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

Microglia-neuron-vascular interactions in ischemia

Cerebral ischemia is a devastating condition that results in impaired blood flow in the brain leading to acute brain injury. As the most common form of stroke, occlusion of cerebral arteries leads to a characteristic sequence of pathophysiological changes in the brain tissue. The mechanisms involved, and comorbidities that determine outcome after an ischemic event appear to be highly heterogeneous. On their own, the processes leading to neuronal injury in the absence of sufficient blood supply to meet the metabolic demand of the cells are complex and manifest at different temporal and spatial scales. While the contribution of non-neuronal cells to stroke pathophysiology is increasingly recognized, recent data show that microglia, the main immune cells of the central nervous system parenchyma, play previously unrecognized roles in basic physiological processes beyond their inflammatory functions, which markedly change during ischemic conditions. In this review, we aim to discuss some of the known microglia-neuron-vascular interactions assumed to contribute to the acute and delayed pathologies after cerebral ischemia. Because the mechanisms of neuronal injury have been extensively discussed in several excellent previous reviews, here we focus on some recently explored pathways that may directly or indirectly shape neuronal injury through microglia-related actions. These discoveries suggest that modulating gliovascular processes in different forms of stroke and other neurological disorders might have presently unexplored therapeutic potential in combination with neuroprotective and flow restoration strategies.

Therapeutic Potential of Targeting the PERK Signaling Pathway in Ischemic Stroke

Many pathologic states can lead to the accumulation of unfolded/misfolded proteins in cells. This causes endoplasmic reticulum (ER) stress and triggers the unfolded protein response (UPR), which encompasses three main adaptive branches. One of these UPR branches is mediated by protein kinase RNA-like ER kinase (PERK), an ER stress sensor. The primary consequence of PERK activation is the suppression of global protein synthesis, which reduces ER workload and facilitates the recovery of ER function. Ischemic stroke induces ER stress and activates the UPR. Studies have demonstrated the involvement of the PERK pathway in stroke pathophysiology; however, its role in stroke outcomes requires further clarification. Importantly, considering mounting evidence that supports the therapeutic potential of the PERK pathway in aging-related cognitive decline and neurodegenerative diseases, this pathway may represent a promising therapeutic target in stroke. Therefore, in this review, our aim is to discuss the current understanding of PERK in ischemic stroke, and to summarize pharmacologic tools for translational stroke research that targets PERK and its associated pathways.

Ferroptosis and endoplasmic reticulum stress in ischemic stroke

Ferroptosis is a form of non-apoptotic programmed cell death, and its mechanisms mainly involve the accumulation of lipid peroxides, imbalance in the amino acid antioxidant system, and disordered iron metabolism. The primary organelle responsible for coordinating external challenges and internal cell demands is the endoplasmic reticulum, and the progression of inflammatory diseases can trigger endoplasmic reticulum stress. Evidence has suggested that ferroptosis may share pathways or interact with endoplasmic reticulum stress in many diseases and plays a role in cell survival. Ferroptosis and endoplasmic reticulum stress may occur after ischemic stroke. However, there are few reports on the interactions of ferroptosis and endoplasmic reticulum stress with ischemic stroke. This review summarized the recent research on the relationships between ferroptosis and endoplasmic reticulum stress and ischemic stroke, aiming to provide a reference for developing treatments for ischemic stroke.

Hypothermia increases adenosine monophosphate and xanthosine monophosphate levels in the mouse hippocampus, preventing their reduction by global cerebral ischemia

Global cerebral ischemia (GCI) caused by clinical conditions such as cardiac arrest leads to delayed neuronal death in the hippocampus, resulting in physical and mental disability. However, the mechanism of delayed neuronal death following GCI remains unclear. To elucidate the mechanism, we performed a metabolome analysis using a mouse model in which hypothermia (HT) during GCI, which was induced by the transient occlusion of the bilateral common carotid arteries, markedly suppressed the development of delayed neuronal death in the hippocampus after reperfusion. Fifteen metabolites whose levels were significantly changed by GCI and 12 metabolites whose levels were significantly changed by HT were identified. Furthermore, the metabolites common for both changes were narrowed down to two, adenosine monophosphate (AMP) and xanthosine monophosphate (XMP). The levels of both AMP and XMP were found to be decreased by GCI, but increased by HT, thereby preventing their decrease. In contrast, the levels of adenosine, inosine, hypoxanthine, xanthine, and guanosine, the downstream metabolites of AMP and XMP, were increased by GCI, but were not affected by HT. Our results may provide a clue to understanding the mechanism by which HT during GCI suppresses the development of delayed neuronal death in the hippocampus.

The mechanistic functional landscape of retinitis pigmentosa: a machine learning-driven approach to therapeutic target discovery

BACKGROUND

Retinitis pigmentosa is the prevailing genetic cause of blindness in developed nations with no effective treatments. In the pursuit of unraveling the intricate dynamics underlying this complex disease, mechanistic models emerge as a tool of proven efficiency rooted in systems biology, to elucidate the interplay between RP genes and their mechanisms. The integration of mechanistic models and drug-target interactions under the umbrella of machine learning methodologies provides a multifaceted approach that can boost the discovery of novel therapeutic targets, facilitating further drug repurposing in RP.

METHODS

By mapping Retinitis Pigmentosa-related genes (obtained from Orphanet, OMIM and HPO databases) onto KEGG signaling pathways, a collection of signaling functional circuits encompassing Retinitis Pigmentosa molecular mechanisms was defined. Next, a mechanistic model of the so-defined disease map, where the effects of interventions can be simulated, was built. Then, an explainable multi-output random forest regressor was trained using normal tissue transcriptomic data to learn causal connections between targets of approved drugs from DrugBank and the functional circuits of the mechanistic disease map. Selected target genes involvement were validated on rd10 mice, a murine model of Retinitis Pigmentosa.

RESULTS

A mechanistic functional map of Retinitis Pigmentosa was constructed resulting in 226 functional circuits belonging to 40 KEGG signaling pathways. The method predicted 109 targets of approved drugs in use with a potential effect over circuits corresponding to nine hallmarks identified. Five of those targets were selected and experimentally validated in rd10 mice: Gabre, Gabra1 (GABARα1 protein), Slc12a5 (KCC2 protein), Grin1 (NR1 protein) and Glr2a. As a result, we provide a resource to evaluate the potential impact of drug target genes in Retinitis Pigmentosa.

CONCLUSIONS

The possibility of building actionable disease models in combination with machine learning algorithms to learn causal drug-disease interactions opens new avenues for boosting drug discovery. Such mechanistically-based hypotheses can guide and accelerate the experimental validations prioritizing drug target candidates. In this work, a mechanistic model describing the functional disease map of Retinitis Pigmentosa was developed, identifying five promising therapeutic candidates targeted by approved drug. Further experimental validation will demonstrate the efficiency of this approach for a systematic application to other rare diseases.

Multi-Omics Profiling Identifies Microglial Annexin A2 as a Key Mediator of NF-κB Pro-inflammatory Signaling in Ischemic Reperfusion Injury

Cerebral stroke is one of the leading causes of mortality and disability worldwide. Restoring the cerebral circulation following a period of occlusion and subsequent tissue oxygenation leads to reperfusion injury. Cerebral ischemic reperfusion (I/R) injury triggers immune and inflammatory responses, apoptosis, neuronal damage, and even death. However, the cellular function and molecular mechanisms underlying cerebral I/R-induced neuronal injury are incompletely understood. By integrating proteomic, phosphoproteomic, and transcriptomic profiling in mouse hippocampi after cerebral I/R, we revealed that the differentially expressed genes and proteins mainly fall into several immune inflammatory response-related pathways. We identified that Annexin 2 (Anxa2) was exclusively upregulated in microglial cells in response to cerebral I/R in vivo and oxygen-glucose deprivation and reoxygenation (OGD/R) in vitro. RNA-seq analysis revealed a critical role of Anxa2 in the expression of inflammation-related genes in microglia via the NF-κB signaling. Mechanistically, microglial Anxa2 is required for nuclear translocation of the p65 subunit of NF-κB and its transcriptional activity upon OGD/R in BV2 microglial cells. Anxa2 knockdown inhibited the OGD/R-induced microglia activation and markedly reduced the expression of pro-inflammatory factors, including TNF-α, IL-1β, and IL-6. Interestingly, conditional medium derived from Anxa2-depleted BV2 cell cultures with OGD/R treatment alleviated neuronal death in vitro. Altogether, our findings revealed that microglia Anxa2 plays a critical role in I/R injury by regulating NF-κB inflammatory responses in a non-cell-autonomous manner, which might be a potential target for the neuroprotection against cerebral I/R injury.

Rapamycin Alleviates Neuronal Injury and Modulates Microglial Activation After Cerebral Ischemia

Neurons and microglia are sensitive to cerebral microcirculation and their responses play a crucial part in the pathological processes, while they are also the main target cells of many drugs used to treat brain diseases. Rapamycin exhibits beneficial effects in many diseases; however, whether it can affect neuronal injury or alter the microglial activation after global cerebral ischemia remains unclear. In this study, we performed global cerebral ischemia combined with rapamycin treatment in CX3CR1GFP/+ mice and explored the effects of rapamycin on neuronal deficit and microglial activation. Our results showed that rapamycin reduced neuronal loss, neurodegeneration, and ultrastructural damage after ischemia by histological staining and transmission electron microscopy (TEM). Interestingly, rapamycin suppressed de-ramification and proliferation of microglia and reduced the density of microglia. Immunofluorescence staining indicated that rapamycin skewed microglial polarization toward an anti-inflammatory state. Furthermore, rapamycin as well suppressed the activation of astrocytes. Meanwhile, quantitative real-time polymerase chain reaction (qRT-PCR) analyses revealed a significant reduction of pro-inflammatory factors as well as an elevation of anti-inflammatory factors upon rapamycin treatment. As a result of these effects, behavioral tests showed that rapamycin significantly alleviated the brain injury after stroke. Together, our study suggested that rapamycin attenuated neuronal injury, altered microglial activation state, and provided a more beneficial immune microenvironment for the brain, which could be used as a promising therapeutic approach to treat ischemic cerebrovascular diseases.

