Circadian rhythms are usually associated with sleepy brains, but it looks like our muscles have a daily routine as well. As the day ticks on, researchers have found that the mixture of lipids, or fats, in our muscles regularly change, regardless of activity levels. This doesn’t necessarily mean that you’re likely to feel weaker or stronger at different times, but it may have implications for other parts of the body, like your liver or fat cells.
Measuring muscle cells
The first phase of this study simply measured the composition of lipids in people’s thigh muscles throughout the day to see if it changed on a regular cycle. Every four hours, a small muscle sample was taken and analyzed. As expected, the lipids found in a single thigh varied according to a 24 hour schedule. However, they also varied greatly between individuals, which muddled things up a bit. To try to really isolate the relationship between lipid composition and circadian rhythm, researchers decided to isolate the muscle cells themselves.
The second phase of the experiment was based around muscle cells living in a petri dish. This allowed for finer control over variables, such as the signals that would normally put muscle cells on a daily rhythm in the first place. A circadian rhythm was then simulated by exposing the muscle cells to signal molecules that the body normally produces on a daily basis. As expected, this triggered the changes in lipid composition that matched what had been previously observed in people’s thighs. To further prove the importance of this signal molecule, genes in the muscle cells that enabled sensitivity to circadian signals were blocked, and the signal molecule no longer affected lipid production.
Interfering with insulin intake
You probably haven’t noticed these changes in your muscles’ lipid production, but your liver and pancreas might have. Lipids are make up part of a cell’s outer membrane, and thus can influence how well substances can pass in and out of a cell. This balance is disrupted in insulin resistant cases of type 2 diabetes, reducing muscle cell’s ability to take in blood sugar. Knowing that the lipids that influence insulin absorption change throughout the day may enable more sophisticated treatment methods. The circadian signaling molecules in our bodies, the treatment that’s a good match for someone’s morning might not be as effective in the evening.
Source: Our muscles measure the time of day, Universite de Geneve