Nucleolin Rescues TDP-43 Toxicity in Yeast and Human Cell Models

Caterina Peggion,Maria Lina Massimino,Alessandro Bertoli,Jessica Agostini,Raissa Bortolotto,Roberto Stella,Geppo Sartori,Raffaele Lopreiato,Fiorella Tonello,Arianna Maldi

doi:10.3389/fncel.2021.625665

Abstract

TDP-43 is a nuclear protein involved in pivotal processes, extensively studied for its implication in neurodegenerative disorders. TDP-43 cytosolic inclusions are a common neuropathologic hallmark in amyotrophic lateral sclerosis (ALS) and related diseases, and it is now established that TDP-43 misfolding and aggregation play a key role in their etiopathology. TDP-43 neurotoxic mechanisms are not yet clarified, but the identification of proteins able to modulate TDP-43-mediated damage may be promising therapeutic targets for TDP-43 proteinopathies. Here we show by the use of refined yeast models that the nucleolar protein nucleolin (NCL) acts as a potent suppressor of TDP-43 toxicity, restoring cell viability. We provide evidence that NCL co-expression is able to alleviate TDP-43-induced damage also in human cells, further supporting its beneficial effects in a more consistent pathophysiological context. Presented data suggest that NCL could promote TDP-43 nuclear retention, reducing the formation of toxic cytosolic TDP-43 inclusions.

Highlights

Neurodegenerative diseases (NDs) represent a huge health problem worldwide
We focused on nucleolin (NCL) in light of multiple aspects, including the following structural and functional features of the protein that are reminiscent of transactive response DNA binding 43 kDa protein (TDP-43) attributes: (i), NCL is able to bind DNA/RNA molecules thanks to multiple RNA recognition motifs (RRM) domains; (ii), NCL carries an intrinsically disordered C-terminal region able to interact with different functional partners; (iii) NCL is one of the most abundant non-ribosomal proteins in the nucleolus, where it plays fundamental roles in nucleolar assembly and function, rRNA and ribosome metabolism (Jia et al, 2017), which are critically perturbed in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) (Lehmkuhl and Zarnescu, 2018)
Since one chromosomally integrated copy of TDP-43 displayed no toxicity to yeast cells (Johnson et al, 2008), we generated novel S. cerevisiae yeast strains in the CEN.PK IMX672 genetic background (Mans et al, 2015; hereafter abbreviated as CENPK), carrying in the yeast genome two (2C) or three (3C) integrated copies of the wild-type (WT) human TDP-43 sequence fused to GFP

Summary

INTRODUCTION

Neurodegenerative diseases (NDs) represent a huge health problem worldwide. In most cases, the origin of neurodegeneration remains largely unknown, but it is commonly accepted that many of these disorders share the accumulation and aggregation of misfolded proteins as a major hallmark of neuropathology (for which they are often referred to as proteinopathies). Some nucleolar proteins have been identified as TDP-43 interactors in systematic mass spectrometry (MS)-based approach in mammalian cells (Freibaum et al, 2010) Among these proteins, we focused on nucleolin (NCL) in light of multiple aspects, including the following structural and functional features of the protein that are reminiscent of TDP-43 attributes: (i), NCL is able to bind DNA/RNA molecules thanks to multiple RNA recognition motifs (RRM) domains; (ii), NCL carries an intrinsically disordered C-terminal region able to interact with different functional partners; (iii) NCL is one of the most abundant non-ribosomal proteins in the nucleolus, where it plays fundamental roles in nucleolar assembly and function, rRNA and ribosome metabolism (Jia et al, 2017), which are critically perturbed in ALS and FTD (Lehmkuhl and Zarnescu, 2018). Additional experiments in mammalian HEK293T cell models further support that the NCL overexpression can prevent TDP-43-dependent toxicity, reducing the formation of detergentinsoluble assemblies and restoring cell viability, possibly by avoiding the non-physiologic translocation of TDP-43 out of the nuclear compartment

MATERIALS AND METHODS

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CONCLUSION

DATA AVAILABILITY STATEMENT