Male pattern baldness, also known as male alopecia, is the most widespread form of hair loss in men. Some studies have estimated that between 30 and 50 percent of men are affected by alopecia by the time they reach 50 years of age.
A team of researchers from the University of California, Irvine (UCI) set out to explore hair growth across the skin surface of the entire body. Their findings - which are published in the journal eLife - may help us to understand and treat male baldness, as well as excessive hair growth, differently.
The researchers were jointly led by Maksim Plikus, an assistant professor of developmental and cell biology, and Qing Nie, a professor of mathematics, both of UCI.
Using a combination of mathematical modeling and biological data, the researchers were able to map hair growth patterns across the entire skin.
As the authors explain, mathematical modeling is a valuable tool for understanding how hair follicles grow across the entire body.
"Our new mathematical model predicted details of signaling communications between hairs, otherwise difficult to reveal with standard biological experiments alone," says Prof. Nie.
Wnt and BMP signaling pathways
For the first time, scientists engineered a mouse model of "baldness" in an attempt to understand how poor hair growth occurs in humans.
They examined the Wnt proteins and bone morphogenetic proteins (BMPs) signaling pathways, as previous research on dorsal skin has shown that these play an important role in the "hair cycle clock." Specifically, previous studies referenced by the authors have shown that defects in either one of these pathways may disrupt hair growth patterns.
Wnt proteins regulate cell proliferation, at first during the development of embryos, and then in the growth and regeneration of other tissues. BMPs are also growth factors that drive development in the embryo and play a key role in the functioning of cells.
Previous research referenced by the authors has indicated how these signaling pathways control hair growth across the body, but what the new study shows is that hair growth is a coordinated process, with different skin areas "communicating" with one another.
Wnt-BMP pathway regulation facilitates this communication, as it was found to occur across the entire surface of the skin.
Communication may prevent baldness
Male pattern baldness tends to occur in the frontal and upper back, or crown, areas of the skull, but not at the lower back. The "communication" between the different hair follicles across the different areas of the head is thought to be interrupted, and hair follicles are believed to grow independently.
"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," says Prof. Plikus.
He also adds that Wnt and BMP signaling can be controlled pharmacologically - in other words, we can come up with drugs that may inhibit or activate these pathways, as needed.
By manipulating these pathways, researchers may, in the future, not only be able to stimulate hair growth, but also stop hair from growing in undesired areas.
"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. Our findings suggest that increased signaling crosstalk among hair follicles could be one major reason for this."
Prof. Maksim Plikus
"Our study identified the types of Wnt-BMP signaling levels that are very favorable for hair growth and the types that prevent it," Prof. Plikus adds. "It provides the road map for optimizing Wnt-BMP levels to achieve enhanced hair growth."
Finally, in addition to the Wnt and BMPs signaling pathways, the new study found more signaling factors that were associated with hair growth. In the future, the researchers plan to further explore these newly discovered factors.