Defects in DNA single-strand break repair (SSBR) are linked with neurological dysfunction but the underlying mechanisms remain poorly understood. Here, we show that hyperactivity of the DNA strand break sensor protein Parp1 in mice in which the central SSBR protein Xrcc1 is conditionally deleted (Xrcc1Nes-Cre ) results in lethal seizures and shortened lifespan. Using electrophysiological recording and synaptic imaging approaches, we demonstrate that aberrant Parp1 activation triggers seizure-like activity in Xrcc1-defective hippocampus ex vivo and deregulated presynaptic calcium signalling in isolated hippocampal neurons in vitro. Moreover, we show that these defects are prevented by Parp1 inhibition or deletion and, in the case of Parp1 deletion, that the lifespan of Xrcc1Nes-Cre mice is greatly extended. This is the first demonstration that lethal seizures can be triggered by aberrant Parp1 activity at unrepaired SSBs, highlighting PARP inhibition as a possible therapeutic approach in hereditary neurological disease.

• Keywords
• DNA strand break, XRCC1, neurodegeneration, poly(ADP-ribose) polymerase, seizures,
• MeSH
• DNA-Binding Proteins * genetics   metabolism   MeSH
• DNA MeSH
• Mice MeSH
• Neurons metabolism   MeSH
• DNA Repair genetics   MeSH
• Poly (ADP-Ribose) Polymerase-1 genetics   metabolism   MeSH
• Calcium * MeSH
• Seizures genetics   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA-Binding Proteins * MeSH
• DNA MeSH
• Poly (ADP-Ribose) Polymerase-1 MeSH
• Calcium * MeSH

Defects in DNA repair frequently lead to neurodevelopmental and neurodegenerative diseases, underscoring the particular importance of DNA repair in long-lived post-mitotic neurons1,2. The cellular genome is subjected to a constant barrage of endogenous DNA damage, but surprisingly little is known about the identity of the lesion(s) that accumulate in neurons and whether they accrue throughout the genome or at specific loci. Here we show that post-mitotic neurons accumulate unexpectedly high levels of DNA single-strand breaks (SSBs) at specific sites within the genome. Genome-wide mapping reveals that SSBs are located within enhancers at or near CpG dinucleotides and sites of DNA demethylation. These SSBs are repaired by PARP1 and XRCC1-dependent mechanisms. Notably, deficiencies in XRCC1-dependent short-patch repair increase DNA repair synthesis at neuronal enhancers, whereas defects in long-patch repair reduce synthesis. The high levels of SSB repair in neuronal enhancers are therefore likely to be sustained by both short-patch and long-patch processes. These data provide the first evidence of site- and cell-type-specific SSB repair, revealing unexpected levels of localized and continuous DNA breakage in neurons. In addition, they suggest an explanation for the neurodegenerative phenotypes that occur in patients with defective SSB repair.

• MeSH
• 5-Methylcytosine metabolism   MeSH
• Cell Line MeSH
• DNA biosynthesis   MeSH
• DNA Breaks, Single-Stranded * MeSH
• Humans MeSH
• Methylation MeSH
• Neurons metabolism   MeSH
• DNA Repair * MeSH
• Poly(ADP-ribose) Polymerases metabolism   MeSH
• DNA Replication MeSH
• Sequence Analysis, DNA MeSH
• Enhancer Elements, Genetic genetics   MeSH
• Check Tag
• Humans MeSH
• Male MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Intramural MeSH
• Names of Substances
• 5-Methylcytosine MeSH
• DNA MeSH
• Poly(ADP-ribose) Polymerases MeSH