Valproic Acid Modifies Synaptic Structure and Accelerates Neurite Outgrowth Via the Glycogen Synthase Kinase‐3β Signaling Pathway in an Alzheimer's Disease Model

Summary Aim Tau hyperphosphorylation and amyloid β‐peptide overproduction, caused by altered localization or abnormal activation of glycogen synthase kinase‐3β ( GSK ‐3β), is a pathogenic mechanism in Alzheimer's disease ( AD ). Valproic acid ( VPA ) attenuates senile plaques and neuronal loss. Here, we confirmed that VPA treatment improved spatial memory in amyloid precursor protein ( APP )/presenilin 1 (PS 1) double‐transgenic mice and investigated the effect of VPA on synaptic structure and neurite outgrowth. Methods We used ultrastructural analysis, immunocytochemistry, immunofluorescence staining, and Western blot analysis to assess the effect of VPA treatment in mice. Results VPA treatment thickened the postsynaptic density, increased the number of presynaptic vesicles, and upregulated the expression of synaptic markers PSD ‐95 and GAP 43. VPA increased neurite length of hippocampal neurons in vivo and in vitro . In VPA ‐treated AD mouse brain, inactivated GSK ‐3β ( pS er9‐ GSK ‐3β) was markedly increased, while hyperphosphorylation of tau at Ser396 and Ser262 was decreased; total tau levels remained similar. VPA treatment notably improved pS er133‐ cAMP response element‐binding protein ( CREB ) and brain‐derived neurotrophic factor ( BDNF ) levels, which are associated with synaptic function and neurite outgrowth. Conclusion VPA improves behavioral deficits in AD , modifies synaptic structure, and accelerates neurite outgrowth, by inhibiting the activity of GSK ‐3β, decreasing hyperphosphorylated tau, enhancing CREB and BDNF expression.