Sci. Aging Knowl. Environ., 6 July 2005
Vol. 2005, Issue 27, p. nf54
[DOI: 10.1126/sageke.2005.27.nf54]


Hair Trigger

Molecule induces skin cells to construct hair follicles

R. John Davenport

Like fertilizer on a sparse lawn, a chemical enticement encourages the skin to fill in hair-growing structures, new results reveal. The finding clarifies which cells produce new follicles and might point toward improved ways of encouraging hair growth in balding oldsters.

Hair sprouts from pouches in the skin known as hair follicles, which progress through a growth cycle. They stimulate a hair fiber to grow for a certain time. The hair subsequently falls out, and stem cells in a part of the follicle known as the bulge replenish the cell types that craft hair. Then the cycle starts anew. People are born with all the follicles they'll ever have, and over time, follicle performance falters. The structures spend more time in the "resting" phase and less in the "growing" phase. Follicles also shrink. These factors contribute to thinning hair. A molecule called {beta} catenin can induce new hair follicles to grow in adult animals, and in new work, Silva-Vargas and colleagues investigated how those follicles form.

To probe this issue, the researchers used mice with a version of the {beta}-catenin gene that is activated by a compound called 4-OHT, allowing the scientists to turn on the gene at will. Animals whose skin was treated with 4-OHT sprouted new hair follicles, matching previous findings. Some researchers have hypothesized that these new follicles originate from stem cells in existing follicles. To address that question, the researchers labeled bulge stem cells by incorporating a dye into the cells' DNA. Because they divide less frequently than surrounding cells do, they hang onto the dye longer. By monitoring when the dye disappeared, the scientists showed that fresh follicles appeared before follicle stem cells divided. Further experiments suggest that the new follicles sprang from surrounding skin cells. This outcome indicates that nonfollicle skin cells, not stem cells in existing follicles, produce the nascent hair factories. Other experiments suggest that the follicles function normally. They produced hair and went through growth and rest cycles. In addition, they contained cells that resemble follicle stem cells and melanocytes, which manufacture pigments (see "Gray Matters").

Additional findings reveal molecular signals through which {beta} catenin prompts follicle formation. After 4-OHT treatment, animals activate genes in the Hedgehog pathway, which guides embryonic development. When the team shackled a Hedgehog component before sparking {beta}-catenin activity, animals didn't grow new hair follicles, showing that the pathway must function for hair follicles to emerge.

"The key thing here is that new hair follicles can be produced from adult skin," says cell biologist Ian Jackson of the Medical Research Council in Edinburgh, U.K. "[They] are forming without stem cells from other hair follicles." Pattern baldness results partly from atrophied follicles, says dermatologist Andrzej Dlugosz of the University of Michigan, Ann Arbor. The new work raises the possibility of reprogramming skin cells to mint new follicles. That approach could also benefit patients with serious wounds, which heal without generating the structures. Although {beta} catenin also promotes tumor growth, says Dlugosz, the work might lead researchers to safe ways of keeping heads lush.

July 6, 2005
  1. V. Silva-Vargas et al., {beta}-catenin and hedgehog signal strength can specify number and location of hair follicles in adult epidermis without recruitment of bulge stem cells. Dev. Cell 9, 121-131 (2005). doi:10.1016/j.devcel.2005.04.013 [CrossRef][Medline]
Citation: R. J. Davenport, Hair Trigger. Sci. Aging Knowl. Environ. 2005 (27), nf54 (2005).

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