salubrinal and Cognition-Disorders

We have previously reported that mild traumatic brain injury (mTBI) induced cognitive deficits as well as apoptotic changes in the brains of mice. Apoptosis may be caused by severe, prolonged accumulation of misfolded proteins, and protein aggregation in the endoplasmic reticulum (ER stress). In an additional study, we have reported that mTBI activated the pro-apoptotic arm of the integrated stress response (ISR). The main goal of the present study was to test the involvement of the adaptive eIF2α/ATF4 pathway in mTBI-affected brains. Head injury was induced with a noninvasive, closed-head weight drop (30 g) to ICR mice. Salubrinal, the selective phosphatase inhibitor of p-eIF2α, was injected immediately and 24 h after mTBI (1 mg/kg, ip). Y-maze and novel object recognition tests to assess spatial and visual memories, respectively, were conducted either 7 or 30 days post-trauma. Salubrinal administration significantly improved memory deficits following mTBI. Slaubrinal also prevented the elevation of degenerating neurons and the reduction of mature neurons in the cortex (as seen by immunofluorescent staining with Fluoro-Jade-B and NeuN antibodies, 72 h and 1 week post-mTBI, respectively). Western blot analysis revealed that salubrinal prevented the significant reduction in eIF2α and ATF4 phosphorylation in mTBI brains 72 h post-injury. Immunofluorescence staining revealed that although the reduction in p-eIF2α did not reach significance, salubrinal administration elevated it dramatically. Our results show that targeting the translational/adaptive arm of the ISR with salubrinal may serve as a therapeutic strategy for brain damage.

Topics: Activating Transcription Factor 4; Animals; Apoptosis; Brain Damage, Chronic; Brain Injuries; Cerebral Cortex; Cinnamates; Cognition Disorders; Drug Evaluation, Preclinical; Endoplasmic Reticulum Stress; Eukaryotic Initiation Factor-2; Exploratory Behavior; Hippocampus; Male; Maze Learning; Mice; Mice, Inbred ICR; Nerve Tissue Proteins; Neurons; Neuroprotective Agents; Phosphorylation; Protein Processing, Post-Translational; Recognition, Psychology; Signal Transduction; Thiourea; Wounds, Nonpenetrating

Long-term exposure to stressful stimuli can reduce hippocampal volume and cause cognitive impairments, but the underlying mechanisms are not well understood. Endoplasmic reticulum stress (ERS) is considered an early or initial response of cells under stress and linked to neuronal death in various neurodegenerative diseases. The present study investigated the involvement of ERS in restraint stress (RS)-induced hippocampal apoptosis and cognitive impairments. Using the rat RS model for 21 consecutive days, we found that the hippocampal apoptotic rate was significantly up-regulated as compared with unstressed controls, and salubrinal (ERS inhibitor) pretreatment effectively reduced the increase. As the marker of ERS, the 78-kDa glucose-regulated protein (GRP78) and the target molecule of the unfolded protein response (UPR), the splice variant of X-box binding protein 1 (sXBP-1) were also markedly increased in RS rats. Furthermore, in the three possible signaling pathways of ERS-induced apoptosis, the protein and mRNA levels of C/EBP homologous protein (CHOP) were significantly up-regulated, and caspase-12 was activated and cleaved, which suggested that these two pathways crucially contributed to hippocampal cell death. However, we found no changes in protein levels of phosphorylated JNK, implying that the JNK pathway was not the primary pathway involved in hippocampal apoptosis. It is more important that the cognitive impairments caused by RS were also effectively alleviated by salubrinal pretreatment. The present results suggested that ERS in hippocampus was excessively activated under stress, and amelioration of ERS could be a novel strategy to prevent and treat impaired cognitive function induced by RS.

Topics: Animals; Apoptosis; Caspase 12; Central Nervous System Agents; Cinnamates; Cognition Disorders; DNA-Binding Proteins; Endoplasmic Reticulum Stress; Heat-Shock Proteins; Hippocampus; Male; MAP Kinase Kinase 4; Maze Learning; Phosphorylation; Protein Isoforms; Rats, Sprague-Dawley; Regulatory Factor X Transcription Factors; RNA, Messenger; Stress, Psychological; Thiourea; Transcription Factors; Unfolded Protein Response