PRODUCTION OF METALLOPROTEINASES AND TIMPS BY GLOMERULAR CELLS

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Glomerulosclerosis occurs in a large number of human kidney diseases, including diabetic nephropathy. It consists of the accumulation of extracellular matrix (ECM) within the glomerulus. Sclerosis may be mediated by dysregulation of both synthesis and degradation of ECM. A large family of matrix metalloproteinases as well as tissue inhibitors of metalloproteinase (TIMPs) play a role in the degradative process. Our preliminary in vitrl work revealed that: 1) normal mouse mesangial and epithelial cells in culture secrete a 72 kD and a 92 kD gelatinase (type IV collagenase) as well as TIMP1; 2) mesangial cells derived from NOD mice and mice transgenic for bovine growth hormone (bGH) secrete mostly the 72 kD gelatinase; 3) bGH mesangial cells lack the 92 kd metalloproteinase; 4) when cells are cultured in the presence of high glucose there is a decrease in the 92kd gelatinase. Recently we examined glomeruli in vivo and found that normal mouse glomeruli contain mRNA coding the 72kD species. This mRNA is increased in mice transgenic for bGH who have sclerotic lesions. TIMP 1 and 2 mRNAs are undectable in mouse glomeruli, a fact which emphasizes the major phenotypic changes that occur in vivo. We found that TIMP3 was expressed in mouse glomeruli and was increased in diabetic mice. In GH mice the upregulation of the 72KD gelatinase is less prominent than that of type IV collagen. This finding may suggest that there is an imbalance between synthesis and degradation of extracellular matrix in certain forms of glomerulosclerosis. Of considerable clinical significance was the fact that the phenotypic changes in the sclerotic glomeruli were stable, at least in vitro. Glomerular mesangial (smooth muscle) cells were isolated and cloned from non-obese diabetic mice, and model of autoimmune insulin-dependent diabetes mellitus. We have previously characterized these cells and the stable phenotypic modulation induced after the appearance of sustained hyperglycemia. We found that matrix metalloproteinases were markedly down regulated in these cells, at the mRNA and protein levels, by the presence of hyperglycemia in the media. Thus, hyperglycemia induces marked changes in cells which have been phenotypically modulated by the diabetic state, but not in cells isolated from pre-diabetic animals or from other non-diabetic strains.