Two familial ALS proteins function in prevention/repair of transcription-associated DNA damage

Abstract

Amyotrophic lateral sclerosis (ALS) is a progressive motor neuron dysfunction disease that leads to paralysis and death. There is currently no established molecular pathogenesis pathway. Multiple proteins involved in RNA processing are linked to ALS, including FUS and TDP43, and we propose a disease mechanism in which loss of function of at least one of these proteins leads to an accumulation of transcription-associated DNA damage contributing to motor neuron cell death and progressive neurological symptoms. In support of this hypothesis, we find that FUS or TDP43 depletion leads to increased sensitivity to a transcription-arresting agent due to increased DNA damage. Thus, these proteins normally contribute to the prevention or repair of transcription-associated DNA damage. In addition, both FUS and TDP43 colocalize with active RNA polymerase II at sites of DNA damage along with the DNA damage repair protein, BRCA1, and FUS and TDP43 participate in the prevention or repair of R loopassociated DNA damage, a manifestation of aberrant transcription and/or RNA processing. Gaining a better understanding of the role(s) that FUS and TDP43 play in transcription-associated DNA damage could shed light on the mechanisms underlying ALS pathogenesis.A myotrophic lateral sclerosis (ALS) is a disease of both upper and lower motor neuron dysfunction that leads to progressive paralysis and eventually death due to respiratory failure. No single model of ALS disease pathogenesis has been revealed; however, multiple disease-associated genes are known (1). The variation in function of these genes suggests that there may be multiple ALS molecular subtypes. That said, the familial ALS gene product list is also enriched in protein groups with related functions.Mutations in multiple RNA processing genes, including FUS (FUS RNA-binding protein), TDP43 (TAR DNA-binding protein), SETX (senataxin), TAF15 (TATA box-binding protein-associated factor 15), EWSR1 (EWS RNA-binding protein 1), HNRNPA1 (heterogeneous nuclear ribonucleoprotein A1), and HNRNPA2B1 (heterogeneous nuclear ribonucleoprotein A2/B1), among others, give rise to familial ALS (fALS) (1). FUS and TDP43 are currently the best studied, given that mutations in these genes lead to classic histologic findings in ALS neural tissue and that similar histologic findings can be found in neural tissue of sporadic ALS cases (2). At autopsy, cytoplasmic TDP43 inclusions are found in ALS motor neurons from patients with (i) TDP43 mutations and (ii) sporadic ALS (i.e., patients with no FUS, TDP43, or other known pathogenic mutation) (2). They are also present in neurons in various parts of the brains of patients with either sporadic or familial versions of the ALS-related disorder, fronto-temporal lobar dementia (FTLD) (2). At autopsy, FUS inclusions were detected in the cytoplasm of motor neurons of FUS mutation-bearing fALS patients and in the cytoplasm of neurons in various regions of the brain in some FTLD patients (2).FUS and TDP43 exhibit a wide range of functions, most of which involv...

SMN deficiency in severe models of spinal muscular atrophy causes widespread intron retention and DNA damage

“…Consequently, defects in splicing, RNA processing, and transport would be expected. Perhaps consistent with this idea, FUS and TDP-43 were recently implicated in the prevention of R-loop-mediated transcription-associated DNA damage in models of ALS (68). As we have demonstrated here, changes in RNA processing due to either to cytoplasmic aggregation or genetic deletion of splicing factors could initiate the formation of DNA double-strand breaks in part through R-loops, leading ultimately to the degeneration of motor neurons in both ALS and SMA.…”

FUS affects circular RNA expression in murine embryonic stem cell-derived motor neurons

“…Briefly, human iPSCs were maintained in Nutristem-XF (Biological Industries) in plates coated with hESC-qualified matrigel (BD Biosciences) and passaged every 4–5 days with 1 mg ml −1 dispase (Gibco). MNs were derived based on a previously described protocol modified to use adherent cells53 as follows. Cells were cultured until confluent.…”

Regulation of transcription termination by FUS and TDP-43

“…TDP-43, on the other hand, binds to GUrich sequences and can compete with termination factors for UG-rich sequences downstream of the polyadenylation signal (66,67). Furthermore, both FUS and TDP-43 are known to suppress the buildup of transcription-associated DNA damage (52,(68)(69)(70)(71)(72). Given that ALS or FTD develops after decades of life, we hypothesize that the accumulation of DNA damage due to the buildup of R-loops at transcription terminators in post-mitotic neurons contributes to neurodegenerative pathology.…”