University of California Berkeley

The L.A. Times gave it's rodent of the week designation to a mighty mouse produced by University of Colorado, Boulder researchers.

The group transplanted muscle stem cells from healthy mice into mice with damaged muscles. Not only did the muscle stem cells spring to action, repairing the damaged muscle, but they maintained the mouse in its newly bulked up state for its entire two-year lifespan.

Researchers at the University of California, Berkeley have found molecular pathways that human muscle stem cells rely on to repair damaged muscle. These pathways are active in younger people but less active in older people, explaining why muscles repair more slowly with age. The group found that younger volunteers had double the number of regenerative muscle stem cells in their thigh muscles compared to older volunteers. After two weeks in a leg cast, both groups began exercise routines to rebuild muscle.

Researchers at UC, Berkeley identified a signaling molecule that interferes with the ability of older skeletal muscle to regenerate. After injury, adult skeletal muscle regenerates by activating muscle stem cells that fuse with the existing muscle cells to repair the damage. This ability to regenerate diminishes with age, not because of a decline in the number of resident stem cells, but because stem cells in the older muscle don't respond when damage occurs. It turns out that older muscles release molecules that actively inhibit the resident stem cells.