Involvement of extracellular regulated kinase and p38 kinase in hippocampal seizure tolerance

Time and age dependent regulation of neuroinflammation in a rat model of mesial temporal lobe epilepsy: Correlation with human data

Acute brain insults trigger diverse cellular and signaling responses and often precipitate epilepsy. The cellular, molecular and signaling events relevant to the emergence of the epileptic brain, however, remain poorly understood. These multiplex structural and functional alterations tend also to be opposing - some homeostatic and reparative while others disruptive; some associated with growth and proliferation while others, with cell death. To differentiate pathological from protective consequences, we compared seizure-induced changes in gene expression hours and days following kainic acid (KA)-induced status epilepticus (SE) in postnatal day (P) 30 and P15 rats by capitalizing on age-dependent differential physiologic responses to KA-SE; only mature rats, not immature rats, have been shown to develop spontaneous recurrent seizures after KA-SE. To correlate gene expression profiles in epileptic rats with epilepsy patients and demonstrate the clinical relevance of our findings, we performed gene analysis on four patient samples obtained from temporal lobectomy and compared to four control brains from NICHD Brain Bank. Pro-inflammatory gene expressions were at higher magnitudes and more sustained in P30. The inflammatory response was driven by the cytokines IL-1β, IL-6, and IL-18 in the acute period up to 72 h and by IL-18 in the subacute period through the 10-day time point. In addition, a panoply of other immune system genes was upregulated, including chemokines, glia markers and adhesion molecules. Genes associated with the mitogen activated protein kinase (MAPK) pathways comprised the largest functional group identified. Through the integration of multiple ontological databases, we analyzed genes belonging to 13 separate pathways linked to Classical MAPK ERK, as well as stress activated protein kinases (SAPKs) p38 and JNK. Interestingly, genes belonging to the Classical MAPK pathways were mostly transiently activated within the first 24 h, while genes in the SAPK pathways had divergent time courses of expression, showing sustained activation only in P30. Genes in P30 also had different regulatory functions than in P15: P30 animals showed marked increases in positive regulators of transcription, of signaling pathways as well as of MAPKKK cascades. Many of the same inflammation-related genes as in epileptic rats were significantly upregulated in human hippocampus, higher than in lateral temporal neocortex. They included glia-associated genes, cytokines, chemokines and adhesion molecules and MAPK pathway genes. Uniquely expressed in human hippocampus were adaptive immune system genes including immune receptors CDs and MHC II HLAs. In the brain, many immune molecules have additional roles in synaptic plasticity and the promotion of neurite outgrowth. We propose that persistent changes in inflammatory gene expression after SE leads not only to structural damage but also to aberrant synaptogenesis that may lead to epileptogenesis. Furthermore, the sustained pattern of inflammatory genes upregulated in the epileptic mature brain was distinct from that of the immature brain that show transient changes and are resistant to cell death and neuropathologic changes. Our data suggest that the epileptogenic process may be a result of failed cellular signaling mechanisms, where insults overwhelm the system beyond a homeostatic threshold.

ERK1/2 kinases and dopamine D2 receptors participate in the anticonvulsant effects of a new derivative of benzoylpyridine oxime and valproic acid

Inhibition of the activity of extracellular signal-regulated kinases (ERK1/2) induced by the activation of the dopamine D2 receptor signalling cascade may be a promising pharmacological target. The aim of this work was to study the involvement of ERK1/2 and dopamine D2 receptor in the mechanism of the anticonvulsant action of valproic acid (VA) and a new benzoylpyridine oxime derivative (GIZH-298), which showed antiepileptic activity in different models of epilepsy. We showed that subchronic exposure to maximal electroshock seizures (MES) for 5 days reduced the density of dopamine D2 receptors in the striatum of mice. GIZH-298 counteracted the decrease in the number of dopamine D2 receptors associated with MES and increased the number of ligand binding sites of dopamine D2 receptors in mice without MES. The affinity of dopamine D2 receptors to the ligand was not changed by GIZH-298. MES caused an increase in ERK1/2 and synapsin I phosphorylation in the striatum while GIZH-298, similar to VA, reduced the levels of both phospho-ERK1/2 and phosphosynapsin I after MES, which correlated with the decrease in the intensity of seizure in mice. In addition, GIZH-298 suppressed ERK1/2 phosphorylation in SH-SY5Y human neuroblastoma cells at therapeutic concentrations, while VA inhibited ERK1/2 phosphorylation in vivo but not in vitro. The data obtained expand the understanding of the mechanisms of action of VA and GIZH-298, which involve regulating the activity of ERK1/2 kinases, probably by modulating dopamine D2 receptors in limbic structures, as well as (in the case of GIZH-298) directly inhibiting of the ERK1/2 cascade.

The Signaling Pathways Involved in the Anticonvulsive Effects of the Adenosine A1 Receptor

Adenosine acts as an endogenous anticonvulsant and seizure terminator in the brain. Many of its anticonvulsive effects are mediated through the activation of the adenosine A₁ receptor, a G protein-coupled receptor with a wide array of targets. Activating A₁ receptors is an effective approach to suppress seizures. This review gives an overview of the neuronal targets of the adenosine A₁ receptor focusing in particular on signaling pathways resulting in neuronal inhibition. These include direct interactions of G protein subunits, the adenyl cyclase pathway and the phospholipase C pathway, which all mediate neuronal hyperpolarization and suppression of synaptic transmission. Additionally, the contribution of the guanyl cyclase and mitogen-activated protein kinase cascades to the seizure-suppressing effects of A₁ receptor activation are discussed. This review ends with the cautionary note that chronic activation of the A₁ receptor might have detrimental effects, which will need to be avoided when pursuing A₁ receptor-based epilepsy therapies.

