Cerebrovascular remodeling and epilepsy

Kv7 channel activation reduces brain endothelial cell permeability and prevents kainic acid-induced blood-brain barrier damage

Ion channels in the blood-brain barrier (BBB) play a main role in controlling the interstitial fluid composition and cerebral blood flow, and their dysfunction contributes to the disruption of the BBB occurring in many neurological diseases such as epilepsy. In this study, using morphological and functional approaches, we evaluated the expression and role in the BBB of Kv7 channels, a family of voltage-gated potassium channels including five members (Kv7.1-5) that play a major role in the regulation of cell excitability and transmembrane flux of potassium ions. Immunofluorescence experiments showed that Kv7.1, Kv7.4, and Kv7.5 were expressed in rat brain microvessels (BMVs), as well as brain primary- and clonal (BEND-3) endothelial cells (ECs). Kv7.5 localized at the cell-to-cell junction sites, whereas Kv7.4 was also found in pericytes. The Kv7 activator retigabine increased transendothelial electrical resistance (TEER) in both primary ECs and BEND-3 cells; moreover, retigabine reduced paracellular dextran flux in BEND-3 cells. These effects were prevented by the selective Kv7 blocker XE-991. Exposure to retigabine also hyperpolarized cell membrane and increased tight junctions (TJs) integrity in BEND-3 cells. BMVs from rats treated with kainic acid (KA) showed a disruption of TJs and a selective reduction of Kv7.5 expression. In BEND-3 cells, retigabine prevented the increase of cell permeability and the reduction of TJs integrity induced by KA. Overall, these findings demonstrate that Kv7 channels are expressed in the BBB, where they modulate barrier properties both in physiological and pathological conditions.NEW & NOTEWORTHY This study describes for the first time the expression and the functional role of Kv7 potassium channels in the blood-brain barrier. We show that the opening of Kv7 channels reduces endothelial cell permeability both in physiological and pathological conditions via the hyperpolarization of cell membrane and the sealing of tight junctions. Therefore, activation of endothelial Kv7 channels might be a useful strategy to treat epilepsy and other neurological disorders characterized by blood-brain barrier dysfunction.

Evidence Implicating Blood-Brain Barrier Impairment in the Pathogenesis of Acquired Epilepsy following Acute Organophosphate Intoxication

Organophosphate (OP) poisoning can trigger cholinergic crisis, a life-threatening toxidrome that includes seizures and status epilepticus. These acute toxic responses are associated with persistent neuroinflammation and spontaneous recurrent seizures (SRS), also known as acquired epilepsy. Blood-brain barrier (BBB) impairment has recently been proposed as a pathogenic mechanism linking acute OP intoxication to chronic adverse neurologic outcomes. In this review, we briefly describe the cellular and molecular components of the BBB, review evidence of altered BBB integrity following acute OP intoxication, and discuss potential mechanisms by which acute OP intoxication may promote BBB dysfunction. We highlight the complex interplay between neuroinflammation and BBB dysfunction that suggests a positive feedforward interaction. Lastly, we examine research from diverse models and disease states that suggest mechanisms by which loss of BBB integrity may contribute to epileptogenic processes. Collectively, the literature identifies BBB impairment as a convergent mechanism of neurologic disease and justifies further mechanistic research into how acute OP intoxication causes BBB impairment and its role in the pathogenesis of SRS and potentially other long-term neurologic sequelae. Such research is critical for evaluating BBB stabilization as a neuroprotective strategy for mitigating OP-induced epilepsy and possibly seizure disorders of other etiologies. SIGNIFICANCE STATEMENT: Clinical and preclinical studies support a link between blood-brain barrier (BBB) dysfunction and epileptogenesis; however, a causal relationship has been difficult to prove. Mechanistic studies to delineate relationships between BBB dysfunction and epilepsy may provide novel insights into BBB stabilization as a neuroprotective strategy for mitigating epilepsy resulting from acute organophosphate (OP) intoxication and non-OP causes and potentially other adverse neurological conditions associated with acute OP intoxication, such as cognitive impairment.

Brain vascularization in deep brain stimulation surgeries: epilepsy, Parkinson's disease, and obsessive-compulsive disorder

BACKGROUND

In our experience, we encountered more blood vessels during deep brain stimulation (DBS) surgeries in epilepsy. In this study, we have quantified and compared the cerebral vascularization in epilepsy, Parkinson's disease (PD) and obsessive-compulsive disorder (OCD).

METHODS

A retrospective observational study in 15 epilepsy and 15 PD patients was performed. The amount, location, and size of blood vessels within 5 millimeters (mm) of all DBS electrode trajectories (N.=120) for both targets (anterior nucleus of the thalamus: ANT and subthalamic nucleus: STN) in both patient groups were quantified and compared on a Medtronic workstation (Dublin, Ireland). Additionally, blood vessels in the trajectories (N.=120) of another group of 15 PD (STN) and 15 OCD (ventral capsule-ventral striatum [VC-VS]) patients were quantified and compared (trajectories N.=120), also to the first group. Statistical analyses were performed with SPSS version 27.0 (descriptive statistics, independent samples t-tests, Mann Whitney U Test, ANOVA Test and post-hoc Tukey Test). A P value <0.05 was considered statistically significant.

RESULTS

Our results showed a significant greater amount of cerebral blood vessels in epilepsy patients (10 SD±4) compared to PD (PD1 6 SD±1 and PD2 5 SD±3) and OCD (5 SD±1) with P<0.0001. Also, all other subanalyses showed more vascularization in the epilepsy group.

CONCLUSIONS

Our results show that the brain of epilepsy patients seems to be more vascularized compared to PD and OCD patients. This can make the surgical planning for DBS more challenging, and the use of multiple trajectories limited.

Combined transcriptomics and proteomics forecast analysis for potential biomarker in the acute phase of temporal lobe epilepsy

Background

Temporal lobe epilepsy (TLE) is a common chronic episodic illness of the nervous system. However, the precise mechanisms of dysfunction and diagnostic biomarkers in the acute phase of TLE are uncertain and hard to diagnose. Thus, we intended to qualify potential biomarkers in the acute phase of TLE for clinical diagnostics and therapeutic purposes.

Methods

An intra-hippocampal injection of kainic acid was used to induce an epileptic model in mice. First, with a TMT/iTRAQ quantitative labeling proteomics approach, we screened for differentially expressed proteins (DEPs) in the acute phase of TLE. Then, differentially expressed genes (DEGs) in the acute phase of TLE were identified by linear modeling on microarray data (limma) and weighted gene co-expression network analysis (WGCNA) using the publicly available microarray dataset GSE88992. Co-expressed genes (proteins) in the acute phase of TLE were identified by overlap analysis of DEPs and DEGs. The least absolute shrinkage and selection operator (LASSO) regression and support vector machine recursive feature elimination (SVM-RFE) algorithms were used to screen Hub genes in the acute phase of TLE, and logistic regression algorithms were applied to develop a novel diagnostic model for the acute phase of TLE, and the sensitivity of the diagnostic model was validated using receiver operating characteristic (ROC) curves.

Results

We screened a total of 10 co-expressed genes (proteins) from TLE-associated DEGs and DEPs utilizing proteomic and transcriptome analysis. LASSO and SVM-RFE algorithms for machine learning were applied to identify three Hub genes: Ctla2a, Hapln2, and Pecam1. A logistic regression algorithm was applied to establish and validate a novel diagnostic model for the acute phase of TLE based on three Hub genes in the publicly accessible datasets GSE88992, GSE49030, and GSE79129.

