Ischaemia-induced protein ubiquitinylation is differentially accompanied with heat-shock protein 70 expression after naïve and preconditioned ischaemia.

The aim of this study was to investigate the effect of transient global brain ischaemia, both naïve and preconditioned, on accumulation of ubiquitinylated proteins and induction of stress/chaperone proteins specific to cytoplasm and endoplasmic reticulum. In addition, possible correlation between stress response and ischaemia/induced translocation of p53 to mitochondria was investigated. Rats were subjected to 15-min forebrain ischaemia followed by 1, 3, 24 and 72 h of reperfusion. Transient cerebral ischaemia induced a massive increase in protein ubiquitinylation in the hippocampus as well as in both cerebral and cerebellar cortex. Enhanced ubiquitinylation of proteins was paralleled with transcriptional activation of hsp70.1 gene but not hsp70.3 gene. However, HSP70 protein level was significantly elevated 24 and 72 h after ischaemia. Neither ischaemia nor ischaemia followed by reperfusion was associated with significant changes of GRP78, GADD34 and GADD153 levels. Ubiquitinylated protein level was elevated 1 and 48 h after sub-lethal 5 min ischaemia. Preconditioned ischaemia (15 min ischaemia followed 48 h after sub-lethal ischaemia) was associated with even enhanced accumulation of ubiquitinylated proteins of molecular mass higher than 110 kDa. HSP70 protein was significantly elevated 48 h after sub-lethal ischaemia as well as after preconditioned ischaemia and all investigated time intervals of reperfusion. The elevated level of HSP70 might represent plausible explanation of inhibition of both translocation of p53 to mitochondria and ischaemia-induced apoptosis observed after preconditioned ischaemia.