O-GlcNAc-Selective-N-Acetyl-[beta]-D-Glucosaminidase Activity and mRNA Expression in Muscle Is Related to Glucosamine-Induced Insulin Resistance

Glucosamine (GlcN)-induced insulin resistance is associated with an increase in O-linked-N-acetylglucosaminylated modified proteins (O-GlcNAcylated proteins). The role played by O-GlcNAc-selective-N-acetyl-β-D-glucosaminidase (O-GlcNAcase), which removes O-N-acetyl-glucosamine residues from O-GlcNAcylated proteins, has not yet been demonstrated. We investigated whether GlcN-induced whole-body insulin resistance is related to tissue O-GlcNAcase activity and mRNA expression. GlcN (30 μmol/kg/min) or physiological saline (control) was intravenously infused into Sprague-Dawley rats for 2 h. After GlcN treatment, rats were subjected to the following: intravenous glucose tolerance test, insulin tolerance test or removal of the liver, muscle and pancreas. GlcN was found to provoke hyperglycemia compared to control (8.6 ± 0.41 vs. 4.82 ± 0.17 mM, p [less than] 0.001). The insulin resistance index (HOMA-IR) increased (15.76 ± 1.47 vs. 10.14 ± 1.41, p [less than] 0.001) and the β-cell function index (HOMA-β) diminished (182.69 ± 22.37 vs. 592.01 ± 103, p [less than] 0.001). Liver glucose concentration was higher in the GlcN group than in the control group (0.37 ± 0.04 vs. 0.24 ± 0.038 mmol/g dry weight, p [less than] 0.001). Insulin release index (insulin/glucose) was less in the GlcN group than in the control (2.2 ± 0.1 vs. 8 ± 0.8 at 120 min, p [less than] 0.001). In the GlcN group, muscle O-GlcNAcase activity diminished (0.28 ± 0.019 vs. 0.36 ± 0.018 nmol of p-nitrophenyl/mg protein/min, p [less than] 0.001), and Km increased (1.51 ± 0.11 vs. 1.12 ± 0.1 mM, p [less than] 0.001) compared to the control. In the GlcN group, O-GlcNAcase activity/mRNA expression was altered (0.6 ± 0.07 vs. 1 ± 0.09 of control, p [less than] 0.05). In conclusion, O-GlcNAcase activity is posttranslationally inhibited during GlcN-induced insulin resistance. Copyright © 2010 S. Karger AG, Basel [PUBLICATION ABSTRACT]