A forebrain ischemic preconditioning model established in C57Black/Crj6 mice

Discovery of novel tryptamine derivatives as GluN2B subunit-containing NMDA receptor antagonists via pharmacophore-merging strategy with orally available therapeutic effect of cerebral ischemia

A series of tryptamine derivatives has been designed and synthesized as novel GluN2B subunit-containing NMDA receptor (GluN2B-NMDAR) antagonists, which could simultaneously manifest the receptor-ligand interactions of representative GluN2B-NMDAR antagonists ifenprodil (1) and EVT-101 (3). In the present study, the neuroprotective potential of these compounds was explored through chemical synthesis and pharmacological characterization. Compound Z25 with significantly better neuroprotective activity than the positive control drug (percentage of protection: 55.8 ± 0.6% vs. 41.0 ± 2.7%) was considered to be an effective antagonist of the human GluN2B-NMDA receptor. Judging from in vitro pharmacological profiling, Z25 could downregulate NMDA-induced increased intracellular Ca²⁺ concentration, and Z25 could also upregulate NMDA-induced decreased intracellular p-ERK 1/2 expression, which suggested that Z25 is an antagonist of the GluN2B-NMDA receptor. Furthermore, the in vitro preliminary evaluation of the drug-like properties of compound Z25 showed remarkable plasma stability. Based on in vivo pharmacokinetic and pharmacodynamic studies in C57 mice, compound Z25 exhibited a relatively short half-life and a low F value (3.12 ± 0.01%), while administration of Z25 substantially improved the cognitive performance of mice in a series of tests of cerebral ischemic injury. Overall, these results support the further development of compound Z25 as a potential lead compound to treat the cerebral ischemic injury by antagonizing GluN2B-NMDA receptor.

Neuronal Pentraxin 1 Promotes Hypoxic-Ischemic Neuronal Injury by Impairing Mitochondrial Biogenesis via Interactions With Active Bax[6A7] and Mitochondrial Hexokinase II

Mitochondrial dysfunction is a key mechanism of cell death in hypoxic-ischemic brain injury. Neuronal pentraxin 1 (NP1) has been shown to play crucial roles in mitochondria-mediated neuronal death. However, the underlying mechanism(s) of NP1-induced mitochondrial dysfunction in hypoxia-ischemia (HI) remains obscure. Here, we report that NP1 induction following HI and its subsequent localization to mitochondria, leads to disruption of key regulatory proteins for mitochondrial biogenesis. Brain mitochondrial DNA (mtDNA) content and mtDNA-encoded subunit I of complex IV (mtCOX-1) expression was increased post-HI, but not the nuclear DNA-encoded subunit of complex II (nSDH-A). Up-regulation of mitochondrial proteins COXIV and HSP60 further supported enhanced mtDNA function. NP1 interaction with active Bax (Bax6A7) was increased in the brain after HI and in oxygen-glucose deprivation (OGD)-induced neuronal cultures. Importantly, NP1 colocalized with mitochondrial hexokinase II (mtHKII) following OGD leading to HKII dissociation from mitochondria. Knockdown of NP1 or SB216763, a GSK-3 inhibitor, prevented OGD-induced mtHKII dissociation and cellular ATP decrease. NP1 also modulated the expression of mitochondrial transcription factor A (Tfam) and peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), regulators of mitochondrial biogenesis, following HI. Together, we reveal crucial roles of NP1 in mitochondrial biogenesis involving interactions with Bax[6A7] and mtHKII in HI brain injury.

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

PURPOSE AND BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Triiodothyronine Aggravates Global Cerebral Ischemia-Reperfusion Injury in Mice

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

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

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

Design, synthesis and biological evaluation of 1-benzyl-5-oxopyrrolidine-2-carboximidamide derivatives as novel neuroprotective agents

A series of 1-benzyl-5-oxopyrrolidine-2-carboximidamide derivatives were designed and synthesized. Their protective activities against N-methyl-d-aspartic acid (NMDA)-induced cytotoxicity were investigated in vitro. All of the compounds exhibited neuroprotective activities, especially 12k, which showed higher potency than reference compound 1 (ifenprodil). Further investigation showed that 12k could attenuate Ca²⁺ influx and suppress the NR2B upregulation induced by NMDA. The docking results indicated that 12k could fit well into binding site of 1 in the NR2B-NMDA receptor. Additionally, 12k exhibited excellent metabolic stability. Furthermore, the results of behavioral tests showed that compound 12k could significantly improve learning and memory in vivo. These results suggested that 12k is a promising neuroprotective drug candidate and that the NR2B-NMDA receptor is a potential target of 12k.

SUMOylation participates in induction of ischemic tolerance in mice

A group of proteins, small ubiquitin-like modifier (SUMO) proteins, has been shown to play a major role in rodent cerebral ischemia. Here, we proved that transient global cerebral ischemia induces a marked increase in protein sumo2/3 conjugation levels, we also find that global sumo2/3 conjugation is involved in ischemic tolerance in mice. Mice preconditioned by sublethal ischemia were less vulnerable to severe ischemia than non-preconditioned mice. Five-minute BCCAO precondition decreased the levels of SUMO2/3-conjugated proteins induced by MCAO. These findings suggest that maintenance of a globally decreased SUMO2/3 (and maybe SUMO-2/3) conjugation level as revealed by immunoblot assays is a component of ischemic tolerance.

