Scientists today claimed a major step forward in the quest for a cure for baldness after making skin regrow lost hair follicles.
It is the first time healthy hair-producing follicles have been regenerated in adult skin, giving researchers hope that a treatment for hair loss could be within reach.
The US research team made the breakthrough in mice by awakening a sequence of long-dormant genes, triggering a flood of stem cells into patches of hairless skin. To the researchers' surprise, the stem cells were able to form new hair follicles.
The findings, reported in the journal Nature, overturned scientists' belief that mammals are born with a set number of hair follicles and are unable to grow new ones.
While newts and salamanders are known to be capable of regenerating entire limbs, researchers believed mammals had a much more restricted ability to regrow body tissues.
They discovered the effect during experiments into the healing mechanisms of the animals. When thin sheets of skin were taken from rodents, researchers found that not only did the skin heal, but it also reformed with new hair follicles.
Tests revealed that a set of genes, which are switched off shortly after the embryo stage of development, had been reawakened, causing stem cells to rush to the site of the wound and generate new follicles.
Further studies showed that injecting a protein called WNT onto the patch of skin doubled the number of hair follicles that formed. By blocking WNT proteins in the animals, the researchers were able to stop the growth of new hair follicles.
George Cotsarelis, a dermatologist at the University of Pennsylvania, which is leading the study, said: "We've found that we can influence wound healing with WNTs or other proteins that allow the skin to heal in a way that has less scarring and includes all the normal structures of skin, such as hair follicles and oil glands, rather than just a scar."
The scientists claim the findings have broader implications than a cure for male pattern baldness, suggesting they raise the possibility of treatments for other follicle-related disorders such as acne, scalp conditions and excessive hair growth.
They are now licencing the technology through a US company called Follica Inc.
"Up to now, we thought that the number of hair follicles we have is set before we were born and can only go downhill from there," Denis Headon, a developmental biologist at Manchester University, said.
"This work shows that new hair follicles are made in adult skin, at least when it is healing a wound."
Desmond Tobin, director of the medical biosciences research group at the University of Bradford, said the findings had revealed that "under the conditions peculiar to the wound-healing environment, the highly complex hair follicle can be created anew from apparently unremarkable cells of the healing epidermis and its underlying dermis".