The effect of transient global ischemia on the interaction of Src and Fyn with the N-methyl-D-aspartate receptor and postsynaptic densities: possible involvement of Src homology 2 domains

Urinary protein biomarkers based on LC-MS/MS analysis to discriminate vascular dementia from Alzheimer's disease in Han Chinese population

Objective

This study aimed to identify the potential urine biomarkers of vascular dementia (VD) and unravel the disease-associated mechanisms by applying Liquid chromatography tandem-mass spectrometry (LC-MS/MS).

Methods

LC-MS/MS proteomic analysis was applied to urine samples from 3 groups, including 14 patients with VD, 9 patients with AD, and 21 normal controls (NC). By searching the MS data by Proteome Discoverer software, analyzing the protein abundances qualitatively and quantitatively, comparing between groups, combining bioinformatics analysis using Gene Ontology (GO) and pathway crosstalk analysis using Kyoto Encyclopedia of Genes and Genomes (KEGG), and literature searching, the differentially expressed proteins (DEPs) of VD can be comprehensively determined at last and were further quantified by receiver operating characteristic (ROC) curve methods.

Results

The proteomic findings showed quantitative changes in patients with VD compared to patients with NC and AD groups; among 4,699 identified urine proteins, 939 and 1,147 proteins displayed quantitative changes unique to VD vs. NC and AD, respectively, including 484 overlapped common DEPs. Then, 10 unique proteins named in KEGG database (including PLOD3, SDCBP, SRC, GPRC5B, TSG101/STP22/VPS23, THY1/CD90, PLCD, CDH16, NARS/asnS, AGRN) were confirmed by a ROC curve method.

Conclusion

Our results suggested that urine proteins enable detection of VD from AD and VC, which may provide an opportunity for intervention.

Fyn Signaling in Ischemia-Reperfusion Injury: Potential and Therapeutic Implications

Ischemic stroke caused by arterial occlusion is the most common type of stroke and is one of the leading causes of disability and death, with the incidence increasing each year. Fyn is a nonreceptor tyrosine kinase belonging to the Src family of kinases (SFKs), which is related to many normal and pathological processes of the nervous system, including neurodevelopment and disease progression. In recent years, more and more evidence suggests that Fyn may be closely related to cerebral ischemia-reperfusion, including energy metabolism disorders, excitatory neurotoxicity, intracellular calcium homeostasis, free radical production, and the activation of apoptotic genes. This paper reviews the role of Fyn in the pathological process of cerebral ischemia-reperfusion, including neuroexcitotoxicity and neuroinflammation, to explore how Fyn affects specific signal cascades and leads to cerebral ischemia-reperfusion injury. In addition, Fyn also promotes the production of superoxide and endogenous NO, so as to quickly react to produce peroxynitrite, which may also mediate cerebral ischemia-reperfusion injury, which is discussed in this paper. Finally, we revealed the treatment methods related to Fyn inhibitors and discussed its potential as a clinical treatment for ischemic stroke.

Is Immune Suppression Involved in the Ischemic Stroke? A Study Based on Computational Biology

Objective

To identify the genetic mechanisms of immunosuppression-related genes implicated in ischemic stroke.

Background

A better understanding of immune-related genes (IGs) involved in the pathophysiology of ischemic stroke may help identify drug targets beneficial for immunomodulatory approaches and reducing stroke-induced immunosuppression complications.

Methods

Two datasets related to ischemic stroke were downloaded from the GEO database. Immunosuppression-associated genes were obtained from three databases (i.e., DisGeNET, HisgAtlas, and Drugbank). The CIBERSORT algorithm was used to calculate the mean proportions of 22 immune-infiltrating cells in the stroke samples. Differential gene expression analysis was performed to identify the differentially expressed genes (DEGs) involved in stroke. Immunosuppression-related crosstalk genes were identified as the overlapping genes between ischemic stroke-DEGs and IGs. Feature selection was performed using the Boruta algorithm and a classifier model was constructed to evaluate the prediction accuracy of the obtained immunosuppression-related crosstalk genes. Functional enrichment analysis, gene-transcriptional factor and gene-drug interaction networks were constructed.

Results

Twenty two immune cell subsets were identified in stroke, where resting CD4 T memory cells were significantly downregulated while M0 macrophages were significantly upregulated. By overlapping the 54 crosstalk genes obtained by feature selection with ischemic stroke-related genes obtained from the DisGenet database, 17 potentially most valuable immunosuppression-related crosstalk genes were obtained, ARG1, CD36, FCN1, GRN, IL7R, JAK2, MAFB, MMP9, PTEN, STAT3, STAT5A, THBS1, TLR2, TLR4, TLR7, TNFSF10, and VASP. Regulatory transcriptional factors targeting key immunosuppression-related crosstalk genes in stroke included STAT3, SPI1, CEPBD, SP1, TP53, NFIL3, STAT1, HIF1A, and JUN. In addition, signaling pathways enriched by the crosstalk genes, including PD-L1 expression and PD-1 checkpoint pathway, NF-kappa B signaling, IL-17 signaling, TNF signaling, and NOD-like receptor signaling, were also identified.

Conclusion

Putative crosstalk genes that link immunosuppression and ischemic stroke were identified using bioinformatics analysis and machine learning approaches. These may be regarded as potential therapeutic targets for ischemic stroke.

Prion Protein: The Molecule of Many Forms and Faces

Cellular prion protein (PrP^C) is a glycosylphosphatidylinositol (GPI)-anchored protein most abundantly found in the outer membrane of neurons. Due to structural characteristics (a flexible tail and structured core), PrP^C interacts with a wide range of partners. Although PrP^C has been proposed to be involved in many physiological functions, only peripheral nerve myelination homeostasis has been confirmed as a bona fide function thus far. PrP^C misfolding causes prion diseases and PrP^C has been shown to mediate β-rich oligomer-induced neurotoxicity in Alzheimer’s and Parkinson’s disease as well as neuroprotection in ischemia. Upon proteolytic cleavage, PrP^C is transformed into released and attached forms of PrP that can, depending on the contained structural characteristics of PrP^C, display protective or toxic properties. In this review, we will outline prion protein and prion protein fragment properties as well as overview their involvement with interacting partners and signal pathways in myelination, neuroprotection and neurodegenerative diseases.

Show Me Your Friends and I Tell You Who You Are: The Many Facets of Prion Protein in Stroke

Ischemic stroke belongs to the leading causes of mortality and disability worldwide. Although treatments for the acute phase of stroke are available, not all patients are eligible. There is a need to search for therapeutic options to promote neurological recovery after stroke. The cellular prion protein (PrPC) has been consistently linked to a neuroprotective role after ischemic damage: it is upregulated in the penumbra area following stroke in humans, and animal models of stroke have shown that lack of PrPC aggravates the ischemic damage and lessens the functional outcome. Mechanistically, these effects can be linked to numerous functions attributed to PrPC: (1) as a signaling partner of the PI3K/Akt and MAPK pathways, (2) as a regulator of glutamate receptors, and (3) promoting stem cell homing mechanisms, leading to angio- and neurogenesis. PrPC can be cleaved at different sites and the proteolytic fragments can account for the manifold functions. Moreover, PrPC is present on extracellular vesicles (EVs), released membrane particles originating from all types of cells that have drawn attention as potential therapeutic tools in stroke and many other diseases. Thus, identification of the many mechanisms underlying PrPC-induced neuroprotection will not only provide further understanding of the physiological functions of PrPC but also new ideas for possible treatment options after ischemic stroke.

NMDA receptors and BDNF are necessary for discrimination of overlapping spatial and non-spatial memories in perirhinal cortex and hippocampus

Successful memory involves not only remembering information over time but also keeping memories distinct and less confusable. Discrimination of overlapping representations has been investigated in the dentate gyrus (DG) of the hippocampus and largely in the perirhinal cortex (Prh). In particular, the DG was shown to be important for discrimination of overlapping spatial memories and Prh was shown to be important for discrimination of overlapping object memories. In the present study, we used both a DG-dependent and a Prh-dependent task and manipulated the load of similarity between either spatial or object stimuli during information encoding. We showed that N-methyl-D-aspartate-type glutamate receptors (NMDAr) and BDNF participate of the same cellular network during consolidation of both overlapping object and spatial memories in the Prh and DG, respectively. This argues in favor of conserved cellular mechanisms across regions despite anatomical differences.

