Intravenous; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D011972:Receptor, Insulin / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; C526296:Irs1 protein, rat; C526299:Irs2 protein, rat; C491584:Irs3 protein, rat; D010750:Phosphoproteins; D014443:Tyrosine; D019869:Phosphatidylinositol 3-Kinases; D011972:Receptor, Insulin; D005944:Glucosamine