Endoplasmic reticulum stress plays critical role in brain damage after cerebral ischemia/reperfusion in rats

Melatonin Protects Against Neuronal Apoptosis via Suppression of the ATF6/CHOP Pathway in a Rat Model of Intracerebral Hemorrhage

Neuronal apoptosis is an important factor accounting for the poor outcomes of intracerebral hemorrhage (ICH). This study first showed that inhibition of activating transcription factor 6 (ATF6) could alleviate secondary brain injury through anti-apoptosis after ICH in rats. Melatonin, ATF6 and CCAAT/enhancer-binding protein homologous protein (CHOP) siRNAs were applied in this study. Brain edema, neurological functions, blood-brain barrier (BBB) integrity were evaluated at 24 h after ICH. Western blot analysis was used to evaluate the protein level of target proteins (ATF6, CHOP, Bip, Bcl-2, Bax, and cleaved caspase-3). Reverse transcription-polymerase chain reaction (RT-PCR) was used to assess the mRNA level of ATF6, CHOP and cleaved caspase-3. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and caspase-3 immunofluorescence staining were applied to evaluate the neuronal cell death. The results suggested that the levels of ATF6 and its downstream protein, CHOP, were upregulated and reached the peak at 24 h after ICH. ATF6 was highly expressed in neurons. The administration of melatonin significantly decreased the mRNA and protein levels of ATF6, and its downstream targets, CHOP and cleaved caspase-3, but increased the Bcl-2/Bax ratio, which ameliorated the neurological functions. The CHOP siRNA significantly reversed the pro-apoptotic effect induced by the increased ATF6 level after ICH. Melatonin could protect against neuronal apoptosis via suppression of ATF6/CHOP arm of ER-stress-response pathway.

Melatonin Upregulates Nuclear Factor Erythroid-2 Related Factor 2 (Nrf2) and Mediates Mitophagy to Protect Against Early Brain Injury After Subarachnoid Hemorrhage

BACKGROUND The aim of this study was to investigate whether melatonin is involved in brain injury following subarachnoid hemorrhage (SAH). MATERIAL AND METHODS An SAH model was established and TUNEL assays were utilized to detect the effect of melatonin on cell apoptosis. Western blot analysis was used to detect the effect of melatonin on expression of autophagic markers and apoptotic factors. Real-time PCR, Western blot analysis, and luciferase assay were performed to study the effect of melatonin on nuclear factor erythroid-2 related factor 2 (NRF2) expression. RESULTS The SAH group displayed a lower neurological score and a higher brain water content, while melatonin treatment increased the neurological score and decreased the brain water content. The administration of melatonin also inhibited the apoptosis of neurons in the brain. In addition, higher Beclin-1 expression and higher conversion ratio from LC3- II to LC3-I were observed in the SAH group. The activation of Beclin-1 and the conversion from LC3-II to LC3-I was further enhanced by melatonin treatment. Furthermore, in the SAH group, the level of Bcl-2 was decreased while the level of Bax and cleaved caspase-3 were increased. However, following melatonin treatment in the SAH group, the level of Bcl-2 was increased while the levels of Bax and cleaved caspase-3 were decreased. CONCLUSIONS Our study indicated that, by increasing the expression of NRF2, the mitophagy induced by melatonin provided protection against brain injury post-SAH.

SH2B1 protects against OGD/R‑induced apoptosis in PC12 cells via activation of the JAK2/STAT3 signaling pathway

Apoptosis acts as the primary pathogenesis of cerebral ischemia/reperfusion (I/R) injury. Prior studies have revealed the effects of src homology 2 (SH2)B adaptor protein 1 (SH2B1) in myocardial infarction; however, involvement of SH2B1 in cerebral I/R injury and the underlying mechanisms remain to be investigated. In the present study, neural-like PC12 cells underwent 6 h of oxygen-glucose deprivation (OGD) followed by 24 h of reoxygenation (OGD/R). PC12 cells were pre-transfected with an adenovirus encoding for SH2B1 or GFP prior to exposure to OGD/R. Cell viability, LDH release and the apoptotic cascade were investigated. Reverse transcription-quantitative polymerase chain reaction and western blotting were employed to analyze mRNA and protein expression levels, respectively. The results of the present study revealed that OGD/R reduced SH2B1 expression in PC12 cells, accompanied by suppressed cell viability and enhanced cell death. Adenovirus-mediated SH2B1 overexpression, however, resulted in increased viability, reduced LDH release and a reduction in the expression levels of proteins associated with the apoptotic cascade in PC12 cells under the OGD/R condition. A mechanistic explanation may be that the positive effects of SH2B1 on neurons were in part derived from the activation of the JAK2/STAT3 signaling pathway. Furthermore, abolishment of JAK2/STAT3 signaling using a pharmacological inhibitor suppressed the inhibitory effects of SH2B1 under the OGD/R condition. The results of the present study suggested that SH2B1 may protect PC12 cells from OGD/R injury partially by the JAK2/STAT3-dependent inhibition of apoptosis and may provide a novel therapeutic target for the treatment of cerebral I/R injury.

Nobiletin protects PC12 cells from ERS-induced apoptosis in OGD/R injury via activation of the PI3K/AKT pathway

Nobiletin (NOB) possesses multiple pharmacological effects, but its anti-apoptotic property has acquired a great deal of attention. Endoplasmic reticulum (ER) stress (ERS)-induced apoptosis acts as the pivotal aetiology in neuronal oxygen-glucose deprivation and reoxygenation (OGD/R) injury. The aim of this study focused on whether NOB exerts neuro-protective effects on OGD/R injury by repressing ERS-induced apoptosis. The PC12 neuronal cell line was subjected to 4 h OGD and 24 h reoxygenation following NOB treatment. A PI3K/AKT inhibitor (LY294002) was added during the mechanistic experiments. Cell viability, lactate dehydrogenase (LDH) release and apoptosis were determined. Western blotting was used to measure protein expression levels. The results showed that OGD/R caused neuronal damageas exhibited by the increase in LDH release and the reduction of cellular viability. Moreover, ERS-induced apoptosis was markedly stimulated by OGD/R in PC12 cells, as evidenced by the elevation in the apoptotic rate and protein levels of C/EBP homologous protein/glucose-regulated protein-78. However, NOB administration significantly reversed neuronal damage and the ERS-induced apoptosis in response to OGD/R injury. Mechanistic detections showed that the neuron-favorable and ERS-repressing contributions of NOB were, in part, a result of the activation of the PI3K/AKT pathway, which was validated by a specific PI3K/AKT inhibitor (LY294002). Therefore, NOB protects PC12 cells from ERS-induced apoptosis in OGD/R injury mainly through enhancement of the PI3K/AKT pathway, which may provide a novel therapeutic avenue for the prevention of cerebral ischemia/reperfusion injury.

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.

