Scientists have identified the mechanics underlying the out-of-control hair development seen in nevi, also known as skin moles.
The process of skin moles is started by aged pigment cells, according to research done by the University of California, Irvine team. The findings, published in the journal Nature, challenge what aging entails for hair loss and may open the door to molecular therapies to treat androgenetic alopecia, a common hair loss condition.
A skin mole is a skin growth brought on by the collection of melanocytes, or pigment cells. Typical moles can occasionally be seen at birth, however, they frequently appear later in infancy. The majority of people continue to develop new moles up until about age 40. Common moles frequently go away as people become older.
Contrary to what may be predicted, given this older cell population, hairy skin exhibits excellent hair growth while having a large percentage of aged pigment cells. According to the study, particular signaling molecules are to blame for the peculiar development.
"We found that senescent pigment cells produce large quantities of a specific signaling molecule called osteopontin, which causes normally dormant and diminutive hair follicles to activate their stem cells for robust growth of long and thick hairs," says lead author Maksim Plikus.
"Senescent cells are typically viewed as detrimental to regeneration and are thought to drive the aging process as they accumulate in tissues throughout the body, but our research clearly shows that cellular senescence has a positive side to it."
By activating stem cells, which divide to allow follicles to make new hairs, the proliferation of hair follicles is carefully regulated. These hairs develop in cycles, with the stem cells of the follicle remaining dormant until the beginning of the following process after each episode of hair growth.
To investigate the nevi, the scientists employed mouse models with pigmented skin regions with hyperactive stem cells and hair development that resembled the mechanisms described in human nevi.
The researchers thoroughly examined the surrounding hair stem cells and senescent pigment cells. High quantities of osteopontin were produced by aged pigment cells, and this receptor, termed CD44, was found in stem cells. Osteopontin and CD44 reacted, activating stem cells and beginning the hair growth cycle.
Studies conducted later on mice models missing the genes encoding either osteopontin or CD44 revealed much slower hair growth rates, supporting the importance of these proteins. Samples taken from human hairy skin nevi were used to confirm osteopontin's impact on hair development further.
"Our findings provide qualitatively new insights into the relationship between senescent cells and tissue's own stem cells and reveal positive effects of senescent cells on hair follicle stem cells," concludes first and co-corresponding author Xiaojie Wang.
"As we learn more, that information can potentially be harnessed to develop new therapies that target properties of senescent cells and treat a wide range of regenerative disorders, including common hair loss."
The team will now investigate additional chemicals found in hairy skin nevi and their capacity to stimulate hair growth. Further investigation will reveal more effective activators.
- Nature. Signalling by senescent melanocytes hyperactivates hair growth
- National Cancer Institute. Common Moles, Dysplastic Nevi, and Risk of Melanoma