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Sleep Loss Encourages Spread of Toxic Alzheimer’s Protein

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Man sleeping
Credit: iStock/bowdenimages

In addition to memory loss and confusion, many people with Alzheimer’s disease have trouble sleeping. Now an NIH-funded team of researchers has evidence that the reverse is also true: a chronic lack of sleep may worsen the disease and its associated memory loss.

The new findings center on a protein called tau, which accumulates in abnormal tangles in the brains of people with Alzheimer’s disease. In the healthy brain, active neurons naturally release some tau during waking hours, but it normally gets cleared away during sleep. Essentially, your brain has a system for taking the garbage out while you’re off in dreamland.

The latest findings in studies of mice and people further suggest that sleep deprivation upsets this balance, allowing more tau to be released, accumulate, and spread in toxic tangles within brain areas important for memory. While more study is needed, the findings suggest that regular and substantial sleep may play an unexpectedly important role in helping to delay or slow down Alzheimer’s disease.

It’s long been recognized that Alzheimer’s disease is associated with the gradual accumulation of beta-amyloid peptides and tau proteins, which form plaques and tangles that are considered hallmarks of the disease. It has only more recently become clear that, while beta-amyloid is an early sign of the disease, tau deposits track more closely with disease progression and a person’s cognitive decline.

Such findings have raised hopes among researchers including David Holtzman, Washington University School of Medicine, St. Louis, that tau-targeting treatments might slow this devastating disease. Though much of the hope has focused on developing the right drugs, some has also focused on sleep and its nightly ability to reset the brain’s metabolic harmony.

In the new study published in Science, Holtzman’s team set out to explore whether tau levels in the brain naturally are tied to the sleep-wake cycle [1]. Earlier studies had shown that tau is released in small amounts by active neurons. But when neurons are chronically activated, more tau gets released. So, do tau levels rise when we’re awake and fall during slumber?

The Holtzman team found that they do. The researchers measured tau levels in brain fluid collected from mice during their normal waking and sleeping hours. (Since mice are nocturnal, they sleep primarily during the day.) The researchers found that tau levels in brain fluid nearly double when the animals are awake. They also found that sleep deprivation caused tau levels in brain fluid to double yet again.

These findings were especially interesting because Holtzman’s team had already made a related finding in people. The team found that healthy adults forced to pull an all-nighter had a 30 percent increase on average in levels of unhealthy beta-amyloid in their cerebrospinal fluid (CSF).

The researchers went back and reanalyzed those same human samples for tau. Sure enough, the tau levels were elevated on average by about 50 percent.

Once tau begins to accumulate in brain tissue, the protein can spread from one brain area to the next along neural connections. So, Holtzman’s team wondered whether a lack of sleep over longer periods also might encourage tau to spread.

To find out, mice engineered to produce human tau fibrils in their brains were made to stay up longer than usual and get less quality sleep over several weeks. Those studies showed that, while less sleep didn’t change the original deposition of tau in the brain, it did lead to a significant increase in tau’s spread. Intriguingly, tau tangles in the animals appeared in the same brain areas affected in people with Alzheimer’s disease.

Another report by Holtzman’s team appearing early last month in Science Translational Medicine found yet another link between tau and poor sleep. That study showed that older people who had more tau tangles in their brains by PET scanning had less slow-wave, deep sleep [2].

Together, these new findings suggest that Alzheimer’s disease and sleep loss are even more intimately intertwined than had been realized. The findings suggest that good sleep habits and/or treatments designed to encourage plenty of high quality Zzzz’s might play an important role in slowing Alzheimer’s disease. On the other hand, poor sleep also might worsen the condition and serve as an early warning sign of Alzheimer’s.

For now, the findings come as an important reminder that all of us should do our best to get a good night’s rest on a regular basis. Sleep deprivation really isn’t a good way to deal with overly busy lives (I’m talking to myself here). It isn’t yet clear if better sleep habits will prevent or delay Alzheimer’s disease, but it surely can’t hurt.

References:

[1] The sleep-wake cycle regulates brain interstitial fluid tau in mice and CSF tau in humans. Holth JK, Fritschi SK, Wang C, Pedersen NP, Cirrito JR, Mahan TE, Finn MB, Manis M, Geerling JC, Fuller PM, Lucey BP, Holtzman DM. Science. 2019 Jan 24.

[2] Reduced non-rapid eye movement sleep is associated with tau pathology in early Alzheimer’s disease. Lucey BP, McCullough A, Landsness EC, Toedebusch CD, McLeland JS, Zaza AM, Fagan AM, McCue L, Xiong C, Morris JC, Benzinger TLS, Holtzman DM. Sci Transl Med. 2019 Jan 9;11(474).

