Protein aggregation after transient cerebral ischemia

Protein aggregates containing ubiquitinated proteins are commonly present i n neurodegenerative disorders and have been considered to cause neuronal de generation. Here, we report that transient cerebral ischemia caused severe protein aggregation in hippocampal CA1 neurons. By using ethanolic phosphot ungstic acid electron microscopy (EM) and ubiquitin immunogold EM, we found that protein aggregates were accumulated in CA1 neurons destined to die 72 hr after 15 min of cerebral ischemia. Protein aggregates appeared as clump s of electron-dense materials that stained heavily for ubiquitin and were a ssociated with various intracellular membranous structures. The protein agg regates appeared at 4 hr and progressively accumulated at 24 and 48 hr of r eperfusion in CA1 dying neurons. However, they were rarely observed in dent ate gyrus neurons that were resistant to ischemia. At 4 hr of reperfusion, protein aggregates were mainly associated with intracellular vesicles in th e soma and dendrites, and the nuclear membrane. By 24 hr of reperfusion, th e aggregates were also associated with mitochondria, the Golgi apparatus, a nd the dendritic plasmalemma. High-resolution confocal microscopy further d emonstrated that protein aggregates containing ubiquitin were persistently and progressively accumulated in all CA1 dying neurons but not in neuronal populations that survive in this model. We conclude that proteins are sever ely aggregated in hippocampal neurons vulnerable to transient brain ischemi a. We hypothesize that the accumulation of protein aggregates cause ischemi c neuronal death.