Role of calpain-5 in cerebral ischemia and reperfusion injury

BACKGROUND

Ischemia and reperfusion (I/R) injury exacerbate the prognosis of ischemic diseases. The cause of this exacerbation is partly a mitochondrial cell death pathway. Mitochondrial calpain-5 is proteolyzed/autolyzed under endoplasmic reticulum stress, resulting in inflammatory caspase-4 activation. However, the role of calpain-5 in I/R injury remains unclear. We hypothesized that calpain-5 is involved in ischemic brain disease.

METHODS

Mitochondria from C57BL/6J mice were extracted via centrifugation with/without proteinase K treatment. The expression and proteolysis/autolysis of calpain-5 were determined using western blotting. The mouse and human brains with I/R injury were analyzed using hematoxylin and eosin staining and immunohistochemistry. HT22 cells were treated with tunicamycin and CAPN5 siRNA.

RESULTS

Calpain-5 was expressed in the mitochondria of mouse tissues. Mitochondrial calpain-5 in mouse brains was responsive to calcium earlier than cytosolic calpain-5 in vitro calcium assays and in vivo bilateral common carotid artery occlusion model mice. Immunohistochemistry revealed that neurons were positive for calpain-5 in the normal brains of mice and humans. The expression of calpain-5 was increased in reactive astrocytes at human infarction sites. The knockdown of calpain-5 suppressed of cleaved caspase-11.

CONCLUSIONS

The neurons of human and mouse brains express calpain-5, which is proteolyzed/autolyzed in the mitochondria in the early stage of I/R injury and upregulated in reactive astrocytes in the end-stage.

GENERAL SIGNIFICANCE

Our results provide a comprehensive understanding of the mechanisms underlying I/R injury. Targeting the expression or activity of mitochondrial calpain-5 may suppress the inflammation during I/R injuries such as cerebrovascular diseases.

Methylmercury-induced brain neuronal death in CHOP-knockout mice

Apoptosis is one of the hallmarks of MeHg-induced neuronal cell death; however, its molecular mechanism remains unclear. We previously reported that MeHg exposure induces neuron-specific ER stress in the mouse brain. Excessive ER stress contributes to apoptosis, and CHOP induction is considered to be one of the major mechanisms. CHOP is also increased by MeHg exposure in the mouse brain, suggesting that it correlates with increased apoptosis. In this study, to clarify whether CHOP mediates MeHg-induced apoptosis, we examined the effect of CHOP deletion on MeHg exposure in CHOP-knockout mice. Our data showed that CHOP deletion had no effect on MeHg exposure-induced weight loss or hindlimb impairment in mice, nor did it increase apoptosis or inhibit neuronal cell loss. Hence, CHOP plays little role in MeHg toxicity, and other apoptotic pathways coupled with ER stress may be involved in MeHg-induced cell death.

Involvement of Proteasomal and Endoplasmic Reticulum Stress in Neurodegeneration After Global Brain Ischemia

A brief period of transient global brain ischemia leads to selective ischemic neurodegeneration associated with death of hippocampal CA1 pyramidal neurons days after reperfusion. The mechanism of such selective and delayed neurodegeneration is still uncertain. Our work aimed to study the involvement of proteasomal and endoplasmic reticulum (ER) stress in ischemic neurodegeneration. We have performed laser scanning confocal microscopy analysis of brain slices from control and experimental animals that underwent global brain ischemia for 15 min and varying times of reperfusion. We have focused on ubiquitin, PUMA, a proapoptotic protein of the Bcl-2 family overexpressed in response to both proteasomal and ER stress, and p53, which controls expression of PUMA. We have also examined the expression of HRD1, an E3 ubiquitin ligase that was shown to be overexpressed after ER stress. We have also examined potential crosstalk between proteasomal and ER stress using cellular models of both proteasomal and ER stress. We demonstrate that global brain ischemia is associated with an appearance of distinct immunoreactivity of ubiquitin, PUMA and p53 in pyramidal neurons of the CA1 layer of the hippocampus 72 h after ischemic insults. Such changes correlate with a delay and selectivity of ischemic neurodegeneration. Immunoreactivity of HRD1 observed in all investigated regions of rat brain was transiently absent in both CA1 and CA3 pyramidal neurones 24 h after ischemia in the hippocampus, which does not correlate with a delay and selectivity of ischemic neurodegeneration. We do not document significant crosstalk between proteasomal and ER stress. Our results favour dysfunction of the ubiquitin proteasome system and consequent p53-induced expression of PUMA as the main mechanisms responsible for selective and delayed degeneration of pyramidal neurons of the hippocampal CA1 layer in response to global brain ischemia.

Cross-talk between bioactive lipid mediators and the unfolded protein response in ischemic stroke

Ischemic cerebral stroke is a severe medical condition that affects about 15 million people every year and is the second leading cause of death and disability globally. Ischemic stroke results in neuronal cell death and neurological impairment. Current therapies may not adequately address the deleterious metabolic changes and may increase neurological damage. Oxygen and nutrient depletion along with the tissue damage result in endoplasmic reticulum (ER) stress, including the Unfolded Protein Response (UPR), and neuroinflammation in the affected area and cause cell death in the lesion core. The spatio-temporal production of lipid mediators, either pro-inflammatory or pro-resolving, decides the course and outcome of stroke. The modulation of the UPR as well as the resolution of inflammation promotes post-stroke cellular viability and neuroprotection. However, studies about the interplay between the UPR and bioactive lipid mediators remain elusive and this review gives insights about the crosstalk between lipid mediators and the UPR in ischemic stroke. Overall, the treatment of ischemic stroke is often inadequate due to lack of effective drugs, thus, this review will provide novel therapeutical strategies that could promote the functional recovery from ischemic stroke.

Modulation of the autophagy-lysosomal pathway and endoplasmic reticulum stress by ketone bodies in experimental models of stroke

Ischemic stroke is a leading cause of disability worldwide. There is no simple treatment to alleviate ischemic brain injury, as thrombolytic therapy is applicable within a narrow time window. During the last years, the ketogenic diet (KD) and the exogenous administration of the ketone body β-hydroxybutyrate (BHB) have been proposed as therapeutic tools for acute neurological disorders and both can reduce ischemic brain injury. However, the mechanisms involved are not completely clear. We have previously shown that the D enantiomer of BHB stimulates the autophagic flux in cultured neurons exposed to glucose deprivation (GD) and in the brain of hypoglycemic rats. Here, we have investigated the effect of the systemic administration of D-BHB, followed by its continuous infusion after middle cerebral artery occlusion (MCAO), on the autophagy-lysosomal pathway and the activation of the unfolded protein response (UPR). Results show for the first time that the protective effect of BHB against MCAO injury is enantiomer selective as only D-BHB, the physiologic enantiomer of BHB, significantly reduced brain injury. D-BHB treatment prevented the cleavage of the lysosomal membrane protein LAMP2 and stimulated the autophagic flux in the ischemic core and the penumbra. In addition, D-BHB notably reduced the activation of the PERK/eIF2α/ATF4 pathway of the UPR and inhibited IRE1α phosphorylation. L-BHB showed no significant effect relative to ischemic animals. In cortical cultures under GD, D-BHB prevented LAMP2 cleavage and decreased lysosomal number. It also abated the activation of the PERK/eIF2α/ATF4 pathway, partially sustained protein synthesis, and reduced pIRE1α. In contrast, L-BHB showed no significant effects. Results suggest that protection elicited by D-BHB treatment post-ischemia prevents lysosomal rupture allowing functional autophagy, preventing the loss of proteostasis and UPR activation.

Brain injury triggers cell-type-specific and time-dependent endoplasmic reticulum stress responses

The unfolded protein response (UPR) is a signal transduction network that responds to endoplasmic reticulum (ER) stress by coordinating protein homeostasis to maintain cell viability. The UPR can also trigger cell death when adaptive responses fail to improve protein homeostasis. Despite accumulating evidence suggesting that the UPR plays a role in neurodegenerative diseases and brain insults, our understanding of how ER stress is induced under neuropathological conditions is limited. Here, we investigated the cell- and time-specific patterns of the ER stress response after brain injury using ER stress-activated indicator (ERAI) mice, which enable monitoring of the UPR in vivo via increased fluorescence of a spliced XBP-1 protein fused with the green fluorescent protein (GFP) variant Venus. Following cortical stab injury of ERAI mice, the GFP signal and number of GFP⁺ cells increased in the ipsilateral cortex throughout the observation period (6 h to 7 days post-injury), confirming the induction of the UPR. GFP signals were observed in injured neurons early (from 6 h) after brain injury. However, non-neuronal cells, mainly endothelial cells followed by astrocytes, accounted for the majority of GFP⁺ cells after brain injury. Similar results were obtained in a mouse model of focal cerebral ischemia. These findings suggest that activation of the UPR in both neuronal and non-neuronal cells, especially endothelial cells and astrocytes, may play an important role in and could be a potential therapeutic target for acute brain injuries.

