Single Prolonged Stress induces ATF6 alpha-dependent Endoplasmic reticulum stress and the apoptotic process in medial Frontal Cortex neurons

Background: In our previous researches, we have found that apoptosis was induced in the medial prefrontal cortex (mPFC) of post-traumatic stress disorder (PTSD) rats. Endoplasmic reticulum (ER) stress-induced apoptosis has been implicated in the development of several disorder diseases. The aim of this study was to investigate whether endoplasmic reticulum-related pathway is involved in single-prolonged stress (SPS) induced apoptosis in the mPFC of PTSD rats by examining the expression levels of ATF6 alpha (ATF6a), two important downstream molecular chaperones of ATF6a in the ER stress: Glucose-regulated protein (GRP) 78 and ERP57, and apoptotic factors caspase 12, caspase 9, and caspase 3. Results: Our results of Morris Water Maze (MWM) test showed that after SPS exposure, a striking increase of the escape latency was observed in SPS rats at day 1 through day 6, and SPS rats had much less time spent in target quadrant compared to control rats (P < 0.01). And From immunofluorescence assays, we found that there was a gradual increase on the protein expression of ATF6a in response to SPS, which indicated ATF6a was activated by SPS. And additionally, immunohistochemistry assays, western blotting and reverse transcription-polymerase chain reaction (RT-PCR) showed that the immunoreactivity, protein and mRNA expression of GRP78 and ERP57 increased on 1, 4 days, and peaked on 7 days after SPS exposure, which revealed that SPS triggered inductions of GRP78 and ERP57 in the mPFC neurons. Moreover, RT-PCR assays demonstrated that there were up-regulations in the transcripts levels of caspase 12, caspase 9, and caspase 3 in response to SPS, which were according with the proteins changes of these apoptotic factors and indicated that ER stress and the activation of caspases contributed to SPS. Conclusion: Current data in this study highlight that SPS induced ATF6a-dependent Endoplasmic reticulum stress and ER-related apoptosis in the mPFC neurons, which indicated that the endoplasmic reticulum pathway may be involved in PTSD-induced apoptosis.