Evaluation of the innate and adaptive immunity in type I and type II focal cortical dysplasias

mTOR and neuroinflammation in epilepsy: implications for disease progression and treatment

Epilepsy remains a major health concern as anti-seizure medications frequently fail, and there is currently no treatment to stop or prevent epileptogenesis, the process underlying the onset and progression of epilepsy. The identification of the pathological processes underlying epileptogenesis is instrumental to the development of drugs that may prevent the generation of seizures or control pharmaco-resistant seizures, which affect about 30% of patients. mTOR signalling and neuroinflammation have been recognized as critical pathways that are activated in brain cells in epilepsy. They represent a potential node of biological convergence in structural epilepsies with either a genetic or an acquired aetiology. Interventional studies in animal models and clinical studies give strong support to the involvement of each pathway in epilepsy. In this Review, we focus on available knowledge about the pathophysiological features of mTOR signalling and the neuroinflammatory brain response, and their interactions, in epilepsy. We discuss mitigation strategies for each pathway that display therapeutic effects in experimental and clinical epilepsy. A deeper understanding of these interconnected molecular cascades could enhance our strategies for managing epilepsy. This could pave the way for new treatments to fill the gaps in the development of preventative or disease-modifying drugs, thus overcoming the limitations of current symptomatic medications.

CNS autoimmune response in the MAM/pilocarpine rat model of epileptogenic cortical malformation

The development of seizures in epilepsy syndromes associated with malformations of cortical development (MCDs) has traditionally been attributed to intrinsic cortical alterations resulting from abnormal network excitability. However, recent analyses at single-cell resolution of human brain samples from MCD patients have indicated the possible involvement of adaptive immunity in the pathogenesis of these disorders. By exploiting the MethylAzoxyMethanol (MAM)/pilocarpine (MP) rat model of drug-resistant epilepsy associated with MCD, we show here that the occurrence of status epilepticus and subsequent spontaneous recurrent seizures in the malformed, but not in the normal brain, are associated with the outbreak of a destructive autoimmune response with encephalitis-like features, involving components of both cell-mediated and humoral immune responses. The MP brain is characterized by blood-brain barrier dysfunction, marked and persisting CD8+ T cell invasion of the brain parenchyma, meningeal B cell accumulation, and complement-dependent cytotoxicity mediated by antineuronal antibodies. Furthermore, the therapeutic treatment of MP rats with the immunomodulatory drug fingolimod promotes both antiepileptogenic and neuroprotective effects. Collectively, these data show that the MP rat could serve as a translational model of epileptogenic cortical malformations associated with a central nervous system autoimmune response. This work indicates that a preexisting brain maldevelopment predisposes to a secondary autoimmune response, which acts as a precipitating factor for epilepsy and suggests immune intervention as a therapeutic option to be further explored in epileptic syndromes associated with MCDs.

Drug resistant epilepsies: A multicentre case series of steroid therapy

PURPOSE

Our study aimed to evaluate the effectiveness of corticosteroids on seizure control in drug-resistant epilepsies (DREs). Our primary goal was to assess the response to steroids for various underlying etiologies, interictal electroencephalographic (EEG) patterns and electroclinical seizure descriptions. Our second goal was to compare steroid responsiveness to different treatment protocols.

METHODS

This is a retrospective multicentre cohort study conducted according to the STROBE guidelines (Strengthening the Reporting of Observational Studies in Epidemiology). The following data were collected for each patient: epilepsy etiology, interictal EEG pattern, seizure types and type of steroid treatment protocol administered.

RESULTS

Thirty patients with DRE were included in the study. After 6 months of therapy, 62.7 % of patients experienced reduced seizure frequency by 50 %, and 6.6 % of patients experienced complete seizure cessation. Findings associated with favourable response to steroids included structural/lesional etiology of epilepsy, immune/infectious etiology and focal interictal abnormalities on EEG. Comparing four different steroid treatment protocols, the most effective for seizure control was treatment with methylprednisolone at the dose of 30 mg/kg/day administered for 3 days, leading to greater than 50 % seizure reduction at 6 months in 85.7 % of patients. Treatment with dexamethasone 6 mg/day for 5 days decreased seizure frequency in 71.4 % of patients. Hydrocortisone 10 mg/kg administered for 3 months showed a good response to treatment in 71 %.

CONCLUSIONS

In our study, two-thirds of patients with DRE experienced a significant seizure reduction following treatment with steroids. We suggest considering steroids as a potential therapeutic option in children with epilepsy not responding to conventional antiseizure medicines (ASM).

Microglia in epilepsy

Epilepsy is one of most common chronic neurological disorders, and the antiseizure medications developed by targeting neurocentric mechanisms have not effectively reduced the proportion of patients with drug-resistant epilepsy. Further exploration of the cellular or molecular mechanism of epilepsy is expected to provide new options for treatment. Recently, more and more researches focus on brain network components other than neurons, among which microglia have attracted much attention for their diverse biological functions. As the resident immune cells of the central nervous system, microglia have highly plastic transcription, morphology and functional characteristics, which can change dynamically in a context-dependent manner during the progression of epilepsy. In the pathogenesis of epilepsy, highly reactive microglia interact with other components in the epileptogenic network by performing crucial functions such as secretion of soluble factors and phagocytosis, thus continuously reshaping the landscape of the epileptic brain microenvironment. Indeed, microglia appear to be both pro-epileptic and anti-epileptic under the different spatiotemporal contexts of disease, rendering interventions targeting microglia biologically complex and challenging. This comprehensive review critically summarizes the pathophysiological role of microglia in epileptic brain homeostasis alterations and explores potential therapeutic or modulatory targets for epilepsy targeting microglia.

Transcriptome analyses of the cortex and white matter of focal cortical dysplasia type II: Insights into pathophysiology and tissue characterization

Introduction

Focal cortical dysplasia (FCD) is a common cause of pharmacoresistant epilepsy. According to the 2022 International League Against Epilepsy classification, FCD type II is characterized by dysmorphic neurons (IIa and IIb) and may be associated with balloon cells (IIb). We present a multicentric study to evaluate the transcriptomes of the gray and white matters of surgical FCD type II specimens. We aimed to contribute to pathophysiology and tissue characterization.

Methods

We investigated FCD II (a and b) and control samples by performing RNA-sequencing followed by immunohistochemical validation employing digital analyses.

Results

We found 342 and 399 transcripts differentially expressed in the gray matter of IIa and IIb lesions compared to controls, respectively. Cholesterol biosynthesis was among the main enriched cellular pathways in both IIa and IIb gray matter. Particularly, the genes HMGCS1, HMGCR, and SQLE were upregulated in both type II groups. We also found 12 differentially expressed genes when comparing transcriptomes of IIa and IIb lesions. Only 1 transcript (MTRNR2L12) was significantly upregulated in FCD IIa. The white matter in IIa and IIb lesions showed 2 and 24 transcripts differentially expressed, respectively, compared to controls. No enriched cellular pathways were detected. GPNMB, not previously described in FCD samples, was upregulated in IIb compared to IIa and control groups. Upregulations of cholesterol biosynthesis enzymes and GPNMB genes in FCD groups were immunohistochemically validated. Such enzymes were mainly detected in both dysmorphic and normal neurons, whereas GPNMB was observed only in balloon cells.

Discussion

Overall, our study contributed to identifying cortical enrichment of cholesterol biosynthesis in FCD type II, which may correspond to a neuroprotective response to seizures. Moreover, specific analyses in either the gray or the white matter revealed upregulations of MTRNR2L12 and GPNMB, which might be potential neuropathological biomarkers of a cortex chronically exposed to seizures and of balloon cells, respectively.

Retinal Tissue Shows Glial Changes in a Dravet Syndrome Knock-in Mouse Model

Dravet syndrome (DS) is an epileptic encephalopathy caused by mutations in the Scn1a gene encoding the α1 subunit of the Nav1.1 sodium channel, which is associated with recurrent and generalized seizures, even leading to death. In experimental models of DS, histological alterations have been found in the brain; however, the retina is a projection of the brain and there are no studies that analyze the possible histological changes that may occur in the disease. This study analyzes the retinal histological changes in glial cells (microglia and astrocytes), retinal ganglion cells (RGCs) and GABAergic amacrine cells in an experimental model of DS (Syn-Cre/Scn1a^WT/A1783V) compared to a control group at postnatal day (PND) 25. Retinal whole-mounts were labeled with anti-GFAP, anti-Iba-1, anti-Brn3a and anti-GAD65/67. Signs of microglial and astroglial activation, and the number of Brn3a+ and GAD65+67+ cells were quantified. We found retinal activation of astroglial and microglial cells but not death of RGCs and GABAergic amacrine cells. These changes are similar to those found at the level of the hippocampus in the same experimental model in PND25, indicating a relationship between brain and retinal changes in DS. This suggests that the retina could serve as a possible biomarker in DS.

