Focal cortical dysplasia II caused by brain somatic mutation of IRS-1 is associated with ERK signaling pathway activation.

Somatic mutations have been identified in 10% to 63% of focal cortical dysplasia type II samples, primarily linked to the mTOR pathway. When the causative genetic mutations are not identified, this opens the possibility of discovering new pathogenic genes or pathways that could be contributing to the condition. In our previous study, we identified a novel candidate pathogenic somatic variant of IRS-1 c.1791dupG in the brain tissue of a child with focal cortical dysplasia type II. This study further explored the variant's role in causing type II focal cortical dysplasia through in vitro overexpression in 293T and SH-SY5Y cells and in vivo evaluation via in utero electroporation in fetal brains, assessing effects on neuronal migration, morphology, and network integrity. It was found that the mutant IRS-1 variant led to hyperactivity of p-ERK, increased cell volume, and was predominantly associated with the MAPK signaling pathway. In vivo, the IRS-1 c.1791dupG variant induced abnormal neuron migration, cytomegaly, and network hyperexcitability. Notably, the ERK inhibitor GDC-0994, rather than the mTOR inhibitor rapamycin, effectively rescued the neuronal defects. This study directly highlighted the ERK signaling pathway's role in the pathogenesis of focal cortical dysplasia II and provided a new therapeutic target for cases of focal cortical dysplasia II that are not treatable by rapamycin analogs.

Spatial omics reveals molecular changes in focal cortical dysplasia type II.

Focal cortical dysplasia (FCD) represents a group of diverse localized cortical lesions that are highly epileptogenic and occur due to abnormal brain development caused by genetic mutations, involving the mammalian target of rapamycin (mTOR). These somatic mutations lead to mosaicism in the affected brain, posing challenges to unravel the direct and indirect functional consequences of these mutations. To comprehensively characterize the impact of mTOR mutations on the brain, we employed here a multimodal approach in a preclinical mouse model of FCD type II (Rheb), focusing on spatial omics techniques to define the proteomic and lipidomic changes. Mass Spectrometry Imaging (MSI) combined with fluorescence imaging and label free proteomics, revealed insight into the brain's lipidome and proteome within the FCD type II affected region in the mouse model. MSI visualized disrupted neuronal migration and differential lipid distribution including a reduction in sulfatides in the FCD type II-affected region, which play a role in brain myelination. MSI-guided laser capture microdissection (LMD) was conducted on FCD type II and control regions, followed by label free proteomics, revealing changes in myelination pathways by oligodendrocytes. Surgical resections of FCD type IIb and postmortem human cortex were analyzed by bulk transcriptomics to unravel the interplay between genetic mutations and molecular changes in FCD type II. Our comparative analysis of protein pathways and enriched Gene Ontology pathways related to myelination in the FCD type II-affected mouse model and human FCD type IIb transcriptomics highlights the animal model's translational value. This dual approach, including mouse model proteomics and human transcriptomics strengthens our understanding of the functional consequences arising from somatic mutations in FCD type II, as well as the identification of pathways that may be used as therapeutic strategies in the future.

Altered expression of the Plexin-B2 system in tuberous sclerosis complex and focal cortical dysplasia IIb lesions.

