Sleep, death and ... the gut?

June 4, 2020

Science Daily/Harvard Medical School

A new study finds a causal link between sleep deprivation and death. In sleep-deprived fruit flies, death is preceded by the accumulation of molecules known as reactive oxidative species in the gut. When fruit flies were given antioxidant compounds that neutralize ROS, sleep-deprived flies remained active and had normal lifespans. The findings may one day inform new approaches to counteract the harmful effects of insufficient sleep in humans.

The first signs of insufficient sleep are universally familiar. There's tiredness and fatigue, difficulty concentrating, perhaps irritability or even tired giggles. Far fewer people have experienced the effects of prolonged sleep deprivation, including disorientation, paranoia and hallucinations.

Total, prolonged sleep deprivation, however, can be fatal. While it has been reported in humans only anecdotally, a widely cited study in rats conducted by Chicago-based researchers in 1983 showed that a total lack of sleep inevitably leads to death. Yet, despite decades of study, a central question has remained unsolved: why do animals die when they don't sleep?

Now, Harvard Medical School neuroscientists have identified an unexpected, causal link between sleep deprivation and premature death. In a study on sleep-deprived fruit flies, researchers found that death is always preceded by the accumulation of molecules known as reactive oxidative species (ROS) in the gut.

When fruit flies were given antioxidant compounds that neutralize and clear ROS from the gut, sleep-deprived flies remained active and had normal lifespans. Additional experiments in mice confirmed that ROS accumulate in the gut when sleep is insufficient.

The findings, published in Cell on June 4, suggest the possibility that animals can indeed survive without sleep under certain circumstances. The results open new avenues of study to understand the full consequences of insufficient sleep and may someday inform the design of approaches to counteract its detrimental effects in humans, the authors said.

"We took an unbiased approach and searched throughout the body for indicators of damage from sleep deprivation. We were surprised to find it was the gut that plays a key role in causing death," said senior study author Dragana Rogulja, assistant professor of neurobiology in the Blavatnik Institute at HMS.

"Even more surprising, we found that premature death could be prevented. Each morning, we would all gather around to look at the flies, with disbelief to be honest. What we saw is that every time we could neutralize ROS in the gut, we could rescue the flies," Rogulja said.

Scientists have long studied sleep, a phenomenon that appears to be fundamental for life, yet one that in many ways remains mysterious. Almost every known animal sleeps or exhibits some form of sleeplike behavior. Without enough of it, serious consequences ensue. In humans, chronic insufficient sleep is associated with heart disease, type 2 diabetes, cancer, obesity, depression and many other conditions.

Previous research has shown that prolonged, total sleep restriction can lead to premature death in animal models. In attempts to answer how sleep deprivation culminates in death, most research efforts have focused on the brain, where sleep originates, but none have yielded conclusive results.

Gut accumulation

Spearheaded by study co-first authors Alexandra Vaccaro and Yosef Kaplan Dor, both research fellows in neurobiology at HMS, the team carried out a series of experiments in fruit flies, which share many sleep-regulating genes with humans, to search for signs of damage caused by sleep deprivation throughout the body. To monitor sleep, the researchers used infrared beams to constantly track the movement of flies housed in individual tubes.

They found that flies can sleep through physical shaking, so the team turned to more sophisticated methods. They genetically manipulated fruit flies to express a heat-sensitive protein in specific neurons, the activity of which are known to suppress sleep. When flies were housed at 29 degrees C (84 degrees F), the protein induced neurons to remain constantly active, thus preventing the flies from sleeping.

After 10 days of temperature-induced sleep deprivation, mortality spiked among the fruit flies and all died by around day 20. Control flies that had normal sleep lived up to approximately 40 days in the same environmental conditions.

Because mortality increased around day 10, the researchers looked for markers of cell damage on that and preceding days. Most tissues, including in the brain, were indistinguishable between sleep-deprived and non-deprived flies, with one notable exception.

The guts of sleep-deprived flies had a dramatic buildup of ROS -- highly reactive, oxygen-containing molecules that in large amounts can damage DNA and other components within cells, leading to cell death. The accumulation of ROS peaked around day 10 of sleep deprivation, and when deprivation was stopped, ROS levels decreased.

