| Alzheimer's disease(AD),a neurodegenerative disease,is clinically characterized by early progressive loss of memory and cognitive dysfunction.It is considered that Aβdesposition,neurofibrillary tangles,selective loss of neurons and their synapses are the main pathological features in AD.However,how the Aβcause the neuropathologic changes and abnormal clinical symptoms,especially the deficits of the learning and memory still remains unknown.Synaptic dysfunction is considered to be the most significant factor contributing to the decline of the memory and cognition.Recentely,studies indicated that dendritic deficits played an important role in the cognitive dysfuntion in AD.P21-activated kinase(PAK),an actin-regulated protein,is well documented to have a critical role in the plasticity of dendritic spines, and PAK signal pathway is reported to be involved in the deficits of cognition in AD. However,it is not clear whether PAK is involved in the early mechanism of the learning and memory loss by affecting the plastic changes of dendritic spines and their synapses.Therefore,the present study investigated the relationships between the Aβaccumulation and the pathologic changes of dendritic spines and synapses in an AD animal model with APP/PS1 double transgenes.At the same time,the mechanism underlining the deficits of PAK was studied.Three parts are included in present thesis.In the first part,the plaques composed of Aβand the levels of Aβ42 in the cerebral cortex and hippocampus of 22w-,32w- and 48w- APP/PS1 transgenic mice were examined by methods of immunohistochemical,ELISA and Morris Water Maze behavior test.The results showed that there was an age-related increase of Aβ42 levels and Aβplaques in the cerebral cortex and hippocampus of APP/PS1 transgenic mice.At the age of 22 weeks,Aβplaque was firstly observed in the cerebral cortex, and the number and volume of the plaques increased with aging.The plaques occurred in the hippocampus were observed at 22 weeks of age,being later than those in the cerebral cortex.At 32 weeks of age,there was increasing Aβplaque deposition. And at 48 weeks of age,the desposition of Aβplaque was significantly increased. Results from ELISA method showed that Aβ42 levels began to increase at 22 weeks of age,and there was a significant increase in Aβ42 levels at 32-,48-week-old APP/PS1 transgenic mice.These results indicated that the increases of Aβplaque and Aβ42 levels were closely related with aging.The results from behaviour analysis by Morris Water Maze revealed that there was evident impairment in the spatial discrimination learning and memory in the 32-week-old APP/PS1 transgenic mice.In the space navigation experiment,the escape time was evident delayed.And in the spatial probe test,the number of platform crossing was obvious decreased.At the 48 weeks of age,the ability of learning and memory further decreased.These results reflected some relative correlation between age-related Aβaccumulation and the decline of learning and memory.In the second part,by the methods of Tunel,Nissl staining,Golgi impregnation and electron microscopy,we studied the morphologic changes of neurons and their synapses.We did not observe the loss of neurons in the cerebral cortex and hippocampus in the 48-week-old APP/PS1 transgenic mice.But there were obvious dendrite abnormal changes,including dendrite distortion,disorder,shorten,thicken and a significant decrease of dendritic spines in the cerebral cortex and hippocampus at 48-week-old APP/PS1 transgenic mice.With aging,the decreases of dendritic loss in the 22-,32-,48-week-old APP/PS1 transgenic mice were significant,indicating an age-related decrease of dendritic spines in the APP/PS1 transgenic mice.Electron microscopy showed that there was an obvious synapse abnormality,including the decrease of the total number of the synapse,less in the type of perforate synapse in the temporal cortex and in the DG of hippocampus at 48-week-old APP/PS1 transgenic mice.All of these results revealed obvious dendrite disorders,the loss of the dendritic spines and their synapses,while no significant loss of neurons in the brain of APP/PS1 transgenic mice at the level of the light microscopy. For the third part,the expression of p21-activated kinase(PAK) and Drebrin in the cerebral cortex and hippocampus of APP/PS1 transgenic mice and wild-type(WT) mice were studied by mean of immunohistochemistry,western blot,intracerebral ventricle injection of PAK18(PAK inhibitor) from different ages,and the relationgships among PAK,Drebrin and the pathologic changes in APP/PS1 transgenic mice were discussed.Western blot showed that there was a significant decrease of the levels of both pPAK and Drebrin at the 32- and 48-week-old APP/PS1 transgenic mice in the cerebral cortex and hippocampus.And with aging,the levels of pPAK and Drebrin were further decreased.But,the expression of PAK3 was not changed.These results indicated a paralleled decrease in the PAK activities and expression level of Drebrin in the brain of APP/PS1 transgenic mice,which involved in the neuropathologic changes of transgenic mice.The experiment of PAK18 injection further revealed a significant decrease of pPAK levels,companied by the decrease of Drebrin levels,in the cerebral cortex and hippocampus of 48-week-old WT mice after intracerebral ventricle injection of PAK18.These results demonstrated that Drebrin levels were closely related to the PAK activity,and the decrease of PAK activity could cause the Drebrin levels decline in WT mice,which indicated that the decrease of Drebrin was caused by PAK activity decline.Taken together,the decrease of PAK activity played a critical role in the pathology process of the APP/PS1 transgenic model mouse of AD.The results above suggested that age-related Aβaccumulation in the brain of the APP/PS1 transgenic mice might cause PAK activity decline and Drebrin levels decrease,which resulted in the dendrite disorders,dendritic spine loss and spine synapse loss.All of the changes might be the cause of the deficits of learning and memory observed in the APP/PS1 transgenic mice of AD. |
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