Evolution of GADD34 expression after focal cerebral ischaemia

Abstract

GADD34, a stress response protein associated with cell rescue, DNA repair and apoptosis, is expressed in the ischaemic brain. The C-terminal region of GADD34 has homology with the Herpes Simplex Virus protein, ICP34.5, which overcomes the protein synthesis block after viral infection by actively dephosphorylating eukaryotic translation initiation factor 2α (eIF2α). The carboxy terminus of GADD34 is also capable of dephosphorylating eIF2α and therefore has the capacity to restore the protein synthesis shutoff associated with ischaemia. This study examines the distribution and time course of GADD34 expression after focal cerebral ischaemia. Focal ischaemia or sham procedure was carried out on Sprague–Dawley rats with survival times of 4, 12, 24 h, 7 and 30 days. Brains were processed for histology and immunohistochemistry. Ischaemic damage was mapped onto line diagrams and GADD34 positive cells counted in selected regions of cortex and caudate. GADD34 immunopositive cells (mainly neurones), expressed as cells/mm 2, were present in ischaemic brains at 4 h (e.g., peri-infarct cortex 20 ± 5; contralateral cortex 3 ± 1, P < 0.05). Of the time points examined, numbers of GADD34 positive cells were highest 24 h after ischaemia (peri-infarct cortex 31 ± 7.3, contralateral cortex 0.1 ± 0.1, P < 0.05). Immunopositive cells, following a similar time course, were identified within the peri-infarct zone in the caudate nucleus and in ipsilateral cingulate cortex (possibly as a consequence of cortical spreading depression). GADD34 positive cells did not co-localise with a marker of irreversible cell death (TUNEL). Taken together, GADD34 positive cells in key neuroanatomical locations pertinent to the evolving ischaemic lesion, the lack of co-localisation with TUNEL and the protein's known effects on restoring protein synthesis, repairing DNA and involvement in ischaemic pre-conditioning suggests that it has the potential to influence cell survival in ischaemically compromised tissue.