One hour of pilocarpine-induced status epilepticus is sufficient to develop chronic epilepsy in mice, and is associated with mossy fiber sprouting but not neuronal death

Small-molecule caspase-1 inhibitor CZL80 terminates refractory status epilepticus via inhibition of glutamatergic transmission

Status epilepticus (SE), a serious and often life-threatening medical emergency, is characterized by abnormally prolonged seizures. It is not effectively managed by present first-line anti-seizure medications and could readily develop into drug resistance without timely treatment. In this study, we highlight the therapeutic potential of CZL80, a small molecule that inhibits caspase-1, in SE termination and its related mechanisms. We found that delayed treatment of diazepam (0.5 h) easily induces resistance in kainic acid (KA)-induced SE. CZL80 dose-dependently terminated diazepam-resistant SE, extending the therapeutic time window to 3 h following SE, and also protected against neuronal damage. Interestingly, the effect of CZL80 on SE termination was model-dependent, as evidenced by ineffectiveness in the pilocarpine-induced SE. Further, we found that CZL80 did not terminate KA-induced SE in Caspase-1-/- mice but partially terminated SE in IL1R1-/- mice, suggesting the SE termination effect of CZL80 was dependent on the caspase-1, but not entirely through the downstream IL-1β pathway. Furthermore, in vivo calcium fiber photometry revealed that CZL80 completely reversed the neuroinflammation-augmented glutamatergic transmission in SE. Together, our results demonstrate that caspase-1 inhibitor CZL80 terminates diazepam-resistant SE by blocking glutamatergic transmission. This may be of great therapeutic significance for the clinical treatment of refractory SE.

Neuronal MeCP2 in the dentate gyrus regulates mossy fiber sprouting of mice with temporal lobe epilepsy

Sprouting of mossy fibers, one of the most consistent findings in tissue from patients with mesial temporal lobe epilepsy, exhibits several uncommon axonal growth features and has been considered a paradigmatic example of circuit plasticity that occurs in the adult brain. Clarifying the mechanisms responsible may provide new insight into epileptogenesis as well as axon misguidance in the central nervous system. Methyl-CpG-binding protein 2 (MeCP2) binds to methylated genomic DNA to regulate a range of physiological functions implicated in neuronal development and adult synaptic plasticity. However, exploring the potential role of MeCP2 in the documented misguidance of axons in the dentate gyrus has not yet been attempted. In this study, a status epilepticus-induced decrease of neuronal MeCP2 was observed in the dentate gyrus (DG). An essential regulatory role of MeCP2 in the development of functional mossy fiber sprouting (MFS) was confirmed through stereotaxic injection of a recombinant adeno-associated virus (AAV) to up- or down-regulate MeCP2 in the dentate neurons. Chromatin immunoprecipitation sequencing (ChIP-seq) was performed to identify the binding profile of native MeCP2 using micro-dissected dentate tissues. In both dentate tissues and HT22 cell lines, we demonstrated that MeCP2 could act as a transcription repressor on miR-682 with the involvement of the DNA methylation mechanism. Further, we found that miR-682 could bind to mRNA of phosphatase and tensin homolog (PTEN) in a sequence specific manner, thus leading to the suppression of PTEN and excessive activation of mTOR. This study therefore presents a novel epigenetic mechanism by identifying MeCP2/miR-682/PTEN/mTOR as an essential signal pathway in regulating the formation of MFS in the temporal lobe epileptic (TLE) mice. SIGNIFICANCE STATEMENT: Understanding the mechanisms that regulate axon guidance is important for a better comprehension of neural disorders. Sprouting of mossy fibers, one of the most consistent findings in patients with mesial temporal lobe epilepsy, has been considered a paradigmatic example of circuit plasticity in the adult brain. Although abnormal regulation of DNA methylation has been observed in both experimental rodents and humans with epilepsy, the potential role of DNA methylation in this well-documented example of sprouting of dentate axon remains elusive. This study demonstrates an essential role of methyl-CpG-binding protein 2 in the formation of mossy fiber sprouting. The underlying signal pathway has been also identified. The data hence provide new insight into epileptogenesis as well as axon misguidance in the central nervous system.

