Sleep is a requirement for all mammals and most other animals. Humans sleep for approximately one third of their lives. However, the beneficial effects of sleep are not well understood at the cellular level. Sleep is regulated by its duration (sleep homeostasis) and frequency (circadian rhythm). Previous studies have shown that humans with insufficient sleep experience psychiatric and metabolic disorders, and cardiovascular disease. These studies were unable to determine whether the outcomes were from the lack of sleep, or the increased stress caused by lack of sleep. Stress in this case refers to the stress on our cells. Reactive oxygen species (ROS) are by-products of metabolism and must be properly neutralized since they can damage proteins, lipids, and DNA. Antioxidants are molecules that help prevent molecular damage inflicted by ROS. When ROS levels exceed the levels of antioxidants present, the cell experiences oxidative stress. One explanation for the function of sleep is known as the free radical flux theory of sleep (dating back to the early 1990’s). This theory proposes that damaging ROS accumulate in neurons while the animal is awake, and sleep enables ROS clearance.
The humble fruit fly has been a very useful model to study how genes influence behaviour. In this article, Hill, et. al. studied fruit flies with a mutant inc gene, which has been shown to cause shortened sleep duration, to investigate how oxidative stress influences sleep. They injected normal and inc mutant flies with two types of oxidizing agents, and observed that inc mutant flies succumbed more rapidly to oxidative stress, which led to death. To determine if ROS levels influenced sleep duration, researchers reduced ROS levels in the brain and observed a decrease in the amount of time the flies slept.
This research provides evidence for a relationship between sleep and oxidative stress. ROS levels in the brain may play a part in the regulation of sleep, extending sleep when ROS levels are high. Sleep appears to mitigate ROS accumulation in the neurons in the brain. These findings can contribute to the overall understanding of sleep, and provide new insight into the mechanisms and treatment of neurodegenerative diseases associated with oxidative stress like Alzheimer’s, Parkinson’s, and Huntington’s diseases.
Summary written by: Jocelyn MacDonald
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A bidirectional relationship between sleep and oxidative stress in Drosophila
