Possible mechanisms involved in the down-regulation of translation during transient global ischaemia in the rat brain

Abstract

The striking correlation between neuronal vulnerability and down-regulation of translation suggests that this cellular process plays a critical part in the cascade of pathogenetic events leading to ischaemic cell death. There is compelling evidence supporting the idea that inhibition of translation is exerted at the polypeptide chain initiation step, and the present study explores the possible mechanism/s implicated. Incomplete forebrain ischaemia (30min) was induced in rats by using the four-vessel occlusion model. Eukaryotic initiation factor (eIF)2, eIF4E and eIF4E-binding protein (4E-BP1) phosphorylation levels, eIF4F complex formation, as well as eIF2B and ribosomal protein S6 kinase (p70S6K) activities, were determined in different subcellular fractions from the cortex and the hippocampus [the CA1-subfield and the remaining hippocampus (RH)], at several post-ischaemic times. Increased phosphorylation of the α subunit of eIF2 (eIF2α) and eIF2B inhibition paralleled the inhibition of translation in the hippocampus, but they normalized to control values, including the CA1-subfield, after 4–6h of reperfusion. eIF4E and 4E-BP1 were significantly dephosphorylated during ischaemia and total eIF4E levels decreased during reperfusion both in the cortex and hippocampus, with values normalizing after 4h of reperfusion only in the cortex. Conversely, p70S6K activity, which was inhibited in both regions during ischaemia, recovered to control values earlier in the hippocampus than in the cortex. eIF4F complex formation diminished both in the cortex and the hippocampus during ischaemia and reperfusion, and it was lower in the CA1-subfield than in the RH, roughly paralleling the observed decrease in eIF4E and eIF4G levels. Our findings are consistent with a potential role for eIF4E, 4E-BP1 and eIF4G in the down-regulation of translation during ischaemia. eIF2α, eIF2B, eIF4G and p70S6K are positively implicated in the translational inhibition induced at early reperfusion, whereas eIF4F complex formation is likely to contribute to the persistent inhibition of translation observed at longer reperfusion times.

Regulatory proteins of eukaryotic initiation factor 2‐alpha subunit (eIF2α) phosphatase, under ischemic reperfusion and tolerance

“…In rats without IT, the peak in eIF2α phosphorylation was reached at R30 and afterwards eIF2(αP) levels significantly decreased all along reperfusion, a result very similar to that previously reported (Burda et al. 1994; Martín de la Vega et al. 2001a,b; García et al.…”

“…In addition, we have previously found that the eIF2α phosphatase activity, characterized as PP1, is inhibited both in vitro and in vivo after reperfusion (Muñoz et al. 2000; Martín de la Vega et al. 2001b).…”

Cerebral ischemia and the unfolded protein response

“…2003). The levels of eIF4E and eIF4G, the initiation factors responsible for delivering the mRNA to the ribosome during translation initiation, have also been shown to decrease following several hours of reperfusion (Martin de la Vega et al . 2001; Mengesdorf et al .…”

Neuroglobin is up‐regulated in the cerebellum of pups exposed to maternal epileptic seizures

“…After ischemia the non‐vulnerable areas return to normal, while the vulnerable areas remain inhibited (Bodsch et al, 1985; Widmann et al, 1991). Studies show that inhibition of protein synthesis after ischemia is accompanied by a dissociation of polyribosomes and endoplasmic reticulum dysfunction (Kleihues et al, 1975; Burda et al, 1994; Martín de la Vega et al, 2001; Paschen, 2004). After ischemia, energy metabolism regenerated only reactive phases of elongation and termination of synthesis, leading to dissociation of polyribosomes and a sustained inhibition of protein synthesis (Hossmann et al, 1992).…”