Identification of Specific Circular RNA Expression Patterns and MicroRNA Interaction Networks in Mesial Temporal Lobe Epilepsy

Aberrant encoding of event saliency in the orbitofrontal cortex following loss of the psychiatric-associated circular RNA, circHomer1

CircHomer1 is an activity-dependent circular RNA (circRNA) isoform produced from back-splicing of the Homer1 transcript. Homer1 isoforms are well-known regulators of homeostatic synaptic plasticity through post-synaptic density scaffold regulation. Homer1 polymorphisms have been associated with psychiatric diseases including schizophrenia (SCZ) and bipolar disorder (BD). Postmortem tissue from patients with SCZ and BD displayed reduced circHomer1 levels within the orbitofrontal cortex (OFC), a region that tracks event saliency important for modulating behavioral flexibility. While dysregulation of circHomer1 expression has recently been identified across multiple psychiatric and neurodegenerative disorders and is associated with impaired behavioral flexibility in mice, it is unknown whether circHomer1 can induce electrophysiological signatures relevant to cognitive dysfunction in these disorders. To examine the role of circHomer1 in neuronal signaling, we bilaterally knocked down circHomer1 in the OFC of C57BL/6 J male mice and recorded neural activity from the OFC during a touchscreen reversal learning task then measured molecular changes of synaptic regulators following knockdown. Knockdown of circHomer1 within the OFC induced choice-dependent changes in multiunit firing rate and local field potential coordination and power to salient stimuli during reversal learning. Further, these electrophysiological changes were associated with transcriptional downregulation of glutamatergic signaling effectors and behavioral alterations leading to impaired cognitive flexibility. CircHomer1 is a stable biomolecule, whose knockdown in rodent OFC produces lasting electrophysiological and transcriptional changes important for efficient reversal learning. This is, to our knowledge, the first demonstration of a psychiatric-associated circRNA contributing to electrophysiological, transcriptional, and behavioral alterations relevant to psychiatric phenotypes.

Silencing miR-155-5p alleviates hippocampal damage in kainic acid-induced epileptic rats via the Dusp14/MAPK pathway

Epilepsy with recurrent seizures is characterized by neuronal damage and glial proliferation induced by brain inflammation. Recurrent seizures can lead to changes in the microRNA (miRNA) spectrum, significantly influencing the inflammatory response of microglia. MiR-155-5p, as a pro-inflammatory miRNA, is increased in the epileptic brain. However, its specific role in acute seizures remains unknown. The study aimed to develop a new strategy for treating epilepsy by investigating how silencing of miR-155-5p initiated its anticonvulsive mechanism. The level of miR-155-5p was up-regulated in the hippocampus of epileptic immature rats induced by kainic acid (KA). The use of antago-miR-155-5p exerted significant beneficial effects on the seizure scores, brain discharges and cognition in immature rats following KA-induced epilepsy. Antago-miR-155-5p also inhibited neuron damage and microglial activation. Moreover, the silencing of miR-155-5p significantly inhibited the Dual-specificity phosphatase 14 (Dusp14)/ mitogen-activated protein kinase (MAPK) axis in vivo. MiR-155-5p interacted with dusp14 to regulate MAPK signaling way expression, verified by a dual-luciferase reporter assay. The results suggested that the silencing of miR-155-5p might reduce hippocampal damage in epileptic immature rats induced by KA via Dusp14/MAPK signaling way. This implied that miR-155-5p could serve as a therapeutic tool to prevent the development of epilepsy.

Advances in Circular RNA in the Pathogenesis of Epilepsy

Recent studies evidenced the involvement of circular RNA (circRNA) in neuroinflammation, apoptosis, and synaptic remodeling suggesting an important role for circRNA in the occurrence and development of epilepsy. This review provides an overview of circRNAs considered to be playing regulatory roles in the process of epilepsy and to be involved in multiple biological epilepsy-related processes, such as hippocampal sclerosis, inflammatory response, cell apoptosis, synaptic remodeling, and cell proliferation and differentiation. This review covers the current research status of differential expression of circRNA-mediated seizures, m6A methylation, demethylation-mediated seizures in post transcriptional circRNA modification, as well as the mechanisms of m5C- and m7G-modified circRNA. In summary, this article reviews the research progress on the relationship between circRNA in non-coding RNA and epilepsy.

Research progress on the relationship between epilepsy and circRNA

OBJECTIVE

This review aims to provide a comprehensive summary of the latest research progress regarding the relationship between epilepsy and circular RNA (circRNA).