Inhibition of p38 MAPK regulates epileptic severity by decreasing expression levels of A1R and ENT1

Epilepsy is a chronic nervous system disease. Excessive increase of the excitatory neurotransmitter glutamate in the body results in an imbalance of neurotransmitters and excessive excitation of neurons, leading to epileptic seizures. Long‑term recurrent seizures lead to behavior and cognitive changes, and even increase the risk of death by 2‑ to 3‑fold relative to the general population. Adenosine A1 receptor (A1R), a member of the adenosine system, has notable anticonvulsant effects, and adenosine levels are controlled by the type 1 equilibrative nucleoside transporter (ENT1); in addition the p38 MAPK signaling pathway is involved in the regulation of ENT1, although the effect of its inhibitors on the expression levels of A1R and ENT1 is unclear. Therefore, in the present study, SB203580 was used to inhibit the p38 MAPK signaling pathway in rats, and the expression levels of A1R and ENT1 in the brain tissue of rats with acute LiCl‑pilocarpine‑induced status epilepticus was detected. SB203580 decreased pathological damage of hippocampal neurons, prolonged seizure latency, reduced the frequency of seizures, and decreased levels of A1R and ENT1 protein in rats.

Sema7A, a brain immune regulator, regulates seizure activity in PTZ-kindled epileptic rats

Aims

Semaphorin7A (Sema7A) plays an important role in the immunoregulation of the brain. In our study, we aimed to investigate the expression patterns of Sema7A in epilepsy and further explore the roles of Sema7A in the regulation of seizure activity and the inflammatory response in PTZ‐kindled epileptic rats.

Methods

First, we measured the Sema7A expression levels in patients with temporal lobe epilepsy (TLE) and in rats of a PTZ‐kindled epilepsy rat model. Second, to explore the role of Sema7A in the regulation of seizure activity, we conducted epilepsy‐related behavioral experiments after knockdown and overexpression of Sema7A in the rat hippocampal dentate gyrus (DG). Possible Sema7A‐related brain immune regulators (eg, ERK phosphorylation, IL‐6, and TNF‐α) were also investigated. Additionally, the growth of mossy fibers was visualized by anterograde tracing using injections of biotinylated dextran amine (BDA) into the DG region.

Results

Sema7A expression was markedly upregulated in the brain tissues of TLE patients and rats of the epileptic model after PTZ kindling. After knockdown of Sema7A, seizure activity was suppressed based on the latency to the first epileptic seizure, number of seizures, and duration of seizures. Conversely, overexpression of Sema7A promoted seizures. Overexpression of Sema7A increased the expression levels of the inflammatory cytokines, IL‐6 and TNF‐α, ERK phosphorylation, and growth of mossy fibers in PTZ‐kindled epileptic rats.

Conclusion

Sema7A is upregulated in the epileptic brain and plays a potential role in the regulation of seizure activity in PTZ‐kindled epileptic rats, which may be related to neuroinflammation. Sema7A promotes the inflammatory cytokines TNF‐α and IL‐6 as well as the growth of mossy fibers through the ERK pathway, suggesting that Sema7A may promote seizures by increasing neuroinflammation and activating pathological neural circuits. Sema7A plays a critical role in epilepsy and could be a potential therapeutic target for this neurological disorder.

D-Serine Contributes to Seizure Development via ERK Signaling

A seizure is one of the leading neurological disorders. NMDA receptor-mediated neuronal excitation has been thought to be essential for epileptogenesis. As an endogenous co-agonist of the NMDA receptor, D-serine has been suggested to play a role in epileptogenesis. However, the underlying mechanisms remain unclear. In the current study, we investigated the effects of antagonizing two key enzymes in D-serine metabolism on the development of seizures and the downstream signaling. Our results showed that serine racemase (SR), a key enzyme in regulating the L-to-D-serine conversion, was significantly up-regulated in hippocampal astrocytes in rats and patients who experienced seizure, in comparison with control rats and patients. L-aspartic acid β-hydroxamate (LaaβH), an inhibitor of SR, significantly prolonged the latencies of seizures, shortened the durations of seizures, and decreased the total EEG power in rats. In contrast, D-amino acid oxidase inhibitor 5-chlorobenzo[d]isoxazol-3-ol (CBIO), which can increase D-serine levels, showed the opposite effects. Furthermore, our data showed that LaaβH and CBIO significantly affected the phosphorylation of Extracellular Signal-regulated Kinase (ERK). Antagonizing or activating ERK could significantly block the effects of LaaβH/CBIO on the occurrence of seizures. In summary, our study revealed that D-serine is involved in the development of epileptic seizures, partially through ERK signaling, indicating that the metabolism of D-serine may be targeted for the treatment of epilepsy.

A role for astrocyte-derived amyloid β peptides in the degeneration of neurons in an animal model of temporal lobe epilepsy

Kainic acid, an analogue of the excitatory neurotransmitter glutamate, can trigger seizures and neurotoxicity in the hippocampus and other limbic structures in a manner that mirrors the neuropathology of human temporal lobe epilepsy (TLE). However, the underlying mechanisms associated with the neurotoxicity remain unclear. Since amyloid-β (Aβ) peptides, which are critical in the development of Alzheimer's disease, can mediate toxicity by activating glutamatergic NMDA receptors, it is likely that the enhanced glutamatergic transmission that renders hippocampal neurons vulnerable to kainic acid treatment may involve Aβ peptides. Thus, we seek to establish what role Aβ plays in kainic acid-induced toxicity using in vivo and in vitro paradigms. Our results show that systemic injection of kainic acid to adult rats triggers seizures, gliosis and loss of hippocampal neurons, along with increased levels/processing of amyloid precursor protein (APP), resulting in the enhanced production of Aβ-related peptides. The changes in APP levels/processing were evident primarily in activated astrocytes, implying a role for astrocytic Aβ in kainic acid-induced toxicity. Accordingly, we showed that treating rat primary cultured astrocytes with kainic acid can lead to increased Aβ production/secretion without any compromise in cell viability. Additionally, we revealed that kainic acid reduces neuronal viability more in neuronal/astrocyte co-cultures than in pure neuronal culture, and this is attenuated by precluding Aβ production. Collectively, these results indicate that increased production/secretion of Aβ-related peptides from activated astrocytes can contribute to neurotoxicity in kainic acid-treated rats. Since kainic acid administration can lead to neuropathological changes resembling TLE, it is likely that APP/Aβ peptides derived from astrocytes may have a role in TLE pathogenesis.

