AsianScientist (Feb. 17, 2016) – Japanese researchers have that discovered DNA damage to stem cells in the hair follicles turns them into skin cells which subsequently leave the scalp. These findings, published in Science, could potentially lead to new treatments for hair loss and other aging-associated diseases.
The hair follicle is an epithelial mini-organ of the skin. As it ages, it naturally shrinks or miniaturizes, and its functions and regenerative ability decline. Hair follicles contain hair follicle stem cells (HFSCs) that activate in cyclical growth phases; the longer the growth phase, the longer the hair.
While aging in organisms has been explained by various theories, not much is known about the role of stem cells in the organ aging process.
Studying hair follicles as mini-organs, Professor Emi K. Nishimura and colleagues from the Department of Stem Cell Biology, Medical Research Institute, Tokyo Medical and Dental University, set out to investigate the impact of aging on HFSCs, and if there was any link to aging-associated hair loss.
In a study of wild-type mice models, they found that HFSCs accumulate DNA damage as they renew during repetitive hair cycles, leading to a breakdown of type XVII collagen (COL17A1) which is crucial for the maintenance of HFSCs.
Once these aged HFSCs are activated during the hair cycle, they eventually leave the follicle, turn into epidermal keratinocytes and are then eliminated from the skin surface.
Then, to see if this was the same for humans as well, the team analyzed healthy human scalp skin from women at ages ranging from 22 to 70 years old. They found that human female scalps from the aged group (55 to 70 years old) contain significantly more miniaturized hair follicles compared with the younger group (35 to 45 years old).
The team’s findings show that hair follicle aging is initially caused by DNA damage that accumulates in renewing HFSCs as they age. This thus leads to hair follicles in mammals miniaturizing and even disappearing from the skin, regardless of gender, in both mice and humans.
It is worth noting that hair follicle aging is also linked to intrinsic genomic instability, as in the case of the genetic disorders such as progeria.
Indeed, this dynamic hair follicle aging program is a good model of how different organs and tissue miniaturize and become less functional with age, the authors wrote.
The article can be found at: Matsumura et al. (2016) Hair Follicle Aging is Driven by Transepidermal Elimination of Stem Cells via COL17A1 Proteolysis.
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