Friday, May 18th, 2007--

Fifty years ago, several researchers reported seeing mammals (rabbits and humans) generate new hair follicles as adults. Hair follicle production was thought to occur only in embryos. A short controversy ensued, but was put to rest when a researcher named William Straile published a paper in the journal Investigative Dermatology concluding that there was no good evidence to support the claim.

Straile’s paper was widely accepted until this week, when George Cotsarelis, Mayumi Ito and colleagues published a new paper in the journal Nature, showing that adult mice can re-grow hair, the mice just have to be seriously wounded to do it.

“There’s no doubt that hair follicles are developing de novo. I think the data is pretty definitive,” says Cotsarelis, a professor at the University of Pennsylvania Medical School and senior author on the paper.

The researchers discovered that when a mouse was wounded deeply enough (a five millimeter scar needed to form), new hair follicles emerged at the middle of the wound and new hair sprouted. “We saw all these stages that looked like hair follicle development in the embryo,” Cotsarelis says.

But the development of hair follicles in the wounded mouse differed slightly from the embryonic development. In embryos, follicles are produced by follicle stem cells; in this case, the follicle stem cells had little to do with follicle generation, Cotsarelis says. “Actually it was the epidermal cells—or cells that don’t normally make hair—which were being reprogrammed to make hair follicles in an adult—so that was very surprising.”

What triggers the the epidermal cells to become hair follicle factories? “We don’t know exactly what is going on,” says Cotsarelis. “We do know that the same molecular pathways that are present during development are also present during this process.”

For example, Wnt signaling—which refers to proteins that help cells communicate with each other—was present. Wnt is activated during hair follicle development in embryos. In the wounded mice, Cotsarelis showed that increased exposure to Wnt proteins led to more hair growth and no hair follicles formed when Wnt exposure was blocked.

Cotsarelis says treating baldness would likely require a wound-Wnt combination approach. Cotsarelis is involved with a start-up called Follica to apply this research to humans: “We’re in pre-clinical stages right now working on this.”

Until now—despite what you may have seen on TV—the two FDA-approved treatments for hair loss "are much better at maintaining what you have rather than regrowing hair. Neither will restore hair to a totally bald area,” Cotsarelis says.

One potential roadblock to using the wound-Wnt method to treat people is that humans are not in the habit of leaving gaping wounds open. But sutured wounds did not produce new hair follicles in mice. “When you have a surgical incision you put the edges together and sew them up," Cotsarelis says. "So it’s possible we’re actually inhibiting this process in normal incisions.”

Although wounding may sound like a drastic solution for regrowing hair, Cotsarelis argues that it is relatively straightforward compared to other options. “It seems simpler than say, gene therapy or tissue engineering, where you’re messing around with cells and separating them and trying to put them back together to get a structure." Hair follicles are complex organs, Cotsarelis says, and difficult to generate artificially. He says, "Here at least you’re triggering these programs that are innate and basically well-orchestrated to allow a new follicle to form.”

What did you think of the story? Send us some feedback.

--Flora Lichtman

Sources

George Cotsarelis
Department Of Dermatology Kligman Laboratories University Of Pennsylvania School Of Medicine Philadelphia, Pennsylvania

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