Ischemic preconditioning mediates cyclooxygenase-2 expression via nuclear factor-kappa B activation in mixed cortical neuronal cultures

Chronic Traumatic Encephalopathy as the Course of Alzheimer's Disease

This editorial investigates chronic traumatic encephalopathy (CTE) as a course of Alzheimer's disease (AD). CTE is a debilitating neurodegenerative disease that is the result of repeated mild traumatic brain injury (TBI). Many epidemiological studies show that experiencing a TBI in early or middle life is associated with an increased risk of dementia later in life. Chronic traumatic encephalopathy (CTE) and Alzheimer's disease (AD) present a series of similar neuropathological features that were investigated in this work like recombinant tau into filaments or the accumulation and aggregation of Aβ protein. However, these two conditions differ from each other in brain-blood barrier damage. The purpose of this review was to evaluate information about CTE and AD from various articles, focusing especially on new therapeutic possibilities for the improvement in cognitive skills.

Research progress of mitophagy in chronic cerebral ischemia

Chronic cerebral ischemia (CCI), a condition that can result in headaches, dizziness, cognitive decline, and stroke, is caused by a sustained decrease in cerebral blood flow. Statistics show that 70% of patients with CCI are aged > 80 years and approximately 30% are 45-50 years. The incidence of CCI tends to be lower, and treatment for CCI is urgent. Studies have confirmed that CCI can activate the corresponding mechanisms that lead to mitochondrial dysfunction, which, in turn, can induce mitophagy to maintain mitochondrial homeostasis. Simultaneously, mitochondrial dysfunction can aggravate the insufficient energy supply to cells and various diseases caused by CCI. Regulation of mitophagy has become a promising therapeutic target for the treatment of CCI. This article reviews the latest progress in the important role of mitophagy in CCI and discusses the induction pathways of mitophagy in CCI, including ATP synthesis disorder, oxidative stress injury, induction of reactive oxygen species, and Ca2+ homeostasis disorder, as well as the role of drugs in CCI by regulating mitophagy.

Alcohol Dependence Modulates Amygdalar mTORC2 and PKCε Expression in a Rodent Model

Multiple alcohol use disorder (AUD)-related behavioral alterations are governed by protein kinase C epsilon (PKCε), particularly in the amygdala. Protein kinase C (PKC) is readily phosphorylated at Ser729 before activation by the mTORC2 protein complex. In keeping with this, the current study was conducted to assess the variations in mTORC2 and PKCε during different ethanol exposure stages. The following groups of rats were employed: control, acute, chronic, ethanol withdrawal (EW), and EW + ethanol (EtOH). Ethanol-containing and non-ethanol-containing modified liquid diets (MLDs) were administered for 27 days. On day 28, either saline or ethanol (2.5 g/kg, 20% v/v) was intraperitoneally administered, followed by bilateral amygdala extraction. PKCε mRNA levels were noticeably increased in the amygdala of the EW + EtOH and EW groups. Following chronic ethanol consumption, the stress-activated map kinase-interacting protein 1 (Sin1) gene expression was markedly decreased. In the EW, EW + EtOH, and chronic ethanol groups, there was a profound increase in the protein expression of mTOR, Sin1, PKCε, and phosphorylated PKCε (Ser729). The PKCε gene and protein expressions showed a statistically significant moderate association, according to a correlation analysis. Our results suggest that an elevated PKCε protein expression in the amygdala during EW and EW + EtOH occurred at the transcriptional level. However, an elevation in the PKCε protein expression, but not its mRNA, after chronic ethanol intake warrants further investigation to fully understand the signaling pathways during different episodes of AUD.

The p38 MAPK/NF-κB pathway mediates GLT-1 up-regulation during cerebral ischemic preconditioning-induced brain ischemic tolerance in rats

Our previous finding suggests that p38 MAPK contributes to the GLT-1 upregulation during induction of brain ischemic tolerance by cerebral ischemic preconditioning (CIP), however, the underlying mechanism is still unclear. Here, we investigated the molecular mechanisms underlying the CIP-induced GLT-1 upregulation by using Western blotting, Co-immunoprecipitation (Co-IP), electrophoretic mobility shift assay (EMSA) and thionin staining in rat hippocampus CA1 subset. We found that application of BAY11-7082 (an inhibitor of NF-κB), or dihydrokainate (an inhibitor of GLT-1), or SB203580 (an inhibitor of p38 MAPK) could attenuate the CIP-induced neuronal protection in hippocampus CA1 region of rats. Moreover, CIP caused rapid activation of NF-κB, as evidenced by nuclear translocation of NF-κB p50 protein, which led to active p50/p65 dimer formation and increased DNA binding activity. GLT-1 was also increased after CIP. Pretreatment with BAY11-7082 blocked the CIP-induced GLT-1 upregulation. The above results suggest that NF-κB participates in GLT-1 up-regulation during the induction of brain ischemic tolerance by CIP. We also found that pretreatment with SB203580 caused significant reduction of NF-κB p50 protein in nucleus, NF-κB p50/p65 dimer nuclear translocation and DNA binding activity of NF-κB. Together, we conclude that p38 MAPK/NF-κB pathway participates in the mediation of GLT-1 up-regulation during the induction of brain ischemic tolerance induced by CIP.

