Neuronal DNA Double Strand Break Damage and Repair Following Sublethal iGluR Activation, and the Neuroprotective Effects of Melatonin

Abstract

DNA double strand break (DSB) damage is among the most lethal forms of DNA damage, and its repair in mature neurons remains largely unexamined, particularly following neuronal excitation. A major cause of DSBs is mediated by endogenous reactive oxygen species (ROS) that lead to a state of oxidative stress. The brain's large oxygen consumption, high metabolic rate and relative low levels of antioxidant defenses, make endogenous ROS the primary cause of neuronal DSBs. Since mature neurons do not divide, they cannot repair DSBs using accurate repair mechanism, and must rely on error-prone pathways to counter DSB damage. These factors suggest that post-mitotic neurons likely endure a slow accumulation of DNA errors over the years that can potentially lead to the onset various neuropathologies. Using a novel implementation of the neutral comet assay, a technique that examines DSBs, we show that neurons sustain DSB DNA damage following sub-lethal ionotropic glutamate receptor (iGluR) activity, leading to an increase in ROS and oxidative stress, and that they are repaired by a faulty repair mechanism. Due to the inherent error-prone quality of neuronal DSB repair, a viable approach in minimizing the deleterious effects associated with DSB damage is thus to minimize ROS generation in the first place. We show that neuronal pretreatment using the brain neurohormone melatonin completely prevents DSB generation, neuronal ROS increase and mitochondria destabilization, caused by iGluR activation, making the use of this neurohormaone a potential strategy to prevent the onset of DNA damage in adult neurons.

Lastly, We begin to examine the role of two key proteins, ATM and DNA-PKcs, involved in DSB repair, and the effects that their inhibition has on neuronal survival.