Hypothermia augments stress response in mammalian cells

Mild hypothermia (32 °C) is routinely used in medical practice to alleviate hypoxic ischemic damage, however, the mechanisms that underlie its protective effects remain uncertain. Using a systems approach based on genome-wide expression screens, reporter assays and biochemical studies, we find that cellular hypothermia response is associated with the augmentation of major stress-inducible transcription factors Nrf2 and HIF1Α affecting the antioxidant system and hypoxia response pathways, respectively. At the same time, NF-κB, a transcription factor involved in the control of immune and inflammatory responses, was not induced by hypothermia. Furthermore, mild hypothermia did not trigger unfolded protein response. Lower temperatures (27 °C and 22 °C) did not activate Nrf2 and HIF1A pathways as efficiently as mild hypothermia. Current findings are discussed in the context of the thermodynamic hypothesis of therapeutic hypothermia. We argue that the therapeutic effects are likely to stem both from metabolic suppression (inhibitory component) and augmentation of stress tolerance (activating component). We argue that systems coping with cellular stressors are plausible targets of therapeutic hypothermia and deserve more attention in clinical hypothermia research.

Mesencephalic Astrocyte-Derived Neurotrophic Factor (MANF) Protects Against Neuronal Apoptosis via Activation of Akt/MDM2/p53 Signaling Pathway in a Rat Model of Intracerebral Hemorrhage

Neuronal apoptosis plays key roles in secondary brain injury caused by intracerebral hemorrhage (ICH). This study first reported the role of mesencephalic astrocyte-derived neurotrophic factor (MANF) in alleviating secondary brain injury through anti-apoptosis in rat model of ICH. The recombinant human-MANF (rh-MANF) and selective Akt inhibitor MK2206 was administrated intracerebroventricularly 1 h after ICH. Brain water content, behavioral assessment, BBB (blood brain barrier) leakage was evaluated 24 h after the induction of ICH. Western blot analysis was used to evaluate the expression level of target proteins (MANF, mouse 3T3 cell double-minute 2 (MDM2), P53, Akt, Bcl-2, Bax, and caspase-3). Terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) was applied to evaluate the neuronal cell death. Besides, whether MANF was expressed in neurons was verified with double immunofluorescence staining. The results suggested that the level of MANF, and its downstream proteins, Akt, MDM2 was upregulated and reached peak at 24 h after ICH. MANF was mainly expressed in neurons. The administration of rh-MANF could significantly increase the level of p-Akt, p-MDM2, Bcl/Bax ratio, but reduce the expression of p53, caspase-3 and neuronal death, thus ameliorate the neurological functions at 24 h after ICH. However, these effects of rh-MANF could be obviously reversed by MK2206. MANF could exert its neuronal anti-apoptotic effects via Akt/MDM2/P53 pathways. Therefore, MANF could be a valuable drug target in the treatment of ICH.

Elucidation of Gene Expression Patterns in the Brain after Spinal Cord Injury

Spinal cord injury (SCI) is a devastating neurological disease. The pathophysiological mechanisms of SCI have been reported to be relevant to central nervous system injury such as brain injury. In this study, gene expression of the brain after SCI was elucidated using transcriptome analysis to characterize the temporal changes in global gene expression patterns in a SCI mouse model. Subjects were randomly classified into 3 groups: sham control, acute (3 h post-injury), and subacute (2 wk post-injury) groups. We sought to confirm the genes differentially expressed between post-injured groups and sham control group. Therefore, we performed transcriptome analysis to investigate the enriched pathways associated with pathophysiology of the brain after SCI using Database for Annotation Visualization, and Integrated Discovery (DAVID), which yielded Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway. Following enriched pathways were found in the brain: oxidative phosphorylation pathway; inflammatory response pathways—cytokine–cytokine receptor interaction and chemokine signaling pathway; and endoplasmic reticulum (ER) stress-related pathways—antigen processing and presentation and mitogen-activated protein kinase signaling pathway. Oxidative phosphorylation pathway was identified at acute phase, while inflammation response and ER stress-related pathways were identified at subacute phase. Since the following pathways—oxidative phosphorylation pathway, inflammatory response pathways, and ER stress-related pathways—have been well known in the SCI, we suggested a link between SCI and brain injury. These mechanisms provide valuable reference data for better understanding pathophysiological processes in the brain after SCI.

Diazoxide inhibits of ER stress‑mediated apoptosis during oxygen‑glucose deprivation in vitro and cerebral ischemia‑reperfusion in vivo

Neuroprotective strategies using diazoxide (DZX) have been demonstrated to limit ischemia/reperfusion (I/R)-induced injury and cell apoptosis. In type 2 diabetes mellitus, DZX has been reported to improve β-cell function and reduce their apoptosis, through suppressing endoplasmic reticulum (ER) stress. However, the effects of DZX on ER stress during I/R-induced neuronal apoptosis in the hippocampus remains to be elucidated. In the present study, pretreatment of hippocampal neurons with DZX was revealed to inhibit oxygen-glucose deprivation (OGD)-stimulated apoptosis in vitro and to alleviate I/R-induced hippocampal injury and behavioral deficits in rats in vivo. Furthermore, OGD and I/R were demonstrated to induce ER stress via upregulating the expression of ER stress-associated proteins, including C/EBP homologous protein, 78 kDa glucose-regulated protein and caspase-12, whereas the exogenous administration of DZX effectively downregulated ER stress-associated protein expression following OGD and I/R. In addition, DZX was revealed to significantly increase the protein expression of B-cell lymphoma (Bcl)-2 and suppress the expression of caspase-3 and Bcl-2-associated X protein. These findings suggested that DZX may protect cells against apoptosis via regulating the expression of ER stress-associated proteins in vitro and in vivo, thus enhancing the survival of hippocampal cells. The present results suggested a novel mechanism that may underlie the protective effect of DZX administration in the central nervous system.

Melatonin protects brain against ischemia/reperfusion injury by attenuating endoplasmic reticulum stress

Endoplasmic reticulum (ER) stress plays a vital role in mediating ischemic reperfusion damage in brain. In this study, we evaluated whether melatonin inhibits ER stress in cultured neurons exposed to oxygen and glucose deprivation (OGD) and in rats subjected to transient focal cerebral ischemia. Sprague-Dawley rats were treated with melatonin (5 mg/kg) or control at reperfusion onset after transient occlusion of the right middle cerebral artery (MCA) for 90 min. Brain infarction and hemorrhage within infarcts were measured. The expression of ER stress proteins of phosphorylation of PRKR-like endoplasmic reticulum kinase (p-PERK), phosphorylation of eukaryotic translation initiation factor 2α (p-eIF2α), activating transcription factor 4 (ATF4) and C/EBP homologous protein (CHOP) were detected by western blotting and immunohistochemistry analysis. The terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling (TUNEL) method, cleaved caspase-3 and cytochrome c were used to investigate cell apoptosis in OGD-induced cultured neurons. Our results demonstrated that animals treated with melatonin had significantly reduced infarction volumes and individual cortical lesion sizes as well as increased numbers of surviving neurons. Melatonin can significantly modulate protein levels by decreasing both p-PERK and p-eIF2α in the ischemic core and penumbra. Moreover, the expressions of ATF4 and CHOP were restrained in the ischemic core and penumbra, respectively. Furthermore, pretreatment with melatonin at 10–100 µM effectively reduced the levels of p-PERK and p-eIF2α in cultured neurons after OGD injury. Melatonin treatment also effectively decreased neuron apoptosis resulting from OGD-induced neuron injury. These results indicate that melatonin effectively attenuated post-ischemic ER stress after ischemic stroke.

