Exercise-induced irisin in bone and systemic irisin administration reveal new regulatory mechanisms of bone metabolism

A fat-burning hormone that is released during exercise also enhances bone formation in mice. A team led by Jake Chen and Qisheng Tu from Tufts University School of Dental Medicine in Boston, USA, examined the expression of genes and proteins involved in producing irisin, the so-called “exercise hormone”, in mice allowed two weeks of voluntary wheel running and in a control group kept under normal cage conditions. They found higher levels of irisin and associated factors in the bone tissue of exercised mice. The researchers also injected mice with irisin or viruses engineered to express the hormone and observed increases in bone thickness. Experiments with bone cell lines showed that irisin induced bone-forming cells and inhibited bone-absorbing cells. The findings illustrate the complex interplay between exercise, muscle, bone and fat tissues.