Abstracts

Rationale:  Epilepsy is characterized by changes in neuronal excitability and is often associated with altered expression or function of ion channels. One example of such a channelopathy in genetic and acquired epilepsy is the reduction of hyperpolarizing A-type potassium currents in the hippocampal CA1 region. These A-type currents are mainly mediated by the voltage-gated potassium channel Kv4.2. MicroRNAs (miRNAs) are small, non-coding RNAs involved in post-transcriptional regulation of protein-coding mRNAs. Emerging evidence suggests miRNAs as crucial regulators of genes involved in epilepsy. We hypothesized that enhancing A-type currents by increasing Kv4.2 expression may reduce seizure severity in a mouse model of chronic epilepsy. Methods:  6-8 weeks old C57BL/6 male mice were injected with intracerebroventricular (ICV) injection of miR-324-5p antagomirs (miRNA inhibitors) and scrambled control to measure the regulation of A-type current in CA1 pyramidal neurons using patch clamp recordings. For the seizure model, 6-8 weeks old male offsprings from C57Bl/6JxFVB breeding were injected with pilocarpine (320 mg/kg, i.p), followed by 3 weeks latent phase to develop spontaneous seizures. Later, cortical EEG electrodes and an ICV cannula were surgically implanted and mice were video-EEG monitored for seizures and effect of antagomir treatment on seizure severity. Results:  Antisense-mediated inhibition of the Kv4.2-targeting microRNA miR-324-5p in mice selectively increased A-type potassium currents in pyramidal neurons of the CA1, while leaving membrane potential, channel properties, and other potassium currents unaltered. We confirm that Kv4.2 protein and mRNA were reduced in the pilocarpine-injected mice. Inhibition of microRNA-induced silencing of Kv4.2 by ICV injection of miR-324-5p antagomirs in the chronically seizing mice caused a reduction in seizure frequency. However, no significant changes in seizure duration were observed. Conclusions:  Our results suggest that the microRNA miR-324-5p regulates specific potassium currents and its manipulation can ameliorate channelopathy-associated neurological disorders. Funding:  Postdoctoral fellowship from American Epilepsy Society (D.T)NIH grant R01NS092705 (C.G.) Grant from Center for Clinical and Translational Science and Training (CCTST).