METHODS

Relevant literature from the PubMed database was meticulously searched and reviewed. The selected articles focused on investigating the association between epilepsy and circRNA, including studies on expression patterns, diagnostic markers, therapeutic targets, and functional mechanisms.

RESULTS

Epilepsy, characterized by recurrent seizures, is a neurological disorder. Numerous studies have demonstrated significant alterations in the expression profiles of circRNA in epileptic brain tissues, animal models, and peripheral blood samples. These differential expressions of circRNA are believed to be closely linked with the occurrence and development of epilepsy. Moreover, circRNA has shown promising potential as diagnostic markers for epilepsy, as well as prognostic indicators for predicting disease outcomes. Furthermore, circRNA has emerged as a potential therapeutic target for epilepsy treatment, offering prospects for gene therapy interventions.

CONCLUSION

The dysregulation of circRNA expression in epilepsy suggests its potential involvement in the pathogenesis and progression of this disorder. Identifying specific circRNA molecules associated with epilepsy may pave the way for novel diagnostic approaches and therapeutic strategies. However, further investigations are imperative to elucidate the precise functional mechanisms of circRNA in epilepsy and validate its clinical utility.

CircRNA-associated ceRNA regulatory networks as emerging mechanisms governing the development and biophysiopathology of epilepsy

The etiology of epilepsy is ascribed to the synchronized aberrant neuronal activity within the brain. Circular RNAs (circRNAs), a class of non-coding RNAs characterized by their circular structures and covalent linkage, exert a substantial influence on this phenomenon. CircRNAs possess stereotyped replication, transience, repetitiveness, and paroxysm. Additionally, MicroRNA (miRNA) plays a crucial role in the regulation of diverse pathological processes, including epilepsy. CircRNA is of particular significance due to its ability to function as a competing endogenous RNA, thereby sequestering or inhibiting miRNA activity through binding to target mRNA. Our review primarily concentrates on elucidating the pathological and functional roles, as well as the underlying mechanisms, of circRNA-miRNA-mRNA networks in epilepsy. Additionally, it explores the potential utility of these networks for early detection and therapeutic intervention.

Circular RNAs: Diagnostic and Therapeutic Perspectives in CNS Diseases

Circular RNAs (circRNAs) are a class of regulatory non-coding RNAs characterized by the presence of covalently closed ends. A growing body of evidence suggests that circRNAs play important roles in physiology and pathology. In particular, accumulating data on circRNA functions in various central nervous system (CNS) diseases and their correlations indicate that circRNAs are critical contributors to the onset and development of brain disorders. In this review, we focus on the regulatory and functional roles of circRNAs in CNS diseases, highlighting their diagnostic and therapeutic potential, with the aim of providing new insights into CNS diseases.

Identification and characterization of circular RNA in the model of autism spectrum disorder from PM2.5 exposure

PM_2.5 induces a series of effects on neurological disorders, including autism spectrum disorder (ASD), however, the mechanism is not completely clear yet. Circular RNAs (circRNAs) are a class of closed-loop structures that can be stably expressed in vivo. In our experiments, rats exposed to PM_2.5 exhibited autism-like phenotypes, such as anxiety, and memory loss. To explore the etiology, we performed transcriptome sequencing and found significant differences in the expression of circRNA. A total of 7770 circRNAs were identified between the control and experimental groups, 18 of which were differentially expressed, we selected ten circRNAs and performed qRT-PCR and Sanger sequencing to validate them. By GO and KEGG enrichment analysis, we found differentially expressed circRNAs that were mainly enriched in processes related to placental development and reproduction. Finally, using bioinformatics, we predicted miRNAs and mRNAs that circ-Mbd5 and circ-Ash1l might regulate and constructed circRNA-miRNA-mRNA networks involving genes associated with ASD, suggesting that circRNAs might regulate the occurrence of ASD.

Emerging Molecular Targets for Anti-Epileptogenic and Epilepsy Modifying Drugs

The pharmacological treatment of epilepsy is purely symptomatic. Despite many decades of intensive research, causal treatment of this common neurologic disorder is still unavailable. Nevertheless, it is expected that advances in modern neuroscience and molecular biology tools, as well as improved animal models may accelerate designing antiepileptogenic and epilepsy-modifying drugs. Epileptogenesis triggers a vast array of genomic, epigenomic and transcriptomic changes, which ultimately lead to morphological and functional transformation of specific neuronal circuits resulting in the occurrence of spontaneous convulsive or nonconvulsive seizures. Recent decades unraveled molecular processes and biochemical signaling pathways involved in the proepileptic transformation of brain circuits including oxidative stress, apoptosis, neuroinflammatory and neurotrophic factors. The "omics" data derived from both human and animal epileptic tissues, as well as electrophysiological, imaging and neurochemical analysis identified a plethora of possible molecular targets for drugs, which could interfere with various stages of epileptogenetic cascade, including inflammatory processes and neuroplastic changes. In this narrative review, we briefly present contemporary views on the neurobiological background of epileptogenesis and discuss the advantages and disadvantages of some more promising molecular targets for antiepileptogenic pharmacotherapy.

