How the brain invokes deep sleep to speed healing

How the brain invokes deep sleep to speed healing

By Mariana Lenharo & Nature magazine

Immune cells rush to the brain and promote deep sleep after a heart attack, according to a new study involving both mice and humans. This heavy sleep promotes recovery by reducing inflammation in the heart, the study found.

The findings, published on October 30 in Naturecould help guide care for people after a heart attack, says co-author Cameron McAlpine of the Icahn School of Medicine at Mount Sinai in New York City, who studies immune function in the cardiovascular and nervous systems. “Getting enough sleep and rest after a heart attack is important for the long-term healing of the heart,” he notes.

The research’s implications go beyond a heart attack, says Rachel Rowe, a sleep and inflammation specialist at the University of Colorado Boulder. “With any type of injury, your body’s natural response would be to help you sleep so your body can heal,” she says.

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The heart needs its sleep

Scientists have long known that sleep and cardiovascular health are linked. For example, people who sleep poorly are at greater risk of developing high blood pressure than healthy sleepers. But how cardiovascular disease affects sleep has been less studied.

To find out more, the authors induced heart attacks in mice and examined the animals’ brain waves. The researchers found that these mice spent much more time in slow-wave sleep – a stage of deep sleep associated with healing – than mice that had not had a heart attack.

The authors then tried to understand what caused that effect. An obvious place to look was the brain, which controls sleep, McAlpine notes. After a heart attack, immune cells trigger a massive inflammatory response in the heart, he says, and the researchers wondered whether these immune changes were also happening in the brain.

The team found that after a mouse’s heart attack, immune cells called monocytes flooded the brain. These cells produced high amounts of a protein called tumor necrosis factor (TNF), which is an important regulator of inflammation and also promotes sleep.

To confirm that these cells were linked to the increased sleep, researchers prevented monocytes from accumulating in the rodents’ brains. As a result, “the mice no longer had this increase in slow-wave sleep after their heart attack,” says McAlpine, supporting the theory that the influx of monocytes to the brain contributes to the sleep boost after a heart attack. Similar experiments confirmed the role of TNF as a messenger for sleep-inducing brain cells.

Slumbering towards recovery

To understand the purpose of the extra sleep, the researchers repeatedly interrupted slow-wave sleep in mice that had had a heart attack. The team found that these mice had more inflammation in both the brain and heart, and had a much worse prognosis than mice that were allowed to sleep undisturbed after a heart attack.

The authors also studied people who had had acute coronary syndrome, a term for conditions, including heart attack, caused by a sudden reduction in blood flow to the heart muscle. Those who reported poor sleep in the weeks after such an episode had a greater risk of developing heart attacks and other serious cardiovascular problems over the next two years than those who were good sleepers.

Given the findings, “physicians should educate patients about the importance of a good night’s sleep” after a heart attack, Rowe says. This should also be taken into account in hospital, where tests and procedures are ideally carried out during the day to minimize sleep interruptions.

She adds that the findings highlight the bidirectional relationship between sleep and the immune system. “When your grandma says, ‘If you don’t get enough sleep, you’re going to get sick,’ there’s a lot of truth in that.”

This article has been reproduced with permission and was published for the first time on October 30, 2024.