Characterization of neuronal and astroglial responses to ER stress in the hippocampal CA1 area in mice following transient forebrain ischemia

Endoplasmic Reticulum Stress and the Unfolded Protein Response in Cerebral Ischemia/Reperfusion Injury

Ischemic stroke is an acute cerebrovascular disease characterized by sudden interruption of blood flow in a certain part of the brain, leading to serious disability and death. At present, treatment methods for ischemic stroke are limited to thrombolysis or thrombus removal, but the treatment window is very narrow. However, recovery of cerebral blood circulation further causes cerebral ischemia/reperfusion injury (CIRI). The endoplasmic reticulum (ER) plays an important role in protein secretion, membrane protein folding, transportation, and maintenance of intracellular calcium homeostasis. Endoplasmic reticulum stress (ERS) plays a crucial role in cerebral ischemia pathophysiology. Mild ERS helps improve cell tolerance and restore cell homeostasis; however, excessive or long-term ERS causes apoptotic pathway activation. Specifically, the protein kinase R-like endoplasmic reticulum kinase (PERK), activating transcription factor 6 (ATF6), and inositol-requiring enzyme 1 (IRE1) pathways are significantly activated following initiation of the unfolded protein response (UPR). CIRI-induced apoptosis leads to nerve cell death, which ultimately aggravates neurological deficits in patients. Therefore, it is necessary and important to comprehensively explore the mechanism of ERS in CIRI to identify methods for preserving brain cells and neuronal function after ischemia.

The Effect of Prosopis farcta and Its Bioactive Luteolin on the Hippocampus of Mice after Induced Ischemia Reperfusion

Background

Ischemia plays an important role in increasing damage to the nervous system. This study aimed to evaluate the effect of Prosopis farcta (PFE) and its bioactive luteolin (Lu) and forced swimming exercise on the hippocampus of mice after induced ischemia reperfusion.

Methods

The bioactive component of PFE (Lu) was identified by HPLC. Fifty-six male mice were divided into different groups. Ischemia was induced by ligation of the common carotid artery. After mice training (swimming exercise, 8 weeks) and consuming PFE and Lu, the mice's memory ability was evaluated in the shuttle box. Histological examination was performed by Nissel staining and immunohistochemistry.

Results

Results showed that the ischemic mice exercised and treated with PFE and Lu had higher step-through latency (STL) compared with the nonexercised mice, and this was confirmed with time spent in the dark compartment (TDC). The number of dark cells in the ischemic group exercising and receiving PFE and Lu decreased compared to that of the other groups in the hippocampus. DCX protein expression was increased in nonexercised groups compared to that of the exercised groups and those treated with PFE and Lu, while NeuN decreased.

Conclusions

Forced swimming exercise following ischemia, as well as consumption of PFE and Lu, has reduced cell death and increased neurogenesis in the hippocampus and thus may help improve memory in ischemia.

Mechanism of Endoplasmic Reticulum Stress in Cerebral Ischemia

Endoplasmic reticulum (ER) is the main organelle for protein synthesis, trafficking and maintaining intracellular Ca²⁺ homeostasis. The stress response of ER results from the disruption of ER homeostasis in neurological disorders. Among these disorders, cerebral ischemia is a prevalent reason of death and disability in the world. ER stress stemed from ischemic injury initiates unfolded protein response (UPR) regarded as a protection mechanism. Important, disruption of Ca²⁺ homeostasis resulted from cytosolic Ca²⁺ overload and depletion of Ca²⁺ in the lumen of the ER could be a trigger of ER stress and the misfolded protein synthesis. Brain cells including neurons, glial cells and endothelial cells are involved in the complex pathophysiology of ischemic stroke. This is generally important for protein underfolding, but even more for cytosolic Ca²⁺ overload. Mild ER stress promotes cells to break away from danger signals and enter the adaptive procedure with the activation of pro-survival mechanism to rescue ischemic injury, while chronic ER stress generally serves as a detrimental role on nerve cells via triggering diverse pro-apoptotic mechanism. What’s more, the determination of some proteins in UPR during cerebral ischemia to cell fate may have two diametrically opposed results which involves in a specialized set of inflammatory and apoptotic signaling pathways. A reasonable understanding and exploration of the underlying molecular mechanism related to ER stress and cerebral ischemia is a prerequisite for a major breakthrough in stroke treatment in the future. This review focuses on recent findings of the ER stress as well as the progress research of mechanism in ischemic stroke prognosis provide a new treatment idea for recovery of cerebral ischemia.

Inhibiting Caspase-12 Mediated Inflammasome Activation protects against Oxygen-Glucose Deprivation Injury in Primary Astrocytes

Stroke is one of the leading causes of death worldwide. Accumulating evidence suggests that NLRP3 inflammasome activation plays an important role in ischemic stroke injury. However, the existence of the NLRP3 inflammasome in astrocytes remains controversial. In this study, we demonstrated the presence of the NLRP3 inflammasome in primary mouse astrocytes and investigated the role of caspase-12 in NLRP3 inflammasome activation and cell injury in an in vitro astrocyte oxygen-glucose deprivation (OGD) model. Astrocytes exposed to 2, 3, and 4 h of OGD exhibited increased cell injury and apoptosis, and the protein levels of caspase-12, cleaved caspase-3, NLRP3 inflammasome components, and IL-1β were also significantly elevated. Interestingly, pretreatment with the caspase-12-specific inhibitor Z-ATAD-FMK attenuated cell injury and apoptosis and decreased the levels of NLRP3, caspase-1, IL-1β, and cleaved caspase-3 in the OGD group. In conclusion, Z-ATAD-FMK protected astrocytes against OGD-induced cell death and inhibited NLPR3-inflammasome activation. Our results indicate that caspase-12 and its potential regulation of NLRP3 inflammasome activation might be a promising target for treatment of ischemic stroke.

