Ischemia-induced neuronal cell death is mediated by the endoplasmic reticulum stress pathway involving CHOP

Downregulation of TRB3 protects neurons against apoptosis induced by global cerebral ischemia and reperfusion injury in rats

Global cerebral ischemia and reperfusion injury (GCI/R) can lead to neuronal apoptosis and contributes to permanent neurological sequelae. However, the underlying mechanism is largely unknown. Therefore, the present study aimed to assess the effects of GCI/R on the tribbles homolog 3 (TRB3) and to explore the role of TRB3 in GCI/R. The GCI/R model was developed in Sprague-Dawley male rats by four-vessel occlusion. Subsequently, the expressions of TRB3, endoplasmic reticulum stress markers, and apoptosis-associated proteins were examined by western blot at 1h, 6h, 12h, 24h, and 72h after GCI/R. TRB3 short-hairpin RNA (shRNA) lentivirus was constructed and used to investigate the role of TRB3 in GCI/R-induced neuronal apoptosis. GCI/R increased the level of TRB3, endoplasmic reticulum stress markers, and pro-apoptotic proteins. The level of protein kinase B (Akt) phosphorylation was reduced during GCI/R. Administration of TRB3 shRNA lentivirus attenuated GCI/R-induced up-regulation of TRB3, endoplasmic reticulum stress, and neuronal apoptosis. Furthermore, TRB3 shRNA lentivirus reversed the reduced level of Akt phosphorylation induced by GCI/R. These data implied that TRB3 participated in the GCI/R-induced neuronal apoptosis. Knocking down TRB3 attenuated endoplasmic reticulum stress, enhanced Akt phosphorylation, and protected neurons from apoptosis in response to GCI/R. These results demonstrated that the downregulation of TRB3 may be a promising approach for treating GCI/R.

The neuroprotective effect of hesperidin in NMDA-induced retinal injury acts by suppressing oxidative stress and excessive calpain activation

We found that hesperidin, a plant-derived bioflavonoid, may be a candidate agent for neuroprotective treatment in the retina, after screening 41 materials for anti-oxidative properties in a primary retinal cell culture under oxidative stress. We found that the intravitreal injection of hesperidin in mice prevented reductions in markers of the retinal ganglion cells (RGCs) and RGC death after N-methyl-D-aspartate (NMDA)-induced excitotoxicity. Hesperidin treatment also reduced calpain activation, reactive oxygen species generation and TNF-α gene expression. Finally, hesperidin treatment improved electrophysiological function, measured with visual evoked potential, and visual function, measured with optomotry. Thus, we found that hesperidin suppressed a number of cytotoxic factors associated with NMDA-induced cell death signaling, such as oxidative stress, over-activation of calpain, and inflammation, thereby protecting the RGCs in mice. Therefore, hesperidin may have potential as a therapeutic supplement for protecting the retina against the damage associated with excitotoxic injury, such as occurs in glaucoma and diabetic retinopathy.

Therapeutic effects of L-Cysteine in newborn mice subjected to hypoxia-ischemia brain injury via the CBS/H2S system: Role of oxidative stress and endoplasmic reticulum stress

Neonatal hypoxic-ischemic (HI) injury is a major cause of neonatal death and neurological dysfunction. H₂S has been shown to protect against hypoxia-induced injury and apoptosis of neurons. L-Cysteine is catalyzed by cystathionine-β-synthase (CBS) in the brain and sequentially produces endogenous H₂S. The present study was designed to investigate whether L-Cysteine could attenuate the acute brain injury and improve neurobehavioral outcomes following HI brain injury in neonatal mice by releasing endogenous H₂S. L-Cysteine treatment significantly attenuated brain edema and decreased infarct volume and neuronal cell death, as shown by a decrease in the Bax/Bcl-2 ratio, suppression of caspase-3 activation, and reduced phosphorylation of Akt and ERK at 72 h after HI. Additionally, L-Cysteine substantially up-regulated NF-E2-related factor 2 and heme oxygenase-1 expression. L-Cysteine also decreased endoplasmic reticulum (ER) stress-associated pro-apoptotic protein expression. Furthermore, L-Cysteine had long-term effects by protecting against the loss of ipsilateral brain tissue and improving neurobehavioral outcomes. Importantly, pre-treatment with a CBS inhibitor significantly attenuated the neuroprotection of L-Cysteine on HI insult. Thus, L-Cysteine exerts neuroprotection against HI-induced injury in neonates via the CBS/H₂S pathway, mediated in part by anti-apoptotic effects and reduced oxidative stress and ER stress. Thus, L-Cysteine may be a promising treatment for HI.

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L-Cysteine administration at 24 h after HI insult has neuroprotective effect.

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L-Cysteine administration attenuated HI-induced oxidative stress and ER stress.

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L-Cysteine administration had long-term effects in improving neurobehavioral function at 14 and 28 days after HI insult.

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Pre-treatment with a CBS inhibitor significantly attenuated the neuroprotection of L-Cysteine on HI in neonatal mice.

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.

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.

Management of glaucoma as a neurodegenerative disease

Glaucoma is a neurodegenerative disease with an estimated prevalence of 60 million people, and the most common cause of irreversible blindness worldwide. The mainstay of treatment has been aimed at lowering intraocular pressure, currently the only modifiable risk factor. Unfortunately, despite adequate pressure control, many patients go on to suffer irreversible visual loss. We first briefly examine currently established intraocular pressure lowering-treatments, with a discussion of their roles in neuroprotection as demonstrated by both animal and clinical studies. The review then examines currently available intraocular pressure independent agents that have shown promise for possessing neuroprotective effects in the management of glaucoma. Finally, we explore potential future treatments such as immune-modulation, stem cell therapy and neural regeneration as they may provide further protection against the neurodegenerative processes involved in glaucomatous optic neuropathy.

Thioredoxin-Interacting Protein Mediates Apoptosis in Early Brain Injury after Subarachnoid Haemorrhage

Early brain injury (EBI) is considered to be the major factor associated with high morbidity and mortality after subarachnoid haemorrhage (SAH). Apoptosis is the major pathological mechanism of EBI, and its pathogenesis has not been fully clarified. Here, we report that thioredoxin-interacting protein (TXNIP), which is induced by protein kinase RNA-like endoplasmic reticulum (ER) kinase (PERK), participates in EBI by promoting apoptosis. By using adult male Sprague-Dawley rats to establish SAH models, as well as Terminal dexynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) staining, immunofluorescence, and western blot, we found that TXNIP expression significantly increased after SAH in comparison to the sham group and peaked at 48 h (up to 3.2-fold). Meanwhile, TXNIP was widely expressed in neurons and colocalized with TUNEL-positive cells in the hippocampus and cortex of SAH rats. After administration of TXNIP inhibitor-resveratrol (60 mg/kg), TXNIP small interfering RNA (siRNA) and the PERK inhibitor GSK2656157, TXNIP expression was significantly reduced, accompanied by an attenuation of apoptosis and prognostic indicators, including SAH grade, neurological deficits, brain water content, and blood-brain barrier (BBB) permeability. Collectively, these results suggest that TXNIP may participate in EBI after SAH by mediating apoptosis. The blockage of TXNIP induced by PERK could be a potential therapeutic strategy for SAH treatment.