Conclusion

Our study establishes a reliable model for screening and diagnosing the acute phase of TLE that provides a theoretical basis for adding diagnostic biomarkers for TLE acute phase genes.

From neurons to the neuro-glio-vascular unit: Seizures and brain homeostasis in networks

While seizures are undoubtedly neuronal events, an ensemble of auxiliary brain cells profoundly shapes synaptic transmission in health and disease conditions. Endothelial-astrocyte-pericyte assemblies at the blood-brain barrier (BBB) and neuroglia within the neuro-glio-vascular unit (NGVU) finely tune brain parenchymal homeostasis, safeguarding the ionic and molecular compositions of the interstitial fluid. BBB permeability with neuroinflammation and the resulting loss of brain homeostatic control are unifying mechanisms sustaining aberrant neuronal discharges, with temporal specificities linked to acute (head trauma, stroke, infections) and pre-existent (genetic) or chronic ( dysplasia, tumors, neurodegenerative disorders) pathological conditions. Within this research template, one hypothesis is that the topography of BBB damage and neuroinflammation could associate with symptoms, e.g., limbic structures for seizures or pre-frontal for psychiatric episodes. Another uncharted matter is whether seizure activity, without tissue lesions or sclerosis, is sufficient to promote stable cellular-level maladaptations in networks. Contingent to localization and duration, BBB damage and inflammation forecast pathological trajectories, and the concept of an epileptic NGVU could enable time-sensitive biomarkers to predict disease progression. The coherence between electrographic, imaging and molecular NGVU biomarkers could be established from the epileptogenic to the propagating zones. This paradigm shift could lead to new diagnostic and therapeutic modalities germane to specific epilepsies or when seizure activity represents a comorbidity.

Effects of leptin treatment immediately after neonatal seizures on serum clusterin and VEGF levels and brain oxidative stress-related proteins and neurobehavioral phenotypes

The developing infant brain has a different response mechanism and repair potential for injury than the adult brain. There is an urgent need for new anticonvulsants to effectively control neonatal seizures while minimizing the drug's toxic damage to the developing brain. Leptin protects neuronal plasma membrane integrity, while it has clinical advantages in terms of anticonvulsant properties as well. This study aimed to evaluate the effect of immediate leptin treatment on the serum concentration of clusterin and vascular endothelial growth factor (VEGF), neuronal plasma membrane integrity-related proteins, and the neurobehavioral phenotypes following neonatal seizures. Leptin was injected i.p at a dose of 4 mg/kg 1 hour after daily 30 minutes prolonged seizures for consecutive 10 days. The serum biomarkers (clusterin and VEGF), and brain protein expression of ATF-4/GRP78/autophagy axis were measured by enzyme-linked immunosorbent assay and western blot in the acute phase (24 hours after the last seizures), respectively. Behavioral and histopathological phenotypes and seizure threshold were conducted from P23 to P34, respectively. There were rapid elevation of serum VEGF and clusterin as well as upregulated protein expression of ATF-4, GRP78, Beclin-1, and LC3 in the cerebral cortex and hippocampus following a neonatal seizure, which was restored by immediate treatment with leptin after seizures. In addition, leptin improved seizure-induced impaired neuropsychological, and cognitive functioning. Furthermore, leptin succeeded in ameliorating markers of neuronal excitability, including seizure threshold and hippocampal mossy fiber sprouting. In conclusion, this study verified that immediate treatment with leptin after neonatal seizures restored both rapid elevation of serum clusterin as well as upregulated protein expression of ATF-4/GRP78/autophagy axis in the cerebral cortex and hippocampus, which contributes to the recovery of neurological function.

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.

Late-Onset Focal Epilepsy: Electroclinical Features and Prognostic Role of Leukoaraiosis

The aim of this study was to describe the electroclinical and prognostic characteristics, and to investigate the role of leukoaraiosis in outpatients with new-onset elderly focal epilepsy aged ≥60 years, referred to a tertiary epilepsy center between 2005 and December 31, 2020. Among the 720 patients who were referred to the center, we retrospectively selected 162 consecutive outpatients, with a first referral for recent-onset focal epilepsy of unknown cause (UC) or structural cause (SC), and collected a clinical and standard-Electroencephalogram (S-EEG), 24-h ambulatory EEG (A-EEG), and neuroimaging data. We also analyzed the seizure prognosis after titration of the first antiseizure medication (ASM). One hundred and four UC and 58 SC patients, followed up for 5.8 ± 5.3 years (mean ± SD), were included. Compared with the SC group, the patients with UC showed a predominance of focal seizures with impaired awareness (51.9% of cases) and focal to bilateral tonic-clonic seizures during sleep (25%); conversely, the SC group, more frequently, had focal to bilateral tonic-clonic seizures during wakefulness (39.6%) and focal aware seizures (25.8%) (p < 0.0001). Oral or gestural automatisms were prevalent in UC epilepsy (20.2 vs. 6.9% in the SC group, p = 0.04). In UC compared to patients with SC, interictal epileptiform discharges showed a preferential temporal lobe localization (p = 0.0007), low expression on S-EEG, and marked activation during deep Non-Rapid Eye Movement (NREM) sleep (p = 0.003). An overall good treatment response was found in the whole sample, with a probability of seizure freedom of 68.9% for 1 year. The cumulative probability of seizure freedom was significantly higher in the UC compared with the SC group (p < 0.0001). The prognosis was worsened by leukoaraiosis (p = 0.012). In the late-onset focal epilepsy of unknown cause, electroclinical findings suggest a temporal lobe origin of the seizures. This group showed a better prognosis compared with the patients with structural epilepsy. Leukoaraiosis, per se, negatively impacted on seizure prognosis.

Role of NDEL1 and VEGF/VEGFR-2 in Mouse Hippocampus After Status Epilepticus

Nuclear-distribution element-like 1 (NDEL1) is associated with the proliferation and migration of neurons. Vascular endothelial growth factor (VEGF) in combination with VEGF receptor-2 (VEGFR-2) regulates the proliferation and migration of neurons. This study was performed to explore undefined alterations in the expression levels of NDEL1 and VEGF/VEGFR-2 within the hippocampus after status epilepticus (SE). Following the creation of pilocarpine-induced epilepsy models using adolescent male C57BL/6 mice, Western blotting and reverse transcription quantitative polymerase chain reaction were applied to assess the levels of NDEL1, VEGF, and VEGFR-2 expression in whole hippocampi at 1, 2, 3, and 4 weeks post-SE, respectively. Immunofluorescent labeling was also employed to detect the colocalization of NDEL1 and VEGF in the hippocampus. Our results indicated that NDEL1 and VEGF have similar patterns of upregulation throughout the hippocampus. Upregulation of VEGFR-2 occurred only in the early stages, and the expression decreased shortly afterward. NDEL1 and VEGF were coexpressed in the cornu ammonis 3 pyramidal cell, granular, and polymorph layers of the dentate gyrus in the hippocampus. This study revealed that NDEL1, VEGF, and VEGFR-2 may work together and are involved in the pathophysiology in the hippocampus after SE.

