ALS/FTD Mutation-Induced Phase Transition of FUS Liquid Droplets and Reversible Hydrogels into Irreversible Hydrogels Impairs RNP Granule Function

Tetsuro Murakami,David Ron,Mei Zhen,Seung-Pil Yang,Eric Rees,Yosuke Wakutani,Michele Vendruscolo,Seema Qamar,William Meadows,Akinori Miyashita,Giorgio Favrin,Weili Lin ,Julie Qiaojin Lin ,Deborah Kronenberg‐Versteeg ,Roger B Dodd ,Christine E Holt ,Fiona Chan ,Clemens F Kaminski ,Paul E Fraser ,Claire H Michel ,Gian Gaetano Tartaglia ,Gabriele S Kaminski Schierle ,Rodylyn Rose Ferry ,Gerold Schmitt‐Ulms ,Ana Rita Costa ,Yang Li ,Dennis W Dickson ,Neil A Shneider ,Dong Liu ,Peter St George-Hyslop

doi:10.1016/j.neuron.2015.10.030

Abstract

SummaryThe mechanisms by which mutations in FUS and other RNA binding proteins cause ALS and FTD remain controversial. We propose a model in which low-complexity (LC) domains of FUS drive its physiologically reversible assembly into membrane-free, liquid droplet and hydrogel-like structures. ALS/FTD mutations in LC or non-LC domains induce further phase transition into poorly soluble fibrillar hydrogels distinct from conventional amyloids. These assemblies are necessary and sufficient for neurotoxicity in a C. elegans model of FUS-dependent neurodegeneration. They trap other ribonucleoprotein (RNP) granule components and disrupt RNP granule function. One consequence is impairment of new protein synthesis by cytoplasmic RNP granules in axon terminals, where RNP granules regulate local RNA metabolism and translation. Nuclear FUS granules may be similarly affected. Inhibiting formation of these fibrillar hydrogel assemblies mitigates neurotoxicity and suggests a potential therapeutic strategy that may also be applicable to ALS/FTD associated with mutations in other RNA binding proteins.

Highlights

To investigate this possibility, we utilized FUS as a tractable example of the RNA binding proteins (RBPs)-proteinopathies
In partial agreement with earlier reports (Han et al, 2012; Kato et al, 2012), we show that in a process driven by the LC domain at the N terminus of FUS, FUS undergoes phase transitions, reversibly shifting between dispersed, liquid droplets, and hydrogel-like phases
We show that these stable ‘‘irreversible’’ FUS assemblies: selectively entrap other ribonucleoproteins, impair local RNP granule function, and attenuate new protein synthesis in the axon terminals of cultured neurons

Summary

Introduction

We utilized FUS as a tractable example of the RBP-proteinopathies. We demonstrate that pathogenic FUS mutants severely limit this ability to reiteratively shift between these phases. FUS mutants increase the propensity of FUS to condense into poorly soluble, stable, fibrillar hydrogel-like assemblies. We show that these stable ‘‘irreversible’’ FUS assemblies: selectively entrap other ribonucleoproteins, impair local RNP granule function, and attenuate new protein synthesis in the axon terminals of cultured neurons. We do not exclude the possibility that formation of fibrillar hydrogels may have similar disruptive effects on nuclear RNP granules. We show that modulation of these protein phase transitions may be a tractable therapeutic strategy

Results

Discussion

Conclusion