Disruption of normal cytoskeletal dynamics may play a key role in the pathogenesis of epilepsy

Girdin deficiency causes developmental and epileptic encephalopathy with hippocampal sclerosis and interneuronopathy

OBJECTIVE

Loss-of-function mutations in the GIRDIN/CCDC88A gene cause developmental epileptic encephalopathy (DEE) in humans. However, its pathogenesis is largely unknown. Global knockout mice of the corresponding orthologous gene (gKOs) have a preweaning lethal phenotype with growth failure, preventing longitudinal analysis. We aimed to overcome this lethality and elucidate DEE pathogenesis.

METHODS

We developed a novel lifelong feeding regimen (NLFR), which consists of providing mash food from postnatal day 14 (P14) until weaning (P28), followed by agar-bound food exclusively after weaning. Videography, electroencephalography (EEG), and histological analyses were performed. Conditional Girdin/Ccdc88a knockout mice (cKOs) of variable lineages (Nestin, Emx1, or Nkx2-1) were generated to identify the region responsible for epilepsy.

RESULTS

Under the NLFR, gKOs survived beyond 1 year and displayed fully penetrant, robust epileptic phenotypes, including early-onset (P22.3 in average) generalized tonic-clonic seizures (GTCSs) (averaging eight per day), which were completely synchronized with fast rhythms on EEG, frequent interictal electroencephalographic spikes (averaging 430 per hour), and progressive deformation of visceral organs. In addition, gKOs had absence seizures, which were not always time-locked to frequent spike waves on EEG. The frequent GTCSs and interictal spikes in gKOs were suppressed by known antiepileptic drugs. Histologically, bilateral hippocampi in gKOs exhibited congenital cornu-ammonis splitting, granule cell dispersion, and astrogliosis. Furthermore, analysis of conditional knockouts using multiple Cre-deleters identified a defect in the delivery of interneuron precursors from the medial ganglionic eminence into the hippocampal primordium during embryogenesis as a major cause of epileptogenesis.

SIGNIFICANCE

These findings give rise to a new approach of lifelong caregiving to overcome the problem of preweaning lethality in animal models. We propose a useful model for studying DEE with hippocampal sclerosis and interneuronopathy. gKOs with NLFR combine the contradictory properties of robust epileptic phenotypes and long-term survivability, which can be used to investigate spontaneous epileptic wave propagation and therapeutic intervention in hippocampal sclerosis.

Exploiting fly models to investigate rare human neurological disorders

Rare neurological diseases, while individually are rare, collectively impact millions globally, leading to diverse and often severe neurological symptoms. Often attributed to genetic mutations that disrupt protein function or structure, understanding their genetic basis is crucial for accurate diagnosis and targeted therapies. To investigate the underlying pathogenesis of these conditions, researchers often use non-mammalian model organisms, such as Drosophila (fruit flies), which is valued for their genetic manipulability, cost-efficiency, and preservation of genes and biological functions across evolutionary time. Genetic tools available in Drosophila, including CRISPR-Cas9, offer a means to manipulate gene expression, allowing for a deep exploration of the genetic underpinnings of rare neurological diseases. Drosophila boasts a versatile genetic toolkit, rapid generation turnover, and ease of large-scale experimentation, making it an invaluable resource for identifying potential drug candidates. Researchers can expose flies carrying disease-associated mutations to various compounds, rapidly pinpointing promising therapeutic agents for further investigation in mammalian models and, ultimately, clinical trials. In this comprehensive review, we explore rare neurological diseases where fly research has significantly contributed to our understanding of their genetic basis, pathophysiology, and potential therapeutic implications. We discuss rare diseases associated with both neuron-expressed and glial-expressed genes. Specific cases include mutations in CDK19 resulting in epilepsy and developmental delay, mutations in TIAM1 leading to a neurodevelopmental disorder with seizures and language delay, and mutations in IRF2BPL causing seizures, a neurodevelopmental disorder with regression, loss of speech, and abnormal movements. And we explore mutations in EMC1 related to cerebellar atrophy, visual impairment, psychomotor retardation, and gain-of-function mutations in ACOX1 causing Mitchell syndrome. Loss-of-function mutations in ACOX1 result in ACOX1 deficiency, characterized by very-long-chain fatty acid accumulation and glial degeneration. Notably, this review highlights how modeling these diseases in Drosophila has provided valuable insights into their pathophysiology, offering a platform for the rapid identification of potential therapeutic interventions. Rare neurological diseases involve a wide range of expression systems, and sometimes common phenotypes can be found among different genes that cause abnormalities in neurons or glia. Furthermore, mutations within the same gene may result in varying functional outcomes, such as complete loss of function, partial loss of function, or gain-of-function mutations. The phenotypes observed in patients can differ significantly, underscoring the complexity of these conditions. In conclusion, Drosophila represents an indispensable and cost-effective tool for investigating rare neurological diseases. By facilitating the modeling of these conditions, Drosophila contributes to a deeper understanding of their genetic basis, pathophysiology, and potential therapies. This approach accelerates the discovery of promising drug candidates, ultimately benefiting patients affected by these complex and understudied diseases.

