Amyloid precursor protein (APP) traffics from the cell surface via endosomes for amyloid β (Aβ) production in the trans-Golgi network

Amyloid precursor protein (APP) is processed sequentially by the beta-site APP cleaving enzyme and gamma-secretase to generate amyloid beta (A beta) peptides, one of the hallmarks of Alzheimer's disease. The intracellular location of A beta production-endosomes or the trans-Golgi network (TGN)-remains uncertain. We investigated the role of different postendocytic trafficking events in A beta(40) production using an RNAi approach. Depletion of Hrs and Tsg101, acting early in the multivesicular body pathway, retained APP in early endosomes and reduced A beta(40) production. Conversely, depletion of CHMP6 and VPS4, acting late in the pathway, rerouted endosomal APP to the TGN for enhanced APP processing. We found that VPS35 (retromer)-mediated APP recycling to the TGN was required for efficient A beta(40) production. An interruption of the bidirectional trafficking of APP between the TGN and endosomes, particularly retromer-mediated retrieval of APP from early endosomes to the TGN, resulted in the accumulation of endocytosed APP in early endosomes with reduced APP processing. These data suggest that A beta(40) is generated predominantly in the TGN, relying on an endocytosed pool of APP recycled from early endosomes to the TGN.