Neuroprotective effects and mechanisms of ischemic/hypoxic preconditioning on neurological diseases

As the organ with the highest demand for oxygen, the brain has a poor tolerance to ischemia and hypoxia. Despite severe ischemia/hypoxia induces the occurrence and development of various central nervous system (CNS) diseases, sublethal insult may induce strong protection against subsequent fatal injuries by improving tolerance. Searching for potential measures to improve brain ischemic/hypoxic is of great significance for treatment of ischemia/hypoxia related CNS diseases. Ischemic/hypoxic preconditioning (I/HPC) refers to the approach to give the body a short period of mild ischemic/hypoxic stimulus which can significantly improve the body's tolerance to subsequent more severe ischemia/hypoxia event. It has been extensively studied and been considered as an effective therapeutic strategy in CNS diseases. Its protective mechanisms involved multiple processes, such as activation of hypoxia signaling pathways, anti-inflammation, antioxidant stress, and autophagy induction, etc. As a strategy to induce endogenous neuroprotection, I/HPC has attracted extensive attention and become one of the research frontiers and hotspots in the field of neurotherapy. In this review, we discuss the basic and clinical research progress of I/HPC on CNS diseases, and summarize its mechanisms. Furthermore, we highlight the limitations and challenges of their translation from basic research to clinical application.

Stem Cell Therapy in Brain Ischemia: The Role of Mitochondrial Transfer

Mitochondrial dysfunction is an important pathological process in the setting of ischemic brain injury. Stem cell-mediated mitochondrial transfer provides an efficient intercellular process to supply additional mitochondria in the ischemic brain tissues. In this review, we summarize the mitochondrial pathology associated with brain ischemia, mechanisms of stem cell-mediated mitochondrial transfer, and in vitro/in vivo experimental findings of mitochondrial transfer from stem cells to ischemic vascular endothelial cells/neurons as potential therapeutic strategy in the management of ischemic brain injury.

Zinc causes the death of hypoxic astrocytes by inducing ROS production through mitochondria dysfunction

Cerebral ischemia triggers a cascade of events that contribute to ischemic brain damages. Zinc release and accumulation has been shown to lead to brain cell death following cerebral ischemia. However, the mechanism underlying remains to be elucidated. Our recently published work showed that suppression of mitochondrial-derived reactive oxygen species (ROS) production significantly reduced ischemic stroke related brain damage within 6 h. Herein, we investigated the relationship between zinc accumulation and mitochondrial-derived ROS production in astrocytes after 3-h hypoxia. We found that inhibition of mitochondrial-derived ROS significantly decreased total amount of ROS generation and cell death in primary astrocytes during hypoxia when zinc was overload. In contrast, the inhibition of NADPH oxidase-derived ROS had less of an effect. Our results also showed that zinc and mitochondria were colocalized in hypoxic astrocytes. Moreover, extracellular zinc addition caused zinc accumulation in the mitochondria and decreased mitochondrial membrane potential, leading to mitochondria dysfunction. These findings provide a novel mechanism that zinc accumulation contributes to hypoxia-induced astrocytes death by disrupting mitochondria function, following cerebral ischemia.

Preactivation of Notch1 in remote ischemic preconditioning reduces cerebral ischemia-reperfusion injury through crosstalk with the NF-κB pathway

Background

Remote ischemic preconditioning (RIPC) initiates endogenous protective pathways in the brain from a distance and represents a new, promising paradigm in neuroprotection against cerebral ischemia-reperfusion (I/R) injury. However, the underlying mechanism of RIPC-mediated cerebral ischemia tolerance is complicated and not well understood. We reported previously that preactivation of Notch1 mediated the neuroprotective effects of cerebral ischemic preconditioning in rats subjected to cerebral I/R injury. The present study seeks to further explore the role of crosstalk between the Notch1 and NF-κB signaling pathways in the process of RIPC-induced neuroprotection.

Methods

Middle cerebral artery occlusion and reperfusion (MCAO/R) in adult male rats and oxygen-glucose deprivation and reoxygenation (OGD/R) in primary hippocampal neurons were used as models of I/R injury in vivo and in vitro, respectively. RIPC was induced by a 3-day procedure with 4 cycles of 5 min of left hind limb ischemia followed by 5 min of reperfusion each day before MCAO/R. Intracerebroventricular DAPT injection and sh-Notch1 lentivirus interference were used to inhibit the Notch1 signaling pathway in vivo and in vitro, respectively. After 24 h of reperfusion, neurological deficit scores, infarct volume, neuronal apoptosis, and cell viability were assessed. The protein expression levels of NICD, Hes1, Phospho-IKKα/β (p-IKK α/β), Phospho-NF-κB p65 (p-NF-κB p65), Bcl-2, and Bax were assessed by Western blotting.

Results

RIPC significantly improved neurological scores and reduced infarct volume and neuronal apoptosis in rats subjected to I/R injury. OGD preconditioning significantly reduced neuronal apoptosis and improved cell viability after I/R injury on days 3 and 7 after OGD/R. However, the neuroprotective effect was reversed by DAPT in vivo and attenuated by Notch1-RNAi in vitro. RIPC significantly upregulated the expression of proteins related to the Notch1 and NF-κB pathways. NF-κB signaling pathway activity was suppressed by a Notch1 signaling pathway inhibitor and Notch1-RNAi.

Conclusions

The neuroprotective effect of RIPC against cerebral I/R injury was associated with preactivation of the Notch1 and NF-κB pathways in neurons. The NF-κB pathway is a downstream target of the Notch1 pathway in RIPC and helps protect focal cerebral I/R injury.