Tuberous sclerosis complex (TSC) and focal cortical dysplasia (FCD) type IIb are the predominant causes of drug-refractory epilepsy in children. Dysmorphic neurons (DNs), giant cells (GCs), and balloon cells (BCs) are the most typical pathogenic profiles in cortical lesions of TSC and FCD IIb patients. However, mechanisms underlying the pathological processes of TSC and FCD IIb remain obscure. The Plexin-B2-Sema4C signalling pathway plays critical roles in neuronal morphogenesis and corticogenesis during the development of the central nervous system. However, the role of the Plexin-B2 system in the pathogenic process of TSC and FCD IIb has not been identified. In the present study, we investigated the expression and cell distribution characteristics of Plexin-B2 and Sema4C in TSC and FCD IIb lesions with molecular technologies. Our results showed that the mRNA and protein levels of Plexin-B2 expression were significantly increased both in TSC and FCD IIb lesions versus that in the control cortex. Notably, Plexin-B2 was also predominantly observed in GCs in TSC epileptic lesions and BCs in FCD IIb lesions. In contrast, the expression of Sema4C, the ligand of Plexin-B2, was significantly decreased in DNs, GCs, and BCs in TSC and FCD IIb epileptic lesions. Additionally, Plexin-B2 and Sema4C were expressed in astrocytes and microglia cells in TSC and FCD IIb lesions. Furthermore, the expression of Plexin-B2 was positively correlated with seizure frequency in TSC and FCD IIb patients. In conclusion, our results showed the Plexin-B2-Sema4C system was abnormally expressed in cortical lesions of TSC and FCD IIb patients, signifying that the Plexin-B2-Sema4C system may play a role in the pathogenic development of TSC and FCD IIb.

Aberrant adenosine signaling in patients with focal cortical dysplasia.

Focal cortical dysplasia (FCD), a common malformation of cortical development, is frequently associated with pharmacoresistant epilepsy in both children and adults. Adenosine is an inhibitory modulator of brain activity and a prospective anti-seizure agent with potential for clinical translation. Our previous results demonstrated that the major adenosine-metabolizing enzyme adenosine kinase (ADK) was upregulated in balloon cells (BCs) within FCD type IIB lesions, suggesting that dysfunction of the adenosine system is implicated in the pathophysiology of FCD. In our current study, we therefore performed a comprehensive analysis of adenosine signaling in surgically resected cortical specimens from patients with FCD type I and type II via immunohistochemistry and immunoblot analysis. Adenosine enzyme signaling was assessed by quantifying the levels of the key enzymes of adenosine metabolism, i.e., ADK, adenosine deaminase (ADA), and ecto-5'-nucleotidase (CD73). Adenosine receptor signaling was assessed by quantifying the levels of adenosine A2A receptor (A2AR) and putative downstream mediators of adenosine, namely, glutamate transporter-1 (GLT-1) and mammalian target of rapamycin (mTOR). Within lesions in FCD specimens, we found that the adenosine-metabolizing enzymes ADK and ADA, as well as the adenosine-producing enzyme CD73, were upregulated. We also observed an increase in A2AR density, as well as a decrease in GLT-1 levels and an increase in mTOR levels, in FCD specimens compared with control tissue. These results suggest that dysregulation of the adenosine system is a common pathologic feature of both FCD type I and type II. The adenosine system might therefore be a therapeutic target for the treatment of epilepsy associated with FCD.

[Expression of cation chloride cotransporter (NKCC1/KCC2) in brain tissue of children with focal cortical dysplasia type â ¡].

Objective: To investigate the expression of cation chloride cotransporter (NKCC1/KCC2) in the neurons from cerebral lesions of children with focal cortical dysplasia (FCD) type Ⅱ, to provide a morphological basis for revealing the possible mechanism of epilepsy. Methods: Eight cases of FCD type Ⅱ diagnosed at Beijing Haidian Hospital, Beijing, China and 12 cases diagnosed at Xuanwu Hospital, Capital Medical University, Beijing, China from February 2017 to December 2019 were included. The expression of NKCC1 and KCC2 in FCD type Ⅱa and FCD type Ⅱb was detected using immunohistochemistry and double immunohistochemical stains. The average optical density of NKCC1 in dysmorphic neurons and normal neurons was also determined using immunohistochemical staining in FCD type Ⅱa (10 cases). Results: The patients were all younger than 14 years of age. Ten cases were classified as FCD type IIa, and 10 cases as FCD type Ⅱb. NKCC1 was expressed in the cytoplasm of normal cerebral cortex neurons and KCC2 expressed on cell membranes. In dysmorphic neurons of FCD type Ⅱa, expression of NKCC1 increased, which was statistically higher than that of normal neurons (P<0.01). Aberrant expression of KCC2 in dysmorphic neurons was also noted in the cytoplasm. In the FCD Ⅱb type, the expression pattern of NKCC1/KCC2 in dysmorphic neurons was the same as that of FCD type Ⅱa. The aberrant expression of NKCC1 in balloon cells was negative or weakly positive on the cell membrane, while the aberrant expression of KCC2 was absent. Conclusions: The expression pattern of NKCC1/KCC2 in dysmorphic neurons and balloon cells is completely different from that of normal neurons. The NKCC1/KCC2 protein-expression changes may affect the transmembrane chloride flow of neurons, modify the effect of inhibitory neurotransmitters γ-aminobutyric acid and increase neuronal excitability. These effects may be related to the occurrence of clinical epileptic symptoms.

