Spurring regeneration of muscle is of interest as as a part of any future rejuvenation biotechnology package because humans and other mammals progressively lose muscle mass and strength with age - aside from the sedentary lifestyle that most older people adopt, there are underlying processes that sap muscle strength even in athletes. Stepping on the gas and telling the body to build new muscle - when it ordinarily would not do so - isn't as good an approach as preventing muscle loss from happening in the first place, or at least attenuating some of the mechanisms involved, but it certainly closer to realization at this point in time.
As a demonstration of that fact, here are researchers building new muscle in mice using one of the many specialist techniques for delivering stem cells that are presently evolving in the laboratory:
Researchers removed a portion of the tibialis anterior leg muscle in several mice (the muscle was chosen because injury to it affects the foot's range of motion but doesn't prevent the mice from walking). In some mice, the injuries were left to heal on their own. In others, the wound was filled with bundles of microthreads seeded with reprogrammed human muscle cells. The untreated mice developed significant scarring at the injury site, with no restoration of muscle function. In sharp contrast, the mice that received the reprogrammed cells grew new muscle fibers and developed very little scarring.
Tests done 10 weeks after implantation showed that the regenerated tibialis anterior muscle functioned with nearly as much strength as an uninjured muscle. The scientists expected that most of the regenerated muscle would be composed of human cells, since the implanted cells were from human muscle. Surprisingly, most of the new muscle fibers were made of mouse cells. The team theorized that the fibrin microthreads, which in their composition and shape are similar to muscle fibers, may encourage resident mouse progenitor cells to migrate into the wound and begin restoring the tissue (they may also forestall the natural inflammatory response that leads to scarring after a major injury).
This surprise finding suggests that fibrin microthreads alone could be used to treat major muscle trauma while research on enhancing regeneration with reprogrammed human cells continues.
Yet another line of research to keep an eye on: the ultimate destination of regenerative medicine is to move away from introducing new cells and towards using signals to tell existing cells to get to work. A lot of these potential signals are being discovered through accident and guided guesswork at the present time, but this will become a more purposeful process of discovery as understanding of the deepest and most complex levels of our biological processes increases.