ER stress, Stroke, CHOP, ATF6
Introduction: Stroke is a leading cause of death and acquired disability worldwide. A hallmark of stroke is impaired function of the endoplasmic reticulum (ER) stress response. In order to restore ER function in stressed cells, the unfolded protein response (UPR) is activated, which then induces three arms of ER stress sensor proteins including activating transcription factor 6 (ATF6). Although a failed ER stress response has been linked to apoptosis, the ATF6 UPR branch has also been found to be crucial to ischemic stroke outcome, via a pro-survival pathway, but the mechanisms are yet to be fully elucidated. We aimed to evaluate ATF6 and CHOP expression in infarcted and normal appearing cerebral tissue, following occlusive stroke and reperfusion.
Methods: Focal ischemic stroke was created by transient (4h) occlusion of the middle cerebral artery in Sprague Dawley rats (n=4/5 per group), followed by 2h full reperfusion or no reperfusion and sham operated controls. ATF6 and CHOP expression was assessed in 30m perfusion-fixed tissue sections by immunohistochemistry.
Approach for statistical analysis: Results were analysed by two-way ANOVA with Bonferroni post-hoc and expressed as mean + SEM.
Results and conclusions: An assessment of ATF6-expression found significantly higher levels in the 4h-occluded ipsilateral hemisphere with (F(1,149)=63.65), p<0.0001) or without reperfusion (F(1,149)=102.8), p<0.0001), but more so in the normal appearing frontal cortex than the lesioned temporal cortex (F(1,149)=37.83), p<0.0001). An assessment of CHOP expression also found significantly higher levels in the 4h-occluded ipsilateral hemisphere, with (F(1,190)=29.5), p<0.0001) or without, reperfusion (F(1,190)=81.19), p<0.0001), when compared to the contralateral hemisphere, particularly in the frontal cortex (F(1,190)=75.27), p<0.0001) in comparison to the lesioned temporal cortex.
High expression of ATF6 and CHOP particularly in the ipsilateral frontal cortex suggests that conflicting pro- and anti-apoptotic signals are present. Promotion of the pro-survival ATF6 arm could be critical if expansion of the lesion is to be prevented.