Imbalanced expression of cation-chloride cotransporters as a potential therapeutic target in an Angelman syndrome mouse model

Abstract

Angelman syndrome is a neurodevelopmental disorder caused by loss of function of the maternally expressed UBE3A gene. Treatments for the main manifestations, including cognitive dysfunction or epilepsy, are still under development. Recently, the Cl− importer Na+-K+-Cl− cotransporter 1 (NKCC1) and the Cl− exporter K+-Cl− cotransporter 2 (KCC2) have garnered attention as therapeutic targets for many neurological disorders. Dysregulation of neuronal intracellular Cl− concentration ([Cl−]i) is generally regarded as one of the mechanisms underlying neuronal dysfunction caused by imbalanced expression of these cation-chloride cotransporters (CCCs). Here, we analyzed the regulation of [Cl−]i and the effects of bumetanide, an NKCC1 inhibitor, in Angelman syndrome models (Ube3am−/p+ mice). We observed increased NKCC1 expression and decreased KCC2 expression in the hippocampi of Ube3am−/p+ mice. The average [Cl−]i of CA1 pyramidal neurons was not significantly different but demonstrated greater variance in Ube3am−/p+ mice. Tonic GABAA receptor-mediated Cl− conductance was reduced, which may have contributed to maintaining the normal average [Cl−]i. Bumetanide administration restores cognitive dysfunction in Ube3am−/p+ mice. Seizure susceptibility was also reduced regardless of the genotype. These results suggest that an imbalanced expression of CCCs is involved in the pathophysiological mechanism of Ube3am−/p+ mice, although the average [Cl−]i is not altered. The blockage of NKCC1 may be a potential therapeutic strategy for patients with Angelman syndrome.