The hexosamine pathway has been implicated in the pathogenesis of diabetic complications. We determined first that hyperglycemia induced a decrease in glyceraldehyde-3-phosphate dehydrogenase activity in bovine aortic endothelial cells via increased production of mitochondrial superoxide and a concomitant 2.4-fold increase in hexosamine pathway activity. Both decreased glyceraldehyde-3-phosphate dehydrogenase activity and increased hexosamine pathway activity were prevented completely by an inhibitor of electron transport complex II (thenoyltrifluoroacetone), an uncoupler of oxidative phosphorylation (carbonyl cyanide m-chlorophenylhydrazone), a superoxide dismutase mimetic [manganese (III) tetrakis(4-benzoic acid) porphyrin], overexpression of either uncoupling protein 1 or manganese superoxide dismutase, and azaserine, an inhibitor of the rate-limiting enzyme in the hexosamine pathway (glutamine:fructose-6-phosphate amidotransferase). Immunoprecipitation of Sp1 followed by Western blotting with antibodies to O-linked GlcNAc, phosphoserine, and phosphothreonine showed that hyperglycemia increased GlcNAc by 1.7-fold, decreased phosphoserine by 80%, and decreased phosphothreonine by 70%. The same inhibitors prevented all these changes. Hyperglycemia increased expression from a transforming growth factor-␤ 1 promoter luciferase reporter by 2-fold and increased expression from a (؊740 to ؉44) plasminogen activator inhibitor-1 promoter luciferase reporter gene by nearly 3-fold. Inhibition of mitochondrial superoxide production or the glucosamine pathway prevented all these changes. Hyperglycemia increased expression from an 85-bp truncated plasminogen activator inhibitor-1 (PAI-1) promoter luciferase reporter containing two Sp1 sites in a similar fashion (3.8-fold). In contrast, hyperglycemia had no effect when the two Sp1 sites were mutated. Thus, hyperglycemia-induced mitochondrial superoxide overproduction increases hexosamine synthesis and O-glycosylation of Sp1, which activates expression of genes that contribute to the pathogenesis of diabetic complications. D iabetic hyperglycemia causes a variety of pathologic changes in small vessels, arteries, and peripheral nerves (1, 2). Three major hypotheses about how hyperglycemia causes diabetic complications have generated extensive data as well as several clinical trials based on specific inhibitors of these pathways (3-6). These three pathways-activation of protein kinase C isoforms (7), increased formation of glucose-derived advanced glycation endproducts (3), and increased glucose flux through the aldose reductase pathway (8)-recently have been shown to be consequences of a single common mechanism, hyperglycemia-induced mitochondrial superoxide overproduction (1).A fourth hypothesis about how hyperglycemia causes diabetic complications has been formulated recently (9, 10), in which glucose is shunted into the hexosamine pathway. Inhibition of the rate-limiting enzyme in the conversion of glucose to glucosamine, glutamine:fructose-6-phosphate amidotransferase, bl...

Emerging evidence suggests that transforming growth factor-␤ (TGF-␤) is an important mediator of diabetic nephropathy. We showed previously that short-term treatment with a neutralizing monoclonal anti-TGF-␤ antibody (␣T) in streptozotocin-diabetic mice prevents early changes of renal hypertrophy and increased matrix mRNA. To establish that overactivity of the renal TGF-␤ system mediates the functional and structural changes of the more advanced stages of nephropathy, we tested whether chronic administration of ␣T prevents renal insufficiency and glomerulosclerosis in the db͞db mouse, a model of type 2 diabetes that develops overt nephropathy. Diabetic db͞db mice and nondiabetic db͞m littermates were treated intraperitoneally with ␣T or control IgG, 300 g three times per week for 8 wk. Treatment with ␣T, but not with IgG, significantly decreased the plasma TGF-␤1 concentration without decreasing the plasma glucose concentration. The IgG-treated db͞db mice developed albuminuria, renal insufficiency, and glomerular mesangial matrix expansion associated with increased renal mRNAs encoding ␣1(IV) collagen and fibronectin. On the other hand, treatment with ␣T completely prevented the increase in plasma creatinine concentration, the decrease in urinary creatinine clearance, and the expansion of mesangial matrix in db͞db mice. The increase in renal matrix mRNAs was substantially attenuated, but the excretion of urinary albumin factored for creatinine clearance was not significantly affected by ␣T treatment. We conclude that chronic inhibition of the biologic actions of TGF-␤ with a neutralizing monoclonal antibody in db͞db mice prevents the glomerulosclerosis and renal insufficiency resulting from type 2 diabetes.