The circadian clocks, or biological, are found everywhere in our body and are essential for its proper functioning. They trigger the release of melatonin during sleep, promote the secretion of digestive enzymes at lunchtime, or keep us awake at the most important times of the day. A “master clock” in the brain synchronizes all the branches in various organs. Researchers from the University of Geneva (UNIGE), Switzerland have found that such a clock is also present in our muscles. But what can it be used for? The results of their research have just been published in the magazine PNAS.
A variation in lipids throughout the day
Researchers have found that the amount of different types of fat (lipids) in our muscle cells varies throughout the day. To make sure that a biological clock was involved, the scientists synchronized the “master” clocks of several volunteers by asking them to adhere to a diet and sleep routine a week before the experiment. They then took, every four hours for 24 hours, a very small sample of muscle tissue from the thigh in order to analyze its lipid composition. The team, from these samples, observed a correlation between the lipid composition of the muscle cell and the time of day.
In a second step, the researchers moved on to an in vitro experiment. They cultured human muscle cells and artificially synchronized them using a signal molecule normally secreted in the body. The researchers observed a periodic variation in the lipid composition of cells, similar to what they observed in human subjects. When they disrupted synchronization, by inhibiting the genes responsible, these periodic variations disappeared.
An impact in type 2 diabetes
“We have clearly shown that this variation in the types of lipids in our muscles is due to our circadian rhythm,” explains lead author Ursula Loizides-Mangold, “But the main question remains“ what is this mechanism for? ”“ Scientists think that the body clock in muscle, with its impact on lipids, could help regulate the sensitivity of cells to insulin. This is because lipids – being a component of the cell membrane – influence the ability of molecules to move in and out of muscle cells. The muscle’s sensitivity to insulin as well as its ability to absorb blood sugar would then vary throughout the day.
Low muscle receptivity to insulin leads to a condition called “insulin resistance”. It is one of the primary causes of Type 2 diabetes. “The studies strongly suggest a link between circadian clocks, insulin resistance and the development of diabetes,” says Charna Dibner, co-director of the study. The team will explore this link in their next study.
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