Getting Excited Through Cyclin: A Role for Endothelial Cdk5 Signaling in Hippocampal Hyperexcitability

Endothelial Cdk5 Deficit Leads to the Development of Spontaneous Epilepsy Through CXCL1/CXCR2-Mediated Reactive Astrogliosis

Liu XX, Yang L, Shao LX, et al. J Exp Med. 2020;217(1):e20180992. DOI: 10.1084/jem.20180992

Blood–brain barrier dysfunction has been suggested to play an important role in epilepsy. However, the mechanism mediating the transition from cerebrovascular damage to epilepsy remains unknown. Here, we report that endothelial cyclin-dependent kinase 5 is a central regulator of neuronal excitability. Endothelial-specific Cdk5 knockout led to spontaneous seizures in mice. Knockout mice showed increased endothelial chemokine (C-X-C motif) ligand 1 (Cxcl1) expression, decreased astrocytic glutamate reuptake through the glutamate transporter 1 (GLT1), and increased glutamate synaptic function. Ceftriaxone restored astrocytic GLT1 function and inhibited seizures in endothelial Cdk5-deficient mice, and these effects were also reversed after silencing Cxcl1 in endothelial cells and its receptor chemokine (C-X-C motif) receptor 2 (Cxcr2) in astrocytes, respectively, in the CA1 by AAV transfection. These results reveal a previously unknown link between cerebrovascular factors and epileptogenesis and provide a rationale for targeting endothelial signaling as a potential treatment for epilepsy.¹

Hippocampal CA3 transcriptional modules associated with granule cell alterations and cognitive impairment in refractory mesial temporal lobe epilepsy patients

In about a third of the patients with epilepsy the seizures are not drug-controlled. The current limitation of the antiepileptic drug therapy derives from an insufficient understanding of epilepsy pathophysiology. In order to overcome this situation, it is necessary to consider epilepsy as a disturbed network of interactions, instead of just looking for changes in single molecular components. Here, we studied CA3 transcriptional signatures and dentate gyrus histopathologic alterations in hippocampal explants surgically obtained from 57 RMTLE patients submitted to corticoamygdalohippocampectomy. By adopting a systems biology approach, integrating clinical, histopathological, and transcriptomic data (weighted gene co-expression network analysis), we were able to identify transcriptional modules highly correlated with age of disease onset, cognitive dysfunctions, and granule cell alterations. The enrichment analysis of transcriptional modules and the functional characterization of the highly connected genes in each trait-correlated module allowed us to unveil the modules’ main biological functions, paving the way for further investigations on their roles in RMTLE pathophysiology. Moreover, we found 15 genes with high gene significance values which have the potential to become novel biomarkers and/or therapeutic targets in RMTLE.

Seizure-Induced Acute Glial Activation in the in vitro Isolated Guinea Pig Brain

Introduction: It has been proposed that seizures induce IL-1β biosynthesis in astrocytes and increase blood brain barrier (BBB) permeability, even without the presence of blood borne inflammatory molecules and leukocytes. In the present study we investigate if seizures induce morphological changes typically observed in activated glial cells. Moreover, we will test if serum albumin extravasation into the brain parenchyma exacerbates neuronal hyperexcitability by inducing astrocytic and microglial activation.

Methods: Epileptiform seizure-like events (SLEs) were induced in limbic regions by arterial perfusion of bicuculline methiodide (BMI; 50 μM) in the in vitro isolated guinea pig brain preparation. Field potentials were recorded in both the hippocampal CA1 region and the medial entorhinal cortex. BBB permeability changes were assessed by analyzing extravasation of arterially perfused fluorescein isothiocyanate (FITC)–albumin. Morphological changes in astrocytes and microglia were evaluated with tridimensional reconstruction and Sholl analysis in the ventral CA1 area of the hippocampus following application of BMI with or without co-perfusion of human serum albumin.

Results: BMI-induced SLE promoted morphological changes of both astrocytes and microglia cells into an activated phenotype, confirmed by the quantification of the number and length of their processes. Human-recombinant albumin extravasation, due to SLE-induced BBB impairment, worsened both SLE duration and the activated glia phenotype.

Discussion: Our study provides the first direct evidence that SLE activity per se is able to promote the activation of astro- and microglial cells, as observed by their changes in phenotype, in brain regions involved in seizure generation; we also hypothesize that gliosis, significantly intensified by h-recombinant albumin extravasation from the bloodstream to the brain parenchyma due to SLE-induced BBB disruption, is responsible for seizure activity reinforcement.

Drug-Resistant Temporal Lobe Epilepsy Alters the Expression and Functional Coupling to Gαi/o Proteins of CB1 and CB2 Receptors in the Microvasculature of the Human Brain

Cannabinoid receptors 1 and 2 (CB1 and CB2, respectively) play an important role in maintaining the integrity of the blood–brain barrier (BBB). On the other hand, BBB dysfunction is a common feature in drug-resistant epilepsy. The focus of the present study was to characterize protein expression levels and Gαi/o protein-induced activation by CB1 and CB2 receptors in the microvascular endothelial cells (MECs) isolated from the brain of patients with drug-resistant mesial temporal lobe epilepsy (DR-MTLE). MECs were isolated from the hippocampus and temporal neocortex of 12 patients with DR-MTLE and 12 non-epileptic autopsies. Immunofluorescence experiments were carried out to determine the localization of CB1 and CB2 receptors in the different cell elements of MECs. Protein expression levels of CB1 and CB2 receptors were determined by Western blot experiments. [³⁵S]-GTPγS binding assay was used to evaluate the Gαi/o protein activation induced by specific agonists. Immunofluorescent double-labeling showed that CB1 and CB2 receptors colocalize with tight junction proteins (claudin-5, occludin, and zonula occludens-1), glial fibrillary acidic protein and platelet-derived growth factor receptor-β. These results support that CB1 and CB2 receptors are expressed in the human isolated microvessels fragments consisting of MECs, astrocyte end feet, and pericytes. The hippocampal microvasculature of patients with DR-MTLE presented lower protein expression of CB1 and CB2 receptors (66 and 43%, respectively; p < 0.001). However, its Gαi/o protein activation was with high efficiency (CB1, 251%, p < 0.0008; CB2, 255%, p < 0.0001). Microvasculature of temporal neocortex presented protein overexpression of CB1 and CB2 receptors (35 and 41%, respectively; p < 0.01). Their coupled Gαi/o protein activation was with higher efficiency for CB1 receptors (103%, p < 0.006), but lower potency (p < 0.004) for CB2 receptors. The present study revealed opposite changes in the protein expression of CB1 and CB2 receptors when hippocampus (diminished expression of CB1 and CB2) and temporal neocortex (increased expression of CB1 and CB2) were compared. However, the exposure to specific CB1 and CB2 agonists results in high efficiency for activation of coupled Gαi/o proteins in the brain microvasculature of patients with DR-MTLE. CB1 and CB2 receptors with high efficiency could represent a therapeutic target to maintain the integrity of the BBB in patients with DR-MTLE.

Astrocytes as Guardians of Neuronal Excitability: Mechanisms Underlying Epileptogenesis

Astrocytes are key homeostatic regulators in the central nervous system and play important roles in physiology. After brain damage caused by e.g., status epilepticus, traumatic brain injury, or stroke, astrocytes may adopt a reactive phenotype. This process of reactive astrogliosis is important to restore brain homeostasis. However, persistent reactive astrogliosis can be detrimental for the brain and contributes to the development of epilepsy. In this review, we will focus on physiological functions of astrocytes in the normal brain as well as pathophysiological functions in the epileptogenic brain, with a focus on acquired epilepsy. We will discuss the role of astrocyte-related processes in epileptogenesis, including reactive astrogliosis, disturbances in energy supply and metabolism, gliotransmission, and extracellular ion concentrations, as well as blood-brain barrier dysfunction and dysregulation of blood flow. Since dysfunction of astrocytes can contribute to epilepsy, we will also discuss their role as potential targets for new therapeutic strategies.