Abnormal cytoskeletal remodeling but normal neuronal excitability in a mouse model of the recurrent developmental and epileptic encephalopathy-susceptibility KCNB1-p.R312H variant

Integrin_K+ Channel_Complexes (IKCs), are implicated in neurodevelopment and cause developmental and epileptic encephalopathy (DEE) through mechanisms that were poorly understood. Here, we investigate the function of neocortical IKCs formed by voltage-gated potassium (Kv) channels Kcnb1 and α5β5 integrin dimers in wild-type (WT) and homozygous knock-in (KI) Kcnb1R312H(+/+) mouse model of DEE. Kcnb1R312H(+/+) mice suffer from severe cognitive deficit and compulsive behavior. Their brains show neuronal damage in multiple areas and disrupted corticocortical and corticothalamic connectivity along with aberrant glutamatergic vesicular transport. Surprisingly, the electrical properties of Kcnb1R312H(+/+) pyramidal neurons are similar to those of WT neurons, indicating that the arginine to histidine replacement does not affect the conducting properties of the mutant channel. In contrast, fluorescence recovery after photobleaching, biochemistry, and immunofluorescence, reveal marked differences in the way WT and Kcnb1R312H(+/+) neurons modulate the remodeling of the actin cytoskeleton, a key player in the processes underlying neurodevelopment. Together these results demonstrate that Kv channels can cause multiple conditions, including epileptic seizures, through mechanisms that do not involve their conducting functions and put forward the idea that the etiology of DEE may be primarily non-ionic.

Role and mechanism of EphB3 in epileptic seizures and epileptogenesis through Kalirin

BACKGROUND

The EphB receptor tyrosine kinase family participates in intricate signaling pathways that orchestrate neural networks, guide neuronal axon development, and modulate synaptic plasticity through interactions with surface-bound ephrinB ligands. Additionally, Kalirin, a Rho guanine nucleotide exchange factor, is notably expressed in the postsynaptic membrane of excitatory neurons and plays a role in synaptic morphogenesis. This study postulates that Kalirin may act as a downstream effector of EphB3 in epilepsy. This investigation focuses on understanding the link between EphB3 and epilepsy.

MATERIALS AND METHODS

Chronic seizure models using LiCl-pilocarpine (LiCl/Pilo) and pentylenetetrazol were developed in rats. Neuronal excitability was gauged through whole-cell patch clamp recordings on rat hippocampal slices. Real-time PCR determined Kalirin's mRNA expression, and Western blotting was employed to quantify EphB3 and Kalirin protein levels. Moreover, dendritic spine density in epileptic rats was evaluated using Golgi staining.

RESULTS

Modulation of EphB3 functionality influenced acute seizure severity, latency duration, and frequency of spontaneous recurrent seizures. Golgi staining disclosed an EphB3-driven alteration in dendritic spine density within the hippocampus of epileptic rats, underscoring its pivotal role in the reconfiguration of hippocampal neural circuits. Furthermore, our data propose Kalirin as a prospective downstream mediator of the EphB3 receptor.

CONCLUSIONS

Our findings elucidate that EphB3 impacts the action potential dynamics in isolated rat hippocampal slices and alters dendritic spine density in the inner molecular layer of epileptic rat hippocampi, likely through Kalirin-mediated pathways. This hints at EphB3's significant role in shaping excitatory circuit loops and recurrent seizure activity via Kalirin.