The Coordination of mTOR Signaling and Non-Coding RNA in Regulating Epileptic Neuroinflammation

Epilepsy accounts for a significant proportion of the burden of neurological disorders. Neuroinflammation acting as the inflammatory response to epileptic seizures is characterized by aberrant regulation of inflammatory cells and molecules, and has been regarded as a key process in epilepsy where mTOR signaling serves as a pivotal modulator. Meanwhile, accumulating evidence has revealed that non-coding RNAs (ncRNAs) interfering with mTOR signaling are involved in neuroinflammation and therefore articipate in the development and progression of epilepsy. In this review, we highlight recent advances in the regulation of mTOR on neuroinflammatory cells and mediators, and feature the progresses of the interaction between ncRNAs and mTOR in epileptic neuroinflammation.

Non-Coding RNAs: New Biomarkers and Therapeutic Targets for Temporal Lobe Epilepsy

Temporal lobe epilepsy (TLE) is the most common form of focal epilepsy; it is considered a network disorder associated with structural changes. Incomplete knowledge of the pathological changes in TLE complicates a therapeutic approach; indeed, 30 to 50% of patients with TLE are refractory to drug treatment. Non-coding RNAs (ncRNAs), acting as epigenetic factors, participate in the regulation of the pathophysiological processes of epilepsy and are dysregulated during epileptogenesis. Abnormal expression of ncRNA is observed in patients with epilepsy and in animal models of epilepsy. Furthermore, ncRNAs could also be used as biomarkers for the diagnosis and prognosis of treatment response in epilepsy. In summary, ncRNAs can represent important mechanisms and targets for the modulation of brain excitability and can provide information on pathomechanisms, biomarkers and novel therapies for epilepsy. In this review, we summarize the latest research advances concerning mainly molecular mechanisms, regulated by ncRNA, such as synaptic plasticity, inflammation and apoptosis, already associated with the pathogenesis of TLE. Moreover, we discuss the role of ncRNAs, such as microRNAs, long non-coding RNAs and circular RNAs, in the pathophysiology of epilepsy, highlighting their use as potential biomarkers for future therapeutic approaches.

Expression of Circ_Satb1 Is Decreased in Mesial Temporal Lobe Epilepsy and Regulates Dendritic Spine Morphology

Mesial temporal lobe epilepsy (mTLE) is a chronic disease characterized by recurrent seizures that originate in the temporal lobes of the brain. Anti-epileptic drugs (AEDs) are the standard treatment for managing seizures in mTLE patients, but are frequently ineffective. Resective surgery is an option for some patients, but does not guarantee a postoperative seizure-free period. Therefore, further insight is needed into the pathogenesis of mTLE to enable the design of new therapeutic strategies. Circular RNAs (circRNAs) have been identified as important regulators of neuronal function and have been implicated in epilepsy. However, the mechanisms through which circRNAs contribute to epileptogenesis remain unknown. Here, we determine the circRNA transcriptome of the hippocampus and cortex of mTLE patients by using RNA-seq. We report 333 differentially expressed (DE) circRNAs between healthy individuals and mTLE patients, of which 23 circRNAs displayed significant adjusted p-values following multiple testing correction. Interestingly, hippocampal expression of circ_Satb1, a circRNA derived from special AT-rich sequence binding protein 1 (SATB1), is decreased in both mTLE patients and in experimental epilepsy. Our work shows that circ_Satb1 displays dynamic patterns of neuronal expression in vitro and in vivo. Further, circ_Satb1-specific knockdown using CRISPR/CasRx approaches in hippocampal cultures leads to defects in dendritic spine morphology, a cellular hallmark of mTLE. Overall, our results identify a novel epilepsy-associated circRNA with disease-specific expression and previously unidentified cellular effects that are relevant for epileptogenesis.