Blood-Brain Barrier-Associated Proteins Are Elevated in Serum of Epilepsy Patients

Blood-brain barrier (BBB) dysfunction emerges as one of the mechanisms underlying the induction of seizures and epileptogenesis. There is growing evidence that seizures also affect BBB, yet only scarce data is available regarding serum levels of BBB-associated proteins in chronic epilepsy. In this study, we aimed to assess serum levels of molecules associated with BBB in patients with epilepsy in the interictal period. Serum levels of MMP-9, MMP-2, TIMP-1, TIMP-2, S100B, CCL-2, ICAM-1, P-selectin, and TSP-2 were examined in a group of 100 patients who were seizure-free for a minimum of seven days and analyzed by ELISA. The results were compared with an age- and sex-matched control group. Serum levels of MMP-9, MMP-2, TIMP-1, TIMP-2 and S100B were higher in patients with epilepsy in comparison to control group (p < 0.0001; <0.0001; 0.001; <0.0001; <0.0001, respectively). Levels of CCL-2, ICAM-1, P-selectin and TSP-2 did not differ between the two groups. Serum levels of MMP-9, MMP-2, TIMP-1, TIMP-2 and S100B are elevated in patients with epilepsy in the interictal period, which suggests chronic processes of BBB disruption and restoration. The pathological process initiating epilepsy, in addition to seizures, is probably the factor contributing to the elevation of serum levels of the examined molecules.

LTBP1 Gene Expression in the Cerebral Cortex and its Neuroprotective Mechanism in Mice with Postischemic Stroke Epilepsy

OBJECTIVE

This study aimed at exploring the expression level of LTBP1 in the mouse model of epilepsy. The mechanism of LTBP1 in epileptic cerebral neural stem cells was deeply investigated to control the occurrence of epilepsy with neuroprotection.

METHODS

qRT-PCR was conducted for the expression levels of LTBP1 in clinical human epileptic tissues and neural stem cells, as well as normal cerebral tissues and neural stem cells. The mouse model of postischemic stroke epilepsy (PSE) was established by the middle cerebral artery occlusion (MCAO). Then, qRT-PCR was conducted again for the expression levels of LTBP1 in mouse epileptic tissues and neural stem cells as well as normal cerebral tissues and neural stem cells. The activation and inhibitory vectors of LTBP1 were constructed to detect the effects of LTBP1 on the proliferation of cerebral neural stem cells in the PSE model combined with CCK-8. Finally, Western blot was conducted for the specific mechanism of LTBP1 affecting the development of epileptic cells.

RESULTS

Racine score and epilepsy index of 15 mice showed epilepsy symptoms after the determination with MCAO, showing a successful establishment of the PSE model. LTBP1 expression in both diseased epileptic tissues and cells was higher than that in normal clinical epileptic tissues and cells. Meanwhile, qRT-PCR showed higher LTBP1 expression in both mouse epileptic tissues and their neural stem cells compared to that in normal tissues and cells. CCK-8 showed that the activation of LTBP1 stimulated the increased proliferative capacity of epileptic cells, while the inhibition of LTBP1 expression controlled the proliferation of epileptic cells. Western blot showed an elevated expression of TGFβ/SMAD signaling pathway-associated protein SMAD1/5/8 after activating LTBP1. The expression of molecular MMP-13 associated with the occurrence of inflammation was also activated.

CONCLUSION

LTBP1 can affect the changes in inflammation-related pathways by activating the TGFβ/SMAD signaling pathway and stimulate the development of epilepsy, and the inhibition of LTBP1 expression can control the occurrence of epilepsy with neuroprotection.

Dendritic spine loss in epileptogenic Type II focal cortical dysplasia: Role of enhanced classical complement pathway activation

Dendritic spines are the postsynaptic sites for most excitatory glutamatergic synapses. We previously demonstrated a severe spine loss and synaptic reorganization in human neocortices presenting Type II focal cortical dysplasia (FCD), a developmental malformation and frequent cause of drug-resistant focal epilepsy. We extend the findings, investigating the potential role of complement components C1q and C3 in synaptic pruning imbalance. Data from Type II FCD were compared with those obtained in focal epilepsies with different etiologies. Neocortical tissues were collected from 20 subjects, mainly adults with a mean age at surgery of 31 years, admitted to epilepsy surgery with a neuropathological diagnosis of: cryptogenic, temporal lobe epilepsy with hippocampal sclerosis, and Type IIa/b FCD. Dendritic spine density quantitation, evaluated in a previous paper using Golgi impregnation, was available in a subgroup. Immunohistochemistry, in situ hybridization, electron microscopy, and organotypic cultures were utilized to study complement/microglial activation patterns. FCD Type II samples presenting dendritic spine loss were characterized by an activation of the classical complement pathway and microglial reactivity. In the same samples, a close relationship between microglial cells and dendritic segments/synapses was found. These features were consistently observed in Type IIb FCD and in 1 of 3 Type IIa cases. In other patient groups and in perilesional areas outside the dysplasia, not presenting spine loss, these features were not observed. In vitro treatment with complement proteins of organotypic slices of cortical tissue with no sign of FCD induced a reduction in dendritic spine density. These data suggest that dysregulation of the complement system plays a role in microglia-mediated spine loss. This mechanism, known to be involved in the removal of redundant synapses during development, is likely reactivated in Type II FCD, particularly in Type IIb; local treatment with anticomplement drugs could in principle modify the course of disease in these patients.

Serum Proteins Associated with Blood-Brain Barrier as Potential Biomarkers for Seizure Prediction

As 30% of epileptic patients remain drug-resistant, seizure prediction is vital. Induction of epileptic seizure is a complex process that can depend on factors such as intrinsic neuronal excitability, changes in extracellular ion concentration, glial cell activity, presence of inflammation and activation of the blood−brain barrier (BBB). In this study, we aimed to assess if levels of serum proteins associated with BBB can predict seizures. Serum levels of MMP-9, MMP-2, TIMP-1, TIMP-2, S100B, CCL-2, ICAM-1, P-selectin, and TSP-2 were examined in a group of 49 patients with epilepsy who were seizure-free for a minimum of seven days and measured by ELISA. The examination was repeated after 12 months. An extensive medical history was taken, and patients were subjected to a follow-up, including a detailed history of seizures. Serum levels of MMP-2, MMP-9, TIMP-1, CCL-2, and P-selectin differed between the two time points (p < 0.0001, p < 0.0001, p < 0.0001, p < 0.0001, p = 0.0035, respectively). General linear model analyses determined the predictors of seizures. Levels of MMP-2, MMP-9, and CCL-2 were found to influence seizure count in 1, 3, 6, and 12 months of observation. Serum levels of MMP-2, MMP-9, and CCL-2 may be considered potential biomarkers for seizure prediction and may indicate BBB activation.

The role of interleukin-17 in epilepsy

Epilepsy is a common neurological disorder that seriously affects human health. It is a chronic central nervous system dysfunction caused by abnormal discharges of neurons. About 50 million patients worldwide are affected by epilepsy. Although epileptic symptoms of most patients are controllable, some patients with refractory epilepsy have no response to antiseizure medications. It is necessary to investigate the pathogenesis of epilepsy and identify new therapeutic targets for refractory epilepsy. Epileptic disorders often accompany cerebral inflammatory reactions. Recently, the role of inflammation in the onset of epilepsy has increasingly attracted attention. The activation of both innate and adaptive immunity plays a significant role in refractory epilepsy. According to several clinical studies, interleukin-17, an essential inflammatory mediator linking innate and adaptive immunity, increased significantly in the body liquid and epileptic focus of patients with epilepsy. Experimental studies also indicated that interleukin-17 participated in epileptogenesis through various mechanisms. This review summarized the current studies about interleukin-17 in epilepsy and aimed at finding new therapeutic targets for refractory epilepsy.