Molecular mechanisms of brain-derived neurotrophic factor in neuro-protection: Recent developments

Neuronal cell injury, as a consequence of acute or chronic neurological trauma, is a significant cause of mortality around the world. On a molecular level, the condition is characterized by widespread cell death and poor regeneration, which can result in severe morbidity in survivors. Potential therapeutics are of major interest, with a promising candidate being brain-derived neurotrophic factor (BDNF), a ubiquitous agent in the brain which has been associated with neural development and may facilitate protective and regenerative effects following injury. This review summarizes the available information on the potential benefits of BDNF and the molecular mechanisms involved in several pathological conditions, including hypoxic brain injury, stroke, Alzheimer's disease and Parkinson's disease. It further explores the methods in which BDNF can be applied in clinical and therapeutic settings, and the potential challenges to overcome.

Overexpression of Human SOD1 Leads to Discrete Defects in the Cerebellar Architecture in the Mouse

The human superoxide dismutase 1 (SOD1) gene is responsible for neutralizing supercharged oxygen radicals within the cell. Mutation in SOD1 gene causes amyotrophic lateral sclerosis (ALS). Recent studies have shown involvement of the cerebellum in ALS, although the cerebellar contribution in SOD1 transgenic mice remains unclear. Using immunohistopathology, we investigated the Purkinje cell phenotype in the vermis of the SOD1 transgenic mice cerebellum. Calbindin 1 (Calb1) and three well-known zone and stripe markers, zebrin II, HSP25, and PLCβ4 have been used to explore possible alteration in zone and stripe. Here we show that Calb1 expression is significantly reduced in a subset of the Purkinje cells that is almost aligned with the cerebellar zones and stripes pattern. The Purkinje cells of SOD1 transgenic mice display a pattern of Calb1 down-regulation, which seems to proceed to Purkinje cell degeneration as the mice age. The onset of Calb1 down-regulation in Purkinje cells begins from the central zone and continues into the nodular zone, however it has not been observed in the anterior and posterior zones. In a subgroup of SOD1 transgenic mice in which gait unsteadiness was apparent, down-regulation of Calb1 is seen in a subset of PLCβ4⁺ Purkinje cells in the anterior zone. These observations suggest that the Calb1^- subset of Purkinje cells in the anterior zone, which receives somatosensory input, causes unsteady gait. Our data suggest that human SOD1 overexpression leads to Calb1 down-regulation in the zone and strip pattern and raise the question of whether SOD1 overexpression leads to Purkinje cells degeneration.

Endoplasmic Reticulum Stress PERK-ATF4-CHOP Pathway Is Associated with Hypothalamic Neuronal Injury in Different Durations of Stress in Rats

The hypothalamus, which is the initial part of the hypothalamic-pituitary-adrenal (HPA) axis, plays a critical role in regulating stress in the central nervous system. The present study aimed to determine whether endoplasmic reticulum stress in hypothalamic neurons is differentially stimulated by varying durations of stress exposure, which ultimately leads to pathological changes in neurons by affecting HPA axis function. There is a need for better morphological evidence of the mechanisms involved in stress-induced neuron injury. A stress model was established in rats by restraining for 8 h and forced ice-water swimming for 5 min each day. The stress-inducing process lasted for 1, 3, 7, 14, and 21 days. Enzyme-linked immunosorbent assay (ELISA) was used to assay serum glucocorticoid levels. Thionine staining was used to observe morphological changes in hypothalamic neurons. Immunohistochemistry and microscopy-based multicolor tissue cytometry (MMTC) was used to detect changes in expression of endoplasmic reticulum stress protein GRP78, ATF4, and CHOP. Serum glucocorticoid levels significantly increased after 3 days of stress exposure and the levels peaked by 7 days. By 21 days, however, the levels were significantly decreased. Thionine staining revealed that prolonged stress exposure resulted in hypothalamic neurons with edema, a lack of Nissl bodies, and pyknotic neurons. Immunohistochemistry and MMTC showed that increasing stress periods significantly decreased GRP78 expression, although ATF4 and CHOP protein expression significantly increased. Stress resulted in pathological changes and significant dynamic changes because of endoplasmic reticulum stress in rat hypothalamic neurons. These results suggested that the endoplasmic reticulum stress PERK-ATF4-CHOP pathway may be associated with hypothalamic neuronal injury.

KUS121, a VCP modulator, attenuates ischemic retinal cell death via suppressing endoplasmic reticulum stress

Ischemic neural damages cause several devastating diseases, including brain stroke and ischemic retinopathies, and endoplasmic reticulum (ER) stress has been proposed to be the underlying mechanism of the neuronal cell death of these conditions. We previously synthesized Kyoto University substances (KUSs) as modulators of valosin-containing protein (VCP); KUSs inhibit VCP ATPase activity and protect cells from different cell death-inducing insults. Here, we examined the efficacy of KUS121 in a rat model of retinal ischemic injury. Systemic administration of KUS121 to rats with ischemic retinal injury significantly suppressed inner retinal thinning and death of retinal ganglion and amacrine cells, with a significant functional maintenance of visual functions, as judged by electroretinography. Furthermore, intravitreal injection of KUS121, which is the clinically preferred route of drug administration for retinal diseases, appeared to show an equal or better neuroprotective efficacy in the ischemic retina compared with systemic administration. Indeed, induction of the ER stress marker C/EBP homologous protein (CHOP) after the ischemic insult was significantly suppressed by KUS121 administration. Our study suggests VCP modulation by KUS as a promising novel therapeutic strategy for ischemic neuronal diseases.

Hydrogen-rich saline attenuates hippocampus endoplasmic reticulum stress after cardiac arrest in rats

BACKGROUND

Hydrogen-rich saline can selectively scavenge reactive oxygen species (ROS) and protect brain against ischemia reperfusion (I/R) injury. Endoplasmic reticulum stress (ERS) has been implicated in the pathological process of cerebral ischemia. However, very little is known about the role of hydrogen-rich saline in mediating pathophysiological reactions to ERS after I/R injury caused by cardiac arrest.

METHODS

The rats were randomly divided into three groups, sham group (n=30), ischemia/reperfusion group (n=40) and hydrogen-rich saline group (n=40). The rats in experimental groups were subjected to 4min of cardiac arrest and followed by resuscitation. Then they were randomized to receive 5ml/kg of either hydrogen-rich saline or normal saline.