Anti‑Nogo‑A antibody promotes brain function recovery after cardiopulmonary resuscitation in rats by reducing apoptosis

Brain injury after cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) is the main cause of neurological dysfunction and death in cardiac arrest. To assess the effect of Nogo-A antibody on brain function in rats following CPR and to explore the underlying mechanisms, CA/CPR (ventricular fibrillation) rats were divided into the CPR+Nogo-A, CPR+saline and sham groups. Hippocampal caspase-3 levels were detected by RT-PCR and immunoblotting. Next, Nogo-A, glucose regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), cysteinyl aspartate specific proteinase-12 (casapse-12), Bcl-2 and Bax protein levels in the hippocampus were detected by immunoblotting. Coronal brain sections were analyzed by TUNEL assay to detect apoptosis at 72 h, while Nissl staining and electron microscopy were performed to detect Nissl bodies and microstructure at 24 h, respectively. Finally, rats were assessed for neurologic deficits at various times. Nissl staining revealed morphological improvement after Nogo-A antibody treatment. Sub-organelle structure was preserved as assessed by electron microscopy in model animals post-antibody treatment; neurological function was improved as well (P<0.05), while the apoptosis index was decreased (26.2±9.85 vs. 46.6±12.95%; P<0.05). Hippocampal caspase-3 mRNA and protein, Nogo-A protein levels were significantly decreased after antibody treatment (P<0.05). Hippocampal Nogo-A expression was positively correlated with caspase-3 (Pearson's correlation; r=0.790, P=0.000). Hippocampal GRP78 and Bcl-2 protein levels were higher after antibody treatment than these levels noted in the model animals (P<0.05), while CHOP, caspase-12 and Bax levels were reduced (P<0.05). Nogo-A antibody ameliorates neurological function after restoration of spontaneous circulation (ROSC), possibly by suppressing apoptosis induced by endoplasmic reticulum stress.

Neuroprotective mechanism of low-dose sodium nitrite in oxygen-glucose deprivation model of cerebral ischemic stroke in PC12 cells

The purpose of this study was to clarify the mechanisms of the protective effects of low-dose sodium nitrite (SN) on oxygen and glucose deprivation (OGD)-induced endoplasmic reticulum (ER) stress in PC12 cells. The PC12 cells were exposed to 4 h of OGD and treated with 100 μmol SN. The expression and activity of ER stress markers, including PKR-like endoplasmic reticulum kinase (PERK), transcription factor 6 (ATF6), CCAAT/enhancer binding protein homologous protein (CHOP), as well as caspase-12 and -3, were detected by immunoblotting assay. Fluorescence staining was used to detect the levels of reactive oxygen species (ROS) and Ca²⁺ release from the ER. Cell viability was also evaluated by MTT assay. It was found that SN significantly inhibited ROS production and Ca²⁺ release from the ER in OGD-injured PC12 cells. Moreover, ER stress marker expression and cleaved fragments of caspase-3 and -12 in OGD-injured PC12 cells were decreased after SN treatment. These findings were accompanied by a significant increase in cell viability. It seems that SN exerts a neuroprotective effect at least partially through reduction of ROS-mediated ER stress caused by OGD insult.

Spatiotemporal Expression of GRP78 in the Blood Vessels of Rats Treated With 3-Nitropropionic Acid Correlates With Blood-Brain Barrier Disruption

Glucose-regulated protein (GRP78) or BiP, a 78-kDa chaperone protein located in the endoplasmic reticulum (ER), has recently been reported to be involved in the neuroglial response to ischemia-induced ER stress. The present study was designed to study the expression patterns of this protein and the cell types involved in the induction of GRP78 expression in rats treated with the mitochondrial toxin 3-nitropropionic acid (3-NP). GRP78 immunoreactivity was almost exclusively localized to striatal neurons in saline-treated controls, but GRP78 expression was induced in activated glial cells, including reactive astrocytes and activated microglia/macrophages, in the striata of rats treated with 3-NP. In the lesion core, increased GRP78 immunoreactivity was observed in the vasculature; this was evident in the lesion periphery of the core at 3 days after lesion induction, and was evenly distributed throughout the lesion core by 7 days after lesion induction. Vascular GRP78 expression was correlated, both temporally and spatially, with infiltration of activated microglia into the lesion core. In addition, this was coincident with the time and pattern of blood-brain barrier (BBB) leakage, detected by the extravasation of fluorescein isothiocyanate-albumin, an established BBB permeability marker. Vascular GRP78-positive cells in the lesion core were identified as endothelial cells, smooth muscle cells, and adventitial fibroblast-like cells, in which GRP78 protein was specifically localized to the cisternae of the rough ER and perinuclear cisternae, but not to other organelles such as mitochondria or nuclei. Thus, our data provide novel insights into the phenotypic and functional heterogeneity of GRP78-positive cells within the lesion core, suggesting the involvement of GRP78 in the activation/recruitment of activated microglia/macrophages and its potential role in BBB impairment in response to a 3-NP-mediated neurotoxic insult.

Postconditioning with sevoflurane ameliorates spatial learning and memory deficit via attenuating endoplasmic reticulum stress induced neuron apoptosis in a rat model of hemorrhage shock and resuscitation

Hemorrhage shock could initiate endoplasmic reticulum stress (ERS) and then induce neuronal apoptosis. The aim of this study was to investigate whether sevoflurane postconditioning could attenuate brain injury via suppressing apoptosis induced by ERS. Seventy male rats were randomized into five groups: sham, shock, low concentration (sevo1, 1.2%), middle concentration (sevo2, 2.4%) and high concentration (sevo3, 3.6%) of sevoflurane postconditioning. Hemorrhage shock was induced by removing 40% of the total blood volume during an interval of 30 min. 1 h after the completion of bleeding, the animals were reinfused with shed blood during the ensuing 30 min. The spatial learning and memory ability of rats were measured by Morris water maze (MWM) test three days after the operation. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) positive cells in the hippocampus CA1 region were assessed after the MWM test. The expression of C/EBP-homologousprotein (CHOP) and glucose-regulated protein 78 (GRP78) in the hippocampus were measured at 24 h after reperfusion. We found that sevoflurane postconditioning with the concentrations of 2.4% and 3.6% significantly ameliorated the spatial learning and memory ability, decreased the TUNEL-positive cells, and reduced the GRP78 and CHOP expression compared with the shock group. These results suggested that sevoflurane postconditioning with the concentrations of 2.4% and 3.6% could ameliorate spatial learning and memory deficit after hemorrhage shock and resuscitation injury via suppressing apoptosis induced by ERS.

