[Regulation of the expression and function of glucose transporter-1 by TGF-beta 1 and high glucose in mesangial cells]

Abstract

Objective: To study the effects of high glucose and transforming growth factor-beta 1 (TGF-beta 1) on the expression and function of glucose transporter-1 (GLUT1) in mouse mesangial cells.

Methods: Cultured mouse mesangial cells were used. The expression of GLUT1 mRNA was detected by Northern Blot; glucose uptake and its kinetics were determined with a 2-Deoxy-[3H]-D-glucose uptake assay.

Results: Mesangial cells exposed to enriched glucose medium (20 mmol/L) for 72 hours demonstrated a decrease in both GLUT1 mRNA and Vmax for uptake of the glucose analog, 2-deoxy-D-glucose (2DOG), as compared to mesangial cells cultured in physiologic glucose concentrations (5.5 mmol/L). In contrast, hypertonic mannitol had no effect on GLUT1 mRNA levels. TGF-beta 1 treatment for 10 hours stimulated 2DOG uptake, both in 5.5 mmol/L and 20 mmol/L glucose medium, by approximately 4.28-fold in a dose-dependent manner (2 ng/ml maximum). Kinetic analysis of 2DOG uptake revealed an increase in Vmax and a decrease in Km in the presence of TGF-beta 1. TGF-beta 1 also up-regulated the expression of GLUT1 mRNA in mesangial cells. The addition of anti-TGF-beta neutralizing antibody (30 micrograms/ml) in mesangial cells cultured in enriched glucose medium (20 mmol/L) led to a 40% decrease in 2DOG uptake.

Conclusions: The expression of GLUT1 can be suppressed by exposure of mesangial cells to high glucose medium, which may serve as a protective mechanism against possible adverse effects of excessive glucose flux into cells. TGF-beta 1 stimulates glucose uptake by enhancing the expression and function of GLUT1 in mesangial cells. This effect is independent of the glucose milieu in the cultured medium.