Effects of mesangium glycation on matrix metalloproteinase activities: possible role in diabetic nephropathy

High glucose concentrations can decrease degradation of mesangium by reducing the activities of matrix metalloproteinases (MMPs). The aim of this study was to investigate the effects of glycation of mesangium matrix on MMP-2, the principal MMP secreted by mesangial cells to degrade type IV collagen. Also examined were membrane type 1 MMP (MT1-MMP), tissue inhibitors of MMPs (TIMP)-1 and -2, and transforming growth factor-beta (TGF-beta), which together regulate MMP-2 activities in an interacting manner. Human fetal mesangial cells were grown on mesangium matrix glycated by incubation in 500 mmol/l ribose, with or without aminoguanidine. The activities and gene expression of the abovementioned enzymes/inhibitors were measured by degradation of radiolabeled mesangium matrix, RT-PCR, and zymography. Glycation of mesangium matrix resulted in a threefold increase in advance glycation end products and reduced by 45% the matrix-degrading activity of MMPs secreted by mesangial cells. Analogous to the direct effects of high glucose concentrations, glycation of matrix increased the gene expression of MMP-2 and TIMP-1 (control 100 +/- 16.9 vs. glycated 197.3 +/- 30.6% and control 100 +/- 5.3 vs. glycated 152.1 +/- 20.1%, respectively; P < 0.05) and decreased MT1-MMP (control 100 +/- 1.17 vs. glycated 54.1 +/- 15.2%; P < 0.05). However, unlike high glucose concentrations, glycation was not associated with decreased activation of MMP-2. Similarly, glycation but not high glucose increased expression of TIMP-2 (control 100 +/- 5.9 vs. glycated 168.2 +/- 31.4%; P < 0.05), and the effects of glycation on degradation can be abolished by anti-TIMP-2 antibody. Glycation of matrix decreased TGF-beta mRNA by 38.2% and total and active TGF-beta by 35.5 and 21.5%, respectively, opposite the effects of high glucose concentrations. Our results indicate that glycation of matrix affects the balance between MMP-2 and its activator and inhibitors, but this phenomenon is not due to TGF-beta. The process of glycation may impart to the mesangium matrix a memory effect that contributes to the long-term toxicity of hyperglycemia.