A team led by USC Stem Cell Principal Investigator Cheng-Ming Chuong has demonstrated that by plucking the specific 200 hairs, they can induce up to 1,200 replacement hairs to grow in a mouse; and they published the results in the journal Cell.
"It is a good example of how basic research can lead to a work with potential translational value," says Chuong, who is a professor of pathology at the Keck School of Medicine of USC. "The work leads to potential new targets for treating alopecia, a form of hair loss."
Initially starting two years ago, the study was based on visiting scholar Chih-Chiang Chen’s knowledge as a dermatologist that hair follicle injury affects its adjacent environment.
The Chuong lab at USC had already established that this environment in turn can influence hair regeneration, and so worked with Chen, from National Yang-Ming University and Veterans General Hospital in Taiwan, reasoning that they might be able to use the environment to activate more follicles.
To test the concept, Chen devised a strategy to pluck 200 hair follicles, one by one, in different configurations on the back of a mouse.
The team found that when plucking the hairs in a low-density pattern from an area exceeding six millimetres in diameter, no hairs regenerated; however, when higher-density plucking from circular areas with diameters between three and five millimeters was implemented, they found it triggered the regeneration of between 450 and 1,300 hairs, including ones outside of the plucked region.
Quorum sensing
Working with Arthur D. Lander from the University of California, the team showed that this regenerative process relies on the principle of ‘quorum sensing,’ which is a system of stimulae and response correlated to population density.
In this case, the scientists say quorum sensing underlies how the hair follicle system responds to the plucking of some, but not all hairs.
The regeneration works as the plucked follicles signal distress by releasing inflammatory proteins which then trigger a response from immune cells.
These immune cells then secrete signalling molecules which, at a certain concentration, communicate to both plucked and unplucked follicles that it's time to grow hair, and voila!
"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," says Chuong.