Neuroprotective and Neurorestorative Effects of Epo and VEGF: Perspectives for New Therapeutic Approaches to Neurological Diseases

BACKGROUND

Erythropoietin (Epo) and vascular endothelial growth factor (VEGF) are two vasoactive molecules with essential trophic effects for brain development. The expression and secretion of both molecules increase in response to neuronal damage and they exert protective and restorative effects, which may also be accompanied by adverse side effects.

OBJECTIVE

We review the most relevant evidence on the neuroprotective and neurorestorative effects of Epo and VEGF in three of the most frequent neurological disorders, namely, stroke, epilepsy and Alzheimer's disease, to develop new therapeutic approaches.

METHODS

Several original scientific manuscripts and reviews that have discussed the evidence in critical way, considering both the beneficial and adverse effects of Epo and VEGF in the selected neurological disorders, were analysed. In addition, throughout this review, we propose several considerations to take into account in the design of therapeutic approaches based on Epo and VEGF signalling.

RESULTS

Although the three selected disorders are triggered by different mechanisms, they evolve through similar processes: excitotoxicity, oxidative stress, neuroinflammation, neuronal death, glial reactivity and vascular remodelling. Epo and VEGF exert neuroprotective and neurorestorative effects by acting on these processes due to their pleiotropism. In general, the evidence shows that both Epo and VEGF reduce neuronal death but that at the vascular level, their effects are contradictory.

CONCLUSION

Because the Epo and VEGF signalling pathways are connected in several ways, we conclude that more experimental studies, primarily studies designed to thoroughly assess the functional interactions between Epo and VEGF in the brain under both physiological and pathophysiological conditions, are needed.

Effects of febrile seizures in mesial temporal lobe epilepsy with hippocampal sclerosis on gene expression using bioinformatical analysis

Background

To investigate the effect of long-term febrile convulsions on gene expression in mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) and explore the molecular mechanism of MTLE-HS.

Methods

Microarray data of MTLE-HS were obtained from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) between MTLE-HS with and without febrile seizure history were screened by the GEO2R software. Pathway enrichment and gene ontology of the DEGs were analyzed using the DAVID online database and FunRich software. Protein–protein interaction (PPI) networks among DEGs were constructed using the STRING database and analyzed by Cytoscape.

Results

A total of 515 DEGs were identified in MTLE-HS samples with a febrile seizure history compared to MTLE-HS samples without febrile seizure, including 25 down-regulated and 490 up-regulated genes. These DEGs were expressed mostly in plasma membrane and synaptic vesicles. The major molecular functions of those genes were voltage-gated ion channel activity, extracellular ligand-gated ion channel activity and calcium ion binding. The DEGs were mainly involved in biological pathways of cell communication signal transduction and transport. Five genes (SNAP25, SLC32A1, SYN1, GRIN1,andGRIA1) were significantly expressed in the MTLE-HS with prolonged febrile seizures.

Conclusion

The pathogenesis of MTLE-HS involves multiple genes, and prolonged febrile seizures could cause differential expression of genes. Thus, investigations of those genes may provide a new perspective into the mechanism of MTLE-HS.

Astrocytes in the regulation of cerebrovascular functions

Astrocytes are the most numerous type of neuroglia in the brain and have a predominant influence on the cerebrovascular system; they control perivascular homeostasis, the integrity of the blood-brain barrier, the dialogue with the peripheral immune system, the transfer of metabolites from the blood, and blood vessel contractility in response to neuronal activity. These regulatory processes occur in a specialized interface composed of perivascular astrocyte extensions that almost completely cover the cerebral blood vessels. Scientists have only recently started to study how this interface is formed and how it influences cerebrovascular functions. Here, we review the literature on the astrocytes' role in the regulation of the cerebrovascular system. We cover the anatomy and development of the gliovascular interface, the known gliovascular functions, and molecular factors, the latter's implication in certain pathophysiological situations, and recent cutting-edge experimental tools developed to examine the astrocytes' role at the vascular interface. Finally, we highlight some open questions in this field of research.

Changes of EEG spectra in rat brains with different patterns of dysplasia in response to pilocarpine-induced seizures

Disorders of neurogenesis at early developmental stages lead to irreversible structural and functional impairments of the brain. As further their consequences, increases in brain excitability and the development of drug-resistant epilepsy can frequently be observed in clinical cases. Mechanisms underlying these phenomena can also be examined on animal models of brain dysplasia. This study was conducted on rats with four degrees of brain dysplasia following exposure to gamma radiation on days 13, 15, 17, or 19 of prenatal development. When reached adulthood, the rats received electroencephalographic (EEG) transmitter implantation. Thereafter, pilocarpine was administered, and significant differences in susceptibility to seizures were detected depending on the degree of brain dysplasia. Before, during, and after the seizures, EEG was recorded in free moving animals. Additionally, the intensity of seizure behavioral symptoms was assessed. Strong and moderate correlations were found between the intensity of seizure behavioral symptoms, the power of particular EEG bands, and volumes of dysplastic brains and their regions. The data drew particular attention to correlations between variations in EEG spectra and changes in the midbrain and pons volumes. The results point to possible significant roles of these regions in the observed changes of susceptibility to seizures. Consequently, the frequently used experimental model was considered here not only as representing cases of cortical dysplasia but also of generalized, diffuse dysplasia of the whole brain.

Expression of VEGF- and tight junction-related proteins in the neocortical microvasculature of patients with drug-resistant temporal lobe epilepsy

The blood-brain barrier (BBB) maintains the optimal microenvironment for brain function. Tight junctions (TJs) allow endothelial cells to adhere to each other, leading to the formation of a barrier that prevents the penetration of most molecules via transcellular routes. Evidence has indicated that seizure-induced vascular endothelial growth factor (VEGF) type 2 receptor (VEGFR-2) pathway activation weakens TJs, inducing vasodilatation and increasing vascular permeability and subsequent brain injury. The present study focused on investigating the expression levels of VEGF-related (VEGF-A and VEGFR-2) and TJ-related proteins (claudin-5, occludin and ZO-1) in the neocortical microvasculature of patients with drug-resistant temporal lobe epilepsy (TLE). The results obtained from hippocampal sclerosis TLE (HS-TLE) patients were compared with those obtained from patients with TLE secondary to lesions (lesion-TLE) and autopsy samples. The Western blotting and immunofluorescence results showed that VEGF-A and VEGFR-2 protein expression levels were increased in HS-TLE and lesion-TLE patients compared to autopsy group. On the other hand, claudin-5 expression was higher in HS-TLE patients and lesion-TLE patients than autopsies. The expression level of occludin and ZO-1 was decreased in HS-TLE patients. Our study described modifications to the integrity of the BBB that may contribute to the pathogenesis of TLE, in which the VEGF system may play an important role. We demonstrated that the same modifications were present in both HS-TLE and lesion-TLE patients, which suggests that seizures modify these systems and that they are not associated with the establishment of epilepsy.

Shedding light on human cerebral lipofuscin: An explorative study on identification and quantification

Increased oxidative stress has been associated with several neurodegenerative diseases such as Alzheimer's disease, but also with neurological diseases sharing pathophysiological pathways like epilepsy. Lipofuscin is a nondegradable end-product of oxidative stress; its cerebral presence reflects the cumulative amount of oxidative stress the brain has endured. In this study, we have observed prominent autofluorescent particles in the pial arterial wall and in neocortical parenchyma of young, drug-resistant epilepsy patients (18-28 years old) who underwent resective brain surgery (n = 6), as well as in older control patients (n = 3). With fluorescence spectroscopic imaging, brightfield microscopy, histochemistry and fluorescence lifetime imaging, these autofluorescent particles were identified as the age pigment lipofuscin. An evaluation of these lipofuscin particles using Imaris© software allowed robust quantification, while the 3D properties allowed visualization of the complex configuration. We elaborate on the usefulness of lipofuscin as a marker of cumulative oxidative stress in the brain. Furthermore, we speculate on the observed differences in particle size and density that we found between young patients and older controls, which could imply a role for lipofuscin in the pathophysiology of epilepsy and possibly other neurological diseases.

