Effects Of Simvastatin On Aβ_1-42-Impaired Neurotoxicity In Mice And Underlying Mechanisms

IntroductionStatins, inhibitors of 3-hydroxy-3-methyl-glytarylcoenzyme A (HMG-CoA) reductase, are widely used to prevent or treat cardiovascular diseases. Alzheimer’s disease (AD) is a progressive neurodegenerative disease that is characterized by cognitive impairment. The neuropathological hallmarks of AD include intracellular neurofibrillary tangles, deposition of β-amyloid peptide (Aβ) which creates senile plaques (SP) and neuronal death. In the general population, the use of statins is associated with a lower risk of AD. Clinical epidemiology study has shown that the treatment with simvastatin (SV) can decrease risk for AD and improve cognition in AD patients. However, the underlying mechanism still remains unclear. Aβ can selectively activate N-methy-D-aspartate receptor (NMDAr) and enhances the Ca2+ influx, leading to Ca2+ overload, neuronal death and cognitive deficits. Previous studies reported that simvastatin can increase the function of NMDAr through reducing the level of NR2B phosphorylation (phospho-NR2B) of NMDAr. Thus, it is proposed that high dose of simvastatin through enhancing NMDAr activity can aggravate the Ap-neurotoxicity.ObjectiveThe aims of the present study were to investigate the effects of SV on the Aβ1-42-neurotoxicity and to explore the molecular mechanisms underlying SV effects in Aβ1-42-mice.Methods1. Preparation of AD animal model:ICR male mice were intracerebroventriculy injected (i.c.v.) with the Aβ1-42 or Aβ42-1 (0.3 nmol/2 μ1/mouse) to prepare the Aβ1-42-mice.2. SV administration:Oral administration (p.o.) of SV at dose of 10-80 mg/kg, daily was given starting at 4 h after Aβ1-42-injection for consecutive 15 days. Oral administration of farnesol (FOH) or farnesyl pyrophosphate (FPP) was administered.3. Behavioral examination:Morris water maze task and Y-maze task were used to test the cognitive performance.4. Histological examination:The pyramidal cells in hippocampal CA1 and CA3 regions were assessed by Toluidine blue staining.5. Hoechst staining was used to examine the number of apoptotic cells.6. Total number of healthy pyramidal cells in CA1 region was counted by stereological analysis.7. Western blot analyses the level of phosphor-NR2B and phosphor-Akt in hippocampus.Results1. Aβ1-42-mice spent longer escape-latency to reach the hidden platform and significantly reduced the alternation rate compared to control mice.2. The treatment of Aβ1-42-mice with SV for continuous 15 days could attenuate the spatial cognitive deficits in a "U" type dose-dependent manner.3. In comparison with control mice, the number of pyramidal cells was reduced and the number of hoechst-positive cells was significantly increased in Aβ1-42-mice.4. The death of pyramidal cells in Aβ1-42-mice was significantly reduced by the SV-treatment at 20 mg/kg, but not at dose of 10 or 40 mg/kg, even was aggravated at dose of 80 mg/kg.5. In comparison with control mice, the CA3-CA1 synaptic transmission in Aβ1-42-mice was impaired with the deficits of LTP induction, which could be improved by the treatment with SV-treatment at 20-40 mg/kg.6. Hippocampal NMDA receptor (NMDAr) NR2B phosphorylation (phosphor-NR2B) was elevated in Aβ1-42-mice, which was further dose-dependently increased by SV-treatment. Replenishment of isoprenoid farnesyl pyrophosphate (FPP) by applying farnesol (FOH) could abolish the SV-increased phosphor-NR2B in Aβ1-42-mice, but had no effect on the or-NR2B.7. NMDAr antagonist MK801 blocked the neurotoxicity of Aβ1-42 and SV (80 mg/kg) in Aβ1-42-mice, whereas FOH only inhibited SV (80 mg/kg)-neurotoxicity.8. The SV-treatment in Aβ1-42-mice corrected the decrease in hippocampal Akt phosphorylation. The PI3K inhibitor abolished the SV (20 mg/kg)-neuroprotection in Aβ1-42-mice.ConclusionThe results indicate that the SV-treatment in Aβ1-42-mice exerts dose-dependent neuroprotection and neurotoxicity through reducing FPP to enhance the phosphorylation of NR2B and Akt.