Cellular and Subcellular Localization of Endoplasmic Reticulum Chaperone GRP78 Following Transient Focal Cerebral Ischemia in Rats

The 78-kDa glucose-regulated protein (GRP78), a chaperone protein located in the endoplasmic reticulum (ER), has been reported to have neuroprotective effects in the injured central nervous system. Our aim was to examine the expression profiles and subcellular distributions of GRP78 and its association with the neuroglial reaction in the rat striatum after transient, focal cerebral ischemia. In sham-operated rats, constitutive, specific immunoreactivity for GRP78 was almost exclusively localized to the rough ER of striatal neurons, with none in the resting, ramified microglia or astrocytes. At 1 day post reperfusion, increased expression was observed in ischemia-resistant cholinergic interneurons, when most striatal neurons had lost GRP78 expression (this occurred earlier than the loss of other neuronal markers). By 3 days post reperfusion, GRP78 expression had re-emerged in association with the activation of glial cells in both infarct and peri-infarct areas but showed different patterns in the two regions. Most of the expression induced in the infarct area could be attributed to brain macrophages, while expression in the peri-infarct area predominantly occurred in neurons and reactive astrocytes. A gradual, sustained induction of GRP78 immunoreactivity occurred in reactive astrocytes localized to the astroglial scar, lasting for at least 28 days post reperfusion. Using correlative light- and electron-microscopy, we found conspicuous GRP78 protein localized to abnormally prominent, dilated rough ER in both glial cell types. Thus, our data indicate a link between GRP78 expression and the activated functional status of neuroglial cells, predominantly microglia/macrophages and astrocytes, occurring in response to ischemia-induced ER stress.

Age-related cataracts: Role of unfolded protein response, Ca2+ mobilization, epigenetic DNA modifications, and loss of Nrf2/Keap1 dependent cytoprotection

Age-related cataracts are closely associated with lens chronological aging, oxidation, calcium imbalance, hydration and crystallin modifications. Accumulating evidence indicates that misfolded proteins are generated in the endoplasmic reticulum (ER) by most cataractogenic stresses. To eliminate misfolded proteins from cells before they can induce senescence, the cells activate a clean-up machinery called the ER stress/unfolded protein response (UPR). The UPR also activates the nuclear factor-erythroid-2-related factor 2 (Nrf2), a central transcriptional factor for cytoprotection against stress. Nrf2 activates nearly 600 cytoprotective target genes. However, if ER stress reaches critically high levels, the UPR activates destructive outputs to trigger programmed cell death. The UPR activates mobilization of ER-Ca2+ to the cytoplasm and results in activation of Ca2+-dependent proteases to cleave various enzymes and proteins which cause the loss of normal lens function. The UPR also enhances the overproduction of reactive oxygen species (ROS), which damage lens constituents and induce failure of the Nrf2 dependent cytoprotection. Kelch-like ECH-associated protein 1 (Keap1) is an oxygen sensor protein and regulates the levels of Nrf2 by the proteasomal degradation. A significant loss of DNA methylation in diabetic cataracts was found in the Keap1 promoter, which overexpresses the Keap1 protein. Overexpressed Keap1 significantly decreases the levels of Nrf2. Lower levels of Nrf2 induces loss of the redox balance toward to oxidative stress thereby leading to failure of lens cytoprotection. Here, this review summarizes the overall view of ER stress, increases in Ca2+ levels, protein cleavage, and loss of the well-established stress protection in somatic lens cells.

Excessive nNOS/NO/AMPK signaling activation mediated by the blockage of the CBS/H2S system contributes to oxygen‑glucose deprivation‑induced endoplasmic reticulum stress in PC12 cells

Hypoxic‑ischemia stress causes severe brain injury, leading to death and disability worldwide. Although it has been reported that endoplasmic reticulum (ER) stress is an essential step in the progression of hypoxia or ischemia‑induced brain injury, the underlying molecular mechanisms are and have not yet been fully elucidated. Accumulating evidence has indicated that both nitric oxide (NO) and hydrogen sulfide (H2S) play an important role in the development of cerebral ischemic injury. In the present study, we aimed to investigate the effect of the association between NO signaling and the cystathionine β‑synthase (CBS)/H2S system on ER stress in a cell model of cerebral hypoxia‑ischemia injury. We found that oxygen‑glucose deprivation (OGD) markedly increased the NO level and neuronal NO synthase (nNOS) activity. 3‑Bromo‑7‑nitroindazole (3‑Br‑7‑NI), a relatively selective nNOS inhibitor, abolished the OGD‑induced inhibition of cell viability and the increased expression of ER stress‑related proteins, including glucose‑regulated protein 78 (GRP78), C/EBP homologous protein (CHOP) and cleaved caspase‑12 in PC12 cells, indicating the contribution of excessive nNOS/NO signaling to OGD‑induced ER stress. Furthermore, we found that OGD increased the phosphorylated AMP‑activated protein kinase (p‑AMPK)/AMPK ratio, and the AMPK activator, 5‑aminoimidazole‑4‑carboxamide‑1‑β‑D‑ribofuranoside (AICAR), attenuated the effects on OGD‑induced ER stress, suggesting that OGD‑induced NO overproduction results in AMPK activation in PC12 cells. We also found that OGD induced the downregulation of the CBS/H2S system, as indicated by the decreased H2S level in the culture supernatant and CBS activity in PC12 cells. In addition, we found that treatment with NaHS (a H2S donor) or S‑adenosyl‑L‑methionine (SAM, a CBS agonist) mitigated OGD‑induced ER stress, as well as the NO level, nNOS activity and AMPK phosphorylation in PC12 cells. On the whole, these results suggest that the inhibition of the CBS/H2S system, which facilitated excessive nNOS/NO/AMPK activation, contributes to OGD‑induced ER stress.

