Hyperexcitability and epilepsy associated with disruption of the mouse neuronal‐specific K–Cl cotransporter gene

Abstract

Four genes encode electroneutral, Na+-independent, K-Cl cotransporters. KCC2, is exclusively expressed in neurons where it is thought to drive intracellular Cl- to low concentrations and shift the reversal potential for Cl- conductances such as GABA(A) or glycine receptor channels, thus participating in the postnatal development of inhibitory mechanisms in the brain. Indeed, expression of the cotransporter is low at birth and increases postnatally, at a time when the intracellular Cl- concentration in neurons decreases and gamma-aminobutyric acid switches its effect from excitatory to inhibitory. To assert the significance of KCC2 in neuronal function, we disrupted the mouse gene encoding this neuronal-specific K-Cl cotransporter. We demonstrate that animals deficient in KCC2 exhibit frequent generalized seizures and die shortly after birth. We also show upregulation of Fos, the product of the immediate early gene c-fos, and the significant loss of parvalbumin-positive interneurons, both indicative of brain injury. The regions most affected are the hippocampus and temporal and entorhinal cortices. Extracellular field potential measurements in the CA1 hippocampus exhibited hyperexcitability. Application of picrotoxin, a blocker of the GABA(A) receptor, further increased hyperexcitability in homozygous hippocampal sections. Pharmacological treatment of pups showed that diazepam relieved the seizures while phenytoin prevented them between postnatal ages P4-P12. Finally, we demonstrate that adult heterozygote animals show increased susceptibility for epileptic seizure and increased resistance to the anticonvulsant effect of propofol. Taken together, these results indicate that KCC2 plays an important role in controlling CNS excitability during both postnatal development and adult life.

Molecular Targets for Antiepileptic Drug Development

“…The importance of these transporters in the regulation of seizure susceptibility is highlighted by the seizure phenotypes of mice deficient in KCC2, a neuronal electroneutral K ϩ and Cl Ϫ cotransporter that drives intracellular Cl Ϫ to low concentrations and shifts the reversal potential for GABA A and glycine receptors so that the channels are hyperpolarizing. Mice lacking KCC2 exhibit severe seizures and die shortly after birth, 175 whereas those in which KCC2 has been reduced by 80 -85% show enhanced susceptibility to PTZ seizures. 176 …”

Neto2 is a KCC2 interacting protein required for neuronal Cl − regulation in hippocampal neurons

“…KCC2 is essential for survival, as KCC2 knockout mice die immediately at birth due to respiratory failure (6). In the adult nervous system, decreased KCC2 expression correlates with neuropathic pain, spasticity following spinal cord injury, and epileptic seizures (5,(7)(8)(9)(10)(11).…”

WNK3 modulates transport of Cl - in and out of cells: Implications for control of cell volume and neuronal excitability

“…Cl Ϫ influx largely occurs via NKCC1, whereas Cl Ϫ efflux is mediated via the neuronalspecific K-Cl cotransporter KCC2 (11,(17)(18)(19). The importance of this regulation is underscored by the consequences of KCC2 deficiency in mouse, which reduces GABA's inhibitory signaling, resulting in motor defects, epilepsy, and anxiety-like behavior (20)(21)(22). The mechanism underlying the dynamic and coordi-nated modulation of NKCC1 and KCC2 activity in neurons is unknown.…”

“…Disruption of NKCC1 in mouse leads to hearing loss, altered pain perception, neuronal excitability, and altered blood pressure (25). Targeted disruption of KCC2 results in epilepsy (20,21).…”