Lipid Rafts and Amyloid Metabolism: Role in Pathogenesis of Alzheimer’s Disease

Abstract

Brain lipids play an important role not only as ubiquitous structural membrane components providing the scaffolding and compartmentalisation outside and within the cells but also participating in various signalling processes either by facilitating them or by acting as signal molecules. Membrane lipids form highly specialised domains, called lipid rafts, which are more ordered structures than the rest of the membrane and are enriched in cholesterol and sphingolipids. These domains provide a platform for specific and targeted protein-lipid and protein-protein interactions and as such facilitate binding and/or enzymatic processes on the surface and within the membranes. These lipid-protein interactions are important for various signalling events and proper cell functioning. When normal structure and functions of lipid rafts is disturbed due to the changes in lipid metabolism, caused by various internal and environmental factors, it results in a cascade of pathological events. Among proteins whose metabolic pathways depend on the lipid raft structure and integrity is amyloid precursor protein (APP) – the protein highly implicated in the pathogenesis of Alzheimer’s disease (AD). Proteolytic processing of APP by a metalloproteinase called β-secretase (BACE1) and a multiprotein complex called γ-secretase results in production of the amyloid β peptide (Aβ) - one of the key molecules leading to development of AD. These events take place in the lipid rafts. Some lipid components of the rafts, including ganglioside GM1, facilitate Aβ aggregation and formation of its toxic oligomers. Understanding the mechanisms regulating lipid-protein interactions in the rafts might result in new therapeutic strategies and treatments. In this review we discuss the implications of lipids in APP processing and Aβ metabolism and possible therapeutic avenues derived from studying lipid raft structure and functions in normal and AD brain.