ABSTRACT
Abnormalities of the endolysosomal and autophagy systems are found in Alzheimer's disease, but it is not clear whether defects in these systems are a cause or consequence of degenerative processes in the disease. In human neuronal models of monogenic Alzheimer's disease, APP and PSEN1 mutations disrupt lysosome function and autophagy, leading to impaired lysosomal proteolysis and defective autophagosome clearance. Processing of APP by γ-secretase is central to the pathogenic changes in the lysosome-autophagy system caused by PSEN1 and APP mutations: reducing production of C-terminal APP by inhibition of BACE1 rescued these phenotypes in both APP and PSEN1 mutant neurons, whereas inhibition of γ-secretase induced lysosomal and autophagic pathology in healthy neurons. Defects in lysosomes and autophagy due to PSEN1 mutations are rescued by CRISPR-knockout of APP. These data demonstrate a key role for proteolysis of the C-terminal of APP by γ-secretase in neuronal dysfunction in monogenic Alzheimer's disease.
Subject(s)
Alzheimer Disease/metabolism , Amyloid Precursor Protein Secretases/metabolism , Amyloid beta-Protein Precursor/metabolism , Autophagosomes/metabolism , Lysosomes/metabolism , Protein Processing, Post-Translational , Alzheimer Disease/genetics , Alzheimer Disease/pathology , Amyloid Precursor Protein Secretases/antagonists & inhibitors , Amyloid beta-Protein Precursor/genetics , Autophagy , Axons/metabolism , CRISPR-Cas Systems/genetics , Cerebral Cortex/pathology , Endosomes/metabolism , Humans , Mutation/genetics , Presenilin-1/genetics , ProteolysisABSTRACT
Neurons rely heavily on axonal transport to deliver materials from the sites of synthesis to the axon terminals over distances that can be many centimetres long. KIF1A is the neuron-specific kinesin with the fastest reported anterograde motor activity. Previous studies have shown that KIF1A transports a subset of synaptic proteins, neurofilaments and dense-core vesicles. Using two-colour live imaging, we showed that beta-secretase 1 (BACE1)-mCherry moves together with KIF1A-GFP in both the anterograde and retrograde directions in superior cervical ganglions (SCG) neurons. We confirmed that KIF1A is functionally required for BACE1 transport by using KIF1A siRNA and a KIF1A mutant construct (KIF1A-T312M) to impair its motor activity. We further identified several cargoes that have little or no co-migration with KIF1A-GFP and also move independently from BACE1-mCherry. Together, these findings support a primary role for KIF1A in the anterograde transport of BACE1 and suggest that axonally transported cargoes are sorted into different classes of carrier vesicles in the cell body and are transported by cargo-specific motor proteins through the axon.
