AP1 transcriptional factor activation and its relation to apoptosis of hippocampal CA1 pyramidal neurons after transient ischemia in gerbils

Mitochondrial dynamics, elimination and biogenesis during post-ischemic recovery in ischemia-resistant and ischemia-vulnerable gerbil hippocampal regions

Transient ischemic attacks (TIA) result from a temporary blockage in blood circulation in the brain. As TIAs cause disabilities and often precede full-scale strokes, the effects of TIA are investigated to develop neuroprotective therapies. We analyzed changes in mitochondrial network dynamics, mitophagy and biogenesis in sections of gerbil hippocampus characterized by a different neuronal survival rate after 5-minute ischemia-reperfusion (I/R) insult. Our research revealed a significantly greater mtDNA/nDNA ratio in CA2-3, DG hippocampal regions (5.8 ± 1.4 vs 3.6 ± 0.8 in CA1) that corresponded to a neuronal resistance to I/R. During reperfusion, an increase of pro-fission (phospho-Ser616-Drp1/Drp1) and pro-fusion proteins (1.6 ± 0.5 and 1.4 ± 0.3 for Mfn2 and Opa1, respectively) was observed in CA2-3, DG. Selective autophagy markers, PINK1 and SQSTM1/p62, were elevated 24-96 h after I/R and accompanied by significant elevation of transcription factors proteins PGC-1α and Nrf1 (1.2 ± 0.4, 1.78 ± 0.6, respectively) and increased respiratory chain proteins (e.g., 1.5 ± 0.3 for complex IV at I/R 96 h). Contrastingly, decreased enzymatic activity of citrate synthase, reduced Hsp60 protein level and electron transport chain subunits (0.88 ± 0.03, 0.74 ± 0.1 and 0.71 ± 0.1 for complex IV at I/R 96 h, respectively) were observed in I/R-vulnerable CA1. The phospho-Ser616-Drp1/Drp1 was increased while Mfn2 and total Opa1 reduced to 0.88 ± 0.1 and 0.77 ± 0.17, respectively. General autophagy, measured as LC3-II/I ratio, was activated 3 h after reperfusion reaching 2.37 ± 0.9 of control. This study demonstrated that enhanced mitochondrial fusion, followed by late and selective mitophagy and mitochondrial biogenesis might together contribute to reduced susceptibility to TIA.

Notch signaling and neuronal death in stroke

Ischemic stroke is a leading cause of morbidity and death, with the outcome largely determined by the amount of hypoxia-related neuronal death in the affected brain regions. Cerebral ischemia and hypoxia activate the Notch1 signaling pathway and four prominent interacting pathways (NF-κB, p53, HIF-1α and Pin1) that converge on a conserved DNA-associated nuclear multi-protein complex, which controls the expression of genes that can determine the fate of neurons. When neurons experience a moderate level of ischemic insult, the nuclear multi-protein complex up-regulates adaptive stress response genes encoding proteins that promote neuronal survival, but when ischemia is more severe the nuclear multi-protein complex induces genes encoding proteins that trigger and execute a neuronal death program. We propose that the nuclear multi-protein transcriptional complex is a molecular mediator of neuronal hormesis and a target for therapeutic intervention in stroke.

Inhibition of soluble epoxide hydrolase after cardiac arrest/cardiopulmonary resuscitation induces a neuroprotective phenotype in activated microglia and improves neuronal survival

Cardiac arrest (CA) causes hippocampal neuronal death that frequently leads to severe loss of memory function in survivors. No specific treatment is available to reduce neuronal death and improve functional outcome. The brain's inflammatory response to ischemia can exacerbate injury and provides a potential treatment target. We hypothesized that microglia are activated by CA and contribute to neuronal loss. We used a mouse model to determine whether pharmacologic inhibition of the proinflammatory microglial enzyme soluble epoxide hydrolase (sEH) after CA alters microglial activation and neuronal death. The sEH inhibitor 4-phenylchalcone oxide (4-PCO) was administered after successful cardiopulmonary resuscitation (CPR). The 4-PCO treatment significantly reduced neuronal death and improved memory function after CA/CPR. We found early activation of microglia and increased expression of inflammatory tumor necrosis factor (TNF)-α and interleukin (IL)-1β in the hippocampus after CA/CPR, which was unchanged after 4-PCO treatment, while expression of antiinflammatory IL-10 increased significantly. We conclude that sEH inhibition after CA/CPR can alter the transcription profile in activated microglia to selectively induce antiinflammatory and neuroprotective IL-10 and reduce subsequent neuronal death. Switching microglial gene expression toward a neuroprotective phenotype is a promising new therapeutic approach for ischemic brain injury.