Early cerebrovascular and long-term neurological modifications ensue following juvenile mild traumatic brain injury in male mice

Clinical evidence suggests that a mild traumatic brain injury occurring at a juvenile age (jmTBI) may be sufficient to elicit pathophysiological modifications. However, clinical reports are not adequately integrated with experimental studies examining brain changes occurring post-jmTBI. We monitored the cerebrovascular modifications and assessed the long-term behavioral and electrographic changes resulting from experimental jmTBI. In vivo photoacoustic imaging demonstrated a decrease of cerebrovascular oxygen saturation levels in the impacted area hours post-jmTBI. Three days post-jmTBI oxygenation returned to pre-jmTBI levels, stabilizing at 7 and 30 days after the injury. At the functional level, cortical arterioles displayed no NMDA vasodilation response, while vasoconstriction induced by thromboxane receptor agonist was enhanced at 1 day post-jmTBI. Arterioles showed abnormal NMDA vasodilation at 3 days post-jmTBI, returning to normality at 7 days post injury. Histology showed changes in vessel diameters from 1 to 30 days post-jmTBI. Neurological evaluation indicated signs of anxiety-like behavior up to 30 days post-jmTBI. EEG recordings performed at the cortical site of impact 30 days post-jmTBI did not indicate seizures activity, although it revealed a reduction of gamma waves as compared to age matched sham. Histology showed decrease of neuronal filament staining. In conclusion, experimental jmTBI triggers an early cerebrovascular hypo‑oxygenation in vivo and faulty vascular reactivity. The exact topographical coherence and the direct casualty between early cerebrovascular changes and the observed long-term neurological modifications remain to be investigated. A potential translational value for cerebro-vascular oxygen monitoring in jmTBI is discussed.

The Isolated Brain Microvessel: A Versatile Experimental Model of the Blood-Brain Barrier

A versatile experimental model for the investigation of the blood-brain barrier (BBB), including the neuro-vascular unit, is the isolated brain microvessel preparation. Brain microvessels are primarily comprised of endothelial cells, but also include pericytes, pre-capillary arteriolar smooth muscle cells, astrocyte foot processes, and occasional nerve endings. These microvessels can be isolated from brain with a 3 h procedure, and the microvessels are free of brain parenchyma. Brain microvessels have been isolated from fresh animal brain, fresh human brain obtained at neurosurgery, as well as fresh or frozen autopsy human brain. Brain microvessels are the starting point for isolation of brain microvessel RNA, which then enables the production of BBB cDNA libraries and a genomics analysis of the brain microvasculature. Brain microvessels, combined with quantitative targeted absolute proteomics, allow for the quantitation of specific transporters or receptors expressed at the brain microvasculature. Brain microvessels, combined with specific antibodies and immune labeling of isolated capillaries, allow for the cellular location of proteins expressed within the neuro-vascular unit. Isolated brain microvessels can be used as an “in vitro” preparation of the BBB for the study of the kinetic parameters of BBB carrier-mediated transport (CMT) systems, or for the determination of dissociation constants of peptide binding to BBB receptor-mediated transport (RMT) systems expressed at either the animal or the human BBB. This review will discuss how the isolated brain microvessel model system has advanced our understanding of the organization and functional properties of the BBB, and highlight recent renewed interest in this 50 year old model of the BBB.

Vascular Abnormalities and the Role of Vascular Endothelial Growth Factor in the Epileptic Brain

Epilepsy is a chronic neurological disorder generally defined to be caused by excessive neuronal activity. Thus, excessive neuronal activity is the main target of the currently used antiepileptic drugs (AEDs). However, as many as 30% of epileptic patients show drug resistance to currently available AEDs, which suggests that epilepsy should be attributed not only to neuronal cells but also to other brain cells, such as glial cells and vascular cells. Astrocytes, pericytes, and endothelial cells in particular comprise the blood–brain barrier (BBB), which tightly regulates the exchange of substances between the brain parenchyma and the circulating blood. It has been proposed that BBB dysfunction, especially barrier leakage, exacerbates epileptic progression, and conversely, that epileptic seizures induce barrier leakage. Furthermore, several studies have shown that BBB dysfunction is one of the main causes of drug resistance in epilepsy. To better understand the mechanisms that link BBB dysfunction and intractable epilepsy to gain insights for the future development of treatments, we review and discuss the relationships between epilepsy and brain vascular abnormalities, mainly by focusing on vascular malformation, BBB dysfunction, and excessive angiogenesis. Because these abnormalities have been reported to be caused by vascular endothelial growth factor (VEGF) in the ischemic brain, we discuss the possible role of VEGF in vascular abnormalities in the epileptic brain, in which the upregulation of VEGF levels has been reported. Both glial cells and endothelial cells express VEGF receptors (VEGFRs); thus, these cells are likely affected by increases in VEGF during seizures, which in turn could cause vascular abnormalities. In this review, we review the possible role of VEGF in epilepsy and discuss the mechanisms that link vascular abnormalities and intractable epilepsy.

Structural, Molecular, and Functional Alterations of the Blood-Brain Barrier during Epileptogenesis and Epilepsy: A Cause, Consequence, or Both?

The blood-brain barrier (BBB) is a dynamic, highly selective barrier primarily formed by endothelial cells connected by tight junctions that separate the circulating blood from the brain extracellular fluid. The endothelial cells lining the brain microvessels are under the inductive influence of neighboring cell types, including astrocytes and pericytes. In addition to the anatomical characteristics of the BBB, various specific transport systems, enzymes and receptors regulate molecular and cellular traffic across the BBB. While the intact BBB prevents many macromolecules and immune cells from entering the brain, following epileptogenic brain insults the BBB changes its properties. Among BBB alterations, albumin extravasation and diapedesis of leucocytes from blood into brain parenchyma occur, inducing or contributing to epileptogenesis. Furthermore, seizures themselves may modulate BBB functions, permitting albumin extravasation, leading to activation of astrocytes and the innate immune system, and eventually modifications of neuronal networks. BBB alterations following seizures are not necessarily associated with enhanced drug penetration into the brain. Increased expression of multidrug efflux transporters such as P-glycoprotein likely act as a 'second line defense' mechanism to protect the brain from toxins. A better understanding of the complex alterations in BBB structure and function following seizures and in epilepsy may lead to novel therapeutic interventions allowing the prevention and treatment of epilepsy as well as other detrimental neuro-psychiatric sequelae of brain injury.

Epilepsy and Alterations of the Blood-Brain Barrier: Cause or Consequence of Epileptic Seizures or Both?

