Adult muscle stem cells, known as satellite cells, have been shown to play an important role in muscle hypertrophic growth, during which time the satellite cells get recruited to existing muscle fibers and fuse with them to promote fiber radial growth. Previous studies, however, have reported that that this recruitment of satellite cells is not obligatory. Here, Kristian Gundersen and colleagues revisit this issue and report that satellite cell depletion prevents fiber hypertrophy in skeletal muscle in mice (p. 2898). They reveal that hypertrophy in two different muscles – the plantaris and the extensor digitorum longus – does not occur in the absence of satellite cells. They base this finding on measurements of the cross-sectional area of fibers rather than on measurements of muscle mass, which the authors propose are a less reliable indicator of fiber hypertrophy. They further report that mechanical overload, which is used to experimentally induce muscle hypertrophy, in fact leads to muscle damage, and that the inclusion of damaged fibers in analyses could mask differences in hypertrophic responses. These, together with other results, lead the authors to propose that satellite cells are obligatory for hypertrophic growth.