Regulation of pannexin channels in the central nervous system by Src family kinases

Pannexins form single membrane channels that regulate the passage of ions, small molecules and metabolites between the intra- and extracellular compartments. In the central nervous system, these channels are integrated into numerous signaling cascades that shape brain physiology and pathology. Post-translational modification of pannexins is complex, with phosphorylation emerging as a prominent form of functional regulation. While much is still not known regarding the specific kinases and modified amino acids, recent reports support a role for Src family tyrosine kinases (SFK) in regulating pannexin channel activity. This review outlines the current evidence supporting SFK-dependent pannexin phosphorylation in the CNS and examines the importance of these modifications in the healthy and diseased brain.

Phosphorylation of Tyrosine 1070 at the GluN2B Subunit Is Regulated by Synaptic Activity and Critical for Surface Expression of N-Methyl-D-aspartate (NMDA) Receptors

The number and subunit composition of synaptic N-methyl-d-aspartate receptors (NMDARs) play critical roles in synaptic plasticity, learning, and memory and are implicated in neurological disorders. Tyrosine phosphorylation provides a powerful means of regulating NMDAR function, but the underling mechanism remains elusive. In this study we identified a tyrosine site on the GluN2B subunit, Tyr-1070, which was phosphorylated by a proto-oncogene tyrosine-protein (Fyn) kinase and critical for the surface expression of GluN2B-containing NMDARs. The phosphorylation of GluN2B at Tyr-1070 was required for binding of Fyn kinase to GluN2B, which up-regulated the phosphorylation of GluN2B at Tyr-1472. Moreover, our results revealed that the phosphorylation change of GluN2B at Tyr-1070 accompanied the Tyr-1472 phosphorylation and Fyn associated with GluN2B in synaptic plasticity induced by both chemical and contextual fear learning. Taken together, our findings provide a new mechanism for regulating the surface expression of NMDARs with implications for synaptic plasticity.

Fyn in Neurodevelopment and Ischemic Brain Injury

The Src family kinases (SFKs) are nonreceptor protein tyrosine kinases that are implicated in many normal and pathological processes in the nervous system. The SFKs Fyn, Src, Yes, Lyn, and Lck are expressed in the brain. This review will focus on Fyn, as Fyn mutant mice have striking phenotypes in the brain and Fyn has been shown to be involved in ischemic brain injury in adult rodents and, with our work, in neonatal animals. An understanding of Fyn's role in neurodevelopment and disease will allow researchers to target pathological pathways while preserving protective ones.

Hemichannels: new pathways for gliotransmitter release

Growing evidence suggests that glial cells express virtually all known types of neurotransmitter receptors, enabling them to sense neuronal activity and microenvironment changes by responding locally via the Ca(2+)-dependent release of bioactive molecules, known as "gliotransmitters". Several mechanisms of gliotransmitter release have been documented. One of these mechanisms involves the opening of plasma membrane channels, known as hemichannels. These channels are composed of six protein subunits consisting of connexins or pannexins, two highly conserved protein families encoded by 21 or 3 genes, respectively, in humans. Most data indicate that under physiological conditions, glial cell hemichannels have low activity, but this activity is sufficient to ensure the release of relevant quantities of gliotransmitters to the extracellular milieu, including ATP, glutamate, adenosine and glutathione. Nevertheless, it has been suggested that dysregulations of hemichannel properties could be critical in the beginning and during the maintenance of homeostatic imbalances observed in several brain diseases. In this study, we review the current knowledge on the hemichannel-dependent release of gliotransmitters in the physiology and pathophysiology of the CNS.

Protein tyrosine phosphorylation in the ischemic brain

Cerebral ischemia, a pathological condition in which brain tissue experiences a shortage of cerebral blood flow, is associated with cerebrovascular disease, brain trauma, epilepsy, and cardiac arrest. A reduction in blood flow leaves the brain tissue unsupplied with oxygen and glucose, thus leading to cell death in the ischemic core as well as subsequent peripheral injury in the penumbra. Neurons in the penumbra, where reperfusion occurs, are functionally inactive but still viable. Many biochemical changes, which may lead to neuronal cell death, thereby induce dysfunction of the central nervous system. However, the mechanisms responsible for ischemic stroke-induced cell damage remain to be determined. Protein phosphorylation has been implicated in the regulation of diverse cellular responses in the brain. Initially, tyrosine phosphorylation was considered to be involved in the regulation of cell growth and development. In addition, a variety of synaptic and cellular functions mediated by tyrosine phosphorylation in the brain were found to be associated with relatively high levels of protein tyrosine kinase activity. However, the involvement of this protein tyrosine kinase activity in ischemic cell death is still not fully understood. This review summarizes recent advances dealing with the possible implications of protein tyrosine phosphorylation in the ischemic brain.

Enhanced NMDA receptor tyrosine phosphorylation and increased brain injury following neonatal hypoxia-ischemia in mice with neuronal Fyn overexpression

The Src family kinases (SFKs) Src and Fyn are implicated in hypoxic-ischemic (HI) injury in the developing brain. However, it is unclear how these particular SFKs contribute to brain injury. Using neuron-specific Fyn overexpressing (OE) mice, we investigated the role of neuronal Fyn in neonatal brain HI. Wild type (WT) and Fyn OE mice were subjected to HI using the Vannucci model at postnatal day 7. Brains were scored five days later for evaluation of damage using cresyl violet and iron staining. Western blotting with postsynaptic density (PSD)-associated synaptic membrane proteins and co-immunoprecipitation with cortical lysates were performed at various time points after HI to determine NMDA receptor tyrosine phosphorylation and Fyn kinase activity. Fyn OE mice had significantly higher mortality and brain injury compared to their WT littermates. Neuronal Fyn overexpression led to sustained NR2A and NR2B tyrosine phosphorylation and enhanced NR2B phosphorylation at tyrosine (Y) 1472 and Y1252 in synaptic membranes. These early changes correlated with higher calpain activity 24h after HI in Fyn OE mice relative to WT animals. Our findings suggest a role for Fyn kinase in neuronal death after neonatal HI, possibly via up-regulation of NMDA receptor tyrosine phosphorylation.

Anoxia-induced NMDA receptor activation opens pannexin channels via Src family kinases

Anoxic depolarization of pyramidal neurons results from a large inward current that is activated, in part, by excessive glutamate release during exposure to anoxia/ischemia. Pannexin-1 (Panx1) channels can be activated both by ischemia and NMDA receptors (NMDARs), but the mechanisms of Panx1 activation are unknown. We used whole-cell recordings to show that pharmacological inhibition or conditional genetic deletion of Panx1 strongly attenuates the anoxic depolarization of CA1 pyramidal neurons in acute brain slices from rats and mice. Anoxia or exogenous NMDA activated Src family kinases (SFKs), as measured by increased phosphorylation of SFKs at Y416. The SFK inhibitor PP2 prevented Src activation and Panx1 opening during anoxia. A newly developed interfering peptide that targets the SFK consensus-like sequence of Panx1 (Y308) attenuated the anoxic depolarization (AD) without affecting SFK activation. Importantly, the NMDAR antagonists, D-APV and R-CPP, attenuated AD currents carried by Panx1, and the combined application of D-APV and (10)panx (a Panx1 blocker) inhibited AD currents to the same extent as either blocker alone. We conclude that activation of NMDARs during anoxia/ischemia recruits SFKs to open Panx1, leading to sustained neuronal depolarizations.

