title: Evidence for a novel TGF-beta1-independent mechanism of fibronectin production in mesangial cells overexpressing glucose transporters.
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)-beta1. 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-beta1 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-beta1 expression.
authors.affiliation: Department of Internal Medicine, Division of Endocrinology, Metabolism and Pathobio-Chemistry, University of Tübingen, Germany.
authors.forename: Cora
authors.initials: C
authors.lastname: Weigert
authors.forename: Katrin
authors.initials: K
authors.lastname: Brodbeck
authors.forename: Frank C
authors.initials: FC
authors.lastname: Brosius
authors.forename: Matthias
authors.initials: M
authors.lastname: Huber
authors.forename: Rainer
authors.initials: R
authors.lastname: Lehmann
authors.forename: Ulrich
authors.initials: U
authors.lastname: Friess
authors.forename: Sonia
authors.initials: S
authors.lastname: Facchin
authors.forename: Steffen
authors.initials: S
authors.lastname: Aulwurm
authors.forename: Hans U
authors.initials: HU
authors.lastname: Häring
authors.forename: Erwin D
authors.initials: ED
authors.lastname: Schleicher
authors.forename: Charles W
authors.initials: CW
authors.lastname: Heilig
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004797:Enzyme-Linked Immunosorbent Assay; D005353:Fibronectins / Q000235:genetics*; D005920:Glomerular Mesangium / Q000187:drug effects / Q000502:physiology*; D005947:Glucose / Q000378:metabolism; D051272:Glucose Transporter Type 1; D006801:Humans; D007773:Lactates / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000235:genetics*; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics; D051381:Rats; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D053773:Transforming Growth Factor beta1
chemical_list: D005353:Fibronectins; D051272:Glucose Transporter Type 1; D007773:Lactates; D009004:Monosaccharide Transport Proteins; D016755:Proto-Oncogene Proteins c-jun; C495677:SLC2A1 protein, human; C495679:Slc2a1 protein, rat; C508960:TGFB1 protein, human; C508962:Tgfb1 protein, rat; D018808:Transcription Factor AP-1; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D005947:Glucose