Unveiling the Unexpected Role of TRF2 in Muscle Repair

A protein traditionally associated with protecting chromosome ends has been found to play a crucial role in helping muscle stem cells remain functional and rebuild injured tissue, according to researchers at the Perelman School of Medicine at the University of Pennsylvania.

The study, published in Science Advances, reveals that TRF2 does much more than shield chromosomes. Within muscle stem cells, it helps preserve the genetic instructions that define the cells and allow them to regenerate muscle after damage.

For years, TRF2 has been viewed as a protein whose primary job is protecting the ends of chromosomes from damage or corruption. However, senior author Foteini Mourkioti, PhD, an associate professor of Orthopedic Surgery at Penn Medicine, notes that rather than simply protecting DNA, TRF2 seems to be key to regenerating muscle throughout life.

Muscle stem cells normally remain inactive until tissue is injured. They then become active, multiply, rebuild the damaged area, and produce replacement stem cells that return to a dormant state. Laboratory experiments showed that TRF2 levels change in a carefully timed pattern as muscle stem cells move through these different stages. The amount of the protein rises and falls as the cells shift between rest, tissue repair, and self-renewal, suggesting that TRF2 helps organize the regeneration process.

To determine what happens without the protein, the researchers removed TRF2 from muscle stem cells in laboratory mice. The animals’ muscles initially looked normal, but their supply of muscle stem cells gradually decreased. The cells did not die, which was unexpected based on the effects of TRF2 loss in other tissues. Instead, they lost the molecular characteristics that allowed them to function as muscle stem cells.

This loss of identity had serious consequences after injury. Rather than rebuilding healthy muscle, the damaged areas accumulated fat and scar tissue. The team also examined TRF2 in a mouse model of Duchenne muscular dystrophy. When the protein was removed from muscle stem cells, the disease advanced much more rapidly. Muscle deterioration became more severe, and the mice had shorter lifespans.

Further investigation revealed how TRF2 produces these effects. The protein does not operate exclusively at chromosome ends. It also attaches to regulatory regions throughout the genome that control genes needed to preserve muscle stem cell identity. Many of those genomic regions contain secondary DNA formations known as G-quadruplexes, which are also being studied as potential targets for cancer therapies.

The findings reveal a biological mechanism that allows muscle stem cells to retain their regenerative abilities. They also show that this mechanism can affect the progression of Duchenne muscular dystrophy in mice. The discovery may help scientists investigate a longstanding puzzle: skeletal muscle has an exceptional ability to regenerate, yet cancers that begin in muscle tissue are relatively uncommon.

Mourkioti and her colleagues are now studying whether this unusual use of TRF2 could lead to new therapeutic approaches for muscular dystrophy. They also hope it will provide insight into cancer biology in tissues that are more vulnerable to the disease.