Effects of metabotropic glutamate mGlu5 receptor antagonist on tyrosine phosphorylation of NMDA receptor subunits and cell death in the hippocampus after brain ischemia in rats

Tyrosine phosphorylation of the N-methyl-D-aspartate (NMDA) receptor appears to be associated with the regulation of the receptor's ion channel. This study focused on the effect of a metabotropic glutamate mGlu5 receptor antagonist on tyrosine phosphorylation of NMDA receptor subunits and cell death in the hippocampal CA1 region after transient global ischemia and sought to explore their mechanisms. Pretreatment with the mGlu5 receptor antagonist reduced cell death in the hippocampal CA1 region on day 3 after the transient ischemia. Transient ischemia increased the tyrosine phosphorylation of NMDA receptor subunits, which are a major target of Src family tyrosine kinases. Therefore, we investigated the effect of the antagonist on tyrosine phosphorylation of the NMDA receptor subunits after transient ischemia. Tyrosine phosphorylation of the NR2A subunit, but not that of the NR2B one, was inhibited by the mGlu5 receptor antagonist. The administration of the antagonist also attenuated the increase in the amount of active form of Src after the reperfusion. We further demonstrated that the administration of a Src-family kinase inhibitor prevented cell death in the hippocampal CA1 region and attenuated the increase in the tyrosine phosphorylation of the NMDA receptor subunits after the reperfusion. These findings suggest that mGlu5 receptor in the hippocampal CA1 region after transient ischemia is involved in the activation of Src and subsequent tyrosine phosphorylation of NMDA receptor subunits, which actions may contribute to alterations of properties of the NMDA receptor and may be related to pathogenic events leading to neuronal cell death.

Chronic zinc exposure decreases the surface expression of NR2A-containing NMDA receptors in cultured hippocampal neurons

BACKGROUND

Zinc distributes widely in the central nervous system, especially in the hippocampus, amygdala and cortex. The dynamic balance of zinc is critical for neuronal functions. Zinc modulates the activity of N-methyl-D-aspartate receptors (NMDARs) through the direct inhibition and various intracellular signaling pathways. Abnormal NMDAR activities have been implicated in the aetiology of many brain diseases. Sustained zinc accumulation in the extracellular fluid is known to link to pathological conditions. However, the mechanism linking this chronic zinc exposure and NMDAR dysfunction is poorly understood.

METHODOLOGY/PRINCIPAL FINDINGS

We reported that chronic zinc exposure reduced the numbers of NR1 and NR2A clusters in cultured hippocampal pyramidal neurons. Whole-cell and synaptic NR2A-mediated currents also decreased. By contrast, zinc did not affect NR2B, suggesting that chronic zinc exposure specifically influences NR2A-containg NMDARs. Surface biotinylation indicated that zinc exposure attenuated the membrane expression of NR1 and NR2A, which might arise from to the dissociation of the NR2A-PSD-95-Src complex.

CONCLUSIONS

Chronic zinc exposure perturbs the interaction of NR2A to PSD-95 and causes the disorder of NMDARs in hippocampal neurons, suggesting a novel action of zinc distinct from its acute effects on NMDAR activity.

Lymphocyte cell kinase activation mediates neuroprotection during ischemic preconditioning

The molecular mechanisms underlying preconditioning (PC), a powerful endogenous neuroprotective phenomenon, remain to be fully elucidated. Once identified, these endogenous mechanisms could be manipulated for therapeutic gain. We investigated whether lymphocyte cell kinase (Lck), a member of the Src kinases family, mediates PC. We used both in vitro primary cortical neurons and in vivo mouse cerebral focal ischemia models of preconditioning, cellular injury, and neuroprotection. Genetically engineered mice deficient in Lck, gene silencing using siRNA, and pharmacological approaches were used. Cortical neurons preconditioned with sublethal exposure to NMDA or oxygen glucose deprivation (OGD) exhibited enhanced Lck kinase activity, and were resistant to injury on subsequent exposure to lethal levels of NMDA or OGD. Lck gene silencing using siRNA abolished tolerance against both stimuli. Lck-/- mice or neurons isolated from Lck-/- mice did not exhibit PC-induced tolerance. An Lck antagonist administered to wild-type mice significantly attenuated the neuroprotective effect of PC in the mouse focal ischemia model. Using pharmacological and gene silencing strategies, we also showed that PKCε is an upstream regulator of Lck, and Fyn is a downstream target of Lck. We have discovered that Lck plays an essential role in PC in both cellular and animal models of stroke. Our data also show that the PKCε-Lck-Fyn axis is a key mediator of PC. These findings provide new opportunities for stroke therapy development.

S-nitrosylation of c-Src via NMDAR-nNOS module promotes c-Src activation and NR2A phosphorylation in cerebral ischemia/reperfusion

Previous studies suggested that activated c-Src promote the tyrosine phosphorylation of NMDA receptor subunit NR2A, and thus aggravate the injury induced by transient cerebral ischemia/reperfusion (I/R) in rat hippocampus CA1 region. In this study, we examined the effect of nitric oxide (NO) on the activation of c-Src and the tyrosine phosphorylation of NMDA receptor NR2A subunit. The results show that S-nitrosylation and the phosphorylation of c-Src were induced after cerebral I/R in rats, and administration of nNOS inhibitor 7-NI, nNOS antisense oligonucleotides and exogenous NO donor sodium nitroprusside diminished the increased S-nitrosylation and phosphorylation of c-Src during cerebral I/R. The cysteine residues of c-Src modified by S-nitrosylation are Cys489, Cys498, and Cys500. On the other hand, NMDAR antagonist MK-801 could attenuate the S-nitrosylation and activation of c-Src. Taken together, the S-nitrosylation of c-Src is provoked by NO derived from endogenous nNOS, which is activated by Ca(2+) influx from NMDA receptors, and promotes the auto-phosphorylation at tyrosines and further phosphorylates NR2A. The molecular mechanism we outlined here is a novel postsynaptic NMDAR-nNOS/c-Src-mediated signaling amplification, the 'NMDAR-nNOS → NO → SNO-c-Src → p-c-Src → NMDAR-nNOS' cycle, which presents the possibility as a potential therapeutic target for stroke treatment.

Protracted Tyrosine Phosphorylation of the Glutamate Receptor Subunit NR2 in the Rat Hippocampus Following Transient Cerebral Ischemia is Prevented by Intra-Ischemic Hypothermia

Changes in the dynamic interactions of macromolecules in cell membranes appear to underlie the robust neuroprotective effect of hypothermia against selective neuronal degeneration in the CA1 region of the rat hippocampus after transient cerebral ischemia, but the detailed mechanisms are still elusive. Using the two-vessel occlusion model of transient normothermic cerebral ischemia of 15 min duration, we investigated the tyrosine phosphorylation of synaptic proteins in general and that of the NMDA receptor subunits in particular, at different times of recirculation. Specifically, the effect of intra-ischemic hypothermia (33°C), which provides neuroprotection to the CA1 region of the hippocampus, was studied. Phosphorylation of tyrosine residues on the NMDA receptor (NR) 2, but not of the NR1 or the AMPA receptor subunit 1 (GluR1) proteins, was markedly enhanced following cerebral ischemia. Protein tyrosine phosphorylation was persistently increased in the postsynaptic densities of the vulnerable CA1 region, but was transient in the CA3/dentate gyrus (DG) neurons where cell death was not evident. The phospho-tyrosine phosphatase activity decreased during reperfusion in the CA1 region but not in CA3/DG. Importantly, decreasing body temperature to 33°C during ischemia modified the dynamics of the protein tyrosine phosphorylation of NR2 in the CA1 region, which was transient and similar in time course to that seen in the CA3/DG region after normothermic ischemia. We conclude that the protracted tyrosine phosphorylation of the NR2 subunit in the hippocampus CA1 region following normothermic ischemia is attenuated by hypothermia and therefore constitutes an important target for hypothermic neuroprotection.

