The effect of circadian rhythm on gene expression in human skin

Skin is the largest organ in the body and serves important barrier, regulatory, and sensory functions. Like other tissues, skin is subject to temporal fluctuations in physiological responses under both homeostatic and stressed states. To gain insight into these fluctuations, we investigated the role of the circadian clock in the transcriptional regulation of human epidermal samples collected in a time-ordered fashion. We also determined whether this circadian patterning could be applied to unordered (i.e., randomly collected) human epidermal samples. The purpose of this study was to gain insight into the evolutionarily-conserved rhythmic patterns of the circadian transcriptome in human skin and how it relates to published transcriptomes from other human tissues. For the time-ordered data, 2mm punch biopsies from the forearm were collected from 20 healthy male subjects over the course of 24 hours (12pm, 6pm, 12am, and 6am the following day). As controls, saliva samples were also collected every 3 hours to measure fluctuations in known circadian oscillators. For the unordered data, single 4mm punch biopsies were collected from the forearms of 152 Caucasian and 67 African-American healthy female subjects All biopsy samples were subjected to laser capure microdissection to isolate the epidermal compartments for subsequent gene expression profiling using Affymetrix U219 array plates.