Cortical Dysplasia and the mTOR Pathway: How the Study of Human Brain Tissue Has Led to Insights into Epileptogenesis.

Type II focal cortical dysplasia (FCD) is a neuropathological entity characterised by cortical dyslamination with the presence of dysmorphic neurons only (FCDIIA) or the presence of both dysmorphic neurons and balloon cells (FCDIIB). The year 2021 marks the 50th anniversary of the recognition of FCD as a cause of drug resistant epilepsy, and it is now the most common reason for epilepsy surgery. The causes of FCD remained unknown until relatively recently. The study of resected human FCD tissue using novel genomic technologies has led to remarkable advances in understanding the genetic basis of FCD. Mechanistic parallels have emerged between these non-neoplastic lesions and neoplastic disorders of cell growth and differentiation, especially through perturbations of the mammalian target of rapamycin (mTOR) signalling pathway. This narrative review presents the advances through which the aetiology of FCDII has been elucidated in chronological order, from recognition of an association between FCD and the mTOR pathway to the identification of somatic mosaicism within FCD tissue. We discuss the role of a two-hit mechanism, highlight current challenges and future directions in detecting somatic mosaicism in brain and discuss how knowledge of FCD may inform novel precision treatments of these focal epileptogenic malformations of human cortical development.

Impaired myelin production due to an intrinsic failure of oligodendrocytes in mTORpathies.

AIMS: We aim to evaluate if the myelin pathology observed in epilepsy-associated focal cortical dysplasia type 2B (FCD2B) and-histologically indistinguishable-cortical tubers of tuberous sclerosis complex (TSC) is primarily related to the underlying malformation or constitutes a secondary phenomenon due to the toxic microenvironment created by epileptic seizures. We also aim to investigate the possible beneficial effect of the mTOR pathway regulator everolimus on white matter pathology. METHODS: Primary mixed glial cell cultures derived from epilepsy surgery specimens of one TSC and seven FCD2B patients were grown on polycaprolactone fibre matrices and analysed using immunofluorescence and electron microscopy. Unaffected white matter from three age-matched epilepsy patients with mild malformations of cortical development (mMCD) and one with FCD3D served as controls. Additionally, TSC2 knock-out was performed using an oligodendroglial cell line. Myelination capacities of nanofibre grown cells in an inflammatory environment after mTOR-inhibitor treatment with everolimus were further investigated. RESULTS: Reduced oligodendroglial turnover, directly related to a lower myelin content was found in the patients' primary cells. In our culture model of myelination dynamics, primary cells grown under 'inflammatory condition' showed decreased myelination, that was repaired by treatment with everolimus. CONCLUSIONS: Results obtained in patient-derived primary oligodendroglial and TSC2 knock-out cells suggest that maturation of oligodendroglia and production of a proper myelin sheath seem to be impaired as a result of mTOR pathway disturbance. Hence, oligodendroglial pathology may reflect a more direct effect of the abnormal genetic programme rather than to be an inactive bystander of chronic epilepsy.

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.

Downregulated GPR30 expression in the epileptogenic foci of female patients with focal cortical dysplasia type IIb and tuberous sclerosis complex is correlated with 18 F-FDG PET-CT values.

