With busy lives and schedules, sleep is usually one of the last things on our mind, and it can be hard to get a good night’s rest. However, getting an adequate amount of sleep is extremely important when it comes to cognition, metabolism, and immunity. And the lack of sleep can actually be detrimental to our health.

A study done by researchers at Harvard Medical School just last year found that severe sleep deprivation not only affects our cognition and brain function, but can potentially cause harm in our gut and gastrointestinal system. Researchers identified that sleep deprivation can lead to the accumulation of reactive oxygen species (ROS) in the gut, which are highly reactive, unstable molecules that drive cellular damage in instances of sleep deprivation, for example. While ROS can be beneficial in terms of cell signaling (Figure 1), an excess of ROS present causes irreversible changes to cell makeup and function through widespread oxidation. Because ROS are so unstable, they begin to react with different components of your cells, such as DNA, and other macromolecules, such as RNA and proteins, causing damage and making these macromolecules unstable as well.

To further examine the implications of sleep deprivation, the researchers first used flies to test their hypothesis. They specifically used the species drosophila, or fruit flies to conduct their study. Fruit flies were used because they require adequate sleep to function normally, and their sleep patterns are very similar to humans. These flies are also a common model organism and are easy to work with due to their short lifespan, their ability to reproduce in large numbers, and because about 60% of their genes are homologous to humans.

The study used three different methods of sleep deprivation on the flies to confirm and further examine if there is a correlation between sleep deprivation and the presence of ROS in the gut. First they used a thermogenetic method, where various neurons in the flies were stimulated at 29°C to suppress sleep. The flies were sleep deprived for 10 days, and it was found that not only did mortality increase, but levels of ROS increased in their gut as well (Figure 2). The flies needed 15 days to recover from the severe sleep deprivation, lowering ROS levels, proving that poor sleep did affect their gut health. 

To examine the presence of ROS levels in these experiments, the researchers used dihydroethidium (DHE) to detect the presence of ROS. DHE is very sensitive to oxidative radicals, so when ROS is present, it emits a bright fluorescence. If oxidative species are not present, then DHE emits a blue fluorescence. In the following experiments and figures, the red-purple, pink, and white colors indicate that ROS was present after severe sleep deprivation.

To confirm these findings, the researchers used another method to suppress sleep in the flies. They exposed the flies to vibrations that affected their sleep. They found that their wings and legs became damaged due to the vibrations, a limitation of the experiment, but ROS still accumulated due to the lack of sleep (Figure 3).

Lastly, they used loss-of-function mutations, induced by RNAi, that targeted the neurons and deprived the flies of sleep. RNAi can be used to target specific genes by neutralizing the mRNA and inhibiting the expression of targeted genes. The genes that were targeted with RNAi were redeye(ryeT227M), sleepless (sssD40), and insomniac(inc2). Once again, their experiments showed that ROS accumulated in the gut, as shown in the following figures.

The researchers also tested their findings on mice to see if their findings were applicable to a mammalian model. They had five mice set up in a little house that had a rotating bar to keep the mice moving to prevent them from sleeping. They also had an additional five mice as a control, who were placed in a house with no rotating bar. After just two days of sleep deprivation, they found elevated ROS levels in the small and large intestines of the mice in the experimental group (Figure 7). After five days of sleep deprivation, DNA damage, stress granules, and cell death were observed due to elevated ROS levels (Figure 8).

You might be wondering if these findings are applicable to humans. The researchers indicated that they first used fruit flies because their sleep is very similar to how humans sleep. Just as we require an adequate amount of sleep to function properly, flies require the same. Humans also share a lot of DNA with fruit flies and scientists have done a lot of research with their genome, especially when it comes to understanding certain diseases, so the findings of this study may be applicable to humans in further research The study also later used mice to understand the effects of sleep deprivation on the gut. Mice have commonly been used to study diseases and have even been used to develop human antibodies, so the findings may be applied to humans. In fact, past research has shown that the lack of sleep does contribute to many gastrointestinal diseases and disorders, so the conclusions of this research can be used to further understand how sleep deprivation in model organisms similar to humans affects their gut health, and further understand the implications of poor sleep. Not getting adequate sleep can affect our bodies and health in many detrimental ways, so making sleep a priority is extremely important for our wellbeing.

References

Ali, Tauseef et al. “Sleep, immunity and inflammation in gastrointestinal disorders.” World journal of gastroenterology vol. 19,48 (2013): 9231-9. doi:10.3748/wjg.v19.i48.9231

Marsh, Aleksandra, and Mullan, Alan. “Advantages of using Drosophila Melanogaster as a Model Organism.” Oxford Instruments. Feb 2019. https://andor.oxinst.com/learning/view/article/advantages-of-using-drosophila-melanogaster-as-a-model-organism

Ray, Paul D et al. “Reactive oxygen species (ROS) homeostasis and redox regulation in cellular signaling.” Cellular signalling vol. 24,5 (2012): 981-90. doi:10.1016/j.cellsig.2012.01.008

Original Study: https://doi.org/10.1016/j.cell.2020.04.049