Ischemic Neuroprotectant PKCε Restores Mitochondrial Glutamate Oxaloacetate Transaminase in the Neuronal NADH Shuttle after Ischemic Injury

The preservation of mitochondrial function is a major protective strategy for cerebral ischemic injuries. Previously, our laboratory demonstrated that protein kinase C epsilon (PKCε) promotes the synthesis of mitochondrial nicotinamide adenine dinucleotide (NAD⁺). NAD⁺ along with its reducing equivalent, NADH, is an essential co-factor needed for energy production from glycolysis and oxidative phosphorylation. Yet, NAD⁺/NADH are impermeable to the inner mitochondrial membrane and their import into the mitochondria requires the activity of specific shuttles. The most important neuronal NAD⁺/NADH shuttle is the malate-aspartate shuttle (MAS). The MAS has been implicated in synaptic function and is potentially dysregulated during cerebral ischemia. The aim of this study was to determine if metabolic changes induced by PKCε preconditioning involved regulation of the MAS. Using primary neuronal cultures, we observed that the activation of PKCε enhanced mitochondrial respiration and glycolysis in vitro. Conversely, inhibition of the MAS resulted in decreased oxidative phosphorylation and glycolytic capacity. We further demonstrated that activation of PKCε increased the phosphorylation of key components of the MAS in rat brain synaptosomal fractions. Additionally, PKCε increased the enzyme activity of glutamic oxaloacetic transaminase 2 (GOT2), an effect that was dependent on the import of PKCε into the mitochondria and phosphorylation of GOT2. Furthermore, PKCε activation was able to rescue decreased GOT2 activity induced by ischemia. These findings reveal novel protective targets and mechanisms against ischemic injury, which involves PKCε-mediated phosphorylation and activation of GOT2 in the MAS.

Estrogen preconditioning: A promising strategy to reduce inflammation in the ischemic brain

During the premenopausal phase of a woman's life, estrogen naturally protects against ischemic brain damage and its debilitating consequence of cognitive decline. However, the decline in estrogen at menopause exponentially increases a women's risk for cerebral ischemia and its severity. Supplementation of estrogen during menopause is the most logical solution to abate this increased risk for cerebral ischemia; however, continuous therapy has proven to be contraindicative. Studies from our laboratory over the past decade have shown that a single bolus or long-term periodic 17β-estradiol treatment(s) two days prior to ischemia mimics ischemic preconditioning-conferred protection of the brain in ovariectomized or reproductively senescent female rats. These studies also demonstrated that 17β-estradiol-induced preconditioning (EPC) requires estrogen receptor (ER)-subtype beta (ER-β) activation. ER-β is expressed throughout the brain, including in the hippocampus, which plays a key role in learning and memory. Because periodic activation of ER-β mitigates post-ischemic cognitive decline in ovariectomized female rats, it can be surmised that EPC has the potential to reduce post-ischemic damage and cognitive decline in females. Estrogens are key anti-inflammatory agents; therefore this review discusses the effects of EPC on the inflammasome. Furthermore, as we now clearly know, the brain acts differently in males and females. Indeed, neurodegenerative diseases, including cerebral ischemia, and pharmacological drugs affect males and females in different ways. Thus, inasmuch as the National Institutes of Health and the Stroke Treatment Academic Industry Roundtable (STAIR) consortium mandate inclusion of female experimental animals, this review also discusses the need to close the gap in our knowledge in future studies of EPC in female animal models of cerebral ischemia.

Silencing of PTGS2 exerts promoting effects on angiogenesis endothelial progenitor cells in mice with ischemic stroke via repression of the NF-κB signaling pathway

The objective of the current study is to investigate the effect of PTGS2 on proliferation, migration, angiogenesis and apoptosis of endothelial progenitor cells (EPCs) in mice with ischemic stroke through the NF-κB signaling pathway. Middle cerebral artery occlusion (MCAO) model was established in mice. EPCs were identified, in which ectopic expression and depletion experiments were conducted. The mRNA and protein expression of related factors in tissues and cells were measured. Besides, proliferation, migration, angiogenesis, and apoptosis, as well as cell cycle distribution, of cells were determined. MCAO mice showed overexpression of interleukin-6 (IL-6), IL-17, and IL-23, and increased positive protein expression of PTGS2, as well as expression of PTGS2, nuclear factor-κB (NF-κB), tumor suppressor region 1 (TSP-1) and Bcl-2-associated X protein (Bax), but underexpression of vascular endothelial growth factor (VEGF), S-phase kinase associated protein 2 (Skp2), and B-cell lymphoma 2 (Bcl-2). Moreover, ectopic expression of tumor necrosis factor-α significantly elevated the expression of PTGS2, NF-κB, TSP-1, and Bax, as well as cell apoptosis and cell cycle arrest, but decreased the expression of VEGF, Skp2, and Bcl-2, as well as proliferation, migration and angiogenesis of EPCs, and the PTGS2-siRNA group showed an opposite trend. Taken together, we conclude that the specific knockdown of PTGS2 expression could repress the NF-κB signaling pathway, thereby inhibits apoptosis and promotes proliferation, migration and angiogenesis of EPCs, providing protective effect on mice with ischemic stroke.

Mitochondrial Dysfunction in Neural Injury

Mitochondria are the double membrane organelles providing most of the energy for cells. In addition, mitochondria also play essential roles in various cellular biological processes such as calcium signaling, apoptosis, ROS generation, cell growth, and cell cycle. Mitochondrial dysfunction is observed in various neurological disorders which harbor acute and chronic neural injury such as neurodegenerative diseases and ischemia, hypoxia-induced brain injury. In this review, we describe how mitochondrial dysfunction contributes to the pathogenesis of neurological disorders which manifest chronic or acute neural injury.

