A biological signaling mechanism that regulates hair growth could hold the key to combat both baldness and excessive growth, a new paper reports.

Male baldness.

Via Alamy.

Turns out hairs, just like people, communicate and coordinate with each other to ensure that everybody does their job. This process is regulated by a single molecular signaling mechanism that adjusts growth by skin region to ensure no bald patches form and to dictate what hair density each area of the body gets. And again, just like people, sometimes these hairs feel the need to disconnect from all the chatter — leading to male pattern baldness or excessive hair growth.

Mice models

In an effort to pry the secrets out of this signaling mechanism, a team from the University of California-Irvine led by Maksim Plikus, assistant professor of developmental and cell biology and Qing Nie, professor of mathematics, developed and used the first mouse model of poor hair growth to analyze human-like hair behavior that leads to baldness.

The team focused their efforts on the interaction between the Wnt signaling pathway, which plays a key role in embryonic development and regeneration, and bone morphogenetic proteins (BMP), which can inhibit hair growth. Previous work has shown that the Wnt-BMP interaction can regulate hair growth in certain regions of the body, but it wasn’t understood how these regions then communicate and coordinate growth with one another.

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However, laboratory experiments can fall short when trying to explain complex biological functions such as skin-wide hair growth patterns. So the team combined Nie’s lab’s expertise in mathematical modeling with the expertise in skin studies from Plikus’ lab and found that Wnt-BMP regulation dictates hair growth on every inch of skin, no matter where on the body.

“In analogy with languages spoken in two neighboring countries, it was unclear how the back skin ‘talks’ with the belly skin to coordinate the tasks of growing hairs,” Plikus said. “We showed that although different signaling ‘dialects’ may exist between belly and back skin, for instance, all hairs can understand one another through the use of similar ‘words’ and ‘sentences.'”

Understanding this signaling mechanism could help uncover the cause of human hair growth irregularities and point to possible solutions. For example, male pattern baldness usually affects the crown and frontal part of the head, but not the back. This seems to be caused by a breakdown of communication via Wnt-BMP, causing each follicle to grow independently — and not very well at that.

“If communication between nonbalding and balding regions can be reactivated, hair growth signals can then start spreading across the entire head skin, preventing regional baldness,” Plikus said.

“Just like scalp skin can show hair growth deficiency, skin in other body sites — such as the face, arms and legs — can often show excessive hair growth that can be cosmetically undesirable,” he added. “Our findings suggest that increased signaling crosstalk among hair follicles could be one major reason for this.”

The good news is that the mechanism can be re-activated and regulated with medication. The team also identified which levels of Wnt-BMP signaling promote or inhibit hair growth, providing “the road map for optimizing Wnt-BMP levels to achieve enhanced hair growth,” Plikus explains. The findings could also further our understanding of how regions of faster and slower regeneration work in coordination in other fast-renewing tissues, such as the intestines and bone marrow.

Plikus adds that their findings suggest there’s an additional signaling factor besides Wnt-BMP which handles heavy hair growth and that the team’s next step will be to identify and examine it.

The paper “A multi-scale model for hair follicles reveals heterogeneous domains driving rapid spatiotemporal hair growth patterning” has been published in the journal eLife.