Pathogenesis and Therapeutic Targets of Focal Cortical Dysplasia Based on Bioinformatics Analysis

Focal cortical dysplasia (FCD), a malformation of cortical development, is the most common cause of intractable epilepsy in children. However, the causes and underlying molecular events of FCD need further investigation. The microarray dataset GSE62019 and GSE97365 were obtained from Gene Expression Omnibus. To examine critical genes and signaling pathways, bioinformatics analysis tools such as protein-protein interaction (PPI) networks, miRNA-mRNA interaction networks, and immune infiltration in FCD samples were used to fully elucidate the pathogenesis of FCD. A total of 534 differentially expressed genes (DEGs) and 71 differentially expressed miRNAs (DEMs) were obtained. The DEGs obtained were enriched in ribosomal, protein targeting, and pathways of neurodegeneration multiple diseases, whereas the target genes of DEMs were enriched in signaling pathways such as transforming growth factor beta, Wnt, PI3K-Akt, etc. Finally, four hub genes (RPL11, FAU, RPS20, RPL27) and five key miRNAs (hsa-let-7b, hsa-miR-185, hsa-miR-23b, hsa-miR-222 and hsa-miR-92b) were obtained by PPI network, miRNA-mRNA network, and ROC analysis. The immune infiltration results showed that the infiltration levels of five immune cells (MDSC, regulatory T cells, activated CD8⁺ T cells, macrophage and effector memory CD8⁺ T cells) were slightly higher in FCD samples than in control samples. Moreover, the gene expressions of RPS19, RPL19, and RPS24 were highly correlated with the infiltration levels and immune characteristics of 28 immune cells. It broadens the understanding of the molecular mechanisms underlying the development of FCD and enlightens the identification of molecular targets and diagnostic biomarkers for FCD.

A companion to the preclinical common data elements and case report forms for neuropathology studies in epilepsy research. A report of the TASK3 WG2 Neuropathology Working Group of the ILAE/AES Joint Translational Task Force

The International League Against Epilepsy/American Epilepsy Society (ILAE/AES) Joint Translational Task Force initiated the TASK3 working group to create common data elements (CDEs) for various aspects of preclinical epilepsy research studies, which could help improve the standardization of experimental designs. This article addresses neuropathological changes associated with seizures and epilepsy in rodent models of epilepsy. We discuss CDEs for histopathological parameters for neurodegeneration, changes in astrocyte morphology and function, mechanisms of inflammation, and changes in the blood-brain barrier and myelin/oligodendrocytes resulting from recurrent seizures in rats and mice. We provide detailed CDE tables and case report forms (CRFs), and with this companion manuscript, we discuss the rationale and methodological aspects of individual neuropathological examinations. The CDEs, CRFs, and companion paper are available to all researchers, and their use will benefit the harmonization and comparability of translational preclinical epilepsy research. The ultimate hope is to facilitate the development of rational therapy concepts for treating epilepsies, seizures, and comorbidities and the development of biomarkers assessing the pathological state of the disease.

Immunity, Ion Channels and Epilepsy

Epilepsy is a common chronic neurological disorder in modern society. One of the major unmet challenges is that current antiseizure medications are basically not disease-modifying. Among the multifaceted etiologies of epilepsy, the role of the immune system has attracted considerable attention in recent years. It is known that both innate and adaptive immunity can be activated in response to insults to the central nervous system, leading to seizures. Moreover, the interaction between ion channels, which have a well-established role in epileptogenesis and epilepsy, and the immune system is complex and is being actively investigated. Some examples, including the interaction between ion channels and mTOR pathways, will be discussed in this paper. Furthermore, there has been substantial progress in our understanding of the pathophysiology of epilepsy associated with autoimmune encephalitis, and numerous neural-specific autoantibodies have been found and documented. Early recognition of immune-mediated epilepsy is important, especially in cases of pharmacoresistant epilepsy and in the presence of signs of autoimmune encephalitis, as early intervention with immunotherapy shows promise.

Cytokines and Neurodegeneration in Epileptogenesis

Epilepsy is a common brain disorder characterized by a heterogenous etiology. Its main features are recurrent seizures. Despite many clinical studies, about 30% of cases are refractory to treatment. Recent studies suggested the important role of immune-system elements in its pathogenesis. It was suggested that a deregulated inflammatory process may lead to aberrant neural connectivity and the hyperexcitability of the neuronal network. The aim of our study was the analysis of the expression of inflammatory mediators in a mouse model of epilepsy and their impact on the neurodegeneration process located in the brain. We used the KA-induced model of epilepsy in SJL/J mice and performed the analysis of gene expression and protein levels. We observed the upregulation of IL1β and CXCL12 in the early phase of KA-induced epilepsy and elevated levels of CCL5 at a later time point, compared with control animals. The most important result obtained in our study is the elevation of CXCL2 expression at both studied time points and its correlation with the neurodegeneration observed in mouse brain. Increasing experimental and clinical data suggest the influence of peripheral inflammation on epileptogenesis. Thus, studies focused on the molecular markers of neuroinflammation are of great value and may help deepen our knowledge about epilepsy, leading to the discovery of new drugs.

Factors not considered in the study of drug-resistant epilepsy: Drug-resistant epilepsy: assessment of neuroinflammation

More than one‐third of people with epilepsy develop drug‐resistant epilepsy (DRE). Different hypotheses have been proposed to explain the origin of DRE. Accumulating evidence suggests the contribution of neuroinflammation, modifications in the integrity of the blood‐brain barrier (BBB), and altered immune responses in the pathophysiology of DRE. The inflammatory response is mainly due to the increase of cytokines and related molecules; these molecules have neuromodulatory effects that contribute to hyperexcitability in neural networks that cause seizure generation. Some patients with DRE display the presence of autoantibodies in the serum and mainly cerebrospinal fluid. These patients are refractory to the different treatments with standard antiseizure medications (ASMs), and they could be responding well to immunomodulatory therapies. This observation emphasizes that the etiopathogenesis of DRE is involved with immunology responses and associated long‐term events and chronic inflammation processes. Furthermore, multiple studies have shown that functional polymorphisms as risk factors are involved in inflammation processes. Several relevant polymorphisms could be considered risk factors involved in inflammation‐related DRE such as receptor for advanced glycation end products (RAGE) and interleukin 1β (IL‐1β). All these evidences sustained the hypothesis that the chronic inflammation process is associated with the DRE. However, the effect of the chronic inflammation process should be investigated in further clinical studies to promote the development of novel therapeutics useful in treatment of DRE.

A systems-level analysis highlights microglial activation as a modifying factor in common epilepsies

AIMS

The causes of distinct patterns of reduced cortical thickness in the common human epilepsies, detectable on neuroimaging and with important clinical consequences, are unknown. We investigated the underlying mechanisms of cortical thinning using a systems-level analysis.

METHODS

Imaging-based cortical structural maps from a large-scale epilepsy neuroimaging study were overlaid with highly spatially resolved human brain gene expression data from the Allen Human Brain Atlas. Cell-type deconvolution, differential expression analysis and cell-type enrichment analyses were used to identify differences in cell-type distribution. These differences were followed up in post-mortem brain tissue from humans with epilepsy using Iba1 immunolabelling. Furthermore, to investigate a causal effect in cortical thinning, cell-type-specific depletion was used in a murine model of acquired epilepsy.

RESULTS

We identified elevated fractions of microglia and endothelial cells in regions of reduced cortical thickness. Differentially expressed genes showed enrichment for microglial markers and, in particular, activated microglial states. Analysis of post-mortem brain tissue from humans with epilepsy confirmed excess activated microglia. In the murine model, transient depletion of activated microglia during the early phase of the disease development prevented cortical thinning and neuronal cell loss in the temporal cortex. Although the development of chronic seizures was unaffected, the epileptic mice with early depletion of activated microglia did not develop deficits in a non-spatial memory test seen in epileptic mice not depleted of microglia.

CONCLUSIONS

These convergent data strongly implicate activated microglia in cortical thinning, representing a new dimension for concern and disease modification in the epilepsies, potentially distinct from seizure control.

