Our research will take a cell biology approach to investigate mechanisms controlling axonal lysosome transport and maturation. Through these efforts we will seek to define how defects in the axonal transport and maturation of lysosomes create a sub-cellular environment that is highly conducive to the amyloidogenic processing of APP and the development of amyloid plaque pathology. These efforts are motivated by human genetics studies that have identified multiple genes encoding endo-lysosomal pathway proteins as AD risk factors as well as the well established but poorly understood local accumulation of lysosomes within swollen axons that surround amyloid plaques. Although such lysosome accumulations are widely found in human AD brain tissue and are recapitulated in transgenic mouse models that develop amyloid plaques, the contributions of these lysosomes (either protective or deleterious) on disease progression or dementia are not known. Based on our previous investigation of the amyloid plaque-associated axonal lysosome accumulations and axonal lysosome transport mechanisms, we hypothesize that defects in axonal lysosome transport and maturation create hotspots for amyloidogenic APP processing. Therefore, to investigate the contribution of defective axonal lysosome transport to APP processing and Aβ peptide production, we aim to: (1) Define mechanisms that control axonal lysosome abundance; (2) Establish the impact of axonal transport defects on amyloid precursor protein processing, Aβ production and the development of amyloid plaque pathology. Central to these proposed studies is our recent discovery of a robust defect in the coordinated process of axonal lysosome transport and maturation in neurons from JNK-interacting protein 3 (JIP3) knockout mice. Through our proposed efforts to dissect the mechanisms whereby JIP3 regulates axonal lysosomes and their ability to serve as sites of APP processing, we will gain new insight into possible pathogenic roles played by these organelles in Alzheimer's disease. Focusing on this specific subcellular environment that is so supportive of the amyloidgenic processing of APP has the potential to identify new strategies to specifically suppress the most dangerous sub-cellular sites for APP processing while sparing potentially beneficial functions of genes such as APP, BACE1 and PSENs. This research could thereby lead to novel therapeutic opportunities focused on manipulating axon lysosome biogenesis and/or transport to limit both Aβ production and neuronal pathology. New insights into the cell biology of neuronal lysosomes revealed by the proposed studies are expected to have additional broad relevance to other neurodegenerative diseases with lysosomal contributions to their pathology such as Parkinson's disease, frontotemporal dementia and hereditary spastic paraplegia.