Enhanced cerebrovascular expression of matrix metalloproteinase-9 and tissue inhibitor of metalloproteinase-1 via the MEK/ERK pathway during cerebral ischemia in the rat

Background: Cerebral ischemia is usually characterized by a reduction in local blood flow and metabolism and by disruption of the blood-brain barrier in the infarct region. The formation of oedema and opening of the blood-brain barrier in stroke is associated with enhanced expression of metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinase-1 (TIMP-1). Results: Here, we found an infarct volume of 24.8 +/- 2% and a reduced neurological function after two hours of middle cerebral artery occlusion (MCAO), followed by 48 hours of recirculation in rat. Immunocytochemistry and confocal microscopy revealed enhanced expression of MMP-9, TIMP-1, and phosphorylated ERK1/2 in the smooth muscle cells of the ischemic MCA and associated intracerebral microvessels. The specific MEK1/2 inhibitor U0126, given intraperitoneal zero or 6 hours after the ischemic event, reduced the infarct volume significantly (11.8 +/- 2% and 14.6 +/- 3%, respectively; P < 0.05), improved neurological function, normalized expression of phosphorylated ERK1/2, and reduced expression of MMP-9 and TIMP-1 in the vessel walls. Administration of U0126 12 hours after MCAO did not alter the expression of MMP-9. Immunocytochemistry showed no overlap in expression between MMP-9/TIMP-1 and the astrocyte/glial cell marker GFAP in the vessel walls. Conclusion: These data are the first to show that the elevated vascular expression of MMP-9 and TIMP-1, associated with breakdown of the blood-brain barrier following focal ischemia, are transcriptionally regulated via the MEK/ERK pathway.