Unfolded protein response in brain ischemia: A timely update

ATF5-Mediated Mitochondrial Unfolded Protein Response (UPRmt) Protects Neurons Against Oxygen-Glucose Deprivation and Cerebral Ischemia

BACKGROUND

The mitochondrial unfolded protein response (UPRmt) is an evolutionarily conserved mitochondrial response that is critical for maintaining mitochondrial and energetic homeostasis under cellular stress after tissue injury and disease. Here, we ask whether UPRmt may be a potential therapeutic target for ischemic stroke.

METHODS

We performed the middle cerebral artery occlusion and oxygen-glucose deprivation models to mimic ischemic stroke in vivo and in vitro, respectively. Oligomycin and meclizine were used to trigger the UPRmt. We used 2,3,5-triphenyltetrazolium chloride staining, behavioral tests, and Nissl staining to evaluate cerebral injury in vivo. The Cell Counting Kit-8 assay and the Calcein AM Assay Kit were conducted to test cerebral injury in vitro.

RESULTS

Inducing UPRmt with oligomycin protected neuronal cultures against oxygen-glucose deprivation. UPRmt could also be triggered with meclizine, and this Food and Drug Administration-approved drug also protected neurons against oxygen-glucose deprivation. Blocking UPRmt with siRNA against activating transcription factor 5 eliminated the neuroprotective effects of meclizine. In a mouse model of focal cerebral ischemia, pretreatment with meclizine was able to induce UPRmt in vivo, which reduced infarction and improved neurological outcomes.

CONCLUSIONS

These findings suggest that the UPRmt is important in maintaining the survival of neurons facing ischemic/hypoxic stress. The UPRmt mechanism may provide a new therapeutic avenue for ischemic stroke.

Nuclear Factor Erythroid 2-Related Factor 2 is Essential for Low-Normobaric Oxygen Treatment-Mediated Blood-Brain Barrier Protection Following Ischemic Stroke

Cerebral ischemia/reperfusion (I/R) injury increases blood-brain barrier (BBB) permeability, leading to hemorrhagic transformation and brain edema. Normobaric oxygen (NBO) is a routine clinical treatment strategy for this condition. However, its neuroprotective effects remain controversial. This study investigated the effect of different NBO concentrations on I/R injury and explores the involvement of the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway in the underlying mechanism. A mouse middle cerebral artery occlusion (MCAO) model, and an oxygen and glucose deprivation (OGD) model featuring mouse brain microvascular endothelial cells (ECs) called bEnd.3, were used to investigate the effect of NBO on I/R injury. A reactive oxygen species (ROS) inducer and Nrf2-knockdown by RNA were used to explore whether the Nrf2 pathway mediates the effect of NBO on cerebrovascular ECs. In the early stage of MCAO, 40% O2 NBO exposure significantly improved blood perfusion in the ischemic area and effectively relieved BBB permeability, cerebral edema, cerebral injury, and neurological function after MCAO. In the OGD model, 40% O2 NBO exposure significantly reduced apoptosis, inhibited ROS generation, reduced ER stress, upregulated the expression of tight junction proteins, and stabilized the permeability of ECs. Blocking the Nrf2 pathway nullified the protective effect of 40% O2 NBO on ECs after OGD. Finally, our study confirmed that low concentrations of NBO have a neuroprotective effect on I/R by activating the Nrf2 pathway in ECs.

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.

Inhibition of OGFOD1 by FG4592 confers neuroprotection by activating unfolded protein response and autophagy after ischemic stroke

BACKGROUND

Acute ischemic stroke is a common neurological disease with a significant financial burden but lacks effective drugs. Hypoxia-inducible factor (HIF) and prolyl hydroxylases (PHDs) participate in the pathophysiological process of ischemia. However, whether FG4592, the first clinically approved PHDs inhibitor, can alleviate ischemic brain injury remains unclear.

METHODS

The infarct volumes and behaviour tests were first analyzed in mice after ischemic stroke with systemic administration of FG4592. The knockdown of HIF-1α and pretreatments of HIF-1/2α inhibitors were then used to verify whether the neuroprotection of FG4592 is HIF-dependent. The targets predicting and molecular docking methods were applied to find other targets of FG4592. Molecular, cell biological and gene knockdown methods were finally conducted to explore the potential neuroprotective mechanisms of FG4592.

RESULTS

We found that the systemic administration of FG4592 decreased infarct volume and improved neurological defects of mice after transient or permanent ischemia. Meanwhile, FG4592 also activated autophagy and inhibited apoptosis in peri-infarct tissue of mice brains. However, in vitro and in vivo results suggested that the neuroprotection of FG4592 was not classical HIF-dependent. 2-oxoglutarate and iron-dependent oxygenase domain-containing protein 1 (OGFOD1) was found to be a novel target of FG4592 and regulated the Pro-62 hydroxylation in the small ribosomal protein s23 (Rps23) with the help of target predicting and molecular docking methods. Subsequently, the knockdown of OGFOD1 protected the cell against ischemia/reperfusion injury and activated unfolded protein response (UPR) and autophagy. Moreover, FG4592 was also found to activate UPR and autophagic flux in HIF-1α independent manner. Blocking UPR attenuated the neuroprotection, pro-autophagy effect and anti-apoptosis ability of FG4592.

CONCLUSION

This study demonstrated that FG4592 could be a candidate drug for treating ischemic stroke. The neuroprotection of FG4592 might be mediated by inhibiting alternative target OGFOD1, which activated the UPR and autophagy and inhibited apoptosis after ischemic injury. The inhibition of OGFOD1 is a novel therapy for ischemic stroke.

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.

Reinventing the Penumbra - the Emerging Clockwork of a Multi-modal Mechanistic Paradigm

The concept of the ischemic penumbra was originally defined as the area around a necrotic stroke core and seen as the tissue at imminent risk of further damage. Today, the penumbra is generally considered as time-sensitive hypoperfused brain tissue with decreased oxygen and glucose availability, salvageable tissue as treated by intervention, and the potential target for neuroprotection in focal stroke. The original concept entailed electrical failure and potassium release but one short of neuronal cell death and was based on experimental stroke models, later confirmed in clinical imaging studies. However, even though the basic mechanisms have translated well, conferring brain protection, and improving neurological outcome after stroke based on the pathophysiological mechanisms in the penumbra has yet to be achieved. Recent findings shape the modern understanding of the penumbra revealing a plethora of molecular and cellular pathophysiological mechanisms. We now propose a new model of the penumbra, one which we hope will lay the foundation for future translational success. We focus on the availability of glucose, the brain's central source of energy, and bioenergetic failure as core pathophysiological concepts. We discuss the relation of mitochondrial function in different cell types to bioenergetics and apoptotic cell death mechanisms, autophagy, and neuroinflammation, to glucose metabolism in what is a dynamic ischemic penumbra.

Research progress on the mechanism of curcumin in cerebral ischemia/reperfusion injury: a narrative review

Cerebral ischemia/reperfusion (I/R) injury can result in different levels of cerebral impairment, and in severe cases, death. Curcumin, an essential bioactive component of turmeric, has a rich history as a traditional medicine for various ailments in numerous countries. Experimental and clinical research has established that curcumin offers a protective effect against cerebral I/R injury. Curcumin exerts its protective effects by acting on specific mechanisms such as antioxidant, anti-inflammatory, inhibition of ferroptosis and pyroptosis, protection of mitochondrial function and structure, reduction of excessive autophagy, and improvement of endoplasmic reticulum (ER) stress, which ultimately help to preserve the blood-brain barrier (BBB) and reducing apoptosis. There is currently a shortage of drugs undergoing clinical trials for the treatment of cerebral I/R injury, highlighting the pressing need for research and development of novel treatments to address this injury. The primary objective of this study is to establish a theoretical basis for future clinical applications of curcumin by delineating the mechanisms and protective effects of curcumin against cerebral I/R injury. Adapted with permission from [1].

The Unfolded Protein Response: A Double-Edged Sword for Brain Health

Efficient brain function requires as much as 20% of the total oxygen intake to support normal neuronal cell function. This level of oxygen usage, however, leads to the generation of free radicals, and thus can lead to oxidative stress and potentially to age-related cognitive decay and even neurodegenerative diseases. The regulation of this system requires a complex monitoring network to maintain proper oxygen homeostasis. Furthermore, the high content of mitochondria in the brain has elevated glucose demands, and thus requires a normal redox balance. Maintaining this is mediated by adaptive stress response pathways that permit cells to survive oxidative stress and to minimize cellular damage. These stress pathways rely on the proper function of the endoplasmic reticulum (ER) and the activation of the unfolded protein response (UPR), a cellular pathway responsible for normal ER function and cell survival. Interestingly, the UPR has two opposing signaling pathways, one that promotes cell survival and one that induces apoptosis. In this narrative review, we discuss the opposing roles of the UPR signaling pathways and how a better understanding of these stress pathways could potentially allow for the development of effective strategies to prevent age-related cognitive decay as well as treat neurodegenerative diseases.

