APP and Bace1: Differential effect of cholesterol enrichment on processing and plasma membrane mobility

High cholesterol levels are a risk factor for the development of Alzheimer’s dis- ease. Experiments investigating the influence of cholesterol on the proteolytic processing of the amyloid precursor protein (APP) by the b-secretase Bace1 and on their proximity in cells have led to conflicting results. By using a fluores- cence bioassay coupled with flow cytometry we found a direct correlation between the increase in membrane cholesterol amount and the degree of APP shedding in living human neuroblastoma cells. Analogue results were obtained for cells overexpressing an APP mutant that cannot be processed by a-secretase, highlighting the major influence of cholesterol enrichment on the cleavage of APP carried out by Bace1. By contrast, the cholesterol content was not correlated with changes in membrane dynamics of APP and Bace1 analyzed with single molecule tracking, indicating that the effect of cholesterol enrichment on APP processing by Bace1 is uncoupled from changes in their lateral diffusion.