Muscle tissue cells contain circadian clocks that control their metabolic response and energy efficiency, according to Northwestern Medicine scientists, who suggest that these cells may be more responsive to exercise during the daytime.

“Oxygen and the internal clock are doing a dance together inside muscle cells to produce energy, and the time of day determines how well that dance is synchronized,” says senior author Dr Joseph Bass, in a media release. “The capacity for a cell to perform its most important functions, to contract, will vary according to the time of day.”

“We’re not saying we can tell athletes when they should work out,” continues Bass, chief of endocrinology, metabolism and molecular medicine, and director of the Center for Diabetes and Metabolism at Northwestern University Feinberg School of Medicine. “But in the future, perhaps, you may be able to take advantage of these insights to optimize muscle function.”

In the study, published in Cell Metabolism, Bass and colleagues studied muscle tissues and fibers in mice that were exercised on a treadmill at different times each day, for expression of genes that are important for exercise. By doing so they determined the impact of deregulation of the circadian clock on muscle fibers in terms of how muscle processes fuel, like sugar and fat, when oxygen levels are low.

“When we manipulated the clock genetically, we noticed there were profound abnormalities in the muscle,” says Bass, also a member of the Robert H. Lurie Comprehensive Cancer Center of Northwestern University. “That set us on a course to understand how the inner muscle clock is important in regulating how well the muscle cell can mobilize energy.”

When mice, which are nocturnal, are exercised during the night, their muscles are better at turning on genes to help them adapt to exercise, scientists found. Since these genes also exist in humans, this suggests humans may also be able to respond better to exercise during the daytime.

The muscle clocks control the metabolic response by interacting with proteins called HIFs that change metabolism when oxygen concentrations get too low in order to allow muscle cells to continue to make energy, the release explains.

Normally when we rest or do low-level exercise, our muscles consume oxygen to make energy. When we start to sprint or exercise strenuously, we consume oxygen faster and quickly run out. That’s when the dip in oxygen triggers HIFs and signals muscles to switch to sugar for energy—which in turn increases lactic acid.

Turning off the muscle clock prevented the normal capacity of exercise to induce sugar consumption and generation of lactic acid. These findings suggest that better exercise capacity may be tied to specific times of day, the release continues.

“In the future, we may discover new ways to manipulate the oxygen response of the cell by resetting the clock,” notes Bass, who also holds the Charles F. Kettering Professorship of Medicine at Feinberg.

“If we can optimize muscle function, it’s also a critical step in understanding how to impact glucose metabolism in diabetes,” he adds.

[Source(s): Northwestern University, Science Daily]