Losing a single night of sleep led to an immediate increase in beta-amyloid, a protein in the brain associated with Alzheimer's disease, according to a small, new study by researchers at the National Institutes of Health. In Alzheimer's disease, amyloid beta proteins cluster to form amyloid plaques, a hallmark of the disease.
Although it is known that acute sleep deprivation raises amyloid beta levels in mice, less is known about the impact of sleep deprivation on beta-amyloid accumulation in the human brain. The study shows that sleep can play an important role in human beta-amyloid clearance.
"This research provides a new insight into the potentially damaging effects of lack of sleep on the brain and has implications for a better characterization of Alzheimer's disease," says George F. Koob, PhD, director of the National Institute on Alcohol Abuse and Alcoholism (NIAAA), in a statement. NIAAA is part of the National Institutes of Health, which funded the study.
Beta amyloid is a metabolic waste product present in the fluid found between brain cells. In Alzheimer's disease, beta-amyloid groups to form amyloid plaques, negatively affecting communication between neurons.
Directed by Ehsan Shokri-Kojori, PhD, and Nora D. Volkow, MD, of the NIAAA Neuroimaging Laboratory, the study is now in Proceedings of the National Academy of Sciences . Volkow is also the director of the National Institute on Drug Abuse at NIH.
To understand the possible link between beta-amyloid accumulation and sleep, the researchers used positron emission tomography (PET) to scan the brains of 20 healthy subjects, at the age of 22 to 72 years, after of a restful night's sleep and after sleep deprivation (being awake for approximately 31 hours). They found beta-amyloid increases of about 5% after losing a night's sleep in the brain regions, including the thalamus and the hippocampus, regions especially vulnerable to damage in the early stages of Alzheimer's disease.
In Alzheimer's disease, beta-amyloid is estimated to increase approximately 43% in affected individuals compared to healthy older adults. It is unknown whether the increase in beta-amyloid in the study participants would decrease after a night's rest.
The investigators also found that study participants with greater increases in beta-amyloid reported worse mood after sleep deprivation.
"Although our sample was small, this study demonstrated the negative effect of sleep deprivation on the amyloid beta load in the human brain. Future studies are needed to evaluate the possibility of generalization to a broader and more diverse population" , says Shokri-Kojori.
It is also important to note that many scientists believe that the link between sleep disorders and Alzheimer's risk is "bidirectional," since elevated beta-amyloid can also cause sleep disturbances.
Image credit: Proceedings of the National Academy of Sciences