Neuronal responses to physiological stress

Physiological stress can be defined as any external or internal condition that challenges the homeostasis of a cell or an organism. It can be divided into three different aspects: environmental stress, intrinsic developmental stress, and aging. Throughout life all living organisms are challenged by changes in the environment. Fluctuations in oxygen levels, temperature, and redox state for example, trigger molecular events that enable an organism to adapt, survive, and reproduce. In addition to external stressors, organisms experience stress associated with morphogenesis and changes in inner chemistry during normal development. For example, conditions such as intrinsic hypoxia and oxidative stress, due to an increase in tissue mass, have to be confronted by developing embryos in order to complete their development. Finally, organisms face the challenge of stochastic accumulation of molecular damage during aging that results in decline and eventual death. Studies have shown that the nervous system plays a pivotal role in responding to stress. Neurons not only receive and process information from the environment but also actively respond to various stresses to promote survival. These responses include changes in the expression of molecules such as transcription factors and microRNAs that regulate stress resistance and adaptation. Moreover, both intrinsic and extrinsic stresses have a tremendous impact on neuronal development and maintenance with implications in many diseases. Here, we review the responses of neurons to various physiological stressors at the molecular and cellular level.

The potential role of metalloproteinases in neurogenesis in the gerbil hippocampus following global forebrain ischemia

BACKGROUND

Matrix metalloproteinases (MMPs) have recently been considered to be involved in the neurogenic response of adult neural stem/progenitor cells. However, there is a lack of information showing direct association between the activation of MMPs and the development of neuronal progenitor cells involving proliferation and/or further differentiation in vulnerable (Cornus Ammoni-CA1) and resistant (dentate gyrus-DG) to ischemic injury areas of the brain hippocampus.

PRINCIPAL FINDINGS

We showed that dynamics of MMPs activation in the dentate gyrus correlated closely with the rate of proliferation and differentiation of progenitor cells into mature neurons. In contrast, in the damaged CA1 pyramidal cells layer, despite the fact that some proliferating cells exhibited antigen specific characteristic of newborn neuronal cells, these did not attain maturity. This coincides with the low, near control-level, activity of MMPs. The above results are supported by our in vitro study showing that MMP inhibitors interfered with both the proliferation and differentiation of the human neural stem cell line derived from umbilical cord blood (HUCB-NSCs) toward the neuronal lineage.

CONCLUSION

Taken together, the spatial and temporal profiles of MMPs activity suggest that these proteinases could be an important component in neurogenesis-associated processes in post-ischemic brain hippocampus.

Comparative analysis of cis-regulation following stroke and seizures in subspaces of conserved eigensystems

BACKGROUND

It is often desirable to separate effects of different regulators on gene expression, or to identify effects of the same regulator across several systems. Here, we focus on the rat brain following stroke or seizures, and demonstrate how the two tasks can be approached simultaneously.

RESULTS

We applied SVD to time-series gene expression datasets from the rat experimental models of stroke and seizures. We demonstrate conservation of two eigensystems, reflecting inflammation and/or apoptosis (eigensystem 2) and neuronal synaptic activity (eigensystem 3), between the stroke and seizures. We analyzed cis-regulation of gene expression in the subspaces of the conserved eigensystems. Bayesian networks analysis was performed separately for either experimental model, with cross-system validation of the highest-ranking features. In this way, we correctly re-discovered the role of AP1 in the regulation of apoptosis, and the involvement of Creb and Egr in the regulation of synaptic activity-related genes. We identified a novel antagonistic effect of the motif recognized by the nuclear matrix attachment region-binding protein Satb1 on AP1-driven transcriptional activation, suggesting a link between chromatin loop structure and gene activation by AP1. The effects of motifs binding Satb1 and Creb on gene expression in brain conform to the assumption of the linear response model of gene regulation. Our data also suggest that numerous enhancers of neuronal-specific genes are important for their responsiveness to the synaptic activity.