PPARα activation alleviates damage to the cytoskeleton during acute myocardial ischemia/reperfusion in rats

The cytoskeleton serves an important role in maintaining cellular morphology and function, and it is a substrate of calpain during myocardial ischemia/reperfusion (I/R) injury (MIRI). Calpain may be activated by endoplasmic reticulum (ER) stress during MIRI. The activation of peroxisome proliferator-activated receptor α (PPARα) may inhibit ischemia/reperfusion damage by regulating stress reactions. The present study aimed to determine whether the activation of PPARα protects against MIRI-induced cytoskeletal degradation, and investigated the underlying mechanism involved. Wistar rats were pretreated with or without fenofibrate and subjected to left anterior descending coronary artery ligation for 45 min, followed by 120 min of reperfusion. Calpain activity and the expression of PPARα, desmin and ER stress parameters were evaluated. Electrocardiography was performed and cardiac function was evaluated. The ultrastructure was observed under transmission electron microscopy. I/R significantly induced damage to the cytoskeleton in cardiomyocytes and cardiac dysfunction, all of which were improved by PPARα activation. In addition, I/R increased ER stress and calpain activity, which were significantly decreased in fenofibrate-pretreated rat heart tissue. The results suggested that PPARα activation may exert a protective effect against I/R in the myocardium, at least in part via ER stress inhibition. Suppression of ER stress may be an effective therapeutic target for protecting the I/R myocardium.

PERK Pathway Activation Promotes Intracerebral Hemorrhage Induced Secondary Brain Injury by Inducing Neuronal Apoptosis Both in Vivo and in Vitro

The protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) signaling pathway was reported to exert an important role in neuronal apoptosis. The present study was designed to investigate the roles of the PERK signaling pathway in the secondary brain injury (SBI) induced by intracerebral hemorrhage (ICH) and its potential mechanisms. Sprague-Dawley rats were used to establish ICH models by injecting autologous blood (100 μl), and cultured primary rat cortical neurons were exposed to oxyhemoglobin (10 μM) to mimic ICH in vitro. The PERK antagonist, GSK2606414, and inhibitor of eukaryotic translation initiation factor 2 subunit α (eIF2α) dephosphorylation, salubrinal, were used to study the roles of PERK signaling pathway in ICH-induced SBI. Our results showed that the protein levels of p-eIF2α and ATF4 were upregulated following ICH, peaking at 48 h. Application of GSK2606414 reversed this increase in vivo and in vitro, thereby preventing ICH-induced neuronal apoptosis. On the contrary, salubrinal inhibited the dephosphorylation of eIF2α, resulting in the elevation of p-eIF2α, which could activate downstream of PERK signaling and induce neuronal apoptosis and necrosis following ICH in vitro and in vivo. Thus, PERK signaling pathway plays an important role in ICH-induced apoptosis and blocking its activation has neuroprotective effects that alleviates SBI, suggesting that targeting this pathway could be a promising therapeutic strategy for improving patient outcome after ICH.

Salubrinal and robenacoxib treatment after global cerebral ischemia. Exploring the interactions between ER stress and inflammation

BACKGROUND

Blood reperfusion of the ischemic tissue after stroke promotes increases in the inflammatory response as well as accumulation of unfolded/misfolded proteins in the cell, leading to endoplasmic reticulum (ER) stress. Both Inflammation and ER stress are critical processes in the delayed death of the cells damaged after ischemia. The aim of this study is to check the putative synergic neuroprotective effect by combining anti-inflammatory and anti-ER stress agents after ischemia.

METHODS

The study was performed on a two-vessel occlusion global cerebral ischemia model. Animals were treated with salubrinal one hour after ischemia and with robenacoxib at 8 h and 32 h after ischemia. Parameters related to the integrity of the blood-brain barrier (BBB), such as matrix metalloproteinase 9 and different cell adhesion molecules (CAMs), were analyzed by qPCR at 24 h and 48 h after ischemia. Microglia and cell components of the neurovascular unit, including neurons, endothelial cells and astrocytes, were analyzed by immunofluorescence after 48 h and seven days of reperfusion.

RESULTS

Pharmacologic control of ER stress by salubrinal treatment after ischemia, revealed a neuroprotective effect over neurons that reduces the transcription of molecules involved in the impairment of the BBB. Robenacoxib treatment stepped neuronal demise forward, revealing a detrimental effect of this anti-inflammatory agent. Combined treatment with robenacoxib and salubrinal after ischemia prevented neuronal loss and changes in components of the neurovascular unit and microglia observed when animals were treated only with robenacoxib.

CONCLUSION

Combined treatment with anti-ER stress and anti-inflammatory agents is able to provide enhanced neuroprotective effects reducing glial activation, which opens new avenues in therapies against stroke.

Are Major Dementias Triggered by Poor Blood Flow to the Brain? Theoretical Considerations

There is growing evidence that chronic brain hypoperfusion plays a central role in the development of Alzheimer's disease (AD) long before dyscognitive symptoms or amyloid-β accumulation in the brain appear. This commentary proposes that dementia with Lewy bodies (DLB), frontotemporal dementia (FTD), and Creutzfeldt-Jakob disease (CJD) may also develop from chronic brain hypoperfusion following a similar but not identical neurometabolic breakdown as AD. The argument to support this conclusion is that chronic brain hypoperfusion, which is found at the early stages of the three dementias reviewed here, will reduce oxygen delivery and lower oxidative phosphorylation promoting a steady decline in the synthesis of the cell energy fuel adenosine triphosphate (ATP). This process is known to lead to oxidative stress. Virtually all neurodegenerative diseases, including FTD, DLB, and CJD, are characterized by oxidative stress that promotes inclusion bodies which differ in structure, location, and origin, as well as which neurological disorder they typify. Inclusion bodies have one thing in common; they are known to diminish autophagic activity, the protective intracellular degradative process that removes malformed proteins, protein aggregates, and damaged subcellular organelles that can disrupt neuronal homeostasis. Neurons are dependent on autophagy for their normal function and survival. When autophagic activity is diminished or impaired in neurons, high levels of unfolded or misfolded proteins overwhelm and downregulate the neuroprotective activity of unfolded protein response which is unable to get rid of dysfunctional organelles such as damaged mitochondria and malformed proteins at the synapse. The endpoint of this neuropathologic process results in damaged synapses, impaired neurotransmission, cognitive decline, and dementia.

Kaempferol mitigates Endoplasmic Reticulum Stress Induced Cell Death by targeting caspase 3/7

The Endoplasmic Reticulum (ER) plays a fundamental role in executing multiple cellular processes required for normal cellular function. Accumulation of misfolded/unfolded proteins in the ER triggers ER stress which contributes to progression of multiple diseases including neurodegenerative disorders. Recent reports have shown that ER stress inhibition could provide positive response against neuronal injury, ischemia and obesity in in vivo models. Our search towards finding an ER stress inhibitor has led to the functional discovery of kaempferol, a phytoestrogen possessing ER stress inhibitory activity in cultured mammalian cells. We have shown that kaempferol pre-incubation significantly inhibits the expression of GRP78 (a chaperone) and CHOP (ER stress associated pro-apoptotic transcription factor) under stressed condition. Also, our investigation in the inhibitory specificity of kaempferol has revealed that it inhibits cell death induced by diverse stimuli. Further study on exploring the molecular mechanism implied that kaempferol renders protection by targeting caspases. Both the in silico docking and in vitro assay using recombinant caspase-3 enzyme confirmed the binding of kaempferol to caspases, through an allosteric mode of competitive inhibition. Altogether, we have demonstrated the ability of kaempferol to alleviate ER stress in in vitro model.