The blood-brain barrier (BBB) is a dynamic, highly selective barrier primarily formed by endothelial cells connected by tight junctions that separate the circulating blood from the brain extracellular fluid, thereby preserving a narrow and stable homeostatic control of the neuronal environment. The endothelial cells lining the brain microvessels are under the inductive influence of neighboring cell types within the "neurovascular unit" including astrocytes and pericytes. In addition to the morphological characteristics of the BBB, various specific transport systems, enzymes, and receptors regulate the molecular and cellular traffic across the barrier. Furthermore, the intact BBB prevents many macromolecules and immune cells from entering the brain. This changes dramatically following epileptogenic brain insults; such insults, among other BBB alterations, lead to albumin extravasation and diapedesis of leukocytes from blood into brain parenchyma, inducing or contributing to epileptogenesis, which finally leads to development of spontaneous recurrent seizures and epilepsy. Furthermore, seizures themselves may cause BBB disruption with albumin extravasation, which has been shown to be associated with activation of astrocytes, activation of innate immune systems, and modifications of neuronal networks. However, seizure-induced BBB disruption is not necessarily associated with enhanced drug penetration into the brain, because the BBB expression of multidrug efflux transporters such as P-glycoprotein increases, most likely as a "second line defense" mechanism to protect the brain from drug toxicity. Hopefully, a better understanding of the complex BBB alterations in response to seizures and epilepsy can lead to novel therapeutic intervention to prevent epileptogenesis and the development of other detrimental sequelae of brain injury.

Synchrotron Radiation-Based Three-Dimensional Visualization of Angioarchitectural Remodeling in Hippocampus of Epileptic Rats

Characterizing the three-dimensional (3D) morphological alterations of microvessels under both normal and seizure conditions is crucial for a better understanding of epilepsy. However, conventional imaging techniques cannot detect microvessels on micron/sub-micron scales without angiography. In this study, synchrotron radiation (SR)-based X-ray in-line phase-contrast imaging (ILPCI) and quantitative 3D characterization were used to acquire high-resolution, high-contrast images of rat brain tissue under both normal and seizure conditions. The number of blood microvessels was markedly increased on days 1 and 14, but decreased on day 60 after seizures. The surface area, diameter distribution, mean tortuosity, and number of bifurcations and network segments also showed similar trends. These pathological changes were confirmed by histological tests. Thus, SR-based ILPCI provides systematic and detailed views of cerebrovascular anatomy at the micron level without using contrast-enhancing agents. This holds considerable promise for better diagnosis and understanding of the pathogenesis and development of epilepsy.

Inflammation and reactive oxygen species as disease modifiers in epilepsy

Neuroinflammation and reactive oxygen and nitrogen species are rapidly induced in the brain after acute cerebral injuries that are associated with an enhanced risk for epilepsy in humans and related animal models. These phenomena reinforce each others and persist during epileptogenesis as well as during chronic spontaneous seizures. Anti-inflammatory and anti-oxidant drugs transiently administered either before, or shortly after the clinical onset of symptomatic epilepsy, similarly block the progression of spontaneous seizures, and may delay their onset. Moreover, neuroprotection and rescue of cognitive deficits are also observed in the treated animals. Therefore, although these treatments do not prevent epilepsy development, they offer clinically relevant disease-modification effects. These therapeutic effects are mediated by targeting molecular signaling pathways such as the IL-1β-IL-1 receptor type 1 and TLR4, P2X7 receptors, the transcriptional anti-oxidant factor Nrf2, while the therapeutic impact of COX-2 inhibition for reducing spontaneous seizures remains controversial. Some anti-inflammatory and anti-oxidant drugs that are endowed of disease modification effects in preclinical models are already in medical use and have a safety profile, therefore, they provide potential re-purposed treatments for improving the disease course and for reducing seizure burden. Markers of neuroinflammation and oxidative stress can be measured in blood or by neuroimaging, therefore they represent testable prognostic and predictive biomarkers for selecting the patient's population at high risk for developing epilepsy therefore eligible for novel treatments. This article is part of the special issue entitled 'New Epilepsy Therapies for the 21st Century - From Antiseizure Drugs to Prevention, Modification and Cure of Epilepsy'.

P2Y4/TSP-1/TGF-β1/pSmad2/3 pathway contributes to acute generalized seizures induced by kainic acid

Epilepsy is accompanied by angiogenesis and blood-brain barrier (BBB) disruption. The transforming growth factor-β1 (TGF-β1)/phosphorylated small mothers against decapentaplegic 2 and 3 (pSmad2/3)/vascular endothelial growth factor (VEGF) pathway, activated by thrombospondin-1 (TSP-1), which is further regulated by Y type P2 purinergic receptor activity, may participate in angiogenesis. We sought to investigate the relationship between the P2R/TSP-1/TGF-β1/pSmad2/3/VEGF pathway, angiogenesis, and BBB damage in a kainic acid (KA) model of acute generalized seizure. Our results demonstrated that KA-induced seizures were accompanied by angiogenesis and BBB damage. In addition, expression of TSP-1, TGF-β1, and pSmad2/3 was increased. Rats treated with pyridoxal phosphate-6-azophenyl-2', 4'-disulfonic acid, a broad P2 receptor antagonist, or Reactive Blue 2, a potent P2Y4 receptor antagonist, showed significant attenuation of TSP-1 expression and Smad2/3 phosphorylation levels. Furthermore, angiogenesis, BBB damage, and acute seizure severity were also reduced. The inhibition of TSP-1 expression by siRNA or TGF-β1 activation by Leu-Ser-Lys-Leu (LSKL) treatment prevented KA-induced phosphorylation of Smad2/3, angiogenesis, BBB damage, and acute seizures. Our results strongly indicate that the P2Y4/TSP-1/TGF-β1/pSmad2/3/VEGF pathway plays an essential role in seizure pathophysiology and angiogenesis. Therapeutic interventions targeting this pathway may offer new treatment options for acute seizures.

Pericyte Plasticity in the Brain

Cerebral pericytes are perivascular cells that stabilize blood vessels. Little is known about the plasticity of pericytes in the adult brain in vivo. Recently, using state-of-the-art technologies, including two-photon microscopy in combination with sophisticated Cre/loxP in vivo tracing techniques, a novel role of pericytes was revealed in vascular remodeling in the adult brain. Strikingly, after pericyte ablation, neighboring pericytes expand their processes and prevent vascular dilatation. This new knowledge provides insights into pericyte plasticity in the adult brain.

A pericyte-glia scarring develops at the leaky capillaries in the hippocampus during seizure activity

OBJECTIVE

Inflammatory cerebrovascular damage occurs in epilepsy. Here, we tested the hypothesis that a pericyte-glia scar forms around the outer wall of hippocampal capillaries in a model of temporal lobe epilepsy associated with hippocampal sclerosis. We studied the participation of stromal cells expressing platelet-derived growth factor receptor beta (PDGFRβ) and extracellular matrix modifications to the perivascular scar during epileptogenesis.

METHODS

We used NG2DsRed/C57BL6 mice and induced status epilepticus (SE) followed by epileptogenesis and spontaneous recurrent seizures (SRS) by means of unilateral intrahippocampal injection of kainic acid (KA). For pharmacological assessment, we used organotypic hippocampal cultures (OHCs) where ictal electrographic activity was elicited by KA or bicuculline.

RESULTS

NG2DsRed pericytes, GFAP astroglia, and IBA1 microglia are reactive and converge to form a pericapillary multicellular scar in the CA hippocampal regions during epileptogenesis and at SRS. The capillaries are leaky as indicated by fluorescein entering the parenchyma from the peripheral blood. Concomitantly, PDGFRβ transcript and protein levels were significantly increased. Within the regional scar, a fibrotic-like PDGFRβ mesh developed around the capillaries, peaking at 1 week post-SE and regressing, but not resolving, at SRS. Abnormal distribution or accumulation of extracellular matrix collagens III/IV occurred in the CA regions during seizure progression. PDGFRβ/DAPI cells were in direct contact with or adjacent to the damaged NG2DsRed pericytes at the capillary interface, consistent with the notion of stromal cell reactivity or fibroblast formation. Inducing electrographic activity in OHCs was sufficient to augment PDGFRβ reactivity around the capillaries. The latter effect was pharmacologically mimicked by treating OHCs with the PDGFRβ agonist PDGF-BB and it was diminished by the PDGFRβ inhibitor imatinib.

