Mice transgenic for bovine growth hormone (bGH) develop progressive mesangial sclerosis resulting in uremia. Mesangial cells from bGH mice were isolated to determine whether the cells maintained a stable phenotypic change in the synthesis and degradation of extracellular matrix, which contribute to the glomerular lesions in vivo. The bGH mesangial cells were 1.2-fold larger than cells from control mice. They had a 1.7-fold increase in doubling time, a 7-fold decrease in labeling index (p< 0.0001), and a 2.4-and 2-fold decrease in c-myc (p< 0.05) and insulin-like growth factor I gene expression, respectively. Collagen synthesis and degradation were studied by PCR, ELISA, and gelatin zymography. bGH mesangial cell alpha 1 collagen IV mRNA levels were increased 2.3-fold (0.47+/-0.25 versus 0.20+/-0.09 attomoles/500 cells, p< 0.01) whereas secreted collagen IV and collagen IV in the cell lysates were increased 1.4-fold (25.1+/-5 versus 17.2+/-4 ng/ml/10 (5) cells) and 1.8-fold (30.5+/-3 versus 16.7+/-3 ng/ml/10 (5), p< 0.05), respectively. There were no differences in collagen I mRNA levels or in the protein content of either the media or cell lysates. We were not able to detect metalloproteinase 9 (MMP-9) mRNA expression or MMP-9 protein in bGH mesangial cell medium, whereas both mRNA and protein were present in controls. MMP-2 mRNA and enzyme activity in bGH cells were, however, elevated 1.5-fold (p< 0.05) and 2.1-fold (p= 0.05) over controls. Transforming growth factor beta 1 mRNA in bGH cells was 1.6-fold higher than that of controls (p< 0.05). The data suggest that (a) mesangial lesions may result from stable, genetically induced, phenotypic changes in mesangial cells, and (b) alterations of MMP-9 and collagen IV expression by mesangial cells may contribute to an imbalance between extracellular matrix synthesis and degradation and play a critical role in the genesis of glomerulosclerosis.