Degradation of glomerular basement membrane by purified mammalian metalloproteinases

Neutral metalloproteinases degrade components of the extracellular matrix, including collagen types I-V, fibronectin, laminin and proteoglycan. However, their ability to degrade intact glomerular basement membrane (GBM) has not previously been investigated. Incubation of [³H]GBM (50,000 c.p.m.; pH 7.5; 24 h at 37°C) with purified gelatinase or stromelysin (2 units) resulted in significant GBM degradation: gelatinase, 46 ± 2.2; stromelysin, 59 ± 5.8 (means ± S.E.M.; percentage release of non-sedimentable radioactivity; n = 4). In contrast, 2 units of collagenase released only 5.6 ± 0.52% (n = 3) of the [³H]GBM radioactivity compared with 2.0 ± 0.15% (n = 7) released from [³H]GBM incubated alone. Sephadex G-200 gel chromatography of supernatants obtained from incubations of [³H]GBM with either gelatinase or stromelysin confirmed the ability of these enzymes to degrade GBM and revealed both high-(800,000) and relatively low-(<20,000) M(r) degradation products for both enzymes. GBM degradation by gelatinase and stromelysin was dose-dependent (range 0.02-2.0 units), near maximal between pH 6.0 and 8.6, and was completely inhibited (> 95%) by 2 mM-o-phenanthroline. Collagenase (2 units) did not enhance the degradation of GBM by either gelatinase (0.02 or 0.2 unit) or stromelysin (0.02 or 0.2 unit). Our results indicate that metalloproteinase-mediated GBM degradation by neutrophils and glomeruli may be attributable to gelatinase (neutrophils) and/or stromelysin (glomeruli) and suggest an important role for these proteinases in glomerular pathophysiology.