A study published on Wednesday in the journal PLOS Genetics found that star-shaped brain cells called astrocytes played an essential role in sleep in fruit flies and might do the same in mammals including humans.
The study lent new clues to the understanding on how sleep works inside the brain and perhaps why people sleep.
"We spend about a third of our lives asleep, and yet we don't really know why," said William Vanderheyden, the study's first author and an assistant research professor in the Elson S. Floyd College of Medicine.
Astrocytes have until recently been thought as mere "glue" that holds the brain together. But more studies suggested that astrocytes were more active than they seemed.
TNF-alpha, a protein involved in inflammation, has been shown to play a critical role in sleep regulation in humans and other mammals, according to the study.
"Fruit flies happen to have a molecule that is very similar to TNF-alpha that is called Eiger," said Vanderheyden.
They bred a generation of flies in which the gene that controlled Eiger was switched off. These flies slept less overall, and their sleep was also more fragmented.
Then, they manipulated the flies so that Eiger was switched off in specific brain cell types, either astrocytes or neurons. They saw a similar reduction in sleep in flies with Eiger switched off in astrocytes, whereas sleep duration in flies with Eiger switched off in neurons did not change.
This suggested that Eiger contributes to the regulation of sleep time in a way that depends on astrocyte signaling, according to Vanderheyden.
Vanderheyden's team is planning to take their hypothesis into mammals by studying whether the same astrocyte-to-neuron pathway regulates sleep in rodents.