Molecular determinants and modifiers of the toxicity, condensate dynamics, and droplet morphology of the ALS/FTD-associated protein Matrin-3.

Abstract

Matrin-3 is a DNA- and RNA-binding protein (RBP) implicated in amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and a distal myopathy. Many RBPs with prion-like domains, including TDP-43 and FUS, have been implicated in ALS/FTD and Matrin-3 has key similarities and differences as compared to these proteins. To better understand the key features of Matrin-3, we have developed a new yeast model of Matrin-3 proteotoxicity and aggregation. We find that Matrin-3 is toxic and forms dynamic shell-like nuclear condensates in yeast, resembling the structures that form from RNA-binding deficient TDP-43. Disease-associated mutations in Matrin-3 impair condensate dynamics and disrupt condensate morphology. Matrin-3 toxicity is largely driven by its RNA-recognition motifs (RRMs). Further, deletion of one or both RRMs drives coalescence of these shell-like condensates. Aberrant phase separation of several different RBPs underpins ALS/FTD, and we have engineered potentiated Hsp104 variants to reverse the misfolding of a range of proteins including TDP-43 and FUS. Here, we demonstrate that these same variants also counter Matrin-3 toxicity, highlighting the importance of restoring proteostasis to counter Matrin-3 toxicity. We suggest that these Hsp104 variants which rescue Matrin-3, TDP-43, and FUS toxicity might be employed to restore impaired condensate dynamics of a range of ALS/FTD-associated proteins. We anticipate that our yeast model could be a useful platform to screen for genetic or small molecule modulators of Matrin-3 misfolding. We will also describe our recent efforts to further characterize the properties of Matrin-3, including its phase separation and RNA binding.