The role of protein glycosylation in the occurrence and outcome of acute ischemic stroke

Acute ischemic stroke (AIS) is a serious and life-threatening disease worldwide. Despite thrombolysis or endovascular thrombectomy, a sizeable fraction of patients with AIS have adverse clinical outcomes. In addition, existing secondary prevention strategies with antiplatelet and anticoagulant drugs therapy are not able to adequately decrease the risk of ischemic stroke recurrence. Thus, exploring novel mechanisms for doing so represents an urgent need for the prevention and treatment of AIS. Recent studies have discovered that protein glycosylation plays a critical role in the occurrence and outcome of AIS. As a common co- and post-translational modification, protein glycosylation participates in a wide variety of physiological and pathological processes by regulating the activity and function of proteins or enzymes. Protein glycosylation is involved in two causes of cerebral emboli in ischemic stroke: atherosclerosis and atrial fibrillation. Following ischemic stroke, the level of brain protein glycosylation becomes dynamically regulated, which significantly affects stroke outcome through influencing inflammatory response, excitotoxicity, neuronal apoptosis, and blood-brain barrier disruption. Drugs targeting glycosylation in the occurrence and progression of stroke may represent a novel therapeutic idea. In this review, we focus on possible perspectives about how glycosylation affects the occurrence and outcome of AIS. We then propose the potential of glycosylation as a therapeutic drug target and prognostic marker for AIS patients in the future.

Protective Effect and Mechanism of Xbp1s Regulating HBP/O-GlcNAcylation through GFAT1 on Brain Injury after SAH

(1) SAH induces cellular stress and endoplasmic reticulum stress, activating the unfolded protein response (UPR) in nerve cells. IRE1 (inositol-requiring enzyme 1) is a protein that plays a critical role in cellular stress response. Its final product, Xbp1s, is essential for adapting to changes in the external environment. This process helps maintain proper cellular function in response to various stressors. O-GlcNAcylation, a means of protein modification, has been found to be involved in SAH pathophysiology. SAH can increase the acute O-GlcNAcylation level of nerve cells, which enhances the stress capacity of nerve cells. The GFAT1 enzyme regulates the level of O-GlcNAc modification in cells, which could be a potential target for neuroprotection in SAH. Investigating the IRE1/XBP1s/GFAT1 axis could offer a promising avenue for future research. (2) Methods: SAH was induced using a suture to perforate an artery in mice. HT22 cells with Xbp1 loss- and gain-of-function in neurons were generated. Thiamet-G was used to increase O-GlcNAcylation; (3) Results: Severe neuroinflammation caused by subarachnoid hemorrhage leads to extensive endoplasmic reticulum stress of nerve cells. Xbp1s, the final product of unfolded proteins induced by endoplasmic reticulum stress, can induce the expression of the hexosamine pathway rate limiting enzyme GFAT1, increase the level of O-GlcNAc modification of cells, and have a protective effect on neural cells; (4) Conclusions: The correlation between Xbp1s displayed by immunohistochemistry and O-GlcNAc modification suggests that the IRE1/XBP1 branch of unfolded protein reaction plays a key role in subarachnoid hemorrhage. IRE1/XBP1 branch is a new idea to regulate protein glycosylation modification, and provides a promising strategy for clinical perioperative prevention and treatment of subarachnoid hemorrhage.

PERK inhibitor, GSK2606414, ameliorates neuropathological damage, memory and motor functional impairments in cerebral ischemia via PERK/p-eIF2ɑ/ATF4/CHOP signaling

The protein kinase R-like endoplasmic reticulum kinase/eukaryotic initiation factor 2ɑ (PERK/eIF2α), the branch of unfolded protein response (UPR), is responsible for transient arrest in translation to counter the enhanced levels of misfolded or unfolded proteins in the endoplasmic reticulum (ER) following any acute condition. In neurological disorders, overactivation of PERK-P/eIF2-P signaling, leads to a prolonged decline in global protein synthesis resulting in synaptic failure and neuronal death. Our study has shown, PERK/ATF4/CHOP pathway gets activated following cerebral ischemia in rats. We have further demonstrated, PERK inhibitor, GSK2606414 ameliorates ischemia induced neuronal damage by preventing additional neuronal loss, minimizing brain infarct, reducing brain edema, and preventing neurological symptoms from appearing. GSK2606414 was found to improve the neurobehavioral deficits and reduce the pyknotic neurons in ischemic rats. Also, it decreased glial activation and apoptotic protein mRNA expression while enhanced the synaptic protein mRNA expression in rat brain following cerebral ischemia. In conclusion, our findings suggest that PERK/ATF4/CHOP activation play a vital role in cerebral ischemia. Thus, PERK inhibitor, GSK2606414 might be a potential neuroprotective agent in cerebral ischemia.

Geraniol-Mediated Suppression of Endoplasmic Reticulum Stress Protects against Cerebral Ischemia-Reperfusion Injury via the PERK-ATF4-CHOP Pathway

Endoplasmic reticulum (ER) stress plays an important role in cerebral ischemia-reperfusion injury (CIRI). Geraniol has antioxidant, antibacterial, and anti-inflammatory activities. Studies have shown that geraniol has a protective effect against CIRI in rats, but the exact mechanism is unclear. Purpose: The aim of this study was to investigate the protective mechanism of geraniol against CIRI. We established a middle cerebral artery occlusion reperfusion model in rats and a PC12 cell oxygen-glucose deprivation/reoxygenation (OGD/R) model to observe the neuroprotective effects of geraniol. Neurological scoring, 2,3,5-triphenyltetrazolium chloride staining, and hematoxylin and eosin staining were used to evaluate the neuroprotective effects of geraniol against CIRI. ER-stress-related and apoptosis-related protein expression was detected via Western blotting and immunofluorescence. Apoptosis was also detected via TUNEL assays and flow cytometry. The fluorescent detection of intracellular calcium was achieved using fluorescent calcium-binding dyes, and transmission electron microscopy was used to assess the neuronal ultrastructure. Geraniol effectively attenuated cerebral infarction and pathological injury after CIRI, had a protective effect against CIRI, significantly reduced the expression of the ER-stress-related proteins P-PERK, ATF4, CHOP, and GRP78 and the pro-apoptotic protein BAX, increased the expression of the anti-apoptotic protein BCL-2, and reduced the occurrence of apoptosis. In the OGD/R model in PC12 cells, the protective effect of geraniol was the same as that in vivo. Our results suggest that geraniol has a protective effect against ischemic stroke by a mechanism possibly related to ER stress via the PERK-ATF4-CHOP pathway.

Leptin alleviates endoplasmic reticulum stress induced by cerebral ischemia/reperfusion injury via the PI3K/Akt signaling pathway

BACKGROUND

Cerebral ischemic/reperfusion injury (CIRI) is a key factor for the prognosis of ischemic stroke (IS), the leading disease in terms of global disability and fatality rates. Recent studies have shown that endoplasmic reticulum stress (ERS) may be a target against CIRI and that leptin, a peptide hormone, has neuroprotective activity to mitigate CIRI.

METHODS

An in vitro CIRI model was induced in primary cortical neurons by oxygen-glucose deprivation and reoxygenation (OGD/R) after pretreatment with LY294002 (10 µmol/L) and/or leptin (0.4 mg/L), and cell viability, neuronal morphology and endoplasmic reticulum (ER) dysfunction were evaluated. An in vivo CIRI model was established in rats by middle cerebral artery occlusion and reperfusion (MCAO/R) after the injection of LY294002 (10 μmol/L) and/or leptin (1 mg/kg), and neurological function, infarct volume, cerebral pathological changes, the expression of ERS-related proteins and cell apoptosis were examined.

RESULTS

In vitro, leptin treatment improved the cell survival rate, ameliorated neuronal pathological morphology and alleviated OGD/R-induced ERS. In vivo, administration of leptin significantly reduced the infarct volume, neurological deficit scores and neuronal apoptosis as well as pathological alterations. In addition, leptin suppressed MCAO/R-induced ERS and may decrease apoptosis by inhibiting ERS-related death and caspase 3 activation. It also regulated expression of the antiapoptotic protein Bcl-2 and the proapoptotic protein Bax in the cortex. Furthermore, the inhibitory effect of leptin on ERS was significantly decreased by the effective phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002.

CONCLUSIONS

These results confirm that ERS plays an important role in CIRI and that leptin can inhibit the activation of ERS through the PI3K/Akt pathway, thereby alleviating CIRI. These findings provide novel therapeutic targets for IS.

Sodium formononetin-3'-sulphonate alleviates cerebral ischemia-reperfusion injury in rats via suppressing endoplasmic reticulum stress-mediated apoptosis

BACKGROUND

Sodium formononetin-3'-sulphonate (Sul-F) may alleviate I/R injury in vivo with uncertain mechanism. Endoplasmic reticulum (ER) stress-mediated apoptosis participates in the process of cerebral ischemia-reperfusion (I/R) injury. Our aim is to figure out the effect of Sul-F on cerebral I/R injury and to verify whether it works through suppressing ER stress-mediated apoptosis.

