A mechanism for the inactivation of Ca2+/calmodulin-dependent protein kinase II during prolonged seizure activity and its consequence after the recovery from seizure activity in rats in vivo

Unveiling the role of CaMKII in retinal degeneration: from biological mechanism to therapeutic strategies

Ca2+/calmodulin-dependent protein kinase II (CaMKII) is a family of broad substrate specificity serine (Ser)/threonine (Thr) protein kinases that play a crucial role in the Ca2+-dependent signaling pathways. Its significance as an intracellular Ca2+ sensor has garnered abundant research interest in the domain of neurodegeneration. Accumulating evidences suggest that CaMKII is implicated in the pathology of degenerative retinopathies such as diabetic retinopathy (DR), age-related macular degeneration (AMD), retinitis pigmentosa (RP) and glaucoma optic neuropathy. CaMKII can induce the aberrant proliferation of retinal blood vessels, influence the synaptic signaling, and exert dual effects on the survival of retinal ganglion cells and pigment epithelial cells. Researchers have put forth multiple therapeutic agents, encompassing small molecules, peptides, and nucleotides that possess the capability to modulate CaMKII activity. Due to its broad range isoforms and splice variants therapeutic strategies seek to inhibit specifically the CaMKII are confronted with considerable challenges. Therefore, it becomes crucial to discern the detrimental and advantageous aspects of CaMKII, thereby facilitating the development of efficacious treatment. In this review, we summarize recent research findings on the cellular and molecular biology of CaMKII, with special emphasis on its metabolic and regulatory mechanisms. We delve into the involvement of CaMKII in the retinal signal transduction pathways and discuss the correlation between CaMKII and calcium overload. Furthermore, we elaborate the therapeutic trials targeting CaMKII, and introduce recent developments in the zone of CaMKII inhibitors. These findings would enrich our knowledge of CaMKII, and shed light on the development of a therapeutic target for degenerative retinopathy.

The Traf2 and NcK interacting kinase inhibitor NCB-0846 suppresses seizure activity involving the decrease of GRIA1

Epilepsy, one of the most common neurological disorders, is characterized by spontaneous recurrent seizures. Temporal lobe epilepsy (TLE) is one of the most common medically intractable seizure disorders. Traf2-and NcK-interacting kinase (TNIK) has recently attracted attention as a critical modulation target of many neurological and psychiatric disorders, but its role in epilepsy remains unclear. In this study, we hypothesized the involvement of TNIK in epilepsy and investigated TNIK expression in patients with intractable TLE and in a pilocarpine-induced rat model of epilepsy by western blotting, immunofluorescence, and immunohistochemistry. A pentylenetetrazole (PTZ)-induced epilepsy rat model was used to determine the effect of the TNIK inhibitor NCB-0846 on behavioral manifestations of epilepsy. Coimmunoprecipitation (Co-IP)/mass spectrometry (MS) was used to identify the potential mechanism. Through Co-IP, we detected and confirmed the main potential TNIK interactors. Subcellular fractionation was used to establish the effect of NCB-0846 on the expression of the main interactors in postsynaptic density (PSD) fractions. We found that TNIK was primarily located in neurons and decreased significantly in epilepsy model rats and TLE patients compared with controls. NCB-0846 delayed kindling progression and decreased seizure severity. Co-IP/MS identified 63 candidate TNIK interactors in rat hippocampi, notably CaMKII. Co-IP showed that TNIK might correlate with endogenous GRIA1, SYN2, PSD-95, CaMKIV, GABRG1, and GABRG2. In addition, the significant decrease in GRIA1 in hippocampal total lysate and PSDs after NCB-0846 treatment might help modify the progression of PTZ kindling. Our results suggest that TNIK contributes to epileptic pathology and is a potential antiepileptic drug target.

Highly dynamic inflammatory and excitability transcriptional profiles in hippocampal CA1 following status epilepticus

Transient brain insults including status epilepticus (SE) can initiate a process termed 'epileptogenesis' that results in chronic temporal lobe epilepsy. As a consequence, the entire tri-synaptic circuit of the hippocampus is fundamentally impaired. A key role in epileptogenesis has been attributed to the CA1 region as the last relay station in the hippocampal circuit and as site of aberrant plasticity, e.g. mediated by acquired channelopathies. The transcriptional profiles of the distinct hippocampal neurons are highly dynamic during epileptogenesis. Here, we aimed to elucidate the early SE-elicited mRNA signature changes and the respective upstream regulatory cascades in CA1. RNA sequencing of CA1 was performed in the mouse pilocarpine-induced SE model at multiple time points ranging from 6 to 72 h after the initial insult. Bioinformatics was used to decipher altered gene expression, signalling cascades and their corresponding cell type profiles. Robust transcriptomic changes were detected at 6 h after SE and at subsequent time points during early epileptogenesis. Major differentially expressed mRNAs encoded primarily immediate early and excitability-related gene products, as well as genes encoding immune signalling factors. Binding sites for the transcription factors Nfkb1, Spi1, Irf8, and two Runx family members, were enriched within promoters of differentially expressed genes related to major inflammatory processes, whereas the transcriptional repressors Suz12, Nfe2l2 and Rest were associated with hyperexcitability and GABA / glutamate receptor activity. CA1 quickly responds to SE by inducing transcription of genes linked to inflammation and excitation stress. Transcription factors mediating this transcriptomic switch represent targets for new highly selected, cell type and time window-specific anti-epileptogenic strategies.

