Pathological Targets for Treating Temporal Lobe Epilepsy: Discoveries From Microscale to Macroscale

Distinct changes to hippocampal and medial entorhinal circuits emerge across the progression of cognitive deficits in epilepsy

Temporal lobe epilepsy (TLE) causes pervasive and progressive memory impairments, yet the specific circuit changes that drive these deficits remain unclear. To investigate how hippocampal-entorhinal dysfunction contributes to progressive memory deficits in epilepsy, we performed simultaneous in vivo electrophysiology in hippocampus (HPC) and medial entorhinal cortex (MEC) of control and epileptic mice 3 or 8 weeks after pilocarpine-induced status epilepticus (Pilo-SE). We found that HPC synchronization deficits (including reduced theta power, coherence, and altered interneuron spike timing) emerged within 3 weeks of Pilo-SE, aligning with early-onset, relatively subtle memory deficits. In contrast, abnormal synchronization within MEC and between HPC-MEC emerged later, by 8 weeks after Pilo-SE, when spatial memory impairment was more severe. Furthermore, a distinct subpopulation of MEC layer 3 excitatory neurons (active at theta troughs) was specifically impaired in epileptic mice. Together, these findings suggest that hippocampal-entorhinal circuit dysfunction accumulates and shifts as cognitive impairment progresses in TLE.

Peripheral blood regulatory B and T cells are decreased in patients with focal epilepsy

Patients with focal epilepsy of unknown cause (FEoUC) may display T cell infiltration in post-surgery brain specimens and increased serum levels of pro-inflammatory cytokines produced by B and T cells, indicating potential involvement of adaptive immunity. Our study aimed to investigate the peripheral blood distribution of B and T cell subgroups to find clues supporting the distinct organization of adaptive immunity in FEoUC. Twenty-two patients with FEoUC and 25 age and sex matched healthy individuals were included. Peripheral blood mononuclear cells were immunophenotyped by flow cytometry. Expression levels of anti-inflammatory cytokines and FOXP3 were measured by real-time PCR. Carboxyfluorescein succinimidyl ester (CFSE) proliferation assay was conducted using CD4+ T cells. Patients with FEoUC showed significantly decreased regulatory B (Breg), B1a, plasmablast and regulatory T (Treg) cell percentages, and increased switched memory B and Th17 cell ratios. Moreover, CD4+CD25+CD49d- Tregs of FEoUC patients displayed significantly reduced TGFB1 and FOXP3, but increased IL10 gene expression levels. CD4+ helper T cells of patients with FEoUC gave more exaggerated proliferation responses to phytohemagglutinin, anti-CD3 and anti-CD28 stimulation. Patients with FEoUC display increased effector lymphocyte, decreased regulatory lymphocyte ratios, and impaired Treg function and enhanced lymphocyte proliferation capacity. Overall, this pro-inflammatory phenotype lends support to the involvement of adaptive immunity in FEoUC.

An imaging review of the hippocampus and its common pathologies

The hippocampus is a complex structure located in the mesial temporal lobe that plays a critical role in cognitive and memory-related processes. The hippocampal formation consists of the dentate gyrus, hippocampus proper, and subiculum, and its importance in the neural circuitry makes it a key anatomic structure to evaluate in neuroimaging studies. Advancements in imaging techniques now allow detailed assessment of hippocampus internal architecture and signal features that has improved identification and characterization of hippocampal abnormalities. This review aims to summarize the neuroimaging features of the hippocampus and its common pathologies. It provides an overview of the hippocampal anatomy on magnetic resonance imaging and discusses how various imaging techniques can be used to assess the hippocampus. The review explores neuroimaging findings related to hippocampal variants (incomplete hippocampal inversion, sulcal remnant and choroidal fissure cysts), and pathologies of neoplastic (astrocytoma and glioma, ganglioglioma, dysembryoplastic neuroepithelial tumor, multinodular and vacuolating neuronal tumor, and metastasis), epileptic (mesial temporal sclerosis and focal cortical dysplasia), neurodegenerative (Alzheimer's disease, progressive primary aphasia, and frontotemporal dementia), infectious (Herpes simplex virus and limbic encephalitis), vascular (ischemic stroke, arteriovenous malformation, and cerebral cavernous malformations), and toxic-metabolic (transient global amnesia and opioid-associated amnestic syndrome) etiologies.

The genetic link between systemic autoimmune disorders and temporal lobe epilepsy: A bioinformatics study

OBJECTIVE

We aimed to explore the underlying pathomechanisms of the comorbidity between three common systemic autoimmune disorders (SADs) [i.e., insulin-dependent diabetes mellitus (IDDM), systemic lupus erythematosus (SLE), and rheumatoid arthritis (RA)] and temporal lobe epilepsy (TLE), using bioinformatics tools. We hypothesized that there are shared genetic variations among these four conditions.

METHODS

Different databases (DisGeNET, Harmonizome, and Enrichr) were searched to find TLE-associated genes with variants; their single nucleotide polymorphisms (SNPs) were gathered from the literature. We also did a separate literature search using PubMed with the following keywords for original articles: "TLE" or "Temporal lobe epilepsy" AND "genetic variation," "single nucleotide polymorphism," "SNP," or "genetic polymorphism." In the next step, the SNPs associated with TLE were searched in the LitVar database to find the shared gene variations with RA, SLE, and IDDM.

