Synergy between a plasminogen cascade and MMP-9 in autoimmune disease
J. Clin. Invest. Zhi Liu, et al. 115:879 doi:10.1172/JCI23977 [Go to this article.]

Figure 4
MMP-9 activation by plasmin in vivo and in vitro. (A) To identify MMP-9 activation in the lesional skin of experimental BP, neonatal Plg^+/+, Plg^–/–, tuPA^+/+, and tuPA^–/– mice were injected i.d. with pathogenic anti-mBP180 IgG. Skin samples were obtained at 4 hours after IgG injection, and protein extracts (30 μg/lane) were analyzed by gelatin zymography. Both proMMP-9 and actMMP-9 were seen in lesional skin samples of IgG-injected +/+ mice (lanes 1 and 3). In contrast, no actMMP-9 was found in skin samples of pathogenic IgG-injected Plg^–/– (lane 2) and tuPA (lane 4) mice. (B) To show MMP-9 activation in a cell system, mouse neutrophils (mPMN; 1 × 10⁵) were stimulated by pathogenic anti-mBP180 IgG (5 μg/ml) plus mBP180 antigen (5 μg/ml) at 37°C for 1 hour. The supernatant was then incubated with plasmin (2 μg/ml) at 37°C for 16 hours. proMMP-9 released by neutrophils was activated by plasmin as shown by gelatin zymography (lane 1) and MMP colorimetric assay (bar 1). n = 6; *P < 0.001. (C) To show MMP-9 activation in vitro, the recombinant mouse proMMP-9 (1 μg) was incubated with plasmin (1 μg) in 100 μl of reaction buffer at 37°C for 6 hours and assayed by gelatin zymography and MMP colorimetric assay. Plasmin converted proMMP-9 to actMMP-9 (lane 2 and bar 2), and the activation was blocked by the plasmin inhibitor α2-AP (lane 3 and bar 3). n = 6; *P < 0.001.