Abstract
It has been long assumed that post-mitotic neurons only utilize the error-prone non-homologous end-joining pathway to repair double-strand breaks (DSBs) associated with oxidative damage to DNA, given the inability of non-replicating neuronal DNA to utilize a sister chromatid template in the less error-prone homologous recombination (HR) repair pathway. However, we and others have found recently that active transcription triggers a replication-independent recombinational repair mechanism in G0/G1 phase of the cell cycle. Here we observed that the HR repair protein RAD52 is recruited to sites of DNA DSBs in terminally differentiated, post-mitotic neurons. This recruitment is dependent on the presence of a nascent mRNA generated during active transcription, providing evidence that an RNA-templated HR repair mechanism exists in non-dividing, terminally differentiated neurons. This recruitment of RAD52 in neurons is decreased by transcription inhibition. Importantly, we found that high concentrations of amyloid β, a toxic protein associated with Alzheimer's disease, inhibits the expression and DNA damage response of RAD52, potentially leading to a defect in the error-free, RNA-templated HR repair mechanism. This study shows a novel RNA-dependent repair mechanism of DSBs in post-mitotic neurons and demonstrates that defects in this pathway may contribute to neuronal genomic instability and consequent neurodegenerative phenotypes such as those seen in Alzheimer's disease.
Highlights
It has been long assumed that post-mitotic neurons only utilize the error-prone non-homologous end–joining pathway to repair double-strand breaks (DSBs) associated with oxidative damage to DNA, given the inability of non-replicating neuronal DNA to utilize a sister chromatid template in the less errorprone homologous recombination (HR) repair pathway
Some findings have shown a link between cell cycle activation in postmitotic neurons and a DNA damage response leading to apoptosis (13)
Studies have shown a correlation between this phosphorylated histone H3 (Ser-10) and mitotic chromosome condensation during early prophase, suggesting that anti-phosphohistone H3 can be used as a mitosis-specific marker (14)
Summary
To understand how non-dividing neurons repair oxidative DNA damage, we first verified that the primary rat cortical neurons utilized for experimentation were post-mitotic. After inhibiting RNA polymerase II, recruitment of RAD52, an essential factor for RNA-templated recombinational repair, was significantly reduced at sites of laser damage in post-mitotic neurons. After treatment with RNase H, RAD52 recruitment was significantly inhibited at sites of laser damage in post-mitotic neurons. After 24 h of treatment, it significantly reduced RAD52 recruitment to damage sites in both post-mitotic neurons and U2OS cancer cells (Fig. 3I). This indicates that A1–42 affects the same repair pathway in both dividing and non-dividing cells, compromising. These in vitro results are consistent with the possibility that RAD52 may bind ssRNA and the co-transcriptional R-loop upon transcriptional stress in postmitotic neurons
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