Edaravone protects against oxygen-glucose-serum deprivation/restoration-induced apoptosis in spinal cord astrocytes by inhibiting integrated stress response

We previously found that oxygen-glucose-serum deprivation/restoration (OGSD/R) induces apoptosis of spinal cord astrocytes, possibly via caspase-12 and the integrated stress response, which involves protein kinase R-like endoplasmic reticulum kinase (PERK), eukaryotic initiation factor 2-alpha (eIF2α) and activating transcription factor 4 (ATF4). We hypothesized that edaravone, a low molecular weight, lipophilic free radical scavenger, would reduce OGSD/R-induced apoptosis of spinal cord astrocytes. To test this, we established primary cultures of rat astrocytes, and exposed them to 8 hours/6 hours of OGSD/R with or without edaravone (0.1, 1, 10, 100 μM) treatment. We found that 100 μM of edaravone significantly suppressed astrocyte apoptosis and inhibited the release of reactive oxygen species. It also inhibited the activation of caspase-12 and caspase-3, and reduced the expression of homologous CCAAT/enhancer binding protein, phosphorylated (p)-PERK, p-eIF2α, and ATF4. These results point to a new use of an established drug in the prevention of OGSD/R-mediated spinal cord astrocyte apoptosis via the integrated stress response.

Melatonin Mediates Protective Effects against Kainic Acid-Induced Neuronal Death through Safeguarding ER Stress and Mitochondrial Disturbance

Kainic acid (KA)-induced neuronal death is linked to mitochondrial dysfunction and ER stress. Melatonin is known to protect hippocampal neurons from KA-induced apoptosis, but the exact mechanisms underlying melatonin protective effects against neuronal mitochondria disorder and ER stress remain uncertain. In this study, we investigated the sheltering roles of melatonin during KA-induced apoptosis by focusing on mitochondrial dysfunction and ER stress mediated signal pathways. KA causes mitochondrial dynamic disorder and dysfunction through calpain activation, leading to neuronal apoptosis. Ca²⁺ chelator BAPTA-AM and calpain inhibitor calpeptin can significantly restore mitochondrial morphology and function. ER stress can also be induced by KA treatment. ER stress inhibitor 4-phenylbutyric acid (PBA) attenuates ER stress-mediated apoptosis and mitochondrial disorder. It is worth noting that calpain activation was also inhibited under PBA administration. Thus, we concluded that melatonin effectively inhibits KA-induced calpain upregulation/activation and mitochondrial deterioration by alleviating Ca²⁺ overload and ER stress.

Valproate Attenuates Endoplasmic Reticulum Stress-Induced Apoptosis in SH-SY5Y Cells via the AKT/GSK3β Signaling Pathway

Endoplasmic reticulum (ER) stress-induced apoptosis plays an important role in a range of neurological disorders, such as neurodegenerative diseases, spinal cord injury, and diabetic neuropathy. Valproate (VPA), a typical antiepileptic drug, is commonly used in the treatment of bipolar disorder and epilepsy. Recently, VPA has been reported to exert neurotrophic effects and promote neurite outgrowth, but its molecular mechanism is still unclear. In the present study, we investigated whether VPA inhibited ER stress and promoted neuroprotection and neuronal restoration in SH-SY5Y cells and in primary rat cortical neurons, respectively, upon exposure to thapsigargin (TG). In SH-SY5Y cells, cell viability was detected by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay, and the expression of ER stress-related apoptotic proteins such as glucose‑regulated protein (GRP78), C/EBP homologous protein (CHOP), and cleaved caspase-12/-3 were analyzed with Western blot analyses and immunofluorescence assays. To explore the pathway involved in VPA-induced cell proliferation, we also examined p-AKT, GSK3β, p-JNK and MMP-9. Moreover, to detect the effect of VPA in primary cortical neurons, immunofluorescence staining of β-III tubulin and Anti-NeuN was analyzed in primary cultured neurons exposed to TG. Our results demonstrated that VPA administration improved cell viability in cells exposed to TG. In addition, VPA increased the levels of GRP78 and p-AKT and decreased the levels of ATF6, XBP-1, GSK3β, p-JNK and MMP-9. Furthermore, the levels of the ER stress-induced apoptosis response proteins CHOP, cleaved caspase-12 and cleaved caspase-3 were inhibited by VPA treatment. Meanwhile, VPA administration also increased the ratio of Bcl-2/Bax. Moreover, VPA can maintain neurite outgrowth of primary cortical neurons. Collectively, the neurotrophic effect of VPA is related to the inhibition of ER stress-induced apoptosis in SH-SY5Y cells and the maintenance of neuronal growth. Collectively, our results suggested a new approach for the therapeutic function of VPA in neurological disorders and neuroprotection.

Expression of Glucose-Regulated Protein 78 and miR-199a in Rat Brain After Fatal Ligature Strangulation

The roles of endoplasmic reticulum (ER) stress and microRNA in the brain tissue after fatal mechanical asphyxia have not been clearly elucidated. We examined the expression of glucose-regulated protein 78 (GRP78), the key regulator of unfolded protein response, and miR-199a in the brain tissues of rats subjected to fatal ligature strangulation to understand the roles of ER stress and microRNA in ligature strangulation. The expressions of GRP78 and miR-199a in rat cortex, hippocampi, and midbrain were measured by immunohistochemistry and Western blot analysis in a rat model of ligature strangulation. Furthermore, the levels of miR-199a-3p and miR-199a-5p were detected by real-time fluorescent quantitative polymerase chain reaction. Glucose-regulated protein 78 was highly expressed in the cortex and midbrain in the ligature strangulation group (P < 0.01) when compared with the control group. The expression of GRP78 in the hippocampi showed no significant difference between the 2 groups. miR-199a-3p in the cortex and midbrain was significantly down-regulated in the ligature strangulation group (P < 0.01). However, miR-199a-5p in each brain region showed no significant difference between the 2 groups. In conclusion, ER stress was involved in the physiological and pathological processes of ligature strangulation. Furthermore, upstream miR-199a may play an important regulatory role in mechanical asphyxia.

Adaptive preconditioning in neurological diseases - therapeutic insights from proteostatic perturbations

In neurological disorders, both acute and chronic neural stress can disrupt cellular proteostasis, resulting in the generation of pathological protein. However in most cases, neurons adapt to these proteostatic perturbations by activating a range of cellular protective and repair responses, thus maintaining cell function. These interconnected adaptive mechanisms comprise a 'proteostasis network' and include the unfolded protein response, the ubiquitin proteasome system and autophagy. Interestingly, several recent studies have shown that these adaptive responses can be stimulated by preconditioning treatments, which confer resistance to a subsequent toxic challenge - the phenomenon known as hormesis. In this review we discuss the impact of adaptive stress responses stimulated in diverse human neuropathologies including Parkinson׳s disease, Wolfram syndrome, brain ischemia, and brain cancer. Further, we examine how these responses and the molecular pathways they recruit might be exploited for therapeutic gain. This article is part of a Special Issue entitled SI:ER stress.

