The body has its own internal clock called the circadian clock. It runs in the background to carry out essential functions, which occur in alignment with certain circadian rhythms, such as the sleep-wake cycle.
A closer look into the factors shaping the circadian clock shows that various cell signals play an integral role in its function.
Researchers from the U.S. and Canada examined the potential effect of various stress signals. They found that they influence how fast the circadian clock runs and how robust it is.
Stress signals improve circadian clock
Cells respond to various stress signals by activating a signal transduction cascade that triggers a series of molecular events. This process involves the protein eIF2?, which plays a major role in protein synthesis in cells.
The team found that stress leads to rhythmic phosphorylation of eIF2? in the central brain clock. In turn, phosphorylation promotes the production of the ATF4 protein. This protein activates the Per2 gene, which makes the circadian clock tick faster. Meanwhile, the activation of the gene is necessary to maintain a robust clock.
Therefore, the researchers concluded that stress signals influence how fast and robust the circadian clock is.
The study provides one of the first pieces of evidence linking the circadian clock to stress response. Furthermore, while scientists know that the circadian clock is disrupted among diseased individuals, they are uncertain why that happens. The study’s findings may help answer this question. According to the researchers, stress responses are often impaired among people with a disease, which can disrupt their body clock.
"Hopefully our work can lead to discovering medicine that can manage the stress level and regulate the clock function in disease to keep people healthier," said co-author Ruifeng Cao, a professor at the University of Minnesota Medical School.
Link between circadian rhythms and stress hormones
In another study, published in the journal Neuroendocrinology, researchers found that stress hormones help control the circadian rhythms of brain cells.
They examined a brain component, the suprachiasmatic nucleus, which is the principal circadian pacemaker in the mammalian brain. It regulates the circadian rhythms of several areas of the brain, including the cerebellum and the cerebral cortex. However, the team noted that these two areas are not directly linked to the suprachiasmatic nucleus by neurons, which implies that there might be other players involved.
They conducted a series of tests on mice by removing the suprachiasmatic nucleus from their brains. This effectively impaired circadian rhythms in the mice. For example, their body temperatures, activity levels and hormone production went from rhythmic to static.
This was reversed when the researchers administered carefully metered doses of a stress hormone called corticosterone at different times of the day and night, mimicking the biological schedules in mice. Corticosterone is the rodent equivalent of cortisol in humans, which plays an important role in helping the body respond to stress.
The researchers conducted more trials to ensure the consistency of their findings. And again, they were able to detect rhythmic activity in the clock genes in rodent cerebellum, even though the suprachiasmatic nucleus was removed.
"This is hugely interesting from a scientific point of view, because it means that we have two systems – the nervous system and the hormonal system – that communicate perfectly and influence one another," said co-author Martin Fredensborg Rath of the University of Copenhagen. (Related: Does stress have benefits? A certain form of stress may be linked to longer life, say scientists.)
The team concluded that circadian rhythms are controlled by means of signaling agents such as corticosterone.
Learn more about the effects of stress at MindBodyScience.news.
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