Mitogen- and Stress-Activated Protein Kinase 1 Regulates Status Epilepticus-Evoked Cell Death in the Hippocampus

Mitogen-activated protein kinase (MAPK) signaling has been implicated in a wide range of neuronal processes, including development, plasticity, and viability. One of the principal downstream targets of both the extracellular signal-regulated kinase/MAPK pathway and the p38 MAPK pathway is Mitogen- and Stress-activated protein Kinase 1 (MSK1). Here, we sought to understand the role that MSK1 plays in neuroprotection against excitotoxic stimulation in the hippocampus. To this end, we utilized immunohistochemical labeling, a MSK1 null mouse line, cell viability assays, and array-based profiling approaches. Initially, we show that MSK1 is broadly expressed within the major neuronal cell layers of the hippocampus and that status epilepticus drives acute induction of MSK1 activation. In response to the status epilepticus paradigm, MSK1 KO mice exhibited a striking increase in vulnerability to pilocarpine-evoked cell death within the CA1 and CA3 cell layers. Further, cultured MSK1 null neurons exhibited a heighted level of N-methyl-D-aspartate-evoked excitotoxicity relative to wild-type neurons, as assessed using the lactate dehydrogenase assay. Given these findings, we examined the hippocampal transcriptional profile of MSK1 null mice. Affymetrix array profiling revealed that MSK1 deletion led to the significant (>1.25-fold) downregulation of 130 genes and an upregulation of 145 genes. Notably, functional analysis indicated that a subset of these genes contribute to neuroprotective signaling networks. Together, these data provide important new insights into the mechanism by which the MAPK/MSK1 signaling cassette confers neuroprotection against excitotoxic insults. Approaches designed to upregulate or mimic the functional effects of MSK1 may prove beneficial against an array of degenerative processes resulting from excitotoxic insults.

An RNAi-mediated screen identifies novel targets for next-generation antiepileptic drugs based on increased expression of the homeostatic regulator pumilio

Despite availability of a diverse range of anti-epileptic drugs (AEDs), only about two-thirds of epilepsy patients respond well to drug treatment. Thus, novel targets are required to catalyse the design of next-generation AEDs. Manipulation of neuron firing-rate homoeostasis, through enhancing Pumilio (Pum) activity, has been shown to be potently anticonvulsant in Drosophila. In this study, we performed a genome-wide RNAi screen in S2R + cells, using a luciferase-based dPum activity reporter and identified 1166 genes involved in dPum regulation. Of these genes, we focused on 699 genes that, on knock-down, potentiate dPum activity/expression. Of this subgroup, 101 genes are activity-dependent based on comparison with genes previously identified as activity-dependent by RNA-sequencing. Functional cluster analysis shows these genes are enriched in pathways involved in DNA damage, regulation of cell cycle and proteasomal protein catabolism. To test for anticonvulsant activity, we utilised an RNA-interference approach in vivo. RNAi-mediated knockdown showed that 57/101 genes (61%) are sufficient to significantly reduce seizure duration in the characterized seizure mutant, para^bss. We further show that chemical inhibitors of protein products of some of the genes targeted are similarly anticonvulsant. Finally, to establish whether the anticonvulsant activity of identified compounds results from increased dpum transcription, we performed a luciferase-based assay to monitor dpum promoter activity. Third instar larvae exposed to sodium fluoride, gemcitabine, metformin, bestatin, WP1066 or valproic acid all showed increased dpum promoter activity. Thus, this study validates Pum as a favourable target for AED design and, moreover, identifies a number of lead compounds capable of increasing the expression of this homeostatic regulator.

SRF modulates seizure occurrence, activity induced gene transcription and hippocampal circuit reorganization in the mouse pilocarpine epilepsy model

A hallmark of temporal lobe epilepsy (TLE) is hippocampal neuronal demise and aberrant mossy fiber sprouting. In addition, unrestrained neuronal activity in TLE patients induces gene expression including immediate early genes (IEGs) such as Fos and Egr1.

We employed the mouse pilocarpine model to analyze the transcription factor (TF) serum response factor (SRF) in epileptogenesis, seizure induced histopathology and IEG induction. SRF is a neuronal activity regulated TF stimulating IEG expression as well as nerve fiber growth and guidance. Adult conditional SRF deficient mice (Srf^CaMKCreERT2) were more refractory to initial status epilepticus (SE) acquisition. Further, SRF deficient mice developed more spontaneous recurrent seizures (SRS). Genome-wide transcriptomic analysis uncovered a requirement of SRF for SE and SRS induced IEG induction (e.g. Fos, Egr1, Arc, Npas4, Btg2, Atf3). SRF was required for epilepsy associated neurodegeneration, mossy fiber sprouting and inflammation. We uncovered MAP kinase signaling as SRF target during epilepsy. Upon SRF ablation, seizure evoked induction of dual specific phosphatases (Dusp5 and Dusp6) was reduced. Lower expression of these negative ERK kinase regulators correlated with altered P-ERK levels in epileptic Srf mutant animals.

Overall, this study uncovered an SRF contribution to several processes of epileptogenesis in the pilocarpine model.

Selective targeting of MAPK family kinases JNK over p38 by rationally designed peptides as potential therapeutics for neurological disorders and epilepsy

A systematic strategy is described to optimize peptide selectivity between the MAPK family kinases JNK and p38 for epilepsy therapy.

Blockade of endothelin B receptor improves the efficacy of levetiracetam in chronic epileptic rats

PURPOSE

To elucidate the mechanisms that regulate p-glycoprotein (PGP) expression and function in pharmacoresistant epilepsy, we investigated the effect of an ETB receptor antagonist (BQ788) and a p38 mitogen-activated protein kinase (p38MAPK) inhibitor (SB202190) on intractable seizures in chronic epileptic rats.

METHODS

Lithium-pilocarpine-induced chronic epileptic rats were used in the present study. Animals were given levetiracetam (LEV), LEV + SB202190, LEV + BQ788, SB202190 or BQ788 over a 3-day period using an osmotic pump. Seizure activity was recorded by video-EEG monitoring with 2h of recording per day at the same time of day. We also performed western blot after EEG analysis.

RESULTS

Compared to control animals, PGP, ETB receptor and p38MAPK expression was increased in the hippocampus of epileptic animals. Neither SB202190 nor BQ788 affected the spontaneous seizure activity in epileptic rats. Three of ten rats were responders and achieved complete seizure control or significant reduction in seizure activity by LEV. In four of ten rats, seizure frequency was unaltered by LEV (non-responders). LEV + SB202190 reduced seizure duration, but not seizure frequency, in both responders and non-responders. LEV + BQ788 alleviated seizure frequency and seizure duration in both responders and non-responders. Compared to responders, PGP and ETB receptor expression was enhanced in the hippocampus of non-responders.