YiQiFuMai Powder Injection Ameliorates Cerebral Ischemia by Inhibiting Endoplasmic Reticulum Stress-Mediated Neuronal Apoptosis

YiQiFuMai (YQFM) powder injection as a modern preparation derived from Sheng Mai San, a traditional Chinese medicine, has been widely used in the treatment of cardiovascular and cerebrovascular diseases. However, its neuroprotective effect and underlying mechanism in cerebral ischemia remain to be explored. The present study was designed to investigate the neuroprotective effect of YQFM on endoplasmic reticulum (ER) stress-mediated neuronal apoptosis in the permanent middle cerebral artery occlusion- (MCAO-) injured mice and the oxygen-glucose deprivation- (OGD-) induced pheochromocytoma (PC12) cells. The results showed that single administration of YQFM (1.342 g/kg, i.p.) could reduce the brain infarction and improve the neurological deficits and the cerebral blood flow (CBF) after MCAO for 24 h in mice. Moreover, incubation with YQFM (100, 200, and 400 μg/mL) could increase the cell viability, decrease the caspase-3 activity, and inhibit the cell apoptosis in OGD-induced PC12 cells for 12 h. In addition, YQFM treatment could significantly modulate cleaved caspase-3 and Bcl-2 expressions and inhibit the expressions of ER stress-related marker proteins and signaling pathways in vivo and in vitro. In conclusion, our findings provide the first evidence that YQFM ameliorates cerebral ischemic injury linked with modulating ER stress-related signaling pathways, which provided some new insights for its prevention and treatment of cerebral ischemia diseases.

δV1-1 Reduces Pulmonary Ischemia Reperfusion-Induced Lung Injury by Inhibiting Necrosis and Mitochondrial Localization of PKCδ and p53

Ischemia-reperfusion (IR)-induced lung injury is one of the major contributing factors of morbidity and mortality after lung transplantation. To determine the IR-induced molecular changes in lung epithelial cells, we developed a cell-culture model that simulates lung preservation and transplantation. Six hours of cold ischemic time (CIT) and reperfusion elicited production of multiple inflammatory cytokines and chemokines and increased expression of endoplasmic reticulum (ER) proteins. Prolonged hypothermic condition (18 h CIT) reduced ER stress protein levels, and induced apoptosis and necrosis (via mechanisms related to mitochondrial permeability transition pore opening). Protein kinase C (PKCδ) was activated during CIT, and its downregulation via small interference (si) (in siRNA) RNA reduced IR-induced cytokine production and apoptotic cell death. δV1-1, a PKCδ peptide inhibitor, reduced translocation of PKCδ and p53 to the mitochondria after 18 h CIT, rescued ER stress protein expression, and converted the major mode of cell death from necrosis to apoptosis. Administration of δV1-1 effectively reduced lung transplantation and IR-induced pulmonary injury in rats. Therefore, inhibition of PKCδ by δV1-1 could be an effective strategy to ameliorate IR-induced lung injury by inhibiting the signaling pathways leading to necrosis.

Transcription factor changes following long term cerebral ischemia/reperfusion injury

The present study established a rat model of cerebral ischemia/reperfusion injury using four-vessel occlusion and found that hippocampal CA1 neuronal morphology was damaged, and that there were reductions in hippocampal neuron number and DNA-binding activity of cAMP response element binding protein and CCAAT/enhancer binding protein, accompanied by decreased learning and memory ability. These findings indicate that decline of hippocampal cAMP response element binding protein and CCAAT/enhancer binding protein DNA-binding activities may contribute to neuronal injury and learning and memory ability reduction induced by cerebral ischemia/reperfusion injury.

3,5,4'-Trihydroxy-6,7,3'-trimethoxyflavone protects astrocytes against oxidative stress via interference with cell signaling and by reducing the levels of intracellular reactive oxygen species

Oxidative stress is tightly involved in various neurodegenerative diseases such as Parkinson's and Alzheimer's diseases, and conditions such as ischemia. Astrocytes, the most abundant glial cells in the brain, protect neurons from reactive oxygen species (ROS) and provide them with trophic support. Therefore, any damage to astrocytes will affect neuronal survival. In a previous study we have demonstrated that an extract prepared from the plant Achillea fragrantissima (Af) prevented the oxidative stress-induced death of astrocytes and attenuated the intracellular accumulation of ROS in astrocytes under oxidative stress. In the present study, using activity guided fractionation, we have purified from this plant the active compound, determined to be a flavonoid named 3,5,4'-trihydroxy-6,7,3'-trimethoxyflavone (TTF). The effects of TTF in any biological system have not been studied previously, and this is the first study to characterize the anti-oxidant and protective effects of this compound in the context of neurodegenerative diseases. Using primary cultures of astrocytes we have found that TTF prevented the hydrogen peroxide (H2O2)-induced death of astrocytes, and attenuated the intracellular accumulation of ROS following treatment of these cells with H2O2 or the peroxyl radicals generating molecule 2,2'-Azobis(amidinopropane) (ABAP). TTF also interfered with cell signaling events and inhibited the phosphorylation of the signaling proteins stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK), extracellular signal regulated kinase (ERK 1/2) and mitogen activated protein kinase kinase (MEK1) and the phosphorylation of the transcription factor cyclic AMP response element-binding protein (CREB). The mechanism of the protective effect of TTF against H2O2-cytotoxicity could not be attributed to a direct H2O2 scavenging but rather to the scavenging of free radicals as was shown in cell free systems. Thus, TTF might be a therapeutic candidate for the prevention/treatment of neurodegenerative diseases where oxidative stress is part of the pathophysiology.

Endoplasmic reticulum stress: relevance and therapeutics in central nervous system diseases

Endoplasmic reticulum (ER) stress plays an important role in a range of neurological disorders, such as neurodegenation diseases, cerebral ischemia, spinal cord injury, sclerosis, and diabetic neuropathy. Protein misfolding and accumulation in the ER lumen initiate unfolded protein response in energy-starved neurons which are relevant to toxic effects. In neurological disorders, such as Alzheimer's disease, Parkinson's disease, and Huntington's disease, ER dysfunction is well recognized, but the mechanisms remain unclear. In stroke and ischemia, spinal cord injury, and amyotrophic lateral sclerosis, chronic activation of ER stress is considered as main pathogeny which causes neuronal disorders. By targeting components of these ER signaling responses, to explore clinical treatment strategies or new drugs in CNS neurological diseases might become possible and valuable in the future.