Apelin-13 attenuates ER stress-mediated neuronal apoptosis by activating Gαi/Gαq-CK2 signaling in ischemic stroke

Cerebral ischemia/reperfusion (I/R) injury-induced neuronal apoptosis contributes to the death and disability in patients with ischemic stroke. However, underlying mechanisms remain elusive and it lacks effective treatment. Here we reported that the expression of casein kinase 2 (CK2) was significantly reduced in brains of middle cerebral artery occlusion/reperfusion (MACO/R) model rats and oxygen-glucose deprivation/reperfusion (OGD/R) model neurons, which was associated with the activation of eIF2-ATF4-CHOP signaling pathway, leading to neuronal apoptosis. Moreover, we found that apelin-13 significantly upregulated CK2 expression and inhibited eIF2-ATF4-CHOP activation, attenuating cerebral I/R injury-induced infarct and neuronal apoptosis in MACO/R model rats and OGD/R model neurons. Furthermore, we demonstrated that the rescue effect of apelin-13 on I/R injury-induced neuronal apoptosis was mediated by Gα_i/Gα_q-CK2-dependent inhibition of eIF2-ATF4-CHOP activation. These data indicated cerebral I/R injury reduced CK2 expression and activated eIF2-ATF4-CHOP signaling contributing to neuronal apoptosis, and apelin-13 can activate Gα_i/Gα_q-CK2 signaling attenuating eIF2-ATF4-CHOP-mediated neuronal apoptosis. It provides a novel insight that not only apelin-13 but also CK2 agonists may have therapeutic potential for protecting neurons from I/R injury-induced apoptosis, facilitating post-stroke recovery.

The Role of IRE1 Signaling in the Central Nervous System Diseases

The accumulation of misfolded or unfolded proteins in endoplasmic reticulum (ER) lumen results in the activation of an adaptive stress process called the unfolded protein response (UPR). As the most conserved signaling branch of the UPR, Inositol-requiring enzyme 1 (IRE1) possesses both Ser/Thr kinase and RNase activities operating as major stress sensors, mediating both adaptive and pro-apoptotic pathways under ER stress. Over the last three decades, a mounting body of evidence has shown that IRE1 signaling dysfunction is involved in the pathology of various neurological disorders. Targeting this pathway has emerged as a promising therapeutic strategy against these diseases. In this review, we provide a general overview about the expression and physiological function of IRE1 signaling and its pathophysiological roles in the central nervous system diseases.

Inhibition of endoplasmic reticulum stress alleviates secondary injury after traumatic brain injury

Apoptosis after traumatic brain injury has been shown to be a major factor influencing prognosis and outcome. Endoplasmic reticulum stress may be involved in mitochondrial mediated neuronal apoptosis. Therefore, endoplasmic reticulum stress has become an important mechanism of secondary injury after traumatic brain injury. In this study, a rat model of traumatic brain injury was established by lateral fluid percussion injury. Fluorescence assays were used to measure reactive oxygen species content in the cerebral cortex. Western blot assays were used to determine expression of endoplasmic reticulum stress-related proteins. Hematoxylin-eosin staining was used to detect pathological changes in the cerebral cortex. Transmission electron microscopy was used to measure ultrastructural changes in the endoplasmic reticulum and mitochondria. Our results showed activation of the endoplasmic reticulum stress-related unfolded protein response. Meanwhile, both the endoplasmic reticulum stress response and mitochondrial apoptotic pathway were activated at different stages post-traumatic brain injury. Furthermore, pretreatment with the endoplasmic reticulum stress inhibitor, salubrinal (1 mg/kg), by intraperitoneal injection 30 minutes before injury significantly inhibited the endoplasmic reticulum stress response and reduced apoptosis. Moreover, salubrinal promoted recovery of mitochondrial function and inhibited activation of the mitochondrial apoptotic pathway post-traumatic brain injury. These results suggest that endoplasmic reticulum stress might be a key factor for secondary brain injury post-traumatic brain injury.

Biochemical targets of drugs mitigating oxidative stress via redox-independent mechanisms

Acute or chronic oxidative stress plays an important role in many pathologies. Two opposite approaches are typically used to prevent the damage induced by reactive oxygen and nitrogen species (RONS), namely treatment either with antioxidants or with weak oxidants that up-regulate endogenous antioxidant mechanisms. This review discusses options for the third pharmacological approach, namely amelioration of oxidative stress by 'redox-inert' compounds, which do not inactivate RONS but either inhibit the basic mechanisms leading to their formation (i.e. inflammation) or help cells to cope with their toxic action. The present study describes biochemical targets of many drugs mitigating acute oxidative stress in animal models of ischemia-reperfusion injury or N-acetyl-p-aminophenol overdose. In addition to the pro-inflammatory molecules, the targets of mitigating drugs include protein kinases and transcription factors involved in regulation of energy metabolism and cell life/death balance, proteins regulating mitochondrial permeability transition, proteins involved in the endoplasmic reticulum stress and unfolded protein response, nuclear receptors such as peroxisome proliferator-activated receptors, and isoprenoid synthesis. The data may help in identification of oxidative stress mitigators that will be effective in human disease on top of the current standard of care.

Low Dose of Apelin-36 Attenuates ER Stress-Associated Apoptosis in Rats with Ischemic Stroke

Cerebral ischemia/reperfusion (I/R) injury-induced cellular apoptosis contributes to neuronal death in ischemic stroke, while endoplasmic reticulum stress (ERS) and subsequently triggered unfolded protein response (UPR) are the major mechanisms of cerebral I/R injury-induced apoptosis. A number of studies indicated that apelin-13 protects neurons from I/R injury-induced apoptosis. Apelin-36, the longest isoform of apelin, has stronger affinity to apelin receptor than apelin-13 does. However, the role of apelin-36 in ischemic stroke is less studied. In addition, preventive administration of apelin was applied in most studies, which could not precisely reflect its therapeutic potential in ischemic stroke. Here, we first reported that low dose of apelin-36, other than apelin-13, administrated after ischemic stroke significantly reduced infarct volume in rats. Moreover, apelin-36 attenuated cerebral I/R injury-induced apoptosis and caspase-3 activation. Furthermore, apelin-36 suppressed I/R injury-induced CHOP and GRP78 elevation, indicating that apelin-36 inhibited ERS/UPR activation. Our study first demonstrated that post-stroke administration of low-dose apelin-36 could attenuate cerebral I/R injury-induced infarct and apoptosis, which is associated with the inhibition of cerebral I/R injury-induced ERS/UPR activation. Our data support the therapeutic potential of apelin-36 in ischemic stroke although further investigation is needed.