The emerging field of epigenetics in neurodegeneration and neuroprotection

Epigenetic mechanisms - including DNA methylation, histone post-translational modifications and changes in nucleosome positioning - regulate gene expression, cellular differentiation and development in almost all tissues, including the brain. In adulthood, changes in the epigenome are crucial for higher cognitive functions such as learning and memory. Striking new evidence implicates the dysregulation of epigenetic mechanisms in neurodegenerative disorders and diseases. Although these disorders differ in their underlying causes and pathophysiologies, many involve the dysregulation of restrictive element 1-silencing transcription factor (REST), which acts via epigenetic mechanisms to regulate gene expression. Although not somatically heritable, epigenetic modifications in neurons are dynamic and reversible, which makes them good targets for therapeutic intervention.

Ischemic preconditioning protects against ischemic brain injury

In this study, we hypothesized that an increase in integrin α_vβ₃ and its co-activator vascular endothelial growth factor play important neuroprotective roles in ischemic injury. We performed ischemic preconditioning with bilateral common carotid artery occlusion for 5 minutes in C57BL/6J mice. This was followed by ischemic injury with bilateral common carotid artery occlusion for 30 minutes. The time interval between ischemic preconditioning and lethal ischemia was 48 hours. Histopathological analysis showed that ischemic preconditioning substantially diminished damage to neurons in the hippocampus 7 days after ischemia. Evans Blue dye assay showed that ischemic preconditioning reduced damage to the blood-brain barrier 24 hours after ischemia. This demonstrates the neuroprotective effect of ischemic preconditioning. Western blot assay revealed a significant reduction in protein levels of integrin α_vβ₃, vascular endothelial growth factor and its receptor in mice given ischemic preconditioning compared with mice not given ischemic preconditioning 24 hours after ischemia. These findings suggest that the neuroprotective effect of ischemic preconditioning is associated with lower integrin α_vβ₃ and vascular endothelial growth factor levels in the brain following ischemia.

In Situ Pluripotency Factor Expression Promotes Functional Recovery From Cerebral Ischemia

Recovery from ischemic tissue injury can be promoted by cell proliferation and neovascularization. Transient expression of four pluripotency factors (Pou5f1, Sox2, Myc, and Klf4) has been used to convert cell types but never been tested as a means to promote functional recovery from ischemic injury. Here we aimed to determine whether transient in situ pluripotency factor expression can improve neurobehavioral function. Cerebral ischemia was induced by transient bilateral common carotid artery occlusion, after which the four pluripotency factors were expressed through either doxycycline administration into the lateral ventricle in transgenic mice in which the four factors are expressed in a doxycycline-inducible manner. Histologic evaluation showed that this transient expression induced the proliferative generation of astrocytes and/or neural progenitors, but not neurons or glial scar, and increased neovascularization with upregulation of angiogenic factors. Furthermore, in vivo pluripotency factor expression caused neuroprotective effects such as increased numbers of mature neurons and levels of synaptic markers in the striatum. Dysplasia or tumor development was not observed. Importantly, neurobehavioral evaluations such as rotarod and ladder walking tests showed that the expression of the four factors dramatically promoted functional restoration from ischemic injury. These results provide a basis for novel therapeutic modality development for cerebral ischemia.

Cerebral Ischemic Preconditioning: the Road So Far…

Cerebral preconditioning constitutes the brain's adaptation to lethal ischemia when first exposed to mild doses of a subtoxic stressor. The phenomenon of preconditioning has been largely studied in the heart, and data from in vivo and in vitro models from past 2-3 decades have provided sufficient evidence that similar machinery exists in the brain as well. Since preconditioning results in a transient protective phenotype labeled as ischemic tolerance, it can open many doors in the medical warfare against stroke, a debilitating cerebrovascular disorder that kills or cripples thousands of people worldwide every year. Preconditioning can be induced by a variety of stimuli from hypoxia to pharmacological anesthetics, and each, in turn, induces tolerance by activating a multitude of proteins, enzymes, receptors, transcription factors, and other biomolecules eventually leading to genomic reprogramming. The intracellular signaling pathways and molecular cascades behind preconditioning are extensively being investigated, and several first-rate papers have come out in the last few years centered on the topic of cerebral ischemic tolerance. However, translating the experimental knowledge into the clinical scaffold still evades practicality and faces several challenges. Of the various preconditioning strategies, remote ischemic preconditioning and pharmacological preconditioning appears to be more clinically relevant for the management of ischemic stroke. In this review, we discuss current developments in the field of cerebral preconditioning and then examine the potential of various preconditioning agents to confer neuroprotection in the brain.

Sigma 1 receptor activation regulates brain-derived neurotrophic factor through NR2A-CaMKIV-TORC1 pathway to rescue the impairment of learning and memory induced by brain ischaemia/reperfusion

RATIONALE

Sigma-1 receptor (Sig-1R) agonists showed anti-amnesic properties in Alzheimer's disease models and anti-inflammatory properties in cerebrum ischaemia models. The agonist of Sig-1R was reported to up-regulate brain-derived neurotrophic factor (BDNF) levels in the hippocampus of mice. Here, we investigate whether the activation of Sig-1R attenuates the learning and memory impairment induced by ischaemia/reperfusion and how it affects the expression of BDNF.

OBJECTIVES

Bilateral common carotid artery occlusion (BCCAO) was induced for 20 min in C57BL/6 mice.

MATERIALS AND METHODS

Sig-1R agonist, PRE084, sigma 1/2 non-selective agonist, DTG, Sig-1R antagonist and BD1047 were injected once daily throughout the experiment. Behavioural tests were performed from day 8. On day 22 after BCCAO, mice were sacrificed for biochemical analysis.