CONCLUSION

Eigensystems conserved between stroke and seizures separate effects of inflammation/apoptosis and neuronal synaptic activity, exerted by different transcription factors, on gene expression in rat brain.

Association of protein kinase C delta and phospholipid scramblase 3 in hippocampal mitochondria correlates with neuronal vulnerability to brain ischemia

Recent findings support the idea that mitochondrial integrity plays an important role in the propagation of excitotoxic ischemic signal and PKC is implicated in the regulation of mitochondrial membranes properties. One of the targets of PKC delta is phospholipid scramblase 3 (PLSCR3), an enzyme responsible for cardiolipin translocation from the inner to outer mitochondrial membrane. To get an insight into in vivo mechanism by which PKC delta mediates ischemia/reperfusion injury of hippocampal neurons, we examined the effects of transient brain ischemia in gerbil on association of PKC delta with mitochondria isolated from ischemia-vulnerable (CA1) and ischemia-resistant regions, and interactions between PKC delta and PLSCR3. Postischemic, biphasic and brain region-specific translocation of PKC delta to mitochondria was observed. First peak was at 30-60 min of reperfusion and the second was observed after 72-96 h following ischemia. PKC delta was translocated to mitochondria only in CA1 region. The PLSCR3 mRNA and protein was detected in brain by RT-PCR and sequence analysis, Western blotting and immunocytochemistry in electron microscopy (EM). Co-immunoprecipitation and double-labeled immuno-EM showed association of PKC delta and PLSCR3 in postischemic CA1 mitochondria. Additionally, the amount of tBid associated with mitochondria was elevated 96 h following ischemia. Our data suggest that in the postischemic brain PKC delta co-localizes with PLSCR3 in mitochondria and this event might influence the mitochondrial membranes architecture and delayed neurons degeneration.

Non-selective cation channels, transient receptor potential channels and ischemic stroke

Several pathways to neural cell death are involved in ischemic stroke, and all require monovalent or divalent cation influx, implicating non-selective cation (NC) channels. NC channels are also likely to be involved in the dysfunction of vascular endothelial cells that leads to formation of edema following cerebral ischemia. Two newly described NC channels have emerged as potential participants in ischemic stroke, the acid sensing ion channel (ASIC), and the sulfonylurea receptor-1 (SUR1)-regulated NC(Ca-ATP) channel. Non-specific blockers of NC channels, including pinokalant (LOE 908 MS) and rimonabant (SR141716A), have beneficial effects in rodent models of ischemic stroke. Evidence is accumulating that NC channels formed by members of the transient receptor potential (TRP) family are also up-regulated in ischemic stroke and may play a direct role in calcium-mediated neuronal death. The nascent field of NC channels, including TRP channels, in ischemic stroke is poised to provide novel mechanistic insights and therapeutic strategies for this often devastating human condition.

Pattern of transcription factor activation in Helicobacter pylori-infected Mongolian gerbils

BACKGROUND AND AIMS

Helicobacter pylori interact with epithelial cells resulting in activation of cellular signaling pathways leading to an inflammatory response. The pattern and timing of transcription factor activation in H pylori-infected gastric mucosa remain unclear. We investigated the roles of transcription factors in the gastric mucosa of H pylori-infected gerbils over the course of the infection.

METHODS

Six-week-old male Mongolian gerbils were inoculated orally with H pylori TN2GF4 or isogenic cagE mutants and examined at 1, 3, 9, and 18 months. We examined the expression of 54 transcription factors using DNA/protein arrays and electrophoretic mobility shift assays. Phosphorylation status of mitogen-activated protein kinases and IkappaB were evaluated by immunoblot and immunohistochemistry.