RESULTS

Hydrogen-rich saline significantly improves survival rate and neurological function. The beneficial effects of hydrogen-rich saline were associated with decreased levels of oxidative products, as well as the increased levels of antioxidant enzymes. Furthermore, the protective effects of hydrogen-rich saline were accompanied by the increased activity of glucose-regulated protein 78 (GRP78), the decreased activity of cysteinyl aspartate specific proteinase-12 (caspase-12) and C/EBP homologous protein (CHOP).

CONCLUSIONS

Hydrogen-rich saline attenuates brain I/R injury may through inhibiting hippocampus ERS after cardiac arrest in rats.

Mitomycin C induces apoptosis in human epidural scar fibroblasts after surgical decompression for spinal cord injury

Numerous studies have shown that topical application of mitomycin C after surgical decompression effectively reduces scar adhesion. However, the underlying mechanisms remain unclear. In this study, we investigated the effect of mitomycin C on the proliferation and apoptosis of human epidural scar fibroblasts. Human epidural scar fibroblasts were treated with various concentrations of mitomycin C (1, 5, 10, 20, 40 μg/mL) for 12, 24 and 48 hours. Mitomycin C suppressed the growth of these cells in a dose- and time-dependent manner. Mitomycin C upregulated the expression levels of Fas, DR4, DR5, cleaved caspase-8/9, Bax, Bim and cleaved caspase-3 proteins, and it downregulated Bcl-2 and Bcl-xL expression. In addition, inhibitors of caspase-8 and caspase-9 (Z-IETD-FMK and Z-LEHD-FMK, respectively) did not fully inhibit mitomycin C-induced apoptosis. Furthermore, mitomycin C induced endoplasmic reticulum stress by increasing the expression of glucose-regulated protein 78, CAAT/enhancer-binding protein homologous protein (CHOP) and caspase-4 in a dose-dependent manner. Salubrinal significantly inhibited the mitomycin C-induced cell viability loss and apoptosis, and these effects were accompanied by a reduction in CHOP expression. Our results support the hypothesis that mitomycin C induces human epidural scar fibroblast apoptosis, at least in part, via the endoplasmic reticulum stress pathway.

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.

Histological detection of dynamic glial responses in the dysmyelinating Tabby-jimpy mutant brain

Oligodendrocytes (OLs) are glial cells that form myelin sheaths surrounding the axons in the central nervous system (CNS). Jimpy (jp) mutant mice are dysmyelinating disease models that show developmental abnormalities in myelinated OLs in the CNS. The causative gene in jp mice is the proteolipid protein (PLP) located on the X chromosome. Mutations in the jp allele result in exon 5 skipping and expression of abnormal PLP containing a C-terminal frame shift. Many lines of evidence suggest that abnormal PLP in OLs results in endoplasmic reticulum (ER) stress and cell death. To histologically detect glial responses in the jp mutant brain, we performed staining with lineage-specific markers. Using OL markers and OL progenitor cell marker staining, we identified reduced numbers of OL lineage cells in the jp mutant brain. Nuclear staining of the transcription factor Olig1 was observed in the Tabby-jp brain, whereas cytoplasmic Olig1 staining was observed in the wild-type brain at postnatal day 21, suggesting that active myelination was present in the mutant brain. Many microglial cells with activated morphology and intensive staining of CD11b microglia marker were observed in the internal capsule of the mutant brain, a region of white matter containing residual OLs. Activated astrocytes with high glial fibrillary acidic protein-immunoreactivity were also mainly observed in white matter. Finally, we performed in situ hybridization using C/EBP homologous protein (CHOP) antisense probes to detect ER stressed cells. CHOP mRNA was strongly expressed in residual OLs in the Tabby-jp mutant mice at postnatal stages. These data show that microglia and astrocytes exhibit dynamic glial activation in response to cell death of OLs during Tabby-jp pathogenesis, and that CHOP antisense probes may be a good marker for the detection of ER-stressed OLs in jp mutant mice.

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.

The novel monoclonal antibody 9F5 reveals expression of a fragment of GPNMB/osteoactivin processed by furin-like protease(s) in a subpopulation of microglia in neonatal rat brain

To differentiate subtypes of microglia (MG), we developed a novel monoclonal antibody, 9F5, against one subtype (type 1) of rat primary MG. The 9F5 showed high selectivity for this cell type in Western blot and immunocytochemical analyses and no cross-reaction with rat peritoneal macrophages (Mφ). We identified the antigen molecule for 9F5: the 50- to 70-kDa fragments of rat glycoprotein nonmetastatic melanoma protein B (GPNMB)/osteoactivin, which started at Lys(170) . In addition, 9F5 immunoreactivity with GPNMB depended on the activity of furin-like protease(s). More important, rat type 1 MG expressed the GPNMB fragments, but type 2 MG and Mφ did not, although all these cells expressed mRNA and the full-length protein for GPNMB. These results suggest that 9F5 reactivity with MG depends greatly on cleavage of GPNMB and that type 1 MG, in contrast to type 2 MG and Mφ, may have furin-like protease(s) for GPNMB cleavage. In neonatal rat brain, amoeboid 9F5+ MG were observed in specific brain areas including forebrain subventricular zone, corpus callosum, and retina. Double-immunοstaining with 9F5 antibody and anti-Iba1 antibody, which reacts with MG throughout the CNS, revealed that 9F5+ MG were a portion of Iba1+ MG, suggesting that MG subtype(s) exist in vivo. We propose that 9F5 is a useful tool to discriminate between rat type 1 MG and other subtypes of MG/Mφ and to reveal the role of the GPNMB fragments during developing brain. GLIA 2016;64:1938-1961.

Melatonin Protects SH-SY5Y Neuronal Cells Against Methamphetamine-Induced Endoplasmic Reticulum Stress and Apoptotic Cell Death

Methamphetamine (METH), a psychostimulant with highly neurotoxic effects, has been known to induce neuronal apoptosis in part through an endoplasmic reticulum (ER) stress pathway. Melatonin is an endogenous antioxidant compound that exerts protective effects against several neurodegenerative conditions, including METH-induced neurotoxicity, via various mechanisms. However, the role of melatonin in ER stress is still relatively unclear. In the present study, we investigated ER stress and neuronal apoptosis following METH treatment and the role of melatonin in METH-mediated ER stress-induced cell death in the SH-SY5Y neuroblastoma cell line. We found that METH caused the overexpression of ER stress-related genes, including C/EBP homologous protein and spliced X-box binding protein 1, in dose- and time-dependent manners. Moreover, METH time-dependently activated caspase-12 and -3, leading to cellular apoptosis. Furthermore, we demonstrated that pretreatment with melatonin attenuated the overexpression of ER stress-related genes and the cleavages of caspase-12 and -3 caused by METH exposure. Flow cytometry revealed that METH-mediated neuronal apoptosis was also prevented by melatonin. These findings suggest the protective effects of melatonin against ER stress and apoptosis caused by METH and other harmful agents.

