Researchers have demonstrated that by plucking 200 hairs in a specific pattern and density, they can induce up to 1,200 replacement hairs to grow in a mouse.
“The work leads to potential new targets for treating alopecia, a form of hair loss,” says Cheng-Ming Chuong, a professor of pathology at the Keck School of Medicine of USC.
As a dermatologist, first author Chih-Chiang Chen knew that hair follicle injury affects its adjacent environment, and the Chuong lab had already established that this environment can, in turn, influence hair regeneration.
Based on this combined knowledge, they researchers reasoned that they might be able to use the environment to activate more follicles.
Hair by hair
To test this concept, Chen devised the strategy of plucking 200 hair follicles, one by one, in different configurations on the back of a mouse.
When plucking the hairs in a low-density pattern from an area exceeding 6 millimeters in diameter, no hairs regenerated. However, higher-density plucking from circular areas with diameters between 3 and 5 millimeters triggered the regeneration of between 450 and 1,300 hairs, including ones outside of the plucked region.
The team showed that this regenerative process relies on the principle of “quorum sensing,” which defines how a system responds to stimuli that affect some, but not all members. In this case, quorum sensing underlies how the hair follicle system responds to the plucking of some, but not all hairs.
Through molecular analyses, the team showed that these plucked follicles signal distress by releasing inflammatory proteins, which recruit immune cells to rush to the site of the injury.
These immune cells then secrete signaling molecules such as tumor necrosis factor alpha (TNF-α), which, at a certain concentration, communicate to both plucked and unplucked follicles that it’s time to grow hair.
“The implication of the work is that parallel processes may also exist in the physiological or pathogenic processes of other organs, although they are not as easily observed as hair regeneration,” Chuong says.
The results are published today in the journal Cell.
Additional coauthors contributed from the Fourth Military Medical University, China; UC Irvine; University of Dundee, Scotland; National Cheng Kong University, Taiwan; National Yang-Ming University and Veterans General Hospital, Taiwan; and the University of Pennsylvania.
Research funding came from the National Institute of Arthritis and Musculoskeletal and Skin Diseases, the Taiwan National Science Council, the Taipei Veterans General Hospital, the National Institutes for Health, the Edward Mallinckrodt Jr. Foundation, the California Institute for Regenerative Medicine, the National Science Foundation, and Cheng Kong University, Taiwan.