Human skin keratinocytes, melanocytes, and fibroblasts contain distinct circadian clock machineries

Abstract

Skin acts as a barrier between the environment and internal organs and performs functions that are critical for the preservation of body homeostasis. In mammals, a complex network of circadian clocks and oscillators adapts physiology and behavior to environmental changes by generating circadian rhythms. These rhythms are induced in the central pacemaker and peripheral tissues by similar transcriptional-translational feedback loops involving clock genes. In this work, we investigated the presence of functional oscillators in the human skin by studying kinetics of clock gene expression in epidermal and dermal cells originating from the same donor and compared their characteristics. Primary cultures of fibroblasts, keratinocytes, and melanocytes were established from an abdominal biopsy and expression of clock genes following dexamethasone synchronization was assessed by qPCR. An original mathematical method was developed to analyze simultaneously up to nine clock genes. By fitting the oscillations to a common period, the phase relationships of the genes could be determined accurately. We thereby show the presence of functional circadian machinery in each cell type. These clockworks display specific periods and phase relationships between clock genes, suggesting regulatory mechanisms that are particular to each cell type. Taken together, our data demonstrate that skin has a complex circadian organization. Oscillators are present not only in fibroblasts but also in epidermal keratinocytes and melanocytes and are likely to act in coordination to drive rhythmic functions within the skin.

Peripheral Circadian Clocks—A Conserved Phenotype?

“…Thus, the tail skin may possess multiple clocks of almost 24 h, but at different phases. This conclusion is in agreement with the opinion of Geyfman and Andersen (2009) and the recent study of Sandu et al (2012). The first paper claimed that it is too simplistic to define the skin as a tissue of a single circadian clock.…”

“…Previous studies in humans and rodents demonstrated circadian rhythms in expression of several core clock genes (especially Per and Bmal1) in each of these tissues. Other experiments concluded that functional circadian clocks tick in the liver, OBs, and in most cell types in the skin (Geyfman & Andersen, 2009Granados-Fuentes et al, 2004;Guilding & Piggins, 2007;Hamada et al, 2011;Hughes et al, 2009;Kornmann et al, 2007;Liu et al, 2007;Sandu et al, 2012;Takata et al, 2002;Tanioka et al, 2009). Contradictory evidence appears to exist for the WBCs (Boivin et al, 2003;Liu et al, 2007;Teboul et al, 2005).…”

“…In the absence of cyclic light conditions, the SCN synchronizes by non-photic-dependent pathways, the various clocks leading to a single and overall circadian phenotype of the skin. Sandu et al (2012) unveiled variability in the temporal pattern of the circadian clock genes transcripts between fibroblasts, keratinocytes, and melanocytes of human skin biopsies.…”

Impaired light detection of the circadian clock in a zebrafish melanoma model

“…33 However, human skin contains different cell types displaying a range of amplitudes in clock gene rhythms, with keratinocyte and dermal fibroblast cultures showing a more robust clock compared to melanocyte cultures. 28 To ensure that the difference in amplitude we observed between normal skin and melanoma tumors in our study is not due to a higher number of melanocytes in tumor samples, we analyzed clock gene expression in zebrafish dysplastic naevi (Fig. S2).…”

“…25,26 Skin cells have been shown to contain a robust biological clock in mammals although the function of this skin clock is generally unknown. [27][28][29][30] There is evidence for a role of the circadian clock in maintaining stem cell heterogeneity in the epidermis and the timing of DNA replication appears to be under clock-control in keratinocytes. 31,32 Analysis of clock gene expression in human skin and melanoma tumor biopsies showed down regulation in tumor samples.…”