TGF-beta 1 stimulates glucose uptake by enhancing GLUT1 expression in mesangial cells

Background. An increase in the expression of transforming growth factor-bet a 1 (TGF-beta 1) has been proposed to play an important role in the excessi ve production of extracellular matrix (ECM) proteins seen in diabetes. Beca use the linkage between glucose metabolism and ECM protein production was f ound in mesangial cells overexpressed with the brain-type glucose transport er (GLUT1), we hypothesized that TGF-beta 1 could affect glucose metabolism . Methods. To prove this hypothesis, we examined the effect of TGF-beta 1 on glucose uptake, the first step of glucose metabolism, in mesangial cells. 2 -Deoxy-D-glucose (2DOG) uptake and the expression of GLUT1 were measured in mesangial cells exposed to various concentrations of TGF-beta 1. The kinet ic constants were determined using 2DOG and 3-O-methyl-D-glucose (3OMG). Th e effect of anti-TGF-beta neutralizing antibody on 2DOG uptake and GLUT1 mR NA was also examined in mesangial cells cultured under high-glucose(22.2 mM ) conditions for 72 hours. Results. TGF-beta 1 stimulated 2DOG uptake in mesangial cells by approximat ely 2.5-fold in a dose- (1.25 ng/ml maximum) and time-dependent manner, wit h a peak stimulation at nine hours. The increase in 2DOG uptake by TGF-beta 1 was completely abolished by the addition of 1 mu g/ml cycloheximide, and kinetic analysis of 2DOG or 3OMG uptake revealed an increase in V-max by T GF-beta 1. Furthermore, TGF-beta 1 enhanced the expression of GLUT1 mRNA fr om one hour, followed by an enhancement of the expression of GLUT1 protein at nine hours. Finally, 2DOG uptake was significantly enhanced in cells cul tured under high-glucose (22.2 mM) conditions as compared with that in cell s under normal glucose (5.6 mM) conditions, and this increase in 2DOG uptak e in cells under high-glucose conditions was inhibited by the addition of a nti-TGF-beta neutralizing antibody. Conclusions. TGF-beta 1 stimulates glucose uptake by enhancing the expressi on of GLUT1 in mesangial cells, which leads to the acceleration of intracel lular metabolic abnormalities in diabetes.