Abstracts

Rationale: Dendrites are sites of most excitatory synaptic input and thus are a critical determinant of brain excitability. The structure and function of dendrites is controlled in part by compartmentalized protein synthesis under the influence of microRNAs (miRNA). These are small non protein-coding RNAs that regulate gene expression networks. MiR-134 was among the first miRNA found to localize to dendrites where it regulates dendrite spine size by repressing Lim kinase-1 (Limk-1) translation. We previously showed that miR-134 is overexpressed in experimental and human temporal lobe epilepsy and that silencing miR-134 using intracerebroventricular injection of antisense oligonucleotides (antagomirs; Ant) potently suppressed evoked and spontaneous seizures in mice. In order to move this approach toward clinical translation we tested systemic delivery of these large macromolecules, timing delivery to coincide with blood-brain barrier (BBB) opening after status epilepticus (SE) in mice. We also explored the mechanism of the potent disease-modifying effects of Ant-134. Methods: Status epilepticus (SE) was induced in C57BL/6 adult mice by an intra-amygdala injection of kainic acid. BBB permeability was assessed by dye injections, extravasation of serum protein into brain parenchyma and 7T magnetic resonance imaging (MRI). The presence of Ant-134 in the hippocampus was confirmed by in situ hybridization. Antagomirs were locked nucleic acid- and cholesterol-modified. Spontaneous seizures were tracked using continuous long-term video-telemetry EEG recording.  Results: BBB opening in this model was apparent 2 h after SE. Systemic injection of Ant-134 at this time point did not alter the duration or severity of status epilepticus in mice but significantly reduced the number of spontaneous seizures (p < 0.008) and the total time spent in epileptic seizures (p < 0.005) recorded in mice compared with controls. These seizure-suppressive effects persisted up to 3 months after the SE. This phenotype could be partly-reversed by knockdown of Lim kinase-1 (p < 0.001), a known target of miR-134.  Conclusions: Systemic delivery of Ant-134 timed with blood-brain barrier opening produced potent and long-lasting disease-modifying effects. These findings suggest efficacious antagomir therapy can be achieved using a clinically-relevant route and provide a rationale for pursuing pre-clinical development of Ant-134 for epilepsy. Funding: EpimiRNA (Framework Programme 7 No. 602130); Health Research Board (HRA-POR-2013-325)