RESULTS

PRE084 and DTG ameliorated learning and memory impairments in the Y maze, novel object recognition, and water maze tasks and prevented the decline of synaptic proteins and BDNF expression in the hippocampus of BCCAO mice. Furthermore, PRE084 and DTG up-regulated the level of NMDA receptor 2A (NR2A), calcium/calmodulin-dependent protein kinase type IV (CaMKIV) and CREB-specific co-activator transducer of regulated CREB activity 1 (TORC1). Additionally, the effects of PRE084 and DTG were antagonised by the co-administration of BD1047.

CONCLUSIONS

Sig-1R activation showed an attenuation in the ischaemia/reperfusion model and the activation of Sig-1R increased the expression of BDNF, possibly through the NR2A-CaMKIV-TORC1 pathway, and Sig-1R agonists might function as neuroprotectant agents in vascular dementia.

Preconditioning provides neuroprotection in models of CNS disease: paradigms and clinical significance

Preconditioning is a phenomenon in which brief episodes of a sublethal insult induce robust protection against subsequent lethal injuries. Preconditioning has been observed in multiple organisms and can occur in the brain as well as other tissues. Extensive animal studies suggest that the brain can be preconditioned to resist acute injuries, such as ischemic stroke, neonatal hypoxia/ischemia, surgical brain injury, trauma, and agents that are used in models of neurodegenerative diseases, such as Parkinson's disease and Alzheimer's disease. Effective preconditioning stimuli are numerous and diverse, ranging from transient ischemia, hypoxia, hyperbaric oxygen, hypothermia and hyperthermia, to exposure to neurotoxins and pharmacological agents. The phenomenon of "cross-tolerance," in which a sublethal stress protects against a different type of injury, suggests that different preconditioning stimuli may confer protection against a wide range of injuries. Research conducted over the past few decades indicates that brain preconditioning is complex, involving multiple effectors such as metabolic inhibition, activation of extra- and intracellular defense mechanisms, a shift in the neuronal excitatory/inhibitory balance, and reduction in inflammatory sequelae. An improved understanding of brain preconditioning should help us identify innovative therapeutic strategies that prevent or at least reduce neuronal damage in susceptible patients. In this review, we focus on the experimental evidence of preconditioning in the brain and systematically survey the models used to develop paradigms for neuroprotection, and then discuss the clinical potential of brain preconditioning.

Cyclophilin B is involved in p300-mediated degradation of CHOP in tumor cell adaptation to hypoxia

The regulation of CCAAT/enhancer-binding protein-homologous protein (CHOP), an endoplasmic reticulum (ER) stress-response factor, is key to cellular survival. Hypoxia is a physiologically important stress that induces cell death in the context of the ER, especially in solid tumors. Although our previous studies have suggested that Cyclophilin B (CypB), a molecular chaperone, has a role in ER stress, currently, there is no direct information supporting its mechanism under hypoxia. Here, we demonstrate for the first time that CypB is associated with p300 E4 ligase, induces ubiquitination and regulates the proteasomal turnover of CHOP, one of the well-known pro-apoptotic molecules under hypoxia. Our findings show that CypB physically interacts with the N-terminal α-helix domain of CHOP under hypoxia and cooperates with p300 to modulate the ubiquitination of CHOP. We also show that CypB is transcriptionally induced through ATF6 under hypoxia. Collectively, these findings demonstrate that CypB prevents hypoxia-induced cell death through modulation of ubiquitin-mediated CHOP protein degradation, suggesting that CypB may have an important role in the tight regulation of CHOP under hypoxia.

Danggui-Jakyak-San ameliorates memory impairment and increase neurogenesis induced by transient forebrain ischemia in mice

Background

Danggui-Jakyak-San (DJS), a traditional herbal prescription, has been used to treat insufficient blood supplies. Recently, regenerative medication for the treatment of cerebral ischemia has drawn the attention of many researchers.

Methods

In this study, we examined whether DJS exerts a neuronal regenerative effect in the hippocampus of a transient forebrain ischemia mice model. Transient forebrain ischemia was induced by bilateral common carotid artery occlusion (BCCAO). Animals were divided into three groups (sham, BCCAO + vehicle, and BCCAO + DJS). To test the effect of DJS on learning and memory, Morris water maze or passive avoidance test was conducted. To test neuroprotective and neurogenic effect, immunohistochemistry and Western blot analysis were used. Statistical significance was analyzed with Student t-test, one-way or two-way analysis of variance.

Results

We found that the administration of DJS ameliorated ischemia-induced spatial memory impairment in the Morris water maze task. Moreover, Akt/glycogen synthase kinase-3β (GSK3β)/β-catenin signaling was increased by DJS, which would be one possible mechanism of DJS for neurogenesis in the hippocampal dentate gyrus region.

Conclusions

These results suggest that DJS is a possible candidate for the treatment of ischemia-induced neuronal degeneration.

Bilateral common carotid artery occlusion as an adequate preconditioning stimulus to induce early ischemic tolerance to focal cerebral ischemia

There is accumulating evidence, that ischemic preconditioning - a non-damaging ischemic challenge to the brain - confers a transient protection to a subsequent damaging ischemic insult. We have established bilateral common carotid artery occlusion as a preconditioning stimulus to induce early ischemic tolerance to transient focal cerebral ischemia in C57Bl6/J mice. In this video, we will demonstrate the methodology used for this study.

