Anahita Kodali, Life Sciences, News, Spring 2020
Figure 1: Even though worms are anatomically very different than humans, they are surprisingly good surrogates when it comes to sleep research. This is because they need sleep, like humans do. However, their neural systems are much less complex than humans are, so researchers understand much more about the functions of their specific neurons. As a result of this, they are able to know exactly which genes and neurons to turn off to turn off sleep. 4
Image Source: Wikimedia Commons
As is commonly known, sleep loss has many negative effects. Chronic sleep deprivation weakens the immune system, resulting in an increased likelihood of getting sick if people do not get the recommended 8 hours of sleep per night. In addition, lack of sleep also has negative impacts on mental well-being as long term sleep debt may lead to depression and anxiety. On the other hand, sufficient sleep prevents diabetes and heart disease and can increase fertility.1One long-studied impact of sleep deprivation is the associated weight gain; researchers found that lack of sleep can have a negative impact on the body’s metabolism. Studies show that when compared to adults sleeping ten hours a night, adults who sleeping only four hours had increases in hunger and appetite, especially for carbohydrate and calorie-rich foods. What’s more, some studies have found links between sleep deprivation and obesity, a very serious health condition.2
The causal relationship between sleep and weight gain, as mentioned above, was long thought to be that sleep induces weight gain. However, a recent study from researchers in the University of Pennsylvania Perelman School of Medicine and University of Nevada, Reno, used data from C. elegans worm studies to show that it may not be sleep that causes weight gain; excess weight may actually be the cause of poor sleep. The neurons that control sleep were turned off in the C. elegans and they were able to behave normally otherwise but could not sleep. They found that the worms’ ATP levels – that is, the body’s energy “currency” – significantly dropped, indicating that sleep is one of the body’s main mechanisms to conserve energy. 3
These findings agreed with other research done by co-author Alexander van der Linden, assistant professor of biology at University of Nevada, Reno. In the previous study, the van der Linden team knocked out the worms’ KIN-29 gene, a gene similar to SIK-3 in humans – both signal for sleep. They found that the worms were unable to sleep, again causing a loss of ATP. Surprisingly, however, the worms concurrently gained fat similar to the human obesity condition. They hypothesized that the excess fat prevented the worms from sleep. To test they manipulated the worms to “free” the accumulated fat deposits, and the worms were able to sleep again4.
Thus, the researchers hypothesize that one reason that people with obesity have sleep problems is because there are signaling problems between brain cells that control sleep and fat deposits. They caution that because the study was done on worms, the results may not translate exactly to humans, but the C. elegans worms do make surprisingly good models for humans (see Figure 1). 4 While there is still much to be learned about sleep and weight gain, these findings will pave the way for further research in worm models. They also may lead to useful findings for treatments for weight gain and for sleep loss.
Bibliography
[1] Why lack of sleep is bad for your health. (n.d.). UK National Health Services. Retrieved from https://www.nhs.uk/live-well/sleep-and-tiredness/why-lack-of-sleep-is-bad-for-your-health/
[2] Zeratsky, K. (2020, April 2). Why skipping sleep leads to weight gain. Mayo Clinic. Retrieved fromhttps://www.mayoclinic.org/healthy-lifestyle/adult-health/expert-answers/sleep-and-weight-gain/faq-20058198
[4] Jeremy J. Grubbs, Lindsey E. Lopes, Alexander M. van der Linden, David M. Raizen. A salt-induced kinase is required for the metabolic regulation of sleep. PLOS Biology, 2020; 18 (4): e3000220 DOI: 10.1371/journal.pbio.3000220
[5] University of Pennsylvania School of Medicine. (2020, April 22). Link between obesity and sleep loss: Energy conservation may be a major function of sleep, according to new study in worms. ScienceDaily. Retrieved from www.sciencedaily.com/releases/2020/04/200422091205.htm