Dendritic Cell-Targeted Therapies to Treat Neurological Disorders

Dendritic cells (DCs) are the immune system's highly specialized antigen-presenting cells. When DCs are sluggish and mature, self-antigen presentation results in tolerance; however, when pathogen-associated molecular patterns stimulate mature DCs, antigen presentation results in the development of antigen-specific immunity. DCs have been identified in various vital organs of mammals (e.g., the skin, heart, lungs, intestines, and spleen), but the brain has long been thought to be devoid of DCs in the absence of neuroinflammation. However, neuroinflammation is becoming more recognized as a factor in a variety of brain illnesses. DCs are present in the brain parenchyma in trace amounts under healthy circumstances, but their numbers rise during neuroinflammation. New therapeutics are being developed that can reduce dendritic cell immunogenicity by inhibiting pro-inflammatory cytokine production and T cell co-stimulatory pathways. Additionally, innovative ways of regulating dendritic cell growth and differentiation and harnessing their tolerogenic capability are being explored. Herein, we described the function of dendritic cells in neurological disorders and discussed the potential for future therapeutic techniques that target dendritic cells and dendritic cell-related targets in the treatment of neurological disorders.

Norwegian population-based study of long-term effects, safety, and predictors of response of vagus nerve stimulation treatment in drug-resistant epilepsy: The NORPulse study

OBJECTIVE

This study was undertaken to evaluate the efficacy of vagus nerve stimulation (VNS) over time, and to determine which patient groups derive the most benefit.

METHODS

Long-term outcomes are reported in 436 epilepsy patients from a VNS quality registry (52.8% adults, 47.2% children), with a median follow-up of 75 months. Patients were stratified according to evolution of response into constant responders, fluctuating responders, and nonresponders. The effect was evaluated at 6, 12, 24, 36, and 60 months. Multivariate regression analysis was used to identify predictors of response.

RESULTS

The cumulative probability of ≥50% seizure reduction was 60%; however, 15% of patients showed a fluctuating course. Of those becoming responders, 89.5% (230/257) did so within 2 years. A steady increase in effect was observed among constant responders, with 48.7% (19/39) of those becoming seizure-free and 29.3% (39/133) with ≥75% seizure reduction achieving these effects within 2-5 years. Some effect (25%-<50%) at 6 months was a positive predictor of becoming a responder (odds ratio [OR] = 10.18, p < .0001) and having ≥75% reduction at 2 years (OR = 3.34, p = .03). Patients without intellectual disability had ORs of 3.34 and 3.11 of having ≥75% reduction at 2 and 5 years, respectively, and an OR of 6.22 of being seizure-free at last observation. Patients with unchanged antiseizure medication over the observation period showed better responder rates at 2 (63.0% vs. 43.1%, p = .002) and 5 years (63.4% vs. 46.3%, p = .031) than patients whose antiseizure medication was modified. Responder rates were higher for posttraumatic (70.6%, p = .048) and poststroke epilepsies (75.0%, p = .05) than other etiologies (46.5%).

SIGNIFICANCE

Our data indicate that the effect of VNS increases over time and that there are important clinical decision points at 6 and 24 months for evaluating and adjusting the treatment. There should be better selection of candidates, as certain patient groups and epilepsy etiologies respond more favorably.

Increased expression of complement components in tuberous sclerosis complex and focal cortical dysplasia type 2B brain lesions

Objective

Increasing evidence supports the contribution of inflammatory mechanisms to the neurological manifestations of epileptogenic developmental pathologies linked to mammalian target of rapamycin (mTOR) pathway dysregulation (mTORopathies), such as tuberous sclerosis complex (TSC) and focal cortical dysplasia (FCD). In this study, we aimed to investigate the expression pattern and cellular distribution of the complement factors C1q and C3 in resected cortical tissue of clinically well‐characterized patients with TSC and FCD2B.

Methods

We applied immunohistochemistry in TSC (n = 29) and FCD2B (n = 32) samples and compared them to autopsy and biopsy controls (n = 27). Furthermore, protein expression was observed via Western blot, and for descriptive colocalization studies immunofluorescence double labeling was performed.

Results

Protein expression for C3 was significantly upregulated in TSC and FCD2B white and gray matter lesions compared to controls. Staining of the synaptic vesicle protein synaptophysin showed a remarkable increase in the white matter of both TSC and FCD2B. Furthermore, confocal imaging revealed colocalization of complement factors with astroglial, microglial, neuronal, and abnormal cells in various patterns.

Significance

Our results demonstrate that the prominent activation of the complement pathway represents a common pathological hallmark of TSC and FCD2B, suggesting that complement overactivation may play a role in these mTORopathies.

The Molecular Dichotomy Between Epileptic and Functional Seizures

Association of Epileptic and Nonepileptic Seizures and Changes in Circulating Plasma Proteins Linked to Neuroinflammation

Gledhill J, Brand E, Pollard J, Clair RS, Wallach T, Crino P. Neurology. 2021;96(10):e1443-e1452. doi:10.1212/WNL.0000000000011552

Objective:

To develop a diagnostic test that stratifies epileptic seizure (ES) from psychogenic nonepileptic seizure (PNES) by developing a multimodal algorithm that integrates plasma concentrations of selected immune response associated proteins and patient clinical risk factors for seizure.

Methods:

Daily blood samples were collected from patients evaluated in the epilepsy monitoring unit (EMU) within 24 hours after EEG confirmed ES or PNES and plasma was isolated. Levels of 51 candidate plasma proteins were quantified using an automated, multiplexed, sandwich ELISA and then integrated and analyzed using our diagnostic algorithm.

Results:

A 51 protein multiplexed ELISA panel was used to determine the plasma concentrations of ES patients, PNES patients, and healthy controls. A combination of protein concentrations, TRAIL, ICAM-1, MCP-2, and TNF-R1 provided a probability that a patient recently experienced a seizure with TRAIL and ICAM-1 higher in PNES than ES, and MCP-2 and TNF-R1 higher in ES than PNES. The diagnostic algorithm yielded an AUC of 0.94 ± 0.07, sensitivity of 82.6% (95% CI: 62.9-93.0), and specificity of 91.6% (95% CI: 74.2-97.7). Further, expanding the diagnostic algorithm to include previously identified PNES risk factors enhanced diagnostic performance with AUC of 0.97 ± 0.05, sensitivity of 91.3% (95% CI: 73.2-97.6), and specificity of 95.8% (95% CI: 79.8-99.3).

Conclusions:

These 4 plasma proteins could provide a rapid, cost-effective, and accurate blood-based diagnostic test to confirm recent ES or PNES.

Classification of Evidence:

This study provides Class III evidence that variable levels of 4 plasma proteins, when analyzed by a diagnostic algorithm, can distinguish PNES from ES with sensitivity of 82.6% and specificity of 91.6%.

HMGB1-RAGE Pathway Contributes to the Abnormal Migration of Endogenous Subventricular Zone Neural Progenitors in an Experimental Model of Focal Microgyria

Abnormal migration of subventricular zone (SVZ)-derived neural progenitor cells (SDNPs) is involved in the pathological and epileptic processes of focal cortical dysplasias (FCDs), but the underlying mechanisms are not clear. Recent studies indicated that high mobility group box 1 (HMGB1)/receptor for advanced glycation end products (RAGE) are widely expressed in epileptic specimens of FCDs, which suggests that the HMGB1-RAGE pathway is involved in the pathological and/or epileptic processes of FCDs. The present study used Nestin-GFP^tg/+ transgenic mice, and we established a model of freezing lesion (FL), as described in our previous report. A "migrating stream" composed of GFP-Nestin⁺ SDNPs was derived from the SVZ region and migrated to the cortical FL area. We found that translocated HMGB1 and RAGE were expressed in cortical lesion in a clustered distribution pattern, which was especially obvious in the early stage of FL compared to the sham group. Notably, the number of GFP-Nestin⁺ SDNPs within the "migrating stream" was significantly decreased when the HMGB1-RAGE pathway was blocked by a RAGE antagonist or deletion of the RAGE gene. The absence of RAGE also decreased the activity of pentylenetetrazol-induced cortical epileptiform discharge. In summary, this study provided experimental evidence that the levels of extranuclear HMGB1 and its receptor RAGE were increased in cortical lesion in the early stage of the FL model. Activation of the HMGB1-RAGE pathway may contribute to the abnormal migration of SDNPs and the hyperexcitability of cortical lesion in the FL model.