Neurons: The Interplay between Cytoskeleton, Ion Channels/Transporters and Mitochondria

Neurons are permanent cells whose key feature is information transmission via chemical and electrical signals. Therefore, a finely tuned homeostasis is necessary to maintain function and preserve neuronal lifelong survival. The cytoskeleton, and in particular microtubules, are far from being inert actors in the maintenance of this complex cellular equilibrium, and they participate in the mobilization of molecular cargos and organelles, thus influencing neuronal migration, neuritis growth and synaptic transmission. Notably, alterations of cytoskeletal dynamics have been linked to alterations of neuronal excitability. In this review, we discuss the characteristics of the neuronal cytoskeleton and provide insights into alterations of this component leading to human diseases, addressing how these might affect excitability/synaptic activity, as well as neuronal functioning. We also provide an overview of the microscopic approaches to visualize and assess the cytoskeleton, with a specific focus on mitochondrial trafficking.

Loss-of-function variants in TIAM1 are associated with developmental delay, intellectual disability, and seizures

TIAM Rac1-associated GEF 1 (TIAM1) regulates RAC1 signaling pathways that affect the control of neuronal morphogenesis and neurite outgrowth by modulating the actin cytoskeletal network. To date, TIAM1 has not been associated with a Mendelian disorder. Here, we describe five individuals with bi-allelic TIAM1 missense variants who have developmental delay, intellectual disability, speech delay, and seizures. Bioinformatic analyses demonstrate that these variants are rare and likely pathogenic. We found that the Drosophila ortholog of TIAM1, still life (sif), is expressed in larval and adult central nervous system (CNS) and is mainly expressed in a subset of neurons, but not in glia. Loss of sif reduces the survival rate, and the surviving adults exhibit climbing defects, are prone to severe seizures, and have a short lifespan. The TIAM1 reference (Ref) cDNA partially rescues the sif loss-of-function (LoF) phenotypes. We also assessed the function associated with three TIAM1 variants carried by two of the probands and compared them to the TIAM1 Ref cDNA function in vivo. TIAM1 p.Arg23Cys has reduced rescue ability when compared to TIAM1 Ref, suggesting that it is a partial LoF variant. In ectopic expression studies, both wild-type sif and TIAM1 Ref are toxic, whereas the three variants (p.Leu862Phe, p.Arg23Cys, and p.Gly328Val) show reduced toxicity, suggesting that they are partial LoF variants. In summary, we provide evidence that sif is important for appropriate neural function and that TIAM1 variants observed in the probands are disruptive, thus implicating loss of TIAM1 in neurological phenotypes in humans.

Effects of altered tau expression on dentate granule cell excitability in mice

Tauopathies, including Alzheimer's disease, are characterized by progressive accumulation of hyperphosphorylated and pathologic tau protein in association with onset of cognitive and behavioral impairment. Tau pathology is also associated with increased susceptibility to seizures and epilepsy, with tau^-/- mice showing seizure resistance in some epilepsy models. To better understand how tau pathology is related to neuronal excitability, we performed whole-cell patch-clamp electrophysiology in dentate gyrus granule cells of tau^-/- and human-tau expressing, htau mice. The htau mouse is unique from other transgenic tau models in that the endogenous murine tau gene has been and replaced with readily phosphorylated human tau. We assessed several measures of neuronal excitability, including evoked action potential frequency and excitatory synaptic responses in dentate granule cells from tau^-/-, htau, and non-transgenic control mice at 1.5, 4, and 9 months of age. Compared to age matched controls, dentate granule cells from both tau^-/- and htau mice had a lower peak frequency of evoked action potentials and greater paired pulse facilitation, suggesting reduced neuronal excitability. Our results suggest that neuronal excitability is more strongly influenced by the absence of functional tau than by the presence of pathologic tau. These results also suggest that tau's effect on neuronal excitability is more complex than previously understood.