RESULTS

The cerebral lesions of middle cerebral artery occlusion (MCAO) model in SD rats were aggravated after 24 h of reperfusion, including impaired neurological function, increased infarct volume, intensified inflammatory response and poor cell morphology. After intervention, the edaravone (EDA, 3 mg/kg) group and Sul-F high-dose (Sul-F-H, 80 mg/kg) group significantly alleviated I/R injury via decreasing neurological score, infarct volume and the serum levels of inflammatory factors (TNF-α, IL-1β and IL-6), as well as alleviating pathological injury. Furthermore, the ER stress level and apoptosis rate were elevated in the ischemic penumbra of MCAO group, and were significantly blocked by EDA and Sul-F-H. In addition, EDA and Sul-F-H significantly down-regulated the ER stress related PERK/eIF2α/ATF4 and IRE1 signal pathways, which led to reduced cell apoptosis rate compared with the MCAO group. Furthermore, there was no difference between the EDA and Sul-F-H group in terms of therapeutic effect on cerebral I/R injury, indicating a therapeutic potential of Sul-F for ischemic stroke.

CONCLUSIONS

Sul-F-H can significantly protects against cerebral I/R injury through inhibiting ER stress-mediated apoptosis in the ischemic penumbra, which might be a novel therapeutic target for ischemic stroke.

AA147 ameliorates post-cardiac arrest cerebral ischemia/reperfusion injury through the co-regulation of the ATF6 and Nrf2 signaling pathways

Ischemia/reperfusion caused by cardiac arrest (CA) disturbs endoplasmic reticulum (ER) homeostasis and redox balance in neurons. AA147, originally developed as a pharmacologic activator of the activating transcription factor 6 (ATF6), can protect multiple tissues from ischemia/reperfusion injury (IRI) by decreasing reactive oxygen species (ROS) and restoring ER function. However, it is unclear whether pharmacologic treatment of AA147 could ameliorate post-CA cerebral IRI and whether it is associated with proteostasis regulation and anti-oxidative stress mechanism. In the present study, mice were subjected to 9 min-CA surgery followed by cardiopulmonary resuscitation (CPR). AA147 or vehicle was administered 1 day before the operation and 15 min after the return of spontaneous circulation. We found that AA147 restored neurological function and reduced dead neurons in mice suffering from CA. Moreover, AA147 inhibited CA/CPR-caused neuronal apoptosis and ER stress, indicated by reduced TUNEL-positive neurons, surged expression of Bcl-2/Bax, and down expression of cleaved caspase-3, caspase-12, C/EBP homologous protein (CHOP). The expression of ATF6 and its regulated gene glucose-regulated protein 78 (GRP78) increased significantly after the administration of AA147, suggesting the activation of the ATF6 pathway. In addition, AA147 also alleviated the upsurge of the ROS generation and MDA levels as well as increased SOD activity, accompanied by enhancement of the nuclear factor E2-related factor 2 (Nrf2) and its modulated heme-oxygenase-1 (HO-1) expressions. Cotreatment of AA147 with inhibitors of the ATF6 or Nrf2 significantly suppressed AA147-dependent reductions in ROS scavenging and neuronal death after CA/CPR. The results suggested that AA147 could confer neuroprotection against post-CA cerebral IRI through inhibition of oxidative stress along with ER stress-associated apoptosis, which is attributed to the coregulation of both ATF6 and Nrf2 signaling pathways activity. Our findings support the potential for AA147 as a therapeutic approach to improve post-CA brain injury.

Beneficial effects of neuronal ATF6 activation in permanent ischemic stroke

Objective: Brain ischemia leads to the accumulation of unfolded/misfolded proteins in the endoplasmic reticulum (ER) lumen and consequently, ER stress. To help cells restore ER function, a series of adaptive stress response pathways, collectively termed the unfolded protein response (UPR), are activated. We have previously demonstrated that the UPR pathway initiated by ATF6 is pro-survival in transient ischemic stroke. However, the effect of ATF6 activation on the outcome after permanent ischemic stroke remains unknown. Here, we addressed this knowledge gap. Method: sATF6-KI mice with functional short-form ATF6 (sATF6) predominantly expressed in forebrain neurons were subjected to two ischemic stroke models: photothrombotic stroke and permanent middle cerebral artery occlusion (pMCAO). Both short-term and long-term functional outcomes were evaluated. Changes in neuroinflammation and cerebrovascular density after pMCAO were also assessed. Results: Compared to littermate controls, sATF6-KI mice performed significantly better in open field, cylinder, and foot fault tests on day 1 or 3 after photothrombotic stroke. However, on days 7 and 14 after stroke, the performance of these functional tests was not significantly different between groups, which is likely related to mild brain damage associated with this stroke model. Thus, to evaluate the long-term effects of ATF6 activation in permanent stroke, we turned to our pMCAO model. We first found that on day 4 after pMCAO, functional outcome was better, and infarct volumes were smaller in sATF6-KI mice vs controls. Next, the 15-day stroke outcome study indicated that compared to control mice, sATF6-KI mice consistently exhibited improved performance in neurologic scoring, tight rope test, and tape removal test, after pMCAO. Moreover, sATF6-KI mice showed higher vascular density and lower activation of both astrocytes and microglia around stroke regions on day 16 after pMCAO. Conclusions: Here, we presented the first evidence that activation of the ATF6 UPR branch is protective in permanent ischemic stroke, which further supports the therapeutic potential of targeting the ATF6 pathway in stroke.

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.

Mitochondrial quality control in acute ischemic stroke

Mitochondria play a central role in the pathophysiological processes of acute ischemic stroke. Disruption of the cerebral blood flow during acute ischemic stroke interrupts oxygen and glucose delivery, leading to the dysfunction of mitochondrial oxidative phosphorylation and cellular bioenergetic stress. Cells can respond to such stress by activating mitochondrial quality control mechanisms, including the mitochondrial unfolded protein response, mitochondrial fission and fusion, mitophagy, mitochondrial biogenesis, and intercellular mitochondrial transfer. Collectively, these adaptive response strategies contribute to retaining the integrity and function of the mitochondrial network, thereby helping to recover the homeostasis of the neurovascular unit. In this review, we focus on mitochondrial quality control mechanisms occurring in acute ischemic stroke. A better understanding of how these regulatory pathways work in maintaining mitochondrial homeostasis will provide a rationale for developing innovative neuroprotectants when these mechanisms fail in acute ischemic stroke.

An update on the unfolded protein response in brain ischemia: Experimental evidence and therapeutic opportunities

After ischemic stroke or cardiac arrest, brain ischemia occurs. Currently, no pharmacologic intervention that targets cellular processes has proven effective in improving neurologic outcome in patients after brain ischemia. Recent experimental research has identified the crucial role of proteostasis in survival and recovery of cells after ischemia. In particular, the unfolded protein response (UPR), a key signaling pathway that safeguards cellular proteostasis, is emerging as a promising therapeutic target for brain ischemia. For some time, the UPR has been known to play a critical role in the pathophysiology of brain ischemia; however, only in the recent years has the field grown substantially, largely due to the extensive use of UPR-specific mouse genetic models and the rapidly expanding availability of pharmacologic tools that target the UPR. In this review, we provide a timely update on the progress in our understanding of the UPR in experimental brain ischemia, and discuss the therapeutic implications of targeting the UPR in ischemic stroke and cardiac arrest.

Activation of the XBP1s/O-GlcNAcylation Pathway Improves Functional Outcome After Cardiac Arrest and Resuscitation in Young and Aged Mice

ABSTRACT

After cardiac arrest (CA) and resuscitation, the unfolded protein response (UPR) is activated in various organs including the brain. However, the role of the UPR in CA outcome remains largely unknown. One UPR branch involves spliced X-box-binding protein-1 (XBP1s). Notably, XBP1s, a transcriptional factor, can upregulate expression of specific enzymes related to glucose metabolism, and subsequently boost O-linked β-N-acetylglucosamine modification (O-GlcNAcylation). The current study is focused on effects of the XBP1 UPR branch and its downstream O-GlcNAcylation on CA outcome. Using both loss-of-function and gain-of-function mouse genetic tools, we provide the first evidence that activation of the XBP1 UPR branch in the post-CA brain is neuroprotective. Specifically, neuron-specific Xbp1 knockout mice had worse CA outcome, while mice with neuron-specific expression of Xbp1s in the brain had better CA outcome. Since it has been shown that the protective role of the XBP1s signaling pathway under ischemic conditions is mediated by increasing O-GlcNAcylation, we then treated young mice with glucosamine, and found that functional deficits were mitigated on day 3 post CA. Finally, after confirming that glucosamine can boost O-GlcNAcylation in the aged brain, we subjected aged mice to 8 min CA, and then treated them with glucosamine. We found that glucosamine-treated aged mice performed significantly better in behavioral tests. Together, our data indicate that the XBP1s/O-GlcNAc pathway is a promising target for CA therapy.