The Dichotomy of Endoplasmic Reticulum Stress Response in Liver Ischemia-Reperfusion Injury

Endoplasmic reticulum (ER) stress plays critical roles in the pathogenesis of liver ischemia-reperfusion injury (IRI). As ER stress triggers an adaptive cellular response, the question of what determines its functional outcome in liver IRI remains to be defined. In a murine liver partial warm ischemia model, we studied how transient (30 minutes) or prolonged (90 minutes) liver ischemia regulated local ER stress response and autophagy activities and their relationship with liver IRI. Effects of chemical chaperon 4-phenylbutyrate (4-PBA) or autophagy inhibitor 3-methyladenine (3-MA) were evaluated. Our results showed that although the activating transcription factor 6 branch of ER stress response was induced in livers by both types of ischemia, liver autophagy was activated by transient, but inhibited by prolonged, ischemia. Although 3-MA had no effects on liver IRI after prolonged ischemia, it significantly increased liver IRI after transient ischemia. The 4-PBA treatment protected livers from IRI after prolonged ischemia by restoring autophagy flux, and the adjunctive 3-MA treatment abrogated its liver protective effect. The same 4-PBA treatment, however, increased liver IRI and disrupted autophagy flux after transient ischemia. Although both types of ischemia activated 5' adenosine monophosphate-activated protein kinase and inactivated protein kinase B (Akt), prolonged ischemia also resulted in downregulations of autophagy-related gene 3 and autophagy-related gene 5 in ischemic livers. These results indicate a functional dichotomy of ER stress response in liver IRI via its regulation of autophagy. Transient ischemia activates autophagy to protect livers from IRI, whereas prolonged ischemia inhibits autophagy to promote the development of liver IRI.

Calcineurin β protects brain after injury by activating the unfolded protein response

The Ca²⁺-dependent phosphatase, calcineurin (CN) is thought to play a detrimental role in damaged neurons; however, its role in astrocytes is unclear. In cultured astrocytes, CNβ expression increased after treatment with a sarco/endoplasmic reticulum Ca²⁺-ATPase inhibitor, thapsigargin, and with oxygen and glucose deprivation, an in vitro model of ischemia. Similarly, CNβ was induced in astrocytes in vivo in two different mouse models of brain injury - photothrombotic stroke and traumatic brain injury (TBI). Immunoprecipitation and chemical activation dimerization methods pointed to physical interaction of CNβ with the unfolded protein response (UPR) sensor, protein kinase RNA-like endoplasmic reticulum kinase (PERK). In accordance, induction of CNβ resulted in oligomerization and activation of PERK. Strikingly, the presence of a phosphatase inhibitor did not interfere with CNβ-mediated activation of PERK, suggesting a hitherto undiscovered non-enzymatic role for CNβ. Importantly, the cytoprotective function of CNβ was PERK-dependent both in vitro and in vivo. Loss of CNβ in vivo resulted in a significant increase in cerebral damage, and correlated with a decrease in astrocyte size, PERK activity and glial fibrillary acidic protein (GFAP) expression. Taken together, these data reveal a critical role for the CNβ-PERK axis in not only prolonging astrocyte cell survival but also in modulating astrogliosis after brain injury.

Hydrogen-rich saline mediates neuroprotection through the regulation of endoplasmic reticulum stress and autophagy under hypoxia-ischemia neonatal brain injury in mice

Hydrogen as a new medical gas exerts organ-protective effects through regulating oxidative stress, inflammation and apoptosis. Multiple lines of evidence reveal the protective effects of hydrogen in various models of brain injury. However, the exact mechanism underlying this protective effect of hydrogen against hypoxic-ischemic brain damage (HIBD) is not fully understood. The present study was designed to investigate whether hydrogen-rich saline (HS) attenuates HIBD in neonatal mice and whether the observed protection is associated with reduced endoplasmic reticulum (ER) stress and regulated autophagy. The results showed that HS treatment significantly improved brain edema and decreased infarct volume. Furthermore, HS significantly attenuated HIBD-induced ER stress responses, including the decreased expression of glucose-regulated protein 78, C/EBP homologous protein, and down-regulated transcription factor. Additionally, we demonstrated that HS induced autophagy, including increased LC3B and Beclin-1 expression and decreased phosphorylation of mTOR and Stat3, as well as phosphorylation of ERK. Taken together, HS exerts neuroprotection against HIBD in neonatal mouse, mediated in part by reducing ER stress and increasing autophagy machinery.

Neuroprotective DAMPs member prothymosin alpha has additional beneficial actions against cerebral ischemia-induced vascular damages

Prothymosin alpha (ProTα) suppresses stress-induced necrosis of cultured cortical neurons. As neuroprotection alone could not explain the long-lasting protective actions against cerebral ischemia by ProTα, we further examined whether ProTα, in addition to neuroprotective effects, has other anti-ischemic activities. When recombinant mouse ProTα (rmProTα) at 0.3 mg/kg was intravenously (i.v.) given 2 h after the start of tMCAO, all mice survived for more than 14 days. In evaluation of CD31- and tomato lectin-labeling as well as IgG and Evans blue leakage, rmProTα treatment (0.1 mg/kg) largely blocked ischemia-induced vascular damages. Therefore, rmProTα has novel beneficial effects against ischemia-induced brain damage through vascular mechanisms.

Hydrogen sulfide exhibits cardioprotective effects by decreasing endoplasmic reticulum stress in a diabetic cardiomyopathy rat model

Endoplasmic reticulum (ER) stress is critical in the occurrence and development of diabetic cardiomyopathy (DC). Hydrogen sulfide (H2S) has been found to be the third gaseous signaling molecule with anti‑ER stress effects. Previous studies have shown that H2S acts as a potent inhibitor of fibrosis in the heart of diabetic rats. This study aimed to demonstrate whether H2S exhibits protective effects on the myocardium of streptozotocin (STZ)‑induced diabetic rats by suppressing ER stress. In this study, diabetic models were established by intraperitoneal (i.p.) injection of 40 mg/kg STZ. The STZ‑treated mice were divided into three groups, and subsequently treated with normal saline, 30 µmol/kg or 100 µmol/kg NaHS, i.p., respectively, for 8 weeks. The extent of myocyte hypertrophy was measured using hematoxylin and eosin‑stained sections and collagen components were investigated using immunostaining. The expression of glucose-regulated protein (Grp78), C/EBP‑homologous protein (CHOP) and caspase‑12 in the heart tissue of each group was detected by western blot analysis. It was demonstrated that H2S could improve myocardial hypertrophy and myocardial collagen deposition in diabetic rats. In addition, it could reduce the expression of Grp78, caspase-12 and CHOP. In conclusion, these findings demonstrate that H2S suppresses STZ‑induced ER stress in the hearts of rats, and it may serve as a novel cardioprotective agent for DC.

