Clock genes, hair growth and aging

Mikhail Geyfman,Bogi Andersen

doi:10.18632/aging.100130

Abstract

Hair follicles undergo continuous cycles of growth, involution and rest. This process, referred to as the hair growth cycle, has a periodicity of weeks to months. At the same time, skin and hair follicles harbor a functional circadian clock that regulates gene expression with a periodicity of approximately twenty four hours. In our recent study we found that circadian clock genes play a role in regulation of the hair growth cycle during synchronized hair follicle cycling, uncovering an unexpected connection between these two timing systems within skin. This work, therefore, indicates a role for circadian clock genes in a cyclical process of much longer periodicity than twenty four hours.

Highlights

Beginning after completion of hair morphogenesis, hair growth cycles commence with catagen, an involution process of the hair follicle during which the majority of its epithelial compartments undergo apoptosis [1]
In order to systematically discover transcriptional activity associated with the hair growth cycle, we profiled mRNA expression at a genome-wide level over multiple time points corresponding to morphogenesis and two synchronized hair growth cycles
The clock genes that we identified as upregulated in telogen/early anagen were all CLOCK/BMAL1 target genes, including Pers, Dbp and Rev-Erbα

Summary

The hair growth cycle

Beginning after completion of hair morphogenesis (postnatal day 14 in the mouse), hair growth cycles commence with catagen, an involution process of the hair follicle during which the majority of its epithelial compartments undergo apoptosis [1]. This stage is followed by telogen during which the hair follicle remains in relative quiescence. Telogen is interrupted by activation of epithelial stem and progenitor cells located in specialized stem cell compartments in the bulge and secondary hair germ, followed by rapid proliferation and differentiation of progeny keratinocytes; this growth phase is referred to as anagen [2]. As the mouse ages, the hair growth cycles become progressively less synchronized [3]

Circadian gene expression is hair growth cycle dependent

Role for circadian clock genes in hair growth cycling

The aging hair follicle

Circadian clock and the aging hair follicle