LncRNA MIAT enhances cerebral ischaemia/reperfusion injury in rat model via interacting with EGLN2 and reduces its ubiquitin-mediated degradation

Long non-coding RNA (lncRNA) MIAT (myocardial infarction associated transcript) has been characterized as a functional lncRNA modulating cerebral ischaemic/reperfusion (I/R) injury. However, the underlying mechanisms remain poorly understood. This study explored the functional partners of MIAT in primary rat neurons and their regulation on I/R injury. Sprague-Dawley rats were used to construct middle cerebral artery occlusion (MCAO) models. Their cerebral cortical neurons were used for in vitro oxygen-glucose deprivation/reoxygenation (OGD/R) models. Results showed that MIAT interacted with EGLN2 in rat cortical neurons. MIAT overexpression or knockdown did not alter EGLN2 transcription. In contrast, MIAT overexpression increased EGLN2 stability after I/R injury via reducing its ubiquitin-mediated degradation. EGLN2 was a substrate of MDM2, a ubiquitin E3 ligase. MDM2 interacted with the N-terminal of EGLN2 and mediated its K48-linked poly-ubiquitination, thereby facilitating its proteasomal degradation. MIAT knockdown enhanced the interaction and reduced EGLN2 stability. MIAT overexpression enhanced infarct volume and induced a higher ratio of neuronal apoptosis. EGLN2 knockdown significantly reversed the injury. MIAT overexpression reduced oxidative pentose phosphate pathway flux and increased oxidized/reduced glutathione ratio, the effects of which were abrogated by EGLN2 knockdown. In conclusion, MIAT might act as a stabilizer of EGLN2 via reducing MDM2 mediated K48 poly-ubiquitination. MIAT-EGLN2 axis exacerbates I/R injury via altering redox homeostasis in neurons.

Activation of the ATF6 (Activating Transcription Factor 6) Signaling Pathway in Neurons Improves Outcome After Cardiac Arrest in Mice

Background Ischemia/reperfusion injury impairs proteostasis, and triggers adaptive cellular responses, such as the unfolded protein response (UPR), which functions to restore endoplasmic reticulum homeostasis. After cardiac arrest (CA) and resuscitation, the UPR is activated in various organs including the brain. However, the role of the UPR in CA has remained largely unknown. Here we aimed to investigate effects of activation of the ATF6 (activating transcription factor 6) UPR branch in CA. Methods and Results Conditional and inducible sATF6-KI (short-form ATF6 knock-in) mice and a selective ATF6 pathway activator 147 were used. CA was induced in mice by KCl injection, followed by cardiopulmonary resuscitation. We first found that neurologic function was significantly improved, and neuronal damage was mitigated after the ATF6 pathway was activated in neurons of sATF6-KI mice subjected to CA/cardiopulmonary resuscitation. Further RNA sequencing analysis indicated that such beneficial effects were likely attributable to increased expression of pro-proteostatic genes regulated by ATF6. Especially, key components of the endoplasmic reticulum-associated degradation process, which clears potentially toxic unfolded/misfolded proteins in the endoplasmic reticulum, were upregulated in the sATF6-KI brain. Accordingly, the CA-induced increase in K48-linked polyubiquitin in the brain was higher in sATF6-KI mice relative to control mice. Finally, CA outcome, including the survival rate, was significantly improved in mice treated with compound 147. Conclusions This is the first experimental study to determine the role of the ATF6 UPR branch in CA outcome. Our data indicate that the ATF6 UPR branch is a prosurvival pathway and may be considered as a therapeutic target for CA.

Polyphenols and Ischemic Stroke: Insight into One of the Best Strategies for Prevention and Treatment

Ischemic stroke (IS) is still among the leading causes of death and disability worldwide. The pathogenic mechanisms beyond its development are several and are complex and this is the main reason why a functional therapy is still missed. The beneficial effects of natural compounds against cardiovascular diseases and IS have been investigated for a long time. In this article, we reviewed the association between the most studied polyphenols and stroke protection in terms of prevention, effect on acute phase, and rehabilitation. We described experimental and epidemiological studies reporting the role of flavonols, phenolic acid, and stilbens on ischemic mechanisms leading to stroke. We analyzed the principal animal models used to evaluate the impact of these micronutrients to cerebral blood flow and to molecular pathways involved in oxidative stress and inflammation modulation, such as sirtuins. We reported the most significant clinical trials demonstrated as the persistent use of polyphenols is clinically relevant in terms of the reduction of vascular risk factors for IS, such as Atrial Fibrillation. Interestingly, different kinds of polyphenols provide brain protection by activating different pathways and mechanisms, like inducing antithrombotic effect, such as Honokiol. For this reason, we discussed an appropriate integrative use of them as a possible therapeutic alternative against stroke.

Regulation of blood-brain barrier permeability by Salvinorin A via alleviating endoplasmic reticulum stress in brain endothelial cell after ischemia stroke

Inhibition of endoplasmic reticulum (ER) stress reduces blood-brain barrier (BBB) injury caused by ischemia/reperfusion (I/R), with indistinct mechanisms. Salvinorin A (SA) relieves I/R-induced BBB leakage; however, whether it is related to the suppression of ER stress is yet unclear. To address this question, we have used both a rat model of middle cerebral artery occlusion (MCAO) and human brain microvascular endothelial cells (HBMECs) with oxygen-glucose deprivation (OGD). SA was injected by tail vein at the terminal of ischemia; Norbinaltorphimine (NB), a kappa opioid antagonist, was administered 30 min prior to SA; 4-phenylbutyric acid (4-PBA), an ER stress inhibitor, was injected intraperitoneally after the onset of ischemia; adenylate-activated protein kinase (AMPK)-specific small interfering RNAs (siRNAs) were transfected to HBMECs before OGD. The assessment was as follows: infarct volume, brain water gain, Evans blue leakage, and modified neurological severity score (mNSS) after MCAO; HBMECs apoptosis rate and permeability, ER stress-related protein, and reactive oxygen species (ROS) and calcium levels after OGD. The results showed that SA significantly reduced the BBB leakage in vivo; SA relieved the apoptotic rates and ER stress in HBMECs, protected the permeability of HBMECs, and reduced ROS and calcium ion level after OGD. Moreover, the SA function was blocked by NB in vivo and AMPK- siRNAs in vitro. We conclude that SA mitigated BBB damage and HBMEC injury after I/R and alleviated ER stress in endothelial cells via AMPK pathway.

Increasing O-GlcNAcylation is neuroprotective in young and aged brains after ischemic stroke

Spliced X-box binding protein-1 (XBP1s) together with the hexosamine biosynthetic pathway (HBP) and O-GlcNAcylation forms the XBP1s/HBP/O-GlcNAc axis. Our previous studies have provided evidence that activation of this axis is neuroprotective after ischemic stroke and critically, ischemia-induced O-GlcNAcylation is impaired in the aged brain. However, the XBP1s' neuroprotective role and its link to O-GlcNAcylation in stroke, as well as the therapeutic potential of targeting this axis in stroke, have not been well established. Moreover, the mechanisms underlying this age-related impairment of O-GlcNAcylation induction after brain ischemia remain completely unknown. In this study, using transient ischemic stroke models, we first demonstrated that neuron-specific overexpression of Xbp1s improved outcome, and pharmacologically boosting O-GlcNAcylation with thiamet-G reversed worse outcome observed in neuron-specific Xbp1 knockout mice. We further showed that thiamet-G treatment improved long-term functional recovery in both young and aged animals after transient ischemic stroke. Mechanistically, using an analytic approach developed here, we discovered that availability of UDP-GlcNAc was compromised in the aged brain, which may constitute a novel mechanism responsible for the impaired O-GlcNAcylation activation in the aged brain after ischemia. Finally, based on this new mechanistic finding, we evaluated and confirmed the therapeutic effects of glucosamine treatment in young and aged animals using both transient and permanent stroke models. Our data together support that increasing O-GlcNAcylation is a promising strategy in stroke therapy.

FABP4 alleviates endoplasmic reticulum stress-mediated ischemia-reperfusion injury in PC12 cells via regulation of PPARγ

Ischemic stroke is a life-threatening complication with a high rate of morbidity. Circulating fatty acid binding protein 4 (FABP4) has been reported to be associated with the outcome of acute ischemic stroke. The present study aimed to illustrate the function of FABP4 in ischemic stroke. PC12 cells exposed to oxygen glucose deprivation/reoxygenation (OGD/R) were used to mimic ischemia-reperfusion (I/R) injury in ischemic stroke. Cell viability was estimated using a Cell Counting Kit-8 assay. The expression of FABP4 in PC12 cells under OGD/R was detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). PC12 cells were transfected with FABP4 small interfering RNA (siRNA), inflammatory cytokines and reactive oxygen species (ROS) were determined via RT-qPCR and ROS assay kit. Western blotting was performed to detect endoplasmic reticulum stress (ERS)-related proteins and peroxisome proliferator-activated receptor γ (PPARγ). Flow cytometry was used to evaluate the cell apoptotic rate. The expression of FABP4 increased gradually with the prolongation of reoxygenation within 8 h. FABP4-knockdown inhibited the transcription of inflammatory cytokines, the production of ROS and decreased cell apoptosis. Furthermore, decreased ERS-related proteins and increased PPARγ were estimated in PC12 cells transfected with FABP4 siRNA. PPARγ inhibitor GW9662 weakened the anti-apoptotic effect of FABP4-knockdown. Taken together, these results indicated that FABP4-knockdown suppressed cell apoptosis via relieving ERS; this effect was reversed by treatment of GW9662.

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.

