Increased Glucose Uptake and Metabolism in Mesangial Cells Overexpressing Glucose Transporter 1 Increases Interleukin-6 and Vascular Endothelial Growth Factor Production: Role of AP-1 and HIF-1α

Abstract

Previous results indicate that enhanced glucose transporter (GLUT)1 expression mediates the deleterious effects of metabolic and hemodynamic perturbations leading to diabetic kidney disease. First screening for altered gene expression in GLUT1 overexpressing cells (GT1) by Affymetrix microarray analysis revealed upregulation of interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF) expression, which was verified by RT-PCR. Subsequently, IL-6 and VEGF protein production was more than 3-fold increased in the GT1 cells. This upregulation was independent from each other. Studies on the underlying transcriptional mechanisms by gelshift assays and siRNA approach implicated activation of AP-1 in the increased expression of both, IL-6 and VEGF. We found also increased nuclear protein levels of hypoxia-inducible factor (HIF)-1α and enhanced DNA binding activity to a hypoxia responsible element located in the VEGF promoter. Knock-down of HIF-1α reduced the VEGF expression to 50% with an additive effect of AP-1 gene silencing down to 24%. The IL-6 expression was not affected by reducing HIF-1α. In conclusion our results link increased GLUT1 levels leading to excess glucose metabolism under normoglycemic conditions and altered gene expression of pathogenetic factors involved in diabetic kidney disease.

GLUT1 enhances mTOR activity independently of TSC2 and AMPK

“…9, the same system that was used by Lee et al for their transient experiments. Such suppression in mTOR activity occurred because reduced GLUT1 levels led to a reduction in glucose utilization, independent of extracellular glucose concentration (11,34), and thereby enhanced Rheb association with GAPDH, reduced Rheb association with mTOR, and inhibited mTOR activation. This presumably protective response did not occur in mesangial cells that were the focus of most of our experiments, nor does it occur in glomeruli in rodent models of diabetic nephropathy (5).…”

“…The KRP buffer was removed and replaced with 0.1 mM unlabeled 2-DOG (Sigma) and 0.5 Ci/ml 3 H-2-DOG (Perkin Elmer, Waltham, MA) in KRP buffer ϩ 1% (wt/vol) BSA Ϯ 20 nM cytochalasin B, an irreversible inhibitor of glucose transport, at 37°C for 5 min. Previous studies showed that uptake is linear for at least 10 min in the control MC line (34). The plates were subsequently washed twice for 5 min each time with cold KRP solution containing 200 M phloretin to quench 2-DOG uptake.…”

“…growth factor and extracellular matrix production (11,34,39,40). Conversely, reduction of GLUT1 expression in mesangial cells exposed to high glucose (12) and in diabetic mice prevents such alterations (5).…”

“…Conversely, reduction of GLUT1 expression in mesangial cells exposed to high glucose (12) and in diabetic mice prevents such alterations (5). Increases in GLUT1 expression result in major enhancement of glucose utilization in mesangial cells (11,34). Thus, it appears that the number of GLUT1 transporters, rather than extracellular glucose concentrations per se, regulates mesangial cell glucose metabolic flux.…”

Hepatitis C virus core protein triggers hepatic angiogenesis by a mechanism including multiple pathways #

“…40 In addition, we specified the mechanistic role of HCV core in the course of the hepatic angiogenesis, during HCV infection.…”