title: Independent regulation of transforming growth factor-beta1 transcription and translation by glucose and platelet-derived growth factor.
abstract: Proximal tubular renal epithelial cells may contribute to the pathogenesis of renal interstitial fibrosis in diabetes by generation of cytokines such as transforming growth factor (TGF)-beta1. We have previously demonstrated that proximal tubular renal epithelial cell TGF-beta1 synthesis may be modulated by elevated glucose concentration and by cytokines such as platelet-derived growth factor (PDGF). The aim of the current study was to characterize the mechanism by which glucose and PDGF synergistically stimulate the generation of TGF-beta1. Addition of either 25 mmol/L of D-glucose or low-dose PDGF increased TGF-beta1 mRNA expression without stimulation of TGF-beta1 protein synthesis. In contrast sequential stimulation with 25 mmol/L of D-glucose for 48 hours followed by low-dose (25 ng/ml) PDGF led to a significant increase in TGF-beta1 synthesis. Elevated glucose concentration stimulated de novo gene transcription as assessed by stimulation of a TGF-beta1 promoter-luciferase construct. This led to induction of a poorly translated TGF-beta1 transcript determined by polysome analysis. PDGF at low dose did not influence TGF-beta1 transcription, but led to alteration in TGF-beta1 mRNA stability and translation. Without a previous glucose-induced increase in the amount of TGF-beta1 transcript, PDGF did not stimulate significant TGF-beta1 protein synthesis. At a high dose (100 ng/ml) PDGF stimulated TGF-beta1 synthesis independent of glucose concentration. This was associated with increased TGF-beta1 gene transcription and alteration in TGF-beta1 mRNA translational efficiency. In conclusion the data suggests that in diabetic nephropathy, the role of glucose is to lower the threshold at which a stimulus such as PDGF stimulates TGF-beta1 protein synthesis. The data also suggest that independent regulation of TGF-beta1 transcription and translation by glucose and PDGF account for their synergistic effect on TGF-beta1 protein synthesis. We hypothesize that the role of glucose in diabetic nephropathy is to prime the kidney for an injurious response to other stimuli.
authors.affiliation: Institute of Nephrology, University of Wales College of Medicine, Heath Park Cardiff, Wales, United Kingdom.
authors.forename: Donald
authors.initials: D
authors.lastname: Fraser
authors.forename: Lalage
authors.initials: L
authors.lastname: Wakefield
authors.forename: Aled
authors.initials: A
authors.lastname: Phillips
mesh_terms: D002461:Cell Line, Transformed; D004357:Drug Synergism; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D014176:Protein Biosynthesis / Q000187:drug effects*; D014158:Transcription, Genetic / Q000187:drug effects*; D016212:Transforming Growth Factor beta / Q000096:biosynthesis* / Q000235:genetics; D053773:Transforming Growth Factor beta1
chemical_list: D010982:Platelet-Derived Growth Factor; C508960:TGFB1 protein, human; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; C075278:platelet-derived growth factor A; D005947:Glucose