Substantial outcome improvement using a refined pilocarpine mouse model of temporal lobe epilepsy

Systemic pilocarpine treatment is one of the most reliable means of inducing temporal lobe epilepsy (TLE). However, the traditional pilocarpine injection protocol using mice was associated with a high death rate, possibly because of cardiorespiratory collapse following status epilepticus (SE). To prevent this, we developed a modified procedure of pilocarpine SE induction, which included a single injection of a moderate dose of caffeine during the induction phase. That new protocol was based on the use of young male mice as well as on a refined Racine's scale. Using that protocol, we report a substantially increased survival rate, thus enabling the generation of a large cohort of mice that exhibited cardinal histological (e.g., mossy fiber sprouting) and electrophysiological (e.g., chronic interictal events and ictal seizures) characteristics associated with TLE. In conclusion, our refined caffeine- and pilocarpine-based protocol substantially improves the outcome of the reliable pilocarpine mouse model of TLE.

Neuronal Glypican4 promotes mossy fiber sprouting through the mTOR pathway after pilocarpine-induced status epilepticus in mice

In temporal lobe epilepsy (TLE), abnormal axon guidance and synapse formation lead to sprouting of mossy fibers in the hippocampus, which is one of the most consistent pathological findings in patients and animal models with TLE. Glypican 4 (Gpc4) belongs to the heparan sulfate proteoglycan family, which play an important role in axon guidance and excitatory synapse formation. However, the role of Gpc4 in the development of mossy fibers sprouting (MFS) and its underlying mechanism remain unknown. Using a pilocarpine-induced mice model of epilepsy, we showed that Gpc4 expression was significantly increased in the stratum granulosum of the dentate gyrus at 1 week after status epilepticus (SE). Using Gpc4 overexpression or Gpc4 shRNA lentivirus to regulate the Gpc4 level in the dentate gyrus, increased or decreased levels of netrin-1, SynI, PSD-95, and Timm score were observed in the dentate gyrus, indicating a crucial role of Gpc4 in modulating the development of functional MFS. The observed effects of Gpc4 on MFS were significantly antagonized when mice were treated with L-leucine or rapamycin, an agonist or antagonist of the mammalian target of rapamycin (mTOR) signal, respectively, demonstrating that mTOR pathway is an essential requirement for Gpc4-regulated MFS. Additionally, the attenuated spontaneous recurrent seizures (SRSs) were observed during chronic stage of the disease by suppressing the Gpc4 expression after SE. Altogether, our findings demonstrate a novel control of neuronal Gpc4 on the development of MFS through the mTOR pathway after pilocarpine-induced SE. Our results also strongly suggest that Gpc4 may serve as a promising target for antiepileptic studies.

Involvement of TRPV4 in changes in rapidly inactivating potassium channels in the early stage of pilocarpine-induced status epilepticus in mice

The rapidly inactivating potassium current (I_A ) is important in controlling neuronal action potentials. Altered I_A function and K⁺ channel expression have been found in epilepsy, and activation of the transient receptor potential vanilloid 4 (TRPV4) channel is involved in epilepsy pathogenesis. This study examined whether TRPV4 affects Kv4.2 and K⁺ channel interacting protein (KCHIP) expression and I_A changes following pilocarpine-induced status epilepticus (PISE) in mice. Herein, hippocampal protein levels of Kv4.2 and KCHIP2 increased 3 h-3 d and decreased 7-30 d; that of KCHIP1 increased 3-24 h and decreased 3-30 d post-PISE. The TRPV4 antagonist HC-067047 attenuated the increased protein levels of Kv4.2 and KCHIP2 but not that of KCHIP1 post-PISE. The TRPV4 agonist GSK1016790A increased hippocampal protein levels of Kv4.2 and KCHIP2 but had no effect on KCHIP1 expression. HC-067047 attenuated the increased I_A in hippocampal pyramidal neurons 24 h and 3 d post-PISE. GSK1016790A increased I_A in hippocampal pyramidal neurons, shifting the voltage-dependent inactivation curve toward depolarization. The GSK1016790A-induced increase of I_A was blocked by protein kinase A and calcium/calmodulin-dependent kinase II antagonists but was unaffected by protein kinase C antagonists. We conclude that TRPV4 activation may be responsible for the increases of Kv4.2 and KCHIP2 expression in hippocampi and I_A in hippocampal pyramidal neurons in PISE mice, which are likely compensatory measures for hyperexcitability at the early stage of epilepsy.

