Potentiating KCC2 activity is sufficient to limit the onset and severity of seizures

Abstract

The type 2 K/Cl cotransporter (KCC2) allows neurons to maintain low intracellular levels of Cl, a prerequisite for efficient synaptic inhibition. Reductions in KCC2 activity are evident in epilepsy; however, whether these deficits directly contribute to the underlying pathophysiology remains controversial. To address this issue, we created knock-in mice in which threonines 906 and 1007 within KCC2 have been mutated to alanines (KCC2-T906A/T1007A), which prevents its phospho-dependent inactivation. The respective mice appeared normal and did not show any overt phenotypes, and basal neuronal excitability was unaffected. KCC2-T906A/T1007A mice exhibited increased basal neuronal Cl extrusion, without altering total or plasma membrane accumulation of KCC2. Critically, activity-induced deficits in synaptic inhibition were reduced in the mutant mice. Consistent with this, enhanced KCC2 was sufficient to limit chemoconvulsant-induced epileptiform activity. Furthermore, this increase in KCC2 function mitigated induction of aberrant high-frequency activity during seizures, highlighting depolarizing GABA as a key contributor to the pathological neuronal synchronization seen in epilepsy. Thus, our results demonstrate that potentiating KCC2 represents a therapeutic strategy to alleviate seizures.

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.…”

Smoothened receptor Signaling regulates the developmental shift of GABA polarity in rat somatosensory cortex

“…Large number of studies have illustrated that the KCC2 dysfunction facilitates initiation of epileptic seizures (Chen et al, 2017;Moore et al, 2018). The changes of KCC2's Ser 940 phosphorylation that modify neuronal chloride homeostasis and depolarizing strength of GABA strongly affect the seizures susceptibilities in KCC2 transgenic mice (Silayeva et al, 2015).…”

Impaired KCC2 phosphorylation leads to neuronal network dysfunction and neurodevelopmental pathogenesis

“…Among multiple KCC2 phosphorylation sites (Payne et al, 1996;Lee et al, 2007Lee et al, , 2010Weber et al, 2014;Agez et al, 2017;Cordshagen et al, 2018), the dual (de)phosphorylation of threonine 906 and 1007 (Thr 906 /Thr 1007 ) is a particularly potent regulator of KCC2 activity (Lee et al, 2007(Lee et al, , 2011Rinehart et al, 2009;Inoue et al, 2012;Friedel et al, 2015;Moore et al, 2018). Thr 906 /Thr 1007 becomes progressively dephosphorylated during neuronal development (Rinehart et al, 2009;Friedel et al, 2015).…”

“…The importance of precise post-translational KCC2 regulation has been corroborated by the identification of mutations that impair these processes in human patients with NDDs, including epilepsy (Kahle et al, 2014;Merner et al, 2015;Stödberg et al, 2015). However, the pathophysiological consequences and mechanisms of impaired K-Cl co-transporters phosphorylation has only begun to be explored in vivo (Silayeva et al, 2015, Kahle et al, 2016aMoore et al, 2018).…”