P26 Investigating the cellular effects of external environmental stressors on human skin circadian rhythm and its associated skin functions
Sotia Iosifidou, Mark Birch-Machin, Clare O’ConnorAbstract
Introduction and aims
As the outermost layer of the body, skin is directly exposed to light, serving as a major environmental cue regulating biological processes through circadian rhythm. This 24-h clock enhances skin protection during daytime and promotes night-time DNA repair, helping defend against ultraviolet (UV)-induced damage. Yet, most existing data are derived from nocturnal rodent models, which may not accurately represent circadian regulation in diurnal humans. Here, we aim to explore the effect of external environmental stressors (complete solar light) on gene and protein expression in human skin cells.
Methods
Human dermal fibroblasts (HDFn) and epidermal keratinocytes (CCD1106) were exposed to varying doses of complete solar light (0.54 SED, 2.16 SED, 8.64 SED, with 2.16 SED approximating 20 min of Mediterranean sun exposure) across multiple timepoints to assess dose-dependent disruptions of the circadian rhythm. Circadian gene expression was quantified using quantitative polymerase chain reaction (qPCR) and protein levels using Western blot analysis.
Results
Four core clock genes (CLOCK, BMAL1, PER1, PER2) were tested. PER1 and PER2 genes showed early induction, across all doses in both cell types, peaking at 6 and 12 h in fibroblasts and at 12 h in keratinocytes. Conversely, CLOCK and BMAL1 exhibited later inductions, peaking at 18 h in fibroblasts and 24 h in keratinocytes. To investigate whether transcriptional changes translated to protein level alterations, CLOCK, BMAL1, PER1 and PER2 were investigated across matched timepoints. Consistent with qPCR data, PER1 and PER2 proteins demonstrated early expression, with peak intensities occurring within the first 12 h, whereas CLOCK and BMAL1 proteins exhibited later rises, mirroring the delayed mRNA induction.
Conclusions
Understanding different mechanisms and disruptions in the circadian clock in the skin can contribute to strategies that mitigate environmental stress on skin, supporting the development of targeted interventions that enhance skin barrier and via night repair formulations improve skin protection and recovery from external insults.