Cholecystokinin Signaling can Rescue Cognition and Synaptic Plasticity in the APP/PS1 Mouse Model of Alzheimer's Disease.

Synaptic impairment and loss are an important pathological feature of Alzheimer's disease (AD). Memory is stored in neural networks through changes in synaptic activity, and synaptic dysfunction can cause cognitive dysfunction and memory loss. Cholecystokinin (CCK) is one of the major neuropeptides in the brain, and plays a role as a neurotransmitter and growth factor. The level of CCK in the cerebrospinal fluid is decreased in AD patients. In this study, a novel CCK analogue was synthesized on the basis of preserving the minimum bioactive fragment of endogenous CCK to investigate whether the novel CCK analogue could improve synaptic plasticity in the hippocampus of the APP/PS1 transgenic mouse model of AD and its possible molecular biological mechanism. Our study found that the CCK analogue could effectively improve spatial learning and memory, enhance synaptic plasticity in the hippocampus, normalize synapse numbers and morphology and the levels of key synaptic proteins, up-regulate the PI3K/Akt signaling pathway and normalize PKA, CREB, BDNF and TrkB receptor levels in APP/PS1 mice. The amyloid plaque load in the brain was reduced by CCK, too. The use of a CCKB receptor antagonist and targeted knockdown of the CCKB receptor (CCKBR) attenuated the neuroprotective effect of the CCK analogue. These results demonstrate that the neuroprotective effect of CCK analogue is achieved by activating the PI3K/Akt as well as the PKA/CREB-BDNF/TrkB signaling pathway that leads to protection of synapses and cognition.