Melatonin Can Modulate Neurodegenerative Diseases by Regulating Endoplasmic Reticulum Stress

As people age, their risks of developing degenerative diseases such as cancer, diabetes, Parkinson's Disease (PD), Alzheimer's Disease (AD), rheumatoid arthritis, and osteoporosis are generally increasing. Millions of people worldwide suffer from these diseases as they age. In most countries, neurodegenerative diseases are generally recognized as the number one cause afflicting the elderly. Endoplasmic reticulum (ER) stress has been suggested to be associated with some human neurological diseases, such as PD and AD. Melatonin, a neuroendocrine hormone mainly synthesized in the pineal gland, is involved in pleiotropically biological functions, including the control of the circadian rhythm, immune enhancement, and antioxidant, anti-aging, and anti-tumor effects. Although there are many papers on the prevention or suppression of diseases by melatonin, there are very few papers about the effects of melatonin on ER stress in neurons and neurodegenerative diseases. This paper aims to summarize and present the effects of melatonin reported so far, focusing on its effects on neurons and neurodegenerative diseases related to ER stress. Studies have shown that the primary target molecule of ER stress for melatonin is CHOP, and PERK and GRP78/BiP are the secondary target molecules. Therefore, melatonin is crucial in protecting neurons and treating neurodegeneration against ER stress.

Mitochondrial unfolded protein response in ischemia-reperfusion injury

Mitochondrial unfolded protein response (UPRmt) is a mitochondrial stress response that activates the transcriptional program of mitochondrial chaperone proteins and proteases to keep protein homeostasis in mitochondria. Ischemia-reperfusion injury results in multiple severe clinical issues linked to high morbidity and mortality in various disorders. The pathophysiology and pathogenesis of ischemia-reperfusion injury are complex and multifactorial. Emerging evidence showed the roles of UPRmt signaling in ischemia-reperfusion injury. Herein, we discuss the regulatory mechanisms underlying UPRmt signaling in C. elegans and mammals. Furthermore, we review the recent studies into the roles and mechanisms of UPRmt signaling in ischemia-reperfusion injury of the heart, brain, kidney, and liver. Further research of UPRmt signaling will potentially develop novel therapeutic strategies against ischemia-reperfusion injury.

Gardenia jasminoides Extract GJ-4 Alleviates Memory Deficiency of Vascular Dementia in Rats through PERK-Mediated Endoplasmic Reticulum Stress Pathway

Endoplasmic reticulum stress (ERS) is involved in the pathological process of vascular dementia (VD). GJ-4 is extracted from Gardenia jasminoides J. Ellis and has been reported to have protective roles in ischemia-related brain damage. However, the role of GJ-4 in ERS has not been elucidated. We established a VD rat model through bilateral common carotid arteries occlusion (2-VO). The rats were intragastrically administrated with GJ-4 (10, 25, and 50[Formula: see text]mg/kg) and nimodipine (10[Formula: see text]mg/kg). Data from a Morris water maze test showed that GJ-4 could significantly alleviate learning and memory deficits in VD rats. Nissl and cleaved caspase-3 staining revealed that GJ-4 can inhibit apoptosis and thus exert a protective role in the brain of 2-VO rats. Western blot results suggested that GJ-4 significantly reduced ERS-related protein expression and inhibited apoptosis through suppression of the PERK/eIF2[Formula: see text]/ATF4/CHOP signaling pathway. For in vitro studies, the oxygen-glucose deprivation (OGD) SH-SY5Y model was employed. Western blot and Hoechst 33342/PI double staining were utilized to explore the effects of crocetin, the main active metabolite of GJ-4. Like GJ-4 in vivo, crocetin in vitro also decreased ERS-related protein expression and inhibited the activation of the PERK/eIF2[Formula: see text]/ATF4/CHOP signaling pathway. Thus, crocetin exerted similar protective roles on OGD challenged SH-SY5Y cells in vitro. In summary, GJ-4 and crocetin reduce the ERS in the brain of VD rats and SY5Y cells subjected to OGD and inhibit neuronal apoptosis through suppression of the PERK/eIF2[Formula: see text]/ATF4/CHOP pathway, suggesting that GJ-4 may be useful for the treatment of VD.

Activation of LRP1 Ameliorates Cerebral Ischemia/Reperfusion Injury and Cognitive Decline by Suppressing Neuroinflammation and Oxidative Stress through TXNIP/NLRP3 Signaling Pathway in Mice

Cerebral ischemia/reperfusion (I/R) injury is a clinical event associated with high morbidity and mortality. Neuroinflammation plays a crucial role in the pathogenesis of I/R-induced brain injury and cognitive decline. Low-density lipoprotein receptor-related protein-1 (LRP1) can exert strong neuroprotection in experimental intracerebral hemorrhage. However, whether LRP1 can confer neuroprotective effects after cerebral I/R is yet to be elucidated. The present study is aimed at investigating the effects of LRP1 activation on cerebral I/R injury and deducing the underlying mechanism involving TXNIP/NLRP3 signaling pathway. Cerebral I/R injury was induced in mice by bilateral common carotid artery occlusion. LPR1 ligand, apoE-mimic peptide COG1410, was administered intraperitoneally. To elucidate the underlying mechanism, overexpression of TXNIP was achieved via the hippocampal injection of AAV-TXNIP before COG1410 treatment. Neurobehavioral tests, brain water content, immunofluorescence, Western blot, enzyme-linked immunosorbent assay, HE, and terminal deoxynucleotidyl transferase dUTP nick end labeling staining were performed. Our results showed that the expressions of endogenous LRP1, TXNIP, NLRP3, procaspase-1, and cleaved caspase-1 were increased after cerebral I/R. COG1410 significantly ameliorated cerebral I/R-induced neurobehavioral deficits, brain edema, histopathological damage, and poor survival rate. Interestingly, COG1410 inhibited microglia proinflammatory polarization and promoted anti-inflammatory polarization, decreased oxidative stress, attenuated apoptosis, and inhibited the expression of the TXNIP/NLRP3 signaling pathway. However, the benefits of COG1410 were abolished by TXNIP overexpression. Thus, our study suggested that LRP1 activation with COG1410 attenuated cerebral I/R injury at least partially related to modulating microglial polarization through TXNIP/NLRP3 signaling pathway in mice. Thus, COG1410 treatment might serve as a promising therapeutic approach in the management of cerebral I/R patients.

Stroke-Induced Neurological Dysfunction in Aged Mice Is Attenuated by Preconditioning with Young Sca-1+ Stem Cells

AIMS

To date, stroke remains one of the leading causes of death and disability worldwide. Nearly three-quarters of all strokes occur in the elderly (>65 years old), and a vast majority of these individuals develop debilitating cognitive impairments that can later progress into dementia. Currently, there are no therapies capable of reversing the cognitive complications which arise following a stroke. Instead, current treatment options focus on preventing secondary injuries, as opposed to improving functional recovery.

METHODS

We reconstituted aged (20-month old) mice with Sca-1+ bone marrow (BM) hematopoietic stem cells isolated from aged or young (2-month old) EGFP+ donor mice. Three months later the chimeric aged mice underwent cerebral ischemia/reperfusion by bilateral common carotid artery occlusion (BCCAO), after which cognitive function was evaluated. Immunohistochemical analysis was performed to evaluate host and recipient cells in the brain following BCCAO.

RESULTS

Young Sca-1+ cells migrate to the aged brain and give rise to beneficial microglial-like cells that ameliorate stroke-induced loss of cognitive function on tasks targeting the hippocampus and cerebellum. We also found that young Sca-1+ cell-derived microglial-like cells possess neuroprotective properties as they do not undergo microgliosis upon migrating to the ischemic hippocampus, whereas the cells originating from old Sca-1+ cells proliferate extensively and skew toward a pro-inflammatory phenotype following injury.

CONCLUSIONS

This study provides a proof-of-principle demonstrating that young BM Sca-1+ cells play a pivotal role in reversing stroke-induced cognitive impairments and protect the aged brain against secondary injury by attenuating the host cell response to injury.

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

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

Targeting the Interaction of GABAB Receptors With CHOP After an Ischemic Insult Restores Receptor Expression and Inhibits Progressive Neuronal Death

GABA_B receptors control neuronal excitability via slow and prolonged inhibition in the central nervous system. One important function of GABA_B receptors under physiological condition is to prevent neurons from shifting into an overexcitation state which can lead to excitotoxic death. However, under ischemic conditions, GABA_B receptors are downregulated, fostering over-excitation and excitotoxicity. One mechanism downregulating GABA_B receptors is mediated via the interaction with the endoplasmic reticulum (ER) stress-induced transcription factor CHOP. In this study, we investigated the hypothesis that preventing the interaction of CHOP with GABA_B receptors after an ischemic insult restores normal expression of GABA_B receptors and reduces neuronal death. For this, we designed an interfering peptide (R2-Pep) that restored the CHOP-induced downregulation of cell surface GABA_B receptors in cultured cortical neurons subjected to oxygen and glucose deprivation (OGD). Administration of R2-Pep after OGD restored normal cell surface expression of GABA_B receptors as well as GABA_B receptor-mediated inhibition. As a result, R2-Pep reduced enhanced neuronal activity and inhibited progressive neuronal death in OGD stressed cultures. Thus, targeting diseases relevant protein-protein interactions might be a promising strategy for developing highly specific novel therapeutics.