Microtubule Dynamics and Neuronal Excitability: Advances on Cytoskeletal Components Implicated in Epileptic Phenomena

Extensive researches have deepened knowledge on the role of synaptic components in epileptogenesis, but limited attention has been devoted to the potential implication of the cytoskeleton. The study of the development of epilepsy and hyperexcitability states involves molecular, synaptic, and structural alterations of neuronal bioelectric activity. In this paper we aim to explore the neurobiological targets involved in microtubule functioning and cytoskeletal transport, i.e. how dynamic scaffolding of microtubules can influence neuronal morphology and excitability, in order to suggest a potential role for microtubule dynamics in the processes turning a normal neuronal network in a hyperexcited one. Pathophysiological alterations of microtubule dynamics inducing neurodegeneration, network remodeling and relative impairment on synaptic transmission were overviewed. Recent researches were reported on the phosphorylation state of microtubule-associated proteins such as tau in neurodegenerative diseases and epileptic states, but also on the effect of microtubule-active agents influencing cytoskeleton destabilization in epilepsy models. The manipulation of microtubule polymerization was found effective in the modulation of hyperexcitability. In addition, it was considered the importance of microtubules and related neurotrophic factors during neural development since they are essential for the formation of a properly functional neuronal network. Otherwise, this can lead to cognitive deficits, hyperexcitability phenomena and neurodevelopmental disorders. Lastly, we evaluated the role of microtubule dynamics on neuronal efficiency considering their importance in the transport of mitochondria, cellular elements fulfilling energy requirements for neuronal activity, and a putative influence on cannabinoid-mediated neuroprotection. This review provides novel perspectives for the implication of microtubule dynamics in the development of epileptic phenomena.

Postnatal Role of the Cytoskeleton in Adult Epileptogenesis

Mutations in cytoskeletal proteins can cause early infantile and childhood epilepsies by misplacing newly born neurons and altering neuronal connectivity. In the adult epileptic brain, cytoskeletal disruption is often viewed as being secondary to aberrant neuronal activity and/or death, and hence simply represents an epiphenomenon. Here, we review the emerging evidence collected in animal models and human studies implicating the cytoskeleton as a potential causative factor in adult epileptogenesis. Based on the emerging evidence, we propose that cytoskeletal disruption may be an important pathogenic mechanism in the mature epileptic brain.

Phosphoproteomic analysis reveals Akt isoform-specific regulation of cytoskeleton proteins in human temporal lobe epilepsy with hippocampal sclerosis

Akt is one of the most important downstream effectors of phosphatidylinositol 3-kinase/mTOR pathway. Hyperactivation and expression of this pathway are seen in a variety of neurological disorders including human temporal lobe epilepsy with hippocampal sclerosis (TLE-HS). Nevertheless, the expression and activation profiles of the Akt isoforms, Akt1, Akt2, and Akt3 and their functional roles in human TLE-HS have not been studied. We examined the protein expression and activation (phosphorylation) patterns of Akt and its isoforms in human hippocampal tissue from TLE and non-TLE patients. A phosphoproteomic approach followed by interactome analysis of each Akt isoform was used to understand protein-protein interactions and their role in TLE-HS pathology. Our results demonstrated activation of the Akt/mTOR pathway as well as activation of Akt downstream substrates like GSK3β, mTOR, and S6 in TLE-HS samples. Akt1 isoform levels were significantly increased in the TLE-HS samples as compared to the non-TLE samples. Most importantly, different isoforms were activated in different TLE-HS samples, Akt2 was activated in three samples, Akt2 and Akt1 were simultaneously activated in one sample and Akt3 was activated in two samples. Our phosphoproteomic screen across six TLE-HS samples identified 183 proteins phosphorylated by Akt isoforms, 29 of these proteins belong to cytoskeletal modification. Also, we were able to identify proteins of several other classes involved in glycolysis, neuronal development, protein folding and excitatory amino acid transport functions as Akt substrates. Taken together, our data offer clues to understand the role of Akt and its isoforms in underlying the pathology of TLE-HS and further, modulation of Akt/mTOR pathway using Akt isoforms specific inhibitors may offer a new therapeutic window for treatment of human TLE-HS.

Epilepsy-associated alterations in hippocampal excitability

The hippocampus exhibits a wide range of epilepsy-related abnormalities and is situated in the mesial temporal lobe, where limbic seizures begin. These abnormalities could affect membrane excitability and lead to overstimulation of neurons. Multiple overlapping processes refer to neural homeostatic responses develop in neurons that work together to restore neuronal firing rates to control levels. Nevertheless, homeostatic mechanisms are unable to restore normal neuronal excitability, and the epileptic hippocampus becomes hyperexcitable or hypoexcitable. Studies show that there is hyperexcitability even before starting recurrent spontaneous seizures, suggesting although hippocampal hyperexcitability may contribute to epileptogenesis, it alone is insufficient to produce epileptic seizures. This supports the concept that the hippocampus is not the only substrate for limbic seizure onset, and a broader hyperexcitable limbic structure may contribute to temporal lobe epilepsy (TLE) seizures. Nevertheless, seizures also occur in conditions where the hippocampus shows a hypoexcitable phenotype. Since TLE seizures most often originate in the hippocampus, it could therefore be assumed that both hippocampal hypoexcitability and hyperexcitability are undesirable states that make the epileptic hippocampal network less stable and may, under certain conditions, trigger seizures.