Focal cortical dysplasia type IIb (FCDIIb) and tuberous sclerosis complex (TSC) are typical causes of developmental delay and refractory epilepsy. G-protein-coupled receptor 30 (GPR30) is a specific estrogen receptor that is critical in neurodevelopment, neuroinflammation, and neuronal excitability, suggesting that it plays a potential role in the epilepsy of patients with FCDIIb and TSC. Therefore, we investigated the role of GPR30 in patients with FCDIIb and TSC. We found that the expression of GPR30 and its downstream protein kinase A (PKA) pathway were decreased and negatively correlated with seizure frequency in female patients with FCDIIb and TSC, but not in male patients. GPR30 was widely distributed in neurons, astrocytes, and microglia, and its downregulation was especially notable in microglia. The GPR30 agonist G-1 increased the expression of PKA and p-PKA in cultured cortical neurons, and the GPR30 antagonist G-15 exhibited the opposite effects of G-1. The NF-κB signaling pathway was also activated in the specimens of female patients with FCDIIb and TSC, and was regulated by G-1 and G-15 in cultured cortical neurons. We also found that GPR30 regulated cortical neuronal excitability by altering the frequency of spontaneous excitatory postsynaptic currents and the expression of NR2A/B. Further, the relationship between GPR30 and glycometabolism was evaluated by analyzing the correlations between GPR30 and 18 F-FDG PET-CT values (standardized uptake values, SUVs). Positive correlations between GPR30 and SUVs were found in female patients, but not in male patients. Intriguingly, GPR30 expression and SUVs were significantly decreased in the epileptogenic tubers of female TSC patients, and ROC curves indicated that SUVs could predict the localization of epileptogenic tubers. Taken together, our results suggest a potential protective effect of GPR30 in the epileptogenesis of female patients with FCDIIb and TSC.

Increased expression of fibroblast growth factor 13 in cortical lesions of the focal cortical dysplasia.

Focal cortical dysplasias (FCDs) are well recognized as important causes of medically intractable epilepsy in both children and adults. To explore the potential role of fibroblast growth factor 13 (FGF13) in intractable epilepsy caused by FCDs, we examined the expression of FGF13 in cortical lesions from 23 patients with FCD type Ia (FCDIa), 24 patients with FCD type IIa (FCDIIa), and 12 patients with FCD type IIb (FCDIIb), and we compared the results with the FGF13 expression levels in control cortex (CTX) brain tissues from 12 nonepileptic normal subjects. Both the mRNA levels and protein levels of FGF13 were significantly higher in the cortical lesions from patients with FCD than in the control cortices. The immunohistochemical results showed that strong FGF13 immunoreactivity was observed in misshapen cells, including neuronal microcolumns, hypertrophic neurons, dysmorphic neurons, and most balloon cells. Moreover, double-label immunofluorescence analyses confirmed that FGF13 was mainly localized in neurons and nearly absent in glia-like cells. Taken together, our results suggest that the overexpression of FGF13 in FCDs and the cell-specific distribution patterns of FGF13 in misshapen neurons in FCDs could potentially contribute to intractable epilepsy caused by FCDs.

mTOR pathway activation in focal cortical dysplasia.