Toward a refined genotype-phenotype classification scheme for the international consensus classification of Focal Cortical Dysplasia

Focal Cortical Dysplasia (FCD) is the most common cause of drug-resistant focal epilepsy in children and young adults. The diagnosis of currently defined FCD subtypes relies on a histopathological assessment of surgical brain tissue. The many ongoing challenges in the diagnosis of FCD and their various subtypes mandate, however, continuous research and consensus agreement to develop a reliable classification scheme. Advanced neuroimaging and genetic studies have proven to augment the diagnosis of FCD subtypes and should be considered for an integrated clinico-pathological and molecular classification. In this review, we will discuss the histopathological foundation of the current FCD classification and potential advancements when using genetic analysis of somatic brain mutations in neurosurgically resected brain specimens and postprocessing of presurgical neuroimaging data. Combining clinical, imaging, histopathology, and molecular studies will help to define the disease spectrum better and finally unveil FCD-specific treatment options.

What value can TSPO PET bring for epilepsy treatment?

Epilepsy is one of the most common neurological disorders and affects both the young and adult populations. The question we asked for this review was how positron emission tomography (PET) imaging with translocator protein (TSPO) radioligands can help inform the epilepsy clinic and the development of future treatments targeting neuroinflammatory processes.Even though the first TSPO PET scans in epilepsy patients were performed over 20 years ago, this imaging modality has not seen wide adoption in the clinic. There is vast scientific evidence from preclinical studies in rodent models of temporal lobe epilepsy which have shown increased levels of TSPO corresponding to neuroinflammatory processes in the brain. These increases peaked sub-acutely (1-2 weeks) after the epileptogenic insult (e.g. status epilepticus) and remained chronically increased, albeit at lower levels. In addition, these studies have shown a correlation between TSPO levels and seizure outcome, pharmacoresistance and behavioural morbidities. Histological assessment points to a complex interplay between different cellular components such as microglial activation, astrogliosis and cell death changing dynamically over time.In epilepsy patients, a highly sensitive biomarker of neuroinflammation would provide value for the optimization of surgical assessment (particularly for extratemporal lobe epilepsy) and support the clinical development path of anti-inflammatory treatments. Clinical studies have shown a systematic increase in asymmetry indices of TSPO PET binding. However, region-based analysis typically does not yield statistical differences and changes are often not restricted to the epileptogenic zone, limiting the ability of this imaging modality to localise pathology for surgery. In this manuscript, we discuss the biological underpinnings of these findings and review for which applications in epilepsy TSPO PET could bring added value.

Balloon cells promote immune system activation in focal cortical dysplasia type 2b

Aims

Focal cortical dysplasia (FCD) type 2 is an epileptogenic malformation of the neocortex associated with somatic mutations in the mammalian target of rapamycin (mTOR) pathway. Histopathologically, FCD 2 is subdivided into FCD 2a and FCD 2b, the only discriminator being the presence of balloon cells (BCs) in FCD 2b. While pro‐epileptogenic immune system activation and inflammatory responses are commonly detected in both subtypes, it is unknown what contextual role BCs play.

Methods

The present study employed RNA sequencing of surgically resected brain tissue from FCD 2a (n = 11) and FCD 2b (n = 20) patients compared to autopsy control (n = 9) focusing on three immune system processes: adaptive immunity, innate immunity and cytokine production. This analysis was followed by immunohistochemistry on a clinically well‐characterised FCD 2 cohort.

Results

Differential expression analysis revealed stronger expression of components of innate immunity, adaptive immunity and cytokine production in FCD 2b than in FCD 2a, particularly complement activation and antigen presentation. Immunohistochemical analysis confirmed these findings, with strong expression of leukocyte antigen I and II in FCD 2b as compared to FCD 2a. Moreover, T‐lymphocyte tissue infiltration was elevated in FCD 2b. Expression of markers of immune system activation in FCD 2b was concentrated in subcortical white matter. Lastly, antigen presentation was strongly correlated with BC load in FCD 2b lesions.

Conclusion

We conclude that, next to mutation‐driven mTOR activation and seizure activity, BCs are crucial drivers of inflammation in FCD 2b. Our findings indicate that therapies targeting inflammation may be beneficial in FCD 2b.

An interictal measurement of cerebral oxygen extraction fraction in MRI-negative refractory epilepsy using quantitative susceptibility mapping

PURPOSE

Oxygen extraction fraction (OEF) can be a factor to identify brain tissue's disability in epileptic patients. This study aimed to assess the OEF's level measurement in refractory epileptic patients (REPs) using a quantitative susceptibility mapping (QSM) method and to determine whether the OEF parameters change.

METHODS

QSM-OEF maps of 26 REPs and 16 healthy subjects were acquired using 3T MRI with a 64-channel coil. Eighteen regions-of-interest (ROIs) were chosen around the cortex in one appropriate slice of the brain and the mean QSM-OEF for each ROI was obtained. The correlations of QSM-OEF among different clinical characteristics of the disease, as well as between the patients and normal subjects, were also investigated.

RESULTS

QSM-OEF was shown to be significantly higher in REPs (44.9 ± 5.8) than that in HS (41.9 ± 6.2) (p < 0.05). Mean QSM-OEF was statistically lower in the ipsilateral side (44.5 ± 6.6) compared to the contralateral side (46.4 ± 6.8) (P < 0.01). QSM-OEF was illustrated to have a strong positive correlation with the attack duration (r = 0.6), and a moderate negative correlation with the attack frequency (r = -0.3). Using an optimized support vector machine algorithm, we could predict the disease in subjects having abnormal OEF values in the brain-selected-ROIs with sensitivity, specificity, AUC, and the precision of 0.96, 1, 0.98, and 1, respectively.

CONCLUSIONS

The results of this study revealed that QSM-OEF of the REPs' brain is higher than that of HS, which indicates that QSM-OEF is associated with disease activity.

Links between Immune Cells from the Periphery and the Brain in the Pathogenesis of Epilepsy: A Narrative Review

Accumulating evidence has demonstrated that the pathogenesis of epilepsy is linked to neuroinflammation and cerebrovascular dysfunction. Peripheral immune cell invasion into the brain, along with these responses, is implicitly involved in epilepsy. This review explored the current literature on the association between the peripheral and central nervous systems in the pathogenesis of epilepsy, and highlights novel research directions for therapeutic interventions targeting these reactions. Previous experimental and human studies have demonstrated the activation of the innate and adaptive immune responses in the brain. The time required for monocytes (responsible for innate immunity) and T cells (involved in acquired immunity) to invade the central nervous system after a seizure varies. Moreover, the time between the leakage associated with blood–brain barrier (BBB) failure and the infiltration of these cells varies. This suggests that cell infiltration is not merely a secondary disruptive event associated with BBB failure, but also a non-disruptive event facilitated by various mediators produced by the neurovascular unit consisting of neurons, perivascular astrocytes, microglia, pericytes, and endothelial cells. Moreover, genetic manipulation has enabled the differentiation between peripheral monocytes and resident microglia, which was previously considered difficult. Thus, the evidence suggests that peripheral monocytes may contribute to the pathogenesis of seizures.

Clonally Focused Public and Private T Cells in Resected Brain Tissue From Surgeries to Treat Children With Intractable Seizures

Using a targeted transcriptomics approach, we have analyzed resected brain tissue from a cohort of 53 pediatric epilepsy surgery cases, and have found that there is a spectrum of involvement of both the innate and adaptive immune systems as evidenced by the differential expression of immune-specific genes in the affected brain tissue. The specimens with the highest expression of immune-specific genes were from two Rasmussen encephalitis cases, which is known to be a neuro-immunological disease, but also from tuberous sclerosis complex (TSC), focal cortical dysplasia, and hemimegalencephaly surgery cases. We obtained T cell receptor (TCR) Vβ chain sequence data from brain tissue and blood from patients with the highest levels of T cell transcripts. The clonality indices and the frequency of the top 50 Vβ clonotypes indicated that T cells in the brain were clonally restricted. The top 50 Vβ clonotypes comprised both public and private (patient specific) clonotypes, and the TCR Vβ chain third complementarity region (CDR3) of the most abundant public Vβ clonotype in each brain sample was strikingly similar to a CDR3 that recognizes an immunodominant epitope in either human cytomegalovirus or Epstein Barr virus, or influenza virus A. We found that the frequency of 14 of the top 50 brain Vβ clonotypes from a TSC surgery case had significantly increased in brain tissue removed to control recurrent seizures 11 months after the first surgery. Conversely, we found that the frequency in the blood of 18 of the top 50 brain clonotypes from a second TSC patient, who was seizure free, had significantly decreased 5 months after surgery indicating that T cell clones found in the brain had contracted in the periphery after removal of the brain area associated with seizure activity and inflammation. However, the frequency of a public and a private clonotype significantly increased in the brain after seizures recurred and the patient underwent a second surgery. Combined single cell gene expression and TCR sequencing of brain-infiltrating leukocytes from the second surgery showed that the two clones were CD8 effector T cells, indicating that they are likely to be pathologically relevant.

