The Effects Of Amyloid Precursor Protein And β-Amyloid On Neuronal Excitability

Objective:Alzheimer’s disease （AD） is a kind of neurodegenerative diseases. The characteristic symptoms of AD are progressive memory impairment, cognitive dysfunction, personality changes and speech disorders. These symptoms seriously affect the patients’ quality of life. The etiology and pathogenesis of AD has not been clearly elucidated. The pathological characteristics of AD are senile plaques which derive from the extracellular β-amyloid （AP） deposits, and neurofibrillary tangles resulting from the hyperphosphorylation of intracellular tau. It has been a long time that researches on amyloid precursor protein （APP） mainly focus the roles of its abnormal metabolic pathways in the progress of AD, as its cleavage product Aβ remains to be the major component of senile plaques. Although the expression of APP, a housekeeping gene, has been found in a variety of human tissues, but little is known about its function. Our previous experimental results showed that in the central nervous system APP specifically clustered and VGSC colocalized at the nodes of Ranvier, which were likely to affect nerve conduction velocity. Therefore, the main purpose of this study is to further develop the relationship between APP/Aβ and neuronal excitability as well as VGSC from the functional perspective, in order to provide a new theoretical basis in revealing the physiological function of the APP in the pathogenesis of AD.Methods:The primary neurons extracted from APP/PS1 transgenic mice were cultured in vitro and the neuronal excitability was investigated using current patch clamp technique. The functional interaction between APP and sodium channel was explored on voltage-gated sodium channel （Nav1.6, Nav1.2） HEK 293 cell line which were transfected to APP by whole-cell patch-clamp technique. Before and after treatment of Aβ_1-42, the changes of neuronal excitability and VGSC currents from primary culture neurons were observed using whole-cell patch-clamp technique.Results:1. APP could increase the amplitude of action potential of neuron.2. APP could reduce the threshold of neuronal action potential.3. APP could increase the frequency of neuronal action potential.4. APP could enhance the sodium currents of HEK 293 Navl.6 cell line.5. APP could speed up the activation of Na+ channel kinetic on HEK 293 Nav1.6 cell line.6. APP could slow down the inactivation of Na+ channel kinetic on HEK 293 Nav1.6 cell line.7. APP may not regulate Na+ channel kinetic on HEK 293 Nav1.2 cell line.8. Aβ_1-42 could reduce the threshold of neuronal action potential.9. Aβ_1-42 could increase the frequency of neuronal action potential.10. Aβ_1-42 showed no effect on the sodium channel currents.Conclusion:1. The overexpression of APP increases the neuronal excitability.2. APP specifically enhances the Navl.6 currents, and does not regulate Nav1.2 currents.3. Aβ_1-42 also increases the excitability of neurons, but does not affect the sodium channel currents.