Endoplasmic Reticulum Stress and Associated ROS

The endoplasmic reticulum (ER) is a fascinating network of tubules through which secretory and transmembrane proteins enter unfolded and exit as either folded or misfolded proteins, after which they are directed either toward other organelles or to degradation, respectively. The ER redox environment dictates the fate of entering proteins, and the level of redox signaling mediators modulates the level of reactive oxygen species (ROS). Accumulating evidence suggests the interrelation of ER stress and ROS with redox signaling mediators such as protein disulfide isomerase (PDI)-endoplasmic reticulum oxidoreductin (ERO)-1, glutathione (GSH)/glutathione disuphide (GSSG), NADPH oxidase 4 (Nox4), NADPH-P450 reductase (NPR), and calcium. Here, we reviewed persistent ER stress and protein misfolding-initiated ROS cascades and their significant roles in the pathogenesis of multiple human disorders, including neurodegenerative diseases, diabetes mellitus, atherosclerosis, inflammation, ischemia, and kidney and liver diseases.

Protective Effect of Gomisin N against Endoplasmic Reticulum Stress-Induced Hepatic Steatosis

Gomisin N is a physiological substance derived from Schisandra chinensis. In the present study, the in vitro and in vivo effects of gomisin N on endoplasmic reticulum (ER) stress and hepatic steatosis were investigated. We quantified the expression of markers of ER stress, including glucose regulated protein 78 (GRP78), CCAAT/enhancer binding protein (C/EBP) homolog protein (CHOP), and X-box-binding protein-1 (XBP-1), and triglyceride (TG) accumulation, in HepG2 cells treated with tunicamycin or palmitate. Tunicamycin treatment in HepG2 cells induced expression of markers of ER stress and increased TG levels; Gomisin N reversed these effects, reducing the expression of markers of ER stress and TG levels. Similar effects were seen following palmitate pretreatment of HepG2 cells. The inhibitory effects of gomisin N were further confirmed in mice injected with tunicamycin. Gomisin N reduced expression of markers of ER stress and decreased TG levels in mouse liver after tunicamycin injection. Furthermore, gomisin N decreased expression of inflammatory and lipogenic genes in palmitate-incubated HepG2 cells. These results suggest that gomisin N inhibits ER stress and ameliorates hepatic steatosis induced by ER stress.

Crosstalk Between Endoplasmic Reticulum Stress, Oxidative Stress, and Autophagy: Potential Therapeutic Targets for Acute CNS Injuries

Endoplasmic reticulum (ER) stress induces a variety of neuronal cell death pathways that play a critical role in the pathophysiology of stroke. ER stress occurs when unfolded/misfolded proteins accumulate and the folding capacity of ER chaperones exceeds the capacity of ER lumen to facilitate their disposal. As a consequence, a complex set of signaling pathways will be induced that transmit from ER to cytosol and nucleus to compensate damage and to restore the normal cellular homeostasis, collectively known as unfolded protein response (UPR). However, failure of UPR due to severe or prolonged stress leads to cell death. Following acute CNS injuries, chronic disturbances in protein folding and oxidative stress prolong ER stress leading to sustained ER dysfunction and neuronal cell death. While ER stress responses have been well studied after stroke, there is an emerging need to study the association of ER stress with other cell pathways that exacerbate neuronal death after an injury. In this review, we summarize the current understanding of the role for ER stress in acute brain injuries, highlighting the diverse molecular mechanisms associated with ER stress and its relation to oxidative stress and autophagy. We also discussed the existing and developing therapeutic options aimed to reduce ER stress to protect the CNS after acute injuries.

Characterization of secretomes from a human blood brain barrier endothelial cells in-vitro model after ischemia by stable isotope labeling with aminoacids in cell culture (SILAC)

The human immortalized brain endothelial cell line hCMEC/D3 is considered a simple in-vitro model of the blood-brain-barrier. Our aim was to characterize changes in the secretome of hCMEC/D3 subjected to oxygen and glucose deprivation (OGD) to identify new proteins altered after ischemia and that might trigger blood-brain-barrier disruption and test their potential as blood biomarkers for ischemic stroke. Using a quantitative proteomic approach based on SILAC, 19 proteins were found differentially secreted between OGD and normoxia/normoglycemia conditions. Among the OGD-secreted proteins, protein folding was the main molecular function identified and for the main canonical pathways there was an enrichment in epithelial adherens junctions and aldosterone signaling. Western blot was used to verify the MS results in a set of 9 differentially secreted proteins and 5 of these were analyzed in serum samples of 38 ischemic stroke patients, 18 stroke-mimicking conditions and 18 healthy controls.

SIGNIFICANCE

"We characterized changes in the secretome of hCMEC/D3 cells after an ischemic insult by SILAC and identified proteins associated with ischemia that might be involved in the disruption of the blood-brain barrier. Besides we analyzed the putative potential of the candidate proteins to become biomarkers for the diagnosis of ischemic stroke.

Cell death induced by endoplasmic reticulum stress

The endoplasmic reticulum is an organelle with multiple functions. The synthesis of transmembrane proteins and proteins that are to be secreted occurs in this organelle. Many conditions that impose stress on cells, including hypoxia, starvation, infections and changes in secretory needs, challenge the folding capacity of the cell and promote endoplasmic reticulum stress. The cellular response involves the activation of sensors that transduce signaling cascades with the aim of restoring homeostasis. This is known as the unfolded protein response, which also intersects with the integrated stress response that reduces protein synthesis through inactivation of the initiation factor eIF2α. Central to the unfolded protein response are the sensors PERK, IRE1 and ATF6, as well as other signaling nodes such as c-Jun N-terminal kinase 1 (JNK) and the downstream transcription factors XBP1, ATF4 and CHOP. These proteins aim to restore homeostasis, but they can also induce cell death, which has been shown to occur by necroptosis and, more commonly, through the regulation of Bcl-2 family proteins (Bim, Noxa and Puma) that leads to mitochondrial apoptosis. In addition, endoplasmic reticulum stress and proteotoxic stress have been shown to induce TRAIL receptors and activation of caspase-8. Endoplasmic reticulum stress is a common feature in the pathology of numerous diseases because it plays a role in neurodegeneration, stroke, cancer, metabolic diseases and inflammation. Understanding how cells react to endoplasmic reticulum stress can accelerate discovery of drugs against these diseases.