Identifying cellular signalling molecules in developmental disorders of the brain: Evidence from focal cortical dysplasia and tuberous sclerosis

AIMS

We understand little of the pathogenesis of developmental cortical lesions, because we understand little of the diversity of the cell types that contribute to the diseases or how those cells interact. We tested the hypothesis that cellular diversity and cell-cell interactions play an important role in these disorders by investigating the signalling molecules in the commonest cortical malformations that lead to childhood epilepsy, focal cortical dysplasia (FCD) and tuberous sclerosis (TS).

METHODS

Transcriptional profiling clustered cases into molecularly distinct groups. Using gene expression data, we identified the secretory signalling molecules in FCD/TS and characterised the cell types expressing these molecules. We developed a functional model using organotypic cultures.

RESULTS

We identified 113 up-regulated secretory molecules in FCDIIB/TS. The top 12 differentially expressed genes (DEGs) were validated by immunohistochemistry. This highlighted two molecules, Chitinase 3-like protein 1 (CHI3L1) and C-C motif chemokine ligand 2 (CCL2) (MCP1) that were expressed in a unique population of small cells in close proximity to balloon cells (BC). We then characterised these cells and developed a functional model in organotypic slice cultures. We found that the number of CHI3L1 and CCL2 expressing cells decreased following inhibition of mTOR, the main aberrant signalling pathway in TS and FCD.

CONCLUSIONS

Our findings highlight previously uncharacterised small cell populations in FCD and TS which express specific signalling molecules. These findings indicate a new level of diversity and cellular interactions in cortical malformations and provide a generalisable approach to understanding cell-cell interactions and cellular heterogeneity in developmental neuropathology.

Neuropathological Characterization of a Dravet Syndrome Knock-In Mouse Model Useful for Investigating Cannabinoid Treatments

Dravet syndrome (DS) is an epileptic syndrome caused by mutations in the Scn1a gene encoding the α1 subunit of the sodium channel Nav1.1, which is associated with febrile seizures that progress to severe tonic-clonic seizures and associated comorbidities. Treatment with cannabidiol has been approved to reduce seizures in DS, but it may also be active against these comorbidities. The aim of this study was to validate a new mouse model of DS having lower mortality than previous models, which may serve to further evaluate therapies for the long-term comorbidities. This new model consists of heterozygous conditional knock-in mice carrying a missense mutation (A1783V) in Scn1a gene expressed exclusively in neurons of the CNS (Syn-Cre/Scn1a^WT/A1783V). These mice have been used here to determine the extent and persistence of the behavioral deterioration in different postnatal days (PND), as well as to investigate the alterations that the disease produces in the endocannabinoid system and the contribution of inflammatory events and impaired neurogenesis in the pathology. Syn-Cre/Scn1a^WT/A1783V mice showed a strong reduction in hindlimb grasp reflex at PND10, whereas at PND25, they presented spontaneous convulsions and a greater susceptibility to pentylenetetrazole-induced seizures, marked hyperactivity, deficient spatial working memory, lower levels of anxiety, and altered social interaction behavior. These differences disappeared at PND40 and PND60, except the changes in social interaction and anxiety. The analysis of CNS structures associated with these behavioral alterations revealed an elevated glial reactivity in the prefrontal cortex and the dentate gyrus. This was associated in the dentate gyrus with a greater cell proliferation detected with Ki67 immunostaining, whereas double-labeling analyses identified that proliferating cells were GFAP-positive suggesting failed neurogenesis but astrocyte proliferation. The analysis of the endocannabinoid system of Syn-Cre/Scn1a^WT/A1783V mice confirmed reductions in CB₁ receptors and MAGL and FAAH enzymes, mainly in the cerebellum but also in other areas, whereas CB₂ receptors became upregulated in the hippocampus. In conclusion, Syn-Cre/Scn1a^WT/A1783V mice showed seizuring susceptibility and several comorbidities (hyperactivity, memory impairment, less anxiety, and altered social behavior), which exhibited a pattern of age expression similar to DS patients. Syn-Cre/Scn1a^WT/A1783V mice also exhibited greater glial reactivity and a reactive response in the neurogenic niche, and regional changes in the status of the endocannabinoid signaling, events that could contribute in behavioral impairment.

Tuberous Sclerosis Complex as Disease Model for Investigating mTOR-Related Gliopathy During Epileptogenesis

Tuberous sclerosis complex (TSC) represents the prototypic monogenic disorder of the mammalian target of rapamycin (mTOR) pathway dysregulation. It provides the rational mechanistic basis of a direct link between gene mutation and brain pathology (structural and functional abnormalities) associated with a complex clinical phenotype including epilepsy, autism, and intellectual disability. So far, research conducted in TSC has been largely neuron-oriented. However, the neuropathological hallmarks of TSC and other malformations of cortical development also include major morphological and functional changes in glial cells involving astrocytes, oligodendrocytes, NG2 glia, and microglia. These cells and their interglial crosstalk may offer new insights into the common neurobiological mechanisms underlying epilepsy and the complex cognitive and behavioral comorbidities that are characteristic of the spectrum of mTOR-associated neurodevelopmental disorders. This review will focus on the role of glial dysfunction, the interaction between glia related to mTOR hyperactivity, and its contribution to epileptogenesis in TSC. Moreover, we will discuss how understanding glial abnormalities in TSC might give valuable insight into the pathophysiological mechanisms that could help to develop novel therapeutic approaches for TSC or other pathologies characterized by glial dysfunction and acquired mTOR hyperactivation.

Neuroinflammation in neocortical epilepsy measured by PET imaging of translocator protein

OBJECTIVES

Neuroinflammation, implicated in epilepsy, can be imaged in humans with positron emission tomography (PET) ligands for translocator protein 18 kDa (TSPO). Previous studies in patients with temporal lobe epilepsy and mesial temporal sclerosis found increased [11C]PBR28 uptake ipsilateral to seizure foci. Neocortical foci present more difficult localization problems and more variable underlying pathology.

METHODS

We studied 11 patients with neocortical seizure foci using [11C]PBR28 or [11C] N,N-diethyl-2-(4-methoxyphenyl)-5,7-dimethylpyrazolo[1,5-a]pyrimidine-3-acetamide (DPA) 713, and 31 healthy volunteers. Seizure foci were identified with structural magnetic resonance imaging (MRI) and ictal video-electroencephalography (EEG) monitoring. Six patients had surgical resections; five had focal cortical dysplasia type 2A or B and one microdysgenesis. Brain regions were delineated using FreeSurfer and T1-weighted MRI. We measured brain radioligand uptake (standardized uptake values [SUVs]) in ipsilateral and contralateral regions, to compare calculated asymmetry indices [AIs; 200% *(ipsilateral - contralateral)/(ipsilateral + contralateral)] between epilepsy patients and controls, as well as absolute [11C]PBR28 binding as the ratio of distribution volume to free fraction (V_T /f_P ) in 9 patients (5 high affinity and 4 medium affinity binders) and 11 age-matched volunteers (5 high-affinity and 6 medium affinity) who had metabolite-corrected arterial input functions measured.

RESULTS

Nine of 11 patients had AIs exceeding control mean 95% confidence intervals in at least one region consistent with the seizure focus. Three of the nine had normal MRI. There was a nonsignificant trend for patients to have higher binding than volunteers both ipsilateral and contralateral to the focus in the group that had absolute binding measured.

