Decreased expression of thyroid receptor-associated protein 220 in temporal lobe tissue of patients with refractory epilepsy

Mediator complex in neurological disease

Neurological diseases, including traumatic brain injuries, stroke (haemorrhagic and ischemic), and inherent neurodegenerative diseases cause acquired disability in humans, representing a leading cause of death worldwide. The Mediator complex (MED) is a large, evolutionarily conserved multiprotein that facilities the interaction between transcription factors and RNA Polymerase II in eukaryotes. Some MED subunits have been found altered in the brain, although their specific functions in neurodegenerative diseases are not fully understood. Mutations in MED subunits were associated with a wide range of genetic diseases for MED12, MED13, MED13L, MED20, MED23, MED25, and CDK8 genes. In addition, MED12 and MED23 were deregulated in the Alzheimer's Disease. Interestingly, most of the genomic mutations have been found in the subunits of the kinase module. To date, there is only one evidence on MED1 involvement in post-stroke cognitive deficits. Although the underlying neurodegenerative disorders may be different, we are confident that the signal cascades of the biological-cognitive mechanisms of brain adaptation, which begin after brain deterioration, may also differ. Here, we analysed relevant studies in English published up to June 2023. They were identified through a search of electronic databases including PubMed, Medline, EMBASE and Scopus, including search terms such as "Mediator complex", "neurological disease", "brains". Thematic content analysis was conducted to collect and summarize all studies demonstrating MED alteration to understand the role of this central transcriptional regulatory complex in the brain. Improved and deeper knowledge of the regulatory mechanisms in neurological diseases can increase the ability of physicians to predict onset and progression, thereby improving diagnostic care and providing appropriate treatment decisions.

Identifying shared genetic factors underlying epilepsy and congenital heart disease in Europeans

Epilepsy (EP) and congenital heart disease (CHD) are two apparently unrelated diseases that nevertheless display substantial mutual comorbidity. Thus, while congenital heart defects are associated with an elevated risk of developing epilepsy, the incidence of epilepsy in CHD patients correlates with CHD severity. Although genetic determinants have been postulated to underlie the comorbidity of EP and CHD, the precise genetic etiology is unknown. We performed variant and gene association analyses on EP and CHD patients separately, using whole exomes of genetically identified Europeans from the UK Biobank and Mount Sinai BioMe Biobank. We prioritized biologically plausible candidate genes and investigated the enriched pathways and other identified comorbidities by biological proximity calculation, pathway analyses, and gene-level phenome-wide association studies. Our variant- and gene-level results point to the Voltage-Gated Calcium Channels (VGCC) pathway as being a unifying framework for EP and CHD comorbidity. Additionally, pathway-level analyses indicated that the functions of disease-associated genes partially overlap between the two disease entities. Finally, phenome-wide association analyses of prioritized candidate genes revealed that cerebral blood flow and ulcerative colitis constitute the two main traits associated with both EP and CHD.

The Impact of the CX3CL1/CX3CR1 Axis in Neurological Disorders

Fractalkine (FKN, CX3CL1) is a transmembrane chemokine expressed by neurons in the central nervous system (CNS). CX3CL1 signals through its unique receptor, CX3CR1, that is expressed in microglia. Within the CNS, fractalkine acts as a regulator of microglia activation in response to brain injury or inflammation. During the last decade, there has been a growing interest in the roles that the CX3CL1/CX3CR1 signaling pathway plays in the neuropathology of a diverse array of brain disorders. However, the reported results have proven controversial, indicating that a disruption of the CX3CL1 axis induces a disease-specific microglial response that may have either beneficial or detrimental effects. Therefore, it has become clear that the understanding of neuron-to-glia signals mediated by CX3CL1/CX3CR1 at different stages of diseases could provide new insight into potential therapeutic targets. Hence, the aim of this review is to provide a summary of the literature on the emerging role of CX3CL1 in animal models of some brain disorders.

Identification of epilepsy-associated neuronal subtypes and gene expression underlying epileptogenesis

Epilepsy is one of the most common neurological disorders, yet its pathophysiology is poorly understood due to the high complexity of affected neuronal circuits. To identify dysfunctional neuronal subtypes underlying seizure activity in the human brain, we have performed single-nucleus transcriptomics analysis of >110,000 neuronal transcriptomes derived from temporal cortex samples of multiple temporal lobe epilepsy and non-epileptic subjects. We found that the largest transcriptomic changes occur in distinct neuronal subtypes from several families of principal neurons (L5-6_Fezf2 and L2-3_Cux2) and GABAergic interneurons (Sst and Pvalb), whereas other subtypes in the same families were less affected. Furthermore, the subtypes with the largest epilepsy-related transcriptomic changes may belong to the same circuit, since we observed coordinated transcriptomic shifts across these subtypes. Glutamate signaling exhibited one of the strongest dysregulations in epilepsy, highlighted by layer-wise transcriptional changes in multiple glutamate receptor genes and strong upregulation of genes coding for AMPA receptor auxiliary subunits. Overall, our data reveal a neuronal subtype-specific molecular phenotype of epilepsy.