Hippocampal Hyperexcitability is Modulated by Microtubule-Active Agent: Evidence from In Vivo and In Vitro Epilepsy Models in the Rat

The involvement of microtubule dynamics on bioelectric activity of neurons and neurotransmission represents a fascinating target of research in the context of neural excitability. It has been reported that alteration of microtubule cytoskeleton can lead to profound modifications of neural functioning, with a putative impact on hyperexcitability phenomena. Altogether, in the present study we pointed at exploring the outcomes of modulating the degree of microtubule polymerization in two electrophysiological models of epileptiform activity in the rat hippocampus. To this aim, we used in vivo maximal dentate activation (MDA) and in vitro hippocampal epileptiform bursting activity (HEBA) paradigms to assess the effects of nocodazole (NOC) and paclitaxel (PAC), that respectively destabilize and stabilize microtubule structures. In particular, in the MDA paroxysmal discharge is electrically induced, whereas the HEBA is obtained by altering extracellular ionic concentrations. Our results provided evidence that NOC 10 μM was able to reduce the severity of MDA seizures, without inducing neurotoxicity as verified by the immunohistochemical assay. In some cases, paroxysmal discharge was completely blocked during the maximal effect of the drug. These data were also in agreement with the outcomes of in vitro HEBA, since NOC markedly decreased burst activity that was even silenced occasionally. In contrast, PAC at 10 μM did not exert a clear action in both paradigms. The present study, targeting cellular mechanisms not much considered so far, suggests the possibility that microtubule-active drugs could modulate brain hyperexcitability. This contributes to the hypothesis that cytoskeleton function may affect synaptic processes, relapsing on bioelectric aspects of epileptic activity.

Reduced Pumilio-2 expression in patients with temporal lobe epilepsy and in the lithium-pilocarpine induced epilepsy rat model

OBJECTIVE

Drosophila Pumilio (Pum), a homolog of mammalian Pum2, plays an important role in translational regulation in the central nervous system (CNS), particularly for dendrite outgrowth and neuronal excitability. We investigated the expression pattern and cellular distribution of Pum2 in patients with drug-refractory temporal lobe epilepsy (TLE) and rats with lithium chloride-pilocarpine-induced epilepsy.

METHODS

Real-time quantitative PCR (RT-qPCR), Western blot, immunohistochemistry, and double-labeled immunofluorescence were utilized to determine the expression level and distribution of Pum2 in temporal neocortex tissues from patients with intractable TLE (n=20) and patients with severe head trauma (n=20) in addition to the hippocampus and adjacent cortex of rats with lithium chloride-pilocarpine-induced TLE and controls.

RESULTS

Pum2 was expressed in the cell bodies and dendrites of neurons but did not colocalize with glial fibrillary acidic protein-positive astrocytes or propidium iodide (PI) in nuclei. The expression of Pum2 was significantly reduced in patients and rats with TLE in comparison to controls (P<0.05).

CONCLUSION

Pum2 expression was less in patients with TLE and a rodent model of epilepsy, suggesting that decreased expression of Pum2 may be involved in the pathogenesis of TLE.

Molecular mechanisms of epilepsy

Decades of experimental work have established an imbalance of excitation and inhibition as the leading mechanism of the transition from normal brain function to seizure. In epilepsy, these transitions are rare and abrupt. Transition processes incorporating positive feedback, such as activity-dependent disinhibition, could provide these uncommon timing features. A rapidly expanding array of genetic etiologies will help delineate the molecular mechanism(s). This delineation will entail quite a bit of cell biology. The genes discovered so far are more remarkable for their diversity than their similarities.