CONCLUSION

To the best of our knowledge, these findings are the first indications of the role of ETB receptor in pharmacoresistant epilepsy. Therefore, the present data suggest that the regulation of the ETB receptor-mediated signaling pathway may be important for identification of new therapeutic strategies for improving antiepileptic drug efficacy.

Contribution of protease-activated receptor 1 in status epilepticus-induced epileptogenesis

Clinical observations and studies on different animal models of acquired epilepsy consistently demonstrate that blood-brain barrier (BBB) leakage can be an important risk factor for developing recurrent seizures. However, the involved signaling pathways remain largely unclear. Given the important role of thrombin and its major receptor in the brain, protease-activated receptor 1 (PAR1), in the pathophysiology of neurological injury, we hypothesized that PAR1 may contribute to status epilepticus (SE)-induced epileptogenesis and that its inhibition shortly after SE will have neuroprotective and antiepileptogenic effects. Adult rats subjected to lithium-pilocarpine SE were administrated with SCH79797 (a PAR1 selective antagonist) after SE termination. Thrombin and PAR1 levels and neuronal cell survival were evaluated 48h following SE. The effect of PAR1 inhibition on animal survival, interictal spikes (IIS) and electrographic seizures during the first two weeks after SE and behavioral seizures during the chronic period was evaluated. SE resulted in a high mortality rate and incidence of IIS and seizures in the surviving animals. There was a marked increase in thrombin, decrease in PAR1 immunoreactivity and hippocampal cell loss in the SE-treated rats. Inhibition of PAR1 following SE resulted in a decrease in mortality and morbidity, increase in neuronal cell survival in the hippocampus and suppression of IIS, electrographic and behavioral seizures following SE. These data suggest that the PAR1 signaling pathway contributes to epileptogenesis following SE. Because breakdown of the BBB occurs frequently in brain injuries, PAR1 inhibition may have beneficial effects in a variety of acquired injuries leading to epilepsy.

Acute anticonvulsant effects of capric acid in seizure tests in mice

Capric acid (CA10) is a 10-carbon medium-chain fatty acid abundant in the medium-chain triglyceride ketogenic diet (MCT KD). The purpose of this study was to characterize acute anticonvulsant effects of CA10 across several seizure tests in mice. Anticonvulsant effects of orally (p.o.) administered CA10 were assessed in the maximal electroshock seizure threshold (MEST), 6-Hz seizure threshold, and intravenous pentylenetetrazole (i.v. PTZ) seizure tests in mice. Acute effects of CA10 on motor coordination were assessed in the grip and chimney tests. Plasma and brain concentrations of CA10 were measured. Co-administration studies with CA10 and another abundant medium-chain fatty acid, caprylic acid (CA8) were performed. CA10 showed significant and dose-dependent anticonvulsant properties by increasing seizure thresholds in the 6-Hz and MEST seizure tests; it was ineffective in the i.v. PTZ seizure test. At higher doses than those effective in the 6-Hz and MEST seizure tests, CA10 impaired motor performance in the grip and chimney tests. An enhanced anticonvulsant response in the 6-Hz seizure test was produced when CA8 and CA10 were co-administered. An acute p.o. administration of CA10 resulted in dose-proportional increases in its plasma and brain concentrations. CA10 exerted acute anticonvulsant effects at doses that produce plasma exposures comparable to those reported in epileptic patients on the MCT KD. An enhanced anticonvulsant effect is observed when CA10 and the other main constituent of the MCT KD, CA8, were co-administered. Thus, acute anticonvulsant properties of CA10 and CA8 may influence the overall clinical efficacy of the MCT KD.

Attenuation of mitochondrial and nuclear p38α signaling: a novel mechanism of estrogen neuroprotection in cerebral ischemia

P38 mitogen-activated protein kinase (MAPK) is a pro-apoptotic and pro-inflammatory protein that is activated in response to cellular stress. While p38 is known to be activated in response to cerebral ischemia, the precise role of p38 and its isoforms in ischemia-induced neuronal apoptosis remains unclear. In the current study, we examined the differential activation and functional roles of p38α and p38β MAPK isoforms in short-term ovariectomized female rats treated with either the neuroprotective ovarian hormone 17beta-estradiol (E2) or placebo in a model of global cerebral ischemia (GCI). GCI induced biphasic activation of total p38 in the hippocampal CA1, with peaks at 30 min and 1 day after 10-min ischemia-reperfusion. Further study demonstrated that activated p38α, but not p38β, translocated to the nucleus 30 min and 3 h post reperfusion, and that this event coincided with increased phosphorylation of activating transcription factor 2 (ATF2), a p38 target protein. Intriguingly, activated p38α was also enhanced in mitochondrial fractions of CA1 neurons 1 day after GCI, and there was loss of mitochondrial membrane potential, as well as enhanced cytochrome c release and caspase-3 cleavage at 2 days post GCI. Importantly, E2 prevented the biphasic activation of p38, as well as both nuclear and mitochondrial translocation of p38α after GCI, and these findings correlated with attenuation of mitochondrial dysfunction and delayed neuronal cell death in the hippocampal CA1. Furthermore, administration of a p38 inhibitor was able to mimic the neuroprotective effects of E2 in the hippocampal CA1 region by preventing nuclear and mitochondrial translocation of p38α, loss of mitochondrial membrane potential, and neuronal apoptosis. As a whole, this study suggests that changes in subcellular localization of the activated p38α isoform are required for neuronal apoptosis following GCI, and that E2 exerts robust neuroprotection, in part, through dual inhibition of activation and subcellular trafficking of p38α.