Towards a quantitative model of the post-synaptic proteome

The postsynaptic compartment of the excitatory glutamatergic synapse contains hundreds of distinct polypeptides with a wide range of functions (signalling, trafficking, cell-adhesion, etc.). Structural dynamics in the post-synaptic density (PSD) are believed to underpin cognitive processes. Although functionally and morphologically diverse, PSD proteins are generally enriched with specific domains, which precisely define the mode of clustering essential for signal processing. We applied a stochastic calculus of domain binding provided by a rule-based modelling approach to formalise the highly combinatorial signalling pathway in the PSD and perform the numerical analysis of the relative distribution of protein complexes and their sizes. We specified the combinatorics of protein interactions in the PSD by rules, taking into account protein domain structure, specific domain affinity and relative protein availability. With this model we interrogated the critical conditions for the protein aggregation into large complexes and distribution of both size and composition. The presented approach extends existing qualitative protein-protein interaction maps by considering the quantitative information for stoichiometry and binding properties for the elements of the network. This results in a more realistic view of the postsynaptic proteome at the molecular level.

Involvement of src-kinase activation in ischemic preconditioning induced protection of mouse brain

AIMS

To investigate the role of src-kinase in ischemic preconditioning induced reversal of ischemia and reperfusion induced cerebral injury in mice.

MAIN METHODS

Bilateral carotid artery occlusion of 17min followed by reperfusion for 24h was employed to produce ischemia and reperfusion induced cerebral injury in mice. Cerebral infarct size was measured using triphenyltetrazolium chloride staining using both by volume and by weight methods differently. Memory was evaluated using elevated plus maze test. Rota rod test was employed to assess motor incoordination.

KEY FINDINGS

Bilateral carotid artery occlusion followed by reperfusion produced cerebral infarction and impaired memory and motor co-ordination. Three preceding episodes of bilateral carotid artery occlusion for 1min and reperfusion of 1min (ischemic preconditioning) prevented markedly ischemia-reperfusion-induced cerebral injury measured in terms of infarct size (38.5±1.3% and 38.5±2.9% mean infarct of control animals was reduced to 24.3±1.2% and 23.5±1.8% of the preconditioning groups respectively), loss of memory (72.2±3.6 mean transfer latency time of control animals was reduced to 25.6±5.2 of the preconditioning group respectively) and motor coordination (78.3±17.6s mean falling down latency time of control animals was increased to a mean value of 180.9±6.5s of the preconditioning groups respectively). SU6656 (2mg/kg, ip) and PP1 (0.1mg/kg, ip), highly selective src-kinase inhibitors, attenuated this neuroprotective effect of ischemic preconditioning.

SIGNIFICANCE

Therefore, neuroprotective effect of ischemic preconditioning may be due to src-kinase linked mechanism.

NADPH oxidase-mediated oxidative damage to proteins in the postsynaptic density after transient cerebral ischemia and reperfusion

NADPH oxidase is an important source of superoxide in the central nervous system. Although NADPH oxidase is localized near the postsynaptic site in neurons, little is known about the pathophysiological role of NADPH oxidase in synapses after cerebral ischemia and reperfusion. In the present study, we sought to determine the role of NADPH oxidase in oxidative damage to postsynaptic density (PSD) proteins, which were isolated from rats subjected to transient focal cerebral ischemia and reperfusion. The amounts of carbonylated PSD proteins were increased after transient focal cerebral ischemia and reperfusion. This change was accompanied by an increase in the level of NADPH oxidase subunits in the PSD. The administration of apocynin, an NADPH oxidase inhibitor, attenuated both the protein carbonylation in the PSD and cerebral infarct volume. We further demonstrated that the decreases seen in the amounts of PSD-associated proteins, such as neuroligin, N-cadherin, and SAP102, in the PSD were prevented by treatment with apocynin. These results suggest that pronounced activation of NADPH oxidase in the PSD after cerebral ischemia and reperfusion may be related to the focal oxidative damage to synaptic functions and subsequent development of ischemia and reperfusion-induced cerebral injury.

Decay accelerating factor (CD55) protects neuronal cells from chemical hypoxia-induced injury

Background

Activated complement system is known to mediate neuroinflammation and neurodegeneration following exposure to hypoxic-ischemic insults. Therefore, inhibition of the complement activation cascade may represent a potential therapeutic strategy for the management of ischemic brain injury. Decay-accelerating factor (DAF, also known as CD55) inhibits complement activation by suppressing the function of C3/C5 convertases, thereby limiting local generation or deposition of C3a/C5a and membrane attack complex (MAC or C5b-9) production. The present study investigates the ability of DAF to protect primary cultured neuronal cells subjected to sodium cyanide (NaCN)-induced hypoxia from degeneration and apoptosis.

Methods

Cultured primary cortical neurons from embryonic Sprague-Dawley rats were assigned one of four groups: control, DAF treatment alone, hypoxic, or hypoxic treated with DAF. Hypoxic cultures were exposed to NaCN for 1 hour, rinsed, followed by 24 hour exposure to 200 ng/ml of recombinant human DAF in normal medium. Human DAF was used in the present study and it has been shown to effectively regulate complement activation in rats. Neuronal cell function, morphology and viability were investigated by measuring plateau depolarization potential, counting the number dendritic spines, and observing TUNEL and MTT assays. Complement C3, C3a, C3a receptor (R) production, C3a-C3aR interaction and MAC formation were assessed along with the generation of activated caspase-9, activated caspase-3, and activated Src.

Results

When compared to controls, hypoxic cells had fewer dendritic spines, reduced plateau depolarization accompanied by increased apoptotic activity and accumulation of MAC, as well as up-regulation of C3, C3a and C3aR, enhancement of C3a-C3aR engagement, and elevated caspase and Src activity. Treatment of hypoxic cells with 200 ng/ml of recombinant human DAF resulted in attenuation of neuronal apoptosis and exerted significant protection against neuronal dendritic spine loss and plateau depolarization reduction. Furthermore, treatment with DAF resulted in decreased accumulation of C3a, MAC, C3a-C3aR interaction, caspase-9, activated caspase-3, and pTyr416-Src (activated Src) tyrosine kinase.

Conclusion

DAF was found to reduce neuronal cell death and apoptosis in NaCN induced hypoxia. This effect is attributed to the ability of DAF to limit complement activation and inhibit the activity of Src and caspases 9 and 3. This study supports the inhibiting of complement as a neuroprotective strategy against CNS ischemia/reperfusion injury.

Inhibition of Src activity decreases tyrosine phosphorylation of occludin in brain capillaries and attenuates increase in permeability of the blood-brain barrier after transient focal cerebral ischemia

Disruption of the blood-brain barrier (BBB) caused by cerebral ischemia can initiate the development and progression of brain injuries, which may lead to irreversible dysfunction of the central nervous system. It is likely that tyrosine phosphorylation of a membrane-associated tight junctional protein, occludin, is important for the interaction of occludin with intracellular proteins, ZO-1 to ZO-3, and it regulates vascular permeability. Little is known about the pathophysiological alterations of tight junctional proteins after transient focal cerebral ischemia. In this study, we examined the tyrosine phosphorylation of occludin in isolated brain capillaries after transient focal cerebral ischemia. We further examined the effects of the Src-family tyrosine kinase inhibitor, PP2, on the tyrosine phosphorylation of occludin and on vascular permeability and infarct volume. Transient focal ischemia increased the tyrosine phosphorylation of occludin in the isolated brain capillaries. The administration of PP2 attenuated this phosphorylation, which was coincident with an inhibition of BBB leakage and a decrease in infarct volume. These results suggest that the increase in the tyrosine phosphorylation of occludin in the brain capillaries may be linked to the disruption of tight junctions, whose disruption can cause dysfunction of the BBB and the consequent increase in infarct volume.

