Stress granules at the intersection of autophagy and ALS

• Pathogenic mutations in ALS-associated genes have been shown to perturb autophagy pathways.
• Many ALS-associated proteins accumulate in cytoplasmic stress granules.
• Mutant ALS-causing proteins such as FUS, TDP-43, and SOD1 have been shown to be cleared by autophagy in cellular and human stem-cell derived neurons.

Amyotrophic lateral sclerosis (ALS) is a progressive, fatal disease caused by loss of upper and lower motor neurons. The majority of ALS cases are classified as sporadic (80–90%), with the remaining considered familial based on patient history. The last decade has seen a surge in the identification of ALS-causing genes – including TARDBP (TDP-43), FUS, MATR3 (Matrin-3), C9ORF72 and several others – providing important insights into the molecular pathways involved in pathogenesis. Most of the protein products of ALS-linked genes fall into two functional categories: RNA-binding/homeostasis and protein-quality control (i.e. autophagy and proteasome). The RNA-binding proteins tend to be aggregation-prone with low-complexity domains similar to the prion-forming domains of yeast. Many also incorporate into stress granules (SGs), which are cytoplasmic ribonucleoprotein complexes that form in response to cellular stress. Mutant forms of TDP-43 and FUS perturb SG dynamics, lengthening their cytoplasmic persistence. Recent evidence suggests that SGs are regulated by the autophagy pathway, suggesting a unifying connection between many of the ALS-linked genes. Persistent SGs may give rise to intractable aggregates that disrupt neuronal homeostasis, thus failure to clear SGs by autophagic processes may promote ALS pathogenesis.This article is part of a Special Issue entitled SI:Autophagy.