ALBUMIN MODIFIED BY AMADORI GLUCOSE ADDUCTS ACTIVATES MESANGIAL CELL TYPE-IV COLLAGEN GENE-TRANSCRIPTION

The direct relationship between elevated glucose concentrations and ac celerated protein glycation has implicated increased glycation as a po tential mechanistic link between hyperglycemia and the pathogenesis of diabetic nephropathy. Albumin modified by Amadori glucose adducts has been shown to stimulate collagen secretion by mesangial cells in vitr o, and to contribute to the overproduction of glomerular mesangial mat rix in vivo. To delineate mechanisms responsible for these effects, we examined the influence of glycated albumin on transcriptional activat ion of the a, (IV) collagen gene in renal glomerular mesangial cells. These experiments used a stably transfected reporter mesangial cell li ne that exhibits responses to media manipulations that are directional ly parallel with those of non-transformed mesangial cells, and that ex presses luciferase driven by 5'-flanking and first intron regions of t he a, (IV) collagen gene. In these cells, purified glycated albumin st imulated collagen IV gene transcription, whereas glucose-free albumin did not. Further, glycated albumin induced a significant increase in m esangial cell collagen IV mRNA, assessed by Northern blot analysis and quantified by calculation of the ratio of collagen IV mRNA to 18S rib osomal RNA after densitometric scanning. The stimulation of collagen g ene transcription and mRNA expression were both prevented by monoclona l antibodies known to specifically recognize Amadori-modified albumin. The findings indicate that glycated albumin promotes mesangial cell t ranscriptional activation and mRNA expression of the a, (TV) collagen gene and further implicate increased glycated albumin in diabetes in t he pathogenesis of diabetic nephropathy.