Author : Christopher Towlson
Publisher :
Page : 496 pages
File Size : 47,98 MB
Release : 2010
Category : Alzheimer's disease
ISBN :
Alzheimer's disease (AD) brain pathology is characterised by the presence of senile plaques containing insoluble aggregates of the amyloid beta peptide (A[beta]). The mechanisms of A[beta] generation are not well understood but previous work has shown that amyloid precursor protein (APP) internalization from the cell surface may be an important step in this process. APP and the amyloidogenic enzymes involved in its processing have been shown to reside in cholesterol rich membrane micro-domains called lipid rafts. Lipid rafts are important cell signalling centres on the plasma membrane and may be involved in certain types of endocytosis. APP processing, including endocytosis, is also modulated by insulin signalling pathways. This thesis describes the generation and expression of APP endocytosis deficient mutants to study the role of APP intemalisation, insulin signalling and lipid rafts in A[beta] generation. -- Subcellular fractionation of cultured cells expressing human APP reveals that [beta]CTF, the direct precursor to A[beta], is found almost exclusively in lipid raft fractions. Furthermore, [beta]CTF is reduced in lipid rafts from cells expressing endocytosis deficient APP mutants. By contrast, APP endocytosis mutations have no effect on the localization of full-length APP or [beta]- and [gamma]-secretases. We also show that insulin treatment increases non-amyloidogenic processing of APP in neuroblastoma cells and primary mouse neurons, possibly by a mechanism involving decreased APP endocytosis. - Taken together, my results are consistent with the notion that plasma membrane bound APP and the [beta]-secretase BACE reside in distinct lipid raft species that merge upon endocytosis, resulting in enzyme and substrate converging in endosomes where APP is cleaved to generate A[beta]. Furthermore, altered APP endocytosis due to insulin resistance may increase the generation of A[beta] in AD.