When muscles get hurt, tiny stem cells inside them wake up and get to work fixing the damage. Scientists at the University of Pennsylvania have now discovered that a protein called TRF2 — long known for protecting the tips of chromosomes — plays a surprising second role: it helps these muscle stem cells remember what they are and keep healing tissues throughout life.
The findings, published in the journal Science Advances, came from researchers at the Perelman School of Medicine at Penn. They noticed that TRF2 levels rise and fall in a precise pattern as muscle stem cells switch between resting, repairing, and replenishing themselves. When they removed TRF2 from the muscle stem cells of lab mice, the animals' muscles looked normal at first. But over time, the stem cell population shrank. The cells did not die — they simply forgot how to be muscle stem cells. Injured muscles failed to heal properly, filling in with scar tissue and fat instead of healthy muscle.
"This completely changes how we think about TRF2's role in these cells," said Foteini Mourkioti, Ph.D., an associate professor of Orthopaedic Surgery at Penn Medicine who led the study. "The loss of identity has severe implications for whether recovery from injury is even possible."
The researchers then tested TRF2 in mice with a condition that mimics Duchenne muscular dystrophy, a disease that causes muscles to weaken over time. When they removed TRF2 from the mice's muscle stem cells, the disease got worse much faster — muscles degenerated more quickly and the animals did not live as long.
The team also uncovered something unexpected about how TRF2 works. Rather than acting only at the protective tips of chromosomes, TRF2 also binds to stretches of DNA across the genome that control muscle identity genes. Many of these stretches contain special DNA structures called G-quadruplexes, which scientists are already studying as targets for cancer treatments.
The discovery may help answer a longstanding puzzle in biology: why are skeletal muscles among the body's best at regenerating themselves, while cancers originating in muscle are relatively rare? Understanding how muscle stem cells use TRF2 differently from other tissues could point toward new treatments for muscular dystrophy — and maybe even insights into cancer prevention.
"Rather than simply protecting DNA, TRF2 seems to be key to regenerating muscle throughout life," Dr. Mourkioti said.
Mourkioti and her team are now exploring whether this unique biological mechanism could lead to new therapies that promote muscle healing without increasing cancer risk.