Protective effects of the p38 MAPK inhibitor SB203580 on NMDA‑induced injury in primary cerebral cortical neurons

The p38 pathway, which is important in mitogen-activated protein kinase (MAPK) family protein signaling, leads to mitochondrial dysfunction and activation of caspase-3. B-cell lymphoma 2 (Bcl‑2) family members are involved in the regulation of activities associated with the survival and death of neurons through apoptosis and have important functions in most types of apoptosis. In the present study, the effects of the p38 MAPK inhibitor SB203580 on N-methyl-d-aspartate (NMDA)-induced cerebral cortical neuron apoptosis were observed to further analyze the possible mechanisms of NMDA-induced neuronal death. Cultured primary cortical neurons were randomly divided into five groups: A control group, NMDA group and three SB203580 interventional groups. The lactate dehydrogenase (LDH) and MTT assays were employed to investigate the effects of the drugs on apoptosis. The morphology of apoptotic cells was observed using acridine orange/ethidium bromide (AO/EB) fluorescence staining. The expression levels of phospho‑(p)‑p38MAPK, Bcl‑2 and Bcl-2-associated X (Bax) were assessed by immunohistochemical methods and western blot analysis to investigate the possible underlying protective mechanisms. The cell viability markedly decreased following incubation with NMDA. The protein levels of cell death repressor Bcl-2 and the levels of Bcl-2/Bax were downregulated. The protein levels of p‑p38MAPK and cell death promoter Bax increased significantly in cells with NMDA treatment. However, these changes were inhibited by SB203580 treatment, particularly in the high‑dose group. Neuronal death induced by NMDA in primary cortical neurons was caused in part by apoptosis, which was mediated through the activation of the p38 signaling pathway by NMDA. SB203580 has neuroprotective effects against NMDA‑induced apoptosis.

The histone lysine demethylase Kdm6b is required for activity-dependent preconditioning of hippocampal neuronal survival

Enzymes that regulate histone lysine methylation play important roles in neuronal differentiation, but little is known about their contributions to activity-regulated gene transcription in differentiated neurons. We characterized activity-regulated expression of lysine demethylases and lysine methyltransferases in the hippocampus of adult male mice following pilocarpine-induced seizure. Pilocarpine drove a 20-fold increase in mRNA encoding the histone H3 lysine 27-specific demethylase Kdm6b selectively in granule neurons of the dentate gyrus, and this induction was recapitulated in cultured hippocampal neurons by bicuculline and 4-aminopyridine (Bic + 4AP) stimulation of synaptic activity. Because activity-regulated gene expression is highly correlated with neuronal survival, we tested the requirement for Kdm6b expression in Bic + 4AP induced preconditioning of neuronal survival. Prior exposure to Bic + 4AP promoted neuronal survival in control neurons upon growth factor withdrawal; however, this effect was ablated when we knocked down Kdm6b expression. Loss of Kdm6b did not disrupt activity-induced expression of most genes, including that of a gene set previously established to promote neuronal survival in this assay. However, using bioinformatic analysis of RNA sequencing data, we discovered that Kdm6b knockdown neurons showed impaired inducibility of a discrete set of genes annotated for their function in inflammation. These data reveal a novel function for Kdm6b in activity-regulated neuronal survival, and they suggest that activity- and Kdm6b-dependent regulation of inflammatory gene pathways may serve as an adaptive pro-survival response to increased neuronal activity.

Early-life seizures in predisposing neuronal preconditioning: a critical review

Although seizures are known to be harmful, recent evidence indicates that they can also lead to adaptations that protect neurons from further insult. For example, a history of two episodes of status epilepticus during a critical period of early development can prolong the time period of resistance to hippocampal injury during the postnatal period. Neonatal seizures may lead to this neuroprotection via a preconditioning mechanism that could be attributed to attenuation of Ca(2+) currents, reduction of inflammation, and induction of survival signaling pathways. Understanding mechanisms underlying neuroprotective preconditioning may elucidate new therapeutic targets and improve outcomes and quality of life for pediatric epilepsy patients. This review will detail the specific cellular and molecular findings involved in neuronal preconditioning predisposed by early-life seizures.

Transcriptome profiling of hippocampal CA1 after early-life seizure-induced preconditioning may elucidate new genetic therapies for epilepsy

Injury of the CA1 subregion induced by a single injection of kainic acid (1 × KA) in juvenile animals (P20) is attenuated in animals with two prior sustained neonatal seizures on P6 and P9. To identify gene candidates involved in the spatially protective effects produced by early-life conditioning seizures we profiled and compared the transcriptomes of CA1 subregions from control, 1 × KA- and 3 × KA-treated animals. More genes were regulated following 3 × KA (9.6%) than after 1 × KA (7.1%). Following 1 × KA, genes supporting oxidative stress, growth, development, inflammation and neurotransmission were upregulated (e.g. Cacng1, Nadsyn1, Kcng1, Aven, S100a4, GFAP, Vim, Hrsp12 and Grik1). After 3 × KA, protective genes were differentially over-expressed [e.g. Cat, Gpx7, Gad1, Hspa12A, Foxn1, adenosine A1 receptor, Ca(2+) adaptor and homeostasis proteins, Cacnb4, Atp2b2, anti-apoptotic Bcl-2 gene members, intracellular trafficking protein, Grasp and suppressor of cytokine signaling (Socs3)]. Distinct anti-inflammatory interleukins (ILs) not observed in adult tissues [e.g. IL-6 transducer, IL-23 and IL-33 or their receptors (IL-F2 )] were also over-expressed. Several transcripts were validated by real-time polymerase chain reaction (QPCR) and immunohistochemistry. QPCR showed that casp 6 was increased after 1 × KA but reduced after 3 × KA; the pro-inflammatory gene Cox1 was either upregulated or unchanged after 1 × KA but reduced by ~70% after 3 × KA. Enhanced GFAP immunostaining following 1 × KA was selectively attenuated in the CA1 subregion after 3 × KA. The observed differential transcriptional responses may contribute to early-life seizure-induced pre-conditioning and neuroprotection by reducing glutamate receptor-mediated Ca(2+) permeability of the hippocampus and redirecting inflammatory and apoptotic pathways. These changes could lead to new genetic therapies for epilepsy.

