| Alzheimer’s disease is the major pathogeny of dementia in the70’s presentingamyloid-beta peptides and neurofibrillary tangles. It contains atypia, senile and preseniletypes according to the age of onset and clinical feature. Moreover, AD also can be classifiedinto sporadic and familial type including three stages, early medium and later. As thedeterioration of it,the clinical symptoms are becoming worse.With the development of technology, more researches concern about the cause of ADaiming to find new therapeutic targets. It is thought that the environment and inheritanceare two main causes of AD. Moreover Presenilin1, Presenilin2, amyloid precursor proteinare important pathologies in this disease. Besides, it has found that aquatic products andvegetables can decrease the morbidity. For the cause of Alzheimer’s disease hasn’t beenidentified, so therapeutic plans are just improving the cognition, mental symptoms andsome psychological or social treatments. Drugs for AD include cholinesterase inhibitorsand NMDA receptor antagonists.Functions of CNS including cranial ganglia, brain and spinal cord are seriouslydamaged in AD mice. And central nervous system are composed of neural cells acceptinginformations. What’s more, as a main part of central nervous system, brain containsforebrain, midbrain and hindbrain. Forebrain is the most complex and significant part,midbrain is the reflex center of vision and auditory, hindbrain is the connection of brain. Sobrain functions a lot in central nervous system, which can be impaired by Alzheimer’sdisease.Past researches maily concern about damage of neurons. However the injury of glialcells hasn’t been widely studied in AD. As siginificant parts of central nervous system,glialcells not only support neurons but regulate internal environment of brain. Furthermore,oligodendrodyte is a kind of glia with amounts of processes and chondriosome. Satellitecell is another kind of oligodendrocyte surrounded by neurons in gray matter. Indeed,functioning a similar role as schwann cell, oligodendroyte forms myelin in the central nervous system. The nuclear of oligodendrocyte is round and small, owning densechromatin in high electron density. It can perform strong motions in vitro as well.To explore new directions of diagnosis and therapy in AD, an increasing researchesdraw attention to the role of oligodendrocyte in AD. Previous studies have found outtoxication of Aβ25-35on neurons, suppressing cells’ proliferation and differentiation.Moreover, recent researches agree that oligodendrocyte can be suppressed by Aβ as well,and finding that3xTg-AD mice’s abnormality of oligodendrocyte before the deposition ofAβ. Furthermore, oligodendrocyte precursor cells transfected by Presenilin presentabnormal distribution of MBP accompanying with the Aβ1-42’s effect. And it is thought thatAβ1-42increases the poison of presenilin in OPCs.Although numerous of researches support the view that Alzheimer’s disease can injurythe myelination in CNS. There are still several unsolvd problems. What’s the etiology ofdemyelination in AD? Whether it contains any interactions between AD and remyelination?What’s the progress of the abnormality? Detail evidences haven’t been found.To discuss the effect of amyloid-beta peptides on myelination in CNS, C57BL/6miceare chosen in this research. And the study is carried out through whole, tissue and cellularlevels. At whole level, Aβ1-42was dissolved and cultured in incubator for7～10days, thenidentified with fibrous deposit. Moreover mice were injected with Aβ1-42in the thirdventricle, and the control group was injected with sterile water in the same area. Further,the mice were weighted and tested every day. As the results showed, mice injected byAβ1-42prsent impaired balance ability and weight loss. At tissue level, Transgenic APP/PS1mice are chosen to identify Aβ’s toxication. Mice were perfused by Zamboni’s and theirbrains were dissected for immunohistochemistry. Results revealed that the MBP’sexpression in the experimental group is much lower than the control group. Furthermore,we found out that Aβ1-42oligomer drmatically affected the proliferation and differentiationof oligodendrocyte precursor cells. So we intend to explore the interactions among Aβ1-42,oligodendrocytes and the caspase pathway.Results are divided into three parts:Part I the effect of amyloid-beta peptides on athletic ability of C57BL/630C57BL/6mice from experimental animal center of third military medical universitywere divided into three groups. Specifically10mice without interference in normal group, 10mice injected by sterile water in contrl group, the others injected by Aβ1-42in experimentgroup,then observing their weight and behavior. As the global