ABSTRACT
Postmenopausal women with Alzheimer's disease (AD) exhibit dramatically reduced sensitivity to estrogen replacement therapy, which is though to be related to an estrogen receptor (ER)α/ERß ratio imbalance arising from a significantly decreased level of ERs of the brain. The aim of our study was to investigate whether valproic acid (VPA) can enhance the beneficial effects of estrogen on cognitive function through restoration of ERα and ERß expression in the brain. We removed the ovaries of female APP/PS1 mice to simulate the low estrogen levels present in postmenopausal women and then administered VPA (30 mg/kg, intraperitoneal injection, once daily), 17ß-estradiol (E2) (2.4 µg, intraperitoneal injection, once daily), liquiritigenin (LG) (50 µg/kg, intragastric infusion, once daily), VPA + E2, or VPA + LG for 4 successive weeks. Compared with treatment with a single drug, treatment with VPA + E2 or VPA + LG significantly increased the level of glycogen synthase kinase 3ß, increased the expression of estrogen receptor α, reduced the expression of small ubiquitin-like modifiers, and increased the level of estrogen receptor ß. This resulted in enhanced sensitivity to estrogen therapy, reduced amyloid ß aggregation, reduced abnormal phosphorylation of the tau protein, reduced neuronal loss, increased dendritic spine and postsynaptic density, and significantly alleviated memory loss and learning impairment in mice. This study was approved by the Chongqing Medical University Animal Protection and Ethics Committee, China on March 6, 2013.
ABSTRACT
AIM: Tau hyperphosphorylation and amyloid ß-peptide overproduction, caused by altered localization or abnormal activation of glycogen synthase kinase-3ß (GSK-3ß), 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 GAP43. VPA increased neurite length of hippocampal neurons in vivo and in vitro. In VPA-treated AD mouse brain, inactivated GSK-3ß (pSer9-GSK-3ß) was markedly increased, while hyperphosphorylation of tau at Ser396 and Ser262 was decreased; total tau levels remained similar. VPA treatment notably improved pSer133-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-3ß, decreasing hyperphosphorylated tau, enhancing CREB and BDNF expression.