Kainic acid dose affects delayed cell death mechanism after status epilepticus

Ceramide signalling in inherited and multifactorial brain metabolic diseases

In recent years, research on sphingolipids, particularly ceramides, has attracted increased attention, revealing the important roles and many functions of these molecules in several human neurological disorders. The nervous system is enriched with important classes of sphingolipids, e.g., ceramide and its derivatives, which compose the major portion of this group, particularly in the form of myelin. Ceramides have also emerged as important nodes for lipid signalling, both inside the cell and between cells. Until recently, knowledge about ceramides in the nervous system was limited, but currently, multiple links between ceramide signalling and neurological diseases have been reported. Alterations in the regulation of ceramide pathobiology have been shown to influence the risk of developing neurometabolic diseases. Thus, these molecules are critically important in the maintenance and development of the nervous system and are culprits or major contributors to the development of brain disorders, either inherited or multifactorial. In the present review, we highlight the critical role of ceramide signalling in several different neurological disorders as well as the effects of their perturbations and discuss how this emerging class of bioactive sphingolipids has attracted interest in the field of neurological diseases.

Inhibition of TRIB3 Protects Against Neurotoxic Injury Induced by Kainic Acid in Rats

Epilepsy refers to a group of neurological disorders of varying etiologies characterized by recurrent seizures, resulting in brain dysfunction. Endoplasmic reticulum (ER) stress is highly activated in the process of epilepsy-related brain injury. However, the mechanisms by which ER stress triggers neuronal apoptosis remain to be fully elucidated. Tribbles pseudokinase 3 (TRIB3) is a pseudokinase that affects a number of cellular functions, and its expression is increased during ER stress. Here, we sought to clarify the role of TRIB3 in neuronal apoptosis mediated by ER stress. In the kainic acid (KA) (10 mg/kg)-induced rat seizure model, we characterized neuronal injury and apoptosis after KA injection. KA induced an ER stress response, as indicated by elevated expression of glucose-regulated protein 78 (GRP78) and C/EBP homologous protein (CHOP). TRIB3 protein was upregulated concomitantly with the downregulation of phosphorylated-protein kinase B (p-AKT) in rats following KA administration. In rat cortical neurons treated with KA, TRIB3 knockdown by siRNA reduced the number of dying neurons, decreased the induction of GRP78 and CHOP and the activation of caspase-3, and blocked the dephosphorylation of AKT after KA treatment. Our findings indicate that TRIB3 is involved in neuronal apoptosis occurring after KA-induced seizure. The knockdown of TRIB3 effectively protects against neuronal apoptosis in vitro, suggesting that TRIB3 may be a potential therapeutic target for the treatment of epilepsy.

Morin Prevents Granule Cell Dispersion and Neurotoxicity via Suppression of mTORC1 in a Kainic Acid-induced Seizure Model

An abnormal reorganization of the dentate gyrus and neurotoxic events are important phenotypes in the hippocampus of patients with temporal lobe epilepsy (TLE). The effects of morin, a bioflavonoid constituent of many herbs and fruits, on epileptic seizures have not yet been elucidated, though its beneficial effects, such as its anti-inflammatory and neuroprotective properties, are well-described in various neurodegenerative diseases. In the present study, we investigated whether treatment with morin hydrate (MH) can reduce the susceptibility to seizures, granule cell dispersion (GCD), mammalian target of rapamycin complex 1 (mTORC1) activity, and the increases in the levels of apoptotic molecules and inflammatory cytokines in the kainic acid (KA)-induced seizure mouse model. Our results showed that oral administration of MH could reduce susceptibility to seizures and lead to the inhibition of GCD and mTORC1 activity in the KA-treated hippocampus. Moreover, treatment with MH significantly reduced the increased levels of apoptotic signaling molecules and pro-inflammatory mediators in the KA-treated hippocampus compared with control mice, suggesting a neuroprotective role. Therefore, these results suggest that morin has a therapeutic potential against epilepsy through its abilities to inhibit GCD and neurotoxic events in the in vivo hippocampus.

