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This bacteria-fighting protein also induces sleep

Infected fruit flies slept more and survived longer when levels of Nemuri surged

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2:03pm, January 31, 2019
fruit fly brain

SLEEPING OFF SICKNESS  A protein called Nemuri (green) is produced in fruit fly brains (purple) and helps the insects stay asleep. Nemuri’s lullaby may also help flies sleep away sickness and stress.

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“Feed a cold, starve a fever,” or so the adage goes. But fruit fly experiments suggest that sleep may be a better remedy.

A microbe-fighting protein helps control how much and how deeply fruit flies sleep, researchers report in the Feb. 1 Science. That’s evidence that sleep speeds recovery from illness, they conclude.

“We finally have a very clear link between being sleepy and fighting an infection,” says Caltech sleep researcher Grigorios Oikonomou, who was not involved in the work. Such a link has been hinted at but never formally demonstrated, says Oikonomou, who coauthored a commentary on the study in the same issue of Science.

Researchers in Amita Sehgal’s lab at the University of Pennsylvania’s Perelman School of Medicine made the discovery while searching for genes that control sleep. Her team looked for proteins that, when overproduced, would cause Drosophila melanogaster fruit flies to sleep more. After combing through more than 8,000 overproduced proteins, the researchers found just one that lulled flies to sleep.

Flies with an overabundance of that protein, produced from the nemuri gene, took more naps during the day and slept longer and deeper at night. Strong bumps from a device called “the hammer” roused only about 18 percent of these Nemuri-overproducing flies in the middle of the night but jolted awake more than 94 percent of normal flies, Sehgal’s team discovered. Flies that lacked Nemuri were more easily awakened than normal flies when researchers flicked lights on and off or wafted an odor into the tubes where the fruit flies were sleeping.

Sehgal’s team discovered that Nemuri is similar to fish proteins known as antimicrobial peptides, short proteins or pieces of protein that can kill microbes. In tests of Nemuri’s effect on two types of bacteria, the protein killed the bacteria in lab dishes and, when overproduced, helped bacteria-infected fruit flies survive longer.

The protein’s lullaby power, not its antimicrobial activity, might be what actually fights infection. Flies made more Nemuri not just when sick but also when sleep deprived and under other types stress. “Sleep helps to fight off these challenges,” Sehgal says. Nemuri may not be as important for daily sleep, except for helping flies stay asleep at night

A dual role of killing bacteria and triggering sleep is new for antimicrobial peptides, says Robert Hancock, a microbiologist and immunologist at the University of British Columbia in Vancouver. “But I’m not shocked,” he says, “because peptides do so many things.”

Antimicrobial peptides generally aren’t all that good at killing microbes in animals, though, Hancock says. Instead, the peptides help regulate the immune system to perform a variety of tasks. It’s possible, though, that mammals, including humans — who have more than 100 antimicrobial peptide genes — may have antimicrobial peptides that induce sleep during illness.

“Causing an animal to go to sleep and concentrate all its resources on fighting infection is useful to host defense,” Hancock says. Or as one Irish proverb goes, “A good laugh and a long sleep are the best cures in the doctor's book.”

Citations

H. Toda et al. A sleep-inducing gene, nemuri, links sleep and immune function in Drosophila. Science. Vol. 363, February 1, 2019, p. 509. doi:10.1126/science.aat1650.

G. Oikonomou and D.A. Prober. Linking immunity and sickness-induced sleep. Science. Vol. 363, February 1, 2019, p.455. doi: 10.1126/science.aaw2113.

Further Reading

A. Cunningham. Lack of sleep is tied to increases in two Alzheimer's proteins. Science News Online, January 24, 2019.

L. Rosenbaum. New studies add evidence to a possible link between Alzheimer’s and herpesvirus. Science News. Vol. 194, July 21, 2018, p. 10.

L. Biel. The brain may clean out Alzheimer’s plaques during sleep. Science News. Vol. 194, July 21, 2018, p. 22.

T.H. Saey. Ions may be in charge of when you sleep and wake. Science News. Vol. 189, May 28, 2016, p. 8.

L. Sanders. Sugar makes mice sleepy. Science News. Vol. 188, August 8, 2015, p. 15.

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