Chrysophanol inhibits endoplasmic reticulum stress in cerebral ischemia and reperfusion mice

Endoplasmic reticulum (ER) stress plays a critical role in mediating ischemia/reperfusion (I/R) damage in the brain. Our previous study showed that Chrysophanol (CHR) alleviated cerebral ischemic injury in mice and nuclear factor-κB (NF-κB) involved in its neuroprotective effect, but the precise mechanism remains not fully understood. The present study investigated the effect of CHR treatment on I/R-induced ER stress. Mice were subjected to middle cerebral artery occlusion (MCAO) for 45min and received either vehicle or CHR (0.1mg/kg) for 14 days after reperfusion. Terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) was used to detect apoptotic cells in penumbral tissue. The expression of ER stress-related factors including glucose-regulated protein 78 (GRP78), phosphorylated eukaryotic initiation factor 2α (p-eIF2α), CCAAT-enhancer-binding protein homologous protein (CHOP), and caspase-12 as well as inhibitory κB-α (IκB-α), the inhibitor of NF-κB, was assessed. Our results demonstrated that CHR treatment reduced MCAO-induced upregulation of GRP78, p-eIF2α, CHOP, and caspase-12 in the ischemic brain. Moreover, the TUNEL-positive neuronal cells, which were colocalized with CHOP and caspase-12, decreased in response to CHR treatment, indicating that CHR protects against I/R injury by inhibiting ER stress-associated neuronal apoptosis. In addition, CHR reversed the decrease in IκB-α level induced by MCAO, which was attributed at least in part to the attenuation of translational inhibition induced by eIF2α phosphorylation, indicating that CHR exerts anti-inflammatory effects following I/R by inhibiting ER stress response. These results suggest that attenuation of ER stress may be involved in the mechanisms of neuroprotective effects of CHR.

RTN1-C mediates cerebral ischemia/reperfusion injury via ER stress and mitochondria-associated apoptosis pathways

The reticulon family has been found to induce apoptosis, inhibit axon regeneration and regulate protein trafficking. However, little is known about the mechanisms of how reticulon proteins are involved in neuronal death-promoting processes during ischemia. Here, we report that the expression of Reticulon Protein 1-C (RTN1-C) was associated with the progression of cerebral ischemia/reperfusion (I/R) injury. Using a combination of rat middle cerebral artery occlusion (MCAO) stroke and oxygen-glucose deprivation followed by reoxygenation (OGD/R) models, we determined that the expression of RTN1-C was significantly increased during cerebral ischemic/reperfusion. RTN1-C overexpression induced apoptosis and increased the cell vulnerability to ischemic injury, whereas RTN1-C knockdown reversed ischemia-induced apoptosis and attenuated the vulnerability of OGD/R-treated neural cells. Mechanistically, we demonstrated that RTN1-C mediated OGD/R-induced apoptosis through ER stress and mitochondria-associated pathways. RTN1-C interacted with Bcl-xL and increased its localization in the ER, thus reducing the anti-apoptotic activity of Bcl-xL. Most importantly, knockdown of Rtn1-c expression in vivo attenuated apoptosis in MCAO rats and reduced the extent of I/R-induced brain injury, as assessed by infarct volume and neurological score. Collectively, these data support for the first time that RTN1-C may represent a novel candidate for therapies against cerebral ischemia/reperfusion injury.

Bisoprolol protects myocardium cells against ischemia/reperfusion injury by attenuating unfolded protein response in rats

Bisoprolol (B) exerts potential cardioprotective effects against myocardial ischemia/reperfusion (I/R) injury. Unfolded protein response (UPR) attenuates I/R injury induced apoptosis by reducing oxidative damage and inflammation response. The current study investigated whether the protective effects of bisoprolol resulted from modulating UPR and anti-inflammatory during myocardial I/R condition and elucidated its potential mechanisms. Sprague-Dawley rats were treated with B in the absence or presence of the injected UPR activator dithiothreitol (DTT) and then subjected to myocardial I/R surgery. In vitro, cultured H9C2 cells were pretreated with B or DTT and then subjected to simulate ischemia reperfusion (SIR) operation. Bisoprolol conferred cardioprotective effects by improving postischemic cardiac function, decreasing infarct size, reducing apoptotic index, diminishing serum creatine kinase and lactate dehydrogenase levels, suppressing TNF-α and IL-6 secretion, inhibiting UPR signal pathways and downregulating caspase-12 and caspase-3 expressions. Consistently, B conferred similar antioxidative and anti-inflammatory effects against SIR injury in cultured H9C2 cardiomyocytes. Pretreatment with DTT or C/EBP homologous protein (CHOP) overexpression mediated by lentivirus administration both abolished these effects. In summary, our results demonstrate that Bisoprolol protects myocardium cells against ischemia/reperfusion injury partly by attenuating unfolded protein response.

Unfolded protein response is activated in the ipsilateral thalamus following focal cerebral infarction in hypertensive rats

Focal cerebral cortical infarction causes secondary neurodegeneration in the remote regions, such as the ventroposterior nucleus of the thalamus. Retrograde degeneration of thalamocortical fibers is considered as the principle mechanism, but the exact molecular events remain to be elucidated. This study aimed to investigate whether unfolded protein response (UPR) is activated in thalamic neurons following distal middle cerebral artery occlusion (MCAO) in stroke-prone renovascular hypertensive rats. Immunostaining and immunoblotting were performed to evaluate the expression of Grp78 and its downstream effectors in the thalamus at 3, 7 and 14 days after MCAO. Secondary thalamic degeneration was assessed with Nissl staining and NeuN immunostaining. Neuronal death was not apparent at 3 days post-ischaemia but was evident in the thalamus at 7 and 14 days after MCAO. Grp78 level was reduced in the ipsilateral thalamus at 3 and 7 days after MCAO. In parallel, phosphorylated eIF2α and ATF4 levels were elevated, indicating the activation of UPR. In contrast, ATF6α and CHOP levels were not changed. These results suggest that UPR is activated before neuronal death in the ipsilateral thalamus after MCAO and may represent a key early event in the secondary thalamic degeneration.

Molecular analysis of oxalate-induced endoplasmic reticulum stress mediated apoptosis in the pathogenesis of kidney stone disease

Oxalate, a non-essential end product of metabolism, causes hyperoxaluria and eventually calcium oxalate (CaOx) stone disease. Kidney cells exposed to oxalate stress results in generation of reactive oxygen species (ROS) and progression of stone formation. Perturbations in endoplasmic reticulum (ER) result in accumulation of misfolded proteins and Ca²⁺ ions homeostasis imbalance and serve as a common pathway for various diseases, including kidney disorders. ER stress induces up-regulation of pro-survival protein glucose-regulated protein 78 (GRP78) and pro-apoptotic signaling protein C/EBP homologous protein (CHOP). Since the association of oxalate toxicity and ER stress on renal cell damage is uncertain, the present study is an attempt to elucidate the interaction of GRP78 with oxalate by computational analysis and study the role of ER stress in oxalate-mediated apoptosis in vitro and in vivo. Molecular docking results showed that GRP78-oxalate/CaOx interaction takes place. Oxalate stress significantly up-regulated expression of ER stress markers GRP78 and CHOP both in vitro and in vivo. Exposure of oxalate increased ROS generation and altered antioxidant enzyme activities. N-Acetyl cysteine treatment significantly ameliorated oxalate-mediated oxidative stress and moderately attenuated ER stress marker expression. The result indicates oxalate toxicity initiated oxidative stress-induced ER stress and also activating ER stress mediated apoptosis directly. In addition, the up-regulation of transforming growth factor β-₁ revealed oxalate may induce kidney fibrosis through ER stress-mediated mechanisms. The present study provide insights into the pathogenic role of oxidative and ER stress by oxalate exposure in the formation of calcium oxalate stone.

