Ischemic preconditioning-induced neuroprotection against transient cerebral ischemic damage via attenuating ubiquitin aggregation

Ubiquitin binds to short-lived proteins, and denatured proteins are produced by various forms of injuries. In the present study, we investigated the effect of ischemic preconditioning (IPC) on free ubiquitin and its mutant form (ubiquitin+ 1) in the gerbil hippocampus induced by transient cerebral ischemia. The animals were randomly assigned to 4 groups (sham-operated-group, ischemia-operated-group, IPC plus (+)-sham-operated-group, and IPC + ischemia-operated-group). IPC was induced by subjecting gerbils to a 2 min of ischemia followed by 1 day of recovery. A significant loss of neurons was observed in the stratum pyramidale (SP) of the hippocampal CA1 region (CA1) in the ischemia-operated-groups 5 days after ischemia-reperfusion (I-R). In all the IPC + ischemia-operated-groups, neurons in the SP were well protected. We found that strong ubiquitin immunoreactivity was detected in the SP in the sham-operated-group and the immunoreactivity was decreased with time after I-R. In all the IPC + ischemia-operated-groups, ubiquitin immunoreactivity in the SP was similar to that in the sham-operated group. Moderate ubiquitin+ 1 immunoreactivity was detected in the SP of the sham-operated-group, and the immunoreactivity was markedly increased 2 days after I-R. Five days after I-R, ubiquitin+ 1 immunoreactivity was very weak in the SP. In all the IPC + ischemia-operated-groups, ubiquitin+ 1 immunoreactivity in the SP was slightly decreased with time after I-R. Western blot analysis showed that, in all the IPC + ischemia-ischemia-groups, the levels of ubiquitin and ubiquitin+ 1 proteins were well maintained after I-R. In brief, our findings suggest that the inhibition of the depletion of free ubiquitin and the formation of ubiquitin+ 1 may have an essential role in inducing cerebral ischemic tolerance by IPC.