BACKGROUND: Focal cortical dysplasia (FCD) is a localized cortical malformation and considerable morphological overlap exists between FCD IIB and neurological lesions associated with Tuberous sclerosis complex (TSC). Abnormal mTOR pathway secondary to somatic mTOR mutation and TSC gene mutation linked to PI3K/AKT/mTOR pathway have supported the hypothesis of common pathogenesis involved. Role of converging pathway, viz. Wnt/ß-Catenin and mTOR is unknown in FCD. We aimed to analyse FCD IIB for TSC1/TSC2 mutations, immunoreactivity of hamartin, tuberin, mTOR and Wnt signalling cascades, and stem cell markers. MATERIALS AND METHODS: Sixteen FCD IIB cases were retrieved along with 16 FCD IIA cases for comparison. Immunohistochemistry was performed for tuberin, hamartin, mTOR pathway markers, markers of stem cell phenotype, and Wnt pathway markers. Mutation analysis for TSC1 and TSC2 was performed by sequencing in 9 FCD cases. RESULTS: All FCD cases showed preserved hamartin and tuberin immunoreactivity. Aberrant immunoreactivity of phospho-P70S6 kinase, S6 ribosomal, phospho-S6 ribosomal and Stat3 was noted in FCD IIB, with variable phospho-4E-BP1 (45%) and absent phospho-Stat3 expression. Immunoreactivity for phospho-P70S6 kinase (100%), S6 ribosomal protein (100%) and Stat3 (100%) was noted in FCD IIA, but not for phospho-S6 ribosomal, phospho-4E-BP1 and phospho-Stat3. c-Myc immunoreactivity was noted in all FCD cases. Nestin (81%) and Sox 2 (88%) stained balloon cells in FCD IIB (44%), while in FCD IIA cases were negative. All FCD cases were immunopositive for Wnt, but were negative for ß-Catenin and cyclin-D1. TSC mutations were detected in two cases of FCD IIB. CONCLUSION: Abnormal mTOR pathway activation exists in FCD IIB and IIA, however, shows differential immunoreactivity profile, indicating varying degrees of dysregulation. Labelling of neuronal stem cell markers in balloon cells suggests they are phenotypically immature. TSC1/2 mutation play role in the pathogenesis of FCD. Deep targeted sequencing is preferred diagnostic technique since conventional sanger sequencing often fails to detect low-allele frequency variants involved in mTOR/TSC pathway genes, commonly found in FCD.

Phosphorylation of S6 Protein as a Potential Biomarker in Surgically Treated Refractory Epilepsy.

The tuberous sclerosis complex (TSC), focal cortical dysplasia IIB (FCD IIB), and hemimegalencephaly (HME) exhibit similar molecular features that are dependent on the hyperactivation of the mTOR pathway. They are all associated with refractory epilepsy and the need for surgical resection with varying outcomes. The phosphorylated protein S6 (pS6) is a downstream target of mTOR, whose increased expression might indicate mTOR hyperactivation, but which is also present when there is no alteration in the pathway (such as in FCD type I). We have performed immunohistochemical marking and quantification of pS6 in resected brain specimens of 26 patients clinically and histologically diagnosed with TSC, FCD IIB, or HME and compared this data to a control group of 25 patients, to measure the extent of pS6 positivity and its correlation with clinical aspects. Our results suggest that pS6 may serve as a reliable biomarker in epilepsy and that a greater percentage of pS6 marking can relate to more severe forms of mTOR-dependent brain anomalies.

Chronic activation of anti-oxidant pathways and iron accumulation in epileptogenic malformations.

AIMS: Oxidative stress is evident in resected epileptogenic brain tissue of patients with developmental brain malformations related to mammalian target of rapamycin activation: tuberous sclerosis complex (TSC) and focal cortical dysplasia type IIb (FCD IIb). Whether chronic activation of anti-oxidant pathways is beneficial or contributes to pathology is not clear. METHODS: We investigated oxidative stress markers, including haem oxygenase 1, ferritin and the inflammation associated microRNA-155 in surgically resected epileptogenic brain tissue of TSC (n = 10) and FCD IIb (n = 8) patients and in a TSC model (Tsc1GFAP-/- mice) using immunohistochemistry, in situ hybridization, real-time quantitative PCR and immunoblotting. Using human foetal astrocytes we performed an in vitro characterization of the anti-oxidant response to acute and chronic oxidative stress and evaluated overexpression of the disease-relevant pro-inflammatory microRNA-155. RESULTS: Resected TSC or FCD IIb tissue displayed higher expression of oxidative stress markers and microRNA-155. Tsc1GFAP-/- mice expressed more microRNA-155 and haem oxygenase 1 in the brain compared to wild-type, preceding the typical development of spontaneous seizures in these animals. In vitro, chronic microRNA-155 overexpression induced haem oxygenase 1, iron regulatory elements and increased susceptibility to oxidative stress. Overexpression of iron regulatory genes was also detected in patients with TSC, FCD IIb and Tsc1GFAP-/- mice. CONCLUSION: Our results demonstrate that early and sustained activation of anti-oxidant signalling and dysregulation of iron metabolism are a pathological hallmark of FCD IIb and TSC. Our findings suggest novel therapeutic strategies aimed at controlling the pathological link between both processes.