Role of Forkhead Box Protein O1 (FoxO1) in Stroke: A Literature Review

Stroke is one of the most prevalent causes of death around the world. When a stroke occurs, many cellular signaling cascades and regulators are activated, which results in severe cellular dysfunction and debilitating long-term disability. One crucial regulator of cell fate and function is mammalian Forkhead box protein O1 (FoxO1). Many studies have found FoxO1 to be implicated in many cellular processes, including regulating gluconeogenesis and glycogenolysis. During a stroke, modifications of FoxO1 have been linked to a variety of functions, such as inducing cell death and inflammation, inhibiting oxidative injury, affecting the blood brain barrier (BBB), and regulating hepatic gluconeogenesis. For these functions of FoxO1, different measures and treatments were applied to FoxO1 after ischemia. However, the subtle mechanisms of post-transcriptional modification and the role of FoxO1 are still elusive and even contradictory in the development of stroke. The determination of these mechanisms will lead to further enlightenment for FoxO1 signal transduction and the identification of targeted drugs. The regulation and function of FoxO1 may provide an important way for the prevention and treatment of diseases. Overall, the functions of FoxO1 are multifactorial, and this paper will summarize all of the significant pathways in which FoxO1 plays an important role during stroke damage and recovery.

Peptidylarginine deiminase 2 promotes T helper 17-like T cell activation and activated T cell-autonomous death (ACAD) through an endoplasmic reticulum stress and autophagy coupling mechanism

Peptididylarginine deiminase type 2 (PADI2) catalyzes the conversion of arginine residues to citrulline residues on proteins. We demonstrate that PADI2 induces T cell activation and investigate how PADI2 promotes activated T cell autonomous death (ACAD). In activated Jurkat T cells, overexpression of PADI2 significantly increases citrullinated proteins and induces endoplasmic reticulum (ER) stress and unfolded protein response (UPR) signaling, ultimately resulting in the expression of autophagy-related proteins and autophagy. PADI2 promoted autophagy and resulted in the early degradation of p62 and the light chain 3B (LC3B)-II accumulation. In Jurkat T cells, silencing the autophagy-related gene (Atg) 12 protein inhibits PADI2-mediated autophagy and promotes ER stress and apoptosis, whereas overexpression of Atg12 decreased ER stress and prolonged autophagy to promote cell survival. Additionally, PADI2 regulates T cell activation and the production of Th17 cytokines in Jurkat T cells (interleukins 6, IL-17A, IL-17F, IL-21, and IL-22). In Jurkat T cells, silencing IL-6 promotes autophagy mediated by PADI2 and inhibits PADI2-induced apoptosis, whereas silencing Beclin-1 increases the activation and survival of Th17-like T cells while decreasing autophagy and apoptosis. PADI2 silencing alleviates ER stress caused by PADI2 and decreases cytokine expression associated with Th17-like T cell activation and ACAD. We propose that PADI2 was involved in Th17 lymphocyte ACAD via a mechanism involving ER stress and autophagy that was tightly regulated by PADI2-mediated citrullination. These findings suggest that inhibiting Th17 T cell activation and the development of severe autoimmune diseases may be possible through the use of novel antagonists that specifically target PADI2.

Zinc Accumulation Aggravates Cerebral Ischemia/Reperfusion Injury Through Inducing Endoplasmic Reticulum Stress

Zinc is highly enriched in the central nervous system. Numerous evidences suggest that high concentration of zinc acts as a critical mediator of neuronal death in the ischemic brain, however, the possible mechanisms of neurotoxicity of zinc during cerebral ischemia/reperfusion (I/R) remain elusive. Endoplasmic reticulum (ER) is a storage location of intracellular zinc. ER stress related genes were up-regulated during zinc-induced neuronal death in vascular-type senile dementia. In the present study, we investigated whether intracellular accumulated zinc aggravates I/R injury through ER stress and ER stress-associated apoptosis. Male Sprague-Dawley rats were subjected to 90 min middle cerebral artery occlusion (MCAO) and received either vehicle or zinc chelator TPEN 15 mg/kg. The expression of ER stress related factors glucose-regulated protein 78 (GRP78) and phosphorylated eukaryotic initiation factor 2α (p-eIF2α), ER stress related apoptotic proteins CCAAT-enhancer-binding protein homologous protein (CHOP) and caspase-12, as well as anti-apoptotic factor B-cell lymphoma-2 (Bcl-2) were assessed 24 h after reperfusion. Our results showed that the levels of GRP78 and p-eIF2α, as well as CHOP and caspase-12, were increased in ischemic brain, indicating that cerebral I/R triggers ER stress. Furthermore, GRP78, CHOP and caspase-12 were all colocalized with the zinc-specific dyes NG, suggesting that there is certain relationship between cytosolic labile zinc and ER stress following cerebral ischemia. Chelating zinc with TPEN reversed the expression of GRP78, p-eIF2α in ischemic rats. Moreover, CHOP and NeuN double staining positive cells, as well as caspase-12 and TUNEL double staining positive cells were also decreased after TPEN treatment, indicating that chelating zinc might inhibit ER stress and decreased ER stress associated neuronal apoptosis. In addition, TPEN treatment reversed the downregulated level of Bcl-2, which localized in the ER membrane and involved in the dysfunction of ER, confirming that the anti-apoptosis effects of chelating zinc following I/R are exerted via inhibition of the ER stress. Taken together, this study demonstrated that excessive zinc activates ER stress and zinc induced neuronal cell death is at least partially due to ER stress specific neuronal apoptosis in ischemic penumbra, which may provide an important mechanism of cerebral I/R injury.

Irisin Protects Cerebral Neurons from Hypoxia/Reoxygenation via Suppression of Apoptosis and Expression of Pro-Inflammatory Cytokines

BACKGROUND

Ischemic stroke is a major health issue that causes high incidents of morbidity and mortality worldwide. Irisin is an excise-induced protein that has exhibited pleiotropic properties. Accumulating evidence reveals its critical roles in the regulation of various cellular functions, including nervous system functions. This study aims to disclose the effect of irisin on rat cerebral neurons suffering from hypoxia/reoxygenation (H/R) treatment and to explore the potential underlying molecular mechanisms.

METHODS

The percentage of rat cerebral neuron cell death was determined by flow cytometry analysis and MTT assay. The expression levels of target genes were measured by western blotting and real-time quantitative reverse transcription PCR assay.

RESULTS

Our results demonstrated that irisin treatment substantially reduced H/R-induced apoptosis of rat cerebral neurons. Further investigation revealed that irisin treatment markedly decreased mitogen-activated protein kinase (MAPK) signaling pathway activation and suppressed pro-informatory cytokine expression in cerebral neurons with H/R challenge. Finally, we showed that the neuroprotective effect and anti-inflammatory effect of irisin were comparable with three MAPK signaling inhibitors.

CONCLUSION

Irisin exerts profound neuroprotective and anti-inflammatory effects on H/R-stimulated cerebral neurons by inhibiting the MAPK signaling activation. Therefore, irisin may serve as a potential drug for the treatment of patients with ischemic stroke.

Ischemic brain injury in diabetes and endoplasmic reticulum stress

Diabetes is a widespread disease characterized by high blood glucose levels due to abnormal insulin activity, production, or both. Chronic diabetes causes many secondary complications including cardiovascular disease: a life-threatening complication. Cerebral ischemia-related mortality, morbidity, and the extent of brain injury are high in diabetes. However, the mechanism of increase in ischemic brain injury during diabetes is not well understood. Multiple mechanisms mediate diabetic hyperglycemia and hypoglycemia-induced increase in ischemic brain injury. Endoplasmic reticulum (ER) stress mediates both brain injury as well as brain protection after ischemia-reperfusion injury. The pathways of ER stress are modulated during diabetes. Free radical generation and mitochondrial dysfunction, two of the prominent mechanisms that mediate diabetic increase in ischemic brain injury, are known to stimulate the pathways of ER stress. Increased ischemic brain injury in diabetes is accompanied by a further increase in the activation of ER stress. As there are many metabolic changes associated with diabetes, differential activation of the pathways of ER stress may mediate pronounced ischemic brain injury in subjects suffering from diabetes. We presently discuss the literature on the significance of ER stress in mediating increased ischemia-reperfusion injury in diabetes.

Neurotherapeutic implications of sense and respond strategies generated by astrocytes and astrocytic tumours to combat pH mechanical stress

Aims

Astrocytes adapt to acute acid stress. Intriguingly, cancer cells with astrocytic differentiation thrive even better in an acidic microenvironment. How changes in extracellular pH (pHe) are sensed and measured by the cell surface assemblies that first intercept the acid stress, and how this information is relayed downstream for an appropriate survival response remains largely uncharacterized.

Methods

In vitro cell‐based studies were combined with an in vivo animal model to delineate the machinery involved in pH microenvironment sensing and generation of mechanoadaptive responses in normal and neoplastic astrocytes. The data was further validated on patient samples from acidosis driven ischaemia and astrocytic tumour tissues.

Results

We demonstrate that low pHe is perceived and interpreted by cells as mechanical stress. GM3 acts as a lipid‐based pH sensor, and in low pHe, its highly protonated state generates plasma membrane deformation stress which activates the IRE1‐sXBP1‐SREBP2‐ACSS2 response axis for cholesterol biosynthesis and surface trafficking. Enhanced surface cholesterol provides mechanical tenacity and prevents acid‐mediated membrane hydrolysis, which would otherwise result in cell leakage and death.

