Genome instability underlies an augmented DNA damage response in familial and sporadic ALS human iPSC-derived motor neurons

Abstract Amyotrophic Lateral Sclerosis (ALS) is characterised by progressive motor neuron degeneration, but there is marked genetic and clinical heterogeneity1. It has been challenging to identify common ALS mechanisms among this diversity; however, a systematic framework examining motor neurons across the ALS spectrum may reveal unifying insights. Here, we present the most comprehensive compendium of ALS human induced pluripotent stem cell-derived motor neurons (iPSNs) from 429 donors, spanning 10 ALS mutations and sporadic ALS, from 15 datasets, including Answer ALS and NeuroLINCS. Using gold-standard reproducible bioinformatic workflows, we identified that ALS iPSNs show a common increase in the DNA damage response, which is characterised by activation of p53 signalling. The strongest p53 activation was observed in C9orf72 repeat expansions but was also found in TARDBP, FUS and sporadic subgroups. p53 activation was replicated in an ALS postmortem spinal cord cohort of 203 samples, indicating that the p53-dependent DNA damage response in ALS begins early and persists into the later stages of the disease. ALS iPSNs showed extensive genomic instability, as evidenced by enrichment of splicing alterations, single nucleotide variants, insertions, deletions and gene fusions, which may contribute to their p53 signature. In summary, by integrating the global landscape of ALS iPSNs, we reveal genome instability and p53 activation as common hallmarks of ALS motor neurons and provide a resource for identifying future ALS drug targets.