Oligodendrocyte lineage and myelination are compromised in the gray matter of focal cortical dysplasia type IIa.

OBJECTIVES: Focal cortical dysplasias (FCDs) are local malformations of the human neocortex and a leading cause of medically intractable epilepsy. FCDs are characterized by local architectural disturbances of the neocortex and often by a blurred gray-white matter boundary indicating abnormal white matter myelination. We have recently shown that myelination is also compromised in the gray matter of dysplastic areas, since transcripts encoding factors for oligodendrocyte differentiation and myelination are downregulated and myelin fibers appear fractured and disorganized. METHODS: Here, we characterized the gray matter-associated myelination pathology in detail by in situ hybridization, immunohistochemistry, and electron microscopy with markers for myelin, mature oligodendrocytes, and oligodendrocyte precursor cells in tissue sections of FCD IIa and control cortices. In addition, we isolated oligodendrocyte precursor cells from resected dysplastic tissue and performed proliferation assays. RESULTS: We show that the proportion of myelinated gray matter is similar in the dysplastic cortex to that in controls and myelinated fibers extend up to layer III. On the ultrastructural level, however, we found that the myelin sheaths of layer V axons are thinner in dysplastic specimens than in controls. In addition, the density of oligodendrocyte precursor cells and of mature oligodendrocytes was reduced. Finally, we show for the first time that oligodendrocyte precursor cells isolated from resected dysplastic cortex have a reduced proliferation capacity in comparison to controls. SIGNIFICANCE: These results indicate that proliferation and differentiation of oligodendrocyte precursor cells and the formation of myelin sheaths are compromised in FCD and might contribute to the epileptogenicity of this cortical malformation.

Functional screening of GATOR1 complex variants reveals a role for mTORC1 deregulation in FCD and focal epilepsy.

Mutations in the GAP activity toward RAGs 1 (GATOR1) complex genes (DEPDC5, NPRL2 and NPRL3) have been associated with focal epilepsy and focal cortical dysplasia (FCD). GATOR1 functions as an inhibitor of the mTORC1 signalling pathway, indicating that the downstream effects of mTORC1 deregulation underpin the disease. However, the vast majority of putative disease-causing variants have not been functionally assessed for mTORC1 repression activity. Here, we develop a novel in vitro functional assay that enables rapid assessment of GATOR1-gene variants. Surprisingly, of the 17 variants tested, we show that only six showed significantly impaired mTORC1 inhibition. To further investigate variant function in vivo, we generated a conditional Depdc5 mouse which modelled a 'second-hit' mechanism of disease. Generation of Depdc5 null 'clones' in the embryonic brain resulted in mTORC1 hyperactivity and modelled epilepsy and FCD symptoms including large dysmorphic neurons, defective migration and lower seizure thresholds. Using this model, we validated DEPDC5 variant F164del to be loss-of-function. We also show that Q542P is not functionally compromised in vivo, consistent with our in vitro findings. Overall, our data show that mTORC1 deregulation is the central pathological mechanism for GATOR1 variants and also indicates that a significant proportion of putative disease variants are pathologically inert, highlighting the importance of GATOR1 variant functional assessment.

Type IIB focal cortical dysplasia with balloon cells in medial temporal lobe epilepsy: Clinical, neuroimaging, and histopathological findings.