SIGNIFICANCE

Our study demonstrates the presence of focal and distributed inflammation in neocortical epilepsy. There may be a role for TSPO PET for evaluation of patients with suspected neocortical seizure foci, particularly when other imaging modalities are unrevealing. However, a complex method, inherent variability, and increased binding in regions outside seizure foci will limit applicability.

mTOR Hyperactivity Levels Influence the Severity of Epilepsy and Associated Neuropathology in an Experimental Model of Tuberous Sclerosis Complex and Focal Cortical Dysplasia

Tuberous sclerosis complex (TSC) and focal cortical dysplasia (FCD) are focal malformations of cortical development (FMCDs) that are highly associated with intractable epilepsy. TSC and FCD are mTORopathies caused by a spectrum of pathogenic variants in the mechanistic target of rapamycin (mTOR) pathway genes leading to differential activation of mTOR signaling. However, whether the degree of mTOR hyperactivity influences disease severity remains unclear. Here, we examined the effects of differential mTOR hyperactivity levels on epilepsy and associated neuropathology in a mouse model of TSC and FCD. Constitutively active Rheb (RhebCA), the canonical activator of mTOR complex 1 (mTORC1), was expressed in mouse embryos of either sex via in utero electroporation at low, intermediate, and high concentrations to induce different mTORC1 activity levels in developing cortical neurons. We found that RhebCA expression induced mTORC1 hyperactivation and increased neuronal soma size and misplacement in a dose-dependent manner. No seizures were detected in the low RhebCA mice, whereas the intermediate and high RhebCA mice displayed spontaneous, recurrent seizures that significantly increased with higher RhebCA concentrations. Seizures were associated with a global increase in microglial activation that was notably higher in the regions containing RhebCA-expressing neurons. These data demonstrate that neuronal mTOR hyperactivity levels influence the severity of epilepsy and associated neuropathology in experimental TSC and FCD. Overall, these findings highlight the importance of evaluating the outcome of individual variants on mTOR activity levels and support personalized medicine strategies based on patient variants and mTOR activity level for TSC, FCD, and potentially other mTORopathies.SIGNIFICANCE STATEMENT Tuberous sclerosis complex (TSC) and focal cortical dysplasia (FCD) are epileptogenic cortical malformations caused by pathogenic variants in mechanistic target of rapamycin (mTOR) pathway genes leading to differential mTOR hyperactivation. Here, we present novel findings that neuronal mTOR hyperactivity levels correlate with the severity of epilepsy and associated neuropathology in a mouse model of TSC and FCD. Our findings suggest the need to evaluate the outcome of individual variants on mTOR activity levels in clinical assessments and support personalized medicine strategies based on patient variants and mTOR activity level. Additionally, we present useful modifications to a previously described mouse model of TSC and FCD that allows for titration of seizure frequency and generation of a mild to severe epilepsy phenotype as applicable for preclinical drug testing and mechanistic studies.

Why Malformations of Cortical Development Cause Epilepsy

Malformations of cortical development (MCDs), a complex family of rare disorders, result from alterations of one or combined developmental steps, including progenitors proliferation, neuronal migration and differentiation. They are an important cause of childhood epilepsy and frequently associate cognitive deficits and behavioral alterations. Though the physiopathological mechanisms of epilepsy in MCD patients remain poorly elucidated, research during the past decade highlighted the contribution of some factors that will be reviewed in this paper and that include: (i) the genes that caused the malformation, that can be responsible for a significant reduction of inhibitory cells (e.g., ARX gene) or be inducing cell-autonomous epileptogenic changes in affected neurons (e.g., mutations on the mTOR pathway); (ii) the alteration of cortical networks development induced by the malformation that will also involve adjacent or distal cortical areas apparently sane so that the epileptogenic focus might be more extended that the malformation or even localized at distance from it; (iii) the normal developmental processes that would influence and determine the onset of epilepsy in MCD patients, particularly precocious in most of the cases.

Evidence for Innate and Adaptive Immune Responses in a Cohort of Intractable Pediatric Epilepsy Surgery Patients

Brain-infiltrating lymphocytes (BILs) were isolated from resected brain tissue from 10 pediatric epilepsy patients who had undergone surgery for Hemimegalencephaly (HME) (n = 1), Tuberous sclerosis complex (TSC) (n = 2), Focal cortical dysplasia (FCD) (n = 4), and Rasmussen encephalitis (RE) (n = 3). Peripheral blood mononuclear cells (PBMCs) were also isolated from blood collected at the time of the surgery. Cells were immunostained with a panel of 20 antibody markers, and analyzed by mass cytometry. To identify and quantify the immune cell types in the samples, an unbiased clustering method was applied to the entire data set. More than 85 percent of the CD45+ cells isolated from resected RE brain tissue comprised T cells; by contrast NK cells and myeloid cells constituted 80-95 percent of the CD45+ cells isolated from the TSC and the FCD brain specimens. Three populations of myeloid cells made up >50 percent of all of the myeloid cells in all of the samples of which a population of HLA-DR+ CD11b+ CD4- cells comprised the vast majority of myeloid cells in the BIL fractions from the FCD and TSC cases. CD45RA+ HLA-DR- CD11b+ CD16+ NK cells constituted the major population of NK cells in the blood from all of the cases. This subset also comprised the majority of NK cells in BILs from the resected RE and HME brain tissue, whereas NK cells defined as CD45RA- HLA-DR+ CD11b- CD16- cells comprised 86-96 percent of the NK cells isolated from the FCD and TSC brain tissue. Thirteen different subsets of CD4 and CD8 αβ T cells and γδ T cells accounted for over 80% of the CD3+ T cells in all of the BIL and PBMC samples. At least 90 percent of the T cells in the RE BILs, 80 percent of the T cells in the HME BILs and 40-66 percent in the TSC and FCD BILs comprised activated antigen-experienced (CD45RO+ HLA-DR+ CD69+) T cells. We conclude that even in cases where there is no evidence for an infection or an immune disorder, activated peripheral immune cells may be present in epileptogenic areas of the brain, possibly in response to seizure-driven brain inflammation.

Pharmacological targeting of brain inflammation in epilepsy: Therapeutic perspectives from experimental and clinical studies

Increasing evidence supports a pathogenic role of unabated neuroinflammation in various central nervous system (CNS) diseases, including epilepsy. Neuroinflammation is not a bystander phenomenon of the diseased brain tissue, but it may contribute to neuronal hyperexcitability underlying seizure generation, cell loss, and neurologic comorbidities. Several molecules, which constitute the inflammatory milieu in the epileptogenic area, activate signaling pathways in neurons and glia resulting in pathologic modifications of cell function, which ultimately lead to alterations in synaptic transmission and plasticity. Herein we report the up-to-date experimental and clinical evidence that supports the neuromodulatory role of inflammatory mediators, their related signaling pathways, and involvement in epilepsy. We discuss how these mechanisms can be harnessed to discover and validate targets for novel therapeutics, which may prevent or control pharmacoresistant epilepsies.

Amygdala enlargement in mesial temporal lobe epilepsy: an alternative imaging presentation of limbic epilepsy

PURPOSE

To assess imaging, clinical, and pathological features of mesial temporal lobe epilepsy (mTLE) patients with amygdala enlargement (AE) in comparison with those with mesial temporal sclerosis (MTS).

METHODS

Clinical, imaging, and pathologic features were retrospectively reviewed in 40 mTLE patients with postoperative follow-up (10 with AE and 30 with MTS). The volumes and signal intensity of the amygdala and hippocampus were assessed in 10 AE, 10 age- and sex-matched MTS patients, and 12 controls (HC).

RESULTS

AE patients had a lower rate of concordant FDG PET (p < 0.05) and required more frequently intracerebral electrodes compared to MTS patients (p < 0.05). AE had larger ipsilateral amygdala (p < 0.0001) and hippocampus volumes (p < 0.0001) compared to MTS and to HC, with no significant differences for other brain structures. Normalized FLAIR signal was higher in the ipsilateral than contralateral amygdala in both AE and MTS (p < 0.001 and p < 0.05, respectively) and higher in the ipsilateral amygdala compared to HC (p < 0.05). In MTS, ADC in the ipsilateral amygdala (867 mm²/s) was higher compared to the contralateral one (804.8 × 10^-6 mm²/s, p < 0.01), compared to HC (773 × 10^-6 mm²/s, p < 0.01) and compared to the ipsilateral amygdala in AE (813.7 × 10^-6 mm²/s, p < 0.05). AE patients had dysplasia (50%) or astrocytic gliosis (50%) of the amygdala extending to the hippocampus and temporal isocortex, and only 2/10 cases had pathologic findings of MTS.

