Presence of a distinct extracellular matrix-degrading metalloproteinase activity in renal tubules.

Abstract

Renal tubular homogenates incubated with [3H]laminin (2 micrograms, 10(5) cpm) at 37 degrees C resulted in time- and protein-dependent laminin degradation (e.g., at 24 h, control = 6,533 +/- 771; experimental = 27,610 +/- 1,023 cpm +/- SE; N = 20). Gel chromatography confirmed that laminin (800 to 900 kd) was degraded to 20- to 50-kd fragments. Laminin degradation was not significantly decreased by serine or cysteine protease inhibitors. In contrast, metal chelators produced marked inhibition (EDTA, 93 +/- 3%; 1,10-phenanthroline, 99 +/- 1%) indicating that, at neutral pH, metalloproteinases were responsible for the laminin degradation. Laminin-degrading activity in renal tubules was not inhibited by the tissue inhibitor of metalloproteinase and was present in an active form. This activity was also present in high concentrations in the renal cortex and medulla but was only minimal in the liver. Further studies of the renal cortex revealed a similar metalloproteinase activity against type IV collagen (11,075 +/- 305; N = 6) and gelatin (41,026 +/- 1,373; N = 6), and this activity was membrane associated (97 +/- 1%; N = 4). Taken together, the characteristics of this renal metalloproteinase indicate that it is distinct from classic matrix-degrading metalloproteinases. The release of this distinct metalloproteinase from damaged renal tubular epithelial cells during injury may result in the production of fragments of laminin or other extracellular matrix components with biologic effects relevant to renal regeneration.