The Vesicular Acetylcholine Transporter Is Required for Neuromuscular Development and Function

Abstract

The vesicular acetylcholine (ACh) transporter (VAChT) mediates ACh storage by synaptic vesicles. However, the VAChT-independent release of ACh is believed to be important during development. Here we generated VAChT knockout mice and tested the physiological relevance of the VAChT-independent release of ACh. Homozygous VAChT knockout mice died shortly after birth, indicating that VAChT-mediated storage of ACh is essential for life. Indeed, synaptosomes obtained from brains of homozygous knockouts were incapable of releasing ACh in response to depolarization. Surprisingly, electrophysiological recordings at the skeletalneuromuscular junction show that VAChT knockout mice present spontaneous miniature end-plate potentials with reduced amplitude and frequency, which are likely the result of a passive transport of ACh into synaptic vesicles. Interestingly, VAChT knockouts exhibit substantial increases in amounts of choline acetyltransferase, high-affinity choline transporter, and ACh. However, the development of the neuromuscular junction in these mice is severely affected. Mutant VAChT mice show increases in motoneuron and nerve terminal numbers. End plates are large, nerves exhibit abnormal sprouting, and muscle is necrotic. The abnormalities are similar to those of mice that cannot synthesize ACh due to a lack of choline acetyltransferase. Our results indicate that VAChT is essential to the normal development of motor neurons and the release of ACh.

Dysautonomia Due to Reduced Cholinergic Neurotransmission Causes Cardiac Remodeling and Heart Failure

“…VAChT-null mice (VAChT del/del ), in which the VAChT open reading frame (ORF) was deleted by using Cre/loxP, were described previously (9). VAChT del/del mice die shortly after birth due to respiratory failure; therefore, experiments were performed with embryonic day 18.5 (E18.5) embryos.…”

“…We have shown previously that a constitutively lack of cholinergic tone affects skeletal muscle function and ability to perform exercise in VAChT KD HOM mice (41). Moreover, the lack of VAChT in KO mice affects skeletal muscle development (9). In order to determine if the constitutive decrease in cholinergic tone could affect cardiomyocytes and, hence, heart physiology, we performed invasive hemodynamic assessments on anesthetized mice.…”

“…ACh-mediated signaling plays important roles in maintaining synaptic connections during development (5,9,32); hence, chronic disturbance of cholinergic tone, as observed in cases of dysautonomia, could contribute to altered myocardial function. Rich cholinergic innervations are found in the sinoatrial node (SAN), the atrial myocardium, the atrioventricular node, and the ventricular conducting system in many species (24).…”

Developmental and Functional Nature of Human iPSC Derived Motoneurons

“…6A). Additionally, motoneurons expressed the vesicular acetylcholine transporter (VAChT), which mediates ACh storage by synaptic vesicles [38] and is a specific marker for "cholinergic" synaptic vesicles [209] (Fig. 6A).…”

Variants in SLC18A3 , vesicular acetylcholine transporter, cause congenital myasthenic syndrome

“…12 Two mouse models of reduced SLC18A3 expression, a knockout mouse and a knockdown mouse, have previously been described and provide strong support for SLC18A3 as a genetic cause of presynaptic congenital myasthenic syndrome. [13][14][15][16] Homozygous SLC18A3 (VAChT , with deletion of a regulatory element within the 59 untranslated region, had a 65% to 70% reduction in VAChT expression. Motor performance and grip strength were impaired, and mice were not able to maintain long periods of physical activity.…”