PDI augments kainic acid-induced seizure activity and neuronal death by inhibiting PP2A-GluA2-PICK1-mediated AMPA receptor internalization in the mouse hippocampus

Protein disulfide isomerase (PDI) is a redox-active enzyme and also serves as a nitric oxide donor causing S-nitrosylation of cysteine residues in various proteins. Although PDI knockdown reduces α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR)-mediated neuronal activity, the underlying mechanisms are largely unknown. In the present study, we found that under physiological condition PDI knockdown increased CaMKII activity (phosphorylation) in the mouse hippocampus. However, PDI siRNA inhibited protein phosphatase (PP) 2A-mediated GluA2 S880 dephosphorylation by increasing PP2A oxidation, independent of S-nitrosylation. PDI siRNA also enhanced glutamate ionotropic receptor AMPA type subunit 1 (GluA1) S831 and GluA2 S880, but not GluA1 S845 and GluA2 Y869/Y873/Y876 phosphorylations, concomitant with the enhanced protein interacting with C kinase 1 (PICK1)-mediated AMPAR internalization. Furthermore, PDI knockdown attenuated seizure activity and neuronal damage in response to kainic acid (a non-desensitizing agonist of AMPAR). Therefore, these findings suggest that PDI may regulate surface AMPAR expression through PP2A-GluA2-PICK1 signaling pathway, and that PDI may be one of the therapeutic targets for epilepsy via AMPAR internalization without altering basal neurotransmission.

In the fast lane: Receptor trafficking during status epilepticus

Status epilepticus (SE) remains a significant cause of morbidity and mortality and often is refractory to standard first-line treatments. A rapid loss of synaptic inhibition and development of pharmacoresistance to benzodiazepines (BZDs) occurs early during SE, while NMDA and AMPA receptor antagonists remain effective treatments after BZDs have failed. Multimodal and subunit-selective receptor trafficking within minutes to an hour of SE involves GABA-A, NMDA, and AMPA receptors and contributes to shifts in the number and subunit composition of surface receptors with differential impacts on the physiology, pharmacology, and strength of GABAergic and glutamatergic currents at synaptic and extrasynaptic sites. During the first hour of SE, synaptic GABA-A receptors containing γ2 subunits move to the cell interior while extrasynaptic GABA-A receptors with δ subunits are preserved. Conversely, NMDA receptors containing N2B subunits are increased at synaptic and extrasynaptic sites, and homomeric GluA1 ("GluA2-lacking") calcium permeant AMPA receptor surface expression also is increased. Molecular mechanisms, largely driven by NMDA receptor or calcium permeant AMPA receptor activation early during circuit hyperactivity, regulate subunit-specific interactions with proteins involved with synaptic scaffolding, adaptin-AP2/clathrin-dependent endocytosis, endoplasmic reticulum (ER) retention, and endosomal recycling. Reviewed here is how SE-induced shifts in receptor subunit composition and surface representation increase the excitatory to inhibitory imbalance that sustains seizures and fuels excitotoxicity contributing to chronic sequela such as "spontaneous recurrent seizures" (SRS). A role for early multimodal therapy is suggested both for treatment of SE and for prevention of long-term comorbidities.

Role of Ca2+/Calmodulin-Dependent Protein Kinase Type II in Mediating Function and Dysfunction at Glutamatergic Synapses

Glutamatergic synapses harbor abundant amounts of the multifunctional Ca²⁺/calmodulin-dependent protein kinase type II (CaMKII). Both in the postsynaptic density as well as in the cytosolic compartment of postsynaptic terminals, CaMKII plays major roles. In addition to its Ca²⁺-stimulated kinase activity, it can also bind to a variety of membrane proteins at the synapse and thus exert spatially restricted activity. The abundance of CaMKII in glutamatergic synapse is akin to scaffolding proteins although its prominent function still appears to be that of a kinase. The multimeric structure of CaMKII also confers several functional capabilities on the enzyme. The versatility of the enzyme has prompted hypotheses proposing several roles for the enzyme such as Ca²⁺ signal transduction, memory molecule function and scaffolding. The article will review the multiple roles played by CaMKII in glutamatergic synapses and how they are affected in disease conditions.

Repeated exposure to microcystin-leucine-arginine potentiates excitotoxicity induced by a low dose of kainate

Microcystin-leucine-arginine (MLCR) is a cyanobacterial toxin, and has been demonstrated to cause neurotoxicity. In addition, MCLR has been identified as an inhibitor of protein phosphatase (PP)1 and PP2A, which are known to regulate the phosphorylation of various molecules related to synaptic excitability. Thus, in the present study, we examined whether MCLR exposure affects seizures induced by a low dose of kainic acid (KA; 0.05 μg, i.c.v.) administration. KA-induced seizure occurrence and seizure score significantly increased after repeated exposure to MCLR (2.5 or 5.0 μg/kg, i.p., once a day for 10 days), but not after acute MCLR exposure (2.5 or 5.0 μg/kg, i.p., 2 h and 30 min prior to KA administration), and hippocampal neuronal loss was consistently facilitated by repeated exposure to MCLR. In addition, repeated MCLR significantly elevated the membrane expression of kainate receptor GluK2 subunits, p-pan-protein kinase C (PKC), and p-extracellular signal-related kinase (ERK) at 1 h after KA. However, KA-induced membrane expression of Ca²⁺/calmodulin-dependent kinase II (CaMKII) was significantly reduced by repeated MCLR exposure. Consistent with the enhanced seizures and neurodegeneration, MCLR exposure significantly potentiated KA-induced oxidative stress and microglial activation, which was accompanied by increased expression of p-ERK and p-PKCδ in the hippocampus. The combined results suggest that repeated MCLR exposure potentiates KA-induced excitotoxicity in the hippocampus by increasing membrane GluK2 expression and enhancing oxidative stress and neuroinflammation through the modulation of p-CaMKII, p-PKC, and p-ERK.

Peripheral blood mononuclear cell activation sustains seizure activity

OBJECTIVE

The influx of immune cells and serum proteins from the periphery into the brain due to a dysfunctional blood-brain barrier (BBB) has been proposed to contribute to the pathogenesis of seizures in various forms of epilepsy and encephalitis. We evaluated the pathophysiological impact of activated peripheral blood mononuclear cells (PBMCs) and serum albumin on neuronal excitability in an in vitro brain preparation.

