Excitatory somatostatin interneurons in the dentate gyrus drive a widespread seizure network in cortical dysplasia.

Seizures due to cortical dysplasia are notorious for their poor prognosis even with medications and surgery, likely due to the widespread seizure network. Previous studies have primarily focused on the disruption of dysplastic lesions, rather than remote regions such as the hippocampus. Here, we first quantified the epileptogenicity of the hippocampus in patients with late-stage cortical dysplasia. We further investigated the cellular substrates leading to the epileptic hippocampus, using multiscale tools including calcium imaging, optogenetics, immunohistochemistry and electrophysiology. For the first time, we revealed the role of hippocampal somatostatin-positive interneurons in cortical dysplasia-related seizures. Somatostatin-positive were recruited during cortical dysplasia-related seizures. Interestingly, optogenetic studies suggested that somatostatin-positive interneurons paradoxically facilitated seizure generalization. By contrast, parvalbumin-positive interneurons retained an inhibitory role as in controls. Electrophysiological recordings and immunohistochemical studies revealed glutamate-mediated excitatory transmission from somatostatin-positive interneurons in the dentate gyrus. Taken together, our study reveals a novel role of excitatory somatostatin-positive neurons in the seizure network and brings new insights into the cellular basis of cortical dysplasia.

CRISPR-Based KCC2 Upregulation Attenuates Drug-Resistant Seizure in Mouse Models of Epilepsy.

OBJECTIVE: The precise intervention of K-Cl cotransporter isoform 2 (KCC2) as a promising target for drug-resistant epilepsy remains elusive. METHODS: Here, we used a CRISPRa system delivered by adeno-associated viruses to specifically upregulate KCC2 in the subiculum to confirm its therapeutic potential in various in vivo epilepsy models. Calcium fiber photometry was used to reveal the role of KCC2 in the restoration of impaired GABAergic inhibition. RESULTS: CRISPRa system effectively upregulated KCC2 expression both in in vitro cell culture and in vivo brain region. Delivery of CRISPRa with adeno-associated viruses resulted in upregulating the subicular KCC2 level, contributing to alleviating the severity of hippocampal seizure and facilitating the anti-seizure effect of diazepam in a hippocampal kindling model. In a kainic acid-induced epilepticus status model, KCC2 upregulation greatly increased the termination percentage of diazepam-resistant epilepticus status with the broadened therapeutic window. More importantly, KCC2 upregulation attenuated valproate-resistant spontaneous seizure in a kainic acid-induced chronic epilepsy model. Finally, calcium fiber photometry showed CRISPRa-mediated KCC2 upregulation partially restored the impaired GABAA -mediated inhibition in epilepsy. INTERPRETATION: These results showed the translational potential of adeno-associated viruses-mediated delivery of CRISPRa for treating neurological disorders by modulating abnormal gene expression that is directly associated with neuronal excitability, validating KCC2 as a promising therapeutic target for treating drug-resistant epilepsy. ANN NEUROL 2023;94:91-105.