Poly(ADP-ribose) Engages the TDP-43 Nuclear-Localization Sequence to Regulate Granulo-Filamentous Aggregation

Abstract

TAR DNA-binding protein of 43 kDa (TDP-43) forms granulo-filamentous aggregates in affected brain regions of >95% of patients with ALS and ~50% of patients with frontotemporal degeneration (FTD). Furthermore, in disease, TDP-43 becomes N-terminally truncated resulting in protein deposits that are mainly composed of the C-terminal prion-like domain (PrLD). The PrLD is inherently aggregation-prone and is hypothesized to drive protein aggregation of TDP-43 in disease. Here, we establish that the N-terminal region of the protein is critical for rapid TDP-43 granulo-filamentous aggregation. We show that the biopolymer poly(ADP-ribose), or PAR, inhibits granulo-filamentous aggregation of TDP-43 by engaging PAR-binding motifs (PBMs) embedded in TDP-43 nuclear-localization sequence. We demonstrate that progressive N-terminal truncation of TDP-43 can decelerate aggregation kinetics and promote formation of thread-like filaments. Thus, the N-terminal region and the PBMs of TDP-43 promote rapid granulo-filamentous aggregation and antagonize formation of thread-like fibrils. These findings illustrate the complexity of TDP-43 aggregation trajectories.

The role of liquid–liquid phase separation in aggregation of the TDP-43 low-complexity domain

“…Our current findings regarding the impact of LLPS on the aggregation properties of TDP-43 are limited to experiments in vitro with a purified LCD. As such, these findings do not account for the potential role of the TDP-43 N-terminal domain, which may alter the aggregation landscape by modulating phase separation and the formation of pathogenic species (10,17,59,60). It is likely that the reported recruitment of TDP-43 to cytoplasmic stress granules in vivo (61,62) may involve similar self-association of TDP-43 molecules, thus triggering robust LLPS-mediated fibrillation.…”

“…Invariably, these CTFs contain the glycine-rich, disordered LCD (residues ϳ267-414) that appears to be of key importance to the intrinsic aggregation propensity of TDP-43 (12). Recent studies indicate, however, that the N-terminal domain is also important, playing a regulatory role in the formation of different types of aggregates (17). Even though the specific nature of TDP-43 aggregates from patient histopathological samples is a topic for discussion (1, 18 -20), the prion-like progressive behavior of TDP-43 proteinopathies (21)(22)(23)(24) suggests that these aggregates have a seeding capacity characteristic of amyloids.…”

TDP-43, a protein central to amyotrophic lateral sclerosis, is destabilized by tankyrase-1 and -2

“…Mounting evidence implicates poly(ADP-ribose) (PAR) activity in the neurotoxicity-associated with ALS/FTD and other neurodegenerative disorders such as ischemic stroke, Parkinson's and Alzheimer's diseases (Duan et al, 2019;Fatokun et al, 2014;Kam et al, 2018;McGurk et al, 2018a;McGurk et al, 2018b;McGurk et al, 2018c;McGurk et al, 2019;Naumann et al, 2018;Rulten et al, 2014). PAR is a reversible posttranslational modification generated by PAR polymerases (PARPs) whereby polymers of ADP-ribose are covalently linked onto target proteins (transPARylation) or the enzymes themselves (autoPARylation) (Gupte et al, 2017).…”

Alphavirus nsP3 ADP-ribosylhydrolase Activity Disrupts Stress Granule Formation

“…Informatics analyses revealed that RNA granule proteins are enriched for low complexity regions and these proteins are preferentially modified by ADP-ribosylation and that PAR-binding proteins are also enriched for low-complexity regions [27,[70][71][72]. Compared with other protein modifications that regulate SG dynamics, ADP-ribosylation is unique in that the polymeric form (i.e., PAR) is able to seed the low-complexity region-containing proteins to form non-membranous structures in vitro [25][26][27][28]70]. Our data suggest that the nsP3 ADP-ribosylhydrolase likely degrades the PAR that seeds SGs in cells, with G3BP1 as a possible ADP-ribosylated substrate (cf.…”

“…Overexpression of these PARPs and PARG isoforms induces and suppresses SG formation, respectively, while PARG knockdown delays SG disassembly [19,25]. PAR, like RNA, has been proposed to seed formation of non-membranous structures by facilitating the high concentration of low complexity region-containing proteins locally through noncovalent binding to the repetitive monomeric units of the polymer [19,[25][26][27][28]. The non-covalent PAR-protein interaction also facilitates the targeting of specific proteins to SGs [25,26,29], such as TDP-43-a key protein involved in several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS).…”