Abstract
Protein misfolding underpins several neurodegenerative disorders including frontotemporal dementia (FTD). In
FTD the misfolding of several different RNA-binding proteins (RBPs) with prion-like domains, including TDP-43
and FUS, are implicated. Prion-like domains are intrinsically disordered, making these proteins highly
aggregation-prone. RBPs are also known to undergo liquid-liquid phase separation (LLPS). LLPS is a
physiological response that allows sequestration and protection of essential cellular components, and for RBPs,
RNA is a key modulator of this process. However, the localized concentration of proteins can be quite high upon
LLPS, further increasing aggregation propensity. Indeed, pathological inclusions of TDP-43 are found in over
half of FTD patients. Further, many other proteins are known to co-aggregate with TDP-43, and synergistic
corruption of protein homeostasis may underpin FTD. Recently Matrin-3 (MATR3) aggregation was implicated
in FTD, and MATR3 has several key similarities and differences as compared to TDP-43 and FUS. However,
MATR3 remains poorly understood, and conflicting results have been reported in different studies. We therefore
aim to leverage our unique skillset to delineate the properties of MATR3 with respect to LLPS, RNA binding, and
interactions with other FTD-linked proteins. Understanding these mechanisms will provide fundamental
knowledge to inform new therapeutic development, particularly for new RNA therapeutics that might restore
physiological LLPS. We hypothesize that corrupted binding of MATR3 to RNA and other FTD-linked proteins can
synergize, driving FTD pathogenesis. In this proposal, we will investigate the specific mechanisms by which
MATR3 undergoes LLPS and how its LLPS is perturbed in FTD. Further, we will investigate the specific
mechanism by which LLPS leads to quality control malfunction in cells. We will also investigate how interactions
of MATR3 with RNA and other FTD-associated proteins synergize in FTD. To test these ideas, my lab has
developed a genetically tractable yeast system to probe the drivers of MATR3 toxicity and aberrant LLPS. We
have also pioneered purification of full-length MATR3, which will allow us to reconstitute its putative interactions
with RNA and other FTD-associated RBPs. Key findings will be validated in mammalian cells. In sum, we will
meet the following aims: 1) Define the molecular determinants of Matrin-3 liquid-liquid phase separation, and
how liquid-liquid phase separation is perturbed in ALS/FTD and 2) Elucidate the interactions of Matrin-3 with
RNA and other ALS/FTD-associated proteins. Successful completion of this project will provide us with new
fundamental knowledge of the factors modulating MATR3 LLPS, how MATR3 LLPS is corrupted in FTD, and
how LLPS might be therapeutically modulated.