Changes in matrix metalloproteinases during the evolution of interstitial renal fibrosis in a rat experimental model

The aim of the present study was to analyze the matrix metalloproteinase (MMP) activity during the evolution of interstitial renal fibrosis in a rat experimental model of unilateral ureteral obstruction. The interstitial type I collagenase and the gelatinolytic activities were analyzed by radiolabeled substrate degradation. Interstitial collagenase activity was low at all times while gelatinolytic activity increased on day 6 of evolution, with a decrease in activity from this point. The use of organomercurials revealed the presence of latent enzyme in all cases. Normal kidney samples contained MMP-9 in both active and proenzyme forms as revealed by zymography. On day 3 MMP-9 dimers appeared, and increased activity was observed until day 6. A decrease in the gelatinolytic activity was detected from days 9-15 of evolution. This observation was confirmed by Western blot analysis that revealed the presence of proMMP-9 mainly from days 6-12. Tissue inhibitor of metalloproteinase-1 (TIMP-1) was also detected alone and in combination with proMMP-1 and MMP-1, particularly from days 6-15 of evolution. The presence of MMP-9 and MMP-1 was detected in the cytoplasm of cortical tubular cells by immunohistochemistry, with no difference between the experimental and the normal kidneys. There was also an increase in collagen concentration from day 3 after surgery that increased during the entire evolution of the experimental model. This work reveals that the decrease in the MMP-9 and MMP-1 enzymatic activity, due to their interaction with TIMP-1 and to the lack of activation of the latent forms, may participate in the excessive collagen deposit during the evolution of experimental interstitial renal fibrosis.