Cytochrome P450 2J2 is protective against global cerebral ischemia in transgenic mice

Cytochrome P450 epoxygenase metabolites of arachidonic acid, EETs, have multiple cardiovascular effects, including reduction of blood pressure, protection against myocardial ischemia-reperfusion injury, and attenuation of endothelial apoptosis. This study investigated the hypothesis that transgenic mice with endothelial overexpression of CYP2J2 (Tie2-CYP2J2-Tr) would be protected against global cerebral ischemia induced by bilateral common carotid artery occlusion (BCCAO) and action mechanisms of EETs on cerebral ischemia in cultures of astrocytes exposed to oxygen-glucose deprivation (OGD). Tie2-CYP2J2-Tr mice had significantly increased CYP2J2 expression, increased 14,15-EET production, increases regional cerebral blood flow (rCBF) and microvascular density, decreased ROS production, decreased brain infarct size and apoptosis after ischemia compared to wild type mice, these were associated with increased activation of the PI3K/AKT and apoptosis-related protein in ischemic brain. Addition of exogenous EETs or CYP2J2 transfection attenuated OGD-induced apoptosis in astrocytes via activation of PI3K/AKT and anti-apoptosis pathways. However, these effects were reduced by pretreatments with inhibitor of the PI3K (LY294002) and 14,15-EET (14,15-EEZE), respectively. These results indicate that CYP2J2 overexpression exerts marked neuroprotective effects against ischemic injury by a mechanism linked to increased level of circulating EETs and increases CBF and reduction of apoptosis.

Acidic preconditioning protects against ischemia-induced brain injury

Ischemic preconditioning protects against cerebral ischemia. Recent investigations indicated that acidic preconditioning (APC) protects against ischemia-induced cardiomyocytes injury. However, it is not clear whether APC can protect against cerebral ischemia. To address this issue, C57BL/6 mice were exposed 3 times at 10-min intervals to a normoxic atmosphere containing 20% CO(2) for 5 min before being further subjected to bilateral common carotid artery occlusion. APC reversed the ischemia-induced brain injury as revealed by improved performance in passive avoidance experiments and decreased neuron loss in the hippocampal CA1 region. Consistently, both APC-treated brain slices and primary cultured neurons were more resistant to oxygen-glucose-deprivation (OGD)-induced injury, in a pH- and time-dependent manner, as revealed by reversed cell/tissue viability. In addition, the APC treatment prevented OGD-induced mitochondrial transmembrane potential loss and apoptosis, which was inhibited by the mitochondrial permeability transport pore opener atractyloside. Taken together, these findings indicated that APC protects against ischemia-induced neuronal injury. The beneficial effects may be attributed, at least in part, to decreased mitochondria-dependent neuronal apoptosis.

Preconditioning-induced ischemic tolerance: a window into endogenous gearing for cerebroprotection

Ischemic tolerance defines transient resistance to lethal ischemia gained by a prior sublethal noxious stimulus (i.e., preconditioning). This adaptive response is thought to be an evolutionarily conserved defense mechanism, observed in a wide variety of species. Preconditioning confers ischemic tolerance if not in all, in most organ systems, including the heart, kidney, liver, and small intestine. Since the first landmark experimental demonstration of ischemic tolerance in the gerbil brain in early 1990's, basic scientific knowledge on the mechanisms of cerebral ischemic tolerance increased substantially. Various noxious stimuli can precondition the brain, presumably through a common mechanism, genomic reprogramming. Ischemic tolerance occurs in two temporally distinct windows. Early tolerance can be achieved within minutes, but wanes also rapidly, within hours. Delayed tolerance develops in hours and lasts for days. The main mechanism involved in early tolerance is adaptation of membrane receptors, whereas gene activation with subsequent de novo protein synthesis dominates delayed tolerance. Ischemic preconditioning is associated with robust cerebroprotection in animals. In humans, transient ischemic attacks may be the clinical correlate of preconditioning leading to ischemic tolerance. Mimicking the mechanisms of this unique endogenous protection process is therefore a potential strategy for stroke prevention. Perhaps new remedies for stroke are very close, right in our cells.

Concurrent Vasculogenesis and Neurogenesis From Adult Neural Stem Cells

Rationale : Recent reports have demonstrated that signals from vascular endothelial cells are necessary for organogenesis that may precede vasculogenesis. However, the origin of these neovascular cells in regenerating tissue has not been clarified.

Objective : Here we tested the hypothesis that adult neural stem cells (NSCs) can differentiate into vascular lineage, as well as neural lineage, in the process of collaborative organogenesis.

Methods and Results : NSCs, clonally isolated from mouse brain, were shown to develop endothelial and smooth muscle phenotypes in vitro. To elucidate whether NSCs can simultaneously differentiate into vascular and neural cells in vivo, genetically labeled NSCs were administered to mice with unilateral sciatic nerve crush injury or operatively induced brain and myocardial ischemia. Two weeks later, necropsy examination disclosed recruitment of the labeled NSCs to sites of injury differentiating into vascular cells (endothelial cells and vascular smooth muscle cells) and Schwann cells in regenerating nerve. Similarly, NSC-derived vascular cells/astrocytes and endothelial cells were identified in ischemic brain tissue and capillaries in myocardium 2 weeks following transplantation, respectively.

Conclusions : These findings, concurrent vasculogenesis and neurogenesis from a common stem cell, suggest that certain somatic stem cells are capable of differentiating into not only somatic cells of identity but also into vascular cells for tissue regeneration.

