Induction of MMP-9 is largely blunted after ureteral obstruction in tPA–/– mice. (a) Zymographic analysis of whole-tissue lysate of the obstructed kidneys at 7 days after UUO in tPA+/+ and tPA–/– mice. Samples equalized for protein content were separated on a polyacrylamide gel containing 1 mg/ml gelatin. Proteolytic activity was demonstrated by digestion of gelatin, resulting in the bands of clearing. The locations of bands corresponding to MMP-9 and MMP-2 are indicated. Representative pictures show the results of two animals per group. (b) Graphic presentation of the relative abundance of MMP-9 (both pro–MMP-9 and active MMP-9) in obstructed kidneys in tPA+/+ and tPA–/– mice. Data are presented as mean ± SEM of five animals per group (n = 5). **P < 0.01, UUO vs. sham-operated. ‡P < 0.05, tPA+/+ vs. tPA–/– mice. (c–h) Immunofluorescence staining of MMP-9 protein in the obstructed kidneys at 7 days after UUO in tPA+/+ and tPA–/– mice (red). Renal proximal tubules were stained with lectin from T. purpureas (green). (c, d, and e) tPA+/+ mice. (f, g, and h) tPA–/– mice. In d and e, asterisk (*) indicates disaggregated, isolated tubular cell clusters on a background of abundant MMP-9 protein. Scale bar, 20 μm.