RESULTS

Ten transcription factors were up-regulated by H pylori infection. Six of these factors, including activator protein-1 (AP-1) and cAMP responsive element binding protein (CREB), reached maximal levels at 3 months and were strongly correlated with cellular inflammation and ulceration. Phosphorylation of extracellular signal-regulated kinase correlated with activation of AP-1 and CREB. Levels of nuclear factor-kappaB and interferon-stimulated responsive element (ISRE) peaked at 18 months and correlated with the presence of severe atrophy and with phosphorylation of Jun-N-terminal kinase (JNK), p38, and IkappaB.

CONCLUSIONS

The gastric mucosal transcription factors induced by H pylori infection differed according to the phase and outcome of infection; AP-1 and CREB levels were early responders related to inflammation and ulceration, whereas NF-kappaB and ISRE were late responders related to atrophy.

Microarray‐based long‐term detection of genes differentially expressed after cortical spreading depression

Spreading depression (SD) is a slowly propagating wave of neuronal depolarization altering ion homeostasis, blood flow and energy metabolism without causing irreversible damage of the tissue. As SD has been implicated in several neurological diseases including migraine and stroke, understanding these disorders requires systematic knowledge of the processes modified by SD. Thus, we induced repetitive SD in the rat cerebral cortex by topical application of 3 m KCl for approximately 2 h and evaluated the kinetics of SD-induced changes in cortical gene expression for up to 30 days using Affymetrix RAE230A arrays. The temporal profile showed a rapid expression of immediate early genes, genes associated with inflammation, metabolism, stress and DNA repair, ion transport, and genes that play a role in growth/differentiation. Stress-response genes could still be detected after 24 h. At this time, induced genes were mainly related to the cell membrane and adhesion, or to the cytoskeleton. A subset of genes was still affected even 30 days after SD. Real-time polymerase chain reactions and immunohistochemistry confirmed the microarray results for several of the transcripts. Our findings demonstrate a temporal pattern of gene expression which might promote tissue remodeling and cortical plasticity, and might probably account for the mediation of neuronal tolerance towards subsequent ischemia.

PTD-XIAP protects against cerebral ischemia by anti-apoptotic and transcriptional regulatory mechanisms

Caspases play a major role in the infarction process that follows occlusion of cerebral arteries and are important targets for stroke therapy. We have generated three fusion proteins that link various domains of the X chromosome-linked inhibitor of apoptosis (XIAP), a potent caspase inhibitor, to the protein transduction domain (PTD) of HIV-1/Tat, and have tested their efficacy after distal occlusion of the middle cerebral artery (dMCAO) in mice. PTD-XIAP failed to accumulate in brain structures after intravenous (iv) delivery, but properly transduced cortical cells when applied topically. Shorter constructs efficiently targeted the lesion after iv delivery. All proteins retained their caspase inhibitory activity and significantly reduced infarct volumes. PTD-XIAP reversed long-term impairments in the water maze test. Sequential activation of transcription factors was observed, suggesting that the effects of XIAP are mediated by both direct inhibition of apoptotic mechanisms and secondary regulation of transcription factors involved in neuronal survival.

Decrease in NF-kappaB, AP-1 and SP-1 activities in neuronal cells expressing presenilin 2

Decreases in activities of the NF-kappaB, AP-1 and SP-1 transcription factors, which could act as antiapoptotic factors, in the presenilin 2 transfected PC12 cells, either in nontreatment conditions or under apoptotic stimulation, were found in this study. Similar results were also found in mice brain cells carrying presenilin 2, especially in the mutant gene expressed ones. These findings suggested that presenilin 2 may be implicated in neuronal cell death by altering the antiapoptotic activity of the transcription factors.

Neuroprotection by cyclosporin A following transient brain ischemia correlates with the inhibition of the early efflux of cytochrome C to cytoplasm