Nobiletin improves brain ischemia-induced learning and memory deficits through stimulation of CaMKII and CREB phosphorylation

Decreased cerebral blood flow causes cognitive impairments and neuronal injury in the progressive age-related neurodegenerative disorders such as Alzheimer's disease (AD) and vascular dementia. In the present study, we for the first time found that nobiletin, a novel leading compound for AD therapy, improved cerebral ischemia-induced memory deficits in vivo. Treatment with 50 mg/kg of nobiletin (i.p.) for the consecutive 7 days before and after brain ischemia significantly inhibited delayed neuronal death in the hippocampal CA1 neurons in a 20-min bilateral common carotid arteries occlusion (BCCAO) ischemia. However, the contextual memory assessed by passive avoidance task was not improved. On the other hand, a 5-min BCCAO-induced contextual memory deficit was significantly improved by the nobiletin treatment. In the 5-min BCCAO mice, Western blot analysis evidently showed that the levels of synaptic proteins, including calcium/calmodulin-dependent protein kinase II (CaMKII), microtubule-associated protein 2 (MAP2) and glutamate receptor 1 (GluR1), significantly decreased in the hippocampal CA1 region. The nobiletin treatment prevented the reduction in CaMKII, MAP2 and GluR1 protein levels in the hippocampal CA1 region, accompanied by restoration of both ERK and CREB phosphorylation and CaMKII autophosphorylation. Consistent with the restored CaMKII and ERK phosphorylation, an electrophysiological study showed that the impaired hippocampal long-term potentiation (LTP) observed in the 5-min ischemic mice was significantly improved by the nobiletin treatment. These findings suggest that the activation of CaMKII and ERK signaling in part mediates improvement of ischemia-induced learning and memory deficits by nobiletin.

Toll-like receptor 4 is involved in neuroprotection afforded by ischemic preconditioning

It has been demonstrated that a short ischemic event (ischemic preconditioning, IPC) results in a subsequent resistance to severe ischemia (ischemic tolerance, IT). We have recently demonstrated the role of innate immunity and in particular of toll-like receptor (TLR) 4 in brain ischemia. Several evidences suggest that TLR4 might also be involved in IT. Therefore, we have now used an in vivo model of IPC to investigate whether TLR4 is involved in IT. A 6-min temporary bilateral common carotid arteries occlusion was used for focal IPC and it was performed on TLR4-deficient mice (C57BL/10ScNJ) and animals that express TLR4 normally (C57BL/10ScSn). To assess the ability of IPC to induce IT, permanent middle cerebral artery occlusion was performed 48 h after IPC. Stroke outcome was evaluated by determination of infarct volume and assessment of neurological scores. IPC caused neuroprotection as shown by a reduction in infarct volume and better outcome in mice expressing TLR4 normally. TLR4-deficient mice showed less IPC-induced neuroprotection than wild-type animals. Western blot analysis of tumor necrosis factor alpha (TNF-alpha), inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) showed an up-regulation in the expression of these proteins in both substrains of mice measured 18, 24 and 48 h after IPC, being higher in mice with TLR4. Similarly, nuclear factor-kappa B (NF-kappaB) activation was observed 18, 24 and 48 h after IPC, being more intense in TLR4-expressing mice. These data demonstrate that TLR4 signalling is involved in brain tolerance as shown by the difference in the percentage of neuroprotection produced by IPC between ScSn and ScNJ (60% vs. 18%). The higher expression of TNF-alpha, iNOS and cyclooxygenase-2 and NF-kappaB activation in mice expressing TLR4 is likely to participate in this endogenous neuroprotective effect.

MR contrast probes that trace gene transcripts for cerebral ischemia in live animals

The aim of this research was to validate transcription magnetic resonance (MR) imaging (MRI) for gene transcript targeting in acute neurological disorders in live subjects. We delivered three MR probe variants with superparamagnetic iron oxide nanoparticles (SPION, a T2 susceptibility agent) linked to a phosphorothioate-modified oligodeoxynucleotide (sODN) complementary to c-fos mRNA (SPION-cfos) or beta-actin mRNA (SPION-beta-actin) and to sODN with random sequence (SPION-Ran). Each probe (1 microg Fe in 2 microl) was delivered via intracerebroventricular infusion to the left cerebral ventricle of male C57Black6 mice. We demonstrated SPION retention, measured as decreased T2* signal or increased R2* value (R2* = 1/T2*). Animals that received the SPION-beta-actin probe exhibited the highest R2* values, followed (in descending order) by SPION-cfos and SPION-Ran. SPION-cfos retention was localized in brain regions where SPION-cfos was present and where hybrids of SPION-cfos and its target c-fos mRNA were detected by in situ reverse transcription PCR. In animals that experienced cerebral ischemia, SPION-cfos retention was significantly increased in locations where c-fos mRNA increased in response to the ischemic insult; these elevations were not observed for SPION-beta-actin and SPION-Ran. This study should enable MR detection of mRNA alteration in disease models of the central nervous system.

Rodent models of focal stroke: size, mechanism, and purpose

Rodent stroke models provide the experimental backbone for the in vivo determination of the mechanisms of cell death and neural repair, and for the initial testing of neuroprotective compounds. Less than 10 rodent models of focal stroke are routinely used in experimental study. These vary widely in their ability to model the human disease, and in their application to the study of cell death or neural repair. Many rodent focal stroke models produce large infarcts that more closely resemble malignant and fatal human infarction than the average sized human stroke. This review focuses on the mechanisms of ischemic damage in rat and mouse stroke models, the relative size of stroke generated in each model, and the purpose with which focal stroke models are applied to the study of ischemic cell death and to neural repair after stroke.

Ischaemic preconditioning: therapeutic implications for stroke?

