Disrupted Autophagy and Neuronal Dysfunction in C. elegans Knockin Models of FUS Amyotrophic Lateral Sclerosis

It remains unclear how mutations in FUS, a ribonucleoprotein, lead to neuronal dysfunction in Amyotrophic Lateral Sclerosis (ALS) patients. To examine mechanisms underlying ALS FUS dysfunction, we generated the first C. elegans knock-in models using CRISPR/Cas9-mediated genome editing, creating R524S and P525L ALS FUS models. Although FUS inclusions were not detected, ALS FUS animals showed defective neuromuscular function, as well as stress-induced locomotion defects. Unlike C. elegans lacking the endogenous FUS ortholog, ALS FUS animals had impaired neuronal autophagy and increased SQST-1 accumulation in ALS FUS motor neurons. Loss of sqst-1, the C. elegans ortholog for ALS-linked, autophagy adaptor protein SQSTM1/p62, suppressed both neuromuscular and stress-induced locomotion defects in ALS FUS animals, but did not suppress neuronal autophagy defects. Therefore, autophagy dysfunction is upstream of, and not dependent on, SQSTM1 function in ALS FUS pathogenesis. Combined, our findings demonstrate that autophagy dysfunction likely contributes to protein homeostasis and neuromuscular defects in ALS FUS knock-in animals.