Therapeutic window of globular adiponectin against cerebral ischemia in diabetic mice: the role of dynamic alteration of adiponectin/adiponectin receptor expression

Recent studies have demonstrated that adiponectin (APN) attenuates cerebral ischemic/reperfusion via globular adiponectin (gAD). However, the therapeutic role of gAD in cerebral ischemic injury in type 1 diabetes mellitus (T1DM) remains unclear. Our results showed that gAD improved neurological scores and reduced the infarct volumes in the 8-week T1DM (T1DM-8W) mice, but not in the 2-week T1DM (T1DM-2W) mice. Moreover, the ischemic penumbra APN levels increased and peaked in T1DM-2W mice, and reduced to normal in T1DM-8W mice, while the APN receptor 1 (AdipoR1) expression change was the opposite. Administration of rosiglitazone in T1DM-2W mice up-regulated the expression of AdipoR1 and restored the neuroprotection of gAD, while intracerebroventricular injection of AdipoR1 small interfering RNA (siRNA) in T1DM-8W mice reversed it. Furthermore, the expression of p-PERK, p-IRE1 and GRP78 were increased whereas the expressions of CHOP and cleaved caspase-12 as well as the number of apoptotic neurons were decreased after gAD treatment in T1DM-8W mice. These beneficial effects of gAD were reversed by pretreatment with AdipoR1 siRNA. These results demonstrated a dynamic dysfunction of APN/AdipoR1 accompanying T1DM progression. Interventions bolstering AdipoR1 expression during early stages and gAD supplementation during advanced stages may potentially reduce the cerebral ischemic injury in diabetic patients.

CCAAT-Enhancer-Binding Protein Homologous Protein Deficiency Attenuates Oxidative Stress and Renal Ischemia-Reperfusion Injury

AIMS

Renal ischemia-reperfusion (I/R) is a major cause of acute renal failure. The mechanisms of I/R injury include endoplasmic reticulum (ER) stress, inflammatory responses, hypoxia, and generation of reactive oxygen species (ROS). CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) is involved in the ER stress signaling pathways. CHOP is a transcription factor and a major mediator of ER stress-induced apoptosis. However, the role of CHOP in renal I/R injury is still undefined. Here, we investigated whether CHOP could regulate I/R-induced renal injury using CHOP-knockout mice and cultured renal tubular cells as models.

RESULTS

In CHOP-knockout mice, loss of renal function induced by I/R was prevented. Renal proximal tubule damage was induced by I/R in wild-type mice; however, the degree of alteration was significantly less in CHOP-knockout mice. CHOP deficiency also decreased the I/R-induced activation of caspase-3 and -8, apoptosis, and lipid peroxidation, whereas the activity of endogenous antioxidants increased. In an in vitro I/R model, small interfering RNA targeting CHOP significantly reversed increases in H2O2 formation, inflammatory signals, and apoptotic signals, while enhancing the activity of endogenous antioxidants in renal tubular cells.

INNOVATION

To the best of our knowledge, this is the first study which demonstrates that CHOP deficiency attenuates oxidative stress and I/R-induced acute renal injury both in vitro and in vivo.

CONCLUSION

These findings suggest that CHOP regulates not only apoptosis-related signaling but also ROS formation and inflammation in renal tubular cells during I/R. CHOP may play an important role in the pathophysiology of I/R-induced renal injury.

ER Stress and Angiogenesis

Proper tissue vascularization is vital for cellular function as it delivers oxygen, nutrients, hormones, and immune cells and helps to clear cellular debris and metabolic waste products. Tissue angiogenesis occurs to satisfy energy requirements and cellular sensors of metabolic imbalance coordinate vessel growth. In this regard, the classical pathways of the unfolded protein response activated under conditions of ER stress have recently been described to generate angiomodulatory or angiostatic signals. This review elaborates on the link between angiogenesis and ER stress and discusses the implications for diseases characterized by altered vascular homeostasis, such as cancer, retinopathies, and atherosclerosis.

Nafamostat mesilate attenuates transient focal ischemia/reperfusion-induced brain injury via the inhibition of endoplasmic reticulum stress

Nafamostat mesilate (NM), a serine protease inhibitor, has a broad range of clinical applications that include use as an anticoagulant during hemodialysis in cerebral hemorrhage patients, as a hemoperfusion anticoagulant for patients with intravascular coagulation, hemorrhagic lesions, and hemorrhagic tendencies, and for the improvement of acute pancreatitis. However, the effects of NM on acute cerebral ischemia have yet to be investigated. Thus, the present study utilized a rat model in which transient middle cerebral artery occlusion (MCAO) was used to induce ischemic injury to investigate the effects of NM on infarct volume and histological and biological changes. NM (1mg/kg) was intravenously administered prior to and after the MCAO procedure. Compared to control rats, the administration of NM significantly decreased infarct size and the extent of brain edema after the induction of focal ischemia via MCAO. Additionally, NM treatment attenuated MCAO-induced neuronal degeneration and activation of microglia and astrocytes. NM treatment also inhibited the MCAO-induced expression levels of glucose-regulated protein 78 (GRP78), CATT/EBP homologous protein (CHOP), and p-eukaryotic initiation factor 2α (eIF2α), which are endoplasmic reticulum (ER) stress markers, in the cerebral cortex. The present findings demonstrate that NM exerts neuroprotective effects in the brain following focal ischemia via, at least in part, the inhibition of ER stress.

Regulation of mitophagy in ischemic brain injury

The selective degradation of damaged or excessive mitochondria by autophagy is termed mitophagy. Mitophagy is crucial for mitochondrial quality control and has been implicated in several neurodegenerative disorders as well as in ischemic brain injury. Emerging evidence suggested that the role of mitophagy in cerebral ischemia may depend on different pathological processes. In particular, a neuroprotective role of mitophagy has been proposed, and the regulation of mitophagy seems to be important in cell survival. For these reasons, extensive investigations aimed to profile the mitophagy process and its underlying molecular mechanisms have been executed in recent years. In this review, we summarize the current knowledge regarding the mitophagy process and its role in cerebral ischemia, and focus on the pathological events and molecules that regulate mitophagy in ischemic brain injury.

