Impaired regulation of KCC2 phosphorylation leads to neuronal network dysfunction and neurodevelopmental pathology

KCC2 is a vital neuronal K⁺/Cl^- cotransporter that is implicated in the etiology of numerous neurological diseases. In normal cells, KCC2 undergoes developmental dephosphorylation at Thr⁹⁰⁶ and Thr¹⁰⁰⁷ We engineered mice with heterozygous phosphomimetic mutations T906E and T1007E (KCC2 ) to prevent the normal developmental dephosphorylation of these sites. Immature (postnatal day 15) but not juvenile (postnatal day 30) KCC2 mice exhibited altered GABAergic inhibition, an increased glutamate/GABA synaptic ratio, and greater susceptibility to seizure. KCC2 mice also had abnormal ultrasonic vocalizations at postnatal days 10 to 12 and impaired social behavior at postnatal day 60. Postnatal bumetanide treatment restored network activity by postnatal day 15 but failed to restore social behavior by postnatal day 60. Our data indicate that posttranslational KCC2 regulation controls the GABAergic developmental sequence in vivo, indicating that deregulation of KCC2 could be a risk factor for the emergence of neurological pathology.