Acute Neural and Proteostasis Messenger Ribonucleic Acid Levels Predict Chronic Locomotor Recovery after Contusive Spinal Cord Injury

One of the difficulties in identifying novel therapeutic strategies to manage central nervous system (CNS) trauma is the need for behavioral assays to assess chronic functional recovery. In vitro assays and/or acute behavioral assessments cannot accurately predict long-term functional outcome. Using data from 13 independent T9 moderate contusive spinal cord injury (SCI) studies, we asked whether the ratio of acute (24-72 h post-injury) changes in the levels of neuron-, oligodendrocyte-, astrocyte-specific and/or endoplasmic reticulum stress response (ERSR) messenger ribonucleic acids (mRNAs) could predict the extent of chronic functional recovery. Increased levels of neuron, oligodendrocyte, and astrocyte mRNAs all correlated with enhanced Basso Mouse Scale (BMS) scores. Reduced levels of the ERSR mRNAs Atf4 and Chop correlate with improved chronic locomotor function. Neither neural or ERSR mRNAs were predictive for chronic recovery across all behavioral changes. The ratio of oligodendrocyte/ERSR mRNAs, however, did predict "improved," "no change," or "worse" functional recovery. Neuronal/ERSR mRNA ratios predicted functional improvement, but could not distinguish between worse or no change outcomes. Astrocyte/ERSR mRNA ratios were not predictive. This approach can be used to confirm biological action of injected drugs in vivo and to optimize dose and therapeutic window. It may prove useful in cervical and lumbar SCI and in other traumatic CNS injuries such as traumatic brain injury and stroke, where prevention of neuronal loss is paramount to functional recovery. Although the current analysis was directed toward ERSR whose activity was targeted in all but one study, acute mRNA markers for other pathophysiological cascades may be as predictive of chronic recovery when those cascades are targeted for neuroprotection.

Endoplasmic reticulum stress serves an important role in cardiac ischemia/reperfusion injury (Review)

Although acute myocardial infarction is one of the most common fatal diseases worldwide, the understanding of its underlying pathogenesis continues to develop. Myocardial ischemia/reperfusion (I/R) can restore myocardial oxygen and nutrient supply. However, a large number of studies have demonstrated that recovery of blood perfusion after acute ischemia causes reperfusion injury to the heart. With progress made in the understanding of the underlying mechanisms of myocardial I/R and oxidative stress, a novel area of research that merits greater study has been identified, that of I/R-induced endoplasmic reticulum (ER) stress (ERS). Cardiac I/R can alter the function of the ER, leading to the accumulation of unfolded/misfolded proteins. The resulting ERS then induces the activation of signal transduction pathways, which in turn contribute to the development of I/R injury. The mechanism of I/R injury, and the causal relationship between I/R and ERS are reviewed in the present article.

Low density lipoprotein receptor related protein 6 (LRP6) protects heart against oxidative stress by the crosstalk of HSF1 and GSK3β

Low density lipoprotein receptor-related protein 6 (LRP6), a Wnt co-receptor, induces multiple functions in various organs. We recently reported cardiac specific LRP6 deficiency caused cardiac dysfunction in mice. Whether cardiomyocyte-expressed LRP6 protects hearts against ischemic stress is largely unknown. Here, we investigated the effects of cardiac LRP6 in response to ischemic reperfusion (I/R) injury. Tamoxifen inducible cardiac specific LRP6 overexpression mice were generated to build I/R model by occlusion of the left anterior descending (LAD) coronary artery for 40 min and subsequent release of specific time. Cardiac specific LRP6 overexpression significantly ameliorated myocardial I/R injury as characterized by the improved cardiac function, strain pattern and infarct area at 24 h after reperfusion. I/R induced-apoptosis and endoplasmic reticulum (ER) stress were greatly inhibited by LRP6 overexpression in cardiomyocytes. LRP6 overexpression enhanced the expression of heat shock transcription factor-1(HSF1) and heat shock proteins (HSPs), the level of p-glycogen synthase kinase 3β(GSK3β)(S9) and p-AMPK under I/R. HSF1 inhibitor deteriorated the apoptosis and decreased p-GSK3β(S9) level in LRP6 overexpressed -cardiomyocytes treated with H2O2. Si-HSF1 or overexpression of active GSK3β significantly attenuated the increased expression of HSF1 and p-AMPK, and the inhibition of apoptosis and ER stress induced by LRP6 overexpression in H2O2-treated cardiomyocytes. AMPK inhibitor suppressed the increase in p-GSK3β (S9) level but didn't alter HSF1 nucleus expression in LRP6 overexpressed-cardiomyocytes treated with H2O2. Active GSK3β, but not AMPK inhibitor, attenuated the inhibition of ubiquitination of HSF1 induced by LRP6-overexpressed-cardiomyocytes treated with H2O2. LRP6 overexpression increased interaction of HSF1 and GSK3β which may be involved in the reciprocal regulation under oxidative stress. In conclusion, cardiac LRP6 overexpression significantly inhibits cardiomyocyte apoptosis and ameliorates myocardial I/R injury by the crosstalk of HSF1 and GSK3β signaling.

Modulation of Cerebral Store-operated Calcium Entry-regulatory Factor (SARAF) and Peripheral Orai1 Following Focal Cerebral Ischemia and Preconditioning in Mice

Store-operated Ca²⁺ entry (SOCE) contributes to Ca²⁺ refilling of endoplasmic reticulum (ER), but also provides Ca²⁺ influx involved in physiological and pathological signalling functions. Upon depletion of Ca²⁺ store, the sensor protein stromal interaction molecule (STIM) activates Orai1, forming an ion-conducting pore highly selective for Ca²⁺. SOCE-associated regulatory factor (SARAF) associates with STIM1 to facilitate a slow form of Ca²⁺-dependent inactivation of SOCE or interacts with Orai1 to stimulate SOCE in STIM1-independent manner. We have investigated whether cerebral ischemic damage and neuroprotection conferred by ischemic preconditioning (PC) in mouse are associated with changes in the expression of the molecular components of SOCE. Ischemic PC induced by 15-min occlusion of the middle cerebral artery (MCAo) resulted in significant amelioration of histological and functional outcomes produced, 72 h later, by a more severe ischemia (1 h MCAo). Neither ischemia, nor PC affected the expression of Orai1 in the frontoparietal cortex. However, the number of Orai1-immunopositive cells, mostly corresponding to Ly-6G+ neutrophils, was significantly elevated in the blood after the ischemic insult, regardless of previous PC. The expression of Stim1 and SARAF, mainly localised in NeuN-immunopositive neurons, was reduced in the ischemic cortex. Interestingly, neuroprotection by ischemic PC prevented the reduction of SARAF expression in the lesioned cortex and this could be interpreted as a compensatory mechanism to restore ER Ca²⁺ refilling in neurons in the absence of STIM1. Thus, preventing SARAF downregulation may represent a pivotal mechanism implicated in neuroprotection provided by ischemic PC and should be exploited as an original target for novel stroke therapies.

Proteomic analysis of the cardiac myocyte secretome reveals extracellular protective functions for the ER stress response

The effects of ER stress on protein secretion by cardiac myocytes are not well understood. In this study, the ER stressor thapsigargin (TG), which depletes ER calcium, induced death of cultured neonatal rat ventricular myocytes (NRVMs) in high media volume but fostered protection in low media volume. In contrast, another ER stressor, tunicamycin (TM), a protein glycosylation inhibitor, induced NRVM death in all media volumes, suggesting that protective proteins were secreted in response to TG but not TM. Proteomic analyses of TG- and TM-conditioned media showed that the secretion of most proteins was inhibited by TG and TM; however, secretion of several ER-resident proteins, including GRP78 was increased by TG but not TM. Simulated ischemia, which decreases ER/SR calcium also increased secretion of these proteins. Mechanistically, secreted GRP78 was shown to enhance survival of NRVMs by collaborating with a cell-surface protein, CRIPTO, to activate protective AKT signaling and to inhibit death-promoting SMAD2 signaling. Thus, proteins secreted during ER stress mediated by ER calcium depletion can enhance cardiac myocyte viability.

Molecular profile of the rat peri-infarct region four days after stroke: Study with MANF

The peri-infarct region after ischemic stroke is the anatomical location for many of the endogenous recovery processes; however, -the molecular events in the peri-infarct region remain poorly characterized. In this study, we examine the molecular profile of the peri-infarct region on post-stroke day four, a time when reparative processes are ongoing. We used a multiomics approach, involving RNA sequencing, and mass spectrometry-based proteomics and metabolomics to characterize molecular changes in the peri-infarct region. We also took advantage of our previously developed method to express transgenes in the peri-infarct region where self-complementary adeno-associated virus (AAV) vectors were injected into the brain parenchyma on post-stroke day 2. We have previously used this method to show that mesencephalic astrocyte-derived neurotrophic factor (MANF) enhances functional recovery from stroke and recruits phagocytic cells to the peri-infarct region. Here, we first analyzed the effects of stroke to the peri-infarct region on post-stroke day 4 in comparison to sham-operated animals, finding that strokeinduced changes in 3345 transcripts, 341 proteins, and 88 metabolites. We found that after stroke, genes related to inflammation, proliferation, apoptosis, and regeneration were upregulated, whereas genes encoding neuroactive ligand receptors and calcium-binding proteins were downregulated. In proteomics, we detected upregulation of proteins related to protein synthesis and downregulation of neuronal proteins. Metabolomic studies indicated that in after stroke tissue there is an increase in saccharides, sugar phosphates, ceramides and free fatty acids and a decrease of adenine, hypoxantine, adenosine and guanosine. We then compared the effects of post-stroke delivery of AAV1-MANF to AAV1-eGFP (enhanced green fluorescent protein). MANF administration increased the expression of 77 genes, most of which were related to immune response. In proteomics, MANF administration reduced S100A8 and S100A9 protein levels. In metabolomics, no significant differences between MANF and eGFP treatment were detected, but relative to sham surgery group, most of the changes in lipids were significant in the AAV-eGFP group only. This work describes the molecular profile of the peri-infarct region during recovery from ischemic stroke, and establishes a resource for further stroke studies. These results provide further support for parenchymal MANF as a modulator of phagocytic function.