The Hypothermic Influence on CHOP and Ero1-α in an Endoplasmic Reticulum Stress Model of Cerebral Ischemia

Hypoxia induced endoplasmic reticulum stress causes accumulation of unfolded proteins in the endoplasmic reticulum and activates the unfolded protein response, resulting in apoptosis through CCAAT-enhancer-binding protein homologous protein (CHOP) activation. In an in vitro and in vivo model of ischemic stroke, we investigated whether hypothermia regulates the unfolded protein response of CHOP and Endoplasmic reticulum oxidoreductin-α (Ero1-α), because Ero1-α is suggested to be a downstream CHOP target. The gene expression of CHOP and Ero1-α was measured using Quantitative-PCR (Q-PCR) in rat hippocampi following global cerebral ischemia, and in hypoxic pheochromocytoma cells during normothermic (37 °C) and hypothermic (31 °C) conditions. As a result of ischemia, a significant increase in expression of CHOP and Ero1-α was observed after three, six and twelve hours of reperfusion following global ischemia. A stable increase in CHOP expression was observed throughout the time course (p < 0.01, p < 0.0001), whereas Ero1-α expression peaked at three to six hours (p < 0.0001). Induced hypothermia in hypoxia stressed PC12 cells resulted in a decreased expression of CHOP after three, six and twelve hours (p < 0.0001). On the contrary, the gene expression of Ero1-α increased as a result of hypothermia and peaked at twelve hours (p < 0.0001). Hypothermia attenuated the expression of CHOP, supporting that hypothermia suppress endoplasmic reticulum stress induced apoptosis in stroke. As hypothermia further induced up-regulation of Ero1-α, and since CHOP and Ero1-α showed differential regulation as a consequence of both disease (hypoxia) and treatment (hypothermia), we conclude that they are regulated independently.

Brain endoplasmic reticulum stress mechanistically distinguishes the saline-intake and hypertensive response to deoxycorticosterone acetate-salt

Endoplasmic reticulum stress has become an important mechanism in hypertension. We examined the role of endoplasmic reticulum stress in mediating the increased saline-intake and hypertensive effects in response to deoxycorticosterone acetate (DOCA)-salt. Intracerebroventricular delivery of the endoplasmic reticulum stress-reducing chemical chaperone tauroursodeoxycholic acid did not affect the magnitude of hypertension, but markedly decreased saline-intake in response to DOCA-salt. Increased saline-intake returned after tauroursodeoxycholic acid was terminated. Decreased saline-intake was also observed after intracerebroventricular infusion of 4-phenylbutyrate, another chemical chaperone. Immunoreactivity to CCAAT homologous binding protein, a marker of irremediable endoplasmic reticulum stress, was increased in the subfornical organ and supraoptic nucleus of DOCA-salt mice, but the signal was absent in control and CCAAT homologous binding protein-deficient mice. Electron microscopy revealed abnormalities in endoplasmic reticulum structure (decrease in membrane length, swollen membranes, and decreased ribosome numbers) in the subfornical organ consistent with endoplasmic reticulum stress. Subfornical organ-targeted adenoviral delivery of GRP78, a resident endoplasmic reticulum chaperone, decreased DOCA-salt-induced saline-intake. The increase in saline-intake in response to DOCA-salt was blunted in CCAAT homologous binding protein-deficient mice, but these mice exhibited a normal hypertensive response. We conclude that (1) brain endoplasmic reticulum stress mediates the saline-intake, but not blood pressure response to DOCA-salt, (2) DOCA-salt causes endoplasmic reticulum stress in the subfornical organ, which when attenuated by GRP78 blunts saline-intake, and (3) CCAAT homologous binding protein may play a functional role in DOCA-salt-induced saline-intake. The results suggest a mechanistic distinction between the importance of endoplasmic reticulum stress in mediating effects of DOCA-salt on saline-intake and blood pressure.

Stress-induced neuroprotective effects of epiregulin and amphiregulin

Members of the epidermal growth factor family play important roles in the regulation of cell growth, proliferation, and survival. However, the specific roles of each epidermal growth factor family member with respect to brain injury are not well understood. Gene chip assay screens have revealed drastic increases in the expression of the epidermal growth factor family members amphiregulin and epiregulin following lipopolysaccharide stimulation, which activates an immune response. Both immune activity and endoplasmic reticulum stress are activated during cerebral ischemia. We found that the expression levels of amphiregulin and epiregulin were significantly increased under conditions of cerebral ischemia. Because endoplasmic reticulum stress increased the expression of amphiregulin and epiregulin in glial cells, endoplasmic reticulum stress may be a key mediatory factor of pathophysiological activity. Recombinant epiregulin and amphiregulin proteins effectively inhibited endoplasmic reticulum stress and the subsequent induction of neuronal cell death. Therefore, the upregulation of the epidermal growth factor family members epiregulin and amphiregulin may play a critical role in preventing endoplasmic reticulum stress-induced cell death, thus providing a potential therapy for brain injury.

Tunicamycin-induced unfolded protein response in the developing mouse brain

Accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER) causes ER stress, resulting in the activation of the unfolded protein response (UPR). ER stress and UPR are associated with many neurodevelopmental and neurodegenerative disorders. The developing brain is particularly susceptible to environmental insults which may cause ER stress. We evaluated the UPR in the brain of postnatal mice. Tunicamycin, a commonly used ER stress inducer, was administered subcutaneously to mice of postnatal days (PDs) 4, 12 and 25. Tunicamycin caused UPR in the cerebral cortex, hippocampus and cerebellum of mice of PD4 and PD12, which was evident by the upregulation of ATF6, XBP1s, p-eIF2α, GRP78, GRP94 and MANF, but failed to induce UPR in the brain of PD25 mice. Tunicamycin-induced UPR in the liver was observed at all stages. In PD4 mice, tunicamycin-induced caspase-3 activation was observed in layer II of the parietal and optical cortex, CA1-CA3 and the subiculum of the hippocampus, the cerebellar external germinal layer and the superior/inferior colliculus. Tunicamycin-induced caspase-3 activation was also shown on PD12 but to a much lesser degree and mainly located in the dentate gyrus of the hippocampus, deep cerebellar nuclei and pons. Tunicamycin did not activate caspase-3 in the brain of PD25 mice and the liver of all stages. Similarly, immature cerebellar neurons were sensitive to tunicamycin-induced cell death in culture, but became resistant as they matured in vitro. These results suggest that the UPR is developmentally regulated and the immature brain is more susceptible to ER stress.

Possible involvement of endoplasmic reticulum stress in the pathogenesis of Alzheimer’s disease

The endoplasmic reticulum (ER) is an organelle that plays a crucial role in protein quality control such as protein folding. Evidence to indicate the involvement of ER in maintaining cellular homeostasis is increasing. However, when cells are exposed to stressful conditions, which perturb ER function, unfolded proteins accumulate leading to ER stress. Cells then activate the unfolded protein response (UPR) to cope with this stressful condition. In the present review, we will discuss and summarize recent advances in research on the basic mechanisms of the UPR. We also discuss the possible involvement of ER stress in the pathogenesis of Alzheimer’s disease (AD). Potential therapeutic opportunities for diseases targeting ER stress is also described.

