Degradation of glomerular basement membrane by a neutral metalloproteinase(s) present in glomeruli isolated from normal rat kidney

Incubation of glomerular homogenates (200ug protein) with glomerular basement membrane (GBM, 30–35ug hydroxyproline) at pH 7.5 for 36h at 37°C resulted in significant GBM degradation as measured by hydroxyproline release (40±6%, n=17). GBM degradation increased with increasing incubation time (12–48h) and glomerular protein concentration (50–250ug). GBM degradation was not significantly decreased by inhibitors of serine or cysteine proteinases or the inhibitor of bacterial metalloproteinases, phosphoramidon. In contrast GBM degradation by glomerular homogenates was markedly inhibited by the metal chelators 10mM EDTA (−95±3%, n=7) and 2mM 1,10-phenanthroline (−96±2%, n=4). Preincubation of glomerular homogenates with trypsin (followed by soya bean trypsin inhibitor) markedly stimulated GBM degradation (+103±20%, n=11). These results document the presence of a GBM-degrading, neutral metalloproteinase(s) in glomeruli suggesting an important role for this enzyme in glomerular pathophysiology.