Involvement of endoplasmic reticulum stress after middle cerebral artery occlusion in mice

The endoplasmic reticulum (ER) plays an important role in ischemic neuronal cell death. ER stress-related markers [immunoglobulin binding protein (BiP)/glucose-regulated protein (GRP) 78, activating transcription factor-4 (ATF-4), and C/EBP-homologous protein (CHOP)] in the striatum and the cortex were investigated after permanent middle cerebral artery occlusion (MCAO) in mice. Using endoplasmic reticulum stress-activated indicator (ERAI) transgenic mice, which show splicing of X-box protein 1 (XBP-1) mRNA as green fluorescence, we monitored the regional changes in fluorescence after MCAO. BiP mRNA (by reverse-transcription polymerase chain reaction [RT-PCR] analysis) was increased in the cortex at 6 h. In immunohistochemical and/or Western blot analysis, the expressions of ER stress-related markers (BiP, ATF-4, and CHOP) were increased in the infarct region, more strongly in the cortex than in the striatum. ERAI fluorescence was observed in the ischemic area starting from 6 and 12 h, respectively, after MCAO, with the peaks at 1 day and the fluorescence co-localized with the 2,3,5-triphenyltetrazolium chloride (TTC)-visible extension of brain infarction. These findings suggest that permanent MCAO induces expression of ER-stress related genes mainly in the periphery of the MCA territory.