The efflux of mitochondrial protein cytochrome C to cytoplasm is one of the key events of mitochondrial dysfunction observed in post-ischemic pathology. We investigated the effect of intra-carotid infusion of 5-10 mg/kg of cyclosporin A (CsA) on the neuronal survival in CA1 sector of hippocampus and on the subcellular localization of cytochrome C in the model of 5 min gerbil brain ischemia. To discriminate between the immunosuppressive and the mitochondria protecting component of CsA action, we compared the effect of CsA with one other immunosuppressant FK506. Almost 75% of neurons in ischemia-affected brain area were saved after CsA but not after FK506 treatment. This protective effect was only observed when the drug was infused immediately upon reperfusion. Early CsA treatment was able to block an initial phase of cytochrome C release, occurring transiently at 30 min post-ischemia, an effect never observed after FK506 administration. We assessed the neuroprotective potency of CsA vs. FK506 in rat cortical primary culture treated with compounds that mimic destructive signals induced by brain ischemia. In all cases, neuronal death and cytochrome C release were evidently suppressed by CsA applied not later than 30 min after the initial insult. Thus, early treatment with CsA in vitro and after bolus intra-carotid injection in vivo can save neurons by inhibition of cytochrome C efflux to cytoplasm.

Acupuncture suppresses ischemia-induced increase in c-Fos expression and apoptosis in the hippocampal CA1 region in gerbils

Acupuncture has been used for the enhancement of functional recovery from various disorders including stroke. In the present study, the effects of acupuncture on the c-Fos expression and apoptosis in the hippocampal CA1 region of gerbils following transient global ischemia were investigated via immunohistochemistry for c-Fos and caspase-3 and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay. Enhanced Fos, TUNEL, and caspase-3 positivities were detected in the hippocampal CA1 region in the ischemic gerbils. Acupunctural treatment suppressed the ischemia-induced increment in the number of Fos-, TUNEL-, and caspase-3-positive cells: the most potent suppressive effect was observed at the Zusanli acupoint. These results suggest that acupunctural treatment alleviates ischemia-induced apoptosis and may aid in the recovery following ischemic cerebral injury.

Transient forebrain ischemia modulates signal transduction from extracellular matrix in gerbil hippocampus

Cell adhesion to the extracellular matrix (ECM) functions as a survival factor and disruption of cell-ECM interaction can lead to cell death. Our previous study has demonstrated ischemia-induced enhancement of activity of extracellular metalloproteinases, which might result in the alteration of adhesive contact with ECM and affect the intracellular signaling pathway. The enzyme thought to play a major role in conveying survival signals from ECM to the cell interior is focal adhesion kinase (pp125(FAK)). In the present study, the temporal relation between activation of extracellular metalloproteinases (MMP-2 and MMP-9), degradation of extracellular matrix protein laminin and the expression of pp125(FAK) after 5 min of global ischemia in gerbil hippocampus were investigated. While significant activation of both investigated metalloproteinases occurred in the course of reperfusion, only changes in MMP-9 activity were correlated with degradation of laminin. These ischemia-induced extracellular events coincide temporarily with proteolytic modification of FAK protein and diminished level of its phosphorylated form, to about 50% of the initial value. These results are indicative of an involvement of ECM-pp125(FAK) signaling pathway in ischemia-induced neuronal degeneration.

Apoptosis and brain ischaemia

There is increasing evidence that some neuronal death after brain ischaemia is mediated by the action of cysteine-requiring aspartate-directed proteases (caspases), the proteases responsible for apoptosis in mammals, although this form of neuronal death is not always accompanied by the morphological changes that are typical of apoptosis in other tissues. Caspase-mediated neuronal death is more extensive after transient than permanent focal brain ischaemia and may contribute to delayed loss of neurons from the penumbral region of infarcts. The activation of caspases after brain ischaemia is largely consequent on the translocation of Bax, Bak, and other BH3-only members of the Bcl-2 family to the mitochondrial outer membrane and the release of cytochrome c, procaspase-9, and apoptosis activating factor-1 (Apaf-1) from the mitochondrial intermembrane space. How exactly ischaemia induces this translocation is still poorly understood. NF-kappaB, the c-jun N-terminal kinase-c-Jun pathway, p53, E2F1, and other transcription factors are probably all involved in regulating the expression of BH3-only proteins after brain ischaemia, and mitochondrial translocation of Bad from sequestering cytosolic proteins is promoted by inactivation of the serine-threonine kinase, Akt. Other processes that are probably involved in the activation of caspases after brain ischaemia include the mitochondrial release of the second mitochondrial activator of caspases (Smac) or direct inhibitor-of-apoptosis-binding protein with low pI (DIABLO), the accumulation of products of lipid peroxidation, a marked reduction in protein synthesis, and the aberrant reentry of neurons into the cell cycle. Non-caspase-mediated neuronal apoptosis may also occur, but there is little evidence to date that this makes a significant contribution to brain damage after ischaemia. The intracellular processes that contribute to caspase-mediated neuronal death after ischaemia are all potential targets for therapy. However, anti-apoptotic interventions in stroke patients will require detailed evaluation using a range of outcome measures, as some such interventions seem simply to delay neuronal death and others to preserve neurons but not neuronal function.