Ischemic Preconditioning Protects Astrocytes against Oxygen Glucose Deprivation Via the Nuclear Erythroid 2-Related Factor 2 Pathway

Induction of ischemic preconditioning (IPC) represents a potential therapy against cerebral ischemia by activation of adaptive pathways and modulation of mitochondria to induce ischemic tolerance to various cells and tissues. Mitochondrial dysfunction has been ascribed to contribute to numerous neurodegenerative conditions and cerebral ischemia. Nuclear erythroid 2-related factor 2 (Nrf2) is a transcription factor that has traditionally been involved in upregulating cellular antioxidant systems to combat oxidative stress in the brain; however, the association of Nrf2 with mitochondria in the brain remains unclear. In the present study, we investigated the effects of Nrf2 on (i) IPC-induced protection of astrocytes; (ii) OXPHOS protein expression; and (iii) mitochondrial supercomplex formation.Oxygen-glucose deprivation (OGD) was used as an in vitro model of cerebral ischemia and IPC in cultured rodent astrocytes derived from WT C57Bl/6J and Nrf2-/- mice. OXPHOS proteins were probed via western blotting, and supercomplexes were determined by blue native gel electrophoresis.IPC-induced cytoprotection in wild-type, but not Nrf2-/- mouse astrocyte cultures following a lethal duration of OGD. In addition, our results suggest that Nrf2 localizes to the outer membrane in non-synaptic brain mitochondria, and that a lack of Nrf2 in vivo produces altered supercomplex formation in mitochondria.Our findings support a role of Nrf2 in mediating IPC-induced protection in astrocytes, which can profoundly impact the ischemic tolerance of neurons. In addition, we provide novel evidence for the association of Nrf2 to brain mitochondria and supercomplex formation. These studies offer new targets and pathways of Nrf2, which may be heavily implicated following cerebral ischemia.

Ischemic preconditioning treatment of astrocytes transfers ischemic tolerance to neurons

Ischemic preconditioning (IPC) represents a potential therapy against cerebral ischemia. While our group has previously shown IPC to induce neuroprotection through various pathways, the role of astrocytes in supporting IPC-induced neuroprotection has not been extensively studied. Astrocyte-derived lactate has gained attention as a potential soluble mediator through which astrocytes could impart ischemic tolerance to neurons. Therefore, the goal of this study was to determine if i) IPC-treatment of astrocytes alone could transfer ischemic tolerance to neurons; ii) if IPC-treatment of astrocytes increases lactate production; and if iii) exogenous lactate administration to neurons could induce neuroprotection against lethal ischemia in vitro. For this purpose, a co-culture system was used and modified from a previous method. This system allows astrocytes and neurons to be separated by a physical barrier, while allowing secreted substances from either cell type to interact with each other. Oxygen-glucose deprivation was used as a model of cerebral ischemia and IPC in cultured rodent astrocytes and neurons. Neurons incubated with IPC-treated astrocytes were significantly protected against lethal ischemic injury compared to neurons incubated with sham-treated astrocytes. In addition, IPC-treatment of astrocytes significantly increased lactate secretion into the extracellular media. Finally, exogenous lactate administration can significantly attenuate cell death in neuronal cultures following exposure to lethal OGD. Our results suggest that IPC-treatment of astrocytes alone can transfer ischemic tolerance to neurons. In addition, the ability of IPC to increase lactate production in astrocytes suggest that lactate could represent a neuroprotective agent to protect neurons against lethal ischemic injury.

(-)-Phenserine inhibits neuronal apoptosis following ischemia/reperfusion injury

Stroke commonly leads to adult disability and death worldwide. Its major symptoms are spastic hemiplegia and discordant motion, consequent to neuronal cell death induced by brain vessel occlusion. Acetylcholinesterase (AChE) is upregulated and allied with inflammation and apoptosis after stroke. Recent studies suggest that AChE inhibition ameliorates ischemia-reperfusion injury and has neuroprotective properties. (-)-Phenserine, a reversible AChE inhibitor, has a broad range of actions independent of its AChE properties, including neuroprotective ones. However, its protective effects and detailed mechanism of action in the rat middle cerebral artery occlusion model (MCAO) remain to be elucidated. This study investigated the therapeutic effects of (-)-phenserine for stroke in the rat focal cerebral ischemia model and oxygen-glucose deprivation/reperfusion (OGD/RP) damage model in SH-SY5Y neuronal cultures. (-)-Phenserine mitigated OGD/PR-induced SH-SY5Y cell death, providing an inverted U-shaped dose-response relationship between concentration and survival. In MCAO challenged rats, (-)-phenserine reduced infarction volume, cell death and improved body asymmetry, a behavioral measure of stoke impact. In both cellular and animal studies, (-)-phenserine elevated brain-derived neurotrophic factor (BDNF) and B-cell lymphoma 2 (Bcl-2) levels, and decreased activated-caspase 3, amyloid precursor protein (APP) and glial fibrillary acidic protein (GFAP) expression, potentially mediated through the ERK-1/2 signaling pathway. These actions mitigated neuronal apoptosis in the stroke penumbra, and decreased matrix metallopeptidase-9 (MMP-9) expression. In synopsis, (-)-phenserine significantly reduced neuronal damage induced by ischemia/reperfusion injury in a rat model of MCAO and cellular model of OGD/RP, demonstrating that its anti-apoptotic/neuroprotective/neurotrophic cholinergic and non-cholinergic properties warrant further evaluation in conditions of brain injury.

