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. 2012 Jul 17;109(29):11758-63.
doi: 10.1073/pnas.1209592109. Epub 2012 Jul 2.

Brain and muscle Arnt-like protein-1 (BMAL1) controls circadian cell proliferation and susceptibility to UVB-induced DNA damage in the epidermis

Mikhail Geyfman  1 , Vivek Kumar, Qiang Liu, Rolando Ruiz, William Gordon, Francisco Espitia, Eric Cam, Sarah E Millar, Padhraic Smyth, Alexander Ihler, Joseph S Takahashi, Bogi Andersen
Affiliations

Brain and muscle Arnt-like protein-1 (BMAL1) controls circadian cell proliferation and susceptibility to UVB-induced DNA damage in the epidermis

Mikhail Geyfman et al. Proc Natl Acad Sci U S A. .

Abstract

The role of the circadian clock in skin and the identity of genes participating in its chronobiology remain largely unknown, leading us to define the circadian transcriptome of mouse skin at two different stages of the hair cycle, telogen and anagen. The circadian transcriptomes of telogen and anagen skin are largely distinct, with the former dominated by genes involved in cell proliferation and metabolism. The expression of many metabolic genes is antiphasic to cell cycle-related genes, the former peaking during the day and the latter at night. Consistently, accumulation of reactive oxygen species, a byproduct of oxidative phosphorylation, and S-phase are antiphasic to each other in telogen skin. Furthermore, the circadian variation in S-phase is controlled by BMAL1 intrinsic to keratinocytes, because keratinocyte-specific deletion of Bmal1 obliterates time-of-day-dependent synchronicity of cell division in the epidermis leading to a constitutively elevated cell proliferation. In agreement with higher cellular susceptibility to UV-induced DNA damage during S-phase, we found that mice are most sensitive to UVB-induced DNA damage in the epidermis at night. Because in the human epidermis maximum numbers of keratinocytes go through S-phase in the late afternoon, we speculate that in humans the circadian clock imposes regulation of epidermal cell proliferation so that skin is at a particularly vulnerable stage during times of maximum UV exposure, thus contributing to the high incidence of human skin cancers.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
The circadian transcriptome of skin. (A and B) Representative histology and heatmaps of the circadian transcriptomes for (A) telogen and (B) anagen skin. (C and D) The five most significantly enriched functional categories among (C) telogen and (D) anagen circadian genes. (E) Heatmaps of telogen circadian genes encoding oxidative phosphorylation and cell-cycle regulators. (F) Quantification of ROS levels in telogen skin at ZT8 and ZT20 from WT, Bmal1+/−, and Bmal1−/− mice. P values were determined by Student’s t test. Two-way ANOVA revealed a significant effect of genotype [F(1,11) = 371.33; P < 0.0001]. Error bars represent SEM for three to seven biological replicates. The LD cycles are indicated below the time-course panels. Numbers above the color scales indicate log2-transformed mean-centered expression values.
Fig. 2.
Fig. 2.
Circadian proliferation in the mouse epidermis. The data were analyzed by ANOVA and sinusoidal wave fitting. Percentage of BrdU-positive nuclei in (A) the telogen interfollicular epidermis [F(2,20) = 14.3; P = 6.8 × 10−7; sine-wave P = 7.6 × 10−4], (B) the telogen upper follicle [F(2,20) = 4.8; P = 0.0016; sine-wave P = 1 × 10−6], (C) the secondary hair germ (SHG) at P23 [F(2,20) = 0.73; P = 0.68; sine-wave P = 1.04 × 10−2], and (D) the matrix at P27 [F(2,20) = 0.68; P = 0.21; sine-wave P = 9.3 × 10−3]. Representative immunohistochemical images of each compartment are shown. The error bars represent SEM for three or four biological replicates. The LD cycles are indicated below the time-course panels.
Fig. 3.
Fig. 3.
BMAL1 regulates the proportion of cells in S-phase in the interfollicular epidermis and upper follicles. Quantification of BrdU incorporation during telogen (P22) in (A) the interfollicular epidermis [two-way ANOVA for genotype, F(1,24) = 21.93; P < 0.0001] and (B) upper follicles [two-way ANOVA for genotype, F(1,24) = 27.5, P < 0.0001] of Bmal1+/− and Bmal1−/− mice. In Bmal1−/− mice circadian variation is lost in the epidermis and upper follicles. The error bars represent SEM for three or four independent biological replicates.
Fig. 4.
Fig. 4.
Keratinocyte-specific Bmal1 deletion has no effect on hair cycle progression but obliterates time-of-day–dependent variation of S-phase in the interfollicular epidermis and upper follicles. (A) Quantification of hair follicle stages at P24 in Bmal1−/−, Bmal1fl/+;K14Cre, and Bmal1fl/fl;K14Cre mice. (B) Quantification of BrdU-positive cells in the interfollicular epidermis of P24 Bmal1fl/+;K14Cre and Bmal1fl/fl;K14Cre mice at the indicated times. (C) Quantification of BrdU-positive cells in the upper hair follicles of P24 Bmal1fl/+;K14Cre and Bmal1fl/fl;K14Cre mice at the indicated times. The error bars represent SEM for three or four biological replicates. P values were determined by Student’s t test.
Fig. 5.
Fig. 5.
BMAL1 is responsible for time-of-day–dependent sensitivity to UVB-induced DNA damage. Quantification of (A) 6-4 photoproducts (64Ps) [two-way ANOVA for genotype, F(1,16) = 7.72; P < 0.013], (B) cyclobutane pyrimidine dimers (CPDs) [two-way ANOVA for genotype, F(1,17) = 5.92; P < 0.026], and (C) phospho (S-139) H2AX-positive cells [two-way ANOVA for genotype, F(1,8) = 62.95; P < 0.001] in the epidermis of Bmal1+/− and Bmal1−/− mice after UVB exposure at the indicated times. (D) A model of antiphasic relationship between time-of-day–dependent ROS accumulation, S-phase, and sensitivity to DNA damage in mouse and human skin. Note that in human skin the highest proportion of epidermal keratinocytes in S-phase (highest susceptibility of DNA damage) occurs at the time of the highest UV intensity, possibly contributing to a high occurrence of human skin cancer. The error bars represent SEM for three biological replicates. P values were determined by Student’s t test.
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References

    1. Lowrey PL, Takahashi JS. Genetics of circadian rhythms in Mammalian model organisms. Adv Genet. 2011;74:175–230. - PMC - PubMed
    1. Yan J, Wang H, Liu Y, Shao C. Analysis of gene regulatory networks in the mammalian circadian rhythm. PLOS Comput Biol. 2008;4:e1000193. - PMC - PubMed
    1. Fuchs E, Horsley V. Ferreting out stem cells from their niches. Nat Cell Biol. 2011;13:513–518. - PMC - PubMed
    1. Rigel DS. Cutaneous ultraviolet exposure and its relationship to the development of skin cancer. J Am Acad Dermatol. 2008 58(5, Suppl 2)S129–S132. - PubMed
    1. Greinert R. Skin cancer: New markers for better prevention. Pathobiology. 2009;76:64–81. - PubMed

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