Resulting abnormal proteins accumulate and then induce ER-stress. However, in some cell types, it has been reported that the depletion, rather than the overload, of ER Ca2+ stores is critical in apoptosis [40], [41]. Thus it is not entirely clear which components of the Ca2+ signaling cascade are important to trigger apoptosis. In our study, we observed Title Loaded From File calcium overload in the hippocampus 1 day after SPS, but the calcium level returned to normal level 4 days after SPS. These studies suggest that SPS compromises cellular Ca2+ homeostasis and that increased intracellular Ca2+ 10457188 could induce ER stress. We also analyzed the level of ca2+/CaM, a ubiquitous Ca2+ sensor protein involved in almost all intracellular events. CaMKIIa is the molecular basis of learning and memory, but in the absence of bound Ca2+/CaM, CaMKIIa is in its inactive conformation. The influx of Ca2+ results in CaMKIIa activation. Ca2+/CaMKIIa is a major mediator of Ca2+ signaling and of particular importance in the brain, contributing significantly to the regulation of nerve functions, including learning and memory [42]. It has been speculated that CaMKIIa responds to a strong and/or repeatedstimulus when the cellular Ca2+ concentration is relatively high. CaMKIIa is highly effective in synaptic plasticity and considered as one of the best candidates for a memory molecule [43]. Our result showed an increase in CaM level at 1 day after SPS, suggesting that the CaM content changed synchronously with changes in the Ca2+ concentration. This occurred as a result of the SPS increasing the intracellular free Ca2+ levels in the hippocampal cells which then induces the overexpression of CaM. The change in CaMKIIa from inactive to active decreased the CaMKIIa level in the hippocampus following SPS exposure. Li from our team has found change in the expression level of cytochrome C in the SPS rats, suggesting SPS induced mitochondria-dependent apoptosis in rat hippocampus. It is not contradictory with our result. It is possible that not only mitochondrial pathway but also endoplasmic reticulum pathway participate in Title Loaded From File SPS-induced apoptosis. ER and mitochondria form close contacts at 20 of the mitochondrial surface [44]. The direct contact between ER and mitochondria are referred to as mitochondrial associated membranes (MAM) [45]. MAM have pivotal roles in numerous cellular functions including Ca2+ signaling, lipid transport, energy metabolism, and cell survival. The interaction between the two organelles is mediated by mitochondrial shaping proteins and key chaperones including calnexin, calreticulin, ERp44, ERp57, GRp75, and sigma-1 receptor. It has been reported prolonged ER stress up-regulated release of cytochrome C and induced change of the mitochondria membrane potential [46]. Anti-apoptotic protein Bcl-2/Bcl-XL inhibited apoptosis induced by ER stress [47].ConclusionWe found that single-prolonged stress induced apoptosis in the hippocampus of rats. Changes in the expression levels of GRP78, caspase-12 and Ca2+/CaM/CaMKIIa, indicate that endoplasmic reticulum pathway participates in SPS-induced apoptosis. In particular, the increase in the expression of GRP78, which protects against apoptosis, may provide important information for the pathogenesis and treatment of PTSD. However, more research is needed to better understand the molecular mechanisms underlying PTSD-induced apoptosis.AcknowledgmentsThe authors would like to thank Prof. de kloet (Leiden University) for his assistanc.Resulting abnormal proteins accumulate and then induce ER-stress. However, in some cell types, it has been reported that the depletion, rather than the overload, of ER Ca2+ stores is critical in apoptosis [40], [41]. Thus it is not entirely clear which components of the Ca2+ signaling cascade are important to trigger apoptosis. In our study, we observed calcium overload in the hippocampus 1 day after SPS, but the calcium level returned to normal level 4 days after SPS. These studies suggest that SPS compromises cellular Ca2+ homeostasis and that increased intracellular Ca2+ 10457188 could induce ER stress. We also analyzed the level of ca2+/CaM, a ubiquitous Ca2+ sensor protein involved in almost all intracellular events. CaMKIIa is the molecular basis of learning and memory, but in the absence of bound Ca2+/CaM, CaMKIIa is in its inactive conformation. The influx of Ca2+ results in CaMKIIa activation. Ca2+/CaMKIIa is a major mediator of Ca2+ signaling and of particular importance in the brain, contributing significantly to the regulation of nerve functions, including learning and memory [42]. It has been speculated that CaMKIIa responds to a strong and/or repeatedstimulus when the cellular Ca2+ concentration is relatively high. CaMKIIa is highly effective in synaptic plasticity and considered as one of the best candidates for a memory molecule [43]. Our result showed an increase in CaM level at 1 day after SPS, suggesting that the CaM content changed synchronously with changes in the Ca2+ concentration. This occurred as a result of the SPS increasing the intracellular free Ca2+ levels in the hippocampal cells which then induces the overexpression of CaM. The change in CaMKIIa from inactive to active decreased the CaMKIIa level in the hippocampus following SPS exposure. Li from our team has found change in the expression level of cytochrome C in the SPS rats, suggesting SPS induced mitochondria-dependent apoptosis in rat hippocampus. It is not contradictory with our result. It is possible that not only mitochondrial pathway but also endoplasmic reticulum pathway participate in SPS-induced apoptosis. ER and mitochondria form close contacts at 20 of the mitochondrial surface [44]. The direct contact between ER and mitochondria are referred to as mitochondrial associated membranes (MAM) [45]. MAM have pivotal roles in numerous cellular functions including Ca2+ signaling, lipid transport, energy metabolism, and cell survival. The interaction between the two organelles is mediated by mitochondrial shaping proteins and key chaperones including calnexin, calreticulin, ERp44, ERp57, GRp75, and sigma-1 receptor. It has been reported prolonged ER stress up-regulated release of cytochrome C and induced change of the mitochondria membrane potential [46]. Anti-apoptotic protein Bcl-2/Bcl-XL inhibited apoptosis induced by ER stress [47].ConclusionWe found that single-prolonged stress induced apoptosis in the hippocampus of rats. Changes in the expression levels of GRP78, caspase-12 and Ca2+/CaM/CaMKIIa, indicate that endoplasmic reticulum pathway participates in SPS-induced apoptosis. In particular, the increase in the expression of GRP78, which protects against apoptosis, may provide important information for the pathogenesis and treatment of PTSD. However, more research is needed to better understand the molecular mechanisms underlying PTSD-induced apoptosis.AcknowledgmentsThe authors would like to thank Prof. de kloet (Leiden University) for his assistanc.