Conclusions

In summary, activating these lipids or the associated downstream machinery in acidosis‐related neurodegeneration may prevent disease progression, while specifically suppressing this key mechanical ‘sense‐respond’ axis should effectively target astrocytic tumour growth.

Isoginkgetin attenuates endoplasmic reticulum stress-induced autophagy of brain after ischemic reperfusion injury

Isoginkgetin is characterized by properties of potent anticancer and anti-inflammation. To explore its effect on ischemic stroke, a rat model of ischemia/reperfusion (I/R) injury was established and induced by transient middle cerebral artery occlusion/reperfusion (MCAO/R). Different doses of isoginkgetin were intraperitoneally injected into each rat. Expressions of ER stress activation-related makers including phosphorylated inositol-requiring enzyme 1 (IRE1), phosphorylated protein kinase RNA-like endoplasmic reticulum kinase (p-PERK), activating transcription factor-6 (ATF6), and two autophagy markers (ratio of LC3II/I and Beclin-1) were detected by western blot. Infarct volume, neurological deficits, and brain water content were detected. The results showed that ER stress and autophagy were activated by cerebral (I/R) injury, which could be effectively attenuated following pre-ischemia isoginkgetin administration. Moreover, autophagy induced by ER stress was triggered by the activation of PERK and IRE1 pathways. ER stress inhibitor (4-PBA) and ER related signaling inhibitors including PERK, GSK, IRE1, and DBSA markedly inhibited ER stress and autophagy induced by I/R. In addition, isoginkgetin markedly mitigated cerebral infarction, edema, neuronal apoptosis as well as neurological impairment induced by I/R injury, while tunicamycin (ER stress activator TM) and rapamycin (autophagy activator RAPA) could eliminate these lesions. This research identified a novel therapeutic agent isoginkgetin, which could effectively attenuate I/R injury by blocking autophagy induced by ER stress.

LncRNA KCNQ1OT1 Regulates Endoplasmic Reticulum Stress to Affect Cerebral Ischemia-Reperfusion Injury Through Targeting miR-30b/GRP78

Endoplasmic reticulum stress (ERS) plays an important role in cerebral ischemia-reperfusion injury (CIRI) by regulating apoptosis. Although the role of long non-coding RNA (LncRNA) KCNQ1OT1 in CIRI has been reported, the specific mechanism is still unclear. In this paper, the regulation of ERS by LncRNA KCNQ1OT1 in CIRI and its mechanism were studied. Transient middle cerebral artery occlusion (tMCAO) model was established in SD rats with KCNQ1OT1 intervention. PC12 cells were used to construct the OGD/R cell model. The expressions of LncRNA KCNQ1OT1 and miR-30b were detected by RT-qPCR. TCC staining was used to detect the extent of cerebral ischemia. TUNEL staining was used to detect apoptosis level, and Western blot was used to detect the expressions of ERS and apoptosis-related proteins. The targeted binding of LncRNA KCNQ1OT1, miR-30b, and GRP78 was detected by double luciferase assay. The expressions of LncRNA KCNQ1OT1 and miR-30b were interfered by cell transfection. Cell proliferation was detected by CCK-8. The level of LncRNA KCNQ1OT1 was increased and that of miR-30b was decreased in the blood samples of patients with CIRI. In tMCAO rats with KCNQ1OT1 intervention, the expression of miR-30b was increased, and the ischemic range of brain tissues was decreased. What's more, the level of ERS was decreased, and the apoptosis of brain tissues was decreased. LncRNA KCNQ1OT1 could regulate miR-30b/GRP78 in OGD/R cells in a targeted way. Intervention of KCNQ1OT1 could promote the proliferation of OGD/R cells, inhibiting the level of ERS and cell apoptosis. Further inhibition of miR-30b could reverse the effect of intervention of KCNQ1OT1. LncRNA KCNQ1OT1 regulates ERS to affect CIRI through targeting miR-30b/GRP78.

Mechanism of Endoplasmic Reticulum Stress in Cerebral Ischemia

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

Inhibition of endoplasmic reticulum stress reverses synaptic plasticity deficits in striatum of DYT1 dystonia mice

Background and objective: Striatal plasticity alterations caused by endoplasmic reticulum (ER) stress is supposed to be critically involved in the mechanism of DYT1 dystonia. In the current study, we expanded this research field by investigating the critical role of ER stress underlying synaptic plasticity impairment imposed by mutant heterozygous Tor1a^+/- in a DYT1 dystonia mouse model.

Methods: Heterozygous Tor1a^+/- mouse model for DYT1 dystonia was established. Wild-type (Tor1a^+/+, N=10) and mutant (Tor1a^+/-, N=10) mice from post-natal day P25 to P35 were randomly distributed to experimental and control groups. Patch-clamp and current-clamp recordings of SPNs were conducted with intracellular electrodes for electrophysiological analyses. Striatal changes of the direct and indirect pathways were investigated via immunofluorescence. Golgi-Cox staining was conducted to observe spine morphology of SPNs. To quantify postsynaptic signaling proteins in striatum, RNA-Seq, qRT-PCR and WB were performed in striatal tissues.

Results: Long-term depression (LTD) was failed to be induced, while long-term potentiation (LTP) was further strengthened in striatal spiny projection neurons (SPNs) from the Tor1a^+/- DYT1 dystonia mice. Spine morphology analyses revealed a significant increase of both number of mushroom type spines and spine width in Tor1a^+/- SPNs. In addition, increased AMPA receptor function and the reduction of NMDA/AMPA ratio in the postsynaptic of Tor1a^+/- SPNs was observed, along with increased ER stress protein levels in striatum of Tor1a^+/- DYT1 dystonia mice. Notably, ER stress inhibitors, tauroursodeoxycholic acid (TUDCA), could rescue LTD as well as AMPA currents.

Conclusion: The current study illustrated the role of ER stress in mediating structural and functional plasticity alterations in Tor1a^+/- SPNs. Inhibition of the ER stress by TUDCA is beneficial in reversing the deficits at the cellular and molecular levels. Remedy of dystonia associated neurological and motor functional impairment by ER stress inhibitors could be a recommendable therapeutic agent in clinical practice.

Voltage-dependent potassium channel Kv4.2 alleviates the ischemic stroke impairments through activating neurogenesis

As well as their ion transportation function, the voltage-dependent potassium channels could act as the cell signal inducer in a variety of pathogenic processes. However, their roles in neurogenesis after stroke insults have not been clearly illustrated. In our preliminary study, the expressions of voltage-dependent potassium channels Kv4.2 was significantly decreased after stroke in cortex, striatum and hippocampus by real-time quantitative PCR assay. To underlie the neuroprotection of Kv4.2 in stroke rehabilitation, recombinant plasmids encoding the cDNAs of mouse Kv4.2 was constructed. Behavioral tests showed that the increased Kv4.2 could be beneficial to the recovery of the sensory, the motor functions and the cognitive deficits after stroke. Temozolomide (TMZ), an inhibitor of neurogenesis, could partially abolish the mentioned protections of Kv4.2. The immunocytochemical staining showed that Kv4.2 could promote the proliferations of neural stem cells and induce the neural stem cells to differentiate into neurons in vitro and in vivo. And Kv4.2 could up-regulate the expressions of ERK1/2, p-ERK1/2, p-STAT3, NGF, p-TrkA, and BDNF, CAMKII and the concentration of intracellular Ca²⁺. Namely, we concluded that Kv4.2 promoted neurogenesis through ERK1/2/STAT3, NGF/TrkA, Ca²⁺/CAMKII signal pathways and rescued the ischemic impairments. Kv4.2 might be a potential drug target for ischemic stroke intervention.

Interleukin-15 modulates the response of cortical neurons to ischemia

OBJECTIVE

Stroke is a major cause of death and disability in the United States. Current acute stroke therapy consists of clot-dissolving drugs, catheter-based interventions and physical rehabilitation. To date, there are no therapies that directly enhance neuronal survival after a stroke. Previous work from our lab demonstrated that Interleukin-15 (IL-15) peptide could rescue cardiomyocytes subjected to hypoxia. We sought to extend these findings to cortical neurons since IL-15 has been implicated to have an important role in neuronal homeostasis.

METHODS

We have evaluated the effect of IL-15 peptide on primary cortical neurons derived from embryonic rats in vitro under conditions of anoxia and glucose deprivation, and in vivo following middle cerebral artery occlusion.

RESULTS

IL-15 administration rescued neuronal cells subjected to anoxia coupled with glucose deprivation (AGD), as well as with reoxygenation. A hallmark of stroke is the ischemic microenvironment and associated oxidative stress, which results in DNA damage and ER stress, both of which contribute to neuronal cell damage and death. The expression of anoxia, ER stress, and DNA damage factors/markers was evaluated via western blot and correlated with the cellular survival effects of IL-15 in vitro. In addition, IL-15 effect of alleviating ER stress and increasing cell survival was also observed in vivo.

INTERPRETATION

Our data indicate, for the first time, that administration of the pleiotropic factor IL-15 reduces neuronal cell death during AGD, which correlates with modulation of multiple cellular stress pathways.