Anticonvulsant profile of caprylic acid, a main constituent of the medium-chain triglyceride (MCT) ketogenic diet, in mice

The purpose of the present study was to evaluate the acute anticonvulsant effects of caprylic acid (CA), the main constituent of the medium-chain triglyceride ketogenic diet (MCT KD), in seizure tests typically used in screening for potential antiepileptic drugs in mice. Pharmacodynamic and pharmacokinetic interactions between CA and valproate (VPA) were also investigated. CA (p.o.) and VPA (i.p.) were administered 30 min before testing. Acute effects on motor coordination were assessed in the chimney test. Total plasma and brain concentrations of CA and VPA, when administered alone or in combination, were determined by high performance liquid chromatography. CA (10-30 mmol/kg) increased the threshold for i.v. pentylenetetrazole-induced myoclonic and clonic convulsions, but not tonic convulsions. CA (5-30 mmol/kg) increased the threshold for 6-Hz psychomotor seizures but was ineffective in the maximal electroshock seizure threshold test. CA (10-60 mmol/kg p.o.) impaired motor performance in the chimney test (TD(50) value, 58.4 mmol/kg). Increasing doses of CA (5-30 mmol/kg) produced proportional increases in plasma and brain exposure with constant brain/plasma partitioning. CA increased anticonvulsant potency of VPA in the maximal electroshock seizure and 6-Hz seizure tests. Co-administration of CA and VPA had no effect on brain and plasma concentrations of either compound. In summary, CA exerts acute anticonvulsant effects and potentiates the anticonvulsant effect of VPA at doses that result in plasma exposures comparable to those reported in epileptic patients on the MCT KD. Thus, this acute anticonvulsant property of CA may benefit and add to the overall clinical efficacy of the MCT KD.

Duplicate preconditioning with sevoflurane in vitro improves neuroprotection in rat brain via activating the extracellular signal-regulated protein kinase

OBJECTIVE

Sevoflurane preconditioning has been demonstrated to reduce cerebral ischemia-reperfusion (IR) injury, but the underlying mechanisms have not been fully elucidated. Besides, different protocols would usually lead to different results. The objective of this study was to determine whether dual exposure to sevoflurane improves the effect of anesthetic preconditioning against oxygen and glucose deprivation (OGD) injury in vitro.

METHODS

Rat hippocampal slices under normoxic conditions (95% O2/5% CO2) were pre-exposed to sevoflurane 1, 2 and 3 minimum alveolar concentration (MAC) for 30 min, once or twice, with 15-min washout after each exposure. The slices were then subjected to 13-min OGD treatment (95% N2/5% CO2, glucose-free), followed by 30-min reoxygenation. The population spikes (PSs) were recorded in the CA1 region of rat hippocampus. The percentage of PS amplitude at the end of 30-min reoxygenation to that before OGD treatment was calculated, since it could indicate the recovery degree of neuronal function. In addition, to assess the role of mitogen-activated protein kinases (MAPKs) in preconditioning, U0126, an inhibitor of extracellular signal-regulated protein kinase (MEK-ERK1/2, ERK1/2 MAPK), and SB203580, an inhibitor of p38 MAPK, were separately added 10 min before sevoflurane exposure.

RESULTS

Preconditioning once with sevoflurane 1, 2, and 3 MAC increased the percentage of PS amplitude at the end of 30-min reoxygenation to that before OGD treatment, from (15.13+/-3.79)% (control) to (31.88+/-5.36)%, (44.00+/-5.01)%, and (49.50+/-6.25)%, respectively, and twice preconditioning with sevoflurane 1, 2, and 3 MAC increased the percentage to (38.53+/-4.36)%, (50.74+/-7.05)% and (55.86+/-6.23)%, respectively. The effect of duplicate preconditioning with sevoflurane 3 MAC was blocked by U0126 [(16.23+/-4.62)%].

CONCLUSION

Sevoflurane preconditioning can induce neuroprotection against OGD injury in vitro, and preconditioning twice enhances this effect. Besides, the activation of extracellular signal-regulated protein kinase (MEK-ERK1/2, ERK1/2 MAPK) may be involved in this process.

Tissue plasminogen activator alters intracellular sequestration of zinc through interaction with the transporter ZIP4

Glutamatergic neurons contain free zinc packaged into neurotransmitter-loaded synaptic vesicles. Upon neuronal activation, the vesicular contents are released into the synaptic space, whereby the zinc modulates activity of postsynaptic neurons though interactions with receptors, transporters and exchangers. However, high extracellular concentrations of zinc trigger seizures and are neurotoxic if substantial amounts of zinc reenter the cells via ion channels and accumulate in the cytoplasm. Tissue plasminogen activator (tPA), a secreted serine protease, is also proepileptic and excitotoxic. However, tPA counters zinc toxicity by promoting zinc import back into the neurons in a sequestered form that is nontoxic. Here, we identify the zinc influx transporter, ZIP4, as the pathway through which tPA mediates the zinc uptake. We show that ZIP4 is upregulated after excitotoxin stimulation of the mouse, male and female, hippocampus. ZIP4 physically interacts with tPA, correlating with an increased intracellular zinc influx and lysosomal sequestration. Changes in prosurvival signals support the idea that this sequestration results in neuroprotection. These experiments identify a mechanism via which neurons use tPA to efficiently neutralize the toxic effects of excessive concentrations of free zinc.

Activation of ERK by spontaneous seizures in neural progenitors of the dentate gyrus in a mouse model of epilepsy

Cellular changes that are associated with spontaneous seizures in temporal lobe epilepsy are not well understood but could influence ongoing epilepsy-related processes. In order to identify cell signaling events that could occur at the time of spontaneous seizures, the localization of phosphorylated extracellular signal-regulated kinase (pERK) was studied in a pilocarpine mouse model of epilepsy at very short intervals (1.5-2.5 min) after detection of a spontaneous seizure. Within the hippocampal formation, immunolabeling of pERK was evident in a subpopulation of cells in the subgranular zone (SGZ) of the dentate gyrus at these short intervals. Many of these cells had a long vertical process and resembled radial glia, while others had short processes and were oriented horizontally. Labeling with a series of developmental markers demonstrated that virtually all pERK-labeled cells were neural progenitor cells (NPCs). A high percentage ( approximately 80%) of the pERK-labeled cells was labeled with either glial fibrillary acidic protein or brain lipid binding protein, indicating that these cells were radial glia-like NPCs. A smaller percentage of labeled cells expressed NeuroD, suggesting that they were later-developing NPCs that were assuming a neuronal identity. Early expression of pERK was not detected in immature neurons. Double labeling with proliferation markers demonstrated that approximately 30% of pERK-labeled NPCs expressed Mcm2, indicating that they were actively proliferating. Furthermore, virtually all radial glia-like NPCs that were in the proliferative cycle expressed pERK. These findings suggest that spontaneous seizures and associated ERK activation could contribute to the proliferation of radial glia-like NPCs in this epilepsy model.

