Evidence for a Novel TGF-β1−Independent Mechanism of Fibronectin Production in Mesangial Cells Overexpressing Glucose Transporters

• Published in: Diabetes (New York, N.Y.) Vol. 52; no. 2; pp. 527 - 535
• Main Authors: Weigert, Cora, Brodbeck, Katrin, Brosius III, Frank C., Huber, Matthias, Lehmann, Rainer, Friess, Ulrich, Facchin, Sonia, Aulwurm, Steffen, Häring, Hans U., Schleicher, Erwin D., Heilig, Charles W.
• Format: Journal Article
• Language: English
• Published: American Diabetes Association 01.02.2003
• Subjects: Development and progression; Diabetic nephropathies; Glucose metabolism; Physiological aspects; Transforming growth factors; Germany
• ISSN: 0012-1797; 1939-327X
• DOI: 10.2337/diabetes.52.2.527

Evidence for a Novel TGF-β1−Independent Mechanism of Fibronectin Production in Mesangial Cells Overexpressing Glucose Transporters Cora Weigert 1 , Katrin Brodbeck 1 , Frank C. Brosius III 3 , Matthias Huber 1 , Rainer Lehmann 1 , Ulrich Friess 1 , Sonia Facchin 1 , Steffen Aulwurm 4 , Hans U. Häring 1 , Erwin D. Schleicher 1 and Charles W. Heilig 2 1 Department of Internal Medicine, Division of Endocrinology, Metabolism and Pathobio-Chemistry, University of Tübingen, Germany 2 III Division of Nephrology, Johns Hopkins School of Medicine, Baltimore, Maryland 3 Department of Medicine, Division of Nephrology, University of Michigan Medical School, Ann Arbor, Michigan 4 Department of Neurology, University of Tübingen, Germany Abstract Recent experimental work indicates that the hyperglycemia-induced increase in mesangial matrix production, which is a hallmark in the development of diabetic nephropathy, is mediated by increased expression of GLUT1. Mesangial cells stably transfected with human GLUT1 mimic the effect of hyperglycemia on the production of the extracellular matrix proteins, particularly fibronectin, when cultured under normoglycemic conditions. Our investigation of the molecular mechanism of this effect has revealed that the enhanced fibronectin production was not mediated by the prosclerotic cytokine transforming growth factor (TGF)-β1. We found markedly increased nuclear content in Jun proteins, leading to enhanced DNA-binding activity of activating protein 1 (AP-1). AP-1 inhibition reduced fibronectin production in a dosage-dependent manner. Moreover, inhibition of classic protein kinase C (PKC) isoforms prevented both the activation of AP-1 and the enhanced fibronectin production. In contrast to mesangial cells exposed to high glucose, no activation of the hexosamine biosynthetic, p38, or extracellular signal–related kinase 1 and 2 mitogen-activated protein kinase pathways nor any increase in TGF-β1 synthesis could be detected, which could be explained by the absence of oxidative stress in cells transfected with the human GLUT1 gene. Our data indicate that increased glucose uptake and metabolism induce PKC-dependent AP-1 activation that is sufficient for enhanced fibronectin production, but not for increased TGF-β1 expression. Footnotes Address correspondence and reprint requests to Dr. Erwin D. Schleicher, Department of Internal Medicine, Division of Endocrinology, Metabolism and Pathobiochemistry, University of Tübingen, Otfried-Müller-Straβe 10, D-72076 Tübingen, Germany. E-mail: enschlei{at}med.uni-tuebingen.de . Received for publication 17 May 2002 and accepted in revised form 4 November 2002. ANG, angiotensin; AP-1, activating protein 1; ATF, activating transcription factor; CRE, cAMP-responsive element; CREB, CRE binding protein; DCFDA; EGF, epidermal growth factor; ELISA, enzyme-linked immunosorbent assay; EMSA, electrophoretic mobility shift assay; ERK, extracellular signal–related kinase; GFAT, glutamine:fructose-6-phosphate amidotransferase; MAPK, mitogen-activated protein kinase; PKC, protein kinase C; PMA, phorbol myristoyl acid; ROS, reactive oxygen species; Sp-1, stimulating protein 1; TGF, transforming growth factor; TRE, PMA responsive element; UDP-GlcNAc, uridine-5′-diphosphate- N -acetylglucosamine. DIABETES