Additional experiments confirmed that ROS builds up in the gut of only those animals that experienced sustained sleep loss, and that the gut is indeed the main source of this apparently lethal ROS.

"We found that sleep-deprived flies were dying at the same pace, every time, and when we looked at markers of cell damage and death, the one tissue that really stood out was the gut," Vaccaro said. "I remember when we did the first experiment, you could immediately tell under the microscope that there was a striking difference. That almost never happens in lab research."

The team also examined whether ROS accumulation occurs in other species by using gentle, continuous mechanical stimulation to keep mice awake for up to five days. Compared to control animals, sleep-deprived mice had elevated ROS levels in the small and large intestines but not in other organs, a finding consistent with the observations in flies.

Death rescue

To find out if ROS in the gut play a causal role in sleep deprivation-induced death, the researchers looked at whether preventing ROS accumulation could prolong survival.

They tested dozens of compounds with antioxidant properties known to neutralize ROS and identified 11 that, when given as a food supplement, allowed sleep-deprived flies to have a normal or near-normal lifespan. These compounds, such as melatonin, lipoic acid and NAD, were particularly effective at clearing ROS from the gut. Notably, supplementation did not extend the lifespan of non-deprived flies.

The role of ROS removal in preventing death was further confirmed by experiments in which flies were genetically manipulated to overproduce antioxidant enzymes in their guts. These flies had normal to near-normal lifespans when sleep-deprived, which was not the case for control flies that overproduced antioxidant enzymes in the nervous system.

The results demonstrate that ROS buildup in the gut plays a central role in causing premature death from sleep deprivation, the researchers said, but cautioned that many questions remain unanswered.

"We still don't know why sleep loss causes ROS accumulation in the gut, and why this is lethal," said Kaplan Dor. "Sleep deprivation could directly affect the gut, but the trigger may also originate in the brain. Similarly, death could be due to damage in the gut or because high levels of ROS have systemic effects, or some combination of these."

Insufficient sleep is known to interfere with the body's hunger signaling pathways, so the team also measured fruit fly food intake to analyze whether there were potential associations between feeding and death. They found that some sleep-deprived flies ate more throughout the day compared with non-deprived controls. However, restricting access to food had no effect on survival, suggesting that factors beyond food intake are involved.

The researchers are now working to identify the biological pathways that lead to ROS accumulation in the gut and subsequent physiological disruptions.

The team hopes that their work will inform the development of approaches or therapies to offset some of the negative consequences of sleep deprivation. One in three American adults gets less than the recommended seven hours of sleep per night, according to the U.S. Centers for Disease Control and Prevention, and insufficient sleep is a normal part of life for many around the world.

"So many of us are chronically sleep deprived. Even if we know staying up late every night is bad, we still do it," Rogulja said. "We believe we've identified a central issue that, when eliminated, allows for survival without sleep, at least in fruit flies."

"We need to understand the biology of how sleep deprivation damages the body, so that we can find ways to prevent this harm," she said.

https://www.sciencedaily.com/releases/2020/06/200604152053.htm

Parents aren't powerless when it comes to sleep-deprived teenagers

January 9, 2020

Science Daily/University of Rochester

Teenagers in the US simply don't get enough shut eye. The consequences of this epidemic of sleep deprivation are extensive and include increasing rates of anxiety and depression among adolescents, as well as suicidal thoughts and actions. Sleep-deprived teens are more likely to be involved in car crashes, and run a higher risk of injury during sports-related activities.

Experts have pointed to various reasons for the chronic teenage sleep deficit: growing homework loads, too many extra-curricular activities, caffeine consumption, school start times that run counter to middle and high schoolers' natural circadian rhythms, and the use of electronic devices and backlit screens, which may disrupt sleep patterns, before bedtime.

But researchers at the University of Rochester have found that a simple and timeworn solution yields solid results: a clear bedtime that parents consistently adhere to.