Oxaloacetate restores the long-term potentiation impaired in rat hippocampus CA1 region by 2-vessel occlusion

Various acute brain pathological conditions are characterized by the presence of elevated glutamate concentrations in the brain interstitial fluids. It has been established that a decrease in the blood glutamate level enhances the brain-to-blood efflux of glutamate, removal of which from the brain may prevent glutamate excitotoxicity and its contribution to the long-lasting neurological deficits seen in stroke. A decrease in blood glutamate level can be achieved by exploiting the glutamate-scavenging properties of the blood-resident enzyme glutamate-oxaloacetate transaminase, which transforms glutamate into 2-ketoglutarate in the presence of the glutamate co-substrate oxaloacetate. The present study had the aim of an evaluation of the effects of the blood glutamate scavenger oxaloacetate on the impaired long-term potentiation (LTP) induced in the 2-vessel occlusion ischaemic model in rat. Transient (30-min) incomplete forebrain ischaemia was produced 72 h before LTP induction. Although the short transient brain hypoperfusion did not induce histologically identifiable injuries in the CA1 region (Fluoro-Jade B, S-100 and cresyl violet), it resulted in an impaired LTP function in the hippocampal CA1 region without damaging the basal synaptic transmission between the Schaffer collaterals and the pyramidal neurons. This impairment could be fended off in a dose-dependent manner by the intravenous administration of oxaloacetate in saline (at doses between 1.5 mmol and 0.1 mumol) immediately after the transient hypoperfusion. Our results suggest that oxaloacetate-mediated blood and brain glutamate scavenging contributes to the restoration of the LTP after its impairment by brain ischaemia.

Inhibition of NR2B phosphorylation restores alterations in NMDA receptor expression and improves functional recovery following traumatic brain injury in mice

Traumatic brain injury (TBI) triggers a massive glutamate efflux, hyperactivation of N-methyl-D-aspartate receptors (NMDARs) and neuronal cell death. Previously it was demonstrated that, 15 min following experimentally induced closed head injury (CHI), the density of activated NMDARs increases in the hippocampus, and decreases in the cortex at the impact site. Here we show that CHI-induced alterations in activated NMDARs correlate with changes in the expression levels of the major NMDARs subunits. In the hippocampus, the expression of NR1, NR2A, and NR2B subunits as well as the GluR1 subunit of the AMPA receptor (AMPAR) were increased, while in the cortex at the impact site, we found a decrease in the expression of these subunits. We demonstrate that CHI-induced increase in the expression of NMDAR subunits and GluR1 in the hippocampus, but not in the cortex, is associated with an increase in NR2B tyrosine phosphorylation. Furthermore, inhibition of NR2B-phosphorylation by the tyrosine kinase inhibitor PP2 restores the expression of this subunit to its normal levels. Finally, a single injection of PP2, prior to the induction of CHI, resulted in a significant improvement in long-term recovery of motor functions observed in CHI mice. These results provide a new mechanism by which acute trauma contributes to the development of secondary damage and functional deficits in the brain, and suggests a possible role for Src tyrosine kinase inhibitors as preoperative therapy for planned neurosurgical procedures.

Postsynaptic density-membrane associated guanylate kinase proteins (PSD-MAGUKs) and their role in CNS disorders

Membrane associated guanylate kinase proteins (MAGUKs) play a key role in the regulation of the intracellular trafficking and synaptic localization of ionotropic glutamate receptors. In particular, the postsynaptic density-95-like subfamily of MAGUKs (PSD-MAGUKs) organizes ionotropic glutamate receptors and their associated signaling proteins in the postsynaptic density of the excitatory synapse regulating the strength of synaptic activity. Several recent observations clearly put forward the idea that alterations of PSD-MAGUK protein function such as alterations of PSD-MAGUK protein interaction with N-methyl-D-aspartate (NMDA) receptors regulatory subunits are common events in several CNS disorders. With this view, a better knowledge and understanding of PSD-MAGUK function as well as of the molecular events regulating PSD-MAGUK-mediated interactions in the glutamatergic synapse could lead to the identification of new pharmaceutical targets for the therapy of CNS disorders.

Neuroprotection of GluR5-containing kainate receptor activation against ischemic brain injury through decreasing tyrosine phosphorylation of N-methyl-D-aspartate receptors mediated by Src kinase

Previous studies indicate that cerebral ischemia breaks the dynamic balance between excitatory and inhibitory inputs. The neural excitotoxicity induced by ionotropic glutamate receptors gain the upper hand during ischemia-reperfusion. In this paper, we investigate whether GluR5 (glutamate receptor 5)-containing kainate receptor activation could lead to a neuroprotective effect against ischemic brain injury and the related mechanism. The results showed that (RS)-2-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl) propanoic acid (ATPA), a selective GluR5 agonist, could suppress Src tyrosine phosphorylation and interactions among N-methyl-D-aspartate (NMDA) receptor subunit 2A (NR2A), postsynaptic density protein 95 (PSD-95), and Src and then decrease NMDA receptor activation through attenuating tyrosine phosphorylation of NR2A and NR2B. More importantly, ATPA had a neuroprotective effect against ischemia-reperfusion-induced neuronal cell death in vivo. However, four separate drugs were found to abolish the effects of ATPA. These were selective GluR5 antagonist NS3763; GluR5 antisense oligodeoxynucleotides; CdCl(2), a broad spectrum blocker of voltage-gated calcium channels; and bicuculline, an antagonist of gamma-aminobutyric acid A (GABA(A)) receptor. GABA(A) receptor agonist muscimol could attenuate Src activation and interactions among NR2A, PSD-95 and Src, resulting the suppression of NMDA receptor tyrosine phosphorylation. Moreover, patch clamp recording proved that the activated GABA(A) receptor could inhibit NMDA receptor-mediated whole-cell currents. Taken together, the results suggest that during ischemia-reperfusion, activated GluR5 may facilitate Ca(2+)-dependent GABA release from interneurons. The released GABA can activate postsynaptic GABA(A) receptors, which then attenuates NMDA receptor tyrosine phosphorylation through inhibiting Src activation and disassembling the signaling module NR2A-PSD-95-Src. The final result of this process is that the pyramidal neurons are rescued from hyperexcitability.

mGluR1 antagonist decreases tyrosine phosphorylation of NMDA receptor and attenuates infarct size after transient focal cerebral ischemia

The contribution of metabotropic glutamate receptors to brain injury after in vivo cerebral ischemia remains to be determined. We investigated the effects of the metabotropic glutamate receptor 1 (mGluR1) antagonist LY367385 on brain injury after transient (90 min) middle cerebral artery occlusion in the rat and sought to explore their mechanisms. The intravenous administration of LY367385 (10 mg/kg) reduced the infarct volume at 24 h after the start of reperfusion. As the Gq-coupled mGluR1 receptor is known to activate the PKC/Src family kinase cascade, we focused on changes in the activation and amount of these kinases. Transient focal ischemia increased the amount of activated tyrosine kinase Src and PKC in the post-synaptic density (PSD) at 4 h of reperfusion. The administration of LY367385 attenuated the increases in the amounts of PSD-associated PKCgamma and Src after transient focal ischemia. We further investigated phosphorylation of the NMDA receptor, which is a major target of Src family kinases to modulate the function of the receptor. Transient focal ischemia increased the tyrosine phosphorylation of NMDA receptor subunits NR2A and NR2B. Tyrosine phosphorylation of NR2A, but not that of NR2B, in the PSD at 4 h of reperfusion was inhibited by LY367385. These results suggest that the mGluR1 after transient focal ischemia is involved in the activation of Src, which may be linked to the modification of properties of the NMDA receptor and the development of cerebral infarction.