Disparity among neural injury models and the unfolded protein response

Endoplasmic reticulum stress is activated following both stroke and traumatic brain injury producing reactive oxgygen species, increasing intracellular calcium levels, and inducing inflammation; however, the timing and duration of activation varies between injuries. Preventing the immediate effects of ischemic/reperfusion injury or traumatic brain injury is challenging due to short onset of injury, but mitigating the secondary effects is a therapeutically targetable option. Preventative therapies using pharmacological agents have been utilized in pre-clinical models of neural injury to ameliorate secondary effects such as apoptosis and neurodegeneration. The connection between ER stress activation, apoptosis, and subsequent neurodegeneration has been proposed, but not yet causally linked. Researchers are now pursuing effective treatment strategies to suppress the secondary effects of neural injury in order to mitigate the development of chronic deficits. Secondary effects such as endoplasimic reticulum stress and neuroinflammation can be prevented in pre-clinical models, but the results have yet to translate to meaningful treatment options for patients. Evidence suggests that targeting the right transcription factors, at the right time, will aid in the prevention of apoptosis and neurodegenerative disease development following neural injury. In this review, we examine therapeutic approaches that target secondary injury and how these may correlate to better treatment options for patients.

Ischemia-like oxygen and glucose deprivation mediates down-regulation of cell surface γ-aminobutyric acidB receptors via the endoplasmic reticulum (ER) stress-induced transcription factor CCAAT/enhancer-binding protein (C/EBP)-homologous protein (CHOP)

Cerebral ischemia frequently leads to long-term disability and death. Excitotoxicity is believed to be the main cause for ischemia-induced neuronal death. Although a role of glutamate receptors in this process has been firmly established, the contribution of metabotropic GABAB receptors, which control excitatory neurotransmission, is less clear. A prominent characteristic of ischemic insults is endoplasmic reticulum (ER) stress associated with the up-regulation of the transcription factor CCAAT/enhancer-binding protein-homologous protein (CHOP). After inducing ER stress in cultured cortical neurons by sustained Ca(2+) release from intracellular stores or by a brief episode of oxygen and glucose deprivation (in vitro model of cerebral ischemia), we observed an increased expression of CHOP accompanied by a strong reduction of cell surface GABAB receptors. Our results indicate that down-regulation of cell surface GABAB receptors is caused by the interaction of the receptors with CHOP in the ER. Binding of CHOP prevented heterodimerization of the receptor subunits GABAB1 and GABAB2 and subsequent forward trafficking of the receptors to the cell surface. The reduced level of cell surface receptors diminished GABAB receptor signaling and, thus, neuronal inhibition. These findings indicate that ischemia-mediated up-regulation of CHOP down-regulates cell surface GABAB receptors by preventing their trafficking from the ER to the plasma membrane. This mechanism leads to diminished neuronal inhibition and may contribute to excitotoxicity in cerebral ischemia.

Role of the ubiquitin-proteasome system in brain ischemia: friend or foe?

The ubiquitin-proteasome system (UPS) is a catalytic machinery that targets numerous cellular proteins for degradation, thus being essential to control a wide range of basic cellular processes and cell survival. Degradation of intracellular proteins via the UPS is a tightly regulated process initiated by tagging a target protein with a specific ubiquitin chain. Neurons are particularly vulnerable to any change in protein composition, and therefore the UPS is a key regulator of neuronal physiology. Alterations in UPS activity may induce pathological responses, ultimately leading to neuronal cell death. Brain ischemia triggers a complex series of biochemical and molecular mechanisms, such as an inflammatory response, an exacerbated production of misfolded and oxidized proteins, due to oxidative stress, and the breakdown of cellular integrity mainly mediated by excitotoxic glutamatergic signaling. Brain ischemia also damages protein degradation pathways which, together with the overproduction of damaged proteins and consequent upregulation of ubiquitin-conjugated proteins, contribute to the accumulation of ubiquitin-containing proteinaceous deposits. Despite recent advances, the factors leading to deposition of such aggregates after cerebral ischemic injury remain poorly understood. This review discusses the current knowledge on the role of the UPS in brain function and the molecular mechanisms contributing to UPS dysfunction in brain ischemia with consequent accumulation of ubiquitin-containing proteins. Chemical inhibitors of the proteasome and small molecule inhibitors of deubiquitinating enzymes, which promote the degradation of proteins by the proteasome, were both shown to provide neuroprotection in brain ischemia, and this apparent contradiction is also discussed in this review.

Mithramycin, an agent for developing new therapeutic drugs for neurodegenerative diseases

Mithramycin A (MTM) has been shown to inhibit cancer growth by blocking the binding of Sp-family transcription factors to gene regulatory elements and is used for the treatment of leukemia and testicular cancer in the United States. In contrast, MTM has also been shown to exert neuroprotective effects in normal cells. An earlier study showed that MTM protected primary cortical neurons against oxidative stress-induced cell death. Recently, we demonstrated that MTM suppressed endoplasmic reticulum (ER) stress-induced neuronal death in organotypic hippocampal slice cultures and cultured hippocampal cells through attenuation of ER stress-associated signal proteins. We also found that MTM decreased neuronal death in area CA1 of the hippocampus after transient global ischemia/reperfusion in mice and restored the ischemia/reperfusion-induced impairment of long-term potentiation in this area. MTM has been shown to prolong the survival of Huntington's disease model mice and to attenuate dopaminergic neurotoxicity in mice after repeated administration of methamphetamine. In this review, we provide an up to date overview of neuroprotective effects of MTM and less toxic MTM analogs, MTM SK and MTM SDK, on some of the neurodegenerative diseases and discuss the promise of MTM as an agent for developing new therapeutic drugs for such diseases.

Role of mitochondrial function in the protective effects of ischaemic postconditioning on ischaemia/reperfusion cerebral damage

Objective

To investigate the effects of ischaemic postconditioning on brain injury and mitochondria in focal ischaemia and reperfusion, in rats.

