TDP43 aggregation at ER-exit sites impairs ER-to-Golgi transport

Protein aggregation plays key roles in age-related degenerative diseases, but how different proteins coalesce to form inclusions that vary in composition, morphology, molecular dynamics and confer physiological consequences is poorly understood. Here we employed a general reporter based on mutant Hsp104 to identify proteins forming aggregates in human cells under common proteotoxic stress. Over 300 proteins were identified, forming different inclusions containing subsets of aggregating proteins. In particular, TDP43, implicated in Amyotrophic Lateral Sclerosis (ALS), partitions dynamically between two distinct types of aggregates: stress granule and a previously unknown solid inclusion at the ER exit sites (ERES). TDP43-ERES coaggregation is induced by diverse proteotoxic stresses and observed in the motor neurons of ALS patients. Such aggregation causes retention of secretory cargos at ERES and therefore delayed ER-to-Golgi transport, providing a link between TDP43 aggregation and compromised cellular function in ALS patients.