Circadian clock and oxidative Stress: functional cross-talk in skin homeostasis

Ozone (O 3 ) is among the most reactive chemical to which living organisms are routinely exposed and due to its critical location, the skin is one of the most susceptible tissues to environmental stressors. It is well known a significant role of the circadian system in the regulation of protein involved in the cellular response to oxidative stress. In this work, we investigated a possible protective role of the circadian system to O 3 induced damage in human keratinocytes evaluating the cross-talk between defensive and inflammatory pathway. Synchronized keratinocytes exhibited a faster cellular response, with a more efficient interplay among these two important pathways, compared to the arrhythmic after O3 exposure. Analysis of clock gene expression in rhythmic cells reveals a more rapid induction of the cardinal clock gene Bmal1. Taken together these data suggest that an adequate coordination of the circadian system and antioxidant/inflammatory pathway might be essential to maintain the skin homeostasis. Alteration of metabolic pathways as occurs in many diseases or simply irregular schedule of life activity (shift work, transcontinental journey) could negatively influence tissue gene expression programs and associated organ physiology via its effect on the circadian system.