A new study examines the molecular mechanisms of hair growth and finds that senescent, or senescent, cells may hold the key to promoting hair growth in humans. Their findings may open the door to the development of new hair loss treatments that harness the innate abilities of these often damaged cells.
Senescent cells get a bad rap because they are associated with hallmarks of aging and many diseases, including cancer, diabetes, cardiovascular disease and Alzheimer’s. But new research finds that senescent cells aren’t all bad.
Cellular senescence is when cells stop dividing but instead of dying they accumulate in the body. This is a normal physiological event that occurs naturally as people age. Now, researchers at the University of California, Irvine (UCI) have taken a closer look at the molecular mechanisms underlying senescent cells in the skin of mice and found that they stimulate hair growth.
The skin contains hair follicles rich in progenitor cells that cycle to renew themselves. This process is initiated by signals that activate hair stem cells, causing them to divide and allowing the follicle to produce new hair. After each cycle, the stem cells remain inactive until the cycle begins again.
The researchers examined mice with pigmented blotches of skin that contained overactive stem cells and showed accelerated hair growth. These spots closely resemble what humans call moles, which are dark, hairy birthmarks. These moles are unique in that they continue to grow thick hair while accumulating large numbers of senescent pigment cells.
Examining the skin spots, the researchers found that their senescent pigment cells produced high levels of a signaling molecule called osteopontin, and that senescent hair stem cells had a matching receptor molecule called CD44. When osteopontin and CD44 interact, the stem cells are activated and produce hair. Mice that were genetically engineered to remove the genes that produce osteopontin or CD44 had significantly slower hair growth.
“We found that senescent pigment cells produce large amounts of a specific signaling molecule called osteopontin, which causes small, normally dormant hair follicles to activate their stem cells, promoting robust growth of long, thick hair,” the study said. said one of the corresponding authors, Maksim Plikus. author. “Senescent cells are generally considered detrimental to regeneration and are thought to drive the aging process as they accumulate in tissues throughout the body, but our study clearly shows that there is a positive side to cellular senescence.”
The researchers also examined human hairy moles by means of RNA sequencing and found significant differences between the moles and adjacent normal facial skin, confirming the role of osteopontin in promoting hair growth in humans.
The researchers say their findings could lead to the development of new treatments for hair loss that exploit the innate properties of senescent cells.
“Our findings provide qualitative new insights into the relationship between senescent cells and the tissue’s own stem cells, and reveal the positive impact of senescent cells on hair follicle stem cells,” said Xiaojie Wang, lead author of the study. “As we learn more, this information has the potential to be used to develop new treatments that target the properties of senescent cells and treat a variety of regenerative diseases, including common hair loss.”
The researchers plan to expand their research to examine other molecular mechanisms of hair growth.
“In addition to osteopontin and CD44, we are also looking more closely at other molecules present in hairy skin nevi and their ability to induce hair growth,” Plikus said. “Our continued research will likely uncover additional potent activators.”
The study was published in the journal nature.
source: University of California, Irvine