Revisiting LAMP1 as a marker for degradative autophagy-lysosomal organelles in the nervous system

ABSTRACTLysosomes serve as the degradation hubs for macroautophagic/autophagic and endocytic components, thus maintaining cellular homeostasis essential for neuronal survival and function. LAMP1 (lysosomal associated membrane protein 1) and LAMP2 are distributed among autophagic and endolysosomal organelles. Despite widespread distribution, LAMP1 is routinely used as a lysosome marker and LAMP1-positive organelles are often referred to as lysosomal compartments. By applying immuno-electron microscopy (iTEM) and confocal imaging combined with Airyscan microscopy, we expand on the limited literature to provide a comprehensive and quantitative analysis of LAMP1 distribution in various autophagic and endolysosomal organelles in neurons. Our study demonstrates that a significant portion of LAMP1-labeled organelles lack major lysosomal hydrolases. BSA-gold pulse-chase assay further shows heterogeneous degradative capacities of LAMP1-labled organelles. In addition, LAMP1 intensity is not a sensitive readout to a...