Intranasal Delivery of miR-146a Mimics Delayed Seizure Onset in the Lithium-Pilocarpine Mouse Model

Abstract

Unveiling the key mechanism of temporal lobe epilepsy (TLE) for the development of novel treatments is of increasing interest, and anti-inflammatory miR-146a is now considered a promising molecular target for TLE. In the current study, a C57BL/6 TLE mouse model was established using the lithium-pilocarpine protocol. The seizure degree was evaluated according to the Racine scale, and level 5 was considered the threshold for generalized convulsions. Animals were sacrificed to analyze the hippocampus at three time points (2 h and 4 and 8 weeks after pilocarpine administration to evaluate the acute, latent, and chronic phases, resp.). After intranasal delivery of miR-146a mimics (30 min before pilocarpine injection), the percent of animals with no induced seizures increased by 6.7%, the latency to generalized convulsions was extended, and seizure severity was reduced. Additionally, hippocampal damage was alleviated. While the relative miR-146a levels significantly increased, the expression of its target mRNAs (IRAK-1 and TRAF-6) and typical inflammatory modulators (NF-κB, TNF-α, IL-1β, and IL-6) decreased, supporting an anti-inflammatory role of miR-146a via the TLR pathway. This study is the first to demonstrate that intranasal delivery of miR-146a mimics can improve seizure onset and hippocampal damage in the acute phase of lithium-pilocarpine-induced seizures, which provides inflammation-based clues for the development of novel TLE treatments.

Loss of the neurodevelopmental disease-associated gene miR-146a impairs neural progenitor differentiation and causes learning and memory deficits

“…miR-146a is 100% conserved between humans and mice; it is expressed broadly in the brain during embryonic development and restricted to neurons at postnatal stages. Importantly, modulating the expression of this particular miRNA was shown to reduce the latency, the duration as well as the intensity of the induced epilepsy in rodent models of telencephalon epilepsy [15,16].…”

Ago2-seq identifies new microRNA targets for seizure control

“…treating patients with pre-existing, refractory epilepsy) 17 , we found eight up- and one down-regulated miRNAs common to all three models (Figure 3B,C). This included miR-132-3p and miR-146a-5p, for which there is already significant functional data linking them to epilepsy 25–28 , and six miRNAs (miR-10a-5p, miR-21a-3p, miR-27a-3p, miR-142a-5p, miR-212-3p and miR-431-5p) for which there is limited or no functional in vivo data linking to epilepsy (Figure 3C).…”

MicroRNA‐induced silencing in epilepsy: Opportunities and challenges for clinical application

“…Lack of complement inhibition can lead to a state of chronic inflammation, not uncommonly found in brains from patients with refractory epilepsy (Vezzani and Viviani, 2015). Future work is needed to reconcile the proseizure functions of miR-146a reported by He et al, with the anti-seizure and -epilepsy functions observed in two other studies (Iori et al, 2017b;Tao et al, 2017).…”

“…Two recent studies showed a seizure‐suppressing effect of miR‐146a supplementation. Intranasal administration of a miR‐146a mimic delayed seizure onset in a lithium‐pilocarpine rat model of TLE (Tao et al, ), and intracerebroventricular injection of a miR‐146a mimic before or after kainic acid‐mediated induction of status epilepticus delayed seizure onset and reduced seizure frequency in mice (Iori et al, ). Iori et al demonstrated that modulation of miR‐146a through intracerebroventricular injection of a mimic 24 hrs and 72 hrs before induction of kainic acid‐induced status epilepticus in mice decreased the time spent in seizure in addition to reducing the overall number of seizures.…”

“…In neurons, activation of TLR4 promotes NMDA receptordependent calcium influx (Maroso et al, 2010). The anti-seizure effects of miR-146a mimics (described above; Iori et al, 2017b;Tao et al, 2017) could thus be partially caused by reduction of NMDA receptor-dependent neuronal excitability, in addition to suppressing neuroinflammation mediated by astrocytes (Vezzani and Viviani, 2015;Iori et al, 2017a). Iori et al also showed that treatment with anti-inflammatory drugs under a similar time course as they used for application of the miR-146a-specific mimic likewise reduced seizure frequency in chronically seizing mice weeks after drug treatment had ended (Iori et al, 2017b).…”