When we get older, our muscles heal more slowly. New research in mice shows why this happens.
Protein That Slows Repair
Scientists at UCLA found that an old muscle cell makes a lot of a protein called NDRG1. This protein acts like a brake. It slows a pathway named mTOR that normally tells cells to grow and fix damage.
In old mice, NDRG1 levels were about three and a half times higher than in young mice.
What Happens When the Brake Is Lifted?
The researchers blocked NDRG1 in mice that were as old as a 75‑year‑old human. The muscle stem cells started acting young again. They moved quickly and helped repair injuries.
But there was a catch. Without the protective brake, many stem cells died sooner, leaving the muscle less able to heal after repeated injuries.
Survival vs. Speed
Think of a sprinter and a marathon runner. Young stem cells are like sprinters – they work fast but tire quickly. Old stem cells are like marathon runners – they are slower but can last longer. The same trait that helps them survive makes them slower to repair.
Why the Protein Grows With Age
The team says the rise of NDRG1 is a kind of "survivorship bias." Cells that don’t have enough NDRG1 die off, leaving only the tougher ones that live longer but work slower.
This is similar to how animals survive harsh times by slowing growth and focusing on staying alive.
What This Means for Future Treatments
Knowing how NDRG1 works could help design medicines that make old muscles heal better. However, boosting repair might also cause the stem cells to disappear faster. There is no free lunch.
The researchers will keep studying how stem cells balance staying alive and fixing damage as we age.
Funding was provided by the National Institutes of Health and several private foundations.