CONCLUSION

AE patients have distinct imaging and pathologic features compared to MTS, and require more extensive preoperative workup. Recognition of AE may improve preoperative assessment in TLE surgical candidates.

Activation of the innate immune system is evident throughout epileptogenesis and is associated with blood-brain barrier dysfunction and seizure progression

OBJECTIVE

Because brain inflammation may contribute to the pathophysiology of temporal lobe epilepsy (TLE), we investigated the expression of various inflammatory markers of the innate and adaptive immune system in the epileptogenic human and rat hippocampus in relation to seizure activity and blood-brain barrier (BBB) dysfunction.

METHODS

Immunohistochemistry was performed using various immune cell markers (for microglia, monocytes, macrophages, T lymphocytes, and dendritic cells) on hippocampal sections of drug-resistant TLE patients and patients who died after status epilepticus. The expression of these markers was also studied in the electrical post-status epilepticus rat model for TLE, during the acute, latent, and chronic epileptic phase. BBB dysfunction was assessed using albumin immunohistochemistry and the BBB tracer fluorescein.

RESULTS

Monocyte infiltration, microglia, and perivascular macrophage activation were persistently increased in both epileptogenic human and rat hippocampus, whereas T lymphocytes and dendritic cells were not or were scarcely detected. In addition to this, increased expression of C-C motif ligand 2 (CCL2) and osteopontin was observed. In humans, the expression of CD68 and CCL2 was related to the duration of epilepsy and type of pathology. In rats, the expression of CD68, CCL2, and the perivascular macrophage marker CD163 was related to the duration of the initial insult and to the number of spontaneous seizures. Interestingly, the number of CD163-positive perivascular macrophages was also positively correlated to BBB dysfunction in chronic epileptic rats.

SIGNIFICANCE

These data suggest a proepileptogenic role for monocytes/macrophages and other cells of the innate immune response, possibly via increased BBB leakage, and indicate that T cells and dendritic cells, which are closely associated with the adaptive immune response, are only sparsely infiltrated during epileptogenesis in the electrical post-status epilepticus rat model. Future studies should reveal the relative importance of these immune cells and whether specific manipulation can modify or prevent epileptogenesis.

Neuroinflammatory Nexus of Pediatric Epilepsy

A rapidly growing body of evidence supports the premise that neuroinflammation plays an important role in initiating and sustaining seizures in a range of pediatric epilepsies. Clinical and experimental evidence indicate that neuroinflammation is both an outcome and a contributor to seizures. In this manner, seizures that arise from an initial insult (e.g. infection, trauma, genetic mutation) contribute to an inflammatory response that subsequently promotes recurrent seizures. This cyclical relationship between seizures and neuroinflammation has been described as a 'vicious cycle.' Studies of human tissue resected for surgical treatment of refractory epilepsy have reported activated inflammatory and immune signaling pathways, while animal models have been used to demonstrate that key inflammatory mediators lead to increased seizure susceptibility. Further characterization of the molecular mechanisms involved in this cycle may ultimately enable the development of new therapeutic approaches for the treatment of epilepsy. In this brief review we focus on key inflammatory mediators that have become prominent in recent literature of epilepsy, including newly characterized microRNAs and their potential role in neuroinflammatory signaling.

MTOR pathway in focal cortical dysplasia type 2: What do we know?

Focal cortical dysplasia (FCD) is the most commonly encountered developmental malformation that causes refractory epilepsy. Focal cortical dysplasia type 2 is one of the most usual neuropathological findings in tissues resected therapeutically from patients with drug-resistant epilepsy. Unlike other types of FCD, it is characterized by laminar disorganization and dysplastic neurons, which compromise the organization of the six histologically known layers in the cortex; the morphology and/or cell location can also be altered. A comprehensive review about the pathogenesis of this disease is important because of the necessity to update the results reported over the past years. Here, we present an updated review through Pubmed about the mammalian target of rapamycin (MTOR) pathway in FCD type 2. A wide variety of aspects was covered in 44 articles related to molecular and cellular biology, including experiments in animal and human models. The first publications appeared in 2004, but there is still a lack of studies specifically for one type of FCD. With the advancement of techniques and greater access to molecular and cellular experiments, such as induced pluripotent stem cells (iPSCs) and organoids, it is believed that the trend is increasing the number of publications contributing to the achievement of new discoveries.

Peripherally derived T regulatory and γδ T cells have opposing roles in the pathogenesis of intractable pediatric epilepsy

Xu et al. provide the first study in patients with intractable epilepsy showing a direct correlation between the phenotype, activation state, cytokine profiles, and ability to cause neuronal apoptosis of brain-infiltrating peripherally derived immune cells with seizure severity using an unbiased flow cytometric approach.

The pathophysiology of drug-resistant pediatric epilepsy is unknown. Flow cytometric analysis of inflammatory leukocytes in resected brain tissues from 29 pediatric patients with genetic (focal cortical dysplasia) or acquired (encephalomalacia) epilepsy demonstrated significant brain infiltration of blood-borne inflammatory myeloid cells and memory CD4⁺ and CD8⁺ T cells. Significantly, proinflammatory (IL-17– and GM-CSF–producing) γδ T cells were concentrated in epileptogenic lesions, and their numbers positively correlated with disease severity. Conversely, numbers of regulatory T (T reg) cells inversely correlated with disease severity. Correspondingly, using the kainic acid model of status epilepticus, we show ameliorated seizure activity in both γδ T cell– and IL-17RA–deficient mice and in recipients of T reg cells, whereas T reg cell depletion heightened seizure severity. Moreover, both IL-17 and GM-CSF induced neuronal hyperexcitability in brain slice cultures. These studies support a major pathological role for peripherally derived innate and adaptive proinflammatory immune responses in the pathogenesis of intractable epilepsy and suggest testing of immunomodulatory therapies.

Seizure progression and inflammatory mediators promote pericytosis and pericyte-microglia clustering at the cerebrovasculature

BACKGROUND

Cerebrovascular dysfunction and inflammation occur in epilepsy. Here we asked whether pericytes, a pivotal cellular component of brain capillaries, undergo pathological modifications during experimental epileptogenesis and in human epilepsy. We evaluated whether pro-inflammatory cytokines, present in the brain during seizures, contribute to pericyte morphological modifications.

METHODS

In vivo, unilateral intra-hippocampal kainic acid (KA) injections were performed in NG2DsRed/C57BL6 mice to induce status epilepticus (SE), epileptogenesis, and spontaneous recurrent seizures (SRS). NG2DsRed mice were used to visualize pericytes during seizure progression. The effect triggered by recombinant IL-1β, TNFα, or IL-6 on pericytes was evaluated in NG2DsRed hippocampal slices and in human-derived cell culture. Human brain specimens obtained from temporal lobe epilepsy (TLE) with or without sclerosis (HS) and focal cortical dysplasia (FCD-IIb) were evaluated for pericyte-microglial cerebrovascular assembly.

RESULTS

A disarray of NG2DsRed⁺ pericyte soma and ramifications was found 72 h post-SE and 1 week post-SE (epileptogenesis) in the hippocampus. Pericyte modifications topographically overlapped with IBA1⁺ microglia clustering around the capillaries with cases of pericytes lodged within the microglial cells. Microglial clustering around the NG2DsRed pericytes lingered at SRS. Pericyte proliferation (Ki67⁺) occurred 72 h post-SE and during epileptogenesis and returned towards control levels at SRS. Human epileptic brain tissues showed pericyte-microglia assemblies with IBA1/HLA microglial cells outlining the capillary wall in TLE-HS and FCD-IIb specimens. Inflammatory mediators contributed to pericyte modifications, in particular IL-1β elicited pericyte morphological changes and pericyte-microglia clustering in NG2DsRed hippocampal slices. Modifications also occurred when pro-inflammatory cytokines were added to an in vitro culture of pericytes.

CONCLUSIONS

These results indicate the occurrence of pericytosis during seizures and introduce a pericyte-microglial mediated mechanism of blood-brain barrier dysfunction in epilepsy.