Ischaemic preconditioning (IPC), also known as ischaemic tolerance (IT), is a phenomenon whereby tissue is exposed to a brief, sublethal period of ischaemia, which activates endogenous protective mechanisms, thereby reducing cellular injury that may be caused by subsequent lethal ischaemic events. The first description of this phenomenon was in the heart, which was reported by Murry and co-workers in 1986. Subsequent studies demonstrated IPC in lung, kidney and liver tissue, whereas more recent studies have concentrated on the brain. The cellular mechanisms underlying the beneficial effects of IPC remain largely unknown. This phenomenon, which has been demonstrated by using various injury paradigms in both cultured neurons and animal brain tissue, may be utilised to identify and characterise therapeutic targets for small-molecule, antibody, or protein intervention. This review will examine the experimental evidence demonstrating the phenomenon termed IPC in models of cerebral ischaemia, the cellular mechanisms that may be involved and the therapeutic implications of these findings.

Hypoxic preconditioning protects against ischemic brain injury

Animals exposed to brief periods of moderate hypoxia (8% to 10% oxygen for 3 hours) are protected against cerebral and cardiac ischemia between 1 and 2 days later. This hypoxia preconditioning requires new RNA and protein synthesis. The mechanism of this hypoxia-induced tolerance correlates with the induction of the hypoxia-inducible factor (HIF), a transcription factor heterodimeric complex composed of inducible HIF-1alpha and constitutive HIF-1beta proteins that bind to the hypoxia response elements in a number of HIF target genes. Our recent studies show that HIF-1alpha correlates with hypoxia induced tolerance in neonatal rat brain. HIF target genes, also induced following hypoxia-induced tolerance, include vascular endothelial growth factor, erythropoietin, glucose transporters, glycolytic enzymes, and many other genes. Some or all of these genes may contribute to hypoxia-induced protection against ischemia. HIF induction of the glycolytic enzymes accounts in part for the Pasteur effect in brain and other tissues. Hypoxia-induced tolerance is not likely to be equivalent to treatment with a single HIF target gene protein since other transcription factors including Egr-1 (NGFI-A) have been implicated in hypoxia regulation of gene expression. Understanding the mechanisms and genes involved in hypoxic tolerance may provide new therapeutic targets to treat ischemic injury and enhance recovery.

Obligatory role of inducible nitric oxide synthase in ischemic preconditioning

Sublethal insults can induce a transient tolerance toward subsequent lethal ischemia, a phenomenon termed ischemic preconditioning (IPC). In the myocardium, nitric oxide derived from 'inducible' nitric oxide synthase (iNOS or NOS II) plays a critical role in the expression of IPC produced by sublethal ischemia. Here, we investigated whether iNOS is involved in IPC in brain. Ischemic preconditioning was produced in mice by three episodes of 1-min bilateral common carotid artery (BCCA) occlusion, each followed by 5 mins of reperfusion. After 24 h, mice underwent middle cerebral artery (MCA) occlusion for 20 mins. Intraischemic cerebral blood flow was monitored during both in BCCA and MCA occlusion (MCAO) by laser-Doppler flowmetry. Mice were killed 3 days after MCAO, and infarct volume was determined in thionine-stained sections. Infarct volume was significantly reduced 24 h after IPC (70%; P<0.05). Treatment with the iNOS inhibitor aminoguanidine (400 mg/kg), abolished the IPC-induced protection. Furthermore, IPC failed to induce ischemic tolerance in iNOS-null mice. In wild-type mice, IPC increased the resistance to Ca(2+)-mediated depolarization in isolated brain mitochondria. However, in iNOS-null mice IPC failed to induce such resistance. We conclude that iNOS is required for the full expression of IPC and that such effect is coupled to an increased resistance of mitochondria to injury. Thus, iNOS-derived nitric oxide, in addition to its deleterious effects on the late stages of ischemic brain damage, can also be beneficial by promoting ischemic tolerance through signaling, ultimately resulting in mitochondrial protection.

Preconditioning enhances the expression of mitochondrial antioxidant thioredoxin-2 in the forebrain of rats exposed to severe hypobaric hypoxia

The impact of severe hypoxia and preconditioning on the expression of the mitochondrial antioxidant thioredoxin-2 (Trx-2) in rat hippocampus (CA1, CA2, CA3 fields, and dentate gyrus) and neocortex was studied by immunocytochemistry. The preconditioning consisted of three trials of mild hypobaric hypoxia (360 Torr, 2 hr) spaced at 24 hr. The last trial was followed by severe hypobaric hypoxia (180 Torr, 3 hr) 24 hr later. Both in hippocampus and in neocortex, severe hypobaric hypoxia resulted in enhanced Trx-2 expression at 3 hr, followed by a slight decline in Trx-2 levels, which nevertheless remained increased at 24 hr elsewhere except for the CA1 region. The preconditioning considerably augmented severe hypoxia-induced Trx-2 immunoreactivity, affecting both the number of immunoreactive cells and the intensity of immunostaining. The findings suggest a role for Trx-2 in the formation of brain hypoxic/ischemic tolerance accomplished by the preconditioning.