Curcumin inhibits endoplasmic reticulum stress induced by cerebral ischemia-reperfusion injury in rats

The aim of the present study was to observe the dynamic changes of the growth arrest and DNA damage-inducible 153 (GADD153) gene and caspase-12 in the brain tissue of rats with cerebral ischemia-reperfusion injury (CIRI) and the impact of curcumin pretreatment. A total of 60 rats were randomly divided into the normal group (N), the sham operation group (S), the dimethyl sulfoxide control group (D) and the curcumin treatment group (C). For group D and C, 12 (T1), 24 (T2) and 72 h (T3) of reperfusion were performed after 2 h ischemia. The expression levels of GADD153 and caspase-12 in the brain tissue were detected and compared among the groups by immunohistochemistry, immunofluorescence double staining and western blotting. The expression levels of GADD153 and caspase-12 were increased at T1compared with groups N and S, and the expression of caspase-12 peaked at T2 in group D, while GADD153 was increased until T3 in group D. Compared with group D, the expression levels of GADD153 and caspase-12 in group C at T2 and T3 were significantly decreased (P<0.05). Endoplasmic reticulum stress is involved in the pathological process of CIRI. Curcumin may decrease the expression levels of the above two factors, thus exhibiting protective effects against CIRI in rats.

The role of the endoplasmic reticulum stress response following cerebral ischemia

Background Cornu ammonis 3 (CA3) hippocampal neurons are resistant to global ischemia, whereas cornu ammonis (CA1) 1 neurons are vulnerable. Hamartin expression in CA3 neurons mediates this endogenous resistance via productive autophagy. Neurons lacking hamartin demonstrate exacerbated endoplasmic reticulum stress and increased cell death. We investigated endoplasmic reticulum stress responses in CA1 and CA3 regions following global cerebral ischemia, and whether pharmacological modulation of endoplasmic reticulum stress or autophagy altered neuronal viability . Methods In vivo: male Wistar rats underwent sham or 10 min of transient global cerebral ischemia. CA1 and CA3 areas were microdissected and endoplasmic reticulum stress protein expression quantified at 3 h and 12 h of reperfusion. In vitro: primary neuronal cultures (E18 Wistar rat embryos) were exposed to 2 h of oxygen and glucose deprivation or normoxia in the presence of an endoplasmic reticulum stress inducer (thapsigargin or tunicamycin), an endoplasmic reticulum stress inhibitor (salubrinal or 4-phenylbutyric acid), an autophagy inducer ([4'-(N-diethylamino) butyl]-2-chlorophenoxazine (10-NCP)) or autophagy inhibitor (3-methyladenine). Results In vivo, decreased endoplasmic reticulum stress protein expression (phospho-eIF2α and ATF4) was observed at 3 h of reperfusion in CA3 neurons following ischemia, and increased in CA1 neurons at 12 h of reperfusion. In vitro, endoplasmic reticulum stress inducers and high doses of the endoplasmic reticulum stress inhibitors also increased cell death. Both induction and inhibition of autophagy also increased cell death. Conclusion Endoplasmic reticulum stress is associated with neuronal cell death following ischemia. Neither reduction of endoplasmic reticulum stress nor induction of autophagy demonstrated neuroprotection in vitro, highlighting their complex role in neuronal biology following ischemia.

Impaired autophagosome clearance contributes to neuronal death in a piglet model of neonatal hypoxic-ischemic encephalopathy

To examine the temporal relationship of cortical autophagic flux with delayed neuronal cell death after hypoxia-ischemia (HI) in neonatal piglets. HI was produced with 45-min hypoxia and 7-min airway occlusion in 3-5-day-old piglets. Markers of autophagic, lysosomal and cell death signaling were studied via immunohistochemistry, immunoblotting, and histochemistry in piglet brains. In vitro, autophagy was impaired in cultured mouse cortical neurons treated with chloroquine with or without rapamycin for 1 d in the presence of Z-VAD-fmk, cyclosporine A, or vehicle control, and cell viability was assessed with the MTT assay. In vivo, neuronal cell death of sensorimotor cortex was delayed by 1-2 days after HI, whereas LC3-II, Beclin-1, PI3KC3, ATG12-ATG-5, and p-ULK1 increased by 1.5-6 h. Autophagosomes accumulated in cortical neurons by 1 d owing to enhanced autophagy and later to decreased autophagosome clearance, as indicated by LC3, Beclin-1, and p62 accumulation. Autophagy flux impairment was attributable to lysosomal dysfunction, as indicated by low lysosomal-associated membrane protein 2, cathepsin B, and cathepsin D levels at 1 d. Ubiquitin levels increased at 1 d. Autophagosome and p62 accumulated predominantly in neurons at 1 d, with p62 puncta occurring in affected cells. Beclin-1 colocalized with markers of caspase-dependent and caspase-independent apoptosis and necrosis in neurons. In vitro, mouse neonatal cortical neurons treated with rapamycin and chloroquine showed increased autophagosomes, but not autolysosomes, and increased cell death that was attenuated by cyclosporine A. Neonatal HI initially increases autophagy but later impairs autophagosome clearance, coinciding with delayed cortical neuronal death.

Activation of cell surface GRP78 decreases endoplasmic reticulum stress and neuronal death

The unfolded protein response (UPR) is an endoplasmic reticulum (ER) -related stress conserved pathway that aims to protect cells from being overwhelmed. However, when prolonged, UPR activation converts to a death signal, which relies on its PERK-eIF2α branch. Overactivation of the UPR has been implicated in many neurological diseases, including cerebral ischaemia. Here, by using an in vivo thromboembolic model of stroke on transgenic ER stress-reporter mice and neuronal in vitro models of ischaemia, we demonstrate that ischaemic stress leads to the deleterious activation of the PERK branch of the UPR. Moreover, we show that the serine protease tissue-type plasminogen activator (tPA) can bind to cell surface Grp78 (78 kD glucose-regulated protein), leading to a decrease of the PERK pathway activation, thus a decrease of the deleterious factor CHOP, and finally promotes neuroprotection. Altogether, this work highlights a new role and a therapeutic potential of the chaperone protein Grp78 as a membrane receptor of tPA capable to prevent from ER stress overactivation.

Neurodegenerative signaling factors and mechanisms in Parkinson's pathology

Parkinson's disease (PD) is a chronic and progressive degenerative disorder of central nervous system which is mainly characterized by selective loss of dopaminergic neurons in the nigrostrial pathway. Clinical symptoms of this devastating disease comprise motor impairments such as resting tremor, bradykinesia, postural instability and rigidity. Current medications only provide symptomatic relief but fail to halt the dopaminergic neuronal death. While the etiology of dopaminergic neuronal death is not fully understood, combination of various molecular mechanisms seems to play a critical role. Studies from experimental animal models have provided crucial insights into the molecular mechanisms in disease pathogenesis and recognized possible targets for therapeutic interventions. Recent findings implicate the involvement of abnormal protein accumulation and phosphorylation, mitochondrial dysfunction, oxidative damage and deregulated kinase signaling as key molecular mechanisms affecting the normal function as well survival of dopaminergic neurons. Here we discuss the relevant findings on the PD pathology related mechanisms and recognition of the cell survival mechanisms which could be used as targets for neuroprotective strategies in preventing this devastating disorder.