SIGNIFICANCE

The reported multicellular activation and scar are traits of perivascular inflammation and hippocampal sclerosis in experimental epilepsy, with an implication for neurovascular dysfunction. Modulation of PDGFRβ could be exploited to target inflammation in this chronic disease setting.

ABC transporters in drug-resistant epilepsy: mechanisms of upregulation and therapeutic approaches

Drug-resistant epilepsy (DRE) affects approximately one third of epileptic patients. Among various theories that try to explain multidrug resistance, the transporter hypothesis is the most extensively studied. Accordingly, the overexpression of efflux transporters in the blood-brain barrier (BBB), mainly from the ATP binding cassette (ABC) superfamily, may be responsible for hampering the access of antiepileptic drugs into the brain. P-glycoprotein and other efflux transporters are known to be upregulated in endothelial cells, astrocytes and neurons of the neurovascular unit, a functional barrier critically involved in the brain penetration of drugs. Inflammation and oxidative stress involved in the pathophysiology of epilepsy together with uncontrolled recurrent seizures, drug-associated induction and genetic polymorphisms are among the possible causes of ABC transporters overexpression in DRE. The aforementioned pathological mechanisms will be herein discussed together with the multiple strategies to overcome the activity of efflux transporters in the BBB - from direct transporters inhibition to down-regulation of gene expression resorting to RNA interference (RNAi), or by targeting key modulators of inflammation and seizure-mediated signalling.

Targeting pericytes for neurovascular regeneration

Pericytes, as a key cellular part of the blood-brain barrier, play an important role in the maintenance of brain neurovascular unit. These cells participate in brain homeostasis by regulating vascular development and integrity mainly through secreting various factors. Pericytes per se show different restorative properties after blood-brain barrier injury. Upon the occurrence of brain acute and chronic diseases, pericytes provoke immune cells to regulate neuro-inflammatory conditions. Loss of pericytes in distinct neurologic disorders intensifies blood-brain barrier permeability and leads to vascular dementia. The therapeutic potential of pericytes is originated from the unique morphological shape, location, and their ability in providing vast paracrine and juxtacrine interactions. A subset of pericytes possesses multipotentiality and exhibit trans-differentiation capacity in the context of damaged tissue. This review article aimed to highlight the critical role of pericytes in restoration of the blood-brain barrier after injury by focusing on the dynamics of pericytes and cross-talk with other cell types.

Proliferation of NG2 cells in the epileptic hippocampus

NG2 cells are oligodendrocyte progenitor cells, and have been shown to receive synaptic input from pyramidal neurons to generate action potentials. Whether any change of these cells occurs after status epilepticus (SE) and subsequent temporal lobe epilepsy remains unknown. In the present study, the expression of NG2 was investigated in the mouse hippocampus after pilocarpine-induced status epilepticus (PISE). We showed that reactive NG2 cells were significantly increased from 1 day to 2 months after PISE. Double immunofluorescence indicated that few NG2 cells differentiated into neurons and astrocytes after PISE, whereas the number of NG2 cells was increased significantly in the stratum lucidum of CA3 area from 1 day onwards after PISE. Our results suggest that the significantly increased reactive NG2 cells from acute to chronic stage after PISE may be involved in epileptogenesis.

Therapeutic potential of endothelial progenitor cells in a rat model of epilepsy: Role of autophagy

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This is the first report showing EPCs therapeutic effects in PTZ-induced epilepsy.

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Intravenously administered EPCs homed into the epileptic rat hippocampus.

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EPCs amend the memory and locomotor activity deficits related to epilepsy.

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EPCs ameliorate epilepsy-associated alterations in neurotransmitters and autophagy.

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EPCs mitigate concomitant histological and vascular anomalies.

Epilepsy is one of the most well-known neurological conditions worldwide. One-third of adult epileptic patients do not respond to antiepileptic drugs or surgical treatment and therefore suffer from the resistant type of epilepsy. Stem cells have been given substantial consideration in the field of epilepsy therapeutics. The implication of pathologic vascular response in sustained seizures and the eminent role of endothelial progenitor cells (EPCs) in maintaining vascular integrity tempted us to investigate the potential therapeutic effects of EPCs in a pentylenetetrazole (PTZ)-induced rat model of epilepsy. Modulation of autophagy, a process that enables neurons to maintain an equilibrium of synthesis, degradation and subsequent reprocessing of cellular components, has been targeted. Intravenously administered EPCs homed into the hippocampus and amended the deficits in memory and locomotor activity. The cells mitigated neurological damage and the associated histopathological alterations and boosted the expression of brain-derived neurotrophic factor. EPCs corrected the perturbations in neurotransmitter activity and enhanced the expression of the downregulated autophagy proteins light chain protein-3 (LC-3), beclin-1, and autophagy-related gene-7 (ATG-7). Generally, these effects were comparable to those achieved by the reference antiepileptic drug, valproic acid. In conclusion, EPCs may confer therapeutic effects against epilepsy and its associated behavioural and biochemical abnormalities at least in part via the upregulation of autophagy. The study warrants further research in experimental and clinical settings to verify the prospect of using EPCs as a valid therapeutic strategy in patients with epilepsy.

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.

Transient Focal Magnetic Resonance Imaging Abnormalities After Status Epilepticus Showed 11C-Methionine Uptake with Positron Emission Tomography in a Patient with Cerebral Cavernous Malformation

BACKGROUND

Transient focal magnetic resonance imaging (MRI) abnormalities after status epilepticus (SE) are rarely seen in patients with benign brain tumors, and the underlying mechanism is still unknown. We report a rare case of cerebral cavernous malformation with transient focal MRI abnormalities around the tumor and accumulation of 11C-methionine on positron emission tomography (PET) after SE. These findings mimicked those of a glioma because the MRI and methionine PET findings were similar. We also speculate about the cause of this phenomenon in relation to pathologic findings of this case.

CASE DESCRIPTION

A 51-year-old man suffered from SE. MRI demonstrated a focal T2/fluid-attenuated inversion recovery hyperintense area. 11C-methionine PET showed high accumulation of methionine in the same lesion. The initial diagnosis was low-grade glioma. However, these MRI abnormalities were transient and completely resolved. The patient underwent surgical removal of the tumor, and the histologic diagnosis was typical cavernous malformation. Pathologic findings of the gyrus around the tumor revealed mild gliosis with proliferating astrocytes but no evidence of glioma.

CONCLUSIONS

This case suggests that transient focal MRI abnormalities after SE may indicate reversible cortical brain edema. Accumulation of 11C-methionine on PET could occur in the corresponding lesion even if no malignant tumor is present. Because distinguishing transient MRI abnormalities after SE from a glioma is difficult, repeated imaging studies should be performed in patients with brain tumor-related seizures.

Review: Roles for astrocytes in epilepsy: insights from malformations of cortical development

Malformations of cortical development (MCDs), such as cortical dysplasia and tuberous sclerosis complex, are common causes of intractable epilepsy, especially in paediatric patients. Recently, mounting evidence points to a common pathology of these disorders. Hyperactivation of mammalian target of rapamycin (mTOR) has been proposed as a central mechanism in most, if not all, MCDs. The transition from mTOR hyperactivation and cellular abnormalities to large-scale functional changes and seizure is, however, not fully understood. In this article we set out to review currently available information regarding MCD pathology, focusing on glial cells - especially astrocytes - and their interactions with the brain vascular system. A large body of evidence points to these elements as potential targets in MCD. Here, we attempt to provide a review of this evidence and propose some hypotheses regarding the possible chain of events linking primary glial dysfunction and epilepsy. We focus on extracellular matrix remodelling, blood-brain barrier leakage and failure of astrocyte-dependent removal of extracellular debris. We posit that the failure of these systems results in a chronically pro-inflammatory environment, maintaining local astrocytes in a state of gliosis, with increased susceptibility to seizures as a consequence.