Enhanced susceptibility of Prnp-deficient mice to kainate-induced seizures, neuronal apoptosis, and death: Role of AMPA/kainate receptors

Normal physiologic functions of the cellular prion protein (PrPc) are still elusive. This GPI-anchored protein exerts many functions, including roles in neuron proliferation, neuroprotection or redox homeostasis. There are, however, conflicting data concerning its role in synaptic transmission. Although several studies report that PrPc participates in NMDA-mediated neurotransmission, parallel studies describe normal behavior of PrPc-mutant mice. Abnormal axon connections have been described in the dentate gyrus of the hippocampi of PrPc-deficient mice similar to those observed in epilepsy. A study indicates increased susceptibility to kainate (KA) in these mutant mice. We extend the observation of these studies by means of several histologic and biochemical analyses of KA-treated mice. PrPc-deficient mice showed increased sensitivity to KA-induced seizures in vivo and in vitro in organotypic slices. In addition, we show that this sensitivity is cell-specific because interference experiments to abolish PrPc expression increased susceptibility to KA in PrPc-expressing cells. We indicate a correlation of susceptibility to KA in cells lacking PrPc with the differential expression of GluR6 and GluR7 KA receptor subunits using real-time RT-PCR methods. These results indicate that PrPc exerts a neuroprotective role against KA-induced neurotoxicity, probably by regulating the expression of KA receptor subunits.

TDAG51 in the anterior temporal neocortex of patients with intractable epilepsy

TDAG51 (T cell death-associated gene 51) is an apoptosis-associated protein. Our aim was to investigate TDAG51 expression in the anterior temporal neocortex of patients with intractable epilepsy (IE), and then to discuss the possible role of TDAG51 in IE. Tissue samples from the anterior temporal neocortex of 33 patients who had surgery for IE were used to detect TDAG51 expression by immunohistochemistry, immunofluorescence, and Western blotting. We compared these tissues with nine histologically normal anterior temporal lobes from intracranial hypertension patients who had decompression procedures. TDAG51 was mainly expressed in the cytoplasm of neurons and glial cells. TDAG51 in IE was significantly higher than that in the controls. These findings were consistently observed using Western blotting, immunofluorescence, and immunohistochemistry techniques. TDAG51 in patients with IE was significantly higher when compared with levels in the controls. This finding suggests TDAG51 is consistent with a possible role of this gene in the evolution of the pathology in IE.

Extracellular signal-regulated protein kinase in human intractable epilepsy

Extracellular signal-regulated kinases (ERK) such as ERK1 [p44 mitogen-activated protein kinase (MAPK)] and ERK2 (p42 MAPK) are activated in the central nervous system under physiological and pathological conditions such as ischemia and epilepsy. Our aim is to investigate ERK1, ERK2, and phosphorylated ERK (p-ERK) (Thr202/Tyr 204) expression in the temporal lobe of patients with intractable epilepsy (IE) and to explore its possible role of ERK in it. Tissue samples from temporal neocortices of 40 patients who had surgery for IE were used to detect ERK1, ERK2, and p-ERK (Thr 202/Tyr 204) expression through immunohistochemistry and western blot. We compared these tissues against 17 histological normal temporal lobes from head-trauma patients. ERK1, ERK2, and p-ERK in IE were significantly higher than those in the controls. They were mainly expressed in the cytoplasm of neurons and glial cells. There was also increased detection of p-ERK in the gliotic cortex of IE compared with the non-gliotic cortex. These findings were consistently observed in western blot and immunohistochemistry techniques. ERK expression in patients with IE was significantly increased compared with the controls. This suggested a probable role of ERK in the pathogenesis of IE.

Histone modifications in the brain

Chromatin remodelling, including histone modifications has been recognized to play a central role in the regulation of gene expression. Histone modifications are mostly based on studies in cell culture systems in vitro. Recent evidence suggests that histone modifications are actively involved in activity-dependent neural plasticity via regulation of critical gene transcription necessary for the biological process in vivo. We have reviewed here the recent works studied on long-term memory formation, visual cortical plasticity during the critical period and drug-induced status epilepticus to elucidate a role for histone modifications in these biological processes. All of the studies indicate that chromatin structure, including histone modifications is highly dynamic within the nervous system and suggest the possibility that chromatin structure itself might be recruited as a target of plasticity-associated signal transduction mechanisms.

Platelet-derived growth factor-mediated gliomagenesis and brain tumor recruitment

Platelet-derived growth factor (PDGF) is a growth factor family of ligands and receptors known to activate phosphatidylinositol 3-kinase, mitogen-activated protein kinase, Jak family kinase, Src family kinase, and phospholipase Cgamma signal transduction pathways, some of which have been causally linked to glioma formation. Extensive involvement of PDGF in development and its implication in a variety of pathologic conditions, including gliomagenesis, are mediated not only by autocrine effects but by paracrine effects. Many researchers view brain tumors as clonal entities derived from the cancer stem cell; however, recent documentation of the importance of the tumor microenvironment for glioma initiation and progression as well as the ability of neural stem or progenitor cells to migrate toward the sites of injury or tumor formation reveals additional complexities in brain tumorigenesis. Paracrine effects of PDGF in animal models of gliomagenesis, continued adult neurogenesis capable of increasing in response to brain injury, and the growth factor-rich environment of brain tumors suggest that recruitment may play a role in gliomagenesis. In this view, glioma formation involves recruitment of cells from the adjacent brain and possibly other sites.

Status epilepticus-induced somatostatinergic hilar interneuron degeneration is regulated by striatal enriched protein tyrosine phosphatase

Excitotoxic cell death is one of the precipitating events in the development of temporal lobe epilepsy. Of particular prominence is the loss of GABAergic hilar neurons. Although the molecular mechanisms responsible for the selective vulnerability of these cells are not well understood, activation of the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) pathway has been implicated in neuroprotective responses to excitotoxicity in other neuronal populations. Here, we report that high levels of the striatal-enriched protein tyrosine phosphatase (STEP), a key regulator of ERK/MAPK signaling, are found in vulnerable somatostatin-immunoreactive hilar interneurons. Under both control conditions and after pilocarpine-induced status epilepticus (SE), ERK/MAPK activation was repressed in STEP-immunoreactive hilar neurons. This contrasts with robust SE-induced ERK/MAPK activation in the granule cell layer of the dentate gyrus, a cell region that does not express STEP. During pilocarpine-induced SE, in vivo disruption of STEP activity allowed activation of the MAPK pathway, leading to immediate-early gene expression and significant rescue from cell death. Thus, STEP increases the sensitivity of neurons to SE-induced excitotoxicity by specifically blocking a latent neuroprotective response initiated by the MAPK pathway. These findings identify a key set of signaling events that render somatostatinergic hilar interneurons vulnerable to SE-induced cell death.