Vinpocetine Inhibits NF-κB-Dependent Inflammation in Acute Ischemic Stroke Patients

Immunity and inflammation play critical roles in the pathogenesis of acute ischemic stroke. Therefore, immune intervention, as a new therapeutic strategy, is worthy of exploration. Here, we tested the inflammation modulator, vinpocetine, for its effect on the outcomes of stroke. For this multi-center study, we recruited 60 patients with anterior cerebral circulation occlusion and onset of stroke that had exceeded 4.5 h but lasted less than 48 h. These patients, after random division into two groups, received either standard management alone (controls) or standard management plus vinpocetine (30 mg per day intravenously for 14 consecutive days, Gedeon Richter Plc., Hungary). Vinpocetine treatment did not change the lymphocyte count; however, nuclear factor kappa-light-chain-enhancer of activated B cell activation was inhibited as seen not only by the increased transcription of IκBα mRNA but also by the impeded phosphorylation and degradation of IκBα and subsequent induction of pro-inflammatory mediators. These effects led to significantly reduced secondary lesion enlargement and an attenuated inflammation reaction. Compared to controls, patients treated with vinpocetine had a better recovery of neurological function and improved clinical outcomes during the acute phase and at 3-month follow-up. These findings identify vinpocetine as an inflammation modulator that could improve clinical outcomes after acute ischemic stroke. This study also indicated the important role of immunity and inflammation in the pathogenesis of acute ischemic stroke and the significance of immunomodulatory treatment.

CLINICAL TRIAL REGISTRATION INFORMATION

www.clinicaltrials.gov . Identifier: NCT02878772.

Neuronal Gene Targets of NF-κB and Their Dysregulation in Alzheimer's Disease

Although, better known for its role in inflammation, the transcription factor nuclear factor kappa B (NF-κB) has more recently been implicated in synaptic plasticity, learning, and memory. This has been, in part, to the discovery of its localization not just in glia, cells that are integral to mediating the inflammatory process in the brain, but also neurons. Several effectors of neuronal NF-κB have been identified, including calcium, inflammatory cytokines (i.e., tumor necrosis factor alpha), and the induction of experimental paradigms thought to reflect learning and memory at the cellular level (i.e., long-term potentiation). NF-κB is also activated after learning and memory formation in vivo. In turn, activation of NF-κB can elicit either suppression or activation of other genes. Studies are only beginning to elucidate the multitude of neuronal gene targets of NF-κB in the normal brain, but research to date has confirmed targets involved in a wide array of cellular processes, including cell signaling and growth, neurotransmission, redox signaling, and gene regulation. Further, several lines of research confirm dysregulation of NF-κB in Alzheimer's disease (AD), a disorder characterized clinically by a profound deficit in the ability to form new memories. AD-related neuropathology includes the characteristic amyloid beta plaque formation and neurofibrillary tangles. Although, such neuropathological findings have been hypothesized to contribute to memory deficits in AD, research has identified perturbations at the cellular and synaptic level that occur even prior to more gross pathologies, including transcriptional dysregulation. Indeed, synaptic disturbances appear to be a significant correlate of cognitive deficits in AD. Given the more recently identified role for NF-κB in memory and synaptic transmission in the normal brain, the expansive network of gene targets of NF-κB, and its dysregulation in AD, a thorough understanding of NF-κB-related signaling in AD is warranted and may have important implications for uncovering treatments for the disease. This review aims to provide a comprehensive view of our current understanding of the gene targets of this transcription factor in neurons in the intact brain and provide an overview of studies investigating NF-κB signaling, including its downstream targets, in the AD brain as a means of uncovering the basic physiological mechanisms by which memory becomes fragile in the disease.

ZNT-1 Expression Reduction Enhances Free Zinc Accumulation in Astrocytes After Ischemic Stroke

Excess intracellular zinc has been implicated in ischemic brain cell death. We previously reported that extracellular zinc increases intracellular free zinc level only in hypoxic astrocytes but not in normoxia astrocytes. However, the underlying mechanisms remain to be elucidated. Zinc transporters ZnTs and ZIPs mediate intracellular zinc efflux and extracellular zinc influx. In the present study, we determined the effect of hypoxia/reoxygenation on ZnT-1 and ZIP-1. Hypoxia/reoxygenation did not change the ZIP-1 level in astrocytes. Remarkably, hypoxia/reoxygenation dramatically decreased ZnT-1 expression, which can be difficult to reverse by the addition of extracellular zinc, although extracellular zinc treatment significantly increased ZnT-1 level at normoxia. These results suggest that hypoxia/reoxygenation blocked zinc efflux, whereas zinc influx may be at a similar level to that in normoxia, providing a novel mechanism for intracellular free zinc accumulation after ischemic stroke.

Rational modulation of the innate immune system for neuroprotection in ischemic stroke

The innate immune system plays a dualistic role in the evolution of ischemic brain damage and has also been implicated in ischemic tolerance produced by different conditioning stimuli. Early after ischemia, perivascular astrocytes release cytokines and activate metalloproteases (MMPs) that contribute to blood–brain barrier (BBB) disruption and vasogenic oedema; whereas at later stages, they provide extracellular glutamate uptake, BBB regeneration and neurotrophic factors release. Similarly, early activation of microglia contributes to ischemic brain injury via the production of inflammatory cytokines, including tumor necrosis factor (TNF) and interleukin (IL)-1, reactive oxygen and nitrogen species and proteases. Nevertheless, microglia also contributes to the resolution of inflammation, by releasing IL-10 and tumor growth factor (TGF)-β, and to the late reparative processes by phagocytic activity and growth factors production. Indeed, after ischemia, microglia/macrophages differentiate toward several phenotypes: the M1 pro-inflammatory phenotype is classically activated via toll-like receptors or interferon-γ, whereas M2 phenotypes are alternatively activated by regulatory mediators, such as ILs 4, 10, 13, or TGF-β. Thus, immune cells exert a dualistic role on the evolution of ischemic brain damage, since the classic phenotypes promote injury, whereas alternatively activated M2 macrophages or N2 neutrophils prompt tissue remodeling and repair. Moreover, a subdued activation of the immune system has been involved in ischemic tolerance, since different preconditioning stimuli act via modulation of inflammatory mediators, including toll-like receptors and cytokine signaling pathways. This further underscores that the immuno-modulatory approach for the treatment of ischemic stroke should be aimed at blocking the detrimental effects, while promoting the beneficial responses of the immune reaction.

