| dc.description.abstract | AD is the most common neurodegenerative disease. The pathological hallmark of extra-cellular β-amyloid (Aβ) deposit is considered as one of the primary factors in inducing Alzheimer’s disease (AD). However, the mechanism of Aβ deposition on the cell membrane and the induced cytotoxicity is still unclear. The major obstacle in designing an effective therapeutic or strategy lies in our incomplete understanding of the mechanism of AD. On the basis of the previous reports and results, the “Recruiting Hypothesis” was proposed on the interaction between the plasma membrane and Aβ.
For “Recruiting Hypothesis” verification , this study is analyzed by kinetic and thermodynamic methods which divided into three parts which shown as follows.
(1) Investigation of the mechanism of beta-amyloid fibril formation
In the aggregation process, the secondary structure of Aβ (1-40) transforms to the β-sheet conformation, which could be described as a two-state model. As the temperature and ionic strength increase, the conformation of Aβ converts to the β-sheet structure with an increased rate. Results of circular dichroism monitoring demonstrate that the rate constant of nucleation is smaller than that of elongation, and the nucleation is the rate-determining step during the overall Aβ aggregation. The β-sheet structure was stabilized by hydrophobic force as revealed by the ITC measurements. The different structural aggregates and forming pathways could be identified and discriminated at high and low ionic strengths, resulting in distinctive fibril conformations. Furthermore, the thermodynamic analysis shows that hydrophobic interaction is the major driving force in the nucleation step.
(2)Studying the interaction between beta-amyloid and artificial cell membranes
Results from SPR and lipid monolayer trough studies showed that the rate of Aβ adsorption onto lipid monolayer/liposome is mainly due to the electrostatic effect which is sensitive to the lipid monolayer/liposome composition. Due to the electrostatic attraction of more number of GM1 by the Aβ leads to the formation of GM1 clusters. The GM1 clusters incurred cholesterol recruitment and form raft-like structure Consequently, the Aβ conformation changed to β-sheet, which acts as a seed and initiates a chain reaction, in that it attract other Aβs to interact with the GM1. This resulted in the accumulation of Aβ on the plasma membrane. At the same time, both GM1 and cholesterol accumulate more and form larger clusters. Finally, each clusters aggregate with each other and form Aβ, GM1 and cholesterol rich phase which resulted in the function of membrane degradation.
(3)Examining the interaction between beta-amyloid and PC12 cell
Monomeric Aβ could attack the plasma membrane resulting in cytotoxicity, however, fibrillar Aβ was found to be less toxic. Aβ (1-40) was more toxic than Aβ (25-35) and the cytotoxcity of Aβ was proportional to its concentration. Besides, the depletion of GM1 from plasma membrane, it would block the Aβ-induced cytotoxicity. Decreasing the cholesterol level by around 30 % could attenuate the cytotoxicity of Aβ. These findings validate our idea that the cholesterol could stabilize the lateral pressure derived from the formation of GM1-Aβ complex on the membrane surface. Furthermore, both GM1 and cholesterol are essential in mechanism of Aβ accumulation and could modulate the cytotoxicity of monomeric Aβ.
All these results list above and published references are support “Recruiting Hypothesis”. Understanding the insight of the interaction between Aβ and cell membrane which provide by “Recruiting Hypothesis” could be helpful in developing medicines and strategies aimed to cure AD.
In addition, a biothermodynamic approach to real-time monitor the heat of metabolism by isothermal titration calorimetry (ITC) during PC12 cell-Aβ (1-40) interaction was provided by this study. This approach with rapid and directly measurement may provide not only real-time information for the interaction between Aβ and live cell but also more options for candidate drug development.
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