Maturational Effects of Single and Multiple Early-Life Seizures on AMPA Receptors in Prepubescent Hippocampus

The effects of single versus multiple episodes of status epilepticus on the expression of AMPA receptors during a critical growth spurt are unknown. To determine whether the pattern of hippocampal AMPA receptor subunit expression depends upon the age of the animal, timing and number of perinatal seizures, we characterized maturational changes in AMPA receptor protein levels of the hippocampus with immunohistochemistry and Western blotting in rats of juvenile ages with and without a history of neonatal seizures. Kainic acid (KA) was used to induce a single episode of status epilepticus (1 x KA) in rats on P20 or P30. Animals with a history of multiple seizures (3 x KA) were given KA on P6, P9, and then on P20 or P30. After 1 x KA, in P20 and P30 rats that are preferentially sensitive to CA1 damage, GluR1 immunoreactivity was depleted remarkably in CA1 stratum pyramidale and stratum lucidum and only morphologically healthy cells were faintly labeled. At P30, GluR2 subunit expression was nearly absent in the healthy cells and increased within the injured CA1 neuronal population. Western blot analysis confirmed that the GluR1/GluR2 ratio was decreased at P20 and further decreased at P30. A history of perinatal seizures (3 x KA) prevented the age-dependent alterations in the CA1. Except for areas of cell loss, NR1 and NR2A/B antibody labeling was relatively stable throughout the hippocampus at both ages and conditions examined. Data suggest that (i) Ca2+ permeable AMPA receptors may not be responsible for neuronal injury or irreversible cell loss and that (ii) the expression of AMPA receptors after status epilepticus depends upon the age of the animal, the timing of the first insult and subsequent formation of AMPA receptor subunit compositions within specific populations of hippocampal neurons.

On the participation of hippocampal p38 mitogen-activated protein kinase in extinction and reacquisition of inhibitory avoidance memory

Inhibitory avoidance (IA) learning relies on the formation of an association between stepping down from a platform present in a certain context (conditioned stimulus; CS) with an aversive unconditioned stimulus (US; i.e. a footshock). A single CS-US pairing establishes a robust long-term memory expressed as an increase in step-down latency at testing. However, repeated retrieval of the avoidance response in the absence of the US induces extinction of IA memory. That is, recurring presentation of the CS alone results in a new learning indicating that the CS no longer predicts the US. Although the signaling pathways involved in the consolidation of IA and other fear-motivated memories have been profusely studied, little is known about the molecular requirements of fear memory extinction. Here we report that, as happens with its consolidation, extinction of IA long-term memory requires activity of the p38 subfamily of mitogen-activated protein kinases (MAPK) in the CA1 region of the dorsal hippocampus. Moreover, we found that inhibition of hippocampal p38MAPK blocked memory reacquisition after extinction without affecting either the increase in IA memory retention induced by a second training session or animal's locomotor/exploratory activity and anxiety state.

Histone modifications in kainate-induced status epilepticus

To understand the molecular actions of status epilepticus at the chromatin level, we studied the effects of kainate-induced status epilepticus on two different histone modifications at amino terminal tails: histone H3 phosphorylation at serine 10 and histone H4 acetylation. In addition to induction of c-fos and c-jun immediate early genes (IEGs) expression in mouse hippocampus, we also found the upregulation of acetylation and phosphorylation of histones, coupled with status epilepticus after kainate administration. c-fos and c-jun mRNA were sequentially induced in response to kainate, in different hippocampal subpopulations, starting from the dentate gyrus (DG) and spreading to the cornus ammonis regions. Immunohistochemical analysis showed that the spatio-temporal distribution of histone H4 hyperacetylation after kainate treatment was well correlated with the expression of c-fos and c-jun genes. Additionally, there was a transient appearance of phosphorylated histone H3 specifically in the DG region. CREB-binding protein or CBP, a well-known transcriptional co-activator with histone acetyltransferase (HAT) activity, was also induced by kainate and its expression pattern well correlated with histone H4 hyperacetylation in the hippocampus. Chromatin immunoprecipitation analysis showed that both histone modifications were associated with c-fos gene promoter after kainate stimulation, but only histone acetylation with c-jun gene. Pretreatment with curcumin, which has a HAT inhibitory activity specific for CBP/p300, attenuated histone modifications, IEGs expression and also the severity of status epilepticus after kainate treatment. Our findings suggest the involvement of histone modifications induced by kainate not only in IEGs expression but also in the development of epilepsy.

Involvement of multitargets in paeoniflorin-induced preconditioning

Paeoniflorin (PF) is the principal component of Paeoniae radix prescribed in traditional Chinese medicine. The delayed neuroprotection induced by PF preconditioning and its underlying mechanisms were investigated in rat middle cerebral artery occlusion (MCAO) and reperfusion model. At a dosage of 20 or 40 mg/kg, PF preconditioning 48 h before MCAO followed by 24-h reperfusion significantly reduced the mortality and infarct volume and reversed the neurological deficits caused by ischemia. Likewise, the ameliorative effects on mortality, infarct size, and neurological impairment induced by MCAO emerged as well when PF was administered 24 h, 48 h, or 5 days before MCAO at the dose of 20 mg/kg. Furthermore, comparative proteomics analysis was adopted to identify the differentially expressed proteins induced by PF preconditioning itself. The relative levels of 42 proteins were altered after PF preconditioning, among which 20 were elevated and 22 reduced. In summary, A(1) receptor-regulator of G protein signaling-K(ATP) signaling, arachidonic acid cascade, nitric oxide system, markers of neuronal damage, mitochondrial damage-related molecules, and the mitogen-activated protein kinase and nuclear factor-kappaB pathway are associated with the mechanisms of PF preconditioning.