A Tokyo Medical and Dental University research team announced in the British journal Science on Feb. 5 that it has uncovered the mechanism through which hair thins out along with the process of aging.
The team, led by professor Emi Nishimura with the university's Department of Stem Cell Biology, found that the protein known as Collagen Type XVII, or COL17A1 -- which protects the hair follicle stem cells that are necessary for the production of hair -- decreases along with age. The hair follicle stem cells move from deep inside the pores up toward the surface of the skin, where they are subsequently sloughed off as dandruff.
Human hair has a lifespan of three to five years, after which time it falls out and is replaced by new hair that grows in at the same spot. At this time, the hair follicle stem cells in the pores are utilized for the regeneration of the cells that go on to become the basis of the hair.
Professor Nishimura and her research team focused upon the fact that mice similarly lose their hair after two years of age. Tracing the movements of the hair follicle stem cells of live mice over a long period of time revealed that they failed to self-replicate as the mice aged. The cells also moved gradually toward the epidermis, and were ultimately shed as dandruff or grime. The new hair that grew in was thinner, and the pores became smaller and eventually disappeared.
The team additionally discovered that the no-longer functioning hair follicle stem cells secreted a substance that worked to break down COL17A1 -- which they attributed to the accumulated damage to the hair follicle stem cells' DNA that occurs with age.
Mice that were genetically manipulated so as not to lose the COL17A1, however, were discovered to have 1.4 times as many 1-millimeter pores by age 2 as compared with regular mice.
In an investigation of healthy women's scalps, it was found that an average of 2.2 percent of the pores had shrunk in the three women aged 35 to 45, whereas the figure was an average of around 15 percent for the five women aged 55 to 70.
"If we can locate a substance that works to suppress the depletion of COL17A1, it is possible that it could go on to become a medical remedy for thinning hair, as well as an effective treatment for the hair loss that occurs when undergoing radiation therapy for cancer," noted professor Nishimura.
"We plan to look for a candidate substance over the coming several years, and put it into practical use within 10 years," she added.