Background: Loss-of-function amyloid precursor protein (APP) and Nav1.6 transgenic mice share similar phenotypes. Results: APP interacts with Nav1.6 and enhances its cell surface expression through a G(o)-coupled JNK pathway. Conclusion: APP regulates Nav1.6 function, likely through a G(o)-coupled JNK pathway. Significance: This finding advances the current understanding of APP functions and has implications for novel therapies for neurodegenerative disorders.
Amyloid precursor protein (APP) is commonly associated with Alzheimer disease, but its physiological function remains unknown. Nav1.6 is a key determinant of neuronal excitability in vivo. Because mouse models of gain of function and loss of function of APP and Nav1.6 share some similar phenotypes, we hypothesized that APP might be a candidate molecule for sodium channel modulation. Here we report that APP colocalized and interacted with Nav1.6 in mouse cortical neurons. Knocking down APP decreased Nav1.6 sodium channel currents and cell surface expression. APP-induced increases in Nav1.6 cell surface expression were G(o) protein-dependent, enhanced by a constitutively active G(o) protein mutant, and blocked by a dominant negative G(o) protein mutant. APP also regulated JNK activity in a G(o) protein-dependent manner. JNK inhibition attenuated increases in cell surface expression of Nav1.6 sodium channels induced by overexpression of APP. JNK, in turn, phosphorylated APP. Nav1.6 sodium channel surface expression was increased by T668E and decreased by T668A, mutations of APP695 mimicking and preventing Thr-668 phosphorylation, respectively. Phosphorylation of APP695 at Thr-668 enhanced its interaction with Nav1.6. Therefore, we show that APP enhances Nav1.6 sodium channel cell surface expression through a G(o)-coupled JNK pathway.
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