Involvement of Proteasome and Endoplasmic Reticulum Stress in Neurodegeneration after Global Brain Ischemia

Abstract

Abstract A brief period of transient global brain ischemia leads to a selective ischemic neurodegeneration associated with death of hippocampal CA1 pyramidal neurons days after reperfusion. The mechanism of such selective and delayed neurodegeneration is still uncertain. The aim of our work was to study an involvement of proteasome and endoplasmic reticulum (ER) stress in ischemic neurodegeneration. We have performed laser scanning confocal microscopy analysis of brain slices from control and experimental animals that underwent global brain ischemia in duration of 15 minutes and varying times of reperfusion. We have focused on ubiquitin, PUMA that is proapoptotic protein of Bcl-2 family overexpressed in response to both proteasome and ER stress, and p53 that controls expression of PUMA. We have also examined expression of HRD1, E3 ubiquitin ligase that was shown to be overexpressed after ER stress. Using cellular models of both proteasome and ER stress, we have examined possible crosstalk between proteasome and ER stress. We demonstrate that global brain ischemia is associated with an appearance of distinct immunoreactivity of ubiquitin, PUMA and p53 in pyramidal neurons of CA1 layer of hippocampus 72 hours after ischemic insults. Such changes corelate with a delay and selectivity of ischemic neurodegeneration. Immunoreactivity of HRD1 observed in all investigated regions of rat brain was transiently absent in both CA1 and CA3 neurones 24 hours after ischemia in hippocampus that does not correlate with a delay and selectivity of ischemic neurodegeneration. We do not document significant crosstalk between proteasome and ER stress. Our results are in favour of dysfunction of ubiquitin proteasome system and consequent p53-induced expression of PUMA as the main mechanisms responsible for selective and delayed degeneration of pyramidal neurons of hippocampal CA1 layer in response to global brain ischemia.