u-0126 and Brain-Infarction

Less disruption of the blood-brain barrier (BBB) after severe ischemic stroke is one of the beneficial outcomes of ischemic preconditioning (IP). However, the effect of IP on tight junctions (TJs), which regulate paracellular permeability of the BBB, is not well understood. In the present study, we examined IP-induced changes in TJs before and after middle cerebral artery occlusion (MCAO) in mice, and the association between changes in TJs and tolerance to a subsequent insult. After IP, we found decreased levels of transmembrane TJ proteins occludin and claudin-5, and widened gaps of TJs with perivascular swelling at the ultrastructural level in the brain. An inflammatory response was also observed. These changes were reversed by inhibition of extracellular signal-regulated kinase1/2 (ERK1/2) via the specific ERK1/2 inhibitor U0126. After MCAO, reduced brain edema and inflammatory responses were associated with altered levels of angiogenic factors and cytokines in preconditioned brains. Pretreatment with U0126 reversed the neuroprotective effects of IP against MCAO. These findings suggest that ERK1/2 activation has a pivotal role in IP-induced changes in TJs and inflammatory response, which serve to protect against BBB breakdown and inflammation after ischemic stroke.

Topics: Animals; Brain Edema; Brain Infarction; Butadienes; Disease Models, Animal; Enzyme Inhibitors; Gene Expression Regulation; Infarction, Middle Cerebral Artery; Ischemic Preconditioning, Myocardial; Male; Mice; Mice, Inbred C57BL; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Muscle Strength; Neurologic Examination; Nitriles; Tight Junctions; Time Factors; Vascular Endothelial Growth Factor A

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).. 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.. 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.

Topics: Actins; Animals; Astrocytes; Brain Infarction; Butadienes; Disease Models, Animal; Extracellular Signal-Regulated MAP Kinases; Gene Expression Regulation; Glial Fibrillary Acidic Protein; Infarction, Middle Cerebral Artery; Male; MAP Kinase Kinase Kinases; Matrix Metalloproteinase 1; Matrix Metalloproteinase 9; Microvessels; Muscle, Smooth; Neurologic Examination; Nitriles; Rats; Rats, Wistar; Signal Transduction; Tetrazolium Salts; Tissue Inhibitor of Metalloproteinase-1