Expression and localisation of brain-type organic cation transporter (BOCT/24p3R/LCN2R) in the normal rat hippocampus and after kainate-induced excitotoxicity

The iron siderophore binding protein lipocalin 2 (LCN2, also known as 24p3, NGAL and siderocalin) may be involved in iron homeostasis, but to date, little is known about expression of its putative receptor, brain-type organic cation transporter (BOCT, also known as BOCT1, 24p3R, NGALR and LCN2R), in the brain during neurodegeneration. The present study was carried out to elucidate the expression of LCN2 and BOCT in hippocampus after excitotoxicity induced by the glutamate analog, kainate (KA) and a possible role of LCN2 in neuronal injury. As reported previously, a rapid and sustained induction in expression of LCN2 was found in the hippocampus after intracerebroventicular injection of KA. BOCT was expressed in neurons of the saline-injected control hippocampus, and immunolabel for BOCT protein was preserved in pyramidal neurons of CA1 at 1 day post-KA injection, likely due to the delayed onset of neurodegeneration after KA injection. At 3 days and 2 weeks after KA injections, loss of immunolabel was observed due to degenerated neurons, although remaining neurons continued to express BOCT, and induction of BOCT was found in OX-42 positive microglia. This resulted in an overall decrease in BOCT mRNA and protein expression after KA treatment. Increased expression of the pro-apoptotic marker, Bim, was found in both neurons and microglia after KA injection, but TUNEL staining indicating apoptosis was found primarily in Bim-expressing neurons, but not microglia. Interaction between LCN2 and BOCT was found by DuoLink assay in cultured hippocampal neurons. Apo-LCN2 without iron caused no significant differences in neuronal Bim expression or cell survival, whereas holo-LCN2 consisting of LCN2:iron:enterochelin complex increased Bim mRNA expression and decreased neuronal survival. Together, results suggest that LCN2 and BOCT may have a role in neuronal injury.

Dynamic Change in Cells Expressing IL-1β in Rat Hippocampus after Status Epilepticus

BACKGROUND

The time course of cytokine dynamics after seizure remains controversial. Here we evaluated the changes in the levels and sites of interleukin (IL)-1β expression over time in the hippocampus after seizure.

METHODS

Status epilepticus (SE) was induced in adult Wistar rats by means of intraperitoneal injection of kainic acid (KA). Subsequently, the time courses of cellular localization and IL-1β concentration in the hippocampus were evaluated by means of immunohistochemical and quantitative assays.

RESULTS

On day 1 after SE, CA3 pyramidal cells showed degeneration and increased IL-1β expression. In the chronic phase (>7 days after SE), glial fibrillary acidic protein (GFAP)—positive reactive astrocytes—appeared in CA1 and became IL-1β immunoreactive. Their IL-1β immunoreactivity increased in proportion to the progressive hypertrophy of astrocytes that led to gliosis. Quantitative analysis showed that hippocampal IL-1β concentration progressively increased during the acute and chronic phases.

CONCLUSION

IL-1β affects the hippocampus after SE. In the acute phase, the main cells expressing IL-1β were CA3 pyramidal cells. In the chronic phase, the main cells expressing IL-1β were reactive astrocytes in CA1.

Delayed treatments with pharmacological modulators of pre- and postsynaptic mGlu receptors rescue the hippocampus from kainate-induced neurodegeneration

Gene expression of mGluR2, mGluR3 and mGluR5 was evaluated in the hippocampus and frontal cortex in Wistar rats in 1 and 4 weeks after bilateral microinjection of kainic acid into the dorsal hippocampus. The time-course of the receptors' expression suggested their adaptive role in response on the induction of excitotoxicity. It was assumed that the decrease of kainate-induced neurodegeneration could be achieved through simultaneous activation of presynaptic mGluRs and inhibition of mGlu postsynaptic receptors. Both negative allosteric modulator of mGluR5, MPEP, and agonist of mGluR2, LY354740, were administered intraperitoneally 5 days after microinjection of kainic acid. As shown by histochemical studies with cresyl violet and Fluoro-Jade, kainate induced significant damage of hippocampal neurons in the CA3 and CA1 fields. Pharmacological treatment with the negative modulator of mGlu5 receptors in common with the agonist of mGluR2 decreased kainate-induced neurodegeneration in dorsal hippocampus.

Involvement of IRE1α signaling in the hippocampus in patients with mesial temporal lobe epilepsy