A mouse model of cerebral oligemia: relation to brain histopathology, cerebral blood flow, and energy state

An animal model involving stepwise occlusion of the common carotid arteries (sCCAO) in DBA/2 mice is presented in which the right and left carotid arteries were permanently ligated within a time interval of four weeks. Thereafter, cerebral functional and structural parameters were determined at acute (15 min) and subchronic (1 day; 3, 7, and 14 days) time points after sCCAO. Quantitative changes in regional cerebral blood flow (rCBF) as determined by the [14C]iodoantipyrine method, energy state (ATP, phosphocreatine, ADP, AMP, adenosine) as shown by HPLC, brain histopathology, and neuronal densities were measured in both hemispheres. Acute sCCAO was accompanied by a drastic reduction in cerebral energy-rich phosphate concentrations, ATP and phosphocreatine, and in rCBF of more than 50%. In contrast, cortical adenosine increased around five-fold. Subchronic sCCAO, however, was associated with normalization in brain energy metabolites and near-complete restoration of rCBF, except in the caudate nucleus (-40%). No marked signs of necrotic or apoptotic cell destruction were detected. Thus, during the subchronic period, compensatory mechanisms are induced to counteract the drastic changes seen after acute vessel occlusion. In conclusion, this sCCAO mouse model may be useful for long-lasting investigations of stepwise deterioration contributing to chronic cerebrovascular disorders.

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

Brain ischemia induces apoptosis in neuronal cells, but the mechanism is not well understood. When wild-type mice were subjected to bilateral common carotid arteries occlusion (BCCAO) for 15 min, apoptosis-associated morphological changes and appearance of TUNEL-positive cells were observed in the striatum and in the hippocampus at 48 h after occlusion. RT-PCR analysis revealed that mRNAs for ER stress-associated proapoptotic factor CHOP and an ER chaperone BiP are markedly induced at 12 h after BCCAO. Immunohistochemical analysis showed that CHOP protein is induced in nuclei of damaged neurons at 24 h after occlusion. In contrast, ischemia-associated apoptotic loss of neurons was decreased in CHOP(-/-) mice. Primary hippocampal neurons from CHOP(-/-) mice were more resistant to hypoxia-reoxygenation-induced apoptosis than those from wild-type animals. These results indicate that ischemia-induced neuronal cell death is mediated by the ER stress pathway involving CHOP induction.

Histopathological and behavioral characterization of a novel model of cardiac arrest and cardiopulmonary resuscitation in mice

Cardiac arrest is associated with high mortality and poor neurological outcome. We characterized functional and histological outcome in a novel mouse model of cardiac arrest and cardiopulmonary resuscitation (CPR) in order to study neuroprotective mechanisms. Cardiac arrest was induced in male C57Bl/6 and 129SVEV mice by i.v. injection of KCl. After 10 min cardiac standstill, CPR was initiated by administration of epinephrine, ventilation with 100% oxygen and chest compressions. Twenty-four hours before and 3 or 7 days after CPR, mice were subjected to behavioral testing using a passive avoidance task, locomotor activity in an open field, and spontaneous alternation in a T-maze. Hippocampal and caudoputamen injury was quantified 3 or 7 days after CPR. At both time points, caudoputamen injury was worse in 129SVEV mice. Post-ischemic mice of both strains showed a reduced number of correct choices in the T-maze up to 7 days after CPR, and were temporarily impaired in learning the passive avoidance task with a retention deficit on day 3 but not on day 7. Locomotor activity showed strain differences with C57Bl/6 mice being more active, but little ischemia-related effects. A dissociation between functional and histological outcome was found emphasizing the importance of combining both outcome measures for evaluation of neuroprotective strategies.

Transforming growth factor-beta 1-mediated neuroprotection against excitotoxic injury in vivo

Ischemic preconditioning is a phenomenon that describes how a sublethal ischemic insult can induce tolerance to subsequent ischemia. This phenomenon has been observed after focal or global ischemia in different animal models. However, the hypothesis that bacterial infection might lead to neuronal tolerance to injury has not been investigated. To mimic cerebral bacterial infection, we injected bacterial lipopolysaccharide (LPS) in the right dorsal hippocampus, followed 24 hours later by an excitotoxic lesion using kainic acid in the mouse model. Quantification of lesion size after cresyl violet counterstaining revealed that LPS pretreatment afforded neuroprotection to CA3 neurons against KA challenge. To investigate the events underlying this protection, we studied the cytokine profile induced after LPS injection. Interleukin (IL)-1 beta and transforming growth factor beta 1 (TGF-beta 1) were the main cytokines expressed at 24 hours after LPS injection. Because IL-1 beta has been described as deleterious in acute injury, we decided to investigate the function of TGF-beta 1. An adenovirus expressing a constitutively active form of TGF-beta 1 was injected intracerebrally 1 week before the induction of excitotoxic lesion, and neuronal protection was observed. To confirm the neuroprotective role of TGF-beta 1, the TGF-beta 1 adenovirus was replaced by recombinant human TGF-beta 1 protein and total neuroprotection was observed. Furthermore, the antibody-mediated blocking of TGF-beta 1 action prevented the protective effect of pretreatment with LPS. We have demonstrated in vivo that the cerebral tolerance phenomenon induced by LPS pretreatment is mediated by TGF-beta 1 cytokine.

Molecular determinants of the prothrombogenic and inflammatory phenotype assumed by the postischemic cerebral microcirculation

BACKGROUND AND PURPOSE

Circulating blood cells have been implicated in the pathogenesis of cerebral ischemia/reperfusion (I/R) injury and stroke. The objective of this study was to define the magnitude and molecular determinants of the platelet- and leukocyte-endothelial cell adhesive interactions induced by I/R in the mouse brain.

METHODS

Bilateral common carotid artery occlusion was induced for 1 hour in C57BL/6 mice, followed by either 40 minutes or 4 hours of reperfusion. Fluorescent platelets were administered intravenously, and the frontal brain surface was observed with intravital fluorescence microscopy. Leukocyte-endothelial cell adhesion was monitored with the use of rhodamine-6G.

