Prion-like Mechanism in Amyotrophic Lateral Sclerosis: are Protein Aggregates the Key?

ALS is a fatal adult-onset motor neuron disease. Motor neurons in the cortex, brain stem and spinal cord gradually degenerate in ALS patients, and most ALS patients die within 3~5 years of disease onset due to respiratory failure. The major pathological hallmark of ALS is abnormal accumulation of protein inclusions containing TDP-43, FUS or SOD1 protein. Moreover, the focality of clinical onset and regional spreading of neurodegeneration are typical features of ALS. These clinical data indicate that neurodegeneration in ALS is an orderly propagating process, which seems to share the signature of a seeded self-propagation with pathogenic prion proteins. In vitro and cell line experimental evidence suggests that SOD1, TDP-43 and FUS form insoluble fibrillar aggregates. Notably, these protein fibrillar aggregates can act as seeds to trigger the aggregation of native counterparts. Collectively, a self-propagation mechanism similar to prion replication and spreading may underlie the pathology of ALS. In this review, we will briefly summarize recent evidence to support the prion-like properties of major ALS-associated proteins and discuss the possible therapeutic strategies for ALS based on a prion-like mechanism.