Mice with deep skin wounds can grow new hair, scientists said on Wednesday in a finding that offers hope for a baldness remedy for humans.
The mice regenerated hair at the site of the wound via molecular processes similar to those used in embryonic development, according to the research, published in the journal Nature.
The findings show mammals possess greater regenerative abilities than commonly believed. While some amphibians can regenerate limbs and some reptiles can regenerate tails, regeneration in mammals is far more limited.
Dr. George Cotsarelis, a dermatology professor at the University of Pennsylvania School of Medicine in Philadelphia who led the study, said the findings dispel the dogma that hair loss is permanent in people and other mammals, and that once they are lost new hair follicles cannot grow.
Cotsarelis said the findings could pave the way for remedies for male-pattern baldness and other types of hair-loss. He said the idea would be to apply compounds to get epidermal cells to turn into hair follicles.
The regenerated follicles functioned normally, cycling through the various stages of hair growth, and the hair was indistinguishable from neighboring hair with a key exception -- it lacked pigmentation and was white.
The otherwise brown-haired mice had patches of white hair marking the site of the wound.
Cotsarelis said the white-hair issue may not materialize in any baldness remedy in people because the human pigmentation system differs from that in mice.
New hairs formed
The researchers made relatively large wounds on the backs of adult mice, and found that if a wound reached a certain size new hairs formed at its center, with the skin undergoing changes mimicking stages of embryonic hair-follicle development.
Dormant embryonic molecular pathways were activated, sending stem cells — master cells able to transform into other cell types — to the damaged skin.
The stem cells that gave rise to the regenerated follicles were not stem cells usually associated with hair-follicle development.
“They’re actually coming from epidermal cells that don’t normally make hair follicles. So they’re somehow reprogrammed and told to make a follicle,” Cotsarelis said.
The researchers also found a way to amplify the natural regeneration process, causing mice to grow twice as many new hairs by giving the skin a specific molecular signal.
Cotsarelis is involved with Follica Inc., a privately held start-up company that has licensed the patent on the process from the University of Pennsylvania. He said it probably would be more than five years before a treatment was possible.
Cotsarelis also envisioned treating wounds in a way that would leave skin with hair follicles, sweat glands and other normal attributes that would be functionally and cosmetically much better than a scar.
Dr. Cheng-Ming Chuong, a professor of pathology at the University of Southern California who was not involved in the study, said it proved the principle that hair can regenerate from adult skin, but cautioned that human skin differs from mouse skin.
“Repair and regeneration appear to be in competition,” Chuong said by e-mail.
“Since fast-closing wounds help the survival of wild animals, repair often dominates regeneration. In the practice of medicine, physicians are trained to close wounds as soon as possible, thus leaving not enough time for regeneration to occur.”