Sustained activation of Src-family tyrosine kinases by ischemia: A potential mechanism mediating extracellular signal-regulated kinase cascades in hippocampal dentate gyrus

In the present report, we investigated the association between the sustained activation of Src family tyrosine kinases (primarily Src kinase) with the biphasic phosphorylation of extracellular signal-regulated kinase (ERK) induced by ischemia in the rat hippocampal CA3/dentate gyrus subfield. Post-ischemia reperfusion resulted in the phosphorylation of ERK in a Ras-dependent manner; down-regulation of NMDA receptors or Src family protein kinases by ketamine or 4-amino-5-(4-chlorophenyl)-7-(t-butyl) pyrazolo[3,4-d] pyrimidine (PP2) potently antagonized the activation of ERK, indicating that NMDA receptors and Src family tyrosine kinases are essential for the up-regulation of ERK activity following ischemic stimuli. Additionally, an ischemia-induced association between RKIP and Raf-1 resulted in the inhibition of the ERK signaling cascade through an inhibition of Src-mediated Raf-1 phosphorylation at Tyr340/341 residues. This ischemia-induced inhibition of ERK was not associated with other downstream pathways involving Raf-1 phosphorylation at Ser 259 elicited by protein kinase B (Akt). Dissociation of Raf-1 from RKIP by 24 h reperfusion or (4S)-3-[(E)-but-2-enoyl]-4-benzyl-2-oxazolidinone (locostatin) influenced the second phase of ERK activation elicited by the Src-Raf cassette. We propose that, following ischemia, the Src family tyrosine kinases are critical for modulation of the Ras/Raf/MEK/ERK cascade, in which RKIP is involved in biphasic phosphorylation of ERK via a blockade of Src-Raf cascades.

Dehydroepiandrosterone sulfate prevents ischemia-induced impairment of long-term potentiation in rat hippocampal CA1 by up-regulating tyrosine phosphorylation of NMDA receptor

We have reported that dehydroepiandrosterone sulfate (DHEAS) reduces the threshold for long-term potentiation (LTP) in Shaffer collateral-CA1 synapses through the amplification of Src-dependent NMDA receptor signaling. The present study is a follow-up of the above reports, aiming at evaluating the effects of DHEAS on the impaired LTP in reversible forebrain ischemic rats. Transient (20 min) incomplete forebrain ischemia led to an impaired LTP in the hippocampal CA1 region without damages to the basal synaptic transmission between the Shaffer collaterals and pyramidal neurons. Repetitive administrations of DHEAS (20 mg/kg for 3 days) from the first 3 h of reperfusion, but not acute DHEAS application (50 microM), prevent the impairment of LTP produced by ischemia. Co-administration of the specific sigma(1) receptor antagonist NE100 with DHEAS completely prevented the protective effect of DHEAS. In contrast, progesterone (PRGO) not only had no protective effect against the ischemic LTP impairment, but also attenuated the protective effect of DHEAS on the impaired LTP. Tyrosine phosphorylation of NMDA receptor subunit 2B (NR2B) significantly decreased after ischemia, whereas that of NR1 had no obvious change. Furthermore, the repetitive administration of DHEAS improved the reduction in tyrosine phosphorylation of NR2B. These findings suggest that the repetitive activation of sigma(1) receptor induced by DHEAS might prevent the ischemic LTP impairment through regulating the tyrosine phosphorylation of NR2B.

New targets for pharmacological intervention in the glutamatergic synapse

Excitotoxicity is thought to be a major mechanism in many human disease states such as ischemia, trauma, epilepsy and chronic neurodegenerative disorders. Briefly, synaptic overactivity leads to the excessive release of glutamate that activates postsynaptic cell membrane receptors, which upon activation open their associated ion channel pore to produce ion influx. To date, although molecular basis of glutamate toxicity remain uncertain, there is general agreement that N-methyl-d-aspartate (NMDA) subtype of ionotropic glutamate receptors plays a key role in mediating at least some aspects of glutamate neurotoxicity. On this view, research has focused in the discovery of new compounds able to either reduce glutamate release or activation of postsynaptic NMDA receptors. Although NMDA receptor antagonists prevent excitotoxicity in cellular and animal models, these drugs have limited usefulness clinically. Side effects such as psychosis, nausea, vomiting, memory impairment, and neuronal cell death accompany complete NMDA receptor blockade, dramatizing the crucial role of the NMDA receptor in normal neuronal processes. Recently, however, well-tolerated compounds such as memantine has been shown to be able to block excitotoxic cell death in a clinically tolerated manner. Understanding the biochemical properties of the multitude of NMDA receptor subtypes offers the possibility of developing more effective and clinically useful drugs. The increasing knowledge of the structure and function of this postsynaptic NMDA complex may improve the identification of specific molecular targets whose pharmacological or genetic manipulation might lead to innovative therapies for brain disorders.

Reappearance of hippocampal CA1 neurons after ischemia is associated with recovery of learning and memory

The pyramidal neurons of the hippocampal CA1 region are essential for cognitive functions such as spatial learning and memory, and are selectively destroyed after cerebral ischemia. To analyze whether degenerated CA1 neurons are replaced by new neurons and whether such regeneration is associated with amelioration in learning and memory deficits, we have used a rat global ischemia model that provides an almost complete disappearance (to approximately 3% of control) of CA1 neurons associated with a robust impairment in spatial learning and memory at two weeks after ischemia. We found that transient cerebral ischemia can evoke a massive formation of new neurons in the CA1 region, reaching approximately 40% of the original number of neurons at 90 days after ischemia (DAI). Co-localization of the mature neuronal marker neuronal nuclei with 5-bromo-2'-deoxyuridine in CA1 confirmed that neurogenesis indeed had occurred after the ischemic insult. Furthermore, we found increased numbers of cells expressing the immature neuron marker polysialic acid neuronal cell adhesion molecule in the adjacent lateral periventricular region, suggesting that the newly formed neurons derive from this region. The reappearance of CA1 neurons was associated with a recovery of ischemia-induced impairments in spatial learning and memory at 90 DAI, suggesting that the newly formed CA1 neurons restore hippocampal CA1 function. In conclusion, these results show that the brain has an endogenous capacity to form new nerve cells after injury, which correlates with a restoration of cognitive functions of the brain.

Experimental subarachnoid hemorrhage induces changes in the levels of hippocampal NMDA receptor subunit mRNA

NMDA receptors may play a crucial role in nerve cell death following subarachnoid hemorrhage (SAH). Changes in NMDA receptor-mediated transmission appear before neuronal death in rodent models of transient ischemia, and NMDA receptor function is known to be dependent on subunit composition. Here, we have investigated whether mRNA expression of the NMDA receptor subunits is altered in the hippocampal formation 3-5 h following experimental SAH, and correlated these early alterations to subsequent delayed cell death. SAH was induced by intraluminal perforation of the internal carotid artery intracranially, and cerebral blood flow (CBF) was bilaterally monitored by laser-Doppler flowmetry. Early changes in NMDA receptor subunit mRNA and early nerve cell death were analyzed at 3-5 h after SAH, and delayed nerve cell death was analyzed at 2-7 days after SAH. Duration of ipsilateral CBF reduction below 30% of baseline (CBF30) was predictive of ipsilateral delayed nerve cell death in the CA1 2-7 days after SAH. At CBF30 > 9 min, we found downregulation of mRNA for NR2A, NR2B, and NR3B at 3-5 h after SAH, whereas the levels of NR1 mRNA were unaffected. The downregulation of NR2A and NR2B mRNA may result in a reduced NMDA receptor function. Such reduction may be sufficient to provide neuroprotection in the dentate gyrus, where no cell death appears, but insufficient to rescue neurons in the hippocampus proper following SAH.

Impairment of conditioned freezing to tone, but not to context, in Fyn-transgenic mice: relationship to NMDA receptor subunit 2B function

We previously demonstrated that transgenic mice overexpressing Fyn tyrosine kinase exhibit higher seizure susceptibility and enhanced tyrosine phosphorylation of several proteins, including the N-methyl-D-aspartate (NMDA) receptor subunit 2B (NR2B). In the present study, we analysed behavioural phenotypes, especially conditioned fear responses, of Fyn-transgenic (TG) mice to better understand the role of Fyn in learned emotional behaviour. Tone-dependent conditioned freezing was significantly attenuated in Fyn-TG mice, whereas context-dependent freezing was unaffected. Neither massed nor spaced conditioning ameliorated the attenuation of tone-dependent freezing. However, the selective NR2B antagonist ifenprodil, when administered before conditioning, restored tone-dependent freezing in Fyn-TG mice at a dose that did not affect freezing in wild-type (WT) mice. These results suggest that impairment of tone-dependent conditioned freezing in Fyn-TG mice is caused by disruption of the NR2B-containing NMDA receptor function. Tyrosine phosphorylation of brain proteins, including NR2B, was enhanced in Fyn-TG mice compared with that in WT mice. We also found that ifenprodil significantly suppressed the enhanced tyrosine phosphorylation. Thus, our data support the notion that NMDA receptor activity is tightly correlated with protein tyrosine phosphorylation, and Fyn might be one key molecule that controls tone-dependent conditioned freezing through the regulation of NMDA receptor function.

