Motor neuron disease-associated loss of nuclear TDP-43 is linked to DNA double-strand break repair defects

Abstract

Genome damage and their defective repair have been etiologically linked to degenerating neurons in many subtypes of amyotrophic lateral sclerosis (ALS) patients; however, the specific mechanisms remain enigmatic. The majority of sporadic ALS patients feature abnormalities in the transactivation response DNA-binding protein of 43 kDa (TDP-43), whose nucleo-cytoplasmic mislocalization is characteristically observed in spinal motor neurons. While emerging evidence suggests involvement of other RNA/DNA binding proteins, like FUS in DNA damage response (DDR), the role of TDP-43 in DDR has not been investigated. Here, we report that TDP-43 is a critical component of the nonhomologous end joining (NHEJ)-mediated DNA double-strand break (DSB) repair pathway. TDP-43 is rapidly recruited at DSB sites to stably interact with DDR and NHEJ factors, specifically acting as a scaffold for the recruitment of break-sealing XRCC4-DNA ligase 4 complex at DSB sites in induced pluripotent stem cell-derived motor neurons. shRNA or CRISPR/Cas9-mediated conditional depletion of TDP-43 markedly increases accumulation of genomic DSBs by impairing NHEJ repair, and thereby, sensitizing neurons to DSB stress. Finally, TDP-43 pathology strongly correlates with DSB repair defects, and damage accumulation in the neuronal genomes of sporadic ALS patients and inCaenorhabditis elegansmutant with TDP-1 loss-of-function. Our findings thus link TDP-43 pathology to impaired DSB repair and persistent DDR signaling in motor neuron disease, and suggest that DSB repair-targeted therapies may ameliorate TDP-43 toxicity-induced genome instability in motor neuron disease.

Dipeptide repeat proteins inhibit homology-directed DNA double strand break repair in C9ORF72 ALS/FTD

“…Nucleolar dysfunction is recognized as a key feature of C9ORF72-related neurodegeneration and, as a consequence of this dysfunction, various inter-related cellular processes are affected [13]. While there is substantial evidence supporting a role for dysregulated RNA metabolism and nucleocytoplasmic transport defects in C9ALS/FTD [10,16], accumulating evidence supports a role for aberrant DNA DSB repair as well [52,[70][71][72][73]. Since the nucleolus is a repository of stress response proteins, and nucleolar proteins directly participate in the restoration of homeostasis [24,27], we sought to investigate the role of NPM1 in DNA DSB repair deficiencies in C9ALS/FTD focusing on the role of arginine-rich DPRs that are most frequently associated with nucleolar dysfunction [9,10].…”

“…In addition to NPM1, several ALS-linked RNA binding proteins have direct roles in DNA DSB repair including valosin-containing protein (VCP), fused in sarcoma (FUS) and TAR DNA binding protein 43 (TDP-43) [70,72,[86][87][88][89][90][91][92]. It is increasingly understood that the RNA processing functions of these proteins are capable of destabilizing co-transcriptional structures called R-loops, which are composed of the nascent RNA hybridized with template DNA and the non-template singlestranded DNA, thereby reducing the potential of persistent R-loops to result in DNA DSBs [73,93,94].…”

Altered Mitochondrial Dynamics in Motor Neuron Disease: An Emerging Perspective

“…Interestingly, recent studies suggested that XRCC4 may localize to mitochondria, where it may collaborate with LIG3 for mitochondria DNA double-strand break repair [151]. In view of our recent discovery of TDP-43 s association with XRCC4, it is likely that TDP-43 function in mitochondrial DNA repair by recruiting the XRCC4-LIG3 complex [149,151]. The potential role of TDP-43 and FUS in maintaining mitochondrial genomic stability requires further investigation.…”

“…For example, FUS is recruited to the DNA damage site in a PARP1-dependent manner, where it recruits XRCC1/LIG3 and is required for efficient function of LIG3 [31]. Our laboratory identified TDP-43 as a key component of NHEJ-mediated DNA double-strand break repair machinery, where it acts as a scaffold for the recruitment of XRCC4-LIG4 [149]. Furthermore, C9ORF72 iPSC differentiated motor neurons show increased oxidative stress and DNA damage in an age-dependent manner [129].…”

The Overlapping Genetics of Amyotrophic Lateral Sclerosis and Frontotemporal Dementia

“…TDP-43 is a DNA and RNA binding protein involved in many aspects of RNA metabolism, including splicing, microRNA biogenesis, transcription, and stabilization of messenger RNA (Buratti et al, 2001;Strong et al, 2007;Buratti and Baralle, 2008;Fiesel et al, 2010;Lagier-Tourenne et al, 2010). Two contrasting mechanisms have been proposed to explain TDP-43 related neurodegeneration, namely (Cleveland and Rothstein, 2001) loss of function arising from sequestration of critical TDP-43 protein within cytoplasmic aggregates leading to nuclear depletion of TDP-43 (Chio et al, 2013;Mitra et al, 2019;Roczniak-Ferguson and Ferguson, 2019) gain of function effect due to some inherent toxic property of the aggregates (Buratti and Baralle, 2012;Hergesheimer et al, 2019). However, the toxic role of aggregated TDP-43 in neurodegeneration is still under debate.…”