"Greater enforcement of parent-set bedtimes for teenagers aged 14-to-17 are associated with longer sleep duration," says Jack Peltz, lead author of a recent study, which was published in the academic journal Sleep. Peltz, now an assistant professor of psychology at Daemen College, earned his PhD in psychology at Rochester in 2013 and conducted the study as part of a research appointment at the University of Rochester Medical Center's Department of Psychiatry.

Study participants included teenagers and their parents. The team asked their teenage participants to keep twice-daily sleep diary entries over seven days, collecting reports of sleep duration, daytime energy levels, and depressive symptoms. Parents, meanwhile, provided information about their enforcement of sleep-related rules and bedtimes.

Among the key findings:

• Parent-enforced bedtimes -- along with later school start times -- are the greatest predictors of sleep duration, daytime energy level, and depressive symptoms.

• More than 50 percent of parent respondents reported no specific or enforced bedtime rules, consistent with rates measured in previous research across families in the US.

• Evening screen time and caffeine consumption did not, contrary to the researchers' hypotheses, significantly affect teenagers' sleep duration over the course of the study.

In 2014, the American Academy of Pediatrics responded to the sleep deprivation epidemic by urging school districts to start classes no earlier than 8:30 am, especially for middle and high schoolers. But to date, only about 14 percent of US high schools have heeded the recommendation, which makes the rule-setting role of parents all the more important.

The researchers acknowledge that setting a bedtime for teenagers might be difficult; but their results suggest that even with pre-bedtime conflict, parents' enforcement of bedtimes yielded better mental health outcomes for their offspring. That said -- "ideally parents should be able to work collaboratively with their teenagers to develop bedtimes that still support the child's autonomy," says Peltz.

The bottom line, according to coauthor Ronald Rogge, an associate professor of psychology at Rochester, is that "even though adolescents start gaining self-sufficiency and independence, they still need sleep and might not prioritize that if left to their own devices."

Absent an iron-clad rule, there are nevertheless healthy ranges, says Heidi Connolly, a professor of pediatrics and chief of the Division of Pediatric Sleep Medicine at Rochester, who is also a coauthor of the study. Most teenagers need 8.5 to 9.5 hours of sleep each night, she says, mirroring recommendations made by the American Academy of Sleep Medicine and endorsed by the American Academy of Pediatrics.

As for an appropriate bedtime, that of course depends on the wake-up time. "It's inherently more difficult for teenagers to fall asleep earlier than later because of their circadian rhythm," says Connolly. "That's why it's so important for high school start times to be later, as the American Academy of Pediatrics has recommended across the board."

The ideal is to feel well rested during the daytime, and spontaneously awaken at around your scheduled wake-up time even when allowed to sleep in.

The team notes that future studies may be necessary to determine if their findings hold true across a range of populations; they caution that their sample was predominantly white, well-educated, and economically advantaged.

https://www.sciencedaily.com/releases/2020/01/200109130203.htm

Sleep deprivation accelerates Alzheimer's brain damage

January 24, 2019

Science Daily/Washington University School of Medicine

A study in mice and people shows that sleep deprivation causes tau levels to rise and tau tangles to spread through the brain. Tau tangles are associated with Alzheimer's disease and brain damage.

Poor sleep has long been linked with Alzheimer's disease, but researchers have understood little about how sleep disruptions drive the disease.

Now, studying mice and people, researchers at Washington University School of Medicine in St. Louis have found that sleep deprivation increases levels of the key Alzheimer's protein tau. And, in follow-up studies in the mice, the research team has shown that sleeplessness accelerates the spread through the brain of toxic clumps of tau - a harbinger of brain damage and decisive step along the path to dementia.

These findings, published online Jan. 24 in the journal Science, indicate that lack of sleep alone helps drive the disease, and suggests that good sleep habits may help preserve brain health.

"The interesting thing about this study is that it suggests that real-life factors such as sleep might affect how fast the disease spreads through the brain," said senior author David Holtzman, MD, the Andrew B. and Gretchen P. Jones Professor and head of the Department of Neurology. "We've known that sleep problems and Alzheimer's are associated in part via a different Alzheimer's protein -- amyloid beta -- but this study shows that sleep disruption causes the damaging protein tau to increase rapidly and to spread over time."

