The Neuroprotective Effect Of VPA On APP/PS1 Double Transgenic Mouse Model

Objective: The present study is aimed at investigating whether valproic acid (VPA) affect behavior and Aβdeposition in the APP/PS1 double transgenic AD mouse model of different gender; whether VPA inhibit neuronal apoptosis so as to rescue neuronal loss in the brain of AD model mice, as well as exploring its underlying mechanism. The outcome of the study will provide the basis for clinical application of VPA on AD.Methods: 1 Offspring which were bred by APP/PS1 double transgenic AD model mice were genotyped. 16 female and 24 male(3-month old) AD model mice were randomly divided into VPA-treated and saline-treated groups(20 for each group, that is, 8 female and 12 male). 30mg/kg.d of VPA and the same amount of saline were peritoneally injected into mice as control for 4 weeks.2 After 4-week treatment, open field test was performed to test autonomous behaviors of male and female AD model mice ; Morris water maze test was conducted to observe the effect of VPA on the capability of spatial learning and memory of mice;Immunohistochemical staining and Thioflavin S staining were carried out to examine the effect of VPA on SP changes in the brains of mice; ELISA analysis was used to investigate the effect of VPA on Aβproduction. Collecting and analyzing the data to check whether the neuroprotective effect of VPA has gender differences.3 Nissl staining and transmission electron microscopy (TEM) were used to observe the morphological structures and number of neurons in the brains of AD model mice. TUNEL staining, Immunohistochemical staining and Western blot techniques were performed to investigate whether VPA inhibits neuronal apoptosis in the brains of AD model mice, and its possible mechanisms.Results: 1 Open field test showed that the activities of VPA treated male mice decreased significantly compared with the control (P <0.05), Manic symptoms were relieved; while there was no significant difference in activity between VPA-treated and saline-treated female groups. Visible platform test of Water maze experiments showed that there was no significant difference in escape latency, path length and swimming speed among 4 groups (P>0.05). Hidden platform test showed that VPA-treated mice had a significantly lesser latency (P<0.01) and fewer path length (P<0.01) to reach the platform compared with control; Meanwhile, both in VPA-treated and control groups, the male mice had a lesser escape latency and path-length than female mice (P<0.05).2 Immuohistochemical staining showed the number of SP in the cerebral cortex and hippocampus of VPA-treated male mice was notably decreased than that in the control group (P<0.01), furthermore, the number of SP in male VPA-treated mice was significantly reduced, as compared with that in the female VPA-treated mice(P<0.05).3 ELISA assay reveled that Aβ40 and Aβ42 level were significantly decreased in the brains of VPA-treated mice compared with control (P<0.01),Aβ40 and Aβ42 in male mice were lower than that in female mice, regardless of treated or control group.4 Nissl staining showed that the swelling neurons in cortex and hippocampus of VPA-treated mice decreased greatly; Nissl bodies were increased notably;Electron microscopy showed that the structure of synapse in the hippocampus of VPA-treated mice was more obvious, the number of synapse was increased, and both anterior and posterior membranes of synapse became thicker than that in control group.5 The number of neurons in VPA- treated mice was significantly increased(P<0.05), compared with control, as revealed by Immuo- histochemical staining and Western blot; while the number of apoptotic neurons was obviously reduced in the brain of VPA-treated mice(P<0.01), as revealed by TUNEL staining.6 Immuohistochemical staining and Western blot revealed that the expression of Caspase-3, Caspase-9 and Caspase-12 were significantly decreased, while the Bcl-2 protein and Bcl-2/Bax ratio were increased dramatically in the brains of VPA-treated mice. Conclusions: 1 VPA can reduce the autonomous behavior and relieve manic symptoms of male APP/PS1 double transgenic mice; VPA can restore spatial learning and memory; VPA can reduce plaques burden, inhibit Aβproduction in the brains of male and female APP/PS1 double transgenic mice, which have gender difference.2 VPA may change the neuronal morphological structures in the brains of APP/PS1 double transgenic mice, that is, decreasing numbers of swelling neurons, increasing the numbers of Nissl bodies and synapses.3 VPA can inhibit neuronal apoptosis, its underlying mechanisms may be related to downregulation of Caspase-3, Caspase-9 and Caspase-12 and up-regulation of Bcl-2.