METHODS

A condition of mild endothelial activation induced by arterial perfusion of lipopolysaccharide (LPS) was induced in the whole brain preparation of guinea pigs maintained in vitro by arterial perfusion. We analyzed the effects of co-perfusion of human recombinant serum albumin with human PBMCs activated with concanavalin A on neuronal excitability, BBB permeability (measured by FITC-albumin extravasation), and microglial activation.

RESULTS

Bioplex analysis in supernatants of concanavalin A-stimulated PBMCs revealed increased levels of several inflammatory mediators, in particular interleukin (IL)-1β, tumor necrosis factor (TNF)-α, interferon (INF)-γ, IL-6, IL-10, IL-17A, and MIP3α. LPS and human albumin arterially co-perfused with either concanavalin A-activated PBMCs or the cytokine-enriched supernatant of activated PBMCs (1) modulated calcium-calmodulin-dependent protein kinase II at excitatory synapses, (2) enhanced BBB permeability, (3) induced microglial activation, and (4) promoted seizure-like events. Separate perfusions of either nonactivated PBMCs or concanavalin A-activated PBMCs without LPS/human albumin (hALB) failed to induce inflammatory and excitability changes.

SIGNIFICANCE

Activated peripheral immune cells, such as PBMCs, and the extravasation of serum proteins in a condition of BBB impairment contribute to seizure generation.

Role of calcium/calmodulin-dependent kinase 2 in neurodevelopmental disorders

Neurodevelopmental disorders are a complex and heterogeneous group of neurological disorders characterized by their early-onset and estimated to affect more than 3% of children worldwide. The rapid advancement of sequencing technologies in the past years allowed the identification of hundreds of variants in several different genes causing neurodevelopmental disorders. Between those, new variants in the Calcium/calmodulin dependent protein kinase II (CAMK2) genes were recently linked to intellectual disability. Despite many years of research on CAMK2, this proves for the first time that this well-known and highly conserved molecule plays an important role in the human brain. In this review, we give an overview of the identified CAMK2 variants, and we speculate on potential mechanisms through which dysfunctions in CAMK2 result in neurodevelopmental disorders. Additionally, we discuss how the identification of CAMK2 variants might result in new exciting discoveries regarding the function of CAMK2 in the human brain.

Mutation in PHACTR1 associated with multifocal epilepsy with infantile spasms and hypsarrhythmia

A young boy with multifocal epilepsy with infantile spasms and hypsarrhythmia with minimal organic lesions of brain structures underwent DNA diagnosis using whole‐exome sequencing. A heterozygous amino‐acid substitution p.L519R in a PHACTR1 gene was identified. PHACTR1 belongs to a protein family of G‐actin binding protein phosphatase 1 (PP1) cofactors and was not previously associated with a human disease. The missense single nucleotide variant in the proband was shown to occur de novo in the paternal allele. The mutation was shown in vitro to reduce the affinity of PHACTR1 for G‐actin, and to increase its propensity to form complexes with the catalytic subunit of PP1. These properties are associated with altered subcellular localization of PHACTR1 and increased ability to induce cytoskeletal rearrangements. Although the molecular role of the PHACTR1 in neuronal excitability and differentiation remains to be defined, PHACTR1 has been previously shown to be involved in Slack channelopathy pathogenesis, consistent with our findings. We conclude that this activating mutation in PHACTR1 causes a severe type of sporadic multifocal epilepsy in the patient.

Assessment of the protective effect of KN-93 drug in systemic epilepsy disorders induced by pilocarpine in male rat

BACKGROUND AND AIMS

Epileptic seizures occur as a consequence of a sudden imbalance between the stimuli and inhibitors within the network of cortical neurons in favor of the stimulus. One of the drugs that induce epilepsy is pilocarpine. Systemic injection of pilocarpine affects on muscarinic receptors. Increasing evidence has addressed the implication of KN-93 by blocking Ca²⁺ /calmodulin-dependent protein kinase II (CaMKII), suppressing oxidative stress and inflammation, and also reducing neuron decay. So, we aimed to evaluate the potential preventive effects of KN-93 in systemic epilepsy disorders induced by pilocarpine.

MATERIALS AND METHODS

In this animal study, male rats were divided into five groups including treatment group (KN-93 with the dose of 5 mM/10 µL dimethyl sulfoxide (DMSO) before inducing epilepsy by 380 mg/kg pilocarpine) KN-93 group (received 5 mM KN-93), control group, epilepsy group (received 380 mg/kg pilocarpine Intraperitoneal), and sham group (received 10 µL DMSO). Oxidative stress was assessed by measuring its indicators including the concentration of malondialdehyde (MDA), nitrite, glutathione (GSH), as well as the antioxidant activity of catalase. In addition, serum levels of proinflammatory mediators including tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were determined.

RESULTS

Pretreatment with KN-93 significantly reduced oxidative stress index by reducing the concentration of MDA, nitrite, and increasing the level of GSH. In addition, low concentrations of TNF-α and IL-1β were observed in hippocampus supernatant of KN-93 pretreated rats in comparison with the pilocarpine groups. Moreover, administration of KN-93 improved neuronal density and attenuated the seizure activity and behavior.

CONCLUSIONS

Overall, our findings suggest that KN-93 can effectively suppress oxidative stress and inflammation. Furthermore, KN-93 is able to attenuate seizure behaviors by preventing its effects on neuron loss, so, it is valuable for the treatment of epileptic seizures.

