Improved ischemic tissue regeneration after PAI-1 inhibitor treatment depends on tPA and MMP-9. (A-J) HL ischemia was induced in tPA^+/+, tPA^−/−, MMP-9^+/+, and MMP-9^−/− mice and the mice were then treated with or without PAI-1 inhibitor daily from days 0-6. (A) Fibrinolytic activity in plasma samples of HL-ischemia–induced tPA^+/+ and tPA^−/− mice was analyzed on day 1 using a fibrin plate assay (n = 3/group). (B) MMP-9 plasma levels were determined in tPA^+/+ and tPA^−/− mice treated with the PAI-1 inhibitor or with vehicle by ELISA (n = 9 for tPA^+/+ mice; n = 3 for tPA^−/− mice). (C,E) Representative images of limb perfusion analyzed using a laser Doppler. (D,F) The limb perfusion ratio (ischemic/nonischemic) over time of tPA^+/+ and tPA^−/− mice (D) and MMP-9^+/+ and MMP-9^−/− mice (F) treated with the PAI-1 inhibitor or with vehicle (n = 3/group). (G-J) Necrotic areas in sections of H&E-stained muscle sections (G,I) from untreated and PAI-1 inhibitor-treated ischemic limbs (scale bars, 200 mm). (H,J) Necrotic areas in ischemic muscle tissue sections were evaluated after 21 days (n = 3/group). Data represent means ± SEM. *P < .05; **P < .01.