Study shows how human sleep is influenced by genetic variations in the brain waves

Why do humans sleep? This has been an unresolved question of the 21st century.

Sleep

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Now a study performed by Sara Marie Ulv Larsen, Sebastian Camillo Holst, and collaborators from the Neurobiology Research Unit at the University Hospital Copenhagen has revealed that the depth of non-rapid-eye-movement (non-REM) sleep in humans is linked with various genetic versions of a gene that is capable of encoding a water channel involved in the brain’s fluid flow.

The study was recently published in the open-access journal PLOS Biology.

The latest insights imply that sleep may allow and encourage the cerebrospinal fluid to flow into the brain, precisely removing the metabolic waste. When this process occurs in experimental animals, it is supported by water channels known as AQP4; these create water-permeable pores via the cell membranes of the brain cells known as astrocytes.

To date, the function of these water channels in the human brain and whether they are related to the regulation of deep non-REM sleep also referred to as slow-wave sleep, has not been investigated.

A haplotype is a general set of genetic variants that are inherited together. A certain haplotype (comprising eight individual DNA variants) was earlier demonstrated to modulate the AQP4 levels.

The study authors closely studied over 100 healthy individuals and discovered that the depth of slow-wave sleep, which can be quantified by examining the brain waves recorded at the time of sleep, varies between a control group and the carriers of this haplotype.

The authors observed that this variance was highly pronounced at the start of the night when the humans’ requirement for sleep is at the peak. Fascinatingly, both haplotype groups also coped differently when they were kept awake for two full days, implying that variations in the flow of fluids in AQP4 water channels may alter the way humans deal with sleep loss.

Since the genetic variants inside the AQP4 haplotype were also linked with the progression of Alzheimer’s disease in the past, the study results may imply that a sleep-driven exchange of fluids via the AQP4 water channels could be associated with the progression of Alzheimer’s disease.

More studies are required to study the potential link between the AQP4 water channels and Alzheimer’s disease.

A more immediate implication of our results is by improving our understanding of the importance of sleep.”

Study Authors

This means this is the first-ever study to demonstrate that the genetics of the AQP4 water channels influence the intensity of deep sleep and the way humans deal with sleep loss.

These discoveries add support to the present-day theory that sleep may play a role in the regulation of “brain clearance,” and as such emphasize the relationship between fluid flow and sleep in the human brain.

Source:
Journal reference:

Ulv Larsen, S. M., et al. (2020) Haplotype of the astrocytic water channel AQP4 is associated with slow wave energy regulation in human NREM sleep. PLOS Biology. doi.org/10.1371/journal.pbio.3000623.

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