Increased phosphorylation and redistribution of NMDA receptors between synaptic lipid rafts and post-synaptic densities following transient global ischemia in the rat brain

Ischemia results in increased phosphorylation of NMDA receptors. To investigate the possible role of lipid rafts in this increase, lipid rafts and post-synaptic densities (PSDs) were isolated by the extraction of rat brain synaptosomes with Triton X-100 followed by sucrose density gradient centrifugation. Lipid rafts accounted for the majority of PSD-95, whereas SAP102 was predominantly located in PSDs. Between 50 and 60% of NMDA receptors were associated with lipid rafts. Greater than 85-90% of Src and Fyn were present in lipid rafts, whereas Pyk2 was mainly associated with PSDs. Lipid rafts and PSDs were isolated from animals subjected to 15 min of global ischemia followed by 6 h of recovery. Ischemia did not affect the yield, density, flotillin-1 or cholesterol content of lipid rafts. Following ischemia, the phosphorylation of NR1 by protein kinase C and tyrosine phosphorylation of NR2A and NR2B was increased in both lipid rafts and PSDs, with a greater increase in tyrosine phosphorylation occurring in the raft fraction. Following ischemia, NR1, NR2A and NR2B levels were elevated in PSDs and reduced in lipid rafts. The findings are consistent with a model involving close interaction between lipid rafts and PSDs and a role for lipid rafts in ischemia-induced signaling pathways.

Transient forebrain ischemia effects interaction of Src, FAK, and PYK2 with the NR2B subunit of N-methyl-d-aspartate receptor in gerbil hippocampus

Two different models of brain ischemia were used to examine the evoked changes in the tyrosine phosphorylation of NMDA receptor subunits 2A and 2B (NR2A and NR2B), as well as their interactions with non-receptor tyrosine kinases (NRTKs: FAK, PYK2 Src), and PSD-95 protein. Only short-term 5 min ischemia followed by 3 h reperfusion resulted in the elevated tyrosine phosphorylation of both investigated NMDA receptor subunits, but in contrast to previously published data, more pronounced in the case of NR2B. Concomitantly, an increased association of NR2B with FAK, PYK2, Src and PSD-95 has been observed. This sharp early reaction to brief ischemia was markedly attenuated during prolonged recovery (72 h) with almost complete return to control values. The initial recruitment of tyrosine kinases to NMDA receptor during the first 3 h of reperfusion is generally consistent with an active postischemic remodeling of PSD and may participate in the induction of the postischemic signal transduction pathway in gerbil hippocampus. In contrast, ischemia of longer duration (up to 30 min) caused an immediate decrease in the protein levels as well as tyrosine phosphorylation of both NR2A and NR2B subunits which was accompanied by the marked attenuation of the association with their investigated molecular partners--PSD-95 and NRTKs. This effect may be mimicked in vitro by Ca2+-dependent activation of endogenous calpains in purified PSD preparation suggesting irreversible deterioration of the synaptic signaling machinery during irreversible long-term ischemia.

Changes in phosphorylation of the NMDA receptor in the rat hippocampus induced by status epilepticus

Systemic administration of pilocarpine preceded by lithium induces status epilepticus (SE) that results in neurodegeneration and may lead to the development of spontaneous recurrent seizures. We investigated the effect of Li/pilocarpine-induced SE on phosphorylation of the NMDA receptor in rat hippocampus. Phosphorylation of NR1 by PKC on Ser890 was decreased to 45% of control values immediately following 1 h of SE. During the first 3 h following the termination of SE, phosphorylation of Ser890 increased 4-fold before declining to control values by 24 h. Phosphorylation of NR1 by PKA was also depressed relative to controls immediately following SE and transiently increased above control values upon the termination of SE. SE was accompanied by a general increase in tyrosine phosphorylation of hippocampal proteins that lasted for several hours following the termination of seizures. Tyrosine phosphorylation of the NR2A and NR2B subunits of the NMDAR increased 3-4-fold over control values during SE, continued to increase during the first hour following SE and then declined to control levels by 24 h. SE resulted in the activation of Src and Pyk2 associated with the postsynaptic apparatus, suggesting a role for these enzymes in the SE-induced increase in tyrosine phosphorylation. Changes in phosphorylation of the NMDA receptor may play a role in the pathophysiological consequences of SE.

Suppression of Pyk2 attenuated the increased tyrosine phosphorylation of NMDA receptor subunit 2A after brain ischemia in rat hippocampus

Effects of suppressing the protein expression of Pyk2 on increased tyrosine phosphorylation of N-methyl-D-aspartate (NMDA) receptor subunit 2A (NR2A) after brain ischemia in rat hippocampus were studied with immunoprecipitation and immunoblot. Transient (15 min) brain ischemia and reperfusion (I/R) was induced by four-vessel occlusion in Sprague-Dawley (SD) rats. I/R led to increases of tyrosine phosphorylation of NR2A and interaction of Pyk2 and Src kinase with NR2A after 6 h of reperfusion. The increases were attenuated by Pyk2 antisense oligonucleotides intracerebroventricularly infused every 24 h for 4 days before ischemia, but not missense oligonucleotides or vehicle. The antisense also inhibited the increased auto-phosphorylation of Pyk2 and Src kinase, while the protein expression of NR2A or Src kinase had no obvious change under the above conditions. The data suggested that Pyk2 may be involved in facilitating NR2A tyrosine phosphorylation by Src kinase after I/R.

Hypoxia-ischemia in the immature brain

The immature brain has long been considered to be resistant to the damaging effects of hypoxia and hypoxia-ischemia (H/I). However, it is now appreciated that there are specific periods of increased vulnerability, which relate to the developmental stage at the time of the insult. Although much of our knowledge of the pathophysiology of cerebral H/I is based on extensive experimental studies in adult animal models, it is important to appreciate the major differences in the immature brain that impact on its response to, and recovery from, H/I. Normal maturation of the mammalian brain is characterized by periods of limitations in glucose transport capacity and increased use of alternative cerebral metabolic fuels such as lactate and ketone bodies, all of which are important during H/I and influence the development of energy failure. Cell death following H/I is mediated by glutamate excitotoxicity and oxidative stress, as well as other events that lead to delayed apoptotic death. The immature brain differs from the adult in its sensitivity to all of these processes. Finally, the ultimate outcome of H/I in the immature brain is determined by the impact on the ensuing cerebral maturation. A hypoxic-ischemic insult of insufficient severity to result in rapid cell death and infarction can lead to prolonged evolution of tissue damage.

Possible mechanisms underlying the protective effects of SY-21, an extract of a traditional Chinese herb, on transient brain ischemia/reperfusion-induced neuronal death in rat hippocampus

We examined the neuroprotective actions of SY-21, a potent ingredient of a traditional Chinese herb, histologically. Transient brain ischemia (15 min) was induced by four-vessel occlusion in Sprague-Dawley rats. Administration of SY-21 20 min before or 6 h after brain ischemia significantly increased the number of surviving hippocampal CA1 pyramidal cells in rats subjected to transient brain ischemia followed by 5 days of reperfusion. Neuronal cell death resulting from ischemic events is associated with abnormal activation of the NMDA receptors. Tyrosine phosphorylation of the NMDA receptor subunit NR2A by Src or Fyn has been implicated in the up-regulation of NMDA receptor activity. In order to investigate the possible mechanism of the neuroprotective action of SY-21, we examined the effects of SY-21 on the ischemia/reperfusion-induced increases in tyrosine phosphorylation of the NMDA receptor subunit 2A (NR2A) and on the interactions involving NR2A, PSD-95 and Src/Fyn. We found that the increase in the tyrosine phosphorylation of NR2A induced by brain ischemia/reperfusion is suppressed by SY-21 administered 15 min before, or instantly after, brain ischemia. Also, SY-21 attenuated the increased interactions involving NR2A, PSD-95, Fyn and Src. These results demonstrate that SY-21 has a prominent neuroprotective action against brain ischemic insult, and the mechanism may involve the regulation of the tyrosine phosphorylation of NR2A by changing the above interactions.