Pharmacological upregulation of GLT-1 alleviates the cognitive impairments in the animal model of temporal lobe epilepsy

It is known that hippocampal epileptogenesis is accompanied by hyperexcitability, glutamate-related neuronal dysfunctions and consequently cognitive deficits. However, the neuroprotective role of astrocytic glutamate uptake through the Glutamate Transporter-1 (GLT-1) remains to be unknown in these processes. Therefore, to assess the effect of glutamate uptake, pharmacological upregulation of GLT-1 using ceftriaxone administration (200 mg/kg/day, i.p, 5 days) was utilized in Li-PIL animal models of temporal lobe epilepsy (TLE). Glutamate concentration and glutamine synthetase activity were analyzed using biochemical assays. In addition, GLT-1 gene expression was assessed by RT-qPCR. Finally, cognitive function was studied using Morris water maze (MWM) test and novel object recognition task (NORT). Our results demonstrated that the acute phase of epileptogenesis (first 72 hours after Status Epilepticus) was accompanied by an increase in the hippocampal glutamate and downregulation of GLT-1 mRNA expression compared to controls. Ceftriaxone administration in epileptic animals led to a reduction of glutamate along with elevation of the level of glutamine synthetase activity and GLT-1 expression in the acute phase. In the chronic phase of epileptogenesis (4 weeks after Status Epilepticus), glutamate levels and GLT-1 expression were decreased compared to controls. Ceftriaxone treatment increased the levels of GLT-1 expression. Furthermore, impaired learning and memory ability in the chronic phase of epileptogenesis was rescued by Ceftriaxone administration. This study shows that astrocytic glutamate uptake can profoundly impact the processes of hippocampal epileptogenesis through the reduction of glutamate-induced excitotoxicity and consequently rescuing of cognitive deficits caused by epilepsy.

Effectiveness of low dose of rapamycin in preventing seizure-induced anxiety-like behaviour, cognitive impairment, and defects in neurogenesis in developing rats

Aims: Previous studies have demonstrated that rapamycin prevents seizure-induced anxiety-like behaviors. However, rapamycin had been used at a higher dose of 3 mg/kg and resulted in side effects in immature animals. This work was designed to explore whether a lower dose of rapamycin has similar efficacy but has milder side effects.Methods: Acute seizures were induced by injection of pilocarpine at postnatal 10-day Sprague-Dawley rats. Western blot analysis was used to detect changes in mammalian target of rapamycin (mTOR) pathway after seizure. Immunofluorescent intensity of doublecortin (DCX) was conducted to evaluate the development of neurons in hippocampus. Morris water maze and Y-maze test were used to assess cognitive functions and open-field test and elevated plus maze were used to detect anxiety-like behaviors 4 weeks after seizure onset.Results: mTOR pathway was abnormally activated with two peaks after pilocarpine-induced seizures, and no difference of DCX-positive cells and body weight were noticed between control and pilocarpine-induced seizure rats. Pilocarpine-induced seizure in postnatal 10 days rats did not exert impairment on cognitive functions, but resulted in obvious anxiety-like behaviors. Low dose of rapamycin at 0.3 mg/kg significantly reversed seizure-induced increase of p-S6 levels as well as abnormal anxiety-like behaviors. In addition, rapamycin at the dose of 0.3mg/kg did not affect normal development and cognitive functions.Conclusion: lower doses of rapamycin should be used in infants compared with older children or adults.

Transient receptor potential vanilloid 4 is involved in the upregulation of connexin expression following pilocarpine-induced status epilepticus in mice

Epilepsy is characterized by spontaneous seizures. Changes in the expression of the connexins (Cxs) have been reported to be involved in epileptogenesis. It has previously been shown that the transient receptor potential vanilloid 4 (TRPV4) plays an important role in the modulation of neuronal excitability, and that application of a TRPV4 antagonist blocks hyperthermia-induced seizures. Accordingly, in the present study, we sought to explore whether TRPV4 is involved in the regulation of Cx expression following pilocarpine-induced status epilepticus (PISE) in mice. We observed that TRPV4 protein levels in hippocampi increased 3 h to 30 d following PISE, peaking 1-3 d after induction, and that pre-application of the TRPV4 antagonist HC-067047 increased the latency to develop SE induced by pilocarpine and reduced the success rate of PISE preparation. We demonstrated that Cx43 protein levels followed a time profile similar to that of TRPV4, and further showed that the increase in Cx43 protein levels on 3 d post-PISE was markedly attenuated by HC-067047. In contrast, the corresponding increase in Cx32 protein levels lagged substantially behind, and these levels were unaffected by HC-067047. Similarly, the TRPV4 agonist GSK1016790A increased the mRNA and protein levels of Cx43, but not those of Cx32. We thus conclude that the upregulation of Cx43 expression by TRPV4 may be involved in the pathophysiology of epilepsy.

