Researchers Discover Role of Circadian Rhythm in Skin Aging

The body’s circadian rhythm is a well known driver of such important processes as the sleep/wake cycle, when we feel hunger, and how efficiently our metabolism operates. However, little is known about the role that it plays in the maintenance and healing of our skin. But researchers from the University of California Irvine have recently taken on an inquiry into the role of the rhythm in the functioning of skin stem cells, their cycles and division. Reporting in the January 6th edition of the journal Cell Reports, the scientists have provided valuable data on how our exposure to predictable daytime and evening cycles keeps stem cell division and differentiation operating appropriately, and what happens when the circadian clock is disrupted. Their finding showed that these disruptions can lead to both aging and the development of cancers. The study was led by professor of biological chemistry and medicine Bogi Amderson and professor of biomedical engineering Enrico Gratto. The two examined the outermost protective layer of the skin known as the epidermis because it is what is most visibly maintained and healed by stem cells, and what is most visibly damaged when stem cells go awry. The researchers were able to take extremely detailed measurements of the metabolic state of single cells within the epidermal tissue through use of novel two-photon excitation and fluorescence lifetime imaging microscopy available through UCI’s Department of Biomedical Engineering’s Laboratory of Fluorescence Dynamics. What they found was that in addition to everything else that is already known about the circadian clock, it also controls one part of the stem cells’ intermediary metabolism called the oxidative phosphorylation. Oxidative phosphorylation is responsible for the creation of oxygen radicals, which have the potential for damaging various parts of an individual cell, including its DNA. In examining the causes of aging, many theorize that it metabolism-generated oxygen radicals cause cumulative damage within the stem cells that would normally be dividing normally and healing damage. The study done by these two UCI scientists has made it clear that when the circadian clock within epidermal stem cells is disrupted, it has an impact on cell division, shifting its timing to the point where DNA damage can easily take place. It also showed that the circadian clock can shift cell division in order to avoid the most damaging impact. One way or another it is apparent through animal studies that if circadian rhythm is disrupted, aging is accelerated, most likely because of the disruption that is also caused in the stem cells and metabolism. Dr. Anderson says, “Our studies were conducted in mice, but the greater implication of the work relates to the fact that circadian disruption is very common in modern society, and one consequence of such disruption could be abnormal function of stem cells and accelerated aging.”