Roles and Therapeutic Implications of Endoplasmic Reticulum Stress and Oxidative Stress in Cardiovascular Diseases

In different pathological states that cause endoplasmic reticulum (ER) calcium depletion, altered glycosylation, nutrient deprivation, oxidative stress, DNA damage or energy perturbation/fluctuations, the protein folding process is disrupted and the ER becomes stressed. Studies in the past decade have demonstrated that ER stress is closely associated with pathogenesis of obesity, insulin resistance and type 2 diabetes. Excess nutrients and inflammatory cytokines associated with metabolic diseases can trigger or worsen ER stress. ER stress plays a critical role in the induction of endothelial dysfunction and atherosclerosis. Signaling pathways including AMP-activated protein kinase and peroxisome proliferator-activated receptor have been identified to regulate ER stress, whilst ER stress contributes to the imbalanced production between nitric oxide (NO) and reactive oxygen species (ROS) causing oxidative stress. Several drugs or herbs have been proved to protect against cardiovascular diseases (CVD) through inhibition of ER stress and oxidative stress. The present article reviews the involvement of ER stress and oxidative stress in cardiovascular dysfunction and the potential therapeutic implications.

Adaptation to mitochondrial stress requires CHOP-directed tuning of ISR

In response to disturbed mitochondrial gene expression and protein synthesis, an adaptive transcriptional response sharing a signature of the integrated stress response (ISR) is activated. We report an intricate interplay between three transcription factors regulating the mitochondrial stress response: CHOP, C/EBPβ, and ATF4. We show that CHOP acts as a rheostat that attenuates prolonged ISR, prevents unfavorable metabolic alterations, and postpones the onset of mitochondrial cardiomyopathy. Upon mitochondrial dysfunction, CHOP interaction with C/EBPβ is needed to adjust ATF4 levels, thus preventing overactivation of the ATF4-regulated transcriptional program. Failure of this interaction switches ISR from an acute to a chronic state, leading to early respiratory chain deficiency, energy crisis, and premature death. Therefore, contrary to its previously proposed role as a transcriptional activator of mitochondrial unfolded protein response, our results highlight a role of CHOP in the fine-tuning of mitochondrial ISR in mammals.

Downregulation of XBP1 protects kidney against ischemia-reperfusion injury via suppressing HRD1-mediated NRF2 ubiquitylation

Ischemia-reperfusion (IR) injury to the renal epithelia is associated with endoplasmic reticulum stress (ERS) and mitochondria dysfunction, which lead to oxidative stress-induced acute kidney injury (AKI). X-box binding protein 1 (XBP1), an ERS response protein, could play a prominent role in IR-induced AKI. In this study, we revealed that XBP1 and its downstream target HRD1 participated in the crosstalk between ERS and mitochondrial dysfunction via regulation of NRF2/HO-1-mediated reactive oxidative stress (ROS) signaling. Mice with reduced expression of XBP1 (heterozygous Xbp1±) were resistant to IR-induced AKI due to the enhanced expression of NRF2/HO-1 and diminished ROS in the kidney. Downregulation of XBP1 in renal epithelial cells resulted in reduced HRD1 expression and increased NRF2/HO-1 function, accompanied with enhanced antioxidant response. Furthermore, HRD1 served as an E3-ligase to facilitate the downregulation of NRF2 through ubiquitination-degradation pathway, and the QSLVPDI motif on NRF2 constituted an active site for its interaction with HRD1. Thus, our findings unveil an important physiological role for XBP1/HRD1 in modulating the antioxidant function of NRF2/HO-1 in the kidney under stress conditions. Molecular therapeutic approaches that target XBP1-HRD1-NRF2 pathway may represent potential effective means to treat renal IR injury.

The aftermath of the interplay between the endoplasmic reticulum stress response and redox signaling

The endoplasmic reticulum (ER) is an essential organelle of eukaryotic cells. Its main functions include protein synthesis, proper protein folding, protein modification, and the transportation of synthesized proteins. Any perturbations in ER function, such as increased demand for protein folding or the accumulation of unfolded or misfolded proteins in the ER lumen, lead to a stress response called the unfolded protein response (UPR). The primary aim of the UPR is to restore cellular homeostasis; however, it triggers apoptotic signaling during prolonged stress. The core mechanisms of the ER stress response, the failure to respond to cellular stress, and the final fate of the cell are not yet clear. Here, we discuss cellular fate during ER stress, cross talk between the ER and mitochondria and its significance, and conditions that can trigger ER stress response failure. We also describe how the redox environment affects the ER stress response, and vice versa, and the aftermath of the ER stress response, integrating a discussion on redox imbalance-induced ER stress response failure progressing to cell death and dynamic pathophysiological changes.

The endoplasmic reticulum (ER), a cellular organelle responsible for protein folding, is sensitive to chemical imbalances that can induce stress, leading to cell death and disease. Researchers in South Korea, led by Han-Jung Chae from Jeonbuk National University in Jeonju and Hyung-Ryong Kim from Dankook University in Cheonan, review how the ER counters changes in its environment that spur protein folding defects by activating a series of signaling pathways, known collectively as the unfolded protein response. Redox imbalance, may fail adaptive ER stress response that can damage the ER and surrounding mitochondria by modifying cysteine residues. The interaction between the two stress systems, ER stress and oxidative stress, has profound negative impacts on normal physiology. Targeting one or both of these stress mechanisms may therefore be an effective means of treating disease.

Dienogest regulates apoptosis, proliferation, and invasiveness of endometriotic cyst stromal cells via endoplasmic reticulum stress induction

Dienogest, a specific progesterone receptor agonist, is used in the treatment of endometriosis. However, it is still unclear as to the mechanisms of therapeutic effects on endometriosis. Our recent study showed that endometriosis may be the result of aberrant endoplasmic reticulum (ER) stress induction due to progesterone resistance. This finding suggests that the regulation of ER stress induction may play a key role in treatment of endometriosis. Therefore, the anti-endometriotic effects of dienogest may be mediated by regulation of ER stress. To test this hypothesis, we elucidate whether dienogest affects endometriotic stromal cell apoptosis, proliferation and invasiveness by modulating ER stress-induced CCAAT/enhancer-binding protein homologous protein (CHOP) expression. Specifically, PRKR-like ER kinase (PERK)/eukaryotic initiation factor 2α (eIF2α)/activating transcription factor 4 (ATF4), inositol-requiring kinase 1 (IRE1)/TNF receptor-associated factor 2 (TRAF2)/apoptosis signal-regulating kinase 1 (ASK1)/c-Jun N-terminal kinase (JNK) signaling, and downstream CHOP were evaluated to determine the involved ER stress-mediated regulation mechanism of CHOP expression. Our results show that progesterone treatment did not have any significant effects on ER stress, apoptosis, proliferation, and invasion in estrogen-treated endometriotic cyst stromal cells (ECSCs). However, dienogest treatment upregulated the induction of ER stress. It also led to increased apoptosis, and decreased proliferation and invasiveness. These dienogest-induced changes in apoptosis, proliferation and invasiveness were reversed by the ER stress inhibitor salubrinal. Furthermore, dienogest-induced ER stress increased CHOP expression through activation of both PERK/elf2α/ATF4 and IRE1/TRAF2/ASK1/JNK signaling. This upregulation was blocked by transfection with PERK and IRE1 siRNA, which decreased apoptosis and increased the proliferation and invasiveness of dienogest-treated ECSCs. Taken together, our findings indicate that dienogest enhances ER stress induction in endometriotic stromal cells, which affects apoptosis, proliferation and invasiveness via CHOP upregulation.

Targeting the integrated stress response in ophthalmology

Purpose: To summarize the Integrated Stress Response (ISR) in the context of ophthalmology, with special interest on the cornea and anterior segment. Results: The ISR is a powerful and conserved signaling pathway that allows for cells to respond to a diverse array of both intracellular and extracellular stressors. The pathway is classically responsible for coordination of the cellular response to amino acid starvation, ultraviolet light, heme dysregulation, viral infection, and unfolded protein. Under normal circumstances, it is considered pro-survival and a necessary mechanism through which protein translation is controlled. However, in cases of severe or prolonged stress the pathway can promote apoptosis, and loss of normal cellular phenotype. The activation of this pathway culminates in the global inhibition of cap-dependent protein translation and the canonical expression of the activating transcription factor 4 (ATF4). Conclusion:The eye is uniquely exposed to ISR responsive stressors due to its environmental exposure and relative isolation from the circulatory system which are necessary for its function. We will discuss how this pathway is critical for the proper function of the tissue, its role in development, as well as how targeting of the pathway could alleviate key aspects of diverse ophthalmic diseases.

GABAB receptor antagonist promotes hippocampal neurogenesis and facilitates cognitive function recovery following acute cerebral ischemia in mice

PURPOSE AND BACKGROUND

Previous studies have suggested that promoting endogenous neurogenesis has great significance for the recovery of cognitive dysfunction caused by cerebral ischemia (CI). Pharmacological inhibition of GABA_B receptor can enhance neurogenesis in adult healthy and depressed mice. In the study, we intended to investigate the effects of GABA_B receptor antagonists on cognitive function and hippocampal neurogenesis in mice following CI.

METHODS

Adult mice were subjected to bilateral common carotid artery occlusion (BCCAO) for 20 min to induce CI and treated with CGP52432 (antagonist of GABA_B receptor, CGP, 10 mg/kg intraperitoneal injection) starting 24 h after CI. The Morris water maze test was performed to test spatial learning and memory at day 28. Immunofluorescence was applied to detect neurogenesis in the DG region at day 14 and 28. In in vitro experiments, cell proliferation was detected by CCK8 and immunofluorescence, and the expression of cAMP/CREB signaling pathway-related proteins was detected by ELISA assay and Western blot.