Opposite reaction of ERK and JNK in ischemia vulnerable and resistant regions of hippocampus: involvement of mitochondria

Delayed ischemic death of neurones is observed selectively in CA1 region of hippocampus at 3-4 days of reperfusion. Signals generated immediately during and after ischemia are further propagated by a variety of kinases, proteases and phosphatases. Tissue samples from dorsal (vulnerable) and abdominal (resistant) parts of gerbil hippocampi were collected to determine the activation state of key signaling molecules: Akt, Raf-1, JNK, ERK1/2 in the course of reperfusion after 5 min of global cerebral ischemia. Western blot analysis of phosphorylated forms of the kinases revealed persistent activation of JNK, being limited mostly to vulnerable CA1 region. On the contrary, activation of ERK, although observed transiently in both parts, was enhanced for a longer time in the abdominal hippocampus. The levels of the active/phosphorylated Akt and Raf-1 kinases did not change significantly during the recovery period. No significant correlation between postischemic JNK activation and c-Jun phosphorylation or its contribution to AP1-like complex formation was found. In contrast, the amount of active JNK linked with mitochondrial membranes was significantly increased and preceded neuronal death in CA1. In the same period of time the AP1 complex, augmented in CA1 region, did not appear to contain a classical c-Fos protein. These results are consistent with the theory that either long-lasting activation of JNK and/or contrasting ERK and JNK activities in critical time of reperfusion, contribute to selective apoptosis of CA1 neurons. This, in connection with the translocation of activated JNK to mitochondria and time/regional differences in AP1 binding protein complexes can affect final postischemic outcome.

Immunoreactivity for Bcl-2 and C-Jun/AP1 in hippocampal corpora amylacea after ischaemia in humans

Corpora amylacea (CAm) are regarded as a hallmark of brain ageing, but little is known about their role in normal and pathological circumstances. CAm contain, in addition to glucose polymers, ageing-, stress- and proinflammatory proteins. In view of their almost universal occurrence and their cumulation with time, formation of CAm may represent a basic mechanism for the management of metabolic degradation products. In this context, we studied samples from post-mortem cases with repetitive brain hypoxic episodes in the past history. We investigated, by immunohistochemistry, the presence of Bcl-2, c-jun and bax in CAm. CAm showed immunoreactivity for the mitochondrial membrane associated protein Bcl-2, and for the major component of activator protein 1 transcriptional factor c-Jun. We found higher numbers of CAm in the hippocampus and the dentate gyrus in cases with repetitive cerebral hypoxia than in controls. We conclude that: (1) the presence of C-Jun and Bcl-2 within the glucose polymer mass of CAm may be related to mitochondrial damage and/or a transient overload of proteolytic systems during cellular injury; and (2) repetitive cellular stress during life may cause the age-related increase of CAm in elderly subjects.