Methods

Adult male Wistar rats ( n = 15 per group) underwent sham surgery, ischaemia (2-h middle cerebral artery occlusion), or ischaemia followed by ischaemic postconditioning (three cycles of 30 s reperfusion/30 s reocclusion). Brain infarction size, neurological function, mitochondrial reactive oxygen species (ROS) production, mitochondrial membrane potential and mitochondrial swelling were evaluated 24 h postsurgery.

Results

Infarct size was significantly smaller, and neurological function was significantly better, in the ischaemic postconditioning group than in the ischaemia group. Ischaemia resulted in significant increases in mitochondrial ROS production and swelling, and a reduction in mitochondrial membrane potential, all of which were significantly reversed by postconditioning.

Conclusions

The protective role of ischaemic postconditioning in focal ischaemia/reperfusion may be due to decreased mitochondrial ROS production, reduced mitochondrial membrane potential and suppressed mitochondria swelling. Mitochondria are potential targets for new therapies to prevent brain damage caused by ischaemia and reperfusion.

Endoplasmic reticulum dysfunction in neurological disease

Endoplasmic reticulum (ER) dysfunction might have an important part to play in a range of neurological disorders, including cerebral ischaemia, sleep apnoea, Alzheimer's disease, multiple sclerosis, amyotrophic lateral sclerosis, the prion diseases, and familial encephalopathy with neuroserpin inclusion bodies. Protein misfolding in the ER initiates the well studied unfolded protein response in energy-starved neurons during stroke, which is relevant to the toxic effects of reperfusion. The toxic peptide amyloid β induces ER stress in Alzheimer's disease, which leads to activation of similar pathways, whereas the accumulation of polymeric neuroserpin in the neuronal ER triggers a poorly understood ER-overload response. In other neurological disorders, such as Parkinson's and Huntington's diseases, ER dysfunction is well recognised but the mechanisms by which it contributes to pathogenesis remain unclear. By targeting components of these signalling responses, amelioration of their toxic effects and so the treatment of a range of neurodegenerative disorders might become possible.

Loss of endoplasmic reticulum Ca2+ homeostasis: contribution to neuronal cell death during cerebral ischemia

The loss of Ca(2+) homeostasis during cerebral ischemia is a hallmark of impending neuronal demise. Accordingly, considerable cellular resources are expended in maintaining low resting cytosolic levels of Ca(2+). These include contributions by a host of proteins involved in the sequestration and transport of Ca(2+), many of which are expressed within intracellular organelles, including lysosomes, mitochondria as well as the endoplasmic reticulum (ER). Ca(2+) sequestration by the ER contributes to cytosolic Ca(2+) dynamics and homeostasis. Furthermore, within the ER Ca(2+) plays a central role in regulating a host of physiological processes. Conversely, impaired ER Ca(2+) homeostasis is an important trigger of pathological processes. Here we review a growing body of evidence suggesting that ER dysfunction is an important factor contributing to neuronal injury and loss post-ischemia. Specifically, the contribution of the ER to cytosolic Ca(2+) elevations during ischemia will be considered, as will the signalling cascades recruited as a consequence of disrupting ER homeostasis and function.

MKP-1 antagonizes C/EBPβ activity and lowers the apoptotic threshold after ischemic injury

The dual specificity phosphatase MAPK phosphatase-1 (MKP-1) feeds back on MAP kinase signaling to regulate metabolic, inflammatory and survival responses. MKP-1 is widely expressed in the central nervous system (CNS) and induced after ischemic stress, although its function in these contexts remains unclear. Here we report that MKP-1 activated several cell death factors, including BCL2 and adenovirus E1B 19 kDa interacting protein 3, and caspases 3 and 12 culminating in apoptotic cell death in vitro. MKP-1 also exerted inhibitory effects on the bZIP transcription factor CCAAT/enhancer-binding protein (C/EBPβ), previously shown to have neuroprotective properties. These effects included reduced expression of the full-length C/EBPβ variant and hypo-phosphorylation at the MEK-ERK1/2-sensitive Thr(188) site. Notably, enforced expression C/EBPβ rescued cells from MKP-1-induced toxicity. Studies performed in knock-out mice indicate that the MKP-1 activity is required to exclude C/EBPβ from the nucleus basally, and that MKP-1 antagonizes C/EBPβ expression after global forebrain ischemia, particularly within the vulnerable CA1 sector of the hippocampus. Overall, MKP-1 appears to lower the cellular apoptotic threshold by inhibiting C/EBPβ and enhancing both BH3 protein expression and cellular caspase activity. Thus, although manipulation of the MKP-1-C/EBPβ axis could have therapeutic value in ischemic disorders, our observations using MKP-1 catalytic mutants suggest that approaches geared towards inhibiting MKP-1's phosphatase activity alone may be ineffective.

CHOP silencing reduces acute brain injury in the rat model of subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Endoplasmic reticulum stress triggers apoptotic cascades in neurons of the central nervous system after subarachnoid hemorrhage. The aim of this work was to study the mechanism of neuroprotection conferred by targeting cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) in the acute brain injury following subarachnoid hemorrhage.

METHODS

A total of 172 rats were used. Endovascular perforation induced subarachnoid hemorrhage. Two small interfering RNAs for CHOP were injected 24 hours before hemorrhage induction. At 24 or 72 hours, rats were neurologically evaluated and euthanized. The brains were recovered for molecular biology and histology studies.

RESULTS

Western blot analysis revealed effective silencing of CHOP associated with suppression of Bim-Caspase-3 apoptotic pathway. Moreover, the antiapoptotic Bcl2 was found upregulated with CHOP siRNA treatment. A reduced number of TUNEL-positive cells in the subcortex and in the hippocampus reflected histological protection. CHOP siRNA treatment ameliorated intracranial sequelae of and improved functional performance.

CONCLUSIONS

We conclude that CHOP silencing alleviates early brain injury following subarachnoid hemorrhage via inhibiting apoptosis and that CHOP siRNA treatment has a clinical potential for patients with this type of hemorrhagic stroke.