The pathophysiology of epilepsy is unclear. Here, the authors present single-nuclei transcriptomic profiling of human temporal lobe epilepsy from patients. They identified epilepsy-associated neuronal subtypes, and a panel of dysregulated genes, predicting neuronal circuits contributing to epilepsy.

Altered Norbin Expression in Patients with Epilepsy and a Rat Model

Norbin is widely distributed in neuronal tissues, is a regulator of Ca2⁺/calmodulin-dependent protein kinase II (CaMKII) phosphorylation. Norbin is also an important endogenous modulator of metabotropic glutamate receptor 5 (mGluR5) signaling, and nervous system-specific homozygous gene disruptions, result in epileptic seizures. In this study, we aimed to investigate norbin expression patterns in epilepsy and to elucidate the relationships between norbin and mGluR5 and p-CaMKII in epilepsy. Double-immunolabeling, immunohistochemistry and immunoblotting studies showed that norbin was downregulated in the temporal neocortex of patients with temporal lobe epilepsy (TLE) compared with control subjects. Moreover, in a rat model of lithium chloride-pilocarpine-induced epilepsy, norbin expression began to decrease at 6 h after the onset of status epilepticus and remained at a low level until 60 days. In addition, p-CaMKII expression was significantly increased in both patients with TLE and in animal model. Norbin and mGluR5 were found to be co-expressed in neurons of epileptic tissues. Finally, norbin over-expression facilitated by injections of adeno-associated viral vector into the rat hippocampus increased latency and survival in the lithium chloride-pilocarpine model. Thus, our results indicate norbin participates in the pathogenesis of epilepsy, perhaps by modulating mGluR5 signaling, regulating CaMKII phosphorylation, and may exert antiepileptic effects.

Thyroid hormones: Possible roles in epilepsy pathology

Thyroid hormones (THs) L-thyroxine and L-triiodothyronine, primarily known as metabolism regulators, are tyrosine-derived hormones produced by the thyroid gland. They play an essential role in normal central nervous system development and physiological function. By binding to nuclear receptors and modulating gene expression, THs influence neuronal migration, differentiation, myelination, synaptogenesis and neurogenesis in developing and adult brains. Any uncorrected THs supply deficiency in early life may result in irreversible neurological and motor deficits. The development and function of GABAergic neurons as well as glutamatergic transmission are also affected by THs. Though the underlying molecular mechanisms still remain unknown, the effects of THs on inhibitory and excitatory neurons may affect brain seizure activity. The enduring predisposition of the brain to generate epileptic seizures leads to a complex chronic brain disorder known as epilepsy. Pathologically, epilepsy may be accompanied by mitochondrial dysfunction, oxidative stress and eventually dysregulation of excitatory glutamatergic and inhibitory GABAergic neurotransmission. Based on the latest evidence on the association between THs and epilepsy, we hypothesize that THs abnormalities may contribute to the pathogenesis of epilepsy. We also review gender differences and the presumed underlying mechanisms through which TH abnormalities may affect epilepsy here.

Altered expression of CX3CL1 in patients with epilepsy and in a rat model

Chemokine C-X3-C motif ligand 1 (CX3CL1, alias fractalkine), is highly expressed in the central nervous system and participates in inflammatory responses. Recent studies indicated that inflammatory processes within the brain constitute a common and crucial mechanism in the pathophysiological characteristics of epilepsy. This study investigated the expression pattern of CX3CL1 in epilepsy and its relationship with neuronal loss. Double immunolabeling, IHC, and immunoblotting results showed that CX3CL1 expression was up-regulated in the temporal neocortex of patients with temporal lobe epilepsy. In a rat model of epilepsy, CX3CL1 up-regulation began 6 hours after epilepsy, with relatively high expression for 60 days. In addition, ELISA revealed that the concentrations of CX3CL1 in cerebrospinal fluid and serum were higher in epileptic patients than in patients with neurosis but lower than in patients with inflammatory neurological diseases. Moreover, H&E staining demonstrated significant neuronal loss in the brains of epileptic patients and in the rat model. Finally, the expression of tumor necrosis factor-related apoptosis-inducing ligand was significantly increased in both patients and the animal model, suggesting that tumor necrosis factor-related apoptosis-inducing ligand may play a role in CX3CL1-induced cell death. Thus, our results indicate that CX3CL1 may serve as a possible biomarker of brain inflammation in epileptic patients.