A study of ER stress in rat model of cerebral venous sinus thrombosis

Cerebral venous sinus thrombosis (CVST) is a rare form of stroke. The role of endoplasmic reticulum (ER) stress markers is well documented in arterial stroke but has not been evaluated in venous stroke. The present study has been undertaken to investigate the role of ER stress in rodent model of CVST. For inducing CVST, a cranial window was made to expose superior sagittal sinus (SSS). A strip of filter paper soaked with 40% ferric chloride was applied on exposed cranial window while in sham operated control 0.9% saline was used. Clinical evaluations were done on day 1, 2, and 7 for neurological deficit. Rota rod test and brain infarction volume were also measured. Brain tissue was collected from infarcted portion for further analysis using real time polymerase chain reaction and western blot technique for ER stress markers. Augmented expression of ER stress markers and up regulation of apoptotic genes were found in infarcted tissue. These markers improved on day 7. It is concluded that ER markers are up regulated at an early stage of CVST and may be important in pathophysiology.

PEITC induces apoptosis of Human Brain Glioblastoma GBM8401 Cells through the extrinsic- and intrinsic -signaling pathways

Glioblastoma is the most common and most aggressive primary brain malignancy. The multimodality treatments for this tumor including surgery, radiotherapy, and chemotherapy, are still not completely satisfied. Phenethyl isothiocyanate (PEITC), one member of the isothiocyanate family, has been shown to induce apoptosis in many human cancer cells. In this study, we investigate the pro-apoptotic effects caused by PETIC in human brain glioblastoma multiforme GBM 8401 cells. In our data, PEITC induced the cell morphological changes and decreased the cell viability of GBM8401 cells in a dose- and time-dependent manner. Moreover, the analysis of cell cycle distribution detected by flow cytometry showed that PEITC induced significantly sub-G1 phase (apoptotic population) in GBM 8401 cells. In addition, PEITC promoted the production of reactive oxygen species (ROS) and increase in [Ca2+]I, but decreased the mitochondrial membrane potential (ΔΨm) in treated cells. PEITC also induced caspases activities in GBM 8401 cells. Results from Western blot analysis indicated that PEITC promoted Fas, FasL, FADD, TRAIL, caspase-8, -9, -3, increased the pro-apoptotic protein (Bax, Bid and Bak), and inhibited the anti-apoptotic proteins (Bcl-2 and Bcl-xl) in GBM 8401 cells. Furthermore, PEITC promoted the release of cytochrome c, AIF and Endo G. GADD153, GRP 78, XBP-1 and IRE-1α, Calpain I and II in GBM 8401 cells. PEITC also promoted the expression of associated protein with endoplasmic reticulum (ER) stress. PEITC induces apoptosis through the extrinsic (death receptor) pathway, dysfunction of mitochondria, ROS induced ER stress, intrinsic (mitochondrial) pathway in GBM 8401 cells. The possible molecular mechanisms and signaling pathways of the anti-cancer properties of PEITC for human brain glioblastoma cells were postulated.

The dynamic changes of endoplasmic reticulum stress pathway markers GRP78 and CHOP in the hippocampus of diabetic mice

Diabetic encephalopathy has recently been recognized late complication of diabetes resulting in progressive cognitive deficits. Emerging evidence has indicated that endoplasmic reticulum (ER) stress-mediated apoptosis is involved in the pathogenesis of diabetic eye and kidney as well as non-diabetic neurodegeneration. However, there was little direct evidence for the involvement of ER stress in diabetic encephalopathy up to now. In the present work, we investigated the role of ER stress in the pathogenesis of diabetic encephalopathy. Our results have demonstrated the existence of ER stress in the hippocampus of streptozotocin (STZ)-induced diabetic mice. STZ injection i.p. rapidly induced up-regulation of the ER stress marker, the prosurvival chaperone glucose-regulated protein 78 (GRP78), as early as 6-24h and persisted at least for up to 72h in the hippocampus of mice, indicating the UPR activation soon after STZ administration. The increased expression of GRP78 in hippocampal cells is to relieve the ER stress. With the development of diabetes, the expression of GRP78 decreases while the expression of UPR-associated proapoptotic transcriptional regulator C/EBP homologous protein (CHOP) increases significantly in the hippocampal neurons of diabetic mice from 1 week after STZ administration to 12 weeks/the end of the study. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling-positive cells in the hippocampus of diabetic mice were largely colocalized with NeuN- and CHOP-positive cells, indicating that the up-regulation of CHOP in hippocampal neurons of diabetic mice may promote neuronal apoptosis and account for the damaged learning and memory ability of diabetic mice. Therefore, our study provides evidence that ER stress may play an important role in the pathogenesis of neuronal degeneration and may contribute to cognitive dysfunction of diabetic encephalopathy.

The role of endoplasmic reticulum stress in human pathology

Numerous genetic and environmental insults impede the ability of cells to properly fold and posttranslationally modify secretory and transmembrane proteins in the endoplasmic reticulum (ER), leading to a buildup of misfolded proteins in this organelle--a condition called ER stress. ER-stressed cells must rapidly restore protein-folding capacity to match protein-folding demand if they are to survive. In the presence of high levels of misfolded proteins in the ER, an intracellular signaling pathway called the unfolded protein response (UPR) induces a set of transcriptional and translational events that restore ER homeostasis. However, if ER stress persists chronically at high levels, a terminal UPR program ensures that cells commit to self-destruction. Chronic ER stress and defects in UPR signaling are emerging as key contributors to a growing list of human diseases, including diabetes, neurodegeneration, and cancer. Hence, there is much interest in targeting components of the UPR as a therapeutic strategy to combat these ER stress-associated pathologies.

Ischemia/reperfusion-induced CHOP expression promotes apoptosis and impairs renal function recovery: the role of acidosis and GPR4

Endoplasmic reticulum (ER) stress-induced apoptosis is implicated in a wide range of diseases, including ischemia/reperfusion injury (IRI). As a common feature of ER stress, the role of CCAT/enhancer-binding protein homologous protein (CHOP) in renal IRI has not been thoroughly investigated. We found that IR led to renal CHOP expression, accompanied by apoptosis induction. Renal IRI was markedly alleviated in CHOP-/- mice. Observations from bone marrow chimeras showed that this was based on CHOP inactivation in renal parenchymal cells rather than inflammatory cells. In vivo and in vitro studies demonstrated that IRI induced CHOP expression in both endothelial and epithelial cells, which was responsible for apoptosis induction. These results were reinforced by the observation that CHOP knockout led to improvement of the postischemic microcirculatory recovery. In vitro studies revealed hypoxia-induced acidosis to be a major inducer of CHOP in endothelial cells, and neutralizing acidosis not only diminished CHOP protein, but also reduced apoptosis. Finally, knockdown of a proton-sensing G protein-coupled receptor GPR4 markedly reduced CHOP expression and endothelial cell apoptosis after hypoxia exposure. These results highlight the importance of hypoxia-acidosis in ER stress signaling regulation in ischemic kidneys and suggest that GPR4 inhibitors or agents targeting CHOP expression may be promising in the treatment of renal IRI.