Autophagy-mediated Regulation of BACE1 Protein Trafficking and Degradation.

β-Site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) is the major neuronal β-secretase for amyloid-β generation and is degraded in lysosomes. The autophagy-lysosomal system plays a key role in the maintenance of cellular homeostasis in neurons. Recent studies established that nascent autophagosomes in distal axons move predominantly in the retrograde direction toward the soma, where mature lysosomes are mainly located. However, it remains unknown whether autophagy plays a critical role in regulation of BACE1 trafficking and degradation. Here, we report that induction of neuronal autophagy enhances BACE1 turnover, which is suppressed by lysosomal inhibition. A significant portion of BACE1 is recruited to the autophagy pathway and co-migrates robustly with autophagic vacuoles along axons. Moreover, we reveal that autophagic vacuole-associated BACE1 is accumulated in the distal axon of Alzheimer's disease-related mutant human APP transgenic neurons and mouse brains. Inducing autophagy in mutant human APP neurons augments autophagic retention of BACE1 in distal axons, leading to enhanced β-cleavage of APP. This phenotype can be reversed by Snapin-enhanced retrograde transport, which facilitates BACE1 trafficking to lysosomes for degradation. Therefore, our study provides new insights into autophagy-mediated regulation of BACE1 turnover and APP processing, thus building a foundation for future development of potential Alzheimer's disease therapeutic strategies.