No Hair Works Alone—Hair Plucking and Growth

Image of woman plucking eyebrow with tweezer

Plucking of mouse hair is often used in the laboratory to investigate the hair cycle and sometimes to remove the pelage covering the skin before applying chemicals, drugs, ultraviolet irradiation or other components of the experimental tool box. An article by a cross-disciplinary team composed of dermatologists, stem cell biologists, developmental biologists, immunologists, mathematical biologists, and tissue engineers have worked together from diverse regions including the US, Taiwan, People’s Republic of China, and the UK. The result is a stimulating article in CELL about a simple principle underlying the population regenerative behavior in a complex biological system (Chen et al., 2015).

Important points:

  • Plucking hairs stimulate regeneration of both plucked follicles and unplucked adjacent follicles at some distance by some signals sent out from plucked follicles.
  • The immune system plays an essential role in this regenerative process. Hair follicles produce proinflammatory cytokines, including the chemokine CCL2, which attracts inflammatory macrophages with tumor necrosis factor alpha. These macrophages are necessary for spreading the signal afar, achieving the two-step signaling propagation.
  • Mathematical modeling of this system is consistent with the process of quorum sensing. Quorum sensing behaviors are often seen in bacteria and social insects such as ants and bees. Here, hair regeneration is shown as an interesting and important quorum phenomena in a mammalian system. “Quorum” in such systems describes a condition in which numbers of individual cells, organisms, or organs (e.g., hair follicles) are necessary for a change rather than an absolute level of chemical mediator.
  • NF-kappa B is one of the important mediators that stimulate hair regeneration.
  • In addition to the detailed mechanism that functions after hair plucking, this article shows that mathematical modeling analyses can helps to reveal a deeper level of understanding of skin diseases.
  • The institutional origin of the investigators is a perfect demonstration of the importance of involving multiple disciplines in research, as well as the broad international nature of skin-related and all research.
  • As investigators use wax or plucking to remove hairs to study their own hypotheses, they must be cognizant of all the quorum processes going on beneath the skin surface.
  • Hair disorders and organs beyond the skin may be co-opting the evolutionarily conserved quorum sensing principles for health or disease.

References        

Chen et al (2015) Organ-level quorum sensing directs regeneration in hair stem cell populations. Cell 161:277-290

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