Circadian clock as possible protective mechanism to pollution induced keratinocytes damage.

Ozone is among the most toxic environmental stressors to which we are continuously exposed. Due to its critical location, skin is one of the most susceptible tissues to oxidative stress damaging effect of ozone. An increasing collection of data suggests a significant role of circadian system in regulation of cellular response to oxidative stress. However, the molecular mechanism linking circadian clock and antioxidant pathway it is not completely understood. Here we investigated a possible protective role of entrained circadian clock to ozone induced damage in keratinocytes, the main cellular component of human epidermis. Our results showed that, clock-synchronized keratinocytes compared to arrhythmic ones exhibited a more efficient antioxidant response, attested by a faster activation of the master antioxidant regulatory factor NRF2. Moreover, analysis of clock gene expression profiles reveals a more rapid induction of the cardinal clock gene Bmal1 in entrained cells. Based on these findings, we suppose that an adequate coordination of circadian system and antioxidant pathway might be essential to maintain homeostasis in the skin. Alteration of metabolic pathways occurred in neurological diseases or in irregular schedule of life activity could negatively influence tissue gene expression programs and associated organ physiology via its effect on the circadian system.