Aims: Perturbation of membrane trafficking can lead to neurodegenerative diseases such as Alzheimer’s disease (AD) which is the most common form of neurodegeneration in aging populations. Accumulation of amyloid plaques in the brain is a hallmark of AD and are formed by the aggregation of amyloid β peptides (Aβ) generated after proteolytic processing of the amyloid precursor protein (APP) by the protease beta secretase (BACE1). Defining the dynamic intracellular trafficking of newly synthesized BACE1 and APP, especially in neurons is required to understand the regulation of Aβ production, development of AD and design of novel therapeutics.
Method: We are investigating the anterograde trafficking of newly synthesized BACE1 and the identity of trafficking machinery using the Retention Using Selective Hooks (RUSH) system (Boncompain et al, 2012). The RUSH system allows us to synchronize and analyse in real time the trafficking of BACE1 in fixed and live cultured cells and primary mouse neurons. We have combined the RUSH system with the knockdown of Golgi adaptors and the use of TIRF microscopy.
Results: We found that BACE1 is transported to the plasma membrane directly after its exit from the TGN. Subsequently, BACE1 is trafficked to the early endosomes then the recycling endosomes compartments. Significantly, we observed that the depletion of AP1, but not AP4, impairs the Golgi exit of BACE1 and its arrival at the plasma membrane. The retention of BACE1 in the Golgi leads to an increase of Aβ production. On the other hand, the Golgi exit of APP in absence of AP1 is not affected.
Conclusion: Our results show that BACE1 and APP trafficking from the Golgi apparatus is tightly regulated by different adaptor proteins, resulting in the partitioning of BACE1 and APP and the regulation of APP processing. Alterations in their anterograde trafficking can lead to a dramatic increase in Aβ production.