Why do some body parts have no hair?

MADRID, 29th November (EUROPA PRESS) –

Why do humans have hair on their arms and legs, but not on the palms and soles of their feet? This is a fundamental question of human evolution on which researchers at the Perelman School of Medicine at the University of Pennsylvania (Penn) in the United States claim to have found clues in a new study: the existence of a natural inhibitor secreted in the development of hairless skin that blocks a signaling pathway, called WNT pathway, which controls hair growth.

"We know that WNT signaling is essential for the development of hair follicles; blocking it means that the skin does not have hair and change it causes more hair to form, "says Sarah E. Millar, lead author of the study, professor of dermatology and director of the resource center on the biology of the skin and Penn's diseases. In this study, we showed that the skin of hairless regions naturally produced an inhibitor that prevented TNO from doing its job, "he summarizes.

The natural inhibitor is Dickkopf 2 (DKK2), a protein found in specific adult and embryonic tissues where it performs a variety of functions. The researchers analyzed the plantar skin of mice, about the equivalent of the inner face of the human wrist, and they found that DKK2 was highly expressed. In addition, when DKK2 was genetically removed, the hairs started to grow in this normally hairless skin area.

"It's important because it tells us that TNF is still present in the hairless regions, but that it's just stuck," said Millar, whose work is detailed in an article published Wednesday in the review 'Cell Reports'.

Some mammals, such as rabbits and polar bears, naturally develop hair on their plantar skin.. The Millar research group found that, unlike mice, DKK2 is not expressed at high levels in the rabbit's plantar skin, which is why hair can grow there. These results suggest that the production of DKK2 in specific areas of the skin has been modified during evolution to allow the formation of different hair-free or hair-based skin patterns depending on the needs of the animal .

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Hair follicles develop during fetal life, but their production stops after birth. As a result, the hair follicles do not regrow after severe burns or deep, deep skin wounds. Millar and his team are currently investigating whether secreted WNT inhibitors inhibit hair follicle development in these scenarios.

Although some areas of the human body are naturally hairless, others become so because of various diseases. According to the American Academy of Dermatology, more than 80 million people in the United States suffer from androgenetic alopecia, also known as male pattern baldness or in women.

Genomic association studies have identified DKK2 as a potential candidate gene associated with alopecia, suggesting that it is a possible therapeutic target.. "We hope that these lines of research reveal new ways to improve wound healing and hair growth, and we plan to pursue these goals in the future," Millar said.