Aberrant topoisomerase-1 DNA lesions are pathogenic in neurodegenerative genome instability syndromes

DNA damage is considered a prime factor in multiple spinocerebellar neurodegenerative diseases; however, the DNA lesions underpinning disease etiology are unknown. Here we identify the endogenous accumulation of pathogenic topoisomerase-1-DNA cleavage complexes (Top1cc) in murine models of ataxia telangiectasia and spinocerebellar ataxia with axonal neuropathy 1. We also show that the defective DNA damage response factors in these two diseases cooperatively modulate Top1cc turnover in a non-epistatic and ATM kinase-independent manner. Furthermore, coincident neural inactivation of ATM and DNA single strand break repair factors including tyrosyl-DNA phosphodiesterase-1 or XRCC1 result in increased Top1cc formation and excessive DNA damage and neurodevelopmental defects. Importantly, direct topoisomerase-1 poisoning to elevate Top1cc levels phenocopies the neuropathology of the mouse models above. Our study identifies a critical endogenous pathogenic lesion associated with neurodegenerative syndromes arising from DNA repair deficiency, indicating the essential role that genome integrity plays in preventing disease in the nervous system.