Increased stathmin expression strengthens fear conditioning in epileptic rats

Patients with temporal lobe epilepsy have inexplicable fear attack as the aura. However, the underlying neural mechanisms of seizure-modulated fear are not clarified. Recent studies identified stathmin as one of the key controlling molecules in learning and innate fear. Stathmin binds to tubulin, inhibits microtubule assembly and promotes microtubule catastrophes. Therefore, stathmin is predicted to play a crucial role in the association of epilepsy seizures with fear conditioning. Firstly, a pilocarpine model of epilepsy in rats was established, and subsequently the fear condition training was performed. The epileptic rats with fear conditioning (epilepsy + fear) had a much longer freezing time compared to each single stimulus. The increased freezing levels revealed a significantly strengthened effect of the epileptic seizures on the learned fear of the tone-shock contextual. Subsequently, the stathmin expression was compared in the hippocampus, the amygdale, the insular cortex and the temporal lobe. The significant change of stathmin expression occurred in the insular and the hippocampus, but not in the amygdale. Stathmin expression and dendritic microtubule stability were compared between fear and epilepsy in rats. Epilepsy was found to strengthen the fear conditioning with increased expression of stathmin and a decrease in microtubule stability. Fear conditioning slightly increased the expression of stathmin, whereas epilepsy with fear conditioning increased it significantly in the hippocampus, insular cortex and hypothalamus. The phosphorylated stathmin slightly increased in the epilepsy with fear conditioning. The increased expression of stathmin was contrary to the decrease of the stathmin microtubule-associated protein (MAP2) and α-tubulin in the epileptic rats with fear conditioning in all three areas of the brain. The most significant change of the ratio of MAP2 and α-tubulin/stathmin occurred in the insular cortex and hippocampus. In conclusion, epilepsy can strengthen the fear conditioning with increased stathmin and decreased microtubule stability, particularly in the insular cortex and hippacampus. Therefore, the insular cortex may play a more important role between fear and epilepsy.

Single point mutation in Rabenosyn-5 in a female with intractable seizures and evidence of defective endocytotic trafficking

BACKGROUND

We report a 6.5 year-old female with a homozygous missense mutation in ZFYVE20, encoding Rabenosyn-5 (Rbsn-5), a highly conserved multi-domain protein implicated in receptor-mediated endocytosis. The clinical presentation includes intractable seizures, developmental delay, microcephaly, dysostosis, osteopenia, craniofacial dysmorphism, macrocytosis and megaloblastoid erythropoiesis. Biochemical findings include transient cobalamin deficiency, severe hypertriglyceridemia upon ketogenic diet, microalbuminuria and partial cathepsin D deficiency.

METHODS AND RESULTS

Whole exome sequencing followed by Sanger sequencing confirmed a rare (frequency:0.003987) homozygous missense mutation, g.15,116,371 G > A (c.1273G > A), in ZFYVE20 resulting in an amino acid change from Glycine to Arginine at position 425 of the Rbsn protein (p.Gly425Arg), as the only mutation segregating with disease in the family. Studies in fibroblasts revealed expression and localization of Rbsn-5G425R in wild-type manner, but a 50% decrease in transferrin accumulation, which is corrected by wild-type allele transfection. Furthermore, the patient's fibroblasts displayed an impaired proliferation rate, cytoskeletal and lysosomal abnormalities.

CONCLUSION

These results are consistent with a functional defect in the early endocytic pathway resulting from mutation in Rbsn-5, which secondarily disrupts multiple cellular functions dependent on endocytosis, leading to a severe multi-organ disorder.

A breach in the scaffold: the possible role of cytoskeleton dysfunction in the pathogenesis of major depression

Depression is one of the most common psychiatric disorders with inadequately understood disease mechanisms. It has long been considered that dendritic regression and decrease in the number of dendritic spines are involved in depression. Dendrites made up of microtubules and actin filaments form synapses with neighboring neurons, which come together as an important communication network. Cytoskeletal proteins undergo post-translational modifications to define their structure and function. In depression and other psychiatric disorders, post-translational modifications may be disrupted that can result in altered cytoskeletal functions. The disruption of microtubule and actin in terms of morphology and functions may be a leading cause of dendritic regression and decrease in dendritic spine in depression.

