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

Abstract

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 (KCC2E/+) to prevent the normal developmental dephosphorylation of these sites. Immature (postnatal day 15) but not juvenile (postnatal day 30) KCC2E/+ mice exhibited altered GABAergic inhibition, an increased glutamate/GABA synaptic ratio, and greater susceptibility to seizure. KCC2E/+ 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.

Molecular basis for regulation of human potassium chloride cotransporters

“…WNK-SPARK/OSR1 system (4,5). The dephosphorylation and phosphorylation mutations activate and inactive KCCs, respectively (6)(7)(8)(9), though activated phosphorylation site was also identified in KCC2 (10). Under the hypertonic environments, the phosphorylated NKCCs are activated to facilitate the ion influx into the cell, while the phosphorylated KCCs are inhibited.…”

“…The extrusion of chloride ion mediated by KCC2 provides the basis for GABAinduced neuron inhibition (21). Inhibitory phosphorylation of T906 and T1007 in KCC2 is reported to be fundamental in the nervous system development (7)(8)(9). KCC3 was identified in 1999 by three groups (22)(23)(24), which is expressed in multiple tissues and organs including brain, kidney, and muscle.…”

The K-Cl co-transporter 2 is a point of convergence for multiple autism spectrum disorder and epilepsy risk gene products

“…In WT mice KCC2 was phosphorylated on up to seven residues including T906, S940, T1007. These play a critical role in regulating KCC2 function (13,69). In addition to this we detected phosphorylation of S1022 consistent with a recent publication (39).…”

“…These changes in neuronal Cl-extrusion reflect a sustained increase in the expression levels of KCC2 after birth, the mRNA levels of which do not reach their maximal levels in humans until 20-25 years of age (7). In addition to this, the appropriate developmental appearance of hyperpolarizing GABAAR currents is also in part determined by the phosphorylation status of KCC2, a process that facilitates its membrane trafficking and surface activity (8)(9)(10)(11)(12)(13).…”

Isolation and characterization of multi-protein complexes enriched in the K-Cl co-transporter 2 from brain plasma membranes

“…These changes in neuronal Clextrusion reflect a sustained increase in the expression levels of Kcc2 after birth, the mRNA levels of which do not reach their maximal levels in humans until 20-25 years of age (7). In addition to this, the appropriate developmental appearance of hyperpolarizing GABAAR currents is also in part determined by the phosphorylation status of Kcc2, a process that facilitates its membrane trafficking and activity (8)(9)(10)(11)(12)(13).…”