Expression of matrix metalloproteinases 2 and 9 and tissue inhibitors of matrix metalloproteinases 2 and 1 in the glomeruli of human glomerular diseases: the results of studies using immunofluorescence, in situ hybridization, and immunoelectron microscopy.

BACKGROUND: It has been reported matrix metalloproteinases (MMPs) and their inhibitors, tissue inhibitors of matrix metalloproteinases (TIMPs), play important roles in the decomposition of the extracellular matrices of the glomerulus during the pathological processes in various glomerular diseases. Although the activity of these enzymes in cases of experimental glomerulonephritis has been described, the expression sites in the glomeruli of human renal diseases have been identified in only a few articles and remain controversial.
METHODS: The expression of the gelatinase group of MMPs (MMP-2 and MMP-9) and their inhibitors (TIMP-2 and TIMP-1) were evaluated in 19 renal biopsies of several types of glomerular diseases by immunofluorescence (IF) labeling. In addition, several samples of immunoglobulin A nephropathy (IgAN) were also investigated by in situ hybridization (ISH) and immunoelectron microscopy (IEM).
RESULTS: The expression of MMP-2 was observed in all the cases examined by IF and ISH. TIMP-2 expression varied from negative to positive among 11 cases of IgAN, but was negative in the cases with lupus nephritis (LN) (n = 3), membranoproliferative glomerulonephritis (MPGN) (n = 2), and post-streptococcal glomerulonephritis (n = 1). However, it was weakly positive in the cases of diabetic nephropathy (DMN) (n = 2). MMP-2 was mainly observed along glomerular capillary loops (GCLs) and Bowman's capsules, whereas TIMP-2 was found in the mesangial area. The expression of MMP-9 in cases of IgAN varied, and was local, not diffuse, if it was present. MMP-9 expression in cases of LN, MPGN, and DMN was diffuse, but the intensity of staining varied. MMP-9 was primarily expressed in the mesangium. TIMP-1 expression was negative in all cases except for those with IgAN. The localization of MMP-2 in patients with IgAN, which was investigated by IEM, was revealed to be mainly on the endothelial cell membranes of GCLs, podocyte membranes, the parietal cell membranes of Bowman's capsules, and some on the membranes of mesangial cells.
CONCLUSION: The study results suggest that the expression levels and patterns of MMPs and TIMPs are generally similar in several types of glomerular diseases, even though each case has a somewhat different distribution and intensity of expression. When these enzymes were present, their main sites were as follows: MMP-2 was found along glomerular basement membrane, TIMP-2 was located in the acellular mesangial area, MMP-9 was seen in the mesangium, and TIMP-1 was hardly detected. MMP-2 expression is clearly demonstrated to exist at the above-described sites by IEM in patients with IgAN.