Tau is normally found in the brain -- even in healthy people -- but under certain conditions it can clump together into tangles that injure nearby tissue and presage cognitive decline. Recent research at the School of Medicine has shown that tau is high in older people who sleep poorly. But it wasn't clear whether lack of sleep was directly forcing tau levels upward, or if the two were associated in some other way. To find out, Holtzman and colleagues including first authors Jerrah Holth, PhD, a staff scientist, and Sarah Fritschi, PhD, a former postdoctoral scholar in Holtzman's lab, measured tau levels in mice and people with normal and disrupted sleep.

Mice are nocturnal creatures. The researchers found that tau levels in the fluid surrounding brain cells were about twice as high at night, when the animals were more awake and active, than during the day, when the mice dozed more frequently. Disturbing the mice's rest during the day caused daytime tau levels to double.

Much the same effect was seen in people. Brendan Lucey, MD, an assistant professor of neurology, obtained cerebrospinal fluid -- which bathes the brain and spinal cord -- from eight people after a normal night of sleep and again after they were kept awake all night. A sleepless night caused tau levels to rise by about 50 percent, the researchers discovered.

Staying up all night makes people stressed and cranky and likely to sleep in the next chance they get. While it's hard to judge the moods of mice, they, too, rebounded from a sleepless day by sleeping more later. To rule out the possibility that stress or behavioral changes accounted for the changes in tau levels, Fritschi created genetically modified mice that could be kept awake for hours at a time by injecting them with a harmless compound. When the compound wears off, the mice return to their normal sleep-wake cycle -- without any signs of stress or apparent desire for extra sleep.

Using these mice, the researchers found that staying awake for prolonged periods causes tau levels to rise. Altogether, the findings suggest that tau is routinely released during waking hours by the normal business of thinking and doing, and then this release is decreased during sleep allowing tau to be cleared away. Sleep deprivation interrupts this cycle, allowing tau to build up and making it more likely that the protein will start accumulating into harmful tangles.

In people with Alzheimer's disease, tau tangles tend to emerge in parts of the brain important for memory -- the hippocampus and entorhinal cortex -- and then spread to other brain regions. As tau tangles mushroom and more areas become affected, people increasingly struggle to think clearly.

To study whether the spread of tau tangles is affected by sleep, the researchers seeded the hippocampi of mice with tiny clumps of tau and then kept the animals awake for long periods each day. A separate group of mice also was injected with tau tangles but was allowed to sleep whenever they liked. After four weeks, tau tangles had spread further in the sleep-deprived mice than their rested counterparts. Notably, the new tangles appeared in the same areas of the brain affected in people with Alzheimer's.

"Getting a good night's sleep is something we should all try to do," Holtzman said. "Our brains need time to recover from the stresses of the day. We don't know yet whether getting adequate sleep as people age will protect against Alzheimer's disease. But it can't hurt, and this and other data suggest that it may even help delay and slow down the disease process if it has begun."

The researchers also found that disrupted sleep increased release of synuclein protein, a hallmark of Parkinson's disease. People with Parkinson's -- like those with Alzheimer's -- often have sleep problems.

https://www.sciencedaily.com/releases/2019/01/190124141536.htm

College Student Sleep Patterns Could Be Detrimental

May 13, 2008

Science Daily/Central Michigan University

A Central Michigan University study has determined that many college students have sleep patterns that could have detrimental effects on their daily performance.

College students are among the most sleep-deprived age group in the U.S. Sleep deprivation can have detrimental effects on daily performance, including academics and driving, and has also been linked to depressed mood and behavioral problems.

A similar study by Forquer and Johnson, published in "Sleep and Hypnosis," found that the use of continuous white noise may help college students get better sleep. The study found that white noise was effective for college students with self-reported sleep problems to decrease difficulty in falling asleep and night wakings.

"These issues are extremely important because not getting enough sleep is associated with impaired attention, school performance, and also can lead to driving accidents as people fall asleep behind the wheel of their car," said Forquer. "Helping students sleep better will hopefully carry over to help them in some of these areas as well."

http://www.sciencedaily.com/releases/2008/05/080512145824.htm