Single target, multiple possibilities: microRNA holds promise for epilepsy treatment

By Vijay Kumar MalesuReviewed by Lily Ramsey, LLMJul 25 2023

In a recent study published in the PNAS Journal, a group of researchers investigated the role of micro-ribonucleic acid (miRNA) miR-335-5p as a potential therapeutic target for epilepsy by regulating neuronal excitability through the modulation of voltage-gated sodium channels (VGSCs).

Study: MicroRNA-335-5p suppresses voltage-gated sodium channel expression and may be a target for seizure control. Image Credit: SewCreamStudio/Shutterstock.com

Background

Epilepsy affects millions of individuals worldwide, and current antiseizure medications (ASMs) target VGSCs. However, some forms of epilepsy, like Dravet syndrome, are treatment-resistant due to loss of VGSC function. To develop better therapies, researchers are exploring miRNAs that regulate gene expression.

MiRNAs can control VGSC expression, making them attractive therapeutic targets. Triangulating miRNA datasets and studying miRNA alterations caused by effective ASMs could reveal potential therapeutic miRNAs for epilepsy.

Cannabidiol (CBD), approved for treatment-resistant epilepsy, is an example of an effective ASM with an unknown mechanism of action, arising the need for further investigation.

About the study

The study focused on investigating epilepsy using animal models. Animals were kept in controlled conditions with a 12-hour light-dark cycle, proper temperature, and humidity, with food and water freely available.

The researchers used two epilepsy models: the PPS model of temporal lobe epilepsy (TLE) in rats and the pentylenetetrazol (PTZ) model in mice. For the perforant path stimulation (PPS) model, electrodes were implanted, and seizures were induced using paired-pulse stimuli. For the PTZ model, mice received a convulsant dose of PTZ to trigger seizures.

Various treatments were administered to investigate their effects on epilepsy. They modulated miRNA through antisense oligonucleotide "antimir" injections and viral particles expressing specific miRNAs. Additionally, they administered CBD, a compound derived from cannabis, to study its potential effects on epilepsy.

The researchers analyzed miRNA and mRNA expression in the brain tissues of the animals. They also identified miRNA-target interactions and performed pathway enrichment analyses to understand the molecular mechanisms involved in epilepsy.

Finally, ex vivo electrophysiological recordings and sodium currents (I_Na) recordings in human-induced pluripotent stem cell-derived neurons were conducted to study the effects of miRNA manipulation.

All experimental procedures, such as the European Communities Council Directive (2010/63/EU), adhered to ethical guidelines.

Study results

This study focused on miR-335-5p as a potential therapeutic target for treatment-resistant epilepsy. They used a triangulation approach, combining data from different datasets to identify miRNAs relevant to epilepsy.

MiR-335-5p stood out as it was consistently altered in rat hippocampal subfields, human plasma samples, and after treatment with CBD in mice.

To better understand the functional role of miR-335-5p, the researchers investigated its targets. They found that miR-335-5p regulates several genes encoding for VGSCs, including sodium voltage-gated channel alpha subunit 1 (SCN1A), sodium voltage-gated channel alpha subunit 2 (SCN2A), and sodium voltage-gated channel alpha subunit 3 (SCN3A), which are crucial for neuronal excitability.

Pathway enrichment analysis revealed that many of the targets of miR-335-5p are involved in pathways related to neuronal excitability, further supporting its potential role in epilepsy.

The authors used human induced pluripotent stem cell (iPSC)-derived neurons to validate the findings in human brain-relevant models. Inhibition of miR-335-5p in these neurons resulted in an upregulation of VGSCs, confirming the regulatory role of miR-335-5p in human neuronal excitability.

Further, inhibiting miR-335-5p increased seizure susceptibility, while overexpressing miR-335-5p using viral vectors reduced seizure severity and increased survival in response to seizures induced by PTZ.

Researchers found that the behavioral tests showed no adverse effects of miR-335-5p modulation on cognition or naturalistic behavior in mice, indicating its potential safety as a therapeutic target.

Discussion

In this study, researchers utilized a combination of model-based, drug-altered, and human epilepsy biomarker datasets to identify miRNAs that regulate neuronal excitability, which could be relevant for seizure control.

Their approach, known as triangulation, led them to focus on miR-335-5p, a miRNA primarily found in the brain. This approach provided additional miRNA targets for epilepsy treatment compared to other methods.

MiR-335-5p was not initially considered a leading candidate when only animal model miRNA profiles were examined, underscoring the importance of including human data and diverse sources of miRNA profiling. Interestingly, miR-335-5p levels appeared to vary among different models, which may be related to temporal and activity-dependent changes in miRNA expression.

The researchers found that miR-335-5p plays a role in regulating the expression of VGSCs, which are crucial for neuronal excitability.

Inhibiting miR-335-5p increased VGSC levels and pyramidal neuron excitability in mice while overexpressing it had the opposite effect, reducing seizure severity. These findings suggest that miR-335-5p could be a potential therapeutic target for modulating neuronal excitability in epilepsy.

Moreover, the study demonstrated that miR-335-5p modulation did not adversely affect cognition or natural behavior in mice, indicating its potential safety as a therapeutic approach.

Conclusions

To summarize, researchers found that targeting miR-335-5p could potentially develop new treatments for epilepsy, as it could influence VGSCs and fine-tune neuronal excitability, providing a bidirectional effect that might be beneficial in different forms of epilepsy.

However, further research is needed to understand the full extent of miR-335-5p's role and its potential as a therapeutic strategy for epilepsy and other neurological disorders.