Humans spend nearly a third of their time sleeping, but sleep is still one of the most enduring mysteries in biology. So far, scientists don’t know which genetic or molecular power is driving people to sleep. In a new study, researchers from the University of Pennsylvania’s Perelman School of Medicine discovered that a gene called Nemuri increased the need for sleep by studying more than 12,000 strains of fruit flies. Related research results are published in the journal of Science.
As an antimicrobial peptide (AMP), NEMURI proteins resist bacteria with their inherent antibacterial activity. It is secreted by cells in the brain and promotes long-term deep sleep after infection.
The author of the paper, Dr. Amita Sehgal, professor of neurobiology at the University of Pennsylvania’s Perelman School of Medicine, said that ‘although it is widely believed that sleep and disease cure are closely related, our research directly relates to sleep and immune systems that links the two up and provides a possible explanation for how sleep increases during illness.’
In the absence of the nemuri gene, fruit flies are more likely to be awakened during daily sleep, and their urgent need to increase sleep due to sleep deprivation or infection is reduced. On the other hand, sleep deprivation, which increases sleep requirements, and, to some extent, infection, promotes the expression of nemuri in a small group of Drosophila neurons near a known sleep-promoting region of the brain. Nemuri overexpression increases sleep of bacterial infection-infected fruit flies and lead to an increase in their survival rate compared to uninfected control flies.
In response to infection, NEMURI seems to be capable to kill bacteria which most likely happen in the peripheral part of the Drosophila body and increase sleep through its role in the brain. The researchers claim that a variety of molecules like NEMURI have a variety of functions that help fight infection, but its sleep-promoting effects may be equally important for host defenses, as the increased sleep can promote the survival of fruit flies during sleep.
Furthermore, these researchers also pointed out that cytokines such as IL-1 are involved in human sleep. IL-1 acts in the same way as AMP, which accumulates after prolonged waking and appears to promote sleep. In mammals, cytokines are capable of inducing AMP production, but AMP may also affect cytokine expression. Based on this intertwined relationship, these researchers concluded that NEMURI is a link between immune function and sleep.
Dr. Hirofumi Toda, the lead author of the paper and a postdoctoral researcher at Sehgal Labs, said, ‘In the case of higher sleep requirements, such as when we get sick, NEMURI protein is the real driving force for normal sleep. In the next phase of our research work, we plan to study the mechanism by which NEMURI promotes sleep.’
H.Toda el al. A sleep-inducing gene, nemuri, links sleep and immune function in Drosophila. Science, 2019, doi:10.1126/science.aat1650.
G.Oikonomou el al. Linking immunity and sickness-induced sleep. Science, 2019, doi:10.1126/science.aaw2113.