Long-term social isolation inhibits autophagy activation, induces postsynaptic dysfunctions and impairs spatial memory

. Moreover, we found that L-PWSI increased the protein expression of p-AKT/AKT, p-mTOR/mTOR and p62, whereas the protein levels of LC3B and Beclin1 were decreased indicating an inhibition in autophagy activity. Intraperitoneal injection of rapamycin significantly potentiated fEPSP slope and cognition-related proteins expression in the L-PWSI mice. These results therefore suggest that L-PWSI induces postsynaptic dysfunction by disrupting the interaction between AMPAR, NMDAR and PSD-95, and inhibit the autophagy activity which led to impaired spatial memory and cognitive function.

Zinc signaling and epilepsy

Evidence from both preclinical and clinical studies suggest the importance of zinc homeostasis in seizures/epilepsy. Undoubtedly, zinc, via modulation of a variety of targets, is necessary for maintaining the balance between neuronal excitation and inhibition, while an imbalance between excitation and inhibition underlies seizures. However, the relationship between zinc signaling and seizures/epilepsy is complex as both extracellular and intracellular zinc may produce either protective or detrimental effects. This review provides an overview of preclinical/behavioral, functional and molecular studies, as well as clinical data on the involvement of zinc in the pathophysiology and treatment of seizures/epilepsy. Furthermore, the potential of targeting elements associated with zinc signaling or homeostasis and zinc levels as a therapeutic strategy for epilepsy is discussed.

Akt Inhibitor Perifosine Prevents Epileptogenesis in a Rat Model of Temporal Lobe Epilepsy

Accumulating data have revealed that abnormal activity of the mTOR (mammalian target of rapamycin) pathway plays an important role in epileptogenesis triggered by various factors. We previously reported that pretreatment with perifosine, an inhibitor of Akt (also called protein kinase B), abolishes the rapamycin-induced paradoxical increase of S6 phosphorylation in a rat model induced by kainic acid (KA). Since Akt is an upstream target in the mTOR signaling pathway, we set out to determine whether perifosine has a preventive effect on epileptogenesis. Here, we explored the effect of perifosine on the model of temporal epilepsy induced by KA in rats and found that pretreatment with perifosine had no effect on the severity or duration of the KA-induced status epilepticus. However, perifosine almost completely inhibited the activation of p-Akt and p-S6 both acutely and chronically following the KA-induced status epilepticus. Perifosine pretreatment suppressed the KA-induced neuronal death and mossy fiber sprouting. The frequency of spontaneous seizures was markedly decreased in rats pretreated with perifosine. Accordingly, rats pretreated with perifosine showed mild impairment in cognitive functions. Collectively, this study provides novel evidence in a KA seizure model that perifosine may be a potential drug for use in anti-epileptogenic therapy.

Relationship between seizure frequency and number of neuronal and non-neuronal cells in the hippocampus throughout the life of rats with epilepsy

The relationship between seizure frequency and cell death has been a subject of controversy. To tackle this issue, we determined the frequency of seizures and the total number of hippocampal cells throughout the life of rats with epilepsy using the pilocarpine model. Seizure frequency varied in animals with epilepsy according to which period of life they were in, with a progressive increase in the number of seizures until 180 days (sixth months) of epileptic life followed by a decrease (330 days-eleventh month) and subsequently stabilization of seizures. Cell counts by means of isotropic fractionation showed a reduction in the number of hippocampal neuronal cells following 30, 90, 180 and 360 days of spontaneous recurrent seizures (SRS) in rats compared to their controls (about 25%-30% of neuronal cell reduction). In addition, animals with 360 days of SRS showed a reduction in the number of neuronal cells when compared with animals with 90 and 180 days of seizures. The total number of hippocampal non-neuronal cells was reduced in rats with epilepsy after 30 days of SRS, but no significant alteration was observed on the 90th, 180th and 360th days. The total number of neuronal cells was negatively correlated with seizure frequency, indicating an association between occurrence of epileptic seizures throughout life and neuronal loss. In sum, our results add novel data to the literature concerning the time-course of SRS and hippocampal cell number throughout epileptic life.

