Abstract
Methylglyoxal (MG), a highly reactive α-dicarbonyl metabolite of glucose degradation pathways, protein and fatty acid metabolism, plays an important role in the pathogenesis of diabetic complications. Hyperglycemia triggers enhanced production of MG and increased generation of advanced glycation endproducts (AGEs). In non-enzymatic reactions, MG reacts with arginine residues of proteins to form the AGEs argpyrimidine and hydroimidazolone. Glyoxalase 1 (GLO1), in combination with glyoxalase 2 and the co-factor glutathione constitute the glyoxalase system, which is responsible for the detoxification of MG. A GLO1 specific knock down results in accumulation of MG in targeted cells. The aim of this study was to investigate the effect of intracellularly accumulated MG on insulin signaling and on the translocation of the glucose transporter 4 (GLUT4). Therefore, L6 cells stably expressing a myc-tagged GLUT4 were examined. For the intracellular accumulation of MG, GLO1, the first enzyme of the glyoxalase pathway, was down regulated by siRNA knock down and cells were cultivated under hyperglycemic conditions (25 mM glucose) for 48 h. Here we show that GLO1 knock down augmented GLUT4 level on the cell surface of L6 myoblasts at least in part through reduction of GLUT4 internalization, resulting in increased glucose uptake. However, intracellular accumulation of MG had no effect on GLUT4 concentration or modification. The antioxidant and MG scavenger NAC prevented the MG-induced GLUT4 translocation. Tiron, which is also a well-known antioxidant, had no impact on MG-induced GLUT4 translocation.
Highlights
Diabetes mellitus is characterized by chronic hyperglycemia which is associated with excessive formation of advanced glycation endproducts (AGEs) and increased plasma levels of the highly reactive a-dicarbonyl methylglyoxal (MG) [1,2,3]
The glucose uptake was analyzed by measuring the uptake of the fluorescent glucose analogue 2-NBDG. 2-NBDG staining of glyoxalase 1 (GLO1) knock down cells showed a significant increase in 2NBDG uptake without insulin stimulation, compared to scrambled siRNA transfected cells under the same cultivation conditions (100.0 6 24.6 vs. 1,701.3 6 175.8 a.u., p,0.001) (Figure 1B)
As a complex metabolic disorder diabetes mellitus is characterized by chronic hyperglycemia due to defects in insulin secretion or insulin resistance
Summary
Diabetes mellitus is characterized by chronic hyperglycemia which is associated with excessive formation of advanced glycation endproducts (AGEs) and increased plasma levels of the highly reactive a-dicarbonyl methylglyoxal (MG) [1,2,3]. Different studies have shown that MG levels are significantly increased in plasma and tissues of diabetic patients, which leads to increased AGE accumulation. The main action of insulin is the regulation of cellular glucose uptake into skeletal muscle cells and adipocytes via glucose transporter 4 (GLUT4) translocation from intracellular vesicles to the plasma membrane [27,28]. Insulin stimulation induces the release of GLUT4 via exocytosis, and cellular GLUT4 content becomes exposed at the cell surface [28,30,31] In both cell types, glucose uptake is accomplished via activation of insulin receptor substrate 1 (IRS-1), the phosphatidylinositol-3-kinase (PI3-Kinase), and Akt. All components of the PI3-Kinase/Akt-mediated signal pathway take part in the GLUT4 translocation [30,31,32,33]. Recent studies point to the close relationship of MG accumulation with insulin resistance and lead to the assumption that MG might have inhibitory effects towards insulin signaling [37,38,39]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
