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

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 ( Ube3a m−/p+ mice). We observed increased NKCC1 expression and decreased KCC2 expression in the hippocampi of Ube3a m−/p+ mice. The average [Cl − ] i of CA1 pyramidal neurons was not significantly different but demonstrated greater variance in Ube3a m−/p+ mice. Tonic GABA A receptor-mediated Cl − conductance was reduced, which may have contributed to maintaining the normal average [Cl − ] i . Bumetanide administration restores cognitive dysfunction in Ube3a m−/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 Ube3a m−/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.