index showed, averageweight of normal group has increased from15.43±0.37g to21.459±1.56g during the stageof the frist meek to the6thweek, which is increased by7.029±1.19g. the control hasincreased from15.41±0.49g to21.415±1.77g in the same stage,which is increased by7.005±1.28g(P>0.05). However, average weight of experimental group has dramaticallydecreased from15.45±0.27g to11.193±0.61g in2weeks,which is decreased by4.257±0.88g(P<0.05). Although the average weight has increased from11.193±0.61g to14.122±0.98g in the following4weeks, which is still decreased by1.328±1.25g(P<0.01)compared with the average weigh without injection. In a word, Aβ1-42oligomer suppressedmice’s weight.To evaluate the athletic and balance ability of mice injected by Aβ1-42, the rota-rod wasused to record the maintain time. Finding out that normal and control groups show normalathletic and balance ability, the average of which are159.02±23.01s and157.07±22.03s(P>0.05). However, the ability of mice injected by Aβ1-42was impaired, the maintaintime of which is80.49±19.72s(P<0.05). Proving that Aβ1-42not only affect physical fitnessbut athletic and balance ability of mice. Moreover it thought to be related to damage ofmyelination in CNS.Part II the effect of amyloid-beta peptides on corpus callosumAPP/PS1mouse is recognized as a successful AD modle in recent years. Morris watermaze has found that transgenic mouse showed unresponsive and deteriorated ability. And itis proved that study ability decreased in transgenic mouse prior to normal mouse consistentwith rota-rod. And it has been identified that APP/PS1mouse showed AD symptoms, butthe test of histological changes of it hasn’t been widely observed.APP is a transmembrane glycoprotein and closely related to Alzheimer’s disease,genesof which is located in21chromosome expressing PP695, APP714, PP751and APP7704.For sudden changes of APP, β-secretase enzyme increases the deposition of Aβ. PS1isconsisted of467amino acids constituting γ-secretase complex with PS2, Aph21andPEN22. Moreover the sudden change of PS1affects the enzymatic activity and increasesthe production of Aβ1-42. To test effects of amyloid-beta peptides on corpus callosum, we choose48-weekAPP/PS1mice and normal C57mice to explore MBP’s expression of corpus callosum. Andresults show that the expression in corpus callosum among APP/PS1mice is lower thannormal ones.Part III The inhibition of Aβ1-42on proliferation and differentiation inoligodendrocyte precursor cellsWe got OPCs with95%purity through B104conditional culture, then Aβ1-42wasadded to medium in a dose-dependent manner. Survival rate of OPCs in the experimentalgroup significantly decreased(P<0.01) in comparasion with control group. Specifically,cells’ proliferation has been dramatically suppressed by Aβ1-42in one hour(P<0.01).Withthe increase of concentration, the effect of drug on OPCs was becoming more obvious,changing from (P<0.05) to (P<0.01). However, there are no differences between control andnormal groups(P>0.05).We got proteins after the interference of Aβ1-42in a time-dependent manner of0,1,2,4and5h. Through western blot, we found out that the level of caspase-3in experimentalgroup was significant higher than control and normal groups in a time and dose dependence(P<0.01).Specifically, the expression of caspase-3significantly increased after the interferenceof Aβ1-42in two hours(P<0.01). Aβ1-42also affected cells in a dose-dependent mannerwhich was0,1,2.5,5and10μm. We found out that the amount of caspase-3has nochanges in normal and experimental groups in1μm, but it showed the increase of caspase-3in2.5μm. In a word, With the increase of concentration, the level of protein was becomingobvious, which changed from (P<0.05) to (P<0.01).The purified OPCs performed processes in2or3days in vitro,and the followingculture increased processes to mature. To test the effect of Aβ1-42on differentiation, weused immunocytochemistry to observe the morphology of oligodendrocyte. Furthermore,we found out that the diameter and processes of oligodendrocytes decreased throughdetecting myelin basic protein.In conclusion, above results showed that Aβ not only affect mice’s weight and athleticability but also decrease the expression of MBP. Besides Aβ suppress the proliferationand differentiation of OPCs and increase the amount of Caspase-3. Apparently amyloid-beta protein dramatically suppress the formation of myelin and itsfunction,which is through affecting OPCs’ proliferation and differentiation by apoptosispathway. So, it is obvious that amyloid-beta protein plays a vital role in remyelinationamong Alerzhimer’s disease,which can provide a new direction in clinical therapy. |
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