Protective action of mithramycin against neurodegeneration and impairment of synaptic plasticity in the hippocampal CA1 area after transient global ischemia

Mithramycin A (MTM) is an antibiotic used for the treatment of hypercalcemia and several types of cancer. We have reported previously that MTM protects against endoplasmic reticulum (ER) stress-induced neuronal death in organotypic hippocampal slice cultures. In the present study, the neuroprotective effect of MTM against ischemia/reperfusion-induced neuronal injury was evaluated in the hippocampus in mice. Neuronal damage was apparent in area CA1 of the hippocampus after transient global ischemia/reperfusion. The expression of C/EBP homologous protein (CHOP), a key transcription factor for ER stress-induced neuronal death, showed a pronounced increase in area CA1 in these mice. Treatment of the mice with MTM significantly decreased both the number of neurons stained with Fluoro-Jade B and the level of CHOP expression in the hippocampus. MTM did not affect the increase of 78-kDa glucose-regulated protein induced by ischemia/reperfusion. MTM also restored the ischemia/reperfusion-induced impairment of long-term potentiation in the hippocampus, without any change in paired pulse facilitation. These results suggest that administration of MTM protects hippocampal neurons against injury induced by transient global ischemia/reperfusion through attenuation of ER stress-associated signals, and ameliorates neuronal injury induced by ischemia/reperfusion in the hippocampus.

3-Bromo-7-nitroindazole attenuates brain ischemic injury in diabetic stroke via inhibition of endoplasmic reticulum stress pathway involving CHOP

AIMS

The role of nitric oxide (NO) and endoplasmic reticulum (ER) stress has been implicated in the pathogenesis of cerebral ischemic/reperfusion (I/R) injury and diabetes. The aim of the study was to investigate the neuroprotective potential of 3-bromo-7-nitroindazole (3-BNI), a potent and selective neuronal nitric oxide synthase (nNOS) inhibitor against ER stress and focal cerebral I/R injury associated with comorbid type 2 diabetes in-vivo.

MAIN METHODS

Type 2 diabetes was induced by feeding high-fat diet and streptozotocin (35 mg/kg) treatment in rats. Focal cerebral ischemia was induced by 2h middle cerebral artery occlusion (MCAO) followed by 22 h of reperfusion. Immunohistochemistry and western blotting methods were employed for the detection and expression of ER stress/apoptosis markers [78 kDa glucose regulated protein (GRP78) and CCAAT/enhancer binding protein homologous protein (CHOP)]. TUNEL assay for DNA fragmentation was also performed.

KEY FINDINGS

The diabetic rats subjected to cerebral I/R had prominent neurological damage and functional deficits compared with sham-operated rats. Massive DNA fragmentation was observed in ischemic penumbral region of diabetic brains. Concomitantly, the enhanced immunoreactivity and expression of ER stress/apoptosis markers were noticed. 3-BNI (30 mg/kg, i.p.) treatment significantly inhibited the cerebral infarct, edema volume and improved functional recovery of neurological deficits. The neuroprotection was further evident by lesser DNA fragmentation with a concomitant reduction of GRP78 and CHOP.

SIGNIFICANCE

The study demonstrates the neuroprotective potential of 3-BNI in diabetic stroke model which may be partly due to inhibition of ER stress pathway involving CHOP.

Neuroprotective effect of mithramycin against endoplasmic reticulum stress-induced neurotoxicity in organotypic hippocampal slice cultures

Endoplasmic reticulum (ER) stress has been implicated in the pathogenesis of various neurodegenerative diseases. Although the underlying mechanisms of these diseases have been suggested by many studies, therapeutic drugs have yet to be found. In this study, experiments were performed to examine the effect of mithramycin (MTM), a clinically approved guanosine-cytosine (GC)-rich DNA sequence-binding antitumor antibiotic, on ER stress-induced neurotoxicity in organotypic hippocampal slice cultures (OHCs). Time-dependent induction of the ER chaperones, glucose-regulated protein (GRP) 78 and GRP94, was observed after treatment with tunicamycin (TM) (80 μg/mL). Western blot analysis showed that treatment of OHCs with TM increased the expression of CHOP and the cleaved forms of caspase-12. Simultaneous application of MTM suppressed TM-induced cell death in all areas of OHCs with a concomitant decrease in the level of CHOP. In contrast, MTM had no effect on excitotoxic cell death induced by ibotenic acid, a potent N-methyl-d-aspartate (NMDA) agonist in OHCs. Moreover, RNA interference to CHOP or simultaneous treatment with MTM attenuated TM-induced cell death in primary cultured hippocampal neurons. These results suggest that CHOP plays a critical role in the mechanisms underlying ER-stress-induced neurotoxicity in the hippocampus, and that MTM could be a protective agent against ER stress-induced hippocampal neuronal death through attenuation of ER stress-associated signal proteins.

Impact of global cerebral ischemia on K+ channel expression and membrane properties of glial cells in the rat hippocampus

Astrocytes and NG2 glia respond to CNS injury by the formation of a glial scar. Since the changes in K(+) currents in astrocytes and NG2 glia that accompany glial scar formation might influence tissue outcome by altering K(+) ion homeostasis, we aimed to characterize the changes in K(+) currents in hippocampal astrocytes and NG2 glia during an extended time window of reperfusion after ischemic injury. Global cerebral ischemia was induced in adult rats by bilateral, 15-min common carotid artery occlusion combined with low-pressure oxygen ventilation. Using the patch-clamp technique, we investigated the membrane properties of hippocampal astrocytes and NG2 glia in situ 2 hours, 6 hours, 1 day, 3 days, 7 days or 5 weeks after ischemia. Astrocytes in the CA1 region of the hippocampus progressively depolarized starting 3 days after ischemia, which coincided with decreased Kir4.1 protein expression in the gliotic tissue. Other K(+) channels described previously in astrocytes, such as Kir2.1, Kir5.1 and TREK1, did not show any changes in their protein content in the hippocampus after ischemia; however, their expression switched from neurons to reactive astrocytes, as visualized by immunohistochemistry. NG2 glia displayed increased input resistance, decreased membrane capacitance, increased delayed outwardly rectifying and A-type K(+) currents and decreased inward K(+) currents 3 days after ischemia, accompanied by their proliferation. Our results show that the membrane properties of astrocytes after ischemia undergo complex alterations, which might profoundly influence the maintenance of K(+) homeostasis in the damaged tissue, while NG2 glia display membrane currents typical of proliferating cells.