Voltage-Dependent Calcium Channels, Calcium Binding Proteins, and Their Interaction in the Pathological Process of Epilepsy

As an important second messenger, the calcium ion (Ca²⁺) plays a vital role in normal brain function and in the pathophysiological process of different neurodegenerative diseases including Alzheimer’s disease (AD), Parkinson’s disease (PD), and epilepsy. Ca²⁺ takes part in the regulation of neuronal excitability, and the imbalance of intracellular Ca²⁺ is a trigger factor for the occurrence of epilepsy. Several anti-epileptic drugs target voltage-dependent calcium channels (VDCCs). Intracellular Ca²⁺ levels are mainly controlled by VDCCs located in the plasma membrane, the calcium-binding proteins (CBPs) inside the cytoplasm, calcium channels located on the intracellular calcium store (particular the endoplasmic reticulum/sarcoplasmic reticulum), and the Ca²⁺-pumps located in the plasma membrane and intracellular calcium store. So far, while many studies have established the relationship between calcium control factors and epilepsy, the mechanism of various Ca²⁺ regulatory factors in epileptogenesis is still unknown. In this paper, we reviewed the function, distribution, and alteration of VDCCs and CBPs in the central nervous system in the pathological process of epilepsy. The interaction of VDCCs with CBPs in the pathological process of epilepsy was also summarized. We hope this review can provide some clues for better understanding the mechanism of epileptogenesis, and for the development of new anti-epileptic drugs targeting on VDCCs and CBPs.

LPS-induced cortical kynurenic acid and neurogranin-NFAT signaling is associated with deficits in stimulus processing during Pavlovian conditioning

The N-Methyl-d-Aspartate receptor (NMDAR) antagonist kynurenic acid (KYNA) and the post-synaptic calmodulin binding protein neurogranin (Nrgn) have been implicated in neurological and neuropsychiatric conditions including Alzheimer's disease and schizophrenia. This study indicates that systemic dual-lipopolysaccharide (LPS) injections increases KYNA in the medial prefrontal cortex (mPFC), which is accompanied with increased phosphorylation of nuclear factor kappa chain of activated B cells (NFκB) and activation of the nuclear factor of activated T- cells (NFAT). Our results also indicate that dual-LPS increases Nrgn phosphorylation and concomitantly reduces phosphorylation of calmodulin kinase-II (CaMKII). We confirmed that systemic blockade of kynurenine-3 monooxygenase in conjunction with kynurenine administration results in significant increases in Nrgn phosphorylation and a significant reduction of CaMKII phosphorylation in the mPFC. Consequently, dual-LPS administration induced significant impairments in stimulus processing during Pavlovian conditioning. Taken together, our study indicates that elevations in KYNA in the mPFC can directly regulate NMDA-Nrgn-CaMKII signaling, suggesting that neuroinflammatory conditions affecting this pathway may be associated with cognitive dysfunction.

CaMKII modulates sodium current in neurons from epileptic Scn2a mutant mice

Monogenic epilepsies with wide-ranging clinical severity have been associated with mutations in voltage-gated sodium channel genes. In the Scn2a^Q54 mouse model of epilepsy, a focal epilepsy phenotype is caused by transgenic expression of an engineered Na_V1.2 mutation displaying enhanced persistent sodium current. Seizure frequency and other phenotypic features in Scn2a^Q54 mice depend on genetic background. We investigated the neurophysiological and molecular correlates of strain-dependent epilepsy severity in this model. Scn2a^Q54 mice on the C57BL/6J background (B6.Q54) exhibit a mild disorder, whereas animals intercrossed with SJL/J mice (F1.Q54) have a severe phenotype. Whole-cell recording revealed that hippocampal pyramidal neurons from B6.Q54 and F1.Q54 animals exhibit spontaneous action potentials, but F1.Q54 neurons exhibited higher firing frequency and greater evoked activity compared with B6.Q54 neurons. These findings correlated with larger persistent sodium current and depolarized inactivation in neurons from F1.Q54 animals. Because calcium/calmodulin protein kinase II (CaMKII) is known to modify persistent current and channel inactivation in the heart, we investigated CaMKII as a plausible modulator of neuronal sodium channels. CaMKII activity in hippocampal protein lysates exhibited a strain-dependence in Scn2a^Q54 mice with higher activity in F1.Q54 animals. Heterologously expressed Na_V1.2 channels exposed to activated CaMKII had enhanced persistent current and depolarized channel inactivation resembling the properties of F1.Q54 neuronal sodium channels. By contrast, inhibition of CaMKII attenuated persistent current, evoked a hyperpolarized channel inactivation, and suppressed neuronal excitability. We conclude that CaMKII-mediated modulation of neuronal sodium current impacts neuronal excitability in Scn2a^Q54 mice and may represent a therapeutic target for the treatment of epilepsy.

Contrasting features of ERK1/2 activity and synapsin I phosphorylation at the ERK1/2-dependent site in the rat brain in status epilepticus induced by kainic acid in vivo

Extracellular signal-regulated kinase 1/2 (ERK1/2) plays diverse roles in the central nervous system. Activation of ERK1/2 has been observed in various types of neuronal excitation, including seizure activity in vivo and in vitro. However, studies examining ERK1/2 activity and its substrate phosphorylation in parallel are scarce especially in seizure models. We have been studying the phosphorylation state of the presynaptic protein, synapsin I at ERK1/2-dependent and -independent sites in various types of seizure models and showed that ERK1/2-dependent phosphorylation of synapsin I was indeed under control of ERK1/2 activity in vivo. To further expand our study, here we examined the effects of prolonged seizure activity on ERK1/2 activity and synapsin I phosphorylation by using status epilepticus induced by kainic acid (KA-SE) in rats in vivo. In KA-SE, robust ERK1/2 activation was observed in the hippocampus, a representative limbic structure, with lesser activation in the parietal cortex, a representative non-limbic structure. In contrast, the phosphorylation level of synapsin I at ERK1/2-dependent phospho-site 4/5 was profoundly decreased, the extent of which was much larger in the hippocampus than in the parietal cortex. In addition, phosphorylation at other ERK1/2-independent phospho-sites in synapsin I also showed an even larger decrease. All these changes disappeared after recovery from KA-SE. These results indicate that the phosphorylation state of synapsin I is dynamically regulated by the balance between kinase and phosphatase activities. The contrasting features of robust ERK1/2 activation yet synapsin I dephosphorylation may be indicative of an irreversible pathological outcome of the epileptic state in vivo.