Effect of Chronic Administration of Low Dose Rapamycin on Development and Immunity in Young Rats

Mammalian target of rapamycin (mTOR) regulates cell growth, cell differentiation and protein synthesis. Rapamycin, an inhibitor of mTOR, has been widely used as an immunosuppressant and anti-cancer drug. Recently, mTOR inhibitors have also been reported to be a potential anti-epileptic drug, which may be effective when used in young patients with genetic epilepsy. Thus, a suitable dose of rapamycin which can maintain the normal function of mTOR and has fewer side effects ideally should be identified. In the present study, we first detected changes in marker proteins of mTOR signaling pathway during development. Then we determined the dose of rapamycin by treating rats of 2 weeks of age with different doses of rapamycin for 3 days and detected its effect on mTOR pathway. Young rats were then treated with a suitable dose of rapamycin for 4 weeks and the effect of rapamycin on mTOR, development and immunity were investigated. We found that the expression of the marker proteins of mTOR pathway was changed during development in brain hippocampus and neocortex. After 3 days of treanent, 0.03 mg/kg rapamycin had no effect on phospho-S6, whereas 0.1, 0.3, 1.0 and 3.0 mg/kg rapamycin inhibited phospho-S6 in a dose-dependent manner. However, only 1.0 mg/kg and 3.0 mg/kg rapamycin inhibited phospho-S6 after 4 weeks treatment of rapamycin. Parallel to this result, rats treated with 0.1 and 0.3 mg/kg rapamycin had no obvious adverse effects, whereas rats treated with 1.0 and 3.0 mg/kg rapamycin showed significant decreases in body, spleen and thymus weight. Additionally, rats treated with 1.0 and 3.0 mg/kg rapamycin exhibited cognitive impairment and anxiety as evident by maze and open field experiments. Furthermore, the content of IL-1β, IL-2, IFN-γ, TNF-α in serum and cerebral cortex were significantly decreased in 1.0 and 3.0 mg/kg rapamycin-treated rats. The expression of DCX was also significantly decreased in 1.0 and 3.0 mg/kg rapamycin-treated rats. However, rats treated with 1.0 mg/ kg rapamycin exhibited fewer and milder side effects than those treated with 3.0 mg/kg. In summary, all these data suggest that there is not a rapamycin dose that can inhibit mTOR for epilepsy without causing any side effects, but 1 mg /kg may be the optimal dose for young rats for suppressing mTOR with relatively few side effects.

Neuroprotective effects of flavonoids extracted from licorice on kainate-induced seizure in mice through their antioxidant properties

A relationship between status epilepticus (SE) and oxidative stress has recently begun to be recognized. To explore whether the flavonoids extracted from licorice (LFs) have any protective effect on kainate (KA)-induced seizure in mice, we treated mice with LFs before and after KA injection. In KA-treated mice, we found that superoxide dismutase (SOD) activity decreased immediately after the onset of seizure at 1 h and then increased at 6 h. It returned to baseline 1 d after seizure and then increased again at 3, 7, and 28 d, while malondialdehyde (MDA) content remained at a high level at 1 h, 6 h, 3 d, 7 d, and 28 d, indicating a more oxidized status related to the presence of more reactive oxygen species (ROS). Treatment with LFs before KA injection reversed the seizure-induced change in SOD activity and MDA content at 1 h, 6 h, 3 d, 7 d, and 28 d. Treatment with LFs after seizure decreased KA-induced SOD activity and MDA content at 7 and 28 d. Also, LF pre- and post-KA treatments decreased seizure-induced neuronal cell death. Subsequently, Morris water maze tests revealed that the escape latency was significantly decreased and the number of target quadrant crossings was markedly increased in the LF-treated groups. Thus, our data indicate that LFs have protective effects on seizure-induced neuronal cell death and cognitive impairment through their anti-oxidative effects.

Role of the mTOR signaling pathway in epilepsy

Epilepsy, a common neurological disorder and cause of significant morbidity and mortality, places an enormous burden on the individual and society. Presently, most drugs for epilepsy primarily suppress seizures as symptomatic therapies but do not possess actual antiepileptogenic or disease-modifying properties. The mTOR (mammalian target of rapamycin) signaling pathway is involved in major multiple cellular functions, including protein synthesis, cell growth and proliferation and synaptic plasticity, which may influence neuronal excitability and be responsible for epileptogenesis. Intriguing findings of the frequent hyperactivation of mTOR signaling in epilepsy make it a potential mechanism in the pathogenesis as well as an attractive target for the therapeutic intervention, and have driven the significant ongoing efforts to pharmacologically target this pathway. This review explores the relevance of the mTOR pathway to epileptogenesis and its potential as a therapeutic target in epilepsy treatment by presenting the current results on mTOR inhibitors, in particular, rapamycin, in animal models of diverse types of epilepsy. Limited clinical studies in human epilepsy, some paradoxical experimental data and outstanding questions have also been discussed.