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A novel rat mesangial matrix protein, MMP-50/100, involved in mesangial glomerulopathies
C J Kootstra1, A Arkema, P C Hogendoorn
1Department of Pathology, University of Leiden, The Netherlands.
Background:
Within the glomerular extracellular matrix, the glomerular basement membrane and the mesangial matrix have different compositions, presumably related to their different functions. In this study, a novel mesangial matrix protein is recognized by mAb ED5 and KiM4R, which were originally selected for reactivity with follicular dendritic cells of rat lymphoid organs.
Experimental Design:
Distribution of this mesangial matrix protein (MMP-50/100) was studied in normal Wistar rat kidneys by indirect immunofluorescence and immunoelectron microscopy. For partial immunobiochemical characterization, ED5-affinity-purified glomerular matrices were subjected to SDS-PAGE analysis. Expression of MMP-50/100 was additionally studied in kidneys of rats depleted for complement and in kidneys of rats depleted for resident macrophages. Functional significance of MMP-50/100 was studied in kidneys of rats with mesangial glomerulopathies.
Results:
Immunoelectron microscopy showed that MMP-50/100 is located in the extracellular matrix of the rat renal mesangium between mesangial cells and the basement membrane and on the mesangial cell membrane. SDS-PAGE analysis of affinity-purified glomerular matrices indicated that MMP-50/100 is a polypeptide glycoprotein with chains of apparent molecular weights of 50 and 100 kDa. Both in vivo and in vitro results indicate that MMP-50/100 does not appear to be a complement factor, or an Fc or complement receptor. In rats partially depleted for resident macrophages, the expression of MMP-50/100 was similar to that in control rats. In rats with BSA-induced chronic serum sickness nephritis, in rats with anti-Thy-1 nephritis, and in rats with uninephrectomy-induced focal glomerular sclerosis, the mesangial expression of MMP-50/100 was significantly increased. In the first model, double-label immunofluorescence demonstrated identical localization of MMP-50/100 with mesangial immune complex deposits.
Conclusions:
We conclude that MMP-50/100 is an intrinsic component of the mesangial matrix, presumably related to the "classic" mesangial cell. Expression of MMP-50/100 is increased in expanded mesangial matrices during development of glomerular disease. Furthermore, MMP-50/100 appears to be involved in the handling of mesangial immune complexes.
Insights
A novel mesangial matrix protein, MMP-50/100, is identified in rat kidneys. Its expression increases in glomerular disease and it appears involved in handling immune complexes.
Area of Science:
- Nephrology
- Molecular Biology
- Immunology
Background:
- The glomerular extracellular matrix has distinct components like the glomerular basement membrane and mesangial matrix.
- A novel mesangial matrix protein, recognized by mAb ED5 and KiM4R, was identified.
Purpose of the Study:
- To characterize a novel mesangial matrix protein (MMP-50/100) and investigate its distribution and functional significance in rat kidneys.
- To determine the role of MMP-50/100 in mesangial glomerulopathies.
Main Methods:
- Indirect immunofluorescence and immunoelectron microscopy were used to study MMP-50/100 distribution in normal rat kidneys.
- SDS-PAGE analysis was performed for biochemical characterization.
- Expression was studied in rats with depleted complement, macrophages, and in models of mesangial glomerulopathies.
Main Results:
- MMP-50/100 is localized in the mesangial extracellular matrix and on mesangial cell membranes.
- Biochemical analysis revealed MMP-50/100 as a polypeptide glycoprotein (50/100 kDa).
- MMP-50/100 expression significantly increased in mesangial glomerulopathies and co-localized with immune deposits.
Conclusions:
- MMP-50/100 is an intrinsic component of the mesangial matrix, associated with mesangial cells.
- Its expression is upregulated in expanded mesangial matrices during glomerular disease.
- MMP-50/100 plays a role in the handling of mesangial immune complexes.