SOD1 is delivered to lysosomes via autophagy to maintain lysosomal function and integrity

The gene encoding superoxide dismutase 1 (SOD1) is often mutated in familial amyotrophic lateral sclerosis (ALS), affecting motor neurons. Compared with ALS-associated mutant SOD1, the function of WT SOD1 is less explored. We demonstrate that during starvation, WT and mutant SOD1 are transported into lysosomes. Genome-wide CRISPR interference (CRISPRi) screening identified autophagy-related proteins and the autophagic receptor TP53INP1 as key mediators. TP53INP1 binds ATG8 family proteins, preferentially LC3C, and directly interacts with SOD1. Within lysosomes, SOD1 retains its enzymatic activity. Starvation induces elevated levels of lysosomal reactive oxygen species (ROS), which are further increased by knocking down SOD1 or TP53INP1. Lysosomal degradation activities and membrane integrity are also compromised in the absence of SOD1 or TP53INP1. We reveal a novel function of SOD1 in maintaining lysosomal activity and integrity, and a previously unrecognized role of autophagy in delivering cytosolic enzymes into lysosomes for catalytic purposes, rather than for degradation.