S u m m a r y :
Your muscles can tell the time thanks to a biological clock in their cells, says a new study published in the Proceedings of the National Academy of Sciences.
A Clock in Your Muscles
Biological clocks, also known as circadian clocks, are found throughout the body. Regulated by a main clock in the brain, they play unique roles in processes like the secretion of certain hormones and enzymes. A newly-discovered circadian clock has now been found in muscles where it allows them to measure the time of the day, a system that, when perturbed, might be involved in the regulation of metabolism and diabetes. The findings were obtained by a team of researchers from University of Geneva (UNIGE), the University of Bath, the Université Claude Bernard, EPFL, the University of Surrey, and the Nestlé Institute of Health Sciences.
Fats in Your Muscle Tell The Time
The discovery was made when the team tested whether the levels of different types of muscle fat varied during the day. The master clock (the main one located in the brain) of the participants was synchronised as follows: the individuals were asked to stick to a certain eating and sleeping routine on a daily basis; this lasted for a week before experimentation began. The fat levels were measured in samples of thigh muscle tissue.
The results show a clear link between the lipid composition of the muscle cells and the time of the day. However, given that the lipids varied from person to person, more investigations had to be carried out to verify the correlation, explains co-author Howard Riezman.
Fat Levels Vary As Per the Time
The next step was an in-vitro experiment. Human muscle cells were cultivated and artificially synchronised without a master clock. Riezman and his colleagues found a periodic variation in the lipid composition of the cells, and this result was comparable to that obtained from human participants. Furthermore, when the clock mechanism was inhibited, the periodic variations were lost.
First author Ursula Loizides-Mangold explains that their experiments show that our circadian rhythm causes the variation of different types of lipids in our muscles.
Clock in Muscles Linked With Diabetes
What is the purpose of this biological clock? According to Riezman, it might be playing a role in the regulation of the sensitivity of cells to insulin because of its effects on lipids. The latter are an important component of cell membranes where they impact on the movement of molecules (which would include hormones like insulin) in and out of cells. Therefore, changes in cell membrane lipids might be influencing muscle cell sensitivity to insulin, and as an extension muscle ability to absorb sugar. As a matter of fact, diabetes type 2 is characterised by a decreased sensitivity of muscles to insulin, a condition called insulin resistance. So, it is believed that the disruption of the muscle circadian clock is linked with diabetes.
Furthermore, previous studies show a possible link between circadian clocks, insulin resistance, and the development of diabetes, explains co-author Charna Dibner.
“If we establish a link between circadian mechanisms and type 2 diabetes via lipid metabolism, this could have important therapeutic implications. Thanks to our new tools for studying human muscle cellular clocks in vitro, we now have the possibility to investigate this hypothesis in our next study,” says Dibner.