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Activation of nuclear factor-κ-B in the rat brain after transient focal ischemia

Abstract:

Nuclear factor-kappaB (NF-κB) becomes activated under inflammatory conditions and triggers induction of gene expression. Here, activation of NF- κB was studied after transient middle cerebral artery occlusion in the rat. Expression of p65 and p50, protein subunits of NF-κB, was examined by Western blotting, and immunohistochemistry for p65 was carried out. Double- labelling with specific markers for astroglia and microglia was used for cell type identification. Neurons located within and surrounding the ischemic core were identified during the first 24 h post-ischemia by using an antibody against 72-kDa heat shock protein. NF-κB binding activity was evaluated at different times post-ischemia with electrophoretic mobility gel shift assays. The results showed constitutive expression of p65 and p50, and NF-κB binding activity. Basal p65 was seen in certain neurons and resting astrocytes. Constitutive NF-κB binding activity was attributable to one main protein complex possibly formed in neurons and astrocytes, although two minor complexes were also detected. At 1 day post-ischemia selective induction of p65 was seen in neurons located in penumbra-like area. At this time, however, no disturbances of basal NF-κB binding activity were found. Western blotting showed delayed induction of p65 several days after ischemia, whereas no changes were detected for p50. From 4 days post-ischemia, a substantial increase in the amount of p65 was detected due to induction in reactive astrocytes and microglia/macrophages. This was correlated with a robust enhancement of NF-κB binding activity with formation of three major specific binding DNA. It is proposed that the highly inducible NF-κB complexes resulted from induction of p65 and activation of NF-κB in post-ischemic reactive glia.