Ischemia preconditioning protects astrocytes from ischemic injury through 14-3-3γ

Stroke is a leading cause of death and disability, and new strategies are required to reduce neuronal injury and improve prognosis. Ischemia preconditioning (IPC) is an intrinsic phenomenon that protects cells from subsequent ischemic injury and might provide promising mechanisms for clinical treatment. In this study, primary astrocytes exhibited significantly less cell death than control when exposed to different durations of IPC (15, 30, 60, or 120 min). A 15-min duration was the most effective IPC to protect astrocytes from 8-hr-ischemia injury. The protective mechanisms of IPC involve the upregulation of protective proteins, including 14-3-3γ, and attenuation of malondialdehyde (MDA) content and ATP depletion. 14-3-3γ is an antiapoptotic intracellular protein that was significantly upregulated for up to 84 hr after IPC. In addition, IPC promoted activation of the c-Jun N-terminal kinase (JNK), extracellular signal-related kinase (ERK)-1/2, p38, and protein kinase B (Akt) signaling pathways. When JNK was specifically inhibited with SP600125, the upregulation of 14-3-3γ induced by IPC was almost completely abolished; however, there was no effect on ATP or MDA levels. This suggests that, even though both energy preservation and 14-3-3γ up-regulation were turned on by IPC, they were controlled by different pathways. The ERK1/2, p38, and Akt signaling pathways were not involved in the 14-3-3γ upregulation and energy preservation. These results indicate that IPC could protect astrocytes from ischemia injury by inducing 14-3-3γ and by alleviating energy depletion through different pathways, suggesting multiple protection of IPC and providing new insights into potential stroke therapies.

Oxidative Stress and the Use of Antioxidants in Stroke

Transient or permanent interruption of cerebral blood flow by occlusion of a cerebral artery gives rise to an ischaemic stroke leading to irreversible damage or dysfunction to the cells within the affected tissue along with permanent or reversible neurological deficit. Extensive research has identified excitotoxicity, oxidative stress, inflammation and cell death as key contributory pathways underlying lesion progression. The cornerstone of treatment for acute ischaemic stroke remains reperfusion therapy with recombinant tissue plasminogen activator (rt-PA). The downstream sequelae of events resulting from spontaneous or pharmacological reperfusion lead to an imbalance in the production of harmful reactive oxygen species (ROS) over endogenous anti-oxidant protection strategies. As such, anti-oxidant therapy has long been investigated as a means to reduce the extent of injury resulting from ischaemic stroke with varying degrees of success. Here we discuss the production and source of these ROS and the various strategies employed to modulate levels. These strategies broadly attempt to inhibit ROS production or increase scavenging or degradation of ROS. While early clinical studies have failed to translate success from bench to bedside, the combination of anti-oxidants with existing thrombolytics or novel neuroprotectants may represent an avenue worthy of clinical investigation. Clearly, there is a pressing need to identify new therapeutic alternatives for the vast majority of patients who are not eligible to receive rt-PA for this debilitating and devastating disease.

Protection of ischemic postconditioning against neuronal apoptosis induced by transient focal ischemia is associated with attenuation of NF-κB/p65 activation

Background and Purpose

Accumulating evidences have demonstrated that nuclear factor κB/p65 plays a protective role in the protection of ischemic preconditioning and detrimental role in lethal ischemia-induced programmed cell death including apoptosis and autophagic death. However, its role in the protection of ischemic postconditioning is still unclear.

Methods

Rat MCAO model was used to produce transient focal ischemia. The procedure of ischemic postconditioning consisted of three cycles of 30 seconds reperfusion/reocclusion of MCA. The volume of cerebral infarction was measured by TTC staining and neuronal apoptosis was detected by TUNEL staining. Western blotting was used to analyze the changes in protein levels of Caspase-3, NF-κB/p65, phosphor- NF-κB/p65, IκBα, phosphor- IκBα, Noxa, Bim and Bax between rats treated with and without ischemic postconditioning. Laser scanning confocal microscopy was used to examine the distribution of NF-κB/p65 and Noxa.

Results

Ischemic postconditioning made transient focal ischemia-induced infarct volume decrease obviously from 38.6%±5.8% to 23.5%±4.3%, and apoptosis rate reduce significantly from 46.5%±6.2 to 29.6%±5.3% at reperfusion 24 h following 2 h focal cerebral ischemia. Western blotting analysis showed that ischemic postconditioning suppressed markedly the reduction of NF-κB/p65 in cytoplasm, but elevated its content in nucleus either at reperfusion 6 h or 24 h. Moreover, the decrease of IκBα and the increase of phosphorylated IκBα and phosphorylated NF-κB/p65 at indicated reperfusion time were reversed by ischemic postconditioning. Correspondingly, proapoptotic proteins Caspase-3, cleaved Caspase-3, Noxa, Bim and Bax were all mitigated significantly by ischemic postconditioning. Confocal microscopy revealed that ischemic postconditioning not only attenuated ischemia-induced translocation of NF-κB/p65 from neuronal cytoplasm to nucleus, but also inhibited the abnormal expression of proapoptotic protein Noxa within neurons.