Emerging role of CaMKII in neuropsychiatric disease

Although it has been known for decades that hippocampal calcium/calmodulin (CaM)-dependent protein kinase II (CaMKII) plays an essential role in learning and memory consolidation, the roles of CaMKII in other brain regions are only recently being explored in depth. A series of recent studies suggest that CaMKII dysfunction throughout the brain may underlie myriad neuropsychiatric disorders, including drug addiction, schizophrenia, depression, epilepsy, and multiple neurodevelopmental disorders, perhaps through maladaptations in glutamate signaling and neuroplasticity. I review here the structure, function, subcellular localization, and expression patterns of CaMKII isoforms, as well as recent advances demonstrating that disturbances in these properties may contribute to psychiatric disorders.

Ca2+/calmodulin-dependent protein kinase II increases the susceptibility to the arrhythmogenic action potential alternans in spontaneously hypertensive rats

Action potential duration alternans (APD-ALT), defined as long-short-long repetitive pattern of APD, potentially leads to lethal ventricular arrhythmia. However, the mechanisms of APD-ALT in the arrhythmogenesis of cardiac hypertrophy remain undetermined. Ca2+/calmodulin-dependent protein kinase II (CaMKII) is known to modulate the function of cardiac sarcoplasmic reticulum and play an important role in Ca2+ cycling. We thus aimed to determine the role of CaMKII in the increased susceptibility to APD-ALT and arrhythmogenesis in the hypertrophied heart. APD was measured by high-resolution optical mapping in left ventricular (LV) anterior wall from normotensive Wistar-Kyoto (WKY; n = 10) and spontaneously hypertensive rats (SHR; n = 10) during rapid ventricular pacing. APD-ALT was evoked at significantly lower pacing rate in SHR compared with WKY (382 ± 43 vs. 465 ± 45 beats/min, P < 0.01). These changes in APD-ALT in SHR were completely reversed by KN-93 (1 μmol/l; n = 5), an inhibitor of CaMKII, but not its inactive analog, KN-92 (1 μmol/l; n = 5). The magnitude of APD-ALT was also significantly greater in SHR than WKY and was completely normalized by KN-93. Ventricular fibrillation (VF) was induced by rapid pacing more frequently in SHR than in WKY (60 vs. 10%; P < 0.05), which was also abolished by KN-93 (0%, P < 0.05). Western blot analyses indicated that the CaMKII autophosphorylation at Thr287 was significantly increased in SHR compared with WKY. The increased susceptibility to APD-ALT and VF during rapid pacing in hypertrophied heart was prevented by KN-93. CaMKII could be an important mechanism of arrhythmogenesis in cardiac hypertrophy.

Anti-epileptic effect of Ganoderma lucidum polysaccharides by inhibition of intracellular calcium accumulation and stimulation of expression of CaMKII α in epileptic hippocampal neurons

Purpose

To investigate the mechanism of the anti-epileptic effect of Ganoderma lucidum polysaccharides (GLP), the changes of intracellular calcium and CaMK II α expression in a model of epileptic neurons were investigated.

Method

Primary hippocampal neurons were divided into: 1) Control group, neurons were cultured with Neurobasal medium, for 3 hours; 2) Model group I: neurons were incubated with Mg²⁺ free medium for 3 hours; 3) Model group II: neurons were incubated with Mg²⁺ free medium for 3 hours then cultured with the normal medium for a further 3 hours; 4) GLP group I: neurons were incubated with Mg²⁺ free medium containing GLP (0.375 mg/ml) for 3 hours; 5) GLP group II: neurons were incubated with Mg²⁺ free medium for 3 hours then cultured with a normal culture medium containing GLP for a further 3 hours. The CaMK II α protein expression was assessed by Western-blot. Ca²⁺ turnover in neurons was assessed using Fluo-3/AM which was added into the replacement medium and Ca²⁺ turnover was observed under a laser scanning confocal microscope.

Results

The CaMK II α expression in the model groups was less than in the control groups, however, in the GLP groups, it was higher than that observed in the model group. Ca²⁺ fluorescence intensity in GLP group I was significantly lower than that in model group I after 30 seconds, while in GLP group II, it was reduced significantly compared to model group II after 5 minutes.

Conclusion

GLP may inhibit calcium overload and promote CaMK II α expression to protect epileptic neurons.

The immature dentate gyrus represents a shared phenotype of mouse models of epilepsy and psychiatric disease

OBJECTIVES

There is accumulating evidence to suggest psychiatric disorders, such as bipolar disorder and schizophrenia, share common etiologies, pathophysiologies, genetics, and drug responses with many of the epilepsies. Here, we explored overlaps in cellular/molecular, electrophysiological, and behavioral phenotypes between putative mouse models of bipolar disorder/schizophrenia and epilepsy. We tested the hypothesis that an immature dentate gyrus (iDG), whose association with psychosis in patients has recently been reported, represents a common phenotype of both diseases.

METHODS

Behaviors of calcium/calmodulin-dependent protein kinase II alpha (α-CaMKII) heterozygous knock-out (KO) mice, which are a representative bipolar disorder/schizophrenia model displaying iDG, and pilocarpine-treated mice, which are a representative epilepsy model, were tested followed by quantitative polymerase chain reaction (qPCR)/immunohistochemistry for mRNA/protein expression associated with an iDG phenotype. In vitro electrophysiology of dentate gyrus granule cells (DG GCs) was examined in pilocarpine-treated epileptic mice.

RESULTS

The two disease models demonstrated similar behavioral deficits, such as hyperactivity, poor working memory performance, and social withdrawal. Significant reductions in mRNA expression and immunoreactivity of the mature neuronal marker calbindin and concomitant increases in mRNA expression and immunoreactivity of the immature neuronal marker calretinin represent iDG signatures that are present in both mice models. Electrophysiologically, we have confirmed that DG GCs from pilocarpine-treated mice represent an immature state. A significant decrease in hippocampal α-CaMKII protein levels was also found in both models.