PURPOSE: Type IIB focal cortical dysplasia (FCD) is an important cause of drug-resistant epilepsy. However, balloon cells located in the medial temporal lobe have been seldom reported. We aimed to discuss the clinical and pathological features of Type IIB FCD with balloon cells in the medial temporal lobe (MTLE-FCDIIB) and the differential diagnosis with other types of mesial temporal lobe epilepsy. METHODS: Three MTLE-FCDIIB cases were enrolled from Peking Union Medical College Hospital. Clinical and neuroimaging data were analyzed and histology features observed on hematoxylin-eosin (H&E) staining and immunochemical staining, including vimentin, nestin, S-100, CD34, neuronal nuclei antigen (Neun), glial fibrillary acidic protein (GFAP), neurofilament heavy chain (SMI32), were discussed. RESULTS: All cases involved drug-resistant epilepsy patients with childhood onset. The semiology of the epileptic seizure was a highly frequent partial seizure with or without generalized tonic-clonic seizures. Magnetic resonance imaging showed hyper-intensity in the medial temporal lobe without atrophy, different from mesial temporal sclerosis. Histological examination indicated the presence of balloon cells in the white matter of the para-hippocampal gyrus, subiculum, and cornu ammonis with cortical disorganization, and SMI32 positive dysmorphic neurons in the gray matter. Balloon cells were immunohistochemically stained with vimentin and nestin. Granular cell dispersion and pyramidal cell loss were not found. CONCLUSIONS: The presence of balloon cells in the medial temporal lobe is observed in a rare subgroup of FCD, named MTLE-FCDIIB. It has distinct clinical manifestations, neuroimaging features, pathological changes, and prognosis, which should be differentiated from mesial temporal lobe sclerosis and mesial temporal lobe tumors. Our findings enable more accurate diagnosis of mesial temporal lobe epilepsy.

Activation of leukocyte immunoglobulin-like receptor B2 signaling pathway in cortical lesions of pediatric patients with focal cortical dysplasia type IIb and tuberous sclerosis complex.

BACKGROUNDS: Focal cortical dysplasia type IIb (FCD IIb) and tuberous sclerosis complex (TSC) are very frequently associated with epilepsy in pediatric patients. Human leukocyte immunoglobulin-like receptor B2 (LILRB2) participates in the process of neurite growth, synaptic plasticity, and inflammatory reaction, suggesting a potential role of LILRB2 in epilepsy. However, little is known about the distribution and expression of LILRB2 in cortical lesions of FCD IIb and cortical tubers of TSC. METHODS: In this study, we have described the distribution and expression of LILRB2 signaling pathway in cortical lesions of pediatric patients with FCD IIb (n = 15) and TSC (n = 12) relative to age-matched autopsy control samples (CTX, n = 10), respectively. The protein levels of LILRB2 pathway molecules were assessed by western blotting and immunohistochemistry. The expression pattern was investigated by immunohistochemistry and double labeling experiment. Spearman correlation analysis to explore the correlation between LILRB2 protein level and seizure frequency. RESULTS: The protein levels of LILRB2 and its downstream molecules POSH, SHROOM3, ROCK1, ROCK2 were increased in cortices of patients compared to CTX. Protein levels of LILRB2 negatively correlated with the frequency of seizures in FCD IIb and TSC patients, respectively. Moreover, all LILRB2 pathway molecules were strongly expressed in dysmorphic neurons, balloon cells, and giant cells, LILRB2 co-localized with neuron marker and astrocyte marker. CONCLUSION: Taken together, the special expression patterns of LILRB2 signaling pathway in cortical lesions of FCD IIb and TSC implies that it may be involved in the process of epilepsy.

Complex Patterns of GABAergic Neuronal Deficiency and Type 2 Potassium-Chloride Cotransporter Immaturity in Human Focal Cortical Dysplasia.

