Neonatal
seizures pose a clinical challenge in their early detection, acute management, and long-term comorbidities. They are often caused by
hypoxic-ischemic encephalopathy and are frequently refractory to the first-line antiseizure medication
phenobarbital. One proposed mechanism for
phenobarbital inefficacy during neonatal
seizures is the reduced abundance and function of the neuron-specific K+/Cl− cotransporter 2 (KCC2), which maintains
chloride homeostasis and promotes GABAergic inhibition upon its phosphorylation during postnatal development. Here, we investigated whether this mechanism is causal and whether it can be rescued by KCC2 functional enhancement. In a CD-1 mouse model of refractory ischemic neonatal
seizures, treatment with the KCC2 functional enhancer CLP290 rescued
phenobarbital efficacy, increased KCC2 abundance, and prevented the development of epileptogenesis, as quantified by video electroencephalogram monitoring. These effects were prevented by knock-in expression of nonphosphorylatable mutants of KCC2 (S940A or T906A and T1007A), indicating that KCC2 phosphorylation regulates both neonatal seizure susceptibility and CLP290-mediated KCC2 functional enhancement. Our findings therefore validate KCC2 as a clinically relevant target for refractory neonatal
seizures and provide insights for future
drug development.