Skeletal muscle also experiences a decline in regenerative potential with ageing, which is manifested by decreased generation of myogenic fibres and their replacement with fibrous tissue in humans, as well as in invertebrate species17. Diminished regeneration is most apparent after injury, with a protracted and incomplete recovery in aged humans18. The regenerative impairment is thought to result from compromised resident stem cells, the so-called satellite cells. With ageing, there are documented decreases in proliferative and differentiation capacity, as well as possible decreases in numbers of satellite stem cells in both mice and humans17,19. Age-associated changes in satellite cells seem to be driven predominantly by an ‘aged microenvironment’ because the functional capacity of satellite cells from aged muscles can be fully restored if exposed to the milieu of young muscles in parabiotic (surgically conjoined) mice20.
