Despite its importance, it wasn't clear whether the circadian rhythms in hepatic transcription were solely controlled by the liver clock in anticipation of food or responded to actual food intake.
To investigate how much influence rhythmic food intake exerts over the hepatic circadian oscillator, graduate student and first author Christopher Vollmers put normal and clock-deficient mice on strictly controlled feeding and fasting schedules while monitoring gene expression across the whole genome.
He found that putting mice on a strict 8-hour feeding/16-hour fasting schedule restored the circadian transcription pattern of most metabolic genes in the liver of mice without a circadian clock. Conversely, during prolonged fasting, only a small subset of genes continued to be transcribed in a circadian pattern even with a functional circadian clock present.
"Food-induced transcription functions like a metabolic sand timer that runs for 24 hours and is continually reset by the feeding schedule while the central circadian clock is driven by self-sustaining rhythms that help us anticipate food, based on our usual eating schedule," says Vollmers. "But in the real world we don't eat at the same time every day and it makes perfect sense to increase the activity of metabolic genes when you need them the most."
For example, genes that encode enzymes needed to break down sugars rise immediately after a meal, while the activity of genes encoding enzymes needed to break down fat is highest when we fast. Consequently a clearly defined daily feeding schedule puts the enzymes of metabolism in shift work and optimizes burning of sugar and fat
|Contact: Gina Kirchweger|