ag-490 and Ischemic-Attack--Transient

Signal transducer and activator of transcription 3 (STAT3) activation in ischemic brain has been verified. However, the mechanism and the role of STAT3 activation after cerebral ischemia-reperfusion are poorly elucidated. In the present study, we sought to test the hypothesis that STAT3 activation after cerebral ischemia-reperfusion was related to reactive oxygen species (ROS) production.. Adult male Sprague-Dawley rats were subjected to focal cerebral ischemia induced by middle cerebral artery occlusion. STAT3 activation was evaluated by immunohistochemistry and Western blotting. Rats were subjected to permanent ischemia or ischemia-reperfusion to clarify the temporal profile of STAT3 activation. The role of ROS in inducing STAT3 activation was assessed by administration of the ROS scavenger dimethylthiourea (DMTU). The effects of DMTU and the STAT3 activation inhibitor AG490 administration on brain ischemic injuries were evaluated by neurologic behavior scores and brain infarct volumes.. The activation of STAT3 after middle cerebral artery occlusion was significantly increased within peri-ischemia neurons and astrocytes. STAT3 activation mainly occurred in the reperfusion phase rather than in the ischemia phase. In addition, DMTU suppressed STAT3 activation in a dose-dependent manner, indicating that STAT3 activation may be a subsequent event after ROS production. DMTU and AG490 significantly reduced infarct sizes and improved neurologic outcomes.. In comparison with ischemia, reperfusion is a more powerful stimulus for STAT3 activation. ROS scavenging is closely correlated with an inhibition of STAT3 activation. Neuroprotective effects are achieved through ROS scavenging and down-regulation of STAT3 activation.

Topics: Animals; Free Radical Scavengers; Ischemic Attack, Transient; Male; Random Allocation; Rats; Rats, Sprague-Dawley; Reactive Oxygen Species; Reperfusion Injury; STAT3 Transcription Factor; Tyrphostins

Increased levels of interleukin-6 (IL-6) play a role in post-ischemic cerebral inflammation. IL-6 binding to its receptors induces phosphorylation of the receptor associated janus kinases (JAKs), and the down-stream signal transducer and activator of transcription (STAT) family of transcription factors, which amplify the IL-6 signal transduction. We evaluated the functional significance of JAK2 and STAT3 activation in focal ischemia-induced neuronal damage. Transient middle cerebral artery occlusion in adult rats led to increased JAK2 and STAT3 phosphorylation in the ipsilateral cortex and striatum after 6-72 h of reperfusion. Fluorescent immunohistochemistry with cell specific markers (NeuN for neurons, glial fibrillary acidic protein for reactive astrocytes and ED1/OX42 for activated macrophages/microglia) showed that both pJAK2 and pSTAT3 staining is predominantly localized in the macrophages/microglia in the post-ischemic brain. Intracerebroventricular infusion of rats with AG490 (a JAK2 phosphorylation inhibitor) prevented the post-ischemic JAK2 and STAT3 phosphorylation and significantly decreased the infarct volume, number of apoptotic cells and neurological deficits, compared to vehicle control. Furthermore, intracerebral injection of siRNA specific for STAT3 led to curtailed STAT3 mRNA expression and phosphorylation, decreased infarct volume, fewer apoptotic cells and improved neurological function following transient middle cerebral artery occlusion. These studies show that JAK2-STAT3 activation plays a role in post-ischemic brain damage.

Topics: Analysis of Variance; Animals; Blotting, Western; Cell Death; Enzyme Activation; Enzyme Inhibitors; Immunohistochemistry; In Situ Nick-End Labeling; Ischemic Attack, Transient; Janus Kinase 2; Nerve Tissue Proteins; Neurologic Examination; Neurons; Protein-Tyrosine Kinases; Proto-Oncogene Proteins; Rats; Reperfusion; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; RNA, Small Interfering; STAT3 Transcription Factor; Time Factors; Tyrphostins