Regulation of the β-secretase processing of the Alzheimer's amyloid precursor protein

In this thesis, the role of lipid rafts and BACE ectodomain shedding in regulating the β-cleavage of APP have been examined. The activation of protein kinase C (PKC) was shown to increase the shedding of BACE and decrease the release of sAPPβ from SH-SY5Y cells over-expressing human BACE (SH-BACE). These PKC-mediated effects may be orchestrated through lipid rafts, since the activation of PKC was shown in this thesis to decrease the association of BACE with rafts. Together, these data show that a decrease in raft-associated BACE following PKC activation is associated with a decrease in APP β-cleavage, suggesting an important role for these membrane domains in APP processing. In addition, the ubiquitous intracellular calcium mediator, calmodulin, was shown to interact with BACE and to increase BACE shedding and decrease sAPPβ release, as with PKC activation. The majority of the previous work linking lipid rafts and APP processing has been carried out using non-neuronal or transformed neuronal cells. As an alternative and more physiologically relevant approach, synaptosomes have been used in this thesis to study the potential role of these domains in APP β-cleavage. APP, BACE and presenilin 1 (PS1) were all detected in the lipid rafts from purified synaptosomes. Notably, the mature form of BACE was found exclusively within the rafts from these neuronal structures, whereas the immature form was predominantly non-raft localised. Therefore, the presence of the mature species in the rafts supports a role for these membrane domains in the β-cleavage of APP. Strategies which target the reduction of cholesterol and hence the removal of BACE from lipid rafts may prove beneficial with regard to the development and/or progression of AD.EThOS - Electronic Theses Online ServiceGBUnited Kingdo