Tissues Respond Independently to Light

During the day, we experience a series of physical, mental, and behavioral changes known as circadian rhythms. These changes are governed by a central clock, located in the hypothalamus, which lies in the center of the brain. This clock is responsible for synchronizing our tissues to ensure that their functions are coordinated together in time.

In a study published yesterday in Cell, scientists at the Institute for Research in Biomedicine have revealed that although each tissue receives information from the central clock in order to coordinate its functions, each one also has the capacity to respond independently to variations in light and to detect changes in light intensity between the day and night. The work confirms that this autonomy allows tissues to maintain minimal functions even when another tissue in our body is failing.

“The results of these studies are likely to be particularly relevant during aging and in diseases in which high tissue interdependence would lead to a general deterioration of the organism,” says senior author Salvador Aznar Benitah.

In order to investigate this question, the researchers used a new mouse model that allowed them to isolate the communication of each tissue from the rest. They compared the circadian rhythms of the epidermis and liver of this mouse model with those of healthy mice and mice with an impaired central clock. Using this approach, they confirmed the autonomy of both tissues in responding to the variation in light that occurs through the day.

However, the autonomous nature of these tissues does not mean there is an absence of communication in the body. “We confirmed that the central clock communicates from the brain with the rest of the body, providing useful information to ensure its correct function, informing, for example, the gastrointestinal tract, liver, and pancreas that it is time to eat and allowing them to prepare for digestion,” Benitah explains. “But when this communication fails, each organ is able to know what time it is and thus to perform their basic functions.”

The results have important health implications. Our current lifestyle exposes us to light when we should be in darkness. Given that each organ is able to respond independently to light, body functions that should occur during the day take place at night. This ‘social jet lag’ might be responsible for premature aging and the development of certain pathologies.