Cumulative evidence suggests that programmed cell death (apoptosis) may contribute to the progressive hippocampal sclerosis seen in patients with refractory mesial temporal lobe epilepsy (MTLE). The endoplasmic reticulum (ER) stress-mediated cell apoptotic pathway has recently emerged as a vital intrinsic pathway, but the molecular mechanisms underlying this process in the epileptic brain remain unclear. We investigated inositol-requiring protein 1α (IRE1α)-mediated ER stress pro-and anti-apoptotic signaling pathways in resected hippocampi from 32 patients with intractable MTLE. Immunoreactivity for the ER stress markers glucose-regulated proteins 78 and 94 was significantly higher in MTLE hippocampi than in controls. The levels of IRE1α, tumor necrosis factor receptor associated factor 2 (TRAF2), apoptosis signal-regulating kinase 1 (ASK1) and c-Jun N-terminal kinase (JNK), which together constitute the IRE1α/TRAF2/ASK1/JNK pro-apoptotic signaling pathway, were significantly upregulated in patients with MTLE. Immunoreactivity for caspase-4, a homologue of caspase-12 that is possibly activated by IRE1α via TRAF2 following ER stress, and caspase-3 which was a downstream effector of caspase-4, were both detected in MTLE tissue samples. In contrast, immunoreactivity for caspase-4 and caspase-3 were low or absent in control samples. Simultaneously, the X-box binding protein 1 (XBP1), a basic leucine zipper (bZIP) family transcription factor downstream of IRE1α which can promote cell survival by upregulation of multiple ER-targeted genes, was also overexpressed and activated in MTLE hippocampi. Our data suggest that chronic epilepsy is associated with ER stress, as well as induction of both IRE1α-mediated pro- and anti-apoptotic signaling pathways.

Excitotoxicity through Ca2+-permeable AMPA receptors requires Ca2+-dependent JNK activation

The GluA4-containing Ca(2+)-permeable α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptors (Ca-AMPARs) were previously shown to mediate excitotoxicity through mechanisms involving the activator protein-1 (AP-1), a c-Jun N-terminal kinase (JNK) substrate. To further investigate JNK involvement in excitotoxic pathways coupled to Ca-AMPARs we used HEK293 cells expressing GluA4-containing Ca-AMPARs (HEK-GluA4). Cell death induced by overstimulation of Ca-AMPARs was mediated, at least in part, by JNK. Importantly, JNK activation downstream of these receptors was dependent on the extracellular Ca(2+) concentration. In our quest for a molecular link between Ca-AMPARs and the JNK pathway we found that the JNK interacting protein-1 (JIP-1) interacts with the GluA4 subunit of AMPARs through the N-terminal domain. In vivo, the excitotoxin kainate promoted the association between GluA4 and JIP-1 in the rat hippocampus. Taken together, our results show that the JNK pathway is activated by Ca-AMPARs upon excitotoxic stimulation and suggest that JIP-1 may contribute to the propagation of the excitotoxic signal.

In vivo glutamate decline associated with kainic acid-induced status epilepticus

Neurophysiological, biochemical, and anatomical evidence implicates glutamatergic mechanisms in epileptic seizures. Until recently, however, longitudinal characterization of in vivo glutamate dynamics was not possible. Here, we present data using in vivo magnetic resonance spectroscopy (MRS) optimized for the detection of glutamate to identify changes that evolve following kainic acid (KA)-induced status epilepticus. Wild-type male Wistar rats underwent whole-brain MR imaging and single-voxel MRS on a clinical 3 T scanner equipped with a high-strength insert gradient coil. Scanning took place before and then 3 days, 28-32 days, and 42-50 days after induction of status epilepticus. Analyses compared 5 seizure (Sz), 5 no-seizure (NoSz; received KA but did not exhibit seizures), and 6 control (Con) animals. This longitudinal study demonstrated reduced glutamate levels in vivo in the dorsal hippocampus 3 days and 1 month following status epilepticus in Sz animals compared with Con animals. Additionally, previous results were replicated: in the Sz group, computed T2 was higher in the ventral hippocampus and limbic cortex 3 days after seizure activity compared with baseline but resolved in both regions at the 1 month scan, suggesting a transient edema. Three days following seizure activity, N-acetylaspartate (NAA) declined and lactate increased in the dorsal hippocampus of the Sz group compared with the Con and NoSz group; both metabolites approached baseline levels by the third scan. Taken together, these results support the conclusion that seizure activity following KA infusion causes loss of glutamatergic neurons.

Vulnerability of postnatal hippocampal neurons to seizures varies regionally with their maturational stage

The mechanism of status epilepticus-induced neuronal death in the immature brain is not fully understood. In the present study, we examined the contribution of caspases in our lithium-pilocarpine model of status epilepticus in 14 days old rat pups. In CA1, upregulation of caspase-8, but not caspase-9, preceded caspase-3 activation in morphologically necrotic cells. Pretreatment with a pan-caspase inhibitor provided neuroprotection, showing that caspase activation was not an epiphenomenon but contributed to neuronal necrosis. By contrast, upregulation of active caspase-9 and caspase-3, but not caspase-8, was detected in apoptotic dentate gyrus neurons, which were immunoreactive for doublecortin and calbindin-negative, two features of immature neurons. These results suggest that, in cells which are aligned in series as parts of the same excitatory hippocampal circuit, the same seizures induce neuronal death through different mechanisms. The regional level of neuronal maturity may be a determining factor in the execution of a specific death program.