Links:

Alzheimer’s Disease and Related Dementias (National Institute on Aging/NIH)

Accelerating Medicines Partnership: Alzheimer’s Disease (NIH)

Holtzman Lab (Washington University School of Medicine, St. Louis)

NIH Support: National Institute on Aging; National Institute of Neurological Disorders and Stroke; National Center for Advancing Translational Sciences; National Cancer Institute; National Institute of Biomedical Imaging and Bioengineering


Antibody Makes Alzheimer’s Protein Detectable in Blood

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Antibodies to Tau

Caption: The protein tau (green) aggregates abnormally in a brain cell (blue). Tau spills out of the cell and enters the bloodstream (red). Research shows that antibodies (blue) can capture tau in the blood that reflect its levels in the  brain.
Credit: Sara Moser

Age can bring moments of forgetfulness. It can also bring concern that the forgetfulness might be a sign of early Alzheimer’s disease. For those who decide to have it checked out, doctors are likely to administer brief memory exams to assess the situation, and medical tests to search for causes of memory loss. Brain imaging and spinal taps can also help to look for signs of the disease. But an absolutely definitive diagnosis of Alzheimer’s disease is only possible today by examining a person’s brain postmortem. A need exists for a simple, less-invasive test to diagnose Alzheimer’s disease and similar neurodegenerative conditions in living people, perhaps even before memory loss becomes obvious.

One answer may lie in a protein called tau, which accumulates in abnormal tangles in the brains of people with Alzheimer’s disease and other “tauopathy” disorders. In recent years, researchers have been busy designing an antibody to target tau in hopes that this immunotherapy approach might slow or even reverse Alzheimer’s devastating symptoms, with promising early results in mice [1, 2]. Now, an NIH-funded research team that developed one such antibody have found it might also open the door to a simple blood test [3].


Alzheimer’s Disease: Tau Protein Predicts Early Memory Loss

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PET imaging of brains affected by Alzheimer's disease

Caption: PET scan images show distribution of tau (top panel) and beta-amyloid (bottom panel) across a brain with early Alzheimer’s disease. Red indicates highest levels of protein binding, dark blue the lowest, yellows and oranges indicate moderate binding.
Credit: Brier et al., Sci Transl Med

In people with Alzheimer’s disease, changes in the brain begin many years before the first sign of memory problems. Those changes include the gradual accumulation of beta-amyloid peptides and tau proteins, which form plaques and tangles that are considered hallmarks of the disease. While amyloid plaques have received much attention as an early indicator of disease, until very recently there hadn’t been any way during life to measure the buildup of tau protein in the brain. As a result, much less is known about the timing and distribution of tau tangles and its relationship to memory loss.

Now, in a study published in Science Translational Medicine, an NIH-supported research team has produced some of the first maps showing where tau proteins build up in the brains of people with early Alzheimer’s disease [1]. The new findings suggest that while beta-amyloid remains a reliable early sign of Alzheimer’s disease, tau may be a more informative predictor of a person’s cognitive decline and potential response to treatment.


Brain Imaging: Tackling Chronic Traumatic Encephalopathy

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Brain scans of CTE and AD

Caption: Left to right, brain PET scans of healthy control; former NFL player with suspected chronic traumatic encephalopathy (CTE); and person with Alzheimer’s disease (AD). Areas with highest levels of abnormal tau protein appear red/yellow; medium, green; and lowest, blue.
Credit: Adapted from Barrio et al., PNAS

If you follow the National Football League (NFL), you may have heard some former players describe their struggles with a type of traumatic brain injury called chronic traumatic encephalopathy (CTE). Known to be associated with repeated, hard blows to the head, this neurodegenerative disorder can diminish the ability to think critically, slow motor skills, and lead to volatile, even suicidal, mood swings. What’s doubly frustrating to both patients and physicians is that CTE has only been possible to diagnose conclusively after death (via autopsy) because it’s indistinguishable from many other brain conditions with current imaging methods.

But help might be starting to move out of the backfield toward the goal line of more accurate diagnosis. In findings published in the journal PNAS [1], NIH-supported scientists from the University of California, Los Angeles (UCLA) and the University of Chicago report they’ve made some progress toward imaging CTE in living people. Following up on their preliminary work published in 2013 [2], the researchers used a specially developed radioactive tracer that lights up a neural protein, called tau, known to deposit in certain areas of the brain in individuals with CTE. They used this approach on PET scans of the brains of 14 former NFL players suspected of having CTE, generating maps of tau distribution throughout various regions of the brain.


Alzheimer’s-in-a-Dish: New Tool for Drug Discovery

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Alzheimer's Disease in a dish

Caption: A plaque (orange) disrupts the normal network of human neurons (green) grown in a three-dimensional gel in the lab, mimicking the brain anatomy of Alzheimer’s patients.
Credit: Doo Yeon Kim and Rudolph E. Tanzi, Massachusetts General Hospital/ Harvard Medical School

Researchers want desperately to develop treatments to help the more than 5 million Americans with Alzheimer’s disease and the millions more at risk. But that’s proven to be extremely challenging for a variety of reasons, including the fact that it’s been extraordinarily difficult to mimic the brain’s complexity in standard laboratory models. So, that’s why I was particularly excited by the recent news that an NIH-supported team, led by Rudolph Tanzi at Boston’s Massachusetts General Hospital, has developed a new model called “Alzheimer’s in a dish.”

So, how did Tanzi’s group succeed where others have run up against a brick wall? The answer appears to lie in their decision to add a third dimension to their disease model.  Previous attempts at growing human brain cells in the lab and inducing them to form the plaques and tangles characteristic of Alzheimer’s disease were performed in a two-dimensional Petri dish system. And, in this flat, 2-D environment, plaques and tangles simply didn’t appear.