Proteolytic Cascade Enzymes Increase in Focal Cerebral Ischemia in Rat

Cerebral infarction initiates a cascade of molecular events, leading to proteolytic cell death. Matrix-degrading metalloproteinases (MMPs) are neutral proteases involved in extracellular matrix damage. Type IV collagenase is an MMP that increases cerebral capillary permeability after intracerebral injection and may be important along with plasminogen activators (PA) in secondary brain edema in stroke. Therefore, we measured MMPs and PAs in spontaneously hypertensive (SHR) or Wistar-Kyoto (WKY) rats with permanent middle cerebral artery occlusion (MCAO). Brain tissue was assayed for MMPs and PAs at 1, 3, 12, and 24 h and 5 days after occlusion, using substrate gel polyacrylamide electrophoresis (zymography). SHR showed an increase in 92-kDa type IV collagenase (gelatinase B) in the infarcted hemisphere compared with the opposite side at 12 and 24 h (p < 0.05). Gelatinase A remained the same in both infarcted and normal tissue until 5 days after injury, when it increased significantly (p < 0.05). Urokinase-type PA was increased significantly at 12 and 24 h and 5 days, while tissue-type PA was decreased significantly at 1, 12, and 24 h in the ischemic compared with the nonischemic hemisphere. Gelatinase B was markedly increased in SHR at 12 and 24 h compared with WKY (p < 0.05). Secondary vasogenic edema is maximal 1-2 days after a stroke, which is the time that gelatinase B was elevated. The time of appearance of gelatinase B suggests a role in secondary tissue damage and vasogenic edema, while gelatinase A may be involved in tissue repair.