MicroRNA-335-5p suppresses voltage-gated sodium channel expression and may be a target for seizure control

Abstract

There remains an urgent need for new therapies for drug-resistant epilepsy (DRE). Sodium channel blockers are effective for seizure control in common forms of epilepsy, but loss of sodium channel function underlies some genetic forms of epilepsy. Approaches that provide bi-directional control of sodium channel expression are needed. MicroRNAs (miRNA) are small non-coding RNAs which negatively regulate gene expression. Here, we show that genome-wide miRNA screening of hippocampal tissue from a rat epilepsy model, mice treated with the novel anti-seizure medicine cannabidiol (CBD) and plasma from patients with DRE, converge on a single target, miR-335-5p. Pathway analysis on predicted and validated miR-335-5p targets identified multiple voltage-gated sodium channels (VGSCs). Intracerebroventricular injection of antisense oligonucleotides against miR-335-5p resulted in upregulation of Scn1a, Scn2a and Scn3a in the mouse brain and an increased action potential rising phase and greater excitability of hippocampal pyramidal neurons in brain slice recordings, consistent with VGSCs as functional targets of miR-335-5p. Blocking of miR-335-5p also increased voltage-gated sodium currents in human iPSC-derived neurons. Inhibition of miR-335-5p increased susceptibility to tonic-clonic seizures in the pentylenetetrazole seizure model, whereas AAV9-mediated overexpression of miR-335-5p reduced seizure severity and improved survival. These studies suggest modulation of miR-335-5p may be a means to regulate VGSCs and affect brain excitability and seizures. Changes to miR-335-5p may reflect compensatory mechanisms to control excitability and could provide new biomarker or therapeutic strategies for different types of drug-resistant epilepsy.

MicroRNAs – small RNAs with a big influence on brain excitability

“…As miR-324-5p represses the expression of Kcnd2, it follows that antisense inhibition of miR-324-5p leads to increased Kv4.2 functional expression and a reduction in neuronal excitability and seizures (Gross et al, 2016;Tiwari et al, 2019). Similarly, a recent study showed that miR-335-5p is able to reduce susceptibility to induced seizures via repression of the voltage-gated sodium channel subunit Scn2a (Heiland et al, 2022).…”

“…It is possible that the impact of species‐specific sequences may be mitigated by the ability of miRNAs to operate with only partial target complementarity, adding complexity to the translation of studies between animal models and the human brain. To overcome this, studies in the epilepsy field have used surgically resected specimens in order to characterise MTIs in the human seizure focus (Heiland et al., 2022). A recent method (Morris et al., 2022) allows for the application of antimiRs to non‐diseased acutely resected human temporal neocortex (note – this tissue was removed during resective epilepsy surgery to give access to the seizure focus within the temporal lobe; whilst the neocortical tissue is assumed healthy, it was taken from the brain of a person with epilepsy and should be interpreted in this context).…”

“…Induced pluripotent stem cell‐based models can also be used to study MTIs in a human‐derived preparation (e.g. Heiland et al., 2022), though these may not form physiologically realistic synaptic connections and networks (Morris, Rowell et al., 2021), possibly affecting the molecular pathways mediating miRNA function that are described in this article. Human models also have limitations (Richardson & Morris, 2022) and should be used carefully in parallel with animal models to better integrate findings between rodent and human brains.…”

MicroRNA 335-5p: The Sodium Channel Silencer

“…The current study by Heiland and colleagues identified miRNA-335-5p as a potential target for modulating VGSCs in a combination of animal and human epilepsy models. 6 Previous reports that aimed to identify miRNAs that were altered in treatment-resistant forms of epilepsy were based on datasets from only rodent models or a single tissue type, which might limit clinical relevance. In contrast, Heiland et al, explored miRNAs that emerged from multiple datasets, including both rodent tissue and human biofluids, to increase the potential of identifying miRNAs that might be common to multiple forms of treatment-resistant epilepsy.…”

“…In contrast, Heiland et al, explored miRNAs that emerged from multiple datasets, including both rodent tissue and human biofluids, to increase the potential of identifying miRNAs that might be common to multiple forms of treatment-resistant epilepsy. 6 The expression datasets that were used were derived from a perforant path stimulation rat model of temporal lobe epilepsy, blood samples from patients with epilepsy, and mouse brain following treatment with cannabidiol (CBD). Out of over 200 candidates, a single miRNA, miR-335-5p, was found to be altered in all 3 datasets, and importantly, the sequence of miR-335-5p is conserved between rodents and humans, highlighting the potential translational relevance of miR-335-5p.…”