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Our sleep patterns, eating habits, body temperature and hormone levels are driven by the rhythmic activity of body's circadian clock. Travel across time zones or shift work can knock those rhythms out of whack, possibly leading to sleep problems, bipolar disorder, metabolic syndrome and even cancer. The lack of convenient and reliable methods to monitor the internal clock's activity has severely limited the study of circadian-related disease, but now, scientists report that they can easily track the circadian rhythms by analyzing a person's plucked hairs. The finding could one day help doctors diagnose and treat patients suffering from circadian dysfunction.
The body's master clock, located in the brain region called the hypothalamus, is set by light, which activates clock genes that are responsible for keeping this timekeeper ticking correctly. Within the past decade, scientists have discovered that organs outside the brain (such as the skin, liver and pancreas) also keep track of time with 24-hour fluctuations in clock gene expression. Previous studies have attempted to monitor molecular timekeeping in blood cells or in cells lining the mouth, but these approaches are technically challenging.
In an attempt to develop a simpler, noninvasive method to clock circadian rhythms, researchers led by Makoto Akashi of the Research Institute for Time Studies at Yamaguchi University in Japan obtained hairs plucked from volunteers' heads or chins and analyzed clock gene expression in hair follicle cells. They report online this week in the Proceedings of the National Academy of Sciences that the patterns of circadian gene expression in the hair follicle cells accurately reflected the subjects' behavioral rhythms, "demonstrating that this strategy is appropriate for evaluating the human peripheral circadian clock."
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When the researchers looked at clock genes in six rotating shift workers during a three-week period, they found that all subjects had, on average, a five-hour lag between gene expression and their activity schedule. Such abnormal patterns might contribute not only to circadian rhythm disorders, but also to increased risk of heart attack, stroke and sudden death, the researchers sspeculate.
"Because circadian clock dysfunction causes various human disorders, characterization of the circadian pacemaker would be of great value in predicting and preventing these diseases," the researchers write in their paper. They conclude, "Qualitative evaluation of clock gene expression in hair follicle cells…may be an effective approach for studying the human circadian clock in the clinical setting."
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