Normal aging is accompanied by reduced ability to regain strength and mobility after muscle injury. That’s because over time, stem cells within muscle tissues dedicated to repairing cell damage become less able to renew themselves or generate new muscle fibers.
Muscle stem cells from older mice exhibit profound changes with age. In fact, two-thirds of them are dysfunctional when compared to muscle stem cells from younger mice.
For the first time, researchers at the Stanford University School of Medicine have identified a process by which older muscle stem cells can be rejuvenated to function like younger stem cells, able to renew themselves and aid in muscle repair like their younger counterparts.
In future these studies may help human patients keep their muscles strong and repair muscle damage as they age.
Muscle stem cells isolated from mice that were 2 years old - which is equivalent to about 80 years of human life - exhibit high levels of activity in a biological pathway known as the p38 MAP kinase pathway. This pathway interferes with proliferation of muscle stem cells - as a result, many old muscle stem cells become unable to renew themselves and gradually reduce in number with aging.
Blocking the p38 MAP kinase pathway in a laboratory setting allowed old muscle stem cells remain functional. Not only that, they begin to divide and self-renew as they do in young mice - in the process making a large number of new stem cells that can continue to repair muscle damage with aging.
When transplanted back into the animal, old muscle stem cells with inactivated p38 MAP kinase pathway provide a long-lasting stem cell reserve that contributes to muscle repair and restores strength to injured muscles of 2-year-old recipient mice. Two months after transplantation, their muscles still continued to function very similar to young, uninjured muscles.
Stanford University researchers plan to continue their research to understand how this novel technique can be used to help aging humans recover from muscle injury in future. They believe that if they could isolate muscle stem cells from an elderly person, expose them in culture to the proper conditions and transfer them back into a site of muscle injury, they may be able to use the person's own cells to aid recovery from trauma and prevent localized muscle weakness and breakdown due to broken bones and other injuries.