Neuroprotection Of Small Molecules Against Oxidative Stress-mediated PC12 Cell Damage

The human brain,which is called the "central processor" of nervous system,controls the feeling,memory,emotions,movement and logical thinking.However,as the changing of human age and the surrounding environment,the brain suffers from multiple insults and may leads to various neurodegenerative diseases,such as Alzheimer's disease,Parkinson's disease,muscular dystrophy,depression and schizophrenia.These diseases seriously affect the life quality of patients and even threat their life.Besides,with the increase of ages,the probability of suffering from such diseases also increases.Therefore,it is extremely important to study the pathogenesis of these diseases and to find effective treatment strategies.Oxidative stress represents the disorder of the redox equilibrium between the production of free radicals and the capability of cells to eliminate them.As subversion of this redox balance is thought to initiate various diseases,living cells keep a redox equilibrium diligently.Oxidative stress can easily damage the brain due to its high content of polyunsaturated fatty acids,which make it vulnerable to free radicals attack.Oxidative stress has been implicated in the pathogenesis of a wide variety of chronic neurodegenerative diseases.Therefore,maintaining redox homeostasis in the brain is critical for the prevention of neurodegenerative diseases.The nuclear factor E2-related factor 2(Nrf2)is the core of cell's main endogenous antioxidant defense against a variety of chronic diseases including neurodegenerative diseases,cardiovascular diseases,and cancers.Under conditions of oxidative stress or electrophilic stress,Nrf2 is able to escape from Kelch-like ECH associated protein 1(Keap1)-mediated degradation and translocate to the nucleus.In nucleus,Nrf2 binds to small Maf proteins that increases the transcription rate of antioxidant response element(ARE)-driven genes expression including heme oxygenase-1(HO-1),NAD(P)H: quinone oxidoreductase 1(NQO1),thioredoxin reductase(TrxR),thioredoxin(Trx),and glutathione(GSH),all of which are able to regulate intracellular redox equilibrium.Hence,studies focusing on molecules that activate the Nrf2 are of vital significance and can form new therapies targeting the treatment of the neurodegenerative disorders.Molecules containing phenoxyl groups and/or Michael acceptor units appear to possess antioxidant and cytoprotective properties.In this paper,we aim to screen such molecules owning the neuroprotection from daily diets or traditional Chinese herbs,and explore the underlying mechanisms.The content of this thesis is summarized and classified as follows:1.A brief review of Keap1-Nrf2-ARE signal pathway was presented in Chapter 1.Meanwhile,the relationship between the Keap1-Nrf2 signaling pathway and neuroprotective diseases and the strategies of Nrf2 activation were also summarized.2.Five natural compounds,including hydroxytyrosol(HT),6-shogaol(6-S),cardomonin(CD),mangiferin(Mg),and costunolide(COS),were identified to have remarkable protection of PC12 cells against hydrogen peroxide(H2O2)-or 6-hydroxydopamine(6-OHDA)-induced cell injury.Mechanistic studies revealed that these compounds were potent Nrf2 activators to promote the nuclear translocation of Nrf2,which facilitated the expression of a series of Nrf2-driven antioxidant molecules,including HO-1,NQO1,GSH,Trx,and TrxR.In addition,knockdown of Nrf2 by shRNA interferance abolished or decreased the cytoprotection,suggesting that activation Nrf2 was the molecular mechanism underlying the cellular action of these compounds in PC12 cells.3.Hispolon and five analogues were designed and synthesized,and their neuroprotective effect against oxidative stress-mediated cell damage in PC12 cells was evaluated.Through a series of biological experiments two compounds(H1 and H6)were chosen for the follow-up studies.The discovery showed that both compounds could activate the Nrf2 in PC12 cells,which confers them to be potential neuroprotective agents.