Focal cortical dysplasia (FCD) is a common histopathologic finding in cortical specimens resected for refractory epilepsy. GABAergic neuronal abnormalities and K-Cl cotransporter type 2 (KCC2) immaturity may be contributing factors for FCD-related epilepsy. We examined surgical specimens from 12 cases diagnosed with FCD, and brain tissues without developmental abnormality obtained from 6 autopsy cases. We found that GABAergic neuronal density was abnormal in FCD with 2 distinct patterns. In 7 of 12 (58%) FCD subjects, the GABAergic neuron density in dysplastic regions and in neighboring nondysplastic regions was equally reduced, hence we call this a "broad pattern." In the remaining cases, GABAergic neuron density was decreased in dysplastic regions but not in the neighboring nondysplastic regions; we designate this "restricted pattern." The different patterns are not associated with pathologic subtypes of FCD. Intracytoplasmic retention of KCC2 is evident in dysmorphic neurons in the majority of FCD type II subjects (5/7) but not in FCD type I. Our study suggests that (1) "broad" GABAergic deficiency may reflect epileptic vulnerability outside the dysplastic area; and (2) abnormal distribution of KCC2 may contribute to seizure generation in patients with FCD type II but not in type I.

Migration and Synaptic Aspects of Neurons Derived from Human Induced Pluripotent Stem Cells from Patients with Focal Cortical Dysplasia II.

Malformations of cortical development (MCDs) include many different Central Nervous System (CNS) disorders related to a complex process of cortex formation. In children with refractory epilepsy to drug treatment undergoing surgery, focal cortical dysplasia (FCD), one of the MCDs, is considered the most common structural brain lesion found. This study aimed to study the possible alterations in neural differentiation process of human induced pluripotent stem cells (hiPSCs) related to migration and synaptic aspects from fibroblasts of two individuals affected by FCD type IIb (45-year-old male and 12-year-old female) and normal individuals. At the days 14th, 22nd and 35th, hiPSCs were neural differentiated and analyzed. Using qRT-PCR approach, the expression of 9 genes associated with synaptic and neural migration were quantified. Diagnostic of both patients was consistent with FCD type IIb. Our results showed that in all processes and groups, individuals with dysplasia presented alterations in most part of the genes in relation to control individuals. According to our results, it is suggested that the different expressions are mainly involved in alterations of the expression of receptors and capture sites, timing, coupling of synaptic vesicles with the presynaptic membrane, regulation of ion channel and synaptic exocytosis, imbalance of the apoptosis process and abnormal microtubules that may also contribute to delays in synaptogenesis. Thus, brain formation with dysplasia is probably influenced by these genes studied.

Genome-wide DNA Methylation and RNAseq Analyses Identify Aberrant Signalling Pathways in Focal Cortical Dysplasia (FCD) Type II.

Focal cortical dysplasia (FCD) is one of the most common pathologies associated with drug-resistant epilepsy (DRE). The pharmacological targets remain obscured, as the molecular mechanisms underlying FCD are unclear. Implications of epigenetically modulated aberrant gene expression in disease progression are reported in various DRE pathologies except FCD. Here we performed genome-wide CpG-DNA methylation profiling by methylated DNA immunoprecipitation (MeDIP) microarray and RNA sequencing (RNAseq) on cortical tissues resected from FCD type II patients. A total of 19088 sites showed altered DNA methylation in all the CpG islands. Of these, 5725 sites were present in the promoter regions, of which 176 genes showed an inverse correlation between methylation and gene expression. Many of these 176 genes were found to belong to a cohesive network of physically interacting proteins linked to several cellular functions. Pathway analysis revealed significant enrichment of receptor tyrosine kinases (RTK), EGFR, PDGFRA, NTRK3, and mTOR signalling pathways. This is the first study that investigates the epigenetic signature associated with FCD type II pathology. The candidate genes and pathways identified in this study may play a crucial role in the regulation of the pathogenic mechanisms of epileptogenesis associated with FCD type II pathologies.