Umka, Jariya.
(2010)
The control of adult neural stem cell proliferation and cognition by valproic acid.
PhD thesis, University of Nottingham.
Abstract
Valproic acid (VPA) is extensively used for the treatment of epilepsy. This drug also functions as an inhibitor of histone deacetylase enzymes and causes the expression of growth arrest genes. It has been reported that mild to moderate cognitive impairments occur in adult patients taking VPA. This investigation aimed to examine the relationship between cognition and changes in cell proliferation within the rat hippocampus, a brain region where continued formation of new neurons is associated with learning and memory. Also, the antiproliferative function of VPA was investigated in rat and mouse hippocampal neural stem cells (NSCs) and cancer cell lines in vitro.
The cognitive and antiproliferative effects of VP A were determined in adult Hooded Lister rats treated with VP A (300mg/kg) by intraperitoneal injection twice daily for 10 days. Cognition was assessed by the Novel Object Location (NOL) and contextual fear conditioning tests. Cell proliferation within the subgranular zone (SGZ) of the dentate gyrus was determined by immunostaining for Ki67. Additionally, levels of the brain-derived neurotrophic factor (BDNF), doublecortin (DCX) and the receptor Notch1 expression were measured by Western blotting. The results showed that animals treated with VPA had a hippocampal specific cognitive impairment as shown by NOL, test but not contextual fear conditioning. This was linked to a significant reduction in cell proliferation within the SGZ. Moreover, VPA treatment statistically significantly decreased levels of BDNF and Notch1, but not DCX within the hippocampus.
The antiproliferative effect of VPA treatment (0.3 and 1 mM) for 24 hours was investigated in hippocampal neural stem cells (NSCs) in vitro. The numbers of neurosphere and cell proliferation assessed in VPA-treated rat and mouse hippocampal NSCs showed significantly decreased in a concentration-dependent manner. Levels of Notch1 , Sox2, nestin and c-Myc gene expression were quantified using qPCR. This revealed that 1 mM VPA reduced expression of Notch1 , Sox2 and nestin but not c-Myc. However, there were no changes in levels of these gene expressions in 0.3 mM VPA.
The influence of VPA on cancer cell proliferation was examined in human Epn1, Med1 and SHSY5Y cell lines by treating with 1,2 and 3 mM VPA for 72 hours. The data of cell proliferation showed that VPA produced a significant reduction of tumour cell growth in a dose-dependent manner in all three cell lines. VPA (1, 2 and 3 mM) induced levels of Notch1 expression in SHSY5Y cell lines. Additionally, the number of dividing cells of Epn1 and Med1 treated with 2.5 mM VPA was significantly decreased compared to untreated cells using Ki67 immunostaining. However, Notch1 expression was not detected in either Epn1 or Med1 cell lines.
These results indicate that VPA treatment induced cognitive deficits in rats and that this was associated with a reduction in hippocampal NSCs both in vivo and in vitro. In addition, VPA reduced BDNF and Notch1 expression in the hippocampus. Moreover, VPA induced a decrease of levels of Notch1, Sox2 and nestin gene expression in hippocampal NSCs. The present study also reveals that antiproliferative effect of VPA was associated with an increase of Notch1 expression in SHSY5Y. However, this action of VPA appeared to have no link with Notch1 expression in Epn1 and Med1 cell lines.
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