Multi-omic strategies applied to the study of pharmacoresistance in mesial temporal lobe epilepsy

Mesial temporal lobe epilepsy (MTLE) is the most common type of focal epilepsy in adults, and hippocampal sclerosis (HS) is a frequent histopathological feature in patients with MTLE. Pharmacoresistance is present in at least one-third of patients with MTLE with HS (MTLE+HS). Several hypotheses have been proposed to explain the mechanisms of pharmacoresistance in epilepsy, including the effect of genetic and molecular factors. In recent years, the increased knowledge generated by high-throughput omic technologies has significantly improved the power of molecular genetic studies to discover new mechanisms leading to disease and response to treatment. In this review, we present and discuss the contribution of different omic modalities to understand the basic mechanisms determining pharmacoresistance in patients with MTLE+HS. We provide an overview and a critical discussion of the findings, limitations, new approaches, and future directions of these studies to improve the understanding of pharmacoresistance in MTLE+HS. However, it is important to point out that, as with other complex traits, pharmacoresistance to anti-seizure medications is likely a multifactorial condition in which gene-gene and gene-environment interactions play an important role. Thus, studies using multidimensional approaches are more likely to unravel these intricate biological processes.

Circ_0084043 Facilitates High Glucose-Induced Retinal Pigment Epithelial Cell Injury by Activating miR-128-3p/TXNIP-Mediated Wnt/β-Catenin Signaling Pathway

ABSTRACT

Diabetic retinopathy is a frequent complication of diabetes mellitus and one of the common causes of blindness. Circular RNAs (circRNAs) can modulate various biological behaviors of human diseases. Circ_0084043 is a novel circRNA, and its function in diabetic retinopathy progression is unclear. Adult retinal pigment epithelial cells (ARPE-19) were treated with high glucose (HG). RNA levels of circ_0084043, microRNA-128-3p (miR-128-3p), and thioredoxin-interacting protein (TXNIP) were detected by quantitative real-time polymerase chain reaction. 3-(4, 5-dimethylthiazole-2-y1)-2, 5-diphenyl tetrazolium bromide and flow cytometry were, respectively, used to examine cell viability and apoptosis. Apoptotic and TNXIP relative protein levels were measured by Western blot. The combination between targets was analyzed through dual-luciferase reporter assay or RNA immunoprecipitation assay. Results showed that HG induced the upregulation of circ_0084043 and the downregulation of miR-128-3p in ARPE-19 cells. Circ_0084043 knockdown or miR-128-3p overexpression mitigated the HG-mediated cell viability inhibition, apoptosis promotion, and inflammatory response. Circ_0084043 targeted miR-128-3p and miR-128-3p inhibitor returned the regulation of si-circ_0084043 in HG-treated cells. TXNIP was the target gene of miR-128-3p and TXNIP overexpression abolished the miR-128-3p-mediated effects after HG treatment. Circ_0084043 regulated the TXNIP expression to activate Wnt/β-catenin signal pathway by targeting miR-128-3p. Our findings unraveled that circ_0084043 promoted the HG-induced retinal pigment epithelial cell injury through activating the Wnt/β-catenin signal pathway by the miR-128-3p/TXNIP axis. Circ_0084043 might be an available biomarker in diabetic retinopathy diagnosis and therapy.

Enrichment of Circular RNA Expression Deregulation at the Transition to Recurrent Spontaneous Seizures in Experimental Temporal Lobe Epilepsy

Mesial temporal lobe epilepsy (mTLE) is a common form of epilepsy and is characterized by recurrent spontaneous seizures originating from the temporal lobe. The majority of mTLE patients develop pharmacoresistance to available anti-epileptic drugs (AEDs) while exhibiting severe pathological changes that can include hippocampal atrophy, neuronal death, gliosis and chronic seizures. The molecular mechanisms leading to mTLE remain incompletely understood, but are known to include defects in post-transcriptional gene expression regulation, including in non-coding RNAs (ncRNAs). Circular RNAs (circRNAs) are a class of recently rediscovered ncRNAs with high levels of expression in the brain and proposed roles in diverse neuronal processes. To explore a potential role for circRNAs in epilepsy, RNA-sequencing (RNA-seq) was performed on hippocampal tissue from a rat perforant pathway stimulation (PPS) model of TLE at different post-stimulation time points. This analysis revealed 218 differentially expressed (DE) circRNAs. Remarkably, the majority of these circRNAs were changed at the time of the occurrence of the first spontaneous seizure (DOFS). The expression pattern of two circRNAs, circ_Arhgap4 and circ_Nav3, was further validated and linked to miR-6328 and miR-10b-3p target regulation, respectively. This is the first study to examine the regulation of circRNAs during the development of epilepsy. It reveals an intriguing link between circRNA deregulation and the transition of brain networks into the state of spontaneous seizure activity. Together, our results provide a molecular framework for further understanding the role and mechanism-of-action of circRNAs in TLE.