CONCLUSIONS

Our data have shown iDG signatures from mouse models of both bipolar disorder/schizophrenia and epilepsy. The evidence suggests that the iDG may, in part, be responsible for the abnormal behavioral phenotype, and that the underlying pathophysiologies in epilepsy and bipolar disorder/schizophrenia are strikingly similar.

Regulation of ERK1/2 mitogen-activated protein kinase by NMDA-receptor-induced seizure activity in cortical slices

Extracellular signal-regulated kinase 1/2 (ERK1/2) that belongs to a subfamily of mitogen-activated protein kinases (MAPKs) plays diverse roles in the central nervous system. Activation of ERK1/2 has been observed in various types of neuronal excitation, including seizure activity in vivo and in vitro, as well as in NMDA-receptor (NMDA-R)-dependent long-term potentiation in the hippocampus. On the other hand, recent studies in cultured neurons have shown that NMDA-R stimulation could result in either ERK1/2 activation or non-activation, depending on the pharmacological manipulations. To assess NMDA-R-dependent regulation of ERK1/2 activity in vivo, here we examined the effect of NMDA-R-induced seizure activity on ERK1/2 activation by using rat cortical slice preparations. NMDA-R-dependent seizure activity introduced by Mg2+ -free condition did not cause ERK1/2 activation. On the other hand, when picrotoxin was added to concurrently suppress GABAA-receptor-mediated inhibition, profound ERK1/2 activation occurred, which was accompanied by strong phospho-ERK1/2-staining in the superficial and deep cortical layer neurons. In this case, prolonged membrane depolarization and enhanced burst action potential firings, both of which were much greater than those in Mg2+ -free condition alone, were observed. Differential ERK1/2 activation was supported by the concurrent selective increase in phosphorylation of a substrate protein, phospho-site 4/5 of synapsin I. These results indicate that NMDA-R activation through a release from Mg2+ -blockade, which accompanies enhancement of both excitatory and inhibitory synaptic transmission, was not enough, but concurrent suppression of GABAergic inhibition, which leads to a selective increase in excitatory synaptic transmission, was necessary for robust ERK1/2 activation to occur within the cortical network.

Neuronal excitability and calcium/calmodulin-dependent protein kinase type II: location, location, location

Calcium/calmodulin-dependent protein kinase type II (CaMKII) is a highly abundant serine/threonine kinase comprising a significant fraction of total protein in mammalian forebrain and forming a major component of the postsynaptic density. CaMKII is essential for certain forms of synaptic plasticity and memory consolidation and this is mediated through substrate binding and intramolecular phosphorylation of holoenzyme subunits. CaMKII is multifunctional; it targets a variety of cellular substrates, and this diversity depends on holoenzyme subunit composition. CaMKII comprises homooligomeric and heterooligomeric complexes generated from four subunits (α, β, δ, and γ) encoded by separate genes that are further expanded by extensive alternative splicing to more than 30 different isoforms. Much attention has been paid to understanding the regulation of CaMKII function through its structural diversity and/or substrate specificity. However, given the importance of subunit composition to holoenzyme activity, it is likely that specificity of cellular expression of CaMKII isoforms also plays a major role in regulation of enzyme function. Herein we review the cellular colocalization of CaMKII isoforms with special regard to the cell-type specificity of isoform expression in brain. In addition, we highlight the remarkable specificity of subcellular localization by the CaMKIIα isoform. In addition, we discuss the role that this cellular specificity of expression might play in propagating the type of recurrent neuronal activity associated with disorders such as temporal lobe epilepsy.

MK-801 prevents overexpression of multidrug resistance protein 2 after status epilepticus

OBJECTIVE

The aim of this study was to investigate whether NMDA receptor was involved in the upregulation of multidrug resistance protein 2 (Mrp2) expression during status epilepticus (SE).

METHODS

The alterations in the expression of Mrp2 at various time points after SE, and the inhibition of glutamate N-methyl-D-aspartate (NMDA) receptor on Mrp2 expression in hippocampus were both tested by quantitative real-time polymerase chain reaction and western blot. Moreover, immunofluorescence was also used to analyze the impact of the NMDA receptor antagonist, MK-801, on the distribution of Mrp2 in different brain areas.

RESULTS

The results showed that gene encoding Mrp2 was upregulated in hippocampus at 6 hours after the end of SE, and this initial increase was followed by gradual normalization. While between 3 and 72 hours after the end of SE, the protein level of Mrp2 was upregulated in hippocampus, with the highest level emerging at 24 hours. The increment of Mrp2 gene and protein induced by SE was prevented by MK-801 at 6 and 24 hours respectively after the end of SE in the hippocampus. Moreover, immunofluorescence showed that seizures-induced increase of Mrp2 expression was attenuated by the administration of MK-801 mainly in capillaries. Rats after SE exhibited a significant upregulation of Mrp2 in the capillary endothelial cells of the cerebral cortex, piriform cortex, and hippocampus, compared with those in control at 24 hours after the end of SE.

CONCLUSION

The results indicated that the NMDA receptor plays an important role in the upregulation of Mrp2 expression in the blood-brain barrier.

Calcium/calmodulin-dependent protein kinase II (CaMKII) inhibition induces neurotoxicity via dysregulation of glutamate/calcium signaling and hyperexcitability

