Long Exposure to High Glucose Concentration Impairs the Responsive Expression of γ-Glutamylcysteine Synthetase by Interleukin-1β and Tumor Necrosis Factor-α in Mouse Endothelial Cells

Abstract

To elucidate the pathological metabolism of glutathione synthesis in diabetic endothelial cells, we studied the expression of γ-glutamylcysteine synthetase (γ-GCS) using a mouse vascular endothelial cell line.Exposing normoglycemic endothelial cells to tumor necrosis factor-α (TNF-α) or interleukin-1β (IL-1β) increased the activity and the mRNA expression of γ-GCS. The addition of inhibitors for nuclear factor κB (NF-κB) to the cells caused a loss of the γ-GCS mRNA expression in response to TNF-α.A shift of the concentration of glucose in the medium from 5.5 to 28 mM glucose and a following incubation for 7 days decreased the expression of γ-GCS mRNA. These cells showed no apparent responses of γ-GCS mRNA or the activity of NF-κB to TNF-α or IL-β. Increase in the GSH concentration of the cells treated with 28 mM glucose restored the expression of γ-GCS mRNA and its response to TNF-α or IL-β, suggesting that redox regulation is involved in the expression of γ-GCS.In summary, the expression of γ-GCS is regulated by TNF-α or IL-1β in endothelial cells mediated by NF-κB stimulation, and impairment of the regulation of γ-GCS in hyperglycemic cells may be a cause of medical complications that develop in diabetes mellitus. To elucidate the pathological metabolism of glutathione synthesis in diabetic endothelial cells, we studied the expression of γ-glutamylcysteine synthetase (γ-GCS) using a mouse vascular endothelial cell line. Exposing normoglycemic endothelial cells to tumor necrosis factor-α (TNF-α) or interleukin-1β (IL-1β) increased the activity and the mRNA expression of γ-GCS. The addition of inhibitors for nuclear factor κB (NF-κB) to the cells caused a loss of the γ-GCS mRNA expression in response to TNF-α. A shift of the concentration of glucose in the medium from 5.5 to 28 mM glucose and a following incubation for 7 days decreased the expression of γ-GCS mRNA. These cells showed no apparent responses of γ-GCS mRNA or the activity of NF-κB to TNF-α or IL-β. Increase in the GSH concentration of the cells treated with 28 mM glucose restored the expression of γ-GCS mRNA and its response to TNF-α or IL-β, suggesting that redox regulation is involved in the expression of γ-GCS. In summary, the expression of γ-GCS is regulated by TNF-α or IL-1β in endothelial cells mediated by NF-κB stimulation, and impairment of the regulation of γ-GCS in hyperglycemic cells may be a cause of medical complications that develop in diabetes mellitus.