UP-REGULATION OF MESANGIAL GROWTH-FACTOR AND EXTRACELLULAR-MATRIX SYNTHESIS BY ADVANCED GLYCATION END-PRODUCTS VIA A RECEPTOR-MEDIATED MECHANISM

Enhanced advanced glycosylation end product (AGE) formation has been s hown to participate in the pathogenesis of diabetes-induced glomerular injury by mediating the increased extracellular matrix (ECM) depositi on and altered cell growth and turnover leading to mesangial expansion . These effects could be exerted via an AGE-receptor-mediated upregula tion of growth factors, such as the IGFs and transforming growth facto r-beta (TGF-beta). We tested this hypothesis in human and rat mesangia l cells grown on nonglycated or native bovine serum albumin (BSA), gly cated BSA with AGE formation (BSA-AGE), or glycated BSA in which AGE f ormation was prevented by the use of aminoguanidine (BSA-AM), in the p resence or absence of an antibody, alpha-p60, directed against the p60 /OST protein named AGE-receptor 1 (AGE-RI), or normal control (pre-imm une) serum. The mRNA and/or protein levels of IGF-I, IGF-II, IGF recep tors, IGF binding proteins (IGFBPs), TGF-beta 1 and the ECM components fibronectin, laminin, and collagen TV were measured, together with ce ll proliferation. Both human and rat mesangial cells grown on BSA-AGE showed increased IGF-I and total and bioactive TGF-beta medium levels and enhanced IGF-I, IGF-II, and TGF-beta 1 gene expression, compared w ith cells grown on BSA, whereas total IGFBP and IGFBP-3 medium content , IGF receptor density and affinity, and IGF-I receptor transcripts we re unchanged. Moreover, cells grown on BSA-AGE showed increased ECM pr otein and mRNA levels versus cells cultured on BSA, whereas cell proli feration was unchanged in human mesangial cells and slightly reduced i n rat mesangial cells. Growing cells on BSA-AIM did not affect any of the measured parameters. Go-incubation of BSA-AGE with anti-AGE-R1, bu t not with pre-immune serum, prevented AGE-induced increases in IGF-I, TGF-beta 1, and ECM production or gene expression; anti-AGE-R1 also r educed growth factor and matrix synthesis in cells grown on BSA. These results demonstrate that mesangial IGF and TGF-PI synthesis is upregu lated by AGE-modified proteins through an AGE-receptor-mediated mechan ism. The parallelism with increased ECM production raises the speculat ion that the enhanced synthesis of these growth factors resulting from advanced nonenzymatic glycation participates in the pathogenesis of h yperglycemia-induced mesangial expansion.