Exploring the genomic basis of pharmacoresistance in epilepsy: an integrative analysis of large-scale gene expression profiling studies on brain tissue from epilepsy surgery

Some patients with pharmacoresistant epilepsy undergo therapeutic resection of the epileptic focus. At least 12 large-scale microarray studies on brain tissue from epilepsy surgery have been published over the last 10 years, but they have failed to make a significant impact upon our understanding of pharmacoresistance, because (1) doubts have been raised about their reproducibility, (2) only a small number of the gene expression changes found in each microarray study have been independently validated and (3) the results of different studies have not been integrated to give a coherent picture of the genetic changes involved in epilepsy pharmacoresistance. To overcome these limitations, we (1) assessed the reproducibility of the microarray studies by calculating the overlap between lists of differentially regulated genes from pairs of microarray studies and determining if this was greater than would be expected by chance alone, (2) used an inter-study cross-validation technique to simultaneously verify the expression changes of large numbers of genes and (3) used the combined results of the different microarray studies to perform an integrative analysis based on enriched gene ontology terms, networks and pathways. Using this approach, we respectively (1) demonstrate that there are statistically significant overlaps between the gene expression changes in different publications, (2) verify the differential expression of 233 genes and (3) identify the biological processes, networks and genes likely to be most important in the development of pharmacoresistant epilepsy. Our analysis provides novel biologically plausible candidate genes and pathways which warrant further investigation to assess their causal relevance.

Overexpression of μ-calpain in the anterior temporal neocortex of patients with intractable epilepsy correlates with clinicopathological characteristics

PURPOSE

This study aims to investigate μ-calpain expression profiles in the anterior temporal neocortex in patients with intractable epilepsy, and to determine whether its pattern of expression is related to pathological changes seen in these patients.

METHODS

The study subjects consisted of 30 patients with intractable epilepsy and a control group of 10 patients with brain trauma who underwent resection of the anterior temporal lobe. μ-Calpain expression in surgically resected anterior temporal cortices of patients with intractable epilepsy were analyzed using the RT-PCR, Western blot, immunohistochemistry and immunofluorescence staining. GFAP expression was detected by immunohistochemical staining. The related pro-inflammatory cytokines were quantified by elisa. Clinicopathological characteristics were evaluated by HE staining.

RESULTS

Analysis by Western blot and RT-PCR revealed that inactive μ-calpain expression and the calpain-cleaved spectrin fragment in surgically resected anterior temporal cortices of patients with intractable epilepsy were significantly increased compared to the tissues from corresponding regions of the control group. Immunohistological staining demonstrated that μ-calpain was overexpressed in the cell cytoplasm of neurons and glial cells in patients with intractable epilepsy and GFAP was overexpressed in the cell cytoplasm of glial cells in patients with intractable epilepsy. The level of pro-inflammatory cytokines, such as IL-1β, IL-6 and TGF-β1 were significantly increased in patients with intractable epilepsy. HE staining indicated μ-calpain overexpression is an independent prognostic factor for pathological changes such as neuronal loss, neuronal degeneration, gliosis and astrocytosis.

CONCLUSION

These data suggest that overexpression of μ-calpain is relationship with intractable epilepsy as well as the clinicopathological characteristics in these patients.

Increased insulin receptor expression in anterior temporal neocortex of patients with intractable epilepsy

The insulin receptor (IR) is a tyrosine kinase receptor that binds to insulin and plays pivotal roles in energy homeostasis, neuronal growth, neuronal survival, synaptic plasticity and cognitive function. The biological mechanisms of intractable epilepsy involve energy metabolism, neuron loss, neurogenesis and abnormal neural networks. Here, we evaluated the expression of the IR in the anterior temporal neocortex of patients with intractable epilepsy (IE) by immunohistochemistry, double-label immunofluorescence and immunoblotting. We compared these tissues against histologically normal anterior temporal lobes from individuals treated for post-trauma intracranial hypertension. We found that the IR was coexpressed with neuron-specific enolase (NSE) and that IR expression increased in the anterior temporal neocortex of epileptic patients. On the basis of the potential physiological effects of IR, our findings suggest that increased expression of the IR is a consequence of epileptic seizures and a cause of IE.