Two types of calcium channels regulating activation of proline-rich tyrosine kinase 2 induced by transient brain ischemia in rat hippocampus

Tyrosine phosphorylation is an important means for regulating post-ischemic signal transduction. In this article, brain ischemia was induced by four-vessel occlusion, and the effect of ischemia/reperfusion on proline-rich tyrosine kinase 2 (Pyk2) was studied. Tyrosine phosphorylation of Pyk2 in Sprague-Dawley rat hippocampus after transient (15 min) brain ischemia and reperfusion was examined by immunoprecipitation and immunoblot. Kinase activity of Pyk2 was examined by the method of (32)P-incorporation into poly(Glu-Tyr). Tyrosine phosphorylation and kinase activity of Pyk2 decreased slightly after ischemia, then increased after reperfusion and reached the peak levels (5.1 and 1.8 times the levels of the sham-operated group, respectively) at 1 h of reperfusion. Both the increases were partly inhibited by NMDA receptor antagonist ketamine and L-type voltage-gated calcium channel antagonist nifedipine administered 20 min before ischemia. The results suggested that Pyk2 was activated after transient brain ischemia and reperfusion, and it might play an important role in mediating post-ischemic signal transduction events.

Inhibition of protein kinase C reduces ischemia-induced tyrosine phosphorylation of the N-methyl-d-aspartate receptor

The role of protein kinase C (PKC) in tyrosine phosphorylation of the N-methyl-d-aspartate receptor (NMDAR) following transient cerebral ischemia was investigated. Transient (15 min) cerebral ischemia was produced in adult rats by four-vessel occlusion and animals allowed to recover for 15 or 45 min. Following ischemia, tyrosine phosphorylation of NR2A and NR2B and activated Src-family kinases (SFKs) and Pyk2 were increased in post-synaptic densities (PSDs). Phosphorylation of NR2B on Y1472 by PSDs isolated from post-ischemic forebrains was inhibited by the SFK specific inhibitor PP2, and by the PKC inhibitors GF109203X (GF), Gö6976 and calphostin C. Intravenous injection of GF immediately following the ischemic challenge resulted in decreased phosphorylation of NR1 on PKC phosphorylation sites and reduced ischemia-induced increases in tyrosine phosphorylation of NR2A and NR2B without affecting the increase in total tyrosine phosphorylation of hippocampal proteins. Ischemia-induced increases in activated Pyk2 and SFKs in PSDs, but not the translocation of PKC, Pyk2 or Src to the PSD, were also inhibited by GF. The inactive homologue of GF, bisindolylmaleimide V, had no effect on these parameters. The results are consistent with a role for PKC in the ischemia-induced increase in tyrosine phosphorylation of the NMDAR, via a pathway involving Pyk2 and Src-family kinases.

Antidepressant effect of the calcium-activated tyrosine kinase Pyk2 in the lateral septum

Accumulating evidence indicates that neural activity in the lateral septum (LS) influences the pathophysiology of depression and therapeutic effectiveness of antidepressant drugs. For example, the development of behavioral deficits in animal screens for antidepressant drug activity corresponds with a blunting of LS activity, whereas chronic treatment with antidepressants enhances cell firing in the LS; however, the molecular mechanisms underlying such behavioral functions of the LS have not been determined. The nonreceptor tyrosine kinase Pyk2 is highly expressed in the LS and plays important roles in regulating cellular excitability and synaptic plasticity, making it an attractive candidate for regulating the effects of stress and antidepressants on LS functioning and behavior. We provide evidence that stress decreases Pyk2 phosphorylation in the LS, whereas enhancing Pyk2 expression in LS neurons has an antidepressant effect behaviorally.Pyk2 messenger ribonucleic acid (mRNA) expression in the rat forebrain was detected by in situ hybridization, and a brief description of the distribution of Pyk2 mRNA in selected areas is presented. Levels of total Pyk2 protein and phosphorylated Pyk2 were subsequently measured in the LS and hippocampus following stress exposure, as were levels of extracellular stimuli-regulated kinase (Erk) and phospho-Erk. Herpes simplex virus (HSV)-mediated gene transfer was then used to enhance Pyk2 expression in the LS, and the effect this had on behavior in the learned helplessness model of depression was evaluated. High levels of Pyk2 mRNA were detected in a number of forebrain regions, including the hippocampus and LS. Following acute stress exposure, subjects showed a decrease in phosphorylated Pyk2 and Erk in the LS but not in the hippocampus. Total levels of Pyk2 and Erk remained unchanged following stress. In the learned helplessness paradigm, injection of HSV-Pyk2 into the LS prevented the active avoidance deficit caused by exposure to inescapable shock, indicative of an antidepressant effect. These results indicate that following acute stress, Pyk2 and Erk activity in the LS are decreased, whereas experimentally increasing Pyk2 activity in LS neurons reverses the behavioral deficits of acute, inescapable stress. These findings establish a role for the tyrosine kinase Pyk2 in the biochemical and behavioral responses to stress and suggest a possible role in the pathophysiology of depression, particularly notable considering Pyk2's role in promoting synaptic plasticity.

L-type voltage-gated calcium channel attends regulation of tyrosine phosphorylation of NMDA receptor subunit 2A induced by transient brain ischemia

To study the mechanism of the L-type voltage-gated calcium channel (L-VGCC) involved in neuronal injury induced by brain ischemia and reperfusion (I/R), transient (15 min) brain ischemia was induced by four-vessel occlusion of Sprague-Dawley (SD) rats. Tyrosine phosphorylation of NR2A and interaction of NR2A with Src and Pyk2 in hippocampus induced by brain ischemia and reperfusion (I/R) were determined by immunoprecipitation and immunoblot(ting). Tyrosine phosphorylation of NR2A in hippocampus was enhanced after I/R. Interaction of NR2A with Src and Pyk2, tyrosine phosphorylation and kinase activity of Src and Pyk2 also increased after I/R. All the increases were partly inhibited by L-VGCC antagonist nifedipine administered to rats 20 min prior to brain ischemia. The results suggested that increase of tyrosine phosphorylation of NR2A induced by I/R had a relation to activation of L-VGCC. Src and Pyk2 interacting with NR2A might also be involved in this regulation of the tyrosine phosphorylation of NR2A induced by I/R.

Tyrosine kinase and tyrosine phosphatase participate in regulation of interactions of NMDA receptor subunit 2A with Src and Fyn mediated by PSD-95 after transient brain ischemia

In this study, we investigated the effects of protein tyrosine kinase (PTK) and protein tyrosine phosphatase (PTP) on the tyrosine phosphorylation of N-methyl-D-aspartate receptor subunit 2A (NR2A) and the interactions among NR2A, postsynaptic density protein 95 (PSD-95), Fyn/Src after brain ischemia/reperfusion (I/R). The following results were observed: (1) the increase in tyrosine phosphorylation of NR2A induced by I/R was suppressed by genistein, an inhibitor of PTK, but was further enhanced by sodium orthovanadate, an inhibitor of PTP, which were administered to the SD rats 20 min before ischemia. (2) Importantly, genistein and sodium orthovanadate increased and decreased the interactions involving NR2A, PSD-95, Fyn and Src, respectively. These results demonstrated that PTK and PTP were involved in regulating tyrosine phosphorylation of NR2A through changing the interaction among NR2A, PSD-95, Fyn/Src.