Protein aggregation after focal brain ischemia and reperfusion

Two hours of transient focal brain ischemia causes acute neuronal death in the striatal core region and a somewhat more delayed type of neuronal death in neocortex. The objective of the current study was to investigate protei n aggregation and neuronal death after focal brain ischemia in rats. Brain ischemia was induced by 2 hours of middle cerebral artery occlusion. Protei n aggregation was analyzed by electron microscopy, laser-scanning confocal microscopy, and Western blotting. Two hours of focal brain ischemia induced protein aggregation in ischemic neocortical neurons at 1 hour of reperfusi on, and protein aggregation persisted until neuronal death at 24 hours of r eperfusion. Protein aggregates were found in the neuronal soma, dendrites, and axons, and they were associated with intracellular membranous structure s during the postischemic phase. High-resolution confocal microscopy showed that clumped protein aggregates surrounding nuclei and along dendrites wer e formed after brain ischemia. On Western blots, ubiquitinated proteins (ub i-proteins) were dramatically increased in neocortical tissues in the posti schemic phase. The ubi-proteins were Triton-insoluble, indicating that they might be irreversibly aggregated. The formation of ubi-protein aggregates after ischemia correlated well with the observed decrease in free ubiquitin and neuronal death. The authors concluded that proteins are severely damag ed and aggregated in neurons after focal ischemia. The authors propose that protein damage or aggregation may contribute to ischemic neuronal death.