Time-course of neuronal death in the mouse pilocarpine model of chronic epilepsy using Fluoro-Jade C staining

Epilepsy is a serious neurological disorder in human beings and the long-term pathological events remain largely obscure. We are interested in elucidating long-term brain injury that may occur in the temporal lobe epilepsy, and time-course of neuronal death was examined in a mouse pilocarpine model of chronic epilepsy by Fluoro-Jade C (FJC) dye that can specifically stain the degenerative neurons in the central nervous system. The FJC stain combined with immunohistochemistry to neuronal nuclear specific protein revealed that pilocarpine-induced status epilepticus (SE) resulted in massive degenerative death of neuronal cells in brains with their dense distribution in the cerebral cortex and hippocampus. The FJC-positive degenerating neurons, most of them also expressed apoptosis signaling molecules such as caspase-9 and activated caspase-3, occurred at 4h, increased into peak levels at 12h-3d, and then gradually went down at 7d-14d after onset of SE. More interestingly, a large percentage (about 88%) of FJC-positive degenerative neurons were GABAergic as indicated with their immunoreactivity to glutamic acid decarboxylase-67, implying that inhibitory function of GABAergic neural system might by seriously damaged in brains subject to SE attack in this mouse pilocarpine model. Taken together with previous studies, time-course of degenerative neurons in the mouse pilocarpine model by Fluoro-Jade C staining further benefits understanding of long-term brain pathological changes and recurrent seizure mechanism, and may also result in finding the most suitable time-window in therapeutic manipulation of the chronic epilepsy in human beings.

Expression of estrogen receptor alpha and beta in reactive astrocytes at the male rat hippocampus after status epilepticus

Estrogen is neuroprotective against status epilepticus (SE)-induced hippocampal damage in female animals. In male animals, estrogen is converted from testosterone via aromatization the activity of which is upregulated by brain damage. However, it is controversial whether estrogen is neuroprotective or neuroinvasive against male hippocampal damage after SE. In order to understand the role of estrogen, it is important to elucidate the distribution manner of estrogen receptor (ER)alpha and beta as the targets of estrogen. In this study, we examined the time course changes of ERs in adult male rat hippocampus after SE using anti-ERalpha antibodies (MC-20 and PA1-309) and anti-ERbeta antibodies (PA1-310B and PA1-311). In control rats, both ERalpha and beta were expressed in the pyramidal cells predominantly at CA1 and CA3. ERalpha was expressed in the cytoplasm and the nucleus, whereas ERbeta was expressed in the cytoplasm of the pyramidal cells. After SE, according to the pyramidal cell loss at CA1, the number of ERalpha- and beta-immunoreactive pyramidal cells decreased up to day 21. On the other hand, reactive astrocytes, which newly appeared after SE and formed gliosis at CA1, were confirmed to express both ERs in the nucleus, cytoplasm, and process. There were no differences in immunoreactivity between antibodies. Our results indicate that endogenous estrogen affects the pyramidal cells through ERalpha and beta under normal circumstances in adult male rats, whereas the targets of estrogen shift to the reactive astrocytes through ERalpha and beta after SE.

VX-induced cell death involves activation of caspase-3 in cultured rat cortical neurons

Exposure of cell cultures to organophosphorous compounds such as VX can result in cell death. However, it is not clear whether VX-induced cell death is necrotic or involves programmed cell death mechanisms. Activation of caspases, a family of cysteine proteases, is often involved in cell death, and in particular, caspase-3 activation appears to be a key event in programmed cell death processes including apoptosis. In this study, we investigated VX-induced neuronal cell death, as well as the underlying mechanism in terms of its effect on caspase-3 activity. Primary cortical neuronal cultures were prepared from gestational days 17 to 19 Sprague Dawley rat fetuses. At maturation, the cells were treated with varying concentrations of VX and cell death was evaluated by lactate dehydrogenase (LDH) release. VX induced an increase in LDH release in a concentration-dependent manner. Morphological VX-induced cell death was also characterized by using nuclear staining with propidium iodide and Hoechst 33342. VX induced a concentration- and time-dependent increase in caspase-3 activation. Caspase-3 activation was also confirmed by the proteolytic cleavage of poly(ADP-ribose)polymerase (PARP), an endogenous caspase-3 substrate. These data suggested that in rat cortical neurons, VX-induced cell death via a programmed cell death pathway that involves changes in caspase-3 protease.