Conclusions

We demonstrated in this study that the protection of ischemic postconditioning on neuronal apoptosis caused by transient focal ischemia is associated with attenuation of the activation of NF-κB/p65 in neurons.

Non-pharmaceutical therapies for stroke: mechanisms and clinical implications

Stroke is deemed a worldwide leading cause of neurological disability and death, however, there is currently no promising pharmacotherapy for acute ischemic stroke aside from intravenous or intra-arterial thrombolysis. Yet because of the narrow therapeutic time window involved, thrombolytic application is very restricted in clinical settings. Accumulating data suggest that non-pharmaceutical therapies for stroke might provide new opportunities for stroke treatment. Here we review recent research progress in the mechanisms and clinical implications of non-pharmaceutical therapies, mainly including neuroprotective approaches such as hypothermia, ischemic/hypoxic conditioning, acupuncture, medical gases and transcranial laser therapy. In addition, we briefly summarize mechanical endovascular recanalization devices and recovery devices for the treatment of the chronic phase of stroke and discuss the relative merits of these devices.

Sunitinib enhances neuronal survival in vitro via NF-κB-mediated signaling and expression of cyclooxygenase-2 and inducible nitric oxide synthase

BACKGROUND

Angiogenesis is tightly linked to inflammation and cancer. Regulation of angiogenesis is mediated primarily through activation of receptor tyrosine kinases, thus kinase inhibitors represent a new paradigm in anti-cancer therapy. However, these inhibitors have broad effects on inflammatory processes and multiple cell types. Sunitinib is a multitarget receptor tyrosine kinase inhibitor, which has shown promise for the treatment of glioblastoma, a highly vascularized tumor. However, there is little information as to the direct effects of sunitinib on brain-derived neurons. The objective of this study is to explore the effects of sunitinib on neuronal survival as well as on the expression of inflammatory protein mediators in primary cerebral neuronal cultures.

METHODS

Primary cortical neurons were exposed to various doses of sunitinib. The drug-treated cultures were assessed for survival by MTT assay and cell death by lactate dehydrogenase release. The ability of sunitinib to affect NF-κB, COX2 and NOS2 expression was determined by western blot. The NF-κB inhibitors dicoumarol, SN50 and BAY11-7085 were employed to assess the role of NF-κB in sunitinib-mediated effects on neuronal survival as well as COX2 and NOS2 expression.

RESULTS

Treatment of neuronal cultures with sunitinib caused a dose-dependent increase in cell survival and decrease in neuronal cell death. Exposure of neurons to sunitinib also induced an increase in the expression of NF-κB, COX2 and NOS2. Inhibiting NF-κB blunted the increase in cell survival and decrease in cell death evoked by sunitinib. Treatment of cell cultures with both sunitinib and NF-κB inhibitors mitigated the increase in COX2 and NOS2 caused by sunitinib.

CONCLUSIONS

Sunitinib increases neuronal survival and this neurotrophic effect is mediated by NF-κB. Also, the inflammatory proteins COX2 and NOS2 are upregulated by sunitinib in an NF-κB-dependent manner. These data are in agreement with a growing literature suggesting beneficial effects for inflammatory mediators such as NF-κB, COX2 and NOS2 in neurons. Further work is needed to fully explore the effects of sunitinib in the brain and its possible use as a treatment for glioblastoma. Finally, sunitinib may be useful for the treatment of a range of central nervous system diseases where neuronal injury is prominent.

Apobec-1 increases cyclooxygenase-2 and aggravates injury in oxygen-deprived neurogenic cells and middle cerebral artery occlusion rats

Given that cyclooxygenase-2 (COX-2) plays a crucial role during cerebral ischemia and Apobec-1 is a critical regulator of COX-2 mRNA stabilization in gastrointestinal settings, the correlation of COX-2 and Apobec-1 was investigated in neurogenic cells and rat model of cerebral ischemia. After neurogenic SH-SY5Y, NG108-15 and PC12 cells were exposed to oxygen-glucose deprivation, cell viability, LDH leakage and Apobec-1 expression were determined. The effect of Apobec-1 overexpression on injury severity of oxygen-glucose deprivation, COX-2 expression, C-to-U editing of COX-2 mRNA were measured in vitro. Then the correlation of Apobec-1 level and injury severity was analyzed in cells with oxygen-glucose deprivation and in rats with middle cerebral artery occlusion. Apobec-1 expression was elevated along with upregulation of COX-2 and injury severity of oxygen-glucose deprivation in the three cell lines. Apobec-1 overexpression aggravated injury of oxygen-glucose deprivation in vitro and could be correlated to injury severity in vivo. Meanwhile, Apobec-1 increased COX-2 expression and COX-2 mRNA stabilization in neurogenic cells, and failed to catalyze C-to-U editing of COX-2 mRNA. Apobec-1 could upregulate COX-2 expression in neurogenic cells by stabilizing COX-2 mRNA, and might aggravate injury of oxygen-glucose deprivation in neurogenic cells as well as in rats with cerebral ischemia.

Ischemic preconditioning and clinical scenarios

PURPOSE OF REVIEW

Ischemic preconditioning (IPC) is gaining attention as a novel neuroprotective therapy and could provide an improved mechanistic understanding of tolerance to cerebral ischemia. The purpose of this article is to review the recent work in the field of IPC and its applications to clinical scenarios.

RECENT FINDINGS

The cellular signaling pathways that are activated following IPC are now better understood and have enabled investigators to identify several IPC mimetics. Most of these studies were performed in rodents, and efficacy of these mimetics remains to be evaluated in human patients. Additionally, remote ischemic preconditioning (RIPC) may have higher translational value than IPC. Repeated cycles of temporary ischemia in a remote organ can activate protective pathways in the target organ, including the heart and brain. Clinical trials are underway to test the efficacy of RIPC in protecting brain against subarachnoid hemorrhage.