Early c-Fos induction after cerebral ischemia: a possible neuroprotective role

The role of c-Fos in neurodegeneration or neuroprotection after cerebral ischemia is controversial. To investigate whether early c-Fos induction after ischemia is associated with neuroprotection, rats were subjected to 10 minutes of transient forebrain ischemia and c-Fos expression was examined. Resistant dentate granule cells and neurons in CA2-4 displayed more robust immunoreactivity than vulnerable neurons in the CA1 region of hippocampus during early hours of reperfusion. By 6 hours after reperfusion, c-Fos immunoreactivity was greatly diminished in all areas of the hippocampus. Administration of N-acetyl-O-methyldopamine (NAMDA), a compound previously shown to protect CA1 neurons against ischemia, increased c-Fos immunoreactivity in the CA1 vulnerable region at 6 hours after ischemia and protected SK-N-BE(2)C neurons from oxygen glucose deprivation. Further in vitro study showed that NAMDA potentiated phorbol-12 myristate-13 acetate (PMA)-induced c-Fos expression, AP1 binding activity, and late gene expression determined by chloramphenicol acetyltransferase (CAT) activity from AP1 containing tyrosine hydroxylase promoter-CAT fusion gene in SK-N-BE(2)C neurons. In vivo and in vitro results showed that a neuroprotectant, NAMDA, in concert with another stimulus (for example, ischemia or PMA) up-regulates c-Fos expression and suggested that the early rise of NAMDA-induced c-Fos expression in vulnerable CA1 neurons may account for neuroprotection by means of up-regulating late gene expression for survival.

Zn(2+) induces stimulation of the c-Jun N-terminal kinase signaling pathway through phosphoinositide 3-Kinase

Zn(2+), one of the most abundant trace metal ions in mammalian cells, modulates the functions of many regulatory proteins associated with a variety of cellular activities. In the central nervous system, Zn(2+) is highly localized in the cerebral cortex and hippocampus. It has been proposed to play a role in normal brain function as well as in the pathophysiology of certain neurodegenerative disorders. We here report that Zn(2+) induced stimulation of the c-Jun N-terminal kinase (JNK) pathway in mouse primary cortical cells and in various cell lines. Exposure of cells to Zn(2+) resulted in the stimulation of JNK and its upstream kinases including stress-activated protein kinase kinase and mitogen-activated protein kinase kinase kinase. Zn(2+) also induced stimulation of phosphoinositide 3-kinase (PI3K) The Zn(2+)-induced JNK stimulation was blocked by LY294002, a PI3K inhibitor, or by a dominant-negative mutant of PI3Kgamma. Furthermore, overexpression of Rac1N17, a dominant negative mutant of Rac1, suppressed the Zn(2+)- and PI3Kgamma-induced JNK stimulation. The stimulatory effect of Zn(2+) on both PI3K and JNK was repressed by the free-radical scavenging agent N-acetylcysteine. Taken together, our data suggest that Zn(2+) induces stimulation of the JNK signaling pathway through PI3K-Rac1 signals and that the free-radical generation may be an important step in the Zn(2+) induction of the JNK stimulation.

Expression of fos-related antigen-2 in rat hippocampus after middle cerebral arterial occlusion

AP-1 transcription factors have been shown to be induced in the brain after ischemic injury. However, their roles in neuronal survival or death have yet to be defined. Here, we report the discovery of elevated nuclear levels of fos-related antigen-2 (FRA-2) in the nuclei of hippocampal neurons seven days after middle cerebral artery occlusion (MCAO). Expression of FRA-2 and AP-1 DNA binding activity is elevated in hippocampi ipsilateral as well as contralateral to MCAO. Using Fluoro-Jade staining as a marker of neurodegeneration, FRA-2 was not found to be expressed in degenerating neurons. Thus, FRA-2 is expressed in neurons that survive ischemic insult suggesting a role for this transcription factor in neuronal adaptation to the post-injury state.

Multiple molecular penumbras after focal cerebral ischemia

Though the ischemic penumbra has been classically described on the basis of blood flow and physiologic parameters, a variety of ischemic penumbras can be described in molecular terms. Apoptosis-related genes induced after focal ischemia may contribute to cell death in the core and the selective cell death adjacent to an infarct. The HSP70 heat shock protein is induced in glia at the edges of an infarct and in neurons often at some distance from the infarct. HSP70 proteins are induced in cells in response to denatured proteins that occur as a result of temporary energy failure. Hypoxia-inducible factor (HIF) is also induced after focal ischemia in regions that can extend beyond the HSP70 induction. The region of HIF induction is proposed to represent the areas of decreased cerebral blood flow and decreased oxygen delivery. Immediate early genes are induced in cortex, hippocampus, thalamus, and other brain regions. These distant changes in gene expression occur because of ischemia-induced spreading depression or depolarization and could contribute to plastic changes in brain after stroke.