PERK (Protein Kinase RNA-Like ER Kinase) Branch of the Unfolded Protein Response Confers Neuroprotection in Ischemic Stroke by Suppressing Protein Synthesis

Background and Purpose- Ischemic stroke impairs endoplasmic reticulum (ER) function, causes ER stress, and activates the unfolded protein response. The unfolded protein response consists of 3 branches controlled by ER stress sensor proteins, which include PERK (protein kinase RNA-like ER kinase). Activated PERK phosphorylates eIF2α (eukaryotic initiation factor 2 alpha), resulting in inhibition of global protein synthesis. Here, we aimed to clarify the role of the PERK unfolded protein response branch in stroke. Methods- Neuron-specific and tamoxifen-inducible PERK conditional knockout (cKO) mice were generated by cross-breeding Camk2a-CreERT2 with Perk^f/f mice. Transient middle cerebral artery occlusion was used to induce stroke. Short- and long-term stroke outcomes were evaluated. Protein synthesis in the brain was assessed using a surface-sensing-of-translation approach. Results- After tamoxifen-induced deletion of Perk in forebrain neurons was confirmed in PERK-cKO mice, PERK-cKO and control mice were subjected to transient middle cerebral artery occlusion and 3 days or 3 weeks recovery. PERK-cKO mice had larger infarcts and worse neurological outcomes compared with control mice, suggesting that PERK-induced eIF2α phosphorylation and subsequent suppression of translation protects neurons from ischemic stress. Indeed, better stroke outcomes were observed in PERK-cKO mice that received postischemic treatment with salubrinal, which can restore the ischemia-induced increase in phosphorylated eIF2α in these mice. Finally, our data showed that post-treatment with salubrinal improved functional recovery after stroke. Conclusions- Here, we presented the first evidence that postischemic suppression of translation induced by PERK activation promotes recovery of neurological function after stroke. This confirms and further extends our previous observations that recovery of ER function impaired by ischemic stress critically contributes to stroke outcome. Therefore, future research should include strategies to improve stroke outcome by targeting unfolded protein response branches to restore protein homeostasis in neurons.

Intranasal Administration of PACAP Is an Efficient Delivery Route to Reduce Infarct Volume and Promote Functional Recovery After Transient and Permanent Middle Cerebral Artery Occlusion

Intranasal (IN) administration appears to be a suitable route for clinical use as it allows direct delivery of bioactive molecules to the central nervous system, reducing systemic exposure and sides effects. Nevertheless, only some molecules can be transported to the brain from the nasal cavity. This led us to compare the efficiency of an IN, intravenous (IV), and intraperitoneal (IP) administration of pituitary adenylate cyclase-activating polypeptide (PACAP) after transient or permanent middle cerebral artery occlusion (MCAO) in C57BL/6 mice. The results show that the neuroprotective effect of PACAP is much more efficient after IN administration than IV injection while IP injection had no effect. IN administration of PACAP reduced the infarct volume when injected within 6 h after the reperfusion and improved functional recovery up to at least 1 week after the ischemia.

The potassium channel KCa3.1 represents a valid pharmacological target for microgliosis-induced neuronal impairment in a mouse model of Parkinson's disease

Background

Recent studies described a critical role for microglia in Parkinson’s disease (PD), where these central nerve system resident immune cells participate in the neuroinflammatory microenvironment that contributes to dopaminergic neurons loss in the substantia nigra. Understanding the phenotype switch of microgliosis in PD could help to identify the molecular mechanism which could attenuate or delay the progressive decline in motor function. KCa3.1 has been reported to regulate the “pro-inflammatory” phenotype switch of microglia in neurodegenerative pathological conditions.

Methods

We here investigated the effects of gene deletion or pharmacological blockade of KCa3.1 activity in wild-type or KCa3.1^−/− mice after treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a mouse model of PD. MPTP-induced PD mouse model was subjected to the rotarod test to evaluate the locomotor ability. Glia activation and neuron loss were measured by immunostaining. Fluo-4 AM was used to measure cytosolic Ca²⁺ level in 1-methyl-4-phenylpyridinium (MPP⁺)-induced microgliosis in vitro.

Results

We report that treatment of MPTP-induced PD mouse model with gene deletion or pharmacological blockade of KCa3.1 with senicapoc improves the locomotor ability and the tyrosine hydroxylase (TH)-positive neuron number and attenuates the microgliosis and neuroinflammation in the substantia nigra pars compacta (SNpc). KCa3.1 involves in store-operated Ca²⁺ entry-induced Ca²⁺ overload and endoplasmic reticulum stress via the protein kinase B (AKT) signaling pathway during microgliosis. Gene deletion or blockade of KCa3.1 restored AKT/mammalian target of rapamycin (mTOR) signaling both in vivo and in vitro.

Conclusions

Taken together, these results demonstrate a key role for KCa3.1 in driving a pro-inflammatory microglia phenotype in PD.

The PERK Pathway Plays a Neuroprotective Role During the Early Phase of Secondary Brain Injury Induced by Experimental Intracerebral Hemorrhage

The protein kinase RNA-like endoplasmic reticulum kinase (PERK) pathway, which is a branch of the unfolded protein response, participates in a range of pathophysiological processes of neurological diseases. However, few studies have investigated the role of the PERK in intracerebral hemorrhage (ICH). The present study evaluated the role of the PERK pathway during the early phase of ICH-induced secondary brain injury (SBI) and its potential mechanisms. An autologous whole blood ICH model was established in rats, and cultured primary cortical neurons were treated with oxyhemoglobin to mimic ICH in vitro. We found that levels of phosphorylated alpha subunit of eukaryotic translation initiation factor 2 (p-eIF2α) and activating transcription factor 4 (ATF4) increased significantly and peaked at 12 h during the early phase of the ICH. To further elucidate the role of the PERK pathway, we assessed the effects of the PERK inhibitor, GSK2606414, and the eIF2α dephosphorylation antagonist, salubrinal, at 12 h after ICH both in vivo and in vitro. Inhibition of PERK with GSK2606414 suppressed the protein levels of p-eIF2α and ATF4, resulting in increase of transcriptional activator CCAAT/enhancer-binding protein homologous protein (CHOP) and caspase-12, which promoted apoptosis and reduced neuronal survival. Treatment with salubrinal yielded opposite results, which suggested that activation of the PERK pathway could promote neuronal survival and reduce apoptosis. In conclusion, the present study has demonstrated the neuroprotective effects of the PERK pathway during the early phase of ICH-induced SBI. These findings highlight the potential value of PERK pathway as a therapeutic target for ICH.

Aggravation of Cerebral Ischemia/Reperfusion Injury by Peroxisome Proliferator-Activated Receptor-Gamma Deficiency via Endoplasmic Reticulum Stress

BACKGROUND Ischemic stroke is a dominant contributor to disability and mortality worldwide and is recognized as an important health concern. As a transcription factor triggered via stress, peroxisome proliferator-activated receptor-gamma (PPAR-γ) has a crucial impact on differentiation, cell death, and cell growth. However, the role of PPAR-γ and its precise mechanism in cerebral ischemia injury (CII) remain unclear. MATERIAL AND METHODS The male C57Bl/6 mice (12 weeks old, n=52) were subjected to middle cerebral artery occlusion (MCAO). Infarct volume was evaluated by 2, 3, 5-Triphenyltetrazolium chloride staining. Cell apoptosis was measured by terminal dUTP nick-end labeling (TUNEL) staining. The expression of apoptotic-related protein was examined by Western blotting. Neuron2A cells were transfected with PPAR-γ-specific siRNA and then were subjected to oxygen-glucose exhaustion and reoxygenation. RESULTS It was observed that PPAR-γ-deficient mice displayed extended infarct trigon in the MCAO stroke model. Neuronal deficiency was more severe in PPAR-γ-deficient models. Additionally, expression of cell death-promoting Bcl-2 associated X and active caspase-3 was reinforced, while that of cell death-counteracting Bcl-2 was repressed in PPAR-γ-deficient mice. This was characterized by reinforced endoplasmic reticulum (ER) stress reactions in in vivo brain specimens as well as in vitro neurons in ischemia/reperfusion (I/R) injury. CONCLUSIONS This research proved that PPAR-γ protected the brain from cerebral I/R injury by repressing ER stress and indicated that PPAR-γ is a potential target in the treatment of ischemia.

