Enhanced hippocampal miR-32-5p promotes neuronal hyperexcitability and epileptic seizures by targeting KCC2.

MicroRNAs (miRNAs) are small noncoding RNAs that control gene expression at the post-transcriptional level and are involved in the pathogenesis of epilepsy. Although miRNA-32-5p (miR-32-5p) is known to be significantly upregulated at seizure onset in patients, its function and mechanism in neuron hyperexcitability and epileptic seizures remain unclear. In this study, we demonstrated elevated levels of miR-32-5p in the plasma of patients with temporal lobe epilepsy and in the hippocampus and plasma of pentylenetetrazol (PTZ)-induced seizure mice. Systemic knockout (KO) and hippocampal-specific knockdown of miR-32-5p mitigated acute seizure discharge and neuronal spiking in the experimental mice. Additionally, miR-32-5p KO attenuated chronic seizure severity and hippocampal neuronal loss of epileptic mice. Furthermore, miR-32-5p KO reversed the expression of immediate early genes (IEGs), which are neuronal activity markers significantly upregulated during acute seizure in mice. Mechanically, we found that potassium-chloride transporter 2 (KCC2), a main cation-chloride cotransporter involved in neuronal circuit excitation/inhibition (E/I) balance, is the key direct target of miR-32-5p. We further verified that miR-32-5p KO re-balanced hippocampal neuronal E/I imbalance underlying epilepsy. Gain-of-function experiment further revealed that the anti-seizure effect of miR-32-5p KO was abolished by hippocampal KCC2 knockdown. Taken together, our findings showed that hippocampal miR-32-5p promotes neuron hyperexcitability and epileptic seizures, and specifically identified miR-32-5p as a putative biomarker and therapeutic target for hippocampus-related epilepsy.