Abstracts

Rationale: Rationale: The contribution of inflammatory processes originating from activated microglia and astrocytes to the pathogenesis of seizures has been demonstrated in experimental models, and is strongly supported by clinical evidence. Glial cells activated by epileptogenic injuries release pro-inflammatory mediators that increase neuronal excitability, thus promoting the establishment of a seizure generating network. A novel mechanism of efficient and upstream control of pathologic brain inflammation in epilepsy is represented by micro(mi)RNAs, acting as a key post-transcriptional regulators of the innate immune response. We studied the anti-inflammatory and anti-ictogenic properties of miR146a which is up-regulated in hippocampus in human and experimental epilepsy, and modulates the activation of the IL-1R/TLR signaling, a major pro-inflammatory and epileptogenic pathway. Methods: Methods: C57BL6 adult male mice were chronically implanted with hippocampal electrodes and indwelling injection cannula. Seizures were evoked by intracerebral kainic acid (KA), monitored and quantified by EEG analysis. Discrete self-remitting acute seizures were induced by intrahippocampal injection of 7 ng KA while chronic spontaneous recurrent seizures (SRS) were induced by intra-amygdala injection of 0.3 µg KA causing status epilepticus (SE). miR146a synthetic mimic, LNA-antisense (antagomir) or their respective negative controls were injected intracerebroventricularly (icv) in naïve mice, or 24 h before KA in the acute seizure model. In the SRS model, mimic or negative control were injected icv for 2 weeks starting treatment at the onset of epilepsy (two spontaneous seizures >48 h after SE onset). mRNA levels were measured by RT-PCR. Results: Results: Antagomir decreased by 50% miR146a and increased significantly IL-1β and TLR4 mRNA hippocampal levels in naïve mice. Antagomir enhanced by 2-fold the time spent in seizures in the acute model. Conversely, mimic increased miR146a several-fold in the hippocampus, decreased its target proteins TRAF6 and IRAK2, and reduced by 50% the number and total duration of acute seizures. In the chronic model, mimic treatment of mice at the onset of epilepsy reduced their SRS frequency at 2 months post-SE by 70% (24/7 EEG monitoring for 2 weeks), and prevented the 2-fold progression in SRS frequency occuring in control mice over 2 months. Conclusions: Conclusions: Implementation of miR146a brain levels by a synthetic mimic reduces acute and chronic seizures and prevents disease progression, likely by inhibiting the ictogenic IL-1R/TLR pro-inflammatory signaling. Anti-inflammatory miRNAs may represent targets for preventing the pathologic consequences of neuroinflammation in epilepsy.