MMP9 and Cerebral ischemia: Gel zymography (Figure 4A) and western blot (Figure 4B) showed that cerebral ischemia and reperfusion induced remarkable increases in MMP-9 activity and its protein levels in the ischemic brain tissue in wild-type mice, while this MMP-9 induction was significantly, but not completely, inhibited when gp91phox was knocked out.