Choline Transporter 1 Maintains Cholinergic Function in Choline Acetyltransferase Haploinsufficiency

Abstract

Choline acetyltransferase (ChAT), the enzyme that synthesizes the neurotransmitter acetylcholine (ACh), is thought to be present in kinetic excess in cholinergic neurons. The rate-limiting factor in ACh production is the provision of choline to ChAT. Cholinergic neurons are relatively unique in their expression of the choline transporter 1 (CHT1), which exhibits high-affinity for choline and catalyzes its uptake from the extracellular space to the neuron. Multiple lines of evidence indicate that the activity of CHT1 is a key determinant of choline supply for ACh synthesis. We examined the interaction of ChAT and ChT activity using mice heterozygous for a null mutation in the Chat gene (Chatϩ/Ϫ). In these mice, brain ChAT activity was reduced by 40 -50% relative to the wild type, but brain ACh levels as well as ACh content and depolarization-evoked ACh release in hippocampal slices were normal. However, the amount of choline taken up by CHT1 and ACh synthesized de novo from choline transported by CHT1 in hippocampal slices, as well as levels of CHT1 mRNA in the septum and CHT1 protein in several regions of the CNS, were 50 -100% higher in Chatϩ/Ϫ than in Chatϩ/ϩ mice. Thus, haploinsufficiency of ChAT leads to an increased expression of CHT1. Increased ChT activity may compensate for the reduced ChAT activity in Chatϩ/Ϫ mice, contributing to the maintenance of apparently normal cholinergic function as reflected by normal performance of these mice in several behavioral assays.

Differential regulation of the high affinity choline transporter and the cholinergic locus by cAMP signaling pathways

“…The overall result of the two processes would be a tight control of ACh synthesis. Indeed, in mice endowed with only 50% of normal ChAT activity (heterozygous for a null mutation in the Chat gene), CHT expression is upregulated and no impairments in ACh synthesis and release are observed (Brandon et al, 2004) The results that ChAT and VAChT mRNA expression decreased below control levels in the presence of the PKA inhibitor H-89 suggest that not only cAMP-stimulated upregulation, but also basal expression of the cholinergic locus is controlled by the PKA pathway. Our results are in agreement with those of Shimojo et al (1998), who reported that PKAII mediates basal expression as well as the cAMP-induced coordinated upregulation of the cholinergic locus in PC12 cells.…”

“…Furthermore, treatment of primary septal cells with 0.1 μM retinoic acid had no effect on CHT mRNA expression, whereas VAChT expression was increased . Another example of differential regulation of CHT in comparison to ChAT was observed in ChAT heterozygotes, where ChAT expression is reduced by 50% and CHT is significantly upregulated (Brandon et al, 2004).…”

Association of the Choline Acetyltransferase Gene with Responsiveness to Acetylcholinesterase Inhibitors in Alzheimer’s Disease

“…In the present study we have examined the polymorphic variations of the genes encoding 3 enzymes involved in the synthesis, transport, and metabolism of acetylcholine in the cholinergic system ( • ▶ Fig. 1) [11,12]. Choline acetyltransferase (ChAT) encoded by the gene CHAT synthesizes acetylcholine, using choline and acetyl-CoA as substrates [11].…”

“…Choline acetyltransferase (ChAT) encoded by the gene CHAT synthesizes acetylcholine, using choline and acetyl-CoA as substrates [11]. The choline transporter (ChT) catalyzes the uptake of choline from the extracellular space to the neuronal cytoplasm, and is encoded by SLC5A7 [12]. Acetylcholine esterase (AChE) is encoded by ACHE and acts to hydrolyze acetylcholine, thereby inactivating the neurotransmitter [11].…”

The cholinergic system in rat testis is of non-neuronal origin

“…Specificity of the CHAT, SLC18A3 and SLC22A2 antisera was tested by pre-absorption with the corresponding antigen. In addition, the specificity of the SLC5A7 antibody has been shown in murine cochlea, brain and spinal cord (SLC5A7, Brandon et al 2004, Bergeron et al 2005.…”