RESULTS

Ninety unique SNPs were identified to be associated with TLE. LitVar search identified two SNPs that were shared between TLE and all three SADs (i.e., IDDM, SLE, and RA). The first SNP was rs16944 on the Interleukin-1β (IL-1β) gene. The second genetic variation was ε4 variation of apolipoprotein E (APOE) gene.

SIGNIFICANCE

The shared genetic variations (i.e., rs16944 on the IL-1β gene and ε4 variation of the APOE gene) may explain the underlying pathomechanisms of the comorbidity between three common SADs (i.e., IDDM, SLE, and RA) and TLE. Exploring such shared genetic variations may help find targeted therapies for patients with TLE, especially those with drug-resistant seizures who also have comorbid SADs.

Peroxiredoxin 6 Regulates Glutathione Peroxidase 1-Medited Glutamine Synthase Preservation in the Hippocampus of Chronic Epilepsy Rats

Clasmatodendrosis (an autophagic astroglial degeneration) plays an important role in the regulation of spontaneous seizure duration but not seizure frequency or behavioral seizure severity in chronic epilepsy rats. Recently, it has been reported that N-acetylcysteine (NAC), a precursor to glutathione (GSH), attenuates clasmatodendritic degeneration and shortens spontaneous seizure duration in chronic epilepsy rats, although the underlying mechanisms of its anti-convulsive effects are not fully understood. To elucidate this, the present study was designed to investigate whether NAC affects astroglial glutamine synthase (GS) expression mediated by GSH peroxidase 1 (GPx1) and/or peroxiredoxin 6 (Prdx6) in the epileptic hippocampus. As compared to control animals, GS and GPx1 expressions were upregulated in reactive CA1 astrocytes of chronic epilepsy rats, while their expressions were significantly decreased in clasmatodendritic CA1 astrocytes and reactive astrocytes within the molecular layer of the dentate gyrus. Prdx6 expression was increased in reactive CA1 astrocytes as well as clasmatodendritic CA1 astrocytes. In the molecular layer of the dentate gyrus, Prdx6 expression levels were similar to those in control animals. NAC ameliorated clasmatodendrosis through the increment of GS and GPx1 expressions, while it abolished Prdx6 upregulation. 1-hexadecyl-3-(trifluoroethgl)-sn-glycerol-2 phosphomethanol (MJ33, a selective inhibitor of aiPLA2 activity of Prdx6) alleviated clasmatodendrosis by enhancing GPx1 and GS expressions in clasmatodendritic CA1 astrocytes without changing the Prdx6 level. NAC or MJ33 did not affect GS, GPx1 and Prdx6 expression in astrocytes within the molecular layer of the dentate gyrus. These findings indicate that upregulated aiPLA2 activity of Prdx6 may abolish GPx1-mediated GS preservation and lead to clasmatodendrosis in CA1 astrocytes, which would extend spontaneous seizure duration due to impaired glutamate-glutamine conversion regulated by GS. Therefore, the present data suggest that aiPLA2 activity of Prdx6 in astrocytes may be one of the upstream effectors of seizure duration in the epileptic hippocampus.

Sp1-Mediated Prdx6 Upregulation Leads to Clasmatodendrosis by Increasing Its aiPLA2 Activity in the CA1 Astrocytes in Chronic Epilepsy Rats

Clasmatodendrosis is an autophagic astroglial degeneration (a non-apoptotic (type II) programmed cell death) whose underlying mechanisms are fully understood. Peroxiredoxin-6 (Prdx6), the “non-selenium glutathione peroxidase (NSGPx)”, is the only member of the 1-cysteine peroxiredoxin family. Unlike the other Prdx family, Prdx6 has multiple functions as glutathione peroxidase (GPx) and acidic calcium-independent phospholipase (aiPLA2). The present study shows that Prdx6 was upregulated in CA1 astrocytes in chronic epilepsy rats. 2-Cyano-3,12-dioxo-oleana-1,9(11)-dien-28-oic acid methyl ester (CDDO-Me) and N-acetylcysteine (NAC, a precursor of glutathione) ameliorated clasmatodendrosis accompanied by reduced Prdx6 level in CA1 astrocytes. Specificity protein 1 (Sp1) expression was upregulated in CA1 astrocyte, which was inhibited by mithramycin A (MMA). MMA alleviated clasmatodendrosis and Prdx6 upregulation. Sp1 expression was also downregulated by CDDO-Me and NAC. Furthermore, 1-hexadecyl-3-(trifluoroethgl)-sn-glycerol-2 phosphomethanol (MJ33, a selective inhibitor of aiPLA2 activity of Prdx6) attenuated clasmatodendrosis without affecting Prdx6 expression. All chemicals shortened spontaneous seizure duration but not seizure frequency and behavioral seizure severity in chronic epilepsy rats. Therefore, our findings suggest that Sp1 activation may upregulate Prdx6, whose aiPLA2 activity would dominate over GPx activity in CA1 astrocytes and may lead to prolonged seizure activity due to autophagic astroglial degeneration.