The mediator complex subunit 1 enhances transcription of genes needed for adrenal androgen production

There are three enzymes involved in the biosynthesis of the adrenal androgen dehydroepiandrosterone (DHEA) sulfate. Cholesterol side-chain cleavage (CYP11A1) and 17alpha-hydroxylase/17,20-lyase (CYP17) metabolize cholesterol into DHEA, whereas steroid sulfotransferase family 2A1 (SULT2A1) is responsible for conversion of DHEA to DHEA sulfate. We previously examined the mechanisms regulating CYP11A1, CYP17, and SULT2A1 transcription and found that each is regulated, in part, by the transcription factor GATA-6. Previous studies suggested that mediator complex subunit 1 (MED1, also called PPARBP or TRAP220) is a cofactor involved in not only the regulation of nuclear receptors but also the activation of GATA-6 transcription. Herein we demonstrated a role for MED1 in the regulation of CYP11A1, CYP17, and SULT2A1 transcription. Transient transfection assays with SULT2A1 deletion and mutation promoter constructs allowed the determination of specific the GATA-6 binding cis-regulatory elements necessary for transactivation of SULT2A1 transcription. Binding of MED1 and GATA-6 was confirmed by coimmunoprecipitation/Western analysis and chromatin immunoprecipitation assay. We demonstrated expression of MED1 mRNA and protein in the human adrenal and determined that knockdown of MED1 expression via specific small interfering RNA attenuated CYP11A1, CYP17, and SULT2A1 expression levels in H295R cells. In addition, we demonstrated that MED1 enhanced GATA-6 stimulated transcription of promoter constructs for each of these genes. Moreover, the activity of MED1 for SULT2A1 promoter was mediated by GATA-6 via the -190 GATA-binding site. These data support the hypothesis that MED1 and GATA-6 are key regulators of SULT2A1 expression, and they play important roles in adrenal androgen production.

Overexpression of N-WASP in the brain of human epilepsy

Neuronal circuit remodeling is the most critical pathological characteristic closely associated with the initiation and maintenance of epilepsy; however, the exact mechanisms of neuronal remodeling need further elucidation. Neuronal Wiskott-Aldrich syndrome protein (N-WASP) is a key regulator of the actin cytoskeleton that causes actin polymerization and thus neurite extension. Our previous research demonstrated that the upstream regulator of N-WASP, cell division cycle 42 GTP-binding protein (Cdc42), is significantly upregulated in the brains of patients with intractable epilepsy (IE). In addition, cDNA microarray analysis has shown that gene expression of N-WASP is notably enhanced in the epileptic brain, suggesting a possible role for N-WASP in epileptogenesis. Here, we investigated the expression of N-WASP and its downstream effector, actin-related protein 2/3 (Arp2/3), at the protein level in the temporal lobe of IE patient brains to explore its possible role in the genesis of IE. Forty surgical samples from brains of patients with IE and 20 control brain tissues were obtained for this study. The expression of N-WASP in the anterior temporal neocortex was detected using immunohistochemistry, immunofluorescence and western blotting; Arp2/3 expression was detected by western blotting. Compared with controls, N-WASP expression in brains of IE patients was significantly higher; similarly, Arp2/3 level was markedly increased in the IE patient group. These results suggest that increased expression of N-WASP in the human brain may be associated with human IE.

TDAG51 in the anterior temporal neocortex of patients with intractable epilepsy

TDAG51 (T cell death-associated gene 51) is an apoptosis-associated protein. Our aim was to investigate TDAG51 expression in the anterior temporal neocortex of patients with intractable epilepsy (IE), and then to discuss the possible role of TDAG51 in IE. Tissue samples from the anterior temporal neocortex of 33 patients who had surgery for IE were used to detect TDAG51 expression by immunohistochemistry, immunofluorescence, and Western blotting. We compared these tissues with nine histologically normal anterior temporal lobes from intracranial hypertension patients who had decompression procedures. TDAG51 was mainly expressed in the cytoplasm of neurons and glial cells. TDAG51 in IE was significantly higher than that in the controls. These findings were consistently observed using Western blotting, immunofluorescence, and immunohistochemistry techniques. TDAG51 in patients with IE was significantly higher when compared with levels in the controls. This finding suggests TDAG51 is consistent with a possible role of this gene in the evolution of the pathology in IE.