The Effect Of Nanoparticles On The Fibrillation Process Of Amyloid-β

Alzheimer’s disease（AD）is a fatal progressive neurodegenerative disorder and the leading cause of dementia in the aging population.And the incidence rate of AD increases rapidly with age.The main clinical symptoms of AD are memory loss,cognitive dysfunction and abnormal behavior,and the typical pathological hallmark is the accumulation of amyloid plaques and neurofibrillary tangles in the brain.The pathogenesis of AD has not been clearly explained due to its complexity.Studies found that the major component of amyloid plaques is amyloid-beta（Aβ）protein which derived through proteolysis of the amyloid precursor protein（APP）withβ-andγ-secretases.Aβmonomers contain 39-43 amino acids and an imbalance between production and clearance causes the increase of the Aβconcentration,it tends to aggregate into oligomers,protofibrils and mature fibrils.In addition,oligomers can be generated through interactions between monomers and fibrils which called secondary nucleation.Recent studies have shown that oligomers are toxic to neurons.Therefore,Aβaggregates are not only the target of AD treatment,but also can be used as a marker of clinical diagnosis of AD.Inhibiting the aggregation of Aβand degradation of Aβfibrils have been a hot topic in recent years.Nanoparticles are widely used because they have many advantages,such as easy preparation,storage stability,easy surface modification,and good biocompatibility.In this paper,a peptide called CE17was designed to synthesize CE17-AuNCs based on a biomineralized method.The functional CE17-AuNCs could self-assemble to form different morphologies such as toroidal and dendritic nanostructures.More importantly,CE17-AuNCs could interfere with the Aβaggregation.Low concentration of CE17-AuNCs prefers to promote the elongation of fibril while high concentration of CE17-AuNCs showed dramatic inhibition of the fibril formation process.And also,we fabricate co-polymer nanoparticles which contain PDPP3T and LPFFD,which are usd to degrade Aβfibrils and inhibit Aβaggregation,the details of the paper are as follows:Chapter 1.IntroductionIn this paper,we first introduce the generation and aggregation process of Aβ,then discuss the mechanism of how oligomers cause nerve toxicity,and meanwhile,we introduce several inhibitors and nanoparticles used in the detection of Aβaggregation,the inhibition of Aβformation process and the degradation of Aβfibrils.Finally,the significance of this work is expounded.Chapter 2.Study on the self-assembly of functional gold nanoclusters and its role in interfering with A?₄₀0 aggregationIn this work,we synthesized the functional gold nanoclusters with the surface modification of Aβ_11-221-22 fragments,and explored its influence on the aggregation process of Aβ₄₀.First of all,a peptide called CE17 was designed to synthesize CE17-AuNCs based on a biomineralized method.We then use fluorescence spectroscopy,transmission electron microscope（TEM）,atomic force microscope（AFM）,matrix-assisted laser desorption/ionization time-of-flight mass spectrometry（MALDI-TOF-MS）to determine its optical properties,morphology,chemical composition,etc.And the results show that CE17-AuNCs have good fluorescence properties,the size is around 2 nm,and the formula of CE17-AuNCs is Au₁₈Peptide₅.Then,due to the particularity of the sequence on CE17-AuNCs surface,we explored the self-assembly behavior of CE17-AuNCs and found that low concentration of CE17-AuNCs tended to form stable toridal structure while high concentration of CE17-AuNCs disorderly aggregate.Finally,the effect of the CE17-AuNCs on the aggregation of Aβ₄₀0 was studied,and the experimental results showed that the low concentration of CE17-AuNCs had a nucleation effect,which promoted the aggregation and the high concentration of CE17-AuNCs effectively inhibited the aggregation of Aβ₄₀.The addition of CE17-AuNCs can alleviate the toxicity caused by Aβ₄₀.Chapter 3.The preparation of Copolymer-NPs@PDPP3T and their application in A?₄₂2 aggregation and degradationIn this work,we fabricated a Copolymer-NPs@PDPP3T which can both inhibit the aggregation of Aβ₄₂2 and degrade Aβ₄₂2 fibrils by photothermal effect.First of all,theβ-sheet breaker peptide（LPFFD）was modified to the hydrophilic end of the DSPE-PEG_2K-COOH by amidation to synthesize DSPE-PEG_2K-LPFFD.Because phospholipid is hydrophobic,and polyethylene glycol is hydrophilic,it can self-assemble to form Copolymer-NPs.Then,we wrapped the semiconductor copolymer PDPP3T in the hydrophobic core of Copolymer-NPs,the PDPP3T has strong absorption in the near infrared region,which could rapidly heat up under the laser irradiation of 808 nm.The synthetic Copolymer-NPs@PDPP3T were co-culturedwithAβ₄₂,theexperimentalresultsshowedthatthe Copolymer-NPs@PDPP3T could effectively inhibit the aggregation of Aβ₄₂.Copolymer-NPs@PDPP3T co-cultured with Aβ₄₂2 which incubated for 72 h,the temperature of the solution rises rapidly and the fibril structure is destroyed under808nm laser irradiation.We can also find the fibril is degraded into disordered fragments.This fully demonstrates that the Copolymer-NPs@PDPP3T we prepared can potentially be applied to the treatment of AD.