Calpain-induced Proteolysis After Transient Global Cerebral Ischemia and Ischemic Tolerance in a Rat Model

Abstract

The activation of the [Ca(2+)]-dependent cysteine protease calpain plays an important role in ischemic injury. Here, the levels of two calpain-specific substrates, p35 protein and eukaryotic initiation factor 4G (eIF4G), as well as its physiological regulator calpastatin, were investigated in a rat model of transient global cerebral ischemia with or without ischemic tolerance (IT). Extracts of the cerebral cortex, whole hippocampus and hippocampal subregions after 30 min of ischemia and different reperfusion times (30 min and 4 h) were used. In rats without IT, the p35 levels slightly decreased after ischemia or reperfusion, whereas the levels of p25 (the truncated form of p35) were much higher than those in sham control rats after ischemia and remained elevated during reperfusion. The eIF4G levels deeply diminished after reperfusion and the decrease was significantly greater in CA1 and the rest of the hippocampus than in the cortex. By contrast, the calpastatin levels did not significantly decrease during ischemia or early reperfusion, but were upregulated after 4 h of reperfusion in the cortex. Although IT did not promote significant changes in p35 and p25 levels, it induced a slight increase in calpastatin and eIF4G levels in the hippocampal subregions after 4 h of reperfusion.

Nitric oxide mediates NMDA-induced persistent inhibition of protein synthesis through dephosphorylation of eukaryotic initiation factor 4E-binding protein 1 and eukaryotic initiation factor 4G proteolysis

“…Our results are in agreement with research showing that ischaemic tolerance, which promotes translation recovery, tends to prevent eIF4G processing and to favour the phosphorylation of 4E-BP1 [47,50].…”

Deregulation of HDAC1 by p25/Cdk5 in Neurotoxicity

“…rats subjected to transient forebrain ischemia. We and other groups have previously demonstrated the involvement of p25 in this model (Garcia-Bonilla et al, 2006; Wang et al, 2003; Wen et al, 2007). Also, p25 is upregulated in human postmortem brains following ischemic stroke (Mitsios et al, 2007).…”

In Vitro Ischemia Triggers a Transcriptional Response to Down-Regulate Synaptic Proteins in Hippocampal Neurons

“…Previous studies have indicated that the intracellular effects of ischemia include the activation of calpains, a family of calcium-activated cysteine proteases which trigger substrate-specific proteolysis that may contribute to neuronal death [21], after both in vivo [22], [23] and in vitro ischemia [24]–[26]. Calpain activation (usually detected as the breakdown products of a preferred substrate, spectrin) can therefore serve as an indirect indicator of the induction of cell death.…”