Disrupted choline clearance and sustained acetylcholine release in vivo by a common choline transporter coding variant associated with poor attentional control in humans

Abstract

Transport of choline via the neuronal high-affinity choline transporter (CHT; SLC5A7) is essential for cholinergic terminals to synthesize and release acetylcholine (ACh). In humans, we previously demonstrated an association between a common CHT coding substitution (rs1013940; Ile89Val) and reduced attentional capacity as well as attenuated frontal cortex activation. Here, we used a CRISPR/Cas9 approach to generate mice expressing the I89V substitution and assessed, using in vivo cortical choline biosensing, CHT-mediated choline transport, and ACh release. CHT-mediated clearance of choline in mice expressing one or two Val89 alleles was reduced by over 7-fold relative to wild type (WT) mice, suggesting dominant-negative effects. Choline clearance in CHT Val89 mice was further reduced by neuronal inactivation. Deficits in ACh release, 5 and 10 min after repeated depolarization at a low, behaviorally relevant frequency, support an attenuated reloading capacity of cholinergic neurons in mutant mice. The density of CHTs in total synaptosomal lysates and neuronal plasma-membrane-enriched fractions was not impacted by the Val89 variant, indicating a selective impact on CHT function. Consistent with this hypothesis, structural modeling revealed that Val89 may attenuate choline transport by changing the ability of choline to induce conformational changes of CHT that support normal transport rates. Our findings suggest that diminished, sustained cholinergic signaling capacity in the frontal cortex underlies perturbed attentional performance in individuals expressing CHT Val89. Our work supports the utility of the CHT Val89 mouse model as a valuable model to study heritable risk for cognitive disorders arising from cholinergic dysfunction.