Proteostasis and Beyond: ATF6 in Ischemic Disease

Endoplasmic reticulum (ER) stress is a pathological hallmark of numerous ischemic diseases, including stroke and myocardial infarction (MI). In these diseases, ER stress leads to activation of the unfolded protein response (UPR) and subsequent adaptation of cellular physiology in ways that dictate cellular fate following ischemia. Recent evidence highlights a protective role for the activating transcription factor 6 (ATF6) arm of the UPR in mitigating adverse outcomes associated with ischemia/reperfusion (I/R) injury in multiple disease models. This suggests ATF6 as a potential therapeutic target for intervening in diverse ischemia-related disorders. Here, we discuss the evidence demonstrating the importance of ATF6 signaling in protecting different tissues against ischemic damage and discuss preclinical results focused on defining the potential for pharmacologically targeting ATF6 to intervene in such diseases.

Impaired capacity to restore proteostasis in the aged brain after ischemia: Implications for translational brain ischemia research

Brain ischemia induced by cardiac arrest or ischemic stroke is a severe form of metabolic stress that substantially disrupts cellular homeostasis, especially protein homeostasis (proteostasis). As proteostasis is fundamental for cellular and organismal health, cells have developed a complex network to restore proteostasis impaired by stress. Many components of this network - including ubiquitination, small ubiquitin-like modifier (SUMO) conjugation, autophagy, and the unfolded protein response (UPR) - are activated in the post-ischemic brain, and play a crucial role in cell survival and recovery of neurologic function. Importantly, recent studies have shown that ischemia-induced activation of these proteostasis-related pathways in the aged brain is impaired, indicating an aging-related decline in the self-healing capacity of the brain. This impaired capacity is a significant factor for consideration in the field of brain ischemia because the vast majority of cardiac arrest and stroke patients are elderly. In this review, we focus on the effects of aging on these critical proteostasis-related pathways in the brain, and discuss their implications in translational brain ischemia research.

Ca2+-dependent endoplasmic reticulum stress correlation with astrogliosis involves upregulation of KCa3.1 and inhibition of AKT/mTOR signaling

BACKGROUND

The intermediate-conductance Ca²⁺-activated K⁺ channel KCa3.1 was recently shown to control the phenotype switch of reactive astrogliosis (RA) in Alzheimer's disease (AD).

METHODS

KCa3.1 channels expression and cell localization in the brains of AD patients and APP/PS1 mice model were measured by immunoblotting and immunostaining. APP/PS1 mice and KCa3.1^-/-/APP/PS1 mice were subjected to Morris water maze test to evaluate the spatial memory deficits. Glia activation and neuron loss was measured by immunostaining. Fluo-4AM was used to measure cytosolic Ca²⁺ level in β-amyloid (Aβ) induced reactive astrocytes in vitro.

RESULTS

KCa3.1 expression was markedly associated with endoplasmic reticulum (ER) stress and unfolded protein response (UPR) in both Aβ-stimulated primary astrocytes and brain lysates of AD patients and APP/PS1 AD mice. The KCa3.1 channel was shown to regulate store-operated Ca²⁺ entry (SOCE) through an interaction with the Ca²⁺ channel Orai1 in primary astrocytes. Gene deletion or pharmacological blockade of KCa3.1 protected against SOCE-induced Ca²⁺ overload and ER stress via the protein kinase B (AKT) signaling pathway in astrocytes. Importantly, gene deletion or blockade of KCa3.1 restored AKT/mechanistic target of rapamycin signaling both in vivo and in vitro. Consistent with these in vitro data, expression levels of the ER stress markers 78-kDa glucose-regulated protein and CCAAT/enhancer-binding protein homologous protein, as well as that of the RA marker glial fibrillary acidic protein were increased in APP/PS1 AD mouse model. Elimination of KCa3.1 in KCa3.1^-/-/APP/PS1 mice corrected these abnormal responses. Moreover, glial activation and neuroinflammation were attenuated in the hippocampi of KCa3.1^-/-/APP/PS1 mice, as compared with APP/PS1 mice. In addition, memory deficits and neuronal loss in APP/PS1 mice were reversed in KCa3.1^-/-/APP/PS1 mice.

CONCLUSIONS

Overall, these results suggest that KCa3.1 is involved in the regulation of Ca²⁺ homeostasis in astrocytes and attenuation of the UPR and ER stress, thus contributing to memory deficits and neuronal loss.

Astrocyte-specific deletion of Kir6.1/K-ATP channel aggravates cerebral ischemia/reperfusion injury through endoplasmic reticulum stress in mice

ATP-sensitive potassium (K-ATP) channels, coupling cell metabolism to cell membrane potential, are involved in brain diseases including stroke. Emerging evidence shows that astrocytes play important roles in the pathophysiology of cerebral ischemia. Kir6.1, a pore-forming subunit of K-ATP channel, is prominently expressed in astrocytes and participates in regulating its function. However, the exact role of astrocytic Kir6.1-containg K-ATP channel (Kir6.1/K-ATP) in ischemic stroke remains unclear. Here, we found that astrocytic Kir6.1 knockout (KO) mice exhibited larger infarct areas and more severe brain edema and neurological deficits in middle cerebral artery occlusion stroke model. Both activated gliosis and neuronal loss were aggravated in astrocytic Kir6.1 KO mice. Furthermore, the protein levels of pro-apoptotic protein Bcl-2 associated X (Bax) and active caspase-3 were up-regulated and the expression of anti-apoptotic protein Bcl-2 was down-regulated in astrocytic Kir6.1 KO mice. This is accompanied by enhanced endoplasmic reticulum stress (ER stress) responses in brain tissues and in astrocytes during ischemia/reperfusion (I/R) injury. Finally, inhibition of ER stress rescued astrocyte apoptosis induced by Kir6.1 deletion during I/R injury. Collectively, our findings reveal that astrocytic Kir6.1/K-ATP channel protects brain from cerebral ischemia/reperfusion injury through inhibiting ER stress and suggest that astrocytic Kir6.1/K-ATP channel is a promising therapeutic target for ischemic stroke.

Estrogen and propofol combination therapy inhibits endoplasmic reticulum stress and remarkably attenuates cerebral ischemia-reperfusion injury and OGD injury in hippocampus

AIM

Endoplasmic reticulum stress (ERS) is vital in inducing apoptosis via caspase-12 and C/EBP homologous protein (CHOP) apoptotic pathway in the hippocampus after ischemia-reperfusion injury. The study aimed to estimate the efficacy of estrogen and propofol combination therapy against ERS-induced apoptosis after cerebral ischemia-reperfusion injury and oxygen-glucose deprivation (OGD) injury in the hippocampus in vivo and in vitro.

METHODS

Rat model of cerebral ischemia-reperfusion injury was generated by middle cerebral artery occlusion (MCAO) strategy with ischemic intervention for 90 min and reperfusion for 24 h. Propofol processing ischemia-reperfusion group (Propofol group) infused 50 mg/kg/h of propofol via the femoral vein at the onset of reperfusion for 30 min. Estrogen processing ischemia-reperfusion group (estrogen group) received 0.0125 mg/kg of estrogen via tail vein at 30 min prior to MCAO. Combination therapy for ischemia-reperfusion group (combination group) received simultaneous processing with propofol and estrogen. In vitro, brain slices were randomly exposed to dimethylsulfoxide (DSMO), 10 μm of propofol, 10 nm of estrogen, or propofol and estrogen. Changes in the orthodromic population spike (OPS) at the end of reoxygenation were recorded. Neurological deficit examination, Nissl staining, and 2,3,5-triphenyltetrazolium chloride (TTC) staining were employed to evaluate the level of cerebral ischemia-reperfusion injury. The expression of caspase-3, caspase-12, glucose-regulated protein 78 (GRP78), and CHOP were investigated by Western blot and immunofluorescence staining assays. Neural apoptotic rate in hippocampus was detected by the flow cytometry trial.

RESULTS

Neurological deficit score, infarct volume, the expression of caspase-3 (P <  0.05), caspase-12, GRP78, CHOP, and neural apoptotic rate of I/R group increased markedly (P <  0.01). When obtaining drug treatment, neurological deficit score (P <  0.05), infarct volume, the expression levels of caspase-12 and GRP78, and neural apoptotic rate of the propofol group decreased significantly (P <  0.01). Furthermore, neurological deficit score, infarct volume, expression levels of caspase-3, caspase-12, GRP78, and CHOP (P <  0.05), and neural apoptotic rate decreased in the estrogen group (P <  0.01) and especially in the combination group (P <  0.01). Compared with the propofol group, the neurological deficit score (P <  0.05), infarct volume, caspase-3, caspase-12, GRP78, CHOP, and neural apoptotic rate of the combination group decreased (P <  0.01). Compared with the estrogen group, the infarct volume, caspase-3 (P <  0.05), GRP78, CHOP, and neural apoptotic rate (P <  0.05) of the combination group decreased (P <  0.01). Compared with the propofol group, the infarct volume, caspase-3, caspase-12 (P <  0.05), and GRP78 (P <  0.05) of the estrogen group decreased (P <  0.01). Propofol and estrogen treatment can delay the abolishing time of OPS and increase the recovery rate and amplitude of OPS, compared with OGD group (P <  0.01), especially in the combination therapy (P <  0.01).

