Nature Cell Biology doi: 10.1038/ncb1231 7, pp 286 - 294

Several diseases arise when muscle growth is not controlled properly, and loss of muscle mass is a major problem during old age and in AIDS patients. Research published in the March issue of Nature Cell Biology determines a new way to regulate muscle growth by increasing the size of muscle cells – an approach that should minimise the chance of unwelcome side effects, unlike present therapies.

Muscle growth can be achieved in two ways: by increasing the number of muscle cells through cell division or by increasing their size. Current therapies for increasing muscle growth try to exploit the first approach but, as a result, bear the risk of inducing uncontrolled cell division and cancer. However, Mario Pende and colleagues have identified a specific regulatory mechanism – and potential therapeutic target – that controls the size, but not the number, of muscle cells.

Nutrient availability and growth factor levels regulate muscle growth through two signalling proteins: the TOR and Akt kinases. The team found that one protein that acts together with the TOR-Akt kinases – S6K1 kinase – exclusively targets cell growth of skeletal muscle cells, but does not affect their division, showing that muscle growth can be regulated separately. Importantly, this could provide the basis for safer therapies against muscle loss. It should therefore be possible to increase muscle mass by activating S6K1, without the risk of potentially harmful side effects on muscle cell division.