The study, to be published in the journal Nature, involved researchers from King's College London, Harvard University and Massachusetts General Hospital.
The study looked at stem cells found inside muscle – which are responsible for repairing injury – to find out why the ability of muscles to regenerate declines with age. A dormant reservoir of stem cells is present inside every muscle, ready to be activated by exercise and injury to repair any damage. When needed, these cells divide into hundreds of new muscle fibres that repair the muscle. At the end of the repairing process some of these cells also replenish the pool of dormant stem cells so that the muscle retains the ability to repair itself again and again.
The researchers carried out a study on old mice and found the number of dormant stem cells present in the pool reduces with age, which could explain the decline in the muscle's ability to repair and regenerate as it gets older. When these old muscles were screened the team found high levels of FGF2, a protein that has the ability to stimulate cells to divide. While encouraging stem cells to divide and repair muscle is a normal and crucial process, they found that FGF2 could also awaken the dormant pool of stem cells even when they were not needed. The continued activation of dormant stem cells meant the pool was depleted over time, so when the muscle really needed stem cells to repair itself the muscle was unable to respond properly.