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.

Proteomic profiling of epileptogenesis in a rat model: Focus on cell stress, extracellular matrix and angiogenesis

Information about epileptogenesis-associated changes in protein expression patterns is of particular interest for future selection of target and biomarker candidates. Bioinformatic analysis of proteomic data sets can increase our knowledge about molecular alterations characterizing the different phases of epilepsy development following an initial epileptogenic insult. Here, we report findings from a focused analysis of proteomic data obtained for the hippocampus and parahippocampal cortex samples collected during the early post-insult phase, latency phase, and chronic phase of a rat model of epileptogenesis. The study focused on proteins functionally associated with cell stress, cell death, extracellular matrix (ECM) remodeling, cell-ECM interaction, cell-cell interaction, angiogenesis, and blood-brain barrier function. The analysis revealed prominent pathway enrichment providing information about the complex expression alterations of the respective protein groups. In the hippocampus, the number of differentially expressed proteins declined over time during the course of epileptogenesis. In contrast, a peak in the regulation of proteins linked with cell stress and death as well as ECM and cell-cell interaction became evident at later phases during epileptogenesis in the parahippocampal cortex. The data sets provide valuable information about the time course of protein expression patterns during epileptogenesis for a series of proteins. Moreover, the findings provide comprehensive novel information about expression alterations of proteins that have not been discussed yet in the context of epileptogenesis. These for instance include different members of the lamin protein family as well as the fermitin family member 2 (FERMT2). Induction of FERMT2 and other selected proteins, CD18 (ITGB2), CD44 and Nucleolin were confirmed by immunohistochemistry. Taken together, focused bioinformatic analysis of the proteomic data sets completes our knowledge about molecular alterations linked with cell death and cellular plasticity during epileptogenesis. The analysis provided can guide future selection of target and biomarker candidates.

Seizure epicenter depth and translaminar field potential synchrony underlie complex variations in tissue oxygenation during ictal initiation

Whether functional hyperemia during epileptic activity is adequate to meet the heightened metabolic demand of such events is controversial. Whereas some studies have demonstrated hyperoxia during ictal onsets, other work has reported transient hypoxic episodes that are spatially dependent on local surface microvasculature. Crucially, how laminar differences in ictal evolution can affect subsequent cerebrovascular responses has not been thus far investigated, and is likely significant in view of possible laminar-dependent neurovascular mechanisms and angioarchitecture. We addressed this open question using a novel multi-modal methodology enabling concurrent measurement of cortical tissue oxygenation, blood flow and hemoglobin concentration, alongside laminar recordings of neural activity, in a urethane anesthetized rat model of recurrent seizures induced by 4-aminopyridine. We reveal there to be a close relationship between seizure epicenter depth, translaminar local field potential (LFP) synchrony and tissue oxygenation during the early stages of recurrent seizures, whereby deep layer seizures are associated with decreased cross laminar synchrony and prolonged periods of hypoxia, and middle layer seizures are accompanied by increased cross-laminar synchrony and hyperoxia. Through comparison with functional activation by somatosensory stimulation and graded hypercapnia, we show that these seizure-related cerebrovascular responses occur in the presence of conserved neural-hemodynamic and blood flow-volume coupling. Our data provide new insights into the laminar dependency of seizure-related neurovascular responses, which may reconcile inconsistent observations of seizure-related hypoxia in the literature, and highlight a potential layer-dependent vulnerability that may contribute to the harmful effects of clinical recurrent seizures. The relevance of our findings to perfusion-related functional neuroimaging techniques in epilepsy are also discussed.

Increased gyrification and aberrant adult neurogenesis of the dentate gyrus in adult rats

A remarkable example of maladaptive plasticity is the development of epilepsy after a brain insult or injury to a normal animal or human. A structure that is considered central to the development of this type of epilepsy is the dentate gyrus (DG), because it is normally a relatively inhibited structure and its quiescence is thought to reduce hippocampal seizure activity. This characteristic of the DG is also considered to be important for normal hippocampal-dependent cognitive functions. It has been suggested that the brain insults which cause epilepsy do so because they cause the DG to be more easily activated. One type of brain insult that is commonly used is induction of severe seizures (status epilepticus; SE) by systemic injection of a convulsant drug. Here we describe an alteration in the DG after this type of experimental SE that may contribute to chronic seizures that has not been described before: large folds or gyri that develop in the DG by 1 month after SE. Large gyri appeared to increase network excitability because epileptiform discharges recorded in hippocampal slices after SE were longer in duration when recorded inside gyri relative to locations outside gyri. Large gyri may also increase excitability because immature adult-born neurons accumulated at the base of gyri with time after SE, and previous studies have suggested that abnormalities in adult-born DG neurons promote seizures after SE. In summary, large gyri after SE are a common finding in adult rats, show increased excitability, and are associated with the development of an abnormal spatial distribution of adult-born neurons. Together these alterations may contribute to chronic seizures and associated cognitive comorbidities after SE.

Pericytes of the neurovascular unit: key functions and signaling pathways

Pericytes are vascular mural cells embedded in the basement membrane of blood microvessels. They extend their processes along capillaries, pre-capillary arterioles and post-capillary venules. CNS pericytes are uniquely positioned in the neurovascular unit between endothelial cells, astrocytes and neurons. They integrate, coordinate and process signals from their neighboring cells to generate diverse functional responses that are critical for CNS functions in health and disease, including regulation of the blood-brain barrier permeability, angiogenesis, clearance of toxic metabolites, capillary hemodynamic responses, neuroinflammation and stem cell activity. Here we examine the key signaling pathways between pericytes and their neighboring endothelial cells, astrocytes and neurons that control neurovascular functions. We also review the role of pericytes in CNS disorders including rare monogenic diseases and complex neurological disorders such as Alzheimer's disease and brain tumors. Finally, we discuss directions for future studies.

Longitudinal In Vivo Imaging of the Cerebrovasculature: Relevance to CNS Diseases

Remodeling of the brain vasculature is a common trait of brain pathologies. In vivo imaging techniques are fundamental to detect cerebrovascular plasticity or damage occurring overtime and in relation to neuronal activity or blood flow. In vivo two-photon microscopy allows the study of the structural and functional plasticity of large cellular units in the living brain. In particular, the thinned-skull window preparation allows the visualization of cortical regions of interest (ROI) without inducing significant brain inflammation. Repetitive imaging sessions of cortical ROI are feasible, providing the characterization of disease hallmarks over time during the progression of numerous CNS diseases. This technique accessing the pial structures within 250 μm of the brain relies on the detection of fluorescent probes encoded by genetic cellular markers and/or vital dyes. The latter (e.g., fluorescent dextrans) are used to map the luminal compartment of cerebrovascular structures. Germane to the protocol described herein is the use of an in vivo marker of amyloid deposits, Methoxy-O4, to assess Alzheimer's disease (AD) progression. We also describe the post-acquisition image processing used to track vascular changes and amyloid depositions. While focusing presently on a model of AD, the described protocol is relevant to other CNS disorders where pathological cerebrovascular changes occur.