Enhancing KCC2 as a novel strategy for treating seizures
Department of Physiology, School of Medical Sciences, UNSW Sydney, Australia.
The K+Cl--cotransporter (KCC2) plays a key role in regulating intracellular Cl-, influencing the efficacy of GABAa-receptor mediated inhibition. To investigate how elevating KCC2 expression affects neuronal function, we used a transgenic mouse in which forebrain-restricted over-expression of KCC2 in pyramidal neurons could be regulated by doxycycline in the diet. In acute brain slices, field potentials were evoked from hippocampal CA1. It was found that KCC2 upregulation did not influence normal excitability, with similar input-output relationships, paired-pulse ratios, and concentration-response to muscimol observed. Interestingly, hyperexcitability was significantly reduced, as measured using the tetanus-induced afterdischarge and Zero-Mg2+ seizure models. This finding was subsequently supported in vivo, where seizures induced by kainic acid (up to 50mg/kg, i.p) were less likely to progress to status epilepticus in KCC2 upregulated mice (1/5 mice vs. 15/15 mice from control cohorts). A recent study found that the clinically available compound prochlorperazine (Stemetil) acutely increases KCC2 expression (Liabeauf et al, 2017). To explore the potential effects of Stemetil on hyperexcitability, we conducted preliminary experiments using the in vitroafterdischarge seizure model. It was found that a 60 min incubation with Stemetil (10μM) reduced afterdischarge bursts (p<0.01) with no effects on basal excitability. Overall, our data support the strategy of enhancing KCC2 to reduce neuronal hyperexcitability, without negatively affecting basal synaptic transmission. This means that increasing KCC2 may enable greater Cl- homeostasis and maintain more efficacious GABAergic inhibition, hence providing a novel strategy to enhance neuronal inhibition. Further, preliminary results support continued investigation into Stemetil as a therapeutically relevant KCC2 enhancer for the treatment of seizures.