Novel mechanism explains how sleep repairs damaged DNA in the brain
We know sleep is important. Virtually every animal on the planet exhibits some kind of sleep-like behavior, and when an organism is deprived of sleep we can see remarkable adverse effects, both physically and psychologically. However, many of the restorative mechanisms underpinning sleep still remain a mystery to scientists.
A team from Israel's Bar-Ilan University has uncovered a previously unknown function of sleep that may explain why the behavior is so fundamental to all complex organisms with a brain.
To home in on the specific function of sleep on a neuronal level, the researchers examined zebrafish, a useful model organism for scientists because they are transparent in their larval stage, allowing for extraordinary insights into normally hidden cellular processes. The hypothesis was that during sleep, a process occurs inside individual neurons whereby DNA damage accumulated in waking hours can be repaired.
Utilizing a high-resolution microscope that allowed the researchers to observe chromosome activity within a single neuron, it was found that during wakefulness there is a continual process of DNA damage accumulating within a neuron. The cell's natural repair processes are constantly working to repair the damage, however, during waking hours the damage seems to accumulate faster than it can be repaired.
When the zebrafish went to sleep the researchers observed a doubling in the rate of chromosome dynamics, significantly increasing the efficacy of this natural DNA repair system. Lior Appelbaum, lead on the study, uses an analogy inspired by road repair to help explain the importance of sleep in repairing the damage, which he dubs the, "price of wakefulness."
"It's like potholes in the road," says Appelbaum. "Roads accumulate wear and tear, especially during daytime rush hours, and it is most convenient and efficient to fix them at night, when there is light traffic."
As part of this intriguing hypothesis the researchers suggest the sense of being tired and needing to sleep is triggered when neurons have accumulated a volume of DNA damage that demands sleep-related repair. It's a compelling idea, but at this stage the research has only been established in a highly-specific animal model. The next step for the work is to find out if this DNA repair process is related to sleep in larger and more complex mammals.
It's not out of the realm of possibility that this research will translate to humans. A recent study from a team of Hong Kong scientists revealed increased levels of DNA damage can be identified in blood samples from doctors after just one night of sleep deprivation. So there is reason to suspect a link exists between sleep deprivation and DNA damage in humans.
Appelbaum is excited about the implications of his team's discovery. If this process can be verified in the brains of more complex animals, it may offer a clue as to why all animals need to sleep, despite the risks involved in being unaware of one's surroundings for such a long stretch of time.
"Despite the risk of reduced awareness to the environment, animals – ranging from jellyfish to zebrafish to humans – have to sleep to allow their neurons to perform efficient DNA maintenance, and this is possibly the reason why sleep has evolved and is so conserved in the animal kingdom," says Appelbaum.
The new study was published in Nature Communications.