Voluntary Exercise Affects The Neurotoxicity Of Aβ25-35on C57/bl6Mice And Its Mechanism

Background:Previous studies showed that the abnormal of β-amyloid (AP) accumulation and removal in brain is implicated as a central factor in Alzheimer’s disease (AD) pathology. A great quantity of Aβ deposition in the brain leads to neuronal apoptosis, synaptic loss, glial inflammation, oxidative stress, as well as brain vascular dysfunction. Therefore, targeting Aβ metabolism may be a reasonable therapeutic strategy in AD.It is well known that long-term regular and moderate exercise is beneficial to improve overall health condition, regulate the immune response, delay consenescence, and prolong life span. Previous studies showed that exercise can prevent or delay the cognitive impairment and the progress of the disease in AD models, its protective mechanisms may include multiple factors, such as improvements of cerebrovascular function, neurogenesis, angiogenesis and synaptic plasticity, antioxidative stress, and inhibition of metabolism-related inflammatory reaction. Therefore, exercise can be an effective method of adjuvant therapy for AD. We also investigated whether voluntary exercise can counteract the toxicity of Aβ directly.Objective:This dissertation aims to explore that if the voluntary exercise can affect the neurotoxicity of Aβ25-35on C57/b16mice and its mechanism. Thereby, it may provide more scientific basis to prevention of AD through exerciseMethods:Bilateral lateral ventricle injection of Aβ25-35for model of learning and memory impairment in C57/bl6mice, and then follow these steps:1) The exercise mice were exposed to exercise for12days before the start of the Y-maze test;2) Mice were tested for spatial learning and memory using Y maze;3) Hematoxylin-eosin (HE) staining was performed to observe neuronal morphology and neuronal loss in the hippocampus of AP25-35treated mice;4) Immunohistochemical staining to observe the express of synaptophysin (SYN), proliferating cell nuclear antigen (PCNA), laminin, glial fibrillary acidic protein (GFAP) and Ionized calcium binding adaptor molecule1(Ibal) in the hippocampus of mice;5) Western blotting to detect the expression level of nitrotyrosine (NTS), peroxiredoxin-1(Prdx-1), receptor for advanced glycation end products (RAGE), low density lipoprotein receptor-related protein-1(LRP1) in the hippocampus of mice.Results:1) The results showed that icv injection of AP25-35in mice caused a lower percentage of correct alternation in Y maze test, with no difference in number of arm entries compared with saline control. The voluntary exercise for12days significantly mitigated Aβ25-35induced memory deficits. These results suggest that Aβ25-35can induce learning and memory deficits, and voluntary exercise may improve it.2) HE staining showed that cell density and cytoarchitecture of pyramidal neurons in the hippocampal CA1region were not obviously changed, but a few populations of them underwent degeneration, characterized by perikaryal cytoplasmic contraction, in Aβ25-35treated mice compared with saline control mice. Quantitative data revealed a higher percentage of degenerated neurons in Aβ25-35treated mice, which was decreased by voluntary exercise. Compared with saline control mice, SYN immunoreactivity significantly decreased in the hippocampus in Aβ25-35treated mice, which was greatly reversed by voluntary exercise. These results suggest that voluntary exercise can ameliorate hippocampal neurodegeneration induced by Aβ25-35.3) Immunohistochemical staining results confirmed that Aβ25-35could induce gliosis in the hippocampus of mice. However, the level of activated astrocytes and microglia expression in hippocampus in Aβ25-35treated mice decreased by 17.86%and26.23%after voluntary exercise, respectively. There were no obvious change in saline control mice before and after exercise.4) we detected the expression levels of oxidative stress marker NTS and antioxidant enzyme marker Prdxl in the hippocampus by using Western blot. The results showed that NTS was significantly increased in Aβ25-35treated mice compared with saline treated control. The NTS increment was significantly suppressed after voluntary exercise treatment. It was noteworthy that the antioxidant Prdxl showed a compensatory increase in Aβ25-35treated mice compared with saline controls, and significantly reduced after voluntary exercise intervention. These results suggest that the protective effects of voluntary exercise on AP25-35induced hippocampal degeneration are related to reducing oxidative stress.5) Immunohistochemical staining results suggested voluntary exercise could induce hippocampus angiogenesis in Aβ25-35treated mice, but had few effects on the neurogenesis.6) Compared with saline control mice, LRP1and RAGE expression compensatory increased in the hippocampus of Aβ25-35treated mice, as revealed by Western blot quantitation. Voluntary exercise caused significant decreases in LRP1and RAGE in both Aβ25-35treated mice and saline control mice. These results indicated that brain Aβ transport system was activated in response to icv injection of Aβ25-35, which was attenuated by the voluntary exercise. Conclusion:The results of experiment confirmed that Aβ25-35could induce learning and memory impairment in mice, and voluntary exercise could against neurotoxic effect of Aβ25-35directly. The mechanisms may include:1) Voluntary exercise inhibit gliosis induced by Aβ25-35, and reduce the express level of oxidative stress in the hippocampus of mice;2) Voluntary exercise increase angiogenesis in the hippocampal of Aβ25-35treated mice and improve cerebral blood flow. Thus decreasing Aβ25-35induced neuronal degeneration and loss of synaptic protein in the hippocampus, and improving learning and memory in Aβ25-35treated mice.