Marc C Daniels1, Donald A McClain1, Errol D Crook2. 1. Veterans Administration Medical Center and Department of Medicine, University of Mississippi Medical Center, Jackson, Mississippi. 2. Veterans Administration Medical Center and Department of Medicine, University of Mississippi Medical Center, Jackson, Mississippi. Electronic address: ecrook@medicine.umsmed.edu.
Abstract
BACKGROUND: The hexosamine biosynthesis pathway (HBP) is hypothesized to mediate many of the adverse effects of hyperglycemia. We have shown previously that increased flux through this pathway leads to induction of the growth factor transforming growth factor-α (TGF-α) and to insulin resistance in cultured cells and transgenic mice. TGF-β is regulated by glucose and is involved in the development of diabetic nephropathy. We therefore hypothesized that the HBP was involved in the regulation of TGF-β by glucose in rat vascular and kidney cells. METHODS: A plasmid containing the promoter region of TGF-β1 cloned upstream of the firefly luciferase gene was electroporated into rat aortic smooth muscle, mesangial, and proximal tubule cells. Luciferase activity was measured in cellular extracts from cells cultured in varying concentrations of glucose and glucosamine. RESULTS: Glucose treatment of all cultured cells led to a time- and dose-dependent stimulation in TGF-β1 transcriptional activity, with high (20 mM) glucose causing a 1.4- to 2.0-fold increase. Glucose stimulation did not occur until after 12 hours and disappeared after 72 hours of treatment. Glucosamine was more potent than glucose, with 3 mM stimulating up to a 4-fold increase in TGFβ1-transcriptional activity. The stimulatory effect of glucosamine was also dose-dependent but was slower to develop and longer lasting than that of glucose. CONCLUSIONS: The metabolism of glucose through the HBP mediates extracellular matrix production, possibly via the stimulation of TGF-β in kidney cells. Hexosamine metabolism therefore, may play a role in the development of diabetic nephropathy.
BACKGROUND: The hexosamine biosynthesis pathway (HBP) is hypothesized to mediate many of the adverse effects of hyperglycemia. We have shown previously that increased flux through this pathway leads to induction of the growth factor transforming growth factor-α (TGF-α) and to insulin resistance in cultured cells and transgenic mice. TGF-β is regulated by glucose and is involved in the development of diabetic nephropathy. We therefore hypothesized that the HBP was involved in the regulation of TGF-β by glucose in rat vascular and kidney cells. METHODS: A plasmid containing the promoter region of TGF-β1 cloned upstream of the firefly luciferase gene was electroporated into rat aortic smooth muscle, mesangial, and proximal tubule cells. Luciferase activity was measured in cellular extracts from cells cultured in varying concentrations of glucose and glucosamine. RESULTS:Glucose treatment of all cultured cells led to a time- and dose-dependent stimulation in TGF-β1 transcriptional activity, with high (20 mM) glucose causing a 1.4- to 2.0-fold increase. Glucose stimulation did not occur until after 12 hours and disappeared after 72 hours of treatment. Glucosamine was more potent than glucose, with 3 mM stimulating up to a 4-fold increase in TGFβ1-transcriptional activity. The stimulatory effect of glucosamine was also dose-dependent but was slower to develop and longer lasting than that of glucose. CONCLUSIONS: The metabolism of glucose through the HBP mediates extracellular matrix production, possibly via the stimulation of TGF-β in kidney cells. Hexosamine metabolism therefore, may play a role in the development of diabetic nephropathy.