RESULTS

CGP significantly improved spatial learning and memory disorders caused by CI, and it enhanced the proliferation of neural stem cells (NSCs), the number of immature neurons, and the differentiation from newborn cells to neurons. In vitro experiments further confirmed that CGP dose-dependently enhanced the cell viability of NSCs, and immunofluorescence staining showed that CGP promoted the proliferation of NSCs. In addition, treatment with CGP increased the expression of cAMP, PKA, and pCREB in cultured NSCs.

CONCLUSION

Inhibition of GABA_B receptor can effectively promote hippocampal neurogenesis and improve spatial learning and memory in adult mice following CI.

Triiodothyronine Aggravates Global Cerebral Ischemia-Reperfusion Injury in Mice

Thyroid hormones (THs) have been suggested to play an important role in both physiological and pathological events in the central nervous system. Hypothyroidism, which is characterized by low levels of serum THs, has been associated with aggravation of ischemic neuronal injuries in stroke patients. We hypothesized that administration of T3, the main active form of THs, may attenuate the ischemic neuronal injuries. In mice, global cerebral ischemia (GCI), which is induced by transient occlusion of the bilateral common carotid artery, causes neuronal injuries by inducing neuronal death and activating inflammatory responses after reperfusion in the hippocampus. In this study, we examined the effect of T3 administration on DNA fragmentation induced by neuronal death and the activation of inflammatory cells such as astrocytes and microglia in the hippocampus following GCI. The content of nucleosomes generated by DNA fragmentation in the hippocampus was increased by GCI and further increased by T3 administration. The protein expression levels of glial fibrillary acidic protein (GFAP), an astrocytic marker, and Ionized calcium binding adaptor protein 1 (Iba1), a microglial marker, in the hippocampus were also increased by GCI and further increased by T3 administration. The levels of T3 in both the serum and hippocampus were elevated by T3 administration. Our results indicate that T3 administration aggravates GCI-reperfusion injury in mice. There may be an increased risk of aggravation of ischemic stroke by the excessive elevation of T3 levels during the drug treatment of hypothyroidism.

Biochanin A Alleviates Cerebral Ischemia/Reperfusion Injury by Suppressing Endoplasmic Reticulum Stress-Induced Apoptosis and p38MAPK Signaling Pathway In Vivo and In Vitro

We have previously shown that biochanin A exhibits neuroprotective properties in the context of cerebral ischemia/reperfusion (I/R) injury. The mechanistic basis for such properties, however, remains poorly understood. This study was therefore designed to explore the manner whereby biochanin A controls endoplasmic reticulum (ER) stress, apoptosis, and inflammation within fetal rat primary cortical neurons in response to oxygen-glucose deprivation/reoxygenation (OGD/R) injury, and in a rat model of middle cerebral artery occlusion and reperfusion (MCAO/R) injury. For the OGD/R in vitro model system, cells were evaluated after a 2 h OGD following a 24 h reoxygenation period, whereas in vivo neurological deficits were evaluated following 2 h of ischemia and 24 h of reperfusion. The expression of proteins associated with apoptosis, ER stress (ERS), and p38 MAPK phosphorylation was evaluated in these samples. Rats treated with biochanin A exhibited reduced neurological deficits relative to control rats following MCAO/R injury. Additionally, GRP78 and CHOP levels rose following I/R modeling both in vitro and in vivo, whereas biochanin A treatment was associated with reductions in CHOP levels but further increases in GRP78 levels. In addition, OGD/R or MCAO/R were associated with markedly enhanced p38 MAPK phosphorylation that was alleviated by biochanin A treatment. Similarly, OGD/R or MCAO/R injury resulted in increases in caspase-3, caspase-12, and Bax levels as well as decreases in Bcl-2 levels, whereas biochanin A treatment was sufficient to reverse these phenotypes. Together, these findings thus demonstrate that biochanin A can alleviate cerebral I/R-induced damage at least in part via suppressing apoptosis, ER stress, and p38 MAPK signaling, thereby serving as a potent neuroprotective agent.

Hydrogen-rich saline protects intestinal epithelial tight junction barrier in rats with intestinal ischemia-reperfusion injury by inhibiting endoplasmic reticulum stress-induced apoptosis pathway

AIM

To investigate the effects of hydrogen-rich saline (HRS) on intestinal epithelial tight junction (TJ) barrier in rats with intestinal ischemia-reperfusion injury (IIRI).

MATERIALS AND METHODS

Thirty-two healthy male Sprague-Dawley (SD) rats were randomly divided into four groups (n = 8 each): Sham group, I/R group, HRS group and 4-PBA group. After 45 min of ischemia and 6 h of reperfusion, the rats were sacrificed to collect serum and ileum for detection. Hematoxylin and eosin (H&E) staining was used to observe the morphology of small intestine. The serum expression levels of intestinal fatty acid binding protein (IFABP), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) were determined by enzyme linked immunosorbent assay (ELISA). Imunohistochemistry, immunofluorescence and Western blot were used to detect key proteins in intestinal epithelial TJs, ERS, and ERS-induced apoptosis, including occludin, zonula occludens-1 (ZO-1), glucose-regulated protein 78 (GRP78), X-box binding protein-1 (XBP1), C/EBP-homologous protein (CHOP) and caspase-3. Data was presented as mean ± SEM and compared using one-way ANOVA. A p-value <0.05 was considered significant.

RESULTS

Compared with rats in the I/R group, the Chiu score of ileum damage in the HRS group and 4-PBA group were lower. The levels of serum IFABP, TNF-α, and IL-1β were statistically significant among the groups. Increased expression of TJ proteins occludin and ZO-1 by reducing various parameters of ERS and ERS-induced apoptosis evidenced by down-regulation of the protein levels of GRP78, XBP1, CHOP and caspase-3 were shown in the HRS and 4-PBA groups.

CONCLUSION

HRS had potential protective effects on intestinal barrier in IIRI rats. This study suggested that inhibition of excessive ERS and ERS-induced apoptosis by HRS may reduce intestinal epithelial cells damage and maintain the integrity of intestinal epithelial TJ barrier in rats with IIRI.

Granulocyte-colony stimulating factor gene therapy as a novel therapeutics for stroke in a mouse model

Background

Global ischemia is the resulting effect of a cardiopulmonary arrest (CPA). Presently there is no effective treatment to address neurological deficits in patients who survived a CPA. Granulocyte-colony stimulating factor is a growth factor (G-CSF) with a plethora of beneficial effects, including neuroprotection. Clinical application of human G-CSF (hG-CSF) is limited due to its plasma half-life of 4 h. Therefore, novel approaches need to be investigated that would (1) enable prolonged manifestation of hG-CSF and (2) demonstrate G-CSF efficacy from studying the underlying protective mechanisms of hG-CSF. In our previous work, we used the self-complementary adeno-associated virus (stereotype2: scAAV2) as a vector to transfect the hG-CSF gene into the global ischemic brain of a mouse. As an extension of that work, we now seek to elucidate the protective mechanisms of hG-CSF gene therapy against endoplasmic reticulum induced stress, mitochondrial dynamics and autophagy in global ischemia.

Method

A single drop of either AAV-CMV-hG-CSF or AAV-CMV-GFP was dropped into the conjunctival sac of the Swiss Webster mouse’s left eye, 30–60 min after bilateral common artery occlusion (BCAO). The efficacy of the expressed hG-CSF gene product was analyzed by monitoring the expression levels of endoplasmic reticulum stress (ER), mitochondrial dynamics and autophagic proteins over 4- and 7-days post-BCAO in vulnerable brain regions including the striatum, overlying cortex (frontal brain regions) and the hippocampus (middle brain regions). Statistical analysis was performed using mostly One-Way Analysis of variance (ANOVA), except for behavioral analysis, which used Repeated Measures Two-Way ANOVA, post hoc analysis was performed using the Tukey test.

Results

Several biomarkers that facilitated cellular death, including CHOP and GRP78 (ER stress) DRP1 (mitochondrial dynamics) and Beclin 1, p62 and LC3-ll (autophagy) were significantly downregulated by hG-CSF gene transfer. hG-CSF gene therapy also significantly upregulated antiapoptotic Bcl2 while downregulating pro-apoptotic Bax. The beneficial effects of hG-CSF gene therapy resulted in an overall improvement in functional behavior.

Conclusion

Taken together, this study has substantiated the approach of sustaining the protein expression of hG-CSF by eye drop administration of the hG-CSF gene. In addition, the study has validated the efficacy of using hG-CSF gene therapy against endoplasmic reticulum induced stress, mitochondrial dynamics and autophagy in global ischemia.

Review Cerebral Ischemic Tolerance and Preconditioning: Methods, Mechanisms, Clinical Applications, and Challenges

Stroke is one of the leading causes of morbidity and mortality worldwide, and it is increasing in prevalence. The limited therapeutic window and potential severe side effects prevent the widespread clinical application of the venous injection of thrombolytic tissue plasminogen activator and thrombectomy, which are regarded as the only approved treatments for acute ischemic stroke. Triggered by various types of mild stressors or stimuli, ischemic preconditioning (IPreC) induces adaptive endogenous tolerance to ischemia/reperfusion (I/R) injury by activating a multitude cascade of biomolecules, for example, proteins, enzymes, receptors, transcription factors, and others, which eventually lead to transcriptional regulation and epigenetic and genomic reprogramming. During the past 30 years, IPreC has been widely studied to confirm its neuroprotection against subsequent I/R injury, mainly including local ischemic preconditioning (LIPreC), remote ischemic preconditioning (RIPreC), and cross preconditioning. Although LIPreC has a strong neuroprotective effect, the clinical application of IPreC for subsequent cerebral ischemia is difficult. There are two main reasons for the above result: Cerebral ischemia is unpredictable, and LIPreC is also capable of inducing unexpected injury with only minor differences to durations or intensity. RIPreC and pharmacological preconditioning, an easy-to-use and non-invasive therapy, can be performed in a variety of clinical settings and appear to be more suitable for the clinical management of ischemic stroke. Hoping to advance our understanding of IPreC, this review mainly focuses on recent advances in IPreC in stroke management, its challenges, and the potential study directions.

