CHT- knock-out mice have a loxP-flanked EGFP gene replacing part of the coding region, including the ATG initiation codon, of the solute carrier family 5 (choline transporter), member 7 (Slc5a7) gene. EGFP is detectable by immunostaining. SLC5A7 (CHT) is a Na(+)-dependent high-affinity transporter that mediates the uptake of choline for acetylcholine (ACh) synthesis in cholinergic neurons. ACh is a neurotransmitter released at the neuromuscular junction (NMJ), as well as at autonomic synapses, of the central and peripheral nervous system. ACh regulates a variety of autonomic, cognitive, and motor functions, and also plays a role in the development and maturation of both presynaptic and postsynaptic aspects of the NMJ. Deficits in ACh synthesis or response have been associated with myasthenic syndromes, while degeneration of the cholinergic neurons of the basal forebrain has been associated with the onset of Alzheimer’s Disease. Heterozygotes CHT+/- mice are viable and fertile, while homozygotes die within an hour after birth due to hypoxia caused by herniation of the diaphragm. Choline uptake and ACh synthesis are lost in the forebrain and hindbrain of CHT-/- mice. The NMJs of the mice exhibit developmental and neurotransmission defects.
Adult CHT+/- mice overcome reductions in CHT protein levels and sustain choline uptake at wild-type levels through posttranslational mechanisms. These heterozygous mice display impaired physical performance with a slower rate of recovery compared to wildtype mice. They also have reduced brain ACh levels, elevated choline levels, and brain region-specific decreased expression of muscarinic acetylcholine receptors. They exhibit age-dependent ventricular dysfunction, as well as tachycardia and hypertension at rest.