Abnormal expression of stathmin 1 in brain tissue of patients with intractable temporal lobe epilepsy and a rat model

Microtubule dynamics have been shown to contribute to neurite outgrowth, branching, and guidance. Stathmin 1 is a potent microtubule-destabilizing factor that is involved in the regulation of microtubule dynamics and plays an essential role in neurite elongation and synaptic plasticity. Here, we investigate the expression of stathmin 1 in the brain tissues of patients with intractable temporal lobe epilepsy (TLE) and experimental animals using immunohistochemistry, immunofluorescence and western blotting. We obtained 32 temporal neocortex tissue samples from patients with intractable TLE and 12 histologically normal temporal lobe tissues as controls. In addition, 48 Sprague Dawley rats were randomly divided into six groups, including one control group and five groups with epilepsy induced by lithium chloride-pilocarpine. Hippocampal and temporal lobe tissues were obtained from control and epileptic rats on Days 1, 7, 14, 30, and 60 after kindling. Stathmin 1 was mainly expressed in the neuronal membrane and cytoplasm in the human controls, and its expression levels were significantly higher in patients with intractable TLE. Moreover, stathmin 1 was also expressed in the neurons of both the control and the experimental rats. Stathmin 1 expression was decreased in the experimental animals from 1 to 14 days postseizure and then significantly increased at Days 30 and 60 compared with the control group. Many protruding neuronal processes were observed in the TLE patients and in the chronic stage epileptic rats. These data suggest that stathmin 1 may participate in the abnormal network reorganization of synapses and contribute to the pathogenesis of TLE.

Potential role of drebrin a, an f-actin binding protein, in reactive synaptic plasticity after pilocarpine-induced seizures: functional implications in epilepsy

Several neurological disorders characterized by cognitive deficits, including Alzheimer's disease, down syndrome, and epilepsy exhibit abnormal spine density and/or morphology. Actin-based cytoskeleton network dynamics is critical for the regulation of spine morphology and synaptic function. In this paper, I consider the functions of drebrin A in cell shaping, spine plasticity, and synaptic function. Developmentally regulated brain protein (drebrin A) is one of the most abundant neuron-specific binding proteins of F-actin and its expression is increased in parallel with synapse formation. Drebrin A is particularly concentrated in dendritic spines receiving excitatory inputs. Our recent findings point to a critical role of DA in dendritic spine structural integrity and stabilization, likely via regulation of actin cytoskeleton dynamics, and glutamatergic synaptic function that underlies the development of spontaneous recurrent seizures in pilocarpine-treated animals. Further research into this area may provide useful insights into the pathology of status epilepticus and epileptogenic mechanisms and ultimately may provide the basis for future treatment options.

Increased expression of calponin-3 in epileptic patients and experimental rats

Calponin-3 is an actin-interacting protein and is expressed in the brain. Our previous microarray scan has found an up-regulation of calponin-3 gene CNN3 in the temporal lobe of patients with drug-resistant epilepsy. Here we investigated in epileptic patients the changes of brain and cerebrospinal fluid (CSF) calponin-3 expressions, and assessed calponin-3 expression pattern in a rat model of pilocarpine-induced epilepsy. We showed that in the temporal neocortices of 30 patients with drug-resistant epilepsy, both mRNA and protein level of calponin-3 were significantly increased. In addition, the augmentation of CSF calponin-3 from 126 epileptic patients was closely correlated with disease duration. Moreover, in the cortices of temporal lobes of pilocarpine-treated rats, calponin-3 increased along with the time and maintained at significant high levels for up to 2 months, while the up-regulation of hippocampal calponin-3 only occurred at 24h and 1 week. The elevated calponin-3 suggests that deregulation of actin filament dynamics in axonal and dendritic outgrowth and synaptic rearrangement may contribute to pathophysiology of epilepsy.

The microtubule cytoskeleton acts as a key downstream effector of neurotransmitter signaling

Microtubules are well known to play a key role in the trafficking of neurotransmitters to the synapse. However, less attention has been paid to their role as downstream effectors of neurotransmitter signaling in the target neuron. Here, we show that neurotransmitter-based signaling to the microtubule cytoskeleton regulates downstream microtubule function through several mechanisms. These include tubulin posttranslational modification, binding of microtubule-associated proteins, release of microtubule-interacting second messenger molecules, and regulation of tubulin expression levels. We review the evidence for neurotransmitter regulation of the microtubule cytoskeleton, focusing on the neurotransmitters serotonin, melatonin, dopamine, glutamate, glycine, and acetylcholine. Some evidence suggests that microtubules may even play a more direct role in propagating action potentials through conductance of electric current. In turn, there is evidence for the regulation of neurotransmission by the microtubule cytoskeleton.