SUMMARY

IPC, RIPC, and IPC mimetics have the potential to be therapeutic in various clinical scenarios. Further understanding of IPC-induced neuroprotection pathways and utilization of clinically relevant animal models are necessary to increase the translational potential of IPC in the near future.

JAK-STAT pathway modulates the roles of iNOS and COX-2 in the cytoprotection of early phase of hydrogen peroxide preconditioning against apoptosis induced by oxidative stress

Our previous studies have demonstrated that preconditioning with hydrogen peroxide (H(2)O(2)) activated the JAK-STAT pathway that played an important role in the cytoprotection, and inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) mediated the late phase of cytoprotection induced by high concentration of H(2)O(2) after preconditioning. Here we sought to identify the downstream targets of the JAK-STAT axis that mediated H(2)O(2) preconditioning and the expression of iNOS and COX-2 in the early phase of H(2)O(2) preconditioning. It was shown that (1) Preconditioning with H(2)O(2) at 100 μmol/L for 90 min in PC12 cells induced significant expression of iNOS and COX-2. (2) Pretreatment with the iNOS inhibitor AG (10 μmol/L) or the COX-2 inhibitor NS-398 (10 μmol/L) respectively 20min before H(2)O(2) preconditioning not only inhibits the increased expression of iNOS or COX-2 but also abrogates the protective effects of H(2)O(2) preconditioning against apoptosis induced by oxidative stress. (3) Pretreatment with the JAK inhibitor AG-490 (10 μmol/L) 20 min before H(2)O(2) preconditioning obviously inhibits the up-regulation of iNOS or COX-2 induced by H(2)O(2) preconditioning. These results suggested that JAK-STAT pathway modulates the roles of iNOS and COX-2 in the cytoprotection of early phase of H(2)O(2) preconditioning.

Phosphorylated mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 may not always represent its kinase activity in a rat model of focal cerebral ischemia with or without ischemic preconditioning

The extracellular signal-regulated kinase (ERK) 1/2 protein requires a dual phosphorylation at conserved threonine and tyrosine residues to be fully activated under normal physiological conditions. Thus, ERK1/2 kinase activity is often defined by the quantity of phosphorylated kinase. However, this may not accurately represent its true activity under certain pathological conditions. We investigated whether ERK1/2 kinase activity is proportional to its phosphorylation state in a rat focal ischemia model with and without rapid ischemic preconditioning. We showed that phosphorylated-ERK1/2 protein levels were increased 2.6±0.07-fold, and ERK1/2 kinase activity was increased 10.6±1.9-fold in animals receiving ischemic preconditioning alone without test ischemia compared with sham group (P<0.05, n=6/group), suggesting that phosphorylated-ERK1/2 protein levels represent its kinase activity under these conditions. However, preconditioning plus test ischemia robustly blocked ERK1/2 kinase activity, whereas it increased phosphorylated-ERK1/2 protein levels beyond those receiving test ischemia alone, suggesting that phosphorylated-ERK1/2 protein levels were not representative of actual kinase activity in this pathological condition. In conclusion, protein phosphorylation levels of ERK1/2 do not always correspond to kinase activity, thus, measuring the true kinase activity is essential.

Signal transducers and activators of transcription: STATs-mediated mitochondrial neuroprotection

Cerebral ischemia is defined as little or no blood flow in cerebral circulation, characterized by low tissue oxygen and glucose levels, which promotes neuronal mitochondria dysfunction leading to cell death. A strategy to counteract cerebral ischemia-induced neuronal cell death is ischemic preconditioning (IPC). IPC results in neuroprotection, which is conferred by a mild ischemic challenge prior to a normally lethal ischemic insult. Although many IPC-induced mechanisms have been described, many cellular and subcellular mechanisms remain undefined. Some reports have suggested key signal transduction pathways of IPC, such as activation of protein kinase C epsilon, mitogen-activated protein kinase, and hypoxia-inducible factors, that are likely involved in IPC-induced mitochondria mediated-neuroprotection. Moreover, recent findings suggest that signal transducers and activators of transcription (STATs), a family of transcription factors involved in many cellular activities, may be intimately involved in IPC-induced ischemic tolerance. In this review, we explore current signal transduction pathways involved in IPC-induced mitochondria mediated-neuroprotection, STAT activation in the mitochondria as it relates to IPC, and functional significance of STATs in cerebral ischemia.

Pathways for ischemic cytoprotection: role of sirtuins in caloric restriction, resveratrol, and ischemic preconditioning

Caloric restriction (CR), resveratrol, and ischemic preconditioning (IPC) have been shown to promote protection against ischemic injury in the heart and brain, as well as in other tissues. The activity of sirtuins, which are enzymes that modulate diverse biologic processes, seems to be vital in the ability of these therapeutic modalities to prevent against cellular dysfunction and death. The protective mechanisms of the yeast Sir2 and the mammalian homolog sirtuin 1 have been extensively studied, but the involvement of other sirtuins in ischemic protection is not yet clear. We examine the roles of mammalian sirtuins in modulating protective pathways against oxidative stress, energy depletion, excitotoxicity, inflammation, DNA damage, and apoptosis. Although many of these sirtuins have not been directly implicated in ischemic protection, they may have unique roles in enhancing function and preventing against stress-mediated cellular damage and death. This review will include in-depth analyses of the roles of CR, resveratrol, and IPC in activating sirtuins and in mediating protection against ischemic damage in the heart and brain.