Figure 1. Exercise messenger. Dana-Farber Cancer Institute researchers have identified a new hormone, irisin, which mediates some of the benefits exercise has on metabolism.

Exercise induces increased expression of peroxisome
proliferation-activated receptor-g coactivator 1a (PPARGC1A; PGC-1a) [a], which boosts expression of the membrane protein fibronectin type III domain containing 5 (FNDC5) [b]. FNDC5 is proteolytically cleaved, resulting in the release of irisin [c], which is carried in the blood to white adipose tissue [d], where it stimulates the browning of white fat [e].

In mice fed a high-fat diet, greater expression of irisin decreased weight gain and increased glucose tolerance compared with
normal irisin expression.