A team of scientists at the University of Texas Southwestern Medical Center has identified the cells that directly give rise to hair as well as the mechanism that causes hair to turn gray. The research is published in the journal Genes & Development.

Layers of the skin. Image credit: M.Komorniczak / Madhero / CC BY-SA 3.0.

With this knowledge, we hope in the future to create a topical compound or to safely deliver the necessary gene to hair follicles to correct these cosmetic problems, said senior author Dr. Lu Le, an associate professor of dermatology with the Harold C. Simmons Comprehensive Cancer Center at the University of Texas Southwestern Medical Center.

Dr. Le and colleagues found that a protein called KROX20 (also termed EGR2), more commonly associated with nerve development, turns on in skin cells that become the hair shaft.

These hair precursor cells then produce a protein called stem cell factor (SCF) that the researchers showed is essential for hair pigmentation.

When the authors deleted the SCF gene (KITLG gene) in the hair progenitor cells in mouse models, the animals hair turned white.

When they deleted the KROX20-producing cells, no hair grew and the mice became bald.

We uncovered this explanation for balding and hair graying while studying a disorder called Neurofibromatosis Type 1, a rare genetic disease that causes tumors to grow on nerves, Dr. Le said.

Scientists already knew that stem cells contained in a bulge area of hair follicles are involved in making hair and that SCF is important for pigmented cells.

What they did not know in detail is what happens after those stem cells move down to the base, or bulb, of hair follicles and which cells in the hair follicles produce SCF or that cells involved in hair shaft creation make the KROX20 protein.

If cells with functioning KROX20 and SCF are present, they move up from the bulb, interact with pigment-producing melanocyte cells, and grow into pigmented hairs.

But without SCF, the hair in mouse models was gray, and then turned white with age. Without KROX20-producing cells, no hair grew.

We will now try to find out if the KROX20 in cells and the SCF gene stop working properly as people age, leading to the graying and hair thinning seen in older people as well as in male pattern baldness, Dr. Le said.

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Chung-Ping Liao et al. Identification of hair shaft progenitors that create a niche for hair pigmentation. Genes & Development, published online May 2, 2017; doi: 10.1101/gad.298703.117

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