Aberrant glutamate and calcium signalings are neurotoxic to specific neuronal populations. Calcium/calmodulin-dependent kinase II (CaMKII), a multifunctional serine/threonine protein kinase in neurons, is believed to regulate neurotransmission and synaptic plasticity in response to calcium signaling produced by neuronal activity. Importantly, several CaMKII substrates control neuronal structure, excitability, and plasticity. Here, we demonstrate that CaMKII inhibition for >4 h using small molecule and peptide inhibitors induces apoptosis in cultured cortical neurons. The neuronal death produced by prolonged CaMKII inhibition is associated with an increase in TUNEL staining and caspase-3 cleavage and is blocked with the translation inhibitor cycloheximide. Thus, this neurotoxicity is consistent with apoptotic mechanisms, a conclusion that is further supported by dysregulated calcium signaling with CaMKII inhibition. CaMKII inhibitory peptides also enhance the number of action potentials generated by a ramp depolarization, suggesting increased neuronal excitability with a loss of CaMKII activity. Extracellular glutamate concentrations are augmented with prolonged inhibition of CaMKII. Enzymatic buffering of extracellular glutamate and antagonism of the NMDA subtype of glutamate receptors prevent the calcium dysregulation and neurotoxicity associated with prolonged CaMKII inhibition. However, in the absence of CaMKII inhibition, elevated glutamate levels do not induce neurotoxicity, suggesting that a combination of CaMKII inhibition and elevated extracellular glutamate levels results in neuronal death. In sum, the loss of CaMKII observed with multiple pathological states in the central nervous system, including epilepsy, brain trauma, and ischemia, likely exacerbates programmed cell death by sensitizing vulnerable neuronal populations to excitotoxic glutamate signaling and inducing an excitotoxic insult itself.

Resveratrol inhibits neuronal apoptosis and elevated Ca2+/calmodulin-dependent protein kinase II activity in diabetic mouse retina

OBJECTIVE

This study investigated the effects of resveratrol, a natural polyphenol with neuroprotective properties, on retinal neuronal cell death mediated by diabetes-induced activation of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII).

RESEARCH DESIGN AND METHODS

Diabetes was induced in C57BL/6 mice by five consecutive intraperitoneal injections of 55 mg/kg streptozotocin (STZ). Control mice received buffer. All mice were killed 2 months after the injections, and the extent of neuronal cell death, CaMKII, and phospho-CaMKII protein expression levels and CaMKII kinase activity were examined in the retinas. To assess the role of CaMKII in the death of retinal neurons, a small-interfering RNA (siRNA) or specific inhibitor of CaMKII was injected into the right vitreous humor, and vehicle only was injected into the left vitreous humor, 2 days before death. Resveratrol (20 mg/kg) was administered by oral gavage daily for 4 weeks, beginning 1 month after the fifth injection of either STZ or buffer.

RESULTS

The death of retinal ganglion cells (RGCs), CaMKII, phospho-CaMKII protein levels, and CaMKII activity were all greatly increased in the retinas of diabetic mice compared with controls, 2 months after induction of diabetes. Terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL)-positive signals co-localized with CaMKII- and phospho-CaMKII immunoreactive RGCs. However, in addition to CaMKII knockdown and inhibition by siRNA or a specific inhibitor, respectively, resveratrol provided complete protection from diabetes-induced retinal cell death.

CONCLUSIONS

In the present study, resveratrol prevented diabetes-induced RGC death via CaMKII downregulation, implying that resveratrol may have potential therapeutic applications for prevention of diabetes-induced visual dysfunction.

Development of the calcium plateau following status epilepticus: role of calcium in epileptogenesis

Status epilepticus is a clinical emergency defined as continuous seizure activity or rapid, recurrent seizures without regaining consciousness and can lead to the development of acquired epilepsy, characterized by spontaneous, recurrent seizures. Understanding epileptogenesis--the transformation of healthy brain tissue into hyperexcitable neuronal networks--is an important challenge and the elucidation of molecular mechanisms can lend insight into new therapeutic targets to halt this progression. It has been demonstrated that intracellular calcium increases during status epilepticus and that these elevations are maintained past the duration of the injury (Ca(2+) plateau). As an important second messenger, Ca(2+) elevations can lead to changes in gene expression, neurotransmitter release and plasticity. Thus, characterization of the post-injury Ca(2+) plateau may be important in eventually understanding the pathophysiology of epileptogenesis and preventing the progression to chronic epilepsy after brain injury.

Kinase-dead knock-in mouse reveals an essential role of kinase activity of Ca2+/calmodulin-dependent protein kinase IIalpha in dendritic spine enlargement, long-term potentiation, and learning

Ca2+/calmodulin-dependent protein kinase IIalpha (CaMKIIalpha) is an essential mediator of activity-dependent synaptic plasticity that possesses multiple protein functions. So far, the autophosphorylation site-mutant mice targeted at T286 and at T305/306 have demonstrated the importance of the autonomous activity and Ca2+/calmodulin-binding capacity of CaMKIIalpha, respectively, in the induction of long-term potentiation (LTP) and hippocampus-dependent learning. However, kinase activity of CaMKIIalpha, the most essential enzymatic function, has not been genetically dissected yet. Here, we generated a novel CaMKIIalpha knock-in mouse that completely lacks its kinase activity by introducing K42R mutation and examined the effects on hippocampal synaptic plasticity and behavioral learning. In homozygous CaMKIIalpha (K42R) mice, kinase activity was reduced to the same level as in CaMKIIalpha-null mice, whereas CaMKII protein expression was well preserved. Tetanic stimulation failed to induce not only LTP but also sustained dendritic spine enlargement, a structural basis for LTP, at the Schaffer collateral-CA1 synapse, whereas activity-dependent postsynaptic translocation of CaMKIIalpha was preserved. In addition, CaMKIIalpha (K42R) mice showed a severe impairment in inhibitory avoidance learning, a form of memory that is dependent on the hippocampus. These results demonstrate that kinase activity of CaMKIIalpha is a common critical gate controlling structural, functional, and behavioral expression of synaptic memory.