RESULTS

Ischemia followed by 40 minutes of reperfusion resulted in the rolling (125.1+/-23.6/mm2) and firm adhesion (109.5+/-25.8/mm2) of leukocytes but not platelets in venules. However, with 4 hours of reperfusion, rolling (138.8+/-24.6/mm2) and firm adhesion (153.7+/-22.3/mm2) of platelets were detected, and this was accompanied by a more intense recruitment of rolling (374.5+/-54.6/mm2) and adherent (445.2+/-57.1/mm2) leukocytes. In mice deficient in either P-selectin (P-selectin-/-) or intercellular adhesion molecule-1 (ICAM-1) (ICAM-1-/-), the I/R-induced platelet-endothelial cell (by 80% and 60%, respectively) and leukocyte-endothelial cell (by 84% and 78%, respectively) interactions were significantly blunted compared with those of wild-type mice.

CONCLUSIONS

These findings indicate that I/R promotes the adhesion of both platelets and leukocytes in cerebral venules, with the accumulation of adherent leukocytes preceding the recruitment of platelets. Both P-selectin and ICAM-1 contribute to the inflammatory and prothrombogenic state induced by cerebral I/R.

Different expression patterns of Bcl-2, Bcl-xl, and Bax proteins after sublethal forebrain ischemia in C57Black/Crj6 mouse striatum

BACKGROUND AND PURPOSE

Ischemic injury in neurons can be strongly reduced by a preceding sublethal ischemic episode, of which the mechanism is poorly understood. Although changes in the expression of apoptosis-related proteins (Bcl-2, Bcl-xl, and Bax) have been considered to be crucially important in ischemic injury, the roles these proteins play in ischemic preconditioning induced by sublethal forebrain ischemia have not been elucidated. Therefore, we investigated the transcription and expression of Bcl-2, Bcl-xl, and Bax in striatum of mice subjected to sublethal forebrain ischemia and lethal ischemia, with or without ischemic preconditioning.

METHODS

Sublethal forebrain ischemia was induced in C57Black/Crj6 (C57BL/6) mice by 6 minutes of bilateral common carotid artery occlusion. The transcription and expression of Bcl-2 family genes were detected by reverse transcription-polymerase chain reaction, Western blot, and immunofluorescent staining.

RESULTS

No detectable neuronal loss was induced in striatum by 6 minutes of bilateral common carotid artery occlusion. Transcription and expression of Bcl-2 and Bcl-xl were increased after sublethal forebrain ischemia, which attenuated the DNA fragmentation induced by lethal ischemia. The transcription and expression of Bax remained unchanged.

CONCLUSIONS

Upregulation of Bcl-2 and Bcl-xl but not Bax may have a role in protective ischemic preconditioning. This result indicates a potential strategy for further ischemic neuronal injury therapies.

Ischemic tolerance

A brief period of cerebral ischemia confers transient tolerance to a subsequent ischemic challenge in the brain. This phenomenon of ischemic tolerance has been confirmed in various animal models of forebrain ischemia and focal cerebral ischemia. Since the ischemic tolerance afforded by preceding ischemia can bring about robust protection of the brain, the mechanism of tolerance induction has been extensively studied. It has been elucidated that ischemic tolerance protects neurons, and at the same time, it preserves brain function. Further experiments have shown that metabolic and physical stresses can also induce cross-tolerance to cerebral ischemia, but the protection by cross-tolerance is relatively modest. The underlying mechanism of ischemic tolerance still is not fully understood. Potential mechanisms may be divided into two categories: (1) A cellular defense function against ischemia may be enhanced by the mechanisms inherent to neurons. They may arise by posttranslational modification of proteins or by expression of new proteins via a signal transduction system to the nucleus. These cascades of events may strengthen the influence of survival factors or may inhibit apoptosis. (2) A cellular stress response and synthesis of stress proteins may lead to an increased capacity for health maintenance inside the cell. These proteins work as cellular "chaperones" by unfolding misfolded cellular proteins and helping the cell to dispose of unneeded denatured proteins. Recent experimental data have demonstrated the importance of the processing of unfolded proteins for cell survival and cell death. The brain may be protected from ischemia by using multiple mechanisms that are available for cellular survival. If tolerance induction can be manipulated and accelerated by a drug treatment that is safe and effective enough, it could greatly improve the treatment of stroke.

Sublethal cerebral ischemia inhibits caspase-3 activation induced by subsequent prolonged ischemia in the C57Black/Crj6 strain mouse

Caspase-3 activation has been implicated in ischemic neuronal death. In the present study, we examined if cerebral ischemic tolerance induced by sublethal ischemia is associated with an attenuation of caspase-3 activation in a mouse forebrain ischemia model. Forebrain ischemia in C57Black/Crj6 strain mice was induced by bilateral common carotid artery occlusion (BCCAO) for 18 min. Two episodes of 6-min ischemia were carried out as preconditioning 48 and 72 h before the 18-min BCCAO. Caspase-3-like activity was determined by fluorescently monitoring the release of amino-4-methylcoumarin from N-acetyl-Asp-Glu-Val-Asp-7-amino-4-methylcoumarin in the striatal protein extracts at 4, 24, and 72 h after reperfusion. The results showed that the ischemic preconditioning significantly attenuated caspase-3 activation at 4, 24, and 72 h after reperfusion, and reduced neuronal loss caused by the 18-min ischemia as examined on the 7th day after reperfusion. The present results suggest that the neuroprotection achieved by ischemic preconditioning is related to an attenuation of caspase-3 activation.