Cerebral Ischemia-induced ER Stress And Stresslin Expression

OBJECTIVETo investigate whether the endoplasmic reticulum (ER) stress will be induced by focal ischemia/reperfusion and whether stresslin expression can be up-regulated under this condition. Meanwhile, the types of the cells that secreting stresslin will be figured out.METHODSMiddle cerebral artery occlusion (MCAO) was performed to establish a focal cerebral ischemia/reperfusion model in rats. Tunicamycin and recombinant tau protein were used to induce ER stress in primarily cultured neurons. HE, immunohistochemistry, and immunofluorescent staining were used to observe ER stress and stesslin expression. The markers of neurons and neuroglial cells were used to determine the types of the cells that secreting stresslin.RESULTSIn normal rats, stresslin expresses a little in many brain regions, including hippocampus, cerebral cortex, thalamus, hypothalamus, substantia nigra, amygdaloid nucleus. It mainly distributes in cytosol. There is no difference in stresslin expression between the samples taken by fixing in vivo and decapitation. The expression of stresslin is not associated with gender. The stresslin-positive cells are more in the conventional rats than that in SPF rats, but there is not significance between them. CHOP was activated in the ischemic regions in unilateral MCAO rats, suggesting that ischemia induced ER stress. We also found that CHOP was in the cytosol in ischemic tissue, which was not reported before. In this case, CHOP was co-localized with stresslin. Additionally, stresslin was more sensitive to ischemia than CHOP.In the unilateral MCAO, stresslin expression was found to increase in ipsilateral hippocampus after 0.5 h ischemia followed by 1 h reperfusion. The stresslin-positive cells appear in hypothalamus and subcommissural organ after 2 h ischemia followed by 2 h reperfusion. Stresslin expression markedly increased in many regions after 4 h ischemia. Then we chased the reperfusion time for 12 h, 24 h, 36 h, 48 h, and 72 h after 4 h ischemia. It was found that stresslin expression went up along with the time prolongation. Moreover, the types of the cells that secreting stresslin were found. It includes neurons, astrocytes, oligodendrocytes, microglial cells, and ependymal cells.Interestingly, we found the number of NeuN-positive cells decreased in the ischemic regions, compared with the sham control. In stresslin-positive cells, the level of NeuN is lower than that in stresslin-negative cells, which suggest an inverse relationship between them. Meanwhile, we found the glial activation was obvious in the ischemic regions, which may contribute to induce ER stress.In the primary cultured neurons, we found that stresslin and CHOP were induced by ER stress inducer tunicamycin and recombinant human full length tau protein.CONCLUSIONS Focal ischemia/reperfusion induced ER stress and up-regulated stresslin expression. Stresslin was found in the cytosol of the neurons and neuroglial cells in the ischemic regions and was more sensitive to ischemia than CHOP. In some neurons, CHOP was found to present in cytosol where it co-localizes with stresslin, besides it appears in nucleus. Recombinant tau protein induces ER stress and stresslin expression in primarily cultured neurons.