Ischemia and status epilepitcus result in enhanced phosphorylation of calcium and calmodulin-stimulated protein kinase II on threonine 253

Ca2+-stimulated protein kinase II (CaMKII) is critically involved in the regulation of synaptic function and is implicated in the neuropathology associated with ischemia and status epilepticus (SE). The activity and localization of CaMKII is regulated by multi-site phosphorylation. In the present study we investigated the effects of global ischemia followed by reperfusion and of SE on the phosphorylation of CaMKII on T253 in rat forebrains and compared this to the phosphorylation of T286. Both ischemia and SE resulted in marked increases in the phosphorylation of T253, and this was particularly marked in the postsynaptic density (PSD). Phosphorylation of T286 decreased rapidly towards basal levels following ischemia whereas phosphorylation of T253 remained elevated for between 1 and 6 h before decreasing to control values. Following SE, phosphorylation of T253 remained elevated for between 1 and 3 h before decreasing to control levels. In contrast, phosphorylation of T286 remained elevated for at least 24 h following the termination of SE. Total CaMKII associated with PSDs transiently increased 10 min following ischemia, but only several hours following SE. The results demonstrate that phoshorylation of CaMKII on T253 is enhanced following both ischemia/reperfusion and SE and indicate that the phosphorylation of T253 and T286 are differentially regulated.

Early exposure to general anesthesia causes significant neuronal deletion in the developing rat brain

Frequent exposure of children to general anesthesia is common practice in modern medicine. Although previously unrecognized, recent in vitro and in vivo animal studies suggest that exposure to clinically relevant general anesthetics at the peak of brain development could be detrimental to immature mammalian neurons, as demonstrated by massive and widespread apoptotic neurodegeneration. The survival of the developing neurons presumably depends on proper and timely formation of synapses, for which synaptic proteins (e.g., synaptophysin, synaptobrevin, amphiphysin, synaptosomal-associated protein 25 [SNAP-25], and Ca(2+)/calmodulin-dependent protein kinase II [CaM kinase II]) are crucially important. Overinhibition of developing neurons impairs synaptic protein function and activity-induced synaptic plasticity, which could in turn result in permanent neuronal loss. To examine the effects of general anesthesia, the pharmacological agents known to cause extensive neuronal inhibition, on synaptic proteins, and neuronal survival at the peak of synaptogenesis, we exposed 7-day-old rat pups to general anesthesia (midazolam, 9 mg/kg of body weight, subcutaneously, followed by 6 h of nitrous oxide 75 vol% and isoflurane 0.75 vol%). We found that this general anesthesia causes permanent neuronal deletion in the most vulnerable brain regions-the cerebral cortex and the thalamus-while transiently modulating protein levels of synaptophysin, synaptobrevin, amphiphysin, SNAP-25, and CaM kinase II.

Epileptogenesis causes an N-methyl-d-aspartate receptor/Ca2+-dependent decrease in Ca2+/calmodulin-dependent protein kinase II activity in a hippocampal neuronal culture model of spontaneous recurrent epileptiform discharges

Alterations in the function of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) have been observed in both in vivo and in vitro models of epileptogenesis; however the molecular mechanism mediating the effects of epileptogenesis on CaM kinase II has not been elucidated. This study was initiated to evaluate the molecular pathways involved in causing the long-lasting decrease in CaM kinase II activity in the hippocampal neuronal culture model of low Mg2+-induced spontaneous recurrent epileptiform discharges (SREDs). We show here that the decrease in CaM kinase II activity associated with SREDs in hippocampal cultures involves a Ca2+/N-methyl-d-aspartate (NMDA) receptor-dependent mechanism. Low Mg2+-induced SREDs result in a significant decrease in Ca2+/calmodulin-dependent substrate phosphorylation of the synthetic peptide autocamtide-2. Reduction of extracellular Ca2+ levels (0.2 mM in treatment solution) or the addition of dl-2-amino-5-phosphonovaleric acid (APV) 25 microM blocked the low Mg2+-induced decrease in CaM kinase II-dependent substrate phosphorylation. Antagonists of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainic acid receptor or L-type voltage sensitive Ca2+ channel had no effect on the low Mg2+-induced decrease in CaM kinase II-dependent substrate phosphorylation. The results of this study demonstrate that the decrease in CaM kinase II activity associated with this model of epileptogenesis involves a selective Ca2+/NMDA receptor-dependent mechanism and may contribute to the production and maintenance of SREDs in this model.

Mechanisms of status epilepticus: an evidence-based review

(1) Status epilepticus is a significant health problem that is under-recognized, yet is associated with major morbidity and mortality. (2) Mechanisms accounting for status epilepticus emergence from a single seizure, and for prolonged status epilepticus duration, remain unclear. (3) No randomized controlled trials, systematic reviews, or meta-analyses were found in any of the databases searched regarding the pathophysiologic mechanisms of status epilepticus in humans. (4) Ongoing and future research is likely to more clearly define the pathogenetic mechanisms of status epilepticus. This, in turn, is likely to encourage better treatment 'targeting' for particular aspects of the condition.

Molecular signaling mechanisms underlying epileptogenesis

Epilepsy, a disorder of recurrent seizures, is a common and frequently devastating neurological condition. Available therapy is only symptomatic and often ineffective. Understanding epileptogenesis, the process by which a normal brain becomes epileptic, may help identify molecular targets for drugs that could prevent epilepsy. A number of acquired and genetic causes of this disorder have been identified, and various in vivo and in vitro models of epileptogenesis have been established. Here, we review current insights into the molecular signaling mechanisms underlying epileptogenesis, focusing on limbic epileptogenesis. Study of different models reveals that activation of various receptors on the surface of neurons can promote epileptogenesis; these receptors include ionotropic and metabotropic glutamate receptors as well as the TrkB neurotrophin receptor. These receptors are all found in the membrane of a discrete signaling domain within a particular type of cortical neuron--the dendritic spine of principal neurons. Activation of any of these receptors results in an increase Ca2+ concentration within the spine. Various Ca2+-regulated enzymes found in spines have been implicated in epileptogenesis; these include the nonreceptor protein tyrosine kinases Src and Fyn and a serine-threonine kinase [Ca2+-calmodulin-dependent protein kinase II (CaMKII)] and phosphatase (calcineurin). Cross-talk between astrocytes and neurons promotes increased dendritic Ca2+ and synchronous firing of neurons, a hallmark of epileptiform activity. The hypothesis is proposed that limbic epilepsy is a maladaptive consequence of homeostatic responses to increases of Ca2+ concentration within dendritic spines induced by abnormal neuronal activity.