Scientists have identified the cells responsible for hair growth as well as the mechanism that causes them to turn grey, a finding that could lead to new treatments for balding and greying hair.
"Although this project was started in an effort to understand how certain kinds of tumours form, we ended up learning why hair turns grey and discovering the identity of the cell that directly gives rise to hair," said Lu Le, associate professor at the University of Texas Southwestern in the US.
"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 Le.
The researchers found that a protein called KROX20, more commonly associated with nerve development, in this case turns on in skin cells that become the hair shaft.
These hair precursor, or progenitor, cells then produce a protein called stem cell factor (SCF) that the researchers showed is essential for hair pigmentation.
When they deleted the SCF gene in the hair progenitor cells in mouse models, the animal's hair turned white. When they deleted the KROX20-producing cells, no hair grew and the mice became bald, according to the study.
The researchers serendipitously uncovered this explanation for balding and hair greying while studying a disorder called Neurofibromatosis Type 1, a rare genetic disease that causes tumours to grow on nerves.
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, said Le.
However, they did not know 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, he said.
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 grey, and then turned white with age, according to the study. Without KROX20-producing cells, no hair grew, the study said.
Researchers will now try to find out if the KROX20 in cells and the SCF gene stop working properly as people age, leading to the greying and hair thinning seen in older people - as well as in male pattern baldness, Le said.
The research also could provide answers about why we age in general as hair greying and hair loss are among the first signs of ageing.
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