Unfolded protein response plays a critical role in heart damage after myocardial ischemia/reperfusion in rats

The unfolded protein response (UPR) plays a critical role in cell death mediated by ischemia/reperfusion (I/R) injury. However, little is known about the exact mechanism of UPR signaling pathways after myocardial I/R injury in rats. An attempt was therefore made to assess whether the myocardial I/R induced UPR, and which branch of UPR (ATF6, IRE1 and PERK) signal pathway was activated. Sprague-Dawley rats were pretreated with UPR stimulator dithiothreitol (DTT) and UPR inhibitor 4-phenylbutyrate (4PBA) and then subjected to myocardial I/R surgery. Compared with sham-operated group, the expression of GRP78, ATF6, CHOP and sXBP1 in the I/R injured group is significantly increased at transcript and protein levels, which indicated that all the three signal pathways of UPR were activated in the myocardial I/R injury. Compared with the I/R injured group, treatment with 4PBA effectively decreased myocardium infarct size, reduced myocardial apoptosis, down-regulated caspase-12 expression, diminished serum creatine kinase and lactate dehydrogenase levels. In contrast, these effects were reversed in DTT treated group. In summary, these results demonstrated that myocardial I/R injury activates UPR and inhibiting cell UPR possesses a cardioprotective effect through the suppression of ER stress-induced apoptosis. Therefore, inhibition of UPR might be used as a therapeutic target during myocardial I/R injury.

Integrated Stress Response as a Therapeutic Target for CNS Injuries

Central nervous system (CNS) injuries, caused by cerebrovascular pathologies or mechanical contusions (e.g., traumatic brain injury, TBI) comprise a diverse group of disorders that share the activation of the integrated stress response (ISR). This pathway is an innate protective mechanism, with encouraging potential as therapeutic target for CNS injury repair. In this review, we will focus on the progress in understanding the role of the ISR and we will discuss the effects of various small molecules that target the ISR on different animal models of CNS injury.

Temporal Expression of Apelin/Apelin Receptor in Ischemic Stroke and its Therapeutic Potential

Stroke is one of the leading causes of death and disability worldwide, and ischemic stroke accounts for approximately 87% of cases. Improving post-stroke recovery is a major challenge in stroke treatment. Accumulated evidence indicates that the apelinergic system, consisting of apelin and apelin receptor (APLNR), is temporally dysregulated in ischemic stroke. Moreover, the apelinergic system plays a pivotal role in post-stroke recovery by inhibiting neuronal apoptosis and facilitating angiogenesis through various molecular pathways. In this review article, we summarize the temporal expression of apelin and APLNR in ischemic stroke and the mechanisms of their dysregulation. In addition, the protective role of the apelinergic system in ischemic stroke and the underlying mechanisms of its protective effects are discussed. Furthermore, critical issues in activating the apelinergic system as a potential therapy will also be discussed. The aim of this review article is to shed light on exploiting the activation of the apelinergic system to treat ischemic stroke.

rAAV8-733-Mediated Gene Transfer of CHIP/Stub-1 Prevents Hippocampal Neuronal Death in Experimental Brain Ischemia

Brain ischemia is a major cause of adult disability and death, and it represents a worldwide health problem with significant economic burden for modern society. The identification of the molecular pathways activated after brain ischemia, together with efficient technologies of gene delivery to the CNS, may lead to novel treatments based on gene therapy. Recombinant adeno-associated virus (rAAV) is an effective platform for gene transfer to the CNS. Here, we used a serotype 8 rAAV bearing the Y733F mutation (rAAV8-733) to overexpress co-chaperone E3 ligase CHIP (also known as Stub-1) in rat hippocampal neurons, both in an oxygen and glucose deprivation model in vitro and in a four-vessel occlusion model of ischemia in vivo. We show that CHIP overexpression prevented neuronal degeneration in both cases and led to a decrease of both eIF2α (serine 51) and AKT (serine 473) phosphorylation, as well as reduced amounts of ubiquitinated proteins following hypoxia or ischemia. These data add to current knowledge of ischemia-related signaling in the brain and suggest that gene therapy based on the role of CHIP in proteostasis may provide a new venue for brain ischemia treatment.

Unfolded protein response in brain ischemia: A timely update

Folding and processing newly synthesized proteins are vital functions of the endoplasmic reticulum that are sensitive to a variety of stress conditions. The unfolded protein response is activated to restore endoplasmic reticulum function impaired by stress. While we know that brain ischemia impairs endoplasmic reticulum function, the role of unfolded protein response activation in post-ischemic recovery of neurologic function is only beginning to emerge. Here, we summarize what is known about endoplasmic reticulum stress and unfolded protein response in brain ischemia and discuss recent findings from myocardial ischemia studies that could help to advance research on endoplasmic reticulum stress and unfolded protein response in brain ischemia.

Neuroprotection and Blood-Brain Barrier Restoration by Salubrinal After a Cortical Stab Injury

Following a central nervous system (CNS) injury, restoration of the blood-brain barrier (BBB) integrity is essential for recovering homeostasis. When this process is delayed or impeded, blood substances and cells enter the CNS parenchyma, initiating an additional inflammatory process that extends the initial injury and causes so-called secondary neuronal loss. Astrocytes and profibrotic mesenchymal cells react to the injury and migrate to the lesion site, creating a new glia limitans that restores the BBB. This process is beneficial for the resolution of the inflammation, neuronal survival, and the initiation of the healing process. Salubrinal is a small molecule with neuroprotective properties in different animal models of stroke and trauma to the CNS. Here, we show that salubrinal increased neuronal survival in the neighbourhood of a cerebral cortex stab injury. Moreover, salubrinal reduced cortical blood leakage into the parenchyma of injured animals compared with injured controls. Adjacent to the site of injury, salubrinal induced immunoreactivity for platelet-derived growth factor subunit B (PDGF-B), a specific mitogenic factor for mesenchymal cells. This effect might be responsible for the increased immunoreactivity for fibronectin and the decreased activation of microglia and macrophages in injured mice treated with salubrinal, compared with injured controls. The immunoreactivity for PDGF-B colocalized with neuronal nuclei (NeuN), suggesting that cortical neurons in the proximity of the injury were the main source of PDGF-B. Our results suggest that after an injury, neurons play an important role in both, the healing process and the restoration of the BBB integrity. J. Cell. Physiol. 232: 1501-1510, 2017. © 2016 Wiley Periodicals, Inc.

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.

Urinary congophilia in women with hypertensive disorders of pregnancy and preexisting proteinuria or hypertension

BACKGROUND

Congophilia indicates the presence of amyloid protein, which is an aggregate of misfolded proteins, that is implicated in the pathophysiologic condition of preeclampsia. Recently, urinary congophilia has been proposed as a test for the diagnosis and prediction of preeclampsia.

OBJECTIVES

The purpose of this study was to determine whether urine congophilia is present in a cohort of women with preeclampsia and in pregnant and nonpregnant women with renal disease.

