Background: Matrix metalloproteinase (MMP)-9, a member of the MMP family with specificity towards type IV collagen, is implicated in the turnover of the extracellular matrix in the kidney. To elucidate its physiological and pathophysiological significance, we examined the expression and localization of MMP-9 in the normal kidney and the changes in these features during the course of anti-glomerular basement membrane (GBM) glomerulonephritis induced in WKY rats, along with the changes in these features of tissue inhibitor of metalloproteinase 1 (TIMP-1) and MMP-2.
Methods: The expression of MMP-9, TIMP-1 and MMP-2 mRNA was quantified by ribonuclease protection assay, and the gelatinolytic activities of MMP-9 and MMP-2 were evaluated by gelatin zymography. The localization of MMP-9 was visualized by immunohistochemistry and immunofluorescence microscopy.
Results: The ribonuclease protection assay indicated the almost exclusive expression of MMP-9 mRNA in the glomerulus of normal kidneys. Immunohistochemistry and double-label immunofluorescence microscopy showed that MMP-9 was localized in the mesangial cells. During the course of anti-GBM glomerulonephritis, the expression of MMP-9 mRNA in glomeruli increased on day 1, peaked on days 3 to 7, and then decreased on day 14. The change in MMP-9 mRNA expression was accompanied by parallel changes in the gelatinolytic activity of the active form of MMP-9, TIMP-1 mRNA expression, and MMP-9 immunoreactivity in mesangial cells. In contrast, glomerular MMP-2 mRNA expression and its activity increased after the decline of MMP-9.
Conclusions: MMP-9 mRNA was predominantly expressed in the glomerulus in normal rat kidneys and MMP-9 was present in the mesangium. The MMP-9 mRNA expression increased in the glomerulus 3 to 7 days after the induction of anti-GBM glomerulonephritis in WKY rats, in parallel with the development of abnormal glomerular histology and injury, suggesting a role of MMP-9 in proteolysis of the GBM during glomerulonephritis. MMP-2 may participate in the later phase of the nephritis.