The circadian rhythm of the human body, the biological process behind its natural sleep and wake cycles, have been linked to all kinds of health outcomes through recent research. These include slowing the growth of cancer cells, driving stress and recently, influencing the body's metabolism. Researchers have again placed this under the microscope by performing the first ever analysis of circadian rhythm within fat cells, finding they appear to have body clocks of their own and use them to share the heavy lifting throughout the day.
The research was led by scientists at the University of Surrey's School of Biosciences and Medicine, and enlisted seven healthy males who were put through carefully designed sleep and wake cycle experiment. This began with controlled sleep-wake cycles and meals leading up to the experiment, and then for its first three days to synchronize the circadian rhythms. The scientists then subjected them to an unregulated 37-hour period free of the typical triggers of outside time, such as changes in light and standard meal times.
Five biopsies were taken from the white adipose tissue of each subject at six-hour intervals and examined for gene expression through microarray analysis. The team highlighted a total of 727 genes in the fat tissue that indicate these cells dance to the beat of their own drum, independently of external environmental factors.
The team's analysis revealed many of the genes perform key metabolic functions at different times of the day, and that around a third of them peaked in the morning and two-thirds of them in the evening. Those that sprung into action in the morning were associated with nucleic acid biology, a key mechanism for cell function, while those on the late shift were linked to redox activity and organic acid metabolism.
This work echoes the findings of recent research investigating links between the circadian clock and the metabolism of the human body. A study published in November last year uncovered new evidence around how our bodies burn calories at different rates throughout the day. Another, published in August, revealed how disrupted circadian rhythms can cause tissue-level molecular changes that drive weight gain.
But by pinpointing a new mechanism in the long-hypothesized idea that disrupted body clocks can be a factor in obesity and adverse health outcomes, the University of Surrey scientists say the results highlight just how closely related circadian rhythms and human physiology might be.
"This is the first time that we have been able to identify such rhythms in human fat," says Dr Jonathan Johnston, lead author on the study. "This provides us with more information about how human metabolism changes across the day and possibly why the body processes foods differently during day and night."
The research was published in the journal Scientific Reports.
Source: University of Surrey