STUDY DESIGN

With the use of a preeclampsia, chronic hypertension, renal disease, and systemic lupus erythematosus cohort, we analyzed urine samples from healthy pregnant control subjects (n = 31) and pregnant women with preeclampsia (n = 23), gestational hypertension (n = 10), chronic hypertension (n = 14), chronic kidney disease; n = 28), chronic kidney disease with superimposed preeclampsia (n = 5), and chronic hypertension and superimposed preeclampsia (n = 12). Samples from nonpregnant control subjects (n = 10) and nonpregnant women with either systemic lupus erythematosus with (n = 25) and without (n = 14) lupus nephritis were analyzed. For each sample, protein concentration was standardized before it was mixed with Congo Red, spotted to nitrocellulose membrane, and rinsed with methanol. The optical density of the residual Congo Red stain was determined; Congo red stain retention was calculated, and groups were compared with the use of the Mann-Whitney test or Kruskal-Wallis analysis of Variance test, as appropriate.

RESULTS

Congophilia was increased in urine from women with preeclampsia (median Congo red stain retention, 47%; interquartile range, 22-68%) compared with healthy pregnant control subjects (Congo red stain retention: 16%; interquartile range, 13-21%; P = .002), women with gestational hypertension (Congo red stain retention, 20%; interquartile range, 13-27%; P = .008), or women with chronic hypertension (Congo red stain retention, 17%; interquartile range, 12-28%; P = .01). There were no differences in Congo red retention between pregnant women with chronic hypertension and normal pregnant control subjects (Congo red stain retention, 17% [interquartile range, 12-28%] vs 16% [interquartile range, 13-21%], respectively; P = .72). Congophilia was present in pregnant women with chronic kidney disease (Congo red stain retention, 32%; interquartile range, 14-57%), being similar to values found in women with preeclampsia (P = .22) and for women with chronic kidney disease and superimposed preeclampsia (Congo red stain retention, 57%; [interquartile range, 29-71%; P = .18). Nonpregnant women with lupus nephritis had higher congophilia levels compared with nonpregnant female control subjects (Congo red stain retention, 38% [interquartile range, 17-73%] vs 9% [7-11%], respectively; P < .001) and nonpregnant women with systemic lupus erythematosus without nephritis (Congo red stain retention, 38% [interquartile range, 17-73%] vs 13% [interquartile range, 11-17%], respectively; P = .001). A significant positive correlation was observed between congophilia and protein:creatinine ratio (Spearman rank correlations, 0.702; 95% confidence interval, 0.618-0.770; P < .001).

CONCLUSION

This study confirms that women with preeclampsia and chronic kidney disease without preeclampsia have elevated urine congophilia levels compared with healthy pregnant women. Nonpregnant women with lupus nephritis also have elevated urine congophilia levels compared with healthy control subjects. An elevated Congo Red stain retention may not be able to differentiate between these conditions; further research is required to explore the use of congophilia in clinical practice.

Heat shock protein 70 protects PC12 cells against ischemia-hypoxia/reoxygenation by maintaining intracellular Ca(2+) homeostasis

Heat shock protein 70 (HSP70) maintains Ca²⁺ homeostasis in PC12 cells, which may protect against apoptosis; however, the mechanisms of neuroprotection are unclear. Therefore, in this study, we examined Ca²⁺ levels in PC12 cells transfected with an exogenous lentiviral HSP70 gene expression construct, and we subsequently subjected the cells to ischemia-hypoxia/reoxygenation injury. HSP70 overexpression increased neuronal viability and ATPase activity, and it decreased cellular reactive oxygen species levels and intracellular Ca²⁺ concentration after hypoxia/reoxygenation. HSP70 overexpression enhanced the protein and mRNA expression levels of sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase (SERCA), but it decreased the protein and mRNA levels of inositol 1,4,5-trisphosphate receptor (IP₃R), thereby leading to decreased intracellular Ca²⁺ concentration after ischemia-hypoxia/reoxygenation. These results suggest that exogenous HSP70 protects against ischemia-hypoxia/reoxygenation injury, at least in part, by maintaining cellular Ca²⁺ homeostasis, by upregulating SERCA expression and by downregulating IP₃R expression.

Hypothermia and Rewarming Activate a Macroglial Unfolded Protein Response Independent of Hypoxic-Ischemic Brain Injury in Neonatal Piglets

Therapeutic hypothermia provides incomplete neuroprotection after hypoxia-ischemia (HI)-induced brain injury in neonates. We previously showed that cortical neuron and white matter apoptosis are promoted by hypothermia and early rewarming in a piglet model of HI. The unfolded protein response (UPR) may be one of the potential mediators of this cell death. Here, neonatal piglets underwent HI or sham surgery followed by 29 h of normothermia, 2 h of normothermia + 27 h of hypothermia or 18 h of hypothermia + rewarming. Piglets recovered for 29 h. Immunohistochemistry for endoplasmic reticulum to nucleus signaling-1 protein (ERN1), a marker of UPR activation, was used to determine the ratios of ERN1+ macroglia and neurons in the motor subcortical white matter and cerebral cortex. The ERN1+ macroglia were immunophenotyped as oligodendrocytes and astrocytes by immunofluorescent colabeling. Temperature (p = 0.046) and HI (p < 0.001) independently affected the ratio of ERN1+ macroglia. In sham piglets, sustained hypothermia (p = 0.011) and rewarming (p = 0.004) increased the ERN1+ macroglia ratio above that in normothermia. HI prior to hypothermia diminished the UPR. Ratios of ERN1+ macroglia correlated with white matter apoptotic profile counts in shams (r = 0.472; p = 0.026), thereby associating UPR activation with white matter apoptosis during hypothermia and rewarming. Accordingly, macroglial cell counts decreased in shams that received sustained hypothermia (p = 0.009) or rewarming (p = 0.007) compared to those in normothermic shams. HI prior to hypothermia neutralized the macroglial cell loss. Neither HI nor temperature affected ERN1+ neuron ratios. In summary, delayed hypothermia and rewarming activate the macroglial UPR, which is associated with white matter apoptosis. HI may decrease the macroglial endoplasmic reticulum stress response after hypothermia and rewarming.

Salubrinal reduces oxidative stress, neuroinflammation and impulsive-like behavior in a rodent model of traumatic brain injury

Traumatic brain injury (TBI) is the leading cause of trauma related morbidity in the developed world. TBI has been shown to trigger secondary injury cascades including endoplasmic reticulum (ER) stress, oxidative stress, and neuroinflammation. The link between secondary injury cascades and behavioral outcome following TBI is poorly understood warranting further investigation. Using our validated rodent blast TBI model, we examined the interaction of secondary injury cascades following single injury and how these interactions may contribute to impulsive-like behavior after a clinically relevant repetitive TBI paradigm. We targeted these secondary pathways acutely following single injury with the cellular stress modulator, salubrinal (SAL). We examined the neuroprotective effects of SAL administration on significantly reducing ER stress: janus-N-terminal kinase (JNK) phosphorylation and C/EBP homology protein (CHOP), oxidative stress: superoxide and carbonyls, and neuroinflammation: nuclear factor kappa beta (NFκB) activity, inducible nitric oxide synthase (iNOS) protein expression, and pro-inflammatory cytokines at 24h post-TBI. We then used the more clinically relevant repeat injury paradigm and observed elevated NFκB and iNOS activity. These injury cascades were associated with impulsive-like behavior measured on the elevated plus maze. SAL administration attenuated secondary iNOS activity at 72h following repetitive TBI, and most importantly prevented impulsive-like behavior. Overall, these results suggest a link between secondary injury cascades and impulsive-like behavior that can be modulated by SAL administration.