Activating Transcription Factor 6 Contributes to Functional Recovery After Spinal Cord Injury in Adult Zebrafish

Spinal cord injury (SCI) is one of the most common devastating injuries, with little possibility of recovery in humans. However, zebrafish efficiently regenerate functional nervous system tissue after SCI. Therefore, the spinal cord transection model of adult zebrafish was applied to explore the role of ATF6 in neuro-recovery. Activating transcription factor 6 (ATF6) is a type-II transmembrane protein in the endoplasmic reticulum (ER). ATF6 target genes could improve ER homeostasis, which contributes to cytoprotection. Herein, we found that the ATF6 level increased at 12 h and 3 days post SCI, and returned to sham levels at 7 days post SCI. ATF6-expressing motor neurons were present in the central canal of the spinal cord and increased at 12 h post SCI. ATF6 morpholino treatment showed that inhibition of ATF6 delayed locomotor recovery and hindered neuron axon regrowth in SCI zebrafish. Furthermore, we investigated the role of both binding immunoglobulin protein (Bip) and C/EBP homologous transcription factor protein (CHOP), the two target genes of ATF6. We found that Bip expression significantly increased in the spinal cord at 7 days after SCI, which served as a pro-survival chaperone. Our results also showed that CHOP expression significantly decreased in the spinal cord at 7 days after SCI, which was identified as a protein involved in apoptosis. Taken together, our data demonstrate that ATF6 may contribute to the functional recovery after SCI in adult zebrafish, via up-regulation of Bip and down-regulation of CHOP to restore the homeostasis of ER.

Characterization of Retinal Microvascular Complications and the Effects of Endoplasmic Reticulum Stress in Mouse Models of Diabetic Atherosclerosis

Purpose

Recent evidence suggests that there is a correlation between the micro- and macrovascular complications of diabetes mellitus. The aim of this study is to investigate the molecular mechanisms by which diabetes promotes the development of microvascular disease (diabetic retinopathy [DR]) through characterization of the effects of hyperglycemia in the retina of mouse models of diabetic atherosclerosis.

Methods

Hyperglycemia was induced in apolipoprotein E-deficient (ApoE-/-) mice, a model of accelerated atherosclerosis, either through streptozotocin (STZ) injection or introduction of the Ins2Akita mutation (ApoE-/-Ins2+/Akita). Another subset of ApoE-/- mice was supplemented with glucosamine (GlcN). To attenuate atherosclerosis, subsets of mice from each experimental group were treated with the chemical chaperone, 4-phenylbutyric acid (4PBA). Eyes from 15-week-old mice were either trypsin digested and stained with periodic acid-Schiff (PAS) or frozen for cryostat sectioning and immunostained for endoplasmic reticulum (ER) stress markers, including C/EBP homologous protein (CHOP) and 78-kDa glucose-regulated protein (GRP78). PAS-stained retinal flatmounts were analyzed for microvessel density, acellular capillaries, and pericyte ghosts.

Results

Features of DR, including pericyte ghosts and reduced microvessel density, were observed in hyperglycemic and GlcN-supplemented mice. Treatment with 4PBA reduced ER stress in the retinal periphery and attenuated DR in the experimental groups.

Conclusions

Mouse models of diabetic atherosclerosis show characteristic pathologies of DR that correlate with atherosclerosis. The increased magnitude of these changes and responses to 4PBA in the peripheral retina suggest that future studies should be aimed at assessing regional differences in mechanisms of ER stress-related pathways in these mouse models.

Pathological Aspects of COVID-19 as a Conformational Disease and the Use of Pharmacological Chaperones as a Potential Therapeutic Strategy

Coronavirus disease 2019 (COVID-19), the seventh human coronavirus infectious disease, was first reported in Wuhan, China, in December 2019, followed by its rapid spread globally (251,059 deaths, on May 5, 2020, by Johns Hopkins University). An early clinical report showed that fever, cough, fatigue, sputum production, and myalgia were initial symptoms, with the development of pneumonia as the disease progressed. Increases in the level of serum liver enzymes, D-dimer, cardiac troponin I, and creatinine have been observed in severely ill patients, indicating that multiple organ failure had occurred in these cases. Lymphopenia and an increase in interleukin-6 (IL-6) were also observed. Although COVID-19 patients are administered glucocorticoid therapy to treat the excessive immune response to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection, the efficacy of this form of therapy is unclear. Viremia is observed in severe cases, suggesting that in addition to type II alveolar epithelial cells, many cell types, such as vascular endothelial cells, cardiomyocytes, renal tubular cells, neuronal cells, and lymphocytes, may be damaged. The improvement of survival rates requires elucidation of the mechanism by which cellular damage occurs during viral infection. Cellular therapy, along with organ support systems such as oxygen therapy, artificial ventilation, extra corporeal membrane oxygenation and dialysis, as well as antiviral therapy, are required. Viral replication in infected host cells may perturb protein folding in the endoplasmic reticulum (ER), causing ER stress. Although an adaptive cellular response, i.e. the unfolded protein response, can compensate for the misfolded protein burden to some extent, continued viral proliferation may induce inflammation and cell death. Therefore, we propose that proteostasis dysfunction may cause conformational disorders in COVID-19. The application of pharmacological chaperone therapy to treat COVID-19 patients is additionally discussed.

Unfolded protein response in cardiovascular disease

The unfolded protein response (UPR) is a highly conserved molecular machinery, which protects the cells against a diverse variety of stimuli. Activation of this element has been associated with both human health and disease. The purpose of the current manuscript is to provide the most updated information on the involvement of UPR towards the improvement; or deterioration of cardiovascular functions. Since UPR is consisted of three distinct elements, namely the activating transcription factor 6, the protein kinase RNA-like endoplasmic reticulum kinase; and the inositol-requiring enzyme-1α, a highly orchestrated manipulation of those molecular branches may provide new therapeutic possibilities against the severe outcomes of cardiovascular disease.

Neuroprotective Effects of Endogenous Secretory Receptor for Advanced Glycation End-products in Brain Ischemia

The receptor for advanced glycation end-products (RAGE) is expressed on human brain endothelial cells (HBEC) and is implicated in neuronal cell death after ischemia. We report that endogenous secretory RAGE (esRAGE) is a splicing variant form of RAGE that functions as a decoy against ischemia-induced neuronal cell damage. This study demonstrated that esRAGE was associated with heparan sulphate proteoglycans on HBEC. The parabiotic experiments between human esRAGE overexpressing transgenic (Tg), RAGE knockout (KO), and wild-type (WT) mice revealed a significant neuronal cell damage in the CA1 region of the WT side of parabiotic WT→WT mice, but not of Tg→WT mice, 7 days after bilateral common carotid artery occlusion. Human esRAGE was detected around the CA1 neurons in the WT side of the parabiotic Tg→WT pair, but not in the KO side of the Tg→KO pair. To elucidate the dynamic transfer of esRAGE into the brain, we used the blood-brain barrier (BBB) system (PharmaCo-Cell) with or without RAGE knockdown in endothelial cells. A RAGE-dependent transfer of esRAGE was demonstrated from the vascular to the brain side. These findings suggested that esRAGE is associated with heparan sulphate proteoglycans and is transferred into the brain via BBB to exert its neuroprotective effects in ischemia.

Circ_002664/miR-182-5p/Herpud1 pathway importantly contributes to OGD/R-induced neuronal cell apoptosis

OBJECTIVE

Apoptosis is a prominent form of neuron death in cerebral ischemia-reperfusion-induced injury. Accompanied with the pathogenesis, Circ_002664 is upregulated. However, its role in the neuron apoptosis and the underlying mechanisms are unknown.

METHODS

In this study, HT22 cells were treated with oxygen glucose deprivation and reoxygenation (OGD/R). The cell viability, apoptosis, proliferation and mitochondrial potential were examined. The expressions of interested genes, Circ_002664, miR-182-5p and Herpud1, were measured. The roles of these genes in OGD/R-induced cell injury were investigated by knockdown, overexpression alone or in combination. Additionally, the interactions between Circ_002664, miR-182-5p and Herpud1 were validated by luciferase report assay. The levels of MAP2, CHOP, Cytochrome C (CYC) and cleaved caspase-3 were determined.

RESULTS

OGD/R treatment significantly increased cell apoptosis, decreased cell proliferation and mitochondrial potential, as well as increased Circ_002664 and Herpud1 expressions, and decreased miR-182-5p level. Circ_002664 knockdown markedly inhibited the effects by OGD/R on cell survival and altered expression of miR-182-5p and Herpud1. MiR-182-5p was observed sponged by Circ_002664 and negatively mediated its effect above mentioned, and this was by directly targeting Herpud1. Additionally, it was observed that CHOP expressions were regulated by Circ_002664/miR-182-5p/Herpud1 pathway, and in turn mediated its regulation in CYC and cleaved caspase-3.

CONCLUSIONS

In summary, our data showed that the Circ_002664 importantly contributed to neuronal cell apoptosis induced by OGD/R treatment, and this might be achieved by directly targeting miR-182-5p/Herpud1 pathway.