CONCLUSION

The neuroprotection of propofol and estrogen combination therapy inhibited excessive ERS-induced apoptosis against cerebral ischemia-reperfusion injury and OGD injury in the hippocampus of rats. Furthermore, the outcomes demonstrated that combination therapy yielded synergistic effects.

ZIKV infection activates the IRE1-XBP1 and ATF6 pathways of unfolded protein response in neural cells

BACKGROUND

Many viruses depend on the extensive membranous network of the endoplasmic reticulum (ER) for their translation, replication, and packaging. Certain membrane modifications of the ER can be a trigger for ER stress, as well as the accumulation of viral protein in the ER by viral infection. Then, unfolded protein response (UPR) is activated to alleviate the stress. Zika virus (ZIKV) is a mosquito-borne flavivirus and its infection causes microcephaly in newborns and serious neurological complications in adults. Here, we investigated ER stress and the regulating model of UPR in ZIKV-infected neural cells in vitro and in vivo.

METHODS

Mice deficient in type I and II IFN receptors were infected with ZIKV via intraperitoneal injection and the nervous tissues of the mice were assayed at 5 days post-infection. The expression of phospho-IRE1, XBP1, and ATF6 which were the key markers of ER stress were analyzed by immunohistochemistry assay in vivo. Additionally, the nuclear localization of XBP1s and ATF6n were analyzed by immunohistofluorescence. Furthermore, two representative neural cells, neuroblastoma cell line (SK-N-SH) and astrocytoma cell line (CCF-STTG1), were selected to verify the ER stress in vitro. The expression of BIP, phospho-elF2α, phospho-IRE1, and ATF6 were analyzed through western blot and the nuclear localization of XBP1s was performed by confocal immunofluorescence microscopy. RT-qPCR was also used to quantify the mRNA level of the UPR downstream genes in vitro and in vivo.

RESULTS

ZIKV infection significantly upregulated the expression of ER stress markers in vitro and in vivo. Phospho-IRE1 and XBP1 expression significantly increased in the cerebellum and mesocephalon, while ATF6 expression significantly increased in the mesocephalon. ATF6n and XBP1s were translocated into the cell nucleus. The levels of BIP, ATF6, phospho-elf2α, and spliced xbp1 also significantly increased in vitro. Furthermore, the downstream genes of UPR were detected to investigate the regulating model of the UPR during ZIKV infection in vitro and in vivo. The transcriptional levels of atf4, gadd34, chop, and edem-1 in vivo and that of gadd34 and chop in vitro significantly increased.

CONCLUSION

Findings in this study demonstrated that ZIKV infection activates ER stress in neural cells. The results offer clues to further study the mechanism of neuropathogenesis caused by ZIKV infection.

Aging Is Associated With Impaired Activation of Protein Homeostasis-Related Pathways After Cardiac Arrest in Mice

Background The mechanisms underlying worse outcome at advanced age after cardiac arrest ( CA ) and resuscitation are not well understood. Because protein homeostasis (proteostasis) is essential for cellular and organismal health, but is impaired after CA , we investigated the effects of age on proteostasis-related prosurvival pathways activated after CA . Methods and Results Young (2-3 months old) and aged (21-22 months old) male C57Bl/6 mice were subjected to CA and cardiopulmonary resuscitation ( CPR ). Functional outcome and organ damage were evaluated by assessing neurologic deficits, histological features, and creatinine level. CA / CPR -related changes in small ubiquitin-like modifier conjugation, ubiquitination, and the unfolded protein response were analyzed by measuring mRNA and protein levels in the brain, kidney, and spinal cord. Thiamet-G was used to increase O-linked β-N-acetylglucosamine modification. After CA / CPR , aged mice had trended lower survival rates, more severe tissue damage in the brain and kidney, and poorer recovery of neurologic function compared with young mice. Furthermore, small ubiquitin-like modifier conjugation, ubiquitination, unfolded protein response, and O-linked β-N-acetylglucosamine modification were activated after CA / CPR in young mice, but their activation was impaired in aged mice. Finally, pharmacologically increasing O-linked β-N-acetylglucosamine modification after CA improved outcome. Conclusions Results suggest that impaired activation of prosurvival pathways contributes to worse outcome after CA / CPR in aged mice because restoration of proteostasis is critical to the survival of cells stressed by ischemia. Therefore, a pharmacologic intervention that targets aging-related impairment of proteostasis-related pathways after CA / CPR may represent a promising therapeutic strategy.

Novel Modification of Potassium Chloride Induced Cardiac Arrest Model for Aged Mice

Experimental cardiac arrest (CA) in aging research is infrequently studied in part due to the limitation of animal models. We aimed to develop an easily performed mouse CA model to meet this need. A standard mouse KCl-induced CA model using chest compressions and intravenous epinephrine for resuscitation was modified by blood withdrawal prior to CA onset, so as to decrease the requisite KCl dose to induce CA by decreasing the circulating blood volume. The modification was then compared to the standard model in young adult mice subjected to 8 min CA. 22-month old mice were then subjected to 8 min CA, resuscitated, and compared to young adult mice. Post-CA functional recovery was evaluated by measuring spontaneous locomotor activity pre-injury, and on post-CA days 1, 2, and 3. Neurological score and brain histology were examined on day 3. Brain elF2α phosphorylation levels were measured at 1 h to verify tissue stress. Compared to the standard model, the modification decreased cardiopulmonary resuscitation duration and increased 3-day survival in young mice. For aged mice, survival was 100 % at 24 h and 54% at 72 h. Neurological deficit was present 3 days post-CA, although more severe versus young mice. Mild neuronal necrosis was present in the cortex and hippocampus. The modified model markedly induced elF2α phosphorylation in both age groups. This modified procedure makes the CA model feasible in aged mice and provides a practical platform for understanding injury mechanisms and developing therapeutics for elderly patients.

KCa3.1 Inhibition Switches the Astrocyte Phenotype during Astrogliosis Associated with Ischemic Stroke Via Endoplasmic Reticulum Stress and MAPK Signaling Pathways

Ischemic stroke is a devastating neurological disease that can initiate a phenotype switch in astrocytes. Reactive astrogliosis is a significant pathological feature of ischemic stroke and is accompanied by changes in gene expression, hypertrophied processes and proliferation. The intermediate-conductance Ca²⁺-activated potassium channel KCa3.1 has been shown to contribute to astrogliosis-induced neuroinflammation in Alzheimer’s disease (AD). We here present evidence, from both astrocytes subjected to oxygen–glucose deprivation (OGD) and from the brains of mice subjected to permanent middle cerebral artery occlusion (pMCAO), that KCa3.1 represents a valid pharmacological target for modulation of astrocyte phenotype during astrogliosis caused by ischemic stroke. In the primary cultured astrocytes, OGD led to increased expression of KCa3.1, which was associated with upregulation of the astrogliosis marker, glial fibrillary acidic protein (GFAP). Pharmacological blockade or genetic deletion of KCa3.1 suppressed OGD-induced up-regulation of GFAP, endoplasmic reticulum (ER) stress marker 78 kDa glucose-regulated protein (GRP78) and phosphorylated eIF-2α through the c-Jun/JNK and ERK1/2 signaling pathways. We next investigated the effect of genetic deletion of KCa3.1 in the pMCAO mouse model. KCa3.1 deficiency also attenuated ER stress and astrogliosis through c-Jun/JNK and ERK1/2 signaling pathways following pMCAO in KCa3.1^−/− mice. Our data suggest that blockade of KCa3.1 might represent a promising strategy for the treatment of ischemic stroke.

Is age a key factor contributing to the disparity between success of neuroprotective strategies in young animals and limited success in elderly stroke patients? Focus on protein homeostasis

Neuroprotection strategies to improve stroke outcome have been successful in the laboratory but not in clinical stroke trials, and thus have come under scrutiny by the medical community. Experimental stroke investigators are therefore under increased pressure to resolve this problem. Acute ischemic stroke represents a severe form of metabolic stress that activates many pathological processes and thereby impairs cellular functions. Traditionally, neuroprotection strategies were designed to improve stroke outcome by interfering with pathological processes triggered by ischemia. However, stroke outcome is also dependent on the brain's capacity to restore cellular functions impaired by ischemia, and this capacity declines with age. It is, therefore, conceivable that this age-dependent decline in the brain's self-healing capacity contributes to the disparity between the success of neuroprotective strategies in young animals, and limited success in elderly stroke patients. Here, prosurvival pathways that restore protein homeostasis impaired by ischemic stress should be considered, because their capacity decreases with increasing age, and maintenance of proteome fidelity is pivotal for cell survival. Boosting such prosurvival pathways pharmacologically to restore protein homeostasis and, thereby, cellular functions impaired by ischemic stress is expected to counterbalance the compromised self-healing capacity of aged brains and thereby help to improve stroke outcome.