It is well known that people who work night shifts or travel often across different time zones have a higher tendency to become overweight and suffer from gut inflammation.
The underlying cause for this phenomenon has been the subject of many studies.
They tried to relate physiological processes with the activity of the brain’s circadian clock, which is generated in response to the daylight cycle.
In a new study, researchers found that the function of a group of immune cells, which are known to be strong contributors to gut health, is directly controlled by the brain’s circadian clock.
The study was done by a group at the Champalimaud Centre for the Unknown in Lisbon, Portugal.
Previous research has shown that sleep deprivation, or altered sleep habits, can have dramatic health consequences, resulting in a range of diseases such as bowel inflammatory diseases.
To understand why this happens, the team started by asking whether immune cells in the gut are influenced by the circadian clock.
Almost all cells in the body have internal genetic machinery that follows the circadian rhythm through the expression of what is commonly known as “clock genes.”
The clock genes work like little clocks that inform cells of the time of day and thereby help the organs and systems that the cells make up together, anticipate what is going to happen, for instance, if it’s time to eat or sleep.
Even though these cell clocks are autonomous, they still need to be synchronized in order to make sure that “everyone is on the same page.”
According to the team, the cells inside the body don’t have direct information about external light, which means that individual cell clocks can be off.
The job of the brain’s clock, which receives direct information about daylight, is to synchronize all of these little clocks inside the body so that all systems are in synch, which is absolutely crucial for our wellbeing.
Among the variety of immune cells that are present in the intestine, the team discovered that Type 3 Innate Lymphoid Cells (ILC3s) were particularly susceptible to perturbations of their clock genes.
These cells fulfill important functions in the gut: they fight infection, control the integrity of the gut epithelium and instruct lipid absorption.
When the team disrupted their clocks, they found that the number of ILC3s in the gut was significantly reduced.
This resulted in severe inflammation, breaching of the gut barrier, and increased fat accumulation.
These results are very exciting because they clarify why gut health becomes compromised in people who are routinely active during the night.
This mechanism can be a beautiful example of evolutionary adaptation. During the day’s active period, which is when you feed, the brain’s circadian clock reduces the activity of ILC3s in order to promote healthy lipid metabolism.
But then, the gut could be damaged during feeding. So after the feeding period is over, the brain’s circadian clock instructs ILC3s to come back into the gut, where they are now needed to fight against invaders and promote regeneration of the epithelium.
The lead author of the study is Henrique Veiga-Fernandes.
The study is published in the scientific journal Nature.
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